Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
  • B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
  • B01J8/1818—Feeding of the fluidising gas
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
  • B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
  • B01J8/1836—Heating and cooling the reactor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B9/00—Making granules
  • B29B9/16—Auxiliary treatment of granules
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/88—Post-polymerisation treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/36—After-treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B9/00—Making granules
  • B29B9/16—Auxiliary treatment of granules
  • B29B2009/165—Crystallizing granules
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B9/00—Making granules
  • B29B9/02—Making granules by dividing preformed material
  • B29B9/06—Making granules by dividing preformed material in the form of filamentary material, e.g. combined with extrusion
  • B29B9/065—Making granules by dividing preformed material in the form of filamentary material, e.g. combined with extrusion under-water, e.g. underwater pelletizers

Definitions

• This invention relates to the removal of residual acetaldehyde from polyester particles.
• a conventional process for the preparation of a polyethylene terephthalate based resin is characterized as a two stage process: a melt phase process which includes the esterification and polycondensation reactions, and a solid state polymerization process for increasing the molecular weight of the polymer in the solid state rather than in the melt.
• PET polyethylene terephthalate based resin
• a solid state polymerization process PET is exposed to temperatures of 200-230 0 C and a constant counter-current flow of nitrogen through the resin for a significant length of time.
• the molecular weight of the resin is increased in the melt phase up to an It.V. of about 0.55 to 0.65, followed by peptization, after which the pellets are crystallized, and then solid state polymerized with an optional annealing step after crystallization.
• the particles are exposed to a counter- current flow of nitrogen gas to carry off ethylene glycol, water, and/or other condensates generated during polycondensation.
• nitrogen also minimizes the oxidative degradation of the PET resin at solid stating temperatures.
• the nitrogen gas also helps safeguard against oxidation of antimony metal in resins containing reduced antimony as a reheat agent.
• a process comprising introducing polyester polymer particles containing residual acetaldehyde into a vessel at a temperature within a range of 13O 0 C to 195 0 C to form a bed of particles within the vessel, flowing a gas through at least a portion of the particle bed, and withdrawing finished particles from the vessel having a reduced amount of residual acetaldehyde.
• it is not necessary to introduce a hot flow of gas at high flow rates otherwise required to heat up cool particles to a temperature sufficient to strip acetaldehyde.
• this process provides a benefit in that, if desired, gas introduced, into the vessel at low flow rates and low temperatures can nevertheless be effective to strip acetaldehyde in a reasonable time because the hot particles quickly heat the low flow of gas to the particle temperature.
• the polyester polymer forming the particles is polymerized in the melt phase to an It.V.
• the particles are partially crystallized before being exposed to the flow of gas, or the polyester polymer particles finished by the above method are dried in a dryer and fed to a melt processing zone without solid state polymerizing the particles, or the finished polyester polymer particles have a residual level of acetaldehyde of less than 5 ppm, or the process comprises a combination of any two or more of these features.
• a process comprising crystallizing polyester polymer particles to produce a hot stream of crystallized polyester polymer particles having an average degree of crystallinity of at least 25% and having a particle temperature in excess of 9O 0 C, continuously feeding the hot stream of particles at a temperature of at least 13O 0 C into a vessel before the temperature of the hot stream drops below 5O 0 C, feeding a flow of gas into the vessel and through the stream of particles in an amount sufficient to form a stream of finished polyester polymer particles having a reduced level of residual acetaldehyde relative to the level residual acetaldehyde prior to entry into the vessel.
• heat energy imparted to particles during crystallization is harnessed as the heat energy transferred to the gas in the stripping vessel needed to reduce the level of residual acetaldehyde on or in the particles.
• a process comprising continuously feeding a stream of polyester polymer particles having a residual acetaldehyde level into a vessel, allowing the particles to form a bed and flow by gravity to the bottom of the vessel, continuously withdrawing finished particles from the vessel having a residual acetaldehyde level which is less than the residual acetaldehyde level of the stream of particles fed to the vessel and in no event greater than 10 ppm, continuously introducing a flow of gas into the vessel, and passing the flow of gas through the particles within the vessel, wherein the particles introduced into the vessel have an It.V. of at least 0.72 dL/g obtained without polymerization in the solid state.
• particles having high It.V. and low levels of residual acetaldehyde are made without the need for solid state polymerization, thereby avoiding the costly solid state polymerization step.
• Figure 1 illustrates an acetaldehyde stripping vessel.
• Figure 2 is a process flow diagram for crystallizing and stripping acetaldehyde from polyester polymer particles.
• Figure 3 illustrates a lab model of a modified chromatograph column used to conduct experiments.
• Ranges may be expressed herein as “within” or “between” or from one value to another. In each case, the end points are included in the range. Ranges expressed as being greater than or less than a value exclude the end point(s).
• “comprising” or “containing” or “having” is meant that at least the named compound, element, particle, or method step etc must be present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, etc, even if the other such compounds, material, particles, method steps etc. have the same function as what is named.
• a temperature means the temperature applied to the polymer unless otherwise expressed as the "actual" polymer temperature.
• polyester polymer particles containing residual acetaldehyde are introduced into a vessel at a temperature within a range of 13O 0 C to 195 0 C to form a bed of particles within the vessel, a flow of gas is allowed to pass through at least a portion of the particle bed, and finished particles are withdrawn from the vessel having a reduced amount of residual acetaldehyde.
