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    • 专利摘要:
    The invention is directed to a process to prepare mixture of powdered waste plastics by cryogenic milling a mixture of different waste polymer products wherein the cryogenic milling is performed using liquid nitrogen as a refrigerant and wherein the liquid nitrogen has been obtained in a cryogenic air separation process. The nitrogen is indirectly or directly reduced in temperature and/or liquified by heat exchange against evaporating liquified natural gas and wherein the cryogenic air separation process also prepares an oxygen product which oxygen product is not used as refrigerant for the cryogenic milling, and wherein the mixture of waste polymer products comprises at least two polymers of the following list of polymers consisting of LDPE (Low-density polyethylene), HDPE (High-density polyethylene); PP (Polypropylene); PS (Polystyrene); PET (Polyethylene terephthalate).
    公开号:NL2027724A
    申请号:NL2027724
    申请日:2021-03-09
    公开日:2021-10-19
    发明作者:Cramwinckel Michiel
    申请人:Cramwinckel Michiel；
    IPC主号:
    专利说明:

    PROCESS FOR CONVERTING DIFFERENT WASTE POLYMER PRODUCTS The invention is directed to a process to convert a mixture of different waste polymer products.
    The recycling of waste polymer products, also referred to as waste plastics, is a specific sector of waste recycling and consists of a set of operations performed on waste composed of plastic materials in order to obtain new material to be reintroduced in production processes. After the sorted waste collection step, the plastic is taken to first selection and treatment plants; it is then separated from other fractions and impurities and then divided by polymer type. In particular, low- and high-density PET and PE are selected. Various methods for mechanical recycling are known which are adapted to obtain flakes or granules which are then used to produce new objects.
    US2007187299 describes a process wherein waste polymers are isolated from other waste by a selection based on the dielectric constant of the material. This separation separates polymer materials having a dielectric constant below a certain threshold, such as polypropylene and polyethylene, polystyrene and ABS from materials having a higher dielectric such as wet or moist wood, foam and rubber.
    US2004226864 describes a process to separate polymer films from garbage by flotation. The publication states that this avoids plastic film products such as plastic bags to end up in a landfill. The publication is however silent how the plastic film is to be further used.
    US4406411 describes a process where chrome plated ABS polymer is milled at cryogenic temperatures to a powder. The metal is separated from the powder by means of a magnetic separation and the cleaned ABS powder is melted and extruded thereby obtaining an ABS extrudate.
    US4483488 describes a process where PVC is recovered from PVC coated fabric by cryogenic milling.
    WO03/041931 describes a process where waste plastics are milled at low temperatures. In this process a gas, like nitrogen, oxygen or their mixtures, is reduced in temperature to minus 170 C by indirect heat exchange against evaporating liquified natural gas (LNG). The gas with the reduced temperature is then used to crush or mill the waste plastic by spraying the gas on the waste plastic while crushing or milling.
    WO2005/068920 describes a process to shredder waste tires in cryogenic conditions using gaseous nitrogen. The gaseous nitrogen has been reduced in temperature by indirect heat exchange against evaporating liquified natural gas (LNG).
    KR100855759 describes a process where waste polymers are pulverised in the presence of liquid nitrogen in a screw type milling apparatus.
    Because plastics cannot be recycled indefinitely and only 50% of the total of plastic waste can be reused validly in a production process the remaining 50% is not suitable for various reasons. These reasons may be for example the excessive degree of contamination of plastics, the loss of technical properties due to past recycling/reuse cycles, the impossibility to perform a selection of the various types of plastic for finer fractions. This remaining 50% of plastic waste is currently disposed by waste-to- energy conversion or by landfill disposal.
    Waste-t0-energy conversion uses waste treatment plants (waste-to- energy plants) which allow to recover the heat generated during the combustion of said waste and use it to generate steam, which is then used to generate electric power or as a heat transfer medium, for example for remote heating. Although modern waste- to-energy conversion plants have many advantages with respect to simple incinerators, waste-to-energy conversion processes remain characterized by negative economic and environmental impacts; in general, they are unable to reach an economic balance only through the generation and sale of thermal and/or electric power. From the environmental standpoint, waste-to-energy conversion processes are characterized by all the negative impacts linked to waste combustion processes, such as, by way of nonlimiting example, carbon dioxide emissions in the atmosphere, production of dangerous and non-dangerous waste and production of wastewater.
    So-called "Plastic-To-Fuel" (PTF) technologies are known which consist of processes aimed at converting waste and plastic materials into liquid fuels or synthetic oils, mainly based on the two processes of simple pyrolysis and catalytic pyrolysis. WO2019003253 describes a PFT process which cracks a mixture of molten plastics in the presence of a liquid catalyst at a temperature between 350 and 500 °C to non-condensable gasses, such as methane and carbon monoxide and liquid hydrocarbon fuel fractions. A disadvantage of this process is that it makes use of a catalyst. The catalyst will have to be recovered from the liquid products making the process complex. A general disadvantage of PTF processes is that the quality of the fuel is such that they are not directly useable as transportation fuels like gasoline or diesel.
