Terephtalic acid crystallization using co 2

Abstract

The present invention is in the field of a method of CO2 assisted crystallization of a chemical species, in particular from a mixture comprising said chemical species, and a crystal obtained by said method. The chemical species is typically provided in a mother liquid, typically being a solution, and crystals are typically obtained directly thereof.

Description

[0001] TEREPHTALIC ACID CRYSTALLIZATION USING CO2

[0002] FIELD OF THE INVENTION

[0003] The present invention is in the field of a method of CO2 assisted crystallization of a chemical species, in particular from a mixture comprising said chemical species, and a crystal obtained by said method. The chemical species is typically provided in a mother liquid, typically being a solution, and crystals are typically obtained directly thereof.

[0004] RELATED APPLICATIONS

[0005] The present application claims the benefit of priority from Dutch Patent Application NL2037821, filed on May 30, 2024, in the name of Feyecon Development & Implementation B.V., The Netherlands.

[0006] The entire contents of the above-referenced applications and of all priority documents referenced in the Application Data Sheet filed herewith are hereby incorporated by reference for all purposes.

[0007] BACKGROUND OF THE INVENTION

[0008] In chemistry, a solution relates to a homogeneous mixture composed of two or more substances. In such a mixture, the so-called solute is a substance dissolved in another substance typically referred to as a solvent. For obtaining such a solution a mixing process may be used, wherein the solutes are dissolved in the solvent; or, the solution may be obtained directly from a source, such as a waste stream, seawater and the like. In the solution usually the solvent forms the larger (volume, and typically also weight) fraction of the mixture. The amount of solute in a given amount of solution or solvent is referred to as the concentration, which may be expressed in terms of mass / volume (kg / 1), in a weight ratio (kg / kg), or in a molarity, wherein the mass of a certain solute is calculated back to an amount of mole by using the molar weight of said solute (mole / 1). The solution typically comprises more than one solute, as (i) typically solutes are present as ions (cations and anions), (ii) more than one type of ions is present inherently. Put different, the solution may comprise a plurality of solutes, of which one, or some, typically form a major part. The term "aqueous solution" is used when one of the solvents is water.

[0009] In order to separate solutes from the solution, and likewise melt, several chemicalphysical processes can be used. One of these processes is crystallization. Typically, rather pure solutes can be obtained thereby. Crystallization is the process by which a solid forms, wherein the atoms or molecules are highly organized into a lattice structure known as a crystal. Typically, many crystals are formed at the same time with a specific structure and under certain dynamic growth conditions. The solid relates to at least one of the solutes or part of the solvent. Some of the ways by which crystals form are crystalizing from a solution, freezing, or more rarely deposition directly from a gas. Typical parameters that are controlled may be temperature, pressure, and solvent / fluid evaporation. Crystallization is considered to occur in two major steps. The first is nucleation (depicted as primary and secondary nucleation), the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent or the like; the supersaturation provides the driving force for crystallization. The second step is known as crystal growth, which is the increase in the size of particles. In view of crystallization, it is noted that minerals, inorganic compounds, and (small) organic molecules typically crystallize easily, and the resulting crystals are generally of good quality, i.e. with high purity.

[0010] In an alternative solidification process precipitation might be considered. In an aqueous solution, precipitation is the process of typically rather instantaneously transforming a dissolved substance into an insoluble solid from a supersaturated solution. The solid formed is then called the precipitate. The precipitate is typically not very pure as it requires a rather large supersaturation to be formed. The precipitation of a compound may occur when its concentration exceeds its solubility. This can be due to temperature changes, solvent evaporation, or by mixing solvents. Precipitation may also occur when an antisolvent (a solvent in which the product is insoluble) is added, such as in the case of a gas anti-solvent, drastically reducing the solubility of the desired product. Precipitation occurs more rapidly from a strongly supersaturated solution. For instance, extreme high pressures may be used in this respect, or a solvent may be removed such as by evaporation, e.g. in case of spraying. Precipitation is also commonly used to isolate the products of an organic reaction during workup and purification operations. Ideally, the product of the reaction is insoluble in the solvent used for the reaction. The latter has not much to do with the present invention. In addition, precipitation is typically not very energy efficient, especially if pure materials to be recovered are envisaged, and not very method efficient, as further work up steps would typically be required. Examples of precipitation processes can be found e.g. in EP 1 212 278 Bl, WO 01 / 16074 A2, WO 90 / 03782 A2, and WO 01 / 16082 A2.

[0011] In order to stress the difference between precipitation and crystallization the following is a summary. Crystallization relates to formation of solid crystals generally from a homogeneous solutions. It happens when solutions become supersaturated, basically meaning it contains more solute than it can be dissolved at a given boundary condition (such as temperature, concentration, solubility, etc.); The crystallization process is a controlled process, wherein the formed crystals have species that are arranging in highly ordered repeating pattern. It is often used in industry as a purification method. Crystallization generically relates with precipitation in some aspects, in that they are both separation techniques. Precipitation is a formation of solid particles from a liquid solution e.g. due to a chemical reaction or a change in conditions. Unlike crystallization, precipitation can result from a reaction of two and more solutions that contains ions or likewise different ions which can form an insoluble compound. The solid particles formed do not have a well-defined crystal structure, do not grow, and can be amorphous, to put it mildly. Generally, precipitation is not considered reproducible for product qualification. Precipitation is never associated with terms as “controlled process”, “purification method”, “crystallinity structure and repetition”.

[0012] In the present invention crystallization is mainly used as a physical -chemi cal solidliquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering, crystallization occurs in a crystallizer which is constructed as such to offer controlled process conditions. Crystallization may be compared to precipitation, although the result is not amorphous, or polycrystalline, or disordered, as in the case of precipitation, but a crystal. Crystallization compared to precipitation yields reproducible results in terms of crystal properties.

[0013] Most chemical compounds, dissolved in most solvents, show a solubility threshold that increases with temperature, i.e. at a higher temperature more solute can be dissolved in the solvent with respect to a lower temperature. The process of crystallization typically makes use of this phenomenon, by decreasing the temperature of the solution, thereby lowering the solubility, and creating the energy for the crystals to be formed. The temperature difference between the maximum solubility at a certain temperature, and the actual, lower temperature, is often referred to as supersaturation. The present invention relates partly to crystallization through cooling.

[0014] There may be limitations in the use of cooling crystallization. For instance, a hydrate instead of an anhydrous crystal may be formed, which may be detrimental, such as in the case of calcium chloride. In the crystallizer a maximum supersaturation will evidently take place in the coldest points. These may be heat exchanger tubes which are sensitive to scaling, and heat exchange may be greatly reduced or discontinued. Due to the decrease in temperature usually an increase of the viscosity of a solution is observed. A too high viscosity may give hydraulic challenges, and the laminar flow thus created may affect the crystallization dynamics. Also, crystallization by cooling is not applicable to compounds having a so- called reverse solubility, a solubility that increases with temperature decrease; in such a case crystallization would be obtained by increasing the temperature.

[0015] Another challenge with crystallization is that it is difficult to crystallize a solute in a continuous mode. In particular production rate, scalability, the above scaling in the heat exchanger, may be problematic. Such is especially the case for fraction crystallization. In chemistry, fractional crystallisation use is made of differences in solubility between solutes being present. It fractionates (forms fractions) via differences in crystallization, which differences may be rather absolute, namely crystallization or not. If a mixture of two or more substances in solution are allowed to crystallize, for example by allowing the temperature of the solution to decrease or increase, the precipitate may contain more of the least soluble substance. The proportion of components in the precipitate depends on their solubility quantified by their so-called solubility products. In a case that the respective solubility products at a given temperature are very similar, a cascade process may be needed to effectuate a complete separation. This technique is often used in chemical engineering to obtain very pure substances, or to recover saleable products from waste solutions.

[0016] Polyethylene terephthalate (PET) stands as one of the most widely used polymers, representing the predominant thermoplastic resin within the polyester family. It finds application in various industries, including clothing fibres, liquid and food containers, thermoforming for manufacturing, and composite materials. As of 2016, global PET production reached an annual estimated 56 million tons, with fibres comprising over 60% of usage and bottle production making up approximately 30% of demand. However, only half of the produced bottles undergo recycling processes, resulting in a mere 15% of total PET production being recycled currently. Recycling of textile fibres comprising PET remains a problem due to their high crystallinity which hampers its depolymerization.

[0017] PET recycling typically involves either chemical or enzymatical processes, utilizing huge volumes of corrosive chemicals to yield its precursors, terephthalic acid (TP A) or its esters, or mechanical methods that maintain or restore the original polymer properties. Transesterification may also occur, incorporating glycols, polyols, or glycerol to produce polyols for use in applications like polyurethane production or PU foam manufacturing. Additionally, PET can be chemically transformed into epoxy-based products, including paints.

[0018] Efforts to recover and reuse PET remain imperative to reduce fossil fuel dependency and achieve more sustainable polymer processing, thereby minimizing CO2 emissions. Among the various PET recovery processes, chemical degradation to TPA or its ester monomers stands out as a particularly promising route. While enzymatic and electrochemical approaches have been explored, they all entail extensive chemical usage, such as buffer solutions, and / or mineral acids, for final TPA precipitation. These challenges make the scale-up process rather difficult due to the involved corrosive chemicals and the utilization of larger volumes of aqueous solutions (mostly with high concentrations of salts). Moreover, TPA recovery via e.g. precipitation is not inherently a purifying method, necessitating additional purification step otherwise cannot be used in a new polymerization cycle(s).

[0019] Many companies and specialized research institutes have tried, over the years, different solutions for TPA recovery, some of them involving a use of gaseous CO2. Recovery of TPA from an aqueous and alkaline solution containing TPA and mono and di-salts of TPA was considered. The recovery relates to a complicated process of precipitating mono and dipotassium salts and further TPA from an alkaline solution in which gaseous CO2 was bubbled through, hence at more or less atmospheric conditions. The recovery process is performed at somewhat elevated temperatures between 30 to 50°C. In view of the strong alkali nature of the process the pH thereof is likely to be rather high, e.g. at least >12. Another approach of recovery of TPA uses rather extreme conditions, that is 300atm and 152°C. The process relates to the TPA purification from a mixture of 4-carboxybenzaldehide. Economically these extreme conditions are not feasible for continuous recovery of TPA. These conditions are considered rather unfavourable and hard to implement in a continuous process with larger volumes.

[0020] The present invention therefore relates to an improved method of recovering a chemical species, such as TP A, and various aspects thereof, and a prepared crystals, which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages.

[0021] SUMMARY OF THE INVENTION

[0022] In order to better address one or more of the aforementioned desires, the present invention relates, in several aspects, to a method for improving the recovery of a chemical species, such as Terephthalic Acid (TP A), from solution, typically utilizing a combination of CO2-assisted crystallization and pH adjustment, and minimizing the use of corrosive solutions. In an exemplary example, by introducing CO2 under controlled pressure conditions which may be followed by seeding with TPA crystals, TPA crystallization is accelerated, resulting in larger crystals with enhanced purity. Additionally, pH adjustment, e.g. by using mineral acids, facilitates the separation of e.g. TPA crystals from optionally co-formed salts, leading to increased process yields and improved colour and purity of the recovered TPA crystals. So, in an exemplary embodiment there is a supersaturation combined with pH variation. Typically, in a carefully orchestrated dance of pressure, temperature and pH, CO2 gently guided the chemical species molecules to form exquisite crystals, all within the original mother liquor. It is noted that carboxylic acids may have speciation (dissolved mono and disalts presence in the mother liquor) and the combination of anti-solvent crystallization with pH shifting may result in the formation and growth of e.g. TPA crystals. The yield of this reaction may depend heavily on the nature of the mother liquor. A pH of buffer solutions is more difficult to correct compared to e.g. a simple alkaline solution. The process can be successfully applied for recovering e.g. TPA from e.g. solutions originated degraded PET packages, PET multilayer plastics, and PET textile. In the case of PET recycling from textile, scCCh discoloration may be used as pre-treat- ment step for improved the L*a*b* and purity of the recovered TPA monomer. This allows the recovery of a pure TPA crystal and prevent the pigments or other impurities to be carried into the TPA crystals. As such their re-use in repolymerization is enhanced. In an exemplary embodiment the present invention provides a novel method for enhancing e.g. TPA recovery directly from solution, involving: 1. Introduction of CO2 under controlled pressure conditions, gradually increasing until (TPA) crystallization which occurs at 5.5 MPa (55 bar). 2. Seeding with (TPA) crystals to promote direct secondary nucleation and accelerate crystallization. 3. pH adjustment of the solution to e.g. 2.5 using mineral acids such as HC1 or H2SO4 to facilitate (TPA) crystal formation from all its speciated mono and di-salts. 4. Filtration of the (TPA) crystals using vacuum filtration on a Buchner filter funnel with Whatman paper of 2.5pm porosity. 5. Washing of (TP A) crystals with hot water (temperature >90°C) to remove residual impurities. 6. Drying of (TP A) crystals overnight at controlled temperature and airflow conditions. The applicant developed a process based on CO2 techniques which allows TPA or its esters crystallization directly in the mother liquor. The process is successfully proved to be used for crystallization of TPA and / or its esters. The process is applied directly to the (TPA) solution (here in called mother liquor) without further intermediate processing. In this case, the mother liquor represents the resulting solution after degradation of the PET back to its monomers. This can be any solution which resulted from a chemical, electrolytic, enzymatic or any other process which yields dissolved chemical species (TPA) in a solvent, such as an aqueous solution of various pHs, mixture of aqueous solution with organic solvents (acetic acid, acetophenone), or organic solvents (DMSO). At the end of the CO2 crystallization processing, the produced (TPA) crystals can be separated from the mother liquid via filtration and further washing with hot water. The crystallization process of chemical species (TPA) can be seen similar for TPA as well as for its esters. The term “TPA crystals” is used which can refer as well to its esters. Optionally the process can involve a preliminary purification step of the mother liquor where activated carbon (AC) is added to the (TPA) solution before crystallization. The mother liquid is heated near the boiling point and AC is added to the solution to absorb impurities. Subsequently, temperature-controlled filtration may be carried out. Various types of activated carbon such as granules, powder, and pellets can be utilized, including Cabot Norit GAC 830W and Desotec DSL22-0082. The filtration under controlled temperature prevents the TPA crystals to be formed while the AC is filtered. Following the purification step, the filtrate may be further exposed to high pressure CO2, typically above 3 MPa, with more suitable conditions being above 5 MPa, and preferably above 5.5 MPa. Alternatively, the process can be conducted around supercritical conditions, typically between 7.37 bar and 30 MPa, in an autoclave to initiate the (TPA) crystallization. In the case of bringing the process to supercritical conditions, the obtained (TPA) crystals are longer, and more needle shaped with a high tendency of agglomeration (see Example 2). The present invention relates to the (TPA) crystallization process conducted directly into the mother liquid containing dissolved chemical species (TPA). This mother liquid may represent the solution in which PET was degraded. Following the chemical or enzymatic PET degradation, the aqueous solution containing dissolved TPA can have different pHs most frequently above pH7, preferred above pH 7.5 and most preferred pH 8.

[0023] The present (TPA) crystallization process runs best directly into the mother liquid assisted by liquid CO2, or scCCE. When utilizing liquid CO2 preferred mild conditions are used in respect to pressure and temperature. The best conditions were achieved between 10°C and 18.3°C, and most preferred between 15 and 18°C. (TP A) crystallization in scCCh uses temperatures between 35 and 60°C and pressures between 73 and 300bar. CO2 plays the role of the antisolvent as well as acidifying the solution, via the formation of carbonic acid (H2CO3). The acidic environment created by carbonic acid further influences the speciation of TPA and its salts, affecting their solubility and precipitation behaviour. Thus, CO2 plays a dual role in enhancing chemical species (TPA) recovery by facilitating both crystallization and acidification of the solution. The pH of the original solution containing dissolved chemical species (TPA) and or its salts can influence the recovery of the species (TPA). The co- existence of mono- and di-TPA salts within a broad pH range suggests a complex equilibrium between different TPA species. Lowering the pH of the solution is found to increase the crystallization of TPA molecules. Consequently, the TPA recovery rate itself is higher at lower pH values, enabling the additional transformation of both mono- and di-salts of TPA. Experimental results indicate that the optimal pH range for TPA recovery lies between 5.5 and 2. Within this range, the highest TPA recovery yields are achieved, with preferable conditions observed between pH 3.5 and 2.5. At these acidic pH levels, the solubility of TPA and its salts is significantly reduced, leading to efficient preferential crystallization and recovery of TPA from solution.

[0024] The addition of the CO2 into the (TPA) solution can be done rather quickly until 3.5-4 MPa and then gradually until pressure reaches 5.5 MPa when (TPA) crystallization occurs. To speed up the process and create possibility of direct secondary nucleation, seeding can be done by injection of small amount of chemical species (TPA) crystals (e.g. O.Olg / L TPA in acidic solution) during second pressurization (after 4 MPa). The crystallization of chemical species (TPA) or its salts can be done also by lowering the pH of the solution with addition of acids. Such acids can be selected from HC1, H2SO4, etc. The obtained (TPA) crystals obtained via this route are rather small and difficult to separate from the other salts which may co-precipitate into the solution when lowering the pH. Using CO2 process allows the crystals to grow (at least twice the dimensions of the ones obtained via an alternative process such as chemical precipitation). This brings certain advantages to the process: easy filtration, high purity of the obtained (TPA) crystals, fast recovery, etc.

[0025] The solution containing the (TPA) crystals was further processed as such: to increase the process yields from 12% to 70% the pH of the solution was corrected to 2.5 using a strong acid such as HC1 or H2SO4 (concentration 0.35M). Then the solution was filtered using simple vacuum filtration on Buchner filter funnel using Whatman paper of 2.5pm porosity. The crystals were further washed directly on the funnel with hot water (t>90°C), then recovered and dried over night at controlled temperature and air flow 40°C under with internal air flow.

[0026] The colour and purity of the dried (TP A) crystals have been assessed. These are more in the approximate of the values of the virgin chemical species, such as TPA. This is a major achievement compared e.g. to the previous recovered TPA (b*=±12) where colour was a big issue in recycling.

[0027] In a first aspect the invention relates to a method of CO2 assisted crystallization of a chemical species, in particular from a fluidic mixture comprising said chemical species, comprising providing an increased-CCh pressure environment at a first pressure and at a first temperature, introducing said chemical species in at least one polar solvent, typically a liquid polar solvent, and wherein the chemical species and at least one polar solvent form a liquid solution, into said pressure environment, providing a supersaturation by increasing CO2 pressure, crystallizing said chemical species from said at least one solvent, in particular crystallizing into mono-crystalline crystals, and obtaining crystallized chemical species. The CO2 is used in that it supports the process of crystallization. The CO2 is not used to dissolve the chemical species, at least substantially not, and is also not used as a gas e.g. bubbling through the mother liquid or the like. In principle the method is applicable to any chemical species which can crystallize, or a mixture thereof. More than one chemical species may be present, of which then typically one thereof is the prime object of crystallization. For instance, in the case of TPA monomers, dimers, possibly trimers, and so on may be present. The mixture is in a fluidic form, typically in a polar solvent. The solvent is often referred to as the mother liquid. The mixture is introduced in an increased CO2 pressure environment, which are readily available. Then crystallization is effected by providing a supersaturation, including increasing a CO2 pressure in the CO2 pressure environment. It is to be understood that the supersaturation typically is increased gradually and controlled, e.g. step by step, or in a continuous mode; the supersaturation is typically also quite minimal, in that it is slightly higher (super) than an at the given temperature and pressure maximum saturation relating to the (maximum) solubility of the chemical species in the at least one polar solvent. The supersaturation therefore typically is e.g. less than 10K relative, typically less than 1 K relative, and / or less than 1 MPa relative, typically less than 0.1 MPa relative. By crystallization typically mono-crystalline, or single crystalline, crystals are obtained. Then crystals are obtained, such as by taking them out of the pressure environment.

[0028] In a second aspect the present invention relates to a crystal obtained by a method according to the invention, wherein the crystal comprises < 1 wt.% colorant, in particular < 10’2wt.% colorant, more in particular < 10'3wt.% colorant, so, most or almost all of the optionally present colorant in the original material, such as a polymer, is removed by the present method, and / or wherein the crystal comprises < 1 wt.% plasticizer, in particular < 10'2wt.% plasticizer, more in particular < 10'3wt.% plasticizer, so, most or almost all of the optionally present plasticizer in the original material, such as a polymer, is removed by the present method, and / or wherein the crystal have an average size of 5-100 pm and a standard size deviation of <5 pm (as measured using SEM), in particular a standard size deviation <1 pm, and / or wherein crystals are (substantially) mono-crystalline also referred to as singlecrystalline. Such results in much purer crystals, much better crystallinity, better work-up if required at all,

[0029] In a third aspect the present invention relates to a system for CO2 assisted crystallization comprising a pressure environment (1) comprising a CCh-inlet, a mixture inlet for a fluidic mixture comprising chemical species to be crystallized, a mixer, a pump (5) in fluidic connection with a CO2 source (4) and with the pressure environment CO2 inlet, in particular a (high) pressurized CO2 source (4), the CO2 source (4) in fluidic connection with pump (5) and with cooler (3), the cooler (3) in fluidic connection with the CO2 source (4) and CO2 recycling buffer tank (2), and optionally with a pressurized CO2 source (7), and a heater (6) in fluidic connection with the pump (5) and the pressure environment (1).

[0030] Thereby the present invention provides a solution to one or more of the above mentioned problems.

[0031] Advantages of the present description are detailed throughout the description. References to the figures are not limiting, and are only intended to guide the person skilled in the art through details of the present invention.

[0032] DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention relates in a first aspect to a method of CO2 assisted crystallization.

[0034] In an exemplary embodiment of the present method said chemical species is selected from carboxylic acids, from dicarboxylic acids, from tri-carboxylic acids, from dimers thereof, from trimers thereof, from speciation thereof, and from esters thereof, and from in the at least one polar solvent solvable inorganic or organic salts, and / or wherein the chemical species comprises C4-C32 carbon atoms, in particular Cs-Ci6 carbon atoms, and / or wherein the chemical species comprises 1-4 aromatic moieties, in particular 1-2 aromatic moieties, and / or wherein the chemical species has at least one pKa. Examples hereof are TPA CAS 100-21-0 and Phthalic acid CAS 88-99-3. So, the present method is particularly suited for relatively small carboxylic acids, and esters thereof. When these carboxylic acids, or chemical species in general, form part of a polymer, and said polymer is recycled by the present method, it particularly contributes to green methods.

[0035] In an exemplary embodiment of the present method a first pressure is >2 MPa (20 bar), in particular < 6 MPa (60 bar), typically at a pressure of 3-6 MPa, and / or a temperature of >5 °C, in particular at a temperature of 10-22 °C. The initial, first pressure is therefore not to high, and the temperature is close to environmental conditions.

[0036] In an exemplary embodiment of the present method supersaturation is provided at a supersaturation pressure of >2 MPa (20 bar), typically at a pressure of 3-30MPa, such as 8- 25 MPa, and / or a supersaturation temperature of >5 °C, in particular at a temperature of 10- 80 °C, typically wherein supersaturation pressure and / or supersaturation temperature are gradually increased from said first pressure and / or decreased from said first temperature. The supersaturation may be provided by a pressure increase and / or a temperature decrease, and may further be assisted by a lowering of the pH, or may be provided by lowering the pH, and may further be assisted by a pressure increase and / or a temperature decrease. The present increased CO2 pressure environment provides such options.

[0037] In an exemplary embodiment of the present method the temperature is from 35-80 °C and the pressure is from 7.37-30 MPa, in particular a temperature from 35-60 °C, in particular a pressure from 8-22 MPa. These conditions may be considered as super-critical, somewhat above minimal requirements thereto.

