Process and apparatus for polymer devolatilization

Abstract

The present invention in general relates to a process or method for reducing volatiles in a polymer melt feed, wherein the polymer melt feed comprises a polylactic acid (PLA) polymer. The present invention also relates to a devolatilization apparatus for removing volatiles from a polymer melt feed, wherein the polymer melt feed comprises a polylactic acid (PLA) polymer.

Description

[0001] PROCESS AND APPARATUS FOR POLYMER DEVOLATILIZATION

[0002] FIELD OF THE INVENTION

[0003] The present invention in general relates to a process or method for reducing volatiles in a polymer melt feed, preferably wherein the polymer melt feed comprises a polylactic acid (PLA). The present invention also relates to a devolatilization apparatus for removing volatiles from a polymer melt feed, wherein the polymer melt feed preferably comprises a polylactic acid (PLA).

[0004] BACKGROUND OF THE INVENTION

[0005] The demand for biodegradable polymers with excellent material properties is rapidly growing. Biodegradable polymers can be used in various applications, from biomedicine, additive technologies, film, fibres, packaging, automotive to agriculture, etc. Polylactide, which is also referred to as polylactic acid and abbreviated as PLA, has been receiving increased attention in recent years for use in these applications, because of its excellent performances in renewability, mechanical properties, biocompatibility, and biodegradability.

[0006] PLA is an aliphatic polyester, which can be manufactured from renewable resources. Such manufacture may involve the fermentation of starch, sugar, or other renewable organic substrates into lactic acid. Polylactide can be produced by direct polycondensation of lactic acid, i.e. lactate monomers. However, this has the drawback that a high molecular weight is not easily reached. Therefore, PLA is usually prepared by ring-opening polymerization (ROP) of lactide, the cyclic dimer of lactic acid, which in turn is usually manufactured by polycondensation of lactic acid into PLA oligomers, followed by de-polymerization of these oligomers by a so-called ‘backbiting’ mechanism in the presence of a suitable catalyst. After purification, the produced lactide can be converted into PLA of controlled molecular weight by means of a ring-opening polymerization reaction (ROP) in the presence of a polymerization catalyst and initiator. Ring-opening polymerization allows to control the polymerization process and thereby the structure of the produced PLA. This method can be used to manufacture PLA of high molecular weight. The molecular weights of the polymer fabricated by the ring opening polymerization can be controlled by residence time, catalyst and initiator concentration, and temperature. The sequence and ratio of L- and D-lactic acid units in the final polymer can also be controlled.

[0007] At the end of the polymerisation step of PLA (polylactide), the polymer, because of the chemical ring-chain equilibrium, always comprises lactide in a concentration which is dependent upon the polymerisation temperature and is between approx. 1 and 5%. This value is independent of whether the PLA is produced by ring-opening polymerisation from lactide or by direct polycondensation from lactic acid. During ring-opening polymerisation, the concentration of the lactide can also assume higher values if the reaction is interrupted even before reaching the chemical equilibrium, e.g., by addition of a substance which deactivates the polymerisation catalyst or by shortening the reaction residence time.

[0008] The unreacted lactide must be removed from the PLA polymer after the polymerization to obtain a PLA product of marketable quality. Lactide concentrations in the PLA of more than 0.5% by weight make the polymer unusable for most commercial purposes. During processing of PLA in the melt, such as spinning of threads, pouring of films, injection moulding etc, they lead to smoke which causes coughing; it also pollutes, and corrodes devices. Lactide-containing PLA granulate absorbs moisture when stored in ambient air, lactide being hydrolysed to form the linear dimer of lactic acid. During processing from the melt, this hydrolysis product leads to the rapid decomposition of the PLA chains because of the high melting temperature required for this purpose of more than 130° C (melting point of PLA), so that the polymer loses technically important properties, such as strength, transparency etc., and becomes unusable. The lower the residual concentration of lactide in the PLA, the more durable are the products produced therefrom and the better it behaves during processing. In the state of the art, such a removal of unreacted lactide can be achieved by means of a devolatilization step conducted at elevated temperature and reduced pressure.

[0009] After polymerization, the final polymer may comprise other undesirable volatile components such as moisture, residual solvents, and degradation by-products. The presence of moisture in PLA can result in reduced mechanical properties, reduced processing stability, and increased risk of degradation. Residual solvents may cause decreased processing stability and reduced material properties. The presence of degradation by-products can cause yellowing, reduced mechanical properties, and increased risk of degradation. To overcome these challenges, various devolatilization methods have been developed, Devolatilization of PLA is necessary to ensure the desired properties and quality of the final product. Without proper devolatilization, the presence of volatile impurities can result in a variety of processing and performance issues.

[0010] The polymer may, for example, be recovered from a polymerization reactor, stabilized by addition of a catalyst killer and fed to a devolatilization sector, where the undesirable components may be removed from the polymer. For example, volatiles may be removed by vacuum distillation, flash devolatilization, stripping, increasing polymer surface area, or combinations thereof. However, these methods are often energy-intensive, require specialized equipment, and can result in degradation of the material. A typical devolatilization section currently available uses a rudimentary setup which is not optimal in terms of quality, because of yellow coloration or black specks present in the final product, which are formed due to excessive residence time and temperature in the devolatilization system.

[0011] Given the commercial and regulatory importance of devolatilization, an ongoing need exists for improved devolatilization processes and associated equipment.

[0012] It is therefore an object of the present invention to provide an improved and / or optimized process for reducing volatiles in a polymer melt feed, and, in particular, in a polymer melt feed comprising a polylactic acid (PLA) polymer, and an improved and / or optimized apparatus for removing volatiles from a polymer melt feed, in particular a PI_A polymer melt feed. It is an object to provide a more efficient process and apparatus. It is an object to provide a process and apparatus that reduces the residual monomers that are present in the polymer melt after devolatilization. It is an object to provide a process or an apparatus that improves the yellowness index of the polymer after devolatilization. It is an object to provide a process or an apparatus that reduces the black specks that are present in a polymer after production of said polymer. It is an object to provide a process and apparatus that lowers the ratio of the capital expenditures over the operating expenditures (capex / opex).

[0013] SUMMARY OF THE INVENTION

[0014] In a first aspect, the present invention provides a process for reducing volatiles in a polymer melt feed, preferably wherein the polymer melt feed comprises a polylactic acid (PLA) polymer. The process preferably comprises one or more, preferably all, of the following steps: providing the polymer melt feed to a first preheater wherein the polymer melt feed is heated to a temperature T 1 under vacuum such that the polymer melt feed is at least partially foamed, thereby generating a foam; directly passing the heated polymer melt feed and the foam from the first preheater to a first devolatilization unit wherein the heated polymer melt feed and the foam are kept at a temperature T2 under vacuum, wherein the first devolatilization unit is in direct connection with the first preheater; and, recovering the volatiles from the foam in the first devolatilization unit through a gas outlet in the first devolatilization unit, thereby generating an at least partially devolatilized heated polymer melt. The inventors have surprisingly found that the formation of a PLA foam in the first preheater facilitates the removal of volatiles while improving the polymer colour, making the polymer less yellow. Moreover, the process of the invention is typically characterized in that foaming of the polymer melt already starts in the first preheater. This results in a reduced density of the polymer melt feed, thereby reducing and minimizing the residence time of the polymer melt in the preheater which is beneficial for the quality of the polymer melt and the final devolatilized polymer. Therefore, the system is also energy efficient, in that it allows to heat just what is needed but nothing more.

[0015] In some preferred embodiments, the process further comprises one or more, preferably all, of the following steps: optionally, passing the at least partially devolatilized heated polymer melt from the first devolatilization unit to a second preheater, wherein the at least partially devolatilized heated polymer melt is kept at a temperature T3; passing the at least partially devolatilized heated polymer melt from the first devolatilization unit or from the second preheater to a polymer distributor located inside and at the top of a second devolatilization unit, the polymer melt being kept at temperature T3 and under vacuum; passing the at least partially devolatilized heated polymer melt from the polymer distributor to the second devolatilization unit wherein the at least partially devolatilized heated polymer is kept at a temperature T4 under vacuum; recovering volatiles from the at least partially devolatilized heated polymer melt in the second devolatilization unit through a gas outlet in the second devolatilization unit, thereby generating a devolatilized polymer; collecting the devolatilized polymer from the second devolatilization unit in a collector; and, recovering the devolatilized polymer from the collector.

