Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfur containing
Patent
1998-10-01
2000-05-02
Kumar, Shailendra
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfur containing
C07C31902
Patent
active
06057481&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the manufacture of methylmercaptopropanal ("MMP"), also known in the art as 3-(Methylthio)-propanal, and more specifically relates to new processes for the conversion of propylene to MMP via an acrolein intermediate.
BACKGROUND OF THE INVENTION
MMP is an intermediate for the manufacture of both d, 1-methionine and 2-hydroxy-4-(methylthio)butanoic acid ("HMBA"). Methionine is an essential amino acid in which components of the animal feed compositions are commonly deficient. HMBA provides a source of methionine, and is widely used as a methionine supplement in animal feed formulations. MMP relatively free of impurities is typically required for the manufacture of HMBA or methionine.
MMP is conventionally produced by the reaction of acrolein with methyl mercaptan. In a conventional process for the preparation of MMP, acrolein and methyl mercaptan are introduced in a liquid phase into a reactor containing liquid-phase MMP product. The reaction takes place batchwise in the liquid phase. In order to produce MMP of the quality typically desired, refined acrolein is typically used in the manufacture of HMBA and methionine.
Acrolein is a highly toxic and flammable material. It is conventionally produced by the vapor-phase oxidation of propylene over a solid-phase catalyst, producing a crude, gaseous reaction product which contains acrolein, water vapor, acrylic acid, acetaldehyde, and other organic by-products. Typically, the gas is treated to remove acrylic acid, then contacted with cooled water for absorption of the acrolein. The resultant aqueous solution is distilled to recover the absorbed acrolein and other organic components. The crude acrolein is then refined to reject lower-boiling impurities such as, for example, acetaldehyde, producing a purified, liquid acrolein product. Since the conventional processes typically use a batch reaction system, condensation and in-process storage of liquid acrolein is necessary as a surge buffer between the acrolein process and the MMP reactor.
Storage of liquid acrolein involves significant toxicity, fire and explosion hazards. High capital and operating costs are consequently incurred in providing for the safe handling of acrolein. Substantial enhancements in the safety of handling acrolein would be achieved if acrolein were transferred directly and continuously from the acrolein manufacturing process to the MMP reactor without intermediate storage. Since the conventional, commercial processes for the preparation of MMP involve liquid-phase reactions, the need to condense the gaseous acrolein product has been considered unavoidable. However, further enhancements in the safety of handling acrolein and the process efficiency of manufacturing MMP could be achieved if the acrolein were transferred to the MMP reactor in the vapor phase, i.e., without significant condensation of the acrolein.
SUMMARY OF THE INVENTION
By the present invention, improved, continuous processes for the conversion of propylene to MMP are provided via the production of acrolein as an intermediate.
In one aspect of the present invention, the acrolein produced in the process is condensed and reacted with methyl mercaptan in a liquid phase to form MMP. In this aspect of the invention, the acrolein reaction is conducted in the presence of a recycle gas containing an effective amount of propane to enhance the efficiency of the acrolein reaction. Operation in this manner represents an improvement over the current processes in several ways. For example, the recycle process of the present invention can provide better distribution of the reaction load over the catalyst resulting in improved acrolein reaction efficiency and less by-product acrylic acid. In addition, in the present processes, oxygen rather than air, as is conventionally used, is fed to the acrolein reactor and unconverted propylene and oxygen are recycled to the acrolein reactor feed rather than purged and incinerated, which is necessary in an air-based process to avoid a build-up of nitro
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J.A. Chem Soc. 1948 vol. 70 pp. 1450-1451.
Brockwell Jonathan L
Etzkorn William G
Maher John M
Warren Barbara K
Young Mark A
Kumar Shailendra
Union Carbide Chemicals & Plastics Technology Corporation
Vollano Jean F
Volles W. K.
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