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Lignin is a promising biopolymer to serve as a sustainable resource for a multitude of applications (e.g., thermoset materials, production of bulk chemicals) thereby substituting fossil-based carbon sources. In this work, the reductive depolymerization of Kraft lignin (KL) was studied in ethanol/water aided by formic acid (FA) as the way forward to valorize lignin. The effect of various process conditions was elucidated using P-31-NMR, pH, GPC, CHNSO, GC-MS and 2D-LC analyses. It is found that the addition of a small amount of FA (3.6 vol%) is beneficial for obtaining smaller lignin fragments with more phenolic OH (PhOH) functionalities upon depolymerization at 250 degrees C for 8 h. Besides, a higher FA concentration causes acid catalyzed lignin repolymerization and a longer reaction time results in only a limited reduction in molecular weight of the obtained lignin fragments. The addition of a supported Pd catalyst leads to a more pronounced depolymerization (smaller lignin fragments with more PhOH functionalities) as well as a stronger decrease in oxygen and sulfur content. Furthermore, several experiments and multiple analysis techniques support the hypothesis that FA acts as H-2 donor under the investigated conditions in this study. In conclusion, KL (M-W similar to 16,436 g mol(-1) and 3.31 mmol g(-1) PhOH) was successfully depolymerized into a low molecular weight lignin (M-W similar to 3250 g mol(-1)) with more PhOH functionalities (5.29 mmol g(-1)).

The inherent reactivity of lignin in conventional biomass processing commonly prevents isolation of native lignin and limits monomer yields from catalytic depolymerization strategies that target aryl-ether bonds. Here we show that flow-through solvolysis with methanol at 225 °C produces native-like lignin from poplar, enabling the study of intrinsic lignin properties and evaluation of steady-state lignin depolymerization processes.

The utilization of lignin and glyoxal as potentially sustainable and less hazardous building blocks for phenolic resins is an emerging research field. Lignin thereby serves as a partial, macromolecular substitute for phenol, while glyoxal fulfills the role of an aldehyde cross-linker. In the first part of this perspective, the industrial context of lignin and glyoxal will be expounded with a focus on their origin and production processes. In the framework of phenolic resins, the use of lignin and glyoxal can be categorized into two research domains: (i) glyoxalation to improve the reactivity of lignin prior to resin synthesis and (ii) direct resin synthesis using lignin and glyoxal with glyoxal immediately serving as the cross-linker. This perspective provides a comprehensive overview of the progress made in both domains, pinpointing the opportunities, blind spots, and challenges that lay ahead.

Lignin is a potential non-fossil resource of diverse functionalized phenolic units. The most important lignin-derived monomers are 4-alkylphenols, 4-hydroxybenzaldehydes, 4-hydroxybenzoic acids, and 4-hydroxycinnamic acids/esters. Efficient transformation of lignin and/or its monomers into valuable aromatics and their derivatives is crucial, not only for a sustainable lignocellulose biorefinery, but also to reduce our dependence on fossil feedstocks. This review provides a concise account of the recent advances in lignocellulose fractionation/lignin depolymerization processes towards lignin-derived monomers. Subsequently, numerous potential atom-efficient catalytic routes for upgrading lignin monomers into drop-in chemicals and new polymer building blocks are discussed.

In-depth structural analysis of biorefined lignin is imperative to understand its physicochemical properties, essential for its efficient valorization to renewable materials and chemicals. Up to now, research on Reductive Catalytic Fractionation (RCF) of lignocellulose biomass, an emerging biorefinery technology, has strongly focused on the formation, separation and quantitative analysis of the abundant lignin-derived phenolic monomers. However, detailed structural information on the linkages in RCF lignin oligomers, constituting up to 50 wt% of RCF lignin, and their quantification, is currently lacking. This study discloses new detailed insights into the pine wood RCF lignin oil's molecular structure through the combination of fractionation and systematic analysis, resulting in the first assignment of the major RCF-derived structural units in the 1H–13C HSQC NMR spectrum of the RCF oligomers. Specifically, β-5 γ-OH, β-5 ethyl, β-1 γ-OH, β-1 ethyl, β-β 2x γ-OH, β-β THF, and 5-5 inter-unit linkages were assigned unambiguously, resulting in the quantification of over 80% of the lignin inter-unit linkages and end-units. Detailed inspection of the native lignin inter-unit linkages and their conversion reveals the occurring hydrogenolysis chemistry and the unambiguous proof of absence of lignin fragment condensation during proper RCF processing. Overall, the study offers an advanced analytical toolbox for future RCF lignin conversion and lignin structural analysis research, and valuable insights for lignin oil valorization purposes., In-depth structural analysis of pine wood RCF lignin discloses new detailed insights into the RCF lignin oil's molecular structure.

