Removal of odorous substances from post-consumer polyolefin waste

Abstract

A process for reducing the content of hydrophobic functional group-containing volatile organic compounds and the content of hydrophilic volatile organic compounds of a recycled polyolefin, said process comprising an acidic washing step followed by a basic / neutral washing step.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for reducing the content of hydrophobic functional group-containing volatile organic compounds and the content of hydrophilic volatile organic compounds of a recycled polyolefin, and the use of said process. BACKGROUND

[0002] In the past decade, concerns about the environmental sustainability of plastics and their use at current quantities have increased. This has led to new regulations regarding the disposal, collection and recycling of polyolefins. Furthermore, many countries have made efforts to increase the percentage of plastic materials that are recycled instead of being sent to landfills.

[0003] In Europe, plastic waste accounts for approximately 27 million tons of waste per year; in 2016, 7.4 million tons of this quantity were disposed of by landfill, 11.27 million tons were burned (to produce energy), and approximately 8.5 million tons were recycled. Polypropylene-based materials are a particular problem because these materials are widely used in packaging. Given the large amount of waste collected compared to the amount of waste that is recycled back into the stream (only about 30%), there is still great potential for intelligent reuse of the plastic waste stream and for mechanical recycling of plastic waste.

[0004] Taking the automotive industry as an example, in Europe, the European Union’s End-of-Life Vehicle (ELV) Directive stipulates that 85% / 95% of the materials from a vehicle should be recyclable or recycled. The current recycling rate of automotive parts is far below this target. On average, a vehicle consists of 9% by weight of plastics, of which currently only 3% by weight is recycled. Therefore, if the target for recycled plastics in the automotive industry is to be achieved, there is still a demand to be met. The present invention focuses in particular on the mechanical recycling of waste streams, rather than “energy recycling” in which polyolefins are burned and used for energy. However, due to cost reasons, poor mechanical properties and poor processing properties, waste streams containing crosslinked polyolefins are often used for energy recycling (e.g. incineration in district heating plants or for heat generation in the cement industry) and are often not recycled into new products.

[0005] One major trend in the polyolefin field is the use of recycled materials derived from a wide variety of sources. Durable goods streams such as those derived from waste electronic equipment (WEE) or end-of-life vehicles (ELV) contain a wide variety of plastics. These materials can be processed to extract recycled acrylonitrile-butadiene-styrene (ABS), high-impact polystyrene (HIPS), polypropylene (PP), and polyethylene (PE) plastics. Separation can be performed in water using density separation, followed by further separation based on fluorescence, near-infrared absorption, or Raman fluorescence. However, it is often difficult to obtain pure recycled polypropylene or pure recycled polyethylene. Often, the recycled quantities of polypropylene on the market are mixtures of both polypropylene (PP) and polyethylene (PE); this is especially true for post-consumer waste streams. Commercial recyclates from post-consumer waste sources have been found to often contain mixtures of PP and PE, with the secondary component up to < 50 wt%.

[0006] The better the quality of the recycled polyolefin, i.e. the higher the purity, the more expensive the material. Furthermore, recycled polyolefin materials are often cross-contaminated with non-polyolefin materials such as polyethylene terephthalate, polyamide, polystyrene, or non-polymeric substances such as wood, paper, glass, or aluminum. Furthermore, materials rich in recycled polypropylene often have much poorer performance than virgin materials, unless the amount of recycled polyolefin added to the final compound is very low. For example, such materials often have poor performance in terms of odor and taste, limited stiffness, limited impact strength, and poor mechanical properties such as, for example, brittleness, so they do not meet consumer requirements.

[0007] The poor mechanical properties can be improved by mixing the recycled polyolefin with virgin polymer, or by using reinforcing fillers, however this does not solve the odor / taste problem.

[0008] Existing methods for removing volatile organic compounds from virgin polymers and from recycled polymers involve aeration of the polymer. This can be achieved, inter alia, by using air, an inert gas, or steam.

[0009] Variants of this method have been known for many years and are described, inter alia, in EP 0 004 601 A1, EP 0 859 809 A1, EP 0 964 877 A1, EP 1 542 777 A2, and EP 3 647 328 A1.

[0010] While these methods can be very effective in removing a wide range of volatile compounds, they can be energy-intensive, which can be disadvantageous in terms of production when the goal is a recycling process that is as environmentally friendly as possible.

[0011] Therefore, there remains a need for other methods for reducing odoriferous volatile compounds from recycled polyolefin compositions.

[0012] The present invention is based on the finding that treating a recycled polyolefin with an inorganic oxyacid, followed by treating the recycled polyolefin with water or a caustic (i.e. alkali containing) solution, allows for the removal of both hydrophilic volatile organic compounds (such as acetic acid and acetaldehyde) and hydrophobic functional group containing volatile organic compounds (such as styrene and limonene). SUMMARY

[0013] The present invention relates to a method for reducing the content of hydrophobic functional group containing volatile organic compounds and the content of hydrophilic volatile organic compounds of a recycled polyolefin, said method comprising the following steps in this order:

[0014] (a) treating a recycled polyolefin containing hydrophobic functional group containing volatile organic compounds and hydrophilic volatile organic compounds with an aqueous solution A of an inorganic oxyacid, wherein said aqueous solution A has a pH value of 2.0 or less,

[0015] (b) removing the aqueous solution A of step (a) from the recycled polyolefin,

[0016] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH value of 7.0 or more,

[0017] (d) removing the aqueous solution B of step (c) from the recycled polyolefin,

[0018] (e) optionally drying, extruding and / or aerating the recycled polyolefin,

[0019] thereby obtaining a recycled polyolefin having a reduced content of hydrophobic functional group containing volatile organic compounds and hydrophilic volatile organic compounds,

[0020] 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,

[0021] hydrophobic compounds are defined as those compounds having a logP (octanol / water) value of more than 1.0, and

[0022] hydrophilic compounds are defined as those compounds having a logP (octanol / water) value of less than or equal to 1.0.

