A process for the preparation of a soft blowing polyether polyol

Abstract

This invention discloses a preparation process for flexible foam polyether polyol, belonging to the field of polyether polyol synthesis technology. The preparation process includes the following steps: S1, mixing and stirring the initiator and strong base catalyst until a particle-free homogeneous mixture is obtained, and then feeding it into a circulating spray reaction system under closed negative pressure conditions; S2, employing a gas-phase + liquid-phase bidirectional displacement mode to simultaneously remove gaseous oxygen and liquid-phase dissolved oxygen; S3, gradient homogenization preheating; S4, continuously feeding mixed epoxides via atomization from the top of the reactor, completing polymerization through two-stage differential switching of circulation flow rates; S5, after the epoxides are added, continuously circulating the top material with a high flow rate to adjust the system to a micro-negative pressure constant temperature curing; S6, after curing, cooling and removing impurities through a two-stage gradient vacuum. This invention, through the coordinated operation of the entire process, suppresses the generation of by-products from the reaction source, achieving stable industrial production with low unsaturated double bonds, ultra-low monomer residue, low VOCs, and low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of polyether polyol synthesis technology, specifically relating to a complete coupled cyclic spray preparation process for flexible foam polyether polyol with low monomer residue and low odor. Background Technology

[0002] Flexible polyether polyols are the core raw material for flexible polyurethane foam, widely used in high-end furniture, automotive interiors, baby products, medical sponges, and other fields. High-end applications have stringent requirements for the residual monomer content, odor, yellowing resistance, and aging resistance of polyether products. Currently, the industry's industrial production routes are mainly divided into two categories: traditional stirred tank processes and conventional external circulation single-stage constant parameter spray polymerization processes. Both processes have inherent technical defects that are difficult to overcome. 1. Traditional stirred tank processes have low mass and heat transfer efficiency, poor material mixing uniformity, and the reaction system is prone to local high temperatures. The final product has a high content of unsaturated double bonds, resulting in poor resilience and aging resistance of the foam prepared from it, which cannot meet the needs of the high-end market. 2. Existing conventional external circulation single-stage constant parameter spray polymerization process uses top atomization feeding throughout the entire process. Relying solely on a fixed atomization particle size and constant circulation flow rate in a single-stage polymerization mode, although atomization increases the gas-liquid contact area, it has several shortcomings: In the early stages of polymerization, the material activity is high, and if a large flow rate atomization feeding is used, it is easy to cause droplet collision and aggregation, local overheating, and a large amount of unsaturated double bond byproducts. In the middle and late stages of polymerization, the monomer concentration decreases, and the mass transfer efficiency of a single constant low flow rate circulation is insufficient, resulting in a high monomer residue. The existing process simply replaces the gas phase air without specifically removing dissolved oxygen and dissolved water in the liquid phase. Trace impurities can cause random termination of molecular chains, resulting in large fluctuations in product quality. High-temperature and atmospheric-pressure static curing is commonly used. High temperature continuously promotes the formation of low molecular weight oligomers, and the atmospheric-pressure environment cannot remove trace dissolved monomers, making it difficult to meet the product odor and VOC (volatile organic compound) standards. The refining stage only uses single-stage vacuum devolatilization, and high and low boiling point impurities are removed simultaneously, resulting in low refining separation efficiency and limited product purity.

[0003] Existing technologies only disclose individual, independent processes in segmented feeding, spray curing, single-stage nitrogen replacement, and single-stage vacuum devolatilization. Using any one or two of these modified processes alone can only alleviate the defects of a single indicator and cannot simultaneously solve common industry pain points such as local overheating, high double bond content, high monomer residue, strong odor, high energy consumption, and poor batch stability. The industry has long lacked an integrated production process that coordinates the entire process from raw material feeding to finished product refining. Summary of the Invention

