Solvent-based plastic recycling using film

Abstract

The invention relates to a method for removing one or more solvent-soluble additives from a polymer comprising less than 40% by weight of polyvinyl chloride or from a mixture of polymers comprising less than 40% by weight of polyvinyl chloride, the method comprises the steps of: a) dissolving the polymer or mixture of polymers comprising the one or more solvent-soluble additives in a solvent or solvent mixture, the solvent or solvent mixture dissolving the polymer or mixture of polymers and also dissolving the one or more additives, b) filtering a solution comprising a dissolved polymer or polymer mixture and one or more dissolved additives over a solvent resistant membrane, whereby the dissolved polymer is trapped by the membrane and the one or more solvent soluble additives permeate through the membrane.

Description

Technical Field

[0001] The present invention relates to membrane filtration and plastic recycling. Background Art

[0002] The use of plastics creates challenges in waste management, leading to a cumulative crisis. Global demand for polymer production has increased dramatically, reaching approximately 350 million metric tons annually. However, it is well known that there are only a few commercially viable and economical methods for reusing polymers. 55% of polymer waste is discarded in the environment or landfills, 25% is burned for energy recovery, and only 25% is recycled.

[0003] The recycling process can be described as recovering and reusing waste materials even in different processes, which creates a cleaner environment and improves the circular economy model. There are many recycling methods such as chemical, mechanical and thermal recycling.

[0004] Chemical recycling requires different reagents and solvents. Furthermore, this method is time-consuming, energy-intensive, and expensive to implement. Consequently, the need for expertise and significant investment has limited this method to investigation by a small number of companies. Thermal recycling involves heating composite materials at temperatures ranging from 350°C to 800°C. However, this method introduces impurities and produces toxic substances during the recycling process. In Europe, 98% of plastics are recycled through mechanical recycling methods, which poses a problem due to the diversity of plastics and additives, as well as the inability to remove and recover these additives.

[0005] Solvent-based purification (dissolution precipitation) is an interesting method for recycling plastics due to the selective solubility of polymers in mixtures of polymers and the dissolution process to separate additives (including organic additives) from the polymers.

[0006] The process is typically based on (1) dissolution of waste polymer material (containing additives) in a solvent, and (2) recovery of the purified polymer by adding a solvent resistant to the polymer, thereby causing its precipitation while keeping the undesired additives in solution.

[0007] EP 4 067 421 discloses a process in which a halogenated polymer is dissolved and contaminants (eg heavy metal residues) are present in a discontinuous phase. The contaminants are removed by separating the discontinuous phase from the continuous phase with the dissolved polymer, for example by centrifugation or filtration. Summary of the Invention

[0008] The present invention relates to the removal of additives from waste plastics by dissolution and solvent-resistant membrane filtration.

[0009] The present invention is summarized in the following statement:

[0010] 1. A process for removing one or more solvent-soluble additives from a polymer comprising less than 40% by weight of polyvinyl chloride or from a mixture of polymers comprising less than 40% by weight of polyvinyl chloride,

[0011] The method comprises the following steps:

[0012] a) dissolving the polymer or polymer mixture comprising the one or more solvent-soluble additives in a solvent or solvent mixture which dissolves the polymer or polymer mixture and also the one or more additives,

[0013] b) filtering a solution comprising the dissolved polymer or polymer mixture and one or more dissolved additives over a solvent resistant membrane, whereby the dissolved polymer is retained by the membrane and the one or more solvent soluble additives permeate through the membrane.

[0014] 2. The process according to statement 1, wherein the polymer comprises less than 20 wt% polyvinyl chloride or wherein the mixture of polymers comprises less than 20 wt% polyvinyl chloride.

[0015] 3. A process according to statement 1 or 2, wherein the polymer comprises less than 10 wt% polyvinyl chloride or wherein the mixture of polymers comprises less than 10 wt% polyvinyl chloride.

[0016] 4. The process according to any one of statements 1 to 3, wherein the polymer comprises less than 5 wt% polyvinyl chloride or wherein the mixture of polymers comprises less than 5 wt% polyvinyl chloride.

[0017] 5. The process according to any one of statements 1 to 4, wherein the polymer comprises less than 1 wt% polyvinyl chloride or wherein the mixture of polymers comprises less than 1 wt% polyvinyl chloride.

[0018] 6. Process according to any one of statements 1 to 5, wherein the membrane has a molecular weight cut-off of less than 20 000 Da.

[0019] 7. The method according to any one of statements 1 to 6, wherein the membrane is a cross-linked polyimide membrane.

[0020] 8. The method according to any one of statements 1 to 6, wherein the membrane is a cross-linked PVDF membrane.

[0021] 9. The process according to any one of statements 1 to 8, wherein the polymer is selected from polystyrene, polyethylene and polypropylene.

[0022] 10. A method according to any one of statements 1 to 9, wherein the solvent-soluble additive has a Mr of less than 1000 Da, less than 750 Da or less than 500 Da.

[0023] 11. A process according to any one of statements 1 to 10, wherein the membrane has a permeability of greater than 3, 4, 5, 6 or 7 L.m-2.h-1.bar-1 and a polystyrene rejection of greater than 90% as compared with a 0.1% (w / v) solution of polystyrene with a Mw between 250 and 300 kDa in n-BiOAc at a temperature of 25°C and a pressure of 5 bar.

[0024] 12. A process according to any one of statements 1 to 11, wherein the membrane has a permeability of greater than 3, 4, 5, 6 or 7 L.m-2.h-1.bar-1 and a polystyrene rejection of greater than 90% as compared to a 0.1% (w / v) solution of polystyrene with a Mw between 250 and 300 kDa in n-BiOAc at a temperature of 100°C and a pressure of 25 bar.

[0025] 13. The process according to any one of statements 1 to 12, wherein the solvent-soluble additive is a dye, a plasticizer or a UV-scavenger, a heat-donating compound or a compound providing stability to thermal radiation.

[0026] 14. The process according to any one of statements 1 to 13, wherein the solvent is selected from NMP, THF, DMF, DMAc, butyl acetate, methyl ethyl ketone, chloroform and dichloromethane.

