Continuous production of biodiesel fuel from vegetable oil using supercritical methanol process

Biodiesel Production from Castor Oil under Subcritical Methanol Conditions

“…This process does not require any catalysts or auxiliary chemicals and does not generate significant wastes [10], [15]. Supercritical methanol was used to obtain biodiesel from different oils such as rapeseed, sunflower, soybean and palm kernel [15], [17]- [19]. The highest conversion efficiency was achieved with reaction temperatures between 280 and 400 º C and pressures between 20 and 45 MPa.…”

Transesterification in Supercritical Conditions

“…The reaction pressure also has a significant effect on the efficiency of the supercritical transesterification reaction below 20.0 MPa, but the effects tend to be negligible above 25.0 MPa (He et al, 2007a;He et al, 2007b), due to the fact that increasing the reaction pressure simultaneously increases both the density of the reaction mixture (Velez et al, 2010) and the degree of hydrogen bonding (Hoffmann & Conradi, 1998) at an otherwise constant temperature and alcohol to oil molar ratio. The transesterification conversion is enhanced with an increased reaction mixture density, due to the resulting increased volumetric concentration of alcohols and the residence time in a tubular reactor, which is commonly used to investigate the effect of pressure.…”

“…This prolonged reaction time might cause a decline in the production efficiency obtained by supercritical transesterification, but it could be shortened by the use of assisting methods, as discussed in Sections 3.2 -3.4. On the other hand, the gradual heating technique in a tubular reactor has been demonstrated to avoid the thermal cracking of unsaturated fatty acids and shorten the reaction time at the same time (He et al, 2007b). For instance, when the reaction mixture is heated in a tubular reactor gradually from 100 ºC at the inlet to 320 ºC at the outlet, the biodiesel product obtained after 25 min of reaction time has an over 96% methyl ester content (He et al, 2007b).…”

“…In the following years, various catalysts were employed to assist the supercritical transesterification to achieve the maximum alkyl esters content but at milder operating conditions (Demirbas, 2007;Yin et al, 2008b). The continuous production of biodiesel in supercritical methanol was reported in 2006 (Bunyakiat et al, 2006) (Minami & Saka, 2006) and 2007 (He et al, 2007b). Therefore, the research focus on the reduction of the elevated operating conditions and continuous process has been ongoing since 2005.…”

“…Therefore, the research focus on the reduction of the elevated operating conditions and continuous process has been ongoing since 2005. 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).…”