Effect of catalyst deactivation on the chemical composition and biological activity of catalytic two-stage coal liquefaction process materials

Samples of pressure filter liquid (PFL), the solids-free portion of the recycle slurry oil, were taken each day of the 25-day demonstration run No. 227-20 of the catalytic two-stage direct coal liquefaction (CTSL) process operated by Hydrocarbon Research Inc. (HRI). Selected samples were chemically characterized by fractionation into chemical classes by adsorption column chromatography using neutral alumina and picric acid-coated alumina adsorbents followed by high resolution gas chromatography, g.c.-m.s. and low voltage probe-inlet mass spectrometry. Selected samples were tested for biological activity using the standard histidine reversion microbial mutagenicity assay with S. typhimurium, TA 98 and an initiation/promotion assay for mouse skin tumorigenicity. Chemical analysis results indicated that there were increased concentrations of heteroatomic components in the PFL as catalyst age increased; the nitrogen-containing polycyclic aromatic compound fraction and hydroxy-substituted polycyclic aromatic hydrocarbon fraction contents of the PFL both increased with increasing pilot plant operation time. In addition, the aliphatic hydrocarbon and hydroaromatic fraction contents of the PFL decreased and the heavier molecular weight PAH compound content increased as the catalyst aged during the demonstration run. Biological testing results indicated that the mutagenic activity increased and that the skin tumour initiating activity of the PFL, as determined by total number of tumours per mouse, also tended to increase with catalyst age and deactivation.     

Effects of solvent and iron-compounds on the liquefaction of brown coal

Hydrogen-donor solvents such as hydrophenanthrene are the most effective aromatic solvents for the liquefaction of brown coal. The hydrogen-donating ability of the solvent is more important for brown coals than for bituminous coals, because the thermal decomposition and subsequent recombination of the structure of the brown coals occurs rapidly. Three-ring aromatic hydrocarbons are more effective solvents than two-ring aromatics, and polar compounds are less effective solvents with brown coals than with bituminous coals. The thermal treatment of brown coal, accompanied by carbon dioxide evolution at temperatures > 300°C, in the presence of hydrogen-donating solvent did not affect the subsequent liquefaction reaction. However, thermal treatment in the absence of solvent strongly suppressed the liquefaction reaction, suggesting that the carbonization reaction occurred after the decarboxylation reaction in the absence of hydrogen donor. To study the effect of various iron compounds, brown coal and its THF-soluble fraction were hydrogenated at 450°C in the presence of ferrocene or iron oxide. The conversion of coal and the yield of degradation products are increased by the addition of the iron compounds, particularly ferrocene, and the yield of carbonaceous materials is decreased.     

Micrinite and exudatinite in some Australian coals,and their relation to the generation of petroleum

The occurrence and microscopic features of micrinite and exudatinite in some Australian coals are reported. The origin of these macerals and also the significance of their occurrence are discussed in connection with hydrocarbon genesis. In Australia, micrinite occurs in bituminous and sub-bituminous coals which are very rich in inertinite, and also in brown coal rich in inertinite. One of the possible progenitors of micrinite is oxidized porigelinite. There is little reason to conclude that micrinite was formed from resinite and other macerals at an early stage of coalification and that liquid hydrocarbons were formed during this process. Exudatinite occurs in sub-bituminous and high-volatile bituminous coals in the Gippsland Basin. There is no positive evidence of a genetic relation between liquid hydrocarbons, exudatinite, micrinite and liptinite macerals. The formation of liquid hydrocarbons from solid liptinite etc. may take place just before and during Teichmüller's so-called ‘2nd coalification jump’.     

