A process for the isomerization of propylene oxide to allyl alcohol

Abstract

This invention provides a method for isomerizing propylene oxide to prepare allyl alcohol. The method includes contacting preheated propylene oxide with a catalyst under an inactive carrier gas to carry out an isomerization reaction. The catalyst is a lithium phosphate catalyst supported on elemental Pt. The loading of elemental Pt in the catalyst is 0.5 wt% to 2 wt% based on the mass of lithium phosphate. The method of this invention has higher conversion rate, selectivity, and better catalytic stability (long catalyst life).

Description

Technical Field

[0001] This invention belongs to the field of fine chemicals, specifically relating to a method for preparing allyl alcohol by isomerization of propylene oxide. Background Technology

[0002] Allyl alcohol is an important fine chemical product and intermediate. Due to the presence of both double bonds and hydroxyl groups in its molecular structure, it is chemically very reactive and can react with aldehydes, esters, etc. Allyl alcohol and its derivatives are widely used as basic chemical raw materials in pharmaceuticals, fragrances, and other organic synthesis.

[0003] Currently, the main methods for industrial production of allyl alcohol include: acrolein reduction, allyl chloride hydrolysis, propylene acetate hydrolysis, and propylene oxide isomerization. Among these, propylene oxide isomerization is further divided into gas-phase and liquid-phase methods, which offer advantages such as simple process, high yield, no equipment corrosion, and high atom utilization. Lithium phosphate is the most effective catalyst for the propylene oxide isomerization reaction.

[0004] The gas-phase method involves isomerizing preheated propylene oxide into allyl alcohol by passing it through a reactor loaded with a catalyst. While simple and easy to operate, the gas-phase process requires high temperature and pressure, achieving a conversion rate of 58%–75% and a selectivity of up to 94%. However, the carbon deposits generated during the reaction affect the catalyst's activity and lifespan, and catalyst regeneration requires acetone, making the process cumbersome. Most domestic and international research focuses on modifying the catalyst to improve its activity and selectivity, and extend its lifespan. For example, Chinese invention patent CN107537526A describes a fluidized bed isomerization catalyst using silica as a support, alkaline lithium phosphate as the main catalyst, and a small amount of additives. By loading the catalyst, the specific surface area can be increased, improving the utilization rate of the active component. Furthermore, using a small amount of additives to further modify the catalyst can enhance its selectivity, achieving a selectivity of over 96%.

[0005] To date, there have been many reports on the gas-phase preparation of allyl alcohol from propylene oxide, but these methods generally suffer from low conversion rates and poor selectivity for allyl alcohol, making subsequent separation and purification complex. Furthermore, the tar produced during isomerization coats the catalyst surface, shortening its lifespan. Summary of the Invention

[0006] To address the problems of low conversion rate and poor reaction selectivity in the preparation of allyl alcohol by isomerization of propylene oxide in the existing technology, this invention provides a method for preparing allyl alcohol by isomerization of propylene oxide. In the method of this invention, the conversion rate of propylene oxide is high, the selectivity of allyl alcohol is high, and the catalytic stability is good (long catalyst life).

[0007] According to one aspect of the present invention, a method for preparing allyl alcohol by isomerization of propylene oxide is provided, the method comprising contacting preheated propylene oxide with a catalyst under an inactive carrier gas to carry out an isomerization reaction.

[0008] The catalyst is a lithium phosphate catalyst supported on elemental Pt.

[0009] The loading of elemental Pt in the catalyst is 0.5 wt% to 2 wt% based on the mass of lithium phosphate.

[0010] The inventors of this invention have discovered that loading Pt onto lithium phosphate effectively improves the conversion rate of propylene oxide and the selectivity of allyl alcohol. Analysis suggests that loading a specific amount of Pt onto lithium phosphate causes charge transfer between the metal carriers, thereby forming Pt. n+ The active center, and this change may help improve the catalytic effect of the catalyst, thereby improving the conversion rate of propylene oxide and the selectivity of allyl alcohol.

