REMOVAL OF ODORANTS FROM POST-CONSUMER POLYOLEFIN WASTE

Abstract

A process for reducing the hydrophobic functional group-containing volatile organic compound content and hydrophilic volatile organic compound content of recycled polyolefin comprising an acid washing step followed by an alkaline/neutral washing step.

Claims

1. A process for reducing the hydrophobic functional group-containing volatile organic compound content and hydrophilic volatile organic compound content of recycled polyolefin comprising, in the given order, the steps of: (a) treating recycled polyolefin, which contains hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, with an aqueous solution A of an inorganic oxoacid, wherein said aqueous solution A has a pH-value of 2.0 or lower, (b) removing aqueous solution A of step (a) from the recycled polyolefin, (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH-value of 7.0 or higher, (d) removing aqueous solution B of step (c) from the recycled polyolefin, (e) optionally drying, extruding and/or aerating the recycled polyolefin, thereby obtaining a recycled polyolefin with reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, wherein volatile organic compounds are defined as organic compounds having an initial boiling point (b.p.) of less than or equal to 250° C. when measured at a standard atmospheric pressure of 101.3 kPa, hydrophobic compounds are defined as those compounds having a logP (octanol/water) value of greater than 1.0, and hydrophilic compounds are defined as those compounds having a logP (octanol/water) value of lower than or equal to 1.0.

2. The process according to claim 1, wherein the recycled polyolefin of step (a) is in flaked form or pelletized form.

3. The process according to claim 1, wherein the treatment of the recycled polyolefin in step (a) with aqueous solution A lasts 5 minutes to 4 hours and step (a) is carried out at a temperature in the range from 10 to 45° C.

4. The process according to claim 1, wherein the treatment of the recycled polyolefin in step (c) with aqueous solution B lasts 5 minutes to 4 hours and step (c) is carried out at a temperature in the range from 20 to 90° C.

5. The process according to claim 1, wherein the inorganic oxoacid is selected from the group consisting of disulphuric acid, sulphuric acid, phosphoric acid, nitric acid, perchloric acid, and mixtures thereof.

6. The process according to claim 1, wherein the pKa of the inorganic oxoacid is in the range from -5.0 to 0.0, and/or wherein the amount of the inorganic oxoacid in aqueous solution A is in the range of 40 to 100 wt.%.

7. The process according to claim 1, wherein aqueous solution B of step (c) is a caustic aqueous solution comprising a base.

8. The process according to claim 7, wherein the amount of the base in the caustic aqueous solution is in the range of 0.5 to 10 wt.%.

9. The process according to claim 7, wherein the base is selected from the group consisting of calcium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium hydroxide and mixtures thereof.

10. The process according to claim 1, wherein the combination of aqueous solution A and the recycled polyolefin in step (a) is subjected to agitation through mechanical mixing, ultrasonic treatment, mechanical grinding or pump around loop, and/or wherein the combination of aqueous solution B and the recycled polyolefin in step (c) is subjected to agitation through mechanical mixing, ultrasonic treatment, mechanical grinding or pump around loop.

11. The process according to claim 1, wherein the process comprises an additional step (b2) of rinsing residue of aqueous solution A and/or any other foreign material and/or degradation products thereof from the recycled polyolefin, which is carried out after step (b), and/or wherein the process comprises an additional step (d2) of rinsing residue of aqueous solution B and/or any other foreign material and/or degradation products thereof from the recycled polyolefin, which is carried out after step (d).

12. The process according to claim 1, wherein the recycled polyolefin originates from post-consumer waste, post industrial waste, or a combination thereof.

13. The process according to claim 1, wherein the recycled polyolefin obtained as a product of the process has: a limonene content, as measured by HS-GC/MS, of less than 30% of the value measured before the process, and/or a styrene content, as measured by HS-GC/MS, of less than 30% of the value measured before the process, and/or an acetic acid content, as measured by HS-GC/MS, of less than 40% of the value measured before the process, and/or an acetaldehyde content, as measured by HS-GC/MS, of less than 20% of the value measured before the process.

14-15. (canceled)

16. The process according to claim 2, wherein the recycled polyolefin in flaked form or pelletized form is shredded prior to the treatment with aqueous solution A.

17. The process according to claim 1, wherein the inorganic oxoacid is sulphuric acid.

18. The process according to claim 7, wherein the caustic aqueous solution comprising a base has a pH-value in the range of 9.0 to 14.0.

