CN115212917B - Catalyst for preparing alkyl lactate by chemical catalysis of 1, 3-dihydroxyacetone as well as preparation method and application thereof - Google Patents

Catalyst for preparing alkyl lactate by chemical catalysis of 1, 3-dihydroxyacetone as well as preparation method and application thereof Download PDF

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CN115212917B
CN115212917B CN202110430951.2A CN202110430951A CN115212917B CN 115212917 B CN115212917 B CN 115212917B CN 202110430951 A CN202110430951 A CN 202110430951A CN 115212917 B CN115212917 B CN 115212917B
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dihydroxyacetone
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唐波
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Tianjin Normal University
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Abstract

The invention discloses a catalyst for preparing alkyl lactate by chemical catalysis of 1, 3-dihydroxyacetone, and a preparation method and application thereof, wherein the preparation method comprises the following steps: uniformly dispersing tetraethyl ammonium hydroxide aqueous solution, sodium metaaluminate, sodium hydroxide and fumed silica after mixing, treating for 1-6 hours at 120-180 ℃ to obtain a pre-crystallized sample, adding a surfactant into the pre-crystallized sample, treating at constant temperature to obtain a crystallized sample, immersing the crystallized sample into acid, carrying out vacuum suction filtration to obtain a filter cake, washing the filter cake to be neutral, and drying to obtain a dried sample; grinding the dried sample and a metal active center Sn precursor to be uniformly dispersed, and roasting for 6-12 hours to obtain the catalyst, wherein the catalyst has the advantages of unique structure, strong Lewis acidity and stable structure, can be recycled for multiple times, and has no obvious reduction in catalytic activity; the catalyst has the advantages of simple preparation process, excellent catalytic performance, low catalytic process cost, environmental protection and no pollution.

Description

Catalyst for preparing alkyl lactate by chemical catalysis of 1, 3-dihydroxyacetone as well as preparation method and application thereof
Technical Field
The invention belongs to the technical field of catalysts of alkyl lactate, and particularly relates to a catalyst for preparing alkyl lactate by using 1, 3-dihydroxyacetone through chemical catalysis, and a preparation method and application thereof.
Background
Lactic acid and alkyl lactate are organic matters with high potential and multiple functions, are widely applied to industries such as food, cosmetics, medicines and the like, and can also be used as chemical raw materials for producing bulk chemicals such as acrylic acid, polylactic acid (degradable thermoplastic high polymer materials) and the like. To date, the industrial production of lactic acid and alkyl lactate mainly adopts a microbial fermentation method, which accounts for more than 90% of the total global export amount, the production process is complicated, the steps of fermentation, neutralization, precipitation, acidification, filtration, recrystallization, esterification and the like are needed, the reaction conditions are harsh, the requirements on the performance of production equipment are high, the complicated separation and purification processes lead to high production cost (accounting for 50-60% of the total cost), and a large amount of salt wastewater is generated in the production link of the process, so that the increasingly severe environmental discharge pressure is faced. Therefore, it is urgent to find a green, efficient and sustainable lactic acid and alkyl lactate production process route.
