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Previously it was shown that wood chip compression or enzyme impregnation prior to refining reduces energy consumption and improves pulp quality. This work characterizes the effect of different magnitudes and rates of compression on the extent of enzymatic hydrolysis. A laboratory compressor and a controlled uniaxial load set-up were used to apply different compression ratios and compression times to mixed-softwood wood chips. The chips were subsequently subjected to enzymatic hydrolysis with a high-yield exoglucanase preparation to demonstrate changes in cellulose hydrolysis. Enzymatic hydrolysis yield increased with compression ratio but was unaffected by compression time. Increasing compression ratio increased removal of soluble molecules such as sugars and acid-soluble lignin. Microscopy imaging showed increased cell wall buckling and fracturing with increased compression. The morphological changes led to improved enzyme diffusion and resulted in higher available surface area. The improved cellulose hydrolysis is due to changes in wood morphology as well as the removal of extractives.

The adsorption of locust bean gum (LBG) onto Northern Bleached Softwood Kraft (NBSK) pulp improved paper tensile and burst strength and lowered refining energy by strengthening inter-fibre bonding. Adsorption kinetics and isotherms were investigated to develop a fundamental understanding of the adsorption mechanism. The adsorption rate followed pseudo-second-order kinetics and the activation energy was 99.34 kJ·mol−1, suggesting chemisorption. The adsorption rate constant increased rapidly with temperature from 25 to 45 °C (k = 1.93 to 24.03 g·mg−1·min−1), but the amount adsorbed at equilibrium decreased (qe = 1.91 to 0.48 mg·g−1 o.d. fibre). LBG adsorption to NBSK at 25 °C was consistent with the Langmuir adsorption model for LBG n = 5.00, and the equilibrium constant Kf = 2.57 mg·g−1·(mg·L−1)−1/n at 25 °C. Favorable adsorption conditions for negatively charged LBG were identified: 25 °C for 10 min, low dosage level ( 150 r.p.m.), acidic or neutral conditions (pH 2–7) without salt addition. Graphic abstract

The fate of hydrogen during glycerol aqueous phase reforming (APR) and the effect of in situ phenol hydrogenation (IGAPH) with Raney Ni on the glycerol APR mechanism were studied. Glycerol APR proc...

The diversity of hemicellulose oligomers enables many potential applications, but controlling yield and oligomer molar mass is challenging. Oligomer production by hydrolysis of softwoods was invest...

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Xylan obtained from birch (betula pendula) by a novel semi-industrial scale aqueous based method was used for studying the hydrolysis and consecutive hydrolysis-hydrogenation processes in continuous reactors. Dowex 50WX2-100 was chosen as the hydrolysis catalyst based on the results of catalyst screening performed previously in batch reactor. It was also observed to perform well in continuous reactor converting xylan to xylose in high yield under the studied reaction conditions. The influence of several reaction parameters were investigated for optimization. Similar experimental conditions used in the hydrolysis were then applied for studying one flow through hydrolysis and hydrogenation of the semi-industrial xylan. A consecutive catalyst bed consisting of ruthenium on carbon was introduced into the continuous reactor downstream from the hydrolysis bed to hydrogenate monosaccharides to xylitol. Hydrogen was co-fed into the reactor with the xylan solution. Reaction parameters, including temperature, residence time and hydrogen pressure, were varied to maximize the xylitol yield. The developed continuous process was demonstrated to be highly selective and efficient for the valorization of the semi-industrial xylan by yielding over 90% xylitol under optimal experimental conditions. It was noticed, that co-feeding hydrogenation decreased the degradation of monosaccharides during hydrolysis, thus improving the selectivity towards the target product and enabling remarkable process intensification. Moreover, mathematical modelling was performed for the hydrolysis and one flow through hydrolysis and hydrogenation processes. The models take into account the consecutive reaction pathways and the influence of the experimental conditions. Good fits of the model to the experimental data were obtained. The conversion of this novel, well characterized wood-based xylan to produce xylose or xylitol in continuous reactors has not been studied previously. The current work contributes significantly to understanding the processing of real feedstock in one flow through employing consecutive reactions and provides necessary data for process intensification.

