Catalyst ethylene oxide 228 - regeneration

Electrochemical Process. Several patents claim that ethylene oxide is produced ia good yields ia addition to faradic quantities of substantially pure hydrogen when water and ethylene react ia an electrochemical cell to form ethylene oxide and hydrogen (206—208). The only raw materials that are utilized ia the ethylene oxide formation are ethylene, water, and electrical energy. The electrolyte is regenerated in situ ie, within the electrolytic cell. The addition of oxygen to the ethylene is activated by a catalyst such as elemental silver or its compounds at the anode or its vicinity (206). The common electrolytes used are water-soluble alkah metal phosphates, borates, sulfates, or chromates at ca 22—25°C (207). The process can be either batch or continuous (see Electrochemicalprocessing). 

If the depolymerization stops short of complete disappearance of polymer because of insufficient catalyst, the reaction can be revived by addition of ethylene oxide but the yield of dioxane is then only about five moles per mole of reacting monomer, a value far below that obtained by direct addition of oxonium ions. This difference is important because conditions after regeneration must resemble those in a polymerizing mixture, but unfortunately the reason for the difference is still far from clear. It is found that the rate of disappearance of monomer under these conditions is essentially independent of monomer concentration so Eastham and co-workers (74) concluded that monomer is involved only in the regeneration of oxonium ions,... 

Meta-4 A process for converting ethylene and 2-butene into propylene by metathesis. The process operates in the liquid phase at low temperatures in the presence of heterogeneous catalyst based on rhenium oxide on alumina. The catalyst is constantly regenerated by coke combustion. Developed by IFP and the Chinese Petroleum Corporation of Taiwan. A demonstration plant was operated from 1988 to 1990 and the process was demonstrated at Kaohsiung, Taiwan, in 1999. Now offered by Axens. 

The homogeneous Wacker Process is normally carried out in aqueous HCl solution, in a two-step process. Early procedures, in which ethylene oxidation and catalyst regeneration were performed in one reactor, ran a serious risk of explosions. In the two-step process ethylene oxidation and catalyst regeneration occur separately. Typical conditions are 7-14 atm ethylene at 100-110 °C, affording 99% product. Palladium reoxidation is done at the same temperature and 7-14 atm O2. 

The tetrachloroethylene is fluorinated with HF in vapor phase (320°C) in the presence of viz., chromium oxides, oxyfluorides or oxychlorides as catalyst to obtain HFC-125. It can also be obtained from dismutation of HCFC-124 and HCFC-123. The fluorination process has lower selectivity. In case of dismutation process, HCFC-124 has to be synthesized first by fluorination of tetrachloro ethylene. Fixed or flow bed reactors are used for the fluorination process. The catalyst can be regenerated by treatment with a mixture of air and HF followed by H treatment. 

Ca.ta.lysis, The most important iadustrial use of a palladium catalyst is the Wacker process. The overall reaction, shown ia equations 7—9, iavolves oxidation of ethylene to acetaldehyde by Pd(II) followed by Cu(II)-cataly2ed reoxidation of the Pd(0) by oxygen (204). Regeneration of the catalyst can be carried out in situ or ia a separate reactor after removing acetaldehyde. The acetaldehyde must be distilled to remove chloriaated by-products. 

Catalytic Pyrolysis. This should not be confused with fluid catalytic cracking, which is used in petroleum refining (see Catalysts, regeneration). Catalytic pyrolysis is aimed at producing primarily ethylene. There are many patents and research articles covering the last 20 years (84—89). Catalytic research until 1988 has been summarized (86). Almost all catalysts produce higher amounts of CO and CO2 than normally obtained with conventional pyrolysis. This indicates that the water gas reaction is also very active with these catalysts, and usually this leads to some deterioration of the olefin yield. Significant amounts of coke have been found in these catalysts, and thus there is a further reduction in olefin yield with on-stream time. Most of these catalysts are based on low surface area alumina catalysts (86). A notable exception is the catalyst developed in the former USSR (89). This catalyst primarily contains vanadium as the active material on pumice (89), and is claimed to produce low levels of carbon oxides. 

