Conversion of cellulose from plant biomass to and its derivatives in ionic liquid media

Transcription

1 The University of Toledo The University of Toledo Digital Repository Theses and Dissertations 2015 Conversion of cellulose from plant biomass to and its derivatives in ionic liquid media Siamak Alipour University of Toledo Follow this and additional works at: Recommended Citation Alipour, Siamak, "Conversion of cellulose from plant biomass to and its derivatives in ionic liquid media" (2015). Theses and Dissertations This Dissertation is brought to you for free and open access by The University of Toledo Digital Repository. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of The University of Toledo Digital Repository. For more information, please see the repository's About page.

2 A Dissertation entitled Conversion of Cellulose from Plant Biomass to 5-(hydroxymethyl)furfural (HMF) and its Derivatives in Ionic Liquid Media by Siamak Alipour Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering Dr. Sasidhar Varanasi, Committee Chair Dr. Sridhar Viamajala, Committee Member Dr. Patricia Relue, Committee Member Dr. Ashok Kumar, Committee Member Dr. Kana Yamamoto, Committee Member Dr. Patricia R. Komuniecki, Dean College of Graduate Studies The University of Toledo May 2015

3 Copyright 2015, Siamak Alipour This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author.

4 Conversion of Cellulose from Plant Biomass to 5-(hydroxymethyl)furfural (HMF) and its Derivatives in Ionic Liquid Media by Siamak Alipour Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering The University of Toledo May 2015 In this study, the main goal is introducing a new method for the production of 5- (hydroxymethyl)furfural (HMF) and its derivatives. I propose an integrated process with low energy input for high-yield production of hydroxymethyl furfural (HMF) from glucose in biomass hydrolysates. Due to the prevalent recognition that HMF is a versatile platform molecule for fuels and chemicals, there is a critical need for economically viable technologies for its production from biomass hydrolysates. Previous attempts to generate HMF in aqueous media (either from untreated biomass or from hydrolysates) have not resulted in high yields due to loss of product to humins and inability to prevent hydrolysis of HMF to levulinic and formic acids. Although biomass hydrolysates typically contain glucose, it is now broadly recognized that the best yields can be obtained by dehydration of the corresponding keto-isomer, fructose, and by executing the reactions in non aqueous reaction media (e.g. DMSO and ionic liquids (ILs)). The challenge then, for costeffective and high-yield HMF production, is to devise a cohesive pathway to efficiently transfer glucose from biomass hydrolysate into the non-aqueous reaction media; produce iii

5 HMF in high yield; and isolate it for downstream processing, all with low energy input and recycling of process streams. The technology addresses this challenge and we propose a hybrid enzyme- and chemo-catalytic process that first converts hydrolysate glucose to its more reactive ketose form and subsequently integrates with a downstream catalytic dehydration step that achieves high yields of HMF. The conversion of hydrolysate glucose to fructose and its near-complete recovery is accomplished through a novel enzyme-based simultaneousisomerization-and-reactive-extraction (SIRE) process. The recovered fructose is then dehydrated to HMF in an acidic ionic liquid (IL) reaction medium and simultaneously extracted into low-boiling tetrahydrofuran (THF) solvent to prevent side reactions, increase process yields and facilitate easy product recovery. Conversion of fructose to HMF in IL-media results in superior yields than in aqueous solutions and also occurs at mild operating conditions (IL rxn T ~ 50 C; aqueous rxn T >160 C). Finally, a key feature of this technology is that it permits recycling and reuse of the catalysts, solvents and reaction media. This method also is proven to be an ideal pathway to produce furfural and HMF simultaneously from mixed C5 and C6 sugars stream. In addition, for the important HMF derivatives namely 5-ethoxy methyl furfural (EMF), levulinic acid and 5- acetoxymethyl furfural (AMF) production this method has modified and successfully applied. iv

6 To my beloved Parents, Hengameh and Babak for their love, support and patience

7 Acknowledgements I would like to sincerely thank my family for their endless support. My wife, parents and brother have encouraged me enormously during my PhD journey. Without their helps my dreams would not be achieved. They were always beside me in any situation that I faced. I would like to thank my advisor Prof., Sasidhar Varanasi for his scientific support, useful hints and patience. Without his considerations my PhD achievement was not possible. I would also like to thank my PhD committee Drs. Sridhar Viamajala, Patricia Relue, Ashok Kumar and Kana Yamamoto for their recommendations and Chemical and Environmental Engineering Department support throughout my PhD. My Colleagues and lab mates have helped me a lot during my experiments; I would like to express my gratitude to them especially to Brook, Heng, Bin and Peng. Also I want to appreciate my best friend, Nima Mansouri, helps and supports. v

8 Table of Contents Abstract... iii Acknowledgements...v Table of Contents... vi List of Tables... xi List of Figures... xii 1 Introduction Preview Dissertation outline High Yield 5-Hydroxymethylfurfural Production from Biomass Sugar at Facile Reaction Conditions: a Hybrid Enzyme- and Chemo-Catalytic Technology Introduction Materials and Methods Chemicals and Materials Preparation of saccharified biomass hydrolysate Simultaneous-isomerization-and-reactive-extraction (SIRE) and backextraction (BE) vi

9 2.2.4 Fructose conversion to HMF in IL reaction media Fructose and xylulose conversion to HMF and furfural in IL reaction media Analytical methods Results and Discussion Step 1 Simultaneous-isomerization-and-reactive-extraction (SIRE) Step 2 Back-extraction (BE) of fructose from the organic phase Step 3 Dehydration of fructose to HMF Biomass Hydrolysate IL Reusability Fructose Loading Mixed fructose and xylulose stream Conclusion High Yield Biomass Hydrolysate Conversion to 5- (ethoxymethyl)furfural Introduction Materials and Methods Chemicals and Materials Fructose conversion to EMF in IL media Glucose conversion to EMF in IL media Analytical methods Results and discussions Reaction Kinetics data Temperature effect on the products yield vii

10 3.3.3 Ethanol loading effect on the products yield Fructose loading effect on the products yield IL reusability Glucose conversion to EMF Conclusion Facile Production and in-situ Esterification of HMF from Biomass Sugars in Ionic Liquid Media Introduction Materials and Methods Chemicals and Materials Experimental procedure Analytical Procedures Results and Discussion Effect of acetic acid loading on the final furan yield H 2 SO 4 loading influence on final furan yield Temperature effects on furan yield Effect of fructose loading on final furan yield IL recycling Extracting Solvent efficiency Effects of modifications to the reactants and IL reaction medium Conclusion Levulinic acid Production in High from Biomass Hydrolysate sugar by Implementing SIRE-BE Technique viii

11 5.1 Introduction Materials and Methods Chemicals and Materials Fructose conversion to Levulinic acid Glucose conversion to Levulinic acid Analytical methods Results and Discussion Acid catalyst loading effect on the levulinic acid yield in the aqueous media Reaction duration effect on the levulinic acid yield in the aqueous media Temperature effect on the levulinic acid yield in the aqueous media Fructose loading effect on the levulinic acid yield in the aqueous media Glucose conversion to the levulinic acid in the aqueous media Levulinic acid production in the [BMIM-SO 3 ]HSO4 and DI water mixture [BMIM-SO 3 ]HSO4 loadings effect on the levulinic acid yield Levulinic acid kinetic data in the [BMIM-SO 3 ]HSO4 and DI water mixture Temperature effect on the levulinic acid yield in the [BMIM-SO 3 ]HSO4 and DI water mixture ix

12 Fructose loading effect on the levulinic acid yield in the [BMIM- SO 3 ]HSO4 and DI water mixture Ionic liquid reusability Ionic liquids replacement effect on the levulinic acid yield Conclusion Conclusion, Alternative Approaches and Suggestions for Future Works Conclusion Alternative implementations of SIRE-BE technique and suggestions References x

13 List of Tables 2.1 IL screening for selective back-extraction of fructose from the organic solvent Fructose dehydration to HMF in [EMIM]HSO4 media Results for dehydration of mixed ketoses back-extracted into [EMIM]HSO Comparison the total furan yield between dehydration and in-situ esterification system and only dehydration reaction Furan yield in the modified experiments Furan yield in the different IL Glucose conversion to LA and HMF xi

14 List of Figures 1-1 HMF as a building Block Schematic representation of the three-step process for production of HMF from the biomass sugar glucose Effect of boronic acid to sugar mole ratio on sugar extraction and ketose selectivity for SIRE Schematic diagram of the 4 stage SIRE followed by BE with the summary of results for a 30 g/l (~165mM) aqueous glucose stream Summary of SIRE-BE results for biomass hydrolysate HMF yield with repeated reuse of the IL dehydration media HMF yield as a function of the initial fructose loading Process schematic for furans production from biomass hydrolysate sugars (glucose and xylose) by the SIRE-BE-Dehydration-in-IL approach The block box diagram of the biomass conversion to value added products Kinetic data of Fructose conversion, EMF, HMF and EL yield Ethanol loading effect on fructose conversion and products yield Fructose loading effect on fructose conversion and products yield [EMIM]HSO4 reusability results xii

15 3-6 Glucose conversion to EMF, LE and HMF results Effects of acetic acid loading on final furan yield Influence of H 2 SO 4 loading on final furan yield Fructose, HMF, and AMF content (mole % relative to initial moles of sugar) versus time at (a) 80 C (b) 100 C (c) 117 C Reaction pathway for fructose dehydration and in-situ HMF esterification Effect of fructose loading on final furan yield Reusability of [EMIM]Cl results Solvents extraction efficiency comparison Effects of glucose and fructose on the products yield Acid catalyst concentration effects on fructose conversion, LA and HMF yield Reaction duration effect on fructose conversion, LA and HMF yield Temperature effect on the fructose conversion, and LA and HMF yield Fructose loading effects on LA and HMF yield [BIMIM-SO 3 ]HSO4 weight percent effects on LA yield Kinetic data of fructose conversion and LA yield in IL aqueous mixture Temperature effect on fructose conversion and LA yield in IL aqueous mixture Fructose loading effect on LA yield in IL aqueous mixture IL aqueous mixture reusability results Fructose conversion, LA and HMF yield in different ILs Schematic diagram for the alternative reactor configuration DMSO weight percent effects on HMF yield xiii

