Carbon-sulphur surface complexes on charcoal

Interaction of charcoal with sulphur, hydrogen sulphide, carbon disulphide and sulphur dioxide at 600°C results in appreciable fixation of sulphur. The amount fixed varies with the nature of the reagent used and, for a given reagent, it depends not so much on surface area as on oxygen and hydrogen contents, extent of surface unsaturation and pore structure of charcoal. There are indications that sulphur is fixed partly by addition at the unsaturated sites and partly by substitution through interaction with certain oxygen groups which come off as carbon monoxide on high temperature evacuation. The carbon-sulphur complex, resulting from fixation of sulphur on charcoal, is highly stable. The products, when heated in a current of nitrogen, evolve largely hydrogen sulphide and carbon disulphide but the entire amount cannot be recovered even at 1200°C. The amount of sulphur recovered as sulphate ion on prolonged treatment with excess of hot concentrated nitric acid varies with the nature of the reagent used in the fixation of sulphur. The results give some indication of the possible nature of sulphur-containing groups and structures formed. The products catalyse sodium azide-iodine reaction to varying extents. The adsorption isotherms of water, methanol and benzene indicate considerable narrowing down of capillary pores of charcoal, as a result of fixation of sulphur.     

Detection of natural oxidation of coking coal by TG-FTIR—mechanistic implications

The natural oxidation/weathering of coal continues to be a subject of interest both scientifically and industrially, in part due to the complexity of the molecular processes at hand as well as to the commercial implications involved. It is widely recognized that coking can be adversely affected by weathering whereas, combustion processes appear to be enhanced as result of oxidation.Combustion techniques are commonly used in the analysis of coal, and organic compounds in general, for the determination of elemental hydrogen, carbon and nitrogen. For oxygen, the method in common practice involves the determination by difference from directly determined values for moisture, ash, sulphur, hydrogen, carbon and nitrogen. This has led us to consider the use of thermogravimetry coupled to gas analysis by infrared spectroscopy (TG-FTIR) to measure organic oxygen in coal directly. Although this technique, developed by Solomon and coworkers, has been extensively used by our group and others, it appears not to have been considered for this particular purpose.Recently, we have shown that TG-FTIR is capable of measuring all the organic oxygen in both fresh and oxidized coal by simultaneous measurement of the three main oxygen-containing gases H₂O, CO and CO₂ evolved during rapid pyrolysis. This gives us a way of measuring quantitatively the oxygen introduced into the coal matrix during oxidation and at least a partial capability of establishing oxygen speciation.We have found, using TG-FTIR, that the early stages of coal oxidation results in the appearance of O-containing functional groups not present in the original coal. The nature of these functional groups is directly related to the oxidation reaction mechanism. These results will be presented and discussed in detail.     

表面活性元素影响钢液脱氮动力学

在４０ｋｇ真空感应炉上进行表面活性元素（氧、硫）影响钢液脱氮动力学的研究，实验采用真空碳脱氧工艺，研究在不同的硫含量条件下，钢中脱氧和脱氮的相互关系．研究结果表明：（１）当钢中硫含量较低时，脱氮速率很快，随着硫含量的逐步增加，脱氮速率相应降低．（２）钢中硫含量较低时，脱氮速率快于脱氧速率；而当硫含量较高时，脱氧速率大于脱氮速率．（３）真空碳脱氧过程中，脱碳、脱氧速率与硫含量关系不大．     

The electrochemistry of gases at metallized membrane electrodes

The electrochemistry of four gases, hydrogen, nitric oxide, nitrogen dioxide and sulphur dioxide at metallized membrane electrodes is reported. It is shown that, as was the case with oxygen and carbon monoxide, it is possible by suitable choice of electrode potential, electrode metal and electrolyte to find conditions where the currents are determined by the rate of diffusion of the electroactive species through the membrane. The experimental data are used to estimate values for the diffusion coefficient and solubility of the gases in the membrane material and the relevance to the design of environmental monitors of these experiments with high partial pressures of gases is discussed.     

