Preparation method and application of MOF-biochar modified activated carbon

Abstract

This invention discloses a method for preparing MOF-biocarbon modified activated carbon and its application, comprising: drying columnar activated carbon; preparing biocarbon by pulverizing and carbonizing biomass raw materials, followed by acidification to obtain acidified biocarbon with oxygen-containing functional groups on the surface; subjecting the pretreated activated carbon to steam-carbon dioxide composite activation to obtain activated activated carbon; using zirconium tetrachloride as a metal source, terephthalic acid as an organic ligand, and DMF as a solvent, mixing and stirring to obtain a MOF precursor solution; mixing the acidified biocarbon and activated activated carbon, adding the MOF precursor solution, and performing hydrothermal synthesis to allow MOF crystals to grow in situ on the surface of biocarbon and inside the pores of activated carbon to obtain a composite intermediate; washing and drying the composite intermediate, then calcining it with a gradient temperature increase, and cooling to obtain a MOF-biocarbon modified activated carbon with ultra-high specific surface area, excellent adsorption capacity for macromolecular hydrocarbons, excellent mechanical strength, and outstanding cycle stability. The MOF-biocarbon modified activated carbon is suitable for oil and gas recovery.

Description

Technical Field

[0001] This invention relates to the field of activated carbon oil and gas adsorption and separation environmental protection materials technology, specifically to a method for preparing MOF-biocarbon modified activated carbon and its application in oil and gas recovery processes. Background Technology

[0002] Oil and gas recovery is a key environmental protection process in industries such as petroleum refining, oil depot storage and transportation, and gas stations. Activated carbon is the mainstream adsorption material in oil and gas recovery processes due to its well-developed pores, low cost, and readily available raw materials. Currently, the specific surface area of ​​commercially available conventional activated carbon is generally 800-1000 m² / g, which has obvious technical defects in practical oil and gas recovery applications: First, its pore structure is simple, mainly micropores, with a very low proportion of mesopores and macropores, resulting in poor adsorption and retention capacity for large long-chain hydrocarbons in crude oil. Large hydrocarbon molecules can easily penetrate the adsorption layer, leading to a low oil and gas recovery purification rate. Second, the material has weak mechanical strength. During the adsorption-high-temperature desorption regeneration cycle, activated carbon particles are easily broken and pulverized, causing increased pressure drop in the adsorption tower and pipeline blockage. Third, the pores are easily blocked by oil and gas colloids and heavy hydrocarbons, making regeneration difficult and shortening the cycle life. Fourth, the adsorption capacity is limited. Conventional activated carbon has a low saturated adsorption capacity for oil and gas, requiring frequent replacement of the adsorbent by enterprises, resulting in high operating costs.

[0003] Therefore, developing a MOF-biocarbon modified activated carbon preparation technology that can optimize pore structure, increase specific surface area, enhance mechanical properties, and adapt to the adsorption of macromolecular hydrocarbons is of great engineering application value. This technology can solve the industry pain points of existing oil and gas recovery adsorption materials, such as low adsorption capacity, poor adsorption of macromolecular hydrocarbons, easy breakage during regeneration, and short lifespan. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing MOF-biocarbon modified activated carbon and its application, resulting in MOF-biocarbon modified activated carbon that possesses ultra-high specific surface area, excellent macromolecular hydrocarbon adsorption capacity, superior mechanical strength, and outstanding cycle stability.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing MOF-biocarbon modified activated carbon, comprising the following steps: S1. Raw material pretreatment: The columnar activated carbon is dried; the biomass raw material is crushed and carbonized to prepare biochar, and then acidified with dilute nitric acid to obtain acidified biochar with oxygen-containing functional groups on the surface; the biomass raw material is either straw or coconut shell. S2. Activated carbon activation: The pretreated activated carbon is activated by steam-carbon dioxide composite activation at 800-900℃ under an inert atmosphere to obtain activated activated carbon. S3. Preparation of MOF precursor solution: Using zirconium tetrachloride as the metal source, terephthalic acid as the organic ligand, and DMF as the solvent, the MOF precursor solution was obtained by mixing and stirring. S4. Composite: Acidified biochar and activated carbon are mixed in proportion, MOF precursor solution is added, and hydrothermal synthesis is carried out at 120-150℃, so that MOF crystals grow in situ on the surface of biochar and inside the pores of activated carbon to obtain composite intermediate. S5. Post-processing: After washing and drying the composite intermediate, it is calcined under an inert atmosphere with a gradient heating. After cooling, MOF-biocarbon modified activated carbon is obtained.

[0006] Furthermore, in step S1, the acidification treatment uses 8%-12% dilute nitric acid by mass and soaks the material at 45-55℃ for 2-3 hours; the biomass raw material has a particle size of 80-100 mesh, a carbonization temperature of 550-650℃, and a carbonization time of 2-3 hours.

[0007] Furthermore, in step S2, the steam flow rate for the steam-carbon dioxide composite activation is 8-12 mL / min, the carbon dioxide flow rate is 5-7 mL / min, the activation time is 1.5-2.5 h, and the heating rate is 5-8 °C / min.