[0027] 15. A process according to any one of statements 1 to 14, wherein the dissolved polymer is present after step a) and before step b) in a concentration between 0.1 wt% and 5 wt%, 10 wt%, 15 wt% or 20 wt%.

[0028] 16. The process according to any one of statements 1 to 15, wherein the filtration is carried out at a temperature between 10°C and 100°C.

[0029] 17. The process according to any one of statements 1 to 16, wherein the filtration is carried out at a pressure of between 1 and 25 bar.

[0030] 18. The process according to any one of statements 1 to 17, wherein the filtration in step b) is a dead-end filtration.

[0031] 19. The process according to any one of statements 1 to 17, wherein the filtration in step b) is a cross-flow filtration.

[0032] 20. The process according to any one of statements 1 to 19, wherein insoluble material is removed after step a) and before step b).

[0033] 21. The process according to any one of statements 1 to 19, wherein after step b) the polymer is recovered by evaporation of the solvent.

[0034] 22. The process according to any one of statements 1 to 19, wherein the additive is recovered after step b) by evaporation of the solvent.

[0035] 23. A method for removing one or more solvent-soluble additives from a polymer other than polyvinyl chloride or from a mixture of polymers other than a mixture comprising polyvinyl chloride, the method comprising the steps of:

[0036] a) dissolving the polymer or the mixture of polymers comprising the one or more solvent-soluble additives in a solvent or a solvent mixture which dissolves the polymer and the one or more additives,

[0037] b) filtering a solution comprising the dissolved polymer and the one or more dissolved additives over a solvent resistant membrane, whereby the dissolved polymer is retained by the membrane and the one or more solvent soluble additives permeate through the membrane.

[0038] 24. A method according to statement 23, wherein the membrane has a molecular weight cut-off (MWCO) of less than 100,000 Da, less than 50,000 Da, less than 20,000 Da, less than 10,000 Da, less than 5,000 Da, less than 2,000 Da, or less than 1,000 Da. ["Less than" refers to the upper limit of the range; the lower limit can be 100, 200, or 500.] A higher upper limit of the MWCO can, on the one hand, result in the loss of a portion of the dissolved polymer as it passes through the membrane. The polymer chains can curl or extend, depending on the solvation of the liquid and the flexibility of the polymer backbone. If high MW polymer chains extend more in the solvent, while low MW polymer chains curl more and are therefore larger in size, the high MW polymer chains may therefore be retained less than the low MW polymer chains. On the other hand, the higher the MWCO, the less additive is retained and the higher the flux. A higher flux allows the use of a smaller surface area of the membrane.

[0039] It is up to the skilled artisan to balance the loss of polymer with enhanced flux and removal of additives.

[0040] 25. A method according to statement 23 or 24, wherein the solvent-resistant membrane has a permeability of greater than 3, 4, 5, 6 or 7 L.m-2.h-1.bar-1 and a polystyrene rejection of greater than 90% compared to a reference measurement with a 0.1% (w / v) polystyrene (Mw 250-300 kDa) solution in n-BiOAc at a temperature of 25°C and a pressure of 5 bar.

[0041] 26. A method according to statement 23 or 24, wherein the solvent-resistant membrane has a permeability greater than 3, 4, 5, 6 or 7 L.m-2.h-1.bar-1 and a polystyrene rejection greater than 90% compared to a reference measurement with a 0.1% (w / v) polystyrene (Mw 250-300 kDa) solution in n-BiOAc at a temperature of 100°C and a pressure of 25 bar.

[0042] 27. A method according to any one of statements 23 to 26, wherein the membrane is a cross-linked polymer membrane, such as a cross-linked polyimide membrane, a cross-linked polysulfone membrane, a cross-linked polyvinylidene fluoride membrane or a cross-linked polyvinyl chloride membrane.

[0043] 28. The method according to any one of statements 23 to 27, wherein the membrane is a cross-linked polyimide membrane or a cross-linked PVDF membrane.

[0044] 29. A process according to any one of statements 23 to 28, wherein the polymer is selected from the group consisting of polystyrene, polyethylene and polypropylene. The present invention is equally applicable to heteropolymers.

[0045] 30. A method according to any one of statements 23 to 29, wherein the solvent-soluble additive has a Mr of less than 1000 Da, less than 750 Da or less than 500 Da.

[0046] 31. A process according to any one of statements 23 to 30, wherein the additive is a dye, a plasticizer or a UV-scavenger, a compound providing thermal or radiation stability.

[0047] 32. A process according to any one of statements 23 to 31, wherein the additive is present in the dissolved polymer in a concentration of between 0.5 and 50% by weight.

[0048] 33. A process according to any one of statements 23 to 32, wherein the solvent is selected from NMP, THF, DMF, DMAc, butyl acetate, methyl ethyl ketone, chloroform, dichloromethane.

[0049] 34. A process according to any one of statements 23 to 33, wherein the dissolved polymer is present after step a) and before step b) at a concentration between 0.1 wt% and 5 wt%, 10 wt%, 15 wt% or 20 wt%.

[0050] Typical starting polymer concentrations are usually as high as possible, typically 5-20% by weight, depending on the viscosity of the solution. This can be even higher if possible. During filtration, viscosity increases, and higher temperatures or pressures may be applied to facilitate the process. If high concentrations of additives are to be removed from the polymer, a filtration process is employed in which the concentrated retentate is first diluted and then filtered again. This dilution-filtration sequence can be repeated several times, and both the dilution and concentration factors can be selected.

[0051] 35. A process according to any one of statements 23 to 34, wherein the filtering is carried out at a temperature between 10 and 100°C.

[0052] 36. The process according to any one of statements 23 to 35, wherein the filtration is carried out at a pressure between 1 and 25 bar.

[0053] 37. The process according to any one of statements 23 to 36, wherein the filtration in step b) is dead-end filtration or cross-flow filtration.

[0054] In industrial processes, membrane filtration is typically run in cross-flow mode. When the permeability drops below 1 Lmh / bar, the process is typically stopped and worked up (e.g. via distillation, non-solvent addition, cooling...) or the retentate is diluted again when operating in diafiltration mode.

