CN111804319B - Preparation method and application of magnetic solid acid catalyst - Google Patents

Preparation method and application of magnetic solid acid catalyst Download PDF

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CN111804319B
CN111804319B CN202010771535.4A CN202010771535A CN111804319B CN 111804319 B CN111804319 B CN 111804319B CN 202010771535 A CN202010771535 A CN 202010771535A CN 111804319 B CN111804319 B CN 111804319B
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蒋平平
聂志欣
刘德开
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王涵颖
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Abstract

A preparation method and application of a magnetic solid acid catalyst belong to the technical field of catalyst preparation. The invention adopts a one-pot method and a two-step method to prepare two magnetic solid acid catalysts loaded with phosphotungstic acid. The catalyst HPW/Fe of the magnetic zirconia supported phosphotungstic acid prepared by the one-pot method is respectively 2 O 3 @ZrO 2 And a catalyst HPW/Fe of magnetic silicon dioxide supported phosphotungstic acid prepared by a two-step method 3 O 4 @SiO 2 . The magnetic solid acid catalyst has larger catalytic specific surface area and proper pore canal structure, is favorable for the adsorption, mass transfer and surface reaction of reactants on the surface of the catalyst, and can be used in the esterification reaction of long-chain fatty acid to obtain better effect. The two catalysts are catalyzedThe esterification reaction of oleic acid and methanol is used as a probe reaction in the test of the chemical activity, so that the method has good oleic acid conversion rate and better esterification catalytic activity.

Description

Preparation method and application of magnetic solid acid catalyst
Technical Field
The invention relates to a preparation method and application of two magnetic solid acid catalysts, which show better catalytic activity in esterification reaction of long-chain fatty acid, and belong to the technical field of catalyst preparation.
Background
In recent decades, with the decrease of fossil fuels, the world is faced with serious energy and environmental crisis with an increasing emission of pollutants and greenhouse gases, which has led to the urgent search for new alternative and sustainable fuels for the environment and society by humans. Biodiesel, which is a clean, efficient, purely natural energy source, minimizes the dependence on fossil fuels and is increasingly favored by people because of its environmental friendliness, non-toxicity and biodegradability. The current method for preparing biodiesel is to use esterification or transesterification, and in the process of synthesizing biodiesel, low-cost raw oil such as waste edible oil, animal fat, palm fatty acid distillate oil and the like is of research interest, but these types of raw materials contain a large amount of free fatty acid, are not suitable for use with alkaline catalysts, and cause saponification problems. Thus, in the reaction for producing biodiesel, an acid catalyst is often used.
In the conventional esterification reaction, homogeneous acid catalysts having high acid strength such as hydrochloric acid, nitric acid, concentrated sulfuric acid, phosphoric acid, etc. are generally used, but these catalysts have some disadvantages such as difficulty in recycling, poor catalyst stability, serious equipment corrosion, etc., and not only cause an increase in production cost but also cause a series of environmental problems, which do not conform to the concept of green chemistry. Therefore, the above problems can be solved by using a solid acid catalyst such as sulfonated carbon and a metal sulfate oxide. The heterogeneous solid acid catalyst is more popular than the homogeneous catalyst because of the advantages of easy separation, regeneration, no need of purification, small influence on environment and the like, and solves a plurality of problems in the traditional esterification reaction.
In recent years, many synthetic routes for solid acid catalysts have emerged for catalyzing the esterification reaction of long chain fatty acids. Among these solid acid catalysts, heteropolyacids have great potential for application. Heteropolyacids are protonated forms of anionic metallo-oxygen clusters, in which H has a Keggin-type structure n [XM 12 O 40 ](wherein X represents a heteroatom such as Si IV , P V And m=mo VI , W VI ) The type heteropolyacid is one of the most representative. The heteropoly acid has extremely high solubility in polar solvents, which limits its application as a heterogeneous catalyst. Therefore, many scholars have studied different carriers for supporting the heteropolyacid to achieve the purpose of applying the heteropolyacid to heterogeneous catalytic reactions, such as mesoporous MCM-41 silica, zirconia or alumina, and the like, have been greatly focused by researchers. Although this method of immobilizing the heteropolyacid on the carrier can solve the problem of using the catalyst in a heterogeneous system to some extent, there is still a disadvantage in that the catalyst is difficult to separate from the reaction system. For this reason, many researchers have developed methods of simultaneously introducing magnetism into catalyst materials. Thus, the preparation of acidic solid acid catalysts with magnetic properties for heterogeneous catalysis is an effective catalyst synthesis direction.
