Polyethylene operating rates

Polyethylene is the highest volume plastic available today. Global consumption of polyethylene was about 150 billion pounds (67.8 million metric tons) in 2006 and is forecast to grow to about 185 billion pounds (82.9 million metric tons) in 2010 Polyethylene demand, total capacity and percent operating rates from 1995 to 2010 are shown in Figure 1 Polyethylene is composed of mainly carbon and hydrogen (with some notable exceptions such as ethylene vinyl acetate copolymer, acid copolymers, etc.) which can be combined in number of ways. Various polyethylene molecular architectures have been commercialized over last 70 years to make different types of polyethylene. These various molecular architectures can be grouped into ten major types of polyethylene ... 

Figure 1. Polyethylene demand, capacity, and percent operating rates from 1995 to 2010. Data provided by Dr. Balaji Singh of Chemical Market Resources Inc., Texas.

Types of air strippers include packed towers, tray towers, and spray towers. Packed towers are packed or filled with small forms made of polyethylene [9002-88-4] stainless steel, poly(vinyl chloride) (PVC) [9002-86-2] or ceramic that provide large surface area to volume ratios which increase transfer rates into the air stream. Packed towers operate in countercurrent mode, that is, the aqueous stream enters at the top of the tower while air is blown in from the bottom. An example of this type of unit is shown in Figure 1. Channeling or short circuiting of the aqueous stream is minimized by... 

Injection moulding and extrusion may be carried out at temperatures in the range of 300-380°C. The polymer has a high melt viscosity and melt fracture occurs at a lower shear rate (about 10 s ) than with low-density polyethylene (about 10 s ) or nylon 66 (about 10 s ). Extruders should thus be designed to operate at low shear rates whilst large runners and gates are employed in injection moulds. 

Analysis and purification of the product solution is best accomplished by gas chromatography. The submitters used a 500 cm. by 0.6 cm. aluminum or polyethylene column packed with 21% oxydipropionitrile on Chromosorb P with column, injector and detector operated at 25° and a flow rate of 50 ml./minute. Under these conditions the retention times of bicyclopentene and cyclopentadiene were 3 and 5 minutes, respectively, beyond that of the coinjected air. Since bioyclo-pentene is extremely labile with respect to acid catalysis any contact with water, hydroxylic solvents, and nonprotic acids should be avoided (Note 11). Bicyclopentene stored at —78° in anhydrous tetrahydro-furan is stable indefinitely. 

This comprehensive article supplies details of a new catalytic process for the degradation of municipal waste plastics in a glass reactor. The degradation of plastics was carried out at atmospheric pressure and 410 degrees C in batch and continuous feed operation. The waste plastics and simulated mixed plastics are composed of polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene, and polyethylene terephthalate. In the study, the degradation rate and yield of fuel oil recovery promoted by the use of silica alumina catalysts are compared with the non-catalytic thermal degradation. 9 refs. lAPAN... 

Sometimes technological problems forbid the size of an operation to exceed a certain value. For instance, in the batch polymerization of polyethylene and polystyrene, it is important to maintain the temperature below a critical value, because otherwise the material will be damaged. Since this is an exothermic reaction, it means the energy must be removed as fast as it is formed. If it is not, the temperature will begin to rise, which will increase the rate of polymerization. This will result in an acceleration of the temperature rise and the result will be a discolored batch. This requirement establishes a limit on the size of the reactor. The practical significance is demonstrated in the polystyrene case-study example following Chapter 5. 

Fig. 9.27 Fully contained ATR/FTIR instrument rated for operation at the depth of 500 m in the ocean. The ATR sensing element is AgCl fiber coated with polyethylene/polypropylene copolymer (reprinted from Kraft et al., 2003)...

LC2) or b) the reaction temperature T2 (if allowed), which affects the rate constant k. Figure 4.4(b) shows that, whenever Da < 2, this strategy requires moderate changes of the manipulated variables. We note that there are many situations when a large reactor cannot be used. For example, in the polyethylene production, the high operating pressure requires a small reactor. In addition, the molecular weight distribution of the final product and difficult heat transfer due to the gel effect favor low conversion, and thus small reactors. 

A similar technique is applied to low-density polyethylene reactors. Some of these systems operate in cooled tubular reactors at a very high pressure. Since the reactor has a thick tube wall, the temperature response to changes in the coolant is slow. Instead, the reaction rate (and thereby temperature.) is controlled by injecting initiator at select places along the length of the reactor tube (see Fig. 4.28). 

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