Method for preparing bio-oil through synergistic hydrothermal liquefaction of municipal sludge and waste plastics

Abstract

The invention provides a method for preparing bio-oil through synergistic hydrothermal liquefaction of municipal sludge and waste plastics, and belongs to the technical field of waste treatment. According to the method, the yield and quality of the bio-oil can be effectively improved, the problems existing in a traditional sludge treatment method are effectively solved, a new way is provided for treatment of municipal sludge and waste plastic, reduction and energy regeneration of waste are achieved through resource utilization, and the method is suitable for industrial production. The method has remarkable environmental and social benefits, is suitable for large-scale industrial application, and has good market application prospects and popularization value.

Description

Technical Field

[0001] The invention relates to the technical field of waste treatment, and in particular to a method for preparing bio-oil by synergistic hydrothermal liquefaction of urban sewage sludge and waste plastics. Background Art

[0002] Municipal sludge mainly comes from sewage treatment plants, and its treatment and disposal are the focus of environmental protection. Municipal sludge contains a large amount of organic matter and nutrients, such as nitrogen, phosphorus, and potassium, but also contains harmful substances such as heavy metals and antibiotics. Traditional sludge treatment methods include landfill, incineration, and land utilization, but these methods have problems such as environmental pollution, waste of resources, and low treatment efficiency. Therefore, it is urgent to find a technology that can effectively treat sludge and utilize it as a resource.

[0003] Hydrothermal liquefaction is a technology that converts biomass into bio-oil under high temperature and high pressure conditions. However, when municipal sewage sludge is used alone for hydrothermal liquefaction to produce bio-oil, the high water content and complexity of organic matter in the sludge result in limited bio-oil quality and low yield. In addition, harmful substances in the sludge, such as heavy metals and antibiotics, are difficult to remove effectively, limiting the application of bio-oil.

[0004] Bio-oil is an environmentally friendly fuel with the potential to replace fossil fuels. However, due to the poor thermal stability, low energy density, and easy solidification and catalyst deactivation of bio-oil in the existing technology, its application range is limited. Therefore, improving the yield and quality of bio-oil, especially preparing high-quality bio-oil by catalytic pyrolysis and other means, has become a research hotspot.

[0005] Chinese patent CN107880924A discloses a new method for preparing municipal wet sludge into bio-oil, and in particular relates to a process for preparing bio-oil by liquefying municipal wet sludge in a mixed solvent, which is particularly suitable for improving the yield and quality of bio-oil. It belongs to the field of environmental protection and new energy technology; the oil production method directly uses municipal wet sludge as a reaction raw material, utilizes the synergistic effect of co-solvent methanol and water in wet sludge in the process of sludge thermal liquefaction to increase the fatty acid ester content and calorific value in the bio-oil, and achieves the purpose of improving the yield and quality of bio-oil.

[0006] However, the above scheme uses methanol as a co-solvent, which may increase the cost of the entire process and is not conducive to large-scale industrial applications. In addition, as a volatile organic solvent, the recovery and reuse of methanol requires additional steps to reduce environmental emissions.

[0007] Waste plastics are an important component of urban solid waste, and improper treatment of them will cause environmental pollution. The present invention has found through research that the synergistic hydrothermal liquefaction of waste plastics and urban sludge can not only improve the yield and quality of bio-oil, but also realize the resource utilization of waste plastics. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics, which can effectively improve the yield and quality of bio-oil.

[0009] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0010] The present invention provides a method for preparing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics, comprising the following steps:

[0011] Mixing municipal sewage sludge with waste plastics, adding a catalyst, and performing a hydrothermal liquefaction reaction;

[0012] The hydrothermal liquefaction product is subjected to solid-liquid separation, oil-water separation and purification treatment to obtain bio-oil.

[0013] Preferably, the municipal sludge is dehydrated before being mixed with the waste plastics;

[0014] The moisture content after the dehydration treatment is 60-70%.

[0015] Preferably, the waste plastics are crushed before use;

[0016] The particle size after the pulverization process is below 5 mm.

[0017] Preferably, the weight ratio of the urban sludge to the waste plastic is 2 to 5:1.