Molar group contributions to the heat of combustion

Experimental results for the gross heat of combustion of over 140 commercial and developmental polymers and small molecules of known chemical structure were used to derive additive molar group contributions to the heat of combustion. The materials examined contained carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, chlorine, fluorine and silicon in linear, branched and cyclic structures. Values for the molar group contributions were summed and divided by the molecular weight of the molecule or polymer repeat unit to yield the gross heat of combustion as determined by oxygen bomb calorimetry. This new method provides an accurate single step method for calculating the heat of combustion. The average relative error of the calculated gross heats of combustion is 2.8%. Published in 2002 by John Wiley & Sons, Ltd.     

Material balance in coal. 2. Oxygen determination and stoichiometry of 33 coals

Chemical coal analysis can be supplemented by the determination of oxygen in high- and low-temperature ash, in coal as received, and in dried coal at 105 °C. The rapid method utilizes fast-neutron activation. The reaction ¹⁶O(np)¹⁶N and counting of the 6.1 and 7.1 MeV gamma radiation of 7.3 s half-life are used. A specially designed dual transfer and simultaneous counting system gives very accurate results. Oxygen in 33 coals ranging from lignite to low-volatile bituminous coal has been determined and results are compared with ‘oxygen by difference’. Considerable discrepancies are observed. Better stoichiometric results are obtained if oxygen in coal ash, in wet coal and the dried coal is determined. This permits the estimation of the true material balances in fuels using data of the ultimate and the proximate coal analysis. The oxygen determination provides the coal chemist with an accurate basis and can be used to rank coal. The summation of the percent of carbon, nitrogen, hydrogen, sulphur and oxygen becomes more meaningful, some errors can be detected, and the state of completeness of coal analysis can be evaluated. Total sulphur can be estimated and oxidation effects during drying can be detected. These affect the moisture determination. It appears that after more data have been collected the interpretation of solid fuel analyses may be facilitated and will be made stoichiometrically more meaningful; the ranks of different coals and other properties such as $\text{O}\text{C}$ plots will become better defined. This approach may help the coal industry in general to quantize further the energy generating processes. It may be possible to simplify the present time-consuming methods of coal analysis. A brief overview of coal analysis methods in relation to direct determination of oxygen is given³.     

Sulphur transformation and removal for Western Kentucky coals

Inhibition isotherms were measured for Western Kentucky No.9 coal. Crushed and sieved coal (?25 + 140 U.S. mesh) was fluidized in 10-g batches in a 22-mm i.d. quartz reactor up to a temperature of 870 °C. The release of hydrogen sulphide during heatup under nitrogen and at the run temperature (usually 1–2 h) under the same gas (pyrolysis), hydrogen, or hydrogen/hydrogen sulphide mixtures was followed by gas chromatography. The residue or char was analysed for pyritic, organic, sulphide, sulphate, and total sulphur. Inhibition isotherms, which are pseudo-equilibria between sulphur in the char and gaseous hydrogen sulphide, were measured at 600 and 870 °C. At the lower temperature the isotherm was found to be independent of the hydrogen sulphide concentration in the gas stream and the char sulphur content remained constant at 2.6%. At 870 °C the sulphur content of the char was greater than that of the original coal when gas mixtures of 1, 3, and 6% hydrogen sulphide in hydrogen were used, indicating the necessity of maintaining low hydrogen sulphide concentration for sulphur removal. In pure hydrogen, sulphur removal increased continuously from 47% at 600 °C to 84% at 870 °C. For pyrolysis under nitrogen, sulphur removal was 40% at 600 °C and increased to 59% at 740 °C. No further removal occurred above this temperature up to 870 °C. In addition to the inhibition isotherms, sulphur-form transformation diagrams were constructed for coal treated with nitrogen, hydrogen, and hydrogen/hydrogen sulphide mixtures. Pyritic sulphur, which comprised 40% of the sulphur in the original coal, was completely converted to ferrous sulphide at 600 °C in hydrogen and 740 °C in nitrogen. At 870 °C the sulphur content of the char produced under hydrogen was 1.1% made up of 48.4% ferrous sulphide, 43.4% organic sulphur, and 8.2% sulphate.     

