CN110624608A - Preparation process and application of Fe-based metal organic framework solid acid catalyst - Google Patents
Preparation process and application of Fe-based metal organic framework solid acid catalyst Download PDFInfo
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Abstract
The invention relates to the technical field of solid acid catalysts for biodiesel production, in particular to a preparation process and application of a Fe-based metal organic framework solid acid catalyst. The process comprises the following steps: 1) placing MIL-100(Fe) in a dilute sulfuric acid solution for hydrothermal reaction; separating out a solid product after the reaction is finished to obtain a precursor; 2) washing the precursor obtained in the step 1) with water until the washing liquid is neutral to obtain a neutral precursor; 3) drying the neutral precursor obtained in the step 1) to obtain the Fe-based metal organic framework solid acid catalyst. The invention is based on metal organic framework material (MIL-100(Fe)), and takes dilute sulphuric acid as a sulfonation reagent to prepare a solid acid catalyst with high catalytic activity and good stability for preparing biodiesel by catalytic esterification.
Description
Technical Field
The invention relates to the technical field of solid acid catalysts for biodiesel production, in particular to a preparation process and application of a Fe-based metal organic framework solid acid catalyst.
Background
The information disclosed in this background of the invention is only for enhancement of understanding of the general background of the invention and is not necessarily to be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Biodiesel is fatty acid alkyl monoester obtained by using animal and vegetable oil, fatty acid and the like as raw materials and carrying out esterification or ester exchange reaction with an alcohol agent (low-carbon chain alcohol such as methanol) under the catalytic action of acid, alkali or biological enzyme. As a green and environment-friendly renewable fuel, the biodiesel has the advantages of high cetane number, low sulfur content, good lubricating property and the like, and is an ideal substitute for common fossil diesel. In the production process of the biodiesel, the raw oil occupies 70-75% of the production cost, and in order to break through the price bottleneck of the biodiesel, cheap and easily available waste cooking oil such as swill-cooked dirty oil, frying waste oil and hogwash oil becomes a research hotspot. Waste cooking oil is rich in triglycerides, but has a high content of free fatty acids due to severe rancidity, and is mixed with impurities such as water. Although the traditional biodiesel production process adopts a homogeneous alkali catalyst with short reaction time and high efficiency, the process has strict requirements on the contents of fatty acid and water in raw oil, particularly the fatty acid and the alkali catalyst are easy to have saponification reaction with the raw oil, so that the catalyst is consumed, and the yield of the biodiesel is reduced seriously. Therefore, before the ester exchange reaction, the waste catering oil needs to be esterified, and fatty acid is directly converted into biodiesel. Common solid acid catalysts used in esterification reactions are cation exchange resins, zeolite molecular sieves, solid superacids, heteropolyacids and carbon-based solid acids, such as chinese patent documents (application nos. 201811518412.9, 201710157289.1, 201510985895.3, 201210312374.8).
Disclosure of Invention
Concentrated sulfuric acid is used as sulfonating agent to load sulfonic acid group (-SO)3H) Is a commonly used solid acid preparation method, however, the present inventors found that: in the preparation process of the catalyst, the solid product needs to be washed by water for many times to remove redundant concentrated sulfuric acid, so that a large amount of acidic wastewater is generated. Meanwhile, sulfonic acid groups are easy to dissolve in water and then run off, and a by-product water is generated in the process of catalytic esterification reaction of the solid acid, so that the service life of the traditional sulfonic acid group solid acid is shortened due to the generation of water in the esterification reaction.
The invention aims to solve the problems of a large amount of acidic wastewater generated by preparing solid acid by using concentrated sulfuric acid as a sulfonating agent to load sulfonic acid groups and short service life of the catalytic esterification reaction of the sulfonic acid group solid acid. Therefore, the invention provides a preparation process and application of a Fe-based metal organic framework solid acid catalyst. The invention is based on metal organic framework material (MIL-100(Fe)), and takes dilute sulphuric acid as a sulfonation reagent to prepare a solid acid catalyst with high catalytic activity and long service life for preparing biodiesel by catalytic esterification reaction.
