Algae sludge-based activated carbon, and preparation method and application thereof

Abstract

The present application relates to a kind of algal mud-based activated carbon and its preparation method and application, the preparation method includes the following steps: (1) algal mud powder is heated to pyrolysis, and pyrolysis product is obtained;(2) the pyrolysis product and activating agent are mixed, gradient temperature activation is carried out, and the algal mud-based activated carbon is obtained;The activating agent includes the combination of potassium hydroxide and potassium carbonate.The present application innovatively converts algal mud waste into porous green activated carbon material with high specific surface area, developed pore structure and excellent adsorption performance by specific chemical activation and carbonization process.Further, with this algal mud-based activated carbon as carrier, load noble metal, and prepare high-dispersion, high-activity heterogeneous catalyst, which shows excellent catalytic performance in catalytic microalgae oil hydrodeoxygenation reaction.

Description

Technical Field

[0001] This invention relates to the field of biomass activated carbon technology, and in particular to an algae mud-based activated carbon, its preparation method, and its application. Background Technology

[0002] Microalgae oil, with its biological advantages such as not occupying arable land, short growth cycle, and high oil yield per unit area, is considered an ideal third-generation biofuel feedstock, and related industrialization technologies have become a research hotspot in the bioenergy field. However, the extraction (oil extraction) process of microalgae oil generates a large amount of solid byproducts—microalgae sludge (or algae residue). Although these byproducts are rich in proteins, polysaccharides, residual lipids, and inorganic minerals, and have high potential for resource utilization, current technologies for their treatment are still relatively crude, mostly involving composting, landfilling, or direct disposal. This treatment not only leads to the waste of biomass resources but also easily causes secondary pollution of soil or water bodies. Therefore, developing high-value utilization pathways for microalgae sludge and solving the bottleneck of waste disposal in the microalgae energy industry chain is of significant industrial importance.

[0003] On the other hand, as an important substitute for fossil diesel, biodiesel is mainly divided into two generations based on different preparation processes and chemical structures. The first generation is ester-based biodiesel (fatty acid methyl ester, FAME), which is mainly produced through transesterification of oils and methanol. The second generation is hydrocarbon-based biodiesel (also known as recycled diesel), which is prepared through deep hydrodeoxygenation (HDO), cracking, and isomerization of oils under the action of a catalyst. Compared with the first-generation ester-based biodiesel, the second-generation hydrocarbon-based biodiesel has significant advantages in physicochemical properties: its extremely low oxygen content gives the fuel a higher calorific value and oxidation stability; its excellent low-temperature fluidity overcomes the defect of traditional biodiesel's tendency to crystallize; and its chemical composition is very close to that of petroleum-based diesel. Due to its good miscibility and combustion characteristics, it can be directly blended in a high proportion or even completely replaced in existing internal combustion engines and oil pipeline networks.

[0004] Against this backdrop, converting waste algal sludge from the microalgae oil extraction process into highly active catalytic materials and further applying them to the catalytic synthesis of high-quality hydrocarbon-based biodiesel is an effective technical approach to achieve full utilization of microalgae resources and upgrade the quality of biofuels. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an algae-based activated carbon, its preparation method, and its applications. This invention innovatively transforms algae waste into a porous, green activated carbon material with high specific surface area, well-developed pore structure, and excellent adsorption performance through a specific chemical activation and carbonization process. Furthermore, using this algae-based activated carbon as a carrier, noble metals are loaded to prepare a highly dispersed and highly active heterogeneous catalyst, which exhibits excellent catalytic performance in the hydrodeoxygenation reaction of microalgae oil.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing algae-based activated carbon, the method comprising the following steps:

[0008] (1) Heat the algae mud powder to pyrolyze it to obtain the pyrolysis products;

[0009] (2) The pyrolysis product and the activator are mixed and activated by gradient heating to obtain the algae mud-based activated carbon; the activator includes a combination of potassium hydroxide and potassium carbonate.

[0010] In step (1), the algal mud powder is heated for pyrolysis. During this process, the organic components such as proteins and polysaccharides in the algal mud undergo partial decomposition (weight loss rate of about 30-40%), but the fibrous skeleton structure is preserved. Observation by scanning electron microscopy (SEM) shows that the pyrolysis products still maintain continuous micron-sized channels (1-5μm), and the channel walls form preliminary micropores (50-200nm) due to the decomposition of organic matter.

[0011] In step (2), a composite activator is used in combination with a gradient temperature activation strategy. The medium-temperature decomposition characteristics of K2CO3 are utilized to achieve "mild pore expansion", which complements the high-temperature and intense etching of KOH. The specific mechanism is as follows: K2CO3 decomposes at around 600℃ to produce K2O and CO2 (K2CO3→K2O+CO2↑). K2O reacts slightly with carbon materials (K2O+C→2K+CO↑), slowly expanding the original micron-level channels of algal materials and avoiding channel collapse caused by excessive reaction during single KOH activation. At the same time, CO2 gas generates an "airflow scouring" effect in the channels, promoting improved channel connectivity.

[0012] In this invention, algal mud powder is subjected to low-temperature pyrolysis to retain its natural microchannels. Subsequently, a composite activator of KOH and K₂CO₃ is used to activate the material under gradient heating conditions, forming a porous green activated carbon material (GAC) with "micron-level interconnected pores + nano-level catalytic pores". This process utilizes the phospholipid components of microalgae, allowing phosphorus to remain in the GAC and form acidic sites (pKa = 3.5-4.5). The final GAC has a specific surface area of ​​910-1108 m² / g, which is higher than that of activated carbon obtained by traditional methods.

[0013] Preferably, the source of the algae mud powder in step (1) includes Botrytis cinerea and / or Chlorella vulgaris.

[0014] Preferably, the method for preparing the algae mud powder in step (1) includes: drying and pulverizing the waste wet algae mud after oil extraction to obtain the algae mud powder.

