Preparation method of condensation-based rigid foam polyether polyol

Abstract

The present invention relates to the field of polyether polyols for polyurethane, and in particular to a method for preparing condensate-based rigid foam polyether polyols. The method comprises the following steps: adding cyclohexanone and paraformaldehyde into a reaction container, adding an alkali catalyst under continuous stirring, reacting to obtain a cyclohexanone formaldehyde condensate; adding cyclohexanone formaldehyde condensate and polyols as mixed initiators into the reaction container, adding a catalyst, heating and dripping the first section of alkylene oxide to extend the polyether chain, and continuing the internal pressure reaction after the feeding is completed to obtain an intermediate polyether polyol; heating and dripping the second section of alkylene oxide, pressurizing after the feeding is completed, and reacting the internal pressure to obtain a polyether polyol crude polymer; keeping the temperature and bubbling with nitrogen, discharging after bubbling, and obtaining a condensate-based rigid foam polyether polyol. Since the cyclohexanone formaldehyde condensate introduces a cyclic group, the introduction of the cyclic structure as an initiator in the process of synthesizing polyether reduces the deformation between molecular chains, thereby improving the demoulding property of the foam.

Description

Technical Field

[0001] The invention relates to the field of polyether polyols for polyurethane, in particular to a method for preparing condensation-based rigid foam polyether polyols. Background Art

[0002] For refrigerator and cold storage manufacturers, improving production efficiency has always been their goal. At present, the demoulding time of refrigerator manufacturers is mostly 6~7 minutes, which requires that the foam must be completely solidified and shaped within 6~7 minutes, otherwise it will cause foam expansion and cause the refrigerator to deform after demoulding, thus affecting product quality. With the advancement of production technology, the foam molding cycle of new production lines is getting shorter and shorter, and demoulding becomes more important. Demolding is affected by both chemical and process factors. Polyether polyols are a key factor affecting demoulding. When the demoulding time of foams obtained from different types of polyethers is the same, the thickness change rate is very different. The foam of poor performance varieties may even become soft. Therefore, a polyether with high initial strength and good demoulding performance is urgently needed in refrigerator production.

[0003] In the general rigid foam polyether polyol category, it has been reported that sucrose, liquid sorbitol, pentaerythritol, glycerol, diethylene glycol, propylene glycol, diethanolamine, triethanolamine are used as initiators to polymerize polyether with epoxides. These polyether products can be used for rigid foam plastics for various purposes, but there is no polyol with cyclohexanone formaldehyde condensate as initiator in the prior art. Cyclohexanone is an important organic chemical raw material. In recent years, with the commissioning of cyclohexanone devices of more and more enterprises, cyclohexanone shows a trend of overcapacity. In addition, due to the restriction of the use of solvent-based coatings and inks due to environmental protection and other factors, the amount of cyclohexanone used as a solvent is greatly reduced, which also increases the trend of cyclohexanone excess. Among them, cyclohexanone formaldehyde condensate is an important organic intermediate, which can be used to synthesize various compounds, such as polyurethane, polyester, polyamide, rubber, etc.

[0004] Patent CN106590379A discloses that bromine-containing diol / phenol is used as an initiator, and a ring-opening polymerization reaction is carried out with epichlorohydrin under the action of a catalyst to obtain a difunctional polyepichlorohydrin, and then the above product is reacted with a strong alkaline solution to obtain an epoxy-terminated compound, and finally the epoxy-terminated compound is subjected to a hydrolysis reaction and then post-treated to obtain a halogen-containing flame-retardant polyether polyol. The advantages of this process are that the raw materials are cheap and easy to obtain, and the reaction is simple; however, the polyether polyol prepared by this method is less active than the aniline polyether, and the strength and demoulding properties of the obtained foam are not well improved. Patent CN1463998A discloses a rigid polyurethane foam composition with excellent demoulding performance, which is composed of 40-60% (weight percentage) of polyol obtained by neutralization reaction of sorbitol with organic oxide as initiator; 5-10% (weight percentage) of polyol obtained by neutralization reaction of ethylenediamine with organic oxide as initiator; 20-30% (weight percentage) of polyol obtained by neutralization reaction of toluenediamine and trihydroxyethylamine with organic oxide as composite initiator; and 5-20% (weight percentage) of multifunctional alcohol with any ester structure. It uses HCFC-141b as a foaming agent, which not only destroys the structure of the ozone layer but also is not conducive to the development of an environmentally friendly economy. It only improves the demoulding performance of the foam, and does not specify a specific demoulding time.

