CN113145159A - Biodiesel catalyst and preparation method thereof - Google Patents

Biodiesel catalyst and preparation method thereof Download PDF

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CN113145159A
CN113145159A CN202110350605.3A CN202110350605A CN113145159A CN 113145159 A CN113145159 A CN 113145159A CN 202110350605 A CN202110350605 A CN 202110350605A CN 113145159 A CN113145159 A CN 113145159A
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biodiesel
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porous carbon
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黄振旭
高海荣
陈凌霞
孙海杰
李会吉
陈建军
潘丽延
宋岩岩
李品
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Zhengzhou Normal University
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Abstract

A preparation method of a biodiesel catalyst comprises the following steps: soaking the nitrogen-doped porous carbon fiber into titanium dioxide hydrosol to prepare a composite carrier; fully grinding and mixing calcium acetate and calcium carbonate, and then preserving heat for 3-10h at the temperature of 160-260 ℃ in an inert gas atmosphere to obtain a precursor; and (3) fully grinding and mixing the composite carrier and the precursor, placing the mixture in the center of a tubular furnace, introducing inert gas, and roasting to obtain the biodiesel catalyst. The method disclosed by the invention is simple to operate, relatively few in steps, the prepared catalyst shows good catalytic activity, the inert gas is used for protection in the preparation process, so that the influence of moisture and carbon dioxide in the air on calcium oxide is avoided in the preparation process of the catalyst, the catalytic activity of the catalyst is improved, the yield is relatively improved and reaches 96.0% -98.5%, the yield of the biodiesel can reach more than 96%, the biodiesel can be repeatedly utilized for 10-12 times, the cost is saved, no corresponding by-product is discharged, and the method is economic and environment-friendly.

Description

Biodiesel catalyst and preparation method thereof
Technical Field
The invention belongs to the technical field of biodiesel catalysts, and particularly relates to a biodiesel catalyst and a preparation method thereof.
Background
The biodiesel is a low-price, safe and convenient biomass clean energy source which is obtained by taking renewable resources such as animal and vegetable oil as raw materials and carrying out esterification or ester exchange reaction with short-chain alcohol such as methanol, and the chemical components of the biodiesel are mainly methyl ester or ethyl ester of long-chain saturated and unsaturated fatty acids such as linolenic acid, palmitic acid, stearic acid, oleic acid, linoleic acid and the like, and the properties of the biodiesel are similar to those of diesel oil. Compared with petroleum diesel, the biodiesel not only has very similar combustion performance, but also has incomparable environmental protection and reproducibility of the petroleum diesel, and has very wide application prospect.
At present, the homogeneous catalysis transesterification method is mainly adopted for the industrial production of the biodiesel at home and abroad. The ester exchange method is to carry out ester exchange reaction between animal and vegetable oil and lower alcohol such as methanol or ethanol to generate corresponding fatty acid methyl ester or ethyl ester. However, the catalyst has the problem of strong corrosion to equipment, products after the reaction are difficult to separate, so that the post-treatment process is complicated, and in addition, the output of the treated waste acid and waste water is large, so that the treatment cost is expensive. In order to solve these problems, heterogeneous catalysts have been developed, which have a simpler reaction process, are easy to separate products after reaction, and can be recycled many times, compared to common homogeneous catalysts.
However, the existing solid heterogeneous catalyst has low loading capacity, is easily poisoned by water and carbon dioxide in the air, and influences the catalytic activity of the catalyst, and in addition, the firmness of the combination between the carriers is relatively poor, so that the repeatability is low, and the service life of the catalyst is influenced.