19. The process according to claim 7, wherein the base is sodium hydroxide.

20. The process according to claim 1, wherein the recycled polyolefin originates from post-consumer waste.

Description

DETAILED DESCRIPTION OF THE INVENTION

Process

[0035] The process for reducing the hydrophobic functional group-containing volatile organic compound content and hydrophilic volatile organic compound content of recycled polyolefin comprises, in the given order, the steps of: [0036] (a) treating recycled polyolefin, which contains hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, with an aqueous solution A of an inorganic oxoacid, wherein said aqueous solution A has a pH-value of 2.0 or lower, [0037] (b) removing aqueous solution A of step (a) from the recycled polyolefin, [0038] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH-value of 7.0 or higher, [0039] (d) removing aqueous solution B of step (c) from the recycled polyolefin, [0040] (e) optionally drying, extruding and/or aerating the recycled polyolefin, [0041] thereby obtaining a recycled polyolefin with reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, wherein volatile organic compounds are defined as organic compounds having an initial boiling point (b.p.) of less than or equal to 250° C. when measured at a standard atmospheric pressure of 101.3 kPa, [0042] hydrophobic compounds are defined as those compounds having a logP (octanol/water) value of greater than 1.0, and [0043] hydrophilic compounds are defined as those compounds having a logP (octanol/water) value of less than or equal to 1.0.

[0044] In an alternative embodiment, the process for reducing the hydrophobic functional group-containing volatile organic compound content and hydrophilic volatile organic compound content of recycled polyolefin comprises, in the given order, the steps of: [0045] (a) treating recycled polyolefin, which contains hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, with an aqueous solution A of an inorganic oxoacid, wherein said aqueous solution A has a pH-value in the range from 0.0 to 2.0, [0046] (b) removing aqueous solution A of step (a) from the recycled polyolefin, [0047] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH-value in the range from 7.0 to 14.0, [0048] (d) removing aqueous solution B of step (c) from the recycled polyolefin, [0049] (e) optionally drying, extruding and/or aerating the recycled polyolefin, [0050] thereby obtaining a recycled polyolefin with reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, wherein volatile organic compounds are defined as organic compounds having an initial boiling point (b.p.) of less than or equal to 250° C. when measured at a standard atmospheric pressure of 101.3 kPa, [0051] hydrophobic compounds are defined as those compounds having a logP (octanol/water) value of greater than 1.0, and [0052] hydrophilic compounds are defined as those compounds having a logP (octanol/water) value of less than or equal to 1.0.

[0053] The recycled polyolefin must contain hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds. These compounds typically result from contamination during the first use of the polymer, often when the polymer is used as packaging material, especially for food and/or personal care compositions.

[0054] It is further preferred that the hydrophobic functional group-containing volatile organic compounds of the present invention contain a covalent bond selected from O—H bonds, C═O bonds and C═C bonds.

[0055] The recycled polyolefin preferably originates from post-consumer waste, post-industrial waste or a combination thereof, most preferably from post-consumer waste.

[0056] Post-consumer waste refers to objects having completed at least a first use cycle (or life cycle), i.e. having already served their first purpose; while industrial waste refers to manufacturing scrap, which does not normally reach a consumer.

[0057] The recycled polyolefin is preferably provided in a flaked form or pelletized form.

[0058] Whilst the process according to the present invention is effective at removing hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds from recycled polyolefin in flaked or pelletized form, it is preferred that the recycled polyolefin is shredded prior to the treatment with aqueous solution A of the inorganic oxoacid. This has been found to improve the extraction of the hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds both as a result of higher effective surface areas and also improved ease of agitation, should agitation be required.

[0059] It is further preferred that the combination of aqueous solution A and the recycled polyolefin in step (a) is subjected to agitation through mechanical mixing, ultrasonic treatment, mechanical grinding or pump around loop. This agitation helps to expose the surface of the recycled polyolefin to fresh aqueous solution A, avoiding that a high concentration of extracted volatile organic compounds at the interface would hinder further extraction.

[0060] It is also preferred that the combination of aqueous solution B and the recycled polyolefin in step (c) is subjected to agitation through mechanical mixing, ultrasonic treatment, mechanical grinding or pump around loop, for the same reasons as given above.

[0061] Steps (b) and (d) involve the removal of aqueous solution A and aqueous solution B, respectively, from the recycled polyolefin. Whilst this process is relatively simple to achieve through decanting and/or filtering the mixture, traces of either aqueous solution A or aqueous solution B can remain on the surface of the recycled polyolefin. These traces of aqueous solution A and/or B contain solubilised volatile organic compounds, as well as the acid and/or base if present, and it is therefore advantageous to remove all trace of the aqueous solutions A and/or B.

[0062] This may be achieved through the use of rinsing steps, whereby any foreign material and/or aqueous solutions are rinsed from the surface of the recycled polyolefin.

[0063] As such, it is preferred that the process comprises an additional step (b2) of rinsing residue of the aqueous solution (A) and/or any other foreign material and/or degradation products thereof from the recycled polyolefin, which is carried out after step (b).

[0064] It is further preferred that the process comprises an additional step (d2) of rinsing residue of the aqueous solution (B) and/or any other foreign material and/or degradation products thereof from the recycled polyolefin, which is carried out after step (d).

