Showing papers on "Pyrolysis published in 1994"

Stability of wood fast pyrolysis oil

Abstract: This study evaluates the effects of storage conditions on physical and chemical properties of biomass fast pyrolysis oils exposed to elevated temperatures over extended periods of time. It was performed on oak pyrolysis oil generated in the NREL vortex reactor. Oil samples were stored at three temperatures: 37, 60 and 90°C in glass vessels. Properties of the oils were measured after hours of storage at 90°C, and after days or weeks at lower temperatures. Chemical changes in the oils were measured using GPC (molecular weight distribution) and FTIR spectroscopy. The oil remained a single phase throughout the studied conditions. Its pH was not affected by storage. The water content, viscosity and molecular weight of the oil increased with the time and temperature of storage. First-order reaction kinetics were successfully used to predict changes in molecular weight of the stored oil. FTIR provided evidence that etherification or esterification are mechanisms for condensation of the oil during storage.

Analytical pyrolysis of humic substances: pitfalls, limitations, and possible solutions

Abstract: Analytical pyrolysis is a technique currently used for investigating structural features of compler macromolecular materials. However, pitfalls appear to be widespread in pyrolysis studies of humic substances, and serious limitations can be experienced during the analytical procedure due to thermal reactions and configuration of the pyrolysis units and chromatographic systems. Pyrolysis presents inconsistencies for chemical studies, and the interpretation of the chemical structure of humic substances in light of information provided by pyrolysis data is, to say the least, hazardous. This paper examines possible solutions to some of the problems encountered in pyrolysis

Pyrolysis of Polyethylene in a Fluidized Bed Reactor

Abstract: A fluidized sand bed reactor was used to study the production of gases from polyethylene (HDPE) at five nominal temperatures (ranging from 500 to 900°C). Both HDPE primary decomposition and wax cracking reactions take place inside the reactor. Yields of 13 pyrolysis products (methane, ethane, ethylene, propane, propylene, acetylene, butane, butylene, pentane, benzene, toluene, xylenes, and styrene) were analyzed as a function of the operating conditions. The results are compared with the data obtained by pyrolysis of HDPE in a Pyroprobe 1000, where secondary wax and tar cracking is small. Correlations between the products analyzed with those of methane are discussed.

Role of transition-metal catalysis in the formation of natural gas

Abstract: THE idea that natural gas is formed by thermal decomposition of sedimentary organic matter1,2 enjoys almost universal acceptance3–6. But pyrolysis experiments on organic matter7–13 have failed to reproduce the composition of natural gas (typically 90% methane). It has recently been suggested14 that natural gas may instead be generated catalytically: transition metals are often found in carbonaceous sedimentary rocks, and might promote the reaction between hydrogen and n-alkenes (which are themselves formed during thermal decomposition of kerogen) to give light hydrocarbons and natural gas. We report here experimental results that support this hypothesis. In particular, we find that n-alkenes, hydrogen and a carbonaceous sedimentary rock containing moderately high concentrations of transition metals react under mild conditions (∼200 °C) to generate a light-hydrocarbon product indistinguishable from natural gas in both molecular and carbon isotope composition. Our results demonstrate that the reaction is indeed catalytic, and could alter the way in which we view the generation and distribution of oil and gas in the Earth.

A unified, global model for the pyrolysis of cellulose

Abstract: Complex interactions occur between the many competing and sequential chemical reactions during the pyrolysis of cellulose, making the prediction of the pyrolysis products relatively difficult. The purpose of this paper is to present cellulose pyrolysis as a comprehensible interaction of time, temperature and pressure. Appropriate kinetic data for seven first-order global reactions for the pyrolysis of cellulose were found in the literature. A mathematical model was developed, in which the seven reactions occurred simultaneously so long as the feedstock for the particular reaction existed. The seven differential equations representing the reaction rates were numerically integrated simultaneously to obtain the products of pyrolysis as a function of time, temperature, heating rate and pressure. This program was used to predict many results and trends observed in both slow and fast pyrolysis: very high yields of condensible vapors (primary oils) were predicted under high heating rates to modest final temperatures; high char yields were predicted for slow heating rates at low temperatures; high gas yields were predicted for fast pyrolysis at high temperatures.

Characterisation of oils from the fluidised bed pyrolysis of biomass with zeolite catalyst upgrading

