Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/02—Separating plastics from other materials
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/06—Recovery or working-up of waste materials of polymers without chemical reactions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/04—Disintegrating plastics, e.g. by milling
  • B29B17/0412—Disintegrating plastics, e.g. by milling to large particles, e.g. beads, granules, flakes, slices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B2017/001—Pretreating the materials before recovery
  • B29B2017/0015—Washing, rinsing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/02—Separating plastics from other materials
  • B29B2017/0213—Specific separating techniques
  • B29B2017/0217—Mechanical separating techniques; devices therefor
  • B29B2017/0237—Mechanical separating techniques; devices therefor using density difference
  • B29B2017/0241—Mechanical separating techniques; devices therefor using density difference in gas, e.g. air flow
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
  • B29K2067/003—PET, i.e. poylethylene terephthalate
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/06—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
  • B29K2105/065—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts containing impurities
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/52—Mechanical processing of waste for the recovery of materials, e.g. crushing, shredding, separation or disassembly
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/62—Plastics recycling; Rubber recycling

Definitions

• the present invention relates to an improved process for the recycling of PET.
• DMT dimethyl terephthalate
• ethylene glycol ethylene glycol
• a typical physical PET recycling process includes washing PET bottles and containers, sorting the bottles and containers and removing any metal therefrom. The bottles and containers are then ground and washed before being dried and extruded and then pelletised.
• the migrating substances must either only be present in dietary concentration at very low levels, i.e. less than 0.5 ppb, or the level is less than 1% of the acceptable daily intake (ADI) for those substances.
• ADI acceptable daily intake
• Another consideration of a recycling process is the effective removal of surrogate contaminants, that is contaminants to which the PET container is exposed to as a result of consumer misuse, for example, the storage of petrol or oil in a bottle which originally stored beverages, say.
• surrogate contaminants that is contaminants to which the PET container is exposed to as a result of consumer misuse, for example, the storage of petrol or oil in a bottle which originally stored beverages, say.
• These surrogate chemicals are selected to represent the wide range of volatile and non- volatile, polar and non-polar materials that can be encountered in the consumer environment.
• an effective recycling process must remove such surrogate contaminants if the recycled material is intended for food contact.
• WO 01/21373 discloses a process for preparing food contact grade PET. The process involves sorting at least some of the non-PET materials from waste material, followed by dividing the PET material into flakes. The flakes are then washed in a hot aqueous medium containing alkaline materials and surfactants. Following washing, the flakes are dried such that absorbed contaminants are removed by heating and stirring the flakes under vacuum. The flakes are then melted, extruded and pelletised.
• WO 2005/037514 discloses a further process for recycling used PET bottles. The process involves washing and grinding the bottles into flakes, said flakes are then separated based upon their mass/density/wall thickness. Interestingly, WO 2005/037514 teaches that contamination is related to the thickness of the flakes, i.e. thicker flakes are more deeply contaminated. Thus, flakes are separated on the basis of their mass/density/wall thickness.
• a process for recycling PET from waste material comprising PET, said process comprising the following steps of: a) optionally washing said waste material; b) sorting at least some non-PET material from said waste material, where present; c) grinding the waste material to form flakes; d) optionally washing said flakes; e) sorting and separating said flakes on the basis of their surface area; f) heating the flakes in order to decontaminate the flakes; and g) melting the decontaminated flakes and extruding the melt.
• the process according to this aspect of the present invention may be used to prepare food grade PET from waste material comprising PET.
• the process of the present invention gives rise to a more efficient and cost effective process since only the flakes that are rapidly decontaminated need be used in the latter stages of the process.
• a further advantage of the process of the present invention is that solid stating is not required. By eliminating a separate solid stating step from the recycling significant capital costs savings are made and energy costs for operating the process are reduced.
• Solid stating is typically used as a way of advancing the intrinsic viscosity of PET resin. This is usually done with virgin resin as a normal way of converting fibre grade resin into bottle grade resin, and involves heating PET granules at elevated temperatures i.e. 200 °C in an anhydrous atmosphere, which may be air or an inert atmosphere. This is typically achieved in a separate step either in a rotating dryer or in a vertical column with control on the residence time which is typically related to the increment in IV that is being achieved by the resin.
• washing of the waste material prior to sorting may be performed using any suitable solvent. This initial washing step is often desirable in order to reduce contaminant levels.
• Preferred solvents include any of the following either alone or in combination: water, ionic or non-ionic detergents up to 0.2% by wt, dilute caustic soda up to 1.0 % by wt.
• non-PET material separated out from the remaining waste material typically includes labels and metal objects, such as caps, etc. It will be appreciated that the present invention may be carried out using pre-sorted waste from which at least some non-PET material has been removed (and which may optionally have been washed).
• the non-PET material is separated out by means well known to those skilled in the art. For example, sieving, air elutriation, sink-float separation, colour separation.
• the waste material is ground to form flakes.
• the flakes are ground such that they have an average size in the range of from 2mm to 20mm.
