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

Abstract

The invention relates to the technical field of waste plastic pyrolysis, in particular to a method and system for increasing the content of paraffin in waste plastic pyrolysis oil gas. The method comprises the steps that 1, saturated paraffin is preheated and then mixed with waste plastic, and a mixture is obtained; and (2) carrying out pyrolytic reaction on the mixture to obtain pyrolytic oil gas and semicoke. According to the method for increasing the content of the paraffin in the waste plastic pyrolysis oil gas, provided by the invention, the saturated paraffin is added during pyrolysis of the waste plastic, and the saturated paraffin can provide small-molecule alkyl free radicals with the carbon number of less than C9 for a pyrolysis reaction, so that the self pyrolysis of the waste plastic can be promoted to generate more paraffin, and the content of light oil fractions in the pyrolysis oil gas is remarkably increased.

Description

Technical Field

[0001] The invention relates to the technical field of waste plastic pyrolysis, and in particular to a method and a system for increasing the content of chain alkanes in waste plastic pyrolysis oil and gas. Background Art

[0002] The existing methods of waste plastic disposal mainly include physical recycling, incineration power generation, landfill, etc. Physical recycling refers to the physical treatment of relatively single, high-value waste plastics, such as PET mineral water bottles, which are remade into plastic products for downgrading. After 2-3 cycles, they cannot be recycled again. Incineration power generation can maximize the reduction of waste plastics, but it causes a lot of carbon emissions. Since the degradation cycle of waste plastics is as long as 200-500 years, landfill cannot fundamentally solve the problem of white pollution, and it also occupies a lot of land resources. Therefore, the international community no longer recommends landfilling of waste plastics.

[0003] Domestically, most high-value waste plastics are physically recycled, while the most used waste plastics such as agricultural films and packaging films are often discarded and incinerated in power plants due to their high recycling costs and low recycling value. This part of waste plastics is often mainly polyolefins, which are mainly composed of C and H and have good recycling potential. Based on literature and field surveys, chemical recycling of polyolefins is considered to be the only process that can achieve sustainable development. Among them, the pyrolysis process has attracted the attention of researchers and companies in various countries due to its environmental protection and high yield. Major international refining and chemical companies all have polyolefin pyrolysis processes with independent intellectual property rights.

[0004] However, one of the main problems with existing thermal cracking technology is that waste plastics, especially polyolefin waste plastics, follow a random chain scission mechanism during the cracking process, so an alkane is inevitably formed at the same time as an alkane, and the olefin content in the thermal product is relatively high. Although pyrolysis under hydrogen conditions can reduce the olefin content, the amount of hydrogen consumed is relatively high, and the pyrolysis catalyst is easily contaminated and difficult to recycle, which has poor economic efficiency. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of high olefin content and low alkane content in the pyrolysis oil and gas obtained by pyrolysis of waste plastics and large hydrogen consumption in the hydrogen pyrolysis technology, and to provide a method and system for increasing the chain alkane content in the pyrolysis oil and gas of waste plastics.

[0006] In order to achieve the above object, the first aspect of the present invention provides a method for increasing the content of paraffin in the oil gas produced by pyrolysis of waste plastics, wherein the method comprises the following steps:

[0007] (1) preheating a saturated paraffin and mixing it with waste plastics to obtain a mixture;

[0008] (2) subjecting the mixture to a pyrolysis reaction to obtain pyrolysis oil gas and semi-coke.

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

[0010] Among them, the preheating device 1, the hopper 2, the screw extruder 3 and the 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 tower 5, the side line production outlet of the distillation tower 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, and the liquid phase outlet of the oil and gas separation device 7 is connected to the hopper 2; the top of the distillation tower 5 is connected to the gas-liquid separator 8, and 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 tower 5 and the hydrogenation device 6.