[0004] Based on the multiple defects of traditional stirred tank and existing conventional constant parameter single-stage spray polymerization processes, such as droplet agglomeration, local micro-area overheating, high residue of unsaturated double bonds and free monomers, strong product odor, high energy consumption, and large batch performance fluctuations, the purpose of this invention is to provide a complete set of coupled cyclic spray preparation process for flexible foam polyether polyols with low monomer residue and low odor. By linking the entire process, the generation of by-products is suppressed from the reaction source, achieving stable industrial production with low unsaturated double bonds, ultra-low monomer residue, low VOC, and low energy consumption.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A preparation process for flexible foam polyether polyols comprises six coupled processes: material pretreatment with negative pressure feeding, gas-liquid two-phase inert displacement, gradient homogenization preheating, small-circuit top atomization pre-initiation + large-circuit top atomization enhanced mass transfer two-stage differentiated ring-opening polymerization, low-temperature negative pressure spray curing, and two-stage gradient vacuum precision refining. The preparation process includes the following steps: S1. Material pretreatment and negative pressure closed feeding: Glycerol and dipropylene glycol compound initiator and strong base catalyst are mixed and stirred until a particle-free homogeneous mixture is formed. It is then fed into the circulating spray reaction system under a closed negative pressure of -0.05~-0.07MPa, and external water vapor and impurities are isolated throughout the process. S2, Gas-liquid two-phase inert replacement: High-purity nitrogen is used to first replace the gas phase space of the reaction system, and then the material spray circulation is started to replace the dissolved gas in the liquid phase. The replacement is repeated 2 to 3 times. After the replacement is completed, the system is maintained at a slight positive pressure of 0.02 to 0.05 MPa, and the total oxygen content of the system is controlled to be ≤80 ppm and the water content to be ≤50 ppm. S3. Gradient homogeneous preheating: Turn on the external circulation heat exchange and spray circulation system of the system, first pre-circulate and uniformly heat at a small flow rate, then raise the temperature to 100~110℃ at a uniform rate of 3~5℃ / min, and maintain the temperature for 20~30min to fully activate the catalyst and eliminate the temperature gradient inside the material. S4. Two-stage variable flow top atomization ring-opening polymerization: Epoxy propylene oxide and ethylene oxide mixed epoxides are continuously added dropwise, with the feed uniformly atomized from the top of the reactor throughout the process. The polymerization is completed in two stages with differentiated switching of circulation flow rates. The first stage starts a small circulation, which, together with the top atomization feed, smoothly pre-initiates the polymerization. The second stage switches to a large circulation, with the remaining epoxides continuously atomized from the top of the reactor along with the large flow circulation material to enhance gas-liquid mass transfer, maintaining a closed-loop coupled gas-liquid circulation throughout the process. S5. Low-temperature negative pressure spray curing: After the epoxide is added, continue to open the high-flow top material spray circulation and adjust the system to a micro negative pressure constant temperature curing for 40~60 minutes to promote the complete reaction of trace residual monomers and inhibit the generation of high-temperature by-products. S6. Two-stage gradient vacuum precision refining: After maturation, the temperature is reduced to 80~90℃, and impurities are removed by two-stage gradient vacuum. First, free epoxide monomers are removed by low vacuum, and then low molecular weight oligomers and moisture are removed by high vacuum. After degassing, the material is cooled to below 40℃ and filtered through a precision filter to obtain the finished flexible foam polyether polyol.

[0006] Preferably, in step S1, the mass ratio of glycerol to dipropylene glycol in the initiator is (3~5):1; the strong base catalyst is potassium hydroxide or sodium hydroxide, and the amount of catalyst added is 0.2%~0.5% of the total mass of the initiator; the water content of the initiator itself is ≤30ppm.

[0007] Preferably, in step S2, the purity of the high-purity nitrogen gas is ≥99.99%; after the replacement is completed, the dissolved oxygen in the liquid phase of the system is ≤30ppm.

[0008] Preferably, in step S3, the flow rate of the pre-circulation is 0.8 to 1.2 times the volumetric flow rate of the reaction system, the overall temperature of the system is maintained at 80 to 90°C during the uniform temperature stage, and the duration of the pre-circulation uniform temperature is 10 to 15 minutes.

[0009] Preferably, in step S4, the mass ratio of propylene oxide to ethylene oxide is (8~10):1; the total mass of epoxide is 8~12 times the total mass of the initiator; and the purity of the epoxide monomer is ≥99.9%.

[0010] Preferably, in step S4, the specific operation of the two-stage variable flow top atomization open-loop polymerization is as follows: The first stage of small circulation top atomization for stable pre-initiation polymerization: the temperature is controlled at 110~120℃, the pressure at 0.15~0.25MPa, the small circulation flow rate is 1.5~2.0 times the volumetric flow rate of the reaction system, 40%~50% of all epoxides are atomized and sprayed from the top of the reactor with a small flow rate of material, the atomization particle size is 50~70μm, and the reaction time is 60~80min; The second stage is a large-scale top-atomization enhanced mass transfer polymerization: the temperature is raised to 125~135℃, the system pressure is maintained at 0.10~0.20MPa, and the flow rate is switched to a large circulation flow rate, which is 2.0~2.5 times the volumetric flow rate of the reaction system. The remaining 50%~60% of the epoxides are continuously atomized and sprayed out from the top with the large-flow circulating material, and the atomized particle size is maintained at 50~70μm. The reaction time is 90~110min.

[0011] Preferably, in step S5, the curing temperature is consistent with the second stage polymerization temperature in step S4, the curing pressure is controlled at -0.02~-0.04MPa, and the curing process is carried out with uninterrupted large-circulation top spray circulation.

[0012] Preferably, the two-stage vacuum purification parameters in step S6 are: the first stage vacuum degree is -0.06~-0.08MPa, and the degassing time is 10~15min; the second stage vacuum degree is -0.085~-0.095MPa, and the degassing time is 10~25min.

[0013] Preferably, in step S6, after degassing, the material is cooled to 35-40°C and then precisely filtered using a 200-300 mesh filter.

[0014] Preferably, the flexible foam polyether polyol prepared by the present invention has a hydroxyl value of 105~115mgKOH / g, a viscosity of 300~450mPa·s at 25℃, an unsaturated double bond value of ≤0.02mmol / g, a free monomer residue of ≤0.01%, and a VOC content of ≤15μg / g.

[0015] The beneficial effects of this invention are: (1) The core innovation of this invention lies in the pioneering two-stage differentiated polymerization system of full top atomization and segmented switching circulation flow, which matches two completely different reaction kinetic conditions: high activity in the early stage of polymerization and high viscosity in the middle and late stages. It is equipped with a complete process design of gas-liquid two-phase deep deoxygenation, dynamic negative pressure spray curing, and two-stage gradient vacuum refining. Only through the coordinated operation of the entire process can multiple effects such as ultra-low unsaturated double bonds, low monomer residue, low VOC, low odor, low energy consumption, and high batch stability be achieved simultaneously, resulting in a synergistic technical effect.

