Composite lithium phosphate catalyst, preparation method and application thereof, and method for preparing allyl alcohol

Abstract

The invention relates to the technical field of catalysis, and provides a composite lithium phosphate catalyst, a preparation method and application thereof, and a method for preparing allyl alcohol. The composite lithium phosphate catalyst provided by the invention comprises a silicon dioxide carrier, a lithium phosphate crystal loaded in the silicon dioxide carrier and copper oxide doped in the lithium phosphate crystal. The carrier and ethyl silicate are added in the lithium phosphate crystallization process, so that the specific surface area and roughness of the catalyst can be improved, and the catalytic activity is improved; by introducing copper oxide, the carbon deposition resistance of the catalyst can be improved, and the service life is prolonged. According to the invention, the catalyst slurry is purged before the reaction, so that the generation of n-propanol can be effectively reduced, and the selectivity of the reaction is improved. Results of the embodiment show that when the method is used for preparing allyl alcohol, the selectivity can reach 95% or above, and the service life of the catalyst exceeds 600h.

Description

Technical Field

[0001] The present invention relates to the field of catalytic technology, and in particular, to a composite lithium phosphate catalyst, a preparation method and an application thereof, and a method for preparing allyl alcohol. Background Art

[0002] Allyl alcohol, also known as propenol and garlic alcohol, is an important fine chemical intermediate. Due to the presence of two functional groups, a double bond and a hydroxyl group, in its molecular structure, its chemical properties are very active and it can participate in chemical reactions such as oxidation, reduction, esterification, etherification, and addition. Allyl alcohol and its derivatives, as basic chemical raw materials, can be used to synthesize many important downstream products and have very wide applications in pharmaceuticals, fragrances, and other organic syntheses.

[0003] At present, there are many methods for preparing allyl alcohol. Among them, the isomerization of propylene oxide is a simple process with advantages such as high atom economy, high yield, no corrosion, and no three wastes. However, this method has two obvious problems: First, the selectivity of the reaction is relatively low. When propylene oxide is isomerized to allyl alcohol, a part of propionaldehyde, acetone, and n-propanol will be produced. The boiling point of n-propanol (97.2 °C) is less than 1 °C different from the boiling point of allyl alcohol (96.9 °C), making the post-treatment difficult. Second, during the isomerization process, due to factors such as carbon deposition poisoning and different physical and chemical conditions, the activity of the catalyst is easily reduced with the increase of the use time, resulting in catalyst deactivation. For example, in the related art, allyl alcohol is prepared by a liquid-phase method, and the catalyst used is fine powder lithium phosphate, which is dissolved in a high-boiling solvent, and the reaction temperature is about 280 °C. The selectivity of this method is less than 90%, and the loss of the high-boiling solvent and the catalyst is very serious, and the single-pass life of the catalyst is less than 200 h.

[0004] In summary, how to improve the selectivity of propylene oxide isomerization and the service life of the catalyst is an urgent problem to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a composite lithium phosphate catalyst, a preparation method and an application thereof, and a method for preparing allyl alcohol. The composite lithium phosphate catalyst prepared by the present invention has high catalytic activity and long service life. When it is applied to the isomerization of propylene oxide to prepare allyl alcohol, it can improve the selectivity of the reaction and realize the large-scale continuous production of allyl alcohol.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions: A preparation method of a composite lithium phosphate catalyst, comprising the following steps: Mix a phosphoric acid aqueous solution and a catalyst carrier to obtain a phosphoric acid-carrier mixed solution; the catalyst carrier is silica; the mass of the catalyst carrier is 1.1 to 1.5 times the mass of phosphoric acid in the phosphoric acid aqueous solution; Mix lithium hydroxide solution and lithium phosphate seeds to obtain a lithium hydroxide-seed mixture liquid. Mix the lithium hydroxide-seed mixture liquid, tetraethyl orthosilicate alcohol solution, copper oxide, and phosphoric acid-carrier mixture liquid for crystallization to obtain a crystallization liquid; age the crystallization liquid to obtain a catalyst precursor; the temperature of the crystallization is 60-80 °C, and the final pH value is 12-12.5. Dry the catalyst precursor and then calcine it to obtain a composite lithium phosphate catalyst.

[0007] Preferably, the concentration of the phosphoric acid aqueous solution is 40-50 wt%; the mass of the catalyst carrier is 1.1-1.5 times the mass of phosphoric acid in the phosphoric acid aqueous solution; the average particle size of the lithium phosphate seeds is 0.4-0.8 μm.

[0008] Preferably, the concentration of the lithium hydroxide solution is 5-12.4 wt%; the molar ratio of lithium hydroxide in the lithium hydroxide solution to phosphoric acid in the phosphoric acid aqueous solution is 3-3.5:1. The dosage ratio of lithium hydroxide in the lithium hydroxide solution to lithium phosphate seeds is (3-3.5) mol:(0.2-5) g. The concentration of the tetraethyl orthosilicate alcohol solution is 10-30 wt%, and the molar ratio of tetraethyl orthosilicate in the tetraethyl orthosilicate alcohol solution to phosphoric acid in the phosphoric acid aqueous solution is 0.01-0.1:1. The particle size of the copper oxide is 5-10 μm, and the mass ratio of copper oxide to phosphoric acid in the phosphoric acid aqueous solution is 0.1-0.5:1.

[0009] Preferably, the crystallization includes: at 60-80 °C, simultaneously dropwise add the tetraethyl orthosilicate alcohol solution and a part of the lithium hydroxide-seed mixture liquid into the phosphoric acid-carrier mixture liquid, after the dropping is completed, mix with copper oxide, and then continue to dropwise add the remaining part of the lithium hydroxide-seed mixture liquid, and stop dropping when the pH value of the system reaches 12-12.5.

