Alkylation of Benzene by Propylene to Cumene

Alkylation of Benzene by Propylene to Cumene Table 6.7 Physical properties of a zeolite catalyst. 

Saponites were synthesised at 90°C and 1 atmosphere from a Si/Al-gel and a solution containing urea and M2+-nitrate (M2+= Zn, Mg, Ni and Co) in only a few hours. The products were characterised by XRD, TEM, BET, 27a1- and 29si-MASNMR. Furthermore, the catalytic properties of the synthetic saponites in the Friedel-Crafts alkylation of benzene with propylene to cumene were tested. Incorporation of Zn, Mg, Ni, Co, or a combination of Zn and Mg, in the octahedral layer, as well as controlling the Si/Al-ratio in the tetrahedral layer between 7.9 and 39 could easily be established. The specific surface areas and the pore volumes of the saponites are extremely high, viz., 100-750 m /g and 0.03-0.32 ml/g, respectively. Zn-saponite with A]3+ in the interlayer exhibited a higher catalytic activity as compared to a commercial SPA-catalyst (Solid Phosphoric Acid). 

Cumene (isopropylbenzene) is made by Friedel-Crafts alkylation of benzene with propylene. Although cumene is a high-octane automotive fuel, almost all of the cumene produced is used to make phenol (C6H5OH) and acetone [(CH3)2CO]. Cumene is easily oxidized to the corresponding hydroperoxide, which is readily cleaved in dilute acid, to yield phenol and acetone. 

A typical phenol plant based on the cumene hydroperoxide process can be divided into two principal areas. In the reaction area, cumene, formed by alkylation of benzene and propylene, is oxidized to form cumene hydroperoxide (CHP). The cumene hydroperoxide is concentrated and cleaved to produce phenol and acetone. By-products of the oxidation reaction are acetophenone and dimethyl benzyl alcohol (DMBA). DMBA is dehydrated in the cleavage reaction to produce alpha-methylstyrene (AMS). 

Production of a-methylstyrene (AMS) from cumene by dehydrogenation was practiced commercially by Dow until 1977. It is now produced as a by-product in the production of phenol and acetone from cumene. Cumene is manufactured by alkylation of benzene with propylene. In the phenol—acetone process, cumene is oxidized in the Hquid phase thermally to cumene hydroperoxide. The hydroperoxide is spHt into phenol and acetone by a cleavage reaction catalyzed by sulfur dioxide. Up to 2% of the cumene is converted to a-methylstyrene. Phenol and acetone are large-volume chemicals and the supply of the by-product a-methylstyrene is weU in excess of its demand. Producers are forced to hydrogenate it back to cumene for recycle to the phenol—acetone plant. Estimated plant capacities of the U.S. producers of a-methylstyrene are Hsted in Table 13 (80). 

CD-Cumene A process for making cumene for subsequent conversion to phenol and acetone. The cumene is made by catalytic alkylation of benzene with propylene in a catalytic distillation reactor. Developed in 1995 by CDTech. 

Sulfated zirconia catalysts showed selectivities comparable to those of AICI3 in the alkylation of benzene with 1-alkenes to linear alkylbenzenes.396 The mesopor-ous sulfated zirconia sample could be regenerated by solvent extraction or thermal treatment. Phosphotungstic acid supported on sulfated zirconia doped with Fe proved to be very active and highly selective in the alkylation of benzene with propylene at 100-150°C to produce cumene both monoalkylation and cumene formation have better than 90% selectivity.397 It can be regenerated at moderate temperature (350°C). 

Desorption of similar products from cumene- and propylene-deactivated parent H-mordenite is a result analogous to that of Venuto and Hamilton (3). They found that deactivation of rare earth X (REX) faujasite by alkylation of benzene with ethylene to ethylbenzene resulted in trapped products similar to those for deactivation with ethylene alone. 

Cumene (isopropylbenzene) is the major intermediate (10.6 Mt/a was the world capacity in 2004) for the manufacture of phenol. It is formed by alkylation of benzene with propylene according to Equation 6. Propylene is believed to react with hydrogen chloride forming the more stable secondary carbocation, which is associated with the tetrachloroaluminate anion. The ion pair reacts further with benzene to give the product. 

Recently, a novel CD process for the alkylation of benzene with propylene using suspended catalyst rather than encasing the catalyst in a rigid structure with 100% conversion for propylene with more than 90% selectivity to high-purity cumene was reported. An improvement of the suspension CD by simultaneous alkylation and transalkylation for producing... 

Isopropylbenzene (Cumene). Oxidation of isopropylbenzene, cumene, to cumene hydroperoxide and the subsequent decomposition to phenol and acetone have become of significant commercial importance in recent years and have, furthermore, pointed the way as a generally useful new route for potential commercial manufacture of other important chemicals. For use in the phenol-plus-acetone process, cumene is usually obtained by the phosphoric acid-catalyzed alkylation of benzene with propylene. 

A more complex example is the manufacture of cumene (isopropyl benzene) by the alkylation of benzene with propylene, taken from the 1997 National Student Design Competition of the AIChE. Cumene is widely used to make acetone and phenol. The fresh feeds are as follows, where the benzene feed is nearly pure, but a refinery cut of a propylene-propane mixture is used rather than a more expensive feed of nearly pure propylene. 

Like ethylene, propylene is produced by the cracking of hydrocarbons. The major use of propylene is to make polypropylene but it is also a feedstock to manufacture other industrial chemicals, including propylene glycol, acrylic acid, propylene oxide, cumene, and isopropyl alcohol. Propylene oxide is made by the oxidation of propylene, and hydrolysis of propylene oxide gives propylene glycol. The alkylation of benzene with propylene gives isopropyl benzene, more commonly called cumene. Note that the product is not n-propyl benzene. This is because the intermediate is the more stable secondary carbocation which results in isopropyl benzene. 

Small quantities of methanol and ethanol are sometimes added to the C3S in pipelines to protect against freezing because of hydrate formation. Although the beta zeolite catalyst is tolerant of these alcohols, removing them from the feed by a water wash may still be desirable to achieve the lowest possible levels of EB or cymene in the cumene product. Cymene is formed by the alkylation of toluene with propylene. The toluene may already be present as an impurity in the benzene feed, or it may be formed in the alkylation reactor from methanol and benzene. Ethylbenzene is primarily formed from ethylene impurities in the propylene feed. However, similar to cymene, EB can also be formed from ethanol. 

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