Carbon nano tube loaded calcium oxide catalyst as well as preparation method and application thereof

Abstract

The invention provides a carbon nano tube loaded calcium oxide catalyst and a preparation method and application thereof, the preparation method of the carbon nano tube loaded calcium oxide catalyst comprises the following steps: S100: mixing a calcium ion-containing solution, a carbon nano tube and a carbonate ion-containing solution, and reacting to generate a precipitate mixture; s200, the precipitate mixture is separated, filtered and washed, and a CaCO3 (at) CNTs precipitate is obtained; and S300, the CaCO3-coated CNTs precipitate is dried and calcined, and the carbon nanotube-loaded calcium oxide catalyst is obtained, the carbon nanotube-loaded calcium oxide catalyst has high conductivity and high dispersity, the conductivity of an electrolytic transesterification reaction system in the biodiesel production process is enhanced, and the biodiesel yield is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of biodiesel, and in particular to a carbon nanotube-supported calcium oxide catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of the global economy, the demand for energy in industry and transportation has also increased. The shortage of fossil fuels has become increasingly prominent. At the same time, the large-scale use of fossil energy has caused serious damage to the global environment. The search for green and clean energy has become a hot topic in current research. Biodiesel, as a clean and renewable energy source, has attracted increasing attention due to its biodegradability, renewability, and environmental friendliness. Biodiesel raw materials mainly come from oil plants or waste cooking oil and animal fats. If waste cooking oil and animal fats can be effectively utilized, they can not only be converted into high-value-added products, but also significantly reduce the burden these wastes place on the environment.

[0003] Traditional methods for producing biodiesel primarily include direct mixing, high-temperature thermal cracking, microemulsion, and transesterification. Transesterification is a common method for biodiesel production, but its catalytic systems still face significant challenges. Acid catalysis suffers from low efficiency, equipment corrosion, and complex catalyst preparation. Enzyme catalysis, while offering advantages such as mild conditions and good selectivity, suffers from poor tolerance to alcohols and high costs, limiting its industrial application. In contrast, base-catalyzed transesterification is widely used due to its fast reaction rate and high conversion rate. However, homogeneous base catalysts are difficult to recycle and reuse, resulting in environmental pollution and increased economic costs. Therefore, heterogeneous base catalysts, due to their ease of separation and reusability, have become a common choice for biodiesel catalytic transesterification. Calcium oxide (CaO) has attracted considerable attention in industrial applications due to its widespread availability, low cost, and high catalytic activity. However, alkaline catalysts are highly sensitive to the acid value and moisture content of the feedstock. High acid values ​​can easily trigger saponification, while moisture can lead to catalyst deactivation. These issues severely restrict the efficiency and yield of biodiesel production.

[0004] To overcome this limitation, electrolytic transesterification has been applied to biodiesel production as an emerging process. Compared with the traditional two-step method, this method simplifies the preparation and purification steps by driving the reaction electrochemically. In the electrolytic transesterification reaction, the high water content of the raw materials facilitates the electrolysis reaction. The water at the anode and cathode in the reactants is electrolyzed to form H + and OH - This electrolysis mechanism not only allows the use of raw materials with high acid value and high water content, but also eliminates the need for dehydration. In the process of preparing biodiesel by electrolytic transesterification, the conductivity of the system has a significant impact on the biodiesel yield. However, the poor dispersion and conductivity of CaO particles in the electrolyte limit the improvement of biodiesel yield. Summary of the Invention

[0005] The purpose of the present invention is to provide a carbon nanotube-loaded calcium oxide catalyst and its preparation method and application. The prepared carbon nanotube-loaded calcium oxide catalyst has high conductivity and dispersibility, enhances the conductivity of the electrolytic transesterification reaction system in the process of producing biodiesel, and improves the yield of biodiesel.

[0006] To achieve the above-mentioned object, the present invention provides a method for preparing a carbon nanotube-loaded calcium oxide catalyst, which comprises the following steps: S100: adding carbon nanotubes to a calcium ion-containing solution and mixing them to obtain a mixed solution, and then adding a carbonate ion-containing solution to the mixed solution to react and generate a precipitate mixture; S200: separating, filtering, and washing the precipitate mixture to obtain a CaCO3@CNTs precipitate; S300: drying and calcining the CaCO3@CNTs precipitate to obtain a carbon nanotube-loaded calcium oxide catalyst.