[0016] (2) Addressing the long-standing common pain points in the industry from the source of the reaction mechanism Traditional industry improvement methods often rely on post-processing remedial measures such as vacuum purification and adsorption deodorization, which only address the symptoms and not the root cause. This invention precisely matches the reaction kinetics through segmented variable flow top atomization polymerization, directly avoiding droplet aggregation and localized high temperatures in the early stages of the polymerization reaction, and suppressing the formation of unsaturated double bonds and low-molecular-weight byproducts from the source of the reaction. Combined with full-process two-phase deoxygenation, dynamic negative pressure ripening, and two-stage gradient vacuum deep purification, a complete closed-loop process route of "source control of byproducts + process impurity removal + end-stage graded refining" is formed, which is significantly superior to existing single-point improvement technologies in terms of technological innovation.

[0017] (3) The overall performance of the product has achieved a leapfrog upgrade, and the indicators have significantly surpassed those of existing industrial products. The product has an unsaturated double bond value of ≤0.02mmol / g and a free monomer residue of ≤0.01%. It has ultra-low odor, low VOC, and excellent anti-yellowing and anti-aging properties. The polyurethane flexible foam prepared from it has a resilience of ≥70% and a compression set of ≤3.0%, which can stably meet the high-demand and high-end application scenarios such as infant products, automotive interiors, and medical sponges. Existing conventional single-stage spray and stirred tank processes cannot stably achieve this range of indicators.

[0018] (4) Industrialized production has multiple economic advantages, including high conversion rate, short cycle and low energy consumption. The entire closed-loop spray coupling reaction achieves a near 100% conversion rate of epoxide monomers, maximizing raw material utilization. Compared to traditional stirred tanks and constant flow single-stage spray processes, the production cycle per batch is shortened by more than 35%, and overall production energy consumption is reduced by 20%. The entire process is highly automated and adaptable, with minimal fluctuations in product performance between batches, significantly improving the stability of continuous industrial production and possessing extremely high industrialization and promotion value. Attached Figure Description

[0019] Figure 1 This is a process flow diagram for preparing flexible foam polyether polyols according to an embodiment of the present invention. Detailed Implementation

[0020] The complete coupled cyclic spray preparation process for flexible foam polyether polyols provided by this invention consists of six coupled and linked processes: material pretreatment with negative pressure feeding, gas-liquid two-phase inert displacement, gradient homogenization preheating, small-circuit top atomization pre-initiation + large-circuit top atomization enhanced mass transfer two-stage differentiated ring-opening polymerization, low-temperature negative pressure spray curing, and two-stage gradient vacuum precision refining. Each process cooperates with each other and is indispensable, working together to achieve low unsaturated double bonds, low monomer residue, low VOC, and low energy consumption production.

[0021] like Figure 1 As shown in the figure, the preparation process of flexible foam polyether polyol includes the following steps as a specific embodiment of the present invention: S1. Material pretreatment and negative pressure closed feeding: Glycerol and dipropylene glycol compound initiator and strong base catalyst are mixed and stirred until a particle-free homogeneous mixture is formed. The mixture is then fed into the circulating spray reaction system under a closed negative pressure of -0.05~-0.07MPa, completely isolating external water vapor and impurities.

[0022] In this step, the mass ratio of glycerol to dipropylene glycol is controlled at 3~5:1; the catalyst is potassium hydroxide or sodium hydroxide, and the amount added is 0.2%~0.5% of the total mass of the initiator; the water content of the initiator is ≤30ppm; the low water content can completely eliminate hydrolysis side reactions, and the compound dual initiators can precisely control the functionality and chain segment flexibility of polyether molecules, which is suitable for the high-end flexible foam requirements of high resilience and uniform opening.

[0023] This step allows for strict control of the raw material's water content from the source, eliminating hydrolysis side reactions and, in conjunction with subsequent gas-liquid two-phase deoxygenation, creating a pure reaction environment with low impurities throughout the process.

[0024] S2. Gas-liquid two-phase inert replacement: High-purity nitrogen (nitrogen purity ≥ 99.99%) is used to first replace the gas phase space of the reaction system, and then the material spray circulation is started to replace the dissolved gas in the liquid phase. The replacement is repeated 2 to 3 times. After the replacement is completed, the system is maintained at a slight positive pressure of 0.02 to 0.05 MPa, and the total oxygen content of the system is controlled to be ≤ 80 ppm and the water content to be ≤ 50 ppm.

[0025] Compared to the industry-standard single gas-phase nitrogen purging, this step adopts a gas-phase + liquid-phase bidirectional displacement mode, simultaneously removing gas-phase oxygen and liquid-phase dissolved oxygen. This prevents material oxidation and molecular chain oxidation and breakage during the polymerization process from the source, ensuring the product's aging resistance. It is a core guarantee for the stable reaction of the two-stage polymerization process.

[0026] S3. Gradient Heating and Homogenization Preheating: Activate the external circulation heat exchange and spray circulation system. First, pre-circulate at a low flow rate to homogenize the temperature. The low flow rate is 0.8 to 1.2 times the volumetric flow rate of the reaction system. During the homogenization phase, maintain the overall system temperature at 80-90℃ for 10-15 minutes. Then, increase the temperature uniformly to 100-110℃ at a rate of 3-5℃ / min and maintain this temperature for 20-30 minutes to fully activate the catalyst and eliminate temperature gradients within the material.

