Preparation method of monoisopropanolamine

Abstract

The invention discloses a method for preparing monoisopropanolamine, which comprises the following steps: using an aqueous solution of triisopropanolamine as a raw material, mixing with liquid ammonia, and then passing it into a reactor in which an imidization catalyst is loaded on the upper part and a hydrogenation catalyst is loaded on the lower part, and hydrogen is simultaneously passed through for reaction to prepare monoisopropanolamine; the imidization catalyst is a ruthenium / tin catalyst with a Lewis acid-modified porous oxide as a carrier; and the hydrogenation catalyst is a Cu-based catalyst with a pyridine-modified silicon-aluminum molecular sieve as a carrier. The present invention uses an aqueous solution of triisopropanolamine as a raw material, first through the action of an imidization catalyst, converting all C-N bonds into C=N bonds after all the C-N bonds are cracked, and then through the action of a hydrogenation catalyst, a highly selective catalytic generation of monoisopropanolamine can be achieved.

Description

Technical Field

[0001] The invention relates to an organic synthesis preparation method, in particular to a preparation method of monoisopropanolamine. Background Art

[0002] Isopropanolamine is an alkyl alcoholamine substance that contains both amino and hydroxyl groups in its structure. It can be used as a surfactant, fiber industry refining agent, antistatic agent, dye, fiber wetting agent, etc. It can also be used to synthesize detergents, cosmetic lubricants, antioxidants for cutting oils, plasticizers, emulsifiers, etc. It has a wide range of applications.

[0003] The traditional synthesis method of isopropanolamine adopts propylene oxide and ammonia to carry out ring-opening reaction, and water is used as catalyst. The reaction is a three-stage series reaction, and the usual reaction product is a mixture of monoisopropanolamine (MIPA), diisopropanolamine (DIPA), and triisopropanolamine (TIPA). After the production is completed, the product is usually distilled and separated by multi-tower joint operation, but because the isopropanolamine series products are heat-sensitive substances, too high a temperature easily leads to an increase in product chromaticity and an increase in impurities. For example, the boiling point of TIPA is as high as 305°C, and the distillation temperature is relatively high. The triisopropanolamine product obtained by distillation has a high chromaticity and low purity, which cannot meet the requirements of the market. Among the triisopropanolamine products currently on sale in the market, the general product purity is only about 85%, of which the water content accounts for about 10-15%.

[0004] In view of the fact that the market values ​​of MIPA, DIPA and TIPA decrease in sequence, how to prepare monoisopropanolamine with high yield is of great significance.

[0005] Patent US4328370A discloses a method of converting low-carbon trialkanolamines such as triethanolamine and triisopropanolamine into corresponding monoalkanolamines and dialkanolamines by reacting with ammonia in the presence of a noble metal hydrogenation catalyst using an intermittent process. Since the method uses a noble metal catalyst, the catalyst cost is relatively high, and the product is still a mixture of monoalkanolamines and dialkanolamines, and the yield of the monoalkanolamine product is relatively low.

[0006] Patent CN114247470A discloses a method for synthesizing monoisopropanolamine by using propylene oxide and liquid ammonia as raw materials via a catalyst in an intermittent process. The method uses hydrogen-type mordenite (H-MOR) modified with a soluble calcium salt as a catalyst. The main drawback of the method is that it is difficult to avoid the product monoisopropanolamine from further reacting with propylene oxide to form diisopropanolamine. The selectivity of diisopropanolamine exceeds 10%, thereby reducing the yield of the target product. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for preparing monoisopropanolamine. The present invention uses an aqueous solution of triisopropanolamine as a raw material, firstly reacts with an imidization catalyst to completely cleave the CN bonds and convert them into C=N bonds, and then reacts with a hydrogenation catalyst to catalyze and generate monoisopropanolamine with high selectivity.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing monoisopropanolamine comprises the following steps:

[0010] An aqueous solution of triisopropanolamine is used as a raw material, mixed with liquid ammonia, and then introduced into a reactor filled with an imidization catalyst on the upper part and a hydrogenation catalyst on the lower part, and hydrogen is introduced at the same time for reaction to prepare monoisopropanolamine;

[0011] The imidization catalyst is a supported catalyst with Lewis acid-modified porous oxide as a carrier and metal Ru and Sn as active components; wherein the loading amount of metal Ru and Sn is 6-21% of the mass of the porous oxide, and the molar ratio of Ru to Sn is 1:(0.01-0.1);

[0012] The hydrogenation catalyst is a Cu-based catalyst with pyridine-modified silica-alumina molecular sieve as a carrier, wherein the loading amount of Cu is 4-30% of the mass of the silica-alumina molecular sieve.

