Optimization of bioethanol production, engine performance and exhaust emissions from Manihot glaziovii and sweet sorghum in a spark ignition engine / Abdi Hanra Sebayang

Abdi Hanra , Sebayang (2020) Optimization of bioethanol production, engine performance and exhaust emissions from Manihot glaziovii and sweet sorghum in a spark ignition engine / Abdi Hanra Sebayang. PhD thesis, Universiti Malaya.

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Abstract

The ever-increasing fossil fuel consumption over the years is attributable to economic and population growth, which in turn, increases greenhouse gas emissions. Bioethanol is one of the promising solutions to address the depletion of fossil fuels as well as environmental problems. Manihot glaziovii tubers and sweet sorghum grains are inedible feedstocks that can be used for bioethanol production. The carbohydrate content (70%) of these biomasses makes them suitable as feedstocks for bioethanol production. In this study, enzymatic hydrolysis (liquefaction and saccharification) was used to obtain the reduction of sugars. The enzymes α-amylase from Bacillus licheniformis Type XII-A and amyloglucosidase from Aspergillus niger were used as the catalysts for liquefaction and saccharification. The reduced sugars were converted into ethanol during the fermentation process by the yeast Saccharomyces cerevisiae. Distillation was carried out to remove water from the bioethanols. Box-Behnken design was used to optimize the enzymatic hydrolysis and fermentation process parameters. The hydrolysis process parameters (substrate loading, α-amylase concentration, amyloglucosidase concentration, and stroke speed) were optimized to maximize the reduction sugar yield. The fermentation process parameters (yeast concentration, reaction temperature, and agitation speed) were optimized to maximize the bioethanol yield. The optimum reduced sugar yields were 196.15 and 170.26 g/L for Manihot glaziovii and sweet sorghum, respectively. The optimum yeast concentration, reaction temperature, and agitation speed were 1.18 g/L, 36.48°C and 217 rpm, respectively, for Manihot glaziovii, and the values were 1.29 g/L, 35.36°C and 188.97 rpm, respectively, for sweet sorghum. The corresponding bioethanol yields were 94.45 and 82.13 g/L for Manihot glaziovii and sweet sorghum, respectively. The physicochemical properties of both the bioethanols fulfilled the specifications of the ASTM D4806 standard. Engine tests were carried out using a single-cylinder four-stroke spark ignition engine to determine the engine performance (engine torque, brake power, brake specific fuel consumption, brake thermal efficiency) and exhaust emissions (carbon monoxide, unburned hydrocarbons, and nitrogen oxides) of the Manihot glaziovii bioethanol-gasoline blends (ME5, ME10, ME15, and ME20) and sweet sorghum bioethanol-gasoline blends (SE5, SE10, SE15, and SE20). In general, the engine performance parameters were better and the exhaust emissions were lower for the bioethanol-gasoline blends compared with those for gasoline. For the ME20 and SE20 blends, the brake specific fuel consumption decreased while the brake thermal efficiency increased at an engine speed of 3200 rpm. The corrosive behavior of copper coupons immersed in the bioethanol-gasoline blends was also investigated in this study. The surface morphological changes of the copper coupons were analyzed using scanning electron microscopy. The rate of copper corrosion was faster for the ME20 and SE20 blends compared with that for gasoline. These blends also had the fastest rate of copper corrosion compared with the all blends tested in this study. Based on the results, it can be concluded that the Manihot glaziovii tubers and sweet sorghum grains have great potential as bioethanol feedstocks and the bioethanol-gasoline blends produced from these biomasses can be used in the spark ignition engine without modifications.

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