Responses of biomass briquetting and pelleting to water-involved pretreatments and subsequent enzymatic hydrolysis

Effect of pelleting on the enzymatic digestibility of corn stover

Pelleting of lignocellulosic biomass to improve its transportation, storage and handling impacts subsequent processing and conversion. This work reports the role of high moisture pelleting in the enzymatic digestibility of corn stover prior to pretreatment, together with associated substrate characteristics. Pelleting increases the digestibility of unpretreated corn stover, from 8.2 to 15.5% glucan conversion, at 5% solid loading using 1 FPU Cellic® CTec2 per g solids. Compositional analysis indicates that loose and pelleted corn stover have similar non-dissolvable compositions, although their extractives are different. Enzymatic hydrolysis of corn stover after size reduction to normalize particle sizes and removal of extractives confirms that pelleting improves corn stover digestibility. Such differences may be explained by the decreased particle size, improved substrate accessibility, and hydrolysis of cross-linking structures induced by pelleting. These findings are useful for the development of processing schemes for sustainable and efficient use of lignocellulose.

Effects of preheating on briquetting and subsequent hydrothermal pretreatment for enzymatic saccharification of wheat straw

Briquetting of plant biomass with low bulk density is an advantage for handling, transport, and storage of the material, and heating of the biomass prior to the briquetting facilitates the densification process and improves the physical properties of the briquettes. This study investigates the effects of preheating prior to briquetting of wheat straw (WS) on subsequent hydrothermal pretreatment and enzymatic conversion to fermentable sugars. WS (11% moisture content) was densified to briquettes under different conditions; without preheating or with preheating at 75 or 125°C for either 5 or 10 min. Subsequent hydrothermal pretreatment was done for both un-briquetted WS and for briquettes. Enzymatic saccharification was afterwards performed for all samples. The results showed that as expected, nonpretreated WS briquettes gave very low sugar yields (22-29% of the cellulose content), even though preheating at 125°C prior to briquetting (without pretreatment) improved sugar yields somewhat. When combined with pretreatment, briquetting with preheating showed neutral or negative effects on sugar yield. This result suggests that moderate preheating (75°C for 5 min) before briquetting improved bulk density and compressive resistance of briquettes without impeding subsequent enzymatic conversion. However, excessive preheating (75 or 125°C for 10 min) before briquetting may result in irreversible structural modifications that hinder the interaction between biomass and water during pretreatment, thereby decreasing the accessibility of cellulose to enzymatic saccharification.

Recycling solvent system in phosphoric acid plus hydrogen peroxide pretreatment towards a more sustainable lignocellulose biorefinery for bioethanol

Pretreating lignocellulosic biomass by phosphoric acid plus hydrogen peroxide (PHP) was integrated with recovering concentrated phosphoric acid (CPA), lignin, and treating phosphorus (P) wastewater. Results indicated no significant effects on cellulose recovery was observed by promoting ethanol addition, but CPA and lignin recovery were improved to 80.0% and 23.3%, respectively. Increasing water addition did not greatly affect CPA recovery (80.0-80.4%), and lignin recovery (22.8-23.6%). Consequently, the ratio of 11:1 (ethanol/PHP solution) and 4:1 (water/de-ethanol liquor) were suggested for solid/liquid separation and lignin precipitation. Average 86.0% CPA was recycled for pretreatment (≥11 runs) with average 96.3% cellulose-glucose conversion. A specially-developed biochar from crab shell was efficient on P removal with maximal adsorption capacity of 261.6 mg/g. Pretreating 1.0 kg wheat straw by 1.1 kg CPA harvested 155.0 g ethanol, 45.0 g high purity lignin and 4.9 kg P-rich biochar fertilizer. Recovering CPA, biochar-fertilizer and lignin, and P wastewater treatment made PHP pretreatment towards more sustainable and cleaner.

Bioethanol production from wheat straw by phosphoric acid plus hydrogen peroxide (PHP) pretreatment via simultaneous saccharification and fermentation (SSF) at high solid loadings

Phosphoric acid plus hydrogen peroxide (PHP) pretreatment was employed on wheat straw for ethanol conversion by simultaneous saccharification and fermentation (SSF) at high loadings. Results showed solid loading of PHP-pretreated wheat straw can be greatly promoted to 20%. Although more enzyme input improved ethanol conversion significantly, it still can be potentially reduced to 10-20 mg protein/g cellulose. Increasing yeast input also promoted ethanol conversion, however, the responses were not significant. Response surface method was employed to optimize SSF conditions with the strategy of maximizing ethanol conversion and concentration and minimizing enzyme and yeast input. Results indicated that ethanol conversion of 88.2% and concentration of 69.9 g/L were obtained after 120 h SSF at solid loading of 15.3%, and CTec2 enzyme and yeast were in lower input of 13.2 mg protein/g cellulose and 1.0 g/L, respectively. Consequently, 15.5 g ethanol was harvested from 100 g wheat straw in the optimal conditions.

Improving agricultural straw preparation logistics stream in bio-methane production: experimental studies and application analysis

Long-term production in commercial straw biogas plants has been rare in China due to inefficiencies in the logistics stream. Biomass densification could be a potential solution to this issue. Therefore, we conducted a study to evaluate whether biomass densification is a more efficient and sustainable option. We performed methane production experiments to investigate fermentation characteristics of briquettes (with a new pretreatment, model II) and rubs (with a common pretreatment, model I). A 3000-m³ biogas plant was used to conduct a comparative analysis with solar eMergy joules. Results showed that the methane yield of briquettes of corn stover was 66.74% higher than that of rubs, and the briquettes had better digestion performance in terms of CH₄ content, VFA, and alcohol. The two models required almost the same eMergy investment input, while model II obtained a greater quantity of net eMergy (16.5% higher) in comparison with model I. The net eMergy yield ratio (EYR) (biogas only) of model I and model II was 0.99 and 1.67, respectively, showing less market competitiveness for commercial operations with model I. Meanwhile, the logistic costs of model II could be reduced to approximately US $34,514 annually.

