MXPA98000121A - Process for the recovery of a polymer microporose polyester, solid, from a recycling current and products made by me - Google Patents

Abstract

The present invention relates to: A method for recovering the polyester polymer as a microporous solid from a recycle stream of the mixed polymer, characterized in that it comprises: a) contacting the recycle stream of mixed polymer at a high temperature with a selective solvent wherein the polyester polymers are soluble and other polymers present in the recycle stream are substantially insoluble to form a solution of polyester polymer in the selective solvent, b) when the concentration of polyester in the solution is below 35% by weight. weight, increase it over that value, c) cool the selective solvent solution to form a solid material that has a phase of interconnection of solid polymer domains rich in polyester polymer and a phase of solvent domains rich in the selective solvent; extract the selective solvent from the solid material to form a micropore solid

Description

PROCESS FOR THE RECOVERY OF A POLYESTER POLYMER MICROPOROSO, SOLID, FROM A RECYCLING CURRENT AND PRODUCTS MADE THROUGH THEMSELVES.

FIELD OF THE INVENTION This invention relates to a process for the preparation of PET pellets with a porous, fibrous and sintered morphology; to porous PET products and to an improved process for the polymerization of PET in the solid state.

BACKGROUND OF THE INVENTION The European Patent Application 0.742.251 discloses a method for recovering PET from recycling streams of the mixed polymer typical of that generated by the collection of recycled plastics from streets after consumption. In general, this procedure included the steps of: (1) contacting the waste stream of the mixed polymer with a solvent that selectively dissolves the PET, (2) separating the selective solvent containing PET from the waste of the residual mixed polymer, ( 3) precipitate the PET from the selective solvent solution by means of the use of a non-solvent for the polyethylene terephthalate or by cooling to form a fine powder precipitate of the REF: 26539 crystalline polyethylene terephthalate polymer and (4) remove the selective solvent or the selective / non-solvent solvent from the precipitated PET. In one of the embodiments described, the recycle stream of the mixed polymer is prepared for recycling through conventional passages, such as washing with water and, additionally, it can be chemically washed after washing with water and before of contacting the selective solvent. The recovered PET can be combined with "virgin" PET and then subjected to processing to increase its molecular weight through solid state polymerization. However, the precipitation technique described in this procedure requires the circulation of a large amount of selective solvent or selective / non-solvent solvent in order to retain a viscosity of slurry and reasonable particle morphologies subsequent to precipitation, which gives result in high capital and operating costs. This invention relates to a process for the recovery of the polyester polymer without the need to use large flow rates of solvent and, without the need to precipitate the polyester polymer from the solution, through the solidification of a concentrated solution of the solubilized polyester polymer. in a selective solvent to form a solid material having an interconnection phase of the polymeric polymer-rich solid polymer domains and a phase of solvent domains rich in selective solvent and, d) extracting the selective solvent from the solid material to form a microporous solid polyester polymer. By a "concentrated solution" reference is made to an effective polyester polymer concentration in order to allow the formation of the described solid with polyester-rich and high-solvent-selective domains and, upon solvent extraction from the solid. The process of this invention comprises recovering the polyester polymer as a microporous solid from a recycle stream of the mixed polymer comprising: a) contacting the recycle stream of the mixed polymer at elevated temperature with a selective solvent in which the polymers polyesters are soluble and the other polymers present in the recycle stream are substantially insoluble to form a polyester polymer solution in the selective solvent; b) if the concentration of polyester in said solution is below 35% by weight, increase it above that value; c) cooling the selective solvent solution to form a solid material having an interconnection phase of polymer-rich solid polymer domains and a phase of solvent domains rich in selective solvent; d) extracting the selective solvent from the solid material to form a microporous solid. The new products produced by this process are a solid polyester polymer that possesses polyester domains and solvent domains, where the solvent is of the type that is a solvent for the polyester polymer; it can be molded, extruded and / or cut to form articles having an open microporous structure, where the average pore diameter is between 0.5 and. 100 microns and, preferably, between 0.5 and 50 microns. The product of the invention is useful for filtering, attenuating sound, providing light weight structural members and the release of substances within the pores over time. The microporous polyester polymer can be polymerized in the solid state by heating at an effective temperature to increase the molecular weight of the polyester polymer and thereby allowing the molecular weight increase.

The polyester polymers include a large variety of condensation polymers formed by the combination of a dicarboxylic acid or diester thereof and an alcohol or dihydric glycol. Polyethylene terephthalate (PET) in the recycle stream is generally formed by repeating units derived from terephthalic acid or a diester thereof and ethylene glycol (1,2-ethanediol). However, it will be understood that PET can also be modified with small amounts of other monomers. Said modified PET may contain small amounts of repeating units derived from diacids other than terephthalic acid and / or glycols in addition to ethylene glycol. For example, amounts of isophthalic acid or a naphthalenedicarboxylic acid can be used in the diacid component used when the PET is prepared. The PET that has been modified with a small amount of a diol containing between 3 and 8 carbon atoms is also representative of said modified PET. By way of example, a small amount of 1,4-butanediol or cyclohexanedimethanol can be used in the glycol component used for the preparation of modified PET. Generally, no more than about 15 weight percent of the repeating units in said modified PET will be formed by diacids (or diesters) or diols other than terephthalic acid and ethylene glycol. Other polyesters include polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) and polybutylene naphthalate (PBN). PPT is derived from terephthalic acid or a diester thereof and propylene glycol (e.g., 1,3-propanediol). The PBT is derived from terephthalic acid or a diester thereof and 1,4-butanediol. PEN is derived from a naphthalenedicarboxylic acid such as 2,6-naphthalene dicarboxylic acid, or a diester thereof, and ethylene glycol. PBN is derived from a naphthalenedicarboxylic acid, or a diester thereof, and 1,4-butanediol. PET is the most common polyester currently present in the recycle stream and will be used in an exemplary manner. However, the present invention can be applied to, and is intended to, comprise a wide variety of polyesters, either individually or in combination.