[0027] In this step, uniform gradient heating combined with low-flow pre-circulation for uniform temperature is used to uniformly activate the catalyst, completely eliminate local temperature differences inside the material, provide a stable temperature control basis for two-stage variable flow top atomization polymerization, and avoid the pre-inducing factors of local overheating side reactions.

[0028] S4. Two-stage variable flow top atomization ring-opening polymerization: propylene oxide and ethylene oxide mixed epoxide are continuously added dropwise, and the entire process is uniformly fed from the top of the reactor. Gradient controllable polymerization is achieved by switching the circulation flow in two stages. The epoxide contains propylene oxide in a mass ratio of 8 to 10:1, the total amount of epoxide is 8 to 12 times the total mass of the initiator, and the purity of the epoxide monomer is ≥99.9%, which reduces the introduction of impurities and ensures the orderly growth of molecular chains.

[0029] The specific operation of two-stage variable flow top atomization open-loop polymerization is as follows: The first stage involves a small-circulation top atomization for stable pre-initiation polymerization: the temperature is controlled at 110~120℃, the pressure at 0.15~0.25MPa, the small-circulation flow rate is 1.5~2.0 times the volumetric flow rate of the reaction system, and 40%~50% of all epoxides are atomized and sprayed from the top of the reactor with a small flow rate of material, with an atomized particle size of 50~70μm and a reaction time of 60~80min. The small circulation reduces the intensity of fluid turbulence, the probability of atomized droplet collision is low, the initial initiation of molecular chains is completed gently, local micro-region overheating is avoided, and the formation of unsaturated double bond byproducts is reduced. The second stage involves top atomization to enhance mass transfer polymerization via a large circulation system: the temperature is raised to 125~135℃, the system pressure is maintained at 0.10~0.20MPa, and the circulation flow rate is increased to 2.0~2.5 times the volumetric flow rate of the reaction system. The remaining 50%~60% of the epoxides are continuously atomized and sprayed out from the top along with the high-flow-rate circulating material, with the atomized particle size maintained at 50~70μm. The reaction time is 90~110min. The large circulation system increases the material turnover rate, continuously renews the gas-liquid interface, overcomes the defects of increased system viscosity and high monomer diffusion resistance in the middle and later stages, and reduces the residue of free monomers.

[0030] From a principle perspective, this invention employs segmented flow rate switching to precisely match reaction kinetics. A low flow rate in the initial stage reduces droplet collision and aggregation, while a large circulation stage enhances gas-liquid mass transfer. These two gradient stages regulate the orderly growth of molecular chains, adapting to the completely different reaction conditions in the two stages. Specifically, 1) The first stage of small circulation top atomization stably pre-initiates polymerization, starts low-load and low-flow external circulation. In the early stage of polymerization, the molecular chain is short and the system is highly reactive. Small circulation reduces the degree of fluid turbulence in the tube and reactor. The atomized droplet movement speed is low and the probability of collision and aggregation is significantly reduced. There are no local overheating hot spots in the system. The molecular chain initiation addition is completed gently and stably, and the generation of unsaturated double bonds is suppressed from the source. 2) The top atomization of the second stage of the large circulation enhances mass transfer polymerization. The large circulation accelerates the overall material renewal rate in the reactor, and the continuous atomization maintains a super large air-liquid contact area, effectively offsetting the mass transfer resistance caused by the increase in material viscosity in the middle and later stages. This allows trace amounts of unreacted epoxides to fully contact the active sites, significantly reducing the content of free monomers in the finished product.

[0031] S5. Low-temperature negative pressure spray curing: After the epoxide is added, the material at the top of the large circulation is continuously sprayed and circulated. The system is adjusted to a micro negative pressure constant temperature curing for 40~60 minutes. The curing temperature is consistent with the mass transfer polymerization temperature of the atomization enhancement at the top of the second stage of the large circulation. The curing pressure is controlled at -0.02~-0.04MPa. This step follows two stages of variable flow atomization polymerization, employing a large-circulation top atomization dynamic spray combined with micro-negative pressure low-temperature curing. The dynamic large-circulation atomization continuously consumes trace amounts of unreacted monomers, while the micro-negative pressure simultaneously removes dissolved small molecules. The low-temperature environment prevents the formation of new low-molecular-weight byproducts. This step differs from existing static atmospheric pressure high-temperature curing processes by consuming trace amounts of residual monomers without generating new byproducts, simultaneously removing dissolved gases from the system, and reducing VOCs and irritating odors in the product.

[0032] S6. Two-stage gradient vacuum precision refining: After maturation, the temperature is reduced to 80~90℃, and impurities are removed by two-stage gradient vacuum. First, free epoxide monomers are removed by low vacuum, and then low molecular weight oligomers and moisture are removed by high vacuum. The material is cooled to below 40℃ and filtered through a 200~300 mesh precision filter to obtain the finished flexible foam polyether polyol.

