Preparation method of alkaline earth metal catalyst and its application

Abstract

The present invention discloses a method for preparing an alkaline earth metal catalyst, comprising: (1) adding an alkaline earth metal compound to a polyether polyol under an inert atmosphere, stirring for reaction; (2) lowering the temperature, dripping an inorganic oxygen-containing acid into the reaction solution, stirring for reaction, and obtaining the alkaline earth metal catalyst. The present invention also discloses a method for synthesizing a water reducer monomer polyether, comprising: (1) adding an initiator and an alkaline earth metal catalyst to a reaction vessel; (2) controlling the reaction temperature and reaction pressure, continuously adding an epoxide, and reacting until the pressure no longer decreases, and obtaining the water reducer monomer polyether. In the process of synthesizing the water reducer monomer polyether catalyzed by the alkaline earth metal catalyst of the present invention, no hydrogen is generated, no moisture is generated, the production process is safe, the product can be obtained by one-step polymerization, no neutralization treatment is required, and the content of by-product polyethylene glycol in the product can be significantly reduced, and the product has the advantages of low production cost and good product performance.

Description

Technical Field

[0001] The invention belongs to the field of polyether polyols, and in particular relates to a method for preparing an alkaline earth metal catalyst and a method for catalytically synthesizing a water reducing agent monomer polyether by using the alkaline earth metal catalyst. Background Art

[0002] Polycarboxylic acid water reducer is a high-performance concrete water reducer with good application prospects, excellent comprehensive performance and green environmental protection. After being added to the concrete mixture, the water reducer has a dispersing effect on cement particles, which can improve its workability, reduce the unit water consumption and improve the fluidity of the concrete mixture. Polycarboxylic acid water reducer is synthesized by copolymerization of water reducer monomer polyether and unsaturated carboxylic acid small molecule monomer under the action of initiator. Water reducer monomer polyether is a vital basic raw material in the polycarboxylic acid water reducer industry.

[0003] At present, the traditional industrial production process of water-reducing agent monomer polyether usually uses metallic sodium or sodium hydride as a catalyst, and a crude product is prepared by ring-opening polymerization of an ene alcohol initiator and an alkylene oxide, and then after neutralization treatment, the final product is obtained by cooling, slicing and granulation.

[0004] The traditional production process of water-reducing agent monomer polyether is complicated and has a long production cycle. When using sodium metal or sodium hydride as a catalyst, flammable and explosive hydrogen is generated, and the process safety is poor. In addition, some initiators have poor solubility in sodium metal and a long dissolution cycle. During the catalytic reaction, a large amount of impurity polyethylene glycol is generated, which produces a large number of bubbles and affects the performance of water-reducing agent products. In addition, after using traditional alkali metal catalysts such as sodium metal to prepare water-reducing agent monomer polyether, further neutralization post-treatment is required, which has a complicated process flow and high production cost.

[0005] Therefore, developing a method for synthesizing water reducing agent monomer polyether by catalysis of alkaline earth metal catalyst with safe process and simple flow has great industrial application value. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for preparing an alkaline earth metal catalyst and a method for synthesizing a water reducer monomer polyether using the alkaline earth metal catalyst, which solves the problems of complex process flow and high production cost in the prior art. The alkaline earth metal catalyst obtained by the method of the present invention has good solubility in the initiator, no hydrogen is generated during the synthesis process, and the synthesized product does not need neutralization post-treatment, which ensures the safety of the water reducer monomer polyether synthesis process, greatly improves product quality, and reduces production costs.

[0007] To achieve its purpose, the present invention adopts the following technical solutions:

[0008] In one aspect of the present invention, it relates to a method for preparing an alkaline earth metal catalyst, the method comprising the following steps:

[0009] (1) under an inert atmosphere, adding an alkaline earth metal compound to a polyether polyol, controlling the temperature to be 80-150° C., preferably 90-120° C., for example, 100° C., 110° C., 130° C. or 140° C., and stirring the reaction;

[0010] (2) lowering the temperature to 10-90°C, preferably 20-50°C, such as 30°C, 40°C, 60°C, 70°C or 80°C, etc., and adding the inorganic oxygen-containing acid dropwise to the reaction solution of step (1), stirring the reaction, and obtaining the alkaline earth metal catalyst.

[0011] In a specific embodiment of the present invention, the alkaline earth metal compound is one or more of magnesium oxide, magnesium hydroxide, magnesium carboxylate, calcium oxide, calcium hydroxide, calcium carboxylate, barium oxide, barium hydroxide, strontium oxide and strontium hydroxide.

