Optimization of Concentrated Sulphuric Acid Hydrolysis of Gadam Sorghum Stalks Found in Kenya for Fermentable Sugar Production

Abstract

Gadam sorghum stalks are agricultural residues which can be hydrolyzed into fermentable sugars that can be used to produce bioethanol which is a renewable source of energy. In order to produce bioethanol from lignocellulosic biomass such as Gadam sorghum stalks, several processes including hydrolysis are involved. However, the use of lignocellulosic biomass for bioethanol production is hindered by the low yield of fermentable sugars obtained during hydrolysis. The lack of sufficient information on optimal conditions governing hydrolysis of lignocellulosic biomass leads to inefficient process which hinders the economic viability of large-scale bioethanol production. The objective of this study was to optimize reaction conditions involved in concentrated sulphuric acid hydrolysis of Gadam sorghum stalks. During hydrolysis, the conditions that were varied included temperature (40°C–80°C), time (30-90 minutes), and concentration of acid (30%-70%, $w/w$ ). Central composite rotatable design was used to optimize and establish optimum level of hydrolysis conditions. Response surface methodology and analysis of variance were used to interprete the results. The results of hydrolysis revealed that the highest yield of glucose was 87.54% ( $w/w$ ) which was realized at 60°C hydrolysis temperature, 60 minutes hydrolysis period, and 50% ( $w/w$ ) concentration of sulphuric acid. In addition, the lowest glucose yield was 45.59% ( $w/w$ ) which was realized at 60°C hydrolysis temperature, 60 minutes hydrolysis period, and 16.36% ( $w/w$ ) sulphuric acid concentration. Concentrated sulphuric acid hydrolysis of Gadam sorghum stalks results in high yield of fermentable sugars. These results reveal that Gadam sorghum stalks are viable substrates for the production of fermentable sugars.