Inferences regarding the nature of solvent-refined coal (SRC)

Solvent-refined coal product has been subjected to numerous analytical techniques in an effort to ascertain its chemical nature. Electron spin resonance, ¹³C and ¹H nuclear magnetic resonance, and mass spectroscopy along with elemental and molecular weight analyses have been employed. High-performance liquid chromatography via gel permeation separates tetrahydrofuran-soluble SRC into several size fractions. Nuclearmagnetic-resonance data strongly suggest that hexamethylphosphoramide-soluble SRC is approximately 95% aromatic in character.     

Conversion of solvent-refined coal to liquid products in the presence of Lewis acids

The formation of liquid products from a solvent-refined coal (SRC) was studied using Lewis acid catalysts in the presence of either benzene or cyclohexane as an extracting solvent. The soluble products were characterized by elemental analysis, ¹H-n.m.r., and, in some experiments, by gel permeation chromatography. Only ZnCl₂ and SnCl₂, the weakest Lewis acids examined, enhanced the dissolution of SRC over that observed in the absence of a catalyst. Increases in solubility were accompanied by increases in $\text{H}\text{C}$ and aliphatic character and by decreases in average molecular weight. These changes are ascribed to the ability of ZnCl₂ and SnCl₂ to promote depolymerization and hydrogenation of the SRC. Alkylation with isopropanol was also found to enhance the solubility of SRC in benzene and cyclohexane.     

Analysis of upgraded SRC-11 and H-coal liquid products

Upgraded coal-derived liquids obtained from catalytic hydroprocessing of SRC-11 and H-coal syncrudes have been studied by i.r., p.m.r., g.c.-m.s., and silica gel chromatography. With increase in residence time, nitrogen, oxygen and aromatics decrease, while naphthenes increase substantially. All the upgraded liquids show low viscosity at 298 K (1.3–1.4 mN s m^?2), even though saturate and aromatic fractions varied with processing severity. In the aromatic-1 fraction, 1 -ring aromatics increase, and 3-ring aromatics decrease, with increase in severity of hydroprocessing. G.c.-m.s. analyses indicate a marked qualitative similarity for saturate and aromatic fractions irrespective of syncrude source. Only the heavier end of the aromatic-1 fraction is noticeably different. Tentative identifications based on m.s. and g.c. retention times are made for most of the significant components. 600 M Hz p.m.r. spectra of the upgraded SRC-11 and H-coal liquids appear identical, but the n.m.r. difference technique revealed slight differences between the two liquids in concentrations of certain species.     

Studies in magnetochemical engineering. 1. A pilot-scale study of high-gradient magnetic desulphurization of solvent-refined coal (SRC)

A pilot-scale high-gradient magnetic separation (HGMS) system for the magnetic filtration of mineral residue from liquefied coal has been designed and constructed. The system is equipped with a specially designed on-line product-sampling device for obtaining time-cut samples of the magnetically cleaned product at elevated temperatures and pressures. Filter feed slurries of Illinois No. 6 and Kentucky No. 9/14 coals obtained from SRC pilot plants at Wilsonville, Alabama and Tacoma, Washington have been magnetically filtered under a wide range of separation conditions. The effects of major separation variables on the removal of inorganic sulphur and extracted solids from SRC filter-feed slurries have been quantitatively investigated. Under optimum separation conditions observed in this study, HGMS effectively removes up to 93 wt % of the inorganic sulphur. A quantitative correlation between the magnetic desulphurization performance and separator capacity applicable over a wide range of separation conditions has been found experimentally. A comparison of the present work and reported exploratory bench-scale studies is given, and a new SRC processing scheme incorporating HGMS capable of achieving over 90 wt % total sulphur removal from pulverized feed coal is also suggested.     

Spectroscopic investigations of solvent-refined coal fractions

The chemical characteristics of Amax solvent-refined coal are investigated on a molecular size and component basis. Gel permeation chromatography (g.p.c.) is used to characterize the tetrahydrofuran-soluble portion of the SRC and to obtain the molecular size distributions, and is also used as a preanalysis step, in which fractions are obtained according to elution time. The THF-soluble portion of the SRC has elution times comparable to asphaltene plus oil. The resultant g.p.c. eluent is divided into six fractions, three of which have molecular sizes and elution times comparable to asphaltene alone, two to oil, and one to asphaltene plus oil. These observations are confirmed by chemical ionization and electron impact mass spectrometry. Various analytical techniques are used to establish further the composition of the fractions, including: infrared spectrometry, elemental analysis, flourescence excitation and emission spectrometry, high-pressure liquid chromatography and gas chromatography.     