• a stream of polyester polymer particles is fed into the vessel at an elevated temperature.
• the elevated temperature is at least 13O 0 C, or at least 14O 0 C, or at least 15O 0 C, or at least 16O 0 C, and preferably under 195 0 C 1 or 19O 0 C or less.
• the polyester polymer particles introduced into the vessel contain a level of residual acetaldehyde.
• the invention reduces the amount of acetaldehyde present in the polyester polymer particles fed to the acetaldehyde stripping vessel.
• the level of residual acetaldehyde present in the particles fed to the vessel is greater than 10 ppm, or greater than 20 ppm, or 30 ppm or more, or 40 ppm or more, and even 50 ppm or more.
• Finished particles are particles treated by a flow of gas and having a level of residual acetaldehyde which is less than the level of residual acetaldehyde present on or in the particles fed to the vessel.
• the level of residual acetaldehyde present on the finished particles is 10 ppm or less, or 7 ppm or less, or 5 ppm or less, or 3 ppm or less, or 2 ppm or less, or 1.5 ppm or less.
• the reduction in acetaldehyde is at least 5 ppm, or at least 10 ppm, or at least 20 ppm, or at least 30 ppm.
• the amount of residual acetaldehyde can be measured according to standard techniques in the industry so long as the same test method is used. Otherwise, the test method used to determine the residual acetaldehyde content is ASTM F2013-00 "Determination of Residual Acetaldehyde in Polyethylene Terephthalate Bottle Polymer Using an Automated Static Head-Space Sampling Device and a Capillary GC with a Flame Ionization Detector".
• the polyester polymer particles are exposed to a flow of gas across the particles in the particle bed within the vessel.
• the temperature of the gas as introduced into the vessel containing the bed of particles is desirably within a range of O 0 C to 200 0 C.
• the gas temperature quickly equilibrates to the particle temperature in the bed within the vessel.
• gas introduced at a temperature higher than the temperature of the particles will quickly equilibrate to the lower particle temperature at low gas flow rates relative to the flow rate of the particles introduced into the vessel.
• gas introduced into the vessel at a temperature lower than the temperature of the particles will quickly equilibrate to the higher particle temperature at low gas flow rates relative to the flow rate of the particles introduced into the vessel. While it is possible to introduce gas at high temperature into the vessel, it is unnecessary and represents a waste of energy to heat the gas.
• the gas is introduced into the vessel at a temperature of 7O 0 C or less, or 6O 0 C or less, or 5O 0 C or less, or 4O 0 C or less, and preferably at 1O 0 C or more, or 15 0 C or more, or 2O 0 C or more, and most preferably is introduced at about the ambient air temperature.
• the temperature of the gas exiting the stripping vessel is preferably 195 0 C or less.
• the gas can be introduced into the vessel by any conventional means, such as by a blower, fans, pumps, and the like.
• the gas may flow co-current to or countercurrent to or across the flow of particles through the vessel.
• the preferred flow of gas through the bed of particles is countercurrent to the particle flow through the bed.
• the gas can be introduced at any desired point on the vessel effective to reduce the level of acetaldehyde on the particles fed to the vessel.
• the gas introduction point in to the lower half of the bed height, and more preferably to the lower ⁇ A of the bed height.
• the gas flows through at least a portion of the particle bed, preferably through at least 50 vo!ume% of the bed, more preferably through at least 75% of the particle bed volume.
• any gas is suitable for use in the invention, such as air, carbon dioxide, and nitrogen.
• gases are more preferred than others due to the ready availability and low cost.
• air rather than nitrogen would lead to significant operating cost improvements.
• nitrogen gas was required in operations which pass a hot flow of gas through a bed of particles, such as in a crystallizer, because nitrogen is inert to the oxidative reactions which would otherwise occur between many polyester polymers and ambient oxygen resulting in pellet discoloration.
• the gas contains less than 90 vol% nitrogen, or less than 85 vol% nitrogen, or less than 80 vol% nitrogen.
• the gas contains oxygen in an amount of 17.5 vol% or more.
• air at ambient composition the composition of the air at the plant site on which the vessel is located
• air which is not separated or purified is preferred.
• ambient air is fed through the gas inlet. While the air can be dried if desired, it is not necessary to dry the air since the object of the invention is to strip acetaldehyde from the particles.
• Any vessel for containing particles and allowing a feed of gas and particles into and out of the vessel is suitable.
• a vessel having at least an inlet for gas, and inlet for the polyester polymer particles, an outlet for the gas, and an outlet for the finished particles.
• the vessel preferably insulated to retain heat.
• the gas inlet and the finished particle outlet is desirably located below the gas outlet and the particle inlet, preferably with the latter being toward the top of the vessel and the former being toward the bottom of the vessel.
• the gas is desirably introduced into the bed within the vessel at about ⁇ A or %, of the bed height within the vessel.
• the particles are preferably introduced at the top of the vessel, and move by gravity to the bottom of the vessel, while the gas preferably flows countercurrent to the direction of the particle flow.
• the particles accumulate within the vessel to form a bed of particles, and the particles slowly descend down the length of the vessel by gravity to the finished particle outlet at the bottom of the vessel.
• the bed height is not limited, but is preferably at a substantially constant height in a continuous process and is at least 75% of the height of the stripping zone containing the particles within the vessel.
