Acidulated Sulfur Dioxide

During vinification, SO2 has historically represented one important tool used by winemakers to control microbiological growth. Due to health concerns (Yang and Purchase, 1985), some wineries have reduced usage dramatically, with a possible increased risk of microbial spoilage. 

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Once deposits and debris are removed and surfaces are visibly clean, the equipment can then be sanitized. Sanitizing agents may include the halogens (e.g., iodine), hot water, ozone, peroxides, quaternary ammonium compounds (QUATS), or acidulated sulfur dioxide. Table 9.1 compares commonly used chemical sanitizers with respect to their relative advantages and disadvantages. 

The anaerobic reaction of sulfur dioxide with aqueous ammonia produces a solution of ammonium sulfite [10192-30-0]. This reaction proceeds efficientiy, even with a gas stream containing as Httie as 1 wt % sulfur dioxide. The sulfur dioxide can be regenerated at a high concentration by acidulation or by stream stripping of the ammonium sulfite solution, or the sulfite can be made to precipitate and the ammonia recovered by addition of lime (243). The process can also be modified to produce ammonium sulfate for use as fertili2er (244) (see Fertilizers). In a variant of this process, the use of electron-beam radiation cataly2es the oxidation of sulfur dioxide in the presence of ammonia to form ammonium sulfate (245). 

The Reich test is used to estimate sulfur dioxide content of a gas by measuring the volume of gas required to decolorize a standard iodine solution (274). Equipment has been developed commercially for continuous monitoring of stack gas by measuring the near-ultraviolet absorption bands of sulfur dioxide (275—277). The deterrnination of sulfur dioxide in food is conducted by distilling the sulfur dioxide from the acidulated sample into a solution of hydrogen peroxide, foUowed by acidimetric titration of the sulfuric acid thus produced (278). Analytical methods for sulfur dioxide have been reviewed (279). 

In kaolin (clay) processing, sulfur dioxide reduces colored impurities, eg, iron compounds. In the bromine industry, sulfur dioxide is used as an antioxidant in spent brine to be reinjected underground. In agriculture, especially in California, sulfur dioxide is used to increase water penetration and the avadabiHty of soil nutrients by virtue of its abiHty to acidulate saline—alkaH soils (327). It is also usefiil for cleaning ferric and manganese oxide deposits from tile drains (328). 

Calcium sulfate may be decomposed to cement clinker and sulfur dioxide gas in a coke-fired rotary kiln at 900-1400°C (Miiller-Kiihne).28 However, the unfavorable economics of this process relegate it to countries that do not have other sources of sulfur. Phospho-gypsum (gypsum produced by the acidulation of phosphate rock) may be decomposed in this way as a means of recycling the sulfur values in the large waste phosphogypsum piles at fertilizer plants (OSW-Krupp and FIPR/Davy... 

Various catalysts have been used, including activated carbon, bauxite, and bimetallic oxides. The sulfur dioxide is then absorbed in a solution of ammonium sulfite and bisulfite acidulation of this yields ammonium sulfate and elemental sulfur. 

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