William H. Calkins

The chemical forms of sulfur in coal : a review

Abstract The sulfur in coal exists in inorganic and organic forms. The inorganic forms are usually sulfides and sulfates, with pyrite the major inorganic sulfur contaminant in most coals. Analytical methods are available for determining these inorganic sulfur components, and various commercial processes exist for the removal of much of the inorganic sulfur from coal. The organic sulfur structures in coals are mainly components of the macromolecular structures of the coal and are not readily separated and analysed without destruction of the macromolecular network. A number of analytical methods have been developed for approximating the sulfur functional group compositions of coals. Some of these are destructive tests depending on pyrolysis or catalytic reduction to H 2 S or oxidation to SO 2 . However various non-destructive X-ray methods are now available which measure sulfur types (aliphatic, aromatic or thiophenic) directly. The organic sulfur components can be broadly divided into aliphatic and aromatic or heterocyclic sulfur structures. The aliphatic types are thermally less stable, form H 2 S on heating or pyrolysis, and are converted at least in part to the more stable heterocyclic structures. The heterocyclic (usually thiophenic forms) vary from single-ring to at least six-ring structures, and often also contain nitrogen and/or oxygen heteroatoms. Many of the heterocyclic sulfur structures contain alkyl substituents of various sizes and complexity. Aromatic sulfides and disulfides are present in high-sulfur coals, but usually in small amounts compared with the heterocyclic sulfur compounds. Low sulfur coals derive their sulfur mainly from the sulfur components in the coal-forming plants. High-sulfur coals, however, are now known to derive most of their sulfur from reduction of sulfate ions to H 2 S in sea or brackish water in the coal beds by microbial processes. The H 2 S is chemically incorporated into the peat during diagenesis. The H 2 S also reacts with ferric ions in the water to produce pyrite in the coal. The mineral sulfur components can be removed or reduced by commercial methods of coal washing, flotation and oil agglomeration. Despite a great deal of research and development, no economically practical processes exist for the chemical removal of all the major organic sulfur components of coal. The aliphatic sulfur structures can be reacted with very strong bases, and the heterocyclic sulfur structures react selectively with single-electron-transfer reagents such as potassium naphthalenide. Certain microorganisms have been shown to consume or convert selectively some of the sulfur components of coal.

Comparison of pyrolytic and x-ray spectroscopic methods for determining organic sulfur species in coal

Publisher Summary This chapter presents the comparison of pyrolytic and X-ray spectroscopic methods for determining organic sulfur species in coal. It presents a few pyrolysis experiments that were conducted at 625–930°C with 105–149 μm fractions in the continuous flow pyrolyze. The coal particles were entrained into a nitrogen stream in the coal feeder and were carried over into the fluidized sand bed at various flash pyrolysis temperatures. X-ray photoelectron spectroscopy spectra were taken on a Vacuum Generator ESCA Lab System using MgK radiation. These spectra were interpreted by using a curve resolution method. The chapter illustrates the comparative results for aliphatic sulfur content on five low pyrite coals run by the pyrolysis and X-ray methods, showing total sulfur and organic sulfur contents and the maf carbon contents as a measure of rank. It is apparent that the pyrolysis values fairly closely track those of the X-ray measurements as far as the aliphatic sulfur contents are concerned.

Distillation of liquid fuels by thermogravimetry

In this paper, design and operation of a custom-built thermogravimetric apparatus for the distillation of liquid fuels are reported. Using a sensitive balance with scale of 0.001 g and ASTM distillation glassware, several petroleum and petroleum-derived samples have been analyzed by the thermogravimetric distillation method. When the ASTM distillation glassware is replaced by a micro-scale unit, sample size could be reduced from 100 g to 5-10 g. A computer program has been developed to transfer the data into a distillation plot, e.g. Weight Percent Distilled vs. Boiling Point. It also generates a report on the characteristic distillation parameters, such as, IBP (Initial Boiling Point), FBP (Final Boiling Point), and boiling point at 50 wt% distilled. Comparison of the boiling point distributions determined by TG (thermogravimetry) with those by SimDis GC (Simulated-Distillation Gas Chromatography) on two liquid fuel samples (i.e. a decanted oil and a filtered crude oil) are also discussed in this paper.

