Cumene synthesis

Fig. 1. UOP catalytic condensation process for cumene synthesis. R = reactor RECT = rectifier DP = depropanizer RC = recycle column ...

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. 

Experimental and computational study of beta, ZSM-12, Y, mordenite and ERB-1 in cumene synthesis. Micropor. Mater., 6, 395-404. 

Treybal, in his book Liquid Extraction [1], works equilibrium material balances with triangular coordinates. The most unique and simple way to show three-phase equilibrium is a triangular diagram (Fig. 7.1), which is used for extraction unit operation in cumene synthesis plants [2], In this process benzene liquid is used as the solvent to extract acetic acid (the solute) from the liquid water phase (the feed-raffinate). The curve D,S,P,F,M is the equilibrium curve. Note that every point inside the triangle has some amount of each of the three components. Points A,... 

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

Figure 6.6 Profile of concentrations and temperature in an adiabatic PFR for cumene synthesis.

Figure 6.14 Catalytic distillation column for cumene synthesis.

Figure 6.15 Flowsheet for cumene synthesis making use of catalytic distillation.

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. 

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