[0012] In a specific embodiment of the present invention, the polyether polyol is polyoxyethylene ether, preferably polyethylene glycol and / or diethylene glycol monoethyl ether.

[0013] In a specific embodiment of the present invention, the inorganic oxygen-containing acid is phosphoric acid, nitric acid or sulfuric acid, preferably sulfuric acid.

[0014] In a specific embodiment of the present invention, in step (1), the weight ratio of the alkaline earth metal compound to the polyether polyol is 0.05:1-1:1, preferably 0.1:1-1:1, for example 0.08:1, 0.15:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1 or 0.9:1, etc.

[0015] In a specific embodiment of the present invention, in step (1), the stirring reaction time is 2-6 hours, such as 3 hours, 4 hours or 5 hours.

[0016] In a specific embodiment of the present invention, in step (2), the molar ratio of the alkaline earth metal compound to the inorganic oxygen-containing acid is 10:1-1:1, preferably 4:1-1.2:1, for example 9:1, 8:1, 7:1, 6:1, 5:1, 3:1, 2.4:1, 2:1, 1.8:1, 1.6:1 or 1.4:1, etc.

[0017] In a specific embodiment of the present invention, in step (2), the stirring reaction time is 1-24 h, for example, 2 h, 6 h, 10 h, 14 h, 16 h, 18 h, 20 h or 22 h, etc.

[0018] In a specific embodiment of the present invention, in step (2), before obtaining the alkaline earth metal catalyst, reduced pressure distillation is performed to remove impurities, and the conditions of the reduced pressure distillation are: temperature 120-240°C, such as 140°C, 160°C, 180°C, 200°C or 220°C, etc.; pressure -0.05Mpa to -0.098Mpa, such as -0.06Mpa, -0.07Mpa, -0.08Mpa or -0.09Mpa, etc.; time 1-8h, such as 2h, 3h, 4h, 5h, 6h or 7h, etc.

[0019] Another aspect of the present invention relates to the use of the alkaline earth metal catalyst prepared by the above method in the synthesis of water reducing agent monomer polyether.

[0020] In another aspect of the present invention, it relates to a method for synthesizing a water reducing agent monomer polyether, the method comprising the following steps:

[0021] (1) using unsaturated alcohols, unsaturated alcohol ethers or unsaturated amines as initiators, and adding the initiators and the alkaline earth metal catalyst prepared by the above method into a reaction container;

[0022] (2) controlling the reaction temperature to be 100-150° C., preferably 110-130° C., for example, 120° C. or 140° C., etc.; controlling the reaction pressure to be 0.1-0.6 MPa, preferably 0.1-0.3 MPa, and continuously adding epoxide according to the target molecular weight, reacting until the pressure no longer decreases, thereby obtaining the water reducer monomer polyether.

[0023] In a specific embodiment of the present invention, the initiator is methyl allyl alcohol, isopentenol, allyl alcohol or vinyl glycol ether.

[0024] In a specific embodiment of the present invention, the epoxide is ethylene oxide.

[0025] In a specific embodiment of the present invention, the amount of the initiator is 1wt%-5wt% of the total product, for example, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt% or 4.5wt%, etc.

[0026] In a specific embodiment of the present invention, the amount of the catalyst used is 0.02wt%-0.5wt% of the total product, for example, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.40wt% or 0.45wt%, etc.

[0027] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects:

[0028] (1) The alkaline earth metal catalyst of the present invention does not generate hydrogen or water during the catalytic synthesis of the water-reducing agent monomer polyether, has good process safety, and contains less byproduct polyethylene glycol in the obtained water-reducing agent monomer polyether;

[0029] (2) The alkaline earth metal catalyst of the present invention has good compatibility with the initiator, produces less foam in the product, and is efficient and simple to use;

[0030] (3) The water-reducing agent monomer polyether of the present invention does not require neutralization treatment during production, the process is green and simple, and the production cycle is short. DETAILED DESCRIPTION

[0031] The method provided by the present invention is described in further detail below, but the present invention is not limited thereby.

[0032] raw material

[0033] Magnesium hydroxide, polyethylene glycol, sulfuric acid, methyl allyl alcohol, calcium hydroxide, ethylene glycol monoethyl ether, strontium hydroxide, isopentenol, and calcium oxide are all analytical grade reagents purchased from Beijing Inokai Technology Co., Ltd. Unless otherwise specified, other raw materials appearing in this article are conventional commercially available raw materials.

