Preparation method and application of sludge liquefaction catalyst

Abstract

The application discloses a preparation method of a sludge liquefaction catalyst, and particularly relates to the following steps: sealing dry municipal sludge and anhydrous ethanol in a high-pressure reaction kettle, carrying out a liquefaction reaction under supercritical conditions in a nitrogen atmosphere, cooling to room temperature after the reaction, carrying out solid-liquid separation on a reaction product to obtain a solid-phase product, washing and drying the solid-phase product, calcining the solid-phase product under a nitrogen atmosphere to obtain the sludge liquefaction catalyst, or adding the calcined product into a saturated alkali solution for impregnation and stirring, carrying out solid-liquid separation, and drying and calcining the solid phase to obtain the sludge liquefaction catalyst; and applying the sludge liquefaction catalyst to catalytic municipal sludge supercritical liquefaction for preparing bio-oil. Experimental results show that the catalyst can improve the yield and quality of bio-oil produced by sludge liquefaction, reduce the cost of catalyst preparation, recycle the solid-phase product of sludge liquefaction, expand the technical route of sludge energy utilization, and has important economic, environmental and social benefits.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sludge utilization, and particularly relates to a preparation method and application of a catalyst for improving the quality of sludge supercritical liquefaction bio-oil. BACKGROUND

[0002] With the expansion of the city scale in China, the amount of municipal sludge produced by treating urban wastewater through the activated sludge method is increasing, and the sludge treatment pressure is increasing. The municipal sludge not only has a high water content and is easy to rot and emit odor, but also has a complex composition structure and contains harmful components such as pathogenic bacteria, heavy metals, refractory organic matter and microplastics. This will seriously harm the ecological system of the earth and even endanger people's health.

[0003] As a biomass with a huge output, the municipal sludge contains not only a large amount of inorganic matter, but also a certain amount of organic matter such as polysaccharides, proteins, lipids and nucleic acid substances, and is a potential energy resource. With the shortage of liquid fuel, countries around the world are working hard to develop sludge energy treatment methods based on the principle of sludge three-treatment, such as thermal chemical conversion technologies for preparing biofuels through sludge pyrolysis, gasification and hydrothermal liquefaction. Both pyrolysis and gasification need to consume heat to treat the water content in the sludge. Sludge supercritical liquefaction can convert macromolecular organic matter such as proteins, lipids and sugars in the sludge into solid, liquid and non-condensable gas phases under the action of water or other solvents.

[0004] The yield of bio-oil is generally between 10% and 48%, and the catalyst is the most significant factor affecting the yield of bio-oil. The addition of a catalyst not only can appropriately reduce the activation energy required for the reaction, improve the conversion efficiency, but also can promote sludge degradation, inhibit side reactions such as polycondensation and re-aggregation to reduce the generation of solid residues and improve the quality of bio-oil. The catalysts are divided into homogeneous catalysts and heterogeneous catalysts. The homogeneous catalysts are difficult to recover and have corrosivity that can damage the reaction kettle equipment, thus limiting their application and development. The heterogeneous catalysts include elemental metals and oxides, supported catalysts and molecular sieve catalysts, which synergistically catalyze through porous active sites to improve the quality of bio-oil. However, the carrier raw material needs a certain cost, and therefore a carrier with low cost and rich porosity is needed to improve the quality of sludge supercritical liquefaction bio-oil. SUMMARY

[0005] The application provides a preparation method of a sludge liquefaction catalyst to reduce the cost of the catalyst carrier and realize the recycling of the solid phase product of sludge supercritical liquefaction. The sludge liquefaction catalyst provided by the application is a solid phase product of sludge supercritical liquefaction, or a catalyst with the solid phase product of sludge supercritical liquefaction as a carrier and further loaded with an alkali. The catalyst improves the quality of bio-oil produced by sludge supercritical liquefaction, reduces the preparation cost of the catalyst, and recycles the solid phase product of sludge liquefaction.

[0006] To achieve the above-mentioned purposes of the application, the present application provides the following technical solutions:

[0007] 1. Preparation of sludge liquefaction catalyst

[0008] (1) Dry municipal sludge is placed in a high-pressure reaction kettle and anhydrous ethanol is added as a solvent, sealed, and nitrogen is introduced to replace the air in the kettle. The liquefaction reaction is carried out under a nitrogen atmosphere and supercritical conditions. After the reaction is completed, heating is stopped, and the kettle body is cooled to room temperature. After the gas in the reaction kettle is emptied, the reaction kettle is opened, and the reaction product is taken out for solid-liquid separation. The solid phase is washed and dried, and then calcined under a nitrogen atmosphere to obtain a sludge liquefaction catalyst;

[0009] The municipal sludge is dried and crushed to a powder of 100-120 mesh at 100-110°C, and the solid phase product is washed with anhydrous ethanol and pure water in sequence;