The high solubility of heteropoly acid in polar solvent limits its application as heterogeneous catalyst, so that it needs to be immobilized on solid carrier to achieve the purpose of applying it in heterogeneous catalytic reaction, for example, zirconia and alumina are very interesting as carriers. Wherein SiO is 2 Has high porosity and large specific surface area,The catalyst has the advantages of small volume density, stable chemical property and the like, and has wide application prospect in the aspect of catalyst carriers; zrO (ZrO) 2 Has high chemical stability, high temperature resistance and large specific surface area, and is often used as a carrier of a catalyst. Thus the invention selects SiO 2 And ZrO(s) 2 Respectively as a carrier to prepare a solid acid catalyst. The method of immobilizing the heteropolyacid on the carrier can solve the problem of using the catalyst in a heterogeneous system to a certain extent, but has the disadvantage that the catalyst is difficult to separate from the reaction system. For this reason, many researchers have developed methods of simultaneously introducing magnetism into catalyst materials. Thus, in the present synthesis method, magnetic core Fe is first prepared 2 O 3 （Fe 3 O 4 ) Then using ZrO 2 （SiO 2 ) Coating it with ZrO on the one hand 2 （SiO 2 ) Can well protect Fe 2 O 3 （Fe 3 O 4 ) So that it is not destroyed in an acidic environment, on the other hand, zrO as a shell layer 2 （SiO 2 ) Having a surface that can be modified creates good conditions for the subsequent introduction of active centers.
Disclosure of Invention
The invention aims to overcome the defects, and provides two preparation methods of the magnetic solid acid catalyst, wherein the magnetic solid acid catalyst has a large catalytic specific surface area and a proper pore structure, is favorable for the adsorption, mass transfer and surface reaction of reactants on the surface of the catalyst, and can be used for esterification reaction of long-chain fatty acid to obtain a good effect.
According to the technical scheme, the method for preparing the magnetic solid acid catalyst by a two-step method comprises the following steps of: coating magnetic Fe with silicon dioxide 3 O 4 Nano-core loaded with phosphotungstic acid to obtain magnetic solid acid catalyst HPW/Fe 3 O 4 @SiO 2 。
Further, the two-step method for preparing the magnetic solid acid catalyst comprises the following steps:
(1) Magnetic Fe 3 O 4 Preparation of the nanonucleus: fe is added to 2+ And Fe (Fe) 3+ Dispersing in deionized water, and dripping NH at uniform speed under stirring 3 ∙H 2 O adjusts the pH of the solution; then aging the obtained suspension at a certain temperature, washing the aged product with distilled water and absolute ethyl alcohol for several times, drying in an oven to obtain magnetic Fe 3 O 4 A nano core;
（2）Fe 3 O 4 @SiO 2 preparation of the carrier: taking the magnetic Fe 3 O 4 The nano-cores are dispersed in a mixed solution of ethanol and water, and the ultrasonic dispersion is uniform; then tetraethyl orthosilicate TEOS and NH are added successively 3 ∙H 2 O, mechanically stirring the mixture 24 and h, and separating Fe by using a magnet 3 O 4 @SiO 2 Washing with ethanol and water for several times, and drying to obtain catalyst carrier with core-shell structure, which is expressed as Fe 3 O 4 @SiO 2 ；
（3）HPW/Fe 3 O 4 @SiO 2 Preparation of the catalyst: taking the Fe 3 O 4 @SiO 2 Dispersing the carrier in deionized water, and performing ultrasonic dispersion; dissolving phosphotungstic acid in a small amount of water, stirring uniformly, adding the aqueous solution, and stirring at normal temperature and a certain rotating speed for 24 h; separating the solid from the solution by using a magnet, washing the solid for a plurality of times by using ethanol and water, and drying the solid to obtain the phosphotungstic acid-loaded magnetic solid acid catalyst HPW/Fe 3 O 4 @SiO 2 。
Further, the Fe in the step (1) 2+ Derived from FeSO 4 ·7H 2 O，Fe 3+ Derived from FeCl 3 ·6H 2 O; the FeSO 4 ·7H 2 O︰FeCl 3 ·6H 2 The molar ratio of O to deionized water is 1:2:200-250;
step (2) Fe 3 O 4 @SiO 2 Fe in the preparation of (2) 3 O 4 Nanoparticles: TEOS: NH (NH) 3 ∙H 2 The mass ratio of O is 1:2-4:2-4;
fe in step (3) 3 O 4 @SiO 2 The mass ratio of the carrier to the phosphotungstic acid is as follows: 1:0.2-1, mechanical stirring speed is 200-500 r·min -1 。
Further, the application of the magnetic solid acid catalyst is that long-chain fatty acid, short-chain alcohol and magnetic solid acid catalyst HPW/Fe are taken 3 O 4 @SiO 2 Heating in an oil bath in a round bottom flask, and mechanically stirring by using a condensation reflux device; under different reaction conditions: different reaction temperatures, alcohols: carrying out catalytic reaction under the conditions of acid molar ratio, reaction time and catalyst dosage; in the reaction process, sampling is carried out at intervals of a certain time, the acid value of the reactant is measured, and the conversion rate of the reaction is calculated by using the acid value; after the reaction, the catalyst was separated by a magnet, washed and dried, and then recycled for the next reaction.