Every twig and splinter used Plant-based production of commodity chemicals faces steep competition from fossil resources, which are often cheaper and easier to partition. Sustainable use of renewable resources requires strategies for converting complex and recalcitrant biomolecules into streams of chemicals with extraordinary efficiency. Liao et al. developed a biorefinery concept in which wood is eventually fully converted into useful chemicals: phenol, propylene, pulp amenable to ethanol production, and phenolic oligomers that can be incorporated into ink production (see the Perspective by Zhang). A life-cycle assessment and techno-economic analysis highlight the efficiency of the process and reveal the potential for such biorefinery strategies to contribute to sustainable chemicals markets. Science , this issue p. 1385 ; see also p. 1305

Correction for ‘Flow-through solvolysis enables production of native-like lignin from biomass’ by David G. Brandner et al., Green Chem., 2021, 23, 5437–5441, DOI: 10.1039/D1GC01591E.

Reductive catalytic fractionation (RCF) of lignocellulose is an emerging biorefinery scheme that combines biomass fractionation with lignin depolymerisation. Central to this scheme is the integration of heterogeneous catalysis, which overcomes the tendency of lignin to repolymerise. Ultimately, this leads to a low-Mw lignin oil comprising a handful of lignin-derived monophenolics in close-to-theoretical yield, as well as a carbohydrate pulp. Both product streams are considered to be valuable resources for the bio-based chemical industry. This Opinion article sheds light on recently achieved milestones and consequent research opportunities. More specifically, mechanistic studies have established a general understanding of the elementary RCF steps, which include (i) lignin extraction, (ii) solvolytic and catalytic depolymerisation and (iii) stabilisation. This insight forms the foundation for recently developed flow-through RCF. Compared to traditional batch, flow-through RCF has the advantage of (i) separating the solvolytic steps from the catalytic steps and (ii) being a semi-continuous process; both of which are beneficial for research purposes and for industrial operation. Although RCF has originally been developed for 'virgin' biomass, researchers have just begun to explore alternative feedstocks. Low-value biomass sources such as agricultural residues, waste wood and bark, are cheap and abundant but are also often more complex. On the other side of the feedstock spectrum are high-value bio-engineered crops, specifically tailored for biorefinery purposes. Advantageous for RCF are feedstocks designed to (i) increase the total monomer yield, (ii) extract lignin more easily, and/or (iii) yield unconventional, high-value products (e.g. alkylated catechols derived from C-lignin). Taking a look at the bigger picture, this Opinion article highlights the multidisciplinary nature of RCF. Collaborative efforts involving chemists, reactor engineers, bioengineers and biologists working closer together are, therefore, strongly encouraged. ispartof: Current Opinion In Biotechnology vol:56 pages:193-201 ispartof: location:England status: published

Herein, we present a full lignocellulose-to-chemicals valorization chain, wherein low molecular weight and highly functional lignin oligomers, obtained from reductive catalytic fractionation (RCF) of pine wood, were used to fully replace bisphenol A (BPA) for synthesizing bio-based epoxy resins.

