Method and system for increasing the content of paraffins in waste plastic pyrolysis oil gas

Abstract

The present application relates to the technical field of waste plastic pyrolysis, and particularly relates to a method and system for increasing the content of alkanes in waste plastic pyrolysis oil gas, which comprises the following steps: (1) mixing saturated alkanes with waste plastics after preheating to obtain a mixture; (2) performing pyrolysis reaction on the mixture to obtain pyrolysis oil gas and semi-coke. The method for increasing the content of alkanes in waste plastic pyrolysis oil gas provided in the present application adds saturated alkanes during waste plastic pyrolysis, and the saturated alkanes can provide small-molecule alkyl radicals below C9 for the pyrolysis reaction, so as to promote the waste plastic itself to produce more alkanes, and significantly increase the content of light oil fraction in the pyrolysis oil gas.

Description

Technical Field

[0001] This invention relates to the field of waste plastic pyrolysis technology, specifically to a method and system for increasing the content of alkanes in the oil and gas from waste plastic pyrolysis. Background Technology

[0002] Existing methods for disposing of waste plastics mainly include physical recycling, incineration for power generation, and landfill. Physical recycling refers to reprocessing relatively simple, high-value waste plastics, such as PET mineral water bottles, into recycled plastic products for reuse. These products can only be recycled 2-3 times before they cannot be reused again. Incineration for power generation can maximize the reduction of waste plastics, but this results in significant carbon emissions. Because waste plastics have a degradation cycle of 200-500 years, landfilling cannot fundamentally solve the problem of white pollution and also occupies a large amount of land resources. Therefore, internationally, landfilling is no longer recommended for waste plastic disposal.

[0003] Domestically, most high-value waste plastics are physically recycled, while the largest-volume waste plastics, such as agricultural film and packaging film, are often discarded and disposed of in incineration power plants due to their high recycling costs and low recycling value. This portion of waste plastics is often dominated by polyolefins, whose composition is primarily C and H, exhibiting good recycling potential. Based on literature and field surveys, chemical recycling of polyolefins is considered the only process capable of achieving sustainable development. Pyrolysis processes, in particular, have attracted attention from researchers and companies worldwide due to their environmental friendliness and high yield rates; major international refining and chemical companies all possess proprietary polyolefin pyrolysis processes.

[0004] However, one of the main problems with existing pyrolysis technologies is that waste plastics, especially polyolefin waste plastics, follow a random chain scission mechanism during pyrolysis. Therefore, while an alkane is generated, an olefin is inevitably formed simultaneously, resulting in a high olefin content in the heat transfer products. Although pyrolysis under hydrogen-containing conditions can reduce the olefin content, the amount of hydrogen consumed is relatively high. Moreover, the pyrolysis catalyst is easily contaminated and difficult to recycle, making it economically unfeasible. Summary of the Invention

[0005] The purpose of this invention is to address the problems of high olefin content, low alkane content, and high hydrogen consumption in pyrolysis oil and gas obtained from waste plastic pyrolysis, and to provide a method and system for increasing the alkane content in waste plastic pyrolysis oil and gas.

[0006] To achieve the above objective, a first aspect of the present invention provides a method for increasing the alkanes content in the pyrolysis oil and gas of waste plastics, wherein the method includes the following steps:

[0007] (1) Saturated alkanes are preheated and then mixed with waste plastics to obtain a mixture;

[0008] (2) The mixture is subjected to pyrolysis to obtain pyrolysis oil and gas and semi-coke.

[0009] A second aspect of the present invention provides a processing system for increasing the content of alkanes in the pyrolysis oil and gas of waste plastics, wherein the system includes a preheating device 1, a hopper 2, a screw extruder 3, a pyrolysis reaction device 4, a distillation column 5, a hydrogenation device 6, an oil and gas separation device 7, a gas-liquid separator 8, and a boiler 9.

[0010] The preheating device 1, hopper 2, screw extruder 3, and pyrolysis reaction device 4 are connected in sequence. The pyrolysis oil and gas outlet of the pyrolysis reaction device 4 is connected to the distillation column 5. The side stream outlet of the distillation column 5 is connected to the hydrogenation device 6. The hydrogenation device 6 is connected to the oil and gas separation device 7. The gas phase outlet of the oil and gas separation device 7 is connected to the hydrogenation device 6. The liquid phase outlet of the oil and gas separation device 7 is connected to the hopper 2. The top of the distillation column 5 is connected to the gas-liquid separator 8. The gas phase outlet of the gas-liquid separator 8 is connected to the boiler 9. The boiler 9 is connected to at least one of the pyrolysis reaction device 4, the distillation column 5, and the hydrogenation device 6.

[0011] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0012] 1) The method for increasing the content of alkanes in waste plastic pyrolysis oil and gas provided in this invention utilizes the improvement of the heat and mass transfer performance of saturated alkanes on the hot melt fluid and the alkyl donation effect to promote the generation of more alkanes from waste plastic pyrolysis and increase the content of light oil fraction in the pyrolysis oil.

[0013] 2) The method for increasing the alkanes content in waste plastic pyrolysis oil provided in this invention can increase the yield of alkanes in waste plastic pyrolysis oil with minimal hydrogen consumption, avoiding the problems of difficult catalyst separation and high catalyst cost in catalytic pyrolysis technology, and can effectively improve the quality of pyrolysis oil products.

[0014] 3) The processing system for increasing the content of alkanes in the pyrolysis oil and gas of waste plastics provided in this invention uses a screw extruder to mix waste plastics and saturated alkanes evenly and then send them to the pyrolysis reaction device. The extrusion of the material in the extruder forms a physical seal to prevent the oil and gas generated by pyrolysis from backflowing into the atmosphere and causing environmental pollution.