[0013] In the present invention, as a possible reaction mechanism, the reaction expression is as follows:

[0014]

[0015] The breakage of CN is a well-known technical difficulty for those skilled in the art. It is difficult to prepare MIPA with high selectivity in one step from TIPA. Therefore, the present invention develops an efficient modified catalyst, and TIPA can be prepared with high selectivity to obtain MIPA through two-step reaction. In the present invention, liquid ammonia dissociates in water, and as a nitrogen source, under the action of an imidization catalyst, all the CN bonds of TIPA are converted into C=N bonds. Among them, the carrier of the imidization catalyst is modified by Lewis acid. Since it is a compound with an electron-deficient structure, it can attract the lone pair of electrons on the nitrogen atom in TIPA and participate in the catalytic reaction. The Sn element can inhibit the reaction of the reaction products to form secondary amines, thereby improving the selectivity of the product MIPA. The imine generated by the reaction is further subjected to a hydrogenation reaction, and the product MIPA is obtained by hydrogenation under the action of an active Cu catalyst.

[0016] As a preferred embodiment of the present invention, the imidization catalyst is prepared by the following method:

[0017] a1. Impregnating the Lewis acid solution into the porous oxide, stirring and treating at 50-70° C. for 2-10 hours to obtain a Lewis acid-modified carrier;

[0018] a2. Add the Lewis acid modified carrier to a mixed solution of ruthenium salt and tin salt, stir and treat at 60-90° C. for 2-12 hours, filter, dry and then roast, press into tablets to obtain an imidization catalyst;

[0019] Preferably, in step a1, the mass concentration of the Lewis acid solution is 0.5-5%, preferably 1-3%; the Lewis acid solution and the porous oxide are impregnated in equal volumes;

[0020] Preferably, the Lewis acid is one or more of AlCl3, BF3, SbCl5, FeBr3, FeCl3, SnCl4, TiCl4, and ZnCl2;

[0021] Preferably, the porous oxide is one or more of γ-Al2O3, SiO2, TiO2, ZrO2, and preferably has a specific surface area of ​​100-300m 2 / g preferably 150-250m 2 / g, the pore volume is 0.2-3ml / g, preferably 1-2ml / g, and the pore size is 2-20nm. The γ-Al2O3 can be in the shape of flake, cylinder, clover, four-leaf clover, etc.

[0022] Preferably, the stirring speed in step a1 is 200-1000 rpm.

[0023] Preferably, after the stirring in step a1 is completed, the filtered solid is dried at 90-150° C. for 2-12 h, preferably at 110-130° C. for 4-8 h.

[0024] As a preferred embodiment of the present invention, in step a2, the ratio of ruthenium salt to tin salt is 1:(0.01-0.1) in terms of metal element molar ratio;

[0025] Preferably, the amount of ruthenium salt and tin salt added is 6-21% of the mass of the porous oxide in the Lewis acid-modified support, based on the total mass of metal ruthenium and tin.

[0026] Preferably, the ruthenium salt can be selected from ruthenium trichloride, ruthenium sulfate, ruthenium nitrate, etc.; the tin salt can be selected from tin tetrachloride, stannous sulfate, tin nitrate, etc.

[0027] Preferably, after the stirring in step a2 is completed, the filtered solid is dried at 100-150° C. for 2-24 h, preferably at 110-140° C. for 8-16 h.

[0028] As a preferred embodiment of the present invention, in step a2, the calcination condition is calcination at 400-600°C for 2-12h;

[0029] Preferably, the stirring speed in step a2 is 100-800 rpm.

[0030] Preferably, before tableting in step a2, the solid obtained by calcination is mixed with graphite accounting for 1-5% of the solid mass.

[0031] As a preferred embodiment of the present invention, the hydrogenation catalyst is prepared by the following method:

[0032] b1. Immerse the pyridine solution in the silicon-aluminum molecular sieve, and stir for 2-10 hours at 50-70° C. to obtain a modified carrier;

[0033] b2. Add the modified carrier to the mixed solution of copper salt, stir and treat at 60-90° C. for 2-12 hours, filter, dry, roast, and press into tablets to obtain a hydrogenation catalyst.

