SYSTEM AND PROCESS FOR CONVERTING PLASTICS TO PETROLEUM
PRODUCTS
FIELD OF THE INVENTION The invention relates to a system and process for converting plastics and other heavy hydrocarbon solids into retail petroleum products by subjecting the plastics to melting, pyrolysis, vapourization, and selective condensation, whereby final in-spec petroleum products are produced. The system and process is energy efficient, as fuels generated during the process are recycled for use upstream in the process. BACKGROUND
Plastic materials represent a valuable source of petroleum-based fuels. Plastics are comprised of hydrocarbons which, when broken down into their substituent compounds, can be used as diesel fuel, gasoline, furnace oil, kerosene, or lower carbon-chain fuels such as methane, butane and propane. The recycling of plastic materials to generate fuel is important for reducing the dependency on obtaining petroleum using costly and environmentally hazardous drilling and extraction means.
Methods of processing plastics into petroleum fuels are known. These are described in, for example, US Patent No. 4,851,601; US Patent No. 5,414,169; US Patent No. 5,608,136; US Patent No. 5,856,599; US Patent No. 6,172,271; US Patent No. 6,866,830; US Patent No. 7,531,703; US Patent Publication 2009/0062581 ; US Patent Publication 2010/0018116; Chinese patent publication CN 101050373; Chinese patent publication CN 1824733; Japanese patent publication 07331251; Japanese patent publication 09316459; Japanese patent publication 11 138125; Japanese patent publication 2003301184; Japanese patent publication 2009209278; Japanese patent publication 2010059329; and PCT publication WO 2000/064997. Typical methods use external sources of fuel to melt and pyrolize plastics into the substituent compounds. The materials are often separated using distillation columns and other means. Generally, previous methods have been inefficient at generating higher quantity and quality on-specification petroleum products. They have often required
higher temperatures to effectively crack the hydrocarbon substituents which, counterproductively, requires more energy input than is generated.
There remains a need, therefore, for a system and method for producing oil from petroleum- based products, such as plastics. This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
SUMMARY The present system and process attempt to address the problems encountered with previous systems and processes for converting plastics to petroleum products.
The present invention provides a system and process for converting plastics into industrial quality petroleum fuels. In accordance with one aspect of the present invention there is provided a system for processing plastics into one or more petroleum products, the system comprising: a) a reactor for subjecting the plastics to pyro lysis and cracking hydrocarbons in the plastics to produce a plastics vapour comprising hydrocarbon substituents; b) one or more separation vessels for separating the plastics vapour into hydrocarbon substitutents based on boiling points of the hydrocarbon substituents; c) one or more condensers for condensing the hydrocarbon substituents into one or more petroleum products; and d) means for collecting the one or more petroleum products.
In accordance with another aspect of the present invention there is provided a process for processing plastics into one or more petroleum products, the process comprising: providing plastics to a pyrolysis reactor; subjecting the plastics to pyrolysis and cracking to produce a plastics vapour, plastics liquids and plastics solids comprising hydrocarbon substituents; separating the plastics vapour in a separation vessel to form a first liquid petroleum product from a gaseous petroleum product; and condensing the gaseous petroleum product into a second liquid petroleum product.
Advantageously, the system and process of the present invention provides a closed loop, which allows the generation not only of on-specification petroleum products, but also petroleum fuels for use within the system and process itself. Further, less input fuel is required, providing environmental and cost benefits. BRIEF DESCRIPTION OF THE FIGURES
Figure 1 shows an overview of a system in accordance with the present invention.
Figure 2 shows a premelt system for use in a system and process according to the present invention.
Figure 3 shows a pyro lysis reactor for use in a system and process according to the present invention.
Figure 4 shows a catalyst tower for use in a system and process according to the present invention.
DETAILED DESCRIPTION
In accordance with one aspect of the present invention, there is provided a system for processing plastics into one or more petroleum products, the system comprising: a) a reactor for subjecting the plastics to pyro lysis and cracking hydrocarbons in the plastics to produce a plastics vapour comprising hydrocarbon substituents; b) one or more separation vessels for separating the plastics vapour into hydrocarbon substitutents based on boiling points of the hydrocarbon substituents; c) one or more condensers for condensing the hydrocarbon substituents into one or more petroleum products; and d) means for collecting the one or more petroleum products.
