103 results found
Costa MJF, Gonçalves AAS, Rinaldi R, et al., 2023, Highly porous niobium-containing silica glasses applied to the microwave-assisted conversion of fructose into HMF, Catalysis Communications, Vol: 174, ISSN: 1566-7367
Metal dispersion is key for designing highly active and well-defined catalytic systems. Herein, to shed light on the effects of Nb dispersion on the conversion of fructose into HMF, highly porous silica glasses grafted with niobium oxide were prepared. Preliminary catalytic screening was done for the microwave-assisted conversion of fructose into 5-hydroxymethylfurfural (HMF) in a biphasic system. The highly porous silica glasses impregnated with niobium oxide presented HMF productivities about 10- to 20 times higher than the mesoporous NbOPO4 reference material. Intriguingly, humin formation correlates with HMF yield regardless of the catalyst employed, although metal dispersion influences the acidity profile.
Rinken R, Posthuma D, Rinaldi R, 2022, Lignin Stabilization and Carbohydrate Nature in H-transfer Reductive Catalytic Fractionation: The Role of Solvent Fractionation of Lignin Oil in Structural Profiling, CHEMSUSCHEM, ISSN: 1864-5631
Kessler M, Rinaldi R, 2022, Kinetic energy dose as a unified metric for comparing ball mills in the mechanocatalytic depolymerization of lignocellulose, Frontiers in Chemistry, Vol: 9, ISSN: 2296-2646
Mechanochemistry utilizes mechanical forces to activate chemical bonds. It offers environmentally benign routes for both (bio) organic and inorganic syntheses. However, direct comparison of mechanochemistry results is often very challenging. In mechanochemical synthetic protocols, ball mill setup (mechanical design and grinding vessel geometry) in addition to experimental parameters (milling frequency, duration, ball count and size) vary broadly. This fact poses a severe issue to further progress in this exciting research area because ball mill setup and experimental parameters govern how much kinetic energy is transferred to a chemical reaction. In this work, we address the challenge of comparing mechanochemical reaction results by taking the energy dose provided by ball mills as a unified metric into account. In this quest, we applied kinematic modeling to two ball mills functioning under distinct working principles to express the energy dose as a mathematical function of the experimental parameters. By examining the effect of energy dose on the extent of the mechanocatalytic depolymerization (MCD) of lignocellulosic biomass (beechwood), we found linear correlations between yield of water-soluble products (WSP) and energy dose for both ball mills. Interestingly, when a substrate layer is formed on the grinding jar wall and/or grinding medium, a weak non-linear correlation between water-soluble products yield and energy dose is identified. We demonstrate that the chemical reaction’s best utilization of kinetic energy is achieved in the linear regime, which presents improved WSP yields for given energy doses. In the broader context, the current analysis outlines the usefulness of the energy dose as a unified metric in mechanochemistry to further the understanding of reaction results obtained from different ball mills operating under varied experimental conditions.
Bartling AW, Stone ML, Hanes RJ, et al., 2021, Techno-economic analysis and life cycle assessment of a biorefinery utilizing reductive catalytic fractionation, Energy and Environmental Science, Vol: 14, Pages: 4147-4168, ISSN: 1754-5692
Reductive catalytic fractionation (RCF) is a promising approach to fractionate lignocellulose and convert lignin to a narrow product slate. To guide research towards commercialization, cost and sustainability must be considered. Here we report a techno-economic analysis (TEA), life cycle assessment (LCA), and air emission analysis of the RCF process, wherein biomass carbohydrates are converted to ethanol and the RCF oil is the lignin-derived product. The base-case process, using a feedstock supply of 2000 dry metric tons per day, methanol as a solvent, and H2 gas as a hydrogen source, predicts a minimum selling price (MSP) of crude RCF oil of $1.13 per kg when ethanol is sold at $2.50 per gallon of gasoline-equivalent ($0.66 per liter of gasoline-equivalent). We estimate that the RCF process accounts for 57% of biorefinery installed capital costs, 77% of positive life cycle global warming potential (GWP) (excluding carbon uptake), and 43% of positive cumulative energy demand (CED). Of $563.7 MM total installed capital costs, the RCF area accounts for $323.5 MM, driven by high-pressure reactors. Solvent