Interrelationship of chemical characterization and rheological behaviour of coal liquefaction bottoms

In the development of the Exxon Donor Solvent (EDS) process, bituminous and subbituminous coals have been processed in a one ton-per-day coal liquefaction pilot plant using the feed coal slurried with solvent and with or without bottoms recycle. The liquefaction bottoms from both once-through and bottoms recycle operation exhibit non-Newtonian viscometric behaviour. The recycled bottoms, however, are more viscosity/shear dependent, less viscosity/temperature dependent and more thermally stable than the once-through bottoms. Chemical characterization of these bottoms reveals that alkyl and phenoxy groups are important functional groups responsible for the viscometric behaviour of bottoms. The increase of bottoms viscosity is postulated to involve the elimination/condensation of methylene units are phenolic functional groups to form the crosslinkages of large aromatic clusters.     

Differences in the behaviour of US bituminous and subbituminous coals during short contact time liquefaction

The short contact time (SCT) liquefaction of Belle Ayr subbituminous coal has been compared with that of Illinois No. 6 and Pittsburgh seam bituminous coals. Each bituminous coal was highly solubilized (90 wt%, daf coal) in 3–4 min at 450 °C and 13–16 MPa hydrogen pressure. More than 80 wt% of each coal was converted to solvent-refined coal (SRC, pyridine-soluble residuum), with only small quantities of distillate oil and C₁–C₄ gas being formed. A longer reaction (up to 30 min) gave only a small increase in total conversion, but gas and distillate yields increased significantly. Iron sulphides did not appear to catalyse coal solubilization. By contrast, only 65 wt% of the Belle Ayr coal dissolved rapidly in SCT liquefaction and pyrite addition catalysed the conversion of the remaining insoluble organic matter (IOM). With an equivalent amount of pyrite present the Belle Ayr coal also gave more C₁–C₄ gas and substantially more distillate in SCT liquefaction than the bituminous coals. These differences in product distributions obtained from bituminous and subbituminous coals in SCT liquefaction can be rationalized on the basis of differences in the structures of the starting coals. However, the origin of high IOM yields with the Belle Ayr coal remains unclear.     

The influence of catalyst regeneration on the composition of zeolite-upgraded biomass pyrolysis oils

The composition of oils derived from the on-line, low pressure zeolite upgrading of biomass pyrolysis oils from a fluidized bed pyrolysis unit have been investigated in relation to the regeneration of the zeolite catalyst. The catalyst used was H-ZSM-5 zeolite. The gases were analysed by packed column gas chromatography. The composition of the oils before catalysis and after catalyst upgrading were analysed by liquid chromatography fractionation, followed by coupled gas chromatography—mass spectrometry of each fraction. In particular, the aromatic and oxygenated aromatic species were identified and quantified. In addition, the oils were analysed for their elemental composition and molecular weight range using size exclusion chromatography. Before catalysis the biomass pyrolysis oil was highly oxygenated but after catalysis a highly aromatic oil was formed with high concentrations of monocyclic aromatic hydrocarbons. In addition, significant concentrations of polycyclic aromatic hydrocarbons (PAH) were formed. Regeneration of the zeolite catalyst showed that continued regeneration reduced the effectiveness of the catalyst in converting biomass pyrolysis oils to an aromatic product. Elemental analysis of the upgraded oils showed an increase in the oxygen content of the oil with increasing regeneration of the catalyst. The molecular weight range of the oils was found to decrease markedly after catalysis, but continued regeneration of the catalyst increased the molecular weight range of the upgraded oils. Detailed analysis of the uncatalysed oils showed they contained low concentrations of aromatic and PAH species which markedly increased in concentration after catalysis. The overall effect of increasing catalyst regeneration was a decrease in the concentration of aromatic hydrocarbons and PAH. Also as the catalyst was regenerated, the number of methyl groups on the parent single ring aromatic compound or PAH increased. The oxygenated aromatic species in the oil before catalysis were mainly, phenols and benzenediols and their alkylated homologues. After catalysis some of the oxygenated species were reduced and some increased in concentration. A dual mechanistic route is suggested for the formation of aromatics and PAH during the catalytic upgrading of biomass pyrolysis oils: (1) the formation of low-molecular-weight hydrocarbons on the catalyst which then undergo aromatization reactions to produce aromatic hydrocarbons and PAH; (2) deoxygenation of oxygenated compounds found in the non-phenolic fraction of the pyrolysis oils which directly form aromatic compounds.     

