Optimization of Levulinic acid production from groundnut shell using Taguchi orthogonal array design

Abstract

The exploitation of lignocellulosic biomass is receiving an increasing attention due to its renewability, abundance and low price value, and can be converted into various valuable platform compounds such as furfural, lactic acid, formic acid and levulinic acid. Among these products, levulinic acid (LA) is the main compound of biomass hydrolysis, which has been classified by the United States Department of Energy as one of the top-12 promising building blocks. This work reported the transformation of groundnut shell into LA. The production of LA was carried out in a 50 cm³ Teflon lined stainless steel reactor. The LA produced was extracted from the aqueous mixture using ethyl acetate, about 1g of sodium sulphate anhydrous were added to remove the water in the organic layer after the aqueous layer was drained and then heated at a temperature of about 78 ^oC for the solvent to evaporate and LA was the residue. The production process was optimized using a Taguchi orthogonal array design, with optimum yield of 74.54 % at reaction conditions of temperature (180 °C), time (3.5 h), and acid concentration (0.3 M). The FT-IR spectrum of the produced LA showed absorption at about 1705.13 cm^-1 and 3039.91 cm^-1 indicating the conjugated carbonyl and the hydroxyl of carboxylic acid functional group. It was recommended that high yields of LA can be achieved across a range of optimization variables as long as two out of the three conditions are met: high acid catalyst concentration, long reaction time or high temperature within the range tested, as LA is relatively stable once formed. Moreover, the results obtained revealed that groundnut shell could be a potential substrate for levulinic acid production.

Keywords: Groundnut shell, Levulinic acid, Optimization, Hydrolysis, Taguchi design.