Performance of AFEX™ pretreated rice straw as source of fermentable sugars: the influence of particle size

Abstract

BackgroundIt is widely believed that reducing the lignocellulosic biomass particle size would improve the biomass digestibility by increasing the total surface area and eliminating mass and heat transfer limitation during hydrolysis reactions. However, past studies demonstrate that particle size influences biomass digestibility to a limited extent. Thus, this paper studies the effect of particle size (milled: 2 mm, 5 mm, cut: 2 cm and 5 cm) on rice straw conversion. Two different Ammonia Fiber Expansion (AFEX) pretreament conditions, AFEX C1 (low severity) and AFEX C2 (high severity) are used to pretreat the rice straw (named as AC1RS and AC2RS substrates respectively) at different particle size.ResultsHydrolysis of AC1RS substrates showed declining sugar conversion trends as the size of milled and cut substrates increased. Hydrolysis of AC2RS substrates demonstrated opposite conversion trends between milled and cut substrates. Increasing the glucan loading to 6% during hydrolysis reduced the sugar conversions significantly in most of AC1RS and AC2RS except for AC1RS-2 mm and AC2RS-5 cm. Both AC1RS-2 mm and AC2RS-5 cm indicated gradual decreasing trends in sugar conversion at high glucan loading. Analysis of SEM imaging for URS and AFEX pretreated rice straw also indicated qualitative agreement with the experimental data of hydrolysis. The largest particle size, AC2RS-5 cm produced the highest sugar yield of 486.12 g/kg of rice straw during hydrolysis at 6% glucan loading equivalent to 76.0% of total theoretical maximum sugar yield, with an average conversion of 85.9% from total glucan and xylan. In contrast, AC1RS-5 cm gave the lowest sugar yield with only 107.6 g/kg of rice straw, about 16.8% of total theoretical maximum sugar yield, and equivalent to one-quarter of AC2RS-5 cm sugar yield.ConclusionsThe larger cut rice straw particles (5 cm) significantly demonstrated higher sugar conversion when compared to small particles during enzymatic hydrolysis when treated using high severity AFEX conditions. Analysis of SEM imaging positively supported the interpretation of the experimental hydrolysis trend and kinetic data.

Rice straw as a feedstock for biofuels: Availability, recalcitrance, and chemical properties

“…Usually SE is carried out at very high pressure and temperature with supplementation of catalysts like ammonia, acid, alkali, or oxidizing agents (i.e., hydrogen peroxide) may help in achieving high efficiency at milder temperatures and pressures. Zhou et al . showed a linear increase in rice straw CrI% (from 38% to 49% and 51%) with increasing temperature (210°C and 220°C, respectively) this was attributed to the reduction in hemicellulose and lignin content (Table ).…”

“…This was partially attributed to its reduced lignin content and its distinct wall polymer features such as cellulose CrI, hemicellulosic Xyl/Ara ratio, and lignin H/G proportion . Instead of burning, if all rice straw were converted into bioethanol, it would become the single largest feedstock for second‐generation ethanol production in the world . In addition, rice straw may also be utilized as a feedstock for producing value‐added chemicals and bio‐derived materials via the biorefinery concept.…”

Producing carbohydrate-rich microalgal biomass grown under mixotrophic conditions as feedstock for biohydrogen production

“…In microalgae, the carbohydrates are either accumulated in the plastids or become the major component of inner cell walls [5]. Due to the lack of lignin in microalgae-based cellulose, saccharification of the microalgal biomass becomes much easier than with lignocellulosic materials [12]. In addition, microalgae grow faster than terrestrial plants, and also have a higher CO 2 fixation rate [16].…”

Study on loading coefficient in steam explosion process of corn stalk

“…This practice creates serious environmental, safety and health issues, and there is a strong desire to find alternative ways to remove the corn stalk after each harvesting season. Recent research findings on bioconversion of lignocellulosic feedstocks to biofuels and high value biochemicals offer a preferable means for farmers wishing to be more environmentally friendly while adding an extra source of income (Alvira et al, 2010;Chen and Qiu, 2010;Harun et al, 2013).…”

“…Bioconversion is an economical and environmentally beneficial way of biomass utilization comparing to open burning and chemical disposal (Chen and Qiu, 2010;Himmel et al, 2007;Harun et al, 2013). Various feedstocks have been evaluated for their potential as a feedstock for bioconversion and as such several common process variables in the overall lignocelluloses-to-ethanol (i.e., pretreatment, enzymatic hydrolysis, fermentation) have been established (Chen, 2013).…”