ITMI20011783A1 - METHACRYLAMIDE (MAA) PREPARATION PROCESS FROM ACETONCIANIDRINA - Google Patents

Description

Description of the industrial invention in the name:

The present invention relates to a process for the preparation of alkyl methacrylates in which the alkyl comprises from 1 to 5 carbon atoms, linear or branched when possible, comprising methacrylamide (MAA) by reaction of acetoncyanhydrin (ACH) with concentrated sulfuric acid and subsequent transformation of the intermediates or-hydroxyisobutyramide (ar-IIBA) and sulphonic monoester of or-hydroxyisobutyramide (α-IIBAS) to methacrylamide (MAA), by heating at 130-150 ° C characterized by the fact that the reaction between sulfuric and acetononehydrin is carried out in the presence of alkyl- or arii-sulphonic acids.

With the process object of the invention it is possible to obtain MAA with high yields of at least 90%, in particular higher than 95%, using molar ratios H2SO4 / ACH lower than 1.1: 1.

The reaction between ACH and concentrated sulfuric acid is normally carried out using a molar ratio between sulfuric acid and acetonchyanhydrin ranging from 1.3: 1 to 1.6: 1 in order to have a reaction mass that is sufficiently fluid to allow the reaction to take place. If a lower quantity of sulfuric acid is used, the viscosity of the reaction mixture obtained is too high and does not allow the reaction to take place.

In the production plants of the MAA starting from ACH, the disposal of the considerable quantities of sulfuric acid that must be used is very important. This disposal involves considerable costs for its transformation and / or recovery.

Patent EP 226,724 describes the reaction between sulfuric acid and ACH with molar ratios between 1.1: 1 and 1.4: 1, carrying out the reaction in the presence of a. C5-C7 hydrocarbon solvent, preferably hexane.

The need was therefore felt to reduce the quantities of sulfuric acid necessary for the process and therefore to be able to operate with molar ratios H2S04 / ACH close to or even lower than the stoichiometric ratio 1: 1, while maintaining a high yield in MAA.

The object of the present invention is to be able to carry out the reaction between concentrated sulfuric acid and ACH using molar ratios substantially stoichiometric or even lower than the stoichiometric and to obtain MAA with high yields.

It has been unexpectedly and surprisingly found that this object is achieved by carrying out the reaction between ACH and sulfuric acid using sulfuric acid in the presence of alkyl- or arii-sulphonic acids.

Therefore, the object of the present invention is a process for the preparation of alkyl methacrylates in which the alkyl comprises from 1 to 5 carbon atoms, linear or branched when possible, comprising the preparation of methacrylamide (MAA) comprising the following steps:

(a) gradual addition of acetoneianhydrin (ACH) to a mixture of sulfuric acid and an alkyl- or arylsulfonic acid, maintained under stirring at a reaction temperature between 50 ° C and 100 ° C, preferably between 70 and 90 ° C , wherein the H2SO4 / ACH molar ratios are comprised between 0.3: 1 and 1.1: 1, preferably between 0.7: 1 and 0.9: 1, with the proviso that the alkyl acid or arii-sulfonic is liquid at the reaction temperature;

(b) heating the reaction mixture obtained in step (a) to temperatures of 120-160 ° C, preferably 130-150 ° C with the obtaining of a reaction mixture containing methacrylamide (MAA), sulfuric acid and alkyl acid - or arii-sulfonic.

The reaction mixture obtained in step (b), optionally after separation of the alkyl- or arii-sulfonic acid, can be subjected to hydrolysis or esterification with water or CV C5 aliphatic alcohols to obtain alkyl-methacrylates, in particular methyl methacrylate (MMA ).

Optionally, step (b) can be followed by step (al) in which the reaction mixture coming from step (b) is reacted with a further quantity of ACH under the same reaction conditions described for step (a), at which is followed by a step (b1) carried out under the same conditions as step (b). It is possible to repeat the above sequence of phases (al), (bl). Generally it is possible to repeat this succession of phases (al), (bl) with the condition that a final overall yield in MAA of at least 90% is obtained.

With the process of the present invention it is possible to obtain global yields in MAA with respect to the fed ACH of at least 90%, in particular higher than 95%.

The sulfuric acid used has a concentration comprised between 98% and 102%, preferably between 99% and 101%, and is preferably added with small quantities, for example 200-400 ppm, of a polymerization inhibitor of MAA, to for example phenothiazine (PTZ).

The alkyl- or arii-sulphonic acid is used in mixture with the sulfuric acid in a weight ratio comprised between 10: 1 and 1: 1, preferably between 4: 1 and 3: 1.

Examples of alkyl- or arii-sulfonic acids usable in the present invention are methanesulfonic acid, trifluoromethanesulfonic acid (triflic acid), dodecylbenzenesulfonic acid, preferably methanesulfonic acid.

Some illustrative but not limitative examples of the present invention follow.

EXAMPLES

EXAMPLE 1

29.2 g of 100% H2SO4, 58 mg of phenothiazine (approx.

400 ppm on the H2S04 / AMS mixture) and 98.7 g of methanesulfonic acid (AMS). The mixture is heated up to 90 ° C and 31.7 g of 99.62% ACH are added under stirring in 51 minutes, achieving a molar ratio of H2SO4 / ACH of 0.8: 1.

It is left to react for 20 minutes and then the mixture is heated up to 140 ° C. After 30 minutes a sample is taken which analyzed in HPLC results to contain 18.2% by weight of MAA and 0.3% by weight of methacrylic acid, with an overall yield with respect to the ACH fed equal to 93.5%. For each gram of MAA produced, 0.988 g of H2S04 was used.

