Polyester textile waste recycling

Abstract

A method for recovering natural fibers from a textile comprising polyester and natural fibers. The method comprises the steps of: providing said textile soaked in a mixture comprising a solvent and a catalyst, providing and maintaining a temperature of said mixture comprising said textile within a range of 80-240° C. during depolymerization of polyester in said textile; and recovering natural fibers after said depolymerization, wherein, in said step of providing said textile soaked in said mixture, said catalyst of said mixture comprises calcium oxide.

Claims

1. A method for recovering natural fibers from a textile comprising polyester and natural fibers, wherein said method comprises the steps of: providing said textile soaked in a mixture comprising a solvent and a catalyst; providing and maintaining a temperature of said mixture comprising said textile within a range of 80-240° C. during depolymerization of polyester in said textile; and recovering natural fibers after said depolymerization, wherein, in said step of providing said textile soaked in said mixture, said catalyst of said mixture comprises calcium oxide.

2. The method according to claim 1, wherein said step of maintaining the temperature of said mixture comprising textile lasts until at least 20% of the polyester in said textile is depolymerized to molecules with a molecular weight lower than 600 g/mol, or at least 50% of the polyester in said textile is depolymerized to molecules with a molecular weight lower than 600 g/mol, or at least 80% of the polyester in said textile is depolymerized to molecules with a molecular weight lower than 600 g/mol.

3. The method according to claim 1, wherein said natural fibers comprise at least one of cotton fibers, viscose fibers, cellulose fibers, and regenerated cotton fibers, such as lyocell type fibers.

4. The method according to claim 3, wherein said natural fibers comprise cotton fibers.

5. The method according to claim 1, wherein said catalyst further comprises an oxide of any periodic table group 2 metal, and/or an oxide of any lanthanide metal.

6. The method according to claim 5, wherein said catalyst further comprises MgO.

7. The method according to claim 1, wherein, after said depolymerization of polyester, reaction products of said depolymerization of polyester are separated from the natural fibers, the natural fibers being present in a solid fraction.

8. The method according to claim 1, wherein the textile comprises at least 10% polyester, or at least 25% polyester, or at least 50% polyester, or at least 75% of polyester.

9. The method according to claim 1, wherein said temperature is above 80° C., or above 90° C., or above 100° C., or above 110° C., or above 120° C., or above 140° C., or above 160° C., or above 180° C.; and/or wherein said temperature is lower than 200° C., or lower than 180° C., or lower than 160° C., or lower than 140° C., or lower than 120° C., or lower than 100° C.

10. The method according to claim 1, wherein said temperature is within a range of 80-170° C., or within a range of 100-150° C.

11. The method of claim 1, wherein, in said step of maintaining said temperature of said mixture comprising said textile, said temperature is maintained for at least 10 min, or at least 20 min, or at least 30 min, or at least 40 min, or at least 50 min, or at least 60 min; and/or wherein said temperature is maintained for at most 300 min, or at most 270 min, or at most 240 min, or at most 200 min, or at most 160 min, or at most 120 min, or at most 90 min, or for at most 60 min.

12. The method according to claim 1, wherein, in said step of maintaining said temperature of said mixture comprising said textile, said temperature is maintained for 10-300 min, or for 30-240 min, or for 60-120 min.

13. The method according to claim 1, wherein said solvent comprises an alcohol or a diol.

14. The method according to claim 1, wherein said textile further comprises additional synthetic fibers.

15. The method according to claim 1, wherein said polyester comprises aromatic polyester; and wherein reaction products of said depolymerization of polyester includes at least one of dimethyl terephthalate, ethylene glycol, 1,3-propanediol, 1,4-butanediol, ethyl methyl terephthalate, dimers of the aromatic polyester, and trimers of the aromatic polyester.

16. The method according to claim 1, wherein said catalyst has a general formula CaO-xO-yO, where x is any periodic table group 2 metal and where y is any lanthanide metal.

