Polymerization hexane slurry

When pure needle-like crystals of -aminobenzoyl chloride are polymerized in a high temperature, nonsolvent process, or alow temperature, slurry process, polymer is obtained which maintains the needle-like appearance of monomer. PBA of inherent viscosity, 4.1 dL/g, has been obtained in a hexane slurry with pyridine as the acid acceptor. Therefore PBA of fiber-forming molecular weight can be prepared in the soHd state. 

Gas phase olefin polymerizations are becoming important as manufacturing processes for high density polyethylene (HOPE) and polypropylene (PP). An understanding of the kinetics of these gas-powder polymerization reactions using a highly active TiCi s catalyst is vital to the careful operation of these processes. Well-proven models for both the hexane slurry process and the bulk process have been published. This article describes an extension of these models to gas phase polymerization in semibatch and continuous backmix reactors. 

The kinetic models for the gas phase polymerization of propylene in semibatch and continuous backmix reactors are based on the respective proven models for hexane slurry polymerization ( ). They are also very similar to the models for bulk polymerization. The primary difference between them lies in the substitution of the appropriate gas phase correlations and parameters for those pertaining to the liquid phase. 

In the presence of an emulsifier, water and AlMes react in hexane to form MAO particles about 5—20 fim in diameter. When contacted with metallocene dichlorides, solid catalysts are formed which give good particle morphology and high bulk density in hexane—slurry polymerizations of ethylene or bulk monomer polymerization of propylene. ... 

Continuous stirred tank reactors are also widely used for hexane slurry ethylene polymerization by many manufacturers. In the Hoechst process, the reaction is carried out in four CSTRs arranged in series such that the slurry phase and the vapor phase move in concurrent flow. Polymerization occurs at 100 psig and 85 C with 98% conversion of ethylene. The residence time in the reactor is about 2.7 hr. The product slurry is pumped into centrifuges, which separate the bulk of the hydrocarbon diluent liquid from the polymer fluff. 

In the Hoechst process, for example, hexane is used as the diluent (108,109). Hexane, ethylene, alpha-olefin, catalyst components, and hydrogen are continuously fed into a stirred reactor for polymerization. The slurry is then transferred into a smaller reactor for post-polymerization, after which the total charge is separated by a centrifuge into a liquid stream (which is returned to the initial reactor) and solid polymer. The wet polymer is steam-stripped from the solvent, dried, and pelletized. The stripped hexane is purified and recycled. Although stirred tanks are most common, loops can also be used in this fashion. In some schemes, a portion of the recycle diluent from the centrifuge is returned to the reactor, and a portion is fed to recycle purification for wax removal. This step removes some of the lowest molecular weight pol5mier, which dissolves in the diluent. 

Polymerization productivity hexane slurry, 70°C, 0.7 MPa, 4 h, with hydrogen for molecular weight control. Values in parentheses are polymerizations performed in liquid propylene at 70°C for 2 h with hydrogen. 

Some slurry processes use continuous stirred tank reactors and relatively heavy solvents (57) these ate employed by such companies as Hoechst, Montedison, Mitsubishi, Dow, and Nissan. In the Hoechst process (Eig. 4), hexane is used as the diluent. Reactors usually operate at 80—90°C and a total pressure of 1—3 MPa (10—30 psi). The solvent, ethylene, catalyst components, and hydrogen are all continuously fed into the reactor. The residence time of catalyst particles in the reactor is two to three hours. The polymer slurry may be transferred into a smaller reactor for post-polymerization. In most cases, molecular weight of polymer is controlled by the addition of hydrogen to both reactors. After the slurry exits the second reactor, the total charge is separated by a centrifuge into a Hquid stream and soHd polymer. The solvent is then steam-stripped from wet polymer, purified, and returned to the main reactor the wet polymer is dried and pelletized. Variations of this process are widely used throughout the world. 