Determination of PAHs in Combustion-Related Samples and in SRM 1597, Complex Mixture of PAHs from Coal Tar

Three types of combustion sample extracts, smokeless coal, smoky coal, and wood, were analyzed for a range of polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic sulfur heterocycles (PASH). Standard Reference Material (SRM) 1597, Complex Mixture of PAHs from Coal Tar, was also analyzed as a control sample and for the determination of a larger number of PAHs relative to those determined previously. Target analytes included many alkyl-substituted PAHs such as dimethylphenanthrenes, methylfluoranthenes, and methylpyrenes. The analytical methods included sample clean-up and the selection of specific stationary phases to accomplish unique separations of PAHs. Clean-up involved the use of normal-phase liquid chromatographic isolation of PAHs based on the number of aromatic carbons and a total PAH fraction, PAHs in the resulting fractions were separated by gas chromatography using two stationary phases with different selectivities and analyzed using mass spectrometry. These methods are discussed below and results are presented with an emphasis on the relative concentrations and distribution of PAHs in the combustion samples.     

Mutagenicity of eluent by hot water extraction of various coals: Effect of chlorination

Six kinds of powdery coals (two bituminous coals, two sub-bituminous coals, and two lignites) were extracted by hot water, and the eluents obtained were analyzed for total organic carbon (TOC), absorbance at 260 nm (A₂₆₀), and pH. The TOC in the eluents decreased in the order, lignites > sub-bituminous coals > bituminous coals. The eluents of lignite gave high A₂₆₀/TOC values and fairly low pH compared to other coals. Chemical structure of the organic matter eluted from coals was discussed with the aid of FTIR analysis. The coal eluents were analyzed by the Ames mutagenicity assay using Salmonella typhimurium TA100 and TA98 strains, and no mutagenicity was observed for all of the six coals. However, especially for the lignites, chlorination of the eluents produced an appreciable mutagenicity, and the expression of mutagenicity was dependent upon the type of coal. The mutagenicity was extinguished when metabolic activation (rat liver homogenate, +S9) was applied.     

Gas composition and temperature profiles in a spouted bed coal gasifier

Verification of scale-up models of the spouted bed gasifier requires experimental gas composition and temperature profiles within the reactor. Radial and axial profiles are presented for key gaseous species in a 0.30-m. dia, atmospheric pressure gasifier fed at about 30 kg coal/h. Low calorific value gases were generated at air/coal mass ratios of 2.87-4.08, while medium calorific value gases were produced at an oxygen/coal mass ratio of 0.84 and steam/coal ratios of 2.23-2.84. The combustion zone within the gasifier is delineated and the effects of operating conditions on gas composition and temperature profiles are illustrated for typical sub-bituminous and bituminous coals. Recycle of char to the bed from the primary cyclone and bed depth show little effect on profile shape.     

Firing a sub-bituminous coal in pulverized coal boilers configured for bituminous coals

It is important to adapt utility boilers to sub-bituminous coals to take advantage of their environmental benefits while limiting operation risks. We discuss the performance impact that Adaro, an Indonesian sub-bituminous coal with high moisture content, has on opposite-wall and tangentially-fired utility boilers which were designed for bituminous coals. Numerical simulations were made with GLACIER, a computational-fluid-dynamic code, to depict combustion behavior. The predictions were verified with full-scale test results. For analysis of the operational parameters for firing Adaro coal in both boilers, we used EXPERT system, an on-line supervision system developed by Israel Electric Corporation. It was concluded that firing Adaro coal, compared to a typical bituminous coal, lowers NO_x and SO₂ emissions, lowers LOI content and improves fouling behavior but can cause load limitation which impacts flexible operation.     