[0008] Furthermore, in step S3, the molar ratio of zirconium tetrachloride, terephthalic acid, and DMF is 1:1.2:45, the stirring speed is 350-450 r / min, and the stirring time is 30-45 min.

[0009] Furthermore, in step S4, the mass ratio of acidified biochar to activated carbon is 1:(3.5-4.5), the solid-liquid ratio is 1g:8-12mL, and the hydrothermal synthesis time is 6-8h.

[0010] Furthermore, in step S5, the calcination temperature is 600-680℃ and the calcination time is 1-1.5h; the gradient heating rate is 3-5℃ / min. After calcination, the outer organic ligand of the MOF crystal is partially carbonized to form a carbonized protective shell with a thickness of 1-3nm. The carbonized protective shell undergoes C-C covalent bonding with the bio-carbon skeleton to form a core-shell interlocking encapsulation structure of the MOF particle.

[0011] Furthermore, in step S5, the drying is carried out under vacuum at a temperature of 80-95°C for 5-7 hours.

[0012] Furthermore, the MOF-biocarbon modified activated carbon preparation method yields MOF-biocarbon modified activated carbon.

[0013] On the other hand, the MOF-biocarbon modified activated carbon is used in oil and gas recovery by filling the modified activated carbon into a fixed-bed adsorption tower for the adsorption treatment of oil and gas generated in petroleum refining, oil depots or gas stations; the adsorption working temperature is from room temperature to 55℃, and the oil and gas inlet flow rate is 0.5-2.0 m³ / h; after adsorption saturation, nitrogen purging desorption regeneration is carried out at 180-220℃, and the regeneration time is 30-50 min.

[0014] Furthermore, the MOF-biocarbon modified activated carbon has a specific surface area of ​​1500-2200 m² / g, a macromolecular hydrocarbon removal rate of over 92%, and a particle breakage rate of ≤2.5% after 50 adsorption-desorption cycles at 180-220℃.

[0015] The method for preparing MOF-biocarbon modified activated carbon of the present invention has the following beneficial effects: 1. By using activated carbon to construct the basic pore structure, biochar as the rigid framework support, and MOF functionalization to optimize surface adsorption sites, a multi-level composite pore structure of micropores, mesopores, and macropores is constructed through the synergistic effect of these three elements. Micropores are responsible for the adsorption of small molecule hydrocarbons, mesopores (2-15nm) precisely match the molecular size of C10-C20 long-chain hydrocarbons, and macropores provide diffusion channels. The specific surface area of ​​the finished product is increased from 800-1000 m² / g of conventional activated carbon to 1500-2200 m² / g. Under optimized process conditions, the saturated adsorption capacity for oil and gas is significantly improved (58.4% higher in Example 1 compared to Comparative Example 1), and the removal rate of large molecule hydrocarbons reaches over 92%, solving the problem of poor adsorption capacity for large molecule hydrocarbons by traditional activated carbon.

[0016] 2. Acidification with dilute nitric acid generates abundant hydroxyl and carboxyl functional groups on the surface of biochar. These functional groups act as nucleation anchors for MOFs during hydrothermal synthesis, chemically bonding with zirconium ions through coordination bonds. This enables the oriented growth of MOF crystals along the surface of biochar, forming a carbon framework-MOF crystal chemical bonding interface, rather than a simple physical coating. This structure significantly improves the compressive strength of the material compared to conventional activated carbon (an increase of 82.9% in Example 1), solving the problems of weak interfacial bonding and easy detachment during high-temperature regeneration in traditional MOF / carbon composite materials.

[0017] 3. Calcination is carried out using a slow temperature gradient of 3-5℃ / min. The controlled carbonization of the outer organic ligands of the MOF forms an ultrathin carbonized protective shell of 1-3nm. This shell undergoes C-C covalent bonding with the bio-carbon framework, encapsulating and locking the MOF particles onto the activated carbon-bio-carbon composite framework. This core-shell interlocking structure prevents the formation of interfacial microcracks during repeated thermal cycling at 180-220℃, and the particle breakage rate is ≤2.5% after 50 adsorption-desorption cycles.

[0018] 4. During calcination, the biochar undergoes partial pyrolysis and shrinkage, releasing the space it occupies in situ, precisely forming 2-15nm mesoporous channels between the MOF crystals and the pore walls of the activated carbon. This pore size range is highly matched with the molecular dynamics diameter of C10-C20 macromolecular hydrocarbons in oil and gas, achieving molecular sieving and directional adsorption of macromolecular hydrocarbons. This is the structural basis for the leap in macromolecular hydrocarbon removal rate from 65.3% of traditional activated carbon to 94.2%.

