Showing papers on "Pyrolysis published in 1997"

Biomass to hydrogen via fast pyrolysis and catalytic steam reforming of the pyrolysis oil or its fractions

Abstract: Pyrolysis of lignocellulosic biomass and reforming of the pyroligneous oils are being studied as a strategy for producing hydrogen A process of this nature has the potential to be cost competitive with conventional means of producing hydrogen We propose a regionalized system of hydrogen production, where small- and medium-sized pyrolysis units (<500 Mg/day) provide bio-oil to a central reforming unit to be catalytically converted to H2 and CO2 Thermodynamic modeling of the major constituents of the bio-oil has shown that reforming is possible within a wide range of temperatures and steam-to-carbon ratios In addition, screening tests aimed at catalytic reforming of model compounds to hydrogen using Ni-based catalysts have achieved essentially complete conversion to H2 Existing data on the catalytic reforming of oxygenates have been studied to guide catalyst selection A process diagram for the pyrolysis and reforming operations is discussed, as are initial production cost estimates A window of opport

Additives To Lower and Stabilize the Viscosity of Pyrolysis Oils during Storage

Abstract: The initial development of additives to stabilize the viscosity of biocrude during long-term storage has produced dramatic results. The additives investigated were ethyl acetate, methyl isobutyl ketone and methanol, acetone, methanol, acetone and methanol, and ethanol. These additives represent three chemical families, which all demonstrated the ability to drastically reduce the aging rate of biocrude, as defined by the increase in viscosity with time. Accelerated aging tests were run at 90 °C to screen the additives. The additives not only lowered the initial viscosity at 40 °C by half but also reduced the aging rate of a hot gas filtered pyrolysis oil made from hybrid poplar (NREL run 175) by factors of 1−18 compared to the original pure oil. With the best additive, methanol, at a 10 wt % level in the pyrolysis oil, the modified biocrude was still a single-phase liquid and still met the ASTM No. 4 diesel fuel specification for viscosity even after 96 h exposure to 90 °C. Based on the aging rate at 90 °C...

A Generalized Biomass Pyrolysis Model Based on Superimposed Cellulose, Hemicelluloseand Liqnin Kinetics

Abstract: The pyrolysis of general biomass materials is modeled via a superposition of cellulose, hemi-cellulose and lignin kinetics. All three of the primary biomass components are modeled with multi-step kinetics involving both competetive primary pyrolysis and secondary tar decomposition reactions. Only “typical” (untreated) feedstocks are considered at atmospheric pyrolysis pressures. The kinetics scheme is then coupled to the porous particle model of Miller and Bellan (1996) along with appropriate properties and heats of reaction to provide a complete model for the pyrolysis of arbitrary biomass feedstocks and sample sizes. Comparisons with past isothermal and thermogravimetry experiments for a variety of biomass materials under both kinetically controlled and diffusion limited conditions show favorable agreement with the model predictions. In addition, discussions are provided which support the use of competetive char production kinetics over single and successive reaction schems which cannot currently be reconciled with observed pyrolysis behavior.

Emissions from smoldering combustion of biomass measured by open-path Fourier transform infrared spectroscopy

Abstract: Biomass samples from a diverse range of ecosystems were burned in the Intermountain Fire Sciences Laboratory open combustion facility. Midinfrared spectra of the nascent emissions were acquired at several heights above the fires with a Fourier transform infrared spectrometer (FTIR) coupled to an open multipass cell. In this report, the results from smoldering combustion during 24 fires are presented including production of carbon dioxide, carbon monoxide, methane, ethene, ethyne, propene, formaldehyde, 2-hydroxyethanal, methanol, phenol, acetic acid, formic acid, ammonia, hydrogen cyanide, and carbonyl sulfide. These were the dominant products observed, and many have significant influence on atmospheric chemistry at the local, regional, and global scale. Included in these results are the first optical, in situ measurements of smoke composition from fires in grasses, hardwoods, and organic soils. About one half of the detected organic emissions arose from fuel pyrolysis which produces white smoke rich in oxygenated organic compounds. These compounds deserve more attention in the assessment of fire impacts on the atmosphere. The compound 2-hydroxyethanal is a significant component of the smoke, and it is reported here for the first time as a product of fires. Most of the observed alkane and ammonia production accompanied visible glowing combustion. NH3 is normally the major nitrogen-containing emission detected from smoldering combustion of biomass, but from some smoldering organic soils, HCN was dominant. Tar condensed on cool surfaces below the fires accounting for ∼1% of the biomass burned, but it was enriched in N by a factor of 6–7 over the parent material, and its possible role in postfire nutrient cycling should be further investigated.