[0016] In some preferred embodiments, the polymer comprises a polylactic acid (PLA) polymer. In preferred embodiments, the polymer comprises a PLA homopolymer, a PLA copolymer, or a combination thereof.

[0017] In some preferred embodiments, the first preheater comprises an inlet part, a polymer heating part, and an outlet part. Said outlet part is preferably in direct contact or direct connection with the first devolatilization unit. In some preferred embodiments, the outlet part of the first preheater is the inlet part of the first devolatilization unit. In some preferred embodiments, the outlet part of the first preheater is located inside the first devolatilization unit. In some preferred embodiments, the heating part, and the outlet part of the first preheater are located at least partly inside the first devolatilization unit. In some further embodiments, the heating part of the first preheater is located at least partly inside the first devolatilization unit and the outlet part of the first preheater is located inside the first devolatilization unit.

[0018] The inventors surprisingly found that by positioning of the outlet part of the first preheater in the first devolatilization unit, a larger surface area is created, resulting in a more efficient devolatilization.

[0019] In some preferred embodiments, the temperatures T1 , T2, T3, and / or T4 are each independently at least 180°C and at most 240°C; preferably at least 190°C and at most 230°C; more preferably at least 195°C and at most 230°C. These temperatures allow for optimal devolatilization without unnecessarily compromising the polymer quality.

[0020] In some preferred embodiments, the vacuum is at least 80.0% vacuum; preferably at least 90.0% vacuum; more preferably at least 95.0% vacuum; even more preferably at least 99.0% vacuum. Preferably, the second devolatilisation unit has a higher level of vacuum compared to the first devolatilisation unit.

[0021] In some preferred embodiments, the pressure in the first devolatilization unit is at least 0.0 mbar abs and at most 100.0 mbar abs; preferably at least 0.01 mbar abs and at most 50.0 mbar abs; more preferably at least 0.1 mbar abs and at most 10.0 mbar abs; even more preferably at least 1 .0 mbar abs and at most 3.0 mbar abs.

[0022] In some preferred embodiments, the pressure in the second devolatilization unit is at least 0.0 mbar abs and at most 100.0 mbar abs; preferably at least 0.01 mbar abs and at most 50.0 mbar abs; more preferably at least 0.1 mbar abs and at most 10.0 mbar abs; even more preferably at least 1.0 mbar abs and at most 3.0 mbar abs.

[0023] In some preferred embodiments, the pressure in the first devolatilization unit and / or the second devolatilization unit is at most 100.0 mbar abs; preferably at most 50.0 mbar abs; more preferably at most 10.0 mbar abs; even more preferably at most 5.0 mbar abs; even more preferably at most 3.0 mbar abs. In some preferred embodiments, the pressure in the second devolatilization unit is lower than the pressure in the first devolatilization unit. The difference in pressure between the first and second devolatilization unit results in an even more efficient devolatilization, in particular since the residuals concentration of the polymer melt in the second devolatilization unit is already lower than the residuals concentration of the polymer melt in the first devolatilization unit.

[0024] In some preferred embodiments, the pressure in the second devolatilization unit is at most 100% of the pressure in the first devolatilization unit; preferably at most 75%; preferably at most 50%; preferably at most 33%; preferably at most 25%; preferably at most 10%. In some preferred embodiments, the pressure in the second devolatilization unit is at least 0.5 mbar abs lower than the pressure in the first devolatilization unit; preferably at least 1 .0 mbar abs lower; preferably at least 1.5 mbar abs lower; preferably at least 2.0 mbar abs lower; preferably at least 3.0 mbar abs lower; preferably at least 4.0 mbar abs lower; preferably at least 5.0 mbar abs lower.

[0025] In some preferred embodiments, the first preheater is a shell and tube preheater, a plate-fin heat exchanger, or a static mixer reactor (SMR); preferably a shell and tube heat exchanger. The use of a shell and tube heat exchanger allows to exactly control the temperature in the preheater, thereby also reducing the residence time of the polymer melt in the preheater.

[0026] In a second aspect, the present invention provides a devolatilization apparatus for removing volatiles from a polymer melt feed, wherein the polymer melt feed comprises a polylactic acid (PLA) polymer. The apparatus is preferably configured to perform the process according to the first aspect, and (preferred) embodiments thereof. (Preferred) embodiments of the first aspect are also (preferred) embodiments of the second aspect; and vice versa.

[0027] More particularly, the invention provides in a devolatilization apparatus for removing volatiles from a polymer melt feed, wherein the polymer melt feed preferably comprises a polylactic acid (PLA) polymer; the apparatus comprising: a first preheater, comprising an inlet part, a polymer heating part, and an outlet part; and, a first devolatilization unit, comprising an inlet part, a devolatilization vessel, a gas outlet, and a polymer outlet part.

[0028] The apparatus is preferably characterized in that the first preheater and the first devolatilization unit are configured to withstand vacuum pressure. The apparatus is preferably also characterized in that the first preheater is configured to at least partially foam a polymer melt feed comprising a polylactic acid (PLA) polymer. The apparatus is preferably also characterized in that the first preheater is in direct connection with the first devolatilization unit.

[0029] In some preferred embodiments, the devolatilization apparatus further comprises optionally, a second preheater; a second devolatilization unit, comprising an inlet part in the form of a polymer distributor, a devolatilization vessel, a gas outlet, and a polymer outlet part; and, a collector, configured to collect the polymer from the second devolatilization unit.

[0030] The apparatus is preferably characterized in that the second preheater and the second devolatilization unit are configured to withstand vacuum pressure.

[0031] In some preferred embodiments, the outlet part of the first preheater is in direct contact or connection with the inlet part of the first devolatilization unit. Preferably, the outlet part of the first preheater is the inlet part of the first devolatilization unit, or the outlet part of the first preheater is located inside the first devolatilization unit. In some preferred embodiments, the heating part of the first preheater is located at least partly inside the first devolatilization unit, and / or the outlet part of the first preheater is located inside the first devolatilization unit.

[0032] In a third aspect, the present invention thereto provides an at least partially devolatilized polymer or a devolatilized polymer, obtained through a process according to the first aspect, and (preferred) embodiments thereof, or with an apparatus according to the second aspect, and (preferred) embodiments thereof. (Preferred) embodiments of the first or second aspect are also (preferred) embodiments of the third aspect; and vice versa. The at least partially devolatilized polymer preferably comprises a residuals concentration of volatiles of at most 15000 ppm for PLA at the outlet of the first devolatilization unit.

[0033] The devolatilized polymer preferably comprises a residuals concentration of volatiles at the outlet of the second devolatilization unit of at most 3 000 ppm for PLA.

[0034] The present invention, and embodiments thereof, provides an improved process for reducing volatiles in a polymer melt feed; preferably a polymer melt comprising PLA, for example by foaming of the polymer melt feed already in the first preheater, and an improved apparatus for removing volatiles from a polymer melt feed; preferably a polymer melt feed comprising PLA, for example by allowing the foaming of the polymer melt feed already in the first preheater. The polymer devolatilization is very efficient. In particular, the foaming of the polymer melt already in the preheater and further the preheater outlet part being inside the first devolatilization result in optimized degassing resulting in the reduction of residual monomer in the final polymer, in an improved yellowness index (for example as measured according to ASTM D1925-70), in reduction of black specks in the final product and in an optimized capex / opex ratio.

[0035] DETAILED DESCRIPTION OF THE FIGURES

[0036] FIG. 1 illustrates a schematic representation of an embodiment of the invention showing a first preheater (1) in combination with a first devolatilization unit (2) comprising a gas outlet (3) wherein the outlet part of the first preheater is in direct contact with the first devolatilization unit.

[0037] FIG. 2 illustrates a schematic representation of an embodiment of the invention showing a first preheater (1) in combination with a first devolatilization unit (2) comprising a gas outlet (3) wherein the outlet part and the preheating part of the first preheater (1) are located at least partly in the first devolatilization unit (2).