• the vessel preferably has an aspect ratio UD of at least 2, or at least 4, or at least 6.
• the process can be conducted in a batch or semi batch mode in which as the particles would not flow and the stream of gas can be passed through the bed of particles in any direction
• the process is preferably continuous in which a stream of particles continuously flows from the particle inlet to the finished particle as the particles are fed to the vessel.
• a suitable gas flow rate introduced into the vessel and passing through at least a portion of the particle bed is one which is sufficient to reduce the amount of residual acetaldehyde on the particles introduced into the vessel.
• the gas flow rate at the gas inlet is low.
• suitable gas flow rates introduced into the vessel are at least 0.0001 standard cubic feet per minute (SCFM), or at least 0.001 SCFM, or at least 0.005 SCFM.
• SCFM standard cubic feet per minute
• High flow rates are also suitable, but not necessary, and should be kept sufficiently low to avoid unnecessary energy consumption by the gas pumps, fans, or blowers.
• the gas flow rate in the process of the invention is preferably not any higher than 0.15 SCFM, or not higher than 0.10 SCFM, or not higher than 0.05 SCFM, or even not higher than 0.01 SCFM for every one (1 ) pound of charged particles per hour.
• the optimal flow rate is desirably set to provide the needed level of acetaldehyde removal without unnecessary energy consumption.
• the gas is quickly heated within the vessel by the hot particles, thereby providing a hot gas throughout a substantial portion of the particle bed within the vessel effective to strip residual acetaldehyde from the particles.
• suitable devices to move the gas through the vessel are advantageously fans or blowers, although any suitable device for providing a motive force to a gas can be used.
• the residence time of the particles can be shortened by increasing the temperature at which stripping occurs. This temperature is largely controlled by the temperature of the particles introduced into the vessel. The heat transfer from the particles rapidly heat the gas after it enters the vessel. At the point where the gas enters the vessel, the particles undergo a temperature change depending on the flow rate and temperature of the gas.
• An additional advantage of this process is the capability to integrate the heat energy between different steps for producing polyester polymer particles in that the hot gas stream exiting the vessel can now be used to provide heat transfer to other suitable parts of a polyester polymer plant or as a source of combustion, such as a source of hot gas to a furnace to lower the energy requirements of the furnace.
• polyester polymer resin becomes much more economical if the crystallized particles introduced into the acetaldehyde stripping zone do not have to be heated up to temperature after crystallization. Allowing the crystallized particles to cool after crystallization, followed by heating the particles back up to the desired introductory temperature for acetaldehyde stripping, wastes energy.
• polyester polymer particles are crystallized in a crystallization zone, discharged as a stream of particles from the crystallization zone at particle temperatures in excess of 9O 0 C, or in excess of 100 0 C 1 or in excess of 12O 0 C, or in excess of 13O 0 C, or even in excess of 14O 0 C, and before the stream of particles is allowed to drop to a temperature below 5O 0 C, or below 7O 0 C, or below 9O 0 C, or below 13O 0 C, the stream of hot particles is fed to an acetaldehyde stripping zone in which a flow of gas is introduced at a temperature within a range of about O 0 C to 25O 0 C, and the gas is passed through the stream of polyester polymer particles in an amount sufficient to form a stream of finished polyester polymer particles having a reduced level of the residual acetaldehyde.
• the degree of crystallinity of the polyester polymer particles is not particularly limited. It is preferred to employ crystallizable polyester polymers.
• the process of the invention is capable of producing high It.V. polyester polymer particles having low levels of residual acetaldehyde ready to be shipped or fed to a dryer feeding an injection molding machine or extruder for making an article, such as sheet or preforms. To reduce the tendency of the particles to stick to each other in the dryer, it is preferred to feed the dryer with partially crystallized particles. Therefore, in one embodiment, the polyester polymer particles fed to the acetaldehyde stripping zone are partially crystallized, preferably to a degree of crystallinity of at least 25%, or at least 30%, or at least 35%, and up to about 60%. The particles can be crystallized to a higher degree of crystallinity, but satisfactory results in decreasing the level of particles agglomeration can be obtained within these ranges.
• the pressure within the vessel is not particularly limited.
• the vessel can be maintained close to ambient conditions, with a slight amount of pressure to force gas into the vessel.
• a slight pressure gradient will exist if hot particles are introduced from the air inlet to the air outlet.
• a pressure gradient also exists due to the pressure drop from friction of the gas on the pellets.
• the pressure within the vessel measured at the gas inlet close to the gas inlet/vessel junction ranges from about 0 psig to about 30 psig, preferably from about 0 psig to about 10 psig, or from about 0 psig to 5 psig.
• the residence time of the particles in contact with the flow of gas within the vessel is also not particularly limited. Suitable residence times range from 2 hours, or from 10 hours, or from 18 hours, and up to about 48 hours, or 36 hours, or 30 hours.
• the process of the invention provides the flexibility of adjusting a number of variables to maintain a constant particle It.V. and to mitigate discoloring the particles.
• the process variables include the.particle introductory temperature, the particle residence time, the gas flow rate, and the gas introductory temperature.