[0015] 4) The processing system for increasing the content of alkanes in the pyrolysis oil and gas of waste plastics provided in this invention has a simple process and is suitable for industrial promotion. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the processing system provided in this invention for increasing the alkanes content in the pyrolysis oil and gas of waste plastics.

[0017] Explanation of reference numerals in the attached figures

[0018] 1. Preheating device; 2. Hopper; 3. Screw extruder

[0019] 4. Pyrolysis reaction apparatus; 5. Distillation column; 6. Hydrogenation unit.

[0020] 7. Oil-gas separation device; 8. Gas-liquid separator; 9. Boiler

[0021] 10. Feeding machine Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] A first aspect of the present invention provides a method for increasing the alkanes content in the pyrolysis oil and gas of waste plastics, wherein the method includes the following steps:

[0024] (1) Saturated alkanes are preheated and then mixed with waste plastics to obtain a mixture;

[0025] (2) The mixture is subjected to pyrolysis to obtain pyrolysis oil and gas and semi-coke.

[0026] In step (1):

[0027] In one embodiment of the present invention, the saturated alkanes contain ≥90wt% saturated alkanes, preferably ≥95wt%, based on the total mass of the saturated alkanes.

[0028] In this invention, saturated alkanes refer to hydrocarbon oils whose main component is saturated alkanes. Besides saturated alkanes, saturated alkanes also contain small amounts of aromatic hydrocarbons, cycloalkanes, and alkenes as impurities. Preferably, the content of aromatic hydrocarbons is ≤8 wt%, more preferably ≤3 wt%, and the total content of cycloalkanes and alkenes is ≤5 wt%, more preferably ≤2 wt%.

[0029] In one embodiment of the present invention, the saturated alkanes have a distillation range of 120-350°C, preferably 150-300°C.

[0030] In this invention, the inventors discovered that polyolefins generally have long carbon chains. During pyrolysis alone, the alkyl radicals formed by the breakage of these long carbon chains are difficult to move within the condensed phase formed by pyrolysis. They can only react with adjacent long-chain hydrocarbons to generate relatively large heavy components, which is detrimental to the lightening of the pyrolysis oil. Based on the pyrolysis mechanism of saturated alkanes, saturated alkanes with a distillation range of 120-350℃ are added during the pyrolysis of waste plastics. Saturated alkanes can provide small alkyl radicals (C9 and below) for the pyrolysis reaction. These small alkyl radicals can attack any position on the long carbon chain of the polyolefin, breaking it into long-chain radicals. These long-chain radicals can further undergo β-position cleavage to form an alkane and an olefin. The generated alkanes and alkenes can further react with small alkyl radicals below C9, thereby further shortening the carbon number of the products. The stable products formed after C9 radicals abstract H radicals generally have boiling points below 151℃ and belong to gasoline fractions. Therefore, it can promote the pyrolysis of waste plastics to generate more alkanes and significantly increase the content of light oil fractions and alkanes in pyrolysis oil and gas.

[0031] In one embodiment of the present invention, the saturated alkanes are selected from one or more of paraffinic diesel oil, waste paraffinic diesel oil recovery oil, paraffinic kerosene, waste paraffinic kerosene recovery oil, and hydrogenated waste plastic pyrolysis oil.

[0032] Among them, paraffinic diesel refers to the diesel fraction obtained from the atmospheric distillation of paraffinic crude oil, and waste paraffinic diesel oil recovery refers to the distillate oil recovered from waste paraffinic diesel. Paraffinic kerosene refers to the kerosene fraction obtained from the atmospheric distillation of paraffinic crude oil, and waste paraffinic kerosene oil recovery refers to the distillate oil recovered from waste paraffinic kerosene.

[0033] In one embodiment of the present invention, the preheating temperature is 100-200°C, preferably 120-150°C.

[0034] In this invention, saturated alkanes are preheated and then mixed with waste plastics. On the one hand, the heat carried by the preheated saturated alkanes can be used to vaporize and discharge the water entrained in the waste plastics. The discharged water vapor can be condensed and sent to a wastewater treatment device for discharge after treatment. On the other hand, it also makes the saturated alkanes liquid rather than solid, which can mix more evenly with the waste plastics, helping to accelerate the reaction of saturated alkanes and waste plastics in the condensed phase during pyrolysis and reduce energy consumption.

[0035] In one embodiment of the present invention, the waste plastic includes polymerized halogen-free waste plastic, water and mechanical impurities, and optionally includes polymerized halogenated waste plastic and / or condensation waste plastic; wherein the polymerized halogen-free waste plastic is selected from one or more of waste polyethylene (PE), waste polypropylene (PP) and waste polystyrene (PS), preferably waste polyethylene and / or waste polypropylene.

[0036] In this invention, the waste plastics are mainly halogen-free polymerized waste plastics, while halogenated polymerized waste plastics can be polyvinyl chloride (PVC), etc., and condensation-polymerized waste plastics can be polyethylene terephthalate (PET), polyamide (PA), polyurethane (PU), etc. Halogenated polymerized waste plastics and / or condensation-polymerized waste plastics can be collectively referred to as other plastics. Mechanical impurities have a generally accepted meaning, referring to impurities such as sand, gravel, soil, sawdust, weeds, and metal. This invention does not impose any special limitations on the form of the waste plastics; the waste plastics can be soft films or rigid shells.