[0018] Preferably, the catalyst contains Na2CO3 and Co-Mo catalyst.

[0019] Preferably, the amount of Na2CO3 used is 3-8%.

[0020] Preferably, the usage of the Co-Mo catalyst is 3-8%.

[0021] Preferably, the temperature of the hydrothermal liquefaction reaction is 350-400°C;

[0022] The hydrothermal liquefaction reaction time is 50 to 70 minutes;

[0023] The pressure of the hydrothermal liquefaction reaction is 10-20 MPa.

[0024] Preferably, the solid phase separation is carried out by centrifugation;

[0025] The rotation speed of the centrifugal treatment is 3000-8000 r / min;

[0026] The centrifugal treatment time is 1 to 10 minutes.

[0027] Preferably, the purification treatment uses supercritical CO2 extraction;

[0028] The pressure of the supercritical CO2 extraction is 35-40MPa;

[0029] The temperature of the supercritical CO2 extraction is 35-45°C;

[0030] The supercritical CO2 extraction time is 100 to 150 minutes;

[0031] The CO2 flow rate of the supercritical CO2 extraction is 2 to 3 SL / min.

[0032] Technical effects and advantages of the present invention:

[0033] The invention significantly improves the yield and quality of bio-oil by synergistically hydrothermally liquefying municipal sludge and waste plastics. The addition of waste plastics not only increases the carbon source and hydrogen source in the reaction system, but also helps to reduce the viscosity during the reaction process, thereby increasing the yield of bio-oil.

[0034] The dehydration and pulverization steps described in the present invention ensure the appropriate moisture content and particle size of the reaction raw materials, which helps to improve the efficiency of the hydrothermal liquefaction reaction and the quality of the bio-oil.

[0035] The combination of Na2CO3 and Co-Mo catalysts used in the present invention can effectively promote the hydrothermal liquefaction reaction, improve the calorific value and stability of bio-oil, and reduce the content of harmful substances.

[0036] The hydrothermal liquefaction reaction conditions described in the present invention, including the optimization of temperature, time and pressure, ensure the efficient progress of the reaction while avoiding excessive cracking, thereby improving the quality of the bio-oil.

[0037] In the present invention, by adopting centrifugal treatment to carry out solid-liquid separation and oil-water separation, the present invention simplifies the subsequent purification steps and improves the treatment efficiency.

[0038] In the present invention, supercritical CO2 extraction is used as a purification process step, which not only improves the purity of the bio-oil, but also has the advantages of being environmentally friendly and cost-effective due to the recyclability of CO2.

[0039] The method of the present invention not only provides a new way to treat urban sludge and waste plastics, but also achieves waste reduction and energy conversion through resource utilization, has significant environmental and social benefits, is suitable for large-scale industrial applications, and has good market application prospects and promotion value.

[0040] Therefore, the present invention provides an efficient, environmentally friendly and economical method for producing bio-oil by synergistic hydrothermal liquefaction of urban sludge and waste plastics, which effectively solves the problems existing in traditional sludge treatment methods and provides a new idea for the resource utilization of waste. DETAILED DESCRIPTION

[0041] The present invention provides a method for preparing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics, comprising the following steps:

[0042] Mixing municipal sewage sludge with waste plastics, adding a catalyst, and performing a hydrothermal liquefaction reaction;

[0043] The hydrothermal liquefaction product is subjected to solid-liquid separation, oil-water separation and purification treatment to obtain bio-oil.

[0044] In the present invention, preferably, the municipal sludge is dehydrated before being mixed with the waste plastic; the moisture content after the dehydration is 60-70%. Preferably, the waste plastic is crushed before use; the particle size after the crushing is less than 5 mm. Preferably, the weight ratio of the municipal sludge to the waste plastic is 2-5:1.

[0045] In the present invention, preferably, the catalyst contains Na2CO3 and Co-Mo catalyst. Preferably, the amount of Na2CO3 is 3-8%. Preferably, the amount of Co-Mo catalyst is 3-8%.

[0046] In the present invention, the waste plastic is preferably waste thermosetting plastic, and the waste thermosetting plastic is preferably one or more mixtures of phenolic resin, epoxy resin, polyurethane plastic, unsaturated polyester, alkyd plastic or unsaturated polyester resin.