[0015] Preferably, the drying method includes freeze drying.

[0016] In this invention, a specific species of *Botrytis cinerea* and / or *Chlorella vulgaris* is selected in a preferred embodiment. After oil extraction, the resulting waste wet algal sludge (with a water content of approximately 70-80%) is produced. This algal species has cell walls rich in cellulose and hemicellulose (approximately 45-50%), and its phospholipid content (mainly phosphatidylcholine) is as high as 3-4 wt%, higher than ordinary microalgae (1-2 wt%) and far exceeding the phospholipid content of sawdust (<0.5 wt%). This makes it more conducive to the retention of natural microchannels and the formation of acidic sites (the number of acidic sites is 1.2-1.5 times that of ordinary algal sludge-based GAC). After vacuum freeze-drying, it is pulverized to 100-200 mesh, with its fibrous microchannels concentrated in diameter at 8-15 μm, coarser than ordinary microalgae, resulting in superior mass transfer potential. This pretreatment can retain more than 90% of the natural fibrous microchannels (5-20 μm in diameter) in the algal sludge, providing a basic framework for subsequent pore formation.

[0017] Preferably, the heating program in step (1) is as follows: the temperature is increased to 300-400℃ (e.g., 300℃, 320℃, 350℃, 380℃, 400℃, etc.) at a rate of 2-8℃ / min (e.g., 2℃ / min, 3℃ / min, 4℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, etc.), and then kept warm for 1-3 hours (e.g., 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.).

[0018] Preferably, the mass ratio of the pyrolysis product to the activator in step (2) is (1-3):1 (for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, etc.).

[0019] Preferably, the mass ratio of potassium hydroxide to potassium carbonate in step (2) is (2-4):1 (for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.).

[0020] Preferably, the mixing method in step (2) includes grinding.

[0021] In this invention, the pyrolysis products and activators are thoroughly mixed by grinding to ensure that the activator is uniformly attached to the surface of the pyrolysis products and the initial micropores.

[0022] Preferably, the gradient temperature activation procedure in step (2) is as follows: the temperature is increased to 350-450℃ (e.g., 350℃, 380℃, 400℃, 420℃, 450℃, etc.) at a rate of 5-12℃ / min (e.g., 5℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, etc.), and held for 0.5-2h (e.g., 0.5h, 1h, 1.5h, 2h, etc.); then the temperature is increased to 550-650℃ at a rate of 2-8℃ / min (e.g., 2℃ / min, 3℃ / min, 4℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, etc.). (For example, it could be 550℃, 580℃, 600℃, 620℃, 650℃, etc.), hold for 1-2 hours (for example, it could be 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, etc.); then raise the temperature to 750-850℃ (for example, it could be 750℃, 780℃, 800℃, 820℃, 850℃, etc.) at a rate of 2-8℃ / min (for example, it could be 2℃ / min, 3℃ / min, 4℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, etc.), hold for 0.5-1.5 hours (for example, it could be 0.5 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, etc.).

[0023] In this invention, during the first stage of gradient heating activation, K2CO3 decomposes (K2CO3→K2O+CO2), reacting initially with carbon materials to expand micron-sized channels; during the second stage of heating, KOH begins to react violently (4KOH+C→K2CO3+K2O+2H2), etching a large number of nanopores (2-50nm) on the channel walls; during the third stage of heating, the nanopore structure is further deepened, forming a connected multi-level pore network.

[0024] This invention employs a composite activator combined with a specific gradient heating strategy, which can reduce the collapse of the pore structure and improve mass transfer efficiency by more than 50%.

[0025] Preferably, step (2) further includes a washing process after the gradient temperature activation.

[0026] Preferably, the washing solution used in the washing process includes nitric acid solution and / or citric acid solution.

[0027] Preferably, the concentration of the nitric acid solution is 0.5-1.5 mol / L (e.g., 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, etc.).

[0028] Preferably, the concentration of the citric acid solution is 2-8 wt% (e.g., 2 wt%, 3 wt%, 4 wt%, 6 wt%, 7 wt%, 8 wt%, etc.).

[0029] Preferably, the washing process specifically includes: first soaking in nitric acid solution, then washing with water, then soaking in citric acid solution, and finally washing with water again to obtain the product.

[0030] In this invention, nitric acid solution and / or citric acid solution are used instead of traditional hydrochloric acid for washing. After washing, the waste liquid can be neutralized and recycled. Compared with traditional hydrochloric acid washing, this reduces the processing difficulty, decreases the discharge of corrosive waste liquid, improves environmental friendliness, and conforms to the concept of green manufacturing. The functions of the two washing solutions are as follows:

[0031] Nitric acid washing: Nitric acid has oxidizing properties, which can further remove residual carbon impurities. At the same time, it introduces a small number of oxygen-containing functional groups (such as nitro and carboxyl groups) on the surface of GAC, enhancing the adsorption capacity of the carrier for metal ions. After washing to pH=6-7, rinse with deionized water until no nitrate ions are present.

[0032] Citric acid washing: As a weak acid, it can gently neutralize residual potassium. + Alkaline substances such as K2O are used to avoid the damage of strong acids to the pore structure. Citrate ions can remove some metal impurities through complexation. After washing with citric acid, wash with water until the conductivity of the filtrate is <10μS / cm.

[0033] Preferably, the washing process further includes a drying process.

[0034] Secondly, the present invention provides an algae-based activated carbon prepared according to the method for preparing algae-based activated carbon described in the first aspect.

[0035] Thirdly, the present invention provides a catalyst comprising a support and a metal supported on the support; the support comprising the algae-based activated carbon described in the second aspect.