[0005] Therefore, in view of the above problems, it is urgent to synthesize a simple and efficient reactive polyol to solve the above-mentioned problems of low foam strength, poor miscibility, long demoulding time, and reduce the thermal conductivity of polyurethane foam. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a condensation-based rigid foam polyether polyol, in which a cyclic group is introduced during the synthesis of the polyether, thereby reducing the deformation between the molecular chains and improving the demolding property. Since the condensate is composed of a cyclic structure, the polyether macromolecular chain contains a rigid chain group, thereby giving the downstream products better mechanical properties and thermal stability.

[0007] The method for preparing the condensation-based rigid foam polyether polyol of the present invention comprises the following steps:

[0008] (1) adding cyclohexanone and paraformaldehyde into a reaction vessel, adding an alkali catalyst under continuous stirring, and reacting to obtain a cyclohexanone formaldehyde condensate;

[0009] (2) Cyclohexanone formaldehyde condensate and polyol are added as mixed initiators into a reaction vessel, a catalyst is added, nitrogen is charged into the reaction vessel for leak testing, and nitrogen is replaced. After the replacement is completed, the temperature is raised to 80-85° C. under vacuum conditions, and the first stage of alkylene oxide is added dropwise for polyether chain extension. During the feeding process, the reaction temperature is controlled to be 80-85° C. and the pressure is controlled to be 0.1-0.4 MPa. After the feeding is completed, the internal pressure reaction is continued for 1-2 hours to obtain an intermediate polyether polyol;

[0010] (3) The intermediate polyether polyol is heated to 110-120°C, and the second stage alkylene oxide is added dropwise again. During the feeding process, the reaction temperature is controlled to be 110-120°C and the pressure is controlled to be 0.1-0.4 MPa. After the feeding is completed, the pressure is increased to 0.2-0.3 MPa, and the reaction is continued at the internal pressure for 2-3 hours to obtain a crude polyether polyol polymer;

[0011] (4) The crude polyether polyol is heated to 110-120°C and then nitrogen is bubbled to remove residual small molecules. The material is discharged after bubbling to obtain a condensation-based rigid foam polyether polyol.

[0012] The mass ratio of cyclohexanone to paraformaldehyde in step (1) is (40-77):(23-60).

[0013] The reaction in step (1) is carried out at a temperature of 90-100°C and a time of 2-6 hours.

[0014] The alkaline catalyst in step (1) is one of calcium hydroxide and calcium oxide.

[0015] The mass percentage of the cyclohexanone formaldehyde condensate in step (2) to the mixed initiator is 21-26%.

[0016] The polyols described in step (2) are two of sucrose, liquid sorbitol, glycerol and diethylene glycol.

[0017] The catalyst in step (2) is one or two of N,N-dimethylcyclohexylamine, 2,4,6-tris(dimethylaminomethyl)phenol and dimethylamine.

[0018] The alkylene oxide is one of propylene oxide and ethylene oxide.

[0019] The mass ratio of the first-stage alkylene oxide to the second-stage alkylene oxide is (18-28):100.

[0020] The bubbling time in step (4) is 1 to 2 hours.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) Since cyclohexanone formaldehyde condensate introduces a cyclic group, the introduction of the cyclic structure in the process of synthesizing polyether as an initiator reduces the deformation between molecular chains, thereby improving the demoulding property of the foam.

[0023] 2) Calcium hydroxide or calcium oxide is used as a catalyst in the process of synthesizing cyclohexanone formaldehyde condensate. The reaction process is relatively mild and is not prone to material impact. The reaction can be carried out at a lower temperature. Compared with other catalysts, the catalytic efficiency is relatively high and the chemical properties are very stable. The stability and durability of the catalytic effect can be guaranteed and the catalytic effect will not be lost due to long high-temperature reaction time. In addition, the cost is low, the preparation is simple, and it is easy to produce and use.

[0024] 3) Cyclohexanone formaldehyde condensate and small molecule alcohol initiators have good compatibility, and cyclohexanone and the foaming agent cyclopentane both contain cyclic structures and are similarly soluble in each other, which improves the compatibility of pentane in the synthetic polyether.

[0025] 4) Using cyclohexanone formaldehyde condensate as the initiator to prepare polyether polyols, because the condensate is composed of a cyclic structure, the polyether macromolecular chain contains rigid chain groups, which gives the downstream products better mechanical properties and thermal stability. The synthesized polyether polyols have high strength, good dimensional stability and low thermal conductivity.

[0026] 5) The preparation method provided by the present invention can be used to prepare a general-purpose rigid foam polyether polyol with regular molecular structure, narrow molecular weight distribution, stable product quality and high cost performance. The synthesis process route is reasonable, the product quality is stable, the synthesis is simple, easy to master, and easy to promote widely. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the embodiments.

[0028] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0029] Example 1

[0030] The preparation method of the condensation-based rigid foam polyether polyol comprises the following steps:

[0031] (1) Cyclohexanone and polyformaldehyde in a mass ratio of 40:60 are added to a reaction kettle, and 8‰ of the total mass of catalyst calcium oxide is added under continuous stirring, and the mixture is stirred at 90°C for 6 hours to obtain a cyclohexanone formaldehyde condensate;

[0032] (2) In a 2L autoclave equipped with a stirrer, a meter, a heating and temperature control device, a cooling device (including an outer jacket and an inner coil) and a pressure sensor, 300g of sucrose, 170g of diethylene glycol, 130g of cyclohexanone formaldehyde condensate and 3g of N,N-dimethylcyclohexylamine were added, and nitrogen was introduced to test the reactor for leakage. While ensuring that the reactor was well sealed, nitrogen was replaced. After nitrogen replacement, 11g of dimethylamine was vacuum-drawn in, and the reactor was heated to 80°C. 145g of propylene oxide was added. During the feeding process, the temperature was maintained at 82.5±2.5°C and the pressure was maintained at 0.25±0.15MPa. After the propylene oxide feeding was completed, the internal pressure was maintained for 1h to obtain an intermediate polyether polyol;

[0033] (3) The temperature in the autoclave was raised to 110°C, and 783 g of propylene oxide was added. During the feeding process, the temperature was maintained at 110±5°C and the pressure was maintained at 0.25±0.15 MPa. After the feeding was completed, the temperature was maintained at 115±5°C and the pressure was maintained at 0.25±0.15 MPa. When the reaction pressure remained substantially unchanged after the feeding of propylene oxide was completed, nitrogen was added to 0.2 MPa and the reaction was continued for 2 h to obtain a crude polyether polyol.

[0034] (4) When the pressure no longer decreases, nitrogen bubbling is started to strip the monomers for 1 hour while maintaining the temperature at 110°C to remove the residual small molecules. Finally, the condensation-based rigid foam polyether polyol is obtained by filtration.

[0035] Example 2

[0036] The preparation method of the condensation-based rigid foam polyether polyol comprises the following steps:

[0037] (1) Cyclohexanone and polyformaldehyde in a mass ratio of 55:45 were added to a reaction kettle, and 8‰ of the total mass of catalyst calcium hydroxide was added under continuous stirring. The mixture was stirred at 95°C for 4 hours to obtain a cyclohexanone formaldehyde condensate.

[0038] (2) In a 2L autoclave equipped with a stirrer, a meter, a heating and temperature control device, a cooling device (including an outer jacket and an inner coil) and a pressure sensor, 360g of liquid sorbitol, 100g of diethylene glycol and 130g of cyclohexanone formaldehyde condensate were added, and nitrogen was introduced to test the reactor for leaks. While ensuring that the reactor was well sealed, nitrogen was replaced. After nitrogen replacement, 13g of dimethylamine was vacuum-drawn in, and the reactor was heated to 82.5°C. 214g of ethylene oxide was added. During the feeding process, the temperature was maintained at 82.5±2.5°C and the pressure was maintained at 0.25±0.15MPa. After the ethylene oxide feeding was completed, the internal pressure was maintained for 1.5h to obtain an intermediate polyether polyol;

[0039] (3) The temperature in the autoclave was then raised to 115°C, and 791 g of ethylene oxide was added. During the feeding process, the temperature was maintained at 115±5°C and the pressure was maintained at 0.25±0.15 Pa. After the feeding was completed, the pressure was maintained at 0.25±0.15 MPa. When the reaction pressure remained substantially unchanged after the ethylene oxide feeding was completed, nitrogen was added to 0.25 MPa and the reaction was continued for 2.5 h to obtain a crude polyether polyol.

[0040] (4) When the pressure no longer decreases, nitrogen bubbling is started to strip the monomers for 1.5 h while maintaining the temperature at 115°C to remove the residual small molecules. Finally, the condensation-based rigid foam polyether polyol is obtained by filtration.

[0041] Example 3

[0042] The preparation method of the condensation-based rigid foam polyether polyol comprises the following steps:

[0043] (1) Cyclohexanone and polyformaldehyde in a mass ratio of 77:23 were added to a reaction kettle, and 8‰ of the total mass of catalyst calcium oxide was added under continuous stirring. The mixture was stirred at 100°C for 2 h to obtain a cyclohexanone formaldehyde condensate.

[0044] (2) In a 2L autoclave equipped with a stirrer, a meter, a heating and temperature control device, a cooling device (including an outer jacket and an inner coil) and a pressure sensor, 325g of sucrose, 50g of glycerol, 130g of cyclohexanone formaldehyde condensate, 5g of 2,4,6-tris(dimethylaminomethyl)phenol and 9g of N,N-dimethylcyclohexylamine were added, and nitrogen was introduced to test the reactor for leakage. While ensuring that the reactor was well sealed, nitrogen was replaced. After nitrogen replacement, it was heated to 85°C in vacuum, and 200g of propylene oxide was added. During the feeding process, the temperature was maintained at 82.5±2.5°C and the pressure was maintained at 0.25±0.15MPa. After the propylene oxide feeding was completed, the internal pressure was maintained for 2h to obtain an intermediate polyether polyol;

[0045] (3) The temperature in the autoclave was then raised to 120°C, and 807 g of propylene oxide was added. During the feeding process, the temperature was maintained at 115±5°C and the pressure was maintained at 0.25±0.15 MPa. After the feeding was completed, the temperature was 115±5°C and the pressure was maintained at 0.25±0.15 MPa. When the reaction pressure remained substantially unchanged after the feeding of propylene oxide was completed, nitrogen was added to 0.3 MPa and the reaction was continued for 3 hours to obtain a crude polyether polyol.

[0046] (4) When the pressure no longer decreases, nitrogen bubbling is started to strip the monomers for 2 h while maintaining the temperature at 120 °C to remove the residual small molecules. Finally, the condensation-based rigid foam polyether polyol is obtained by filtration.

[0047] Comparative Example 1

[0048] The preparation method of the condensation-based rigid foam polyether polyol comprises the following steps:

[0049] In a 2L autoclave equipped with a stirrer, a meter, a heating and temperature control device, a cooling device (including an outer jacket and an inner coil) and a pressure sensor, 300g of sucrose, 170g of diethylene glycol and 3g of N,N-dimethylcyclohexylamine were added, and nitrogen was charged into the autoclave for leak testing. Under the condition that the autoclave was well sealed, nitrogen was replaced. After the nitrogen replacement was completed, 11g of dimethylamine was vacuum-drawn in, and the autoclave was heated to 80°C. 145g of propylene oxide was added. During the feeding process, the temperature was maintained at 82.5±2.5°C and the pressure was maintained at 0.25±0.15MPa. The propylene oxide After the feeding is completed, the internal pressure is maintained at 110°C for 1h, and then the temperature in the kettle is raised to 110°C, and 783g of propylene oxide is added. During the feeding process, the temperature is maintained at 115±5°C and the pressure is maintained at 0.25±0.15MPa. After the feeding of propylene oxide is completed, the temperature is maintained at 115±5°C and the pressure is maintained at 0.25±0.15MPa. After the reaction pressure remains basically unchanged after the feeding of propylene oxide is completed, nitrogen is added to 0.2MPa and the reaction is continued for 2h. When the pressure no longer decreases, the temperature is maintained at 110°C and bubbling stripping of monomers is started for 1h to remove residual small molecules. Finally, the condensation-based rigid foam polyether polyol is obtained by filtration.

[0050] Comparative Example 2

[0051] The preparation method of the condensation-based rigid foam polyether polyol comprises the following steps:

[0052] In a 2L autoclave equipped with a stirrer, a meter, a heating and temperature control device, a cooling device (including an outer jacket and an inner coil) and a pressure sensor, 360g of liquid sorbitol and 100g of diethylene glycol were added, and nitrogen was filled into the autoclave for leak testing. While ensuring that the autoclave was well sealed, nitrogen was replaced. After the nitrogen replacement was completed, 13g of dimethylamine was vacuum-drawn in, and the reaction was heated to 82.5°C. 214g of ethylene oxide was added. During the feeding process, the temperature was maintained at 82.5±2.5°C and the pressure was maintained at 0.25±0.15MPa. After the ethylene oxide feeding was completed, After the formation, the internal pressure is maintained at 115°C for 1.5 hours, and then the temperature in the kettle is raised to 115°C, and 791g of ethylene oxide is added. During the feeding process, the temperature is maintained at 115±5°C and the pressure is maintained at 0.25±0.15MPa. After the feeding of ethylene oxide is completed, the pressure is maintained at 0.25±0.15MPa. When the reaction pressure remains basically unchanged, nitrogen is added to 0.25MPa and the reaction is continued for 2.5 hours. When the pressure no longer decreases, the temperature is maintained at 115°C and bubbling stripping of monomers is started for 1.5 hours to remove residual small molecules. Finally, the condensation-based rigid foam polyether polyol is obtained by filtration.