Mechanisms leading to process improvements in lignite liquefaction using CO and H2S

Optimum distillate yields from US lignites can be as high on a dry, ash-free basis as those obtained from bituminous coals, but only if the vacuum bottoms are recycled. Lignites are more readily liquefied if the reducing gas contains some carbon monoxide and water, which together with bottoms recycle has proven to yield the highest conversions and the best bench-unit operability. The recycle solvent in the reported tests consisted of unseparated product slurry, including coal mineral constituents. Variability in coal minerals among nine widely representative US low-rank coals did not appear to correlate with liquefaction behaviour. Addition of iron pyrite did, however, improve yields and product quality, as measured by hydrogen-to-carbon ratio. Future improvements in liquefaction processes for lignite must maintain high liquid yields at reduced levels of temperature, pressure, and reaction time whilst using less reductant, preferably in the form of synthesis gas (CO + H₂) and water instead of the more expensive pure hydrogen. Understanding the process chemistry of carbon monoxide and sulphur (including H₂S) during lignite liquefaction is a key factor in accomplishing these improvements. This Paper reviews proposed mechanisms for such reactions from the viewpoint of their relative importance in affecting process improvements. The alkali formate mechanism first proposed to explain the reduction by CO does not adequately explain its role in lignite liquefaction. Other possible mechanisms include an isoformate intermediate, a formic acid intermediate, a carbon monoxide radical anion, direct reaction with lignite, and the activation of CO by alkali and alkaline earth cations and by hydrogen sulphide. Hydrogen sulphide reacts with model compounds which represent key bond types in low-rank coal in the following ways: (1) hydrocracking; (2) hydrogen donor; (3) insertion reactions in aromatic rings; (4) hydrogen abstraction, with elemental sulphur as a reaction intermediate; and (5) catalysis of the water-gas shift reaction. It appears that all of these reaction pathways may be operative when catalytic amounts of H₂S are added during liquefaction of lignite. In bench recycle tests, the addition of H₂S as a homogeneous catalyst reduced reductant consumption as much as three-fold whilst maintaining high yield levels when the reaction temperature was reduced by 60°C. Attainment of the high distillate yield at 400°C was accompanied by a marked decrease in the production of hydrocarbon gases, which normally is a major cause of unproductive hydrogen consumption and solvent degradation via hydrocracking. Processing with synthesis gas and inherent coal moisture using bottoms recycle and H₂S as a catalyst appears to be the most promising alternative combination of conditions for producing liquids from lignite at reduced cost.     

A kinetic investigation of coal liquefaction at short reaction times

Coal liquefaction kinetics have been studied at very short reaction times (less than 250 seconds) in order to emphasize the initial underlying physical and chemical processes involved. These studies were made possible by the use of a continuous flow stirred tank reactor (CSTR) which avoids the problems of slow heat up and cool down associated with the massive equipment required for running high-temperature and high-pressure liquefaction reactions. Preliminary physical (NMR and ESR) and chemical analytical results are presented on the coal liquids and reaction residues from Illinois No. 6 hv bituminous and Wyodak Black Thunder subbituminous coals.

ESR results showed that radical concentration in the solid residue changed during coal liquefaction. These changes were accompanied by changes in the NMR-derived aromaticity. The rate of decrease of organic-based radicals was different for Wyodak Black Thunder and Illinois No. 6 coals, perhaps indicating a different mechanism for the quenching of radicals in these bituminous and subbituminous coals. NMR spectra of the liquid products indicated that the initially produced material was relatively aromatic, and that subsequent products had lower aromatic content. This is consistent with secondary hydrogenation of the primary liquefaction products. Finally, the total oxygen contents of the coal residues decreased gradually during the first three minutes of coal liquefaction at 390°C. A corresponding decrease in the hydroxyl content of these residues was also noted.     