17. The method according to claim 1, wherein said depolymerization is performed in an autoclave.

18. The method according to claim 15, wherein said method further comprises the step of: recovering said at least one of dimethyl terephthalate, ethylene glycol, 1,3-propanediol, 1,4-butanediol, ethyl methyl terephthalate, dimers of aromatic polyester, and trimers of aromatic polyester.

19. The method according to claim 1, wherein said method further comprises the step of: producing new textile from recovered natural fibers.

20. A recovered natural fiber obtainable by depolymerization of polyester in a textile comprising polyester and natural fibers, and recovery of natural fibers after said depolymerization.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 shows a schematic view of the method in accordance with at least one embodiment of the invention;

(3) FIG. 2 shows a schematic view of the method in accordance with at least one embodiment of the invention;

(4) FIG. 3 shows photographs of the different steps comprised in the method in accordance with at least one embodiment of the invention;

(5) FIG. 4 shows graphs of the molecular weight distribution of cotton before and after depolymerization of polyester in accordance with at least one example embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) In the present detailed description, embodiments of the present invention will be discussed with the accompanying figures. It should be noted that this by no means limits the scope of the invention, which is also applicable in other circumstances for instance with other types or variants of methods for recycling polyester from a polyester textile than the embodiments shown in the appended drawings. Further, that specific features are mentioned in connection to an embodiment of the invention does not mean that those components cannot be used to an advantage together with other embodiments of the invention.

(7) FIG. 1 shows a schematic view of a method 1 for recycling polyester from a polyester textile. The method comprises two steps 2, 4. The first step comprising providing a polyester textile soaked in a mixture comprising a solvent and a catalyst. The second step 4 comprises providing and maintaining a temperature of the mixture within a range of 80-240° C. during depolymerization of polyester in the polyester textile. For example, the temperature which is provided and maintained may be 100° C., or 120° C., or 150° C., or 170° C. The temperature is according to at least one example embodiment maintained until at least 20% of the polyester in the polyester textile is depolymerized to molecules with a molecular weight lower than 600 g/mol. In other embodiments the temperature is maintained until at least 50% or at least 80% of the polyester in said polyester textile is depolymerized to molecules with a molecular weight lower than 600 g/mol. The temperature may e.g. be maintained for 10-300 min.

(8) The polyester textile may comprise at least 10%, or 25%, or 50% or 75% of polyester and it may further comprise a natural fiber, e.g. cotton, regenerated cotton or viscose. Alternatively, the polyester textile may also comprise 100% polyester fibers. The polyester may for example be an aromatic polyester, such as a polyalkylene terephthalate. Examples of such polyalkylene terephthalate is polyethylene terephthalate, polytrimethyl terephthalate and polybutylene terephthalate. The catalyst comprises calcium oxide. It may for example be CaO, or it may be CaO—CeO.sub.2, or it may be CaO—MgO—CeO.sub.2. In the latter case the ration may be 1:4:1, i.e. the catalyst used may be 1CaO-4MgO-1CeO.sub.2. The solvent may comprise an alcohol or a diol.

(9) FIG. 2 shows a schematic view of a method 201. The two first steps 202, 204 of the method 201 in FIG. 2 are the same as the two steps 2, 4 of the method 1 in FIG. 1. Hence, focus on the description related to FIG. 2 will be on the differences compared to the method 1 of FIG. 1.

(10) The method 201 has a third step 206, which comprises recovering of said at least one of dimethyl terephthalate, ethylene glycol, 1,3-propanediol, 1,4-butanediol, ethyl methyl terephthalate, dimers of aromatic polyester, and trimers of aromatic polyester. The third step 206 may also comprise recovering of any dye, any natural fiber e.g. cotton and/or any additional component e.g. elastane. This step may be divided into one or several sub-steps. Examples of such sub-steps are precipitation, filtration, extraction, soxhlet extraction, distillation. These sub-steps may be combined in various ways in order to recover any component of the polyester textile. In addition, the third step may comprise recovering of any natural fiber, any further material and/or any dye which may be present in the polyester textile.

