Disclosure of Invention
In view of the above, it is necessary to provide a solid carbon sulfonic acid catalyst and a preparation method thereof, and tributyl citrate and a preparation method thereof, in order to solve the problem of how to improve the repeated practicability of the catalyst.
A preparation method of a solid carbon sulfonic acid catalyst comprises the following steps:
soaking the bamboo powder in a sodium silicate solution for 15-20 h, then soaking the bamboo powder in deionized water to reach adsorption balance, filtering and drying, and then carrying out heat treatment at 130-150 ℃ for 3-5 h to obtain bamboo powder subjected to alkaline pretreatment;
mixing the bamboo powder subjected to the alkaline pretreatment with hydrochloric acid, adding p-toluenesulfonic acid after complete reaction, uniformly mixing, and then carrying out heat treatment at 140-200 ℃ for 1-3 h to obtain bamboo powder subjected to the acidic pretreatment;
carbonizing the bamboo powder subjected to the acidic pretreatment to obtain carbonized bamboo powder; and
and sulfonating the carbonized bamboo powder to obtain the solid carbon sulfonic acid catalyst.
In one embodiment, the bamboo powder is prepared by the following steps:
bamboo is used as a raw material, washed with water and dried, and then milled in a crusher, sieved by a sieve with 50 meshes to 70 meshes and dried in vacuum at the temperature of 50 ℃ in sequence to obtain the bamboo powder.
In one embodiment, the carbonization of the bamboo powder after the acidic pretreatment comprises the following steps:
putting the bamboo powder into a stainless steel reaction tube, then putting the stainless steel reaction tube into a flat tube type electric furnace, vacuumizing the stainless steel reaction tube by using a circulating water type multipurpose vacuum pump, and then starting program heating; the temperature is controlled to rise by adopting a temperature programming mode, and the steps are divided into 4 sections: in the first stage, the temperature is increased to 250 ℃ at the heating rate of 10 ℃/min; in the second stage, the temperature is continuously increased to 300-350 ℃ at the temperature increase rate of 5 ℃/min; the temperature of the third section is increased to 380 ℃ at the heating rate of 1 ℃/min; and finally keeping the temperature at 380 ℃ for 3h, and cooling to room temperature to obtain the carbonized bamboo powder.
In one embodiment, the sulfonation of the carbonized bamboo powder is performed by:
and (3) sulfonation reaction: grinding the carbonized bamboo powder, then soaking the bamboo powder into 50% fuming sulfuric acid, and sulfonating in a nitrogen atmosphere at the reaction temperature: 373K, reaction time: 3 h;
and adding deionized water after the reaction is cooled to terminate the reaction: washing with distilled water, decocting in boiling water bath for half an hour, filtering, repeating for three times, and adding BaCl2And (4) checking the solution until no white precipitate is generated in the filtrate, and finally drying the bamboo charcoal sulfonic acid to obtain the solid carbon sulfonic acid catalyst.
In one embodiment, the mass ratio of the carbonized bamboo powder to 50% fuming sulfuric acid is 1: 4-6.
In one embodiment, the operation of preparing the acidic pretreated bamboo powder comprises:
and mixing the bamboo powder subjected to the alkaline pretreatment with hydrochloric acid, adding 5% of p-toluenesulfonic acid after complete reaction, uniformly mixing, introducing steam into a tube furnace for heat treatment at 140 ℃, and heating to 200 ℃ for treatment for 2 hours to obtain the bamboo powder subjected to the acidic pretreatment.
The solid carbon sulfonic acid catalyst is prepared by the preparation method of the solid carbon sulfonic acid catalyst.
A preparation method of tributyl citrate comprises the following steps:
and (3) uniformly mixing citric acid, n-butanol and the solid carbon sulfonic acid catalyst, and reacting for 4-5 h at the temperature of 130-150 ℃ to obtain tributyl citrate.
In one embodiment, the ratio of the citric acid, the n-butanol, and the solid carbon sulfonic acid catalyst is 1 mol: 4.5 mol: 1 g;
the reaction temperature is 145 ℃, and the reaction time is 4 h.
Tributyl citrate is prepared by the preparation method of the tributyl citrate.
