VEGETABLE OIL-BASED FUELS, ADDITIVES AND COPRODUCTS
Location: Bio-oils Research Unit
Title: Complete utilization of spent coffee to biodiesel, bio-oil and biochar
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2012
Publication Date: June 25, 2012
Citation: Sharma, B.K., Vardon, D., Moser, B.R., Zheng, W., Witkin, K., Evangelista, R.L., Rajagopalan, N. 2012. Complete utilization of spent coffee to biodiesel, bio-oil and biochar [abstract]. 6th International Conference on Environmental Science and Technology, June 25-29, Houston, TX. p. 136.
Energy production from renewable or waste biomass/material is a more attractive alternative compared to conventional feedstocks, such as corn and soybean. The objective of this study is to maximize utilization of any waste organic carbon material to produce renewable energy. This study presents total utilization of a waste material, spent coffee grounds, through a two-step process. The waste coffee grounds were selected as a waste organic carbon material, collected from local coffee shops and dried in an oven to remove excess moisture.
In the first step, triacylglycerol oil was extracted from spent coffee grounds using hexane Soxhlet extraction. The extracted oil properties were studied and found suitable for producing biodiesel. This extracted coffee oil was transesterified using conventional alkaline-catalyzed methanolysis to prepare the corresponding fatty acid methyl esters (FAMEs) (biodiesel). This biodiesel and their 5 and 20% blends in ultra low sulfur diesel were studied for various fuel properties such as oxidative stability, cold flow properties, kinematic viscosity, iodine value, acid value, free and total glycerol content, energy content, and lubricity. While the FAMEs prepared from spent coffee oil are not compliant with biodiesel standards, their 5% blends did meet most of the specifications.
In the second step, the defatted spent coffee grounds were converted into bio-oil and biochar using a thermochemical process (slow pyrolysis) at 450 deg C under nitrogen atmosphere. It was found that spent coffee grounds produced more bio-oil and less biochar compared to defatted coffee grounds. The bio-oils were analyzed for their physical properties such as viscosity, density, elemental analysis, heating value, boiling point, and molecular weight distribution. The spent coffee bio-oil approached the higher heating value (HHV) of Illinois shale oil (41 MJ/kg), which falls within the range for conventional petroleum crudes (41-48 MJ/kg). Structural characterization of bio-oils was carried out using advanced spectroscopic and chromatographic techniques such as NMR, FTIR, GPC, and GC-MS to provide insight on average structures, carbon and hydrogen distribution, functional groups, and major components present in bio-oils.
The bio-chars produced from spent and defatted coffee grounds have the potential to be used as fuel and also as soil amendment material. These biochars were characterized for their BET surface area, energy content, acid value, ultimate and proximate analysis. To demonstrate their soil amendment properties, these biochars were used in green house experiments to show how they can help reduce the amount of chemical fertilizer needed. The implications of reduction of chemical fertilizers in the field are improvements in the quality of agricultural runoff water, which will decrease nitrogen and phosphorous in streams and rivers and finally help prevent gulf hypoxia. This will also reduce the energy input required to produce fertilizers.