Temperature heat removal from ethylene

Free radical polymerization of neat monomer in the absence of solvent and with only initiator present is called bulk or mass polymerization. Monomer in the liquid or vapor state is well mixed with initiator in a heated or cooled reactor as appropriate. The advantages of this method are that it is simple, and because of the few interacting components present, there is less possibility for contamination. However, vinyl-type polymerizations are highly exothermic so that control of the temperature of bulk polymerization may be difficult. Also, in the absence of a solvent viscosities may become very high toward the end of a polymerization, which could make stirring difficult, and add to the difficulty of heat removal from the system. The advantages of this system, however, are sufficiently attractive for this to be used commercially for the free radical polymerization of styrene, methyl methacrylate, vinyl chloride, and also for some of the polymerization processes of ethylene [7]. 

The "gas-phase" (fluidized-bed) process is much like the slurry process in that polymer particles are formed at similar temperatures, but a liquid hydrocarbon diluent is not used. A bed of catalyst/polymer is stirred either by mechanical means, or, more often, by fluidization, while ethylene, N2, and other hydrocarbons that act as a coolant are circulated [718-722], Although the "gas phase" process offers many advantages, including the lack of a diluent that can cause polymer swelling, its weak point is poor heat removal from the polymer particles, because of the low heat capacity of a gas. Thus, reactor fouling still occurs,... 

Direct chlorination of ethylene is usually conducted in liquid EDC in a bubble column reactor. Under typical process conditions, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor. Feme chloride is a highly selective and efficient catalyst for llus reaction, and is widely used commercially. The direct chlorination process may be run with a slight excess of either ethylene or chlorine, depending on how effluent gases from the reactor are subsequently processed. Conversion of the limiting component is essentially 100%. and selectivity to EDC is greater than 99%. The direct chlorination reaction is exothermic (AH = — 180 kJ/mol foreq. 1) and requires heat removal for temperature control. 

In oxychlorination. ethylene reacts with dry HC1 and either air or pure oxygen to produce EDC and water. While commercial oxychlorination processes may differ from one another to some extent because they were developed independently by many different vinyl chloride producers, in each case the reaction is carried out in the vapor phase in either a fixed- or fluidized-bed reactor containing a modified Deacon catalyst. Cupnc chloride is usually the primary active ingredient of the catalyst, supported on a porous substrate such as alumina, silica-alumina, or diatomaceous earth. The oxychlorination reaction is highly exothermic (AH = —239 kJ/mol for eq. 3) and requires heat removal for temperature control. 

Application Inovyl s high temperature chlorination (HTC) is an energy-efficient process to produce ethylene dichloride (EDC) from ethylene and chlorine. Energy is conserved by using the exothermic heat of reaction to vaporize the EDC, thus product purification can be done by fractional distillation. Unlike with the LTC process, waterwashing the product to remove dissolved ferric chloride is not necessary. Therefore, no aqueous effluent treatment is required. 

Example 1-1 Ethylene oxide is produced by direct oxidation with air using a bed of catalyst particles (silver on a suitable carrier). Suppose that the stream enters the flow reactor at 200°C and contains 5 mole % ethylene and 95% air. If the exit temperature does not exceed 260°C, it is possible to convert 50% of the ethylene to the oxide, although 40% is also completely burned to carbon dioxide. How much heat must be removed from the reaction, per mole of ethylene fed, in order not to exceed the limiting temperature The average molal heat capacity of. ethylene may be taken as 18 Btu/(lb mole) (°R) between 25 and 200°C and as 19 Btu/(lb mole)(°R) between 25 and 260°C. Similar values for ethylene oxide are 20 and 21 Btu/(lb mole)(°R). The pressure is essentially atmospheric. 

Temperature Programmed Oxidation. These measurements characterize both the amount and chemical nature of the carbon on the surface. After a surface is exposed to ethylene and pretreated as desired, it receives a 6 L dose of O2 at 323 K. The TPO spectrum is the CO desorption signal at a 6 K/sec programming rate. CO2 accounts for less than 1% of the oxidation, so the CO signal accounts for essentially all of the carbon removed. O2 dosing is repeated until no further CO is evolved during heating. SIMS results show that all carbon has been removed from the surface at the TPO end point. 

Ethylene is compressed to 2,700 bar and a free-radical initiator, e.g., trace amounts of oxygen or a peroxide, is injected into the feed stream to promote the free-radical polymerization. The polyethylene polymer that is formed remains dissolved in the supercritical ethylene phase at the operating temperature, which ranges from 140 to 250°C. The heat of reaction is removed by through-wall heat transfer when the tubular reactor is used and by regulating the rate of addition of initiator when the autoclave reactor is used. 

Freshly distilled carbon tetrachloride (210 g, 1.36 moles), water (35 g), and benzoyl peroxide (0.47 g, 0.00194 mole) are placed in a stainless steel autoclave (capacity about 350 ml) fitted with a gas-inlet tube and a thermoelement for temperature measurement. Air is removed from the autoclave, and ethylene is pressed in to 35 atm. The autoclave is then shaken in a horizontal position and heated when the temperature of the mixture reaches 70°, more ethylene is pressed in, to give a pressure of about 100 atm. The mixture is then kept at 95° for 5 h, more ethylene being pressed in to keep the pressure at 85-100 atm. Finally the autoclave is cooled and the product is removed, separated from the water, and dried over anhydrous magnesium sulfate. After unchanged carbon tetrachloride has been distilled off, fractionation of the telomer gives the following yields ... 

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