Further, the reaction temperature is 60-100 ℃, alcohol: the molar ratio of the acid is 7-19, the reaction time is 0.5-6 h, and the catalyst is 1-5 wt% of the total amount of the starting materials.
The method for preparing the magnetic solid acid catalyst by the one-pot method comprises the following steps: the magnetic zirconia is adopted to load phosphotungstic acid, and the magnetic zirconia solid acid catalyst HPW/Fe of the loaded phosphotungstic acid is obtained 2 O 3 @ZrO 2 。
Further, the preparation method of the magnetic solid acid catalyst by the one-pot method comprises the following steps:
(1) One-pot method for preparing magnetic zirconia catalyst carrier: fe is added to 2+ 、Fe 3+ And Zr (Zr) 4+ Dissolving in a certain amount of deionized water, and dropwise adding NaOH aqueous solution at a constant speed under the stirring condition to adjust the pH of the solution; then aging the obtained suspension at a certain temperature, washing the aged product with distilled water and absolute ethyl alcohol for several times, drying in an oven, and finally roasting in a tube furnace to form a stable crystal structure to obtain the magnetic zirconia catalyst carrier Fe 2 O 3 @ZrO 2 ；
(2) Loading of active centers: introducing phosphotungstic acid onto a magnetic zirconia catalyst support by impregnation; weighing different amounts of phosphotungstic acid to be dissolved in 0.1 mol.L -1 Adding the magnetic zirconia catalyst carrier prepared in the step (1) into the hydrochloric acid solution of phosphotungstic acidIn the method, after stirring, dipping, finally drying in an oven to obtain the magnetic zirconia solid acid catalyst HPW/Fe with different phosphotungstic acid loadings 2 O 3 @ZrO 2 。
Further, the Fe in the step (1) 2+ Derived from FeSO 4 ·7H 2 O，Fe 3+ Derived from FeCl 3 ·6H 2 O，Zr 4+ Derived from ZrOCl 2 ·8H 2 O; the FeSO 4 ·7H 2 O︰FeCl 3 ·6H 2 O︰ZrOCl 2 ·8H 2 The molar ratio of O/deionized water is 1:2:6-8:220-240; the aging temperature is 50-70 ℃ and the aging time is 16-24 h; roasting the prepared catalyst carrier at 500-600 ℃ in oxygen or air atmosphere for 4-8 h;
in the step (2), the mass ratio of the added phosphotungstic acid, the catalyst carrier and the hydrochloric acid solution is 0.2-1:1:50-200.
Further, the application of the magnetic solid acid catalyst is used for catalyzing esterification reaction of long-chain fatty acid by the catalyst; heating long-chain fatty acid, short-chain alcohol and magnetic zirconia supported phosphotungstic acid catalyst in a round bottom flask in an oil bath, and mechanically stirring by using a traditional condensing reflux device; catalytic reaction is carried out under different reaction conditions, namely different reaction temperatures, alkyd molar ratios, reaction time and catalyst dosage; in the reaction process, sampling is carried out at intervals of a certain time, the acid value of the reactant is measured, and the conversion rate of the reaction is calculated by using the acid value; after the reaction, the catalyst was separated by a magnet, washed and dried, and then recycled for the next reaction.
