Polyethylene plant

Polyethylene was soon seen to have many properties suitable for this purpose and manufacture on a commercial scale was authorised. The polyethylene plant came on stream on 1st September 1939, just before the outbreak of World War II. 

A similar but more serious incident occurred in a polyethylene plant in 1989. A take-off branch was dismantled to clear a choke. The 8-in. valve isolating it from the reactor loop (the Demco valve in Figure 1-2) was open, and hot ethylene under pressure came out and exploded, killing 23... 

Pasadena, Texas (Ref. 14) 23 (unknown number in buildings) An isobutane and ethylene release in a polyethylene plant resulted in an explosion that destroyed the facility, including the control room, and also damaged an administration building 0.5 mi (0.8 km) away. 

A 100,000 ton/yr polyethylene plant costs 8,500,000 to construct.20 If polyethylene sells for 0.080 a pound, what is the return on investment for this plant if a 10% profit is to be expected after taxes ... 

A massive explosion in Pasadena, Texas, on October 23,1989, resulted in 23 fatalities, 314 injuries, and capital losses of over 715 million. This explosion occurred in a high-density polyethylene plant after the accidental release of 85,000 pounds of a flammable mixture containing ethylene, isobutane, hexane, and hydrogen. The release formed a large gas cloud instantaneously because the system was under high pressure and temperature. The cloud was ignited about 2 minutes after the release by an unidentified ignition source. 

Figure 1-12 Polyethylene plant settling leg and product takeoff system.

The OSHA investigation13 found that (1) no process hazard analysis had been performed in the polyethylene plant, and as a result, many serious safety deficiencies were ignored or overlooked (2) the single-block (DEMCO) valve on the settling leg was not designed to fail to a safe closed position when the air failed (3) rather than relying on a single-block valve, a double-... 

The explosions were felt 6 miles away. Twelve buildings were destroyed, and fire and explosion damage occurred throughout the polyethylene plant. The damage was estimated at over 15 million. 

Polyethylene The first commercial fluidized-bed polyethylene plant was constructed by Union Carbide in 1968. Modern units operate at a temperature of approximately 100°C and a pressure of... 

The slurry phase, the traditional route to PP, uses Ziegler-Natta type catalyst, a hydrocarbon solvent like hexane or heptane and polymer grade propylene (99.5%). Like the stringent requirements for polyethylene plant feeds, propylene must be high purity. Water, oxygen, carbon monoxide, or carbon dioxide will poison the catalyst. The reaction takes place in the liquid phase at 150—160°C and 100—400 psi. When the isotactic polymer particles form, they remain suspended in the diluent as slurry. The atactic polymers dissolve in the diluent. 

A VaporSep system was installed at a polyethylene plant to recover 290 lb of ethylene per hour (Ib/hr) from a gas stream consisting of 18% hydrogen, 22% nitrogen, 30% methane, and 30% ethylene. The capital costs for the system were 200,000. Based on an ethylene value of 300 per ton, the plant would save 370,000 per year using the VaporSep system to purify and recycle the ethylene (D205549, p. 5). 

Loss prevention of polyethylene plants is outlined in Chapter 7.2. The major hazard that can occur is the runaway of the high-pressure reactor and decomposition of ethylene besides fire and disintegration of high-pressure separators, pipes, and compressors. The critical conditions for runaway and ethylene decomposition during homo- and copolymerization are revealed together with the influence of decomposition sensitizers. Relief devices and venting systems are described. 

A.W. Guill, Safety in High Pressure Polyethylene Plants, American Inst, of Chem. Engng. 1973, 49-52. 

R.G. Ziefle, Designing Safe High Pressure Polyethylene Plants, Chem. Eng. Progress Technical Manual, American Institute of Chemical Engineers, New York, 1973. 

The distances between process equipment were in violation of accepted engineering practices and did not allow personnel to leave the polyethylene plants safely during the initial vapor release nor was there sufficient separation between reactors and the control room to carry out emergency shutdown procedures. The control room, in fact, was destroyed by the initial explosion. Of the 22 victims bodies recovered at the scene, all were located within 250 ft of the vapor release point. 

According to OSHA, Phillips had not conducted a process hazard analysis or equivalent (such as HAZOP) in its polyethylene plants. 

Figure 6.5 Ethylene compressor for ELENAC low density polyethylene plant (France).

The first commercial fluidized bed polyethylene plant was constructed by Union Carbide in 1968. Modem units operate at 100°C and 32 MPa (300 psig). The bed is fluidized with ethylene at about 0.5 m/s and probably operates near the turbulent fluidization regime. The excellent mixing provided by the fluidized bed is necessary to prevent hot spots, since the unit is operated near the melting point of the product. A model of the reactor (Fig. 17-25) that couples kinetics to the hydrodynamics was given by Choi and Ray, Chem. Eng. Sci., 40, 2261, 1985. 

Keywords Economic criteria, Enviromnental criteria, MOO, Williams and Otto Process, Low-density polyethylene plant. Industrial ecosystems. 

To prepare a titanated catalyst, surface silanol groups on the silica react with a titanium ester or halide. Unreacted organic or halide groups left on the Ti are then replaced by oxide during subsequent calcination. Titanation can be accomplished in various solvents, such as hydrocarbons, alcohols, or even sometimes water, or by vapor-phase deposition. The simplicity of the approach allows any commercial silica to be so modified with up to 5-8 wt% Ti, at which point (depending on the surface area) saturation is reached. Catalyst manufacturers practice titanation but some procedures have also been developed by many polyethylene producers as well. These recipes can be practiced in a commercial polyethylene plant, because the titanium compound is applied as a vapor during the catalyst activation step. 

In the preceding discussion of the operation of the tubular reactor polymerization scheme, we stated that the heat of reaction is removed by through-wall heat transfer. What exactly occurs in the vicinity of the wall If the characteristic of the high-pressure (300 bar) naphthalene isobar is interpreted as a schematic representation of the solubility of polyethylene in ethylene at a pressure of 2,700 bar, we can use it to predict that polyethylene will precipitate in the boundary layer near any relatively cold surfaces in the reactor or downstream lines. If the precipitation of polyethylene does occur on these internal surfaces and if it is not appropriately removed, the buildup of the polymer on the wall can result in decreased heat transfer from the hot gas-polymer solution, and the attendant decrease in heat transfer can lead to the runaway reaction that is occasionally encountered in high-pressure polyethylene plants. 

Much of the growth in LLDPE demand will be at the expense of other polyolefins, especially conventional high-pressure, LDPE. Its proponents claim that LLDPE can replace LDPE in 70 to 80% of its markets and that "the last conventional polyethylene plant has been built." Another sign of the times is the fact that ICI, originator of the high-pressure process, has now ceased production. 

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