    WO2018/224482 describes a process to recycle polystyrene containing plastic waste mixture by pyrolysis to obtain styrene. A disadvantage is that although styrene yields are high also significant amounts of by-products are formed.
    The aim of the present invention is to provide a simple process that is capable of processing a large part of the polymer products which are disposed as waste.
    This object is achieved by the following process. Process to prepare mixture of powdered waste plastics by cryogenic milling a mixture of different waste polymer products wherein the cryogenic milling is performed using a liquid nitrogen as a refrigerant and wherein the liquid nitrogen has been obtained in a cryogenic air separation process wherein nitrogen is indirectly or directly reduced in temperature and/or liquified by heat exchange against evaporating liquified natural gas and wherein the cryogenic air separation process also prepares an oxygen product, which oxygen product is not used as refrigerant for the cryogenic milling, and wherein the mixture of waste polymer products comprises at least two polymers of the following list of polymers consisting of LDPE (Low-density polyethylene), HDPE (High-density polyethylene); PP (Polypropylene); PS (Polystyrene); PET (Polyethylene terephthalate).
    Applicants found that with this process a powder can be obtained having a more or less constant composition making the powder suited to be easier used in various downstream processes. Further it has been found that the starting mixture of different waste polymer products does not have to be separated prior to the milling in different fractions per polymer type. Instead the mixture, even containing contaminants like sand and food rests, can be used as feedstock for this process. find use in various downstream processes. Further an oxygen product is obtained which may be advantageously be used for combustion or partial combustion processes yielding a combustion gas from which carbon dioxide may be easily isolated and stored. This co-generation of oxygen was not described in the prior art publications.
    In the cryogenic milling step the liquid nitrogen refrigerant is used which has been indirectly or directly reduced in temperature by evaporating liquified natural gas. In prior art processes the required energy for performing the cryogenic milling at the very low temperature ranges is high. In the present process a large part of the required energy is obtained when evaporating liquified natural gas (LNG). LNG is made by condensing natural gas at remote locations like northern Australia, Sakhalin, Nigeria and Qatar and transporting the liquified natural gas by ship to for example South Korea, Japan, China, Indonesia, India, Italy, France and The Netherlands. Once unloaded the LNG is typically evaporated, in so-called LNG regas plants, to gaseous natural gas to be used in industry and for domestic heating and cooking. The gaseous natural gas is typically transported in pipelines to its end users. In the present process the part of the energy used to condense the natural gas to LNG at a remote location is now used to perform the cryogenic milling at the required low temperatures at a location where one will find abundant quantities of waste plastic products. This energy is as it were transported by ship from a remote refrigerator to where the process according to the present invention takes place.
    As stated above, one of the advantages of the present process is that waste plastic feedstock originating from different sources may be cryogenically milled without having to perform substantial pre-treatment of the waste plastic feedstock, such as separation into different fractions per polymer type. This allows one to cryogenically mill different waste plastic feedstocks having varying compositions in time.
    This results in powders of waste plastic feedstocks having different compositions.
    Preferably these powders are homogenised to obtain a powder of the waste plastic feedstock having a substantially constant performance in the catalytic cracking process. 5 Homogenisation may be simply performed in the storage vessels for the powder by mixing the content of the vessel.
    For example the powder obtained in at least a 2 hour period may be homogenised, preferably the powder obtained in at least a 12 hour period may be homogenised, more preferably the powder obtained in at least a 24 hour period may be homogenised, even more preferably the powder obtained in a 60 hour period may be homogenised.
    The homogenisation results in a homogenised product.
    The preferred time period may also depend on the variation in time of the composition of the waste plastic products to be milled and the available mixing vessels.
    Homogenisation may also be performed by mixing powders obtained from different cryogenic milling processes using different waste plastic products as starting material.
    The homogenisation is preferably performed to achieve a powder having an atomic carbon content, an atomic hydrogen content and optionally an atomic oxygen content and atomic nitrogen content which contents vary in time for less than 20%, more preferably less than 10% and even more preferably less than 5% from an average content.
    The mixture of different waste polymer products suitably comprises two polymers of the following list of polymers consisting of LDPE (Low-density polyethylene), HDPE (High-density polyethylene), PP (Polypropylene), PS (Polystyrene); PVC (Polyvinyl chloride); PET (Polyethylene terephthalate); PUT (Polyurethanes) and PP&A fibres (Polyphthalamide fibres), PVC (polyvinylchloride), polyvinylidene chloride, PU (polyurethane), ABS (acrylonitrile-butadiene-styrene), nylon, aramid and fluorinated polymers.
    Preferably the waste polymer products are substantially only hydrocarbons consisting of only carbon, hydrogen and optionally oxygen.
    This avoids the formation of nitrogen based combustion gasses and chlorine gasses when PVC is present when the powder is used as a fuel in a combustion process. Small amounts of these other polymers may be present as contaminants. Preferably the mixture of different waste polymer products at least comprises two polymers of the following list of polymers consisting of LDPE (Low-density polyethylene), HDPE (High-density polyethylene); PP (Polypropylene) and PS (Polystyrene) and PET (Polyethylene terephthalate). Preferably the powder of the waste plastic feedstock comprise for more than 50 wt%, more preferably for more than 70 wt%, even more preferably for more than 80 wt% and even more preferably for more than 95 wt% of the listed polymers above.
