Chapter One - Catalytic valorization of biomass and bioplatforms to chemicals through deoxygenation

https://doi.org/10.1016/bs.acat.2020.09.002Get rights and content

Abstract

Catalytic valorization of biomass as a renewable resource into building-block chemicals or synthetic intermediates would contribute to establishing a sustainable chemical industry. Because of the high oxygen content in lignocellulosic biomass, it is necessary to develop methods and systems to remove specific oxygen atoms selectively from the biomass or biomass-derived platform compounds (bioplatforms) to produce value-added chemicals that can be directly used in the chemical industry. This review highlights advances in the past decade in the catalytic valorization of biomass and bioplatforms to a variety of chemicals by deoxygenation. Emphases are put on the selective cleavage of specific C–O bonds of cellulose, the most abundant component in lignocellulosic biomass, furanic and phenolic compounds that can be derived from hemicellulose and lignin to form ethanol, adipic acid, 1,6-hexanediol, methyl furan, dimethyl furan, p-xylene and arene products. Since multiple C–OH bonds exist in biomass and bioplatforms, this review analyzes different strategies that can be exploited to remove one or more –OH groups to offer ethanol or adipic acid. Furanic compounds have both C–O–C bonds in furan ring and C–OH/C = O bonds connected to the ring, and thus the cleavage of different C–O bonds can lead to either linear or aromatic products. The methods and catalytic systems for the transformations of furanic compounds such as 5-hydroxymethylfurfural and furfural to 1,6-hexanediol, methyl furan, dimethyl furan and p-xylene are summarized. The deoxygenation of lignin-derived phenolic compounds to arene products by hydrogenolysis is briefly described. This review also highlights recent advances in understanding the reaction mechanisms for deoxygenation of biomass and bioplatforms. Key factors determining the product selectivity as well as activity will also be discussed.

Introduction

Sustainable production of chemicals and fuels from renewable and abundant resources would contribute to alleviating the energy and environmental issues caused by over-consumption of fossil resources. As an important renewable carbon resource in nature, lignocellulosic biomass may serve as a feedstock to replace fossil resources, in particular petroleum, to produce a wide range of chemicals 1, 2, 3, 4, 5, 6. Unlike petroleum, lignocellulosic biomass is an over-oxygenated feedstock with oxygen content of ~ 40% in weight percentage (7), and thus the catalytic transformation of biomass should be quite different from the petroleum refinery. In petrochemical industry, hydrocarbons, the major component of petroleum, generally require selective oxidation or other types of functionalization to gain functional groups, forming a variety of basic chemicals. In contrast, the partial deoxygenation of excess oxygen atoms from biomass plays crucial roles in the biomass utilization. As a consequence, catalyst requirements and catalytic mechanisms for biomass transformations would be distinct from that in conventional petroleum refinery. However, because of the complex structure of lignocellulosic biomass, it is challenging to precisely remove specific oxygen-containing groups for the synthesis of target products.

Lignocellulosic biomass is composed of cellulose (35–50%), hemicellulose (25–30%), and lignin (15–30%) 8, 9. Cellulose consists of d-glucose units connected through linkage of β-1,4-glycosidic bonds (Fig. 1). Such a linkage facilitates the formation of side-by-side arrangement of glucose units in a chain-like manner, which generates extensive intramolecular hydrogen bonding networks between the hydroxyl groups nearby the glycosidic bonds. These hydrogen bonds make the crystalline structure of cellulose highly robust, and hence the depolymerization of cellulose becomes difficult under mild conditions. Hemicellulose is a macro-polymer consisting of different sugar units including hexoses (e.g., glucose, mannose, galactose, and rhamnose) and pentoses (e.g., xylose and arabinose). In particular, xylose constitutes the dominant component in hemicellulose (10). Although these sugar units are linked with glycosidic bonds, their nonuniform feature makes hemicellulose an amorphous and highly branched polymer (Fig. 1). Compared to cellulose, the crystallinity of hemicellulose is much lower. Consequently, the reactivity of hemicellulose is significantly higher than that of cellulose (10). Lignin is a cross-linked aromatic biopolymer consisting of methoxylated phenylpropane units (Fig. 1) 11, 12. Although the exact structure of lignin is not determined, three primary monomers in lignin have been identified as p-coumaryl, coniferyl and sinapyl alcohols. The relative abundance of these monomers varies depending on the origin of biomass. For example, coniferyl alcohols accounts for about 90% in softwood, whereas roughly equal proportions of coniferyl alcohol and sinapyl alcohol exist in hardwood (12). These monomers are linked by various C–O bonds and C–C bonds. In typical lignocellulosic biomass, cellulose and hemicellulose are encapsulated in a lignin shelter and fixed by hydrogen bonds and covalent bonds.