[0037] In one embodiment of the present invention, before mixing the waste plastic with the preheated saturated alkanes, the waste plastic can be washed, dried and crushed to further reduce the content of water and mechanical impurities in the waste plastic.

[0038] In one embodiment of the present invention, based on the total mass of the waste plastics, the content of the polymerized halogen-free waste plastics is ≥80wt%, preferably ≥90wt%, more preferably ≥95wt%; the water content is ≤5wt%, preferably ≤2wt%; and the mechanical impurities content is ≤5wt%.

[0039] In one embodiment of the present invention, based on the total mass of the waste plastics, the content of the polymerized halogenated waste plastics is ≤4wt%, preferably ≤2wt%; and the content of the condensation-polymerized plastics is ≤5wt%.

[0040] In one embodiment of the present invention, the mass ratio of the saturated alkanes to waste plastics is 1:0.1-0.9, preferably 1:0.3-0.7.

[0041] In this invention, if the amount of saturated alkanes added is too small, the provided small molecule alkyl radicals are insufficient, resulting in poor improvement of the light oil fraction in the pyrolysis oil gas. If the amount of saturated alkanes added is too large, too many small molecule alkyl radicals will undergo β-site cracking to form pyrolysis gas, which can easily lead to resource waste and reduce the yield of pyrolysis oil in the pyrolysis oil gas. When the mass ratio of saturated alkanes to waste plastics is within the above-defined range, the effect of lightening the pyrolysis oil is better and a large amount of pyrolysis gas will not be generated.

[0042] In one embodiment of the present invention, the temperature of the mixture is 80-130°C, preferably 95-105°C. In this invention, controlling the temperature of the mixture reduces the difficulty of conveying it.

[0043] In step (2):

[0044] In one embodiment of the present invention, the pyrolysis reaction is carried out under an inert gas; wherein the inert gas is selected from one or more of nitrogen, carbon dioxide, helium, and argon, preferably nitrogen. Carrying the reaction under an inert gas helps to improve the safety of the pyrolysis reaction.

[0045] In one embodiment of the present invention, the operating conditions of the pyrolysis reaction include: a pyrolysis reaction temperature of 450-600℃, preferably 500-550℃; a pyrolysis reaction pressure of -0.5 to 0.5 MPa, preferably 0-0.2 MPa; and a pyrolysis reaction residence time of 5-60 min, preferably 15-30 min.

[0046] In this invention, the pyrolysis reaction is carried out in a pyrolysis reactor, and the pyrolysis residence time refers to the time elapsed from when the mixture enters the pyrolysis reactor to when the reaction residue is discharged from the pyrolysis reactor.

[0047] In one embodiment of the present invention, the method further includes the following steps:

[0048] (3) The pyrolysis oil and gas are distilled to obtain the top fraction with a boiling point < T1, the middle fraction with a boiling point of T2 and the heavy oil fraction with a boiling point > T3; wherein, T1 is 140-160℃, T2 is 140-310℃ and T3 is 290-310℃.

[0049] (4) The middle fraction is divided into at least part A and part B, wherein part A is contacted with fresh hydrogen and hydrogenation catalyst to carry out hydrogenation reaction to obtain hydrogenation product;

[0050] (5) The hydrogenation product is subjected to oil-gas separation to obtain recycled hydrogen and hydrogenated oil; wherein at least part of the hydrogenated oil is returned to step (1) as saturated alkanes;

[0051] (6) The top fraction of the column is subjected to gas-liquid separation to obtain pyrolysis gas with a boiling point < T4 and light oil fraction with a boiling point ≥ T4; wherein, T4 is 40-60℃.

[0052] In step (3):

[0053] In one embodiment of the present invention, T1 is 140-150℃, T2 is 140-310℃, and T3 is 300-310℃.

[0054] In this invention, distillation is not specifically limited; any operation that can cut pyrolysis oil and gas according to T1, T2, and T3 can be used in this invention. The heavy oil fraction separated from the pyrolysis oil and gas can be directly output as a product after cooling.

[0055] In step (4):

[0056] In one embodiment of the present invention, portion A accounts for 50-100% of the total mass of the intermediate distillate, preferably 65-75%; portion B accounts for 0-50% of the total mass of the intermediate distillate, preferably 25-35%. Portion B, after cooling, is directly output as a product.

[0057] In one embodiment of the present invention, the hydrogenation catalyst comprises 10-50 wt% of an active metal component and 50-90 wt% of a support, based on the total mass of the hydrogenation catalyst.

[0058] The active metal component is selected from one or more of Group VIB and Group VIII, preferably from one or more of Ni, W, Mo, and Co; the support is selected from one or more of aluminum silicate, magnesium silicate, molecular sieve, activated carbon, and alumina, preferably alumina and / or molecular sieve.

[0059] In this invention, the content of the active metal component is calculated as a metal element, and the active metal component may exist in the form of metal oxides, metal sulfides, or elemental metal particles. This invention does not impose any special limitations on the hydrogenation catalyst; conventional hydrogenation catalysts in the art can be used in this invention.

[0060] In one embodiment of the present invention, the operating conditions of the hydrogenation reaction include: a hydrogenation reaction temperature of 100-500℃, preferably 400-500℃; a hydrogenation reaction pressure of atmospheric pressure -5MPa, preferably atmospheric pressure -1MPa; and a hydrogen-to-oil ratio (m) of the hydrogenation reaction. 3 / m 3 The value is 1-1000, preferably 100-500; the reaction volume hourly space velocity is 1-20 h⁻¹. -1 5-10 hours is preferred. -1 The term "atmospheric pressure" has a generally accepted meaning, and this invention does not impose any specific limitations on it.