[0019] 5. The process is simple, the raw materials (straw / coconut shell, commercial activated carbon) are cheap and readily available, the reaction conditions are mild, there are no toxic or harmful byproducts, it can be mass-produced, and it is directly compatible with various oil and gas recovery fixed bed adsorption devices in petroleum refining, oil depots, gas stations and other facilities. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a method for preparing MOF-biocarbon modified activated carbon, comprising the following steps: S1. Raw material pretreatment: The columnar activated carbon is dried; the biomass raw material is crushed and carbonized to prepare biochar, and then acidified with dilute nitric acid to obtain acidified biochar with oxygen-containing functional groups on the surface. S2. Activated carbon activation: The pretreated activated carbon is activated by steam-carbon dioxide composite activation at 800-900℃ under an inert atmosphere to obtain activated activated carbon. Preparation of S3MOF precursor solution: Using zirconium tetrachloride as the metal source, terephthalic acid as the organic ligand, and DMF as the solvent, the MOF precursor solution was obtained by mixing and stirring. S4. Composite: Acidified biochar and activated carbon are mixed in proportion, MOF precursor solution is added, and hydrothermal synthesis is carried out at 120-150℃, so that MOF crystals grow in situ on the surface of biochar and inside the pores of activated carbon to obtain composite intermediate. S5. Post-processing: The filtered composite intermediate is washed alternately with anhydrous ethanol and deionized water 3-5 times to thoroughly remove residual DMF solvent and unreacted precursors. After washing, the product is placed in a vacuum drying oven and dried at 80-95℃ for 5-7 hours. Finally, it is subjected to gradient calcination under a nitrogen inert atmosphere at a temperature of 600-680℃ for 1-1.5 hours, with a heating rate controlled at 3-5℃ / min. After cooling, it is sieved to obtain the MOF-biocarbon modified activated carbon product. The preparation method of this invention is as follows: using the oxygen-containing functional groups on the surface of acidified biochar as the nucleation anchoring points of MOF, chemical bonding between MOF and carbon skeleton is achieved through hydrothermal in-situ growth; then, through precisely controlled gradient calcination, on the one hand, the outer layer of MOF is partially carbonized to form a core-shell interlocking structure, and on the other hand, the pyrolysis and shrinkage of biochar generates mesoporous channels in situ that match the size of macromolecular hydrocarbons, ultimately obtaining a MOF-biochar modified activated carbon with ultra-high specific surface area, excellent macromolecular hydrocarbon adsorption capacity, excellent mechanical strength and outstanding cycle stability.

[0022] In step S1, commercial columnar activated carbon is selected as the matrix, with a preferred particle size of 2-4 mm. It is placed in a constant temperature drying oven and dried at 105-120℃ for 4-6 hours to remove surface free moisture and impurities, which facilitates subsequent activation treatment.

[0023] In step S1, either agricultural waste straw or coconut shell is selected as the biomass raw material. After washing and removing impurities, it is pulverized to 80-100 mesh and carbonized at 550-650℃ for 2-3 hours under a nitrogen inert atmosphere. After natural cooling, it is ground to obtain powdered biochar. The obtained biochar is placed in a dilute nitric acid solution with a mass fraction of 8%-12% and soaked and acidified at 45-55℃ for 2-3 hours. Then, it is repeatedly washed with deionized water until neutral and dried at 110℃ for later use. After acidification with dilute nitric acid, abundant oxygen-containing functional groups (mainly including hydroxyl-OH and carboxyl-COOH) will be generated on the surface of the biochar. These functional groups will play a key role in subsequent steps: firstly, as active sites for MOF crystal nucleation and chemical anchoring, inducing MOF to grow along the biochar surface; secondly, enhancing the interfacial bonding force between biochar and activated carbon matrix and MOF precursor.

[0024] Straw and coconut shells are both agricultural wastes with high yield and low cost. Using them as raw materials to prepare biochar aligns with the concepts of green environmental protection and resource utilization. Crushing the raw materials to 80-100 mesh ensures uniform heating during carbonization, guaranteeing the homogeneity of the carbonized products. A carbonization temperature of 550-650℃ is an optimal balance range: too low a temperature results in incomplete biomass carbonization, low fixed carbon content, and insufficient skeletal strength; too high a temperature increases the graphitization of the carbonized products, reducing the number of surface functional groups, which is detrimental to the subsequent acidification treatment that introduces oxygen-containing functional groups. A dilute nitric acid solution with a mass fraction of 8%-12% is used. Too low a concentration results in insufficient oxidizing power, making it difficult to generate sufficient oxygen-containing functional groups on the biochar surface; too high a concentration leads to over-oxidation, causing excessive etching of the biochar skeleton and a decrease in its strength. Medium-temperature soaking at 45-55℃ ensures the acidification reaction rate while avoiding high-temperature decomposition of functional groups. The biochar treated under these conditions exhibits a significant increase in the content of oxygen-containing functional groups such as hydroxyl and carboxyl groups on its surface. This provides abundant and strongly binding chemical anchoring sites for the MOF precursor during the hydrothermal synthesis process in step S4, thereby achieving a strong chemical bond between the MOF crystal and the biochar surface. This is crucial for improving the structural stability of the material during multiple high-temperature regeneration cycles.

