GB2568500A - Method for separating polymers - Google Patents

Method for separating polymers Download PDF

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Publication number
GB2568500A
GB2568500A GB1719040.6A GB201719040A GB2568500A GB 2568500 A GB2568500 A GB 2568500A GB 201719040 A GB201719040 A GB 201719040A GB 2568500 A GB2568500 A GB 2568500A
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United Kingdom
Prior art keywords
silicone fluid
range
mixture
suspension
polymer fraction
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Granted
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GB1719040.6A
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GB2568500B (en
GB201719040D0 (en
Inventor
Donaldson James
Neave Chris
Stark Ian
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Sortology Ltd
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Sortology Ltd
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Priority to GB1719040.6A priority Critical patent/GB2568500B/en
Publication of GB201719040D0 publication Critical patent/GB201719040D0/en
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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
    • 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
    • B29B2017/0203—Separating plastics from plastics
    • 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
    • B29B2017/0231—Centrifugating, cyclones
    • 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
    • B29B2017/0234—Mechanical separating techniques; devices therefor using gravity, e.g. separating by weight differences in a wind sifter
    • 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
    • B29B2017/0244—Mechanical separating techniques; devices therefor using density difference in liquids
    • 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
    • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
    • B29K2023/04—Polymers of ethylene
    • 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
    • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
    • B29K2023/10—Polymers of propylene
    • B29K2023/12—PP, i.e. polypropylene
    • 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

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  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Centrifugal Separators (AREA)

Abstract

A method of separating polyethylene (PE) and polypropylene (PP) from a mixture thereof comprising subjecting a suspension of PE and PP in a silicone fluid to an acceleration greater than gravity to form a light and heavy polymer fraction; removing the light and/or heavy polymer fraction to provide a polymer mixture enriched in PP (light fraction) and/or PE (heavy fraction) wherein the silicone fluid has a density from 0.90-0.95kg/l at 35°C. The enhanced gravity may be achieved using a centrifuge, preferably a three phase decanter centrifuge, or a hydrocyclone, wherein the acceleration provided may be greater than 1000g and below 3000g. The use of silicone fluid in the method is also provided. The silicone fluid may comprise a mixture of two different silicones.

