Marc Bisschops

Internal Sherwood numbers for diffusion in sorption operations

Abstract An approximate mathematical description of diffusion in sorption operations, based on the assumption of a linear driving force (LDF) for the diffusion process, is investigated. A method is presented to employ the LDF model as a useful tool for data analysis and process design for various sorption process types, by which elaborate numerical solution methods can be omitted or simplified considerably. The principal variable of the LDF model is an internal Sherwood number for the sorbent phase. It is shown that the internal Sherwood number is time dependent and a function of the second order time-derivative of the sorbate concentration in the sorbent particle at the surface. Correlative expressions for the internal Sherwood number are derived and their application to sorption process calculations is examined.

RECOVERY OF DILUTED COMPONENTS FROM LARGE AQUEOUS STREAMS BY AN EXTREMELY COMPACT, CENTRIFUGAL COUNTERCURRENT ADSORPTION SYSTEM

The development of efficient and generally applicable recovery techniques for dilute, non-volatile species from large industrial streams or waste flows has been a technological challenge for many decades. The generality of this problem can be illustrated by many examples, such as the purification of diluted biopharmaceutical proteins from fermentation broth, removal of dissolved organic contaminants from petrochemical waste streams and the recovery of precious metals such as uranium from leach streams. The use of adsorbent or ion exchange agents is usually preferred over other separation techniques, because of their high selectivities towards the desired product, the possibility of recycling the auxiliary (sorbent) material, the relatively low regeneration cost, and the variety of possible, efficient processes. A typical example of this category of equipment was described by Cloete and Streat in 1962,1 and was considered breakthrough technology at that time. However, the available equipment is without exception inherently voluminous, and may contain tens to hundreds of cubic meters of adsorbent material for processing flows in the order 10 to 100 m3 per hour. In this work, we present a novel technique, Centrifugal Adsorption Technology (CAT), to process similar liquid streams with a high recovery efficiency, but in very compact equipment, typically 100 to 1000 times smaller than the previous equipment.