EXAMPLE 2

In the apparatus used in example 1, 29.2 g of 100% H2S04, 58 mg of phenothiazine (about 400 ppm on the H2S04 / AMS mixture) and 98.7 g of methanesulfonic acid (AMS) are introduced. The mixture is heated up to 90 ° C and 36.5 g of 99.5% ACH are added under stirring in 51 minutes, achieving a molar ratio of H2SO4 / ACH of 0.7: 1.

It is left to react for 10 minutes and then the mixture is heated up to 140 ° C. After 20 minutes a sample is taken which analyzed in HPLC results to contain 19.7% by weight of MAA and 0.5% by weight of methacrylic acid, with an overall yield with respect to the ACH fed equal to 91.4%. Approximately 0.88 g of H2S04 were therefore used for each gram of MAA produced.

EXAMPLE 3

Example 1 was repeated but carrying out the reaction between sulfuric acid and 99.5% ACH at a temperature of 80 ° C for a time of 10 minutes. Subsequently the obtained mixture is heated up to 140 ° C.

After 20 minutes a sample is taken which analyzed in HPLC results to contain 18.4% by weight of MAA and 0.4% by weight of methacrylic acid, with an overall yield with respect to the ACH fed equal to 95%. Approximately 0.97 g of H2S04 were therefore used for each gram of MAA produced.

EXAMPLE 4 (comparative)

Example 1 was repeated with the exception that methanesulfonic acid (AMS) was not fed but only sulfuric acid.

With the gradual addition of the ACH, the viscosity of the reaction mixture suddenly increases, after an addition of only 24 g of ACH, making it impossible to stir the reaction mixture and blocking the reaction.

EXAMPLE 5 (comparative)

Example 1 was repeated but using 127.9 g of methanesulfonic acyclo (AMS) in place of the AMS / H2SO4 mixture. The mixture is heated up to 90 ° C and 31.7 g of 99.57% ACH are added under stirring in 42 minutes.

It is left to react for 10 minutes and then the mixture is heated up to 140 ° C. After 20 minutes a sample is taken which analyzed in HPLC results to contain 1.03% by weight of MAA and 0.09% by weight of methacrylic acid (AMA), with an overall yield with respect to the fed ACH equal to 5.68%.

EXAMPLE 6 (comparative)

Example 1 was repeated with the exception that the methanesulfonic acid (AMS) was replaced with an equal amount of hexane. During the reaction there was a formation of sensitive quantities of a precipitate which sticks to the reactor walls. Then the reacted mass contained in the reactor is heated to about 70 ° C, that is to the boiling temperature of the hexane.

After 20 minutes the reaction mixture is cooled and the liquid phase is separated from the precipitate. The precipitate is dissolved in water and both homogeneous liquid phases thus obtained are analyzed in HPLC.

The set of the two liquid phases thus results to contain 2.05% by weight of MAA and 0.02% by weight of methacrylic acid (AMA), with an overall yield with respect to the fed ACH of 10.46%. Approximately 8.84 g of H2S04 were used for each gram of MAA produced.

EXAMPLE 7 (comparative)

Example 1 was repeated but using trifluoroacetic acid in place of methanesulfonic acid in the AMS / H2S04 mixture.

To the mixture of 29.2 g of H2S04 and 98.7 g of trifluoroacetic acid, maintained at 80 ° C (boiling temperature of trifluoroacetic acid), 31.7 g of 99.34% ACH are added under stirring in 51 minutes obtaining a molar ratio H2S04 / ACH equal to 0.8. It is left to react for 10 minutes, then the mixture is heated up to 105 ° C. After 30 minutes a sample is taken which on HPLC analysis is found to contain 10.72% by weight of MAA and 0.14% by weight of methacrylic acid, with an overall yield with respect to the ACH fed equal to 55.04% .

Approximately 1.68 g of sulfuric acid was used for each gram of MAA produced.

Claims (5)

CLAIMS 1. Process for the preparation of alkyl methacrylates in which the alkyl comprises from 1 to 5 carbon atoms, linear or branched whenever possible, comprising the preparation of methacrylamide (MAA) comprising the following steps: (a) gradual addition of acetone cyanohydrin ( ACH) to a mixture of sulfuric acid and an alkyl- or ari-sulphonic acid, maintained under stirring at a reaction temperature between 50 ° C and 100 ° C, preferably between 70 and 90 ° C, in which the molar ratios H2S04 / ACH are between 0.3: 1 and 1.1: 1, preferably between 0.7: 1 and 0.9: 1, with the proviso that the alkyl- or arii-sulfonic acid is liquid at the temperature of reaction; (b) heating the reaction mixture obtained in step (a) to temperatures of 120-160 ° C, preferably 130-150 ° C with the obtaining of a reaction mixture containing methacrylamide (MAA), sulfuric acid and alkyl acid - or arii-sulfonic. 2. Process according to claim 1 wherein a mixture of alkyl- or arii-sulfonic acid and sulfuric acid in a weight ratio between 10: 1 and 1: 1, preferably between 4: 1 and 3: 1, is used. 3. Process according to claims 1-2 wherein the alkyl- or arii-sulfonic acid is selected from the group formed by methanesulfonic acid, trifluoromethanesulfonic acid (triflic acid), dodecylbenzenesulfonic acid, preferably methanesulfonic acid. 4. Process according to claims 1-3 wherein step (b) is followed by step (al) in which the reaction mixture coming from step (b) is reacted with a further quantity of ACH under the same reaction conditions described for step (a), which is followed by a step (bl) carried out under the same conditions as step (b), optionally the aforementioned sequence of steps (al), (bl) can be repeated. 5. Process according to claims 1-4 wherein the alkyl in the alkyl methacrylates is -CH3.