Date of Award

Fall 2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering - (Ph.D.)

Department

Chemical Engineering

First Advisor

Kamalesh K. Sirkar

Second Advisor

Marino Xanthos

Third Advisor

S. Mitra

Fourth Advisor

Jing Wu

Fifth Advisor

Michael Jaffe

Abstract

The separation and purification of organic-solvent-based process streams may be carried out by membrane processes such as nanofiltration/ultrafiltration/microfiltration and membrane solvent extraction. Lack of solvent stability and chemical stability of most commercially available membranes is limiting the utilization of the above mentioned membrane technologies. This dissertation was primarily focused on developing solvent resistant hollow fiber and flat film membranes for separation and purification of organic-solvent-based process streams.

Available porous polymeric supports (Polypropylene (PP), Polyethersulfone (PES) and Nylon) suitable for the required solvent-stable applications were chosen first and then the supports were modified to satisfy the requirements for the applications. Membrane modification techniques employed were interfacial polymerization (IP) and poly(ethyleneimine) (PEI) self crosslinking. Thin film composite (TFC) nanofiltration and ultrafiltration membranes were fabricated on PBS, Nylon and hydrophilized PP support membranes. Before carrying out IP, PP was hydrophilized by pre-wetting with acetone and treating with hot chromic acid solution. The introduced procedure of “modified IP” involved wetting next with the aqueous monomer solution followed by the organic monomer solution. Nanofiltration membranes were characterized using solutes, safranin 0 (MW 351) and brilliant blue R (MW 826) dyes in methanol; ultrafiltration membranes were characterized with a 70% alcoholic solution of zein (MW 35,000). These membranes were also studied for long term solvent stability in ethanol and toluene. The membrane based on PP was first hydrophilized by the techniques of “modified [P” and PHI self crosslinking. For possible applications in microfiltration of aqueous systems, these hydrophilized membranes were characterized by the water permeation rate. Crosslinking of PHI was implemented on the lumen side of the Nylon hollow fibers to reduce the pore size; then, their performance in membrane solvent back extraction was studied. Extraction of phenol from MIBK into an aqueous caustic solution was studied as a model system for reactive back extraction; extraction of acetic acid from MIBK into water was studied as a model system for nonreactive back extraction. Hollow fibers of PBS were coated on the lumen side by IP. The IP layer was again coated with silicone to make the IP coating impervious to water. The coated PES fibers were then tested for heat transfer performance. All modified membranes were also characterized using scanning electron microscopy.

Thin film composite nanofiltration and ultrafiltration membranes were successfully fabricated on PP and PBS hollow fiber supports; high rejections of solutes and high solvent fluxes were achieved in UF and NT membranes. However, only the PP-based TFC membranes retained their characteristics after solvent exposure for the studied period of time. Permanent hydrophilization of PP was achieved by the “modified IP procedure. Reduced pores on the lumen side of Nylon hollow fibers provided stable aqueous-organic interface for solute transport in membrane solvent back extraction; the coating improved the extraction performance of the membranes. Better heat transfer performance was achieved in the coated PBS hollow fibers when compared with the nonporous PP hollow fibers.

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