Process for recycling polyethylene terephthalate determined by intrinsic viscosity of polyethylene terephthalate

Abstract

One aspect is a method for producing a first intermediate product. A feedstock is provided that comprises a first polyester. The feedstock is contacted with a first amount of a first organic compound in a volume section V.sub.1 to obtain a first initial mixture. The first amount is in the form of a liquid. The first polyester is contacted with a further organic compound in a volume section V.sub.3 to obtain a further initial mixture. A weight average molar mass of the first polyester is reduced in the volume section V.sub.3 to obtain a first intermediate mixture. The first intermediate mixture comprises a first intermediate product and the further organic compound. The first polyester is transported in a first direction that is at least partially opposite the direction of gravity when the first polyester has an intrinsic viscosity that is larger than or equal to Y.sub.IV,1, where Y.sub.IV,1 is 0.10 dL/g, and in further direction that is at least partially along the direction of gravity when the first polyester has an intrinsic viscosity that is less than or equal to Y.sub.IV,2, where Y.sub.IV,2 is 0.09 dL/g.

Claims

1. A method for producing a first intermediate product, comprising the steps of a. providing a feedstock that comprises a first polyester; b. contacting the feedstock with a first amount of a first organic compound in a volume section V.sub.1 to obtain a first initial mixture, wherein the first amount is in the form of a liquid and wherein the intrinsic viscosity of the first polyester in the volume section V.sub.1 varies by less than 15%; c. transporting the first polyester to a volume section V.sub.2 from the volume section V.sub.1; d. contacting the first polyester with a further amount of the first organic compound in the volume section V.sub.2; e. reducing an intrinsic viscosity of the first polyester in the volume section V.sub.2, wherein after the reduction step has been completed in the volume section V.sub.2, the first polyester has an intrinsic viscosity in the range of 0.10 dL/g to 0.45 dL/g; f. transporting the first polyester to a volume section V.sub.3; g. contacting the first polyester with a further organic compound in the volume section V.sub.3 to obtain a further initial mixture; h. reducing a weight average molar mass of the first polyester in the volume section V.sub.3 to obtain a first intermediate mixture, wherein the first intermediate mixture comprises i. a first intermediate product that has an intrinsic viscosity in the range of 0.010 dL/g to 0.090 dL/g, ii. the further organic compound; wherein the first polyester is transported I./ in a first direction that is at least partially opposite the direction of gravity when the first polyester has an intrinsic viscosity that is larger than or equal to Y.sub.IV,1, where Y.sub.IV,1 is 0.10 dL/g; II./ in further direction that is at least partially along the direction of gravity when the first polyester has an intrinsic viscosity that is less than or equal to Y.sub.IV,2, where Y.sub.IV,2 is 0.09 dL/g; and III./ the transport of the first polyester along the first direction comprises transport from the volume section V.sub.1 to the volume section V and transport through the volume section V.sub.2, with the intrinsic viscosity determined according to the method described herein.

2. The method according to claim 1, wherein the first polyester is selected from the group consisting of a polyethylene terephthalate, a polybutylene terephthalate, a polylactide, a polytrimethylene terephthalate, a polyethylene naphthalate, a polycarbonate, a polyester carbonate, a polyarylate, a polyester resin, and a combination of two or more thereof.

3. The method according to claim 1, wherein the first organic compound has at least one or all of the following properties: a. comprises at least two hydroxyl groups; b. a molar mass of at least 60 g/mol; c. a boiling point of at least 192 C.

4. The method according to claim 1, wherein the first polyester in the volume section V.sub.1 has an intrinsic viscosity in the range of 0.50 dL/g to 1.00 dL/g, with the intrinsic viscosity determined according to the method described herein.

5. The method according to claim 1, wherein the method further comprises the step of reducing the following in the volume section V.sub.2: a. the weight average molar mass of the first polyester.

6. The method according to claim 5, wherein after the reduction step has been completed in the volume section V.sub.2, the first polyester has the following property: a weight average molar mass in the range of 3 000 Da to 7 500 Da with the weight average molar mass determined according to the method described herein.

7. The method according to claim 1, wherein the further organic compound has at least one or all of the following properties: a. comprises at least two hydroxyl groups; b. a molar mass of at least 60 g/mol; c. a boiling point of at least 192 C.

8. The method according to claim 1, wherein at least 40 wt-% of the first intermediate product is in the form of oligomers that have in the range of 2 to 35 repeating units, with the wt-% determined according to the method described herein.

Description

FIGURES

List of Figures

(1) The figures serve to exemplify the present invention, and should not be viewed as limiting the invention. Furthermore, the figures are not drawn to scale.

(2) FIGS. 1A to 1C: schematic illustration of an assembly and a method, according to the invention, for producing a first intermediate product and a further polyester.

(3) FIGS. 2A and 2B: schematic illustration of the angle between the even-further direction and a horizontal plane.

(4) FIG. 3: flow diagram showing the steps of an embodiment of a method, according to the invention, for producing a first intermediate product.

(5) FIG. 4: flow diagram showing the steps of an embodiment of a method, according to the invention, for producing a further intermediate product.

(6) FIGS. 5A and 5B: orientation of a direction with respect to gravity.

