CN108559543A - The technique that supercritical water is heat-treated waste plastics and stalk mixture production hydrocarbon ils - Google Patents

Abstract

The present invention relates to a supercritical hydrothermal treatment process of waste plastics and straw mixture to produce hydrocarbon oil products. The active species produced by the easy cracking of the straws of waste plants in the farmland under supercritical hydrothermal conditions can be used to trigger the cracking of plastic macromolecules, without The use of a catalyst avoids the problem of difficult separation of the catalyst and the product. At the same time, the components produced by the plant cracking also have a solvent effect, which can significantly reduce the viscosity of the plastic cracking oil. Supercritical water can not only act as a solvent and dispersant to avoid system coking in the process of waste plastic cracking, but also reduce the unsaturation of plastic cracking products through its own hydrogen transfer and improve the stability of the product. The method comprehensively utilizes waste plastics and farmland waste straw as raw materials, has low cost, simple operation, does not require hydrogen source, does not require catalyst, has high yield of hydrocarbon oil, and has no pollution to the environment.

Description

Process of supercritical hydrothermal treatment of waste plastic and straw mixture to produce hydrocarbon oil

technical field

The invention relates to a process for producing hydrocarbon oil by supercritical hydrothermal treatment of waste plastics and straw mixture, which belongs to the field of solid waste treatment and biomass energy in the field of resource recovery and utilization.

Background technique

Discarded plastic products have become a major urban solid waste, among which polyolefin waste plastics (such as PE, PP, PS) account for more than 80%. Since plastics are difficult to degrade in nature for a long time, finding a way to make them reusable is related to the development of human beings and the continuation of civilization. Recycled plastic products produced by technical means such as mechanical processing or physical and chemical modification and regeneration have poor performance and can only be used in downgrades. Converting waste plastics into liquid oil by means of pyrolysis is an effective way to recycle waste plastics.

Patent CN106520174 discloses a method for preparing aromatics by catalytic pyrolysis of waste polyolefin plastics. In the method, niobic acid is used as a catalyst and nitrogen is used as a carrier gas, and polyolefin plastics are quickly cracked to synthesize liquid aromatics in a catalytic pyrolysis reactor.

Patent CN107191950 discloses a method for suspension catalytic cracking and catalytic oxidation flameless combustion of waste plastics. The method is to homogenize and modify waste plastics with a liquid catalytic cracking combustion aid first, and then crack them in the decomposition furnace of the dry-process cement production line system at a temperature of 850°C to 1200°C, and use the cracked oil as a cement production process. fuel.

Patent CN107446610 discloses a method specially used for industrial processing of plastics in sorted garbage. The method is to send waste plastics to a liquefaction tank for liquefaction treatment at 350°C, and then send the liquefied plastics to a cracking tank for cracking reaction.

Patent CN107434979 discloses a method of refining waste plastics. The method is to mix waste plastics with dechlorination agent and solvent oil at 350°C, and then inject the mixed oil of dechlorination and dechlorination agent into the next reaction The catalytic cracking reaction is carried out in the kettle.

my country is a large agricultural country, and a large amount of waste straw is produced every year. The traditional incineration treatment will produce a large amount of harmful gas and pollute the environment. If it is converted into biomass oil for use, it is a win-win way that not only conforms to the concept of circular economy but also avoids environmental pollution. .

Patent CN102618312 discloses a method for co-pyrolyzing biomass and waste plastics to prepare fuel oil. The biomass and waste plastics are evenly mixed, placed in a cracking reactor, and heated to start the pyrolysis reaction. The gas produced by pyrolysis enters the refining reaction tower for catalytic reforming. The liquid product after reforming is rectified to obtain different fractions of fuel oil. The flammable gas and residue produced are returned to the pyrolysis reactor for combustion as an auxiliary heat source. Biomass includes aquatic biomass, agricultural production waste and forestry production waste, and waste plastics include PP, HDPE, LDPE. This pyrolysis requires the use of a catalyst, and there is a problem that it is difficult to separate the catalyst from the residue.

