Methionine Hydroxy Analog from Acrolein, Methyl Mercaptan and HCN

The process under analysis comprises three major sections: (1) HMBN Synthesis; (2) MHA Synthesis; and (3) Purification.

HMBN Synthesis. Liquid MMP is continuously fed to the HMBN reactor, while gaseous hydrogen cyanide is fed through its bottom. The reaction is catalyzed by a mixture of pyridine and acetic acid. MMP is completely converted, with high selectivity to HMBN, and few heavier by-products. The effluent from this reactor is conducted to a nitrogen stripping column to remove unconverted hydrogen cyanide, the HCN free stream is then directed to the MHA synthesis.

MHA Synthesis. HMBN undergoes hydrolysis in three steps. At first, HMBN is introduced into a continuously stirred tank reactor (CSTR) along with process water and sulfuric acid stream. HMBN reacts with water to form an amide, 2-hydroxy-4-methylthiobutanamide, and sulfuric acid behaves as a catalyst. The effluent from this reactor and additional process water are introduced into a second CSTR, operated at higher temperature. The amide content is hydrolyzed in a reaction with water and sulfuric acid forming MHA and ammonium bisulfate. The effluent from this second reactor is fed to a plug flow reactor to guarantee complete hydrolysis of the amide formed in the first step.

Purification. MHA is extracted with methyl isobutyl ketone (MIBK). The extract, rich in MHA and solvent, is steam stripped. The water and solvent are recovered from the top product and a concentrated MHA stream is recovered from the bottom. The final product composition is corrected with process water. The raffinate from the extraction, mostly water and ammonium bisulfate, is also steam stripped. The water is recovered from the top and an aqueous solution containing ammonium bisulfate is recovered from the bottoms and disposed as waste.