Process for recycling pla

Abstract

The invention relates to a process for recycling polylactic acid (PLA) into lactic acid, comprising the steps of: a) hydrolysing a PLA waste thereby obtaining a crude lactic acid composition; b) diluting the crude lactic acid composition in water, thereby producing a diluted crude lactic acid composition; c) equilibrating the diluted crude lactic acid composition for a equilibration period te at a equilibration temperature of at least Te, thereby producing an equilibrated crude lactic acid composition; d) concentrating the equilibrated crude lactic acid composition, thereby producing a concentrated crude lactic acid composition; e) optionally, distilling the concentrated crude lactic acid composition thereby producing a distilled lactic acid composition; and f) crystallizing the concentrated crude lactic acid composition obtained in step d), or the distilled lactic acid composition obtained in step e), thereby recovering lactic acid. The invention also relates to lactic acid obtained when carrying out the process of the invention and their use in the preparation of lactide and / or polylactide.

Description

[0001] PROCESS FOR RECYCLING PLA

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the technical field of PLA recycling, and more particularly to a process for recycling PLA waste. The present invention provides a process for recycling PLA waste, e.g. post-industrial and post-consumer PLA, into lactic acid, particularly into lactic acid crystals. The present invention also related to the use of the lactic acid obtained from recycled PLA waste, for the preparation of lactide and / or PLA.

[0004] BACKGROUND OF THE INVENTION

[0005] Polylactic acid (PLA) is a linear, aliphatic thermoplastic 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. PLA can be produced by direct polycondensation of lactic acid, i.e. lactate monomers. More frequently, PLA is prepared by ringopening 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 depolymerization 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 by means of a ring-opening polymerization reaction (ROP) in the presence of a polymerization catalyst and initiator. Besides the fact that it can be obtained from renewable resources, PLA also has the advantage that it can be biodegraded, thus allowing it to be more readily disposed of after use. These two advantageous properties have led to a significant increase in the use of PLA for various applications, ranging from food packaging to biomedical products, textiles, cards, electronic appliances and others.

[0006] In order to make PLA suitable for various different applications, usually different types of additives are added to improve the properties of PLA. This can be achieved by blending PLA with additives, such as for example mineral charges, impact modifiers, plasticizers, colouring agents, and / or other polymers. However, such additives may negatively affect the biodegradability properties of PLA.

[0007] From an economic and ecological viewpoint, there is a demand for PLA waste to be degraded, after use, into a product that still has some use, instead of PLA being degraded on a landfill whereby most material properties of PLA are lost. Especially in certain applications, where collection, washing and sorting after use is feasible, it may be interesting to recycle PLA waste. This can, for example, be achieved by depolymerizing the used polylactic acid product back into its essential building blocks, i.e. lactic acid or lactide, said building blocks can then be reused to, for example, produce new PLA (recycled PLA, r-PLA) or can be reused for other purposes. For instance, it may be possible to recover lactic acid that may be used as monomer in the polylactic acid polymerisation process. It has been shown that in doing so, the total carbon emissions of the obtained lactic acid may be significantly less than for virgin lactic acid which typically is produced via fermentation.

[0008] However, to enable the production of recycled PLA (r-PLA), starting from such recovered lactic acid, there is a demand for a high purity of the recovered lactic acid. Some additives, dyes or comonomers commonly used in the formation of PLA articles, are notoriously difficult to remove in a recycling process, and are moreover reason for lack of food contact approvals for mechanical recycling. Impurities remaining in recovered lactic acid can cause detrimental effects during lactide production, cause a decrease in yield, and decrease purity of the final recycled PLA.

[0009] It is also known to those skilled in the art that industrial scale, high molecular weight PLA production proceeds via the preparation of lactide intermediates, which in turn need to be prepared starting from high purity lactic acid. Color formation and racemization are prominent causes for yield loss in the overall lactic acid-to-PLA process and as such need to be minimized.

[0010] In view of the above, there remains a need in the art for an improved process for recycling polylactic acid containing waste streams.

[0011] It is therefore an object of the present invention to provide an improved and broadly applicable process for recovering lactic acid with high purity from polylactic acid-based waste streams which are obtained from various resources and which may contain various amounts and types of impurities.

[0012] It is also an object of the present invention to recover lactic acid, having a high starting stereochemical purity, from PLA waste, as this allows it to be used for preparing polylactic acid with tuneable thermal properties, and for preparing tailored PLA grades suitable for a plethora of applications.

[0013] SUMMARY OF THE INVENTION

[0014] It has now surprisingly been found that some or all of the above needs and objectives can be attained either individually or in any combination by the process for recycling PLA into lactic acid according to the present invention. The present invention thereto provides a process to recover lactic acid from polylactic acid present in waste containing polylactic acid, by recycling such PLA waste into lactic acid via a specific sequence of process steps. The process according the present invention allows to recover lactic acid in high purity and with a desired stereochemistry from polylactic acid present in polylactic acid based waste stream (PLA waste), which may comprise a wide variety of impurities in various amounts.

[0015] In particular, in a first aspect, the present invention relates to a process for recycling polylactic acid (PLA), comprising the steps of: a) hydrolysing a PLA waste thereby obtaining a crude lactic acid composition; b) diluting the crude lactic acid composition in water, thereby producing a diluted crude lactic acid composition; c) equilibrating the diluted crude lactic acid composition for a equilibration period teat a equilibration temperature of at least Te, thereby producing an equilibrated crude lactic acid composition; d) concentrating the equilibrated crude lactic acid composition, thereby producing a concentrated crude lactic acid composition; e) optionally, distilling the concentrated crude lactic acid composition thereby producing a distilled lactic acid composition; and f) crystallizing the concentrated crude lactic acid composition obtained in step d), or the distilled lactic acid composition obtained in step e), thereby recovering lactic acid.

[0016] The present invention advantageously provides a process that allows to purify PLA waste, from its additives and (un)intended impurities, via a crystallization step of lactic acid. After hydrolysis of the PLA waste, a contaminated lactic acid stream is obtained, which is diluted, equilibrated and concentrated in accordance with the present process, after which the resulting concentrated lactic acid composition may be crystallized either directly (step f) of the process), or after distillation, preferably flash distillation, of the acid, as provided in step e) of the present process.

[0017] In some preferred embodiments of the process of the invention, the PLA waste comprises polylactic acid containing waste from domestic and / or industrial areas, and for instance, comprises post-consumer PLA and / or post-industrial PLA.

[0018] In some preferred embodiments of the process of the invention the PLA waste has a stereochemical purity of at least 80.0 % L-Lactate, such as at least 85.0 %, at least 90.0 %, at least 92.0 %, at least 95.0 %, at least 96.0 % L-Lactate. In some other preferred embodiments of the process of the invention, the PLA waste has a stereochemical purity of at least 80.0 % D- Lactate, such as at least 85.0 %, at least 90.0 %, at least 92.0 %, at least 95.0 %, at least 96.0 % D- Lactate.

[0019] In accordance with the process of the invention, the dilution step comprises dilution of the crude lactic acid composition in water, preferably in deionised water or reverse osmosis water. In some preferred embodiments, the diluted crude lactic acid composition has a total acid concentration of between 50.0 and 80.0 wt%, wherein the wt% is expressed compared to the total weight of the diluted crude lactic acid composition.

[0020] In some preferred embodiments of the process of the invention, the equilibrating step is continued until the ratio of the weight percentage of free acid in the equilibrated crude lactic acid composition, over the weight percentage of the total acid in the equilibrated crude lactic acid composition is at least 0.70, preferably at least 0.75, preferably at least 0.80, preferably at least 0.85, preferably at least 0.90.

[0021] In some embodiments of the present process, it is preferred that the time between the end of the equilibrating step and the beginning of the concentrating step is at most 36.0 hours, preferably at most 30.0 hours, preferably at most 24.0 hours, preferably at most 18.0 hours, preferably at most 12.0 hours, preferably at most 6.0 hours, preferably at most 3.0 hour, preferably at most 2.0 hour, preferably at most 1.0 hour.

[0022] In some preferred embodiments of the process of the invention, concentrating is done by evaporating water from the equilibrated crude lactic acid composition. In some preferred embodiments, the concentrated crude lactic acid composition has a total acid concentration of at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, preferably at least 95.0 wt%, wherein the wt% is expressed compared to the total weight of the concentrated crude lactic acid composition.

[0023] In some preferred embodiments, crystallization is solvent crystallization or melt crystallization, wherein said either solvent or melt crystallization is performed as a suspension crystallization or layer crystallization. In some preferred embodiments the crystallisation step f) comprises seeding the concentrated crude lactic acid composition obtained in step d) or the distilled lactic acid composition obtained in step e) with lactic acid crystals, preferably with lactic acid crystals of a suitable and desired isomeric purity. In some preferred embodiments, the crystallisation temperature Tcin step f) is at most 50°C, preferably at most 47°C, preferably at most 46°C, preferably at most 45°C.

[0024] In some preferred embodiments, the crystallisation step f) comprises lowering the temperature of the concentrated crude lactic acid composition obtained in step d), or of the distilled lactic acid composition obtained in step e), below crystallisation temperature Tc, preferably at least 1.0°C below Tc, preferably at least 2.0°C below Tc, preferably at least 3.0°C below Tc.