(7) FIGS. 6A to 6C: calibration plots used in the method for measuring molar mass.

(8) FIG. 7: scanning electron microscope image of a PET flake showing impurities on the surface of the PET flake.

(9) FIG. 8: graph showing the pore diameter distribution of the first particulated material.

(10) FIG. 9: illustration of the test method for determining the mass ratio of the feedstock, more preferably the first polyester, to the first organic compound in the volume section V.sub.1.

DESCRIPTION OF FIGURES

(11) In the figure descriptions, reference is made to a feedstock that comprises PET flakes which are obtained by the shredding of PET plastic bottles. Additionally or alternatively, the feedstock may comprise textile fragments and/or threads that are obtained by the shredding of textiles. Therefore, in the figure descriptions, the term PET flakes should preferably be understood as collectively referring to PET flakes obtained from the shredding of bottles and/or the textile fragments and/or threads obtained from shredding textiles.

(12) FIG. 1 is a schematic illustration of an assembly and a method, according to the invention, for producing a first intermediate product and a further polyester, such as PET. More specifically, FIG. 1 shows an assembly and method for recycling used PET.

(13) FIG. 1A shows a cross-section of a first part of the assembly, viewed from the side. A feedstock 101, comprising PET flakes (a first polyester in the form of a plurality of fragments), is provided. Residual impurities such as glue, polyvinyl chloride (PVC) labels, food preservatives, and flavouring agents, adhere to the surfaces of the PET flakes. The feedstock may also contain other impurities such as sand. The PET flakes are obtained by shredding PET plastic bottles that were used for beverages. The feedstock 101 is placed in a hopper 102. The feedstock 101 is transported from the hopper 102 to a volume section V.sub.1 103. The transportation of the feedstock 101 can be performed using, e.g., conveying screws, gravity, or a combination thereof. The volume section V.sub.1 103 can be e.g., a receptacle, a tank, or a reactor, such as a washing reactor.

(14) Liquid MEG (a first amount of a first organic compound) is added to the volume section V.sub.1 103 via inlet 104 and mixed (contacted) with the PET flakes and impurities making up the feedstock 101 to obtain a first initial mixture 105 that comprises the PET flakes and the liquid MEG. The first initial mixture 105 is agitated (the agitation means is not shown) to improve the mixing of the PET flakes and MEG. The agitation is performed using mechanical means. The MEG can remove impurities from the surfaces of the PET flakes. This is partly due to the fact that MEG is a powerful solvent and at moderate temperatures its ability to remove organic contaminants is enhanced. Agitating the first initial mixture 105 also at least partly enables the removal of glue from the surfaces of the PET flakes by friction between the PET flakes.

(15) At least a fraction of the impurities, e.g., fragments of bottle caps which comprise polyolefins, float on a surface 106 of the first initial mixture 105. These floating impurities can be removed by using, e.g., skimming or filtration. The impurities are removed from the volume section V.sub.1 103 via the outlet 123. By contrast, the PET flakes in the first initial mixture 105 sink to a bottom 107 of the volume section V.sub.1 103.

(16) The PET flakes, as well as some of the MEG in the first initial mixture 105, are transported to a volume section V.sub.2 108 that is partially filled with MEG. The transport is performed using conveying screw 109 (an Archimedean screw) and a siphon (not shown) that is in fluid communication with the conveying screw 109 and the volume section V.sub.2 108. Further means of transportation, such as additional conveying screws or pumps, can also be used, and are not shown. Furthermore, the volume section V.sub.2 108 is in fluid communication with the volume section V.sub.1 103. The volume section V.sub.2 108 can be e.g., a receptacle, a tank, or a reactor, such as a pre-glycolysis reactor. The conveying screw 109 is arranged such that the PET flakes that are transported to the volume section V.sub.2 108 are transported along a direction 110 (an even-further direction) that is at least partially opposite the direction of gravity 161.

(17) The PET flakes enter the volume section V.sub.2 108 via an inlet of a first kind 115. In FIG. 1A, the inlet of the first kind 115 is an opening in the volume section V.sub.2 108. In addition, MEG (a further amount of the first organic compound) is injected into the volume section V.sub.2 108. A first fraction of the MEG is injected in the form of a vapour via an inlet of a further kind 116. The first fraction may possibly include MEG that was in vapour form, but which has condensed prior to being injected into the volume section V.sub.2 108. The inlet of the further kind 116 is a nozzle that is adapted and arranged to inject the MEG vapour into the volume section V.sub.2 108 under pressure. Although only one inlet of the further kind 116 is shown, it is also possible that there are more than one inlet of the further kind 116. A further fraction of the MEG is injected in the form of a liquid via an inlet of an even-further kind 117. The inlet of the even-further kind 117 is a nozzle that is adapted and arranged to spray the liquid MEG into the volume section V.sub.2 108. The PET flakes in volume section V.sub.2 108 are partially depolymerised (reducing a weight average molar mass) via glycolysis, thereby reducing the weight average molar mass of the PET flakes in the volume section V.sub.2. Part of the PET flakes may be depolymerised to oligomers in the volume section V.sub.2.

