Organic Sulfur In Coal Research Articles

95/04441 Study on chemical stability of organic sulfur in coal and its structure

95/04441 Study on chemical stability of organic sulfur in coal and its structure

95/01132 Chemical stability and structure of organic sulfur in coal

95/01132 Chemical stability and structure of organic sulfur in coal

STUDY ON CHEMICAL STABILITY OF ORGANIC SULFUR IN COAL AND ITS STRUCTURE*

ABSTRACT In this paper, two high-sulfur coals were selected from Yazhou and Donglin mines of China. Inorganic sulfur was completely removed first, then the tested samples were experimented under various conditions: hydrolysis, oxidation, reduction, and supercritical extraction with methanol. The change in organic sulfur was investigated. It was found that approximately 40-60% organic sulfur in coal was released at the temperature of 350°C. The removed organic sulfur was thioalcohol and thioether, while the remaining part in coal was thiophenic sulfur.

Speciation of organic sulfur in coal using sulfur L-edge X-ray absorption spectroscopy

Speciation of organic sulfur in coal using sulfur L-edge X-ray absorption spectroscopy

EFFECT OF FILTRATION TEMPERATURE ON ORGANIC SULFUR REMOVAL FROM COAL BY PERCHLOROETHYLENE COAL CLEANING PROCESS

Abstract The perchloroethylene extraction desulfurization process removes the organic sulfur in coal via a hybrid mechanism of solvent extraction and chemical reaction. The nature and extent of the reaction is controlled by the extraction time and temperature of operation. Although the extraction temperature is kept identical for all types of coals (120°C), the organosulfur extraction time still depends upon the type of coal. If the reaction mixture is left too long in the extraction environment, the intermediate labile sulfur released by the reaction forms cross-links with the organic matter in the macromolecule of coal. This is detrimental to the process efficiency. Constant temperature has to be maintained throughout the extraction, till coal is separated from the solvent. If not, the extracted labile sulfur re-enters the coal macromolecule to form inter-penetrating polymer networks with the organic matter in coal. In this paper, it has been established that the time required for separation and isother...

EFFECT OF PERCHLOROETHYLENE DESULFURIZATION OF COAL ON ITS HYDROCARBON CONTENT AND CALORIFIC VALUE

Most of the coal treatment processes involve changes in hydrocarbon content and calorific values of the treated coals. Depending upon the end-use of desulfurized coal, its hydrocarbon content as well as its calorific value and combustion efficiency are the key factors in determining the process efficiency and economics. The perchloroethylene coal cleaning process is capable of selectively removing the organic sulfur in coal. In this paper, the effect of the process on the calorific value and hydrocarbon content of coal has been studied. The effect on its hydrocarbon content was determined by comparing the ultimate analyses of raw and extracted coals. The calorific values were computed using Dulong formula

Oxidation of Dibenzothiophene Catalyzed by Hemoglobin and Other Hemoproteins in Various Aqueous-Organic Media

Biocatalytic oxidation of dibenzothiophene (a model of organic sulfur in coal) with hydrogen peroxide was investigated. It was found that various hemoproteins, both enzymic (e.g., horseradish peroxidase) and nonenzymic (e.g., bovine blood hemoglobin), readily oxidized dibensothiophene to its S-oxide and, to a minor extent, further to its S-dioxide (sulfone). This process catalyzed by hemoglobin (a slaughterhouse waste protein) was studied in a number of monophasic aqueousorganic mixtures. Although hemoglobin was competent as an oxidation catalyst even in nearly dry organic solvents (with protic, acidic solvents being optimal), the highest conversions were observed in predominantly aqueous media. The hemoglobin-catalyzed oxidation of dibenzothiophene at low concentrations of the protein stopped long before all the substrate was oxidized. This phenomenon was caused by inactivation of hemoglobin by hydrogen peroxide that destroyed the heme moiety. The maximal degree of the hemoglobin-catalyzed dibenzothiophene oxidation was predicted, and found, to be strongly dependent on the reaction medium composition.

Reduction of sulphur from polysulphidic model compounds by the hyperthermophilic archaebacterium Pyrococcus furiosus

Several polysulphidic model compounds were studied for their reducibility by a hyperthermophilic archaebacterium, Pyrococcus furiosus. Model compounds that may represent forms of organic sulphur in coal were selected for study including model compounds with bulky alkyl and aryl groups surrounding the sulphur atoms and polymeric polysulphides. P. furiosus reduced these organic polysulphides to hydrogen sulphide with varying efficiency. The use of complex model compounds may be more realistic than simple model compounds for evaluating the potential for microbial removal of organic sulphur from coal.