Disclosure of Invention
The technical problems to be solved by the invention are that the existing catalyst is low in loading capacity, easy to be poisoned by water and carbon dioxide in the air, and low in repeatability, and the catalytic activity of the catalyst is influenced.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a preparation method of a biodiesel catalyst comprises the following steps:
s1 preparation of composite carrier
S1.1 preparation of Nitrogen-doped porous carbon fiber
Placing microcrystalline cellulose in the center of a tube furnace, introducing nitrogen, heating to 300 ℃, preserving heat for 1-5 h, then heating to 500 ℃, and preserving heat for 1-10 h to obtain nitrogen-doped porous carbon fiber; wherein the dosage ratio of the microcrystalline cellulose to the nitrogen is 1 g: 80-120 mL/min;
s1.2 preparation of titanium dioxide hydrosol
Dropwise adding acetic acid and lactic acid in a volume ratio of 1:1 into an ethylenediamine solution, wherein the volume ratio of the lactic acid to the ethylenediamine is 1: 0.5-1, so as to obtain a solution A; slowly dripping tetrabutyl titanate into the solution A, uniformly stirring, and then slowly dripping deionized water, wherein the volume ratio of the tetrabutyl titanate to the solution A to the deionized water is (1-3): 1: (60-100), continuously stirring uniformly after the dripping is finished, and obtaining a titanium dioxide aqueous solution;
s1.3, soaking the nitrogen-doped porous carbon fiber into titanium dioxide hydrosol, adjusting the pH value to 7.0-8.0, soaking for 6-10h, centrifuging, filtering, drying, and roasting at 500 ℃ for 5-8h in an inert gas atmosphere to obtain a composite carrier;
s2 preparation of precursor
Fully grinding and mixing calcium acetate and calcium carbonate, and then preserving heat for 3-10h at the temperature of 160-260 ℃ in an inert gas atmosphere to obtain a precursor;
s3 preparation of biodiesel catalyst
And (3) fully grinding and mixing the composite carrier obtained in the step S1 and the precursor obtained in the step S2, placing the mixture in the center of a tubular furnace, introducing inert gas, gradually heating the tubular furnace to 260 ℃, preserving heat for 3-6h, heating to 500 ℃ and 600 ℃, roasting, and preserving heat for 6-12h to obtain the biodiesel catalyst.
S1.1, in the preparation step of the nitrogen-doped porous carbon fiber, the temperature rise speed is 5-10 ℃/min.
S1.2 the reaction temperature for preparing the titanium dioxide hydrosol is 20-30 ℃.
S1.3, the mass ratio of the nitrogen-doped porous carbon fiber to the titanium dioxide hydrosol is 1: 5-10.
The mass ratio of calcium acetate to calcium carbonate in S2 is 1: 1.
The mass ratio of the S3 precursor to the composite carrier is 1: 20 to 30.
The heating rate in the roasting process of S1, S2 and S3 is 3-8 ℃/min.
The inert gas in S1.3, S2 and S3 is any one of nitrogen, argon, helium and neon.
The biodiesel catalyst prepared by the preparation method.
Compared with the prior art, the preparation method of the biodiesel catalyst provided by the invention has the following beneficial effects:
1. according to the invention, firstly, the microcrystalline cellulose is subjected to nitrogen doping carbonization to prepare the nitrogen-doped porous carbon fiber, the strength and the carrier activity of the porous carbon fiber are improved by doping nitrogen elements on the porous carbon fiber, so that the porous carbon fiber can be combined with titanium dioxide to form a composite carrier to form a stable combined phase, and then the combined phase is roasted with calcium oxide to form a stable structure, so that the specific surface area and the pore size of the catalyst are increased, and the loading capacity is improved. Meanwhile, in the process of roasting the composite carrier of the nitrogen-doped porous carbon fiber and the precursor at high temperature, a certain crystalline phase structure is obtained through the synergistic effect of element molecules, and the crystalline phase structure not only can improve the wear-resistant and wear-reducing effects of the catalyst, but also can enhance the crushing strength of the catalyst so as to prolong the service life of the catalyst.
2. The method disclosed by the invention is simple in operation process and relatively few in steps, the prepared catalyst shows good catalytic activity, the inert gas nitrogen is used for protection in the preparation process, so that the influence of moisture and carbon dioxide in the air on calcium oxide is avoided in the preparation process of the catalyst, the catalytic activity of the catalyst is improved, the yield is relatively improved and reaches 96.0-98.5%, when the method is applied to the preparation process of the biodiesel, the yield of the biodiesel can reach more than 96%, the biodiesel can be recycled for 10-12 times, the cost is saved, no corresponding by-product is discharged, and the method is economical and environment-friendly.
Drawings
FIG. 1 is a plot of the nitrogen adsorption-desorption isotherm of a biodiesel catalyst at-196 ℃.
FIG. 2 is a pore size distribution plot for a biodiesel catalyst.
