Cumene oxidation process

Gumylphenol. -Cumylphenol (PGP) or 4-(1-methyl-l-phenylethyl)phenol is produced by the alkylation of phenol with a-methylstyrene under acid catalysis. a-Methylstyrene is a by-product from the production of phenol via the cumene oxidation process. The principal by-products from the production of 4-cumylphenol result from the dimerization and intramolecular alkylation of a-methylstyrene to yield substituted indanes. 4-Cumylphenol [599-64-4] is purified by either fractional distillation or crystallization from a suitable solvent. Purification by crystallization results in the easy separation of the substituted indanes from the product and yields a soHd material which is packaged in plastic or paper bags (20 kg net weight). Purification of 4-cumylphenol by fractional distillation yields a product which is almost totally free of any dicumylphenol. The molten product resulting from purification by distillation can be flaked to yield a soHd form however, the soHd form of 4-cumylphenol sinters severely over time. PGP is best stored and transported as a molten material. 

More than 95% of the cumene produced is used as feedstock for the production of phenol (qv) and its coproduct acetone (qv). The cumene oxidation process for phenol synthesis has been growing in popularity since the 1960s and is prominent today. The first step of this process is the formation of cumene hydroperoxide [80-15-9]. The hydroperoxide is then selectively cleaved to phenol [108-95-2] and acetone [67-64-1/ in an acidic environment (21). 

The acetone supply is strongly influenced by the production of phenol, and so the small difference between total demand and the acetone suppHed by the cumene oxidation process is made up from other sources. The largest use for acetone is in solvents although increasing amounts ate used to make bisphenol A [80-05-7] and methyl methacrylate [80-62-6]. a-Methylstyrene [98-83-9] is produced in controlled quantities from the cleavage of cumene hydroperoxide, or it can be made directly by the dehydrogenation of cumene. About 2% of the cumene produced in 1987 went to a-methylstyrene manufacture for use in poly (a-methylstyrene) and as an ingredient that imparts heat-resistant quaUties to polystyrene plastics. 

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. 

Fermentation and distillation techniques for acetone production were replaced starting in the 1950s with the cumene oxidation process (Figure 2.1). In this process, cumene is oxidized to cumene hydroperoxide, which is then decomposed using acid to acetone and phenol. This is the primary method used to produce phenol, and acetone is produced as a co-product in the process, with a yield of about 0.6 1 of acetone to phenol. 

Cumene manufacture consumed about 10 percent (2.2 billion lb) of the propylene used for chemicals in the United States in 1998. It is prepared in near stoichiometric yield from propylene and benzene with acidic catalysts (scheme below). Many catalysts have been used commercially, but most cumene is made using a solid phosphoric acid catalyst. Recently, there has been a major industry shift to zeolite-based catalyst. The new process has better catalyst productivity and also eliminates the environmental waste from spent phosphoric acid catalyst. It significantly improves the product yield and lowers the production cost. Cumene is used almost exclusively as feed to the cumene oxidation process, which has phenol and acetone as its coproducts. 

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Phenol and acetone are produced from benzene and propene by the cumene route, which can be divided into cumene process and cumene oxidation process [1]. Benzene and propene react to cumene in the cumene process. In the cumene oxidation process, cumene is oxidized to cumene hydroperoxide (CHP), which is converted into phenol and acetone in a successive reaction, the so-called cleavage. The oxidation of cumene to CHP is described in detail in the following sections. 

The cleavage of CHP into phenol and acetone was first reported by Hock and Lang [2]. Hence, the cumene oxidation process for the production of phenol and acetone is known as the Hock process. As claimed by Zakoshansky [3], the reaction route was supposedly discovered in parallel in the former USSR. 

Minor amounts of CHP are used as an initiator in polymerization processes. However, the dominant use of CHP is as an intermediate product in the cumene oxidation process. Based on the worldwide phenol production capacity (in 2013) of approximately 11.4x 10 t, the production capacity of CHP can be estimated to be 18.8xl0 t/a. 

In the cumene oxidation process, in a first reaction cumene is oxidized to CHP. In a second reaction, CHP is cleaved to phenol and acetone by using a strong mineral acid as catalyst. The reaction heat is 117kJ/mol for the oxidation and 252 kJ/mol for the cleavage. The oxidation is carried out at pressures ranging from atmospheric to approximately 7 bar and temperatures between 80 and 120 C. The cleavage is performed around atmospheric pressure and temperatures in the range between 40 and 80 °C. 

In commercial cumene oxidation processes, the radicals from the thermal decomposition of CHP are the initiators for the free-radical chain reaction. Therefore, the reaction towards CHP in the cumene oxidation is called autooxidation. 

Figure 2.3 gives an overview of the cumene oxidation process, which includes the oxidation of cumene to CHP. A more detailed description is given in [1]. 

Figure 2.3 Block diagram of the cumene oxidation process.

In the beginning of the cumene oxidation process, oxidation was carried out as a three-phase reaction [25—27], the so-called wet oxidation. In addition to cumene and air, an aqueous sodium carbonate solution was continuously added to the reactors to extract and neutralize organic acids that are formed during oxidation. Phenolchemie, now INEOS Phenol, was the first to operate reactors without adding any caustic soda or sodium carbonate [28], which is called dry oxidation. Such a process is easier to handle and even leads to higher yields. 

In the recent past, the focus of new developments was on alternative phenol processes that overcome the disadvantage of the coupled product acetone in the cumene oxidation process. These processes are based on the oxidation of benzene with nitrous oxide or hydrogen peroxide [7]. The main research on the cumene oxidation process is process intensification by improving the oxidation reaction and improved process and reactor design. 

The oxidation reaction is a radical chain reaction, which can be influenced by radical scavengers, such as phenol. As phenol is produced from GHP, the risk of phenol recycling within the cumene oxidation process is always present. To reduce the... 

Probably the most intensively studied derivative of styrene with regard to its polymerization behavior is a-methylstyrene. It is produced commercially by the dehydrogenation of isopropyl-benzene (cumene) and also as a by-product in the production of phenol and acetone by the cumene oxidation process. The polymerization characteristics of ot-methylstyrene are considerably dilferent from those of styrene. Whereas radical polymerization of the pure monomer proceeds very slowly and is therefore not a practical technique [196], both ionic and coordination-type polymerization can be used to prepare poly(a-methylstyrene) (PMS). 

Cyclohexanone peroxide compounds (R OOR ) in the presence of tetraethylammonium bromide initiate the cumene oxidation reaction even at 308 - 340K (Fig. 1). Tetraethylammonium bromide as well as peroxide compounds I and II don t initiate cumene oxidation process at mentioned temperature interval. 

Isopropyl alcohol (IPA) has been called the first petrochemical. Both historically and today, it is prepared by sulfuric acid-mediated indirect hydration of propylene (see equations below and Fig. 22.28). Originally it was the source of most of the acetone used in the world. Now, this route must compete with acetone derived from the cumene oxidation process, in which cumene is converted to equimolar amounts of phenol and acetone. Between 1959 and 1978 the amount of acetone derived from IPA dehydrogenation declined from 80 percent to 34 percent, and the amount of IPA used for this purpose declined from 47 percent in 1978 to 12 percent in 1990. 

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