The first object of the present invention: provides a preparation process of a Fe-based metal organic framework solid acid catalyst.
The second object of the present invention: provides the application of the Fe-based metal organic framework solid acid catalyst prepared by the process.
In order to achieve the purpose, the invention discloses the following scheme:
firstly, a preparation process of a Fe-based metal organic framework solid acid catalyst is disclosed, which comprises the following steps:
(1) placing MIL-100(Fe) in a dilute sulfuric acid solution for hydrothermal reaction; separating out a solid product after the reaction is finished to obtain a precursor;
(2) washing the precursor obtained in the step (1) with water until the washing liquid is neutral to obtain a neutral precursor;
(3) drying the neutral precursor obtained in the step (1) to obtain a Fe-based metal organic framework solid acid catalyst; the drying aims to activate the precursor and improve the catalytic activity.
As a further technical scheme, in the step (1), the MIL-100(Fe) is prepared by the method in chinese patent document 201910439556.3 (application number).
As a further technical scheme, in the step (1), the concentration of the dilute sulfuric acid solution is 0.1-1.0mol/L, and more preferably 0.8-0.9mol/L, and tests show that when the concentration of the dilute sulfuric acid solution is in the range, the catalytic activity of the obtained catalyst is higher.
As a further technical scheme, in the step (1), the hydrothermal reaction time is 1-30h, the sulfonation temperature is 60-300 ℃, and the reaction time is preferably 10h at the temperature of 120-160 ℃, and tests show that when the temperature is in the range, the catalytic activity of the obtained catalyst is higher.
As a further technical scheme, in the step (2), the washing temperature is 40-80 ℃ and the time is 20-35 min.
As a further technical scheme, in the step (3), the drying method comprises firstly air-blast drying and then vacuum drying, wherein the temperatures adopted by the two drying methods are both 100-130 ℃, the air-blast drying time is 20-24h, and the vacuum drying time is 6-24 h.
One of the characteristics of the solid acid catalyst of the invention is as follows: the Metal Organic Framework (MOF) is a porous crystalline material with a periodic multidimensional network structure formed by self-assembly of Metal ions or Metal cluster units and organic ligands through coordination, the MOF material has certain hydrophobic property due to periodic arrangement of the organic ligands, and the hydrophobic property of the solid acid can be enhanced by grafting sulfonic acid groups on the MOF material serving as a matrix to prepare the solid acid, so that the reusability of the solid acid is improved. Moreover, the porosity of the MOF is beneficial to the mass transfer process of the esterification reaction, and the esterification efficiency is improved.
The solid acid catalyst of the invention is characterized by the following two: dilute sulfuric acid is used as a sulfonation reagent, so that the solid product does not need to be washed by water for many times, and a large amount of acidic wastewater cannot be generated.
Secondly, the invention discloses the application of the Fe-based metal organic framework solid acid catalyst in the preparation of biodiesel; preferably, the esterification reaction of the oleic acid and the methanol is catalyzed to produce the biodiesel, and the specific method comprises the following steps: mixing methanol and oleic acid according to a set alcohol acid molar ratio, stirring and heating for esterification reaction, then adding the Fe-based metal organic framework solid acid catalyst, keeping condensation and reflux, centrifugally separating out the catalyst after the reaction is finished, standing and layering the liquid product, and obtaining the upper layer, namely the biodiesel.
As a further technical solution, the heating method comprises: the water bath was heated to 50-90 ℃.
As a further technical scheme, the addition amount of the Fe-based metal organic framework solid acid catalyst is 1-15% of the mass of the oleic acid.
