Nitrogen bases in solvent-refined coal

The basic components contained in a coal liquefaction product obtained from the Wilsonville, Alabama coal liquefaction pilot plant were examined by means of capillary-column Chromatographic-mass spectroscopy. A total of 62 of the 150 components observed were identified. The most interesting of the newly identified compounds are phenoxazine, butyl quinolines and isoquinolines, diarylamines and aminobiphenyl derivatives. The possibility of removing amino aromatics from coal liquefaction products by condensing them with the phenols in the mixture is discussed.     

Transmission electron microscope observations of porosity in coal

Samples of a high-volatile bituminous coal (HVab) were examined by means of transmis sion electron microscopy in a high-voltage electron microscope (1 MeV). The porosity observed within the exinite and inertinite constituents of this coal falls primarily into the mesopore size range (2–50 nm). Small particles (≈25 nm in diameter) were seen in a majority of the exinite pores and are believed to have acted as catalysts in the pore formation.     

Catalyst performance in hydroprocessing solvent-refined coal

The hydroprocessing of solvent-refined coal (SRC) was studied in a fixed-catalyst basket reactor using modified Shell 324 NiMo catalyst supported on alumina. At a reaction temperature of 775°F (413°C), a hydrogen pressure of 2000 psig, and a space velocity of 0.9 g feed/(g catalyst h), the SRC conversion was 57%. As expected, SRC conversion, hydrocarbon gas production, total desulfurization, and hydrogen consumption increased with increasing reaction temperature. However, oil production, which was also expected to increase, changed only slightly with increasing temperature. The effect of time on stream on SRC conversion and catalyst activity was determined at 775°F (413°C), while other process conditions were maintained constant. Catalyst activity changed only slightly during the first 294 h (catalyst age = 246 g SRC/g catalyst) of SRC hydroprocessing. However, catalyst activity decreased drastically thereafter. Analysis of the spent catalyst revealed that catalyst surface area, pore volume, and pore diameter decreased significantly, while chemical analysis showed an unusually high level of sodium deposition (4.2%), which was probably due to the high sodium level in the feed. A mass balance on the metals in the feed revealed that only small amounts of iron and titanium from the feed SRC were deposited on the catalyst, whereas most of the sodium was retained by the catalyst. The decrease in catalyst activity could have been due to a reduction in intraparticle diffusion due to coke and metals deposition, to catalyst poisoning by sodium, or both. Finally, it was concluded that the SRC hydroprocessing experiments should be carried out long enough to cover the entire range of catalyst activity to obtain a meaningful catalyst replacement rate.     

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.     

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.     

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.     

Analysis of upgraded solvent-refined coal (SRC) liquid products

Upgraded coal-derived liquids obtained from catalytic hydroprocessing of a 30–70(wt%) blend of SRC-1 with SRC-II have been studied by infrared and proton magnetic resonance spectroscopy, and gel permeation chromatography techniques. Compared with the feed blend, the upgraded liquids exhibit a lower C/H ratio and decreased aromatic, heteroatom and pentane-insoluble contents, along with decreased specific gravity and viscosity. The amount of hydrogen-bonded structure in the upgraded liquid decreases with increases in residence time and processing temperature. The pseudo-first-order disappearance of phenolic OH and total nitrogen during processing indicates a relative reactivity of 2:1 of hydroxyl oxygen removal to total nitrogen removal in the upgrading process. Conversion of pentaneinsolubles to soluble oil also follows a pseudo-first-order reaction; under mild processing conditions, the heteroatom functionalities play a dominant role in the ease and extent of this conversion. Higher temperatures increase thermal cracking and hydrocracking of the ring structure resulting in more conversion of asphaltene to oil. The linear dependence of the logarithm of viscosity on the content of heteroatoms and toluene-insolubles (TI) indicates the importance of molecular interactions involving polar functional groups in defining the viscosity of coal-derived liquid.     

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).     

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.     

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.     

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.     

Comparison of solvent-refined lignite with solvent-refined bituminous coals

Comparison of laboratory-deashed samples of solvent-refined lignite, subbituminous and bituminous coals on the basis of gross combustion analysis, acid and basic titres, molecular weight, nuclear magnetic resonance, ultraviolet and electron spin resonance spectra including various derived parameters indicated that there is relatively little difference between the range of values for lignite- and bituminous coal-derived solvent-refined products. The probability that coal nitrogen content is reflected in the solvent-refined product was noted.     

Minor and trace metal analysis of a solvent-refined coal by flameless atomic absorption

Solvent-refined coal (SRC), THF¹-insoluble SRC, THF-soluble SRC and three of its ‘size-separated’ fractions have been analysed for eleven metallic elements via flameless atomic absorption spectroscopy. Prior to analysis each sample was wet ashed with equal quantities of concentrated H₂SO₄ and 30% H₂O₂. Matrix effects were compensated for by the method of standard additions and deuterium-arc background correction. Mg, Al, K and Fe were found in greatest concentration in all samples. The concentration of Pb and Cd was measurable only in THF-insoluble SRC.     

Trace metal distribution in fractions of solvent-refined coal by ICP-OES and implications regarding metal speciation

Separations of Amax solvent-refined coal according to its acid/base/neutral components and by selective elution from a silica column (SESC) to yield nine fractions have been carried-out. After ashing with H₂O₂-H₂SO₄, twenty metals (Mg, Al, P, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Mo, Cd, Sr, Zr, W, Hg and Ba) were analysed by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). A majority of elements (Zn, Cd, Hg, Cr, Mo, W, and Fe) were found concentrated in the acid fraction while Co, Ni and Cu preferred the neutral and base fraction. In the step gradient SESC fractions, the greatest concentration of metal was found in fractions that had been characterized as enriched with phenols.     

Characterization of organic fractions in solvent-refined coal by quantitative n.m.r. spectroscopy

A solvent-refined coal product obtained from Pittsburgh No. 8 coal has been preparatively separated into four sized fractions by gel permeation chromatography. Quantitative ¹H and ¹³C Fourier-transform nuclear-magnetic-resonance results for the separated fractions are reported along with elemental and molecular weight analysis data. Observed trends for several average molecular parameters for these fractions (e.g. $\text{(}\text{H}\text{C}\text{)}{}_{\mathrm{alp}}$, $\text{(}\text{H}\text{C}\text{)}{}_{\mathrm{aro}}$, etc.) are discussed. The absence of certain organic functional groups, such as carbonyls, is also noted.     

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.     

Coal liquefaction. 1. Further liquefaction of solvent-refined coal by controlled low-temperature air oxidation in quinoline

Low-temperature air autoxidation of SRC in quinoline followed by an ærobic thermolysis yields as much as 30% of low-molecular-weight (< 210) compounds. Preliminary autoxidation of the quinoline-soluble portion of a bituminous coal gave a significant yield of similar low-molecular-weight compounds. These are highly aromatic.     

Optimizing slurry separation in coal preparation

In processing slurry with cationic polyelectrolytes, the final concentration of the suspended particulates in the water beyond the slurry tank in the coal-preparation shop is no more than 10 mg/l. Consequently, this water may be reused in industrial systems.