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1 Electronic Supplementary Material (ESI) for Green Chemistry. This journal is The Royal Society of Chemistry 2019 AROMATICS FROM LIGNIN THROUGH ULTRAFAST REACTIONS IN WATER. Nerea Abad-Fernández a, Eduardo Pérez b and María José Cocero a* a Bioeconomy research Institute BioeEcoUva. Research group High Pressure Processes. EII, Sede Mergelina, Universidad de Valladolid, Valladolid, Spain. * mjcocero@iq.uva.es b Bioeconomy research Institute BioeEcoUva. Research Group TERMOCAL, Thermodynamics and Calibration, EII, Paseo del Cauce 59, Universidad de Valladolid, Valladolid, Spain. Supporting Information 1. Calculations For calculating yields of the fractions, %Y i, the following equation is used: Ci % Yi 100 C Lg Where C i and C Lg are the concentration of the fraction i obtained and of lignin in the reactor respectively, expressed in g/l. Analogously, the yield of the monomers %Y x, present in the light oil is referred to the total amount of lignin loaded and calculated as: oil Cx X x Coil oil % Y X Y C C x x oil Lg Lg Where C x is the concentration of the monomer x in the product mixture and X oil x is the mass fraction of the monomer x in the light oil. 2. Fractionation of depolymerization products Product mixture was acidified by adding concentrated H 2 SO 4 dropwise until the solution reached ph=2. The water-insoluble solids precipitate and a brown suspension is formed. After centrifugation, the supernatant was carefully recovered by a pipette and the wet solid was washed with acidified water at ph=2. After washing, the solid fraction was extracted with ethyl acetate and centrifuged, obtaining solution of a solid extract and a solid residue. The solvent was evaporated and the remaining material was dried, weighted and labeled as heavy oil. The solid residue was dried, weighed and labeled as char. The aqueous fraction (L) was extracted with ethyl acetate to give an aqueous extract and the 1

2 aqueous residue. The solvent was evaporated from the aqueous extract, this fraction was dried, weighed and labeled as light oil. Finally, the water was removed from the aqueous residue, weighed and labeled as aqueous residue. The fractionation of the products obtained from the process performed in neutral medium (without NaOH addition) was identical, except no acidification was needed to precipitate the solid. Due to the small amount of solid obtained, the ethyl acetate extraction was not performed to this fraction. Figure S1. Separation sequence for product fractionation after lignin depolymerization. 3. Characterization procedures 3.1. GC-MS analysis of the oil fractions Compounds were detected by a gas chromatograph equipped with a quadrupole mass spectrometer detector (5977A-Agilent Technologies, USA). Data of the chromatographic separations were acquired using a capillary column HP-5ms, 30 m x mm x 0.25 μm (Agilent Technologies, USA). The equipment was in splitless mode. The oven temperature was programmed as follows: initial temperature was set at 32 ºC and kept for 10 min, then temperature was raised to 52 ºC at 2ºC/min, and kept for 2 min; to 65ºC at 2ºC/min, and kept for 2 min; to 93ºC at 4ºC/min, and kept for 2 min; to 230ºC at 2ºC/min and kept for 3 min; and finally, to 300ºC at 15ºC/min, and kept for 3 min. This oven ramp was chosen after several runs as the best option to obtain clear chromatograms with a good separation between peaks. To eliminate the acquisition of the solvent (acetone) by the MS, a solvent delay was programed at 3.70 minutes after confirming that no compounds were removed with the solvent. For compound identification, the data 2

3 obtained in the GC-MS analysis were compared with m/z values compiled in the spectrum library Wiley. Data analysis was performed using the Agilent Mass Hunter software (Agilent Technologies, USA). Validation of compound identification was carried out by comparison of their MS spectra and their retention times with standards. Quantification was carried out employing the internal standard method. With this calibration method, the peak area of each compound was normalized to the peak area of the internal standard. Some calibration curves are represented in Figure S2. Figure S2. Calibration curves for guaiacol, vanillin and syringol using the internal standard method for GC-MS Other analytical techniques Gel Permeation Chromatography (GPC) The molecular weight distribution of the different samples was determined by gel permeation chromatography (GPC) with a Jordi Gel Sulphonated Plus Å 250 x 10 mm column and using a Waters IR detector 2414 (210 nm) and a Waters dual λ absorbance detector 2487 (254 nm). The column was operated at 35 ºC. The mobile phase was a solution water:methanol 90:10 vol, adjusted to ph = 12 at a flow rate of 1 ml/min. Samples were dissolved directly in the eluent with concentration between 2 and 6 mg/ml The injection volume was 25 µl. Further details can be found in reference 2. 3

