CN108603122A - For by cracking by converting-plastics be gas, liquid fuel and wax method - Google Patents

Abstract

The present invention relates to a kind of methods for converting the mixture comprising plastics and at least one oxygenatedchemicals to gas, liquid fuel and wax by cracking.This method includes deoxygenation step and subsequent hydrocracking step, during the hydrocracking step, so that the mixture is subjected to cracking conditions to obtain the product stream containing the gas, liquid fuel and wax.

Description

Method for converting plastics into gases, liquid fuels and waxes by cracking

This application claims priority from European Application No. EP 16306634.3 filed on December 7, 2016, the entire content of said application being incorporated by reference into this application for all purposes.

technical field

The invention relates to a process for converting a mixture comprising plastic and at least one oxygenate into gas, liquid fuel and wax by cracking. The process comprises a deoxygenation step followed by a cracking step during which the mixture is subjected to cracking conditions to obtain a product stream comprising said gas, liquid fuel and wax.

current technology

Given the increasing importance of polymers as alternatives to conventional construction materials such as glass, metal, paper and wood, there is a perceived need for safe non-renewable resources such as petroleum and the dwindling amount of landfill capacity available for disposal of waste , the problem of recovering, recuperating, recycling, or in some way repurposing waste plastics has attracted considerable attention in recent years.

Pyrolysis or catalytic cracking of waste plastics has been proposed in order to convert high molecular weight polymers into volatile compounds with much lower molecular weights. Depending on the method employed, these volatile compounds can be relatively high boiling liquid hydrocarbons useful as fuel oils or fuel oil extenders, or light to medium boiling carbon atoms useful as gasoline-type fuels or other chemicals. Furthermore, these volatile compounds may be waxes, or at least may contain waxes.

Cracking of mixed waste plastics is a method well known to those skilled in the art. For example, US 5,216,149 discloses a method for controlling the pyrolysis of complex waste streams of plastics to convert such streams into useful high-value monomers or other chemicals by identifying catalysts and temperature conditions that allow a given polymer to decompose .

Known methods for the depolymerization of plastics by thermal or catalytic cracking generally result in the formation of five main products, which can be classified according to their carbon chain length from short to long: gas, gasoline, diesel, kerosene and wax (or HCO = heavy cycle oil).

The inventors of the present invention have found that the available technologies have the disadvantage that the oxygenates present in the raw materials are in most cases detrimental since they increase the oxygen content in the resulting product, thereby reducing its quality. Therefore, it would be desirable to produce high value products with low oxygen content from mixtures comprising plastics and oxygenates (Pavel T. Williams, "Waste treatment and disposal", 2nd ed., John W. John Wiley and Sons, Chichester, 2005, p 334).

A process for converting oxygenated hydrocarbons to hydrocarbons is described in US 4,308,411. The process starts with solid waste, including cellulosic material, from which an inorganic fraction is separated. In these examples, the organic fraction is dried and then pyrolyzed at a temperature from about 300°C to about 800°C (eg, 550°C). The vapors thus obtained comprising oxygenated hydrocarbons are separated, and these oxygenated hydrocarbons are subsequently contacted with crystalline aluminosilicate zeolites for conversion into hydrocarbons. Although this method allows the reduction of oxygenated hydrocarbons, it has the disadvantage that the organic fraction of the solid waste first has to be pyrolyzed at high temperature. At such high temperatures, plastics in solid waste also depolymerize and the depolymerization products may react with these oxygenates, leading to undesirably high oxygen content of the resulting gases, liquid fuels and waxes.

Therefore, there remains a need to further improve the cracking of plastics, in particular the conversion of mixtures comprising plastics and at least one oxygenate into gases, liquid fuels and waxes with a low oxygen content.

Contents of the invention

The inventors of the present invention have now found that oxygenates can be removed from mixtures comprising plastics and these oxygenates at considerably lower temperatures. Furthermore, the inventors have found that the density of the condensate of the gas stream obtained from the heated mixture is a suitable marker for determining the end of the deoxygenation process. At the beginning of the process, the density of the condensate is high. During deoxygenation, the density of the condensate decreases. At a certain density, a large amount of undesired oxygenates has been removed from the mixture, so that a product stream containing high quality and low oxygen content gases, liquid fuels and waxes is obtained during the subsequent cracking steps.

