Plastic depolymerization using supported ionic liquid catalysts

Abstract

A method of depolymerizing plastic waste using supported ionic liquid catalyst is described herein. The method provides with high efficiency a high quality liquid depolymerization product usable as cracker feedstock.

Description

PLASTIC DEPOLYMERIZATION USING SUPPORTED IONIC LIQUIDCATALYSTSFIELD OF THE DISCLOSURE

[0001] This disclosure relates to a catalytic method for depolymerizing plastic feedstock, and to certain catalyst for the depolymerization. More particularly, it relates to methods for the depolymerizing plastic feedstock in the presence of supported ionic liquids catalysts.BACKGROUND OF THE DISCLOSURE

[0002] Plastics are inexpensive and durable materials, which can be used to manufacture a variety of products that find use in a wide range of applications, so that the production of plastics has increased dramatically over the last decades. Due to the durability of the polymers involved in plastic production, an increasing amount of plastics are filling up landfill sites and occupying natural habitats worldwide, resulting in environmental problems. Even degradable and biodegradable plastics may persist for decades depending on local environmental factors, like levels of ultraviolet light exposure, temperature, presence of suitable microorganisms and other factors.

[0003] Currently plastic recycling primarily includes mechanical recycling and chemical recycling. Globally speaking, mechanical recycling is the most used method for new uses of plastics, and through this method, plastics are mechanically transformed without changing their chemical structure, so they can be used to produce new materials. Typical mechanical recycling steps include collecting plastic wastes; sorting plastic wastes into different types of plastics and colors; packaging plastics by pressing or milling plastics; washing and drying the plastics; reprocessing the plastics into pellets by agglutinating, extruding and cooling the plastics; and finally recycled raw materials are obtained. This is the most widely used technology for the polyolefins like polyethylene (PE) and polypropylene (PP).

[0004] Chemical recycling, on the other hand, reprocesses plastics and modify their structure so that they can be used as raw material for different industries or as a basic input or feedstock for manufacturing new plastic products. Chemical recycling typically includes the steps of collecting plastics, followed by heating the plastics to a temperature at which the polymers break down into small fragments. This process, also called depolymerization, is abasic process whereby plastic waste material is converted to liquid fuel by thermal degradation (cracking) in the absence of oxygen. Plastic waste is typically first melted within a stainless steel chamber under an inert purging gas, such as nitrogen. This chamber then heats the molten material to a gaseous state that is drawn and then condensed in one or more condensers to yield a hydrocarbon distillate comprising straight and branched chain aliphatic, cyclic aliphatic and aromatic hydrocarbons. Molecules having one or more double bonds can also be found. The resulting mixture can then be used as a fuel or used as a feedstock for further thermocatalytic process in order to obtain refined chemicals such as monomers that can be reintroduced into the plastic manufacturing cycle.

[0005] The step of converting the molten plastic mass into a gaseous stream can in principle take place only by the action of the heat (thermal depolymerization). However, it has been proved that the presence of a catalyst in this stage allow the depolymerization to take place at a lower temperature and more efficiently.

[0006] To this end, various catalysts have been proposed although sometimes without confirming their capability to depolymerize. WO2018 / 000014 suggests a process for the depolymerization of a mixed polymeric / biomass feedstock carried out in the presence ionic liquids acting simultaneously as catalysts and solvents for the feedstock. Although the specific amounts are not mentioned, from the function they have to perform it can be inferred that the amount of ionic liquid must be at least comparable and probably higher than the amount of feedstock. In any case, the said reference does not provide any data concerning catalyst effectiveness.

[0007] The applicant has surprisingly found that supported ionic liquids are very effective in plastic waste depolymerization even if used in small amounts.SUMMARY OF THE DISCLOSURE

[0008] It is therefore an aspect of the present disclosure a process for depolymerizing plastics, comprising the steps of: a) providing a melt plastic waste feedstock comprising at least a polyolefin fraction and; b) subjecting the melt product obtained in (a) to a temperature ranging from 280°C to 600°C to obtain a depolymerization product; said process being characterized by the fact that either or both of the melt product and depolymerization product are contacted with a supported ionic liquid catalyst.