recycle and water removal via distillation incur a process heat demand equivalent to 73% of the biomass energy content, and accounts for 35% of total operating costs. In contrast, H2 cost and catalyst recycle are relatively minor contributors to operating costs and environmental impacts. In the carbohydrate-rich pulps, polysaccharide retention is predicted not to substantially affect the RCF oil MSP. Analysis of cases using different solvents and hemicellulose as an in situ hydrogen donor reveals that reducing reactor pressure and the use of low vapor pressure solvents could reduce both capital costs and environmental impacts. Processes that reduce the energy demand for solvent separation also improve GWP, CED, and air emissions. Additionally, despite requiring natural gas imports, converting lignin as a biorefinery co-product could significantly reduce non-greenhouse
Dierks M, Cao Z, Rinaldi R, 2021, Design of task-specific metal phosphides for the sustainable manufacture of advanced biofuels, CATALYSIS IN BIOMASS CONVERSION, Editors: Ford, VanEldik, Publisher: ELSEVIER ACADEMIC PRESS INC, Pages: 219-239
Abu-Omar MM, Barta K, Beckham GT, et al., 2020, Guidelines for performing lignin-first biorefining, Energy & Environmental Science, Vol: 14, Pages: 262-292, ISSN: 1754-5692
The valorisation of the plant biopolymer lignin is now recognised as essential to enabling the economic viability of the lignocellulosic biorefining industry. In this context, the “lignin-first” biorefining approach, in which lignin valorisation is considered in the design phase, has demonstrated the fullest utilisation of lignocellulose. We define lignin-first methods as active stabilisation approaches that solubilise lignin from native lignocellulosic biomass while avoiding condensation reactions that lead to more recalcitrant lignin polymers. This active stabilisation can be accomplished by solvolysis and catalytic conversion of reactive intermediates to stable products or by protection-group chemistry of lignin oligomers or reactive monomers. Across the growing body of literature in this field, there are disparate approaches to report and analyse the results from lignin-first approaches, thus making quantitative comparisons between studies challenging. To that end, we present herein a set of guidelines for analysing critical data from lignin-first approaches, including feedstock analysis and process parameters, with the ambition of uniting the lignin-first research community around a common set of reportable metrics. These guidelines comprise standards and best practices or minimum requirements for feedstock analysis, stressing reporting of the fractionation efficiency, product yields, solvent mass balances, catalyst efficiency, and the requirements for additional reagents such as reducing, oxidising, or capping agents. Our goal is to establish best practices for the research community at large primarily to enable direct comparisons between studies from different laboratories. The use of these guidelines will be helpful for the newcomers to this field and pivotal for further progress in this exciting research area.
Kessler M, Ahorsu R, Medina F, et al., 2020, An integrated cellulase‐free approach to produce sugars from lignocellulose at high quality for fermentation processes, Chemie Ingenieur Technik, Vol: 92, Pages: 1263-1263, ISSN: 0009-286X
Leal GF, Lima S, Graca I, et al., 2019, Design of nickel supported on water-tolerant Nb2O5 catalysts for the hydrotreating of lignin streams obtained from lignin-first biorefining, iScience, Vol: 15, Pages: 467-488, ISSN: 2589-0042
In biomass conversion, Nb2O5 has attracted increasing attention as a catalyst support presenting water-tolerant Lewis acid sites. Herein, we address the design of Ni/Nb2O5 catalysts for hydrotreating of lignin to hydrocarbons. To optimize the balance between acidic and hydrogenating properties, the catalysts were first evaluated in the hydrotreating of diphenyl ether. The best catalyst candidate was further explored in the conversion of lignin oil obtained by catalytic upstream biorefining of poplar. As primary products, cycloalkanes were obtained, demonstrating the potential of Ni/Nb2O5 catalysts for the lignin-to-fuels route. However, the Lewis acidity of Nb2O5 also catalyzes coke formation via lignin species condensation. Thereby, an acidity threshold should be found so that dehydration reactions essential to the hydrotreatment are not affected, but the condensation of lignin species prevented. This article provides a critical “beginning-to-end” analysis of aspects crucial to the catalyst design to produce lignin biofuels.