(18) A screw conveyor (not shown) transports the PET flakes (and the PET oligomers, if present) in the volume section V.sub.2 108 in a transport direction 118 that is upward. The vapour MEG that enters the volume section V.sub.2 108, via the inlet of the further kind 116, also flows in an upward direction, i.e., along the transport direction 118. By contrast, the liquid MEG that enters the volume section V.sub.2 108, via the inlet of the even-further kind 117, flows in a downward direction, i.e., opposite the transport direction 118.

(19) The liquid MEG in the volume section V.sub.2 108 comprises liquid MEG that was transported from the volume section V.sub.1 103, liquid MEG that was injected via the inlet of the even-further kind 117, and any MEG vapour (injected via the inlet of the further kind 116) that has condensed. The liquid MEG does not completely fill the volume section V.sub.2 108. The surface (or level) of the liquid MEG therefore forms a boundary 119 that divides the volume section V.sub.2 108 into a first zone 120 and a further zone 121. The further zone 121 is downstream the first zone 120.

(20) The first zone 120 is filled with an even-further initial mixture, which comprises a mixture of PET flakes (and PET oligomers, if present) that are submerged in MEG. The further zone 121 comprises PET flakes and any liquid MEG that adheres to surfaces of the PET flakes, as well as MEG vapour. The further zone 121 may also comprise PET oligomers.

(21) As shown in FIG. 1A, a level 111 of MEG in the volume section V.sub.1 103 is below a level of MEG 113 in the volume section V.sub.2 108. FIG. 1A further shows that the MEG levels 111 and 113 are measured from the ground 114 (e.g., a floor of the recycling plant) to the surfaces of the liquid MEG in the volume section V.sub.1 103 and V.sub.2 108. As a result of this difference in the MEG levels 111 and 113, a fraction of the liquid MEG in the volume section V.sub.2 108 flows back to the volume section V.sub.1 103 via the conveying screw 109. Floatable impurities that were not removed in the volume section V.sub.1 103, and which were transported to the volume section V.sub.2 108 (along with the transport of the PET flakes), can thus be transported back to the volume section V.sub.1 103. The PET flakes with MEG that is adhering to their surfaces (and PET oligomers, if present) exit the volume section V.sub.2 108 via an outlet 122.

(22) FIG. 1B shows a cross-section of a further part of the assembly, viewed from the side. The PET flakes (and PET oligomers, if present) that exit via outlet 122 are transported to a volume section V.sub.3 124, which is a reactor (e.g., a glycolysis reactor). The volume section V.sub.3 124 is in fluid communication with the volume section V.sub.2 108. The PET flakes (and PET oligomers, if present) enter the volume section V.sub.3 124 via the inlet 125, and flow through the volume section V.sub.3 124 as indicated by the arrow 136. The inlet 125 of the volume section V.sub.3 124 is also below the outlet 122 of the volume section V.sub.2 108. In other words, when the PET flakes (and PET oligomers, if present) are transported from the volume section V.sub.2 108 to the volume section V.sub.3 124, the PET flakes (and PET oligomers, if present) are transported at least partially along the direction of gravity.

(23) The volume section V.sub.3 124 is fed with MEG (a further organic compound) via an inlet 143. The mixing of the PET with MEG (fed to the volume section V.sub.3) leads to the obtaining of a further initial mixture that comprises the PET flakes (and PET oligomers, if present) and MEG. The MEG in the further initial mixture causes the partly depolymerised PET flakes (and PET oligomers, if present) to undergo further glycolysis (reducing a weight average molar mass of the first polyester) as the further initial mixture flows through the volume section V.sub.3 124. A first intermediate mixture is thereby obtained. A transport pipe 144, in fluid communication with an outlet 126, is located inside the volume section V.sub.3 124. The first intermediate mixture exits the volume section V.sub.3 124 via the transport pipe 144 and the outlet 126. The first intermediate mixture that exits the outlet 126 of the volume section V.sub.3 124 comprises free MEG and a first intermediate product (comprising BHET and PET oligomers). The oligomers are polymers with more than one repeating unit (e.g., dimers, trimers, and oligomers with more than three repeating units). Some PET flakes which are not depolymerised to oligomers or BHET may also be present in the first intermediate mixture.

(24) As shown by the arrows in FIG. 1B, after exiting the volume section V.sub.3 124 via an outlet 126, the first intermediate mixture is transported to a volume section V.sub.4 127, which is in fluid communication with the volume section V.sub.3 124. The volume section V.sub.4 127 can be e.g., a receptacle, or a tank, such as a stirred tank. The first intermediate mixture enters the volume section V.sub.4 127 via an inlet 128. In the volume section V.sub.4 127 the first intermediate mixture is mixed with diatomaceous earth (first particulated material). The first intermediate mixture in the volume section V.sub.4 127 is agitated in order to improve the mixing of the first intermediate mixture and the diatomaceous earth.

