EP3341462B1

EP3341462B1 - Process for cleaning contaminated plastic material for recycling

Info

Publication number: EP3341462B1
Application number: EP16757261.9A
Authority: EP
Inventors: Jan KOLIJN
Original assignee: Eindhoven Technical University
Current assignee: Eindhoven Technical University
Priority date: 2015-08-28
Filing date: 2016-08-26
Publication date: 2019-08-07
Anticipated expiration: 2036-08-26
Also published as: WO2017036977A1; EP3341462A1

Description

FIELD OF THE INVENTION

The present invention relates to a process for cleaning a contaminated plastic material for recycling.

BACKGROUND OF THE INVENTION

The recycling of plastic containers is becoming increasingly important from both environmental and economical perspective. The plastic containers to be recycled usually contain contaminants in the form of residues of the material they once contained. Such materials include for instance detergents, motor oils, milk, frying oils and cooking oils. In order to remove residues of these materials from the plastic containers, the plastic containers are usually grinded and the plastic particles so obtained are subjected to a cleaning process. Cleaning processes commonly used for this purpose are energy intensive processes because of the high temperatures and/or high pressure that need to be applied and/or are environmentally unfriendly since use is made of combustible or flammable solvents and/or corrosive cleaning agents.
US Patent No. 6,114,401 discloses an industrial plastic reclamation process, the process comprising agitating plastic pieces with an aqueous alkaline solvent. The cleaning step is performed at a temperatures well above room temperature and at a pressure well above atmospheric pressure. For obvious reasons, it is desirable to avoid alkaline pH, elevated temperature and elevated pressure from an environmental point of view.
Furthermore, EP-A1-0 474 053 discloses a cleaning process that uses 2 phases of liquid cleaning composition, the latter containing a liquid hydrocarbon solvent, an emulsifier and a dibasic ester. In the examples of this document, the dibasic ester was found to perform more effectively than C9- or C10 primary alcohol acetates.
Object of the present invention is to provide a process for cleaning a contaminated plastic materials for recycling which is less energy intensive and/or which is environmentally friendly with respect to the solvents used and/or which allows recycling the solvents.

SUMMARY OF THE INVENTION

It has now been found that this can be established when use is made of a particular physical mixture in the cleaning process.
Accordingly, the present invention relates to a process for cleaning a contaminated plastic material for recycling comprising a cleaning step wherein a contaminated plastic material is contacted with a physical mixture of liquid phase 1 and liquid phase 2 and wherein the solvent of liquid phase 1 is water and the solvent of liquid phase 2 is an organic phase comprising an acetate.
The acetate is an acetate ester having the general formula (I), of C-COO-R, wherein R is an alkyl group comprising 4, 6 or 8 carbon atoms, as as they have been shown to have a very good cleaning efficiency.
The physical mixture suitably comprises liquid phase 2 in an amount from about 8 to 55 wt. % based on the total weight of the physical mixture and/or liquid phase 1 in an amount of more than about 45 wt. % based on the total weight of the physical mixture. In a preferred embodiment, the physical mixture comprises liquid phase 1 and liquid phase 2 in a ratio of liquid phase 1: liquid phase 2 from about 92:8 to about 45:55 based on the total weight of the physical mixture and wherein liquid phase 1 and liquid phase 2 adds up to 100 wt. % of the physical mixture.
Liquid phase 1 suitably has a pH from about 6 to about 8, such as from about 6.5 to about 7.5 or about 7.
Suitably, the cleaning step is performed at temperature from of from 5-35 °C and/or at atmospheric pressure.
In one embodiment of the present invention, liquid phase 1 and/or liquid phase 2 are recycled by collecting the physical mixture obtained from the separation step in a separation vessel (150) in which liquid phase 1 and liquid phase 2 are allowed to separate into their respective phases. Subsequently, liquid phase 1 and/or liquid phase 2 can be refed from separation vessel (150) into the cleaning step.
A major advantage of the present invention resides in the fact that the present process can be carried out at a low temperature at atmospheric pressure, whereas at the same time the use of a combustible or flammable solvent is not needed, allowing for an environmentally safe cleaning process. Furthermore, the process according to the present invention allows for not only recycling the plastic cleaned in the process but also the solvents used in the cleaning process.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: Figure 1 shows a flowchart with an example of how to perform the cleaning process of the present invention and furthermore the pre-cleaning separation step of separating desired contaminated plastic material for recycling from unwanted material and a post-washing drying step of drying the cleaned plastic material.
- A = pre-cleaning separation step
- B = cleaning step
- C = drying step
- 110 = waste material comprising plastic mix, and unwanted material such as, glass, metal and sand
- 120 = Plastic separation vessel (separating desired plastic from unwanted material)
- 130 = Unwanted material including unwanted plastic material
- 140 = Desired type of plastic
- 150 = Liquid Separation vessel (separating liquid 1 from liquid 2)
- 160 = input of liquid 1 into cleaning vessel
- 170 = input of liquid 2 into collection vessel
- 180 = Collection vessel
- 190 = input of liquid 2 into cleaning vessel
- 200 = cleaning vessel
- 210 = transfer of cleaned plastic material from cleaning vessel to drying vessel
- 220 = transfer of used physical mixture comprising liquids 1 and 2 from cleaning vessel to liquid separation vessel
- 230 = drying vessel
- 240 = output of cleaned and dried plastic material
- 250 = transfer of used cleaning mixture comprising liquids 1 and 2 from drying vessel to liquid separation vessel.
Figure 2: Cleaning efficiency of clean frying oil depending on the amount of different acetates used as liquid phase 2 in wt. % based on the total amount of physical mixture. Y-axis is cleaning efficiency in wt. % and x-axis is amount of liquid phase 2 in water given in wt. %.
Figure 3: Residual amount of fat in the form of clean frying oil on the plastic surface depending on the amount of different acetates used as liquid phase 2 in wt. % based on the total amount of physical mixture. Y-axis is residual amount of fat in wt. % and x-axis is amount of liquid phase 2 in water given in wt. %.
Figure 4: Cleaning efficiency of used frying oil depending on the amount of octyl acetate used as liquid phase 2 in wt. % based on the total amount of physical mixture. Y-axis is cleaning efficiency in wt. % and x-axis is amount of octyl acetate in water given in wt. %.
Figure 5: Residual amount of fat in the form of used frying oil on the plastic surface depending on the amount of octyl acetate used as liquid phase 2 in wt. % based on the total amount of physical mixture. Y-axis is residual amount of fat in wt. % and x-axis is amount of octyl acetate in water given in wt. %.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an environmentally friendly process for removing soil, such as grease and oil, from plastic so that the plastic can be reused. The process of the present invention uses only water and an acetate solvent with low toxicity, low volatility, high biodegradability and which readily phase-separates from an aqueous phase. Furthermore, the acetate solvents used in the present invention are natural products that can be derived from fruit. The process can take place at room temperature and there is no need of applying any pressure. Furthermore, the process according to the invention also allows for both the water phase and the acetate phase to be reused thereby further minimizing the ecological footprint of cleaning plastic to be recycled. The process for cleaning a contaminated plastic material for recycling according to the present invention comprises a cleaning step wherein a contaminated plastic material is contacted with a physical mixture of liquid phase 1 and liquid phase 2 and wherein the solvent of liquid phase 1 is water and the solvent of liquid phase 2 is an organic phase comprising an acetate. The cleaning step is shown as B in figure 1.

