Studies in Solid-Liquid Extraction

MacDonald, Bruce Beacom (1958) Studies in Solid-Liquid Extraction. PhD thesis, University of Glasgow.

Abstract

The object of the work was to investigate the effects of temperature and solute concentration on the process of diffusion in porous solids. This was done by immersing previously impregnated earthenware slabs in a moving stream of liquid and allowing absorption or desorption of the solute to proceed for measured intervale of time. The experimental results indicated that the mass transfer was in accordance with Fick's law and that values of D, the diffusion coefficient, could be estimated from semi-log plots of the fraction of solute absorbed or desorbed against t, time in seconds. The derived values of D were correlated with temperature T in the customary relationship, D = A exp (-E/RT) where A = a constant E = an activation energy. It was found that the activation energy E was not independent of the solute concentration. With KCI as solute, it was apparent that for desorption experiments, the calculated values of E were very nearly identical for N and 3N solutions. Absorption experiments, however, give results which differed markedly from those for desorption. The general tendency was for the values of D to be smaller at lower temperatures but to increase more rapidly with increasing temperature than the corresponding values for desorption. Consequently, the derived values of E were much higher for absorption than desorption. The results for sucrose were similar but, in this case, desorption proceeded more rapidly than absorption though again solute concentration appeared to be the dominating factor in determining the relative rates of absorption for 0. 3M and M solutions. Experiments were carried out with slabs of different physical characteristics and in one series of experiments. (slabs whose mean pore diameter was one micron and solute M sucrose) there appeared to be an interaction between the slab structure and the diffusing molecules. Comparison of the apparent lengths of the paths followed by the diffusing molecules seemed to indicate that the diameter of the smaller pores and the length of a sucrose molecule may well be of comparable dimensions. From consideration of the experimental results, there would appear to be certain fundamental differences between the rates of absorption and desorption. The explanation for these differences is not obvious though it is felt that the pore distribution, particularly the number and diameters of the smaller pores making up the voidage, play an important part in determining rates of mass transfer to or from the slabs.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Physical chemistry
• Date of Award: 1958
• Depositing User: Enlighten Team
• Unique ID: glathesis:1958-79245
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 31 Mar 2020 09:09
• Last Modified: 31 Mar 2020 09:09
• URI: https://theses.gla.ac.uk/id/eprint/79245