[0010] Preferably, the aging temperature is 60-80 °C, and the time is 0.5-1.5 h; the drying temperature is 70-110 °C, and the time is 1-2 h; the calcination temperature is 250-380 °C, and the time is 0.5-4 h.

[0011] The present invention also provides a composite lithium phosphate catalyst prepared by the preparation method described above, including a silica carrier, lithium phosphate crystals loaded in the silica carrier, and copper oxide doped in the lithium phosphate crystals.

[0012] The present invention also provides the application of the composite lithium phosphate catalyst described above in the isomerization of propylene oxide to prepare allyl alcohol.

[0013] The present invention also provides a method for preparing allyl alcohol by isomerization of propylene oxide, comprising the following steps: Mix the composite lithium phosphate catalyst described in the above solution with a dispersion medium to obtain a catalyst slurry; Purge the catalyst slurry with an inert gas, and then co-feed propylene oxide vapor and an inert gas into the catalyst slurry for isomerization reaction to obtain allyl alcohol.

[0014] Preferably, the device used for the isomerization reaction is a slurry bed reactor; The propylene oxide vapor is obtained by vaporizing propylene oxide liquid, and the dosage of the propylene oxide liquid is 121.2 - 206.4 g / h / L of the catalyst slurry; The dispersion medium is an inert liquid; the mass ratio of the composite lithium phosphate catalyst to the dispersion medium is 1:1 - 10; The temperature of the catalyst slurry during purging is 230 - 280 °C; the temperature of the isomerization reaction is 230 - 280 °C; During purging, the per-minute feeding amount of the inert gas is 8 - 13 times the volume of the catalyst slurry; During the isomerization reaction, the per-minute feeding amount of the inert gas is 1.5 - 2.5 times the volume of the catalyst slurry.

[0015] The present invention provides a method for preparing a composite lithium phosphate catalyst, comprising the following steps: Mix an aqueous phosphoric acid solution with a catalyst support to obtain a phosphoric acid - support mixture liquid; the catalyst support is silica; the mass of the catalyst support is 1.1 - 1.5 times the mass of phosphoric acid in the aqueous phosphoric acid solution; Mix a lithium hydroxide solution with lithium phosphate seeds to obtain a lithium hydroxide - seed mixture liquid; Mix the lithium hydroxide - seed mixture liquid, tetraethyl orthosilicate alcohol solution, copper oxide, and the phosphoric acid - support mixture liquid for crystallization to obtain a reaction liquid; Age the reaction liquid to obtain a catalyst precursor; The temperature of the crystallization reaction is 60 - 80 °C, and the end-point pH value is 12 - 12.5; Calcinate the catalyst precursor to obtain a composite lithium phosphate catalyst. In the present invention, a support is added during the crystallization of lithium phosphate to guide nucleation, making the catalyst particles finer and the specific surface area larger, thereby improving the catalytic activity; In the present invention, tetraethyl orthosilicate is added during the crystallization of lithium phosphate, and the hydrolysis of tetraethyl orthosilicate generates small particles of silica, which can make the catalyst morphology rougher, and the remaining tetraethyl orthosilicate decomposes during calcination, which can play a role in secondary pore formation, further increasing the specific surface area of the catalyst and improving the catalytic activity; In the present invention, copper oxide is introduced into the composite lithium phosphate catalyst, which can improve the anti-coking performance of the catalyst and extend the service life.

[0016] The present invention also provides a method for preparing allyl alcohol by isomerization of propylene oxide, which comprises the following steps: mixing the composite lithium phosphate catalyst described in the above solution with a dispersion medium to obtain a catalyst slurry; purging the catalyst slurry with an inert gas, and then introducing propylene oxide and the inert gas into the catalyst slurry together for isomerization reaction to obtain allyl alcohol. Before the isomerization reaction, the present invention purges the catalyst slurry to remove residual crystal water, thereby effectively reducing the generation of n-propanol and improving the selectivity of the reaction; further, the present invention uses a slurry bed reactor for the isomerization reaction of propylene oxide, and the residence time of the raw materials is short, which can reduce the side reaction of allyl alcohol generating n-propanol, thereby improving the selectivity. The results of the examples show that when the method of the present invention is used to prepare allyl alcohol, the selectivity can reach more than 95%, the conversion rate of n-propanol reaches more than 50%, and the service life of the catalyst exceeds 600 h. Detailed implementation mode

[0017] The present invention provides a method for preparing a composite lithium phosphate catalyst, which comprises the following steps: Mixing an aqueous phosphoric acid solution with a catalyst support to obtain a phosphoric acid-support mixed solution; the catalyst support is silicon dioxide; the mass of the catalyst support is 1.1 to 1.5 times the mass of phosphoric acid in the aqueous phosphoric acid solution; Mixing a lithium hydroxide solution with lithium phosphate seeds to obtain a lithium hydroxide-seed mixed solution; Mixing the lithium hydroxide-seed mixed solution, tetraethyl orthosilicate alcohol solution, copper oxide and the phosphoric acid-support mixed solution for crystallization to obtain a reaction solution; aging the reaction solution to obtain a catalyst precursor; the temperature of the crystallization is 60 to 80 °C, and the end point pH value is 12 to 12.5; Drying the catalyst precursor and then calcining it to obtain the composite lithium phosphate catalyst.

[0018] The present invention mixes an aqueous phosphoric acid solution with a catalyst support to obtain a phosphoric acid-support mixed solution. In the present invention, the catalyst support is silicon dioxide, preferably white carbon black; the concentration of the aqueous phosphoric acid solution is preferably 40 to 50 wt%, more preferably 45.5 wt%; the mass of the catalyst support is 1.1 to 1.5 times the mass of phosphoric acid in the aqueous phosphoric acid solution, preferably 1.184 to 1.549 times, and further preferably 1.2 times.