In-situ glycerol aqueous phase reforming and phenol hydrogenation (IGAPH) was conducted with Raney Ni® at 180–240 °C for phenol to glycerol ratios from 0 to 4.88. Thermodynamic analysis of the complex IGAPH reaction system revealed the need to balance endothermic glycerol aqueous phase reforming (APR) and exothermic phenol hydrogenation reactions. It was found that maximum glycerol carbon selectivity for APR and maximum hydrogen selectivity for phenol hydrogenation occurred at 220 °C. Addition of phenol to glycerol APR increased glycerol conversion and glycerol carbon selectivity for APR. These observations can be attributed to an equilibrium shift to the forward APR reaction due to hydrogen consumption and suppression of competing parallel reactions by phenol hydrogenation. An initial rate model of the system suggests that IGAPH proceeds via the Langmuir-Hinshelwood mechanism and is rate-limited by phenol hydrogenation. Perspectives for future process development in terms of reaction heat and catalyst stability are provided.

Author(s): Jung, Seokwon; Trajano, Heather L; Yoo, Chang Geun; Foston, Marcus B; Hu, Fan; Tolbert, Allison K; Wyman, Charles E; Ragauskas, Arthur J

Enzyme recycling by adsorption from supernatant to fresh substrate is a promising strategy to reduce enzyme expenses and the production cost of lignocellulosic ethanol. The study was performed using oxygen-delignified wheat straw, and the effect of lignin content, enzyme loading, and hydrolysis time on recycling was determined. The percent of recycled cellulases, 0–35% of initial cellulase loading, increased with increasing enzyme loading and hydrolysis time but decreased with increasing lignin content. Cellulose conversions of 10–71% were achieved during the second hydrolysis round using only recycled cellulases indicating the existence of a highly active subset of enzymes. To achieve constant production of sugars during enzyme recycling, fresh cellulases were loaded before the second hydrolysis round to match the cellulase loading used in the first round. Subsequently, similar glucose, xylose, and protein concentrations were obtained at the end of the first and second rounds for all conditions. Recyclin...

Open foam structures are very beneficial as heterogeneous catalysts for three-phase processes, because they have high efficiency and low pressure drop. A mathematical model for open foam catalyst structures was developed. It was based on the concept of axial dispersion as flow pattern, on liquid-solid mass transfer effects and intrinsic kinetics on the active sites of the catalyst. Rate equations were presented for the hydrogenation of individual sugars and binary sugar mixtures on Ru/C catalysts and they were implemented in the mass transfer and flow models of the open foam catalyst. The flow pattern in the foam structure was confirmed with step change experiments with an inert tracer. The multiphase model was applied on the hydrogenation of arabinose and galactose in a laboratory-scale open foam catalyst bed. The model was able to reproduce the main features of the experimental observations, both for individual sugars and binary sugar mixtures.

To improve the efficiency of enzymatic hemicellulose removal from bamboo pre-hydrolysis kraft pulp, mechanical refining was conducted prior to enzyme treatment. Refining significantly improved the subsequent hemicellulose removal efficiency by xylanase treatment. Results showed that when PFI refining was followed by 3 h xylanase treatment, the xylan content of the bamboo pre-hydrolysis kraft pulp (after first stage oxygen delignification) could be decreased to 2.72% (w/w). After bleaching of enzyme treated pulp, the alpha-cellulose content was 93.4% (w/w) while the xylan content was only 2.38%. The effect of refining on fibre properties was investigated in terms of freeness, water retention value, fibre length and fibrillation characteristics. The brightness, reactivity and viscosity were also determined to characterize the quality of final pulp. Results demonstrated the feasibility of combining refining and xylanase treatment to produce high quality bamboo dissolving pulp.

This study presents high temperature water-only continuous flowthrough pretreatment coupled with nuclear magnetic resonance (NMR) as a promising analytical tool to examine the plant cell wall, to understand its recalcitrance (i.e., cell wall resistance to deconstruction), and to probe the chemistry occurring during batch pretreatment of biomass. (13)C-enriched corn stover stems were pretreated at 170°C for 60min with a hot-water flow rate of 20mL/min to control fractionation of the cell wall. This approach helped elucidate the nature of plant cell wall chemical recalcitrance and biomass pretreatment chemistry by tracking cell wall fragmentation as a function of time. Fractions of the reactor effluent were collected in a time-resolved fashion and characterized by various NMR techniques to determine the degree and sequence of fragments released, as well as, the chemical composition, molecular structure, and relative molecular weight of those released fragments.

Previous studies defined easy and difficult to hydrolyze fractions of hemicellulose that may result from bonds among cellulose, hemicellulose, and lignin. To understand how such bonds affect hydrolysis, Populus trichocarpa × Populus deltoides, holocellulose isolated from P. trichocarpa × P. deltoides and birchwood xylan were subjected to hydrothermal flow-through pretreatment. Samples were characterized by glycome profiling, HPLC, and UPLC-MS. Glycome profiling revealed steady fragmentation and removal of glycans from solids during hydrolysis. The extent of polysaccharide fragmentation, hydrolysis rate, and total xylose yield were lowest for P. trichocarpa × P. deltoides and greatest for birchwood xylan. Comparison of results from P. trichocarpa × P. deltoides and holocellulose suggested that lignin-carbohydrate complexes reduce hydrolysis rates and limit release of large xylooligomers. Smaller differences between results with holocellulose and birchwood xylan suggest xylan-cellulose hydrogen bonds limited hydrolysis, but to a lesser extent. These findings imply cell wall structure strongly influences hydrolysis.

