Hydrothermal liquefaction of spent coffee grounds followed by biocatalytic upgradation to produce biofuel: a circular economy approach

Abstract

Hydrothermal liquefaction (HTL) of wet spent coffee grounds was performed in a batch reactor for bioenergy production. The effects of spent coffee grounds to water ratio, temperature and reactor volume occupation on product yield were investigated. A maximum 19.1 wt% bio-oil yield with HHV of 38.5 MJ/kg was obtained from wet spent coffee grounds. Subsequently, the bio-oil synthesized via hydrothermal liquefaction was upgraded biocatalytically to bring down the acid value and to convert the bio-oil into a higher quality liquid biofuel. During this process the fatty acids present in the bio-oil were converted into fatty acid methyl esters (biodiesel) using lipase. Novozyme-435 converted ∼ 85% of fatty acids in the bio-oil into fatty acid methyl esters at 35 °C after 14 h, as determined by ¹H NMR. In addition, FTIR analysis confirmed the presence of fatty acid esters in the product. The acid number of the bio-oil decreased significantly after the enzymatic reaction. The results shows that lipase is an effective biocatalyst for crude bio-oil upgradation.

Keywords:

• Hydrothermal liquefaction
• spent coffee grounds
• lipase
• biorefinery
• circular economy

Disclosure statement

No potential conflict of interest was reported by the author(s).