Further, the long-chain fatty acid is oleic acid, and the short-chain alcohol is methanol; the reaction temperature is 60-100 ℃, alcohol: the molar ratio of the acid is 7-19, the reaction time is 0.5-6 h, and the catalyst is 1-5 wt% of the total amount of the starting materials.
The invention has the beneficial effects that: the synthesized silicon dioxide coated magnetic Fe prepared by the two-step method of the invention 3 O 4 Nano core loaded phosphotungstic acid catalyst HPW/Fe 3 O 4 @SiO 2 Catalytic activity testing with oleic acidThe esterification reaction with methanol is used as a probe reaction, and the probe reaction has good oleic acid conversion rate and better esterification catalytic activity.
The synthesized phosphotungstic acid-loaded magnetic zirconia solid acid catalyst HPW/Fe prepared by the one-pot method 2 O 3 @ZrO 2 The catalytic activity test is carried out, and the esterification reaction of oleic acid and methanol is used as a probe reaction, so that the method has good oleic acid conversion rate and better esterification catalytic activity.
Drawings
FIG. 1 shows the magnetic Fe synthesized in example 1 3 O 4 Nano core, fe 3 O 4 @SiO 2 Support and HPW/Fe 3 O 4 @SiO 2 Infrared (FTIR) plot of the catalyst.
FIG. 2 is a silica-coated magnetic Fe synthesized in example 1 3 O 4 Nano core loaded phosphotungstic acid catalyst HPW/Fe 3 O 4 @SiO 2 SEM images of (a).
FIG. 3 is a silica-coated magnetic Fe synthesized in example 1 3 O 4 Nano core loaded phosphotungstic acid catalyst HPW/Fe 3 O 4 @SiO 2 Is a TEM image of (1).
FIG. 4 is a magnetic Fe synthesized in example 1 3 O 4 Nano core, fe 3 O 4 @SiO 2 Support and HPW/Fe 3 O 4 @SiO 2 VSM plot of catalyst.
FIG. 5 is a silica-coated magnetic Fe synthesized in example 1 3 O 4 Nano core loaded phosphotungstic acid catalyst HPW/Fe 3 O 4 @SiO 2 And a catalytic esterification effect graph of oleic acid.
FIG. 6 is an infrared (FTIR) image of a magnetic zirconia support, a phosphotungstic acid supported magnetic zirconia solid acid catalyst synthesized in example 7.
FIG. 7 is a graph showing the catalytic esterification effect of the phosphotungstic acid-supported magnetic zirconia solid acid catalyst synthesized in example 7 on oleic acid.
FIG. 8 is a graph showing the effect of separating the phosphotungstic acid-supported magnetic zirconia solid acid catalyst synthesized in example 7 from the reaction system under the action of external magnet.
Detailed Description
EXAMPLE 1 HPW/Fe 3 O 4 @SiO 2 Is prepared from
(1) Magnetic Fe 3 O 4 Preparation of the nanonucleus: 0.04 mol FeSO 4 ·7H 2 O and 0.08 mol FeCl 3 ·6H 2 O is dissolved in 150 mL water and then is dissolved in 300 r min -1 Adding NH dropwise under stirring 3 ∙H 2 O adjusts the solution ph=7. Then the obtained suspension is placed in a baking oven at 70 ℃, aged 16 h, the aged products are respectively washed twice by deionized water and absolute ethyl alcohol, and dried in the baking oven to obtain the magnetic Fe 3 O 4 A nano-core.
