Document Type

Dissertation

Date of Award

Spring 5-31-1997

Degree Name

Doctor of Philosophy in Environmental Science - (Ph.D.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Richard B. Trattner

Third Advisor

Barbara B. Kebbekus

Fourth Advisor

Leonard Dauerman

Fifth Advisor

Paul C. Chan

Abstract

The objective of this study is to develop air sampling techniques using membrane permeation. Two novel techniques for sampling and analysis of trace level VOCs from air via membrane permeation are presented:

  1. selective concentration of VOCs into a canister using a membrane permeator;
  2. on-line membrane extraction for direct introduction of VOCs from air emissions into a gas chromatograph.

In the membrane permeator-canister sampling system (MPCS), the air sample containing trace level VOCs as well as some interferences such as moisture are passed through the membrane module. Polydimethyl siloxane membrane used in this research is highly permeable to organic compounds, but relatively impermeable to air and water. The membrane permeator used in the experiments acts as a barrier that allows selective diffusion of the organics and elimination of water. Parameters that control the membrane permeation, such as the effect of membrane thickness, the effect of membrane module configuration, as well as the effect of operating parameters, i.e., temperature, sample flow rate, pressure difference, sampling time etc., were investigated. The MPCS system was evaluated by collecting real ambient air samples. The study demonstrated that membrane sampling can offer several advantages, such as, elimination of water vapor from the background matrix and sample preconcentration thus enhancing the sensitivity.

In the second project, an on-line membrane extraction microtrap GC (OLMEM-GC) monitoring system was developed for selectively extracting and monitoring trace volatile organic compounds from an emission stream. A laboratory scale catalytic incinerator was used to generate emission streams containing VOCs. The conversion efficiency of the incinerator was evaluated using the OLMEM-GC system. Continuous monitoring of VOCs was achieved by first selectively permeating VOCs through the semipermeable membrane and then using a microtrap to concentrate and inject the permeated VOCs into the GC. The method detection limit, precision, system linearity, response time, as well as the effects of operating parameters such as pressure difference, sample flow rate, temperature, and moisture content were investigated.

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