Downstream process for separating a mixture of depolymerized polyester products produced from methanolysis

Abstract

Disclosed herein are methods and compositions used to separate and recover high-purity individual monomers from a mixture of deconstructed products from a catalyzed methanolysis depolymerization process of mixed polyester wastes.

Description

DOWNSTREAM PROCESS FOR SEPARATING A MIXTURE OF DEPOLYMERIZED POLYESTER PRODUCTS PRODUCED FROM METHANOLYSISCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. § 119 to U.S. provisional patent application no. 63 / 512,804 filed on 10Jul2023, the contents of which are hereby incorporated in their entirety.CONTRACTUAL ORIGIN

[0002] The United States Government has rights in this invention under Contract No. DE- AC36-08GO28308 between the United States Department of Energy and Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory.BACKGROUND

[0003] Feedstock heterogeneity is the most significant challenge in recycling real-world plastic wastes. Technologies for depolymerizing the most prominent polyester, PET, are known and currently being scaled to handle currently unrecyclable forms of the polymer. However, three key technical hurdles have limited widespread commercial success: (1) lack of technologies for handling increasingly heterogeneous polyester waste streams, (2) resilience to various contaminations in deconstruction and separation processes, (3) precise separation and recovery of high-purity individual products from mixed feedstocks. Therefore, developing robust and scalable technologies for high-purity product recovery from a mixture of deconstructed monomers is critical to the future of plastic recycling.

[0004] The methods disclosed herein are useful to overcome the existing technical hurdles by designing a downstream separation process that can remove contaminants and recover individual monomers from depolymerized mixed polyesters with high purity. Meanwhile, methodsdisclosed herein also fill the gap between deconstruction and redesign by enabling direct reuse of recovered monomers for making new polymers and / or other valuable products. With the developed downstream process, the processing cost, GHG emissions, and energy footprints for the plastic upcycling process can be much lower than the conventional manufacturing or separation approaches. As mentioned, the post depolymerization separation process can be challenging as the feedstock compositions are complex and varied. This invented process can be applicable to the wide range of the depolymerized product compositions and from various types of polyesters.SUMMARY

[0005] In an aspect, disclosed herein are methods for isolating a monomer product from a mixture of polyester polymers, the method comprising the steps of a methanolysis reaction of the mixture of polyester polymers, a solid-liquid separation of the resulting mixture of monomer products from the methanolysis reaction, purifying the mixture of monomer products, and isolating a monomer product from the mixture of monomer products. In an embodiment, the solid-liquid separation comprises microfdtration to remove large solid contaminants from the methanolysis reaction. In an embodiment, the microfdtration takes place at a temperature above room temperature. In an embodiment, the separated monomer products from the methanolysis reaction are further purified using activated carbon. In an embodiment, the separated monomer products from the methanolysis reaction are further purified using column chromatography comprising an ion exchange resin. In an embodiment, the monomer is isolated through meltcrystallization. In an embodiment, the isolated monomer is further purified using activated carbon. In an embodiment, the isolated monomer is further purified using column chromatography comprising an ion exchange resin. In an embodiment, the method further comprises distilling the methanolysis reaction solvent to isolate constituent solvents from oneanother. In an embodiment, the isolated solvents can be reused in the methanolysis reaction. In an embodiment, the monomers comprise MLA, DMT, dimethyl adipate (DMA), and dimethyl succinate (DMS). In an embodiment, the mixture of polyester polymers comprises polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polyethylene terephthalate (PET) and polybutylene succinate (PBS). In an embodiment, the methanolysis reaction comprises methanol, a catalyst, 1-4-butanediol (BDO), and ethylene glycol (EG). In an embodiment, BDO is isolated from EG. In an embodiment, the BDO is isolated from EG through a step comprising distillation, melt crystallization, liquid chromatography or solvent extraction methods. In an embodiment, the MLA is the isolated monomer product. In an embodiment, the DMT is the isolated monomer product. In an embodiment, the DMA is the isolated monomer product. In an embodiment, the DMS is the isolated monomer product. In an embodiment, the monomer product is isolated from the mixture of monomer products through distillation means.

[0006] Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 depicts a scheme for overview of the downstream process flow diagram (PLA: Polylactic acid, PBAT: Polybutylene adipate terephthalate, PET: Polyethylene terephthalate, PBS: Polybutylene succinate, MLA: methyl lactate, DMT: dimethyl terephthalate, DMA: dimethyl adipate, DMS: dimethyl succinate, BDO: 1,4-butanediol, EG: ethylene glycol).

