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Title: Freeze concentration of aqueous solutions by clathration
Author: Aaron, Stuart Wilson
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1969
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Current interest in direct—contact heat transfer, in which a volatile dispersed Phase evaporates into a continuous medium, has stimulated a study into the possible use of this technique for concentrating liquid foodstuffs The immiscible refrigerant selected for its low toxicity, difluorodichloromethane, combines with water to form a crystalline clathrate, or hydrate, Bench—scale tests were conducted with aqueous sucrose solutions in a well—stirred 5 litre reactor which was operated both batchwise and as a flow reactor. Eydrate equilibrium data and agent solubility for the sucrose system have been determined. in the batch reactor. Material and energy balances have been established and the degree and rate of concentration effectively analysed in terms of the experimental variables — power input, sucrose concentration, reactor temperature and pressure and slurry viscosity. The ,process offers a convenient method of concentrating aqueous feedstocks. 20% of the water contained in the sucrose feed nay be removed as hydrate in a single stage and the hydrate crystals may be washed free of occluded mother liquor. The experimental results show that the rate-controlling mechanism is the transfer of agent through the continuous-phase boundary layer surrounding the agent bubbles. A correlation for the volumetric liquid-film mass-transfer coefficient has been derived, which makes it possible to predict the performance of a single stage reactor. Comparative tests were conducted in the same equipment with propane as the hydrating agent. A comparison of the results suggests that the correlation developed for the Freon-12 system may not be extended to include other hydrate formers. The experimental coefficients also differ substantially from those predicted by established two-phase correlations and it is considered that these differences are due to the effects of the boiling liquid phase and the reactor pressure. Tests with growth and decomposition of the hydrate indicate a fundamental dependence on operating pressure.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available