[0019] The lithium hydroxide solution and lithium phosphate seeds are mixed in the present invention to obtain a lithium hydroxide-seed mixture solution. In the present invention, the concentration of the lithium hydroxide solution is preferably 5-12.4 wt%; the solvent of the lithium hydroxide solution is preferably water; in a specific embodiment of the present invention, lithium hydroxide is preferably added to water and heated to 80 °C to completely dissolve the lithium hydroxide; the lithium hydroxide is preferably lithium hydroxide monohydrate; the molar ratio of lithium hydroxide in the lithium hydroxide solution to phosphoric acid in the phosphoric acid aqueous solution is preferably 3-3.5:1, more preferably 3.2:1; in the present invention, the average particle size of the lithium phosphate seeds is preferably 0.4-0.8 μm, more preferably 0.52 μm; the dosage ratio of lithium hydroxide in the lithium hydroxide solution to lithium phosphate seeds is preferably (3-3.5) mol:(0.2-5) g, more preferably 3.2 mol:1 g.

[0020] In the present invention, the preparation method of the lithium phosphate seeds preferably includes: stirring and mixing a dilute lithium hydroxide solution and a phosphoric acid alcohol solution to precipitate lithium phosphate seeds; the concentration of the dilute lithium hydroxide solution is preferably 0.15 mol / L, the solvent of the dilute lithium hydroxide solution is preferably water; the concentration of the phosphoric acid alcohol solution is preferably 0.1 mol / L; the solvent of the phosphoric acid alcohol solution is preferably ethanol; the molar ratio of lithium hydroxide in the dilute lithium hydroxide solution to phosphoric acid in the phosphoric acid alcohol solution is preferably 14-16:1, more preferably 15:1; the temperature of the stirring and mixing is preferably 60-80 °C, and the time is preferably 15 min; in a specific embodiment of the present invention, the dilute lithium hydroxide solution is preferably heated to 60-80 °C first, and then the phosphoric acid alcohol solution is quickly added for stirring. After precipitating the lithium phosphate seeds, the present invention preferably filters the obtained slurry by suction and dries the obtained solid product to obtain the lithium phosphate seeds; the drying temperature is preferably 90 °C.

[0021] After obtaining the lithium hydroxide-seed mixture solution and the phosphoric acid-carrier mixture solution, the present invention mixes the lithium hydroxide-seed mixture solution, the tetraethyl orthosilicate alcohol solution, copper oxide, and the phosphoric acid-carrier mixture solution for crystallization to obtain a reaction solution. In the present invention, the concentration of the tetraethyl orthosilicate alcohol solution is preferably 10-30 wt%, more preferably 15-25 wt%; the solvent of the tetraethyl orthosilicate alcohol solution is preferably ethanol; the molar ratio of tetraethyl orthosilicate in the tetraethyl orthosilicate alcohol solution to phosphoric acid in the phosphoric acid aqueous solution is preferably 0.01-0.1:1, specifically 0.01:1, 0.03:1, 0.05:1 or 0.1:1; the copper oxide is specifically copper oxide powder, the particle size of the copper oxide is preferably 5-10 μm, and the purity of the copper oxide is preferably above 99%; the mass ratio of the copper oxide to phosphoric acid in the phosphoric acid aqueous solution is 0.1-0.5:1, specifically 0.2:1, 0.25:1, 0.3:1 or 0.5:1.

[0022] In the present invention, the crystallization temperature is preferably 60 to 80 °C, and the final pH value is preferably 12 to 12.5, specifically it can be 12 or 12.5, and more preferably 12. By controlling the crystallization temperature and pH value, the present invention can control the precipitation rate of lithium phosphate crystals, not only making the precipitation of lithium phosphate more complete, but also reducing the deposition of lithium phosphate on the surface of large crystals, and obtaining lithium phosphate crystals with more uniform morphology.

[0023] In the present invention, the crystallization preferably includes: at 60 to 80 °C, simultaneously dropping an ethyl silicate alcohol solution and a partial lithium hydroxide-seed mixture solution into the phosphoric acid-carrier mixture solution, after the dropping is completed, mixing with copper oxide, and then continuing to drop the remaining part of the lithium hydroxide-seed mixture solution. When the pH value of the system reaches 12 to 12.5, stop dropping; in the present invention, the time for simultaneously dropping the ethyl silicate alcohol solution and the partial lithium hydroxide-seed mixture solution is preferably 0.5 to 3 h, specifically it can be 1 h, 2 h or 3 h; the volume of the partial lithium hydroxide-seed mixture solution is preferably 93 to 95% of the total volume of the lithium hydroxide-seed mixture solution, and more preferably 93.75%; when simultaneously dropping the ethyl silicate alcohol solution and the partial lithium hydroxide-seed mixture solution, adding copper oxide and dropping the remaining part of the lithium hydroxide-seed mixture solution, it is all preferably carried out under stirring conditions; in the present invention, first dropping a part of the lithium hydroxide-seed mixture solution, and then continuing to drop after adding copper oxide can make copper oxide uniformly doped in lithium phosphate crystals.

[0024] After the pH value reaches the requirement, stop dropping the lithium hydroxide-seed mixture solution, and then age the obtained reaction solution; the aging temperature is preferably 60 to 80 °C, the time is preferably 0.5 to 1.5 h, more preferably 1 h, and the aging is preferably carried out under stirring conditions. After aging is completed, it is preferably to filter the obtained material solution, and the obtained solid is the catalyst precursor.