Description

Abstract Title: Method of separating polyethylene and polypropylene (57) A method of separating polyethylene (PE) and polypropylene (PP) from a mixture thereof comprising subjecting a suspension of PE and PP in a silicone fluid to an acceleration greater than gravity to form a light and heavy polymer fraction; removing the light and/or heavy polymer fraction to provide a polymer mixture enriched in PP (light fraction) and/or PE (heavy fraction) wherein the silicone fluid has a density from 0.90-0.95kg/l at 35°C. The enhanced gravity may be achieved using a centrifuge, preferably a three phase decanter centrifuge, or a hydrocyclone, wherein the acceleration provided may be greater than 1000g and below 3000g. The use of silicone fluid in the method is also provided. The silicone fluid may comprise a mixture of two different silicones.
Diagram of separating plastic using Silicone solution and three phase decanter centrifuge
At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.
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Temp [C]
Method for separating polymers [0001] This invention relates to a method of separating polyethylene and polypropylene from a mixture thereof. Polyethylene and polypropylene are typically both present in both the post-consumer and post-industrial plastic waste streams and the methods of the invention find particular application in the sorting of these waste streams for recycling.
BACKGROUND [0002] Polyethylene (PE) and polypropylene (PP) polymers are widely used in food packaging and other consumer applications. They both float on water so they are readily recovered as a mixture from plastic waste streams by wet sink float recycling processes. However, the utility of such a mixture is limited and the two polymer types are difficult to separate. While a number of techniques have been developed to separate PE and PP from each other, the methods of doing so tend to be expensive and/or impractical for large scale application.
[0003] One way to separate PE and PP is to use solvents in which polyethylene (the more dense of the two polymers) sinks while the polypropylene (the less dense of the two polymer) floats. Example solvents include acetone /water mixtures and glycol ethers. However, these solvents are either unsafe due to their volatility and resultant fire risk (acetone) or have a strong chemical odour (glycol ethers) that can be difficult to remove from the obtained polymers.
BRIEF SUMMARY OF THE DISCLOSURE [0004] In a first aspect of the present invention is provided a method of separating polyethylene (PE) and polypropylene (PP) from a mixture thereof; the method comprising:
a) subjecting the suspension of PE and PP in a silicone fluid to an acceleration greater than g to form a light polymer fraction and a heavy polymer fraction;
b) removing the light polymer fraction and/or the heavy polymer fraction from the suspension to provide a polymer mixture enriched in PP (the light polymer fraction) and/or a polymer mixture enriched in PE (the heavy polymer fraction);
wherein the silicone fluid has a density in the range from 0.90 to 0.95 kg/l at 35 °C.
[0005] The inventors have found that silicone fluids are capable of separating PE from PP under enhanced gravity. Silicone fluids offer a number of advantages over prior art solvents: they offer no fire risk, they are non-toxic (the silicone fluids used in the examples of this application are often found in shampoos) and they are odour free.
[0006] The silicone fluid may have a viscosity in the range 2 to 20 centistokes. The low viscosity of many silicone fluids means that they drain well from the polymer product under the enhanced gravity conditions of the process of the invention, providing a clean product and allowing the fluid to be reused.
[0007] The silicone fluid may have a surface tension in the range 19 to 25 mN/m.
[0008] The silicone fluid may comprise a single silicone.
[0009] The silicone fluid may be a mixture of at least two different silicones. The different silicones may have, for example, different densities and/or viscosities and can be blended to obtain a particular density or viscosity of separation fluid for use in the method.
[0010] The silicone fluid may have a density in the range from 0.91 to 0.93 kg/l at 35 °C. The silicone fluid may have a density in the range from 0.915 to 0.925 kg/l at 35 °C. Unfilled PP has a density in the range 0.89 to 0.92 kg/l, unfilled high-density PE has a density in the range from 0.93 to 0.98 kg/l and unfilled low-density PE has a density in the range 0.92 to 0.93 kg/l. The inventors have found that a density of around 0.92 kg/l at 35 °C provides effective separation for most applications. However, the precise density of the fluid can be tailored to the nature of the polymer mixture and/or the desired purity of the product(s). If a very high purity of PE is desired, the density of the fluid may be selected to be closer to the upper end of the ranges mentioned above. If a very high purity of PP is desired, the density of the fluid may be selected to be closer to the lower end of the ranges mentioned above.
