Of ethylbenzene hydroperoxide

Ethylbenzene Hydroperoxide Process. Figure 4 shows the process flow sheet for production of propylene oxide and styrene via the use of ethylbenzene hydroperoxide (EBHP). Liquid-phase oxidation of ethylbenzene with air or oxygen occurs at 206—275 kPa (30—40 psia) and 140—150°C, and 2—2.5 h are required for a 10—15% conversion to the hydroperoxide. Recycle of an inert gas, such as nitrogen, is used to control reactor temperature. Impurities ia the ethylbenzene, such as water, are controlled to minimize decomposition of the hydroperoxide product and are sometimes added to enhance product formation. Selectivity to by-products include 8—10% acetophenone, 5—7% 1-phenylethanol, and <1% organic acids. EBHP is concentrated to 30—35% by distillation. The overhead ethylbenzene is recycled back to the oxidation reactor (170—172). 

PO—SM Coproduction. The copioduction of propylene oxide and styrene (40—49) includes three reaction steps (/) oxidation of ethylbenzene to ethylbenzene hydroperoxide, (2) epoxidation of ethylbenzene hydroperoxide with propylene to form a-phenylethanol and propylene oxide, and (3) dehydration of a-phenylethanol to styrene. 

The oxidation step is similar to the oxidation of cumene to cumene hydroperoxide that was developed earlier and is widely used in the production of phenol and acetone. It is carried out with air bubbling through the Hquid reaction mixture in a series of reactors with decreasing temperatures from 150 to 130°C, approximately. The epoxidation of ethylbenzene hydroperoxide to a-phenylethanol and propylene oxide is the key development in the process. 

Styrene is manufactured nearly entirely by the direct dehydrogenation of ethylbenzene. Smaller amounts are obtained indirectly, as a co product, from the production of propy. lene oxide by the Oxirane and Shell technologies, industrialized in the United States, the Netherlands and Spain, and whose essential intermediate step is the formation of ethylbenzene hydroperoxide, or from the production of aniline, by a technique develop jn the USSR, which combines the highly exothermic hydrogenation of nitrobenzene with the highly endothermic dehydrogenation of ethylbenzene. 

In the ethylbenzene process the 1-methylbenzyl alcohol (MBA) co-product is dehydrated to monomeric styrene (SM). The theoretical SM/PO ratio is 1.8 1 and commercial plants operate in the range 2.2-2.7 l, indicating that the selectivity of ethylbenzene hydroperoxide (EBHP) formation is much higher than that of... 

A group of Russian workers has produced a series of technical reports, currently to number 11, that deal with the epoxidation of cyclohexene by ethylbenzene hydroperoxide, using molbydenum catalysts. The reports explore the effects of modifications of the catalyst on reaction efficiency. The use of molybdenum catalysts in the oxidation of cyclohexene by cumyl peroxide has been studied, using i.r. and e.s.r. spectroscopyE.s.r. spectroscopy has also been used to investigate the decomposition of ethylbenzene hydroperoxide in the presence of molybdenum naphthenate. ... 

As follows from Figures 7.4 and 7.5 the calculated kinetic curves on the accumulation of ethylbenzene hydroperoxide describe experimental results with reasonable accuracy for the ethylbenzene oxidation inhibited by the /Jora-methylphenol and without the inhibition at 60°C and 120°C. 

Figure 7.5. Kinetic curves of the ethylbenzene hydroperoxide accumulation (1) and / ara-methylphenol consumption (2) for liquid-phase oxidation of ethylbenzene at 120 °C. Initial concentrations of ethylbenzene hydroperoxide andpora-methylphenol were 5-10 M and 7.5-10 M, respectively (points experimental lines - calculation).

Figure 7.8. Calculated kinetic curves of /jara-methylphenol consumption (1), accumulation of para-methylphenoxyl radical (2), hydroperoxide of ethylbenzene (3) and peroxyl radical (4) for the liquid-phase inhibited oxidation of ethylbenzene at 60 °C. Initial concentration of ethylbenzene hydroperoxide was 10 M.

Figure 7.12. Kinetic curves of oxygen absorption for ethylbenzene oxidation in the absence (1) and presence (2 and 3) of BHT. [BHT]o=6.5 10 M (2) and I TO " M (3), respectively, T= 120 °C. The initial concentration of ethylbenzene hydroperoxide was I TO M (points - experimental curves -calculation).

Figure 7.16. Reduced value contributions of individual steps over the induction period for liquid-phase oxidation of ethylbenzene inhibited by BHT at different initial concentrations lO M, 10 M and 10 M, T=60 °C. The initial concentration of ethylbenzene hydroperoxide was 10 M. Step contributions are numbered according to the steps. Conversion of BHT makes up 7-10%.

In the peroxidation reactor ethylbenzene is converted with air at 146 °C and 2 bar to form a 12-14 wt% solution of ethylbenzene hydroperoxide in ethylbenzene. The reaction takes place in the liquid phase and conversion is limited to 10% for safety reasons. The reactor is a bubble tray reactor with nine separate reaction zones. To avoid decomposition of the formed peroxide the temperature is reduced from 146 °C to 132 °C over the trays. In the epoxidation reactor the reaction solution is mixed with a homogeneous molybdenum naphthenate catalyst. Epoxidation of propylene in the liquid phase is carried out at 100-130 °C and 1-35 bar. The crude product stream (containing PO, unreacted propylene, a-phenylethanol, acetophenone, and other impurities) is sent to the recycle column to remove propylene. The catalyst can be removed by an aqueous alkali wash and phase separation. The crude PO, obtained as head stream in the crude PO column, is purified by distillations. The unconverted reactant ethylbenzene can be recycled in the second recycle column. The bottom stream containing a-phenylethanol is sent to the dehydration reactor. The vapor-phase dehydration of a-phenylethanol to styrene takes place over a titanium/alumina oxide catalyst at 200-280 °C and 0.35 bar (conversion 85%, selectivity 95%). 