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

[0012] 1) The method for increasing the content of paraffins in the pyrolysis oil and gas of waste plastics provided in the present invention utilizes the improvement of the heat transfer and mass transfer performance of the hot melt fluid by saturated paraffins and the role of providing alkyl groups to achieve the purpose of promoting the pyrolysis of waste plastics to generate more paraffins and increasing the content of light oil fractions in the pyrolysis oil;

[0013] 2) The method for increasing the content of chain alkanes in the waste plastic pyrolysis oil gas provided in the present invention can increase the yield of alkanes in the waste plastic pyrolysis oil with minimal hydrogen consumption, avoids the difficulties of 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 paraffin in the pyrolysis oil and gas of waste plastics provided in the present invention uses a screw extruder to evenly mix the waste plastics with saturated paraffins and then sends them to a pyrolysis reaction device, and uses the extrusion of the materials in the extruder to form a physical seal to prevent the oil and gas generated by pyrolysis from escaping into the atmosphere and causing environmental pollution;

[0015] 4) The processing system for increasing the content of chain alkanes in the pyrolysis oil and gas of waste plastics provided in the present invention has a simple process and is suitable for industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of a processing system for increasing the content of chain alkanes in the oil gas produced by pyrolysis of waste plastics provided in the present invention.

[0017] Description of Reference Numerals

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

[0019] 4. Pyrolysis reaction device 5. Distillation tower 6. Hydrogenation device

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

[0021] 10. Loading machine DETAILED DESCRIPTION

[0022] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0023] The first aspect of the present invention provides a method for increasing the content of paraffin in waste plastic pyrolysis oil gas, wherein the method comprises the following steps:

[0024] (1) preheating a saturated paraffin and mixing it with waste plastics to obtain a mixture;

[0025] (2) subjecting the mixture to a pyrolysis reaction to obtain pyrolysis oil gas and semi-coke.

[0026] In step (1):

[0027] In one embodiment of the present invention, based on the total mass of the saturated paraffins, the content of saturated paraffins in the saturated paraffins is ≥ 90 wt%, preferably ≥ 95 wt%.

[0028] In the present invention, saturated paraffin refers to hydrocarbon oil with saturated paraffin as the main component, and the saturated paraffin contains a small amount of impurity components such as aromatic hydrocarbons, cycloalkanes and olefins in addition to saturated paraffins. Preferably, the content of aromatic hydrocarbons is ≤8wt%, preferably ≤3wt%, and the total content of cycloalkanes and olefins is ≤5wt%, preferably ≤2wt%.

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

[0030] Among them, in the present invention, the inventors have found through research that the carbon chain of polyolefins is generally relatively long. When pyrolyzed alone, the alkyl radicals formed by the breakage of the long carbon chain of polyolefins are difficult to move in the condensed phase formed by pyrolysis, and can only react with adjacent long-chain hydrocarbons to generate heavy components with relatively large molecules, which is not conducive to the lightness of pyrolysis oil. Based on the pyrolysis mechanism of saturated chain alkanes, saturated chain alkanes with a distillation range of 120-350°C are added during the pyrolysis of waste plastics. Saturated chain alkanes can provide small molecular alkyl radicals below C9 for the pyrolysis reaction. Small molecular alkyl radicals can attack any position of the long carbon chain of polyolefins and break the long carbon chain of polyolefins into long carbon chain radicals. The long carbon chain radicals further break at the β position to form an alkane and an olefin. The generated alkanes and olefins can further react with small molecular alkyl radicals below C9, thereby further shortening the carbon number of the product. The boiling point of the stable product formed after the C9 radical captures the H radical is generally lower than 151°C, which belongs to the gasoline fraction. Therefore, it can promote the pyrolysis of waste plastics to generate more chain alkanes and significantly increase the content of light oil fractions and alkanes in the pyrolysis oil and gas.

[0031] In one embodiment of the present invention, the saturated paraffin is selected from one or more of paraffin-based diesel, waste paraffin-based diesel recovered oil, paraffin-based kerosene, waste paraffin-based kerosene recovered oil, and waste plastic pyrolysis oil hydrogenated oil.

[0032] Among them, paraffin-based diesel refers to the diesel fraction obtained by atmospheric pressure distillation of paraffin-based crude oil, and waste paraffin-based diesel recovered oil refers to the distillate oil recovered from waste paraffin-based diesel. Paraffin-based kerosene refers to the kerosene fraction obtained by atmospheric pressure distillation of paraffin-based crude oil, and waste paraffin-based kerosene recovered oil refers to the distillate oil recovered from waste paraffin-based kerosene.

