Absorption hydrogen sulfide

Solvents used for hydrogen sulfide absorption include aqueous solutions of ethanolamine (monoethano1 amine, MEA), diethanolamine (DEA), and diisopropanolarnine (DIPA) among others ... 

A minor variant to the amine scrubbing process described above is the Sulfinol process, which still uses an alkanolamine base, diisopropanolamine (35%), but in a solvent consisting of a mixture of sulfolane (40%), tetramethy-lene sulfone (CH2)4S02, a good hydrogen sulfide solvent) and water [29]. Other processes are based on hydrogen sulfide absorption in aqueous alkaline carbonate solutions, such as the Catacarb and Benfield systems (Eqs. 9.16 and 9.17). 

Cai, R.-X., and Chang, H.-G., 1992, Selective Hydrogen Sulfide Absorption in Hindered Amine Aqueous Solution, Journal of Natural Gas Chemistry, No. 2, p. 175. 

The need to employ dilute solutions to prevent the formation of thiosulfate resulted in very large circulation rates and considerable power consumption. Furthermore, the formation of elemental sulfur was slow from an industrial standpoint, requiring large reaction tanks and large liquid inventories. In addition, to obtain satisfactory rates of hydrogen sulfide absorption when treating gas streams containing appreciable amounts of carbon dioxide, partial decarbonation of the solution was required before recycle to the absorber. 

The reaction is exothermic, with the heat of reaction amounting to 3.S80 Btu per pound of sulfur. The overall reaction can be subdivided into three separate consecutive steps. These steps are a) hydrogen sulfide absorption, b) conversion of hydrogen sulfide to elemental sulfur, and c) vanadium reoxidation. 

Hydrogen Sulfide Absorption. In the Stretford process, the wash liquor in circulation typically contains a total of 30 grams per liter of sodium carbonate and sodium bicarbonate, whose proportions are established by the partial pressure of carbon dioxide above the solution. 

Excellent discussions on the properties of purification materials have been presented by Smith (1957) and Ward (1964). The physical mechanism of hydrogen sulfide absorption by iron oxide was investigated by Avery (1939) and Dent and Moignard (1950). The studies showed that under proper conditions of temperature, moisture content, and pH, the sulfur formed on the oxide particle is continuously displaced by iron oxide, which migrates from the particle center to the surface, thus exposing ftesh oxide for further reaction with hydrogen sulfide and oxygen. 

Carbonate is measured by evolution of carbon dioxide on treating the sample with sulfuric acid. The gas train should iaclude a silver acetate absorber to remove hydrogen sulfide, a magnesium perchlorate drying unit, and a CO2-absorption bulb. Sulfide is determined by distilling hydrogen sulfide from an acidified slurry of the sample iato an ammoniacal cadmium chloride solution, and titrating the precipitated cadmium sulfide iodimetrically. 

In a typical batch operation, carbon disulfide is added to four molar equivalents of 25—30 wt % aqueous ammonia in a stirred vessel, which is kept closed for the first one to two hours. The reaction is moderately exothermic and requires cooling. After two to three hours, when substantially all of the disulfide has reacted, the reaction mixture is heated to decompose dithiocarbamate and trithiocarbonate and vented to an absorption system to collect ammonia, hydrogen sulfide, and any unreacted carbon disulfide. 

Conversion Processes. Most of the adsorption and absorption processes remove hydrogen sulfide from sour gas streams thus producing both a sweetened product stream and an enriched hydrogen sulfide stream. In addition to the hydrogen sulfide, this latter stream can contain other co-absorbed species, potentially including carbon dioxide, hydrocarbons, and other sulfur compounds. Conversion processes treat the hydrogen sulfide stream to recover the sulfur as a salable product. 

As worldwide attention has been focused on the dangers of acid rain, the demand to reduce sulfur dioxide [7446-09-5] emissions has risen. Several processes have been developed to remove and recover sulfur dioxide. Sulfur can be recovered from sulfur dioxide as Hquid sulfur dioxide, sulfuric acid, or elemental sulfur. As for the case of hydrogen sulfide, sulfur dioxide removal processes are categorized as adsorption, absorption, or conversion processes. 

Barium hydro sulfide [25417-81-6], Ba(HS)2, is formed by absorption of hydrogen sulfide into barium sulfide solution. On addition of alcohol, barium hydrosulfide tetrahydrate [12230-74-9], Ba(HS)2 4H2O, crystallizes as yellow rhombic crystals that decompose at 50 °C. Sohd barium hydro sulfide is very unstable. Its solubility in water is... 

SolubiHty of carbon dioxide in ethanolamines is affected by temperature, amine solution strength, and carbon dioxide partial pressure. Information on the performance of amines is available in the Hterature and from amine manufacturers. Values for the solubiHty of carbon dioxide and hydrogen sulfide mixtures in monoethanolamine and for the solubiHty of carbon dioxide in diethanolamine are given (36,37). SolubiHty of carbon dioxide in monoethanolamine is provided (38). The effects of catalysts have been studied to improve the activity of amines and provide absorption data for carbon dioxide in both mono- and diethanolamine solutions with and without sodium arsenite as a catalyst (39). Absorption kinetics over a range of contact times for carbon dioxide in monoethanolamine have also been investigated (40). 

Figure 14-12 illustrates the influence of system composition and degree of reaetant eonversion upon the numerical values of for the absorption of CO9 into sodium hydroxide solutions at constant conditions of temperature, pressure, and type of packing. An excellent experimental study of the influence of operating variables upon overall values is that of Field et al. (Pilot-Plant Studie.s of the Hot Carbonate Proce.s.s for Removing Carbon Dioxide and Hydrogen Sulfide, U.S. Bureau of Mines Bulletin 597, 1962). 

Absorption of pollutant gases is accomplished by using a selective liquid in a wet scrubber, packed tower, or bubble tower. Pollutant gases commonly controlled by absorption include sulfur dioxide, hydrogen sulfide, hydrogen chloride, chlorine, ammonia, oxides of nitrogen, and low-boiling hydrocarbons. 

By-product processing Hydrogen sulfide Conversion to elemental sulfur or sulfuric acid by liquid absorption, wet oxidation to elemental sulfur, combustion to SO2... 

Since the Claus process by itself removes only about 90% of the hydrogen sulfide in the gas stream, the Beaven, SCOT, or Wellman-Lord processes are often used to further recover sulfur. In the Beaven process, the hydrogen sulfide in the relatively low concentration gas stream from the Claus process can be almost completely removed by absorption in a quinone solution. 

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