Valorization of Quercus suber Bark toward Hydrocarbon Bio-Oil and 4

5 days ago - The bark as a whole possesses a lower degree of oxygenation than the heartwood. The O:C ratio of the present Quercus suber bark was measu...
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Valorization of Quercus suber bark towards hydrocarbon bio-oil and 4-ethylguaiacol Ivan Kumaniaev, and Joseph S. M. Samec ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00537 • Publication Date (Web): 30 Mar 2018 Downloaded from http://pubs.acs.org on March 31, 2018

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Valorization of Quercus suber bark towards hydrocarbon bio-oil and 4-ethylguaiacol Ivan Kumaniaev† and Joseph S. M. Samec*† * E-mail: [email protected]

Department of Organic Chemistry, Stockholm University, Svante Arrhenius väg 16C,

SE 106 91, Stockholm, Sweden KEYWORDS: suberin; hydrodeoxygenation; bark; cork; biomass

ABSTRACT: A reductive fractionation process for the valorization of Quercus suber bark towards hydrocarbons in gasoline and diesel ranges and optionally 4-ethylguaiacol has been developed. The procedure involves three steps: 1) tandem hydrogen-free Pd/C-catalyzed transfer hydrogenolysis of lignin where the carbohydrates serve as an inherent hydrogen donor under slightly alkaline conditions to also facilitate the depolymerization of suberin; 2) optional distillation, to isolate the 4-ethylguaiacol; 3) hydrodeoxygenation of the mixture from the first step by a Pt-MoO3/TiO2 catalyst generated hydrocarbons in gasoline and diesel ranges. The yield of 4-ethylguaiacol (90% purity) is 2.6% of dry bark weight (12% of acid insoluble lignin), and yield of hydrocarbon bio-oil is 42% of dry bark weight and this corresponds to a theoretical maximum yield of 77% for lignin and suberin. The carbon yield of the obtained bio-oil is thereby 64% from the total initial bark.

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INTRODUCTION. Lignocellulose is the most abundant biomass and is considered to be a potential feedstock for future biorefinery platforms1,2. Therefore, production of renewable chemicals and fuels from lignocellulose has been widely studied3. When transforming lignocellulose or other types of biomass into biofuels, the main challenge is deoxygenation since the biomass has a high oxygen content4. For lignocellulose, a range of hydrodeoxygenation procedures has been investigated, focusing on conversion of both lignin5,6 and carbohydrates7 where especially the latter has a high O:C ratio. Lignin (Scheme 1, b) is a polymer with higher oxygen content (25–30 wt%). Taking this into account, the quest for a cost-efficient transformations of lignin into a biofuel is challenging. Though a wide scope of strategies for hydrodeoxygenation of lignin-derived momomers towards alkanes and alkanols has been developed8, full conversion of lignin and its oils remains a challenge9. On the other hand, lignin derivatives formed upon partial deoxygenation and depolymerization comprise functional groups and can serve as precursors for valuable chemicals, such as pharmaceuticals or polymers10,11,12. For instance, it was recently shown that ligninderived monophenolic compounds are promising building blocks for the synthesis of sustainable polymer building blocks13,14,15. Recent findings by several groups including Rinaldi, Sels, AbuOmar, and our own have shown that employing a hydrogenolysis or transfer hydrogenolysis step in tandem to organosolv pulping, often referred to as “Lignin First Approach”, “Catalytic Fractionation”, or “Catalytic Upgrading Biorefinery” can depolymerize lignin and stabilize the resulting monophenolic compounds to prevent recondensation9,16,17,32,39. Thereby, the approach leads to both valorized carbohydrate as well as lignin streams. Another important plant tissue is bark, the external layer of stems and roots of woody plants. At the moment, bark is mainly treated as waste and burnt to produce process heat and in some

