Wouter Schutyser

Reductive lignocellulose fractionation into soluble lignin-derived phenolic monomers and dimers and processable carbohydrate pulps

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.

Tuning the acid/metal balance of carbon nanofiber-supported nickel catalysts for hydrolytic hydrogenation of cellulose.

Carbon nanofibers (CNFs) are a class of graphitic support materials with considerable potential for catalytic conversion of biomass. Earlier, we demonstrated the hydrolytic hydrogenation of cellulose over reshaped nickel particles attached at the tip of CNFs. The aim of this follow-up study was to find a relationship between the acid/metal balance of the Ni/CNFs and their performance in the catalytic conversion of cellulose. After oxidation and incipient wetness impregnation with Ni, the Ni/CNFs were characterized by various analytical methods. To prepare a selective Ni/CNF catalyst, the influences of the nature of oxidation agent, Ni activation, and Ni loading were investigated. Under the applied reaction conditions, the best result, that is, 76 % yield in hexitols with 69 % sorbitol selectivity at 93 % conversion of cellulose, was obtained on a 7.5 wt % Ni/CNF catalyst prepared by chemical vapor deposition of CH(4) on a Ni/γ-Al(2)O(3) catalyst, followed by oxidation in HNO(3) (twice for 1 h at 383 K), incipient wetness impregnation, and reduction at 773 K under H(2). This preparation method leads to a properly balanced Ni/CNF catalyst in terms of Ni dispersion and hydrogenation capacity on the one hand, and the number of acidic surface-oxygen groups responsible for the acid-catalyzed hydrolysis on the other.

Influence of bio-based solvents on the catalytic reductive fractionation of birch wood

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.

Selective nickel-catalyzed conversion of model and lignin-derived phenolic compounds to cyclohexanone-based polymer building blocks

Valorization of lignin is essential for the economics of future lignocellulosic biorefineries. Lignin is converted into novel polymer building blocks through four steps: catalytic hydroprocessing of softwood to form 4-alkylguaiacols, their conversion into 4-alkylcyclohexanols, followed by dehydrogenation to form cyclohexanones, and Baeyer-Villiger oxidation to give caprolactones. The formation of alkylated cyclohexanols is one of the most difficult steps in the series. A liquid-phase process in the presence of nickel on CeO2 or ZrO2 catalysts is demonstrated herein to give the highest cyclohexanol yields. The catalytic reaction with 4-alkylguaiacols follows two parallel pathways with comparable rates: 1) ring hydrogenation with the formation of the corresponding alkylated 2-methoxycyclohexanol, and 2) demethoxylation to form 4-alkylphenol. Although subsequent phenol to cyclohexanol conversion is fast, the rate is limited for the removal of the methoxy group from 2-methoxycyclohexanol. Overall, this last reaction is the rate-limiting step and requires a sufficient temperature (>250 °C) to overcome the energy barrier. Substrate reactivity (with respect to the type of alkyl chain) and details of the catalyst properties (nickel loading and nickel particle size) on the reaction rates are reported in detail for the Ni/CeO2 catalyst. The best Ni/CeO2 catalyst reaches 4-alkylcyclohexanol yields over 80 %, is even able to convert real softwood-derived guaiacol mixtures and can be reused in subsequent experiments. A proof of principle of the projected cascade conversion of lignocellulose feedstock entirely into caprolactone is demonstrated by using Cu/ZrO2 for the dehydrogenation step to produce the resultant cyclohexanones (≈80 %) and tin-containing beta zeolite to form 4-alkyl-ε-caprolactones in high yields, according to a Baeyer-Villiger-type oxidation with H2 O2 .

Alkylphenols to phenol and olefins by zeolite catalysis: a pathway to valorize raw and fossilized lignocellulose

Selective conversion of alkylphenols to phenol and olefins is presented as a challenging key step in upgrading raw and fossilized lignocellulose. An exceptional and stable dealkylation performance is achieved by application of an acidic ZSM-5 zeolite, in which co-feeding of water is crucial to maintain catalytic activity. The role of water is attributed to competitive adsorption of water and phenol. The lignin-first pathway towards phenol yields a tenfold improvement of phenol compared to the state-of-the-art single-step lignocellullosic depolymerization techniques.

Sustainable bisphenols from renewable softwood lignin feedstock for polycarbonates and cyanate ester resins

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.

Regioselective synthesis of renewable bisphenols from 2,3-pentanedione and their application as plasticizers

2,3-Pentanedione (2,3-PD), a bio-based chemical derived from lactic acid, has the potential to serve as a precursor for the synthesis of novel bisphenols. We developed a solvent-free catalytic strategy for the condensation of phenol with 2,3-PD by using acid catalysts at temperatures ranging from 323 to 373 K. Various soluble and solid acids exhibit high activity, while a high chemoselectivity to bisphenol requires a high phenol to 2,3-PD molar ratio. Bisphenol yields as high as 84% are for instance reported in an excess of phenol in the presence of Nafion NR50. Recycling of the Nafion catalyst after washing with ethanol at room temperature is demonstrated. The regioselectivity in the bisphenol fraction is influenced by the acid strength. A clear trend is presented in which the regioselectivity towards the desired p,p′-isomers increases with increasing acid strength, showing p,p′/o,p′-isomer ratios as high as 100. A tentative mechanism is discussed based on the ionic versus non-ionic pathway. The purified 2,3-PD-derived p,p′-bisphenols are assessed as plasticizers for polyethylene terephthalate (PET), showing promising properties similar to that of the reference bisphenol A, but with a broader processing window due to the lower melting point and higher thermal stability under an inert atmosphere.

Promising bulk production of a potentially benign bisphenol A replacement from a hardwood lignin platform

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 (

Conversion of biomass to chemicals: The catalytic role of zeolites

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 BPAs 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.

Catalytic Strategies Towards Lignin-Derived Chemicals

Abstract Since the mid-20th century zeolites have been successfully applied in oil refining and petrochemistry, owing to the strong Bronsted acidity of their protonated form in a porous crystalline matrix. Yet, concerns about the excessive use of fossil fuels force researchers to develop processes for the production of fuels and chemicals from CO2-neutral feedstocks such as biomass, considered as the alternative and sustainable source of carbon for the production of future bio-derived chemicals. With their success in refinery and petrochemistry, there is increasing interest in the use of zeolites in biomass processing, and this has already resulted in the gradual entrance of zeolites in the conversion of biomass feedstocks. Many interesting biomass conversions have been demonstrated today using the unique acid and redox chemistry of zeolites. However, there are disadvantages inherent to the biomass conversion that need to be overcome before zeolite chemistry can play as important a role in the conversion of biomass as in the conversion of fossil feedstocks. These disadvantages include unstable products and complex conversion network schemes, the stability of zeolites in often polar (condensed) media and active site accessibility of large biomolecules. This chapter presents the major organic compounds in biomass feedstock and provides an overview of the numerous chemical reactions with these chemicals using zeolites in the bulk and fine chemistry. Developments and future challenges in the area are summarized.