[0023] The present invention also relates to the use of the method of the present invention for reducing the content of hydrophobic functional group containing volatile organic compounds and hydrophilic volatile organic compounds, wherein the content of limonene, measured by HS-GC / MS, is reduced to less than 30% of the value measured prior to said method, and / or wherein the content of styrene, measured by HS-GC / MS, is reduced to less than 30% of the value measured prior to said method.

[0024] Definitions

[0025] In the context of the present application, the term "volatile organic compound" refers to any organic compound having an initial boiling point less than or equal to 250°C, as defined by the European Union in the VOC Solvent Emission Directive 1999 / 13 / EC.

[0026] The term "hydrophilic" is used in the present application to mean having a partition function between octanol and water (log P(octanol / water)) less than or equal to 1.0.

[0027] The term "hydrophobic" is used in the present application to mean having a partition function between octanol and water (log P(octanol / water)) greater than 1.0.

[0028] The term "functional group-containing" means that the compound must contain atoms other than carbon and hydrogen and / or must contain a double or triple bond or an aromatic system. Suitable examples of functional groups include hydroxyl, amino, carbonyl (aldehyde or ketone), alkene, alkyne, benzene ring, etc.

[0029] In the context of the present application, the term "acid" refers to a compound that acts as a proton donor in aqueous solution, i.e. a Bronsted acid (H acid). The acid can be monoprotic or polyprotic. In the following, "pKa" (logarithm of the acid dissociation constant) refers to the first dissociation step of the acid.

[0030] "Inorganic oxoacid" is any compound in which the acidic hydrogen is bound to an oxygen atom, wherein the acid does not contain a hydrocarbon chain or ring structure (i.e. an organic moiety). These inorganic oxoacids typically (although not strictly always) have the type of formula H m XO n wherein X is an atom that acts as the central atom, while the parameters m and n depend on the oxidation state of the element X. In most cases, the element X is a non-metal, although certain metals (e.g. chromium and manganese) can form oxoacids (when in their highest oxidation state). Because the oxidation state of the central atom X is typically high, the conjugate base of such oxoacids can act as an oxidizing agent.

[0031] The skilled person will realize that pH values greater than 14.0 and lower than 0.0 are theoretically possible; however, they will also realize that the determination of such pH values using conventional pH probes is extremely difficult. Therefore, in the context of the present application, an aqueous solution having an effective pH greater than 14.0 is considered to have a pH of 14.0, and an aqueous solution having an effective pH lower than 0.0 is considered to have a pH of 0.0.

[0032] In the context of the present invention, the term "flushing" is used to denote the addition of a solvent, typically water, which serves to remove foreign material or residual liquids from the surface of the polyolefin. This can be achieved in a very short time, i.e. less than 5 minutes, typically less than 1 minute, in sharp contrast to the "washing" step which typically requires a longer time and agitation to extract volatile organic compounds from the polyolefin.

[0033] Where the term "comprising" is used in the present specification and claims, it does not exclude other un-specified elements or steps. For the purposes of the present invention, the term "consisting of" is to be understood as meaning that the specified elements or steps are the only ones that are present in the combination. If, in the following text, a combination is defined to comprise at least a certain number of elements, this is to be understood as meaning that, in addition to these elements, other elements can also be present, provided that the overall number of elements in the combination is at least the number specified.

[0034] Where an indefinite or definite article is used when referring to a singular noun e.g. "an", "a" or "the", this includes a plural of that noun unless specifically stated otherwise. DETAILED DESCRIPTION

[0035] Method

[0036] The method for reducing the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds of a recycled polyolefin comprises the following steps in this order:

[0037] (a) treating a recycled polyolefin containing hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds with an aqueous solution A of a mineral oxyacid, wherein the aqueous solution A has a pH value of 2.0 or less,

[0038] (b) removing the aqueous solution A of step (a) from the recycled polyolefin,

[0039] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH value of 7.0 or more,

[0040] (d) removing the aqueous solution B of step (c) from the recycled polyolefin,

[0041] (e) optionally drying, extruding and / or aerating the recycled polyolefin,

[0042] thereby obtaining a recycled polyolefin having a reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds,

[0043] wherein a volatile organic compound is defined as an organic compound 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,

[0044] Hydrophobic compounds are defined as those compounds having a logP (octanol / water) value greater than 1.0, and

[0045] Hydrophilic compounds are defined as those compounds having a logP (octanol / water) value less than or equal to 1.0.

[0046] In an alternative embodiment, the process for reducing the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds of a recycled polyolefin comprises the following steps in this order:

[0047] (a) treating a recycled polyolefin containing hydrophobic functional group- containing volatile organic compounds and hydrophilic volatile organic compounds with an aqueous solution A of a mineral oxyacid, wherein the aqueous solution A has a pH value in the range of 0.0 to 2.0,

[0048] (b) removing the aqueous solution A of step (a) from the recycled polyolefin,

[0049] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH value in the range of 7.0 to 14.0,

[0050] (d) removing the aqueous solution B of step (c) from the recycled polyolefin,

[0051] (e) optionally drying, extruding and / or aerating the recycled polyolefin,

[0052] thereby obtaining a recycled polyolefin having a reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds,

[0053] wherein volatile organic compounds are defined as organic compounds having an initial boiling point (b.p.) less than or equal to 250°C when measured at a standard atmospheric pressure of 101.3 kPa,

[0054] Hydrophobic compounds are defined as those compounds having a logP (octanol / water) value greater than 1.0, and

[0055] Hydrophilic compounds are defined as those compounds having a logP (octanol / water) value less than or equal to 1.0.