[0007] The technical effect achieved by adopting this technical solution is as follows: CaCO3 is generated by the precipitation of calcium ions and carbonate ions on the surface of carbon nanotubes (CNTs), obtaining a carbon nanotube-loaded calcium carbonate (CaCO3@CNTs) precipitate, and a carbon nanotube-loaded calcium oxide (CaO@CNTs) catalyst is obtained after calcination. This not only makes use of the conductivity of CNTs to make the CaO@CNTs catalyst have high conductivity, but also achieves uniform loading and structural stability of the CaO active component, avoids particle agglomeration, has high dispersibility, and has a simple preparation process and is easy to scale up.

[0008] Furthermore, step S100 includes the following steps: S110: adding carbon nanotubes to a solution containing calcium ions and mixing them to obtain a mixed solution; S120: adding a solution containing carbonate ions to the mixed solution to react and generate a precipitate mixture.

[0009] The technical effect achieved by adopting this technical solution is as follows: by first uniformly dispersing the carbon nanotubes in a calcium ion-containing solution and then adding a carbonate ion-containing solution, the full reaction of the carbonate ions and the calcium ions can be promoted to ensure the complete generation of calcium carbonate. At the same time, the pre-uniform dispersion of the carbon nanotubes is utilized to enable the generated calcium carbonate to fully contact with them, ensuring that the calcium carbonate is uniformly loaded on the surface of the carbon nanotubes, and ultimately obtaining a uniformly distributed carbon nanotube-loaded calcium oxide catalyst, which significantly improves the performance and stability of the catalyst.

[0010] Furthermore, the calcium ion solution is selected from at least one of CaCl2, Ca(NO3)2, and Ca(CH3COO)2, and the concentration of the calcium ion solution is 0.5~2mol / L; and / or the carbonate ion solution is selected from at least one of Na2CO3, K2CO3, and (NH4)2CO3, and the concentration of the carbonate ion solution is 0.5~2mol / L.

[0011] The technical effect achieved after adopting this technical solution is: the selection of calcium salts and carbonates with higher solubility and appropriate concentrations can promote the rapid reaction on the surface of CNTs to form a uniform CaCO3 deposition layer, which is conducive to the uniform distribution of CaO and CNTs in the CaO@CNTs catalyst.

[0012] Furthermore, separation is performed using a centrifuge at a speed of 2000-5000 r / min and a separation time of 8-12 min; and / or the drying temperature is 80-120° C. and the drying time is 1-3 h; and / or the calcination temperature is 550-950° C., the calcination heating rate is 5-10° C. / min, and the calcination time is 0.5-3 h.

[0013] The technical effects achieved after adopting this technical solution are as follows: a centrifuge is used to separate the precipitation mixture, and the appropriate centrifuge speed and separation time can not only improve the separation purity of the precipitation in the precipitation mixture, but also help to form loose precipitation particles; the CaCO3@CNTs precipitate is dried, and mild drying conditions avoid particle collapse and pore blockage caused by rapid dehydration, thereby retaining the pore structure of the catalyst; the optimized calcination heating rate, calcination temperature and calcination time promote the complete conversion of CaCO3 to CaO, while regulating the grain size and crystal structure, enhancing the basic site density and sintering resistance of the catalyst, and ultimately improving its catalytic activity and stability.

[0014] The present invention also provides a carbon nanotube-supported calcium oxide catalyst, which is prepared using the above-mentioned preparation method; wherein the mass of the carbon nanotubes accounts for 10-20wt% of the total mass of the carbon nanotube-supported calcium oxide catalyst.

[0015] The technical effect achieved after adopting this technical solution is: when the CNTs content in the CaO@CNTs catalyst is too high, it will shield the CaO active sites and affect the activity of the CaO@CNTs catalyst. When the CNTs content in the CaO@CNTs catalyst is too low, it will cause the electrical conductivity of the catalyst to decrease. Therefore, the CNTs content in the CaO@CNTs catalyst will affect the performance of the CaO@CNTs catalyst.

[0016] The present invention also provides a biodiesel, which is prepared by using the carbon nanotube-supported calcium oxide catalyst.

[0017] The technical effect achieved after adopting this technical solution is: when using an electrolytic transesterification reaction system to produce biodiesel, the high conductivity and high dispersibility of the catalyst have a direct impact on increasing the yield of biodiesel. Therefore, the use of CaO@CNTs catalyst increases the yield of biodiesel produced from oil and fat, thereby improving the economic and environmental benefits of biodiesel enterprises.