Detailed ways

Therefore, the present invention relates to a method for converting by cracking a mixture comprising plastic and at least one oxygenate into gas, liquid fuel and wax, the method comprising:

a deoxygenation step performed by heating the mixture to a temperature of at least 200° C. for a period of time until the condensate of the gas stream obtained from the heated mixture has a density of about 0.94 g/cm or ^less ;

and a cracking step following the deoxygenation step, during which the mixture is subjected to cracking conditions to obtain a product stream containing said gas, liquid fuel and wax.

In the cracking of plastics, several compound fractions are obtained. Typically, gas fractions containing light compounds (having less than 5 carbon atoms) are present. The gasoline fraction contains compounds with low boiling points, for example below 150°C. This fraction contains compounds having 5 to 9 carbon atoms. Kerosene and diesel fractions have higher boiling points, eg 150°C to 359°C. This fraction generally contains compounds having 10 to 21 carbon atoms. The even higher boiling fractions are often designated heavy cycle oil (or HCO) and waxes. In all these fractions, the compounds are hydrocarbons optionally containing heteroatoms such as N, O, and the like. Thus, "wax" in the sense of the present invention denotes a hydrocarbon optionally comprising heteroatoms. It is solid at room temperature (23°C) in most cases and it has a softening point generally above 26°C. Definitions of the resulting fractions are provided in the experimental section below.

Plastics are mostly composed of a specific polymer, and the plastic is often named after that specific polymer. Preferably, the plastic comprises more than 25% by weight, preferably more than 40% by weight, and more preferably more than 50% by weight of this particular polymer relative to its total weight. Other components in plastics are for example additives such as fillers, reinforcements, processing aids, plasticizers, pigments, light stabilizers, lubricants, impact modifiers, antistatic agents, inks, antioxidants and the like. Often, plastics contain more than one additive.

Plastics used in the method of the present invention include polyolefins and polystyrenes such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), ethylene-propylene-diene monomer (EPDM), polypropylene (PP ) and polystyrene (PS). Hybrid plastics consisting essentially of polyolefins and/or polystyrene are preferred.

Other plastics such as polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, polyurethane (PU), acrylonitrile-butadiene-styrene (ABS), ethylene vinyl alcohol (EVA), Polyvinyl acetate, polycarbonate, polyacrylate, polymethylmethacrylate (PMMA), nylon and fluorinated polymers are less desirable. If present in the plastic, they are preferably present in an amount of less than 50% by weight, preferably less than 30% by weight, more preferably less than 20% by weight, even more preferably less than 10% by weight of the total weight of the dry weight plastic a small amount exists.

Preferably, the plastic comprises one or more thermoplastic polymers and is substantially free of thermosetting polymers. In this regard, substantially free is intended to mean that the content of thermosetting polymer is less than 15% by weight, preferably less than 10% by weight, and even more preferably less than 5% by weight of the plastic starting material.

The plastic used in the method of the invention can be selected from:

Single waste plastics, single virgin plastics qualified or unqualified, mixed plastic wastes, rubber wastes, organic wastes, biomass or mixtures thereof. Single plastic waste, single off-spec virgin plastic, mixed plastic waste, rubber waste or mixtures thereof are preferred. Rejected single virgin plastics, mixed waste plastics or mixtures thereof are particularly preferred. Mixing plastic waste usually yields good results.

Prior to the method of the invention, the mixture may be pretreated by physico-chemical methods comprising one or more operations such as size reduction, grinding, crushing, sieving, chipping, melt removal, foreign matter removal, Dedusting, drying, degassing, melting, solidification and agglomeration.

Usually, waste plastics contain other undesired components, ie, foreign matter, such as glass, stone, metal, and the like. Limited amounts of such unpyrolizable components are acceptable as inlet feedstock contaminants. For example, the mixture used in the method of the invention may comprise less than 50% by weight, preferably less than 20% by weight, more preferably less than 10% by weight of non-pyrolyzable components, based on the total weight of the dry mixture.

