Patent Application
20240191052
The present invention generally relates to solvent based recycling processes of polyolefins. More particularly, the present invention relates to a solvent-based recycling process for polyolefins, which produces virgin-like polymers, has low requirements on heavy-duty equipment of the process equipment, and can preferably be carried out in a continuous manner.
The challenge of the disposal of accumulated waste plastics and corresponding environmental issues have received widespread attention from the public and academician. Therefore, besides the concepts of the prevention of plastic waste in general and the prevention of leakage of plastic waste into the environment in particular, recycling of waste plastics material has become an important topic. Waste plastics can be turned into resources for new plastic products. Hence, environmental and economic aspects can be combined in recycling and reusing waste plastics material.
Mid of the 90-ies, several European countries have implemented a more differentiating waste collection system (Recycling Management System, Circular Economy Law), which actually allows a more target orientated collection and separation of plastic materials from other waste materials. Thus, a more or less efficient separation of polymer types from each other can be managed to achieve, after the treatment, finally polymer types enriched and thus more easily recyclable secondary plastic material fractions. The build-up of a suitable waste collection system and especially the set-up of a suitable waste separation infrastructure took place within the last decades to generate a secondary petrochemical raw material source resp. market. Parallel, several plastic recycling processes have been developed resp. in particular improved, primary with the target to increase the achievable product quality of the recyclable polymer materials.
There are different methods of plastic recycling commonly known including mechanical [material recycling], advanced physical or solvent based [solution] and chemical processing [(feedstock recycling, thermochemical such as pyrolysis or gasification, solvolysis]. Among these methods, mechanical recycling and chemical recycling are the most widely practiced.
Although, EU-public collection and pre-sorting systems reached plastic collection rates up to 76 [wt. % (Ger)] in 2018, the direct plastic material recycling rates have been on a lower level for mechanical advanced recycling processes (e.g. 12[%] for Germany in 2018). Today, advanced mechanical recycling includes separation steps such as shredding, vibrating, rotary sieving, advanced sorting methods supported by spectrometric-methods [e.g. NIR/VIS] and wash operations to reduce organic, biologic and partly odour contaminants primary from the surface of the recyclable plastic material, as well as achieving a polymer type enriched and more homogeneous polymer recyclate fraction. Thereby, plastic type-enriched resp. especially polyolefin-enriched secondary mass streams (>85; <95 [wt. %] PO-content) can be obtained such as for example Polypropylene (PP), High-Density-Polyethylene (HDPE), Low-Density-Polyethylene (LDPE), Polyethylene-Terephthalate (PET) and/or Polystyrene (PS). Following, these separated mass streams will be processed to granules (extrusion) and material specific into products converted. Nevertheless, the achievable product quality remains relatively poor and does not allow both food contact and high performance applications and thus products such as flower pots, paint buckets or shampoo bottles are typically for the mechanically recycled materials today.
Especially improved and better performing sorting methods (e.g. colouring flake sorting) should effect both higher concentrations within the specific polymer type fraction and secondary wash operations to reduce more efficiently disturbing contaminants resp. to increase the product quality of the final secondary polymer raw material. Latter includes additionally expenditures concerning a complex process design, waste water treatment, exhaust gas treatment and intermediate product drying coupled with an increased total energy consumption, while keeping emissions as low as feasible.
However, the challenges of difficulties to remanufacture directly mechanical polymer recyclates into high-quality end applications remain, caused by waste components such as multi-layer materials resp. films or mixed flexible film waste materials. Further, important reason can be found in the less predictable and controllable homogeneity of the polymer type material mixture concerning especially historically applied polymerization technology (define material properties such as polymer density, average molecular weight, molecular weight distribution, molecular structure, cross-linking level) and historically applied compounding technology (additive-, filler concentrations and finally multiple pigment compositions). All these quality concerning factors remain inside the mechanically processed bulk mass mixture and cannot be covered by mechanical sorting and applied purification methods, which interact in best case onto the surface of the recyclable polymer material mixture.
A further approach to overcome the lower quality in advanced mechanical polymer recycling can be found in blending mechanical polymer recyclates with virgin polymers, finally to achieve a tolerable, marketable quality for the end application (non-food), whereby the implementable content of mechanically recycled polymer materials stays on a lower level (several [wt. %]), especially for high-quality/high performance end applications.