The recycle stream of the mixed polymer collected by commercial recyclers (by means of street collections, etc.) will generally have PET contents between 25 weight percent and 75 weight percent. Due to economic reasons, it is convenient to increase the PET content in this stream. In general, this is achieved by physical separation of non-PET containers from PET bottles. This can be done manually or with an automatic device. Optionally, colored PET containers (e.g., carbonated soft green beverage bottles) can be sorted by the recycler, leaving a recycle stream predominantly free of PET. The classification of the bottles will typically increase the PET content of the recycle stream from 65 weight percent and up to 90 weight percent is generally limited by foreign materials used for labels, caps and bases . PET in the recycle feed stream will usually derive from molded PET in the form of bottles, tray and other containers although they may also derive from other items such as fibers, molded sheets, blister packs, belts and films. Typically, the PET is milled or crushed in the form of "flakes" and loaded into a container filled with water in which many extraneous plastics (high density polyethylene, polypropylene, expanded polystyrene, etc.) will float and can be extracted. easily. By combining bottle separation and a simple dip / float step, the PET fraction can easily be increased to 90 percent by weight or more. PET beverage bottles are generally crushed into flakes that have a cross-sectional area between 10 mm2 and 150 mm.2, in general, between 40 mm2 and 100 mm2. The thickness of the flakes will vary according to the thickness of the wall of the bottles that will be subjected to recycling. PET can contain catalyst deactivators, for example phosphates and other additives such as impact modifiers, process aids, fillers, pigments and dyes (organic and inorganic), ultraviolet light stabilizers and antidegradants. Before the waste containing polyester comes into contact with the selective solvent, it can be subjected to the process through a variety of optional pretreatments. In an optional pre-treatment, the recycle stream of the mixed polymer is contacted with a gum washing solvent to remove the various impurities in the recycle stream of the mixed polymer. Such impurities include, for example, glues, inks, toxic materials, for example pesticides, as well as organoleptic materials. The chemical wash solvent can also remove selected non-PET polymers such as, for example, polyvinyl chloride and polystyrene, from the recycle stream of the mixed polymer. Additionally, the chemical wash solvent serves to reduce the water content, which can also be considered as an impurity, of a recycle stream of the mixed polymer washed with water. The chemical washing solvent of the invention is a solvent that will selectively dissolve at least polyvinyl chloride and, preferably, also polystyrene while not dissolving or depolymerizing PET significantly. Preferred chemical wash solvents dissolve less than 1 part per hundred (pph) of PET, measured as PET parts per 100 parts of solvent at room temperature. Suitable chemical washing solvents can be broadly classified as moderately polar, oxygenated hydrocarbon materials that will not depolymerize PET and, in general, boiling points between 50 ° C and 200 ° C, in order to enable effective dissolution. of the polyvinyl chloride and / or other polymers present in the recycle stream of the mixed polymer. The oxygenated hydrocarbon cites include esters, ethers and ketones with a total ranging from three to sixteen carbon atoms. Such oxygenated hydrocarbons can be aliphatic or cyclic but, in general, they are non-aromatic. In cases where the compounds include alkyl groups, such alkyl groups generally contain between one and four carbon atoms.

