Hydrogen sulfide reaction with ferric oxides

The liquid is circulated at such a rate that a two- to threefold excess of ferric hydroxide over the stoichiometric quantity necessary for the complete reaction with hydrogen sulfide is present. Gollmar (1945) states that the process can be operated with less than the stoichiometric concentration of iron oxide and interprets the function of the iron as a catalytic oxygen carrier. Available historical data from several plants indicate that operation with an excess of iron oxide over the stoichiometric amount was commonly practiced. This excess seems to be required for complete removal of hydrogen sulfide and, also, to minimize thiosulfate formation in the thionizer. For a coal gas plant with a 10 MMsef/day capacity and a hydrogen sulfide removal rate of 400 grains/lOO scf, the chemical requirements are approximately 3,500 Ib/day of sodium carbonate and 2,800 Ib/day of iron. 

Benzoyl disulfide has been obtained by the reaction of benzoyl chloride with hydrogen sulfide, hydrogen disulfide, hydrogen trisulfide, potassium sulfide, sodium disulfide, lead sulfide, sodium hydrosulfite, sodium thiosulfate, sulfhydrylmagnesium bromide, and thiobenzamide. It is also formed by reaction of benzoic anhydride with hydrogen sulfide. The better preparative methods involve the oxidation of thiobenzoic add by means of air,hydrogen peroxide or sulfur monochloride, or of the sodium or potassium salt by means of air, - chlorine, iodine, copper sulfate, - potassium ferricyanide, - or ferric chloride. - ... 

Fixed-bed noncatalytic reactors. Fixed-bed reactors can be used to react a gas and a solid. For example, hydrogen sulfide can be removed from fuel gases by reaction with ferric oxide ... 

Iron Sponge Also called Dry box. An obsolete process for removing hydrogen sulfide from gas streams by reaction with iron oxide monohydrate. The ferric sulfide that is formed is periodically re-oxidized to regenerate ferric oxide and elemental sulfur. When this process becomes inefficient because of pore-blockage, the sulfur is either oxidized to sulfur dioxide for conversion to sulfuric acid, or is extracted with carbon disulfide. 

Most powerful poisons are lethal because they inhibit enzymes required for life. Hydrogen cyanide and hydrogen sulfide liberate ions, CN" and HS . that combine with ferric iron atoms in the cytochromes, which are heme enzymes that catalyze the cellular oxidation reactions required for life. Many drugs are enzyme inhibitors. 

One can also frequently choose between a purely mass-transfer operation and a chemical reaction or a combination of both. Water can be removed from an ethanol-water solution either by causing it to react with unslaked lime or by special methods of distillation, for example. Hydrogen sulfide can be separated from other gases either by absorption in a liquid solvent with or without simultaneous chemical reaction or by chemical reaction with ferric oxide. Chemical methods ordinarily destroy the substance removed, while mass-transfer methods usually permit its eventual recoveiy in unaltered form without great difficulty. 

The Cataban process was developed by Rhodia Inc. of New York, and described in some detail by Meuly and Ruff (1972) and Meuly (1973). It is no longer a commercially active process. The basis of the process is the oxidation of hydrogen sulfide to elemental sulfur by reduction of ferric ions to the ferrous state, followed by oxidation of the ferrous ions to ferric state by contact with air. The reactions involved can be expressed in the following equations ... 

The sodium ferrite/ferrate solution is very alkaline and lends to absorb other acid gases such as HCN, CO2. and S02- HCN is a weak acid that reacts with the alkaline solution to form NaCN by a reversible acid/base reaction. Since it is not destroyed (as is H2S) the NaCN builds up in the solution until the vapor pressure of HCN over the solution is high enough to impede absorption. At this point most of the HCN in the feed gas leaves the absorber with the product gas. A small fraction of the HCN will react with solution components to form NaSCN and ferric ferrocyanide (Prussian blue). This fetrocyanide complex is identical to the oxygen carrier employed in the Staatsmijnen-Otto process, and contributes to the oxidation of hydrogen sulfide to elemental sulfur. 

Historiad Background. The first installations utilized a simple form of the iron oxide (or dry-box) process. In this form of the process, hydrogen sulfide was removed completely by reaction with hydrated ferric oxide, resulting in the formation of ferric sulfide. After removal from the box and exposure to atmospheric oxygen, the ferric sulfide oxidized to elemental sulfur and ferric oxide. The oxidized mixture was reloaded into the box and used to react with additional hydrogen sulfide. The cycle could be repeated several times before the material lost activity due to the presence of excessive amounts of elemental sulfur. 

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