Contaminated plastic material for recycling

The contaminated plastic material for recycling will usually be provided in the form of a mixture of plastic flakes or particles that are obtained by grinding contaminated plastic containers. The plastic containers may be containers for motor oils, food products such as milk, motor oil, detergents, and in particular frying oils and cooking oils, including used frying and cooking oils, or other greasy materials. Accordingly, the contaminated plastic material subjected to the process according to the present invention may be contaminated with contaminants including oils such as motor oils, frying oils and cooking oils; dairy products such as milk; detergents and mixtures thereof. As used herein, the terms "grease", "oil" and "fat" are used interchangeably. The typical size of the provided plastic flakes from about 20 to about 1600 cm², such as from about 100 to about 900 cm² or about 400 cm². However, any size and shape enabling all sides of the plastic material to be in contact with the physical mixture of liquid phase 1 and liquid phase 2 is suitable for use in the process of the present invention.
A wide variety of plastic material can be cleaned in accordance with the present invention. The plastic material can suitably be selected from the group consisting of a high density polyethylene material, low density polyethylene material, polyethylene terephthalate material, polypropylene material, polyvinylchloride material, polyamide material, polybutylene terephthalate material, polycarbonate material, polymethylmethacrylate material and polyoxymethylene material. Copolymers of any of these recyclable polymer materials can also suitably be used in accordance with the present invention. In addition, the plastic material to be used in the present invention can also suitably be a laminated polymer composite in which two or more these polymer materials have been laminated onto each other. The process according to the present invention does not optimally work for styrene-comprising plastics (polymers or co-polymers comprising styrene) since the solvent of liquid phase 2 renders the surface of such materials sticky, indicating that it partly dissolves these materials. Accordingly, the contaminated plastic material for recycling according to the present invention is preferably not a polymer or co-polymer comprising styrene. Furthermore, the contaminated plastic material for recycling according to the present invention preferably comprises no or essentially no polymers or co-polymers comprising styrene. If the contaminated plastic material for recycling according to the present invention comprises polymers or co-polymers comprising styrene it is best to use other acetate esters than butyl acetate and ethyl acetate, as these are the ones known to dissolve styrene comprising plastics.
Depending on the purpose of the process, there may be types of plastic materials that are more desirable for recycling than others. For example, it is currently most economically viable to clean PP (polypropylene) and PE (polyethylene) for recycling than other types of plastics, and thereby more desirable. In a preferred embodiment of the present invention the plastic material for recycling comprises more than 80 w/w%, such as more than 85 w/w%, 90 w/w%, 95 w/w% of a desired one or more types of plastic material. In a more preferred embodiment the plastic material for recycling essentially consist of one or more desired types of plastic material. In yet another preferred embodiment, the one or more desired types of plastic for recycling is PP and/or PE. In one embodiment of the present invention, desired types of plastic are separated from undesired types of plastic in a pre-cleaning separation step A preceding the cleaning step B. The process of the present invention will in this embodiment further comprise a separation step A, wherein the plastic material for recycling is separated from unwanted other waste material before subjecting said plastic material to the cleaning step. The separation can achieved based on e.g. the density of the materials, given that the undesired materials such as, glass, sand, metal and/or undesired forms of plastic having a different density than the desired forms of plastic. Alternatively, a variety of separation systems can be used in the separation step. Suitably, the separation system is a cyclone. Other suitable separation systems include sink-float tanks. Suitably, the water phase can contain one or more salts to establish a so-called heavy medium. Another example of a process that separates the desired plastic from the undesired materials is a NIR (Near-infrared) selection unit or a combination of separation processes, e.g. based on demetallization by magnets and/or an eddy current non-magnetic metal separator. However, preferably the mixed plastic material is already sorted on before-hand rendering the pre-cleaning separation step redundant.

Physical mixture

The cleaning liquid used in the present invention is a physical mixture of an aqueous phase and an organic phase, which remove water-soluble contaminants and greasy contaminants present on the contaminated plastic, respectively. As described herein, the aqueous phase is called "liquid phase 1" and the organic phase is called "liquid phase 2".
Since liquid phase 2 according to the present invention has a high viscosity, it is important that it is well mixed with liquid phase 1 when in contact with the plastic material in order to avoid that it sticks to the plastic material. This is achieved by mixing liquid phase 1 and 2 such that they flow together like one liquid. In the process according to the present invention it is also important that liquid phases 1 and 2 only flow together like one liquid upon the application of physical force, such as by physical mixing, but that they readily phase-separate into their respective phases in the absence of either physical mixing or emulsifying agents. The rapid and complete phase-separation between liquid phases 1 and 2 is advantageous in order to be able to reuse both phases in the cleaning process. Accordingly, in a preferred embodiment of the present invention, the physical mixture comprises no or essentially no emulsifying agents from the outset (i.e. before the cleaning process starts).
As used herein, the term "physical mixture" means a mixture of liquid phase 1 and liquid phase 2, which flow together as one liquid. In other words the physical mixture according to the present invention behaves as an unstable emulsion formed upon physical mixing of liquid phases 1 and 2, and in a preferred embodiment it is an unstable emulsion. A suitable way of performing the cleaning step is therefore contacting the contaminated plastic material with a premixed physical mixture of liquid phase 1 and liquid phase 2 or with liquid phase 1 and liquid phase 2 upon physical mixing ensuring the formation of a physical mixture of liquid phase 1 and liquid phase 2. What is important during the cleaning step is that liquid phases 1 and 2 are physically mixed such that they form a physical mixture at the point in time, where they are in contact with the contaminated plastic material. As used herein, the terms "physical mixture" and "cleaning mixture" are used interchangeably.
As used herein, the term "physical mixing" means any form of ensuring that liquid phase 1 and liquid phase 2 are mixed in such a way that they effectively form a physical mixture of the two phases. Examples of physically mixing the two liquid phases are premixing the two liquid phases in a separate vessel by agitation or stirring, or spraying the two liquid phases onto the contaminated plastic material using nozzles, thus creating tiny droplets of the two liquid phases, resulting in the formation of physical mixture of the two liquid phases, liquid phase 1 and liquid phase 2. The simultaneous spraying with liquid phase 1 and 2, respectively, serves both the purpose of contacting the contacting the contaminated plastic as well as physically mixing the two phases in order to obtain a physical mixture of them on the plastic material. Furthermore, the force by which liquid phases 1 and 2 are sprayed onto the plastic material will in itself assist the cleaning process.

Liquid phase 1

Liquid phase 1 is an aqueous phase as the solvent of liquid phase 1 is water. Preferably, liquid phase 1 is clean water at the beginning of the cleaning step or before reusing it in further cleaning steps. Preferably, liquid phase 1 comprises no salts or essentially no salts due to salts corrosive effect on the equipment used in the process. Suitably, the water phase can contain one or more salts to establish a so-called heavy medium. Preferably, liquid phase 1 has a pH from about 6 to about 8, such as from about 6.5 to about 7.5 or about 7. This is advantageous as an aqueous phase of neutral pH is less hazardous to the environment and to the equipment than either acidic or alkaline aqueous phases.
During the cleaning of the plastic material, liquid phase 1 will gradually also comprise more and more water-soluble contaminants present on the plastic material being cleaned.

Liquid phase 2

Liquid phase 2 is an organic phase, the solvent of which comprises an acetate. The organic phase is the phase that removes the greasy material the plastic material is contaminated with in order for it to be usable for recycling. During the cleaning of the plastic material, liquid phase 2 will gradually also comprise more and more greasy contaminants present on the plastic material being cleaned. According to the present invention, the organic phase comprises an acetate, which has been shown to effectively clean the contaminated plastic material even when present in low amounts compared to liquid phase 1 and which readily phase separates from an aqueous phase when no physical mixing or emulsifying agents are present. This is important in the present invention as will become apparent in the below. Furthermore, a solvent comprising an acetate according to the present invention has the advantages of having low toxicity, low volatility, high biodegradability and being able to readily phase-separate from the aqueous liquid phase 1, rendering these solvents environmentally friendly and recyclable. Preferably, the solvent of liquid phase 2 essentially consists of an acetate. More preferably, the solvent of liquid phase 2 is an acetate.
The acetate is an acetate ester having the general formula (I) of C-COO-R, wherein R is an alkyl group comprising 4, 6 or 8 carbon atoms. The lower the number of carbon atoms in the alkyl group of an acetate ester, the higher its volatility. It is preferred that the solvent of liquid phase 2 has a low volatility, as the lower the volatility, the less combustible and flammable is the solvent. Acetate esters comprising alkyl groups with higher number of carbon atoms are less volatile than acetate esters comprising alkyl groups with lower number of carbon atoms. From this perspective, acetate esters comprising an alkyl group with more than 4, such as more than 6 carbon atoms are preferred. Acetate esters comprising an alkyl group with 8 carbon atoms is most preferred as it can be used in an open air process without the need of exhaustion.
On the other hand, it is also preferred that the solvent of liquid phase 2 has a low viscosity, as a low viscosity sticks less to the plastic material and is easier to mix with liquid phase 1 such as to obtain a physical mixture of liquid phases 1 and 2. Acetate esters comprising alkyl groups with lower number of carbon atoms are less viscous than acetate esters comprising alkyl groups with higher number of carbon atoms. From this perspective, acetate esters comprise an alkyl group with 8 or less carbon atoms.
Furthermore, acetate esters comprising alkyl groups with lower number of carbon atoms are cheaper than acetate esters comprising alkyl groups with higher number of carbon atoms. From this perspective, acetate esters comprise an alkyl group with 4 carbon atoms. Using acetate esters in this range will require that the process is performed in a closed system or in the presence of exhaustion.
The length of the alkyl group of the preferred acetate esters is therefore a trade-off between volatility on one hand and viscosity on the other hand. To this end, in the present invention the acetate is an acetate ester having the general formula (I) of C-COO-R, wherein R is an alkyl group comprising 4, 6 or 8 carbon atoms. In a more preferred embodiment of the present invention the acetate is an acetate ester having the general formula (I) of C-COO-R, wherein R is an alkyl group comprising 8 carbon atoms (octyl acetate). It has been shown in the present invention that butyl acetate, hexyl acetate and octyl acetate all have very good and similar cleaning efficiencies, where butyl acetate comprises an alkyl group with 4 carbon atoms, hexyl acetate comprises an alkyl group with 6 carbon atoms and octyl acetate comprises an alkyl group with 8 carbon atoms. Accordingly, from a cleaning efficiency perspective it is preferred to use an acetate ester having the general formula (I) of C-COO-R, wherein R is an alkyl group comprising an even number of between 4-8 carbon atoms. Acetate esters comprising alkyl groups with even number of carbon atoms are cheaper to purchase. Thus, acetates to be used in accordance with the present invention are selected from the group consisting of butyl acetate, hexyl acetate and octyl acetate. More preferably, the acetate is hexyl acetate or octyl acetate and most preferably, the acetate is octyl acetate.

