Direct transesterification of spent coffee grounds for biodiesel production

Authors: LIU, YANG - University Of Cincinnati; TU, QINGSHI - University Of Cincinnati; Knothe, Gerhard; LU, MINGMING - University Of Cincinnati

Submitted to: Fuel
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2017
Publication Date: 3/3/2017
Publication URL: https://handle.nal.usda.gov/10113/5832872
Citation: Liu, Y., Tu, Q., Knothe, G., Lu, M. 2017. Direct transesterification of spent coffee grounds for biodiesel production. Fuel. 199:157-161.

Interpretive Summary: Replacing fuels obtained from finite petroleum by those produced from renewable resources remains a priority to ensure energy supply. Biodiesel, which is made from materials such as vegetable oils and other plant oils, is such a fuel. In order to enhance economics and augment supply of biodiesel, inexpensive sources, and favorable production methods are important factors. In this connection, this work describes biodiesel production from an inexpensive source, spent coffee grounds, by an improved method for this feedstock. Such work has the potential to make more biodiesel available for use.

Technical Abstract: 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, 20wt.% 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 inoleate) were the major components of the coffee biodiesel.