Gas Permeation through Micropores of Carbon Molecular Sieve Membranes Derived from Kapton Polyimide

Abstract: The evolution of micropores and the gas permeation properties have been investigated on carbon molecular sieve dense membranes prepared by pyrolysis of Kapton polyimide films under several conditions. With decreasing the pore sizes upon pyrolization under vacuum, the gas permeability decreased, whereas the permselectivity increased. The change in the heating rate was found to affect the permeation properties to a lesser extent; however, the pyrolysis atmosphere (vacuum or inert purge pyrolysis) did not appreciably influence the properties within the experimental conditions studied. The highest permselectivities attained by a membrane were H2/N2 4700, He/N2 2800, CO2/N2 122, and O2/N2 36, respectively, at 308 K. The permeabilities of the selected gases were shown to be in the order H2 > He > CO2 > O2 > N2 for almost all the membranes, whose order was not exactly in accordance with the order of kinetic gas diameters. From the temperature dependencies of permeability, diffusivity, and sorptivity of the membr...

Kinetics of the low-temperature pyrolysis of polyethene, polypropene and polystyrene modeling, experimental determination and comparison with literature models and data

Abstract: The pyrolysis kinetics of low-density polyethylene, high-density polyethylene, polypropylene, and polystyrene has been studied at temperatures below 450 C. In addition, a literature review on the low-temperature pyrolysis of these polymers has been conducted and has revealed that the scatter in the reported kinetic data is significant, which is most probably due to the use of simple first-order kinetic models to interpret the experimental data. This model type is only applicable in a small conversion range, but was used by many authors over a much wider conversion range. In this investigation the pyrolysis kinetics of the forementioned polymers and a mixture of polymers has been studied at temperatures below 450 C by performing isothermal thermogravimetric analysis (TGA) experiments. The TGA experimental data was used to determine the kinetic parameters on the basis of a simple first-order model for high conversions (70-90%) and a model developed in the present study, termed the random chain dissociation (RCD) model, for the entire conversion range. The influence of important parameters, such as molecular weight, extent of branching and -scission on the pyrolysis kinetics was studied with the RCD model. This model was also used to calculate the primary product spectrum of the pyrolysis process. The effect of the extent of branching and the initial molecular weight on the pyrolysis process was also studied experimentally. The effect of the extent of branching was found to be quite significant, but the effect of the initial molecular weight was minor. These results were found to agree quite well with the predictions obtained from the RCD model. Finally, the behavior of mixtures of the aforementioned polymers was studied and it was found that the pyrolysis kinetics of the polymers in the mixture remains unaltered in comparison with the pyrolysis kinetics of the pure polymers.

Alkali Metal Emission during Pyrolysis of Biomass

Abstract: The alkali metal release during pyrolysis of biomass is investigated with a surface ionization method. Wheat straw samples (20 mg) are pyrolyzed in a laboratory unit under N2 atmosphere, and two characteristic temperature intervals for alkali metal emission are identified. A small fraction of the alkali metal content is released in a low-temperature region (180−500 °C) and is attributed to a connection with the decomposition of the organic structure. The two most pronounced emission processes below 500 °C are well described by a first-order rate behavior, and the activation energies are found to be 156 ± 11 and 178 ± 8 kJ/mol. The major part of the alkali metal release takes place in the high-temperature region (>500 °C), and activation energies of alkali metal emission from the ash residues are found in the range 168−238 kJ/mol. A high chlorine content is found to enhance the alkali metal emission from the ash, while the alkali metal release in the low-temperature region cannot be correlated with the chl...