Desulfurization of single coal macerals

The main objective of this study is to investigate the desulfurization behavior of individual coal macerals. The sporinite and vitrinite macerals which contain most of the organic sulfur in coal are more reactive toward desulfurization processes than any of the other materials that were studied. They also give the highest desulfurization levels. Since they are more reactive than whole coals or floated samples, the other constituents in the coal matrix must reduce sulfur removals. This phenomenon has not been reported previously. It implies that the inertinite macerals may behave in a manner similar to activated charcoal and chemically absorb copious amounts of sulfur during the desulfurization processes. The practical result of this phenomenon is that selection of coals on the basis of maceral composition could be necessary to optimize thermal-chemical desulfurization.

Chemical and microbiological problems associated with research on the biodesulfurization of coal. A review

The study of microbial processes for the removal of organic and inorganic sulfur from coals is complicated by the lack of direct methods of measurement for organic sulfur content and the related incomplete understanding of the specific forms of organic sulfur in coal. In addition, the accessibility of specific chemical groups in the coal matrix to microorganisms and their enzymes is uncertain, raising questions about the nature and validity of model compound studies. Thus, interpretation of data from numerous efforts focussed on the microbial removal of inorganic and organic sulfur from coals remains controversial. The discussion here reviews recent developments in the chemical characterization of coal sulfur related to bioprocessing research and describes some recent efforts in involving sulfur transformation by hyperthermophilic archaebacteria.

Investigation of the molecular structure of organic sulfur in coal by XAFS spectroscopy

Investigation of the molecular structure of organic sulfur in coal by XAFS spectroscopy

Microbial leaching of sulfate from Illinois no. 6 coal

Abstract Coal which had been pre-treated to reduce the amount of pyritic sulfur was used in enrichment cultures to select heterotrophic bacteria capable of oxidizing the organic sulfur in coal. With the assumption that sulfate would be released upon the oxidation of thiophenic sulfur, sulfate concentrations in culture fluids were measured and used as the criterion to select cultures. Microbial cultures in coal slurries made with acidic media (pH 3.5) had sulfate concentrations that were comparable to sulfate concentrations in abiotic controls. Sulfate was probably leached from coal by the acidic conditions of the media and not by microbial activity. Microbial cultures in coal slurries made with media buffered near neutrality (pH 7) had sulfate concentrations that were greater than those of the abiotic controls. However, sulfate concentrations in these cultures were similar to sulfate concentrations in coal slurries made with either acidic culture media (pH 3.5) or acidic solutions (pH 1–pH 4). Even though microbial cultures at pH 7 released sulfate from coal, it appeared that this activity may have been due to the leaching of sulfate from coal and not due to the oxidation of organic sulfur.

Use of stable sulphur isotopes to monitor directly the behaviour of sulphur in coal during thermal desulphurization

A method has been developed using stable sulphur isotope analyses to monitor the behaviour of sulphur forms in a coal during thermal desulphurization. In this method, the natural stable isotopic composition of the pyritic and organic sulphur in coal is used as a tracer to follow their mobility during the desulphurization process. This tracer method is based on the fact that the isotopic compositions of pyritic and organic sulphur are significantly different in some coals. Isotopic results of pyrolysis experiments at temperatures ranging from 350 to 750 °C indicate that the sulphur released with the volatiles is predominantly organic sulphur. The pyritic sulphur is evolved in significant quantities only when pyrolysis temperatures exceed 500 °C. The presence of pyrite seems to have no effect on the amount of organic sulphur evolved during pyrolysis. The chemical and isotopic mass balances achieved from three different samples of the Herrin (No. 6) coal of the Illinois Basin demonstrate that this stable isotope tracer method is quantitative. The main disadvantage of this tracing technique is that not all coals contain isotopically distinct organic and pyritic sulphur.

Correlation between the δ34S of pyritic and organic sulfur in coal and oil shale

The δ 34S of pyritic ( Y) and organic ( X) sulfur in high-sulfur Illinois Basin coals and the Saline Zone of the Piceance Creek Basin, Colorado, U.S.A., oil shale of the Green River Formation exhibit a linear relationship ( Y = 1.16 X − 4.8; R 2 = 0.98). This relationship implies that a common mechanism resulted in the incorporation of sulfur in two different depositional settings. They were formed in an environment where bacterial sulfate reduction and plant assimilation were the two major pathways of sulfur incorporation and where dissolved sulfate concentration was high. Bacterial sulfate reduction has apparently produced large kinetic isotope fractionation effects in the high-sulfate-concentration environment. In contrast, low-sulfur coals from the Illinois Basin and the Leached and Mahogany Zones of the Piceance Creek were apparently formed in environments where the dissolved sulfate concentration was lower and where bacterial sulfate reduction, if it occurred, did not produce significant kinetic isotope fractionation.

Thermomagnetometry and evolved gas analysis in the identification of organic and pyritic sulphur in coal and oil shale

Potential difficulties of using a new TG/TM technique for measuring the pyrite content of coals that also contain siderite are discussed briefly. Direct measurement of the SO 2 evolved on heating pyrite in an oxidizing atmosphere is a possible alternative and this may also provide information on amounts of organic sulphur in the coal.