Co-carbonization of fractions of solvent-refined coal with a non-coking coal

Co-carbonizations of solubility fractions of a solvent-refined coal with a high-volatile, inertinite-rich non-coking coal are reported. Both chloroform-soluble and chloroform-insoluble fractions give rise to improved fusion in the cokes derived from the blends, but only the coke derived from the blend containing the chloroform-insoluble fraction contains areas of anisotropic microtexture.     

Structural characterization of filter cake solids from a solvent-refined coal process (SRC-1)

A study has been undertaken to characterize the structural aspects of the solids that have been recovered from solvent refined coal (SRC-I). Both the mineral matter as well as the organic materials are characterized through the utilization of various analytical techniques: chemical analysis, X-ray techniques, optical microscopy and electron microscopy studies, surface area measurements, density gradient separation, electron spin resonance, magnetic susceptibility and ESCA studies. A comparison is being made of the solids from this particular process with solids derived from another SRC process. Some of the main findings of this study include the following. Major minerals are pyrrhotite and α-quartz. Organic inerts consist of fusinite, semifusinite, micrinite and macrinite. The least dense fraction is essentially organic, while the high density fraction contains much of the pyrrhotite. The e.s.r.-free-radical measurements show that the solids contain few reactive species.     

Optical microscope observations of electrokinetic separation in solvent-refined coal

The response of the particulate matter in solvent-refined coal dispersions to electric perturbations was observed by optical microscopy, as a function of frequency (0–10⁴ Hz), voltage (0–3000 v), and time of application of the field. Cells giving uniform and radial electric field geometries, and having both all-metal and polymer-insulated electrode configurations, were used. Initially the field induces dipoles and orients and aggregates the particles into chains parallel to the field direction. Electrokinetic migration then leads to separation. A steady-field electrophoretic effect is seen, consistent with a net positive, low density, surface charge on the particles. Dielectrophoretic migration of induced-dipole structures towards the most intense field also occurs. It is strongest at steady and low frequency voltages and falls off with frequency in general agreement with the permittivity-frequency characteristics of solvent-refined coal dispersions. The microscopic mechanism is based on the surface polarization of elastically-bound ions in the electric double layer of the colloidal particles. The intrinsic electrophoretic and dielectrophoretic phenomena are complicated by electronic charging and discharging at the electrodes and the concomitant attraction and repulsion effects. These extrinsic phenomena become more important with increasing voltage and decreasing frequency but are significantly reduced by insulating one electrode. The results suggest that electrokinetic separation (as distinct from ‘electrostatic’ separation) is potentially useful for removing residual carbonaceous solids and mineral matter from the crude products of coal liquefaction. It is worthy of quantitative investigation on a larger scale.     

Characteristics of coal upgraded with heavy oils

We investigated the ability of an oil coating to upgrade Indonesian low-rank coal, which has a low ash content and a moisture content of approximately 30%. Proximate and ultimate analyses of the characteristics of coal samples containing different amounts of asphalt (ASP) and palm fatty acid distillate (PFAD) were studied, including the samples’ calorific values, crossing-point temperatures (CPT), specific surface areas, pore sizes, structural changes, and moisture readsorption. The results showed that the 0.5% PFAD-coated coal was the highest quality. This coal showed few physical and chemical changes, and it had a low surface area and a high CPT value.     

Removal of mineral material from solvent-refined coal by solvent extractions

Solvent refined coal (SRC), a coal extract which is highly polyaromatic in character and relatively high in N, O and S content, is derived from the direct liquefaction of coal. SRC contains mineral matter in the form of soluble organometallic compounds which can not be removed by filtration. These soluble species can be detrimental to the hydrocracking catalyst used in the upgrading of the SRC to high-value liquid fuels. These species, however, can be separated from the SRC by extraction with benzene or tetralin as solvents so that the mineral matter is mainly concentrated in the solvent-insoluble fraction, the other fraction are then readily hydrocracked, as demonstrated in this work.     

