Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2001-12-03
2004-03-09
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S492000, C422S245100, C422S251000, C422S253000
Reexamination Certificate
active
06703479
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for cooling or heating polymer in a polymerization reactor. The invention specifically relates to cooling polymerized solids in a polycondensation reactor. The invention particularly relates to cooling polyester, polyamide or polycarbonate chips in a solid-state polycondensation (SSP) reactor.
BACKGROUND OF THE INVENTION
Polymer resins are molded into a variety of useful products. One such polymer resin is polyethylene terephthalate (PET) resin. It is well known that aromatic polyester resins, particularly PET, copolymers of terephthalic acid with lower proportions of isophthalic acid and polybutylene terephthalate are used in the production of beverage containers, films, fibers, packages and tire cord. U.S. Pat. No. 4,064,112 B1 discloses a solid-state polycondensation or polymerization (SSP) process for the production of PET resins.
While for fibers and films the intrinsic viscosity of the resin must generally be between 0.6 and 0.75 dl/g, higher values are necessary for molding materials such as containers and tire cord. Higher intrinsic viscosity such as greater than 0.75 dl/g can only with difficulty be obtained directly through polycondensation of molten PET, commonly called the melt phase process. The SSP process pushes polymerization to a higher degree thereby increasing the molecular weight of the polymer by the heating and removal of reaction products. The polymer with higher molecular weight has greater mechanical strength and other properties useful for production of containers, fibers and films, for example.
The SSP process starts with polymer chips that are in an amorphous state. U.S. Pat. No. 4,064,112 B1 teaches crystallizing and heating the chips in a crystallizer vessel under agitation to a density of 1.403 to 1.415 g/cm
3
and a temperature ranging between 230° and 245° C. (446° and 473° F.) before entering into the SSP reactor. Otherwise the tacky chips tend to stick together.
The SSP reactor may consist of a cylindrical reactive section containing a vertical mobile bed into which the polymer chips are introduced from above and a frusto-conical portion of a dispensing section at the base for dispensing the product chips. The polycondensation reactor typically operates at temperatures between 210°. and 220° C. (410° and 428° F.).
The polyester chips move through the cylindrical reactive section of the polycondensation reactor by gravity in plug-flow. However, when the chips enter the frusto-conical portion of the dispensing section at the base of the polycondensation reactor, they enter into a non-flat velocity profile which interjects a non-uniformity in the amount of time that the chips are in the polycondensation reactor. Accordingly, a chip-to-chip variation in the degree of polymerization occurs due to the variation in residence time. Moreover, at the transition from the cylinder to the cone, the chips are subjected to a consolidation pressure that may be several times the normal radial axial pressure to which the chip had previously been subjected. The chips that are in a glassy region have a strong sticking tendency. Hence, the consolidation pressure can cause lumping of chips and interruption of flow.
Various reactions occur during polycondensation of PET. The main reaction that increases the molecular weight of PET is the elimination of the ethylene glycol group:
PET—COO—CH
2
—CH
2
—OH+HO—CH
2
—CH
2
—OOC—PET→PET—COO—CH
2
—CH
2
—OOC—PET+HO—CH
2
—CH
2
—OH
Inert gas such as nitrogen is introduced into the crystallizer vessel and the polycondensation reactor to strip the developing polymer of volatile impurities generated by the polycondensation reaction. Impurities include ethylene glycol and acetaldehyde if PET is produced. U.S. Pat. No. 5,708,124 B1 discloses maintaining the ratio of the mass flow rate of inert gas to the mass flow rate of PET polymer solids to below 0.6 in an SSP reactor.
The conventional method used for the purification of an inert gaseous stream recycled from an SSP process includes an oxidation step for converting the organic impurities to CO
2
and a drying step to eliminate the water formed in the polymerization process and the oxidation step. The oxidation step is carried out with gas containing oxygen by using an oxygen concentration of no more than in slight excess of the stoichiometric quantity with respect to the organic impurities. The oxidation step is controlled according to U.S. Pat. No. 5,612,011 B1 so that the inert gaseous stream at the outlet contains an oxygen concentration of not more than 250 ppm and preferably according to U.S. Pat. No. 5,547,652 B1 so that the inert gaseous stream at the outlet contains an oxygen concentration of not more than 10 ppm. These patents taught that a previously required deoxidation step of reducing the oxygen with hydrogen between the oxidation and drying steps was not required. Typically, the inert gaseous stream must be heated before it is recycled to the polycondensation reactor requiring additional utility cost.
It is also well known that polyamide resins, and among them particularly PA6, PA6,6, PA11, PA12 and their copolymers, find wide application both in the fiber and flexible packaging sectors, and in the manufactured articles production by blow and extrusion technology. While the resin relative viscosity for fibers is low at about 2.4 to 3.0, higher relative viscosities of 3.2 to 5.0 are needed for articles produced by blow and extrusion technologies. The relative viscosity is increased to above 3.0 by means of an SSP process operating at temperatures of between 140° and 230° C. (284° and 446° F.), depending on the polyamide types used. U.S. Pat. No. 4,460,762 B1 describes an SSP process for a polyamide and different methods to accelerate this reaction.
An SSP process for polyamide resins is also described in the article “Nylon 6 Polymerization in the Solid State,” R. J. Gaymans et al.,
Journal of Applied Polymer Science
, Vol. 27, 2515-2526 (1982) which points out the use of nitrogen as a heating and flushing aid. The reaction is carried out at 145° C. (293° F.).
It is also known that the molecular weight of polycarbonate can be increased through an SSP process.
The polymer chips exiting from an SSP reactor must be cooled to below the glass transition temperature for packaging purposes, especially to avoid heat damage to packaging containers, such as sacks and boxes. The desired packaging temperature is below 80° C. (176° F.) for PET chips. U.S. Pat. No. 5,817,747 B1 teaches two-stage cooling of the polymer chips after exiting the polycondensation reactor. The first cooling stage is a bed fluidized with nitrogen used for purging impurities from the SSP process after the nitrogen has been purified. The fluidizing gas entrains and separates the polymer dust from the polymer chips while cooling them to 160° to 180° C. (320° to 356° F.). The polymer dust is formed in the processing apparatuses by the action of rotating parts of an agitator in contact with the polymer chips in the crystallizer vessel and the sliding friction between the chips and the walls of the polycondensation reactor. The second cooling stage is a shell and tube or wall-type heat exchange cooler which uses water as the cooling fluid to cool the chips to between 40° and 60° C. (104° and 140° F.).
U.S. Pat. No. 5,662,870 B1 discloses a fluidized bed with two chambers for cooling polymer chips exiting the SSP reactor in a single stage. Fluidizing gas from the hotter chamber into which hot chips enter from the SSP reactor is recycled to heat the SSP reactor after it is de-dusted through a cyclone. Fluidizing gas from the cooler chamber is also de-dusted through a cyclone and recycled to the fluidizing bed. The amount of dust collected in the fluidizing gas from a fluidized bed is significant and must be removed.
JP 5-253468 A1 teaches introducing a nitrogen gas into a vessel surrounding a dispensing cone at the bottom of a reaction chamber to indirectly cool a product, solid-gas mixture in the cone without causing turbulence wit
Boveri Giuseppina R.
McGehee James F.
Sechrist Paul A.
Acquah Samuel A.
Paschall James C.
Tolomei John G.
UOP LLC
LandOfFree
Process and apparatus for cooling polymer in a reactor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and apparatus for cooling polymer in a reactor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and apparatus for cooling polymer in a reactor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3234964