Studies of the oil extraction kinetics of repeseen (canola)

Abstract

Experimental data on the rate of extraction of oil from rapeseed were collected on a bench scale batch extractor, using commercial hexane (Skelly F) as a solvent. The experimental data were then used to fit a two stage washing/diffusion mathematical model. The effects of variables such as particle thickness, extraction temperature, cooking, degree of agitation, change of total mass of seed and solvent, as well as, the seed to solvent ratio, on the rate of extraction were studied. The reason for examining so many variables in this project was to make certain that in general the mathematical model would be applicable to any operating condition of the extraction process, without any restrictions. The extraction process was found, indeed, to be the summation of two processes involving a washing and a diffusion process. The washing process was very rapid and took place in the early stage of the extraction in which the oil was removed from the surface of the crushed seeds. The diffusion process, however, was slow, took place in the latter stage of the extraction, and two mechanisms appeared to be involved; one slow and one very slow. The slow mechanism was responsible for the removal of a portion of oil which was held in the partially broken cells, whereas, the very slow mechanism was responsible for the removal of a portion of oil within the unruptured cells. Kinetic coefficients of both (cooked and uncooked) prepressed and flaked seed were obtained for the model and ranged from 0.79 to 9.35 min⁻¹ for the washing stage, 0.056 to 0.38 min⁻¹ for the unhindered diffusion stage, and 0. 0015 to 0. 01 6 min⁻¹ for the hindered diffusion stage over the following range of conditions: particle size from 0.76 mm to 0.06 mm, solvent to seed ratio 0 of 4, agitation speed of 170 rpm and at the temperature of 40°C. A reduction in particle thickness, an increase in temperature of extraction and heat treatment of the seed prior to extraction increased the rate of extraction. The rate of extraction also increased as a result of increasing the agitation speed of the stirrer and increasing the seed to solvent ratio. Also, the rate of extraction increased as the total mass of seed and solvent increased.