[0025] In step S2, the dried columnar activated carbon is placed in an activation furnace and activated using a steam-carbon dioxide composite method under inert nitrogen protection. The activation temperature is 800-900℃, the activation time is 1.5-2.5h, and the heating rate is 5-8℃ / min. The steam flow rate is 8-12mL / min, and the carbon dioxide flow rate is 5-7mL / min. After activation, the carbon dioxide is cooled to room temperature under an inert atmosphere, and surface ash is removed to obtain activated carbon. This step uses a synergistic activation of steam and carbon dioxide. The steam mainly acts on the interior of the carbon matrix, generating and expanding micropores; the carbon dioxide moderately etches the carbon surface, forming some mesoporous rudiments. The coupled effect of these two methods can construct the basic hierarchical pore framework required for subsequent MOF and biochar loading, while avoiding the decrease in framework strength caused by excessive etching by a single activator.

[0026] In step S3, the molar ratio of zirconium tetrachloride (ZrCl4), terephthalic acid (H2BDC), and DMF is 1:1.2:45. This ratio ensures sufficient coordination of the zirconium ions from the metal source, reduces internal defects in the MOF crystal, and improves crystallinity. The stirring speed is 350-450 r / min, and the stirring time is 30-45 min, forming a uniform and transparent MOF precursor mixed solution. The selected Zr-MOF exhibits excellent temperature resistance and hydrocarbon corrosion resistance, making it suitable for the high-temperature desorption conditions of 180-220℃ in oil and gas recovery processes, and its structure remains stable after long-term regeneration.

[0027] In step S4, the mass ratio of acidified biochar to activated carbon is 1:(3.5-4.5). At this ratio, if the proportion of biochar is too low, the framework support is insignificant; if the proportion is too high, it will occupy too much of the effective adsorption pore volume of the activated carbon, reducing the overall specific surface area. The solid-liquid ratio is 1g:8-12mL, ensuring that the MOF precursor solution fully wets the solid mixture, providing sufficient material supply for in-situ MOF growth. The hydrothermal synthesis time is 6-8 hours. Acidified biochar and activated carbon are added to the MOF precursor solution, and the mixture is transferred to a hydrothermal reactor for hydrothermal synthesis at 120-150℃ for 6-8 hours. After the reaction, the mixture is naturally cooled to room temperature, and the solid product is filtered to obtain the composite intermediate. During the hydrothermal synthesis, the oxygen-containing functional groups on the surface of the acidified biochar serve as MOF nucleation anchors, inducing MOF crystals to grow along the biochar surface, forming a chemically bonded carbon framework-MOF interface structure. The technical effect of this step is that it acidifies the -OH and -COOH functional groups on the surface of biochar and reacts with Zr. 4+ A strong coordination interaction occurs between them, acting as molecular rivets, anchoring the MOF crystals to the surface of biochar through chemical bonding, rather than simple physical adhesion. This chemically bonded interface effectively inhibits the shedding and aggregation of MOF particles during subsequent high-temperature calcination and multiple thermal cycling desorption and regeneration processes, which is the key structural basis for the extremely low cycle breakage rate of the product of this invention.

[0028] In step S5, the calcination temperature is 600-680℃, and the calcination time is 1-1.5h. The gradient heating rate is 3-5℃ / min. After calcination, the outer organic ligands of the MOF crystal partially carbonize to form a carbonized protective shell with a thickness of 1-3nm. The carbonized protective shell undergoes C-C covalent bonding with the bio-carbon skeleton, constituting the core-shell interlocking encapsulation structure of the MOF particle. The heating rate is strictly controlled within a relatively slow range of 3-5℃ / min to avoid pore collapse and MOF crystal structure damage caused by excessively rapid high-temperature processes. At the suitable calcination temperature of 600-680℃, the terephthalic acid organic ligands on the outer layer of the MOF undergo controlled pyrolysis under an inert atmosphere, partially carbonizing to form an ultrathin amorphous carbon shell with a thickness of only 1-3nm. This shell is sufficient to protect the active structure of the internal MOF crystal without significantly blocking the pores or reducing the specific surface area. More importantly, this carbonized shell layer undergoes C-C covalent bonding with the biomass-derived biocarbon framework under thermodynamic drive, forming a strong chemical bond that encapsulates and locks the MOF particles onto the activated carbon-biocarbon composite framework. This core-shell interlocking encapsulation structure endows the modified activated carbon with excellent thermal shock resistance. In subsequent applications, even after undergoing multiple severe thermal cycles of high-temperature desorption at 180-220℃ and adsorption at room temperature, no microcracks are generated at the material interface, and the MOF does not detach.