[0038] In an exemplary embodiment of the present method said mixture comprises as further components 0-20 wt.% of a structural analogue, in particular 0.1-7 wt.% structural analogue, more in particular 1-5 wt.% structural analogue, 0-7 wt.% of a natural or synthetic colorant selected from at least one of a pigment, a dye, a metal oxide, in particular 0,01-1 wt.%, such as 0, 1-0,3 wt.%, 0-20 wt.% of a plasticiser, in particular 0,01-1 wt.%, such as 0, 1-0,3 wt.%, 0-10 wt.% of a surfactant, in particular 0,01-1 wt.%, such as 0, 1-0,3 wt.%, and 0-20 wt.% of a filler, in particular 0,5-12 wt.%, such as 1-8 wt.%, and wherein the further components are substantially removed from the crystallized chemical species. A structural analogue is considered to relate to a compound, also known as a chemical analog or simply an analog, having a structure similar to that of another compound, but differing from it in respect to a certain component ((https : / zen wikipedi a . org / wiki / S tru ciuraf alog) . As the present chemical species may be relate to a degradation product of a polymer and the like, the polymer being formed in a process using further compounds, such as the components mentioned above, and, as the degradation product may comprise structural analogues of the present chemical species to be crystallized, one or more of these components may be present in the present mixture.

[0039] In an exemplary embodiment of the present method said at least one polar solvent is selected from at least one of water, C1-C4 alcohol, a liquid acid, an ionic liquid, a polar organic solvent [miscible with water], and a deep eutectic solvent. The present chemical species is typically provided as a liquid, such as a solution, with one or more of the aforementioned as solvent.

[0040] In an exemplary embodiment the present method further comprises lowering a pH, in particular to <5.5, more in particular to <pKa, even more in particular to < (pKa-1), wherein the pKa(cs) is the lowest pKa of the chemical species (cs), and / or adding a mineral acid, in particular wherein the mineral acid (ma) is selected from acids with a pKa (ma) < pKa(cs), more in particular pKa (ma) < 1, such as pKa < -1, even more in particular selected from at least one of HC1, H2SO4, and HN03. In an exemplary embodiment the present method further comprises introducing seed crystals of said chemical species into said pressure environment, in particular before and / or during providing the supersaturation, in particular introducing seed crystals near saturation. By providing the seed crystals it is found that crystallization is supported, and that better quality crystals are obtained.

[0041] In an exemplary embodiment of the present method the mixture comprising said chemical species is provided by de-polymerization, in particular by hydrolysis of a polymer, more in particular provided by degradation of a polymer comprising product, such as textile. As mentioned above, the present chemical species may relate to a degradation product.

[0042] In an exemplary embodiment the present method further comprises re-crystallizing the crystallized chemical species, in particular under said supersaturation conditions. In order to obtain even better and purer crystals for instance, the obtained crystals can be recrystallized.

[0043] In an exemplary embodiment of the present method further comprises filtering the crystallized chemical species, in particular over a Buchner filter (and Whatman 2.5 um porosity filter paper), and / or washing the crystallized chemical species with water at an elevated temperature, e.g. >70 C, e.g. > 90 C, and / or drying the crystallized chemical species. These are typical steps that may be performed after obtaining crystals, e.g. in order to provide directly reusable chemical species.

[0044] In an exemplary embodiment of the present method the mixture is flown over and / or surrounds the crystals and wherein the mixture is contacting the crystals. With intimate contact between the mixture and the crystals being formed a homogeneous mother liquid is provided, with well controlled parameters, such as supersaturation. As such good quality crystals are obtained.

[0045] In an exemplary embodiment of the present method crystallizing is performed during a period of > 1 minute, in particular 5-200 minutes, more in particular 60-180 minutes.

[0046] In an exemplary embodiment of the present method the CO2 is refreshed or circulated through the reactor with a circulation pump, in particular circulated through a conduit from the reactor, to a circulation pump, and back to the reactor, more in particular wherein the pressure in the reactor is substantially remained constant, in particular wherein circulation is continuous or wherein circulation is intermittent, or wherein the CO2 is circulated and replaced at least once.

[0047] In an exemplary embodiment of the present method the increased-pressure environment is a closed-cycle gas turbine or an autoclave. In case of the gas -turbine approach, an extra internal motor can be used to recirculate the CO2 inside the reactor during the reaction. The CO2 is generally circulated through the reactor and back to the recirculation pump and during depressurization the CO2 is circulated thorough the buffer thanks for cleaning and re-pressurization to the cycle pressure conditions. From the CO2 recycling buffer tank, at the end of the process, after depressurization, impurities which were carried out by CO2 can be collected. This process allows a recovery of the CChwith high purity.

[0048] The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art, it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

[0049] SUMMARY OF FIGURES

[0050] Figure 1. An example of the autoclave.

[0051] Figure 2. Schematic presentation of the machine

[0052] Figure 3. Schematic presentation of the TPA recovery process (e.g. example 4)

[0053] Figure 4. Scanning Electron Microscope (SEM) images of TPA crystal obtained from CO2 crystallization (example 1, figs. 4a-b represents TPA crystals obtained using first pressurization; example 2, figs 4c-e SEM images of TPA crystal obtained from SCCO2 crystallization).

[0054] Fig. 5a-b TPA solids recovered from CO2 first pressure crystallization, before washing (a) and after washing (b) of example 3.

[0055] Figs. 6a-p, Differences in colour of the recovered TPA from discoloured textile and coloured textile (example 5). 6a & 6j : discoloured PET fabrics; 6b & 6k: blue PET fabrics; 6c: PET fabrics in alkaline solution, left discoloured, right blue; 6d: Intermediate reaction time (9 hours) PET partially 6a:degraded and 6b: discoloured, 6e: Intermediate reaction time (20 hours), 6f: End reaction time (30 hours); 6d-f for discoloured textile, 6g-i for coloured textile; 61-6p PET degradation in alkaline solution with surfactant;6m & 60 intermediate reaction (1.5h); 6p &6n end reaction (3h) [example 5]

[0056] Figs. 7a-b Differences in colour of the recovered TPA from discoloured textile and coloured textile [example 5],

[0057] Fig. 8; obtained TPA crystals from coloured PET textile compared with the ones obtained from discoloured PET textile.