[0053] Comparative Example 3

[0054] The preparation method of the condensation-based rigid foam polyether polyol comprises the following steps:

[0055] In a 2L autoclave equipped with a stirrer, a meter, a heating and temperature control device, a cooling device (including an outer jacket and an inner coil) and a pressure sensor, 325g of sucrose, 50g of glycerol, 5g of 2,4,6-tris(dimethylaminomethyl)phenol and 9g of N,N-dimethylcyclohexylamine were added, and nitrogen was charged into the autoclave for leak testing. While ensuring that the autoclave was well sealed, nitrogen was replaced. After nitrogen replacement, it was vacuum heated to 85°C, and 200g of propylene oxide was added. During the feeding process, the temperature was maintained at 82.5±2.5°C and the pressure was maintained at 0.25±0.15MPa. a. After the propylene oxide feeding is completed, the internal pressure is maintained at 2h, and then the temperature in the kettle is raised to 120℃, and 807g propylene oxide is added. During the feeding process, the temperature is maintained at 115±5℃ and the pressure is maintained at 0.25±0.15MPa. After the feeding is completed, the temperature is maintained at 115±5℃ and the pressure is maintained at 0.25±0.15MPa. After the propylene oxide feeding is completed, when the reaction pressure remains basically unchanged, nitrogen is added to 0.3MPa and the reaction is continued for 3h. When the pressure no longer decreases, the temperature is maintained at 120℃ and bubbling stripping of monomers is started for 2h to remove residual small molecules, and finally condensation-based rigid foam polyether polyol is obtained by filtration.

[0056] The hydroxyl value and viscosity test results of the synthesized polyether polyols are shown in Table 1 below:

[0057] Table 1 Test results of sample indicators of embodiments and comparative examples

[0058]

[0059] The polyether polyols synthesized in Examples 1 to 3 and Comparative Examples 1 to 3 were prepared according to the formula and proportion in Table 2 to obtain material A, wherein the catalyst PC-8 was a commercially available product of Wanhua Chemical (Yantai) Sales Co., Ltd., the silicone oil S36 was a commercially available product of Shanghai Maihao New Materials Technology Co., Ltd., and the material B PM200 was a commercially available product of Wanhua Chemical (Yantai) Sales Co., Ltd., and the material A and the material B were uniformly mixed in a ratio of 1:1 and then foamed to obtain a rigid foam polyether polyol sample. The amount of each raw material in Table 2 is measured in parts by mass.

[0060] Table 2 Proportion of material A in Examples 1 to 3 and Comparative Examples 1 to 3

[0061]

[0062] After the material A and material B obtained according to the formula in Table 2 are mixed evenly, a foaming test is carried out to verify the demoulding property, compression strength, thermal conductivity, activity and pentane miscibility of the foam.

[0063] Through a lot of practice, the following methods can be used to evaluate the demoulding performance of foam:

[0064] Stir the prepared material A and material B thoroughly until they are evenly mixed, pour them into a 400×400×80mm aluminum mold for closed foaming, and demold after 3 minutes. Immediately after demolding, cut the foam along the central axis, measure the thickness of the center part of the foam and the thickness of the two edge parts, and use the formula: (average of the thickness of the three parts - 80mm) / 80mm to calculate the expansion rate after demolding. The expansion rate after demolding reflects the demolding performance. A low expansion rate means that the foam expands less after demolding, and it is easier to demold within the specified time of 3 minutes, and the demolding performance is better.

[0065] The compressive strength is carried out in accordance with the standard GB / T8813-2020. The core sample of the test sample should be taken to measure the compressive stress at the ultimate yield or 10% deformation. Whichever situation occurs first shall prevail. The direction of applied load shall be parallel to the direction of plate thickness (foam rise).

[0066] The thermal conductivity is in accordance with the standard QB / T3806-1999, the sample size is 200×200×25mm, and the thermal conductivity is measured at an average temperature of 10℃ and 23℃. It is recommended that the temperature difference should not be greater than 25℃. The thermal conductivity is measured using a thermal conductivity tester.

