PARAMETER-PROGRAMMING IN SEPARATIONS: CONTINUOUS TWO-DIMENSIONAL REGENERATIVE EXTRACTION AND MULTICOMPONENT PRESSURE SWING ADSORPTION

SHANKAR NATARAJ, Purdue University

Abstract

In Part I, the basic idea of continuous two-dimensional extraction is presented, and synthesized with a scheme for making the process self-regenerate its separating agent (solvent). The possibilities and advantages of diluent recycle in such cascades are illustrated. Experimental runs conducted with a laboratory cascade--a 4 x 4 array of mixers-settlers--on the system diethylamine (solute)-toluene (solvent)-water (diluent)-temperature (parameter) are described. Results show that a 4 x 4 cascade is reproducibly operable in the once-through mode, with small amounts of phase entrainment. The separation factors obtained ranged from 1.9 to 2.2, compared to model predictions of about 2.7. Further experiments show that a 2 x 4 cascade with diluent recycle is operable without phase entrainment, yielding separation factors of 2.35-2.45, as opposed to predictions of about 2.8. For linear systems, a matrix-theoretic analysis enables certain cascade-types be mathematically represented by a so-called "configuration-matrix" whose structure is exploited to make some general deductions of cascade properties. For example, the existence and shape of saturation self-preserving concentration profiles is predicted. For non-linear systems, a continuum theory based on the method of characteristics is developed. It predicts and explains certain transitions in the concentration topology. For highly non-linear systems, with simple geometric constructions, it is possible to estimate the concentration topology quantitatively. In Part II, two schemes are proposed for fractionating multicomponent mixtures using Pressure Swing Adsorption. For two solutes both schemes use a sequence of three adsorption columns, each at a different pressure and operating cyclically, 120(DEGREES) out-of-phase with each other. Both schemes can be extended to a system of N solutes requiring N + 1 columns. The goal of the process is to produce pure carrier gas and N streams containing a single solute enriched in the carrier gas. The local equilibrium model is used to enunciate the mathematical inequalities which govern the production of uncontaminated products. These are analyzed to identify regions of feasibility. The analysis shows that for some chemical systems neither scheme will work contamination-free, while for others, one or both of the schemes will work. The analysis also identifies regimes of operation potentially more efficient. A sample design for the separation of ethylene and acetylene in nitrogen using activated carbon is presented.

Degree

Ph.D.

Subject Area

Chemical engineering

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