Characteristics of direct transesterification using ultrasound on oil extracted from spent coffee grounds

Abstract

Spent coffee grounds (SCG), the residue after brewing coffee beverage, is a promising biodiesel feedstock due to its high oil contents (15‒20%). However, SCG should be pretreated to reduce the high free fatty acid content, which hampers transesterification reaction. To overcome this, we explored a direct transesterification reaction of SCG using ultrasound irradiation and identified the optimal sonication parameters. A high fatty acid methyl ester (FAME) content, up to 97.2%, could be achieved with ultrasound amplitude of 99.2 <i>μ</i>m, irradiation time of 10 min, and methanol to oil ratio of 7:1 in the presence of potassium hydroxide concentration of 1.25 wt.%. In addition, we demonstrated that ultrasound irradiation is an efficient method to produce biodiesel from untreated SCG in a short time with less energy than the conventional mechanical stirring method. The physical and chemical properties of the SCG biodiesel met the requirements for an alternative fuel to the current commercial biodiesel.

Solid Fuel Characteristics of Pellets Comprising Spent Coffee Grounds and Wood Powder

“…According to previous studies, a feedstock with a high oil content (>6.5%) adversely affects the interparticle bonding force during pelletization, resulting in reduced durability [36]. Given the high oil content of SCG (15%-20%) [22], the durability decreased as the SCG proportion increased. This effect is due to interference with interparticle bonding, which results from a decrease in pelletization pressure [36].…”

“…SCG contains 15%-20% oil; thus, it has a high calorific value (19-26.9 MJ/kg). After it is converted into solid fuel, it can replace currently-used wood pellets [8,22]. However, raw materials with a high oil content tend to impair the densification of pellets, and they need to be mixed with other biomass or waste products [23].…”