(25) As shown by the arrows in FIG. 1B, the first intermediate mixture, which comprises the diatomaceous earth, exits the volume section V.sub.4 127 via an outlet 129, and is transported to a vertical leaf filter 130 (filtering means), which is in fluid communication with the volume section V.sub.4 127. The first intermediate mixture, which comprises the diatomaceous earth, enters the vertical leaf filter 130 via an inlet 131. The first intermediate mixture flows through the leaf filter 130 and is re-circulated (not shown) between the leaf filter 130 and the volume section V.sub.4 127, thereby allowing the individual filters of the leaf filter 130 to be coated with the diatomaceous earth. Initially the filtrate (the intermediate mixture) will be turbid. However, if the individual filters have been sufficiently coated, the filtrate will become clear. Once the filtrate has become clear, the intermediate mixture is allowed to exit the vertical leaf filter 130 via an outlet 132. The vertical leaf filter 130 filters out the diatomaceous earth and other particulated material (i.e., impurities) in the first intermediate mixture, as well as any PET flakes that have not been depolymerised to oligomers or BHET. The first intermediate mixture which exits the vertical leaf filter 130 via outlet 132 has only trace amounts of impurities and diatomaceous earth.

(26) As shown by the arrows in FIG. 1B, the first intermediate mixture that exits the vertical leaf filter 130, via the outlet 132, is transported to a volume section V.sub.5 133, which is in fluid communication with the vertical leaf filter 130. The first intermediate mixture enters the volume section V.sub.5 133 via an inlet 134. The volume section V.sub.5 133 can be e.g., a receptacle, or a tank, such as a rectification tank. The volume section V.sub.5 133 is used to determine and correct the colour of the first intermediate mixture. If necessary, at least one colouring agent is added to the first intermediate mixture in the volume section V.sub.5 133. If at least one colouring agent is added to the first intermediate mixture, the first intermediate mixture is agitated in order to better mix the first intermediate mixture with the at least one colouring agent. The first intermediate mixture, which possibly comprises the at least one colouring agent, exits the volume section V.sub.5 133 via an outlet 135.

(27) FIG. 1C shows a cross-section of a further part of the assembly, viewed from the side. The first intermediate mixture, that possibly comprises the at least one colouring agent, is transported from the outlet 135 to a volume section V.sub.6 137, which is in fluid communication with the volume section V.sub.5 133. The first intermediate mixture enters the volume section V.sub.6 137 via an inlet 138. Prior to entering the volume section V.sub.6 137, a catalyst and stabiliser may be added to the first intermediate mixture. The PET flakes in the feedstock are obtained by shredding used PET bottles. During the production of the PET used for the bottles, a catalyst is often added. Therefore, the PET flakes of the feedstock very often already contain a catalyst, and it may this not be necessary to add further catalyst during the recycling process. The volume section V.sub.6 137 is a pre-polymerisation reactor that polymerises the oligomers and BHET (increasing the weight average molar mass of the first intermediate product) in the first intermediate mixture to obtain polymers (the further intermediate product). A further intermediate mixture comprising polymers (i.e., PET polymers) and MEG is thereby obtained. In the volume section V.sub.6 137, up to 95% of excess MEG is evaporated under vacuum conditions. The excess MEG comprises both free MEG that was transported into the volume section V.sub.6, as well as bound MEG that was released by the polymerisation. The further intermediate mixture exits the volume section V.sub.6 137 via an outlet 139.

(28) As shown by the arrows in FIG. 1C, the further intermediate mixture that exits the volume section V.sub.6 137, via the outlet 139, is transported to a volume section V.sub.7 140, which is in fluid communication with the volume section V.sub.6 137. The further intermediate mixture enters the volume section V.sub.7 140 via an inlet 141. The volume section V.sub.7 140 is a polymerisation reactor, such as a disc-cage reactor, that is used to further increase the weight average molar mass (via polymerisation) of the polymers, and any remaining oligomers, in the further intermediate mixture. In addition, any remaining MEG in the further intermediate mixture is also evaporated under vacuum conditions in the volume section V.sub.7 140. The remaining MEG comprises both free MEG that was transported into the volume section V.sub.7, as well as bound MEG that was released by the polymerisation. The further intermediate mixture, comprising the further intermediate product, exits the volume section V.sub.7 140 via the outlet 142. The further intermediate product (i.e., recycled PET) that is obtained, following the completion of the polymerisation in the volume section V.sub.7 140, is in the form of a hot melt. The hot melt can be used to produce yarn (an example of a product), as well as granules, commonly referred to as chips. The chips can be obtained by extruding and cooling the hot melt. The further intermediate product is thus a further polyester.

(29) Although not shown, the transport of the first intermediate mixture between volume sections V.sub.3, V.sub.4, V.sub.5, V.sub.6, and the vertical leaf filter is achieved by pumping the first intermediate mixture. This also holds for the further intermediate mixture, i.e., the further intermediate mixture is pumped between the volume sections V.sub.6 and V.sub.7.

(30) (Not shown in the figures): the further intermediate product can subsequently be used to produce further products, such as yarn for textiles. For example, the further intermediate product, in molten form, is pumped through spin-packs. A spin-pack is conceptually similar to a domestic shower head. The number of apertures in the spin-pack determine the filament count of the yarn that is produced. The molten, further intermediate product streams that exit the spin-packs are cooled, and coalesce into a single yarn. The single yarn is then wound onto bobbins. The further intermediate product is also obtained without using virgin PET. E.g., virgin PET monomers and oligomers are not mixed with the first intermediate product prior to polymerisation. E.g., virgin PET polymers are also not mixed with the further intermediate product.

