Oxidation of Propylene to Acetone

The Wacker chemistry can also be used to oxidize higher olefins. Terminal olefins are converted to methylketones. In general rates and yields of ketone formation decrease with increasing alkyl chain length. Hence only propylene to acetone has found commercial application. 

Three processes are currently used for acetone manufacture  

Most important is the cumene process with an 80-85% share worldwide cumene (isopropylbenzene obtained from alkylation of benzene with propylene) is oxidized to the corresponding hydroperoxide which is decomposed to a mixture of phenol and acetone. In Japan the second most important process for acetone production is the direct oxidation of propylene with a 12% share. 

The Wacker-Hoechst process has been practised commercially since 1964. In this liquid phase process propylene is oxidized to acetone with air at 110-120°C and 10-14 bar in the presence of a catalyst system containing PdCl2. As in the oxidation of ethylene, Pd(II) oxidizes propylene to acetone and is reduced to Pd(0) in a stoichiometric reaction, and is then reoxidized with the CuCl2/CuCl redox system. The selectivity to acetone is 92% propionaldehyde is also formed with a selectivity of 2-4%. The conversion of propylene is more than 99%. 

As in the acetaldehyde process, this can be carried out commercially in either a single-step or a two-step process. The latter is economically more favourable because a propylene/propane mixture (made by petroleum cracking) can be directly used as the feedstock. Propane behaves like an inert gas and does not participate in the reaction. Acetone is separated from lower and higher boiling compounds in a two-step distillation. 

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Production of acetone by dehydrogenation of isopropyl alcohol began in the early 1920s and remained the dominant production method through the 1960s. In the mid-1960s virtually all United States acetone was produced from propylene. A process for direct oxidation of propylene to acetone was developed by Wacker Chemie (12), but is not beheved to have been used in the United States. However, by the mid-1970s 60% of United States acetone capacity was based on cumene hydroperoxide [80-15-9], which accounted for about 65% of the acetone produced. 

Cu Pd -TSM catalyzes the oxidation of propylene to acetone selectively in the presence of water vapor. Because Cu Pd -TSM swells with water, the interlayer region is considered to be filled with a solution similar to that used in the Wacker reaction. However, the interlayer spacing of Cu Pd -TSM is not wide enough for the reactant molecule to diffuse into the interlayers, and a great number of the Pd ions located at the inside of the interlayers are thought not to contribute in the reaction. For the... 

As shown above, the oxidation of the ethylene is thought to proceed via nucleophilic attack of a hydroxide on the ethylene. Palladium(ll) chloride will also catalyse the oxidation of propylene to acetone and cis- and trans-butenes to methylethyl ketone [116a]. Kinetic studies on these reactions suggest that the rate-determining step is the addition of hydroxide to the co-ordinated olefin, viz. ... 

The attack of OH obeys the Markovnikov rule. Higher alkenes are oxidized to ketones and this unique oxidation of alkenes has extensive synthetic appli-cations[23]. The oxidation of propylene affords acetone. Propionaldehyde is... 

In summary, the total oxidation of propylene to C02 occurred at a higher rate than partial oxidation to propylene oxide and acetone total and partial oxidations occurred in parallel pathways. The existence of the parallel reaction pathways over Rh/Al203 suggest that the selective poisoning of total oxidation sites could be a promising approach to obtain high selectivity toward PO under high propylene conversion. 

Moiseev and coworkers showed [10,13] that giant palladium clusters with an idealized formula Pd56iL5o(OAc)igo (L = phenanthroline or bipyridine) are highly active catalysts for allylic oxidation of olefins. The catalytically active solution was prepared by reduction of Pd(OAc)2, e. g. with H2, in the presence of the ligand, L, followed by oxidation with O2. The giant palladium cluster catalyzed the oxidation of propylene to allyl acetate under mild conditions. Even in 10% aqueous acetic acid, allyl acetate selectivity was 95-98 % [10]. Oxidation catalyzed by Pd-561 in water afforded a mixture of allylic alcohol (14%), acrolein (2%), and acrylic acid (60%), and only 5% acetone [10]. 

Conditions for the direct oxidation of propylene to acrolein include use of a catalyst of cuprous oxide deposited on granular silicon carbide, catalyst temperature of 375 C, feed stream composition by volume of 20 per cent propylene, 20 per cent air, and 60 per cent steam, and contact time of 1 sec. Recovery and primary purification of the acrolein from the reaction product are effected by quench scrubbing the reactor effluent with water and wth liquid propylene. The composition of the carbonylic compounds in the product is, approximately, acrolein, 90 per cent by weight acetaldehyde, 6 per cent propionaldehyde, 2 per cent and acetone, 2 per cent. At reaction temperatures of about 300 C and conversions of about 50 per cent, a selectivity to acrolein of about 40 per cent is reported for 10 per cent propylene-in-air mixtures. ... 

Catal54ic oxidations of hydrocarbons have relatively low selectivities. Reactions with interesting perspectives are the direct oxidation of propylene to propylene oxide, of benzene to phenol, and of propane to isopropanol and acetone. 