（2）Fe 3 O 4 @SiO 2 Preparation of the carrier: taking the Fe 3 O 4 Nanoparticle 2 g was dispersed in a mixed solution of ethanol 70 mL and water 10 mL, and dispersed uniformly by sonication for 15 min. Then, 5 mL tetraethyl orthosilicate (TEOS) and 5 mL NH were added successively 3 ∙H 2 O (25-28 wt%), the mixture was stirred under mechanical stirring for 24 h, and Fe was separated by a magnet 3 O 4 @SiO 2 Washing with ethanol and water for several times, and drying to obtain catalyst carrier with core-shell structure, which is expressed as Fe 3 O 4 @SiO 2 。
（3）HPW/Fe 3 O 4 @SiO 2 Preparation of the catalyst: dispersing the carrier 2 g in 30 mL deionized water, and performing ultrasonic dispersion for 30min. Dissolving 0.5. 0.5 g phosphotungstic acid in 5 mL deionized water, stirring, adding above water solution, and standing at normal temperature for 300 r min -1 Stirring 24 h under conditions. Separating the solid from the solution with magnet, washing with ethanol and water for 3 times, and drying to obtain SiO 2 Coated magnetic Fe 3 O 4 Nanoparticle supported phosphotungstic acid catalyst and expressed as HPW/Fe 3 O 4 @SiO 2 。
For magnetic Fe in example 1 3 O 4 Nano core, fe 3 O 4 @SiO 2 Support and HPW/Fe 3 O 4 @SiO 2 The catalyst was subjected to infrared analysis and the results are shown in fig. 1. Three samples at 583 cm -1 Peaks are formed at the positions corresponding to the stretching vibration of Fe-O bond in magnetite, which proves that the magnetic Fe 3 O 4 Is a successful synthesis of (a). Comparative Fe 3 O 4 And Fe (Fe) 3 O 4 @SiO 2 Can be found by the infrared curve of Fe 3 O 4 @SiO 2 At 1070 cm -1 、796 cm -1 And 950 cm -1 Obvious absorption peaks respectively represent asymmetric stretching vibration of Si-O-Si, symmetric stretching vibration peak of Si-O-Si and symmetric stretching vibration of Si-OH appear, which proves that Fe 3 O 4 @SiO 2 Is a successful synthesis of (a). Fe is added to 3 O 4 @SiO 2 Support and HPW/Fe 3 O 4 @SiO 2 Comparing the infrared curves of the two, the HPW/Fe can be found 3 O 4 @SiO 2 1070 cm in the infrared curve of (a) -1 Sum 980 cm -1 There are two distinct absorption peaks representing P-O bonds and w=o, respectively t The antisymmetric stretching vibration of the bond proves that the active center phosphotungstic acid is successfully introduced to the surface of the carrier.
SEM and TEM analyses were performed on the catalyst in example 1, and the results are shown in fig. 2 and 3. From the SEM images, it can be seen that the catalyst is in the form of nano-scale spherical particles. As can be seen from TEM image, the nano particles of the catalyst have a core-shell structure, and the dark core is magnetic Fe 3 O 4 Particles, the outer light-colored part being SiO 2 A shell. Demonstration of SiO 2 Coated magnetic Fe 3 O 4 The nano particle supported phosphotungstic acid catalyst has an obvious core-shell structure.
For magnetic Fe in example 1 3 O 4 Nano core, fe 3 O 4 @SiO 2 Support and HPW/Fe 3 O 4 @SiO 2 The catalysts were each subjected to VSM characterization and the results are shown in fig. 4. From the figure it can be seen that the M-H curves of all samples show no hysteresis loop, and that these samples have no remanence and coercivity, which suggests that they have superparamagnetic behaviour. From the curves, it can be seen that the saturation magnetization of the three samples is approximately 65.3 emu/g, 37.1 emu/g and 22.3 emu/g.The saturation magnetization of the catalyst is 22.3 emu/g, which is reduced compared with the former two, but still belongs to a higher level, which shows that the catalyst can rapidly respond to the change of an external magnetic field and obtain high magnetic induction with low loss, thereby laying a foundation for obtaining higher recovery rate of the catalyst.
EXAMPLE 2 HPW/Fe 3 O 4 @SiO 2 Is prepared from
The amount of tetraethyl orthosilicate in example 1 was changed to 8 mL, and the other steps were unchanged.
EXAMPLE 3 HPW/Fe 3 O 4 @SiO 2 Is prepared from
Only NH in example 1 3 ∙H 2 The dosage of O is changed to 10 mL, and other steps are unchanged.
EXAMPLE 4 HPW/Fe 3 O 4 @SiO 2 Is prepared from
The quality of phosphotungstic acid in example 1 was changed to 1 g, and the other steps were unchanged.
EXAMPLE 5 HPW/Fe 3 O 4 @SiO 2 Is prepared from
The speed of mechanical stirring in example 1 was changed to 400 r. Min -1 The other steps are unchanged.
