Sulfur acid tower operation

The calcium bisulfite acid used in the manufacture of sulfite cellulose is the product of reaction between gaseous sulfur dioxide, liquid water, and limestone. The reaction is normally carried out in trickle-bed reactors by the so-called Jenssen tower operation (E3). The use of gas-liquid fluidized beds has been suggested for this purpose (V7). The process is an example of a noncatalytic process involving three phases. 

SOLINOX SO,. Linde NO,] A process for removing both NOx and SOx from fluegases. The SOx is removed by scrubbing with tetra-ethylene glycol dimethyl ether, circulated in a packed tower (the Selexol process). The NOx is destroyed by Selective Catalytic Reduction ( SCR). The sorbent is regenerated with steam the SOx is recovered for conversion to sulfuric acid. Developed by Linde in 1985 and used in a lead smelter in Austria and several power stations in Germany. In 1990 it was announced that it would be used at the titanium pigment plant in The Netherlands operated by Sachtleben. 

Later it was synthesized in a batch process from dimethyl ether and sulfur thoxide (93) and this combination was adapted for continuous operation. Gaseous dimethyl ether was bubbled at 15.4 kg/h into the bottom of a tower 20 cm in diameter and 365 cm high and filled with the reaction product dimethyl sulfate. Liquid sulfur thoxide was introduced at 26.5 kg/h at the top of the tower. The mildly exothermic reaction was controlled at 45—47°C, and the reaction product (96—97 wt % dimethyl sulfate, sulfuric acid, and methyl hydrogen sulfate) was continuously withdrawn and purified by vacuum distillation over sodium sulfate. The yield was almost quantitative, and the product was a clear, colorless, mobile liquid. A modified process is described in Reference 94. Properties are listed in Table 3. 

In contrast to the Western economy, the Russia continued expansion of wood hydrolysis facilities, and about 40 such plants are presently in operation. All the Russian plants are based on dilute sulfuric acid in percolation towers. In the West interest in producing alcohols from wood was revitalized by the dramatic increase in the price of petroleum in the 1970s and the push to decrease oil imports by substituting gasohol, which is one part alcohol in nine parts gasoline, for 100 percent gasoline at gas pumps. Both ethanol and methanol can be used in gasohol blends. 

Complete simulation models have been formulated for cascade and Stratco sulfuric acid alkylation units and studies have confirmed the accuracy of the models. Application studies include cases in which model usage Identified profitable unit modifications, determined optimal unit capacity and optimal distillation tower operation, and compared the performance of cascade and Stratco units. "Isostripper" deisobutanizer operation was determined to be relatively unprofitable for sulfuric acid alkylation units and acid consumption on a modified cascade unit was found to be 36% below that expected for a Stratco unit. The examples presented suggest the broad applicability of the simulation models for improving alkylation unit operation. Use of the models not only pinpoints areas where significant improvements are possible, but also quantifies incentives needed to get them implemented quickly. 

Sulfuric acid is utilized with gaseous ammonia, the heat of neutralization then being sufficient to evaporate all the water. In a process operated in Japan, sulfuric acid is fed in at the top of a tower and gaseous ammonia at the bottom. The ammonium sulfate can be drawn off from the bottom, which requires no further drying. 

There has also been concern over the potential air pollution problem that can be caused by the ammonia present in the off-gas. However, it has been reported (12) that the ammonia concentration in the off-gas from a stripping tower seldom exceeds 10 mg/m even before its dispersion in the surrounding air. The threshold for odor is about 35 mg/m therefore, there is little likelihood for the ammonia-stripping operation to cause an odor problem. However, small concentrations of ammonia in air may react with sulfur dioxide to form aerosols or fog. Under such a situation, ammonia can be removed from the offgas by a scrubber of by bubbling it through a dilute sulfuric acid solution. 

One commercial method to obtain nitric acid concentrations above 68% uses concentrated sulfuric acid to dehydrate the azeotropic composition. Hot nitric acid vapor is passed upward against concentrated sulfuric acid, which moved downward (countercurrent) in a tower packed with chemical stoneware to obtain 90+%HNO3 and a diluted sulfuric acid stream (Fig. 11.6). If this process is practiced on only a small scale, the sulfuric acid may be reconcentrated by addition of oleum, and a portion of the buildup of sulfuric acid in this circuit may be used to make up a commercial nitrating mixture with some of the fuming nitric acid made. Larger scale operation requires the use of a sulfuric acid boiler and a large heat input to reconcentrate the dehydration acid. There is also a noticeable sulfate contamination of the nitric acid product from this process. 

Cooling the gases leaving the ammoxidation reactor are quenched at about 380 to 400°C, first in a boiler designed to produce low-pressure steam, and then by direct contact in a tower operating in the presence of sulfuric acid af the bottom zone to neutralize the residual ammonia, and water in the top section. The ammonium sulfate withdrawn can be treated subsequently to extract the organic compounds which it contains. 

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