The second arising plastic recycling route is chemical or feedstock recycling, concerning solvolysis and thermochemical processing. In 2018 the technology share rate of chemical plastic recycling was less than 2[%] in total. A technology prognosis indicates, that the thermochemical recycling share rate should significantly increase from less than 2[%] (2018) up to 13[%] until 2030. However, chemical plastic recycling provides a promising opportunity to recover pre-sorted and pre-treated solid plastic waste anyhow to obtain feedstock for the petrochemical industry, which can be processed to plastics again, as well as to chemical commodities and fuels. To degrade the polymeric structure of the plastic solid mixture to shorter hydrocarbons up to monomeric building blocks, heat, catalysts and solvents have to be applied. Depending on the specific technology, chemical recycling approaches have much higher tolerances towards mixed plastic fractions and impurities and thus are principally capable to deal with contaminated and polymer material mixtures resp. secondary polymeric raw materials. Nevertheless, cross-contaminations of polyolefinic material mixtures with heteroatomic polymers (N/O/S, Halogene) should be preferably avoided.
Nevertheless, abstraction of especially thermochemical plastic processing, especially polyolefin recycling technologies illustrates rather the substitution of fossil based crude oil fractions to already fossil based secondary polymer recyclate materials by applying well-known traditional thermochemical unit operations, which have to be adapted costly to the secondary feedstock source. The specific energy demand remain, concerning the heat-intensive endothermic C—C resp. C—H bonding breakages (cracking, degradation), so that finally the total energy input is significantly higher in comparison to crude oil to virgin polymer processing—principally the degradation of a short chain molecule (e.g. Naphtha within crude oil fractionation) will be replaced by cracking long chain and branched polymers. Independently, the extravagant and energy-consuming thermal degradation remains. Furthermore, the CO2-emissions of such processes are also higher as long as the necessary applied energy carrier could not easily switched to renewable/sustainable energy carriers.
The third plastic recycling route is advanced physical or Solvent based Recycling (SbR), which showed a plastic recycling market share of less than 1% in 2018 in Germany. In SbR-processing the polymer will be initially dissolved in an appropriate solvent and following, either the solubility of the dissolved polymer will be decreased by the addition of a non-solvent (dissolution/precipitation) and/or a solidification of the polymer will be caused by the preferably complete separation of the solvent from the solidified polymer by thermal unit operations (evaporation, drying etc.).
Polyolefin-SbR-processing show similarities to traditional PO-polymerization processes, whereby the solvent for the monomers (olefins) and temporary formed oligomers (waxes) and short chain polymers is for example a refinery fraction (e.g. kerosene) until the solubility limits will be exceeded (long chain polyolefins are formed during polymerization) and the final polyolefin precipitates forming a polyolefin-solvent slurry (e.g. Chevron slurry process). An extraordinary polyolefin process is the solution PO-polymerisation process, whereby the olefin is initially dissolved in a paraffinic solvent blend, polymerized and the finalized polyolefin will stay in solution until the process conditions will significantly change by depressurization resp. flash devolatilization.
The framework of commonly known waste plastics material solvent based recycling processes includes the removal of impurities, dissolution, and reprecipitation/recrystallization and/or devolatilization of the polymer. Specifically, the one or more polymer is dissolved in one or more solvent, and subsequently, each polymer is selectively precipitated/crystallized. Ideally, if a solvent can dissolve either the target polymer or all the other polymers except the target polymer, it can be used for selective dissolution.
It is generally a desire to produce virgin-like polymers by waste plastics material solvent based recycling processes, whereas virgin-like is defined as contaminant-free, pigment-free, odor-free, homogeneous and generally similar in properties to freshly polymerized polymers. The need for high quality, virgin-like recycled resins is especially important for food and drug contact applications, such as food packaging. In addition to being contaminated with impurities and mixed colorants, many recycled resin products are often heterogeneous in chemical composition and may contain a significant amount of polymeric contamination, such as polyethylene contamination in recycled polypropylene and vice versa.
EP 3 339 361 (A1) describes a polymer solvent based recycling process including the step of contacting a waste polymer at a temperature of 110 t0 170° C. and at a pressure of 1,100 psig to 2,100 psig with n-butane. This step is repeated four times. The residue of this step is subsequently dissolved again in n-butane at 130 to 180° C. and 2,000 psig to 3,000 psig. Furthermore, settling and removal of non-dissolved polymer is performed and an adsorption step is added using a pure silica bed followed by an aluminium-oxide (zeolite) bed at 130 to 180° C. and 350 psig to 20,000 psig. The polymer is then precipitated from the solvent.