[0033] This step employs staged vacuum devolatilization, combined with the preceding curing process, to achieve deep purification. Staged vacuum selectively separates impurities with different boiling points: low vacuum preferentially removes volatile free monomers, while high vacuum deeply removes high-boiling-point, low-molecular-weight oligomers. Separating these two types of impurities significantly improves purification efficiency. The two-stage vacuum purification parameters are: first-stage vacuum degree -0.06~-0.08MPa, degassing for 10~15min; second-stage vacuum degree -0.085~-0.095MPa, degassing for 10~25min; the material is cooled to below 40℃, preferably 35~40℃. This range balances filtration flow rate and impurity removal effect, avoiding incomplete filtration at excessively high temperatures and filter blockage due to increased viscosity at excessively low temperatures; the filter screen is selected from 200 to 300 mesh. 200 mesh is suitable for conventional batch production, while 300 mesh is suitable for high-end, low-impurity products, providing a wider range of process adaptability.

[0034] The technical solution of the present invention will be described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0035] Product performance testing standards and methods: (1) Hydroxyl value: determined according to the phthalic anhydride method in GB / T 12008.3-2009 "Plastic Polyether Polyols Part 3: Determination of Hydroxyl Value"; (2) Viscosity at 25℃: According to GB / T 12008.7-2010 "Plastic Polyether Polyols Part 7: Determination of Viscosity", a rotational viscometer was used to test at a constant temperature of 25℃; (3) Unsaturated double bond value: The content of unsaturated bonds in polyether was determined by iodometric titration according to GB / T 12008.6-2010; (4) Residual free epoxy monomers: Quantitative detection of total residual propylene oxide and ethylene oxide by gas chromatography (GC-FID, headspace injection) (general laboratory method). (5) VOC content: Tested by headspace gas chromatography at 280℃, in accordance with GB / T 23986-2009; (6) Resilience of polyurethane flexible foam: According to GB / T 6670-2008 "Determination of resilience of flexible foam polymer materials by falling ball method"; (7) Compression permanent deformation: According to GB / T 6669-2008, the compression is 50%, and the temperature is kept constant at 70℃ for 22 hours before recovery test.

[0036] Example 1

[0037] S1. Material pretreatment and negative pressure closed feeding: Take 400 kg of glycerol and 100 kg of dipropylene glycol as a compound initiator with a mass ratio of 4:1 and a water content of ≤30 ppm initiator; add 1.5 kg of potassium hydroxide catalyst and stir at high speed for 30 min until the system is completely homogeneous; feed it into the circulating spray reaction system under a negative pressure of -0.06 MPa, and seal it to isolate water vapor and external impurities.

[0038] S2, Gas-liquid two-phase inert replacement: Using 99.99% high-purity nitrogen, first replace the gas phase space of the system, then start the spray circulation to replace the dissolved gas in the liquid phase, repeat the replacement twice; the system is stably maintained at a slight positive pressure of 0.03MPa, and the gas phase oxygen content is detected to be 70ppm, the liquid phase dissolved oxygen is 25ppm, and the total water content of the system is 40ppm.

[0039] S3, Gradient heating and homogenization preheating: Turn on the external circulation heat exchange system and spray circulation, first pre-circulate at a small flow rate to uniformly heat the temperature, then heat up to 105℃ at a uniform rate of 4℃ / min, and maintain the temperature for 25 minutes.

[0040] S4. Two-stage variable flow top atomization polymerization: 4500 kg of propylene oxide and 500 kg of ethylene oxide are mixed with epoxides at a mass ratio of 9:1, and the monomer purity is 99.95%. The first stage of small-circulation top atomization for stable pre-initiation polymerization: temperature 115℃, pressure 0.20MPa, small circulation is started, flow rate is 1.8 times the system volumetric flow rate, 2250kg of mixed epoxide is sprayed out with the top atomization of the circulating material, atomization particle size is 60μm, reaction time is 70min; small circulation low-speed atomization gently completes the initial initiation of molecular chains, without droplet agglomeration or local overheating; The second stage involves top atomization to enhance mass transfer polymerization in a large circulation system: the temperature is raised to 130℃ and the system pressure is 0.15MPa. The circulation pump is switched to increase the circulation flow rate to 2.2 times the system volumetric flow rate. The remaining 2750kg of epoxide is continuously atomized and sprayed from the top with an atomized particle size of 60μm. The reaction time is 100min. The large circulation system improves material turnover efficiency, and the fine atomization enhances gas-liquid mass transfer and reduces monomer residue.

[0041] S5. Low-temperature negative pressure spray curing: Maintain a constant temperature of 130℃, continuously open the top spray circulation of the large circulation system throughout the process, adjust the system pressure to -0.03MPa, and dynamically cure for 50 minutes.

[0042] S6. Two-stage gradient vacuum precision refining: Gradual cooling to 85℃; First-stage vacuum degree -0.07MPa degassing for 12min to remove free monomers; Second-stage vacuum degree -0.09MPa degassing for 20min to remove low molecular weight oligomers and moisture; The material is cooled to 36℃ and filtered through a 260-mesh precision filter to obtain the finished flexible foam polyether polyol.

[0043] Finished product testing indicators: hydroxyl value of 110mgKOH / g, viscosity at 25℃ of 380mPa·s, unsaturated double bond value of 0.018mmol / g, monomer residue of 0.008%, VOC content of 11μg / g; the prepared foam has a resilience of 71%, compression set of 2.8%, and is odorless and resistant to yellowing.

