Sequential separation of lignin and fatty acid methyl ester from spent coffee grounds

Abstract

The objective of this study was to investigate optimal conditions of organosolv pretreatment for sequential separation of both fatty acid methyl ester (FAME) and lignin from spent coffee grounds (SCG). The effects of conditions (reaction temperature, concentration of sulfuric acid and ratio of SCG-to-solvent) of organosolv pretreatment on yields of FAME and lignin was observed using rotatable central composite design (CCD) and response surface methodology (RSM). The ranges of independents for the RSM were 110~180 ℃ of reaction temperature (T), 1~5 v/v % of concentration of sulfuric acid (C) and 2~4 g/ml of ratio of SCG-to-solvent (R). Among those experimental conditions, the maximal yield of lignin from SCG showed 60.73 % at 110 ℃, 4.61 % H2SO4 and 2 g/ml. FAME were extracted with maximum yields of 58.71 % at 159.5 ℃, 3.86 % H2SO4 and 3.71 g/ml. The optimal conditions for sequentially extracting both FAME and lignin from SCG were 148.13 ℃, 4.44 % H2SO4 and 4 g/ml, yielding 58.53 % for lignin and 58.01 % for biodiesel, respectively. Compositions of extracted FAME were occupied with 41.7 % of C16 and 48.16 % of C18, indicating being appropriate for usage as a biodiesel, but further treatment is required considering the relatively low FAME yields. The sequential extraction of FAME and lignin from SCG may increase in usage of total biomass up to 25.03 %, comparing only 17.04 % and 8.75 % increase in biomass usage for the single extraction of lignin and biodiesel, respectively.