(11) FIG. 3 shows photographs visualizing the different steps of method 201. In this example embodiment the polyester textile 220 comprises polyethylene terephthalate (PET) and a dye. During the depolymerization the polyethylene terephthalate will depolymerize into its monomers, i.e. dimethyl terephthalate and ethylene glycol as well as dimers and trimers of the polyester. The textile 220 is soaked in a mixture comprising a solvent and a catalyst. In other words, the polyester textile is provided soaked in a mixture comprising a solvent and a catalyst 202. Subsequently, a temperature will be provided and maintained during depolymerization of polyester in the polyester textile 204. After depolymerization the reaction mixture 222 contains a solid fraction 222a and a liquid fraction 222b. The reaction mixture 222 will subsequently go through the third step 206 of the method in order to recover reaction products, dye and solvent. This third step 206 is divided into several sub-steps. After the reaction the reaction mixture may be cooled for precipitating some of the reaction products, e.g. dimethyl terephthalate as well as dimers and trimers of the polyester such that they become a part of the solid fraction. Hence, after precipitation the solid fraction 222a comprises the precipitated reaction products, the catalyst and undepolymerized polyester if present. The liquid fraction 222b comprises the solvent, dye and ethylene glycol. The liquid fraction 222b will be separated from the solid fraction via filtration. The solid fraction will undergo extraction or soxhlet extraction 206b using methanol such that dimethyl terephthalate 224 is recovered and separated from the remaining solid fraction. This liquid fraction 222b comprises dye, ethylene glycol and methanol and is subsequently or simultaneously distillated 206c. During distillation 206c, ethylene glycol 230 is recovered and separated from a solution comprising methanol and dye. The methanol may be evaporated 206d in order to recover the dye 228.

(12) FIG. 4 shows the molecular weight of cotton present in the polyester textile before (solid line) and after depolymerization of polyester at 165° C. (dotted line) and at 190° C. (dashed line). The graph shows that a lower temperature for depolymerization does not affect, i.e. lower, the molecular weight distribution of the cotton fraction of the polyester textile as much as a higher temperature. Hence, it is favorable to be able to keep the temperature which is maintained during depolymerization as low as possible.

(13) The skilled person realizes that a number of modifications of the embodiments described herein are possible without departing from the scope of the invention, which is defined in the appended claims. For instance, textiles of different compositions or different polyesters may be recycled using this method.

EXAMPLES

(14) Several catalysts were tested at different temperatures in order to find a catalyst working at low temperature.

(15) Table 1 indicates which catalyst that were working at the different temperatures. In table 1, x means that the catalyst does not work and ✓ means that the catalyst work. It shall be understood, the by working it means that the catalyst will trigger the depolymerization of the polyester in the polyester textile.

(16) TABLE-US-00001 Low Medium High temperature temperature temperature Name <160° C. 160-200 >200 Al.sub.2O.sub.3 x X x Fe.sub.3O.sub.4 x X x CaO ✓ ✓ ✓ MgO x X ✓ CeO.sub.2 x X ✓ CaO—CeO.sub.2 ✓ ✓ ✓ MgO—CeO.sub.2 x X ✓ 1CaO.sup.−4MgO.sup.−1CeO.sub.2 ✓ ✓ ✓ 4MgO—CeO.sub.2—Fe.sub.3O.sub.4 x X ✓ 4MgO—PrOx—CeO.sub.2 x X ✓

(17) From this first screening of temperatures the three catalysts: CaO, CaO—CeO.sub.2 and CaO-4MgO-1CeO.sub.2, which were working were further tested at even lower temperatures (cf. Example 1-8 below). Table 3 shows results from these tests.