Study of Irreversible Capacities for Li Insertion in Hard and Graphitic Carbons

Abstract: The irreversible capacity of carbon electrodes for lithium is a critical parameter which must be minimized in practical Li ion cells. This paper reports studies of the origin of the irreversible capacity in high-capacity carbons derived from sugar, and for comparison, in graphitic carbons made from mesocarbon microbeads. Tablet electrodes (∼0.4 mm thick) of sugar carbon or of mesocarbon microbeads (mixed with 10% pitch) were prepared by pyrolysis of the precursors at 1050°C under a vacuum of about 10 mTorr. Tablets exposed to different gases were used in carbon/Li coin cells, in order to study the effect of different gas exposures on irreversible capacities, C irr , for Li insertion. Carbon electrodes exposed only to argon or nitrogen demonstrated a dramatic reduction in irreversible capacity: C irr 50 and 10 mAh/g for sugar carbon and mesocarbon microbead tablet cells, respectively, compared to C irr 180 and 30 mAh/g for the corresponding conventional doctor-blade spread electrode cells where the electrodes had been exposed to laboratory air for several days. Tablet electrodes were also exposed to CO 2 , O 2 , water, steam, and air, respectively, for different periods of time. Tablets exposed to each of these reactive gases showed a dramatic increase in irreversible capacity. The irreversible capacity for hard carbons results from two sources: (i) electrolyte decomposition on nominally clean carbon surfaces and (ii) reactions with surface groups which form on carbons exposed to reactive gases. The amount of irreversible capacity from the latter source depends on the gas exposure time and involves reactions with species such as hydroxyl, carboxyl functional groups, or adsorbed water

Release of Chlorine from Biomass at Pyrolysis and Gasification Conditions1

Abstract: The working hypothesis for the study was that the main part of the chlorine in biomass is in an inorganic form and therefore should not vaporize appreciably below the melting point of the corresponding salt (around 700 °C) because the vapor pressure over solid salt is negligible. In the study, biomass fuels (sugarcane trash, switch grass, lucerne, straw rape) were subjected to pyrolysis in a flow of nitrogen, and the weight of the residue and its chlorine content were measured and compared to the original fuel. Contrary to the hypothesis, the results showed that during pyrolysis of biomass 20−50% of the total chlorine evaporated already at 400 °C, although the majority of the chlorine was water soluble (in grass 93%) and therefore most probably ionic species. At 900 °C, 30−60% of the chlorine was still left in the char. At 200 °C less than 10% of chlorine had evaporated from the fuel, indicating that the chlorine is not associated with water. Another result was that there was no significant difference in ...

Corannulene. A Three-Step Synthesis1

Abstract: Thermal cyclization of 7,10-diethynylfluoranthene (3) in the gas phase gives corannulene (2), the smallest bowl-shaped polycyclic hydrocarbon fragment of C60 with fullerene-like curvature. Bromocorannulene (10) and 1,6-dibromocorannulene (9) have also been obtained from flash pyrolysis of 7,10-bis(2,2-dibromovinyl)fluoranthene (8). Short, practical syntheses of several corannulene precursors from acenaphthenequinone are described which have made corannulene available in gram quantities.

Nitrogen-containing carbon nanotubes

Abstract: Carbon nanotubes containing small amounts of nitrogen are produced by the pyrolysis of aza-aromatics such as pyridine, methylpyrimidine and triazine over cobalt nanoparticles in an Ar atmosphere; good yields of such nanotubes are obtained by carrying out the pyrolysis of a mixture of pyridine and Fe(CO)(5) in flowing Ar + H-2.