Most commercial processes produce polypropylene by a Hquid-phase slurry process. Hexane or heptane are the most commonly used diluents. However, there are a few examples in which Hquid propylene is used as the diluent. The leading companies involved in propylene processes are Amoco Chemicals (Standard OH, Indiana), El Paso (formerly Dart Industries), Exxon Chemical, Hercules, Hoechst, ICl, Mitsubishi Chemical Industries, Mitsubishi Petrochemical, Mitsui Petrochemical, Mitsui Toatsu, Montedison, Phillips Petroleum, SheU, Solvay, and Sumimoto Chemical. Eastman Kodak has developed and commercialized a Hquid-phase solution process. BASE has developed and commercialized a gas-phase process, and Amoco has developed a vapor-phase polymerization process that has been in commercial operation since early 1980. 

Slurry phase (or suspension) process. The uniquedooldng equipment in Figure 23—5 is a loop reactor. This process also takes place in a solvent (in this case, normal hexane, isobutane, or isopentane) so that the mixture can be pumped continuously in a loop while the polymerization is taking place. Feeds (the solvent, comonomer if any, ethylene and Ziegler-Natta catalyst) are pumped into the loop and circulated. Polymerization rakes place continuously at temperatures below the melting point of the polyethylene allowing solid polymer particles to form enough to form slurry. The reaction takes place at 185—212°F and 75—150 psi. A slurry of HOPE in hexane is drawn off continuously or intermittently. 

The manufacture of linear low-density polyethylene (LLDPE) by slurry polymerization in hexane (see Sections 6.2 and 6.8) is carried out by Hoechst, Mitsui, and a number of other chemical manufacturers in a series of continuous stirred tank reactors. The manufacture of butyraldehyde from CO, H2, and propylene using a soluble rhodium phosphine complex (see Sections 5.2 and 5.5) is also carried out in a continuous stirred tank reactor. 

The Unipol process employs a fluidized bed reactor (see Section 3.1.2) for the preparation of polyethylene and polypropylene. A gas-liquid fluid solid reactor, where both liquid and gas fluidize the solids, is used for Ziegler-Natta catalyzed ethylene polymerization. Hoechst, Mitsui, Montedison, Solvay et Cie, and a number of other producers use a Ziegler-type catalyst for the manufacture of LLDPE by slurry polymerization in hexane solvent (Fig. 6.11). The system consists of a series of continuous stirred tank reactors to achieve the desired residence time. 1-Butene is used a comonomer, and hydrogen is used for controlling molecular weight. The polymer beads are separated from the liquid by centrifugation followed by steam stripping. 

Finally, the HDPE slurry from the second reactor is sent to the postreactor (3) to reduce dissolved monomer, and no monomer recycling is needed. In the decanter (4), the polymer is separated from the dispersing medium. The polymer containing the remaining hexane is dried in a fluidized bed dryer (5) and then pelletized in the extrusion section. The separated and collected dispersing medium of the fluid separation step (6) with the dissolved co-catalyst and comonomer is recycled to the polymerization reactors. A small part of the dispersing medium is distilled to maintain the composition of the diluent. 

The catalyst is only fed to the first reactor. Polymerization occurs in a dispersing medium like n-hexane using a Ziegler catalyst with very high activity. No deactivation and catalyst removal is necessary because a very low level of catalyst residue remains in the polymer. For unimodal-grade production, the catalyst, dispersing medium, monomer and hydrogen are fed to the first reactor (1) where the first polymerization takes place. The slurry is then sent to the post reac-... 

Reagents. Hydroxyethyl methacrylate (HEMA) was extracted with hexane to remove bis-esters and distilled in vacuo, b.p. 69 / 0.1 mm Hg. p-Mltrobenzenesulfonyl isocyanate (b.p. 160 /A mm Hg) was synthesized in 63% yield by phosgenatlon of p-nltrobenzene-sulfonamlde in the presence of butyl isocyanate (9 ). Homo- and copolymers of HEMA were prepared by solution polymerization in DMF in the presence of benzoyl peroxide and the results are summarized in Table I. The hydrolytic stability of the hydrogels was estimated by slurrying 0.5-1.0 g of polymer in 5.0 mL 0.35 KOH in 10 mL culture tubes equipped with teflon lined screw caps. The samples were heated at 100 for up to 24 hr in an aluminum constant temperature block. Immediately upon removal from the heating block, the samples were cooled and acidified with 6N HCl. The precipitated gel was washed and soaked in distilled water for 30 min before the carboxylic acid content was estimated by titration with standard NaOH. 