[0034] As a preferred embodiment of the present invention, in step b1, the mass concentration of the pyridine solution is 1-5%, preferably 1.5-4.5%; the pyridine solution and the silica-alumina molecular sieve are impregnated in equal volumes;

[0035] Preferably, the silicon-aluminum molecular sieve is at least one of type A molecular sieve, type X molecular sieve, type Y molecular sieve, ZSM-5, and SAPO.

[0036] Preferably, the stirring speed in step b1 is 200-1000 rpm.

[0037] Preferably, after the stirring in step b1 is completed, the filtered solid is dried at 90-150° C. for 2-12 h, preferably at 110-130° C. for 4-8 h.

[0038] As a preferred embodiment of the present invention, in step b2, the amount of copper salt added is 4-30% of the mass of the silica-alumina molecular sieve in the modified carrier, calculated on the basis of the mass of metal Cu.

[0039] Preferably, the copper salt can be selected from copper chloride, copper sulfate, copper nitrate and the like.

[0040] As a preferred embodiment of the present invention, in step b2, the calcination condition is calcination at 400-600°C for 2-12h;

[0041] Preferably, the stirring speed in step b2 is 100-800 rpm.

[0042] Preferably, after the stirring in step b2 is completed, the filtered solid is dried at 100-150° C. for 2-24 h, preferably at 110-140° C. for 8-16 h.

[0043] Preferably, before tableting in step a2, the solid obtained by calcination is mixed with graphite accounting for 1-5% of the solid mass.

[0044] As a preferred embodiment of the present invention, the mass ratio of triisopropanolamine, liquid ammonia and hydrogen is 1:(1.05-3.14):(2.46-4.93), preferably 1:(1.58-2.62):(3.08-4.31), the reaction temperature is 150-200°C, preferably 160-180°C; the absolute reaction pressure is 8-14MPa, preferably 10-12MPa; the space velocity of triisopropanolamine is 0.17-0.68h -1 , preferably 0.34-0.51h -1 ;

[0045] Preferably, the imidization catalyst and the hydrogenation catalyst are both subjected to hydrogen reduction activation treatment before use. For example, the activation temperature is 300-500°C, preferably 350-450°C; the absolute pressure is 5-12MPa, preferably 6-8MPa; the hydrogen space velocity during the activation process is 0.009-0.036h -1 , preferably 0.018-0.027h -1 , the reduction time is 6-32h, preferably 12-24h.

[0046] Preferably, the aqueous solution of triisopropanolamine may be a triisopropanolamine solution with a mass concentration of 80-98%, for example, 85%, 90%, 95%, etc.

[0047] The imidization catalyst and the hydrogenation catalyst are loaded in a reactor to prepare monoisopropanolamine. The reactor can be a tubular reactor, preferably a fixed bed tubular reactor. The production process of the monoisopropanolamine is preferably a continuous production process.

[0048] As a preferred embodiment of the present invention, after the reaction is completed, the reaction liquid is distilled and purified to obtain a monoisopropanolamine product;

[0049] Preferably, the distillation conditions are: temperature 100-140° C., preferably 110-130° C., absolute pressure 2-20 kPa, preferably 6-12 kPa, residence time 1-6 h, preferably 2-4 h.

[0050] The beneficial effects of the present invention are as follows:

[0051] (1) The introduction of Lewis acid in the imidization catalyst enhances the electrophilicity of the catalyst and improves the catalyst activity; at the same time, under the activation of water, the transition metals Ru and Sn work together to convert all CN bond groups into C=N bonds, thereby improving the selectivity and yield of small molecule imine products in the first step of the imidization reaction.

[0052] (2) After the silica-alumina molecular sieve is modified by pyridine, the alkalinity of the carrier is improved, which can further activate NH3. Cu is loaded on the silica-alumina molecular sieve as a heterogeneous solid acid catalyst, and the silica-alumina molecular sieve with a high specific surface area is used as a carrier to provide more active centers for the catalyst, and the generated imine is more efficiently converted into MIPA in the presence of NH3 and hydrogen.