Physical characterisation of biomass-based pyrolysis liquids: Application of standard fuel oil analyses

Abstract: The main purpose of the study was to test the applicability of standard fuel oil methods developed for petroleum-based fuels to pyrolysis liquids. In addition, research on sampling, homogeneity, stability, miscibility and corrosivity was carried out. The standard methods have been tested for several different pyrolysis liquids. Recommendations on sampling, sample size and small modifications of standard methods are presented. In general, most of the methods can be used as such but the accuracy of the analysis can be improved by minor modifications. Fuel oil analyses not suitable for pyrolysis liquids have been identified. Homogeneity of the liquids is the most critical factor in accurate analysis. The presence of air bubbles may disturb in several analyses. Sample preheating and prefiltration should be avoided when possible. The former may cause changes in the composition and structure of the pyrolysis liquid. The latter may remove part of organic material with particles. The size of the sample should be determined on the basis of the homogeneity and the water content of the liquid. The basic analyses of the Technical Research Centre of Finland (VTT) include water, pH, solids, ash, Conradson carbon residue, heating value, CHN, density, viscosity, pourpoint, flash point, and stability. Additional analyses are carried out when needed. (orig.) 53 refs.

The pyrolysis of individual plastics and a plastic mixture in a fixed bed reactor

Abstract: Six thermoplastics, which represent more than two-thirds of all polymer production in western Europe, were pyrolysed in a static batch reactor in a nitrogen atmosphere. These were high density polyethylene (HDPE), low density polyethylene (LDPE), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET) and polyvinyl chloride (PVC). The heating rate used was 25°C/min to a final temperature of 700°C. These six plastics were then mixed together to simulate the plastic fraction of municipal solid waste found in Europe. The effect of mixing on the product yield and composition was examined. The results showed that the polymers studied did not react independently, but some interaction between samples was observed. The product yield for the mixture of plastics at 700°C was 9.63% gas, 75.11% oil, 2.87% char and 2.31% HCl. The gases identified were H 2 , CH 4 , C 2 H 4 , C 2 H 6 , C 3 H 6 , C 3 H 8 , C 4 H 8 , C 4 H 10 , CO 2 and CO. The composition of oils were determined using Fourier Transform infrared spectrometry and size exclusion chromatography. Analysis showed the presence mainly of aliphatic compounds with small amounts of aromatic compounds.

Pyrolyzed Polysiloxanes for Use as Anode Materials in Lithium‐Ion Batteries

Abstract: More than sixty siloxane polymers containing various organofunctional siloxane units were synthesized. The synthesized siloxane polymers were pyrolyzed in inert gas at 1000°C. Chemical analysis showed that the products of pyrolysis were distributed over a well-defined region in the Si-C-O Gibbs phase diagram. The electrochemical and structural properties of these materials were measured using coin-type test cells and x-ray powder diffraction, respectively. The most interesting materials are found near the line in the Si-C-O Gibbs triangle connecting carbon to SiO 1.3 . Materials with the largest reversible specific capacity for lithium (about 900 mAh/g) are on this line and were at about 43% carbon, 32% oxygen, and 25% silicon (atomic percent). Materials which were almost pure carbon showed diffraction patterns characteristic of disordered carbons. Along the line from carbon to SiO 1.3 the sample structure can be described as a mixture of single or small groups of graphene sheets mixed with regions of Si-C-O amorphous glass. The amount and composition of the glass changed according to the overall sample composition. Moving from carbon to SiO 1.3 , the reversible capacity first rises from about 340 mAh/g for pure carbon, to a maximum of 900 mAh/g near 50% carbon, and then falls to near zero mAh/g at 0% carbon. This suggests that the amorphous glass can reversibly react with lithium, provided the carbon is present to provide a path for electrons and Li ions. However, the hysteresis in the voltage profile (difference between charge and discharge voltages) and the irreversible capacity increase almost linearly along this line. There is a clear correlation between both the irreversible capacity and hysteresis in these materials with their oxygen content. Along the line connecting carbon to silicon, the reversible capacity rises from 340 mAh/g for pure carbon to about 600 mAh/g for samples with about 15 atomic percent Si. It then decreases to near zero as the composition nears SiC. Along the C-SiC line, the irreversible capacities remain below about 200 mAh/g. We are quite convinced that optimized silicon-containing carbons can be good alternatives to pure carbons as anode materials in lithium-ion batteries

