Effect of co-solvents on production of biodiesel via transesterification in supercritical methanol

Abstract

Previous studies on the transesterification of vegetable oil in supercritical methanol in a batch reactor resulted in a non-saponified product with high methyl esters content and high glycerol purity. For the continuous reactor, the high viscosity of vegetable oil might result in problems in the flow system. This study selected THF and hexane as co-solvents to reduce the viscosity of the vegetable oil. The effect of co-solvents was investigated in both 250 mL and 5.5 mL batch reactors by 2-replicate 2 3 factorial design at temperatures from 290-350 uC, a molar ratio of methanol to vegetable oil from 12-42 and a molar ratio of co-solvent to vegetable oil from 0-5. The reaction time was fixed at 10 min. The products from the employed and unemployed co-solvent process were analyzed by GC-MS to confirm that the reaction among the vegetable oil, methanol and cosolvent was non-existent. However, some thermal cracking was observed in a 250 mL reactor at 350 uC and 30 min reaction time. The amount of co-solvents had no significant effect on methyl esters content and also did not allow the reaction to be completed under milder conditions. Thus, it was concluded that both THF and hexane were appropriate co-solvents to reduce the viscosity of vegetable oil for the continuous production of biodiesel in supercritical methanol.

A Comparison Between Raw Material and Technologies for a Sustainable Biodiesel Production Industry

“…The absence of a catalyst allows the system to treat triglycerides, fatty acids, and water with no concerns. Even more, in order to reduce the amount of alcohol, some works have shown that is possible to reduce the alcohol molar ratio by increasing secondary supercritical fluids such as CO 2 , hexane, heptanes, propane or tetrahydrofuran, being those much cheaper (Sawangkeaw et al, 2007, Tan et al, 2010, Yin et al, 2008, Han et al, 2005. In some cases, it could be found that a catalyst could be introduced into the system (Demirbaş, 2007) making possible to achieved good final conversions without compromising the down streaming separation and purification.…”

Transesterification in Supercritical Conditions

“…In 2007, the gradual heating technique was introduced to limit or prevent thermal cracking of the unsaturated fatty acids and so prevent the reduction in the final methyl esters content obtained (He et al, 2007b). At the same time, the effect of using co-solvents to reduce the viscosity of vegetable oils was successfully investigated (Sawangkeaw et al, 2007). Supercritical transesterification in ethanol was studied in a continuous reactor in 2008 (Vieitez et al, 2008).…”

“…Both types of co-solvents have different purposes and advantages that will be presented accordingly. The liquid co-solvents are added into the supercritical transesterification reaction to reduce the viscosity of the vegetable oils, which might otherwise pose some pumping problems in a continuous process (Sawangkeaw et al, 2007). Since hexane is the conventional solvent for vegetable oil extraction, it could be possible to combine the supercritical transesterification after the extraction process using hexane for both.…”

Catalyst-Free Biodiesel Production Methods: A Comparative Technical and Environmental Evaluation

“…Points: data based on the experimental data obtained by Minami and Saka [25]. Lines: fitted lines using Equation (7).…”

“…Some of these studies include the exploration of alternative biodiesel production pathways such as catalyst-free subcritical and supercritical biodiesel production processes [2,3] for enhanced biodiesel yields in short reaction times, the use of unconventional biodiesel feedstocks such as meat processing DAF sludge [1] and sewage sludge [4] as alternative lipid sources to improve economic performances and the modification of existing biodiesel production processes such as application of in-situ approaches to enhance biodiesel productivity [5]. Current investigations however highlight scientific interest in catalyst-free biodiesel production processes due to reduced reaction times (<10 min) and high percentage conversions (>95%) typically recorded in experimental work [2,6,7]. Conventional catalyst-free biodiesel production processes are essentially transesterification reactions occurring under supercritical conditions of the reacting alcohols.…”