Process Optimization For Production Of Bioethanol From Sugarcane Bagasse

Abstract

Sugarcane bagasse, a byproduct of sugar processing, is a cellulosic biomass that comprises of lignocellulose molecule. Nowadays, it is becoming an increasingly popular, environmentally safe and renewable alternative source of energy to petroleum fuel. The Ethiopian sugar estates produce huge and surplus amount of bagasse annually. However, only 85-90% used for cogeneration while rest quantity was wasted. In order to convert this valuable byproduct to bio ethanol, pretreatment and process optimization are the primary requirements. In spite of the importance of bio-ethanol and huge wastage of bagasse in Ethiopian sugar estates, there is no research effort made so far on pretreatment and process optimization to valorize and utilize bagasse as alternative source of bio-ethanol energy. Therefore, this study was aimed to optimize pretreatment, hydrolysis and fermentation processes to produce bio-ethanol from sugarcane bagasse. Accordingly, in pretreatment optimization experiment, the effect of NaOH (0.5, 2.5, and 5 %) and pressure (10, 15, 20 Psi) under different reaction times (5, 20, 35 minutes) was evaluated. For hydrolysis experiment, the effects of H2SO4 (1, 2 and 3 %), temperature (160,190 and 220 OC) and hydrolysis time (20, 40 and 60 minutes) were evaluated while the fermentation experiment consists of different incubation temperatures (30, 35 and 40 OC) and incubation periods (24, 48 and 72 hours) under different initial pH (4, 5 and 6). All the three experiments were arranged in randomized complete block design with three factor factorial. Each treatment was arranged in two replications. In pretreatment experiments, data on cellulose, hemicellulose and lignin, in the hydrolysis experiment data on reducing sugar and on fermentation experiment data on ethanol yield were collected. After quality test, the collected data were subjected to statistical analysis and model optimization using design expert statistical software version 7.0. Results of the statistical analysis on pretreatment optimization revealed that 2.5 % NaOH and 15 psi pressure at 35 minutes gave the maximum extraction of cellulose (81.25) with maximum removal of hemicellulose (8.41) and lignin (6.02%). For pretreated bagasse hydrolysis, 2.05 % H2SO4 at a temperature 205.92 OC within 60 minutes produced maximum yield of reducing sugar (80.89 g/l) while the maximum ethanol produced at optimized conditions (6 initial PH, 30 OC incubation temperature and 71.83 hours incubation period) was 42.98 g/l. From these results, it can be deduced that the treatments that gave optimum results for pretreatment, hydrolysis and fermentation can be used to produce bio-ethanol from sugarcane bagasse.