16 Chapter 1 Introduction 1-1 Preview The steady growth of world energy consumption, energy security, diminishing fossil fuel resources, and environmental impact require the usage of renewable alternative energy resources [1,2]. Solar energy, wind energy, hydropower, geothermal energy and biomass are major renewable alternative energy resources [3]. Among these energy resources, biomass is the only one that is based on carbon, while others are suitable to produce electrical energy. Based on the constituent biopolymers, biomass could be classified into lignocellulosic and non-ligneous biomass. Lignocellulosic biomass is the most abundant class of biomass: agricultural residue (e.g. wheat straw, sugarcane bagasse, corn stover), forest products (hardwood and softwood), and dedicated crops (switchgrass, salix) [4] are examples of lignocellulosic materials that can be used as renewable sources of energy. Non-ligneous biomass are lignin-deficient feedstocks include micro- or macro-algae, oleaginous feedstocks, bacteria, fungi, etc. [5, 6]. 1

17 Initially edible biomass such as corn or cane sugar were studied and used for the production of chemicals and biofuels. However, this usage can cause shortages in these food sources. As a result, it will increase food prices and raises the food versus fuel debate. Such issues have driven researchers to develop technologies to process non-edible biomass (e.g., lignocellulosic biomass) to produce biofuel and chemicals sustainably without affecting food supplies. In addition, lignocellulosic biomass has two important advantages over edible biomass feedstocks: it is more abundant and can be grown faster and at lower costs as well [7]. Lignocellulosic biomass is composed of cellulose (40 50%), hemicellulose (25 35%), and lignin (15 20%) [8]. Cellulose is a polymer of glucose units linked via β- glycosidic bonds, and is typically embedded as crystalline fibrils within the complex of lignin/hemicellulose matrix, which makes it largely inaccessible to hydrolysis in untreated biomass. Since the cellulose is the major part of the lignocellulosic biomass, its transformation to chemical and fuels is essential to build a sustainable chain of products. The hemicellulose fraction of lignocellulosic biomass is also an amorphous polymer that is comprised of up to five different sugar monomers: D-xylose, L-arabinose, D-galactose, D-glucose, and D-mannose; xylose is the most abundant among these sugars [8-9]. The last part of the lignocellulosic biomass, lignin, is a cross-linked polymer network of methoxylated phenylpropane structures, that included coniferyl alcohol, sinapyl alcohol, and coumaryl alcohol [10-11]. Production of chemicals and fuels from lignocellulosic biomass feedstock requires various innovative approaches and multistep processes due to its high degree of chemical and structural complexity. In general, the biomass is first fractionated into its major 2

18 components, and the individual components are then converted into suitable products [12]. The lignocellulosic biomass has a very rigid structure to protect it in nature; its fractionation, accordingly, requires a special pretreatment followed by hydrolysis. The pretreatment can include physical (e.g. milling, comminuting) and chemical (e.g. acid or base hydrolysis) methods. Following the pretreatment step, the hydrolysis of crystalline cellulose is affected via enzyme hydrolysis. The resulting sugars can then be converted to value-added compounds through conventional chemical and/or biochemical routes. This approach is popularly referred to as the sugar platform. The following seven petro-chemical compounds: toluene, benzene, xylene, 1,3- butadiene, propylene, ethane, and methane form the platform chemicals in a traditional petroleum refinery based approach for manufacturing high-value chemicals [13]. In an analogous bio-refinery based approach to chemicals and fuels, carbohydrate-derived sugars, and lignin-derived phenolics would serve as starting compounds that can be converted to a different set of platform-molecules [14]. One such class of platform molecules are furans obtained via dehydration of C6 and C5 sugars. They are important building blocks that can be further processed to produce solvents and fuels. For instance, 5-hydroxymethyl-furfural (HMF), furfural, and 2, 5-furan-di-carboxylic acid are mentioned in the DOE top 10 list of platform chemicals [15], and in a recent update by Bozell et. al. [16], these were included in the 10+4 list as well. 3

19 Figure 1-1: HMF as a building Block [17] Figure 1-1 presents some of the important compounds that can be produced from HMF. In view of these important chemical and material precursors that can result from HMF, finding pathways that economically produce HMF from cellulose in high yields is the crucial first step in bio-refining and is the principal objective of this thesis. The recent discovery that cellulose can be dissolved in some ILs [18-20] opened the possibility for using these ILs as reaction media for cellulose-derived chemicals and materials. For instance, cellulose, which is insoluble in aqueous media, requires heterogeneous reaction conditions and the use of cellulase enzyme cocktails to affect its hydrolysis to glucose in water. In contrast, depolymerization/hydrolysis of cellulose in presence of mineral acid catalysts becomes feasible in ILs under homogeneous reaction conditions, as ILs are able to dissolve appreciable amounts of cellulose. Here, the 4

20 hydrolysis of β (1 4) glycosidic linkages is catalyzed by the protons. Different solid acids (Amberlyst, Nafion, alumina, sulfonated zircona, and zeolithes) have also been shown to hydrolyze both microcrystalline cellulose or α-cellulose in the IL butyl-methyl imadazolium chloride, [BMIM]Cl [21-22]. In addition, some preliminary investigations on dehydration of the monosaccharaides to furans was also reported in IL media, In these reactions, the acidity of the IL medium [23] and its water content [24] play an important role. In most of these early studies, the furan yields were low and the reaction conditions were rather severe. In the present work, it has been proposed to exploit the unique reaction environment offered by the ILs to produce furans and furan-derived compounds from major biomass sugars, namely, glucose (six-carbon sugar) and xylose (five-carbon sugar). Several innovative strategies are proposed to maximize product yields, while conducting the involved reaction steps under facile conditions. Strategies for recovering and reusing the reaction media are also proposed. Overall, the objective of this Dissertation is to develop technologies that can make large scale production of furans and furan-derived compounds from biomass sugars economically viable. 1-2 Dissertation outline In order to gain the goals of this work, HMF and its derivatives production have studied in detail. The investigation results are presented in the separate chapters for each component. Consequently the dissertation is organized as follows: 5

21 In the first chapter the introduction has provided. The importance of topic and motivation for this study are highlighted in this section. Also the pathway for the aim of the dissertation is provided. The second chapter presents a complete image of simultaneous isomerization and reactive extraction (SIRE) - back extraction (BE) and dehydration process. This chapter includes the process mechanism description and data of HMF production form biomass hydrolysate. Besides, chapter two shows the results of implementing SIRE-BE- Dehydration process for simultaneous HMF and furfural production from a mixed xylose and glucose stream. In order to obtain optimum conditions for this method different operating parameters have investigated in detail. Chapter three illustrates the results of modifications in SIRE-BE-Dehydration process to produce 5-ethoxy methyl furfural (EMF) from C6 sugars. The data also present EMF, EL, and HMF yields changes due to variations in the different parameters such as temperature, reactants loading, reaction duration etc. Chapter four includes the one-pot 5-acetoxy methyl furfural (AMF) production from C6 sugars. Prepared data provide the effects of reactants and catalyst loading, reaction temperature and duration, different reaction media, and various precursors on the AMF yield. Besides reusability of reaction media and extracting organic solvent efficiency has shown. Chapter five demonstrates the results of levulinic acid preparation from biomass hydrolysate. The results provide optimum operating conditions (e. g. temperature, 6

22 reaction duration, catalysts and reactants loadings). In addition, in order to produce levulinic acid in high yield various reaction media has investigated. Chapter six provides the conclusions, alternative approaches and comments for future studies. 7

23 Chapter 2 High Yield 5-Hydroxymethylfurfural Production from Biomass Sugar at Facile Reaction Conditions: a Hybrid Enzyme- and Chemo-Catalytic Technology 2.1 Introduction Lignocellulosic biomass can serve as a sustainable feedstock for producing liquid transportation fuels and chemical and material precursors, augmenting petroleum resources in this role. Pretreatment processes and saccharification depolymerize the biomass cellulose and hemicellulose to produce monomeric sugars. These carbohydratederived sugars are the starting compounds for conversion into a diverse set of platformmolecules [15,16] such as furans. The furan 5-(hydroxymethyl)furfural (HMF) produced from dehydration of glucose is an important intermediate. Hydrodeoxygenation of HMF condensation products provide drop-in liquid transportation fuels [25-30], while hydrogenation products e.g. dimethylfuran and dimethyl-tetrahydrofuran, are good fuel additives [31-34]. Furan dicarboxylic acid (FDCA) obtained from catalytic oxidation of 8

24 HMF is a viable replacement for terephthalic acid the petrochemical precursor for PET plastic [35]. Since HMF is formed via acid-catalyzed sugar-dehydration reactions, aqueous phase hydrothermal conversion of untreated lignocellulosic feedstocks or saccharified hydrolysates has naturally received the most attention [17]. However, these processes are generally considered unviable due to high energy demand of the processes (up to 220 C), low carbon efficiency (< 60%) due to char/humin formation, and HMF rehydration to levulinic acid and formic acid [17, 36]. For example, the Biofine process produces levulinic acid (from cellulose) and furfural (from hemicellulose) but not HMF [36]. In addition to relatively low yields, the products are dilute and require energy-intensive product recovery steps [37]. From several recent studies with pure sugars, two themes have consistently emerged. The first is that due to the very stable nature of the glucose ring structure, high reaction temperatures are required to offset side-reactions and increase HMF yield. Glucose s keto-isomer fructose gives much higher HMF yields and at relatively milder reaction conditions [38-41]. However, if HMF is to be produced from biomass feedstocks, it is imperative that its conversion be achieved starting from glucose produced via saccharification. Isomerization of glucose to fructose is thus the necessary first step for efficient HMF production. Unfortunately, this isomerization reaction is plagued by an unfavorable aldose to ketose ratio at equilibrium (~1:1). At present, the absence of cost-effective methods for achieving high fructose yields is a barrier to using this more-suitable isomer for HMF production [38]. 9

