CN111253238B - Method for preparing lactic acid - Google Patents

Abstract

The present invention relates to a method for preparing lactic acid, the method comprising: contacting methylglyoxal and water with a catalyst in a reactor and reacting to obtain a product containing lactic acid; wherein the molar ratio of methylglyoxal to water is 1: (40-350), the temperature of reaction is 30-180 ℃, and the reaction time is 1-10h, and described catalyzer contains the mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve, aceguv aldehyde and titanium-silicon molecular sieve and tin-silicon molecular sieve in dry basis weight The weight ratio of the mixture of molecular sieves is 1:(0.1-6). The process of the invention has a high conversion of methylglyoxal and a yield of lactic acid.

Description

A kind of method for preparing lactic acid

technical field

The present invention relates to a method for preparing lactic acid.

Background technique

Lactic acid (scientific name: 2-hydroxypropionic acid) is a chemical compound with the molecular formula C ₃ H ₆ O ₃ , which plays a role in various biochemical processes. It is a carboxylic acid containing a hydroxyl group and is therefore an alpha-hydroxy acid. In aqueous solution, its carboxyl group releases a proton to produce lactate ion. Lactate dehydrogenase converts pyruvate to L-lactate during fermentation. Lactate is continuously produced during normal metabolism and exercise, but its concentration generally does not rise. Lactic acid is a colorless liquid, and the industrial product is a colorless to pale yellow liquid. Odorless, hygroscopic, relative density 1.200, melting point 18°C, boiling point 122°C, flash point greater than 110°C, miscible with ethanol, ether, water, glycerin, insoluble in chloroform, carbon disulfide and petroleum ether, widely used in the food industry , pharmaceutical industry, industry, cosmetics industry, agriculture and livestock industry.

Traditional lactic acid production methods mainly use sugar fermentation and chemical synthesis. The fermentation method uses carbohydrates as raw materials, and the pH value of the fermentation system needs to be maintained in the range of 5.5-6.5, but with the continuous generation of lactic acid, the pH value gradually decreases, so it is necessary to continuously add calcium oxide or calcium carbonate during the reaction process. Balance the pH of the system. The generated calcium lactate is treated with sulfuric acid to obtain crude lactic acid, and a large amount of waste salt (calcium sulfate) is produced at the same time. However, it is difficult to separate crude lactic acid, which needs to be reacted with alcohol to form lactic acid ester with a relatively low boiling point, and then separated by distillation and hydrolyzed to obtain high-purity lactic acid. The process has a long reaction route, high production cost, and produces a large amount of solid waste, which makes it impossible to realize large-scale production and application of lactic acid at present. The commonly used chemical synthesis methods are the lactonitrile method and the propionic acid method. The lactonitrile method uses acetaldehyde and highly toxic hydrocyanic acid as the reaction raw materials, and concentrated sulfuric acid as the catalyst. Therefore, the production process is seriously polluted and has potential safety hazards. The propionic acid method uses toxic chlorine gas as a raw material, which not only requires high operational safety and airtightness, but also easily pollutes the atmospheric environment.

Contents of the invention

The object of the present invention is to provide a kind of method for preparing lactic acid, the method of the present invention has high aceglyoxal conversion rate and the productive rate of lactic acid.

In order to achieve the above object, the present invention provides a method for preparing lactic acid, the method comprising:

Contacting and reacting methylglyoxal and water with a catalyst in a reactor to obtain a product containing lactic acid; wherein, the molar ratio of methylglyoxal to water is 1: (40-350), and the reaction temperature is 30-180°C, The reaction time is 1-10h, the catalyst contains a mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve, and the weight ratio of methylglyoxal to the mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve in dry basis weight is 1: (0.1-6) .

Optionally, the tin-silicon molecular sieve is selected from MFI tin-silicon molecular sieves, MEL tin-silicon molecular sieves, BEA tin-silicon molecular sieves, MWW tin-silicon molecular sieves, MOR tin-silicon molecular sieves, hexagonal tin-silicon molecular sieves and FAU tin-silicon molecular sieves. One or more of silicon molecular sieves.

Optionally, the titanium-silicon molecular sieve is selected from MFI-type titanium-silicon molecular sieves, MEL-type titanium-silicon molecular sieves, BEA-type titanium-silicon molecular sieves, MWW-type titanium-silicon molecular sieves, MOR-type titanium-silicon molecular sieves, TUN-type titanium-silicon molecular sieves and hexagonal structure titanium One or more of silicon molecular sieves.

Optionally, the tin-silicon molecular sieve is selected from Sn-MFI molecular sieve, Sn-MEL molecular sieve, Sn-Beta molecular sieve, Sn-MCM-22 molecular sieve, Sn-MOR molecular sieve, Sn-MCM-41 molecular sieve, Sn-SBA-15 molecular sieve One or more of molecular sieves and Sn-USY molecular sieves.

