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.

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

Mallee wood fast pyrolysis: Effects of alkali and alkaline earth metallic species on the yield and composition of bio-oil

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 ...

Release of Chlorine from Biomass at Pyrolysis and Gasification Conditions1

Cellulosic biomass can be directly converted to hydrocarbon transportation fuels through the use of hydropyrolysis or integrated hydropyrolysis plus hydroconversion (IH2). Hydropyrolysis performed in a fast fluidized bed under 14–35 bar of hydrogen pressure with an effective deoxygenation catalyst directly produces a fungible hydrocarbon product with less than 1 total acid number which can either be directly fed to a refinery or polished in an integrated hydroconversion reactor to produce gasoline and diesel with less than 1% oxygen. Experimental data from a 0.45 kg/h semi-continuous IH2 pilot plant is presented. Economics and life cycle analysis data will be presented later in this series, and will show that by employing IH2 technology, biomass can be converted to gasoline and diesel fuels at delivered costs of less and in some cases significantly less than $1.80/gallon with greater than 90% reduction in greenhouse gas emissions. Larger (2.08 kg/h) long-term continuous pilot-scale testing of the IH2 process will commence in the near future. As a biomass-to-fuels conversion technology, IH2 has the potential to substantially reduce US dependence on foreign oil, thereby reducing the price of transportation fuels and significantly lowering worldwide greenhouse gas emissions. © American Institute of Chemical Engineers Environ Prog, 2011

Integrated hydropyrolysis and hydroconversion (IH2) for the direct production of gasoline and diesel fuels or blending components from biomass, part 1: Proof of principle testing

Biological markers in fossil fuel production

Identification of large molecular mass material in high temperature coal tars and pitches by laser desorption mass spectroscopy

Coal tar analysis by mass spectrometry — a comparison of methods

Identification of straight-chain fatty acids in coal extracts and their geochemical relation with straight-chain alkanes

Low intensity hydropyrolysis of biomass has been investigated as a likely process route for upgrading agricultural and municipal waste, aiming to produce less highly oxygenated bio-oils with more stable storage characteristics than atmospheric pressure pyrolysis oils. A high-pressure wire-mesh pyrolysis reactor, recently re-designed to allow continuous sweeping of volatile products away from the reaction zone, was used during these experiments. This reactor configuration allows the determination of bio-oil yields and the recovery of condensible products for analytical characterisation in the relative absence of extra-particle secondary reactions. Samples of Swedish pine-wood and pine-wood lignin have been pyrolysed at temperatures between 300–700°C, at hydrogen pressures up to 70 bar. Product bio-oils have been characterised by size exclusion chromatography (SEC), UV-fluorescence spectroscopy (UV-F) and gas chromatography-mass spectrometry (GC-MS). Bio-oil yields from both pine-wood and lignin decreased by relatively small amounts over the pressure range, but significant changes in liquid product structures were observed: product bio-oils with progressively smaller molecular masses and lower polarity have been obtained with increasing pressure. Nevertheless, product bio-oils were characterised by a preponderance of oxygenates, including syringol and guaiacol derivatives and carboxylic acids, rather than alcohols, ketones, terpenoid and polynuclear aromatic hydrocarbons. Considerable differences have been observed between hydropyrolysis yields from pinewood and lignin: bio-oil and total volatile yields from the parent wood were greater than those observed for the lignin sample by about 30%. Comparison by GC-MS and UV-F suggests that the lignin derived bio-oils contain considerably more aromatic and less polar structures than the wood derived oils. At 70 bars, traces of di- and tri-bromodibenzodioxins have been detected in pinewood bio-oils from experiments at 400 and 700°C, apparently liberated from the wood during hydropyrolysis; it is presumed that the precursor fungicide molecules had previously been incorporated into the wood structure.

Effect of H2-pressure on the structures of bio-oils from the mild hydropyrolysis of biomass

Conventionally, coal-derived tars are separated by solvent fractionation into pentane solubles, asphaltenes (pentane insoluble, benzene soluble) and preasphaltenes (benzene insoluble) with further separation of the pentane solubles into saturated, aromatic and polar fractions by open-column chromatography on silica.Normal-phase HPLC, using hexane with a gradient to dichloromethane-methanol (95 + 5) coupled to a mass spectrometer by a moving-belt interface, has indicated that the so-called aromatic fraction of a low-temperature hydropyrolysis coal tar contains some saturates (alkanes and cycloalkanes including hopanes, up to C64) and an appreciable amount of polar materials which may represent 50% of the aromatic fraction, in addition to aromatics from alkylbenzenes to alkylrubicenes as extensive homologous series.Mass spectrometry with electron impact and chemical ionisation using ammonia and isobutane has given new structural information on the polar materials present in this “aromatic” fraction. Fast atom bombardment of asphaltenes and benzene-insolubles indicated that their structures resemble those of the polar compounds and differ from those of the aromatics. Size-exclusion chromatography confirmed the relative molecular mass ranges detected by mass spectrometry, GC-MS with a capillary column proved inadequate for defining many of the aromatics. The relevance of the work to the structure of coal is considered.

Brian J. Stokes

Papers

Identification of large molecular mass material in high temperature coal tars and pitches by laser desorption mass spectroscopy

Coal tar analysis by mass spectrometry — a comparison of methods

Identification of straight-chain fatty acids in coal extracts and their geochemical relation with straight-chain alkanes

Effect of H2-pressure on the structures of bio-oils from the mild hydropyrolysis of biomass

Liquid chromatographic-mass spectrometric analysis of coal tar fractions