[0053] (3) Through the two-step reaction, the conversion rate of TIPA and the selectivity of MIPA were greatly improved, and the high added value utilization of TIPA aqueous solution was achieved.

[0054] (4) The process flow of the present invention is simple, the conditions in the production process are mild, and the product purity is high. DETAILED DESCRIPTION

[0055] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0056] Gas chromatograph: Agilent 7890, detection conditions are as follows: chromatographic column is DB-5; injector and detector temperature is 280°C; initial column temperature is 50°C; heating rate is 20°C / min to 280°C and retained for 10 min.

[0057] TIPA aqueous solution was purchased from Hongbaoli Group Co., Ltd., 85% TIPA aqueous solution; liquid ammonia was purchased from Air Liquide Co., Ltd., purity was 99.5%; hydrogen was purchased from Air Liquide Co., Ltd., purity was 99.999%. Other raw materials and reagents were purchased from commercial finished products unless otherwise specified.

[0058] [Example 1]

[0059] (1) Preparation of imidization catalyst

[0060] Prepare a 3% mass concentration AlCl3 ethanol solution, pour 2000g of γ-Al2O3 carrier into the solution according to equal volume, impregnate at 60℃, stir at 600 rpm for 6h, and dry the carrier at 120℃ for 8h after impregnation to obtain a modified carrier. Weigh 262g of RuCl3·3H2O and 13.05g of anhydrous SnCl4, add 2L of deionized water to prepare an impregnation solution, take 1200g of the modified carrier and put it into the impregnation solution, impregnate at 75℃, stir at 500 rpm for 8h, filter and dry the solid at 120℃ for 12h, and then calcine at 500℃ for 8h. Add 3% of the mass of graphite to the calcined solid, press and shape it to obtain an imidization catalyst A with a diameter of 3mm.

[0061] (2) Preparation of hydrogenation catalyst

[0062] Prepare a 3% mass concentration pyridine aqueous solution, pour 2000g ZSM-5 molecular sieve carrier into the solution according to equal volume, impregnate for 6h at 60℃ and 600 rpm stirring speed, dry the carrier at 120℃ for 8h after impregnation to obtain a modified carrier. Weigh 300g CuCl2, add 2L deionized water to prepare an impregnation solution, take 1200g modified carrier and put it into the above impregnation solution, impregnate for 8h at 75℃ and 500 rpm stirring speed, dry the solid at 120℃ for 12h after filtration, and then roast at 500℃ for 8h. Add 3% of the mass of graphite to the roasted solid, press and shape it to obtain a hydrogenation catalyst A with a diameter of 3mm.

[0063] (3) The upper part of the fixed bed tubular reactor was loaded with imidization catalyst A, and the lower part was loaded with hydrogenation catalyst A. The reactor was activated with hydrogen at 400°C and 8 MPa absolute pressure for 24 h, with a hydrogen hourly velocity of 0.02 h -1 After activation, the mixture of TIPA: liquid ammonia: hydrogen = 1:1.8:3.5 was introduced into the reactor. The reaction temperature was 180°C, the absolute pressure was 10MPa, and the TIPA space velocity was 0.43h -1 The reaction was carried out, and the obtained reaction mother liquid was distilled at 120° C. and an absolute pressure of 10 kPa for 3 hours to remove liquid ammonia, water and small molecular byproducts to obtain pure monoisopropanolamine. According to chromatographic analysis, the TIPA conversion rate in this embodiment was 98.6%, and the MIPA selectivity was 99.2%.

[0064] [Example 2]

[0065] (1) Preparation of imidization catalyst

[0066] Prepare an AlCl3 ethanol solution with a mass concentration of 0.5%, and pour 2000g of SiO2 carrier into the solution according to equal volume, and impregnate it at 50℃ with a stirring speed of 200 rpm for 10h. After impregnation, the carrier is dried at 90℃ for 12h to obtain a modified carrier. Weigh 262g of RuCl3·3H2O and 26.1g of anhydrous SnCl4, add 4L of deionized water to prepare an impregnation solution, take 1200g of the modified carrier and put it into the above impregnation solution, and impregnate it at 60℃ with a stirring speed of 800 rpm for 2h. After filtering, the solid is dried at 150℃ for 2h, and then calcined at 400℃ for 12h. Add 1% of the mass of graphite to the calcined solid, press and shape it, and obtain an imidization catalyst B with a diameter of 2mm.