[0038] FIG. 3 illustrates a schematic representation of an embodiment of the invention showing a second preheater (4) in combination with a second devolatilization unit (5) comprising a polymer distributor (6) in the form of a nozzle comprising a number of apertures to form polymer strands.

[0039] DETAILED DESCRIPTION OF THE INVENTION

[0040] When describing the invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0041] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

[0042] In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0043] As used herein, the singular forms “a”, “an”, and “the” include both singular and plural referents unless the context clearly dictates otherwise. By way of example, “a polymer” means one polymer or more than one polymer. The terms "comprising", "comprises" and "comprised of as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements, or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of, "consists" and "consists of.

[0044] The terms “apparatus”, “device” may be used herein as synonyms.

[0045] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g., 1 to 5 can include 1 , 2, 3, 4 when referring to, for example, a number of elements, and can also include 1 .5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0046] The term "about" as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + / -10% or less, preferably + / -5% or less, more preferably + / -1 % or less, of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier "about" refers is itself also specifically, and preferably, disclosed.

[0047] The terms “wt%,” “vol%”, or “mol%” refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, which includes the component.

[0048] All references cited in the present specification are hereby incorporated by reference in their entirety. In particular, the teachings of all references herein specifically referred to are incorporated by reference.

[0049] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some, but not other, features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art.

[0050] The terms described above, and others used in the specification are well understood to those skilled in the art.

[0051] Preferred statements (features) and embodiments, resins and uses of this invention are set herein below. Each statement and embodiment of the invention so defined may be combined with any other statement and / or embodiment unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features or statements indicated as being preferred or advantageous. Hereto, the present invention is, in particular, captured by any one or any combination of one or more of the below numbered aspects and embodiments, with any other statement and / or embodiment.

[0052] 1 . Process for reducing volatiles in a polymer melt feed, the process comprising the steps of: providing the polymer melt feed to a first preheater wherein the polymer melt feed is heated to a temperature T 1 under vacuum such that the polymer melt feed is at least partially foamed, thereby generating a foam; directly passing the heated polymer melt feed and the foam from the first preheater to a first devolatilization unit wherein the heated polymer melt feed and the foam are kept at a temperature T2 under vacuum, wherein the first devolatilization unit is in direct connection with the first preheater; and, recovering the volatiles from the foam in the first devolatilization unit through a gas outlet in the first devolatilization unit, thereby generating an at least partially devolatilized heated polymer melt.

[0053] 2. The process according to the preceding statement or according to some embodiments herein, further comprising: optionally, passing the at least partially devolatilized heated polymer melt from the first devolatilization unit to a second preheater, wherein the at least partially devolatilized heated polymer melt is heated at a temperature T3; passing the at least partially devolatilized heated polymer melt from the first devolatilization unit or from the second preheater to a polymer distributor located inside and at the top of a second devolatilization unit, the polymer being kept at a temperature T3 and under vacuum; passing the at least partially devolatilized heated polymer melt from the polymer distributor to the second devolatilization unit, wherein the at least partially devolatilized heated polymer is kept at a temperature T4 under vacuum; recovering volatiles from the at least partially devolatilized heated polymer melt in the second devolatilization unit through a gas outlet in the second devolatilization unit, thereby generating a devolatilized polymer; collecting the devolatilized polymer from the second devolatilization unit in a collector; and, recovering the devolatilized polymer from the collector.

[0054] 3. The process according to any of the preceding statements or according to some embodiments herein, wherein the polymer comprises a polylactic acid (PLA) polymer.

[0055] 4. The process according to any of the preceding statements or according to some embodiments herein, wherein the polymer comprises a PLA homopolymer, a PLA copolymer, or a combination thereof.

[0056] 5. The process according to any of the preceding statements or according to some embodiments herein, wherein the first preheater comprises an inlet part, a polymer heating part, and an outlet part; preferably wherein said outlet part is in direct contact or direct connection with the first devolatilization unit.

[0057] 6. The process according to any of the preceding statements or according to some embodiments herein, wherein the outlet part of the first preheater is the inlet part of the first devolatilization unit.

[0058] 7. The process according to any of the preceding statements or according to some embodiments herein, wherein the outlet part of the first preheater is located in the first devolatilization unit.

[0059] 8. The process according to any of the preceding statements or according to some embodiments herein, wherein both the heating part and the outlet part of the first preheater are at least partly located inside the first devolatilization unit. 9. The process according to any of the preceding statements or according to some embodiments herein, wherein the heating part of the first preheater is located at least partly in the first devolatilization unit and / or wherein the outlet part is located in the first devolatilization unit.

[0060] 10. The process according to any of the preceding statements or according to some embodiments herein, wherein the temperatures T1 , T2, T3 and / or T4 are each independently at least 180°C and at most 240°C; preferably at least 195°C and at most 230°C.

[0061] 11 . The process according to any of the preceding statements or according to some embodiments herein, wherein the temperature T1 is at least 180°C and at most 240°C; preferably at least 195°C and at most 230°C.

[0062] 12. The process according to any of the preceding statements or according to some embodiments herein, wherein the temperature T2 is at least 180°C and at most 240°C; preferably at least 195°C and at most 230°C.

[0063] 13. The process according to any of the preceding statements or according to some embodiments herein, wherein the temperature T3 is at least 180°C and at most 240°C; preferably at least 195°C and at most 230°C.

[0064] 14. The process according to any of the preceding statements or according to some embodiments herein, wherein the temperature T4 is at least 180°C and at most 240°C; preferably at least 195°C and at most 230°C.

[0065] 15. The process according to any of the preceding statements or according to some embodiments herein, wherein the vacuum is at least 80.0% vacuum; preferably at least 90.0% vacuum; more preferably at least 95.0% vacuum; even more preferably at least 99.0% vacuum.

[0066] 16. The process according to any of the preceding statements or according to some embodiments herein, wherein the pressure in the first devolatilization unit is at least 0.0 mbar abs and at most 100.0 mbar abs; preferably at least 0.01 mbar abs and at most 50.0 mbar abs; more preferably at least 0.1 mbar abs and at most 10.0 mbar abs; even more preferably at least 1.0 mbar abs and at most 3.0 mbar abs.

[0067] 17. The process according to any of the preceding statements or according to some embodiments herein, wherein the pressure in the second devolatilization unit is at least 0.0 mbar abs and at most 100.0 mbar abs; preferably at least 0.01 mbar abs and at most 50.0 mbar abs; more preferably at least 0.1 mbar abs and at most 10.0 mbar abs; even more preferably at least 1.0 mbar abs and at most 3.0 mbar abs. 18. The process according to any of the preceding statements or according to some embodiments herein, wherein the pressure in the second devolatilization unit is lower than the pressure in the first devolatilization unit; preferably wherein the pressure in the second devolatilization unit is at most 100% of the pressure in the first devolatilization unit; preferably at most 75%; preferably at most 50%; preferably at most 33%; preferably at most 25%; preferably at most 10%; preferably wherein the pressure in the second devolatilization unit is at least 0.5 mbar abs lower than the pressure in the first devolatilization unit; preferably at least 1 .0 mbar abs lower; preferably at least 1.5 mbar abs lower; preferably at least 2.0 mbar abs lower; preferably at least 3.0 mbar abs lower; preferably at least 4.0 mbar abs lower; preferably at least 5.0 mbar abs lower.

[0068] 19. The process according to any of the preceding statements or according to some embodiments herein, wherein the first preheater is a shell and tube heat exchanger, a plate-fin heat exchanger, or a static mixer reactor (SMR); preferably a shell and tube heat exchanger.

[0069] 20. The process according to any of the preceding statements or according to some embodiments herein, wherein the ratio of length to diameter (L / D) of the shell and tube preheater is at least 0.5 and at most 6.0; preferably at least 1 .0 and at most 3.0.

[0070] 21 . The process according to any of the preceding statements or according to some embodiments herein, wherein the internal tube diameter of the shell and tube preheater is at least 14.0 mm and at most 30.0 mm; preferably at least 16.0 mm and at most 22.0 mm.