[0044] Example 2

[0045] S1. Material pretreatment and negative pressure closed feeding: Take 375kg glycerol + 125kg dipropylene glycol compound initiator with a mass ratio of 3:1, add 2.0kg sodium hydroxide catalyst and stir to homogenize, and send it into the circulating spray reaction system under a negative pressure of -0.05MPa.

[0046] S2, Gas-liquid two-phase inert replacement: Using 99.99% high-purity nitrogen, first replace the gas phase space of the system, then start the spray circulation to replace the dissolved gas in the liquid phase. Repeat the replacement 3 times. The system maintains a slight positive pressure of 0.04MPa. The gas phase oxygen is detected at 65ppm and the liquid phase dissolved oxygen at 22ppm.

[0047] S3, Gradient heating and homogenization preheating: Turn on the external circulation heat exchange system and spray circulation, first pre-circulate at a small flow rate to uniformly heat the temperature, then heat up to 110℃ at a uniform rate of 3℃ / min, and maintain the temperature for 20 minutes.

[0048] S4, Two-stage variable flow top atomization polymerization: 4800 kg of propylene oxide and 480 kg of ethylene oxide are mixed with epoxides at a mass ratio of 10:1, with a monomer purity of 99.95%; The first stage of small circulation top atomization for stable pre-initiation polymerization: temperature 120℃, pressure 0.25MPa, small circulation started, flow rate 2.0 times the system volume flow rate, 50% epoxide top atomization feed, atomization particle size 50μm, reaction 65min; The second stage of large-circulation top atomization enhances mass transfer polymerization: the temperature is raised to 135℃ and 0.20MPa, the large circulation flow rate is switched to 2.5 times the system volume flow rate, the remaining epoxide is continuously atomized and sprayed out from the top, the atomized particle size is 50μm, and the reaction is carried out for 90min.

[0049] S5. Low-temperature negative pressure spray curing: Maintain a constant temperature of 135℃, adjust the system pressure to -0.04MPa, and perform full-process large-circulation top spray curing for 45 minutes.

[0050] S6. Two-stage gradient vacuum refining: Cool to 80℃; degas under first-stage vacuum of -0.08MPa for 10 minutes, and under second-stage vacuum of -0.095MPa for 25 minutes; cool to 38℃ and filter through a 220-mesh filter to obtain the finished product.

[0051] Finished product testing indicators: hydroxyl value is 112 mg KOH / g, viscosity at 25℃ is 420 mPa·s, unsaturated double bond value is 0.019 mmol / g, monomer residue is 0.009%, VOC content is 13 μg / g; foam resilience is 69%, compression set is 2.9%.

[0052] Comparative Example 1 (existing constant top atomizing spray process, refer to patent document CN103739838A) The raw material ratio is exactly the same as in Example 1; S1: 400kg glycerol + 100kg dipropylene glycol, 1.5kg KOH, -0.06MPa negative pressure feed; S2: Only a single gas phase nitrogen replacement, without liquid phase circulation deoxygenation, the total oxygen in the system is 145 ppm; S3: Gradient-free uniform temperature, directly heating to 105℃ at 5℃ / min, without pre-circulation uniform temperature step; S4: The entire process uses a single constant circulation flow rate (2.0 times the system volumetric flow rate), with all epoxides continuously fed from the top atomization in one go, at a constant temperature of 120℃, for a total reaction time of 170 min, without any two-stage flow rate switching; S5: After the addition is complete, statically mature at 130℃ and normal pressure for 50 minutes without spray circulation; S6: Single-stage vacuum -0.09MPa degassing for 32 minutes, followed by cooling and filtration; Finished product testing indicators: hydroxyl value is 111 mg KOH / g, viscosity at 25℃ is 405 mPa·s, unsaturated double bond value is 0.042 mmol / g, monomer residue is 0.035%, VOC content is 48 μg / g; foam resilience is 63%, compression set is 4.2%, the product has a slight odor, and batch performance fluctuates significantly.

[0053] Comparative Example 2 (Traditional Stirred Tank Process) The raw material ratio is exactly the same as in Example 1; S1: Same as Example 1, negative pressure closed feeding; S2: Only one gas phase nitrogen purging, no liquid phase deoxygenation, total oxygen 170ppm; S3: The stirred tank is directly heated to 105℃, with uniform preheating without external circulation spray; S4: Stirred reaction with a paddle, no top atomized feed, continuous droplet addition of epoxide, reaction at a constant temperature of 125℃ for 180 min; S5: Static curing at 130℃ and normal pressure for 50 minutes; S6: Single-stage vacuum -0.09MPa degassing for 35 minutes; Finished product testing indicators: hydroxyl value is 114 mg KOH / g, viscosity at 25℃ is 440 mPa·s, unsaturated double bond value is 0.055 mmol / g, monomer residue is 0.050%, VOC content is 65 μg / g; foam resilience is 60%, compression set is 4.8%, and the product performance has significant defects.