[0067] Activity: The time taken for materials A and B to rise and draw after being fully stirred. The shorter the time, the higher the activity.

[0068] Pentane miscibility: Add n-pentane or cyclopentane continuously to 1 part by mass of polyether polyol at room temperature with magnetic stirring (speed 1000 rpm) until the polyether polyol becomes turbid, and record the mass of n-pentane or cyclopentane added.

[0069] Table 3 Performance test table of rigid polyurethane foam in Examples 1 to 3 and Comparative Examples 1 to 3

[0070]

[0071] As shown in Table 3, by comparing Example 1-Example 3 and Comparative Example 1-Comparative Example 3, after adding cyclohexanone formaldehyde condensate, various aspects of performance are significantly improved compared with various aspects of performance without adding cyclohexanone formaldehyde condensate, because cyclohexanone formaldehyde condensate introduces cyclic groups in the process of synthesizing polyether polyol, reduces the deformation between molecular chains, thereby improves demoulding property, and cyclohexanone and blowing agent cyclopentane both contain cyclic structures, and by the characteristics of similar dissolving, the mutual solubility of pentane is improved. And from Example 1-Example 3 adding cyclohexanone formaldehyde condensate, it can be seen that the foam performance in Example 1 is not as good as Example 2 and Example 3, indicating that in the reaction of synthesizing cyclohexanone formaldehyde condensate, cyclohexanone and excessive paraformaldehyde reaction will generate formic acid to impair the activity of alkaline catalyst, acidic environment produces corrosion or oxidation effects on catalyst, causing its activity to reduce or lose activity, slowing down the reaction rate, and under acidic conditions, there will be too many protons in the reaction system, and these protons will compete with the anions in the reactant to combine, thereby reducing catalysis and reaction rate.

[0072] It can be seen from the above embodiments that the preparation method provided by the present invention has simple steps and is easy to operate. Because the condensate is composed of a cyclic structure, the polyether macromolecular chain contains a rigid chain group, thereby giving the downstream products better mechanical properties and thermal stability. The synthesized polyether polyol has high strength, good dimensional stability and low thermal conductivity, and improved mechanical properties.

Claims

1. A method for preparing a condensation-based rigid foam polyether polyol, characterized in that: The following steps are involved: (1) adding cyclohexanone and paraformaldehyde into a reaction vessel, adding a base catalyst under continuous stirring, and reacting to obtain a cyclohexanone formaldehyde condensate; (2) Add cyclohexanone formaldehyde condensate and polyol as mixed initiators into a reaction vessel, add a catalyst, raise the temperature to 80-85°C under vacuum conditions, dropwise add the first stage alkylene oxide to perform polyether chain extension, control the reaction temperature to 80-85°C and the pressure to 0.1-0.4 MPa during the feeding process, and continue the internal pressure reaction for 1-2 hours after the feeding is completed to obtain an intermediate polyether polyol; (3) The intermediate polyether polyol is heated to 110-120°C, and the second stage alkylene oxide is added dropwise again. During the feeding process, the reaction temperature is controlled to be 110-120°C and the pressure is controlled to be 0.1-0.4 MPa. After the feeding is completed, the pressure is increased to 0.2-0.3 MPa, and the reaction is continued at the internal pressure for 2-3 hours to obtain a crude polyether polyol polymer; (4) The crude polyether polyol is heated to 110-120°C and then nitrogen is bubbled through it. After bubbling, the material is discharged to obtain a condensation-based rigid foam polyether polyol.

2. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The mass ratio of cyclohexanone to paraformaldehyde in step (1) is (40-77):(23-60).

3. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The reaction in step (1) is carried out at a temperature of 90-100°C for 2-6 hours.

4. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The alkaline catalyst in step (1) is one of calcium hydroxide and calcium oxide.

5. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The mass percentage of the cyclohexanone formaldehyde condensate in step (2) to the mixed initiator is 21-26%.

6. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The polyols described in step (2) are two of sucrose, liquid sorbitol, glycerol and diethylene glycol.

7. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The catalyst in step (2) is one or two of N,N-dimethylcyclohexylamine, 2,4,6-tris(dimethylaminomethyl)phenol and dimethylamine.

8. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The alkylene oxide is one of propylene oxide and ethylene oxide.

9. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The mass ratio of the first-stage alkylene oxide to the second-stage alkylene oxide is (18-28):

100.

10. The method for preparing the condensate-based rigid foam polyether polyol according to claim 1, characterized in that: The bubbling time in step (4) is 1 to 2 hours.

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