Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1998-10-09
2001-02-13
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S041000, C568S470000, C568S449000, C568S862000, C549S356000, C549S369000, C549S430000, C560S177000
Reexamination Certificate
active
06187963
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the manufacture of acrolein derivatives by the conversion of propylene to acrolein in the presence of propane.
BACKGROUND OF THE INVENTION
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 often necessary as a surge buffer between the acrolein production process and the process to produce derivatives of acrolein.
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 acrolein derivative reaction zone without intermediate storage. Since the conventional, commercial processes for the preparation of acrolein derivatives, e.g., methylmercaptopropanal, also known in the art as 3- (methylthio)-propanal (“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 acrolein derivative could be achieved if the acrolein were transferred to the acrolein derivative 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 acrolein derivatives are provided via the production of acrolein in the presence of propane.
In one aspect of the present invention, the acrolein produced in the process can be condensed and reacted with a co-reactant in a liquid phase to form the acrolein derivative. 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 typical acrolein production 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 nitrogen. The increased utilization of raw materials can substantially reduce operating expenses.
In addition, in accordance with a preferred aspect of the present invention, the acrolein derivative reaction is continuous and is directly coupled to the acrolein process. Storage of significant volumes of highly purified acrolein, which is required in order to provide inventory for a batchwise acrolein derivative reaction, is eliminated and a much higher level of inherent process safety can be achieved.
In another aspect of the invention, propane is used as the feed source. Existing processes for acrolein derivative production typically use propylene as a feedstock for the production of acrolein, which is a process intermediate. Propane is substantially cheaper than propylene, as well as being more widely available and more stable in price. In a preferred aspect of the present invention, oxydehydrogenation is used for the conversion of propane to propylene. This is particularly well-suited for integration of the propane conversion step and the acrolein derivative process. By operating at low propane conversions, the selectivity to propylene can be made quite high, e.g., between 80 and 100 mole percent. Since the feed to the acrolein reactor need only contain propylene in low concentration, e.g., 5 to 40 mole percent, the low conversion/high selectivity mode of operation can be highly efficient provided unreacted propane is recycled to the oxydehydrogenation reactor. Such recycle operation is feasible because typical oxydehydrocatalysts are unaffected by species such as carbon oxides and water which are formed in the acrolein reactor. Hence, after recovery of the acrolein, the noncondensable gas stream may be recycled without expensive purification steps.
In another aspect of the invention, the acrolein produced in the process can be reacted with a co-reactant in a vapor phase to form the acrolein derivative. Significant enhancements in reaction efficiency can be achieved by passing the acrolein product to the acrolein derivative reactor in the vapor phase. Preferably, this operation is made possible using a diluent which is anhydrous. The low water content of the effluent from the anhydrous diluent (only the water of reaction is present) makes direct introduction into the acrolein reactor feasible. By-products in the crude acrolein stream pass unreacted through the acrolein derivative reactor.
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Brockwell Jonathan Lester
Etzkorn William George
Galley Richard A.
Maher John Michael
Snead Thomas E.
Padmanabhan Sreeni
Union Carbide Chemicals & Plastics Technology Corporation
Volles W. K.
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