The role of heteroatoms in carbon nanotubes for hydrogen storage

Carbon materials should have specific centers for hydrogen adsorption/absorption. The Universal Force Field and Density Functional Theory have been used to find the role of heteroatom substitution in carbon nanotubes as an activator. The effect of various heteroatoms like nitrogen, phosphorus, sulphur and boron for hydrogen activation and their geometrical positions has been identified for easy hydrogenation. This will be one of the possible centers where hydrogen adsorption/absorption is initiated.     

The influence of nitric acid oxidation of low rank coal and its impact on coal structure☆

FT-i.r. was used to examine the behaviour of a Spanish lignite during its oxidative treatment with nitric acid with a view to assessing the different forms of sulphur reduction and the changes produced in the coal structure, as a result of the action of the reagent. Inorganic sulphur decreases rapidly and practically disappears, even under mild attack conditions (50 °C, 20% acid concentration). At first, organic sulphur undergoes a rapid decrease but more energetic conditions are required to maintain the reduction. Reduction may even reach 53% under such conditions.Unfortunately, energetic attacks (90 °C) lead to a high-level of coal organic matter solubilization and an increase in oxygen content. Basically, the oxygen appears as carbonyl group within the desulphurized coal.The nitric acid causes effective nitration of the coal, the nitrogen being incorporated especially as aromatic nitrogen. The substitution is easily produced (50 °C) when there are two adjacent aromatic hydrogens per ring. The isolated hydrogens in aryl- or polycyclic aromatic structures, are more resistant to attack under mild conditions but not so at 90 °C. As nitration progresses, more electrophilic molecules appear and aliphatic hydrogen tends to increase after initially decreasing under mild attack and increases more so under more energetic condition. This aliphatic hydrogen compensates for the decrease in aromatic hydrogen.     

Structural aspects of chemisorption at Cu(110) revealed at the atomic level

We illustrate the impact that scanning tunnelling microscopy (STM) has made on our understanding of chemisorption and catalysis at metal surfaces at the atomic level by considering four examples where information from surface sensitive techniques was also available. The advantages of STM and the limitations of some of the other experimental methods are discussed. (1) Through a combination of STM and X-ray photoelectron spectroscopy (XPS) we have established that a number of distinct oxygen chemisorbed states can exist at a Cu(110) surface. These are metastable and temperature dependent. Furthermore, the presence of chemisorbed sulphur is shown to promote a specific oxygen state – isolated oxygen strings – which are likely to be more chemically reactive than the oxygen overlayer present at Cu(110). In this sense the sulphur is a structural promoter. (2) The oxidation of ammonia under ammonia-rich conditions results in the growth of imide (NH) strings at a Cu(110) surface and this has been followed quantitatively by STM. The reactive surface oxygen state participates in an oxydehydrogenation reaction generating NH-radical species which undergo surface diffusion and result in string growth. (3) Nitric oxide dissociates at Cu(110) to generate a two-phase system of chemisorbed nitrogen and oxygen adatoms. The oxygen is present in a well ordered (2 × 1) structure and the nitrogen in a (3 × 2) structure. The limitations of an earlier LEED study are discussed. (4) Structural aspects of chemisorbed sulphur generated by the dissociative chemisorption of hydrogen sulphide and methyl mercaptan are discussed. In the latter case carbon–sulphur bond cleavage results in the formation of a sulphide overlayer at 450 K with complete removal of carbon as desorbed hydrocarbons. Various sulphur structures have been delineated over a wide temperature range. This revised version was published online in August 2006 with corrections to the Cover Date.     