Comparison of fractions of pyridine extract and solvent-refined coal from Illinois No. 6 coal

A pyridine extract of Illinois No. 6 coal and a solvent-refined coal from the same coal have been fractionated. Parallels between the two sets of fractions in composition and molecular weight and some experiments on phenol-pyridine interactions lead to the conclusion that solvent refining cleaves ether links and removes much of the organic 0 and S, without much change in acidic and basic groups. Gel-permeation chromatograms of the fractions indicate that they have moderately narrow molecular weight distributions. A plot of number-average molecular weights against retention times for both sets of fractions gives a smooth curve that is consistent with relations for polystyrene and poly(ethylene oxide).     

Study of Ti in solvent-refined coal by X-ray absorption spectroscopy

The chemical environment of titanium in solvent-refined coal (SRC-I and SRC-II) has been studied using X-ray absorption spectroscopy. Evidence that organic complexes of Ti are produced in the liquefaction process from mineral forms of Ti present in the feed coal is presented, based on the pre-edge structure of the X-ray absorption spectra.     

煤焦油馏分微波萃取神府煤热解液体产物的研究

为提高煤在萃取过程中的转化率,考察微波辅助萃取煤的工业化可行性。在微波辅助下,以神府低温煤焦油馏分为溶剂,在最优操作条件下萃取神府煤,将萃取混合液在510℃条件下热解,分析了热解液体产物的性质及组成,得到了加工方案。结果表明:液体产物主要由酚类化合物、芳烃化合物及烷烃组成,酚类含量较高,其在萃取热解液体产物中的比例均达到50%以上,主要由苯酚、C1～C4苯酚组成,大于C4苯酚的含量很小,其中由苯酚、C1-苯酚、C2-苯酚组成的低级酚含量占总酚含量的70%以上,因此对液体产物进行加工时,需要将低级酚类化合物从液体产物中先分离出来。     

Characterization of a complex mixture of aromatic and heterocyclic acids obtained from oxidation of lignite coal and its solvent-refined products

This study reports the results from the oxidation, using sodium dichromate, of a solvent-refined lignite (SRL) and its feed coal and the effects of varying the ratio of oxidant to coal. The numerous aromatic and heteroaromatic carboxylic acids isolated were identified as their methyl esters by g.c./m.s. and h.r.m.s. Oxidation of SRL with a limited amount of dichromate yielded a large number of polycyclic aromatic and heteroaromatic acids not found in the oxidation of the lignite. These results indicate that the SRL process produces highly-condensed aromatic molecules.     

Investigation of retrogressive reactions leading to the carbonization of solvent-refined coal

The carbonization of solvent-refined coal (SRC) samples produced by the liquefaction of an HVc bituminous coal has been studied. Carbonization conditions were 450 °C, 34.4 MPa, for 1 and 5 h hold times. The original SRCs and pyridine-insoluble fractions of the carbonization products have been characterized by Fourier-transform infrared spectroscopy. Spectral changes demonstrate that the formation of larger molecules during carbonization involve the joining together of aromatic molecules that were originally present, without increasing their size significantly. This is accomplished by the elimination of methylene units and condensation of phenolic functional groups originally present on the aromatic groups in the SRCs.     

Hydrogen solubility in coal liquid (SRC-II)

Experimental results are presented for hydrogen solubility in hydrogenated coal liquid (SRC-II) and coal-liquid partial pressure in the hydrogen-coal-liquid system, over temperature and pressure ranges of 420–680 K and 4–11 MPa. Two in situ hydrogen probes were used to determine the hydrogen partial pressure in the system. No coking was observed at these temperature levels. The results are in good agreement with hydrogen solubility data for similar hydrogen-bearing systems reported in the literature. The hydrogen solubility exhibits an inversion with increasing temperature at constant total pressure, which can be interpreted in terms of the strong dependence of the coal-liquid partial pressure on temperature.     