Measurement and prediction of the emission of pollutants from the combustion of coal and biomass in a fixed bed furnace

The effect of co-combustion of coal and biomass has been studied for a fixed bed appliance originally designed for coal and in widespread use in many parts of the world especially Eastern Europe. Organic, inorganic and gaseous emissions have been measured. Organic compounds have been determined for a range of fuel combinations. These include polycyclic aromatic hydrocarbons PAH, alkyl PAH, a range of oxygenated compounds (including phenols, aldehydes and ketones, oxygenated polycyclic aromatic compounds (O-PAC) and dioxins), polycyclic aromatic sulphur hydrocarbons (PASH), nitrogenated polycyclic aromatic compounds (N-PAC) and common volatile organic compounds (VOC). Inorganic species include trace heavy metals, as well as the gases, CO, CO₂, SO_x and NO_x. The concentration of the trace metals in the ash and fly ash have been compared to equilibrium calculations of the emission profiles during co-combustion.     

Separation and characterization of large-ring number polycyclic aromatic hydrocarbons in non-distillable, pyridine soluble coal-liquids

Low-pressure liquid chromatography, high-performance liquid chromatography, and field ionization mass spectrometry (f.i.m.s.) were used to obtain compositional information on large-ring number polycyclic aromatic hydrocarbon (PAH) present in a non-distillable coal liquid sample. A highly selective h.p.l.c. method for the separation of (PAH) from polar compounds was applied to nitrogen-compound fractions derived from a Wyodak non-distillable ( > 427 °C) coal-liquid sample. F.i.m.s. analyses revealed that the PAH subfractions isolated by the h.p.l.c. procedure contained large-ring number PAH and relatively few nitrogen compounds. The methods developed can generally be applied to the analyses of complex organic mixtures, and in conjunction with other methods, can yield detailed polycyclic aromatic hydrocarbon compositional information.     

Determination of Sulfur-Containing Polycyclic Aromatic Compounds in Coal Extracts using Capillary Column Gas Chromatography with Radio Frequency Plasma Detection

Detailed identification of sulfur-containing polycyclic aromatic compounds (S-PAC) was accomplished for solvent extracts of five different coals. The S-PAC were isolated by ligand-exchange chromatography. Due to the great complexities of these samples, capillary gas chromatography (GC) was employed for their analysis. An element selective radio frequency plasma detector was used to provide sulfur selective detection. Gas chromatography-mass spectrometry was used to identify individual compounds in isolated sulfur fractions. Condensed thiophenic compounds were found to be the major constituents in all five S-PAC fractions. Diaryl sulfides were also detected in the high volatile bituminous Illinois #6 coal. The prevalence of various S-PAC in different coal extracts was observed as a function of their rank.     

Ash deposition characteristics of Moolarben coal and its blends during coal combustion

We report a systematic and comprehensive laboratory investigation of the ash deposition behavior of Moolarben (MO) coal, which has recently begun to be imported into Korea. Ash deposition experiments were conducted in a drop tube reactor, and a water-cooled ash deposit probe was inserted into the reactor to affix the ash. The tests were conducted using five types of single coals (two bituminous and three sub-bituminous, including MO coal) and blended coals (bituminous coal blended with sub-bituminous coal). Two indices represent ash deposition behavior: capture efficiency and energy-based growth rate. A thermomechanical analysis evaluated the melting behavior of the resulting ash deposits. The MO coal had the least ash deposition of the single coals due to its high melting temperature, indicated by high ash silica content. Indonesian sub-bituminous coals formed larger ash deposits and were sticky at low temperatures due to relatively high alkali content. However, blends with MO coal had greater ash deposition than blends with other bituminous coals. This non-additive behavior of MO coal blends is likely due to interactions between ash particles. Coals with higher silica content more effectively retain alkali species, resulting in lower melting temperatures and larger ash deposits. Therefore, we recommend that when blending in a boiler, silica-rich coals (SiO₂>80%, SiO₂/Al₂O₃> 5) should be blended with relatively low-alkali coals (Na₂O+K₂O<3%), and the blending ratio of the silica-rich coals indicates less than 10%, which can safely operate the boiler.     