[0071] 22. The process according to any of the preceding statements or according to some embodiments herein, wherein a pressure drop is present across the first preheater and the first devolatilization unit; preferably wherein the pressure drop is at least 0.1 bar and at most 60.0 bar; preferably at least 0.5 bar and at most 15.0 bar.

[0072] 23. The process according to any of the preceding statements or according to some embodiments herein, wherein the residence time of the polymer melt feed in the first preheater is between 0.1 and 20 minutes; preferably between 0.5 and 15 minutes; more preferably between 1 and 10 minutes.

[0073] 24. The process according to any of the preceding statements or according to some embodiments herein, wherein the second devolatilization unit comprises an inlet part in the form of a polymer distributor, a devolatilization vessel, a gas outlet, and a polymer outlet part.

[0074] 25. The process according to any of the preceding statements or according to some embodiments herein, wherein the polymer distributor in the inlet part of the second devolatilization unit is a devolatilization nozzle, the nozzle comprising an inlet part, a polymer distribution part comprising headers, and an outlet part comprising a number of apertures.

[0075] 26. The process according to any of the preceding statements or according to some embodiments herein, wherein the at least partially devolatilized heated polymer melt in the second devolatilization unit is provided to the devolatilization nozzle and passes through the apertures of the nozzle, thereby forming polymer strands in the second devolatilization unit.

[0076] 27. The process according to any of the preceding statements or according to some embodiments herein, wherein the polymer strands are collected in the collector by letting the polymer strands drop over a strand drop height into the collector, thereby obtaining a devolatilized polymer in the collector.

[0077] 28. A devolatilization apparatus for removing volatiles from a polymer melt feed; preferably wherein the polymer melt feed comprises a polylactic acid (PLA) polymer; preferably a polylactic acid (PI_A) polymer; the apparatus configured to perform the process according to any of the preceding statements or according to some embodiments herein.

[0078] 29. A devolatilization apparatus for removing volatiles from a polymer melt feed; preferably wherein the polymer melt feed comprises a polylactic acid (PLA) polymer; preferably a polylactic acid (PLA) polymer; preferably according to any of the preceding statements or according to some embodiments herein, the apparatus comprising: a first preheater, comprising an inlet part, a polymer heating part, and an outlet part; and, a first devolatilization unit, comprising an inlet part, a devolatilization vessel, a gas outlet, and a polymer outlet part; preferably characterized in that the first preheater and the first devolatilization unit are configured to withstand vacuum pressure; and preferably characterized in that the first preheater is configured to at least partially foam a polymer melt feed comprising a polylactic acid (PLA) polymer; preferably a polylactic acid (PLA) polymer; and preferably wherein the first devolatilization unit is in direct connection with the first preheater.

[0079] 30. The devolatilization apparatus according to any of the preceding statements or according to some embodiments herein, further comprising optionally, a second preheater, comprising an inlet part, a polymer heating part, and an outlet part; a second devolatilization unit, comprising an inlet part in the form of a polymer distributor, a devolatilization vessel, a gas outlet, and a polymer outlet part; and, a collector, configured to collect the polymer from the second devolatilization unit; preferably characterized in that the second preheater and the second devolatilization unit are configured to withstand vacuum pressure.

[0080] 31 . The devolatilization apparatus according to any of the preceding statements or according to some embodiments herein, wherein the outlet part of the first preheater is in direct contact or in direct connection with the inlet part of the first devolatilization unit.

[0081] 32. The devolatilization apparatus according to any of the preceding statements or according to some embodiments herein, wherein the outlet part of the first preheater is the inlet part of the first devolatilization unit.

[0082] 33. The devolatilization apparatus according to any of the preceding statements or according to some embodiments herein, wherein the outlet part of the first preheater is located in the first devolatilization unit.

[0083] 34. The devolatilization apparatus according to any of the preceding statements or according to some embodiments herein, wherein the outlet part of the first preheater is located in the first devolatilization unit and / or the heating part is located at least partly in the first devolatilization unit.

[0084] 35. An at least partially devolatilized polymer, obtained through a process according to any of the preceding statements or according to some embodiments herein, the polymer preferably comprising a residuals concentration of volatiles of at most 15 000 ppm.

[0085] 36. An at least partially devolatilized polymer obtained with an apparatus according to any of the preceding statements or according to some embodiments herein, the polymer preferably comprising a residuals concentration of volatiles of at most 15 000 ppm in the case of a PI_A polymer.

[0086] 37. A devolatilized polymer, obtained through a process according to any of the preceding statements or according to some embodiments herein, the polymer preferably comprising a residuals concentration of volatiles of at most 3 000 ppm in the case of a PLA polymer. 38. A devolatilized polymer obtained with an apparatus according to any of the preceding statements or according to some embodiments herein, the polymer preferably comprising a residuals concentration of volatiles of at most 3 000 ppm in the case of a PLA polymer.

[0087] In a first aspect, the present invention provides a process for reducing volatiles in a polymer melt feed, preferably wherein the polymer melt feed comprises a polylactic acid (PLA) polymer. The process preferably comprises one or more, preferably all, of the following steps: providing the polymer melt feed to a first preheater wherein the polymer melt feed is heated to a temperature T 1 under vacuum such that the polymer melt feed is at least partially foamed, thereby generating a foam; directly passing the heated polymer melt feed and the foam from the first preheater to a first devolatilization unit wherein the heated polymer melt feed and the foam are kept at a temperature T2 under vacuum, wherein the first devolatilization unit is in direct connection with the first preheater; and, recovering the volatiles from the foam in the first devolatilization unit through a gas outlet in the first devolatilization unit, thereby generating an at least partially devolatilized heated polymer melt.

[0088] The devolatilization process or apparatus as described herein may be used to remove volatile components from a polymer prior to further polymer manufacturing processes such as pelletising and forming.

[0089] The inventors have found that the formation of foam in the first preheater facilitates the removal of volatiles from a polymer melt feed, particularly a PLA polymer melt feed.

[0090] The inventors have found that a particular set of process conditions may provide an optimum for PLA polymer devolatilization in combination with reduced presence of black specks and improved yellowness index in the obtained polymer. Typically for the invention, foaming of the polymer melt feed is already initiated during the first preheating step, which results in improved devolatilization of the polymer melt already after the first devolatilization step. Also, foaming of the polymer melt in the first preheater tremendously reduces the residence time of the polymer melt feed in the first preheater, which is beneficial for the product quality of the obtained devolatilized polymer. More specific, the residence time of the polymer melt feed in the first preheater in the process of the invention may be reduced to less than 20 minutes; even less than 15 minutes; and even further to less than 10 minutes; in comparison to more than 20 minutes for devolatilization processes or setups known in the art. As a consequence of the reduced residence time, the colour of the obtained devolatilized polymer is greatly improved, evidenced by a yellowness index of 30 or lower, preferably of 25 or lower, preferably of 23 or lower. Further, the reduced residence time also results in less presence of black specks in the obtained polymer, with typically a reduction of about 75% as compared to devolatilization processes with a standard setup known in the art.

[0091] As used herein, the yellowness index of PLA is a measure of the extent to which the material has yellowed over time. Yellowing is a common degradation process that occurs in thermoplastics such as PLA and is caused by exposure to light, heat, and other environmental factors. The yellowness index is a numerical value that represents the extent of yellowing, with higher values indicating greater yellowing. The yellowness index is typically measured using a spectrophotometer, which measures the amount of light absorbed by the sample at a specific wavelength. The measurement is performed by comparing the sample's optical properties with those of a reference material, such as a virgin PLA sample that has not been exposed to environmental conditions. The yellowness index is usually expressed in units of AL*, where AL* represents the change in the L* value (a measure of the lightness of the sample) between the reference material and the sample being tested. As used herein, the yellowness index may be measured according to standard ASTM D1925-70.

[0092] Furthermore, the configuration of the outlet part of the first preheater being located inside the first devolatilization unit increases the surface exchange area, which helps further reduce the residuals concentration in the polymer melt.

