Semi-volatile Components Research Articles

Microwave-Enhanced Thermal Decontamination of Soil

Results of bench-scale and pilot-scale investigations on the remediation of contaminated sand and soil using microwave energy are presented. Microwave radiation penetrates the soil and heats water and contaminants. Developing vapors are withdrawn from the soil. The experiments suggest that microwave heating is an effective soil remediation technology. The process is rapid as compared to other methods, and its efficiency depends on the dielectric and physicochemical properties of the soil and the contaminant. It allows for the removal of volatile and semivolatile components, and it is especially effective in the case of polar compounds. In the presence of soil moisture, the removal of both polar and nonpolar compounds can be described quantitatively in terms of steam distillation. The remediation proceeds at a temperature not exceeding 100 °C. It is of particular importance in the case of soil rich in organic matter, where too high a temperature could result in carbonization of humic substances. The remediation of trichloroethylene-contaminated sand in a pilot-scale microwave heating system simulating the in-situ process is also reported. The profiles of temperature and contaminant concentration in the remediation zone are presented. The pilot-scale investigations indicate a possibility of the use of microwave heating as an in-situ remediation technique. The use of inexpensive low-power generators for the supply of power to individual antennas may help to reduce costs and allow for an unconstrained design of the array of antennas in the ground.

Multicomponent coagulation and condensation of toxic metals in combustors

The temporal evolution of the size-segregated composition of multiple, heavy metal, combustion-generated aerosols was investigated. The purpose was to gain insight into the competition between metal condensation and aerosol coagulation processes that affect the partitioning of toxic, heavy metals during combustion and their impact on the environment. Experiments were conducted on a2-to 16-kW downflow combustor, which supported a natural gas flame through which aqueous solutions of metal salts were sprayed. The behavior of both single metals and binary mixtures of lead and cadmium (which are both considered semivolatile) and of cadmium and nickel (the latter of which is refractory) was investigated. Particulate samples were withdrawn isokinetically through a rapid-dilution sampling probe from which they were quickly size segregated in a Berner low pressure impactor, allowing physical and chemical resolution in the submicron particle size range. Experimental data agreed with theoretical predictions using an existing literature model. This model solved the general dynamic equation numerically but was modified here to include the effects of film condensation in a simple manner. For samples withdrawn above the semivolatile metal dew points, theory showed that nucleation of the semivolatile metal in the probe, followed by coagulation, could explain completely, the measured size-segregated composition. With similar dew points and number concentrations, cadmium and lead particles interacted primarily through coagulation. However, cadmium and nickel particles did not interact by coagulation in the probe because of disparties in particle size and number concentrations. Further down the furnace, both model and data showed that compositions of particles were determined by condensation on existing nickel particles, rather than by nucleation of the semivolatile component (cadmium), followed by coagulation. These results are consistent with a literature hypothesis, on the effect of temperature quench rate on pertinent aerosol mechanisms.

Behavior of Hazardous and Radioactive Metals in a Laboratory Furnace and a Demonstration-Scale Incinerator

The behaviors of hazardous and radioactive metals in analytical and real combustion conditions were observed to understand their vaporization and to predict their release into the atmosphere at a real incineration plant. In the laboratory furnace experiment, vaporization fluxes were obtained based on the measurement of weight losses with temperatures. Vaporization fluxes were compared to maximum theoretical fluxes obtained from the Herz-Knudsen's kinetic theory of gas. The vaporization coefficient, α, for volatile metal chloride appears to be a characteristic value of the evaporating substance, not varying with increasing temperatures. With some theoretical considerations on interfacial equilibrium, mass transfer coefficient of vaporization, KG, was determined as a function of absolute temperature. To evaluate the behavior of metals and radionuclides in an incinerator and off-gas treatment system, test burns of simulated waste containing several toxic metals and radioisotopes were performed at the demonstration-scale incineration plant. The previously analyzed characteristics of volatilization of hazardous metals and radioactive nuclides were used to explain their distributions in the demonstration plant. The decontamination factor for low-volatility species was above 105, which was equivalent to the removal efficiency of particulate matter in the plant. The factors for semivolatile components were in the range between 102 and 104, showing the strong dependency on volatility. Key words: Metal; radionuclide; volatility; incineration; removal efficiency