Amounts of liquid phase 1 and liquid phase 2 in the physical mixture

As can be seen in figure 2, the cleaning efficiency of the physical mixture is a steeply increasing curve in the range of 0-10 wt. % of liquid phase 2 based on the total weight of the physical mixture. The curve is approximately flat between 10-50% wt. % of liquid 2 based on the total weight of the physical mixture. At higher than 50 wt. % of liquid phase 2 based on the total weight of the physical mixture, the cleaning efficiency is still about 90% or more, meaning that about 90% or more of the contaminating frying oil has been removed. Accordingly, the physical mixture according to the present invention, comprises more than 8 wt. %, such as more than 10 wt. % of liquid 2 based on the total amount of the physical mixture. Since it is for both environmental and economic reasons preferred to use as little liquid phase 2 as possible, it is preferred that the physical mixture according to the invention comprises liquid phase 2 in an amount from about 8 to 55 wt. % based on the total weight of the physical mixture. More preferably, the physical mixture according to the invention comprises liquid phase 2 in an amount of from about 10 to about 50 wt. %, such as, from about 10 to about 45 wt. %, from about 10 to about 40 wt. %, from about 10 to about 35 wt. %, from about 10 to about 30 wt. %, from about 10 to about 25 wt. %, from about 10 to about 20 wt. %or from about 12 to about 18 wt. %, based on the total weight of the physical mixture.
Likewise, the physical mixture of liquid phase 1 and liquid phase 2 used in the present invention preferably comprises liquid phase 1 in an amount of more than about 45 wt. % based on the total weight of the physical mixture. For environmental and economic reasons it is advantageous that the liquid mixture of liquid phase 1 and liquid phase 2 comprises as much water as possible while maintaining the cleaning efficiency. Accordingly, it is more preferable that the physical mixture comprises liquid phase 1 in amount of more than about 50 wt. %, such as more than about 55 wt. %, 60 wt. %, 65 wt. %, 70 wt. % or 75 wt. % based on the total weight of the physical mixture. Most preferable, the physical mixture comprises liquid phase 1 in an amount of more than about 80 wt. % based on the total weight of the physical mixture. Preferably, the physical mixture according to the present invention comprises liquid phase 1 and liquid phase 2 in a ratio of liquid phase 1: liquid phase 2 from about 92:8 to about 45:55 such as from about 90:10 to about 50:50, from about 90:10 to about 55:45, from about 90:10 to about 60:40, from about from about 90:10 to about 65:35, from about 90:10 to about 70:30, from about 90:10 to about 75:25, from about 90:10 to about 80:20 or from about 88:12 to about 72:18 based on the total weight of the physical mixture, where liquid phase 1 and liquid phase 2 adds up to 100 wt. % of the physical mixture.

