From carbonyl sulfide

Carbonyl sulfide reacts slowly with aqueous alkah metal hydroxides, which can therefore be used to free carbonyl sulfide from acidic gases. The half-hfe at pH 12 (0.01 N KOH) is 3 min at 22°C. The product initially formed from carbonyl sulfide and aLkaU is the thiocarbonate [534-18-9] which then breaks down to carbonate and sulfide ... 

For each of the three precursors of hydrogen sulfide, i.e. sulfur dioxide/sulfite, sulfate, and cysteine, a different biosynthetic pathway has been established. Figure 1 gives an overall view of these three pathways a suggestion for a path of synthesis of hydrogen sulfide from carbonyl sulfide is included. 

A variation to this latter route is to start from carbonyl sulfide, thus incorporating both N and S in the first step... 

Hydroxy-THISs react with electron-deficient alkynes to give nonisol-able adducts that extrude carbonyl sulfide, affording pyrroles (23). Compound 16 (X = 0) seems particularly reactive (Scheme 16) (25). The cycloaddition to benzyne yields isoindoles in low- yield. Further cyclo-addition between isoindole and benzyne leads to an iminoanthracene as the main product (Scheme 17). The cycloadducts derived from electron-deficient alkenes are stable (23, 25) unless highly strained. Thus the two adducts, 18a (R = H, R = COOMe) and 18b (R = COOMe, R = H), formed from 7, both extrude furan and COS under the reaction conditions producing the pyrroles (19. R = H or COOMe) (Scheme 18). Similarly, the cycloadduct formed between 16 (X = 0) and dimethylfumarate... 

The reaction is carried out at low temperature in aqueous medium and then allowed to stand overnight (221). Ammonium thiocarbamate is prepared from a cold saturated solution of ammonium thiocyanate, which is gradually added to dilute sulfuric acid at 25°C. The liberated carbonyl sulfide is passed into a saturated solution of alcoholic ammonia at about 10°C (221). The fairly low yield indicates that the reaction has not been greatly developed. 

Solid-Bed Caustic Treatment. SoHd-bed caustic units utilizing methanol [67-56-1] injection into the LPG feed stream can be used for carbonyl sulfide removal. The methanol—caustic solution must be drained periodically from the beds and discarded. When the soHd bed is exhausted, the spent caustic must be discarded and replaced. The LPG from the treater has a low enough water content to meet the propane specification. 

Nickel [7440-02-0] Ni, recognized as an element as early as 1754 (1), was not isolated until 1820 (2). It was mined from arsenic sulfide mineral deposits (3) and first used in an alloy called German Silver (4). Soon after, nickel was used as an anode in solutions of nickel sulfate [7786-81 A] NiSO, and nickel chloride [7718-54-9] NiCl, to electroplate jewelry. Nickel carbonyl [13463-39-3] Ni(C02)4, was discovered in 1890 (see Carbonyls). This material, distilled as a hquid, decomposes into carbon monoxide and pure nickel powder, a method used in nickel refining (5) (see Nickel and nickel alloys). 

It is good practice to keep concentrations of airborne nickel in any chemical form as low as possible and certainly below the relevant standard. Local exhaust ventilation is the preferred method, particularly for powders, but personal respirator protection may be employed where necessary. In the United States, the Occupational Safety and Health Administration (OSHA) personal exposure limit (PEL) for all forms of nickel except nickel carbonyl is 1 mg/m. The ACGIH TLVs are respectively 1 mg/m for Ni metal, insoluble compounds, and fume and dust from nickel sulfide roasting, and 0.1 mg/m for soluble nickel compounds. The ACGIH is considering whether to lower the TLVs for all forms of nickel to 0.05 mg/m, based on nonmalignant respiratory effects in experimental animals. 

Physica.1 Properties. Carbonyl sulfide [463-58-1] (carbon oxysulfide), COS, is a colorless gas that is odorless when pure however, it has been described as having a foul odor. Physical constants and thermodynamic properties are Hsted ia Table 1 (17,18). The vapor pressure has been fitted to an equation, and a detailed study has been made of the phase equiUbria of the carbonyl sulfide—propane system, which is important ia the purification of propane fuel (19,20). Carbonyl sulfide can be adsorbed on molecular sieves (qv) as a means for removal from propane (21). This approach has been compared to the use of various solvents and reagents (22). 

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). 

Carbonyl sulfide is overall the most abundant sulfur-beating compound ia the earth s atmosphere 430—570 parts per trillion (10 ), although it is exceeded by H2S and SO2 ia some iadustrial urban atmospheres (27). Carbonyl sulfide is beheved to origiaate from microbes, volcanoes, and the burning of vegetation, as well as from iadustrial processes. It may be the main cause of atmospheric sulfur corrosion (28). 