Abstract: Biomass in the form of pine wood was pyrolysed in an externally heated 7.5 cm diameter, 100 cm high fluidised bed pyrolysis reactor with nitrogen as the fluidising gas. A section of the freeboard of the reactor was packed with zeolite ZSM-5 catalyst. The pyrolysis oils before and after catalysis were collected in a series of condensers and cold traps. In addition, gases were analysed off-line by packed column gas chromatography. The compositions of the oils and gases were determined in relation to the primary fluidised bed and after catalysis at increasing catalyst bed temperatures from 400° to 550°C. The oils were analysed by a number of techniques to determine composition, including liquid chromatography, gas chromatography/mass spectrometry. Fourier transform infrared spectroscopy and size exclusion chromatography. The results showed that the oils before catalysis were highly oxygenated; after catalysis the oils were markedly reduced in oxygenated species with an increase in aromatic and polycyclic aromatic species. The gases evolved from the fluidised bed pyrolysis of biomass were CO2, CO, H2, CH4, C2H4, C3H6 and minor concentrations of other hydrocarbon gases. After catalysis the concentrations of CO2 and CO were increased. The conversion of oxygenated compounds was mainly to H2O at lower catalyst temperatures and CO2 and CO at high catalyst temperatures. Detailed analysis of the oils showed that there were high concentrations of biologically active polycyclic aromatic species in the catalysed oil which increased with increasing catalyst temperature. The oxygenated compounds in the uncatalysed oil were mainly phenols and car☐ylic acids. After catalysis these decreased in concentration with increasing catalyst temperature

Structural Characterization of Sol-Gel Derived Oxycarbide Glasses. 1. Study of the Pyrolysis Process

Abstract: A gel resulting from the cohydrolysis of dimethyldiethoxysilane, a silane precursor, and tetraethoxysilane, a silica precursor, has been pyrolyzed to a silicon oxycarbide network. This conversion has been carefully characterized using various structural techniques: thermogravimetric analysis coupled with mass spectrometry, multinuclear solid-state magic angle spinning nuclear magnetic resonance ( 29 Si, 1 H, and 13 C), infrared spectroscopy, and electronic spin resonance. The pyrolysis process can be divided in two main stages. In the 400-650 °C temperature range, redistribution reactions between Si-O and Si-C bonds occur with evolution of low molecular weight siloxanes. New Si sites are created, but the methyl groups remain intact. From 650 to 1000 °C, the conversion of the polymeric network into an inorganic material takes place. Cleavage of C-H, Si-C, but also Si-O bonds occurs with evolution of methane, hydrogen and water. Aromatic carbon units are formed. Heat treatment at 1000 °C in argon flow leads to the formation of an amorphous silicon oxycarbide phase, characterized by SiC x O 4-x units. The presence of a free carbon phase has also been shown.

Coke Formation in the Thermal Cracking of Hydrocarbons. 4. Modeling of Coke Formation in Naphtha Cracking

Abstract: An extensive experimental program has been carried out in a pilot unit for the thermal cracking of hydrocarbons. On the basis of the experimental information and the insight in the mechanisms for coke formation in pyrolysis reactors, a mathematical model describing the coke formation has been derived. This model has been incorporated in the existing simulation tools at the Laboratorium voor Petrochemische Techniek, and the run length of an industrial naphtha cracking furnace has been accurately simulated. In this way the coking model has been validated.

Investigation of the Kinetics of Pyrolysis of PVC by TG-MS-Analysis

Abstract: Pyrolysis or combustion of plastics are of interest from different points of view: on the one hand polymers from which harmful substances may arise are involved in fires or are fed to incinerators; on the other hand plastic refuses are an alternative resource of energy or chemical raw materials. For designing recycling procedures the behaviour of the decomposition of polymers with regard to the decomposition products and the kinetics of decomposition must be known. Plastic refuses encompass chlorine- and/or nitrogen-containing polymers which may form toxic or corrosive products under pyrolytic conditions or in combustion. These components must be separated before processing or the troublesome elements have to be eliminated by pretreatment. The aim of this work was to investigate the kinetics of pyrolysis of polyfvinyl chloride) and mixtures of poly(vinyl chloride) with polyethylene, polypropylene, polystyrene and polyamide 6. By means of simultaneous thermogravimetry-mass spectrometry the kinetic...

Removal of metal ions from aqueous solution by activated carbons obtained from different raw materials

Abstract: The adsorption of Pb 2+ , Cu 2+ , Zn 2+ and Cd 2+ from aqueous solution at 293 K by activated carbons obtained from different raw materials was studied. These carbons were prepared by water vapour pyrolysis of the raw materials-apricot stones, coconut shells and lignite coal. The influence of the solution pH on the adsorption processes has been studied. The presence of other metal ions in the solution decreases the adsorption of each of the ions. The selective adsorption of the metal ions is observed but the ones preferentially adsorbed do not completely prevent the adsorption of other ions. The chemical nature of the carbon surface and metal ions have great significance for the adsorption process

Ablative plate pyrolysis of biomass for liquids

Abstract: Ablative pyrolysis is one of a range of fast or flash pyrolysis technologies for the production of liquids in high yields which offers the potential for high reactor specific throughputs with reduced equipment size, costs and improved controllability. The main objectives of the work are to design, construct and operate an ablative pyrolysis reactor and a pyrolysis liquids collection system which includes identification of key process parameters, exploration of relationships between parameters and product quality and the development of a new model to account for the ablative pyrolysis process. A reactor has been operated at temperatures from 450° to 600°C and at dry reacted wood feedrates up to 2.5 kg/h. Run times of 45 min have been achieved at steady state. Total liquid yields up to 81 wt% on dry ablatively pyrolysed wood basis have been achieved.

