Continuous Production Of Biodiesel From Soybean Oil Using Supercritical Methanol In The Vertical Tube Reactor: Phase Holdup And Kinetics

In this paper, we studied the process conditions, the distribution ofintermediate products, phase holdup distribution of methanol and oil inthe vertical tube without catalyst. We also study adding a co-solvent toenhance reaction process.The technology of producing biodiesel by using supercriticalmethanol is a green synthesis technique. In this paper a detail study hasbeen carried out in a vertical tube reactor with the length of3700mm andthe diameter of20mm at275-375℃and15MPa, and the molar ratio ofmethanol to soybean oil40:1. The phase holdup, intermediate product,yield and axial distribution of methyl ester were studied. It isdemonstrated that，（1）the phase holdup of methanol increases, however,the phase holdup of oil decreases along the axial direction.（2）When thetemperature reaches300℃that the critical temperature of system, the MEyield increases up to50%, however, when the temperature is kept onrising, the methyl ester yield increases distinctly. At the same time, it isfound that at375℃, the decomposition rate of methyl ester is greater thanthe reaction rate of methyl ester and methyl ester begins to reduce whenthe reaction time is beyond1200s.We studied the effect of co-solvent on the methyl ester yield andintermediate products. The condition of the reaction temperature, reactionpressure, the molar ratio of methanol to oil were275-375℃,11-15MPa,30:1-40:1respectively. The results showed that the methyl ester yieldsignificantly enhance by adding co-solvent THF at a lower temperature.As the temperature increased, the effect of co-solvent on the methyl esteryield gradually weakened. It can be inferred that the oil and methnaol hadnot been completely mixed at lower temperatures. When co-solvent isadded, the mixture of methnaol and oil had been improved, so the methylester yield significantly increased. Co-solvent accelerated the reactionrate. Contrast to without co-solvent, the intermediate products reach to a equilibrium concentration in a very short period with co-solvent. We alsofound that the harsh conditions of supercritical reaction can be reduced byadding co-solvent. Under the conditions of350℃and the molar ratio ofco-solvent THF to methanol0.02, when the pressure dropped from15MPa to11MPa and the molar ratio of methanol to oil dropped from40:1to30:1, the methyl ester yield changed little.