© 2018, The Author(s), under exclusive licence to Springer Nature Limited. There is an urgent need to address environmental problems caused by our transportation systems, which include the reduction of associated CO2 emissions. In the short term, renewable drop-in fuels are ideal, as they allow a direct integration into the existing infrastructure. However, preferably they would perform better than current alternatives (for example, bioethanol) and be synthesized in a more efficient way. Here we demonstrate the production of biogasoline with a direct upstream integration into processes in existing petrorefinery facilities that targets the 10% bio-based carbon in accordance with the current European Union directives (for 2020) for biofuels. To achieve this goal, we show the valorization of (hemi)cellulose pulp into light naphtha using a two-phase (H2O:organic) catalytic slurry process. A C5–C6 alkane stream, enriched with bio-derived carbon and compatible with further downstream petrorefinery operations for (bio)gasoline production, is automatically obtained by utilizing fossil light straight run naphtha as the organic phase. The ease of integration pleads for a joint petro/bio effort to gradually produce bio-enriched gasolines, wherein the chemical compounds of the bio-derived fraction are indistinguishable from those in current high-quality gasoline compositions. ispartof: Nature Energy vol:3 issue:11 pages:969-977 status: published

A full lignin-to-chemicals valorisation chain – from hardwood over bissyringols to aromatic polyesters (APEs) – is established for renewable 4-n-propylsyringol (PS), the main product from catalytic hydrogenolysis of (native) hardwood lignin. To do so, reagent-grade PS was produced from birch wood via reductive catalytic fractionation (RCF) and isolated in 34 wt% yield on lignin basis. Additional early-stage theoretical calculations, based on both relative volatility (α) and distillation resistance (Ω) as well as Aspen Plus® simulations, predict that the isolation of PS by means of distillation is economically feasible at industrial scales ($85–95 per ton of propylphenolics at 200–400 kt a−1 scale). Subsequent stoichiometric acid-catalysed condensation with formaldehyde unveils a remarkably high 92 wt% selectivity towards the dimer 3,3′-methylenebis(4-n-propylsyringol) (m,m′-BSF-4P), which is isolated in >99% purity by facile single-step crystallisation. The striking dimer selectivity is ascribed to the synergetic interplay between the activating methoxy groups and the oligomerisation-inhibiting propyl chain. Next, an in vitro human oestrogen receptor α (hERα) assay was performed to ensure safe(r) chemical design. The bissyringyl scaffold displays reduced potency (∼19–45-times lower affinity than bisphenol A) and lower efficacy (∼36–45% of BPA's maximum activity). Lastly, to assess the functionality of the safe(r) bissyringol scaffold, it was converted into an APE. The APE displays a Mw = 43.0 kDa, Mn = 24.4 kDa, Tg = 157 °C and Td,5% = 345 °C. In short, (i) the feasibility and scalability of the feedstock, (ii) the simplified process conditions, (iii) the reduced in vitro oestrogenicity, and (iv) the functionality towards polymerisation, make this bissyringol a renewable and potentially benign bisphenol replacement, capable for production at bulk scale.

© 2018 The Royal Society of Chemistry. Lignocellulose constitutes an alluring renewable feedstock for the production of bio-based chemicals. In this contribution, we propose a chemocatalytic biorefinery concept that aims to convert lignocellulosic biomass (Eucalyptus sawdust) into (i) lignin-derived (mono)phenolics, (ii) hemicellulose-derived polyols, and (iii) a cellulose pulp. This is achieved by processing biomass in an equivolumetric mixture of n-butanol and water at elevated temperature (200 °C), in the presence of Ru/C and pressurised hydrogen (30 bar). During this one-pot Reductive Catalytic Fractionation (RCF) process, the hot liquor enables the extraction and solvolytic depolymerisation of both lignin and hemicellulose, while the catalyst and reductive environment are essential to hydrogenate reactive intermediates (coniferyl/sinapyl alcohol and sugars) toward stable target products (phenolics and polyols, respectively). After the catalytic reaction, the solid carbohydrate pulp (mainly cellulose) is easily retrieved upon filtration. Phase separation of n-butanol and water occurs upon cooling the liquor (