Optionally, the titanium silicon molecular sieve is selected from TS-1 molecular sieve, TS-2 molecular sieve, Ti-Beta molecular sieve, Ti-MCM-22 molecular sieve, Ti-MOR molecular sieve, Ti-TUN molecular sieve, Ti-MCM-41 molecular sieve, One or more of Ti-SBA-15 molecular sieve and Ti-ZSM-48 molecular sieve.

Optionally, the mixing weight ratio of titanium-silicon molecular sieves and tin-silicon molecular sieves in the catalyst is 1:(0.1-10).

Optionally, the molar ratio of titanium dioxide to silicon dioxide in the titanium-silicon molecular sieve is (0.01-10):100, preferably (0.05-5):100.

Optionally, the molar ratio of tin dioxide to silicon dioxide in the tin-silicon molecular sieve is (0.01-10):100, preferably (0.05-5):100.

Optionally, the molar ratio of methylglyoxal to water is 1:(60-200), and the weight ratio of methylglyoxal to the mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve in dry basis weight is 1:(0.2-3 ), the reaction temperature is 40-120°C, the reaction time is 2-8h, the reaction pressure is 0.1-3MPa, and the reaction pressure is preferably 0.1-2MPa.

Optionally, the reactor is a tank reactor, a fixed bed reactor, a moving bed, a suspension bed or a slurry bed reactor.

The method of the invention adopts a catalyst containing a mixture of tin-silicon molecular sieve and titanium-silicon molecular sieve, wherein the skeleton titanium atoms of the titanium-silicon molecular sieve and the skeleton tin atoms of the tin-silicon molecular sieve synergistically catalyze the generation of lactic acid from aceguvaldehyde, thereby improving the reaction efficiency. Compared with the existing technology, a higher conversion rate of aceglyoxal and a yield of lactic acid can be obtained under milder reaction conditions in a short period of time, the subsequent separation of products consumes less energy, and the process is safer and more efficient, suitable for large-scale industrial production applications .

Other features and advantages of the present invention will be described in detail in the following detailed description.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, together with the following specific embodiments, are used to explain the present invention, but do not constitute a limitation to the present invention. In the attached picture:

Fig. 1 is the reaction mechanism diagram that the present invention relates to the conversion of methylglyoxal into lactic acid.

Detailed ways

Specific embodiments of the present invention will be described in detail below. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

In the present invention, the weight on a dry basis refers to the weight measured after the sample is calcined at 550° C. for 3 hours.

The invention provides a method for preparing lactic acid, the method comprising: contacting methylglyoxal and water with a catalyst in a reactor and reacting to obtain a product containing lactic acid; wherein the molar ratio of methylglyoxal to water is 1: (40-350), the reaction temperature is 30-180 ℃, and the reaction time is 1-10h, the catalyst contains the mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve, aceguvaldehyde and titanium-silicon molecular sieve and tin-silicon molecular sieve in dry basis weight The weight ratio of the molecular sieve mixture is 1:(0.1-6). The reaction mechanism diagram is shown in Figure 1.

According to the present invention, a tin-silicon molecular sieve refers to a molecular sieve obtained by substituting tin atoms for a part of the silicon atoms in the molecular sieve lattice framework, and a titanium-silicon molecular sieve refers to a molecular sieve obtained by replacing a part of the silicon atoms in the molecular sieve lattice framework with titanium atoms. The present invention combines the two molecular sieves Mechanical Mixing The resulting mechanical mixture is used as a catalyst or as a component of a catalyst. The content of tin atoms and titanium atoms in the molecular sieve can be measured by conventional XRF methods in this field, while the tin atoms and titanium atoms in the molecular sieve framework can be measured by ultraviolet or infrared spectroscopy, for example, using ultraviolet spectroscopy to analyze tin-silicon molecular sieve samples, The characteristic absorption peak of the skeleton tin atom appears around 190nm; the characteristic absorption peak of the skeleton Ti atom appears near 210nm when analyzing the titanium silicon molecular sieve sample. The peak of pyridine infrared spectrum at 1450cm ^-1 reflects the L-acidity characteristic of molecular sieve, which is provided by the skeleton tin atoms and skeleton titanium atoms.