Patent CN106433733 discloses a device and method for cracking straw and waste plastics to produce liquid fuel. The method is to preheat the straw and waste plastic particles through a low-temperature (100°C-150°C) preheating system, add Ni/HZSM-5 or Ni/HZSM-22 as a catalyst, and then send them into a high-temperature (500°C) The pyrolysis system conducts pyrolysis, the generated gas enters the solid-gas separation system, the carbon residue will be intercepted, and the volatile gas enters the condensation recovery system. The condensable gas will become liquid fuel after cooling, and the non-condensable gas will be introduced into the low-temperature preheating system through the recovery pipe. . The mass ratio of the straw to the waste plastic is (1:5) to (5:1), and the amount of the catalyst added is 5% to 20% of the total weight of the straw and the waste plastic. Although this method uses co-thermal cracking of straw and waste plastics to improve the yield and quality of liquid fuels, this method requires the use of solid catalysts, and the coke produced by the cracking is likely to deactivate the catalysts. The operation period is short and it is difficult to industrialize.

Contents of the invention

The invention provides a process for producing hydrocarbon oil by supercritical hydrothermal treatment of waste plastics and straw. The purpose of the present invention is to use the active species produced by the easy cracking of the stalks of abandoned plants in the farmland under supercritical hydrothermal conditions to trigger the cracking of plastic macromolecules without using a catalyst and avoiding the problem of difficult separation of the catalyst and the product. At the same time, the plant The components produced by cracking also have a solvent effect, which can significantly reduce the viscosity of plastic cracking oil. Supercritical water can not only act as a solvent and dispersant to avoid system coking in the process of waste plastic cracking, but also reduce the unsaturation of plastic cracking products through its own hydrogen transfer, and improve the stability of the product. The method comprehensively utilizes waste plastics and waste straw from farmland as raw materials, has low cost, simple operation, does not require hydrogen source, does not require catalyst, has high yield of hydrocarbon oil, and has no pollution to the environment.

A process for producing hydrocarbon oil by supercritical hydrothermal treatment of waste plastics and straw mixture, comprising the following steps:

1) Crushing waste plastics and straw plants;

2) Mix crushed waste plastics and straw plants according to a mass ratio of 0.1-10:1 to obtain a mixed raw material, mix and stir the mixed raw material with water to form a slurry material, and the mass ratio of water to mixed raw material is 0.5-2 : 1;

3) adding the slurry material into the reactor, and sealing the reactor;

4) Heating the reactor in two steps. The first step is to heat to 200-380°C and maintain a constant temperature for 5-30 minutes. The second step is to raise the temperature to 400-430°C. The pressure is self-generated pressure;

5) discharge the fluid mixture from the reactor to the condenser, let the mixture pass through the heat exchange unit to cool down to below 20°C, and collect the condensate, which is an oil-water mixture;

6) Oil and water are separated by centrifugation or static stratification to obtain hydrocarbon oil produced by pyrolysis of waste plastic and straw mixture through supercritical hydrothermal treatment.

The waste plastics include: polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC) and other plastics, and the farmland waste straw includes corn cobs, corn stalks, sorghum stalks , sunflower stalks, straw or wheat straw.

The preferred first-stage reaction temperature is 250-310° C., and the reaction time is 10-20 minutes.

The preferred second-stage reaction temperature is 410-420° C., and the reaction time is 20-30 minutes.

Preferably the mass ratio of plastic to straw is 1-5:1

Preferably, the mass ratio of water to the mixed raw material of pulverized plastic and straw is 1-1.5:1.

The reactor is a tube-and-tube reactor, and the arrangement of the tubes and tubes in the reactor is based on that of a conventional tube-and-tube heat exchanger. Critical aquathermolysis reaction to generate a mixture of hydrocarbon oil and water. The shell side of the tubular reactor is fed with heating medium. One end of the reactor is connected to the slurry delivery pump through a valve, and the other end of the reactor is connected to the heat exchange pump through a valve. The unit is connected, and the heat exchange unit is connected with the phase separator.