The cleaning step

To meet the cleaning standards after this cleaning process, mixing of the physical mixture comprising the two liquid phases and the plastic material is desired in order to spread the physical mixture evenly and increase the contact between the physical mixture and the plastic and furthermore in order to maintain liquid phase 1 and liquid phase 2 as a physical mixture by not allowing their complete phase separation. Suitable ways of mixing the plastic material with the physical mixture are any ways that will ensure that each plastic flake is subjected to a dynamic contact with the physical mixture, meaning that the physical mixture that each individual plastic flake is in contact with is continuously replaced. This mixing can for example be achieved by agitation of the plastic material in contact with the physical mixture. The cleaning vessel 200 may therefore suitably be designed in such a way that physical mixing of all three phases is ensured. Suitably, the physical mixing of the plastic material and the physical mixture is performed by agitation. Accordingly, the cleaning vessel or tank 200 may therefore be provided with a mixing system to agitate the contents of the vessel or tank and to establish sufficient contact between the plastic material and the physical mixture in the cleaning step. By mixing the physical mixture and the plastic material in the cleaning step a slurry which comprises plastic flakes or particles and physical mixture comprising liquid phases 1 and 2 will be obtained. Physical mixing of the plastic material with the physical mixture of liquid phase 1 and liquid phase 2 can for example be obtained by using a rotating vessel or counter-current flow of the liquid phases with the contaminated plastic material.
If desired, the cleaning step can be carried out in a series of cleaning vessels or tanks which are interconnected with each other. In this way, the cleaning step can be carried out in a number of stages, ensuring that contaminants are sufficiently removed from the contaminated plastic material. It is also possible to carry out the cleaning step in a batch mode of operation in which separate tanks or vessels are operated one after each other. Alternatively, the cleaning step may be performed as a continuous process in a cleaning vessel, wherein the liquid phases 1 and 2 are continuously sprayed onto the plastic material. Suitably, liquid phase 1 may be sprayed onto the plastic material with a pressure of about 3 to 6 bar, and preferably at a pressure of about 4 to 5 bar. Liquid phase 2 may suitably be sprayed onto the plastic material with a pressure of from about 6 to 11 bar, such as from about 7 to 9 bar or at about 8 bar. Since the liquid phases are fed to the mixing vessel, the amount of liquid in the vessel builds up. To prevent excessive amounts of liquid in the mixing vessel, a physical mixture of the two liquid phases is continuously removed from the cleaning vessel, e.g. by an overflow system, draining or by using a pump.
During the cleaning step, the contaminated plastic material for recycling is contacted with the physical mixture at a temperature in the range of from 5-35 °C with the physical mixture according to the present invention, which comprises liquid phase 1 and liquid phase 2 to remove contaminants from the contaminated plastic material for recycling. The temperature during the cleaning step is preferably in the range of from 15-30 °C, more preferably in the range of from 15-25 °C. Even more preferably, the temperature during the cleaning step is room temperature, which is typically between 20-25 °C.
The cleaning step can suitably be carried out at a variety of pressures, but preferably the cleaning step is carried out at atmospheric pressure. If the cleaning step is performed in a closed system, it is however advantageous to perform the cleaning step in a cleaning vessel under a minor under-pressure compared to atmospheric pressure in order to avoid waste of the physical mixture.
The cleaning step is suitably carried out for a predetermined length of time. Preferably, the cleaning step is carried out over a relatively short period of time. Preferably, the cleaning step is carried out for a period of time in the range of at least 15 seconds, such as at least 20, 25, 30, 35, 40, 45, 50, 55 or 60 seconds depending also on the other conditions under which the cleaning step is performed.

Separation of physical mixture from plastic material

At the end of the cleaning step, the plastic material is separated from the physical mixture, which physical mixture contains contaminants removed from the contaminated plastic material. To establish this, the slurry which comprises plastic material and physical mixture as obtained in the cleaning step can suitably be passed to a separation system in which the cleaned plastic material in the form of particles will be separated from the physical mixture that contains contaminants. Accordingly, the cleaning step may further comprise a separation step 220, in which the physical mixture which contains contaminants removed from the contaminated plastic material is separated from the plastic material after having been in contact with the plastic material for a predetermined time. As mentioned in the above, this predetermined length of time may suitably be in the range of in the range of at least 15 seconds, such as at least 20, 25, 30, 35, 40, 45, 50, 55 or 60 seconds depending also on the other conditions under which the cleaning step is performed. The separation may be performed in any suitable way, such as by an overflow system, draining or by using a pump. The separation step can suitably be carried out at the same temperature ranges and pressure ranges as those described for the cleaning step.
Preferably, the cleaning step further comprises rinsing the plastic material with liquid phase 1 or with water after the physical mixture has been separated from said plastic material, in order to remove liquid phase 2 from the plastic material and enabling recycling of as much of liquid phase 2 as possible. The rinsing with water can suitably be carried out by spraying excessive amounts of water onto the plastic material after the cleaning and separation steps.

Recycling of

liquid phases

1 and 2

For economic and environmental reasons, it is advantageous to recycle both of the liquid phases of the physical mixture. Liquid phase 2 being the most expensive and least environmentally friendly of the two, is therefore most important to recycle. Accordingly, the process according to the present invention preferably comprises collecting the physical mixture obtained from the separation step in a separation vessel 150 in which liquid phase 1 and liquid phase 2 are allowed to separate into their respective phases. This phase-separation may take from a few seconds when liquid phase 2 is clean (not yet contaminated) to about an hour if liquid phase 2 is very contaminated. Once the liquid phases 1 and 2 have separated, liquid phase 1 and 2 can be refed from the separation vessel 150 into the cleaning step, where the cleaning step is suitably carried out in a cleaning vessel 200. In the case of liquid phase 2, it can suitably be refed from separation vessel 150 via collection vessel 180. Apart from allowing for recycling of the liquid phases 1 and 2, this separation from the plastic material followed by the phase separation in the separation vessel and refeeding the liquid phases 1 and 2 into the cleaning step also assists in spreading the physical mixture of the liquid phases evenly over the plastic material. It also allows for refeeding the liquid phases with a certain force or a certain pressure, as also described in the above, which assists the cleaning process by partly removing the contaminants physically.
The liquid phases collected in the separation vessel comprises the contaminants removed from the contaminated plastic during one or more previous cleaning steps. Liquid phase 1 will comprise the water-soluble contaminants and liquid phase 2 will comprise the greasy/oily contaminants. The liquid phases will therefore need to be cleaned and/or partly or fully replaced when saturated, i.e. when it no longer results in a good cleaning efficiency or gets too viscous.
In one embodiment, liquid phase 2 is transferred from separation vessel 150 to a collection vessel 180 from which it is refed into the cleaning step, suitably by use of a pump. Collection vessel 180 can be replaced when liquid phase 2 gets too contaminated with greasy/oily contaminants removed from the plastic material.
In a further embodiment of the present invention, used liquid phase 2 is cleaned, e.g. by distillation or by membrane or extraction techniques, and used again. This also allows for the isolation of the greasy/oily contaminants present in the used liquid phase 2, which can then also be recycled. In a preferred embodiment, the greasy/oily contaminants are used as fuel for this distillation process or other machines used in the process.

