IL33840A - Process for the preparation of methionine - Google Patents

Description

npsnV Process for the preparation oi ethionine from It is known that methionine can be prepared by the hydrolysis of the hydantoin indicated The hydrolysis is effected by heating the if under in the presence o and of certain substances of alkaline Prom the solution of methionine salts thus obtained the methionine is precipitated by neutralization of the solution with an the hydrolysis may be effected by means of an acid and the methionine be separated by neutralization with an alkaline As alkaline substances there may be used alkali metal hydroxides or alkaline earth metal such as sodium hydroxide or barium while sulfuric or hydrochloric acid may be used as the Patent Specification It is also known to use as an alkaline substance sodium or potassium carbonate and as an acid a lower aliphatic ox lie acid such as acetic acid Patent fication It is further know to as alkaline substances for reaction with mixtures of an alkali metal carbonate and an alkali and carbon dioxide as an Published Application The hydrolysis also produces gaseous According to a new process these substances are eliminated the reaction system during the reaction in order to increase the yield of Published Application 65 In all these considerable amounts of salts are formed by the alkali metal or alkaline earth metal alkali metal alkali metal acetates or alkali metal depending on the alkaline substances and acids The separation and purification of the methionine from these whose molar proportion is times several times in excess over that of the is rather especially if a high yield of methionine is to be A further disadvantage of the known processes for the preparation of methionine consists in the required continuous consumption of the alkaline substances and while on the other hand the salts thus formed can not be Since their separation from the mother liquor is not economical are usually discarded with the mother This results in considerable amounts of waste and a certain amount of methionine is always lost with the mother invention consists in a process for the thio paration of methionine wherein hydantoin is subjected to hydrolysis with an aqueous alkali metal carbonate or bicarbonate at elevated temperature and under elevated the ammonia and carbon dioxide formed are separated during the the methionine is separated from the solution after the hydrolysis by means of carbon and the mother liquor containing alkali bicarbonate is recycled to the hydrolysis reaction By the ammonia and carbon dioxide are split off from the Under the conditions of the reaction the and carbon dioxide are gases and escape from the reaction mixture together with water In addition carbon dioxide is liberated from the alkali metal bicarbonate solution by the methionine by the The residual reaction liquor is alkaline with a above and contains the methionine as alkali metal In order to s eparate the methionine carbon dioxide is if at elevated pressure into the In this manner the of the solution is as a rule it becomes stable at to and the alkali metal inate is converted into the more difficultly soluble Instead of gaseous carbon liquid or solid carbon dioxide may be The methionine precipitate can then be separated without difficulty by filtration from the It has a purity higher than The liquor remaining after the separation of the methionine is recycled and used for hydrolysis of a further amount of Thus no waste liquids are except for the small amount of mother liquor which has from time to time to be discarded in ord r to avoid the accumulation of Since these small portions of mother liquor can easily be freed from methionine and alkali metal carbonate or the losses in these compounds are extremel The ield of methionine is as hi h as gaseous substances escaping during the hydrolysis carbon dioxide and can completely be recycled in the Ammonia and a ponding part of the carbon dioxide is used in aqueous solution for the preparation of hydantoin from aldehyde while the remaining part of the carbon dioxide is used for precipitating the methionine fro the reaction For carrying out the process according to the tion aqueous solutions of alkali metal carbonate or alkali metal bicarbonate or a mixture thereof may be recycled liquor is used after the separation of the methionine by saturation with carbon is in fact an alkali metal bicarbonate In the mother liquor contains depending on the reaction conditions 20 to 50 grams of dissolved methionine per litre which escapes separation under the precipitating conditions of the process but can be recycled without any Among the alkali metal bicarbonates and carbonates the potassium salts are Preferred ratios of hydantoin to alkali metal salt are up to preferably to The hydrolysis of the hydantoin is preferably effected in the temperature range of 120 to preferably from 140 to Corresponding to this temperature the operation is conducted under elevated which is generally slightly higher than the water vapour pressure corresponding to this The removal of the ammonia and carbon dioxide formed during the hydrolysis is facilitated if steam or an inert such as is passed through the reaction The residual reaction which is free of if be decolorized with active For the separation of the so much carbon dioxide is introduced into the solution at room if desired under that the solution becomes The mother liquor can repeatedly be reused for the hydrolysis without If it is made up wit alkali metal carbonate or As a rule it is only after about 100 cycles that such an amount of or decomposition products such as has accumulated in the mother liquor that the methionine recovered has no longer the required and the mother liquor has to be It is that an amount of 1 to of the mother liquor is withdrawn at each From this withdrawn portion of the mother liquor and bicarbonate the recovered by saturation with carbon dioxide at as low a temperature as possible and with 2 