Propylene oxide selectivity

Gas-phase oxidation of propylene using oxygen in the presence of a molten nitrate salt such as sodium nitrate, potassium nitrate, or lithium nitrate and a co-catalyst such as sodium hydroxide results in propylene oxide selectivities greater than 50%. The principal by-products are acetaldehyde, carbon monoxide, carbon dioxide, and acrolein (206—207). This same catalyst system oxidizes propane to propylene oxide and a host of other by-products (208). 

Propylene oxide selectivity, 20 806-807 Propylene oxide vapors, 20 811 Propylene oxide-styrene (PO-SM)... 

EBHP in the feed. Propylene oxide selectivity was defined as the percentage of EBHP reacfed fo PO (i.e., propylene oxide selectivity = propylene oxide yield/EBHP conversion). 

TABLE 14.2 Effects of deposition temperature (Tj), oxidants, and supports on propylene oxide selectivity (%)... 

Reaction temperature, 423 K TOS = 3 h. Propylene Oxide selectivity (mol %). —> represents the next pretreatment step. 

Propylene Oxidation. The propylene oxidation process is attractive because of the availabihty of highly active and selective catalysts and the relatively low cost of propylene. The process proceeds in two stages giving first acrolein and then acryUc acid (39) (see Acrolein and derivatives). 

In this process, the fine powder of lithium phosphate used as catalyst is dispersed, and propylene oxide is fed at 300°C to the reactor, and the product, ahyl alcohol, together with unreacted propylene oxide is removed by distihation (25). By-products such as acetone and propionaldehyde, which are isomers of propylene oxide, are formed, but the conversion of propylene oxide is 40% and the selectivity to ahyl alcohol reaches more than 90% (25). However, ahyl alcohol obtained by this process contains approximately 0.6% of propanol. Until 1984, ah ahyl alcohol manufacturers were using this process. Since 1985 Showa Denko K.K. has produced ahyl alcohol industriahy by a new process which they developed (6,7). This process, which was developed partiy for the purpose of producing epichlorohydrin via ahyl alcohol as the intermediate, has the potential to be the main process for production of ahyl alcohol. The reaction scheme is as fohows ... 

An excess of 2—10 mol propylene to liydiopeioxide is used to maximize conversion of hydroperoxide and selectivity to propylene oxide. Temperature is... 

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). 

EBHP is mixed with a catalyst solution and fed to a horizontal compartmentalized reactor where propylene is introduced into each compartment. The reactor operates at 95—130°C and 2500—4000 kPa (360—580 psi) for 1—2 h, and 5—7 mol propylene/1 mol EBHP are used for a 95—99% conversion of EBHP and a 92—96% selectivity to propylene oxide. The homogeneous catalyst is made from molybdenum, tungsten, or titanium and an organic acid, such as acetate, naphthenate, stearate, etc (170,173). Heterogeneous catalysts consist of titanium oxides on a siUca support (174—176). 

Direct Oxidation of Propylene to Propylene Oxide. Comparison of ethylene (qv) and propylene gas-phase oxidation on supported silver and silver—gold catalysts shows propylene oxide formation to be 17 times slower than ethylene oxide (qv) formation and the CO2 formation in the propylene system to be six times faster, accounting for the lower selectivity to propylene oxide than for ethylene oxide. Increasing gold content in the catalyst results in increasing acrolein selectivity (198). In propylene oxidation a polymer forms on the catalyst surface that is oxidized to CO2 (199—201). Studies of propylene oxide oxidation to CO2 on a silver catalyst showed a rate oscillation, presumably owing to polymerization on the catalyst surface upon subsequent oxidation (202). 

Noncatalytic oxidation of propylene to propylene oxide is also possible. Use of a small amount of aldehyde in the gas-phase oxidation of propylene at 200—350°C and up to 6900 kPa (1000 psi) results in about 44% selectivity to propylene oxide. About 10% conversion of propylene results (214—215). Photochemical oxidation of propylene with oxygen to propylene oxide has been demonstrated in the presence of a-diketone sensitizers and an aprotic solvent (216). 

Selectivity of propylene oxide from propylene has been reported as high as 97% (222). Use of a gas cathode where oxygen is the gas, reduces required voltage and eliminates the formation of hydrogen (223). Addition of carbonate and bicarbonate salts to the electrolyte enhances ceU performance and product selectivity (224). Reference 225 shows that use of alternating current results in reduced current efficiencies, especiaHy as the frequency is increased. Electrochemical epoxidation of propylene is also accompHshed by using anolyte-containing silver—pyridine complexes (226) or thallium acetate complexes (227,228). 

Recently (79MI50500) Sharpless and coworkers have shown that r-butyl hydroperoxide (TBHP) epoxidations, catalyzed by molybdenum or vanadium compounds, offer advantages over peroxy acids with regard to safety, cost and, sometimes, selectivity, e.g. Scheme 73, although this is not always the case (Scheme 74). The oxidation of propene by 1-phenylethyl hydroperoxide is an important industrial route to methyloxirane (propylene oxide) (79MI5501). 

Both fixed and fluid-bed reactors are used to produce acrylonitrile, but most modern processes use fluid-bed systems. The Montedison-UOP process (Figure 8-2) uses a highly active catalyst that gives 95.6% propylene conversion and a selectivity above 80% for acrylonitrile. The catalysts used in ammoxidation are similar to those used in propylene oxidation to acrolein. Oxidation of propylene occurs readily at... 