[0018] The present invention also provides a method for preparing biodiesel, which comprises the following steps: S10: adding oil, low-carbon alcohol, carbon nanotube-loaded calcium oxide catalyst and electrolyte solution into an electrolytic cell device and stirring to react to obtain a mixed oil liquid; S20: allowing the mixed oil liquid to stand and separate into layers, and taking the upper layer of oil liquid; S30: centrifuging the upper layer of oil liquid to obtain biodiesel.

[0019] The technical effect achieved after adopting this technical solution: Since waste cooking oil and animal fats are raw materials with high acid value and high water content, an electrolytic ester exchange reaction system and a high-conductivity catalyst are adopted. This method is simple, has high yield and low production cost.

[0020] Furthermore, the stirring includes one of mechanical stirring, magnetic stirring, and ultrasonic-assisted stirring, the stirring speed is 400~1000r / min, the stirring temperature is 55~105°C, and the stirring time is 60~150min; and / or the electrolytic cell device is one of a single-chamber electrolytic cell reactor and a double-chamber electrolytic cell reactor, the voltage of the electrolytic reactor is 15~35V; and / or the centrifugal separation uses a centrifuge, the centrifuge speed is 5000~10000r / min, and the centrifugal separation time is 5~15min.

[0021] The technical effects achieved after adopting this technical solution are as follows: stirring ensures uniform mixing of the electrolytic transesterification reaction system, overcomes the interphase mass transfer resistance of oil, low-carbon alcohol and catalyst in the transesterification reaction, the stirring temperature is in the medium and high temperature range, reduces the viscosity of the reaction system, accelerates molecular motion, and avoids excessive temperature causing volatilization of low-carbon alcohol or side reactions; the voltage of the electrolytic reactor is moderate, which balances the reaction kinetics and energy consumption, and avoids side reactions caused by excessive voltage; high-speed centrifugation effectively separates biodiesel, glycerol by-products and unreacted products, shortens the traditional standing stratification time, and improves the purity of biodiesel.

[0022] Furthermore, the amount of the carbon nanotube-supported calcium oxide catalyst added is 1-10 wt% relative to the mass of the oil; and / or the molar ratio of the low-carbon alcohol to the oil is (5-20):1.

[0023] The technical effects achieved by adopting this technical solution are as follows: when the CaO@CNTs catalyst content is too low, the electrolytic ester exchange reaction is incomplete, the triglyceride conversion rate is low, and the biodiesel yield is reduced. When the CaO@CNTs catalyst content is too high, the separation difficulty increases, so an appropriate amount of CaO@CNTs catalyst is very important; low-carbon alcohols and oils produce biodiesel under the conditions of CaO@CNTs catalysts. Too little low-carbon alcohols lead to insufficient oil reaction, and too much low-carbon alcohols lead to increased separation burden and cost, so an appropriate amount of low-carbon alcohols is also important.

[0024] Furthermore, the oil includes at least one of lard, fish oil, and beef tallow; and / or the low-carbon alcohol includes at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, ethylene glycol, and allyl alcohol; and / or the electrolyte solution includes at least one of sodium chloride, potassium chloride, and sodium sulfate.

[0025] The technical effect achieved after adopting this technical solution: This method for preparing biodiesel is widely used, with a large selection of low-carbon alcohols, and an electrolyte solution is added to the electrolytic ester exchange system to enhance the conductivity of the system, thereby increasing the yield of biodiesel.

[0026] Compared with the existing technology, the following technical effects can be achieved: (1) The CaO@CNTs catalyst prepared by the present invention utilizes the excellent conductive properties of CNTs materials to load the catalytic active substance CaO to form a CaO@CNTs catalyst, which improves the conductivity of the electrolytic transesterification reaction system for preparing biodiesel and enhances the dispersibility of the CaO catalyst to increase the yield of biodiesel.

[0027] (2) The CaO@CNTs catalyst prepared by the present invention increases the conductivity of the electrolytic transesterification reaction system to 7.71 μS / cm, significantly enhancing the conductivity of the electrolytic transesterification reaction system.

[0028] (3) The CaO@CNTs catalyst prepared by the present invention achieved a biodiesel yield of up to 96.34%.