Sultan Z, Graça I, Li Y, et al., 2019, Membrane fractionation of liquors from lignin-first biorefining, ChemSusChem, Vol: 12, Pages: 1203-1212, ISSN: 1864-5631
For the purposing of each lignin fraction in the lignin liquors, the development of separation strategies to fractionate the lignin streams by MW ranges constitutes a timely challenge to be tackled. Herein, membrane separation was applied to the refining of lignin streams obtained from a lignin-first biorefining process based on H-transfer reactions catalyzed by Raney Ni, using 2-propanol as a part of the lignin extraction liquor and as an H-donor. A two-stage membrane cascade was considered to separate and concentrate the monophenol-rich fraction from the CUB liquor. Building on the experimental results, an economic evaluation of the potential of membrane separation for the refining of lignin streams was undertaken. The membrane performance represents the bottleneck of the costs associated with the separation process. Accordingly, we present a detailed analysis of future developments in the performance required to debottleneck the utilization of membrane separation for lignin refining.
Rinaldi R, Woodward RT, Ferrini P, et al., 2019, Lignin-first biorefining of lignocellulose: the impact of process severity on the uniformity of lignin oil composition, Journal of the Brazilian Chemical Society, Vol: 30, Pages: 479-491, ISSN: 0103-5053
In lignin-first biorefining via reductive processes, lignocellulosic materials are deconstructed by the solvent extraction of lignin in the presence of a hydrogenation catalyst. This approach provides a route to the successful extraction and reductive passivation of lignin fragments to produce low molar mass lignin oils together with high-quality pulps. Herein, we present an investigation into the impact of process severity (i.e., cooking temperature) on the reductive processes taking place on the lignin fragments and uniformity of the product mixture. In addition to improving overall delignification yields (up to 87%) and producing low molar mass fragments, higher process temperatures led to the preferential cleavage of hydroxyl groups in monolignol sidechains via hydrodeoxygenation, yielding oils with lower oxygen content. By comparing products from both lignin-first biorefining and organosolv processes at various temperatures, we elucidate key performance differences and outline routes to increased chemical uniformity in lignin streams. Overall, this study outlines clearly the importance of process temperature in the deconstruction of lignocellulose by lignin-first biorefining when producing highly depolymerized lignin products. This study points out a trade-off in the effect of temperature upon delignification and increase in product mixture complexity, which needs to be carefully optimized for the scale-up of lignin-first technologies.
Graca I, Woodward RT, Kennema M, et al., 2018, Formation and fate of carboxylic acids in the lignin-first biorefining of lignocellulose via H-transfer catalyzed by Raney Ni, ACS Sustainable Chemistry and Engineering, Vol: 6, Pages: 13408-13419, ISSN: 2168-0485
Lignin-first biorefining constitutes a new research field in which the overarching objective is the prevention of lignin recalcitrance while providing high-quality pulps. For this purpose, the solvent extraction of lignin is performed in the presence of a hydrogenation catalyst, employing H2 pressure or an H-donor solvent (e.g., 2-propanol), and thus leading to passivation of reactive lignin fragments via reductive processes. As a result, lignin-first biorefining methods generate high-quality pulps in addition to low-molecular-weight lignin streams with high molecular uniformity. Nonetheless, upon cooking lignocellulose in solvent mixtures containing water, other processes on the lignocellulosic matrix take place, releasing soluble intermediates. In fact, hemicellulose undergoes deacetylation, to a variable extent, releasing acetic acid into the liquor. Moreover, formic acid can also be formed as a degradation product of hemicellulose C6-sugars also released into the liquor. However, despite this general notion, the formation and fate of these