[0034] Test Method

[0035] Hydroxyl value: GB12008.3-2009;

[0036] Polyethylene glycol content: GB / T17830-1999;

[0037] Double bond retention rate: GB / T12008.7-2010;

[0038] pH (1% aqueous solution): GB / T12008.2-2010.

[0039] Example

[0040] Example 1

[0041] Catalyst preparation

[0042] Under nitrogen atmosphere and reflux condensation, 10g of magnesium hydroxide was added to 100g of polyethylene glycol (molecular weight: 400g / mol), and the temperature was controlled at 120°C and stirred for 2h. The temperature of the reaction liquid was lowered to 50°C, 4.3g of sulfuric acid (98%) was slowly added dropwise thereto, and the reaction was continued to stir for 5h, then the temperature was raised to 160°C, the pressure was reduced to -0.08Mpa, and impurities were removed for 3h to obtain 105g of alkaline earth metal catalyst with a moisture content of less than 0.1%.

[0043] Synthesis of Polyether Monomer for Water Reducing Agent

[0044] 500g of methyl allyl alcohol and 17g of the above alkaline earth metal catalyst are added to a 25L reactor. First, nitrogen is passed to make the reactor pressure 0.3Mpa, then the pressure is discharged to 0Mpa, and then vacuumed to -0.098Mpa. This operation is repeated three times to complete nitrogen replacement. The temperature is raised to 130°C, and 16860g of ethylene oxide is continuously added to the reaction vessel. During the reaction, the reaction temperature is controlled at 110-130°C, and the reaction pressure is controlled at 0.2-0.3Mpa, not higher than 0.4Mpa. After the addition of epoxide is completed, the reactor is aged until the pressure in the reactor no longer decreases, and a water reducer monomer polyether is obtained.

[0045] The water reducing agent monomer polyether prepared in this example was tested for its indicators: hydroxyl value: 22.3 mgKOH / g; polyethylene glycol: 1.1 wt %; double bond retention rate: 97.3%; pH (1% aqueous solution): 6.58.

[0046] Example 2

[0047] Catalyst preparation

[0048] Under nitrogen atmosphere and reflux condensation, 20g of calcium hydroxide was added to 120g of diethylene glycol monoethyl ether, and the temperature was controlled at 90°C and stirred for 5h. The temperature of the reaction liquid was lowered to 30°C, 10.5g of nitric acid (68%) was slowly added dropwise thereto, and the reaction was continued with stirring for 8h, then the temperature was raised to 220°C, the pressure was reduced to -0.05Mpa, and impurities were removed for 5h to obtain 141g of alkaline earth metal catalyst with a moisture content of less than 0.1%.

[0049] Synthesis of Polyether Monomer for Water Reducing Agent

[0050] 500g of isopentenol and 20g of the above alkaline earth metal catalyst are added to a 25L reactor. First, nitrogen is passed to make the reactor pressure 0.3Mpa, then the pressure is discharged to 0Mpa, and then vacuumed to -0.098Mpa. This operation is repeated three times to complete nitrogen replacement. The temperature is raised to 115°C, and 14035g of ethylene oxide is continuously added to the reaction vessel. During the reaction, the reaction temperature is controlled at 115-130°C, and the reaction pressure is controlled at 0.2-0.6Mpa, not higher than 0.6Mpa. After the addition of epoxide is completed, the reactor is aged until the pressure in the reactor no longer decreases, and a water reducer monomer polyether is obtained.

[0051] The water reducing agent monomer polyether prepared in this example was tested for its indicators: hydroxyl value: 22.1 mgKOH / g; polyethylene glycol: 0.9 wt %; double bond retention rate: 96.9 %; pH (1 % aqueous solution): 6.82.

[0052] Example 3

[0053] Catalyst preparation

[0054] Under nitrogen atmosphere and reflux condensation, 15g of calcium hydroxide was added to 100g of diethylene glycol monoethyl ether, and the temperature was controlled at 130°C and stirred for 4h. The temperature of the reaction liquid was lowered to 80°C, 2.3g of sulfuric acid (98%) was slowly added dropwise thereto, and the reaction was continued to be stirred for 16h, then the temperature was raised to 120°C, the pressure was reduced to -0.06Mpa, and impurities were removed for 3h to obtain 117g of alkaline earth metal catalyst with a moisture content of less than 0.1%.