[0065] Step (a) itself involves the treatment of the recycled polyolefin with an aqueous solution A of an inorganic oxoacid. Without wishing to be bound by theory, it is believed that this inorganic oxoacid decomposes/reacts with the functional group-containing hydrophobic volatile organic compounds, such as styrene and limonene, present in the recycled polyolefin, converting them into more hydrophilic and/or more volatile compounds, enabling them to be extracted into the aqueous solution A.

[0066] In order to achieve this hypothesized oxidation/acidic degradation, the acid must be an inorganic oxoacid, since the counteranions of such acids can act as oxidants.

[0067] It is preferred that the inorganic oxoacid is selected from the group consisting of disulphuric acid, sulphuric acid, phosphoric acid, nitric acid, perchloric acid, and mixtures thereof.

[0068] In a particularly preferred embodiment, the inorganic oxoacid is sulphuric acid.

[0069] It is preferred that the pKa of the inorganic oxoacid is in the range from -5.0 to 5.0, preferably in the range from -5.0 to 0.0.

[0070] It is additionally preferred that the amount of the inorganic oxoacid in aqueous solution A is in the range of 40 to 100 wt.-% (corresponding for sulphuric acid to a molarity of 5.3 to 18.65 M), more preferably in the range from 70 to 98 wt.-% (corresponds to 11.5 M to 18.4 M, most preferably from 94 to 98 wt.-% (corresponds to 17.8 M to 18.4 M).

[0071] The aqueous solution A may comprise more than one inorganic oxoacid. The above-mentioned concentration and pKa values refer to each individual acid.

[0072] It is particularly preferred that aqueous solution A is an aqueous solution of sulphuric acid at a concentration in the range from 94 to 98 wt.-%.

[0073] The pH of aqueous solution A must be less than 2.0, more preferably less than 1.0, most preferably less than 0.5.

[0074] Alternatively, the pH must be in the range from 0.0 to 2.0, more preferably in the range from 0.0 to 1.0, most preferably in the range from 0.0 to 0.5.

[0075] The treatment of the recycled polyolefin with the aqueous solution A in step (a) is a washing step, as opposed to a rinsing step as defined herein, and consequently typically lasts 5 minutes or longer, like 5 minutes to 24 hours.

[0076] The treatment of the recycled polyolefin with the aqueous solution A in step (a) preferably lasts 5 minutes to 4 hours, preferably 30 minutes to 3 hours, most preferably 1 to 2 hours.

[0077] It is further preferred that step (a) is carried out at a temperature in the range from 10 to 45° C., more preferably in the range from 20 to 35° C.

[0078] Whilst step (a) may be effective for the removal of some hydrophilic volatile organic compounds, the highly acidic nature of aqueous solution A may make the extraction of many hydrophilic compounds, especially acidic examples, less effective than would be the case for a simple water wash.

[0079] As such, treatment of the recycled polyolefin that results from step (b) with an aqueous solution B in step (c) is used to remove any remaining hydrophilic volatile organic compounds.

[0080] Treatment with water may be used to remove the hydrophilic volatile organic compounds; however, improved results can be obtained when aqueous solution B contains a base, i.e. aqueous solution B is a caustic aqueous solution comprising a base.

[0081] It is preferred that the caustic aqueous solution comprises a base in an amount in the range from 0.5 to 10 wt.-%, more preferably 1 to 5 wt.-%.

[0082] The choice of base is not crucial, however it is preferred that the base is selected from the group consisting of calcium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium hydroxide and mixtures thereof.

[0083] It is particularly preferred that the base is sodium hydroxide.

[0084] In one particularly preferred embodiment, aqueous solution B is a sodium hydroxide solution having a sodium hydroxide concentration in the range from 3 to 10 wt.-%.

[0085] The presence of a base means that the pH of aqueous solution B is increased above 7.0.

[0086] It is preferred that the pH of the caustic aqueous solution is in the range greater than or equal to 9.0, more preferably greater than or equal to 11.0, most preferably greater than or equal to 12.0.

[0087] It is alternatively preferred that the pH of the caustic aqueous solution is in the range of 9.0 to 14.0, more preferably in the range from 11.0 to 14.0, most preferably in the range from 12.0 to 14.0.

[0088] The treatment of the recycled polyolefin with the aqueous solution B in step (c) is a washing step, as opposed to a rinsing step as defined herein, and consequently typically lasts 5 minutes or longer, like 5 minutes to 24 hours.

[0089] The treatment of the recycled polyolefin with the aqueous solution B in step (c) preferably lasts 5 minutes to 4 hours, preferably 30 minutes to 3 hours, most preferably 1 to 2 hours. It is further preferred that step (c) is carried out at a temperature in the range from 20 to 90° C., more preferably in the range from 50 to 80° C.

[0090] In a particularly preferred embodiment, aqueous solution A is an aqueous solution of sulphuric acid at a concentration in the range from 94 to 98 wt.-% and aqueous solution B is a sodium hydroxide solution having a sodium hydroxide concentration in the range from 3 to 10 wt.-%.

