Carbonyl sulfide hydrolysis

Measured total sulfide levels confirm the major features of the hypotheses of Elliott and coworkers (8-11). in that sulfide seems to exist in remote oxic waters at concentrations approaching nanomolar, sufficient for meaningful metal interactions. The amplitude of the diurnal variation is too strong, however, for carbonyl sulfide hydrolysis to be the primary input, or for direct oxidation by O2 to be the sole sink, and alternate cycling processes are indicated. 

Elhott S., Lu E., and Rowland F. S. (1987) Carbonyl sulfide hydrolysis as a source of hydrogen-sulfide in open ocean seawater. Geophys. Res. Lett. 14(2), 131 — 134. 

Fiedorow, R. Leaute, R. Dalla Lana, 1. G. A study of the kinetics and mechanism of carbonyl sulfide hydrolysis over alumina. J. Catal. 1984, 85(2), 339-48. 

Alternative means for removal of carbonyl sulfide for gas streams iavolve hydrogenation. For example, the Beavon process for removal of sulfur compounds remaining ia Claus unit tail gases iavolves hydrolysis and hydrogenation over cobalt molybdate catalyst resulting ia the conversion of carbonyl sulfide, carbon disulfide, and other sulfur compounds to hydrogen sulfide (25). 

To effectively remove carbonyl sulfide from a gas stream, special alkaline scmbbiag Hquors are used. These contain sodium aluminate or sodium plumbite, or they are made of alkaUes with a hydrolysis catalyst based on Zn, Fe, Ni, or Cu. Diethanolamine, diglycolamine, or other alkanolamines (qv) mixed with water remove carbonyl sulfide from sour, ie, acid-gas-containing, gas streams (25,26) (see Carbon dioxide). 

Carbon disulfide is essentially unreactive with water at room temperature, but above about 150°C in the vapor phase some reaction occurs forming carbonyl sulfide (carbon oxysulfide) [463-58-1] and hydrogen sulfide [7783-06-4]. Carbonyl sulfide is an intermediate in the hydrolysis reaction ... 

The genus Thiobacillus, especially the species T. denitrificans catalyzed the oxidation reactions of hydrogen sulfide yielding soluble hydrosulfide compounds, elemental sulfur, and sulfuric acid. Carbonyl sulfide and carbon disulfide are converted to hydrogen sulfide by hydrolysis. Additionally, they are oxidized to SOx and sulfates via microbial action. The reported oxidation reactions of thiosulfate using nitrate as electron acceptor are ... 

COMBISULF A process for removing sulfur compounds from the gases from combined-cycle power plants with integrated coal gasification. Carbonyl sulfide is removed by catalytic hydrolysis hydrogen sulfide is removed by selective absorbtion in aqueous MEDA and the sulfur is recovered from both processes by a modified Claus unit. Developed by Krupp Koppers and first operated in Spain in 1996. See PRENFLO. 

These species are ubiquitous in soil (Kelly and Harrison 1989). In a recent laboratory investigation of the fate of ionic thiocyanate in six different soils, Brown and Morra (1993) concluded that microbial degradation is the primary mechanism for thiocyanate disappearance at or below 30 °C, with carbonyl sulfide proposed as a possible hydrolysis product. Loss of thiocyanate at higher temperatures (50-60 °C) did not appear to result from microbial degradation the observed decreases in thiocyanate concentrations of soil extracts with incubation time at elevated temperatures were postulated to result primarily from increased sorption or increased sorption kinetics, but abiotic catalysis of thiocyanate degradation was also noted as a possible cause. 

Adewuyi, Y.G. and Carmichael, G.R. Kinetics of hydrolysis and oxidation of carbon disulfide by hydrogen peroxide in alkaline medium and application to carbonyl sulfide, Environ. Sci. Technol, 21(2) 170-177, 1987. 