As a further technical scheme, the molar ratio of the methanol to the oleic acid is 4:1-15: 1.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention is based on metal organic framework material MIL-100(Fe), dilute sulphuric acid is taken as a sulfonation reagent, and sulfonic acid group (-SO) is subjected to hydrothermal method3H) Grafted to MIL-100(Fe) to obtain the solid acid catalyst with high catalytic activity and long service life. The catalyst can be directly used for catalyzing fatty acid and methanol to carry out esterification reaction to produce biodiesel, and can also be used for acid reduction treatment in the transesterification process of high-acid-value waste oil.
(2) The solid acid catalyst obtained by the invention has the advantages of high catalytic activity, long service life and easy product separation. In the biodiesel production process, the activity and the repeated use times of the catalyst can be improved, the production cost of the biodiesel is reduced, the environmental pollution is favorably treated, and the method has a very strong industrial application prospect.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is an FTIR spectrum of a solid acid catalyst prepared in example 5 of the present invention.
FIG. 2 shows a spectrum of Py-FTIR of the solid acid catalyst prepared in example 5 of the present invention.
FIG. 3 is an SEM topography of MIL-100(Fe) used in example 5 of the present invention.
FIG. 4 is an SEM topography of a solid acid catalyst prepared in example 5 of the present invention.
Detailed Description
It is to be noted that, unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
As described above, the current preparation of solid acid by using concentrated sulfuric acid as sulfonating agent to load sulfonic acid groups has the problem of generating a large amount of acidic wastewater. For this purpose, the invention is based on (MIL-100(Fe)) preparing a solid acid catalyst with dilute sulfuric acid as sulfonating agent. The invention will now be further described with reference to the drawings and detailed description.
In the following examples, the MIL-100(Fe) was prepared by the method of example 1 in Chinese patent document 201910439556.3 (application No.).
Example 1
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) preparing a dilute sulfuric acid solution with the concentration of 0.8mol/L, then weighing 2g of MIL-100(Fe), adding the solution into 25mL of the dilute sulfuric acid solution, stirring the solution at room temperature for 60min, pouring the mixed material into a hydrothermal reaction kettle, heating the reaction kettle to 60 ℃ by using an air-blast drying oven, heating the reaction kettle for 30h, and cooling the reaction kettle to room temperature.
(2) And (3) placing the mixed material in the reaction kettle in a centrifuge, centrifuging for 30min at 3000r/min, removing supernatant, placing the obtained solid material in 200mL of deionized water, stirring and washing for 30min at 60 ℃, filtering and separating a solid product, repeating the step if the pH of the filtrate is less than 7 until the pH of the filtrate is 7, and filtering to obtain a washed material.
(3) And drying the washed materials in a 130 ℃ forced air drying oven for 20h, then transferring to a vacuum drying oven, drying for 6h at 130 ℃ to obtain a solid acid catalyst, and sealing and storing.
The catalyst prepared in the embodiment is used for catalyzing esterification reaction of oleic acid and methanol, and the esterification efficiency is 65.52% under the conditions that the molar ratio of the alcohol acid to the alcohol acid is 8:1, the addition amount of the catalyst is 8% of the mass of the oleic acid, the reaction temperature is 70 ℃ and the reaction time is 2 hours.
Example 2
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) preparing a dilute sulfuric acid solution with the concentration of 0.9mol/L, then weighing 2g of MIL-100(Fe), adding the solution into 25mL of the dilute sulfuric acid solution, stirring the solution at room temperature for 60min, pouring the mixed material into a hydrothermal reaction kettle, heating the reaction kettle to 160 ℃ by using an air-blast drying oven, heating the reaction kettle for 15h, and cooling the reaction kettle to room temperature.
(2) And (3) placing the mixed material in the reaction kettle in a centrifuge, centrifuging for 30min at 3000r/min, removing supernatant, placing the obtained solid material in 200mL of deionized water, stirring and washing for 20min at 80 ℃, filtering and separating a solid product, repeating the step if the pH of the filtrate is less than 7 until the pH of the filtrate is 7, and filtering to obtain a washed material.
