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PubMed2004

Parallel replica dynamics with a heterogeneous distribution of barriers: application to n-hexadecane pyrolysis.

Parallel replica dynamics simulation methods appropriate for the simulation of chemical reactions in molecular systems with many conformational degrees of freedom have been developed and applied to study the microsecond-scale pyrolysis of n-hexadecane in the temperature range of 2100-2500 K. The algorithm uses a transition detection scheme that is based on molecular topology, rather than energetic basins. This algorithm allows efficient parallelization of small systems even when using more processors than particles (in contrast to more traditional parallelization algorithms), and even when there are frequent conformational transitions (in contrast to previous implementations of the parallel replica algorithm). The parallel efficiency for pyrolysis initiation reactions was over 90% on 61 processors for this 50-atom system. The parallel replica dynamics technique results in reaction probabilities that are statistically indistinguishable from those obtained from direct molecular dynamics, under conditions where both are feasible, but allows simulations at temperatures as much as 1000 K lower than direct molecular dynamics simulations. The rate of initiation displayed Arrhenius behavior over the entire temperature range, with an activation energy and frequency factor of E(a) = 79.7 kcal/mol and log A/s(-1) = 14.8, respectively, in reasonable agreement with experiment and empirical kinetic models. Several interesting unimolecular reaction mechanisms were observed in simulations of the chain propagation reactions above 2000 K, which are not included in most coarse-grained kinetic models. More studies are needed in order to determine whether these mechanisms are experimentally relevant, or specific to the potential energy surface used.

Journal Article↗

PubMed2000

Laser pyrolysis fabrication of ferromagnetic gamma'-Fe4N and FeC nanoparticles.

Using the laser pyrolysis method, single phase gamma'-Fe4N nanoparticles were prepared by a two step method involving preparation of nanoscale iron oxide and a subsequent gas-solid nitridation reaction. Single phase Fe3C and Fe7C3 could be prepared by laser pyrolysis from Fe(CO)5 and 3C2H4 directly. Characterization techniques such as XRD, TEM and vibrating sample magnetometer were used to measure phase structure, particle size and magnetic properties of these nanoscale nitride and carbide particles.

Carbon Compounds, Inorganic↗

PubMedDate not supplied

Hydraulic fluids and jet engine oil: pyrolysis and aircraft air quality.

Incidents of smoke in aircraft cabins often result from jet engine oil and/or hydraulic fluid that leaks into ventilation air, which can be subjected to temperatures that exceed 500 degrees C. Exposed flight-crew members have reported symptoms, including dizziness, nausea, disorientation, blurred vision, and tingling in the legs and arms. In this study, the authors investigated pyrolysis products of one jet engine oil and two hydraulic fluids at 525 degrees C. Engine oil was an important source of carbon monoxide. Volatile agents and organophosphate constituents were released from all the agents tested; however, the neurotoxin trimethyl propane phosphate was not found. The authors hypothesized that localized condensation of pyrolysis products in ventilation ducts, followed by mobilization when cabin heat demand was high, accounted for mid-flight incidents. The authors recommended that carbon monoxide data be logged continuously to capture levels during future incidents.

Air Pollutants↗

PubMed1975

Polyvinyl chloride pyrolysis products. A potential cause for respiratory impairment.

A limited investigation of respiratory and other symptom prevalence, plus before and after shift ventilatory capacity was conducted among a group of 17 meat wrappers exposed to pyrolysis products of polyvinyl chloride and a group of 21 control subjects. Exposed meat wrappers showed a higher prevalence of cough, phlegm, hay fever, and asthma than did the control group. The exposed group also demonstrated relative decreases in forced expiratory volume, one second (FEV1.0) and forced expiratory flow 50% (FEF50) after one shift of work; whereas, the controls showed an opposite tendency. These findings suggest that meat wrappers exposed to pyrolysis products of polyvinyl chloride might be adversely affected. The results, while suggestive, are not totally conclusive owing to the fact that there was not ideal matching of the exposed and control groups in regard to age, height, race, sex, and smoking status.

Age Factors↗

PubMed2003

Pyrolysis of composite plastic waste.