Bisguaiacol F (BGF), a potentially safer and renewable bisphenol A (BPA) replacement made from lignin-derivable vanillyl alcohol (p-VA), is a promising building block for future aromatic biopolymers. Unfortunately, like BPA synthesis, this electrophilic condensation reaction is also prone to regioselectivity issues, giving rise to m,p′- and o,p′-BGF byproducts. In this work, the hitherto unconsidered influence of m,p′-BGF, viz. the main isomeric byproduct of p,p′-BGF synthesis, on the physicochemical properties of poly(BGF carbonate) (BGF-PC) was systematically investigated by random copolymerisation with different fractions of pure m,p′-BGF (25, 50 and 75 wt%). To do so, the elusive m,p′-isomer was made in unparalleled regioselectivity (72%) by alkylation condensation of isovanillyl alcohol (m-VA) with guaiacol. Surprisingly, no isomeric scrambling due to acid-catalysed isomerisation was encountered for pure BGF isomers, which strongly facilitates their synthesis in contrast to petrochemical bisphenol F (BPF). Furthermore, to ensure safer chemical design, an in vitro human oestrogen receptor α (hERα) transactivation assay was performed. Both pure m,p′- and p,p′-BGF displayed a significantly reduced oestrogenic potency (∼426–457 times lower affinity than BPA) and oestrogenic efficacy (∼39–50% of BPA's maximum induction). Interestingly, mutual comparison between p,p′-BPF and p,p′-BGF reveals and proves for the first time the direct link between ortho-methoxy substitution and reduced in vitro oestrogenic activity (for transactivation of hERα). In contrast to o,p′-BPA, viz. the main byproduct of p,p′-BPA synthesis, m,p′-BGF was proven suitable for utilization in thermoplastics, thereby avoiding time-consuming and labour-intensive (re)crystallizations to obtain regioisomerically pure p,p′-BGF.

Tree bark is a major waste stream from the wood processing industries, and thus an alluring feedstock for biorefineries. This contribution explores a catalytic biorefining strategy for black locust (Robinia pseudoacacia) bark. In this Reductive Catalytic Fractionation (RCF) strategy, bark is processed in methanol at elevated temperatures (200–250 °C) in the presence of a heterogeneous hydrogenation catalyst (e.g. Ru/C) and pressurized hydrogen. This enables the (partial) extraction and solvolytic depolymerization of lignin, suberin and hemicellulose which are present in bark. The formed lignin intermediates are effectively stabilized via catalytic hydrogenation, thereby avoiding repolymerization reactions and thus enabling the formation of a highly depolymerized lignin fraction. RCF of black locust bark results in a solid phase (mainly cellulose and residual lignin) and a process liquor. The soluble products were further separated via liquid/liquid extraction into an aqueous phase, containing glycerol and carbohydrate derivatives, and an organic phase, containing phenolic mono-, di- and oligomers as well as suberin-derived, long-chain aliphatic monomers (mainly α,ω-dimethyl esters and ω-OH methyl esters, next to alkanols and methyl esters). A comparison with black locust wood (hardwood) was made, highlighting the presence of suberin and the more condensed lignin structure in bark. Furthermore, this contribution examines the effect of various process parameters (e.g. temperature, reaction time, catalyst type and loading) on the extraction and depolymerization of lignin and suberin polymers. Finally, a heptane extraction was executed on the bark oil (i.e. dried organic phase) as a proof-of-concept separation of the suberin-derived aliphatics on one hand and the lignin phenolics on the other.

Reductive catalytic fractionation (RCF) of lignocellulosic biomass is a promising lignin-first biorefinery strategy that yields nearly theoretical amounts of phenolic monomers by performing solvolytic delignification and lignin depolymerization in presence of a reducing catalyst, here Ni-Al2O3. This contribution attempts to elucidate the precise role of the catalyst, with respect to lignin solubilization, depolymerization and stabilization. The presented experiments unambiguously show that the solvent, under the applied conditions (methanol at 523 K), is largely responsible for both the initial release of lignin fragments from the lignocellulose matrix and their further depolymerization to shorter phenolics. The catalyst is merely responsible for the hydrogenation of reactive unsaturated side-chains in the solubilized lignin intermediates, leading to the formation of stable phenolic monomers and short oligomers. This catalytic reduction essentially prevents undesirable repolymerization reactions towards a condensed (high MW) lignin product. Since a solid–solid interaction between catalyst and wood is not required for the stabilization of soluble lignin products, the use of catalyst pellets (confined in a reactor basket) as a means to facilitate catalyst recuperation and clean pulp production, is justified. After optimizing the process with regard to mass transfer limitations, above 90% delignification of birch wood is achieved, producing a lignin oil that contains over 40% phenolic monomers, of which 70% consists of 4-n-propanolguaiacol and -syringol. In addition, multiple catalyst recycling experiments are successfully performed. Catalyst fouling is appointed as a primary cause of deactivation, though catalytic activity can be fully restored by thermal H2-treatment. Simple filtration of the reaction mixture finally affords a catalyst-free and delignified pulp, containing most of the initial cellulose and hemicellulose (93% glucose and 83% xylose retention). This pulp is converted into bio-ethanol, through simultaneous saccharification (accelerase trio enzyme mix) and fermentation (GSE16-T18-HAA1* yeast). A first and unprecedented trial led to a 73% bio-ethanol yield.

