A method for preparing a biological oil denitrification catalyst by using sewage sludge hydrothermal liquefaction residue

Abstract

The application discloses a method for preparing a biological oil denitrification catalyst by using sewage sludge hydrothermal liquefaction residues, and comprises the following steps: taking the solid-phase residues obtained by preparing biological oil through sludge hydrothermal liquefaction as raw materials, extracting metal elements in the solid-phase residues through a physical and chemical method, and constructing a metal nitrate / sulfate homogeneous catalyst of the metal elements. The method uses the solid-phase residues obtained by preparing biological oil through sludge hydrothermal liquefaction as raw materials to prepare a homogeneous catalyst, and uses the catalyst in a catalytic denitrification reaction process of sludge hydrothermal liquefaction biological oil, so that high-value utilization of the solid-phase products of sludge hydrothermal liquefaction is realized, and a new idea is provided for comprehensive treatment and disposal of sludge components.

Description

Technical Field

[0001] This invention relates to the fields of environmental protection and new energy technologies, and in particular to a method for preparing a bio-oil denitrification catalyst using wastewater sludge hydrothermal liquefaction residue. Background Technology

[0002] The preparation of bio-oil from sewage sludge using hydrothermal liquefaction technology is an important approach to achieving high-value utilization of sludge. It not only achieves the harmlessness and volume reduction of sewage sludge but also enables energy recovery in the form of bio-oil, thus attracting widespread attention from scholars both domestically and internationally. Sludge (dry basis) contains approximately 70% inorganic components. After hydrothermal liquefaction, organic matter is converted into bio-oil, while a large amount of inorganic components remain in the solid residue. Only a small amount of macromolecular organic matter undergoes polymerization to form the residue. With the enrichment of heavy metals in the solid phase, the treatment and disposal of the high-ash and high-heavy-metal content solid residue obtained after the reaction cannot be ignored. Currently, the utilization of solid residue from sludge hydrothermal liquefaction is very limited. Due to the dense structure of sludge, the pore structure and specific surface area of ​​its solid residue are unsuitable for use as biochar or other methods. Furthermore, the solid residue contains a large amount of heavy metals, and direct utilization poses certain environmental risks. Therefore, further development of sludge hydrothermal liquefaction urgently requires safer and more resource-efficient solid residue treatment and disposal methods.

[0003] The heavy metal content in the solid residue after hydrothermal liquefaction of sludge, from highest to lowest, is Zn, Cu, Cr, Pb, and Cd, and it also contains large amounts of Fe, Al, and Mg. Studies have shown that some metal elements have a significant positive catalytic effect during hydrothermal liquefaction. For example, the presence of Zn helps reduce the O content in bio-oil and increases its calorific value. During the hydrothermal carbonization of sludge, Fe(NO3)3 can significantly reduce TOC, NH3-N, and TN in the liquid phase products and increase the enrichment of C, H, and O in the solid phase products. CuSO4 not only increases the relative content of light components in bio-oil but also improves its yield and energy recovery rate; furthermore, CuSO4 can significantly reduce the content of pollutants such as S and N in bio-oil. Similarly, heavy metal chlorides also improve the yield and calorific value of bio-oil to varying degrees. In summary, various metal salts may exhibit varying degrees of positive catalytic effects in the process of preparing bio-oil from biomass through hydrothermal liquefaction. Therefore, it is of great significance to extract the metal elements contained in sludge residue and change their form to give them catalytic efficacy and use them to improve the quality of bio-oil.

[0004] The journal *Molecular Catalysis*, Volume 514, September 2021, publication number 111823, "Fe(NO3)3 assisted hydrothermal carbonization of sewage sludge: Focusing on characteristics of hydro-char and aqueous phase," proposes a method for the hydrothermal carbonization of sewage sludge catalyzed by Fe(NO3)3: (1) 20 g of sewage sludge and 20 mL of distilled water are added to a stainless steel high-pressure reactor, and 5% and 15% of Fe(NO3)3 are mixed evenly, respectively, and kept at 180-240 °C for 60 min; (2) After the reaction time is completed, the mixture is cooled to room temperature, and the product is separated by vacuum filtration; (3) The solid residue is placed in an oven at 105 °C for 24 h to remove moisture. This method yields a liquid phase product with lower nitrogen content, demonstrating that Fe(NO3)3 can effectively play a role in the hydrothermal liquefaction of sewage sludge.