(3) Drying the washed materials in a 120 ℃ air-blast drying oven for 24h, then transferring to a vacuum drying oven, drying for 12h at 120 ℃ to obtain a solid acid catalyst, and sealing and storing.
The catalyst prepared in the embodiment is used for catalyzing esterification reaction of oleic acid and methanol, and the esterification efficiency is 88.54% under the conditions that the molar ratio of the alcohol acid to the alcohol acid is 15:1, the addition amount of the catalyst is 15% of the mass of the oleic acid, the reaction temperature is 70 ℃ and the reaction time is 2 hours.
Example 3
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) preparing a dilute sulfuric acid solution with the concentration of 1.0mol/L, then weighing 2g of MIL-100(Fe), adding the solution into 25mL of the dilute sulfuric acid solution, stirring the solution at room temperature for 60min, pouring the mixed material into a hydrothermal reaction kettle, heating the reaction kettle to 300 ℃ by using an air-blast drying oven, heating the reaction kettle for 1h, and cooling the reaction kettle to room temperature.
(2) And (3) placing the mixed material in the reaction kettle in a centrifuge, centrifuging for 30min at 3000r/min, removing supernatant, placing the obtained solid material in 200mL of deionized water, stirring and washing for 35min at 40 ℃, filtering and separating a solid product, repeating the step if the pH of the filtrate is less than 7 until the pH of the filtrate is 7, and filtering to obtain a washed material.
(3) And drying the washed materials in a 100 ℃ forced air drying oven for 24h, then transferring to a vacuum drying oven, drying for 24h at 100 ℃ to obtain a solid acid catalyst, and sealing and storing.
The catalyst prepared in the embodiment is used for catalyzing esterification reaction of oleic acid and methanol, and the esterification efficiency is 81.77% under the conditions that the molar ratio of the alcohol acid to the alcohol acid is 8:1, the addition amount of the catalyst is 8% of the mass of the oleic acid, the reaction temperature is 70 ℃ and the reaction time is 2 hours.
Example 4
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) preparing a dilute sulfuric acid solution with the concentration of 0.1mol/L, then weighing 2g of MIL-100(Fe), adding into 12.5mL of the dilute sulfuric acid solution, stirring at room temperature for 60min, pouring the mixed material into a hydrothermal reaction kettle, heating the reaction kettle to 160 ℃ by using an air-blast drying box, heating for 10h, and cooling to room temperature.
(2) And (3) placing the mixed material in the reaction kettle in a centrifuge, centrifuging for 30min at 3000r/min, removing supernatant, placing the obtained solid material in 200mL of deionized water, stirring and washing for 30min at 60 ℃, filtering and separating a solid product, repeating the step if the pH of the filtrate is less than 7 until the pH of the filtrate is 7, and filtering to obtain a washed material.
(3) And drying the washed materials in a 120 ℃ forced air drying oven for 24 hours, then transferring to a vacuum drying oven, drying for 12 hours at 120 ℃ to obtain a solid acid catalyst, and sealing and storing.
The catalyst prepared in the embodiment is used for catalyzing esterification reaction of oleic acid and methanol, and the esterification efficiency is 40.97% under the conditions that the molar ratio of the alcohol acid to the alcohol acid is 4:1, the addition amount of the catalyst is 1% of the mass of the oleic acid, the reaction temperature is 50 ℃ and the reaction time is 2 hours.
Example 5
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) preparing a dilute sulfuric acid solution with the concentration of 0.9mol/L, then weighing 2g of MIL-100(Fe) and adding the mixture into 25mL of dilute sulfuric acid solution, stirring the mixture at room temperature for 60min, pouring the mixture into a hydrothermal reaction kettle, heating the reaction kettle to 160 ℃ by using an air-blast drying oven, heating the reaction kettle for 10h, and cooling the reaction kettle to room temperature.
