Preparation method and application of micron-sized Au / TS-1 catalyst for gas-phase propylene epoxidation reaction in hydrogen-oxygen system

Abstract

The invention belongs to the field of petrochemical catalysis technology, discloses a preparation method and application of a micron-sized Au / TS-1 catalyst for propylene gas phase epoxidation reaction under a hydrogen-oxygen system, and applies it to propylene gas phase epoxidation reaction under a hydrogen-oxygen system. Micron-sized TS-1 is synthesized by spray drying assisted hydrothermal method, and gold is loaded on the TS-1 carrier by deposition precipitation method. This method solves the problem that the TS-1 carrier prepared by the classical hydrothermal synthesis method is not easy to separate, and has a high degree of crystallinity and skeleton titanium content. The obtained micron-sized Au / TS-1 catalyst shows good catalytic performance and stability in propylene gas phase epoxidation reaction, and the propylene oxide generation rate is better than the small-grain Au / TS-1 catalyst synthesized by the classical hydrothermal method, and has industrial application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical catalysis, and in particular relates to a method for preparing a micron-sized Au / TS-1 catalyst for propylene gas phase epoxidation reaction, in particular to a catalyst for propylene gas phase epoxidation reaction under hydrogen and oxygen system conditions. Background Art

[0002] Propylene oxide (PO) is an important chemical raw material for the production of polyether polyols, propylene glycol, dimethyl carbonate and other substances, and the market demand is huge. In 1998, the Haruta research group (Research on chemical intermediates, 1998, 24.3: 329-336.) first reported the gas-phase epoxidation of propylene by co-feeding hydrogen, oxygen and propylene under the Au-Ti based catalyst system. The epoxidation process has high atomic utilization rate and the main by-product is water, which is a green catalytic process.

[0003] Titanium silicate molecular sieve (TS-1) is widely used as a catalyst carrier in the gas-phase epoxidation reaction of propylene. Currently, the preparation of TS-1 mainly adopts the hydrothermal crystallization method. After the crystallization is completed, the product is separated, washed, dried and calcined to obtain the target product TS-1 molecular sieve. The size of TS-1 molecular sieve prepared in the classical hydrothermal synthesis system is mainly concentrated in 200-500nm. Therefore, the current public literature and patents mainly focus on the modification, reduction method and feed composition of small-grain Au / TS-1.

[0004] For example, Huang Jiahui et al.'s patent (CN109928942A) discloses the use of two alkaline metal (Li, Cs, Na and Rb) salts (carbonates, nitrates, sulfates, phosphates) mixed as precipitants to prepare a gold catalyst modified with a bimetallic additive, thereby improving the performance of the catalyst. Patent (CN109926098A) uses alkaline gas to modify the loaded Au / TS-1 catalyst, and the production rate of propylene oxide is greatly improved after the modification. Patent (CN107961814A) discloses the use of raw materials propylene, oxygen and hydrogen as catalysts for pretreatment, and then propylene epoxidation reaction is carried out under normal pressure. The catalyst reduced by this method shows very good activity in the propylene epoxidation reaction, and the generation rate of propylene oxide is also greatly improved. Patent (CN112871205A) discloses that defective site additives (such as soluble starch, polyacrylamide, etc.) and S-containing additives (such as sodium sulfite, potassium bisulfite, etc.) are added during the preparation of the catalyst, and a titanium-rich catalyst having a large number of defective sites suitable for Au loading is obtained. At the same time, the amorphous titanium species on the catalyst is stabilized by the S species, thereby obtaining a highly active propylene gas phase epoxidation catalyst. The alkali metal ions introduced simultaneously with the S additive can reduce the selectivity of by-products, greatly improve the conversion rate of propylene, the selectivity of PO, and the hydrogen efficiency. Chen Xiaohui et al. disclosed Ga and Fe-modified Au / TS-1 catalysts in patents (CN109529927A, CN109569716A), respectively, which improved the performance of the catalyst to varying degrees. Patent (CN113368895A) discloses the modification of Au / TS-1 by biomass activator and ammonium salt, which can better anchor gold atoms during the modification preparation process, improve the capture rate of gold and increase the number of effective gold sites, so that the production rate of propylene oxide is increased by 15 times. Patent (CN113912571A) of Zhao Chenyang et al. discloses the introduction of a small amount of propane into the feed gas, which significantly prolongs the service life of the catalyst in the propylene epoxidation reaction, and also improves the reaction selectivity and propylene conversion rate.

