الفهرس 
Chapter (I): IntroductionOnly 14 pages are availabe for public view
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Abstract
This study represents the first step in evaluating the using of sub-critical water technology as a new pathway for extraction of compounds from biomass. In this work, we used the sub-critical water for cottonseed oil extraction. The first part covered the investigation of the effect of the different parameters affecting the extraction processes. The results reveled that the optimum temperature of extraction was found to be 270 oC for extracting time of 30 minutes using a solvent (water) to feed ratio 1:1 and cottonseeds with particle size of less than 0.5 mm.
Then, in the second part we studied the kinetics and thermodynamics of the oil extraction process as well as the overall extraction process of the cottonseed constitutes in the range of 190-270 0C. The obtained kinetic data for the oil extraction process were correlated well with a consecutive unimolecular-type first order reaction mechanism. The oil extraction rate constants were found to be 0.036, 0.040 and 0.055 min-1 while the decomposition rate constants were 0.21, 0.14 and 0.13 at extraction temperatures of 230, 250, and 270 oC, respectively. The overall extraction process was found to follow a reaction of 2.3 order. The overall extraction rate constants were found to be 1.1 × 10-5, 7.07 × 10-5 and 1.7 × 10-4 (mol. L-1)1.3. min-1 at extraction temperatures of 190, 200, and 210 oC, respectively.
Using the Arrhenius and Eyring equations, we calculated the thermodynamic parameters. The values of activation energy (E) and frequency factor (A) for both oil and overall extraction processes were 254, 1.1 kJ.mol-1 and 7.7 × 1023(mol. L-1)1.3. min-1, 3.9 × 1012 min-1, respectively.
To have deeper understanding for the extraction process, the change in enthalpy of activation (∆H#) and entropy of activation (∆S#) were calculated using the transit-state theory. The calculated values of ∆H# and ∆S# for both oil and overall extraction processes were found to be -25.1, -19.69 kJ.mol-1 and 0.201, -0.237 kJ.K-1.mol-1, respectively.
The values of the change in Gibbs free energy of activation (∆G#) for the overall extraction were -118.2, -120.2, and -122.2 kJ.mol-1 at 190, 200 and 210 oC, while for the oil extraction process were 99, 104, 109 kJ.mol-1 at 230, 250 and 270 oC, respectively.
At the end, the enthalpy change (∆H) and the entropy change (∆S) of the oil extraction process were calculated to be 120.4 kJ.mol-1 and 0.222 kJ.K-1.mol-1, respectively.
Based on the measured thermodynamic parameters it could be finally concluded that that the change in enthalpy of the oil extraction process was found to be positive which indicted that the process is endothermic. Moreover, the values of the change in the free energy of the oil extraction step was changing from being positive at relatively lower extraction temperature and converted to be negative at higher temperature, indicating the shifting from non-spontaneous to spontaneous process by increasing in the extraction temperature.
Based on the obtained data it could be concluded that the new proposed extraction process could be a cost effective alternative for the traditional hexane method for cottonseed oil extraction. However, more studies are needed for the investigating the possibility and feasibly of the commercialization of the process.