(2) And (3) placing the mixed material in the reaction kettle in a centrifuge, centrifuging for 30min at 3000r/min, removing supernatant, placing the obtained solid material in 200mL of deionized water, stirring and washing for 30min at 60 ℃, filtering and separating a solid product, repeating the step if the pH of the filtrate is less than 7 until the pH of the filtrate is 7, and filtering to obtain a washed material.
(3) And drying the washed materials in a 120 ℃ forced air drying oven for 24 hours, then transferring to a vacuum drying oven, drying for 12 hours at 120 ℃ to obtain a solid acid catalyst, and sealing and storing.
The catalyst prepared in the embodiment is used for catalyzing esterification reaction of oleic acid and methanol, and the esterification efficiency is 93.24% under the conditions that the molar ratio of the alcohol acid to the alcohol acid is 8:1, the addition amount of the catalyst is 8% of the mass of the oleic acid, the reaction temperature is 70 ℃ and the reaction time is 2 hours.
Example 6
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) preparing a dilute sulfuric acid solution with the concentration of 0.9mol/L, then weighing 2g of MIL-100(Fe), adding into 50mL of the dilute sulfuric acid solution, stirring at room temperature for 60min, pouring the mixed material into a hydrothermal reaction kettle, heating the reaction kettle to 160 ℃ by using an air-blast drying oven, heating for 10h, and cooling to room temperature.
(2) And (3) placing the mixed material in the reaction kettle in a centrifuge, centrifuging for 30min at 3000r/min, removing supernatant, placing the obtained solid material in 200mL of deionized water, stirring and washing for 30min at 60 ℃, filtering and separating a solid product, repeating the step if the pH of the filtrate is less than 7 until the pH of the filtrate is 7, and filtering to obtain a washed material.
(3) And drying the washed materials in a 120 ℃ forced air drying oven for 24 hours, then transferring to a vacuum drying oven, drying for 12 hours at 120 ℃ to obtain a solid acid catalyst, and sealing and storing.
The catalyst prepared in the embodiment is used for catalyzing esterification reaction of oleic acid and methanol, and the esterification efficiency is 73.13% under the conditions that the molar ratio of the alcohol acid to the alcohol acid is 8:1, the addition amount of the catalyst is 8% of the mass of the oleic acid, the reaction temperature is 90 ℃ and the reaction time is 2 hours.
Example 7
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) preparing a dilute sulfuric acid solution with the concentration of 0.9mol/L, then weighing 2g of MIL-100(Fe), adding the solution into 25mL of the dilute sulfuric acid solution, stirring the solution at room temperature for 60min, pouring the mixed material into a hydrothermal reaction kettle, heating the reaction kettle to 120 ℃ by using an air-blast drying oven, heating the reaction kettle for 10h, and cooling the reaction kettle to room temperature.
(2) And (3) placing the mixed material in the reaction kettle in a centrifuge, centrifuging for 30min at 3000r/min, removing supernatant, placing the obtained solid material in 200mL of deionized water, stirring and washing for 30min at 60 ℃, filtering and separating a solid product, repeating the step if the pH of the filtrate is less than 7 until the pH of the filtrate is 7, and filtering to obtain a washed material.
(3) And drying the washed materials in a 120 ℃ forced air drying oven for 24 hours, then transferring to a vacuum drying oven, drying for 12 hours at 120 ℃ to obtain a solid acid catalyst, and sealing and storing.
The catalyst prepared in the embodiment is used for catalyzing esterification reaction of oleic acid and methanol, and the esterification efficiency is 82.76% under the conditions that the molar ratio of the alcohol acid to the alcohol acid is 8:1, the addition amount of the catalyst is 8% of the mass of the oleic acid, the reaction temperature is 70 ℃ and the reaction time is 2 hours.