Example 1

(18) A mixture of 6 g of polyethylene terephthalate (PET) fiber soaked of 60 ml methanol and 0.12 g of CaO were put in an autoclave. The autoclave was heated to and maintained at 80° C. during the depolymerization. After 14 h, the autoclave was quenched to room temperature by cold water allowing precipitation of dimethyl terephthalate (DMT) as well as dimers and trimers of the polyester. The liquid fraction was separated from the solid fraction by filtration. 3.11 g of DMT was extracted from the solid fraction by methanol. Methanol and ethylene glycol were recovered by distillation of the liquid fraction.

Example 2

(19) A mixture of 6 g of PET-fiber soaked 60 ml methanol and 0.12 g of a CaO—CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heated to and maintained at 100° C. during the depolymerization. After 4.5 h, the autoclave was quenched to room temperature by cold water allowing precipitation of DMT as well as dimers and trimers of the polyester. The liquid fraction was separated from the solid fraction by filtration. 4.07 g of DMT was extracted from the solid fraction by methanol. Methanol and ethylene glycol were recovered by distillation of the liquid fraction.

Example 3

(20) A mixture of 6 g of PET fiber soaked in 60 ml of methanol and 0.12 g of a 1CaO-4MgO-1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heated to and maintained at 135° C. After 4.5 h, the autoclave was quenched to room temperature by cold water allowing precipitation of DMT as well as dimers and trimers of the polyester. The liquid fraction was separated from the solid fraction by filtration. 4.61 g of DMT was extracted from the solid fraction by methanol. Methanol and ethylene glycol were recovered by distillation of the liquid fraction.

Example 4

(21) A mixture of 6 g of PET fiber soaked in 60 ml methanol and 0.12 g of a 1CaO-4MgO-1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heated to and maintained at 165° C. during the depolymerization. After 2 h, the autoclave was quenched to room temperature by cold water. The reaction mixture was put in freezer for 1 h in order to further precipitate DMT as well as dimers and trimers of the polyester. The liquid fraction was separated from the solid fraction by filtration. 5.31 g of DMT was extracted from the solid fraction by methanol. The methanol and ethylene glycol was recovered by distillation.

Example 5

(22) A mixture of 8 g of PET textile waste with different colors soaked in 60 ml methanol and 0.12 g of a 1CaO-4MgO-1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heated to and maintained at 165° C. during the depolymerization. After 2 h, the autoclave was quenched to room temperature by cold water. The reaction mixture was put in freezer for 1 h to further precipitate DMT as well as dimers and trimers of the polyester. The liquid fraction was separated from the solid fraction by filtration. DMT was extracted from the solid fraction by methanol. The extracted DMT was further purified by distillation to generate a higher purity. The liquid fraction comprising methanol, ethylene glycol and dye was distilled.

Example 6

(23) A mixture of 6 g of PET textile waste with one color soaked in 60 ml methanol and 0.12 g of a 1CaO-4MgO-1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heated to and maintained at 165° C. during the depolymerization. After 2 h, the autoclave was quenched to room temperature by cold water. The reaction mixture was put in freezer for 1 h to further precipitate DMT as well as dimers and trimers of the polyester. The liquid fraction was separated from the solid fraction by filtration. DMT was extracted from the solid fraction by methanol. The extracted DMT was further purified by recrystallization to generate a higher purity. The liquid fraction comprising methanol, ethylene glycol and dye was distilled.

Example 7

(24) 10 g of white PET/cotton mixed textile waste with a weight ratio of 1:1 (PET to cotton) soaked in 100 ml methanol and 0.2 g of a 1CaO-4MgO-1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heated to and maintained at 165° C. during the depolymerization. After 2 h, the autoclave was quenched to room temperature by cold water allowing for precipitation of DMT as well as dimers and trimers of the polyester. The liquid fraction was separated from the solid fraction by filtration. Here, the solid fraction mainly contains DMT and cotton. DMT was extracted from solid fraction by methanol. The remaining cotton was then dried at 35° C. overnight. The dried cotton can be reused through a wet-spinning process to produce regenerated cellulose fiber. Table 2 shows the mechanical properties of regenerated cotton fiber made from the recovered cotton. The methanol and ethylene glycol in liquid phase was recovered by distillation.