A group of chemical washing solvents that is preferred includes methyl ethyl ketone; tetrahydrofuran, tetrahydropyran, cyclopentanone, alkyl substituted cyclopentanones, hexanones, hexanediones, heptanediones, octanediones, alkyl malonates, dioldiacetates (for example, ethylene glycol diacetate, propanediol diacetate and butanediol diacetate), alkyl substituted acetoacetate, 1,3-dioxane , 1,4-dioxane, 1,3-dioxolane, 2-methoxyethyl ether, diethoxymethane, cyclohexanone, alkyl-substituted cyclohexanones, cycloheptanone, alkyl-substituted cycloheptanones, amyl acetate, amyl propionate, mesityl oxide, dibutyl phthalate and dialkylformamide and, all of them will dissolve both polyvinyl chloride and polystyrene. Any of these chemical solvents can be used wet, combined with water. For example, an azeotropic mixture of tetrahydrofuran and water may be employed as the chemical wash solvent. Cyclohexanone, cycloheptanone, alkyl substituted cyclohexanones, alkyl substituted cycloheptanones, amyl acetate, amyl propionate, dioldiacetates, dibutyl phthalate, heptandione and mesityl oxide are particularly useful if polyolefins are present in the recycle stream of the mixed polymer, since these solvents dissolve polyolefins in addition to dissolving polyvinyl chloride and polystyrene. The chemical wash solvent is contacted with the recycle stream of the mixed polymer in ratios ranging from 0.5: 1 to 10: 1 and, preferably, between 1: 1 and 3: 1, based on the weight of the solvent of chemical washing and mixed polymer. The step of chemical washing can be completed with a cycle in which the chemical washing solvent is contacted with the mixed polymer or with multiple washes. When multiple washings are used, the ratio between the solvent and the polymer is lower than that used for a single wash and can provide a purer product. It is also possible to resort to the use of continuous washing, with a subsequent reduction in the amount of washing solvent required in the weight of the polymer. Countercurrent washing is another useful method. The chemical wash solvent can be used at ambient air temperatures and in mild conditions. In order to minimize the necessary contact time, in general, it is preferred to use the chemical washing solvent at elevated temperatures, preferably, between 50 ° C and 200 ° C. Lower temperatures may be required, according to the boiling point of the chemical wash solvent. By way of example, when cyclohexanone is used, the preferred temperature range goes from 125 ° C to 160 ° C. The ceiling limit for the temperature is determined by the boiling point of the chemical washing solvent and the stability of the polymers, and it should not be so high as to decompose the polymers. The contact time necessary to substantially dissolve the polyvinyl chloride and / or other polymers present will vary according to the solvent and the wash temperature but will generally range from about 5 minutes to 60 minutes. Preferably, the chemical washing step is carried out at or near atmospheric pressure, although higher pressures may also be used. The PET can be contacted with the chemical wash solvent following any conventional method and through the use of conventional equipment for the operating conditions employed. The chemical wash step is carried out, for example, by combining the PET and the chemical wash solvent in a stirred tank reactor or in a series of stirred tank reactors. The resulting contaminated chemical wash solvent can be separated from the recycle stream of the residual mixed polymer by gravity separation, filtering, sieving, centrifugation, or other equivalent methods. It is preferable that both chemical wash solvent and practical solvent be removed from the chemically washed residual mixed polymer, since any entrained chemical wash solvent will retain the impurities removed from the mixed polymer. A preferred method for separating the chemical wash solvent from the residual mixed polymer includes the removal of the chemical wash solvent by gravity separation followed by displacement with another solvent, which may be the PET-selective solvent. In the step of dissolving the polyester polymer, the polyester polymer, either PET or a different polyester polymer, is contacted at an elevated temperature with the selective solvent to form a polyester polymer solution solubilized in the solvent. The solvent selectively dissolves the polyester polymer while maintaining the polyester polymer in polymer form and substantially rejects the dissolution of the other polymers present in the recycle stream of the mixed polymer. The size of the polyester polymer particles affects the rate of dissolution of the polyester polymer in the selective solvent (the small particles dissolve more rapidly than the larger particles due to a larger surface area exposed to the solvent). Agitation of the polyester polymer particles in the selective solvent will accelerate the dissolution of the polyester polymer as well as increase the temperature of the selective solvent, provided that the temperature is not so high as to cause the decomposition of the polymers present. The selective solvent used in the invention is a solvent that selectively dissolves the polyester polymer without significantly dissolving other polymers that may be present such as, for example, polyethylene, polypropylene, polystyrene and polyvinyl chloride. Some reduction in the molecular weight of the polyester polymer can be produced, however, the polyester polymer is largely maintained in the form of a polymer. The reduction in molecular weight that occurs in the polyester polymer is adjusted through subsequent processes such as, for example, solid state polymerization, in order to reconstruct the molecular weight. Suitable selective solvents can be broadly classified as moderately polar, aprotic materials that do not disconnate the polyester polymer and boast above 180 ° C in order to allow effective dissolution of the polyester polymer at an elevated temperature. Preferred solvents dissolve less than 1 pph of the other polymers that may be present in the recycle stream of the mixed polymer, measured as polymer parts individually dissolved in a given solvent at elevated temperature (generally comprised between 170 ° C and 250 ° C). ° C). Such solvents include diethyl glutarate, dimethyl succinate, dimethyl sulfoxide, diphenylsulfone, N-methylpyrrolidone and sulpholane. A group of solvents that is preferred includes those considered "natural" for the recovered polyester polymer, which means that the solvent decomposes or can decompose to form raw materials that are useful for the realization of a polyester polymer and similar polyester polymers. Dicarboxylic acids such as terephthalic acid and, glycols such as ethylene glycol, are not included within the group of solvents since these materials will depolymerize the polyester polymer. However, the diesters of dicarboxylic acids, such as dimethyl terephthalate and ethylene carbonate, which will decompose to form ethylene glycol and carbon dioxide upon exposure to water, fall within this group of solvents. Specifically, a group of selective solvents which is particularly preferred includes dialkyl terephthalates, dialkyl phthalates, dialkyl isophthalates, dialkyl naphthalates and mixtures thereof as well as alkylene carbonates and mixtures thereof. Some specific examples of the selective solvents that are particularly preferred include dimethyl terephthalate, dimethyl phthalate, diethyl terephthalate, dimethyl isophthalate, dimethyl-2,6-naphthalene dicarboxylate and their mixtures as well as ethylene carbonate, propylene carbonate and mixtures thereof. the same. Although these preferred selective solvents are characterized as non-depolymerizing, some reduction in the molecular weight of the polyester polymer may occur which coincides with the dissolution in the solvent. The amount of molecular weight reduction that occurs can be controlled by careful selection of the selective solvent and, minimizing the amount of impurities present in the selective solvent. It is expected that some water will be present in the selective solvent, and / or transported with the waste stream of the mixed polymer, which will result in some hydrolysis and reduction in the molecular weight of the polyester polymer. Additionally, some of the selective solvents that are preferred such as, for example, ethylene carbonate, can generate decomposition byproducts, in particular, at elevated temperatures. The presence of ethylene glycol (a by-product of decomposition) in the ethylene carbonate solvent will also cause a reduction in the molecular weight of the polyester polymer. Also, other glycols may be present in ethylene carbonate or the other alkylene carbonate solvents. The diesters appear less susceptible to the generation of such impurities and provide greater retention of the molecular weight in the recovered polyester polymer product. The presence of impurities in the selective solvent can be used to control the molecular weight or the intrinsic viscosity of the recovered polyester polymer product. For example, if an alkylene carbonate such as ethylene carbonate is used as the selective solvent, it will contain some impurities such as water and ethylene glycol, which will hydrolyze and reduce the molecular weight of the recovered polyester polymer product. Some impurities, for example ethylene glycol, can be generated by the use of ethylene carbonate under normal operating conditions. The level of such impurities can be controlled or maintained (by adding or removing impurities from the selective solvent) to levels that will provide a product of the polyester polymer recovered with a certain molecular weight or intrinsic viscosity. Other variables, such as the contact time of the polyester polymer with the selective solvent and the temperature of the selective solvent, will also influence the product of the recovered polyester polymer. Those skilled in the art will be able to adjust the digestion time, temperature and impurity levels in order to achieve the desired molecular weight or intrinsic viscosity for the recovered polyester polymer product, to allow optimum utilization of the polymer product. polyester in a subsequent processing. By minimizing the presence of water, ethylene glycol and other materials that will generate a reduction in the molecular weight of the polyester polymer is an alternative, and this can be achieved through the use of relatively pure solvents and maximizing the removal of water from the subsequent polyester polymer. if a step of washing with water in the processing is compromised. By way of example, when ethylene carbonate is used as the selective solvent, it is preferred that the ethylene carbonate contains less than 35 parts per million (ppm) of water and less than 25 ppm of ethylene glycol. A preferred method to reduce impurities, such as water, of the ethylene carbonate is through the use of zeolite or molecular sieve absorbents. While some reduction in the molecular weight of the polyester polymer is expected, it remains in polymer form. For example, the polyester polymer should contain at least 16 repeating units in the polymer chain. It has been found that selective aromatic ester solvents such as, for example, dimethyl phthalate, provide a PET polymer with a higher molecular weight recovered after dissolution, due to a higher molecular weight retention in the dissolution step. This molecular weight retention is convenient since less processing is required to reconstruct the molecular weight in the recycled polyester polymer product. Alkylene carbonates also offer an advantage. Although the molecular weight of the PET polymer recovered after dissolution in the selective solvent may be lower due to the presence of impurities that are present in the alkylene carbonates, the molecular weight distribution in the recovered PET polymer indicates a polydispersity of about 2, essentially equal to that of a virgin molten polymerized PET polymer, even though the recycle stream of the mixed polymer has a polydispersity greater than 2. This indicates that the PET polymers that are present in the polymer recycle stream the mixed are substantially balanced and, that the fractions with high and low molecular weights are adjusted to provide a polydispersity of about 2. If it is convenient to obtain a PET polymer recovered with a polydispersity comparable to that of the virgin polymer, the use of solvents is preferred selective alkylene carbonate. If it is convenient to maintain the polydispersity of the recycle stream of the mixed polymer, the use of selective aromatic ester solvents is preferred. The amount of selective solvent used should be sufficient to dissolve the polyester polymer within a reasonable period. Conveniently, the selective solvent is contacted with the recycle stream of the mixed polymer at ratios between 1: 1 and 19: 1, preferably between 1.5: 1 and 9: 1, and especially between 2: 1 and 5: 1 based on the total weight of the selective solvent and the polyester polymer present in the mixed polymer. The selective solvent is contacted with the recycle stream of the mixed polymer in amounts sufficient to produce a solution of selective solvent containing between 5 weight percent and less than 75 weight percent, preferably 10% and 40% by weight and, in particular, between 15% to 35% by weight of the polyester polymer.

The selective solvent and the polyester polymer are contacted at an elevated temperature sufficient to ensure that the temperature of the polyester polymer solution in the selective solvent is above the solidification temperature of said solution, suitably, between 140 ° C. and 285 ° C, preferably, between 170 ° C and 250 ° C and, more preferably, between 200 ° C and 230 ° C. The dissolution step of the polyester polymer is preferably carried out at or approximately at atmospheric pressure, although higher pressures may be employed. The polyester polymer can be contacted with the selective solvent by any conventional method and resorting to the use of conventional equipment for the operating conditions employed. The passage of the polyester polymer solution is carried out, for example, by combining the polyester polymer and the selective solvent in a stirred tank reactor or a series of stirred tank reactors. The resulting solvent-containing polyester polymer can be separated from the waste waste stream by means of filtration, gravity separation, or other eguivalent medium and using conventional equipment. Unless the polyolefins present in the recycle stream of the mixed polymer are removed before proceeding with the dissolution of the polyester polymer, any polyolefin present will melt and form a liquid phase separate from the selective solvent for the polyester polymer. In addition, if the polyester polymer contains encapsulated polyolefins (e.g., PET trays containing a small portion of a polyolefin), the solution of the polyester polymer in the selective solvent can release the encapsulated polyolefins, which contributes to the polyolefin layer. This polyolefin layer, which typically floats on the solvent, is removed from the solvent by phase separation, foaming, decanting or other equivalent means. If it is desired to dissolve a polymer-polyester other than polyethylene terephthalate, the same principles as stated above will be applied, that is, a selective solvent will be selected to dissolve the appropriate polyester polymer (s) and substantially reject the dissolution of the others. Polymers of polyesters at the temperatures, pressures and concentrations of the solvent most effective for the dissolution of the desired polyester polymer (s). As mentioned earlier, by the phrase "concentrated solution" reference is made to an effective polyester polymer concentration to allow both the formation of the described solid having polyester-rich and solvent-rich domains in selective solvent and solvent extraction from the solid. This concentration can already be present in the dissolution step a) mentioned above, when the concentration of the polyethylene terephthalate in the ceiling of the range ranges between 35% and 50% by weight. In these cases, it is not necessary to have a separate step of increasing the concentration of the polyester polymer solution that goes beyond the concentration used in the dissolution step. However, in the roof of the concentration range, the polyester polymer solution becomes highly viscous, which makes it very difficult to impossible to dissolve all the polyethylene terephthalate and effectively eliminates all that impurity from the solution in an effective manner. In this way, the use of a large excess of the solvent in the dissolution step is preferred in order to keep the viscosity of the polyethylene terephthalate solution low, which allows a shorter dissolution time and a more efficient elimination of the impurities. . The concentration of polyethylene terephthalate that is preferred in the dissolution stage is within the range of 15% to 25% by weight of polyethylene terephthalate in the selective solvent. Once the polyethylene terephthalate has completely dissolved in the solution and the impurities have been removed, the concentration of the solution can be increased. The increase in the concentration of polyethylene terephthalate in solution above the concentration of polyethylene terephthalate in the dissolution step is necessary if the concentration of the polyethylene terephthalate in the dissolution step is too low to allow the formation of domains in the polyethylene terephthalate. solid and the extraction of the selective solvent from the solid. As an alternative, however, it may be convenient to increase the concentration of the polyethylene terephthalate in solution even when the minimum concentration necessary to eventually form a microporous polyester polymer is present, in order to decrease the amount of the solvent that must be recovered during the extraction stage. The concentration of the solution can be increased by heating the solution to evaporate a portion of the selective solvent immediately. The solution can be heated to temperatures between 200 ° C and 400 ° C, conveniently, at superatmospheric pressures sufficient to avoid boiling of the selective solvent, for example between 5 and 50 bar and, at a time of residence so brief as possible. The particular temperature, pressure and residence time will vary according to the nature of the solution to be heated. Once it has been heated, the solution can be expelled inside a flash chamber maintained at a pressure low enough to generate an amount of immediate evaporation of the desired selective solvent, leaving a solution with a concentration of polyethylene terephthalate highest. The selective solvent evaporated immediately can then be condensed and recycled to the solution step. This step may optionally be followed by the addition of the virgin polyester polymer in the solution to bring the concentration to the desired point. Some examples of suitable amounts of virgin polyethylene terephthalate that can be added to the solution to increase its concentration reach up to 75% of the total polymer content. The various types of containers suitable for immediately evaporating the selective solvent include rectified and non-rectified flash drums, rubbed film evaporators and fractionation columns. The various types of containers suitable for the addition of the additional virgin polymer include stirred tank reactors or elements for in-line mixing. Other methods for increasing the concentration of the polyethylene terephthalate polymer in solution include the fractionation of inert gas into fractionation columns. The concentration of the polyethylene terephthalate polymer in effective solution to form a microporous polyethylene terephthalate polymer of good quality, generally ranges from 40% by weight and less than 75% in weight. It was observed that, at concentrations of 75% by weight or more, extraction of the solid selective polyester-solvent polymer material by washing with a second solvent was ineffective. It is believed that at such high concentrations of polyethylene terephthalate, the polyethylene terephthalate-rich domains and the selective solvent-rich domains are not formed. At concentrations below 40% by weight, the porosity of the solid decreases rapidly and becomes increasingly friable, which makes it difficult to handle with conventional processing equipment. Once the concentration of suitable polyester solution is obtained, the hot concentrated solution is subjected to a solidification step whereby both the polyester polymer and the selective solvent are solidified to form a solid material containing a polymeric phase of interconnection of the solid polymer domains rich in the polyester polymer and a solvent phase rich in the selective solvent. The polymer phase is a solid at the operating temperatures during the subsequent extraction when the selective solvent is extracted from the solid material. In the above procedures which employ the precipitation technique, a hot polyester polymer solution is poured into a liquid solvent bath which is a non-solvent for the polyester polymer and a good solvent for the solvent used in making the polymer solution polyester. In this manner, the polyester polymer is precipitated out of the solution as a solid and the solvent that was used to make the solution of the hot polyester polymer out of the polyester polymer, while solidifying, is dissolved in the liquid solvent bath. However, in this invention a method for solidification is employed which results in a solid mass which retains a discrete phase of the selective solvent used to make the hot polyester polymer solution within the solid polyester polymer network. The solidification step of the invention produces a solid material having an interconnected phase of domains rich in solid polyester polymer (ie, at least 80% by weight and, preferably, at least 9% by weight) and a solvent phase rich (ie, at least 80% by weight and, preferably, at least 90% by weight) in the selective solvent. The selective solvent domains may be liquids or solids at room temperature or at the operating temperature. Whether the selective solvent is a liquid or a solid will depend on the freezing point of the selective solvent and the temperature at which the solid mass was maintained. It has been found that at room temperature, selective solvents such as dimethyl isophthalate and ethylene carbonate are solid, and that selective solvents such as propylene carbonate or orthodimethyl phthalate are a liquid in the solidified material. Some impurities may be present in the domains, which are derived from the impurities present in the hot solution of the polyester polymer. Other impurities may be introduced during the solidification technique from a clear bath of a particular type of solvent, discussed below, and containing small amounts of contaminants. Alternatively, the concentration of the polymer or the selective solvent may change slightly if they are slightly soluble in the liquid bath solvent in which the hot polyester polymer solution contacts. In any case, however, the domains present in the solid mass formed during the solidification step possess at least 80% by weight of the respective polyester polymer or selective solvent. The domains rich in the polyester polymer may consist of a single polyester polymer or a mixture of polyester polymers. Similarly, the domains rich in the selective solvent may contain a single type of selective solvent or a mixture of selective solvents. A mixture of selective solvents can be formed by using a mixture of selective solvents in the dissolution phase or if during the solidification phase the concentrated polyester solution is contacted with a liquid bath thatIn addition, it is a selective solvent for the polyester solution, which is discussed later. A concentration of 80% by weight of the selective solvent would include single selective solvents or selective solvent mixtures. The same is true for the polyester polymer richness. For example, a domain containing a mixture of 50/40% by weight of two types of selective solvents and the rest consisting of impurities, is considered as a domain rich in selective solvent. The polyester polymer will form a discrete phase of a solid polymer network of interconnection through the solid material. The solid material also contains discrete selective solvent domains, which may be continuous or discontinuous, solid or liguid. The advantages of the solid material produced by the solidification technique are that it can be transported, processed and shaped into an open microporous body in any desired way. Unlike the precipitation technique that produces a fine powder filtered from the selective solvent and subsequently dried, the solidification technique produces a solid material with the mass and structural integrity sufficient to transport, wet or dry, without the loss of fines which occurs when a powder is transported. Additionally, unlike the precipitation technique that produces a solid with a shape that is limited to the shape of the polyester solution poured into it, the non-solvent liquid bath has been contacted, usually a sphere or a particle with irregular shape, the solidification technique used in the invention produces a polyester polymer with a solid mass that can be elaborated and shaped which contains the selective solvent. This presents numerous opportunities to realize a wide variety of molded or cut bodies with a continuous porous structure because the solid material containing the selective solvent can be made and shaped into the shape of a body in any desired form, after which is extracted the selective solvent for 1 leaving a microporous polyester polymer of open cells that retains the shaped form. The solid material produced by the solidification technique can be extruded in a continuous form and cut with a blade, an air knife, a liquid jet or other means, to form shorter segments in a continuous manner such as, for example, pellets. Since the solidification technique of the invention produces a solid mass with a reasonable tension and hardness, a polymer can be made with any size and shape by hot pressing or molding, by mechanical cutting of the solid, or by the combination of these techniques The solidification technique can be used to make pellets, stars, strand and cubes with rounded ends. Additionally, the solidification technique can be used to make shaped articles with the desired shapes such as filter bodies, sponges, bricks, porous tubes and porous gas bodies containing the selective solvent which, when subsequently extracted, leave the already formed porous polyester polymer. The solidification technique of the invention takes advantage of the cooling to solidify the polyester polymer. The cooling temperature must be determined to solidify the polyester polymer in the concentrated solution at an effective rate so as to form a solid mass having an interconnection domain rich in the polyester polymer and discrete domain / s of the selective solvent. The particular cooling temperature and speed will vary according to the concentration of the solution and the types of polyester polymer and selective solvent used. However, in general, for the majority of polyester polymers, selective solvents and solution concentrations, the desired morphology can be obtained by cooling the hot concentrated polyester solution (temperatures between 180 ° C and 50 ° C). 250 ° C) at temperatures ranging from 20 ° C to 60 ° C. Higher or lower temperatures can be used, especially if the temperature is lowered at an effective rate to allow the polyester polymer to crystallize in the continuous domain structure described herein A cooling method comprises simply pouring or spreading, optionally with a matrix, the concentrated polyester polymer solution on a solid surface whose surface temperature is lower than the temperature of the hot solution. An example of such a solid surface is a chilled metal conveyor belt.The tapes can have a surface of metal or polymeric, such as Teflon. According to the solvent system and the production method used, the transport speed can vary from cm to many meters per minute. Subsequently, the mass of polyester polymer-cooled solid selective solvent can be cut into cubes, granulated or crushed. In another method, the concentrated hot polyester solution is contacted with a liquid solvent bath with temperature control. The liquid bath solvent that comes in contact with the concentrated polyester solution must be either a solvent for the polyester polymer or a non-solvent for both the polyester polymer and the selective solvent. The precipitation of the polyester polymer should be avoided. In the case where the liquid is a solvent for the polyester polymer, the type of liquid used can be a solvent or a non-solvent for the selective solvent in the hot polyester solution. A liquid bath solvent that is a solvent for both the polyester polymer and the selective solvent is a selective solvent. The co-mixing between the liquid bath solvent and the polyester solution solvent will occur, without any harmful effect occurring during the formation of selective solvent domains in the solidified material since both solvents are selective solvents that dissolve the polymer polyester and prevent it from being precipitated. In fact, the liquid bath solvent can be of the same type of the selective solvent that is used in the concentrated polyester solution. Some examples of liquid bath solvents which are solvents for both the polyester polymer and the selective solvent are the selective solvents described above as well as HFIPA and the protic solvents. Another type of cooling liquid that can be used to form a solid material with the described morphology is a liquid that is both a non-solvent for the polyester polymer and a non-solvent for the selective solvent. This dual non-solvent liquid can be used without precipitating the polyester polymer from the solution because the selective solvent does not dissolve in the liquid bath and still maintains the dissolved polyester polymer until the polyester polymer has the opportunity to slowly crystallize forming a solid phase of the polymer. interconnect and trap the selective solvent within the interstices of the polymer in formation. Some examples of liguid solvents that are non-solvent for both the polyester polymer and the selective solvent are the fluorocarbons or the n-paraffins for the ethylene carbonate and the water for the dimetyl phthalate.

The concentrated polyester solution can be introduced into the liquid bath by pouring the concentrated polyester solution into the bath directly or on a conveyor that transports the solution through the cooling bath. The cooling bath should be controlled by temperature in order to maintain a constant temperature throughout the bath or maintain a temperature gradient throughout the bath. In another cooling method, the concentrated polyester solution is contacted with a vapor having a temperature below the temperature of the hot solution. The formation of the solid material in the vapor occurs, either by transfer of heat from the hot concentrated polyester solution to the vapor in order to avoid rapid cooling and detachment of the layers, or the vapor will prevent the detachment of layers by maintaining the polyester polymer in solution on the surface long enough to have a continuous surface morphology with and similar to the interior of the solid mass. Examples of suitable vapors are not limited and include inert gases, a solvent of the type in which the polyester is soluble, a solvent of the type in which the selective solvent is soluble or mixtures thereof. While the solvents of the latter type, in which the selective solvent is soluble and which is a non-solvent for the polyester polymer, are not suitable in liquid form when the hot solution is passed through a liquid bath as discussed above, the They can be used in the form of steam without affecting the ability of the polyester solution to solidify in crystalline domains of polyester polymer and selective solvent. Specific examples of vapors that are suitable include nitrogen gas, methyl ethyl ketone, acetone, tetrahydrofuran, hexanones, 1,4-dioxane, diethoxymethane, dioldiacetates, dibutyl phthalate, dimethyl terephthalate, dimethyl phthalate, dimethyl isophthalate, dimethyl naphthalate. , ethylene carbonate, propylene carbonate or their mixtures. The methods for contacting the hot solution in a vapor are a countercurrent contact with gases or vapors in a granulation tower. A granulated tower dispenses the liquid in the form of drops with a diameter of 50 ^ m to 500 ^ 111 approximately. The gas flow velocity is sufficient to capture the heat and extract it from the drops in cooling. They can be cooled and the vapors recirculated. The vapor velocity should be low enough to avoid droplet entrainment.