[0061] In step (5):

[0062] In one embodiment of the present invention, the operation of the oil-gas separation device is not particularly limited; any operation that can separate circulating hydrogen from the hydrogenation products can be used in the present invention. For example, oil-gas separation can be carried out in a fractionation tower.

[0063] In one embodiment of the present invention, the hydrogen content in the circulating hydrogen is ≥85v%, preferably ≥90v%.

[0064] In one embodiment of the invention, the recycled hydrogen is returned to the hydrogenation reaction for recycling.

[0065] In this invention, when recycled hydrogen is returned to the hydrogenation reaction for reuse, the amount of fresh hydrogen used can be reduced while maintaining the same hydrogen-to-oil ratio. In this case, the amount of fresh hydrogen used can be 5-15% of the total hydrogen feed to the hydrogenation reaction.

[0066] In one embodiment of the invention, the hydrogenated oil is entirely returned to step (1) as a saturated alkane.

[0067] In this invention, the hydrogenated oil remaining after separating the recycled hydrogen is mainly composed of saturated alkanes and can be recycled back to step (1). When the hydrogenated oil is recycled back to step (1), the amount of saturated alkanes added can be reduced accordingly, and preferably, the addition of saturated alkanes is stopped.

[0068] In step (6):

[0069] In one embodiment of the present invention, T4 is 45-50°C. The present invention does not specifically limit the gas-liquid separation operation of the overhead fraction; any operation that can separate pyrolysis gas with a boiling point ≤ T4 from the overhead fraction can be used in the present invention. The pyrolysis gas separated from the overhead fraction can be used as fuel to heat at least one of the following reactions: pyrolysis, distillation, and hydrogenation. The separated light oil fraction, after cooling to room temperature, can be output as a product.

[0070] A second aspect of the present invention provides a processing system for increasing the content of alkanes in the pyrolysis oil and gas of waste plastics, wherein the system includes a preheating device 1, a hopper 2, a screw extruder 3, a pyrolysis reaction device 4, a distillation column 5, a hydrogenation device 6, an oil and gas separation device 7, a gas-liquid separator 8, and a boiler 9.

[0071] The preheating device 1, hopper 2, screw extruder 3, and pyrolysis reaction device 4 are connected in sequence. The pyrolysis oil and gas outlet of the pyrolysis reaction device 4 is connected to the distillation column 5. The side stream outlet of the distillation column 5 is connected to the hydrogenation device 6. The hydrogenation device 6 is connected to the oil and gas separation device 7. The gas phase outlet of the oil and gas separation device 7 is connected to the hydrogenation device 6. The liquid phase outlet of the oil and gas separation device 7 is connected to the hopper 2. The top of the distillation column 5 is connected to the gas-liquid separator 8. The gas phase outlet of the gas-liquid separator 8 is connected to the boiler 9. The boiler 9 is connected to at least one of the pyrolysis reaction device 4, the distillation column 5, and the hydrogenation device 6.

[0072] In this invention, a preheating device is used to preheat saturated alkanes; a silo is used to mix waste plastics and preheated saturated alkanes to obtain a mixture; a screw extruder is used to transport the mixture to a pyrolysis reactor; the pyrolysis reactor is used to carry out the pyrolysis reaction of the mixture to obtain pyrolysis oil and gas and semi-coke; a distillation column is used to cut the obtained pyrolysis oil and gas to obtain a top fraction with a boiling point < T1, a middle fraction with a boiling point of T2, and a heavy oil fraction with a boiling point > T3; a hydrogenation device is used to carry out the hydrogenation reaction of the middle fraction to obtain hydrogenation products; an oil-gas separation device is used to separate the obtained hydrogenation products to obtain circulating hydrogen and hydrogenated oil; a gas-liquid separation device is used to separate the obtained top fraction to obtain pyrolysis gas and light oil fraction; and a boiler is used to burn the pyrolysis gas to provide heat for at least one of the pyrolysis reactor, distillation column, and hydrogenation device.

[0073] In one embodiment of the present invention, the preheating device is not specifically limited. Any heating device capable of heating saturated aliphatic hydrocarbons can be used in the present invention, such as a heat exchanger.

[0074] In one embodiment of the present invention, the system further includes a feeder, wherein the feeder is connected to the hopper and is used to convey waste plastic to the hopper.

[0075] In this invention, the feeder is selected from one or more of the following: bucket elevator, vacuum feeder, screw feeder, vibrating feeder, and bag feeder. Preferably, the feeder is equipped with a sealed outer cover to prevent moisture and saturated alkane vapors from escaping from the system. To prevent the hydrogenated oil from rebounding out of the system when returning to the hopper and to save the volume of the locking hopper, the positions of the sealed outer cover, hopper, and screw extruder can be adjusted according to conventional operation in the art.

[0076] In one embodiment of the invention, the hopper is provided with a feed inlet, a discharge outlet, an air outlet, an external heat insulation cover, and a built-in agitator.

[0077] In this invention, the feed inlet can be set to one, in which case the waste plastic and saturated alkanes enter the hopper through the same inlet; alternatively, the feed inlet can be set to two, in which case the waste plastic and saturated alkanes enter the hopper through different inlets. The heat insulation cover slows down the heat loss of the preheated saturated alkanes, thus improving the drying effect. Inside the hopper, the heat carried by the saturated alkanes vaporizes the moisture in the waste plastic, and the vaporized moisture is discharged from the outlet. The built-in agitator thoroughly mixes the waste plastic and saturated alkanes, accelerating the vaporization of moisture. The water vapor discharged from the hopper can be condensed by an air-cooled or water-cooled heat exchanger and stored in a wastewater tank or directly sent to a wastewater treatment plant for processing.