The production of amines from biomass is a growing field of interest. Particularly the amination of bio-based alcohols receives a lot of attention. In this review, we discuss recent progress in the development of efficient heterogeneous catalysts. The substrate scope for the production of bio-based amines is not limited to (hemi)cellulosic alcohols. Other platform chemicals that originate from different biomass fractions, such as lignin, oils, chitin and protein, are also suitable feedstock for the production of amines. This comprehensive review first provides an overview of the available bio-based feedstock candidates. The following section is devoted to the sustainable reaction routes that are available to carry out the desired amination reactions. Next, state-of-the-art technologies are summarized for each substrate class, focussing on heterogeneous catalysis. Special attention is dedicated to the sustainability of the discussed reaction routes. Finally, a critical discussion is provided, together with current challenges and future perspectives regarding the industrial production of bio-based amine chemicals.

The selective reductive catalytic depolymerisation of softwood lignin (e.g. pine, spruce) yields predominantly 4-n-propylguaiacol (4PG; 15–20 wt% on lignin basis), an interesting platform chemical for bio-based chemistry. This contribution specifically shows promising technical, sustainable and environmental advantages of such a bio-phenol for various polymer applications. The bisphenolic polymer precursor, 5,5′-methylenebis(4-n-propylguaiacol) (m,m′-BGF-4P), was therefore first synthesized by acid-catalysed condensation, and its synthesis and isolation are compared with shorter chain analogs, viz. 4-methyl- and 4-ethylguaiacol. A thorough GC-GPC/SEC analysis of the crude condensation mixture was developed to assess the purity of the isolated dimers. Isolation is done by a single-step crystallization, yielding 57 wt% of m,m′-BGF-4P in >99% purity. This pure m,m′-BGF-4P bisphenol displays a notably reduced potency to activate human estrogen receptor alpha (hERα; EC50 at 10−5 M) in comparison with commercial bisphenols, and is therefore useful for future polymer applications. As a proof of concept, polycarbonates and cyanate ester resins were prepared from m,m′-BGF-4P and compared to other bisphenols. The polycarbonate had Mn = 5182 g mol−1, Tg = 99 °C, Tm = 213 °C, Td,5% = 360 °C, and displayed improved processability in common solvents, as opposed to the methylated and ethylated bisguaiacols. A fully cured resin disk exhibited a Tg = 193 °C, Td,5% = 389 °C and a water uptake of only 1.18% after being immersed in 85 °C water for four days. These results underscore the potential of the intrinsic functionality of lignin-derived building blocks to transcend the scope of renewability.

