摘要:

Coal is one of the carbonaceous materials which, under certain conditions, can combust spontaneously as a result of its oxidation with atmospheric oxygen. Coal oxidation is an irreversible exothermic reaction and its rate increases with temperature. In mines or in storage, the deficiency of the heat dissipation capacity of the coal bulk with respect to its heat generation capacity can result in heat accumulation which subsequently leads to higher oxidation rates due to higher temperatures. This process, if not averted with appropriate action, results in the spontaneous combustion of the coal.

ISSN:0884-3759    

DOI:10.1080/08843759508947726

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Oxidation of asphalt causes the degradation and failure of asphalt pavement. Due to the molecular complexity and relatively high molecular weight of asphalt, the oxidation mechanism is complicated by the interactions among the molecules of different types. To minimize the interactions, the asphalt sample was chromatographically separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes. These Corbett fractions were then oxidized under ultraviolet irradiation. Fourier-transform infrared spectroscopy was used to analyze the structural changes of the Corbett fractions during photooxidation. All Corbett fractions have shown significant spectral changes in the region of 3500 − 3100 cm−1characterized the stretching vibrations of hydroxyl or nitrogen-hydrogen groups, the peak around 1700 cm−1featured carbonyl groups, and in the region of 1320 − 1000 cm−1characterized the formation of sulfur-containing functional groups. Strong evidence has shown that sulfates are produced in the oxidation of asphalt. The formation of sulfates provides an essential explanation for the deterioration of asphalt pavement.

ISSN:0884-3759    

DOI:10.1080/08843759508947727

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Due to environmental constraints, sulfur content of diesel fuel has been restricted to very low levels (500 ppm maximum) in many countries. As a result, a greater emphasis has been placed in recent years on the development of catalysts and processes for deep desulfurization of diesel blending streams to produce low sulfur diesel fuel. In the present work we have compared the performance of a conventional Co-Mo catalyst with that of high metal loading Co-Mo and Ni-Mo catalysts in deep desulfurization of Kuwait atmospheric gas oil. The tests were carried out in a fixed bed reactor unit using 75 ml of catalyst under the conditions: P=32 bar; LHSV = 4h−1; H2/oil ratio = 100 ml/ml; temperature range = 330 − 390°C. HDS activity of the high molybdenum Co-Mo catalyst was superior to that of the conventional Co-Mo hydrotreating catalyst. High metal loading Co-Mo/Al2O3catalyst also showed a substantially higher HDS activity than the Ni-Mo/Al2O3catalyst containing a similar high metal loading. The unreacted sulfur compounds remaining in the product after high severity hydrotreating were identified as dibenzothiophenes with alkyl substituents next to the sulfur atom. The desulfiirization of such low reactive alkyl dibenzothiophenes was found to occur at a substantially lower temperature over the high metal loading Co-Mo catalyst compared with the conventional Co-Mo catalyst. The results have been explained on the basis of the stacking and dispersion of MoS2slabs as well as in terms of the nature of the sulfur vacancies in the MoS2layers in these catalyst systems.

ISSN:0884-3759    

DOI:10.1080/08843759508947728

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Mass spectrometry (MS) of the porphyrin fraction of a demetallated shale oil from the LLNL Hot-Recycled-Solids retorting process exhibited homologous series of C25to C33(C28maximum) for etio and C26to C36(C30maximum) for DPEP (isocyclic) porphyrins, respectively. The sum of intensities after baseline correction yielded a ΣDPEP/Σetio ratio of 1/1. The petroporphyrin fraction was prepared by demetallation of the whole shale oil using methane sulfonic acid followed by isolation which involved extraction and purification by alumina chromatography. MS examination of silica purified fractions showed another type of homologous series, tentatively assigned as tetrahydrobenzo-DPEP por-phyrin. MS examination of porphyrin fractions isolated by alumina or alumina/silica chromatography without demetallation indicated Ni(etio) and Ni(DPEP) (isocyclic) porphyrins were observed with the same homologous series as seen in the demetallated fraction.

ISSN:0884-3759    

DOI:10.1080/08843759508947729

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Asphaltene onset concentration and bulk deposition were measured for a typical live reservoir oil titrated withn-C6H14,n-C5H12,n-C4H10, C3H8, C2H6, CH4and CO2at 100° C (212 ° F) and 29.9 MPa (4340 psia). The concentration of titrant at asphaltene onset was observed to decrease approximately in a linear fashion with decreasing molecular weight of the paraffinic solvent; CH4did not induce any asphaltene precipitation. Bulk deposition experiments were performed using a solvent: oil volume ratio of 10:1; the results indicated that the weight percent of asphaltenes precipitated increased exponentially with decreasing molecular weight of the paraffinic solvents. More importantly, the asphaltene molecular weight showed a maximum forn-C4H10precipitated asphaltenes. Possible explanations for this unusual result are presented.

ISSN:0884-3759    

DOI:10.1080/08843759508947730

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A two step process of organorefining (successive solvolytic extractions) using anthracene oi1-ethylenediamine-liquid paraffin followed by steam carbonization of coal afforded clean fuels from coal with higher heating values. Effect of heating rate and final temperature of pyrolysis on the pyrolysis of residual coal obtained after organorefining was studied. More than 60% coal was recovered as clean fuels by this process. Pretreatments such as reduction, depolymerization and reductive-depolymerization enhance the devoiati1ization yield through steam pyrolysis. The use of steam in pyrolysis inhibited condensation reactions and promoted the cracking of phenolic and condensed polycyclic aromatic ring structures. Dynamics of the two stage process has been studied. The observation that coal consists of 5 different types of molecules has been supported by the evidence. Behaviour of different types of coal molecules in the stepwise coal conversion is explained. Successive extraction by selected solvents followed by pyrolysis of residual coal obtained can be a useful technique for the studies of organic chemical structure of coal.

ISSN:0884-3759    

DOI:10.1080/08843759508947731

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper is a brief, but not exhaustive review of the literature of the catalytic mild hydrocracking processes. It includes data characterizing reactivities, reaction network and kinetics of mild hydrocracking reactions. This review is designed for use as a reference for further research and development work in the field of mild hydrocracking.

ISSN:0884-3759    

DOI:10.1080/08843759508947732

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Ag-Rh/SiO2catalysts which exhibit activity and selectivity for oxygenate and hydrocarbon synthesis have been characterized by X-ray diffraction (XRD). XRD patterns show that the catalysts prepared using Rh chloride precursor contain Rh, Ag, AgCl, and AgClO2crystallites. The size of these crystallites varied with the amount of Ag in the catalyst. The variation in crystallite size of Rh, Ag, AgCl, and AgClO2with Ag/Rh ratio has an impact on the activity and selectivity for synthesis of oxygenates and hydrocarbons during CO hydrogenation and ethylene hydroformylation reactions. The selectivity towards oxygenates is decreased on the Ag-Rh catalysts due to the presence of AgCl and AgClO2crystallites on the catalyst surface. Ag-Rh catalyst with Ag/Rh ratio of 0.5 gives a higher activity and selectivity for ethanol and propanol during CO hydrogenation and ethylene hydroformylation than the other Ag-Rh catalysts. Ag-Rh catalysts prepared from Rh chloride and Ag nitrate precursors are less active and selective for oxygenate synthesis than those prepared from nitrate precursors. Ag-Rh catalysts for oxygenate synthesis should be prepared using nitrate precursors.

ISSN:0884-3759    

DOI:10.1080/08843759508947733

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0884-3759    

DOI:10.1080/08843759508947725

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor