Process and apparatus for polymer devolatilization

Abstract

The present invention generally relates to processes or methods for reducing volatiles in a polymer melt feed, wherein the polymer melt feed comprises a polylactic acid (PLA) polymer. The invention also relates to a devolatilizer for removing volatiles from a polymer melt feed, wherein the polymer melt feed comprises a polylactic acid (PLA) polymer.

Description

Technical Field

[0001] The present invention generally relates to a process or method for reducing volatiles in a polymer melt feed, preferably wherein the polymer melt feed comprises polylactic acid (PLA). The present invention also relates to a devolatilization apparatus for removing volatiles from a polymer melt feed, preferably wherein the polymer melt feed comprises polylactic acid (PLA). Background Art

[0002] The demand for biodegradable polymers with excellent material properties is rapidly growing. Biodegradable polymers are used in a wide range of applications, from biomedicine and additive technology to membranes, fibers, packaging, automotive, and agriculture. Polylactide, also known as polylactic acid and abbreviated as PLA, has gained increasing attention in recent years for its use in these applications due to its excellent properties in terms of renewability, mechanical properties, biocompatibility, and biodegradability.

[0003] PLA is an aliphatic polyester that can be produced from renewable resources. Such production can involve fermenting 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 disadvantage of not being able to easily achieve high molecular weights. Therefore, PLA is typically produced by ring-opening polymerization (ROP) of lactide, a cyclic dimer of lactic acid. This, in turn, is typically produced by polycondensing lactic acid into PLA oligomers, which are then depolymerized in the presence of a suitable catalyst via a so-called "backbiting" mechanism. After purification, the produced lactide can be converted into PLA with a controlled molecular weight via ring-opening polymerization (ROP) in the presence of a polymerization catalyst and initiator. Ring-opening polymerization allows control of the polymerization process, thereby controlling the structure of the produced PLA. This method can be used to produce high-molecular-weight PLA. The molecular weight of the polymer produced by ring-opening polymerization can be controlled by residence time, catalyst and initiator concentrations, and temperature. The sequence and ratio of L-lactic acid units and D-lactic acid units in the final polymer can also be controlled.

[0004] At the end of the PLA (polylactide) polymerization step, due to chemical ring-chain equilibrium, the polymer always contains lactide, with a lactide concentration that depends on the polymerization temperature and ranges from approximately 1 to 5%. This value is independent of whether the PLA is produced from lactide via ring-opening polymerization or from lactic acid via direct polycondensation. During ring-opening polymerization, if the reaction is interrupted even before chemical equilibrium is reached, for example by adding a substance that deactivates the polymerization catalyst or by shortening the reaction residence time, the lactide concentration can also reach higher values.

[0005] Unreacted lactide must be removed from PLA polymer after polymerization to obtain marketable PLA products. Lactide concentrations greater than 0.5% by weight in PLA render the polymer unusable for most commercial purposes. During processing of PLA in the melt (e.g., spinning, film casting, injection molding, etc.), it produces smoke that causes coughing; it also contaminates and corrodes equipment. When stored in ambient air, lactide-containing PLA pellets absorb moisture, and the lactide is hydrolyzed to form linear dimers of lactic acid. During processing from the melt, these hydrolysis products, due to the required high melt temperature (over 130°C, the melting point of PLA), rapidly decompose the PLA chains, causing the polymer to lose technologically important properties such as strength and transparency, rendering it unusable. The lower the residual lactide concentration in PLA, the more durable the products produced from it are, and the better they perform during processing. In the prior art, such removal of unreacted lactide is accomplished through a devolatilization step conducted at elevated temperature and reduced pressure.

[0006] After polymerization, the final polymer may contain other undesirable volatile components, such as moisture, residual solvents, and degradation byproducts. The presence of moisture in PLA can lead to reduced mechanical properties, reduced processing stability, and increased degradation risk. Residual solvents can lead to reduced processing stability and reduced material properties. The presence of degradation byproducts can lead to yellowing, reduced mechanical properties, and increased degradation risk. To overcome these challenges, a variety of devolatilization methods have been developed. Devolatilization of PLA is essential to ensure the desired properties and quality of the final product. Without proper devolatilization, the presence of volatile impurities can lead to various processing and performance problems.

[0007] The polymer can be recovered, for example, from a polymerization reactor, stabilized by adding a catalyst deactivator, and fed to a devolatilization zone where undesirable components can be removed from the polymer. For example, volatiles can be removed by vacuum distillation, flash devolatilization, steam stripping, increasing the polymer surface area, or a combination thereof. However, these methods are often energy intensive, require specialized equipment, and may result in degradation of the material.

[0008] Typical devolatilization sections currently available use a basic setup that is not optimal in terms of quality, since yellow coloration or black specks are present in the final product, which are formed due to excessive residence times and temperatures in the devolatilization system.

[0009] Given the commercial and regulatory importance of devolatilization, there is a continuing need for improved devolatilization processes and related equipment.

[0010] Therefore, the object of the present invention is to provide an improved and / or optimized process for reducing volatiles in a polymer melt feed, in particular a polymer melt feed comprising polylactic acid (PLA) polymer, and an improved and / or optimized apparatus for removing volatiles from a polymer melt feed, in particular a PLA polymer melt feed. The object of the present invention is to provide a more efficient process and apparatus. The object of the present invention is to provide a process and apparatus that reduce the residual monomers present in the polymer melt after devolatilization. The object of the present invention is to provide a process or apparatus that improves the yellowness index of the polymer after devolatilization. The object of the present invention is to provide a process or apparatus that reduces the black specks present in the polymer after polymer production. The object of the present invention is to provide a process and apparatus that reduces the ratio of capital expenditure to operating expenditure (capex / opex). Summary of the Invention

[0011] 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:

[0012] - providing the polymer melt feed to a first preheater, wherein the polymer melt feed is heated to a temperature T1 under vacuum, such that the polymer melt feed is at least partially foamed, thereby generating foam;

[0013] - passing the heated polymer melt feed and the foam from the first preheater directly to a first devolatilization unit, wherein the heated polymer melt feed and the foam are maintained at a temperature T2 under vacuum, wherein the first devolatilization unit is directly connected to the first preheater; and,

[0014] - withdrawing volatiles from the foam in the first devolatilization unit through a gas outlet in the first devolatilization unit, thereby producing an at least partially devolatilized heated polymer melt.