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modern paper mills to produce electricity18. However, taking into account its composition of mainly fatty acids and lignin it would be a great alternative to fossil feedstocks in the production of fuels and fine chemicals or polymer building blocks. Typically, bark contains 10–20 wt% of extractives19 (mainly triglycerides), 20–40% of suberin20, 10–20% of lignin, and 10–30% of polysaccharides21. Thereby, bark comprises high energy components (waxes, fats, and lignin) to a higher extent than the woody parts of biomass where the carbohydrates dominate. When developing a procedure that will enable bark components into biorefinery streams, attention should be given to suberin which is not present in other tissues20. Structure-wise, suberin (Scheme 1, a) is an insoluble hydrophobic aliphatic polyester. It is the major component of growing and frontier plant tissues and serves as a protective barrier, participates in damage repairing, and provides control of water loss22. Typical suberin monomers are fatty hydroxycarboxylic acids, however aromatic phenolic derivatives, mainly ferulic acid, are also found in the methanolysates23. The bonding of the suberin monomers is realized through ester bonds of the carboxylic group of one monomer by the hydroxyl group of another one. The advantage of suberin as a potential biofuel feedstock lies in its low oxygen content (10– 15 wt%). The bark as a whole possesses lower degree of oxygenation than the heartwood. The O:C ratio of the present Quercus suber bark was measured to be 0.46 (see SI, section 5), which is significantly lower than for wood (0.6–0.7)24. Thereby, bark exhibits higher energetic capacity in comparison with other types of woody biomass where the heat of bark combustion is 24 MJ·kg–1 which is significantly higher than for wood (21 MJ·kg–1)24. Furthermore, the oxygen of bark can be readily removed where processes for hydrodeoxygenation of carboxylic acids, esters, and alcohols towards hydrocarbons are well developed25 and would be easy to apply to suberin.

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O O

O

a.

O O O O

MeO O HO

O

OMe

HO OH

b.

HO O

O HO

OMe MeO

O MeO

Scheme 1. Nominal structures of suberin (a) and lignin (b). Thereby, the chemical composition of bark provides an opportunity to develop a strategy which would produce both hydrocarbons and functionalized phenols. Catalytic fractionation of bark in organosolv conditions has been reported previously18,26. These developed procedures include transformation of suberin into fatty acids but not alkanes. Herein, we report a three-step procedure for the fractionation and valorization of Quercus suber bark towards hydrocarbon oil and 4-ethylguaiacol (4-EG) (Figure 1).

Figure 1. General representation of the developed process of bark valorization.

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RESULTS AND DISCUSSION. An efficient bark fractionation requires both lignin and suberin to be depolymerized, i.e. both ether and ester linkages to be cleaved. Combining these two processes together is a challenging task since they are favored by different pH values of the reaction media. Lignin depolymerization towards monomers is known to proceed more smoothly in acidic or neutral conditions27 in which suberin cannot be hydrolyzed. On the contrary, alkaline conditions are required for suberin hydrolysis but will reduce the yield of lignin monomers and may increase the degree of lignin reassembling as recently showed for metal-catalyzed reductive depolymerization of lignocellulosic biomass27. As a starting point, we considered a tandem organosolv and palladium-catalyzed hydrogenolysis of lignin that has previously been developed in our group.28 The bark biomass was treated in a water–methanol mixture at 200 °C in neutral, acidic, or basic reaction conditions in the presence of 5% Pd/C catalyst (1:200 Pd:bark mass ratio) for 2 hours.29,28 Under these reaction conditions, the bark was delignified and the released organosolv lignin was reductively cleaved and transformed by an ingenious hydrogen donor. The carbohydrates present in bark tissue29, formates released during the pulping16, as well as solvent (MeOH)30,31,41 can serve as the sources of hydrogen which is transferred to lignin by the Pd/C catalyst. Thereby, no external hydrogen source is required in this initial transformation. In addition, MeOH has also facilitates suberin depolymerization (methanolysis is a widely used analytical procedure for suberin isolation23). The reaction conditions were optimized with respect to both depolymerization of lignin and suberin. The reaction mixture was analyzed by GC-MS in which the total ion current (TIC) ratio towards an internal standard was used to measure the relative yields of compounds. First, we focused on the lignin cleavage and performed the reactions under slightly acidic (H3PO4 2.8 g·L–

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) or neutral conditions in a standard solvent mixture MeOH–H2O 2:1 v/v was used (Figure 2, A,

B).

