A method for preparing propylene glycol monomethyl ether by catalytic liquid-phase oxidative alcoholysis of propylene using bifunctional TiSn-MFI molecular sieves.

Abstract

This invention belongs to the field of industrial catalysis and discloses a method for preparing propylene glycol monomethyl ether (PPD) by catalyzing the liquid-phase oxidative alcoholysis of propylene using a bifunctional TiSn-MFI molecular sieve. The steps are as follows: propylene, methanol, hydrogen peroxide aqueous solution, and catalyst are mixed and reacted in the same batch reactor to obtain PPD in one step. The catalyst is a bifunctional TiSn-MFI zeolite molecular sieve containing framework titanium and tin active sites. This synthesis method can catalyze the production of PPD from propylene using the same reactor and the same catalyst, shortening the reaction process of producing propylene oxide from propylene, followed by ring-opening alcoholysis of propylene oxide to obtain PPD, reducing energy consumption and reaction costs. Furthermore, the use of a bimetallic doped molecular sieve catalyst with two closely spaced active centers is beneficial for catalyzing a series of reactions. Compared with previous composite catalyst preparation methods, this method is simpler and has promising industrial applications. The synthesized TiSn-MFI catalyst does not contain non-framework titanium and tin species, has an irregular morphology of stacked crystals, and exhibits high hydrogen peroxide conversion and PPD selectivity.

Description

Technical Field

[0001] This invention belongs to the field of industrial catalysis and relates to a method for preparing propylene glycol monomethyl ether by catalyzing the liquid-phase oxidative alcoholysis of propylene using bifunctional TiSn-MFI molecular sieve. Background Technology

[0002] Propylene glycol monomethyl ether (PGME), also known as propylene glycol methyl ether, has the molecular formula C4H. 10 O2 has two isomers: 1-methoxy-2-propanol and 2-methoxy-1-propanol. Propylene glycol monomethyl ether is a colorless, transparent, flammable, and volatile liquid with a characteristic odor. It possesses two functional groups: a hydrophilic hydroxyl group and a lipophilic ether bond, giving it strong dissolving power, hence its reputation as a universal solvent. Propylene glycol monomethyl ether has similar solubility to other alcohol ethers such as ethylene glycol ethers. However, propylene glycol monomethyl ether can be converted into propylene glycol in vivo, and further into carbon dioxide and water. It has low toxicity, therefore, propylene glycol monomethyl ether has replaced other alcohol ethers and is widely used in coatings, pharmaceuticals, pesticides, printing, electronics manufacturing, and many other fields.

[0003] Currently reported synthetic routes for propylene glycol monomethyl ether include the acetal method, the Williamson method, the epoxide-based propylene oxide method, the propylene oxide alcoholysis method, and the propylene oxidative alcoholysis method. The first three methods have not been industrialized due to their complexity or high cost, while the propylene oxide alcoholysis method is currently the main industrial synthesis method. The most environmentally friendly production method for propylene oxide is the HPPO method using propylene as a raw material. Therefore, the one-pot method for preparing propylene glycol monomethyl ether through propylene epoxidation and ring-opening alcoholysis reduces the need for intermediate propylene oxide separation and purification, lowers energy consumption, and saves costs.

[0004] Patent USP6239315 discloses a method for producing propylene glycol ethers by combining titanium, vanadium, chromium, and tin-containing molecular sieves as epoxidizing agents with acidic resins or acidic molecular sieve solid alkylation catalysts. However, this synthesis method involves complex catalyst preparation, harsh synthesis conditions, and low selectivity of propylene glycol ethers, making industrial production impossible.

[0005] Patent CN1944365A discloses a one-step synthesis method for propylene glycol ethers from propylene. This method uses catalysts such as titanium silicate molecular sieves, titanium silicate molecular sieves with alkali, or titanium silicate molecular sieves with sodium (potassium) alkoxides to catalyze the synthesis of propylene glycol ethers. The propylene glycol monomethyl ether obtained by this method exhibits high selectivity. However, this method requires high reaction temperatures and pressures, particularly necessitating two separate reactors. The second reactor requires a temperature as high as 200°C and a pressure as high as 8.5 MPa.