[0091] The process as described above results in the reduction of hydrophobic functional group-containing volatile organic compound content and hydrophilic volatile organic compound content of the recycled polyolefin.

[0092] It is particularly preferred that the recycled polyolefin obtained as a product of the process has a limonene content, as measured by HS-GC/MS, of less than 30% of the value measured before the process.

[0093] It is further preferred that the recycled polyolefin obtained as a product of the process has a styrene content, as measured by HS-GC/MS, of less than 30% of the value measured before the process.

[0094] It is additionally preferred that the recycled polyolefin obtained as a product of the process has an acetic acid content, as measured by HS-GC/MS, of less than 40% of the value measured before the process.

[0095] It is furthermore preferred that the recycled polyolefin obtained as a product of the process has an acetaldehyde content, as measured by HS-GC/MS, of less than 20% of the value measured before the process.

[0096] In a particularly preferred embodiment, the recycled polyolefin obtained as a product of the process has a limonene content, as measured by HS-GC/MS, of less than 30% of the value measured before the process, a styrene content, as measured by HS-GC/MS, of less than 30% of the value measured before the process, an acetic acid content, as measured by HS-GC/MS, of less than 40% of the value measured before the process, and an acetaldehyde content, as measured by HS-GC/MS, of less than 20% of the value measured before the process.

Use

[0097] The present invention is also directed to a use of the process as described above. All preferable features and preferred embodiments apply equally to the use of the process, as to the process itself.

[0098] In one embodiment, the process can be used for the reduction of the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in recycled polyolefin, wherein the limonene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process.

[0099] In an alternative embodiment, the process can be used for the reduction of the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in recycled polyolefin, wherein the styrene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process.

[0100] In a preferred embodiment the process can be used for the reduction of the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in recycled polyolefin, wherein the limonene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process and wherein the styrene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process.

[0101] In each of these embodiments, it is preferred that the acetic acid content, as measured by HS-GC/MS, decreases to less than 40% of the value measured before the process.

[0102] It is equally preferred that the acetaldehyde content, as measured by HS-GC/MS, decreases to less than 20% of the value measured before the process.

[0103] It is particularly preferred that the acetic acid content, as measured by HS-GC/MS, decreases to less than 40% of the value measured before the process and that the acetaldehyde content, as measured by HS-GC/MS, decreases to less than 20% of the value measured before the process.

[0104] In a yet further preferred embodiment, the process can be used for the reduction of the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in recycled polyolefin, wherein the limonene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process, the styrene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process, the acetic acid content, as measured by HS-GC/MS, decreases to less than 40% of the value measured before the process and the acetaldehyde content, as measured by HS-GC/MS, decreases to less than 20% of the value measured before the process.