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

[0034] Among them, in the present invention, the saturated chain alkane is preheated and then mixed with the waste plastic. On the one hand, the heat carried by the preheated saturated chain alkane can be used to vaporize and discharge the water entrained in the waste plastic. The discharged water vapor can be sent to a sewage treatment device after condensation and discharged after being treated to be qualified; on the other hand, the saturated chain alkane can be made liquid rather than solid, and can be mixed with the waste plastic more evenly, which helps to accelerate the reaction of the saturated chain alkane and the waste plastic in the condensed phase during the pyrolysis process and reduce energy consumption.

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

[0036] Among them, in the present invention, the waste plastics are mainly halogen-free waste plastics of addition polymerization type, halogen-containing waste plastics of addition polymerization type can be polyvinyl chloride (PVC) and the like, and condensation-polymerized waste plastics can be polyethylene terephthalate (PET), polyamide (PA), polyurethane (PU) and the like. Addition polymerization type halogen-containing waste plastics and / or condensation-polymerized waste plastics can be collectively referred to as other plastics. Mechanical impurities have a well-known meaning, and refer to impurities such as sand, soil, wood chips, weeds, and metals. The present invention does not specifically limit the form of waste plastics, and the waste plastics can be a soft film or a hard shell.

[0037] In one embodiment of the present invention, before the waste plastics are mixed with the preheated saturated paraffin, the waste plastics may be washed, dried and crushed, thereby further reducing the content of water and mechanical impurities in the waste plastics.

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

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

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

[0041] Among them, in the present invention, if the amount of saturated paraffin added is too little, the small molecular alkyl free radicals provided are insufficient, and the effect of improving the light oil fraction in the pyrolysis oil and gas is not good; if the amount of saturated paraffin added is too much, too many small molecular alkyl free radicals undergo β-position cracking to form pyrolysis gas, which easily leads to waste of resources and reduces the yield of pyrolysis oil in pyrolysis oil gas; when the mass ratio of saturated paraffin to waste plastics is within the above-defined range, the pyrolysis oil lightweighting effect is better and no large amount of pyrolysis gas is generated.

[0042] In one embodiment of the present invention, the temperature of the mixed material is 80-130° C., preferably 95-105° C. In the present invention, the difficulty of conveying the mixed material can be reduced by controlling the temperature of the mixed material.

[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 out the pyrolysis 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: the pyrolysis reaction temperature is 450-600°C, preferably 500-550°C; the pyrolysis reaction pressure is -0.5 to 0.5MPa, preferably 0-0.2MPa; the pyrolysis reaction residence time is 5-60min, preferably 15-30min.

[0046] The pyrolysis reaction in the present invention is carried out in a pyrolysis reactor, and the pyrolysis residence time refers to the time 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 comprises the following steps:

[0048] (3) distilling the pyrolysis oil gas to obtain a boiling point <T 1 The top fraction has a boiling point of T 2 The middle fraction and boiling point of 3 Heavy oil fraction; among them, T 1 140-160℃, T 2 140-310℃, T 3 290-310℃;

[0049] (4) dividing the middle fraction into at least a portion A and a portion B, wherein the portion A is contacted with fresh hydrogen and a hydrogenation catalyst to undergo a hydrogenation reaction to obtain a hydrogenated product;

[0050] (5) separating the hydrogenation product into oil and gas to obtain circulating hydrogen and hydrogenated oil; wherein at least a portion of the hydrogenated oil is returned to step (1) to be used as saturated paraffin;

[0051] (6) separating the top fraction into gas and liquid to obtain a boiling point <T 4 Thermal decomposition gas and boiling point ≥T 4 Light oil fraction; among which, T 4 is 40-60℃.

[0052] In step (3):

[0053] In one embodiment of the present invention, the T 1 140-150℃, T 2 140-310℃, T 3 It is 300-310℃.

[0054] In the present invention, the present invention does not specifically limit the distillation. 1 , T 2 and T 3 The cutting operation can be used in the present invention. The heavy oil fraction separated from the pyrolysis oil gas can be directly output as a product after cooling.

[0055] In step (4):

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

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

[0058] Among them, the active metal component is selected from one or more of Group VIB and Group VIII, preferably selected from one or more of Ni, W, Mo, and Co; the carrier 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 the present invention, the content of the metal active component is calculated as metal element, and the metal active component can exist in the form of metal oxide, metal sulfide, or metal single substance particles. The present invention does not specifically limit the hydrogenation catalyst, and conventional hydrogenation catalysts in the art can be used in the present invention.