Drying step C

After the plastic is cleaned and free from greasy residues, it still comprises water and/or physical mixture to a higher or lesser degree depending on the way the physical mixture has been separated from the cleaned plastic material. If for instance the separation step performed only involves draining the cleaned plastic material for physical mixture or pumping the physical mixture out of the cleaning vessel, the cleaned plastic will still comprise a relatively high amount of water. Since dry plastic is much easier to handle, it is desirable to further comprising subjecting the plastic material obtained in the separation step to a drying step C. The drying step may involve all kind of conventional drying methods and combinations thereof. The choice and sequence of drying methods will depend on how wet the cleaned plastic is and how dry an end-product is desired. Examples of drying methods used in the drying step are centrifugation, heating, air blowing and combinations thereof. The drying step can suitably be carried out at the same temperature ranges and pressure ranges as those described for the cleaning step. However, if the drying method involves heating or blowing with hot air, the drying step can also be carried out at higher temperatures.
After recovery of the cleaned, and in some instances dried, plastic material it can subsequently be used to make new plastic objects like containers such as bottles.
The cleaning step of the present invention may be executed batch-wise, but it is preferably operated in a continued process, enabling a large amount of plastics, e.g. 2000 kg/hour, to be cleaned continuously. The same applies mutatis mutandis to the pre-cleaning separation step and the drying step, which steps are suitably performed together with the cleaning process in one continuous process comprising the steps of a pre-cleaning separation step A, a cleaning step B and a drying step C.
In one embodiment, the present invention relates to a process of cleaning plastic as outlined in fig. 1:
A mixture of waste, for example grinded or pre-shredded plastic containers, e.g. containers for cooking oil or frying oil, milk, motor oil or containers of other greasy materials is supplied via an input 110 into a plastic separation vessel 120. The grinded plastic containers waste contains a large amount of mixed plastic (desired and undesired types of plastic), as well as small amounts of glass, metal and sand. Preferably, this mixture contains only desired plastic, e.g. PP and PE.
On the surface of all desired and undesired materials, a greasy contaminant is present. This greasy contaminant may consist of frying oil or other cooking oils, or other types of greasy pollution, such as milk or motor oil. To remove the greasy contaminant, a cleaning step B according to the invention is performed in cleaning vessel 200 in order to remove the greasy/oily contaminant from a contaminated plastic material for recycling.
The cleaning step may be preceded by a pre-cleaning separation step A performed in plastic separation vessel 120 in order to remove unwanted material 130, such as undesired plastic material, glass, metal and sand from desired contaminated plastic material for recycling 140. Furthermore, the cleaned plastic material 210 obtained from the cleaning step of the present invention may further be subjected to a drying step C in drying vessel 230.
For the cleaning step, the desired plastic material for recycling is fed to a cleaning vessel 200, in which liquid phase 1 (called "Liq 1" in figure 1) and liquid phase 2 (called "Liq 2" in figure 1) are separately sprayed onto the contaminated plastic material via liquid phase 1 distributor (called "Liq 1 distr" in figure 1) and liquid phase 2 distributor (called "Liq 2 distr" in figure 1), respectively.
Since the liquid phases are continuously sprayed onto the plastic material in the cleaning vessel, the amount of physical mixture in the vessel builds up. To prevent excessive amounts of liquid in the cleaning vessel, the physical mixture of the two liquid phases is continuously removed 220 from the cleaning vessel, e.g. by an overflow system or by using a pump of some kind. This physical mixture is collected in separation vessel 150. Since liquid phase 1 and liquid phase 2 according to the present invention are chosen in such a way that the two liquid phases phase-separate when left standing, the two phases readily phase-separate into their respective phases when left standing, in the separation vessel. From the separation vessel, one or both of the liquid phases 1 and 2 can be refed into the cleaning step. Liquid phase 1 is directly fed back to the cleaning step in cleaning vessel 150 via input 160. Liquid phase 2 now contains not only the solvent of liquid phase 2, but also the greasy contaminant. Liquid phase 2 is also refed from separation vessel 150 to the cleaning step in cleaning vessel 200, either directly or via collection vessel 180, until the liquid is saturated with greasy contaminants and does not clean the plastic anymore. At that point, the collection vessel 180 is replaced with a new collection vessel, filled with new liquid phase 2 which is not yet polluted with greasy residues.
After the cleaning step, the plastic is cleaned and free greasy contaminants, but still contains liquid phases 1 and 2. Preferably, the plastic material is rinsed liquid phase 1 or water in order to remove liquid phase 2 before subjecting the cleaned plastic material to a drying step. This rinsing can suitably be performed by only spraying the plastic material with liquid phase 1 or water in the end of the cleaning step. The cleaning step ends with separating the physical mixture 220 from the cleaned plastic material 230, which may be subjected to a drying step. During the drying step, remaining liquid phase 1 and/or 2, is removed from the surface of the plastic in drying vessel 230.

EXAMPLES

EXAMPLE 1:

Oil contaminated HDPE flakes were cut to pieces of 1-2 cm. 8 grams of these flakes were added to a 100 mL vial. A physical mixture of 8 mL octyl acetate and 42 mL water was prepared in a separate 50 mL vial at room temperature. The cleaning mixture was added to the flakes, followed by mixing at 480 rpm on an automatic shaker plate for 1 minute at room temperature. Subsequently, the flakes were washed three times with water to remove the physical mixture and dried in an oven at 120 °C for 1 hr.
Using the measured weights of the flakes before and afterwashing treatment, it was calculated that the plastic contained 7 wt% frying oil and that 98% of the frying oil was removed by the acetate-water physical mixture.