[0008] FIG. 2 depicts embodiments of chromatographic methods disclosed herein. FIG. 2A depicts batch column separation of EG and BDO. FIG. 2B depicts SMB zone configuration (2-2-2-2). FIG. 2C depicts column profile reached at a steady state. FIG. 2D depicts extract effluent histories. FIG. 2E depicts raffinate effluent histories. Operating conditions: column size (i.d. 1.5cm, Lc 60 cm), particle size = 500 micron, mobile phase - water, linear isotherm (partition coefficient) for EG and BDO = 0.318, 0.732 for adsorption coefficient (L / g), diffusivity coefficient = 0.005 cm2 / min, port switching time = 15.29 min, feed = 50 mL / min, extract 73.0 mL / min, raffinate 88.9 mL / min, desorbent = 111.8 mL / min.

[0009] FIG. 3 depicts downstream methods for contamination removal and monomer reclamation. FIG. 3 A depicts simplified process flow diagram for ACM of PET, PLA, PBAT, and PBS delineated by process area. FIG. 3B depicts normalized monomer yields through the downstream separation process for a 50:23:23:4 PET:PLA:PBAT:PBS feedstock. FIG. 3C depicts dye and metals removal via activated carbon treatment of post-crystallization soluble monomer fractions. Metal concentrations in the liquid samples were determined via inductively couple plasma-mass spectrometry (ICP-MS). FIG. 3D depicts separation efficiency of diesters from diols via single-solvent liquid liquid extraction (LLE) with heptane. The monomer mixture contains BDO, EG, DMA, and DMS in a volume ratio of 1 : 1 : 1 : 1. One-step LLE involved mixing the monomer mixture with the solvent once, followed by phase separation. The two-step LLE started with mixing half the total volume of solvent with the monomer mixture, separating the upper phase, then mixing the remaining solvent with the aqueous phase, and finally separating the phases again.DETAILED DESCRIPTION

[0010] Methods, processes and systems disclosed herein are useful to separate and recover high-purity individual monomers from a mixture of deconstructed products from a catalyzed methanolysis depolymerization process of mixed polyester wastes. A mixture of waste polyesters including PET, PBAT, PLA, PBS and others, can be depolymerized together via methanolysis to produce mixed products, e.g., DMT, MLA, DMA, DMS, BDO, EG. The depolymerization can also be done sequentially in a way afforded by the thermophysical properties of the polymers(e g., a difference in melting points) or by way of difference in their thermodynamic behavior (e.g., difference in rates of reaction of polymers). Each product generated is efficiently separated with high yield and high purity using sequential separation operations. This approach has the benefit of selectively depolymerizing polyester materials to their monomeric forms which can be directly re-used in polymerization. It also has the benefit of obviating the need for complete upstream separation by polyester type which would require many steps and which would be uneconomical due to the small volumes and variance of individual polyesters such as PLA, PBAT and PBS.

[0011] The overview of an embodiment of the downstream process is shown in Figure 1. The deconstructed products first undergo a solid-liquid separation step (e.g., filtered with microfiltration to remove large solid contaminants) at elevated temperature, and are then purified with activated carbon and / or an ion exchange resin to remove residual colorants, metals, and other contaminants from the product stream. Next, DMT is crystallized from the solution and recovered as a solid when the feedstock cools down. Further purification of DMT can be performed via melt-recrystallization and optional treatment with activated carbon and / or ion exchange resin. The leftover solution (i.e., the mother liquor) is distilled to separate methanol and MLA from other products. The resultant distillate is then further distilled to recover the methanol and purify the MLA. The leftover products are collected from the bottom stream of the distillation and separated by a solvent extraction process. In the solvent extraction process, DMA and DMS are effectively separated from BDO and EG via liquid-liquid phase separation by adding at least one organic solvent and / or water. DMA and DMS form an organic phase and can be separated from each other via distillation. Meanwhile, the organic solvent can be recovered in the distillation process and then reused for liquid-liquid extraction. BDO and EG form a separate phase and can be further separated via distillation, melt crystallization, liquid chromatography(any adsorption and SMB, and CCC approaches), or solvent extraction method (counter-current extraction). Recovery of water if being used in the liquid-liquid extraction step can be conducted via reverse osmosis, pervaporation or distillation.

