Document Type

Thesis

Date of Award

5-31-1989

Degree Name

Master of Science in Environmental Science - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Joseph W. Bozzelli

Second Advisor

Richard B. Trattner

Third Advisor

Peter Varuntanya

Abstract

The purpose of this thesis is to study the thermal desorption behavior of toxic organic compounds, specifically o-xylene, p-xylene, ethyl benzene, p-chlorotoluene, and anthracene, from soil with respect to temperature and time, and to develop a mathematical model that will describe this desorption behavior. The model will allow prediction of the concentration of an organic contaminant in commercial soil desorption system over time given a known set of parameters of the specific chemical as well as flow rate and temperature. For this purpose, two sets of experiments were done: These are identified as 1. Thermal desorption and 2. plug flow experiments.

In the plug flow experiments, 1 microliter (ul) of the selected organic chemical was injected into a heated packed soil column with purge flow, residing in a constant temperature oven. The desorption curves resulting from the adsorption and desorption of the chemical to the soil-like packing materials were analysed for change in retention time versus the inverse temperature. Runs were made with four packing materials: organic soil, sand, gaschrom-R and silica gel. An equation was developed for each material. These plug flow runs were made with ethyl benzene, p-chlorotoluene, p-xylene, and o-xylene. Results demonstrate that the retention time decreased with increases in temperature. Correlation factors of the fitted data for all runs were greater than .93, according to the following equation:

Rt = AieBi/T

(See text for parameter definitions)

Thermal desorption runs consisted of heating a soil matrix, uniformly precontaminated with anthracene, in a quartz tube reactor and purging the contaminated soil with nitrogen. The nitrogen flow through the soil matrices was constant at 30 cm3/min, at a nearly constant temperature. The analysis of the desorbed organic was done with a gas chromatograph (GC) equipped with a flame ionization detector (FID). A relationship was developed based on time and temperature requirements for complete desorption of the selected pollutant species with inert gas purge. This relationship was used to develop an engineering equation where for any given hydrocarbon compound the time necessary for removal from soil, can be predicted for any given temperature close to the boiling point (±40 0C). The results showed that the rate of desorption from soil of anthracene increased with increases in temperature as shown in the following mathematical relationship:

C(t)/Co = e-kt

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