25 The second emergent theme is that non-aqueous reaction media stabilize HMF and prevent its further conversion to levulinic and formic acids (with the accompanying loss of carbon efficiency) and cross-condensation to humins. This has been substantiated in several investigations showing high HMF yield from fructose dehydration in solutions of water and polar organics (DMSO, sulfolane, N-methylpyrrolidone, γ-valerolactone, tetrahydrofuran, and dimethyl acetamide) containing mineral or solid-acid catalysts [34, 40-47]. Dehydration of fructose in acidic ILs have also shown comparable HMF productivity [48], with the additional advantage of milder reaction temperatures ( 50 C) [49] relative to polar organic media (>100 C) [46]. Adoption of non-aqueous reaction media, in particular ILs, for HMF production is to-date hindered by a lack of effective strategies for getting biomass sugars into the reaction media, isolating the HMF product, and recovering the reaction medium for reuse. In this chapter, a cohesive pathway is presented to efficiently transfer glucose from biomass hydrolysate into a non-aqueous reaction medium as fructose; produce HMF in high yield; and isolate the HMF for downstream processing. The three main steps for this process as envisioned in Figure 2-1 have low energy input and recyclable process streams. We have implemented a simultaneous-isomerization-and-reactive extraction (SIRE) process to convert glucose to fructose and overcome the unfavorable aldose-toketose transformation equilibrium [50,51]. Reactive-extraction of fructose into an immiscible organic phase (octanol) is achieved through selective binding with the lipophilic aryl boronic acid (ABA) napthalene-2-boronic acid (N2B). Fructose is recovered in a nearly-pure, concentrated form by back-extraction (BE) into an immiscible acidic IL reaction medium ([EMIM]HSO4). Fructose dehydration is conducted in the IL 10

26 at 50 C with in situ extraction into tetrahydrofuran (THF). Evaporation of the low-boiling point THF (nbp 66 C) can be used to recover the HMF in an energy-efficient manner. This scheme permits recycle of the organic extraction phase, the IL, and THF, with all steps operating at <70ºC and at ambient pressure. This process has also been implemented with biomass hydrolysate produced from dilute-acid pretreatment of corn stover. Due to the specificity of the reactive-extraction and differences in partitioning capacities between the three media, impurities from the hydrolysate do not transfer into the IL reaction media. Hence, the process has the potential for implementation with hydrolysates derived through diverse methods. SIRE- BE is also well-suited for concentrating (>5 fold) dilute hydrolysates through use of low organic-to-hydrolysate (in SIRE) and IL-to-organic (in BE) volume ratios [50]. Thus, energy-intense evaporation methods for concentrating sugar streams are avoided. Besides, the feasibility of converting the mixed glucose and xylose stream by the implementing proposed process has studied. 11

27 Step 1: Simultaneous isomerization of glucose and reactive-extraction (SIRE) of fructose to organic phase organic phase recycle Step 2: Back-extraction (BE) of fructose from organic phase to ionic liquid (IL) Step 3: Dehydration of fructose to HMF with in situ extraction immobilized GXI column G F aqueous glucose solution organic w/ ABA F ph 8.5 T = 60 C F-ABA sugar-depleted medium fructose-rich organic F-ABA F Acidic IL T = 50 C fructose-rich IL IL recycle F HMF T = 50 C Low bp organic HMF fluid flow path add/withdraw material at a specific time Figure 2-1: Schematic representation of the three-step process for production of HMF from the biomass sugar glucose. Glucose is isomerized to fructose using immobilized glucose/xylose isomerase (GXI), and the fructose is selectively-extracted into an organic phase via complexation with a lipophilic aryl boronic acid (ABA). The fructose-rich organic phase releases fructose when contacted with an acidic ionic liquid (IL) reaction media. Fructose is dehydrated to HMF and simultaneously extracted into an immiscible organic to increase HMF yield. The dotted arrows represent addition/removal of the media at a specified time in the process; the solid arrows indicate continuous recirculation of the process stream during a batch experiment. 2.2 Materials and Methods Chemicals and Materials Glucose, fructose, HMF, xylose, furfural, sec-butylphenol, sec-butanol, tetrahydrofuran (THF), phosphotungstic acid hydrate (12-TPA), Aliquat 336, sodium acetate and napthalene-2-boronic acid (N2B) were purchased from Sigma Aldrich Co. (St. Louis, MO). All ionic liquids (ILs) 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl, 98% purity), 1-butyl-3-methylimidazolium methyl sulfate ([EMIM]CH3SO4, 97% purity), 1-ethyl-3-methylimidazolium hydrogen sulfate ([EMIM]HSO4, 95% purity), and 1-ethyl-3-methylimidazolium 12

28 trifluoromethanesulfonate ([EMIM]TFO, 98% purity) were also purchased from Sigma Aldrich Co. Wet Amberlyst 15 (Acros Organic Co., Geel, Belgium) and Amberlyst 70 (Dow Chemical Co., Midland, MI) were used as received. Immobilized xylose isomerase (Gensweet IGI, GXI) and Spezyme CP were a kind gift from Genencor International (Rochester, NY); Novozyme 188 (Novozyme Corp., Denmark) was purchased from Sigma-Aldrich. All other chemicals and solvents were purchased from Thermo Fisher Scientific Inc. (Pittsburgh, PA) Preparation of saccharified biomass hydrolysate Dilute acid pre-treated corn stover biomass was received from NREL (Golden, CO). The solids-containing slurry (predominantly cellulose and lignin) was washed twice with DI water, and the solids were separated by filtration with Whatman type 42 ashless filter paper. For saccharification, 160 g of wet biomass was added to 500 ml of 50 mm sodium acetate buffer in DI water and the ph was adjusted to 4.8 with HCl. Two saccharification enzymes cocktails were added, 15 FPU/g glucan of Spezyme CP and 30 CBU/g glucan of Novozyme 188, and the slurry was mixed continuously at 200 rpm in a shaker/incubator and 50 C for 72 hr. The biomass hydrolysate was separated from the remaining solids by centrifugation at 5000 rpm for 10 min followed by filtration with Whatman type 42 ashless filter paper. The hydrolysate was stored at 4 C until use for SIRE-BE Simultaneous-isomerization-and-reactive-extraction (SIRE) and backextraction (BE) The SIRE-BE method was used to produce a high purity, concentrated solution of fructose from glucose at high yield. To conduct the SIRE step, a 165 mm (30g/l) glucose 13

29 solution was prepared, either by mixing pure glucose or diluting biomass hydrolysate in 50 mm sodium phosphate buffer, buffered to ph 8.5. The glucose solution was isomerized overnight with 4.5g/l GXI to reach an equilibrium conversion of glucose to fructose (~45%). The aqueous glucose/fructose solution was contacted with an immiscible octanol phase containing 165 mm N2B and mm Aliquat 336 for 3 hrs to preferentially extract fructose from the solution and drive the isomerization towards more fructose formation. All steps in SIRE were conducted at 60 C and NaOH was added as needed to keep the ph at 8.5. After SIRE was complete, organic and aqueous phases were separated by centrifugation at 5000 rpm for 10 min. To recover and concentrate the extracted fructose, the organic phase was contacted with a reduced volume of IL (IL-to-organic volume ratio <1). The organic phase and IL were separated by centrifugation at 5000 rpm for 10 min. The fructose-rich IL was used as the reaction phase for fructose dehydration. Results from the SIRE process are reported as: Fructose extraction selectivity = Sugar extraction efficiency = Fructose in the organic phase Fructose and glucose in the organic phase Sugar in the organic phase Initial sugar in the aqueous phase Fructose conversion to HMF in IL reaction media Dehydration of fructose to HMF was conducted in an IL reaction mixture composed of 1000 mg [EMIM]HSO4, fructose (2-20 wt% fructose to IL), and acid catalysts. The reaction media (~1 ml total volume) was added to a mm glass vial. In experiments where HCl was used as the acid catalyst and the amount of fructose was varied, the molar ratio of HCl to fructose was held constant at In experiments with in situ product extraction, 12 ml of an organic solvent (THF or MIBK) was also added to 14

30 the reaction vial. To initiate dehydration, a magnetic stir bar was added to the vial, and the vial was capped and placed in an oil bath on a stirring hotplate with the temperature set at either 50 or 100 C. After a specified reaction period, the vial was rapidly cooled by ice-water bath to quench the reaction, and the phases were separated by centrifugation at 5000 rpm for 10 min. The IL and organic phase compositions were analyzed by high performance liquid chromatography (HPLC) and gas chromatography (GC) as described in the following section Fructose and xylulose conversion to HMF and furfural in IL reaction media Simultaneous dehydration of Ketoses to furans was conducted in an IL reaction mixture composed of 1000 mg [EMIM]HSO4, fructose (10 wt% fructose to IL), xylulose (3 wt% fructose to IL) and HCl as the acid catalysts. The experimental protocol has used for this experiment is similar to the pervious section. Also fructose and xylulose were prepared from glucose and xylose as described in section Analytical methods Calibration standards for glucose, fructose, xylose, xylulose, furfural and HMF were prepared in deionized water. Calibration standards and IL reaction media samples, diluted with water as needed, were analyzed by HPLC using an Agilent 1100 HPLC system equipped with a refractive index detector (RID). Two Shodex SH1011 columns (300 8 mm, from Showa Denko K.K, Japan) in series were used for analysis of the sugars and HMF. A mobile phase of 5 mm H 2 SO 4 was run at 0.6 ml/min; the column and RID detector temperatures used were 50 C and 35 C, respectively, for optimal peak resolution and detection. For HMF quantification in THF, HPLC with an Agilent Zorbax SB-C18 reverse-phase column was used with a UV detector. The mobile phase used was 15