Pretreating wheat straw by phosphoric acid plus hydrogen peroxide for enzymatic saccharification and ethanol production at high solid loading

Wheat straw was pretreated by phosphoric acid plus hydrogen peroxide (PHP) for enzymatic hydrolysis and ethanol fermentation at high solid loadings. Results indicated solid loading could reach 20% with 77.4% cellulose-glucose conversion and glucose concentration of 164.9g/L in hydrolysate, it even was promoted to 25% with only 3.4% decrease on cellulose-glucose conversion as the pretreated-wheat straw was dewatered by air-drying. 72.9% cellulose-glucose conversion still was achieved as the minimized enzyme input of 20mg protein/g cellulose was employed for hydrolysis at 20% solid loading. In the corresponding conditions, 100g wheat straw can yield 11.2g ethanol with concentration of 71.2g/L by simultaneous saccharification and fermentation. Thus, PHP-pretreatment benefitted the glucose or ethanol yield at high solid loadings with lower enzyme input. Additionally, decreases on the maximal cellulase adsorption and the direct-orange/direct-blue indicated drying the PHP-pretreated substrates negatively affected the hydrolysis due to the shrinkage of cellulase-size-accommodable pores.

An Experimental Study of Briquetting Process of Torrefied Rubber Seed Kernel and Palm Oil Shell

Torrefaction process of biomass material is essential in converting them into biofuel with improved calorific value and physical strength. However, the production of torrefied biomass is loose, powdery, and nonuniform. One method of upgrading this material to improve their handling and combustion properties is by densification into briquettes of higher density than the original bulk density of the material. The effects of critical parameters of briquetting process that includes the type of biomass material used for torrefaction and briquetting, densification temperature, and composition of binder for torrefied biomass are studied and characterized. Starch is used as a binder in the study. The results showed that the briquette of torrefied rubber seed kernel (RSK) is better than torrefied palm oil shell (POS) in both calorific value and compressive strength. The best quality of briquettes is yielded from torrefied RSK at the ambient temperature of briquetting process with the composition of 60% water and 5% binder. The maximum compressive load for the briquettes of torrefied RSK is 141 N and the calorific value is 16 MJ/kg. Based on the economic evaluation analysis, the return of investment (ROI) for the mass production of both RSK and POS briquettes is estimated in 2-year period and the annual profit after payback was approximately 107,428.6 USD.

Pretreating wheat straw by the concentrated phosphoric acid plus hydrogen peroxide (PHP): Investigations on pretreatment conditions and structure changes

Wheat straw was pretreated by PHP (the concentrated H3PO4 plus H2O2) to clarify effects of temperature, time and H3PO4 proportion on hemicellulose removal, delignification, cellulose recovery and enzymatic digestibility. Overall, hemicellulose removal was intensified by PHP comparing to the concentrated H3PO4. Moreover, efficient delignification specially happened in PHP pretreatment. Hemicellulose removal and delignification by PHP positively responded to temperature and time. Increasing H3PO4 proportion in PHP can promote hemicellulose removal, however, decrease the delignification. Maximum hemicellulose removal and delignification were achieved at 100% and 83.7% by PHP. Enzymatic digestibility of PHP-pretreated wheat straw was greatly improved by increasing temperature, time and H3PO4 proportion, and complete hydrolysis can be achieved consequently. As temperature of 30-40°C, time of 2.0 h and H3PO4 proportion of 60% were employed, more than 92% cellulose was retained in the pretreated wheat straw, and 29.1-32.6g glucose can be harvested from 100g wheat straw.

Effects of biomass densification on anaerobic digestion for biogas production

To elucidate the possibility of applying biomass densification in anaerobic digestion, pelleting and briquetting were investigated for biogas production, and anaerobic digestion using densified biomass at higher solid content was also discussed.

Pretreating lignocellulosic biomass by the concentrated phosphoric acid plus hydrogen peroxide (PHP) for enzymatic hydrolysis: evaluating the pretreatment flexibility on feedstocks and particle sizes

In order to seek a high-efficient pretreatment path for converting lignocellulosic feedstocks to fermentable sugars by enzymatic hydrolysis, the concentrated H₃PO₄ plus H₂O₂ (PHP) was attempted to pretreat different lignocellulosic biomass for evaluating the pretreatment flexibility on feedstocks. Meanwhile, the responses of pretreatment to particle sizes were also evaluated. When the PHP-pretreatment was employed (final H₂O₂ and H₃PO₄ concentration of 1.77% and 80.0%), 71-96% lignin and more than 95% hemicellulose in various feedstocks (agricultural residues, hardwood, softwood, bamboo, and their mixture, and garden wastes mixture) can be removed. Consequently, more than 90% glucose conversion was uniformly achieved indicating PHP greatly improved the pretreatment flexibility to different feedstocks. Moreover, when wheat straw and oak chips were PHP-pretreated with different sizes, the average glucose conversion reached 94.9% and 100% with lower coefficient of variation (7.9% and 0.0%), which implied PHP-pretreatment can significantly weaken the negative effects of feedstock sizes on subsequent conversion.