[0011] The silicone fluid may comprise (or may entirely consist of) linear polymeric siloxanes. The silicone fluid may comprise (or may entirely consist of) polydimethylsiloxanes. Illustrative silicones include the DowXiameter® PMX200 range and, in particular, the 2, 5, 10 and 20 centistokes products.
[0012] The suspension of PE and PP in a silicone fluid may be subjected to an acceleration greater than 500 g. The suspension of PE and PP in a silicone fluid may be subjected to an acceleration greater than 1000 g. The suspension of PE and PP in a silicone fluid may be subjected to an acceleration greater than 1500 g. The suspension of PE and PP in a silicone fluid may be subjected to an acceleration below 3000 g. The suspension of PE and PP in a silicone fluid may be subjected to an acceleration below 2300 g.
[0013] The enhanced gravity may be achieved using a centrifuge or a hydrocyclone. In particular, a three phase decanter centrifuge allows steps a) and b) to be performed in a single step. Illustrative three phase decanter centrifuges include the Censor plastics recycling centrifuge from Andritz Separation and the Sorticanter® from Flottweg Separation Technology.
[0014] A three phase decanter centrifuge typically comprises a vessel, having a tubular portion and a conical portion, that rotates at a predetermined speed, inside of which vessel, but positioned in such a way as to not be in contact with the sides of the tubular end of the vessel, is a screw conveyor that rotates at a higher speed (typically a speed from 0.5 to 5% faster) than the vessel. The conical portion, which at its widest point has substantially the same diameter as the tubular portion and in which the diameter of the vessel narrows the more distant it is from the tubular portion, provides a sloped beach. When the suspension of PE and PP is added to the centrifuge and the centrifuge is rotating, the heavy polymer fraction progresses to the outer surface of the annulus formed by the silicone fluid and is passed by the screw conveyor towards the conical portion and deposited on the sloped beach, from which the heavy polymer fraction can be removed. The light fraction progresses to the inner surface of the annulus formed by the silicone fluid and is carried by fluid flow along the tubular portion in a direction away from the conical portion, allowing it to be recovered from the opposite end of the vessel to the heavy fraction.
[0015] The vessel may comprise a second conical portion at the opposite end of the tubular portion to the first conical portion, said second conical portion, which at its widest point has a narrower diameter than the tubular portion and in which the diameter of the vessel narrows the more distant it is from the tubular portion, provides a second sloped beach. There may also be a second screw conveyor that deposits the light fraction onto the second beach from which the light fraction can be removed. The second screw conveyor may be mounted on the same shaft as the first screw propeller and have the screw blades configured to drive material in the opposite direction to the first screw propeller.
[0016] The tubular portion of the vessel may have a diameter in the range from 200 to 2000 mm. The tubular portion of the vessel may have a diameter in the range from 400 to 1000 mm. The tubular portion of the vessel may have a diameter in the range from 500 to 700 mm.
[0017] The tubular portion of the vessel may rotate at a speed from 500 to 4000 rpm. The tubular vessel may rotate at a speed from 1000 to 3000 rpm. The tubular vessel may rotate at a speed from 1500 to 2500 rpm.
[0018] The angle that the conical portion (or first conical potion, where there are two) forms with the sides of the tubular portion may be from 10° to 20°. The angle that the second conical portion (where there are two) forms with the sides of the tubular portion may be from 10° to 20°.
[0019] The term ‘conical’ is intended to encompass both conical and frustoconical portions. Typically the conical portion or each conical portion will be frustoconical.
[0020] The screw conveyor will typically rotate at a speed from 0.5 to 5% faster, e.g. from 1 to 3% faster, than the tubular vessel.
[0021] The PE and PP are typically in the form of particles. The particles may be flakes, cubes, spheres or any non-uniform shape. The particles will typically have been obtained by chopping or shredding the polymer mixture. The PE and PP particles may have a largest dimension in the range from 2 to 30 mm, e.g. from 12.5 to 22.5 mm or from 15 to 20 mm.