[0058] Figs. 9a-b: SEM images of TPA crystal obtained via CO2 crystallization from PET fabric hydrolysis: discoloured PET (a) and blue PET (b)[example 5],

[0059] DETAILED DESCRIPTION OF FIGURES

[0060] The figures are further detailed in the description of the experiments below.

[0061] EXAMPLES / EXPERIMENTS

[0062] An analysis is made in view of TPA crystals.

[0063] Table 1. Colour characteristics of TPA crystals obtained from CO2 crystallization processes.

[0064] Experiment TP A crystal colour (b*)

[0065] CO2 crystallization +5.32

[0066] CO2 crystallization + hot water washing +4.66 C02crystallization + AC treatment + hot water +3.09 washing

[0067] CO2 and acid crystallization + hot water washing +0.57 b* does not have a unit it is a colour spectrum shift in colour space.

[0068] The colour of the TPA crystals do not differ significantly from the ones recovered after addition AC purification step. That is considered a major benefit.

[0069] The same CO2 process was applied for TPA crystallization and recovery from a mother liquor resulted from PET textile degradation.

[0070] The two PET samples used for degradation originated from:

[0071] - blue sample from scCCh dyeing (blue colour)

[0072] - discoloured sample also made via scCCh discoloration.

[0073] Both samples were exposed to a solution made of >1 M sodium hydroxide, preferred between 1.2 and 1.5M at temperatures >80°C, preferred between 90-100°C.

[0074] Degradation of PET

[0075] The degradation of the PET textile material was twice faster in the case of discoloured PET textile. The resulted solution from both samples have been filtered, exposed to CO2 for crystallization, and recovery of TPA. (See example 5). The PET degradation using surfactant was lOx faster than without surfactant for the same process conditions.

[0076] The increased CO2 pressure machine is provided with a quick-closure autoclave, CO2 pump, integrated cooling / heating system and a small control panel where the operator can control the process parameters. The machine is fully automated (plug and play system) and uses CO2 from bottles or external cryogenic tank. CO2 utilized in such processes can originate from recovered (Carbon capture) sources or fresh CO2. The ratio CCh / solution depends mainly on the pressure and temperature conditions. Higher temperatures (40-90°C) and pressures will induce a fast crystal growth compared to lower temperatures. Preferred conditions are a ratio of CCh / solution between 0.01-5, most preferably between 0.03-1.

[0077] When the process was finalized, the depressurization could be done in dissimilar stages with >95% CO2 recovery. Solubility of the CO2 in the polar solvent, e.g. aqueous solution, depends mainly on the pressure rate of the process. The solubility of the CO2 is found to determine the pH drop via the formation of the carbonic acid. The final pH attained depends amongst others on the initial pH of the TPA solution. The variation of the pH under CO2 conditions can be corrected between 1-3 units, most frequently between 1-2 units; that is considered a limited correction, quite often not sufficient in view of e.g. higher yields, better crystals, etc.

[0078] In an alternative inventors used a high-pressure autoclave with injection system for liquid or scCCh which should be in direct contact with the solution containing the dissolved chemical species, such as TPA. An additional mixer, such as a stirring device, can be used to ensure a better contact between CO2 and the solution. The stirring rate may adjustably the same as the CO2 flow. A temperature is monitored inside the autoclave via a PT 100 sensor and reading thereof is registered during the entire process. Depressurization is done via a controlled system.

[0079] The machine used is fully automated but can work as well in manual controlled mode.

[0080] An example of the aimed process is outlined here:

[0081] Example 1 CO2 crystallization of TPA and its esters applied directly in the hydrolysed solution.

[0082] Inventors used CO2 as anti-solvent for inducing TPA crystallization directly in mother liquor solution. The TPA solution used resulted from PET enzymatic hydrolysis. It is noted that next to TPA the hydrolysate solution (initial pH between 7-8, TPA concentration 70 g / L, containing 0.2M sodium phosphate buffer, IM NaCl, and 2M NaOH) contains a lot of salts as well (Na, K, phosphates, carbonates, etc.) along with organic impurities resulted for PET processing into final products. The TPA solution was processed inside an autoclave where CO2 was added gradually from a bottle. The TPA crystallization started at 5.5MPa, and crystal growth depended on the process time and TPA seeding. The process temperature was 180°C. When seeding was used, between 4-5MPa, it allowed direct secondary nucleation of TPA with further growth. The growth of the TPA crystals is rather slow and it is found influenced by stirring rate and solution saturation. The bigger the crystals, the better handling and more purified they were. After Ih the process is stopped and the TPA (or its esters) crystals were directly filtered (Whatman filter paper) and washed with hot water, dried overnight at 40°C (moisture content <0.5%) and then sent to re-polymerization. The process yield is determined by the pH of the final solution. The lower the pH the better yields were found. When the original solution of TPA is a buffer solution with higher pH, after exposing to CO2 crystallization, the pH of the solution can be further corrected (lowering further to reach 2-2.5 which is required to attain higher recovery yields. A maximum recovery yield is obtained around pH=2, best between pH=2 and pH 2.8, and preferred at pH 2.5.

[0083] The collected TPA (or its esters) can be further filtered and washed directly on the filter with hot demineralized water (T>90°C) to obtain purified TPA crystals (or its esters). Depending on the crystallization time, saturation of TPA and temperature, the crystal size produced by CO2- induced crystallization is ranging from 5-70pm.