[0078] In one embodiment of the present invention, the shortest distance between the spiral stirring blades of the built-in agitator and the inner wall of the hopper is 0.1-5cm, preferably 1-2cm.

[0079] In this invention, the lower end of the hopper is a conical head, and the outermost edge of the spiral stirring blades is parallel to the inner wall of the hopper. The spiral stirring blades can be a conical plate or a conical frame that matches the conical head. The discharge port is located at the bottom of the conical head, and the lower end of the stirrer extends into the interior of the conical head. The distance between the bottom of the stirrer and the opening at the bottom of the conical head is 1-50 cm, preferably 5-15 cm.

[0080] In one embodiment of the present invention, the discharge port of the hopper is directly connected to the feed port of the screw extruder. In this invention, to ensure smooth flow of the mixture, the diameter of the hopper discharge port is 4-10 times the diameter of the waste plastic.

[0081] In one embodiment of the present invention, the screw extruder is selected from a single-screw screw extruder and / or a twin-screw screw extruder, preferably a twin-screw screw extruder.

[0082] In this invention, the rotation direction of the screw in the twin-screw extruder is not specifically limited; it can be internal rotation, external rotation, rotation in the same direction, or rotation in opposite directions, with rotation in the same direction being preferred.

[0083] In one embodiment of the present invention, the pyrolysis reaction device is a horizontal reactor with an external heating jacket and an internal descaling device.

[0084] In this invention, the external heating jacket is equipped with a heat medium inlet and a heat medium outlet, through which the flowing heat medium provides heat for the pyrolysis reaction. A descaling device is used to periodically remove the residue generated by the pyrolysis reaction from the pyrolysis reaction apparatus.

[0085] In one embodiment of the present invention, the horizontal reactor is provided with a mixture inlet, a semi-coke outlet, and a pyrolysis oil and gas outlet; wherein, the waste plastic inlet is located at the feed end of the horizontal reactor, and the semi-coke outlet and the pyrolysis oil and gas outlet are located at the discharge end of the horizontal reactor.

[0086] In one embodiment of the present invention, the angle between the central axis of the horizontal reactor and the horizontal line is α, where 0° < α ≤ 5°.

[0087] In this invention, the horizontal reactor is placed at an angle, and the height of the feed end is higher than that of the discharge end, which facilitates feeding and reduces the difficulty of coke removal.

[0088] In one embodiment of the present invention, the present invention does not impose any special limitation on the distillation column, and packed or plate distillation columns known in the art can be used in the present invention.

[0089] In this invention, the pyrolysis oil and gas outlet of the pyrolysis reactor is directly connected to the feed inlet of the distillation column. To minimize heat loss, the connecting pipeline between the pyrolysis reactor and the distillation column is preferably insulated. If necessary, a stream of high-temperature steam and / or high-temperature flue gas can be introduced from a boiler to heat the pipeline. Alternatively, the heat source required for distillation in the distillation column can also be supplied by a boiler.

[0090] In one embodiment of the present invention, the hydrogenation device is a fixed-bed reactor. The present invention does not impose any particular limitation on the fixed-bed reactor; any fixed-bed reactor known in the art can be used in the present invention. The present invention also does not impose any particular limitation on the number of fixed-bed reactors; there can be one fixed-bed reactor or multiple fixed-bed reactors connected in series.

[0091] In one embodiment of the present invention, the present invention does not specifically limit the oil-gas separation device, gas-liquid separator, and boiler; oil-gas separation devices, gas-liquid separators, and boilers known in the art can all be used in the present invention. In this present invention, the heat medium provided by the boiler can be steam or flue gas.

[0092] The present invention will be described in detail below through embodiments.

[0093] Among them, the embodiments are in Figure 1 The processing is carried out in the system shown. The processing system includes, in sequence, a screw feeder, a preheater, a hopper, a co-rotating twin-screw extruder, a pyrolysis reactor, a plate distillation column, a fixed-bed reactor, an oil-gas separation unit, a gas-liquid separator, and a boiler;

[0094] The screw conveyor is equipped with a sealed outer cover, and the hopper is covered with an insulation cover. The upper end of the hopper has a feed inlet and an air outlet, and the lower end is a conical head. The discharge outlet is located at the bottom of the conical head and has a diameter of 120mm. The hopper is equipped with an agitator. The agitator blades are conical plates that match the conical head. The outermost edge of the conical plate is parallel to the inner wall of the hopper, and the distance between the two is 1cm. The lower end of the agitator extends into the conical head, and the distance between the bottom of the agitator and the lower opening of the conical head is 10cm.

[0095] The pyrolysis reactor is a horizontal reactor with an external heating jacket and an internal coke removal device. The angle α between the central axis of the horizontal reactor and the horizontal line is 5°. The external heating jacket is equipped with a heat medium inlet and a heat medium outlet, wherein the heat medium inlet is connected to the boiler.

[0096] Hydrogenation catalyst: Contains 20 wt% Ni, 10 wt% W, and 70 wt% Al2O3 by mass of Ni and W elements.

[0097] Example 1

[0098] (1) The crushed waste plastic with a particle size of 20 mm (PE content of 60 wt%, PP content of 25 wt%, PS content of 10 wt%, moisture content of 2 wt%, and mechanical impurity content of 3 wt%) is conveyed to the hopper by a screw feeder. The saturated alkanes are preheated to 120°C by a preheater. The preheated saturated alkanes are added to the hopper and mixed with the waste plastic to obtain a mixture at a temperature of 105°C. The saturated alkanes are paraffinic kerosene with a distillation range of 150-300°C. The content of saturated alkanes is 95 wt%, the content of cycloalkanes is 2 wt%, and the content of aromatic hydrocarbons is 3 wt%.