The disadvantage of this process lies in the higher pressure used during processing, which needs heavy duty equipment and causes high investment costs, as the material strength of the plant must be sufficiently dimensioned.
DE 102016015199 A1 is using an atmospheric dissolving process for the separation of post-industrial consumer waste, in particular the separation of polyamide, polyethylene and/or polypropylene. Solvent is a higher non-polar gasoline (kerosene) fraction having boiling point temperatures of 80 to 140° C.
Disadvantage of this process is the high residual solvent content in the intermediate polymer product (up to 5 vol.-%). Removing these unwanted solvent requires complex and expensive post-treatment processing by thin film evaporators (low throughput) and dryers. The exhaust gas contains hydrocarbons and thus high volume off-gas treatment plants are needed.
Therefore, generally, the polymer solvent based recycling processes and in particular the polyolefin solvent based recycling processes known in the prior art either are high pressure processes having the disadvantage of high costs and efforts or are directed to high boiling point solvents causing problems in the after process-treatment in particular in view of removing the solvent, thus not being able to provide virgin-like recycled polyolefins.
Furthermore, many of the solvent based recycling processes of polyolefins described in the prior art are designed in a way that no continuous process is possible. As already mentioned earlier, one problem can be high pressure process technique. However, also the feeding process technique and the sorting might affect the possibility of performing the process in a continuous manner.
It is therefore an object of the present invention to find a solvent based recycling process for polyolefins allowing for the production of virgin-like polyolefins and having low requirements in view of material strengths, staff experience and costs.
It is a further object of the invention to provide a continuous solvent based recycling process of polyolefins.
It has now surprisingly found that said object can be achieved by a solvent based recycling process for recycling waste polymer material, the waste polymer material comprising at least one polyolefin, the process comprising the steps of obtaining the waste polymer material comprising the at least one polyolefin; contacting the waste polymer material with at least one dissolving solvent yielding a slurry stream of polymer solution and undissolved solids; screening the slurry stream yielding the undissolved solids and a stream of the polymer solution; vapor-liquid separating the stream of the polymer solution into a polymer-lean vapor stream and a polymer-rich condensed stream; recovering the at least one polyolefin from the polymer-rich condensed stream; wherein the at least one dissolving solvent has a boiling point temperature at 1 bar of equal to or more than 70° C.
The advantage of the process of the present invention is that the solvent-based recycling process can be performed at lower pressures than shown in the prior art and at the same time maintain the ability to remove solvents readily and economically from the final polymer. Furthermore, the recycled solvents can be reintroduced into the solvent based recycling process, further reducing energy and material demand and also costs. Furthermore, the process uses a low number of unit operations reducing maintenance effort and downtime probability. Moreover, the process of the present invention is able to separate more than one polymer during recycling. Finally, the produced polymer has no significant amount of polymeric cross contamination, is essentially colorless, and essentially odorless (i.e. virgin-like).
The expression ‘volatiles’ or ‘volatile compounds’ as used herein has to be understood as compounds having significantly lower molecular weight in comparison to the polyolefin separated in the process of the invention. Such compounds typically are present in the gaseous form when being exposed to a flash separator. Commonly, the volatile compounds are a mixture of volatile hydrocarbons. Preferably, the mixture of volatile hydrocarbons comprises at least one solvent.
‘Flash separators’ have been known in the prior art for decades (also as low-pressure separators). As it is well known in the art, a liquid feed is passed to a flash vessel operated at a reduced pressure. Thereby a part of the liquid phase vaporizes and can be withdrawn as an overhead stream (or a vapor stream) from the low pressure separator. The part remaining in liquid phase is then withdrawn as a bottom stream or a liquid stream from the flash vessel. Operating the low pressure separator under conditions such that both vapor and liquid phases are present in the flash vessel describes this situation.
‘Gravity separators’ or ‘liquid-liquid separators’ as used herein comprise a vessel in which a two-phase (i.e. liquid/liquid) system can be separated. The liquid phase with the lower relative density (polymer-lean stream) is withdrawn from the upper end of the vessel whereas the liquid phase with the higher relative density (in the present case the polymer-rich stream) is withdrawn from the bottom end of the vessel.