    Other plastics, such as polyvinylchloride (PVC), polyvinylidene chloride, polyurethane (PU), acrylonitrile-butadiene-styrene (ABS), nylon, aramid and fluorinated polymers are less desirable. The powder of the waste plastic feedstock comprise suitably comprise less than 50% by weight, preferably less than 30 wt. %, more preferably less than 20 wt.%, even more preferably less than 10 wt.% of these listed less desirable polymers. An example of a suitable mixture of waste polymer products is the so-called Non-Recycled Plastic (NRP). This is a waste stream from which it is difficult to recycle the polymer from. Such a mixture may comprise foils of the polymer product. Another example of a suitable mixture of waste polymer products is the so-called DKR 350 which comprise PE, eg LDPE and HDPE, PP, PS and PET, less than 10 wt% impurities, wherein the impurities contribute to at most 5 wt% paper and cardboard, at most 2 wt% metals, at most 4 wt% PET bottles, at most 0.5 wt% PVC and at most 3 wt% of a mixture which consists of glass, composite paper and cardboard, for example beverage cartons, rubber, stones, wood, textiles, nappies and/or compostable waste. A next example is so-called plastic waste from mechanical plastic recycling processes. Such mixtures may consist for the majority of PP and PE. Other sources of difficult to mechanically recycle mono-streams are for example PET trays. All these waste polymer products may be used for this process. Chlorine and fluorinated plastics are preferably not part of the waste plastic feedstock. The higher density chlorine and fluorinated plastics, such as PVC and fluorinated ethylene propylene may be separated from the lower density LDPE {Low- density polyethylene), HDPE (High-density polyethylene); PP (Polypropylene) and PS (Polystyrene) type polymers by making use of their difference in density. Suitably the chlorine and fluorinated plastics, such as PVC and fluorinated ethylene propylene are separated from a mixture of waste polymers products by means of flotation in a suitably liquid, preferably water. A suitable waste plastic feedstock may therefore be the floating plastic waste as collected in rivers and/or oceans.
    If these chlorinated or fluorinated polymers are part of the mixture of different waste polymer products it may be preferred to separate the mixture of powdered waste plastics is into at least a light fraction having an average particle density of below 1100 kg/m3 and a heavy fraction having an average particle density of above 1100 kg/m3. The heavier fraction will then be enriched in the chlorinated and/or fluorinated polymer products and optional contaminants such as soil, glass, metals, minerals and salts.
    The polymers having a density of below 1100 kg/m3 preferably comprises at least one of the following list of polymers consisting of LDPE (Low-density polyethylene), HDPE (High-density polyethylene), PP (Polypropylene) and PS (Polystyrene).
    The polymers having a density of above 1100 kg/m3 preferably comprises at least one of the following list of polymers consisting of PVC (Polyvinyl chloride); PET (Polyethylene terephthalate); PUT (Polyurethanes) and PP&A fibres (Polyphthalamide fibres), polyvinylidene chloride, PU (polyurethane), ABS (acrylonitrile-butadiene-styrene), nylon, aramid and fluorinated polymers.
    The separation into a light and heavy fraction may be performed by separation processes which make use of the difference in particle density. This may be by means of flotation in a liquid medium. Preferably methods are used which avoid the use of a liquid medium. One such method is by flowing gas through a zig-zag channel upwards and the powder of the waste plastic feedstock downwards. The light fraction will be entrained by the gas flow and be collected at the top and the heavy fraction is collected at the bottom of the zig-zag fraction. More preferably the separation is performed In a fluidized bed wherein the heavy fraction is obtained at a lower end of the fluidized bed and the light fraction is obtained at a higher end of the fluidized bed. The fluidized bed is preferably operated in a continuous mode wherein at an intermediate position the powder of the waste plastic feedstock is continuously supplied and wherein at the lower end of the fluidized bed the heavy fraction is continuously discharged from the fluidized bed and wherein from the higher end of the fluidized bed the light fraction is continuously discharged from the fluidized bed. At the lower end a fluidization medium is supplied. Examples of suitable fluidization media are inert gasses, such as steam, carbon dioxide and nitrogen. The nitrogen is preferably nitrogen as obtained in the below described air separation process or as used in the cryogenic milling. The rate of this fluidization medium is at least sufficient to achieve minimum fluidization and at most prior to the start of bubbling of the fluidized bed. The fluidization medium is suitably discharged from the upper end of the fluidized bed separate from the light fraction. The fluidization medium as discharged may contain fines which can be separated from this medium by means of sieves, filters, like for example a candle filter, and/or cyclones. Such a process is for example described in US5397066.
    The fluidized bed is suitably an vertical elongated column providing a high fluidized bed height to column diameter ratio, preferably above 4: 1 and more preferably above 6:1. This to minimize back mixing in the vertical direction in the column. The fluidized bed may be provided with means to charge parts of the column to attract electrostatically charged polymer particles to further enhance the separation. The application of such electrostatically charged parts of the column will depend on the type of polymers present in the powder of the waste plastic feedstock.