Direct measurement of organic sulphur in coal

A method of direct determination of the organic sulphur content of coal has been developed using the transmission electron microscope. An electron beam is focussed on a thinned section of coal and X-rays emitted from the elements in the volume irradiated by the electrons are measured by X-ray emission spectroscopic methods. Both the characteristic K α line of sulphur and the bremsstrahlung from the material in the irradiated volume are detected by a solid-state detector. An analytical method has been developed which uses these two measurements for a direct determination of the organic sulphur concentration. Minerals can easily be avoided since they are plainly seen by conventional electron microscope techniques. Several measurements of the organic sulphur concentration in coals have been made; they agree with the conventional chemical values reported for these coals. Of most importance, though, is the use of this technique to detect spatial variations of sulphur over small distances within the coal maceral.

Mild oxidations of coal: 1. Hydrogen peroxide oxidation

Mild oxidation of Pittsburgh bed coal was carried out to investigate the removal of organic sulphur. It was postulated that the organic sulphur in coal might first be oxidized to sulphonic acids and then removed through known desulphonation methods. The coal was oxidized with hydrogen peroxide or mixtures of hydrogen peroxide and acid. After oxidation, the coal was treated with water or phosphoric acid at reflux. Under the mild conditions used, coal oxidation led to slight changes in the organic sulphur content. The ensuing treatment of the oxidized coal with water or phosphoric acid again affected the organic sulphur content, generally decreasing the organic sulphur level. Pyritic sulphur removal varied considerably depending upon the reagent system and reaction conditions.

Automated determination of organic sulphur in coal: Use of scanning electron microscopy and energy-dispersive X-ray microanalysis

Scanning electron microscopy combined with energy-dispersive X-ray microanalysis in fully automated form was used for the determination of organic sulphur in coal. The values found by this technique are in good agreement with those found by the usual classical methods, provided the coal has a low content of pyrite. For coals high in pyrite, however, SEM/XRMA gives considerably lower values of organic sulphur. The discrepancy is probably due to the incomplete extraction of pyrite inclusions in the wet analysis leading to a low value for the pyrite content, and consequently, a high value for organic sulphur. Apart from primarily being a method for the determination of organic sulphur, the method presented affords additional information; for example, it may enable a differentiation to be made between a single coal sample and a blend of several types of coal.

Direct determination of organic sulphur in raw and chemically desulphurized coals

An electron beam technique has been developed for the direct determination of organic sulphur in coal, using a scanning electron microscope coupled with an energy-dispersive X-ray analysis system with quantitative data reduction capabilities. The direct measurement of organic sulphur is performed on a number of particles of the maceral vitrinite, previously located within the mounted coal sample by reflected light microscopy. The particles are first examined by SEM at ≈5000 × magnification to allow proper identification of most mineral inclusions and to avoid these areas during analysis. The X-rays generated from an area 3 μm in diameter are monitored quantitatively by EDX for sulphur and iron, as well as for calcium, aluminium and silicon. After ensuring that no other elements, indicating mineral matter, are present at the point of analysis, the sulphur value obtained is taken as a measure of the organic sulphur in coal. The results obtained by this technique also allow estimation of the intra- and inter-particle variation in the organic sulphur level. Statistical methods can be used to construct confidence bands about the mean sulphur levels and estimate standard deviations within and between particles. This permits evaluation of the precision of the analysis on a sample-by-sample basis and provides a measure of the heterogeneity of the coal. The SEM-EDX method has been applied to a large number of raw coals and coals chemically desulphurized by the Ames, PETC and Ledgemont oxydesulphurization processes, as well as the molten caustic (Gravimelt) process of TRW Systems Inc. The results of this direct technique agree fairly well with those of the ASTM procedure, for both raw and chemically processed coals, although for the latter the SEM values often show less desulphurization than the ASTM values.

Production of Acetylene Using a New Plasma Gasifier (III)

Using a new 100kW plasma gasifier with three torches, coal gasification was studied. The highest acetylene yield attained so far was 59g/kWh. At the same time, a considerable amount of plasma carbon black was obtained as byproduct.Fundamental data were collected to find the applications of the plasma carbon black. Heating loss, iodine adsorption number, DBP absorption number, ash content, etc. were examined in accordance with JIS (K 6221). Inorganic substance, sulfur, adsorbed oil, and volatile material in the carbon black were analyzed. Also, the separation of the plasma carbon black was tried.One of the peculiarities of the carbon black was that the volatile content was more than 15% including adsorbed oil. Another was its relatively high ash content even in the case of the separated carbon black. It was estimated that a considerable amount of the organic sulfur in coal was converted into inorganic sulfur, and resided in the inner part of deposited carbon black in the form of metal sulfide. In order to find commercial applications of the plasma carbon black, it will be necessary to develop a dry separation process and a practical distillation process.