Example 8
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) preparing a dilute sulfuric acid solution with the concentration of 0.9mol/L, then weighing 2g of MIL-100(Fe), adding the solution into 25mL of the dilute sulfuric acid solution, stirring the solution at room temperature for 60min, pouring the mixed material into a hydrothermal reaction kettle, heating the reaction kettle to 200 ℃ by using an air-blast drying oven, heating the reaction kettle for 10h, and cooling the reaction kettle to room temperature.
(2) And (3) placing the mixed material in the reaction kettle in a centrifuge, centrifuging for 30min at 3000r/min, removing supernatant, placing the obtained solid material in 200mL of deionized water, stirring and washing for 30min at 60 ℃, filtering and separating a solid product, repeating the step if the pH of the filtrate is less than 7 until the pH of the filtrate is 7, and filtering to obtain a washed material.
(3) And drying the washed solid material in a 120 ℃ forced air drying oven for 24h, then transferring to a vacuum drying oven, drying at 120 ℃ for 12h to obtain the solid acid catalyst, and sealing and storing.
The catalyst prepared in the embodiment is used for catalyzing esterification reaction of oleic acid and methanol, and the esterification efficiency is 74.45% under the conditions that the molar ratio of the alcohol acid to the alcohol acid is 8:1, the addition amount of the catalyst is 8% of the mass of the oleic acid, the reaction temperature is 70 ℃ and the reaction time is 2 hours.
Example 9
A preparation process of a Fe-based metal organic framework solid acid catalyst comprises the following steps:
(1) the solid acid prepared in example 5 was used as a catalyst to catalyze the esterification reaction of oleic acid and methanol at an alkyd molar ratio of 10:1 and a catalyst amount of 8 wt.%, at a reaction temperature of 70 ℃ for 2 hours, and the esterification efficiency was found to be 95.86%.
(2) After the esterification reaction is finished, the catalyst is recovered by a centrifuge, the fresh oleic acid and the fresh methanol are directly catalyzed under the same esterification reaction working condition without any treatment, the process is repeated for 5 times, and the reusability test of the solid acid is carried out, and the result shows that the catalytic activity is only reduced by 7.36 percent in a 5-time cycle period, which shows that the solid acid catalyst disclosed by the invention not only has high catalytic activity, but also has high stability.
Performance testing
(1) The difference among the examples 1, 2 and 3 is that the concentration of dilute sulfuric acid is 0.8mol/L, 0.9mol/L and 1.0mol/L, the concentration of sulfuric acid is too low, the number of sulfonic acid groups in unit volume is small, and the number of sulfonic acid groups grafted on the organic ligand is reduced; the sulfuric acid concentration is too high, so that MIL-100(Fe) becomes unstable, and the loading of sulfonic acid groups is not facilitated. The catalytic activity result shows that the solid acid has the best catalytic activity when the concentration of the dilute sulfuric acid is 0.9 mol/L.
Example 5, example 7, and example 8 are different in that sulfonation temperatures are 160 ℃, 120 ℃, and 200 ℃, respectively, and when the sulfonation temperature is too low, the energy provided by the reaction system is insufficient to replace H atoms on the organic ligand with sulfonic acid groups, and when the sulfonation temperature is too high, the thermal stability of MIL-100(Fe) is reduced in the hydrothermal reaction system, thereby reducing the solid acid catalytic activity. The catalytic activity results show that the solid acid catalytic activity is the best when the sulfonation temperature is 160 ℃.
The solid acid catalyst prepared in example 5 was characterized by Fourier transform Infrared Spectroscopy (FTIR), pyridine Fourier Infrared Spectroscopy (Py-FTIR) and Scanning Electron Microscopy (SEM).
As can be seen from the FTIR spectrum of FIG. 1, the wavenumber is 1080cm-1Has S-O stretching vibration peak at 1148cm-1And 1308cm-1There is a stretching vibration peak of O ═ S ═ O, indicating that sulfonic acid groups (-SO3H) have been successfully embedded in the MIL-100(Fe) skeleton.