[0099] (2) The above mixture is transported to a horizontal reactor using a twin-screw extruder, and inert gas N2 is introduced. The mixture is then subjected to pyrolysis at 550°C and 0.1 MPa for 30 min to obtain pyrolysis oil and gas and semi-coke.

[0100] (3) The obtained pyrolysis oil and gas are transported to a distillation column for distillation to obtain the top fraction with a boiling point of <150℃, the middle fraction with a boiling point of 150-300℃ and the heavy oil fraction with a boiling point of >300℃; the extracted heavy oil fraction is cooled to room temperature and output as a product.

[0101] (4) The collected middle distillate is divided into part A and part B, with part A accounting for 70% of the total mass of the middle distillate and part B accounting for 30% of the total mass of the middle distillate. Part A is contacted with fresh hydrogen and a hydrogenation catalyst in a fixed-bed reactor to carry out a hydrogenation reaction to obtain the hydrogenated product; wherein, the hydrogenation reaction temperature is 450℃, the hydrogenation reaction pressure is 1MPa, and the hydrogen-to-oil ratio (m) of the hydrogenation reaction is... 3 / m 3 The value is 400, and the volume hourly space velocity (VHSV) is 8 h⁻¹. -1 Part B is cooled to room temperature and then output as the product.

[0102] (5) The obtained hydrogenation product is introduced into an oil-gas separation unit for oil-gas separation to obtain recycled hydrogen and hydrogenated oil; wherein, the hydrogen content in the recycled hydrogen is 92v%, the recycled hydrogen is returned to the hydrogenation reaction for recycling, and the amount of fresh hydrogen can be 10v% of the total hydrogen feed of the hydrogenation reaction; all the obtained hydrogenated oil is returned to step (1) as saturated alkanes.

[0103] (6) The collected top fraction is introduced into a gas-liquid separator to obtain pyrolysis gas with a boiling point of <50℃ and light oil fraction with a boiling point of ≥50℃; the light oil fraction is cooled to room temperature and output as a product; the pyrolysis gas is transported to a boiler as fuel, and the flue gas generated by the boiler is introduced into a horizontal reactor as a heat source.

[0104] Example 2

[0105] Same as Example 1, except that the waste plastic composition is as follows: PE content is 68wt%, PP content is 9wt%, PS content is 12wt%, moisture content is 4wt%, PVC content is 1.3wt%, PET and PA content is 3wt%, and mechanical impurities content is 2.7wt%.

[0106] Example 3

[0107] Same as Example 1, except that: the saturated alkanes are hydrogenated oil from waste plastic pyrolysis oil (prepared according to Example 1).

[0108] Example 4

[0109] Same as Example 1, except that: part A accounts for 50% of the total mass of the middle distillate, and part B accounts for 50% of the total mass of the middle distillate.

[0110] Example 5

[0111] Same as Example 1, except that: the hydrogenation reaction temperature is 300°C, the hydrogenation reaction pressure is 3 MPa, and the hydrogen-to-oil ratio (m) of the hydrogenation reaction is... 3 / m 3 The value is 700, and the reaction volume hourly space velocity is 12 h⁻¹. -1 .

[0112] Comparative Example 1

[0113] (1) The crushed waste plastic with a particle size of 20 mm (same as in Example 1) is conveyed into the hopper using a screw feeder;

[0114] (2) Waste plastic from the hopper is transported to a horizontal reactor using a twin-screw extruder, and inert nitrogen gas is introduced. The pyrolysis reaction is carried out at 550℃ and 0.1MPa for 30 minutes to obtain pyrolysis oil and gas and semi-coke.

[0115] (3) The obtained pyrolysis oil and gas are transported to a distillation column for distillation to obtain the top fraction with a boiling point <150℃, the middle fraction with a boiling point of 150-300℃ and the heavy oil fraction with a boiling point >300℃.

[0116] (4) The extracted pyrolysis gas is transported to the boiler as fuel, and the flue gas generated by the boiler is introduced into the horizontal reactor as a heat source.

[0117] Comparative Example 2

[0118] Similar to Example 1, except that the hydrogenation process of part A in step (4) is omitted, and part A is directly used for recycling.

[0119] Example 1: Drying and Ash-Free Three-Phase Yield Test of Waste Plastics

[0120] The pyrolysis feedstock of this invention includes waste plastics and saturated alkanes. Under the same conditions, the saturated alkanes are pyrolyzed separately, and the amounts of pyrolysis oil, pyrolysis gas, and pyrolysis coke produced are analyzed. Then, combined with the amounts of residue, pyrolysis oil, and pyrolysis gas produced in Examples 1-5 and Comparative Example 2, the dry ash-free three-phase yield of the waste plastics themselves can be calculated. The dry ash-free three-phase yields of pyrolysis coke, pyrolysis oil, and pyrolysis gas from the waste plastics in Examples 1-5 and Comparative Examples 1-2 are shown in Table 1.

[0121] The moisture and ash content of waste plastics were determined using the industrial analysis methods for coal (GB / T 212-2008). The mass of residue and pyrolysis oil was obtained by weighing, and the mass of pyrolysis semi-coke was equal to the mass of residue minus the mass of ash.