[0009] Preferably, the amount of catalyst used ranges from 0.1 to 20 wt.%, more preferably 0.1-10 wt.% and especially from 0.1 to 5 wt.% with respect to the total weight of plastic waste feedstock and catalyst.

[0010] Preferably, the plastic waste feedstock comprises a mixture of polyethylene and polypropylene in a weight ratio 85:15 to 15:85 more preferably 80:20 to 20:80. The polyethylene can be one or more of high density polyethylene (HDPE), low-density polyethylene (LDPE), linear low density polyethylene (LLDPE). Polypropylene (PP) can be either propylene homopolymer or a propylene copolymer with lower amount of ethylene and / or butene. In addition, the feedstock may comprise other polyolefins like polybutene. In a particular embodiment, the feedstock may comprise also polymeric mixtures that incorporates other materials like polystyrene (PS), ethyl-vinyl acetate copolymer (EVA), ethyl-vinyl alcohol copolymer (EVOH), polyvinyl chloride (PVC), or mixtures thereof. In a preferred embodiment, the feedstock is constituted by more than 80% wt of a mixture between polyethylene and polypropylene in which polypropylene accounts for more than 50%wt of the polypropylene / polyethylene mixture.

[0011] When carrying out the depolymerization process, care should be taken for not introducing oxygen containing atmosphere into the depolymerization system. The barrier to the potentially oxygen-containing atmosphere can be obtained with a series of expedients such as nitrogen blanketing and vacuum system connected to a barrel of the extruder.

[0012] More specifically, the plastic feedstock mixture, can be charged into the feeding system of the depolymerization reactor by means of a hopper, or two or more hoppers in parallel, and the oxygen present in the atmosphere of the plastic waste material is substantially eliminated inside the hopper(s).

[0013] Plastic feedstock can be fed directly into the depolymerization reactor for small scale tests. For larger scale it is preferred to fed to the depolymerization reactor by means of an extruder which is turn fed with the plastic feedstock.

[0014] Preferably, plastic scrap is brought to a temperature at which substantially all the mass is melted and then injected into the depolymerization reactor. The extruder receives the plastic scrap cut in small pieces into the feed hopper, conveys the stream in the melting section and heat the polymer by combined action of mixing energy and heat supplied by barrel heaters. Usually, the melting temperature ranges from 250°C to 350°C.

[0015] Additives can optionally be incorporated in the melt aimed at reducing corrosivity of plastic scrap or improving depolymerization efficiency.

[0016] During the extrusion, one or more degassing steps can be foreseen to remove residual humidity present in the product.

[0017] Before being fed to the reactor, the melt stream can be filtered by in order to remove solid impurities present in the plastic waste.

[0018] Any extrusion systems can be applied, as single screw extruders, twin screw extruders, twin screw extruders with gear pump, or combination of the above.

[0019] The mixing of the plastic waste feedstock and catalyst can take place either directly into the depolymerization reactor or beforehand outside the reactor. When the mixing takes place in the depolymerization reactor, the catalyst can be fed according to several options. The simplest one, preferably used in small scale systems, is to directly pour the solid catalyst in the reactor under a nitrogen atmosphere. According to another option, the powdery catalyst may be fed to the reactor in a form of a liquid hydrocarbon slurry or a semisolid paste using dedicated devices.

[0020] As an alternative, the mixing can take place outside the depolymerization reactor. Also in this case several options are possible. According to one of them, catalyst is mixed with plastic scrap in a homogenizer apparatus and the mixture is then pelletized. The so obtained pellets, which can also contain other additives, may then be charged to the extruder hopper which is used to feed the polymerization reactor. It is also possible to charge into the hopper plastic scrap and catalysts separately. In this case, the mixing can take place into the extruder at the time of plastic scrap melting which is subsequently fed to the depolymerization reactor.

[0021] The depolymerization reactor is preferably an agitated vessel operated at temperature ranging from 300°C to 550°C, more preferably from 350°C to 500°C and especially from 350°C to 450°C with inlet for plastic feedstock and catalyst and outlet for the gaseous depolymerization product.