Conversion of biomass platform compounds into high value-added chemicals is an important way to achieve efficient utilization and sustainable development of biomass resources, and has attracted wide attention in industry and academia in recent years. Compared with the traditional fermentation process, the preparation of lactic acid and alkyl lactate by using the biomass-based platform compound through the chemical catalysis process has the advantages of simple preparation route, low cost, no salt wastewater and the like, and is a sustainable production process with great prospect. Among the numerous catalytic systems, sn-Beta molecular sieves formed from isolated Sn ion isomorphously substituted BEA frameworks, which have an open pore structure and advanced Lewis acidity, are recognized as the most heterogeneous catalysts for achieving this catalytic process. However, the following problems exist in the preparation and practical application processes of the Sn-Beta molecular sieve prepared by the traditional hydrothermal method, and the problems need to be solved: a tedious synthesis process and an ultra long synthesis period (> 20 days), a limited skeletal Sn content (< 1.5 wt%), a large grain size (> 1 μm) and the use of environmentally hazardous fluorides. It is particularly pointed out that in liquid phase catalytic systems, larger grain sizes and smaller framework channels (< 0.7 nm) greatly block the molecules of biomass-based platform compounds from entering Sn-Beta molecular sieve crystals and reduce the intra-crystalline diffusion efficiency thereof, which is very likely to cause the reduction of catalytic activity and the deposition of a large amount of coke on the catalyst surface to cause the deactivation of the catalyst. Based on the current situation, the exploration and development of a novel Sn-Beta molecular sieve catalyst with excellent performance is of great significance to the chemical process route from a biomass-based platform compound with high structure efficiency to lactic acid and alkyl lactate.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a preparation method of a catalyst for preparing alkyl lactate by using 1, 3-dihydroxyacetone chemical catalysis, which synthesizes a molecular sieve precursor (a crystallized sample) under hydrothermal conditions through a pre-prepared molecular sieve guiding agent (a pre-crystallized sample) and a surfactant, and introduces active metal centers through acid treatment and roasting to prepare the catalyst.
The catalyst has novel structure, unique petal-shaped nano lamellar structure and advanced Lewis acidity, can obtain excellent catalytic activity and target product selectivity under the condition of being close to room temperature (40 ℃) in the reaction of catalyzing dihydroxyacetone to prepare the alkyl lactate, and can solve the problems of severe reaction conditions, complicated preparation process, high cost, environmental pollution and the like of the traditional alkyl lactate biological fermentation.
The aim of the invention is achieved by the following technical scheme.
A method for preparing a catalyst for preparing alkyl lactate by chemical catalysis of 1, 3-dihydroxyacetone, which comprises the following steps:
1) At room temperature of 20-25 ℃, uniformly dispersing a tetraethyl ammonium hydroxide aqueous solution, sodium metaaluminate, sodium hydroxide and fumed silica after mixing, and treating for 1-6 hours at 120-180 ℃ for pre-crystallization to obtain a pre-crystallized sample, wherein the ratio of the tetraethyl ammonium hydroxide to the sodium metaaluminate to the sodium hydroxide to the fumed silica in the tetraethyl ammonium hydroxide aqueous solution is (0.6-1.0): 0.04-0.05): 0.014-0.020): 1.0 in parts by weight;
in the step 1), the concentration of tetraethylammonium hydroxide in the tetraethylammonium hydroxide aqueous solution is 25 to 40wt%.
2) Adding a surfactant into the pre-crystallized sample, and performing constant temperature treatment for 3-7 d at 140-180 ℃ for crystallization to obtain a crystallized sample, wherein the surfactant is dodecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide or hexadecyl trimethyl ammonium bromide, and the ratio of the pre-crystallized sample to the surfactant is (0.26-0.6) 1.0 in parts by weight;
3) Immersing the crystallized sample in acid at 25-150 ℃ for 1-20 h, carrying out vacuum filtration to obtain a filter cake, washing the filter cake to be neutral, and drying to obtain a dried sample;
in the step 3), the acid is a mixture of hydrochloric acid/nitric acid/sulfuric acid and water, and the mass concentration of the hydrochloric acid/nitric acid/sulfuric acid in the acid is 5.0-10.0 mol/L.
In the step 3), the drying temperature is 85-120 ℃, and the drying time is at least 6h.
4) Grinding the dried sample and a metal active center Sn precursor to be uniformly dispersed, and roasting at 350-650 ℃ for 6-12 h to obtain the catalyst (Sn-Beta-L), wherein the metal active center Sn precursor is dimethyl tin dichloride, tin (II) acetate or tin tetrachloride, and the ratio of Sn in the dried sample to the metal active center Sn precursor is 1.0 (0.019-0.093) in parts by mass.