[0084] Elemental identification of TPA crystals obtained from CO2 crystallization shows Carbon 72.97 (atom Concentration) and 66.96 (relative weight), and Oxygen 27.03 (atom Concentration) and 33.04 (relative weight). This is in line with expectations. The recovered TPA obtained by this method showed a purity of 98-100% according to XRF analysis. Example 2. Crystallization of TPA using scCCh

[0085] For the crystallization of the TPA from same hydrolysed solution (see example 1) supercritical CO2 was used as anti-solvent and pH correction for inducing TPA crystallization. The solution contains TPA (70g / L) along with other contaminants, such as enzymatic residue, and aromatic compounds used as additives, such as plasticizers and surfactants, for PET polymerization. The process was carried out at moderate temperatures (35-60°C) and moderate pressure (8-12 MPa) above a critical point of CO2. Additional stirring was applied (stirring rates between 300-540 rpm). The stirring increases the contact between CO2 and mother liquor. The process takes place in a closed autoclave with controlled temperature, pressure, and stirring rate. The CO2 flow rate was kept constant at lOkg / h during the process. At the end of the process the solid TPA (or its esters) crystals can be directly filtered (Whatman filter paper) and washed with hot water, dried overnight at 40°C, and then sent to re-polymerization. The produced TPA crystal ranged between 10 and 100pm. These crystals were almost twice bigger than TPA crystals produced in example 1, for similar processing time. The TPA crystals have a needle-like shape (much thinner than in Example 1) and tend to agglomerate. The agglomerates can reach 200pm in diameter.

[0086] Example 3. Purification of TPA using AC and hot water

[0087] In this experiment inventors used a same type of TPA solution (hydrolysed PET) as in Examples 1 & 2. In this example inventors have pre-purified the hydrolysate using active (or likewise activated) carbon filtration (AC) prior to TPA crystallization. Inventors used Cabot Norit GAC 830W and Desotec DSL22-0082. AC was added directly to hot hydrolysate solution at a temperature between near the boiling point (95°C) under low constant stirring (<200rpm). The salts started to precipitate above 70°C. The solution was kept under stirring for min. 30min, and preferably Ih. Then the solution was filtered using a Whatman filter paper 2.5pm. The recovered filtrate which contains AC and TPA salts was further washed with hot demineralized water. The filtrate was further used for TPA crystallization following procedure described in Example 1. The recovered solid TPA was further washed with hot DI water approximately 3 times volume of the filtrate, preferably at boiling temperature. The post-purification from hot water washing improved the coloration of the TPA solids and significantly reduced the salts measured (before washing 27000 p pm, after washing <380ppm) in the recovered materials.

[0088] Example 4. Re-use of the filtrate

[0089] PET hydrolysate following the CO2 crystallization process, depending on the pH of the initial solution can be further acidified with mineral acids (HC1 or H2 SO4) to reach a pH around 2-3. After filtration of the obtained TPA, the filtrate can be partially reused for pH correction and partially send to salt recovery via cooling crystallization or evaporation. The resulted water can be further used for washing final TPA crystals or in making new acidic solution. The recovered salts can be re-used. The TPA resulted after filtration is washed directly on the filter with hot water and then dried overnight at 40°C. The filtrate resulted after washing TPA crystals can be send to re-cycle (cooling crystallization or evaporation) see figure 3.

[0090] Example 5. TPA recovered from alkaline hydrolysis of PET fibre.

[0091] PET fibres were degraded by alkaline hydrolysis using 1.5M NaOH (pH 14) producing di sodium terephthalate which mimics the condition obtained via PET enzymatic degradation. Similar solution was made using NaOH (1.5M) with Ig / mL cetyltrimethylammonium chloride as cationic surfactant.

[0092] PET fabrics are notably high in crystallinity, requiring exposure to harsh chemical conditions (extremely high or low pH) and higher temperatures (>100°C) to initiate the depolymerization process. In this example, approximately 0.2 g of discoloured and blue-coloured PET fabrics were degraded under an alkaline hydrolysis condition using 1.5 M sodium hydroxide at 100 °C. At intermediate reaction time (9 hours), the original fabric was readily degraded while the blue fabric was still intact while undergoing decolorization. Only after 20 hours did the coloured PET fabric start to decompose. The depolymerization reaction of the original PET fabric proceeded two times faster than that of the coloured materials, indicating that the presence of additives, in this instance, colorants, hindered the depolymerization process. The reaction was stopped after 30 hours by quenching the reaction in an ice bath. In the case of using cationic surfactant the reaction rate was increased to 3h for total textile degradation at 100°C. A slightly faster degradation of the discoloured textile was observed. The remaining PET residues were filtered out prior to the TPA recovery. Recovery of the dissolved TPA from the solution can be initiated via same procedure as mentioned in example 1. The TPA recovery yield is directly correlated to the initial pH of the hydrolysed solution with higher yield obtained from lower pH solution, preferably between pH 6-8.

[0093] Following the PET degradation, the two solutions were filtered, and the pH of the filtrate was slightly corrected to 6 before exposure to CO2. The CO2 crystallization of TPA was done according to example 1.

[0094] After crystallization, the TPA was recovered via filtration and the TPA crystals were washed with hot water and dried at 40°C. The coloured textile yielded a slightly pink TPA as the discoloured textile was yielding white TPA crystals. It is obvious that the discoloration step is necessary for obtaining white TPA crystals.

[0095] The crystals were characterized using scanning electron microscope (SEM).

[0096] Example 6. TPA recovered from alkaline solution.

[0097] TPA recovered from CCh-induced crystallization can be further recrystallized from an alkaline solution NaOH (pH 10.4) to further increase its purity or crystal size. For this purpose, TPA solid (Concentration of 65mM) was redissolved in alkaline solution (pH 10.4) at 70°C and re precipitated using CO2. The final pH after pressure release measured 3.5-3.7-unit reduction. The pH of the mother liquor can be further corrected with very small amounts of mineral acids (H2SO4). This situation depends on the starting pH of the alkaline solution and in correlation with the targeted pH of 2.5-3 when all TPA speciation will be transformed into TPA. The TPA crystals were further filtered and washed with hot DI water directly on the filter. The recovery yield was 18-20% higher then using the buffer solution. Using solution with pH between 8- 10, preferably 8 can be used to directly crystallize TPA using CO2. At the end of the process the TPA (or its esters) can be directly filtered and washed with hot water, dried overnight at 40°C, and then sent to re-polymerization. The alkaline filtrate can be reused for recrystallization solvents for another batch of TPA solids.

[0098] It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the inventive concept of the invention.

Claims

CLAIMS1. A method of CO2 assisted crystallization of a chemical species, in particular from a fluidic mixture comprising said chemical species, comprisingProviding an increased-CCh pressure environment at a first pressure and at a first temperature,Introducing said chemical species in at least one polar solvent therewith forming a fluidic solution into said pressure environment,Providing a supersaturation by increasing CO2 pressure,Crystallizing said chemical species from said at least one polar solvent at said increased CO2 pressure, in particular crystallizing into mono-crystalline crystals, andObtaining crystallized chemical species.