[0122] The composition of the pyrolysis gas was analyzed by gas chromatography. The volumetric flow rate of the pyrolysis gas was obtained by reading the gas meter before it was sent to the boiler. Then, the mass flow rate was calculated based on the composition of the pyrolysis gas, and the mass of the pyrolysis gas was obtained by integration. The calculation method is as follows:

[0123]

[0124] In the formula, m gas The mass of the pyrolysis gas is g; t is the product calculation cycle time in seconds; V i V is the volumetric flow rate of pyrolysis gas component i, in L / s; i denoted as , where i is the molar mass of the pyrolysis gas component, in g / mol.

[0125] Based on the mass of the three-phase products, the dry ash-free three-phase yield is calculated using the following formula:

[0126]

[0127]

[0128]

[0129] In the formula y oil y gas y char The dry ash-free yields (%) of pyrolysis oil, pyrolysis gas, and pyrolysis semi-coke from waste plastics; m, m oil m gas m char M represents the mass (g) of waste plastic, pyrolysis oil, pyrolysis gas, and pyrolysis semi-coke obtained during the co-pyrolysis of waste plastic and saturated alkanes; ad and A adThese represent the moisture and ash content (%) in waste plastics; m oil-agent m gas-agent m char-agent The values ​​are, in grams, the masses of pyrolysis oil, pyrolysis gas, and pyrolysis semi-coke produced when saturated alkanes added during the pyrolysis process are pyrolyzed separately under the same reaction conditions.

[0130] Table 1

[0131]

[0132] Example 2: Test on the distillation range and hydrocarbon composition of pyrolysis oil generated from waste plastics:

[0133] The pyrolysis oil in this invention is derived partly from waste plastics and partly from saturated alkanes. Saturated alkanes are pyrolyzed separately under the same conditions, and the resulting pyrolysis oil's distillation range and hydrocarbon composition are analyzed. Then, by combining the distillation range and hydrocarbon composition of the pyrolysis oils from Examples 1-5 and Comparative Example 2, the distillation range and hydrocarbon composition of the pyrolysis oil generated from the waste plastics themselves can be calculated.

[0134] The boiling range of the pyrolysis oils obtained in Examples 1-5 and Comparative Examples 1-2 was analyzed using the petroleum fraction boiling range distribution determination method (gas chromatography, GC-D2887), and the hydrocarbon composition of the pyrolysis oils obtained in Examples 1-5 and Comparative Examples 1-2 was analyzed using GC-MS.

[0135] The distillation range and hydrocarbon composition of pyrolysis oil generated from waste plastics can be calculated using the following formula:

[0136]

[0137] In the formula, y i-plastic The content of product component i, in % based on waste plastics; m total The total mass of waste plastics and saturated alkanes from the pyrolysis process is expressed in g; y i-total The content (%) of component i in the co-pyrolysis oil of waste plastics and saturated alkanes; m agent The mass of the pyrolysis oil obtained when saturated alkanes are added during the pyrolysis process and pyrolyzed alone is expressed in g; y i-agent The percentage represents the content of component i in the pyrolysis oil when saturated alkanes are pyrolyzed alone.

[0138] Table 2

[0139]

[0140]

[0141] As shown in the table above, the method provided in this invention can significantly increase the content of alkanes in pyrolysis oil and the yield of light oil fractions.

[0142] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for increasing the alkanes content in the pyrolysis oil and gas of waste plastics, characterized in that, The method includes the following steps: (1) The saturated alkane oil is preheated and then mixed with waste plastics to obtain a mixture; (2) The mixture is subjected to a pyrolysis reaction to obtain pyrolysis oil and gas and semi-coke; Wherein, based on the total mass of the saturated alkane hydrocarbon oil, the content of saturated alkanes in the saturated alkane hydrocarbon oil is ≥95wt%, the content of aromatic hydrocarbons is ≤3wt%, and the total content of cycloalkanes and olefins is ≤2wt%; The saturated alkane oil has a distillation range of 150-300℃.

2. The method according to claim 1, wherein, The saturated alkane hydrocarbon oil is selected from one or more of paraffinic diesel oil, paraffinic kerosene, and hydrogenated waste plastic pyrolysis oil.

3. The method according to claim 1, wherein, The saturated alkane hydrocarbon oil is selected from one or more of waste paraffin-based diesel oil and waste paraffin-based kerosene oil.

4. The method according to claim 1, wherein, The preheating temperature is 100-200℃.

5. The method according to claim 4, wherein, The preheating temperature is 120-150℃.

6. The method according to any one of claims 1-5, wherein, The waste plastics include polymerized halogen-free waste plastics, water, and mechanical impurities, and optionally include polymerized halogenated waste plastics and / or condensation waste plastics; wherein the polymerized halogen-free waste plastics are selected from one or more of waste polyethylene, waste polypropylene, and waste polystyrene.

7. The method according to claim 6, wherein, The polymerized halogen-free waste plastics are waste polyethylene and / or waste polypropylene.

8. The method according to claim 6, wherein, Based on the total mass of the waste plastics, the content of the polymerized halogen-free waste plastics is ≥80wt%; the water content is ≤5wt%; and the mechanical impurities content is ≤5wt%.

9. The method according to claim 8, wherein, Based on the total mass of the waste plastics, the content of the polymerized halogen-free waste plastics is ≥90wt%; and the water content is ≤2wt%.

10. The method according to claim 9, wherein, Based on the total mass of the waste plastics, the content of the polymerized halogen-free waste plastics is ≥95wt%.

11. The method according to claim 6, wherein, Based on the total mass of the waste plastics, the content of the addition-polymerized halogenated waste plastics is ≤4wt%; the content of the condensation-polymerized plastics is ≤5wt%.