According to the present invention, the tin-silicon molecular sieve is a product in which tin atoms replace part of the skeleton silicon of various topological molecular sieves. The topological structure of the molecular sieve can refer to the website of the International Zeolite Association (IZA, International Zeolite Association). For example, the tin-silicon molecular sieve can be selected from One or more of MFI tin-silicon molecular sieves, MEL tin-silicon molecular sieves, BEA tin-silicon molecular sieves, MWW tin-silicon molecular sieves, MOR tin-silicon molecular sieves, hexagonal tin-silicon molecular sieves and FAU tin-silicon molecular sieves. The MFI-type tin-silicon molecular sieve is, for example, Sn-MFI molecular sieve, the MEL-type tin-silicon molecular sieve is, for example, Sn-MEL molecular sieve, the BEA-type tin-silicon molecular sieve is, for example, Sn-Beta molecular sieve, and the MWW-type tin-silicon molecular sieve is, for example, Sn-MCM-22 Molecular sieves, MOR-type tin-silicon molecular sieves are, for example, Sn-MOR molecular sieves, hexagonal-structure tin-silicon molecular sieves are, for example, Sn-MCM-41 molecular sieves, Sn-SBA-15 molecular sieves, and FAU-type tin-silicon molecular sieves are, for example, Sn-USY molecular sieves.锡硅分子筛的具体制备方法可以参考中国专利CN104549549A、CN107162014A、CN105271294A、CN103964461A、CN105314649A、CN104557629A、CN104557632A、CN103204806A、CN103204830A、CN103204775A、CN103204792A、CN103204777A、CN103204835A等。 Further preferably, the tin-silicon molecular sieve is an MFI-type tin-silicon molecular sieve. The MFI-type tin-silicon molecular sieve can be obtained commercially, or according to the literature (Mal N K, Ramaswamy V, Rajamohanan P R, et al.Sn-MFI molecular sieves: synthesis methods, 29Si liquid and solid MAS-NMR, 119Sn static and MAS NMRstudies [J]. Microporous Materials, 1997, 12 (4-6): 331-340.) prepared by the method.

According to the present invention, titanium-silicon molecular sieves are products in which titanium atoms replace part of the skeleton silicon of molecular sieves with various topological structures. One or more of titanium-silicon molecular sieves, MOR-type titanium-silicon molecular sieves, TUN-type titanium-silicon molecular sieves and hexagonal titanium-silicon molecular sieves. The MFI-type titanium-silicon molecular sieve is, for example, TS-1 molecular sieve, the MEL-type titanium-silicon molecular sieve is, for example, TS-2 molecular sieve, the BEA-type titanium-silicon molecular sieve is, for example, Ti-Beta molecular sieve, and the MWW-type titanium-silicon molecular sieve is, for example, Ti-MCM-22 Molecular sieves, MOR-type titanium-silicon molecular sieves such as Ti-MOR molecular sieves, TUN-type titanium-silicon molecular sieves such as Ti-TUN molecular sieves, hexagonal titanium-silicon molecular sieves such as Ti-MCM-41 molecular sieves, Ti-SBA-15 molecular sieves, and other structures The preferred titanium silicon molecular sieve is, for example, Ti-ZSM-48 molecular sieve.钛硅分子筛的具体制备方法可以参考中国专利CN107879357A、CN107879354A、CN107879356A、CN107879355A、CN107986293A、CN107986294A、CN108002404A、CN107539999A、CN107537559A、CN107539998A、CN103182323A、CN103183355A、CN106964400A、CN106904633A、CN107986292A、CN103182320A、CN103182322A、CN103183356A、CN101439300A、CN106145151A , CN107840347A, CN106145148A, CN106145149A, CN106145147A and CN107840344A, etc., preferably, the titanium-silicon molecular sieve is at least one selected from MFI-type titanium-silicon molecular sieves, MEL-type titanium-silicon molecular sieves and BEA-type titanium-silicon molecular sieves. Further preferably, the titanium-silicon molecular sieve is an MFI-type titanium-silicon molecular sieve. The MFI-type titanium-silicon molecular sieve can be obtained commercially, or can be prepared according to the method in the literature (Studies on the synthesis of titanium silicalite, TS-1 Zeolites, 1992, 12(8), 943-50).

In the present invention, the titanium atoms of the skeleton of the titanium-silicon molecular sieve and the tin atoms of the skeleton of the tin-silicon molecular sieve synergistically catalyze aceguvaldehyde to generate lactic acid. The titanium-silicon molecular sieve and the tin-silicon molecular sieve in the catalyst can be mixed in any proportion. Preferably, the titanium-silicon molecular sieve in the catalyst The mixing weight ratio with tin-silicon molecular sieve is 1: (0.001-1000), further preferably, the mixing weight ratio of titanium-silicon molecular sieve and tin-silicon molecular sieve in the catalyst is 1: (0.01-100), even more preferably, The mixing weight ratio of titanium-silicon molecular sieves and tin-silicon molecular sieves in the catalyst is 1:(0.1-10).

According to the present invention, titanium atoms and tin atoms can replace silicon atoms in part of the molecular sieve, for example, the molar ratio of titanium dioxide to silicon dioxide in the titanium-silicon molecular sieve can be (0.01-10): 100, preferably (0.05-5 ): 100; the molar ratio of tin dioxide to silicon dioxide in the tin-silicon molecular sieve can be (0.01-10): 100, preferably (0.05-5): 100.