[0056] The recycled polyolefin must contain hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds. These compounds are typically generated by contamination during the first use of the polymer, usually when the polymer is used as a packaging material, especially for food and / or personal care compositions.

[0057] It is further preferred that the hydrophobic functional group containing volatile organic compound of the present application contains a covalent bond selected from the group consisting of an O-H bond, a C=0 bond and a C=C bond.

[0058] The recycled polyolefin is preferably derived from post-consumer waste, post-industrial waste or a combination thereof, most preferably from post-consumer waste.

[0059] Post-consumer waste refers to objects that have at least completed their first life cycle, i.e. have served their first purpose; whereas post-industrial waste refers to manufacturing scrap, which typically does not reach the consumer.

[0060] The recycled polyolefin is preferably provided in the form of flakes or pellets.

[0061] While the process according to the present application is effective in removing both the hydrophobic functional group containing volatile organic compound and the hydrophilic volatile organic compound from the recycled polyolefin in the form of flakes or pellets, it is preferred that the recycled polyolefin is shredded prior to the treatment with the aqueous solution of inorganic oxoacid A. It has been found that this improves the extraction of both the hydrophobic functional group containing volatile organic compound and the hydrophilic volatile organic compound due to the higher effective surface area and improved ease of stirring, if stirring is required.

[0062] It is further preferred that the combination of the aqueous solution A and the recycled polyolefin in step (a) is subjected to stirring by mechanical mixing, ultrasonication, mechanical grinding or circulation pumping. This stirring helps to expose the surface of the recycled polyolefin to fresh aqueous solution A, thereby avoiding that a high concentration of the extracted volatile organic compound at the interface hinders further extraction.

[0063] It is also preferred that the combination of the aqueous solution B and the recycled polyolefin in step (c) is subjected to stirring by mechanical mixing, ultrasonication, mechanical grinding or circulation pumping for the same reasons as mentioned above.

[0064] Steps (b) and (d) involve the removal of the aqueous solution A and the aqueous solution B, respectively, from the recycled polyolefin. While this process is relatively simple to achieve by decanting and / or filtering the mixture, traces of the aqueous solution A or the aqueous solution B can remain on the surface of the recycled polyolefin. These traces of the aqueous solution A and / or B contain the dissolved volatile organic compounds, as well as the acid and / or base, if present, and it is therefore advantageous to remove all traces of the aqueous solution A and / or B.

[0065] This can be achieved by using a rinsing step, in which any foreign material and / or aqueous solution is rinsed off from the surface of the recycled polyolefin.

[0066] It is therefore preferred that the process comprises an additional step (b2) of rinsing the recovered polyolefin from the residual of the aqueous solution (A) and / or any other foreign material and / or degradation products thereof, which is carried out after step (b).

[0067] It is further preferred that the process comprises an additional step (d2) of rinsing the recovered polyolefin from the residual of the aqueous solution (B) and / or any other foreign material and / or degradation products thereof, which is carried out after step (d).

[0068] Step (a) itself involves treating the recovered 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 present in the recovered polyolefin, such as styrene and limonene, thereby converting them into more hydrophilic and / or more volatile compounds, enabling their extraction into the aqueous solution A.

[0069] In order to achieve this hypothesized oxidative / acidic degradation, the acid must be an inorganic oxoacid, as the counterion of such an acid can act as an oxidizing agent.

[0070] It is preferred that the inorganic oxoacid is selected from the group consisting of pyrosulfuric acid, sulfuric acid, phosphoric acid, nitric acid, perchloric acid, and mixtures thereof.

[0071] In a particularly preferred embodiment, the inorganic oxoacid is sulfuric acid.

[0072] It is preferred that the inorganic oxoacid has a pKa in the range of -5.0 to 5.0, preferably in the range of -5.0 to 0.0.

[0073] It is additionally preferred that the amount of inorganic oxoacid in the aqueous solution A is in the range of 40 to 100 wt.-% (corresponding to a molar concentration of 5.3 to 18.65 M for sulfuric acid), more preferably in the range of 70 to 98 wt.-% (corresponding to 11.5 M to 18.4 M, most preferably 94 to 98 wt.-% (corresponding to 17.8 M to 18.4 M) for sulfuric acid.

[0074] The aqueous solution A can comprise more than one inorganic oxoacid. The above-mentioned concentrations and pKa values refer to each individual acid.

[0075] It is particularly preferred that the aqueous solution A is an aqueous solution of sulfuric acid having a concentration in the range of 94 to 98 wt.-%.

[0076] The pH of the aqueous solution A must be less than 2.0, more preferably less than 1.0, most preferably less than 0.5.

[0077] Optionally, the pH must be in the range of 0.0 to 2.0, more preferably in the range of 0.0 to 1.0, most preferably in the range of 0.0 to 0.5.

[0078] The treatment of the recovered polyolefin with aqueous solution A in step (a) is a washing step, which is different from the rinsing step as defined herein, and is thus typically for 5 minutes or more, such as 5 minutes to 24 hours.

[0079] The treatment of the recovered polyolefin with aqueous solution A in step (a) is preferably for 5 minutes to 4 hours, preferably 30 minutes to 3 hours, most preferably 1 to 2 hours.

[0080] It is further preferred that step (a) is carried out at a temperature in the range of 10 to 45 °C, more preferably in the range of 20 to 35 °C.

[0081] While step (a) is effective for the removal of some hydrophilic volatile organic compounds, the highly acidic nature of aqueous solution A can make the extraction of many hydrophilic compounds, especially acidic examples, less effective than the case of a simple water wash.

[0082] Accordingly, the treatment of the recovered polyolefin from step (b) with aqueous solution B in step (c) serves to remove any remaining hydrophilic volatile organic compounds.

[0083] The treatment with water can serve 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.

