Yong Tang

Prehydrolysis and cold caustic extraction (CCE) are two effective approaches to convert the traditional Kraft pulp to a dissolving‐grade pulp. Compared to prehydrolysis, CCE has several positive attributes but reduces final pulp reactivity. To gain insight into the factors that influence the reactivity of CCE treated cellulose, we compared the surface morphology, supramolecular properties and fibre properties of commercial dissolving pulp from prehydrolysis to dissolving grade cellulose upgraded using CCE. CCE treatment promoted the fibril aggregation and modified the initial cellulose I on Kraft pulps to cellulose II, thus decreasing final pulp reactivity. Various “post‐treatments” such as mechanical refining, steam explosion, induction of fibre kink and curl, sulfuric acid hydrolysis and endoglucanase hydrolysis effectively recover the reactivity lost during the production of dissolving pulp cellulose using a CCE step. Mechanical refining combined with endoglucanase treatment had the greatest effect increasing the reactivity from 32% to 75%.

The merit of deacetylation of corn stover prior to pretreatment is decreasing the formation of inhibitors and improving enzyme hydrolysis, proved in dilute acid pretreatment. However, few studies are done on how deacetylation would affect bioconversion process containing steam explosion. In this study, the effect of deacetylation on steam explosion was conducted using poplar as substrate. About 57 to 90% of acetyl group in poplar, depending on alkaline types and concentration, was removed by dilute alkaline deacetylation in 6 h. Deacetylation eliminated over 85% of inhibitor formation during downstream steam explosion. However, deacetylation prior to steam explosion decreased the dissolution of hemicellulose, thus reducing the cellulose accessibility of pretreated poplar, finally resulting in 5–20% decrease in glucose yield and 20–35% decrease in xylose yield. The addition of 5% SO₂ during steam explosion significantly improved the hydrolysis of deacetylated and pretreated poplar without significantly increasing the concentration of inhibitors. Incorporating 45 mmol/kg sulfoacid group in lignin fraction of deacetylated and then pretreated poplar dramatically improved the xylose yield to about 100% and increased the glucose yield by 30%.

Industrial wastes that are well pre-treated during related upstream industrial processes, such as cassava residuals and furfural residuals, are becoming promising feedstocks for producing biofuels. To better use these wastes, an approach must be flexible in their use during biologically based ethanol production. In the current study, three scenarios, including the cellulosic ethanol process, the starchy ethanol process, and the integration of 1 G and 2 G ethanol, were compared for ethanol production from CR, FR, and corn. Compared with the starch ethanol process, the cellulosic ethanol process and integration of 1 G and 2 G ethanol produced ethanol at a higher ethanol concentration and yield. Of the three processes, the integrated process utilized over 75% of polysaccharides when using multiple materials as feedstocks. Protein, cellulose, and starch were yield-determining components in the high-solid integration process. Protein provided important nutrients for yeast cells. The influences of cellulose and starch were associated with product inhibition of cellulases and viscosity. Lignin had a low or negligible influence. For an integration process at a 20% (w/w) substrate loading, the optimum concentrations of protein, cellulose, and starch included >1%, from 4% to 5%, and from 8% to 11%, respectively. At the optimum concentrations, the integration process obtained a final ethanol concentration of about 70 g L⁻¹ and an ethanol yield of about 80%.

Furfural residue (FR) is a waste lignocellulosic material with enormous potential for bioethanol production. In this study, bioethanol production from FR after delignification was compared. Hydrophilic variation was measured by conductometric titration to detect the relationship between hydrophilicity and bioethanol production. It was found that ethanol yield increased as delignification enhanced, and it reached up to 75.6% of theoretical yield for samples with 8.7% lignin. The amount of by-products decreased as delignification increased. New inflection points appeared in conductometric titration curves of samples that were partially delignified, but they vanished in the curves of the highly delignified samples. Total charges and carboxyl levels increased after slight delignification, and they decreased upon further delignification. These phenomena suggested some new hydrophilic groups were formed during pretreated delignification, which would be beneficial to enzymatic hydrolysis. However, some newly formed groups may act as toxicant to the yeast during simultaneous saccharification and fermentation.

Enhancement of enzymatic digestibility by some supplementations could reduce enzyme loading and cost, which is still too high to realize economical production of lignocellulosic biofuels. A recent study indicates that yeast hydrolysates (YH) have improved the efficiency of cellulases on digestibility of furfural residues (FR). In the current work, the components of YH were separated by centrifugation and size exclusion chromatography and finally characterized in order to better understand this positive effect.

Effect of Ultrasonic-assisted Pretreatment on Hydrolysis and Fermentation of Acorn Starch

Xylitol fermentation production from corncob acid hydrolysate has become an attractive and promising process. However, corncob acid hydrolysate cannot be directly used as fermentation substrate owing to various inhibitors. In this work, soaking in aqueous ammonia (SAA) pretreatment was employed to reduce the inhibitors in acid hydrolysate. After detoxification, the corncob acid hydrolysate was fermented by immobilizedCandida tropicaliscell to produce xylitol. Results revealed that SAA pretreatment showed high delignification and efficient removal of acetyl group compounds without effect on cellulose and xylan content. Acetic acid was completely removed, and the content of phenolic compounds was reduced by 80%. Furthermore, kinetic behaviors of xylitol production by immobilizedC. tropicaliscell were elucidated from corncob acid hydrolysate detoxified with SAA pretreatment and two-step adsorption method, respectively. The immobilizedC. tropicaliscell showed higher productivity efficiency using the corncob acid hydrolysate as fermentation substrate after detoxification with SAA pretreatment than by two-step adsorption method in the five successive batch fermentation rounds. After the fifth round fermentation, about 60 g xylitol/L fermentation substrate was obtained for SAA pretreatment detoxification, while about 30 g xylitol/L fermentation substrate was obtained for two-step adsorption detoxification.