[0015] The inventors surprisingly discovered that forming PLA foam in the first preheater facilitates the removal of volatiles while simultaneously improving polymer color, making it less yellow. Furthermore, a characteristic feature of the present method is that foaming of the polymer melt begins already in the first preheater. This results in a lower density of the polymer melt feed, thereby reducing and minimizing the residence time of the polymer melt in the preheater, which benefits the quality of the polymer melt and the resulting devolatilized polymer. Consequently, the system is also energy-efficient, as it allows heating only what is needed, not more.

[0016] In some preferred embodiments, the process further comprises one or more, preferably all, of the following steps:

[0017] - optionally, sending 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 maintained at a temperature T3;

[0018] - conveying 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 on top of the second devolatilization unit, the polymer melt being maintained at temperature T3 and under vacuum;

[0019] - 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 maintained at a temperature T4 under vacuum;

[0020] - withdrawing 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 producing a devolatilized polymer;

[0021] - collecting the devolatilized polymer from the second devolatilization unit in a collector; and,

[0022] - Recovering the devolatilized polymer from the collector.

[0023] 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.

[0024] In some preferred embodiments, the first preheater comprises an inlet portion, a polymer heating portion, and an outlet portion. The outlet portion is preferably in direct contact with or directly connected to the first devolatilization unit. In some preferred embodiments, the outlet portion of the first preheater is the inlet portion of the first devolatilization unit. In some preferred embodiments, the outlet portion of the first preheater is located inside the first devolatilization unit. In some preferred embodiments, the heating portion and the outlet portion of the first preheater are at least partially located inside the first devolatilization unit. In some further embodiments, the heating portion of the first preheater is at least partially located inside the first devolatilization unit, and the outlet portion of the first preheater is located inside the first devolatilization unit.

[0025] The inventors surprisingly found that by positioning the outlet portion of the first preheater in the first devolatilization unit, a larger surface area is created, resulting in more efficient devolatilization.

[0026] In some preferred embodiments, 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 polymer quality.

[0027] 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 devolatilization unit has a higher vacuum level than the first devolatilization unit.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] In some preferred embodiments, the pressure in the second devolatilization unit is lower than the pressure in the first devolatilization unit. The pressure difference between the first and second devolatilization units leads to an even more efficient devolatilization, in particular because the residual concentration of the polymer melt in the second devolatilization unit is already lower than the residual concentration of the polymer melt in the first devolatilization unit.

[0032] 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.

[0033] 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 for precise control of the temperature in the preheater, thereby also reducing the residence time of the polymer melt in the preheater.

[0034] 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 a 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.

[0035] More specifically, the present invention provides a devolatilizer for removing volatiles from a polymer melt feed, wherein the polymer melt feed preferably comprises a polylactic acid (PLA) polymer; the apparatus comprising:

[0036] - a first preheater comprising an inlet section, a polymer heating section, and an outlet section; and,

[0037] - A first devolatilization unit comprising an inlet section, a devolatilization vessel, a gas outlet and a polymer outlet section.

[0038] Preferably, the apparatus is characterized in that the first preheater and the first devolatilization unit are configured to withstand vacuum pressure. Preferably, the apparatus is further characterized in that the first preheater is configured to at least partially foam a polymer melt feed comprising polylactic acid (PLA) polymer. Preferably, the apparatus is further characterized in that the first preheater is directly connected to the first devolatilization unit.

[0039] In some preferred embodiments, the devolatilizer further comprises

[0040] - Optionally, a second preheater;

[0041] - a second devolatilization unit comprising an inlet section in the form of a polymer distributor, a devolatilization vessel, a gas outlet and a polymer outlet section; and,

[0042] - a collector configured to collect polymer from the second devolatilization unit.

[0043] Preferably, the apparatus is characterized in that the second preheater and the second devolatilization unit are configured to withstand vacuum pressure.

[0044] In some preferred embodiments, the outlet portion of the first preheater is in direct contact with or connected to the inlet portion of the first devolatilization unit. Preferably, the outlet portion of the first preheater is the inlet portion of the first devolatilization unit, or the outlet portion of the first preheater is located within the first devolatilization unit. In some preferred embodiments, the heating portion of the first preheater is at least partially located within the first devolatilization unit, and / or the outlet portion of the first preheater is located within the first devolatilization unit.

[0045] In a third aspect, the present invention provides an at least partially devolatilized polymer, or a devolatilized polymer, obtained by a process according to the first aspect and its (preferred) embodiments, or using an apparatus according to the second aspect and its (preferred) embodiments. (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 has a residual concentration of volatiles of at most 15,000 ppm for PLA at the outlet of the first devolatilization unit.

[0046] The devolatilized polymer preferably comprises, at the outlet of the second devolatilization unit, a residual concentration of volatiles of at most 3 000 ppm for PLA.

[0047] The present invention and embodiments thereof provide an improved process for reducing volatiles in a polymer melt feed, preferably a polymer melt comprising PLA, such as by foaming the polymer melt feed already in a first preheater, and an improved apparatus for removing volatiles from a polymer melt feed, preferably a polymer melt feed comprising PLA, such as by allowing the polymer melt feed already in a first preheater to foam.

