Production of Cellulosic Ethanol from Wood Sawdust
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Date
2016-07
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Addis Ababa University
Abstract
Production of cellulosic ethanol was investigated in this study. The wood sawdust has
lignocelluloses content, which make it suitable as fermentable sugars, when hydrolyzed. The
dried sawdust with uniform particle size was hydrolyzed with sulfuric acid for breaking the bond
that binds sugar monomers together. The black residue or lignin was removed and the reduced
sugars were neutralized for catalyst activity in the fermentation process. Four experimental
parameters were investigated during hydrolysis. They are particle size (1-3mm), acid
concentration (3-7%), temperature (90-110oC) and time (120-240 minutes). The total reduced
sugars content of hydrolyzed solutions were analyzed using phenol sulfuric acid method. The
result of stastical analysis showed a maximum sugar content of 72.51% (w/w) during the
hydrolysis of 10% (w/v) wood sawdust of 2mm particle size at 5% (v/v) sulfuric acid
concentration at 100oC and 180 minutes. The minimum yield of 41.24% (w/w) was achieved at
1mm particle size, 3% (v/v) sulfuric acid concentration, 90oC and 120 minutes. The reduced
sugars were fermented using Saccharomyces cerevisiae in anaerobic condition and the residual
solutions were distilled every 150 minutes by rotary evaporator. The ethanol concentrations
were measured by Alcoholmeter. And maximum and minimum ethanol concentrations of
73.10% (v/v) and 35.20% (v/v) with 90% (0.46 g/g) of the theoretical conversion (0.51g/g) in 72
hours were achieved respectively. Response surface methodology (RSM) employing the central
composite design (CCD) was used to optimize the total reduced sugar using acid hydrolysis. The
optimum result was obtained at 1.72mm particle size, 4.21% (v/v) acid concentration, 102.46oC
and 156.60 minutes. The total reduced sugar yield of 67.56% (w/w) was achieved under these
conditions. The rough feasibility analysis evaluation indicates that, this project is beneficial. The
cost estimation studies provide the rate of return on investment as 52.4%. The payback period
shows the return of the total investment cost in 3 years with the net present value of 22.73
million Birr.
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Keywords
Wood sawdust, Acid hydrolysis, Reduced sugars, Phenol-Sulphuric acid, Fermentation, Saccharomyces cerevisiae, Cellulosic ethanol, Alcoholmeter, Optimization