In both cases, lignin monomers were generated, however, no suberin hydrolysis was

observed. The solvent system was varied: using pure MeOH or MeOH–H2O 1:2 v/v in neutral conditions resulted in a lower yield of lignin monomers and almost the same negligible yield of suberin. We then switched to a basic reaction media (NaOH was added) to facilitate the hydrolysis of suberin. As expected, the yield of free fatty acids raised gradually as the concentration of the base increased from 0.9 to 6.0 g·L–1 (Figure 2, C, D, E) and the yield of lignin monomers was reduced. Nevertheless, it was decided to continue using the alkaline medium for two reasons. Firstly, it enabled us to carry out both Pd-catalyzed transfer hydrogenolysis of lignin and base-catalyzed hydrolysis of suberin in one step. Secondly, the selectivity of the reaction in alkaline media increased significantly where 4-EG could be generated in 90% purity (see SI, sections 3.2 and 6.2). This is in contrast with the results obtained in the cases of neutral or acidic media, where the selectivity towards main product 4propenylguaiacol was around 50% (GC TIC data). The loss of one carbon atom from C3 side chain of monolignolic compounds under alkaline pulping conditions has previously been reported and proceeds through an elimination of formaldehyde from a quinone methide intermediate27,32,40. However, model study of decarboxylation of ferullic acid showed that this reaction also generates 4-EG (see SI, section 10.2).

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Figure 2. Relative yields of different suberin- and lignin-derived monomeric compounds in the reaction of reductive bark depolymerization. A, acidic medium (H3PO4 2.8 g·L–1); B, neutral medium; C, D, E, alkaline media (0.9, 2.8. 6.0 g·L–1 NaOH, respectively). Under the optimized reaction conditions, the depolymerization of suberin was not complete. The two main products observed from the hydrolysis were 18-hydroxy-9-octadecenoic acid (7) and 22-hydroxydocosanoic acid (8). Other suberin monomers which were detected by the compositional analysis of bark (see SI, section 2.4), such as 20-hydroxyicosanoic acid and 24-

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hydroxytetracosanoic acid, were not observed in the reaction mixture. Therefore, the depolymerization of suberin was not complete under the employed reaction conditions and consequently some part of suberin will enter the next step of the valorization in oligomeric form. This hypothesis was confirmed with a kinetic study of the hydrodeoxygenation process (see below). Simple distillation was utilized to separate the monomeric lignin derivatives from oligomeric ones and suberin. Thus, the bio-oil obtained from the first step was subjected to distillation in Kugelrohr (150 °C, 1 mbar). 4-EG of 90% purity was obtained as a colorless liquid. The resulting yield of 4-EG was 3.0% of the hydrolysate obtained at the first step, i.e. 2.6% of initial bark weight or 12% of acid insoluble lignin (AIL). In addition to 4-EG, guaiacol and 4-propylguaiacol were other components of this fraction (Figure 3).

Figure 3. Gas chromatograms of products obtained at different steps of the process. a) Step 1: partial depolymerization, formation of monomeric phenols; a1 – alkaline, a2 – neutral media. b) Step 2: monomeric phenolic compounds obtained in b1 – alkaline and b2 – neutral media, separated by distillation. The bio-oil residue that remained after distillation contained partially depolymerized suberin, lignin oligomers, and lignin monomers. In contrast with the bark as a whole, this material