(31) Returning to FIGS. 1A and 1B: these figures show that the PET flakes are transported in a first direction that is at least partially opposite the direction of gravity when the PET flakes have an intrinsic viscosity that is larger than or equal to a value Y.sub.IV,1, and transported in further direction that is at least partially along the direction of gravity when the PET flakes have an intrinsic viscosity that is less than a value Y.sub.IV,2 (here Y.sub.IV,1 and Y.sub.IV,2 represents variables, with Y.sub.IV,1>Y.sub.IV,2).

(32) As shown in FIG. 1A, after being contacted with MEG in the volume section V.sub.1 103, the PET flakes are transported to volume section V.sub.2 108 along the direction 110, which is at least partially opposite the direction of gravity 161. In the volume section V.sub.2 108 the PET flakes are transported in the transport direction 118, which is directed opposite the direction of gravity 161, i.e., the average transport direction of the PET flakes in the volume section V.sub.2 108 is upward. In the context of FIG. 1A, the first direction can be defined as the direction from the bottom 107 of the volume section V.sub.1 103 to the outlet 122 of the volume section V.sub.2 108. The preceding should, however, not be seen as the general definition of the first direction. The transporting of PET (e.g., in the form of flakes) in the first direction should generally be understood to mean that PET fragments (e.g., in the form of flakes) is transported at least partially against the direction of gravity as long as the intrinsic viscosity of the PET fragments is larger than or equal to a value Y.sub.IV,1.

(33) As shown in FIG. 1B, when the PET flakes enter the volume section V.sub.3 124, via the inlet 125, the PET flakes are transported along the direction 136, which is directed along the direction of gravity 161. In the context of FIG. 1B, the direction 136 defines the further direction. The preceding should, however, not be seen as the general definition of the further direction. The transporting of PET (e.g., in the form of flakes) in the further direction should generally be understood to mean that PET fragments (e.g., in the form of flakes) is transported at least partially along the direction of gravity as long as the intrinsic viscosity of the PET fragments is less than or equal to a value Y.sub.IV,2. However, once the PET has been depolymerised, the PET oligomers and/or monomers can be transported either against gravity, or along the direction of gravity.

(34) FIG. 2 is a schematic illustration 200 showing how the angle between the even-further direction 210 and a horizontal plane 214 is measured. The horizontal plane 214 is perpendicular to the direction of gravity 261. The angle is measured as the smallest angle between the even-further direction 210 and the horizontal plane 214. This is illustrated in FIG. 2A and FIG. 2B. In each of these figures, the angle 262 is defined as the angle between the even-further direction 210 and the horizontal plane 214, and not the angle to 263.

(35) FIG. 3 is flow diagram showing the steps of an embodiment of a method 300, according to the invention, for producing a first intermediate product. Optional steps in FIG. 3 are indicated with a dashed box. The description of the method steps are given below.

(36) TABLE-US-00005 Step: Description: 301 Providing a feedstock that comprises a first polyester. 302 Contacting the feedstock with a first amount of a first organic compound in a volume section V.sub.1 to obtain a first initial mixture, wherein the first amount is in the form of a liquid. 303 Optionally, transporting the first polyester to a volume section V.sub.2 from the volume section V.sub.1. 304 Optionally, contacting the first polyester with a further amount of the first organic compound in the volume section V.sub.2. 305 Optionally, reducing a weight average molar mass of the first polyester in the volume section V.sub.2. 306 Optionally, transporting the first polyester to a volume section V.sub.3 from the volume section V.sub.2. 307 Contacting the first polyester with a further organic compound, in the volume section V.sub.3, to obtain a further initial mixture. 308 Reducing the weight average molar mass of the first polyester, in the volume section V.sub.3, to obtain a first intermediate mixture, wherein the first intermediate mixture comprises a first intermediate product and the further organic compound. 309 Optionally, transporting the first intermediate mixture to a volume section V.sub.4 from the volume section V.sub.3. 310 Optionally, adding first particulated material to the first intermediate mixture in the volume section V.sub.4. 311 Optionally, transporting the first intermediate mixture to a filtering means from the volume section V.sub.4. 312 Optionally, at least partially removing the following, using the filtering means, from the first intermediate mixture: the first particulated material, at least one impurity. 313 Optionally, transporting the first intermediate mixture to a volume section V.sub.5 from the filtering means. 314 Optionally, adding at least one colouring agent to the first intermediate mixture in the volume section V.sub.5.

(37) In FIG. 3, the first polyester is transported in a first direction that is at least partially opposite the direction of gravity when the first polyester has an intrinsic viscosity that is larger than or equal to Y.sub.IV,1, where Y.sub.IV,1 is 0.10 dL/g; and in further direction that is at least partially along the direction of gravity when the first polyester has an intrinsic viscosity that is less than or equal to Y.sub.IV,2, where Y.sub.IV,2 is 0.09 dL/g. Here the transport can be between two different volume section, through a volume section, or both. For example, the first direction is preferably from the volume section V.sub.1 to the volume section V.sub.2, and through the volume section V.sub.2. For example, the further direction is through the volume section V.sub.3.

