Peracidox process

With the double contact process it is unnecessary to purify the tail gases to reduce their sulfur dioxide content still further, whereas tail gases from single contact plants have to be purified. This can be realized either by scrubbing with ammonia or with an aqueous solution of sodium sulfite and sodium hydrogen sulfite (Wellman-Lord process), absorption on activated charcoal (sulfacid process from Lurgi) or by oxidative gas purification such as in the peracidox process (oxidation of sulfur dioxide with hydrogen peroxide or peroxomonosulfuric acid). 

Indirect electrochemical process with homogeneous redox mediator called as Peracidox process (Saraberg-Holter-Lurgi-SHL) has been... 

Peracidox A process for removing sulfur dioxide from the tail gases from sulfuric acid plants by absorption in peroxomonosulfuric acid (Caro s acid). The peroxomonosulfuric acid is generated on-site by the electrolytic oxidation of sulfuric acid. Developed by Lurgi and Sud-Chemie and first operated in 1972. 

Tail gas emissions are controlled by improving the S02 conversion efficiency and by scrubbing the tail gas. In a double absorption process plant, a five-bed converter has 0.3 percent unconverted S02, as compared with 0.5 percent for a four-bed converter. A Lurgi Peracidox scrubber may be used to remove up to 90 percent of the residual S02 in the tail gas from a double absorption plant. Hydrogen peroxide or electrolytically produced peroxymonosulfuric acid is used to convert the S02 to H2S04 in the Lurgi scrubber. 

One example [54] uses Cr(VI) ions and also simultaneously treats the NO c components of the flue gas. Both the SO2 and the are oxidised to the corresponding acids. A similar process is based on the use of the Ce(III)/Ce(IV) redox couple. Lurgi have developed a process (Peracidox) using an intrinsic redox mediator based on lead/lead dioxide. Current efficiencies of 97% can be achieved at electrode potentials of 1.61 V. 

Of all these methods indirect oxidation of SO2 using redox mediators and electrochemically promoted oxidation seem to be the nearest alternatives to the commercial applications. The removal of SO2 by using redox mediators has already been tested in commercial scale in the processes named Peracidox and Ispra Mark HI. Westinghouse Process is another commercial application in terms of hydrogen production via hybrid sulfur cycle. 

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See also in sourсe #XX -- [ ]

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