PROCESS FOR PRODUCING AN AMORPHOUS ALPHA-OLEFIN POLYMER

Abstract: A circulation loop is provided between a point next to the outlet of an amorphous polyalphaolefin polymerization zone and a flash zone, carrying a stream of molten devaporized polymer product.

Description: The present invention relates to a bulk polymerization process for the direct production of substantially amorphous α-olefin polymers, especially amorphous propylene homopolymers or interpolymers. The amorphous polymer is the only product of the process and after separation of unreacted monomers, deactivation of catalyst residues in the polymer and polymer stabilization against heat and oxidation, a final product is recovered from the process. In conventional slurry polymerization processes for the production of highly crystalline isotactic propylene polymer using a high activity polymerization catalyst, the polymer leaves the polymerization reactor as a solution in liquid propylene at elevated temperatures and pressures, usually at temperatures between 54 and 79.4°C (130°F and 175°F) and at pressures between 2.76 and 3.79 MPa gauge (400 psig and 550 psig). The reactor effluent is then merely passed to a vaporization zone, usually a cyclone-bag filter combination, maintained at relatively low pressure, in which zone separation or flashing of unreacted propylene monomer occurs overhead while solid and substantially dry and free flowing polymer in powder form is recovered from the bottoms of the vaporization zone. Such an arrangement is completely unsuitable in a process producing an amorphous polymer due to the physical characteristics of the polymer product, i.e. the high viscosity and "stickiness" which prevent it from being recovered as a powder solid on a non-plugging filter. In addition, due to the inherent lowering in temperature in a flashing operation at reduced pressure, the product stream removed from the reactor tends to freeze and plug the conduits leading to the vaporization zone. The present invention seeks to provide a process for the separation of amorphous α-olefin polymer from unreacted monomer(s). THE INVENTION In accordance with the invention there is provided a process for the production of an amorphous α-olefin polymer in fluid form which comprises: (a) withdrawing through a valve from a bulk polymerization zone maintained at a temperature between 54 and 79.4°C (130°F and 175°F) and at a pressure between 2.76 and 3.79 MPa gauge (400 psig and 550 psig) a reactor effluent comprising amorphous α-olefin polymer and liquid unreacted monomer; (b) directly contacting said effluent immediately upon withdrawal through said valve with a heated devaporized amorphous α-olefin polymer obtained in step (f) below and having a temperature of from 177 to 218°C (350°F to 425°F); (c) passing the resulting mixture from step (b) to a flash zone maintained at a pressure from 276 to 552 KPa gauge (40 to 80 psig) and a temperature between 149 and 191°C (300°F and 375°F); (d) withdrawing a vapor stream of unreacted monomer from said flash zone; (e) withdrawing devaporized amorphous α-olefin polymer from said flash zone, and (f) heating a portion of said devaporized α-olefin polymer from step (e) by indirect heat exchange and passing the heated portion to step (b) above. It is not important to the success of the present invention what slurry polymerization conditions and catalyst system are chosen in the preparation of the amorphous α-olefin polymer. Nor is it important whether the polymer is a homopolymer or a copolymer. The polymer products of the process of this invention have excellent properties making them useful in a variety of applications, such as for adhesives, caulking and sealing compounds, and roofing compositions. For a better understanding of the invention, reference is directed to the accompanying drawing which is a flow diagram of one embodiment of the process of the invention. A reactor effluent containing an amorphous copolymer of a major proportion of propylene with ethylene as the remainder, e.g. about 85 wt % propylene and about 15 wt % ethylene, is provided in line 10. The effluent typically is a solution of the polymer (say a 30 to 60% by weight solution) in liquid unreacted monomer. The effluent, which typically contains from 40 to 70 wt % of unreacted monomers and hydrogen used for molecular weight control, is passed through a cyclic discharge valve or "blipper" valve 11, which is of the type that opens and closes continuously so that the effluent withdrawn from the polymerization vessel (not shown) simulates a continuous discharge operation. The effluent is subsequently heated as close as possible to the outlet of the "blipper" valve 11, by means of intermixing of molten amorphous polymer from line 12 having a temperature of from 177 to 218°C (350°F to 425°F). The weight ratio of amorphous polyolefins in line 12 and line 10 (monomer free basis) should range between 10:1 and 15:1. The mixed stream 13 is introduced into a flash tank 14 maintained at a pressure from 276 to 552 KPa gauge (40 to 80 psig). Unreacted monomer vapors (and also small quantities of hydrogen used as a polymer molecular weight control agent) flow from flash tank 14 via line 16 through a separator 17 to remove small amounts of entrained polymer and then to purification and recycle to the polymerization reactor (not shown). Devaporized polymer is withdrawn in line 21 and the net polymer product having a temperature between 149 and 191°C (300°F and 375°F) flows by means of level control 19 through line 21 to product storage (not shown). The remaining portion of the withdrawn polymer is circulated by means of pump 22 through a shell and tube type exchanger 24 located in conduit 23. The heating medium is high pressure steam, e.g. at about 4.1 MPa gauge (600 psig), provided in line 26 and its flow is regulated by means of temperature control valve 27. Hot oil could also be used as the heating medium. There are several advantages of the process of this invention. Among these are: 1) it provides a simple yet extremely efficient method of vaporization and subsequent separation of unreacted monomers from the polymer product; and 2) it enables trouble free flow of pumpable product throughout the entire process equipment, i.e. from the outlet of the reactor, through the separation equipment and finally to product storage or to heated vehicles used to transport the final product to the user. Preferred embodiments of the invention are disclosed in the Claims 2 and 3

Claims: A process for the production of an amorphous α-olefin polymer in fluid form which comprises: (a) withdrawing through a valve from a bulk polymerization zone maintained at a temperature between 54 and 79.4°C (130°F and 175°F) and at a pressure between 2.76 and 3.79 MPa gauge (400 psig and 550 psig) a reactor effluent comprising amorphous α-olefin polymer and liquid unreacted monomer; (b) directly contacting said effluent immediately upon withdrawal through said valve with a heated devaporized amorphous α-olefin polymer obtained in step (f) below and having a temperature of from 177 to 218°C (350°F to 425°F); (c) passing the resulting mixture from step (b) to a flash zone maintained at a pressure from 276 to 552 KPa gauge (40 to 80 psig) and a temperature between 149 and 191°C (300°F and 375°F); (d) withdrawing a vapor stream of unreacted monomer from said flash zone; (e) withdrawing devaporized amorphous α-olefin polymer from said flash zone, and (f) heating a portion of said devaporized α-olefin polymer from step (e) by indirect heat exchange and passing the heated portion to step (b) above. A process according to claim 1, wherein the weight ratio of the heated devaporised polymer in step (b) to the amorphous α-olefin polymer withdrawn in step (a) is between 10:1 and 15:1. A process according to claim 1 or 2 wherein the amorphous α-olefin polymer is a propylene-based polymer selected from amorphous propylene homopolymer, amorphous copolymers of propylene and ethylene and amorphous interpolymers of propylene, ethylene and another alpha-olefin having from 4 to 8 carbon atoms per molecule.

Inventors: OETTING, STEVEN LOUIS
Applicants: REXENE PRODUCTS COMPANY (A DELAWARE CORPORATION)
Application year: 1987
Main classification: C08F10
IPC codes: C08F6, C08F10