Sulfur H2SO4 production

Up until the 1940s the manufacture of heavy chemicals in India was insignificant. For example, the production of H2SO4 was only 18,000 tons as contrasted with 7 million tons in the United States. Until the establishment of the first contact acid plant in 1948, all production involved the chamber process. The installed annual capacity in 1948 was 175,000 tons, distributed among 49 different factories. Because India does not have a source of free sulfur, the production of H2SO4 is one of the critical chemical industries. Development of the large deposits of iron pyrite in the northern part of the country would alleviate this problem. 

When H2S is passed into a solution of copper(II) sulfate acidified with H2SO4, copper(II) sulfide precipitates. When concentrated H2SO4 is heated with metallic Cu, the principal sulfur-containing product is SO2 but a residue of copper(II) sulfide is also formed. Account for these reactions. 

We discuss catalysts in Chapter 16 and H2SO4 production in Chapter 21. These two sulfur oxides also form when sulfur impurities in coal burn and then oxidize further. In contact with rain, they form H2SO3 and H2SO4 and contribute to a major pollution problem that we discuss in Chapter 19. 

FIGURE 10.16 Estimates for the characteristic time required for the condensation of sulfuric acid vapor on preexisting particles (r ) and the characteristic time required for nucleation of H2SO4-H2O aerosols (xs) as a function of relative humidity. Two H2SO4 production rates... 

The type and concentration of the acid(s) can have a marked effect on the neutralisation process, largely owing to the solubility of the reaction product(s). The acids most commonly found in waste water are nitric (HNO3), hydrochloric (HCl), sulfuric (H2SO4), hydrofluoric (HF) and phosphoric (H3PO4). The solubilities of their calcium and magnesium salts are summarised in Table 28.6 [28.7] (N.B., all sodium salts are soluble). 

Prior to 2000, heavy duty vehicles coped with the same problems as passenger cars the need for high SOF conversion combined with as little H2SO4 production as possible. Ceria and vanadia-promoted Pt were used until the reduced sulfur content of the fuel rendered them no longer necessary. This, of course, mirrors the situation just described for LDD vehicles. 

Production level 1,200 tpd of 93%-96% sulfuric acid calculated on 100% H2SO4 (sulfur burnir ). Production level 1,050 tpd of 93%-96% sulfuric acid calculated on 100% H2SO4 (pyrite gas treatment). 

Practically all processes of sulfuric acid production presently in use are based on catalytic oxidation of sulfur dioxide to sulfur trioxide and subsequent absorption in recirculating sulfuric acid to form H2SO4. The process of oxidation is accomplished most commonly in multibed converters on vanadium pentoxide catalyst. 

Fig. 1.3. Top of H2S04-making ( absorption ) tower, courtesy Monsanto Enviro-Chem Systems, Inc. www.enviro-chem.com The tower is packed with ceramic saddles. 98.5 mass% H2SO4, 1.5 mass% H2O sulfuric acid is distributed uniformly across this packed bed. Distributor headers and downcomer pipes are shown. The acid flows through slots in the downcomers down across the bed (see buried downcomers below the right distributor). It descends around the saddles while S03-rich gas ascends, giving excellent gas-liquid contact. The result is efficient H2SO4 production by Reaction (1.2). A tower is 7 m diameter. Its packed bed is 4 m deep. About 25 m of acid descends per minute while 3000 Nm of gas ascends per minute.

Fig. 2.1. World sulfuric acid production, 1950-2003, in millions of tonnes of contained H2SO4. The increase in production with time is notable. It is due to the increased use of phosphate and sulfate fertilizers, virtually all of which are made with sulfuric acid. Data sources ...

Fig. 5.1. Spent sulfuric acid regeneration flowsheet. H2SO4(0 the contaminated spent acid is decomposed to S02(g), 02(g) and H20(g) in a mildly oxidizing, 1300 K fuel fired furnace. The fiunace offgas (6-14 volume% SO2,2 volume% O2, remainder N2, H2O, CO2) is cooled, cleaned and dried. It is then sent to catalytic SO2 + AO2 SO3 oxidation and H2SO4 making, Eqn. (1.2). Air is added just before dehydration (top right) to provide O2 for catalytic SO2 oxidation. Molten sulfur is often burnt as fuel in the decomposition fiimace. It provides heat for H2SO4 decomposition and SO2 for additional H2SO4 production. Tables 5.2 and 5.3 give details of industrial operations.

Heat for this reaction is mainly provided by burning molten sulfur and other fuels with preheated air (occasionally oxygen-enriched) and the O2 from Reaction (5.1). A small amount of heat is obtained from oxidizing the spent acid s hydrocarbons. Sulfur burning has the advantages that it increases SO2 concentration in decomposition furnace offgas and H2SO4 production rate. 

Catalytic oxidation of S02(g) to S03(g) is a key step in sulfuric acid production. It produces the SO3 required for H2SO4 making. Chapter 9. 

Catalytic S02(g) + /202(g) -> S03(g) oxidation is a key step in sulfuric acid manufacture. It makes SO3 for subsequent H2SO4 production, Reaction (1.2). Efficient SO2 oxidation contributes to efficient acid production and small emission of SO2. 

Fig. 23.1. Simplified single contact sulfuric acid production flowsheet. Its inputs are moist feed gas and water. Its outputs are 98 mass% H2SO4, 2 mass% H2O sulfuric acid and dilute SO2, O2, N2 gas. The acid output combines gas dehydration tower acid, H2SO4 making tower acid and liquid water. The equivalent sulfur burning acid plant sends moist air (rather than moist feed gas) to dehydration. Appendix V gives an example sulfur burning calculation.

Fig. 4. Staple fiber washing sequence 1, a hot acid wash (2% H2SO4 at 90°C) decomposes and washes out most of the insoluble zinc salts. This wash completes the regeneration of xanthate and removes as much sulfur as possible in the form of recoverable CS2 and H2S 2, an alkaline sodium sulfide desulfurization bath solubilizes sulfurous by-products and converts them into easily removed sulfides 3, a sulfide wash to remove the sulfides created in bath 2 4, a bleach bath (optional) uses very dilute hypochlorite or peroxide to improve fiber whiteness 5, a dilute acid or sour bath removes any remaining traces of metal ions and guarantees that any residual bleaching chemicals are destroyed 6, a controlled-pH freshwater final wash removes the last traces of acid and salt prior to drsdng and 7, a finish bath gives the fiber a soft handle for easy drying and subsequent processing.

Scheme 6.83. A suite of reactions that accounts for the production of the nitronium ion (N02 ) by the sulfuric (H2SO4) acid promoted dehydration of nitric (HNO3) acid. It is important to notice the stoichiometry of the summed reaction since cryoscopic measurements identify four ionic species.

Absorption with reaction Sulfuric acid production SOj in H2SO4 Packed column... 

In contrast to sulfur oxidation to SO2, the oxidation to SO3 is limited by thermodynamic constraints (Example 4.2.3), and is the crucial reaction step in H2SO4 production. According to Eqs. (4.2.19) and (4.2.20), the equilibrium constant Ky based on the molar fractions of SO2, O2, and SO3 (with p as total pressure) is given by ... 

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