It should be understood that steps c″) and d) can occur multiple times in a row, therefore they can be denoted as c″1 or d2, whereas the index points to the order in the serial processing of the steps (i.e. 1→first, 2→second). The same holds for streams connected downstream to said multiple processes as well as processes connected downstream thereto (i.e. e2)
The process according to the present invention is a solvent based recycling process for recycling waste polymer material (1), the waste polymer material (1) comprising at least one polyolefin (2), the process comprising the steps of
The waste polymer material (1), can contain different plastics such as polyethylene (PE) or polypropylene (PP), in particular high density polyethylene (HDPE), low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), poly(ethylene terephthalate) (PET), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PS), polycarbonate (PC), polyurethanes (PUR) and polyamides (PA). Preferably, the waste polymer material (1) has a polyolefin content of higher than 75 wt.-%, more preferably of higher than 80 wt.-% and most preferably higher than 85 wt.-%. The waste polymer material (1) further can comprise waste impurities, such as common additives, such as antioxidants, food residues, residual perfume components, dyes and pigments, and generally components inevitably introduced in plastic waste material by production and usage. In addition to contaminations, many recycled resin products are often heterogeneous in chemical composition and may contain a significant amount of polymeric contamination, such as PE contamination in recycled PP and vice versa.
The polyolefin (2) recycled by the process of the present invention can be a mixture of polyolefin classes such as polypropylene or polyethylene. Preferably, however, the polyolefin (2) comprises, preferably consists of a single polyolefin class. Most preferably, the polyolefin (2) comprises, preferably consists of polypropylene. It should be understood that in the latter case polyethylene residues can be again dissolved at increased temperatures and residence times with the same dissolving solvent (3) and separated according to the present invention.
Generally, the dissolving solvent (3) must be able to solve polyolefins, in particular the polyolefin (2). Therefore, preferably, the dissolving solvent (3) is a non-polar solvent or a mixture thereof. Therefore, the solvent preferably is a hydrocarbon or a mixture of hydrocarbons. More preferably, the dissolving solvent (3) is a paraffinic solvent or a mixture of paraffinic solvents due to paraffinic nature of polyolefins (‘Similia similibus solventum’). Aromatic hydrocarbon solvents are known for good solvent properties and can therefore also be considered. Nevertheless, a drawback of aromatic hydrocarbons lies in enhanced dissolution of polystyrene. On the other hand, e.g. n-alkanes are known as not dissolving polystyrene. Most importantly, the solvent should not dissolve polar polymers such as PET, PVC, PA, PC, PUR, or bio-based fractions such as cellulose or lignin. Furthermore, the boiling point at 1 bar pressure of the dissolving solvent (3) must be higher than 70° C. Therefore, preferably, the dissolving solvent is selected from the list of low boiling solvents and high boiling solvents or mixtures thereof. Low boiling solvents comprise n-alkanes and aromatic hydrocarbons, such as toluene and xylene. The advantage of low boiling solvents is that they can be separated from dissolved polyolefins via evaporation. High-boiling solvents comprise paraffinic gas oil or vacuum gas oil. Such solvents have the disadvantage that they are difficult to be removed from the product. Therefore, preferably, the dissolving solvent (3) is selected from n-alkanes or mixtures thereof having a boiling point at 1 bar pressure of more than 70° C. and preferably not more than 150° C., more preferably not more than 140° C., even more preferably not more than 100° C. and most preferably not more than 90° C. Most preferably, the dissolving solvent (3) is selected from the group consisting of n-heptane, n-octane, n-nonane, and n-decane or mixtures thereof.
The step a) of obtaining the waste polymer (1) comprises the steps of preparing the waste polymer (1) from general waste, including washing the waste with aqueous and/or caustic solutions to remove unwanted material from the waste polymer (cf.
The step b) of contacting the waste polymer (1) with at least one dissolving solvent (3) is preferably a dissolution step (cf.
The step b) of contacting can be carried out in that only a single target polyolefin is dissolved by the dissolving solvent (3). Such a configuration is in particular applicable, if the target polyolefin dissolves at lower temperatures than all other polyolefins present in the waste polymer material (1). In another embodiment of step b), the conditions are chosen so that even two or more polyolefins are dissolved, i.e. polymer A and polymer B. In such a case, subsequent liquid-liquid separation steps are beneficial to separate the solubilized polymers from each other (cf. below). Mainly polypropylene can be dissolved from a polyethylene/polypropylene mixture using non-polar solvents with Hansen solubility parameters, which are similar/nearby to those of the polypropylene. Preferably, the conditions are chosen to exhibit temperatures between 100 and 300° C., more preferably between 110 to 290° C., and most preferably between 120 to 280° C. Preferably, the pressure used in step b) is in the range of 5 to 50 bar, preferably from 7 to 45 bar, and most preferably from 10 to 40 bar.