[0067] (2) Preparation of hydrogenation catalyst

[0068] Prepare a 1% mass concentration pyridine aqueous solution, pour 2000g SAPO molecular sieve carrier into the solution according to equal volume, impregnate at 50°C, stir at 200 rpm for 10h, and dry the carrier at 90°C for 12h to obtain a modified carrier. Weigh 100g CuCl2, add 2L deionized water to prepare an impregnation solution, take 1000g modified carrier and put it into the impregnation solution, impregnate at 60°C, stir at 800 rpm for 2h, filter and dry the solid at 150°C for 2h, and then calcine at 400°C for 12h. Add 1% of graphite to the calcined solid, press and shape, and obtain hydrogenation catalyst B with a diameter of 2mm.

[0069] (3) The upper part of the fixed bed tubular reactor was loaded with imidization catalyst B, and the lower part was loaded with hydrogenation catalyst B. The reactor was activated with hydrogen at 300°C and 12 MPa absolute pressure for 32 h, with a hydrogen hourly velocity of 0.009 h -1 After activation, the mixture was mixed with TIPA: liquid ammonia: hydrogen = 1:1.05:2.46 and then entered the reactor. The reaction temperature was 150°C, the absolute pressure was 14 MPa, and the TIPA space velocity was 0.17 h -1 The reaction was carried out, and the obtained reaction mother liquid was distilled at 100° C. and an absolute pressure of 2 kPa for 6 h to remove liquid ammonia, water and small molecular byproducts to obtain pure monoisopropanolamine. According to chromatographic analysis, the TIPA conversion rate in this embodiment was 98.1%, and the MIPA selectivity was 99.4%.

[0070] [Example 3]

[0071] (1) Preparation of imidization catalyst

[0072] Prepare a 5% mass concentration BF3 ethanol solution, pour 2000g TiO2 carrier into the solution according to equal volume, impregnate at 70℃, stir at 1000 rpm for 2h, and dry the carrier at 150℃ for 2h after impregnation to obtain a modified carrier. Weigh 262g RuCl3·3H2O and 2.61g anhydrous SnCl4, add 1L deionized water to prepare an impregnation solution, take 500g modified carrier and put it into the impregnation solution, impregnate at 90℃, stir at 100 rpm for 12h, filter and dry the solid at 100℃ for 24h, and then calcine at 600℃ for 2h. Add 5% of the mass of graphite to the calcined solid, press and shape, and obtain imidization catalyst C with a diameter of 5mm.

[0073] (2) Preparation of hydrogenation catalyst

[0074] Prepare a 5% mass concentration pyridine aqueous solution, pour 2000g of type A molecular sieve carrier into the solution according to equal volume, impregnate at 70°C, with a stirring speed of 1000 rpm for 2h, and dry the carrier at 150°C for 2h after impregnation to obtain a modified carrier. Weigh 600g CuCl2, add 2L deionized water to prepare an impregnation solution, take 1000g of the modified carrier and put it into the above impregnation solution, impregnate at 90°C, with a stirring speed of 100 rpm for 12h, filter the solid, dry it at 100°C for 24h, and then roast it at 600°C for 2h. Add 5% of the mass of graphite to the roasted solid, press and shape it, and obtain a hydrogenation catalyst C with a diameter of 5mm.

[0075] (3) The upper part of the fixed bed tubular reactor was loaded with imidization catalyst C, and the lower part was loaded with hydrogenation catalyst C. The reactor was activated with hydrogen at 500°C and 5 MPa absolute pressure for 6 h, with a hydrogen hourly velocity of 0.036 h -1 After activation, the mixture was mixed with TIPA: liquid ammonia: hydrogen = 1:3.14:4.93 and then entered the reactor. The reaction temperature was 200°C, the absolute pressure was 8MPa, and the TIPA space velocity was 0.68h -1 The reaction was carried out, and the obtained reaction mother liquid was distilled at 140° C. and an absolute pressure of 20 kPa for 1 hour to remove liquid ammonia, water and small molecular byproducts to obtain pure monoisopropanolamine. According to chromatographic analysis, the TIPA conversion rate in this embodiment was 99.2%, and the MIPA selectivity was 99.6%.

