US20190345393A1

US20190345393A1 - Process for converting plastic into gases, liquid fuels and waxes by cracking

Info

Publication number: US20190345393A1
Application number: US16/466,788
Authority: US
Inventors: Stéphane Streiff; Dominique Balthasart; Marco PICCININI; Avelino Corma; Miriam CERRO-ALARCÓN; Jesús MENGUAL
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2016-12-07
Filing date: 2017-12-06
Publication date: 2019-11-14
Also published as: WO2018104401A1; JP2020513453A; EP3551726A1; KR20190092487A; CN108603122A

Abstract

The present invention relates to a process for converting a mixture comprising plastic and at least one oxygenated compound into gases, liquid fuels and waxes by cracking. The process comprises a deoxygenation step and subsequently a cracking step during which the mixture is subjected to cracking conditions for obtaining a product stream containing said gases, liquid fuels and waxes.

Description

This application claims priority to European application No. EP 16306634.3 filed on Dec. 7, 2016, the whole content of this application being incorporated herein by reference for all purposes.

TECHNICAL FIELD

PRIOR ART

In view of the increasing importance of polymers as substitutes for conventional materials of construction, such as glass, metal, paper and wood, the perceived need to safe non-renewable resources such as petroleum and dwindling amounts of landfilled capacity available for the disposal of waste products, considerable attention has been devoted in recent years to the problem of recovering, reclaiming, recycling or in some way reusing waste plastic.
It has been proposed to pyrolyze or catalytically crack the waste plastic so as to convert high molecular weight polymers into volatile compounds having much lower molecular weight. The volatile compounds, depending on the process employed, can be either relatively high-boiling liquid hydrocarbons useful as fuel oils or fuel oil supplements or light- to medium-boiling carbon atoms useful as gasoline-type fuels or as other chemicals. Furthermore, the volatile compounds can be or at least can include waxes.
Cracking of a mixed waste plastic is a process well-known to the person skilled in the art. For example, U.S. Pat. No. 5,216,149 discloses a method for controlling the pyrolysis of complex waste stream of plastics to convert such stream into useful high-value monomers or other chemicals, by identifying catalyst and temperature conditions that permit decomposition of a given polymer.
The known processes for plastic depolymerization by thermal or catalytic cracking usually leads to the formation of five main products that can be categorized according to their carbon chain length, from shorter to longer: gases, gasoline, diesel, kerosene and waxes (or HCO=Heavy Cycle Oil).
The present inventors found that available technologies have the drawback that oxygenated compounds being present in the raw material are in most cases detrimental as they increase the oxygen content in the obtained products thereby lowering their quality. The production of high-value products that have low oxygen content from mixtures comprising plastic and oxygenated compounds would therefore by desirable (Pavel T. Williams in “Waste treatment and disposal”, 2^nded., John Wiley and Sons, Chichester, 2005, p 334).
A process for converting oxygenated hydrocarbons into hydrocarbons is described in U.S. Pat. No. 4,308,411. This process starts from solid waste, including cellulosic materials, from which an inorganic fraction is separated. The organic fraction is dried and then pyrolyzed at a temperature of from about 300° C. to about 800° C., such as 550° C. in the examples. The thus obtained vapor comprising oxygenated hydrocarbons is separated and subsequently the oxygenated hydrocarbons are contacted with a crystalline aluminosilicate zeolite for conversion into hydrocarbons. While this process allows for the reduction of oxygenated hydrocarbons, it has the drawback that the organic fraction of the solid waste first has to be pyrolyzed at high temperature. At such high temperature, the plastic in the solid waste also depolymerizes and the depolymerization products can react with the oxygenized compounds resulting in an undesired high oxygen content of the obtained gases, liquid fuels and waxes.
There is therefore still a need for further improving the cracking of plastic, in particular for converting a mixture comprising plastic and at least one oxygenated compound into gases, liquid fuels and waxes having a low oxygen content.

BRIEF DESCRIPTION OF THE INVENTION

The present inventors now found that oxygenated compounds can be removed from a mixture comprising plastic and the oxygenated compounds at a rather low temperature. Additionally, the inventors 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 substantial amount of the undesired oxygenated compound has been removed from the mixture so that during the subsequent cracking step a product stream containing gases, liquid fuels and waxes of high quality and low oxygen content is obtained.

