Kinetics of hydroxide‐catalyzed methanolysis of crude sunflower oil for the production of fuel‐grade methyl esters

Abstract

Methyl esters from crude sunflower oil were produced via methanolysis reaction using sodium hydroxide catalyst. Methanolysis was carried out at different agitation speeds (200-600 rpm), temperatures (25-60• C), catalyst loadings (0.25-1.00% by weight of oil), and methanol:oil mole ratios (6:1-20:1). Mass-transfer limitation was effectively minimized at agitation speeds of 400-600 rpm with no apparent lag period. Lowering the temperature resulted in a fall in the rate of reaction prolonging the reaction time necessary to achieve maximum production of methyl ester. Using 0.50% hydroxide catalyst was found to be adequate, resulting in 97-98% conversion without compromising recovery due to soap formation. Increasing the methanol:oil mole ratio beyond the usual amount of 6:1 tended to speed up the initial rate of methanolysis and was found to lower the bonded glycerol content, especially the amount of diglyceride in the sample. Kinetic rate constants were derived from experimental results using second-order rate expressions, and values of activation energy for glyceride methanolysis have been established.

Modelling the Kinetics of Jatropha Oil Transesterification

“…It is interesting to note that methyl ester conversion was high even at the initial stage of 5 minutes (73%) and there was no time lag at this stage that was reported in [5]- [8] [10] [11]. This can be explained by the fact that high mixing intensity used (600 rpm) and high temperature (55˚C) produced homogeneous oil-methanol mixture where mass transfer control was negligible.…”

“…The reaction had not reached completion after two hours. Reasons could be due to low catalyst loading (0.5% wt of oil) as opposed to the recommended literature value of 1% (wt of oil) [5] [7] [8].…”

“…The intermolecular forces are broken down by the intensity of mixing making the oil-methanol solution homogeneous without phase formation. Noureddini and Zhu [7] reported that at stirring speed of 600 rpm, the mass transfer controlled reaction is eliminated while [8] reported the value of 400 rpm. It can be observed that after 30 minutes of the reaction, increasing mixing intensity becomes unnecessary because the methyl ester produced is soluble in oil and in methanol and it acts as a co-solvent where the system is homogeneous and only chemical reaction controls the kinetic (Figure 5).…”

“…A research on the kinetics of transesterification of soybean oil with methanol using a shunt reaction reported that mass transfer control reaction is negligible with the stirring speed of 600 rpm and the kinetically controlled chemical reaction was second-order [7]. A study on the kinetics of hydroxide-catalysed methanolysis of crude sunflower oil for the production of fuel-grade methyl esters reported the mass transfer region to be effectively minimized using agitation speeds between 400 and 600 rpm [8]. A kinetic study on the methanolysis of sunflower oil at low temperatures using simplified rate equations reported a sigmoidal kinetic where mass transfer initially control the kinetic followed by a chemically controlled kinetic region [9].…”

Monitoring of Biodiesel Transesterification Process Using Impedance Measurement

“…Previous work has identified agitation methods such as the use of magnetic stirrer, static stirrer, ultrasound and ultra turrax. Bambase et al [11] reported that the using of a higher agitation speed (magnetic stirrer) reduces the mass transfer resistant significantly. For the transesterification of crude sunflower oil it was shown that the mass transfer limitation was reduced to an effective zero time lag by selecting a 400-600 rev/min agitation speed.…”