Volatilization thermal enhancement

Remediation activities at American Thermostat included the excavation and thermal treatment of over 13,000 cubic yards of soil and sediments contaminated primarily with perchloroethylene, trichloroethylene, and solvents. The soil was excavated and treated using a thermal treatment unit called the low-temperature enhanced volatilization facility (LTEVF). The performance test for the site s thermal unit had just been completed at the time of the inspection, so there was limited activity. 

Thermal enhancement of volatilization.19 21 Volatility of contaminants increases greatly with temperature, so several techniques have been developed to raise soil temperature, including the injection of hot air or steam, electrical resistance heating, and radio frequency heating. 

Of the four enhanced volatilization methods described above, documentation exists to support the contention that the low-temperature thermal stripping system has the greatest ability to successfully remove contaminants that are similar to gasoline constituents (i.e., compounds with high vapor pressures) from soil. The limitations of some enhanced volatization techniques can be attributed to the following ... 

Thermally enhanced extraction is another experimental approach for DNAPL source removal. Commonly know as steam injection, this technique for the recovery of fluids from porous media is not new in that it has been used for enhanced oil recovery in the petroleum industry for decades, but its use in aquifer restoration goes back to the early 1980s. Steam injection heats the solid-phase porous media and causes displacement of the pore water below the water table. As a result of pore water displacement, DNAPL and aqueous-phase chlorinated solvent compounds are dissolved and volatilized. The heat front developed during steam injection is controlled by temperature gradients and heat capacity of the porous media. Pressure gradients and permeability play a less important role. 

Heron, G. and Christensen, T. H, 1998, Thermally Enhanced Remediation at DNAPL Sites The Competition between Downward Mobilization and Upward Volatilization In Nonaque-ous-Phase Liquids — Remediation of Chlorinated and Recalcitrant Compounds (edited by G. B. Wickramanayake and R. E. Hinchee), Battelle Press, Columbus, OH, pp. 193-198. 

The steam-enhanced recovery process (SERF) is an in situ technology designed to remove and treat volatile and semivolatile organic compounds (VOCs and SVOCs) in contaminated soils by using steam injection and vacuum extraction. The technology is based on the idea that added heat (thermal enhancement) increases the volatility and mobility of SVOCs and VOCs and thus facilitates the extraction of soil contaminants. The process works by injecting high-quality steam... 

Steam-enhanced extraction (SEE) is a thermally enhanced, in situ, extraction technology that removes volatile organic compounds (VOCs) and semivolatUe organic compounds (SVOCs),... 

Heron G, Christensen TH, Heron T, Larsen T. (1998). Thermally enhanced remediation at DNAPL sites The competition between downward mobilization and upward volatilization. Proceedings of the First International Conference on Remediation of Chlorinated and Recalcitrant Compounds. Columbus, OH Battelle Press, pp. 193-198. 

For gas chromatography and mass spectrometry, the addition of the TMS group(s) to polar compounds confers thermal and chemical stability in addition to enhanced volatility. Although dimethylsilyl ether derivatives are more volatile, they lack the chemical stability required for routine application [1]. The properties of the most commonly used reagents for trimethylsilylation are given below. 

Thermal revaporization mainly concerns the most volatile component of the deposited aerosol. Thus, in the experiments of Benson and Bowsher (1988), cadmium was primarily volatilized from a deposited control rod aerosol, with the residue enriched in silver and indium. Similarly, deposited volatile fission products may be revaporized when the temperature at a given location tends to increase over the course of an accident. Finally, as an example of chemical resuspension, when such a deposit of control rod aerosols is heated in steam, indium will show an enhanced volatilization due to the formation of volatile indium monohydroxide InOH. In contrast, revolatilization of deposited cadmium is not significantly reduced in the presence of steam, in spite of the possible formation of low-volatility CdO. 

Optical transparency Thermal stabifity Volatility Resolution enhancement... 

Roughly speaking among the whole molecules (100%), about 30% of them could be treated with GC, including those formed through derivatization to enhance volatility or thermal stabihty, while LC can be apphed about 85% of them provided that some proper solvents can he found even for polymers. However, the insoluble substances between the ranges above B cannot be treated by any chromatographic techniques. 

Gas chromatography-mass spectrometry has proven to be a powerful analytical tool for detection of drugs of abuse in biological matrices. In particular, the use of the SIM mode has enhanced the sensitivity of the GC-MS method for detection of drugs of abuse. The versatility of the method has been extended by the use and development of novel derivatization procedures that have allowed a more diverse array of illicit drugs and their metabolites to be converted to thermally stable, volatile compounds. In addition, SPE and SPME methods also have improved the sensitivities of detection due to their capabilities for preconcentration of the targeted analytes. 

Various authors have described on-line LC-SFC coupling [947,948]. Coupling of LC to SFC with conventional-size LC columns, where only a small fraction of the peak of interest is transferred to the SFC, allows only for qualitative results, and does not address the need for improved sensitivity in cSFC. Cortes et al. [948] have described relatively large-volume sample introductions (>10 xL) into cSFC, using microcolumn LC in the first dimension. LVI-LC-cSFC provides enhanced sensitivity compared with conventional cSFC injection techniques. LC-cSFC is expected to be of utility in the characterisation of complex samples, and in the determination of components which are thermally labile do not contain significant chromophores or do not have sufficient volatility to be analysed by GC. 

An initial experiment involved determination of Arapahoe Smoke Chamber results for samples with and without the zinc coating present. Data are presented in Table II. Depending upon orientation of the sample, an increase in char occurred for some samples with zinc present, while no change in smoke formation was seen. Initial pyrolysis GC/mass spectroscopy results at 90CPC in helium showed no difference in volatiles formed with or without zinc. These results suggested enhanced char formation as the origin of the Radiant Panel results for zinc on modified-polyphenylene oxide (m-PPO). Zinc oxide is a known, effective thermal stabilizer in the alloy. The next work then focused on DSC/TGA studies. 

Drugs and toxicants are metabolized in the human body in such a way that more polar compounds are usually formed. Therefore to decrease the polarity and increase the volatility and thermal stability of the analytes, the derivatization step is an unavoidable requirement for GC analysis. This step enhances the detectability of the analytes and provides very characteristic mass spectra that can be relevant for identification purposes. Most analytes do not require derivatization for LC separation and MS detection. 

---