[0011] Optionally, the loading of the elemental Pt, based on the mass of lithium phosphate, is 0.6 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 1.9 wt%, or any value between any two of the above.

[0012] Optionally, the temperature of the preheated propylene oxide is 180–260°C; the pressure of the propylene oxide is 0.8–1.2 bar; and the mass hourly space velocity (HSV) of the propylene oxide is 1 h⁻¹. -1 ~10h -1 4h preferred -1 ~6h -1 The pressure of the propylene oxide is the pressure at the preheating temperature.

[0013] The pressure in this invention is gauge pressure.

[0014] Optionally, the conditions for the isomerization reaction include: a temperature of 260–340°C and a time of 4–8 hours.

[0015] Optionally, the inactive carrier gas includes at least one of nitrogen, helium, argon and neon, preferably nitrogen.

[0016] Optionally, the flow rate of the inactive carrier gas is 1-40 ml / min relative to 1 g of the catalyst.

[0017] Optionally, relative to 1g of the catalyst, the flow rate of the inactive carrier gas is 1ml / min, 5ml / min, 10ml / min, 15ml / min, 20ml / min, 25ml / min, 30ml / min, 35ml / min, 40ml / min, or any value between any two of the above points.

[0018] Optionally, the catalyst preparation method includes adding a reducing agent dropwise to a solution containing lithium phosphate and platinum precursors to carry out a reduction reaction.

[0019] Optionally, the molar ratio of lithium phosphate, reducing agent, and platinum precursor is 58–336:6–12:1, wherein the amount of platinum precursor is calculated as platinum element.

[0020] Optionally, the platinum precursor is selected from at least one of chloroplatinic acid, sodium chloroplatinate, and potassium chloroplatinate.

[0021] Optionally, the reducing agent is selected from at least one of NaBH4, formaldehyde, and ethylene glycol.

[0022] Optionally, the rate of adding the reducing agent is 0.5-1 mol / min, preferably 0.6-0.8 mol / min, relative to 1 mol of reducing agent.

[0023] Optionally, the dropping rate relative to 1 mol of reducing agent is 0.5 mol / min, 0.6 mol / min, 0.7 mol / min, 0.8 mol / min, 0.9 mol / min, 1 mol / min, or any value between any two of the above points.

[0024] Optionally, the reduction reaction can be carried out for 2 to 6 hours.

[0025] Optionally, the reaction time is 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or any value between any two of the above points.

[0026] Optionally, the method for preparing the lithium phosphate includes:

[0027] (1) Add LiOH solution dropwise to Na3PO4 solution to carry out the reaction;

[0028] (2) Filter the precipitate, wash the precipitate with water until the pH of the filtrate is 10-12, then dry and calcine.

[0029] Optionally, the solvent in the Na3PO4 solution is water or a mixture of ethanol and water; the solvent in the LiOH solution is water or a mixture of ethanol and water; the volume ratio of water to ethanol in the mixture is 3:1 to 1:3.

[0030] Optionally, the molar mass ratio of Na3PO4 to LiOH is 1:3 to 5.

[0031] Optionally, the molar mass ratio of Na3PO4 to LiOH is 1:3.5, 1:4, 1:4.5, 1:5, or any value between any two of the above.

[0032] Optionally, in step (1), the reaction conditions include: a reaction time of 2 to 6 hours and a reaction temperature of 70 to 90°C.

[0033] Optionally, in step (2), the drying temperature is 100-160°C and the drying time is 10-16 hours.

[0034] Optionally, in step (2), the calcination temperature is 260–350°C and the calcination time is 6–12 hours.

[0035] As one embodiment of the present invention, a method for synthesizing a modified lithium phosphate catalyst includes:

[0036] (1) Dissolve Na3PO4 and LiOH·H2O in distilled water at 80℃ respectively. After dissolution, slowly add the LiOH solution to the Na3PO4 solution while stirring. After the addition is complete, continue stirring and reacting for 4 hours. Filter the obtained precipitate and wash it with water until the pH is 10-12, preferably 12. Dry the obtained precipitate in an oven at 120℃ for 12 hours, and then calcine it in a muffle furnace at 300℃ for 8 hours to obtain lithium phosphate.