Allyl alcohol is produced by the catalytic isomerization of propylene oxide at approximately 280°C. The reaction is catalyzed with lithium phosphate. A selectivity around 98% could be obtained at a propylene oxide conversion around 25% ... 

Synthesis of New Propellants Explosives , Quarterly Progress Rept No 5, US Rubber Co, Passaic, Contract Nord 10129 (1948), 36-37 4a) G.O. Curme, Jr F. Johnston, Glycols , ACS Monograph No 114, Reinhold, NY (1952) 4b) A.F, Gait, "Propylene Oxide in E.G. Hancock, Ed, Propylene and Its Industrial Derivatives , Wiley Sons, NY (1973), 273-97 5) R.C. Crews, Effects of Propylene Oxide on Selected Species of Fishes , AFATL TR-74-183 (1974) 6) Bretherick (1975), 364 7) Anon,... 

Epoxides such as ethylene oxide and higher olefin oxides may be produced by the catalytic oxidation of olefins in gas-liquid-particle operations of the slurry type (S7). The finely divided catalyst (for example, silver oxide on silica gel carrier) is suspended in a chemically inactive liquid, such as dibutyl-phthalate. The liquid functions as a heat sink and a heat-transfer medium, as in the three-phase Fischer-Tropsch processes. It is claimed that the process, because of the superior heat-transfer properties of the slurry reactor, may be operated at high olefin concentrations in the gaseous process stream without loss with respect to yield and selectivity, and that propylene oxide and higher... 

Phosphoric acid esters based on alkylene oxide adducts are of great interest. Their properties can be altered by the length and structure of the hydrophobic alkyl chain. But they are also controlled by the kind and length of the hydrophilic alkyleneoxide chain. The latter can easily be tailored by selection between ethylene oxide and propylene oxide and by the degree of alkoxylation. 

M. Stoukides, and C.G. Vayenas, The effect of electrochemical oxygen pumping on the Rate and Selectivity of Propylene Oxidation on Silver in a Solid Electrolyte Cell, J. Electrochem. Soc. 131(4), 839-845 (1984). 

A qualitatively similar behaviour was obtained during C3H6 epoxidation on Ag 43 Enhancement factor A values of the order of 150 were measured.43 Both the rates of epoxidation and oxidation to C02 increase with I>0 and decrease with I<0. The intrinsic selectivity to propylene oxide was very low, typically 0.03 and could be increased only up to 0.04 by using positive currents. This was again an exploratory study, as no reference electrode was used, thus T and UWr could not be measured 43... 

Extensive studies of stereoselective polymerization of epoxides were carried out by Tsuruta et al.21 s. Copolymerization of a racemic mixture of propylene oxide with a diethylzinc-methanol catalyst yielded a crystalline polymer, which was resolved into optically active polymers216 217. Asymmetric selective polymerization of d-propylene oxide from a racemic mixture occurs with asymmetric catalysts such as diethyzinc- (+) bomeol218. This reaction is explained by the asymmetric adsorption of monomers onto the enantiomorphic catalyst site219. Furukawa220 compared the selectivities of asymmetric catalysts composed of diethylzinc amino acid combinations and attributed the selectivity to the bulkiness of the substituents in the amino acid. With propylene sulfide, excellent asymmetric selective polymerization was observed with a catalyst consisting of diethylzinc and a tertiary-butyl substituted a-glycol221,222. ... 

The structure of the single phase bismuth-iron molybdate compound of composition Bl3FeMo20.2 related to the scheellte structure of Bi2Mo30-2( ). It is reported(, ) that the catalytic activity and selectivity of bismuth-iron molybdate for propylene oxidation and ammoxidatlon is not greater than that of bismuth molybdate. 

In reactor 1 2,6-xylenol is condensed with propylene oxide in the presence of NaOH at elevated temperature and pressure. The reaction is reasonably selective. However, some isomers are also formed in minor proportions. Therefore, the crude DMFP is dissolved in the organic solvent / and crystallized in tank 2, separated from the mother liquor in centrifuge 3, and dried in drier 4. 

Other TUD-l catalysts proven for selective oxidation (16) include Au/Ti-Si-TUD-1 for converting propylene to propylene oxide (96% selectivity at 3.5% conversion see also (17), Ag/Ti-Si-TUD-1 for oxidizing ethylene to ethylene oxide (29% selectivity at 19.8% conversion), and Cr-Si-TUD-1 for cyclohexene to cyclohexene epoxide (94% selectivity at 46% conversion). 

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. 

On the basis of this approach, a triblock copolymer of ethylene oxide (EO) and propylene oxide (PO), HO(EO) (PO)m(EO) OH was analyzed with respect to the PPO inner block and the PEO outer blocks by LCCC and SEC (Adrian et al., 1998). For the selective separation of the block copolymer with respect to the PPO block, experiments were conducted using chromatographic conditions, corresponding to the critical point of PEO. These could be established on a RP-18 stationary phase when an eluent of methanol-water 86 14 (v/v) is used. The separation of the triblock copolymer at the critical point of PEO is shown in Fig. 17.15. 

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