DETAILED DESCRIPTION OF THE INVENTION

The present invention therefore relates to a process for converting a mixture comprising plastic and at least one oxygenated compound into gases, liquid fuels and waxes by cracking, the process comprising:

- a deoxygenation step which is conducted by heating the mixture to a temperature of at least 200° C. for a period until the condensate of the gas stream obtained from the heated mixture has a density of about 0.94 g/cm³or lower;
- and subsequently to the deoxygenation step a cracking step during which the mixture is subjected to cracking conditions for obtaining a product stream containing said gases, liquid fuels and waxes.

In the cracking of plastic several fractions of chemical compounds are obtained. Usually, there is a gas fraction containing light-weight chemical compounds with less than 5 carbon atoms. The gasoline fraction contains compounds having a low boiling point of for example below 150° C. This fractions includes compounds having 5 to 9 carbon atoms. The kerosene and diesel fraction has a higher boiling point of for example 150° C. to 359° C. This fraction generally contains compounds having 10 to 21 carbon atoms. The even higher-boiling fractions are generally designated as heavy cycle oil (or HCO) and waxes. In all these fractions, the compounds are hydrocarbons which optionally comprise heteroatoms, such as N, O, etc. “Waxes” in the sense of the present invention therefore designate hydrocarbons which optionally contain heteroatoms. In most cases, they are solid at room temperature (23° C.) and have a softening point of generally above 26° C. A definition of the obtained fractions is provided in the experimental section below.
A plastic is mostly constituted of a particular polymer and the plastic is generally named by this particular polymer. Preferably, a plastic contains more than 25% by weight of its total weight of the particular polymer, preferably more than 40% by weight and more preferably more than 50% by weight. Other components in plastic are for example additives, such as fillers, re-enforcers, processing aids, plasticizers, pigments, light stabilizers, lubricants, impact modifiers, antistatic agents, inks, antioxidants, etc. Generally, a plastic comprises more than one additive.
Plastics used in the process of the present invention include polyolefins and polystyrene, such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), ethylene-propylene-diene monomer (EPDM), polypropylene (PP), and polystyrene (PS). Mixed plastics mostly constituted of polyolefin and/or polystyrene are preferred.
Other plastics, such as polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, polyurethane (PU), acrylonitrile-butadiene-styrene (ABS), ethylene vinyl alcohol polymer (EVA), polyvinylacetate, polycarbonate, polyacrylate, polymethylmetacrylate (PMMA), nylon and fluorinated polymers are less desirable. If present in the plastic, they are preferably present in a minor 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.
Preferably, the plastic comprises one or more thermoplastic polymers and is essentially free of thermosetting polymers. Essentially free in this regard is intended to denote a content of thermosetting polymers of less than 15, preferably less than 10 and even more preferably less than 5% by weight of the plastic starting material.
The plastic used in the process of the present invention can be selected among:

- single waste plastic, single virgin plastic on spec or off spec, mixed waste plastic, rubber waste, organic waste, biomass or a mixture thereof. Single plastic waste, single virgin plastic off spec, mixed waste plastic, rubber waste or a mixture thereof are preferred. Single virgin plastic off-spec, mixed waste plastic or a mixture thereof particularly preferred. Mixed plastic waste gives usually good results.

