Direct transesterification of spent coffee grounds for biodiesel production

- A one step process to directly making biodiesel from SCGs without solvent extraction.
- 17.08 wt.% of coffee biodiesel yield, oil-to-biodiesel conversion rate of 98.61 wt.%.
- The optimal reaction condition: 12 h; 70 °C with 20 wt.% H2SO4 impregnated catalyst.

Studies of spent coffee grounds (SCGs) as a potential biodiesel feedstock in recent years mostly started from solvent extraction to obtain coffee oil, and then converted it into coffee biodiesel in two steps, acid esterification followed by alkaline transesterification. This paper presents a direct transesterification (in situ) method that produces biodiesel from SCGs without the need for oil extraction and esterification steps. Prior to the direct transesterification, SCGs were impregnated with sulfuric acid as the catalyst for subsequent direct transesterification, and moisture was removed from the impregnated SCGs. The effects of H2SO4 concentration, reaction time, and reaction temperature on biodiesel yield were investigated. The coffee biodiesel yield (wt.% of dried SCGs) reached 17.08 ± 0.70 wt.% under the optimal condition of 70 °C, 20 wt.% sulfuric acid and 12-h reaction time, which was equivalent to an oil-to-biodiesel conversion rate of 98.61 wt.%. 28.87 ml methanol/g oil was used in the in situ method. Compositional analysis of fatty acid methyl esters (FAME) indicated that C16:0 (methyl palmitate) and C18:2 (methyl linoleate) were the major components of the coffee biodiesel.