[0006] Patent CN108002986B discloses a method for producing propylene glycol monomethyl ether from propylene. This method involves contacting propylene, methanol, hydrogen peroxide, and a catalyst under oxidative reaction conditions. The catalyst used is a composite catalyst of modified titanium silicate molecular sieve and polymetallic oxyacids and / or polymetallic oxysalts. This reaction achieves high propylene conversion and high selectivity for propylene glycol monomethyl ether. However, the catalyst preparation is complex, and the modification of the titanium silicate molecular sieve requires high-temperature treatment (up to 350°C) for a period of time in a modifying solution containing nitric acid and at least one peroxide.

[0007] The catalysts mentioned above generally require a combination of two catalysts to complete the catalytic effect of a series of reactions. However, the two active sites of the composite catalyst are far apart, which is not conducive to the progress of the series of reactions. Therefore, it is necessary to develop a bifunctional catalyst for the synthesis of propylene glycol monomethyl ether with a simpler synthesis method, for a method of highly selective preparation of propylene glycol monomethyl ether. Summary of the Invention

[0008] This invention provides a bifunctional catalyst for the synthesis of propylene glycol monomethyl ether from propylene, which has a relatively simple synthesis method, and a method for the highly selective preparation of propylene glycol monomethyl ether.

[0009] This invention provides a method for the liquid-phase production of propylene glycol monomethyl ether. The method is carried out in a batch reactor, where propylene, methanol, and hydrogen peroxide are brought into contact under certain reaction conditions and catalysis to produce propylene glycol monomethyl ether.

[0010] The technical solution of this invention:

[0011] A method for preparing propylene glycol monomethyl ether by catalytic liquid-phase oxidative alcoholysis of propylene using bifunctional TiSn-MFI molecular sieves involves mixing and reacting propylene, methanol, and hydrogen peroxide in a batch reactor under certain reaction conditions and with the catalysis of a catalyst to generate propylene glycol monomethyl ether.

[0012] The catalyst is a TiSn-MFI molecular sieve.

[0013] The concentrations of the hydrogen peroxide solution and the methanol solution are 0.5 mol / L to 3.0 mol / L, preferably 0.7 mol / L to 1.3 mol / L;

[0014] The molar ratio of hydrogen peroxide to methanol is 0.02-0.10, preferably 0.035-0.06.

[0015] The reaction temperature is 50℃-100℃, preferably 85℃-95℃; the reaction time is 1h-6h, preferably 3-5h; the reaction pressure is 0.2MPa-0.8MPa, preferably 0.5MPa-0.7MPa.

[0016] The preparation steps of the TiSn-MFI molecular sieve include:

[0017] (1) The silicon source, titanium source and tin source are respectively mixed with alkaline template agent and water for hydrolysis to obtain the corresponding silicon source, titanium source and tin source hydrolysate;

[0018] (2) After mixing the tin source hydrolysate and the titanium source hydrolysate, add them dropwise to the silicon source hydrolysate and stir to mix evenly. The molar ratio of the mixed gel is: 1SiO2:0.01-0.02TiO2:0.01-0.02SnO2:0.15-0.4TPAOH:25H2O;

[0019] (3) Under hydrothermal crystallization conditions, the mixed gel is transferred into a stainless steel high-pressure reactor with a polytetrafluoroethylene liner and crystallized at a temperature of 150-190℃ for 4-96 hours.

[0020] (4) After crystallization, the crystallization mixture is separated by centrifugation. The solid catalyst sample is washed until neutral and then dried in an oven at 110°C overnight. After calcination at 550°C for 6 hours, TiSn-MFI molecular sieve is obtained.

[0021] The alkaline template agent is one or a mixture of two or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, and tetrapropylammonium fluoride.

[0022] The silicon source is one or a mixture of two or more of tetraethyl orthosilicate, tetramethyl orthosilicate, tetrapropyl orthosilicate, or one or a mixture of two of silica sol and silica.

[0023] The tin source is an inorganic tin salt.

[0024] The titanium source is an organic titanium source.