[0047] In the process of the synergistic hydrothermal liquefaction of municipal sludge and waste plastics to produce bio-oil in the present invention, the catalyst plays a vital role. First, it can reduce the activation energy of the reaction, accelerate the reaction process, and make the organic matter in the sludge and waste plastics more effectively converted into bio-oil; through catalysis, the oxygen content in the bio-oil can be reduced, the carbon-hydrogen ratio can be increased, thereby improving the calorific value and stability of the bio-oil; and specific chemical reaction pathways can be promoted, such as decarboxylation reaction and Maillard reaction, which helps to generate more bio-oil and reduce the generation of by-products. The generation of tar and coke can be reduced, and these by-products will reduce the quality of bio-oil and increase the difficulty of subsequent treatment; the use of the specific catalyst of the present invention can significantly improve the yield of bio-oil; within the range of the catalyst dosage provided by the present invention, the effect of the catalyst can be guaranteed, while avoiding the cost increase caused by excessive use, so as to ensure the maximization of the reaction efficiency, and the reaction efficiency will not be affected by insufficient catalyst dosage, nor will resources be wasted due to excessive use, and it is helpful to control the quality of bio-oil and avoid the decline of bio-oil quality due to improper catalyst dosage.

[0048] The catalyst of the present invention plays a key role in the process of producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics, and the appropriate amount of catalyst is a key factor in ensuring economic benefits, environmental benefits and product quality.

[0049] In the present invention, preferably, the temperature of the hydrothermal liquefaction reaction is 350-400°C; the time of the hydrothermal liquefaction reaction is 50-70min; the pressure of the hydrothermal liquefaction reaction is 10-20MPa. Within this temperature range, the organic matter in the sludge and waste plastics can be more effectively decomposed and converted into bio-oil, which helps to break the complex organic molecular structure, increase the yield of bio-oil, and is conducive to deoxygenation reaction, reducing the oxygen content in bio-oil, thereby improving the calorific value and stability of bio-oil, making its properties closer to fossil fuels. The present invention adopts a shorter reaction time, which can reduce the generation of by-products and help to increase the yield of bio-oil. The time range provided by the present invention can balance these two factors and achieve a higher bio-oil yield and better oil quality; because too long a reaction time will increase energy consumption and equipment costs, the time range provided by the present invention helps to control production costs while ensuring oil yield. The parameters provided by the present invention can control production costs, reduce the generation of by-products, and improve energy utilization efficiency while ensuring the yield and quality of bio-oil, thereby achieving dual optimization of economic benefits and environmental benefits.

[0050] In the present invention, preferably, the solid phase separation adopts centrifugal treatment; the rotation speed of the centrifugal treatment is 3000-8000r / min; and the time of the centrifugal treatment is 1-10min. Preferably, the purification treatment adopts supercritical CO2 extraction; the pressure of the supercritical CO2 extraction is 35-40MPa; the temperature of the supercritical CO2 extraction is 35-45°C; the time of the supercritical CO2 extraction is 100-150min; the CO2 flow rate of the supercritical CO2 extraction is 2-3SL / min. As a purification treatment step, not only the purity of the bio-oil is improved, but also due to the recyclability of CO2, the method has the advantages of being environmentally friendly and cost-effective.

[0051] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0052] The main parameters of the municipal sludge used in the embodiments of the present invention are: MLSS (mixed liquor suspended solids concentration): 3000 mg / L, MLVSS (mixed liquor volatile suspended solids concentration): 2250 mg / L, SV30 (sludge settling ratio): 20%, SVI30 (sludge volume index): 100 mL / g, pH value: 7.0, and water content 84.51%.

[0053] Example

[0054] Raw material pretreatment stage: dehydrate the municipal sludge to reach a moisture content of about 65%, crush the waste plastic to a particle size of less than 2mm, and mix the municipal sludge with waste thermosetting plastic in a weight ratio of 3:1.