The present invention also provides a process for processing plastics into one or more petroleum products, the process comprising: providing plastics to a pyrolysis reactor; subjecting the plastics to pyrolysis and cracking to produce a plastics vapour, plastics liquids and plastics solids comprising hydrocarbon substituents; separating the plastics vapour in a separation vessel to form a first liquid petroleum product from a gaseous petroleum product; and condensing the gaseous petroleum product into a second liquid petroleum product.
The entire process is typically performed at atmospheric pressure.
As used herein, "plastics" refers generally to synthetic or semi-synthetic plastic-based materials, such as those comprising polymers of high molecular mass, which are derived primarily from petroleum and natural gas. Examples include high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), polyvinylchloride (PVC), polyurethanes, cellulose-based plastics, and the like.
As used herein, "petroleum" refers generally to hydrocarbon-based flammable liquids that are used as fuels, such as, for example, diesel fuel, naphtha, gasoline, kerosene, methane, ethane, propane, butane, and the like.
An overview of a system according to the present invention is generally shown in Figure 1. The system comprises components for treating and converting waste plastics to petroleum products. It is understood that modifications within the system - such as, for example, the dimensions of the individual components, number of components within the system, or types of materials used for the components - may be contemplated within the scope of invention.
As shown in the embodiment of Figure 1, the system comprises one or more conveyor belts 21 for introducing plastics 22 into the system. The plastics feedstock which is added to the system can come from any number of sources, such as directly from sanitation trucks used for collecting waste plastics from residential or industrial locations. The plastics can include plastic containers (such as beverage and food containers), plastic scrap, grocery bags, and the like, and of different sizes and shapes. Soft and hard plastics can similarly be processed. Plastics feedstock containing contaminants, such as metals, halogenated hydrocarbons and other undesirable materials, may also be processed, but larger contaminating items are preferably removed by hand from the conveyor belt. The plastics are placed onto the conveyor belt in loose or packaged baled form, and can be added directly from a receptacle or into a hopper 200 to facilitate the process. The conveyor belts 21 are sufficiently long and wide to accept plastics of a wide range of sizes. The one or more conveyor belts 21 lead
to a feed 24 which guides the plastics to feeder 201. Alternatively, the feed can include a shredder 25 for reducing the plastics into smaller material.
Figure 2 illustrates a pre-melt reactor. Before undergoing pyrolysis, the plastics 22 can transported through a conveyor 100 into a pre-melt reactor 2 (hereinafter "premelter"). The premelter 2 is part of a pre-melt system generally shown in Figure 2. The premelter 2 melts the plastics feedstock 5 to provide a liquid material to facilitate extraction of petroleum therefrom. It can also be used to separate contaminants from the plastics.
The premelter 2 is housed within a heating chamber 3. The premelter 2 is heated to about 250°C to 340°C to melt the plastics therein and boil off any undesired contaminants. Desirably, the heat for the heating chamber 3 can be provided from hot air that has been used to heat the reactor (see below) via a flue gas pipe 4 connected to the heating chamber 3.
The premelter 2 is typically a rotary kiln. At the end of the screw feeder 100 a rotary seal can be provided attach the screw feeder 100 to the premelter 2. In one embodiment, the premelter 2 has a diameter of about 7 feet and a length of about 18-20 feet. However, the premelter 2 can be much larger depending on the application and the need for higher throughput, such as having a diameter of about 8 feet and length of about 60 feet, for example. Within the premelter 2, the plastic feedstock 5 is liquefied to produce liquefied plastics, non-aqueous vapours (which can include halides, if present in the feedstock), water vapour, and contaminant solids, such as metals. Optionally, a lifter 9 is present in the premelter 2 to shuttle molten plastic and residue from the bottom 8 of the premelter 2 for removal thereform. An outlet screw 19, which can be similar to the screw feeder 100 at the entry to the premelter 2, transports molten plastic from the premelter 2. The outlet screw 19 is within a larger pipe sleeve in such a way that waste solids, unmelted plastics, and other solid and liquid residue settle to the bottom of the outlet screw 19, while residue vapour which is collected in the pipe sleeve 16 and sent to a residue condenser 17. Condensed vapour and residue are collected from the residue condenser 17. A residue removal tank 11 is positioned below the outlet screw 19 to collect the residue 12. Solid residue is collected in residue barrel 13 via a residue screw 15 and may contain acids or other vendible products,
or can be discarded. Liquid residue is removed from the residue removal tank 11 via a liquid plastics pump 16, and sent to the pyro lysis reactor.
