Showing papers on "Pyrolysis published in 1989"

Kinetic modelling of the pyrolysis of biomass and biomass components

Abstract: The kinetics of the pyrolysis of lignocellulosic materials was studied with a view of providing simple kinetic models for engineering purposes. Experimental data obtained by means of thermal analysis techniques suggest that the pyrolysis of fine particles (below 1 mm) can be considered to be controlled by pyrolysis kinetics. The rate of pyrolysis of one biomass type can be represented by the sum of the corresponding rates of the main biomass components (cellulose, lignin, hemicellulose). The kinetics of each of these components was simulated by a kinetic scheme capable of predicting the pyrolysis rate and the final weight-loss for a wide range of pyrolysis parameters including various heating conditions.

Product yields and kinetics from the vapor phase cracking of wood pyrolysis tars

Abstract: The homogeneous vapor phase cracking of newly formed wood pyrolysis tar was studied at low molar concentrations as a function of temperature (773 - 1.073 K), at residence times of 0.9 - 2.2 s. Tar conversions ranged from about 5 to 88%. The tars were generated by low heating rate (0.2 K/s) pyrolysis of --2 cm deep beds of sweet gum hardwood, and then rapidly conveyed to an adjacent reactor for controlled thermal treatment. Quantitative yields and kinetics were obtained for tar cracking and resulting product formation. The major tar conversion product was carbon monoxide, which accounted for over two-thirds of the tar lost at high severities. Corresponding ethylene and methane yields were each about 10% of the converted tar. Coke formation was negligible and weight-average tar molecular weight declined with increasing tar conversion.

Heterogeneous cracking of wood pyrolysis tars over fresh wood char surfaces

Abstract: Char-induced conversion of newly formed wood pyrolysis tars was measured for independent variations in temperature and tar-char space time. Tar vapors were generated by controlled devolatilization of shallow (∼2 cm deep) packed beds of 45-250 μm particles of sweet gum hardwood. Heterogeneous conversion was significant but essentially constant at 14±7 wt% of tar (to 2 standard deviations), for temperatures from 400 to 600 o C and space times from 2.5 to 100 ms. In contrast, vapor-phase tar conversion upstream of the char bed ranged from 0% at 400 o C to 30% (wt% of vapor-phase tar conversion upstream of the char bed ranged from 0% at 400 o C to 30% (wt% of tar) at 600 o C. The implication is that an otherwise thermally stable fraction of newly formed wood pyrolysis tars is very reactive in the presence of wood char

Preceramic Polymer Pyrolysis. I. Pyrolytic Properties of Polysilazanes.

Abstract: The physicochemical behaviour of characterized polysilazanes has been examined during their pyrolytic transformation into amorphous silicon-based ceramics. Selected polysilazanes bearing different substituents at silicon and nitrogen were synthesized by ruthenium catalysed dehydrocoupling of Si-H bonds with N-H bonds. The relationships between the structure and chemical content of polymers and their pyrolysed ceramic compositions and yields are discussed. Possible reactions occurring during pyrolysis are described in terms of a set of mechanisms based on known behaviour of silazane monomers. The decomposition product patterns at different temperature levels and the compositions of the final ceramics suggest specific kinetically or thermodynamically controlled thermolysis pathways. Additional chemical reactivity has been observed when the amorphous ceramic products at 800° C are heated and crystallized at 1600° C.

Structural models for catalytic cracking. 1. Model compound reactions

Abstract: Data on the catalytic cracking reactions of model compounds over an amorphous silica-alumina-zirconia catalyst are organized into a general framework based on carbon centers. Each hydrocarbon in a petroleum mixture consists of a collection of carbon centers, and the reaction behavior of individual compounds can be described by the reaction behavior of the carbon centers. The cracking behavior of the carbon centers has been deduced from pure compound studies available in the literature. The carbon center approach results in predictions that are in reasonbable agreement with the experimental data. The models of pure components are used as a basis for modeling the cataytic cracking reactions of hydrocarbon mixtures.