[0022] The method may comprise the step of obtaining the mixture of PE and PP. The method may comprise the step of chopping or shredding the mixture of PE and PP. Alternatively, the mixture of PE and PP may be obtained in a chopped or shredded form. This may be the case, for example, where the PE and PP are obtained as a mixture from an earlier separation process.
[0023] The mixture of PE and PP may be washed before being suspended and/or have undergone a process or processes to remove any metal, glass, cardboard, dirt, mineral (e.g. stones, soil, sand, brick, concrete, cement) and/or paper content. The mixture of PE and PP may be washed before being suspended and/or have undergone a process or processes to remove any polymeric materials other than PE and PP.
[0024] The mixture of PE and PP may be screened to remove particles below a certain size or above a certain size from the mixture.
[0025] The method may comprise the step of suspending the mixture of PE and PP in the silicone fluid to form the suspension.
[0026] The heavy and/or light fraction may be washed or dried once it has been removed from the suspension.
[0027] The heavy and/or light fraction may be melted and formed into pellets. The heavy and/or light fraction may be melted and formed directly into a product, e.g. a packaging product.
[0028] The heavy polymer fraction obtained in the process may contain over 75% PE by weight. The heavy polymer fraction obtained in the process may contain over 85% PE by weight. The heavy polymer fraction obtained in the process may contain over 95% PE by weight.
[0029] The light polymer fraction obtained in the process may contain over 75% PP by weight. The light polymer fraction obtained in the process may contain over 85% PP by weight. The light polymer fraction obtained in the process may contain over 95% PP by weight.
[0030] The method may comprise the step of separating the heavy polymer fraction obtained into low-density polyethylene (LDPE) and high density polyethylene (HDPE). This may be achieved using a method similar to that of the invention, e.g. using silicone fluid of an appropriate density (e.g. a density somewhere between 0.91 and 0.94 kg/l, depending on the desired end purity) and a centrifuge or hydrocyclone.
[0031] In a second aspect of the present invention is provided a use of a silicone fluid having a density in the range from 0.90 to 0.95 kg/l at 35 °C to separate polyethylene (PE) and polypropylene (PP) from a mixture thereof, the use comprising subjecting a suspension of PE and PP in the silicone fluid to an acceleration greater than g.
[0032] In a third aspect of the invention is provided PE and/or PP obtainable (or obtained) according to the methods of the first aspect of the invention. The PE and/or PP may comprise trace amounts (e.g. greater than 0.001 % by weight) of the silicone fluid.
[0033] The embodiments described above in relation to the first aspect of the invention apply equally, where appropriate, to the second and third aspects of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS [0034] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:
Figure 1,2 and 3 are cross-sectional views of an apparatus suitable for carrying out the methods of the invention in certain embodiments;
Figure 4 is a schematic of an embodiment of a method of the invention;
Figure 5 shows differential scanning calorimeter (DSC) analysis of the HDPE obtained by the process of example 1
DETAILED DESCRIPTION [0035] The suspension is subjected to an acceleration greater than g wherein g is the acceleration due to gravity at the Earth’s surface, i.e. roughly 9.8 m/s2. For example, an acceleration that is greater than 500 g is an acceleration that is greater than 500 times the acceleration due to gravity at the Earth’s surface. In the methods of the invention the acceleration greater than g to which the suspension is subjected is usually achieved by the application of centrifugal force, e.g. using a centrifuge, or centripetal force, e.g. using a hydrocyclone.
[0036] A silicone is a polymeric siloxane. Silicones have the general formula [SiRaRbO]n where Ra and Rb are each alkyl groups (e.g. methyl, ethyl, propyl) or other organic groups (e.g. phenyl). Silicones may be linear (in which case Ra and Rb will typically be simple alkyl groups or phenyl) or they may be crosslinked (in which a proportion of Ra or Rb may be attached to a further siloxane unit). The silicone fluids of the invention are typically made up of one or more silicone oils, a silicone oil being a linear polymeric siloxane.
[0037] Figure 1 shows a decanter centrifuge comprising a vessel, having a tubular portion 1, a frustoconical portion 2 and a screw conveyor 3 that rotates at a faster velocity than the vessel. When the suspension of PE and PP is added to the centrifuge and the centrifuge is rotating, a centrifugal force acts on the heavy polymer fraction such that it progresses to the outer surface of the annulus 4 formed by the silicone fluid and is passed by the screw conveyor towards the frustoconical portion and deposited on the sloped beach, from which the heavy polymer fraction can be removed (arrow A).