[0029] (4) The CaO@CNTs catalyst prepared by the present invention can be recycled. After five cycles, the yield of biodiesel produced by this catalyst is still 79.79%, and the yield is only reduced by 16.55% compared with the first use, showing good reusability and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which: Figure 1This is the XRD pattern of the CaO@CNTs catalyst provided in Example 1 of the present invention; Figure 2 This is the FESEM image of the CaO@CNTs catalyst provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0032] An embodiment of the present invention provides a method for preparing a carbon nanotube-supported calcium oxide catalyst, which comprises the following steps: S100: adding carbon nanotubes to a calcium ion-containing solution and mixing them to obtain a mixed solution, and then adding a carbonate ion-containing solution to the mixed solution to react and generate a precipitate mixture; S200: separating, filtering, and washing the precipitate mixture to obtain a CaCO3@CNTs precipitate; and S300: drying and calcining the CaCO3@CNTs precipitate to obtain a carbon nanotube-supported calcium oxide catalyst.

[0033] This embodiment provides a method for preparing a carbon nanotube-supported calcium oxide catalyst. Calcium ions and carbonate ions are precipitated on the surface of carbon nanotubes to generate CaCO3. The resulting CaO@CNTs catalyst, obtained after calcination, not only has high electrical conductivity due to the electrical conductivity of CNTs, but also achieves uniform loading and structural stability of CaO active sites, avoids particle agglomeration, and has high dispersibility. In addition, the preparation process is simple and easy to scale up.

[0034] In some embodiments of the present application, step S100 includes the following steps: S110: adding the carbon nanotubes to the calcium ion-containing solution and mixing to obtain a mixed solution; S120: adding the carbonate ion-containing solution to the mixed solution to react and generate the precipitation mixture.

[0035] In a preparation process of a carbon nanotube-loaded calcium oxide catalyst, the carbon nanotubes are first uniformly dispersed in a calcium ion solution, and then a carbonate ion solution is added. This can promote the full reaction of the carbonate ions and the calcium ions, ensuring the complete generation of calcium carbonate. At the same time, the pre-uniform dispersion of the carbon nanotubes allows the generated calcium carbonate to fully contact with the calcium ions, ensuring that the calcium carbonate is uniformly loaded on the surface of the carbon nanotubes. Ultimately, a uniformly distributed carbon nanotube-loaded calcium oxide catalyst is obtained, significantly improving the performance and stability of the catalyst.

[0036] In some embodiments of the present application, the calcium ion solution is selected from at least one of CaCl2, Ca(NO3)2, and Ca(CH3COO)2, and the concentration of the calcium ion solution is 0.5~2 mol / L; and / or the carbonate ion solution is selected from at least one of Na2CO3, K2CO3, and (NH4)2CO3, and the concentration of the carbonate ion solution is 0.5~2 mol / L.

[0037] In the preparation of a carbon nanotube-supported calcium oxide catalyst, selecting highly soluble calcium salts and carbonates at appropriate concentrations can promote a rapid reaction on the surface of the CNTs to form a uniform CaCO3 deposition layer, which promotes uniform distribution of CaO and CNTs in the CaO@CNTs catalyst. Preferably, the calcium ion solution is selected from CaCl2, and the carbonate ion solution is selected from Na2CO3.

[0038] In some embodiments of the present application, the separation in S200 is performed using a centrifuge, the rotation speed of the centrifuge is 2000~5000r / min, and the centrifugation time is 8~12min; and / or the drying temperature in step S300 is 80~120°C, and the drying time is 1~3h; and / or the calcination temperature in step S300 is 550~950°C, the calcination heating rate is 5~10°C / min, and the calcination time is 0.5~3h.

[0039] In the preparation process of a carbon nanotube-loaded calcium oxide catalyst, a centrifuge is used to separate the precipitate mixture. The appropriate centrifuge speed and separation time can not only improve the separation purity of the precipitate in the precipitate mixture, but also help to form loose precipitate particles; the CaCO3@CNTs precipitate is dried, and mild drying conditions avoid particle collapse and pore blockage caused by rapid dehydration, thereby retaining the pore structure of the catalyst; the optimized calcination heating rate, calcination temperature and calcination time promote the complete conversion of CaCO3 to CaO, while regulating the grain size and crystal structure, enhancing the basic site density and sintering resistance of the catalyst, and ultimately improving its catalytic activity and stability.

[0040] An embodiment of the present invention further provides a carbon nanotube-supported calcium oxide catalyst, which is prepared using the above-mentioned preparation method.