[0005] Chinese patent CN202210596771.6 discloses a method for preparing a cold-rolled sludge catalyst: (1) cold-rolled sludge is ground to a particle size of less than 200 mesh to obtain cold-rolled sludge powder; (2) the cold-rolled sludge powder is mixed evenly with deionized water and stirred at a temperature of 50-70℃ for 1-2 hours to obtain a suspension; (3) the suspension is filtered, the filter cake is washed with deionized water, dried, and then heated at a constant temperature to 300-600℃ and calcined at a constant temperature for 3-7 hours to obtain powder A; (4) powder A is added to an equal volume of sulfuric acid solution and ultrasonically etched for 1-3 hours to obtain slurry B; (5) slurry B is dried, and then heated at a constant temperature to 300-600℃ and calcined at a constant temperature for 3-7 hours to obtain powder C; (6) active components are added to powder C and mixed evenly to obtain a mixture. After the mixture is formed, it is calcined at a temperature of 400-600℃ for 3-5 hours to obtain the cold-rolled sludge catalyst. This method utilizes cold-rolled sludge containing metals such as Fe, Mn, and Ca to prepare SCR denitrification catalysts. Although the raw materials are different from sludge hydrothermal liquefaction residues, it demonstrates that sludge-based mixed metal catalysts have high catalytic performance.

[0006] Resource utilization of sludge hydrothermal liquefaction residue is of great significance for improving the overall conversion efficiency of sludge. The two technologies mentioned above have respectively demonstrated the positive catalytic effect of metal salt catalysts on bio-oil reforming and the feasibility of extracting multiple metal elements from sludge and preparing catalysts. Summary of the Invention

[0007] In view of this, the present invention discloses a method for preparing a bio-oil denitrification catalyst using the residue from hydrothermal liquefaction of sewage sludge. The catalyst obtained by this method is used in the catalytic denitrification reaction process of bio-oil from hydrothermal liquefaction of sludge, realizing the high-value utilization of the solid products from hydrothermal liquefaction of sludge.

[0008] The technical solution provided by this invention is specifically a method for preparing a bio-oil denitrification catalyst using wastewater sludge hydrothermal liquefaction residue, comprising: using the solid residue obtained from preparing bio-oil by sludge hydrothermal liquefaction as raw material, extracting the metal elements therein by physicochemical methods, and constructing a metal nitrate / sulfate homogeneous catalyst of the metal elements.

[0009] Specifically, the above methods include:

[0010] Step 1: Remove organic components from the dried solid residue;

[0011] Step 2: Add excess dilute H2SO4 to the residue obtained in Step 1 and stir thoroughly to dissolve the metal ions in the residue into the liquid phase, wherein the concentration of dilute H2SO4 is 1-5 mol / L;

[0012] Step 3: After solid-liquid separation, the product obtained in Step 2 is retained in liquid phase;

[0013] Step 4: Add excess NaOH solution to the liquid phase to convert the metal ions in the liquid phase into precipitate. After adding NaOH solution until no new precipitate is formed, separate the precipitate from the liquid phase using a centrifuge and retain the precipitate.

[0014] Step 5: Repeatedly add deionized water to the precipitate, wash the precipitate three times, centrifuge to remove excess Na2SO4, and dry the final solid phase in an oven at 105℃.

[0015] Step 6: Grind all the dried solid blocks into powder and sieve.

[0016] Step 7: Place the powder in a colorimetric tube, add HNO3 and shake until the solid is completely dissolved. The resulting solution is a 5% nitrate catalyst.

[0017] Step 8: Place the powder in a colorimetric tube, add H2SO4, and shake until the solid is completely dissolved. The resulting solution is a 5% sulfate catalyst.

[0018] Specifically, step 1 involves placing the dried solid residue in a muffle furnace and calcining it at 600°C for 3 hours to remove the organic components from the residue.

[0019] Specifically, the catalyst is used in the catalytic denitrification of bio-oil.

[0020] Specifically, the application of the catalyst in the catalytic denitrification of bio-oil includes the following steps:

[0021] Step 1: Weigh out the bio-oil and solvent separately, mix them with 5% and 10% of the catalyst respectively, and pour them into a stainless steel high-pressure reactor;

[0022] Step 2: Check the airtightness of the device, the circuit and pipelines for unobstructed flow. After confirming that the above conditions are good, introduce N2 into the reactor and keep it for 2 minutes to replace the air in the reactor. After the gas replacement is completed, close the gas valve and open the agitator cooling water valve.