According to the present invention, the mol ratio of described methylglyoxal and water is preferably 1:(60-200), and the weight ratio of methylglyoxal and the mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve in dry basis weight is preferably 1:(0.2 -3), the reaction temperature is preferably 40-120°C, the reaction time is preferably 2-8h, the reaction pressure (absolute pressure) can be 0.1-3MPa, and the reaction pressure is preferably 0.1-2MPa.

According to the present invention, the reaction described in the present invention can be carried out in conventional catalytic reactor, and the present invention does not do special limitation, for example, the reaction of the present invention can be carried out in batch tank reactor or three-necked flask, or in suitable In other reactors such as fixed bed, moving bed, suspended bed etc., preferably carry out in tank reactor, fixed bed reactor, moving bed, suspended bed or slurry bed reactor, the specific mode of operation of above-mentioned reactor is this Those skilled in the art are well-known, and the present invention will not repeat them here.

According to the present invention, those skilled in the art can understand that, depending on the reactor used, the tin-silicon molecular sieve and/or titanium-silicon molecular sieve described in the present invention can be the original powder of molecular sieve, or can be formed by mixing molecular sieve and carrier. The final shaped catalyst. The separation of the product containing lactic acid and the catalyst can be achieved in many ways. For example, when the original powdery molecular sieve is used as the catalyst, the separation of the product and the recovery of the catalyst can be realized by means of sedimentation, filtration, centrifugation, evaporation, membrane separation, etc. Alternatively, the catalyst can also be molded and loaded into a fixed-bed reactor, and the catalyst can be recovered after the reaction is completed. The separation and recovery methods of various catalysts are mostly involved in the existing literature, and will not be repeated here.

The present invention will be further described below by way of examples, but content of the present invention is not limited thereto.

Unless otherwise specified, the raw materials used in the preparation examples, preparation comparative examples, examples and comparative examples are all chemically pure reagents.

In the present invention, the analysis of each component in the activity evaluation system is carried out by gas chromatography, and the analysis results are quantified by the internal standard method, and the internal standard is naphthalene. Among them, the chromatographic analysis conditions are: Agilent-6890 chromatograph, HP-5 capillary chromatographic column, injection volume 0.5 μL, inlet temperature 280°C. The column temperature was kept at 100°C for 2min, then increased to 200°C at a rate of 15°C/min, and kept for 3min. FID detector, detector temperature 300°C.

In each embodiment and comparative example:

Methylglyoxal conversion %=(the molar number of methylglyoxal in the raw material-the molar number of methylglyoxal in the product)/the molar number of methylglyoxal in the raw material * 100%;

Lactic acid selectivity %=the molar number of lactic acid in the product/(the molar number of methylglyoxal in the raw material-the molar number of methylglyoxal in the product)×100%;

Lactic acid yield%=the molar number of lactic acid in the product/the molar number of methylglyoxal in the raw material×100%, that is, the lactic acid yield%=lactic acid selectivity%×the conversion rate of methylglyoxal.

Preparation Examples and Preparation Comparative Examples are used to provide catalysts used in Examples and Comparative Examples.

Preparation Example 1

This preparation example prepares Sn-MFI molecular sieve, and specific preparation method is:

Dissolve tin tetrachloride pentahydrate (SnCl ₄ .5H ₂ O) in water, add tetrapropylammonium hydroxide (TPAOH, 20% aqueous solution) to this aqueous solution and stir with tetraethyl orthosilicate (TEOS) and water, continuously stirred for 30 minutes to obtain a clear liquid with a chemical composition of 0.03SnO ₂ : SiO ₂ :0.45TPA: 35H ₂ O, and then crystallized at a temperature of 433K for 2 days, after which the obtained solid was filtered and washed with distilled water , dried at 393K for 5 hours, and then calcined at 823K for 10 hours to obtain a molecular sieve sample. Among them, 15.31 g of TEOS, 33.67 g of TPAOH, 0.38 g of SnCl ₄ .5H ₂ O, and 39.64 g of water are used.

Preparation Example 2

This preparation example references "Nemeth L, Moscoso J, Erdman N, et al.Synthesis and characterization of Sn-Beta as a selective oxidation catalyst [J]. Studies in Surface Science & Catalysis, 2004, 154 (04): 2626-2631" Method prepares Sn-Beta molecular sieve, the preparation method of the adopted Sn-Beta molecular sieve is:

Dissolve tin tetrachloride pentahydrate (SnCl ₄ .5H ₂ O) in water, add this aqueous solution to ethyl orthosilicate (TEOS) and stir, add tetraethylammonium hydroxide (TEAOH) under stirring, stir until TEOS Evaporation gave the alcohol, and hydrogen fluoride (HF) was added to the clear liquid to form a creamy thin layer. Finally, a suspension of dealuminated nano Beta seeds (20nm) and water was added to obtain a clear liquid with a chemical composition of 0.03SnO ₂ : SiO ₂ : 6TEA: 15H ₂ O: 10HF, and then crystallized at 413K for 10 days. Afterwards, the obtained solid was filtered, washed with distilled water, dried at 393K for 5 hours, and then calcined at 823K for 10 hours to obtain a molecular sieve sample. Among them, the amount of TEOS is 20.81g, the amount of TEAOH is 88.42g, the amount of SnCl ₄ .5H ₂ O is 1.05g, the amount of water is 27.01g, and the amount of HF is 20g.