[0005] Public literature (Journal of Materials Chemistry A 6.20(2018):9473-9479.) reports that smaller crystal size is conducive to the catalyst exposing more active sites and better diffusion performance. Public literature (Chemical Engineering Science 227(2020):115907.) reports that small-sized TS-1 improves PO generation rate, selectivity, and hydrogen efficiency ratio due to the synergistic effect of Au-Ti. As a carrier of Au / TS-1 catalyst, in order to obtain more reactive active sites and shorten the diffusion distance of organic matter in the catalyst and improve the reaction performance of the catalyst, researchers have made a lot of attempts to synthesize small-sized TS-1. Public literature has shown that the crystal size can be further reduced by increasing the amount of organic template (Nanoscale., 2013, 5, 6693-6703.), solid conversion method (Micropor. Mesopor. Mater., 2015, 217, 96-101.), using organosilane as a silicon source (Mater. Lett., 2012, 68, 1-3.), introducing seed crystals to shorten the crystal synthesis time (patent CN109250726A) and other strategies.

[0006] From the perspective of the carrier, small-grain TS-1 is not conducive to solid-liquid separation, and membrane filtration is generally used in industry. In order to solve the problem of low separation efficiency, people often use methods such as adding ammonium salts, alkalis, or mixtures of alkalis and salts to the molecular sieve slurry to promote molecular sieve flocculation and improve filtration efficiency, but at the same time, other heteroatoms are also introduced, affecting the catalytic performance of the molecular sieve. Due to the low separation efficiency of centrifugal separation technology, it is generally only suitable for small-scale separation in the laboratory. Compared with small-grain TS-1, the separation method of micron-sized TS-1 is relatively simple. At present, several large domestic companies generally use plate and frame filtration methods, which are more efficient and quick in the solid-liquid separation link. Therefore, the synthesis of Au / TS-1 catalysts with easy-to-separate carriers and good catalytic performance can simplify the synthesis steps and reduce energy consumption, which is of great significance for the application of this catalyst. Summary of the invention

[0007] The present invention relates to a method for preparing an Au / TS-1 catalyst suitable for gas-phase epoxidation of propylene in a hydrogen-oxygen system. Spray drying-assisted hydrothermal synthesis of molecular sieve technology is adopted, and a TS-1 carrier with a micron size of (2-5um) is prepared by adjusting the molar ratio of H2O:SiO2 in a hydrothermal crystallization system at a low template dosage (TPAOH:SiO2 molar ratio is 0.05). The product is easy to separate solid from liquid, and has a high crystallinity and good titanium distribution. The micron-sized Au / TS-1 catalyst prepared by the gold deposition precipitation method exhibits good catalytic performance and stability in the gas-phase epoxidation of propylene, and has potential industrial application prospects.

[0008] The technical solution of the present invention:

[0009] A method for preparing a micron-sized Au / TS-1 catalyst for gas-phase epoxidation of propylene in a hydrogen-oxygen system, the method comprising the following steps:

[0010] (1) A titanium source is dropped into hydrochloric acid, and then deionized water is added and stirred until the solution is clear; then a silicon source is added and stirred for 30 minutes to obtain a clear solution, wherein the molar ratio of each component is: SiO2: TiO2: H2O: HCl = 1: 0.0167-0.0333: 20: 0.067; the obtained solution is sprayed by a spray drying device, and after drying, a titanium silicon amorphous powder A is obtained; the conditions of the spray drying device are: a vaporization chamber temperature of 180-300°C, a peristaltic pump feed rate of 7-20 mL min -1 , fan frequency 80Hz;

[0011] (2) Add 25wt% or 40wt% template aqueous solution and deionized water to titanium silicon amorphous powder A, stir to make the titanium silicon amorphous powder A completely immersed in the template aqueous solution, and the molar ratio of the components of the final mixture is: SiO2:TiO2:template:H2O=1:(0.01-0.033):(0.05-0.2):(0.85-3.4);

[0012] (3) placing the mixture obtained in step (2) into a stainless steel crystallization kettle lined with polytetrafluoroethylene, and then placing it into a rotary oven for rolling or static crystallization at a temperature of 130°C-210°C. After 24-72 hours of crystallization, washing with deionized water until neutral, drying at 90-110°C, and finally calcining at 450-650°C for 10 hours to remove the template, thereby obtaining a TS-1 molecular sieve;

[0013] (4) Take the concentration as 7.6x10 -3mol / L chloroauric acid aqueous solution, add the TS-1 molecular sieve carrier obtained in step (3), the mass ratio of TS-1 molecular sieve carrier to chloroauric acid is (9-10):1, and adjust the pH value of the system to between 7.9 and 8.0 with 1M and 0.1M Na2CO3 solutions respectively. After stirring at 35°C for 6h, filter and wash, and then dry under vacuum at 35°C for 10h. The obtained product is pressed into tablets and sieved with 20-40 mesh, and reduced at 300°C in a mixed atmosphere of hydrogen, propylene and nitrogen with a volume ratio of 1:1:7 for 2h to obtain Au / TS-1 catalyst.