[0076] [Example 4]

[0077] (1) Preparation of imidization catalyst

[0078] Prepare a 1% mass concentration ZnCl2 ethanol solution, pour 2000g ZrO2 carrier into the solution according to equal volume, impregnate at 55℃, stir at 400 rpm for 4h, dry at 100℃ for 10h after impregnation to obtain a modified carrier. Weigh 262g RuCl3·3H2O and 20.88g anhydrous SnCl4, add 2.5L deionized water to prepare an impregnation solution, take 1500g catalyst precursor and put it into the impregnation solution, impregnate at 70℃, stir at 300 rpm for 6h, filter and dry the solid at 110℃ for 6h, and then calcine at 450℃ for 10h. Add 2% of the mass of graphite to the calcined solid, press and shape to obtain imidization catalyst D with a diameter of 5mm.

[0079] (2) Preparation of hydrogenation catalyst

[0080] Prepare a 3% mass concentration pyridine aqueous solution, pour 2000g of Y-type molecular sieve carrier into the solution according to equal volume, impregnate at 55°C, stir at 400 rpm for 4h, and dry the carrier at 100°C for 10h to obtain a modified carrier. Weigh 200g of CuCl2, add 2L of deionized water to prepare an impregnation solution, take 1000g of the modified carrier and put it into the above impregnation solution, impregnate at 70°C, stir at 300 rpm for 6h, filter and dry the solid at 110°C for 6h, and then calcine at 450°C for 10h. Add 2% of the mass of graphite to the calcined solid, press and shape it to obtain a hydrogenation catalyst D with a diameter of 3mm.

[0081] (3) The upper part of the fixed bed tubular reactor was loaded with imidization catalyst D, and the lower part was loaded with hydrogenation catalyst D. The reactor was activated with hydrogen at 350°C and 10 MPa absolute pressure for 18 h, with a hydrogen hourly velocity of 0.015 h -1 After activation, TIPA: liquid ammonia: hydrogen = 1:1.2:3 was mixed and then entered the reactor. The reaction temperature was 160°C, the absolute reaction pressure was 12MPa, and the TIPA space velocity was 0.34h -1 The reaction was carried out, and the obtained reaction mother liquid was distilled at 110° C. and an absolute pressure of 14 kPa for 2 h to remove liquid ammonia, water and small molecular byproducts to obtain pure monoisopropanolamine. According to chromatographic analysis, the TIPA conversion rate in this embodiment was 98.3%, and the MIPA selectivity was 99.1%.

[0082] [Example 5]

[0083] (1) Preparation of imidization catalyst

[0084] Prepare a 4% mass concentration AlCl3 ethanol solution, pour 2000g of γ-Al2O3 carrier into the solution according to equal volume, impregnate at 65℃, stir at 800 rpm for 8h, and dry the carrier at 140℃ for 4h after impregnation to obtain a modified carrier. Weigh 262g of RuCl3·3H2O and 7.83g of anhydrous SnCl4, add 1.25L of deionized water to prepare an impregnation solution, take 750g of the modified carrier and put it into the impregnation solution, impregnate at 80℃, stir at 600 rpm for 10h, filter and dry the solid at 140℃ for 16h, and then calcine at 550℃ for 6h. Add 4% of the mass of graphite to the calcined solid, press and shape it to obtain an imidization catalyst E with a diameter of 4mm.

[0085] (2) Preparation of hydrogenation catalyst

[0086] Prepare a 4% mass concentration pyridine aqueous solution, pour 2000g ZSM-5 molecular sieve carrier into the solution according to equal volume, impregnate at 65°C, stir at 800 rpm for 8h, and dry the carrier at 140°C for 4h after impregnation to obtain a modified carrier. Weigh 400g CuCl2, add 2L deionized water to prepare an impregnation solution, take 1000g modified carrier and put it into the above impregnation solution, impregnate at 80°C, stir at 600 rpm for 10h, filter and dry the solid at 140°C for 16h, and then calcine at 550°C for 6h. Add 4% of the mass of graphite to the calcined solid, press and shape it to obtain a hydrogenation catalyst E with a diameter of 4mm.