Preparation Example 3

References for this preparation example "Yang X, Wu L, Wang Z, et al. Conversion of dihydroxyacetone to methyl lactate catalyzed by highly active hierarchical Sn-USY at room temperature [J]. Catalysis Science & Technology, 2016, 6 (6): 1757- 1763" method to prepare Sn-USY molecular sieve, the preparation method of the adopted Sn-USY molecular sieve is:

H-USY molecular sieve was mixed with nitric acid, treated at 85°C for 8h, the sample was filtered and washed with deionized water, and dried at 120°C for 12h to obtain a solid sample. The solid sample was mixed with tin tetrachloride pentahydrate (SnCl ₄ .5H ₂ O) for 1 hour to obtain a mixed liquid with a chemical composition of 0.03SnO ₂ : 100SiO ₂ , dried at 100°C for 12 hours, and finally calcined at 550°C for 3 hours to obtain Molecular sieve samples. Among them, the amount of H-USY is 2.0 g, the amount of nitric acid is 50 mL, and the amount of SnCl ₄ .5H ₂ O is 0.6 g.

Preparation Example 4

This preparation example prepares TS-1 molecular sieve, and the specific preparation method is:

Add about 3/4 of the tetrapropylammonium hydroxide (TPAOH, 20%) solution to the tetraethyl orthosilicate (TEOS) solution to obtain a liquid mixture with a pH of about 13, and then to the The required amount of n-butyl titanate [Ti(OBu) ₄ ] in anhydrous isopropanol was added dropwise to the obtained liquid mixture, and a clear liquid was obtained after stirring for 15 minutes. Finally, the remaining TPAOH was slowly added to the In the clear liquid, stir at 348-353K for about 3 hours to obtain a sol with a chemical composition of 0.03TiO ₂ : SiO ₂ :0.36TPA: 35H ₂ O, and then crystallize at 443K for 3 days, and then the obtained solid Filter, wash with distilled water, dry at 373K for 5 hours, and then roast at 823K for 10 hours to obtain a molecular sieve sample. Wherein, the consumption of TEOS is 42g, the consumption of TPAOH is 73g, the consumption of Ti(OBu) ₄ is 2g, the consumption of anhydrous isopropanol is 10g, and the consumption of water is 68g.

Preparation Example 5

This preparation example prepares TS-2 molecular sieve, the specific preparation method is:

A certain amount of tetrabutylammonium hydroxide solution (TBAOH, 20%) is mixed with tetraethyl orthosilicate (TEOS), and then the required amount of n-butyl titanate is added dropwise to the obtained transparent liquid mixture under vigorous stirring Anhydrous isopropanol solution of [Ti(OBu) ₄ ] was stirred for 30 minutes to obtain a clear liquid after hydrolysis was completed. Finally, 2 times the required amount of distilled water was added, and the resulting sol was stirred at 348-353K for 2 hours to remove alcohol. The chemical composition of the obtained sol is 0.03TiO ₂ : SiO ₂ :0.2TBA:20H ₂ O. The sol was crystallized at 443K for 3 days, and the obtained crystallized product was filtered, washed with water, dried at 373K for 6 hours, and then calcined at 823K for 16 hours to obtain a molecular sieve sample. Wherein, the consumption of TEOS is 42g, the consumption of TBAOH is 52g, the consumption of Ti(OBu) ₄ is 2g, the consumption of anhydrous isopropanol is 10g, and the consumption of water is 30g.

Preparation Example 6

This preparation example prepares Ti-Beta molecular sieve, and concrete preparation method is:

A certain amount of tetraethylammonium hydroxide solution (TEAOH, 20%) and hydrogen peroxide was added into a solution of measured tetraethylammonium hydroxide solution (TEAOH, 20%), and hydrolyzed for 2 hours under stirring. Then add the weighed anhydrous isopropanol solution of tetrabutyl titanate [Ti(OBu) ₄ ] into the hydrolyzed solution of ethyl orthosilicate, and continue to stir for 3 hours to remove alcohol, and finally the chemical composition can be obtained as TiO ₂ : Sol of 60SiO ₂ :33TEA:400H ₂ O:20H ₂ O ₂ . Finally, dealuminated P-type molecular sieve seed crystals were added and vigorously stirred (the amount of seed crystals added was calculated as sol by silica, and 100 g of silica was added with 4 g of seed crystals). After the obtained mixture was crystallized at 413K for 14 days, the resulting slurry was filtered, washed with water, dried at 373K for 6 hours, and then calcined at 823K for 12 hours to obtain a molecular sieve sample. Wherein, the consumption of TEOS is 42g, the consumption of TEAOH is 81g, the consumption of Ti(OBu) ₄ is 1.16g, the consumption of anhydrous isopropanol is 10g, and the consumption of hydrogen peroxide is 7.5g.