Headspace gas analysis of salad oils by mass spectrometry

A mass spectrometer was used to analyze the content of hydrogen, nitrogen, oxygen, carbon dioxide and argon in headspace gas of commercially packaged soybean, cottonseed and corn salad oils. A leakproof sampling system was designed to avoid air contamination and obtain a representative headspace gas sample. Some edible oils are packaged under pure nitrogen, whereas other samples contained various amounts of oxygen in the headspace gas. The presence or absence of argon in the headspace gas indicates that some oils are packaged with pure nitrogen and others with nitrogen obtained by controlled burning of hydrocarbons to remove all the oxygen in air. The presence of hydrogen in some samples where argon was also present suggested that catalytic purifiers were used to remove the last traces of oxygen and to ensure pure nitrogen for packaging oils. The decrease in oxygen of oils bottled in air was followed during storage at room and at elevated temperatures. No. Market. and Nutr. Res. Div., ARS, USDA.     

Hetero-atoms as activation centers for hydrogen absorption in carbon nanotubes

Carbon materials should have specific centers for hydrogen adsorption/absorption. The role of heteroatom substitution in carbon nanotubes as an activator has been identified by Density Functional Theory. The effect of various hetero-atoms like nitrogen, phosphorus, sulphur and boron for hydrogen activation and their geometrical positions has been recognized as the one of the possible reasons for easy hydrogenation. Experimentally, nitrogen and boron containing carbon nanotubes have been synthesized by using template method. The hydrogen absorption capacity of these materials has been evaluated. It is shown that, there is a need to stabilize nitrogen in the carbon nanotube framework for reproducible hydrogen uptake. In the case of boron containing carbon nanotubes, two different chemical environment of boron facilitates hydrogen interaction. They exhibit a maximum of 2 wt.% of hydrogen storage capacity at 80 bar and 300 K. This configuration has a bearing in hydrogen sorption characteristics.     

X-ray photoelectron spectroscopic investigation of coal

X-ray photoelectron spectroscopy (XPS) has been used to study the carbon, oxygen and sulphur content of several coking coals, a series of sink—float fractions from a high-volatile coking coal, and several inorganic minerals that are commonly found in coals. Single carbon and oxygen peaks were obtained that corresponded to carbon 1s orbital and oxygen 1s orbital electron binding energies which are expressed in units of electron volts (eV). Two sulphur 2p (S 2p) peaks were found. The 169–171 eV S 2p peak corresponded to the sulphates resulting from the oxidation of pyrite (FeS₂), while the 163–164 eV S 2p peak was assigned to the iron sulphide compounds such as pyrite or marcasite. No separate organic sulphur peaks were found for coal, because the majority of the organic sulphur peaks are probably overlapped by the inorganic sulphide line at 163–164 eV. The total carbon and sulphur determined using the XPS peak height correlated with the chemical analysis, although the accuracy of the XPS determinations seems to be lower. A possible direct quantitative method for determining the organic sulphur in coal by XPS is discussed.     

Heavy media separation of SRC-II feedstocks: 1. Effect on coal properties

The objectives of this investigation were to determine the effects of coal preparation on the properties of Run-of-Mine (ROM) and washed Powhatan and Ireland Mine coals and to assess the potential effects on SRC-II liquefaction yields. The effect of washing on the two coals was found to be quite similar. For both coals, the properties were altered more significantly by changes in separation media gravity than by changes in the coal size. The elemental composition of the Powhatan and Ireland washed coals was correlated with carbon content. It was shown that both the hydrogen and oxygen levels increased linearly with the carbon content of the coal samples. However, the $\text{H}\text{C}$ and $\text{O}\text{C}$ ratios were not changed significantly by coal cleaning. Only small variations in the nitrogen and organic sulphur levels were observed while the sulphate sulphur and chlorine levels were not affected by coal cleaning. The major impact of the coal cleaning was to reduce the pyritic sulphur (and hence the total sulphur) content of the coals. Most of the pyritic sulphur was shifted into the middling coal and refuse fractions while the clean coals had much lower contents and the pyritic sulphur level decreased with increasing carbon content. Coal cleaning did not significantly alter the maceral contents of vitrinite, exinite, total reactive macerals (TRM), or the reflectance of vitrinite; all these parameters varied over a very narrow range, probably within the precision of the measurement technique.     

