Density and Conversion in Biodiesel Production with Supercritical Methanol

Abstract

The densities of reacting mixtures of vegetable oils + methanol were measured by loading a closed vessel with a known amount of an oil/alcohol mixture of a given molar ratio. For each studied condition, the mixture was brought to a temperature at which the system became homogeneous. The isochoric (constant-volume) relation between temperature and pressure at this particular density and composition was recorded. In the temperature range of 550−630 K, a high conversion of the oil to the corresponding fatty esters and glycerin was obtained. The densities of sunflower oil with methanol for two different alcohol/oil ratios, namely, 40:1 and 25:1, were measured. Densities of coconut oil + methanol and methyl oleate + methanol mixtures were also measured. The effect of global density on conversion was studied at long reaction times (3−4 h). Strong evidence of the phase transitions of the reacting mixtures, from heterogeneous to homogeneous, was obtained from the experimental results.

Continuous production of biofuel from refined and used palm olein oil with supercritical methanol at a low molar ratio

“…This method has been used by several researchers for obtaining accurate densities and phase transition [22][23][24][25]. The isochoric method was first proposed for biodiesel production from vegetable oils with supercritical alcohols by Velez et al [26,27]. They employed coconut and sunflower oils as feedstocks with methanol to coconut oil molar ratios of 40:1 and 25:1, and an ethanol to sunflower oil molar ratio of 40:1.…”

“…The main operating parameters that influence the transesterification under supercritical conditions are temperature, pressure, alcohol to oil molar ratio, and reaction time. As shown in Table 1, the supercritical reaction of a variety of refined vegetable oils has been investigated over a wide range of operating temperatures (280-350°C), pressures (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35), and reaction times (4-30 min), depending on the types of feedstock and reactor.…”

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.…”

Phase equilibria of triolein to biodiesel reactor systems

“…The most advanced equations-of-state (EoS) used for supercritical systems have been the Cubic Plus Association (CPA) EoS, which was used to study supercritical alcohols [9][10][11][12][13][14][15], and the soft-SAFT, which was used to study binary systems of CO 2 and water, and CO 2 and FAME [16].…”