ABSTRACT

This development of a bioethanol batch production process compares to continuous processes in product quality but eliminates the need for high energy cooking and cooling processes, which is a major problem with batch production processes. Other major problems associated with continuous processes addressed by this design include easy adaptability of operating conditions to varying raw material quality, problems in maintaining a high fermentation rate, and the need for continuous sterilization of the medium requiring expensive control and automation equipment leading to high investment costs. The improved small scale bioethanol process plant comprises of a steam boiler, a bioreactor and a distillation column. Production of bioethanol from the plant using cassava starch involves five main steps which are feedstock preparation, cooking, starch hydrolysis, yeast fermentation and distillation. A low energy cooking process that distinguishes it from the conventional process by subjecting liquefied starch to saccharification at lower temperatures (60- 70°C) through gluco-amylase obtained generally from Aspergillus niger or Rhizopus species was applied, eliminating the need for high energy cooking and cooling processes. Distilling 20 liters of fermented cassava (starch) mash produced 4210.75 ml of ethanol in 350 minutes, having a total of 1050.68 gmol of the mash with 0.20 mole fraction of Ethanol. The plant accomplished this process using a packed column of 0.001 m diameter, with 8 theoretical plates and a height equivalent of a theoretical plate of 0.094 m. A performance evaluation of the distillation column using different packing material showed that the fluid dynamics and mass transfer are affected by the geometry and structure of materials in the column. The ethanol product collected for the stainless steel wool scrubbers packing material was larger compared to that collected for the marble bead packing material. The stainless steel wool scrubber packing material gave a higher product distribution which ranged from 94.5% to 94.4% by volume thus the distillation column design using stainless steel wool scrubbers can be used domestically for distillation of fermented cassava (starch) mash especially in developing economies to reduce cost of production and the amount of energy that would be consumed during the process. This research will offer the potential for carbon neutral, cost-effective, sustainable biofuel production, provide jobs and encourage agriculture for sustainable development.