The extraction of the selective solvent from the solid selective polyester-solvent material is obtained by contacting the solid material with a solvent for the selective solvent and with a non-solvent for the polyester polymer. The non-solvents for the polyester polymer and the solvents for the selective solvent can be selected from a wide variety of materials. In general, these materials are less polar than the selective solvents. An optional criterion for the selection is that they may have lower boiling points than those of the selective solvent for the purpose of simpler recovery and recycling. They must be soluble with the selective solvent in the range of desired operating conditions. If a chemical wash is used in the pretreatment of the polyester polymer before proceeding with the dissolution phase, it would be convenient to use the same gum washing in the extraction phase in order to reduce the type necessary for the recycling of the solvent.

Some examples of the solvents that may be used to extract the selective solvent include acetone, methyl ethyl ketone, tetrahydrofuran, tetrahydropyran, cyclopentanone, alkyl substituted cyclopentanones, hexanones, hexanediones, heptanediones, octanediones, alkyl malonates, dioldiacetates (eg, ethylene glycol diacetate, propanediol diacetate and butanediol diacetate), acetoacetate substituted with alkyl, 1,3-dioxane, 1,4-dioxane, 1,3-dioxolane, 2-methoxyethyl ethyl ether, diethoxymethane, cyclohexanone, alkyl-substituted cyclohexanones, cycloheptanone, alkyl-substituted cycloheptanones, amyl acetate, propionate of amyl, mesityl oxide and dialkylformamide. You can use any of these chemical solvents wet, in combination with water. For example, an azeotropic mixture of tetrahydrofuran and water may be used as the extraction solvent. A group of solvents which is preferred include acetone, methyl ethyl ketone, tetrahydrofuran and cyclohexanone. Methods for contacting and extracting the selective solvent from the solid material are not limited as long as the selective solvent is removed from the solid material to leave the porous polyester polymer. A method for the extraction may take place in a continuous moving bed of the solid material, preferably in the form of particles, with a countercurrent of the extraction solvent flowing through the particle surfaces. Instead of a moving bed, a series of mixers-decanters can be used. The number of wash cycles required to remove all of the selective polyester polymer solvent will depend on the type of selective solvent, the type of extraction solvent, the wash ratio between the extraction solvent and the polyester polymer, and the amount of selective solvent residual that remains in the porous polyester and that can be tolerated for the final application. The number of theoretical steps required, N, to separate the selective solvent from the polyester polymer can be calculated as follows: Log [(yb - yb *) / (ya - ya *)] N = log [(yb - ya) / (yb * - ya *)] where y * is the concentration of the selective solvent of the liguid in equilibrium with the incoming solid, and b * is the concentration of the selective solvent of the liquid leaving the N stage, and b is the concentration of the selective solvent in the extraction solvent that enters the Stage N and, is already the concentration of the selective solvent of the liguid left by the first stage. The greater the number of extraction stages used, the lower the amount of residual selective solvent remaining in the porous polyester polymer. However, an issue of revenue reduction arises, because the amounts of selective residual solvent remaining in the porous polyester polymer can be tolerated, especially when the selective solvent is of the type that can be polymerized in the form of the polymer backbone. polyester during the solid state polymerization without significantly affecting the desired molecular weight of the final polymer. However, in general, the porous polyester polymer should not have more than 500 ppm of residual selective solvent remaining in the porous polymer. The temperature of the extraction solvent is not particularly limited and we have shown that the amount of the selective solvent leached from the polyester polymer using an extraction solvent is independent of the temperature when the extraction solvent is easily dissolved in the selective solvent at room temperature. However, in cases in which the type of extraction solvent used does not easily dissolve the selective solvent at room temperature, but does so at elevated temperatures, it would be convenient to increase the temperature of the extraction solvent that is contacted with the solid mass. The pressures that are applied to the solid mass and / or the extraction solvent during extraction are also not limited. However, it would be convenient to apply vacuum to the solid selective polyester-solvent polymer material on a surface such as, for example, the lower surface, and to contact the solid material with the extraction solvent on a different surface, for example on the upper surface, to force the extraction solvent by the mass of the polymer at a flow rate greater than the flow rate that can be reached with gravity. This would reduce the extraction time or increase the amount of selective solvent that is eliminated at a certain time, so that the number of stages necessary for extraction is reduced. The relationship between the extraction solvent and the solid selective polyester-solvent polymer material is also not limited. An equilibrium can be found by taking, within the desired contact period, the amount of extraction steps desired, the desired purity of the porous solid of the residual selective solvent and the amount of extraction solvent that can be handled economically in the process. The number of stages for the extraction decreases rapidly to the extent that the ratio between the extraction solvent and the solid mass increases from more than 1: 1 to approximately 8: 1, by weight and, thereafter, the subsequent increases in the extraction solvent ratios will not generate abrupt reductions in the amount of extraction steps necessary to eliminate the selective solvent. The optimum ratios between the extraction solvent and the solid are generally between about 3: 1 and 6: 1 by weight. Once the selective solvent has been extracted from the porous polyester polymer, the solids can be dried by evaporation and the recovery of any residual extraction solvent that can remain on and within the porous solid. Evaporation can occur at elevated temperatures. Extraction solvents such as, for example, THF or acetone, are readily volatilized from the pores of the solid by fractionation with nitrogen at temperatures below the glass transition temperature of the polyester polymer in order to avoid hydrolysis of the polymer, usually between 36 ° and 100 ° C approximately, and it is also possible at lower temperatures if the drying occurs at subatmospheric pressures. While it is preferred to recover the polyester polymer with a molecular weight comparable to that of the polyester polymer in the recycle polymer stream, in general, the process of the invention will generate a reduction in the molecular weight of the recovered polyester polymer product. The porous polyester polymer recovered from the invention can be subjected to another process to increase its molecular weight, which is known as solid state polymerization. In a typical PET polymerization process, terephthalic acid (or dimethyl terephthalate) and ethylene glycol are combined and polymerized in a liquid or molten phase. The melt phase polymerization process generally comprises a series of reactors in which the molecular weight of the polymer is increased sequentially until the PET reaches an intrinsic viscosity (VI) not exceeding 0.6 dl / g, equivalent to a molecular weight of average number of around 18,600. The molten polymer is extruded, cooled and granulated to form an amorphous prepolymer product. Subsequently, this prepolymer is heated to increase its crystallinity and then further polymerized in the "solid state until reaching a VI of about 0.7 dl / g or more and, preferably, a VI of at least 0.8 dl / g One of the novel aspects of the present invention is the combination of the porous polyester polymer product recovered with the polyester polymer manufactured from typical raw materials for further processing, for example, the polyester polymer can be added. porous recovered in a melt phase polymerization reactor containing a polymer with approximately the same VI range of the recovered porous polyester polymer.