[0023] Step 3: Turn on the computer program controlling the reactor, set the reactor temperature to 260℃, set the stirrer speed to 50r / min, and set the residence time to 30min after reaching the target temperature;

[0024] Step 4: After the reaction is complete, use a fan to lower the temperature inside the reactor to room temperature, then open the exhaust valve and purge the reactor with N2 until the 1L gas bag is full.

[0025] Step 5: After pouring out the product, wash the inner wall of the reactor three times with acetone; filter the washing liquid and the product together under vacuum; evaporate the obtained filtrate under reduced pressure to remove acetone and ethanol, and the remaining brown viscous liquid is the oil phase product; place the remaining black solid on the filter paper into an oven to dry and obtain the solid phase product.

[0026] The solvent in step 1 of the application is ethanol.

[0027] This invention provides a method for preparing bio-oil denitrification catalysts using wastewater sludge hydrothermal liquefaction residue. This method utilizes the fact that the wastewater sludge hydrothermal liquefaction residue contains a certain amount of heavy metals. Using the solid residue obtained from the preparation of bio-oil by wastewater hydrothermal liquefaction as raw material, the metal elements are extracted through physicochemical methods, and sulfate and nitrate catalysts are constructed. After extracting the metal elements through this method, not only is the resource utilization of metals realized, but the environmental risk of the residue can also be effectively reduced. It has the advantages of being renewable, economical and environmentally friendly.

[0028] Furthermore, the method provided by this invention also improves the comprehensive utilization efficiency of organic and inorganic components of municipal sludge, and provides a new approach for improving the sludge hydrothermal liquefaction reaction system and promoting large-scale development.

[0029] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the disclosure of the present invention. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a flowchart of a method for preparing a bio-oil denitrification catalyst using wastewater sludge hydrothermal liquefaction residue, as disclosed in an embodiment of the present invention. Detailed Implementation

[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of systems consistent with some aspects of the invention as detailed in the appended claims.

[0034] This implementation scheme extracts metal elements such as Fe, Mn, Al, Zn and Cu from the solid residue of sludge hydrothermal liquefaction, prepares a metal nitrate / sulfate homogeneous catalyst, and uses it in the catalytic conversion reaction process of sludge hydrothermal liquefaction bio-oil. It can reduce the nitrogen content of bio-oil and promote the hydrodeoxygenation of bio-oil, realizing the high-value utilization of solid products from sludge hydrothermal liquefaction.

[0035] This implementation plan includes the following steps:

[0036] Step 1: Place the dried solid residue in a muffle furnace and calcine at 600°C for 3 hours to remove the organic components from the residue;

[0037] Step 2: After the residue cools to room temperature, the metal in the residue mainly exists in the form of oxides. Add excess dilute H2SO4 (1-5 mol / L) to the residue and stir thoroughly to dissolve the metal ions in the residue into the liquid phase.

[0038] Step 3: Separate the solid and liquid phases by vacuum filtration, retaining the liquid phase;

[0039] Step 4: Add excess NaOH solution to the liquid phase to convert metal ions such as Fe, Al, Mg, Zn and Cu in the liquid phase into precipitates. After adding NaOH solution until no new precipitate is formed, separate the precipitate from the liquid phase using a centrifuge and retain the precipitate.

[0040] Step 5: Repeatedly add deionized water to the precipitate, wash the precipitate three times, centrifuge to remove excess Na2SO4, and dry the final solid phase in an oven at 105℃.

[0041] Step 6: Grind all the solid blocks into powder using a mortar and pestle, and then pass the powder through a 200-mesh sieve;

[0042] Step 7: Take 0.3252g of powder and place it in a colorimetric tube. Add 0.18mL of HNO3 and shake until the solid is completely dissolved. The resulting solution is a 5% nitrate catalyst (containing Fe(NO3)3, Al(NO3)3, Mg(NO3)2, Zn(NO3)2 and Cu(NO3)2, etc.).

[0043] Step 8: Place 0.3252g of powder in a colorimetric tube, add 0.28mL of H2SO4, and shake until the solid is completely dissolved. The resulting solution is a 5% sulfate catalyst (containing Fe2(SO4)3, Al2(SO4)3, MgSO4, ZnSO4, and CuSO4, etc.).

