Influence of pre-treatment and variation of briquetting parameters on the mechanical refinement of spent coffee grounds

Abstract

Coffee is an essential agricultural product and offers the spent coffee grounds (SCG) after brewing. In order to intensify the utilisation of this by-product, various approaches have been investigated into. The mechanical refinement of the SCG by briquetting plays an important role for further upgrading processes. In this work, the briquetting of dried SCG was investigated with and without pre-treatment of the SCG by solid-liquid extraction with toluene or pyrolysis. Furthermore the addition of 5% cellulose as binder and the variation of moisture content from 5% up to 10% and briquetting pressure in the range of 120 MPa–160 MPa was investigated. To evaluate the briquette quality, raw density, compressive strength, and abrasion resistance were determined. The results show that briquetting of pre-treated SCG by extraction leads to an increasing briquette quality, since the oil fraction of 16.12% was removed. Whereas an increasing in briquetting pressure from 120 MPa to 140 MPa leads to a slight increase in briquette quality, a further increase in briquetting pressure results in a decreasing briquette quality. The best briquetting results were achieved for SCG with 10% tapioca starch as binder. At a briquetting pressure of 140 MPa the briquette quality was significantly increased.