    More than one of the elongated columns may be operated in series wherein the powder obtained at the lower end of an upstream column is fed to a downstream column and wherein the powder obtained at the lower end of the most downstream column is the heavy fraction and wherein the powder obtained at the upper ends of the columns is combined as the light fraction.
    Any iron, nickel and/or cobalt and/or their alloys as present in the mixture of powdered waste plastics or the light fraction or the heavy fraction may be separated from the powder of the waste plastic feedstock and/or from the heavy fraction by means of magnetic separators.
    From the mixture of powdered waste plastics, the light fraction and/or from the heavy fraction individual fractions of substantially pure polymers may be isolated by means of an electrostatic separation. Such a separation is suitably performed after the above described magnetic separation. In such a separation use is made of the fact that when two dissimilar non-conducting polymer particles come into contact, charge is transferred; one of the particles becomes negatively charged and the other positively charged. The charge polarity is determined by the so-called triboelectric series. Any polymer higher in the below list will in contact with one lower in the table charge negatively. For example, polyethylens (PE) will charge negatively in contact with polyethylene-terephihalate (PET), but will charge positively in contact with polyvinyl chloride (FV), PTFE, Teflon BVC, polyvinyl chloride PE, polyethyiene PP, polypropylene PS, polystyrene PET, polyethylene terephthalate Acrylic A mixture of different polymers powders may be charged by mixing the different polymer particles in Tor example a rotating drum. Because of the multiple and repeated contacts between the particles become positively or negatively charged as described above. These opposite charged particles are subsequently separated making use of their different charges. This may be by passing the particles through a strong electric field wherein the positive negatively charged particles are drawn toward the positive electrode while the positively charged particles are drawn toward the negative electrode. Such electrostatic separation is suitably performed when the ight fraction comprises LDPE {Low-density polyethylene) and/or HDPE (High-
    density polyethylene) and PP (Polypropylene). LDPE (Low-density polyethylene) andfor HDPE (High-density polyethylene) may so be separated from PP {Polypropylene} by means of an electrostatic separation. PVC and PET powder particles as may be present in the heavy fraction may be separated from each other by means of an electrostatic separation.
    Electrostatic separation may be used io separate polymers as present in the powder mixture in a series of two or more electrostatic separation steps. For example a fist separation divides the mixture in two first sub fractions. Each first sub fraction can be further divided into two second sub fractions. Eventually the separation of such a further fraction will result in obtaining a substantially pure polymer.
    Electrostatic separation is a known technology for separating the above cited polymers and is for example described in US2012187227, US8498313, US4885642, DE19711340, DE102004024754 and US8541708. The above electrostatic separation may also be used to separate a mixture of polymers into two or more fractions of substantially pure polymers types. The mixture of polymers is obtained by a process to prepare mixture of powdered waste plastics by cryogenic milling a mixture of different waste polymer products, suitably using liquid nitrogen as a refrigerant, and wherein the mixture of waste polymer products comprises at least two polymers of the following list of polymers consisting of LDPE (Low-density polyethylene), HDPE (High-density polyethylene); PP (Polypropylene), PS (Polystyrene), PET {Polyethylene terephthalate}. In this embodiment the liquid nitrogen does not necessarily have to be obtained In a process which is heat integraied with evaporating liquified natural gas (LNG). The remaining relevant parts of the description applies also to this invention.
    Cryogenic milling is known and for example described in US4406411, US4483488, US3885744 and US5203511. The milling itself may be performed in a grinding mill in the presence of a refrigerant. The refrigerant is suitably nitrogen and preferably liquid nitrogen. Nitrogen is used to avoid conditions at which the powder of plastics may ignite and explode. The temperature at which the milling takes place is suitably well below the glass transition temperature of the plastic products present in the mixture. The temperature is suitably below minus 150 °C (- 150 °C) and preferably below minus 180 (-180 °C). The refrigerant may be evaporating liquified natural gas (LNG). In such an embodiment an indirect heat exchange suitably takes place between the evaporating LNG and the mixture of different waste polymer products. Preferably only part of the LNG evaporates bringing the temperature of the partly evaporated LNG down to about minus 160 C. The partly liquid gas having such a reduced temperature may for example be provided to an annular shell as present at the exterior of a tubular conduit. Through said conduit the mixture of different waste polymer products is passed and cooled down to be eryogenically milled downstream said conduit. For safety reasons it is preferred to use another refrigerant which has been indirectly or directly reduced in temperature by evaporating liquified natural gas. In this manner any leakage will not directly result in that natural gas and the mixture of different waste polymer products come into contact and form an explosive mixture. This other refrigerant may be used to indirectly or directly cool the mixture of differant waste polymer products prior and/or during the cryogenic milling. By indirect cooling is here meant a method of cooling similar to described above wherein to an annular shell as present at the exterior of a tubular conduit the refrigerant is supplied and wherein through said conduit the mixture of different waste polymer products is passed and cooled down to be cryogenicaliy milled downstream said conduit. By direct coding is here meant that the refrigerant is in direct contact when cryogenicaliy milling.
    it may be efficient to combine both methods of cooling wherein first the mixture of different waste polymer products is reduced in temperature by indirect heat exchange, as for example described above, with the other refrigerant and further reduced in temperature, suitably when performing the cryogenic milling, by directly contacting the cooled mixture of different waste polymer products with the other refrigerant. The other refrigerant, suitably nitrogen, as used in the cryogenic milling may be recovered downstream the milling and reused as the other refrigerant.