Several different composite plastics were pyrolysed in a fixed bed reactor at final temperatures between 350 and 800 degrees C. The composites studied were polyester, phenolic, epoxy, vinylester, polypropylene and PET resins, reinforced with glass and/or carbon fibre. The product yields of oil gas and solid residue were determined together with a detailed composition of the derived gases. There was evidence to suggest that calcium carbonate filler, present in the polyester and phenolic composites, decomposed to form carbon dioxide at 800 degrees C, which was subsequently involved in char gasification reactions. Polyester, phenolic and epoxy composites generated highly aromatic, oxygenated condensable products. There was no noticeable correlation between the composition of these products and the final pyrolysis temperature. The tensile strength of recovered glass fibre was lower than that of virgin fibre and decreased markedly as the final pyrolysis temperature increased from 650 to 800 degrees C.

Conservation of Natural Resources↗

PubMed2000

Production of activated carbons from pyrolysis of waste tires impregnated with potassium hydroxide.

Activated carbons were produced from waste tires using a chemical activation method. The carbon production process consisted of potassium hydroxide (KOH) impregnation followed by pyrolysis in N2 at 600-900 degrees C for 0-2 hr. The activation method can produce carbons with a surface area (SA) and total pore volume as high as 470 m2/g and 0.57 cm3/g, respectively. The influence of different parameters during chemical activation, such as pyrolysis temperature, holding time, and KOH/tire ratio, on the carbon yield and the surface characteristics was explored, and the optimum preparation conditions were recommended. The pore volume of the resulting carbons generally increases with the extent of carbon gasified by KOH and its derivatives, whereas the SA increases with degree of gasification to reach a maximum value, and then decreases upon further gasification.

Air Pollutants, Occupational↗

PubMed2006

Pyrolysis behavior of tire-derived fuels at different temperatures and heating rates.

Pyrolytic product distribution rates and pyrolysis behavior of tire-derived fuels (TDF) were investigated using thermogravimetric analyzer (TGA) techniques. A TGA was designed and built to investigate the behavior and products of pyrolysis of typical TDF specimens. The fundamental knowledge of TGA analysis and principal fuel analysis are applied in this study. Thermogravimetry of the degradation temperature of the TDF confirms the overall decomposition rate of the volatile products during the depolymerization reaction. The principal fuel analysis (proximate and ultimate analysis) of the pyrolytic char products show the correlation of volatilization into the gas and liquid phases and the existence of fixed carbon and other compounds that remain as a solid char. The kinetic parameters were calculated using least square with minimizing sum of error square technique. The results show that the average kinetic parameters of TDF are the activation energy, E = 1322 +/- 244 kJ/mol, a pre-exponential constant of A = 2.06 +/- 3.47 x 10(10) min(-1), and a reaction order n = 1.62 +/- 0.31. The model-predicted rate equations agree with the experimental data. The overall TDF weight conversion represents the carbon weight conversion in the sample.

Conservation of Natural Resources↗

PubMed1978

Pyrolysis gas chromatography of enzymes.

Pyrolysis gas chromatography (PGC) has been shown to be useful for differentiating enzymes. The enzymes alpha-chymotrypsin, lactate dehydrogenase, catalase, and urease were easily "fingerprinted" on a 1.8 m 0.5% Carbowax 20 M column. Also, in some cases, isoenzymes of lactate dehydrogenase could be distinguished. Based on the pyrolyses of the free aromatic amino acids, four major enzyme pyrolysis peaks were tentatively identified as organic compounds derived from tyrosine and tryptophan. The use of a nitrogen-selective detector in conjunction with the FID and measurement of peak retention times by computer on three different types of columns permitted confirmations of peak identity.

Acetylcholinesterase↗

PubMed2000

Forensic discrimination of automotive paint samples using pyrolysis-gas chromatography-mass spectrometry with multivariate statistics

Analytical pyrolysis-gas chromatography (Py-GC) has been a standard method for the forensic analysis of automotive paint for a number of decades. Automotive paints are often identified by visual comparison of pyrograms for peak presence and intensities; however, such analyses can be subjective and time consuming. A preliminary investigation based on Py-GC-mass spectrometric analysis of 100 automobile paint samples of five different colors is presented. Designed experiments are employed to select pyrolysis conditions for adequate discrimination. Pattern recognition techniques including principal component analysis and canonical variates analysis are used to visualize clustering of pyrograms to validate comparisons between different automotive paint pyrograms. These methods have the potential to ease the interpretation task for data sets involving a large number of comparisons.