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possesses low oxygen content as the carbohydrates have been consumed in the Pd/C catalyzed transfer hydrogenolysis of the lignin polymer, and therefore can more easily undergo hydrodeoxygenation into hydrocarbons. Thus, the oil was subjected to a catalytic hydrotreatment. Pd/C and Pt/C as catalysts were initially examined but no reactivity was observed,

even

though

these

catalysts

were

found

to

be

reactive

in

the

hydrodeoxygenation/decarboxylation of model compound stearic acid into octadecane and heptadecane with ~90–100% selectivety towards the latter (see SI, section 10). Bimetallic PtMoO3/TiO2 catalyst, recently reported to be efficient for hydrodeoxygenation of carboxylic acids and esters33, was then explored. The catalyst afforded almost full deoxygenation (less than 1% of residual suberin carboxylic acids remained and full lignin conversion as shown by GC-MS) in 20 h at 350 °C. Two different hydrogen sources were tested: exogenous free hydrogen (50 bar) and formic acid of the corresponding amount, both leading to similar results. However, reactions using hydrogen gas gave better reproducibility. We found that the first step of the catalytic process is cleavage of suberin oligomers left from the alkaline pulping. The resulting monomeric fatty acids were then deoxygenated into alkanes. Kinetic experiments at 350 °C showed that these fatty acids, for instance ω-hydroxyoctadecenoic acid, were formed and accumulated in the mixture during the first hours of the reaction (Figure 4), and then these monomeric compounds were hydrodeoxygenated to yield alkanes. Since monometallic Pd and Pt catalysts did not show any reactivity, we propose that the oligoester cleavage occurs at the Lewis-acidic Mon+ sites, present in the structure of Pt-MoO3/TiO2 catalyst. These sites bond to the Lewis-basic oxygen atoms of the substrates, thus promote cleavage of ester bonds. The general mechanism studied on a variety of model oxygenated substrates was reported in the original articles by Shimizu.33,34,37,38 The necessity to apply harsh hydrotreatment

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conditions (350 °C) instead of previously reported reaction conditions for fatty acids (180–300 °C) is likely due to the presence of polyester which is necessary to cleave. Noteworthy, the PtMoO3/TiO2 catalyst was not reactive in the direct hydrotreatment of bark without an initial transfer hydrogenolysis (no monomeric products were observed). A possible explanation is that the generated fatty acids, waxes and monophenolics from step 1, serve as a carrier liquid in hydrodeoxygenation reaction.

Figure 4. Time dependence of concentrations of 4-ethylguaiacol, octadecane and ωhydroxyoctadecenoic acid in the hydrodeoxygenation reactions. Gas chromatogram of the obtained bio-oil exhibits two major regions that overlap. The first region contains signals of linear and/or slightly branched alkanes derived from fatty acids of suberin, while the second region contains signals of cyclic and unsaturated hydrocarbons derived from both lignin oligomers and suberin (Figure 5). Also, a minor region was observed, containing cyclohexanes derived from the hydrodearomatization reaction of residual lignin

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monomers. Cyclic hydrocarbons are easily distinguished form acyclic ones due to the difference of fragmentation patterns (see SI, section 7). The most abundant components of the mixture (~30 mol% according to MS TIC) are C10–C20 alkanes. 2D GC (SI, section 9) was used for a more indepth investigation of the chemical composition of the obtained bio-oil. Although only acids with even numbers of carbon atoms are present in initial suberin, the whole range of hydrocarbons C6–C27 was found among the products of the HDO reaction (Table 1). This is likely due to cracking processes, including exchange of carbocations which proceeds on the acidic sites of the catalyst. Distribution of the major components by the carbon atom number is shown in Figure 6.

Figure 5. Step 3: hydrodeoxygenation of suberin and lignin residue (material obtained in alkaline medium after distillation). Simulated distillation (Figure 7; SI, section 8) results were in accordance with 2D GC data and showed that the obtained bio-oil includes components with boiling point ranges typical for different types of hydrocarbon fuels, such as gasoline, diesel, and heavy gas oil35. Hydrocarbons of heavy gas and wax regions can be used as lubricants or cracked to yield fuel range fractions36.