Thermal stability of a PCS-derived SiC fibre with a low oxygen content (Hi-Nicalon)

Abstract: The oxygen free Si–C fibre (Hi-Nicalon) consists of β-SiC nanocrystals (≈5nm) and stacked carbon layers of 2–3nm in extension, in the form of carbon network along the fibre. This microstructure gives rise to a high density, tensile strength, stiffness and electrical conductivity. With respect to a Si–C–O fibre (Nicalon NL202), the Si–C fibres have a much greater thermal stability owing to the absence of the unstable SiOxCy phase. Despite its high chemical stability, it is nevertheless subject to a slight structural evolution at high temperatures of both SiC and free carbon phases, beginning at pyrolysis temperatures in the range 1200–1400°C and improving with increasing pyrolysis temperature and annealing time. A moderate superficial decomposition is also observed beyond 1400°C, in the form of a carbon enriched layer whose thickness increases as the pyrolysis temperature and annealing time are raised. The strength reduction at ambient for pyrolysis temperatures below 1600°C could be caused by SiC coarsening or superficial degradation. Si–C fibres have a good oxidation resistance up to 1400°C, due to the formation of a protective silica layer.

Investigation of the Catalytic Pyrolysis of High-Density Polyethylene over a HZSM-5 Catalyst in a Laboratory Fluidized-Bed Reactor

Abstract: High-density polyethylene (HDPE) was pyrolyzed over HZSM-5 catalyst using a specially developed laboratory fluidized-bed reactor operating isothermally at ambient pressure. The influence of reaction conditions including temperature, ratios of HDPE to catalyst feed, and flow rates of fluidizing gas was examined. The sodium form of siliceous ZSM-5, silicalite, containing very few or no catalytically active sites, gave very low conversions of polymer to volatile hydrocarbons compared with HZSM-5 (Si/Al = 17.5) under the same reaction conditions. Experiments carried out with HZSM-5 gave good yields of volatile hydrocarbons with differing selectivities in the final products dependent on reaction conditions. Catalytic pyrolysis of HDPE performed in the fluidized-bed reactor was shown to produce valuable hydrocarbons in the range of C3−C5 carbon number with a high olefinic content. The production of olefins with potential value as a chemical feedstock is potentially attractive and may offer greater profitability...

Pyrolysis Kinetics of Acid-Leached Rice Husk

Abstract: A highly pure mixture of carbon and silica was obtained on pyrolysis rice husk leached with acid at high temperature in a nonoxidizing atmosphere. The product was suitable for use as a starting material in the the manufacture of silicon nitride powder. The effect of treatment including the kind and concentration of acid and the pyrolysis temperature on the constituents of the specimen was presented. Kinetic tests on pyrolysis of rice husk in a nitrogen atmosphere were carried out with a thermal gravimetric analysis (TGA) technique at heating rates 2, 3, and 5 K/min. The results indicated that thermal degradation of rice husk consisted of two distinct pyrolysis stages. The corresponding kinetic parameters including the activation energy were determined. A reasonable pyrolysis mechanism was proposed, which agreed satisfactorily with the experimental results.

Carbon aerogels from dilute catalysis of resorcinol with formaldehyde

Abstract: Aqueous polycondensation of resorcinol with formaldehyde leads to organic gels the structure of which can be controlled by the reaction parameters. The amount of catalyst controls the size of the particles constituting the gel network. We could show that for very low catalyst concentrations in a high dilution of reactants, the particle growth can be further enhanced if the reaction temperature is kept low, and the gel time is prolonged. The resultant structure is largely affected by this treatment, producing particles with sizes of about 2 μm and average pore sizes of up to 7 μm. Due to these coarse structures it is possible to dry these RF gels subcritically with very little shrinkage. The structure has been studied by nitrogen sorption, small angle X-ray scattering and acoustic sound propagation. The change of the elastic modulus caused by pyrolysis at around 1000°C has been investigated. Mechanical properties of carbon aerogels are correlated with their electrical properties. The derived carbon aerogels have large specific surface areas, very little mesopore volume however, micron-sized macropores.