FIG. 3 is an SEM morphology photograph of a biodiesel catalyst.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific examples, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort belong to the protection scope of the present invention.
A preparation method of a biodiesel catalyst comprises the following steps:
s1 preparation of composite carrier
S1.1 preparation of Nitrogen-doped porous carbon fiber
Placing microcrystalline cellulose in the center of a tube furnace, introducing nitrogen, heating to 300 ℃, preserving heat for 1-5 h, then heating to 500 ℃, and preserving heat for 1-10 h to obtain nitrogen-doped porous carbon fiber; wherein the dosage ratio of the microcrystalline cellulose to the nitrogen is 1 g: 80-120 mL/min;
s1.2 preparation of titanium dioxide hydrosol
Dropwise adding acetic acid and lactic acid in a volume ratio of 1:1 into an ethylenediamine solution, wherein the volume ratio of the lactic acid to the ethylenediamine is 1: 0.5-1, so as to obtain a solution A; slowly dripping tetrabutyl titanate into the solution A, uniformly stirring, and then slowly dripping deionized water, wherein the volume ratio of the tetrabutyl titanate to the solution A to the deionized water is (1-3): 1: (60-100), continuously stirring uniformly after the dripping is finished, and obtaining a titanium dioxide aqueous solution;
s1.3, soaking the nitrogen-doped porous carbon fiber into titanium dioxide hydrosol, adjusting the pH value to 7.0-8.0, soaking for 6-10h, centrifuging, filtering, drying, and roasting at 500 ℃ for 5-8h in an inert gas atmosphere to obtain a composite carrier;
s2 preparation of precursor
Fully grinding and mixing calcium acetate and calcium carbonate, and then preserving heat for 3-10h at the temperature of 160-260 ℃ in an inert gas atmosphere to obtain a precursor;
s3 preparation of biodiesel catalyst
And (3) fully grinding and mixing the composite carrier obtained in the step S1 and the precursor obtained in the step S2, placing the mixture in the center of a tubular furnace, introducing inert gas, gradually heating the tubular furnace to 260 ℃, preserving heat for 3-6h, heating to 500 ℃ and 600 ℃, roasting, and preserving heat for 6-12h to obtain the biodiesel catalyst.
S1.1, in the preparation step of the nitrogen-doped porous carbon fiber, the temperature rise speed is 5-10 ℃/min.
S1.2 the reaction temperature for preparing the titanium dioxide hydrosol is 20-30 ℃.
S1.3, the mass ratio of the nitrogen-doped porous carbon fiber to the titanium dioxide hydrosol is 1: 5-10.
The mass ratio of calcium acetate to calcium carbonate in S2 is 1: 1.
The mass ratio of the S3 precursor to the composite carrier is 1: 20 to 30.
The heating rate in the roasting process of S1, S2 and S3 is 3-8 ℃/min.
The inert gas in S1.3, S2 and S3 is any one of nitrogen, argon, helium and neon.
The biodiesel catalyst prepared by the preparation method.
Compared with the prior art, the preparation method of the biodiesel catalyst provided by the invention has the following beneficial effects:
1. according to the invention, firstly, microcrystalline cellulose is subjected to nitrogen doping carbonization to prepare nitrogen-doped porous carbon fiber, and nitrogen element is doped on the porous carbon fiber to improve the strength and the carrier activity of the porous carbon fiber, so that the porous carbon fiber can be combined with titanium dioxide to form a composite carrier, and a relatively stable combined phase is formed; and S3, fully grinding and mixing the composite carrier and the precursor, placing the tubular furnace in the tubular furnace, introducing inert gas, gradually heating the tubular furnace to 260 ℃, preserving the heat for 3-6h, heating to 500-600 ℃ for roasting, decomposing calcium acetate and calcium carbonate into calcium oxide, and roasting the composite carrier and the calcium oxide to form a stable structure, so that the specific surface area and the pore size of the catalyst are increased, and the loading capacity is improved. Meanwhile, in the process of roasting the composite carrier of the nitrogen-doped porous carbon fiber and the precursor at high temperature, a certain crystalline phase structure is obtained through the synergistic effect of element molecules, and the crystalline phase structure not only can improve the wear-resistant and wear-reducing effects of the catalyst, but also can enhance the crushing strength of the catalyst so as to prolong the service life of the catalyst.