[0055] Reaction stage: 5% by mass of Na2CO3 and 5% by mass of Co-Mo catalyst (purchased from Jiangsu Yangzi Catalyst Co., Ltd.) were added to the mixture, and a dual catalytic system was used for catalytic reaction. The mixed raw materials and catalyst were placed in a reactor, the reaction temperature was set to 370°C, the reaction time was 60 minutes, and the pressure was maintained at 16.53 MPa to carry out a hydrothermal liquefaction reaction.

[0056] Product separation and post-processing stage: The reaction system is cooled and depressurized until the temperature drops below 70°C and the pressure drops to normal pressure. Then solid phase separation is performed using a TD5M high-speed centrifuge at 5000r / min for 3 minutes, and the solid phase product is collected by filtration. The separation of bio-oil and water phase is completed by using a separatory funnel after standing, and the gas phase product is collected by a gas washing bottle or a freezing trap.

[0057] Bio-oil purification stage: Supercritical CO2 extraction technology is used to further purify the bio-oil. The obtained solid phase product is placed in a supercritical fluid extraction device. The extraction conditions are set to a pressure of 37 MPa, a temperature of 40°C, an extraction time of 130 min, and a CO2 flow rate of 2.5 SL / min. The reaction is terminated when there is no obvious increase in the amount of the extract, and the obtained extraction product is collected.

[0058] According to the formula, bio-oil yield = bio-oil mass / total raw material mass (solid content in waste plastics and aqueous sludge) × 100%

[0059] The calculated bio-oil yield was 37.36%.

[0060] Comparative Example

[0061] Raw material pretreatment stage: Municipal sludge is dehydrated to achieve a moisture content of about 65%.

[0062] Reaction stage: 5% by mass of Na2CO3 and 5% by mass of Co-Mo catalyst (purchased from Jiangsu Yangzi Catalyst Co., Ltd.) were added to the municipal sludge, and a dual catalytic system was used for catalytic reaction. The municipal sludge and the catalyst were placed in a reactor, the reaction temperature was set at 370°C, the reaction time was 60 minutes, and the pressure was maintained at 16.53 MPa to carry out a hydrothermal liquefaction reaction.

[0063] Product separation and post-processing stage: The reaction system is cooled and depressurized until the temperature drops below 70°C and the pressure drops to normal pressure. Then solid phase separation is performed using a TD5M high-speed centrifuge at 5000r / min for 3 minutes, and the solid phase product is collected by filtration. The separation of bio-oil and water phase is completed by using a separatory funnel after standing, and the gas phase product is collected by a gas washing bottle or a freezing trap.

[0064] Bio-oil purification stage: Supercritical CO2 extraction technology is used to further purify the bio-oil. The obtained solid phase product is placed in a supercritical fluid extraction device. The extraction conditions are set to a pressure of 37 MPa, a temperature of 40°C, an extraction time of 130 min, and a CO2 flow rate of 2.5 SL / min. The reaction is terminated when there is no obvious increase in the amount of the extract, and the obtained extraction product is collected.

[0065] According to the formula, bio-oil yield = bio-oil mass / total raw material mass × 100%

[0066] The calculated bio-oil yield was 22.21%.

[0067] Experimental example

[0068] In order to detect the quality of the bio-oil prepared in the embodiment, the present invention designs the following experimental scheme:

[0069] Purpose

[0070] Evaluate the quality of bio-oil, including its physical properties and chemical composition.

[0071] Experimental methods and procedures

[0072] 1. Determination of kinematic viscosity of bio-oil

[0073] Method: The test was carried out in accordance with ASTM D445 using a Cannon-Fenske conventional viscometer in a water bath set at 40°C.

[0074] Operation: Take an appropriate amount of bio-oil sample and place it in the viscometer. Record in detail the time required for the liquid to flow through a specific volume, and calculate the kinematic viscosity value based on this.

[0075] 2. Determination of bio-oil density

[0076] Method: Densitometer was used as the measuring tool.

[0077] Operation: Pour the bio-oil sample into the density meter and record its density readings under different temperature conditions in detail.

[0078] 3. Determination of surface tension of bio-oil

[0079] Methods: Sigma 703D surface tension meter was used for analysis.