[0093] In some preferred embodiments, the process further comprises one or more, preferably all, of the following steps: optionally, passing the at least partially devolatilized heated polymer melt from the first devolatilization unit to a second preheater, wherein the at least partially devolatilized heated polymer melt is kept at a temperature T3; passing the at least partially devolatilized heated polymer melt from the first devolatilization unit or from the second preheater to a polymer distributor located inside the second devolatilization unit, the polymer being kept at temperature T3 and under vacuum; passing the at least partially devolatilized heated polymer from the polymer distributor to the second devolatilization unit wherein the at least partially devolatilized heated polymer is kept at a temperature T4 under vacuum; recovering volatiles from the at least partially devolatilized heated polymer melt in the second devolatilization unit through a gas outlet in the second devolatilization unit, thereby generating a devolatilized polymer; collecting the devolatilized polymer from the second devolatilization unit in a collector; and, recovering the devolatilized polymer from the collector.

[0094] In some preferred embodiments, the polymer is a PLA polymer; preferably a PLA polymer that comprises a PLA homopolymer, a PLA copolymer, or a combination thereof. The Mw range can be for example from at least 50 000 to at most 400 000 g / mol.

[0095] The process and apparatus of the present invention are typically suitable for devolatilization of polymer melt feeds comprising a polymer, such as a PLA polymer. In some embodiments, the PLA polymer is PLA homopolymer. In some embodiments, the PLA polymer is a PLA copolymer. In some embodiments, the PLA polymer is a combination of a PLA homopolymer and a PLA copolymer.

[0096] The terms “PLA”, “polylactic polymer”, and “polylactic acid” are used herein as synonyms.

[0097] A “PLA polymer” as used herein refers to a polymer of lactide (monomers). Lactide can exist in three different geometric structures, which have a diastereomeric relationship. The term “lactide” (or “lactide monomer”) as used herein may therefore be L-lactide (derived from two L-lactic acid molecules), D-lactide (derived from two D-lactic acid molecules), meso-lactide (derived from a L- lactic acid molecule and a D-lactic acid molecule), or a mixture of two or more of the above. A 50 / 50 mixture of L-lactide and D-lactide with a melting point of about 126°C is often referred to in the literature as D, L-lactide or racemic lactide (and is also denoted as “rac-Lactide” or “racemic lactide” or “rac-lactide” herein). A PLA polymer as defined herein may thus be a polymer of lactide (monomer) selected from the group comprising L-lactide, D-lactide, meso-lactide, racemic lactide and any mixture of two or more thereof.

[0098] In certain embodiments, a PLA polymer as defined herein is a polymer of lactide (monomer) as defined herein only, i.e., such polymer does not comprise any other monomer which is not a lactide. In certain embodiments, a PLA polymer which does not comprise any monomer which is not a lactide, is also denoted herein as a “PLA homopolymer”. Such PLA homopolymer may thus consist of lactide, e.g., lactide which is selected from the group comprising L-lactide, D-lactide, meso-lactide, racemic lactide and any mixture of two or more thereof. In certain embodiments, the PLA polymer is selected from the group comprising, and preferably consisting of, poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), and poly(L-,D-lactic acid) (PLDLA), and any mixture thereof. Stereo-complexes of PLLA and PDLA, as described for example in WO 2010 / 097463, can also be used as PLA polymer.

[0099] The process for preparing PLA is well-known by the person skilled in the art.

[0100] In certain embodiments, the PLA polymer may comprise limited amounts of a comonomer which is not a lactide as defined herein. More in particular, the PLA polymer may include a PLA copolymer, i.e., a copolymer of a lactide and a non-lactide comonomer. The term “PLA copolymer” as used herein intends to refer to a polymer of lactide (monomer) (as defined herein) and a comonomer which is not lactide (i.e., a non-lactide comonomer).

[0101] In a certain embodiment, a non-lactide comonomer is selected from the group comprising glycolide, urethanes, carbonates, lactones; preferably glycolide. For instance, copolymers of lactide and trimethylene carbonate may be used. For instance, copolymers of lactide and urethanes may be used. For instance, copolymers of lactide and lactones may be used. In a preferred embodiment, said comonomer is a lactone. Preferably said lactone is selected from the group comprising caprolactone, valerolactone, and butyrolactone. For instance, copolymers of lactide and caprolactone may be used in the polymer composition.

[0102] In some embodiments, the introduction of comonomers to PLA increases the ductility (i.e., decreases the brittleness) of the PLA. Additionally, it is appreciated that if polymer composition comprises a PLA copolymer, as defined herein such PLA copolymer comprises a non-lactide comonomer content in a very specific range. Preferably, the amount of a non-lactide comonomer in a PLA copolymer, for use in the present invention, is at most 30 % by weight, based on the total weight of the PLA copolymer, and preferably comprised between 1 and 20 % by weight or between 1 and 10 % by weight, or between 2 and 7 % by weight, or between 2 and 5 % by weight, based on the total weight of the PLA copolymer. A PLA copolymer as applied herein can be understood to mean any type of copolymer, including but not limited to a random copolymer, a block copolymer, a gradient copolymer, and a statistical copolymer.

[0103] In some preferred embodiments, the temperatures T1 , T2, T3, and / or T4 are each independently at least 180°C and at most 240°C; preferably at least 190°C and at most 230°C; more preferably at least 195°C and at most 230°C.

[0104] It is to be noted that optimum temperature varies from one type of polymer to the other, as well as, for a given type of polymer, from one grade to another. The ranges provided here usually correspond to the targeted foaming capacity of the polymer melt. The polymer temperature may be measured by a thermowell temperature probe at the entrance, i.e. the inlet part, of the first preheater, the first devolatilization unit, the second preheater or the second devolatilization unit. For example, the temperature may be measured using a thermowell type sensor from WIKA model TW10.

[0105] The inventors have found that a temperature range of at least 185°C and at most 240°C; preferably at least 195°C and at most 230°C in the first preheater, i.e. temperature T1 , and in the first devolatilization unit, i.e. temperature T2, provides an optimum for foaming of the polymer melt feed, and thus provides an optimum for the devolatilization of most of the polymers, in particular polymers comprising a PLA polymer.

[0106] Although one might think that higher temperatures as such might result in a better devolatilization efficiency, it means also higher risk of thermal degradation. Also, higher temperatures typically results in lower viscosity, a lower pressure drop across the first preheater and first devolatilization unit, and a risk of less efficient devolatilization. If the temperature is lower, then it means lower devolatilization efficiency, and due to high viscosity higher capes and opex.

[0107] Excessive temperature results in the modification of the polymer properties, which is not desirable. The temperature is preferably adapted depending on the stability of the polymer, its viscosity, and the nature of the volatiles to be removed.

[0108] In some embodiments, the polymer temperature during the process according to the invention or in the devolatilization apparatus according to the invention is at least 150°C and at most 300°C; preferably at least 190°C and at most 280°C; more preferably at least 180°C and at most 240°C; more preferably at least 190°C and at most 240°C; more preferably at least 195°C and at most 230°C.

[0109] In some embodiments, the temperature T1 , which is the temperature to which the polymer melt feed is heated in the first preheater is at least 150°C and at most 300°C; preferably at least 190°C and at most 280°C; more preferably at least 180°C and at most 240°C; more preferably at least 190°C and at most 240°C; more preferably at least 195°C and at most 230°C.

[0110] In some embodiments, the temperature T2, which is the temperature to which the polymer melt feed is heated in the first devolatilization unit is at least 150°C and at most 300°C; preferably at least 190°C and at most 280°C; more preferably at least 180°C and at most 240°C; more preferably at least 190°C and at most 240°C; more preferably at least 195°C and at most 230°C. In some embodiments, the temperature T3, which is the temperature to which the at least partially devolatilized polymer is heated in the second preheater is at least 150°C and at most 300°C; preferably at least 190°C and at most 280°C; more preferably at least 180°C and at most 240°C; more preferably at least 190°C and at most 240°C; more preferably at least 195°C and at most 230°C.

[0111] In some embodiments, the temperature T4, which is the temperature to which the at least partially devolatilized polymer is heated in the second devolatilization unit is at least 150°C and at most 300°C; preferably at least 190°C and at most 280°C; more preferably at least 180°C and at most 240°C; more preferably at least 190°C and at most 240°C; more preferably at least 195°C and at most 230°C.

[0112] As taught herein, the preheating and devolatilization in the first part, and in the optional second part of the system are all preferably performed under vacuum to allow optimized foaming of the polymer melt feed.

