Although NEDOL process is one of the highest yield processes of coal liquefaction, part of coal remain as a coal liquefaction residue. A usage of the coal liquefaction residue needs to be developed for the establishment of NEDOL process. The studies on the characterization of the coal liquefaction residue began by using various measurements. In this paper, solid-state 13C-NMR spectroscopy has been applied to structural characterization of the pyridine soluble matter of the coal liquefaction residue. The analysis of carbon functional groups was performed by curve-fitting techniques of the conventional CP/MAS spectrum. The apparent ratio of quaternary to tertiary aromatic carbons was determined with dipolar dephasing experiments on the sample. Using this ratio and the distributions of carbon functional groups, several parameters can be obtained on its average chemical structure. Pyridine soluble matter of the coal liquefaction residue was evaluated to consist of four to five aromatic rings with a few methyl and hydroxyl groups and naphthene rings.
vacuum residue (IL-S3) of Illinois No.6 coal from NEDOL coal liquefaction process was analyzed by 13C-NMR, FT-IR, and pyrolysis GC-MS. The IL-S3, was separated into two soluble fractions, HS (31.8%) and HI/PS (54.4%, ash free basis). The FT-IR analyses of the raw coal, the residue, and two soluble fractions of IL-S3 indicated that the residue and its soluble fractions have much more amount of aromatic hydrogen and less amount of hydroxyl groups. From absorption at 3150-3000 and 2700-3000cm-1, we could estimate the ratio of aromatic (Har) to aliphatic hydrogen (Hal) contained in IL-S3 and its HI/PS fraction. The 13C-NMR spectra of the raw coal, the IL-S3, and the soluble fractions revealed that carbon aromaticity (fa) of the residue and two soluble fractions was a little higher than that of raw coal while the number of carbon atoms attached to oxygen (CH3O and Ar-O) of the residue was lower than that of the raw coal. Curie-point pyrolysis GC of the residue showed the presence of phenanthrene, pyrene and chrysene and their monomethylated derivatives in it, while the pyrolysis of the raw coal gave aliphatic hydrocarbons, alkylbenzenes (-C4), alkylphe-nols (-C3), and alkylnaphthalenes (-C4). These results strongly suggest that deal-kylation, deoxygenation, and condensation of aromatic hydrocarbons took place during the NEDOL coal liquefaction process.
Molecular weight distributions of heavy products are very important factors necessary to understand the mechanism of coal liquefaction reaction. GPC is a promising method for heavy organic materials such as preasphaltenes (benzene insoluble-pyridine soluble fractions) derived from coal. In this paper, GPC analysis was applied to characterize the preasphaltenes using N-methyl-2-pyrolidinone (NMP), which is a preferable solvent for the preasphaltenes, as an elution solvent in GPC. In the GPC analysis of the preasphaltenes, two characteristic peaks were observed in the region of the molecular weight of 103 and 105-7 correlated by polystyrene standards. A peak corresponding to 105-7 shifted to the lower-molecular-weight region after addition of LiBr into the solvent. Besides the preasphaltenes, phenol novolak resin showed the same GPC profile using NMP as the solvent. These results suggested that the origin of the peak in the higher-molecular-weight region was the oxygen-containing polar components in the preasphaltenes. The peak separation and the peak shift after LiBr addition were also observed in the reversed phase liquid chromatography of preasphaltenes and phenol resin using NMP as the solvent. It was therefore suggested that the peak observed in the higher-molecular-weight region was ascribed to the decrease of the interaction between polar components and the column packings, because of the enhanced ionic properties of the polar components caused by NMP. Therefore, it was realized that the evaluation of the molecular weight distributions of these polar components was needed to analyze the preasphaltenes, and the phenol resin was one of the promising candidates for the standards to be used in the correlation of molecular weight.
ydrogen-donating abilities of coal liquefaction residues (CLR) were evaluated in the temperature range of 380-450°C with four molecular probes such as bibenzyl, trans-stilbene, 9-benzylphenanthrene and benzophenone for the purpose of effective utilization of donatable hydrogens in CLR. CLR stabilized arylmethyl radicals such as benzyl, 1-naphthylmethyl, 1, 2-diphenylethyl and 1, 2-dipheny1-3-(1-naphthyl)-1-propyl, and their magnitudes of steric hindrance affected the radical-capping ability of CLR. Molecule-induced hydrogen atom transfer was also promoted by CLR, and its additive effect depended on the chemical affinities of the hydrogen acceptors with CLR and their hydrogen-accepting abilities.