[0029] In step S5, the drying is performed under vacuum at a temperature of 80-95℃ for 5-7 hours. During calcination, the biochar undergoes partial pyrolysis and shrinkage, releasing in situ between the MOF crystals and the activated carbon pore walls to form mesoporous channels with a pore size of 2-15 nm. The size of these mesoporous channels matches the molecular size of large hydrocarbon molecules in oil and gas, achieving molecular sieving and directional adsorption of C10-C20 large hydrocarbon molecules. During calcination at 600-680℃, the acidified biochar introduced in step S1 undergoes further partial pyrolysis and shrinkage. The space it originally occupied is released in situ after volume reduction, precisely creating mesoporous channels with a size of 2-15 nm between the closely adjacent MOF crystals and activated carbon pore walls. This pore size range is highly matched with the molecular dynamics diameter of C10-C20 large chain hydrocarbon molecules in oil and gas, enabling molecular sieving and directional enrichment of target pollutants. This is the fundamental reason why the product of this invention can achieve a large hydrocarbon removal rate of over 92%. Traditional activated carbon is mainly composed of micropores, which makes it difficult for large hydrocarbon molecules to enter the pores and thus they are trapped. However, this invention perfectly overcomes this adsorption barrier by constructing a mesoporous network in situ through the self-templating effect of bio-carbon.

[0030] An application of the MOF-biocarbon modified activated carbon in oil and gas recovery is described. In this application, the modified activated carbon is packed into a fixed-bed adsorption tower for the adsorption treatment of oil and gas generated in petroleum refining, oil depots, or gas stations. The adsorption operating temperature is from room temperature to 55°C, and the oil and gas inlet flow rate is 0.5-2.0 m³ / h. After adsorption saturation, nitrogen purging and desorption regeneration are performed at 180-220°C for 30-50 minutes. After regeneration, the carbon is cooled to the operating temperature before being put into the next adsorption cycle.

[0031] Testing revealed that the MOF-biocarbon modified activated carbon prepared using the method of this invention has a specific surface area of ​​1500-2200 m² / g, possessing a multi-level composite pore structure of micropores, mesopores, and macropores. MOF crystals are chemically bonded and interlocked with the carbonized shell core, encapsulating within the activated carbon-biocarbon composite framework. This results in ultra-high specific surface area, excellent adsorption capacity for large molecular hydrocarbons, superior mechanical strength, and strong resistance to thermal shock cycling. Under optimized process conditions, the removal rate of large molecular hydrocarbons reaches over 92% (except for 89.7% in Example 3). After 50 adsorption-desorption cycles at 180-220℃, the particle breakage rate is ≤2.5%. The saturated oil and gas adsorption capacity of Example 1 is increased by 58.4% compared to Comparative Example 1, and the compressive strength is increased by 82.9%.

[0032] The beneficial technical effects of the present invention will be further illustrated below through several embodiments and comparative examples.

[0033] Example 1 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h; select straw biomass, wash and remove impurities, crush it to 90 mesh, and carbonize it at 600℃ for 2.5h under nitrogen atmosphere to obtain powdered biochar; use 10% dilute nitric acid to soak the biochar at 50℃ for 2.5h, wash it with deionized water until neutral, and dry it at 110℃ to obtain acidified biochar.

[0034] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 850℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0035] S3, MOF precursor solution preparation: Zirconium tetrachloride, terephthalic acid and DMF were mixed in a molar ratio of 1:1.2:45 and magnetically stirred at room temperature for 40 min at a speed of 400 r / min to obtain a homogeneous precursor solution.

[0036] S4. Composite: Acidified biochar and activated carbon are mixed uniformly at a mass ratio of 1:4. MOF precursor solution is added at a solid-liquid ratio of 1g:10mL. The mixture is transferred to a hydrothermal reactor and hydrothermally synthesized at 135℃ for 7 hours. After natural cooling, the mixture is filtered.

[0037] S5. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 4℃ / min under a nitrogen atmosphere, and calcined at 650℃ for 1.2 hours. After cooling, it was sieved to obtain the MOF-biocarbon modified activated carbon product.

[0038] Example 2 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h; select straw biomass, wash and remove impurities, crush it to 90 mesh, and carbonize it at 600℃ for 2.5h under nitrogen atmosphere to obtain powdered biochar; use 10% dilute nitric acid to soak the biochar at 50℃ for 2.5h, wash it with deionized water until neutral, and dry it at 110℃ to obtain acidified biochar.

[0039] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 850℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0040] S3, MOF precursor solution preparation: Zirconium tetrachloride, terephthalic acid and DMF were mixed in a molar ratio of 1:1.2:45 and magnetically stirred at room temperature for 40 min at a speed of 400 r / min to obtain a homogeneous precursor solution.

[0041] S4. Composite: Acidified biochar and activated carbon are mixed uniformly at a mass ratio of 1:3.5. MOF precursor solution is added at a solid-liquid ratio of 1g:10mL. The mixture is transferred to a hydrothermal reactor and hydrothermally synthesized at 120℃ for 8 hours. After natural cooling, the mixture is filtered.

[0042] S5. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 4℃ / min under a nitrogen atmosphere, and calcined at 650℃ for 1.2 hours. After cooling, it was sieved to obtain the MOF-biocarbon modified activated carbon product.

[0043] Example 3 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h; select straw biomass, wash and remove impurities, crush it to 90 mesh, and carbonize it at 600℃ for 2.5h under nitrogen atmosphere to obtain powdered biochar; use 10% dilute nitric acid to soak the biochar at 50℃ for 2.5h, wash it with deionized water until neutral, and dry it at 110℃ to obtain acidified biochar.