2. The method of CO2 assisted crystallization according to claim 1, wherein said chemical species is selected from carboxylic acids, from dicarboxylic acids, from tri-carboxylic acids, from dimers thereof, from trimers thereof, from speciation thereof, and from esters thereof, and from in the at least one polar solvent solvable inorganic or organic salts, and / or Wherein the chemical species comprises C4-C32 carbon atoms, and / orWherein the chemical species comprises 1-4 aromatic moieties, and / or Wherein the chemical species has at least one pKa.

3. The method of CO2 assisted crystallization according to claim 1 or 2, wherein a first pressure is >2 MPa (20 bar), in particular < 6 MPa (60 bar), typically at a pressure of 3-6 MPa (30-60 bar), and / or a first temperature of >5 °C, in particular at a temperature of 10-22 °C.

4. The method of CO2 assisted crystallization according to any of claims 1-3, wherein supersaturation is provided at a supersaturation increased CO2 pressure of >2 MPa (20 bar), typically at a pressure of 3-30MPa (30-300bar), such as 8-25 MPa (80-250 bar), and / or a supersaturation temperature of >5 °C, in particular at a supersaturation temperature of 10- 80 °C, typically, wherein supersaturation pressure and / or supersaturation temperature are gradually increased from said first pressure and / or decreased from said first temperature, or wherein the first temperature is from 35-80 °C and the first pressure is from 7.37-30 MPa (73.7-300 bar), in particular a first temperature from 35-60 °C, in particular a first pressure from 8-22 MPa (80-220 bar).

5. The method of CO2 assisted crystallization according to any of claims 1-4, wherein said mixture comprises as further components0-20 wt.% of a structural analogue, in particular 0.1-7 wt.% structural analogue, 0-7 wt.% of a natural or synthetic colorant selected from at least one of a pigment, a dye, a metal oxide,0-20 wt.% of a plasticiser,0-10 wt.% of a surfactant, and0-20 wt.% of a filler, andWherein the further components are substantially removed from the crystallized chemical species.

6. The method of CO2 assisted crystallization according to any of claims 1-5, wherein said at least one polar solvent is selected from at least one of water, C1-C4 alcohol, a liquid acid, an ionic liquid, a polar organic solvent [miscible with water], and a deep eutectic solvent.

7. The method of CO2 assisted crystallization according to any of claims 1-6, further comprising lowering a pH, in particular to <5.5, more in particular to <pKa, even more in particular to < (pKa-1), wherein the pKa(cs) is the lowest pKa of the chemical species (cs), and / or Adding a mineral acid, in particular wherein the mineral acid (ma) is selected from acids with a pKa (ma) < pKa(cs), more in particular pKa (ma) < 1, such as < -1, even more in particular selected from at least one of HC1, H2SO4, and HNO3.

8. The method of CO2 assisted crystallization according to any of claims 1-7, further comprising introducing seed crystals of said chemical species into said pressure environment, in particular before and / or during providing the supersaturation, in particular introducing seed crystals near saturation.

9. The method of CO2 assisted crystallization according to any of claims 1-8, wherein the mixture comprising said chemical species is provided by de-polymerization, in particular by hydrolysis of a polymer, more in particular provided by degradation of a polymer comprising product, such as textile.

10. The method of CO2 assisted crystallization according to any of claims 1-9, further comprising re-crystallizing the crystallized chemical species, in particular under said supersaturation conditions.

11. The method of CO2 assisted crystallization according to any of claims 1-10, further comprising filtering the crystallized chemical species, in particular over a Buchner filter (and Whatman 2.5 um porosity filter paper), and / orWashing the crystallized chemical species with water at an elevated temperature, e.g. >70 C, e.g. > 90 C, and / orDrying the crystallized chemical species.

12. The method of CO2 assisted crystallization according to any of claims 1-11, Wherein the mixture is flown over and / or surrounds the crystals and wherein the mixture is contacting the crystals.

13. The method of CO2 assisted crystallization according to any of claims 1-12, wherein crystallizing is performed during a period of > 1 minute, in particular 5-200 minutes, more in particular 60-180 minutes.

14. The method of CO2 assisted crystallization according to any of claims 1-13, whereinthe CO2 is refreshed or circulated through the reactor with a circulation pump, in particular circulated through a conduit from the reactor, to a circulation pump, and back to the reactor, more in particular wherein the pressure in the reactor is substantially remained constant, in particular wherein circulation is continuous or wherein circulation is intermittent, or wherein the CO2 is circulated and replaced at least once.

15. The method of CO2 assisted crystallization according to any of claims 1-14, wherein the increased-pressure environment is a closed-cycle gas turbine or an autoclave16. A crystal obtained by a method according to any of claims 1-15, wherein the crystal comprises < 1 wt.% colorant, in particular < 10'1wt.% colorant, more in particular < 10'2wt.% colorant, and / or wherein the crystal comprises < 1 wt.% plasticizer, in particular < 10'1wt.% plasticizer, more in particular < 10'2wt.% plasticizer, and / or wherein the crystal has an average size of 5-100 pm and a standard size deviation of <5 pm (as measured using SEM), in particular a standard size deviation <1 pm, and / or wherein crystals are mono-crystalline.

17. A system for CO2 assisted crystallization comprising a pressure environment (1) comprising a CCh-inlet, a mixture inlet for a fluidic mixture comprising chemical species to be crystallized, a mixer, in particular a stirrer, and optionally a temperature sensor, and a pressure sensor, a pump (5) in fluidic connection with a CO2 source (4) and with the pressure environment CO2 inlet, in particular a pressurized CO2 source (4), the CO2 source (4) in fluidic connection with pump (5) and with cooler (3), the cooler (3) in fluidic connection with the CO2 source (4) and CO2 recycling buffer tank (2), and optionally with a pressurized CO2 source (7), and a heater (6) in fluidic connection with the pump (5) and the pressure environment (1).

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