to times its volume of a solvent such as an especially methanol or preferably After filtration the solvent is recovered from the mother liquor by The invention is illustrated by the following Examples to which it is not 1 A recycled mother liquor contains 327 g of 60 g of potassium 27 g of potassium 20 g of methionine and g of To this solution 314 g of an aqueous solution containing 86 g of the same hydantoin is The mixture is heated to in an autoclave provided with a stirrer and maintained at this temperature for 40 minutes at a pressure of 7 atmospheres During this time 212 g of vapours consisting of ammonia and carbon di ide are continuously withdrawn and end of the reaction is recognized by the is released fact that no more After release of pressure and cooling to the reaction solution is admixed with g of active further cooled to and From the filtrate the methionine is by introduction of carbon dioxide in a first stage at normal pressure in a second stage under a pressure of 3 solution absorbs 40 g of carbon the of the solution drops from to The separated methionine is filtered and washed with 100 g of 73 g of methionine are This corresponds to a yield of 99 calculated on the amount of hydantoin The methionine contains as impurity of potassium The filtrate amounts to g of mother liquor which is freed from 130 g of water and 20 g of carbon dioxide by mother liquor has then mately the game composition as the starting It is reused for the In order to keep the composition of the mother liquor constant as it is recycled to the hydrolysis of new hydantoin and to avoid an accumulation of 10 g of the mother liquor are separated before each reuse and worked up the recovery of the dissolved methionine and carbonate the solution is cooled to and mixed with a double amount of acetone and saturated at normal pressure with carbon 10 g of mother liquor g of methionine and g of potassium bicarbonate are recovered and are returned to the After the recovery of the acetone by distillation the mother liquor is From the vapours escaping during the hydrolysis an aqueous ammonium carbonate solution is this is used for the preparation of the solution of hydantoin and hydrocyanic Excess carbon or the carbon dioxide recovered by the evaporation of the mother is used again for the precipitation of the 2 To 1200 ml of a solution in which 110 g of potassium carbonate and g of methionine are there is added 285 ml of an aqueous solution containing 81 g of The mixture is heated for 4 hours at 135 to and a pressure of 2 to while 150 to 170 ml of aqueous ammonia together with carbon dioxide are The methionine is recovered by the procedure described in By introduction of carbon dioxide into the solution the of the latter is lowered from to 69 of methionine are recoveredj this corresponds to a yield calculated on the hydantoin The ionine has a purity of and a melting point between 272 and The whole mother liquor used for After 50 cycles the has still the purity as after the first In order to remove the the whole amount of mother liquor purified with acetone as described in whereby of the dissolved methionine and potassium bicarbonate are To 1200 of a solution in which 220 g potassium bicarbonate 55 of methionine are there is added 285 of an aqueous solution containing 81 g of mixture is heated for hours at to and to The yield and the purity of the methionine produced are the same as in Example litres of a solution containing 1600 g of sodium and g of there is added a solution of 1620 g of in 5 litres of solution is heated for 4 hours to At the beginning of the reaction the pressure is about and at the end of the reaction it is The distillation of aqueous ammonia and carbon dioxide amounts to 3 to litres per After cooling to the solution is diluted with water to a volume of 25 The methionine is cipitated by the introduction of carbon The pH of the solution drops from to and when the carbon dioxide pressure is raised to 3 gauge the pH drops further to As described in Example 2 the mother liquor is used for further hydrolysis 1360 g of methionine are this corresponds to a yield of calculated on the hydantoin The purity of the methionine is EXAMPLE 5 A solution of 100 kg of potassium 28 kg thio of methionine and 41 kg of in 400 litres of water is fed by means of a metering to a continuously operating pressure apparatus consisting of three recycle evaporators connected in The solution is prepared continuously by the tion of a aqueous solution of hydantoin to the recycled mother Quantitative version requires an average residence time of 2 to hours at 155 to and of 15 to 20 minutes at 175 to 70 to 100 of steam of 160 to are passed through the reaction mixture in order to expel the ammonia and carbon dioxide The further procedure is essentially the same as described in Example kg hour of methionine are this corresponds to a yield of calculated on the hydantoin Similar results are achieved if nitrogen is used instead of steam for the entrainment of the ammonia and carbon insufficientOCRQuality

Claims (1)

CLAIMS A process for preparation of methionine wherein is subjected to hydrolysis with an aqueous alkali metal carbonate or bicarbonate at vated temperature and under elevated the ammonia and carbon dioxide formed are separated during the the methionine is separated from the solution after the tiydrolysis by means of carbon and the mother liquor containing alkali metal bicarbonate is recycled to the hydrolysis A process according to Claim wherein the alkali metal carbonate and bicarbonate used are those of A process according to
1. Claim 1 or wherein ammonia and carbon dioxide are entrained from the reaction mixture by steam or an inert gas such as A process according to any of Claims 1 to wherein a portion of the mother liquor is withdrawn from time to time or continuously from the process cycle and admixed at a low temperature with a preferably for precipitating methionine and bicarbonate contained For the Applicants insufficientOCRQuality