[0025] After obtaining the catalyst precursor, the present invention dries the catalyst precursor and then calcines it to obtain a composite lithium phosphate catalyst. In the present invention, the drying temperature is preferably 70-110 °C, specifically 90 °C or 100 °C, and the drying time is preferably 1-2 h, more preferably 1.5 h. After drying, it is preferred to grind the dried material and then calcine it; the calcination temperature is preferably 250-380 °C, specifically 300 °C, 330 °C or 350 °C, and the calcination time is preferably 0.5-4 h, specifically 2 h, 3 h or 4 h. During the calcination process, the residual solvent in the catalyst is removed, and the incompletely decomposed tetraethyl orthosilicate is further hydrolyzed and condensed, realizing the function of secondary pore formation of tetraethyl orthosilicate on the surface of the catalyst and increasing the specific surface area of the catalyst. After the calcination is completed, the present invention preferably screens the obtained calcined material to obtain a product with a particle size of less than 50 μm, which is the composite lithium phosphate catalyst of the present invention. The product with a particle size greater than 50 μm is preferably ground until the particle size meets the requirements; the mesh number of the sieve used for screening is preferably 300 mesh.

[0026] The present invention also provides a composite lithium phosphate catalyst prepared by the preparation method described in the above solution, including a silica carrier, lithium phosphate crystals loaded in the silica carrier, and copper oxide doped in the lithium phosphate crystals; in the present invention, the particle size of the composite lithium phosphate catalyst is preferably less than 50 μm, and the specific surface area is preferably 135-162 m 2 / g, the lithium phosphate content is preferably 38-50 wt%, preferably 45-50 wt%, and further preferably 48.5 wt%.

[0027] The present invention also provides the application of the composite lithium phosphate catalyst described in the above solution in the isomerization of propylene oxide to prepare allyl alcohol.

[0028] The present invention also provides a method for isomerizing propylene oxide to prepare allyl alcohol, including the following steps: Mix the composite lithium phosphate catalyst described in the above solution and a dispersion medium to obtain a catalyst slurry; Purge the catalyst slurry with an inert gas, and then co-feed propylene oxide vapor and an inert gas into the catalyst slurry for isomerization reaction to obtain allyl alcohol.

[0029] In the present invention, the device used for the isomerization reaction is preferably a slurry bed reactor; a stirring paddle is preferably arranged in the slurry bed reactor, and the stirring paddle preferably includes a stirring shaft and blades arranged on the stirring shaft; an inlet for propylene oxide vapor is preferably arranged at the bottom of the slurry bed reactor; in a specific embodiment of the present invention, an inert gas can be introduced into the slurry bed reactor from the same inlet as the propylene oxide vapor, or an additional inlet for the inert gas is arranged at the bottom of the slurry bed reactor; the device used for the isomerization reaction preferably further includes a raw material tank, a vaporizer, a condensation device and a storage tank; the raw material tank is used for storing liquid propylene oxide; the vaporizer is used for vaporizing the liquid propylene oxide; the condensation device is used for condensing the gas products generated by the isomerization reaction; the storage tank is used for storing the condensed products; the inlet for propylene oxide vapor of the slurry bed reactor is preferably connected to the vaporizer; the inlet of the vaporizer is preferably connected to the raw material tank; the gas outlet of the slurry bed reactor is preferably connected to the condensation device; the inlet of the storage tank is preferably communicated with the outlet of the condensation device.

[0030] In the present invention, the dispersion medium is preferably an inert liquid, specifically therminol 55 heat transfer oil; the mass ratio of the composite lithium phosphate catalyst to the dispersion medium is preferably 1:1 to 10, specifically 1:1, 1:3, 1:5, 1:6, 1:6.4, 1:7 or 1:10; in the present invention, the dispersion medium and the composite lithium phosphate catalyst are preferably added into the slurry bed reactor and stirred by the stirring paddle in the slurry bed reactor to make the catalyst slurry evenly distributed.

[0031] In the present invention, the inert gas is preferably nitrogen or an inert gas, more preferably nitrogen; the temperature of the catalyst slurry during purging is preferably 230 to 280 °C, more preferably 250 °C; during purging, the amount of the inert gas introduced per minute is preferably 8 to 13 times the volume of the catalyst slurry, more preferably 10 times; the purging time is preferably 1 to 2 h, more preferably 1.5 h; in a specific embodiment of the present invention, the catalyst slurry is preferably first heated to the target temperature, and then nitrogen is introduced from the bottom of the slurry bed reactor to purge the catalyst slurry; through high-temperature purging, the present invention can remove the low-boiling components in the catalyst slurry and remove the crystal water, thereby reducing the generation of n-propanol and improving the selectivity of the reaction.

[0032] In the present invention, the temperature of the isomerization reaction is preferably 230 to 280 °C, more preferably 250 °C; in the isomerization reaction, the hourly feed rate of the inert gas is preferably 1.5 to 2.5 times the volume of the catalyst slurry, more preferably 2 times; the propylene oxide vapor is obtained by vaporizing propylene oxide liquid, and the amount of the propylene oxide liquid is preferably 121.2 - 206.4 g / h / L of the catalyst slurry, more preferably 121.2 to 182.4 g / h / L of the catalyst slurry. In a specific embodiment of the present invention, the propylene oxide liquid in the raw material tank is preferably fed into a vaporizer to be vaporized into propylene oxide gas, and then together with the inert gas is bubbled into the catalyst slurry from the bottom of the slurry bed reactor; the feeding rate of the propylene oxide liquid is preferably controlled by a metering pump.

[0033] After the propylene oxide gas and the inert gas enter the catalyst slurry in the form of bubbles and react, the resulting gas product enters a condensing device from the gas outlet at the top of the slurry bed reactor for condensation, and the resulting condensate enters a storage tank for storage.