carboxylic acids during the cooking of lignocellulosic substrates, and the effects these acids may have on hydrogenation catalyst performance remain poorly understood. In this report, we examine both the formation and subsequent fate of formic acid and acetic acid during lignocellulose deconstruction for both a lignin-first biorefining method (via H-transfer reactions in the presence of Raney Ni catalyst) and its equivalent Organosolv process with no added acid or hydrogenation catalyst. A mechanism for the mitigation of formic acid formation in the presence of Raney Ni catalyst is outlined via the hydrogenation of sugars to sugar alcohols. Furthermore, the effects of the carboxylic acids on Raney Ni performance are assessed, using the transfer-hydrogenation of phenol to cyclohexanol/cyclohexanone as a model reaction, elucidating inhibition rates of the acids. Finally, we conclude with the implications of these results for the
de Castro IBD, Graca I, Rodriguez-Garcia L, et al., 2018, Elucidating the reactivity of methoxyphenol positional isomers towards hydrogen-transfer reactions by ATR-IR spectroscopy of the liquid-solid interface of RANEY (R) Ni, Catalysis Science and Technology, Vol: 8, Pages: 3107-3114, ISSN: 2044-4753
In the valorisation of lignin, the application of catalytic hydrogen transfer reactions (e.g. in catalytic upstream biorefining or lignin-first biorefining) has brought a renewed interest in the fundamental understanding of hydrogen-transfer processes in the defunctionalisation of lignin-derived phenolics. In this report, we address fundamental questions underlining the distinct reactivity patterns of positional isomers of guaiacol towards H-transfer reactions in the presence of RANEY® Ni and 2-PrOH (solvent and H-donor). We studied the relationship between reactivity patterns of 2-, 3- and 4-methoxyphenols and their interactions at the liquid–solid interface of RANEY® Ni as probed by attenuated total reflection infrared (ATR-IR) spectroscopy. Regarding the reactivity patterns, 2-methoxyphenol or guaiacol is predominantly converted into cyclohexanol through a sequence of reactions including demethoxylation of 2-methoxyphenol to phenol followed by hydrogenation of phenol to cyclohexanol. By contrast, for the conversion of the two non-lignin related positional isomers, the corresponding 3- and 4-methoxycyclohexanols are the major reaction products. The ATR-IR spectra of the liquid–solid interface of RANEY® Ni revealed that the adsorbed 2-methoxyphenol assumes a parallel orientation to the catalyst surface, which allows a strong interaction between the methoxy C–O bond and the surface. Conversely, the adsorption of 3- or 4-methoxyphenol leads to a tilted surface complex in which the methoxy C–O bond establishes no interaction with the catalyst. These observations are also corroborated by a smaller activation entropy found for the conversion of 2-methoxyphenol relative to those of the other two positional isomers.
Cao Z, Dierks M, Clough MT, et al., 2018, A convergent approach for a deep converting lignin-first biorefinery rendering high-energy-density drop-in fuels, Joule, Vol: 2, Pages: 1118-1133, ISSN: 2542-4351
Herein, a lignin-centered convergent approach to produce either aliphatic or aromatic bio-hydrocarbons is introduced. First, poplar or spruce wood was deconstructed by a lignin-first biorefining process, a technique based on the early-stage catalytic conversion of lignin, yielding lignin oils along with cellulosic pulps. Next, the lignin oils were catalytically upgraded in the presence of a phosphidated Ni/SiO2 catalyst under H2 pressure. Notably, selectivity toward aliphatics or aromatics can simply be adjusted by changes in H2 pressure and temperature. The process renders two distinct main cuts of branched hydrocarbons (gasoline: C6-C10, and kerosene/diesel: C14-C20). As the approach is H2-intensive, we examined the utilization of pulp as an H2 source via gasification. For several biomass sources, the H2 obtainable by gasification stoichiometrically meets the H2 demand of the deep converting lignin-first biorefinery, making this concept plausible for the production of high-energy-density drop-in biofuels.