[0022] In fact, as a result of the depolymerization process, a gaseous stream is generated that is sent to a condensation unit which totally or partially liquifies said stream.

[0023] The condensation section receives effluent gases from the depolymerization reactor and partially condense them in an oily depolymerized product substantially made up ofhydrocarbons. A fraction of incondensable gases can be collected and stored separately. The condensation section can be composed by one or more stages, operated in pressure or not, at different temperatures in order to recover the maximum amount of products according to the volatility of the resulting formed compounds. The temperature range can vary of course depending on the operative pressure.

[0024] Preferably, the condensation section has at least two condensation stages preferably operating at descending temperatures. As an example, in small scale equipment the first condensation stage is operated at a temperature range of 100-120°C and the second at a temperature range of from 2°C to -20°C:

[0025] The depolymerization process can take place also in a reactor set-up comprising two depolymerization reactors, preferably connected in series in which the second depolymerization reactor can be operated under similar conditions described for the previous depolymerization stage. When operating with two reactors, there are different possibilities for the catalyst feeding. According to one preferred embodiment, the catalyst is fed in the first reactor, preferably together with the plastic waste melt, and then transferred to the second reactor together with the first reactor content.

[0026] According to another embodiment, the catalyst can be fed to the second reactor where it can operate on the partially depolymerized material coming from the first reactor. When operating with this set-up, it is also preferred to recycle back the catalyst and part of the liquid or semiliquid mass to the first depolymerization reactor from which the solid residue is discharged. In analogy with the first depolymerization step, the gaseous effluent can be condensed in a subsequent condensation stage.

[0027] At the end of the process preferably at least 80% wt., and preferably at 90% wt., of the plastic feedstock has been converted in liquid or gaseous depolymerization product.

[0028] As mentioned above, the main use of the depolymerization product according to the present disclosure can be as a cracker feedstock. In this connection, it would be preferred to generate from the depolymerization process a high yield in liquid depolymerization product. In a preferred embodiment the amount of liquid depolymerization product is higher than 60%wt more preferably from 65 to 85% wt. of the plastic waste feedstock.

[0029] Moreover, it would also be preferable for the liquid depolymerization product to have a composition as much as possible suited for a cracker feedstock. This involves having a very low amount, or even absence, of fractions with C28 or higher. Preferably, in the liquiddepolymerization product the amount of the higher than C28 fraction is equal to, or lower than, 4%, preferably lower than 3% and more preferably lower than 2% with respect to the total amount of liquid depolymerization product.

[0030] Also, the quality of cracker feedstock is higher when the depolymerization oil obtained from real plastic waste has low values of C6-C8 aromatics and Internal Olefin Index. This latter is defined as the molar ratio between internal double bonds with respect to double bond in chain end position (alfa-olefins) determined as described in the characterization section. Preferably, in the liquid depolymerization product the Internal Olefin Index is lower than l%wt and more preferably lower than 0.5%wt.

[0031] As used herein, “C6-C8 aromatics” refer to a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle, wherein total of 6 to 8 carbon atoms are present. Preferably, the content of aromatics C6-C8 aromatics in the liquid depolymerization product is lower than 2%mol and preferably lower than 1.5%mol.

[0032] As already mentioned, the catalyst comprises ionic liquids deposited on a solid support.

[0033] Ionic Liquids are known in the art and include compounds having different structures and properties. According to the present disclosure, ionic liquid are considered those ionic organic compounds that have a melting temperature at 550°C or below.

[0034] Preferred ionic liquids have a melting temperature lower than 400°C, more preferably lower than 350°C and especially lower than 300°C.

[0035] Preferably, said ionic liquids do not decompose at, or below, the depolymerization temperature.

[0036] Cation and anions of the ionic liquids can be preferably chosen from those represented below:cation(organic)phosphonium pyrrolidinium sulfoniumalkylsulfate tosylate methanesulfonate anion(organic) anion(inorganic)bis (trifluoromethyl- hexaf luo ro- tetrafluoro- halide sulfonyl)imide phosphate borate where Ri to R4 groups are, independently, selected from C1-C20 alkyl or arylalkyl and C6-C20 aryl or alkylaryl groups.