Analysis of extracts fromcedrela toona (meliaceae) by on-line and off-line supercritical fluid extraction-capillary gas chromatography

A quantitative comparison between off-line supercritical fluid extraction (SFE) and a classical solvent extraction of a limonoid compound is discussed. A two-level three factor factorial analysis was used to optimize the variables, pressure, temperature, and the length of extraction time. By a statistical analysis of variance on the preliminary data collected, pressure and temperature were the significant variables influencing the yields of the limonoid cedrelone from the ground wood of Cedrela toona (Meliaceae). The cedrelone in the extracts was analyzed by capillary gas chromatography with flame ionization and mass spectrometric detection. On-line combination of micro-SFE with gas chromatography (SFE-GC) was also performed on the wood and bark to show the applicability of the technique in the analysis of semi-volatile components in natural products. Results for on-line and off-line SFE-GC were comparable and indicated that the on-line studies could be used to predict results obtainable from large scale SFE. © 1996 John Wiley & Sons, Inc.

Development and validation of a method for removal of normal paraffin hydrocarbon in radioactive waste samples prior to analysis of semivolatile components

A method has been developed at Pacific Northwest Laboratory (PNL) to remove normal paraffin hydrocarbon (NPH) from radioactive waste samples prior to gas chromotography/mass spectrometry analysis of semivolatile components. The effectiveness of the cleanup procedure was demonstrated for all the EPA semivolatile target list compounds. Blanks and spiked actual waste samples were utilized in the development and validation study. Approximately 95% of the NPH was removed from the single-shell tank samples. The recoveries were good for most of the target compounds. Results were compared with those obtained by utilizing EPA method 3630. The recoveries were much better for the PNL-developed method.

Examination of the emission of (semi-)volatile organic compounds from polymer materials used as interior trim materials in automobiles

Examinations of thermally-conditioned emissions from polymer materials used as interior trim in automobiles are presented. It is shown that a comprehensive description of the emission behaviour of polymer materials in the motor vehicle interior is only possible when the volatile as well as the semi-volatile emission components are taken into consideration. The influence of the manufacturing steps on the emission behaviour of interior parts is discussed on the basis of an example (instrument panel).

The Volatile and Semivolatile Components of Supercritical Fluid and Methylene Chloride Extracts of Selected Tobaccos

ABSTRACT Employing the hyphenated technique, gas chromatography/vapor phase infrared spectrometry/mass spectrometry (GC/VP-IR/MSD), the major volatile and semivolatile constituents of essential oils prepared by supercritical fluid (CO2) and methylene chloride extractions of selected tobaccos are presented. The major volatile and semivolatile components of both the supercritical fluid and methylene chloride extracts are nicotine, neophytadiene and hexadecanoic acid comprising approximately 85% by weight. Acids, ketones, amines and alcohols comprise the balance of the volatile and semivolatile components. All of the components of the extracts (supercritical fluid or methylene chloride) identified in this study have been previously identified in tobacco and/or tobacco smoke. The qualitative nature of these extracts is similar to those previously reported. The supercritical fluid extraction (SFE) approach provides a significant improvement over currently employed techniques such as solvent and Soxhlet extractions. Notable areas of improvement include reductions in lab space requirements, sample process time, material costs, potential solvent residual contamination and manpower requirements.

A review of pyrolysis studies to unravel reaction steps in burning tobacco

The chemical constituents of tobacco smoke are generated in the burning zone of the cigarette where the processes of combustion, pyrolysis, distillation and aerosol formation occur. Tobacco itself consists of many different chemical components and consequently a large number of reactions occur in parallel as the cigarette burns. Relationships between tobacco components and smoke products are complex and difficult to unravel. Pyrolysis experiments have commonly been used to establish such relationships. However, unless they are performed under dynamic conditions that are relevant to those that occur during tobacco burning, results can be obtained which have little resemblance to those obtained during cigarette smoking. Bearing in mind this limitation, a variety of pyrolysis studies are reviewed which give insights into the mechanisms and reaction pathways occurring in the cigarette. The oxides of carbon are formed by thermal decomposition and combustion of tobacco constituents, and carbon dioxide is further converted to carbon monoxide by carbonaceous reduction. Pyrolysis studies used to elucidate these three processes are discussed. Pyrolysis results are presented which indicate that the majority of the so-called semi-volatile components of cigarette smoke are formed from tobacco at temperatures below 600° C. A literature survey of the tobacco component-semi-volatile product routes has been summarised. It indicates that their formation is complex and only partially understood. A few components (e.g. nicotine and other alkaloids) are transferred directlyfrom the tobacco; most are formed principally as a result of pyrolytic decomposition of many tobacco components in parallel.

