Reactive Distillation/Extraction

Removal of reaction products can shift the equilibrium, forcing the reaction to go to completion. This can be effected by evaporation of products from the reaction mixture (reactive distillations), extraction (including supercritical extraction) of products from the reaction mixture (reactive extractions), or membrane processes. Counter- and cocurrent operation also falls within this category. If the reaction is equilibrium-limited or inhibited by reaction products countercurrent operation outperforms cocurrent operation. 

Integration of reaction and separation in a single unit is a powerful tool to increase efficiency and economic advantages of many chemical processes. Reactive distillation, extraction, and adsorption are well-known examples of this technological resource. Recently, a very promising solution is offered by membrane reactors... 

Reactive distillation/ extraction/ crystallization, HIGEE Reaction window = distillation windovs reaction equilibrium can be shifted by removing one or more of the species from the reaction space. 

Reactive distillation Extraction of metal salts Pulsated tray column... 

Of these five methods all but pressure-swing distillation can also be used to separate low volatiUty mixtures and all but reactive distillation are discussed herein. It is also possible to combine distillation and other separation techniques such as Hquid—Hquid extraction (see Extraction, liquid-liquid), adsorption (qv), melt crystallization (qv), or pervaporation to complete the separation of azeotropic mixtures. 

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... 

Reactive distillation is a technique for combining a number of process operations in a single device. One company has developed a reactive distillation process for the manufacture of methyl acetate that reduces the number of distillation columns from eight to three, also eliminating an extraction column and a separate reactor (Agreda et al., 1990 Doherty and Buzad, 1992 Siirola, 1995). Inventory is reduced... 

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

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 reactor system may consist of a number of reactors which can be continuous stirred tank reactors, plug flow reactors, or any representation between the two above extremes, and they may operate isothermally, adiabatically or nonisothermally. The separation system depending on the reactor system effluent may involve only liquid separation, only vapor separation or both liquid and vapor separation schemes. The liquid separation scheme may include flash units, distillation columns or trains of distillation columns, extraction units, or crystallization units. If distillation is employed, then we may have simple sharp columns, nonsharp columns, or even single complex distillation columns and complex column sequences. Also, depending on the reactor effluent characteristics, extractive distillation, azeotropic distillation, or reactive distillation may be employed. The vapor separation scheme may involve absorption columns, adsorption units,... 

Reactive distillation Membrane-based reactive separations Reactive adsorption Reactive absorption Reactive extraction Reactive crystallization... 

The most important examples of reactive separation processes (RSPs) are reactive distillation (RD), reactive absorption (RA), and reactive extraction (RE). In RD, 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 recycling of unused reactants. The RD process can be efficient in both 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 RD processes are etherifications, nitrations, esterifications, transesterifications, condensations, and alcylations (2). 

This chapter concerns the most important reactive separation processes reactive absorption, reactive distillation, and reactive extraction. These operations combining the separation and reaction steps inside a single column are advantageous as compared to traditional unit operations. The three considered processes are similar and at the same time very different. Therefore, their common modeling basis is discussed and their peculiarities are illustrated with a number of industrially relevant case studies. The theoretical description is supported by the results of laboratory-, pilot-, and industrial-scale experimental investigations. Both steady-state and dynamic issues are treated in addition, the design of column internals is addressed. 

Reactive absorption, reactive distillation, and reactive extraction occur in multicomponent multiphase fluid systems, and thus a single modeling framework for these processes is desirable. In this respect, different possible ways to build such a framework are discussed, and it is advocated that the rate-based approach provides the most rigorous and appropriate way. By this approach, direct consideration... 

Hydrazine is produced in the hydrated form with one mole of water added. Although a significant fraction of hydrazine is used as the hydrate, numerous applications (such as rocket propulsion) require anhydrous hydrazine. Because of the azeotrope at 68% hydrazine, reactive distillation or extractive distillation must be used to produce pure hydrazine. 

At first sight, adsorption and reaction are well-matched functionalities for integrated chemical processes. Their compatibility extends over a wide temperature range, and their respective kinetics are usually rapid enough so as not to constrain either process, whereas the permeation rate in membrane reactors commonly lags behind that of the catalytic reaction [9]. The phase slippage observed in extractive processes [10], for example, is absent and the choice of the adsorbent offers a powerful degree of freedom in the selective manipulation of concentration profiles that lies at the heart of all multifunctional reactor operation [11]. Furthermore, in contrast to reactive distillation, the effective independence of concentration and temperature profiles... 

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. 

Modelling and optimisation of batch reactive and extractive distillation processes... 

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. 

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