[0025] In some preferred embodiments, the crystallisation step f) comprises lowering the temperature of the concentrated crude lactic acid composition obtained in step d), or of the distilled lactic acid composition obtained in step e) at a rate of at most 10.0°C / min, preferably at most 7.5°C / min, preferably at most 5.0°C / min, preferably at most 3.0°C / min, preferably at most 2.0°C / min, preferably at most 1 .0°C / min.

[0026] In some preferred embodiments, the lactic acid, obtained in step f) has a stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % L-Lactate. In some other preferred embodiments, the lactic acid obtained in step f) have a stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % D-Lactate.

[0027] In some preferred embodiments, the process of the invention further comprising the step of processing the lactic acid, obtained in step f), optionally in combination with virgin lactic acid, into lactide, optionally followed by polymerising said lactide into polylactic acid.

[0028] In a second aspect, the present invention relates to lactic acid obtainable or obtained by carrying out a process according the invention. Lactic acid, obtainable or obtained by carrying out a process according the invention, may in certain embodiments have high stereochemical purity, such as at least 85.0 %, such as at least 90.0 %, at least 95.0 %, at least 99.0 % L-Lactate, or at least 85.0 %, such as at least 90.0 %, at least 95.0 %, at least 99.0 % D-Lactate.

[0029] In a third aspect, the present invention relates to the use of lactic acid, obtainable or obtained by carrying out a process according to the present invention, optionally in combination with virgin lactic acid, as a starting material for preparing lactide.

[0030] The present invention also relates to the use of lactic acid, obtainable or obtained by carrying out a process according to the present invention, optionally in combination with virgin lactic acid, as a starting material in a process for preparing polylactide acid, for instance, via the preparation of lactide intermediates, which are subsequently processed into polylactic acid. The independent and dependent claims set out particular and preferred features of the invention. Features from the dependent claims may be combined with features of the independent or other dependent claims as appropriate.

[0031] The present invention will now be further described. 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 or statement indicated as being preferred or advantageous may be combined with any other features or statements indicated as being preferred or advantageous.

[0032] DETAILED DESCRIPTION OF THE FIGURE

[0033] Figure 1 shows a block diagram of a process for recovering lactic acid from polylactic acid waste according to an embodiment of the present invention. Some steps in the process (dashed lines) are optional.

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] When describing the invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0036] 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.

[0037] 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.

[0038] 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. For example, in the following claims and statements, any one of the embodiments can be used in any combination.

[0039] 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.

[0040] As used in the specification and the appended claims, the singular forms "a", "an," and "the" include plural referents unless the context clearly dictates otherwise. By way of example, "a step" means one step or more than one step.

[0041] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art.

[0042] 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 endpoints 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.

[0043] 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.

[0044] 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, that includes the component.

[0045] When describing the present invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise. The terms “isomeric purity” and “stereochemical purity” are used herein interchangeably, and are expressed as wt%, and refer to the amount of a stated stereoisomer expressed as percentage of the total amount of stereoisomers having a given chiral center.

[0046] Preferred statements (features) and embodiments 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 statements and embodiments, with any other aspect and / or embodiment.

[0047] 1 . A process for recycling polylactic acid (PLA), comprising the steps of: a) hydrolysing a PLA waste thereby obtaining a crude lactic acid composition; b) diluting the crude lactic acid composition in water, thereby producing a diluted crude lactic acid composition; c) equilibrating the diluted crude lactic acid composition for a equilibration period teat a equilibration temperature of at least Te, thereby producing an equilibrated crude lactic acid composition; d) concentrating the equilibrated crude lactic acid composition, thereby producing a concentrated crude lactic acid composition; e) optionally, distilling the concentrated crude lactic acid composition thereby producing a distilled lactic acid composition; and f) crystallizing the concentrated crude lactic acid composition obtained in step d), or the distilled lactic acid composition obtained in step e), thereby recovering lactic acid.

[0048] 2. The process according to statement 1 , wherein the lactic acid obtained in step f) is in the form of lactic acid crystals.

[0049] 3. The process according to any one of the previous statements, wherein the PLA waste comprises polylactic acid containing waste from domestic and / or industrial areas, and for instance, comprises post-consumer PLA and / or post-industrial PLA.

[0050] 4. The process according to any one of the previous statements, wherein the PLA waste is melted, filtered, and re-solidified before the hydrolysis step a). The process according to any one of the previous statements, wherein hydrolysis of said PLA waste is catalysed via enzymatic, microbial, alkaline, or acidic species, or any combination thereof. The process according to any one of the previous statements, wherein the PLA waste has a stereochemical purity of at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 96.0 % L-Lactate. The process according to any one of the previous statements, wherein the PLA waste has a stereochemical purity of at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 96.0 % D-Lactate. The process according to any one of the previous statements, wherein the crude lactic acid composition is diluted in deionised water or reverse osmosis water. The process according to any one of the previous statements, wherein the diluted crude lactic acid composition has a total acid (TA) concentration of between 50.0 and 80.0 wt%, preferably of between 55.0 and 77.0 wt%, preferably of between 60.0 wt% and 75.0 wt%, wherein the wt% is expressed compared to the total weight of the diluted crude lactic acid composition. The process according to any one of the previous statements, wherein the equilibrating step is continued until the ratio of the weight percentage of free acid in the equilibrated crude lactic acid composition, over the weight percentage of the total acid in the equilibrated crude lactic acid composition is at least 0.70, preferably at least 0.75, preferably at least 0.80, preferably at least 0.85, preferably at least 0.90. The process according to any one of the previous statements, wherein the equilibration period feis at least 0.25 hour, preferably at least 0.5 hour, preferably at least 0.75 hour, preferably at least 1.0 hour, preferably at least 2.0 hours, preferably at least 4.0 hours, preferably at least 6.0 hours, preferably at least 8.0 hours, preferably at least 10.0 hours, preferably at least 12.0 hours, preferably at least 14.0 hours, preferably at least 16.0 hours preferably at least 18.0 hours, preferably at least 20.0 hours, preferably at least 21 .0 hours. The process according to any one of the previous statements, wherein the equilibration temperature Teis at least 20.0°C, preferably at least 35.0°C, preferably at least 40.0°C, preferably at least 50.0°C, preferably at least 55.0°C, preferably at least 60.0°C, preferably at least 65.0°C, preferably at least 70.0°C. 13. The process according to any one of the previous statements, wherein the equilibration temperature Teis at most 150.0°C, preferably at most 125.0°C, preferably at most 110.0°C, preferably at most 105.0°C, preferably at most 100.0°C, preferably at most 90.0°C, preferably at most 80.0°C.

[0051] 14. The process according to any one of the previous statements, wherein the equilibration temperature Teis at least 20.0°C to at most 150.0°C, preferably at least 35.0°C to at most 125.0°C, preferably at least 40.0°C to at most 110.0°C, preferably at least 50.0°C to at most 105.0°C, preferably at least 55.0°C to at most 100.0°C, preferably at least 60.0°C to at most 90.0°C, preferably at least 75.0°C to at most 85.0°C.

[0052] 15. The process according to any one of the previous statements, wherein concentrating is done by evaporating water from the equilibrated crude lactic acid composition.

[0053] 16. The process according to any one of the previous statements, concentrating is done by evaporating at a temperature of at least 50.0°C, preferably at least 75.0°C, preferably at least 90.0°C, preferably at least 100°C, preferably at least 110.0°C.

[0054] 17. The process according to any one of the previous statements, wherein concentrating is done by evaporating at a temperature at most 200.0°C, preferably at most 175.0°C, preferably at most 150.0°C, preferably at most 130.0°C, preferably at most 120.0°C.

[0055] 18. The process according to any one of the previous statements, wherein concentrating is done by evaporating at a temperature of at least 50.0°C to at most 200.0°C, preferably at least 75.0°C to at most 175.0°C, preferably at least 90.0°C to at most 150.0°C, preferably at least 100°C to at most 130.0°C, preferably at least 110.0°C to at most 120.0°C.

[0056] 19. The process according to any one of the previous statements, wherein concentrating is done by evaporating at a pressure of at most 1000 mbar, preferably at most 750 mbar, preferably at most 500 mbar, preferably at most 400 mbar, preferably at most 300 mbar, preferably at most 250 mbar, preferably at most 100 mbar, preferably at most 75 mbar, preferably at most 50 mbar, preferably at most 25 mbar, preferably at most 20 mbar, preferably at most 15 mbar, preferably at most 10 mbar, preferably at most 5 mbar.

[0057] 20. The process according to any one of the previous statements, wherein the concentrated crude lactic acid composition has a total acid concentration of at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, preferably at least 95.0 wt%, wherein the wt% is expressed compared to the total weight of the concentrated crude lactic acid composition. 21 . The process according to any one of the previous statements, wherein the concentrated crude lactic acid composition has a free acid concentration of at least 70.0 wt%, preferably at least 75.0 wt%, preferably at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, wherein the wt% is expressed compared to the total weight of the concentrated crude lactic acid composition.

[0058] 22. The process according to any one of the previous statements, wherein the ratio of the weight percentage of free acid in the concentrated crude lactic acid composition, over the weight percentage of total acid in the concentrated crude lactic acid composition is at least 0.70, preferably at least 0.75, preferably at least 0.80, preferably at least 0.85, preferably at least 0.90, preferably at least 0.95.

[0059] 23. The process according to any one of the previous statements, comprising the step of distilling the concentrated crude lactic acid composition prior to crystallisation by means of a flash distillation, a short path distillation, or a wiped film distillation, thereby producing a distilled lactic acid composition.