31 a 1:4 v/v methanol:water (ph=2 with H 2 SO 4 ) solution at a flow rate of 0.7 ml/min, and the column temperature was 35 C. The concentration of HMF in MIBK was analyzed by GC on a Shimadzu 2010 chromatograph with an RTX -Biodiesel column (15m 0.32 mm I.D.) using a flame ionization detector (FID). The oven temperature was programmed for a 1 min hold at 60 C followed by a 10 C/min ramp to 300 C. Helium was used as the carrier gas at a flow rate of 1.0 ml/min. The injector was used in split mode; the injector and the detector temperature were 300 C. 2.3 Results and Discussion As mentioned before, the proposed process consists of three steps that will be described in this section with experimental results provided for each step. In addition to pure sugar data the process performance on biomass hydrolysate is also presented Step 1 Simultaneous-isomerization-and-reactive-extraction (SIRE) In order for SIRE to be effective, it must be conducted at a ph suitable for both isomerization and reactive-extraction. In our implementation, a glucose solution at ph 8.5 was first isomerized by the GXI enzyme which catalyzes the isomerization of glucose to fructose. The partially-isomerized sugar solution was contacted with an immiscible organic phase of octanol containing the lipophilic boronic acid N2B and a quaternary ammonium salt Aliquat 336 to promote the extraction of fructose from the aqueous to the organic phase. These components have been previously demonstrated to be effective in SIRE for xylose isomerization to xylulose [50]. To understand how the combination of N2B and Aliquat 336 promotes fructose extraction, it should be noted that ABAs form esters with sugar in a ph-dependent and 16

32 reversible manner. At high ph (> 8.5), lipophilic ABAs exist predominantly in their conjugate-base form (ABA - ) at the organic-aqueous interface. The conjugate-base is able to bind with sugar to form a tetragonal ester (ABAS - ) which accumulates at the interface. Addition of a lipophilic quaternary ammonium salt (Q + Cl - ) such as Aliquat 336 to the organic phase makes it possible to dissolve the negatively charged ABA in the organic phase. Ion pair formation between the lipophilic ammonium cation (Q + ) and the ABAS - yields neutral (Q + )(ABAS - ), which is soluble in the organic phase. The net result of the esterification of fructose with the ABA and ion-pair formation is extraction of sugar from the aqueous phase to the organic phase. Due to the selective complexation and extraction of fructose from the aqueous phase, additional glucose isomerizes to restore the fructose/glucose equilibrium. The isomerization of glucose and extraction of fructose to the organic phase continues until the binding of fructose to the ABA reaches equilibrium. The mole ratios of N2B to sugars and Aliquat 336 to N2B are important factors that can affect sugar extraction and sugar selectivity. As shown in Figure 2-2 increasing the mole ratio of N2B to sugars will increases the fructose and glucose extraction, but will also reduce fructose selectivity. For Aliquat 336 to N2B mole ratios greater than 1.5, the sugar extraction and fructose selectivity are comparable. Since any glucose that extracts is lost in downstream processing, operation conditions were chosen that maximize sugar extraction with very high fructose selectivity. 17

33 Sugar extraction efficiency or Fructose extraction selectivity, % A:N2B 0.5 A:N2B 1.5 A:N2B 2 A:N2B N2B:Sugar mole ratio Figure 2-2: Effect of boronic acid to sugar mole ratio on sugar extraction (closed symbols) and ketose selectivity (open symbols) for SIRE. N2B in the organic phase was 165 mm; glucose in the aqueous phase was 30 g/l (166.7 mm). The volumes of the two phases were adjusted to achieve different N2B to sugar mole ratios. The concentration of Aliquat 336 was in the organic phase was varied to test several different molar ratios to N2B (A:N2B) as shown in the legend. Results shown are for equilibrium isomerization and extraction data in individual experiments [These data are prepared by help of Peng Zhang] Step 2 Back-extraction (BE) of fructose from the organic phase BE media selection The stability of the sugar-aba ester is reduced at low ph. Thus, by contacting the sugar-laden organic phase with an immiscible, acidic solvent, the ABA reverts to its uncharged acid form and fructose is back-extracted into the low ph solvent. In our 18

34 experiments, the back-extraction (BE) of fructose is accomplished by contacting the organic phase with an acidic ionic liquid (IL). In evaluating candidate ionic liquids for fructose back-extraction and its dehydration in this process, three primary requirements were considered. First, the IL be immiscible with the organic phase used for SIRE. The IL must also be capable of extracting the sugar from the organic phase during the backextraction phase. Finally, the IL must be a suitable medium for the efficient dehydration of fructose to HMF In general, imidazolium-based ILs have been preferred for dehydration reactions, with [EMIM]Cl and [EMIM]HSO4 reported as very suitable reaction media for fructose dehydration at low temperatures [48,52]. Table 2-1 summarizes the evaluation of four imidazolium based ILs for octanol immiscibility and fructose extraction efficiency. Only [EMIM]HSO4 and [EMIM]TFO were immiscible with octanol, making them candidates for fructose extraction and subsequent dehydration. In evaluating their ability to extract sugar from the organic phase, [EMIM]HSO4 was able to back-extract all of the sugar, while [EMIM]TFO was only able to strip 50%. As such, [EMIM]HSO4 was used as the medium for all subsequent BE and fructose dehydration experiments. At room temperature, where dehydration is insignificant, 92% of fructose recovery was observed with overnight BE. Since dehydration readily occur at 60 C, the time used for BE of fructose must be limited to prevent extraction of HMF into the organic phase. When 165 mm N2B is used for SIRE, a 5 min contact between organic phase and IL for BE results in 84% BE efficacy at 60 C. 19

35 Table 2.1: IL screening for selective back-extraction of fructose from the organic solvent. Suitable ILs must be immiscible with octanol and facilitate selective fructose extraction. A 30 mm glucose solution was pre-isomerized and used for SIRE with an octanol phase containing 30 mm N2B and 75 mm Aliquat 336. After SIRE reacted equilibrium, the sugar in the organic phase was back-extracted using a volume ratio of the organic phase to IL of 2:1. The fructose back-extracted is the percentage of fructose in the organic phase that was recovered into the ionic liquid. Ionic liquid Immiscible with octanol? Fructose backextracted (%) [BMIM]CH3SO4 No NA * [EMIM]Cl No NA * [EMIM]HSO4 Yes 100 [EMIM]TFO Yes 50 ** * Not applicable due to solvent/il miscibility; ** 50 mm HCl added SIRE-BE validation After selecting an appropriate organic phase composition for SIRE and [EMIM]HSO4 for fructose BE, the complete SIRE-BE process was tested with a 30 g/l glucose solution. In order to increase the extraction of fructose with N2B under the conditions required for high fructose selectivity, the aqueous phase was subjected to four sequential stages of SIRE to increase fructose isomerization and recovery as illustrated in Figure 2-3. In each stage, a fresh volume of the organic phase was contacted with the aqueous sugar isomerization phase in a volume ratio that produced sugar extraction efficiency of 60% and fructose extraction selectivity of 90%. The net results of the SIRE- BE process for production of fructose from the 30g/l glucose solution are shown in 20

36 Figure 2-3. For glucose isomerization under these conditions without reactive extraction, fructose yield is around 45%. However, the 4-stage SIRE results in a shift in the overall isomerization of glucose to fructose from 45% to 89%. After 4 stages, 97% of the initial sugar is transferred to the organic phase; 90% of this sugar is fructose. After completing the SIRE steps, sugar was back extracted to the [EMIM]HSO4. The organic phase to IL volume ratio adjusted such that the fructose concentration in the IL media would be ~10 wt% (g fructose/ g IL) in the [EMIM]HSO4. The SIRE-BE process is able to produce, purify, and concentrate fructose from a glucose solution with minimal energy inputs (all steps are conducted at 60 C). An additional benefit of using SIRE-BE to transfer sugar to the IL for dehydration is that glucose (and fructose) in the aqueous phase after SIRE can be recycled to the feed inlet for reprocessing unlike, other approaches in which the isomerization and dehydration occur in a single vessel [53]. 21

37 Figure 2-3: Schematic diagram of the 4 stage SIRE followed by BE with the summary of results for a 30 g/l (~165 mm) aqueous glucose stream contacted with octanol containing 165 mm N2B and mm Aliquat 336. These data show results for multi-stage extraction of fructose during SIRE and the concentration of sugar during the BE step. The aqueous phase (1) was preisomerized to equilibrium (2) prior to four sequential stages of SIRE, each with 3 hr contact between the organic and aqueous phases. The molar ratio of N2B to sugar in each stage of SIRE was adjusted to achieve optimal sugar extraction and fructose selectivity by changing the organic phase volume. N2B to sugar molar ratios used were as follows: Stage I (streams 2 & 10) 1:1; Stage II (streams 3 & 11) 2:1; Stage III (streams 4 & 12) 3:1; and Stage IV (streams 5 & 13) 3.5: Step 3 Dehydration of fructose to HMF. Fructose dehydration to HMF was conducted under a variety of different conditions using 10 wt% fructose. Dehydration was accomplished at low temperatures (50 or 100 C) and some experiments included the addition of a dehydration catalyst and/or an immiscible organic media for in situ HMF extraction from the IL reaction 22

