Patent ID: 7655072

Claim:
Process for preparing methionine comprising the steps of converting the following components: 3-methylmercaptopropionaldehyde (MMP), hydrogen cyanide, ammonia and carbon dioxide, or sources of those components, to 5-(2-methylmercaptoethyl)hydantoin, hydrolyzing said 5-(2-methylmercaptoethyl)hydantoin and precipitating the methionine with introduction of CO 2 , subjecting CO 2 -containing offgas exiting from a hydantoin synthesis reactor to a scrubbing process for purifying the CO 2 -containing offgas stream having a content of methyl mercaptan, the scrubbing process of the gas stream comprising the specified sequence of steps: a) scrubbing with water or with water in which methylmercapto-propionaldehyde (MMP) is present dissolved up to a maximum of solubility limit, b) subsequently scrubbing with MMP, c) then scrubbing with water to obtain a purified CO 2 , d) recycling the purified CO 2 gas stream is recycled into the production process, e) then recycling resulting scrubbing liquids into the process for preparing methionine or its precursors, and f) introducing the purified CO 2 gas stream into a reactor containing a solution of an alkali metal salt solution of methionine, and precipitating methionine from said alkali metal, in which scrubbing liquid from the first scrubbing step a) is passed into the hydantoin synthesis reactor.