The liquefaction residues discharged from the NEDOL process, were extracted with carbon disulfide-N-methyl-2-pyrrolidinone mixed solvent at room temperature. The extraction yields were 86.1%, 91.1%, 90.1% for Illinois, Wyoming, Wandoan coal liquefaction-residues, respectively. The fractionation of the extract showed that the amount of acetone-soluble fraction was 53%-64%. From ultimate analysis and FTIR measurements, the extract fractions had a higher aromaticity and a lower content of oxygen (especially hydroxyl group) than those for the corresponding raw coals. Heat treatment of the liquefaction residue with a bituminous coal was carried out at 250°C to evaluate the hydrogen donating ability of the liquefaction residue to the bituminous coal. The content of soluble fraction increased by the heat treatment with the bituminous coal, compared to that calculated from the heat treatment of each component alone, indicating that the liquefaction residue donated hydrogens to the raw coal moiety even at temperature as low as 250°C.
The object of this paper is to reduce production of residue discharged from coal liquefaction. Some kinds of residue, for example difference of reaction temperature, have been examined for their boiling point distribution. From these results, the process of retrogressive products is estimated. In addition, to make sure the mechanism of retrogressive reaction on coal liquefaction, the corresponding raw coal was reacted at various conditions.
In the BCL process, the CLB, non-distillable fractions of the primary hydrogenation products is treated in the solvent de-ashing section to remove ash and parts of preasphaltenes. Then the recovered de-ashed oil (DAO) is mixed together with the solvent fraction, followed by hydrotreatment of the mixture at a fixed bed reactor in the secondary hydrogenation section. The secondary hydrogenation reactivity is affected by the primary hydrogenation conditions producing the CLB. In this paper, effects of the chemical structure of DAO on the secondary hydrogenation were inestigated by using a fixed bed reactor with DAO produced under the different primary hydrogenation conditions in the 50t/d pilot plant. Several experiments were carried out to investigate the effect of catalyst bed length and liquid velocity on the rate of secondary hydrogenation of DAO. The rate of secondary hydrogenation reaction can be expressed by a liquid hold-up model in trickle bed reactors proposed by Henry and Gilbert. DA0 conversion decreased with fa and N/C atomic ratio in DAO, and increased with the amount of HI-BS and 0/C atomic ratio in DAO, while the selectivity of the reaction products and the aparent activation energy were almost constant. The calculated values from the regression analysis for DAO conversion were agreement with experimental values. The characteristic structual parameters showed that the aromaticity of DAO increased with reaction temperature in the primary hydrogenation section, whereas the average molecular weight of DAO measured by VPO and the amount of preasphaltenes decreased. From results of structural analysis, the average molecular structure of DAO may be considered to consist of roughly 2 unit structure of clusters including 3 to 4 aromatic rings. These results indicated that the rate of DAO coversion to 420°C fractions decreased with the increase of aromaticity, such as the number of aromatic ring in the unit structure of DAO, affected by the reaction temperature in the primary hydrogenation section producing the CLB.
