Method of producing methyl methacrylate or methacrylic acid

Abstract

There is described a method of reducing polymer tar build-up in the production of methyl methacrylate and/or methacrylic acid by the acetone cyanohydrin process. In the method a stabiliser is contacted with the amide stage reaction medium. The stabiliser includes a hydrocarbon moiety capable of donating a labile hydrogen atom to a methacrylamide derivative capable of reaction with said labile hydrogen atom under the conditions in the said medium. The method herein is especially useful for the continuous production of methyl methacrylate and/or methacrylic acid.

Claims

1. A method of reducing polymer tar build-up in the production of methyl methacrylate and/or methacrylic acid by an acetone cyanohydrin (ACH) process comprising an amide stage reaction medium, wherein a stabilizer is contacted with the amide stage reaction medium, which stabilizer includes a hydrocarbon moiety capable of donating a labile hydrogen atom to a methacrylamide derivative capable of reaction with said labile hydrogen atom under the conditions in the amide stage reaction medium, wherein the stabilizer is selected from one or more of the group consisting of an isoprenoid, 9,10-dihydroanthracene; adamantane; tert-dodecyl polysulfide; tetralin; fluorene; decalin; and 5,12-dihydrotetracene; dihydrocoumarin; anthrone; squalene; hemisqualane; camphor; 4-methylnonane; triacontane; bicyclohexyl; petroleum diesel; butyl cyclohexane; and decane.

2. A method of producing methyl methacrylate or methacrylic acid comprising the steps of: a. contacting acetone cyanohydrin (ACH) with an excess of concentrated sulphuric acid to produce a mixture of sulphatoisobutyramide (SIBAM), hydroxyisobutyramide (HIBAM) and optionally methacrylamide; and b. thermally converting SIBAM and/or HIBAM to methacrylamide in concentrated sulphuric acid medium; and c. contacting the methacrylamide with water or with water and methanol; wherein a stabilizer is present during step b, which stabilizer is added as a hydrocarbon moiety capable of donating a labile hydrogen atom to a methacrylamide derivative capable of reaction with said labile hydrogen atom under the conditions in the said medium, wherein the stabilizer is selected from one or more of the group consisting of an isoprenoid, 9,10-dihydroanthracene; adamantane; tert-dodecyl polysulfide; tetralin; fluorene; decalin; and 5,12-dihydrotetracene; dihydrocoumarin; anthrone; squalene; hemisqualane; camphor; 4-methylnonane; triacontane; bicyclohexyl; petroleum diesel; butyl cyclohexane; and decane.

3. The method according to claim 1, wherein the stabilizer includes a hydrocarbon moiety capable of donating a labile hydrogen atom to a methacrylamide derivative capable of reaction with said labile hydrogen atom under the conditions in concentrated sulphuric acid medium.

4. The method according to claim 1, wherein the stabilizer is a hydrogen transfer agent that is operable to take part in a hydrogen atom transfer reaction under the conditions found in the amide stage of the ACH process wherein a hydrogen atom is transferred to a chemically reactive species in the same medium and in so doing prevents some or all of the side reactions that the species could otherwise take part in.

5. The method according to claim 1, wherein the stabilizer is selected from one or more of the group consisting of 9,10-dihydroanthracene; squalane; anthrone; hemisqualane; camphor; 4-methylnonane; petroleum diesel; decane and tert-dodecyl polysulfide.

6. The method according to claim 1, wherein the stabilizer is present in the reaction mixture in an amount of ≥0.005% w/w.

7. The method according to claim 1, wherein a concentrated sulphuric acid medium in which the stabilizer is capable of donating a labile hydrogen atom to a methacrylamide derivative is in the form of the amide stage reaction medium.

Description

EXAMPLES

(1) The effectiveness of a wide range of stabiliser compounds according to the invention for the amide stages of the ACH route to methacrylate monomers was measured by observing the concentration of MAM remaining after 30 minutes of exposure to a temperature of 160° C.

(2) See Table 1 for a complete list of all the inventive and comparative compounds tested, as well as the results.

(3) To measure the effectiveness of the compounds, they were each tested by making up a solution of methacrylamide (1% w/w) plus stabiliser compound (0.1% w/w), in deutero sulphuric acid (D.sub.2SO.sub.4). Handling operations were carried out in a nitrogen filled glove box in order to eliminate uptake of moisture and oxygen, as in practise the amide process steps in the ACH route to methacrylate monomers are carried out under an inert or reducing gas atmosphere. Eight, 5 mm diameter high pressure nmr tubes were then filled with the solution, before the tubes were sealed by securely adding gas tight screw caps. The tubes were removed from the nitrogen atmosphere, and seven were placed in an oil bath, with the temperature of the oil set at 160° C. Six of the tubes were removed one at a time at ten minute intervals over a period of 60 minutes, followed by a final seventh tube at 90 minutes and each cooled immediately after removal by immersion in water at ambient temperature thus generating a set of solutions that had been exposed to 160° C. temperature for varying lengths of time. .sup.1Hnmr spectra were collected directly on the tubes at ambient temperature, and with the solutions remaining unexposed to air. It was possible to resolve and integrate peaks due to methacrylamide. By conducting the experiments in this way it was possible to produce a graph showing the extent of decomposition of Methacrylamide vs. time for each candidate compound. If the points making up the graph showed a regular curve pattern this was taken as an indication that the quality of the data was good, before selecting out the value at 30 minutes as a means of comparing the effectiveness of the candidate compounds. By comparison of the results to comparative examples 1 (no stabiliser present) and 2 (well known prior art stabiliser PTZ), the effectiveness of the respective stabilisers can be displayed, as shown in Table 1.

(4) TABLE-US-00001 TABLE 1 Results % MAM Remaining after 30 Stabiliser Structure minutes at 160° C. Comparative None n/a 18.0 example 1 Comparative Example 2 Phenothiazine (PTZ) 75.4 Example 1 9,10- Dihydroanthracene 84.4, Example 2 1,2,3,4- Tetrahydro- quinoline 76.5 Example 3 Anthrone 81.8 Example 4 Squalane (2,6,10,15,19,23- Hexamethyl- tetracosane) 95.7 Example 5 Hemisqualane C.sub.15 half length version of Squalane, with three C—H labile hydrogen sites 89.3 Example 6 Camphor (R and S Camphor) 82.4 Example 7 4-methylnonane 81.4 Example 8 Adamantane 0 76.0 Example 9 Triacontane 75.5 Example 10 Vitamin E (Tocopherol, mixture of all four possible optical isomers) 81.8 Example 11 Petroleum diesel* 84.6 (aka petrodiesel, automotive fuel) Example 12 n-Decane 84.0 Example 13 Tert-Dodecyl Polysulfide, No. S atoms per molecule x = 3 92.9 *Mixture of C.sub.10 to C.sub.15 Hydrocarbons, made up of approximately 75% n, iso and cyclic saturated hydrocarbons, plus 25% aromatic hydrocarbons. The average chemical formula for the mixture is C.sub.12H.sub.23, ranging from C.sub.10H.sub.20 to C.sub.15H.sub.28. Hydrocarbons have varying levels of unsaturation and branching.

(5) In comparative example 1 MAM is shown to breakdown in the presence of concentrated sulphuric acid thereby providing a cause of tar build-up. The examples according to the present invention show superior stabiliser benefits over the known stabiliser PTZ.

(6) Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

(7) All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

(8) Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(9) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.