Valorisation of Lignocellulosic Waste and the Potential for Supercritical Water and Wet Air Oxidation Part 1

Transcription

1 Queens University Belfast Valorisation of Lignocellulosic Waste and the Potential for Supercritical Water and Wet Air Oxidation Part 1 Dr Gary Sheldrake School of Chemistry and Chemical Engineering Queen s University Belfast Workshop Technology Foresight Conference, Cologne University of Applied Sciences, Campus Gummersbach, April 23rd to 25th 2013

2 This Presentation This is a two part presentation from Queen s University Belfast on the recovery of value from Tree Bark Part 1: Valorisation of Lignocellulosic Waste Added value chemicals from the catalytic processing of tree bark Part 2: Supercritical Water and Wet Air Oxidation of tree bark + + = 2

3 The Biorefinery Dream? 3

4 The reality..?..or the reality? The challenge for renewable fuels / chemicals is to resolve the tension between crops and chemicals by greater utilisation of waste biomass 4

5 Forestry and Wood Industries Up to 60% of felled timber is left in the forest to rot and nearly 50% of the harvested timber is wasted as sawdust and offcuts, particularly bark, twigs and small branches An increasing amount of the waste is being pelletised for biofuel but still low in percentage terms Ca. 50 Mt lignin/lignosulfonate is produced globally as a by product of wood pulping Much of this lignin is discarded or used for low tech applications such as low grade fuel and cement binders Wood bark contains varying amounts of suberin a potential source of ω functionalised fatty acids among others 5

6 Why Tree Bark? Tree Bark has several biological functions including: ridding the tree of wastes by absorbing and locking them into dead cells and resins; phloem transport of nutrients throughout the tree; providing a water resistant coating preventing ingress of pathogens. But bark is a waste by product of the wood processing industry Bark contains several components of potential value for processing to chemical intermediates Suberin Lignin Carbohydrates 6

7 The Challenge of Lignin Challenging, complex polymeric structure Currently a waste product or at best low value material Potential source of aromatic fine chemicals for a sustainable chemical industry Some current industrial precedence via oxidative depolymerisation to vanillin Extensive literature but mostly >30 years old so potential for new catalytic approaches 7

8 Lignin hydrogenolysis source comparison Substrate Catalyst Total organic yield Wood chips Rh/C 23 % Ru/C, NaOH 12 % Rh/C, NaOH 10 % No catalyst 4 5 % Rh/C 1 2 % Wood chips Lignosulfonate Wood chips Organosolve lignin Typical conditions: 40 bar H2, 200 C, 50 % aqueous dioxane solvent 3 g substrate, 0.5 g catalyst (5% metal loading) The greater the extent of biomass processing to separate lignin from other biopolymers, the lower the conversion to isolable products. Lignin becomes progressively more cross-linked and intractable under chemical treatment conditions 8

9 Suberin Suberin: Natural aliphatic aromatic cross linked polymer 9

10 Bark processing Grinding to 200 μm Suberin Cat. hydrogenolysis + other ligno cellulosic material Extraction Fatty Acids + Aromatics CH3 (CH2)X CH2 CH2 CO2H HOCH2 (CH2)X CH2 CH2 CO2H Tree bark waste from wood industry HO2C CH2 (CH2)X CH2 CO2H Examples of products isolated from suberin processing R OMe OH 10

11 Catalytic hydrogenolysis of barks at QUB 3 barks chosen: Bark species % suberin* % lignin Spruce <10 ~25 Sycamore 26 ~25 Cork 40 ~25 *literature figures Klason analysis Previous research at QUB on the hydrogenolysis of wood showed Rh/C and Pd/C to be the most active catalysts for lignin hydrogenolysis Initial work has demonstrated the possibility of releasing aromatic products from lignin like sections of suberin and lignin itself as well as aliphatic fatty acids/alcohols from the suberin polyesters Prototype laboratory scale conditions: powdered bark 3 g, catalyst 0.5 g, 200 C, 4 hr, dioxane/water, 40 Bar H2 11

12 Hydrogenolysis of wood and bark Mass balance Reaction mixture Mass Balance by Wt Filtered solid Organic extract Aqueous extract Cellular water Klason analysis of the filtered solid shows 30 50% of the starting lignin may still be present and not depolymerised The intractable solids, containing residual lignin as well as metal catalyst, and the aqueous, largely carbohydrate containing fraction from the extraction currently constitute two waste by products which require valorisation to make the process economically viable 12

13 The Objectives of This Investigative Work From Catalytic Chemical Processing To investigate precious metal catalytic processing of tree bark waste to deliver high added value organic products To investigate the solid and aqueous waste streams from this process for further treatment Or to bypass the catalytic chemical processing and treat the bark biomass with WAO and / or SCWO directly or integrate the two into a single process stream 13

14 Questions for Workshop Why Tree bark? Forestry by product of low current economic value: could it be used for something of more value? The current prototype process is a biphasic heterogeneous reaction in aqueous dioxane. Can we find a better co solvent (or no co solvent)? The focus for the current project has been on isolation of aromatic and fatty acid products: is there more value to be obtained from the aqueous phase of the process before further treatment? E.g. sugars? Will it be possible to develop an integrated process combining the chemical catalytic steps with the WAO / SCWO? Analytical challenges: product analysis from the depolymerisation reactions is complex. Some expertise in QUB but elsewhere as well? 14