[0025] The beneficial effects of this invention are as follows: The catalyst used in this invention is a bimetallic TiSn-MFI molecular sieve synthesized by hydrothermal method. This catalyst simultaneously possesses active centers for both the production of propylene oxide from propylene and the production of propylene glycol monomethyl ether from propylene oxide, eliminating the need for combining two catalysts and simplifying the synthesis method. Furthermore, the close proximity of the two active centers in this invention facilitates a series of reactions, resulting in high hydrogen peroxide conversion and high selectivity for the target product, propylene glycol monomethyl ether. Attached Figure Description

[0026] Figure 1 XRD patterns of Examples 1-2 of this invention;

[0027] Figure 2 UV-Vis patterns of Examples 1-2 of this invention;

[0028] Figure 3(a) is a SEM image of Preparation Example 1 (TiSn-MFI-1) of the present invention;

[0029] Figure 3(b) is a SEM image of preparation example 2 (TiSn-MFI-2) of the present invention;

[0030] Figure 4 This is a SEM image of a TiSn-MFI molecular sieve used to catalyze the production of propylene glycol monomethyl ether. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0032] In the following examples, the concentration change of hydrogen peroxide before and after the reaction was determined by iodometric titration. Gas chromatography was used to determine the composition of the reaction products, and the results were quantified using the internal standard method, with acetonitrile selected as the internal standard. The gas chromatography conditions were: PEG-20M (50m × 0.32mm × 0.5μm) column, column temperature 80℃ for 1 min, then increased to 160℃ at a rate of 10℃ / min and held for 4 min; FID detector 200℃; injector 220℃. The conversion rate of hydrogen peroxide and the selectivity of propylene oxide and propylene glycol monomethyl ether were calculated using the following formulas.

[0033] The conversion rate of hydrogen peroxide (%) = (molar amount of hydrogen peroxide in the feed - molar amount of hydrogen peroxide after the reaction) / molar amount of hydrogen peroxide in the feed × 100%.

[0034] Selectivity of propylene oxide (%) = molar amount of propylene oxide after reaction / (molar amount of propylene glycol monomethyl ether after reaction + molar amount of propylene oxide after reaction + molar amount of 1,2-propanediol after reaction) × 100%.

[0035] Selectivity of propylene glycol monomethyl ether (%) = molar amount of propylene glycol monomethyl ether after reaction / (molar amount of propylene glycol monomethyl ether after reaction + molar amount of propylene oxide after reaction + molar amount of 1,2-propanediol after reaction) × 100%.

[0036] Catalyst Example 1

[0037] 21.15 g of tetraethyl orthosilicate (TEOS) was added dropwise to a template agent solution containing 6.61 g of a 40 wt% tetrapropylammonium hydroxide (TPAOH) aqueous solution and 23.03 g of water. The mixture was stirred until homogeneous hydrolysis was achieved, yielding silicon-based hydrolysate A. 0.3517 g of SnCl₄·5H₂O was dissolved in a mixture of 11.17 g of water and 5.08 g of a 40 wt% TPAOH aqueous solution. The mixture was stirred until homogeneous hydrolysis was achieved, yielding tin-based hydrolysate B. 0.3563 g of tetrabutyl titanate (TBOT) was added dropwise to a 4.53 g hydrogen peroxide aqueous solution (30 wt%). After homogeneous mixing, 1.02 g of a 40 wt% TPAOH aqueous solution was added dropwise. The mixture was stirred until homogeneous hydrolysis was achieved, yielding titanium-based hydrolysate C. Hydrolysate B and C were mixed thoroughly and then added dropwise to hydrolysate A. The mixture was stirred until homogeneous and heated at 70-90°C to remove alcohol, yielding a mixed gel. The gel was transferred to a crystallization reactor and crystallized in an oven at 170°C for 48 hours. The crystallized product was cooled and washed until the filtrate was neutral, dried overnight at 110°C, and calcined in air at 550°C for 6 hours to obtain TiSn-MFI-1.

[0038] Catalyst Example 2

[0039] This embodiment uses the same method as Example 1, except that the amount of Ti source added is changed to 0.5209 g, the amount of tin source added is changed to 0.5312 g, the crystallization temperature is changed to 170 °C, and the crystallization time is changed to 24 h. TiSn-MFI-2 can then be obtained.