[0037] (2) The lithium phosphate obtained in the previous step and the prepared chloroplatinic acid solution were mixed and stirred. NaBH4 solution was slowly added dropwise (the rate of addition of NaBH4 was 0.5-1 mol / min, preferably 0.6-0.8 mol / min, relative to 1 mol of NaBH4). The mixture was stirred for 4 hours. After the reaction was completed, the mixture was filtered and the precipitate was washed with distilled water until the filtrate was neutral. Then it was dried at 120°C to obtain Pt / Li3PO4 catalysts modified with different Pt contents.

[0038] In the above synthesis method, the concentration of chloroplatinic acid in step (2) is 20 mg / ml. It can be diluted to different degrees according to the loading, so that the loading of Pt in the modified catalyst after reduction is 0.5 wt% to 2 wt%.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] This invention provides a method for preparing allyl alcohol by isomerization of propylene oxide, using a lithium phosphate catalyst supported on elemental Pt for the isomerization of propylene oxide to prepare allyl alcohol, achieving higher propylene oxide conversion (up to 76% or more), allyl alcohol selectivity (up to 85.8% or more), and better catalytic stability (long catalyst life). Attached Figure Description

[0041] Figure 1 This is a graph showing the catalyst stability test results in Example 2. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0043] The gas chromatograph used in this application was a Perkin Elmer Clarus-580. The test conditions were: high-purity N2 carrier gas, flow rate 1 mL / min, split ratio 30:1, injector temperature 250℃, and column temperature program: column temperature 50℃, residence time 2 min, heating rate 10℃ / min, heating to 260℃, residence time 10 min. External standard method was used for quantitative analysis.

[0044] Preparation Example 1

[0045] Preparation of modified lithium phosphate catalyst: 1 molar Na3PO4 and 4 molar LiOH·H2O were dissolved separately in distilled water at 80℃. The LiOH solution was slowly added dropwise to the Na3PO4 solution while stirring. After the addition was complete, the reaction was stirred for 4 hours. The resulting precipitate was filtered and washed with water until the pH reached 12. The precipitate was dried in an oven at 120℃ for 12 hours, and then calcined in a muffle furnace at 300℃ for 8 hours to obtain lithium phosphate. 4.7 g of the lithium phosphate obtained in the previous step and a prepared chloroplatinic acid solution (concentration 20 mg / ml, volume 2.5 ml) were added to 50 ml of distilled water and mixed with stirring. NaBH4 solution (volume 2.5 ml, concentration 0.5 mol / L, dropping rate 2 ml / min) was slowly added dropwise while stirring for 4 hours. After the reaction was complete, the mixture was filtered and the precipitate was washed with distilled water until the filtrate was neutral. Then, it was dried at 120℃ to obtain a 0.5 wt% Pt modified Pt / Li3PO4 catalyst.

[0046] Preparation Example 2

[0047] Preparation of modified lithium phosphate catalyst: 1 molar Na3PO4 and 4 molar LiOH·H2O were dissolved separately in distilled water at 80℃. After dissolution, the LiOH solution was slowly added dropwise to the Na3PO4 solution while stirring. After the addition was complete, the reaction was stirred for 4 hours. The resulting precipitate was filtered and washed with water until the pH reached 12. The precipitate was dried in an oven at 120℃ for 12 hours, and then calcined in a muffle furnace at 300℃ for 8 hours to obtain lithium phosphate. 4.7 g of the lithium phosphate obtained in the previous step was mixed with a prepared chloroplatinic acid solution (concentration 20 mg / ml, volume 5 ml) and stirred. NaBH4 solution (volume 5 ml, concentration 0.5 mol / L, dropping rate 4 ml / min) was slowly added dropwise while stirring for 4 hours. After the reaction was complete, the mixture was filtered and the precipitate was washed with distilled water until the filtrate was neutral. Then, it was dried at 120℃ to obtain a 1 wt% Pt modified Pt / Li3PO4 catalyst.