[0037] Particularly preferred are the ionic liquids in which the cation has the formula (Phosponium + halogen) where the Ri to R4 groups are phenyl groups or C3-C8 alkyl groups preferably hexyl groups and the halogen is chlorine.

[0038] The support is preferably an inorganic support which can be either spherical or granular. Examples of solids of this type, are aluminum oxide, silicon dioxide (silica gel), titanium dioxide or their mixed oxides or cogels, or aluminum phosphate. Preferably, in the process according to the present disclosure, the solid inorganic support is selected from inorganic oxides and more preferably from AI2O3, SiCh and TiCh. Preferably, the support is based on AI2O3, SiCh, or mixed silica / alumina composition. Support based on SiCh is especially preferred.

[0039] Preferably, the support particles have a pore volume which is preferably in the range between 0.5 and 3.0 cm3 / g, more preferably in the range from 0.7 and 3.0 cm3 / g, and especially in the range from 0.8 cm3 / g to 2.0 cm3 / g.7SUBSTITUTE SHEET (RULE 26)

[0040] Preferably the support particles have a pore diameter which is preferably in the range below 200A, more preferably in the range below 150 A, particularly preferably in the range from 50 A to 130A.

[0041] Preferably the support particles have a particle size (D50 in volume) measured with laser diffraction, ranging from 10 to 200 pm, more preferably from 20 to 110pm.

[0042] The surface area of the inorganic support can range from 100 m2 / g to 1000 m2 / g, preferably in the range from 150 m2 / g to 700 m2 / g and particularly preferably, especially when the support is silica, in the range from 200 m2 / g to 600 m2 / g. The specific surface area of the support particles is the surface area of the particles determined by means of nitrogen adsorption in accordance with the BET technique.

[0043] The apparent density of the inorganic supports for catalysts is preferably in the range from 250 g / 1 to 1200 g / 1, with the apparent density being able to vary as a function of the water content of the support. Particularly when the support is silica, the apparent density of water-containing support particles is preferably in the range from 500 g / 1 to 1000 g / 1, more preferably in the range from 600 g / 1 to 950 g / 1 and particularly preferably in the range from 650 g / 1 to 900 g / 1. In the case of supports which contain very little if any water, the apparent density is preferably from 250 g / 1 to 600 g / 1.

[0044] Silica supports of the above defined features are commercially available.

[0045] Silica supports can be anyway prepared by several methods known in the art. According to one of them, which is also preferred, the support is prepared starting from a silica hydrogel by acidic or basic precipitation from water glass as described in EP1778748A1 the specific disclosure of which is herein incorporated by reference.

[0046] The support preferably comprises a high proportion of SiCh. Preference is given to the silicon content of the support being in the range >10% by weight, preferably in the range >15% by weight, more preferably in the range >20% by weight, particularly preferably in the range >25% by weight, more particularly preferably in the range >30% by weight, especially in the range > 40% by weight, very particularly preferably in the range > 50% by weight, based on the total weight of the support.

[0047] The support material can also be partially or fully modified before use in the process of the invention. The support material can, for example, be treated under oxidizing or nonoxidizing conditions at temperatures of from 200 to 1000°C, if appropriate in the presence of fluorinating agents such as ammonium hexafluorosilicate. In this way, it is possible, interalia, to vary the water content and / or OH group content. Also, it is possible to dope the support with metal compounds different from those on which the support is based on.

[0048] The amount of ionic liquid fixed on the final supported catalyst, before use in depolymerization, could range from 0.5 to 55%wt, preferably from 2 to 50%wt and more preferably from 4 to 40%wt based on the total weight of supported catalyst.

[0049] The supportation process can be carried out according to several methods available to the skilled in the art. According to one of the preferred methods, the process for the preparation of a supported ionic liquid catalyst is based on the incipient wetness technique. In particular, the process may comprise the following steps: a) contacting a solution of ionic liquid (IL) in a polar solvent with the solid inorganic support under conditions and amount such that the ratio (PFR) between the volume of IL solution and the total pore volume relative to the amount of support used is equal to, or lower than 1.20; b) drying the product obtained from previous step keeping while keeping it in substantially continuous motion.