Stable discharge of coal liquefaction residue (CLR) from a vacuum distillation tower is required to get high oil yield and stable operation of the NEDOL process. From this point of view, fluidity of CLR was investigated by measuring the viscosity of three kinds of CLR produced in the 1 t/d Process Supporting Unit (PSU). The relationship between viscosity and temperature showed that apparent activation energy for flow of CLR differs in temperature ranges and its value below a certain temperature (Tr) is greater than that above Tr. This Tr had a good linear relationship to the softening temperature of CLR. Since CLR viscosity was considered to be remrkably influenced by ash content and organic entity viscosity, the effects of these factors were studied. Viscosity of CLR drastically increased as ash content of CLR went up to over 32 mass %, because the ash content reached to its critical value for viscous flow of CLR, i.e., 38 to 40 mass %. On the other hand, organic entity viscosity of CLR estimated by the Mori-Ototake's equation modified using present experimental results increased with the increase in carbon content of raw coal.
Themoplastic property of liquefaction residue produced at NEDOL lt/d Process Supporting Unit using Wandoan and Wyoming coals was studied by Gieseler plastometer under atmospheric and elevated pressure. Effect of air oxidation on thermoplasticity was also investigated. Gieseler fluidity of residue was successfully reduced to zero by air oxidation at 150°C. Pressure dependency of fluidity of oxidized residue was different from that of caking coal. Fluidity was more reduced under higher pressure. Photoacoustic FT-IR spectra were measured for oxidized residues. Oxidation of residues was also observed in-situ by diffuse reflectance FT-IR spectrometer equipped with controlled environment chamber. IR spectra obtained showed that oxidation reaction of residue seemed to be similar to that of coal. Increase in absorption at around 1700 and 3400cm-1 along with decrease in absorption at 2800 to 3050cm-1 was observed as oxidation reaction proceeds, indicating formation of carbonyl and hydroxyl groups and dehydrogenation from methylene group mainly in aliphatic compounds.
In order to examine the feasibility of catalyst recovery from liquefaction residue, fundamental study on the properties of catalyst in the residue was carried out by using XRD, SEM/XMA, XAFS and XPS techniques. Residues were obtained from lt/d NEDOL PSU plant which uses Wandoan, Illinois and Wyoming coals as feedstocks and synthetic pyrite as catalyst. Special attention has been paid on the interaction of catalyst with mineral matter and heavy organics in coal. It was found that the catalyst converted to pyrrhotite during liquefaction was covered with organic materials which can be removed by treating with CS2/N-methyl pyrolidinone solvent.
In order to improve the pyrolysis efficiency in utilization of a coal liquefaction vacuum residue (CLVR) from the NEDOL process, the characteristic of the CLVR and the conditions of its pyrolysis and required apparatus were experimentally studies. Concerning the characteristics, it was clarified that the amount of volatile matter of CLVR is closely related to the softening point of CLVR rather than the degree of coalfication of raw coal. More over, the solvent insoluble composition of CLVR was related to raw coal properties, and the softening point depended on the amount of toluene insolubles of CLVR. Pyrolysis experiments of three kinds of CLVR were carried out by using ordinary pressure thermo-balance, high pressure thermobalance, slot oven type (metallurgical coke oven type) and two types of flash pyrolysis apparatuses. Pyrolysis experiments by slot oven type, high pressure thermobalance and flash pyrolysis apparatus showed higher oil yield in that order. Aromaticity and molecular weight of all recovery oils were higher than those of the recycle solvent in the NEDOL process. In the case of the pyrolysis by slot oven type, the yield of products such as oil, char and gas changed with the softening point of CLVR, and the properties of recovery oil were depended on the raw coal properties. Separation of solvent insoluble components, sulfur and nitrogen removement from CLVR and handling of CLVR in its utilization process will be important subjects in future for improving of the utilization efficiency of CLVR.