The catalyst obtained by the preparation method.
The catalyst is applied to the chemical catalysis of 1, 3-dihydroxyacetone to prepare alkyl lactate.
In the technical scheme, the method for preparing the alkyl lactate by using the catalyst in the chemical catalysis of the 1, 3-dihydroxyacetone comprises the following steps: mixing the catalyst, 1, 3-dihydroxyacetone and alcohol, washing with nitrogen, sealing, and heating for reaction under stirring to obtain the alkyl lactate.
In the technical scheme, the ratio of the mass parts of the catalyst to the mass parts of the 1, 3-dihydroxyacetone to the volume parts of the alcohol is (6-12): (0.15-0.35): 1.0, wherein the mass parts are in mg, the mass parts are in mmol, and the volume parts are in mL.
In the above technical scheme, the alcohol is methanol, ethanol, propanol, butanol or isoamyl alcohol.
In the above technical scheme, the alkyl lactate is methyl lactate, ethyl lactate, propyl lactate, butyl lactate or isoamyl lactate.
In the technical scheme, the temperature of the heating reaction is 40-80 ℃, and the stirring rotation speed is 800-1200 rpm.
In the technical scheme, the heating reaction time is 1-5 h.
The Sn-Beta-L catalyst has a unique structure, strong Lewis acidity and stable structure, can be used for preparing alkyl lactate by chemical catalysis of 1, 3-dihydroxyacetone under the mild condition of 40 ℃, shows excellent catalytic activity and target product selectivity, can be recycled for multiple times, and has no obvious reduction in catalytic activity; the catalyst has the advantages of simple preparation process, excellent catalytic performance, low catalytic process cost, environmental protection and no pollution, and can be popularized and applied in a large scale in the reaction of preparing the alkyl lactate from the 1, 3-dihydroxyacetone.
Drawings
FIG. 1 is a SEM image, wherein a is the catalyst obtained in example 3, b is the catalyst obtained in example 3, c is the Sn-Beta catalyst obtained in comparative example 1;
FIG. 2 is an XRD pattern of the catalyst prepared in example 3;
FIG. 3 is a UV-vis diagram of the catalyst prepared in example 3;
FIG. 4 is a pyridine adsorption FT-IR spectrum of the catalyst prepared in example 3;
FIG. 5 is a schematic structural view of a pressure reactor (a flat plate heating device is arranged below the pressure reactor).
Detailed Description
The technical scheme of the invention is further described below with reference to specific embodiments.
Examples 1 to 19
A method for preparing a catalyst (Sn-Beta-L catalyst) for preparing alkyl lactate by chemical catalysis of 1, 3-dihydroxyacetone, which comprises the following steps:
1) Mixing tetraethyl ammonium hydroxide aqueous solution, sodium metaaluminate, sodium hydroxide and fumed silica serving as molecular sieve guiding agents at room temperature of 20-25 ℃, stirring until the mixture is uniformly dispersed, filling the mixture into a hydrothermal kettle with a polytetrafluoroethylene lining, and then treating the mixture at T1 ℃ for T1 h in a blast drying box for pre-crystallization to obtain a pre-crystallized sample, wherein the ratio of the tetraethyl ammonium hydroxide to the sodium metaaluminate to the sodium hydroxide to the fumed silica in the tetraethyl ammonium hydroxide aqueous solution is 0.75:0.048:0.016:1.0, and the concentration of the tetraethyl ammonium hydroxide in the tetraethyl ammonium hydroxide aqueous solution is 25wt%;
2) Adding a surfactant into the pre-crystallized sample, and performing constant temperature treatment for 4d (24 hours per day) at 140 ℃ in a forced air drying oven for crystallization to obtain a crystallized sample, wherein the surfactant is shown in a table 1, and the ratio of the pre-crystallized sample to the surfactant is 0.45:1.0 in parts by weight;
3) Immersing the crystallized sample in 100 ℃ acid for 20 hours, carrying out vacuum suction filtration to obtain a filter cake, washing the filter cake to be neutral, and drying the filter cake in a forced air drying oven at 120 ℃ for 6 hours to obtain a dried sample, wherein the acid is concentrated nitric acid, and the mass concentration of nitric acid in the concentrated nitric acid is 6mol/L;
4) And fully grinding the dried sample and a metal active center Sn precursor to be uniformly dispersed, and roasting in a muffle furnace at 550 ℃ for 6 hours to obtain the catalyst (Sn-Beta-L), wherein the metal active center Sn precursor is shown in the table 1, and the ratio of Sn in the dried sample to the metal active center Sn precursor is X in parts by weight.
