Slurry polymerization

The Phillips-type catalyst can be used in solution polymerization, slurry polymerization, and gas-phase polymerization to produce both high density polyethylene homopolymers and copolymers with olefins such as 1-butene and 1-hexene. The less crystalline copolymers satisfy needs for materials with more suitable properties for certain uses that require greater toughness and flexibiUty, especially at low temperatures. 

The polymer is separated from the polymerization slurry and slurried with acetic anhydride and sodium acetate catalyst. Acetylation of polymer end groups is carried out in a series of stirred tank reactors at temperatures up to 140°C. End-capped polymer is separated by filtration and washed at least twice, once with acetone and then with water. 

The catalyst is mixed with propane diluent and fed into the compact prepolymerization reactor. Cocatalyst, ethylene, comonomer and hydrogen are also fed into this reactor. The pre-polymerized slurry is then fed into a second larger slurry loop reactor, which is designed for supercritical conditions and is typically operated at 75°C—100°C... 

Phillips Petroleum Co. Polyethylene, LLDPE-HDPE Ethylene Energy efficient loop-reactor technology polymerizes slurry with catalyst 20 1998... 

Material that was in previous editions (e.g.. polymerization, slurry reactors, and chemical vapor disposition reactors) that has been omitted from the printed version of the fourth edition... 

Gas-phase fluidized bed polymerization, solution polymerization, slurry polymerization, and polymerization in melt under high ethylene pressure... 

Uses Dispersant esp. for pigments in aq. sol ns. stabilizer in latex emulsions dispersant in inorg. filler/pigment dispersions, trade sales flat paints, emulsion polymerization, slurries, latex, water treatment, agriculture, cosmetic base makeup, industrial cleaners, in large particle suspensions Features Very low foaming very high efficient ... 

The different polymerization classes discussed above can be implemented in several ways bulk polymerization, solution polymerization, gas-phase polymerization, slurry polymerization, suspension polymerization and emulsion polymerization. 

Polymerizations slurry polymerization is achieved in the same conditions preyiously described for propane polymerization a >, except temperature 80 C, total pressure 8 bars. 

Polymerization. Slurry polymerization was performed in a 1 1 autoclave under a constant pressure of ethylene. A prescribed amount of AlBt, and 500 ml of n-hexane were introduced into the reactor in a nitrogen stream. 1-Hexene was also introduced in the case of copolymerization. After evacuation, ethylene was introduced at the polymerization temperature. Polymerization was started by breaking the glass ampoule containing the prescribed amount of catalyst. The rate of polymerization was determined from the rate of ethylene consumption, measured by a hot-wire flowmeter with a personal computer directly connected to it through A/D converter. Details of polymerization procedures were described elsewhere . 

Several recent patents describe improvements in the basic belt process. In one case a higher soHds polymerization is achieved by cooling the starting monomer until some monomer crystallizes and then introducing the resulting monomer slurry onto the belt as above. The latent heat of fusion of the monomer crystals absorbs some of the heat of polymerization, which otherwise limits the soHds content of the polymerization (87). In another patent a concave belt is described which becomes flat near the end. This change leads to improved release of polymer (88). 

The monomer recovery process may vary ia commercial practice. A less desirable sequence is to filter or centrifuge the slurry to recover the polymer and then pass the filtrate through a conventional distillation tower to recover the unreacted monomer. The need for monomer recovery may be minimized by usiag two-stage filtration with filtrate recycle after the first stage. Nonvolatile monomers, such as sodium styrene sulfonate, can be partially recovered ia this manner. This often makes process control more difficult because some reaction by-products can affect the rate of polymerization and often the composition may vary. When recycle is used it is often done to control discharges iato the environment rather than to reduce monomer losses. 

Stabilizers and pigments are normally slurried with macroglycol and added to the polymeric glycol charge, prior to diisocyanate addition. Therefore, care must be taken to avoid additives that react significantly with diisocyanates or diamines under processing conditions. Also, stabilizers should be chosen that have no adverse catalytic effect on the prepolymer or chain-extension reactions. 

Sodium sihcate is usually added to slurries as a dispersant (see Dispersants). Small amounts of sodium siUcate are used as flocculants. The active species are polymeric siUcates formed by hydrolysis. 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

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. 

An alternative polymerization process utilizes a slurry of calcium chloride in NMP as the polymerization medium. The solubiHty of calcium chloride is only 6% at 20°C however, the salt continues to dissolve as conversion of monomers to polymer proceeds and calcium chloride/polyamide complexes are formed. Polymer molecular weight is further increased by the addition of /V, /V- dim ethyl a n i1 in e as an acid acceptor. This solvent system produces fiber-forming polymer of molecular weights comparable to that formed in HMPA/NMP. 

The polymerization of monomers to form hydrocarbon resins is typically carried out by either the direct addition of catalyst to a hydrocarbon fraction or by the addition of feed to a solvent—catalyst slurry or solution. Most commercial manufacturers use a continuous polymerization process as opposed to a batch process. Reactor temperatures are typically in the range of 0—120°C. 

Polymerization in Solution or Slurry. Many hydrocarbon solvents dissolve PE at elevated temperatures of 120—150°C. Polymerization reactions in solution requite, as theit last step, the stripping of solvent. A variety of catalysts can be used in these processes. 

Polymerization in a hydrocarbon slurry (usually a light-saturated hydrocarbon) was the first commercial polymerization process to utilize Phillips and Ziegler catalysts. These processes enjoy high popularity because of theit versatihty. 

AH technologies employed for catalytic polymerization processes in general are widely used for the manufacture of HDPE. The two most often used technologies are slurry polymerization and gas-phase polymerization. Catalysts are usuaHy fine-tuned for a particular process. 

Slurry (Suspension) Polymerization. This polymerization technology is the oldest used for HDPE production and is widely employed because of process engineering refinement and flexibHity. In a slurry process, catalyst and polymer particles are suspended in an inert solvent, ie, a light or a... 

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. 

Processes for HDPE with Broad MWD. Synthesis of HDPE with a relatively high molecular weight and a very broad MWD (broader than that of HDPE prepared with chromium oxide catalysts) can be achieved by two separate approaches. The first is to use mixed catalysts containing two types of active centers with widely different properties (50—55) the second is to employ two or more polymerization reactors in a series. In the second approach, polymerization conditions in each reactor are set drastically differendy in order to produce, within each polymer particle, an essential mixture of macromolecules with vasdy different molecular weights. Special plants, both slurry and gas-phase, can produce such resins (74,91—94). 

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