[0084] It is preferred that the caustic aqueous solution comprises the base in an amount in the range of 0.5 to 10 wt.%, more preferably 1 to 5 wt.%.

[0085] The choice of base is not critical, 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.

[0086] It is particularly preferred that the base is sodium hydroxide.

[0087] In a particularly preferred embodiment, aqueous solution B is a sodium hydroxide solution having a concentration of sodium hydroxide in the range of 3 to 10 wt.%.

[0088] The presence of the base means that the pH of aqueous solution B is increased to above 7.0.

[0089] It is preferred that the pH of the caustic aqueous solution is in the range of 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.

[0090] It is alternatively preferred that the aqueous caustic solution has a pH in the range of 9.0 to 14.0, more preferably in the range of 11.0 to 14.0, most preferably in the range of 12.0 to 14.0.

[0091] The treatment of the recovered polyolefin with the aqueous solution B in step (c) is a washing step, which is different from the rinsing step as defined herein, and thus typically lasts for 5 minutes or more, such as 5 minutes to 24 hours.

[0092] The treatment of the recovered polyolefin with the aqueous solution B in step (c) preferably lasts for 5 minutes to 4 hours, preferably 30 minutes to 3 hours, most preferably 1 to 2 hours.

[0093] It is further preferred that step (c) is carried out at a temperature in the range of 20 to 90 °C, more preferably in the range of 50 to 80 °C.

[0094] In a particularly preferred embodiment, the aqueous solution A is an aqueous solution of sulfuric acid having a concentration in the range of 94 to 98 wt.-%, and the aqueous solution B is a sodium hydroxide solution having a concentration of sodium hydroxide in the range of 3 to 10 wt.-%.

[0095] The process as described above leads to a reduction of the hydrophobic functional group-containing volatile organic compound content and the hydrophilic volatile organic compound content of the recovered polyolefin.

[0096] It is particularly preferred that the recovered polyolefin obtained as product of the process has a limonene content as measured by HS-GC / MS which is less than 30% of the value measured prior to the process.

[0097] It is further preferred that the recovered polyolefin obtained as product of the process has a styrene content as measured by HS-GC / MS which is less than 30% of the value measured prior to the process.

[0098] It is additionally preferred that the recovered polyolefin obtained as product of the process has an acetic acid content as measured by HS-GC / MS which is less than 40% of the value measured prior to the process.

[0099] It is further preferred that the recovered polyolefin obtained as product of the process has an acetaldehyde content as measured by HS-GC / MS which is less than 20% of the value measured prior to the process.

[0100] In a particularly preferred embodiment, the recovered polyolefin obtained as product of the process has a limonene content measured by HS-GC / MS of less than 30% of the value measured before the process, a styrene content measured by HS-GC / MS of less than 30% of the value measured before the process, an acetic acid content measured by HS-GC / MS of less than 40% of the value measured before the process and an acetaldehyde content measured by HS-GC / MS of less than 20% of the value measured before the process.

[0101] Use

[0102] The present application also relates to the use of the process as described above. All preferred features and preferred embodiments applicable to the process itself are equally applicable to the use of the process.

[0103] In one embodiment, the process can be used to reduce the content of hydrophobic functional group containing volatile organic compounds and hydrophilic volatile organic compounds in the recovered polyolefin, wherein the limonene content measured by HS-GC / MS is reduced to less than 30% of the value measured before the process.

[0104] In an alternative embodiment, the process can be used to reduce the content of hydrophobic functional group containing volatile organic compounds and hydrophilic volatile organic compounds in the recovered polyolefin, wherein the styrene content measured by HS-GC / MS is reduced to less than 30% of the value measured before the process.

[0105] In a preferred embodiment, the process can be used to reduce the content of hydrophobic functional group containing volatile organic compounds and hydrophilic volatile organic compounds in the recovered polyolefin, wherein the limonene content measured by HS-GC / MS is reduced to less than 30% of the value measured before the process and wherein the styrene content measured by HS-GC / MS is reduced to less than 30% of the value measured before the process.

[0106] In each of these embodiments, it is preferred that the acetic acid content measured by HS-GC / MS is reduced to less than 40% of the value measured before the process.

[0107] It is also preferred that the acetaldehyde content measured by HS-GC / MS is reduced to less than 20% of the value measured before the process.

[0108] It is particularly preferred that the acetic acid content measured by HS-GC / MS is reduced to less than 40% of the value measured before the process and that the acetaldehyde content measured by HS-GC / MS is reduced to less than 20% of the value measured before the process.

[0109] In yet another preferred embodiment, the method can be used to reduce the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in the recycled polyolefin, wherein the limonene content measured by HS-GC / MS is reduced to less than 30% of the value measured prior to the method, the styrene content measured by HS-GC / MS is reduced to less than 30% of the value measured prior to the method, the acetic acid content measured by HS-GC / MS is reduced to less than 40% of the value measured prior to the method and the acetaldehyde content measured by HS-GC / MS is reduced to less than 20% of the value measured prior to the method.

[0110] The present application can feature the following:

[0111] 1. A method for reducing the content of hydrophobic functional group-containing volatile organic compounds and the content of hydrophilic volatile organic compounds in a recycled polyolefin, the method comprising the following steps in this order:

[0112] (a) treating the recycled polyolefin with an aqueous solution A of a mineral oxyacid, the recycled polyolefin containing hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, wherein the aqueous solution A has a pH value of 2.0 or less,

[0113] (b) removing the aqueous solution A of step (a) from the recycled polyolefin,

[0114] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH value of 7.0 or more,

[0115] (d) removing the aqueous solution B of step (c) from the recycled polyolefin,

[0116] (e) optionally drying, extruding and / or aerating the recycled polyolefin,

[0117] thereby obtaining a recycled polyolefin having a reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds,

[0118] 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,

[0119] hydrophobic compounds are defined as those compounds having a logP (octanol / water) value of more than 1.0, and

[0120] hydrophilic compounds are defined as those compounds having a logP (octanol / water) value of less than or equal to 1.0.