[0050] Preferably, the drying is carried out under vacuum and the drying temperature ranges from 40 to 150°C with the proviso that if the temperature chosen is higher than 90°C the drying time at that temperature is lower than 16 hours.

[0051] Preferably the support particles have a pore volume measured with liquid titration method of at least 0.3 cm3 / g, preferably at least 0.5 cm3 / g and most preferably at least 0.7 cm3 / g and a particle size (D50) ranging from 5 to 200 pm

[0052] A poison-suppressing agent can be used in association with the catalyst. Preferably, it can be selected from the group consisting of Ca(OH)2, Mg(OH)2, Ba(OH)2, Sr(OH)2, CaO, AI2O3, aluminosilicates such as bentonite, and Zr(HPCL)2 and mixtures thereof. Among them, the use of Ca(OH)2, aluminosilicates Zr(HPO4)2 is preferred.

[0053] The data reported in the present disclosure show that the process according to the present disclosure allows conversion of virgin resins, and also complex plastic waste, in a liquid depolymerization product which is obtained in high yields and composition that makes it suitable for use as a cracker feedstock.CHARACTERIZATIONThe properties are determined according to the following methods.Analytical Methods

[0054] Characterization of liquid products: The liquid products from the two traps were characterized by Gas Chromatography (GC) and proton NMR (*H NMR).

[0055] The GC analysis of the liquid product for each run was performed using an Agilent 7890 GC (Agilent Technologies, Santa Clara, CA) equipped with a standard non-polar column and a flame ionization detector. For the GC data, the weight percent for x < nC7 (having boiling point <98°C named LF1), nC7 < x < nCl l (having boiling point 98°C <BP< 203 °C named LF2), nC12 < x < nC28 (having boiling point 203°C <BP< 434°C named LF3) , x > C28 (having boiling point >434°C named LF4) were used to characterize the liquid product.

[0056] NMR data were used to characterize the percent of aromatic protons, paraffinic protons and olefinic protons in the liquid product. The examples were analyzed with an addition of CDC13 (0.6 g of depolymerize polymer / metal oxide mixture with 0.4 g of CDC13). The data were collected on a Broker AV500 MHz NMR spectrometer (Broker Corporation, Billerica, MA) at 25°C with a 5mm Prodigy probe. One dimension 1H NMR data were processed using TOPSPIN® software (Broker) with an exponential line broadening window function. Quantitative measurements were performed with a 15 second relaxation delay, a 30° flip angle pulse, and 32 scans to facilitate accurate integrals. The spectral integrations for aromatic olefinic, and paraffinic protons were obtained and used to quantify relative ratios of these protons.

[0057] Determination of Al

[0058] The determination of Al content in the solid catalyst component has been carried out via inductively coupled plasma emission spectroscopy on “LC.P Spectrometer ARL Accuris”. The sample was prepared by analytically weighting, in a “Fluxy” platinum crucible”, 0.R0.3 grams of catalyst and 2 grams of lithium metaborate / tetraborate 1 / 1 mixture. After addition of some drops of KI solution, the crucible is inserted in a special apparatus "Claisse Fluxy” for the complete burning. The residue is collected with a 5% v / v HN03 solution and then analyzed via ICP at the following wavelength: aluminum, 394.40 nm.

[0059] Determination of Si

[0060] The determination of Si content in the solid catalyst component has been carried out via inductively coupled plasma emission spectroscopy on “I.C.P Spectrometer leap 7000”. The sample was prepared by analytically weighting, in a plastic 100 mL volumetric flask 0.01-^0.10 grams of catalyst. 20 mL of hydrofluoric acid (48%) were diluted at ten percent in demineralized water and added into the flask. Subsequently, a cold solution of 1.5 g of boric acid (purity > 99.5%) in 50 mL of demineralized water was also added. Finally, the content of the flask is make up to the mark with demineralized water and mix. The resulting solution was then directly analyzed via ICP at the following wavelength: silicon, 212.412 nm.