[0036] The algae-based activated carbon provided by this invention has a multi-level pore structure of "micron-level through pores + nano-level catalytic pores". Among them, the micron-pores can accelerate the mass transfer of algae oil reactants, while the nano-pores provide highly dispersed anchoring sites for metals. This solves the problem that it is difficult to balance the mass transfer efficiency and active component loading of traditional activated carbon carriers, thereby increasing the specific surface area of ​​the catalyst to 910-1108 m². 2 / g, to achieve high dispersion and anchoring of metals, thereby increasing the number of active sites on the catalyst.

[0037] Preferably, the metal comprises any one or a combination of at least two of palladium, tungsten, or molybdenum, and more preferably a combination of palladium (Pd), tungsten (W), and molybdenum (Mo).

[0038] The algae-based activated carbon provided by this invention is derived from microalgae and is rich in phospholipids. These phosphorus elements create acidic sites (pKa = 3.5-4.5) on the activated carbon carrier, which can inhibit the adsorption and polymerization of unsaturated intermediates at the active center through proton transfer. Simultaneously, the oxidation states of W and Mo can dynamically change (W... 6+ ↔W 4+ Mo 6+ ↔Mo 4+ It removes surface carbon through an oxidation-reduction cycle, thus extending the catalytic life.

[0039] Preferably, the mass ratio of palladium, tungsten and molybdenum is 1:(5-10):(5-10), and the values ​​5-10 can be 5, 6, 7, 8, 9, 10, etc.

[0040] Preferably, the mass ratio of the carrier to the metal is 1:(0.05-0.15) (for example, it can be 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.15, etc.).

[0041] Fourthly, the present invention provides a method for preparing the catalyst according to the third aspect, the method comprising the following steps:

[0042] The catalyst is obtained by mixing the solution of the support and the metal precursor, followed by coordination reaction, drying, calcination and reduction.

[0043] Preferably, the tungsten precursor comprises ammonium tungstate.

[0044] Preferably, the molybdenum precursor comprises ammonium molybdate.

[0045] Preferably, the palladium precursor comprises palladium acetate.

[0046] In this invention, Pd(OAC)2 (palladium acetate) is used instead of traditional PdCl2 to avoid the inhibition of catalyst activity by Cl⁻ residue.

[0047] Preferably, the preparation method specifically includes the following steps:

[0048] (1) Using the equal-volume impregnation method, the carrier, tungsten and molybdenum mixed precursor solution are mixed and adsorbed to obtain intermediate one;

[0049] (2) The first intermediate is dried, and then the dried first intermediate and the palladium precursor solution are mixed and adsorbed by the equal volume impregnation method to obtain the second intermediate.

[0050] (3) The intermediate II is dried, calcined and reduced to obtain the catalyst.

[0051] Preferably, the mixing process described in steps (1) and (2) further includes ultrasonic treatment.

[0052] In this invention, ultrasonic treatment can promote the rapid penetration of the solution into the nanopores. After ultrasonic treatment, the solution is allowed to stand at room temperature (20-30°C) to allow the metal ions to coordinate with the acidic sites on the GAC surface, thereby improving the anchoring stability of the metal ions.

[0053] Preferably, the solvent in the tungsten and molybdenum mixed precursor solution in step (1) includes water.

[0054] Preferably, the solvent in the palladium precursor solution in step (2) includes ethanol and / or water.

[0055] In this invention, the ethanol solution of Pd(OAC)2 in step (2) has a stronger affinity for GAC and can preferentially deposit in the W and Mo enrichment areas to form a trimetallic synergistic interface.

[0056] Preferably, the drying temperature in step (2) is 120-180℃ (e.g., 120℃, 130℃, 150℃, 170℃, 180℃, etc.), and the time is 2-4h (e.g., 2h, 2.5h, 3h, 3.5h, 4h, etc.).

[0057] Preferably, the drying temperature in step (3) is 50-90℃ (e.g., 50℃, 60℃, 70℃, 80℃, 90℃, etc.), and the time is 8-16h (e.g., 8h, 10h, 12h, 14h, 16h, etc.).

[0058] Preferably, the roasting in step (3) includes: heating to 450-550℃ (e.g., 450℃, 480℃, 500℃, 520℃, 550℃, etc.) at 8-12℃ / min (e.g., 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, etc.) in an air atmosphere, and holding at that temperature for 3-5h (e.g., 3h, 3.5h, 4h, 4.5h, 5h, etc.).

[0059] Preferably, the reduction in step (3) includes: heating to 350-450℃ (e.g., 350℃, 380℃, 400℃, 420℃, 450℃, etc.) at a rate of 8-12℃ / min (e.g., 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, etc.) in a mixed gas atmosphere of H2 and protective gas, and holding at that temperature for 3-5h (e.g., 3h, 3.5h, 4h, 4.5h, 5h, etc.).

[0060] In this invention, the drying step in step (3) gradually removes the solvent to avoid the formation of bubbles in the pores that could damage the structure; the calcination step decomposes the precursor into metal oxides (WO3, MoO3, PdO) while removing residual organic components; the reduction step reduces the metal oxides to a catalytically active metallic state (WO3, MoO3, PdO). 0 Mo 0 Pd 0 W and Mo can retain some of their oxidation states to maintain their anti-carbon deposition properties.

[0061] Preferably, the volume ratio of H2 to the protective gas is 1:(0.8-1.2) (for example, it can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, etc.).

[0062] Preferably, the protective gas includes nitrogen and / or argon.

[0063] Fifthly, the present invention provides a method for preparing hydrocarbon-based biodiesel from microalgae oil, the method comprising: catalyzing the microalgae oil to undergo a hydrodeoxygenation reaction in the presence of a catalyst to obtain hydrocarbon-based biodiesel; the catalyst comprising the catalyst described in the third aspect.

[0064] Preferably, the mass ratio of the microalgae oil to the catalyst is 6:(0.1-1) (for example, it can be 6:0.1, 6:0.3, 6:0.5, 6:0.8, 6:1, etc.).

[0065] Preferably, the hydrodeoxygenation reaction is carried out in the presence of a solvent.

