The present invention provides a method for purifying carbon dioxide gas characterized in that carbon dioxide gas containing at least one of 3-methylmercaptopropionaldehyde and acrolein is contacted with activated carbon to remove at least one of the 3-methylmercaptopropionaldehyde and acrolein. The present invention provides also a method for producing methionine comprising the purification step of the recovered carbon dioxide.

The present invention provides a method for purifying carbon dioxide gas characterized in that carbon dioxide gas containing at least one of 3-methylmercaptopropionaldehyde and acrolein is contacted with activated carbon to remove at least one of the 3-methylmercaptopropionaldehyde and acrolein. The present invention provides also a method for producing methionine comprising the purification step of the recovered carbon dioxide.

A process for the preparation of a polyunsaturated thiol comprising: (1) reacting a polyunsaturated alcohol in the presence of a compound of formula R.sub.2—SO.sub.2Hal wherein R.sub.2 is a C.sub.1-20 hydrocarbyl group, such an C.sub.1-10 alkyl group, to form a polyunsaturated sulphonyl ester; (2) converting the polyunsaturated sulphonyl ester to a polyunsaturated thioester by reacting with an anion of formula .sup.−SC(═O)R.sub.4 wherein R.sub.4 is a C.sub.1-20 hydrocarbyl group; (3) converting the polyunsaturated thioester to form a polyunsaturated thiol optionally in the presence of an antioxidant, e.g. using a metal carbonate. (4) reacting said polyunsaturated thiol with a compound (LG)R.sup.3COX wherein X is an electron withdrawing group and R.sup.3 is an alkylene group carrying a leaving group (LG), such as LG-CH.sub.2— forming

##STR00001## where X is an electron withdrawing group and LG is a leaving group; optionally in the presence of an antioxidant, so as to form a polyunsaturated ketone compound.

A process for the preparation of a polyunsaturated thiol comprising: (1) reacting a polyunsaturated alcohol in the presence of a compound of formula R.sub.2—SO.sub.2Hal wherein R.sub.2 is a C.sub.1-20 hydrocarbyl group, such an C.sub.1-10 alkyl group, to form a polyunsaturated sulphonyl ester; (2) converting the polyunsaturated sulphonyl ester to a polyunsaturated thioester by reacting with an anion of formula .sup.−SC(═O)R.sub.4 wherein R.sub.4 is a C.sub.1-20 hydrocarbyl group; (3) converting the polyunsaturated thioester to form a polyunsaturated thiol optionally in the presence of an antioxidant, e.g. using a metal carbonate. (4) reacting said polyunsaturated thiol with a compound (LG)R.sup.3COX wherein X is an electron withdrawing group and R.sup.3 is an alkylene group carrying a leaving group (LG), such as LG-CH.sub.2— forming

##STR00001## where X is an electron withdrawing group and LG is a leaving group; optionally in the presence of an antioxidant, so as to form a polyunsaturated ketone compound.

A process for the preparation of a polyunsaturated thiol comprising: (1) reacting a polyunsaturated alcohol in the presence of a compound of formula R.sub.2—SO.sub.2Hal wherein R.sub.2 is a C.sub.1-20 hydrocarbyl group, such an C.sub.1-10 alkyl group, to form a polyunsaturated sulphonyl ester; (2) converting the polyunsaturated sulphonyl ester to a polyunsaturated thioester by reacting with an anion of formula .sup.−SC(═O)R.sub.4 wherein R.sub.4 is a C.sub.1-20 hydrocarbyl group; (3) converting the polyunsaturated thioester to form a polyunsaturated thiol optionally in the presence of an antioxidant, e.g. using a metal carbonate. (4) reacting said polyunsaturated thiol with a compound (LG)R.sup.3COX wherein X is an electron withdrawing group and R.sup.3 is an alkylene group carrying a leaving group (LG), such as LG-CH.sub.2— forming

##STR00001## where X is an electron withdrawing group and LG is a leaving group; optionally in the presence of an antioxidant, so as to form a polyunsaturated ketone compound.

The present disclosure relates to a method for preparing L-cysteine crystals, and L-cysteine crystals prepared by the method. Through the method for preparing L-cysteine crystals of the present disclosure, L-cysteine crystals can be obtained from a natural L-cysteine fermentation broth with a high recovery rate and/or purity without a chemical reaction or the use of an artificial synthetic compound.

The present disclosure relates to a method for preparing L-cysteine crystals, and L-cysteine crystals prepared by the method. Through the method for preparing L-cysteine crystals of the present disclosure, L-cysteine crystals can be obtained from a natural L-cysteine fermentation broth with a high recovery rate and/or purity without a chemical reaction or the use of an artificial synthetic compound.

The present disclosure relates to an additive used in a methionine preparation process, and a methionine preparation method. The additive provided by the present disclosure is a mixture containing components A, B, and C; component A has a structure represented by the following general formula (1); component B has a structure represented by the following general formula (2); component C is silicone oil; RCON(CH.sub.3)CH.sub.2CH.sub.2SO.sub.3Na (1). The methionine preparation method provided in the present invention comprises subjecting methionine to crystallization and/or recrystallization in the presence of the additive provided by the present disclosure. The additive provided by the present disclosure results in uniform emulsification, has good stability, can be used stably for a long time, and is suitable for a continuous crystallization process. The prepared methionine crystal has a good crystal form, a large bulk density, and good flowability. In addition, according to the methionine preparation method of the present disclosure, a crystallization system can operate continuously and stably for a long time without obvious foaming, and the crystallization process of the methionine product can proceed smoothly.

##STR00001##

The present disclosure relates to an additive used in a methionine preparation process, and a methionine preparation method. The additive provided by the present disclosure is a mixture containing components A, B, and C; component A has a structure represented by the following general formula (1); component B has a structure represented by the following general formula (2); component C is silicone oil; RCON(CH.sub.3)CH.sub.2CH.sub.2SO.sub.3Na (1). The methionine preparation method provided in the present invention comprises subjecting methionine to crystallization and/or recrystallization in the presence of the additive provided by the present disclosure. The additive provided by the present disclosure results in uniform emulsification, has good stability, can be used stably for a long time, and is suitable for a continuous crystallization process. The prepared methionine crystal has a good crystal form, a large bulk density, and good flowability. In addition, according to the methionine preparation method of the present disclosure, a crystallization system can operate continuously and stably for a long time without obvious foaming, and the crystallization process of the methionine product can proceed smoothly.

##STR00001##

Provided in the present disclosure is a mixture, comprising 86-89 wt % of a methionine hydroxy analog and an oligomer thereof, more than 99.95 wt % being a monomer, dimer and trimer, and the ratio of monomer:dimer:trimer by weight being 77-80:18.5-19.5:3-4; 9.2-13.5 wt % of water; and less than 0.5 wt % of ammonium sulfate and ammonium bisulfate. The viscosity of the mixture at 10° C. is lower than 200 mPa.Math.s. Further provided is a method for processing a mixture containing a methionine hydroxy analog and an oligomer thereof.