4 Micro-elemental analysis CHNS LECO CHNS-932 and VTF-900 analyzer equipped with an automatic sampler with capacity for 50 samples and an ultra-microbalance SARTORIUS M2P (precision ± mg). Proportion of each element was corrected to exclude the moisture according to the following equations: 0 % C % C % moist. 0 2 % H % moist. % 18 H % moist. moist. 0 % S % S % % C, % H, % S are the corrected percentages for C, H and S respectively; % C0, % H0, % 0 S are the nominal percentages. % moist. is the percentage of moisture Fourier Transform Infrared Spectroscopy (FT-IR) The equipment used for FT-IR analysis of lignin and char was a Bruker Tensor 27. The spectra are recorded in mode Attenuated Total Reflection (ATR). The base line was corrected, and the peaks were normalized to the area between 1393 and 1816 cm -1 (aromatic skeletal vibration) Thermo Gravimetrical Analysis (TGA) TGA analysis were carried out in a TGA/SDTA RSI analyzer of Mettler Toledo. Samples of approximately 5 mg were heated at a rate of 20 ºC/min under N 2 atmosphere (60 ml/min flow) from a temperature of 50 ºC up to temperatures around 850 ºC. Keeping a constant temperature of 850ºC, air was flowing during 5 min with a flow of 60 ml/min. Content of moisture was determined from TGA traces as the mass loss within temperature up to 120 ºC. The amounts measured were very low: 4.4% for Kraft lignin and an average of % for the hydrochar. The values for the rest of the fractions 4

5 were not determined but they should be of the same order of magnitude according to the FTIR traces (see Figure S10) NMR NMR spectra were collected using an Agilent DD2 500 instrument equipped with cryoprobe, operating at MHz for 1 H and at MHz for 13 C. 4. Additional results 4.1. Yield for the different fractions Figure S3 shows a comparison between the light oil yield obtained with NaOH and without catalyst. The maximum in yield appear at similar reaction times but the magnitude is significantly higher. Figure S3. Yield of light oil vs reaction time at 386 ºC comparison between using NaOH and without catalyst. Figure S3 shows the yield of light oil and solid fractions at 300 ºC. The minimum in yield of solid fractions is displaced to around 2500 ms, nearly matching the maximum in light oil, as it happened at 386 ºC. This fact suggests that the reactions involved are somewhat related. 5

6 Figure S4. Yield of light oil (red) and solid fractions (black) vs reaction time at 300 ºC in absence of catalyst. The shape of the curve of solid fraction yield along with that of figure 1 in the main article, agree with the hypothesis of a very rapid initial reaction that yields a solid fraction (not necessarily recondensed fragments). At 300 ºC, kinetics are slowed enough to appreciate the evolution of this first reaction as there is a certain tendency starting from zero solid yield at t = 0 up to 500 ms Yield of monomers Figure S5. Yield of the different monomers identified in the light oil. Figure S5 shows the yield of the monomers identified in the light oil obtained from kraft lignin depolymerization at 386 ºC using NaOH as catalyst. The monomers are obtained simultaneously and they reach a maximum at 300 ms. 6

7 A closer examination of the GC-MS data utilized to quantify the monomers obtained revealed one unknown peak that appeared at a retention time of 58.5 s. The area is maxima at a reaction time of 109 ms. The MS spectra shows one parent peak at m/z = 177 with some minor peaks at 1. This could be an aldehyde at m/z = 178 as it is known that the MS spectra of the latter presents M and M-1 peaks and a major daughter ion at m/z=149 (M-29) characteristic of a -cleavage. Figure S6. a) Evolution of the area of the GC-MS peak at retention time 58.5 min. b) Chromatogram of aromatic oil at 109 ms and MS spectrum of the peak at 58.5 min Molecular weight of depolymerized products Figure S7 (left) shows the normalized GPC chromatogram for kraft lignin and some hydrochars obtained at different times. Retention time of the maxima increases (i.e. the molecular weight decreases) with reaction time up to 240 ms, being those hydrochars lighter than the original lignin. At 300 ms, the hydrochar reaches the molecular weight of lignin, indicating that the repolymerization starts in this point. Above 300 ms, the retention time of the maxima decreases with time, so the molecular weight of the hydrochar increases, indicating that the repolymerization continues. In figure S7 (right) the same information than in figure S7 (left) can be observed, where the retention time of the maxima of hydrochars at different reaction times is represented with the respective reaction time. In this figure the affirmations done above can be seen clearly. 7

