Optimization of in-situ transesterification process for soybean and spent coffee grounds biodiesel

Abstract

Soybean and spent coffee ground (SCG) were applied as biodiesel feedstock in the reactive extraction process named in-situ transesterification (in-situ TE). This process reduced the complexity of biodiesel production by combining vegetable oil extraction and biodiesel synthesis into a single step. Several parameters were evaluated for the effect on biodiesel yield. The optimal process conditions using different alcohol systems showed that the stronger hydrophobicity of alcohol system provided the higher biodiesel yield. It also reduced the alcohol and catalyst loading, lower the reaction temperature and shorten the operation time. Simply washing SCG by methanol could reduce acidify of SCG. Elevating temperature could compensate the coarse particle size of SCG. The kinetic results showed that 80% of biodiesel yield could be obtained within 3 h using 4 kg SCG loading. SCG biodiesel produced from in-situ TE had high oxidative stability index due to the co-extraction of antioxidant. LCA results showed that producing SCG biodiesel at an on-site instant coffee process via in-situ TE had lower impacts at industrial level in terms of respiratory organ and land occupation than those of conventional approach because of the absence of n-hexane and transportation. However, it consumed much more energy during methanol recovery step, resulting in more impacts in the overall of health, ecosystem quality, climate change and resource. The sensitivity analysis suggested that producing biodiesel at an on-site was more favorable in term of energy usage once the transportation distance was >180 km with 7 km/L of fuel consumption rate. In the future work to improve energy usage and environmental impact of our process, we could directly reuse catalyzed methanol in the process, or apply countercurrent extraction technique which could reduce the amount of methanol and catalyst in the process.