Phase processing operations

Older methods use a liquid phase process (Figure 10-11). ° New gas-phase processes operate at higher temperatures with noble metal catalysts. Using high temperatures accelerates the reaction (faster rate). The hydrogenation of benzene to cyclohexane is characterized by a highly exothermic reaction and a significant decrease in the product volume... 

Phillips (1) A process for polymerizing ethylene and other linear olefins and di-olefins to make linear polymers. This is a liquid-phase process, operated in a hydrocarbon solvent at an intermediate pressure, using a heterogeneous oxide catalyst such as chromia on silica/ alumina. Developed in the 1950s by the Phillips Petroleum Company, Bartlesville, OK, and first commercialized at its plant in Pasadena, TX. In 1991, 77 reaction fines were either operating or under construction worldwide, accounting for 34 percent of worldwide capacity for linear polyethylene. 

Xyloflning [Xylol refining] A process for isomerizing a petrochemical feedstock containing ethylbenzene and xylenes. The xylenes are mostly converted to the equilibrium mixture of xylenes the ethylbenzene is dealkylated to benzene and ethylene. This is a catalytic, vapor-phase process, operated at approximately 360°C. The catalyst (Encilite-1) is a ZSM-5-type zeolite in which some of the aluminum has been replaced by iron. The catalyst was developed in India in 1981, jointly by the National Chemical Laboratory and Associated Cement Companies. The process was piloted by Indian Petrochemicals Corporation in 1985 and commercialized by that company at Baroda in 1991. 

Ethyl Chloride. Hydrochlorination of ethylene with HC1 is carried out in either the vapor or the liquid phase, in the presence of a catalyst.182-184 Ethyl chloride or 1,2-dichloroethane containing less than 1% A1C13 is the reaction medium in the liquid-phase process operating under mild conditions (30-90°C, 3-5 atm). In new plants supported AlClj or ZnCl2 is used in the vapor phase. Equimolar amounts of the dry reagents are reacted in a fluidized- or fixed-bed reactor at elevated temperature and pressure (250-400°C, 5-15 atm). Both processes provide ethyl chloride with high (98-99%) selectivity. 

An ion pair of the type, H" AlCl4, is believed to be the actual catalyst in the liquid-phase process operating at ca. 90 °C. As is well known in electrophilic aromatic substitution, electron-releasing substituents favour alkylation thus ethylbenzene can undergo further alkylation to diethylbenzenes. To limit overalkylation, benzene must be used in large excess. The peralkylated benzenes, however, can be recycled to obtain ethylbenzene by exchange with... 

The catalyst systems employed are based on molybdenum and phosphorus. They also contain Various additives (oxides of bismuth, antimony, thorium, chromium, copper, zirconium, etc.) and occur in the form of complex phosphomolybdates, or preferably heteropolyacids deposited on an inert support (silicon carbide, a-alumina, diatomaceous earths, titanium dioxide, etc.). This makes them quite different from the catalysts used to produce acrylic acid, which do not offer sufficient activity in this case. With residence times of 2 to 5 s, once-through conversion is better than 90 to 95 per cent, and the molar yield of methacrylic acid is up to 85 to 90 per cent The main by-products formed are acetic add, acetone, acrylic add, CO, C02, etc. The major developments in this area were conducted by Asahi Glass, Daicel, Japan Catalytic Chemical, Japanese Gem, Mitsubishi Rayon, Nippon Kayaku, Standard Oil, Sumitomo Chemical, Toyo Soda, Ube, etc. A number of liquid phase processes, operating at about 30°C, in die presence of a catalyst based on silver or cobalt in alkaline medium, have been developed by ARCO (Atlantic Richfield Co,), Asahi, Sumitomo, Union Carbide, etc. 

Description The melamine process is a catalytic vapor-phase process operated at pressures below 10 bar. 

Polymerization conditions may vary over a wide range, where polymerization temperatiues vary from 60-110 C and total reactor pressure from 100-350 psig. Comonomers are usually limited to 1 -butene or 1-hexene to control polymer density, but 1-octene may be used if a particular catalyst exhibits a relatively high reactivity with 1-octene such as metallocene catalyst systems. Resin production rates are controlled by primarily two variables catalyst feed rate and ethylene partial pressure. In a modern gas-phase process, operating in what Univation designates as supercondens-ing mode, production rates for many grades of polyethylene of at least 125,000 Ibs/hr are reached. 

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