Kinetics determination of soybean oil transesterification in the design of a continuous biodiesel production process

One-step batch transesterification consisting of three stepwise reversible reactions of pure soybean oil with methanol was conducted at two different mixing speeds (600 and 300 rpm) to produce soybean oil fatty acid methyl esters (biodiesel). In both batch reactions, sodium methoxide (1.09 wt% based on soybean oil) was used as the catalyst, the reaction temperature was 60oC, and the methanol-to-oil molar ratio was 6:1. The objectives were to determine and/or investigate: 1) the mechanism and order of the reaction, 2) the reaction rate constants, 3) the effect of changes in mixing intensity on the reaction rate, 4) the comparison of the reaction mechanism and kinetic rate constants calculated with established literature references (for validation), and 5) how to interpret and utilize the kinetics analysis in the design of a continuous pilot-scale biodiesel production process. The kinetics analysis from the experiment showed that a second-order kinetic mechanism provided a good fit for the reaction. Kinetic rate constants at both mixing speeds were calculated and ranged from -3.10 x 10-3 - 0.028 (wt% min)-1 for the triglyceride, monoglyceride, and diglyceride forward reactions. The rate constants were slightly higher at the 600 rpm mixing speed. Higher mixing intensity also resulted in an increased purity of methyl esters (95.2 wt %). At both mixing speeds, monoglycerides showed the smallest percent elimination of all reaction intermediates at approximately 30%. The rate constants calculated for monoglycerides were the lowest as well. The monoglyceride rate constant of 0.0149 (wt% min)-1 was used in the design of a continuous process in a 100 gallon vessel, which is a scale of operation that could be easily adopted by a cooperative of oil seed producers or geographically isolated plant-oil producing villages. This Honors thesis was a component of a Biological and Agricultural Engineering team Senior Design project which consisted of designing a continuous biodiesel process from production to purification