Sulfur recovery catalyst

Desiccite25. [Engelhard] Alumina sulfur recovery catalysts. 

Beside the above-mentioned catalysts used for the production processes of ammonia, hydrogen, urea and other important inorganic chemicals, some other catalysts might be used during some accessorial processes. They are N2 production catalysts, CO selective oxidation catalysts, sulfur recovery catalysts, CO2 dehydrogenation catalysts, molecular sieve desiccants and de-poison catalysts such as desulfurization, dechlorination, and dearsenization, etc. 

Sulfur recovery catalysts. Sulfur reclaim is to transform the acidic gas containing H2S produced during processes into sulfate, and then sulfate is recycled. The sulfur recovery has many methods, such as iron oxide process, ADA process, G-V process, hypermanganate process, dichromate process, catalytic combustion process and Claus method etc. Herein, the Claus method will be introduced briefly. 

The sulfur recovery catalysts are mainly used at refineries, petrochemical companies and ammonia plants with drege oil or coal as raw materials. Except for a few companies where bauxite is used, most plants adopt Al203-catalysts. LS822, LS821, CT6-2 and CT6-3 are the catalysts made in China for sulfur recovery. 

When treating Claus unit tail gas, the process is capable of overall sulfur recoveries of up to 99.6% The number of reactors included is dependent on the feed gas concentration and the required sulfur recovery. Catalyst selectivity is maximized at a MODOP reactor outlet temperatures of 250°-270°C (482°-518 F). As the oxidation reaction is highly exothermic, additional stages must be employed to limit the reactor outlet temperature to below 320°C (608°F) at high concentrations of H2S in the feed gas. 

The Claus process is the most widely used to convert hydrogen sulfide to sulfur. The process, developed by C. F. Claus in 1883, was significantly modified in the late 1930s by I. G. Farbenindustrie AG, but did not become widely used until the 1950s. Figure 5 illustrates the basic process scheme. A Claus sulfur recovery unit consists of a combustion furnace, waste heat boiler, sulfur condenser, and a series of catalytic stages each of which employs reheat, catalyst bed, and sulfur condenser. Typically, two or three catalytic stages are employed. 

A derivative of the Claus process is the Recycle Selectox process, developed by Parsons and Unocal and Hcensed through UOP. Once-Thm Selectox is suitable for very lean acid gas streams (1—5 mol % hydrogen sulfide), which cannot be effectively processed in a Claus unit. As shown in Figure 9, the process is similar to a standard Claus plant, except that the thermal combustor and waste heat boiler have been replaced with a catalytic reactor. The Selectox catalyst promotes the selective oxidation of hydrogen sulfide to sulfur dioxide, ie, hydrocarbons in the feed are not oxidized. These plants typically employ two Claus catalytic stages downstream of the Selectox reactor, to achieve an overall sulfur recovery of 90—95%. 

In two processes under development as of 1997, the sulfur dioxide stream reacts with reduciag gas over a proprietary catalyst to form elemental sulfur. Both processes have achieved a sulfur recovery of 96% ia a single reactor. Multiple reactor systems are expected to achieve 99+% recovery of the feed sulfur. The direct sulfur recovery process (DSRP), under development at Research Triangle Institute, operates at high temperature and pressure. A similar process being developed at Lawrence Berkeley Laboratory is expected to operate near atmospheric pressure. 

The H2S comes out with the reactor products, goes through the product-recovery system of the FCCU, and eventually goes to a Claus plant for sulfur recovery. The metal oxide adsorbent recirculates with the spent cracking catalyst back to the regenerator for the next SO adsorption cycle. 

Fluid catalyst regenerator Fuel gas combustion Claus sulfur recovery TRS X Storage tanks... 

Occurs in nature in abundance the principal forms are bauxites and lat-erites. The mineral corundum is used to produce precious gems, such as ruhy and sapphire. Activated aluminas are used extensively as adsorbents because of their affinity for water and other polar molecules and as catalysts because of their large surface area and appropriate pore sturcture. As adsorbents, they are used for drying gases and liquids and in adsorption chromatography. Catalytic properties may be attributed to the presence of surface active sites (primarily OFT, 02, and AF+ ions). Such catalytic applications include sulfur recovery from H2S (Clauss catalysis) dehydration of alcohols, isomerization of olefins and as a catalyst support in petroleum refining. 

Although the Claus catalytic conversion is a highly efficient process as presently employed in sulfur recovery plants the continuing efforts to reduce sulfur emissions to atmosphere demand that the last possible ounce of efficiency be squeezed from the process. Whether further small but critical improvements in the already high sulfur recovery efficiency can be achieved by more fine tuning of the converters and their catalyst charge remains to be seen. What cannot be accomplished in the catalytic converters will be achieved in the tail gas desulfurization processes. 

In this new process the H2S/SO2 reaction is carried out in liquid sulfur at pressures in excess of five atmospheres. Typical Claus catalysts are still employed but temperatures are lower (below the dewpoint of sulfur) and thus the redox reaction occurs in the liquid sulfur phase at the surface of the catalyst. Vapor losses due to sulfur mist entrainment are reduced and interstage condensers in the tradition Claus train are not required thus avoiding wasteful heat transfer problems. The authors claim that overall sulfur recoveries in excess of 99% are possible without the use of tail gas clean up units. 

The overall sulfur recovery achievable by the recycle Selec-tox process increases with higher H2S concentration and with the number of catalystic stages used. Vfe may expect 94 to 95 percent recovery from 10 percent H2S feed with three catalystic stages ... 

Catalysts help customers comply cost-effectively with clean-air regulations. Hydrocarbons, carbon monoxide, and nitrogen oxides can be removed using supported precious metal catalysts. Organic sulfur compounds are converted to H2S using nickel/molybdenum or cobalt/molyb-denum on alumina catalysts. Sulfur can be recovered in a Claus process unit. The Claus catalytic converter is the heart of a sulfur recovery plant. 

UCBSRP [University of California Berkeley Sulfur Recovery Process] A process for removing hydrogen sulfide and sulfur dioxide from natural gas. These gases react together in a polyglycol solvent with a catalyst, yielding elemental sulfur. Not piloted as of 1997. 

New processes include synthesis of /V-alkylated anilines from olefins and aniline in an inert solvent with at least one catalyst from a range that includes alkali metal alcoholates, alkaline earth metal alcoholates, alkali metal amides and alkaline earth amides36. The uses for /V,/V-dimethylaniline (11) include in the manufacture of polyester resins, sulfur recovery (in copper refining), insecticides and fungicides, dyes, pharmaceuticals, explosives, rubber products, specialty isocyanates and petroleum additives. The /V-ethylaniline (26) is a dye intermediate and rubber additive, and is used for bum control in explosives, while /V,/V-diclhylaniline is used in production of polyester resins, pharmaceuticals, diazo prints (lithographic), and dyes, and as a petroleum additive37. 

---