The beneficial effects of the process of supercritical hydrothermal treatment of waste plastics and straw mixture to produce hydrocarbon oil provided by the present invention are: the supercritical water environment can inhibit the coking of the cracking system and reduce the generation of toxic and harmful gases; the straw decomposes in the supercritical water environment to produce active Molecules can promote the cracking of plastic macromolecules, increase the yield of cracked oil, reduce the viscosity of cracked hydrocarbon oil, and increase its fluidity. The supercritical hydrothermal cracking products of plastic and straw mixture are mainly saturated hydrocarbons and aromatics, while the content of unsaturated hydrocarbons and oxygenated compounds is very low, and the oil has good stability. The process technology is simple, easy to control, does not need to use hydrogen and hydrogen supply agent, does not need catalyst, and does not need to dilute raw materials. It can also solve the problem of waste straw treatment in farmland, and is energy-saving and environmentally friendly.

Description of drawings

Fig. 1 tubular reaction device;

Among them: 1-tube reactor, 2-temperature monitor, 3-pressure gauge, 4-explosion-proof valve, 5-screw pump, 6-raw material mixing tank, 7-heat exchange unit, 8-phase separator, 9 - gas product storage tank, 10-liquid product storage tank, 11-residual oil storage tank, 12-feeding pipeline valve, 13-cleaning spare port valve, 14-discharging pipeline valve, 15-gas phase production pipeline valve, 16 -Liquid phase production pipeline valve, 17-residual oil production pipeline valve, 18-heating medium inlet, 19-heating medium outlet, 20-reactor insulation layer.

Detailed ways

The present invention is further elaborated below by embodiment, and its purpose is to understand content of the present invention better but not limit the protection scope of the present invention.

Example 1

This embodiment adopts the reaction device shown in Fig. 1, and this device is connected feed pump 5, heat exchange unit 7, phase separator 8, gas storage tank 9, liquid storage tank 10 and Residual oil storage tank 11 is formed. The reactor is 60cm long and 12cm in diameter, and 7 reaction tubes are arranged in the reactor, and the diameter of the reaction tubes is 2cm. One end of the reactor is connected to the screw pump 5 through the valve 12 , the other end of the reactor is connected to the heat exchange unit 7 through the valve 14 , and the heat exchange unit is connected to the gas-liquid separator 8 .

Grinding the transparent PE pipe and corn cob, mixing the crushed plastic and corn cob according to the mass ratio of 5:1 to obtain the mixed raw material, mixing the pulverized mixed raw material and distilled water in the raw material mixing tank 6 to form a slurry material, and mixing the water and The mass ratio of raw materials is 1.5:1. The slurry state material is sent into the tube side of the reactor 1 with a screw pump 5, and the reactor is sealed. Circulate molten salt on the shell side of the reactor to heat the reaction tube, and heat the reactor in two steps. The first step is to heat to 300°C, and the temperature is maintained at this temperature for 10 minutes. The second step is to raise the temperature to 410°C, and the reaction proceeds for 30 minutes. Minutes, the pressure in the reactor tube is autogenous. After the reaction is over, open the valve 14 quickly, and use the pressure inside the reactor to quickly discharge the fluid mixture. The mixture enters the heat exchange unit 7 through the pipeline valve 14 and cools down to 20°C, and then enters the phase separator 8 to separate the oil-water mixture condensate, collect In the liquid storage tank 10 , the uncondensed gas is collected in the gas storage tank 9 , and the residual oil is collected in the residual oil storage tank 11 . The condensate is separated into an oil phase and a water phase by centrifugation, and the oil phase is the hydrocarbon oil produced by cracking the waste plastic and straw mixture through supercritical hydrothermal treatment. The yield of hydrocarbon oil was 88.61%, residual oil was 5.72%, and gas was 5.67%. The gas mainly contains chain hydrocarbons with carbon 3 to carbon 5. The viscosity and group composition of hydrocarbon oil products were analyzed, and the results were as follows: the viscosity was 47cP (50°C), saturated hydrocarbons were 63.40wt%, aromatics were 30.47wt%, olefins were 4.67wt%, and oxygen-containing organic compounds were 1.46wt%.

