(281b) Hot-Gas Pressure Swing Adsorption for Drying Reactive Monomers

A wide variety of unit operations may be used to break an organic + water azeotrope in order to produce a dry organic product.  These include temperature-swing and pressure-swing adsorption; membrane-based pervaporation and vapor permeation; and azeotropic, extractive, and pressure-swing distillation.   However, in applications involving a polymerizable or otherwise reactive monomer, the viability and operability of these processes can come into question.  This presentation will describe the use of Hot-Gas Pressure Swing Adsorption (HGPSA) to dry a reactive monomer from 3 wt% water (a typical azeotropic amount) down to trace ppm levels.  HGPSA is well-known as a commercial process for breaking alcohol + water azeotropes such as ethanol-water and isopropanol-water.  It differs from classic PSA processes in that the feed is not a gas but a liquid that must be completely vaporized and superheated prior to processing.  Our HGPSA pilot work shows how very dry monomer can be produced with no detectable polymerization – by avoiding any condensation during processing and by taking measures to ensure inhibitor is present during the initial vaporization step and on condensation of the dry product.  Results of process simulation using Aspen ASDIM, process design, and pilot-scale operation will be presented, and the applicability of the technology for processing reactive monomers in general will be discussed.  Key process design considerations include selection of adsorbent, the amount of superheat in centrigrade degrees above the dew point, adsorption and desorption pressures, the desorption factor (a kind of reflux ratio), and PSA cycle time.