2. The method disclosed by the invention is simple in operation process and relatively few in steps, the prepared catalyst shows good catalytic activity, the inert gas nitrogen is used for protection in the preparation process, so that the influence of moisture and carbon dioxide in the air on calcium oxide is avoided in the preparation process of the catalyst, the catalytic activity of the catalyst is improved, the yield is relatively improved and reaches 96.0-98.5%, when the method is applied to the preparation process of the biodiesel, the yield of the biodiesel can reach more than 96%, the biodiesel can be recycled for 10-12 times, the cost is saved, no corresponding by-product is discharged, and the method is economic and environment-friendly.
Example 1:
a preparation method of a biodiesel catalyst comprises the following steps:
s1 preparation of composite carrier
S1.1 preparation of nitrogen-doped porous carbon fiber
Placing 1g of microcrystalline cellulose at the central hot area of a tubular furnace, introducing nitrogen into the tubular furnace, wherein the flow rate of the nitrogen is 100mL/min, heating from room temperature to 300 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 1h, then continuously heating to 500 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 1h, and obtaining nitrogen-doped porous carbon fiber after the tubular furnace is naturally cooled to room temperature;
s1.2, preparation of titanium dioxide hydrosol
Slowly dripping 0.5mL of acetic acid and 0.5mL of lactic acid into 0.5mL of ethylenediamine solution at room temperature (20-30 ℃), and continuously stirring for 10min after dripping is finished to obtain a solution A;
slowly dripping 1.5mL of tetrabutyl titanate into the solution A at the dripping speed of 1mL/min, continuously stirring for 60min after finishing dripping, slowly dripping 60mL of deionized water at the dripping speed of 6mL/min, and continuously stirring for 60min after finishing dripping to obtain titanium dioxide hydrosol;
s1.3, soaking 0.5g of nitrogen-doped porous carbon fiber into 2.5g of titanium dioxide hydrosol, adjusting the pH to 7.0 by using a sodium hydroxide solution with a solute mass fraction of 15%, soaking for 6h, centrifuging, filtering, drying, heating to 500 ℃ at a heating speed of 3 ℃/min, roasting for 5h at 500 ℃, introducing nitrogen at a speed of 80ml/min during roasting, and keeping the nitrogen atmosphere to obtain a composite carrier;
s2 preparation of precursor
Fully grinding and mixing calcium acetate and calcium carbonate according to the mass ratio of 1:1, and preserving heat of 1g of mixture for 10 hours at 160 ℃ in a nitrogen atmosphere to obtain a precursor;
s3 preparation of biodiesel catalyst
And (2) fully grinding and mixing 0.033g of the precursor and 0.66g of the composite carrier, placing the mixture at the central hot area of the tubular furnace, introducing nitrogen into the tubular furnace at the flow rate of 80mL/min, heating the temperature of the tubular furnace to 260 ℃ at the heating rate of 3 ℃/min, preserving heat for 3h, heating to 500 ℃ at the heating rate of 3 ℃/min, and preserving heat for 6h to obtain the biodiesel catalyst.