The waste polymer material (1) can be brought into contact with the dissolving solvent (3) either in solid or in molten form. Preferably, the waste polymer material (3) is molten allowing for a quick and thorough mixing of both, the polymeric material and the dissolving solvent (3), i.e. reducing the time necessary for completely solving the polymer material (cf.
In step c) the undissolved solids (6) are preferably removed from the polymer solution (5) by solid-liquid separation (cf.
Furthermore, even more preferably, in step c) also other unwanted materials still solubilized in the polymer solution (2) are screened from the said polymer solution (2). Such materials include additive, colors, antioxidants, odors and mixtures thereof. Most preferably, the screening step is performed by desorption of the unwanted materials. Preferably, the desorption process is carried out with the help of a sorption helper, to which the unwanted materials adsorb or into which the unwanted materials absorb. The sorption helper might also bind the unwanted materials by size exclusion, ion exclusion, ion exchange, and other mechanisms. Furthermore, pigments and other materials commonly found in the waste polymer material may be polar compounds and may preferentially interact with the sorption helper, which therefore may also be at least slightly polar. The polar-polar interactions are especially favorable when non-polar solvents, such as alkanes, are used as the dissolving step solvent.
The sorption helper is preferably selected from the group consisting of inorganic substances, carbon-based substances, and mixtures thereof. Non-limiting examples of inorganic substances are silicon oxide (silica), silica gel, aluminum oxide (alumina), iron oxide, aluminum silicate, magnesium silicate, amorphous volcanic glass, reclaimed glass, sand, quartz, diatomaceous earth, zeolite, perlite, clay, fuller's earth, bentonite clay, metal organic framework (MOF), covalent organic framework (COF), and zeolitic imidazolate framework (ZIF). Non-limiting examples of carbon-based substances are anthracite coal, carbon black, coke, and activated carbon. In one embodiment of the present invention, said inorganic substances are selected from the group consisting of silicon oxide (silica), silica gel, aluminum oxide (alumina), iron oxide, aluminum silicate, magnesium silicate, amorphous volcanic glass, reclaimed glass, sand, quartz, diatomaceous earth, zeolite, perlite, clay, fuller's earth, bentonite clay, metal organic framework (MOF), covalent organic framework (COF), zeolitic imidazolate framework (ZIF), and mixtures thereof. In another embodiment of the present invention, said inorganic substances are selected from the group consisting of silicon oxide (silica), silica gel, aluminum oxide (alumina), amorphous volcanic glass, reclaimed glass, sand, quartz, diatomaceous earth, zeolite, clay, fuller's earth, bentonite clay, and mixtures thereof. In yet another embodiment of the present invention, said carbon-based substances are selected from the group consisting of anthracite coal, carbon black, coke, activated carbon, and mixtures thereof.
In a preferred embodiment of the solution, the polymer solution (5) is subsequently fed to a step c″) of liquid-liquid separation into a polymer-lean stream (7) and a polymer-rich stream (8). Under certain conditions of temperature and pressure, the polymer solution can phase separate into two distinct liquid phases, one which is “lean” in dissolved polymer and one which is “rich” in dissolved polymer. Phase separation occurs at the lower critical solution temperature (LCST), also known as the “cloud point” (cf.
Increasing the temperature or decreasing the pressure at the cloud point leads to further phase separation. In other words, phase separation is encouraged by higher temperatures and/or by lower pressures. The cloud point is determined in part by the pressure, temperature, solution composition and the solvent used for polymerization.
With reference to
In case a step c″) is used (cf.
In an even more preferred embodiment of the invention involving a step c″) as set out above, another step c′) subsequent to step c) and preceding step c″) is carried out (cf.
If the polymer-lean stream (7) from step c″) comprises mainly solvent, it can be reintroduced into the contacting step b) after purification of the solvent (cf.
The vapor-liquid separating step d) of separating the polymer-rich stream (8) into a polymer-lean vapor stream (9) and a polymer-rich condensed stream (10) is preferably carried out as a flash separation step (cf.