Biorefineries of second generation (2G) are receiving more attention nowadays as an option for the development of bioeconomy all over the world. One of the main pretreatments utilized in this type of facilities for the conversion of lignocellulosic biomass is the use of hydrothermal processing using only water/steam as catalyst under different forms of heating (steam, electric heating jackets, or microwave radiation) at different temperatures. Currently, biorefineries are focused on obtaining feedstocks to produce biofuels, but the current position of these on the market shows that the new biorefineries must be integrated systems and so there is a need to focus on the valorization of the whole coproducts. One of them is hemicellulose, from which for instance oligomers could be derived and used in different areas as pharmaceutical products, food ingredients, fuels, chemicals, and bioplastics. In Mexico, avocado represents an important source for agro-industrial residues. These residues are in a process of valorization under the biorefinery concept, to obtain different types of bioproducts. This chapter describes the concepts usually utilized for the definition and understanding of biorefinery, especially the utilization of hydrothermal pretreatments. It focuses also on linking the concept of bioeconomy with biorefineries, and it introduces the utilization of avocado residues as an example of a Mexican residue with potential importance in the global market.

Considerable effort has been devoted to the development of biofuels from renewable lignocellulosic biomass. To resolve the challenges associated with the structural barrier of lignocellulosic biomass, hydrothermal pretreatment is applied to alter the structure and improve the accessibility of carbohydrate sugars to microorganisms or chemicals in the subsequent conversion processes. Hydrothermal pretreatment takes advantage of high moisture content of biomass and efficiently converts polysaccharides into monomeric sugars and their corresponding degradation products. To achieve this goal, multiple technologies have been explored using liquid water as the media, with or without addition of chemicals (acids or alkalis). However, there are difficulties in developing an optimized and universal treatment approach due to the heterogeneity of biomass. In this chapter, four major biomass types, wood, bamboo, agricultural residues, and agave, are discussed and compared with respect to feedstock composition and response to the various hydrothermal pretreatments. Moreover, the reaction pathways of individual biomass components (hemicellulose, cellulose, lignin, extractive, and ash) under different treatment conditions (acidic and alkaline) are also comparatively reviewed. Finally, the effects of pH, biomass solid loading, and reactor selection on pretreatment are presented.

Background During pretreatment, hemicellulose is removed from biomass via proton-catalyzed hydrolysis to produce soluble poly- and mono-saccharides. Many kinetic models have been proposed but the dependence of rate on proton concentration is not well-defined; autohydrolysis and dilute-acid hydrolysis models apply very different treatments despite having similar chemistries. In this work, evolution of proton concentration is examined during both autohydrolysis and dilute-acid hydrolysis of hemicellulose from green bamboo. An approximate mathematical model, or “toy model”, to describe proton concentration based upon conservation of mass and charge during deacetylation and ash neutralization coupled with a number of competing equilibria, was derived. The model was qualitatively compared to experiments where pH was measured as a function of time, temperature, and initial acid level. Proton evolution was also examined at room temperature to decouple the effect of ash neutralization from deacetylation. Results The toy model predicts the existence of a steady-state proton concentration dictated by equilibrium constants, initial acetyl groups, and initial added acid. At room temperature, it was found that pH remains essentially constant both at low initial pH and autohydrolysis conditions. Acid is likely in excess of the neutralization potential of the ash, in the former case, and the kinetics of neutralization become exceedingly small in the latter case due to the low proton concentration. Finally, when the hydrolysis reaction proceeded at elevated temperatures, one case of non-monotonic behavior in which the pH initially increased, and then decreased at longer times, was found. This is likely due to the difference in rates between neutralization and deacetylation. Conclusions The model and experimental work demonstrate that the evolution of proton concentration during hydrolysis follows complex behavior that depends upon the acetyl group and ash content of biomass, initial acid levels and temperature. In the limit of excess added acid, pH varies very weakly with time. Below this limit, complex schemes are found primarily related to the selectivity of deacetylation in comparison to neutralization. These findings indicate that a more rigorous approach to models of hemicellulose hydrolysis is needed. Improved models will lead to more efficient acid utilization and facilitate process scale-up.