[0044] The application of the above catalysts in the catalytic denitrification process of bio-oil includes:

[0045] Step 1: Weigh 2g of raw material and 20g of solvent respectively, mix them with 5% and 10% of catalyst respectively, and pour them into a 100mL stainless steel high-pressure reactor; the raw material is the hydrothermal liquefaction product of sludge, and the solvent is ethanol.

[0046] Step 2: Check the airtightness of the device, the circuit and pipelines for unobstructed flow. After confirming that the above conditions are good, introduce N2 into the reactor and keep it for 2 minutes to replace the air in the reactor. After the gas replacement is completed, close the gas valve and open the agitator cooling water valve.

[0047] Step 3: Turn on the computer program controlling the reactor, set the reactor temperature to 260℃, set the stirrer speed to 50r / min, and set the residence time to 30min after reaching the target temperature;

[0048] Step 4: After the reaction is complete, use a fan to lower the temperature inside the reactor to room temperature, then open the exhaust valve and purge the reactor with N2 until the 1L gas bag is full.

[0049] Step 5: After pouring out the product, wash the inner wall of the reactor three times with acetone; filter the washing liquid and the product together under vacuum; evaporate the obtained filtrate at 58°C under reduced pressure to remove acetone and ethanol, and the remaining brown viscous liquid is the oil phase product; the black solid remaining on the filter paper is placed in an oven at 105°C and dried for 24 hours to obtain the solid phase product.

[0050] The acetone and ethanol used in this implementation plan are all analytical grade, and the NaOH, HNO3, and H2SO4 are of superior grade; the N2 is high-purity N2. The aforementioned bio-oil is a product of sludge hydrothermal liquefaction.

[0051] The renewable metal nitrate catalyst prepared in this embodiment exhibits good catalytic performance in the catalytic denitrification process of bio-oil, reducing the nitrogen content in bio-oil by 32%, and has the same denitrification effect as other precious metal catalysts.

[0052] Example 1:

[0053] 2g of bio-oil (calorific value 27.17 MJ / kg, nitrogen content 2.4%) was weighed and mixed with 20g of anhydrous ethanol and 5% metal sulfate, then poured into a reactor. The reactor was purged with N2 for 2 minutes to replace the air inside; the reactor temperature was set to 260℃, the stirrer speed to 50 rpm, and the residence time to 30 minutes. After the reaction, the reactor was cooled to room temperature with a fan, the exhaust valve was opened, and the reactor was purged with N2 until a 1L gas bag was filled; the product was poured out, and the inner wall of the reactor was washed three times with acetone; the washing liquid and the product were vacuum filtered together; the filtrate was evaporated under reduced pressure at 58℃ to remove acetone and ethanol, and the remaining brown viscous liquid was the oil phase product; the black solid remaining on the filter paper was dried in an oven at 105℃ for 24 hours to obtain the solid phase product. In this reaction, the bio-oil had a calorific value of 37.13 MJ / kg, an H / C ratio of 0.12, and a nitrogen content of 1.51%.

[0054] Example 2:

[0055] 2g of bio-oil (calorific value 27.17 MJ / kg, nitrogen content 2.4%) was weighed and mixed with 20g of anhydrous ethanol and 10% metal sulfate, then poured into a reactor. The reactor was purged with N2 for 2 minutes to replace the air inside; the reactor temperature was set to 260℃, the stirrer speed was 50 rpm, and the residence time was 30 minutes. After the reaction, the reactor was cooled to room temperature with a fan, the exhaust valve was opened, and the reactor was purged with N2 until a 1L gas bag was filled; the product was poured out, and the inner wall of the reactor was washed three times with acetone; the washing liquid and the product were vacuum filtered together; the filtrate was evaporated under reduced pressure at 58℃ to remove acetone and ethanol, and the remaining brown viscous liquid was the oil phase product; the black solid remaining on the filter paper was dried in an oven at 105℃ for 24 hours to obtain the solid phase product. In this reaction, the bio-oil had a calorific value of 37.52 MJ / kg, an H / C ratio of 0.12, and a nitrogen content of 1.50%.