[0041] This application proposes a carbon nanotube-supported calcium oxide catalyst using the aforementioned preparation method. During the preparation process, carbon nanotubes are introduced to impart electrical conductivity to the catalyst, wherein the mass of the carbon nanotubes accounts for 10-20 wt% of the total mass of the carbon nanotube-supported calcium oxide catalyst. Excessive CNT content in the CaO@CNTs catalyst can shield the CaO active sites, affecting the activity of the CaO@CNTs catalyst. Excessive CNT content in the CaO@CNTs catalyst can reduce the electrical conductivity of the catalyst, while low CNT content can affect its performance.

[0042] An embodiment of the present invention further provides a biodiesel, which is prepared using the carbon nanotube-supported calcium oxide catalyst as described above.

[0043] The present application adopts the aforementioned carbon nanotube-loaded calcium oxide catalyst. When an electrolytic transesterification reaction system is used to produce biodiesel, this CaO@CNTs catalyst is used to increase the yield of biodiesel produced from oil and fat, thereby improving the economic and environmental benefits of biodiesel enterprises.

[0044] An embodiment of the present invention also provides a method for preparing biodiesel, which comprises the following steps: S10: adding oil, low-carbon alcohol, carbon nanotube-loaded calcium oxide catalyst and electrolyte solution into an electrolytic cell device and stirring to react to obtain a mixed oil liquid; S20: allowing the mixed oil liquid to stand and separate into layers, and taking the upper layer of oil liquid; S30: centrifuging the upper layer of oil liquid to obtain biodiesel.

[0045] In one biodiesel production process, waste cooking oil and animal fats, which have high acid values ​​and high water content, are used. Therefore, an electrolytic transesterification reaction system and a highly conductive CaO@CNTs catalyst are employed. This method is simple, offers high yields, and reduces production costs. Specifically, a transesterification reaction between low-carbon alcohols and fats occurs over the CaO@CNTs catalyst, producing biodiesel and glycerol as a byproduct. The biodiesel is then purified through stratification and centrifugation.

[0046] In some embodiments of the present application, the stirring in step S10 includes one of mechanical stirring, magnetic stirring, and ultrasonic-assisted stirring, the stirring speed is 400~1000r / min, the stirring temperature is 55~105°C, and the stirring time is 60~150min; and / or the electrolytic cell device in step S10 is one of a single-chamber electrolytic cell reactor and a double-chamber electrolytic cell reactor, and the voltage of the electrolytic cell device is 15~35V; and / or the centrifugal separation in step S30 uses a centrifuge, the speed of the centrifuge is 5000~10000r / min, and the centrifugal separation time is 5~15min.

[0047] In a biodiesel preparation process, stirring ensures uniform mixing of the electrolytic transesterification reaction system, overcomes the interphase mass transfer resistance of oil, low-carbon alcohol and catalyst in the transesterification reaction, and the stirring temperature is in the medium-high temperature range, which reduces the viscosity of the reaction system and accelerates molecular motion, while avoiding excessive temperature causing volatilization of low-carbon alcohol or side reactions; the voltage of the electrolytic reactor is moderate, balancing reaction kinetics and energy consumption, and avoiding side reactions caused by excessive voltage; high-speed centrifugation effectively separates biodiesel, glycerol byproducts and unreacted products, shortens traditional static stratification time, and improves the purity of biodiesel.

[0048] In some embodiments of the present application, the amount of the carbon nanotube-supported calcium oxide catalyst added is 1-10 wt % relative to the mass of the oil; and / or the molar ratio of the low-carbon alcohol to the oil is (5-20):1.

[0049] In the preparation process of biodiesel, when the CaO@CNTs catalyst content is too low, the electrolytic ester exchange reaction is incomplete and the triglyceride conversion rate is low, resulting in a decrease in biodiesel yield. When the CaO@CNTs catalyst content is too high, the separation difficulty increases, so an appropriate amount of CaO@CNTs catalyst is very important. When low-carbon alcohols and oils produce biodiesel under the conditions of CaO@CNTs catalysts, too little low-carbon alcohols will lead to insufficient oil reaction; too much low-carbon alcohols will increase the separation burden and cost, so an appropriate amount of low-carbon alcohols is also important.

[0050] In some embodiments of the present application, the oil includes at least one of lard, fish oil, and beef tallow; and / or the low-carbon alcohol includes at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, ethylene glycol, and allyl alcohol; and / or the electrolyte solution includes at least one of sodium chloride, potassium chloride, and sodium sulfate.