Cataljdic reactions performed in fluid beds are not too numerous. Among these are the oxidation of o-xylene to phthalic anhydride, the Deacon process for oxidizing HCl to CI2, producing acrylonitrile from propylene and ammonia in an oxidation, and the ethylene dichloride process. In the petroleum industry, cataljdic cracking and catalyst regeneration is done in fluid beds as well as some hydroforming reactions. 

Compounds considered carcinogenic that may be present in air emissions include benzene, butadiene, 1,2-dichloroethane, and vinyl chloride. A typical naphtha cracker at a petrochemical complex may release annually about 2,500 metric tons of alkenes, such as propylenes and ethylene, in producing 500,000 metric tons of ethylene. Boilers, process heaters, flares, and other process equipment (which in some cases may include catalyst regenerators) are responsible for the emission of PM (particulate matter), carbon monoxide, nitrogen oxides (200 tpy), based on 500,000 tpy of ethylene capacity, and sulfur oxides (600 tpy). 

Other functionalized supports that are able to serve in the asymmetric dihydroxylation of alkenes were reported by the groups of Sharpless (catalyst 25) [88], Sal-vadori (catalyst 26) [89-91] and Cmdden (catalyst 27) (Scheme 4.13) [92]. Commonly, the oxidations were carried out using K3Fe(CN)g as secondary oxidant in acetone/water or tert-butyl alcohol/water as solvents. For reasons of comparison, the dihydroxylation of trons-stilbene is depicted in Scheme 4.13. The polymeric catalysts could be reused but had to be regenerated after each experiment by treatment with small amounts of osmium tetroxide. A systematic study on the role of the polymeric support and the influence of the alkoxy or aryloxy group in the C-9 position of the immobilized cinchona alkaloids was conducted by Salvadori and coworkers [89-91]. Co-polymerization of a dihydroquinidine phthalazine derivative with hydroxyethylmethacrylate and ethylene glycol dimethacrylate afforded a functionalized polymer (26) with better swelling properties in polar solvents and hence improved performance in the dihydroxylation process [90]. 

The cycle approach for oxidation has been adopted at an industrial level for the Wacker-Chemie process for acetaldehyde production, in which ethylene is first put in contact with the oxidized catalyst solution, containing palladium chloride, and in the second step the solution containing the reduced catalyst is sent to a regeneration reactor containing cupric chloride and inside which also air is fed. The regenerated catalyst solution is returned to the first oxidation stage. Another industrial application is the Lummus process for the anaerobic ammoxidation of o-xylene to o-phthaloni-trile [68]. Du Pont has developed the oxidation of n-butane to maleic anhydride catalyzed by V/P/O, in a CFBR reactor, and built a demonstration unit in Spain [69] however, a few years ago the plant was shut down, due to the bad economics. 

The in situ regeneration of Pd(II) from Pd(0) should not be counted as being an easy process, and the appropriate solvents, reaction conditions, and oxidants should be selected to carry out smooth catalytic reactions. In many cases, an efficient catalytic cycle is not easy to achieve, and stoichiometric reactions are tolerable only for the synthesis of rather expensive organic compounds in limited quantities. This is a serious limitation of synthetic applications of oxidation reactions involving Pd(II). However it should be pointed out that some Pd(II)-promoted reactions have been developed as commercial processes, in which supported Pd catalysts are used. For example, vinyl acetate, allyl acetate and 1,4-diacetoxy-2-butene are commercially produced by oxidative acetoxylation of ethylene, propylene and butadiene in gas or liquid phases using Pd supported on silica. It is likely that Pd(OAc)2 is generated on the surface of the catalyst by the oxidation of Pd with AcOH and 02, and reacts with alkenes. 

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