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.
Highlights
The second-generation ethanol production is based on waste lignocellulosic biomass, sometimes even solving problems with waste management; it does not compete for raw materials used for food or feed production (Balat 2011; Sarkar et al 2012)
In the first stage of research, we examined the impact of the conditions of microwave hydrotropic extraction on biomass extractives, enzymatic hydrolysis of cellulose, and the composition of biomass
We analyzed the effect of various combinations of conditions of microwave hydrotropic treatment, i.e., NaCS concentration (0, 10, 20% v/v), exposure time (10, 20, 30 min), and pressure (39, 78, 117 PSI) on the extraction of biomass components, changes in biomass composition, and the amount of glucose released from pre-processed biomass as after hydrolysis with cellulases
Summary
The second-generation ethanol production is based on waste lignocellulosic biomass, sometimes even solving problems with waste management; it does not compete for raw materials used for food or feed production (Balat 2011; Sarkar et al 2012). Our and other authors’ studies clearly pointed to the usefulness of microwave pretreatment in a diluted sulfuric acid environment in the degradation of lignocellulose to simple sugars, which can be used in bioconversion and biosynthesis processes (Ethaib et al 2016; Germec et al 2017; Amini et al 2018; Mikulski et al 2019; Mikulski and Kłosowski 2020a; Bhardwaj et al 2020). Hydrotropes, i.e., low molecular weight sodium or potassium salts of benzoic or arylsulfonic acid with a substituted alkyl group, are used. Similar to surfactants, they have an amphiphilic structure and reduce surface tension. It leads to a decrease in lignin concentration and to a high level of glucose released during enzymatic hydrolysis of cellulose (Devendra and Pandey 2016; Olsson et al 2019; Mikulski and Kłosowski 2020b)
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