A coal liquefaction residue (CLR) was impregnated into coals at 200-250°C and was pyrolyzed by using three types of reactors. Effectiveness of impregnation was evaluated by the improvement of CLR handling and by the stabilization fragment radicals of coal with donatable hydrogen contained in CLR. When the CLR/coal weight ratio was less than 30/70 for Wandoan coal and less than 50/50 for Morwell brown coal, no agglomerated particles were formed in coal/CLR composites. A good contact between coals and CLR at the molecular level was confirmed from the results of solvent extraction and SEM observation of impregnated coals. In pyrolysis, negative synergism was found in the yield of hydrogen gas, indicating the hydrogen transfer from CLR to coal. The amount of transferred hydrogen normalized by the coal mass was 4.5mol/kg coal at a CLR/coal ratio of 70/30. The yields of hydrocarbon gases and inorganic gases also showed negative synergism. This result suggests that the CLR suppressed the fromation of cross-links accompanied by the evolution of these gases. Hydrogen transfer and suppression of cross-linking reactions contributed to the increase in yield of light aromatics such as BTX and PCX.
Steam gasification of liquefaction residue was carried out in a thermo-balance. The chemical structure of Fe liquefaction catalyst in residue during gasification was investigated with XRD. Fe catalyst was contained in residue as FeS, transformed to Fe3O4 in the steam gasification stage and then to Fe2O3 after burning. Fe catalyst contained in residue showed small catalytic activity for the steam gasification of residue, however, the reactivity of the char produced from liquefaction residue was quite lower than that of raw coal char. In order to develop an effective gasification process of liquefaction residue, Ca catalyst and K catalyst were added to the residue. The catalysts added enhanced the steam gasification rate of residue. The effectiveness of the catalyst depended on the method of catalyst addition, the catalyst type and the catalyst loading. The catalytic effect of Ca catalyst prepared from lime milk was larger than that of K2CO3 catalyst in the range of less than 10wt% of catalyst loading, while the gasification rate of the sample with 20wt% of potassium was significantly higher than that of the sample with 20wt% of calcium. Highly dispersed Ca catalyst was also quite effective for SO2 removal during char combustion.
Coal easily reacted with CrO3 in aqueous solution, while CrO3 was reduced to Cr2O3 at the temperature of coal pyrolysis. In hydrocracking of coal treated with CrO3, coal was hydrocracked to more liquefied products under reducing temperature from CrO3 to Cr2O3. In present report, hydrocracking of Yubari residue treated with CrO3 was carried out from repetition to repetition at the same conditions, and the activity of chromium oxide catalyst formed by the reduction of CrO3 was estimated. HS (hexane soluble fraction) yield linearly increased up to four times and then slowly increased continuously with increasing number of reaction. Especially, BS (hexane insoluble-benzene soluble fraction) linearly increased with more number of reaction. Not a large difference was observed in the average structures of liquefied products from parent coal and CrO3 treated coal, while 1H-NMR spectra of HS were largely affected by the number of reaction. These results indicated that activity of chromium oxide catalyst was kept constant during of 1-8th reactions.
Effects of reaction conditions on the yields and characteristics of the residue have been studied based on operating results of the 1t/d process supporting unit (PSU). The PSU plant has been operated using Wandoan coal, Illinois No.6 coal and Wyoming coal under the various reaction conditions. It is found that there is a liner relationship between residue yield and yields of each component in the residue, such as asphaltenes, preasphaltenes and insoluble organic matter, in the range of the reaction conditions employed in this study and that the yield of residue from any kind of coals employed mainly depends on the yield of asphaltenes. These results imply that the asphaltenes are converted into lighter materials with more severe reaction conditions engaged for reducing the residue yield and that in the results from the same coal, the yield of each component comes to the same value in the same redidue yield produced even from the different reaction conditions.
The boiling ranges of the solvent soluble fractions from coal liquefaction residues (Wandoan, Wyoming and Illinois coals) were determined by the TG method. 40-50% of the residues were dissolved into benzene and 4-5% into n-hexane. Illinois coal residue contains a slightly larger amount of benzene soluble fraction. The coal liquefaction residues showed 40-50% of weight decrease up to 800-950°C by TG at 100°C/min of heating rate under 1Torr. About 70-80% of benzene solubles were distilled up to 700°C. The n-hexane soluble fractions were the lighter ones in this study, which should contain heavier constituents than crysene by GC. It is concluded that the organic constituents from coal liquefaction residues were very heavy.