Determination of limiting separation effects in membrane based air separation for perfectly mixed and cross flow patterns

Abstract

The aim of this work is to investigate the single-stage separation of atmospheric air through silicone rubber membrane assuming cross-flow and ideal-mixing pattern. The novel graphical procedure for obtaining the permeate and retentate compositions as a function of permeate to retentate pressure ratio, γ, membrane selectivity, α*and fraction of feed permeated, θ was developed. The maximum oxygen concentration in the permeate stream was found to be 37 mol % for both models. However, the cross-flow pattern predicts the 100 % pure nitrogen to be obtained in the retentate stream at the q value of unity. In most cases, the cross-flow pattern is preferred when the production of nitrogen-enriched air is concerned, whereas the ideal-mixing pattern is preferred when the oxygen-enriched air is the desirable product. The membrane area requirements are higher for cross-flow pattern, and the deviations between the two models presented here are more pronounced at higher fractions of feed permeated.

U raduje izvršena numerička analiza procesa membranske separacije vazduha pomoću mem­brane od silikonske gume, primenom modela idealnog mešanja i modela unakrsnog toka. Predložen je nov grafički postupak određivanja sastava permeata i retentata u funkciji od odnosa pritisaka permeata i retentata, γ, selektivnosti membrane, α*i stepena permeacije, θ, zasnivan na primeni ravnotežnog xe - ye dijagrama. Rezultati ukazuju da model unakrsnog toka omogućava bolje separacione efekte od modela idealnog mešanja, posebno sa aspekta dobijanja vazduha obogaćenog azotom. Međutim, potrebna membranska površina je pri istom stepenu permeacije veća pri unakrsnom toku faza nego pri idealnom mešanju. Oba modela daju iste rezultate pri nultom stepenu permeacije.