(38) In an aspect of the embodiment in FIG. 3, it is preferred that steps 304 and 305 are performed at least partially simultaneously. In an aspect of the embodiment in FIG. 3, it is preferred that steps 307 and 308 are performed at least partially simultaneously.

(39) FIG. 4 is flow diagram showing the steps of an embodiment of a method 400, according to the invention, for producing a further intermediate product. Optional steps in FIG. 4 are indicated with a dashed box. The description of the method steps are given below.

(40) TABLE-US-00006 Step: Description: 401 Providing a first intermediate mixture that comprises a first intermediate product. The first intermediate product and the first intermediate mixture are obtained from the method of FIG. 3. The first intermediate mixture is provided in a volume section V.sub.6 by transporting the first intermediate mixture from the filtering means to the volume section V.sub.6. 402 Increasing the weight average molar mass of the first intermediate product in the first intermediate mixture, in the volume section V.sub.6, to obtain a further intermediate mixture that comprises a further intermediate product. The further intermediate mixture further comprises at least one or all of the following: the first organic compound, the further organic compound. 403 Optionally, transporting the further intermediate mixture to a volume section V.sub.7. 404 Optionally, further increasing the weight average molar mass of the further intermediate product in the further intermediate mixture in the volume section V.sub.7. 405 Optionally, at least partially removing at least one organic compound, e.g., the first organic compound or the further organic compound, from the further intermediate mixture. This step can be performed at least partially simultaneously with at least one or all of the steps 402 and 404.

(41) In an aspect of the embodiment in FIG. 4, it is preferred that step 405 is performed at least partially simultaneously with at least one or all of the steps 402 and 405. In a preferred embodiment of the invention, a method, according to the invention, for producing a further intermediate product comprises the steps 301 to 314, as well as the steps 401 to 405. E.g., the steps of FIG. 3 can be combined with the steps of FIG. 4, where the steps of FIG. 3 are performed prior to the steps of FIG. 4. In such a combination, optional steps described in FIGS. 3 and 4 remain optional.

(42) FIG. 5 shows how an orientation of a direction with respect to gravity is defined. FIG. 5A shows a direction 570 that is at least partially opposite the direction of gravity 561. The direction 570 can be decomposed into three components. The direction 570 has a component 571 parallel to the direction of gravity 561, and a component 572 perpendicular to the direction of gravity (the other component perpendicular to the direction of gravity is not shown). The direction of the component 571 is opposite the direction of gravity.

(43) FIG. 5B shows a direction 570 that is at least partially along the direction of gravity 561. Similar to FIG. 5A, the direction 570 has a component 571 parallel to the direction of gravity 561, and a component 572 perpendicular to direction of gravity. However, in contrast to FIG. 5A, the direction of the component 571 in FIG. 5B is along the direction of gravity.

(44) An SEM image of a PET flake is shown in FIG. 7. The impurities on the surface of the PET flakes can be identified as the white particles. Three impurities, 781a, 781b, and 781c, are indicated in FIG. 7. FIG. 7 is an example of the SEM image to determine the particle count per area of the at least one impurity.

(45) FIG. 8 shows the distribution of the pore diameter of the first particulated material. As can be seen from FIG. 8, the first particulated material has modes at approximately 17 100 nm, 15 100 nm, 12 300 nm, 10 600 nm, and 9 300 nm. A mode is where the quantity dV/d log D has a maximum value (either a local maximum or a global maximum). dV is the differential volume and d log D is the differential of the logarithm of the pore diameter of the first particulated material. A primary mode refers to the global maximum of dV/d log D. A secondary mode refers to the second largest maximum of dV/d log D. FIG. 8 also shows the cumulative pore volume for the first particulated material.

(46) FIG. 9 is an illustration of the test method for determining the mass ratio of the feedstock, more preferably the first polyester, to the first organic compound in the volume section V.sub.1. FIG. 9 shows an enlargement of the cross-section of the volume section V.sub.1 103 of FIG. 1A (for illustration purposes the dimension of the volume section V.sub.1 103 in FIG. 9 has been changed compared to the dimensions of the volume section V.sub.1 in FIG. 1A).

(47) The first initial mixture 105 in the volume section V.sub.1 is divided into a number of height sections H as shown in FIG. 9. The first height section H1 is bordered by the bottom 107 of the volume section V.sub.1 103 and a height A1, the second height section H2 is bordered by the heights A1 and A2, etc. The last height section H6 is bordered by the height A5 and the surface 106 of the first initial mixture 105. While FIG. 9 shows 6 height sections H, the number of height sections is determined by the fill height of the first initial mixture 105 in the volume section V.sub.1 103. The height sections should each have a height of 20 cm, with the exception of the last height section bordered by the surface of the first initial mixture (height section H6 in FIG. 9). E.g., if the fill height of the first initial mixture in the volume section V.sub.1 is 150 cm, then the first initial mixture is divided into 8 height sections, with 7 height section have a height of 20 cm, and the last height section having a height of 10 cm. The height of the first height section H1, bordered by the bottom 107, is measured from the lowest point of the bottom 107. 5 samples of the first initial mixture are taken in each height section. Each sample taken has a volume of 250 ml. All samples taken are then combined to obtain a collective sample. The mass ratio is determined using the collective sample.