[0061] Determination of Cl

[0062] The determination of Cl content in the solid catalyst component has been carried out by potentiometric titration with silver nitrate. In a 250 mL beaker were subsequently charged 5 mL of a sodium hydroxide solution 10% wt. / vol. in water and 0. 0.3 grams of catalyst. After 20 min stirring at room temperature, 40 mL of a nitric acid solution 3.6 M in water were added and stirring continued for additional 10 min. After dilution with 100 mL of demineralized water, the titration started with an AgNO3 solution 0.1 N in water. As soon as the point of equivalence was found, the amount of titrant used was calculated and the chlorine amount present in the catalyst quantified

[0063] Commercial samples of Silicon Dioxide SiCh (White sand) and Aluminum (III) oxide AI2O3 as well as Titanium Dioxide TiCh are commercially available from common providers such as Grace, PQ, Sigma Aldrich.

[0064] Ionic Liquids used in the different examples are commercially available from common suppliers like Merck and Sigma Aldrich.EXAMPLESGeneral Depolymerization Procedure

[0065] General procedure for depolymerization test in a 500 ml round glass reactor

[0066] 30 g of real plastic waste were loaded in a 500 mL round glass reactor having three necks equipped with thermocouple and nitrogen inlet.

[0067] The real plastic waste used in the examples originated from municipal collection and, after sorting, it resulted to be composed of about 97wt% of polyolefin in which the PP / PE ratio was about 30 / 70) with the residual containing traces of other common polymers (PET, PS, PA, PU) plus inorganic contaminants.

[0068] The solid catalyst (2.5wt% with respect to plastics) is then introduced in the proper amount into the glass reactor. Blank test without any catalyst can be also performed. Two glass condenser are connected in series and kept at 110°C and -8°C respectively using an oil bath (Cryostat Julabo). The reactor is placed in electrically heating system (mantle bath), and setting the desired power, the temperature was raised up to 450°C. The pyrolysis process takes place and the following experimental parameters are recorded:• L%, sum of the yield of liquid condensable at 110°C + liquid condensable at -8°C (with respect the polymer charged)• S%, yield of solid / waxy residue in the reactor, excluding catalyst (with respect to the polymer charged)• G% yield in gaseous products not condensable in both condensers (with respect the polymer charged)Comparative example 1

[0069] A depolymerization run was carried out according to the general depolymerization procedure disclosed above without using a depolymerization catalyst. The results are reported in Table 1.Example 1

[0070] Preparation of TPPC (Tetra Phenyl Phosphonium Chloride) based catalyst

[0071] Tetra Phenyl Phosphonium Chloride (TPPC, 5.7 g) was dissolved at r.t. into 75 mL of anhydrous ethanol, obtaining a solution which was slowly added to silica Sylopol XPO 2107 (50.0 g), previously charged at room temperature into a 500 mL round-bottom flask, equipped with mechanical stirrer. The mechanical stirring was continued for 4 h at room temperature, thus all mixture was transferred into a rotary evaporator. The mixing last 12 h at room temperature by using the rotary evaporator. Drying step was carried out at 100°C for 14 h under vacuum until constant weight. The final compound is a free flowing white powder (55.3 g).

[0072] Characterization:

[0073] Si = 39.4%wt., Cl = l.l%wt.

[0074] The so obtained catalyst was used in a depolymerization run carried out according to the general depolymerization procedure disclosed above. The results are reported in Table 1.Example 2

[0075] A depolymerization run was carried out as described in Example 1 with the difference that 0.75 gr. of Fulcat 435 was used as poison suppressing agent. The results are reported in Table 1.Example 3

[0076] A depolymerization run was carried out as described in Example 1 with the difference that 0.75 gr. of Ca(OH)2 was used as poison suppressing agent. The results are reported in Table 1.Comparative Example 2 Test 700

[0077] A depolymerization run was carried out according to the general depolymerization procedure but using a non-supported ionic liquid of example 1 as a depolymerization catalyst. The results are reported in Table 1.Example 4

[0078] Preparation of TTPC (Trihexyl Tetradecyl Phosphonium Chloride) based catalyst

[0079] Trihexyl Tetradecyl Phosphonium Chloride (TTPC, 2.0 g) was dissolved at r.t. into 20 mL of anhydrous ethanol, obtaining a solution which was slowly added to silica Sylopol XPO 2107 (18.0 g), previously charged at room temperature into a 250 mL round-bottom flask, equipped with mechanical stirrer. Additional 50 mL of anhydrous ethanol were added in order to obtain a homogeneous slurry. The mechanical stirring was continued for 5 h at room temperature, thus all mixture was filtered on a G4 frit, the solid washed with ethanol and subsequently dried at 90°C for 16 h under vacuum until constant weight. The final compound is a free flowing white powder (17.8 g).