The polyester polymer may or may not be further polymerized in the molten phase. Alternatively, if the recovered polyester polymer has an LV comparable to that of the extrusion melt polymer, the recovered polyester polymer can be combined with virgin polyester polymer before it enters the extruder or into the extruder. In addition, the recovered porous polyester polymer can be combined with virgin polyester polymer in other melt processing operations such as, for example, a granulator or spinneret in a fiber making operation. One of the advantages of combining the recovered porous polyester polymer with the virgin polyester polymer that is not obtained from the recycled polyester polymer is that it facilitates the production of a polyester polymer product containing less than 100% recycled polyester polymer. The resins of the polyester polymer with recycled content in square contain, at present, less than 50% by weight of recycled polyester polymer. A recycling content of between 15% by weight and approximately 35% by weight is typical, and a recycle content of about 25% by weight is common. The production of a polyester polymer resin containing 100% recycle content is technically possible with the present invention and can be used for some applications. After the combination of the porous recovered polyethylene terephthalate with virgin polyethylene terephthalate in a molten phase or, instead of this combination, the polyester polymer can be polymerized in the solid state at temperatures between more than its polymerization temperature and less than its polymerization temperature. stickiness temperature. In general, suitable temperatures for increasing the molecular weight of the polyethylene terephthalate polymer will range from about 205 ° C to about 230 ° C, which may subsequently increase gradually while the polymerization reaction occurs. The porous polyester polymer solids produced by the method of the invention exhibit accelerated solid state polymerization rates because the high surface area of the porous solid results in shorter average free path lengths for polymerization byproducts such as water and ethylene glycol. , to diffuse or evaporate the low permeability polymer phase. The porous polyester polymer can be polymerized in the solid state, optionally in a mixture with virgin polyester polymer, in batch form or continuously, under vacuum or in a stream of inert gas which is dispersed homogeneously by the reaction zone. The reactor bed can be fixed, static, fluidized or mobile. In one example, the porous polyester polymer in the solid state can be polymerized within a tubular reactor by circulating from the top to the bottom of the tube at a rate controlled by the discharge velocity at the bottom of the tube, at a rate of countercurrent of inert gas by the polyester polymer at a rate lower than the fluidization rate of the porous solids. Byproducts, such as water and ethylene glycol, are volatilized and removed from the reaction zone in the inert gas stream. In the solid state process, the VI of the polyester polymer can be increased to 0.7 dl / g or more, according to the residence time and the temperature of the polymer in the reaction zone. It is convenient to obtain a porous polyester product recovered with a VI between about 0.2 dl / g and 0.8 dl / g. Once the recovered porous polyester product has been polymerized in solid state, with or without combined virgin polyester, it preferably has a VI ranging from about 0.6 dl / g to 5.0 dl / g. Typically, the VI is used as an indicator for the molecular weight of the polyester polymers, however, such polymers can also be characterized by the average number molecular weight. It is convenient to obtain a recycled porous polyester product with an average number average molecular weight between 3,700 and 150,000. VI is defined as the limit of the fraction (In v) / C as C, the concentration of the polymer in solution, which approaches zero, where v is the relative viscosity that is measured for different concentrations of polymer in a given solvent. For PET, a mixed solvent system of 60:40 phenol: tetrachloroethane at 30 ° C was used. Different solvent systems can be used for the other polyester polymers, according to the molecular weight of the polyester. The molecular weight distributions for the polyester polymers can be determined by the use of Gel Penetration Chromatography (GPC). The PET samples for the GPC analysis can be prepared by dissolving PET hexafluoisopropanol at a concentration ranging from 0.5 to 1.0 milligrams of PET per milliliter of solvent. The GPC system can use columns filled with silica beads or styrenedivinylbenzene. The GPC system can be eguided with detectors calibrated to known standards for PEI. The density of the porous polymer-polyester is lower than the density of the same non-porous polyester polymer with equal VI and crystallinity. The density of the porous polyester polymers produced by the above-described method ranges from 25% to 75% of the density of the same non-porous polyester polymer. The size of the micropores in the products of the invention ranges from 0.5 to 75 microns, usually between about 20 and 50 microns. The pores have a substantially spherical shape and are typically connected to each other in irregular shapes and have a spherical portion protruding from the connected mass. It was within these pores that the selective solvent was located and extreme. The invention will be further illustrated through the illustrative examples presented below, said examples should not be construed as limiting the invention.

Example 1 In this example, the development of a microporous polyethylene terephthalate polymer on a laboratory bench scale was demonstrated. A polyethylene terephthalate resin, PET resin 8006 Cleartuf (Trade Mark) was dried in a vacuum oven at temperatures above 120 ° C and at a pressure lower than 650 Pa. The solvent used was dimethyl phthalate (DMP) which it was stored at molecular sieves other than 4A. Approximately 200 grams of a 50 percent PET solution were made by mixing these two components in a 500 ml flask eguipated with a paddle agitator, nitrogen purge and thermocouple at approximately 215 ° C. Dissolution of the PET in the DMP solvent occurred over a period of about 30 minutes with vigorous stirring. After dissolution, the 50 percent PET solution was cured in the form of hardened sheets by pouring the contents of the bottle into a clean stainless steel centrifuge vessel maintained at room temperature. While the material was cooling, the solution became opaque for a period of about two minutes, which indicated that the PET crystals were being formed. The 200 gram load formed a sheet of about 0.1 m2 area and about 3 mm thick. After completing the cooling, the material was broken into plates and stored in containers. Examination of the 50 percent PET solution in DMP under a microscope after curing revealed a solid with grains of material having a diameter of approximately 20-50 microns.

