Distillation-reaction methyl acetate synthesis

In this process, coal is gasified to give synthesis gas, which is then converted to methanol by a heterogeneous catalytic process. Reaction of methanol with acetic acid by reactive distillation gives methyl acetate, which is then reacted with CO to give acetic anhydride. The cellulose ester is made by reacting acetic anhydride with cellulose. The acetic acid required for the synthesis of methyl acetate comes from recycling the acetic acid produced in the manufacture of cellulose ester. 

The modeling of RD processes is illustrated with the heterogenously catalyzed synthesis of methyl acetate and MTBE. The complex character of reactive distillation processes requires a detailed mathematical description of the interaction of mass transfer and chemical reaction and the dynamic column behavior. The most detailed model is based on a rigorous dynamic rate-based approach that takes into account diffusional interactions via the Maxwell-Stefan equations and overall reaction kinetics for the determination of the total conversion. All major influences of the column internals and the periphery can be considered by this approach. 

Chemical Co. s methyl acetate reactive distillation process and processes for the synthesis of fuel ethers are classic success stories in reactive distillation. Improvements for the Eastman process are very high five-times lower investment and five-times lower energy use than the traditional process. However, combining reaction and distillation is not always advantageous and in some cases it may not even be feasible. The methyl acetate process based on reactive distillation has fewer vessels, pumps, flanges, valves, piping and instruments. This is an advantage also in terms of safety and maintenance. However, a reactive distillation column itself is more complex (multiple unit operations occur within one vessel) and thus more difficult to control and operate. It is thus not possible to make unique conclusions. 

Sometimes reaction rates can be enhanced by using multifunctional reactors, i.e., reactors in which more than one function (or operation) can be performed. Examples of reactors with such multifunctional capability, or combo reactors, are distillation column reactors in which one of the products of a reversible reaction is continuously removed by distillation thus driving the reaction forward extractive reaction biphasing membrane reactors in which separation is accomplished by using a reactor with membrane walls and simulated moving-bed (SMB) reactors in which reaction is combined with adsorption. Typical industrial applications of multifunctional reactors are esterification of acetic acid to methyl acetate in a distillation column reactor, synthesis of methyl-fer-butyl ether (MTBE) in a similar reactor, vitamin K synthesis in a membrane reactor, oxidative coupling of methane to produce ethane and ethylene in a similar reactor, and esterification of acetic acid to ethyl acetate in an SMB reactor. These specialized reactors are increasingly used in industry, mainly because of the obvious reduction in the number of equipment. These reactors are considered by Eair in Chapter 12. 

In reactive distillation, both the chemical reaction and the distillative separation of the product mixture are carried out simultaneously. This integrative strategy allows us to overcome chemical equilibrium limitations. For an exothermic reaction, the heat of reaction can be used directly for distillation. The term catalytic distillation is also used for such systems where a catalyst (homogeneous or heterogeneous) is used to accelerate the reaction. The synthesis of methyl acetate and MTBE (methyl tertiary butyl ether) are the two most prominent examples, where reactive distillation is used on an industrial scale (for MTBE see Section 4.10.8.1). It is beyond the scope of this textbook to discuss more details of this technology. Details can be found in the literature (Sundmacher and Kienle, 2002 Harmsen, 2007 Taylor and Krishna, 2000 Krishna, 2002 Stankiewicz, 2003). 

Variations of the above procedures are sometimes employed. /S-Keto esters may be obtained by alcoholysis of the intermediate diacyl esters by sodium methoxide in methanol, as in the preparation of methyl /3-oxocaprylate (88%). The starting /S-keto ester can be converted to the new /S-keto ester in a single step. Thus, in the synthesis of ethyl ben- > zoylacetate (55%)> ethyl acetoacetate and ethyl benzoate are converted directly to this keto ester by distilling the lower-boiling product, ethyl acetate, thereby forcing the reaction to completion. ... 

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