Example 2

The reaction device used in this embodiment is the same as in Example 1. Grinding the PP film and corn stalks, mixing the crushed plastic and corn stalks at a mass ratio of 1:1 to obtain a mixed raw material, mixing the crushed mixed raw material and distilled water in the raw material mixing tank 6 to form a slurry material, water and mixed raw material The mass ratio is 1:1. The slurry state material is sent into the tube side of the reactor 1 with a screw pump 5, and the reactor is sealed. Circulate the molten salt on the shell side of the reactor to heat the reaction tube, and heat the reactor in two steps. The first step is to heat to 250°C and maintain a constant temperature for 20 minutes. The second step is to raise the temperature to 420°C, and the reaction is carried out for 20 minutes. The pressure inside the tube is self-generated pressure. After the reaction is over, open the valve 14 quickly, and use the pressure inside the reactor to quickly discharge the fluid mixture. The mixture enters the heat exchange unit 7 through the pipeline valve 14 and cools down to 20°C, and then enters the phase separator 8 to separate the oil-water mixture condensate, collect In the liquid storage tank 10 , the uncondensed gas is collected in the gas storage tank 9 , and the residual oil is collected in the residual oil storage tank 11 . The condensate is separated into an oil phase and a water phase by centrifugation, and the oil phase is the hydrocarbon oil produced by cracking the waste plastic and straw mixture through supercritical hydrothermal treatment. The yield of hydrocarbon oil was 89.69%, residual oil was 6.15%, and gas was 4.16%. The gas mainly contains chain hydrocarbons with carbon 3 to carbon 5. The viscosity and group composition of the hydrocarbon oil product were analyzed, and the results were as follows: the viscosity was 50cP (50°C), saturated hydrocarbons were 62.05wt%, aromatics were 31.17wt%, olefins were 5.53wt%, and oxygen-containing organic compounds were 1.25wt%.

Example 3

The reaction device used in this embodiment is the same as in Example 1. Grinding the transparent PS lunch box and sorghum stalks, mixing the crushed plastic and sorghum stalks at a mass ratio of 1:5 to obtain mixed raw materials, mixing the crushed mixed raw materials and distilled water in the raw material mixing tank 6 to form a slurry material, water and The mass ratio of the mixed raw materials is 1:2. The slurry state material is sent into the tube side of the reactor 1 with a screw pump 5, and the reactor is sealed. Circulate the molten salt on the shell side of the reactor to heat the reaction tube, and heat the reactor in two steps. The first step is to heat to 200°C and keep it constant for 30 minutes. The second step is to raise the temperature to 430°C, and the reaction is carried out for 10 minutes. The pressure inside the tube is self-generated pressure. After the reaction is over, open the valve 14 quickly, and use the pressure inside the reactor to quickly discharge the fluid mixture. The mixture enters the heat exchange unit 7 through the pipeline valve 14 and cools down to 20°C, and then enters the phase separator 8 to separate the oil-water mixture condensate, collect In the liquid storage tank 10 , the uncondensed gas is collected in the gas storage tank 9 , and the residual oil is collected in the residual oil storage tank 11 . The condensate is separated into an oil phase and a water phase by centrifugation, and the oil phase is the hydrocarbon oil produced by cracking the waste plastic and straw mixture through supercritical hydrothermal treatment. The yield of hydrocarbon oil was 86.82%, residual oil was 7.31%, and gas was 5.87%. The viscosity and family composition of the hydrocarbon oil product were analyzed, and the results were as follows: its viscosity was 95cP (50°C), saturated hydrocarbons were 48.99wt%, aromatics were 34.30wt%, olefins were 2.92wt%, and oxygen-containing organic compounds were 13.79wt%.