Subsequently, the plates were crushed within the vessels to form a powder with a nominal particle diameter of 1.5 mm or less with a dedicated laboratory grinder. Three different types of extraction solvents were analyzed for the removal of the DMP in the solid. They were tetrahydrofuran (THT), methyl ethyl ketone (MEK) and cyclohexanone. Several relationships between extraction solids and solids were analyzed by contacting the powder and the extraction solvent in 40 ml EPA flasks with agitation discs and a block heater with Reactivial agitation. The relationships between the extraction solvent and the solid for each extraction solvent analyzed varied between 8:19 and 150: 1. After contact with each wash solvent for a period of 12 hours, a sample of the liquid was taken and filtered to perform the HPLC analysis. Solvent wash solids were filtered in a filter flask with air circulation for a few minutes to evaporate the entire wash solvent. The HPLC method for DMP used UV detection at 254 nm and an internal standard of toluene. The elution was controlled by a gradient of methanol-acetonitrile solvent and a C18 column of 25 cm by 5 mm with 5 micron silica particles.

The same procedure was repeated using 75 percent by weight PET solution in DMP. This solution also hardened successfully and led to obtaining a material that had a granular matrix. The extraction of DMP from 50 percent by weight hardened PET was carried out successfully in each of the analyzed washing solvents. Analysis of the 50 percent by weight PET solid after proceeding with THF extraction revealed a fairly porous material in nature. Since PET is essentially insoluble in THF at room temperature, it was concluded that DMP had been leached from the solid matrix. On the other hand, attempts to remove the DMP from the 75 percent by weight hardened PET solution by means of THF extraction was unsuccessful. It was concluded that it was very likely that the material with a higher concentration of PET could not form the structure of interconnected pores so that the DMP could be fractionated with cooling.

Example 2 Solid PET-DMP material was made using the same procedure as described in the aforementioned Example 1. This time, PET / DMP particles with different sizes were obtained by grinding the solid mass and sieving the desired particle size ranges. Two particle sizes were formed, one with the grind to a nominal particle diameter of 1.5 mm or less, and the other 3 mm x 6 mm particles were cut from a hardened plate of the material. However, in this example, instead of waiting for the completion of a twelve-hour period before taking the sample, the contact procedure was modified in such a way that a sample of the supernatant was taken at regular intervals without affecting the stirring a solid in the sample bottles. Subsequently, the content of DMP was determined by the HPLC method. In the first series of experiments, a sample of particles of less than 1.5 mm PET / DMP was washed with THF and a second sample of 3 mm x 6 mm PET / DMP particles was washed with THF. Each of the samples was stirred at the same speed and washed at the same phase ratios. All that was needed was a contact time of about 5 minutes in order to reach equilibrium for the particles with a size of 1.5 mm or less. A longer wash time was needed for the particles with a larger size, most likely due to the formation of a thin layer of polymer on the PET / DMP plate that was formed during the cooling of the melt. In this way, the control of the cooling rate of the selective polyester-solvent polymer solid can minimize the thickness of the film that can develop on the surface of the plate. To minimize the thickness of the surface film and increase the free surface area of a surface film, it would be convenient to pour the PET dissolved in the selective solvent onto a cooled belt followed by grinding with, for example, a grinder in tubes .

Claims (11)

1. A process for recovering the polyester polymer as a microporous solid, characterized by a recycle stream of the mixed polymer comprising: - a) contacting the mixed recycle stream of the mixed polymer at elevated temperature with a selective solvent in which the polymers polyesters are soluble and the other polymers present in the recycle stream are substantially insoluble to form a polyester polymer solution in the selective solvent; b) if the concentration of polyester in said solution is below 35% by weight, increase it above that value; c) cooling the selective solvent solution to form a solid material having an interconnection phase of polymer-rich solid polymer domains and a phase of solvent domains rich in selective solvent; d) extracting the selective solvent from the solid material to form a microporous solid.

2. The procedure, according to the claim 1, 'characterized in that the selective solvent is an alkylene carbonate or dialkyl phthalate.

3. The procedure, according to the claim or 2, characterized in that the concentration of polyester in step b) is increased by means of the immediate evaporation or elimination by evaporation of the selective solvent.

4. The method according to claim 3, characterized in that the proportions between the recycle stream of the polymer and the selective solvent are selected in order to obtain a solution containing between 15% and 25% of the polyester polymer in the selective solvent , which is increased from 35% and up to 50% by weight by means of the elimination of the selective solvent.

5. The method according to any of claims 1 to 4, characterized in that step a) is carried out at a temperature comprised between 140 ° and 285 °.

6. The process, according to any of the aforementioned claims, characterized in that the cooling step c) is carried out by contacting the selective solvent solution at a temperature comprised between 180 ° and 250 ° C with a solid surface, a liquid or a vapor, cooled below 60 ° C, suitably at room temperature or at 20 ° C.

7. The method according to claim 6, characterized in that the cooling is carried out by means of contact with a cooled metal surface.

8. The method, according to any of the aforementioned claims, characterized in that the selective solvent is extracted from the solid material by causing it to come into contact with a liquid that is a solvent for the selective solvent and a non-solvent for the polyester polymer.

9. The process according to claim 8, characterized in that the liquid is acetone, tetrahydrofuran, methyl ethyl ketone or a mixture thereof.

The method, according to any of the preceding claims, characterized in that the process conditions are selected to produce, in step c), a solid material containing at least 80% by weight of rich domains in polyester polymer.

11. A microporous solid polyester polymer produced by a process according to any of claims 1 to 10. SUMMARY A process for recovering a polyester polymer as a microporous solid from a recycle stream of the mixed polymer comprising: - a) contacting the recycle stream of the mixed polymer at elevated temperature with a selective solvent in which the polyester polymers they are soluble and the other polymers present in the recycle stream are substantially insoluble to form a polyester polymer solution in the selective solvent; b) if the concentration of polyester in said solution is below 35% by weight, increase it by that value; c) cooling the selective solvent solution to form a solid material having an interconnected phase of solid polymer domains rich in polyester polymer and a phase of solvent domains rich in selective solvent; d) extracting the selective solvent from the solid material to form a microporous solid. Also, an article is provided comprising a solid, molded, extruded or cut terephthalatopolyethylenelene polymer having an open microporous structure and the average pore diameter is between 0.5 and 50 microns.