[0060] 24. The process according to any one of the previous statements, wherein the distilled lactic acid composition has a total acid concentration of at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, preferably at least 95.0 wt%, wherein the wt% is expressed compared to the total weight of the distilled lactic acid composition.

[0061] 25. The process according to any one of the previous statements, wherein the distilled lactic acid composition has a free acid concentration of at least 70.0 wt%, preferably at least 75.0 wt%, preferably at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, wherein the wt% is expressed compared to the total weight of the distilled lactic acid composition.

[0062] 26. The process according to any one of the previous statements, wherein distillation is carried out at a temperature of at least 50.0°C, preferably at least 75.0°C, preferably at least 90.0°C, preferably at least 100°C, preferably at least 110.0°C, preferably at least 120.0°C.

[0063] 27. The process according to any one of the previous statements, wherein the distillation is carried out at a temperature of at most 200.0°C, preferably at most 175.0°C, preferably at most 150.0°C, preferably at most 140.0°C, preferably at most 130.0°C.

[0064] 28. The process according to any one of the previous statements, wherein distillation is carried out at a temperature of at least 50.0°C to at most 200.0°C, preferably at least 75.0°C to at most 175.0°C, preferably at least 90.0°C to at most 150.0°C, preferably at least 100°C to at most 140.0°C, preferably at least 110.0°C to at most 130.0°C.

[0065] 29. The process according to any one of the previous statements, wherein distillation is carried out at a pressure of at most 100 mbar, preferably at most 75 mbar, preferably at most 50 mbar, preferably at most 25 mbar, preferably at most 20 mbar, preferably at most 15 mbar, preferably at most 10 mbar, preferably at most 5 mbar.

[0066] 30. The process according to any one of the previous statements, wherein crystallization is solvent crystallization or melt crystallization, wherein said either solvent or melt crystallization is performed as a suspension crystallization or layer crystallization.

[0067] 31 . The process according to any one of the preceding statements, wherein crystallization is melt crystallization.

[0068] 32. The process according to any one of the previous statements, wherein crystallisation step f) comprises seeding the concentrated crude lactic acid composition obtained in step d) or the distilled lactic acid composition obtained in step e) with lactic acid crystals.

[0069] 33. The process according to any one of the previous statements 1 to 6 and 8 to 32, wherein crystallisation step f) comprises seeding the concentrated crude lactic acid composition obtained in step d) or the distilled lactic acid composition obtained in step e) with L-lactic acid crystals.

[0070] 34. The process according to any one of the previous statements 1 to 5 and 7 to 32, wherein crystallisation step f) comprises seeding the concentrated crude lactic acid composition obtained in step d) or the distilled lactic acid composition obtained in step e) with D-lactic acid crystals.

[0071] 35. The process according to any one of the previous statements, wherein the crystallisation temperature Tcin step f) is at most 50°C, preferably at most 47°C, preferably at most 46°C, preferably at most 45°C.

[0072] 36. The process according to any one of the previous statements, wherein crystallisation step f) comprises lowering the temperature of the concentrated crude lactic acid composition obtained in step d), or of the distilled lactic acid composition obtained in step e) below crystallisation temperature Tc, preferably at least 1.0°C below Tc, preferably at least 2.0°C below Tc, preferably at least 3.0°C below Tc, 37. The process according to any one of the previous statements, wherein crystallisation step f) comprises lowering the temperature at a rate of at most 10.0°C / min, preferably at most 7.5°C / min, preferably at most 5.0°C / min, preferably at most 3.0°C / min, preferably at most 2.0°C / min, preferably at most 1.0°C / min.

[0073] 38. The process according to any one of the previous statements, further comprising the step of washing the lactic acid obtained in step f).

[0074] 39. The process according to any one of the previous statements, wherein the time between the end of the equilibrating step and the beginning of the concentrating step is at most 36.0 hours, preferably at most 30.0 hours, preferably at most 24.0 hours, preferably at most 18.0 hours, preferably at most 12.0 hours, preferably at most 6.0 hours, preferably at most 3.0 hour, preferably at most 2.0 hour, preferably at most 1 .0 hour.

[0075] 40. The process according to any one of the previous statements, wherein the time between the end of the equilibrating step and the beginning of the crystallizing step is at most 36.0 hours, preferably at most 30.0 hours, preferably at most 24.0 hours, preferably at most 18.0 hours, preferably at most 12.0 hours, preferably at most 6.0 hours, preferably at most 3.0 hour, preferably at most 2.0 hour, preferably at most 1 .0 hour.

[0076] 41. The process according to any one of the previous statements, wherein the process further comprises a purification step, such as filtration, adsorption, passing over a carbon or ion exchange column.

[0077] 42. The process according to any one of the previous statements, wherein said purification step may be applied after any one of steps a), b), c), and d).

[0078] 43. The process according to any one of the previous statements 1 to 6, 8 to 33, and 35 to 42, wherein the lactic acid, obtained in step f) have a stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % L-Lactate.

[0079] 44. The process according to any one of the previous statements 1 to 5, 7 to 32, 34 to 42, wherein the lactic acid obtained in step f) have a stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % D-Lactate.

[0080] 45. The process according to any one of the previous statements, wherein the lactic acid, obtained in step f) have a free acid content of at least 95.0 wt%, preferably at least 96.0 wt%, preferably at least 97.0 wt%, wherein the wt% is expressed compared to the total weight of lactic acid crystals.

[0081] 46. The process according to any one of the previous statements, wherein the lactic acid, obtained in step f) have a total acid content of at least at least 95.0 wt%, preferably at least 96.0 wt%, preferably at least 97.0 wt%, preferably at least 98.0 wt%, preferably at least 99.0 wt%, wherein the wt% is expressed compared to the total weight of lactic acid crystals.

[0082] 47. The process according to any one of the previous statements, wherein the lactic acid obtained in step f), has a sodium content of at most 10.0 ppm, preferably at most 7.5 ppm, preferably at most 5.0 ppm, preferably at most 4.0 ppm, wherein the ppm are weight parts expressed compared to the total weight of the lactic acid.

[0083] 48. The process according to any one of the previous statements, further comprising the step of processing the lactic acid obtained in step f), optionally in combination with virgin lactic acid, into lactide, optionally followed by polymerising said lactide into polylactic acid.

[0084] 49. The process according to any one of the previous statements, further comprising feeding the lactic acid obtained in step f); optionally in combination with a virgin lactic acid; as starting material into a lactide preparation process.

[0085] 50. The process according to any one of the previous statements, further comprising the step of feeding the lactic acid obtained in step f); optionally in combination with virgin lactic acid; as starting material into a polylactide preparation process.

[0086] 51. Lactic acid obtainable or obtained by carrying out a process according to any one of statements 1 to 50.

[0087] 52. The lactic acid according to statement 51 , wherein said lactic acid is / are as defined in any one of the previous statements 43 to 47.

[0088] 53. Use of a lactic acid obtainable or obtained by carrying out a process according to any one of statements 1 to 47, or as defined in any one of statements 51-52, optionally in combination with virgin lactic acid; as a starting material for preparing lactide.

[0089] 54. Use of a lactic acid obtainable or obtained by carrying out a process according to any one of statements 1 to 47, or as defined in any one of statements 51-52, optionally in combination with virgin lactic acid; as a starting material for preparing polylactic acid.

[0090] Lactic acid, sometimes abbreviated as HLA, has the preferred IUPAC name of 2- hydroxypropanoic acid, and can be represented by the following formula: HO-CH(CH3)-COOH. Lactic acid carries 50-21-5 as CAS number for the racemic mixture, and 79-33-4 for the L- enantiomer, and 10326-41-7 for the D-enantiomer. Lactic acid is a building block in the production of polylactic acid.

[0091] The present invention is directed to a process for recycling PLA. The present invention provides a process for recovering lactic acid from PLA waste.

[0092] With the terms or “PLA waste” or "PLA waste stream" as used herein, the complete flow of polylactic acid containing waste from domestic or industrial areas such as homes, businesses, institutions and manufacturing plants, is meant. This term includes post-consumer polylactic acid based products (post-consumer PLA) such as used packaging materials, fibers, films, cups, cards, bottles, containers, toys, furniture, bags, etc., or any polylactic acid based industrial waste (post-industrial PLA), such as polylactic acid waste generated in a PLA production facility or a PLA processing facility, the latter of which can be, for instance, in the shape of film and textile edge trim, spin ware, and thermoforming skeleton

[0093] PLA waste may contain non-PLA impurities and contaminants, which in certain instances cannot be sorted prior to applying the present process. Such impurities may comprise mineral charges, pigments, plasticizers, impact modifiers, metals, titanium oxide, paper, cellulosic materials, adhesives, polymers, or combinations thereof. The present process allows to purify PLA from such impurities and contaminants by hydrolyzing the PLA waste, and subjecting the resulting contaminated lactic acid stream to a sequence of pre-treatment steps, followed by a crystallization step of lactic acid.

[0094] More particularly, the present invention is directed to a process for recycling PLA comprising the steps of: a) hydrolysing a PLA waste thereby obtaining a crude lactic acid composition; b) diluting the crude lactic acid composition, thereby producing a diluted crude lactic acid composition; c) equilibrating the diluted crude lactic acid composition for a equilibration period teat a equilibration temperature of at least Te, thereby producing an equilibrated crude lactic acid composition; d) concentrating the equilibrated crude lactic acid composition, thereby producing a concentrated crude lactic acid composition; e) optionally, distilling the concentrated crude lactic acid composition thereby producing a distilled lactic acid composition; and f) crystallizing the concentrated crude lactic acid composition obtained in step d), or the distilled lactic acid composition obtained in step e), thereby recovering lactic acid.

[0095] In accordance with the process of the invention, the crude lactic acid composition is diluted in water, by adding water to the crude lactic acid composition of step a).

[0096] The present process may be applied on a lactic acid composition obtained by hydrolysis of PLA waste and advantageously permits to remove impurities present in the PLA waste. The present invention also permits to obtain lactic acid with a high stereochemical purity.

[0097] It was found that by carrying out the process of the present invention, and in particular by applying a diluting step followed by an equilibration step, it is possible to prepare a concentrated lactic acid composition from such equilibrated composition having a high amount of monomeric lactic acid in solution (hence limited oligomer content). The equilibration step as provided in the present process, advantageously improves the formation of lactic acid monomers. It was further shown that such concentrated lactic acid solution turned out to be particularly suitable for being crystallised, yielding lactic acid, for instance in the form of crystals, with a high purity (i.e. with a reduced level to no level of contaminants). An even higher purity level may be obtained when the lactic acid composition is distilled before crystallisation.

[0098] As used herein, the terms “total acid”, “total acid content”, “total acid concentration”, sometimes abbreviated to “TA”, are used interchangeably and refer to the acid content after saponification of intermolecular ester bonds with an excess of base and is determined by back titration with acid. The total acid content is the total amount of all the available carboxylate groups in the composition, i.e., carboxylate groups that are both free in the composition and those that are bound, for example in ester groups. The total acid content of a lactic acid composition as provided herein may be determined by the method as disclosed in the example section.

[0099] As used herein, the terms “free acid”, “free acid content”, “free acid concentration”, sometimes abbreviated to “FA”, are used interchangeably and refer to the concentration of free titratable carboxylic acid groups in a sample. The free acid content is determined by direct titration with base without sample pre-treatment. The free acid content of a lactic acid composition as provided herein may be determined by the method as disclosed in the example section.

[0100] In a first step of the present process, a PLA waste, as defined herein, is hydrolysed. The PLA waste may be provided to step a) of the present process in the form of flakes or pellets. Optionally, the PLA waste may undergo a pre-treatment before being subjected to hydrolysis. Suitable pre-treatment step involve, but are not limited to extrusion, carbon treatment, separation / sorting, grinding, etc. In certain preferred embodiments of the present process, the PLA waste may be melted, filtered, and re-solidified before the hydrolysis step a).

[0101] In a preferred embodiment, the PLA waste is heated to a temperature in the range of 45 to 240°C, such as from about 100 to 180°C in the presence of water and / or light oligomers until the reaction is complete, which can be between 0.5 and 30 hours, such as between 0.5 and 5 hours. Hydrolysis of a PLA waste, as provided in step a) of the present process, can be catalysed via enzymatic, microbial, alkaline, or acidic species, or any combination thereof.

[0102] In certain preferred embodiments of the present process, it is preferred that the PLA waste, preferably the PLA within the waste stream, has a stereochemical purity of at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 96.0 % L-Lactate. In certain other preferred embodiments of the present process, it is preferred that the PLA waste, preferably the PLA within the waste stream, has a stereochemical purity of at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 96.0 % D-Lactate.

[0103] Stereochemical purity of PLA can be assessed using methods known in the art. In an example, the stereochemical purity of a PLA (waste) can be assessed after destructive methylation. To that end 0.1 g of a sample to be analyzed is brought into a crimp cap vial, subsequently 2.0 g of dichloromethane (pure, Acros Organics) and 5.0 g of methanol (J.T. Baker) are added and the sample is allowed to dissolve for 2 hours at 70°C. After cooling down to room temperature, 3.0 g of Amberlyst 15 (ion exchange resin, dry, Acros Organics) is added and the reaction is allowed to proceed for 22 hours at 80°C. After cooling down to room temperature, the sample is subjected to chiral gas chromatography separation on a Thermo Focus GO equipped with a CP-Chirasil- dex CB separation column. This achieves separation of the D- (or R) and L- (orS-)methyl lactates, the ratio of which finally determines the stereochemical purity of the sample.

[0104] The hydrolysis step results in the formation of a crude lactic acid composition, which will be further treated in accordance with the present process. As used herein the term “crude composition” as in “a crude lactic acid composition” refers to a composition that may comprise impurities and / or lactic acid oligomers in concentrations which are undesirable in downstream processes, e.g. for the preparation of lactide or PLA. Step b) of the present process comprises a dilution of the crude lactic acid composition obtained after hydrolysis, such that a diluted crude lactic acid composition is thereby obtained. The crude lactic acid composition is diluted in water.

[0105] In accordance with the process of the invention, the crude lactic acid composition is diluted by adding water to the crude lactic acid composition of step a). It is in particular preferred that the crude lactide composition obtained after hydrolysis is diluted in deionised water or in reverse osmosis water. Diluting in water may push the equilibrium between lactic acid oligomers and free (lactic) acid towards free acid. The use of deionised water or reverse osmosis water reduces or avoids the introduction of impurities (such as sodium species) in the lactic acid composition.

[0106] In accordance with the present process the diluted crude lactic acid composition obtained in step b) has a total acid (TA) concentration of between 50.0 and 80.0 wt%, preferably of between 55.0 and 77.0 wt%, preferably of between 60.0 wt% and 75.0 wt%, wherein the wt% is expressed compared to the total weight of the diluted crude lactic acid composition. Such diluted compositions may result in a high amount of free acid after equilibration.

[0107] In step c) of the present process, the diluted crude lactic acid composition is equilibrated for a equilibration period teat a equilibration temperature of at least Te, thereby producing an equilibrated crude lactic acid composition.

[0108] In some embodiments of the present process, the equilibrating step is continued until the ratio of weight percentage of free acid in the equilibrated crude lactic acid composition, over the weight percentage of total acid in the equilibrated crude lactic acid composition (FA / TA weight % ratio at equilibrium) is at least 0.70, preferably at least 0.75, preferably at least 0.80, preferably at least 0.85, preferably at least 0.90. This ensures a high enough free acid content to be formed, and allows to carry out the subsequent process steps.

[0109] In some embodiments of the present process, the equilibration period teis at least 0.25 hour, preferably at least 0.5 hour, preferably at least 0.75 hour, preferably at least 1.0 hour, preferably at least 2.0 hours, preferably at least 4.0 hours, preferably at least 6.0 hours, preferably at least 8.0 hours, preferably at least 10.0 hours, preferably at least 12.0 hours, preferably at least 14.0 hours, preferably at least 16.0 hours preferably at least 18.0 hours, preferably at least 20.0 hours, preferably at least 21.0 hours. Such equilibration period advantageously allows oligomeric lactic acid species to decompose into free lactic acid, and preferably establish a new equilibrium.

[0110] In some embodiments of the present process, the equilibration temperature Teis at least 20.0°C, preferably at least 35.0°C, preferably at least 40.0°C, preferably at least 50.0°C, preferably at least 55.0°C, preferably at least 60.0°C, preferably at least 65.0°C, preferably at least 70.0°C. Such temperatures favour a high free acid content in the lactic acid composition, and also induce a faster equilibration process.

[0111] In some embodiments of the present process, the equilibration temperature Teis at most 150.0°C, preferably at most 125.0°C, preferably at most 110.0°C, preferably at most 105.0°C, preferably at most 100.0°C, preferably at most 90.0°C, preferably at most 80.0°C. Such temperatures avoid the evaporation of water and / or lactic acid, decreasing the yield or acid content of the composition.

[0112] For instance, in certain embodiments of the present process, the equilibration temperature Teis at least 20.0°C to at most 150.0°C, preferably at least 35.0°C to at most 125.0°C, preferably at least 40.0°C to at most 110.0°C, preferably at least 50.0°C to at most 105.0°C, preferably at least 55.0°C to at most 100.0°C, preferably at least 60.0°C to at most 90.0°C, preferably at least 75.0°C to at most 85.0°C.

[0113] In some embodiments of the present process, it is preferred that the time between the end of the equilibrating step and the beginning of the concentrating step is at most 36.0 hours. Preferably such time is at most 30.0 hours, preferably at most 24.0 hours, preferably at most 18.0 hours, preferably at most 12.0 hours, preferably at most 6.0 hours, preferably at most 3.0 hour, preferably at most 2.0 hour, preferably at most 1 .0 hour.

[0114] In some embodiments of the present process, it is further preferred that, the time between the end of the equilibrating step and the beginning of the crystallizing step is at most 36.0 hours, preferably at most 30.0 hours, preferably at most 24.0 hours, preferably at most 18.0 hours, preferably at most 12.0 hours, preferably at most 6.0 hours, preferably at most 3.0 hour, preferably at most 2.0 hour, preferably at most 1 .0 hour.

[0115] Limiting the time between the end of the equilibrating step and the beginning of the concentrating step and / or between the end of the equilibrating step and the beginning of the crystallizing step within the above ranges permits to reduce the amount of oligomerization of the lactic acid after the equilibrating step.

[0116] In step d) of the present process, the equilibrated crude lactic acid composition is concentrated to obtain a concentrated crude lactic acid composition. The concentration step is preferably done by evaporating water / solvent from the equilibrated crude lactic acid composition.