[0051] This method for preparing biodiesel is widely used, with a wide selection of low-carbon alcohols. Furthermore, adding an electrolyte solution to the electrolytic transesterification reaction system enhances the conductivity of the system, thereby increasing the yield of biodiesel. Preferably, the low-carbon alcohol is selected from methanol.

[0052] Example 1 An embodiment of the present invention provides a method for preparing biodiesel, comprising the following steps: S1: 0.75 g of carbon nanotubes were added to a 1 mol / L CaCl2 solution and ultrasonically mixed for 50 min to obtain a mixed solution. 1 mol / L Na2CO3 solution was then added to the mixed solution to react and generate a precipitate mixture. S2: The precipitated mixture is centrifuged, filtered, and washed, wherein the centrifuge speed is 3000 r / min and the centrifuge rotation time is 10 min to obtain a CaCO3@CNTs precipitate; S3: The CaCO3@CNTs precipitate was placed in an oven for drying at 105°C for 2 h. The dried CaCO3@CNTs precipitate was placed in a tube furnace and calcined and decomposed at 750°C in a nitrogen atmosphere at a heating rate of 10°C / min for 1 h to obtain the CaO@CNTs catalyst. S4: 20 g of lard, 9.275 g of low-carbon alcohol, 0.05 g of NaCl, and 0.4 g of CaO@CNTs catalyst were placed in a 100 mL electrolytic cell device, with a molar ratio of low-carbon alcohol to oil of 12:1. The amount of CaO@CNTs catalyst added was 2 wt% of the oil mass, and NaCl formed an electrolyte solution. A DC power supply was used to connect the positive and negative electrodes of the graphite electrodes to provide a stable voltage of 25 V to the electrolytic cell device. Magnetic stirring was used at a stirring speed of 500 r / min, a stirring time of 90 min, and a stirring temperature of 65°C to obtain a mixed oil liquid; S5: Let the mixed oil stand for 10 hours, wait for the layers to separate, and take the upper layer of oil; S6: The upper layer of oil is placed in a centrifuge for centrifugal separation. The speed of the centrifuge is 8000 r / min and the rotation time of the centrifuge is 10 minutes. Biodiesel is obtained after separation.

[0053] The analysis and characterization of the CaO@CNTs catalyst prepared in Example 1 is shown in Figure 1 and Figure 2 ,in Figure 1 This is the XRD pattern of the CaO@CNTs catalyst provided in Example 1 of the present invention; Figure 2 This is the FESEM image of the CaO@CNTs catalyst provided in Example 1 of the present invention.

[0054] In the preparation of biodiesel in Example 1, the conductivity of the electrolytic transesterification reaction system in the electrolytic cell device was 7.71 μS / cm, and the biodiesel yield measured by gas chromatograph (GC) was 96.34%.

[0055] Comparative Example 1 S1: Add 1 mol / L Na2CO3 solution to 1 mol / L CaCl2 solution and mix by ultrasonic for 50 min to generate a precipitate mixture; S2: centrifuge the precipitated mixture, filter, and wash it, wherein the centrifuge speed is 3000 r / min and the centrifuge rotation time is 10 min to obtain a CaCO3 precipitate; S3: The CaCO3 precipitate was placed in an oven for drying at 105°C for 2 h. The dried CaCO3 precipitate was placed in a tube furnace and calcined and decomposed at 750°C in a N2 atmosphere at a heating rate of 10°C / min for 1 h to obtain a CaO catalyst. S4: 20 g of lard, 9.275 g of low-carbon alcohol, 0.05 g of NaCl, and 0.4 g of CaO catalyst were placed in an electrolytic cell device with a volume of 100 mL, with the molar ratio of low-carbon alcohol to oil being 12:1. The amount of CaO catalyst added was 2 wt % of the oil mass, and NaCl formed an electrolyte solution. A DC power supply was connected to the positive and negative electrodes of the graphite electrodes to provide a stable voltage of 25 V to the electrolytic cell device. Magnetic stirring was used at a stirring speed of 500 r / min, a stirring time of 90 min, and a stirring temperature of 65° C. to react to obtain a mixed oil liquid; S5: Let the mixed oil stand for 10 hours, wait for the layers to separate, and take the upper layer of oil; S6: The upper layer of oil is placed in a centrifuge for centrifugal separation. The speed of the centrifuge is 8000 r / min and the rotation time of the centrifuge is 10 minutes. Biodiesel is obtained after separation.