8 Figure S8 shows the GPC traces for the hydrochar, light oil and heavy oil obtained after fractionation for the reactions of kraft lignin at 240 and 348 ms, times right before and after of the repolymerization starting (300 ms). These graphs are shown just to see clearly how the moment right before to the repolymerization, the hydrochar is lighter than lignin, but in the moment right after to the repolymerization, the hydrochar is already heavier than lignin. Moreover, it is possible to see that at 240 ms, heavy oil is slightly heavier than light oil, but at 348 ms, LO has oligomers slightly heavier than HO, in addition to monomers as at 240 ms. Figure S9 shows the GPC traces for the fractions obtained in the black liquor (left) and Kraft-BL (right) depolymerization at 300 ms and 386 ºC with NaOH as catalyst. Kraft lignin obtained from the black liquor has a molecular weight distribution slightly heavier than black liquor itself. That may be because the isolation procedure introduces further modification to the molecules of lignin leading to a certain degree of association. When the fractions are analyzed separately, their molecular weight distribution is very different. Hydrochar molecules are heavier than the rest of the fractions and the molecular weight distribution homogeneous as the peaks are sharp and the maxima appear at the same retention time. The peaks for the heavy and light oils are however different and depends on the starting material. The main difference observed is that the heavy oil for the black liquor is lighter than the light oil so terms should be redefined in this case. It is possible that the fractionation is affected by the presence of other ionic species dissolved. It is also important to notice that the fact that the hydrochar obtained from black liquor and kraft-bl depolymerization at 300 ms is heavier that the original lignin and it doesn t have the same molecular weight as in the case of kraft lignin from Sigma can be due to kraft-sigma lignin is the heaviest lignin used in this study. Thus, it is probable that the repolymerization of black liquor and kraft-bl, which are lighter lignins, starts before than 300 ms. 8

9 Figure S7. Left: GPC traces for hydrochars obtained at different reaction times from kraft lignin depolymerization in alkaline SCW (386 ºC); Right: Curve of the retention times at which the 254 nm signal is maximum for the hydrochars at different reaction times vs the respective reaction time. The dotted line represents the retention time of maximum UV signal for kraft lignin. Figure S8. GPC traces for the fractions obtained after depolymerization of kraft lignin at 240 ms (left) and 348 ms (right). LO is light oil and HO is heavy oil. Figure S9. GPC traces for the fractions obtained after depolymerization of lignins from Técnicas Reunidas at 300 ms in alkaline SCW (386 ºC). Left: black liquor; Right: kraft-bl lignin. 9

10 4.4. Characterization of the structure of the fractions FT-IR and TGA Figure S10 shows the FTIR spectra of some fractions obtained from the depolymerization of kraft lignin. The aqueous residue has a very similar spectra that the original lignin indicating that this fraction is composed essentially by non-depolymerized kraft lignin. Light oil and hydrochar present some differences in the structure compared to kraft lignin, particularly in the region of C-O bonds whose signals appear within 1000 and 1300 cm -1. Also carbonyl groups ( cm -1 ) are present in these fractions. Small peaks are present between 800 and 900 cm-1 in hydrochar revealing the presence of C=C double bonds. The aromatic structure remains unaltered during SCW treatment because the region between 400 and 1650 cm -1 does not change significantly. None of the samples seem to contain a significant proportion of water because the band H-O-H bending (1635 cm -1 ) is not too intense. Figure S10. FTIR spectra for some samples obtained from depolymerization of kraft lignin (black). Aqueous residue (red, 150 ms no NaOH); light oil (magenta, 110 ms, No NAOH); hydrochar (blue, 296 ms, NaOH). Figure S11 show TGA and FT-IR analysis done to the hydrochar at 386 ºC and different reaction times. A clear change of tendency is observed at times higher than 296 ms. TGA derivative traces indicate that for higher reaction times the material is more stable because decomposition peaks at higher temperatures are appearing. FTIR also indicates a change in the C-O bond vibrations. 10

11 Figure S11. Analysis of the hydrochar fraction obtained at 386 ºC in alkaline conditions, at different reaction times. a) TGA; b) FT-IR D HMBC NMR 2D NMR Heteronuclear Multiple Bond Correlation (HMBC) technique detects 13 C- 1 H coupling trough three or four covalent bonds. It was used to provide additional evidence of loss of aliphatic hydroxy groups. Figure S8 show the HMBC spectra for the region of R 1 R 2 CH-O protons for kraft lignin and the hydrochar obtained at 62 ms. A large signal can be appreciated at ca. H= ppm; C= ppm for both spectra, characteristic of the methoxy groups of the aromatic units. In the spectra of lignin, however, additional smaller signals appear, which are likely to correspond to protons attached to C, C and/or C of the aliphatic backbone. These signals have disappeared upon SCW treatment. Figure S12. HMBC spectra for the region of R 1 R 2 CH-O protons for a) kraft lignin and b) hydrochar obtained at 62 ms. 11

12 5. Proposed mechanisms for the production of vanillin and acetovanillone. Figure S13 depicts a scheme of some proposed reaction routes to generate vanillin and acetovanillone from a typical lignin moiety during SCW depolymerization via radicalary mechanisms. The starting species would be generated by H-abstraction (Figure 5) on different parts of the aliphatic sidechain. They would proceed to vanillin or acetovanillone through reactions analogous to glycerol decomposition in SCW. Figure S13. Possible routes for the generation of vanillin or acetovanillone via radicalary mechanisms. 12