[0055] 38. A process according to any one of statements 23 to 37, wherein the solution in step b) contains less than 10, 8, 6, 4, 2, 1, 0.5, 0% water.

[0056] 39. A process according to any one of statements 23 to 38, wherein insoluble material is removed (by filtration, centrifugation, sedimentation, decantation) after step a) and before step b).

[0057] 40. The process according to any one of statements 23 to 39, wherein the solution is stirred during step b).

[0058] 41. The process according to any one of statements 23 to 40, wherein after step b) the polymer is recovered by evaporation of the solvent and / or wherein the additive is recovered by evaporation of the solvent. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 Graphical depiction of the results of filtration experiments using XL-PI (cross-linked polyimide) membranes made from PI-doped solutions with varying Matrimid concentrations (15, 16, 17, and 18 wt%) and a 0.1 w / v feed solution consisting of three different types of polystyrene (PS) (A, B, and C). The average polystyrene retention is depicted by the gray bars, and the average permeability is shown as red dots, both obtained from a set of four data points. Error bars depict the standard deviation.

[0060] Figure 2Graphical depiction of a) the effect of operating temperature (°C) at a constant pressure of 5 bar on the PI-XL membrane and pure n-BuOAc as the feed solution, b) the effect of operating pressure (bar) at room temperature (25°C) on the PI-XL membrane and pure n-BuOAc as the feed solution, and c) the effect of operating pressure (bar) at RT on the flux of the PI-XL membrane and pure n-BuOAc as the feed solution.

[0061] Figure 3 a) Effect of increasing concentration (w / v%) of three different PS (A, B, C) solutions in n-BuOAc on membrane permeability and feed solution viscosity, and b) graphical depiction of the average rejection of PS (A, B, C) solutions from 1 w / v% to 8 w / v%.

[0062] Figure 4 Membrane permeability of three different polystyrene solutions (A, B, C) as a function of temperature (°C) on the left (green line) and as a function of viscosity (mPa.s) on the right (red line). The thermal conditions were investigated using two polystyrene solution concentrations of 1 and 5 w / v%.

[0063] Figure 5 Arrhenius plot of the effect of temperature (K) on the flux of three different polystyrene solutions (A, B, C), where the concentrations of the two polystyrene solutions are 1 w / v% and 5 w / v%.

[0064] Figure 6 Permeability values for three different polystyrene solutions (A, B, C) as a function of operating pressure (bar). The pressure conditions were investigated using two polystyrene solution concentrations, 1 and 5 w / v%, shown in two columns. a: PS A, 1 w / v%, b: PS A, 5 w / v%, c: PS B, 1 w / v%, d: PS B, 5 w / v%, e: PS C, 1 w / v%, f: PS C, 5 w / v%.

[0065] Figure 7 Dead-end filtration under operating pressure was investigated for two polymer solution concentrations (1 w / v% and 5 w / v%) of three different polystyrenes (A, B, C) at RT and 40°C (on two rows, two columns). a: 1 w / v% PS (A, B, C) solution at RT, b: 5 w / v% PS (A, B, C) solution at RT, c: 1 w / v% PS (A, B, C) solution at 40°C, d: 5 w / v% PS (A, B, C) solution at 40°C.

[0066] Figure 8The P-value is interpreted as the significance level of all inputs (temperature, pressure, concentration and combination of these) on the output (permeability) as it is considered to be less than 0.05 (vertical line indicated by arrow) to show the maximum probability for each variable. DETAILED DESCRIPTION

[0067] Throughout this invention, whenever reference is made to "polymer" as a general term, it limits or excludes halogenated vinyl polymers, and more particularly limits or excludes polyvinyl chloride (PVC).

[0068] By polymer is thus meant a polymer comprising less than 40% by weight of halogenated vinyl polymers or PVC, comprising less than 30% by weight of halogenated vinyl polymers or PVC, comprising less than 20% by weight of halogenated vinyl polymers or PVC, comprising less than 10% by weight of halogenated vinyl polymers or PVC, comprising less than 5% by weight of halogenated vinyl polymers or PVC, or comprising less than 1% by weight of halogenated vinyl polymers or PVC.

[0069] "Polymer mixture" means a mixture of dissolved polymers having a PVC concentration of less than 40 wt%, less than 30 wt%, less than 20 wt%, less than 10 wt%, less than 5 wt%, or less than 1 wt%.

[0070] The present invention relates to the use of ultrafiltration using, for example, a cross-linked polyimide membrane for recycling polymers under different operating conditions, such as the effects of operating pressure, temperature, concentration and viscosity of the feed solution on the membrane permeability of the polymer, in order to find the optimal conditions for separating dissolved polymers (e.g., polystyrene) from solvents (e.g., n-butyl acetate (n-BuOAc)). The pure solvent performance is investigated under operation with gradually increasing pressure and temperature and then gradually reducing them in a continuous process.

[0071] Operating pressure, temperature, feed solution concentration, and viscosity have a significant impact on membrane separation performance. Increasing pressure, feed solution concentration, and viscosity decreases membrane permeability due to concentration polarization and accumulation of solutes on the membrane surface. Membrane permeability increases with increasing temperature and activation energy. Hysteresis lines are observed in pure solvent filtration during the return process at operating pressures and temperatures, respectively, related to compaction of the feed solution into the membrane and changes in membrane polymer chains at high temperatures.

[0072] The present invention discloses a method for recycling polymers and obtaining high-quality original-like plastics. Membrane technology is a reliable and repeatable separation process that has shown various applications in chemistry, environment and water treatment. Solvent-resistant nanofiltration-ultrafiltration (SRNF-SRUF) is a method with excellent separation performance and long-term stability even in harsh solvents. Compared with other methods, polymer membranes have shown many advantages, such as the ability to adjust separation properties, selectivity, greener, faster production, lower cost and energy, easier processing and mechanical stability. Due to its heat resistance and chemical resistance, easy preparation and commercial expansion, PI membranes are currently used in various applications [Vanherck et al. (2008) J.Membrane Sci.320,468-476].

