Alkylation cumene synthesis

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. 

For cumene synthesis through alkylation of benzene by propylene, four dififerent zeolites are used industrially (Table 2) MCM-22, mordenite. Beta, and Y zeolites. The ZSM-5 zeolite caimot be used because of its restrictive pore size. 

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 Friedel-Crafts alkylation of aromatic compounds is of great importance in laboratory synthesis and industrial production. For example, the industrial processes for ethylbenzene, cumene and linear alkylbenzenes, etc., are on the base of this kind of reaction. It is well known that the drawbacks of the traditional acid catalysts such as A1Q3, H SO, and HF do great harm to the equipment and the environment, and these catalysts cannot be reused after the usual aqueous work-up besides, most of the reactions are carried out in the harmful and volatile organic solvents which can cause the environmental pollution aU of these problems need the replacement of the solvents or the acid catalysts. In this context, room-temperature ionic liquids have been iuCTeasingly employed as green solvents. 

The key stage is the alkylation of cumene. From its reaction in the liquid phase at 300°C in the presence of a silica/alumina catalyst with 3 moles of propene the 1,4-isomer required for hydroquinone is separated by fractionation (ref.30) and the mixture of 1,2- and 1,3-di-isopropylbenzenes together with the tri-isopropyl isomer equilibrated with benzene at 270°C with the same catalyst to enrich the proportion of the 1,3-compound required for the synthesis of resorcinol. The sequence of steps for hydroquinone is shown. By-product 4-isopropylphenol is mostly reoxidised and recycled giving a total yield of 71% based on di-isopropylbenzene (ref.31). 

Another important potential application is the class of benzene alkylation, as the manufacture of ethylbenzene or isopropyl-benzene (cumene). The synthesis is described by a set of parallel-consecutive equilibrium reactions, as for example ... 

Suppose that the reactant A is totally consumed. If the reaction rate is not infinite, the reactant B must be recycled at a convenient rate, in such a way that the resulting reaction rate leads to the total consumption of A. Therefore, we may speak about total conversion of the one-pass reactant, and partial conversion of the recycled reactant. Because the feed of fresh reactants must respect the stoichiometry, the feed policy of B must be adapted to fulfil the dynamic material balance. The above situation can be found often in industry, as for instance the synthesis of ethers from alchene-oxides and alcohols, the alkylation of benzene with ethylene or propylene to ethylbenzene or cumene, the addition of HCN to ketones, etc. 

The main group in chemical catalysts is general organic synthesis. It includes catalysts for esterification, hydrolysis, alkylation (dominated by cumene and ethylbenzene), and halogenation. A special class of this area are oxidation catalysts. About one-half of this market by value is the silver catalyst for etiiylene oxide. Relatively cheap catalysts are those for the oxychlorination of ethylene, they make up one-third by weight but only 5 % by value. 

One of the important processes in the petrochemical industry is the production of phenol. Phenol is an important raw material for the synthesis of petrochemicals, agrochemicals, and plastics. Examples of employment of phenol as an intermediate are production of bisphenol A, phenolic resins, caprolactam, alkyl phenols, aniline, and other useful chemicals. Current worldwide capacity for phenol production is nearly 7 milUon metric tons per year. More than the 95% of phenol is produced by the common industrial process known as Hock or cumene process involving three successive reaction steps ... 

The mechanism of each of the reactions in the synthesis of phenol from benzene and propene via cumene hydroperoxide requires some comment. The first reaction is a familiar one. The isopropyl cation generated by the reaction of propene with the acid (H3PO4) alkylates benzene in a typical Friedel-Crafts electrophilic aromatic substitution ... 

The toluene, xylene, cumene, and alkylnaphthalene sulfonates, specifically considered in this chapter, are generally prepared by sulfonation of the corresponding aromatic hydrocarbon followed by neutralization with the appropriate base. Gilbert s monograph on sulfonation reactions [1] forms the primary basis for the discussion on their synthesis, that is, the sulfonation of the aromatic portion of the starting raw materials—alkylbenzenes and alkyl naphthalenes. 

The reactivity of propylene is a result of the olefinic double bond in H2C=CHCH2, which gives rise to addition reactions. Consequently, propylene is used in the synthesis of many industrially important compoimds, including propylene oxide, acrylonitrile, cumene, and isopropyl alcohol. The consumption of propylene in the production of polymers, however, is greater than the total for all other chemicals. Propylene is also used in alkylating feedstocks for gasoline. 

From Cumene Hydroperoxide. This process illustrates industrial chemistry at its best. Overall, it is a method for converting two relatively inexpensive organic compounds— benzene and propene—into two more valuable ones—phenol and acetone. The only other substance consumed in the process is oxygen from air. Most of the worldwide production of phenol is now based on this method. The synthesis begins with the Friedel-Crafts alkylation of benzene with propene to produce cumene (isopropylbenzene) ... 

Another method to remove benzene is to react it with propylene or ethylene (benzene alkylation) to produce propylbenzene (cumene) or ethylbenzene. Commercial benzene alkylation processes in the chemical industry have been known for many years. Typically these processes require fairly pure benzene and ethylene feed. The shape selective ZMS-5 catalyst is used as a basis for ethylbenzene synthesis in the Mobil-Badger process (Chen et. al, 1989). ZSM-5 is very selective in this process as a result this process is currently used in the chemical industry to produce about 25% of world s ethylbenzene. Currently there are 12 operating Mobil-Badger EB units including a recent Shell Chemical unit which uses FCC off-gas as the ethylene feedstock source. 

The aromatics alkylation with olefins is a well-known technology, especially in the case of ethylbenzene (a Mobil-Badger process [109]) and cumene production [110], Ethylbenzene synthesis can be catalyzed by diverse modified HZSM-5, BEA, rare-earth Y, and MCM-22 zeohtes. In most cases, the selectivity is pretty high (99%), but the process must be carried out at a large excess of benzene and the conversion of the latter typically does not exceed 20-25% at 400°C and WHSV= 3 h . For cumene production, a few commercial processes have been developed by CD-Tech (Y zeolite), Lummus-Unocal (Y zeolite), Enichem (H-BEA), Mobil-Raytheon (MCM-22), Dow Chemical (dealuminated mordenite (MOR)), and UOP (a Q-Max process with MgSAPO-31). 

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