In addition, waste plastics often contain other undesirable components, mainly cellulosic substrates such as wood, cardboard, paper, tissue, etc. Most of these pyrolyzable components are oxygenated compounds, such as oxygenated hydrocarbons, which during the cracking of plastics lead to an undesired increase in the oxygen content of the resulting gases, liquid fuels and waxes.

However, "oxygenates" in the sense of the present invention are not limited to organic compounds, but may also include inorganic compounds which contain oxygen atoms bonded to other atoms but which are chemically unstable under cracking conditions. H ₂ O is not considered an oxygenate in the sense of the present invention.

These oxygenates are believed to be difficult to remove because pyrolysis of oxygenates such as cellulosic materials as proposed in US 4,308,411 requires high temperatures at which plastic cracking can occur.

The inventors of the present invention have now surprisingly found that in a mixture comprising a plastic and at least one oxygenate, the temperature required to convert the oxygenate into a gas is considerably lower. However, the following problem remains: Under certain conditions, plastics may also crack at low temperatures. It is therefore necessary to determine parameters suitable for distinguishing between deoxygenation processes, during which oxygenates are removed from the mixture, and cracking processes, during which plastics are converted into desired products. After further research, the inventors of the present invention found that the density of the condensate of the gas stream obtained from the heated mixture is a suitable parameter to differentiate between the deoxygenation step and the cracking step.

The inventors have found that, during batch operation, at the beginning of conversion of the mixture comprising plastic and oxygenates, the density of the condensate of the gas stream obtained from the heated mixture is rather high. As the reaction proceeds, the density drops. It was found that when the condensate reached a density of about 0.94 g/cm ³ , a substantial amount or even substantially all of the undesired oxygenates had been removed from the mixture. The remaining mixture thus contains the majority of the plastic present in the initial mixture and a significantly reduced amount of undesired oxygenates. Thus, if the mixture remaining after the deoxygenation step is subjected to cracking conditions, a product stream is obtained comprising high quality gases, liquid fuels and waxes, especially with respect to the reduced oxygen content. At the same time, only a small amount of the plastic present in the initial mixture is depolymerized during this deoxidation step. Thus, the measurement of the density of the condensate of the gas stream obtained from the heated mixture allows to optimize not only the quality of the gas, liquid fuel and wax obtained, but also their yield.

In a preferred embodiment of the invention, the deoxygenation step is carried out until the condensate of the gas stream obtained from the heated mixture has a density in the range of 0.90 g/cm ³ to 0.93 g/cm ³ , preferably 0.91 g/cm 3 cm ³ to 0.93 g/cm ³ , more preferably in the range of 0.920 g/cm ³ to 0.928 g/cm ³ , even more preferably in the range of 0.923 g/cm ³ to 0.927 g/cm ³ , and most preferably about 0.925 g/cm ³ .

In the context of the present invention, "condensate of a gaseous stream obtained from a heated mixture" is understood as the fraction of gaseous products obtained from a mixture heated to at least 200° C. after cooling the hot gaseous stream to 40 obtained at °C. Those components of the gas stream that do not condense at 40°C are discharged. The condensate was then further cooled to a temperature of 25°C. At this temperature, the density of the condensate is measured. Possibly, the condensate can be split into an aqueous fraction and an oil fraction. Therefore, the density of the condensate is defined as the ratio of the sample weight to the sample volume, regardless of any possible liquid phase splitting. This measurement can be made simply by using the apparent weight and apparent volume of the "mixed" condensate.

In order to measure the density of condensate, a certain volume of condensate is required. If the flow rate of condensate obtained during the deoxygenation step is high enough, the density of the condensate can be measured continuously or at least semi-continuously. However, it may be preferable to collect a volume of condensate before measuring its density. For example, especially in a batch process, a suitable volume can be chosen relative to the amount of plastic in the starting mixture introduced into the reactor. In this case, the volume may be in the range of 0.1 to 250 cm ³ /kg plastic, preferably 0.15 to 100 cm ³ /kg plastic, more preferably 0.2 to 20 cm ³ /kg plastic. In another embodiment, a suitable volume may range, for example, from 0.5 to 10 cm ³ , preferably from 0.5 to 5 cm ³ , more preferably from 0.5 to 4 cm ³ . The smaller the volume that is collected for density measurement, the more precise the decision when to end the deoxygenation step and start the cracking step can be more precise. Alternatively, condensate may be collected for a certain period of time and then the density of the condensate collected during this time measured. The time interval during which the condensate is collected depends, for example, on the composition and amount of the mixture comprising plastics and oxygenates, the size of the reactor, the catalyst, the heating power, the flow rate of the condensate, etc., and can be, for example, between 1 and 120 minutes, Preferably in the range of 1 to 90 minutes, more preferably in the range of 1 to 60 minutes, for example in the range of 2 to 30 minutes. Furthermore, the shorter the time interval during which the condensate is collected to measure its density, the higher the accuracy in determining the end of the deoxygenation step and the beginning of the cracking step.