To utilize the whole lignocellulosic biomass in a single process, there are two thermochemical strategies based on the breaking of biomass into mixtures of small molecules prior to producing value-added chemicals or fuels. The one is the high-temperature (973–1473 K) gasification of lignocellulosic biomass to produce syngas (a mixture of CO and H2) 13, 14, 15, which is a versatile platform for the production of chemicals or hydrocarbon fuels via Fischer-Tropsch synthesis (16). The other is the fast pyrolysis or thermal liquefication aiming at converting biomass into liquid products such as bio-oils, which are composed of a complex mixture of condensable oxygenates such as acids, furanic and phenolic compounds 15, 17, 18, 19. Due to the low quality and complex compositions of these mixed compounds, they need further separation and upgrading to be applied to transport fuels or chemical production. As compared to the direct gasification and pyrolysis or liquefication, independent transformation of cellulose, hemicellulose, lignin or their derivatives is more attractive because target products with high selectivity can be achieved. Furthermore, many strategies for isolation of the three components from lignocellulosic biomass have been established, making their independent conversions feasible (12). For example, acid-hydrolysis of biomass can readily separate hemicellulose from cellulose and lignin by producing soluble C5 and C6 sugars in high yields (10). After simple filtration, both cellulose and lignin could be recovered as solid residues. In the pulp and paper industries, kraft and sulfite pulping processes are usually employed to separate cellulose from lignin. In the former process, lignin is depolymerized by a large amount of aqueous sodium hydroxide and sodium sulfide, leaving cellulose almost intact. The later process is generally performed by using salts of sulfurous acid (sulfites or bi-sulfites) of diverse cations (sodium, potassium, calcium or magnesium) as pulping chemicals. Moreover, an effective approach using sequential combination of organic acid (e.g., oxalic acid) and base (e.g., tetramethylammonium hydroxide) hydrolysis has been developed to convert lignocellulosic biomass 20, 21, 22, 23, 24. The treatment with oxalic acid leads to the partial hydrolysis of cellulose to sugars and furanic compounds, and generates amorphous-like structure in the remained cellulose, making its further conversion much easier. The sequential base-treatment readily facilitates the hydrolysis of remained cellulose, and moreover, depolymerizes lignin to phenolic compounds 20, 21.

Additionally, the use of organic solvents as fractionation agents provides another effective approach for isolation of cellulose and lignin. After the organosolv treatment by alcohols or alcohol/water mixtures, cellulose solid is separated by filtration, whereas lignin can be recovered from the reaction media by evaporation or precipitation by antisolvents 10, 25. Recently, lignin-first fractionation, that is, the catalytic valorization of native lignin in biomass in the first step, has emerged as another new strategy to utilize the entire lignocellulosic biomass in a more efficient manner 26, 27, 28, 29, 30. In this process, lignin can be mostly depolymerized into aromatic monomers without considerably modifying the aryl rings or forming undesirable re-polymerized oligomers, which are commonly generated in the kraft and sulfite pulping processes. As a result, lignin monomers, cellulose and hemicellulose sustain their original forms during fractionation, and each component can be selectively transformed into various target products according to their structure features.

Because cellulose, hemicellulose and lignin are different in composition and structures, the development of appropriate catalytic systems holds the key to the deoxygenation of each component into value-added chemicals. The cleavage of specific C–O bonds is a common and crucial step for the deoxygenation of all these components and their derivatives. For cellulose, the hydrogenolysis-promoted cleavage of one C–OH bond and two C–C bonds inside the glucose unit is able to directly convert cellulose into ethanol. When two or more C–OH groups are selectively cleaved via deoxygendehydration, cellulose or the derived sugar acids such as mucic acid and glucaric acid, can be transformed to industrially important monomers such as adipic acid (Fig. 1). Moreover, 5-hydroxymethylfurfural (HMF), a key bioplatform from the hydrolysis/dehydration of cellulose (31), may undergo different catalytic deoxygenation to form a series of chemicals. For instance, hydrogenolysis of C–OH and C = O bonds leads to the formation of dimethyl furfural, while selective cleavage of C–O–C bonds in the furan ring gives linear products such as 1,6-hexanediol (1,6-HD). If Diels-Alder reaction is coupled with dehydration, the furan ring oxygen can be removed from HMF or related furan compounds to form arene products such as p-xylene (PX). For hemicellulose, the high reactivity makes it considerably easier to be transformed into monosaccharides such as xylose via acid-catalyzed hydrolysis (10). Further hydration of xylose produces furfural (31), which has similar structure and properties to HMF and can also be employed as a bioplatform to produce chemicals via deoxygenation. In the case of lignin, the linkage of C–O bonds can be cleaved by hydrolysis, hydrogenolysis, pyrolysis, oxidation and hydrotreating, providing various phenolic compounds as the main products (12). Due to the high reactivity, in particular those produced under pyrolysis or hydrotreating conditions, these phenolic products have high tendency to undergo further side reactions, leading to low selectivity of aromatic compounds (12). Accordingly, much effort has been devoted to breaking down certain C–O bonds (e.g., Caryl–OH and Caryl–OCH3) to upgrade these compounds to value-added arene compounds (Fig. 1).