• Optimal process conditions to minimize oxidation reactions, discoloration, maintain the It.V. of the particles , and remove acetaldehyde while keeping the production costs low are to introduce the gas at ambient temperature, to feed particles within a range of 15O 0 C to 17O 0 C into a vertical cylindrical vessel at an air flow rate ranging from 0.002 SCFM to 0.009 SCFM per 1 Ib of PET.
• the size of the vessel is such that the residence time of the pellets averages about 10 to 24 hours.
• the process of the invention provides an advantageous low cost means for reducing residual acetaldehyde from a polyester polymer having a high molecular weight and high It.V., such as at least 0.70 dL/g.
• the low level of acetaldehyde may also be obtained without the need for adding an acetaldehyde scavenging compound into the melt phase for the production of the high It.V. polyester polymer.
• a polyester polymer resin having an It.V. of at least 0.70 dL/g and 5 ppm or less acetaldehyde without solid state polymerizing the polymer;
• the polyester polymer is polymerized in the melt to a relatively low It.V. of 0.5 to about 0.65 dL/g partly because a further increase in It.V. results in the build up of unacceptably high levels of acetaldehyde.
• the molecular weight of the polymer is further advanced in the solid state rather than in a melt to avoid further increased, and to actually decrease, the levels of residual acetaldehyde.
• to solid state polymerization process may be avoided altogether while obtaining a particle with low residual acetaldehyde.
• a stream of polyester polymer particles having a residual acetaldehyde level are fed continuously into a vessel, allowed to form a bed and flow by gravity to the bottom of the vessel, continuously withdrawn from the vessel as finished particlesl having a residual acetaldehyde level which is less than the residual acetaldehyde level of the stream of particles fed to the vessel and in no event greater than 10 ppm, continuously introducing a flow of gas into the vessel, and passing the flow of gas through the particles within the vessel, wherein the particles introduced into the vessel have an ItV. of at least 0.72 dL/g obtained without polymerization in the solid state.
• the finished particles are directly or indirectly packaged into shipping containers, which are then shipped to customers or distributors. It is preferred to subject the crystallized particles to any process embodiment described herein without solid state polymerizing the particles at any point prior to packaging the particles into shipping containers. With the exception of solid state polymerization, the particles may be subjected to numerous additional processing steps in-between any of the expressed steps.
• Shipping containers are containers used for shipping over land, sea or air. Examples include railcars, semi-containers, Gaylord boxes, and ship hulls.
• the stripping process is conducted at a temperature low enough where the polymer does not polycondense and build up molecular weight.
• process conditions are established such that the It.V. differential measured as the ItV. of the finished polyester polymer and the It.V. of the polyester polymer fed to the acetaldehyde stripping zone, is less than +0.025 dL/g, or +0.020 dL/g or less, or +0.015 dL/g or less, or +0.010 dL/g or less, and preferably -0.02 dl_/g or more, or -0.01 dL/g or more, and most preferably close to 0, within experimental error.
• the intrinsic viscosity is the limiting value at infinite dilution of the specific viscosity of a polymer. It is defined by the following equation:
• Instrument calibration involves replicate testing of a standard reference material and then applying appropriate mathematical equations to produce the "accepted" I. V. values.
• the intrinsic viscosity (ItV or ⁇ int ) may be estimated using the Billmeyer equation as follows:
• L* finished polyester polymer - L* of the particle feed is 5 or less, or 3 or less, or 2 or less, and desirably greater than -3, or greater than -2, or greater than -1.
• Preferred L* value differentials are close to 0. While positive changes where the L* is actually increased in the finished polymer are acceptable and even desirable, consideration should be taken into account as to the reason why the L* is increased. In some cases, L* can increase due to the oxidation of a metal, which may or may not be a significant consideration depending upon the function of the metal. If the metal is present as a reheat additive, its function as a reheat additive will diminish if oxidized even though the L* color brightness increases.
• the amount of metal present can be increased proportionately to allow for the presence of sufficient elemental metal to act as a reheat additive, but in many cases, the amount of metal remaining after its oxidation to function as a reheat agent is a balance against the additional brightness obtained as indicated by the increase in L*.
• the particular end use application and cost will control the degree of increase in L* and reduction in reheat which can be tolerated. However, if the function of the metal is already served or not impacted by an oxidation reaction, then an increase in L* to any degree may actually be desired.
• Another advantage of the invention is that the stripping process is conducted under conditions to prevent the polymer from exhibiting a significant change in color in the direction toward more yellowness. Accordingly, there is provided another embodiment in which process conditions are established such that the b* color value of the finished polyester polymer is less than the b* color value of the polyester polymer fed to the acetaldehyde stripping zone, or is unchanged, or is greater than by not more than 1.0, but is preferably unchanged or less.
• a finished particle b* color value of -2.1 is less than a feed particle b* color value of -1.5.
• a finished b* color value of +2.0 is less than a feed particle b* color value of +2.7.
• b * color value shifts in the direction toward the blue end of the b* color spectrum is desirable. In this way, the process conditions do not add a substantially greater yellow hue to the particles.
• the measurements of L*, a*, and b* color values are conducted according to the following methods.