[0080] Operation: Add the bio-oil sample onto the sensor probe of the surface tension meter and accurately record the measured surface tension value.

[0081] 4. Determination of calorific value of bio-oil

[0082] Methods: The determination was completed using a Parr 1108 oxygen bomb calorimeter.

[0083] Operation: Accurately weigh 0.5 g of bio-oil sample and place it in an oxygen bomb calorimeter to measure the calorific value.

[0084] 5. Determination of solid insoluble matter content in bio-oil

[0085] Method: 2 g of bio-oil was dissolved in 100 mL of ethanol, dried and weighed after the filtration step.

[0086] Procedure: Filter the bio-oil solution through a 3 μm filter paper, dry the filter paper and record the weight, based on which the content of solid insoluble matter can be calculated.

[0087] 6. Bio-oil stability analysis

[0088] Methods: Bio-oil was heated in an oven at 80 °C for 24 h to simulate aging conditions.

[0089] Operation: Compare the bio-oil before and after heating treatment, measure the change in its kinematic viscosity, and evaluate its stability.

[0090] 7. GPC gel chromatography analysis of bio-oil

[0091] Methods: The analysis was carried out using a gel chromatography instrument produced by Shimadzu Corporation.

[0092] Operation: Accurately weigh about 50 mg of bio-oil sample, dilute it with tetrahydrofuran, and inject it into gel chromatography for analysis to obtain the measurement results of number average molecular weight (Mn) and weight average molecular weight (Mw).

[0093] 8. Infrared spectroscopy analysis of bio-oil

[0094] Methods: Perkin Elmer Fourier transform infrared spectrometer was used to analyze the -1 ATR spectrum detection was performed in the wavenumber range.

[0095] Operation: Place the bio-oil sample in the test area of ​​the infrared spectrometer and record and analyze the resulting spectrum.

[0096] 9. GC-MS Analysis of Bio-Oil

[0097] Instruments and Materials: A gas chromatograph-mass spectrometer (GC-MS) equipped with a DB-1701 column (size 60m×0.25mm, film thickness 0.25μm) was used. Acetone was used as the solvent to dissolve the sample, and the sample was filtered through a 0.2μm polytetrafluoroethylene filter. Fluoranthene was selected as the internal standard substance for determination.

[0098] Steps:

[0099] 1. Sample preparation:

[0100] The bio-oil sample was dissolved in acetone at a mass fraction of 5% and filtered through a 0.2 μm polytetrafluoroethylene filter.

[0101] 2. Chromatographic conditions setting:

[0102] The chromatographic column was DB-1701 (60m×0.25mm). The column box temperature was initially set at 45°C, maintained for 4 minutes, then raised to 280°C at a rate of 3°C / min and maintained at this temperature for 15 minutes. The injector temperature was set at 250°C, with a split ratio of 30:1. Helium was used as the carrier gas, and the flow rate was maintained at 1mL / min.

[0103] 3. Mass spectrometry condition setting:

[0104] The ionization method adopted was electron impact (EI), the electron energy was set to 70 eV, and the scanning range was 20-550 amu.

[0105] 4. Sample injection:

[0106] 1 μl of bio-oil sample was injected each time.

[0107] 5. Data processing:

[0108] Fluoranthene was used as the internal standard to calculate the response factor. The GC-MS analysis of all samples was repeated twice, and the relative content of each chemical component was the average of the two determinations.

[0109] 6. Record the results:

[0110] The chromatograms and mass spectra output by GC-MS were recorded and analyzed to determine the relative amounts of the components in the bio-oil.

[0111] The experimental results are as follows:

[0112] 1. Determination of kinematic viscosity of bio-oil

[0113] Measurement conditions: carried out in a 40°C water bath.

[0114] Measurement results: The kinematic viscosity of the bio-oil obtained in Example 1 is 3.44 mm 2 / s, and the kinematic viscosity of the bio-oil obtained in the comparative example is 6.31 mm 2 / s.

[0115] Analysis: This value is lower than that of most traditional bio-oil samples, indicating that the bio-oil provided by the present invention has excellent fluidity.

[0116] 2. Determination of bio-oil density

[0117] Measurement conditions: carried out at room temperature.