EXAMPLE 6 HPW/Fe 3 O 4 @SiO 2 Applications of (2)
The esterification of oleic acid was carried out in a round bottom flask using a conventional condensing reflux apparatus, heated with an oil bath, and mechanically stirred. Oleic acid 0.3 g, methanol 0.34 g and the catalyst 0.0192 g prepared above are taken in a round bottom flask, and the reaction conditions are controlled as follows: the acid molar ratio was 10:1, the reaction time was 3 h, and the catalyst was used in an amount of 3 wt% of the total starting material. During the reaction, samples are taken at regular intervals, the acid value of the reactant is measured, and the conversion rate of the reaction is calculated by using the acid value. After the reaction, the catalyst was separated by a magnet, washed and dried, and then recycled for the next reaction.
FIG. 5 is SiO in example 1 2 Coated magnetic Fe 3 O 4 Nanoparticle Supported phosphotungstic acid catalyst example 6 stripsThe catalytic effect of the catalyst on oleic acid and methanol is shown in the graph, and the catalyst can reach 98.6% of oleic acid conversion rate under the condition of example 6, so that the catalyst has good catalytic activity on esterification reaction of oleic acid and methanol.
EXAMPLE 7 phosphotungstic acid-supported magnetic zirconia solid acid catalyst HPW/Fe 2 O 3 @ZrO 2 Is prepared from
(1) Preparation of the carrier: 0.03 mol FeSO 4 ·7H 2 O、0.06 mol FeCl 3 ·6H 2 O and 0.23 mol ZrOCl 2 ·8H 2 O is dissolved in 125 mL water and then is dissolved in 300 r min -1 Under stirring, the mixture was stirred with a constant pressure dropping funnel at 3 mL min -1 Dripping 6 mol.L -1 NaOH to adjust the solution ph=7. Then placing the obtained suspension in a 60 ℃ oven, aging 18 h, respectively washing the aged product with distilled water and absolute ethyl alcohol for several times, drying, and calcining in a 550 ℃ tubular furnace under oxygen atmosphere for 6 h to obtain the catalyst carrier Fe 2 O 3 @ZrO 2 。
(2) Loading of phosphotungstic acid: weighing 0.06 g phosphotungstic acid and dissolving in 10 mL and 0.1 mol.L -1 Adding 0.2. 0.2 g carrier into the solution, stirring, soaking, drying to obtain the magnetic zirconia solid acid catalyst HPW/Fe with 20 wt percent phosphotungstic acid loading 2 O 3 @ZrO 2 。
The catalyst carrier and the catalyst prepared in this example were subjected to infrared analysis, and the results are shown in fig. 6. The carrier and the catalyst are 3429 and 3429 cm -1 、1627 cm -1 And 690 cm -1 Peaks are present at the sites, which correspond to the ≡Zr-OH, the physically adsorbed H, respectively 2 The stretching vibration of O molecules and Fe-O-Fe groups proves the successful synthesis of magnetic zirconia. Comparing the two infrared curves can find that the catalyst after supporting phosphotungstic acid is 980 cm -1 And 1070 cm -1 There are distinct peaks, which represent w=o respectively t And a P-O stretching vibration peak, which proves that the phosphotungstic acid is successfully introduced to the surface of the carrier.
Example 8
Only ZrOCl in example 7 2 ·8H 2 The O consumption is changed to 0.18 mol, and other steps are unchanged.
Example 9
The aging temperature was changed to 70℃and the aging time was changed to 16 h in example 7, and the other steps were unchanged.
Example 10
The atmosphere for firing the carrier in example 7 was changed to air. All other steps are unchanged.
Example 11
The amount of phosphotungstic acid in example 7 was changed to 0.1. 0.1 g, and all other steps were unchanged.
Example 12
The esterification of oleic acid was carried out in a round bottom flask using a conventional condensing reflux apparatus, heated with an oil bath, and mechanically stirred. Oleic acid 0.2 g, methanol 0.27 g, catalyst 0.024 g prepared in example 7 were taken in a round bottom flask under reaction conditions of 80 ℃ reaction temperature, alcohol: the acid molar ratio was 12:1, the reaction time was 4 h, and the catalyst was used in an amount of 3: 3 wt% of the total starting material. During the reaction, samples are taken at regular intervals, the acid value of the reactant is measured, and the conversion rate of the reaction is calculated by using the acid value. After the reaction, the catalyst was separated by a magnet, washed and dried, and then recycled for the next reaction.