[0060] In one embodiment of the present invention, the operating conditions of the hydrogenation reaction include: the hydrogenation reaction temperature is 100-500°C, preferably 400-500°C; the hydrogenation reaction pressure is normal pressure-5MPa, preferably normal pressure-1MPa; the hydrogen-to-oil ratio (m 3 / m 3 ) is 1-1000, preferably 100-500; the reaction volume space velocity is 1-20h -1 , preferably 5-10h -1 Wherein, normal pressure has a well-known meaning and is not particularly limited in the present invention.

[0061] In step (5):

[0062] In one embodiment of the present invention, the present invention does not specifically limit the operation of the oil-gas separation device, and any operation that can separate the circulating hydrogen from the hydrogenation product can be used in the present invention. For example, the oil-gas separation can be performed in a fractionation tower.

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

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

[0065] In the present invention, when the recycled hydrogen is returned to the hydrogenation reaction for recycling, the amount of fresh hydrogen can be reduced accordingly while ensuring that the hydrogen-to-oil ratio remains unchanged. At this time, the amount of fresh hydrogen can be 5-15v% of the total hydrogen feed amount of the hydrogenation reaction.

[0066] In one embodiment of the present invention, the hydrogenated oil is entirely returned to step (1) to be used as saturated paraffin.

[0067] In the present invention, the hydrogenated oil remaining after separating the circulating hydrogen is mainly composed of saturated paraffins, which can be returned to step (1) for recycling. When the hydrogenated oil is returned to step (1) for recycling, the amount of saturated paraffin added can be reduced accordingly, and preferably the addition of saturated paraffin is stopped.

[0068] In step (6):

[0069] In one embodiment of the present invention, the T 4 The present invention does not impose any special restrictions on the gas-liquid separation operation of the tower top fraction. 4 The pyrolysis gas separated from the tower top fraction can be used in the present invention. The pyrolysis gas separated from the tower top fraction can be used as fuel to provide heat for at least one of the pyrolysis reaction, distillation, and hydrogenation reactions. The separated light oil fraction can be output as a product after being cooled to room temperature.

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

[0071] Among them, the preheating device 1, the hopper 2, the screw extruder 3 and the 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 tower 5, the side line production outlet of the distillation tower 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, and the liquid phase outlet of the oil and gas separation device 7 is connected to the hopper 2; the top of the distillation tower 5 is connected to the gas-liquid separator 8, and 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 tower 5 and the hydrogenation device 6.

[0072] In the present invention, the preheating device is used to preheat the saturated paraffin, the silo is used to mix the waste plastics and the preheated saturated paraffin to obtain a mixture; the screw extruder is used to transport the mixture to the pyrolysis reaction device; the pyrolysis reaction device is used to perform pyrolysis reaction of the mixture to obtain pyrolysis oil gas and semi-coke; the distillation tower is used to cut the obtained pyrolysis oil gas to obtain a boiling point <T 1 The top fraction has a boiling point of T 2 The middle fraction and boiling point of 3 The heavy oil fraction is used for the hydrogenation reaction of the intermediate fraction to obtain the hydrogenation product; the oil-gas separation device is used to separate the obtained hydrogenation product to obtain circulating hydrogen and hydrogenated oil; the gas-liquid separation is used to separate the obtained tower top fraction to obtain pyrolysis gas and light oil fraction; the boiler is used to burn the pyrolysis gas to provide heat for at least one of the pyrolysis reaction device, the distillation tower and the hydrogenation device.

[0073] In one embodiment of the present invention, the present invention does not specifically limit the preheating device, and any heating device that can heat saturated aliphatic hydrocarbons can be used in the present invention, for example, a heat exchanger.

[0074] In one embodiment of the present invention, the system further comprises a loader, wherein the loader is connected to the hopper and is used for conveying waste plastics to the hopper.

[0075] Among them, in the present invention, the feeder is selected from one or more of a bucket elevator, a vacuum feeder, a screw feeder, a vibrating feeder, and a bag feeder. Preferably, a sealed cover is provided on the feeder to prevent moisture and saturated paraffin vapor from escaping the system. In order to prevent the hydrogenated oil from being thrown back out of the system when it returns to the hopper and save the volume of the locked hopper, the setting positions of the sealed cover, the hopper and the screw extruder can be adjusted according to conventional operations in the field.