[0044] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 800℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0045] S3, MOF precursor solution preparation: Zirconium tetrachloride, terephthalic acid and DMF were mixed in a molar ratio of 1:1.2:45 and magnetically stirred at room temperature for 40 min at a speed of 400 r / min to obtain a homogeneous precursor solution.

[0046] S4. Composite: Acidified biochar and activated carbon are mixed uniformly at a mass ratio of 1:4. MOF precursor solution is added at a solid-liquid ratio of 1g:8mL. The mixture is transferred to a hydrothermal reactor and hydrothermally synthesized at 135℃ for 7 hours. After natural cooling, the mixture is filtered.

[0047] S5. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 4℃ / min under a nitrogen atmosphere, and calcined at 600℃ for 1.2 hours. After cooling, it was sieved to obtain the MOF-biocarbon modified activated carbon product.

[0048] Example 4 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h; select straw biomass, wash and remove impurities, crush it to 90 mesh, and carbonize it at 600℃ for 2.5h under nitrogen atmosphere to obtain powdered biochar; use 10% dilute nitric acid to soak the biochar at 50℃ for 2.5h, wash it with deionized water until neutral, and dry it at 110℃ to obtain acidified biochar.

[0049] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 850℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0050] S3, MOF precursor solution preparation: Zirconium tetrachloride, terephthalic acid and DMF were mixed in a molar ratio of 1:1.2:45 and magnetically stirred at room temperature for 40 min at a speed of 400 r / min to obtain a homogeneous precursor solution.

[0051] S4. Composite: Acidified biochar and activated carbon are mixed uniformly at a mass ratio of 1:4.5. MOF precursor solution is added at a solid-liquid ratio of 1g:10mL. The mixture is transferred to a hydrothermal reactor and hydrothermally synthesized at 150℃ for 7 hours. After natural cooling, the mixture is filtered.

[0052] S5. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 4℃ / min under a nitrogen atmosphere, and calcined at 650℃ for 1.2 hours. After cooling, it was sieved to obtain the MOF-biocarbon modified activated carbon product.

[0053] Example 5 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h; select straw biomass, wash and remove impurities, crush it to 90 mesh, and carbonize it at 600℃ for 2.5h under nitrogen atmosphere to obtain powdered biochar; use 10% dilute nitric acid to soak the biochar at 50℃ for 2.5h, wash it with deionized water until neutral, and dry it at 110℃ to obtain acidified biochar.

[0054] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 850℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0055] S3, MOF precursor solution preparation: Zirconium tetrachloride, terephthalic acid and DMF were mixed in a molar ratio of 1:1.2:45 and magnetically stirred at room temperature for 40 min at a speed of 400 r / min to obtain a homogeneous precursor solution.

[0056] S4. Composite: Acidified biochar and activated carbon are mixed uniformly at a mass ratio of 1:3.5. MOF precursor solution is added at a solid-liquid ratio of 1g:8mL. The mixture is transferred to a hydrothermal reactor and hydrothermally synthesized at 120℃ for 8 hours. After natural cooling, the mixture is filtered.

[0057] S5. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 4℃ / min under a nitrogen atmosphere, and calcined at 650℃ for 1.2 hours. After cooling, it was sieved to obtain the MOF-biocarbon modified activated carbon product.

[0058] Example 6 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h; select straw biomass, wash and remove impurities, crush it to 90 mesh, and carbonize it at 600℃ for 2.5h under nitrogen atmosphere to obtain powdered biochar; use 10% dilute nitric acid to soak the biochar at 50℃ for 2.5h, wash it with deionized water until neutral, and dry it at 110℃ to obtain acidified biochar.

[0059] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 850℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0060] S3, MOF precursor solution preparation: Zirconium tetrachloride, terephthalic acid and DMF were mixed in a molar ratio of 1:1.2:45 and magnetically stirred at room temperature for 40 min at a speed of 400 r / min to obtain a homogeneous precursor solution.

[0061] S4. Composite: Acidified biochar and activated carbon are mixed uniformly at a mass ratio of 1:4. MOF precursor solution is added at a solid-liquid ratio of 1g:10mL. The mixture is transferred to a hydrothermal reactor and hydrothermally synthesized at 135℃ for 7 hours. After natural cooling, the mixture is filtered.

[0062] S5. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 10℃ / min under a nitrogen atmosphere, and calcined at 650℃ for 1.2 hours. After cooling, it was sieved to obtain the MOF-biocarbon modified activated carbon product.

[0063] Comparative Example 1 The commonly used columnar activated carbon for oil and gas recovery is selected from the market and has not undergone any modification treatment. Its basic parameters are: specific surface area 915m² / g and compressive strength 38N / particle.

[0064] Comparative Example 2 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h.

[0065] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 850℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0066] S3, MOF precursor solution preparation: Zirconium tetrachloride, terephthalic acid and DMF were mixed in a molar ratio of 1:1.2:45 and magnetically stirred at room temperature for 40 min at a speed of 400 r / min to obtain a homogeneous precursor solution.