[0113] In some embodiments, the polymer melt feed is heated in the first preheater under vacuum. In some embodiments, the polymer melt feed and the generated foam are heated in the first devolatilization unit under vacuum.

[0114] In some preferred embodiments, the vacuum is at least 80.0% vacuum; preferably at least 90.0% vacuum; more preferably at least 95.0% vacuum; even more preferably at least 99.0% vacuum.

[0115] In some preferred embodiments, the pressure in the first devolatilization unit is at least 0.0 mbar abs and at most 100.0 mbar abs; preferably at least 0.01 mbar abs and at most 75.0 mbar abs; more preferably at least 0.01 mbar abs and at most 50.0 mbar abs; more preferably at least 0.1 mbar abs and at most 20.0 mbar abs; more preferably at least 0.1 mbar abs and at most 10.0 mbar abs; more preferably at least 0.2 mbar abs and at most 8.0 mbar abs; more preferably at least 0.5 mbar abs and at most 5.0 mbar abs; more preferably at least 0.8 mbar abs and at most 4.0 mbar abs; even more preferably at least 1 .0 mbar abs and at most 3.0 mbar abs.

[0116] In some preferred embodiments, the pressure in the second devolatilization unit is at least 0.0 mbar abs and at most 100.0 mbar abs; preferably at least 0.01 mbar abs and at most 75.0 mbar abs; more preferably at least 0.01 mbar abs and at most 50.0 mbar abs; more preferably at least 0.1 mbar abs and at most 20.0 mbar abs; more preferably at least 0.1 mbar abs and at most 10.0 mbar abs; more preferably at least 0.2 mbar abs and at most 8.0 mbar abs; more preferably at least 0.5 mbar abs and at most 5.0 mbar abs; more preferably at least 0.8 mbar abs and at most 4.0 mbar abs; even more preferably at least 1 .0 mbar abs and at most 3.0 mbar abs. In some preferred embodiments, the pressure in the second devolatilization unit is lower than the pressure in the first devolatilization unit. For example, in some embodiments, the pressure in the first devolatilization unit is about 3.0 mbar abs, whereas the pressure in the second devolatilization unit is about 1.0 mbar abs. In some preferred embodiments, the pressure in the second devolatilization unit is at most 100% of the pressure in the first devolatilization unit; preferably at most 75%; preferably at most 50%; preferably at most 33%; preferably at most 25%; preferably at most 10%. In some preferred embodiments, the pressure in the second devolatilization unit is at least 0.5 mbar abs lower than the pressure in the first devolatilization unit; preferably at least 1 .0 mbar abs lower; preferably at least 1.5 mbar abs lower; preferably at least 2.0 mbar abs lower; preferably at least 3.0 mbar abs lower; preferably at least 4.0 mbar abs lower; preferably at least 5.0 mbar abs lower. For example, if the pressure in the first devolatilization unit is 3.0 mbar abs, the pressure in the second devolatilization unit may be 1.0 mbar abs, i.e. 33% of the pressure of the first devolatilization unit or 2.0 mbar abs less.

[0117] The difference in pressure between the first and second devolatilization unit results in an even more efficient devolatilization. After all, the residuals concentration of the polymer melt in the second devolatilization unit is already lower than the residuals concentration of the polymer melt in the first devolatilization unit; and thus requires an even lower pressure to obtain an efficient devolatilization.

[0118] In some embodiments, a pressure drop is present across the first preheater, hereby providing an optimum for foaming and devolatilization of the polymer. The pressure drop may be defined as the difference between inlet pressure and outlet pressure. The pressure at the outlet of the preheater is the pressure of the devolatilization unit, typically a vacuum.

[0119] In some preferred embodiments, said pressure drop is at least 0.1 bar and at most 60.0 bar; preferably at least 0.2 bar and at most 40.0 bar; more preferably at least 0.5 bar and at most 30.0 bar; more preferably at least 0.5 bar and at most 15.0 bar.

[0120] As taught herein, the inventors have found that with the process and apparatus according to the invention, the residence time of the polymer melt feed in the first preheater can be greatly reduced as compared to processes and apparatuses known in the art. More specifically, the process or apparatus of the present invention has a residence time of the polymer melt feed in the first preheater of between 0.1 and 20 minutes; preferably between 0.1 and 15 minutes; more preferably between 0.5 and 15 minutes; more preferably between 1.0 and 10.0 minutes. In a second aspect, the present invention provides a devolatilization apparatus for removing volatiles from a polymer melt feed, wherein the polymer melt feed comprises a polylactic acid (PLA) polymer; preferably a PLA polymer. The apparatus is preferably configured to perform the process according to the first aspect, and (preferred) embodiments thereof. (Preferred) embodiments of the first aspect are also (preferred) embodiments of the second aspect; and vice versa.

[0121] The present invention also relates to a process for reducing volatiles in a polymer melt feed that comprises a PI_A polymer, using the devolatilization apparatus as described herein, and (preferred) embodiments thereof.

[0122] The present invention also relates to the use of the devolatilization apparatus as described herein, and (preferred) embodiments thereof, for reducing volatiles in a polymer melt feed comprising a PLA polymer.

[0123] More particularly, the invention provides in a devolatilization apparatus for removing volatiles from a polymer melt feed, wherein the polymer melt feed comprises a polylactic acid (PLA) polymer, the apparatus comprising: a first preheater, comprising an inlet part, a polymer heating part, and an outlet part; and, a first devolatilization unit, comprising an inlet part, a devolatilization vessel, a gas outlet, and a polymer outlet part.

[0124] The apparatus is preferably characterized in that the first preheater and the first devolatilization unit are configured to withstand vacuum pressure. The apparatus is preferably also characterized in that the first preheater is configured to at least partially foam a polymer melt feed comprising a polylactic acid (PLA) polymer. The apparatus is preferably also characterized in that the first devolatilization unit is in direct connection with the first preheater.

[0125] In some preferred embodiments, the outlet part of the first preheater is in direct contact or direct connection with the inlet part of the first devolatilization unit. Preferably, the outlet part of the first preheater is the inlet part of the first devolatilization unit, or the outlet part of the first preheater is located inside the first devolatilization unit; or the heating part is locating at least partly in the first devolatilization unit and the outlet part of the first preheater is located inside the first devolatilization unit. The process of the invention is typically characterized in that foaming of the polymer melt feed already starts during the first preheating phase in the first preheater. In the first preheater, the polymer melt feed is heated to a temperature T 1 under vacuum such that the polymer melt feed is at least partially foamed, thereby generating a foam in the first preheater to facilitate the removal of volatiles. Since the foaming of the polymer melt occurs already in the first preheater, the density of the foam is low, thereby reducing the residence time of the polymer melt feed in the first preheater.

[0126] In some preferred embodiments, the first preheater comprises an inlet part, a polymer heating part, and an outlet part. Said outlet part is preferably in direct contact with the first devolatilization unit. In some preferred embodiments, the outlet part of the first preheater is the inlet part of the first devolatilization unit. In some preferred embodiments, the outlet part of the first preheater is located inside the first devolatilization unit. In some preferred embodiments, the heating part and the outlet part of the first preheater are located at least partly inside the first devolatilization unit. In some preferred embodiments, the heating part a of the first preheater is located at least partly inside the first devolatilization unit, and the outlet part of the first preheater is located inside the first devolatilization unit.

[0127] As used herein, “in direct contact” is to be understood as the configuration wherein the outlet part of the first preheater is directly connected to the first devolatilization unit. In other words, the polymer melt feed and foam are transported from the outlet part of the first preheater directly into the first devolatilization unit.

[0128] In some embodiments, the outlet part of the first preheater (1) is the inlet part of the first devolatilization unit (2), for example as shown in FIG. 1. More specific, the outlet part of the first preheater and the inlet part of the first devolatilization unit are the same such that the first preheater and the first devolatilization unit are directly connected to each other.

[0129] In some embodiments, the outlet part of the first preheater (1) is located in the first devolatilization unit (2). In some further embodiments, the heating part and the outlet part of the first preheater are located at least partly in the first devolatilization unit, for example as shown in FIG. 2.

