Slurry-loop process

Phillips catalysts, 17 702 20 151-152 active chromium species on, 20 156 Phillips chromium catalyst, 20 152 Phillips Petroleum loop slurry process, 20 168... 

One of the most economical routes to most commercial grades of olefin polymers is the loop slurry process with a paraffin diluent. This process was introduced by Chevron Phillips in 1960 (7). There, a mixture of catalyst particles, growing polymer particles, comonomers, and diluent is pumped in a loop. The polymer particles are harvested by guiding a side stream of the slurry to settling chambers, where the polymer particles settle toward the bottom. 

The polymerization process can be carried out at a temperature low enough that the resulting polymer is largely insoluble in the diluent. The pressures in the loop slurry process are in the range of 2.5-4 MPa. 

ChevronPhillips HDPE, MDPE, LLDPE slurry supported Cr, Ziegler-Natta, single site So-called "particle form loop slurry process" used... 

Polymerizations that use supported chromium (Phillips) catalysts are conducted predominantly in slurry processes (though a small portion employs the gas phase process, see below). The historical development of the Phillips process has been expertly reviewed by Hogan (5, 6) and McDaniel (7-9). The slurry process originally developed by Phillips Petroleum (now Chevron Phillips) has been called the "particle form loop slurry process" and the "slurry loop reactor process" for production of HDPE and LLDPE (10). Hexene-1 is most often used as comonomer for LLDPE in the Phillips process. A simplified process flow diagram for the Phillips loop-slurry reactor process is shown in Figure 7.3 and key operating features are summarized in Table 7.4. 

Figure 7.3 Schematic process flow diagram for Chevron Phillips loop slurry process for production of linear low density polyethylene. (Reprinted with permission of John Wiley Sons, Inc., Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley and Sons, Inc., 6 edition, 2006).

Features - particles of growing polymer form as suspension in hydrocarbon diluent - catalyst residence time 1 hour for Phillips loop slurry process - morphology and psd of catalyst are important - wide range of comonomers may be used... 

A higher concentration of slurry, which can contain up to 50% polymer by weight and 80% by settled volume, contributes to the improved economic efficiency of the loop-slurry process. The diluent serves to transfer heat and to keep the catalyst in contact with ethylene and other reactants. Isobutane is now used almost entirely as the diluent. This diluent allows the polymer to be separated by a flash separation, which is generally rather simple in comparison with the separation in the solution processes. 

The initial development of a slurry process for Ziegler-based catalysts did not face the same problems as scientists at Phillips. Since Ziegler catalysts are much more sensitive to hydrogen, molecular weight control does not rely on precise control of high reactor temperatures, as it did for the chromium oxide based loop slurry process. Therefore, lower reactor temperatures and heavier hydrocarbons were possible, and there was no need to go beyond a stirred tank. Hoechst developed the first such process, but Montedison, Mitsui, Solvay, and others have also developed similar processes. 

One of the most efficient implementations of the slurry process was developed by Phillips Petroleum Company in 1961 (Eig. 5). Nearly one-third of all HDPE produced in the 1990s is by this process. The reactor consists of a folded loop with four long (- 50 m) vertical mns of a pipe (0.5—1.0 m dia) coimected by short horizontal lengths (around 5 m) (58—60). The entire length of the loop is jacketed for cooling. A slurry of HDPE and catalyst particles in a light solvent (isobutane or isopentane) circulates by a pump at a velocity of 5—12 m/s. This rapid circulation ensures a turbulent flow, removes the heat of polymeriza tion, and prevents polymer deposition on the reactor walls. 

Phillips Petroleum Company developed an efficient slurry process used for the production of both HDPE and LLDPE (Eig. 6). The reactor is built as a large folder loop containing long mns of pipe from 0.5 to 1 m ia diameter coimected by short horizontal stretches of pipe. The reactor is filled with a light solvent (usually isobutane) which circulates through the loop at high speed. A mixed stream containing ethylene and comonomers (1-butene,... 