Relaxation of 13C and 15N nuclei by solvent-refined coal

The effects of changing various spectroscopic parameters on the solid-state and solution ¹³C-nuclear magnetic resonance (n.m.r.) spectra of solvent-refined coal have been investigated. Solution spectra were obtained with the use of broad band decoupling, inverse gated decoupling and coupling techniques. Conventional relaxation reagent (Cr(acac)₃) was sometimes added to the solvent-refined coal. The effects of pulse delay on the total signal intensity, and on the intensity of the signal from aromatic carbon have been measured. The results show that inverse gated decoupling with pulse delays of 10 s is needed for complete relaxation of solvent-refined coal, but pulse delays of 6 s can give accurate estimations of aromaticity. However, it is recommended that conventional relaxation reagent such as Cr(acac)₃ be added to ensure relaxation if shorter pulse delays are used. The effect of solvent-refined coal on relaxation of some pure compounds in solution has also been studied. Solvent-refined coal acts as a relaxation reagent on ¹³C nuclei in benzene, toluene and ethylbenzene. It can also relax ¹⁵N nuclei in aniline, N,N-dimethylaniline and nitromethane. Spin-lattice relaxation times (T₁'s) of selected nuclei have been measured and the contribution of solvent-refined coal to relaxation (T₁SRC) has been calculated. Solid-state 13C-n.m.r. spectra have been obtained using the cross-polarization (CP) technique with magic-angle sample spinning (MASS). A variety of cross-polarization times and recycle times have been used. The results show that no serious errors in measurement of aromaticity (f_a) are caused by using a contact time as short as 1 ms and a recycle time of 0.3 s. There is good agreement between f_a's obtained by solution and solid-state n.m.r., and as solid-state spectra can be obtained in only a fraction of the time needed to obtain a solution spectrum (≈$\text{1}\text{20th}$), CP-n.m.r. is the method of choice for analysis of f_a of solvent-refined coal. The results also show that CP-MASS n.m.r. can be used to estimate the fraction of aromatic carbon which is unprotonated in solvent-refined coal and, hence, indirectly, the fraction of hydrogen which is aromatic.     

Ash deposition behavior of upgraded brown coal in pulverized coal combustion boiler

Ash with a low melting point causes slagging and fouling problems in pulverized coal combustion boilers. Ash deposition on heat exchanger tubes reduces the overall heat transfer coefficient due to its low thermal conductivity. The purpose of this study is to evaluate the ash deposition for Upgraded Brown Coal (UBC) and bituminous coal in a 145 MW practical coal combustion boiler. The UBC stands for Upgraded Brown Coal. The melting temperature of UBC ash is relatively lower than that of bituminous coal ashes. Combustion tests were conducted on blended coal consisting 20 wt.% of UBC and 80 wt.% of bituminous coal. Before actual ash deposition tests, the molten slag fractions in those coal ashes were estimated by means of chemical equilibrium calculations. The calculation results showed the molten slag fraction for UBC ash reached approximately 90% at 1523 K. However, that for blended coal ash decreased to 50%. These calculation results mean that blending UBC with bituminous coal played a role in decreasing the molten slag fraction. This phenomenon occurred because the coal blending led to the formation of alumino-silicates compounds as a solid phase. Next, ash deposition tests were conducted using a practical pulverized coal combustion boiler. A water-cooled stainless-steel tube was inserted in locations at both 1523 K and 1273 K in the boiler to measure the amount of ash deposits. The results showed that the mass of ash deposition for blended coal did not greatly increase, compared with that for bituminous coal alone. Therefore, appropriately blending UBC with bituminous coal enabled the use of UBC without any ash deposition problems in practical boilers.     

Carbonization and liquid-crystal (mesophase) development. 10. The co-carbonization of coals with solvent-refined coals and coal extracts

Coals (NCB rank 102 to 902) were co-carbonized with solvent-refined coals and coal extracts, mixing ratio of 7:3, to 873 K, heating at 10 K min^?1 with a soak period of 1 h. Resultant cokes were examined in polished section using reflected polarized-light microscopy and optical textures were recorded photographically. These optical textures were compared to assess the ability of the additive pitch to modify both the size and extent of optical texture of resultant cokes. The objective of the study is to provide a fundamental understanding of the use of pitch materials in co-carbonizations of lower-rank coals to make metallurgical coke. A Gulf SRC was able to modify the optical texture of cokes from all coals except the anthracite. Soluble fractions of this Gulf SRC were less effective than the parent SRC. A coal extract (NCB D112) modified coke optical texture, the extent being enhanced as the rank of coal being extracted was increased. Hydrogenation of the coal extract increased the penetration of the pitch into the coal particles but simultaneously reduced the size of the optical texture relative to the non-hydrogenated pitch. This indicates a positive interaction of pitch with coal in the co-carbonization process. The optical texture of the cokes from the hydrogenated coal extract in single carbonizations was larger than that from the non-hydrogenated material. Mechanisms explaining these effects are briefly described.