[0080] Characterization:

[0081] Si = 45.0%wt., Cl = 0.35%wt., H2O = 0.2%wt.

[0082] The so obtained catalyst was used in a depolymerization run carried out according to the depolymerization procedure of example 2. The results are reported in Table 1.Example 5

[0083] Preparation of TTPC (Trihexyl Tetradecyl Phosphonium Chloride) based catalyst

[0084] Trihexyl Tetradecyl Phosphonium Chloride (TTPC, 5.4 g) was dissolved at r.t. into 20 mL of anhydrous ethanol, obtaining a solution which was slowly added to acidic activated aluminum oxide AI2O3 (18.0 g), previously charged at room temperature into a 250 mL round-bottom flask, equipped with mechanical stirrer. The homogeneous slurry so obtained was mechanically stirred for 6 h at room temperature. All mixture was thus filtered on a G4 frit, the solid washed with ethanol and subsequently dried at 90°C for 16 h under vacuum until constant weight. The final compound is a free flowing white powder (18.6 g).

[0085] Characterization:

[0086] Al = 49.4%wt., Cl = 1.0%wt., H2O = 0.8%wt.

[0087] The so obtained catalyst was used in a depolymerization run carried out according to the depolymerization procedure of example 2. The results are reported in Table 1.Example 6

[0088] Preparation of TPPC (Tetra Phenyl Phosphonium Chloride) based catalyst

[0089] Tetra Phenyl Phosphonium Chloride (TPPC, 2.3 g) was dissolved at r.t. into 30 mL of anhydrous ethanol, obtaining a solution which was slowly added to silica Sylopol XPO 2107 (10.0 g), previously charged at room temperature into a 250 mL round-bottom flask, equipped with mechanical stirrer. The mechanical stirring was continued for 4 h at room temperature, thus all mixture was transferred into a rotary evaporator. The mixing last 12 h at room temperature by using the rotary evaporator. Drying step was carried out at 100°C for 14 h under vacuum until constant weight. The final compound is a free flowing white powder (12.1 g).

[0090] Characterization:

[0091] Si = 36.8%wt., Cl = 1.9%wt.

[0092] A depolymerization run was carried out as described in Example 1 with the difference that 0.75 gr. of Fulcat 435 was used as poison suppressing agent. The results are reported in Table 1.Example 7

[0093] Preparation of TPPC (Tetra Phenyl Phosphonium Chloride) based catalyst

[0094] Tetra Phenyl Phosphonium Chloride (TPPC, 1.8 g) was dissolved at r.t. into 25 mL of anhydrous acetonitrile, obtaining a solution which was slowly added to zeolite CFG-1 (15.0 g), previously charged at room temperature into a 250 mL round-bottom flask, equipped with mechanical stirrer. The mechanical stirring was continued for 4 h at room temperature, thus all mixture was transferred into a rotary evaporator. The mixing last 12 h at room temperature by using the rotary evaporator. Drying step was carried out at 100°C for 14 h under vacuum until constant weight. The final compound is a free flowing white powder (16.5 g).

[0095] Characterization:

[0096] Si = 26.8 %wt., Al = 10.0%wt., Cl = 1.1 %wt., H2O = 2.2%wt.