(48) If the volume section V.sub.1 is agitated during the normal operation of the PET recycling process, the samples should be taken while the volume section V.sub.1 is being agitated. In this case, the 5 samples taken in a height section should be taken at the same position in the height section, with the taking of two subsequent samples being separated by a two-minute interval. This is illustrated in FIG. 9, where the 5 samples in the height section H1 are taken at position B1, with the samples taken at two-minute intervals. The position in a height section where the five samples are taken can be anywhere in the height section.

(49) If the agitation means is a physical agitation means (e.g., 164 in FIG. 9) which does not allow for the taking of samples below a certain height, the lowest height A.sub.min where it is possible to take a sample without interfering with the agitation means replaces the bottom 107 in the procedure above, i.e., the first height section is bordered by A.sub.min. The new height sections I, adjusted for the presence of the agitation means 164, are shown in FIG. 9. Similar to the height sections H, the height sections I also have a height of 20 cm, with the exception of the height section 15 bordered by the surface 106.

(50) If the volume section V.sub.1 is not agitated during the normal operation of the PET recycling process, the 5 samples taken in a height section should be taken at positions that are evenly spread out in a direction that is perpendicular to the height of the first initial mixture. This is shown as positions C.sub.1 to C.sub.5 in FIG. 9.

EXAMPLES

(51) The invention is illustrated further by way of examples. The invention is not restricted to the examples. In the tables given in the examples, the size of a technical effect is indicated by one or more or +. The scale, arranged from lowest to highest, is as follows: , , , +, ++, +++. A value of Ref indicates a reference value, i.e., the increase or decrease of a technical effect is relative to the Ref value. A value of O indicates no change with respect to the reference value. When a Ref value is used, the scale, arranged from lowest to highest, is as follows: , , , Ref, +, ++, +++.

(52) Basic Set-Up

(53) Unless specified otherwise, the basic set-up described below applies to all examples.

(54) A feedstock comprising PET flakes is provided. The PET flakes were obtained by processing (e.g., shredding) used PET bottles. The PET flakes subjected to the method steps as described in FIG. 1A. In other words, the PET flakes are transported through the volume sections V.sub.1 and V.sub.2, where the volume section V.sub.2 has a first zone and a further zone. In both the volume sections V.sub.1 and V.sub.2, the PET flakes are contacted with MEG. The following parameters are used for the volume section V.sub.1: a mass ratio of PET to MEG in the range of 0.06-0.25, a temperature in the range of 60 C. to 65 C., a pressure in the range of 98 kPa to 103 kPa, and a residence time in the range of 20 minutes to 30 minutes. The following parameters are used for the volume section V.sub.2: a mass ratio of PET to MEG at an inlet of the volume section V.sub.2 in the range of 0.3-0.5, a mass ratio of PET to MEG at an outlet of the volume section V.sub.2 in the range of 5-20, a temperature in the range of 60 C. to 200 C., an overpressure in the range of 4 kPa to 8 kPa, and a residence time in the range of 110 minutes to 150 minutes.

(55) As described in FIG. 1B, the PET flakes are subsequently transported from the volume section V.sub.2 to the volume section V.sub.3 (a glycolysis reactor). The PET flakes in the volume section V.sub.3 are also contacted with MEG. The following parameters are used for the glycolysis process in the volume section V.sub.3: a temperature in the range of 195 C. to 240 C., an overpressure in the range of 0.7 kPa to 0.9 kPa, and a residence time in the range of 250 minutes to 420 minutes.

(56) As a result of the depolymerisation (via glycolysis) in V.sub.3, a first intermediate mixture comprising BHET, PET oligomers and free MEG is obtained. The first intermediate mixture comprises a first intermediate product (BHET and PET oligomers) free MEG, and residual impurities (to be filtered out).

(57) As is also described in FIG. 1B, the intermediate product is transported from the volume section V.sub.3 to a volume section V.sub.4. The first intermediate mixture is agitated in the volume section V.sub.4 while first particulated material is added to the first intermediate mixture. The first intermediate mixture, now comprising the first particulated material, is transported from the volume section V.sub.4 to a filtering means, where the first intermediate mixture is subjected to a filtering step. This filtering step also includes the pre-coating step described in FIG. 1B. The filtered, first intermediate mixture is subsequently subjected to polymerisation as described in FIG. 1C. Recycled PET is thus obtained. The recycled PET is used to produce yarn.

Example 1

(58) The example was repeated using different set-ups, as shown in Table 1. Table 1 shows whether the PET flakes are transported along or against gravity when the PET flakes have an intrinsic viscosity that is 0.20 dL/g, and whether the PET flakes are transported along or against gravity when the PET flakes have an intrinsic viscosity that is 0.09 dL/g. Table 1 also shows the effects of transporting the PET flakes either against or along gravity depending on the intrinsic viscosity of the PET flakes.

(59) The PET flakes are transported against gravity when the PET flakes are transported from the volume section V.sub.1 to the volume section V.sub.2, as described in FIG. 1A. The PET flakes are also transported against gravity from a bottom to a top of the volume section V.sub.2. Once the PET flakes have entered the volume section V.sub.3, the PET flakes are transported along gravity, as described in FIG. 1B.

