Distillation, reactive

Reverse-flow reactors Reactive distillation Reactive extraction Reactive crystalization Chromatographic reactors Periodic separating reactors Membrane reactors Reactive extrusion Reactive comminution Fuel cells... 

Figure 13.24 Hybrid reaction and distillation - reactive distillation.

In this paper only isothermal simulations have been conducted to show the important features of the model to describe mass transfer with chemical reaction. In many industrial processes, distillation, reactive distillation and some absorption processes, heat effects play an important role and therefore cannot be neglected. These effects will be discussed in Part II. 

Cieutat, D., 1989, La distillation reactive la technologie et ses applications. Petrole et Techn. 350, 36-40. 

Mikitenko, P., 1986, La distillation reactive principe, applications et perspectives. Petrole et Technol. 329, 34-38. 

The best-known and (commercially) most successful example of combining reaction and separation is the reactive distillation. Reactive distillation has been investigated widely [3, 4 see also Chapters 3, 4, and 5] and is applied to many processes [5], However, the integration of more than one functionality in an apparatus leads to a loss in degrees of freedom. For a successful integration, the feasible window of operation concerning process conditions such as pressure and temperature must coincide for the reaction, the separation and the apparatus (Fig. 8.1). 

Despite the clear importance of reactive absorption, its behavior is still not properly understood. This can be attributed to a very complex combination of process thermodynamics and kinetics, with intricate reaction schemes including ionic species, reaction rates varying over a wide range, and complex mass transfer-reaction coupling. As compared to distillation, reactive absorption is a fully rate-controlled process and it occurs definitely far from the equilibrium state. Therefore, both practitioners and theoreticians are highly interested to establish a proper understanding and description of this process. 

In addition, a reactor may perform a function other than reaction alone. Multifunctional reactors may provide both reaction and mass transfer (e.g., reactive distillation, reactive crystallization, reactive membranes, etc.), or reaction and heat transfer. This coupling of functions within the reactor inevitably leads to additional operating constraints on one or the other function. Multifunctional reactors are often discussed in the context of process intensification. The primary driver for multifunctional reactors is functional synergy and equipment cost savings. 

Figure 1.3 shows a typical semi-batch (semi-continuous) distillation column. The operation of such columns is very similar to CBD columns except that a feed is introduced to the column in a continuous or semi-continuous mode. This type of column is suitable for extractive distillation, reactive distillation, etc. (Lang and coworkers, 1994, 1995 Mujtaba, 1999). Further details of semi-batch distillation in extractive mode of operation are provided in Chapter 10. 

Among the most important examples of RS processes are reactive distillation, reactive absorption, reactive stripping and reactive extraction. For instance, in reactive distillation, reaction and distillation take place within the same zone of a distillation column. Reactants are converted to products with simultaneous separation of the products and recycle of unused reactants. The reactive distillation process can be both efficient in size and cost of capital equipment and in energy used to achieve a complete conversion of reactants. Since reactor costs are often less than 10% of the capital investment, the combination of a relatively cheap reactor with a distillation column offers great potential for overall savings. Among suitable reactive distillation processes are etherifications, nitrations, esterifications, transesterifications, condensations and alcylations (Doherty and Buzad, 1992). 

The reversible reactions deserve particular attention. The in-situ removal of a product by reactive distillation, reactive extraction or by using selective membrane diffusion should be investigated. 

James Douglas Let me add two more things. I think reactive crystallization and reactive extraction will become more important in the future, as has reactive distillation. Reactive distillation is receiving a lot of attention at present, but reactive separations should find more applications. 

III HI distillation (reactive and distractive) H2SO4 from Section I Corrosion products from other sections... 

If a chemical reaction occurs inside a distillation colmnn, with reactants and products subject to the usual requirements of the distillation process (phase eqniUbria, fractionation, and contacting device hydraulics), it is possible to shift the reaction eqnilibrimn in a favorable direction. A soluble or insoluble catalyst is likely to be involved thns, the operation is often known as catalytic distillation. Reactive distillation has been nsed snccessfnlly for etherification and esterification reactions and, to some extent, for alkylation, nitration, and amidation reactions. In most applications, the reaction has occurred in the liqnid phase, and an example of this application, where methyl acetate is produced from methanol and acetic acid nsing a solnble catalyst, has been described in detail. Flows for a generalized reactive colmnn are shown in Figm-e 12.21. 

Reactive distillation Reactive stripping Large scale reactors... 

There are two distinct categories of reactive separations. In one category, the reaction aids separation and in the other separation aids the reaction. In the former, decreasing or eliminating the mass-transfer resistance on the liquid side by allowing the solute to react with a non-volatile non-diffusing component as in the absorption of CO2 into an amine solution enhances the mass-transfer rate. Absorption with reaction has been practised for the removal of CO2 and H2S over the past several decades, and an extensive literature is available. Similarly, in distillation, reactive entrainers are used to separate close boiling or azeotropic mixtures [19]). 

Hybrid reactors reverse flow, reactive distillation, reactive extraction, reactive crystallization, chromatographic reactions, membrane reactions, fuel cells... 

Dr. Ruiz-Mercado is currently leading and developing research projects in areas of sustainable development. He is a coinventor and developer of the GREENSCOPE process sustainability methodology and tool. In addition he has a pubhshed record of contributions in research areas such as sustainable product and process design, energy efficient multicomponent distillation, reactive separation processes, sustainabUity evaluation, and life cycle approaches. 

Pervaporation, as a non-integrated process, is typically utilized for dehydration and for the recovery or removal of organics from aqueous solutions and sometimes also for the separation of organic mixtures (Neel, 1995). Also many hybrid processes have been developed where PV is coupled with other processes, such as different membrane processes (e.g., reverse osmosis, or organophilic pervaporation coupled with hydrophilic pervaporation), distillation, reactive distillation and, of course, reaction. With these aspects in mind, PV appears particularly suitable to keep the concentration of a by-product low, or to continuously recover a product while it is formed. Note that these are the main objectives typically pursued in membrane reactors. 

Thermodynamic effects. Many performance limitations are related to a thermodynamic equilibrium, which is the case for numerous reversible reactions. Existing solutions consist in coupling the reaction with a separation system (reactive distillation, reactive chromatography, etc.) and can even be coupled to geometric structuring [11]. 

In this section reactive distillation, reactive extraction, reactive adsorption and membrane reactors are discussed. The references cited in this section are recommended for those wishing to seek out more detail on these or other reactive extractions. 

Multi-functional operations are discussed under two sections of reactive separations and hybrid separation platforms. Reactive separations of reactive distillation, reactive adsorption, and membrane reactors are presented in more detail including their principles, advantages and applicability to different systems. Hybrid separations incorporating different unit operations are discussed briefly along with their application and scope. 

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