[0010] The calcined product can also be added to a saturated alkali solution for immersion and stirring, solid-liquid separation, and drying and calcination of the solid phase to obtain a sludge liquefaction catalyst. The alkali is Na2CO3;

[0011] The supercritical conditions are 290-300°C, 10.94-11.84 MPa, and the liquefaction time is 30-45 min;

[0012] In the above method, the drying temperature is 105-110°C, and the time is 24-48 h; the calcination temperature is 600-700°C, and the calcination time is 3-5 h;

[0013] (2) The sludge liquefaction catalyst prepared by the above method is applied in the catalytic sludge supercritical liquefaction for preparing bio-oil, and the results show that the former catalyst increases the calorific value of bio-oil by 3.09±0.03% and the yield by 1.495±0.165%; the supported catalyst increases the calorific value of bio-oil by 10.86±0.81% and the yield by 24.115±2.955%.

[0014] Advantages and technical effects of the present application:

[0015] The sludge liquefaction catalyst provided by the present application uses municipal sludge as a raw material to prepare a solid phase product under supercritical conditions. The solid phase product has abundant porosity and a large specific surface area, which can improve the yield and quality of bio-oil in subsequent catalytic applications. The catalyst prepared by loading alkali on the solid phase product as a carrier can further improve the yield and quality of bio-oil produced by sludge liquefaction, reducing the preparation cost of the catalyst. The sludge liquefaction solid phase product is recycled, effectively reducing the content of O, N, and S elements in the sludge, expanding the technical approach of sludge energy utilization, and having important economic, environmental, and social benefits. DETAILED DESCRIPTION

[0016] The present application is further illustrated by the following examples, but the scope of the present application is not limited to the following examples, the methods in the examples are all conventional methods unless otherwise specified, and the reagents used are all conventional commercially available reagents or reagents prepared by conventional methods unless otherwise specified;

[0017] The elemental composition of the municipal sludge used in the following examples is shown in the following table:

[0018] Example 1

[0019] After mixing 12 g of dried municipal sludge (100-120 mesh) and 150 mL of anhydrous ethanol, pour them into a 500 mL high-pressure reaction kettle. Continuously introduce nitrogen into the reaction kettle until the pressure in the kettle reaches 0.2 MPa to replace the air in the kettle. Repeat 3 times, then close the outlet valve and inlet valve in turn, open the cooling water and magnetic stirrer, stir at 200 rmp / min, install the electric heating jacket and connect the temperature sensor, heat to 300℃ at a heating rate of 5℃ / min, and stay at 300℃ and 11.84 MPa for 30 min. Then open the cooling water to cool to room temperature. Use a wrench to gradually remove the bolts on the reaction kettle, open the reaction kettle, transfer the liquefied product in the kettle to a 1000 mL beaker, repeatedly clean the reaction kettle pipeline and the inside of the kettle with anhydrous ethanol, and transfer the cleaning liquid to the liquefied product. Use a circulating water pump and a filtration device to separate the liquefied product into solid and liquid. The solid is the solid-phase product. The solid-phase product is washed with anhydrous ethanol for 3 min and then with pure water for 5 min. After drying in a 105℃ oven for 48 h, place it in a tube furnace and treat it at 600℃ under nitrogen protection for 5 h to obtain a sludge liquefaction catalyst. The porosity analysis data of the catalyst are shown in the following table:

[0020] Example 2

[0021] After 12 g of dried municipal sludge (100-120 mesh) and 150 mL of anhydrous ethanol were mixed, they were poured into a 500 mL high-pressure reaction kettle. Nitrogen was continuously introduced into the reaction kettle until the pressure in the kettle was 0.3 MPa to replace the air in the kettle. After repeating three times, the outlet valve and the inlet valve were closed in turn, the cooling water and the magnetic stirrer were turned on, the stirring speed was 250 rpm, the electric heating jacket was installed and connected to the temperature sensor, the heating rate was 5 ℃ / min, the temperature was heated to 290 ℃, and the pressure was 10.94 MPa. After staying for 45 min, the cooling water was turned on to cool to room temperature. The bolts on the reaction kettle were gradually removed using a wrench, the reaction kettle was opened, the liquefied product in the kettle was transferred to a 1000 mL beaker, the reaction kettle pipeline and the kettle body were repeatedly cleaned with anhydrous ethanol, and the cleaning liquid was transferred to the liquefied product. The liquefied product was subjected to solid-liquid separation using a circulating water pump and a filtration device. The solid was the solid-phase product. The solid-phase product was washed in anhydrous ethanol for 1 min, then washed with pure water for 4 min, dried in an oven at 110 ℃ for 24 h, and then treated at 700 ℃ for 3 h under nitrogen protection in a tube furnace to obtain a sludge liquefaction catalyst. Example 3