Thermodynamics of the transformations of oxygen- and sulphur-containing functional groups during coal liquefaction in hydrogen and hydrogen donor

The thermodynamic equilibrium constants for the reduction of oxygen and sulphur functional groups in hydrogen and in tetralin were calculated for the temperature range 327–527 °C. All the reduction reactions of the oxygen groups are thermodynamically favourable both with hydrogen and with tetralin. The reduction reactions of all the sulphur functional groups in tetralin are favourable except for the reductions of thiophenes below 407 °C. However, molecular hydrogen cannot reduce thiophenes or aryl sulphides below about 590 °C. Reactions in which oxygen from water is captured by the organic matrix are not favourable reactions; however, capturing of sulphur from hydrogen sulphide or alkyl thiols can occur in this range of temperatures. The most stable products are condensed thiophenic structures.     

Determination of hydrogen content, gross heat of combustion, and net heat of combustion of diesel fuel using FTIR spectroscopy and multivariate calibration

The precise determination of the heat of combustion is of great importance for trading automotive diesel. The net heat of combustion (NHC) of fuel is related to the hydrogen elemental composition of fuel as obtained by elemental analysis. Heat of combustion expressed as gross heat of combustion (GHC) and net heat of combustion (NHC) have been predicted from data obtained by proximate analysis (density, ash, water and sulphur content) (ASTM D4868). GHC was obtained using bomb calorimetry (ASTM D240). The results of ASTM D4868 and ASTM D240 were found in good agreement. GHC and NHC fall within the relatively narrow range 45.24-46.08 and 41.91-43.27 MJ/kg, respectively. GHCs of tested diesel samples are, on average, about 7% greater than NHCs. The present paper also present a simple analytical method for determination of hydrogen content, GHC, and NHC of automotive diesel fuel using FTIR spectroscopy and partial-least squares calibration (PLS-1). PLS-1 had a high prediction power for prediction of hydrogen from FTIR spectra of diesel samples. The spectral ranges used in calibration were 400-670 and 2846-2970 cm⁻¹. On the other hand, classical least squares calibration (CLS) was found invalid for determination of hydrogen content in diesel. The results obtained by the proposed analytical method were almost to those obtained by ASTM D4868 and ASTM D240. PLS-1 method, offers a simple and reliable analytical method for quantification of hydrogen content in diesel samples without running expensive analysis like those carried out using carbon, hydrogen, and nitrogen (CHN) instruments.     

Hydrogen sulphide — air equilibria under claus furnace conditions

Equilibrium compositions of mixtures resulting from reactions between hydrogen sulphide and air at atmospheric pressure were calculated for temperatures and O₂/H₂S ratios ranging from 600 to 2000°K and 0.05 to 1.0, respectively. Forty-four compounds containing nitrogen, hydrogen, oxygen and sulphur were assumed to be formed but only 25 had concentrations exceeding 0.1 ppm. These compounds should not, as in previous studies, be omitted from equilibrium calculations. Sulphur yields are shown to be increased by approximately 10% if O₂/H₂S ratios less than stoichiometric are used. Reasons for this and implications for Claus plant operation are provided.     