Determination of products of combustion from fires involving solvents commonly carried by rail

The apparatus and protocols used to determine the semi-volatile products of combustion from controlled laboratory-scale fires are presented. Products of combustion were collected in a sampling train consisting of a filter (heated to 160°C) and Tenax and charcoal sorbent tubes. The Tenax tubes were extracted with cyclohexane and the extracts analyzed. Quantitative measurement of the semi-volatile components was made using gas chromatography/flame ionization detection and identification of the products was performed using gas chromatography/mass spectrometry. The results for sixteen solvents commonly carried by rail are presented.

SELECTIVE ADSORPTION OF THE VAPOR PHASE COMPONENTS OF CIGARETTE SMOKE BY ACTIVATED CARBON FIBERS

Adsorption of the components in the vapor phase of cigarette smoke by activated carbon fibers (ACF) with micropore radii from 8 to 29A was measured in order to study the relation between the adsorption efficiencies and the physical properties of ACFs. The adsorption efficiency increased with the size of the micropores and, with the exception of a few components, all ACFs have high adsorption ability for high boiling point components such as limonene. An ACF having a micropore radius of 8A showed an extremely low adsorption ability and an ACF having micropore radius of 10A uniformly adsorbed the components in the vapor phase. When compared with the semivolatile components, the molecular sieving effect and the competitive adsorption due to the difference of the boiling points were clearly observed. The competitive adsorption was thought to be the main reason for the dynamic change of adsorption with puffing. Consequently, the possibility was recognized that an increase in the amount of ACFs having wide micropores decreased the adsorption efficiency of the low boiling point components.

The Characterization of Cigarette Smoke from Cytrel® Smoking Products and its Comparison to Smoke from Flue-Cured Tobacco: II. Semi-Volatile Phase Analysis

AbstractMajor semi-volatile components from Cytrel cigarette smoke have been characterized and compared to the smoke from flue-cured tobacco cigarettes. Significantly greater numbers of cigarettes are required to produce the Cytrel scans due to the very low tar deliveries of these cigarettes. Even so, the CytreI scans are far simpler than those from tobacco-containing samples. Using triacetin delivered from the cigarette filters as an internal standard, numerical data have been derived to compare semi-volatile components from 100 % Cytrel with 100 % flue-cured tobacco and with a 50 % blend with tobacco on an approximately equal cigarette basis. Of the 128 semi-volatile components compared, 37 were found only in tobacco-containing samples and 66 others were present in significantly greater amounts in tobacco than in CytreI. No components were found in CytreI semi-volatiles that were not also present in tobacco smoke. GlyceroI, which is present in Cytrel smoke, does not appear in the 130°C semi-volatile fraction obtained by the capsule sampling technique.

Selective Removal of Semivolatile Components of Cigarette Smoke by Various Filters

Abstract The semivolatile portion of cigarette smoke contains acidic, basic, and neutral compounds that are important to the flavour and in some cases the physiological effects of smoke. A rapid method that could be used routinely for the gas chromatographic analysis of this portion of smoke was developed. A 160 mm glass capillary column was used to resolve approximately 150 semivolatile smoke components. Gas chromatography - mass spectrometry was used to identify about 35 of these components. Twenty known semivolatile compounds with different functional groups and boiling points were used to determine the effects of various filters on their removal from smoke. Standard cellulose acetate filters, cellulose acetate filters with glycerin, cellulose acetate filters with PEG 600, and cellulose acetate filters with activated carbon were evaluated. The cellulose acetate filters with glycerin and PEG 600 were more selective for the removal of aromatic hydrocarbons than were the standard cellulose acetate filters. The cellulose acetate filters with activated carbon were more selective for the removaI of the low-boiling semivolatile compounds than were the other filters tested.