    The other refrigerant may be reduced in temperature directly against evaporating LNG or indirectly. By indirectly is here meant that another refrigerant, Ike nitrogen, is used as intermediate cooling medium, The intermediate cooling medium is reduced in temperature by indirect heat exchange against evaporating LNG as describe above. The cooled intermediate cooling medium in tum is used to cool the other refrigerant by indirect heat exchange to a temperature suited for carrying out the cryogenic milling. The pressure of the intermediate cooling medium is preferably higher than the pressure of the LNG. This avoids leakage of natural gas to the intermediate cooling medium. When nitrogen is used the pressure may be such that in the cooling step against evaporating LNG the nitrogen liguifies, for example by the process described in US5137558, US5139547 US5141543% US2008216512 and EP2669613. The liquid nitrogen may then cool the other refrigerant in an indirect heat exchange step wherein the liquid nitrogen evaporates in the intermediate cooling loop.
    Many cryogenic milling processes use evaporating liquid nitrogen as the cooling medium to cool the solids to be milled by directly contacting the liquid nitrogen with the solids to be milled. The liquid nitrogen may be obtained by a process which involves a heat exchange against evaporating LNG as described above.
    The cryogenic milling may be performed using liquid nitrogen using the cooling and grinding technology called PolarFit® Cryogenic Reduction Solutions as offered by Air Products. In such a process the liquid nitrogen may be added directly to the mill chamber of the grinding mill. The liquid gas may also be provided to a conveyor, like a screw conveyor, where the waste polymer product is cooled to its desired low temperature before it enters the mill chamber as for example described in US3771729. For larger shaped waste plastic feedstock it may be desirable to contact the waste plastic feedstock in a so-called tunnel freezer as for example described in US4175396.
    The milling suitably results in a powder of which at least 90 wt% will pass through a 12 mesh screen and more preferably at least 90 wt% will pass through a 30 mesh screen.
    The liquid nitrogen is obtained in a cryogenic distillation of air wherein also an oxygen gas product, ie a gas stream rich in oxygen, is obtained as for example described in US5137558. Preferably the cryogenic distillation process of air prepares a gaseous nitrogen product, a liquid nitrogen product, an oxygen gas product and a liquid oxygen product. The production of the liquid nitrogen product and the optional liquid oxygen product is advantageous because these products can be easily stored. This is especially advantageous for LNG regas plants which have the function to diversify supply of methane gas to the natural gas grid as an alternative for pipeline gas. Such a plant may not continuously prepare the required nitrogen and/or oxygen products while the downstream processes like the cryogenic milling or the processes described below may require a constant flow of these products. By storing a buffer volume of liquid nitrogen and optionally liquid oxygen the desired constant flow may be achieved while the LNG regassification may temporarily produce at a low production rate.
    Preferably the cryogenic distillation of an air feed is performed by a process wherein the air feed is compressed, cleaned of impurities that will freeze out at cryogenic temperatures such as water and carbon dioxide, and subsequently fed into an cryogenic air separation process (hereafter "cryogenic ASU") comprising a main heat exchanger and a distillation column system which are contained in a large insulated box (generally referred to as the "cold box" in the industry). In a next step the air feed is cooled in the main heat exchanger by indirectly heat exchanging the air feed against at least a portion of the effluent streams from the distillation column system. The cooled air feed is separated in the distillation column system into effluent streams including a stream enriched in nitrogen, a stream enriched in oxygen and, optionally, respective streams enriched in the remaining components of the air feed including argon, krypton and xenon. The distillation column system typically comprises a first column (hereafter "high pressure column" or "HP column") which separates the air feed into effluent streams including a nitrogen-enriched vapor stream and a crude liquid oxygen stream; and a second column (hereafter, "low pressure column" or "LP column") which (i) operates at a relatively lower pressure than the HP column, (ii) separates the crude liquid oxygen stream into effluent streams including an oxygen product stream and one or more additional nitrogen-enriched vapor streams and (iii) is thermally linked with the HP column such that at least a portion of the nitrogen-enriched vapor from the HP column is condensed in a reboiler/condenser against boiling oxygen-rich liquid that collects in the bottom (or sump) of the LP column. Further refrigeration is achieved by indirectly heat exchanging the evaporating LNG in a heat exchanger against one or more nitrogen-enriched vapor streams withdrawn from the distillation column system as for example described in US7552599. The compressor of the cryogenic air separation process may be powered by expansion of steam. Preferably the compressor is powered by electricity and more preferably by electricity which is generated by wind turbines and/or by solar panels. The cryogenic air separation process may be powered by the heat integration with the LNG evaporation facility according to this invention and by electricity. LNG is typically evaporated in periods of high electricity demands to supply the natural gas power plants thereby lowering the electricity demands of the cryogenic air separation process. When no LNG is evaporated a situation of oversupply of electricity may occur. By using this oversupply to run the compressor of the cryogenic air separation process an efficient process is obtained.