Conversion of Polyethylene to Transportation Fuels through Pyrolysis and Catalytic Cracking

Abstract: A high-density polyethylene was thermally cracked in both a closed tubing-bomb reactor at 450-500 °C and an open system using the same reactor at 480 °C. In the closed system, distillate yield increased at a higher temperature which also accelerated the formation of gases and coke. Secondary reactions such as saturation, isomerization, cyclization, and aromatization were found at high severity. In contrast, the open system produced less naphtha but more gas oil. Compositionally, the distillates contained more olefins, less saturates, and very little aromatics, compared with those from the closed system. Pyrolytic waxy products from polyethylene were catalytically cracked in a fixed-bed reactor at 470 and 510 °C, respectively. High yields of gasoline of improved quality and liquefied petroleum gas were obtained along with a small amount of low-value products such as dry gas, heavy cycle oil and coke.

Silicon oxycarbide glasses from gels

Abstract: Silicon-oxycarbide glasses can be synthesized from modified silica gels through a pyrolysis process in inert atmosphere. A critical analysis of the literature suggests a close relationship between oxygen content in the gel precursors and the amount of carbon atoms covalently bonded to silicon atoms in the corresponding silicon-oxycarbide phase. The problem of the formation of a free carbon phase will be discussed and related to the amount of carbon in the starting gel. An example of successful synthesis of an almost pure carbon-rich oxycarbide phase will also be presented.

Hydrogen sulfide sensor based on tin oxide deposited by spray pyrolysis and microwave plasma chemical vapor deposition

Abstract: Spray pyrolysis and microwave plasma chemical vapor deposition techniques have been employed successfully for the deposition of CuO impregnated SnO2 films suitable for sensing hydrogen sulfide and methyl mercaptan. The observed change in conductivity of these films upon exposure to H2S gas in air has been explained on the basis of the band theory of solids.

Water, alkali and char in flash pyrolysis oils

Abstract: Several biomass flash pyrolysis oils were analyzed to determine the forms of water, alkali and char in the oil. Representative oil samples were produced from oak, pine and switchgrass as representatives of hardwood, softwood and herbaceous biomass, respectively. Separations of the oil were undertaken to confirm the site of the alkali in the oil. Consideration was given to potential for char-encased alkali or alkali precipitation as char; alkali salts in water micro-droplets or alkali soap micelle formations; and organo-alkali component solution in the organic phase. Separations attempted included centrifugation, filtration, water dilutions and phase separations. Microscopic analysis of the oils was also attempted as well as scanning electron microscopic analysis of solids. A separate aqueous phase could not be found in the oil. Size distribution of char particulates showed a range primarily from 1 to 10 μ m. Inorganic components were concentrated in the char particles. Component analysis of the oils affirmed earlier analytical data found in the literature for flash pyrolysis oils.

Hydrogen-Transferring Pyrolysis of Long-Chain Alkanes and Thermal Stability Improvement of Jet Fuels by Hydrogen Donors

Abstract: Hydrogen-transferring pyrolysis refers to the thermal decomposition of hydrocarbons in the presence of hydrogen donors. Relative to the pyrolysis of pure n-tetradecane (C[sub 14]H[sub 28]) at 450 C, adding 10 vol % of H-donor tetralin suppressed n-C[sub 14] conversion by 68 % after 12 min of residence time, by about 66% after 21 min, and by 37% after 30 min. The presence of tetralin not only inhibited the n-C[sub 14] decomposition, but also altered the product distribution. The decomposition and isomerization of primary radicals are strongly suppressed, leading to a much higher ratio of the 1-alkene to n-alkane with 12 carbon atoms and slightly higher alkene/alkane ratio for the other product groups. The overall reaction mechanism for the initial stage of hydrogen-transferring pyrolysis is characterized by a one-step [beta]-scission of secondary radical followed by H-abstraction of the resulting primary radical. Moreover, desirable effects of the H-donor are also observed even after 240 min at 450 C, especially for inhibiting solid deposition. The authors also examined the effect of tetralin addition on the deposit formation from a paraffinic jet fuel JP-8 which is rich in C[sub 9]-C[sub 16] long-chain alkanes, and an aromatic compound, n-butylbenzene. Adding 10 vol % tetralin tomore » a JP-8 jet fuel, n-C[sub 14], and n-butylbenzene reduced the formation of deposits by 90% (from 3.1 to 0.3 wt %), 77 % (from 3.0 to 0.7 wt %), and 54 % (from 5.6 to 2.6 wt %), respectively. These results suggest that, by taking advantage of H-transferring pyrolysis, hydrocarbon jet fuels may be used at high operating temperatures with little or no solid deposition.« less

Control of pore size of porous silica by means of pyrolysis of an organic–inorganic polymer hybrid

Abstract: Pyrolysis of a silica gel hybrid with a starburst dendrimer gives porous silica, in which the pore-size is successfully controlled by the size of the organic component used.