Catalysts cumene synthesis

Since zeolite catalysts are successfully introduced in the refining and petrochemical industries, it is not surprising that most of the recent advances concern incremental improvements of existing processes with the development of new generations of catalysts (e.g., dewaxing, ethylbenzene and cumene synthesis). The number of newer applications is much more limited, for example, direct synthesis of phenol from benzene and aromatization of short-chain alkanes, etc. However, both the improvement and development of processes contribute significantly to environmental advances. 

Table 6.5 Selectivity obtained with different zeolite catalysts in cumene synthesis [4].

Current zeolite catalysts already operate at process temperatures that require minimal external heat addition. Heat integration and heat management will be of increasing concern at the lower benzene to propylene ratios because the cumene synthesis reaction is highly exothermic (AHf= -98 kJ/mole). Recycle, particularly in the alkylation reactor, is likely to become increasingly important as a heat management strategy. The key will be how to limit the build-up of byproducts and feed impurities in these recycle loops, particularly as manufacturers seek cheaper and consequently lower quality feedstocks. As in the case of ethylbenzene, process and catalyst innovations will have to develop concurrently. 

Although SPA remains a viable catalyst for cumene synthesis, it has several important limitations 1) cumene yield is limited to about 95% because of the oligomerization of propylene and the formation of heavy alkylate by-products 2) the process requires a relatively high benzene/propylene (B/P) molar feed ratio on the order of 7/1 to maintain such a cumene yield and 3) the catalyst is not regenerable and must be disposed of at the end of each short catalyst cycle. Also, in recent years, producers have been given increasing incentives for better cumene product quality to improve the quality of the phenol, acetone, and especially a-methylstyrene (e.g., cumene requires a low butylbenzene content) produced from the downstream phenol units. 

This example shows that the problem of avoiding liquid acid waste was already solved for cumene synthesis using supported phosphoric acid, but the main problems were (i) the loss of H3PO4, which also causes problems of corrosion and deactivation, (ii) the impossibility of regeneration of the catalyst due to the type of carbon-species that accumulate on it and (iii) the formation of relatively high amounts of diisopropylbenzene (3.0-3.5%), which, even if converted by trans-... 

Transalkylation of DIPB isomers with benzene is an effective way for utilizing this byproduct and increasing the cumene yield again. Therefore, it was of some interest to investigate the efficiency and catalytic behaviour of triflic acid as catalyst for cumene synthesis with a higher yield from DIPB isomers (p-, and m-) by isomerization and transalkylation reactions at room temperature. 

Sales demand for acetophenone is largely satisfied through distikative by-product recovery from residues produced in the Hock process for phenol (qv) manufacture. Acetophenone is produced in the Hock process by decomposition of cumene hydroperoxide. A more selective synthesis of acetophenone, by cleavage of cumene hydroperoxide over a cupric catalyst, has been patented (341). Acetophenone can also be produced by oxidizing the methylphenylcarbinol intermediate which is formed in styrene (qv) production processes using ethylbenzene oxidation, such as the ARCO and Halcon process and older technologies (342,343). 

Phenol is the starting material for numerous intermediates and finished products. About 90% of the worldwide production of phenol is by Hock process (cumene oxidation process) and the rest by toluene oxidation process. Both the commercial processes for phenol production are multi step processes and thereby inherently unclean [1]. Therefore, there is need for a cleaner production method for phenol, which is economically and environmentally viable. There is great interest amongst researchers to develop a new method for the synthesis of phenol in a one step process [2]. Activated carbon materials, which have large surface areas, have been used as adsorbents, catalysts and catalyst supports [3,4], Activated carbons also have favorable hydrophobicity/ hydrophilicity, which make them suitable for the benzene hydroxylation. Transition metals have been widely used as catalytically active materials for the oxidation/hydroxylation of various aromatic compounds. 

Currently, benzene alkylation to produce ethylbenzene and cumene is routinely carried out using zeohtes. We performed a study comparing a zeohte Y embedded in TUD-1 to a commercial zeolite Y for ethylbenzene synthesis. Two different particle diameters (0.3 and 1.3 mm) were used for each catalyst. In Figure 41.7, the first-order rate constants were plotted versus particle diameter, which is analogous to a linear plot of effectiveness factor versus Thiele modulus. In this way, the rate constants were fitted for both catalysts. 

The related manufacture of cumene (isopropylbenzene) through the alkylation of benzene with propylene is a further industrially important process, since cumene is used in the synthesis of phenol and acetone. Alkylation with propylene occurs more readily (at lower temperature) with catalysts (but also with hydrogen fluoride and acidic resins) similar to those used with ethylene, as well as with weaker acids, such as supported phosphoric acid (see further discussion in Section 5.5.3). 

The problem of separating the catalyst at the end of the operation can be eased in some cases by attaching the catalyst to a solid support, for instance, liquid phosphoric add in the pores of a solid carrier for the vapor phase synthesis of cumene and the fairly wide application of enzymes that are attached (immobilized) by... 

The advantages of the catalyzed version are particularly apparent in the case of allyl alcohol whose epoxide, glycidol (2), is unstable to the catalyst.2 It can be obtained by catalyzed epoxidation at 0° with cumene hydroperoxide instead of t-butyl hydroperoxide in 65% yield and 90% ee. However, for use in a synthesis of the P-adrenergic blocking agent (2S)-propranolol (5), the epoxide is not isolated but treated with sodium a-naphthoxide to furnish the diol 3. The synthesis of 5 is completed by conversion to an epoxide (4) and ring opening with isopropylamine. 

In conclusion no catalysts with good performances (>5% conversion and >50% selectivity, simultaneously) have been discovered to date. New selective catalysts for direct phenol synthesis from benzene with 02 are essential for the novel industrial process replacing the cumene process - there are many problems to be resolved. 

Multibed unit with interstage injection of temperature controlled process fluid or inert fluid for temperature control of the process. In the synthesis of cumene from propylene and benzene in the presence of supported phosphoric add catalyst, interstage injection of cold process gas and water is used for temperature control and maintenance of catalyst activity (Figure 13.18(g)). Autothermal multitubular unit with heat interchange between feed on the shell side and reacting gas in the packed tubes and between feed and reacted gas in an external or built-in... 

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