Recovery of sulfuric acid during sugar purification from pretreated wheat straw hydrolysate using electro-electrodialysis system for 2G bioethanol production

Abstract

Concentrated acid hydrolysis (CAH) of lignocellulosic biomass (LCB) is an established method to obtain a near theoretical yield of monomeric sugars from the biomass. The CAH process produced 83.23 % of glucose from pretreated wheat straw (PWS) at optimum conditions (i.e., stage I = 74 % w/w acid, 1:2 biomass loading, and 50 °C for 1 h; and stage II = 30 % w/w acid, 90 °C for 2 h). However, the separation of sugar from acidic hydrolysate is a major constraint of this technology. In this study, an electro-electrodialysis (EED) process using a novel anion exchange membrane (AEM) has been developed to recover sulfuric acid from biomass hydrolysate. The synthetic hydrolysate (i.e., feed acid concentration = 2 M; glucose = 80 g L−1) was used to optimize the EED process parameters. The acid was successfully recovered from alkali pretreated wheat straw (PWS) hydrolysate using the most effective EED process parameters. This resulted in an 82.72 % acid recovery in the permeate under the following conditions: current density of 88 mA cm−2, flow rate of 3 L h−1, and feed acid content of 2 M. During the EED process, the highest glucose recovery in the feed was 90.98 %, achieved with a maximum current efficiency of 93.57 % and the lowest energy consumption of 0.052 kW h mol−1 at optimal conditions using PWS Hydrolysate. Saccharomyces cerevisiae fermented the acid-free PWS hydrolysate, resulting in a maximum ethanol yield of 92.3 %. The EED process cost of $0.049 kg H2SO4−1 and total revenue was $0.02 kg biomass−1 from the second batch onwards suggest the feasibility of the EED process for large-scale 2G bioethanol productions.