Technical possibilities of bioethanol production from coffee pulp: a renewable feedstock

The present paper investigated the technical possibilities of bioethanol production from coffee pulp in a sustainable manner. Coffee pulp is a largely underutilized waste stream and has the potential to become a bioethanol feedstock if processing is economically viable. This study aimed to characterize the chemical composition of coffee pulp with relevance to bioethanol production and to compare results to other bioethanol feedstocks. Based on the total sugar yield, we investigated bioethanol production using AspenPlus simulation software. In the sugar characterization part, total carbohydrates were measured after complete acid hydrolysis of dry pulp, while water-soluble carbohydrates were measured after acid hydrolysis of soxhlet extracted solutions. Moisture, lignin, and ash contents were measured gravimetrically after appropriate heating treatments. The results showed sugar contents, expressed as percentages of dry mass, as follows: 5.8, 5.2, 20.2, 4.2, and 4.7 % for arabinose, galactose, glucose, xylose, and mannose, respectively. Arabinose, galactose, and glucose were the only water-extracted simple sugars, at 1.0, 1.4, and 2.6 % of dry mass, respectively. AspenPlus simulation was based on processing 10,000 ton/day of coffee pulp. The results demonstrated sugar and ethanol yield of 2100 and 1050 ton/day, respectively. This would make annually profit of $0.13 million. The simulation estimated the capital investment cost was about $2 million. In order to satisfy the process economy, the process operation cost must be operated at minimum of $1.87 million annually. The life-cycle analysis showed the net value of energy of the whole process is an economical as well as the balance of CO₂ emission/reduction was on the environmental favor.