[0056] In the preparation of biodiesel in Comparative Example 1, the conductivity of the electrolytic transesterification reaction system in the electrolytic cell device was 1.18 μS / cm, and the biodiesel yield measured by gas chromatograph (GC) was 60.50%.

[0057] Comparative Example 2 S1: Add 1 mol / L Na2CO3 solution to 1 mol / L CaCl2 solution and mix by ultrasonic for 50 min to generate a precipitate mixture; S2: centrifuge the precipitated mixture, filter, and wash it, wherein the centrifuge speed is 3000 r / min and the centrifuge rotation time is 10 min to obtain a CaCO3 precipitate; S3: The CaCO3 precipitate was placed in an oven for drying at 105°C for 2 h. The dried CaCO3 precipitate was placed in a tube furnace and calcined and decomposed at 750°C in a nitrogen atmosphere at a heating rate of 10°C / min for 1 h to obtain CaO. The obtained CaO was magnetically stirred and mixed with 0.75 g of carbon nanotubes and stirred for 30 min to obtain a calcium oxide and carbon nanotube mixed (CaO+CNTs) catalyst. S4: 20 g of lard, 9.275 g of low-carbon alcohol, 0.05 g of NaCl, and 0.4 g of CaO+CNTs catalyst were placed in a 100 mL electrolytic cell device, with a molar ratio of low-carbon alcohol to oil of 12:1. The amount of CaO+CNTs catalyst added was 2 wt % of the oil mass, and NaCl formed an electrolyte solution. A DC power supply was used to connect the positive and negative electrodes of the graphite electrodes to provide a stable voltage of 25 V to the electrolytic cell device. Magnetic stirring was used at a stirring speed of 500 r / min, a stirring time of 90 min, and a stirring temperature of 65°C to obtain a mixed oil liquid; S5: Let the mixed oil stand for 10 hours, wait for the layers to separate, and take the upper layer of oil; S6: The upper layer of oil is placed in a centrifuge for centrifugal separation. The speed of the centrifuge is 8000 r / min and the rotation time of the centrifuge is 10 minutes. Biodiesel is obtained after separation.

[0058] In the preparation of biodiesel in Comparative Example 2, the conductivity of the electrolytic transesterification reaction system in the electrolytic cell device was 5.32 μS / cm, and the biodiesel yield measured by gas chromatograph (GC) was 70.79%.

[0059] Table 1 Application test results of the catalysts of Examples and Comparative Examples 1-2 From the conductivity of the electrolytic transesterification reaction system in the electrolytic cell device, it can be seen that the CaO@CNTs catalyst prepared in Example 1 not only retains the high conductivity of CNTs, but also greatly improves the yield of biodiesel preparation.

[0060] Example 2 The embodiment of the present invention provides a method for preparing biodiesel, wherein the relevant process conditions in Example 1 remain unchanged, except that the voltage in step S4 is 20 V and the amount of CaO@CNTs catalyst added is 3 wt % of the mass of the oil.

[0061] The yield of biodiesel prepared in Example 2 was 93.57%.

[0062] Example 3 The embodiment of the present invention provides a method for preparing biodiesel, wherein the relevant process conditions in Example 1 remain unchanged, except that the amount of CaO@CNTs catalyst added in step S4 is 3 wt % of the mass of the oil, and the stirring time is 120 min.

[0063] The yield of biodiesel prepared in Example 3 was 92.30%.

[0064] Example 4 An embodiment of the present invention provides a method for preparing biodiesel. The relevant process conditions in Example 1 remain unchanged, except that in step S4, the amount of CaO@CNTs catalyst added is 3 wt % of the mass of the oil, and the amount of methanol added is 6.956 g, so that the molar ratio of low-carbon alcohol to oil is 9:1.

[0065] The yield of biodiesel prepared in Example 4 was 90.90%.

[0066] Example 5 The embodiment of the present invention provides a method for preparing biodiesel, wherein the relevant process conditions in Example 1 remain unchanged, except that the amount of CaO@CNTs catalyst added in step S4 is 3 wt % of the mass of the oil, and the stirring time is 60 min.

[0067] The yield of biodiesel prepared in Example 5 was 91.33%.