[0048] Preparation Example 3

[0049] Preparation of modified lithium phosphate catalyst: 1 molar Na3PO4 and 4 molar LiOH·H2O were dissolved separately in distilled water at 80℃. After dissolution, the LiOH solution was slowly added dropwise to the Na3PO4 solution while stirring. After the addition was complete, the reaction was stirred for 4 hours. The resulting precipitate was filtered and washed with water until the pH reached 12. The precipitate was dried in an oven at 120℃ for 12 hours, and then calcined in a muffle furnace at 300℃ for 8 hours to obtain lithium phosphate. 4.7 g of the lithium phosphate obtained in the previous step was mixed with a prepared chloroplatinic acid solution (concentration 20 mg / ml, volume 10 ml) and stirred. NaBH4 solution (volume 10 ml, concentration 0.5 mol / L, dropping rate 6 ml / min) was slowly added dropwise while stirring for 4 hours. After the reaction was complete, the mixture was filtered and the precipitate was washed with distilled water until the filtrate was neutral. Then, it was dried at 120℃ to obtain a 2 wt% Pt modified Pt / Li3PO4 catalyst.

[0050] Example 1

[0051] Propylene oxide isomerization reaction: 30 g of the modified lithium phosphate catalyst prepared in Preparation Example 1 was packed into a fixed-bed reactor. Preheated propylene oxide and nitrogen were introduced, with a nitrogen flow rate of 50 ml / min, a preheating temperature of 260 °C, a preheating pressure of 1 bar, an isomerization reaction temperature of 280 °C, and a propylene oxide mass hourly space velocity (WHSV) of 2 h⁻¹. -1 The reaction time was 4 hours. The reacted material was discharged from the bottom of the reactor, cooled by a cooler to obtain the product, and samples of the product were periodically sampled and analyzed by gas chromatography. The conversion rate of propylene oxide was 84.5%, and the selectivity of allyl alcohol was 92.0%.

[0052] Example 2

[0053] Propylene oxide isomerization reaction: 30 g of the modified lithium phosphate catalyst prepared in Preparation Example 2 above was packed into a fixed-bed reactor. Preheated propylene oxide and nitrogen were introduced, with a nitrogen flow rate of 50 ml / min, a preheating temperature of 260 °C, a preheating pressure of 1 bar, an isomerization reaction temperature of 300 °C, and a propylene oxide mass hourly space velocity of 4 h⁻¹. -1 The reaction time was 6 hours. The reactants were discharged from the bottom of the reactor, and the product was cooled by a cooler. The resulting product was analyzed by gas chromatography. The conversion rate of propylene oxide was 91.2%, and the selectivity of allyl alcohol was 98.1%.

[0054] Catalyst stability study: After 3000 hours of continuous operation, the propylene oxide conversion rate was no less than 86%, and the selectivity of allyl alcohol was no less than 96%. The results are as follows: Figure 1 As shown.

[0055] Example 3

[0056] Propylene oxide isomerization reaction: 30 g of the modified lithium phosphate catalyst prepared in Preparation Example 3 above was packed into a fixed-bed reactor. Preheated propylene oxide and nitrogen were introduced, with a nitrogen flow rate of 50 ml / min, a preheating temperature of 260 °C, a preheating pressure of 1 bar, an isomerization reaction temperature of 320 °C, and a propylene oxide mass hourly space velocity of 6 h⁻¹. -1 The reaction time was 8 hours. The reactants were discharged from the bottom of the reactor, and the product was cooled by a cooler. The resulting product was analyzed by gas chromatography. The conversion rate of propylene oxide was 88.6%, and the selectivity of allyl alcohol was 95.3%.