Thus, during the deoxygenation step, the condensate obtained is collected for a certain period of time, or until a certain volume is obtained. The density of the condensate thus obtained is measured, and if the density is above about 0.94 g/cm ³ , the deoxygenation step is continued and an additional condensate sample is collected for the next density measurement. Collection is continued for a certain period of time for each sample, or until a certain volume is obtained.

So far, the invention has been described in relation to batch operations. However, the process according to the invention can also be carried out continuously, for example by using reactors, such as rotating drum reactors or screw reactors, in which the mixture comprising plastic and at least one oxygenate is continuously moved from one reaction zone to the next reaction zone. A gas stream was collected from each reaction zone and the density of the condensate of this gas stream was measured as described above. As long as the gas stream obtained from a given reaction zone has a density above about 0.94 g/ ^cm3 , that reaction zone will be operated under deoxygenated conditions. Once the mixture moves into a reaction zone where the condensate of the resulting gas stream has a density of about 0.94 g/ ^cm3 or less, this and subsequent reaction zones are operated at cracking conditions to obtain the desired Product streams of gases, liquid fuels and waxes.

The gas stream obtained during the deoxygenation step contains the gaseous products into which the oxygenates are converted. By removing this gas stream from the heated mixture, oxygenates are removed and a residue is obtained which consists mainly of plastic (and optionally the aforementioned non-pyrolyzable components and small amounts of plastic pyrolysis products). This residue is then subjected to cracking conditions.

In addition, it was also found that the temperature at which oxygenates are converted to gaseous products depends on the plastics in the mixture. For example, if the plastic is polyethylene, the oxygenates convert to gas at a temperature slightly below 350°C, and if the plastic is polypropylene, at a temperature slightly below 300°C. This suggests that the plastic in a mixture comprising plastic and at least one oxygenate affects the temperature at which the oxygenate is converted to gas.

As an important step of the method according to the invention, the gas produced during the deoxygenation step is removed as a first gas stream. This gas stream contains unwanted oxygenate products, which are therefore removed before the plastic cracks. Removal of this first gas stream may eg be performed by purging the space above the heated mixture with a gas such as air, preferably an inert gas such as nitrogen. Alternatively or additionally, the first gas flow may be removed by applying reduced pressure.

In a preferred embodiment of the invention, the gas stream obtained during the deoxygenation step is removed for a period sufficient to remove at least 50% by weight of the at least one oxygenate from the mixture (based on the amount of oxygen present in the mixture prior to the deoxygenation step total weight of at least one oxygenate) time. More preferably, at least 70% by weight, even more preferably at least 80% by weight and most preferably substantially all of the at least one oxygenate is removed from the mixture prior to the cracking step. In this context, "substantially all of the at least one oxygenate" is understood such that at least 90% by weight, preferably Preferably at least 95% by weight, and even more preferably at least 97% by weight is removed prior to the cracking step.

A residue is obtained by removing the first gas stream from the heated mixture. This residue comprises plastic that has not been depolymerized at the first temperature, optionally remaining amounts of oxygenates and optionally the aforementioned non-pyrolyzable components. If the heating of the mixture at the first temperature has been carried out in the presence of a catalyst, this catalyst is also contained in the residue.

In the next step of the process according to the invention, this residue is subjected to cracking conditions. Under these conditions, plastic cracking occurs, producing a product stream comprising the desired gas, liquid fuel and wax. The product stream was removed from the heated residue.

Cracking of plastics can be carried out under usual conditions known to those skilled in the art. For example, the temperature during cracking of the plastic is generally above 350°C, preferably above 400°C, more preferably at least 425°C, for example in the range above 400°C to 650°C, even more preferably between 425°C and 550°C In the range.