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

[0077] Among them, in the present invention, the feed port can be set to one, in which case the waste plastics and saturated paraffins enter the hopper from the same port; the feed port can also be set to two, in which case the waste plastics and saturated paraffins enter the hopper from different ports respectively. The setting of the heat preservation cover can slow down the heat loss of the saturated paraffins after preheating to improve the drying effect. In the hopper, the heat carried by the saturated paraffins can vaporize the moisture in the waste plastics, and the moisture is discharged from the outlet after vaporization. The built-in agitator can fully mix the waste plastics and saturated paraffins to accelerate the vaporization of moisture. The water vapor discharged from the hopper can be condensed by an air-cooled heat exchanger or a water-cooled heat exchanger and stored in a wastewater tank or directly sent to a wastewater treatment plant for treatment.

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

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

[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 the present invention, to ensure the smooth flow of the mixed material, the diameter of the discharge port of the hopper 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] The present invention does not impose any special limitation on the rotation direction of the screw in the twin-screw extruder, and the screw can be internally rotated, externally rotated, rotated in the same direction, or rotated in the opposite direction, preferably rotated in the same direction.

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

[0084] In the present invention, a heat medium inlet and a heat medium outlet are provided on the external heating jacket, and the heat medium flowing in provides heat for the pyrolysis reaction. The decoking device is used to regularly clean the residue generated by the pyrolysis reaction out of the pyrolysis reaction device.

[0085] In one embodiment of the present invention, the horizontal reactor is provided with a mixed material inlet, a semi-coke outlet, and a pyrolysis oil and gas outlet; wherein the waste plastic inlet is arranged at the feed end of the horizontal reactor, and the semi-coke outlet and the pyrolysis oil and gas outlet are arranged 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, 0°<α≤5°.

[0087] Among them, in the present invention, the horizontal reactor is placed at an angle, and the height of the feed end is made higher than that of the discharge end, which can facilitate feeding and reduce the difficulty of coke removal.

[0088] In one embodiment of the present invention, the present invention does not specifically limit the distillation tower, and any packed or plate distillation tower known in the art can be used in the present invention.

[0089] In the present invention, the pyrolysis oil and gas outlet of the pyrolysis reaction device is directly connected to the feed port of the distillation tower. In order to minimize heat loss, it is preferred to perform insulation treatment on the connecting pipeline between the pyrolysis reaction device and the distillation tower. If necessary, a stream of high-temperature steam and / or high-temperature flue gas can be introduced from the boiler to heat the pipeline. In addition, the heat source required for distillation in the distillation tower can also be supplied by the boiler.

[0090] In one embodiment of the present invention, the hydrogenation device is a fixed bed reactor, and the present invention does not specifically limit the fixed bed reactor, and any fixed bed reactor known in the art can be used in the present invention. The present invention does not specifically limit the number of fixed bed reactors, and the fixed bed reactor can be one 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, and the oil-gas separation device, gas-liquid separator and boiler known in the art can be used in the present invention. In the 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 examples.

[0093] Among them, the embodiment is Figure 1 The processing system shown in the figure includes a screw feeder, a preheater, a hopper, a co-rotating twin-screw screw extruder, a pyrolysis reaction device, a plate distillation tower, a fixed bed reactor, an oil-gas separation device, a gas-liquid separator and a boiler connected in sequence;

[0094] Among them, the spiral feeder is provided with a closed outer cover, the outside of the hopper is provided with a heat preservation cover, the upper end of the hopper is provided with a feed port and an air outlet, the lower end is a conical head, and the discharge port is provided at the lowest end of the conical head with a diameter of 120mm; an agitator is provided inside the hopper, and the stirring blades of the agitator are conical plates matching 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 end of the agitator and the lower end opening of the conical head is 10cm;

[0095] The pyrolysis reaction device is a horizontal reactor with an external heating jacket and a built-in decoking device. The angle α between the central axis of the horizontal reactor and the horizontal line is 5°. The external heating jacket is provided with a heat medium inlet and a heat medium outlet, wherein the heat medium inlet is connected to the boiler.

[0096] Hydrogenation catalyst: Based on the mass of Ni and W elements, it contains 20wt% Ni, 10wt% W, 70wt% Al 2 O 3 .