[0048] The polymer devolatilization is very efficient. In particular, the foaming of the polymer melt already in the preheater and also of the preheater outlet portion within the first devolatilization leads to optimized degassing, to a reduction in residual monomers in the final polymer, to an improved yellowness index (e.g., as measured in accordance with ASTM D1925-70), to a reduction in black spots in the final product, and to an optimized capital expenditure / operating expenditure (capex / opex) ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic diagram of one embodiment of the present invention is shown, which shows a first preheater (1) in combination with a first devolatilization unit (2) comprising a gas outlet (3), wherein the outlet portion of the first preheater is in direct contact with the first devolatilization unit.

[0050] Figure 2 A schematic diagram of an embodiment of the present invention is shown, which shows a combination of a first preheater (1) and a first devolatilization unit (2) comprising a gas outlet (3), wherein the outlet section of the first preheater (1) and the preheating section are at least partially located in the first devolatilization unit (2).

[0051] Figure 3 A schematic diagram of one embodiment of the present invention is shown 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 plurality of holes to form polymer strands. DETAILED DESCRIPTION

[0052] When describing the present invention, the terms used should be interpreted according to the following definitions, unless the context requires otherwise.

[0053] Unless otherwise defined, all terms used to disclose the present invention, including technical and scientific terms, have the meaning commonly understood by those skilled in the art to which the present invention belongs. By way of further guidance, term definitions are included to better understand the teachings of the present invention.

[0054] In the following paragraphs, different aspects of the present invention are defined in more detail. Each aspect so defined can be combined with any other one or more aspects, unless clearly indicated to the contrary. In particular, any feature indicated as preferred or advantageous can be combined with any other one or more features indicated as preferred or advantageous.

[0055] As used herein, the singular forms "a," "an," and "the" include singular and plural referents unless the context clearly dictates otherwise. For example, "a polymer" means one polymer or more than one polymer.

[0056] As used herein, the terms "comprising," "comprises," and "comprised of" are synonymous with "including," "includes," or "containing," and are inclusive or open-ended and do not exclude additional, unrecited members, elements, or method steps. It will be understood that the term "comprising," as used herein, includes the terms "consisting of," "consists of," and "consists of."

[0057] The terms "device" and "apparatus" may be used as synonyms herein.

[0058] Numerical ranges expressed by endpoints include all integers and, where appropriate, fractions contained within the range (e.g., 1 to 5 when referring to, for example, the number of elements, may include 1, 2, 3, and 4, and when referring to, for example, measurements, may also include 1.5, 2, 2.75, and 3.80). The recitation of endpoints also includes the endpoint values ​​themselves (e.g., 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all subranges contained therein.

[0059] As used herein, the term "about" when referring to a measurable value, such as a parameter, amount, duration, etc., is intended to encompass variations of the specified value, including + / - 10% or less, preferably + / - 5% or less, and more preferably + / - 1% or less, from the specified value, provided such variations are suitable for use in the disclosed invention. It is understood that the value to which the modifier "about" refers is itself also specifically and preferably disclosed.

[0060] The terms "wt%", "vol%" or "mol%" refer to the weight percent, volume percent or mole percent of a component, respectively, based on the total weight, total volume or total moles of the material including the component.

[0061] All references cited in this specification are incorporated by reference in their entirety. In particular, the teachings of all references specifically mentioned herein are incorporated by reference.

[0062] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the phrases "in one embodiment" or "in an embodiment" appearing in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner, as will be apparent to those skilled in the art from this disclosure. Furthermore, while some embodiments described herein include some features included in other embodiments and not other features, combinations of features from different embodiments are intended to be within the scope of the invention and to form different embodiments, as will be appreciated by those skilled in the art.

[0063] The above terms and other terms used in the specification are well understood by those skilled in the art.

[0064] Preferred statements (features) and embodiments, resins and uses of the invention are set forth herein below. Each statement and embodiment of the invention so defined may be combined with any other statement and / or embodiment unless expressly indicated to the contrary. In particular, any feature indicated as preferred or advantageous may be combined with any other feature or features or statements indicated as preferred or advantageous. To this end, the invention is particularly captured by any one or one or more of the following numbered aspects and embodiments in any combination with any other statement and / or embodiment.

[0065] 1. A process for reducing volatiles in a polymer melt feed, the process comprising the steps of:

[0066] - providing the polymer melt feed to a first preheater, wherein the polymer melt feed is heated to a temperature T1 under vacuum, such that the polymer melt feed is at least partially foamed, thereby generating foam;

[0067] - sending the heated polymer melt feed and the foam from the first preheater directly to a first devolatilization unit, wherein the heated polymer melt feed and the foam are maintained at a temperature T2 under vacuum, wherein the first devolatilization unit is directly connected to the first preheater; and,

[0068] - withdrawing volatiles from the foam in the first devolatilization unit through a gas outlet in the first devolatilization unit, thereby producing an at least partially devolatilized heated polymer melt.

[0069] 2. A process according to the preceding statements or according to some embodiments herein, further comprising:

[0070] - optionally, sending 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;

[0071] - conveying 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 on top of the second devolatilization unit, the polymer melt being maintained at temperature T3 and under vacuum;

[0072] - 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 maintained at a temperature T4 under vacuum;

[0073] - withdrawing 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 producing a devolatilized polymer;

[0074] - collecting the devolatilized polymer from the second devolatilization unit in a collector; and,

[0075] - Recovering the devolatilized polymer from the collector.

[0076] 3. The process according to any one of the preceding statements or according to some embodiments herein, wherein the polymer comprises a polylactic acid (PLA) polymer.

[0077] 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.

[0078] 5. The process according to any of the preceding statements or according to some embodiments herein, wherein the first preheater comprises an inlet section, a polymer heating section, and an outlet section; preferably, wherein the outlet section is in direct contact with or directly connected to the first devolatilization unit.

[0079] 6. The process according to any of the preceding statements or according to some embodiments herein, wherein the outlet portion of the first preheater is the inlet portion of the first devolatilization unit.