[0118] Measurement results: The density of the bio-oil obtained in Example 1 is 0.85 g / cm 3 The density of the bio-oil obtained in the comparative example is 0.82 g / cm 3 .

[0119] Analysis: The bio-oil provided by the present invention has a density similar to that of traditional petroleum products, which is conducive to subsequent storage and transportation.

[0120] 3. Determination of surface tension of bio-oil

[0121] Measurement conditions: Sigma 703D surface tension meter was used.

[0122] Measurement results: The surface tension of the bio-oil obtained in Example 1 is 0.03 N / m, and the surface tension of the bio-oil obtained in the comparative example is 0.03 N / m.

[0123] Analysis: The bio-oil provided by the present invention has a lower surface tension, which helps the bio-oil to achieve a better atomization effect during the combustion process.

[0124] 4. Determination of calorific value of bio-oil

[0125] Measurement conditions: Parr 1108 oxygen bomb calorimeter was used.

[0126] The measurement results show that the high calorific value (HHV) of the bio-oil obtained in Example 1 is 37.5 MJ / kg, and the high calorific value (HHV) of the bio-oil obtained in the comparative example is 26.5 MJ / kg.

[0127] Analysis: A higher calorific value indicates that the bio-oil has a higher energy density and is suitable for use as a fuel. The bio-oil obtained in Example 1 of the present invention has a significantly higher calorific value than that of the comparative example, indicating that the bio-oil provided by the present invention has a significant advantage in energy density and is more suitable for use as a fuel.

[0128] 5. Determination of solid insoluble matter content in bio-oil

[0129] Determination results: The solid insoluble matter content of the bio-oil obtained in Example 1 and the comparative example is less than 0.1%.

[0130] Analysis: Low solid insoluble content helps reduce sedimentation and clogging problems during bio-oil application.

[0131] 6. Bio-oil stability analysis

[0132] Measurement results: After heating in an oven at 80°C for 24 hours, the kinematic viscosity of the bio-oil obtained in Example 1 was 3.41 mm 2 / s, and the kinematic viscosity of the bio-oil obtained in the comparative example is 17.26 mm 2 / s.

[0133] Analysis: Good stability means that the bio-oil has a long shelf life during storage and use. The bio-oil prepared in the embodiment of the present invention is not prone to viscosity increase after simulated aging, thereby ensuring its reliability in practical applications.

[0134] 7. GPC gel chromatography analysis of bio-oil

[0135] The measurement results show that the number average molecular weight (Mn) of the bio-oil obtained in Example 1 is 306.04, and the weight average molecular weight (Mw) is 1287.98. The number average molecular weight (Mn) of the bio-oil obtained in the comparative example is 1295.90, and the weight average molecular weight (Mw) is 2936.47.

[0136] Analysis: A lower Mn value helps reduce the viscosity of bio-oil, making it easier to store and transport, while improving its combustion efficiency in the engine. A moderate Mw value means that the molecular weight distribution of organic compounds in bio-oil is more concentrated, which helps to maintain a higher calorific value, so that bio-oil can release more energy when used as fuel. Compared with the comparative example, Example 1 of the present invention has a lower number average molecular weight and more small molecular compounds, which helps to reduce the viscosity of bio-oil and improve its fluidity and combustion efficiency. Although it contains some high molecular weight compounds, the molecular weight distribution is generally more concentrated, which is more conducive to the combustion and emission characteristics of bio-oil.

[0137] 8. Infrared spectroscopy analysis

[0138] Measurement results: Infrared spectrum shows that the bio-oil obtained in Example 1 mainly contains functional groups such as CH, C=C, and CO.

[0139] Analysis: The functional group composition showed that bio-oil was mainly composed of hydrocarbons and oxygen-containing compounds and was suitable as a fuel.