Journal Article↗

PubMed2001

Thin-layer chromatography-pyrolysis-gas chromatography-mass spectrometry: a multidimensional approach to marine lipid class and molecular species analysis.

A new multidimensional chromatographic method is described in which material separated into lipid-class bands on silica-coated quartz thin-layer chromatography (TLC) rods (Chromarods) is desorbed using a pyrolysis unit interface and introduced directly into a gas chromatograph-mass spectrometer for molecular species analysis. Steryl esters, wax esters, hydrocarbons, ketones, and fatty-acid methyl esters (FAMEs) are thermally desorbed without pretreatment. In order to desorb free sterols, monoacylglycerols (MAGs), aliphatic alcohols, and free fatty acids, the esters are converted to trimethylsilyl derivatives on the rod. Triacylglycerols and phospholipids are converted to FAMEs by thermochemolysis with tetramethylammonium hydroxide. The method's utility is demonstrated with lipids from seawater particulate matter by first confirming the identity of lipid bands with the appropriate standards. The wax ester-steryl ester TLC band contained no more than 8% steryl esters. Wax esters of up to C42 are detected. In six individual acyl lipid classes, C14-C22 fatty acids are detected with C16 acids predominant in all but wax esters. C16-C22 MAGs are identified in the complex acetone-mobile polar lipid band. The method successfully extends the scope of latroscan TLC-flame-ionization detection on Chromarods, which is a widely used technique for lipid-class analysis. Modification of the pyrolysis probe to handle intact TLC rods is a future objective.

Journal Article↗

PubMed1986

Pyrolysis gas chromatography-mass spectrometry of mycobacterial mycolic acid methyl esters and its application to the identification of Mycobacterium leprae.

Pyrolysis gas chromatography-mass spectrometry of methyl mycolates from 32 species of mycobacteria, including Mycobacterium leprae, was carried out. The mycobacteria could be classified into four groups in respect of the fatty acid ester patterns detected within the range C20 to C26. The applicability of this pyrolysis-gas chromatographic method for identifying M. leprae is discussed.

Chromatography, Gas↗

PubMed1989

A pyrolysis mass spectrometry study of fusobacteria.

Strains of fusobacteria (143) were examined by pyrolysis mass spectrometry (Py-MS) with a Horizon Instruments PYMS 200X. Fusobacterium necrogenes, F. necrophorum, F. nucleatum, F. mortiferum, F. varium, F. gonidiaformans, F. naviforme, F. russii and Leptotrichia buccalis were discriminated. Strains of fusobacteria isolated from tropical ulcers, although similar to F. mortiferum in conventional tests, were discriminated from each of these species in Py-MS. Identification of 416 spectra to species level agreed with conventional bacteriological methods in 91.8% of cases, was equivocal in 3.4% and disagreed in 4.8%. Classification based on pyrolysis data resolved groups largely corresponding to the recognised species. However, F. nucleatum strains were divided between two distinct groups. The tropical ulcer strains were resolved as a distinct homogeneous group. Py-MS is a rapid, inexpensive and convenient procedure for characterisation of bacteria, with the capacity for a high throughput of samples, although the initial cost of the apparatus is high.

Fusobacterium↗

PubMed1988

Reproducibility of pyrolysis mass spectrometry: effect of growth medium and instrument stability on the differentiation of selected Bacillus species.

The discrimination of a set of 53 strains, taken from four closely related Bacillus species (Bacillus subtilis, B. pumilus, B. licheniformis and B. amyloliquefaciens), was examined using pyrolysis mass spectrometry. Strains were grown on six different media to examine the effect of media variation, especially batch-to-batch variation of a single medium, on the pyrolysis mass spectra and strain discrimination achieved. Long-term reproducibility over a period of 14 months was also examined. It was shown that batch-to-batch media variation is insufficient to affect spectra and strain discrimination significantly, but different media types do affect this. It was shown that species groups could still be recovered from the data, however, with an appropriate data-handling system. It was not possible to directly compare spectra produced 14 months apart, but the strain and species discrimination achieved using each data-set were highly comparable.

Bacillus↗

PubMed1993

Artificial neural network analysis of pyrolysis mass spectrometric data in the identification of Streptomyces strains.

