Ethylene with fluidized catalysts

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. 

In gas-phase processes, gaseous ethylene or propylene is contacted with solid catalysts, sometimes dispersed in dry polymer powder. The industry uses two different methods of carrying out this reaction, depending on the method of heat removal. In one class of processes, a fluidized bed is used, and in the other, a mechanically agitated dry powder bed is used with evaporative cooling in vertical and horizontal autoclaves. The advantage of a gas-phase process is that no solvent recovery is necessary so that the energy requirement is less. 

Description The SUPERFLEX process is a proprietary technology patented by ARCO Chemical Tech nology, Inc. (now Lyondell Chemical Co.), and is exclusively offered for license by Kellogg Brown Root. It uses a fluidized catalytic reactor system with a proprietary catalyst to convert low-value feedstocks to desirable propylene and ethylene products. The catalyst is very robust thus, no feed pretreatment is required for typical contaminants such as sulfur, water, oxygenates or nitrogen. Attractive feedstocks include C4 and CB... 

Chemically, LLDPE can be described as linear polyethylene copolymers with alpha-olefin comonomers in the ethylene chain. They are produced primarily at low pressures and temperatures by the copolymerization of ethylene with various alpha-olefins such as butene, hexane, octane, etc., in the presence of suitable catalysts. Either gas-phase fluidized-bed reactors or liquid-phase solution-process reactors are used. (In contrast, LDPE is produced at very high pressures and temperatures either in autoclaves or tubular reactors.)... 

In addition to suspension, a gas-phase process was developed. No diluent is used in the polymerization step. Highly purified ethylene gas is combined continuously with a dry-powdery catalyst and then fed into a vertical fluidized-bed reactor. The reaction is carried out at 270 psi and 85-100 °C. The circulating ethylene gas fluidizes the bed of growing granular polymer and serves... 

There are some well known examples of large scale industrial processes of this type, such as the steam cracking of hydrocarbons, the cracking of ethylene dichloiide to vinyl chloride, the c ytic leforming.of methane to synthesis gas, and the synthesis of melamine from urea These processes are often carried out in tubular reactors, the latter two with solid catalysts. A well known version of the melamine process is carried out in a fluidized bed reactpr. 

In oxychlorination, ethylene reacts with dry HCl and either air or pure oxygen to produce EDC and water. Various commercial oxychlorination processes differ from one another to some extent because they were developed independentiy by several different vinyl chloride producers (78,83), but 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. Unlike the Deacon process for chlorine production, oxychlorination of ethylene occurs readily at temperatures weU below those requited for HCl oxidation. 

Oxychlorination of Ethylene or Dichloroethane. Ethylene or dichloroethane can be chlorinated to a mixture of tetrachoroethylene and trichloroethylene in the presence of oxygen and catalysts. The reaction is carried out in a fluidized-bed reactor at 425°C and 138—207 kPa (20—30 psi). The most common catalysts ate mixtures of potassium and cupric chlorides. Conversion to chlotocatbons ranges from 85—90%, with 10—15% lost as carbon monoxide and carbon dioxide (24). Temperature control is critical. Below 425°C, tetrachloroethane becomes the dominant product, 57.3 wt % of cmde product at 330°C (30). Above 480°C, excessive burning and decomposition reactions occur. Product ratios can be controlled but less readily than in the chlorination process. Reaction vessels must be constmcted of corrosion-resistant alloys. 

Halogenation—Hydrohalogenation. The most important iatermediate is ethylene dichloride [107-06-2] (EDC) which is produced from ethylene either by direct chlorination or by oxychloriaation. Direct chlorination is carried out ia the Hquid or vapor phase over catalysts of iron, alumiaum, copper, or antimony chlorides, and at conditions of 60°C. Oxychloriaation is carried out ia a fixed or fluidized bed at 220°C with a suitable soHd chloride catalyst. 

Activated alumina and phosphoric acid on a suitable support have become the choices for an iadustrial process. Ziac oxide with alumina has also been claimed to be a good catalyst. The actual mechanism of dehydration is not known. In iadustrial production, the ethylene yield is 94 to 99% of the theoretical value depending on the processiag scheme. Traces of aldehyde, acids, higher hydrocarbons, and carbon oxides, as well as water, have to be removed. Fixed-bed processes developed at the beginning of this century have been commercialized in many countries, and small-scale industries are still in operation in Brazil and India. New fluid-bed processes have been developed to reduce the plant investment and operating costs (102,103). Commercially available processes include the Lummus processes (fixed and fluidized-bed processes), Halcon/Scientific Design process, NIKK/JGC process, and the Petrobras process. In all these processes, typical ethylene yield is between 94 and 99%. 

UNIPOL [Union Carbide Polymerization] A process for polymerizing ethylene to polyethylene, and propylene to polypropylene. It is a low-pressure, gas-phase, fluidized-bed process, in contrast to the Ziegler-Natta process, which is conducted in the liquid phase. The catalyst powder is continuously added to the bed and the granular product is continuously withdrawn. A co-monomer such as 1-butene is normally used. The polyethylene process was developed by F. J. Karol and his colleagues at Union Carbide Corporation the polypropylene process was developed jointly with the Shell Chemical Company. The development of the ethylene process started in the mid 1960s, the propylene process was first commercialized in 1983. It is currently used under license by 75 producers in 26 countries, in a total of 96 reactors with a combined capacity of over 12 million tonnes/y. It is now available through Univation, the joint licensing subsidiary of Union Carbide and Exxon Chemical. A supported metallocene catalyst is used today. 

In Figure 23—6, polymer grade ethylene and any comonomers are blown into the-base of a fluidized bed reacton A very reactive catalyst (based on-titanium and magnesium chlorides) is injected and admixes with the ethylene. Polymerization takes place at 150-212 F and 300 psi, and polymer particles stay in the fluidized state as the ethylene swirls through the reactor. Since the temperature is controlled at or below the melting point, the particles form a white powder. 

Three processes are used commercially to make linear polyethylene-solution, slurry, and gas phase. All are called low-pressure processes (< 50 atm) to distinguish them from the free radical or high-pressure process that makes highly branched polyethylene. In the solution mode a hydrocarbon solvent at 125-170°C dissolves the polymer as it forms. The reaction usually slows as the solution becomes viscous because it becomes difficult to stir ethylene into the liquid phase. In contrast, The slurry process uses a poor solvent and low temperature (60-110°C) to prevent dissolving or even swelling of the polymer. Each catalyst particle creates a polymer particle several thousand times larger than itself. There is no viscosity limitation in the slurry method the diluent serves to transfer heat and to keep the catalyst in contact with ethylene and other reactants. Finally, the gas-phase process is much like the slurry method in that polymer particles are formed at similar temperatures. A bed of catalyst/polymer is fluidized by circulating ethylene, which also serves as a coolant. 

A fluidized-bed catalytic reactor system developed by C. E. Lummus (323) offers several advantages over fixed-bed systems in temperature control, heat and mass transfer, and continuity of operation. Higher catalyst activity levels and higher ethylene yields (99% compared to 94—96% with fixed-bed systems) are accomplished by continuous circulation of catalyst between reactor and regenerator for carbon bum-off and continuous replacement of catalyst through attrition. 

---