• the flakes have an average size in the range of from 4mm to
• the 'size' of a flake is intended to mean the size as measured across the widest part of the flake.
• the size distribution of the flakes may vary. Ideally, at least 80% ( ⁇ 10%) of the flakes fall within the above mentioned size ranges. It has been realised that upon grinding two types of flakes are produced. These flake types differ in respect of their surface area per unit mass.
• the thinner sections of the waste PET for example, walls of bottles, form flakes having a larger surface area than the thicker sections of the waste PET, for example neck and base regions of the bottles.
• larger surface area means flakes having a surface area to mass ratio of about 15mm 2 /g or greater. Therefore, flakes having a smaller surface area are those having a surface area to mass ratio less than about 15mm 2 /g.
• the thinner PET waste is generally more contaminated than the less abundant thicker neck and base sections.
• the waste PET material is ground such as to form discrete pieces or flakes.
• the grinding process produces two distinct types of flakes which differ in their surface area.
• the grinding step may be carried out by any of the techniques known in the art. For instance, grinding is generally performed by cutting the bottles against a fixed size aperture screen, for example 4 mm to 15 mm, with rotary blades. As the bottles are cut, the fragments pass through the screen. The thicker sections of the bottle such as the neck and base end up with generally these dimensions of screen size and thickness. Grinding in this manner ensures that flakes formed from the thinner wall sections have a larger surface area than those formed from the thicker base and neck sections. This is the key to the separation of the flakes which is discussed below.
• the flakes are optionally washed after grinding. This may be desirable to reduce surface contamination, such as inorganic deposits.
• the flakes are typically washed at temperatures above 80°C with 85-90°C being the preferred temperature.
• the flakes may be washed using any suitable solvent, such as water, an aqueous solution of caustic soda at 1 to 1.5% by wt, or an aqueous solution of an ionic or non ionic detergent at 0.1 to 0.5 % by wt.
• the flakes are preferably dried.
• the flakes may be dried by any conventional drying technique, for example using a fluidised bed drier, recirculating air drier or and desiccant drier. Suitable conditions used for the drying step are well known to those skilled in the art.
• a key step in the process of the present invention is the separation of the more contaminated flakes from the less contaminated flakes.
• the flakes having a larger surface area to mass ratio, which are more contaminated, are separated from the less contaminated flakes which have a smaller surface area to mass ratio.
• a destoner effectively separates heavier-than-product debris, such as glass, stones and metal from a large amount of lighter product.
• the principle is that an inclined plate is vibrated and under set pressure the lighter flakes move down the plate.
• the lighter flakes are the flakes having the larger surface area to mass ratio.
• separation is achieved by air classifiers.
• Air classifiers work by using the principle of terminal velocity for a specific product to classify and separate particles.
• the flakes having a larger surface area have a different terminal velocity from the flakes having a smaller surface area.
• By using multiple aspirators, and variable air flow rates appropriate separation can be achieved.
• the separation technique used in the present invention may include one or more passes. For example, each pass lifts approximately 75% of the flakes having a larger surface area. This leaves a balance of 25% of the flakes having a large surface area in the through stock. On a unit having two passes a second pass would also remove approximately 75% of the particles having a larger surface area (i.e. 75% of the remaining 25%), leaving 6.25% of the flakes having a larger surface area in the through stock. Therefore, a dual pass system has 93.75% efficiency.
• the efficiency of the separation process can be maximised by tailoring the separation conditions.
• the invention permits the selection of only the less contaminated PET flakes, i.e. those having a smaller surface area to mass ratio, for decontamination in the next step of the process.
• Heat treatment to decontaminate the flakes may be carried out at any suitable temperature.
• the heat treatment may be carried out at temperatures of 140 0 C or above. Higher temperatures are generally preferred, as the heating time is reduced as the temperature increases, which is economically beneficial. More favourable results are achieved at temperatures of 16O 0 C or above, preferably 17O 0 C or above, more preferably 180 0 C or above, and still more preferably 190 0 C or above.
• a temperature of about 200 0 C ( ⁇ 5°C, more preferably ⁇ 2°C) has been shown to be particularly suitable.
• the heating time varies depending upon the temperature of the heat treatment. At around 200 0 C, by way of example a heating time of about 4 hours has been found to give good results. As the temperature is reduced, the heating time should be increased accordingly.
• the flakes may be heated for about 8 hours, at around 180 0 C the flakes may be heated for about 16 hours, at around 170 0 C the flakes may be heated for about 32 hours, at around 160 0 C the flakes may be heated for about 32 hours, etc.
• the heating conditions may be routinely varied by the person skilled in the art.
• the process of the present invention preferably employs high temperature decontamination, which is preferably conducted in an inert atmosphere.
• the inert atmosphere protects the polymer, minimising degradation and discoloration of the polymer at high temperatures. It is especially desirable to employ an inert atmosphere at heating temperatures of 17O 0 C and or where there is prolonged heating.