[0097] Example 1

[0098] (1) waste plastics (PE content of 60wt%, PP content of 25wt%, PS content of 10wt%, moisture content of 2wt%, mechanical impurity content of 3wt%) with a particle size of 20mm after crushing are conveyed into a hopper by a screw feeder, saturated paraffin is preheated to 120°C by a preheater, and the preheated saturated paraffin is added into the hopper and mixed with the waste plastics to obtain a mixture with a temperature of 105°C; wherein the saturated paraffin is paraffin-based kerosene, has a distillation range of 150-300°C, has a saturated paraffin content of 95wt%, a cycloparaffin content of 2wt%, and an aromatic hydrocarbon content of 3wt%;

[0099] (2) The mixed material is transported to a horizontal reactor by a twin-screw extruder and an inert gas N is introduced. 2 , pyrolysis reaction was carried out at 550℃, 0.1MPa, and the residence time of pyrolysis reaction was 30min, and pyrolysis oil gas and semi-coke were obtained;

[0100] (3) transporting the obtained pyrolysis oil and gas to a distillation tower for distillation to obtain a tower top fraction with a boiling point of less than 150° C., an intermediate fraction with a boiling point of 150-300° C., and a heavy oil fraction with a boiling point of more than 300° C.; cooling the produced heavy oil fraction to room temperature and then outputting it as a product;

[0101] (4) The extracted middle distillate is divided into a portion A and a portion B, wherein the portion A accounts for 70% of the total mass of the middle distillate and the portion B accounts for 30% of the total mass of the middle distillate. The portion A is contacted with fresh hydrogen and a hydrogenation catalyst in a fixed bed reactor to carry out a hydrogenation reaction to obtain a hydrogenated product; wherein the hydrogenation reaction temperature is 450° C., the hydrogenation reaction pressure is 1 MPa, and the hydrogen-to-oil ratio (m / s) of the hydrogenation reaction is 100%. 3 / m 3 ) is 400, and the reaction volume space velocity is 8h -1 ; Cool part B to room temperature and output it as a product;

[0102] (5) introducing the obtained hydrogenation product into an oil-gas separation device for oil-gas separation to obtain circulating hydrogen and hydrogenated oil; wherein the content of hydrogen in the circulating hydrogen is 92% by volume, and the circulating hydrogen is returned to the hydrogenation reaction for recycling, and the amount of fresh hydrogen can be 10% by volume of the total hydrogen feed amount of the hydrogenation reaction; the obtained hydrogenated oil is returned to step (1) for use as saturated paraffin;

[0103] (6) The extracted top fraction is introduced into a gas-liquid separator to obtain a pyrolysis gas with a boiling point of less than 50° C. and a light oil fraction with a boiling point of ≥50° C.; wherein the light oil fraction is cooled to room temperature and then 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] The same as Example 1, except that the waste plastics composition is: 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 are 3wt%, and mechanical impurity content is 2.7wt%.

[0106] Example 3

[0107] The same as Example 1, except that the saturated paraffin is hydrogenated oil of waste plastic pyrolysis oil (prepared with reference to Example 1).

[0108] Example 4

[0109] The 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] The same as Example 1, except that the hydrogenation reaction temperature is 300°C, the hydrogenation reaction pressure is 3MPa, and the hydrogen-to-oil ratio (m 3 / m 3 ) is 700, and the reaction volume space velocity is 12h -1 .

[0112] Comparative Example 1

[0113] (1) The waste plastics with a particle size of 20 mm after crushing (the same as in Example 1) are transported into a hopper by a screw feeder;

[0114] (2) The waste plastics from the hopper are transported to a horizontal reactor by a twin-screw screw extruder, and inert gas nitrogen is introduced to perform pyrolysis reaction at 550° C. and 0.1 MPa. The residence time of the pyrolysis reaction is 30 min to obtain pyrolysis oil gas and semi-coke;

[0115] (3) transporting the obtained pyrolysis oil and gas to a distillation tower for distillation to obtain a top fraction with a boiling point of less than 150° C., a middle fraction with a boiling point of 150-300° C., and a heavy oil fraction with a boiling point of more than 300° C.;

[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] The same as Example 1, except that there is no hydrogenation process for part A in step (4), and part A is directly used for circulation.