Example 4

The reaction device used in this embodiment is the same as in Example 1. Grinding the colorless PC honeycomb board and sunflower stalks, mixing the crushed plastic and sunflower stalks at a mass ratio of 10:1 to obtain mixed raw materials, mixing the crushed mixed raw materials and distilled water in the raw material mixing tank 6 to form slurry materials, water The mass ratio to the mixed raw material is 2:1. The slurry state material is sent into the tube side of the reactor 1 with a screw pump 5, and the reactor is sealed. Circulate the molten salt on the shell side of the reactor to heat the reaction tube, and heat the reactor in two steps. The first step is to heat to 350°C and maintain a constant temperature for 5 minutes. The second step is to raise the temperature to 400°C, and the reaction is carried out for 40 minutes. The pressure inside the tube is self-generated pressure. After the reaction is over, open the valve 14 quickly, and use the pressure inside the reactor to quickly discharge the fluid mixture. The mixture enters the heat exchange unit 7 through the pipeline valve 14 and cools down to 20°C, and then enters the phase separator 8 to separate the oil-water mixture condensate, collect In the liquid storage tank 10 , the uncondensed gas is collected in the gas storage tank 9 , and the residual oil is collected in the residual oil storage tank 11 . The condensate is separated into an oil phase and a water phase by centrifugation, and the oil phase is the hydrocarbon oil produced by cracking the waste plastic and straw mixture through supercritical hydrothermal treatment. The yield of hydrocarbon oil was 90.75%, residual oil was 3.95%, and gas was 5.30%. The analyzed gas composition is mainly chain hydrocarbons with carbon 3 to carbon 5. The viscosity and family composition of the hydrocarbon oil product were analyzed, and the results were as follows: its viscosity was 84cP (50°C), saturated hydrocarbons were 59.26wt%, aromatics were 28.73wt%, olefins were 2.76wt%, and oxygen-containing organic compounds were 9.25wt%.

Claims (7)

1. A kind of supercritical hydrothermal treatment waste plastics and the technology of stalk mixture production hydrocarbon oil, it is characterized in that comprising the following steps: 1) Crushing waste plastics and straw plants; 2) Mixing the crushed waste plastics and straw plants according to the mass ratio of 0.1-10:1 to obtain a mixed raw material, mixing the mixed raw material with water and stirring to form a slurry material, and the mass ratio of water to the mixed raw material is 0.5-2:1; 3) adding the slurry material into the reactor, and sealing the reactor; 4) Heating the reactor in two steps. The first step is to heat to 200-380°C and maintain a constant temperature for 5-30 minutes. The second step is to raise the temperature to 400-430°C. The pressure is self-generated pressure; 5) discharge the fluid mixture from the reactor to the condenser, let the mixture pass through the heat exchange unit to cool down to below 20°C, and collect the condensate, which is an oil-water mixture; 6) Oil and water are separated by centrifugation or static stratification to obtain hydrocarbon oil produced by pyrolysis of waste plastic and straw mixture through supercritical hydrothermal treatment. 2. The process according to claim 1, wherein said waste plastics comprise: polyethylene (PE), polypropylene (PP), polystyrene (PS) or polycarbonate (PC) plastics; The farmland waste straw includes corn cobs, corn stalks, sorghum stalks, sunflower stalks, rice straw or wheat straw. 3. The process according to claim 1, characterized in that the first step reaction temperature is 250-310° C., and the reaction time is 10-20 minutes. 4. The process according to claim 1, characterized in that the reaction temperature of the second step is 410-420° C., and the reaction time is 20-30 minutes. 5. The process according to claim 1, characterized in that the mass ratio of plastics to straw is 1 to 5:1. 6. The process according to claim 1, characterized in that the mass ratio of water to the mixed raw material of crushed plastics and straw is 1 to 1.5:1. 7. The process as claimed in claim 1, characterized in that the reactor is a tube-and-tube reactor, and the arrangement of the tubes and tubes in the reactor is based on the arrangement of the tubes and tubes of a conventional tube-and-tube heat exchanger. The tube side of the tubular reactor undergoes a supercritical hydrothermal cracking reaction to generate a mixture of hydrocarbon oil and water. The shell side of the tubular reactor is fed with a heating medium, and one end of the reactor is connected to the slurry delivery pump through a valve. The other end of the device is connected to the heat exchange unit through a valve, and the heat exchange unit is connected to the phase separator.