Pyrolysis of Argonne premium coals: activation energy distributions and related chemistry

Abstract: We report pyrolysis yields and kinetics at heating rates of several degrees Celsius per minute measured by modified Rock-Eval pyrolysis and by pyrolysis interfaced to triple-quadrupole mass spectrometry (TQMS). Pyrolysis temperatures from pyrolysis-TQMS were consistent with those from Rock-Eval considering that compounds less than about C 8 only were monitored by the TQMS. Rate data at three heating rates from the Rock-Eval apparatus were analyzed by using Gaussian and discrete activation energy distribution models

The gas phase pyrolysis of phenol

Abstract: Phenol pyrolysis has been studied in a turbulent flow reactor by analyzing concentration-time profiles of three major decomposition products: carbon monoxide, cyclopentadiene, and benzene. Experimental conditions were P = 1 atm, T = 1064 − 1162 K, and initial phenol concentrations of 500−2016 ppm. The major experimental observations were that the decomposition product profiles were nearly linear as a function of time and that the overall rate of carbon monoxide production was greater than that of cyclopentadiene. The rate difference is explained by a mechanism which includes a radical combination reaction of cyclopentadienyl and phenoxy. With literature and approximate rate coefficient data, the mechanism reproduced the experimental observations very well. The mechanism and data provide estimates of rate coefficients for the phenol decomposition initiation step, abstraction of hydrogen from phenol by cyclopentadienyl, and the phenoxy-cyclopentadienyl combination, all of which have not been available in the literature.

Pyrolysis of Preceramic Polymers in Ammonia: Preparation of Silicon Nitride Powders

Abstract: The pyrolysis of cross-linked polycarbosilanes, polysilanes and polysilazanes in an ammonia atmosphere to 1473 K yields amorphous, low-carbon silicon nitride powders. The efficacy of carbon removal is independent of the polymer's structure or functionality but is partially dependent on the initial cross-linking temperature. The amorphous silicon nitride powders partially crystallize to α-Si3N4 by 1773 K.

Conversion of lignins to hydrocarbon fuels

Abstract: A pyrolytic lignin (one extracted from a crude biomass pyrolysis oil) has been upgraded in a laboratory nonisothermal plug flow catalytic reactor to give yields of 60-65% hydrocarbon liquids (carbon conversion of 78%). The light hydrocarbon liquid was about 62% aliphatics and 38% aromatics with 50% estimated boiling in the gasoline range. The liquid product contained only about 0.5% oxygen. It is suggested that other lignin by-products could be similary converted if not excessively degraded during the recovery process

Synthesis of Amorphous Boron Nitride by Pressure Pyrolysis of Borazine

Abstract: Amorphous BN that contains hydrogen could be synthesized by pressure pyrolysis of borazine below 700°C at 100 MPa. The fraction of B and N bonded to H in the pyrolysis product could be controlled by changing the pressure pyrolysis condition. The pyrolysis product at 700°C and 100 MPa showed formation of B-N-B bonds of the hexagonal structure in the amorphous state with some B-H and N-H bonding remaining. Spherulitic BN could be prepared only by pyrolysis below 400°C and 100 MPa. The yield of amorphous BN from borazine was as high as about 60% by this pressure pyrolysis. Amorphous BN formed from borazine could be readily converted to cubic BN by reacting it with AIN at 1200°C and 6.5 GPa.

Preparation of organo palladium particles from thermal decomposition of its organic complex in organic solvents

Abstract: Preparation d'une suspension de particules de Palladium par decomposition thermique de Pd (acac) 2 (acac=acetylacetonate) dans differents solvants organiques

Carbon films from polyacrylonitrile

Abstract: Polyacrylonitrile (PAN) films have been fabricated by both spin and solvent casting techniques, and pyrolyzed to produce carbon films in the thickness range of 200--50 000 A. These films have higher electrical conductivities than carbon films produced from most other precursors at similar temperatures. The chemical structure of the films at different stages of processing was investigated by UV, IR, Raman, and XPS spectroscopies. An extra degree of control over the final electrical conductivity was obtained by varying the PAN content of copolymer precursors. Oxidation rates and an activation energy were determined. Finally, processing techniques are described which allow both dry and wet film transfer and lithographic patterning.