[0067] S4. Composite: Add activated carbon to the MOF precursor solution at a solid-liquid ratio of 1g:10mL, transfer to a hydrothermal reactor, and synthesize hydrothermally at 135℃ for 7h. After natural cooling, filter.

[0068] S5. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 4℃ / min under a nitrogen atmosphere, and calcined at 650℃ for 1.2 hours. After cooling, it was sieved to obtain the activated carbon product.

[0069] Comparative Example 3 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h; select straw biomass, wash and remove impurities, crush it to 90 mesh, and carbonize it at 600℃ for 2.5h under nitrogen atmosphere to obtain powdered biochar; use 10% dilute nitric acid to soak the biochar at 50℃ for 2.5h, wash it with deionized water until neutral, and dry it at 110℃ to obtain acidified biochar.

[0070] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 850℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0071] S3. Composite: Acidified biochar and activated carbon are mixed uniformly at a mass ratio of 1:4, an equal amount of DMF solvent is added, and the mixture is transferred to a hydrothermal reactor. The mixture is then hydrothermally synthesized at 135℃ for 7 hours, and filtered after natural cooling.

[0072] S4. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 4℃ / min under a nitrogen atmosphere, and calcined at 650℃ for 1.2 hours. After cooling, it was sieved to obtain the activated carbon product.

[0073] Comparative Example 4 S1. Raw material pretreatment: Select commercial columnar activated carbon with a particle size of 3mm and dry it at 110℃ for 5h; select straw biomass, wash and remove impurities, crush it to 90 mesh, and carbonize it at 600℃ for 2.5h under nitrogen atmosphere to obtain powdered biochar (without acidification treatment).

[0074] S2. Activated carbon activation: Place the dried activated carbon in an activation furnace and heat it to 850℃ under nitrogen protection at a rate of 6℃ / min. The steam flow rate is 10mL / min and the carbon dioxide flow rate is 6mL / min. The carbon dioxide is then introduced and kept at this temperature for 2 hours for combined activation. After cooling to room temperature, the surface ash is removed.

[0075] S3, MOF precursor solution preparation: Zirconium tetrachloride, terephthalic acid and DMF were mixed in a molar ratio of 1:1.2:45 and magnetically stirred at room temperature for 40 min at a speed of 400 r / min to obtain a homogeneous precursor solution.

[0076] S4. Composite: Powdered biochar and activated carbon are mixed uniformly at a mass ratio of 1:4. MOF precursor solution is added at a solid-liquid ratio of 1g:10mL. The mixture is transferred to a hydrothermal reactor and hydrothermally synthesized at 135℃ for 7 hours. After natural cooling, the mixture is filtered.

[0077] S5. Post-treatment: The filtered product was washed four times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 90℃ for 6 hours. It was then subjected to gradient calcination at a heating rate of 4℃ / min under a nitrogen atmosphere, and calcined at 650℃ for 1.2 hours. After cooling, it was sieved to obtain the activated carbon product.

[0078] Table 1 Performance parameters of finished products from Examples 1-6 and Comparative Examples 1-4

[0079] According to Table 1: (1) Example 1 is the optimal solution of the present invention, with a specific surface area of ​​2086 m² / g, oil and gas adsorption capacity of 198 mg / g, macromolecular hydrocarbon removal rate of 94.2%, and a 50-cycle breakage rate of 1.2%, all of which are optimal. Comparative Example 1 is commercially available unmodified activated carbon, with all indicators being the worst. Compared with Comparative Example 1, Example 1 has a 58.4% increase in oil and gas adsorption capacity and an 82.9% increase in compressive strength, fully demonstrating the effectiveness of the overall technical solution of the present invention.

[0080] (2) Examples 2 to 5 were prepared under different combinations of process parameters, with a specific surface area of ​​1538-1980 m² / g, an adsorption capacity of 171-190 mg / g, a macromolecular hydrocarbon removal rate of 89.7%-92.8%, and a breakage rate of 1.5%-2.1% after 50 cycles. Although the performance of each example is different and slightly lower than that of Example 1, it is still at an excellent level.

[0081] (3) Comparative Example 2 used only MOF and activated carbon composite without adding biochar. Its 50-cycle breakage rate was as high as 13.5%, and its compressive strength was only 42 N / particle, which is in stark contrast to 1.2% and 69.5 N / particle in Example 1. This shows that biochar plays an indispensable role in the mechanical strength and cycle stability of the material. Comparative Example 3 used only biochar and activated carbon composite without adding MOF. Its specific surface area was only 1120 m² / g, its oil and gas adsorption capacity was only 148 mg / g, and its macromolecular hydrocarbon removal rate was only 72.6%. This shows that MOF is the core component that provides high specific surface area and adsorption functional sites. Comparative Example 4 used untreated biochar. Its 50-cycle breakage rate reached 7.2%, which is significantly higher than 1.2% in Example 1. This shows that the oxygen-containing functional groups introduced by the acid treatment are the key pretreatment step to achieve MOF chemical anchoring and ensure cycle stability.