[0117] In some embodiments, evaporation is performed at a temperature of at least 50.0°C, preferably at least 75.0°C, preferably at least 90.0°C, preferably at least 100°C, preferably at least 110.0°C. In some embodiments, evaporation is performed at a temperature at most 200.0°C, preferably at most 175.0°C, preferably at most 150.0°C, preferably at most 130.0°C, preferably at most 120.0°C.

[0118] For instance, in certain preferred embodiments, evaporation is performed at a temperature of at least 50.0°C to at most 200.0°C, preferably at least 75.0°C to at most 175.0°C, preferably at least 90.0°C to at most 150.0°C, preferably at least 100°C to at most 130.0°C, preferably at least 110.0°C to at most 120.0°C. Such evaporation temperatures advantageously speed up the concentrating step, which in turn may prevent the formation of large amount of oligomeric lactic acid in the composition.

[0119] In certain embodiments of the present invention, it is preferred that evaporation is performed at a pressure of at most 1000 mbar, preferably at most 750 mbar, preferably at most 500 mbar, preferably at most 400 mbar, preferably at most 300 mbar, preferably at most 250 mbar, preferably at most 100 mbar, preferably at most 75 mbar, preferably at most 50 mbar, preferably at most 25 mbar, preferably at most 20 mbar, preferably at most 15 mbar, preferably at most 10 mbar, preferably at most 5 mbar. At the indicated pressures, concentration may be speed up, which advantageously reduces or prevents the formation of large amount of oligomeric lactic acid in the composition.

[0120] The concentration step in the present process yields a concentrated crude lactic acid composition, which preferably has a total acid concentration of at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, preferably at least 95.0 wt%, wherein the wt% is expressed compared to the total weight of the concentrated crude lactic acid composition, and / or a free acid concentration of at least 70.0 wt%, preferably at least 75.0 wt, preferably at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, wherein the wt% is expressed compared to the total weight of the concentrated crude lactic acid composition.

[0121] In certain embodiments of the present invention, it is also preferred that the ratio of the weight percentage of free acid in the concentrated crude lactic acid composition, over the weight percentage of total acid in the concentrated crude lactic acid composition, i.e. the FA / TA weight % ratio at concentration, is at least 0.70, preferably at least 0.75, preferably at least 0.80, preferably at least 0.85, preferably at least 0.90, preferably at least 0.95. Such ratios allow for an easy crystallisation of the lactic acid composition. The above total and free acid concentrations and wt% ratio’s thereof have the advantage of facilitating crystallisation of the lactic acid composition in a subsequent step. A high lactic acid oligomer content, hence low FA content, may interfere with the crystallisation.

[0122] In certain embodiments of the present invention, the present process may include a step e), which comprises a distillation of the concentrated crude lactic acid composition, obtained in step d), to obtain a distilled lactic acid composition. Distillation is preferably performed by means of flash distillation , wiped film distillation, or short path distillation. Apparatuses for carrying these types of distillation are commonly known in the art. The distillation step may have the advantage that a reoligomerisation of lactic acid is not given the time to be significant, and the free acid content of the composition remains high.

[0123] In some embodiments of the present process, distillation is carried out at a temperature of at least 50.0°C, preferably at least 75.0°C, preferably at least 90.0°C, preferably at least 100°C, preferably at least 110.0°C, preferably at least 120.0°C. In some embodiments of the present process, distillation is carried out the distillation occurs at a temperature of at most 200.0°C, preferably at most 175.0°C, preferably at most 150.0°C, preferably at most 140.0°C, preferably at most 130.0°C. In some embodiments of the present process, distillation is carried out at a temperature of at least 50.0°C to at most 200.0°C, preferably at least 75.0°C to at most 175.0°C, preferably at least 90.0°C to at most 150.0°C, preferably at least 100°C to at most 140.0°C, preferably at least 110.0°C to at most 130.0°C.

[0124] In some embodiments of the present process, distillation is carried out at a pressure of at most 100 mbar, preferably at most 75 mbar, preferably at most 50 mbar, preferably at most 25 mbar, preferably at most 20 mbar, preferably at most 15 mbar, preferably at most 10 mbar, preferably at most 5 mbar.

[0125] The above distillation temperatures and / or pressures may speed up the concentrating step, which prevents or reduces the formation of large amount of oligomeric lactic acid in the composition. Furthermore, the present distillation step may further improve the removal of impurities, which are comprised within the concentrated lactic acid composition.

[0126] In some embodiments of the present process, it is preferred that the distilled lactic acid composition obtained in step e) has: a total acid concentration of at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, preferably at least 95.0 wt%, wherein the wt% is expressed compared to the total weight of the distilled lactic acid composition, and / or a free acid concentration of at least 70.0 wt%, preferably at least 75.0 wt%, preferably at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, wherein the wt% is expressed compared to the total weight of the distilled lactic acid composition.

[0127] In certain embodiments of the present invention, it is also preferred that the ratio of the weight percentage of free acid in the distilled lactic acid composition, over the weight percentage of total acid in the distilled lactic acid composition, i.e., the FA / TA weight % ratio at distillation, is at least 0.70, preferably at least 0.75, preferably at least 0.80, preferably at least 0.85, preferably at least 0.90, preferably at least 0.92.

[0128] The above total and free acid concentrations and wt% ratio’s thereof have the advantage of facilitating crystallisation of the lactic acid composition in a subsequent step. A high lactic acid oligomer content (hence low FA content) may interfere with the crystallisation.

[0129] In step f) of the present process, the concentrated crude lactic acid composition obtained in step d), or the distilled lactic acid composition obtained in step e), is crystallised thereby obtaining lactic acid. In principle, different crystallization techniques can be employed.

[0130] In certain preferred embodiments, crystallisation is a melt crystallization. Melt crystallization is a process in which a crystalline material is obtained from a melt of the material to be crystallized. Melt crystallisation (cooling crystallization), involves direct cooling of the concentrate or distillate containing the lactic acid (as obtained in step d) or e) herein) in the molten state, so that the lactic acid crystallizes out. No solvent in used.

[0131] In certain preferred embodiments, crystallisation is a solvent crystallization. Examples of suitable solvents that may be applied in such crystallisation step include, but are not limited to water, alcohols, acetone, ethyl acetate, cyclohexane, etc.

[0132] The melt crystallisation or solvent crystallization can be carried out with the aid of a suspension crystallization or a layer crystallization, possibly in conjunction with a wash column or a centrifuge, or some other purification technique.

[0133] In certain particularly preferred embodiments, crystallization as applied in step f) is melt crystallization. In an embodiment, crystallisation may be performed using a static melt crystallizer.

[0134] The lactic acid which has crystallized out can then be separated from the remaining liquid, or mother liquor, in the known ways of solid-liquid separation. Examples of suitable separation techniques for separating the lactic acid crystals from the mother liquor are centrifugation, decanting, filtration, separation with the aid of one or more wash columns, or a combination of two or more of these techniques. For instance, separation of the lactic acid crystals from the mother liquor may be performed by centrifugation over a membrane. For instance, such membrane may have a mesh size of at most 1000.0 pm, preferably at most 750.0 pm, preferably at most 500.0 pm, preferably at most 250.0 pm, preferably at most 200.0 pm, preferably at most 150.0 pm, preferably at most 100.0 pm. The mother liquor obtained may still contain considerable quantities of lactic acid. For optimal process control it is therefore preferable to recycle said mother liquor into the present process. Preferably, the mother liquor is recycled to the dilution step, to allow subsequent re-equilibration, hydrolysis of oligomers, and maximizing monomeric lactic acid content.

[0135] Preferably, the crystallization step involves the addition of seed (seeding) a product, e.g. crystals, to the concentrated lactic acid solution. For instance, the crystallisation step f) comprises seeding the concentrated crude lactic acid composition obtained in step d) or the distilled lactic acid composition obtained in step e) with lactic acid, such as lactic acid crystals. This may speed up the crystallisation step. It is to be understood that in embodiments wherein seed crystals are added, seed crystals of a desired isomeric purity are used. Hence, the lactic acid crystals used as seed (seeding) crystals can be L-lactic acid crystals or D-lactic acid crystals.

[0136] For instance, when a process according to the invention starts from PLA waste comprising PLA that predominantly has L-lactate stereochemical purity as defined herein, i.e. , comprising at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 96.0 % L-Lactate, said seeding crystals will preferably be L-lactic acid crystals. Alternatively, when a process according to the invention starts from PLA waste comprising PLA that predominantly has D-lactate stereochemical purity as defined herein, i.e., comprising at least 80.0 %, preferably at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 96.0 % D-Lactate, said seeding crystals will preferably be D-lactic acid crystals.

[0137] It is preferable to keep the temperature at which crystallization occurs (the crystallization temperature) as low as possible, so that the formation of oligomers and polymers of lactic acid is limited as far as possible. In some embodiments, it is preferred that the crystallisation temperature Tcis at most 50°C, preferably at most 47°C, preferably at most 46°C, preferably at most 45°C.

[0138] In certain embodiments, crystallisation of the concentrated crude lactic acid composition obtained in step d), or the distilled lactic acid composition obtained in step e), comprises lowering the temperature of the respective compositions below the crystallisation temperature Tc, preferably at least 1.0°C below Tc, preferably at least 2.0°C below Tc, preferably at least 3.0°C below Tc. This may influence the speed and / or size of the lactic acid to be formed.

[0139] In some embodiments, lowering the temperature occurs at a rate of at most 10.0°C / min, preferably at most 7.5°C / min, preferably at most 5.0°C / min, preferably at most 3.0°C / min, preferably at most 2.0°C / min, preferably at most 1.0°C / min.

