Completed Research
Characterization of Mass Transfer Parameters in Soybean Oil Hydrogenation Process Under Industrial Conditions
Benoit Thierry Fillion, PhD, 2001
(Thesis: UMI Dissertation Publishing)
The hydrogenation of soybean oil is an important process in the fat industry due to its wide applications to produce margarine, shortenings and frying oils. The purpose of this process is to increase the melting point and to improve the oxidation and frying properties. This means that the control of hydrogen during the process has a great impact on the quality of the processed soybean oil and the process economics. The industrial process is typically carried out in a 3-phase autoclave reactor operating at 393-473 K and 1-5 bar with a Nickel-based catalyst loading, ranging from 0.01-0.2 wt.%. Literature reports that in most of the commercial reactors, the rate limiting-step is the gas-liquid mass transfer. Therefore, the purpose of this study was to investigate the solubility, the mass transfer parameters (kLa, kL) and the hydrodynamic parameters (QG,GIR, dS, & εG) for N2 and H2 in soybean oil, in a 4-liter surface aerated (SAR), gas-inducing (GIR) and gas-sparging agitated reactor (GSR) operating under typical industrial conditions. The kinetics data were also measured and coupled with mass and heat transfer parameters in order to model the hydrogenation process. The mass transfer and hydrodynamic data were measured in wide ranges of temperatures (373-473 K), pressures (1-5 bar), mixing speeds (10-23.3 Hz) and liquid heights (0.171-0.268 m) in the SAR and GIR or gas flowrate in the GSR. The transient physical gas absorption technique was employed to measure kLa in all three reactors and the central composite statistical design approach was used to distribute the experiments. The kinetics for soybean oil hydrogenation using a commercial Ni/Al2O3 catalyst were investigated in a 2-liter agitated reaction calorimeter. The reaction data were measured in wide range of temperatures (383-443K), pressures (1.2-6.8 bar) and catalyst loadings (0.02-0.16 Ni-wt.%). A simple model (Model 1) and a novel comprehensive model (Model 2) were developed to describe the hydrogenation process based on Langmuir-Hinshelwood kinetic expressions. The catalyst activity and mass transfer coefficients were incorporated in both models. Modeling results showed that decreasing gas-liquid mass transfer resistance decreases the trans fatty acid (TFA) content in the partially hydrogenated soybean oil, and good heat transfer control is required to minimize the production of TFA. Also, the gas-liquid mass transfer appeared to be the rate-limiting step of the overall process and accordingly proper gas-liquid mixing is of prime importance in commercial soybean oil hydrogenation reactors.