Fig. 7 is a graph showing the catalytic effect of the phosphotungstic acid-supported magnetic zirconia solid acid catalyst of example 7 on oleic acid and methanol under the condition of example 12, and it can be seen from the graph that the catalyst can reach 98.4% of oleic acid conversion rate under the condition of example 12, and the catalyst has good catalytic activity on esterification reaction of oleic acid and methanol.
FIG. 8 is a graph showing the effect of separating the catalyst from the reaction system by using an external magnet in example 12, and it can be seen from the graph that the catalyst contains magnetism enough to be attracted by the external magnet, so as to achieve the effect of rapid separation from the reaction system, which greatly simplifies the separation process of the product and the catalyst after the reaction is finished.

Claims (3)

1. A method for preparing a magnetic solid acid catalyst by a one-pot method is characterized by comprising the following steps: the magnetic zirconia is adopted to load phosphotungstic acid, and the magnetic zirconia solid acid catalyst HPW/Fe of the loaded phosphotungstic acid is obtained 2 O 3 @ZrO 2 The method comprises the steps of carrying out a first treatment on the surface of the The method comprises the following steps:
(1) One-pot method for preparing magnetic zirconia catalyst carrier: fe is added to 2+ 、Fe 3+ And Zr (Zr) 4+ Dissolving in a certain amount of deionized water, and dropwise adding NaOH aqueous solution at a constant speed under the stirring condition to adjust the pH of the solution; then aging the obtained suspension at a certain temperature, washing the aged product with distilled water and absolute ethyl alcohol for several times, drying in an oven, and finally roasting in a tube furnace to form a stable crystal structure to obtain the magnetic zirconia catalyst carrier Fe 2 O 3 @ZrO 2 ；
The Fe is 2+ Derived from FeSO 4 ·7H 2 O，Fe 3+ Derived from FeCl 3 ·6H 2 O，Zr 4+ Derived from ZrOCl 2 ·8H 2 O; the FeSO 4 ·7H 2 O︰FeCl 3 ·6H 2 O︰ZrOCl 2 ·8H 2 The molar ratio of O/deionized water is 1:2:6-8:220-240; the aging temperature is 50-70 ℃ and the aging time is 16-24 h; roasting the prepared catalyst carrier at 500-600 ℃ in oxygen or air atmosphere for 4-8 h;
(2) Loading of active centers: introducing phosphotungstic acid onto a magnetic zirconia catalyst support by impregnation; weighing different amounts of phosphotungstic acid to be dissolved in 0.1 mol.L -1 Adding the magnetic zirconia catalyst carrier prepared in the step (1) into the hydrochloric acid solution of the phosphotungstic acid, wherein the mass ratio of the phosphotungstic acid to the catalyst carrier to the hydrochloric acid solution is 0.2-1:1:50-200 parts; stirring, soaking, and finally drying in an oven to obtain the magnetic zirconia solid acid catalyst HPW/Fe with different phosphotungstic acid loadings 2 O 3 @ZrO 2 。
2. The use of a magnetic solid acid catalyst prepared by the method of claim 1, characterized in that: the catalyst is used for catalyzing esterification reaction of long-chain fatty acid; heating a long-chain fatty acid, a short-chain alcohol and a phosphotungstic acid-loaded magnetic zirconia solid acid catalyst in a round-bottom flask in an oil bath, and mechanically stirring by using a traditional condensation reflux device; catalytic reaction is carried out under different reaction conditions, namely different reaction temperatures, alkyd molar ratios, reaction time and catalyst dosage; in the reaction process, sampling is carried out at intervals of a certain time, the acid value of the reactant is measured, and the conversion rate of the reaction is calculated by using the acid value; after the reaction, the catalyst was separated by a magnet, washed and dried, and then recycled for the next reaction.
3. The use of a magnetic solid acid catalyst according to claim 2, wherein: the long-chain fatty acid is oleic acid, and the short-chain alcohol is methanol; the reaction temperature is 60-100 ℃, alcohol: the molar ratio of the acid is 7-19, the reaction time is 0.5-6 h, and the catalyst is 1-5 wt% of the total amount of the starting materials.
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