[0034] In the present invention, the composite lithium phosphate catalyst in the slurry bed reactor is suspended in a dispersion medium, and the propylene oxide gas is bubbled into the liquid for reaction. In specific implementation, an opening can be made on the side wall of the slurry bed reactor, and the catalyst slurry is pumped out by a pump and enters a regeneration device for activation and regeneration, while continuously replenishing the activated catalyst slurry into the reactor, so as to achieve large-scale continuous production. In the present invention, the method of activation and regeneration is preferably calcination activation or polar solvent immersion activation, and the activity of the catalyst is restored by removing carbon deposits through activation and regeneration; specifically, the calcination activation preferably includes: filtering the used catalyst slurry to obtain catalyst solids, passing steam into the catalyst solids to remove carbon deposits, and then performing calcination under air conditions; the temperature of the steam is preferably 270 °C, and the temperature of the calcination is preferably 300 to 400 °C; the polar solvent immersion activation preferably includes: filtering the used catalyst slurry, immersing the obtained catalyst solids in a polar solvent, and then filtering out the catalyst for drying and calcination; the polar solvent used for the polar solvent immersion is preferably acetone, and the tar on the surface layer of the catalyst is dissolved by the polar solvent immersion; the temperature of the calcination is preferably 300 to 400 °C, and the calcination atmosphere is preferably air. The polar solvent immersion method causes less damage to the catalyst, and the present invention preferably uses the polar solvent immersion method to activate and regenerate the catalyst.

[0035] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0036] Example 1 2.3 g of phosphoric acid with a concentration of 85 wt% (0.02 mol) was added to 200 g of ethanol and dissolved to obtain a phosphoric acid-ethanol solution for standby. In a flask, 12.6 g of lithium hydroxide monohydrate was added to 2 L of water and dissolved to obtain a dilute lithium hydroxide solution (0.15 mol / L); the dilute lithium hydroxide solution was heated to 60 °C, and the phosphoric acid-ethanol solution was quickly added to the flask. After stirring for 15 min, the turbid slurry was filtered by suction, and the filter cake was dried at 90 °C to obtain a white solid powder, which was the lithium phosphate seed crystal. Tested with an X-ray powder diffractometer (model RIGAKU Ultima IV), the average particle size of the lithium phosphate seed crystal was 0.52 μm.

[0037] 134.4 g of lithium hydroxide monohydrate (3.2 mol) was added to 544 mL of water and heated to 80 °C (saturated) for dissolution, then 1.0 g of lithium phosphate seed crystal was added and stirred evenly to obtain a lithium hydroxide-seed crystal mixture solution for standby. 10.4 g of tetraethyl orthosilicate was dissolved in 50 g of ethanol to obtain a tetraethyl orthosilicate-ethanol solution for standby.

[0038] 115.3 g of phosphoric acid with a concentration of 85 wt% (1 mol) was added to the reaction kettle, diluted with 100 g of water, and 116 g of white carbon black was added, and quickly stirred evenly to obtain a phosphoric acid-carrier mixture solution. The prepared lithium hydroxide-seed crystal mixture solution was slowly and evenly added to the reaction kettle. During this period, the temperature of the reaction kettle was maintained at 80 °C by heating, and continuous stirring was carried out. 636 g of the lithium hydroxide-seed crystal mixture solution was added within 1 h. While dropping the lithium hydroxide-seed crystal mixture solution, the tetraethyl orthosilicate-ethanol solution was also slowly added, and the dropping rate was controlled to be completed within 1 h. Then 30 g of powdered copper oxide was added to the kettle, stirred, and the pH value of the solution in the kettle was detected with a pH meter. The lithium hydroxide-seed crystal mixture solution was continuously added until the pH value of the reaction solution in the kettle reached 12.0. Then the reaction solution was kept warm at 80 °C and continuously stirred for 1 h. The solid in the kettle was filtered out under pressure, and the solid was placed in an oven and dried at 100 °C for 1.5 h. The dried solid was transferred to a grinder and ground for 30 min, and then the solid was transferred to a muffle furnace and calcined at 330 °C for 2 h. The obtained solid product was sieved with a 300-mesh sieve to separate out particles with a particle size of less than 50 microns, which was used as the composite lithium phosphate catalyst of the present invention, and the remaining solid was returned to the grinder for further crushing. Elemental analysis of the obtained composite lithium phosphate catalyst was carried out using an inductively coupled plasma optical emission spectrometer (model Optima-7000 DV). The results showed that the lithium phosphate content was 48.5 wt%; measured with a specific surface area and porosity analyzer (model Quadrasorb SI-MP), the results showed that the specific surface area of the composite lithium phosphate catalyst was 162 m 2 / g.

[0039] Example 2 The reaction device includes a raw material tank, a vaporizer, a slurry bed reactor, a condensation device and a storage tank. The slurry bed reactor is 0.5 m high and 4 cm in inner diameter, and is stirred by multiple groups of blades on the stirring shaft. An inlet for propylene oxide vapor is provided at the bottom of the slurry bed reactor and is connected to the propylene oxide vaporizer, and the inlet of the vaporizer is connected to the raw material tank; a gas outlet is provided at the top of the slurry bed reactor and is connected to the condensation device, and the outlet of the condensation device is connected to the storage tank.

[0040] Take 50 g of catalyst powder and mix it with 320 g (volume about 0.45 L) of the dispersing medium therminol 55 heat transfer oil and load it into the slurry bed reactor. Start stirring to mix the catalyst solid and the heat transfer oil to obtain a catalyst slurry, and start heating to raise the temperature of the slurry to 250 °C. Nitrogen is introduced at a rate of 5 L / min for 90 min to activate the catalyst and remove the crystal water remaining in the catalyst. Reduce the nitrogen rate to 1 L / min, and feed liquid propylene oxide into the vaporizer at a rate of 1.01 g / min to be converted into propylene oxide vapor, and introduce it into the catalyst slurry through the feed port at the bottom of the kettle. The condensation device at the top of the reactor cools the reaction products and the remaining raw materials together and stores them in the storage tank. After the device runs for 10 min, the reaction proceeds stably. A small amount of condensate is taken from the condenser and analyzed by gas chromatography for the composition of the condensate material, which contains 47.9 wt% of propylene oxide, 49.7 wt% of allyl alcohol, 0.90 wt% of acetone, 1.29 wt% of propionaldehyde, and 0.21 wt% of n-propanol.