[0073] The present invention relates to methods for removing one or more solvent-soluble additives from polymers other than polyvinyl chloride or polymer mixtures. These methods comprise the steps of (a) dissolving the polymer and the additives and (b) filtering the polymer.

[0074] The polymer or polymer mixture comprising one or more solvent-soluble additives is dissolved in step a) in a solvent or solvent mixture which dissolves the polymer or polymer mixture and the additive or additives which the skilled person wants to remove from the polymer.

[0075] In step b) the solution comprising the dissolved polymer or a mixture thereof and one or more dissolved additives is filtered over a solvent-resistant membrane.

[0076] In this filtration step, the dissolved polymer is retained by the membrane and the solvent dissolved additive(s) permeate through the membrane.

[0077] Listed below is a non-limiting list of polymers contemplated for the methods of the present invention, along with exemplary solvents in which the polymers are dissolved.

[0078] Table 1. Solvents for representative homopolymers. The left column mentions the repeating unit of the polymer. [Information from Aldrich]

[0079]

[0080]

[0081] The solvent resistance of a membrane can be tested by comparing the behavior of the membrane under aqueous conditions and in a chosen solvent, for example with respect to physical stability, flowability, retention of large compounds and passage of small compounds.

[0082] There is a wide choice of MWCO of the membranes considered, depending on the size of the polymer, the size of the additives and the desired flux.

[0083] In an embodiment of the inventive method, the membrane has a molecular weight lower than 100,000Da, lower than 50,000Da, lower than 20,000Da, lower than 10,000Da, lower than 5000Da, lower than 2000Da, lower than 1000Da. ["lower than" refers to the upper limit of the range, the lower limit can be 100, 200 or 500]. The higher upper limit of the MWCO can, on the one hand, result in the loss of a portion of the dissolved polymer when the dissolved polymer passes through the membrane. The polymer chain can curl or extend, depending on the solvation of the liquid and the flexibility of the polymer backbone. If the high MW polymer chain extends more in the solvent, and the low MW polymer chain curls more and is therefore larger in size, the high MW polymer chain can therefore be retained less than the low MW polymer chain. On the other hand, the higher the MWCO, the less additive is retained and the higher the flux will be. Higher flux allows the use of a smaller surface area of the membrane.

[0084] It is up to the skilled artisan to balance the loss of polymer with enhanced flux and removal of additives.

[0085] To further guide the skilled artisan in the use of membranes that filter additives from polymers, the Examples section provides reference tests for identifying such membranes.

[0086] In a less stringent test, a reference measurement was performed with a 0.1% (w / v) polystyrene (Mw 250-300 kDa) solution in n-BiOAc at a temperature of 25°C and a pressure of 5 bar, and the solvent-resistant membranes had a relative humidity of greater than 3, 4, 5, 6 or 7 L.m -2 .h - 1 .bar -1 The permeability is 100% and the polystyrene rejection is greater than 90%.

[0087] In a more stringent test, a reference measurement was performed with a 0.1% (w / v) polystyrene (Mw 250-300 kDa) solution in n-BiOAc at a temperature of 100°C and a pressure of 25 bar, and the solvent-resistant membranes had a viscosity greater than 3, 4, 5, 6, or 7 L.m -2 .h - 1 .bar -1 The permeability is 100% and the polystyrene rejection is greater than 90%.

[0088] Regarding the physicochemical composition, the membrane is typically a cross-linked (XL) polymer membrane. Examples thereof are polyimide XL, polysulfone XL, polyvinylidene fluoride, and polyvinyl chloride XL membranes.

[0089] The specific membrane of the method of the present invention is a cross-linked polyimide membrane or a cross-linked PVDF membrane.

[0090] Specific polymers for use in the process of the present invention are polystyrene, polyethylene and polypropylene.

[0091] Depending on the MWCO of the membrane, a wide variety of additives can be removed. In specific embodiments, the solvent soluble additive has a Mr of less than 1000 Da, less than 750 Da, or less than 500 Da.

[0092] Examples of additives are dyes, plasticizers, UV-scavengers or compounds which provide thermal or radiation stabilization.

[0093] Other non-limiting examples are blowing agents, epoxy compounds, 1,3-dicarbonyl compounds, polyols, lubricants, antioxidants, fillers, impact modifiers, processing aids, antistatic agents, antimicrobial agents, metal deactivators, fluorescent brighteners, flame retardants and anti-fog agents [such compounds are disclosed in more detail in EP4067421].

[0094] The additive may be present in the polymer at a concentration between 0.5 and 50% by weight.

[0095] To maximize the removal of additives, the dissolved polymer concentrated at the end of the filtration cycle is diluted and subjected to a further filtration step.

[0096] Solvents that dissolve polymers are known to the skilled person. Such solvents are equally tested for dissolving the additives to be removed.

[0097] Examples of such solvents are NMP (N-methylpyrrolidone), THF (tetrahydrofuran), DMF (dimethylformamide), DMAc (dimethylacetamide), butyl acetate, methyl ethyl ketone, chloroform, dichloromethane, dimethicone, alkane, acetone, ethyl acetate, halogenated organic solvents, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone and methyl isobutyl ketone.

[0098] In an embodiment of the process according to the invention, the dissolved polymer is present after step a) and before step b) in a concentration between 0.1% and 5%, 10%, 15% or 20% by weight.

[0099] Typical starting polymer concentrations are usually as high as possible, typically 5-20% by weight, depending on the viscosity of the solution. This can be even higher if possible. During filtration, viscosity increases, and higher temperatures or pressures may be applied to facilitate the process. If high concentrations of additives are to be removed from the polymer, a filtration process is employed in which the concentrated retentate is first diluted and then filtered again. This dilution-filtration sequence can be repeated several times, and both the dilution and concentration factors can be selected.

[0100] In an embodiment of the present invention, filtration is carried out at a temperature between 10°C, 20°C, 30°C, 40°C and 60°C, 70°C, 80°C, 90°C, 100°C. All ranges of lower and upper temperature values are hereby explicitly disclosed. The optimal choice of temperature can be influenced by factors such as the viscosity of the polymer solution, the thermal stability of the additive, or the boiling point of the additive.