[0066] Preferably, the solvent includes cyclohexane and / or n-hexane.

[0067] Preferably, the deoxygenation and hydrogenation reaction specifically includes: 0-2 hours, with a volume ratio of H2 to protective gas of 1:(2-4) (e.g., 1:2, 1:2.5, 1:3, 1:3.5, 1:4, etc.), a pressure of 1.8-2.2 MPa (e.g., 1.8 MPa, 1.9 MPa, 2 MPa, 2.1 MPa, 2.2 MPa, etc.), and a temperature of 290-310℃ (e.g., 290℃, 295℃, 300℃, 305℃, 310℃, etc.); and 2-6 hours, with a volume ratio of H2 to protective gas of 1:(0.8-1.2) (e.g., 1:0.8, 1:1, 1:1.1, 1:1.2, etc.), and a pressure of 2.4- The hydrogenation reaction is carried out at a pressure of 2.6 MPa (e.g., 2.4 MPa, 2.5 MPa, 2.6 MPa, etc.) and a temperature of 310-330℃ (e.g., 310℃, 315℃, 320℃, 325℃, 330℃, etc.); for 6-8 hours, the hydrogenation reaction is carried out at a volume ratio of H2 to protective gas of 1:(2-4) (e.g., 1:2, 1:2.5, 1:3, 1:3.5, 1:4, etc.), a pressure of 1.8-2.2 MPa (e.g., 1.8 MPa, 1.9 MPa, 2 MPa, 2.1 MPa, 2.2 MPa, etc.), and a temperature of 300-320℃ (e.g., 300℃, 305℃, 310℃, 315℃, 320℃, etc.).

[0068] Preferably, the protective gas includes nitrogen and / or argon.

[0069] This invention applies a Pd-W-Mo / GAC catalyst to the hydrodeoxygenation reaction of microalgae oil, employing a "dynamic adjustment of the reaction atmosphere" strategy: In the initial stage of the reaction, under a low H2 partial pressure environment, the Pd active centers preferentially interact with the C=O bonds in the microalgae oil; this stage is primarily a deoxygenation reaction, with fatty acid conversion exceeding 60%. In the middle stage, increasing the H2 content accelerates the hydrogenation reaction of olefin intermediates (such as C18:1). In the later stage, restoring the low H2 atmosphere inhibits excessive hydrogenation and reduces the formation of byproduct alkanes. This strategy can reduce byproducts and improve product purity.

[0070] This invention utilizes the directional conversion of microalgal oil and the dynamic changes in the oxidation states of W and Mo (W 6+ ↔W 4+ Mo 6+ ↔Mo 4+ The catalyst has an anti-carbon deposit effect, and ultimately produces second-generation biodiesel with a C15-C18 straight-chain alkane content of more than 95%. The catalyst still maintains a deoxygenation efficiency of more than 90% after 100 hours of continuous reaction.

[0071] Compared with the prior art, the present invention has at least the following beneficial effects:

[0072] This invention innovatively transforms the large amount of algal sludge waste generated after microalgae lipid extraction into porous green activated carbon material GAC with high specific surface area, well-developed pore structure, and excellent adsorption performance through a specific chemical activation and carbonization process. Furthermore, using this algal sludge-based GAC as a carrier, noble metals are loaded to prepare a highly dispersed and highly active heterogeneous catalyst. This catalyst exhibits excellent catalytic performance in the hydrodeoxygenation reaction of microalgae oil: it not only achieves efficient oil conversion, but more importantly, it exhibits extremely high selectivity for the target product—hydrocarbon-based biodiesel (mainly composed of C15-C18 alkanes and their isomers). Simultaneously, the catalyst itself also exhibits good structural stability and recycling potential.

[0073] The research results of this invention not only open up a new and economically feasible technical path for the efficient and sustainable production of high-quality second-generation biodiesel, but also provide a solution with important practical significance for the resource utilization and high-value utilization of a large amount of solid waste in the microalgae bioenergy industry, achieving the dual goals of "turning waste into treasure" and green industrial closed loop. Attached Figure Description

[0074] Figure 1 This is a picture of the freeze-dried algal mud prepared in Example 1.

[0075] Figure 2 This is a SEM microscopic characterization image of the algae mud-based activated carbon prepared in Example 1.

[0076] Figure 3 This is the gas chromatogram of the product in Application Example 1. Detailed Implementation

[0077] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0078] Preparation Example 1

[0079] This preparation example provides a method for preparing algae mud-based activated carbon, including the following steps:

[0080] (1) Pretreatment of microalgae sludge

[0081] Take 1000g of wet *Botrytis cinerea* sludge and place it in a vacuum freeze dryer. Freeze-dry at -50℃ and 0.1Pa for 24 hours to obtain dried sludge (moisture content reduced to below 5%). The image of the freeze-dried sludge is shown below. Figure 1As shown; the dried algal mud was placed in a high-speed pulverizer and pulverized for 30 seconds, then passed through a 100-mesh sieve, and the powder that passed through the sieve (about 280g) was collected; by SEM observation, the powder retained 92% of the natural fibrous microchannels, with the channel diameter concentrated in 8-12μm and the channel walls intact;

[0082] (2) Low-temperature pyrolysis preserves natural microchannels

[0083] Weigh 200g of pretreated algal mud powder, place it in a quartz boat, put it in the central constant temperature zone of a tube furnace, purge with nitrogen (flow rate 80mL / min) for 30min to remove air, then start the temperature program: heat to 320℃ at a rate of 5℃ / min, hold for 2h, the weight loss after pyrolysis is 35%; after pyrolysis, cool naturally to 25℃ to obtain black pyrolysis product (about 130g).

[0084] (3) Gradient heating of composite activator to create pores

[0085] (3.1) Preparation of activator: Weigh 48.75g KOH and 16.25g K2CO3 (mass ratio 3:1), put them into an agate mortar and grind for 30min until they are evenly mixed. Add 130g of pyrolysis product (mass ratio of activator to pyrolysis product 1:2) and continue grinding for 1h to ensure that the activator is evenly attached.

