A. A. Herod

A two-stage fixed-bed reactor for direct hydrotreatment of volatiles from the hydropyrolysis of biomass: effect of catalyst temperature, pressure and catalyst ageing time on product characteristics

This investigation involved the hydropyrolysis of biomass (eucalyptus globulus) and the immediate catalytic hydrocracking of pyrolytic oils in the second stage of the reactor. The effects of temperature, pressure and the catalyst ageing time on the final product tar have been studied using the catalyst Zeolite H-ZSM5. The catalytically hydrocracked tar/oil products were characterised and compared with the hydropyrolysis product from the first stage of the reactor to determine the effect of catalytic hydrocracking. The carbon deposition on the catalyst has been examined using thermogravimetric analysis. The tar yields after catalytic hydrocracking decreased with increasing pressure and temperature of the cracking stage. The tar yields at 10 bar pressure were greater than those at 40 bar pressure. The fresh zeolite catalyst trapped more than 40% of the product from the hydropyrolysis stage and TGA evidence indicated that this was not as carbon deposition but as volatiles trapped in the zeolite matrix. Reuse of the catalyst resulted in little more uptake of volatiles; however, extended use of the catalyst did not result in increased yields of liquid products but in increased production of light volatiles or gas. The H-ZSM5 catalyst appeared to act as a more active cracking catalyst rather than to promote hydrogenation or deoxygenation of the liquids produced in the hydropyrolysis stage. Characterisation of the liquids by SEC and UV fluoresence indicated that structural changes were relatively minor despite the significant changes in yields of liquids with process conditions. Available reaction routes do not appear to allow specific deoxygenation pathways to predominate without disintegration of parent molecules to lighter volatiles, under the conditions used here.

Determination of 17 trace elements in coal and ash reference materials by ICP-MS applied to milligram sample sizes

This paper describes the evaluation of two digestion methods used to extract 17 elements (Be, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Mo, Cd, Sn, Sb, Ba and Pb) from coal and coal ash, obtained as standard reference materials. An acid digestion method in open vessels using sulfuric, hydrofluoric, perchloric and nitric acid was compared with a sealed microwave digestion method using nitric acid only. The microwave method cannot break down silicates, which harbour many trace elements, but can extract As and Se quantitatively. Volatile elements such as As and Se might be lost during the open vessel digestion; therefore, the closed vessel is the method of choice. The effect of reducing the sample size from several hundred milligrams to amounts as small as 5 mg on the accuracy of determinations was investigated. No significant differences were observed so long as the total dissolved solids and the dilution factors of the final solutions remained constant.

Chromatographic separations enabling the structural characterisation of heavy petroleum residues

Abstract Two petroleum residues from European crudes have been fractionated using solvent (heptane) separation and column chromatography. The residues and the separated fractions have been characterised by size exclusion chromatography (SEC) and by UV-fluorescence spectroscopy (UV-F). Matrix assisted laser desorption/ionisation-mass spectrometry of the whole residues and the heptane insoluble fractions indicated that the bulk of the residues covered the mass range m / z 300–2000, while the heptane insolubles (1–2% of the whole) contained material in the mass range from about m / z 300 to 10 000. The upper mass ranges indicated by SEC using polystyrene standards were higher; the earliest eluting material from both distillation residues eluted at times corresponding to polystyrene standards of MMs above 1.85 million u. Possible reasons for the different observations are given. Data from UV-F suggests that the heptane solubility separation method was the most successful for the separation of the largest molecular mass and also probably the most polar materials in these residues. However, all three fractionation methods produced similar trends, showing greater polarity of the fractions to correlate with increasing molecular mass. The shift of maximum intensity of fluorescence towards longer wavelengths (in UV-fluorescence) with increasing molecular size, as indicated by SEC, strongly suggests that the fluorescing molecules are large rather than aggregates of small molecules. Differences in comparison with American petroleum residues can be observed.