38 medium. The results of these experiments are summarized in Table 2-2. Runs 1-3 are the baseline results for HMF yield for [EMIM]HSO4 and fructose at 50 C. The HMF yield increases from 25% to 30% with increased reaction time of 180 min to 540 min. However, this extended reaction time is difficult to justify given the marginal improvement in the yield. As an alternate method to increase HMF yield, an organic solvent immiscible with the IL was used to achieve in situ HMF extraction. Y. Pagan- Torres et al. [39] have used sec-butyl phenol (SBP) for HMF extraction from aqueous media; it has also proven viable for extraction of furfural from aqueous media [51]. However, SBP is not suitable here as it is miscible with [EMIM]HSO4. Two proven HMF extraction solvents [54,55] that are immiscible with [EMIM]HSO4 - THF and MIBK - were tested for their ability to increase HMF yield in IL. As shown in runs 4 and 5, the benefit was comparable to that achieved with the extended 9 hr dehydration time. Another means to increase the HMF yield is the addition of solid and mineral acid catalysts to the reaction system. The addition of 12-TPA (run 6) provided no improvement over in situ extraction into THF (run 4), but Amberlyst 15 addition increased HMF yield to 47% (runs 7 and 8). These solid acid catalysts, while being easily recovered, did not catalyze the dehydration as efficiently as HCl (runs 10 and 11) at this temperature (HMF yield of 68% with THF). For the aqueous phase HCl-catalyzed dehydration of C5 sugars to furfural, addition of NaCl has been reported to further increase furan yield [56,57]. As shown in runs 12 and 13, addition of 0.7 M NaCl resulted in a 10-12% increase in HMF yield over HCl alone, with in situ extraction of HMF into THF achieving an 80% HMF yield. 23

39 From a product recovery standpoint, THF is attractive as its normal boiling point (66 C) allows its economical separation from HMF by evaporation. To determine if in situ HMF extraction under a higher reaction temperature could significantly improve HMF yield, a higher boiling point solvent was needed. MIBK was used for this purpose. In comparing runs 11 and 15 with in situ extraction and HCl as the catalyst, the increased reaction temperature resulted in a 10% increase in HMF yield and a significant reduction in reaction time. Addition of NaCl produced a slight increase in HMF yield from 78 to 83% (see runs 15 & 16); however, this is only a 3% increase in yield as compared to in situ THF extraction at 50 C using HCl with NaCl (run 13). Performance of solid acid catalysts are improved at 100 C (runs 17-20) but still results in lower HMF yield than the combination of HCl/NaCl. Although [EMIM]TFO was not effective in extracting fructose from the octanol phase during back-extraction, dehydration was performed in this IL to compare its performance to [EMIM]HSO4 as a reaction medium. As shown in runs 15 and 21, HMF yield in [EMIM]HSO4 was nearly double that in [EMIM]TFO under the same experimental conditions. Thus, selection of the IL is crucial for both fructose extraction and dehydration. 24

40 Table 2.2: Fructose dehydration to HMF in [EMIM]HSO4 media. All experiments were conducted with 1000 mg [EMIM]HSO4 and 100 mg fructose. For experiments with in situ HMF extraction, 12 ml of organic solvent were used. Total HMF yield includes HMF in both the IL and solvent phases. Run Catalyst In situ extraction solvent 25 Reaction conditions Total HMF yield (mol %) C, 180 min C, 360 min C, 540 min THF 50 C, 180 min MIBK 50 C, 180 min TPA (50 mg) THF 50 C, 180 min 31 7 Amberlyst 15 (50 mg) THF 50 C, 180 min 41 8 Amberlyst 15 (50 mg) THF 50 C, 360 min 47 9 Amberlyst 15 (100 mg) THF 50 C, 180 min mm HCl - 50 C, 180 min mm HCl THF 50 C, 180 min mm HCl; 0.7 M NaCl - 50 C, 180 min mm HCl; 0.7 M NaCl THF 50 C, 180 min * 3.4 M HCl; 0.7 M NaCl THF 50 C, 180 min mm HCl MIBK 100 C, 30 min mm HCl; 0.7 M NaCl MIBK 100 C, 30 min Amberlyst 15 (50 mg) C, 75 min Amberlyst 15 (50 mg) MIBK 100 C, 75 min TPA (50 mg) MIBK 100 C, 180 min Amberlyst 70 (50 mg) MIBK 100 C, 75 min ** 0.42 mm HCl MIBK 100 C, 30 min 40 *Dehydration conducted on the fructose from BE step. **[EMIM]TFO used instead of [EMIM]HSO4

41 2.3.4 Biomass Hydrolysate In addition to pure sugar, the feasibility of using saccharified biomass hydrolysate as a feed for the SIRE-BE process was also evaluated. Glucose-rich biomass hydrolysate was produced by enzymatic saccharification of the solids remaining after dilute acid pretreatment of corn stover. Results for SIRE-BE are shown in Figure 2-4. When compared to the results for pure glucose (Table 2-2 and Figure 2-3), the fructose extraction selectivity, sugar extraction efficiency, the total fructose yield, and HMF yield are very comparable g/l G g/l F g/l G 1.47 g/l F 0.45 g/l G 0.43 g/l F Figure 2-4: Summary of SIRE-BE results for biomass hydrolysate produced from corn stover. Biomass hydrolysate was diluted to 165 mm glucose to allow comparison of the SIRE- BE-Dehydration results to those of pure glucose in Figure 2-3. Experimental conditions used for SIRE were the same as describe in Figure 2-3. Dehydration conditions are those described in Table 2-2 for Run IL Reusability Due to the costs associated with an ionic liquid reaction phase, it is highly appropriate to determine if the IL reaction media can be reused for multiple cycles of 26

42 back-extraction and dehydration. If so, conversion of glucose to fructose to HMF could be implemented in a semi-continuous process with the IL phase as a closed loop as shown in Figure 2-1. To assess IL reusability, fructose was back-extracted into the IL reaction media, and the mixture was held at 50 C for 180 min for dehydration with THF used for in situ HMF extraction. After the reaction, the THF/HMF phase was removed, and the IL/HCl media was used for two additional rounds of BE and dehydration. Results of repeated dehydration in the recycled IL, reported as HMF yield, are shown in Figure 2-5. No reduction in HMF yield was observed after 3 cycles of dehydration, with recycling of the [EMIM]HSO4/HCl reaction media. HMF yield, mol % Run number Figure 2-5: HMF yield with repeated reuse of the IL dehydration media. Dehydration was conducted in 1000 mg [EMIM]HSO4 and 10 wt% fructose loading with 0.42 mm HCl as a catalyst at 50 C for 180 min and 12 ml of THF for in situ extraction (Table 2, Run 11); fructose conversion was 100%. Following phase separation, the IL phase was contacted with an additional 10 ml of THF to extract residual HMF and minimize carryover to the next reaction cycle; no HMF was detected in the IL at the end of Run 3. HMF yield is based on HMF extracted into the combined 22 ml of THF. 27

43 2.3.6 Fructose Loading Since both the IL and HCl serve as catalysts for the dehydration reaction, we investigated the effect of the fructose loading in the IL on the overall HMF yield. These experiments were conducted with in situ extraction of HMF into THF at 50 C for 180 min. The yields of HMF achieved are shown in Figure 2-6. These results indicate that for fructose loadings up to 10 wt% the HMF yield is unchanged. When, the loading was increased from 10 to 20 wt % a reduction in HMF yield from 80% to 74% was observed. Figure 2-6: HMF yield as a function of the initial fructose loading. Dehydration was conducted in 1000 mg [EMIM]HSO4 with 0.42 mm HCl and 0.7 mm NaCl as a catalyst at 50 C for 180 min. The volume of THF used for in situ extraction of HMF was scaled at 1.2 ml THF per 1 wt% fructose based on the initial fructose loading in the IL. Fructose conversion was 100% in each experiment. The HMF yield is based on the combined content in both the IL and THF phases. 28

44 2.3.7 Mixed fructose and xylulose stream Based on the biomass pretreatment method the biomass hydrolysate contains the mixture of xylose and glucose. Thus it is important to investigate the feasibility of implementing our state of the art SIRE-BE-Dehydration process for simultaneous conversion of biomass sugars (glucose and xylose) to HMF and furfural with facile reaction conditions. The process conceptual schematic is shown in Figure 2-7. Described principle for single sugar (glucose) conversion to furan (HMF) is also valid for this case. STEP 1 Simultaneous isomerization & reactive extraction (SIRE) of biomass sugars (50-60 o C) STEP 2 Back extraction (BE) of ketose sugars into IL reaction media STEP 3 Dehydration with in situ furan extraction (50 o C) Biomass hydrolysate organic acidic ionic liquid (IL) low bp with added XI pellets w/ ABA organic (THF) Glucose Fructose Fructose HMF HMF Xylose Xylulose Xylulose Furfural Furfural Figure 2-7: Process schematic for furans production F 92% from biomass HMF hydrolysate 79% HMF sugars 79% Cumulative molar yields: Xu 94% Fur 82% Fur 82% (glucose and xylose) by the SIRE-BE-Dehydration-in-IL approach. The three steps of the SIRE-BE-dehydration process have successfully implemented at laboratory scale employing the system schematically depicted in Figure 2-1. Starting feed was glucose- and xylose-rich streams. Each stream was subjected to SIRE to generate organic phases containing ketose sugar that were subsequently back-extracted into [EMIM]HSO4 (containing HCl and NaCl) by contacting the phases for 10 min to obtain at 10 wt% fructose or a 3 wt% xylulose solution (Table 2-3, column 1) in IL. These ketose sugars were dehydrated with in situ extraction into THF which resulted in high isolated yields of HMF and furfural. 29

45 Table 2-3: Results for dehydration of mixed ketoses back-extracted into [EMIM]HSO4. The ketoses were produced from SIRE performed on dilute acid pretreated corn stover biomass hydrolysate received from NREL. The dehydration was conducted with in situ extraction into THF at 50 C. Ketose loading in IL, wt% (g ketose/g IL) Catalyst Reaction conditions Furan yield, mol% 10 wt% fructose 3 wt% xylulose 0.42 mm HCl; 0.7 M NaCl 2.45 mm HCl; 0.7 M NaCl 50 C, 180 min 86 (HMF) 50 C, 180 min 88 (Furfural) 2.4 Conclusion Our process innovations overcome several key technical barriers in the pathway to furan production. The unfavorable aldose-to-ketose transformation equilibrium is overcome through reactive-extraction of the ketose sugars into an immiscible organic phase through selective binding with ABA. The hurdle for efficient transfer of hydrolysate sugars into a non-aqueous reaction medium is overcome through backextraction of the isomerized and concentrated sugars into [EMIM]HSO4. Finally, the economically-viable isolation of furan from the reaction medium is accomplished through in-situ extraction of furans from IL into THF. 30