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16 Queens University Belfast Valorisation of Lignocellulosic Waste and the Potential for Supercritical Water and Wet Air Oxidation Workshop - Technology Foresight Conference, Cologne University of Applied Science Campus Gummersbach, April 23rd to 25th 2013

17 Part 2 Supercritical Water and Wet Air Oxidation of tree bark + + = 17

18 Overview of Currently Proposed Process A catalytic / chemical process on tree bark leaving a lignocellusioc material, followed by a Wet Air and / or a Supercritical Water Oxidation process (WAO and SCWO) 18

19 The Waste for WAO and / or SCWO The waste to be processed by WAO and / or SCWO is the liquid and solid Lignocellulosic material by-products of the catalytic / chemical treatment of bark Bark itself and intermediate compounds between bark and Lignocellulosic may also be processed by WAO and SCWO at specific pressures and temperatures in or approaching these conditions Lignocellulosic contains aromatics, carbohydrates and fatty acids and we seek to recover the catalyst metals and potentially small organics plus other in the WAO and / or SCWO processes 19

20 The Objectives of the Investigative Work From WAO and / or SCWO To investigate the use of WAO and SCWO in terms of the operating regions to determine what and how efficiently can be recovered from the bark / Lignocellulosic waste Supercritical pressure and temperatures Subcritical pressure with supercritical temperatures Two phase region To potentially investigate other wet air oxidation and supercritical oxidation media other than water CO2? 20

21 Properties of Water for WAO and SCWO Pressure / Enthalpy Diagram for water 220 BAR 374 C SUPERCRITICAL 21

22 Properties of Water for WAO Subcritical Liquid water is a polar solvent at subcritical conditions Dipole dipole molecular attraction Helping molecules form ions, dissolving in solution Water will react chemically in the hydrolysis of carbohydrates, esters, etc reducing the polymer sizes Polar components of biomass will dissolve and react in WAO If metal retained from chemical processing may assist in catalytic WAO reactions 22

23 Properties of Water for SCWO Supercritical Supercritical water behaves more like a non polar solvent at supercritical conditions due to the density decrease or molecular proximity weakening dipole to dipole bonding As a result, non-polar compounds such as most hydrocarbons including the non polar components of biomass and gases (e.g., O2, N2) are more soluble in supercritical water and polar compounds such as inorganic salts are insoluble in supercritical water and precipitate out of solution A complete reversal of water s sub critical behaviour 23

24 WAO and SCWO What are they? Both WAO and SCWO use water and oxygen as a medium to promote the solubility of materials to facilitate the oxidation of organic compounds. SCWO results in total oxidation to CO2 water and energy, WAO is incomplete and leaves small orgnaics Water also provides a uniform thermal environment that provides stable conditions that facilitiates specific and controllable reactions 24

25 WAO and SCWO What are they? SCWO was developed to destroy hazardeous compounds such as nerve agents as it gives complete oxidation There is significnat interest in SCWO and is an obvious choice for aqueous waste with water already there 25

26 WAO and SCWO What are they? WAO being at lower temperatures has much lower reaction rates, lower solubility and lower transport properties giving slower less complete reactions Catalyst are often used to assist WAO SCWO has % complete oxidation reactions with organic compounds to water and carbon dioxide With SCWO precious metals are precipitated as metal oxides which is a more easily handled form for re-processing 26

27 The Main Problems with SCWO SCWO has advantages over WAO in terms of reaction rate and the completeness of the reaction It has great potential on its own or after as WAO process as will be investigated in this research work The problems with SCWO are related to High Pressures with high temperatures presents a significnat engineering challenge Precipitataion of salts in the process can block pipes Acids and electrolytic corrosion destroying the reactor 27

28 A Generic SCWO Plant Layout Generic SCWO plant 28

29 The Potential of WAO and SCWO in Processing Tree Bark Water in WAO or SCWO provides a mechanisms and a medium that stabilises and facilitates control of reaction conditions Given this, WAO and SCWO at specific pressure, temperature and concentration conditions, with the possible addition of other reactants, have the potential to facilitate a series of controlled extraction processes for value products from tree bark QUB will map the WAO and SCWO operating regions and investing tree bark and tree bark derivative reactions with various applied reactants 29

30 QUB Batch tester High Pressure Batch Reactor with Laminar Flame Speed, Internal Condition and Sample Analysis Experimental Capability Main Specification Maximum operating pressure: 270 bar Maximum vessel temperature: C (to be confirmed) Internal diameter: 175 mm Volume: 2.8 litres Required bolt load: 2 MN (200 tonnes) (approximately) Ports and Instrumentation 1 absolute WC pressure transducer 1 dynamic WC pressure transducer 2 thermocouples 2 ionisation probes 2 spark igniter probes 2 top inlet ports 1 top sampling/exhaust port 1 top burst disc 1 base sampling/drain ports 30

31 Questions for Workshop Why water? green, clean, cheap and abundant Why not water bar and 374 C are difficult to reach and maintain Is there any other medium other than water? Analysis of product streams, who, when and where? 31

32 Additional Information 32

33 Properties of Water Water Solvation or density properties Most supercritical fluids have a density (or solvating power) closer to that of a liquid but mass transport properties (such as viscosity and diffusivity) closer to that of a gas Non Polar behaviour And at 250 bar 33

34 Properties of Water Liquid water is a polar solvent at subcritical conditions Dipole dipole molecular attraction Helping molecules form ions, dissolving in solution Polar Salt dissolved in water 34