Integration of Autohydrolysis and Organosolv Delignification for Efficient Acetone, Butanol, and Ethanol Production and Lignin Recovery

Abstract

A two-stage pretreatment, i.e., autohydrolysis and organosolv delignification, was used prior to enzymatic hydrolysis and fermentation by Clostridium acetobutylicum for the improvement of acetone, butanol, and ethanol (ABE) production from rice straw, pine, and elm. Through the autohydrolysis, a liquid, "autohydrolysate", containing 2−7 g/L sugar and 13−27 g/L oligomer, and a pretreated solid were obtained. The solid was subjected to organosolv delignification leading to 490−600 g of pretreated lignocelluloses (70%−74% cellulose) and 100−140 g lignin from each kilogram of lignocelluloses. The pretreated lignocelluloses were hydrolyzed to "cellulosic hydrolysates" and fermented to 6−10 g/L ABE. Through this process, 70−123 g of ABE was produced from each kilogram of lignocelluloses. "Overall hydrolysates" with further sugar concentrations of 16−50 g/L were obtained by hydrolysis of pretreated solid in the autohydrolysate. The yield of ABE production was progressed to 133 g ABE/kg elm by fermenting its overall hydrolysate.

Two‐step fractionation of Pinus radiata by autohydrolysis and organosolv delignification for enzymatic hydrolysis

“…For autocatalyzed organosolv solids, the cellulose content varied between 65 and 75% (Table ). These values are similar to those obtained by Amiri and Karimi (70–74%). The highest value (75%) was reached by the run AH 150 ‐ORG 200 , in which the value of DD obtained was also the highest (76%).…”

“…For the second step (ORG), autohydrolyzed wood (15 g) was loaded in the reactor with an ethanol/water mixture (50:50, w/w) at a wood/solvent ratio of 1:8 (w/v) . This pretreatment was carried out under autocatalyzed conditions (ORG 200 ) and acid‐catalyzed conditions (ORG A,185 ).…”

“…This pretreatment was carried out under autocatalyzed conditions (ORG 200 ) and acid‐catalyzed conditions (ORG A,185 ). In the acid organosolv step, the catalyst employed was sulfuric acid, whose dosage was fixed at 1% (w/w) . The operation mode in the reactor was the same as described for the AH step.…”

“…The main product of the organosolv step is a pretreated solid rich in cellulose, which can be subjected to a step of enzymatic hydrolysis or simultaneous saccharification and fermentation (SSF) for glucose obtainment or bioethanol production, respectively . Furthermore, this delignification with an organic solvent allows the production of lignin with high purity and high chemical reactivity, which is considered as a valuable byproduct in the development of bio‐based materials and chemicals . For instance, organosolv wheat straw lignin has been applied as a substitute for phenol in a phenol–formaldehyde–resol resin .…”

“…These works show the current interest in this pretreatment to achieve the fractionation of agricultural wastes and woody materials and allow the utilization of the separated fractions in subsequent steps, such as enzymatic hydrolysis. However, the use of softwood as raw material in this type of sequential pretreatment is limited …”