Hilgert J, Lima S, Aho A, et al., 2018, The impact of salts formed by the neutralisation of (ligno)cellulose hydrolysates on the hydrogenation of sugars, ChemCatChem, Vol: 10, Pages: 2409-2416, ISSN: 1867-3880
Dilute acid hydrolysis of lignocellulose often requires a neutralisation step to utilise the hydrolysate's sugars. In this context, very little is known regarding the impact of low levels of acids or their corresponding salts produced by neutralisation on the catalyst performance in the hydrogenation of sugars. In this work, the influence of a series of ammonium and alkali metal salts (that is, NH4NO3, NaNO3, (NH4)2SO4, Na2SO4 and K2SO4) on the hydrogenation of glucose and xylose is addressed. This study also encompasses “real‐world” hydrolysates obtained by the mechanocatalytic depolymerisation of α‐cellulose and beechwood. The impact of low levels of acids and their salts upon the hydrogenation of sugars to sugar alcohols (alditols) was examined, in the presence of a commercial Ru/C catalyst (Ru/C, 0.7 wt % Ru) at 110 °C using batch and trickle‐bed reactors. The results show that the presence of salts leads to a considerable decrease in the alditols yields. Notably, salt anions exert an effect stronger than that of cations in the catalyst deactivation. Surprisingly, nitrates had a more significant effect on the decrease in the alditols yield than sulfates, and chlorides had the lowest impact. In this study, we also present the effect of sugars’ degradation products (e.g. 5‐(hydroxymethyl)furfural and furfural) upon hydrogenation of lignocellulose hydrolysates. The activated carbon pre‐treatments of the hydrolysates showed a positive effect on the catalyst activity, adsorbing hydrolysis by‐products. Overall, this study has significant implications for the practical aspects of hydrogenation of lignocellulose hydrolysates, which are often neglected in the current literature.
Dierks M, Cao Z, Manayil JC, et al., 2018, Impact of hydrophobic organohybrid silicas on the stability of Ni<inf>2</inf>P catalyst phase in the hydrodeoxygenation of biophenols, ChemCatChem, Vol: 10, Pages: 2219-2231, ISSN: 1867-3880
Hydrodeoxygenation (HDO) of lignocellulose-derived pyrolysis oils offers an option to produce fuel substitutes. However, catalyst deactivation and stability constitute a significant issue. Herein, the dependence of stability and activity of Ni 2 P/SiO 2 HDO catalysts on the support surface polarity is addressed in detail. The support surface polarity was adjusted by copolymerizing tetraethyl orthosilicate (TEOS) with different types and amounts of organosilanes by a sol-gel process in the presence of nickel nitrate and citric acid. After thermal treatment under an inert atmosphere, Ni/SiO 2 precursors were formed. They were converted into Ni 2 P/SiO 2 catalysts by using NaH 2 PO 2 as a PH 3 source. The catalyst surface polarity was characterized by inverse gas chromatography measurements of the free energy of methanol adsorption, and specific and dispersive surface energies derived from polar and nonpolar probe molecule adsorption. The correlation between catalyst performance and support surface polarity indicates that, to prevent deactivation of the catalyst by water under reaction conditions, the affinity of the support towards polar substances must be decreased below a threshold value.
Dierks M, Cao Z, Manayil JC, et al., 2018, Front Cover: Impact of Hydrophobic Organohybrid Silicas on the Stability of Ni2P Catalyst Phase in the Hydrodeoxygenation of Biophenols (ChemCatChem 10/2018), ChemCatChem, Vol: 10, Pages: 2115-2115, ISSN: 1867-3880
Woodward RT, Kessler M, Lima S, et al., 2018, Hypercrosslinked microporous polymer sorbents for the efficient recycling of a soluble acid catalyst in cellulose hydrolysis, Green Chemistry, Vol: 20, Pages: 2374-2381, ISSN: 1463-9262
Difficulties in the recycling of soluble acid catalysts within the lignocellulosic biorefinery constitute a serious issue to the sustainability of cellulose hydrolysis and several other transformations. Herein, we demonstrate a simple and effective method for the removal and recovery of p-toluenesulfonic acid (p-TSA) employed as a replacement of H2SO4 in the saccharification of cellulose by a mechanocatalytic route. p-TSA is recovered from its diluted aqueous solutions using a non-expensive hypercrosslinked polymer adsorbent. In a batch process, around 97% p-TSA acid was removed from a 5 mM solution after exposure to the hypercrosslinked polymer. Notably, a flow-through process was able to selectively remove the catalyst completely from even lower initial concentrations. Importantly, the efficient recovery of the p-TSA is achieved by washing the spent polymer with methanol. In the purification of a stream derived from the saccharification of cellulose, the extraction of p-TSA catalyst in addition to 5-hydroxymethylfurfural (HMF) and furfural was also achieved. With the rational choice of solvents, p-TSA and furfurals were separately recovered. In the broader context, the current findings represent a step forward towards the acid management from the acid-catalyzed saccharification of cellulose. Moreover, this approach is conducive for the purification of sugars for bioconversion in which even low levels of furfurals may exert a strong inhibitory effect upon yeast cultures.