[0040] Catalyst Comparative Example 1

[0041] This preparation method is a comparative preparation of TS-1 molecular sieves. The specific preparation method is the same as that in the preparation method of Example 1, except that the addition of the tin source is removed.

[0042] Catalyst Comparative Example 2

[0043] This preparation method is a comparative preparation of Sn-MFI molecular sieves, specifically prepared by removing the addition of the titanium source from the method in Preparation Example 2.

[0044] Example 1

[0045] 0.4 g of TiSn-MFI-1 and 30 ml of 1.3 mol / L hydrogen peroxide methanol solution were added to a 300 ml high-pressure batch reactor. 1.237 g of acetonitrile was added as an internal standard. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 80 °C for 2 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0046] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 80.3%, the effective utilization rate of hydrogen peroxide was 91.6%, the selectivity of propylene oxide was 35.5%, and the selectivity of propylene glycol monomethyl ether was 55.6%.

[0047] Example 2

[0048] 0.4 g of TS-1, 30 ml of 1.3 mol / L hydrogen peroxide methanol solution, and 1.237 g of acetonitrile as an internal standard were added to a 300 ml high-pressure batch reactor. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 80 °C for 2 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0049] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 84.7%, the effective utilization rate of hydrogen peroxide was 92.8%, the selectivity of propylene oxide was 83.2%, and the selectivity of propylene glycol monomethyl ether was 13.9%.

[0050] Example 3

[0051] 0.4 g of Sn-MFI, 30 ml of 1.3 mol / L hydrogen peroxide methanol solution, and 1.237 g of acetonitrile as an internal standard were added to a 300 ml high-pressure batch reactor. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 80 °C for 2 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0052] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 9.7%, the effective utilization rate of hydrogen peroxide was 34.8%, the selectivity of propylene oxide was 54%, and the selectivity of propylene glycol monomethyl ether was 34.4%.

[0053] Example 4

[0054] 0.4 g of TiSn-MFI-2 and 30 ml of 1.3 mol / L hydrogen peroxide methanol solution were added to a 300 ml high-pressure batch reactor. 1.237 g of acetonitrile was added as an internal standard. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 80 °C for 2 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0055] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 83.2%, the effective utilization rate of hydrogen peroxide was 83.4%, the selectivity of propylene oxide was 28.9%, and the selectivity of propylene glycol monomethyl ether was 61.2%.

[0056] Example 5

[0057] 0.4 g of TiSn-MFI-2 molecular sieve and 30 ml of 1.3 mol / L hydrogen peroxide methanol solution were added to a 300 ml high-pressure batch reactor, along with 1.237 g of acetonitrile as an internal standard. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 60 °C for 2 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0058] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 64.2%, the effective utilization rate of hydrogen peroxide was 85.2%, the selectivity of propylene oxide was 52.1%, and the selectivity of propylene glycol monomethyl ether was 42.2%.

[0059] Example 6

[0060] 0.4 g of TiSn-MFI-2 molecular sieve and 30 ml of 1.3 mol / L hydrogen peroxide methanol solution were added to a 300 ml high-pressure batch reactor, along with 1.237 g of acetonitrile as an internal standard. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 90 °C for 2 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0061] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 84.7%, the effective utilization rate of hydrogen peroxide was 80.8%, the selectivity of propylene oxide was 22.6%, and the selectivity of propylene glycol monomethyl ether was 65.8%.

[0062] Example 7

[0063] 0.4 g of TiSn-MFI-2 molecular sieve and 30 ml of 1.3 mol / L hydrogen peroxide methanol solution were added to a 300 ml high-pressure batch reactor. 1.237 g of acetonitrile was added as an internal standard. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 90 °C for 4 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0064] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 96.3%, the effective utilization rate of hydrogen peroxide was 80.5%, the selectivity of propylene oxide was 4.8%, and the selectivity of propylene glycol monomethyl ether was 80.0%.

[0065] Example 8

[0066] 0.4 g of TiSn-MFI-2 molecular sieve and 30 ml of 1.3 mol / L hydrogen peroxide methanol solution were added to a 300 ml high-pressure batch reactor. 1.237 g of acetonitrile was added as an internal standard. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 90 °C for 4 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0067] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 96.3%, the effective utilization rate of hydrogen peroxide was 80.5%, the selectivity of propylene oxide was 4.8%, and the selectivity of propylene glycol monomethyl ether was 80.0%.