[0014] Furthermore, in step (1), the stirring temperature is 25-40° C. and the stirring time is 2-12 h; and in step (2), the stirring temperature is room temperature.

[0015] Furthermore, in step (1), the silicon source is one or a mixture of two or more of tetraethyl orthosilicate, tetramethyl orthosilicate, tetrapropyl orthosilicate and tetrabutyl orthosilicate, or one or a mixture of two of silica sol and white carbon black.

[0016] Furthermore, in step (2), the template is one or a mixture of two or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, and tetrapropylammonium fluoride.

[0017] Furthermore, the silicon-titanium molar ratio of the titanium silicon molecular sieve is 30-100; the skeleton titanium content is 1.3-4.2wt%; the molar ratio of the substances in the silicon-titanium amorphous powder A in step (2) is SiO2:TiO2:template:H2O=1:0.0167-0.0333:0.05:0.85-3.4.

[0018] Furthermore, in step (3), the calcination atmosphere is one or a mixture of two or more gases selected from the group consisting of air, nitrogen, argon, helium and ammonia.

[0019] The catalyst prepared by the above method is used in the gas phase epoxidation of propylene to produce propylene oxide in a hydrogen-oxygen system. The reaction is carried out in a fixed bed reactor at normal pressure, the reaction temperature is 80-300°C, the volume ratio of the reaction gas composition is C3H6 / H2 / O2 / N2=1 / 1 / 1 / 7, and the space velocity is 4000-20000mL·h -1 Kg -1 cat.

[0020] The beneficial effects of the present invention are as follows: the micron-sized TS-1 carrier solves the problem that TS-1 synthesized by the classical hydrothermal method is not easy to separate, and has a high crystallinity ( Figure 2 ) and skeleton titanium content ( Figure 3 The Au / TS-1 catalyst showed good catalytic performance and stability in the gas-phase epoxidation of propylene ( Figure 4), propylene oxide generation rate (213.4g PO Kg cat· -1 ·h -1 ) is superior to the Au / TS-1 catalyst (138.1 g) synthesized by the classical hydrothermal method. PO Kg cat· -1 ·h -1 ), which has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1( a) is a SEM image of a carrier of Example 3 of the present invention;

[0022] FIG1( b) is a SEM image of the carrier of Example 2 of the present invention;

[0023] FIG1( c ) is a SEM image of the carrier of Example 1 of the present invention;

[0024] FIG1( d ) is a particle size distribution diagram of the carrier of Example 3 of the present invention;

[0025] FIG1( e ) is a particle size distribution diagram of the carrier of Example 2 of the present invention;

[0026] FIG1( f) is a particle size distribution diagram of the carrier of Example 1 of the present invention;

[0027] Figure 2 XRD diagram of the carrier of Example 1-3 of the present invention;

[0028] Figure 3 The UV-Vis images of the carriers of Examples 1 to 3 of the present invention and the carrier of Comparative Example 1;

[0029] Figure 4 This is a graph showing the change in PO generation rate over time for the catalysts of Examples 1-3 of the present invention and the catalyst of Comparative Example 1. DETAILED DESCRIPTION

[0030] Example 1

[0031] 4.26 g of tetrabutyl titanate (TBOT) was added dropwise to 5 g of hydrochloric acid (12 mol / L), and after sufficient stirring, 270 g of water was added. After stirring in a water bath for 10-15 min, 156.3 g of tetraethyl orthosilicate (TEOS) was added, and stirring was continued for 2 h to obtain a solution A with Si / Ti=60.

[0032] The prepared solution A was spray dried at 220°C using an aerosol spray device to obtain an amorphous precursor powder of titanium silicon with a Si / Ti ratio of 60, denoted as A1. Weigh 15g of the precursor powder A, add 3.4g of a 25wt.% tetrapropylammonium hydroxide (TPAOH) aqueous solution, add 2.55g of water, stir evenly, put into a reactor, and roll crystallize at 170°C for 48h. The crystallized product was cooled and washed until the filtrate was neutral, dried at 110°C overnight, and calcined at 550°C in air atmosphere for 10h to obtain a TS-1(60)-3.4 carrier with an average size of about 2976nm, as shown in Figures 1(c) and (f).