Tests prove that the solid carbon sulfonic acid catalyst and the preparation method thereof, and the tributyl citrate and the preparation method thereof have the following advantages:
(1) in the solid carbon sulfonic acid catalyst obtained by the preparation method of the solid carbon sulfonic acid catalyst, compared with the stability of the traditional bamboo charcoal sulfonic acid, the sulfonic acid group has better improvement effect, and the repeated practicability of the catalyst can be improved;
(2) the bamboo powder is treated by sodium silicate alkali and then is subjected to acid hydrolysis pretreatment by hydrochloric acid, and can be successfully inserted into the bamboo charcoal material in the form of silicon dioxide, so that the mechanical strength and the thermal stability of sulfonated sulfonic groups of the bamboo charcoal material are improved;
(3) the carbonized bamboo powder and the solid carbon sulfonic acid catalyst are analyzed in aspects of FT-IR, TG, XRD, N2 adsorption and desorption, acid amount measurement and the like, and the results show that: the carbonized bamboo powder has a condensed ring aromatic structure with various oxygen-containing functional groups, and the sulfonated sulfonic acid functional groups replace hydrogen on aromatic rings and are bonded to a carbon skeleton; the catalyst is an amorphous macroporous material; it is excellent in thermal stability; the acid content of the bamboo charcoal sulfonic acid is measured by an acid-base titration method, and the measured sulfonic acid content of the improved bamboo charcoal sulfonic acid is 1.55 mmol-g-1Left and right;
(4) through the comparative investigation on the catalytic performance of the solid carbon sulfonic acid catalyst, the bamboo charcoal sulfonic acid prepared by the preparation method of the solid carbon sulfonic acid catalyst shows better catalytic activity in the esterification reaction of catalytic citric acid and n-butyl alcohol than the traditional bamboo charcoal sulfonic acid prepared by direct reduced pressure carbonization under the same reaction condition by comparing catalysis, and the thermal stability and the mechanical strength are improved to a certain extent.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
Unless defined otherwise, 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. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
A method of preparing a solid carbon sulfonic acid catalyst according to an embodiment includes the steps of:
s10, soaking the bamboo powder in a sodium silicate solution for 15-20 h, soaking the bamboo powder in deionized water to reach adsorption balance, filtering and drying, and then carrying out heat treatment at 130-150 ℃ for 3-5 h to obtain the bamboo powder subjected to alkaline pretreatment.
Preferably, the bamboo powder is prepared by the following steps:
bamboo is used as a raw material, washed with water and dried, and then milled in a crusher, sieved by a sieve with 50 meshes to 70 meshes and dried in vacuum at the temperature of 50 ℃ in sequence to obtain the bamboo powder.
The purpose of carrying out alkaline pretreatment on the bamboo powder is to ensure that sodium silicate is saturated and adsorbed in the bamboo powder structure and no residual sodium silicate is attached to the surface layer of the bamboo powder.
S20, mixing the bamboo powder subjected to the alkaline pretreatment obtained in the step S10 with hydrochloric acid, adding p-toluenesulfonic acid after complete reaction, uniformly mixing, and then carrying out heat treatment at 140-200 ℃ for 1-3 h to obtain the bamboo powder subjected to the acidic pretreatment.
The mixing reaction of the bamboo powder and the hydrochloric acid can completely convert the sodium silicate in the bamboo powder into silicic acid. The purpose of carrying out acid pretreatment on the bamboo powder is to hydrolyze lignin in the bamboo powder under an acid condition, destroy the internal structure of the bamboo powder and enable silicon dioxide to be successfully and uniformly inserted into the bamboo powder to form a stable structure.
Preferably, the operation of preparing the bamboo powder after the acidic pretreatment is as follows:
and mixing the bamboo powder subjected to the alkaline pretreatment with hydrochloric acid, adding 5% of p-toluenesulfonic acid after complete reaction, uniformly mixing, introducing steam into a tube furnace for heat treatment at 140 ℃, and heating to 200 ℃ for treatment for 2 hours to obtain the bamboo powder subjected to the acidic pretreatment.
And S30, carbonizing the bamboo powder subjected to the acidic pretreatment obtained in the step S20 to obtain the carbonized bamboo powder.
Preferably, the carbonization operation of the bamboo powder after the acidic pretreatment comprises the following steps:
putting the bamboo powder into a stainless steel reaction tube, then putting the stainless steel reaction tube into a flat tube type electric furnace, vacuumizing the stainless steel reaction tube by using a circulating water type multipurpose vacuum pump, and then starting program heating; the temperature is controlled to rise by adopting a temperature programming mode, and the steps are divided into 4 sections: in the first stage, the temperature is increased to 250 ℃ at the heating rate of 10 ℃/min; in the second stage, the temperature is continuously increased to 300-350 ℃ at the temperature increase rate of 5 ℃/min; the temperature of the third section is increased to 380 ℃ at the heating rate of 1 ℃/min; and finally keeping the temperature at 380 ℃ for 3h, and cooling to room temperature to obtain the carbonized bamboo powder.
