Reactive distillation methyl acetate production

FIG. 13-80 Reactive extracting distillation for methyl acetate production, (a) Composition profile, (b) Temperature profile. 

An important industrial application of reactive distillation is the production of methyl acetate from methanol and acetic acid. This system exhibits several azeotropes, which make the downstream processing of the products very difficult, see Fig. 11.5-1 (Siirola 1996). The conventional process consists of eight distillation columns, one extractor, and one decanter. 

Methyl acetate production Combined unit ops - reactive distillation... 

Reactive distillation is a process where the chemical reactor is also the still. Separation of the product from the reaction mixture does not need a separate distillation step, which saves energy (for heating) and materials. A case study on reactive distillation (on the production of methyl acetate) is presented in Chapter 10. It is a manifestation of the merits of reactive distillation. 

Methyl acetate production is a classical example of reactive distillation technology. A single reactive distillation column could replace the conventional process train consisting of 11 units. This significant reduction in number of units led to tremendous improvement in process economics via improved conversions and reduced equipment and operating costs. Various reactions that are suitable for reactive distillation are given in Table 1.1. These reactions... 

Methyl acetate-methanol Minimum boiling azeotrope None Element of recovery system for alternative to production of methyl acetate by reactive distillation alternative to azeotropic, extractive... 

FIG. 13-79 Integrated reactive-extractive distillation column for the production of methyl acetate. 

A major challenge will be to develop new processes or step-up technologies that increase the yield and/or selectivity, use cheaper raw materials, decrease energy consumption, minimize the product separation and purification needs and lower capital investment. Iimoyative step-out technologies can still have a major impact on existing processes. An excellent example of such an accomplishment is the reactive distillation process developed by Eastman Chemicals for production of methyl acetate by via the reaction [2]... 

Reactive distillation is one of the classic techniques of process intensification. This combination of reaction and distillation was first developed by Eastman Kodak under the 1984 patent in which methyl acetate was produced from methanol and acetic acid. One of the key elements of the design is to use the acetic acid as both a reactant and an extraction solvent within the system, thereby breaking the azeotrope that exists within the system. Likewise, the addition of the catalyst to the system allowed sufficient residence time such that high yields could be obtained, making the process commercially viable. Other examples in which reactive distillation may enhance selectivity include those of serial reactions, in which the intermediate is the desired product, and the reaction and separation rates can be systematically controlled to optimize the yield of the desired intermediate. ... 

The catalyst components are generally dissolved in methyl acetate which acts as both reactant and solvent. Other solvents may be used and in fact, upon several batch recycles where lower boiling products are distilled off, the solvent is an ethylidene diacetate-acetic acid mixture. Any water introduced in the reaction mixture will be consumed via ester and anhydride hydrolysis, therefore anhydrous conditions are warranted. Typical batch reaction examples are presented in Table 1. There is generally sufficient reactivity when carbon monoxide and hydrogen are present at 200-500 psi. Similar results were obtained from the pilot plant using a continuous stirred tank reactor (CSTR). The reaction can also be run continuously over a supported catalyst with a feed of methyl acetate, methyl iodide, CO, and hydrogen. 

Systems that have the most potential for reactive distillation are those where the reaction is reversible, heat of reaction is not excessively large, and the products have the correct volatilities in relation to the reactants. Those systems reach chemical equilibrium (i.e., reaction stops) unless the reactants are in large excess or the products are continuously removed. An example system has been reported in the literature by Eastman Chemical (Agreda et al., 1990) for the production of methyl acetate from methanol and acetic acid. The discussion about process operation and the control strategy shown in the paper certainlv adhere to the plantwide control principles we have outlined in this book. 

Reactive distillation is used in the production of methyl tertiary butyl ether (MTBE) and methyl acetate. 

The high boiling reactant is fed as feed 1 and the low boiling reactant as feed 2. Between the two feeds, there is the reaction zone. As a special application, feed 1 can serve as an extractive agent, e.g. in the case of the production of methyl acetate, acetic acid serves as an entrainer for the binary azeotropic mixture methanol and methylacetate. The ensemble is then a reactive extractive distillation column. 

In reactive distillation, the type of the catalysis is important. Homogeneous catalysis is possible in most cases but needs a separation step to recycle the catalyst. This can be avoided in heterogeneous catalysis, but here special constructions are necessary to fix the catalyst in the reaction zone. If everything harmonizes, considerable advantages arise as can be seen with reference to the Eastman-Kodak Chemicals process for the production of methyl acetate. As can be seen in Figure 4 only one column is needed if reactive distillation is used as opposed to nine and a reactor if it is not used. 

Figure 4 Production of methyl acetate at Eastman-Kodak with/without reactive distillation...

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