Peter D. Clark

Conversion of CS2 and COS over alumina and titania under Claus process conditions: reaction with H2O and SO2

Catalytic conversion of CS2 in the Claus process using either alumina or titania has always been assumed to proceed via hydrolysis. Although this conclusion is supported by the results of this study, data reported here show that the high CS2 conversion activity of titania may be due, in part, to the reaction of CS2 with SO2, a process which proceeds almost quantitatively at 320°C. This reaction was also shown to have an appreciable rate at 250°C, suggesting that some of the CS2 conversion activity of titania at second Claus converter conditions may be due to reaction with SO2. COS was identified as an intermediate product of the reaction of CS2 with SO2. Although these studies confirmed that alumina promotes hydrolysis of CS2, the industrial observation that it is not as efficient a catalyst as titania for the conversion of CS2 may be due to the limited ability of alumina to promote reaction of CS2 with SO2.

Chemistry of organosulphur compound types occurring in heavy oil sands:: 1. High temperature hydrolysis and thermolysis of tetrahydrothiophene in relation to steam stimulation processes

Abstract Studies have been made of the high temperature, high pressure hydrolysis and thermolysis of tetrahydrothiophene as part of a study of the reactivity of organosulphur compounds during in situ steam stimulation processes for heavy oil recovery. It was found that hydrolysis of tetrahydrothiophene produces hydrogen sulphide, carbon dioxide and hydrocarbon gases, together with a complex array of liquid products. A mechanism for this reaction is proposed and investigations into the aqueous decomposition of butanal have been carried out to support this mechanism. A comparative study of the dry thermolysis of tetrahydrothiophene has been carried out.

Some chemistry of organosulphur compound types occurring in heavy oil sands: 2. Influence of pH on the high temperature hydrolysis of tetrahydrothiophene and thiophene

Abstract The hydrolysis of thiophene at high temperatures and pressures has been examined in relation to the steam-stimulated recovery of high-sulphur tar sands and heavy oils. The influence of pH has been examined in the hydrolysis of both thiophene and tetrahydrothiophene considered to be reasonable models for organosulphur molecular types in heavy oils. Mechanisms are proposed to account for the products observed under acidic, neutral and basic conditions.

The chemistry of organosulphur compound types occurring in heavy oils: 4. the high-temperature reaction of thiophene and tetrahydrothiophene with aqueous solutions of aluminium and first-row transition-metal cations

In the reactions of thiophene and tetrahydrothiophene with aqueous solutions of first-row transition-metal and aluminium cations at 240 °C and 3.4 MPa all the metal species accelerated the decomposition of the thiophenes in relation to equivalent reactions with pure water. Al3+, Sc3+, VO2+, Cr3+, Ni2+ and Cu2+ were most reactive towards thiophene and Al3+, VO2+, Cr3+ and Cu2+ were most reactive towards tetrahydrothiophene. Principal products were H2S and complex mixtures of organic products. The presence of CO2 and oxygen-containing organic products revealed that water was involved in direct chemical reaction with the substrates. It is likely that these model reactions parallel more complex processes that occur during the steam-stimulated recovery of oil-sand bitumen and other high-sulphur oils.

Chemistry of organosulphur compound types occurring in heavy oil sands: 3. Reaction of thiophene and tetrahydrothiophene with vanadyl and nickel salts

Abstract As part of a study of the chemistry of the steam-stimulated recovery of heavy oils, the hydrolysis and subsequent desulphurization of tetrahydrothiophene and thiophene by aqueous solutions of vanadyl and nickel salts was investigated. Vanadyl sulphate and vanadyl chloride were shown to behave very differently, emphasizing that these salts have different molecular species in aqueous solutions.