Prepare comparative example 1

The hollow titanium-silicon molecular sieve HTS prepared in this preparation comparison example is prepared according to the method described in Example 1 of the Chinese patent CN1301599A specification, and the specific preparation method is as follows:

Mix 22.5 grams of tetraethyl orthosilicate with 7.0 grams of tetrapropylammonium hydroxide, add 59.8 grams of distilled water, mix well, and then hydrolyze at normal pressure and 60°C for 1.0 hour to obtain a hydrolysis solution of tetraethyl orthosilicate A solution consisting of 1.1 g of tetrabutyl titanate and 5.0 g of anhydrous isopropanol was slowly added under vigorous stirring, and the resulting mixture was stirred at 75° C. for 3 hours to obtain a clear transparent colloid. Put this colloid into a stainless steel sealed reaction kettle, and place it at a constant temperature of 170°C and autogenous pressure for 6 days to obtain a mixture of crystallized products; filter the mixture, wash with water until the pH is 6-8, and dry at 110°C After 60 minutes, unroasted TS-1 powder was obtained. The TS-1 raw powder was calcined in air atmosphere at 550°C for 4 hours to obtain TS-1 molecular sieve.

Get the obtained TS-1 molecular sieve according to the ratio of molecular sieve (gram): sulfuric acid (mol): water (mol) = 100: 0.15: 150 and mix evenly, react at 90 ℃ for 5.0 hours, then filter, wash and dry according to conventional methods , to obtain acid-treated TS-1 molecular sieves.

The above-mentioned acid-treated TS-1 molecular sieves were mixed uniformly according to the ratio of molecular sieve (gram): triethanolamine (mol): tetrapropylammonium hydroxide (mol): water (mol) = 100: 0.20: 0.15: 180, and put into A stainless steel sealed reaction kettle was placed at a constant temperature of 190°C and autogenous pressure for 0.5 days. After cooling and pressure relief, it was filtered, washed, dried according to conventional methods, and roasted in an air atmosphere at 550°C for 3 hours to obtain HTS molecular sieves.

The HTS molecular sieve has a hollow structure with a radial length of 5-100 nanometers, and the benzene adsorption measured by static adsorption method at 25°C, P/P0=0.10, and adsorption time of 1 hour is 85 mg/gram molecular sieve; The adsorption isotherm and desorption isotherm of low-temperature nitrogen adsorption determined according to the ASTM D4222-98 standard method show that there is a hysteresis loop between the adsorption isotherm and desorption isotherm of low-temperature nitrogen adsorption.

Prepare comparative example 2

The preparation method of the titanium-silicon molecular sieve Sn/TS-1 loaded with tin used in this preparation comparative example is as follows:

Tin tetrachloride pentahydrate (SnCl ₄ .5H ₂ O) and TS-1 molecular sieve (prepared by the method of Comparative Example 1) were mechanically mixed directly and then calcined at 550°C for 5 hours to obtain a chemical composition of 0.03TiO ₂ :SiO ₂ : 0.03SnO ₂ molecular sieve. Wherein, the amount of TS-1 is 2 g, and the amount of SnCl ₄ .5H ₂ O is 0.76 g.

The examples and comparative examples are used to illustrate the method for preparing lactic acid from methylglyoxal catalyzed by different catalysts.

Example 1

Weigh 0.15g of the tin-silicon molecular sieve Sn-MFI prepared in Preparation Example 1 and 0.15g of the titanium-silicon molecular sieve TS-1 prepared in Preparation Example 4 as catalysts and put them in a 15mL glass reaction tube, then add a magnetic stirrer and 8g of water in sequence , 0.1g of methylglyoxal, screw on the lid of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Comparative example 1

Weigh 0.3 g of the tin-silica molecular sieve Sn-MFI catalyst prepared in Preparation Example 1 and put it in a 15 mL glass reaction tube, then add a magnetic stirrer, 8 g of water, and 0.1 g of aceglyoxal in sequence, and screw on the glass reaction tube cover. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Comparative example 2

