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
R. P. T. Tomkins
Third Advisor
Peter C. Veruntanya
Abstract
The purpose of this research project was to determine feasiblity to remove organic contaminants from various soil matrices by thermal desorption and gas purge. The volatization and gas purge of organic contaminants from the soil increases under the influence of heat and inert gas.
The work was done in two parts. First, under isothermal conditions, organic compounds were injected as a plug unto columns that contained real or simulated soil matrices. These columns were continuously purged with a carrier gas (nitrogen) and a gas chromatogragh equipped with Flame Ionization Detector but no added column other than the soil was used to measure the axial dispersion and the rate of passage of the organic contaminants through various soil matrices. The soil matrices used were Gas Chrom R, organic soil, and Poropak T. For the soil matrix, the organic contaminants studied were tetrachloroethylene, p-xylene, o dichlorobenzene, m-dichlorobenzene, o-xylene, and chlorotoluene at six different temperatures. For the Poropak T matrix and gas chrom R matrices the organic contaminants were studied at five different temperatures.
The compounds studied were:
Tetrachloroethylene
p-xylene
o-dichlorobenzene
This plug injection experiment demonstrated that Poropak T has the strongest affinity and Gas Chrom R was found to have the weakest affinity for the organic pollutants studied. It also demonstrated that as the temperature of the column increased, the retention time or time for passage decreased. This process was then modeled using an exponential decay rate model and a statistics program was used to regress the data. Values for the adsorption equilibrium constant (Ka) were determined from this model. A plot of the natural log of equilibrium constant versus inverse of temperature for a particular organic compound and soil matrix were performed. The slope of this plot, (δHads/R) was used to calculate the heat of adsorption.
A second desorption system was constructed to study uniformly contaminated soil matrices. It incorporated purge with a 6-way switching valve system, a desorbing oven, and a gas chromatograph now equipped with a column and a flame ionization detector. The organic compound studied was m-dichlorobenzene (BP = 178 C). A soil sample was prepared with a known uniform concentration of contaminant and was placed into a quartz tube and then into an oven at isothermal conditions. The contaminant was desorbed from the soil column, using a carrier gas (nitrogen). The flow of the carrier gas was maintained at 30m1/min throughout the process. The six-way switching valve was used to direct the vapors either to a Flame Ionization Detector for analysis or into a traps filled with activated carbon for collection, and later analysis by solvent extraction. Solvent extractions (acetone) were performed on both the soil samples and activated carbon to provide for mass balance.
The rate of which the organic contaminant desorbed from the soil was a function of the temperature. A mathematical model based on δHvaporization or boiling point and molecular mass was developed to determine the time required to remove the compound under other isothermal conditions. From these experiments and the developed, a design could be suggested for a larger scale desorption system.
Recommended Citation
Calandra, Sarah, "Thermal desorption of hazardous and toxic organic compounds from soil matrices" (1989). Theses. 2724.
https://digitalcommons.njit.edu/theses/2724