We also investigated the possibility of using a slurry system in which the monomer, dissolved in a refluxing hydrocarbon (hexane), was polymerized in the presence of a soluble initiator such as TBP. It turned... 

The main polymerization reaction is done by adding lactone to a stirred slurry of prepolymer in refluxing hexane. A chain-transfer agent... 

Process description The INNOVENE S process utilizes a proprietary vertical slurry-loop reactor, as shown in the flow diagram. Two reactors are used for bimodal capability. Isobutane is normally used as the hydrocarbon diluent in the process, although hexane may be used as an alternative. The diluent is used as a catalyst carrier and as the polymerization reactor suspension and heat transfer medium. Hexene-1 and/or butene-1 can be used as a comonomer. Hydrogen is used for molecular weight control when using the Zieglerg catalyst platform. Titanium-based and chromium-based catalysts are both used. 

Commercial production of crystalline polypropylene (PP) was first put on stream in late 1959 by Hercules in the United States, by Montecatini in Italy, and by Farbenwerke Hoechst AG in Germany. The workhorse process for commercial production of PP has been slurry polymerizations in liquid hydrocarbon diluent, for example, hexane or heptane. These are carried out either in stirred batch or... 

In the HDPE plant ethylene is polymerized in hexane, at 70-90 C and 4-10 bars in the presence of titanium-based MgCl2-supported catalysts and alkyl aluminium co-catalysts Together with the slurry of HDPE powder in hexane a small amount of PE wax is formed. Due to its low molecular weight... 

PP is produced by a variety of processes, most of them by a diluent phase propylene polymerization utihzing a Ziegler-Natta-activated titanium trichloride catalyst in the presence of low- to high-boiling hydrocarbons. Residual catalyst removal followed by hydrocarbon slurry centrifugation is the immediate upstream operation prior to thermal drying. Hexane is the solvent used in the major PP processes in operation today. As a result these polymers are solvent wet. 

The earliest commercial methods used slurry polymerizations with liquid hydrocarbon diluents, like hexane or heptane. These diluents carried the propylene and the catalyst. Small amounts of hydrogen were fed into the reaction mixtures to control molecular weights. The catalyst system consisted of a deep purple or violet-colored TiCls reacted with diethyl aluminum chloride. The TiCb was often prepared by reduction of TiCU with an aluminum powder. These reactions were carried out in stirred autoclaves at temperatures below 90 °C and at pressures sufficient to maintain a liquid phase. The concentration of propylene in the reaction mixtures ranged between 10-20%. The products formed in discrete particles and were removed at 20-40% concentrations of solids. Unreacted monomer was withdrawn from the product mixtures and reused. The catalysts were deactivated and dissolved out of the products with alcohol containing some HCl, or removed by steam extraction. This was followed by extraction of the amorphous fractions with hot liquid hydrocarbons. 

The Mitsui CX process is typical of a modem slurry process for HDPE production (Figure 2.37). It consists of two CSTRs (hexane is used as diluent), a centrifuge to separate the diluent from the polymer, a dryer to remove the residual diluent, and a diluent recovery system to separate the low molecular weight polymer or wax that is dissolved in the diluent. The two polymerization reactors can be operated in series or in parallel. When run in... 

The medium for polymerization can be liquid or gaseous propylene or an inert hydrocarbon diluent such as hexane. Today about 25% of PP is produced in inert hydrocarbon slurry processes. Their relative proportion will steadily decrease because practically all new plants and investments are based on gas phase, bulk or combined bulk/gas phase technologies. 

Two versions of the slurry process are most frequently applied. In the autoclave or Hoechst process (named after the former company Hoechst that introduced this version of the slurry process) the reaction temperature is 80-90 °C. Typical ethene pressures in the polymerization reactor are 5-10 bar, allowing the application of very large reactors (typically 100 m ). The catalyst compound and the aluminum alkyl activator are premixed in the catalyst preparation vessel with the diluent hexane. This mixture is fed to the polymerization reactor. Figure 6.20.3 shows a schematic view of the process with one polymerization reactor, but cascades of two or more polymerization reactors are also frequently found (allowing additional freedom in achieving specific molecular mass distributions of the PE product - see also picture at the beginning of the section, Hostalen ACP technology). 

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