[0041] After the reactor runs continuously for 400 h, a small amount of condensate is taken again for gas chromatography analysis: it contains 48.3 wt% of propylene oxide, 49.3 wt% of allyl alcohol, 1.17 wt% of acetone, 1.03 wt% of propionaldehyde, and 0.20 wt% of n-propanol, and the catalyst activity does not decrease significantly.

[0042] After the reactor runs continuously for 600 h, a small amount of condensate is taken again for gas chromatography analysis: it contains 53.3 wt% of propylene oxide, 44.5 wt% of allyl alcohol, 0.88 wt% of acetone, 1.13 wt% of propionaldehyde, and 0.19 wt% of n-propanol, and the catalyst activity decreases slightly.

[0043] Example 3 According to the same scheme as in Example 1, only when adding the lithium hydroxide-seed mixture liquid, the pH of the reaction liquid is finally stabilized at 12.5. Other subsequent preparation conditions are the same as those in Example 1 to obtain a composite lithium phosphate catalyst. Sampling and testing show that the specific surface area of the catalyst is 144 m 2 / g. Using the composite lithium phosphate catalyst prepared in Example 3, the isomerization reaction of propylene oxide was carried out according to the same scheme as in Example 2. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0044] Comparative Example 1 According to the same scheme as in Example 1, only when adding the lithium hydroxide-seed mixture solution, the pH of the reaction solution was finally stabilized at 13. Other subsequent preparation conditions were the same as those in Example 1, and a composite lithium phosphate catalyst was obtained. Sampling and testing showed that the specific surface area of the catalyst was 102 m 2 / g. Using the lithium phosphate catalyst prepared in Comparative Example 1, the isomerization reaction of propylene oxide was carried out according to the same scheme as in Example 2. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0045] Example 4 According to the same scheme as in Example 1, when adding the lithium hydroxide-seed mixture solution, tetraethyl orthosilicate ethanol solution and copper oxide, the heating temperature was controlled at 70 °C; after dropping the lithium hydroxide solution, it was kept at 70 °C for 1 h. Other subsequent preparation conditions were the same as those in Example 1, and a composite lithium phosphate catalyst was obtained. Sampling and testing showed that the specific surface area of the catalyst was 144 m 2 / g. Sampling the catalyst for elemental analysis, the lithium phosphate content was 44.1 wt%. Using the lithium phosphate catalyst prepared in Example 4, the isomerization reaction of propylene oxide was carried out according to the same scheme as in Example 2. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0046] Example 5 According to the same scheme as in Example 1, when adding the lithium hydroxide-seed mixture solution, tetraethyl orthosilicate ethanol solution and copper oxide, the heating temperature was controlled at 60 °C; after dropping the lithium hydroxide solution, it was kept at 60 °C for 1 h. Other preparation conditions were the same as those in Example 1, and a composite lithium phosphate catalyst was obtained. Sampling and testing showed that the specific surface area of the catalyst was 135 m 2 / g. Sampling the catalyst for elemental analysis, the lithium phosphate content was 42.6 wt%. Using the lithium phosphate catalyst prepared in Example 5, the isomerization reaction of propylene oxide was carried out according to the same scheme as in Example 2. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0047] Comparative Example 2 According to the same scheme as in Example 1, when adding the lithium hydroxide-seed mixture solution, tetraethyl orthosilicate ethanol solution and copper oxide, the heating temperature was controlled at 50 °C; after dropping the lithium hydroxide solution, it was kept at 50 °C for 1 h. Other subsequent preparation conditions were the same as those in Example 1, and a composite lithium phosphate catalyst was obtained. Sampling and testing showed that the specific surface area of the catalyst was 113 m 2 / g. The catalyst was sampled for elemental analysis, and the lithium phosphate content was 38.4 wt%. The lithium phosphate catalyst prepared in Comparative Example 2 was used for the isomerization reaction of propylene oxide according to the same scheme as in Example 2. After the reaction was stabilized, the material composition of the condensate was analyzed by gas chromatography.

[0048] Example 6 According to the same scheme as in Example 1, only the amount of silica was changed to 143 g. Other subsequent preparation conditions were the same as those in Example 1, and a composite lithium phosphate catalyst was obtained. The sample was taken for elemental analysis, and the lithium phosphate content was 38.7 wt%. The lithium phosphate catalyst prepared in Example 6 was used for the isomerization reaction of propylene oxide according to the same scheme as in Example 2. After the reaction was stabilized, the material composition of the condensate was analyzed by gas chromatography.

[0049] Comparative Example 3 According to the same scheme as in Example 1, only the amount of silica was changed to 190 g. Other subsequent preparation conditions were the same as those in Example 1, and a composite lithium phosphate catalyst was obtained. The sample was taken for elemental analysis, and the lithium phosphate content was 21.2 wt%. The lithium phosphate catalyst prepared in Comparative Example 3 was used for the isomerization reaction of propylene oxide according to the same scheme as in Example 2. After the reaction was stabilized, the material composition of the condensate was analyzed by gas chromatography.

[0050] Example 7 According to the same scheme as in Example 2, the composite lithium phosphate catalyst prepared in Example 1 was used for the isomerization experiment of propylene oxide. The metering valve was controlled to control the addition amount of propylene oxide at 1.52 g / min. Other subsequent reaction conditions were the same as those in Example 2. After the reaction was stabilized, the material composition of the condensate was analyzed by gas chromatography.