Rinaldi R, 2018, Early-stage Conversion of Lignin over Hydrogenation Catalysts, Lignin Valorization: Emerging Approaches, Editors: Beckham, Publisher: Royal Society of Chemistry, Pages: 108-127, ISBN: 9781782625544
The deconstruction of lignocellulosic materials producing high-quality pulps together with lignin streams of low molecular weight (Mw) with controlled molecular diversity constitutes the overarching objective of catalytic upstream biorefining (CUB) based on the early-stage catalytic conversion of lignin (ECCL). The CUB process based on ECCL or, simply, a “lignin first” approach builds on the lignin extraction with organic solvents in the presence of a hydrogenation catalyst under hydrogen pressure or employing an H-donor solvent (e.g. 2-propanol). Subjected to a hydrogenation catalyst, the lignin fragments undergo reductive processes, which decrease their reactivity and propensity to recondensation, directly upon their release from the lignocellulosic matrix. As a result, the isolated lignin fraction is a mixture of compounds of Mw 100–600 Da, with a high content of individual components. Herein, key concepts required for the rational deconstruction of lignocellulose based on ECCL are addressed. Notably, catalysis is now applied to the “pulping process” itself, opening up new horizons for the realistic valorization of lignin and full utilization of lignocellulose via downstream catalytic processing of better-defined lignin streams.
Lanziano CAS, Moya SF, Barrett DH, et al., 2018, Hybrid-organic-inorganic anatase as a bifunctional catalyst for enhanced production of HMF from glucose in water, ChemSusChem, Vol: 11, Pages: 872-880, ISSN: 0003-4592
Herein, we report a synthetic route for the preparation of hybrid-organic-inorganic anatase (hybrid-TiO2) via a facile hydrothermal synthesis method employing citric acid. The synthetic approach results in a high surface area nanocrystalline anatase polymorph of TiO2. The uncalcined hybrid-TiO2 is directly studied here as the catalyst for the conversion of glucose into HMF. In the presence of the hybrid-TiO2, HMF yields up to 45% at glucose conversions up to 75% were achieved in water at 130 oC in a monophasic batch reactor. As identified by Ti K-edge XANES, hybrid-TiO2 contains a large fraction of five-fold coordinatively unsaturated Ti(IV) sites, which act as the Lewis acid catalyst for the conversion of glucose into fructose. As citric acid is anchored in the structure of hybrid-TiO2, carboxylate groups seem to catalyze the sequential conversion of fructose into HMF. The fate of citric acid bounded to anatase and the Ti(IV) Lewis acid sites throughout recycling experiments is also investigated. In a broader context, the contribution outlines the importance of hydrothermal synthesis for the creation of water-resistant Lewis acid sites for the conversion of sugars. Most importantly, the utilization of the hybrid-TiO2 with no calcination step contributes to dramatically decreasing the energy consumption in the catalyst preparation.