[0130] The inventors have found that a particular set of geometrical parameters may provide an optimum for polymer devolatilization. Preferably the process is performed with an apparatus at these values. For example, the dimensions of the preheater, such as the diameter and the length of the tubes, are typically optimized to obtain an optimized pressure drop and residence time in the system. In some embodiments, the first preheater is a shell and tube heat exchanger, a plate-fin heat exchanger, or a Static Mixer Reactor (SMR) type preheater with a simple distribution tube sheet at the outlet. In some preferred embodiments, the first preheater is a shell and tube preheater.

[0131] In some further embodiments the ratio of length to diameter (L / D) of the shell and tube preheater is at least 0.3 and at most 6.0; preferably at least 0.5 and at most 3.0.

[0132] In some embodiments, the internal diameter of the first preheater, such as a shell and tube preheater, is at least 10.0 mm and at most 50.0 mm; preferably at least 14.0 mm and at most 30.0 mm; more preferably at least 15.0 mm and at most 30.0 mm; more preferably at least 16.0 mm and at most 22.0 mm.

[0133] In some embodiments, a pressure drop is present across the first preheater and the first devolatilization unit. In some further embodiments, the pressure drop is at least 0.1 bar and at most 60.0 bar; preferably at least 0.5 bar and at most 20.0 bar.

[0134] In some embodiments, the residence time of the polymer melt feed in the first preheater is between 0.5 and 10 minutes; preferably between 1 and 5 minutes.

[0135] In some embodiments, the at least partially devolatilized heated polymer melt from the first devolatilization unit is passed through a second preheater and second devolatilization unit. The configuration of said second preheater and second devolatilization unit can be any configuration known to the skilled person.

[0136] In some preferred embodiments, the devolatilization apparatus further comprises optionally, a second preheater, comprising an inlet part, a polymer heating part, and an outlet part; a second devolatilization unit, comprising an inlet part in the form of a polymer distributor, a devolatilization vessel, a gas outlet, and a polymer outlet part; and, a collector, configured to collect the polymer from the second devolatilization unit.

[0137] The apparatus is preferably characterized in that the second devolatilization unit, and optionally the second preheater, are configured to withstand vacuum pressure.

[0138] In some embodiments, the second devolatilization unit comprises an inlet part in the form of a polymer distributor, a polymer distributing part, and an outlet part. In some specific embodiments, the polymer distributor in the inlet part is a devolatilization nozzle, said nozzle comprising an inlet part, a polymer distribution part comprising headers, and an outlet part comprising a number of apertures.

[0139] In some embodiments, the inlet part of the second devolatilization unit (5) thus comprises polymer distributor (6) which is a devolatilization nozzle comprising an inlet part, a polymer distribution part comprising headers, and an outlet part comprising a number of apertures, configured to form polymer strands in the devolatilization unit, for example as shown in FIG. 3.

[0140] In some embodiments, the average aperture diameter of the aperture in the devolatilization nozzle is at least 0.5 mm and at most 10 mm; preferably at least 0.8 mm and at most 6.0 mm; more preferably at least 1 .0 mm and at most 4.0 mm.

[0141] The inventors have found that this diameter provides an optimum for the devolatilization of the polymer in the second depolymerization unit, particularly when also considering the capex and opex. Larger diameters result in a lower pressure drop and a lower devolatilization efficiency (a higher amount of residual volatiles). Smaller diameters may result in higher pressure drop or might even risk blocking of the aperture. The increased pressure drop as a result may reach the maximum mechanical resistance in the nozzle. At very low aperture diameters, drag forces result in excessive pressure drop, with excessive energy consumption as a result.

[0142] In some embodiments, the at least partially devolatilized heated polymer melt in the second devolatilization unit is provided to the devolatilization nozzle and passes through the apertures of the nozzle, thereby forming polymer strands in the second devolatilization unit. In some embodiments, said polymer strands are collected in the collector by letting the polymer strands drop over a strand drop height into the collector, thereby obtaining a devolatilized polymer in the collector.

[0143] The strands may sway while dropping into the collector. Swaying comes from the gas stream constituted by volatiles leaving the strands. Bigger strands are less prone to swaying, while less gas flow perturbation occurs as the free strand surface is lower.

[0144] In some further embodiments, the at least partially devolatilized heated polymer melt in the second devolatilization unit is provided to the devolatilization nozzle and passes through the apertures of the nozzle, thereby forming polymer strands in the second devolatilization unit.

[0145] In some further embodiments, the polymer strands are collected in the collector by letting the polymer strands drop over a strand drop height into the collector, thereby obtaining a devolatilized polymer in the collector. As taught herein, the first and second devolatilization unit preferably comprise a gas outlet (3, 7) to remove and / or recover the volatiles, including monomers, from the polymer melt in respectively the first and second devolatilization unit. Said gas outlet in the first devolatilization unit and in the second devolatilization unit may be connected at or near the top of the devolatilization unit and is used to remove the volatiles that exit the polymer within the vessel. The gas outlet may comprise one or more pipes, connections, or pipes and connections in order to balance vapour flows.

[0146] Elements of the apparatus are preferably composed of a material capable of withstanding a differential pressure and vacuum as well as an elevated operating temperature. Without indenting to be limiting, an example of a suitable material may be steel. In case the polymer material, such as a polymer comprising PLA, may cause corrosion, appropriate steel alloys may be used, such as 316L or duplex steel grades. Elements of the apparatus may optionally comprise additional elements such as insulation or reinforcement plating.

[0147] The inventors have found that with the process and apparatus according to the invention the residuals concentration in a polymer after polymerization is greatly reduced as compared to known processes or apparatuses in the art.

[0148] In a third aspect, the present invention thereto provides an at least partially devolatilized polymer or a devolatilized polymer, obtained through a process according to the first aspect, and (preferred) embodiments thereof, or with an apparatus according to the second aspect, and (preferred) embodiments thereof. (Preferred) embodiments of the first or second aspect are also (preferred) embodiments of the third aspect; and vice versa. The at least partially devolatilized PLA polymer preferably comprises a residuals concentration of volatiles of at most 15 000 ppm.

[0149] The devolatilized PLA polymer preferably comprises a residuals concentration of volatiles at the collector of the second devolatilization unit of at most 3 000 ppm.

[0150] As used herein, the term “residuals concentration” refers to the total concentration of left-over monomer, co-monomer, and / or solvent remaining in the polymer after devolatilization. As used herein, the term “monomer concentration” refers to the concentration of left-over monomer remaining in the polymer.

[0151] For example, for polylactic acid (PLA), the term “residuals concentration” may refer to lactide.

[0152] In some embodiments, and particularly when the polymer comprises polylactic acid, the polymer melt feed comprises a residuals concentration at the inlet of the first preheater of at most 100 000 ppm; preferably at most 50 000 ppm; In some preferred embodiments, and particular when the polymer comprises polylactic acid, the polymer melt feed comprises a monomer concentration at the inlet of the first preheater of at least

[0153] 1 000 ppm to at most 100 000 ppm; preferably at least 2 000 ppm to at most 50 000 ppm; more preferably at least 5 000 ppm to at most 50 000 ppm.

[0154] In some preferred embodiments, and particular when the polymer comprises polylactic acid, the at least partially devolatilized polymer comprises a residuals concentration at the outlet of the first devolatilization unit of at most 20 000 ppm; more preferably at most 15 000 ppm.

[0155] In some preferred embodiments, and particular when the polymer comprises polylactic acid, the partially devolatilized polymer comprises a residuals concentration at the outlet of the second devolatilization unit of at most 5 000 ppm; preferably at most 3 000 ppm; more preferably at most

[0156] 2 000 ppm.

[0157] In some preferred embodiments, the residuals concentration of volatiles at the outlet of the first devolatilization unit is at most 40% of the residuals concentration of volatiles at the inlet of the first devolatilization unit; preferably at most 30%; more preferably at most 20%; more preferably at most 10.0%.

[0158] In some preferred embodiments, the residuals concentration of volatiles at the outlet of the second devolatilization unit is at most 75% of the residuals concentration of volatiles at the inlet of the second devolatilization unit; preferably at most 60%; more preferably at most 40%; more preferably at most 20.0. For example, the first devolatilization unit may reduce the residuals concentration of volatiles from 5% going to 0.6% (outlet is 12% of feed at inlet), while the second devolatilization unit may further reduce the residuals concentration of volatiles from 0.6% to 0.3% (outlet is 50% of feed at inlet).