[0119] Dry ash-free three-phase yield test example 1 of waste plastics

[0120] The pyrolysis raw materials of the present invention include waste plastics and saturated paraffins. Under the same conditions, the saturated paraffins are subjected to pyrolysis reaction alone, and the generated amounts of pyrolysis oil, pyrolysis gas and pyrolysis semi-coke are analyzed; and then the dry ash-free three-phase yield of the waste plastics themselves can be calculated by combining the generated amounts of residue, pyrolysis oil and pyrolysis gas in Examples 1-5 and Comparative Example 2. The dry ash-free three-phase yields of the pyrolysis semi-coke, pyrolysis oil and pyrolysis gas of the waste plastics themselves in Examples 1-5 and Comparative Example 1-2 are shown in Table 1.

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

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

[0123]

[0124] In the formula, m gasis the mass of pyrolysis gas, g; t is the product calculation cycle time, s; V i is the volume flow rate of pyrolysis gas component i, L / s; V i is the molar mass of pyrolysis gas component i, g / mol.

[0125] According to the mass of the three-phase product, the dry ash-free three-phase yield is calculated according to the following formula:

[0126]

[0127]

[0128]

[0129] Where y oil ,y gas ,y char are the dry ash-free yields of pyrolysis oil, pyrolysis gas and pyrolysis semi-coke of waste plastics, %; m, m oil 、m gas 、m char are the masses of waste plastics, pyrolysis oil, pyrolysis gas and pyrolysis semi-coke obtained during the pyrolysis of waste plastics and saturated paraffins, g; M ad and A ad are respectively the moisture and ash contents in waste plastics, %; m oil-agent 、m gas-agent 、m char-agent They are respectively the masses of pyrolysis oil, pyrolysis gas and pyrolysis semi-coke generated when the saturated paraffin added in the pyrolysis process is pyrolyzed alone under the same reaction conditions, g.

[0130] Table 1

[0131]

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

[0133] The pyrolysis oil in the present invention is partly derived from waste plastics and partly derived from saturated paraffins. Under the same conditions, the saturated paraffins are subjected to pyrolysis reaction alone, and the distillation range and hydrocarbon composition of the pyrolysis oil generated are analyzed; and then the distillation range and hydrocarbon composition of the pyrolysis oil in Examples 1-5 and Comparative Example 2 are combined to calculate the distillation range and hydrocarbons of the pyrolysis oil generated by the waste plastics themselves.

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

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

[0136]

[0137] In the formula, y i-plastic is the content of product component i based on waste plastics, %; m total is the total mass of waste plastics and saturated paraffins during pyrolysis, g; y i-total is the content of a certain component i in the co-pyrolysis oil of waste plastics and saturated paraffins, %; m agent is the mass of pyrolysis oil obtained when saturated paraffin is added to the pyrolysis process and pyrolyzed alone, g; y i-agent is the content of component i in the pyrolysis oil when saturated paraffin is pyrolyzed alone, %.

[0138] Table 2

[0139]

[0140]

[0141] Among them, it can be seen from the above table that the method provided in the present invention can significantly increase the content of paraffins in pyrolysis oil and the yield of light oil fraction.

[0142] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for increasing the content of paraffin in the oil gas produced by pyrolysis of waste plastics, characterized in that: The method comprises the following steps: (1) preheating a saturated paraffin and mixing it with waste plastics to obtain a mixture; (2) subjecting the mixture to a pyrolysis reaction to obtain pyrolysis oil gas and semi-coke.

2. The method according to claim 1, wherein: The content of saturated paraffin in the saturated paraffin is ≥ 90 wt %, preferably ≥ 95 wt %, based on the total mass of the saturated paraffin; Preferably, the distillation range of the saturated paraffin is 120-350°C, preferably 150-300°C; Preferably, the saturated paraffinic hydrocarbon is selected from one or more of paraffin-based diesel, waste paraffin-based diesel recovery oil, paraffin-based kerosene, waste paraffin-based kerosene recovery oil, and waste plastic pyrolysis oil hydrogenation oil; Preferably, the preheating temperature is 100-200°C, preferably 120-150°C.