The hydrogen sulfides (H2S, SH-, S2 and their metal complexes) are well known in restricted reducing regions of the world ocean such as anoxic basins (1), but they have traditionally been dismissed as unimportant for, or even nonexistent in, most oxic seawaters 12-41. Several lines of reasoning are now beginning to suggest that sulfides actually do exist in the surface ocean, and enter into a rich metal chemistiy there. Extensive measurements of carbonyl sulfide (OCS) in seawater (5.61 permit the quantification of a mixed layer source, the hydrolysis reactions f7-111... 

Table L Average Surface Carbonyl Sulfide Concentrations for Various Productivity Zones (6), and Bisulfide Ion Levels Corresponding to them in the Hydrolysis-Oxidation Steady State (Equations 1,2, and 3). Units are Picomolar...

S. Elliot, E. Lu, F.S. Rowland (1989). Rates and mechanisms for hydrolysis of carbonyl sulfide in natural waters. Environ. Sci. Technol., 23,458-461. 

During the combustion of the hydrogen sulfide some of the sulfur reacts with hydrocarbons normally present to form carbon disulfide and methyl mercaptan. Carbonyl sulfide is also formed either by the partial hydrolysis of carbon disulfide and/or by the reaction of carbon dioxide and hydrogen sulfide. Some hydrogen and carbon monoxide are also formed in the Claus combustion step. 

While carbon disulfide and carbonyl sulfide can also be converted to hydrogen sulfide by hydrogenation, both are predominantly converted by hydrolysis. The supply of hydrogen is supplemented by the carbon monoxide content of the reactor feed gas which undergoes Reaction 7, the water-gas shift reaction ... 

After a dry dust filter and final wet scrubbing to remove fly ash, the coal gas is slightly reheated for catalytic hydrolysis of trace amounts of hydrogen cyanide and carbonyl sulfide to ammoma and hydrogen sulfide, respectively. This step simplifies and improves the efficiency of the water treatment and sulfor recovery systems. The plant is designed to operate at zero water discharge. 

Sharma, M. M., 1965, Kinetics of Reaction of Carbonyl Sulfide and Carbon Dioxide with Amines and Catalysis by Brmisted Bases of the Hydrolysis of COS, Trans. Faraday Soc., VoL61,p.681. 

In commercial plants all of the carbonyl sulfide present in the feed gas does not react with monoethanolamine. Pearce et al. (1%1) and Berlie et al. (1965) report that the major portion of the CX>S undergoes hydrolysis, forming H2S and CO2, and only about 15 to 20% of the COS reacts irreversibly with the monethanolamine. The addition of strong alkalis, such as sodium carbonate or sodium hydroxide, to monoethanolamine solutions reduces losses due to reaction with COS substantially, probably by increasing tiie rate of COS hydrolysis (Pearce et al., 1961). Although monoetiianolamine losses can be reduced by this method, use of diethanolamine is preferred if the gas to be treated contains appreciable amounts of COS. 

Carbonyl sulfide is hydrolyzed almost quantitatively to hydrogen sulfide and carbon dioxide and better than 99% removal can be achieved. Carbon disulfide is hydrolyzed in two steps— first to carbonyl sulfide and hydrogen sulfide, followed by hydrolysis of the carbonyl sulfide to hydrogen sulfide and carbon dioxide. The two-step reaction is slower than the simple hydrolysis of carbonyl sulfide with the result that only about 75 to 85% carbon disulfide removal is obtained under normal operating conditions. 

Various reaction mechanisms have been proposed for the formation of carbonyl sulfide and carbon disulfide and for their subsequent hydrolysis to hydrogen sulfide and carbon dioxide (Paskall and Sames, 1992). The plant data available indicate that carbonyl sulfide is formed primarily from the reaction between elemental sulfur and carbon monoxide, which in turn are derived from hydrogen suUide and carbon oxides present during combustion of the feed gas in the Claus thermal stage. The production of carlxin disulfide in the thermal stage is usually attributed to the presence of hydrocarbons in the feed gas because carbon disulfide is produced commercially by reacting elemental sulfur with saturated hydrocarbons. The... 

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