Kessler M, Woodward RT, Wong N, et al., 2018, Kinematic Modeling of Mechanocatalytic Depolymerization of α-Cellulose and Beechwood, ChemSusChem, Vol: 11, Pages: 552-561, ISSN: 1864-5631
Kessler M, Woodward RT, Wong N, et al., 2018, Front Cover: Kinematic Modeling of Mechanocatalytic Depolymerization of α-Cellulose and Beechwood (ChemSusChem 3/2018), ChemSusChem, Vol: 11, Pages: 503-503, ISSN: 1864-5631
Kessler M, Woodward RT, Wong N, et al., 2018, Kinematic Modeling of Mechanocatalytic Depolymerization of Α-Cellulose and Beechwood, ChemSusChem, Vol: 11, Pages: 552-561, ISSN: 1864-5631
Mechanocatalytic depolymerization of lignocellulose presents a promising method for the solid‐state transformation of acidified raw biomass into water‐soluble products (WSPs). However, the mechanisms underlining the utilization of mechanical forces in the depolymerization are poorly understood. A kinematic model of the milling process is applied to assess the energy dose transferred to cellulose during its mechanocatalytic depolymerization under varied conditions (rotational speed, milling time, ball size, and substrate loading). The data set is compared to the apparent energy dose calculated from the kinematic model and reveals key features of the mechanocatalytic process. At low energy doses, a rapid rise in the WSP yield associated with the apparent energy dose is observed. However, at a higher energy dose obtained by extended milling duration or high milling speeds, the formation of a substrate cake layer on the mill vials appear to buffer the mechanical forces, preventing full cellulose conversion into WSPs. By contrast, for beechwood, there exists a good linear dependence between the WSP yield and the energy dose provided to the substrate over the entire range of WSP yields. As the formation of a substrate cake in depolymerization of beechwood is less severe than that for the cellulose experiments, the current results verify the hypothesis regarding the negative effect of a substrate layer formed on the mill vials upon the depolymerization process. Overall, the current findings provide valuable insight into relationships between the energy dose and the extent of cellulose depolymerization effected by the mechanocatalytic process.
Rinaldi R, 2017, A Tandem for Lignin-First Biorefinery, Joule, Vol: 1, Pages: 427-428, ISSN: 2542-4351
Heterogeneous catalysis is no longer restricted to the catalytic upgrading of recalcitrant lignin wastes from the pulping and paper industry. This discipline now offers innovative solutions for the lignocellulose deconstruction, generating “easy-to-upgrade” lignin streams along with cellulose pulps. In this issue of Joule, Beckham, Román-Leshkov, and colleagues report the first example of “tandem” lignin-first biorefining in which the formation and extraction of lignin oligomers in addition to the reductive processes leading to further depolymerization and passivation of lignin fragments are performed in two-sequential flow-through reactors. Heterogeneous catalysis is no longer restricted to the catalytic upgrading of recalcitrant lignin wastes from the pulping and paper industry. This discipline now offers innovative solutions for the lignocellulose deconstruction, generating “easy-to-upgrade” lignin streams along with cellulose pulps. In this issue of Joule, Beckham, Román-Leshkov, and colleauges report the first example of “tandem” lignin-first biorefining in which the formation and extraction of lignin oligomers in addition to the reductive processes leading to further depolymerization and passivation of lignin fragments are performed in two-sequential flow-through reactors.
Ferrini P, Chesi C, Parkin N, et al., 2017, Effect of methanol in controlling defunctionalization of the propyl side chain of phenolics from catalytic upstream biorefining, Faraday Discussions, Vol: 202, Pages: 403-413, ISSN: 1359-6640
In recent years, lignin valorization has gained upward momentum owing to advances in both plant bioengineering and catalytic processing of lignin. In this new horizon, catalysis is now applied to the ‘pulping process’ itself, creating efficient methods for lignocellulose fractionation or deconstruction (here referred to as Catalytic Upstream Biorefining or ‘CUB’). These processes render, together with delignified pulps, lignin streams of low molecular weight (Mw) and low molecular diversity. Recently, we introduced a CUB process based on Early-stage Catalytic Conversion of Lignin (ECCL) through H-transfer reactions catalyzed by RANEY® Ni. This approach renders a lignin stream obtained as a viscous oil, comprising up to 60 wt% monophenolic compounds (Mw < 250 Da). The remaining oil fraction (40 wt%) is mainly composed of lignin oligomers, and as minor products, holocellulose-derived polyols and lignin-derived species of high Mw (0.25–2 kDa). Simultaneously, the process yields a holocellulose pulp with a low content of residual lignin (<5 wt%). Despite the efficiency of aqueous solutions of 2-propanol as a solvent for