When propylene was used for a fuel instead of ethylene, partial oxidation of propylene to acrolein was performed with a 96 % selectivity under short circuit conditions. Acrolein is a Jt-allyl oxidation product at a Pd° catalyst and is not a Wacker oxidation product at a Pd catalyst. When the oxidation rate of propylene was accelerated by an apphed voltage, acetone was produced with 90 % selectivity [5]. The anode potentials in operation were lower than a redox potential of Pd (+0.74 V (Ag/AgCl)) under short circuit conditions. On the other hand, the potentials were higher than the redox potential under applying voltage conditions [6, 7]. The oxidation state of Pd at the anode was Pd° under the former conditions and was Pd " under the latter conditions. The product selectivities to acrolein and acetone were able to control in the propylene oxidation by tuning anode potentials in operation. 

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. 

Other Derivatives and Reactions. The vapor-phase condensation of ethanol to give acetone has been well documented in the Hterature (376—385) however, acetone is usually obtained as a by-product from the cumene (qv) process, by the direct oxidation of propylene, or from 2-propanol. 

The more expedient, direct catalytic oxidation route to acetone was developed in Germany in the 1960s. If you had been in charge of building the acetone business from scratch, you d probably not have built any IPA-to-acetone plants if you had known about the Wacker process. It s a catalytic oxidation of propylene at 200—250°F and 125—200 psi over palladium chloride with a cupric (copper) chloride promoter. The yields are 91-94%. The hardware for the Wacker process is probably less than for the combined IPA/acetone plants. But once the latter plants were built, the economies of the Wacker process were not sufficient to shut them down and start all over. So the new technology never took hold in the United States. 

Contrary to the ionic mechanism suggested by Tsuji, an insertion mechanism explains the facts much better. An external attack of carbon monoxide at the most positive carbon atom of propylene in a palladium chloride complex, as Tsuji proposed, would be expected to produce 3-chloro-2-methylpropionyl chloride rather than the observed product, 3-chlorobutyryl chloride. Since oxidation of propylene by Pd (II) ion gives acetone rather than propionalydehyde, a CO insertion reaction and elimination should produce the observed compound, 3-chlorobutyryl chloride... 

The single-step production of acetone by the catalytic oxidation of propylene in the gas phase is a desirable goal, which can be achieved mainly by binary oxides.552 Acetone is obtained with better than 90% selectivity at 100-160°C when propylene is oxidized with H2O-O2 on SnC -MoOj.553 Ketone formation proceeds via hydration of the carbocation intermediate to form an adsorbed alcoholic species followed by oxydehydrogenation 553,554... 

As a consequence of the experimental results for catalyst Sets A and B, appropriate rhodium-containing catalysts were tested as Set C. Figure 3.38 shows the reactor outlet concentration for propylene oxide, acrolein and acetone. A large number of the catalysts tested produce high concentrations of propylene oxide of up to 2000 ppm at 1% conversion of propylene. The combinations Rh-Sn and Rh-In are very effective for propylene oxide formation. In most cases the binary catalysts have higher activity at lower propylene loading. In Figure 3.38, it can also be seen... 

A rather interesting application of zeolite-based alkene oxidation catalysis has been demonstrated by Japanese workers (46, 47). In particular, a Pd2 +, Cu2 +Y zeolite was shown to be an active and stable heterogeneous oxidation catalyst which is analogous to the well-known homogeneous Wacker catalyst system containing PdCl2 and CuCl2 (48). Under Wacker conditions (i.e., alkene/02/H20) the zeolite Y catalyst was shown to convert ethylene to acetaldehyde and propylene to acetone with selectivities in excess of 90% with C02 as the major by-product. 

Catalysis (27-30) which allows for the direct oxidation of benzene to produce phenol. Economic analyses have shown that these are attractive only in specific instances where, for example, a cheap source of N20 is available. Nevertheless, these developments have shown that direct oxidation is possible and further innovations in this area should probably be expected. The demands for acetone and phenol have generally tended to follow each other. However, as bisphenol A becomes an even more important end use for phenol and acetone, there will be a need for a separate source of phenol. The synthesis of bisphenol A requires two moles of phenol for every one mole of acetone, while the peroxidation of cumene produces one mole of each. Still, processes such as the direct oxidation of benzene are unlikely to have a major impact on cumene demand in the short term since there are competing processes such as Mitsui s for converting acetone back to propylene. 

Cu " Pd " -, Cu " -, and Pd -TSMs are completely different from each other in catalytic activity. Cu - and Pd " -TSMs catalyze no reaction and the total oxidation of propylene, respectively, whereas Cu Pd " -TSM catalyzes the oxidation to form acetone selectively, suggesting that the Wacker type oxidation takes place over the catalyst (41). The results are shown in Fig. 6. The higher initial activity is observed for Cu Pd -TSM with the lower Cu Pd ratio, namely the higher Pd " loading. This might be explainable by the second order dependency of the reaction rate on Pd " concentration, observed for the homogeneous system by Vargaftik et al. in the... 

The Pt black sample active for the epoxidation of 1-hexene and 2-hexenes was also tested in the oxidation of propylene. Figure 5 shows the results of propylene oxidation as a function of the applied voltage across the cell. The oxidation of propylene was initiated at an applied voltage higher than ca. 1.1 V. The formation of propylene oxide and acetone were remarkably enhanced at an applied voltage >1.1 V. The maximum oxidation efficiency for the propylene oxide was 25% and the selectivity to propylene oxide was 53% at 1.7 V. These results indicate that the epoxidation of propylene by the oxidative activation of H O proceeds with fairly good current efficiency and selectivity on the Pt black anode [17]. 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

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