S40, sulfonating the carbonized bamboo powder obtained in the step S30 to obtain a solid carbon sulfonic acid catalyst.
Preferably, the sulfonation operation of the carbonized bamboo powder is as follows:
and (3) sulfonation reaction: grinding the carbonized bamboo powder, then soaking the bamboo powder into 50% fuming sulfuric acid, and sulfonating in a nitrogen atmosphere at the reaction temperature: 373K, reaction time: 3 h;
and adding deionized water after the reaction is cooled to terminate the reaction: washing with distilled water, decocting in boiling water bath for half an hour, filtering, repeating for three times, and adding BaCl2And (4) checking the solution until no white precipitate is generated in the filtrate, and finally drying the bamboo charcoal sulfonic acid to obtain the solid carbon sulfonic acid catalyst.
Preferably, the mass ratio of the carbonized bamboo powder to 50% fuming sulfuric acid is 1: 4-6.
The solid carbon sulfonic acid catalyst of an embodiment is prepared by the above-mentioned preparation method of a solid carbon sulfonic acid catalyst.
The method for preparing tributyl citrate according to an embodiment includes the following steps:
and (3) uniformly mixing citric acid, n-butanol and the solid carbon sulfonic acid catalyst, and reacting for 4-5 h at the temperature of 130-150 ℃ to obtain tributyl citrate.
Preferably, the ratio of citric acid, n-butanol to solid carbon sulfonic acid catalyst is 1 mol: 4.5 mol: 1 g.
Preferably, the reaction temperature is 145 ℃ and the reaction time is 4 h.
The tributyl citrate of an embodiment is prepared by the preparation method of tributyl citrate.
Tests prove that the solid carbon sulfonic acid catalyst and the preparation method thereof, and the tributyl citrate and the preparation method thereof have the following advantages:
(1) in the solid carbon sulfonic acid catalyst obtained by the preparation method of the solid carbon sulfonic acid catalyst, compared with the stability of the traditional bamboo charcoal sulfonic acid, the sulfonic acid group has better improvement effect, and the repeated practicability of the catalyst can be improved;
(2) the bamboo powder is treated by sodium silicate alkali and then is subjected to acid hydrolysis pretreatment by hydrochloric acid, and can be successfully inserted into the bamboo charcoal material in the form of silicon dioxide, so that the mechanical strength and the thermal stability of sulfonated sulfonic groups of the bamboo charcoal material are improved;
(3) the carbonized bamboo powder and the solid carbon sulfonic acid catalyst are analyzed in aspects of FT-IR, TG, XRD, N2 adsorption and desorption, acid amount measurement and the like, and the results show that: the carbonized bamboo powder has a condensed ring aromatic structure with various oxygen-containing functional groups, and the sulfonated sulfonic acid functional groups replace hydrogen on aromatic rings and are bonded to a carbon skeleton; the catalyst is an amorphous macroporous material; it is excellent in thermal stability; the acid content of the bamboo charcoal sulfonic acid is measured by an acid-base titration method, and the measured sulfonic acid content of the improved bamboo charcoal sulfonic acid is 1.55 mmol-g-1Left and right;
(4) through the comparative investigation on the catalytic performance of the solid carbon sulfonic acid catalyst, the bamboo charcoal sulfonic acid prepared by the preparation method of the solid carbon sulfonic acid catalyst shows better catalytic activity in the esterification reaction of catalytic citric acid and n-butyl alcohol than the traditional bamboo charcoal sulfonic acid prepared by direct reduced pressure carbonization under the same reaction condition by comparing catalysis, and the thermal stability and the mechanical strength are improved to a certain extent.
The solid carbon sulfonic acid catalyst and the preparation method thereof, and tributyl citrate and the preparation method thereof according to the present invention will be further described with reference to the following specific examples.
Example 1 preparation of solid carbon sulfonic acid catalyst
Sieving the bamboo powder pulverized by pulverizer with 60 mesh sieve, and vacuum drying at 50 deg.C. After cooling, the bamboo powder was taken out and 10g of dried bamboo powder was quickly weighed. Soaking bamboo powder in 10% sodium silicate solution for 16 hr, soaking in deionized water to reach adsorption balance, filtering, drying, and heat treating with steam at 140 deg.C for 4 hr.