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Table 1. Molar contents and average molecular formulas of the bark-derived hydrocarbon oil. Type of compounds n-alkanes iso-alkanes Cycloalkanes and alkenes Alkylbenzenes Tetralins, indans and naphtalenes Higher aromatics Others Total

Content, mol. % 32.6 12.3 25.9 7.7

Average molecular formula C16.9H35.8 C17.3H36.7 C13.8H27.6 C11.6H17.2

11.1

C11.7H14.5

4.5 5.9 100.0

C14.5H11.1O0.06 – C14.9H28.4O0.00–0.06

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Figure 6. Molar amounts of hydrocarbons with different carbon atom numbers in the obtained bio-oil, according to 2D GC data.

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Figure 7. Simulated distillation curve for the obtained bio-oil. The starting material (bark) and the product of the first stage was subjected to elemental analysis (SI, section 5) while the elemental composition of the final product (hydrocarbon bio-oil) was determined according to the 2D GC data (SI, section 9). H:C ratio (Figure 7) changes throughout the process, from 1.47 for dry bark to, 1.51 for the depolymerized bark (stage 1), 1.56 for the distillated residue (stage 2), and 1.90 for the hydrogenated oil (stage 3). The O:C ratio changes substantially from 0.46 for bark to 0.26–0.30 for the products of the first and the second stages, and then to less than 0.004 for the hydrocarbon bio-oil. The higher heating value (HHV) of such a fuel is estimated to 46–49 MJ·kg–1 (see SI, section 5). The elemental analysis data show that 64% of bark carbon atoms are included in the obtained hydrocarbon oil (yield of hydrocarbon oil is 42% of dry bark weight or 77% of the sum of lignin and suberin contents). It should be noted that some of the energy from the carbohydrates is conserved in the lignin oil.

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Figure 8. Van Krevelen plot representing the changes of the elemental composition of the material throughout the process. CONCLUSIONS: We have demonstrated a three-step process of bark fractionation and valorization towards monomeric phenolic compounds and hydrocarbons. Lignin was converted into 4-ethylguaiacol with high selectivity (90%). Due to the high degree of functionalization, this product can serve as a synthetic precursor for valuable compounds. Moreover, lignin also provided a range of cyclic hydrocarbons, while suberin was transformed into a range of acyclic hydrocarbons. The obtained hydrocarbon bio-oil was characterized with GC-MS, 2D GC, and simulated distillation methods. The product has the average molecular formula of C14.9H28.4O0.00– 0.06

and the yield of valorized products is 42% of the initial bark weight and this corresponds to

64% carbon yield, which is 77% of the sum of lignin and suberin. The carbohydrate part is partially conserved as it serves as hydrogen equivalents in the transfer hydrogenolysis of lignin

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in the first step. Therefore, bark has a good potential as a renewable feedstock for the production of chemicals and fuels.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: Experimental details for the procedures of valorization and analysis of the feedstock, NMR and MS spectra, 2D GC data, elemental analysis data (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID Joseph S. M. Samec: 0000-0001-8735-5397 Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS We acknowledge the Swedish Energy Agency for financial support.

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Chimie, 2017, 20, 1006–1016. DOI: 10.1016/j.crci.2017.10.005 (15)

Francois, C.; Pourchet, S.; Boni, G.; Fontaine, S.; Gaillard, Y.; Placet, V.; Galkin, M. V.;

Orebom, A.; Samec, J.; Plasseraud, L. Diglycidylether of iso-eugenol: a suitable lignin-derived synthon

for

epoxy

thermoset

applications,

RSC

Advances,

2016, 6, 68732–68738.

DOI: 10.1039/C6RA15200G (16)

Galkin, M.V.; Samec, J.S.M. Lignin Valorization through Catalytic Lignocellulose

Fractionation: A Fundamental Platform for the Future Biorefinery. ChemSusChem 2016, 9, 1544–1558. DOI: 10.1002/cssc.201600237 (17)

Renders, T.; Van den Bosch, S.; Koelewijn, S.-F.; Schutyser, W.; Sels, B.F. Lignin-first

biomass fractionation: the advent of active stabilisation strategies. Energy Environ. Sci., 2017, 10, 1551–1557. DOI: 10.1039/C7EE01298E (18)

Koumba-Yoya, G.; Stevanovic, T. Transformation of Sugar Maple Bark through

Catalytic Organosolv Pulping. Catalysts 2017, 7, 294. DOI: 10.3390/catal7100294 (19)

Schreiber, L.; Franke, R.; Hartmann, K. Wax and suberin development of native and

wound periderm of potato (Solanum tuberosum L.) and its relation to peridermal transpiration. Planta 2005, 220, 520–530. DOI: 10.1007/s00425-004-1364-9 (20)

Graça, J. Suberin: the biopolyester at the frontier of plants. Front. Chem. 2015, 3, 62.

DOI: 10.3389/fchem.2015.00062

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Sen, A.; Zhianski, M.; Glushkova, M.; Petkova, K.; Ferreira, J.; Pereira, H. Chemical

composition and cellular structure of corks from Quercus suber trees planted in Bulgaria and Turkey. Wood Sci. Technol. 2016, 50, 1261–1276. DOI: 10.1007/s00226-016-0836-y (22)

Vishwanath, S.J.; Delude, C.; Domergue, F.; Rowland, O. Suberin: biosynthesis,

regulation, and polymer assembly of a protective extracellular barrier. Plant Cell Reports 2015, 34, 573–586. DOI: 10.1007/s00299-014-1727-z (23)

Karnaouri, A.; Lange, H.; Crestini, C.; Rova, U.; Christakopoulos, P. Chemoenzymatic

Fractionation and Characterization of Pretreated Birch Outer Bark. ACS Sustainable Chem. Eng. 2016, 4, 5289–5302. DOI: 10.1021/acssuschemeng.6b01204 (24)

Rossi, A. Progress in Biomass Converstion, chapter 2 – Fuel Characteristics of Wood and

Nonwood Biomass Fuels (Eds.: David A. Tillman, Edwin C. Jahn), Academic Press 1984, p. 92. (25)

Murzin, D.Yu.; Mäki-Arvela, P. Catalytic Deoxygenation of Fatty Acids and their

Derivatives for the Production of Renewable Diesel. Chapter 19 (Ed.: M. Crocker), Thermochemical Conversion of Biomass to Liquid Fuels and Chemicals; The Royal Society of Chemistry 2011, pp. 496–510. DOI: 10.1039/9781849732260 (26)

Garrett, M.D.; Bennett, S.C.; Hardacre, C.; Patrick, R.; Sheldrake, G.N. New methods in

biomass depolymerisation: catalytic hydrogenolysis of barks. RSC Adv., 2013, 3, 21552–21557. DOI: 10.1039/C3RA44382E (27)

Renders, T.; Schutyser, W.; Bosch, S. Van den; Koelewijn, S.-F.; Vangeel, T.; Courtin,

C.M.; Sels, B.F. Influence of Acidic (H3PO4) and Alkaline (NaOH) Additives on the Catalytic Reductive Fractionation of Lignocellulose. ACS Catal. 2016, 6, 2055–2066. DOI: 10.1021/acscatal.5b02906

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Galkin, M. V.; Samec, J. S. M. Selective Route to 2-Propenyl Aryls Directly from Wood

by a Tandem Organosolv and Palladium-Catalysed Transfer Hydrogenolysis. ChemSusChem 2014, 7, 2154–2158. DOI: 10.1002/cssc.201402017 (29)

Kumaniaev, I.; Subbotina, E.; Sävmarker, J.; Larhed, M.; Galkin, M.V.; Samec, J.S.M.