During the past decade, a growing scientific community is eagerly seeking for effective lignin valorisation approaches. Thought-out utilisation of the world's most abundant resource of bio-aromatics could substantially augment the profitability of future lignocellulosic biorefineries. From a multitude of complementary valorisation opportunities (e.g., composite materials, dispersants, carbon fibres), harnessing lignin as renewable feedstock for chemicals forms an alluring challenge. However, a root cause that hampers its full exploitation, is an historically grown and deeply ingrained (mis)conception, stating that lignin is merely considered as a subordinate opportunity to derive some extra added-value, without being of primary concern. Unfortunately, this mind-set doesn't reckon with the fact that lignin is prone to irreversible degradation, leading to recalcitrant condensed structures which are difficult to disassemble into a handful of chemicals. In response, new biorefinery schemes are being developed, wherein the valorisation of lignin is regarded as one of the primary targets. At the heart of these alternative biorefineries are fractionation strategies that aim to prevent structural lignin degradation, hereby enabling an efficient and selective lignin-to-aromatic conversion. Of particular interest are fractionation methods that implement active stabilisation mechanisms that prohibit the problem of lignin condensation, without compromising the structural integrity of the carbohydrates. This new and emerging biorefinery paradigm is termed lignin-first, and includes two distinct strategies to actively prevent structural degradation during biomass fractionation, namely (i) tandem depolymerisation–stabilisation of native lignin, and (ii) active preservation of β-O-4 bonds.

One of the foremost challenges in lignocellulose conversion encompasses the integration of effective lignin valorization in current carbohydrate-oriented biorefinery schemes. Catalytic reductive fractionation (CRF) of lignocellulose offers a technology to simultaneously produce lignin-derived platform chemicals and a carbohydrate-enriched pulp via the combined action of lignin solvolysis and metal-catalyzed hydrogenolysis. Herein, the solvent (composition) plays a crucial role. In this contribution, we study the influence of alcohol/water mixtures by processing poplar sawdust in varying MeOH/water and EtOH/water blends. The results show particular effects that strongly depend on the applied water concentration. Low water concentrations enhance the removal of lignin from the biomass, while the majority of the carbohydrates are left untouched (scenario A). Contrarily, high water concentrations favor the solubilization of both hemicellulose and lignin, resulting in a more pure cellulosic residue (scenario B)...

Recent lignin-first catalytic lignocellulosic biorefineries produce large quantities of two potential platform chemicals, 4-n-propylguaiacol (PG) and 4-n-propylsyringol. Because conversion into 4-n-propylcyclohexanol (PCol), a precursor for novel polymer building blocks, presents a promising valorization route, reductive demethoxylation of PG was examined here in the liquid-phase over three commercial hydrogenation catalysts, viz. 5 wt % Ru/C, 5 wt % Pd/C and 65 wt % Ni/SiO2–Al2O3, at elevated temperatures ranging from 200 to 300 °C under hydrogen atmosphere. Kinetic profiles suggest two parallel conversion pathways: Pathway I involves PG hydrogenation to 4-n-propyl-2-methoxycyclohexanol (PMCol), followed by its demethoxylation to PCol, whereas Pathway II constitutes PG hydrodemethoxylation to 4-n-propylphenol (PPh), followed by its hydrogenation into PCol. The slowest step in the catalytic formation of PCol is the reductive methoxy removal from PMCol. Moreover, under the applied reaction conditions, PCol...

Reductive catalytic fractionation of lignocellulose is a promising “lignin-first” biorefinery strategy wherein lignin is solvolytically extracted from the cell wall matrix and simultaneously disassembled, resulting in a stable lignin oil and a solid carbohydrate-rich residue. Herein, we report on the different influence of acidic (H3PO4) and alkaline (NaOH) additives on the Pd/C-catalyzed reductive processing of poplar wood in methanol (MeOH). It was found that the addition of small quantities of H3PO4 results in three rather than two product streams, since under acidic conditions both delignification and alcoholysis of hemicellulose are promoted, leaving behind a cellulose-rich pulp. The simultaneous acid-catalyzed fractionation of the carbohydrates into separate cellulose and hemicellulose streams provides opportunities for more efficient downstream conversion, as processing parameters can be tailored to the needs of both streams. Alkaline conditions, on the other hand, also enhance delignification, but...