Adding hydrochloric acid into the bamboo powder subjected to the alkaline pretreatment of the sodium silicate, and adjusting the pH value to convert the sodium silicate in the bamboo powder into silicic acid. And treating the bamboo powder with 5% of p-toluenesulfonic acid, introducing steam into a tube furnace for heat treatment at 140 ℃, and then heating to 200 ℃ for treatment for 2 hours to obtain the pretreated composite bamboo material.
Putting the bamboo powder into a stainless steel reaction tube, then putting the stainless steel reaction tube into a flat tube type electric furnace, vacuumizing the stainless steel reaction tube by using a circulating water type multipurpose vacuum pump, and then starting program heating; the temperature is controlled to rise by adopting a temperature programming mode, and the steps are divided into 4 sections: in the first stage, the temperature is increased to 250 ℃ at the heating rate of 10 ℃/min; in the second stage, the temperature is continuously increased to 300-350 ℃ at the temperature increase rate of 5 ℃/min; the temperature of the third section is increased to 380 ℃ at the heating rate of 1 ℃/min; and finally keeping the temperature at 380 ℃ for 3h, and cooling to room temperature to obtain the carbonized bamboo powder.
Grinding the carbonized bamboo powder, then soaking the bamboo powder into 50% fuming sulfuric acid, sulfonating the bamboo powder in a nitrogen atmosphere, wherein the reaction temperature is as follows: 373K, reaction time: and 3 h. And adding deionized water after the reaction is cooled to terminate the reaction: washing with distilled water, decocting in boiling water bath for half an hour, filtering, repeating for three times, and adding BaCl2And (4) checking the solution until no white precipitate is generated in the filtrate, and finally drying the bamboo charcoal sulfonic acid to obtain the solid carbon sulfonic acid catalyst.
EXAMPLE 2 preparation of tributyl citrate
Adding 0.1mol of citric acid and 0.45mol of n-butyl alcohol into a 150ml three-neck flask provided with a water separator, a thermometer, a reflux condenser and a stirrer according to a mol ratio, adding 0.1g of solid carbon sulfonic acid catalyst, uniformly mixing, simultaneously taking reaction liquid, recording the acid value before reaction, heating and stirring by using a heat collection type constant temperature heating magnetic stirrer, stirring and heating to a certain value, keeping the temperature for refluxing for 4 hours, and sampling at regular time to measure the acid value of the reaction liquid (according to the method of GB/T1668[93 ]).
The three-necked flask with the water separator and reflux device was heated to reflux for the calculated time and stopped when no water droplets were separated. And (3) cooling and soaking the product, pouring out the reaction liquid, distilling at normal pressure to recover n-butyl alcohol, cooling to room temperature, filtering, washing the filtrate to be neutral by using a sodium carbonate solution, removing a water layer, distilling the oily liquid under reduced pressure, and collecting 178-180 ℃/400Pa fraction to obtain tributyl citrate, wherein the product is yellowish oily liquid.
Comparative example 1 preparation of solid carbon sulfonic acid catalyst
The bamboo is used as raw material, and is washed and dried, and then is milled, sieved and dried in a pulverizer to obtain dry bamboo powder for later use.
Weighing a certain amount of bamboo powder, putting the bamboo powder into a stainless steel reaction tube, putting the stainless steel reaction tube into a flat-placed tube type electric furnace, vacuumizing the stainless steel reaction tube by using a circulating water type multipurpose vacuum pump, and then starting program heating. The temperature is controlled to rise by adopting a temperature programming mode, and the steps are divided into 4 sections: in the first stage, the temperature is increased to a certain temperature at the heating rate of 10 ℃/min; in the second stage, the temperature is continuously increased at the temperature increasing rate of 5 ℃/min; in the third stage, the temperature is increased to the set temperature at the heating rate of 1 ℃/min; and finally keeping the temperature constant at the temperature for 3 hours, and cooling to room temperature to obtain the bamboo charcoal material expressed as BC. The final temperatures were 250 deg.C, 300 deg.C, 350 deg.C, and 380 deg.C, respectively.
Grinding the black brown bamboo charcoal solid prepared in the carbonization process by using a mortar, adding the ground black brown bamboo charcoal solid into a three-neck flask, carefully adding a certain amount of 50% fuming sulfuric acid to immerse the bamboo charcoal into the 50% fuming sulfuric acid, sulfonating in a nitrogen atmosphere at the reaction temperature: 373K, reaction time: and 3 h. After the reaction is cooled, deionized water is added to stop the reaction. Washing with distilled water, decocting in boiling water bath for half an hour, filtering, repeating for three times, and adding BaCl2Checking the solution until no SO is in the filtrate4 2-Ion, i.e. no white precipitate was formed in the filtrate. And finally, placing the bamboo charcoal sulfonic acid into a drying oven with the temperature T being 110 ℃ for drying, and marking as: BC-SO3H-1。
Comparative example 2 preparation of tributyl citrate
The difference from example 2 is that: the solid carbon sulfonic acid catalyst of comparative example 1 was used.