Prior to the process of the invention, the mixture can be pretreated by a physico-chemical process including one or more operations as size reduction, grinding, shredding, screening, chipping, melt removal, foreign material removal, dust removal, drying, degassing, melting, solidifying and agglomerating.
Usually, waste plastic contains other non-desired components, namely foreign materials such as glass, stone, metal, etc. Limited quantities of such unpyrolizable components as contaminant of the inlet raw material are acceptable. For example, the mixture used in the process of the present invention may contain less than 50% by weight, preferably less than 20% by weight, more preferably less than 10% by weight of the total weight of the dry mixture unpyrolizable components.
Additionally, waste plastic very often contains other non-desired components, mainly cellulosic base materials, such as wood, cardboard, paper, tissue, etc. These pyrolizable components are mostly oxygenated compounds, such as oxygenated hydrocarbons, which during cracking of plastic result in an undesired increase in oxygen content of the obtained gases, liquid fuels and waxes.
“Oxygenated compounds” in the sense of the present invention are, however, not limited to organic compounds but may also include inorganic compounds which comprise oxygen atoms being bound to other atoms but which are chemically not stable under the cracking conditions. H₂O is not considered as an oxygenated compound in the sense of the present invention.
It was believed that these oxygenated compounds are difficult to remove because pyrolysis of oxygenated compounds, such as cellulosic materials, as suggested in U.S. Pat. No. 4,308,411 requires high temperatures at which cracking of the plastic may occur.
The present inventors now surprisingly found that in a mixture comprising plastic and at least one oxygenated compound the temperature required for converting the oxygenated compound into gases is rather low. There remained, however, the problem that under specific conditions also plastics can be cracked at low temperatures. It was therefore necessary to determine a parameter suitable for distinguishing between the deoxygenation process during which the oxygenated compounds are removed from the mixture and the cracking process during which the plastic is converted into the desired products. Upon further investigation, the present inventors found that the density of the condensate of the gas stream obtained from the heated mixture is a suitable parameter to distinguish between the deoxygenation step and the cracking step.
The inventors found that during a batch operation at the beginning of the conversion of the mixture comprising plastic and oxygenated compounds, the density of the condensate of the gas stream obtained from the heated mixture is rather high. When the reaction proceeds, the density decreases. It was found that when the condensate reaches a density of about 0.94 g/cm³, a considerable amount or even substantially all of the undesired oxygenated compounds has been removed from the mixture. The thus remaining mixture comprises most of the plastic being present in the initial mixture and a considerably reduced amount of undesired oxygenated compounds. Thus, if the mixture remaining after the deoxygenation step is subjected to cracking conditions, a product stream containing gases, liquid fuels and waxes of high quality in particular with respect to reduced oxygen content is obtained. At the same time, only a small amount of the plastic being present in the initial mixture is depolymerized during the deoxygenation step. Thus, the measurement of the density of the condensate of the gas stream obtained from the heated mixture allows for an optimization not only of the quality of the obtained gases, liquid fuels and waxes but also of their yield.
In preferred embodiments of the present invention, the deoxygenation step is conducted until the condensate of the gas stream obtained from the heated mixture has a density in the range of 0.90 g/cm³to 0.93 g/cm³, preferably in the range of 0.91 g/cm³to 0.93 g/cm³, more preferably in the range of 0.920 g/cm³to 0.928 g/cm³, even more preferably in the range of 0.923 g/cm³to 0.927 g/cm³, and most preferably about 0.925 g/cm³.
In the context of the present invention, the “condensate of the gas stream obtained from the heated mixture” is to be understood as the fraction of gaseous products obtained from the mixture being heated to at least 200° C. which is obtained when cooling the hot gas stream to 40° C. Those components of the gas stream which do not condense at 40° C. are discharged. The condensate is then further cooled to a temperature of 25° C. At this temperature the density of the condensate is measured. Possibly, the condensate may split into an aqueous fraction and an oil fraction. Therefore, the density of the condensate is defined as the ratio of the weight of the sample to the volume of the sample without taking into account any possible liquid phase split. This measurement can be conducted by simply using the apparent weight and apparent volume of the “mixed” condensate.
For measuring the density of the condensate a certain volume of the condensate is required. If the flow of condensate obtained during the deoxygenation step is high enough, the density of the condensate can be measured continuously or at least semi-continuously. It can, however, be preferred to collect a certain volume of the condensate before measuring its density. For example, in particular in a patch process, a suitable volume can be selected relative to the amount of plastic in the starting mixture being introduced into the reactor. In this case, the volume can be in the range of 0.1 to 250 cm³/kg of the plastic, preferably 0.15 to 100 cm³/kg of the plastic, more preferably 0.2 to 20 cm³/kg of the plastic. In another embodiment a suitable volume can be in the range of for example 0.5 to 10 cm³, preferably 0.5 to 5 cm³, more preferably from 0.5 to 4 cm³. The smaller the volume collected for measurement of the density the higher the precision in deciding when the deoxygenation step ends and the cracking step starts can be. Alternatively, the condensate can be collected for a certain time before the density of the condensate collected during this time is measured. The time interval during which the condensate is collected depends for example on the composition and amount of the mixture comprising the plastic and the oxygenated compound, the size of the reactor, the catalyst, the heating powder, the flow of the condensate, etc. and can be in the range of for example 1 to 120 minutes, preferably 1 to 90 minutes, more preferably 1 to 60 minutes, such as in the range of 2 to 30 minutes. Again, the shorter the time interval during which the condensate is collected for the measurement of its density, the higher is the precision in determining the end of the deoxygenation step and the beginning of the cracking step.