• the instrument used for measuring color should have the capabilities of a HunterLab UltraScan XE, model U3350, using the CIELab Scale(L*, a*, b*), D65 (ASTM) illuminant, 10° observer, integrating sphere geometry. Particles are measured in RSIN reflection, specular component included mode according to ASTM D6290, "Standard Test Method for Color Determination of Plastic Pellets". Plastic pellets are placed in a 33-mm path length optical glass cell, available from HunterLab, and allowed to settle by vibrating the sample cell using a laboratory Mini-Vortexer (VWR International, West Chester, PA). The instrument for measuring color is set up under ASTM E1164 "Standard Practice for Obtaining Spectrophotometric Data for Object- Color Evaluation.” Color is determined on a sample by using its absolute value - the value determined by the instrument.
• ⁇ Hm is the heat of melting of the polymer determined by integrating the area under the curve (Joule / gram) of the melting transition(s) observed during the first scan of 25 0 C to 300 0 C at 2O 0 C per minute in a Perkin Elmer differential scanning calorimeter and ⁇ Hm 0 is a reference value of 140.1 J/g and represents the heat of melting if the polyethylene terephthalate is 100% crystalline.
• the shape of the polyester polymer particles is not limited, and can include regular or irregular shaped discrete particles without limitation on their dimensions, including , stars, spheres, spheroids, globoids, cylindrically shaped pellets, conventional pellets, pastilles, and any other shape, but particles are distinguished from a sheet, film, preforms, strands or fibers.
• the number average weight (not to be confused with the number average molecular weight) of the particles is not particularly limited. Desirably, the particles have a number average weight of at least 0.10 g per 100 particles, more preferably greater than 1.0 g per 100 particles, and up to about 100 g per 100 particles.
• the polyester polymer of this invention is any thermoplastic polyester polymer.
• a polyester thermoplastic polymers of the invention are distinguishable from liquid crystal polymers and thermosetting polymers in that thermoplastic polymers have no ordered structure while in the liquid (melt) phase, they can be remelted and reshaped into a molded article, and liquid crystal polymers and thermosetting polymers are unsuitable for the intended applications such as packaging or stretching in a mold to make a container.
• polyester polymer desirably contains alkylene terephthalate or alkylene naphthalate units in the polymer chain. More preferred are polyester polymers which comprise:
• a carboxylic acid component comprising at least 80 mole% of the residues of terephthaiic acid, derivates of terephthalic acid, naphthalene- 2,6-dicarboxylic acid, derivatives of naphthalene-2,6-dicarboxylic acid, or mixtures thereof, and
• a hydroxyl component comprising at least 60 mole%, or at least 80 mole%, of the residues of ethylene glycol or propane diol, based on 100 mole percent of carboxylic acid component residues and 100 mole percent of hydroxyl component residues in the polyester polymer.
• polyesters such as polyethylene terephthalate are made by reacting a diol such as ethylene glycol with a dicarboxylic acid as the free acid or its dimethyl ester to produce an ester monomer and/or oligomers, which are then polycondensed to produce the polyester. More than one compound containing carboxylic acid group(s) or derivative(s) thereof can be reacted during the process. All the compounds containing carboxylic acid group(s) or derivative(s) thereof that are in the product comprise the "carboxylic acid component.” The mole % of all the compounds containing carboxylic acid group(s) or derivative(s) thereof that are in the product add up to 100.
• the “residues” of compound(s) containing carboxylic acid group(s) or derivative(s) thereof that are in the product refers to the portion of said compound(s) which remains in the oligomer and/or polymer chain after the condensation reaction with a compound(s) containing hydroxyl group(s).
• More than one compound containing hydroxyl group(s) or derivatives thereof can become part of the polyester polymer product(s). All the compounds containing hydroxyl group(s) or derivatives thereof that become part of said product(s) comprise the hydroxyl component. The mole % of all the compounds containing hydroxyl group(s) or derivatives thereof that become part of said product(s) add up to 100. The residues of hydroxyl functional compound(s) or derivatives thereof that become part of said product refers to the portion of said compound(s) which remains in said product after said compound(s) is condensed with a compound(s) containing carboxylic acid group(s) or derivative(s) thereof and further polycondensed with polyester polymer chains of varying length.
• the mole% of the hydroxyl residues and carboxylic acid residues in the product(s) can be determined by proton NMR.
• the polyester polymer comprises:
• a carboxylic acid component comprising at least 90 mole%, or at least 92 mole%, or at least 96 mole% of the residues of terephthalic acid, derivates of terephthalic acid, naphthalene-2,6-dicarboxylic acid, derivatives of naphthalene-2,6-dicarboxylic acid, or mixtures thereof, and
• a hydroxyl component comprising at least 90 mole%, or at least 92 mole%, or at least 96 mole % of the residues of ethylene glycol, based on 100 mole percent of the carboxylic acid component residues and 100 mole percent of the hydroxyl component residues in the polyester polymer.
• the reaction of the carboxylic acid component with the hydroxyl component during the preparation of the polyester polymer is not restricted to the stated mole percentages since one may utilize a large excess of the hydroxyl component if desired, e.g. on the order of up to 200 mole% relative to the 100 mole% of carboxylic acid component used.
• the polyester polymer made by the reaction will, however, contain the stated amounts of aromatic dicarboxylic acid residues and ethylene glycol residues.
• Derivates of terephthalic acid and naphthalane dicarboxylic acid include C 1 - C 4 dialkylterephthalat.es and Ci - C 4 dialkylnaphthalates, such as dimethylterephthalate and dimethylnaphthalate.
• the carboxylic acid component(s) of the present polyester may include one or more additional modifier carboxylic acid compounds.