[0068] Example 6 An embodiment of the present invention provides a method for preparing biodiesel, wherein the relevant process conditions in Example 1 remain unchanged, except that in step S4, the amount of CaO@CNTs catalyst added is 1 wt % of the mass of the oil, and the amount of methanol added is 14.12 g, so that the molar ratio of low-carbon alcohol to oil is 15:1.

[0069] The yield of biodiesel prepared in Example 6 was 93.08%.

[0070] Table 2 Test results of biodiesel preparation in Examples 1-6 It can be seen from the biodiesel prepared by the preparation method of the above Examples 1-11 that the yield of the prepared biodiesel is the highest when the molar ratio of low-carbon alcohol to oil is 12:1, the addition amount of CaO@CNTs catalyst is 2wt%, the voltage is 25V, and the stirring time is 90min.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a carbon nanotube-supported calcium oxide catalyst, characterized in that: The preparation method comprises the following steps: S100: mixing a solution containing calcium ions, carbon nanotubes, and a solution containing carbonate ions to react and generate a precipitate mixture; S200: separating, filtering, and washing the precipitated mixture to obtain a CaCO3@CNTs precipitate; S300: drying and calcining the CaCO3@CNTs precipitate to obtain the carbon nanotube-supported calcium oxide catalyst.

2. The preparation method according to claim 1, characterized in that The step S100 includes the following steps: S110: adding the carbon nanotubes to the calcium ion-containing solution and mixing them to obtain a mixed solution; S120: adding the carbonate ion-containing solution to the mixed solution to react and generate the precipitation mixture.

3. The preparation method according to claim 1, characterized in that The calcium ion solution is selected from at least one of CaCl2, Ca(NO3)2, and Ca(CH3COO)2, and the concentration of the calcium ion solution is 0.5-2 mol / L; and / or The carbonate ion-containing solution is selected from at least one of Na2CO3, K2CO3, and (NH4)2CO3, and the concentration of the carbonate ion-containing solution is 0.5~2mol / L.

4. The preparation method according to claim 1, characterized in that The separation is performed using a centrifuge with a rotation speed of 2000-5000 r / min and a separation time of 8-12 min; and / or The drying temperature is 80-120° C. and the drying time is 1-3 hours; and / or The calcination temperature is 550-950° C., the calcination heating rate is 5-10° C. / min, and the calcination time is 0.5-3 h.

5. A carbon nanotube-supported calcium oxide catalyst, characterized in that: The carbon nanotube-supported calcium oxide catalyst is prepared by the preparation method according to any one of claims 1 to 4; wherein the mass of the carbon nanotubes accounts for 10 to 20 wt % of the total mass of the carbon nanotube-supported calcium oxide catalyst.

6. A biodiesel, characterized in that: The biodiesel is prepared using the carbon nanotube-supported calcium oxide catalyst as claimed in claim 5.

7. A method for preparing biodiesel, characterized in that: The biodiesel preparation method is used to prepare the biodiesel according to claim 6, and the biodiesel preparation method comprises the following steps: S10: adding oil, low-carbon alcohol, the carbon nanotube-supported calcium oxide catalyst and the electrolyte solution into an electrolytic cell device and stirring to react to obtain a mixed oil liquid; S20: allowing the mixed oil to stand and separate into layers, and taking the upper layer of oil; S30: Centrifugally separating the upper oil to obtain the biodiesel.

8. The method for preparing biodiesel according to claim 7, characterized in that: The stirring comprises one of mechanical stirring, magnetic stirring, and ultrasonic-assisted stirring, the stirring speed is 400-1000 r / min, the stirring temperature is 55-105° C., and the stirring time is 60-150 min; and / or The electrolytic cell device is one of a single-chamber electrolytic cell reactor and a double-chamber electrolytic cell reactor, and the voltage of the electrolytic cell device is 15-35V; and / or The centrifugal separation is performed using a centrifuge with a rotation speed of 5000-10000 r / min and a centrifugal separation time of 5-15 min.

9. The method for preparing biodiesel according to claim 7, wherein: The amount of the carbon nanotube-supported calcium oxide catalyst added is 1 to 10 wt % relative to the mass of the oil; and / or The molar ratio of the low-carbon alcohol to the oil is (5-20):

1.

10. The method for preparing biodiesel according to claim 7, characterized in that: The oil comprises at least one of lard, fish oil and beef tallow; and / or The low-carbon alcohol includes at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, ethylene glycol, and allyl alcohol; and / or The electrolyte solution includes at least one of sodium chloride, potassium chloride, and sodium sulfate.

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