Example 2:
a preparation method of a biodiesel catalyst comprises the following steps:
s1 preparation of composite carrier
S1.1 preparation of nitrogen-doped porous carbon fiber
Placing 1g of microcrystalline cellulose at the central hot area of a tubular furnace, introducing nitrogen into the tubular furnace, wherein the flow rate of the nitrogen is 80mL/min, heating to 300 ℃ from room temperature at the heating rate of 10 ℃/min, keeping the temperature for 5h, then continuously heating to 500 ℃ at the heating rate of 10 ℃/min, keeping the temperature for 10h, and obtaining nitrogen-doped porous carbon fiber after the tubular furnace is naturally cooled to room temperature;
s1.2, preparation of titanium dioxide hydrosol
Slowly dripping 0.5mL of acetic acid and 0.5mL of lactic acid into 0.25mL of ethylenediamine solution at room temperature (20-30 ℃), and continuously stirring for 10min after dripping is finished to obtain a solution A;
slowly dripping 3.75mL of tetrabutyl titanate into the solution A at the dripping speed of 1mL/min, continuously stirring for 60min after finishing dripping, slowly dripping 125mL of deionized water at the dripping speed of 5mL/min, and continuously stirring for 60min after finishing dripping to obtain titanium dioxide hydrosol;
s1.3, soaking 0.5g of nitrogen-doped porous carbon fiber into 5g of titanium dioxide hydrosol, adjusting the pH to 8.0 by using a sodium hydroxide solution with a solute mass fraction of 15%, after soaking for 10h, centrifuging, filtering, drying, heating to 500 ℃ at a heating speed of 8 ℃/min, roasting for 8h at 500 ℃, introducing nitrogen gas at a flow rate of 80ml/min during roasting, and maintaining the nitrogen gas atmosphere to obtain a composite carrier;
s2 preparation of precursor
Fully grinding and mixing calcium acetate and calcium carbonate according to the mass ratio of 1:1, and preserving heat of 1g of mixture for 3 hours at 260 ℃ in a nitrogen atmosphere to obtain a precursor;
s3 preparation of biodiesel catalyst
And (2) fully grinding and mixing 0.033g of the precursor and 0.99g of the composite carrier, placing the mixture at the central hot area of a tubular furnace, introducing nitrogen into the tubular furnace, wherein the flow rate of the nitrogen is 80mL/min, heating the temperature of the tubular furnace to 260 ℃ at the heating rate of 8 ℃/min, preserving the heat for 6 hours, heating to 600 ℃ at the heating rate of 8 ℃/min, and preserving the heat for 12 hours to obtain the biodiesel catalyst.
Example 3:
a preparation method of a biodiesel catalyst comprises the following steps:
s1 preparation of composite carrier
S1.1 preparation of nitrogen-doped porous carbon fiber
Placing 1g of microcrystalline cellulose at the central hot area of a tubular furnace, introducing nitrogen into the tubular furnace, wherein the flow rate of the nitrogen is 120mL/min, heating to 300 ℃ from room temperature at the heating rate of 8 ℃/min, keeping the temperature for 3h, then continuously heating to 500 ℃ at the heating rate of 8 ℃/min, keeping the temperature for 5h, and obtaining nitrogen-doped porous carbon fiber after the tubular furnace is naturally cooled to room temperature;
s1.2, preparation of titanium dioxide hydrosol
Slowly dripping 0.5mL of acetic acid and 0.5mL of lactic acid into 0.3mL of ethylenediamine solution at room temperature (20-30 ℃), and continuously stirring for 10min after dripping is finished to obtain a solution A;
slowly dripping 2.6mL of tetrabutyl titanate into the solution A at the dripping speed of 1mL/min, continuously stirring for 60min after finishing dripping, slowly dripping 100mL of deionized water at the dripping speed of 5mL/min, and continuously stirring for 60min after finishing dripping to obtain titanium dioxide hydrosol;
s1.3, soaking 0.5g of nitrogen-doped porous carbon fiber into 4g of titanium dioxide hydrosol, adjusting the pH to 7.5 by using a sodium hydroxide solution with a solute mass fraction of 15%, after soaking for 8h, centrifuging, filtering, drying, heating to 500 ℃ at a heating rate of 5 ℃/min, roasting for 6h at 500 ℃, introducing nitrogen gas at a flow rate of 80ml/min during roasting, and keeping an argon atmosphere to obtain a composite carrier;
s2 preparation of precursor
Fully grinding and mixing calcium acetate and calcium carbonate in a mass ratio of 1:1, and preserving heat of 1g of mixture for 5 hours at 200 ℃ in an argon atmosphere to obtain a precursor;
s3 preparation of biodiesel catalyst
And (2) fully grinding and mixing 0.033g of the precursor and 0.83g of the composite carrier, placing the mixture at the central hot area of a tubular furnace, introducing argon into the tubular furnace, wherein the flow rate of the argon is 80mL/min, heating the temperature of the tubular furnace to 260 ℃ at the heating rate of 5 ℃/min, preserving the temperature for 5h, heating to 550 ℃ at the heating rate of 5 ℃/min, and preserving the temperature for 8h to obtain the biodiesel catalyst.