[0105] The present invention may be characterized by the following items: [0106] 1. A process for reducing the hydrophobic functional group-containing volatile organic compound content and hydrophilic volatile organic compound content of recycled polyolefin comprising, in the given order, the steps of: [0107] (a) treating recycled polyolefin, which contains hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, with an aqueous solution A of an inorganic oxoacid, wherein said aqueous solution A has a pH-value of 2.0 or lower, [0108] (b) removing aqueous solution A of step (a) from the recycled polyolefin, [0109] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH-value of 7.0 or higher, [0110] (d) removing aqueous solution B of step (c) from the recycled polyolefin, [0111] (e) optionally drying, extruding and/or aerating the recycled polyolefin, thereby obtaining a recycled polyolefin with reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, [0112] wherein volatile organic compounds are defined as organic compounds having an initial boiling point (b.p.) of less than or equal to 250° C. when measured at a standard atmospheric pressure of 101.3 kPa, [0113] hydrophobic compounds are defined as those compounds having a logP (octanol/water) value of greater than 1.0, and [0114] hydrophilic compounds are defined as those compounds having a logP (octanol/water) value of lower than or equal to 1.0. [0115] 2. A process for reducing the hydrophobic functional group-containing volatile organic compound content and hydrophilic volatile organic compound content of recycled polyolefin comprising, in the given order, the steps of: [0116] (a) treating recycled polyolefin, which contains hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, with an aqueous solution A of an inorganic oxoacid, wherein said aqueous solution A has a pH-value in the range from 0.0 to 2.0, [0117] (b) removing aqueous solution A of step (a) from the recycled polyolefin, [0118] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH-value in the range from 7.0 to 14.0, [0119] (d) removing aqueous solution B of step (c) from the recycled polyolefin, [0120] (e) optionally drying, extruding and/or aerating the recycled polyolefin, [0121] thereby obtaining a recycled polyolefin with reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, [0122] wherein volatile organic compounds are defined as organic compounds having an initial boiling point (b.p.) of less than or equal to 250° C. when measured at a standard atmospheric pressure of 101.3 kPa, [0123] hydrophobic compounds are defined as those compounds having a logP (octanol/water) value of greater than 1.0, and [0124] hydrophilic compounds are defined as those compounds having a logP (octanol/water) value of lower than or equal to 1.0. [0125] 3. The process according to either item 1 or item 2, wherein the functional group-containing volatile organic compounds contain a covalent bond selected from O—H bonds, C═O bonds and C═C bonds. [0126] 4. The process according to any one of the preceding items wherein the recycled polyolefin of step (a) is in flaked form or pelletized form. [0127] 5. The process according to item 4, wherein the recycled polyolefin in flaked form or pelletized form is shredded prior to the treatment with aqueous solution A. [0128] 6. The process according to any one of the preceding items, wherein the treatment of the recycled polyolefin in step (a) with aqueous solution A lasts 5 minutes to 4 hours. [0129] 7. The process according to any one of the preceding items, wherein step (a) is carried out at a temperature in the range from 10 to 45° C. [0130] 8. The process according to any one of the preceding items, wherein the treatment of the recycled polyolefin in step (c) with aqueous solution B lasts 5 minutes to 4 hours. [0131] 9. The process according to any one of the preceding items, wherein step (c) is carried out at a temperature in the range from 20 to 90° C. [0132] 10. The process according to any one of the preceding items, wherein the inorganic oxoacid is selected from the group consisting of disulphuric acid, sulphuric acid, phosphoric acid, nitric acid, perchloric acid, and mixtures thereof. [0133] 11. The process according to item 10 wherein the inorganic oxoacid is sulphuric acid. [0134] 12. The process according to any one of the preceding items, wherein the pKa of the inorganic oxoacid is in the range from -5.0 to 5.0, preferably in the range from -5.0 to 0.0. [0135] 13. The process according to any one of the preceding items, wherein the amount of the inorganic oxoacid in aqueous solution A is in the range of 40 to 100 wt.-%. [0136] 14. The process according to any one of the preceding items, wherein aqueous solution B of step (c) is a caustic aqueous solution comprising a base. [0137] 15. The process according to item 14, wherein the amount of the base in the caustic aqueous solution is in the range of 0.5 to 10 wt.-%. [0138] 16. The process according to either item 14 or 15, wherein the base is selected from the group consisting of calcium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium hydroxide and mixtures thereof. [0139] 17. Process according to any one of items 14 to 16, wherein the base is sodium hydroxide. [0140] 18. The process according to any one of items 14 to 17, wherein the caustic aqueous solution comprising a base has a pH-value in the range of 9.0 to 14.0. [0141] 19. The process according to any one of the preceding items, wherein the combination of aqueous solution A and the recycled polyolefin in step (a) is subjected to agitation through mechanical mixing, ultrasonic treatment, mechanical grinding or pump around loop. [0142] 20. The process according to any one of the preceding items, wherein the combination of aqueous solution B and the recycled polyolefin in step (c) is subjected to agitation through mechanical mixing, ultrasonic treatment, mechanical grinding or pump around loop. [0143] 21. The process according to any one of the preceding items, wherein the process comprises an additional step (b2) of rinsing residue of aqueous solution A and/or any other foreign material and/or degradation products thereof from the recycled polyolefin, which is carried out after step (b). [0144] 22. The process according to any one of the preceding items, wherein the process comprises an additional step (d2) of rinsing residue of aqueous solution B and/or any other foreign material and/or degradation products thereof from the recycled polyolefin, which is carried out after step (d). [0145] 23. The process according to any one of the preceding items, wherein the recycled polyolefin originates from post-consumer waste, post-industrial waste, or a combination thereof. [0146] 24. The process according to item 23, wherein the recycled polyolefin originates from post-consumer waste. [0147] 25. The process according to any one of the preceding items, wherein the recycled polyolefin obtained as a product of the process has a limonene content, as measured by HS-GC/MS, of less than 30% of the value measured before the process. [0148] 26. The process according to any one of the preceding items, wherein the recycled polyolefin obtained as a product of the process has a styrene content, as measured by HS-GC/MS, of less than 30% of the value measured before the process. [0149] 27. The process according to any one of the preceding items, wherein the recycled polyolefin obtained as a product of the process has an acetic acid content, as measured by HS-GC/MS, of less than 40% of the value measured before the process. [0150] 28. The process according to any one of the preceding items, wherein the recycled polyolefin obtained as a product of the process has an acetaldehyde content, as measured by HS-GC/MS, of less than 20% of the value measured before the process. [0151] 29. A use of the process according to any one of the preceding items, for the reduction of the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in recycled polyolefin, wherein the limonene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process. [0152] 30. A use of the process according to any one of items 1 to 24, for the reduction of the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in recycled polyolefin, wherein the styrene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process. [0153] 31. A use of the process according to either of items 1 or 24, for the reduction of the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in recycled polyolefin, wherein the limonene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process and wherein the styrene content, as measured by HS-GC/MS, decreases to less than 30% of the value measured before the process. [0154] 32. The use according to any one of items 29 to 31, wherein the acetic acid content, as measured by HS-GC/MS, decreases to less than 40% of the value measured before the process. [0155] 33. The use according to any one of items 29 to 32, wherein the acetaldehyde content, as measured by HS-GC/MS, decreases to less than 20% of the value measured before the process.