Lignin valorization represents a crucial, yet underexploited component in current lignocellulosic biorefineries. An alluring opportunity is the selective depolymerization of lignin towards chemicals. Although challenged by lignin's recalcitrant nature, several successful (catalytic) strategies have emerged. This review provides an overview of different approaches to cope with detrimental lignin structural alterations at an early stage of the biorefinery process, thus enabling effective routes towards lignin-derived chemicals. A first general strategy is to isolate lignin with a better preserved native-like structure and therefore an increased amenability towards depolymerization in a subsequent step. Both mild process conditions as well as active stabilization methods will be discussed. An alternative is the simultaneous depolymerization-stabilization of native lignin towards stable lignin monomers. This approach requires a fast and efficient stabilization of reactive lignin intermediates in order to minimize lignin repolymerization and maximize the envisioned production of chemicals. Finally, the obtained lignin-derived compounds can serve as a platform towards a broad range of bio-based products. Their implementation will improve the sustainability of the chemical industry, but equally important will generate opportunities towards product innovations based on unique biobased chemical structures. ispartof: Topics in Current Chemistry vol:376 issue:5 ispartof: location:Switzerland status: published

In pursuit of more sustainable and competitive biorefineries, the effective valorisation of lignin is key. An alluring opportunity is the exploitation of lignin as a resource for chemicals. Three technological biorefinery aspects will determine the realisation of a successful lignin-to-chemicals valorisation chain, namely (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. This review provides a summary and perspective of the extensive research that has been devoted to each of these three interconnected biorefinery aspects, ranging from industrially well-established techniques to the latest cutting edge innovations. To navigate the reader through the overwhelming collection of literature on each topic, distinct strategies/topics were delineated and summarised in comprehensive overview figures. Upon closer inspection, conceptual principles arise that rationalise the success of certain methodologies, and more importantly, can guide future research to further expand the portfolio of promising technologies. When targeting chemicals, a key objective during the fractionation and depolymerisation stage is to minimise lignin condensation (i.e. formation of resistive carbon-carbon linkages). During fractionation, this can be achieved by either (i) preserving the (native) lignin structure or (ii) by tolerating depolymerisation of the lignin polymer but preventing condensation through chemical quenching or physical removal of reactive intermediates. The latter strategy is also commonly applied in the lignin depolymerisation stage, while an alternative approach is to augment the relative rate of depolymerisation vs. condensation by enhancing the reactivity of the lignin structure towards depolymerisation. Finally, because depolymerised lignins often consist of a complex mixture of various compounds, upgrading of the raw product mixture through convergent transformations embodies a promising approach to decrease the complexity. This particular upgrading approach is termed funneling, and includes both chemocatalytic and biological strategies. ispartof: CHEMICAL SOCIETY REVIEWS vol:47 issue:3 pages:852-908 ispartof: location:England status: published

Herein, we demonstrate a practical high yield preparation of large macrocyclic oligo(butadiene)s, preferably the C16 to C44 fraction, from commercial 1,4-polybutadiene by exploring intramolecular backbiting using a series of commercially available Ru catalysts. Product contamination with linear fragments is restricted by using high molecular weight 1,4-polybutadiene with a low content of 1,2-constructs (vinyl groups). The distribution of the cyclic compounds is largely dependent on the nature of the ligand structure of the Ru catalyst. Kinetic inspection of the reaction reveals a two-step mechanism involving (i) backbiting of the linear polymer with initial formation of large macrocycles followed by (ii) tandem ring-opening ring-closing metathesis predominantly leading to thermodynamically favorable t,t,t-cyclododecatriene (CDT). In particular, second-generation Ru catalysts with N-heterocyclic carbene (NHC) ligands favor undesired CDT formation. First-generation catalysts, presumably due to their high barriers for formation of the intermediate metallacyclobutane, selectively form the C16 to C44 macrocyclic oligo(butadiene) fraction. For example, reaction of (HMW, 98% cis)-polybutadiene with a first-generation Ru catalyst almost yields 90% C16–C44 cyclic oligo(butadiene)s.

