Reaction-separation technology

In many gaseous state reactions of technological importance, short-lived intermediate molecules which are formed by die decomposition of reacting species play a significant role in die reaction kinetics. Thus reactions involving die mediane molecule, CH4, show die presence of a well-defined dissociation product, CH3, die mediyl radical, which has a finite lifetime as a separate entity and which plays an important part in a sequence or chain of chemical reactions. 

Around the world chemical professionals continually commercialize new products and processes. Much of this activity results in batch processing. Fine and custom chemicals can involve as many as ten to twenty batch reactions in series, sometimes with multi-step parallel paths, with various separation technologies between reaction steps. This paper is an attempt to reflect the experience of many individuals as seen through the author s eyes over almost four decades, with several very typical situations. 

As for the former problem, the researchers of GA found that the mixed acid solution produced by the Bunsen reaction separates spontaneously into two liquid phases in the presence of excess amount of iodine [17]. The heavier phase is mainly composed of HI, I2, and H20, and is called "Hix" solution. The main components of the lighter phase are H2S04 and H20. The phenomenon (liquid-liquid (LL)-phase separation) offered an easy way of separating the hydriodic acid and the sulfuric acid. As for the HI processing, some ideas have been proposed by GA [17], RWTH Aachen [18], and JAEA. JAEA studied the utilization of membrane technologies for concentrating the Hix solution to facilitate the HI separation and also for enhancing the one-pass conversion of HI decomposition [19,20]. 

Porous oxide catalytic materials are commonly subdivided into microporous (pore diameter <2nm) and mesoporous (2-50 nm) materials. Zeolites are aluminosilicates with pore sizes in the range of 0.3-1.2 nm. Their high acidic strength, which is the consequence of the presence of aluminium atoms in the framework, combined with a high surface area and small pore-size distribution, has made them valuable in applications such as shape-selective catalysis and separation technology. The introduction of redox-active heteroatoms has broadened the applicability of crystalline microporous materials towards reactions other than acid-catalysed ones. 

N Itoh, Simultaneous operation of reaction and separation by a membrane reactor in Future Oportunities in Catalytic and Separation Technologies, Studies in Surface Science and Catalysis, Vol 54, 248 283, Elsevier, Amsterdam,... 

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