[0140] In certain embodiments of the present invention, it may be desired to wash the lactic acid, obtained in crystallisation step f). This is especially advantageous when a mother liquor (containing the impurities) cannot be sufficiently separated from the lactic acid crystals. Preferred washing liquids include for instance, but are not limited, to water and (racemic) lactic acid.

[0141] In certain embodiments, the lactic acid, that has been isolated (and optionally washed), is dissolved in a suitable solvent, generally water, to prevent the hygroscopic lactic acid (crystals) from caking together. The concentration of the lactic acid solution thus obtained can, in principle, have any desired value. Such lactic acid solution is particularly stable and may be stored for later use.

[0142] In an alternative embodiment, the lactic acid product (e.g. crystals) obtained in step f) can also be stored in solid form for later use.

[0143] In certain embodiments of the present invention, it is preferred that the process further comprises a purification step. Such purification step may be applied after any one of steps a), b), c), and d).

[0144] Purification may for instance include filtration, absorption, adsorption, passing over a carbon or ion exchange column, etc.

[0145] For instance, in some embodiments, the crude lactic acid composition is filtered before the diluting step is performed. In some embodiments, the diluted crude lactic acid composition is filtered before the equilibrating step is performed. In some embodiments, the equilibrated crude lactic acid composition is filtered before the concentrating step is performed. In some embodiments, the concentrated crude lactic acid composition is filtered before the crystallizing step is performed. The present invention also encompasses a combination of one or more of the aforementioned filtration steps.

[0146] In another example, the process of the invention may also include a purification step wherein the crude lactic acid composition is contacted with an adsorbent, such as activated carbon, before the diluting step is performed. In some embodiments, the diluted crude lactic acid composition is contacted with an adsorbent, such as activated carbon, before the equilibrating step is performed. In some embodiments, the equilibrated crude lactic acid composition is contacted with an adsorbent, such as activated carbon, before the concentrating step is performed. In some embodiments, the concentrated crude lactic acid composition is contacted with an adsorbent, such as activated carbon, before the crystallizing step is performed. The present invention also encompasses a combination of one or more of the aforementioned filtration steps.

[0147] In some embodiments, the present process further comprising the step of re-using the lactic acid, obtained in step f).

[0148] In certain preferred embodiments, the process of the invention further comprising the step of processing the lactic acid, obtained in step f), optionally in combination with virgin lactic acid, into lactide, optionally followed by polymerising said lactide into polylactic acid, n certain preferred embodiments, the process of the invention further comprises feeding the lactic acid obtained in step f); optionally in combination with a virgin lactic acid; as starting material into a lactide preparation process.

[0149] In certain preferred embodiments, the process of the invention may also further comprise the step of feeding the lactic acid obtained in step f); optionally in combination with virgin lactic acid; as starting material into a polylactide preparation process.

[0150] The lactic acid obtained in step f) of the present process, may have an stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % L-Lactate, and may be used, optionally in a mixture with virgin L-lactic acid, to produce lactide, preferably L-lactide, and / or to produce poly-lactic acid (PLA), preferably poly-L-lactic acid (PLLA).

[0151] Alternatively, the lactic acid obtained in step f) of the present process, may have an stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % D-Lactate, and may be used, optionally in a mixture with virgin D-lactic acid, to produce lactide, preferably D-lactide, and / or to produce polylactic acid (PLA), preferably poly-D-lactic acid (PDLA).

[0152] Figure 1 shows a block diagram of a process according to an embodiment of the present invention. Some of the represented process steps (indicated in dashed lines) are optional. The process starts with providing a polylactic acid waste (1). In the present example, the PLA waste may for instance be discarded post-consumer PLA products, e.g. PLA cups or bottles. The PLA waste may optionally be pretreated (101) before being subjected to a hydrolysis step (102). For instance, the PLA waste may be sorted and washed before being used in the process of the present invention in order to increase the relative amount of PLA in the waste compared to non- PLA materials, and to provide a first purification of non-thermoplastic components. The PI_A waste may also be melted, filtered and re-solidified before subjecting it to hydrolysis. The pre-treatment step (101) is optional. Hydrolysis (102) of the PLA waste may involve treatment with catalysts, such as enzymes or alkaline compounds (e.g. MgOH2, or NH4OH). More preferably, hydrolysis involves the treatment of the PLA waste in water at an elevated temperature, as described herein. As a result of the hydrolysis step, a crude lactic acid composition is obtained, which is subsequently diluted (103) e.g. to a TA content of about 60.0 wt% through the addition of water (3), and equilibrated (103), e.g. by keeping the diluted composition at about 60-80°C for about 20-24 hours. Optionally the obtained diluted and equilibrated lactic acid composition may undergo one or more purification step(s) (104) before being concentrated. Purification may for instance involve a filtration of the obtained composition and / or a treatment involving passing the composition over a carbon column. The -optionally purified composition- is subsequently concentrated (105), e.g. by evaporating water (4) from the composition to obtain a concentrated composition comprising lactic acid, e.g. having more than 90 wt% FA and more than 95 wt% TA. Prior to being subjected to a crystallisation step (107), the concentrated composition may optionally undergo distillation (106) to remove additional impurities and / or contaminants that are present in the concentrated composition. The concentrated composition, optionally after distillation (106) is then subjected to a crystallisation (107), e.g. melt crystallisation, yielding purified crystalline lactic acid (2).

[0153] In accordance with the present process, lactic acid, obtained in step f) of the present process, has high stereochemical purity. In certain embodiments, lactic acid, obtained in step f) of the present process, has a stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % L- Lactate. In certain other embodiments, lactic acid obtained in step f) of the present process, has a stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % D-Lactate.

[0154] In certain embodiments, lactic acid, obtained in step f) of the present process, has: a free acid content of at least at least 95.0 wt%, preferably at least 96.0 wt%, preferably at least 97.0 wt%, wherein the wt% is expressed compared to the total weight of lactic acid, and / or a total acid content of at least at least 95.0 wt%, preferably at least 96.0 wt%, preferably at least 97.0 wt%, preferably at least 98.0 wt%, preferably at least 99.0 wt%, wherein the wt% is expressed compared to the total weight of lactic acid.

[0155] In certain embodiments, lactic acid, preferably the lactic acid crystals, obtained in step f) of the present process, may also be characterised by their color. For instance, in certain embodiments, the lactic acid, preferably the lactic acid crystals, obtained in step f), have a colour, as determined in accordance with ASTM D 5386-93 under non-heated (fresh) conditions, of not more than 10 APHA units. In certain embodiments, the lactic acid, preferably the lactic acid crystals, obtained in step f), have a colour, as determined in accordance with ASTM D 5386-93 after heating at 180°C for about two hours under reflux, of not more than 20 APHA units. Such colour characteristics may allow the lactic acid -obtained with the present process- to be (re-)used in high-end applications and have a colour similar to virgin lactic acid.

[0156] In certain other embodiments, lactic acid, preferably the lactic acid crystals, obtained in step f) of the present process, are characterized by having a sodium content of at most 10.0 ppm, preferably at most 7.5 ppm, preferably at most 5.0 ppm, preferably at most 4.0 ppm, wherein the ppm are weight parts expressed compared to the total weight of the lactic acid crystals.

[0157] Another aspect of the present invention concerns lactic acid, preferably lactic acid crystals, that may be obtainable or obtained by carrying out the present process, and preferably having features as defined herein.

[0158] In preferred embodiments of the present invention, the lactic acid, preferably lactic acid crystals, as obtained in accordance with the present process, are of high purity and / or high stereochemical purity, rendering them particularly suitable for being re-used in a lactic acid-to-PLA process. For instance, the present invention provides for the use of a lactic acid obtainable or obtained by carrying out a process as given herein, or having the features as defined herein, optionally in combination with virgin lactic acid, as a starting material for preparing lactide. The invention further provides for the use of a lactic acid obtainable or obtained by carrying out a process as given herein, or having the features as defined herein, optionally in combination with virgin lactic acid, as a starting material for preparing polylactic acid and the intermediate lactide.

[0159] The following examples serve to merely illustrate the invention and should not be construed as limiting its scope in any way. While the invention has been shown in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes and modifications without departing from the scope of the invention. EXAMPLES

[0160] MATERIALS & METHODS

[0161] Lactic acid material

[0162] In the present example section, lactic acid, commercially available from Corbion, Gorinchem, The Netherlands, and known under the name PURAC®HS100 was applied.

[0163] Process steps

[0164] In the below example section, certain process steps were carried out as follows.

[0165] Concentration by evaporation of water was performed on a UIC KDL-4 short path distillation apparatus (UIC GmbH, Germany), at a continuous feed of 7mL / min, at a pressure of about 250 mbar, and at a temperature of about 110 to 120°C.

[0166] Distillation of lactic acid, when applied, was performed on the same UIC KDL-4 short path distillation apparatus, at 2 to 4 mbar, 130°C at a feed rate of 7ml / min. Feeds were provided at room temperature of 21 °C.

[0167] Crystallization was performed in a double-walled, 300mL suspension crystallization vessel equipped with a magnetic stirrer and water heating bath. For each experiment a single batch of 150-200g of concentrated lactic acid composition was used. Crystallization points were determined by cooling at 1 K / min from the melt under constant seeding of monomeric lactic acid seed crystals. After determination of the crystallization point, the crystal suspension was further cooled and solid-liquid separation was achieved using centrifugation over a 100 micron cloth. Mother liquor and crystal fractions were collected, yield was recorded and analyzed for free and total acid content, stereochemical purity, and residual impurities, were applicable.