[0054] Comparative Example 3 (This invention uses two-stage variable flow atomization polymerization, but eliminates the gas-liquid two-phase inert displacement, and only uses single-phase nitrogen displacement). The raw material ratio is exactly the same as in Example 1; S1: Same as Example 1; S2: Only a single gas phase nitrogen replacement is used, without starting the liquid phase spray circulation replacement. Replacement is done once, without liquid phase deoxygenation operation. The total oxygen content of the system is 160ppm, the liquid phase dissolved oxygen is 95ppm, and the water content is 72ppm. S3~S6: All parameters are used in Example 1; Finished product testing indicators: The hydroxyl value is 111 mg KOH / g, the viscosity at 25℃ is 390 mPa·s, the unsaturated double bond value is 0.023 mmol / g, the free monomer residue is 0.011%, and the VOC content is 32 μg / g; the foam resilience rate is 66%, and the compression set is 3.9%; the material showed slight yellowing after 7 days of storage, and its aging resistance decreased significantly.

[0055] Comparative Example 4 (Complete two-phase deoxygenation + two-stage variable flow polymerization, low-temperature negative pressure spray curing was cancelled and replaced with normal pressure high-temperature static curing) The raw material ratios and S1~S4 are the same as in Example 1; S5: After the epoxide is added, maintain static curing at 130℃ and normal pressure for 50 minutes without high-flow top spray circulation; S6: Same as Example 1; Complete set of testing indicators for finished products: The hydroxyl value is 110 mg KOH / g, the viscosity at 25℃ is 385 mPa·s, the unsaturated double bond value is 0.020 mmol / g, the free monomer residue is 0.026%, the VOC content is 41 μg / g; the foam resilience is 67%, the compression set is 3.7%, and the product has a distinctly pungent odor.

[0056] Comparative Example 5 (complete S1-S5 process, eliminating the two-stage gradient vacuum and using a single-stage vacuum to simultaneously remove monomers and low-molecular-weight impurities) The raw material ratios and S1~S5 are the same as in Example 1; S6: After curing, cool to 85°C and degas under a single vacuum of -0.09MPa for 32 minutes to simultaneously remove free monomers and low molecular weight oligomers; cooling and filtration are the same as in Example 1; Finished product testing indicators: The hydroxyl value is 113 mg KOH / g, the viscosity at 25℃ is 410 mPa·s, the unsaturated double bond value is 0.019 mmol / g, the free monomer residue is 0.016%, and the VOC content is 29 μg / g; the foam resilience is 68%, the compression set is 3.5%, and the low molecular weight oligomer residue is relatively high.

[0057] Comparative analysis (1) Comparative Examples 1 and 2 represent mainstream mature industrial processes in the industry, representing the best level of existing technology. The raw material ratios are completely consistent with the embodiments of this invention, with only the process route being different. The test data fully demonstrates that the two-stage coupled process of this invention, namely "pre-initiation of small circulation top atomization and enhanced mass transfer of large circulation top atomization", breaks through the upper limit of existing process performance. Only by relying on segmented flow gradient control, combined with gas-liquid two-phase deoxygenation, dynamic negative pressure curing, and a two-stage gradient vacuum integrated system, can the core indicators of the product be optimized in leapfrog manner. This complete coupled process has outstanding creativity and industrial promotion value.

[0058] (2) By comparing the data of Comparative Examples 3-5 with that of Example 1, it can be seen that the present invention has a strong process synergy effect, and the absence of any core process will prevent the achievement of all excellent indicators.

[0059] ① In Example 1, the dissolved oxygen in the liquid phase was 25 ppm, VOC was 11 μg / g, and the foam rebound was 71%; in Comparative Example 3, the dissolved oxygen in the liquid phase was 95 ppm, VOC increased to 32 μg / g, the foam rebound decreased to 66%, and the sample showed obvious yellowing in a short period of time. The comparison shows that using only two-stage variable flow atomization polymerization and single gas-phase nitrogen replacement, without using two-phase deoxygenation, will lead to an increase in dissolved oxygen in the liquid phase, causing molecular chain oxidation and breakage, and a significant decrease in the product's aging resistance. ② In Example 1, the free monomer content was 0.008% and the VOC content was 11 μg / g; in Comparative Example 4, after static curing at normal pressure, the monomer residue was 0.026%, and the VOC content reached 41 μg / g, with a pungent odor. The comparison shows that using two-stage variable flow atomization polymerization + two-phase deoxygenation, without low-temperature negative pressure dynamic curing, resulted in a more than three-fold increase in trace monomer residue, and the product's odor and VOC levels seriously exceeded the standards. ③ In Example 1, the monomer residue was 0.008% and VOC was 11 μg / g; in Comparative Example 5, after single-stage vacuum devolatilization, the monomer residue was 0.016%, and the enrichment of low-molecular-weight impurities led to an increase in VOC to 29 μg / g, resulting in poorer permanent deformation of the foam during compression. The comparison shows that the first five processes were complete, but without a two-stage gradient vacuum, high and low boiling point impurities could not be separated in stages, and the residue of small-molecule oligomers increased significantly.

