Showing papers on "Pyrolysis published in 1999"

Fast pyrolysis of biomass : a handbook

Abstract: This handbook is based on the final report of the International Energy Agency's (IEA) Bioenergy sponsored Pyrolysis Activity. Topics reviewed cover the fast pyrolysis of biomass for producing fuels and chemicals; the IEA pyrolysis fundamentals review; the nature and properties of biomass pyrolysis materials; storage and handling of flash pyrolysis oil; testing standard methods; new methods for chemical and physical characterisation and Round Robin testing; proposed specifications for various grades of pyrolysis oils; the determination of biodegradation rates of bio-oil by respirometry; environment, health and safety issues; and the toxicity of biomass pyrolysis liquids.

Product Distribution from Pyrolysis of Wood and Agricultural Residues

Abstract: The pyrolysis characteristics of agricultural residues (wheat straw, olive husks, grape residues, and rice husks) and wood chips have been investigated on a bench scale. The experimental system establishes the conditions encountered by a thin (4 × 10-2 m diameter) packed bed of biomass particles suddenly exposed in a high-temperature environment, simulated by a radiant furnace. Product yields (gases, liquids, and char) and gas composition, measured for surface bed temperatures in the range 650−1000 K, reproduce trends already observed for wood. However, differences are quantitatively large. Pyrolysis of agricultural residues is always associated with much higher solid yields (up to a factor of 2) and lower liquid yields. Differences are lower for the total gas, and approximate relationships exist among the ratios of the main gas species yields, indicating comparable activation energies for the corresponding apparent kinetics of formation. However, while the ratios are about the same for wood chips, rice h...

Silicon Oxycarbide Glasses

Abstract: The first attempts to introduce carbon into glass date back to 1951. But up until recently, the use of carbon or carbide raw materials, and the oxidation, volatilization and decomposition that accompany high temperature melting, have limited the synthesis of true silicon oxycarbide glasses. Here, the term silicon-oxycarbide refers specifically to a carbon-containing silicate glass wherein oxygen and carbon atoms share bonds with silicon in the amorphous, network structure. Thus, there is a distinction between black glass, which contains only a second-phase dispersion of elemental carbon, and oxycarbide glasses which usually contain both network carbon and elemental carbon. In addition to exploring the unique properties and applications of these glasses, per se, they are also of interest for developing models of the residual amorphous phases in polymer-derived silicon-carbide and silicon-nitride ceramics. The application of sol/gel techniques to glass synthesis has significantly advanced the development and characterization of silicon oxycarbide glasses. In this approach, alkyl-substituted silicon alkoxides, which are molecular precursors containing oxygen and carbon functionalities on the silicon, can be hydrolyzed and condensed without decomposition or loss of the carbon functional group. A low-temperature (<1000°C) heat-treatment of the gel creates a glassy silicate material whose molecular structure consists of an oxygen/carbon anionic network. In addition, there is always a blackening of the material due to elemental carbon, which forms during pyrolysis and densification of the gel. The nature of the network carbon, and especially the distribution and form of the elemental carbon, are fundamental to the structure and properties of these novel materials. Their chemical and physical characteristics as revealed by NMR, Raman and TEM are discussed in the overview. In addition, the high temperature stability of these glasses (up to 1750°C), and the effect of hot-pressing, are described. It will be shown that the silicon oxycarbide network is stable up to 1000–1200°C. The network carbon is terminated with hydrogen (i.e., CH, =CH2 and –CH3), and with polyaromatic carbon (i.e., nC6Hx) wherein most of the elemental carbon resides. These glasses can be described as molecular composites of polyaromatic graphene-rings dispersed in a silicon oxycarbide network. After heating to temperatures in excess of 1000–1200°C, the oxycarbide network decomposes through the loss of hydrogen, and a two- or three-phase glass-ceramic consisting of nanocrystalline graphite, silicon carbide, and amorphous silica or cristobalite, is created. Some of the properties and applications of these glasses/glass-ceramics for coatings, composites and porous solids are summarized.

Ceramic Fibers for Matrix Composites in High-Temperature Engine Applications

Abstract: High-temperature engine applications have been limited by the performance of metal alloys and carbide fiber composites at elevated temperatures. Random inorganic networks composed of silicon, boron, nitrogen, and carbon represent a novel class of ceramics with outstanding durability at elevated temperatures. SiBN(3)C was synthesized by pyrolysis of a preceramic N-methylpolyborosilazane made from the single-source precursor Cl(3)Si-NH-BCl(2). The polymer can be processed to a green fiber by melt-spinning, which then undergoes an intermediate curing step and successive pyrolysis. The ceramic fibers, which are presently produced on a semitechnical scale, combine several desired properties relevant for an application in fiber-reinforced ceramic composites: thermal stability, mechanical strength, high-temperature creep resistivity, low density, and stability against oxidation or molten silicon.

Interaction of Plastics in Mixed-Plastics Pyrolysis

Abstract: The pyrolysis of mixed-plastic waste has been proposed as a means of recycling to produce petrochemical feedstock. The interaction of the main plastic types in plastic mixtures is significant in predicting the likely yield and composition of products from different plastic mixtures. The six main plastics in municipal solid waste are high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), and poly(ethylene terephthalate) (PET). Each of the plastics was pyrolyzed individually in a fixed-bed reactor heated at 25 °C min-1 to a final temperature of 700 °C. Polystyrene was then mixed with each of the other five plastics in a ratio of 1:1 and pyrolyzed in the fixed-bed reactor under the same pyrolysis conditions. The yield and composition of the derived oil/wax and gases was determined. The main gases produced from the individual plastics were hydrogen, methane, ethane, ethene, propane, propene, butane, and butene and for the PET plasti...