[0168] Determination of free acid content (FA) and total acid content (TA)

[0169] Free- and total acid were determined using a Metrohm titrator. Direct titration was used to determine the amount of free acid and back titration was used to determine the amount of total acid. To that end ~1 g of lactic acid is weighed accurately to 0.0001 g. MilliQ water is then added to a sample that is to be analyzed, followed by 30 ml ethanol. Next, titration is carried out using 1 M NaOH. The free acidity is then calculated, represented in wt% monomeric lactic acid using the amount of ml NaOH used to reach the equivalence point (NaOH, EP1).

[0170] A total amount of 20 ml NaOH is added and the sample is stirred for 3 minutes for saponification. A back titration is then carried out using 1 M HOI to determine the amount of total acid. The total acid amount may then be calculated in wt% monomeric lactic acid using the amount of ml HCL to neutralize the excess NaOH using the following formulae:

[0171] Free Acid ( NaOH.EPi * 9.008 * titcrao ^ / rnsampie S Ze

[0172] The following example illustrates the methodology.

[0173] Free- and total acid of an 88% lactic acid solution was determined. 0.9803 g of the solution was used for the titrations. Titration with 1.0000 M NaOH was done and the titration end point 1 (EP1) was determined at pH 8.794 using 7.9187 ml NaOH. After saponification, back titration was done with 1.0000 M HOI. titration end point 2 (EP2) was determined at pH 8.405 using 10.3296 ml HOI.

[0174] Applying the formulae above yields the following result:

[0175] Free Acid = (7.9187*9.008*1.0000) I 0.9803 = 72.77 %(w / w)

[0176] Total Acid = (((20*1.0000)-(10.3296*1 ,0000))*9.008) I 0.9803 = 88.86 %(w / w)

[0177] COMPARATIVE EXAM PLE 1

[0178] The following example illustrates crystallization of sample of lactic acid. The lactic acid sample applied in this example was not diluted, nor equilibrated prior to crystallization thereof.

[0179] More specifically, a sample of lactic acid (PURAC® HS100 was applied. Analysis revealed that the sample consisted of 99.1 wt% total acid and 65.7 wt% free acid, with wt% expressed as compared to the total weight of the sample, at the start of the present example.

[0180] The sample was heated to 50°C within 30 min and cooled at 5K / h to 2°C while seeding in order to establish a crystallization point. However, no crystallization point could be found, which illustrates that the FA content of the sample (65.7 wt%) was too low, and the amount of water and oligomeric components was too high to allow crystallization.

[0181] COMPARATIVE EXAMPLE 2

[0182] A sample of lactic acid (PURAC® HS100) (having 99.1wt% total acid and 65.7 wt% free acid, see comparative example 1 above) was diluted by addition of reverse osmosis water to obtain a diluted lactic acid solution. Titration analysis showed that this non-equilibrated solution contained 48.3 wt% total acid and had a free acid content of 32.5 wt% (wt% ratio: FA / TA = 0.67). The non-equilibrated 48.3 wt% lactic acid composition was subsequently concentrated by evaporation of water as described above. Analysis of the resulting concentrated composition revealed that the composition comprised 102.2 wt% total acid and 68.2 wt% free acid.

[0183] This concentrated composition was subsequently used within one hour as feed for melt crystallization. The mixture was cooled as low as 4°C while seeding with lactic acid crystals, but no crystals could be formed.

[0184] This comparative example shows that it is necessary to apply an equilibration step after dilution, to allow oligomeric lactic acid species to hydrolyze into monomeric lactic acid.

[0185] EXAMPLE 1 : CRYSTALLIZATION OF LACTIC ACID AFTER CONCENTRATION

[0186] The following example illustrates the crystallization of a sample of a concentrated lactic acid composition.

[0187] A sample of lactic acid (PURAC® HS100) (having 99.1 wt% total acid and 65.7 wt% free acid, see comparative example 1 above) was diluted by addition of reverse osmosis water to obtain a diluted lactic acid solution (51 .4 wt% total acid). The diluted lactic acid solution was subsequently heated at 60°C for 21 h, allowing to equilibrate the solution. Titration analysis showed that this equilibrated solution contained 51.4 wt% total acid and had a free acid content of 46.6 wt% (wt% ratio: FA / TA = 0.91).

[0188] The equilibrated 51 .4 wt% lactic acid composition was subsequently concentrated by evaporation of water as described above. Analysis of the resulting concentrated composition revealed that the composition comprised 91.3 wt% total acid and 84.6 wt% free acid. This concentrated composition was subsequently used as feed for melt crystallization within one hour. The crystallization point was found to be 45.1 °C, and purified white lactic acid crystals were obtained. Analysis using titration as explained above, revealed that the obtained lactic acid crystals contained 97.0 wt% free acid and 100.0 wt% total acid. Table 1 provides an overview of the acid content (TA and FA) as measured using the method as defined in the methodology section above for the lactic acid composition obtained in the different process step as illustrated in this example.

[0189] Table 1 : Acid concentration of lactic acid compositions obtained throughout this example

[0190] This example shows that lactic acid may be successfully crystallized in accordance with the process of the invention, as opposed to the process set out in the above comparative example 1 or 2, which uses the same starting material, but fails to produce lactic acid crystals.

[0191] EXAMPLE 2: RECOVERING LACTIC ACID FROM RECYCLED POLYLACTIC ACID

[0192] The following example illustrates the recovery of lactic acid from PLA waste in accordance with a process of the invention. The PLA waste in this example consisted of post-industrial PLA (r-PLA), which was received in the form of fiber waste with an average stereochemical purity of 96.2% L- lactate and containing 250-350 ppm sodium.

[0193] The r-PLA was depolymerized in the presence of water, at a temperature in the range of about 140 to 160°C for about 12 hours. The resulting mixture was diluted to 50.0 wt% total acid content and was subsequently heated at 60°C for 21 h, allowing to equilibrate the solution.

[0194] After the equilibration step, the lactic acid solution was concentrated by evaporating water as described above, to reach a concentrated lactic acid composition of 90.0 wt% free acid and 90.0 wt% total acid.

[0195] The concentrated lactic acid composition was kept at room temperature and used within one hour as feed for crystallization as described above. The crystallization point was determined to be 33.0°C. The suspension was cooled further to 20.3°C at which point a thick crystal slurry was obtained. The crystals were isolated by centrifugation. Titration analysis showed that the crystals had about 98.0 wt% free acid and 99.0 wt% total acid content. Stereochemical purity of the crystals was 99.7% L-lactate and no residual sodium could be detected (at a limit of detection (LOD) of <4ppm). Table 2 provides an overview of the acid content (TA and FA) as measured using the method as defined in the method section above for the lactic acid composition obtained in the different process step as illustrated in this example.

[0196] Table 2: Acid concentration of lactic acid compositions obtained throughout this example

[0197] This example shows that post-industrial PLA waste may be converted into purified lactic acid crystals by applying a process according to the invention. Furthermore, the example illustrates that lactic acid with high stereochemical purity can be obtained by applying the present process.

[0198] EXAM PLE 3: RECOVERING LACTIC ACID FROM RECYCLED POLYLACTIC ACID

[0199] The following example illustrates another embodiment of the process of the invention for the recovery of lactic acid from PLA waste.

[0200] The PLA waste in this example consisted of post-industrial PLA (r-PLA), which was received in the form of fiber waste with an average stereochemical purity of 96.2% L-lactate and containing 250-350 ppm sodium. The r-PLA was depolymerized and diluted to 50.0%TA as per Example 2. A crude lactic acid solution was obtained, which was subsequently heated at 60°C for 21 h, allowing to equilibrate the solution After the equilibration step, the lactic acid solution was concentrated by evaporating water as described above, to reach a concentrated lactic acid composition of 90.0 wt% free acid and 90.0 wt% total acid.

[0201] The resulting concentrated lactic acid was further flash distilled as described in the methodology section above. The distilled lactic acid showed a composition of 94.0 wt% free acid and 98.0 wt% total acid.

[0202] The distilled lactic acid was kept at room temperature and was used within one hour as feed for crystallization. The crystallization point was determined to be 45.6°C and after further cooling to 30.0°C, crystals were isolated by centrifugation. The crystals obtained showed 98.0 wt% free and 99.0 wt% total acid and had a stereochemical purity of 99.3% L-lactate. No residual sodium was detected (at an LOD of <4ppm).

[0203] Table 3 provides an overview of the acid content (TA and FA) as measured using the method as defined in the method section above for the lactic acid composition obtained in the different process step as illustrated in this example.

[0204] Table 3: Acid concentration of lactic acid compositions obtained throughout this example

[0205] This example shows that post-industrial PLA waste may be converted into purified lactic acid crystals of high stereochemical purity high when applying a process according to the invention. When comparing the present example 3 to example 2 above, the present example further illustrates that a lactic acid distillation step prior to crystallization allows to increase feed purity to the crystallization step, since the distillation step increases crystallization point and final yield.

[0206] EXAMPLE 4: RECOVERY OF PURIFIED LACTIC ACID

[0207] The present example illustrates the recovery of purified lactic acid starting from an impure lactic acid feed. The impure lactic acid feed applied in the present example provides a model for a PLA waste containing additives.

