Sequential Production of Methylester, Bioethanol and Briquette from SCG

Abstract

Muluken Eshetu

In this study, methyl-ester, bioethanol and briquette samples were sequentially produced from spent coffee ground. The oil extracted from spent coffee ground with solvent extraction route at hexane to spent coffee ground ratio of 22.5g/g with an extraction time of 30.4min resulting in 11.892% of oil yield. This was comparable with literature values and subsequently used for methyl-ester production experiments using a 1% by wt of NaOH at reaction temperatures and residence times ranging from 50 to 65 °C and 20 to 60min, respectively. The optimization carried out using central composite design methodology gave 81.507% of methyl-ester yield at a reaction temperature of 57.133°C and reaction time (residence time) of 45.117 min with model determination coefficient (R2 ) of 0.9465 while the optimum reducing sugar yield for dilute acid hydrolysis experiments for ranges of operating parameters of temperature (70-100°C) and (1-3M )of H2 SO4 concentrations was found to be 39.161% at a temperature of 98.313°C and H2 SO4 acid concentration of 2.962M.The central composite design optimization results for trans-esterification and dilute acid hydrolysis experiments were verified by running experiments at optimum conditions and in turn resulted 79.65% of Methyl Esteryield(out of 11.892g of oil) and reducing sugars yield of 37.28%(out of the hydrolysate). This implied that the verification experimental results weren’t far from the predicted values so that the experimental results were sufficiently represented by the central composite design models. The bio ethanol produced by simple distillation having alcohol by volume yield of 55% can be considered as a good result and it can be easily concentrated to a fuel grade ethanol by using fractionating column. Moreover, the characteristics of the Methyl Ester produced were in good agreement with ASTM and EN standards. The end product of the process which is briquette has been produced from 75% wt of dilute acid hydrolysis residue and 25% wt of glycerol, resulted a calorific value of 13.35MJ/kg, volatile matter value of 88.15%, ash content of 3.95%, and fixed carbon contents of 1.74% with its easily moldable physical status showed that it can as well be used for fueling purpose like firewood and charcoal. This study signifies the value addition that can be affected from spent coffee ground and the potential and results obtained in this regard are discussed

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