[0121] 2. A process for reducing the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds of a recycled polyolefin, the process comprising the following steps in this order:

[0122] (a) treating a recycled polyolefin containing hydrophobic functional group- containing volatile organic compounds and hydrophilic volatile organic compounds with an aqueous solution A of a mineral oxyacid, wherein the aqueous solution A has a pH value in the range of 0.0 to 2.0,

[0123] (b) removing the aqueous solution A of step (a) from the recycled polyolefin,

[0124] (c) treating the recycled polyolefin of step (b) with an aqueous solution B having a pH value in the range of 7.0 to 14.0,

[0125] (d) removing the aqueous solution B of step (c) from the recycled polyolefin,

[0126] (e) optionally drying, extruding and / or aerating the recycled polyolefin,

[0127] thereby obtaining a recycled polyolefin having a reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds,

[0128] wherein volatile organic compounds are defined as organic compounds having an initial boiling point (b.p.) less than or equal to 250°C when measured at a standard atmospheric pressure of 101.3 kPa,

[0129] hydrophobic compounds are defined as those compounds having a logP (octanol / water) value greater than 1.0, and

[0130] hydrophilic compounds are defined as those compounds having a logP (octanol / water) value less than or equal to 1.0.

[0131] 3. The process according to item 1 or item 2, wherein the functional group-containing volatile organic compounds contain covalent bonds selected from O-H bonds, C=0 bonds and C=C bonds.

[0132] 4. The process according to any one of the preceding items, wherein the recycled polyolefin of step (a) is in the form of flakes or in the form of pellets.

[0133] 5. The process according to item 4, wherein the recycled polyolefin in the form of flakes or in the form of pellets is shredded prior to the treatment with the aqueous solution A.

[0134] 6. The process according to any one of the preceding items, wherein the recycled polyolefin is treated with the aqueous solution A in step (a) for a period of 5 minutes to 4 hours.

[0135] 7. The process according to any one of the preceding items, wherein step (a) is carried out at a temperature in the range of 10 to 45 °C.

[0136] 8. The process according to any one of the preceding items, wherein the recovered polyolefin is treated with aqueous solution B in step (c) for a period of 5 minutes to 4 hours.

[0137] 9. The process according to any one of the preceding items, wherein step (c) is carried out at a temperature in the range of 20 to 90 °C.

[0138] 10. The process according to any one of the preceding items, wherein the inorganic oxoacid is selected from the group consisting of pyrosulfuric acid, sulfuric acid, phosphoric acid, nitric acid, perchloric acid and mixtures thereof.

[0139] 11. The process according to item 10, wherein the inorganic oxoacid is sulfuric acid.

[0140] 12. The process according to any one of the preceding items, wherein the pKa of the inorganic oxoacid is in the range of -5.0 to 5.0, preferably in the range of -5.0 to 0.0.

[0141] 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.-%.

[0142] 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.

[0143] 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.-%.

[0144] 16. The process according to 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.

[0145] 17. The process according to any one of items 14 to 16, wherein the base is sodium hydroxide.

[0146] 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.

[0147] 19. The process according to any one of the preceding items, wherein the combination of aqueous solution A and the recovered polyolefin in step (a) is subjected to agitation by mechanical mixing, ultrasonication, mechanical milling or circulation pumping.

[0148] 20. The process according to any of the preceding items, wherein the combination of aqueous solution B in step (c) and the recycled polyolefin is subjected to agitation by mechanical mixing, ultrasonication, mechanical grinding or circulation pumping.

[0149] 21. The process according to any of the preceding items, wherein the process comprises an additional step (b2) of rinsing the recycled polyolefin from the residue of aqueous solution A and / or any other foreign material and / or degradation products thereof, which is carried out after step (b).

[0150] 22. The process according to any of the preceding items, wherein the process comprises an additional step (d2) of rinsing the recycled polyolefin from the residue of aqueous solution B and / or any other foreign material and / or degradation products thereof, which is carried out after step (d).

[0151] 23. The process according to any of the preceding items, wherein the recycled polyolefin is derived from post-consumer waste, post-industrial waste or a combination thereof.

[0152] 24. The process according to item 23, wherein the recycled polyolefin is derived from post-consumer waste.

[0153] 25. The process according to any of the preceding items, wherein the recycled polyolefin obtained as product of the process has a limonene content as measured by HS-GC / MS which is less than 30% of the value measured prior to the process.

[0154] 26. The process according to any of the preceding items, wherein the recycled polyolefin obtained as product of the process has a styrene content as measured by HS-GC / MS which is less than 30% of the value measured prior to the process.

[0155] 27. The process according to any of the preceding items, wherein the recycled polyolefin obtained as product of the process has an acetic acid content as measured by HS-GC / MS which is less than 40% of the value measured prior to the process.

[0156] 28. The process according to any of the preceding items, wherein the recycled polyolefin obtained as product of the process has an acetaldehyde content as measured by HS-GC / MS which is less than 20% of the value measured prior to the process.

[0157] 29. Use of the process according to any of the preceding items for reducing the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds in the recycled polyolefin, wherein the limonene content as measured by HS-GC / MS is reduced to less than 30% of the value measured prior to the process.

[0158] 30. Use of the method according to any one of items 1 to 24 for reducing the content of hydrophobic functional group containing volatile organic compounds and hydrophilic volatile organic compounds in a recycled polyolefin, wherein the content of styrene as measured by HS-GC / MS is reduced to less than 30% of the value measured prior to the method.