• additional modifier carboxylic acid compounds include mono-carboxylic acid compounds, dicarboxylic acid compounds, and compounds with a higher number of carboxylic acid groups.
• Examples include aromatic dicarboxylic acids preferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 12 carbon atoms, or cycloaliphatic dicarboxylic acids preferably having 8 to 12 carbon atoms.
• modifier dicarboxylic acids useful as an acid component(s) are phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyI-4,4'-dicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like, with isophthalic acid, naphthalene-2,6-dicarboxylic acid, and cyclohexanedicarboxylic acid being most preferable.
• the hydroxyl component of the present polyester may include additional modifier mono-ols, diols, or compounds with a higher number of hydroxyl groups.
• modifier hydroxyl compounds include cycloaliphatic diols preferably having 6 to 20 carbon atoms and/or aliphatic diols preferably having 3 to 20 carbon atoms.
• diols include diethylene glycol; triethylene glycol; 1,4-cyclohexanedimethanol; propane-1,3-diol; butane-1,4-diol; pentane-1 ,5-diol; hexane-1,6-diol; 3-methylpentanediol- (2,4); 2- methylpentanediol-(1 ,4); 2,2,4-trimethylpentane-diol-(1 ,3); 2,5- ethylhexanediol- (1,3); 2,2-diethyl propane-diol-(1 , 3); hexanediol-(1,3); 1 ,4-di-(hydroxyethoxy)- benzene; 2,2-bis-(4-hydroxycyclohexyl)-propane; 2,4- dihydroxy-1, 1,3,3- tetramethyl-cyclobutane;
• the polyester pellet compositions may include blends of polyalkylene terephthalates and/or polyalkylene naphthalates along with other thermoplastic polymers such as polycarbonate (PC) and polyamides. It is preferred that the polyester composition should comprise a majority of the polyester polymers, more preferably in an amount of at least 80 wt.%, or at least 95 wt.%, and most preferably 100 wt.%, based on the weight of all thermoplastic polymers (excluding fillers, inorganic compounds or particles, fibers, impact modifiers, or other polymers which may form a discontinuous phase). It is also preferred that the polyester polymers do not contain any fillers, fibers, or impact modifiers or other polymers which form a discontinuous phase.
• polyester compositions can be prepared by polymerization procedures known in the art sufficient to effect esterification and polycondensation.
• Polyester melt phase manufacturing processes include direct condensation of a dicarboxylic acid with the diol, optionally in the presence of esterification catalysts, in the esterification zone, followed by polycondensation in the prepolymer and finishing zones in the presence of a polycondensation catalyst; or ester exchange usually in the presence of a transesterification catalyst in the ester exchange zone, followed by prepolymerization and finishing in the presence of a polycondensation catalyst, and each may optionally be solid stated according to known methods.
• the method for solidifying the polyester polymer from the melt phase process is not limited.
• molten polyester polymer from the melt phase may be directed through a die, or merely cut, or both directed through a die followed by cutting the molten polymer.
• a gear pump may be used as the motive force to drive the molten polyester polymer through the die.
• the molten polyester polymer may be fed into a single or twin screw extruder and extruded through a die, optionally at a temperature of 19O 0 C or more at the extruder nozzle.
• the polyester polymer can be drawn into strands, contacted with a cool fluid, and cut into pellets, or the polymer can be pelletized at the die head, optionally underwater.
• the polyester polymer melt is optionally filtered to remove particulates over a designated size before being cut.
• Any conventional hot pelletization or dicing method and apparatus can be used, including but not limited to dicing, strand pelletizing and strand (forced conveyance) pelletizing, pastillators, water ring pelletizers, hot face pelletizers, underwater pelletizers and centrifuged pelletizers.
• the polyester polymer may also be crystallized if desired as noted above.
• the method and apparatus used to crystallize the polyester polymer is not limited, and includes thermal crystallization in a gas or liquid.
• the crystallization may occur in a mechanically agitated vessel; a fluidized bed; a bed agitated by fluid movement; an un-agitated vessel or pipe; crystallized in a liquid medium above the T 9 of the polyester polymer, preferably at 140 0 C to 190 0 C; or any other means known in the art.
• the polymer may be strain crystallized.
• the polymer may also be fed to a crystallizer at a polymer temperature below its T 9 (from the glass), or it may be fed to a crystallizer at a polymer temperature above its T 9 .
• molten polymer from the melt phase polymerization reactor may be fed through a die plate and cut underwater, and then immediately fed to an underwater thermal crystallization reactor where the polymer is crystallized underwater.
• the molten polymer may be cut, allowed to cool to below its T 9 , and then fed to an underwater thermal crystallization apparatus or any other suitable crystallization apparatus.
• the molten polymer may be cut in any conventional manner, allowed to cool to below its T 9 , optionally stored, and then crystallized.
• the articles of manufacture are not limited, and include sheet and bottle preforms.
• the bottle preforms can be stretch blow molded into bottles by conventional processes.
• the bottles made from the particles of the invention, or made by any of the processes of the invention, or made by any conventional melt processing technique using the particles of the invention.
• containers be made from particles made according to the process of this invention, but other items such as sheet, film, bottles, trays, other packaging, rods, tubes, lids, filaments and fibers, and other molded articles may also be manufactured using the polyester particles of the invention.