lignin fragments and an H-donor, there is scant information regarding the CUB process carried out in the presence of primary alcohols, which often inhibit the catalytic activity of RANEY® Ni, as revealed in model compound studies performed at low temperature. Considering the composition of the lignin oils obtained from CUB based on ECCL, the processes commonly render ortho-(di)methoxy-4-propylphenol derivatives with a varied degree of defunctionalization of the propyl side chain. In this contribution, we present the role of the alcohol solvent (methanol or 2-propanol) and Ni catalyst (Ni/C or RANEY® Ni) in control over selectivity of phenolic products. The current results indicate that solvent effects on the catalytic processes could hold the key for improving control over the degree of functionalization of
Rinaldi R, 2017, What is lignin recalcitrance? A critical analysis of lignins derived from mechanocatalytic biorefining and organosolv process, 254th National Meeting and Exposition of the American-Chemical-Society (ACS) on Chemistry's Impact on the Global Economy, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Clough MT, Fares C, Rinaldi R, 2017, 1D and 2D NMR Spectroscopy of Bonding Interactions within Stable and Phase-Separating Organic Electrolyte-Cellulose Solutions, ChemSusChem, Vol: 10, Pages: 3452-3458, ISSN: 0003-4592
Organic electrolyte solutions (i.e. mixtures containing an ionic liquid and a polar, molecular co-solvent) are highly versatile solvents for cellulose. However, the underlying solvent–solvent and solvent–solute interactions are not yet fully understood. Herein, mixtures of the ionic liquid 1-ethyl-3-methylimidazolium acetate, the co-solvent 1,3-dimethyl-2-imidazolidinone, and cellulose are investigated using 1D and 2D NMR spectroscopy. The use of a triply-13C-labelled ionic liquid enhances the signal-to-noise ratio for 13C NMR spectroscopy, enabling changes in bonding interactions to be accurately pinpointed. Current observations reveal an additional degree of complexity regarding the distinct roles of cation, anion, and co-solvent toward maintaining cellulose solubility and phase stability. Unexpectedly, the interactions between the dialkylimidazolium ring C2−H substituent and cellulose become more pronounced at high temperatures, counteracted by a net weakening of acetate–cellulose interactions. Moreover, for mixtures that exhibit critical solution behavior, phase separation is accompanied by the apparent recombination of cation–anion pairs.
Calvaruso G, Clough MT, Rechulski MDK, et al., 2017, On the Meaning and Origins of Lignin Recalcitrance: A Critical Analysis of the Catalytic Upgrading of Lignins Obtained from Mechanocatalytic Biorefining and Organosolv Pulping, CHEMCATCHEM, Vol: 9, Pages: 2691-2700, ISSN: 1867-3880
Kennema M, de Castro IBD, Meemken F, et al., 2017, Liquid-phase H-transfer from 2-propanol to phenol on Raney Ni: surface processes and inhibition, ACS Catalysis, Vol: 7, Pages: 2437-2445, ISSN: 2155-5435
Raney Ni is perhaps the most widely used catalyst for the transformation of biogenic molecules in industrial practice (e.g., as in the production of sugar alcohols and hardening of vegetable oils). Currently, Raney Ni has found another key application; the catalytic upstream biorefining (CUB) of lignocellulose in which the soluble products released from the lignocellulosic matrix undergo reductive processes, rendering depolymerized lignin oils in addition to high-quality holocellulosic pulps. Despite the industrial importance of Raney Ni, its surface chemistry is poorly understood. In this study, using the H-transfer reaction between 2-propanol (2-PrOH) and phenol as a model reaction, we studied the influence of various alcohols on the catalytic performance of Raney Ni. For the H-transfer hydrogenation of phenol to cyclohexanol, the inhibition of the catalyst increases in the order of secondary alcohols < primary alcohols < polyols at 130 °C. To better understand the observed inhibition, we also studied the molecular interactions of the various alcohols at the catalytic solid–liquid interface using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. The in situ spectroscopic data revealed that 2-PrOH adsorbs on at least two chemically different sites on the surface of Raney Ni. One of these two adsorption sites was attributed to the Ni site responsible for the saturation of the phenolic ring. The ATR-IR spectroscopic data also shows that the adsorption of phenol involves its hydroxyl group. Notably, the phenolic ring was found to be tilted with respect to the surface. Competitive adsorption of various other alcohols was also investigated at the catalytic solid–liquid interface. The presence of methanol inhibited the adsorption of 2-PrOH to a significantly greater degree than phenol. Therefore, it is proposed that hydrogen transfer hydrogenation of the phenolic ring is inhibited in the presence of additional alcohols mainly due t
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