[0082] (4) In Example 6, rapid calcination at 10℃ / min resulted in a decrease in specific surface area to 1410m² / g, a decrease in macromolecular hydrocarbon removal rate to 82.4%, and an increase in breakage rate to 6.8% after 50 cycles. All performance characteristics were significantly worse than in Example 1. This indicates that slow gradient calcination is a necessary process condition for forming a core-shell interlocking structure and self-templating mesoporous channels, and the heating rate is a crucial parameter.

[0083] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing MOF-biochar modified activated carbon, characterized in that: Includes the following steps: S1. Raw material pretreatment: Drying the columnar activated carbon; Biochar is prepared by crushing and carbonizing biomass raw materials, and then acidified with dilute nitric acid to obtain acidified biochar with oxygen-containing functional groups on its surface; the biomass raw materials are either straw or coconut shells. S2. Activated carbon activation: The pretreated activated carbon is activated by steam-carbon dioxide composite activation at 800-900℃ under an inert atmosphere to obtain activated activated carbon. S3. Preparation of MOF precursor solution: Using zirconium tetrachloride as the metal source, terephthalic acid as the organic ligand, and DMF as the solvent, the MOF precursor solution was obtained by mixing and stirring. S4. Composite: Acidified biochar and activated carbon are mixed in proportion, MOF precursor solution is added, and hydrothermal synthesis is carried out at 120-150℃, so that MOF crystals grow in situ on the surface of biochar and inside the pores of activated carbon to obtain composite intermediate. S5. Post-processing: After washing and drying the composite intermediate, it is calcined under an inert atmosphere with a gradient heating. After cooling, MOF-biocarbon modified activated carbon is obtained.

2. The method of claim 1, wherein the MOF-biochar modified activated carbon is prepared by the following steps: In step S1, the acidification treatment uses 8%-12% dilute nitric acid by mass and soaks the biomass raw material at 45-55℃ for 2-3 hours; the particle size of the biomass raw material is 80-100 mesh, the carbonization temperature is 550-650℃, and the carbonization time is 2-3 hours.

3. The method of claim 1, wherein the MOF-biochar modified activated carbon is prepared by the following steps: (1) mixing a MOF and a biochar to obtain a mixture; (2) drying the mixture; (3) heating the mixture to obtain the MOF-biochar modified activated carbon. In step S2, the steam flow rate for the steam-carbon dioxide composite activation is 8-12 mL / min, the carbon dioxide flow rate is 5-7 mL / min, the activation time is 1.5-2.5 h, and the heating rate is 5-8 °C / min.

4. The method of claim 1, wherein the MOF-biochar modified activated carbon is prepared by the following steps: (1) mixing a MOF and a biochar to obtain a mixture; (2) drying the mixture; (3) heating the mixture to obtain a MOF-biochar modified activated carbon. In step S3, the molar ratio of zirconium tetrachloride, terephthalic acid, and DMF is 1:1.2:45, the stirring speed is 350-450 r / min, and the stirring time is 30-45 min.

5. The method for preparing MOF-biocarbon modified activated carbon according to claim 1, characterized in that: In step S4, the mass ratio of acidified biochar to activated carbon is 1:(3.5-4.5), the solid-liquid ratio is 1g:8-12mL, and the hydrothermal synthesis time is 6-8h.

6. The method for preparing MOF-biocarbon modified activated carbon according to claim 1, characterized in that: In step S5, the calcination temperature is 600-680℃ and the calcination time is 1-1.5h; the gradient heating rate is 3-5℃ / min. After calcination, the outer organic ligand of the MOF crystal is partially carbonized to form a carbonized protective shell with a thickness of 1-3nm. The carbonized protective shell is covalently bonded to the biocarbon skeleton, forming a core-shell interlocking encapsulation structure of the MOF particle.

7. The method for preparing MOF-biocarbon modified activated carbon according to claim 6, characterized in that: In step S5, the drying is carried out under vacuum at a temperature of 80-95°C for 5-7 hours.

8. MOF-biocarbon-modified activated carbon prepared by the method according to any one of claims 1 to 7.

9. The application of MOF-biocarbon modified activated carbon according to claim 8 in oil and gas recovery, characterized in that: The modified activated carbon is packed into a fixed-bed adsorption tower for the adsorption treatment of oil and gas generated in petroleum refining, oil depots or gas stations; the adsorption operating temperature is from room temperature to 55℃, and the oil and gas inlet flow rate is 0.5-2.0 m³ / h; after adsorption saturation, nitrogen purging desorption regeneration is carried out at 180-220℃, and the regeneration time is 30-50 min.

10. The application according to claim 9, characterized in that, The MOF-biocarbon modified activated carbon has a specific surface area of ​​1500-2200 m² / g, a macromolecular hydrocarbon removal rate of over 92%, and a particle breakage rate of ≤2.5% after 50 adsorption-desorption cycles at 180-220℃.

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