[0022] After 12 g of dried municipal sludge (100-120 mesh) and 150 mL of anhydrous ethanol were mixed, they were poured into a 500 mL high-pressure reaction kettle. Nitrogen was continuously introduced into the reaction kettle until the pressure in the kettle was 0.3 MPa to replace the air in the kettle. After repeating three times, the outlet valve and the inlet valve were closed in turn, the cooling water and the magnetic stirrer were turned on, the stirring speed was 250 rpm, the electric heating jacket was installed and connected to the temperature sensor, the heating rate was 5 ℃ / min, the temperature was heated to 290 ℃, and the pressure was 10.94 MPa. After staying for 45 min, the cooling water was turned on to cool to room temperature. The bolts on the reaction kettle were gradually removed using a wrench, the reaction kettle was opened, the liquefied product in the kettle was transferred to a 1000 mL beaker, the reaction kettle pipeline and the kettle body were repeatedly cleaned with anhydrous ethanol, and the cleaning liquid was transferred to the liquefied product. The liquefied product was subjected to solid-liquid separation using a circulating water pump and a filtration device. The solid was the solid-phase product. The solid-phase product was washed in anhydrous ethanol for 1 min, then washed with pure water for 4 min, dried in an oven at 110 ℃ for 24 h, and then treated at 700 ℃ for 3 h under nitrogen protection in a tube furnace to obtain a sludge liquefaction catalyst. Example 4

[0023] After 12 g of dried municipal sludge (100-120 mesh) and 150 mL of anhydrous ethanol were mixed, they were poured into a 500 mL high-pressure reaction kettle. The reaction kettle was continuously purged with nitrogen until the pressure in the kettle reached 0.3 MPa to replace the air in the kettle. After repeating this process three times, the outlet valve and the inlet valve were closed in turn, the cooling water and the magnetic stirrer were turned on at 250 rpm / min, the electric heating jacket was installed and connected to the temperature sensor, and the temperature was raised to 290°C at a rate of 5°C / min. After staying at 290°C and 10.94 MPa for 45 min, the cooling water was turned on to cool to room temperature. The bolts on the reaction kettle were gradually removed using a wrench, the reaction kettle was opened, and the liquefied product in the kettle was transferred to a 1000 mL beaker. The reaction kettle lines and the kettle body were repeatedly cleaned with anhydrous ethanol, and the cleaning liquid was transferred to the liquefied product. The liquefied product was separated by solid-liquid separation using a circulating water pump and a filtration device. The solid phase product was washed in anhydrous ethanol for 1 min and then in pure water for 4 min. After drying in an oven at 110°C for 24 h, the product was calcined at 700°C for 3 h under nitrogen protection in a tube furnace. The calcined product was added to a saturated Na2CO3 solution and stirred at room temperature and 500 rpm / min for 15 h. After filtration, the solid was dried at 110°C for 24 h and then calcined at 700°C for 3 h in a muffle furnace to obtain a sludge liquefaction catalyst.

[0024] The liquefaction reaction of municipal sludge was carried out under supercritical conditions of 300°C and 11.84 MPa. 12 g of dried municipal sludge was mixed with 150 mL of anhydrous ethanol and placed in a high-pressure reaction kettle. 0.6 g of the catalyst prepared in Examples 1-4 was added, and the reaction was carried out under a nitrogen atmosphere for 30 min. The catalytic effect of each catalyst was tested, and the test results are shown in the table below:

[0025]

[0026] Elemental composition of bio-oil

[0027]

[0028] From the results of the catalytic effect, it can be seen that in Examples 1-2, the O element content of the bio-oil decreased by 3.04±0.01%, the N element content decreased by 3.96±0.71%, the S element content decreased by 5.56%, the heat value of the bio-oil increased by 3.09±0.03%, and the yield increased by 1.495±0.165%; in Examples 3-4, the O element content of the bio-oil decreased by 13.81±0.27%, the N element content decreased by 22.66±1.12%, the S element content decreased by 16.67%, the heat value of the bio-oil increased by 10.86±0.81%, and the yield increased by 24.115±2.955%.

Claims

1. Application of a sludge liquefaction catalyst in catalytic supercritical liquefaction of municipal sludge to prepare bio-oil, characterized in that: the sludge liquefaction catalyst is prepared by sealing dry municipal sludge and anhydrous ethanol in a high-pressure reactor, conducting a liquefaction reaction under supercritical conditions in a nitrogen atmosphere, cooling to room temperature after the reaction, and then separating the solid and liquid phases to obtain a solid-phase product, which is washed and dried, calcined in a nitrogen atmosphere, impregnated and stirred in a saturated alkali solution after calcination, and then separated and dried and calcined to obtain the sludge liquefaction catalyst. The supercritical conditions are 290-300℃ and 10.94-11.84MPa, the calcination temperature is 600-700℃, and the calcination time is 3-5h. The solid-phase product is sequentially washed with anhydrous ethanol and pure water, and dried at a temperature of 105-110℃ for 24-48h.

2. Use according to claim 1, characterized in that: ​

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