    The oxygen gas and/or liquid oxygen gas product is suitably used to partially or fully combust the mixture of powdered waste plastics or the light fraction or the heavy fraction to a flue gas comprising of carbon dioxide and water. In case of a partial combustion a mixture comprising of carbon monoxide and hydrogen is obtained. The oxygen gas or liquid oxygen product suitably has an oxygen content of more than 80 vol.% , preferably more than 90 vol.%, more preferably more than 95 vol.% and even more preferably more than 99 vol. %.
    The fully combustion of the mixture of powdered waste plastics or the light fraction or the heavy fraction to a flue gas comprising of carbon dioxide and water may for example be performed in a coal fired power plant. By replacing the coal by the polymer particles as feed and the air by the oxygen gas product a process is obtained which can reuse the cola fired power plant, use waste polymers to make energy and generate a concentrated carbon dioxide stream which can be stored in underground reservoirs. The fired boiler may have to be adapted. By making use of carbon dioxide as a carrier gas for the polymer particles in the feed to the burners of the coal fired power plant and/or by adding carbon dioxide when combusting one has means to control the temperature without diluting the flue gas in carbon dioxide. Preferably polymer particles are used having a low level of contaminants or no contaminants. This will result in that no ash is formed which simplifies the process.
    The above combustion may also be performed in an oxy-fired coal power plants as known as for example described in US2019/0024583, US2015369483, US2015079526, US2015330628, US2015323179, WO12078269 or US2011073022. Instead of using coal the polymer particles may be used. Preferably polymer particles are used having a low or no contaminants for the same reasons as explained above. The heat integration with the air separation process as described in for example US2015330628, US2015323179 may be applied.
    The concentrated and suitably dried carbon dioxide stream obtained in such a process may be liquified to liquified carbon dioxide by using a refrigerant and wherein the refrigerant is evaporating liquified natural gas (LNG) or another refrigerant which has been indirectly or directly reduced in temperature by evaporating liquified natural gas. This may be performed in a distillation column wherein gaseous impurities like nitrous oxides may be separated from the liquid carbon dioxide. The carbon dioxide may be permanently stored in a carbon capture and storage (CCS) set-up. For example in a sub sea former natural gas field.
    The mixture of powdered waste plastics or the light fraction or the heavy fraction may also be partially combusted. In such a process a sub-stoichiometric amount of oxygen is used resulting in a syngas mixture comprising of hydrogen and carbon monoxide as the main compounds. Such a process is also referred to as gasification. The gasification may be performed by any technology which partly oxidises the waste polymer particles to carbon monoxide and hydrogen. The oxygen is preferably the oxygen gas or liquid oxygen product as described above. The gasification reaction is suitably performed above 600 °C, more preferably above 900 °C and even more preferably above 1000 °C and even more preferably between 1300 and 1500 °C. The pressure may be around atmospheric and more preferably between 2 and 10 MPa.
    When the polymer particles do not comprise high contents of ash forming compounds the gasification may be performed in well-known reactors used in the Shell Gasification Process (SGP) wherein the burner is adapted to bring a stream of solid polymer particles into contact with a stream of oxygen. Further a stream of steam may also be supplied. A suitable burner for this use are the burners developed for the so-called Shell Coal Gasification Process (SCGP). Examples of coal gasification burners suited for use in the present invention are described in US2012100496, US2003196576, US2003197071, US5127346, US4858538, US4865542, US4510874 , US4523529, DE202017107808U. Other exemplary gasification processes are described in US2008/0149316, US2009/0224209. The gasification reactor is suitably connected to a downstream waste heat boiler in which steam and super-heated steam may be prepared. This steam may be used to generate power, in the gasification reaction itself or in downstream water gas shift reactions. The heat of the partially combusted gasses may also be used to drive downstream endothermal reactions, like for example the ammonia forming reaction. Examples of possible waste heat boilers are described in EP774103B, EP2021960, US2008/0149316 and US2009/0236084.
    The polymer particles may suitably be transported to the above burner by a carrier gas. Such a carrier gas is preferably nitrogen. When the polymer particles are obtained in a nitrogen gas environment in the cryogenic milling no separation of this gas is required when subsequently using the obtained polymer particles in such a gasification step.