The loops are pipes of 10- to 20-inch diameters, about 50 feet high, with a total length of 250—300 feet. They hold about 600 cubic feet of slurry and are water-jacketed to control the heat. The reaction temperature in the process is less than 212°F, with pressures of only a couple of hundred pounds, so the process is more economical (energy saving) than the others already discussed. After the slurry is withdrawn from the loop reactor, processing is the same as that downstream of the reactor in Figure 23—2. This process needs only small amounts of catalyst so catalyst separation from the... 

The primary product in the slurry units is HDPE with MDPE as a secondary product. With single-site catalysts production of mLLDPE in slurry loop reactors is also possible. Today for example, Chevron Phillips, BP Solvay, Basell, Borealis and Sumitomo Mitsui have their own slurry process technology-... 

Slurry processes in hydrocarbon diluent are used in the production of HDPE, including bimodal polymers produced in the cascade process in which different hydrogen concentrations are applied in two or more reactors in series. Liquid loop reactors are generally used with a light hydrocarbon diluent such as isobutane, whereas heavier hydrocarbon diluents are typically used in continuous stirred tank reactors. 

In PP manufacture, modern bulk (liquid monomer) and gas-phase processes have largely replaced the earlier slurry processes in which polymerization was carried out in hydrocarbon diluent. The most widely adopted process for PP is Basell s Spheripol process.317 Homopolymer production involves a pre-polymerization step at relatively low temperature, followed by polymerization in a loop reactor using liquid propylene random co-polymers are produced by introducing small quantities of ethylene into the feed. The pre-polymerization step gives a pre-polymer particle with the capacity to withstand the reaction peak, which occurs on entering the main loop reactor. The addition of one or two gas-phase reactors for EP co-polymerization makes it possible to produce heterophasic co-polymers containing up to 40% of E/P rubber within the homopolymer matrix. 

Stripped for solvent removal. The later Phillips "particle form" process is a slurry process in which the polymer precipitates as it forms. This process uses a circulating-loop reactor. Because of improved catalyst use efficiency, catalyst removal from the polymer is unnecessary. 

Linear polyethylenes are produced in solution, slurry, and increasingly, gas-phase low-pressure processes. The Phillips process developed during the mid 1950s used supported chromium trioxide catalysts in a continuous slurry process (or particle-form process) carried out in loop reactors. Earlier, Standard Oil of Indiana patented a process using a supported molybdenum oxide catalyst. The polyethylenes made by both these processes are HDPE with densities of 0.950-0.965 g/cm and they are linear with very few side-chain branches and have a high degree of crystallinity. 

In addition to the general type of slurry loop process described above, slightly different loop reactor processes also exist. A short summary of two of these processes is shown below. 

Slurry process with horizontal loop reactors... 

Slurry process with loop reactors using hexane as the diluent... 

The first United States patent that described the vertical pipe-loop slurry polymerization reactor illustrated in Figure 5.11 was issued to Donald D. Norwood on April 26,1966, as U.S. Patent 3,248,179 and assigned to Phillips Petroleum Company. Earlier applications filed in 1959 were abandoned, thus explaining the relatively late issue date on the Norwood patent. Although Donald Norwood was the only name on the first United States patent issued to Phillips Petroleum, Philips Petroleum credits three process engineers, D. D. Norwood, S. J. Marwil and R G. Rohling, for the design of the vertical loop reactor [24]. 

The Chevron-Phillips (CP) slurry process is a leading licensor of the slurry loop process for the manufacture of HOPE and LLDPE worldwide. Between 1997 and 2008, the CP process has accounted for the addition of approximately 5.8 billion Ibs/year of global polyethylene capacity. Much of the capacity has been added to emerging markets with line capacity exceeding one billion Ibs/year. Some capacity additions are summarized in Table 5.19. 

Finally, I would like to thank Dr. Max P. McDaniel of Chevron Phillips Chemical Company in Bartlesville, Oklahoma, for many helpful discussions on the development of the Phillips loop process and catalyst systems developed by Phillips Petroleum Company, and later by Chevron Phillips Chemical Company for the slurry 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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