[0051] Example 8 According to the same scheme as in Example 2, the composite lithium phosphate catalyst prepared in Example 1 was used for the isomerization experiment of propylene oxide. The metering valve was controlled to control the addition amount of propylene oxide at 1.72 g / min. Other subsequent reaction conditions were the same as those in Example 2. After the reaction was stabilized, the material composition of the condensate was analyzed by gas chromatography.

[0052] Comparative Example 4 According to the same scheme as in Example 2, the composite lithium phosphate catalyst prepared in Example 1 was used for the isomerization experiment of propylene oxide. The metering valve was controlled to control the addition amount of propylene oxide at 0.81 g / min. Other subsequent reaction conditions were the same as those in Example 2. After the reaction was stabilized, the material composition of the condensate was analyzed by gas chromatography.

[0053] Example 9 According to the same scheme as in Example 2, the isomerization experiment of propylene oxide was carried out using the composite lithium phosphate catalyst prepared in Example 1. Before the reaction started, the amount of the catalyst was changed to 100 g, and the amount of the heat transfer oil was 300 g. The subsequent other reaction conditions were the same as those in Example 2. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0054] Example 10 According to the same scheme as in Example 2, the isomerization experiment of propylene oxide was carried out using the composite lithium phosphate catalyst prepared in Example 1. Before the reaction started, the amount of the catalyst was changed to 200 g, and the amount of the heat transfer oil was 200 g. The subsequent other reaction conditions were the same as those in Example 2. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0055] Example 11 According to the same scheme as in Example 2, the isomerization experiment of propylene oxide was carried out using the composite lithium phosphate catalyst prepared in Example 1. Before the reaction started, the amount of the catalyst was changed to 40 g, and the amount of the heat transfer oil was 400 g. The subsequent other reaction conditions were the same as those in Example 2. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0056] The variable summary of each example is shown in Table 1: Table 1 Summary of experimental condition variables for Examples 2 - 11 and Comparative Examples 1 - 4

[0057] Comparative Example 5 Using the composite lithium phosphate catalyst prepared in Example 1, the catalyst and the heat transfer oil were mixed to prepare a catalyst slurry. The catalyst slurry was not purged with nitrogen and was directly applied to the experiment of preparing allyl alcohol by isomerization of propylene oxide. The subsequent other steps were carried out according to the same scheme as in Example 2. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0058] Comparative Example 6 The composite lithium phosphate catalyst was prepared according to the scheme in Example 1, and only the amount of silica was changed to 0. The other preparation steps were the same as those in Example 1 to obtain a carrier - free composite lithium phosphate catalyst. According to the same scheme as in Example 2, 50 g of the above - mentioned carrier - free lithium phosphate catalyst was used for the isomerization reaction of propylene oxide. After the reaction was stable, the material composition of the condensate was analyzed by gas chromatography.

[0059] Comparative Example 7 Prepare the composite lithium phosphate catalyst according to the scheme in Example 1, only change the dosage of copper oxide powder to 0, and keep other preparation steps the same as those in Example 1 to obtain the composite lithium phosphate catalyst without copper oxide. Carry out the isomerization reaction of propylene oxide using the above-mentioned copper-oxide-free lithium phosphate catalyst according to the same scheme as in Example 2. After the reaction is stable, use gas chromatography to analyze the material composition of the condensate. After the reactor runs continuously for 400 h and 600 h, take a small amount of condensate again for gas chromatography analysis.

[0060] The analysis data of the product components in each example and comparative example are shown in Table 2.

[0061] Table 2 Analysis results of product components in Examples 2 - 11 and Comparative Examples 1 - 7

[0062] It can be seen from the results of Examples 2 - 3 and Comparative Example 1, Examples 4 - 5 and Comparative Example 2 that during the preparation of the composite lithium phosphate catalyst, the temperature and pH value during the precipitation of lithium phosphate crystals have an obvious influence on the performance of the catalyst. An excessively high pH value will affect the crystallization process of lithium phosphate, causing lithium phosphate crystals to agglomerate into large particles too much, and also affecting the combination of lithium phosphate and the carrier, reducing the effective area of the catalyst, resulting in a low reaction conversion rate during the use of the catalyst. At the same time, since the catalyst lithium phosphate contains more basic centers, the reaction selectivity decreases, and the by-products acetone and propionaldehyde increase. The temperature during crystallization affects the precipitation rate of lithium phosphate and the self-repair process of lithium phosphate crystals during the aging process. A higher temperature can not only make the precipitation of lithium phosphate more complete, but also reduce the deposition of lithium phosphate on the surface of large crystals, and lithium phosphate with a more uniform morphology can be obtained. The results of Example 6 and Comparative Example 3 show that the change in the carrier content during the catalyst preparation process will affect the reaction conversion rate during the use of the catalyst, and has no obvious influence on the reaction selectivity.

[0063] The results in Examples 7 - 8 and Comparative Example 4, Examples 9 - 11 show that when the composite lithium phosphate catalyst catalyzes the isomerization reaction of propylene oxide, changing the raw material feeding rate and the catalyst dosage will both affect the conversion rate and selectivity of the reaction. When the feeding rate is too low or the catalyst dosage increases, the catalyst in the catalyst slurry can act more effectively on propylene oxide molecules, increasing the reaction conversion rate, but also resulting in a slight decrease in the reaction selectivity. Therefore, appropriate catalyst dosage and feeding rate need to be selected for the reaction to balance the conversion rate and selectivity.

[0064] In Comparative Example 5, the step of purging the catalyst slurry was omitted. Compared with Example 2, the selectivity of the reaction decreased significantly, which demonstrated the necessity of using nitrogen to purge the catalyst slurry before the reaction. By promoting the departure of the crystal water in the catalyst, the influence of moisture on the reaction during the subsequent reaction process was reduced, and the formation of the by-product n-propanol could be effectively reduced.