Figure 3 illustrates one embodiment of a pyro lysis reactor (hereinafter "reactor") in accordance with the present invention. Liquid plastics from the pre-melt system (if used) is pumped to the reactor 27 via pipe 20. The liquid plastics is essentially free of halogens, water and most contaminants. If no pre-melt system is used, a conveyor 21 similar to described above can be used to transport solid (shredded) plastics to a feeder 201 and into reactor 27.
The feeder 201 can be any transport mechanism for shuttling the plastics, but in one embodiment is a channel comprising a screw-type feeder. The feeder 201 transports the nitrogen- laden plastics into the reactor 27. The feeder can have a hollow-flight screw. Coolant, such as water, is sent through the screw as well as through an air jacket around the feeder 201. The purpose of both of these is to maintain the plastic feed at a temperature below its melting point so that it can be transported into the reactor as a solid, thus reducing gumming residue.
A nitrogen source can be connected to the feeder 201 for supplying nitrogen to a sealed intermediate space between the feeder and the reactor. The nitrogen is used to displace oxygen so as to minimize the amount of oxygen entering the process, thus reducing the yield of undesirable C02 end product. A slide gate (not shown) at the entry of the intermediate space opens and allows the plastics to enter therein. At the same time, the nitrogen source supplies nitrogen into the intermediate space. The plastics becomes packed in the intermediate space and filed with nitrogen. Once the plastics have been exposed and saturated with the nitrogen, a door on the opposite end of the intermediate space opens, and the nitrogenated plastics exit the intermediate space and enter the reactor. The reactor 27 is a vessel, ideally large enough to handle large quantities of plastics, such as about 2000-5000 lbs of raw plastics, for efficient flowthrough of the feedstock through to processing. Ideally, the reactor 27 can have a length of about 22 feet to about 100 feet, typically 22 feet to about 40 feet, more typically 18 feet. Longer reactors may be desired to
increase the interior volume, throughput and efficiency. The diameter of the reactor 27 is typically between about 3-10 feet, or about 6 feet.
The feed rate to the reactor can be controlled to maintain an efficient use of heat in the reactor 27, the rate of fuel being produced, temperature and pressure of gasses in reactor 27, and temperature of gasses downstream, for example. As one example, the feed rate can be controlled such that material is fed into the reactor until the reactor cools to below a target temperature, or within a target temperature range, such as at or below 360°C. A thermocouple (not shown) can be added to a side of the reactor 27 to indicate the amount of liquid in the reactor; with more liquid present, the temperature is generally lower, and the addition of plastics to the reactor can be reduced. The addition or reduction of plastics can be controlled through manual or automatic means, such as through a computer-based algorithm or the like.
The reactor 27 can be made of any suitable material, but ideally iron as a major component. In one embodiment, the reactor has a shell 23 comprising 99.5% iron and up to 0.5% manganese. Chromium oxide formed by the reaction protects the iron from rusting. While a stainless steel reactor may be used, it can be damaged by various impurities (such as halides, for example) in the plastics, requiring it to be replaced more frequently and adding to the expense of the operation.
The reactor 27 is effectively a gradient system comprising different zones therein. The reactor receives the plastics from the feeder 201 (as raw feedstock 22 or molten plastic from the premelter 2, if such is used, via pipe 20). The reactor 27 can be of the rotary type which is rotated during pyrolysis of the plastics so that its internal surfaces are hot enough to vapourize the liquid/solid plastics, forming hydrocarbon vapour and carbon black. A catalyst can be mixed with the liquid or hard plastic in the reactor 27 to facilitate selective cracking of hydrocarbons. A catalyst may be selected according to the desired fuel to be generated from the overall process. For example, catalysts such as aluminum oxide or calcium hydroxide can be added to facilitate the removal of halogens, such as chlorine. In other embodiments, a Group VIII metal can be added to the reaction mixture. This can facilitate a reaction whereby water is broken down, carbon monoxide, unsaturated
hydrocarbons, and hydrogen gas react to form saturated hydrocarbons and carbon dioxide. H2 gas is particularly beneficial for effecting hydrogen saturation of the fuel downstream. This reduces the need for more costly additives, such as in current methods which require an external H2 source and a platinum catalyst under high pressure (300 psi), to facilitate hydrogen saturation. Within the reactor 27 is a reaction zone 202 where the liquid and solids are vapourized, producing a hydrocarbon stream, and solid residue. The vapourized hydrocarbons are cracked to molecules having carbon chains ranging from CI to about C49 or C50. Higher length carbon chains are cracked until they are within the lower range. The solid residue comprises primarily carbon black. The reactor operates in a range of about 340 to 445°C, ideally about 350 to 425°C, or about 400°C. The heat required for this temperature can be obtained with a furnace which uses hydrogen gas, methane and ethane as fuel. Ideally, the fuel can be obtained downstream in the process of the current invention. Typically, this combination of gases burns at approximately 2,300°F. The hot combustion gases are then circulated through a spiral duct that runs around the outside of the reactor. The spiral duct is typically a spiral refractory with heat on end and exhaust on the other. The residence time of the plastics in the reactor for any desired length of time, such as, for example, between 10 minutes to 1 hour or more.