Examples 4 to 15
The specific steps of the preparation method of the biodiesel catalyst in the embodiments 4 to 15 are the same as those of the embodiment 1, except that the preparation process parameters of S1.1, the preparation of the nitrogen-doped porous carbon fiber and S1.2, the preparation process parameters of the titanium dioxide hydrosol are shown in Table 1, the preparation process parameters of S1.3 and S2, the preparation process parameters of the precursor are shown in Table 2, and the preparation process parameters of the biodiesel catalyst are shown in Table 3.
TABLE 1
Figure RE-GDA0003087660340000071
TABLE 2
Figure RE-GDA0003087660340000081
Comparative example 1:
a preparation method of a biodiesel catalyst, which is the same as the preparation method of example 3, except that:
s1.1 preparation of nitrogen-doped porous carbon fiber
Placing 1g of microcrystalline cellulose at the central hot area of a tubular furnace, introducing nitrogen into the tubular furnace at a gas flow rate of 80mL/min, heating from room temperature to 500 ℃ at a heating rate of 8 ℃/min, preserving heat for 5h, and naturally cooling the tubular furnace to room temperature to obtain the porous carbon fiber.
Comparative example 2:
a preparation method of a biodiesel catalyst, which is the same as the preparation method of example 3, except that:
s1.3, soaking 0.5g of nitrogen-doped porous carbon fiber into 4g of titanium dioxide hydrosol, adjusting the pH value to 7.5 by using a 15% sodium hydroxide solution, soaking for 8 hours, centrifuging, filtering, drying, heating to 500 ℃ at a heating rate of 5 ℃/min, and roasting at 500 ℃ for 6 hours to obtain the composite carrier.
Comparative example 3:
a preparation method of a biodiesel catalyst is the same as that of example 3, except that,
s2 preparation of precursor
Fully grinding and mixing calcium acetate and calcium carbonate according to the mass ratio of 1:1 to obtain a precursor.
The physical performance indexes of the biodiesel catalysts prepared in the examples 1-3 and the comparative examples 1-3 are tested, wherein the crushing strength of the catalyst is measured by the existing domestic enterprise standard method, the tester is a DL-II particle strength tester, and the measured crushing strength of the catalyst is axial crushing strength which can be borne by a unit area and is measured in a unit of N/cm2. Specific results of physical property indexes of the biodiesel catalysts prepared in examples 1 to 3 and comparative examples 1 to 3 are shown in Table 1.
TABLE 1
Figure 372764DEST_PATH_IMAGE004
As can be seen from table 1, the biodiesel catalysts prepared in examples 1 to 3 all have large specific surface areas, and have high crush strength due to high-temperature calcination and multi-component synergistic effect, which is related to fibrous crystals of nitrogen-doped porous carbon fibers and to a crystal system after loading titanium dioxide and precursors. The titanium dioxide and the precursor are adsorbed on the surface of the porous carbon fiber doped with nitrogen at the same time, the surface of the porous carbon fiber is modified, the surface structure of fibrous crystals is further adjusted by controlling the mass fraction of the titanium dioxide and the precursor, the specific surface area is further increased, the larger specific surface area is beneficial to loading more active substances, and more precursor substances can be combined on the porous structure of the composite carrier. In addition, due to the introduction of the precursor, the crushing strength of the catalyst is obviously improved in the chemical change process of the composite carrier, the combination is relatively firm, the abrasion-resistant and wear-reducing effects of the catalyst are improved, the service life of the prepared biodiesel catalyst can be prolonged, the prepared catalyst can be reused for 10-12 times, and the cost is further saved.
Comparative example 1 a certain amount of argon gas was introduced during the preparation of porous carbon fibers, and the temperature rise process was continued, so that during the preparation of porous carbon fibers, nitrogen doping and carbonization could not be performed, so that a stable binding phase could not be formed, and the strength was reduced to a certain extent, and the anti-wear effect was reduced.
Comparative example 2 is not protected by nitrogen gas during the preparation of the composite carrier, so that a part of air and a small amount of moisture are doped during the preparation, thereby affecting the catalytic activity of the catalyst and the combination of the precursor.
And in the comparative example 3, the precursor is not roasted in the preparation process, so that when the calcium acetate is combined with the composite carrier, the catalytic activity of the catalyst is influenced by the moisture combined with the calcium acetate, and the service life is shortened.
