Pressure ethylene epoxidation

Activation of Silver Powder for Ethylene Epoxidation at Vacuum and Atmospheric Pressures... 

Transient response techniques are used to investigate the activation of silver powder for ethylene epoxidation at vacuum and atmospheric pressures. Results indicate that the activation process is qualitatively the same in both pressure regimes. Numerical simulation of the process indicates that activation involves the concurrent incorporation of oxygen into surface and subsurface sites. The reaction selectivity parallels the incorporation of oxygen into the subsurface. 

Ethylene epoxidation. Stoukides and Vayenas studied the epoxidation of ethylene over silver between 250 and 450°C at atmospheric pressure.70 Three reactions occurred,... 

Ethylene epoxidation reaction experiments over all studied catalysts were conducted in a differential flow reacfor, which was operafed at a constant pressure of 3.6 MPa and different reaction temperatures. The tubular reactor having 10-mm internal diameter was placed in a furnace equipped wifh a temperafure confroller. T)q)ically, 30 mg of a catalysf sample was placed inside the Pyrex tube reactor and secured with Pyrex glass wool plugs. The packed catalyst was initially pretreated... 

Figure 7. Effect of catalyst potential and gas-phase 1,2-T C2H4CI2 partial pressure on the selectivity of ethylene epoxidation on A.gl "-M20y (reprinted with permission from ref. [24])...

High reaction pressures are needed for many other systems as well in order to convert the surface into a uniquely reactive state such as has been found for ethylene epoxidation. The epoxidation reaction of ethylene catalyzed by silver shows a distinct pressure gap. Higher oxygen pressures are needed in order to convert the silver surface into a silver-oxide overlayer where weakly adsorbed oxygen atoms are formed, that selectively epoxidize ethylene ]. 

Earlier exploratory studies of ethylene epoxidation on Ag/j "-Al203 at atmospheric pressure and T = 410°C had shown that both the activity and selectivity of Ag can be markedly affected via NEMCA." ... 

Because the epoxidation with Tl(III) is stoichiometric to produce Tl(I), reoxidation is needed. Halcon has patented processes based on such epoxidation to yield ethylene oxide (200—203). The primary benefits of such a process are claimed to be high yields of ethylene oxide, fiexibihty to produce either propylene oxide or ethylene oxide, and the potential of a useful by-product (acetaldehyde). Advances usiag organic hydroperoxides ia place of oxygen for reoxidation offer considerable promise, siace reaction rates are rapid and low pressures can be used. 

The epoxidation of C2H4 on Ag/p"-Al203 was investigated22 at temperatures 250° to 300°C and high pressure (5 bar) in the presence of C2H4CI2 moderators in order to simulate industrial practice.22 It was found that technologically important ethylene oxide selectivity values (Sc2H40ss 8%) can... 

The first reported study of a reaction of wood with an epoxide appears to be that of McMillan (1963). This involved the use of gaseous ethylene oxide (Figure 4.9, R=H) at a temperature of 93 °C and a pressure of 3 atmospheres (0.3 MPa). In some cases, the wood was diffusion pre-treated with trimethylamine vapour as the catalyst. A 65 % ASE at 20 % WPG was obtained, attributed to a bulking effect due to in situ polymerization of the epoxide. There was no effect on the static bending strength of samples, and the modified wood became distinctly brown at higher levels of treatment. 

Two reports have appeared on the catalyzed reaction of C02 with epoxides to form alkylene carbonates. One of the processes uses phosphine complexes of zerovalent nickel as the catalyst (157), and appears closely related to the more recent isolation of (PCy3)2Ni(C02) (115). Ethylene oxide reacts in benzene under 500 psi pressure of C02 in a stainless steel autoclave at 100°C to form ethylene carbonate with 95% selectivity, (77), using as the catalysts NiL2, L = PCy3 or PPh3. 

Cobalt tetracarbonyl anion in such hydroxylic solvents as water or methanol also reacts with epoxides at temperatures of 60—100 and at an elevated pressure of carbon monoxide (2000 Ib./in. ) to give esters of j8-hydroxy acids. Thus, ethylene oxide has been found to react with sodium cobalt tetracarbonyl and carbon monoxide in methanol solution at 65 and 2000 Ib./in. to give methyl 3-hydroxy-propionate in a yield of 55% the remainder of the product was acetaldehyde and an involatile oil. It was also shown that this reaction proceeds almost as well at a much lower pressure (three or four atmospheres of carbon monoxide). ... 

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