[0065] In Comparative Example 6, a carrier-free composite lithium phosphate catalyst was used. Compared with Example 2, the conversion rate of the reaction was lower. This was because lithium phosphate precipitated on the surface of the carrier during the precipitation process. By adding a carrier, the amount of lithium phosphate used was reduced to save costs, and the addition of the carrier not only did not reduce the active components of the catalyst, but instead provided more nucleation centers when lithium phosphate precipitated, making the catalyst particles smaller and more uniform in size. Combining Example 6 and Comparative Example 3, it can be seen that the addition amount of the carrier within a certain range is beneficial to the overall catalytic effect of the catalyst.

[0066] In Comparative Example 7, the addition of copper oxide was omitted. Compared with Example 2, the service life of the catalyst decreased significantly, which demonstrated the role of the added copper oxide in the composite catalyst in delaying carbon deposition and extending the service life of the catalyst. The single-pass service life of the conventional lithium phosphate catalyst was about 200 h. In Comparative Example 7, the reaction conversion rate decreased significantly after the catalyst was used for 400 h, and it was almost completely deactivated after being used for 600 h. However, the catalyst in Example 2 could still maintain a high conversion rate and selectivity after being used for 600 h, reducing the frequency of catalyst regeneration. Combining this with the characteristics of the slurry bed reactor used in the present invention, which can continuously extract the slurry into the regeneration process and supplement new catalyst slurry, large-scale continuous production of propylene oxide isomerization reaction can be realized.

[0067] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a composite lithium phosphate catalyst, characterized in that: The following steps are involved: The phosphoric acid aqueous solution and the catalyst carrier are mixed to obtain a phosphoric acid-carrier mixed liquid; the catalyst carrier is silicon dioxide; the mass of the catalyst carrier is 1.1 to 1.5 times the mass of the phosphoric acid in the phosphoric acid aqueous solution; Mixing a lithium hydroxide solution and lithium phosphate seed crystals to obtain a lithium hydroxide-seed crystal mixed solution; The lithium hydroxide-seed mixed liquid, ethyl silicate alcohol solution, copper oxide and phosphoric acid-carrier mixed liquid are mixed and crystallized to obtain a reaction liquid; the reaction liquid is aged to obtain a catalyst precursor; the crystallization temperature is 60-80° C., and the endpoint pH value is 12-12.5; The catalyst precursor is dried and then calcined to obtain a composite lithium phosphate catalyst.

2. The preparation method according to claim 1, characterized in that: The concentration of the phosphoric acid aqueous solution is 40-50 wt %; the average particle size of the lithium phosphate seed crystals is 0.4-0.8 μm.

3. The preparation method according to claim 1, characterized in that: The concentration of the lithium hydroxide solution is 5-12.4wt%; the molar ratio of the lithium hydroxide in the lithium hydroxide solution to the phosphoric acid in the phosphoric acid aqueous solution is 3-3.5:1; the amount ratio of the lithium hydroxide in the lithium hydroxide solution to the lithium phosphate seed is (3-3.5) mol: (0.2-5) g.

4. The preparation method according to claim 1, characterized in that: The concentration of the ethyl silicate alcohol solution is 10-30 wt %, and the molar ratio of ethyl silicate in the ethyl silicate alcohol solution to phosphoric acid in the phosphoric acid aqueous solution is 0.01-0.1:1; The particle size of the copper oxide is 5-10 μm, and the mass ratio of the copper oxide to the phosphoric acid in the phosphoric acid aqueous solution is 0.1-0.5:

1.

5. The preparation method according to claim 1, 3 or 4, characterized in that: The crystallization comprises: at 60-80° C., simultaneously dropping an ethyl silicate alcohol solution and a portion of a lithium hydroxide-seed mixture into a phosphoric acid-carrier mixture, mixing with copper oxide after the dropping is complete, and then continuing to drop the remaining portion of the lithium hydroxide-seed mixture, and stopping the dropping when the pH value of the system reaches 12-12.

5.

6. The preparation method according to claim 1, characterized in that: The aging temperature is 60-80° C., and the time is 0.5-1.5 h; the drying temperature is 70-110° C., and the time is 1-2 h; the calcination temperature is 250-380° C., and the time is 0.5-4 h.

7. The composite lithium phosphate catalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The invention comprises a silicon dioxide carrier, lithium phosphate crystals loaded in the silicon dioxide carrier and copper oxide doped in the lithium phosphate crystals.

8. Use of the composite lithium phosphate catalyst according to claim 7 in the isomerization of propylene oxide to prepare allyl alcohol.

9. A method for preparing allyl alcohol by isomerization of propylene oxide, characterized in that: The following steps are involved: Mixing the composite lithium phosphate catalyst according to claim 7 and a dispersion medium to obtain a catalyst slurry; The catalyst slurry is purged with an inactive gas, and then propylene oxide vapor and the inactive gas are introduced into the catalyst slurry to perform an isomerization reaction to obtain allyl alcohol.

10. The method according to claim 9, characterized in that The device used in the isomerization reaction is a slurry bed reactor; The propylene oxide vapor is obtained by gasifying propylene oxide liquid, and the amount of the propylene oxide liquid is 121.2-206.4 g / h / L catalyst slurry; The dispersion medium is an inert liquid; the mass ratio of the composite lithium phosphate catalyst to the dispersion medium is 1:1-10; The temperature of the catalyst slurry during the purge is 230-280°C; the temperature of the isomerization reaction is 230-280°C; During the purging, the amount of inactive gas introduced per minute is 8 to 13 times the volume of the catalyst slurry; In the isomerization reaction, the amount of inactive gas introduced per minute is 1.5 to 2.5 times the volume of the catalyst slurry.

Images