[0068] Example 9

[0069] 0.4 g of TiSn-MFI-2 molecular sieve and 30 ml of 1.0 mol / L hydrogen peroxide methanol solution were added to a 300 ml high-pressure batch reactor, along with 1.237 g of acetonitrile as an internal standard. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 90 °C for 4 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0070] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 98.0%, the effective utilization rate of hydrogen peroxide was 82.4%, the selectivity of propylene oxide was 5.3%, and the selectivity of propylene glycol monomethyl ether was 79.8%.

[0071] Example 10

[0072] 0.2 g of TiSn-MFI-2 molecular sieve and 30 ml of 1.0 mol / L hydrogen peroxide methanol solution were added to a 300 ml high-pressure batch reactor, along with 1.237 g of acetonitrile as an internal standard. The reactor was checked for leaks and the air inside was purged with high-purity nitrogen. Propylene was introduced into the high-pressure reactor at 0.6 MPa, and the reaction was stirred at 90 °C for 4 h. After the reaction was complete, the reactor was cooled with circulating cooling water, and the reaction mixture was separated by centrifugation. The supernatant was analyzed by gas chromatography, and the concentration of hydrogen peroxide was determined by iodometric titration.

[0073] Under the above reaction conditions, the conversion rate of hydrogen peroxide was 96.2%, the effective utilization rate of hydrogen peroxide was 85.4%, the selectivity of propylene oxide was 17.9%, and the selectivity of propylene glycol monomethyl ether was 72.0%.

Claims

1. A method for preparing propylene glycol monomethyl ether by catalytic liquid-phase oxidative alcoholysis of propylene using bifunctional TiSn-MFI molecular sieve, characterized in that, In a batch reactor, under certain reaction conditions and with the catalysis of a catalyst, propylene, methanol, and hydrogen peroxide are mixed and reacted to produce propylene glycol monomethyl ether. The catalyst is a TiSn-MFI molecular sieve; The molar ratio of hydrogen peroxide to methanol is 0.02-0.10; The reaction temperature is 50℃-100℃; the reaction time is 1h-6h; the reaction pressure is 0.2MPa-0.8MPa. The preparation steps of the TiSn-MFI molecular sieve include: (1) The silicon source, titanium source and tin source are respectively mixed with alkaline template agent and water for hydrolysis to obtain the corresponding silicon source, titanium source and tin source hydrolysate; (2) After mixing the tin source hydrolysate and the titanium source hydrolysate, add them dropwise to the silicon source hydrolysate and stir to mix evenly. The molar ratio of the mixed gel is: 1SiO2: 0.01-0.02TiO2: 0.01-0.02SnO2: 0.15-0.4TPAOH: 25H2O; (3) Under hydrothermal crystallization conditions, the mixed gel was transferred into a stainless steel high-pressure reactor with a polytetrafluoroethylene liner and crystallized at a temperature of 150-190℃ for 4-96 h. (4) After crystallization, the crystallization mixture is separated by centrifugation. The solid catalyst sample is washed until neutral and then dried in an oven at 110°C overnight. After calcination at 550°C for 6 hours, TiSn-MFI molecular sieve is obtained.

2. The method for preparing propylene glycol monomethyl ether by catalytic liquid-phase oxidative alcoholysis of propylene using TiSn-MFI molecular sieve according to claim 1, characterized in that, The silicon source is one or a mixture of two or more of tetraethyl orthosilicate, tetramethyl orthosilicate, tetrapropyl orthosilicate, or one or a mixture of two of silica sol and silica.

3. The method for preparing propylene glycol monomethyl ether by catalytic liquid-phase oxidative alcoholysis of propylene using TiSn-MFI molecular sieve according to claim 1, characterized in that, The tin source is an inorganic tin salt.

4. The method for preparing propylene glycol monomethyl ether by catalytic liquid-phase oxidative alcoholysis of propylene using TiSn-MFI molecular sieve according to claim 1, characterized in that, The titanium source mentioned is an organic titanium source.

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