EXAMPLES

1. Definitions/Determination Methods

Determination of Acetic Acid, Styrene and Limonene Content via HS-GC/MS

Static Headspace Analysis for Marker Substance Determination

[0156] The parameters of the applied headspace gas chromatography mass spectrometry (HS/GC/MS) method are described here.

[0157] For the measurement of a benzene standard 5 .Math.l of a standard solution containing 100 .Math.g/ml benzene in methanol were injected into a 20 ml HS vial and tightly closed with a PTFE cap. Each HS/GC/MS test sequence of sample measurements included the analysis of such a benzene standard. The benzene signal of the corresponding sequence was used for the calculation of the relative normalised area as described further below.

[0158] The samples were also analysed by HS/GC/MS in order to determine potential odorant and hazardous marker substances. Therefore, 2.000 ± 0.100 g samples were weighed in a 20 ml HS vial and tightly sealed with a PTFE cap. For each washing experiment a double determination of the respective sample was performed.

[0159] Applied headspace parameters for the analyses of standards and samples differed in the vial equilibration time and the HS oven temperature. Apart from that, method parameters were kept the same for standard and sample runs. The mass spectrometer was operated in scan mode and a total ion chromatogram (TIC) was recorded for each analysis. The detected substances were tentatively identified by the aid of deconvolution and a minimum match of 800 when the hit was subsequently compared to a mass spectral library. More detailed information on method parameters and data evaluation software is given below:

TABLE-US-00001 HS parameter (Agilent G1888 Headspace Sampler) Vial equilibration time: 5 min (benzene standard), 120 min (sample) Oven temperature: 200° C. (benzene standard), 100° C. (sample) Loop temperature: 205° C. Transfer line temperature: 210° C. Low shaking GC parameter (Agilent 7890A GC System) Column: ZB-WAX 7HG-G007-22 (30 m × 250 .Math.m × 1 .Math.m) Carrier gas: Helium 5.0 Flow: 2 ml/min Split: 5:1 GC oven program: 35° C. for 0.1 min 10° C./min until 250° C. 250° C. for 1 min MS parameter (Agilent 5975C inert XL MSD) Acquisition mode: Scan Scan parameters: Low mass: 20 High mass: 200 Threshold: 10 Software/Data evaluation MSD ChemStation E.02.02.1431 MassHunter GC/MS Acquisition B.07.05.2479 AMDIS GC/MS Analysis Version 2.71 NIST Mass Spectral Library (Version 2011) Microsoft Excel 2016

Data Evaluation

[0160] The benzene standard was evaluated with the same parameters as the sample runs. Therefore, extracted ion chromatograms (EICs) of the measured benzene standards and samples were created. The peak areas required for the further data evaluation were obtained by integrating the corresponding substance peak of the EIC. The applied integration parameters and substance specific ions (m/z ratios) of all marker substances are listed in tables 1 and 2.

TABLE-US-00002 Retention times and substance specific ions of selected marker substances Substance Retention time / min Substance specific ion of the corresponding EIC (m/z) Acetaldehyde 1.7 44 Benzene.sup.1 3.9 78 Toluene 5.3 91 Ethylbenzene 6.6 106 o-Xylene 7.5 106 D-Limonene 7.6 136 Styrene 8.6 104 Acetic acid.sup.∗ 11.5 60 Benzaldehyde 12.5 106 Acetophenone 14.2 105 .sup.1Relevant for both, standards and samples.

[0161] .sup.∗*In the HS-GC/MS analysis the acetic acid peak was not sufficiently separated from the peak corresponding to ethylhexanol. Therefore, the area of the acetic acid peak also includes the ethylhexanol impurity. This minor impurity has not been observed to have a significant influence on the values obtained in the data presented below. In general it is not possible to exclude the possibility of overlapping peaks in other regions of the HS-GC/MS readout.

TABLE-US-00003 Integration parameters for the determination of the peak areas Integration event Value Initial area reject 1000 Initial peak width 0.005 Shoulder detection OFF Initial threshold 10.5

[0162] The substance specific ion peak areas (Area(EIC).sub.x) were normalised by the extracted ion peak area of benzene (Area(EIC).sub.Benzene) and the sample amount in order to obtain the normalised area (norm. Area.sub.x, see equation 1).