[0097] A depolymerization run was carried out as described in Example 1 with the difference that 0.75 gr. of Fulcat 435 was used as poison suppressing agent. The results are reported in Table 1.Example 8

[0098] Preparation of TPPC (Tetra Phenyl Phosphonium Chloride) based catalyst

[0099] Tetra Phenyl Phosphonium Chloride (TPPC, 4.6 g) was dissolved at r.t. into 25 mL of anhydrous ethanol, obtaining a solution which was slowly added to silica / aluminas support Siral 40 HPV (10.0 g), previously charged at room temperature into a 250 mL roundbottom flask, equipped with mechanical stirrer. Additional 20 mL of anhydrous ethanol were added in order to obtain a homogeneous slurry. The mechanical stirring was continued for 4 h at room temperature, thus all mixture was transferred into a rotary evaporator. The mixing last 12 h at room temperature by using the rotary evaporator. Drying step was carried out at 75°C for 7 h under vacuum until constant weight. The final compound is a free flowing white powder (14.0 g).

[0100] Characterization:

[0101] Si = 11.2 %wt., Al = 19.1%wt., Cl = 3.1 %wt.

[0102] A depolymerization run was carried out as described in Example 1 with the difference that 0.75 gr. of Fulcat 435 was used as poison suppressing agent. The results are reported in Table 1.Table 1SRR= Solid Residue Reduction (% vs no cat)LOT. = internal olefin index (1H-NMR)

Claims

CLAIMSWhat is claimed is:

1. A process for depolymerizing plastics, comprising the steps of: a) providing a melt plastic waste feedstock comprising at least a polyolefin fraction and b) subjecting the melt product obtained in (a) to a temperature ranging from 280°C to 550°C to obtain a depolymerization product; said process being characterized by the fact that either or both of the melt product and depolymerization product are contacted with a supported ionic liquid catalyst.

2. The process of claim 1 wherein the amount of catalyst ranges from 0.1 -20 wt.%, preferably 0.1-10 wt.% and especially from 0.1 to 5 wt.% with respect to the total weight of plastic waste feedstock and catalyst.

3. The process according to one or more of the preceding claims in which the plastic waste feedstock comprises a mixture of polyethylene and polypropylene in a weight ratio 85:15 to 15:85 more preferably 80:20 to 20:80.

4. The process according to one or more of the preceding claims in which the ionic liquid has a melting temperature lower than 400°C.

5. The process according to claim 4 in which the ionic liquid has a melting temperature lower than 350°C and especially lower than 300°C.

6. The process according to one or more of the preceding claims in which the ionic liquid hascations and anions selected from the following formulas: cation(organic)phosphonium pyrrolidinium sulfoniumalkylsulfate tosylate methanesulfonate anion(organio) anion(inorganic)bis (trifluoromethyl- hexafluorotetrafluoro- halide sulfonyljimide phosphate borate where Ri to R4 groups are, independently, selected from C1-C20 alkyl or arylalkyl and Ce- C20 aryl or alkyl aryl groups.

7. The process according to claim 1 in which the support is an inorganic support which can be either spherical or granular.

8. The process according to claim 7 in which the support is selected from aluminum oxide, silicon dioxide (silica gel), titanium dioxide or their mixed oxides or cogels, or aluminum phosphate.

9. The process according to claim 8 in which the support is selected from inorganic oxides and more preferably from AI2O3, SiCh and TiCh.

10. The process according to one or more of the preceding claims in which the support particles have a pore volume which is in the range between 0.5 and 3.0 cm3 / g, more preferably in the range from 0.7 and 3.0 cm3 / g, and especially in the range from 0.8 cm3 / g18SUBSTITUTE SHEET (RULE 26)to 2.0 cm3 / g..

11. The process according to one or more of the preceding claims wherein step (b) is carried out in the presence of a poison suppressing agent.

12. The process according to claim 11 in which the poison suppressing agent is selected from the group consisting of Ca(OH)2, Mg(OH)2, Ba(OH)2, Sr(OH)2, CaO, AI2O3, aluminosilicates such as bentonite, Zr(HPO4)2 and mixtures thereof.

13. The process according to claim 12 in which the poison suppressing agent is selected from the group consisting Ca(OH)2, aluminosilicates, Zr(HPO4)2.

14. The process according to one or more of the preceding claims in which the amount of the higher than C28 fraction in the liquid depolymerization product is equal to, or lower than, 4%wt, with respect to the total amount of liquid depolymerization product.

15. The process according to one or more of the preceding claims in which the content of aromatics in the liquid depolymerization product is lower than 2%mol and preferably lower than 1.5%mol.

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