TABLE 1
Comparative example 1
The preparation of Sn-Beta catalysts is described in detail in reference A.Corma, L.T.Nemeth, M.Renz, S.Valencia, nature,2001,412,423 ～ 425. The specific surface area of the synthesized Sn-Beta catalyst is 410m 2 And/g, sn species content is 1.2wt%.
The catalyst is applied to the chemical catalysis of 1, 3-dihydroxyacetone to prepare alkyl lactate. The method for preparing the alkyl lactate by using the catalyst in the chemical catalysis of the 1, 3-dihydroxyacetone comprises the following steps: 20mg of the catalyst of one of examples 1 to 19 and comparative example 1, 0.62mmol of 1, 3-dihydroxyacetone and 2.5mL of methanol were mixed in a pressure reactor with a polytetrafluoroethylene liner, purged 3 times with high-purity nitrogen (99.999%), the pressure reactor was sealed, and heated at T2℃under stirring at 800rpm for reaction for T3 hours to obtain alkyl lactate, wherein T2 and T3 are shown in Table 2.
The product was analyzed by gas chromatography. The gas chromatograph used was Agilent 7890B gas chromatograph, with FID detector, and the capillary column model was HP-FFAP (30 m×0.32mm×1 μm). The product is separated by adopting temperature programming, and the temperature programming steps are as follows: the initial temperature was 120℃and the temperature was raised to 200℃at a rate of 15℃per minute. The conversion of the raw materials and the selectivity of the target product were calculated by the internal standard method, and the specific results are shown in Table 2.
Conversion (%) of 1, 3-dihydroxyacetone= (amount of reacted 1, 3-dihydroxyacetone substance/amount of 1, 3-dihydroxyacetone initial substance) ×100%
Yield (%) of alkyl lactate= (amount of material of alkyl lactate produced/amount of material of 1, 3-dihydroxyacetone initial material) ×100%
Selectivity (%) = (yield of alkyl lactate/conversion of 1, 3-dihydroxyacetone) ×100% of alkyl lactate
TABLE 2
The instrument used in FIG. 1 is a Nova Nano 230 model field emission scanning electron microscope manufactured by FEI company. The Sn-Beta-L catalyst (shown in figures 1, a and b) provided by the invention has uniform morphology, shows a unique petal-shaped nano lamellar structure, has the lamellar thickness of about tens of nanometers, and is obviously smaller than the size of a Sn-Beta catalyst sample (shown in figures 1 and c) prepared by traditional hydrothermal method>1 μm), which is favorable for remarkably increasing the specific surface area (680 m) of the Sn-Beta-L catalyst 2 g -1 ) Thereby exposing more Lewis acid active sites (128 mu mol/g vs Sn-Beta 51 mu mol/g), and in addition, the nano lamellar structure can effectively improve the molecular diffusion performance, thereby improving the catalytic performance.
The apparatus used in FIG. 2 is a Bruker D8X-ray powder diffractometer manufactured by Bruker company. As can be seen from the figure, the Sn-Beta-L catalyst shows two strong diffraction peaks, a "broad peak" at around 7.7o and a "sharp peak" at around 22.5o, respectively, which are attributed to the characteristic diffraction peaks of the BEA topology (M.A.Camblor, J.P erez-paraient, zeolites,1991,11,202).