• Beverage bottles made from polyethylene terephthalate suitable for holding water or carbonated beverages, and heat set beverage bottle suitable for holding beverages which are hot filled into the bottle are examples of the types of bottles which are made from the crystallized pellets of the invention.
• Figures 1 and 2 illustrate non-limiting process flow embodiments describing how the invention could be practiced.
• a stream of hot crystalline polyester particles containing a level of residual AA greater than 10 ppm is introduced into a vessel 105 through particle inlet pipe 101.
• the particles form a bed 106 within the vessel 105 and move downward toward the vessel outlet 103 to form a stream of crystalline polyester particles having a reduced level of residual acetaldehyde of 10 ppm or less.
• a stream of gas is fed into the vessel through a side inlet 103 toward the lower 1/3 of the vessel height.
• Other suitable locations include a bottom inlet closer toward the particle outlet 103, or a top feed.
• the gas is removed from the vessel 105 through gas outlet 104.
• the location of 103 and 104 relative to each other are preferably chosen so that gas flows across the majority of the particles in the bed 106.
• the polyester particle stream flowing into particle inlet 101 are at a temperature of 120 to 180 0 C, and contain more than 10 ppm acetaldehyde.
• the stream rate of the particles is not limited as this process will be effective at a very wide range of rates.
• the size of the vessel 105 is sufficient to contain the bed 106.
• the vessel 105 is insulated to prevent unnecessary heat losses.
• the average temperature of the particles in the bed 106 is within 12O 0 C and 180 0 C and will depend primarily on the temperature, rate, and feed location of particle stream though particle inlet 101, the temperature, rate, and feed location of gas through inlet 102, and heat losses from the vessel 105. At low inlet gas rates, the gas stream will not have a large impact on the average temperature of particles in the bed 106.
• Particles are removed 106 from the vessel containing less than 10 ppm acetaldehyde.
• the temperature of stream 103 is not limited and depends primarily on the temperature and rate of incoming particles 101 the temperature and rate of inlet gas 102, and heat losses from the vessel 105.
• the level of acetaldehyde in stream 103 depends primarily on the rate and acetaldehyde content of particles in inlet stream 101, the temperature and mass of particles in bed 106, the rate and temperature of gas 102, fed to the vessel, and the rate at which acetaldehyde is chemically generated in the polymer during the stripping process.
• the rate of pellet removal 106 is on average the same as the rate of particles at the inlet 101.
• these rates may be intentionally set differently to adjust the mass of the bed 106.
• the rate at the gas inlet 102 is preferably greater than 0.0001 SCFM per Ib/hr of particles 101 fed to the stripper. There is a balance between having sufficient gas to dilute the acetaldehyde and ensure a large driving force for acetaldehyde to leave the polymer particles, versus the cost of providing higher gas rates to the stripper. At the low gas rates that are preferred, the temperature of the gas is not limited as it does not have a large impact on the temperature of particles in the bed 106.
• the gas temperature can have a significant impact on the temperature of bed 106 and must be chosen to give a bed temperature between 120 and 180 0 C.
• the inlet gas stream 102 is preferably air substantially free of acetaldehyde.
• the rate at the gas outlet 104 is on average the same as the average rate of the gas inlet 102.
• the temperature is not limited, and will depend primarily on the temperature of the bed 106 through which the gas has last flowed before exiting the vessel.
• the concentration of acetaldehyde at the gas outlet 104 will depend on the amount of acetaldehyde removed from the polymer particles and the gas flow rate.
• FIG 2 is another non-limiting example of an embodiment in which the heat energy from the particles imparted during crystallization is integrated with the energy required for stripping AA.
• a molten polyester polymer stream is fed to an underfluid cutter 203 through line 201 using a gear pump 202 as the motive force. While an underfluid cutter is illustrated, any conventional type of pelletizer can be employed to make pellets which are eventually fed to a crystallizer.
• the source of the molten polymer may be from pellets fed through an extruder to the gear pump 202 or from the melt phase high polymerizer or finisher (not shown) fed to the gear pump 202.
• the liquid medium is fed into cutter 203 through a feed pipe 206 into the cutter 203.
• a suitable liquid medium comprises water entering the housing at a fluid velocity of 1 ft/s to 8 ft/s, preferably 1 ft/s to 4 ft/s.
• the flow of liquid medium through the cutter 203 sweeps the cut particles away from the cutter and into the outlet pipe 208 for transport into a crystallizer 209.
• the crystallizer 209 is an underfluid crystallizer having a high liquid temperature in which the liquid is kept under a pressure equal to or greater than the vapor pressure of the liquid to keep the fluid in the liquid state.
• Crystallizer 203 comprises of a series of pipes in a coil or stacked to form a three dimensional box or any other shape, including a long linear tube.
• the liquid (e.g. water) temperature at the outlet pipe 208 and through the crystallizer pipes 209 is above the T 9 of the particles, and preferably at any temperature within a range of greater than 100 0 C to 190 0 C, and more preferably from 140 to 18O 0 C. While underfluid crystallizer is illustrated, any conventional crystallizer is suitable.
• a suitable crystallization method includes passing a countercurrent gas of hot nitrogen or air or both at a gas feed temperature of 16O 0 C to 22O 0 C through a bed of solid pellets agitated by the gas flow or by mechanical agitation, or alternatively, the heat source to the pellets is provided by heat transfer through the jacketed walls of a vessel.