Thus, during the deoxygenation step the obtained condensate is collected either for a certain period of time or until a certain volume is obtained. The density of the thus obtained condensate is measured and, if the density is above about 0.94 g/cm³, the deoxygenation step is continued and a further sample of the condensate is collected for the next density measurement. Each sample is collected for a certain period of time or until a certain volume is obtained.
So far, the invention has been described with respect to a batch operation. However, the process of the invention can also be conducted continuously for example by using a reactor, like a rotating drum reactor or a screw reactor wherein the mixture comprising plastic and at least one oxygenated compound is continuously moved from one reaction zone to the next. From each reaction zone, a gas stream is collected and the density of the condensate of the gas stream is measured as described above. As long as the gas stream obtained from a given reaction zone has a density of above about 0.94 g/cm³, the reaction zone is operated under deoxygenation conditions. Once the mixture has moved into a reaction zone where the density of the condensate of the obtained gas stream is about 0.94 g/cm³or lower, this and the subsequent reaction zones are operated under cracking conditions for obtaining product streams containing the desired gases, liquid fuels and waxes.
The gas stream obtained during the deoxygenation step contains gaseous products to which the oxygenated compounds are converted. By removing this gas stream from the heated mixture, the oxygenated compounds are removed and a residue mainly consisting of the plastic (and optionally the above described unpyrolyzable components and small amounts of plastic pyrolysis products) is obtained. This residue is subsequently subjected to cracking conditions.
It was furthermore found that the temperature at which oxygenated compounds are converted into gaseous products depends on the plastic in the mixture. For example, oxygenated compounds are converted into gases at a temperature slightly lower than 350° C. if the plastic is polyethylene and at a temperature slightly lower than 300° C. if the plastic is polypropylene. This demonstrates that the plastic in the mixture comprising plastic and the at least one oxygenated compound influences the temperature at which the oxygenated compound is converted into gases.
As an important step of the process according to the invention the gases produced during the deoxygenation step are removed as a first gas stream. This gas stream contains the products of the undesired oxygen-containing compounds which are thereby removed before the plastic is cracked. Removing of the first gas stream can for example be conducted 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 stream can be removed by applying a reduced pressure.
In a preferred embodiment of the present invention, the gas stream obtained during the deoxygenation step is removed for a time sufficient to remove at least 50% by weight of the at least one oxygenated compound from the mixture, based on the total weight of the at least one oxygenated compound being present in the mixture prior to the deoxygenation step. 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 oxygenated compound is removed from the mixture prior to the cracking step. In this context “substantially all of the at least one oxygenated compound” is understood such that at least 90% by weight, preferably at least 95% by weight and even more preferably at least 97% by weight based on the total weight of the at least one oxygenated compound being present in the mixture prior to the deoxygenation step is removed prior to the cracking step.
By removing the first gas stream from the heated mixture, a residue is obtained. This residue comprises the plastic which was not depolymerized at the first temperature, optionally remaining amounts of oxygenated compounds, and optionally the above described unpyrolizable components. If the heating of the mixture at the first temperature has been conducted in the presence of the catalyst, this catalyst is also comprised within the residue.
In the next step of the process according to the invention, the residue is submitted to cracking conditions. At these conditions, cracking of the plastic occurs thereby producing a product stream containing the desired gases, liquid fuels and waxes. This product stream is removed from the heated residue.
Cracking of the plastic can be conducted under usual conditions known to a person skilled in the art. For example, the temperature during cracking of the plastic usually is above 350° C., preferably above 400° C., more preferably at least 425° C., such as in the range of above 400° C. to 650° C., even more preferably in the range of 425° C. to 550° C.
In one embodiment, the cracking may be conducted in an air depleted atmosphere. An air depleted atmosphere can for examples contain or consist of one or more inert gases, such as nitrogen, or can be at reduced pressure.
In a further embodiment, the cracking may be conducted in the presence of a catalyst. It is, however, also possible that a catalyst is present also during the deoxygenation step. In this case, it is preferred that the deoxygenation step and the cracking step are conducted in the presence of a catalyst, preferably the same catalyst. It is, however, also possible that the two steps are conducted in the presence of two different catalysts or that a further, different catalyst is added to the cracking step. Finally, it is possible, but less desired, that only the deoxygenation step is conducted in the presence of a catalyst, which, however, must then be removed prior to the cracking of the residue.
