Rancang bangun proses produksi bioetanol dari lignoselulosa sebagai energi terbarukan dengan pendekatan ekoefisiensi

Abstract

Corn stover, as an agricultural residue, is one of the lignocellulosic biomass abundantly available in Indonesia. It is an attractive material for bioethanol fuel production. Conversion of lignocellulosic to ethanol consists of four major unit operations: pretreatment, hydrolysis, fermentation and ethanol purification. Biomass pretreatment is one of the main processing steps which have significant contribution to the cost effectiveness of cellulosic biomass conversion to ethanol. The purpose of this research was to elucidate the ethanol production from lignocellulosic biomass through development of pretreatment technology as well as simultaneous saccharification and co-fermentation (SSCF) technology. The pretreatment consisted of the delignification using Ca(OH)2 and two stages hydrothermolysis at 121 OC for one hour and at 180-190 OC for 20 minutes respectively, while the SSCF elaborated the use of cellulase and xylanase enzymes for saccharification and the use of mixed culture fermentation. An optimum process condition for chemical pretreatment was achieved at Ca(OH)2 loading of 0.075 g/g biomass and the use of 6.25 ml water/g biomass, heated at 69.61 OC for 2 hours. Hydrothermolysis produced solid fraction that contained 42.68% of cellulose and 34.68% of hemicellulose. The highest ethanol concentration (43.08 g/l) was obtained after 48 hours of incubation. The energy required for ethanol production was 44.154 MJ/L ethanol and the Net Energy Ratio (NER) value was 5.60, while the water demand reached 114.08 L/L ethanol. Consequently, this production system emitted CO2 (21.93 kg/L ethanol), N2O (0.00003 kg/L ethanol), and CH4 (0.0000002 kg/L ethanol). The suitable design of production process had a negative impact on global warming potential, because the emitted greenhouse gas was 6.578 ton CO2-eq annually. The techno-economic analysis showed that the investment needed to produce 1000 L ethanol per day was Rp 1,891,508,861.00, with working capital of Rp 466,230,881.00 and production costs of Rp 2,797,385,287.00 per year. The production was feasible because its Net Present Value (NPV) value was Rp 957,794.270.00, the Internal Rate of Return (IRR) was 19.29%, which was higher than interest rate 12%, and the payback period was 4.96 years. With the raw materials intensity of 7,881 kg/L, the environmental impact was equivalent to 248.68 tons of CO2-eq. If the price of CO2 was Rp 270,000 per ton (based on 2020), then the ratio of value-added and environmental impact, which called ecoefficiency value, was 0.032.