3. The method according to claim 1 or 2, wherein: The waste plastics include addition polymerized halogen-free waste plastics, water and mechanical impurities, and optionally include addition polymerized halogen-containing waste plastics and / or condensation polymerized waste plastics; wherein the addition polymerized halogen-free waste plastics are selected from one or more of waste polyethylene, waste polypropylene, and waste polystyrene, preferably waste polyethylene and / or waste polypropylene; Preferably, based on the total mass of the waste plastics, the content of the addition-polymerized halogen-free waste plastics is ≥80wt%, preferably ≥90wt%, and further preferably ≥95wt%; the content of water is ≤5wt%, preferably ≤2wt%; the content of mechanical impurities is ≤5wt%; Preferably, based on the total mass of the waste plastics, the content of the addition-polymerized halogen-containing waste plastics is ≤4wt%, preferably ≤2wt%; the content of the condensation-polymerized plastics is ≤5wt%; Preferably, the mass ratio of the saturated paraffin to the waste plastic is 1:0.1-0.9, preferably 1:0.3-0.7; Preferably, the temperature of the mixture is 80-130°C, preferably 95-105°C.

4. The method according to any one of claims 1 to 3, 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, preferably nitrogen; Preferably, the operating conditions of the pyrolysis reaction include: the pyrolysis reaction temperature is 450-600°C, preferably 500-550°C; the pyrolysis reaction pressure is -0.5 to 0.5MPa, preferably 0-0.2MPa; the pyrolysis reaction residence time is 5-60min, preferably 15-30min.

5. The method according to any one of claims 1 to 4, wherein: The method further comprises the following steps: (3) distilling the pyrolysis oil and gas to obtain a top fraction with a boiling point <T1, an intermediate fraction with a boiling point T2, and a heavy oil fraction with a boiling point >T3; wherein T1 is 140-160°C, T2 is 140-310°C, and T3 is 290-310°C; (4) dividing the middle fraction into at least a portion A and a portion B, wherein the portion A is contacted with fresh hydrogen and a hydrogenation catalyst to undergo a hydrogenation reaction to obtain a hydrogenated product; (5) separating the hydrogenation product into oil and gas to obtain circulating hydrogen and hydrogenated oil; wherein at least a portion of the hydrogenated oil is returned to step (1) to be used as saturated paraffin; (6) separating the top fraction into gas and liquid to obtain a pyrolysis gas with a boiling point < T4 and a light oil fraction with a boiling point ≥ T4; wherein T4 is 40-60°C.

6. The method according to claim 5, wherein: The T1 is 140-150°C, T2 is 140-310°C, and T3 is 300-310°C.

7. The method according to claim 5 or 6, 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; Preferably, 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 carrier; The active metal component is selected from one or more of Group VIB and Group VIII, preferably one or more of Ni, W, Mo, and Co; the carrier is selected from one or more of aluminum silicate, magnesium silicate, molecular sieve, activated carbon, and alumina, preferably alumina and / or molecular sieve; Preferably, the operating conditions of the hydrogenation reaction include: the hydrogenation reaction temperature is 100-500°C, preferably 400-500°C; the hydrogenation reaction pressure is normal pressure-5MPa, preferably normal pressure-1MPa; the hydrogen-to-oil ratio (m 3 / m 3 ) is 1-1000, preferably 100-500; the reaction volume space velocity is 1-20h -1 , preferably 5-10h -1 .

8. The method according to any one of claims 5 to 7, wherein: The oil-gas separation is carried out in an oil-gas separation device; Preferably, the content of hydrogen in the circulating hydrogen is ≥85v%, preferably ≥90v%; Preferably, the circulating hydrogen is returned to the hydrogenation reaction for cyclic use; Preferably, the hydrogenated oil is entirely returned to step (1) to be used as saturated paraffin.

9. The method according to any one of claims 5 to 8, wherein: The T4 is 45-50°C.

10. A processing system for increasing the content of paraffin in the oil gas produced by pyrolysis of waste plastics, characterized in that: The system comprises a preheating device (1), a hopper (2), a screw extruder (3), a pyrolysis reaction device (4), a rectification tower (5), a hydrogenation device (6), an oil-gas separation device (7), a gas-liquid separator (8) and a boiler (9); The preheating device (1), the hopper (2), the screw extruder (3) and the 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 tower (5); the side line outlet of the distillation tower (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 tower (5) is connected to a gas-liquid separator (8); the boiler (9) is connected to at least one of the pyrolysis reaction device (4), the distillation tower (5) and the hydrogenation device (6).

Images