Short Contact Time Direct Coal Liquefaction Using a Novel Batch Reactor

The primary objective of this research is to optimize the design and operation of the bench scale batch reactor (SCTBR) for studying direct coal liquefaction at short contact times (.01 to 10 minutes or longer). Additional objectives are to study the kinetics of direct coal liquefaction particularly at short reaction times and to investigate the role of organic oxygen components of coal and their reaction pathways during coal liquefaction. Many of those objectives have already been achieved. This quarterly report discusses further kinetic studies of the liquefaction in tetralin of a Montana Lignite, Wyodak-Anderson subbituminous coal, Illinois #6 hv bituminous coal, Pittsburgh #8 hv bituminous coals, and Pocohontas lV bituminous coal at short contact times. All of these coals showed a distinct extraction stage. Further work has also been done to attempt to clarify the role of the liquefaction solvent in the direct liquefaction process.

Short Contact Time Direct Coal Liquefactionn Using a Novel Batch Reactor. Quarterly Report. May 16 - August 15, 1996

The objective of this research is to optimize the design and operation of the bench scale batch reactor (SCTBR) for studying direct coal liquefaction at short contact times (.01 to 10 minutes or longer). Additional objectives are to study the kinetics of direct coal liquefaction particularly at short reaction times and to investigate the role of organic oxygen components of coal and their reaction pathways during coal liquefaction. Many of those objectives have already been achieved. This quarterly report discusses further kinetic studies of the liquefaction of Illinois #6 bituminous coal, Wyodak-Anderson subbituminous coal, and Pittsburgh #8 bituminous coal. The thermodynamic characteristics of the extraction stage at the start of the liquefaction process in the liquefaction of Illinois #6 coal is also discussed. Further work has also been done to attempt to clarify the role of the liquefaction solvent in the direct liquefaction process.

Kinetics of thermal and catalyzed coal liquefaction at very short reaction times using a novel batch reactor and thermogravimetric analysis

Publisher Summary This chapter discusses the kinetics of thermal and catalyzed coal liquefaction using a batch reactor and thermogravimetric analysis. Coal liquefaction consists of an initial rapid extraction of material soluble in tetralin and an induction period followed by the slow breakdown of the coal structure. As the temperature increases, the amount of extraction increases and the induction period becomes shorter. The volatile matter of the coal is removed. Some of the coal structure is converted to coal liquids. The formation of fixed carbon, which is a precursor to the retrograde processes, becomes more important as the temperature increases. The use of a known hydrogenation catalyst increases the coal liquefaction rate and yield and reduces the formation of the fixed carbon. In the absence of an added catalyst, the mineral matter in the coal catalyzes coal liquefaction in the presence of hydrogen. The pyrite in the coal appears to be a weak catalyst for the reaction.

Use of a novel short contact time batch reactor and thermogravimetric analysis to follow the conversion of coal-derived resids during hydroprocessing

The conversion of two coal-derived nondistillable residua (resids) in tetralin during hydroprocessing has been examined. A novel laboratory scale batch reactor capable of operation up to 450°C and 17 MPa (2500 psi) under well-defined contact times from a few seconds to 30 min or longer was used. Thermogravimetric analyses, augmented by gas chromatography and gas chromatography/mass spectrometry, were used to follow the course of the conversion. Two resids, one derived from Wyodak subbituminous coal and another from Pittsburgh bituminous coal, were found to differ in their reactivity toward conversion to soluble or lower boiling materials. In the absence of a catalyst, the insoluble resids became solubilized in tetralin to some degree. However, even at long reaction times and high temperatures there was no indication of a breakdown in molecular weight or molecular structure as shown by thermogravimetric analysis and laser desorption high resolution mass spectrometry. In the presence of a presulfided Ni/Mo on alumina catalyst there was a much higher degree of solubilization and a definite indication of molecular breakdown