[0056] Example 3:

[0057] 2g of bio-oil (calorific value 27.17 MJ / kg, nitrogen content 2.4%) was weighed and mixed with 20g of anhydrous ethanol and 5% nitrate, then poured into a reactor. The reactor was purged with N2 for 2 minutes to replace the air inside; the reactor temperature was set to 260℃, the stirrer speed to 50 rpm, and the residence time to 30 minutes. After the reaction, the reactor was cooled to room temperature with a fan, the exhaust valve was opened, and the reactor was purged with N2 until a 1L gas bag was filled; the product was poured out, and the inner wall of the reactor was washed three times with acetone; the washing liquid and the product were vacuum filtered together; the filtrate was evaporated under reduced pressure at 58℃ to remove acetone and ethanol, and the remaining brown viscous liquid was the oil phase product; the black solid remaining on the filter paper was dried in an oven at 105℃ for 24 hours to obtain the solid phase product. In this reaction, the bio-oil had a calorific value of 39.29 MJ / kg, an H / C ratio of 0.13, and a nitrogen content of 1.10%.

[0058] Example 4:

[0059] 2g of bio-oil (calorific value 27.17 MJ / kg, nitrogen content 2.4%) was weighed and mixed with 20g of anhydrous ethanol and 10% nitrate, then poured into a reactor. The reactor was purged with N2 for 2 minutes to replace the air inside; the reactor temperature was set to 260℃, the stirrer speed to 50 rpm, and the residence time to 30 minutes. After the reaction, the reactor was cooled to room temperature with a fan, the exhaust valve was opened, and the reactor was purged with N2 until a 1L gas bag was filled; the product was poured out, and the inner wall of the reactor was washed three times with acetone; the washing liquid and the product were vacuum filtered together; the filtrate was evaporated under reduced pressure at 58℃ to remove acetone and ethanol, and the remaining brown viscous liquid was the oil phase product; the black solid remaining on the filter paper was dried in an oven at 105℃ for 24 hours to obtain the solid phase product. In this reaction, the bio-oil had a calorific value of 38.83 MJ / kg, an H / C ratio of 0.13, and a nitrogen content of 1.34%.

[0060] In summary, after adding nitrate catalysts, the metal elements in the catalyst will undergo chelation and precipitation reactions with nitrogen, becoming fixed in the solid residue; secondly, the nitrogen in bio-oil may also be released as NH4+. + The nitrogen (N) in the bio-oil can be partially removed by reacting with HNO3 free radicals in the form of NH3. Furthermore, ethanol, as a solvent, acts as a hydrogen donor in the upgrading reaction, providing a hydrogen source for the hydrodeoxygenation process of the bio-oil. Therefore, the calorific value of the reformed bio-oil is significantly increased, and the nitrogen content is significantly decreased. This demonstrates that the method of extracting metal elements from the hydrothermal liquefaction residue of sludge to prepare a catalyst for upgrading bio-oil is highly effective.

[0061] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims.

Claims

1. A method for preparing a bio-oil denitrification catalyst using wastewater sludge hydrothermal liquefaction residue, characterized in that, include: Using the solid residue obtained from the hydrothermal liquefaction of sludge to prepare bio-oil as raw material, metal elements are extracted from it by physicochemical methods, and a homogeneous catalyst of metal nitrate / sulfate of the metal elements is constructed. Specifically, it includes: Step 1: Remove organic components from the dried solid residue; Step 2: Add excess dilute H2SO4 to the residue obtained in Step 1 and stir thoroughly to dissolve the metal ions in the residue into the liquid phase, wherein the concentration of dilute H2SO4 is 1-5 mol / L; Step 3: After solid-liquid separation, the product obtained in Step 2 is retained in liquid phase; Step 4: Add excess NaOH solution to the liquid phase to convert the metal ions in the liquid phase into precipitate. After adding NaOH solution until no new precipitate is formed, separate the precipitate from the liquid phase using a centrifuge and retain the precipitate. Step 5: Repeatedly add deionized water to the precipitate, wash the precipitate three times, centrifuge to remove excess Na2SO4, and dry the final solid phase in an oven at 105 ℃. Step 6: Grind all the dried solid blocks into powder and sieve. Step 7: Place the powder in a colorimetric tube, add HNO3 and shake until the solid is completely dissolved. The resulting solution is a 5% nitrate catalyst. Step 8: Place the powder in a colorimetric tube, add H2SO4, and shake until the solid is completely dissolved. The resulting solution is a 5% sulfate catalyst.

2. The method for preparing a bio-oil denitrification catalyst using wastewater sludge hydrothermal liquefaction residue according to claim 1, characterized in that, Step 1: Place the dried solid residue in a muffle furnace and calcine at 600 °C for 3 h to remove the organic components in the residue.

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