[0159] 31. Use of the method according to item 1 or 24 for reducing the content of hydrophobic functional group containing volatile organic compounds and hydrophilic volatile organic compounds in a recycled polyolefin, wherein the content of limonene as measured by HS-GC / MS is reduced to less than 30% of the value measured prior to the method and wherein the content of styrene as measured by HS-GC / MS is reduced to less than 30% of the value measured prior to the method.

[0160] 32. Use according to any one of items 29 to 31, wherein the content of acetic acid as measured by HS-GC / MS is reduced to less than 40% of the value measured prior to the method.

[0161] 33. Use according to any one of items 29 to 32, wherein the content of acetaldehyde as measured by HS-GC / MS is reduced to less than 20% of the value measured prior to the method.

[0162] Example

[0163] 1. Definition / assay method:

[0164] Determination of acetic acid, styrene and limonene content via HS-GC / MS

[0165] Static headspace analysis for marker substance determination

[0166] Herein the parameters of the applied headspace gas chromatography mass spectrometry (HS / GC / MS) method are described.

[0167] For the measurement of the benzene standard, 5 μl of a standard solution containing 100 μg / ml benzene in methanol were injected into a 20 ml HS vial and closed with a PTFE cap. Each HS / GC / MS test sequence of sample measurements included an analysis of such a benzene standard. The benzene signal of the corresponding sequence was used for the calculation of the relative normalized area as further described below.

[0168] The samples were also analyzed by HS / GC / MS to determine potential odor and hazard marker substances. Therefore, 2.000 ± 0.100 g of sample were weighed into a 20 ml HS vial and sealed with a PTFE cap. For each washing experiment, a duplicate determination was performed for the respective sample.

[0169] The headspace parameters for the analysis of standards and samples differ in vial equilibration time and HS oven temperature. In addition to this, the method parameters remain the same for both standard and sample runs. The mass spectrometer is operated in scan mode and a total ion chromatogram (TIC) is recorded for each analysis. The detected substances are preliminarily identified by deconvolution and aided by a minimum match of 800 when it is subsequently compared to a mass spectral library. More details on the method parameters and data evaluation software are given below:

[0170] • HS parameters (Agilent G1888 headspace sampler)

[0171] Vial equilibration time: 5 min (benzene standard), 120 min (sample)

[0172] Oven temperature: 200 °C (benzene standard), 100 °C (sample)

[0173] Loop temperature: 205 °C

[0174] Transfer line temperature: 210 °C

[0175] Low shaking

[0176] • GC parameters (Agilent 7890A GC system)

[0177] Column: ZB-WAX 7HG-G007-22 (30 m x 250 pm x 1 pm)

[0178] Carrier gas: Helium 5.0

[0179] Flow: 2 milliliters / minute

[0180] Split ratio: 5:1

[0181] GC oven program: 35 °C for 0.1 min

[0182] 10 °C / min until 250 °C

[0183] 250 °C for 1 min

[0184] • MS parameters (Agilent 5975C inert XL MSD)

[0185] Acquisition mode: Scan

[0186] Scan parameters:

[0187] Low mass: 20

[0188] High mass: 200

[0189] Threshold: 10

[0190] • Software / data evaluation

[0191] MSD ChemStation E.02.02.1431

[0192] MassHunter GC / MS Acquisition B.07.05.2479

[0193] AMDIS GC / MS Analysis Version 2.71

[0194] NIST Mass Spectral Library (2011 version)

[0195] Microsoft Excel 2016

[0196] Data evaluation

[0197] The benzene standard was evaluated using the same parameters as for the sample run. Therefore, extracted ion chromatograms (EIC) of the measured benzene standard and sample were created. The peak areas required for further data evaluation were obtained by integration of the corresponding substance peaks of the EIC. The integration parameters and substance specific ions (m / z ratios) applied for all marker substances are listed in Tables 1 and 2.

[0198] Table 1: Retention times and substance specific ions of the selected marker substances.

[0199]

[0200] 1 Related to both standard and sample.

[0201] * 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 small amount of impurity has not been observed to have a significant influence on the values obtained in the data presented below. In general, the possibility of overlapping peaks in other areas of the HS-GC / MS readout cannot be ruled out.

[0202] Table 2: Integration parameters for determining peak areas.

[0203]

[0204] The substance specific ion peak area (area (EIC) X ) was normalized by the extracted ion peak area (area (EIC) 苯 ) of benzene and the sample amount to obtain the normalized area (normalized area X , see equation 1).

[0205]

[0206] For each wash experiment, the normalized average area (normalized area X1 , normalized area X2 ) of both individual analyses (normalized area (see equation 2) was calculated by using the Excel function AVERAGE.

[0207]

[0208] To obtain the relative normalized area (relative normalized area X ), the normalized average area (normalized area of the respective substance was divided by the normalized average area (normalized area R ) of the reference sample, as described in equation 3.

[0209]

[0210] For data evaluation, three different cases need to be distinguished.

[0211] 1) In both analytical runs of the duplicate determination, substance-specific ion peaks were evaluable. The relative normalized area was obtained by applying equations 1, 2 and 3, as described below.

[0212] 2) Substance-specific ion peaks were only evaluable in one analytical run of the duplicate determination. Accordingly, the normalized average area equals the normalized area (normalized area X ). The relative normalized area (relative normalized area X ) thus obtained is marked with an asterisk (“*”) in the result table.

[0213] 3) In both analytical runs of the duplicate determination, substance-specific ion peaks were not evaluable. Therefore, the calculation of the relative normalized area (relative normalized area X ) was not applicable (“n.a.”), which is indicated in the result table.

[0214] To estimate the deviation of two individual analyses of one corresponding wash experiment, the relative standard deviation (RSD X ) was calculated (only applicable for case 1). Therefore, the standard deviation of both normalized areas (normalized area X1 , normalized area X2 ) was determined by using the Excel function STDEV.S. To calculate the RSD X , the standard deviation (STDEV.S) was divided by the normalized average area (normalized area see equation 4).