[0033] Take 5 mL of 0.04867 mol / L chloroauric acid aqueous solution, add 27 mL of deionized water to dilute, add 0.8 g of the TS-1 molecular sieve carrier obtained above, adjust the pH value of the system to between 7.9 and 8.0 with 1 M and 0.1 M Na2CO3 solutions respectively, stir at 35°C for 6 hours, filter and wash, and then dry at 35°C under vacuum for about 10 hours. The obtained product is pressed into tablets and sieved with 20-40 mesh. Take 0.15 g and reduce it in a hydrogen, propylene and nitrogen atmosphere at 300°C for 2 hours to obtain Au / TS-1(60)-2976nm catalyst.

[0034] Example 2

[0035] 4.26 g of tetrabutyl titanate (TBOT) was added dropwise to 5 g of hydrochloric acid (12 mol / L), and after sufficient stirring, 270 g of water was added. After stirring in a water bath for 10-15 min, 156.3 g of tetraethyl orthosilicate (TEOS) was added, and stirring was continued for 2 h to obtain a solution A with Si / Ti=60.

[0036] The prepared solution A was spray dried at 220°C using an aerosol spray device to obtain an amorphous precursor powder of titanium silicon with a Si / Ti ratio of 60, denoted as A1. Weigh 5 g of the precursor powder A1, add 3.4 g of a 25 wt.% tetrapropylammonium hydroxide (TPAOH) aqueous solution, stir evenly, put into a reactor, and roll crystallize at 170°C for 48 hours. The crystallized product was cooled and washed until the filtrate was neutral, dried at 110°C overnight, and calcined at 550°C in air atmosphere for 10 hours to obtain a TS-1(60)-1.7 carrier with an average size of about 802 nm, as shown in Figures 1(b) and (e).

[0037] Take 5 mL of 0.04867 mol / L chloroauric acid aqueous solution, add 27 mL of deionized water to dilute, add 0.8 g of the TS-1 molecular sieve carrier obtained above, adjust the pH value of the system to between 7.9 and 8.0 with 1 M and 0.1 M Na2CO3 solutions respectively, stir at 35°C for 6 hours, filter and wash, and then dry at 35°C under vacuum for about 10 hours. The obtained product is pressed into tablets and sieved with 20-40 mesh. Take 0.15 g and reduce it in a hydrogen, propylene and nitrogen atmosphere at 300°C for 2 hours to obtain Au / TS-1(60)-1.7 catalyst.

[0038] Example 3

[0039] 4.26 g of tetrabutyl titanate (TBOT) was added dropwise to 5 g of hydrochloric acid (12 mol / L), and after sufficient stirring, 270 g of water was added. After stirring in a water bath for 10-15 min, 156.3 g of tetraethyl orthosilicate (TEOS) was added, and stirring was continued for 2 h to obtain a solution A with Si / Ti=60.

[0040] The prepared solution A was spray dried at 220°C using an aerosol spray device to obtain an amorphous precursor powder of titanium silicon with a Si / Ti ratio of 60, denoted as A1. Weigh 5 g of the precursor powder A1, add 3.4 g of a 40 wt.% tetrapropylammonium hydroxide (TPAOH) aqueous solution, stir evenly, put into a reactor, and roll crystallize at 170°C for 48 hours. The crystallized product was cooled and washed until the filtrate was neutral, dried at 110°C overnight, and calcined at 550°C in air atmosphere for 10 hours to obtain a TS-1(60)-0.85 carrier with an average size of about 277 nm, as shown in Figures 1(a) and (d).

[0041] Take 5 mL of 0.04867 mol / L chloroauric acid aqueous solution, add 27 mL of deionized water to dilute, add 0.8 g of the TS-1 molecular sieve carrier obtained above, adjust the pH value of the system to between 7.9 and 8.0 with 1 M and 0.1 M Na2CO3 solutions respectively, stir at 35°C for 6 hours, filter and wash, and then dry at 35°C under vacuum for about 10 hours. The obtained product is pressed into tablets and sieved with 20-40 mesh. Take 0.15 g and reduce it in a hydrogen, propylene and nitrogen atmosphere at 300°C for 2 hours to obtain Au / TS-1(60)-0.85 catalyst.