The liquefied plastic is moved at a slow rate until reaching the end of reactor 27. Solids from the reactor 27 are removed by lifters 29 and chutes 31 inside the reactor 27. Metal solids form a bed in within reactor 27. Similar with the outlet 19 on the premelt 2, liquid passes through the outlet residue pipe 32 surrounded by a sleeve pipe which collects vapour and sends it to through vapour pipe 35 and preventing backflow of the vapour into the reactor 27, while solid residue settles on the bottom of the channel and is collected in a residue drum 34. The solid residue is discarded using appropriate disposal means in accordance with local regulations. Whereas larger metal solids and biomass are typically removed from the feedstock in the premelter 2, finer solids are removed from the reactor 27.
A cyclone 37 may also be used to remove any of the solid residue from the reactor discharge. Hydrocarbon vapour flows out of reactor 27 through pipe 35 to the cyclone 37. The cyclone 37 removes any entrained particulate matter from the vapour steam. The particulate matter falls out through opening 36 into the residue drum 34. Vapour from the
cyclone 37 then heads to a catalyst tower via a pipe 39. Ideally, a pipe having a 16 inch diameter (including at the inlet end) can be used.
The solids-free vapours are then cracked, treated and condensed in one or more catalyst towers, such as catalyst towers T2 and T3, shown in Figure 4. The catalyst towers are separation vessels which, as a type of reactor, separate vapours into petroleum products based on the boiling points of the hydrocarbon constituents. Typically, the catalyst tower T2,T3 is about 20 feet high having a diameter of about 3 feet, although any size as appropriate can be used. Each catalyst tower T2,T3 consists of one, two or more catalyst zones 40,41 separated by one or more weirs 45 to treat the hydrocarbons and facilitate selective hydrocarbon cracking. Each catalyst tower T2,T3 produces and blends a petroleum product within a particular specification. Petroleum products which are out of specification are pumped either out of the catalyst towers T2,T3 for further processing. For example, off-spec petroleum products are collected in receptacle 44 and are sent by a pump 210 back to the reactor 27. The off-spec petroleum can also be collected and pumped via pump 211, condensed in condenser 212 and added back to the tower at nozzle 42. Alternatively, these hydrocarbons can be collected and taken out of the system for use as fuel (such as furnace oil #4, #5 or heavy diesel, depending on the operation). From further downstream catalyst towers, such as T3, off-spec petroleum products are pumped back to catalyst tower 40 via pump P3 and pipe (400). The shunting of the different petroleum products can also be performed automatically, such as with automatic ball valves controlled by the system, for example. The system open or closes the valve, depending on the amount of movement of fuels, and any blending of the fuels, between the towers to achieve the desired fuel product.
The temperatures of the catalyst towers vary T2,T3, and generally decrease from upstream to downstream when multiple towers are used. Heat from the hydrocarbon vapours maintains the interior of the towers within a broad range. For example, the temperature in T2 can be about 400°C, while the temperature in T3 can be up to 320°C. This difference in temperatures permits petroleum products of differing boiling points to precipitate from the vapour. There is also an oil jacket around each tower (not shown) which has hot oil circulating through it, which can also maintain the temperature in each tower within a very
narrow range. No other external heat source is required to maintain the temperature ranges within the catalyst towers, other than the heat from the hydrocarbon vapours. Further, hydrocarbon vapours from a downstream catalyst tower (such as T3) which are sent back to an upstream catalyst tower (such as T2) can change and regulate the temperature of the upstream tower, and vice versa.
