Integrated volarization of spent coffee grounds to biofuels

Abstract

HIGHLIGHTSBiodiesel is a renewable energy source produced from natural oils and fats, and is being used as a substitute for petroleum diesel. The aim of this study was to investigate the potential of using spent coffee grounds for biodiesel production and its byproducts to produce pelletized fuel, which is expected to help the biodiesel production process achieve zero waste. For this experiment, spent coffee grounds sample was collected from Kaldis coffee, Addis Ababa, Ethiopia. Extraction of the spent coffee grounds oil was then conducted using n-hexane, ether and mixture of isopropanol to hexane ratio (50:50 %vol), and resulted in oil yield of 15.6, 17.5 and 21.5 %w/w respectively. A two-step process was used in biodiesel production with conversion of about 82 %w/w. The biodiesel quality parameters were evaluated using the American Standard for Testing Material (ASTM D 6751). The major fatty acid compositions found by Gas chromatography were linoleic acid (37.6%), palmitic acid (39.8%), oleic (11.7%), and stearic acid (8.6%). In addition, solid waste remaining after oil extraction and glycerin ratio (glycerin content from 20-40%) was evaluated for fuel pellet (19.3-21.6 MJ/Kg) applications. Therefore, the results of this work could offer a new perspective to the production of biofuel from waste materials without growing plants and/or converting food to fuel.

Effect of Solvent Extraction Parameters on the Recovery of Oil From Spent Coffee Grounds for Biofuel Production

“…These results are in good agreement with SCG oil FA profiles obtained from previous studies [6,11,43,46]. Very similar FA profiles were found by Jenkins et al, who demonstrated that the majority of examined coffee oils from fresh and waste samples have similar composition irrespective of the origin, type of bean and brewing process [11].…”

“…The standard deviations calculated from three experimental repeats are also presented, while the oil contents were achieved with a coffee to solvent ratio of 1:9 w/v after 8 h of extraction. The measured SCG moisture contents are similar to those reported by Kondamudi [10] (18-45% w/w) and Ahangari and Sargolzaei (48% w/w) [6,7,9,10,13,16,26]. The variance of the moisture results can be likely attributed to the different coffee brewing procedures that significantly increase the moisture content of SCGs, however there is not a clear difference between ICG and RCG samples (Table 2).…”

“…The lipid content of SCGs on a dry weight basis has been found to range between 7 and 27.8% w/w according to previous studies [6][7][8][10][11][12][13][14][15][16][17] and is significant relative to other major biodiesel feedstocks such as rapeseed oil (37-50%), soybean oil (20%) and palm oil (20%) [18]. Coffee oil consists primarily of triglycerides, diglycerides, monoglycerides and FFAs that combined account for 85-90% of the total lipid content and are principally composed of linoleic, palmitic, oleic and stearic acids in decreasing order of magnitude and in proportions not unlike those found in other common edible vegetable oils [6,11,13,16,19].…”

“…Several approaches to the valorization of SCGs have been made, including utilization as fertilizers or wood powder, as a source of antioxidant and polysaccharide material or as an absorbent for removing cationic dyes in wastewater treatments, however these strategies have not been routinely implemented at an industrial scale [3,5,6]. Meanwhile, there has recently been increased interest in using SCGs as a biodiesel feedstock [7].…”

“…Coffee oil consists primarily of triglycerides, diglycerides, monoglycerides and FFAs that combined account for 85-90% of the total lipid content and are principally composed of linoleic, palmitic, oleic and stearic acids in decreasing order of magnitude and in proportions not unlike those found in other common edible vegetable oils [6,11,13,16,19]. The FA composition of the extracted oil is significant as it affects the properties of the derived FAMEs, while the presence of FFAs is a major factor affecting the potential for efficient further processing into biodiesel as high FFA levels increase susceptibility to oxidation, speed up degradation and inhibit alkaline catalyzed transesterification [20][21][22].…”