The instrument used in FIG. 3 was a Hitachi U-4100 model ultraviolet/visible/near infrared spectrophotometer manufactured by Shimadzu corporation. The Sn-Beta-L catalyst shows a strong absorption peak at 210nm, which is caused by the charge transition (LMCT) from the O atoms of the molecular sieve framework to the Sn atoms of the metal, so that the Sn species in the sample can be judged to exist in the Beta molecular sieve framework in a highly dispersed isolated state (C.Hammond, S.Conrad, I.Hermans, angew.Chem.Int.Ed.,2012,51,11736-11739).
The apparatus used in FIG. 4 was a Bruker Tensor 27 type infrared spectrometer (equipped with a high temperature reaction cell manufactured by Harrick Scientific company) manufactured by Bruker company. Three absorption peaks 1611, 1490 and 1451cm-1 can be clearly observed in the pyridine adsorption FT-IR spectrum of the Sn-Beta-L catalyst, which are related to pyridine molecules adsorbed by Lewis acid sites (B.Tang, W.L.Dai, G.J.Wu, N.J.Guan, L.D.Li, M.Hunger, ACS Catal.,2014,4,2801-2810), and the intensities of the absorption peaks 1611, 1490 and 1451cm-1 only slightly decrease with the increase of the desorption temperature, indicating that the Sn-Beta-L catalyst has stronger Lewis acidity.
As can be seen from example 22 and comparative example 2, in the reaction of preparing methyl lactate from 1, 3-dihydroxyacetone, the Sn-Beta-L catalyst provided by the invention has the performance remarkably superior to that of the Sn-Beta catalyst prepared by traditional hydrothermal method, the 1, 3-dihydroxyacetone conversion rate is as high as 98% after only 5 hours of reaction, compared with the traditional Sn-Beta catalyst which needs longer reaction time (20 hours), and the selectivity (96%) of the Sn-Beta-L catalyst to methyl lactate is also remarkably superior to that of the traditional Sn-Beta catalyst (89%). The excellent catalytic performance exhibited by the Sn-Beta-L catalyst benefits from its relatively high specific surface area (680 m 2 g -1 ) And the more open nano lamellar structure thereof, so that the Sn-Beta-L catalyst exposes more Lewis acid active sites and simultaneously the mass transfer performance of substrate molecules in the pore channels of the Sn-Beta-L catalyst is obviously improved. In addition, a higher Sn species content (3.8 wt% vs Sn-Beta 1.2 wt%) in the Sn-Beta-L catalyst can provide more catalytically active sites for the substrate molecules.
As can be seen from a comparison of examples 20-23, the Sn-Beta-L catalysts prepared by different pre-crystallization times of the molecular sieve directing agent have obvious differences in the conversion rate of 1, 3-dihydroxyacetone and the selectivity of methyl lactate under the same reaction conditions. The Sn-Beta-L catalyst prepared after 4 hours of pre-crystallization of the molecular sieve directing agent has the optimal activity, and the pre-crystallization time is less than or more than 4 hours, so that the conversion rate of 1, 3-dihydroxyacetone and the selectivity of methyl lactate are reduced.
As can be seen from comparison of examples 22, 24-26, the Sn-Beta-L catalyst prepared from the pre-crystallized molecular sieve guide agent at different temperatures shows significantly different catalytic performances in the reaction of catalyzing 1, 3-dihydroxyacetone to prepare methyl lactate. The Sn-Beta-L catalyst synthesized by the pre-crystallization at 140 ℃ has the most outstanding performance, and compared with the methyl lactate with the other pre-crystallization temperatures, the yield is obviously lower.
