Polyethylene solution phase process

Producers use four routes to make polyechylencj the bulk- or high-pressure process, the solution-phase process, the slurry-phase process, and the gas-phase process. Organizing your thinking around processes and products is not all that straightforward. Some of the processes can be used to produce ail the polyethylene forms, some only a few or one. That calls for a few words first by product and then more by process. 

BUC Buchelli, A. and Todd, W.G., On-line liquid-liquid phase separation predictor in the high-density polyethylene solution polymerization process,/ [Pg.181]

In some processes, a diluent, like benzene or chlorobenzene are used as the solvent. At high pressure and temperature, both the polyethylene and the monomers dissolve in these solvents so that the reaction occur in a solution phase. In a typical process, 10-30 per cent of the monomer is converted to polymer per cycle. Rest of monomer is recycled. Extensive chain transfer reactions take place during polymerisation to yield a branched polyethylene. Apart from long branches it is also having a large number of short branches of unto 5 carbon atoms formed by intramolecular chain transfer reactions. A typical molecule of Low density polyethylene is having a short branch for about every 50 carbon atoms and one or two long branches per molecule. 

Commerical polymerizations of ethylene, propene, and other a-olefins are carried out as slurry (suspension) and gas-phase processes [Beach and Kissin, 1986 Diedrich, 1975 Lieberman and Barbe, 1988 Magovern, 1979 Vandenberg and Repka, 1977 Weissermel et al., 1975]. Solution polymerization has been used in the past for ethylene polymerization at 140-150°C, pressures of up to 8 MPa (1 MPa = 145 psi = 9.869 atm), using a solvent such as cyclohexane. The solution process with its higher temperatures was employed for polymerization with the relatively low efficiency early Phillips initiators. (Polyethylene, but not the initiator, is soluble in the reaction medium under the process conditions.) The development of a variety of high-efficiency initiators has allowed their use in lower-temperature suspension and gas-phase processes, which are more advantageous from many... 

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. 

The three processes differ by the operating conditions as reaction temperature, type of heat control and degree of system heterophasicity. Moreover, different processes could bring about also different thermal effects inside the polymer particle The solution process mainly yields polyethylene with a medium to very narrow (Q values of 2 or 3) MWD, while both slurry and vapor phase processes give... 

In slurry, bulk-monomer, or gas-phase processes, the polymer is usually of higher density or crystallinity (e.g.. high-density polyethylene, linear-low-density polyethylene, isotactic polypropylene) and is thus insoluble in the reactor diluent or fluidizing gas stream. The continuous operation of these processes suggests the use of morphologically uniform catalyst particles which can be fed into the reactor smoothly without clumping, which in turn implies fixing the solution-soluble catalyst on an insoluble carrier. 

The technology used for the production of ethylene is schematically represented in Figure 11.4. The final conversion from efhylene into polyethylene will make use of different processes being for Braskem a slurry and gas phase process, while the Dow/Mitsui joint venture may aim for a solution process. Furthermore, ethylene can also be used for other basic chemical derivatives production besides polyethylene. In 2013 the 2007 started project, however, is put on hold in view of changed Ethanol economics (see http //www.worldindustrialreporter.com/ dow-mitsui-postpone-l-5b-sugarcane-to-plastic-brazil-plant/, accessed 22 August 2013). 

What are the industrial conditions for preparations of high-density polyethylene Describe the continuous solution process, the slurry process, and the gas-phase process. 

The polymerization of ethylene might be carried out in solution or in a slurry process. But these processes are complicated by the need for a separation step to isolate the resin product from solution. The newer installations favor the gas-phase process that can produce both the low- and high-densily resins. Older plants lack this versatility and are able to produce only either the high-density or the low-density type of polyethylene. 

Chlorinated Polyethylene (CPE). The first patent on the chlorination of PE was awarded to ICl in 1938. CPE is polymerized by substituting select hydrogen atoms on the backbone of either HDPE or LDPE with chlorine. Chlorination can occur in the gaseous phase, in solution, or as an emulsion. In the solution phase, chlorination is random, while the emulsion process can result in uneven chlorination due to the crystalline regions. The chlorination process generally occurs by a free-radical mechanism, shown in Fig. 2.25, where the chlorine free radical is catalyzed by ultraviolet light or initiators. 

MA1 Matsuo, M., Miyoshi, S., Aztrrrra, M., Bin, Y., Agari, Y., Sato, Y., arrd Korrdo, A., Phase separation of several kirtds of polyethylene solution rrrtder the gelation/ crystalhzation process, Macro io/ecM/e5, 38,6688, 2005. 

Polyethylene is made in a continuous fashion by solution, slurry, and gas-phase processes. In a solution process, the reaction is run at high temperatures (maybe 200-300 °C) in the presence of an organic solvent such as hexane. At the reaction temperature, the ethylene and the polyethylene remain in solution during the polymerization. After the reaction, the pressure is released and the solvent removed. In a slurry process, the temperature is lower and the polyethylene forms as a slurry in the organic solvent. In a gas-phase process, solid polyethylene seeds are suspended in a gaseous stream of ethylene and the ethylene polymerizes onto these suspended seeds. These descriptions are gross oversimplifications and much process research has been, and continues to be, done in this area. Details of each of these processes and recent improvements can be found by consulting the patent literature. 

It is important to understand that the introduction of linear low-density polyethylene (LLDPE) in the 1960s and late 1970s, manufactured by the solution process and the gas-phase process, both operating at relatively low pressure utilizing a transition metal-based catalyst, provided a new type of polyethylene with unique properties that did not result in the elimination of the high-pressure process from commercial use. It opened new markets and applications for the polyethylene industry and resulted in its continued rapid growth. 

Based on the requirements outlined above, industrial scientists recognized soon after the discovery of single-site catalysts based on zircono-cene/MAO solutions that this type of catalyst needed to be supported on a solid support in order to manufacture polyethylene in commercial reactors based on the slurry process and the gas-phase process. Therefore, suitable supports for the single-site Zr/MAO catalyst systems must meet similar requirements as other catalysts in order to perform satisfactorily as particle-form catalysts. 

Chapter 5 is a summary of the processes used to manufacture polyethylene, which includes the tubular and autoclave high-pressure process and the three methods that operate at relatively low-pressure—the slurry process, gas-phase process and solution process. 

The polymerization of olefins with coordination catalysts is performed in a large variety of polymerization processes and reactor configurations that can be classified broadly into solution, gas-phase, or slurry processes. In solution processes, both the catalyst and the polymer are soluble in the reaction medium. These processes are used to produce most of the commercial EPDM rubbers and some polyethylene resins. Solution processes are performed in autoclave, tubular, and loop reactors. In slurry and gas-phase processes, the polymer is formed around heterogeneous catalyst particles in the way described by the multigrain model. Slurry processes can be subdivided into slurry-diluent and slurry-bulk. In slurry-diluent processes, an inert diluent is used to suspend the polymer particles while gaseous (ethylene and propylene) and liquid (higher a-olefins) monomers are fed into the reactor. On the other hand, only liquid monomer is used in the slurry-bulk pro-... 

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