[0057] Example 4

[0058] The modified lithium phosphate catalyst was prepared using a method essentially the same as that used in Example 2. The difference was that, during the preparation process, the precipitate after the reaction of LiOH solution and Na3PO4 solution was filtered and washed with water until the pH reached 10. Under the isomerization conditions of Example 2, the conversion rate of propylene oxide was 80.1%, and the selectivity of allyl alcohol was 90.3%.

[0059] Example 5

[0060] The modified lithium phosphate catalyst was prepared using essentially the same method as in Example 2, except that the precipitate from the reaction of LiOH and Na3PO4 solutions was dried and then calcined in a muffle furnace at 350°C for 8 hours. Under the isomerization conditions of Example 2, the conversion rate of propylene oxide was 83.1%, and the selectivity of allyl alcohol was 92.8%.

[0061] Example 6

[0062] The modified lithium phosphate catalyst was prepared using a method essentially the same as that used in Example 2, except that the precipitate after the reaction of LiOH solution and Na3PO4 solution was filtered and washed with water until the pH reached 8. Under the isomerization conditions of Example 2, the conversion rate of propylene oxide was 76.4%, and the selectivity of allyl alcohol was 85.8%.

[0063] Comparative Example 1

[0064] The propylene oxide isomerization reaction was carried out using essentially the same method as in Example 2, except that a single lithium phosphate catalyst was used, i.e., unsupported elemental Pt. Under the catalytic conditions of Example 2, the propylene oxide conversion was 72.1%, and the allyl alcohol selectivity was 88.3%. After 500 hours of operation, the propylene oxide conversion decreased to 63.2%, and the allyl alcohol selectivity decreased to 70.6%.

[0065] Comparative Example 2

[0066] The modified lithium phosphate catalyst was prepared using essentially the same method as in Example 2, except that a reducing agent was not used during the preparation process. Specifically, after mixing and stirring lithium phosphate and chloroplatinic acid solution, the mixture was filtered, dried at 110°C, and then calcined at 300°C in air for 2 hours. Under the isomerization conditions of Example 2, the conversion rate of propylene oxide was 66.3%, and the selectivity for allyl alcohol was 70.2%.

[0067] Comparative Example 3

[0068] The modified lithium phosphate catalyst was prepared using essentially the same method as in Example 2, except that during the preparation process, 4.7 g of the lithium phosphate obtained in the previous step was mixed and stirred with a prepared copper acetate-ethanol solution (0.15 g copper acetate, 50 ml ethanol). The pH was adjusted to 13 with 1 mol / L NaOH solution, and stirring was continued for 3 hours at room temperature, followed by centrifugation. After washing once, it was dried at 120 °C for 3 hours and then calcined at 300 °C for 4 hours. A modified Cu / Li3PO4 catalyst with a Cu content of 1 wt% was obtained.

[0069] Under the isomerization conditions of Example 2, the conversion rate of propylene oxide was 64.8%, and the selectivity of allyl alcohol was 89.5%.

[0070] Comparative Example 4

[0071] The modified lithium phosphate catalyst was prepared using essentially the same method as in Example 2, except that the chloroplatinic acid solution (concentration 20 mg / ml, volume 5 ml) was replaced with HAuCl4 (concentration 0.0488 mol / ml, volume 5 ml). The pH was adjusted to 11 with 1 mol / L sodium hydroxide solution, and stirring was continued for 2 hours. The resulting precipitate was filtered, washed, dried at 100 °C, and then calcined at 300 °C for 4 hours. A modified Au / Li3PO4 catalyst with an Au content of 1 wt% was obtained.

[0072] Under the isomerization conditions of Example 2, the conversion rate of propylene oxide was 70.2%, and the selectivity of allyl alcohol was 82.1%.

[0073] As can be seen from the above embodiments and comparative examples, the preferred embodiments of the present invention, namely Examples 1-3, have better propylene oxide conversion and allyl alcohol selectivity.