The polymer-lean vapor stream (9) can be reintroduced into the contacting step b) after purification and upon adjustment of temperature and pressure to the requirements of the dissolution occurring in step b) (cf.
Step d) can be repeated multiple times, preferably up to 3 times in a row. Hence, in such a setup, the polymer-lean vapor phase (8) leaving the first step d) is again subject to a second flash separation step d′), thereby creating a second polymer-lean vapor phase (8′), which again can be subject to a third flash separation step d″). Each of the flash separating steps d) to d″) produces a polymer-rich condensed stream (10), which can either be combined or further processed separately from each other. If the step d) is carried out multiple times in a row, the pressure is lowered step after step and the temperature is increased step after step. Thereby, the preference levels as described for the temperature and the pressure of step d) preferably determine the temperature and pressure used in steps d), d′) and d″). In case a liquid-liquid separation step c″) is also used preceding step d), the pressure can already be below 10 bar before entering step d). Therefore, the conditions in step d) need to be respectively changed, i.e. either the pressure of the polymer-rich stream of step c″) increased or the temperature in step d) increased.
The step e) of recovering the polymer from the polymer-rich condensed stream (10), each of the polymer-rich condensed streams (10) to (102) or the combined polymer-rich condensed streams (10) to (102) is preferably carried out in an extruder (cf.
Hence, in a preferred embodiment according to
Moreover, in a preferred embodiment according to
Moreover, in a preferred embodiment according to
This particular embodiment has the advantage that two polymers can be dissolved at the same time in the process and can be therefore separated in a single, continuous process, enhancing process economics.
Preferably, the process of the present invention comprises a pre-treatment step a′) subsequently to the step a) of obtaining the waste polymer material (1) and step b) of contacting the waste polymer material (1) with the dissolving solvent (3) (cf.
In case the pre-treatment step a′) comprises an extraction step, the waste polymer material (1) is contacted with an extracting solvent (3e) to remove unwanted material present in the waste polymer material (1). Therefore, the extracting solvent (3e) has preferably the same boiling point at 1 bar pressure as the dissolving solvent (3). More preferably, the extracting solvent (3e) is identical to the dissolving solvent (3). Generally, the conditions chosen in step a′) are milder than those in step b), whereas milder defines lower temperatures and lower pressures. Generally, the conditions in step a′) are chosen not to dissolve the target polyolefin, but only other components.
In case the pre-treatment step a′) comprises a melting step, the waste polymer material (1) is fed to an extruder, where the polymer is firstly melted (cf.
In case the pre-treatment step a′) comprises a melting step, the extracting solvent (3e) is mixed with the molten polymer in a mixing device, preferably downstream of the melt pump. This enhances rapid mixing of the extracting solvent (3e) with the molten polymer. The final concentration of the extracting solvent (3e) in the mixture of molten polymer and extracting solvent (3e) is preferably from 1.0 to 95 wt.-%. Preferably, the mixing device is a static mixer or a dynamic mixer, more preferably a static mixer having the advantage of low maintenance costs (cf.
During the mixing between the extracting solvent (3e) and the molten polymer a homogenous polymer mixture can be created. In such a case it is beneficial, if the extracting solvent (3e) is identical to the dissolving solvent (3) used in the dissolving step b). Such a setup has the advantage that the dissolution times in the dissolving step b) are significantly reduced. Furthermore, the process can be performed in an continuous manner.
In case the extracting solvent (3e) is again removed from the polymer melt, the step can be considered as the second extraction step following up the melting step.
The addition of extracting solvent (3e) can be carried out in a single step or in multiple steps. Multiple steps can enhance the extraction and dissolution even further. Preferably, the temperatures and pressures used in step a′) are from 150 to 250° C. and from 50 to 150 bar.
A major advantage of the step of melting the polymer is that preferably the melt can be filtered and therefore impurities not being in the molten state can be removed before step b). Furthermore, such a setup provides the possibility to degass gaseous components such as water and volatiles if a degassing dome is additionally being used. Another advantage is that the melt bulk density is relatively high in comparison to the solid polymer. This enhances the flowability and makes it easier to feed the polymer to the contacting step b). Moreover, the process can now be carried out in continuous mode and can be simplified by removal of the extraction step. Finally, in case the extraction step is removed from the process, only one solvent cycle is needed, further not only reducing the complexity of the process, but also the need for material and energy consumption.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21168674.6 | Apr 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/059962 | 4/13/2022 | WO |