COMPARATIVE EXAMPLE 1:

Oil contaminated HDPE flakes were cut to pieces of 1-2 cm. 8 grams of these flakes were added to a 100 mL vial. 50 mL water was prepared in a separate 50 mL vial at room temperature. The cleaning mixture was added to the flakes, followed by mixing at 480 rpm on an automatic shaker plate for 1 minute at room temperature. Subsequently, the flakes were washed three times with water to remove the physical mixture and dried in an oven at 120 °C for 1 hr.
Using the measured weights of the flakes before and after the washing treatment, it was calculated that the plastic contained 4 wt% frying oil and that only 33% of the frying oil was removed by water only.

EXAMPLE 2:

Oil contaminated HDPE flakes were cut to pieces of 1-2 cm. 8 grams of these flakes were added to a 100 mL vial. A physical mixture of 8 mL octyl acetate and 42 mL of a saturated solution of table salt in water was prepared in a separate 50 mL vial at room temperature. The cleaning mixture was added to the flakes, followed by mixing at 480 rpm on an automatic shaker plate for 1 minute at room temperature. Subsequently, the flakes were washed three times with water to remove the physical mixture and dried in an oven at 120 °C for 1 hr.
Using the measured weights of the flakes before and the washing treatment, it was calculated that the plastic contained 6 wt% frying oil and that 95% of the frying oil was removed by the acetate-water physical mixture.

COMPARATIVE EXAMPLE 2:

Oil contaminated HDPE flakes were cut to pieces of 1-2 cm. 8 grams of these flakes were added to a 100 mL vial. 50 mL of a saturated solution of table salt in water was prepared in a separate 50 mL vial at room temperature. The cleaning mixture was added to the flakes, followed by mixing at 480 rpm on an automatic shaker plate for 1 minute at room temperature. Subsequently, the flakes were washed three times with water to remove the physical mixture and dried in an oven at 120 °C for 1 hr.
Using the measured weights of the flakes before and after the washing treatment, it was calculated that the plastic contained 4 wt% frying oil and that only 22% of the frying oil was removed by salt water only.

EXAMPLE 3:

Oil contaminated PET flakes were cut to pieces of 1-2 cm. 8 grams of these flakes were added to a 100 mL vial. A physical mixture of 8 mL octyl acetate and 42 mL water was prepared in a separate 50 mL vial at room temperature. The cleaning mixture was added to the flakes, followed by mixing at 480 rpm on an automatic shaker plate for 1 minute at room temperature. Subsequently, the flakes were washed three times with water to remove the physical mixture and dried in an oven at 120 °C for 1 hr.
Using the measured weights of the flakes before and after the washing treatment, it was calculated that the plastic contained 21 wt% frying oil and that 84% of the frying oil was removed by the acetate-water physical mixture.

COMPARATIVE EXAMPLE 3:

Oil contaminated PET flakes were cut to pieces of 1-2 cm. 8 grams of these flakes were added to a 100 mL vial. 50 mL water was prepared in a separate 50 mL vial at room temperature. The cleaning mixture was added to the flakes, followed by mixing at 480 rpm on an automatic shaker plate for 1 minute at room temperature. Subsequently, the flakes were washed three times with water to remove the physical mixture and dried in an oven at 120 °C for 1 hr.
Using the measured weights of the flakes before and after the washing treatment, it was calculated that the plastic contained 5 wt% frying oil and that only 37% of the frying oil was removed by water only.

EXAMPLE 4: Effect of type and amount of three different acetates in the physical mixture for cleaning plastic contaminated with fresh frying oil.

Goal: To analyze the efficiency of a physical mixture according to the invention to remove fat and oil from the surface of plastics using different amounts of butyl acetate, hexyl acetate or octyl acetate as liquid phase 2.
Experimental: PP sheets (thickness 500 micron) were cut into 10 mm x 10 mm pieces. 7 grams PP pieces were placed in a 70 mL glass jar. 1 g of fresh frying oil (AH Frituurolie) was added and thoroughly mixed to make sure the entire plastic surface was covered with a layer of fat. In a separate jar, water and cleaner were mixed, in total 50 grams of liquid, e.g. 37.5 grams of water as liquid phase 1 and 12.5 grams of butyl, hexyl or octyl acetate as liquid phase 2. The physical mixtures of liquid phases 1 and 2 were added to the greasy plastics and shaken gently for 1 minute.
After shaking, the liquids were filtered off and the PP pieces were rinsed thoroughly with water. The wet PP flakes were dried in an oven for 24 hrs at 130 °C. After drying, the mass of the flakes was determined. The cleaning efficiency and the remaining amount of fat (both in wt. %) were determined according to the below equations, where "Mass PP" is the mass before washing (PP and fat) and the total mass after cleaning were used to calculate the remaining amount of oil on the plastic surface and the cleaning efficiency. The equations below were used to calculate these quantities. $\begin{array}{l} Remaining amount of oil = \frac{Mass remaing oil}{Mass PP} \times 100 % \\ = \frac{Mass after wash - Mass PP}{Mass PP} \times 100 % \end{array}$
$\begin{array}{l} Cleaning efficiency = \frac{Mass remaining oil}{Mass added oil} \times 100 % \\ = \frac{Mass after whashing - Mass PP}{Mass added oil} \times 100 % \end{array}$
Experiments were also performed without any liquid phase 2, and without a washing step, to show that washing with a certain amount of liquid phase 2 is necessary to remove a large amount of oil from the surface of the plastic flakes.

The fresh frying oil was removed very efficiently, as can be seen in Table 1 and figures 2 (cleaning efficiency) and 3 (residual amount of fat).

Table 1: Cleaning efficiency and remaining amount of oil after washing with physical mixtures comprising different acetates as liquid phase 2 in various concentrations.