[0215]

[0216] In order to refer the standard deviation to the relative normalized area X The RSD X is multiplied by the relative normalized area X as described in equation 5.

[0217] The relative RSD X = RSD X * relative normalized area X Equation 5

[0218] 2. Experimental results:

[0219] In the following experiments, the materials used were as follows:

[0220] Reclaimed polyolefin:

[0221] The reclaimed polyolefin used in the following experiments was obtained directly from mtm plastics GmbH, Niedegebra, Germany, and was a pre-sorted, unwashed polymer mixture used by mtm plastics GmbH in the production of Dipolen S. Therefore, the composition of this reclaimed polyolefin with respect to the content of polyethylene and polypropylene was the same as Dipolen S; however, the content of small molecule contaminants can have differed.

[0222] Dipolen S is a reclaimed polymer mixture comprising polyethylene and polypropylene obtained from mtm plastics GmbH, Niedegebra, Germany, and the polyethylene content was determined by DSC analysis to be 40 wt.%. The melting points determined by DSC were 162 °C (PP) and 128 °C (PE).

[0223] In the following experiments, the reclaimed polyolefin was obtained in flake form; it was then cryogenically ground prior to the following experiments in order to be able to perform the experiments on a smaller scale than the case of the industrial process.

[0224] Sulfuric acid:

[0225] Concentrated sulfuric acid (96%) was obtained from Sigma Aldrich Corporation. Sulfuric acid with lower concentrations was obtained by dilution with distilled water (acid was added to water, not water to acid).

[0226] Table 3. Lipophilicity and volatility of the odorants tested

[0227] contaminants logP 辛醇 / 水 ]]> b.p. reviews d-limonene 4.2 176℃ hydrophobic contaminants styrene 2.3 145℃ (moderately) hydrophobic contaminants acetaldehyde 0.45 20℃ (moderately) hydrophilic contaminants acetic acid -0.54 118℃ hydrophilic contaminants and oxidation products

[0228] Table 4. Washing efficiency of water wash, NaOH wash, sulfuric acid wash, and sulfuric acid / NaOH wash expressed as percentage of remaining contaminants after treatment with the respective washing solvent (based on contaminant content before treatment).

[0229]

[0230] * Substance specific ion peaks were only evaluable in one analytical run of the duplicate determination.

[0231] n.a. - Substance specific ion peaks were not evaluable in either of the two analytical runs of the duplicate determination, i.e. the contaminants appeared to be present in an amount below the detection limit in the washed sample.

[0232] Example 1:

[0233] 500 mL of demineralized water were added to 50 g of cryogenically ground rPO and the suspension was allowed to mix at room temperature for 2 hours with the aid of an overhead stirrer. The solution was then filtered through a Büchner system and the rPO was recovered. 500 mL of fresh demineralized water were then added to the washed plastic and stirred for a few seconds. The plastic was filtered again. This step was repeated twice more. The rPO was then dried in a vacuum oven at 70 °C for 1 hour.

[0234] Example 2:

[0235] 500 mL of a 5% aqueous NaOH solution were added to 50 g of cryogenically ground rPO and the suspension was allowed to mix at room temperature for 2 hours with the aid of an overhead stirrer. The solution was then filtered through a Büchner system and the rPO was recovered. 500 mL of fresh demineralized water were then added to the washed plastic and stirred for a few seconds. The plastic was filtered again. This step was repeated once more. The rPO was then dried in a vacuum oven at 70 °C for 1 hour.

[0236] Example 3:

[0237] 500 mL of H2SO4 (50%) were added to 50 g of cryogenically ground rPO and the suspension was allowed to mix at room temperature for 2 hours with the aid of an overhead stirrer. After stirring, the mixture was added to 1 kg of ice to dilute the concentrated acid. The ice served as a control for the exothermic reaction that takes place between H2SO4 and water. The solution was then filtered through a Büchner system and the rPO was recovered. 500 mL of fresh demineralized water were then added to the washed plastic and stirred for a few seconds. The plastic was filtered again. This step was repeated twice more. The rPO was then dried in a vacuum oven at 70 °C for 1 hour.

[0238] Example 4:

[0239] Example 3: 500 mL of H2SO4 (95%) was added to 50 g of cryogenically ground rPO and the suspension was allowed to mix at room temperature for 2 hours with the aid of an overhead stirrer. After stirring, the mixture was added to 1 kg of ice to dilute the concentrated acid. The solution was then filtered through a Buchner system and the rPO was recovered. Then, 500 mL of fresh demineralized water was added to the washed plastic sheeting, which was then removed from the slurry directly by filtration. This rinsing step was repeated twice more. The rPO was then dried in a vacuum oven at 70°C for 1 hour.

[0240] Example 4: 500 mL of a 5% aqueous NaOH solution was then added to the washed plastic and stirred for 1 hour, after which the wash liquid was removed by filtration. An additional rinsing step was performed using 500 mL of fresh demineralized water. The rPO was then dried in a vacuum oven at 70°C for 1 hour.

[0241] Example 5:

[0242] Example 3: 500 mL of H2SO4 (95%) was added to 50 g of cryogenically ground rPO and the suspension was allowed to mix at room temperature for 2 hours with the aid of an overhead stirrer. After stirring, the mixture was added to 1 kg of ice to dilute the concentrated acid. The solution was then filtered through a Buchner system and the rPO was recovered. Then, 500 mL of fresh demineralized water was added to the washed plastic sheeting, which was then removed from the slurry directly by filtration. This rinsing step was repeated twice more. The rPO was then dried in a vacuum oven at 70°C for 1 hour.

[0243] Example 4: 500 mL of a 5% aqueous NaOH solution was then added to the washed plastic and stirred for 1 hour, after which the wash liquid was removed by filtration. An additional rinsing step was performed using 500 mL of fresh demineralized water. The rPO was then dried in a vacuum oven at 70°C for 1 hour.