Health and Safety Factors. Carbonyl sulfide is dangerously poisonous, more so because it is practically odorless when pure. It is lethal to rats at 2900 ppm. Studies show an LD q (rat, ip) of 22.5 mg/kg. The mechanism of toxic action appears to iavolve breakdowa to hydrogea sulfide (36). It acts principally on the central nervous system with death resulting mainly from respiratory paralysis. Little is known regarding the health effects of subacute or chronic exposure to carbonyl sulfide a 400-p.g/m max level has been suggested until more data are available (37). Carbon oxysulfide has a reported inhalation toxicity in mice LD q (mouse) = 2900 ppm (37). 

Other components in the feed gas may react with and degrade the amine solution. Many of these latter reactions can be reversed by appHcation of heat, as in a reclaimer. Some reaction products cannot be reclaimed, however. Thus to keep the concentration of these materials at an acceptable level, the solution must be purged and fresh amine added periodically. The principal sources of degradation products are the reactions with carbon dioxide, carbonyl sulfide, and carbon disulfide. In refineries, sour gas streams from vacuum distillation or from fluidized catalytic cracking (FCC) units can contain oxygen or sulfur dioxide which form heat-stable salts with the amine solution (see Fluidization Petroleum). 

Carbonyl sulfide can be either a starting or intermediate material (108—110), or it can be used as a fluidizing gas in a carbon fluid-bed process (111). Making carbon disulfide from boiler flue gas by catalyticaHy reducing SO2 with CO to COS, and then converting COS to CS2 over an alumina catalyst has been proposed (112). 

Although the continuous-countercurrent type of operation has found limited application in the removal of gaseous pollutants from process streams (Tor example, the removal of carbon dioxide and sulfur compounds such as hydrogen sulfide and carbonyl sulfide), by far the most common type of operation presently in use is the fixed-bed adsorber. The relatively high cost of continuously transporting solid particles as required in steady-state operations makes fixed-bed adsorption an attractive, economical alternative. If intermittent or batch operation is practical, a simple one-bed system, cycling alternately between the adsorption and regeneration phases, 1 suffice. 

These reactions are reversible by changing the system temperature. ME A also reacts with carbonyl sulfide (COS) and carbon disulfide (CSi) to form heat-stable salts that cannot be regenerated. At temperatures above 245°F a side reaction with CO2 exists that produces oxazolidone-2. a heat-stable salt, and consumes MEA from the process. 

Sodium azide does not react with carbonyl sulfide to form 5-hydroxy-1,2,3,4-thiatriazole, nor with carboxymethyl xanthates, RO-CS SCH2COOH, to form 5-alkoxy-l,2,3,4-thiatriazoles. The latter, however, could be prepared from xanthogenhydrazides (RO-CS NHNH2) and nitrous acid. They are very unstable and may decompose explosively at room temperature only the ethoxy compound (6) has been examined in detail. This is a solid which decomposes rapidly at room temperature and even at 0°C is transformed after some months into a mixture of sulfur and triethyl isocyanurate. In ethereal solution at 20° C the decomposition takes place according to Eq. (16)... 

Adip [Possibly an acronym of DIPA, di-isopropanolamine] A process for removing hydrogen sulfide, mercaptans, carbonyl sulfide, and carbon dioxide from refinery streams by extraction into an aqueous solution of di-isopropanolamine or methyl diethanolamine. Developed and licensed by the Shell Oil Company, Houston, TX. More than 320 units were operating in 1992. 

Beavon [Beavon Sulfur Removal] Also called BSR. A process for removing residual sulfur compounds from the effluent gases from the Claus process. Catalytic hydrogenation over a cobalt/molybdena catalyst converts carbonyl sulfide, carbon disulfide, and other... 

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. 

Katasorbon A process for removing carbonyl sulfide and other organic sulfur compounds from syngas by combined catalysis and adsorption. Offered by Lurgi. 

Malaprop A process for removing carbonyl sulfide from gas streams by scrubbing with diethylene glycolamine (DGA). 

Sulfinol A process for removing hydrogen sulfide, carbon dioxide, carbonyl sulfide, and organic sulfur compounds from natural gas by scrubbing with di-isopropanolamine dissolved in a mixture of sulfolane and water. Developed in the 1960s by Shell International Research Mij N.V, The Netherlands and Shell Development Company, Houston. In 1996, over 180 commercial units were operating or under construction. 

Carbonyl sulfide is an intermediate in this reaction. A mixture of sulfur dioxide and oxygen was blown into the bottom of coke-fired reduction furnace and sulfur vapor condensed from the off-gases. Trail is the location of a large mine and smelter in British Columbia. The process was originally used in the 1930s for abating air pollution from the smelter, but when the demand for sulfuric acid for fertilizer production increased in 1943 it became obsolete. See also Boliden (1), RESOX. 

Butyl S-methylthiolcarbonate has been prepared from sodium /-butoxide, carbonyl sulfide, and methyl iodide 3 and from methyl... 

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