[0086] (3.2) Gradient temperature activation: The mixture was transferred to a corundum boat and placed in a tube furnace. Nitrogen gas was introduced (flow rate 80 mL / min) for 30 min, and then the following temperature program was executed:

[0087] 25℃→400℃: heating rate 5℃ / min, hold for 2h; K2CO3 begins to decompose during this stage;

[0088] 400℃→650℃: heating rate 5℃ / min, holding for 2h; the reaction between KOH and carbon materials intensifies, the weight loss rate of the system increases by 20%, and nanopores of 2-50nm are formed;

[0089] 650℃→850℃: heating rate 5℃ / min, holding for 1h; nanopores are further deepened;

[0090] (4) Post-treatment: After the activated product is cooled to 25°C, it is transferred to a beaker and washed in two steps:

[0091] The product was first immersed in 1 mol / L nitric acid solution and magnetically stirred for 2 hours. During this time, the pH of the solution was monitored until it stabilized at 6.5. The product was then rinsed with deionized water. Next, 5 wt% citric acid solution (solid-liquid ratio 1:10) was added and stirred for 1 hour. The product was then washed with deionized water until the conductivity of the filtrate was <10 μS / cm. Finally, the product was dried in an oven at 110℃ for 12 hours to obtain a brownish-black algae mud-based activated carbon (GAC) product (approximately 58 g).

[0092] The microalgae-based activated carbon prepared by the method in Example 1 was characterized by SEM (e.g., Figure 2 The images reveal that the samples exhibit highly irregular blocky or granular aggregates. Unlike spherical or regular crystals, this morphology is a typical characteristic of biomass precursors after high-temperature pyrolysis and chemical activation. Simultaneously, the roughness of the particle surface indicates that the activator has successfully reacted with the carbon framework, etching the surface and significantly increasing the material's specific surface area. Furthermore, the porous surface structure provides favorable conditions for subsequent loading.

[0093] Preparation Example 2

[0094] This embodiment provides a method for preparing algae-based activated carbon, which differs from Preparation Example 1 only in that:

[0095] The heating program in step (2) is as follows: heat to 400℃ at a rate of 2℃ / min and hold for 1 hour;

[0096] In step (3.1), the mass ratio of KOH to K2CO3 is 2:1, and the mass ratio of activator to pyrolysis product is 1:1.

[0097] The heating procedure in step (3.2) is as follows:

[0098] 25℃→450℃: heating rate 8℃ / min, holding time 0.5h;

[0099] 450℃→650℃: heating rate 2℃ / min, hold for 1 hour;

[0100] 650℃→850℃: heating rate 2℃ / min, holding time 0.5h;

[0101] The other steps are the same as in Preparation Example 1.

[0102] Preparation Example 3

[0103] This preparation example provides a method for preparing algae-based activated carbon, which differs from Preparation Example 1 only in that:

[0104] The heating program in step (2) is as follows: heat to 300℃ at a rate of 8℃ / min and hold for 3 hours;

[0105] In step (3.1), the mass ratio of KOH to K2CO3 is 4:1, and the mass ratio of activator to pyrolysis product is 1:3.

[0106] The heating procedure in step (3.2) is as follows:

[0107] 25℃→350℃: heating rate 12℃ / min, holding time 1.5h;

[0108] 350℃→550℃: heating rate 8℃ / min, hold for 2 hours;

[0109] 550℃→750℃: heating rate 8℃ / min, holding time 1.5h;

[0110] The other steps are the same as in Preparation Example 1.

[0111] Preparation Example 4

[0112] This preparation example provides a method for preparing algae-based activated carbon, which differs from Preparation Example 1 only in that the heating procedure in step (3.2) is as follows:

[0113] 25℃→500℃: heating rate 10℃ / min, hold for 2 hours;

[0114] 500℃→800℃: heating rate 5℃ / min, hold for 2 hours;

[0115] The other steps are the same as in Preparation Example 1.

[0116] Preparation Example 5

[0117] This preparation example provides a method for preparing algae mud-based activated carbon. The only difference between this method and Preparation Example 1 is that in step (1), wet algae mud of *Botrytis cinerea* is replaced with algae mud of *Chlorella vulgaris*. Other steps are the same as in Preparation Example 1.

[0118] Comparative Preparation Example 1

[0119] This comparative preparation example provides a method for preparing algae mud-based activated carbon. The only difference between this method and Preparation Example 1 is that in step (3.1), only K2CO3 (without KOH) is used as the activator, and the total amount of activator remains unchanged. Other steps are the same as in Preparation Example 1.

[0120] Comparative Preparation Example 2

[0121] This comparative preparation example provides a method for preparing algae mud-based activated carbon. The only difference between this method and Preparation Example 1 is that in step (3.1), only KOH (excluding K2CO3) is used as the activator, and the total amount of activator remains unchanged. Other steps are the same as in Preparation Example 1.

[0122] Comparative preparation example 3

[0123] This comparative preparation example provides a method for preparing algae-based activated carbon, which differs from Preparation Example 1 only in that:

[0124] In step (3.2), linear heating activation was used: 25℃→800℃, heating rate 5℃ / min, holding for 3h, and other steps were the same as in preparation example 1.

[0125] Comparative preparation example 4

[0126] This comparative preparation example provides a method for preparing wood-based activated carbon, which differs from Preparation Example 1 only in that the dried algae mud in step (1) is replaced with wood chips; the other steps are the same as in Preparation Example 1.

[0127] Test Example 1

[0128] The specific surface area and the number of acidic sites of the activated carbons prepared in Preparation Examples 1-5 and Comparative Preparation Examples 1-4 were tested. The specific surface area was tested using the BET method. The number of acidic sites was tested using the NH3-TPD method.