And (3) testing:
1. specific surface area analysis was performed for example 1 and comparative example 1
Adopts 3H-2000PS2 type N2The specific surface area and the pore structure characteristics of the sample are analyzed under the liquid nitrogen condition of an adsorption-desorption instrument, the specific surface area is calculated by a Brunauer-Emmett-Teller (BET) method, the pore volume is calculated by a Barrett-Joyner-Halenda (BJH) method, and the results are shown in Table 1.
TABLE 1 specific surface area and pore structure of bamboo, bamboo charcoal and example 1, comparative example 1 bamboo charcoal sulfonic acid
According to the data analysis of the table 1, the specific surface area of the bamboo powder is smaller, the specific surface area of the carbonized bamboo charcoal material is increased, the pore diameter is reduced, and the specific surface area of the bamboo charcoal sulfonic acid is not obviously changed compared with that of the bamboo charcoal. The specific surface area and the pore structure of the bamboo charcoal are not influenced after the bamboo charcoal is sulfonated.
2. The carbonized bamboo powder of example 1 and a solid carbon sulfonic acid catalyst were subjected to X-ray diffraction analysis
The instrument comprises the following steps: Y-2000X-ray powder diffractometer (Dandong X-ray apparatus, China). The scanning mode is as follows: continuous scanning; initial range: 10 degrees to 60 degrees; scanning speed: 0.1 °/s; a driving mode: double-shaft linkage; sampling time: 0.5 s; a detector: a proportional detector. The results are shown in FIG. 1.
As is apparent from FIG. 1, both the carbonized bamboo powder of example 1 and the solid carbon sulfonic acid catalyst have amorphous SiO with a wide and gentle width in the range of 10-30 deg2The diffraction peak of the solid carbon sulfonic acid catalyst of example 1 is slightly shifted to the high angle direction compared with the X-ray diffraction peak of the carbonized bamboo powder, which indicates that the carbonized material has a low degree of order and does not form a regular graphite structure, and the amorphous bamboo charcoal material is prepared. And further charring was demonstrated to occur during sulfonation.
3. Infrared analysis
The modified bamboo charcoal sample of example 1 and the modified bamboo charcoal sulfonic acid were thoroughly dried and then subjected to infrared spectroscopic analysis by potassium bromide tableting. The instrument model is as follows: AVATAR 370 type Fourier infrared spectrometer with wave band of 400cm-1To 4000cm-1The signal scans are accumulated.
FIG. 2 shows the infrared spectra of the modified bamboo charcoal and the modified bamboo charcoal sulfonic acid obtained by the vacuum pyrolysis carbonization sulfonation method. As shown in FIG. 2, the sulfonated bamboo charcoal obtained by pyrolyzing and carbonizing bamboo powder under reduced pressure is located at 3450cm-1The characteristic peaks of the left and right O-H stretching vibration are obviously narrowed and strengthened, which shows that the sulfonated bamboo charcoal sulphurthe-OH content on the acid is increased, which can prove that the carboxyl on the bamboo charcoal sulfonic acid is increased. Compared with the carbonized material, the infrared spectrogram of the bamboo charcoal sulfonic acid has some new characteristic peaks, 1125-1150cm-1And 1030cm-1The left and the right appear as S ═ O expansion vibration characteristic peak, 1125-1150cm-1Is represented by-SO2-asymmetric stretching vibrations; 1030cm-1Left and right are-SO2-symmetric telescopic vibration; 700cm-1~600cm-1The position is a C-S stretching vibration peak, and the appearance of the C-S stretching vibration characteristic peak indicates that the sulfonic acid group is successfully grafted on the active site. Observed and found at 1095cm-1Strong absorption peaks appear nearby, which indicates that the bamboo charcoal contains a certain amount of silicon elements. The results of these analyses are in agreement with literature data.