46 Chapter 3 High Yield Biomass Hydrolysate Conversion to 5- (ethoxymethyl)furfural 3.1 Introduction During the past century crude-oil has been used as a resource for production of bulk-chemicals and transportation fuels. Due to declining fossil resources, steady growth of demand for fuels and chemicals, environmental impact and political issues associated with fossil resources, it is necessary to replace this important energy source with alternative sustainable resources. Lignocellulosic biomass proves to be a viable alternative for production of transportation fuels and chemicals based on its abundant availability (production rate ( tons per year)) and high carbon content. In order to synthesize required products from biomass, first the carbohydrates of biomass should be converted to one of the several building block molecules [15]. 5-(hydroxymethyl) furfural (HMF) is a promising platform molecule and its important role has been highlighted in the recent reviews [16,17]. 31

47 HMF is a versatile compound which is formed by acid-catalyzed dehydration of C6 sugars. Apart from its important role in the synthesis of renewable plastics, it has been reported as a fuel additive or transportation fuel precursor. For instance, HMF has been hydrogenated to 2,5-dimethylfuran which can be used as octane booster [33]. In another pathway, HMF was subjected to aldol condensation reaction; then, the resulting C9-C15 molecules were hydrogenated to produce diesel-range fuels [27,58]. Recently 5- (ethoxymethyl) furfural (EMF), product of HMF etherification with ethanol, has been reported as a diesel fuel additive [59]. EMF as fuel additive has promising properties: it has high energy density [60]; its production does not require hydrogenation, and its presence in the blend in the diesel engine has decreased fine particulate and SO x emission [61]. In addition, EMF has low toxicity concerns since it has been used as a flavoring agent in beverage industries [31]. Ethyl levulinate (EL) is, often, produced during EMF synthesis as a byproduct. EL also has been reported as a diesel fuel additive [62]. Different acid catalysts have been reported that catalyzed HMF conversion to EMF in high yield [63-65]. Considering that fructose dehydration to HMF is also conducted in presence of acid catalysts, different research groups have studied one-pot fructose conversion to EMF. For instance, Brown et. al. [66] have used fructose as the feed with ion-exchange resin as acid catalyst to produce EMF, but selectivity was low. Bing and co-workers have used [MIMBS] 3 PW 12 O 40 [67], Wang and co-workers [68] have conducted fructose conversion to EMF in presence of phosophotungstic acid catalyst, moreover cellulose sulfuric acid catalyst has been reported as a bio-supported solid acid catalyst [69] to produce EMF from fructose. Balakrishnan et. al. [31] have studied the performance of different solid and mineral acid catalysts along with the role 32

48 of other parameters on the conversion of fructose or HMF to EMF, and proposed a possible reaction pathway. Kraus and Guney [70] also have conducted one-pot fructose conversion to EMF in acid functionalized ionic liquid. Although these groups have reported promising results, to make the EMF production process economically feasible, glucose should be used as the feed, since glucose is the most abundant C6 sugar produced via depolymerization of biomass carbohydrates with a much lower price compared to fructose. In this regard, some efforts have been made to produce EMF directly from glucose. Abu-Omar s group [71] has used AlCl 3 as an acid catalyst and conducted onepot glucose conversion to EMF at high temperature (> 130 C). Liu et al [72] also used AlCl 3 ; however, they conducted the reaction at different conditions: a lower temperature (100 C) and longer reaction duration. Unfortunately the reported EMF yields are low, less than 40 mol%. Riisager and co-workers [73] have used sulfonic acid functionalized ionic liquid; however, the glucose was converted to ethyl D-glucopyranoside in the IL medium. A completely different approach for EMF production was suggested by Mascal et. al. [74-76]. In the first step, they have converted C6 sugars or cellulose directly to 5- (chloromethyl) furfural (CMF). Then, in presence of ethanol, the Cl atom in the CMF was replaced by an ethoxy group to produce EMF and HCl. Despite high reported EMF yields, this method has not scaled up due to some concerns, such as the recyclability of produced acid (HCl) and the effects of non- reacted halides on the automobile fuel system [31]. Here in we report a novel approach to synthesize EMF in high yield from biomass hydrolysate glucose. This approach takes advantage of the previously described Simultaneous-Isomerization-and-Reactive-Extraction (SIRE) followed by Back- 33

49 Extraction (BE) approach to convert glucose (in biomass hydrolysate) to a concentrated fructose-solution in IL; Dehydration of fructose to HMF, with in-situ etherification of HMF to EMF, is achieved by conducting the sequential reactions in the [EMIM]HSO4 medium in presence of ethanol and an acid catalyst. Different reaction parameters have been investigated to establish optimum conditions. 3.2 Materials and Methods Chemicals and Materials Fructose, glucose, HMF, ethanol, EMF, EL, and 1-ethyl-3-methylimidazolium hydrogen sulfate ([EMIM]HSO4, 95% purity), were purchased from Sigma Aldrich Co. (St. Louis, MO). All other chemicals and solvents were used as received from Thermo Fisher Scientific Inc. (Pittsburgh, PA) Fructose conversion to EMF in IL media Fructose conversion to EMF and EL was conducted in a reaction mixture composed of 1g ([EMIM]HSO4, ml ethanol, fructose (10 wt% fructose to IL) and HCl as the acid catalyst with molar ratio of HCl to fructose held constant at The reaction media was added to a mm glass vial. To initiate dehydration, a magnetic stir bar was added to the vial, and the vial was capped and placed in an oil bath on a stirring hotplate with the temperature set at the desired value. After a specified reaction period, the vial was rapidly cooled by ice-water bath to quench the reaction. The IL phase compositions were analyzed by high performance liquid chromatography (HPLC). EL was extracted by toluene and analyzed by gas chromatography (GC). 34

50 3.2.3 Glucose conversion to EMF in IL media Glucose (pure or from biomass hydrolysate) was converted to fructose by implementing the SRE-BE process. Described procedure in chapter 2 was followed in this regard, and then fructose was converted to EMF as mentioned in the previous section Analytical methods Calibration standards for fructose, HMF, and EMF were prepared in deionized water. IL reaction media samples, diluted with water as needed, and calibration standards were analyzed by HPLC using an Agilent 1100 HPLC system equipped with a refractive index detector (RID). A single Shodex SH1011 column (300 8 mm, from Showa Denko K.K, Japan) was used for analysis of the sugar, HMF and levulinic acid. A mobile phase of 5 mm H 2 SO 4 was run at 0.6 ml/min; the column and RID detector were maintained at 65 C and 35 C, respectively, for optimal peak resolution and detection. The concentration of EL in toluene was determined by GC on a Shimadzu 2010 chromatograph with an RTX -Biodiesel column (15m 0.32 mm I.D.) using a flame ionization detector (FID). The oven temperature was programmed for a 1 min hold at 60 C followed by a 10 C/min ramp to 300 C. Helium was used as the carrier gas at a flow rate of 1.0 ml/min. The injector was used in split mode; the injector and the detector temperature was 300 C. All the experiments were repeated at least two times and the reported results are the average of these multiple runs; the standard deviation was less than 2% among different runs. 35

51 3.3 Results and discussions The block box diagram of the developed process for converting biomass hydrolysate sugar (Glucose) to EMF and EL is presented in Figure 3-1. Briefly, in the first step of the process, acid pretreated biomass is saccharified to release sugar. In the second step by implementing SIRE-BE method glucose from biomass hydrolysate is isomerized to fructose and selectively extracted to an immiscible organic phase. Then, fructose is back extracted into [EMIM]HSO4. Finally, in presence of ethanol, fructose dehydration to HMF and simultaneous HMF etherification to EMF is conducted in the IL. Isolation of the products from reaction media can perform via fractional distillation due to the large differences in the boiling points of ethanol (78 C), HMF (116 C), EMF (254 C), EL (203 C) and [EMIM]HSO4 (bp >350 C). In order to determine the optimum operating conditions for the proposed process, we first investigate different parameters effects on the fructose dehydration to HMF and in-situ HMF etherification to EMF and then by merging the obtained results with the provided data in chapter 2, the optimum parameters will be established for the process. Biomass Saccharification SIRE-BE Fructose Dehydration & HMF Etherification Products Separation EMF EL HMF Figure 3-1: The block box diagram of the biomass conversion to value added products 36

52 3.3.1 Reaction Kinetics data Figure 3-2 presents the kinetic data at temperature levels of 80 C, 90 C and 100 C for fructose dehydration to HMF and in-situ conversion of HMF to EMF via etherification reaction with ethanol. Data demonstrate that at these temperatures almost all of the fructose is consumed within the first thirty minutes beyond this time, the dominant reaction is the etherification of HMF to the EMF, as seen by the continuous drop in HMF concentration and increase in EMF concentration. In addition the results show that at higher temperature the reactions kinetic are faster and EMF has produced sooner. The yield kinetics of EMF and EL display the behavior typical of final products in a reactions-in-series case, i.e., they increase steadily with time. Yield/Conversion Time (min) 80 C Fructose Conversion HMF Yield EMF Yield EL Yield 37

53 Yield/Conversion Time (min) 90 C Fructose Conversion HMF Yield EMF Yield EL Yield 100 Yield/Conversion Time (min) 100 C Fructose Conversion HMF Yield EMF Yield EL Yield Figure 3-2: Kinetic data of Fructose conversion, EMF, HMF, EL yield at 80 C, 90 C and 100 C, 1g [EMIM]HSO4, 2ml ethanol, 100mg fructose, 0.36 mmol HCl as acid catalyst Temperature effect on the products yield The results presented in the Figure 3-2 show the temperature effect on the products distribution. Comparing the products yield at these temperature levels show that 38