FIG. 1 is a nitrogen adsorption-desorption isotherm plot at-196 ℃ for a biodiesel catalyst prepared from nitrogen-doped porous carbon fibers prepared in example 3. As can be seen from fig. 1, the isotherm of the catalyst exhibits a typical type iv adsorption-desorption curve and has a relatively clear hysteresis loop of type H1, which indicates the presence of mesopores in the catalyst, which also reflects a broader pore size distribution of the catalyst; when the relative pressure is less than 0.1, the adsorption quantity rapidly rises, which shows that the catalyst has a large number of micropores, and when the relative pressure is 0.2-0.8, a hysteresis loop shows that the catalyst also contains a certain amount of mesopores. The catalyst has wider pore size distribution, which indicates that the adsorption capacity of the catalyst is stronger, so the activity of the catalyst is higher.
Fig. 2 is a pore size distribution diagram of the biodiesel catalyst prepared from the nitrogen-doped porous carbon fiber prepared in example 3, and it can be seen from fig. 2 that the pore size of the catalyst is mainly distributed between 0.6 nm and 0.8nm, and a large number of micropores are formed, which is beneficial to improving the activity of the catalyst.
Figure 3 gives an SEM topography photograph of a biodiesel catalyst prepared from nitrogen doped porous carbon fibers. As can be seen from FIG. 3, the carbon fiber carrier for preparing the biodiesel catalyst has uniform thickness, and from the appearance, the carbon fiber also maintains the original shape and is uniformly distributed, and the carbon fiber is not obviously damaged in the preparation process of the catalyst. The diameter of the fiber is about 30 μm, active component particles with small particle size are uniformly dispersed on the surface of the fiber, the particle size is uniform, and the active component particles are dispersed and loaded on the carbon fiber. The active ingredient particles can also repair surface portion defects, thereby suppressing the generation of cracks and improving tensile strength. In addition, a small amount of flaky active components are arranged on the periphery of the carbon fibers, and no large particles are agglomerated, so that better contact between the carbon fibers can be promoted, the binding force between fiber matrixes is improved, and the strength of the catalyst is improved.
The biodiesel catalysts prepared in examples 1-3 and comparative examples 1-3 are applied to transesterification of soybean oil and methanol, and the specific process is as follows:
adding soybean oil into a three-neck flask provided with a condensing tube, heating to 60 ℃, adding a biodiesel catalyst and methanol under a stirring state, wherein the mass ratio of the soybean oil to the methanol is 5:1, the dosage of the biodiesel catalyst accounts for 1.2% of the mass of the soybean oil, reacting for 2 hours at 60-80 ℃, distilling at normal pressure after the reaction is finished, recovering the methanol, and separating out a glycerin layer to obtain a biodiesel crude product;
refining the crude product of the biodiesel by adopting a steam distillation method, controlling the liquid phase temperature in a distillation flask to be 200-280 ℃, the gas phase temperature to be 120-220 ℃, the steam temperature to be about 100 ℃, introducing 5L/min of steam, distilling out the biodiesel from the distillation flask, cooling, and then carrying out oil-water separation to obtain the biodiesel.
The performance of the biodiesel prepared in examples 1 to 3 and comparative examples 1 to 3 was tested, and the specific results are shown in table 2, and the yield of the prepared biodiesel is shown in table 3.
TABLE 2
Figure 418081DEST_PATH_IMAGE006
Table 2 shows the indexes of the biodiesel prepared by using the biodiesel catalysts prepared in examples 1-3 and comparative examples 1-3, such as flash point, kinematic viscosity, water content and the like, and from Table 2, it can be concluded that the biodiesel prepared by using the biodiesel catalyst prepared by the preparation method disclosed by the invention meets the standard requirements of the biodiesel (BD100) for blending GB/T20828-2007 diesel fuel.
TABLE 3
Item Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3
Yield of 96.0% 97.2% 98.5% 92.1% 91.4% 90.6%
From table 3, it can be seen that when the biodiesel catalyst prepared by the preparation method disclosed by the invention is applied to the preparation process of biodiesel, the yield of biodiesel is high and can reach more than 96%, the biodiesel can be recycled for 10-12 times, the cost is saved, no corresponding byproduct is discharged, and the method is economical and environment-friendly.
