Hydrogen sulfide catalyst poison

Compounds containing these elements sometimes are toxic but sometimes are promoters, depending on the type of catalyst. It is the character of non-metal compounds. For instance, water is harmful to solid acid catalysts, but is a promoter for hydrogenation reactions on ruthenium catalyst. Hydrogen sulfide can poison a nickel catal3 t, but a sulfate does not. If hydrogen sulfide is oxidized to form a shield-type structure, it is a non-toxic substance. 

Sweetening. Another significant purification appHcation area for adsorption is sweetening. Hydrogen sulfide, mercaptans, organic sulfides and disulfides, and COS need to be removed to prevent corrosion and catalyst poisoning. They ate to be found in H2, natural gas, deethanizer overhead, and biogas. Often adsorption is attractive because it dries the stream as it sweetens. 

Rhenium oxides have been studied as catalyst materials in oxidation reactions of sulfur dioxide to sulfur trioxide, sulfite to sulfate, and nitrite to nitrate. There has been no commercial development in this area. These compounds have also been used as catalysts for reductions, but appear not to have exceptional properties. Rhenium sulfide catalysts have been used for hydrogenations of organic compounds, including benzene and styrene, and for dehydrogenation of alcohols to give aldehydes (qv) and ketones (qv). The significant property of these catalyst systems is that they are not poisoned by sulfur compounds. 

Metal oxides, sulfides, and hydrides form a transition between acid/base and metal catalysts. They catalyze hydrogenation/dehydro-genation as well as many of the reactions catalyzed by acids, such as cracking and isomerization. Their oxidation activity is related to the possibility of two valence states which allow oxygen to be released and reabsorbed alternately. Common examples are oxides of cobalt, iron, zinc, and chromium and hydrides of precious metals that can release hydrogen readily. Sulfide catalysts are more resistant than metals to the formation of coke deposits and to poisoning by sulfur compounds their main application is in hydrodesulfurization. 

In the feed preparation section, those materials are removed from the reactor feed which would either poison the catalyst or which would give rise to compounds detrimental to product quality. Hydrogen sulfide is removed in the DBA tower, and mercaptans are taken out in the caustic wash. The water wash removes traces of caustic and DBA, both of which are serious catalyst poisons. Also, the water wash is used to control the water content of the reactor feed (which has to be kept at a predetermined level to keep the polymerization catalyst properly hydrated) and remove NH3, which would poison the catalyst. Diolefins and oxygen should also be kept out of poly feed for good operation. 

In general, mercaptans are more malodorous than sulfides and hydrogen sulfide. The presence of significant amounts of sulfur can induce catalyst poisoning during the refining of crude oil. 

Sulfur. It is not readily predictable from existing thermodynamic data that sulfur would be a poison of nickel catalysts. The action of sulfur is undoubtedly through the reaction of hydrogen sulfide with nickel, according to ... 

The equilibrium ratios of hydrogen-to-hydrogen sulfide for the reaction, derived (34) from available thermodynamic data (35), are plotted in Figure 10 as a function of temperature. When Ph2/Ph2s over the catalyst is less than the equilibrium value, the nickel can be sulfided and hence poisoned. Conversely, when this ratio is greater than the equi-... 

It is apparent that a new synthetic methodology, preferably catalytic, is needed for the synthesis of this important class of 2-(perfinoroalkyl)ethane thiols. In this context, a variety of catalysts was examined to determine if they wonld catalyze the hydrogenolysis of 2-(perfinorohexyl)ethane thiocyanate. In the conrse of this study, much to our surprise, it was discovered that a carbon supported Pd-Sn would catalyze the reaction. It is known that palladium and other group Vtll metal catalysts are poisoned by the product thiol, traces of hydrogen sulfide byproduct, and the hydrogen cyanide co-prodnct (6), but our observations are that this catalyst is surprisingly robust in the reaction medium. 

The thiol was obtained in >98% yield with trace amounts of the disulfide at 175°C and 700 psig H2 reactor pressnre in 1.5 honrs at a 900 1 substrate catalyst molar ratio. As discussed above, it is known that palladinm and other groups 8 to 10 metal catalysts are poisoned by the prodnct thiol, traces of hydrogen sulfide byproduct, and hydrogen cyanide coprodnct (6), bnt it is surprising that this catalyst is so robnst The effects of solvents, temperature, pressure, catalyst, and recycle will be discnssed. The characterization of the catalyst by various techniques will help to explain some of these observations. 

It is well known that palladium on carbon catalysts are poisoned by hydrogen cyanide and thiol products or hydrogen sulfide (6). Therefore, it was of interest to investigate the reduction of perfluoroalkyl thiocyanates as a function of tin concentration, keeping the concentration of palladium and reaction conditions constant. Figure 15.1 delineates the % conversion vs. Sn/Pd ratio, under the same reaction conditions of 175°C, 700 psig H2 for 2 hours with 5% Pd on carbon catalysts in ethyl acetate solvent at a 1000 1 substrate catalyst molar ratio. The increase in... 

Metal sulfides may be prepared by simply passing a sulfur-containing compound over the metal in a stream of hydrogen. Such catalysts are fairly immune to typical nonmetallic poisons. 

The hydrogen sulfide and ammonia can be removed by amine extraction and acid washes respectively. Hydrotreating also removes metals from the feed that would otherwise poison the reforming and cracking catalysts. 

The poisoning of a catalyst may be shown by adding some hydrogen sulfide solution to the hydrogen peroxide before the colloidal platinum is introduced. No decomposition of the peroxide is observed in this case, since the platinum has been poisoned by the presence of the hydrogen sulfide. This method is applicable to most of the metals below hydrogen in the electrochemical series. 

In contrast to poisoning with water vapor, the poisoning of ammonia synthesis catalysts by hydrogen sulfide is irreversible. It was studied using H2S labeled with H 5S (123) that made the radiochemical technique applicable to the determination of sulfur content in catalysts. 

Significant effort is underway in the United States to develop and commercialize coal gasification processes for producing gaseous fuels One of the major obstacles in the development of such a process is the presence of undesirable contaminants in the product gas stream. The major contaminant in coal gasification is hydrogen sulfide (H2S), which is toxic, poisonous to downstream catalysts and extremely corrosive in nature. Control of H2S in the fuel gas to a safe level is therefore essential. The H2S removal requirements are even more critical when the fuel gas is used in combined cycle power generation or in fuel cells. 

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