Matrix-assisted Laser Desorption/Ionization Mass Spectrometry of Pitch Fractions Separated by Planar Chromatography

Molecular mass distributions of coal-tar pitch fractions separated by planar chromatography (P-C) have been compared by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, carried out in the absence of added matrix. Solvent pairs used in the P-C separation were pyridine-acetonitrile, pyridine-N,ZVdimethylformamide and tetrahydrofuran-toluene. Molecular complexity and average molecular masses were found to increase with decreasing mobilities of the fractions. UV-fluorescence spectroscopy showed shifts of peak intensities to longer wavelengths and decreasing quantum yields, suggesting the presence of progressively greater concentrations of large polynuclear aromatic systems with decreasing mobility of samples in P-C. Fractions immobile in pyridine gave MALDI mass spectra of low intensity, indicating that larger molecules are less easily desorbed or ionized. The observed similarity of upper-mass limits of planar-chromatographic fractions of different mobility is thought to suggest the presence of relatively large-molecular mass (MM) materials of variable polarity in coal-tar pitch. The results were consistent with earlier investigations showing the presence of high molecular mass materials in coal-derived liquids. MM-distributions determined by size exclusion chromatography (SEC) were also observed to increase with decreusing mobility of the fractions on P-C plates. This qualitative agreement with results from MALDI-MS indicates that reported shifts of polar molecules to shorter elution times in SEC (i.e. to apparently larger-MMs) were not of a sufficient magnitude to distort the relative ordering of MM-distributions of PC-fractions observed by SEC. A number of problems relating to the refinement of MALDI-MS determinations on complex mixtures are discussed.

Planar chromatographic separation of petroleum residues and coal-derived liquids

Abstract Vacuum distillation residues from two petroleum crudes, a coal liquefaction extract and a coal tar pitch have been fractionated by planar chromatography (PC) using two solvent sequences: pyridine–acetonitrile and tetrahydrofuran (THF)–toluene. Fractions recovered from PC were examined by UV-fluorescence spectroscopy (UV-F), size-exclusion chromatography (SEC). UV-F and SEC of the whole samples showed differences in aromatic cluster size and molecular mass (MM) ranges which could be related to the different origins of the samples. The MM ranges indicated by SEC were greater for the vacuum residues than for coal-derived materials. However, the UV-F spectra of the fractions indicated that the petroleum residue fractions contained similar aromatic types, whereas the fractions from coal liquids contained significantly different aromatic types. SEC profiles of the fractions indicated a separation of coal-derived samples by increasing molecular size with increasing immobility in PC, whereas for petroleum fractions, the same trend was not apparent. MALDI-mass spectra of the set of original samples showed broadly similar ranges of MM distributions but additional work is necessary to identify appropriate matrices and procedures in order to improve the MALDI spectra.

Fractionation of a wood tar pitch by planar chromatography for the characterisation of large molecular mass materials

Abstract A commercial tar pitch derived from pine wood – Massen Pine ( Pinus Massonia ) and sold as Stockholm tar has been fractionated by planar chromatography with examination of the fractions by size exclusion chromatography in NMP eluent, by UV-fluorescence and by matrix assisted laser desorption mass spectrometry. The relatively small molecules, mobile in planar chromatography, are shown to be non-polar. Large molecules were found in each fraction, corresponding in SEC elution times up to polystyrenes of molecular mass of at least 1.8 million. Size exclusion chromatography profiles by UV light absorbance showed differences in relative absorbance of different wavelengths for large and small molecules, implying differences in structures. MALDI mass spectra indicated molecules of mass of several thousand mass units with the upper limit of mass not defined. Planar chromatography provides a fast, cheap method of isolating large molecular mass fractions of this biomass tar.

Changes in sample reactivity and catalyst deactivation during early stages of the hydrocracking of a coal extract

Abstract Changes in sample reactivity and catalyst deactivation during the early stages of the hydrocracking of coal liquefaction extracts, using presulphided supported NiMo/Al 2 O 3 and a dispersed Mo catalyst, have been investigated. The characterisation of the liquefaction extract and the hydrocracking products has been made using size exclusion chromatography (SEC), UV-fluorescence spectroscopy (UV-F), matrix assisted laser desorption ionisation (MALDI-ms) and thermo-gravimetric analysis (TGA). A complex sequence of events has been resolved involving the simultaneous development of catalyst activity with parallel deactivation due to carbon deposition alongside thermal cracking of the extract. The balance of evidence suggests that the sharp reduction in the rate of reaction early in the hydrocracking process reported in earlier work is primarily caused by loss of sample reactivity.

