Design modifications and scale-up of a novel soxhlet apparatus: Optimization of batch extraction of a biofuel oil from Crotalaria juncea seeds

Till date, a soxhlet extractor is found to be the most versatile equipment for extracting oil from oil-bearing seeds. Use of a conventional soxhlet apparatus is limited by the long extraction time to complete a certain quantity of transfer of solute due to inefficient contact between the extractant and solute. A novel design of a modified soxhlet apparatus, including an additional packed column inserted within the soxhlet thimble, is proposed to overcome the limitations. It is evident from the study that cylindrical and annular packed columns (inserted within the thimble) perform better as compared to the elliptical ones. An annular packed bed ensures better oil yield in comparison to the cylindrical one due to enhancement of mass transfer by multiple factors. In order to commercialize the production of juncea seed oil, an effective modeling, based on a comprehensive dimensional analysis (following similarity criteria), is applied for a scale-up. Four key dimensionless groups, namely, soxhlet specific shape factor (Ss), Reynolds number (Res),Froude number (Frs) and Peclet number (Pes) are identified. Oil yield is represented by another dimensionless group, soxhlet specific Stanton number (Sts). A multiple-factor regression analysis, using Central Composite Design (CCD) based response surface methodology, is used to develop some rational correlations of various combinations of the dimensionless groups. Necessary and sufficient understanding of the effects of the dimensionless groups [Ss, Res,Frs, and Pes] on the oil yield is important to choose proper scale-up criteria. A novel dimensionless number, the soxhlet number, S, is evolved. S determines the soxhlet performance in terms of oil yield. Maximization of S gives forms a basis of scale-up. This specific approach of scaling-up a soxhlet apparatus can be utilized in commercializing the production of juncea oil.