[0074] Compared to Comparative Example 1, which used a single lithium phosphate catalyst for the isomerization of propylene oxide to prepare allyl alcohol, Example 2 used the modified catalyst of supported elemental Pt from Preparation Example 2 for the isomerization of propylene oxide to prepare allyl alcohol. It exhibited higher catalytic stability, with a propylene oxide conversion rate of not less than 86% and an allyl alcohol selectivity of not less than 96% after 3000 hours of continuous operation, indicating that the catalyst prepared in Preparation Example 2 had a longer service life.

[0075] Compared to Comparative Example 3, which used modified lithium phosphate to support elemental Cu, Example 2 used the modified catalyst of elemental Pt supported in Preparation Example 2 for the isomerization of propylene oxide to prepare allyl alcohol, and obtained higher propylene oxide conversion and allyl alcohol selectivity.

[0076] Compared to Comparative Example 4, which used modified lithium phosphate to support elemental Au, Example 2 used the modified catalyst of elemental Pt supported in Preparation Example 2 for the isomerization of propylene oxide to prepare allyl alcohol, which has higher propylene oxide conversion and allyl alcohol selectivity.

[0077] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A process for the isomerization of propylene oxide to allyl alcohol, characterized in that The method includes: contacting preheated propylene oxide with a catalyst under an inactive carrier gas to carry out an isomerization reaction; The catalyst is a lithium phosphate catalyst supported on elemental Pt; the loading of elemental Pt in the catalyst is 0.5 wt% to 2 wt% based on the mass of lithium phosphate.

2. The method of claim 1, wherein, The preheated propylene oxide has a temperature of 180 to 260°C, a pressure of 0.8 to 1.2 bar, a mass space velocity of 1 h -1 ~ 10 h -1 ; And / or, the conditions for the isomerization reaction include: a temperature of 260–340°C and a time of 4–8 hours; And / or, the inactive carrier gas includes at least one of nitrogen, helium, argon and neon; And / or, relative to 1g of the catalyst, the flow rate of the inactive gas carrier gas is 1-40ml / min.

3. The method according to claim 1 or 2, characterized in that, The catalyst is prepared by adding a reducing agent dropwise to a solution containing lithium phosphate and platinum precursor to carry out a reduction reaction.

4. The method of claim 3, wherein, The molar ratio of lithium phosphate, reducing agent, and platinum precursor is 58–336:6–12:1, wherein the amount of platinum precursor is calculated as platinum element. And / or, the platinum precursor is selected from at least one of chloroplatinic acid, sodium chloroplatinate, and potassium chloroplatinate; And / or, the reducing agent is selected from at least one of NaBH4, formaldehyde, and ethylene glycol.

5. The method according to claim 3 or 4, characterized in that, The rate at which the reducing agent is added is 0.5-1 mol / min relative to 1 mol of reducing agent; And / or, the reduction reaction takes 2 to 6 hours.

6. The method according to any one of claims 3-5, characterized in that, The method for preparing the lithium phosphate includes: (1) Add LiOH solution dropwise to Na3PO4 solution to carry out the reaction; (2) Filter the precipitate, wash the precipitate with water until the pH of the filtrate is 10-12, then dry and calcine.

7. The method of claim 6, wherein, The solvent in the Na3PO4 solution is water or a mixture of ethanol and water; the solvent in the LiOH solution is water or a mixture of ethanol and water; the volume ratio of water to ethanol in the mixture is 3:1 to 1:

3.

8. The method according to claim 6 or 7, characterized in that, The molar ratio of Na3PO4 to LiOH is 1:3 to 5; And / or, in step (1), the reaction conditions include: a reaction time of 2 to 6 hours and a reaction temperature of 70 to 90°C.

9. The method according to any one of claims 6-8, characterized in that, In step (2), the drying temperature is 100-160℃ and the drying time is 10-16 hours.

10. The method according to any one of claims 6-9, characterized in that, In step (2), the calcination temperature is 260-350℃ and the calcination time is 6-12 hours.

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