54 at the lowest temperature (80 C) HMF yield is higher than EMF even after continuing the reaction for 180 min. At 90 C EMF yield is higher than HMF; however there are significant amount of HMF available which has not converted. The results also indicate that by increasing temperature to 100 C the majority of HMF will be converted to EMF and EL. In another words, although fructose has disappeared very fast even at 80 C, higher temperature is required to completely convert HMF to EMF. Despite different product distributions, the total product yield remains almost constant at all of the temperatures Ethanol loading effect on the products yield In addition, we also studied the effect of different amounts of ethanol (as a nonlimiting reactant) on the yields of products and their distribution. The presented results in Figure 3-3 demonstrate that at low ethanol loading (mole ratio of ethanol to fructose: 15) the total products yield is lower compared to highest ethanol loading (mole ratio of ethanol to fructose: 60). 39

55 100 Yield/Conversion HMF Yield EL Yield EMF Yıeld Total Product Yield Fructose Conversion Ethanol to fructose mole ratio Figure 3-3: Ethanol loading effect on fructose conversion and products yield. 1g [EMIM]HSO4, 100mg fructose, 100 C, 2hr, 0.36 mmol HCl as acid catalyst Fructose loading effect on the products yield The influence of the fructose initial concentration on the EMF, EL and HMF yield is investigated. The experiment with 10% fructose to IL mass ratio (referred to as the original experiment) is repeated at 7%, 15% and 20% initial fructose loadings. The results demonstrated in Figure 3-4 indicate that there are not any appreciable changes in the total products yield. 40

56 100 Yield/Conversion HMF Yield EL yield EMF Yield Total Product Yield Fructose conversion Fructose (wt%) Figure 3-4: Fructose loading effect on fructose conversion and products yield. 1g [EMIM]HSO4, 100 C, 2hr, Ethanol mole ratio to fructose:60, HCl mole ratio to fructose: IL reusability In order to investigate the reusability of the [EMIM]HSO4, the fructose dehydration and in-situ HMF etherification reaction has repeated for three consecutive cycle. The results presented in Figure 3-5 show that the total products yield remains constant and proves the feasibility of IL recycling. 41

57 90 75 Yield (mol%) Total Product Yield Cycle Number Figure 3-5: [EMIM]HSO4 reusability results. reaction condition in each run: 2ml ethanol 1g [EMIM]HSO4, 100mg fructose, 100 C, 120min, mmol HCl as acid catalyst, Total products yield is summation of EMF, HMF and LE yield Glucose conversion to EMF The main object of this chapter is providing a pathway that converts biomass hydrolysate sugar to EMF. Therefore, first glucose is prepared from biomass hydrolysate solution, then SIRE-BE process implemented to convert glucose to fructose in high yield, finally EMF and EL are produced from fructose dehydration and in-situ HMF etherification in [EMIM]HSO4 and ethanol mixture. The results of glucose conversion to EMF by applying this technique for two different feed cases: a) pure glucose and b) glucose from biomass hydrolysate solution are presented in Figure 3-6. The glucose isomerizations to fructose yield and fructose back extraction efficiency are similar to the reported data in chapter 2 and have not presented here. EMF, EL, and HMF yield are similar for two cases which prove the advantage of the SIRE-BE process that can use 42

58 glucose from saccharified biomass hydrolysate solution without any demand for purification process. Although glucose usage as the feed is the main advantage of the proposed process, comparing products yield in Figure 3-2 and 3-6 shows that higher yield has reported while fructose has used. This lost can be attributed to presence of small amount of octanol which remains on top of the [EMIM]HSO4 phase after BE step and contributes in the etherification reaction with HMF, consequently decreases the EMF yield. This phenomenon is proven by adding different amount of octanol to the reaction media containing [EMIM]HSO4, ethanol, HCl, and fructose. The EMF yield decreases from 63% to 53% and 43% as the octanol increases in the range of zero to 250µl and 500µl respectively. It is worth noting that the produced ether from HMF and octanol does not express as a carbon lost to undesired side products. Since, Gruter and co-worker from Furanix Technologies [77] have studied HMF etherification in presence of different alcohols (included ethanol, isobutanol and octanol) and reported that the mixture of produced ethers can be used as fuel additives. 43

59 50 40 Yield (mol%) Pure Glucose Biomass Hydrolysate 0 HMF EMF EL Products Figure 3-6: Glucose conversion to EMF, LE and HMF results 3.4 Conclusion A new approach is developed for the converting glucose from biomass hydrolysate in high yields to ethoxymethyl furfural (EMF). The new approach couples a novel SIRE-BE technology that provides a path for transferring glucose in the form of concentrated fructose into an IL medium, with the unique traits offered by [EMIM]HSO4 media in affecting fructose conversion to EMF under facile conditions. In addition to EMF, a smaller quantity of EL is also produced. The total product yield, defined as (EMF+EL+HMF) yields, in excess of 87% is possible while using fructose as the feed. Of this 66% is EMF, 12% is EL and 9% is HMF. Various parameters effects on the products yield have investigated and optimum conditions determined. 44

60 Chapter 4 Facile Production and in-situ Esterification of HMF from Biomass Sugars in Ionic Liquid Media 4.1 Introduction Fossil fuels have been used as energy and chemical source for several decades. However, this source is finite, has security concerns and imposes great impact on climate changes by CO 2 emission. To overcome these issues a new sustainable energy source should be used. Biomass is the answer for these demands since it is the most abundant ( ton per year global production) renewable resources [78]. To build a chain from biomass to fuel and chemical precursor, the crucial step is converting sugars prepared from biomass to components called building blocks. Among these 5- (hydroxymethyl)furfural (HMF) is an important one since it provides a bridge between carbohydrate chemistry and mineral oil-based industrial organic chemistry [79]. Typically, the starting point for producing biomass-based HMF is the glucose-rich hydrolysates obtained through pretreatment and enzyme hydrolysis of the biomass. It 45

61 would be ideal if the glucose in the hydrolysate could be dehydrated directly in the aqueous phase itself to HMF. While Bronstead acid catalyzed dehydration of glucose has been investigated, the product yield is low due to HMF rehydration to levulinic and formic acid and in particular, humin formation and loss of sugar results from cross condensation of HMF with sugar and/or resinification of HMF in aqueous environment. Changing reaction media from aqueous to others that stabilize HMF such as DMSO or insitu extraction of HMF into an immiscible organic phase, i.e., biphasic system has been reported [40]. HMF is a very important intermediate building block, however almost it is not used as a final product. In addition, it is rather unstable under the conditions that it forms. Thus it is interesting to find out the applications of HMF derivatives, especially those derivatives that can be produce in-situ. Simultaneous HMF production and conversion to more stable form in the reaction medium can avoid the need for in-situ extraction of HMF. Furthermore, if the resulting compound is less hydrophilic compared to HMF, it can be more completely extracted into a low-boiling point organic solvent to reduce isolation costs and extraction can be carried out after the reaction under room temperature condition which lower the operating cost. Beside, this strategy will increase the total yield of sugar conversion to furans compared to the case that only HMF is produced in single phase reactor, since HMF contribution in the undesired side reactions will be prevented. A distinguished example for this approach is HMF production by sugar dehydration in IL media and in-situ esterification to 5-acetoxymethylfurfural (AMF) with acetic acid, since AMF is more stable compared to HMF. It can be used as the 2, 5-46

62 furandicarboxylic acid (FDCA) precursor and easily extracted from reaction media. Partenheimer and Grushin [80] have recognized AMF during HMF oxidation to 2, 5- diformylfuran (DFF) and FDCA as a byproduct and Furanix Technologies [81] results have proved that at a provided temperature and pressure AMF oxidation to FDCA occurs in high yield. It is worth noting that FDCA has broad range of applications, thus its important role in the bio-refinery has highlighted by in the DOE report [15] and recent update by Bozell et. al. [16]. For instance, based on the Gandini and co-workers [82] FDCA can take place of the terephtalic acid in the manufacture of polyethylenterphatalate (PET). The other polymeric applications of FDCA are the preparation of furanic modified amine based curatives for polyesters, hybrid epoxy and urea-urethanes [83], and as polyester polyols in production of corrosion and flame resistance coating [84]. The goal of this chapter is introducing a new pathway that conducts simultaneous sugar dehydration and HMF esterification in IL media in presences of Bronsted acid catalysts. Due to novelty in the HMF ester application and lack of the knowledge related to its production, a deep investigation on parameters affecting AMF production in IL media is required. Thus, we will investigate different IL media, reaction conditions (temperature, time etc.), reactant loading, and acid catalyst concentrations to optimize AMF production yield. In addition the feasibility of modification for this new pathway will be explored. 47

63 4.2 Materials and Methods Chemicals and Materials Glucose, Fructose, HMF, AMF, 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl), 1-ethyl-3-methylimidazolium hydrogen sulfate ([EMIM]HSO4), 1-ethyl-3- methylimidazolium trifluoromethanesulfonate ([EMIM]TFO), acetic acid, and acetic anhydride were purchased from Sigma Aldrich Co. (St. Louis, MO, USA). Methyl isobutyl ketone (MIBK), tetrahydrofuran (THF), and other chemicals were prepared from Thermo Fisher Scientific Inc. (Pittsburgh, PA, USA) and were used as received Experimental procedure The sugar dehydration to HMF and its in-situ esterification to AMF was conducted in IL medium in a single-pot arrangement. In a standard experiment, 1000 mg of [EMIM]Cl, 100 mg fructose, 0.16 mmole acid catalyst (H 2 SO 4 ), and 35 mmole acetic acid were loaded into mm glass vials. The vials were capped and heated in an oil bath over a hot plate, while constantly stirring the contents of each vial using a magnetic stirrer. After rapidly raising the temperature of the reaction mixture to 80 o C (~ 3min), the reaction was allowed to proceed for a pre-specified time period, at which time the vial was cooled to room temperature and the immiscible organic solvent, MIBK, was added to the reaction mixture in a 8:1 (v/v) (in case of [EMIM]Cl) or 3:1 (v/v) (in case of [EMIM]HSO4) proportion. Following the addition of an organic solvent, the vials were sealed and the two phases were vigorously stirred together for 10 minutes to selectively extract AMF and HMF from the IL medium. Next, the vials were centrifuged at 5000 rpm for 10 minutes to separate the organic and IL phases. 48