Improvement in coal liquefaction solvent quality by dewaxing

Recycle oils from the Integrated Two-Stage Liquefaction (ITSL), H-Coal and Solvent Refined Coal (SRC) processes were dewaxed by variants of commercial dewaxing processes—the ketone and the urea adduction techniques — yielding up to 47 wt % ‘wax’. Feed oils and product fractions were characterized by elemental analysis, ¹H n.m.r. and gas chromatography. The clean waxes were nearly pure mixtures of n-paraffins. The dewaxed oils were substantially better coal liquefaction solvents than the original (non-dewaxed) oils in batch liquefaction tests. For example, in one case, dewaxing improved the conversion of a bituminous coal to tetrahydrofuran-solubles under standard reaction conditions from 71 wt% (dafb) with the original oil to 87 wt % (dafb). These data provide a direct indication of the inimical effect of paraffinic components on solvent quality. The impact of solvent quality is particularly relevant to liquefaction processes in which thermal reactions proceed in a recycle solvent. In addition, the results indicate the technical feasibility of dewaxing coal liquefaction recycle oils by commercially available technology to improve solvent quality and to produce a useful by-product. Dewaxing could be applied in any liquefaction process that uses a deasphalted (preferably distillate) recycle stream.     

Comparison of coal gasification in fluidized and spouted beds

Two sub-bituminous coals, a bituminous coal and a reject coal of 55% ash were gasified with steam and air in a 0.31-m dia. reactor operated in the fluidized and spouted bed modes. Inert beds of 1.1 mm dia. Ottawa sand and 2.1 mm dia. gravel provided stable fluidization and spouting respectively, at superficial velocities in the range 1.3–1.6 m/s. Coals of 1.19–3.36 mm diameter were fed to the gasifier at rates up to 45 kg/h and a range of air/coal ratios. For a given coal, results in the two systems were basically similar, although differences in gas heating value, gas yield and thermal efficiency were noted for some coals.     

Effects of oxygenate concentration on species mole fractions in premixed n-heptane flames

Atmospheric pressure, laminar, premixed, fuel-rich flames of n-heptane/oxygen/argon and n-heptane/oxygenate/oxygen/argon were studied at an equivalence ratio of 1.97 to determine the effects of oxygenate concentration on species mole fractions. The oxygen weight percents in n-heptane/oxygenate mixtures were 2.7 and 3.4. Three different fuel oxygenates (i.e. MTBE, methanol, and ethanol) were tested. A heated quartz micro-probe coupled to an on-line gas chromatography/mass spectrometry has been used to establish the identities and absolute concentrations of stable major, minor, and trace species by the direct analysis of samples, withdrawn from the flames. The oxygenate addition has increased the maximum flame temperatures and reduced the mole fractions of CO, low-molecular-weight hydrocarbons, aromatics, and polycyclic aromatic hydrocarbons. The reduction in mole fractions of aromatic and polycyclic aromatic hydrocarbon species by an increase in oxygenate concentration was more significant.     

The behavior of n-paraffins under coal liquefaction conditions

In order to evaluate the concentration and the distribution of n-paraffins in recycle solvent of coal liquefaction processes, the behavior of n-paraffins under coal liquefaction conditions was investigated. Four coals (Wandoan, Taiheiyo, Wyodak, Illinois No. 6) were liquefied and n-paraffins produced were analyzed. For example, n-paraffins, produced from liquefaction of Wandoan coal at 450°C for 1 h, contain approximately 5.2 wt.% (dry coal base) hydrocarbons in the range C₁₀C₃₆.Furthermore, cracking reactions of n-paraffins were carried out and their behavior under coal liquefaction conditions was analyzed. The cracking conversions of n-paraffins increased with increasing carbon numbers of n-paraffins, and the rate constants for cracking of n-paraffins were directly proportional to carbon numbers. The product distribution in the cracking of n-paraffins was evaluated by using bond dissociation energy. On the basis of these results, the concentrations of n-paraffins in the recycle solvents were calculated and these calculated values agreed well with those observed in the coal liquefaction process.