[0080] 7. The process according to any of the preceding statements or according to some embodiments herein, wherein the outlet portion of the first preheater is located in the first devolatilization unit.

[0081] 8. The process according to any of the preceding statements or according to some embodiments herein, wherein both the heating portion and the outlet portion of the first preheater are at least partially located inside the first devolatilization unit.

[0082] 9. The process according to any of the preceding statements or according to some embodiments herein, wherein the heating portion of the first preheater is at least partially located in the first devolatilization unit and / or wherein the outlet portion is located in the first devolatilization unit.

[0083] 10. The process according to any of the preceding statements or according to some embodiments herein, wherein 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 14. The process according to any of the preceding statements or according to some embodiments herein, wherein temperature T4 is at least 180°C and at most 240°C; preferably at least 195°C and at most 230°C.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 20. The process according to any of the preceding statements or according to some embodiments herein, wherein the shell and tube preheater has a length to diameter ratio (L / D) of at least 0.5 and at most 6.0; preferably at least 1.0 and at most 3.0.

[0094] 21. The process according to any of the preceding statements or according to some embodiments herein, wherein the inner 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.

[0095] 22. The process according to any of the preceding statements or according to some embodiments herein, wherein there is a pressure drop 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.

[0096] 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.

[0097] 24. The process according to any of the preceding statements or according to some embodiments herein, wherein the second devolatilization unit comprises an inlet section in the form of a polymer distributor, a devolatilization vessel, a gas outlet, and a polymer outlet section.

[0098] 25. The process according to any of the preceding statements or according to some embodiments herein, wherein the polymer distributor in the inlet portion of the second devolatilization unit is a devolatilization nozzle comprising an inlet portion, a polymer distribution portion comprising a header, and an outlet portion comprising a plurality of holes.

[0099] 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 through the holes of the nozzle, thereby forming polymer strands in the second devolatilization unit.

[0100] 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 allowing the polymer strands to fall into the collector over a strand drop height, thereby obtaining devolatilized polymer in the collector.

[0101] 28. A devolatilizer 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; the apparatus being configured to carry out a process according to any of the preceding statements or according to some embodiments herein.

[0102] 29. A devolatilizer 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:

[0103] - a first preheater comprising an inlet section, a polymer heating section, and an outlet section; and,

[0104] - a first devolatilization unit comprising an inlet section, a devolatilization vessel, a gas outlet and a polymer outlet section;

[0105] 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 directly connected to the first preheater.

[0106] 30. The devolatilizer according to any of the preceding statements or according to some embodiments herein, further comprising

[0107] - optionally, a second preheater comprising an inlet section, a polymer heating section and an outlet section;

[0108] - a second devolatilization unit comprising an inlet section in the form of a polymer distributor, a devolatilization vessel, a gas outlet and a polymer outlet section; and,

[0109] - a collector configured to collect polymer from the second devolatilization unit;

[0110] Preferably, it is characterized in that the second preheater and the second devolatilization unit are configured to withstand vacuum pressure.

[0111] 31. The devolatilizer according to any of the preceding statements or according to some embodiments herein, wherein the outlet portion of the first preheater is in direct contact or directly connected to the inlet portion of the first devolatilization unit.

[0112] 32. The devolatilizer according to any of the preceding statements or according to some embodiments herein, wherein the outlet portion of the first preheater is the inlet portion of the first devolatilization unit.

[0113] 33. The devolatilizer according to any of the preceding statements or according to some embodiments herein, wherein the outlet portion of the first preheater is located in the first devolatilization unit.

[0114] 34. The devolatilizer according to any of the preceding statements or according to some embodiments herein, wherein the outlet portion of the first preheater is located in the first devolatilization unit and / or the heating portion is located at least partially in the first devolatilization unit.

[0115] 35. An at least partially devolatilized polymer obtained by a process according to any of the preceding statements or according to some embodiments herein, said polymer preferably comprising a residual concentration of volatiles of at most 15 000 ppm.

[0116] 36. An at least partially devolatilized polymer obtained with an apparatus according to any of the preceding statements or according to some embodiments herein, said polymer preferably comprising, in the case of a PLA polymer, a residual concentration of volatiles of at most 15 000 ppm.

[0117] 37. Devolatilized polymer obtained by a process according to any of the preceding statements or according to some embodiments herein, said polymer preferably comprising, in the case of a PLA polymer, a residual concentration of volatiles of at most 3 000 ppm.

[0118] 38. Devolatilized polymer obtained with the apparatus according to any of the preceding statements or according to some embodiments herein, said polymer preferably comprising, in the case of a PLA polymer, a residual concentration of volatiles of at most 3 000 ppm.

[0119] 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:

[0120] - providing the polymer melt feed to a first preheater, wherein the polymer melt feed is heated to a temperature T1 under vacuum, such that the polymer melt feed is at least partially foamed, thereby generating foam;

[0121] - passing the heated polymer melt feed and the foam from the first preheater directly to a first devolatilization unit, wherein the heated polymer melt feed and the foam are maintained at a temperature T2 under vacuum, wherein the first devolatilization unit is directly connected to the first preheater; and,

[0122] - withdrawing volatiles from the foam in the first devolatilization unit through a gas outlet in the first devolatilization unit, thereby producing an at least partially devolatilized heated polymer melt.

[0123] The devolatilization process or apparatus as described herein can be used to remove volatile components from a polymer prior to further polymer manufacturing processes such as pelletizing and shaping.

[0124] The inventors have discovered that forming a foam in the first preheater aids in removing volatiles from the polymer melt feed, particularly PLA polymer melt feed.