64 4.2.3 Analytical Procedures The organic phase was analyzed using GC while the IL phase was analyzed by HPLC. The products in the organic phase, in addition to external standards of HMF and AMF, were analyzed using a Shimadzu 2010 Gas Chromatograph with an RTX - Biodiesel column (15m 0.32mm I.D.) and a Flame Ionization Detector (FID). The injector was used in a split mode; the injector temperature was set at 250 C. The detector temperature was set at 300 C. The oven temperature was programmed as follows: hold for 1 min at 60 C and ramp up to 300 C at 10 C/min. Helium was used as the carrier gas at flow rate of 1.0 ml/min. The high performance liquid chromatography (HPLC) was used to analyze the IL phase. The analysis was carried out using an Agilent 1100 HPLC with a Shodex SH1011 column (300 8 mm from Showa Denko K. K, Japan) using a refractive index detector (RID). During the HPLC analysis, column temperature was maintained at 65 C, and the mobile phase employed was 5 mm H 2 SO 4 at a flow rate of 0.55 ml/min. Based on the measured quantities of the HMF and AMF, the yields for these compounds are defined as follows: HMF yield (mol%) = (moles of HMF in the organic and IL phases) 100/ initial moles of fructose in the IL AMF yield (mol%) = (moles of AMF in the organic and IL phases) 100/ initial moles of fructose in the IL Total furans yield (mol%) = (moles of (HMF + AMF) in the organic and IL phases) 100/ initial moles of fructose in the IL 49

65 4.3 Results and Discussion Effect of acetic acid loading on the final furan yield As noted in the Introduction, addition of acetic acid to the IL medium is expected to facilitate the in-situ esterification of HMF (produced via fructose dehydration) to AMF, thereby reducing the participation of HMF in undesirable side reactions that lead to loss of furan. Figure 4-1 shows the effect of acetic acid loading on the HMF, AMF and total furans yields. As shown in the figure, raising the acetic acid to fructose mole ratio not only affects the conversion of HMF to AMF as expected but also leads to an improvement in the total furans yield, confirming that in-situ esterification strategy mitigates the loss of HMF to side-reactions. As seen in Figure 4-1, the total furans yield goes up significantly as the acetic acid to fructose mole ratio is raised at a fixed initial fructose loading, The total furans yield reaches 80%, at an acetic acid to fructose mole ratio of 64, in contrast to the 60% yield of HMF seen in the base case with no acetic acid. In addition, most of these furans (about 80%) will be in the form of AMF, which is a more desirable starting chemical for producing furan dicraboxylic acid (FDCA). Increasing, acetic acid loading beyond a mole ratio of 64 does not lead to any additional improvement in AMF or total furans yield. Thus, the mole ratio of acetic acid to fructose of 64 is considered the optimum and was used in all the other experiments. Using stoichiometric excess of acetic acid in the reaction medium also has other advantages: acetic acid dissolves in [EMIM]Cl in all proportions forming a homogenous solution that has a much lower viscosity compared to the neat IL; consequently, not only the energy requirements for mixing are reduced but also more rapid reaction kinetics are ensured. 50

66 Also, after isolating the furans into an IL-immiscible organic solvent following the completion of the reaction, most of the acetic acid will be left behind in the IL and can be reused in subsequent runs, along with the recycled IL medium thus making the process cost effective. Figure 4-1: Effects of acetic acid loading on final furan yield; Reaction conditions: 1000 mg [EMIM]Cl 100 mg fructose, mole ratio of H 2 SO 4 to sugar:0.28, Reaction duration:6hrs, temperature:80 C H 2 SO 4 loading influence on final furan yield In general esterification reaction is conducted in presence of an acid catalyst; in addition fructose dehydration to HMF is catalyzed by an acid catalyst. Thus H 2 SO 4 is chosen as a low price acid catalyst for this study. The H 2 SO 4 loading effects on AMF and HMF yields are demonstrated in Figure 4-2. The results indicate that increasing H 2 SO 4 mole ratio to fructose mole from 0.07 to 0.28 improves the AMF yield significantly. However, further addition of H 2 SO 4 slightly decreases the total furan yield due to HMF 51

67 contribution in side reactions. Moreover, when dehydration was carried out, with no in situ esterification (data not shown), we observed about 60% yield of HMF at H 2 SO 4 to fructose mole ratio of Thus, in-situ esterification does not significantly increase H 2 SO 4 requirement. Figure 4-2: Influence of H 2 SO 4 loading on final furan yield, Reaction conditions: 1000 mg [EMIM]Cl, 100 mg fructose, mole ratio of acetic acid to sugar:64, Reaction time:6hrs, temperature:80 C Temperature effects on furan yield The one-pot fructose dehydration to HMF and its in-situ esterification to AMF have been investigated at three different temperatures (80, 100, & 117 C). The results shown in Figure 4-3 present a typical behavior of two reactions in series, in which fructose concentration rapidly decreases, HMF concentration first increases then reaches 52

68 a maximum finally decreases, and AMF concentration steadily increases. This reaction pathway is shown in Figure 4-4. Figure 4-3 a demonstrates that at the 80 C almost all of the fructose is consumed within the first thirty minutes at which time the concentration of HMF reaches its maximum. Beyond the first thirty minutes, the dominant reaction is the esterification of HMF to the AMF, as seen by the continuous drop in HMF concentration and increase in AMF concentration. The fact that the total furans (HMF + AMF) is not decreasing over this period indicates that there is no loss of furan to rehydration to levulinic acid or humins. At the end of the reaction, we are seeing a total furans yield of 80% of which almost 60% is AMF yield and the remaining is HMF yield. Comparing the total furans yield in this system with the similar case that only fructose dehydrates to HMF was conducted (see Table 4-1 run 1), indicates 20% increase in the total furan yield. That means in-situ esterification prevents HMF lost in undesired side reactions. In addition, the kinetic studies are repeated at two higher temperatures (Figure 4-3 b and c). While the kinetics, as expected, is faster, the total furans yield is slightly lower, indicating that higher temperatures are not preferred. The highest AMF yield at 100 C and 117 C are 56.5% and 54.6% respectively. Runs 2 and 3 in Table 4-1 compare the total furan yield for simultaneous dehydration and esterification with the identical cases that only dehydration were conducted at these temperature (100 C and 117 C). Results indicates that in-situ esterification raise total furan yield up 20% for these experiments. 53

69 (a) (b) 54

70 (c) Figure 4-3: Fructose, HMF and AMF content (mole % relative to initial moles of sugar) versus time at (a)80 C (b)100 C (c)117 C; Reactant :1000 mg [EMIM]Cl, 100 mg fructose, mole ratio of acetic acid to sugar:64, mole ratio of H 2 SO 4 to sugar:0.28 Figure 4-4: Reaction pathway for fructose dehydration and in-situ HMF esterification 55

71 Run Table 4.1: Comparison the total furans yield between dehydration and in-situ esterification system and only dehydration reaction (total furans yield= AMF yield + HMF yield) Time (min) Temperature ( C) Total furans yield at dehydration & in-situ esterification (mol%) * HMF yield at dehydration (mol%) ** * Reactants amount are identical with reported one in Figure 3. ** Reactants: 1000 mg [EMIM]Cl 100 mg fructose, mole ratio of H 2 SO 4 to sugar: Effect of fructose loading on final furan yield The influence of the fructose initial concentration on the AMF and HMF yields is demonstrated in Figure 4-5. The experiment with 10% fructose to IL mass ratio (referred to as the original experiment) is repeated at two other initial fructose loadings: one at half the original loading, and the other at double the initial loading. We did not observe any appreciable change in the total yield of HMF or AMF. This is an advantage of IL medium compared to aqueous phase in fructose dehydration reaction. Since increasing fructose loading from 4.5wt% to 18wt% raise losses from 20% to 35% of sugar to humins [85]. This result is in parallel with X. Qi et.al. [86] findings that in the IL media fructose initial concentration has not a negative effect on the HMF yield in the fructose dehydration reaction. 56

72 Figure 4-5: Effect of fructose loading on final furan yield, reaction conditions: 1000 mg [EMIM]Cl, mole ratio of acetic acid to sugar:64, mole ratio of H 2 SO 4 to sugar:0.28, Reaction time:6 hrs, temperature:80 C IL recycling After in-situ esterification, the furans can be completely extracted from IL medium into an organic solvent such as MIBK or THF at room temperature, and IL will be reused for next dehydration and esterification reactions. Removal of acetic acid and H 2 SO 4 from the IL medium is not necessary as they are the required components of the reaction mixture, when the IL medium is reused. In order to test this idea, first simultaneous dehydration and esterification were conducted, then furans separated from IL by MIBK, then reactions repeated with the residual IL medium for a second time. The results of these experiments presented in Figure 4-6 prove the feasibility of the IL recycling. In addition, as shown esterification of IL is not compromised in the second run. 57

73 90 80 Yield (mol%) AMF HMF Total Cycle number Figure 4-6: Reusability of [EMIM]Cl results, total yield is summation of AMF and HMF yields, reaction conditions: 1000 mg [EMIM]Cl, 100 mg fructose, mole ratio of acetic acid to sugar:64, mole ratio of H 2 SO 4 to sugar:0.28, Reaction time:6 hrs, temperature:80 C Extracting Solvent efficiency MIBK have been reported as a reaction medium in the HMF oxidation to FDA [87] and FDCA [88]. Thus in this study we also have used that as an extracting solvent despite its high normal boiling point. In addition, it is possible to use THF (normal boiling point 66 C) in order to save energy while separating and isolating AMF (normal boiling point 122 C) from reaction media and THF. The extraction efficiency of THF is 96% which is higher than 85% for MIBK (see Figure 4-7). Thus in a case that pure AMF is required, THF is more desired solvent compared to MIBK due to its better performance and low energy demand for separation. 58