Hydrogen from Biomass: Steam Reforming of Model Compounds of Fast-Pyrolysis Oil

Abstract: We investigated the production of hydrogen by the catalytic steam reforming of model compounds of biomass fast-pyrolysis oil (bio-oil). Acetic acid, m-cresol, dibenzyl ether, glucose, xylose, and sucrose were reformed using two commercial nickel-based catalysts for steam reforming naphtha. The experiments were conducted at a methane-equivalent gas hourly space velocity (GC1HSV) from 500 to 11790 h-1. Steam-to-carbon ratios (S/C) of 3 and 6 and catalyst temperatures from 550 to 810 °C were selected. Rapid coking of the catalyst was observed during acetic acid reforming at temperatures lower than 650 °C. Acetic acid, m-cresol, and dibenzyl ether were completely converted to hydrogen and carbon oxides above this temperature, and hydrogen yields ranged from 70 to 90% of the stoichiometric potential, depending on the feedstock and reforming conditions. Sugars were difficult to reform because they readily decomposed through pyrolysis in the freeboard of the reactor. This led to the formation of char and gases b...

Effects of Heating Rate and Ion-Exchangeable Cations on the Pyrolysis Yields from a Victorian Brown Coal

Abstract: A Victorian low-rank coal (Loy Yang) was acid-washed and ion-exchanged with Na and Ca to prepare the H-form, Na-form, and Ca-form coal samples. Two more H-form samples were also prepared by rewashing the Na-form and Ca-form samples with acid. These coal samples were pyrolyzed in a wire-mesh reactor where the secondary reactions of the evolved volatiles were minimized. The ion-exchanged coal samples were found to give very different tar yields from those of the raw coal samples. While the tar yields from the pyrolysis of the raw and H-form coal samples were observed to be very sensitive to changes in heating rate, the tar yields from the Ca-form and Na-form samples showed little heating rate sensitivity. Unlike higher rank coals studied previously, the tar yields from the pyrolysis of the raw coal and the H-form coal samples at 600 °C were found to increase much more than the corresponding increases in the total volatile yields as the heating rate was increased from 1 to 2000 K s-1. Reexchanging Na in the ...

Control of the composition and structure of silicon oxycarbide and oxynitride glasses derived from polysiloxane precursors

Abstract: The reactions involved in the preparation of silicon oxycarbide and oxynitride glasses by pyrolysis of polysiloxane precursors respectively under argon and ammonia are reviewed The influence of the composition and structure of the precursor and of these pyrolysis reactions on the pyrolysis yield, the composition, and the structure of the glass is discussed The free-carbon content of the glass depends on the substituents in the precursor and on the nature of the pyrolysis atmosphere The composition of the oxynitride or the oxycarbide phase depends on the O/Si ratio of the precursor The structure of these phases is not directly related to the structure of the precursors, but rather depends on their composition and on the pyrolysis temperature

Molecular insight into soil carbon turnover

Abstract: Curie-point pyrolysis-gas chromatography coupled on-line to mass spectrometry (Py-GC/MS) and isotope ratio mass spectrometry (Py-GC/IRMS) were used to determine the individual turnover rate of specific carbohydrates, lignin, lipids and N-containing compounds from French arable soils. The analysed soils were cultivated, either continuously with a C3 plant (wheat delta(13)C-value = -25.2 per thousand), or transferred to a C4 plant (maize delta(13)C-value = -11.4 per thousand) cropping 23 years ago. Most pyrolysis products identified were related to carbohydrates (furans), lipids (hydrocarbons and derivatives of benzene), proteins (nitriles and pyrrole) and lignins (phenols). The relative yield of all individual pyrolysis products was similar in the samples from the maize and control wheat soil. The isotopic enrichment between identical pyrolysis products from the two soils varied from 1 to 12 delta (delta) units, indicating that after 23 years of cultivation 7 to 90% of their C was derived from maize. This suggests a slow mean turnover time varying from 9 to 220 years. Based on the differences in isotopic enrichment of chemical structures after vegetation change the pyrolysis products could be divided into three groups: (i) pyrolysis products with a nearly complete C4 signal, e. g. phenol, derived from lignin degradation products, (ii) pyrolysis products with an intermediate isotopic enrichment of 6-8 per thousand, most likely to be a composite of remaining (possibly physically protected) fragments derived from both maize and native wheat, and (iii) pyrolysis products showing only low enrichments in (13)C of 1-3 per thousand. Most of their precursors were found to be proteinaceaous materials. This indicates that proteins or peptides are indeed preserved during decomposition and humification processes occurring in the soil. Our study highlights the potential of Py-GC/MS-C-IRMS to further novel insights into the dynamics of soil organic constituents. Copyright 1999 John Wiley & Sons, Ltd.

Sonolysis of tert-butyl alcohol in aqueous solution

Abstract: A product study of the sonolysis of the volatile substrate t-butanol in aqueous solution indicates that substrate decomposition is practically completely determined, even at concentrations as low as millimolar, by oxidative pyrolysis going on in the gas phase within the collapsing cavitational bubble. OH-Radical-induced reactions in solution are insignificant since the volatility of this substrate, its gas-phase concentration within the bubble enhanced by a certain degree of hydrophobicity, causes OH radicals generated thermolytically from water vapour to be intercepted before they can reach the aqueous phase. The nature of the products, as well as the t-butanol-concentration dependence of the product yields, can be qualitatively explained on the basis of the t-butanol-pyrolysis mechanism. Kinetic considerations involving the relative yields of the pyrolysis products ethane, ethylene and acetylene lead to an estimate of a value of 3600 K for the average pyrolysis temperature at a t-butanol bulk concentration of 10–3 molar.