(25) Table 2 shows mechanical properties of regenerated cotton fiber produced through a lyocell spinning process.

(26) TABLE-US-00002 Dry Wet measurement measurement Titer, dtex 8.63 8.52 Tenacity,cN/dtex 3.68 2.93

Example 8

(27) A mixture of 4.8 g PET fiber mixed with 1.2 g spandex fiber soaked in 60 ml methanol and 0.2 g of a 1CaO-4MgO-1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heated to and maintained at 165° C. during the depolymerization. After 2 h, the autoclave was quenched to room temperature by cold water allowing precipitation of DMT as well as dimers and trimers of the polyester. The liquid fraction was separated from the solid fraction by filtration. Here, the solid fraction mainly contains DMT and depolymerized spandex fraction which is not soluble in methanol. DMT was extracted from the solid fraction by methanol and then purified by a distillation to generate higher purity. The liquid fraction comprising methanol, ethylene glycol and polyether from depolymerized spandex was separated by distillation.

Example 9

(28) 6 g of PET fiber, 30 ml of ethanolamine and 0.12 g of 1CaO.4MgO.1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heat up to 115° C. and kept it at 115° C. during the depolymerization. After 2 h, the autoclave was quenched to room temperature by cold water. The reaction products in the reactor were mixed with 150 ml of hot deionised water. The obtained slurry from reactor was heated up to the boiling point and then filtered immediately. The filtrate from filtration was kept in 4° C. overnight. During the storage time, the bis(2-hydroxyethyl) terephthalamide (BHETA) crystallized in the filtrate. The PET was completely depolymerized and around 5.6 g of BHETA was obtained.

Example 10

(29) 6 g of Polylactic acid (PLA) pellets, 60 ml of methanol and 0.12 g of 1CaO.4MgO.1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heat up to 175° C. and kept it at 175° C. during the depolymerization. After 2 h, the autoclave was quenched to room temperature by cold water. The reaction mixture was separated by filtration. The PLA was completely depolymerized. The filtrate from filtration was distilled to remove methanol. After distillation, 4.25 g of methyl lactate was obtained.

Example 11

(30) 6 g of Polytrimethylene terephthalate (PTT) fiber, 60 ml of methanol and 0.12 g of 1CaO.4MgO.1CeO.sub.2 mixed oxide were put in an autoclave. The autoclave was heat up to 175° C. and kept it at 175° C. during the depolymerization. After 2 h, the autoclave was quenched to room temperature by cold water. The reaction mixture was separated by filtration. PTT was completely depolymerized and 2.6 g of DMT was extracted from solid fraction by methanol. The liquid fraction was distilled and got methanol and 1,3-Propanediol. The obtained methanol will be recycled.

(31) Table 3 shows the depolymerization efficiency and the yield of extracted DMT using different catalyst at different temperatures.

(32) TABLE-US-00003 Reaction temperature 80° C. CaO CaO.sup.−CeO.sub.2 Depolymerization  58.5% 43.6% efficiency Yield of Extracted DMT  51.8% 18.7% Reaction temperature 100° C. CaO.sup.−CeO.sub.2 1CaO.sup.−4MgO.sup.−1CeO.sub.2 Depolymerization  83.5% 46.6% efficiency Yield of Extracted DMT  67.8% 32.6% Reaction temperature 135°C CaO CaO.sup.−CeO.sub.2 1CaO.sup.−4MgO.sup.−1CeO.sub.2 Depolymerization 100%   100%   100%   efficiency Yield of Extracted DMT  68.8%  63.8%  76.8% Reaction temperature 165°C CaO CaO.sup.−CeO.sub.2 1CaO.sup.−4MgO.sup.−1CeO.sub.2 Depolymerization 100%   100%   100%   efficiency Yield of Extracted DMT  75.8%  79.8%  88.5%