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). 

Commercially, autoxidation is used in the production of a-cumyl hydroperoxide, tert-huty hydroperoxide, -diisopropylbenzene monohydroperoxide, -diisopropylbenzene dihydroperoxide, -menthane hydroperoxide, pinane hydroperoxide, and ethylbenzene hydroperoxide. 

The second important process for propylene oxide is epoxidation with peroxides. Many hydroperoxides have been used as oxygen carriers for this reaction. Examples are t-butylhydroperoxide, ethylbenzene hydroperoxide, and peracetic acid. An important advantage of the process is that the coproducts from epoxidation have appreciable economic values. 

Epoxidation of propylene with ethylbenzene hydroperoxide is carried out at approximately 130°C and 35 atmospheres in presence of molybdenum catalyst. A conversion of 98% on the hydroperoxide has been reported ... 

Ethylbenzene hydroperoxide is produced by the uncatalyzed reaction of ethylbenzene with oxygen ... 

A 9 g sample of the freshly prepared hydroperoxide decomposed after 20 min at ambient temperature, bursting the 20 ml glass container. A 30% solution of the hydroperoxide in ethylbenzene is stable. 

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

The reverse micelles stabilized by SDS retard the autoxidation of ethylbenzene [27]. It was proved that the SDS micelles catalyze hydroperoxide decomposition without the formation of free radicals. The introduction of cyclohexanol and cyclohexanone in the system decreases the rate of hydroperoxide decay (ethylbenzene, 363 K, [SDS] = 10 3mol L [cyclohexanol] =0.03 mol L-1, and [cyclohexanone] = 0.01 mol L 1 [27]). Such an effect proves that the decay of MePhCHOOH proceeds in the layer of polar molecules surrounding the micelle. The addition of alcohol or ketone lowers the hydroperoxide concentration in such a layer and, therefore, retards hydroperoxide decomposition. The surfactant AOT apparently creates such a layer around water moleculesthat is very thick and creates difficulties for the penetration of hydroperoxide molecules close to polar water. The phenomenology of micellar catalysis is close to that of heterogeneous catalysis and inhibition (see Chapters 10 and 20). 

These reactions produce free radicals, as follows from the fact of consumption of free radical acceptor [42]. The oxidation of ethylbenzene in the presence of thiophenol is accompanied by CL induced by peroxyl radicals of ethylbenzene [43]. Dilauryl dithiopropionate induces the pro-oxidative effect in the oxidation of cumene in the presence of cumyl hydroperoxide [44] provided that the latter is added at a sufficiently high proportion ([sulfide]/[ROOH] > 2). By analogy with similar systems, it can be suggested that sulfide should react with ROOH both heterolytically (the major reaction) and homolytically producing free radicals. When dilauryl dithiopropionate reacts with cumyl hydroperoxide in chlorobenzene, the rate constants of these reactions (molecular m and homolytic i) in chlorobenzene are [42]... 

The resulting products, such as sulfenic acid or sulfur dioxide, are reactive and induce an acid-catalyzed breakdown of hydroperoxides. The important role of intermediate molecular sulfur has been reported [68-72]. Zinc (or other metal) forms a precipitate composed of ZnO and ZnS04. The decomposition of ROOH by dialkyl thiophosphates is an autocata-lytic process. The interaction of ROOH with zinc dialkyl thiophosphate gives rise to free radicals, due to which this reaction accelerates oxidation of hydrocarbons, excites CL during oxidation of ethylbenzene, and intensifies the consumption of acceptors, e.g., stable nitroxyl radicals [68], The induction period is often absent because of the rapid formation of intermediates, and the kinetics of decomposition is described by a simple bimolecular kinetic equation... 

Since approximately 2.2 lb of /-butyl alcohol would be produced per 1 lb of propylene oxide, an alternative reactant in this method is ethylbenzene hydroperoxide. This eventually forms phenylmethylcarbinol along with the propylene oxide. The alcohol is dehydrated to styrene. This chemistry was covered in Chapter 9, Section 6 as one of the syntheses of styrene. Thus the side product can be varied depending on the demand for substances such as /-butyl alcohol or styrene. Research is being done on a direct oxidation of propylene with oxygen, analogous to that used in the manufacture of ethylene oxide from ethylene and oxygen (Chapter 9, Section 7). But the proper catalyst and conditions have not yet been found. The methyl group is very sensitive to oxidation conditions. 

The activity of titanium based catalysts for the oxidation of organic compounds is well known. Wulff et al. in 1971 [1] patented for Shell Oil a process for the selective epoxidation of propylene with hydroperoxides like ethylbenzene hydroperoxide (EBH) or tertiary-butyl hydroperoxide (TBH) with the use of a catalyst made of Ti02 deposited on high surface area Si02. A Shell Oil plant for the production of 130,000 tons/y of propylene oxide at Moerdijk, Holland, is based on this technology. 

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