Regeneration of sulfuric acid from sulfate by-products of 2-hydoxy-4-(methylthio) butyric acid manufacture

A process for the preparation of sulfuric acid comprising the steps of:

• introducing a feed mixture comprising a sulfate feed solution into a combustion zone in which a fuel is burned with a gas comprising oxygen, said sulfate feed solution comprising a by product of a process for the preparation of 2-hydroxy-4-(methylthio)butyric acid by hydrolysis of 2-hydroxy-4-(methylthio)butyronitrile with sulfuric acid to produce a hydrolyzate solution containing 2-hydroxy-4-(methylthio)butyric acid and a sulfate source selected from the group consisting of ammonium sulfate, ammonium bisulfate, sulfuric acid, and mixtures thereof, said sulfate feed solution comprising said sulfate source, said feed mixture further comprising volatile organic sulfur compounds that have been purged from said process for the preparation of 2-hydroxy-4-(methylthio)butyric acid, said volatile organic sulfur compounds comprising precursors of 2-hydroxy-4-(methylthio)butyric acid or by-products of the preparation of 2-hydroxy-4-(methylthio)butyric acid or its precursors, oxidizable components of said feed solution being burned in said combustion zone to produce a combustion gas containing sulfur dioxide, carbon dioxide, nitrogen, and water vapor, said sulfate feed solution being contacted in a first stage of said combustion zone with a reducing flame in which ammonia, nitriles and any amines released from the solution are oxidized to produce nitrogen gas and any oxides of nitrogen are reduced to nitrogen gas, thereby producing a partial combustion gas substantially free of oxides of nitrogen, said partial combustion gas being contacted with additional gas containing oxygen to oxidize unburned fuel and any carbon monoxide contained in the partial combustion gas, thereby producing said combustion gas;
• introducing oxygen into said combustion gas to produce a feed gas containing sulfur dioxide and at least about 0.9 moles of oxygen per mole of sulfur dioxide;
• passing said feed gas over a catalyst for the conversion of sulfur dioxide to sulfur trioxide at a temperature effective for said conversion;
• and
• thereafter contacting the gas that has been passed over said catalyst with sulfuric acid for the absorption of sulfur trioxide and the formation of sulfuric acid.

A process for the manufacture of 2-hydroxy-4-(methylthio)butyric acid in a facility for said process using sulfuric acid recycled from a spent acid recovery unit that is associated with said facility, the process comprising:

• hydrolyzing 2-hydroxy-4-(methylthio)butyronitrile with sulfuric acid to produce 2-hydroxy-4-(methylthio)butyric acid and a by-product sulfate solution;
• introducing into a combustion zone of said spent acid recovery unit a feed mixture comprising said by-product sulfate solution and 2-hydroxy-4-(methylthio)butyric acid;
• burning a fuel and 2-hydroxy-4-(methylthio)butyric acid contained in said by-product sulfate solution in a combustion zone with a gas comprising oxygen to produce a combustion gas containing sulfur dioxide, carbon dioxide, nitrogen, and water vapor, said feed solution being contacted in a first stage of said combustion zone with a reducing flame in which ammonia, nitriles and any amines released from the solution are oxidized to produce nitrogen gas and any oxides of nitrogen are reduced to nitrogen gas, thereby producing a partial combustion gas substantially free of oxides of nitrogen, said partial combustion gas being contacted with additional gas containing oxygen to oxidize unburned fuel and any carbon monoxide in the partial combustion gas, thereby producing said combustion gas;
• introducing oxygen into said combustion gas to produce a feed gas containing sulfur dioxide and at least about 0.9 moles of oxygen per mole of sulfur dioxide;
• passing said feed gas over a catalyst for the conversion of sulfur dioxide to sulfur trioxide at a temperature effective for said conversion;
• thereafter contacting the gas that has been passed over said catalyst with sulfuric acid for the absorption of sulfur trioxide and the formation of sulfur acid;
• recycling sulfuric acid formed by said absorbtion to said facility for the manufacture of 2-hydroxy-4-(methylthio)butyric acid;
• purging sufficient water from the process such that the strength of said recycled sulfuric acid is greater than about 50% by weight on an organic free basis;
• and
• contacting said recycled sulfuric acid with 2-hydroxy-4-(methylthio)butyronitrile for the preparation of 2-hydroxy-4-(methylthio)butyric acid.