[0087] (3) The upper part of the fixed bed tubular reactor was loaded with imidization catalyst E, and the lower part was loaded with hydrogenation catalyst E. The reactor was activated with hydrogen at 450°C and 6 MPa absolute pressure for 12 h, with a hydrogen hourly velocity of 0.03 h -1 After activation, TIPA: liquid ammonia: hydrogen = 1:2.4:4.1 was mixed and then entered the reactor. The reaction temperature was 190°C, the absolute reaction pressure was 9MPa, and the TIPA space velocity was 0.51h -1 The reaction was carried out, and the obtained reaction mother liquid was distilled at 130° C. and an absolute pressure of 6 kPa for 5 hours to remove liquid ammonia, water and small molecular byproducts to obtain pure monoisopropanolamine. According to chromatographic analysis, the TIPA conversion rate in this embodiment was 98.5%, and the MIPA selectivity was 99.2%.

[0088] [Comparative Example 1]

[0089] Monoisopropanolamine was prepared in substantially the same manner as in Example 1, except that the support was not modified with Lewis acid AlCl3 during the preparation of the imidization catalyst.

[0090] According to chromatographic analysis, the conversion rate of TIPA in this comparative example is 85.4%, and the selectivity of MIPA is 92.5%.

[0091] [Comparative Example 2]

[0092] Monoisopropanolamine was prepared in substantially the same manner as in Example 1, except that anhydrous SnCl4 was not added during the preparation of the imidization catalyst.

[0093] According to chromatographic analysis, the conversion rate of TIPA in this comparative example was 88.7%, and the selectivity of MIPA was 95.1%.

[0094] [Comparative Example 3]

[0095] Monoisopropanolamine was prepared in substantially the same manner as in Example 1, except that the support was not modified with pyridine during the preparation of the hydrogenation catalyst.

[0096] According to chromatographic analysis, the conversion rate of TIPA in this comparative example was 91.5%, and the selectivity of MIPA was 94.2%.

[0097] [Comparative Example 4]

[0098] Monoisopropanolamine was prepared in a method substantially the same as that in Example 1, except that in step (3), the imidization catalyst A was loaded only in the upper half of the fixed bed tubular reactor, and no hydrogenation catalyst A was loaded.

[0099] According to chromatographic analysis, the conversion rate of TIPA in this comparative example is 80.3%, and the selectivity of MIPA is 22.5%. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the method of the present invention, several improvements and supplements can be made, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing monoisopropanolamine, characterized in that: The following steps are involved: An aqueous solution of triisopropanolamine is used as a raw material, mixed with liquid ammonia, and then introduced into a reactor filled with an imidization catalyst on the upper part and a hydrogenation catalyst on the lower part, and hydrogen is introduced at the same time for reaction to prepare monoisopropanolamine; The imidization catalyst is a supported catalyst with a Lewis acid-modified porous oxide as a carrier and metal Ru and Sn as active components; wherein the loading amount of metal Ru and Sn is 6-21% of the mass of the porous oxide, and the molar ratio of Ru to Sn is 1:(0.01-0.1); the Lewis acid is one or more of AlCl3, BF3, SbCl5, FeBr3, FeCl3, SnCl4, TiCl4, and ZnCl2; the porous oxide is one or more of γ-Al2O3, SiO2, TiO2, and ZrO2; the Lewis acid solution is impregnated in the porous oxide, and stirred at 50-70°C for 2-10h to obtain a Lewis acid-modified porous oxide carrier; The hydrogenation catalyst is a Cu-based catalyst with a pyridine-modified silica-alumina molecular sieve as a carrier, wherein the Cu loading is 4-30% of the mass of the silica-alumina molecular sieve; the silica-alumina molecular sieve is at least one of an A-type molecular sieve, an X-type molecular sieve, a Y-type molecular sieve, ZSM-5, and SAPO; a pyridine solution is impregnated into the silica-alumina molecular sieve, and stirred at 50-70° C. for 2-10 hours to obtain a pyridine-modified silica-alumina molecular sieve carrier.

2. The method for preparing monoisopropanolamine according to claim 1, characterized in that: The imidization catalyst is prepared by the following method: a1. Impregnating the Lewis acid solution into the porous oxide, stirring and treating at 50-70° C. for 2-10 hours to obtain a Lewis acid-modified porous oxide support; a2. Add the Lewis acid-modified porous oxide support to a mixed solution of ruthenium salt and tin salt, stir and treat at 60-90° C. for 2-12 hours, filter, dry, roast, and press into tablets to obtain an imidization catalyst.