The catalyst used in the process of the present invention can be any suitable catalyst. Preferred catalysts are those used in FCC operations such as fresh FCC catalyst, spent FCC catalyst, equilibrated FCC catalyst, BCA (bottom cracking additives) or any mixture thereof.
For example, the catalyst can comprise a zeolite-type catalyst. Such catalysts may be selected from crystalline microporous zeolites which are known to the person skilled in the art and which are commercially available. Preferred examples for zeolite-type catalysts are described in WO 2010/135273, the content of which is incorporated herein by reference. Specific examples for 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, boralite-C, boralite-D, BCA, and mixtures thereof. Alternatively or additionally, the catalyst may comprise an amorphous-type catalyst which may comprise for example silica, alumina, kaolin, or any mixture thereof. Silica, in particular in the form of sand, is well known for FCC catalyst applications.
The skilled person is aware of suitable apparatus and equipment for carrying out the process in accordance with the present invention and he will select the suitable system based on his professional experience, so that no further extensive details need to be given here.
Examples of suitable reactor types are fluidized bed, entrained bed, spouted bed, downcomer, fixed bed, rotating drum, rotating cone, screw cone, screw auger, extruder, molecular distillation, thin film evaporator, kneader, cyclone and the like. Fluidized bed, entrained bed, spouted bed, screw auger and rotating drum are preferred. Screw auger and rotating drum are particularly preferred.
In one embodiment of the process according to the invention, the deoxygenation step and the cracking step are conducted in two different reactors.
In another embodiment of the process according to the invention, the deoxygenation step and the cracking step are conducted in the same reactor. This can be done subsequently in the same section of a reactor or in two or more different sections of the same reactor, for example in a rotary drum or an auger where different sections are operated at different temperatures.
The process according to the invention can be conducted batchwise, semi-batchwise or continuously. In the semi-batchwise mode, any feed stream and any product stream can 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 present invention furthermore relates to a process for removing oxygenated compounds from a mixture comprising plastic and at least one oxygenated compound, the process comprises: heating the mixture to a temperature of at least 200° C. for a period until the condensate of the gas stream obtained from the heated mixture has a density of about 0.94 g/cm³or lower. In this process, the preferred embodiments are those as described above.
Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.
The process of the present invention and its effects are now explained in more detail with reference to the following examples.
The examples below were conducted according to the following general experimental procedure:
In each catalytic run in semibatch mode, 30 g of plastic (20% Polypropylene, 80% Polyethylene) were loaded inside the reactor and a defined amount of catalyst (approximately 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 150 mL/min nitrogen flow. When the internal temperature reached the melting point of the plastic, stirring was started and was slowly increased to 690 rpm. The temperature was held at 200° C. for several minutes for plastic melting and homogenization. During this heating process, nitrogen coming out from the reactor was collected in a gas sampling bag and no condensates are recovered in the liquids traps. Meanwhile, the catalyst storage tank containing the catalyst was purged with nitrogen several times.
After this first pretreatment step, temperature was increased to less than 425° C. at a heating rate of 10° C./min. During this time the collection of gases and nitrogen was done in another gas sampling bag. Thereafter, the temperature was further increased to the cracking temperature of 425° C. When the internal temperature reached the cracking temperature, the catalyst was introduced inside the reactor, and the circulation of the gaseous products was commuted to another pair of glass traps and corresponding gas sampling bag.
During selected time periods, liquid and gaseous products were collected in a pair of glass traps and their associated gas sampling bag, respectively. At the end of the experiment the reactor was cooled to room temperature. During this cooling step, liquids and gases were also collected.
The reaction products were classified into 3 groups: i) gases, ii) liquid hydrocarbons and iii) residue (waxy compounds, ashes and coke accumulated on the catalyst). Quantification of the gases was done by gas chromatography (GC) using nitrogen as the internal standard, while quantification of liquids and residue was done by weight. Glass traps (along with their corresponding caps) were weighed before and after the collection of liquids, while the reactor vessel was weighed before and after each run.
The simulated distillation (SIM-DIS) GC method allowed determination of the different fractions in the liquid samples (according to the selected cuts), the detailed hydrocarbon analysis (DHA) GC method allows determination of the PIONAU (P: paraffins, I: iso-paraffins, =: olefins, N: naphthenes, A: aromatics, U: unidentified) components in the gasoline fraction of the last withdrawn sample (C5-C11: Boiling point<216.1° C.; what includes C5-C6 in the gas sample and C7-C11 in the liquid samples), and GCxGC allows the determination of saturates, mono-, di- and tri-aromatics in the diesel fraction of the last withdrawn liquid samples (C12-C21; 216.1<BP<359° C.).
Depending on the source and purity of the plastic, two phase liquid samples were obtained. In this case, THF was used as solvent in order to obtain a homogeneous liquid sample, and then SIM-DIS, DHA and GCxGC was performed. Besides, determination of the concentration of water in these liquid THF-diluted samples was done by the Karl-Fischer titration method.
In the examples, HCO refers to heavy cycle oil which is considered as hydrocarbon molecules with at least 22 carbon atoms (+C22). Waxes refer to hydrocarbon molecules with at least 20 carbon atoms (+C20). In general:

- Gasolines: contains C5s and C6s in gases +liquids with bp (boiling point)<150° C. (ca. C5-C9)
- Kerosene: liquids with boiling point 150<bp<250° C. (ca. C10-C14)
- Diesel: liquids with boiling point 250<bp<359° C. (ca. C15-C21)
- HCO: products with boiling point>359° C. (C22 and +)
- Waxes: products with boiling point>330° C. (C20 and +)

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

Example 1

The experiment was carried out following the general procedure described above. Experiments were carried out using 80 wt % HDPE and 20 wt % PP (pure plastic that does not contain oxygenated compounds for comparison in example 1.1 and plastic coming from a recycling plant and containing impurities such as paper, metal foil, etc. in examples 1.2 and 1.3) preheated at ca. 105° C. to remove moisture as raw materials and 20 g of an amorphous catalyst, namely SiO₂. Catalyst to dry plastic mixture weight ratio was equal to 20/30 by wt. The results are summarized in Table 1 below.

Example 2

The experiment was carried out following the general procedure described above. Experiments were carried out using 80 wt % HDPE and 20 wt % PP (coming from a recycling plant and containing impurities such as paper, metal foil, etc.) preheated at ca. 105° C. to remove moisture as raw materials and 20 g of a equilibrated Fluidized Catalytic Cracking Catalyst (ECATDC) provided by Equilibrium Catalyst Inc. Catalyst to dry plastic mixture weight ratio was equal to 20/30 by wt. Three mixtures of waste HDPE and PP were prepared and submitted for catalytic depolymerization (examples 2.1 and 2.2). The results are summarized in Table 1 below.

Example 3

The experiment was carried out following the general procedure described above. Experiments were carried out using 80 wt % HDPE and 20 wt % PP (coming from a recycling plant and containing impurities such as paper, metal foil, etc.) preheated at ca. 105° C. to remove moisture as raw materials and 20 g of a bottom cracking additive catalyst BCA-105 provided by Johnson Matthey. Catalyst to dry plastic mixture weight ratio was equal to 20/30 by wt (example 3.1). The results are summarized in Table 1 below.