The hydrocarbon vapours pass through the weirs 45 containing a catalyst 43. These catalysts can include platinum, the catalysts are composed predominantly of compounds such as a Group II, Group VI and/or Group VIII XIII metal compound sulfides, oxides and hydroxides, for example, molybdenum sulfide (MoS2), and a zeolite depending on the fuel to be produced. Particularly preferred zeolites are synthetic Y-type zeolite and ZSM-5. Hydrocarbon vapours meeting specification pass through pipe 50, ideally platinum plated and having a diameter of about 8 inches, at the top of the reactor and proceed to the next catalyst tower or hydrocarbon condensation system, depending on the desired products to be obtained from the process. The platinum can act as a catalyst to facilitate the saturation of unsaturated hydrocarbons before leaving the catalyst towers to be condensed. Hydrogen and highly reactive low boilers are in the stream to facilitate saturation.
Hydrocarbons are condensed from heavy to light, depending on the desired petroleum product, and each requires its own hydrocarbon condensing system stage. One or more heat exchangers (C1-C4) are in fluid communication with the catalyst tower T2 (or, if two or more catalyst towers are used, the one most downstream T3), to receive vapours coming from the top of the catalyst tower(s) and condense the vapours. The temperature in the heat exchanger(s) is regulated by a hot oil system coiled around the outside of the heat exchanger 212, which provides water, hot oil or air cooling within a very narrow range to ensure the right selection of products is obtained. The products are flows into and is collected in pipe 53.
The petroleum product passes through a manometer 55 and is further cooled (if required) by a 3-phase separator and heat exchanger 56. The petroleum product may be treated in-line with fuel additives required to bring the fuel in specification. The additives are metered into the system through a pump 64 and flow to the liquid petroleum product, which is blended in
the pipe 53. Fuel additives can be lubricity additives, antioxidants, and other common industry fuel additives. An automation system controls the pump 64 to ensure the proper ratio of fuel additive and fuel. Petroleum product in the 3-phase separator 56 is cooled to room temperature and sent to a centrifuge (401) and filtered by a simple strainer and into a storage tank (402).
Multiple condensers and heat exchangers permit different fuels to be precipitated out of the hydrocarbon vapour. The temperature of the cooling system is set based on the hydrocarbon product the condensation system is intended to condense, and based on the temperature of the catalyst towers. For example the temperature is set at 170°C to 180°C for diesel or heating oil #2, 240°C for heating oil #6, and about 20°C for gasoline. At 230°C, the fuel is fairly light (i.e., a mixture of C5-C8 hydrocarbons depending on the degree of blending of the fuels at higher temperatures. At 280°C, 60-70% diesel and 30-40% gasoline is obtained, whereas at 235°C, the ratio is about 60-70%) gas and 10-15%) diesel. Beyond 280°C, paraffin wax (C20-C40) is obtained. As shown best in Fig. 1, the selective condensation system condenses diesel at approximately 170°C to 180°C, the light naphtha (or gasoline) is condensed at 20°C. The remaining hydrocarbon low boilers pass through a fuel seal that ensure oxygen cannot pass back through the process. The low boilers (ethane, methane, butane, propane, and hydrogen) are compressed by a compressor or blower and routed to the furnace to provide fuel.
Residual vapours then pass through pipe 62 to a petroleum water seal 63 within tank 64. The vapours from pipe 62 condenses any water remaining in the vapour stream. This water condenses and falls into the bottom of the tank 64. The vapour bubbles through the water. The water acts as a seal to exclude oxygen from passing back through the system. The remaining vapour consists of hydrogen and hydrocarbons having low boiling points (such as methane, ethane, butane, and propane).
Optionally, a pH meter may be connected to the bottom of the tank 63 to monitor for any halides that got into (or through) the system. The vapour is sent via pipe 65 drawn to an off- gas compressor to pressurize the off-gas (to about 1000 psi) for use as fuel for furnace
burners, such as for heating the premelter 2 and/or the reactor 27, or for other uses, such as propane for barbecue tank fuel. No thermal oxidizers, scrubbers, or filters are required for the flue gas. Ambient air is mixed with syngas by the burner 204 and burned to provide heat for the reactor 27. The flue gas exhaust from the furnace indirectly heats both the premelter 2 and the reactor 27, and then is routed to a stack (404) via an exhaust fan (403). Overall, solid waste plastic is converted to approximately 86.7% liquid petroleum products, 1-5% residue, and 8% syngas used to provide fuel for the furnace.
All publications, patents and patent applications mentioned in this Specification are indicative of the level of skill of those skilled in the art to which this invention pertains and are herein incorporated by reference to the same extent as if each individual publication, patent, or patent applications was specifically and individually indicated to be incorporated by reference.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.