[0125] The inventors have discovered that a specific set of process conditions can provide optimal conditions for devolatilization of PLA polymer, combined with reduced presence of black specks and an improved yellowness index in the resulting polymer. Typically, for the present invention, foaming of the polymer melt feed begins already during the first preheating step, resulting in improved devolatilization of the polymer melt after the first devolatilization step. Furthermore, foaming of the polymer melt in the first preheater significantly reduces the residence time of the polymer melt feed in the first preheater, which benefits the product quality of the devolatilized polymer obtained. More specifically, in the process of the present invention, the residence time of the polymer melt feed in the first preheater can be reduced to less than 20 minutes; even less than 15 minutes; and even further, less than 10 minutes, compared to greater than 20 minutes for devolatilization processes or apparatus known in the art. Due to the reduced residence time, the color of the devolatilized polymer obtained is significantly improved, as evidenced by a yellowness index of 30 or less, preferably 25 or less, and more preferably 23 or less. Furthermore, the reduced residence time also results in a lower presence of black specks in the resulting polymer, with a typical reduction of about 75% compared to a devolatilization process using standard setups known in the art.

[0126] As used herein, the yellowness index of PLA is a measure of the extent to which a 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 indicates the degree 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 a sample at a specific wavelength. It is measured by comparing the optical properties of a sample with the optical properties of a reference material (e.g., a pristine PLA sample that has not been exposed to environmental conditions). The yellowness index is usually expressed as The unit indicates that Indicates the difference between the reference material and the sample being tested. As used herein, the yellowness index can be measured according to standard ASTM D1925-70.

[0127] Furthermore, the configuration of the outlet portion of the first preheater inside the first devolatilization unit increases the surface exchange area, which helps to further reduce the residue concentration in the polymer melt.

[0128] In some preferred embodiments, the process further comprises one or more, preferably all, of the following steps:

[0129] - optionally, sending 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 maintained at a temperature T3;

[0130] - conveying 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 melt being maintained at temperature T3 and under vacuum;

[0131] - 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 maintained at a temperature T4 under vacuum;

[0132] - withdrawing 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 producing a devolatilized polymer;

[0133] - collecting the devolatilized polymer from the second devolatilization unit in a collector; and,

[0134] - Recovering the devolatilized polymer from the collector.

[0135] In some preferred embodiments, the polymer is a PLA polymer; preferably, the PLA polymer comprises a PLA homopolymer, a PLA copolymer, or a combination thereof. The Mw range can be, for example, at least 50,000 to at most 400,000 g / mol.

[0136] The process and apparatus of the present invention are typically suitable for devolatilization of a polymer melt feed comprising a polymer, such as a PLA polymer. In some embodiments, the PLA polymer is a 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.

[0137] The terms "PLA," "polylactic acid polymer," and "polylactic acid" are used synonymously herein.

[0138] As used herein, "PLA polymer" refers to a polymer of lactide (monomer). Lactide can exist in three different geometric structures, which have a diastereomeric relationship. Therefore, the term "lactide" (or "lactide monomer") used herein can be L-lactide (derived from two L-lactic acid molecules), D-lactide (derived from two D-lactic acid molecules), meso-lactide (derived from an 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 approximately 126°C is often referred to in the literature as D,L-lactide or racemic lactide (and also denoted herein as "rac-lactide" or "racemic lactide"). Thus, the PLA polymer as defined herein may be a polymer of lactide (monomer) selected from L-lactide, D-lactide, meso-lactide, racemic lactide, and any mixture of two or more thereof.

[0139] In certain embodiments, a PLA polymer as defined herein is a polymer consisting solely of lactide (monomer) as defined herein, i.e., such a polymer does not contain any other monomers other than lactide. In certain embodiments, a PLA polymer that does not contain any monomers other than lactide is also referred to herein as a "PLA homopolymer." Thus, such a PLA homopolymer can be composed of lactide, for example, a lactide selected from L-lactide, D-lactide, meso-lactide, racemic-lactide, and any mixtures of two or more thereof.

[0140] 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. Stereocomplexes of PLLA and PDLA, such as those described in WO 2010 / 097463, may also be used as PLA polymers.

[0141] Processes for preparing PLA are well known to those skilled in the art.

[0142] In certain embodiments, the PLA polymer may include a limited amount of a comonomer that is not lactide as defined herein. More particularly, the PLA polymer may include a PLA copolymer, i.e., a copolymer of lactide and a non-lactide comonomer. As used herein, the term "PLA copolymer" is intended to refer to a polymer of lactide (monomer) (as defined herein) and a comonomer that is not lactide (i.e., a non-lactide comonomer).

[0143] In certain embodiments, the non-lactide comonomer is selected from glycolide, carbamate, carbonate, and lactone; preferably glycolide. For example, a copolymer of lactide and trimethylene carbonate can be used. For example, a copolymer of lactide and carbamate can be used. For example, a copolymer of lactide and lactone can be used. In a preferred embodiment, the comonomer is a lactone. Preferably, the lactone is selected from caprolactone, valerolactone, and butyrolactone. For example, a copolymer of lactide and caprolactone can be used in the polymer composition.

[0144] In some embodiments, the introduction of comonomers to PLA increases the ductility of PLA (i.e., reduces brittleness). In addition, it is understood that if the polymer composition comprises a PLA copolymer, then as defined herein, such a PLA copolymer is included in a non-lactide comonomer content within a very specific range. Preferably, the amount of the non-lactide comonomer in the PLA copolymer used in the present invention is at most 30 weight %, based on the gross weight of the PLA copolymer, and preferably includes between 1 and 20 weight %, or between 1 and 10 weight %, or between 2 and 7 weight %, or between 2 and 5 weight %, based on the gross weight of the PLA copolymer. PLA copolymers as used herein are understood to mean any type of copolymer, including but not limited to random copolymers, block copolymers, gradient copolymers, and statistical copolymers.

[0145] In some preferred embodiments, 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.