[0159] In some embodiments, the polymer is passed through the devolatilization apparatus. In some embodiments, the polymer is passed multiple times through the devolatilization apparatus. This allows a further reduction of residuals content in the final polymer.

[0160] EXAMPLES

[0161] Different PLA polymer melts were prepared starting from lactide and in the presence of a polymerisation catalyst and an initiator (Table 1). After devolatilization, the quality of the recovered and devolatilized polymer is determined based on the following parameters: presence of residual monomer, yellowness index (based on ASTM D1925-70), presence of black specks >0.5 mm, and the presence of black specks with a size in between 0.1 -0.5 mm.

[0162] Two different setups for the process of devolatilization were tested (Table 1):

[0163] In the “Upflow DV1 PH” setup, the PLA polymer melt feed was fed into a first preheater (DV1 preheater), wherein the polymer melt feed was heated to a temperature of 220°C under vacuum (3 mbar abs). In this setup, the first preheater (DV1 preheater) was connected via an outlet chamber to a piping spool piece. Said piping spool piece was then connected to a side nozzle of the first devolatilization unit (DV1).

[0164] In the “Downflow DV1 PH” setup, the PLA polymer melt feed was also fed into a first preheater (DV1 preheater), wherein the polymer melt feed was heated to a temperature of 220°C under vacuum (3 mbar abs). In this setup, the first preheater (DV1 preheater) was directly connected to the first devolatilization unit (DV1), in particular to the top nozzle of the first devolatilization unit. This Downflow DV1 PH setup is a setup according to an embodiment of the invention.

[0165] In all setups, the first and second preheaters are shell and tube heat exchangers (TEMA).

[0166] After passage through the first devolatilization unit, the polymer melt was then fed into a second preheater (DV2 preheater) followed by passage through a second devolatilization unit (DV2).

[0167] Both in the first and in the second devolatilization unit, volatiles were recovered and the devolatilized polymer was finally recovered from the second devolatilization unit and analysed for the following parameters: presence of residual monomer, yellowness index (based on ASTM D1925-70), presence of black specks >0.5 mm, and presence of black specks with a size in between 0.1 -0.5 mm.

[0168] In Table 1 , the technical settings of two examples (Example 1 and 2) are presented using either the Upflow DV1 PH setup or the Downflow DV1 PH setup.

[0169] Table 1 : Settings that were applied for two examples in the Upflow DV1 PH and Downflow DV1 PH setup during the devolatilization of a polymer.

[0170]

[0171] As shown in Table 2, the Downflow DV1 PH setup results in both Examples 1 and 2 in an improved quality of the recovered devolatilized polymer, as evidenced by reduced presence of residual monomer, reduced yellowness index, and reduced presence of black specks of different sizes.

[0172] Table 2. Quality of the devolatilized polymer obtained after a devolatilization process using either the Upflow DV1 PH setup or the Downflow DV1 PH setup. Two different types of polymer melts were evaluated (Example 1 and 2).

Claims

CLAIMS1. Process for reducing volatiles in a polymer melt feed, wherein the polymer comprises a polylactic acid (PLA) polymer, the process comprising the steps of: providing the polymer melt feed to a first preheater wherein the polymer melt feed is heated to a temperature T 1 under vacuum such that the polymer melt feed is at least partially foamed, thereby generating a foam; directly passing the heated polymer melt feed and the foam from the first preheater to a first devolatilization unit wherein the heated polymer melt feed and the foam are kept at a temperature T2 under vacuum, wherein the first devolatilization unit is in direct connection with the first preheater; and, recovering the volatiles from the foam in the first devolatilization unit through a gas outlet in the first devolatilization unit, thereby generating an at least partially devolatilized heated polymer melt.

2. The process according to claim 1 , further comprising: optionally, passing the at least partially devolatilized heated polymer melt from the first devolatilization unit to a second preheater, wherein the at least partially devolatilized heated polymer melt is heated at a temperature T3. passing the at least partially devolatilized heated polymer melt from the first devolatilization unit or from the optional second preheater to a polymer distributor located inside and at the top of a second devolatilization unit, the polymer being kept at temperature T3 and under vacuum; passing the at least partially devolatilized heated polymer melt from the polymer distributor to the second devolatilization unit wherein the at least partially devolatilized heated polymer is kept at a temperature T4 under vacuum; recovering volatiles from the at least partially devolatilized heated polymer melt in the second devolatilization unit through a gas outlet in the second devolatilization unit, thereby generating a devolatilized polymer; collecting the devolatilized polymer from the second devolatilization unit in a collector; and,recovering the devolatilized polymer from the collector.

3. The process according to claim 2; wherein the pressure in the second devolatilization unit is lower than the pressure in the first devolatilization unit; preferably wherein the pressure in the second devolatilization unit is at most 100% of the pressure in the first devolatilization unit; preferably at most 75%; preferably at most 50%; preferably at most 33%; preferably at most 25%; preferably at most 10%.

4. The process according to any one of claims 1 to 3, wherein the polymer comprises a PLA homopolymer, a PLA copolymer, or a combination thereof.

5. The process according to any one of claims 1 to 4, wherein the first preheater comprises an inlet part, a polymer heating part, and an outlet part; wherein said outlet part is in direct connection with the first devolatilization unit.

6. The process according to claim 5, wherein the outlet part of the first preheater is the inlet part of the first devolatilization unit, and / or wherein the outlet part of the first preheater is located in the first devolatilization unit.

7. The process according to claim 6, wherein the heating part of the first preheater is located at least partly inside the first devolatilization unit and the outlet part of the first preheater is located inside the first devolatilization unit.

8. The process according to any one of claims 1 to 7, wherein the first preheater is a shell and tube heat exchanger, a plate-fin heat exchanger, or a static mixer reactor (SMR); preferably a shell and tube heat exchanger.

9. The process according to any one of claims 1 to 8, wherein the temperatures T1 , T2, T3, and / or T4 are each independently at least 180°C and at most 240°C; preferably at least 195°C and at most 230°C.

10. The process according to any one of claims 1 to 9, wherein the pressure in the first devolatilization unit and in the second devolatilization unit are each independently at least 0.0 mbar abs and at most 100.0 mbar abs; preferably at least 0.01 mbar abs and at most 50.0 mbar abs; more preferably at least 0.1 mbar abs and at most 10.0 mbar abs; even more preferably at least 1 .0 mbar abs and at most 3.0 mbar abs.

11. A devolatilization apparatus for removing volatiles from a polymer melt feed, wherein the polymer melt feed comprises a polylactic acid (PLA) polymer, wherein the apparatus is configured to perform the process according to any one of claims 1 to 10.

12. A devolatilization apparatus for removing volatiles from a polymer melt feed, preferably according to claim 11 , the apparatus comprising at least: a first preheater, comprising an inlet part, a polymer heating part, and an outlet part; and, a first devolatilization unit, comprising an inlet part, a devolatilization vessel, a gas outlet, and a polymer outlet part; characterized in that: the first preheater and the first devolatilization unit are configured to withstand vacuum pressure; the first preheater is configured to at least partially foam a polymer melt feed comprising a polylactic acid (PLA); and the first devolatilization unit is in direct connection with the first preheater.

13. The devolatilization apparatus of claim 12 further comprising: optionally, a second preheater; a second devolatilization unit, comprising an inlet part in the form of a polymer distributor, a devolatilization vessel, a gas outlet, and a polymer outlet part; and, a collector, configured to collect the polymer at the bottom of the second devolatilization unit; characterized in that the second devolatilization unit, and optionally the second preheater, are configured to withstand vacuum pressure.

14. The devolatilization apparatus according to any one of claims 11 to 13, wherein the outlet part of the first preheater is in direct connection with the inlet part of the first devolatilization unit; preferably wherein the outlet part of the first preheater is the inlet part of the first devolatilization unit.

15. The process according to any one of claims 1 to 10, performed with a devolatilization apparatus according to any one of claims 11 to 14.

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