12. The method according to claim 11, wherein, Based on the total mass of the waste plastics, the content of the polymerized halogenated waste plastics is ≤2wt%.

13. The method according to any one of claims 1-5, wherein, The mass ratio of the saturated alkane oil to waste plastic is 1:0.1-0.

9.

14. The method according to claim 13, wherein, The mass ratio of the saturated alkane oil to waste plastic is 1:0.3-0.

7.

15. The method according to any one of claims 1-5, wherein, The temperature of the mixture is 80-130℃.

16. The method according to claim 15, wherein, The temperature of the mixture is 95-105℃.

17. The method according to any one of claims 1-5, wherein, The pyrolysis reaction is carried out under an inert gas; wherein the inert gas is selected from one or more of nitrogen, carbon dioxide, helium, and argon.

18. The method according to any one of claims 1-5, wherein, The operating conditions for the pyrolysis reaction include: a pyrolysis reaction temperature of 450-600℃; a pyrolysis reaction pressure of -0.5 to 0.5 MPa; and a pyrolysis reaction residence time of 5-60 min.

19. The method according to claim 18, wherein, The operating conditions for the pyrolysis reaction include: a pyrolysis reaction temperature of 500-550℃; a pyrolysis reaction pressure of 0-0.2MPa; and a pyrolysis reaction residence time of 15-30min.

20. The method according to any one of claims 1-5, wherein, The method further includes the following steps: (3) The pyrolysis oil and gas are distilled to obtain the top fraction with a boiling point < T1, the middle fraction with a boiling point of T2 and the heavy oil fraction with a boiling point > T3; wherein, T1 is 140-160℃, T2 is 140-310℃ and T3 is 290-310℃. (4) The middle fraction is divided into at least part A and part B, wherein part A is contacted with fresh hydrogen and hydrogenation catalyst to carry out hydrogenation reaction to obtain hydrogenation product; (5) The hydrogenation product is subjected to oil-gas separation to obtain recycled hydrogen and hydrogenated oil; wherein at least part of the hydrogenated oil is returned to step (1) as saturated alkanes; (6) The top fraction of the column is subjected to gas-liquid separation to obtain pyrolysis gas with a boiling point < T4 and light oil fraction with a boiling point ≥ T4; wherein, T4 is 40-60℃.

21. The method according to claim 20, wherein, The T1 is 140-150℃, the T2 is 140-310℃, and the T3 is 300-310℃.

22. The method according to claim 20, wherein, The A portion accounts for 50-100% of the total mass of the middle distillate, and the B portion accounts for 0-50% of the total mass of the middle distillate.

23. The method of claim 20, wherein, Based on the total mass of the hydrogenation catalyst, the hydrogenation catalyst comprises 10-50 wt% of an active metal component and 50-90 wt% of a support; The active metal component is selected from one or more of Group VIB and Group VIII; the support is selected from one or more of aluminum silicate, magnesium silicate, molecular sieve, activated carbon, and alumina.

24. The method according to claim 23, wherein, The active metal component is selected from one or more of Ni, W, Mo, and Co; the support is alumina and / or molecular sieve.

25. The method according to claim 20, wherein, The operating conditions for the hydrogenation reaction include: a hydrogenation reaction temperature of 100-500℃; a hydrogenation reaction pressure of atmospheric pressure to 5 MPa; and a hydrogen-to-oil ratio of 1-1000 m³ / s. 3 / m 3 The reaction volume hourly space velocity is 1-20 h⁻¹. -1 .

26. The method of claim 25, wherein, The operating conditions for the hydrogenation reaction include: a hydrogenation reaction temperature of 400-500℃; a hydrogenation reaction pressure of atmospheric pressure to 1 MPa; and a hydrogen-to-oil ratio of 100-500 m³ / s. 3 / m 3 The reaction volume hourly space velocity is 5-10 h⁻¹. -1 .

27. The method according to any one of claims 21-26, wherein, The oil-gas separation is carried out in an oil-gas separation device.

28. The method according to any one of claims 21-26, wherein, The hydrogen content in the circulating hydrogen is ≥85% v%; The recycled hydrogen is returned to the hydrogenation reaction for reuse. All of the hydrogenated oil is returned to step (1) for use as saturated alkanes.

29. The method according to claim 28, wherein, The hydrogen content in the circulating hydrogen is ≥90%.

30. The method according to any one of claims 21-26, wherein, The T4 temperature is 45-50℃.

31. The method according to any one of claims 1-5, wherein, The method for increasing the alkane content in the pyrolysis oil and gas of waste plastics is carried out in a processing system, which includes a preheating device (1), a hopper (2), a screw extruder (3), a pyrolysis reaction device (4), a distillation column (5), a hydrogenation device (6), an oil and gas separation device (7), a gas-liquid separator (8), and a boiler (9). The preheating device (1), hopper (2), screw extruder (3) and pyrolysis reaction device (4) are connected in sequence. The pyrolysis oil and gas outlet of the pyrolysis reaction device (4) is connected to the distillation column (5). The side-stream outlet of the distillation column (5) is connected to the hydrogenation device (6). The hydrogenation device (6) is connected to the oil and gas separation device (7). The gas phase outlet of the oil and gas separation device (7) is connected to the hydrogenation device (6). The liquid phase outlet of the oil and gas separation device (7) is connected to the hopper (2). The top of the distillation column (5) is connected to the gas-liquid separator (8). The boiler (9) is connected to at least one of the pyrolysis reaction device (4), the distillation column (5) and the hydrogenation device (6).

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