[0146] It should be noted that the optimal temperature varies from one type of polymer to another, and for a given type of polymer, from one grade to another. The ranges provided here generally correspond to the target foaming capacity of the polymer melt. The polymer temperature can be measured at the inlet (i.e., the inlet portion) of the first preheater, the first devolatilization unit, the second preheater, or the second devolatilization unit using a thermowell temperature probe. For example, a thermowell-type sensor from WIKA model TW10 can be used to measure the temperature.

[0147] 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 optimal conditions for foaming of the polymer melt feed and, therefore, for devolatilization of most polymers, in particular polymers including PLA polymers.

[0148] While one might think that higher temperatures inherently lead to better devolatilization efficiency, this also implies a higher risk of thermal degradation. Furthermore, higher temperatures typically result in lower viscosity, lower pressure drop across the first preheater and first devolatilization unit, and the risk of less efficient devolatilization. Lower temperatures imply lower devolatilization efficiency and, due to the higher viscosity, higher capes and opex.

[0149] Too high a temperature leads to changes in the properties of the polymer, which is undesirable. The temperature is preferably adjusted according to the stability of the polymer, its viscosity and the nature of the volatiles to be removed.

[0150] In some embodiments, the polymer temperature during the process according to the invention or in the devolatilizer 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.

[0151] In some embodiments, 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.

[0152] In some embodiments, 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.

[0153] In some embodiments, 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.

[0154] In some embodiments, 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.

[0155] As taught herein, both preheating and devolatilization in the first and optional second sections of the system are preferably performed under vacuum to allow for optimized foaming of the polymer melt feed.

[0156] In some embodiments, the polymer melt feed is heated in a first preheater under vacuum. In some embodiments, the polymer melt feed and the resulting foam are heated in the first devolatilization unit under vacuum.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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, while 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, ie 33% of the pressure in the first devolatilization unit or less than 2.0 mbar abs.

[0161] The pressure difference between the first and second devolatilization units results in an even more efficient devolatilization. After all, the residual concentration of the polymer melt in the second devolatilization unit is already lower than the residual concentration of the polymer melt in the first devolatilization unit; and therefore an even lower pressure is required to obtain efficient devolatilization.

[0162] In some embodiments, there is a pressure drop across the first preheater to provide optimal conditions for foaming and devolatilization of the polymer. The pressure drop can be defined as the difference between the inlet pressure and the outlet pressure. The pressure at the outlet of the preheater is the pressure of the devolatilization unit, which is typically a vacuum.

[0163] In some preferred embodiments, the 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.

[0164] As taught herein, the inventors have discovered that, using the process and apparatus according to the present invention, the residence time of the polymer melt feed in the first preheater can be significantly reduced compared to processes and apparatus 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; and more preferably between 1.0 and 10.0 minutes.

[0165] 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 a 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.

[0166] The present invention also relates to a process for reducing volatiles in a polymer melt feed comprising PLA polymer using a devolatilizer as described herein and (preferred) embodiments thereof.

[0167] The present invention also relates to the use of a devolatilizer as described herein and (preferred) embodiments thereof for reducing volatiles in a polymer melt feed comprising PLA polymer.

[0168] More specifically, the present invention provides a devolatilizer for removing volatiles from a polymer melt feed, wherein the polymer melt feed comprises polylactic acid (PLA) polymer, the apparatus comprising:

[0169] - a first preheater comprising an inlet section, a polymer heating section, and an outlet section; and,

[0170] - A first devolatilization unit comprising an inlet section, a devolatilization vessel, a gas outlet and a polymer outlet section.

[0171] Preferably, the apparatus is characterized in that the first preheater and the first devolatilization unit are configured to withstand vacuum pressure. Preferably, the apparatus is further characterized in that the first preheater is configured to at least partially foam a polymer melt feed comprising polylactic acid (PLA) polymer. Preferably, the apparatus is further characterized in that the first devolatilization unit is directly connected to the first preheater.

[0172] In some preferred embodiments, the outlet of the first preheater is in direct contact with or connected to the inlet of the first devolatilization unit. Preferably, the outlet of the first preheater is the inlet of the first devolatilization unit, or the outlet of the first preheater is located inside the first devolatilization unit; or the heating section is at least partially located in the first devolatilization unit, and the outlet of the first preheater is located inside the first devolatilization unit.

[0173] A typical feature of the process of the present invention is that foaming of the polymer melt feed begins during the first preheating stage in the first preheater. In the first preheater, the polymer melt feed is heated to a temperature T1 under vacuum, causing it to at least partially foam, thereby generating foam in the first preheater to facilitate the removal of volatiles. Because foaming of the polymer melt has already occurred in the first preheater, the foam has a low density, thereby reducing the residence time of the polymer melt feed in the first preheater.

[0174] In some preferred embodiments, the first preheater comprises an inlet portion, a polymer heating portion, and an outlet portion. The outlet portion is preferably in direct contact with the first devolatilization unit. In some preferred embodiments, the outlet portion of the first preheater is the inlet portion of the first devolatilization unit. In some preferred embodiments, the outlet portion of the first preheater is located inside the first devolatilization unit. In some preferred embodiments, the heating portion and the outlet portion of the first preheater are at least partially located inside the first devolatilization unit. In some preferred embodiments, the heating portion of the first preheater is at least partially located inside the first devolatilization unit, and the outlet portion of the first preheater is located inside the first devolatilization unit.

[0175] As used herein, "direct contact" is understood to be a configuration (configuration) in which the outlet portion of the first preheater is directly connected to the first devolatilization unit. In other words, the polymer melt feed and foam are directly conveyed from the outlet portion of the first preheater to the first devolatilization unit.

[0176] In some embodiments, the outlet portion of the first preheater (1) is the inlet portion of the first devolatilization unit (2), for example Figure 1 More specifically, the outlet portion of the first preheater and the inlet portion of the first devolatilization unit are the same, so that the first preheater and the first devolatilization unit are directly connected to each other.