[0038] Figure 2 shows a decanter centrifuge comprising a vessel, having a tubular portion 1, a first frustoconical portion 2 and a first screw conveyor 3 that rotates at a faster velocity than the vessel. When the suspension of PE and PP is added to the centrifuge and the centrifuge is rotating, a centrifugal force acts on the heavy polymer fraction such that it progresses to the outer surface of the annulus 4 formed by the silicone fluid and is passed by the screw conveyor towards the frustoconical portion and deposited on the sloped beach, from which the heavy polymer fraction can be removed (arrow A). The vessel also comprises a second frustoconical portion 5 at the opposite end of the tubular portion to the first frustoconical portion and a second screw conveyor 6 that deposits the light fraction onto the second beach from which the light fraction can be removed (arrow B). The second frustoconical portion 5 has, at its widest point, a narrower diameter than the tubular portion 1. The second screw conveyor 6 is mounted on the same shaft as the first screw propeller 3 and has the screw blades configured to drive material in the opposite direction to the first screw propeller.
[0039] Figure 3 shows a particular example of a decanter centrifuge having a vessel comprising a tubular portion 1; a frustoconical portion 2; a screw conveyor 3 that rotates at a higher speed than the vessel; a second frustoconical portion 5 at the opposite end of the tubular portion to the first frustoconical portion 2 and having, at its widest point, a narrower diameter than the tubular portion 1; and a second screw conveyor 6 mounted on the same shaft as the first screw propeller 3 and having the screw blades configured to drive material in the opposite direction to the first screw propeller 3. The suspension of PE and PP 11 is added to the centrifuge via the inlet 7 (arrow C) as the centrifuge is rotating a centrifugal force acts on the heavy polymer fraction 12 such that it progresses to the outer surface of the annulus 4 formed by the silicone fluid and is passed by the first screw conveyor 3 towards the first frustoconical portion and deposited on the sloped beach, from which the heavy polymer fraction can be removed (arrow A) via outlet 8. The light fraction is passed by the second screw conveyor 6 towards the second frustoconical portion 5 onto the second beach from which the light fraction can be removed (direction B) via outlet 9. The fluid 14 can be removed via outlet 10 (arrow D).
[0040] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
[0041] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
[0042] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
EXAMPLE [0043] The input material for the process was sorted mixed polyolefin cap from a postconsumer PET bottle recycler. The polymer material, rejected from the process to recover PET, was sorted to remove any heavy polymers (mainly PET, PVC) and contained only
PE, PP in flake (and some film) form. Typically, the mixture was 80% HDPE and 20% PP. The flaked material was in the form of thin (1mm) flakes with an average size of 10mm. Film content is derived from the labels on the bottles.
[0044] A Sorticanter® from Flottweg Separation Technology was used. This is a three phase decanter centrifuge. The Sorticanter® was set up to run at full speed 2100 rpm (1528 g) and with the minimum scroll differential (25 rpm). This maximises the ‘drying’ effect of the Sorticanter®- maximum acceleration and maximum time on beach (liquid drains back to annulus).
[0045] The Sorticanter® system was charged with 1000 litres of 5 cs Silicone Oil (Xiameter 200) and 1000 litres of 10cs Silicone Oil (Xiameter 200). The machine was then circulated for 20 minutes to bring the Silicone Oil temperature up from room temperature. The density of the warm oil was measured at 0.92 kg/L.
[0046] The polymer material was augured into the Sorticanter® feed tank at a rate of 1600 kg/hr. After a few minutes, pure HDPE is discharged from the heavies auger and shortly after PP discharged from the lights auger. The discharge was largely flakes but any film present was sorted as well. Both streams were blown to a film separator before going into the respective bagging stations. The material was blown as this reduces slightly any remaining silicone coating the flakes.
[0047] On this run 5 bags of PP were produced for every 18 bags of HDPE - so 22% PP. An analysis of the two materials is shown below:
Material PE (purified)
Density (kg/l 0.955
Melt Flow Index (MFI) (190°C, 2.16kg) 3.72 g/10 mins.
DSC - Fig 5 Pure HDPE
Material Pure HDPE regrind, injection grade.
Material PP (purified)
Density (kg/l 0.910
Melt Flow Index (MFI) (210°C, 2.16kg) 22.60 g/10 mins.
Material Pure PP regrind, injection grade.