    The polymer particles may also be provided to a gasification burner of a gasification reactor as a slurry in water, liquid carbon dioxide or a hydrocarbon fluid. Examples of suitable slurry burners and gasification processes are described in US5307996 and US2019/0194560. The liquid phase of such a slurry may be water, liquid carbon dioxide or a hydrocarbon liquid. Exemplary hydrocarbon liquids may be by-products of downstream processes, like for example Fischer-Tropsch processes. The hydrocarbon fluids may also be refinery streams such as vacuum distillates and vacuum residues obtained when refining crude petroleum. For example the invention can be applied by mixing in polymer particles in the vacuum distillates and/or residues feed of a process wherein syngas or hydrogen is prepared in for example a refinery. The syngas mixture as prepared by the above process may be directly used as fuel for example to generate electricity. The syngas mixture may be subjected to a water gas shift reaction to convert part of all of the carbon monoxide to carbon dioxide and water to hydrogen. Such a water gas shift reaction could be beneficial to increase the hydrogen to carbon monoxide ratio as required in downstream processes or to produce hydrogen. The concentrated carbon dioxide stream may be liquified as described above. The carbon dioxide may be permanently stored in a carbon capture and storage (CCS) set-up. For example in a sub sea former natural gas field. The hydrogen can for example be used as fuel for fuel cells, fuels for hydrogen powered combustion engines and gas turbines or it can be mixed into the natural gas grid. Thus a process is provided which can prepare so-called blue hydrogen from waste plastic in an efficient manner wherein the produced carbon dioxide can be permanently stored. Preferably the obtained syngas mixture is used as feedstock in various processes to make chemicals and fuels, such as the Fischer- Tropsch process, methanation process to make Synthetic Natural Gas (SNG), methanol process, acetic acid process, ammonia process, DME process. For example the Fischer-Tropsch process can prepare kerosene as an aviation fuel. Thus an efficient waste plastic to aviation fuel process is provided by this invention.
    The mixture of powdered waste plastics, the homogenised product, the light fraction or the optional heavy fraction may be advantageously be used as feed to a catalytic cracking process. In such a catalytic cracking process the feed is suitably catalytically cracked by contacting the feed with a cracking catalyst suitably at a temperature of between 550 and 750 °C. In such a process liquid hydrocarbon products and lower olefins and coke are formed. Lower olefins are ethylene, propylene and/or butylene compounds. The liquid hydrocarbon products may be recycled to the catalytic cracking process such to improve the yield to lower olefins. In this manner the waste plastic is converted to building blocks to prepare new polymer products.
    The cracking catalyst is suitably a fluidized catalytic cracking (FCC) catalyst.
    The FCC catalyst is comprised of at least one of a X-type zeolite, a Y-type zeolite, a USY-zeolite, mordenite, Faujasite, nano-crystalline zeolites, MCM mesoporous materials, SBA-15, a silica-alumino phosphate, a gallophosphate, medium pore size zeolite and a titanophosphate.
    Preferably the FCC catalyst is comprised of at least one of a Y-type zeolite and a USY-zeolite.
    Preferably a medium pore size zeolite is used as the cracking catalyst or is present in admixture with the above described cracking catalyst.
    The medium pore size zeolites generally have a pore size from about 0.5 nm, to about 0.7 nm and include, for example, MFI, MFS, MEL, MTW, EUO, MTT, HEU, FER, and TON structure type zeolites (IUPAC Commission of Zeolite Nomenclature). Non-limiting examples of such medium pore size zeolites, include ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, silicalite and silicalite 2. One suitable zeolite is ZSM-5. Medium pore zeolites are known to improve the selectivity to lower olefins, such as ethylene and especially propylene.
    This is advantageous because ethylene and propylene are the monomers of a large part of the polymers present in the light fraction.
    The medium pore zeolites may be used in combination with the other listed cracking catalyst such as especially the Y-type zeolite and a USY-zeolite.
    The cracking catalyst may have a size ranging in diameter between 40 and 80 microns.
    The process may be performed in any possible known reactor configuration suited to intimately contact the cracking catalyst and the powder of the waste plastic feedstock.
    Preferably such a reactor is a fluidised bed, such as a circulating fluidised bed including a riser.
    Preferably the powder is mixed with a liquid hydrocarbon stream and the resulting suspension is used in a typical FCC unit comprising a riser and a regenerator.
    The liquid hydrocarbon may be a liquid product as obtained in this cracking process and/or another hydrocarbon stream, which may be a typical FCC refinery feed.
    The coke is suitably removed from the process by combustion in a separate fluidized bed regenerator.
    Combustion is preferably performed by contacting the coke particles and the coke deposited on the cracking catalyst with an oxygen comprising gas whereby the coke is combusted to carbon dioxide.
    Suitably part of the catalyst present in the fluidised bed reactor and any coke is continuously sent to the fluidised bed regenerator.
    In the fluidised bed regenerator coke is combusted and wherein part of the catalyst as present in the fluidised bed regenerator is sent to the fluidised bed reactor as regenerated catalyst.
    The regeneration may be performed in a comparable manner as in a FCC process.
    The temperature in the fluidised bed regenerator is generally between 620 and 760 °C and preferably between 680 and 720 °C.
    The residence time of the cracking catalyst in the fluidised bed regenerator is between 1 and 6 minutes.
    The fluidized bed regenerator may be provided with additional cooling means.
    This may be required when a powder of a plastic feedstock is used which yields a high coke make.
    The cooling means may be conduits present in the fluidised bed through which water flows and where steam is produced.
    This steam may be used to generate rotational power which in turn may be used to generate electricity.