Reductive catalytic fractionation constitutes a promising approach to separate lignocellulose into a solid carbohydrate pulp and a stable liquid lignin oil. The process is able to extract and convert most of the lignin into soluble mono-, di- and oligomers, while retaining most of the carbohydrates in the pulp. This contribution studies the impact of the solvent choice on both pulp retention and delignification efficiency. Several bio-derivable solvents with varying properties were therefore tested in the Pd/C-catalyzed reductive liquid processing of birch wood. Though a high solvent polarity favors delignification, a too polar solvent like water causes significant solubilization of carbohydrates. A new empirical descriptor, denoted as ‘lignin-first delignification efficiency’ (LFDE), is introduced as a measure of efficient wood processing into soluble lignin derivatives and solid sugar pulp. Of all tested solvents, methanol and ethylene glycol showed the highest LFDE values, and these values could be increased by increasing both reaction time and temperature. Moreover, substantial differences regarding the process characteristics and analyzed product fractions between these two different solvents were discussed extensively. Most striking is the impact of the solvent on the pulp macrostructure, with methanol yielding a pulp composed of aggregated fiber cells, whereas the ethylene glycol pulp comprises nicely separated fiber cells.

Liquid reductive processing of birch wood in the presence of commercial Ru/C or Pd/C catalysts yields about 50% of a select set of phenolic monomers and a variety of phenolic di- and oligomers, next to a solid carbohydrate pulp. Changing the catalyst from Ru/C to Pd/C drastically increases the OH-content of the lignin-derived products, in particular for the phenolic monomers.

Linear, branched and cyclic alkanes are important intermediates and end products of the chemical industry and are nowadays mainly obtained from fossil resources. In search for alternatives, biomass feedstocks are often presented as a renewable carbon source for the production of fuels, chemicals and materials. However, providing a complete market for all these applications seems unrealistic due to both financial and logistic issues. Despite the very large scale of current alkane-based fuel applications, biomass definitely has the potential to offer a partial solution to the fuel business. For the smaller market of chemicals and materials, a transition to biomass as main carbon source is more realistic and even probably unavoidable in the long term. The appropriate use and further development of integrated chemo- and biotechnological (catalytic) process strategies will be crucial to successfully accomplish this petro-to-bio feedstock transition. Furthermore, a selection of the most promising technologies from the available chemo- and biocatalytic tool box is presented. New opportunities will certainly arise when multidisciplinary approaches are further explored in the future. In an attempt to select the most appropriate biomass sources for each specific alkane-based application, a diagram inspired by van Krevelen is applied, taking into account both the C-number and the relative functionality of the product molecules.

© The Royal Society of Chemistry 2015. A catalytic lignocellulose biorefinery process is presented, valorizing both polysaccharide and lignin components into a handful of chemicals. To that end, birch sawdust is efficiently delignified through simultaneous solvolysis and catalytic hydrogenolysis in the presence of a Ru on carbon catalyst (Ru/C) in methanol under a H2 atmosphere at elevated temperature, resulting in a carbohydrate pulp and a lignin oil. The lignin oil yields above 50% of phenolic monomers (mainly 4-n-propylguaiacol and 4-n-propylsyringol) and about 20% of a set of phenolic dimers, relative to the original lignin content, next to phenolic oligomers. The structural features of the lignin monomers, dimers and oligomers were identified by a combination of GC/MS, GPC and 2D HSQC NMR techniques, showing interesting functionalities for forthcoming polymer applications. The effect of several key parameters like temperature, reaction time, wood particle size, reactor loading, catalyst reusability and the influence of solvent and gas were examined in view of the phenolic product yield, the degree of delignification and the sugar retention as a first assessment of the techno-economic feasibility of this biorefinery process. The separated carbohydrate pulp contains up to 92% of the initial polysaccharides, with a nearly quantitative retention of cellulose. Pulp valorization was demonstrated by its chemocatalytic conversion to sugar polyols, showing the multiple use of Ru/C, initially applied in the hydrogenolysis process. Various lignocellulosic substrates, including genetically modified lines of Arabidopsis thaliana, were finally processed in the hydrogenolytic biorefinery, indicating lignocellulose rich in syringyl-type lignin, as found in hardwoods, as the ideal feedstock for the production of chemicals. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: W. J. J. Huijgen (ResearcherID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0) history: Received 20 January 2015; Accepted 20 April 2015; Accepted Manuscript published 20 April 2015; Advance Article published 30 April 2015; Version of Record published 3 June 2015 ispartof: Energy & Environmental Science vol:8 issue:6 pages:1748-1763 status: published