Amino acid recovery using a multistage fluidized bed contactor
Abstract
The main goal of this study is to design and operate a Cloete-Streat fluidized bed contactor for the recovery of amino acids. This device has applications in product recovery from feeds with suspended solids such as fermentation broths. One of the major aims achieved was the introduction of a new process scheme involving pH gradient recovery of amino acids. This operation enhances the recovery of trace feed components by building up their concentrations within the column to well above feed level. The Cloete-Streat contactor is a multistage fluidized-bed system. It achieves countercurrent operation between liquid and solid streams by periodically stopping liquid flow and allowing the downflow of a fixed amount of resin (solids). The determination of design parameters such as: liquid flowrates, the time period between resin downflows (cycle time), the time needed for the column to reach steady-state as well as the investigation of different operating schemes required the development of various predictive models. A lumped film mass transfer (LMT) model was developed to describe the periodic or cyclic operation of the Cloete-Streat contactor. This model can use either linear or nonlinear isotherms. It can also model the effects of running the contactor with two or more of its sections at different solute affinities. This latter technique helps to model the pH gradient operation of the contactor. LMT model results have shown that the system reaches a periodic overall steady-state. At this overall column steady-state, each cycle continues to experience repetitive or periodic transient behavior. In other words, these cyclic transients continue to display an effluent history pattern for each stage which repeats itself. The average of these concentrations stays the same and is what constitutes a periodic overall steady-state condition for the Cloete-Streat contactor. Furthermore, it has been shown that it is important in modeling the contactor to include the liquid gaps or supernatant liquid sections between fluidized bed regions. Including supernatant regions accounts for the differences in effluent histories between fluidized resin and supernatant liquid sections observed at short cycle times. This aspect is novel with respect to past mathematical studies of the device. Experimentally, recoveries of 92% have been obtained for the amino acid, phenylalanine (phe), under isocratic (constant pH) operation. The resin used in this study was Rohm and Haas Duolite C-20 (20-50 mesh size)--a sulfonated polystyrene, cross-linked with divinylbenzene. The separate 5 stage pH gradient operation of the device has produced concentration build-ups of 1.87 and 2.5 times the feed concentration for phenylalanine and lysine, respectively. The individual cycle transients have also been studied for a 5 stage pH gradient system.
Degree
Ph.D.
Advisors
Wang, Purdue University.
Subject Area
Chemical engineering
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