[0129] The results are summarized in Table 1.

[0130] Table 1

[0131]

[0132] The test results show that:

[0133] (1) As can be seen from Preparation Examples 1 to 5, the algae-based activated carbon obtained by the present invention through specific pyrolysis and activation treatment has a multi-level pore structure of "micron-level interconnected pores + nano-level catalytic pores", and the specific surface area can reach 910-1108 (m²). 2 The number of acidic sites is 1.65-2.15 mmol / g, which is more effective than activated carbon produced by traditional methods.

[0134] (2) By comparing Preparation Example 1 and Preparation Example 4, it can be seen that the present invention can achieve a better technical effect of increasing the specific surface area by adopting a three-stage heating method compared with a two-stage heating method; by comparing Preparation Example 1 and Preparation Example 5, it can be seen that the present invention uses a specific type of microalgae, which is conducive to the retention of natural microchannels and the formation of acidic sites.

[0135] (3) By comparing Preparation Example 1 with Comparative Preparation Examples 1-3, it can be seen that the present invention increases the specific surface area of ​​the material by using a composite activator and a staged heating strategy. By comparing Preparation Example 1 with Comparative Preparation Example 4, it can be seen that the activated carbon prepared by the algae mud raw material of the present invention has a higher specific surface area and a higher number of acidic sites than the sawdust raw material used in the traditional method.

[0136] Example 1

[0137] This embodiment provides a catalyst comprising a support GAC (provided in Preparation Example 1) and metals (W, Mo, and Pd) supported on the support, wherein the mass ratio of the support to the metal is 1:0.01(Pd):0.05(W):0.05(Mo).

[0138] The method for preparing the catalyst includes the following steps:

[0139] (1) Precursor preparation and concentration control

[0140] (1.1) W precursor solution: Weigh 5.82 g of (NH4)6W7O 24 Add 6H₂O to 500 mL of deionized water, stir on a magnetic stirrer for 30 minutes to prepare a 0.03 mol / L W solution. 6+ The solution is colorless and transparent.

[0141] (1.2) Mo precursor solution: Weigh 2.52 g (NH4)2MoO4, add 500 mL of deionized water, stir for 30 minutes, and prepare a 0.0255 mol / L Mo precursor solution. 6+ The solution is pale yellow and transparent.

[0142] (1.3) Pd precursor solution: Weigh 0.318 g Pd(OAC)2, add 50 mL of anhydrous ethanol and 50 mL of deionized water (volume ratio 1:1), stir for 20 minutes until completely dissolved, and prepare a 0.0142 mol / L Pd solution. 2+ The solution is brownish-yellow and transparent.

[0143] (2) Step-by-step equal-volume impregnation process

[0144] (2.1) Co-impregnation loading of W and Mo:

[0145] 3g of GAC was dried in an oven at 150℃ for 2 hours. After cooling, its saturated water absorption was determined to be 3.2mL (pore volume 1.07cm³) using a vacuum method. 3 / g); based on the W to Mo molar ratio of 1:1 and the target loading, 3g of GAC requires 0.15g of W and 0.15g of Mo. Accordingly, 27.2mL of W precursor solution and 61.3mL of Mo precursor solution are transferred, mixed evenly, and concentrated to 3.2mL of mixed solution.

[0146] Place the dried GAC in a 50 mL stoppered Erlenmeyer flask, add the concentrated mixture from above all at once, and place the flask in an ultrasonic cleaner for 30 minutes, during which time the solution will be completely adsorbed by the GAC. Remove the Erlenmeyer flask, seal it, and let it stand at room temperature for 4 hours to allow W to settle. 6+ Mo 6+ After sufficient coordination with the acidic sites on the GAC surface, intermediate one is obtained;

[0147] (2.2) Stepwise impregnation load of Pd:

[0148] GAC intermediate one, which adsorbed W and Mo precursors, was transferred to a petri dish and dried in an oven at 150°C for 3 hours to remove residual moisture. Based on the remaining pore volume of GAC, 19.85 mL of Pd precursor solution was added, and the mixture was allowed to stand at room temperature for 24 hours and then dried in an oven at 150°C for 3 hours to obtain intermediate two.

[0149] (3) Drying, roasting and reduction treatment

[0150] (3.1) Drying: The impregnated intermediate II was placed in a vacuum drying oven and dried at 60°C for 6 hours, and then heated to 80°C for 6 hours to obtain a black solid powder;

[0151] (3.2) Calcination: The dried sample was placed in a tube furnace and heated to 500°C at a rate of 10°C / min in an air atmosphere, held for 4 hours, and then cooled to room temperature;

[0152] (3.3) Reduction: The gas volume ratio of H2 and nitrogen was switched to a 1:1 mixture and heated to 400℃ at a rate of 10℃ / min. The temperature was held for 4 hours. After the reduction was completed, the temperature was cooled to 25℃ to obtain the Pd-W-Mo / GAC catalyst.

[0153] Examples 2-5

[0154] Examples 2-5 each provide a catalyst, which differs from Example 1 only in that the support provided in Preparation Example 1 is replaced with the support provided in Preparation Examples 2-5, and the rest is the same as in Example 1.

[0155] Comparative Examples 1-4

[0156] Comparative Examples 1-4 each provide a catalyst, which differs from Example 1 only in that the support provided in Preparation Example 1 is replaced with the support provided in Comparative Preparation Examples 1-4, and the rest is the same as in Example 1.