[0012] EG / BDO separation using SMB

[0013] SMB separation for EG and BDO was studied using a simulation approach. Figure A1A shows an HPLC column experimental result separating EG and BDO in the cation exchange column (Biorad 87H with 0.01M sulfuric acid mobile phase. The retention time of EG and BDO peaks was at 15.9 and 21.1min, respectively, regardless of concentrations up to 500 g / L. This result indicates that the EG and BDO have a linear isotherm in this system. Thus, we designed SMB process using the cation exchange (hydrogen saturated) column and the same mobile phase. Based on the retention time, the partition coefficients of EG and BDO from the HPLC results were calculated from the solute movement theory equation and the retention time, which shown as 0.318 and 0.732, respectively, with a selectivity (BDO / EG) of 2.3. Using those parameters, we estimated a scale-up process with a continuous process in SMB. Figure A1B shows a SMB configuration (2-2-2-2) that used in this study. Four pumps and step time were optimized to separate EG and BDO with high yield and high purity.

[0014] Figures 2C-2E depicts an example of SMB process at pilot scale operation. Here, 250 g / L of each EG and BDO in water was separated under 0.0 IM sulfuric acid continuously. The process reached at a steady state after 1000 min. Here, EG and BDO were separately eluted out to raffinate and extract ports, respectively, with >99% yield and >99% purity.

[0015] Figure 3 shows the results for the downstream for contamination removal and monomer reclamation combining results from the process modeling and the experimental work.

[0016] Embodiments of methods disclosed herein contemplate a continuous process operating on real-life, complex substrates.

[0017] To separate out crystallizable monomers such as DMT, embodiments disclosed herein use a hot filtration to keep the DMT solubilized and remove solid contaminants.

[0018] As disclosed herein, we use an induced phase separation of a larger mixture of methyl esters and diol compounds (dimethyl adipate, dimethyl succinate, 1,4-butanediol, and ethylene glycol) versus just dimethyl adipate and 1,4-butanediol as in the cited technology. This phase separation is novel.

[0019] In an embodiment, processes disclosed herein also undergo further purification of monomers (e.g., activated carbon treatment).

[0020] Separation of diol monomers

[0021] Diols are notoriously difficult to separate from each other and from water mixtures due to prominent hydrogen bonding of the molecules. In an embodiment, processes disclosed herein are able to produce a mixture of diols in the absence of water which is an improvement over existing processes.

[0022] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting.

Claims

CLAIMSWe claim:

1. A method for isolating a monomer product from a mixture of polyester polymers, the method comprising the steps of a methanolysis reaction of the mixture of polyester polymers, a solid-liquid separation of the resulting mixture of monomer products from the methanolysis reaction, purifying the mixture of monomer products, and isolating a monomer product from the mixture of monomer products.

2. The method of claim 1 wherein the solid-liquid separation comprises microfiltration to remove large solid contaminants from the methanolysis reaction.

3. The method of claim 2 wherein the microfiltration takes place at a temperature above room temperature.

4. The method of claim 1 wherein the separated monomer products from the methanolysis reaction are further purified using activated carbon.

5. The method of claim 1 wherein the separated monomer products from the methanolysis reaction are further purified using column chromatography comprising an ion exchange resin.

6. The method of claim 1 wherein the monomer is isolated through melt-crystallization.

7. The method of claim 6 wherein the isolated monomer is further purified using activated carbon.

8. The method of claim 7 wherein the isolated monomer is further purified using column chromatography comprising an ion exchange resin.

9. The method of claim 6 further comprising distilling the methanolysis reaction solvent to isolate constituent solvents from one another.

10. The method of claim 9 wherein the isolated solvents can be reused in the methanolysis reaction.

11. The method of claim 1 wherein the monomers comprise MLA, DMT, dimethyl adipate (DMA), and dimethyl succinate (DMS).

12. The method of claim 1 wherein the mixture of polyester polymers comprises polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polyethylene terephthalate (PET) and polybutylene succinate (PBS).

13. The method of claim 1 wherein the methanolysis reaction comprises methanol, a catalyst, 1-4-butanediol (BDO), and ethylene glycol (EG).

14. The method of claim 13 wherein BDO is isolated from EG.

15. The method of claim 14 wherein BDO is isolated from EG through a step comprising distillation, melt crystallization, liquid chromatography or solvent extraction methods.

16. The method of claim 11 wherein MLA is the isolated monomer product.

17. The method of claim 11 wherein DMT is the isolated monomer product.

18. The method of claim 11 wherein DMA is the isolated monomer product.

19. The method of claim 11 wherein DMS is the isolated monomer product.

20. The method of claim 1 wherein the monomer product is isolated from the mixture of monomer products through distillation means.

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