• the inert atmosphere may be, for example, nitrogen or argon, and is preferably nitrogen.
• the inert atmosphere may take the form of a blanket covering the flakes, thereby preventing oxidation.
• decontamination conducted at about 200 0 C in an inert atmosphere reduces the contaminants in the flakes by approximately 99.8 to 99.9 %.
• these percentages differ depending upon the contaminant, but nevertheless demonstrate the efficiency of the process of the present invention.
• the flakes are melted and extruded into strands which are typically pelletised.
• a twin screw extruder may be used to extrude the flakes. Extrusion may take place at any suitable temperature, for example at a temperature within the range of from 280 0 C to 290 C. The extruder may be twin or triple vented. During extrusion, the melt may be filtered to remove residual particles having a diameter above 75 microns.
• the extrusion step avoids solid stating and it increases the intrinsic viscosity of the PET thereby eliminating the need to use rotary vacuum dryers which in turn reduces the capital cost of the process of the present invention.
• the material obtained from the process of the present invention i.e. the output material
• the material used in the process i.e. the input material.
• the more contaminated flakes having a larger surface area can still be processed as food grade, but may not meet the exacting standards required by large corporations.
• recycled PET produced by a process as described herein.
• a third aspect of the present invention there is provided the use of recycled PET produced by a process as described herein for the preparation of PET containers.
• the containers may be for food contact applications.
• the containers may be bottles for beverages.
• the two flake types are those having a large surface area to mass ratio, i.e. more contaminated, light flakes (LF), and those having a small surface area to mass ratio, i.e. less contaminated, heavy flakes (HF). It was also assumed that separation of these flake types will improve the decontamination process.
• LF light flakes
• HF heavy flakes
• the surface area of the two types of flakes is significantly different, with a flat particle having at least 4 times the surface area of a spherical particle of equal weight.
• the theoretical ratio of the surface area is defined by the ratio D/3T, where D is the diameter of a sphere (i.e. a heavy flake) and T is the thickness of a flake (i.e. a light flake) of equal weight).
• D is the diameter of a sphere (i.e. a heavy flake)
• T is the thickness of a flake (i.e. a light flake) of equal weight.
• Fraunhofer IVV results in unavoidable differentiation between the contamination levels imposed on the two different types of particles.
• Table 3 shows that by varying the volumetric flow rate of the air, it is possible to achieve a wide range of separation percentages.
• the results shown in Table 3 were generated using a multi aspirator air classifier to separate five different samples of 500g.
• Table 3 shows that by find adjustment of the air setting, the desired percentage of liftings can be achieved accurately and consistently.
• Table 4 shows the efficiency of decontamination of PET bottles having had various surrogate chemicals stored therein prior to recycling.
• the data presented is for recycled PET at various stages in the process of the present invention, i.e. initial contaminated flake, flake after washing step, flake after high temperature decontamination, pellet after vacuum extrusion and the test bottles made from 100% recycled PET according to the present invention.
• the flakes used to generate the data of Table 4 are light flakes (i.e. high surface area to mass ratio flakes).
• Table 4 Table 5 shows the decontamination efficiencies as percentages.
• the most significant decontamination step is the heat treatment step at about
• the data for the surrogate chemicals in the flake is worthy of noting.
• the levels are very low and would potentially indicate that this process may well meet the requirements of beverage companies based on the levels of volatile chemical being well under 3ppm and the non- volatile chemicals being well under lOppm.
• the results for the test bottles show that the levels of surrogate contaminants are present at very low levels and based on USFDA submissions it is expected that these bottles will meet the requirements of the migration tests.
• the data for the pellet contamination levels shows slightly higher levels of contaminants compared to the flake. It is thought that this variation is due to the arrangement used during testing where the flake was sampled from the top of the bed of flake being dried indicating that the distribution of gas flowing over the flakes may not have been ideal during the trial. This situation would not be expected under normal production conditions where each flake would have the same residence time and consequently the same residual surrogate contaminants. This anomaly means that the level of contaminants in the bottles would be even lower than recorded in the current tests and shown in Table 3.
• the key issue is the migration of any residual surrogate chemicals into the 95% ethanol solution, which is an aggressive extractant for PET used as a food stimulant.
• the process of the present invention produces food grade recycled PET that meets the ILSI and EU conditions and that the resin can be used at filling conditions up to 100 0 C.
• Table 7 shows melt flow and intrinsic viscosity (IV) of the recycled PET.
• Table 8 shows melt flow and IV data for pellets made by the process of the present invention.
• the final IV is in the range of 0.80 ⁇ 0.02 is a very satisfactory result since the IV of virgin resin is typically also 0.80. It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of example only.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Mechanical Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)

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• 2006
  • 2006-08-09 GB GB0615765A patent/GB0615765D0/en not_active Ceased
• 2007
  • 2007-08-09 WO PCT/GB2007/003022 patent/WO2008017843A1/en not_active Ceased
  • 2007-08-09 EP EP07789156A patent/EP2054207A1/de not_active Withdrawn

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