In the past decade, significant advances have been achieved in the catalytic transformations of cellulose, hemicellulose and lignin into value-added chemicals and fuels. Although a number of elegant review articles have summarized the developments of catalytic systems for these transformations 12, 28, 29, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, less attention has been paid to the selective deoxygenation of oxygen atoms from the biomass or their bioplatforms 45, 46, 47, 48. In this chapter, we provide a review on recent advances in the catalytic deoxygenation of cellulose/hemicellulose, the derived furan compounds and lignin-derived phenolic compounds into value-added chemicals via selective cleavage of specific C–O bonds. Emphases are placed on the key factors that determine the catalytic performance. The reaction mechanisms are also discussed to understand in-depth the activation and cleavage of C–O bonds in these compounds. We hope that such accumulated knowledge on the selective deoxygenation will be helpful to the development of more efficient catalytic systems for future biomass valorization.

Section snippets

Hydrogenolysis

Hydrogenolysis can cleave carbon-carbon or carbon-heteroatom single bonds by hydrogen and has been extensively applied to hydrotreating in conventional petroleum refineries to remove sulfur, nitrogen, and oxygen heteroatoms from hydrocarbons or for hydrocarbon cracking (49). Hydrogenolysis has also become an efficient approach for the transformation of biomass to a broad range of chemicals such as polyols (50), furan derivatives (51), and alkanes (52). This section mainly focuses on the

Advances in the deoxygenation of furanic compounds

Furfural and 5-hydroxymethylfurfural (HMF) are two typical furanic compounds that can be produced by hydrolysis/dehydration of hemicellulose and cellulose, respectively. Both of them have a furan ring linked with a carbonyl group, and in addition, HMF contains one more hydroxymethyl group. Because of those functional groups, furfural and HMF can serve as versatile platforms for production of value-added chemicals and fuels. For example, many other furanic compounds such as furfural alcohol,

Advances in the deoxygenation of phenolic compounds

Lignin is a phenolic macromolecule composed of three major monomers, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, which are linked by various C–O and C–C bonds. To obtain aromatics from lignin requires cleaving the C–O and C–C linkages while keeping the benzene ring intact. Chemical approaches such as pyrolysis, oxidation and hydrotreating have been developed for depolymerization of lignin, providing a complex pool of oxygen-containing phenolic compounds 12, 189, 190. The product

Concluding remarks and future perspectives

Sustainable production of chemicals and fuels from lignocellulosic biomass as a renewable feedstock has become a field of extensive research in the past decades. Due to the presence of high oxygen contents in lignocellulosic biomass, it is necessary to selectively remove some oxygen atoms through hydrogenolysis or deoxydehydration methods, wherein hydrogen generally serves as a reducing agent. The catalyst which is capable of activating hydrogen has been developed to catalyze the

Acknowledgments

Financial support from the National Key R&D program of China (No. 218YFB1501602) and the National Natural Science Foundation of China (Nos. 21690082 and 91545203) is gratefully acknowledged.

Longfei Yan received his BSc degree from the Northeast Forestry University in June 2015 and received his MSc degree from the Harbin Institute of Technology in June 2017. He is pursuing his Ph.D. in Prof. Ye Wang's group. His research interests is catalytic transformation of biomass.

References (308)

  • S. Li et al.

    J. Energy Chem.

    (2019)
  • J. Kopyscinski et al.

    Fuel

    (2010)
  • M. Balat et al.

    Energ. Conver. Manage.

    (2009)
  • S. Pang

    Biotechnol. Adv.

    (2019)
  • K. Cheng et al.

    Adv. Catal.

    (2017)
  • A.V. Bridgwater et al.

    Renew. Sustain. Energy Rev.

    (2000)
  • M. Balat et al.

    Energ. Conver. Manage.

    (2009)
  • X. Hu et al.

    J. Energy Chem.

    (2019)
  • S. Jin et al.

    Biomass Bioenergy

    (2020)
  • L. Penín et al.

    Bioresour. Technol.

    (2020)
  • M. Yabushita et al.