[0055] Synthesis of Polyether Monomer for Water Reducing Agent

[0056] 500g of methyl allyl alcohol and 80g of the above alkaline earth metal catalyst are added to a 25L reactor. First, nitrogen is passed to make the reactor pressure 0.3Mpa, then the pressure is discharged to 0Mpa, and then the pressure is evacuated to -0.098Mpa. This operation is repeated three times to complete nitrogen replacement. The temperature is raised to 120°C, and 16167g of ethylene oxide is continuously added to the reaction vessel. During the reaction, the reaction temperature is controlled at 110-120°C, and the reaction pressure is controlled at 0.1-0.2Mpa, not higher than 0.3Mpa. After the addition of epoxide is completed, the reactor is aged until the pressure in the reactor no longer decreases, and a water reducer monomer polyether is obtained.

[0057] The water reducing agent monomer polyether prepared in this example was tested for its indicators: hydroxyl value: 23.4 mgKOH / g; polyethylene glycol: 1.2 wt %; double bond retention rate: 96.8 %; pH (1 % aqueous solution): 6.98.

[0058] Example 4

[0059] Catalyst preparation

[0060] Under nitrogen atmosphere and reflux condensation, 10 g of strontium hydroxide was added to 120 g of diethylene glycol monoethyl ether, and the temperature was controlled at 150°C and stirred for 5 hours. The temperature of the reaction liquid was lowered to 20°C, 5.5 g of nitric acid (68%) was slowly added dropwise thereto, and the reaction was continued to be stirred for 6 hours, then the temperature was raised to 180°C, the pressure was reduced to -0.098 MPa, and impurities were removed for 8 hours to obtain 128 g of alkaline earth metal catalyst with a moisture content of less than 0.1%.

[0061] Synthesis of Polyether Monomer for Water Reducing Agent

[0062] 500g of isopentenol and 18g of the above alkaline earth metal catalyst are added to a 25L reactor. First, nitrogen is passed to make the reactor pressure 0.3Mpa, then the pressure is discharged to 0Mpa, and then vacuumed to -0.098Mpa. This operation is repeated three times to complete nitrogen replacement. The temperature is raised to 120°C, and 16941g of ethylene oxide is continuously added to the reaction vessel. During the reaction, the reaction temperature is controlled at 115-130°C, and the reaction pressure is controlled at 0.2-0.3Mpa, not higher than 0.4Mpa. After the addition of epoxide is completed, the reactor is aged until the pressure in the reactor no longer decreases, and a water reducer monomer polyether is obtained.

[0063] The water reducing agent monomer polyether prepared in this example was tested for its indicators: hydroxyl value: 18.7 mgKOH / g; polyethylene glycol: 1.1 wt %; double bond retention rate: 97.1 %; pH (1 % aqueous solution): 6.66.

[0064] Example 5

[0065] Catalyst preparation

[0066] Under nitrogen atmosphere and reflux condensation, 10g of calcium oxide was added to 100g of diethylene glycol monoethyl ether, and the temperature was controlled at 80°C and stirred for 6h. The temperature of the reaction liquid was lowered to 50°C, 8.3g of sulfuric acid (98%) was slowly added dropwise thereto, and the reaction was continued with stirring for 12h, then the temperature was raised to 180°C, the pressure was reduced to -0.08Mpa, and impurities were removed for 1h to obtain 128g of alkaline earth metal catalyst with a moisture content of less than 0.1%.

[0067] Synthesis of Polyether Monomer for Water Reducing Agent

[0068] 500g of methyl allyl alcohol and 15g of the above alkaline earth metal catalyst are added to a 25L reactor. First, nitrogen is passed to make the reactor pressure 0.3Mpa, then the pressure is discharged to 0Mpa, and then vacuumed to -0.098Mpa. This operation is repeated three times to complete nitrogen replacement. The temperature is raised to 115°C, and 16860g of ethylene oxide is continuously added to the reaction vessel. During the reaction, the reaction temperature is controlled at 115-130°C, and the reaction pressure is controlled at 0.2-0.3Mpa, not higher than 0.4Mpa. After the addition of epoxide is completed, the reactor is aged until the pressure in the reactor no longer decreases, and a water reducer monomer polyether is obtained.

[0069] The water reducing agent monomer polyether prepared in this example was tested for its indicators: hydroxyl value: 23.3 mgKOH / g; polyethylene glycol: 1.0 wt %; double bond retention rate: 98.6%; pH (1% aqueous solution): 6.73.