[0042] Comparative Example 1

[0043] 2g of Tween 20 and 32g of deionized water were stirred and mixed in a three-necked flask at 40°C, 18.8g of 40wt.% TPAOH aqueous solution was added and stirred for a while at 40°C, and then 35.6g of TEOS was added and stirred thoroughly at 40°C for hydrolysis.

[0044] 0.97 g of tetrabutyl titanate was dissolved in 7.15 g of isopropanol and mixed evenly to obtain a titanium-containing solution. The titanium-containing solution was added dropwise into the silica sol. After the addition was completed, the temperature was raised to 80°C. The stopper of the three-necked flask was opened and the alcohol was removed by stirring at 80°C for 1 hour. Finally, the obtained solution was charged into a crystallization kettle and crystallized at 170°C for 48 hours. The crystallized product was washed by centrifugation until the filtrate was neutral, dried at 110°C overnight, and calcined in air at 550°C for 10 hours to obtain the TS-1(60)-N carrier.

[0045] Take 5 mL of 0.04867 mol / L chloroauric acid aqueous solution, add 27 mL of deionized water to dilute, add 0.8 g of the TS-1 molecular sieve carrier obtained above, adjust the pH value of the system to between 7.9 and 8.0 with 1 M and 0.1 M Na2CO3 solutions respectively, stir at 35°C for 6 hours, filter and wash, and then dry at 35°C under vacuum for about 10 hours. The obtained product is pressed into tablets and sieved with 20-40 mesh. Take 0.15 g and reduce it in a hydrogen, propylene and nitrogen atmosphere at 300°C for 2 hours to obtain Au / TS-1(60)-N catalyst.

[0046] Table 1 shows the product distribution and PO generation rate at 20h of the catalysts of Examples 1-3 of the present invention and the catalyst of Comparative Example 1.

[0047]

[0048] Reaction conditions: C3H6 / O2 / H2 / N2=1 / 1 / 1 / 7 (volume ratio), reaction temperature: 160°C, reaction pressure: 0.1 MPa, space velocity: 14000 mL h -1 g cat -1 All data are taken from the 20th hour after the reaction runs smoothly.

Claims

1. A method for preparing a micron-sized Au / TS-1 catalyst for gas-phase epoxidation of propylene in a hydrogen-oxygen system, characterized in that: 4.26 g of tetrabutyl titanate was added dropwise to 5 g of 12 mol / L hydrochloric acid, and 270 g of water was added after sufficient stirring. After stirring in a water bath for 10-15 min, 156.3 g of ethyl orthosilicate was added, and stirring was continued for 2 h to obtain a solution A with Si / Ti=60. The prepared solution A was spray dried at 220°C using an aerosol spray device to obtain a titanium silicon amorphous precursor powder with a Si / Ti ratio of 60, which was recorded as A1; 15 g of the precursor powder A was weighed, 3.4 g of a 25 wt.% tetrapropylammonium hydroxide aqueous solution was added, 2.55 g of water was added, and the mixture was stirred evenly. The mixture was placed in a reactor and rolled for crystallization at 170°C for 48 h; the crystallized product was cooled and washed until the filtrate was neutral, dried at 110°C overnight, and calcined at 550°C in an air atmosphere for 10 h to obtain the TS-1 carrier; Take 5 mL of 0.04867 mol / L chloroauric acid aqueous solution, add 27 mL of deionized water to dilute, add 0.8 g of the TS-1 molecular sieve carrier obtained above, adjust the pH value of the system to between 7.9 and 8.0 with 1 M and 0.1 M Na2CO3 solutions respectively, stir at 35°C for 6 hours, filter and wash, and then dry under vacuum at 35°C for 10 hours. The obtained product is pressed into tablets and sieved with 20-40 mesh. Take 0.15 g and reduce it in a mixed atmosphere of hydrogen, propylene and nitrogen at 300°C for 2 hours to obtain Au / TS-1 catalyst.

2. Use of the catalyst prepared by the preparation method according to claim 1 in gas phase epoxidation of propylene to produce propylene oxide in a hydrogen-oxygen system, characterized in that: The reaction was carried out in a fixed bed reactor at normal pressure, with a reaction temperature of 160°C, a reaction pressure of 0.1 MPa, a reaction gas composition volume ratio of C3H6 / H2 / O2 / N2=1 / 1 / 1 / 7, and a space velocity of 14000 mL·h -1 ·g -1 cat.

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