From examples 22 and 27-28, the Sn-Beta-L synthesized by cetyl trimethyl ammonium bromide as the surfactant has the most excellent catalytic performance, and the yield of methyl lactate is up to 94%; whereas the yield of methyl lactate was only 70% and 47% when the surfactant was dodecyl trimethyl ammonium bromide and tetradecyl trimethyl ammonium bromide.
From examples 22, 29-32 it can be seen that: with the increase of the nitric acid treatment time, the conversion rate of the 1, 3-dihydroxyacetone and the selectivity of the methyl lactate are correspondingly improved, when the acid treatment time is 20 hours, the yield of the methyl lactate reaches 94 percent, and when the acid treatment time is continuously prolonged to 40 hours, the yield of the methyl lactate is not obviously changed.
From examples 22, 33-34, it is seen that the yield of methyl lactate is highest up to 94% when dimethyltin dichloride is the metal active site Sn precursor, whereas the yields of methyl lactate are not as good as 78% and 63% when tin (II) acetate and tin tetrachloride are the metal active site Sn precursors, respectively.
From examples 22, 35-38, as the ratio of Sn in the dried sample and the metal active site Sn precursor gradually decreased, the conversion of 1, 3-dihydroxyacetone and the selectivity to methyl lactate tended to increase, and when the ratio of Sn in the dried sample and the metal active site Sn precursor was 1.0:0.073, the 1, 3-dihydroxyacetone conversion and the methyl lactate selectivity reached 98 and 96%, respectively, whereas when the ratio of Sn in the dried sample and the metal active site Sn precursor was further decreased to 1.0:0.093, the 1, 3-dihydroxyacetone conversion and the methyl lactate selectivity did not continue to increase.
As is clear from examples 22, 39-41, the 1, 3-dihydroxyacetone conversion rate and the methyl lactate yield increased with the extension of the reaction time, but the methyl lactate selectivity did not change; as can be seen from the table, the conversion of 1, 3-dihydroxyacetone and the yield of methyl lactate reached the highest values, 98% and 94%, respectively, when the reaction time was 5h.
As is clear from examples 22, 42-43, the Sn-Beta-L catalyst showed 1, 3-dihydroxyacetone conversion and methyl lactate selectivity comparable to those at higher temperatures (60 and 80 ℃) even at reaction temperatures approaching room temperature (40 ℃), showing the superiority of the Sn-Beta-L catalyst of the present invention.
Example 44
The reaction conditions in this example were the same as in example 22, after the completion of the reaction, the reaction mixture was centrifuged, and the solid samples obtained after centrifugation were washed three times with methanol and acetone, respectively, and dried in a forced air drying oven at 100℃for 4 hours, and the dried samples were continued for the next reaction.
This example examined the recycling performance of Sn-Beta-L catalyst in the preparation of methyl lactate from 1, 3-dihydroxyacetone under optimal reaction conditions. The catalyst recycling results are shown in Table 3:
TABLE 3 Table 3
According to the embodiment, after the Sn-Beta-L catalyst is recycled for at least 4 times, the catalytic performance of the Sn-Beta-L catalyst does not have obvious deactivation phenomenon, and the excellent recycling performance is that the Sn-Beta-L catalyst has a higher specific surface area and an open nano lamellar structure, so that the diffusion efficiency of substrate molecules in crystals is greatly improved, and further, the formation of carbon deposit is effectively inhibited.
Example 45
This example is essentially the same as example 22, except that the methanol in example 22 is replaced with ethanol, propanol, butanol and isoamyl alcohol, respectively, in sequence, corresponding to the obtained products ethyl lactate, propyl lactate, butyl lactate and isoamyl lactate, respectively.
TABLE 4 Table 4
As can be seen from the example, the Sn-Beta-L catalyst has a wide substrate application range and can be used for efficiently catalyzing and synthesizing various types of alkyl lactate.
Description of sponsored research or development: the invention is sponsored by national natural science foundation young fund project (project number: 22002108) and Tianjin university student innovation startup training plan project (project number: 202010065038).