TABLE 1

Reaction	Density of	% H2O

Reaction

Temper-

time

Mass produced during reaction time range (g)

conden-

removal

Exam-

Sam-

time

ature/

range

HCO

Waxes

sate

at T <

ple

(min)

° C.

(min-min)

Gases

Gasoline

Kerosene

Diesel

(+C22)

(+C20)

H₂O

TOTAL

[g/cm³]

425° C.

1.1	#0	30.5	200-425	0-30.5	0.14	0.15	0.11	0.05	0.02	0.03		0.48	0.782
	#1	25	425	0-25	0.72	1.89	1.38	0.67	0.25	0.35		4.91	0.782
	#2	40	425	25-40	0.27	0.71	0.78	0.64	0.04	0.10		2.44	0.786
	#3	60	425	40-60	0.44	1.10	1.37	1.32	0.09	0.24		4.32	0.790
	#4	90	425	60-90	0.66	1.68	2.29	3.98	1.71	2.78		10.30	0.822
1.2	#0	56	RT-425	0-56	0.82	0.17	0.21	0.12	0.04	0.05	2.02	3.38	0.947	89
	#1	25	425	0-25	0.86	0.91	2.18	1.47	0.59	0.81	0.14	6.15	0.809
	#2	40	425	25-40	0.32	0.40	0.97	1.28	0.38	0.63	0.05	3.40	0.818
	#3	60	425	40-60	0.31	0.45	0.98	1.58	0.75	1.09	0.03	4.11	0.829
	#4	90.5	425	60-90.5	0.19	0.19	0.41	0.99	1.12	1.40	0.03	2.93	0.865
1.3	#0	58	RT-425	0-58	0.85	0.19	0.24	0.09	0.10	0.10	1.97	3.43	0.944	91
	#1	14	425	0-14	0.61	0.62	1.47	0.86	0.58	0.71	0.11	4.25	0.816
	#2	34	425	14-34	0.44	0.58	1.25	1.52	0.45	0.75	0.04	4.28	0.815
	#3	54	425	34-54	0.21	0.36	0.51	0.86	0.45	0.65	0.02	2.41	0.828
	#4	75	425	54-75	0.15	0.27	0.38	0.74	0.56	0.74	0.02	2.10	0.841
2.1	#0	81.5	RT-425	0-81.5	1.63	0.22	0.17	0.07	0.03	0.03	1.84	3.96	0.944	85
	#1	3.5	425	0-3.5	0.35	0.59	1.32	0.34	0.04	0.06	0.13	2.76	0.791
	#2	8.5	425	3.5-8.5	0.32	0.54	1.36	0.61	0.07	0.12	0.09	2.99	0.795
	#3	14.5	425	8.5-14.5	0.35	0.64	1.58	0.90	0.18	0.29	0.05	3.70	0.797
	#4	23	425	14.5-23	0.39	0.63	1.35	0.96	0.31	0.44	0.04	3.68	0.804
2.2	#0	64	RT-425	0-64	0.64	0.06	0.30	0.09	0.02	0.04	1.86	2.98	0.950	82
	#1	2.5	425	0-2.5	0.25	1.09	1.43	0.24	0.02	0.05	0.24	3.27	0.787
	#2	6	425	2.5-6	0.27	0.82	1.48	0.43	0.06	0.12	0.10	3.16	0.787
	#3	11	425	6-11.0	0.26	0.70	0.87	0.38	0.10	0.16	0.04	2.36	0.788
	#4	16	425	11-16.0	0.18	0.52	0.61	0.30	0.09	0.14	0.03	1.73	0.790
3.1	#0	55.3	RT-425	0-55.3	0.67	0.27	0.20	0.06	0.01	0.02	2.02	3.23	0.942	80
	#1	9	425	0-9	0.49	0.67	0.79	0.27	0.07	0.12	0.36	2.65	0.811
	#2	20	425	9-20.0	0.30	0.70	0.76	0.34	0.09	0.15	0.04	2.22	0.787
	#3	33	425	20-33	0.29	0.64	0.96	0.68	0.17	0.28	0.05	2.79	0.798
	#4	50	425	33-50	0.32	0.60	0.81	0.80	0.15	0.31	0.05	2.73	0.801