• the particles attain a degree of crystallization ranging from 20% to about 65%, or about 25% to about 50% after discharge from the crystallizers.
• the crystallized particles are fed through pipe 210 to a particle/liquid separator 211.
• a separator 211 is not needed, however, if conventional crystallization techniques are applied which use a gas or the walls of a vessel as the heat transfer source.
• the method or equipment for separating particles from liquid is not limited. Examples of suitable separators include centrifugal dryers, solid or screen bowl centrifuges, pusher centrifuges, or simple filters or screens into which the particle/liquid slurry is fed with the liquid flowing through the screen and out through liquid outlet pipe 212.
• the liquid in pipe 212 may optionally be re-circulated as a source of liquid for the feed into the underfluid cutter
• the particles are discharged from separator 211 through particle outlet pipe 213 and fed into vessel 105, the AA stripping vessel.
• the particles can be fed directly or indirectly from the crystallizer to the AA stripping vessel 105.
• the particles fed to the vessel 105 have high heat energy imparted by the crystallizer 209. The heat energy in the particles is used as the source of heat transferred to the gas supplied to the vessel 105 through line 103 which flows through the particle bed 106.
• the polyester particle stream is fed into vessel 105 at a temperature of at least 5O 0 C.
• the crystallized particle stream discharged from the separator 211, or discharged from a conventional crystallizer is typically at a temperature in excess of 9O 0 C, or in excess of 12O 0 C, or in excess of 13O 0 C.
• the particles may cool somewhat through heat losses to the piping, or heat losses in the separator 211 , or within optional equipment between the separator 211 and the vessel 105.
• the temperature of the crystallized particles preferably does not drop below 5O 0 C, or does not drop below 75 0 C, or does not drop below 9O 0 C, or does not drop below 100 0 C, or does not drop below 110 0 C.
• the stream of crystallized particles is fed into the stripping vessel 105 through particle inlet pipe 101 at a temperature of at least 13O 0 C, while a flow of gas is fed through gas inlet 102 and through the bed of crystallized particles 106.
• the feed temperature of at least 13O 0 C is preferred because at lower temperatures, the residence time of the particles in th vessel is undesirably long.
• Finished particles are discharged through particle outlet line 103 and the gas is discharged preferably toward the top of the vessel 105 through a gas discharge line 104.
• the stream of crystallized particles can be reheated to at least 13O 0 C by any conventional heating means. Even though thermal energy may be to be applied to reheat the stream of crystallized particles, the integrated process requires the application of less energy than would be required if, for example, the particle temperature falls to ambient temperature. Suitable heating devices include pre-heaters or thermal screws.
• This set of experiments illustrates the effects of time and temperature on the residual acetaldehyde, molecular weight, color, and crystallinity of the polyester polymer particles.
• Three different polyethylene terephthalate based polymers representing three different geometries were placed in a fluidized bed reactor and exposed to either 15O 0 C, 16O 0 C, or 185 0 C temperatures and a low air flow rate for at least 24 hours. More specifically, the experiments were conducted in a column reactor comprised of a modified chromatography column to allow for the introduction of a gas stream over the polymer particles and to regulate the temperature of the polymer particles, a round bottom flask, and a condensor.
• the column reactor is illustrated in Figure 3.
• the outside glass wall 301 contains an inside glass wall 302 within which is a chamber303 for polymer particles.
• a fritted glass support 304 At the bottom of the chamber 303 is a fritted glass support 304, through which is fed a gas at a gas inlet port 306 flowing through a coil of glass tubing 305.
• a connector 307 for a round bottom flask and a connector 308 for a condenser is provided on the outside glass wall.
• the temperature of the column reactor, polymer particles within the column and the gas flowing over the polymer particles in the column is regulated by refluxing a suitable solvent in a round bottom flask connected to the column at inlet 307 .
• the experiments were conducted in two stages by charging the vessel with 1.5 pounds (680 g) of a partially crystallized PET resin.
• the resin was charged to the vessel at 7:00 a.m., and about 60 grams samples were collected at each time interval indicated on Table 1.
• the resin was charged to the vessel at 5:00 p.m., and about 60 grams samples were collected at each time interval as indicated on Table 1 below.
• the samples were submitted for residual acetaldehyde analysis using the test method as described above, for inherent viscosity test measurements as described above, to color (reflectance) analysis as described above, and for %crystallinity analysis as described above.
• the polyester polymer was a polyethylene terephthalate based polymer having 2.0 mol% (of total dicarboxylic acid content) isophthalic acid modification.
• the average particle dimensions were about 1.84 x 2.68 x 2.43 mm, 2.45 x 3.09 x 3.90 mm, and 2.75 mm diameter, respectively.
• the air flow for each experiment was set at 0.0067 SCFM using ambient plant air.
• the amount of solvent charged to the round bottom flask connected to the column reactor was 1000 ml.
• the residence time of the particles was varied and are detailed in Tables 1 through 7.in each case.
• the polymer charge was 1.5 lbs in each case..
• the polymer was added to the column reactor after the column had reached the target temperature of 15O 0 C, 16O 0 C, or 185 0 C, depending upon the solvent used in each set of experiments.
• the temperature of the polymer particles was measured by a thermocouple placed on the fritted glass support (4 in Figure 3)

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