Sixteen representatives of three morphologically distinct groups of streptomycetes were recovered from soil using selective isolation procedures. Duplicated batches of the test strains were examined by Curie-point pyrolysis mass spectrometry and the first data set used for conventional multivariate statistical analyses and as a training set for an artificial neural network. The second set of data was used for 'operational fingerprinting' and for testing the artificial neural network. All of the test strains were correctly identified using the artificial neural network whereas only fifteen of the sixteen strains were assigned to the correct group using the conventional operational fingerprinting procedure. Artificial neural network analysis of pyrolysis mass spectrometric data provides a rapid, cost-effective and reproducible way of identifying and typing large numbers of microorganisms.

Bacterial Typing Techniques↗

PubMed1984

Pyrolysis mass spectrometry of complex organic materials.

Pyrolysis mass spectrometry in combination with computerized multivariate statistical analysis enables qualitative and quantitative analysis of nonvolatile organic materials containing molecular assemblies of a complexity and size far beyond the capabilities of direct mass spectrometry. The state of the art in pyrolysis mass spectrometry techniques is illustrated through specific applications, including structural determination and quality control of synthetic polymers, quantitative analysis of polymer mixtures, classification and structural characterization of fossil organic matter, and nonsupervised numerical extraction of component patterns from complex biological samples.

Biochemical Phenomena↗

PubMed1980

Virulence prediction of Yersinia enterocolitica by pyrolysis gas-liquid chromatography.

Pyrolysis gas-liquid chromatography (PGLC) was used to differentiate between HeLa cell-invasive and noninvasive strains of Yersinia enterocolitica and between Sereny-positive and -negative strains. A temperature-programmed gas-liquid chromatograph, equipped with a high-resolution Carbowax 20M coated capillary column, separated the volatiles from pyrolyzed whole cells preparations and cell wall fractions. The resulting pyrolysis elution patterns (pyrograms) were divided into 313 30-s time interval areas. The time interval areas were normalized in relation to the entire pyrogram area and were evaluated by stepwise linear discriminant analysis. The results of the PGLC-statistical analyses showed good correlation in prediction of the HeLa cell invasivity test. The technique of PGLC coupled with statistical analyses is objective, in contrast to traditional methods of determining pathogenicity of Y. enterocolitica.

Bacteriological Techniques↗

PubMed1970

Pyrolysis-gas-liquid chromatography of fungi: differentiation of species and strains of several members of the Aspergillus flavus group.

Four fungi of the Aspergillus flavus group were differentiated to the species level and strain level by pyrolysis-gas-liquid chromotography. Comparisons of pyrochromatograms revealed more similarities than dissimilarities among both species and strains in the pyrolytic elution patterns. Quantitative analysis was made by comparing the number of peaks in which two strains or reference species agreed or disagreed, the degree of superimposability between the pyrolytic elution patterns of strains and reference species, and the presence or absence of peaks for strain pairs within each species. The accuracy and precision of these techniques suggest that pyrolysis-gas-liquid chromatography may have wide application in the detection, enumeration, and identification of fungi by nonmycologically trained personnel.

Aspergillus↗

PubMed1999

Development of amplified 16S ribosomal DNA restriction analysis for identification of Actinomyces species and comparison with pyrolysis-mass spectrometry and conventional biochemical tests.

Identification of Actinomyces spp. by conventional phenotypic methods is notoriously difficult and unreliable. Recently, the application of chemotaxonomic and molecular methods has clarified the taxonomy of the group and has led to the recognition of several new species. A practical and discriminatory identification method is now needed for routine identification of clinical isolates. Amplified 16S ribosomal DNA restriction analysis (ARDRA) was applied to reference strains (n = 27) and clinical isolates (n = 36) of Actinomyces spp. and other gram-positive rods. Clinical strains were identified initially to the species level by conventional biochemical tests. However, given the low degree of confidence in conventional methods, the findings obtained by ARDRA were also compared with those obtained by pyrolysis-mass spectrometry. The ARDRA profiles generated by the combination of HaeIII and HpaII endonuclease digestion differentiated all reference strains to the species or subspecies level. The profiles correlated well with the findings obtained by pyrolysis-mass spectrometry and by conventional tests and enabled the identification of 31 of 36 clinical isolates to the species level. ARDRA was shown to be a simple, rapid, cost-effective, and highly discriminatory method for routine identification of Actinomyces spp. of clinical origin.

Actinomyces↗