DE2129920C3 - Process for the production of methacrylic acid or its esters - Google Patents

Description

15th

So far, there are various processes for the production of ^ methacrylic acid or its esters from isobutyric acid or their esters have been proposed. For example is a process for the production of Methacrylic acid ester known from the dehydrogenation of an isobutyric acid ester in the presence of iodine (US-PS 27 19 171, JA-AS 7 208/68, JA-AS 12902/63, JA-AS 21 613/65). A process based on the oxidative Dehydrogenation in the presence of sulfuric vapor as a catalyst is based on the JA-AS 8 208/69 known. In this process, the oxidative dehydrogenation is carried out using a oxygen-containing gas in the presence of vaporous Sulfur as a catalyst.

Processes are also known in which the dehydration is carried out with the aid of a solid catalyst (US-PS 2945 057 and 33 70 087).

Furthermore, a process for the preparation of methacrylic acid by dehydrogenation of isobutyric acid in the presence of a hydrogen iodide hydrate Known catalyst (JA-AS 26484/68).

In the process based on dehydration in the presence of iodine or hydrogen iodide hydrate however, the selectivity for methacrylic acid or its esters is limited, even if one large amount of iodine or hydriodic iodide is used and the process is therefore more economical Aspects not advantageous The methods based on the solid catalyst also have the disadvantage that the yields of methacrylic acid or its esters are very low. If on the other hand Sulfur is used as a catalyst, this has the disadvantage that the selectivity for methacrylic acid esters is lower, because of the oxidative dehydration reaction, which is based on a reaction between isobutyric acid ester and oxygen.

In contrast, the invention relates to a process for the preparation of methacrylic acid or its esters by oxidative dehydrogenation of isobutyric acid or its esters at 300 to 700 ⁰ C in the presence of vaporous sulfur, which is characterized in that one mole of isobutyric acid or its esters in the absence of Reacts oxygen with 0.2 to 1 mole of sulfur.

The implementation according to the invention proceeds according to the following equation:

H ₂ C

CHCOOR + S > C ■ COOR + H ₂ S

H ₃ CH ₃ C

in which R is a group C ₁₁ H _{2n +} , (η = 0 to 8). If, for example, methyl isobutyrate is reacted with sulfur vapors according to the invention, the following examples and comparative examples a show that methyl methacrylate can be produced with a higher selectivity compared to other processes, as the following table shows.

Reaction conditions MIB *), S / MIB J ₂ / MIB Oj / MIB Reaction result MMA **), MMA, Additive reaction Partial pressure MlB, yield selectivity temperature sales volume at a (Molver (Molver (Mol ver Passage (%) ratio) ratio) ratio) (%) (%) (C) 32.0 0.3 __ (%) 6.5 80.3 S 500 32.0 0.005 - - 8.1 track - S 580 32.0 0.08 - - 1.3 - S 580 32.0 - 0.005 0.4 - 13.5 45.5 O ₂ + J ₂₅₀₀ 32.0 0.1 - 0.4 30.3 14.2 56.8 O ₂ + S 500 25.1 *) Methyl isobutyrate. **) Methyl methacrylate.

When carrying out the process according to the invention, 0.2 to 1.0 mol of sulfur vapors are used per 1 mol of isobutyric acid or its ester. If less than 0.1 mol of sulfur vapors is added to the reaction system, the yields of methacrylic acid and its ester decrease considerably, as can be seen from Comparative Examples .

Although methacrylic acid and its esters over the specified temperature range also be formed, the yields of methacrylic acid and its esters can be considerably lowered when the reaction temperature is lower than 300 ⁰ C. When the reaction temperature is higher than 700 ⁰ C, the methacrylic acid and its esters are decomposed and a lively side reaction Lindet instead. As long as a gaseous phase can be maintained under the reaction conditions, any elevated, atmospheric or reduced pressure can be used as the reaction pressure.

In carrying out the present invention, an inert gas may exist in the reaction system.

Example I.

Raschig rings were packed in a quartz glass reactor tube as a heat transfer medium, and the tube was kept ^{at 500 ° C. in a tubular electric furnace.} A mixed gas of methyl isobutyrate, sulfur vapors and nitrogen (volume ratio 32: 8: 60) was then ^{passed through at a space velocity of 150 hours "1.} The composition of the effluent gas was analyzed by gas chromatography to find that the conversion of methyl isobutyrate was 76% and that The yield of methyl methacrylate based on the converted methyl isobutyrate was 81.8%.

Comparative example 1

The following reaction was carried out under the same conditions as those of Example 1. A mixed gas of methyl isobutyrate and nitrogen (volume ratio 32:68) was passed through the reactor tube at a space velocity of 150 · h " ^1. As a result of the reaction, no methyl methacrylate was found.

Example 2 * ⁵

The reactor tube was kept at 520 ° C in the same manner as in Example 1. A gas mixture of ethyl isobutyrate, sulfur vapors and nitrogen (volume ratio 32:10:58) was then ^{passed through at a space velocity of 200 · h "1.} After this time, the conversion of ethyl isobutyrate was 11.5% and the yield of ethyl methacrylate, based on the converted ethyl isobutyrate, 78.5%.

Example 3

The reactor tube was kept at 500 ° C. in the same manner as in Example 1. A gas mixture of methyl isobutyrate, sulfur vapors and nitrogen (volume ratio 30:30:40) was ^{passed through at a space velocity of 150 h "1.} After this time, the conversion of methyl isobutyrate was 52.3% and the yield of methyl methacrylate, based on the converted Methyl isobutyrate, 76.8%.

Example 4

The reactor tube was kept at 490 ^° C. in the same way as in example 1. A gas mixture of n-butyl isobutyrate, sulfur vapors and nitrogen (volume ratio 30:10:60) was ^{passed through at a space velocity of 150 · h "1.} After this time, the conversion of n-butyl isobutyrate was 6.8% and the yield of n- Butyl methacrylate based on the converted n-butyl isobutyrate, 72.5%.

Example 5

The reactor tube was kept at 500 ^° C. in the same way as in example 1. A gas mixture of isobutyric acid, sulfur vapors and nitrogen (volume ratio 30:10:60) was ^{passed through at a space velocity of 150-h "1.} After this time the conversion of isobutyric acid was 48% and the yield of methacrylic acid, based on the converted isobutyric acid, 72.8%.

Comparative example 2

The following reaction was carried out under the same conditions as in Example 1. A gas mixture of isobutyric acid and nitrogen (volume ratio 30:70) was passed through the reactor tube at a space velocity of 150 · h " ^1. The reaction did not give methacrylic acid.

Claims (1)

Claim: Process for the production of methacrylic acid or its ester by oxidative dehydration from. Isobutyric acid or its esters at 300 to 700 ° G in the presence of vaporous sulfur, characterized in that one mole of isobutyric acid or its esters in the absence reacts of oxygen with 0.2 to 1 mol of sulfur