4. Comparison of sulfonic acid amounts after traditional and improved catalyst reuse
Preparing tributyl citrate as a catalytic reaction, under the optimal conditions: 0.1mol of citric acid, 0.45mol of n-butanol, and the mol ratio of acid to alcohol of 1: 4.5, the reaction temperature is 145 ℃, and the reaction lasts for 4 hours under the reflux state. Inspecting the amount of sulfonic acid catalyzed by two traditional and improved bamboo charcoal sulfonic acid catalysts, filtering the catalysts when the catalysts are hot after each reaction is finished, washing a small amount of acid, alcohol and ester possibly adsorbed on the surfaces of the catalysts by absolute ethyl alcohol, and drying the washed catalysts in an electric heating constant-temperature air drying oven for detection. As shown in fig. 3, it is understood that the amount of sulfonic acid of the conventional and improved bamboo charcoal sulfonic acid is gradually decreased with the increase of the number of reaction times due to the deactivation of a part of the active sites of the catalyst and the physical loss of the catalyst. However, it is obvious that the amount of the sulfonic acid of the modified bamboo charcoal sulfonic acid is reduced not so fast as compared with the amount of the sulfonic acid of the traditional bamboo charcoal sulfonic acid, and the fact that the inserted silicon element has a certain stabilizing effect on the sulfonic acid group of the catalyst can be shown.
TABLE 2
Percentage reduction of sulfonic acid group in bamboo charcoal sulfonic acid repeated test
From the percentage of sulfonic acid group reduction in the repeated tests of the bamboo charcoal sulfonic acid, it can be seen that the sulfonic acid amount of the traditional and improved bamboo charcoal sulfonic acids is gradually reduced along with the increase of the reaction times as shown in table 2, and the ratio of the sulfonic acid group reduction is compared to the ratio of the sulfonic acid group reduction after the catalyst is recovered after each experiment, which shows that the sulfonic acid group of the improved bamboo charcoal sulfonic acid has better improvement effect compared to the stability of the traditional bamboo charcoal sulfonic acid.
5. Investigation of traditional and improved bamboo charcoal sulfonic acid catalyst catalytic performance
According to the experimental results, the optimal reaction conditions for synthesizing tributyl citrate by improving the bamboo charcoal sulfonic acid catalyst are as follows: 0.1mol of citric acid, 0.45mol of n-butanol, 1: 4.5mol of acid alcohol, 145 ℃ of reaction temperature, 0.1g of bamboo charcoal sulfonic acid catalyst is added, and the reaction is carried out for 4 hours under reflux state. Under these reaction conditions, the comparison of catalytic performances of the conventional and the improved catalysts was studied, giving fig. 4 and table 3.
TABLE 3
As can be seen from fig. 4, we examined the synthesis of tributyl citrate with conventional bamboo charcoal sulfonic acid and modified bamboo charcoal sulfonic acid, and it is obvious that the reuse of conventional bamboo charcoal sulfonic acid is much worse than that of modified bamboo charcoal sulfonic acid. Although, the esterification rate of the conventional bamboo charcoal sulfonic acid is higher than that of the modified bamboo charcoal sulfonic acid in the first reaction, the reason is that the amount of the sulfonic acid of the initial conventional bamboo charcoal sulfonic acid is higher than that of the modified bamboo charcoal sulfonic acid. However, as can be seen from the second, third and fourth reactions, the improved bamboo charcoal sulfonic acid has a higher esterification rate than the traditional bamboo charcoal sulfonic acid, and the determination of the sulfonic acid amount of the bamboo charcoal sulfonic acid by the recovery catalyst shows that the sulfonic acid amount after the improved bamboo charcoal sulfonic acid is recovered is higher than that of the traditional bamboo charcoal sulfonic acid catalyst, because the sulfonic acid active center of the bamboo charcoal sulfonic acid falls off, the sulfonic acid amount is reduced, and the catalytic efficiency is reduced. Meanwhile, in the recovery process, the traditional catalyst is found to be more fragile and smaller in granularity in the stirring reaction than the improved catalyst, the loss of the traditional catalyst is relatively serious, and the thermal stability and the mechanical strength of the improved bamboo charcoal sulfonic acid are improved to a certain extent under the same catalysis condition. The esterification rate reduction percentage in the repeated tests of the bamboo charcoal sulfonic acid is improved, the reduction ratio of the improved bamboo charcoal sulfonic acid is improved, the bamboo charcoal sulfonic acid prepared by the improved method shows better catalytic activity in catalyzing the esterification reaction of citric acid and n-butyl alcohol compared with the traditional bamboo charcoal sulfonic acid prepared by direct heat pressure reduction carbonization, and the repeated use performance of the bamboo charcoal sulfonic acid is greatly improved.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.