[0070] Example 6

[0071] Catalyst preparation

[0072] Under nitrogen atmosphere and reflux condensation, 100g of magnesium hydroxide was added to 100g of polyethylene glycol (molecular weight: 400g / mol), and the temperature was controlled at 120°C and stirred for 3h. The temperature of the reaction liquid was lowered to 10°C, 18.3g of sulfuric acid (98%) was slowly added dropwise thereto, and the reaction was continued to stir for 24h, then the temperature was raised to 160°C, the pressure was reduced to -0.098Mpa, and impurities were removed for 6h to obtain 210g of alkaline earth metal catalyst with a moisture content of less than 0.1%.

[0073] Synthesis of Polyether Monomer for Water Reducing Agent

[0074] 500g of methyl allyl alcohol and 5g of the above alkaline earth metal catalyst are added to a 25L reactor. First, nitrogen is passed to make the reactor pressure 0.3Mpa, then the pressure is discharged to 0Mpa, and then vacuumed to -0.098Mpa. This operation is repeated three times to complete nitrogen replacement. The temperature is raised to 130°C, and 16860g of ethylene oxide is continuously added to the reaction vessel. During the reaction, the reaction temperature is controlled at 110-130°C, and the reaction pressure is controlled at 0.2-0.3Mpa, not higher than 0.4Mpa. After the addition of epoxide is completed, the reactor is aged until the pressure in the reactor no longer decreases, and a water reducer monomer polyether is obtained.

[0075] The water reducing agent monomer polyether prepared in this example was tested for its indicators: hydroxyl value: 22.3 mgKOH / g; polyethylene glycol: 1.1 wt %; double bond retention rate: 97.3%; pH (1% aqueous solution): 6.58.

[0076] Comparative Example 1

[0077] The difference between this comparative example and the above-described embodiment 1 is that this comparative example uses metallic sodium as a catalyst in the synthesis of water-reducing agent monomer polyether. 500g methyl allyl alcohol and 17g metallic sodium catalyst are added to a 25L reactor to react and blast nitrogen at the same time, and the pressure is a slight positive pressure (0-0.02Mpa), and the venting pipeline valve is opened at the same time to vent hydrogen. The reaction temperature is controlled within the range of 25-35°C. After the catalyst is added, the reaction is dissolved for 3 hours, and it is confirmed that the metallic sodium has been dissolved, and then the nitrogen is passed to make the reactor pressure 0.3Mpa, and the rear row is pressed to 0Mpa, and vacuumized to -0.098Mpa, and nitrogen replacement is completed 3 times in this operation. It is warming up to 130°C, and 16860g of ethylene oxide is continuously added to the reaction vessel, and the reaction temperature is controlled to 110-130°C during the reaction, and the reaction pressure is controlled to 0.2-0.3Mpa at the same time, which is not higher than 0.4Mpa. After the addition of the epoxide is completed, the reaction vessel is aged until the pressure in the reaction vessel no longer decreases, and then the reaction vessel is neutralized with glacial acetic acid to obtain a water reducer monomer polyether.

[0078] The water reducing agent monomer polyether prepared in this comparative example was taken to detect its indicators: hydroxyl value: 22.4 mgKOH / g; polyethylene glycol: 2.8 wt %; double bond retention rate: 96.3%; pH (1% aqueous solution): 6.58.

[0079] Comparative Example 2

[0080] The difference between this comparative example and the above-mentioned Example 2 is that in this comparative example, metallic sodium is used as a catalyst in the synthesis of the water reducing agent monomer polyether.

[0081] 500g of isopentenol and 20g of sodium metal catalyst are added to a 25L reactor to react and blast nitrogen at the same time, the pressure is a slight positive pressure (0-0.02Mpa), and the venting pipeline valve is opened at the same time to vent hydrogen. The reaction temperature is controlled within the range of 25-35°C. After the catalyst is added, the reaction is dissolved for 6 hours, and it is confirmed that the sodium metal is dissolved. Then nitrogen is passed to make the reactor pressure 0.3Mpa, the rear row is pressed to 0Mpa, and vacuumized to -0.098Mpa, and nitrogen replacement is completed 3 times in this operation. It is warmed to 115°C, and 14035g of ethylene oxide is continuously added to the reaction vessel. During the reaction, the reaction temperature is controlled to 115-130°C, and the reaction pressure is controlled to 0.2-0.6Mpa, which is not higher than 0.6Mpa. After the addition of epoxide is completed, it is aged to the pressure in the reactor and no longer decreases, and a water reducer monomer polyether is obtained after neutralization with glacial acetic acid.