For further validation, the catalyst was subjected toThe infrared characterization of pyridine is carried out, as shown in figure 2, and the result shows that the solid acid obtained by the invention is 1450cm-1And 1608cm-1Obvious coordination pyridine absorption peak appears, which indicates that the catalyst contains Lewis acid site and is 1540cm-1A peak of pyridinium ion appeared indicating that the catalyst had Bronsted acid sites. Meanwhile, the common absorption peak of Lewis acid and Bronsted acid appears at 1490cm-1To (3). Therefore, the catalyst obtained by the invention is double-acid type solid acid (B acid and L acid), the active sites (sulfonic acid groups) of the B acid are easy to be lost after being dissolved in water, the B acid and the L acid can play a role in synergistically stabilizing the catalyst, the stability of the catalyst is favorably improved, the acid density of the catalyst is 3.72mmol/g, and the acid strength is more than 3.3 and more than H measured by a Hammett indicator method-< 4.8 agent.
In addition, as shown in fig. 3 and 4, the comparison between the apparent morphology of the solid acid catalyst and MIL-100(Fe) shows that the solid acid surface prepared by using dilute sulfuric acid as the sulfonation reagent has an octahedral structure although the edge angle is somewhat fuzzy compared with MIL-100(Fe), which indicates that the use of dilute sulfuric acid as the sulfonation reagent has little influence on the structure of the material itself, and can maintain the original structural characteristics of MIL-100(Fe), thereby avoiding the problem that the original structure is damaged by the traditional sulfonation of concentrated sulfuric acid, fully utilizing the advantages of MOF pore structure and the like, and improving the esterification efficiency.
Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention. Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (10)
1. A preparation process of a Fe-based metal organic framework solid acid catalyst is characterized by comprising the following steps:
(1) placing MIL-100(Fe) in a dilute sulfuric acid solution for hydrothermal reaction; separating out a solid product after the reaction is finished to obtain a precursor;
(2) washing the precursor obtained in the step (1) with water until the washing liquid is neutral to obtain a neutral precursor;
(3) and (2) drying the neutral precursor obtained in the step (1) to obtain the Fe-based metal organic framework solid acid catalyst.
2. The process of claim 1, wherein in step (1), the MIL-100(Fe) is prepared by the method of chinese patent application No. 201910439556.3.
3. The process according to claim 1, wherein in step (1), the dilute sulfuric acid solution has a concentration of 0.1 to 1.0mol/L, preferably 0.8 to 0.9 mol/L.
4. The preparation process according to claim 1, wherein in the step (1), the hydrothermal reaction time is 1-30h, and the sulfonation temperature is 60-300 ℃; preferably, in the step (2), the washing temperature is 40-80 ℃ and the time is 20-35 min.
5. The preparation process as claimed in claim 1, wherein in the step (3), the drying method comprises air-blast drying and then vacuum drying, the temperatures adopted by the two drying methods are both 100 ℃ and 130 ℃, the air-blast drying time is 20-24h, and the vacuum drying time is 6-24 h.
6. Use of the Fe-based metal-organic framework solid acid catalyst obtained by the process as claimed in any one of claims 1 to 5 in the production of biodiesel.
7. The use as claimed in claim 6 for catalyzing the esterification of oleic acid with methanol to produce biodiesel.
8. The application of claim 7, wherein the specific method is as follows: mixing methanol and oleic acid according to a set alcohol acid molar ratio, stirring and heating for esterification reaction, then adding the Fe-based metal organic framework solid acid catalyst, keeping condensation and reflux, centrifugally separating out the catalyst after the reaction is finished, standing and layering the liquid product, and obtaining the upper layer, namely the biodiesel.
9. The use of claim 8, wherein the heating is by: the water bath was heated to 50-90 ℃.
10. The use of claim 8, wherein the Fe-based metal-organic framework solid acid catalyst is added in an amount of 1-15% by mass of oleic acid; preferably, the methanol to oleic acid molar ratio is from 4:1 to 15: 1.
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