Pyrolysis of Baltic amber in a wire-mesh pyrolysis reactor: structural comparison of the tars with amber extracts in NMP

Abstract A sample of Baltic amber believed to be about 40 million years old, has been pyrolysed in a wire-mesh reactor. Nearly all (99%) of the sample was found to volatilise; the condensable tar yield was about 82%. These tars and extracts in 1-methyl-2-pyrrolidinone (NMP), ∼20% of the original amber sample, have been characterised by size exclusion chromatography (SEC) and UV-fluorescence spectroscopy (UV-F). Size exclusion chromatograms of the soluble fraction of the amber gave relatively low intensity signal, indicating the lack of strongly absorbing chromophores. The profiles of the pyrolysis tar were more intense, suggesting that the pyrolytic process promoted aromatisation of the original structures. SEC of the amber extracts showed the presence of apparently large molecular mass material, possibly up to several million units. The SEC of the tar showed lower molecular mass material than that of the extract, with less absorbance at longer wavelengths, suggesting the presence of smaller polynuclear aromatic groups. Synchronous UV-fluorescence spectra suggest that the tar consisted mainly of fragmentation products of larger molecular mass material, deriving mostly from the insoluble, probably partly cross-linked part of the original sample.

Control of gasifier mercury emissions in a hot gas filter: the effect of temperature

Analyses of solid streams from a pilot-scale coal gasifier equipped with hot-gas filtration at 580°C have indicated that all coal-derived mercury was carried away by the fuel gas. Calculations using a thermodynamic equilibrium model have confirmed that there was little potential for removal of mercury in the hot gas filter at these temperatures. In this work, several experimental capture/recovery methods have been used in attempting to quantify the amount of mercury carried in the fuel gas. Standard ‘wet’ sampling methods have not worked well. A ‘dry’ mercury-capture method has been evaluated for determinations of mercury release from a pilot-scale gasifier equipped with a hot gas filter. At temperatures below 200°C, the fine dust on the hot gas filter was able to capture significant amounts of mercury. The findings from pilot-scale experiments have been examined by work in a specially designed bench-scale apparatus. Mercury removal was shown to be due to a reaction with the carbonaceous dust from the gasifier; the dust had substantial capacity for mercury capture at temperatures below 200°C. The effect of the dust in modifying the bulk thermodynamic properties of the hot gas filter system composition is attributed to chemisorption of HgS. The capacity of the dust for mercury capture was observed to be much greater in the laboratory-scale reactor than in the hot gas filter of the pilot plant. This observation is believed to be due to the main mechanism of dust collection by the filter being gravity separation directly to the hopper, rather than deposition as a filter cake.

Structural features of large molecular mass material in coal-derived liquids: catalytic hydrocracking of the pyridine-insoluble fraction of a coal-tar pitch

The pyridine-insoluble fraction of a coal-tar pitch has been catalytically hydrocracked. The starting sample contained no material that could be observed by gas chromatography/mass spectrometry (GC/MS) or by heated-probe mass spectrometry. The aim of the study was to generate structural information on this narrow cut of large-molecular-mass material, which consisted mainly of compounds boiling above 450°C. A much broader boiling-point distribution was found for hydrocracked products; evidence from all analytical techniques used (size-exclusion chromatography, UV-fluorescence spectroscopy and heated-probe mass spectrometry) indicated a significant reduction of the molecular mass range. A wide variety of aromatic groups was identified in hydrocracked products by heated-probe mass spectrometry, ranging from phenanthrene (m/z 178) to beyond dibenzocoronene (m/z 400). Ions corresponding to alkyl (m/z 43, 57, 71 and 85) and alkenyl groups (m/z 41, 55, 69 and 83) were detected. The results reflect the ability of the hydrocracking process to cleave bonds within large pitch molecules, releasing the structural units which form the molecules. The structure of the original pyridine-insoluble material may thus be seen as a series of aromatic groups linked by short bridges or small groups, but with some longer aliphatic bridges (C12 and C17) as shown by pyrolysis-GC/MS. Clearly, some molecular species were reduced in mass but still lay above the range of detection by heated-probe mass spectrometry and could not be identified. Although the extent to which large polycyclic aromatic entities themselves have been cracked (or otherwise reduced to smaller polycyclic aromatic groups) cannot be quantitatively discerned from the present data, the hydrocracking of isolated fractions of intractable coal-derived material appears to offer a useful method for probing their structural features.