    The rotational energy and/or electricity may be used to drive the compressor of the air separation process directly or indirectly.
    Preferably the regeneration is performed by combustion of the coke making use of the oxygen gas or liquid oxygen product as obtained in the above described cryogenic air separation process which also produces the liquid nitrogen.
    Such an oxygen gas or liquid oxygen product is preferably diluted with a carbon dioxide comprising recycle gas.
    The flue gas as formed will contain almost no nitrogen and be comprised of mainly water and carbon dioxide.
    After separating the water the carbon dioxide may be liquified and stored, preferably permanently stored in a carbon capture and storage (CCS) set-up.
    Part of the carbon dioxide is recycled as diluent for the oxygen enriched gas.
    This recycle may be the water containing carbon dioxide and/or the dried carbon dioxide.
    The carbon dioxide may be liquified to liquified carbon dioxide by using a refrigerant and wherein the refrigerant is evaporating liquified natural gas (LNG) or another refrigerant which has been indirectly or directly reduced in temperature by evaporating liquified natural gas.
    This may be performed in a distillation column wherein gaseous impurities like nitrous oxides may be separated from the liquid carbon dioxide.
    权利要求:
    Claims (14)
    [1]
    A method for preparing powdered waste plastic by cryogenically grinding a mixture of various polymer waste products, wherein the cryogenically grinding is performed using liquid nitrogen as a refrigerant, and wherein the liquid nitrogen was obtained in a cryogenic air separation process, in which the temperature of the nitrogen is indirectly or directly reduced and/or in which the nitrogen is liquefied by means of a heat exchange with evaporating liquefied natural gas, and in which the cryogenic air separation process also an oxygen product is produced, this oxygen product is not used as a coolant for cryogenic grinding, and the mixture of polymer waste products comprises at least two polymers from the following list of polymers consisting of LDPE (Low Density Polyethylene}, HDPE (polyethylene n high density), PP (polypropylene), PS (polystyrene), PET (polyethylene terephthalate).
    [2]
    A method according to claim 1, wherein a liquid oxygen product is also produced using the cryogenic air separation process.
    [3]
    A method according to any one of claims 1 to 2, wherein the oxygen gas product or the liquid oxygen product is used to partially or completely burn the mixture of powdered waste plastics, whereby, in the case of partial combustion, a mixture is obtained which consists of carbon monoxide and hydrogen.
    [4]
    The method of claim 3, wherein the mixture consisting of carbon monoxide and hydrogen is subjected to a water gas reaction to produce hydrogen and carbon dioxide, and wherein hydrogen is separated from carbon dioxide.
    [5]
    The method of claim 4, wherein the separated carbon dioxide is permanently stored in a carbon capture and storage set-up (CCS).
    [6]
    The method of claim 5, wherein the carbon dioxide is stored in a former subsea natural gas field.
    [7]
    A method according to any one of claims 1 to 6, wherein an electrically driven compressor is used in the cryogenic air separation process.
    [8]
    A method according to any one of claims 1 to 7, wherein the mixture of polymeric waste products comprises greater than 50% by weight of the listed polymers.
    [9]
    A method according to claim 8, wherein the mixture of polymeric waste products is obtained by collecting floating plastic waste on rivers and/or oceans.
    [10]
    The method of any one of claims 8 to 9, wherein the blend of polymer waste products comprises less than 10% by weight of impurities, the impurities comprising up to 5% by weight of paper and paperboard, up to 2% by weight. in metals, not more than 4% by weight of PET bottles, not more than 0.5% by weight of PVC, and not more than 3% by weight of a mixture consisting of glass, composite paper and cardboard, rubber, stones, wood, textiles, diapers, and/or compostable waste.
    [11]
    A method according to any one of claims 1 to 10, wherein the mixture of powdered waste plastics consists of powder particles of which at least 90% by weight is transmitted through a 30 mesh screen.
    [12]
    A method according to any one of claims 1 to 11, wherein the mixture of powdered waste plastic, such as that obtained by cryogenic grinding for at least 2 hours, is homogenized, resulting in a homogenized product, on a such that the atomic carbon and atomic hydrogen content of the homogenized product varies less than 10% over time from an average content.
    [13]
    A method of separating a mixture of polymer waste products comprising at least two polymers from the following polymer list consisting of LDPE (Low Density Polyethylene}, HDPE (High Density Polyethylene); PP (Polypropylene), PS (polystyrene), PET (polyethylene terephthalate), by cryogenically grinding this mixture into a powder, and by separating the powder into two or more fractions of substantially pure polymer types, using one or more electrostatic separation steps.
    [14]
    The method of claim 13, wherein the mixture of polymer waste products comprises less than 10% by weight of impurities, the impurities comprising up to 5% by weight of paper and paperboard, up to 2% by weight of metals, up to 4 % by weight of PET bottles, not more than 0.5% by weight of PVC, and not more than 3% by weight of a mixture consisting of glass, composite paper and cardboard, rubber, stones, wood, textiles, diapers, and/ or compostable waste.
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    NL2027724B1|2022-02-21|
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