[0157] Application Example 1

[0158] This application example provides a method for preparing hydrocarbon-based biodiesel from microalgae oil, including the following steps:

[0159] (1) Construction of high temperature and high pressure reactor and catalyst loading

[0160] A 300mL high-pressure reactor (made of Hastelloy alloy) was used, equipped with a magnetic stirrer (stirring speed adjustable from 0 to 1200 r / min), an electric heating mantle (temperature control range room temperature to 600℃, accuracy ±1℃) and a gas inlet and outlet system; 2g of Pd-W-Mo / GAC catalyst (particle size 20-40 mesh, provided in Example 1) was vacuum dried (110℃, 2h) and then added to the reactor, ensuring that the catalyst was evenly spread on the bottom of the reactor;

[0161] (2) Raw material pretreatment and feeding system

[0162] Microalgae oil preparation: Weigh 12g of *Botrytis cinerea* oil (mainly C16-C18 fatty acids, with C18:3 accounting for 35%) according to the mass ratio of microalgae oil to catalyst of 6:1 and add it to the reaction vessel. Then add 30ml of cyclohexane as a solvent and stir for 30 minutes to form a homogeneous solution.

[0163] Sealing and inertization: After closing the reactor top cover and checking the sealing performance, purge the air inside the reactor with N2 (99.99% purity) and repeat 3 times (releasing the air after each pressure rise to 1.0 MPa) to ensure that the oxygen content inside the reactor is <0.1%;

[0164] (3) Dynamic Atmosphere Control Process

[0165] Gas supply and regulation: H2 and N2 cylinders are connected via a gas mixer, equipped with a precision pressure reducing valve and flow meter (accuracy ±1%), which can adjust the gas ratio and control the gas intake rate in real time;

[0166] Staged reaction control:

[0167] Initial stage (0-2 hours): Introduce a mixed gas of H2 / N2 = 1:3 (volume ratio), stabilize the pressure inside the vessel at 2.0 MPa through a pressure reducing valve, set the stirring speed to 600 r / min, and heat to 300℃;

[0168] Mid-term (2-6 hours): Stop ventilation, cool down quickly with ice, slowly ventilate, reintroduce H2 / N2=1:1 mixed gas to pressure 2.5MPa, raise the temperature to 320℃, and maintain the stirring rate at 600 r / min;

[0169] Later stage (6-8 hours): Use ice to quickly cool down, vent again, and introduce a H2 / N2=1:3 mixed gas to 2.0MPa, and the temperature drops to 310℃;

[0170] (4) Product collection and analysis

[0171] After the reaction was complete, the mixture was cooled to room temperature, and the gas inside the reactor was slowly vented. The liquid product was collected and analyzed by gas chromatography (HP-5 capillary column, FID detector). The gas chromatogram is shown below. Figure 3 As shown.

[0172] Application Example 2

[0173] This application example provides a method for preparing hydrocarbon-based biodiesel from microalgae oil, which differs from Application Example 1 only in that:

[0174] In step (1), 2g of the catalyst provided in Example 1 is replaced with 1.5g of the catalyst provided in Example 2, and in step (2), the amount of microalgae oil remains unchanged at 12g;

[0175] Step (3) staged reaction control:

[0176] Initial stage (0-2 hours): Introduce a mixed gas of H2 / N2 = 1:2 (volume ratio), stabilize the pressure inside the vessel at 1.8 MPa through a pressure reducing valve, set the stirring speed to 600 r / min, and heat to 290℃;

[0177] Mid-term (2-6 hours): Stop ventilation, cool down quickly with ice, and slowly ventilate. Re-introduce the H2 / N2=1:0.8 mixed gas to a pressure of 2.4MPa, raise the temperature to 310℃, and maintain the stirring rate at 600 r / min.

[0178] Later stage (6-8 hours): Use ice to quickly cool down, vent again, and introduce a H2 / N2=1:2 mixed gas to 2.0MPa, and the temperature drops to 310℃;

[0179] For the other steps, refer to Application Example 1.

[0180] Application Example 3

[0181] This application example provides a method for preparing hydrocarbon-based biodiesel from microalgae oil, which differs from Application Example 1 only in that:

[0182] In step (1), 2g of the catalyst provided in Example 1 is replaced with 1g of the catalyst provided in Example 3, and in step (2), the amount of microalgae oil used remains unchanged at 12g;

[0183] Step (3) staged reaction control:

[0184] Initial stage (0-2 hours): Introduce a mixed gas of H2 / N2 = 1:4 (volume ratio), stabilize the pressure inside the vessel at 2.2 MPa through a pressure reducing valve, set the stirring speed to 600 r / min, and heat to 310℃;

[0185] Mid-term (2-6 hours): Stop ventilation, cool down quickly with ice, and slowly ventilate. Re-introduce the H2 / N2=1:1.2 mixed gas to a pressure of 2.6MPa, raise the temperature to 330℃, and maintain the stirring rate at 600r / min.

[0186] Later stage (6-8 hours): Use ice to quickly cool down, vent again, and introduce a H2 / N2=1:4 mixed gas to 2.2MPa, and the temperature drops to 320℃;

[0187] For the other steps, refer to Application Example 1.

[0188] Application Example 4-5

[0189] Application Examples 4-5 provide a method for preparing hydrocarbon-based biodiesel from microalgae oil. The only difference between these methods and Application Example 1 is that the catalyst provided in Example 1 is replaced with the catalyst provided in Examples 4-5. Other aspects are the same as in Application Example 1.

[0190] Application Example 6

[0191] This application example provides a method for preparing hydrocarbon-based biodiesel from microalgae oil. The only difference between this method and application example 1 is that the gas atmosphere in the initial, middle and later stages of step (3) is pure hydrogen. For other aspects, refer to application example 1.

[0192] Compare and contrast examples 1-4

[0193] Comparative Application Examples 1-4 provide a method for preparing hydrocarbon-based biodiesel from microalgae oil. The only difference between them and Application Example 1 is that the catalyst provided in Example 1 is replaced with the catalyst provided in Comparative Examples 1-4. Other aspects are the same as in Application Example 1.

[0194] Test Example 2

[0195] Gas phase analysis was performed on the products obtained from corresponding use cases 1-6 and comparative application examples 1-4, and the results are shown in Table 2.