[00001]$\begin{array}{cc}norm.Are{a}_X=\frac{Area{\left(EIC\right)}_X}{Area{\left(EIC\right)}_{Benzene}\ast sampleamount\left[\text{g}\right]}& \text{­­­Equation 1}\end{array}$

[0163] For each washing experiment the normalised mean area (norm. Area.sub.x) of the two individual analyses (norm. Area.sub.X1, norm. Area.sub.X2) was calculated by using the Excel function AVERAGE (see equation 2).

[00002]$\begin{array}{cc}\overline{norm.Are{a}_X}=AVERAGE\left(norm.Are{a}_{X1}:norm.Are{a}_{X2}\right)& \text{­­­Equation 2}\end{array}$

[0164] To obtain the relative normalised area (rel. norm. Area.sub.x), the normalised mean area of the respective substance (norm. Area.sub.x) was divided by the normalised mean area of the reference sample (norm. Area.sub.R) as stated in equation 3.

[00003]$\begin{array}{cc}rel.norm.Are{a}_X=\frac{\overline{norm.Are{a}_X}}{norm.Are{a}_R}& \text{­­­Equation 3}\end{array}$

[0165] For the data evaluation three different cases must be distinguished. [0166] 1) The substance specific ion peak was evaluable in both analysis runs of the double determination. The relative normalised area was obtained by applying equations 1, 2 and 3 as described below. [0167] 2) The substance specific ion peak was evaluable in only one analysis run of the double determination. Consequently, the normalised mean area (norm.Area.sub.X) is equal to the normalised area (norm.Area.sub.X). Thus, the so obtained relative normalised area (rel.norm. Area.sub.x) was asterisked (“.sup.∗”) in the result table. [0168] 3) The substance specific ion peak was not evaluable in neither of the two analysis runs of the double determination. Therefore, the calculation of the relative normalised area (rel. norm. Area.sub.x) was not applicable (“n.a.”) which was indicated in the result table.

[0169] In order to estimate the deviation of the two individual analyses of one corresponding washing experiment the relative standard deviation (RSD.sub.X) was calculated (only applicable to case 1). Therefore, the standard deviation of the two normalised areas (norm. Area.sub.X1, norm. Area.sub.X2) was determined by using the Excel function STDEV.S. To calculate RSD.sub.X the standard deviation (STDEV.S) was divided by the normalised mean area (norm. Area.sub.x, see equation 4).

[00004]$\begin{array}{cc}RS{D}_X=\frac{STDEV.S\left(norm.Are{a}_{X1}:norm.Are{a}_{X2}\right)}{\overline{norm.Are{a}_X}}& \text{­­­Equation 4}\end{array}$

[0170] To refer the standard deviation to the rel. norm. Area.sub.x, the RSD.sub.X was multiplied by the rel. norm. Area.sub.X as described in equation 5.

[00005]$\begin{array}{cc}rel.RS{D}_X=RS{D}_X\ast rel.norm.Are{a}_X& \text{­­­Equation 5}\end{array}$

2. Experimental Results

[0171] In the following experiments, the materials used were as follows:

Recycled Polyolefin:

[0172] The recycled polyolefin employed in the following experiments was obtained directed from mtm plastics GmbH, Niedegebra, Germany, and is a pre-sorted, unwashed polymer mixture used by mtm plastics GmbH in the preparation of Dipolen S. Consequently the composition of the recycled polyolefin with regard to the content of polyethylene and polypropylene is identical to that of Dipolen S; however the content of small molecule contaminants is likely to be different.

[0173] Dipolen S is a recycled polymer mixture comprising polyethylene and polypropylene obtained from mtm plastics GmbH, Niedergebra, Germany and has a polyethylene content of 40 wt% determined by DSC analysis. The melting points determined by DSC were 162° C. (PP) and 128° C. (PE).

[0174] In the following experiments, the recycled polyolefin was obtained in a flaked form; cryomilling was then undertaken prior to the below experiments in order to enable the experiments to be carried out on a smaller scale than would be the case for the industrial process.

Sulfuric Acid:

[0175] Concentrated sulfuric acid (96%) was obtained from Sigma Aldrich Corporation. Sulfuric acid having a lower concentration was obtained by dilution with distilled water (addition of acid to water, NOT water to acid).

TABLE-US-00004 Lipophilicity and volatility of tested odorants Contaminant log P.sub.octanol/water b.p. Comment D-limonene 4.2 176° C. Hydrophobic contaminant Styrene 2.3 145° C. (Moderate) hydrophobic contaminant Acetaldehyde 0.45 20° C. (Moderate) hydrophilic contaminant Acetic acid -0.54 118° C. Hydrophilic contaminant and oxidation product

TABLE-US-00005 Washing efficiency of water-, NaOH-, sulphuric acid- and sulphuric acid/NaOH wash in terms of the percentage of remaining contaminants (based on contaminants content before the treatment) after the treatment with the respective wash solvent Wash solvent Acetic acid Acetaldehyde Styrene D-Limonene 1 H.sub.2O wash, RT 32% 18% 77% 70% 2 NaOH (5%), RT 3% 7% 55% 69% 3 H.sub.2SO.sub.4 (50%), RT 337% 9% 55% 3%* 4 H.sub.2SO.sub.4 (95%, RT) 79% 2% 12% n.a. 5 H.sub.2SO.sub.4 (95%, RT), NaOH (5%, RT) 33% 1% 20% n.a. .sup.∗The substance specific ion peak was evaluable in only one analysis run of the double determination. n.a. - In the washed sample the substance specific ion peak was not evaluable in either of the two analysis runs of the double determination, i.e. the contaminant appears to be present in amounts below the detection limit.