[0177] In some embodiments, the outlet portion of the first preheater (1) is located in the first devolatilization unit (2). In some other embodiments, the heating portion and the outlet portion of the first preheater are at least partially located in the first devolatilization unit, for example Figure 2 As shown in .

[0178] The present inventors have discovered that a specific set of geometric parameters can provide optimal conditions for polymer devolatilization. Preferably, the process is performed using an apparatus within these values. For example, the dimensions of the preheater, such as the diameter and length of the tubes, are typically optimized to achieve an optimal pressure drop and residence time in the system.

[0179] 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.

[0180] In some further embodiments, the shell and tube preheater has a length to diameter ratio (L / D) of at least 0.3 and at most 6.0; preferably at least 0.5 and at most 3.0.

[0181] In some embodiments, the inner diameter of the first preheater, eg, 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.

[0182] In some embodiments, there is a pressure drop 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.

[0183] 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.

[0184] In some embodiments, the at least partially devolatilized heated polymer melt from the first devolatilization unit is passed through a second preheater and a second devolatilization unit.The configuration of the second preheater and the second devolatilization unit can be any configuration known to the skilled person.

[0185] In some preferred embodiments, the devolatilizer further comprises

[0186] - optionally, a second preheater comprising an inlet section, a polymer heating section and an outlet section;

[0187] - a second devolatilization unit comprising an inlet section in the form of a polymer distributor, a devolatilization vessel, a gas outlet and a polymer outlet section; and,

[0188] - a collector configured to collect polymer from the second devolatilization unit.

[0189] Preferably, the apparatus is characterized in that the second devolatilization unit and optionally the second preheater are configured to withstand vacuum pressure.

[0190] In some embodiments, the second devolatilization unit comprises an inlet portion in the form of a polymer distributor, a polymer distribution portion, and an outlet portion. In some specific embodiments, the polymer distributor in the inlet portion is a devolatilization nozzle comprising an inlet portion, a polymer distribution portion comprising a manifold, and an outlet portion comprising a plurality of holes.

[0191] In some embodiments, the inlet portion of the second devolatilization unit (5) thus comprises a polymer distributor (6) as a devolatilization nozzle, comprising an inlet portion, a polymer distribution portion comprising a manifold, and an outlet portion comprising a plurality of holes, which are configured to form polymer strands in the devolatilization unit, e.g. Figure 3 As shown in .

[0192] In some embodiments, the holes in the devolatilization nozzle have an average hole diameter of 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.

[0193] The inventors have found that this diameter provides the best conditions for devolatilization of the polymer in the second depolymerization unit, particularly when capital and operating expenses are also taken into account. Larger diameters lead to lower pressure drops and lower devolatilization efficiency (higher amounts of residual volatiles). Smaller diameters may result in higher pressure drops or even the risk of blocking the orifice. Thus, the increased pressure drop can reach the maximum mechanical resistance in the nozzle. At very low orifice diameters, drag forces lead to excessive pressure drops and, as a result, excessive energy consumption.

[0194] In some embodiments, the at least partially devolatilized heated polymer melt in the second devolatilization unit is provided to a devolatilization nozzle and passes through the orifice of the nozzle, thereby forming polymer strands in the second devolatilization unit. In some embodiments, the polymer strands are collected in a collector by allowing the polymer strands to fall into the collector at a strand drop height, thereby obtaining devolatilized polymer in the collector.

[0195] As the strands fall into the collector, they may sway. The swaying comes from the airflow made up of volatiles leaving the strands. Larger strands sway less easily, and when the free strand surface is low, less airflow disturbance occurs.

[0196] In some additional embodiments, the at least partially devolatilized heated polymer melt in the second devolatilization unit is provided to a devolatilization nozzle and passes through the orifices of the nozzle to form polymer strands in the second devolatilization unit.

[0197] In some further embodiments, the polymer strands are collected in a collector by allowing the polymer strands to fall into the collector at a strand drop height, thereby obtaining devolatilized polymer in the collector.

[0198] As taught herein, the first and second devolatilization units preferably include gas outlets (3, 7) to remove and / or recover volatiles, including monomers, from the polymer melt in the first and second devolatilization units, respectively. The gas outlets in the first and second devolatilization units can be connected at or near the top of the devolatilization units and used to remove volatiles from the polymer within the vessel. The gas outlets can include one or more pipes, connectors, or both to balance the steam flow.

[0199] The components of the device are preferably constructed of materials capable of withstanding pressure differentials and vacuum as well as elevated operating temperatures. Without limiting indentation, an example of a suitable material is steel. Where polymeric materials, such as those containing PLA, may cause corrosion, suitable steel alloys, such as 316L or duplex steel grades, may be used. The components of the device may optionally include additional elements, such as insulation or reinforcement coatings.

[0200] The inventors have found that using the process and apparatus according to the invention the concentration of residues in the polymer after polymerisation is strongly reduced compared to processes or apparatus known in the art.

[0201] In a third aspect, the present invention provides an at least partially devolatilized polymer, or a devolatilized polymer, obtained by a process according to the first aspect and its (preferred) embodiments, or using an apparatus according to the second aspect and its (preferred) embodiments. (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 has a volatile residue concentration of at most 15,000 ppm.

[0202] The devolatilized PLA polymer preferably comprises a volatile residue concentration of at most 3 000 ppm at the collector of the second devolatilization unit.

[0203] As used herein, the term "residual concentration" refers to the total concentration of remaining monomer, comonomer, and / or solvent remaining in the polymer after devolatilization. As used herein, the term "monomer concentration" refers to the concentration of remaining monomer remaining in the polymer.

[0204] For example, for polylactic acid (PLA), the term "residual concentration" may refer to lactide.

[0205] In some embodiments, in particular when the polymer comprises polylactic acid, the polymer melt feed comprises a residue concentration at the inlet of the first preheater of at most 100 000 ppm; preferably at most 50 000 ppm;

[0206] In some preferred embodiments, and particularly when the polymer comprises polylactic acid, the polymer melt feed comprises a monomer concentration at the inlet to the first preheater of at least 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.