[0101] In an embodiment of the present invention, the filtration is carried out at a pressure between 1 bar, 5 bar, 10 bar to 10 bar, 15 bar, 20 bar and 25 bar. All ranges of lower and higher pressure values are hereby explicitly disclosed.

[0102] The filtration in step b) can be dead-end filtration or cross-flow filtration.

[0103] In industrial processes, membrane filtration is typically run in cross-flow mode. When the permeability drops below 1 Lmh / bar, the process is typically stopped and worked up (e.g. via distillation, non-solvent addition, cooling...) or the retentate is diluted again when operating in diafiltration mode.

[0104] In an embodiment of the invention, the solution with dissolved polymer applied in step b) contains less than 10, 8, 6, 4, 2, 1, 0.5 or contains 0% water.

[0105] In a specific embodiment, insoluble material is removed after step a) and before step b) (by filtration, centrifugation, sedimentation, decantation).The choice of solvent can be chosen so that the maximum amount of additives is insoluble and can be removed before the filtration process of b).

[0106] In order to increase the throughput of the process, the solution is stirred during step b).Alternatively or additionally, the solution in step b) may be diluted and subjected to further filtration.

[0107] After removal of the additives, the polymer can be recovered by evaporation of the solvent.

[0108] Equally, additives that pass through the membrane can be recovered by evaporation of the solvent, or rendered insoluble.

[0109] One aspect of the present invention involves an energy-efficient and waste-free membrane technology for purifying additives from dissolved polymers, such as PCV. This potentially avoids the use of non-solvents, ultimately saving significantly more CO₂ per ton of recycled polymer. Because non-solvents can be eliminated, a wider selection of solvents can also be used for polymer recycling.

[0110] The invention allows the production of polymers of near virgin quality without the energy requirement of cracking the polymer. Furthermore, it allows the additives to remain intact, thereby avoiding a range of by-products.

[0111] In an embodiment of the present invention, the stability of the polymer membrane under high temperature and pressure is evaluated by pure solvent permeability (n-BuOAc). In addition, the influence of operating pressure, temperature, concentration and viscosity of feed solution (polystyrene (PS) in n-BuOAc) on the performance of cross-linked polyimide membrane is measured. The viscosity of the reduction is observed by the increase of temperature, resulting in a higher permeability compared with the room temperature (RT) filtration process. The polymer solution viscosity is higher than the solution viscosity at higher temperatures under RT. The membrane permeability is improved and accelerated under low viscosity. In general, the membrane flux is improved by increasing the temperature, which is related to the increase of activation energy, solvent diffusion coefficient and polymer chain mobility. This can be calculated to predict the temperature-dependent process by the Arrhenius equation. At higher temperatures, molecular energy can overcome activation energy. Increasing the filtration process temperature causes fouling resistance, which is more conducive to filter performance.

[0112] Solute characteristics such as molecular weight, viscosity, shape and size play a role in filtration process permeability due to concentration polarization (CP) and fouling.The viscosity of a polymer in an ideal solvent with high solubility is also attributed to the molecular weight of the polymer.

[0113] By increasing the feed solution concentration, osmotic pressure is induced and CP may occur (due to the accumulation of solute (polystyrene) on the membrane surface), and a decrease in permeability is expected. The effect of polystyrene solution concentration on viscosity is increased by increasing the concentration. The high viscosity of the feed solution may lead to the formation of a layer on the top of the membrane, which acts as a barrier to membrane flux.

[0114] The separation process and permeability are also affected by pressure. When the pressure increases, a large molecular cake layer is formed on the top of the membrane and the scaling tendency increases. Feed solutions containing organic macromolecules (polymers, proteins) inevitably lead to membrane scaling. The membrane pores are blocked by scaling, which leads to the formation of a cake layer at the membrane surface and a decrease in permeability.

[0115] The present invention provides highly stable membranes for dissolving polymers. The molecular weight cut-off values are typically in the range of 200-1000 Da in nanofiltration or greater than 1000 Da in UF. The chemical cross-linking of the membranes makes them suitable for use in solvents that dissolve polymers.

[0116] The Examples section provides reference tests for determining which types of membranes have the desired permeability and dissolved polymer rejection. The membranes listed below allow separations with MWCO values between 100 and 1000 Da. Most of these commercially available membranes currently available have been designed to prevent excessive swelling in organic media. This is primarily achieved by cross-linking the membrane material through the creation of covalent bonds (typically resulting in amide bonds), such as in Duramem®. TMHowever, these amide bonds limit their use in the presence of, for example, acids and bases. Excessive swelling and thermal expansion also strongly reduce membrane selectivity at higher temperatures.

[0117]

[0118]

[0119]

[0120] Example

[0121] Example 1 Materials and Methods for Polystyrene (PS) and High Impact Polystyrene (HIPS)

[0122] Material

[0123] n-Butyl acetate (n-BuOAc) 99% and 1-methyl-2-pyrrolidone (NMP) 99% were purchased from Fisher Chemical and Acros Organics, respectively. Matrimid polyimide powder (5218) Huntsman (Switzerland) was dried at 100°C for 24 hours before use. Three different commercial polystyrenes were obtained from Ineos (see Table 3). Support polypropylene / polyethylene (PP / PE) fabric ( Novatexx 2471) was obtained from Reudenberg Vliesstoffe (Germany). 1,6-Hexanediamine (HDA) 99.5% was obtained from Alfa Aesar.

[0124] Feed solution preparation

[0125] 15 g of a solution (0.1 w / v %) was prepared by dissolving polystyrene in n-BuOAc while stirring in a closed vial at room temperature.

[0126] Molecular weight measurement

[0127] The molecular weight and dispersibility of different types of polystyrene in THF were measured using gel permeation chromatography (GPC) (SHIMADZU, LC-10ADvp). The results of these experiments are shown in Table 1.

[0128] Table 3: Molecular weight and dispersibility of different types of polystyrene in THF

[0129] polymer PS(A) PS(B) PS(C) Mw(kDa) 260 290 310 Mn(kDa) 181 116 166 Mz(kDa) 359 511 485 Mw / Mn 1.47 2.57 1.87 Mz / Mw 1.35 1.71 1.56

[0130] Viscosity measurement

[0131] The viscosity of different PS solutions (concentration 1-8 w / v %) was measured using SVM 3001 (Anton Paar) at different operating temperatures (25-100°C).