In one embodiment, cracking may be performed in an air-depleted atmosphere. The air-depleted atmosphere may, for example, contain or consist of one or more inert gases, such as nitrogen, or may be under reduced pressure.

In another embodiment, cracking may be performed in the presence of a catalyst. However, it is also possible that a catalyst is also present during the deoxygenation step. In this case it is preferred that the deoxygenation step and the cracking step are carried out in the presence of a catalyst, preferably the same catalyst. However, it is also possible that the two steps are carried out in the presence of two different catalysts, or that another different catalyst is added to the cracking step. Finally, it is possible, but less desirable, that only the deoxygenation step is carried out in the presence of a catalyst which must then, however, be removed before the residue is cracked.

The catalyst used in the process of the invention may be any suitable catalyst. Preferred catalysts are those used in FCC operations, such as fresh FCC catalyst, used FCC catalyst, equilibrated FCC catalyst, BCA (bottoms cracking additive) or any mixture thereof.

For example, the catalyst may comprise a zeolite-type catalyst. Such catalysts may be selected from crystalline microporous zeolites known to those skilled in the art and commercially available. Preferred examples of zeolite-type catalysts are described in WO 2010/135273, the contents of which are incorporated herein by reference. Specific examples of suitable zeolite-type catalysts include, but are not limited to, ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, TS-1, TS-2, SSZ- 46. MCM-22, MCM-49, FU-9, PSH-3, ITQ-1, EU-1, NU-10, silicalite-1, silicalite-2, borosilicate-C, borosilicate- D, BCA and their mixtures. Alternatively or in addition, the catalyst may comprise an amorphous catalyst which may comprise, for example, silica, alumina, kaolin, or any mixture thereof. Silica, especially in the form of sand, is well known for FCC catalyst applications.

The skilled person knows suitable apparatus and equipment for carrying out the method according to the invention and he will select a suitable system on the basis of his professional experience, so that further details need not be given here.

Examples of suitable reactor types are fluidized bed, entrained bed, spouted bed, downcomer, fixed bed, rotating drum, rotating cone, spiral cone, auger, extruder, molecular distillation, thin film evaporator, kneader machine, cyclone separator, etc. Fluidized beds, entrained beds, spouted beds, augers and rotating drums are preferred. Augers and rotating drums are particularly preferred.

In one embodiment of the method according to the invention, the deoxygenation step and the cracking step are carried out in two different reactors.

In another embodiment of the method according to the invention, the deoxygenation step and the cracking step are carried out in the same reactor. This can then be done in the same part of the reactor or in two or more different parts of the same reactor, for example in a rotating drum or auger where the different parts are operated at different temperatures.

The process according to the invention can be carried out batchwise, semi-batchwise or continuously. In semi-batch mode, any feed stream and any product stream may be continuous, but at least one feed stream or one product stream is discontinuous and/or at least one feed stream or one product stream is continuous.

The invention furthermore relates to a method for removing oxygenates from a mixture comprising a plastic and at least one oxygenate, the method comprising: heating the mixture to a temperature of at least 200° C. for a period of time until the heated The condensate of the gaseous stream obtained from the mixture has a density of about 0.94 g/cm ³ or less. In this method, preferred embodiments are those described above.

Should the disclosure of any patents, patent applications, and publications incorporated by reference into this application conflict with the description of this application to the extent that it may render a term unclear, the present description shall take precedence.

The method of the present invention and its effects are now explained in more detail with reference to the following examples.

The following examples were performed according to the following general experimental procedure:

In each catalytic run in semi-batch mode, 30 g of plastic (20% polypropylene, 80% polyethylene) were charged into the reactor and a defined amount of catalyst (about 20 g) was stored in the catalyst storage tank. The reactor was closed and heated from room temperature to 200°C while simultaneously purging with a nitrogen flow of 150 mL/min. When the internal temperature reaches the melting point of the plastic, start stirring and slowly increase to 690rpm. The temperature is maintained at 200° C. for several minutes for melting and homogenization of the plastic. During this heating process, the nitrogen vented from the reactor was collected in a gas sampling bag and no condensate was recovered in the liquid trap. At the same time, the catalyst storage tank containing the catalyst was purged several times with nitrogen.