Rapid and simple determination by combustion of total sulphur in coal

A simple and rapid procedure for determining total sulphur in coal is described. A stoichiometric recovery from a wide variety of coal types containing 0.1–8 wt% sulphur is obtained by ignition at 1160–1180 °C in the commonly available resistance-type tube furnaces such as those used for carbon determinations. The procedure is accurate and uses readily available materials. It is particularly rapid as it consists of only two steps: sample weighing and mixing with a solid oxidant and combustion in a furnace for 7.5–9 min in an alternating nitrogen-oxygen stream with an accompanying titration. The sample and oxidant (vanadium pentoxide and chromic oxide) are heated to ≈1170 °C, any sulphur trioxide produced is reduced to sulphur dioxide by copper heated to near its melting point and chlorine is removed by a hot aluminium gauze plug. To ensure complete recovery of sulphur, oxygen is introduced in brief cycles into the nitrogen carrier flow system. The resulting sulphur dioxide is absorbed in perchloric acid solution and titrated with potassium iodate.     

Activated carbon catalyst for selective oxidation of hydrogen sulphide: On the influence of pore structure, surface characteristics, and catalytically-active nitrogen

The catalytic oxidation of hydrogen sulphide (H₂S) on various activated carbon materials was studied. The effects of pore structure, surface characteristics, and nitrogen content on the activity and selectivity of the carbons towards oxidation of H₂S were investigated. It was found that a high volume of both micropores and small mesopores, in combination with a relatively narrow pore size distribution, were crucial for the retention of sulphur dioxide (SO₂), a by-product of H₂S oxidation. For the retention of carbonyl sulphide (COS), another H₂S oxidation by-product, high surface reactivity with a significant amount of basic groups were found to be important. The only carbon with all these characteristics, and consequently the carbon that was able to retain both H₂S and COS for an extended period of time, was an experimental product, “WSC”. This carbon was found to be superior to the other carbons studied, exhibiting high activity and selectivity for oxidation of H₂S to sulphur. H₂S breakthrough capacities and selectivity values of the carbons were found to be dependent on the nitrogen content of the carbons. In a hydrogen stream, carbons possessing the highest nitrogen contents exhibited the greatest H₂S breakthrough capacities but, at the same time, the lowest selectivity with respect to sulphur formation. In reformate streams, the maximum breakthrough capacity and greatest selectivity were exhibited by carbons with a nitrogen content of about 1-1.5 wt%.     

Catalytic combustion of gasified biomass: poisoning by sulphur in the feed

The influence of sulphur on the catalytic combustion of gasified biomass for gas turbine applications has been studied over precious metal and metal oxide based catalysts, namely Pd/LaAl₁₁O₁₈, Pt/LaAl₁₁O₁₈, Pt/La_0.5Ba_0.5Mn_0.5Fe_0.5Al₁₁O₁₉, La_0.5Ba_0.5Mn_0.5Fe_0.5Al₁₁O₁₉ and LaMnAl₁₁O₁₉. The samples were washcoated on cordierite monoliths and tested in a bench-scale reactor with a synthetic low-heating value fuel mixed with air. The fuel gas, that resembles the gas from air-blown fluidised bed gasification of wood, was composed of hydrogen, carbon monoxide, methane, ethene, carbon dioxide, water and nitrogen. Different concentrations of hydrogen sulphide as well as sulphur dioxide were added to the fuel gas. The results show that all samples were deactivated to some extent by addition of sulphur, although poisoning of the catalytic combustion for each fuel component varied depending both on the active phase and on the support and generally was reversible. The palladium catalyst was severely deactivated for combustion of methane, although activity for carbon monoxide and hydrogen was almost maintained. Platinum catalysts were more severely poisoned for carbon monoxide and hydrogen, but not for methane. Metal oxide catalysts were severely deactivated for all fuel components, especially for carbon monoxide, and the La_0.5Ba_0.5Mn_0.5Fe_0.5Al₁₁O₁₉-sample was irreversibly poisoned. The samples were also characterised by BET, XRD, ICP, SEM–EDX, XPS and SIMS.