Weigh 0.3g of the titanium-silicon molecular sieve TS-1 catalyst prepared in Preparation Example 4 and put it in a 15mL glass reaction tube, then add a magnetic stirrer, 8g of water, and 0.1g of aceguvaldehyde in sequence, and screw on the cap of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Comparative example 3

Weigh 0.3g of the hollow titanium-silicon molecular sieve HTS catalyst prepared in Preparation Comparative Example 1 and put it in a 15mL glass reaction tube, then add a magnetic stirrer, 8g of water, and 0.1g of aceglyoxal in sequence, and screw on the glass reaction tube cover. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Comparative example 4

Weigh 0.3g of the tin-loaded titanium-silicon molecular sieve Sn/TS-1 catalyst prepared in Comparative Example 2 and put it in a 15mL glass reaction tube, then add a magnetic stirrer, 8g of water, and 0.1g of aceglyoxal in sequence, and screw on the glass reaction tube cover. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Comparative example 5

It is basically the same as Example 1, except that the reaction temperature is 10° C., and the reaction time is 0.5 hour. The specific reaction results are shown in Table 1.

Comparative example 6

It is basically the same as Example 1, except that the reaction temperature is 200° C., and the reaction time is 12 hours. The reaction raw materials and the catalyst are packed into a polytetrafluoroethylene liner, and then sealed in a stainless steel reactor. react in a phase reactor. The specific reaction results are shown in Table 1.

Example 2

Weigh 0.15g of the tin-silicon molecular sieve Sn-Beta prepared in Preparation Example 2 and 0.15g of the titanium-silicon molecular sieve TS-1 prepared in Preparation Example 4 as catalysts and put them in a 15mL glass reaction tube, then add a magnetic stirrer, 8g of water , 0.1g of methylglyoxal, screw on the lid of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Example 3

Weigh 0.15g of the tin-silicon molecular sieve Sn-USY prepared in Preparation Example 3 and 0.15g of the titanium-silicon molecular sieve TS-1 prepared in Preparation Example 4 as catalysts and put them in a 15mL glass reaction tube, then add a magnetic stirrer and 8g of water in sequence , 0.1g of methylglyoxal, screw on the lid of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Example 4

Weigh 0.15g of the silicon molecular sieve Sn-MFI prepared in Preparation Example 1 and 0.15g of the titanium silicon molecular sieve TS-2 prepared in Preparation Example 5 as catalysts and put them in a 15mL glass reaction tube, then add a magnetic stirrer, 8g of water, 0.1g of methylglyoxal, screw on the lid of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Example 5

Weigh 0.15g of the tin-silicon molecular sieve Sn-MFI prepared in Preparation Example 1 and 0.15g of the titanium-silicon molecular sieve Ti-Beta prepared in Preparation Example 6 as catalysts and put them in a 15mL glass reaction tube, then add a magnetic stirrer, 8g of water , 0.1g of methylglyoxal, screw on the lid of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 60° C., and the reaction was carried out for 7 hours. The specific reaction results are shown in Table 1.

Example 6

Weigh 0.5g of the tin-silicon molecular sieve Sn-MFI prepared in Preparation Example 1 and 0.5g of the titanium-silicon molecular sieve TS-1 prepared in Preparation Example 4 as catalysts and put them in a 15mL glass reaction tube, then add a magnetic stirrer and 8g of water in sequence , 0.2g of methylglyoxal, screw on the lid of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 30° C., and the reaction was carried out for 10 hours. The specific reaction results are shown in Table 1.

Example 7

Weigh 0.01g of the tin-silicon molecular sieve Sn-MFI prepared in Preparation Example 1 and 0.03g of the titanium-silicon molecular sieve TS-1 prepared in Preparation Example 4 as a catalyst and put them in a 15mL glass reaction tube, then add a magnetic stirrer and 8g of water in sequence , 0.2g of methylglyoxal, screw on the lid of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 70° C., and the reaction was carried out for 8 hours.

Example 8

Weigh 0.1g of the tin-silicon molecular sieve Sn-MFI prepared in Preparation Example 1 and 0.1g of the titanium-silicon molecular sieve TS-1 prepared in Preparation Example 4 as catalysts and put them in a 15mL glass reaction tube, then add a magnetic stirrer and 8g of water in sequence , 0.7g of methylglyoxal, screw on the lid of the glass reaction tube. Put the glass reaction tube in an oil bath on a temperature-controlled magnetic stirrer, start the magnetic stirrer and heating device, and start the reaction. The reaction temperature was controlled at about 50° C., and the reaction was carried out for 4 hours. The specific reaction results are shown in Table 1.

Example 9

It is basically the same as Example 1, except that the molar ratio of methylglyoxal to water is 1:40, the reaction temperature is 30°C, the reaction time is 1 hour, and the weight of the mixture of methylglyoxal and titanium-silicon molecular sieve and tin-silicon molecular sieve The ratio is 1:0.1, and the mixing weight ratio of titanium-silicon molecular sieves and tin-silicon molecular sieves is 1:0.1. The specific reaction results are shown in Table 1.