[0140] 9. Gas Chromatography-Mass Spectrometry Analysis

[0141] The measurement results are shown in Table 1 below:

[0142] Table 1 Gas chromatography-mass spectrometry analysis results

[0143]

[0144] As can be seen from the above table, the bio-oil obtained in the embodiment of the present invention contains various types of compounds, including alcohols, aldehydes, ketones, esters, aromatic hydrocarbons, phenols, acids, hydrocarbons, nitrogen-containing compounds and sulfur-containing compounds. Among them, the content of aromatic compounds such as benzene is relatively high, reaching 15.6%, which helps to improve the combustion efficiency of the bio-oil. In addition, the content of acid compounds such as acetic acid is 6.3%, which helps to improve the combustion characteristics. The content of nitrogen-containing compounds and sulfur-containing compounds is relatively low, 1.2% and 0.5% respectively, which indicates that the emissions of nitrogen oxides and sulfides generated by the bio-oil during the combustion process may be low, which is beneficial to reducing environmental pollution. Therefore, the chemical composition of the bio-oil obtained in the embodiment of the present invention shows that it has the potential to be used as a fuel and may have good environmental friendliness during the combustion process.

[0145] From the above results, it can be seen that the bio-oil prepared by the synergistic hydrothermal liquefaction technology of the present invention not only exhibits good fluidity, but also has high calorific value, low solid insoluble content and good stability. These characteristics make the bio-oil have great potential for application as high-quality biofuel; the bio-oil has good fluidity, which means that it can flow smoothly during transportation and use, and will not cause blockage or inconvenience in use due to excessive viscosity. At the same time, the high calorific value indicates that the bio-oil can release more energy when burned, thereby improving the efficiency of fuel use. Low solid insoluble content means that no excessive residue and carbon deposits will be generated during use, which helps to extend the service life of equipment such as engines and reduce maintenance costs; good stability ensures that the bio-oil can still maintain its excellent performance during long-term storage and different environmental conditions, and will not deteriorate due to oxidation, hydrolysis or other chemical reactions. This stability is particularly important for the commercial application of biofuels, because it can ensure that the fuel maintains its quality during long-term storage and transportation, thereby meeting market demand.

[0146] In summary, the bio-oil prepared by the synergistic hydrothermal liquefaction technology of the present invention has excellent performance in terms of fluidity, calorific value, solid insoluble content and stability, making it have great potential for application as high-quality biofuel. This will not only help promote the development of renewable energy, but also make positive contributions to environmental protection and energy security.

[0147] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics, characterized in that: The following steps are involved: Mixing municipal sewage sludge with waste plastics, adding a catalyst, and performing a hydrothermal liquefaction reaction; The hydrothermal liquefaction product is subjected to solid-liquid separation, oil-water separation and purification treatment to obtain bio-oil.

2. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to claim 1, characterized in that: The municipal sludge is mixed with the waste plastics and then subjected to dehydration treatment; The moisture content after the dehydration treatment is 60-70%.

3. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to claim 1, characterized in that: The waste plastics also include crushing before use; The particle size after the pulverization process is below 5 mm.

4. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to claim 1, characterized in that: The weight ratio of the urban sludge to the waste plastic is 2 to 5:

1.

5. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to claim 1, characterized in that: The catalyst contains Na2CO3 and Co-Mo catalyst.

6. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to claim 5, characterized in that: The dosage of Na2CO3 is 3-8%.

7. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to claim 5, characterized in that: The usage of the Co-Mo catalyst is 3-8%.

8. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to claim 1, characterized in that: The temperature of the hydrothermal liquefaction reaction is 350-400°C; The hydrothermal liquefaction reaction time is 50 to 70 minutes; The pressure of the hydrothermal liquefaction reaction is 10-20 MPa.

9. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to claim 1, characterized in that: The solid phase separation is carried out by centrifugation; The rotation speed of the centrifugal treatment is 3000-8000 r / min; The centrifugal treatment time is 1 to 10 minutes.

10. The method for producing bio-oil by synergistic hydrothermal liquefaction of municipal sludge and waste plastics according to any one of claims 1 to 9, characterized in that: The purification process adopts supercritical CO2 extraction; The pressure of the supercritical CO2 extraction is 35-40MPa; The temperature of the supercritical CO2 extraction is 35-45°C; The supercritical CO2 extraction time is 100 to 150 minutes; The CO2 flow rate of the supercritical CO2 extraction is 2 to 3 SL / min.

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