[0207] In some preferred embodiments, and in particular when the polymer comprises polylactic acid, the at least partially devolatilized polymer comprises a residue concentration at the outlet of the first devolatilization unit of at most 20 000 ppm; more preferably at most 15 000 ppm.

[0208] In some preferred embodiments, and in particular when the polymer comprises polylactic acid, the partially devolatilized polymer comprises a residue 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 2 000 ppm.

[0209] In some preferred embodiments, the residual concentration of volatiles at the outlet of the first devolatilization unit is at most 40% of the residual 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%.

[0210] In some preferred embodiments, the residual concentration of volatiles at the outlet of the second devolatilization unit is at most 75% of the residual 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 can reduce the residual concentration of volatiles from 5% to 0.6% (the outlet is 12% of the feed at the inlet), and the second devolatilization unit can further reduce the residual concentration of volatiles from 0.6% to 0.3% (the outlet is 50% of the feed at the inlet).

[0211] In some embodiments, the polymer is passed through a devolatilizer. In some embodiments, the polymer is passed through a devolatilizer multiple times. This allows for further reduction of the residue content in the final polymer.

[0212] Example

[0213] Starting from lactide and in the presence of a polymerization catalyst and initiator, different PLA polymer melts were prepared (Table 1). After devolatilization, the quality of the recovered and devolatilized polymer was determined based on the following parameters: presence of residual monomers, yellowness index (based on ASTM D1925-70), presence of black specks >0.5 mm, and presence of black specks with a size between 0.1 and 0.5 mm.

[0214] Two different setups for the devolatilization process were tested (Table 1):

[0215] In the "upflow DV1 PH" setup, the PLA polymer melt feed was fed into the first preheater (DV1 preheater), where 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 to a spool piece via an outlet chamber. The spool piece was then connected to the side nozzle of the first devolatilization unit (DV1).

[0216] In a "downflow DV1 PH" setup, the PLA polymer melt feed is also fed into a first preheater (DV1 preheater), where the polymer melt feed is heated to a temperature of 220° C. under vacuum (3 mbar abs). In this setup, the first preheater (DV1 preheater) is 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 one embodiment of the present invention.

[0217] In all arrangements, the first and second preheaters are shell and tube heat exchangers (TEMA).

[0218] After passing through the first devolatilization unit, the polymer melt is then fed into a second preheater (DV2 preheater) and subsequently passed through a second devolatilization unit (DV2).

[0219] In both the first and second devolatilization units, the volatiles were taken off and finally the devolatilized polymer was taken off from the second devolatilization unit and analyzed for the following parameters: presence of residual monomers, yellowness index (based on ASTM D1925-70), presence of black specks > 0.5 mm and presence of black specks with a size between 0.1 and 0.5 mm.

[0220] In Table 1, the technical setup of two examples (Examples 1 and 2) is presented using either an upflow DV1 PH setup or a downflow DV1 PH setup.

[0221] Table 1 : Settings applied for two examples during devolatilization of the polymer in an upflow DV1 PH and a downflow DV1 PH setup.

[0222]

[0223] As shown in Table 2, the downflow DV1 PH setting in both Examples 1 and 2 resulted in 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 varying sizes.

[0224] Table 2. Quality of devolatilized polymer obtained after the devolatilization process using an upflow DV1 PH setup or a downflow DV1 PH setup. Two different types of polymer melts were evaluated (Examples 1 and 2).

[0225]

Claims

1. A 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 T1 under vacuum, such that the polymer melt feed is at least partially foamed, thereby generating foam; - passing the heated polymer melt feed and the foam from the first preheater directly to a first devolatilization unit, wherein the heated polymer melt feed and the foam are maintained at a temperature T2 under vacuum, wherein the first devolatilization unit is directly connected to the first preheater; and, - withdrawing volatiles from the foam in the first devolatilization unit through a gas outlet in the first devolatilization unit, thereby producing an at least partially devolatilized heated polymer melt.

2. The process according to claim 1, further comprising: - optionally, sending 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, - conveying 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 on top of the second devolatilization unit, the polymer being maintained 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 maintained at a temperature T4 under vacuum; - withdrawing 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 producing 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 of 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 section, a polymer heating section and an outlet section; wherein the outlet section is directly connected to the first devolatilization unit.

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

7. The process of claim 6, wherein the heating portion of the first preheater is at least partially located inside the first devolatilization unit, and the outlet portion 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 the second devolatilization unit is 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 devolatilizer for removing volatiles from a polymer melt feed, wherein the polymer melt feed comprises polylactic acid (PLA) polymer, wherein the apparatus is configured to carry out the process according to any one of claims 1 to 10.

12. A devolatilizer for removing volatiles from a polymer melt feed, preferably a devolatilizer according to claim 11, comprising at least: - a first preheater comprising an inlet section, a polymer heating section and an outlet section; as well as, - a first devolatilization unit comprising an inlet section, a devolatilization vessel, a gas outlet and a polymer outlet section; Its characteristics are: - 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 polylactic acid (PLA); and - The first devolatilization unit is directly connected to the first preheater.

13. The devolatilizer of claim 12, further comprising: - Optionally, a second preheater; - a second devolatilization unit comprising an inlet section in the form of a polymer distributor, a devolatilization vessel, a gas outlet and a polymer outlet section; and, - a collector configured to collect 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 devolatilizer according to any one of claims 11 to 13, wherein the outlet portion of the first preheater is directly connected to the inlet portion of the first devolatilization unit; preferably, wherein the outlet portion of the first preheater is the inlet portion of the first devolatilization unit.

15. The process according to any one of claims 1 to 10, which is carried out using a devolatilizer according to any one of claims 11 to 14.

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