Fluidized catalyst beds industrial

The design of reactors, preparation of catalysts, control of tempera-tim and other topics of practical importance are summarized by Pokrovskii in excellent reviews1 84.1885 which encompass the literature up to 13o5. Reference should be made to these sources for numerous patent disclosures that will not be considered in the present disoussicn Among the significant problems examined by Pokrovskii from the standpoint of industrial technology are relative merits of fixed and fluidized catalyst beds, optimum composition of the reaction mixture in terms of both yield and safety, and properties of catalysts—selectivity, activity, durability, etc,—that arc vita] to the success of the enterprise. 

Fluidized catalytic reactions have been industrially operated in the fluid bed conditions, but most of the research has been carried out for the teeter bed. Several studies of fluidized catalytic reaction are listed in Table VI, which are of interest in considering transport phenomena in fluidized catalyst beds. 

Recently many inventions about fluidized catalyst beds, which are useful in industrial applications, have been reported (16-8), initiating trends... 

Problems on the optimization of industrial fluidized catalyst beds are still left unsolved. Certainly optimization in a rigorous sense is impossible. 

With the Sohio technology, fluidized catalyst bed processes represent the most widespread industrial method. Lying far behind in the number of units installed, the PCUK/Distillers fixed bed technique is nevertheless the most widely used of competing processes. 

Heterogeneous catalytic gas-phase reactions are most important in industrial processes, especially in petrochemistry and related fields, in which most petrochemical and chemical products are manufactured by this method. These reactions are currently being studied in many laboratories, and the results of this research can be also used for synthetic purposes. The reactions are usually performed [61] in a continuous system on a fixed catalyst bed (exceptionally a fluidized bed). 

Table 11.14 gives tcchnico-economic data concerning the two principal processes for manufacturing acrylonitrile currently industrialized, and which involve the ammoxi-dation of propylene in a fluidized bed or a fixed catalyst bed. 

Direct Process. Passing methyl chloride vapors through a bed of copper and silicon at temperatures near 300°C 5delds a mixture of methylchlorosilanes. The efficiency of this process is critically dependent on reactor design and chemistry. Optimization of the fluidized-bed reactor is a critical part of the industrial process (22). The rate of methylchlorosilane (MCS) production and selectivity for dichlorodimethylsilane are significantly affected by trace elements in the catalyst bed very pure copper and silicon give poor rate and selectivity (23-25). 

Activated alumina and phosphoric acid on a suitable support have become the choices for an iadustrial process. Ziac oxide with alumina has also been claimed to be a good catalyst. The actual mechanism of dehydration is not known. In iadustrial production, the ethylene yield is 94 to 99% of the theoretical value depending on the processiag scheme. Traces of aldehyde, acids, higher hydrocarbons, and carbon oxides, as well as water, have to be removed. Fixed-bed processes developed at the beginning of this century have been commercialized in many countries, and small-scale industries are still in operation in Brazil and India. New fluid-bed processes have been developed to reduce the plant investment and operating costs (102,103). Commercially available processes include the Lummus processes (fixed and fluidized-bed processes), Halcon/Scientific Design process, NIKK/JGC process, and the Petrobras process. In all these processes, typical ethylene yield is between 94 and 99%. 

Another industrially important reaction of propylene, related to the one above, is its partial oxidation in the presence of ammonia, resulting in acrylonitrile, H2C=CHCN. This ammoxidation reaction is also catalyzed by mixed metal oxide catalysts, such as bismuth-molybdate or iron antimonate, to which a large number of promoters is added (Fig. 9.19). Being strongly exothermic, ammoxidation is carried out in a fluidized-bed reactor to enable sufficient heat transfer and temperature control (400-500 °C). 

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