[0132] Membrane preparation

[0133] Matrimid was dissolved in NMP overnight at room temperature to give a doping solution having a concentration of 15 to 18 w / v%. The doping solution was degassed by placing the open vial containing the doping solution in a vacuum oven (Dwards, Sheldon, INC) at room temperature for 15 minutes at 160 mbar. The doping solution was cast on an automatic casting apparatus (Promoter, Belgium) using a casting blade thickness of 250 μm at a rate of 0.02 ms. -1 A uniform PI solution was cast onto a porous PE / PP nonwoven at room temperature at a casting speed of 100 nm. The temperature and humidity in the casting setup were controlled at 20 ± 2°C and 50 ± 10% relative humidity, respectively. Immediately after casting, the PI film was immersed in a non-solvent (deionized water) bath containing 3 w / v% HDA for 20 minutes for curing and simultaneous crosslinking [Vanherck et al. (2008) cited above]. The crosslinked PI film was stored in deionized water for 24 hours to remove any residual solvent before filtration experiments.

[0134] Filtration experiment

[0135] Under controlled temperature and pressure, 2 Dead-end filtration was performed using the cross-linked PI membrane described above with an active filtration area of 100 mL and a volumetric capacity of 250 mL. The membrane was placed on a sintered disk and sealed with an EPDM O-ring. The tank was exposed to nitrogen to generate the required pressure, and the feed solution was stirred at 300 rpm. For each experiment, the average of the two sample values is reported.

[0136] Pure solvent permeability

[0137] Dead-end filtration was performed on pure n-BuOAc (no dissolved polymer). The experiment was performed by increasing the operating pressure by 5 bar (5, 10, 15, 20, 25 bar) every hour and, conversely, decreasing the operating pressure every hour [at 25°C]. A similar experiment (at 5 bar and vice versa) was performed by increasing the temperature by 5 bar every hour and a half from 25°C to 100°C (thus taking about 30 minutes to reach the desired temperature). After each step of changing the pressure or temperature, the membrane permeability was measured.

[0138] Filtration experiments using PS feed solution

[0139] To investigate the effect of operating temperature on membrane performance, filtration processes (different polystyrene concentrations in n-BuOAc) were performed at a constant pressure of 5 bar by gradually increasing the temperature from 25°C (RT) to 100°C. For each step, fresh feed solution and a new cross-linked PI membrane as described above were used. Samples were collected after the membrane had stabilized for one hour after the center disk reached the desired T.

[0140] To investigate the effect of operating pressure, the pressure at which the filtration process occurs was increased stepwise from 5 to 25 bar, while the temperature was kept constant at 25°C. This increase was performed either continuously or as a series of separate experiments. In the latter case, each different pressure was tested using a new membrane and fresh feed solution. The membrane was allowed to stabilize at the desired pressure for 1 hour, after which samples were collected.

[0141] In order to determine the maximum feasible polystyrene concentration of the feed solution, filtration experiments were performed at RT at 5 bar. The limit was set at 0.05 L / m 2 .h.bar.

[0142] Membrane performance

[0143] The membrane permeability (J) was calculated using Equation 1.

[0144]

[0145] Where V is the permeate volume (L), A is the membrane effective area (0.003m 2 ) and t is the time necessary to collect the permeate volume (h), and Δp is the operating pressure (bar).

[0146] The removal rate (R) of polystyrene is defined by Equation 2.

[0147]

[0148] Among them C r is the concentration of polystyrene in the retentate and C p is the concentration of polystyrene in the permeate [Verbeke et al. (2020) J. Membrane Sci. 612, 118438]. The concentration was determined using UV-Vis spectroscopy (Shimadzu, Uv-1800) at approximately 270-280 nm.

[0149] Data Analysis

[0150] Quantitative analysis of the data was performed using SPSS (developed by IBM) and JMP (SAS Institute) data management statistical software.

[0151] p calculated by SPSS -The value is interpreted as the significance level of all inputs (temperature, pressure, concentration and their combination) on the output (permeability). The maximum probability for each variable is considered to have a p value less than 0.05. - value, which is determined by Figure 8 The blue line depicts the more "extreme" results from these experiments showing the minimum p - Value [Gibbons & Pratt (1975) Am. Stat. 29 (1), 20-25].

[0152] The prediction profiler calculated by JMP displays the relationships between multiple factors and responses in an experiment. This simulation study is used to evaluate the performance of new conditions in a method, design experiments, and explore new variances. It is a combination of a matrix of plots, including prediction variance plots. The independent and dependent variables are displayed on the x- and y-axes, respectively, of each plot.

[0153] Example 2. Membrane selection

[0154] To identify membranes suitable for filtering additives from polymer solutions, dead-end filtration was performed on several cross-linked polyimide membranes, where the polyimide concentration in the casting agent was varied from 15% to 18% by weight. The feed solution used in these filtrations consisted of three different types of polystyrene (properties of the polystyrenes are described in Table 3) dissolved in n-BiOAc at a concentration of 0.1% w / v. The results of these filtrations are shown in Table 3. Figure 1 In this context, as the PI concentration increases, the rejection increases and the permeability decreases. For filtering additives from polymer solutions, a rejection of polymers greater than 95% with high permeability is preferred. Thus, a cross-linked PI membrane prepared as above (having an 18 wt% PI concentration (rejection greater than 97% and permeability of 7 L.m -2 .h -1 .bar -1 )) were used for further experiments.

[0155] Example 3. Membrane stability at high temperature and pressure

[0156] The effects of temperature and pressure on the performance of the prepared membranes were evaluated by measuring the permeability of pure solvent (n-BuOAc) under different operating conditions. In this way, the membranes were tested for their behavior in solvent under temperature and pressure conditions, without the influence of polymers or additives.

[0157] Figure 2 a shows the effect of operating temperature at constant pressure (5 bar), and Figure 2 .b shows the effect of operating pressure at constant temperature (RT, 20-25° C.) First both parameters were increased stepwise to arbitrarily chosen values.