(60) When the PET flakes have an intrinsic viscosity that is less than 0.20 dL/g and more than 0.09 dL/g, the PET flakes are transported along the direction of gravity. This happens when the PET flakes are transported from the volume section V.sub.2 to the volume section V.sub.3.

(61) TABLE-US-00007 TABLE 1 Example 1.1 1.2 1.3 1.4 Set-up Intrinsic 0.20 Transport Against Along Against Along viscosity of PET 0.09 direction Against Along Along Against flakes [dL/g] Technical effects Concentration 0 ++ Ref ++ of impurities remaining after depolymerisation Embrittling ++ ++ of PET flakes Heating rate + 0 0 Energy More Less Ref Slightly required during less depolymerisation Transport + efficiency Yield of first 30-40 60-68 55-60 40-50 intermediate product (BHET and PET oligomers) [wt-%] Filter lifetime 150 75 132 110 [hours] Colour quality Satisfac- Not Good Not of recycled tory ac- ac- PET cept- cept- able able

(62) The technical effects described in Table 1 are as follows: Concentration of impurities remaining after depolymerisation: the concentration of impurities that are present in the first intermediate mixture that is obtained after depolymerisation, i.e., the mixture that exits the volume section V.sub.3. It is desired to decrease the concentration of impurities. Embrittling of PET flakes: the increase in the brittleness of the PET flakes during the residence of the PET flakes in the volume section V.sub.2. It is desired to increase the brittleness of the PET flakes. Heating rate: how effectively the PET flakes can be heating when the intrinsic viscosity of the PET flakes is larger than or equal to 0.5 dL/g. It is desired to increase the heating rate. Energy required during depolymerisation: the amount of energy required to depolymerise the PET flakes in the volume sections V.sub.2 and V.sub.3. It is desired to reduce the energy. Transport efficiency: how efficiently the PET flakes (in the feedstock and/or partially depolymerised PET flakes) can be transported through the recycling plant without a blockage occurring in a component (e.g., an Archimedean screw). It is desired to increase the transport efficiency and to reduce the occurrence of blockages. Yield of first intermediate product: the wt-% of BHET and PET oligomers that are obtained after depolymerisation in the volume section V.sub.3. The wt-% values are based on a total mass of the first intermediate mixture. It is desired to increase the yield. Filter lifetime: the number of hours that filters in the recycling plant can be used before requiring cleaning or exchange. This is, for example, the filters that are used to filter the first intermediate mixture that comprises the oligomers that are obtained from the depolymerised PET flakes. It is desired to increase the filter lifetime Colour quality of recycled PET: it is desired that the recycled PET melt obtained after polymerisation has been completed has the following Hunter Lab colour coordinates: an L value of at least 55, and a b value in the range of 2 to 4. Although colouring agents can be used during the recycling process to improve the colour coordinates, it is desired to reduce the amount of colouring agents used. Note that if the colour quality is poor, it is generally not possibly to improve the colour by adding colouring agents.

REFERENCE LIST

(63) 100 Assembly and method for producing a further polyester 101 Feedstock 102 Hopper 103 Volume section V.sub.1 104 Inlet of volume section V.sub.1 105 First initial mixture 106 Surface of the first initial mixture 107 Bottom of volume section V.sub.1 108 Volume section V.sub.2 109 Conveying screw 110 Even-further direction 111 Level H, of first organic compound 112 Bottom of volume section V.sub.2 113 Level H.sub.2 of first organic compound 114 Ground 115 Inlet of the first kind of volume section V.sub.2 116 Inlet of the further kind of volume section V.sub.2 117 Inlet of the even-further kind of volume section V.sub.2 118 Transport direction 119 Boundary 120 First zone 121 Further zone 122 Outlet of volume section V.sub.2 123 Outlet of volume section V.sub.1 124 Volume section V.sub.3 125 Inlet of volume section V.sub.3 126 Outlet of volume section V.sub.3 127 Volume section V.sub.4 128 Inlet of volume section V.sub.4 129 Outlet of volume section V.sub.4 130 Vertical leaf filter 131 Inlet of vertical leaf filter 132 Outlet of vertical leaf filter 133 Volume section V.sub.5 134 Inlet of volume section V.sub.5 135 Outlet of volume section V.sub.5 136 Direction of flow through volume section V.sub.3 137 Volume section V.sub.6 138 Inlet of volume section V.sub.6 139 Outlet of volume section V.sub.6 140 Volume section V.sub.7 141 Inlet of volume section V.sub.7 142 Outlet of volume section V.sub.7 143 Inlet of volume section V.sub.3 144 Transport pipe 161 Direction of gravity 200 Measuring angle between even-further direction and horizontal plane 210 Even-further direction 214 Horizontal plane 261 Direction of gravity 262 Angle defining orientation of even-further direction with respect to a horizontal plane 263 Incorrect angle 500 Orientation of a direction 561 Direction of gravity 570 Direction 571 Component parallel to gravity 572 Component perpendicular to gravity 700 SEM image used for determining particle count per area of the impurities 781 Impurities