Vapors, H2SO4 production

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... 

Acid circulated over SO absorbing towers is maintained at about 98.5% to minimize its vapor pressure. Where lower concentration product acid is desired, it is made either in separate dilution faciUties, or in drying towers operated at 93—96% H2SO4. 

A clear example of the possible use of acid and/or superacid solids as catalysts is the alkylation of isobutane with butenes. Isobutane alkylation with low-molecular-weight olefins is one of the most important refining process for the production of high-octane number (RON and MON), low red vapor pressure (RVP) gasoline. Currently, the reaction is carried out using H2SO4 or HF (Table 13.1), although several catalytic systems have been studied in the last few years. 

Figure 9.5 illustrates the sulfuric acid concentrations that lead to the production of higher concentrations of nitric acid. At a concentration of 67 weight % H2SO4, the azeotropic point has vanished, and 99 weight % nitric acid can be distilled. The nitric acid is the lighter phase and is extracted as vapor. These vapors are condensed overhead and a portion of the nitric acid is returned to the distillation column as reflux. The sulfuric acid and water go with the bottom liquid phase and are concentrated for reuse in the process104,220. 

A kinetics reaction order of about 0.5 with respect to O2 was found in several studies when H2S was in excess, and of zero order for H2S/O2 < 1 [130,131]. The reaction is first order with respect to H2S. The reaction can be performed at temperatures as low as ambient. The presence of water vapor enhances the breakthrough capacity [132]. At first, only elemental sulfur was found as a reaction product, but later, with some carbons, SO2 and H2SO4 were also observed [130,133]. The formation of H2SO4 requires the presence of water vapor usually, a relative humidity of 80% is used. The selectivity to sulfur oxides increases with increasing reaction temperature. However, H2SO4 is obtained exclusively with some carbons, even at room temperature (e.g., with activated carbon fibers [134]... 

Due to the Clean Air Act, increasing attention is paid to the production of alkylates, which is a very clean burning fuel and has a high MON (motor octane number) with a low octane sensitivity and moderate vapor pressure. Commercially operated alkylate production uses a liquid acid catalyst such as H2SO4 or HE, resulting in problems associated with cost, apparatus and the environment [47]. New synthetic methods utilizing solid acid catalysts have been developed but no commercial process has emerged due to fast catalyst deactivation [48]. 

The characteristic time r/v to achieve a certain nucleation rate is calculated as follows. We assume that the production rate Rg of H2SO4 vapor is constant. At r = 0, = 0... 

A particular feature of operation of EDLC with AC electrodes is the formation of a certain amount of CO2 in the course of operation at the potentials above 1V (NHE). Analysis of the gas collected in the case of EDLC with electrolyte of 38% H2SO4 showed that it consisted predominantly of N2 and O2 with traces of CO2 and H2O at potentials below 1V. Eor charged EDLC, the gas consists mostly of CO2 with small amounts of Nj, O2, and HjO vapors. Presence of water vapors shows that the performance of the capacitor can decrease with time because of loss of electrolyte, which results in a decrease in capacitance of the capacitor. This, however, can occur only in unsealed EDLCs. Carbon dioxide is a product of oxidation of carbon electrodes. Its amount strongly depends on the voltage applied. To prevent CO2 accumulation in the course of EDLC operation, a release valve is used in some schemes. In most schemes, however, no valves are used. 

H2S04(f) is not made by reacting 803(g) with water. This is because Reaction (1.2) is so exothermic that the product of the 863(g) + H20(f) H2SO4 reaction would be hot H28O4 vapor - which is difficult and expensive to condense. 

Armitt et al. investigated the influence of acid vapors (98% H2SO4,35% H2SO4, and 37% HCl) on the decomposition of a solid sample of TATP placed into a crimped vial, where the TATP was separated from the deposited 100 pL liquid acid sample by a plug of cotton wool [62]. The headspace in the sealed vials was sampled with polydimethylsiloxane/Carboxen/divinylbenzene (PDMS/Carboxen/DVB) SPME fibers of film thickness 30 and 50 pm, at 1, 3, 5, and 8 h, and at 1,3, 7, and 10 days. Analysis of the headspace from the TATP samples exposed to vapor from the two sulfuric acids produced similar results, with the sample exposed to the 98% sulfuric acid vapor decomposing at a more rapid rate. The principle decomposition products were DADP and acetone, with some minor production of acetic acid. After 7 days, acetone was the major species observed in the headspace. The analysis of the headspace of the TATP samples exposed to HCl vapors showed rapid decomposition of TATP, with no detection of TATP or DADP after 1 day. Additionally, various chlorinated acetones were also observed, indicating a different decomposition pathway than that observed for the TATP exposed to sulfuric acid vapors. 

The evolved SO3 and H2SO4 vapors will react with the atmospheric moisture in a complicated way. The final product of these reactions is H2SO4 aerosol. In most cases the cloud will initially be denser than air, with numerous processes occurring in it. Only after some distance of travel downwind, allowing adequate dilution with air, will transition to passive behavior occur. By this point, all the SO3 and H2SO4 vapor is consumed and only H2SO4 aerosol is present in the cloud. The processes that occur in the cloud can be considered in three stages, as shown in Fig. 37.3. 

Fig. 6.4 Schematic illustration of the key pathways in the atmospheric cycle of S involving (7) the natural emissions of reduced S compounds such as H2S frran terrestrial biota and dimethyl sulfide (CH3SCH3) from oceanic biota (2) anthropogenic emissions of S compounds, principally SO2 (3) the oxidation of reduced S compounds by OH and other photochemical oxidants leading to the production of intermediate oxidation state S compotmds such as SO2 and methane sulfonic acid (MSA) (4) the oxidation of these mtermediate oxidation state compounds within the gas phase by OH-producing H2SO4 vapor (5) the conversion of intermediate oxidation state compounds within liquid could droplets, which upon evaporation yield sulfate-containing particles (6) the conversion of H2SO4 to sulfate-containing particles and (7) the ultimate removal of S fiom the atmosphere by wet and dry deposition (Chameides and Perdue 1997)...

Figure XIV-16 depicts the coupling of the PBMR with the sulphuric acid decomposition reactor and vaporizer and the HI decomposition reactor. A 0.25 mile separation would exist between the PBMR and the hydrogen plant. The PBMR provides heated helium to the hydrogen plant reactors. The hydrogen plant circulates H2SO4 and productions from the HI reactor at low temperatures and includes three major chemical reactions.

Figure XIV-17 depicts the PBMRTWestinghouse process interface for the production of hydrogen. This is a co-generation application for the PBMR, supplying electricity and heated helium. A 0.25 mile interface exists between the PBMR and the hydrogen production process. However, this process utilizes an electrolizer rather then the HI reactor, and circulates H2SO4 and other products from the decomposition reactor and vaporizer at low temperatures and requires only a single chemical reaction and single heat transmission.

The maximum theoretical product concentration is 98.5 mass% H2SO4 due to the increase in SO3 and decrease in H20(g) vapor pressures at higher acid concentrations (Fig. 9.4). 

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