3. The method for preparing monoisopropanolamine according to claim 2, characterized in that: In step a1, the mass concentration of the Lewis acid solution is 0.5-5%; the Lewis acid solution and the porous oxide are impregnated in equal volumes.

4. The method for preparing monoisopropanolamine according to claim 3, characterized in that: In step a1, the mass concentration of the Lewis acid solution is 1-3%.

5. The method for preparing monoisopropanolamine according to claim 2, characterized in that: The porous oxide has a specific surface area of ​​100-300m 2 / g, γ-Al2O3 with a pore volume of 0.2-3ml / g and a pore diameter of 2-20nm.

6. The method for preparing monoisopropanolamine according to claim 2, characterized in that: In step a2, the ratio of ruthenium salt to tin salt is 1:(0.01-0.1) based on the molar ratio of metal elements.

7. The method for preparing monoisopropanolamine according to claim 6, characterized in that: The added amount of ruthenium salt and tin salt is 6-21% of the mass of the porous oxide in the Lewis acid-modified carrier, calculated based on the total mass of metal ruthenium and tin.

8. The method for preparing monoisopropanolamine according to claim 6, characterized in that: In step a2, the calcination condition is 400-600° C. for 2-12 hours.

9. The method for preparing monoisopropanolamine according to claim 8, characterized in that: Before tableting in step a2, the solid obtained by calcination is mixed with graphite accounting for 1-5% of the solid mass.

10. The method for preparing monoisopropanolamine according to any one of claims 1 to 9, characterized in that: The hydrogenation catalyst is prepared by the following method: b1. Immerse the pyridine solution in the silicon-aluminum molecular sieve, and stir for 2-10 hours at 50-70° C. to obtain a modified carrier; b2. Add the modified carrier to the mixed solution of copper salt, stir and treat at 60-90° C. for 2-12 hours, filter, dry, roast, and press into tablets to obtain a hydrogenation catalyst.

11. The method for preparing monoisopropanolamine according to claim 10, characterized in that: In step b1, the mass concentration of the pyridine solution is 1-5%; the pyridine solution and the silica-alumina molecular sieve are impregnated in equal volumes.

12. The method for preparing monoisopropanolamine according to claim 11, characterized in that: In step b1, the mass concentration of the pyridine solution is 1.5-4.5%.

13. The method for preparing monoisopropanolamine according to claim 11, characterized in that: In step b2, the amount of copper salt added is 4-30% of the mass of the silica-alumina molecular sieve in the modified carrier, calculated on the basis of the mass of metal Cu.

14. The method for preparing monoisopropanolamine according to claim 13, characterized in that: In step b2, the calcination condition is 400-600° C. for 2-12 hours.

15. The method for preparing monoisopropanolamine according to claim 14, characterized in that: Before tableting in step b2, the solid obtained by calcination is mixed with graphite accounting for 1-5% of the solid mass.

16. The method for preparing monoisopropanolamine according to any one of claims 1 to 9, characterized in that: The mass ratio of triisopropanolamine, liquid ammonia and hydrogen is 1:(1.05-3.14):(2.46-4.93), the reaction temperature is 150-200°C; the absolute reaction pressure is 8-14MPa; the space velocity of triisopropanolamine is 0.17-0.68h -1 .

17. The method for preparing monoisopropanolamine according to claim 16, characterized in that: The mass ratio of triisopropanolamine, liquid ammonia and hydrogen is 1:(1.58-2.62):(3.08-4.31), the reaction temperature is 160-180°C; the absolute reaction pressure is 10-12MPa; the space velocity of triisopropanolamine is 0.34-0.51h -1 .

18. The method for preparing monoisopropanolamine according to claim 17, characterized in that: The imidization catalyst and the hydrogenation catalyst are both treated with hydrogen reduction activation before use.

19. The method for preparing monoisopropanolamine according to claim 16, characterized in that: After the reaction is completed, the reaction liquid is distilled and purified to obtain a monoisopropanolamine product.

20. The method for preparing monoisopropanolamine according to claim 19, characterized in that: The distillation conditions are: temperature 100-140°C, absolute pressure 2-20kPa, and residence time 1-6h.

21. The method for preparing monoisopropanolamine according to claim 20, characterized in that: The distillation conditions are: temperature 110-130°C, absolute pressure 6-12 kPa, and residence time 2-4 h.

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