Microwave-assisted hydrotropic pretreatment as a new and highly efficient way to cellulosic ethanol production from maize distillery stillage

Abstract

Aim of the study was to assess the suitability of the combined use of microwave radiation and sodium cumene sulfonate under optimized process conditions for the preparation of maize stillage biomass as a raw material for the production of cellulosic ethanol. The key parameter guaranteeing a high level of lignin removal from biomass (ca. 44%) was concentration of hydrotrope. Even at high biomass concentration (16% w/v) and a cellulase enzyme dose of about 4 filter-paper units/g, maize stillage biomass subjected to microwave-assisted hydrotropic pretreatment was highly susceptible to enzymatic degradation, which resulted in 80% hydrolysis yield. It is possible to obtain a fermentation medium with a very high glucose concentration (up to 80 g/L), without fermentation inhibitors and, as a consequence, to reach a very high level of sugar conversion to ethanol (concentration above 40 g/L), even as much as 95% of theoretical yield. Microwave hydrotropic treatment with sodium cumene sulfonate is a very effective way to prepare waste maize stillage biomass for the production of cellulosic ethanol. The degradation of the lignocellulose structure by the simultaneous use of microwaves and hydrotropes ensured a high degree of conversion of structural polysaccharides to bioethanol. The method provides a high level of enzymatic degradation of cellulose, leading to a medium with high content of released sugars suitable for bioconversion, which is in line with assumptions of the second-generation ethanol production technology. Key points • Microwave-assisted hydrotropic pretreatment is a new way to cellulosic ethanol production. • Microwave-assisted hydrotropic delignification removes 44% of lignin from biomass. • No fermentation inhibitors are obtained after microwave-assisted hydrotropic pretreatment. • High ethanol concentration (above 40 g/L) and fermentation yield (95% of theoretical yield) from biomass after microwave-assisted hydrotropic pretreatment.

Microwave-Assisted Urea-Based-Hydrotropic Pretreatment of Rice Straw: Experimental Data and Mechanistic Kinetic Models

“…However, the absence of inhibitor formation in hydrotropic pretreatments was reported by several researchers. It was found that there was no inhibitor produced in microwave-assisted hydrotropic pretreatment of maize distillery stillage and in hydrotropic pretreatment of cotton stalk . Moreover, although some literatures reported the absence of inhibitor production in their microwave-assisted pretreatment, in this kinetic model, the formation of inhibitors was represented by the term of formation of soluble lignin from lignin (eq b) as well as formation of soluble hemicellulose from hemicellulose (eq ).…”

“…16,19,20 The combination of microwave heating and hydrotrope in biomass pretreatment was also reported. 21 It was reported that the cellulose concentration increased, while 44% of lignin was removed from the distillery stillage which was pretreated with sodium cumene sulfonate under microwave heating. 21 Moreover, although the main objective of the pretreatment is lignin removal, it is important to note that pretreatment with chemical agents as well as microwave heating also resulted in the solubilization of cellulose and hemicellulose.…”

“…Microwave heating is characterized as a high-energy-efficient process due to its rapid, uniform, direct, and selective heating. The low-energy requirement, the low-reaction temperature, the simplicity of the process, and the higher ability in removing the acetyl groups in hemicellulose are some interesting features of the microwave-assisted pretreatment process. − A myriad of literature on lignocellulose pretreatment have also reported the combination of the microwave process with several chemicals such as alkali, deep eutectic solvents, subcritical water, ethanol, and acetic acid. ,, The combination of microwave heating and hydrotrope in biomass pretreatment was also reported . It was reported that the cellulose concentration increased, while 44% of lignin was removed from the distillery stillage which was pretreated with sodium cumene sulfonate under microwave heating …”

Delignification efficiency of various types of biomass using microwave-assisted hydrotropic pretreatment

“…Waste distillery stillage biomass is a by-product of the technology of production of first generation ethanol involving starch raw materials. Some technologies are marked by barothermal processing of the raw material (5–6 atm, 50 min) affecting the structure of lignocelulose 35 . The effectiveness of the delignification of sugarcane bagasse using sodium xylene sulfonate (NaXS) also increases by ca.…”

Recent advances in hydrotropic solvent systems for lignocellulosic biomass utilization

“…The authors used microwave radiation to overcome the limitation of aqueous salt solution. 135 High concentrations of ethanol (≥40 g L −1 ) were obtained from biomass using this process, achieving 95% of the theoretical fermentation yield. This microwave-assisted hydrotropic fractionation method removed 44% of lignin from biomass without generating any fermentation inhibitors.…”