Claims (20)

1. A method of separating polyethylene (PE) and polypropylene (PP) from a mixture thereof; the method comprising:
a) subjecting a suspension of PE and PP in a silicone fluid to an acceleration greater than g to form a light polymer fraction and a heavy polymer fraction;
b) removing the light polymer fraction and/or the heavy polymer fraction from the suspension to provide a polymer mixture enriched in PP (the light polymer fraction) and/or a polymer mixture enriched in PE (the heavy polymer fraction);
wherein the silicone fluid has a density in the range from 0.90 to 0.95 kg/l at 35 °C.
2. IA method of claim 1, wherein the suspension of PE and PP in a silicone fluid is subjected to an acceleration greater than 1000 g.
3. A method of claim 1 or claim 2, wherein the suspension of PE and PP in a silicone fluid is subjected to an acceleration below 3000 g.
4. A method of any one of claims 1 to 3, wherein the enhanced gravity is achieved using a centrifuge or a hydrocyclone.
5. A method of claim 4, wherein steps a) and b) are performed in a three phase decanter centrifuge.
6. A method of any one of claims 1 to 5, wherein the silicone fluid has a viscosity in the range 2 to 20 centistokes.
7. A method of any one of claims 1 to 6, wherein the silicone fluid has a surface tension in the range 19 to 25 mN/m.
8. A method of any one of claims 1 to 7, wherein silicone fluid is a mixture of at least two different silicones.
9. A method of any one of claims 1 to 8, wherein the silicone fluid has a density in the range from 0.91 to 0.93 kg/l at 35 °C.
10. A method of any one of claims 1 to 9, wherein the PE and PP are in the form of particles having a largest dimension in the range from 2 to 30 mm.
11. A use of a silicone fluid having a density in the range from 0.90 to 0.95 kg/l at 35 °C to separate polyethylene (PE) and polypropylene (PP) from a mixture thereof the use comprising subjecting a suspension of PE and PP in the silicone fluid to an acceleration greater than g.
12. A use of claim 11, wherein the suspension of PE and PP in the silicone fluid is subjected to an acceleration greater than 1000 g.
13. A use of claim 11 or claim 12, wherein the silicone fluid has a viscosity in the range 2 to 20 centistokes.
5
14. A use of any one of claims 11 to 13, wherein the silicone fluid has a surface tension in the range 19 to 25 mN/m.
15. A use of any one of claims 11 to 14, wherein silicone fluid is a mixture of at least two different silicones.
16. A use of any one of claims 11 to 15, wherein the silicone fluid has a density in the 10 range from 0.91 to 0.93 kg/l at 35 °C.
17. Polyethylene (PE) obtainable by the method of any one of claims 1 to 10.
18. A PE of claim 17, that comprises trace amounts of the silicone fluid.
19. Polypropylene (PP) obtainable by the method of any one of claims 1 to 10.
20. A PP of claim 19, that comprises trace amounts of the silicone fluid.
Intellectual Property Office
Application No: GB 1719040.6
Claims searched: 1-20
Examiner: Heather Webber
Date of search: 23 May 2018
Patents Act 1977: Search Report under Section 17
Documents considered to be relevant:
Category Relevant to claims Identity of document and passage or figure of particular relevance A - DE43 04726 A (SIEBERT MARTIN) see whole document A - W098/08609 Al (F & P SORTIERTECHNIK GMBH et al) see whole document A - JP2004098522 A (UNIV WASEDA et al) see especially paragraphs [0024, 0045, 0047, 0052, 0053] and figures
Categories:
X Document indicating lack of novelty or inventive step A Document indicating technological background and/or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention. same category. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.
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Search of GB, EP, WO & US patent documents classified in the following areas of the UKCX :
GB1719040.6A 2017-11-17 2017-11-17 Method for separating polymers Active GB2568500B (en)

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GB2568500A true GB2568500A (en) 2019-05-22
GB2568500B GB2568500B (en) 2022-04-20

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4304726A1 (en) * 1993-02-14 1994-08-18 Siebert Martin Process for the separation of plastics using their different thermal expansion behaviour
WO1998008609A1 (en) * 1996-08-29 1998-03-05 F & P Sortiertechnik Gmbh Process for separating low density plastic fractions
JP2004098522A (en) * 2002-09-10 2004-04-02 Univ Waseda Method for sorting plastics and sorting device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4304726A1 (en) * 1993-02-14 1994-08-18 Siebert Martin Process for the separation of plastics using their different thermal expansion behaviour
WO1998008609A1 (en) * 1996-08-29 1998-03-05 F & P Sortiertechnik Gmbh Process for separating low density plastic fractions
JP2004098522A (en) * 2002-09-10 2004-04-02 Univ Waseda Method for sorting plastics and sorting device

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GB2568500B (en) 2022-04-20
GB201719040D0 (en) 2018-01-03

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