Selectivity cumene synthesis

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

Cumene synthesis Dealuminated mordenite MCM-22 beta Y omega Lower inputities Transalkylation function Lower benzene-to-propylene ratio allows higher capacity, great unit efficiency High selectivity Regenerable, non-hazardous, non-corrosive... 

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). 

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 three-step cumene process, including the liquid-phase reactions, is energyconsuming, environmentally unfavorable and disadvantageous for practical operation. The process also produces the unnecessary by-product acetone stoichio-metrically. Furthermore, the intermediate, cumene hydroperoxide, is explosive and cannot be concentrated in the final step, resulting in low phenol yield ( 5%, based on the amount of benzene initially used). Thus, direct phenol synthesis from benzene in a one-step reaction with high benzene conversion and high phenol selectivity is most desirable from the viewpoints of environment-friendly green process and economical efficiency. 

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. 

There is also the prospect of increased demand for some of the cumene byproducts such as diisopropylbezene (DIPB). The production of diphenols from DIPB is important for synthesis of resorcinol (from meta-DIPB) and hydroquinone (from para-DIPB). It is likely that the market may soon see the introduction of cumene based processes that specifically produce these isomers with high degrees of selectivity. 

Aerobic selective oxidation of alkylaromatics, including cumene (CU), ethylbenzene (EtB), and cyclohexylbenzene (CyB), to the corresponding hydroperoxides (CHPs) represents a key step for several large-scale productions, including the Hock process for the synthesis of phenol (see Chapter 2) [15] and the Shell styrene monomer/propylene oxide (SM/PO) process for the production of propylene oxide (PO) and styrene monomer (SM) [16]. 

A brief screen of potential radical mediators revealed that most oxidants facilitated the tosyl group elimination (Table 4). However, two lead reagents were identified, azobisisobutyronitrile (AIBN) and cumene hydroperoxide (CHP), both of which delivered the product in >80% solution yield, while minimizing over-oxidation. Ultimately, CHP was selected due to its commercial availability and ease of handling—CHP is used in the commercial synthesis of acetone and phenol (via the Hock rearrangement)." ... 

In conclusion, the epoxidation of propylene with bulky oxidants (such as cumene or TBHP) can be successfully achieved using titanium-containing mesoporous materials as catalysts. The catalytic chemistry of the active sites can be controlled via the synthesis conditions and postsynthesis modifications. The hydrophobicity of the catalyst is of great importance to achieve a highly selective catalyst. The Ti-MCM-41-based heterogeneous catalyst has demonstrated excellent performance in the commercial process for PO manufacture. 

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 catalytic activity of some of these polymers for the decomposition of hydrazine (19, 59), isopropanol (19), formic acid (19), hydrogen peroxide (60) and for the oxidation of cumene to its hydroperoxide has been studied (55). 2,5-Dihydroxybenzoquinone selectively precipitates thorium and zirconium in the presence of other rare earths (55). Analysis of beryllium by spectro-photometric studies of its complexes with naphthazarin and/or alkannin has been developed into a rapid, sensitive, and accurate method (134). The synthesis of many of the polymers in Table IX.2 (pp. 274-279) for use as dyes was performed in 1912 (48). 

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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