M. P. García-Aparicio

Enhancing the enzymatic digestibility of sugarcane bagasse through the application of an ionic liquid in combination with an acid catalyst.

Various ionic liquids have been identified as effective pretreatment solvents that can enhance the cellulose digestibility of lignocellulose by removing lignin, one of the main factors contributing to the recalcitrant nature of lignocellulose. 1‐Butyl‐3‐methylimidazolium methylsulfate ([BMiM]MeSO4) is a potential delignification reagent, hence its application as a pretreatment solvent for sugarcane bagasse (SB) was investigated. The study also evaluated the benefit of an acid catalyst (i.e., H2SO4) and the effect of pretreatment conditions, which varied within a time and temperature range of 0–240 min and 50–150°C, respectively. The use of an acid catalyst contributed to a more digestible solid and a higher degree of delignification. However, the [BMiM]MeSO4‐H2SO4 combination failed to produce a fully digestible solid, as a maximum cellulose digestibility of 77% (w/w) was obtained at the optimum pretreatment condition of 125°C for 120 min. Furthermore, up to half of the lignin content could be extracted during pretreatment, while simultaneously extensive, sometimes complete, removal of xylan, the presence of which, also hampers cellulose digestibility. Hence, [BMiM]MeSO4 has been identified an effective pretreatment solvent for SB as the application thereof both significantly improved digestibility, and simultaneously removed two of the main factors contributing to the recalcitrant nature of lignocellulose. As xylan and lignin have potential value as precursor chemicals, the existing process may in future be extended toward substrate fractionation, a biorefinery concept where value is added to all feedstock constituents.

Evaluation of steam-treated giant bamboo for production of fermentable sugars

Giant bamboo plantations are currently being established in the Southern Africa region and can be considered as potential lignocellulosic feedstock for the production of second generation bioethanol. In this study, giant bamboo internodal material was subjected to sulphur dioxide (SO2) impregnated steam pretreatment prior to enzymatic hydrolysis. The effect of temperature, residence time, and acidity on the overall sugar recovery and byproduct formation was studied using response surface response technology according to a central composite experimental design (CCD) at a fixed SO2 concentration of 2.5% (w/w liquid) after impregnation. The results showed that pretreatment conditions with combined severity factor (CSF) values and enzyme dosages greater than 1.72 and 30 FPU/g water insoluble solid, respectively, were required to obtain an efficient glucan digestibility and a good overall glucose recovery. Up to 81.2% of the sugar in the raw material was recovered for a CSF of 2.25. However, considering overall sugar yield and byproducts concentration, the pretreated material obtained with a CSF of 1.62 can be considered as the most appropriate for SSF experiments using a xylose‐utilizing yeast. At these conditions, it could be possible to obtain up to 247 L of ethanol per dry ton of giant bamboo considering hexose and pentose sugars fermentation. This amount could be increased up to 292 L of ethanol per dry ton of giant bamboo with the maximum sugar yield obtained (CSF = 2.25) if the microorganism possesses robust fermentative characteristics as well as a high resistance to pretreatment by‐products.

Steam explosion pretreatment of triticale (× Triticosecale Wittmack) straw for sugar production.

Triticale, a non-food based, low-cost and well-adapted crop in marginal lands has been considered as a potential 1G and 2G feedstock for bio-ethanol production. In this work, triticale straw was evaluated as a source of fermentable sugars by combination of uncatalyzed steam explosion and enzymatic hydrolysis. Pretreatment conditions with severities from 3.05 to 4.12 were compared in order to identify conditions that favour the recovery of hemicellulose-derived sugars, cellulose digestibility or the combined sugars yield (CSY) from the pretreatment-enzymatic hydrolysis. Xylose oligosaccharide was the major sugar in hydrolysates from all pretreatment conditions. Maximum hemicellulose-sugars recovery (52% of the feedstock content) was obtained at 200 °C and 5 min. The highest cellulose digestibility (95%) was found at 200 °C - 15 min, although glucose recovery from hydrolysis was maximised at 200 °C - 10 min (digestibility >92%) due to higher mass yield of pretreated solids. The maximum CSY (nearly 77% of theoretical content) was obtained at 200 °C - 5 min. Sugar loss after pretreatment was observed to higher extent at harsher severities. However, the concentrations of sugar degradation products and acetic acid were at levels below tolerance limits of the downstream biological conversions. Steam explosion pretreatment without acid impregnation is a good technology for production of fermentable sugars from triticale straw. This work provides foundation for future autohydrolysis steam explosion optimization studies to enhanced sugars recovery and digestibility of triticale straw.

Lignin enrichment and enzyme deactivation as the root cause of enzymatic hydrolysis slowdown of steam pretreated sugarcane bagasse

The enzymatic hydrolysis (EH) rate normally decreases during the hydrolysis, leaving unhydrolyzed material as residue. This phenomenon occurs during the hydrolysis of both cellulose (avicel) and lignocellulosic material, in nature or even pretreated. The progression of EH of steam pretreated sugarcane bagasse was associated with an initial (fast), intermediate (slower) and recalcitrant (slowest) phases, at glucan to glucose conversion yields of 61.7, 81.6 and 86%, respectively. Even though the EH of avicel as a simpler material than steam pretreated sugarcane bagasse, EH slowdown was present. The less thermo-stable endo-xylanase lost 58% of initial enzyme activity, followed by β-glucosidase that lost 16%, culminating in FPase activity loss of 30% in the first 24hours. After 72hours of EH the total loss of FPase activity was 40% compared to the initial activity. Analysis of the solid residue from EH showed that lignin content, phenolic compounds and ash increased while glucan decreased as hydrolysis progressed. During the initial fast phase of EH, the total solid residue surface area consisted predominantly of internal surface area. Thereafter, in the intermediate and recalcitrant phases of EH, the ratio of external:internal surface area increased. The proposed fiber damage and decrease in internal surface area, probably by EH action, was visualized by scanning electron microscopy imagery. The higher lignin/glucan ratio as EH progressed and enzyme deactivation by thermo instability were the main effects observed, respectively to substrate and enzyme.

Effect of Alkaline Hemicellulose Extraction on Kraft Pulp Fibers from Eucalyptus Grandis

Abstract The alkaline extraction of hemicelluloses from hardwoods prior to pulping, for further conversion to value-added products, seems to be a promising pathway for paper mills to increase profit and improve sustainability. However, the amount of hemicellulose extracted will be limited by the requirement to maintain pulp quality and pulp yield in comparison to existing pulping processes. The effects of NaOH concentration, temperature, and time on hemicellulose extraction of Eucalyptus grandis were studied using a statistical experimental design. Extracted wood chips were subjected to kraft pulping to evaluate the effect of the extraction on cooking chemicals, pulp quality, and handsheet paper strengths. The selective xylan recovery (12.4% dry mass) from E. grandis combined with low-cooking, active alkali charge, and less cooking time advantaged the xylan extraction and subsequent modified kraft pulping process under the studied conditions. Pulp viscosity, breaking strength, and tensile index of handsheets were slightly improved.

Biomass Conversion to Bioenergy Products

The rendering of bioenergy products such as heat, fuel and electricity requires the conversion of sustainably produced biomass feedstock by means of thermochemical and biological processes. Such processes convert feedstocks into higher energy-value products amenable to industrial and domestic applications. This chapter deals with the nature of the conversion processes, the biomass feedstock requirements for these processes and the resulting quality of bioenergy products. In addition, the present chapter will also consider the application potential of different conversion technologies to both industrial and rural areas in the Southern Hemisphere.