After this first pretreatment step, the temperature was raised below 425°C at a heating rate of 10°C/min. During this time, gas and nitrogen collection was done in another gas sampling bag. Thereafter, the temperature was further increased to a cracking temperature of 425°C. When the internal temperature reaches this cracking temperature, the catalyst is introduced into the reactor and the circulation of the gaseous products is switched to another pair of glass traps and corresponding gas sampling bags.

During selected time periods, liquid and gaseous products were collected separately in a pair of glass traps and their associated gas sampling bags. At the end of the experiment, the reactor was cooled to room temperature. During this cooling step, liquid and gas were also collected.

The reaction products are divided into three groups: i) gases, ii) liquid hydrocarbons and iii) residues (waxy compounds, ash and coke accumulated on the catalyst). Quantification of gases was done by gas chromatography (GC) using nitrogen as an internal standard, whereas quantification of liquids and residues was done by weighing. Glass traps (with their corresponding lids) were weighed before and after collecting liquid, while reactor vessels were weighed before and after each run.

The Simulated Distillation (SIM-DIS) GC method allows the determination of different fractions in a liquid sample (according to the selected fraction), the Detailed Hydrocarbon Analysis (DHA) GC method allows the determination of the gasoline fraction (C5-C11: boiling point < 216.1 °C; it includes C5-C6 in gas samples and C7-C11 in liquid samples) in PIONAU (P: paraffin, I: isoparaffin, O=: olefin, N: naphthene, A: aromatic, U: unidentified) components, and GCxGC allowed the determination of saturates, mono-, di-, and tri-aromatics in the diesel fraction (C12-C21; 216.1 °C < BP < 359 °C) of the last liquid sample taken.

Depending on the source and purity of the plastic, a two-phase liquid sample is obtained. In this case, THF was used as solvent in order to obtain a homogeneous liquid sample, and then SIM-DIS, DHA and GCxGC were performed. Furthermore, the determination of the water concentration in these liquid THF-diluted samples was performed by Karl-Fischer titration.

In these examples, HCO refers to heavy cycle oil considered to be hydrocarbon molecules having at least 22 carbon atoms (+C22). Waxes refer to hydrocarbon molecules having at least 20 carbon atoms (+C20). In general:

Gasoline: C5 and C6 including gas + liquid with bp (boiling point) < 150°C (about C5-C9)

Kerosene: a liquid with a boiling point of 150°C<bp<250°C (about C10-C14)

Diesel: liquid with a boiling point of 250°C<bp<359°C (about C15-C21)

●HCO: products with a boiling point >359°C (C22 and above)

Waxes: products with a boiling point >330°C (C20 and above)

Determination of the different fractions was carried out by gas chromatography by simulated distillation method and according to ASTM-D-2887 standard.

Example 1

Experiments were performed following the general procedure described above. 80 wt% HDPE and 20 wt% PP preheated at about 105°C to remove moisture were used (in Example 1.1, pure plastics containing no oxygenates were used for comparison; and in Examples 1.2 and 1.3, from re Plastics that are recycled and contain impurities such as paper, metal foil, etc. for comparison) were used as raw material for experiments along with 20 g of amorphous catalyst (ie, SiO ₂ ). The weight ratio of catalyst to dry plastic mixture is equal to 20/30 (by weight). These results are summarized in Table 1 below.

Example 2

Experiments were performed following the general procedure described above. 80 wt% HDPE and 20 wt% PP (from a recycling plant and containing impurities such as paper, metal foil, etc.) preheated at about 105°C to remove moisture were used as feedstock and 20 g of a balanced fluid catalytic cracking catalyst (ECATDC ) was tested, and the catalyst was provided by Equilibrium Catalyst Inc. The weight ratio of catalyst to dry plastic mixture is equal to 20/30 (by weight). Three mixtures of spent HDPE and PP were prepared and subjected to catalytic depolymerization (Examples 2.1 and 2.2). These results are summarized in Table 1 below.