Cleaning agent	Percentage cleaner in water	Cleaner	Water	Total wt% fat	Residual wt% fat	Cleaning effiency
	(wt%)	(g)	(g)	(wt%)	(wt%)	(wt%)
Octyl acetate	1	0,5	52,4	14%	5,2%	64%
Octyl acetate	2	1,0	49,6	14%	4,2%	70%
Octyl acetate	5	2,5	47,6	14%	2,7%	81%
Octyl acetate	8	4,0	47,4	14%	1,6%	89%
Octyl acetate	10	5,0	45,1	14%	0,3%	98%
Octyl acetate	25	12,6	37,6	14%	0,3%	98%
Octyl acetate	50	25,0	25,1	16%	0,0%	100%
Octyl acetate	59	30,0	20,6	14%	1,1%	93%
Octyl acetate	75	37,6	12,5	14%	1,0%	93%
Octyl acetate	100	50,0	0,0	14%	1,4%	90%
Butyl acetate	5	2,5	47,6	14%	1,7%	88%
Butyl acetate	10	5,0	45,1	17%	1,1%	94%
Butyl acetate	25	12,6	37,5	14%	0,6%	96%
Butyl acetate	50	25,0	25,2	15%	0,5%	97%
Hexyl acetate	5	2,5	47,9	14%	1,6%	89%
Hexyl acetate	9	5,0	47,8	15%	1,0%	93%
Hexyl acetate	25	12,5	37,6	14%	0,5%	97%
Hexyl acetate	50	25,0	25,1	14%	0,5%	97%
Blanc (water only)	0	0,0	50,1	14%	6,0%	57%

EXAMPLE 5: Effect of amounts of octyl acetate in wt % of the total amount of physical mixture on the removal of used frying oil.

In order to test the cleaning efficiency on used cooking oil a sample of used cooking oil was obtained from Rotie Amsterdam, labeled 2004 30-5 MK. This oil is partly hydrogenated and therefore thicker than unused oil.
PP sheets (thickness 500 micron) were cut into 10 mm x 10 mm pieces. 10 grams PP pieces were placed in a 70 mL glass jar. 1 g of used frying oil (Rotie Amsterdam 2004 30-5 MK) was added and thoroughly mixed to make sure the entire plastic surface was covered with a layer of fat. In a separate jar, water and cleaner were mixed, in total 50 grams of liquid, e.g. 37.5 grams of water and 12.5 grams of liquid phase 2. A physical mixture of liquid phase 1 (here water) and liquid phase 2 (here octyl acetate) were added to the greasy plastics and shaken gently for 1 minute.
After shaking, the liquids were filtered off and the PP pieces were rinsed thoroughly with water. The wet PP flakes were dried in an oven for 24 hrs at 130 °C. After drying, the mass of the flakes was determined.

The cleaning efficiency and the remaining amount of fat (both in wt. %) were determined in the same way as described in Example 4. The results are shown in Table 2, Figure 4 (Cleaning efficiency) and Figure 5 (Remaining amount of oil). As can be seen the used frying oil is harder to remove than the fresh frying oil, but the process of the invention still provides a satisfactory result.

Table 2: Cleaning efficiency and remaining amount of oil after washing with octyl acetate at different concentrations.

Cleaning agent	Percentage cleaner in water	Cleaner	Water	Total wt% fat	R esidual wt% fat	C leaning efficiency
	(wt%)	(g)	(g)	(wt%)	(wt%)	(wt%)
Octyl acetate	25	12,4	37,7	10%	1,2%	88%
Octyl acetate
	50	25,1	25,0	10%	1,0%	90%
Water (blanc)	0	0,0	49,9	10%	8,8%	14%
Effect drying	NO washing !!!			10%	9,9%	1%

Claims

A recycling process for cleaning a contaminated plastic material, comprising a cleaning step (B) wherein a contaminated plastic material is contacted with a physical mixture of liquid phase 1 and liquid phase 2 and wherein the solvent of liquid phase 1 is water and the solvent of liquid phase 2 is an organic phase comprising an acetate ester having the general formula (I) of C-COO-R, wherein R is an alkyl group comprising 4, 6 or 8 carbon atoms.
A process according to claim 1, wherein the physical mixture comprises liquid phase 2 in an amount from about 8 to 55 wt. % based on the total weight of the physical mixture.
A process according to any of claims 1 and 2, wherein the physical mixture of liquid phase 1 and liquid phase 2 comprises liquid phase 1 in an amount of more than about 45 wt. % based on the total weight of the physical mixture.
A process to any of the preceding claims, wherein physical mixture comprises liquid phase 1 and liquid phase 2 in a ratio of liquid phase 1: liquid phase 2 from about 92:8 to about 45:55 based on the total weight of the physical mixture and wherein liquid phase 1 and liquid phase 2 adds up to 100 wt. % of the physical mixture.
A process according to any of the preceding claims, wherein liquid phase 1 has a pH from about 6 to about 8, such as from about 6.5 to about 7.5 or about 7.
A process according to any of the preceding claims, wherein the cleaning step is performed at temperature from of from 5-35 °C.
A process according to any of the preceding claims, wherein the cleaning step is carried out at atmospheric pressure.
A process according to any of the preceding claims, wherein the cleaning step further comprises a separation step (220), in which the physical mixture which contains contaminants removed from the contaminated plastic material is separated from the plastic material after having been in contact with the plastic material for a predetermined time.
A process according to claim 8, wherein the cleaning step further comprises rinsing the plastic material with liquid phase 1 or with water after the physical mixture has been separated from said plastic material.
A process according to any of claims 8 and 9, further comprising collecting the physical mixture obtained from the separation step in a separation vessel (150) in which liquid phase 1 and liquid phase 2 are allowed to separate into their respective phases.
A process according to claim 10, further comprising refeeding liquid phase 1 from separation vessel (150) into the cleaning step.
A process according to any of claims 10 and 11, further comprising refeeding liquid phase 2 from the separation vessel (150) into the cleaning step.