[0158] As for temperature, the permeability value increases from 25°C to 100°C.

[0159] As for the pressure, the permeability values decrease from 5 bar to 25 bar.

[0160] In the following, the corresponding parameters were then reduced in the same stepwise manner. It was observed that both temperature and pressure had an impact on the membrane performance after each corresponding cycle. It can be seen that the permeability increased slightly after the temperature cycle (from 44.66 to 48.64 L / m 2 .h.bar), while the permeability decreased significantly after the pressure cycle (from 44.66 to 34.36 L / m 2 .h.bar).

[0161] A possible explanation is that at higher temperatures the polymer chains in the membrane rearrange themselves, leading to an increase in permeability.

[0162] The decrease in permeability after pressure cycling may be due to the compaction of the polymer. Since the flux values increase with increasing pressure (see Figure 2 c), so increasing the pressure is still an effective option to enhance filtration for more viscous solutions. These experiments show that the membrane is stable at pressures up to 25 bar, which provides a feasible window for subsequent experiments.

[0163] Example 4. Membrane permeability under different operating conditions

[0164] Effect of feed solution concentration on filtration process

[0165] A significant decrease in permeability was observed when increasing the polystyrene concentration in the feed solution (from 1 w / v% to 8 w / v%). Figure 3 Increasing the polystyrene concentration significantly leads to the formation of a solute layer on top of the membrane, which, combined with concentration polarization, leads to a significant decrease in permeability. In addition, the increased viscosity of the polymer solution due to increasing polymer concentration plays a role in the decrease in permeability (see Figure 3 ).

[0166] The type of polymer also has an impact on permeability. Polystyrene A solution with the smallest Mw has the lowest viscosity, resulting in the highest permeability [Zhao, S. & Zou (2011) J. Membrane Sci. 379, 459-467].

[0167] The intrinsic viscosity of polystyrene in an ideal solvent with high solubility is measured by Equation 3:

[0168] [η] = KM 1 / 2 (3)

[0169] where K is a constant independent of the molecular weight of polystyrene at a given temperature, and M is the molecular weight [Krigbaum and Flory, (1953) J. Pol. Sci. 11(1), 37-51].

[0170] Dead-end filtration experiments at room temperature were limited to a polystyrene concentration of 8 w / v% due to a severe decrease in permeability values. The change in polystyrene retention was negligible (greater than 95%) for all concentrations. Figure 3 The average retention of all polystyrene solutions (1 w / v % to 8 w / v %) is presented in b.

[0171] Example 5. Effect of operating temperature on membrane permeability

[0172] Figure 4 The membrane permeability [18% PI cross-linked membrane] of three different polystyrenes (A, B, C) at two concentrations (1 wt / v% and 5 wt / v% in n-BuOAc) is shown as a function of temperature (°C) on the left (green line) and as a function of viscosity (mPa.s) on the right (red line).

[0173] The membrane permeability increases with increasing temperature.

[0174] At higher temperatures the mass transfer resistance decreases, which can lead to higher permeabilities even for feed solutions with higher polymer concentrations (5 w / v %), see Figure 4 Right column. Because polystyrene solution viscosity is affected by temperature, higher permeabilities are observed as the solution viscosity decreases.

[0175] Compared with the 5 w / v% polystyrene solution in the range of 25℃-100℃, the permeability of the filtration process in the lower concentration (1 w / v%) polystyrene solution was more affected by temperature [3.32-22.16 L / m in polystyrene A]. 2 .h.bar, 3.57-21.98L / m in polystyrene B 2 .h.bar and polystyrene C 2.3-16.04L / m 2 .h.bar], which was smaller at higher concentrations (5w / v%) [2.1-7.47 L / m in polystyrene A]. 2 .h.bar, 2.58-10.68L / m in polystyrene B 2 .h.bar and polystyrene C 1.7-8.56L / m 2 .h.bar].

[0176] The membrane permeability was determined at each temperature (25°C-100°C), pressure (5 bar-25 bar) and feed solution concentration (1 w / v% to 8 w / v%). The permeability results were affected by the solute (a i The activity is defined by the concentration and the activation coefficient, Eq.

[0177] a i =m i γ i (4)

[0178] The activation energy was calculated by the Arrhenius equation, Eq. 5.

[0179]

[0180] Where A is dependent on the activation energy (E a ), J is the permeation activation energy, R is the gas constant, and T is the absolute temperature (Kelvin) [Machado et al. (1999) J. Membrane Sci. 163, 93-102].

[0181] Because viscosity is affected by temperature and leads to an increase in membrane permeability, the viscosity activation energy is calculated by Equation 6:

[0182]

[0183] Figure 5 Arrhenius plot showing the effect of temperature (K) for three different PS (A, B, C) solutions, each at two different concentrations of 1 w / v% and 5 w / v%. Activation energy values were measured for six different polystyrene solutions (PS A, PS B, PS C at 1 and 5 w / v%) and are summarized in Table 4. The activation energy values depend on temperature and concentration. Increasing the temperature results in higher motion of the feed solution molecules and lower viscosity, leading to an increase in permeability. Figure 5 It is shown in Figure 2 that increasing the concentration of the polymer solution at the same temperature results in higher activation energy and flux.

[0184] Table 4: Activation energy values measured for 6 different polystyrene solutions (PS A, PS B, PS C, at concentrations of 1 and 5 w / v %).

[0185] PS solution activation energy PS A, 1w / v% -13.68 PS A,5w / v% -3.62 PS B, 1w / v% -11.43 PS B,5w / v% -6.21 PS C,1w / v% -9.71 PS C,5w / v% -4.62

[0186] Example 6. Effect of operating pressure

[0187] Figure 6The permeability values of three different polystyrene solutions (A, B, C) at different operating pressures (bar) are shown in Figure 1. The effect of pressure was studied at two polystyrene solution concentrations (1 and 5 w / v% polystyrene), which are shown in two columns: a: PSA, 1 w / v%, b: PS A, 5 w / v%, c: PS B, 1 w / v%, d: PS B, 5 w / v%, e: PS C, 1 w / v%, f: PS C, 5 w / v%.