Example 3

Experiments were performed following the general procedure described above. Carried out using 80wt% HDPE and 20wt% PP (from recycling plants and containing impurities like paper, metal foil, etc.) preheated at about 105°C to remove moisture as feedstock and 20 g of bottoms cracking additive catalyst BCA-105 Experiment, the catalyst was provided by Johnson Matthey (Johnson Matthey). The weight ratio of catalyst to dry plastic mixture was equal to 20/30 (by weight) (Example 3.1). These results are summarized in Table 1 below.

The data in Table 1 above indicate that most of the oxygenates are removed from the plastic mixture during the deoxygenation step (oxygenate removal was determined by measuring the water content in sample #0). On the other hand, the amount of water measured in the samples obtained in the cracking step (samples #1-#4) was only low. This shows that the method of the invention allows the removal of oxygenates from mixtures comprising plastics and oxygenates, so that the gases, liquid fuels and waxes obtained by cracking contain only little oxygen. At the same time, only a small amount of plastic is cracked during the deoxygenation step, so that the overall yield of the desired low oxygen content gases, liquid fuels and waxes remains good. Furthermore, a comparison of the product obtained in comparative example 1.1 (using pure plastic not containing oxygenates) with the products of Examples 1.2-3.1 shows that the removal of undesired oxygenates before the cracking step does not change the product distribution significantly.

Claims (15)

1. Process for converting a mixture comprising plastic and at least one oxygenate into gas, liquid fuel and wax by cracking, the process comprising: a deoxygenation step performed by heating the mixture to a temperature of at least 200° C. for a period of time until the condensate of the gas stream obtained from the heated mixture has a density of about 0.94 g/cm ³ or less; and a cracking step following the deoxygenation step, during which the mixture is subjected to cracking conditions to obtain a product stream containing said gas, liquid fuel and wax. 2. The method according to claim 1, wherein the deoxygenation step is carried out until the condensate of the gas stream obtained from the heated mixture has a density in the range of 0.90 g/cm ^{to 0.93} g/cm , preferably in the range of 0.91 g/cm ³ to 0.93 g/cm ³ , more preferably in the range of 0.920 g/cm ³ to 0.928 g/cm ³ , even more preferably in the range of 0.923 g/cm ³ to 0.927 g/cm ³ , and most preferably about 0.925 g/cm ³ . 3. The method according to claim 1 or 2, wherein the temperature in the deoxidation step is in the range of 250°C to 400°C, preferably in the range of 250°C to 380°C, more preferably in the range of 270°C to 350°C within the range of °C. 4. The method according to any one of claims 1 to 3, wherein the gas stream and the product stream obtained during the deoxygenation step are kept separate from each other. 5. The method according to any one of the preceding claims, wherein the gas stream obtained in the deoxygenation step is removed continuously enough to remove from the mixture based on the at least one gas present in the mixture before the deoxygenation step At least 50% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, even more preferably substantially all of the at least one oxygenate of the total weight of the oxygenate. 6. The method according to any one of the preceding claims, wherein the plastic comprises waste plastic, such as mixed waste plastic, preferably post-consumer waste plastic, off-spec plastic and/or industrial waste plastic. 7. The method according to any one of the preceding claims, wherein the plastic comprises more than 50% by weight of polystyrene and/or polyolefin, based on the total weight of the plastic. 8. A method according to any one of the preceding claims, wherein the cracking step is carried out in the presence of a catalyst. 9. The method according to claim 8, wherein the deoxygenation step and the cracking step are carried out in the presence of a catalyst. 10. The method according to claim 8 or 9, wherein the catalyst is a zeolite type catalyst and/or an amorphous type catalyst such as silica, alumina, kaolin or mixtures thereof. 11. The method of any one of claims 8 to 10, wherein the catalyst is fresh catalyst, equilibrated catalyst or a mixture thereof. 12. The method according to any one of the preceding claims, wherein the deoxygenation step and the cracking step are carried out in two different reactors. 13. The method according to any one of claims 1 to 11, wherein the deoxygenation step and the cracking step are carried out in the same reactor. 14. The method according to any one of the preceding claims, carried out batchwise, semi-batchwise or continuously. 15. A method for removing oxygenates from a mixture comprising plastic and at least one oxygenate, the method comprising: The mixture is heated to a temperature of at least 200° C. for a period of time until the condensate of the gas stream obtained from the heated mixture has a density of about 0.94 g/cm ³ or less.