Claims

1. A preparation process for flexible foam polyether polyol, characterized in that, Includes the following steps: S1. Material pretreatment and negative pressure closed feeding: Glycerol and dipropylene glycol compound initiator and strong base catalyst are mixed and stirred until a particle-free homogeneous mixture is formed. It is then fed into the circulating spray reaction system under a closed negative pressure of -0.05~-0.07MPa, and external water vapor and impurities are isolated throughout the process. S2, Gas-liquid two-phase inert replacement: High-purity nitrogen is used to first replace the gas phase space of the reaction system, and then the material spray circulation is started to replace the dissolved gas in the liquid phase. The replacement is repeated 2 to 3 times. After the replacement is completed, the system is maintained at a slight positive pressure of 0.02 to 0.05 MPa, and the total oxygen content of the system is controlled to be ≤80 ppm and the water content to be ≤50 ppm. S3. Gradient homogeneous preheating: Turn on the external circulation heat exchange and spray circulation system of the system, first pre-circulate and uniformly heat at a small flow rate, then raise the temperature to 100~110℃ at a uniform rate of 3~5℃ / min, and maintain the temperature for 20~30min to fully activate the catalyst and eliminate the temperature gradient inside the material. S4. Two-stage variable flow top atomization ring-opening polymerization: propylene oxide and ethylene oxide mixed epoxide are continuously added dropwise, and the entire process is uniformly fed from the top of the reactor. The polymerization is completed by switching the circulating flow rate in two stages. The first stage starts a small circulation, which, together with the top atomized feed, smoothly pre-initiates polymerization; the second stage switches to a large circulation, where the remaining epoxides are continuously atomized and sprayed out from the top of the reactor along with the high-flow-rate circulating material to enhance gas-liquid mass transfer, maintaining a closed-loop coupled gas-liquid circulation throughout the process. S5. Low-temperature negative pressure spray curing: After the epoxide is added, continue to open the high-flow top material spray circulation and adjust the system to a micro negative pressure constant temperature curing for 40~60 minutes to promote the complete reaction of trace residual monomers and inhibit the generation of high-temperature by-products. S6. Two-stage gradient vacuum precision refining: After maturation, the temperature is reduced to 80~90℃, and impurities are removed by two-stage gradient vacuum. First, free epoxide monomers are removed by low vacuum, and then low molecular weight oligomers and moisture are removed by high vacuum. After degassing, the material is cooled to below 40℃ and filtered through a precision filter to obtain the finished flexible foam polyether polyol.

2. The preparation process of flexible foam polyether polyol according to claim 1, characterized in that: In step S1, the mass ratio of glycerol to dipropylene glycol is (3~5):1; the strong base catalyst is potassium hydroxide or sodium hydroxide, and the amount of catalyst added is 0.2%~0.5% of the total mass of the initiator; the water content of the initiator itself is ≤30ppm.

3. The preparation process of flexible foam polyether polyol according to claim 1, characterized in that: In step S2, the purity of the high-purity nitrogen gas is ≥99.99%; after the replacement is completed, the dissolved oxygen in the liquid phase of the system is ≤30ppm.

4. The preparation process of flexible foam polyether polyol according to claim 1, characterized in that: In step S3, the pre-circulation flow rate is 0.8 to 1.2 times the volumetric flow rate of the reaction system. During the uniform temperature stage, the overall temperature of the system is maintained at 80 to 90°C, and the duration of the pre-circulation uniform temperature stage is 10 to 15 minutes.

5. The preparation process of flexible foam polyether polyol according to claim 1, characterized in that: In step S4, the mass ratio of propylene oxide to ethylene oxide is (8~10):1; the total mass of epoxides is 8~12 times the total mass of the initiator, and the purity of the epoxide monomer is ≥99.9%.

6. The preparation process of the flexible foam polyether polyol according to claim 1, characterized in that, In step S4, the specific operation of the two-stage variable flow top atomization open-loop polymerization is as follows: The first stage of small circulation top atomization for stable pre-initiation polymerization: the temperature is controlled at 110~120℃, the pressure at 0.15~0.25MPa, the small circulation flow rate is 1.5~2.0 times the volumetric flow rate of the reaction system, 40%~50% of all epoxides are atomized and sprayed from the top of the reactor with a small flow rate of material, the atomization particle size is 50~70μm, and the reaction time is 60~80min; The second stage is a large-scale top-atomization enhanced mass transfer polymerization: the temperature is raised to 125~135℃, the system pressure is maintained at 0.10~0.20MPa, and the flow rate is switched to a large circulation flow rate, which is 2.0~2.5 times the volumetric flow rate of the reaction system. The remaining 50%~60% of the epoxides are continuously atomized and sprayed out from the top with the large-flow circulating material, and the atomized particle size is maintained at 50~70μm. The reaction time is 90~110min.

7. The preparation process of flexible foam polyether polyol according to claim 1, characterized in that: In step S5, the curing temperature is consistent with the second stage polymerization temperature in step S4, and the curing pressure is controlled at -0.02~-0.04MPa. The curing process is carried out with uninterrupted large-circulation top spray circulation.

8. The preparation process of flexible foam polyether polyol according to claim 1, characterized in that: Step S6 Two-stage vacuum purification parameters: First stage vacuum degree is -0.06~-0.08MPa, degassing for 10~15min; Second stage vacuum degree is -0.085~-0.095MPa, degassing for 10~25min.

9. The preparation process of the flexible foam polyether polyol according to any one of claims 1 to 8, characterized in that: After degassing, the material is cooled to 35-40℃ and then filtered precisely using a 200-300 mesh filter.

10. The preparation process of the flexible foam polyether polyol according to any one of claims 1 to 8, characterized in that: The prepared flexible foam polyether polyol has a hydroxyl value of 105~115mgKOH / g, a viscosity of 300~450mPa·s at 25℃, an unsaturated double bond value of ≤0.02mmol / g, a free monomer residue of ≤0.01%, and a VOC content of ≤15μg / g.

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