[0188] Since the feed solution is highly compacted on the membrane, increasing the operating pressure reduces the permeability. Therefore, high permeability is hindered by increasing pressure.

[0189] Such pressure increases can be avoided or reduced by cross-flow filtration to avoid the formation of a solute layer on top of the membrane.By increasing the operating pressure, the permeability drops rapidly due to the formation of a solute layer on the membrane surface, scaling and CP (concentration polarization).

[0190] At higher temperatures, the viscosity of the feed solution is higher and more polymer accumulates on the membrane surface, resulting in more membrane fouling and reduced membrane permeability. Figure 6 The nonlinear behavior observed in the operating pressure on three different types of polystyrene feed solutions during the filtration process is described.

[0191] Example 7. Simultaneous effects of operating pressure, temperature and feed solution concentration on the filtration process

[0192] Figure 7 The dead-end filtration process at different operating pressures (5, 10, 15, 20 and 25 bar) was investigated for two polymer solution concentrations (1 w / v% and 5 w / v%) of three different types of polystyrene (A, B, C) at two different temperatures (RT and 40°C), a: 1 w / v% PS (A, B, C) solution at RT, b: 5 w / v% PS (A, B, C) solution at RT, c: 1 w / v% PS (A, B, C) solution at 40°C, d: 5 w / v% PS (A, B, C) solution at 40°C.

[0193] By increasing the feed solution concentration and pressure, the permeability decreases due to the accumulation of solutes on the membrane surface, but the membrane permeability can be increased by increasing the temperature due to increasing the activation energy and decreasing the viscosity. Figure 7 It is shown that an increase of 15°C (from 25°C to 40°C, c and d) doubles the permeability. Temperature reduces the limiting effects of pressure and feed solution concentration and can improve permeability by increasing temperature. R of 0.94 2 The values show a high correlation of the independent inputs (temperature, pressure and concentration) to the dependent output (permeability).

Claims

1. A process for removing one or more solvent-soluble additives from a polymer comprising less than 40% by weight of polyvinyl chloride or from a mixture of polymers comprising less than 40% by weight of polyvinyl chloride, the process comprising the steps of: a) dissolving the polymer or polymer mixture comprising the one or more solvent-soluble additives in a solvent or solvent mixture which dissolves the polymer or polymer mixture and also the one or more additives, b) filtering a solution comprising the dissolved polymer or polymer mixture and one or more dissolved additives over a solvent resistant membrane, whereby the dissolved polymer is retained by the membrane and the one or more solvent soluble additives permeate through the membrane.

2. The method of claim 1, wherein the polymer comprises less than 20 wt% polyvinyl chloride or wherein the mixture of polymers comprises less than 20 wt% polyvinyl chloride.

3. The method of claim 1 or 2, wherein the polymer comprises less than 10 wt% polyvinyl chloride or wherein the mixture of polymers comprises less than 10 wt% polyvinyl chloride.

4. The process according to any one of claims 1 to 3, wherein the polymer comprises less than 5 wt% polyvinyl chloride or wherein the mixture of polymers comprises less than 5 wt% polyvinyl chloride.

5. The method of any one of claims 1 to 4, wherein the polymer comprises less than 1 wt% polyvinyl chloride or wherein the mixture of polymers comprises less than 1 wt% polyvinyl chloride.

6. The method according to any one of claims 1 to 5, wherein the membrane has a molecular weight cut-off of less than 20 000 Da.

7. The method according to any one of claims 1 to 6, wherein the membrane is a cross-linked polyimide membrane.

8. The method according to any one of claims 1 to 6, wherein the membrane is a cross-linked PVDF membrane.

9. The method according to any one of claims 1 to 8, wherein the polymer is selected from polystyrene, polyethylene and polypropylene.

10. The method of any one of claims 1 to 9, wherein the solvent-soluble additive has a Mr of less than 1000 Da, less than 750 Da, or less than 500 Da.

11. The method according to any one of claims 1 to 10, wherein the membrane has a thickness greater than 3, 4, 5, 6 or 7 L.m 2 at a temperature of 25° C. and a pressure of 5 bar, as compared with a 0.1% (w / v) solution of polystyrene having a Mw between 250 and 300 kDa in n-BiOAc. -2 .h -1 .bar -1 The permeability is 100% and the polystyrene rejection is greater than 90%.

12. The method according to any one of claims 1 to 11, wherein the reference measurement is carried out with a 0.1% (w / v) solution of polystyrene with a Mw between 250 and 300 kDa in n-BiOAc at a temperature of 100°C and a pressure of 25 bar, the membrane having a viscosity greater than 3, 4, 5, 6 or 7 L.m -2 .h -1 .bar -1 The permeability is 100% and the polystyrene rejection is greater than 90%.

13. The method according to any one of claims 1 to 12, wherein the solvent-soluble additive is a dye, a plasticizer or a UV-scavenger, a heat-donating compound or a compound providing stability to thermal radiation.

14. The process according to any one of claims 1 to 13, wherein the solvent is selected from NMP, THF, DMF, DMAc, butyl acetate, methyl ethyl ketone, chloroform and dichloromethane.

15. The method of any one of claims 1 to 14, wherein the dissolved polymer is present after step a) and before step b) at a concentration between 0.1 wt% and 5 wt%, 10 wt%, 15 wt% or 20 wt%.

16. The process according to any one of claims 1 to 15, wherein the filtration is performed at a temperature between 10°C and 100°C.

17. The process according to any one of claims 1 to 16, wherein the filtration is carried out at a pressure between 1 and 25 bar.

18. The method according to any one of claims 1 to 17, wherein the filtration in step b) is a dead-end filtration.

19. The process according to any one of claims 1 to 17, wherein the filtration in step b) is a cross-flow filtration.

20. The method according to any one of claims 1 to 19, wherein insoluble material is removed after step a) and before step b).

21. The process according to any one of claims 1 to 20, wherein the polymer is recovered after step b) by evaporation of the solvent.

22. The process according to any one of claims 1 to 20, wherein the additive is recovered after step b) by evaporation of the solvent.

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