Example 1:

[0176] 500 mL of demineralized water were added to 50 g of the cryo-milled rPO and the suspension was allowed to mix by means of an overhead stirrer for 2 hours at room temperature. The solution was then filtrated over a Büchner system and the rPO was recovered. 500 mL of fresh demineralized water was then added to the washed plastic and stirred for a couple of seconds. The plastic was filtrated once again. This step was repeated an additional two times. The rPO was then dried in a vacuum oven at 70° C. for 1 hour.

Example 2:

[0177] 500 mL of a 5 % NaOH aqueous solution were added to 50 g of the cryo-milled rPO and the suspension was allowed to mix by means of an overhead stirrer for 2 hours at room temperature. The solution was then filtrated over a Büchner system and the rPO was recovered. 500 mL of fresh demineralized water was then added to the washed plastic and stirred for a couple of seconds. The plastic was filtrated once again. This step was repeated an additional time. The rPO was then dried in a vacuum oven at 70° C. for 1 hour.

Example 3:

[0178] 500 mL of H.sub.2SO.sub.4 (50 %) were added to 50 g of cryo-milled rPO and the suspension was allowed to mix by means of an overhead stirrer for 2 hours at room temperature. After stirring, the mixture was added to 1 kg of ice in order to dilute the concentrated acid. The ice serves as control for the exothermic reaction taking place between H.sub.2SO.sub.4 and water. The solution was then filtrated over a Büchner system and the rPO is recovered. 500 mL of fresh demineralized water was then added to the washed plastic and stirred for a couple of seconds. The plastic was filtrated once again. This step was repeated an additional two times. The rPO was then dried in a vacuum oven at 70° C. for 1 hour.

Example 4:

[0179] 500 mL of H.sub.2SO.sub.4 (95 %) were added to 50 g of cryo-milled rPO and the suspension was allowed to mix by means of an overhead stirrer for 2 hours at room temperature. After stirring, the mixture was added to 1 kg of ice in order to dilute the concentrated acid. The solution was then filtrated over a Büchner system and the rPO was recovered.

[0180] 500 mL of fresh demineralized water was then added to the washed plastic flakes, directly followed by removal of the water from the slurry by filtration. This rinsing step was repeated an additional two times. The rPO was then dried in a vacuum oven at 70° C. for 1 hour.

Example 5:

[0181] 500 mL of H.sub.2SO.sub.4 (95 %) were added to 50 g of cryo-milled rPO and the suspension was allowed to mix by means of an overhead stirrer for 2 hours at room temperature. After stirring, the mixture was added to 1 kg of ice in order to dilute the concentrated acid. The solution was then filtrated over a Büchner system and the rPO was recovered. 500 mL of fresh demineralized water was then added to the washed plastic flakes, directly followed by removal of the water from the slurry by filtration.

[0182] 500 mL of a 5 % NaOH aqueous solution was then added to the washed plastic and stirred for 1 hour, followed by removal of the wash liquid by filtration. An additional rinsing step with 500 mL of fresh demineralized water was performed. The rPO was then dried in a vacuum oven at 70° C. for 1 hour.

[0183] As can be seen from Table 4, a simple pH-neutral aqueous wash is effective at removing hydrophilic contaminants such as acetic acid and acetaldehyde, however only a very limited removal of hydrophobic contaminants is observed (Example 1). Example 2 demonstrates that a caustic aqueous wash is similarly effective to the pH-neutral wash for most contaminants, however is superior in terms of acetic acid removal. Washing the recycled polyolefin with a relatively dilute acid (Example 3) has the effect of drastically reducing the amount of limonene present in the recycled polyolefin; however, the styrene removal efficiency is essentially no different to the caustic wash of example 2. Interestingly the mildly acidic wash appears to increase the content of acetic acid, possibly due to acid-catalyzed ester hydrolysis processes that form acetic acid.

[0184] Concentrated sulfuric acid has a dramatically improved effect on the content of all of the measured hydrophobic functional group-containing contaminants, thought to be due to the increased oxidizing ability of concentrated sulfuric acid, with the styrene content much lower than previously possible, although the amount of acetic acid is still quite high.

[0185] The process according to the present invention (i.e. Example 5), wherein a (potentially oxidizing) acid wash is combined with a caustic wash, is the only example to show good removal of all of the measured contaminants regardless of their logP values.