Reaction with Product Separation

Fig-1 Sim ultaneous reaction and product separation (two liquid phases). 

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Tauscher, W., and SchUtz, G.. Static Mixing Elements. Sulzer Technical Review, 2/1973. Sladig, W.P.. Catalytic Distillation Combining Chemical Reaction with Product Separation, Chemical Processing, February 1987. 

Stadig, W.P. Catalytic distillation combining chemical reaction with product separation. Chem. Proc. 1987, 50, 27-32. 

Reactive distillation is the name given to the process where the chemical reaction and product separation are carried out simultaneously in one unit. Carrying out the reaction, with separation and purification of the product by distillation, gives the following advantages ... 

In the ideal biphasic hydrogenation process, the substrate will be more soluble or partially soluble in the immobilization solvent and the hydrogenation product will be insoluble as this facilitates both reaction and product separation. Mixing problems are sometimes encountered with biphasic processes and much work has been conducted to elucidate exactly where catalysis takes place (see Chapter 2). Clearly, if the substrates are soluble in the catalyst support phase, then mixing is not an issue. The hydrogenation of benzene to cyclohexane in tetrafluoroborate ionic liquids exploits the differing solubilities of the substrate and product. The solubility of benzene and cyclohexane has been measured in... 

Fig. 6 Typical ion-exchange separation of amino acids followed by postcolumn reaction with ninhydrin. Separation was achieved employing Beckman 6300 amino acid analyzer with cation-exchange column. Three sodium buffers were used with a stepwise elution scheme as supplied/recommended by the manufacturer. Detection was the sum of 440-nm and 570-nm absorbance. Standard three-letter abbreviations for amino acids are used also, CA = cysteic acid, tau = taurine, and nle = norleucine. Data was supplied by Stephen D. Smith, Ross Products Division of Abbott Laboratories, Columbus, OH.

Finally, it is worth mentioning that a successful integration of catalytic reaction steps with product separation and catalyst recovery operations will also be dependent on innovative chemical reaction engineering. This will require the widespread application of sustainable engineering principles [48].In this context process intensification , which involves the design of novel reactors of increased volumetric productivity and selectivity with the aim of integrating different unit operations to reactor design, and miniaturization will play pivotal roles [49, 50]. 

The conversion could be enhanced for the forward reaction if the reverse reaction involving ethene and 2-butene is minimized. Further, since 2-butene desorption is a controlling factor due to its strong sorptive properties, 2-butene removal, in particular, will allow improved rate of reaction and product separation with the use of a sorbent such as y-Al203. The effect of the PSR operation (cycle time = 40 sec) on the reactor performance was tested through simulations and by conducting experiments. Step inputs in inlet feed composition containing propene with helium carrier were conducted with clean sorbent beds and constant total gas flow rates. The results, compared with theoretical predictions, are shown in Fig. 9. Because ethene has... 

In situ polymerization of aniline is generally carried out in aqueous (NH4)2S208/HC1. The glass support is typically removed from the reaction mixture during the polymerization at the stage when a blue/violet film of pernigraniline salt has formed on its surface. This film is then reduced to the green ES product by reaction with a separate... 

The easiest technique to combine catalysis in a polar medium with product separation is shown in Figure 1. Both operations are done in the same unit at the same time. The nonpolar product phase is deposited from the polar catalyst phase and can be separated at the top of the reaction column. The SHOP oligomerization of ethene works in this way. The catalytic phase, consisting of 1,4-butanediol and nickel catalyst, always remains in the reaction unit. In the technical plant the reaction takes place not in only one reactor but in a series of tanks. This is so that the heat of reaction may be removed by water-cooled heat exchangers which are placed between the different reactor tanks. The flow scheme of the SHOP process is shown in Section 7.1. 

If a development engineer has to design an industrial column purely on the basis of miniplant experiments, he has to maintain not only the separation performance but also the ratio of separation performance/reactor performance so that main and secondary reactions proceed to a comparable extent in the industrial-scale reaction column. One way in which this can be achieved is in terms of construction by separating reaction and product separation from one another both in miniplant tests and on an industrial scale. This is possible, for example, when the reaction is carried out in the presence of a heterogeneous catalyst in the downcoming stream or with side reactors at the column. An alternative is to use structured packing with well-defined paths for the liquid flow. This problem has not yet been solved, the main reason being the lack of reference columns on an industrial scale. As we see it, the way forward is either ... 

Equation 25.41 can be solved numerically for different values of 0 corresponding to the extent to which the product is removed. Some results of numerical integration are shown in Figure 25.5. Clearly, the conversion increases with an increase in 0. The maximum conversion is obtained when the product is instantaneously removed from the reaction mixture. At 0 = 0, the conversion approaches the value corresponding to the limiting condition of reaction with no separation. 

Combining OCM reaction and product separation in a simulated countercurrent moving bed chromatographic reactor where a series of high-temperature catalytic reactors operating at low conversion and low-temperature separation columns with adsorbent are interconnected [39-41]. Yields of C2 hydrocarbons up to 50% can be reached under optimal conditions. However, such reactor operation is very complicated and the different temperature levels for the reactor and separation units are costly. Therefore, at present it has low chance to be applied in industry. 

Using knowledge bases of the type mentioned in Section 4.2 these systems propose economic alternatives for chemical processes. The. systems start with basic information about the chemical reaction system, available raw materials and data about the desired products and their quality. Based on these data they allow development of a complete process including raw material preparation, chemical reaction and product separation. ... 

Reactive distillation (RD) is one of the most important reactive separations with potential industrial applications. Here, both reaction and distillation take place within the same zone of a distillation column. It facilitates the instantaneous removal of products in pure form by using distillation principle. New vapor phase of products can be created by either using the heat of reaction in case of exothermic reactions, or by supplying external heat in case of endothermic reactions. Thus reactive distillation provides effective utilization of heat of reaction for product separation and thereby leads to significant reduction in utility consumption. In addition, in-situ removal of products results in improved conversions and yields in case of equilibrium limited reactions, thereby contributing significantly to the overall intensification of the existing process. 

Product removal during reaction. Sometimes the equilibrium conversion can be increased by removing the product (or one of the products) continuously from the reactor as the reaction progresses, e.g., by allowing it to vaporize from a liquid-phase reactor. Another way is to carry out the reaction in stages with intermediate separation of the products. As an example of intermediate separation, consider the production of sulfuric acid as illustrated in Fig. 2.4. Sulfur dioxide is oxidized to sulfur trioxide ... 

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