[0082] The water reducing agent monomer polyether prepared in this example was tested for its indicators: hydroxyl value: 22.3 mgKOH / g; polyethylene glycol: 2.1 wt %; double bond retention rate: 96.1 %; pH (1 % aqueous solution): 6.76.

[0083] It can be seen from the above examples and comparative examples that when the alkaline earth metal catalyst obtained by the method of the present invention is used to prepare a water reducer monomer polyether, the catalyst can be used immediately after being added, no hydrogen is generated, no neutralization treatment is required after the reaction is completed, the synthesis cycle is significantly shortened, and the polyethylene glycol impurity content in the prepared product is low, which has good prospects for industrial application.

[0084] Although the present invention has been described in detail for the purpose of illustration in the foregoing text, it should be understood that these detailed descriptions are only for illustration and can be modified by those skilled in the art without departing from the spirit and scope of the present invention. The present invention is limited only by the claims.

Claims

1. A method for preparing an alkaline earth metal catalyst, the method comprising the following steps: (1) Under an inert atmosphere, an alkaline earth metal compound is added to a polyether polyol, the temperature is controlled at 80-150° C., and the reaction is stirred; (2) lowering the temperature to 10-90° C., adding an inorganic oxygen-containing acid dropwise to the reaction solution of step (1), stirring for reaction, and obtaining the alkaline earth metal catalyst; Wherein, the alkaline earth metal compound is one or more of magnesium oxide, magnesium hydroxide, magnesium carboxylate, calcium oxide, calcium hydroxide, calcium carboxylate, barium oxide, barium hydroxide, strontium oxide and strontium hydroxide; Wherein, the polyether polyol is polyoxyethylene ether; Wherein, the inorganic oxygen-containing acid is phosphoric acid, nitric acid or sulfuric acid; In step (1), the weight ratio of the alkaline earth metal compound to the polyether polyol is 0.05:1-1:1; In step (2), the molar ratio of the alkaline earth metal compound to the inorganic oxygen-containing acid is 10:1-1:

1.

2. The method according to claim 1, wherein: In step (1), the temperature is controlled to be 90-120°C; and / or, in step (2), the temperature is lowered to 20-50°C.

3. The method according to claim 1, wherein: The polyether polyol is polyethylene glycol and / or diethylene glycol monoethyl ether.

4. The method according to any one of claims 1 to 3, wherein: In step (1), the weight ratio of the alkaline earth metal compound to the polyether polyol is 0.1:1-1:1; and / or, the stirring reaction time is 2-6 hours; and / or, In step (2), the molar ratio of the alkaline earth metal compound to the inorganic oxygen-containing acid is 4:1-1.2:1; and / or the stirring reaction time is 1-24 hours; and / or, before obtaining the alkaline earth metal catalyst, reduced pressure distillation is performed to remove impurities, and the conditions of the reduced pressure distillation are: temperature 120-240°C, pressure -0.05Mpa to -0.098Mpa, time 1-8h.

5. Use of the alkaline earth metal catalyst prepared by the method according to any one of claims 1 to 4 in the synthesis of water reducing agent monomer polyether.

6. A method for synthesizing a water reducing agent monomer polyether, the method comprising the following steps: (1) using unsaturated alcohols, unsaturated alcohol ethers or unsaturated amines as initiators, and adding the initiators and the alkaline earth metal catalyst prepared by the method according to any one of claims 1 to 4 into a reaction vessel; (2) controlling the reaction temperature to 100-150° C.; controlling the reaction pressure to 0.1-0.6 MPa, continuously adding epoxide according to the target molecular weight, and reacting until the pressure no longer decreases, thereby obtaining the water reducer monomer polyether.

7. The method according to claim 6, wherein: In step (2), the reaction temperature is controlled at 110-130°C; the reaction pressure is controlled at 0.1-0.3Mpa.

8. The method according to claim 6, wherein: The initiator is methyl allyl alcohol, isopentanol, allyl alcohol or vinyl glycol ether.

9. The method according to claim 6, wherein: The epoxide is ethylene oxide.

10. The method according to any one of claims 6 to 9, wherein: The amount of the initiator used is 1wt%-5wt% of the total product; and / or the amount of the catalyst used is 0.02wt%-0.5wt% of the total product.