[0208] A feed mixture was generated by mixing PURAC® HS100 (see material section above) at room temperature (21 °C) with three additives that are typically used in polymer processing. The resulting mixture (composition A) is shown in Table 4 and provides a model for a possible composition of a PLA waste comprising contaminants / impurities, which are challenging to remove in a recycling process.

[0209] Table 4: Feed mixture

[0210] The obtained lactic acid composition A was then diluted by addition of de-ionized water. This resulting diluted lactic acid solution was then equilibrated for 24 hours at 80 °C. Titration revealed that the equilibrated lactic acid composition comprises 43.6% free acid and 49.1 % total acid (wt ratio FA / TA = 0.89). It was a yellow to orange inhomogeneous mixture which was filtered twice in order to remove insolubles using 597 Whatman 7 pm paper filter.

[0211] The filtered solution was concentrated and the acid was flash distilled to obtain a distilled lactic acid with a 95.5 wt% total acid and a 94.0 wt% free acid content. Concentration and subsequent acid distillation steps were performed on the same apparatus (see method section above), by first applying a mild vacuum for water evaporation, after which the obtained concentrate was once more passed over that equipment at a deeper vacuum to finally distill lactic acid.

[0212] The obtained distillate was subjected to a crystallization step. From this distillate, yellow crystalline lactic acid could be obtained (crystallization point 41°C, final end temperature of crystallization 15°C) at a targeted yield of 76% and stereochemical purity of 99.7% L. Analyses showed that prior to crystallization, 6-hydroxycaproic acid (hydrolysis product of caprolactone) was still present, while after the crystallization step, most of the 6-hydroxycaproic acid was removed. The crystallization resulted in yellow crystals caused by a remaining 300ppm of dye. Table 5 provides an overview of the composition of the treated feed mixture at different process stages as applied in this example.

[0213] Table 5: Compositional analysis of the treated feed mixture throughout this example nm = not measured

[0214] (*) as 6-hydroxycaproic acid (**) as elemental Ti per ICP elemental analysis

[0215] EXAM PLE 5: RECOVERY OF PURIFIED LACTIC ACID

[0216] The present example provides another illustration of the recovery of purified lactic acid starting from an impure lactic acid feed. The same model composition as reported in Example 4 (Table 4) was subjected to the same dilution, equilibration, filtration steps, as reported in example 4. However in the present example, the filtrated solution was carbon treated before concentration, flash distillation, and crystallization.

[0217] The filtered solution (as obtained in Example 4) was passed over a carbon column (Chemviron carbon, type CPG-LF 12x40, Ref FE13220B) at 2 bed volumes per hour. The carbon column was slightly heated using a water bath set to 50 °C. The first 1-8 bed volumes typically were colorless indicating removal of Yellow 7 (textile dye), which was confirmed by analyses. Bed volumes beyond 8 typically showed slight yellow color, indicating saturation of the column with Yellow 7.

[0218] The filtered and carbon treated solution was then concentrated and flash distilled to obtain a lactic acid with a 98.3 wt% total acid and a 91 .9% free acid content. From this distillate, white crystalline lactic acid could be obtained (crystallization point 45°C, final end temperature of crystallization 36°C) at a targeted yield of 40% and stereochemical purity of 99.9% L. Analyses showed that prior to crystallization, 6-hydroxycaproic acid (hydrolysis product of caprolactone) was still present, while after the crystallization step, most of the 6-hydroxycaproic acid was removed. Table 6 provides an overview of the composition of the treated feed mixture at different process stages as applied in this example.

[0219] Table 6: Compositional analysis of the treated feed mixture throughout this example nm = not measured

[0220] (*) as 6-hydroxycaproic acid

[0221] (**) as elemental Ti per ICP elemental analysis Examples 4 and 5 show that by conducting a process according to the invention a variety of contaminants / impurities may be removed, while allowing to recover lactic acid with a high free acid content. Example 5 further illustrates that by applying a carbon treatment on a diluted and equilibrated acid solution before concentration thereof, may be particularly useful for removing dyes.

Claims

CLAIMS1 . A process for recycling polylactic acid (PLA), comprising the steps of: a) hydrolysing a PLA waste thereby obtaining a crude lactic acid composition; b) diluting the crude lactic acid composition in water, thereby producing a diluted crude lactic acid composition; c) equilibrating the diluted crude lactic acid composition for a equilibration period teat a equilibration temperature of at least Te, thereby producing an equilibrated crude lactic acid composition; d) concentrating the equilibrated crude lactic acid composition, thereby producing a concentrated crude lactic acid composition; e) optionally, distilling the concentrated crude lactic acid composition thereby producing a distilled lactic acid composition; and f) crystallizing the concentrated crude lactic acid composition obtained in step d), or the distilled lactic acid composition obtained in step e), thereby recovering lactic acid.

2. Process according to claim 1 , wherein the PLA waste comprises polylactic acid containing waste from domestic and / or industrial areas, and for instance, comprises post-consumer PLA and / or post-industrial PLA.

3. Process according to claim 1 or 2, wherein the PLA waste has a stereochemical purity of at least 80.0 % L-Lactate.

4. The process according to any one of the previous claims, wherein the crude lactic acid composition is diluted in deionised water or reverse osmosis water.

5. The process according to any one of the previous claims, wherein the diluted crude lactic acid composition has a total acid concentration of between 50.0 and 80.0 wt%, wherein the wt% is expressed compared to the total weight of the diluted crude lactic acid composition.

6. The process according to any one of the previous claims, wherein the equilibrating step is continued until the ratio of the weight percentage of free acid in the equilibrated crude lactic acid composition, over the weight percentage of the total acid in the equilibrated crude lactic acid composition is at least 0.70, preferably at least 0.75, preferably at least 0.80, preferably at least 0.85, preferably at least 0.90.

7. The process according to any one of the previous claims, wherein the equilibration period teis at least 0.25 hour.

8. The process according to any one of the previous claims, wherein the equilibration temperature Teis at least 20.0°C.

9. The process according to any one of the previous claims, wherein the equilibration temperature Teis at most 150.0°C.

10. The process according to any one of the previous claims, wherein the concentrated crude lactic acid composition has a total acid concentration of at least 80.0 wt%, preferably at least 85.0 wt%, preferably at least 90.0 wt%, preferably at least 95.0 wt%, wherein the wt% is expressed compared to the total weight of the concentrated crude lactic acid composition.11 . The process according to any one of the previous claims, wherein crystallization is solvent crystallization or melt crystallization, wherein said either solvent or melt crystallization is performed as a suspension crystallization or layer crystallization.

12. The process according to any one of the previous claims, wherein crystallisation step f) comprises seeding the concentrated crude lactic acid composition obtained in step d) or the distilled lactic acid composition obtained in step e) with lactic acid crystals.

13. The process according to any one of the previous claims, wherein the crystallisation temperature Tcin step f) is at most 50°C, preferably at most 47°C, preferably at most 45°C.

14. The process according to any one of the previous claims, wherein crystallisation step f) comprises lowering the temperature of the concentrated crude lactic acid composition obtained in step d), or of the distilled lactic acid composition obtained in step e), below crystallisation temperature Tc, preferably at least 1.0°C below Tc, preferably at least 2.0°C below Tc, preferably at least 3.0°C below Tc.

15. The process according to any one of the previous claims, wherein crystallisation step f) comprises lowering the temperature of the concentrated crude lactic acid composition obtained in step d), or of the distilled lactic acid composition obtained in step e) at a rate of at most 10.0°C / min, preferably at most 7.5°C / min, preferably at most 5.0°C / min, preferably at most 3.0°C / min, preferably at most 2.0°C / min, preferably at most 1.0°C / min.

16. The process according to any one of the previous claims, wherein the time between the end of the equilibrating step and the beginning of the concentrating step is at most 36.0 hours, preferably at most 30.0 hours, preferably at most 24.0 hours, preferably at most 18.0 hours,preferably at most 12.0 hours, preferably at most 6.0 hours, preferably at most 3.0 hour, preferably at most 2.0 hour, preferably at most 1 .0 hour.

17. The process according to any one of the previous claims, wherein the time between the end of the equilibrating step and the beginning of the crystallizing step is at most 36.0 hours, preferably at most 30.0 hours, preferably at most 24.0 hours, preferably at most 18.0 hours, preferably at most 12.0 hours, preferably at most 6.0 hours, preferably at most 3.0 hour, preferably at most 2.0 hour, preferably at most 1 .0 hour.

18. The process according to any one of the previous claims, wherein the lactic acid obtained in step f) has a stereochemical purity of at least 85.0 %, preferably at least 90.0 %, preferably at least 92.0 %, preferably at least 95.0 %, preferably at least 97.0 %, preferably at least 99.0 % L- Lactate.

19. The process according to any one of the previous claims, wherein the lactic acid, obtained in step f) has a free acid content of at least 95.0 wt%, preferably at least 96.0 wt%, preferably at least 97.0 wt%, wherein the wt% is expressed compared to the total weight of lactic acid crystals.

20. The process according to any one of the previous claims, wherein the lactic acid, obtained in step f) has a total acid content of at least at least 95.0 wt%, preferably at least 96.0 wt%, preferably at least 97.0 wt%, preferably at least 98.0 wt%, preferably at least 99.0 wt%, wherein the wt% is expressed compared to the total weight of lactic acid crystals.

21. The process according to any one of the previous claims, further comprising the step of processing the lactic acid, obtained in step f), optionally in combination with virgin lactic acid, into lactide, optionally followed by polymerising said lactide into polylactic acid.

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