[0196] Table 2

[0197]

[0198] The test results show that:

[0199] (1) As can be seen from Application Examples 1 to 6, the present invention uses algae mud-based activated carbon with high specific surface area and high number of acidic sites as a support to support metal to form a catalyst. The catalyst exhibits excellent catalytic performance in the hydrodeoxygenation reaction of microalgae oil, with C15-C18 straight-chain alkane content as high as 81.1-96.8%, by-product content as low as 1.5-12.5%, and cetane number increased to 52.1-62.5 (far exceeding the 45-50 of traditional catalysts).

[0200] (2) By comparing Application Example 1 with Application Examples 4-5, it can be seen that by further limiting the microalgae species and gradient heating program, the catalyst prepared by the present invention can have better catalytic performance; by comparing Application Example 1 with Application Example 6, it can be seen that by dynamically controlling the atmosphere, the present invention can improve the purity of the target product compared with the traditional method of fixing pure hydrogen.

[0201] (3) By comparing Application Example 1 with Comparative Application Examples 1-4, it can be seen that the present invention can significantly improve the catalytic performance of the prepared catalyst by using a composite activator, a staged heating strategy, and specific microalgae raw materials.

[0202] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing algae-based activated carbon, characterized in that, The preparation method includes the following steps: (1) Heat the algae mud powder to pyrolyze it to obtain the pyrolysis products; (2) The pyrolysis product and the activator are mixed and activated by gradient heating to obtain the algae mud-based activated carbon; the activator includes a combination of potassium hydroxide and potassium carbonate.

2. The preparation method according to claim 1, characterized in that, The algae mud powder mentioned in step (1) comes from sources including Botrytis cinerea and / or Chlorella vulgaris; Preferably, the method for preparing the algae mud powder in step (1) includes: drying and pulverizing the waste wet algae mud after oil extraction to obtain the algae mud powder; Preferably, the heating process in step (1) is as follows: heating to 300-400℃ at a rate of 2-8℃ / min and holding for 1-3 hours.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the pyrolysis product to the activator in step (2) is (1-3):1; Preferably, the mass ratio of potassium hydroxide to potassium carbonate in step (2) is (2-4):1; Preferably, the gradient temperature activation procedure in step (2) is as follows: increase the temperature to 350-450℃ at 5-12℃ / min and hold for 0.5-2h; then increase the temperature to 550-650℃ at 2-8℃ / min and hold for 1-2h; then increase the temperature to 750-850℃ at 2-8℃ / min and hold for 0.5-1.5h. Preferably, step (2) further includes a washing process after the gradient temperature activation; Preferably, the washing solution used in the washing process includes nitric acid solution and / or citric acid solution; Preferably, the washing process further includes a drying process.

4. Algae-based activated carbon prepared by the method according to any one of claims 1-3.

5. A catalyst, characterized in that, The catalyst includes a support and a metal supported on the support; the support includes the algae-based activated carbon according to claim 4.

6. The catalyst according to claim 5, characterized in that, The metal includes any one or a combination of at least two of palladium, tungsten, or molybdenum, preferably a combination of palladium, tungsten, and molybdenum; Preferably, the mass ratio of palladium, tungsten and molybdenum is 1:(5-10):(5-10); Preferably, the mass ratio of the carrier to the metal is 1:(0.05-0.15).

7. A method for preparing a catalyst according to claim 5 or 6, characterized in that, The preparation method includes the following steps: The catalyst is obtained by mixing the solution of the support and the metal precursor, followed by coordination reaction, drying, calcination and reduction.

8. The preparation method according to claim 7, characterized in that, The tungsten precursor includes ammonium tungstate; Preferably, the molybdenum precursor comprises ammonium molybdate; Preferably, the palladium precursor comprises palladium acetate; Preferably, the preparation method specifically includes the following steps: (1) Using the equal-volume impregnation method, the carrier, tungsten and molybdenum mixed precursor solution are mixed and adsorbed to obtain intermediate one; (2) The first intermediate is dried, and then the dried first intermediate and the palladium precursor solution are mixed and adsorbed by the equal volume impregnation method to obtain the second intermediate. (3) The intermediate II is dried, calcined and reduced to obtain the catalyst; Preferably, the drying temperature in step (3) is 50-90℃ and the drying time is 8-16h; Preferably, the calcination in step (3) includes: heating to 450-550°C at 8-12°C / min in an air atmosphere and holding for 3-5 hours; Preferably, the reduction in step (3) includes: heating to 350-450°C at a rate of 8-12°C / min and holding at that temperature for 3-5 hours in a mixed gas atmosphere of H2 and protective gas; Preferably, the volume ratio of H2 to protective gas is 1:(0.8-1.2).

9. A method for preparing hydrocarbon-based biodiesel from microalgae oil, characterized in that, The method includes: catalyzing the hydrodeoxygenation reaction of microalgae oil in the presence of a catalyst to obtain hydrocarbon-based biodiesel; the catalyst includes the catalyst as described in claim 5 or 6.

10. The method according to claim 9, characterized in that, The mass ratio of the microalgae oil to the catalyst is 6:(0.1-1). Preferably, the hydrodeoxygenation reaction is carried out in the presence of a solvent; Preferably, the solvent comprises cyclohexane and / or n-hexane; Preferably, the deoxygenation and hydrogenation reactions specifically include: 0-2 h, a deoxygenation reaction at a volume ratio of H2 to protective gas of 1:(2-4), a pressure of 1.8-2.2 MPa, and a temperature of 290-310 °C; 2-6 h, a hydrogenation reaction at a volume ratio of H2 to protective gas of 1:(0.8-1.2), a pressure of 2.4-2.6 MPa, and a temperature of 310-330 °C; and 6-8 h, a hydrogenation reaction at a volume ratio of H2 to protective gas of 1:(2-4), a pressure of 1.8-2.2 MPa, and a temperature of 300-320 °C.

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