The foregoing has described exemplary embodiments of the invention, it being understood that any simple variations, modifications, or other equivalent arrangements which would not unduly obscure the invention may be made by those skilled in the art without departing from the spirit of the invention.

Claims (10)

1. A method for preparing a catalyst for preparing alkyl lactate by chemical catalysis of 1, 3-dihydroxyacetone, which is characterized by comprising the following steps:
1) At room temperature of 20-25 ℃, uniformly dispersing a tetraethyl ammonium hydroxide aqueous solution, sodium metaaluminate, sodium hydroxide and fumed silica after mixing, and treating for 1-6 hours at 120-180 ℃ for pre-crystallization to obtain a pre-crystallized sample, wherein the ratio of the tetraethyl ammonium hydroxide to the sodium metaaluminate to the sodium hydroxide to the fumed silica in the tetraethyl ammonium hydroxide aqueous solution is (0.6-1.0): 0.04-0.05): 0.014-0.020): 1.0 in parts by weight;
2) Adding a surfactant into the pre-crystallized sample, and performing constant temperature treatment for 3-7 d at 140-180 ℃ for crystallization to obtain a crystallized sample, wherein the surfactant is dodecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide or hexadecyl trimethyl ammonium bromide, and the ratio of the pre-crystallized sample to the surfactant is (0.26-0.6) 1.0 in parts by weight;
3) Immersing the crystallized sample in acid at 25-150 ℃ for 1-20 h, carrying out vacuum filtration to obtain a filter cake, washing the filter cake to be neutral, and drying to obtain a dried sample;
4) Grinding the dried sample and a metal active center Sn precursor to be uniformly dispersed, and roasting at 350-650 ℃ for 6-12 hours to obtain the catalyst, wherein the metal active center Sn precursor is dimethyl tin dichloride, tin acetate or tin tetrachloride, and the ratio of Sn in the dried sample to the metal active center Sn precursor is 1.0 (0.019-0.093) in parts by weight.
2. The method according to claim 1, wherein in the step 1), the concentration of tetraethylammonium hydroxide in the aqueous tetraethylammonium hydroxide solution is 25 to 40wt%;
in the step 3), the acid is a mixture of hydrochloric acid/nitric acid/sulfuric acid and water, and the mass concentration of the hydrochloric acid/nitric acid/sulfuric acid in the acid is 5.0-10.0 mol/L;
in the step 3), the drying temperature is 85-120 ℃, and the drying time is at least 6h.
3. A catalyst obtainable by the process of claim 1 or 2.
4. Use of the catalyst according to claim 3 for the chemical catalytic preparation of alkyl lactate from 1, 3-dihydroxyacetone.
5. The use according to claim 4, wherein the alkyl lactate is methyl lactate, ethyl lactate, propyl lactate, butyl lactate or isoamyl lactate.
6. The use according to claim 5, wherein the catalyst is used for the chemical catalytic preparation of alkyl lactate in 1, 3-dihydroxyacetone by the following method: mixing the catalyst, 1, 3-dihydroxyacetone and alcohol, washing with nitrogen, sealing, and heating for reaction under stirring to obtain the alkyl lactate.
7. The use according to claim 6, wherein the ratio of the parts by weight of the catalyst, the parts by weight of the 1, 3-dihydroxyacetone and the parts by volume of the alcohol is (6-12): (0.15-0.35): 1.0, wherein the parts by weight are in mg, the parts by weight are in mmol, and the parts by volume are in mL.
8. The use according to claim 7, wherein the alcohol is methanol, ethanol, propanol, butanol or isoamyl alcohol.
9. The method according to claim 6, wherein the temperature of the heating reaction is 40-80℃and the stirring speed is 800-1200 rpm.
10. Use according to claim 9, characterized in that the heating reaction takes 1 to 5 hours.
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