Chemistry of organosulphur compound types occurring in heavy oil sands: 5. Reaction of thiophene and tetrahydrothiophene with aqueous Group VIIIB metal species at high temperature

Abstract As part of a study of organosulphur compounds in heavy oil sands, the interaction of thiophene (1) and tetrahydrothiophene (10) with aqueous solutions of Group VIIIB metal species at 200–240 °C has been investigated. Thiophene was the more reactive and the greatest degree of reaction was observed with the second- and third-row members of the Group VIIIB metals. Aqueous Pt(IV) gave most reaction for both substances. Desulphurization of the sulphur compounds was significant, although conversion to more complex organic substances, including dithienyls and benzothiophene, account for > 50 wt % of the total reaction for most metal species. The presence of CO2 in the products showed that water was involved in the reaction. Reactions with thiophene produced only minor amounts of C1C4 hydrocarbons, but significant quantities were obtained from reactions with tetrahydrothiophene.

COMMENTS ON THE ROLE OF H2S IN THE CHEMISTRY OF EARTH'S EARLY ATMOSPHERE AND IN PREBIOTIC SYNTHESIS

Abstract: Free energy calculations and experimental measurements have been used to show that H2S/CO2 mixtures outgassing from a prebiotic Earths crust would have produced a reducing gas mixture containing CO, H2, H2O, and Sx as principal components. Due to rapid recombination of H2, CO, and Sx to H2S and CO2 on cooling from a high temperature to ambient conditions, reducing components would have been retained only if efficient quenching of the reduced gas mixture had been possible. Consequently, subsea vents or vents with efficient infusion of water would have been ideal sites for retention of reduced species and for prebiotic organic synthesis. It is suggested that C/H/O/S ratios are important factors in controlling the degree of prebiotic organic synthesis and, hence, the emergence of life, since if oxygen is abundant, CO2 and SO2 would have been dominant species.

CLAY-CATALYZED THIOALKYLATION OF THIOPHENES AND BENZO[b]THIOPHENES

Abstract A method for the direct thioalkylation of thiophene (1) and benzo[b]thiophene (7) by reaction of either heterocycle with an alkyldisulfide using a ZnCl2-modified montmorillonite clay catalyst is described. The clay-catalyzed reaction of 1 with excess dimethyl disulfide (DMDS) over 24 hours in refluxing chlorobenzene yielded a mixture of bis-, tris-, and tetrakis(methylthio)thiophenes (2–5) from which 2,3,5-tris(methylthio)thiophene (4a) and tetrakis(methylthio)thiophene (5) could be isolated in modest yield. Prolonging the reaction time gave (4a) and 5 in isolated yields of 21 and 16% respectively. Carrying out the same reaction in a sealed autoclave at 150°C with an air overpressure resulted in a clean and rapid (5 h) conversion of thiophene to the tetramethylthio-derivative 5 in moderate isolated yield (50%). In a similar manner 7 could be converted to 2,3-bis(methylthio)benzo[b]thiophene (8a) or 2,3,6-tris- and 2,3,6,7-tetrakis(methylthio) derivatives 9 and 10a by clay catalyzed reactions with...

Benzylation of thiophene using zinc and iron chloride modified montmorillinite clay

Montmorillinite clays, modified with either Zn(II) or Fe(III) chlorides have been used to catalyze the Friedel-Crafts alkylation of thiophene. High yields (ca. 80%) of 2- and 3-benzylthiophene mixtures were obtained using either catalyst in chlorobenzene or nitrobenzene solvent at 80°C. The ratio of 2–3-products was found to be controlled by their relative stability. Reactions were most rapid in nitrobenzene solution (<5 min) and resulted in formation of the 2-isomer as the only mono-substituted product. This is believed to be the first example in which an alkylation of thiophene has been limited to one regio-isomer.

C-S bond formation in aromatic substrates using Mn(II)-promoted montmorillonite clays

Direct introduction of -SCH3 groups into activated aromatic and hetero aromatic compounds has been achieved by reaction with dimethyldisulfide over a MnCl2-promoted K-10 montmorillonite. Unlike ZnCl2/K-10, the Mn- promoted clay appears to promote reaction by coordination of the aromatic substrate at the active site followed by attack of the disulfide at the activated aromatic.