Lignin depolymerization to monophenolic compounds in a flow-through system. Green Chem. 2017, 19, 5767–5771. DOI: 10.1039/c7gc02731a (30)

Rousu, P.; Rousu, P.; Anttila, J. Resources. Sustainable pulp production from agricultural

waste. Conservation and Recycling 2002, 35, 85–103. DOI: 10.1016/S0921-3449(01)00124-0 (31)

Galkin, M.V.; Samec, J.S.M. Lignin Valorization through Catalytic Lignocellulose

Fractionation: A Fundamental Platform for the Future Biorefinery. ChemSusChem 2016, 9, 1544–1558. DOI: 10.1002/cssc.201600237 (32)

Schutyser, W.; Renders, T.; Van den Bosch, S.; Koelewijn, S.-F.; Beckham, G.T.; Sels,

B.F. Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading. Chem. Soc. Rev. 2018, 47, 852–908. DOI: 10.1039/C7CS00566K (33)

Kon, K.; Toyao, T.; Onodera, W.; Siddiki, S.M.A.H.; Shimizu, K. Hydrodeoxygenation

of Fatty Acids, Triglycerides, and Ketones to Liquid Alkanes by a Pt–MoOx/TiO2 Catalyst. ChemCatChem 2017, 9, 2822–2827. DOI: 10.1002/cctc.201700219 (34)

Kon, K.; Onodera, W.; Takakusagi, S.; Shimizu, K. Hydrodeoxygenation of fatty acids

and triglycerides by Pt-loaded Nb2O5 catalysts. Catal. Sci. Technol. 2014, 4, 3705–3712. DOI: 10.1039/C4CY00757C (35)

Riazi, M.R. Characterization and Properties of Petroleum Fractions. ASTM manual series

MNL50 2005, p. 8.

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Alam, M.S.; Zeraati-Rezaei, S.; Stark, C.P.; Liang, Z.; Xu, H.; Harrison, R.M. The

characterisation of diesel exhaust particles – composition, size distribution and partitioning. Faraday Discuss. 2016, 189, 69–84. DOI: 10.1039/C5FD00185D (37)

Touchy, A.S.; Hakim Siddiki, S.M.A.; Onodera, W.; Kon, K.; Shimizu, K.

Hydrodeoxygenation of sulfoxides to sulfides by a Pt and MoOx co-loaded TiO2 catalyst. Green Chem. 2016, 18, 2554–2560. DOI: 10.1039/C5GC02806J (38)

Touchy, A.S.; Hakim Siddiki, S.M.A.; Kon, K.; Shimizu, K. Heterogeneous Pt Catalysts

for Reductive Amination of Levulinic Acid to Pyrrolidones. ACS Catal. 2014, 4, 3045–3050. DOI: 10.1021/cs500757k. (39)

Luo, H.; Klein, I.M.; Jiang, Y.; Zhu, H.; Liu, B.; Kenttämaa, H.I.; Abu-Omar, M.M.

Total Utilization of Miscanthus Biomass, Lignin and Carbohydrates, Using Earth Abundant Nickel Catalyst. ACS Sustainable Chem. Eng. 2016, 4, 2316−2322. DOI: 10.1021/cs500757k (40)

Loubinoux, B.; Heitz, M.; Coudert, G.; Guillaumet, G. Hydrogenolysis of lignins: nickel

boride catalyst. Tetrahedron lett. 1980, 21, 4991–4994. DOI: 10.1016/S0040-4039(00)71174-9 (41)

Song, Q.; Wang, F.; Cai, J.; Yehong, W.; Zhang, J.; Yu, W.; Xu, J. Lignin

depolymerization (LDP) in alcohol over nickel-based catalysts via a fragmentation– hydrogenolysis process. Energy Environ. Sci. 2013, 6, 994–1007. DOI: 10.1039/C2EE23741E

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ACS Sustainable Chemistry & Engineering

For Table of Contents Use Only Synopsis: In this work, we describe a procedure of tree bark valorization for producing hydrocarbons which are currently derived from fossil sources, and also valuable phenolic compounds.

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