Example 10

Basically the same as Example 1, the difference is: the molar ratio of methylglyoxal to water is 1:350, the reaction temperature is 180°C, the reaction time is 10 hours, the weight of the mixture of methylglyoxal and titanium-silicon molecular sieve and tin-silicon molecular sieve The ratio is 1:6, the mixing weight ratio of titanium-silicon molecular sieve and tin-silicon molecular sieve is 1:10, the reaction raw materials and catalysts are packed into a polytetrafluoroethylene liner, and then placed in a stainless steel reactor to seal and react in a homogeneous phase reaction in the vessel. The specific reaction results are shown in Table 1.

As can be seen from the results of the foregoing examples and comparative examples, the method of the present invention is used to prepare lactic acid, the operation process is simple, the reaction conditions are mild, and the conversion rate of raw materials and the selectivity of lactic acid are higher; For molecular sieve mechanical mixtures, preferably the molar ratio of methylglyoxal to water is 1: (40-350), the reaction temperature is 30-180°C, the reaction time is 1-10h, and the reaction pressure is 0.1-3.0MPa, more preferably acetone The molar ratio of aldehyde to water is 1:(60-200), the reaction temperature is 40-120°C, the reaction time is 2-8h, and the reaction pressure is 0.1-2.0MPa, which is more conducive to improving the conversion rate of methylglyoxal and lactic acid yield.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention. These simple modifications All belong to the protection scope of the present invention.

In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way if there is no contradiction. The combination method will not be described separately.

In addition, various combinations of different embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the idea of the present invention, they should also be regarded as the content of the present invention.

Table 1

serial number Methylglyoxal conversion rate/% Lactic acid selectivity/% Example 1 96 95 Example 2 93 95 Example 3 93 94 Example 4 92 94 Example 5 94 93 Example 6 86 88 Example 7 85 86 Example 8 85 84 Example 9 83 82 Example 10 95 84 Comparative example 1 81 76 Comparative example 2 50 twenty three Comparative example 3 57 28 Comparative example 4 68 63 Comparative example 5 13 14 Comparative example 6 91 72

Claims (10)

1. A method for preparing lactic acid, the method comprising: Methylglyoxal and water are contacted with the catalyst in a reactor and reacted to obtain a product containing lactic acid; wherein, the molar ratio of the methylglyoxal to water is 1: (200-350), and the reaction temperature is 40-120°C, The reaction time is 1-10h, the catalyst contains a mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve, and the weight ratio of methylglyoxal to the mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve in dry basis weight is 1: (0.1-6) The mixing weight ratio of titanium-silicon molecular sieve and tin-silicon molecular sieve in the catalyst is 1: (0.1-10), and the tin-silicon molecular sieve is selected from MFI type tin-silicon molecular sieve, MEL type tin-silicon molecular sieve, BEA type tin-silicon molecular sieve and One or more of FAU-type tin-silicon molecular sieves, wherein the titanium-silicon molecular sieve is selected from one or more of MFI-type titanium-silicon molecular sieves, MEL-type titanium-silicon molecular sieves and BEA-type titanium-silicon molecular sieves. 2. The method according to claim 1, wherein the tin-silicon molecular sieve is selected from one or more of Sn-MFI molecular sieves, Sn-MEL molecular sieves, Sn-Beta molecular sieves and Sn-USY molecular sieves. 3. The method according to claim 1, wherein the titanium silicon molecular sieve is selected from one or more of TS-1 molecular sieves, TS-2 molecular sieves and Ti-Beta molecular sieves. 4. The method according to claim 1, wherein the molar ratio of titanium dioxide to silicon dioxide in the titanium-silicon molecular sieve is (0.01-10):100. 5. The method according to claim 4, wherein the molar ratio of titanium dioxide to silicon dioxide in the titanium-silicon molecular sieve is (0.05-5):100. 6. The method according to claim 1, wherein the molar ratio of tin dioxide to silicon dioxide in the tin-silicon molecular sieve is (0.01-10):100. 7. The method according to claim 6, wherein the molar ratio of tin dioxide to silicon dioxide in the tin-silicon molecular sieve is (0.05-5):100. 8. The method according to claim 1, wherein, the weight ratio of methylglyoxal and the mixture of titanium-silicon molecular sieve and tin-silicon molecular sieve in dry basis weight is 1: (0.2-3), and the reaction times is 2-8h, The reaction pressure is 0.1-3MPa. 9. The method according to claim 1, wherein the reaction pressure is 0.1-2 MPa. 10. The method according to claim 1, wherein the reactor is a tank reactor, a fixed bed reactor, a moving bed, a suspension bed or a slurry bed reactor.

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