    Appl. Catal. Environ.

    (2014)
  • Y. Jing et al.

    Chem

    (2019)
  • J. Ma et al.

    J. Energy Chem.

    (2019)
  • M. Yang et al.

    Joule

    (2019)
  • M.A. Vuurman et al.

    J. Mol. Catal.

    (1992)
  • G.W. Huber et al.

    Chem. Rev.

    (2006)
  • Y. Lin et al.

    Energ. Environ. Sci.

    (2009)
  • D.M. Alonso et al.

    Chem. Soc. Rev.

    (2012)
  • S. Santoro et al.

    Green Chem.

    (2017)
  • S. Li et al.

    ChemSusChem

    (2018)
  • L.T. Mika et al.

    Chem. Rev.

    (2018)
  • R. Rinaldi et al.

    ChemSusChem

    (2009)
  • B.M. Upton et al.

    Chem. Rev.

    (2016)
  • P. Mäki-Arvela et al.

    Chem. Rev.

    (2011)
  • A.J. Ragauskas et al.

    Science

    (2014)
  • J. Zakzeski et al.

    Chem. Rev.

    (2010)
  • U. Wongsiriwan et al.

    Energy Fuel

    (2010)
  • Y. Noda et al.

    Energy Fuel

    (2012)
  • T.V. Stein et al.

    Green Chem.

    (2010)
  • J. Wang et al.

    Green Chem.

    (2015)
  • M.V. Galkin et al.

    ChemSusChem

    (2016)
  • T. Renders et al.

    Energ. Environ. Sci.

    (2017)
  • Z. Sun et al.

    Chem. Rev.

    (2018)
  • W. Schutyser et al.

    Chem. Soc. Rev.

    (2018)
  • X. Wu et al.

    Nat. Catal.

    (2018)
  • C. Xu et al.

    Chem. Soc. Rev.

    (2020)
  • A. Corma et al.

    Chem. Rev.

    (2007)
  • C.H. Zhou et al.

    Chem. Soc. Rev.

    (2011)
  • R.A. Sheldon

    Green Chem.

    (2014)
  • C. Li et al.

    Chem. Rev.

    (2015)
  • Z. Zhang et al.

    Chem. Rev.

    (2017)
  • M. Wang et al.

    ACS Catal.

    (2018)
  • P. Sudarsanam et al.

    Chem. Soc. Rev.

    (2018)
  • M. Wang et al.

    Adv. Mater.

    (2019)
  • T. Ren et al.

    ChemCatChem

    (2019)
  • S.S. Wong et al.

    Chem. Soc. Rev.

    (2020)
  • M. Shiramizu et al.

    Angew. Chem. Int. Ed.

    (2012)
  • K.A. Rogers et al.

    ChemSusChem

    (2016)
  • S. Kim et al.

    Green Chem.

    (2019)
  • J. Zhang et al.

    Green Chem.

    (2020)
  • Cited by (0)

    Longfei Yan received his BSc degree from the Northeast Forestry University in June 2015 and received his MSc degree from the Harbin Institute of Technology in June 2017. He is pursuing his Ph.D. in Prof. Ye Wang's group. His research interests is catalytic transformation of biomass.

    Qihui Zhang received his BSc degree from the Fuzhou University. He is pursuing his Master degree in Prof. Ye Wang's group. His research interest is catalytic transformation of biomass.

    Dr. Weiping Deng obtained his PhD degree from Xiamen University in 2009. He joined Xiamen University as engineer of the National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters in 2010. He became assistant professor in the College of Chemistry and Chemical Engineering in 2015 and was promoted to associate professor in 2018. His research interest focuses on biomass transformation catalysis.

    Prof. Qinghong Zhang received her BS and MSc degrees from Nanjing University, and obtained her PhD degree from Hiroshima University of Japan in 2002. She joined Xiamen University as an associate professor in October of 2002 and was promoted to full professor in 2010. Her research interests include the synthesis, characterization and catalytic applications of novel catalytic materials for C1 and sustainable chemistry.

    Prof. Ye Wang received his BS degree from Nanjing University and obtained his PhD degree in 1996 from Tokyo Institute of Technology. He then worked at Tokyo Institute of Technology, Tohoku University and Hiroshima University, and was promoted to associate professor at Hiroshima University in 2001. He became full professor of Xiamen University in August 2001. He serves as associate editor of ACS Catalysis and council member of International Association of Catalysis Societies. The research interest of Prof. Ye Wang's group is catalysis for C1 and sustainable chemistry, including C–O/C–C cleavage chemistry for cellulose/lignin valorization, C–H activation and C–C coupling of C1 molecules.

    View full text