RT: room temperature

The data in the above Table 1 demonstrate that during the deoxygenation step a major portion of the oxygenated compounds is removed from the plastic mixture (removal of the oxygenated compounds is determined by measurement of the water content in sample #0). On the other hand, the amount of water determined in the samples obtained in the cracking step (samples #1-#4) was only low. This demonstrates that the process of the present invention allows for the removal of oxygenated compounds from a mixture comprising plastic and oxygenated compounds so that the gases, liquid fuels and waxes obtained by cracking contain only little oxygen. Simultaneously, only small amounts of plastic are cracked during the deoxygenation step so that the overall yield of the desired gases, liquid fuels and waxes of low oxygen content is still good. Furthermore, a comparison of the products obtained in comparative examples 1.1 using pure plastic that does not contain oxygenated compounds with the products of examples 1.2-3.1 demonstrates that removal of the undesired oxygenated compounds prior to the cracking step does not significantly change the product distribution.

Claims

1. A process for converting a mixture comprising plastic and at least one oxygenated compound into gases, liquid fuels and waxes by cracking, the process comprising:

a deoxygenation step which is conducted by heating the mixture to a temperature of at least 200° C. for a period until the condensate of the gas stream obtained from the heated mixture has a density of about 0.94 g/cm³or lower;

and subsequently to the deoxygenation step a cracking step during which the mixture is subjected to cracking conditions for obtaining a product stream containing said gases, liquid fuels and waxes.

2. The process according to claim 1, wherein the deoxygenation step is conducted until the condensate of the gas stream obtained from the heated mixture has a density in the range of 0.90 g/cm³to 0.93 g/cm³.

3. The process according to claim 1, wherein the temperature in the deoxygenation step is in the range of 250° C. to 400° C.

4. The process according to claim 1, wherein the gas stream obtained during the deoxygenation step and the product stream are kept separate from each other.

5. The process according to claim 1, wherein the gas stream obtained in the deoxygenation step is removed for a time sufficient to remove at least 50% by weight, based on the total weight of the at least one oxygenated compound being present in the mixture prior to the deoxygenation step.

6. The process according to claim 1, wherein the plastic comprises waste plastic.

7. The process according to claim 1, wherein the plastic comprises more than 50% by weight of polystyrene and/or polyolefin based on the total weight of plastic.

8. The process according to claim 1, wherein the cracking step is conducted in the presence of a catalyst.

9. The process according to claim 8, wherein the deoxygenation step and the cracking step are conducted in the presence of a catalyst.

10. The process according to claim 8, wherein the catalyst is a zeolite-type catalyst and/or an amorphous-type catalyst.

11. The process according to claim 8, wherein the catalyst is fresh catalyst, equilibrated catalyst, or a mixture thereof.

12. The process according to claim 1, wherein the deoxygenation step and the cracking step are conducted in two different reactors.

13. The process according to claim 1, wherein the deoxygenation step and the cracking step are conducted in the same reactor.

14. The process according to claim 1, which wherein the process is conducted batchwise, semi-batchwise or continuously.

15. A process for removing oxygenated compounds from a mixture comprising plastic and at least one oxygenated compound, the process comprising:

heating the mixture to a temperature of at least 200° C. for a period until the condensate of the gas stream obtained from the heated mixture has a density of about 0.94 g/cm³or lower.

16. The process according to claim 2, wherein the deoxygenation step is conducted until the condensate of the gas stream obtained from the heated mixture has a density in the range of 0.91 g/cm³to 0.93 g/cm³.

17. The process according to claim 3, wherein the temperature in the deoxygenation step is in the range of 250° C. to 380° C.

18. The process according to claim 5, wherein the gas stream obtained in the deoxygenation step is removed for a time sufficient to remove at least 70% by weight, based on the total weight of the at least one oxygenated compound being present in the mixture prior to the deoxygenation step.

19. The process according to claim 6, wherein the plastic comprises mixed waste plastic.

20. The process according to claim 10, wherein the catalyst is silica, alumina, kaolin, or a mixture thereof.