In summary, in the process of preparing the biodiesel catalyst, the porous carbon fibers need to be subjected to nitrogen doping modification, so that the strength of the catalyst is improved, the anti-wear effect of the catalyst is improved, and the service life of the catalyst is prolonged. The preparation process needs protection of nitrogen, and the influence of gases such as moisture in air and carbon dioxide on the catalytic activity of the catalyst is avoided. Therefore, the catalysts prepared in comparative examples 1 to 3 were relatively low in all of loading, catalytic activity and service life, compared to examples 1 to 3 of the present invention.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A preparation method of a biodiesel catalyst is characterized by comprising the following steps:
s1 preparation of composite carrier
Preparation of nitrogen-doped porous carbon fibers
Placing microcrystalline cellulose in the center of a tube furnace, introducing nitrogen, heating to 300 ℃, preserving heat for 1-5 h, then heating to 500 ℃, and preserving heat for 1-10 h to obtain nitrogen-doped porous carbon fiber; wherein the dosage ratio of the microcrystalline cellulose to the nitrogen is 1 g: 80-120 mL/min;
preparation of titanium dioxide hydrosol
Dropwise adding acetic acid and lactic acid in a volume ratio of 1:1 into an ethylenediamine solution, wherein the volume ratio of the lactic acid to the ethylenediamine is 1: 0.5-1, so as to obtain a solution A; slowly dripping tetrabutyl titanate into the solution A, uniformly stirring, and then slowly dripping deionized water, wherein the volume ratio of the tetrabutyl titanate to the solution A to the deionized water is (1-3): 1: (60-100), continuously stirring uniformly after the dripping is finished, and obtaining a titanium dioxide aqueous solution;
soaking the nitrogen-doped porous carbon fiber into titanium dioxide hydrosol, adjusting the pH value to 7.0-8.0, soaking for 6-10h, centrifuging, filtering, drying, and roasting at 500 ℃ for 5-8h in an inert gas atmosphere to obtain a composite carrier;
s2 preparation of precursor
Fully grinding and mixing calcium acetate and calcium carbonate, and then preserving heat for 3-10h at the temperature of 160-260 ℃ in an inert gas atmosphere to obtain a precursor;
s3 preparation of biodiesel catalyst
And (3) fully grinding and mixing the composite carrier obtained in the step S1 and the precursor obtained in the step S2, placing the mixture in the center of a tubular furnace, introducing inert gas, gradually heating the tubular furnace to 260 ℃, preserving heat for 3-6h, heating to 500 ℃ and 600 ℃, roasting, and preserving heat for 6-12h to obtain the biodiesel catalyst.
2. The preparation method of the biodiesel catalyst according to claim 1, wherein the temperature rise rate in the preparation step of the S1.1 nitrogen-doped porous carbon fiber is 5-10 ℃/min.
3. The preparation method of the biodiesel catalyst according to claim 1, wherein the reaction temperature of the S1.2 titanium dioxide hydrosol during preparation is 20-30 ℃.
4. The preparation method of the biodiesel catalyst according to claim 1, wherein the mass ratio of the S1.3 nitrogen-doped porous carbon fiber to the titanium dioxide hydrosol is 1: 5-10.
5. The method for preparing the biodiesel catalyst according to claim 1, wherein the mass ratio of calcium acetate to calcium carbonate in S2 is 1: 1.
6. The preparation method of the biodiesel catalyst according to claim 1, wherein the mass ratio of the S3 precursor to the composite carrier is 1: 20 to 30.
7. The preparation method of the biodiesel catalyst according to claim 1, wherein the temperature rise rate in the roasting process in S1.3 and S3 is 3-8 ℃/min.
8. The method for preparing a biodiesel catalyst according to claim 1, wherein the inert gas in S1.3, S2, S3 is any one of nitrogen, argon, helium, and neon.
9. A biodiesel catalyst obtained by the production process according to any one of claims 1 to 8.
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CN101402058A (en) * 2008-10-10 2009-04-08 广东海洋大学 Process for producing solid alkali biodiesel catalyst with shell powder as carrier
CN101972662A (en) * 2010-10-27 2011-02-16 华北电力大学（保定） Preparation and use methods of nitrogen-vanadium co-doped modified titanium dioxide catalyst
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