[0244] As can be seen from Table 4, a simple pH neutral water wash was effective in removing hydrophilic contaminants such as acetic acid and acetaldehyde, but only very limited removal of hydrophobic contaminants was observed (Example 1). Example 2 demonstrated that for most contaminants, a caustic water wash was similar in effectiveness to a pH neutral wash, although superior in removing acetic acid. Washing the recovered polyolefin with a relatively dilute acid (Example 3) had the effect of significantly reducing the amount of limonene present in the recovered polyolefin; however, the removal efficiency of styrene was essentially indistinguishable from the caustic wash of Example 2. Of interest, the mild acidic wash appeared to increase the acetic acid content, likely due to the acid catalyzed ester hydrolysis process forming acetic acid.

[0245] Concentrated sulfuric acid had a dramatically improved effect on the content of all measured contaminants containing hydrophobic functional groups, which is believed to be due to the increased oxidative capacity of concentrated sulfuric acid, where despite the high amount of acetic acid, the styrene content was far lower than previously possible.

[0246] The process according to the application in which the (potentially oxidizing) acidic wash is combined with a caustic wash (i.e. Example 5) is the only example showing good removal of all measured contaminants, regardless of their logP value.

Claims

1. A process for reducing the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds of a recycled polyolefin, said process comprising the following steps in this order: (a) treating a recycled polyolefin containing hydrophobic functional group- containing volatile organic compounds and hydrophilic volatile organic compounds with an aqueous solution A of a mineral oxyacid, wherein the aqueous solution A has a pH value of 2.0 or less and the mineral oxyacid is sulfuric acid, (b) removing the 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 more, (d) removing the 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 having a reduced content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, wherein a volatile organic compound is defined as an organic compound 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 log P 辛醇 / 水 values greater than 1.0, and Hydrophilic compounds are defined as those compounds having a log P value less than or equal to 1.

0. 辛醇 / 水 Hydrophilic compounds are defined as those compounds having a log P value less than or equal to 1.

0.

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

3. The process according to claim 2, wherein the recycled polyolefin in the form of flakes or pellets is shredded prior to the treatment with the aqueous solution A.

4. The process according to any one of claims 1 to 3, wherein the recycled polyolefin is treated with the aqueous solution A in step (a) for 5 minutes to 4 hours and step (a) is conducted at a temperature in the range of 10 to 45°C.

5. The process according to any one of claims 1 to 3, wherein the recycled polyolefin is treated with the aqueous solution B in step (c) for 5 minutes to 4 hours and step (c) is conducted at a temperature in the range of 20 to 90°C.

6. The process according to any one of claims 1 to 3, wherein the amount of the mineral oxyacid in the aqueous solution A is in the range of 40 to 100% by weight.

7. The process according to any one of claims 1 to 3, wherein the aqueous solution B of step (c) is a caustic aqueous solution comprising a base.

8. 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.

9. 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% by weight.

10. 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.

11. The process according to any one of claims 1 to 3, wherein the combination of the aqueous solution A and the recycled polyolefin in step (a) is subjected to agitation by mechanical mixing, ultrasonication, mechanical milling or circulation pumping, and / or wherein the combination of aqueous solution B and the recovered polyolefin is subjected to agitation in step (c) by mechanical mixing, ultrasonication, mechanical grinding or circulation pumping.

12. The process according to any one of claims 1 to 3, wherein the process comprises an additional step (b2) of rinsing the residue of the aqueous solution A of recovered polyolefin and / or any other foreign material and / or degradation products thereof, which is carried out after step (b), and / or wherein the process comprises an additional step (d2) of rinsing the residue of the aqueous solution B of recovered polyolefin and / or any other foreign material and / or degradation products thereof, which is carried out after step (d).

13. The process according to any one of claims 1 to 3, wherein the recovered polyolefin is derived from post-consumer waste, post-industrial waste or a combination thereof.

14. The process according to any one of claims 1 to 3, wherein the recovered polyolefin obtained as product of the process has: a limonene content measured by HS-GC / MS of less than 30% of the value measured prior to the process, and / or a styrene content measured by HS-GC / MS of less than 30% of the value measured prior to the process, and / or an acetic acid content measured by HS-GC / MS of less than 40% of the value measured prior to the process, and / or an acetaldehyde content measured by HS-GC / MS of less than 20% of the value measured prior to the process.

15. Use of the process according to any one of claims 1 to 14 for reducing the content of hydrophobic functional group-containing volatile organic compounds and hydrophilic volatile organic compounds, wherein the limonene content measured by HS-GC / MS is reduced to less than 30% of the value measured prior to the process, and / or wherein the styrene content measured by HS-GC / MS is reduced to less than 30% of the value measured prior to the process.

16. Use according to claim 15, wherein the acetic acid content measured by HS-GC / MS is reduced to less than 40% of the value measured prior to the process, and / or wherein the acetaldehyde content measured by HS-GC / MS is reduced to less than 20% of the value measured prior to the process.

17. Process according to any one of claims 1 to 14, wherein the process is carried out at a temperature of 20 to 60°C, preferably 25 to 50°C, more preferably 30 to 40°C.

18. Process according to any one of claims 1 to 14, wherein the process is carried out at a pH of 2 to 12, preferably 3 to 10, more preferably 4 to 8.

19. Process according to any one of claims 1 to 14, wherein the process is carried out at a temperature of 20 to 60°C and a pH of 2 to 12.

20. Process according to any one of claims 1 to 14, wherein the process is carried out at a temperature of 20 to 60°C and a pH of 3 to 10.

21. Process according to any one of claims 1 to 14, wherein the process is carried out at a temperature of 20 to 60°C and a pH of 4 to 8.

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