Production process of citric acid type polycarbonate polyether polyol

Abstract

The invention belongs to the technical field of polycarbonate polyether polyol, and provides a production process of citric acid type polycarbonate polyether polyol, the production process is carried out in a tubular reaction device, and the tubular reaction device comprises a premixing unit, a reaction unit and a post-treatment unit, the premixing unit adopts a partitioned premixing form to prevent citric acid from passivating the activation center of the catalyst; a gas-liquid mass transfer area with a specific proportion is arranged in a tubular reactor of a reaction unit, a gas-liquid double-circulation mode is adopted, a double-flow atomization nozzle with a specific structure is designed, a static mixer is arranged in the reaction area, and the material circulation flow rate and the range temperature are accurately controlled; compared with the prior art, the preparation method has the advantages that the conversion rate of the epoxypropane and the functionality of the citric acid type polycarbonate polyether polyol are effectively improved, the content of byproducts is reduced, the mechanical property of the citric acid type polycarbonate polyether polyol in polyurethane foaming application is improved, and the production efficiency and the product quality can be remarkably improved in industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of polycarbonate polyether polyols, and in particular relates to a production process of citric acid type polycarbonate polyether polyols. Background Art

[0002] Polycarbonate polyether polyols are a type of polyols with carbonate groups in the molecule and hydroxyl groups at the ends of the molecular chain. Double metal cyanide (abbreviated as DMC) catalysts are widely used in the synthesis process of polycarbonate polyether polyols because of their simple preparation, low cost, and residual heavy metals in the product below 30ppm. Carbon dioxide, one of the raw materials, is cheap and easy to obtain, non-toxic and non-flammable, and has a clear chemical fixation effect of carbon dioxide. The temperature required for the reaction is not high, and the energy consumption required is low. The copolymerization method of carbon dioxide and epoxy compounds has broad application prospects and high industrial value. Polycarbonate polyether polyols have high modulus, high hydrogen bond density, high weather resistance and wear resistance brought by carbonate bonds, and fluidity and flexibility brought by ether bonds. They are widely used in polyurethane coatings, adhesives, foams and other fields, and have broad market prospects.

[0003] Citric acid is a tetrafunctional initiator, which contains a total of 4 functional groups (3 primary hydroxyl groups and 1 tertiary hydroxyl group) in its structure. The 3 primary hydroxyl groups are highly reactive and theoretically all of them can react in the polymerization reaction. However, due to the uncontrollable nature of the actual reaction and the weak reactivity of the tertiary hydroxyl group, it is difficult for the -OH bond to break. Therefore, when citric acid is used as an initiator to produce polycarbonate polyether polyols, the theoretical functionality should be 4. However, due to the fact that the reactivity of the tertiary hydroxyl group is difficult to reach 4, the functionality of the ideal citric acid-based polycarbonate polyether polyol is as close to 4 as possible.

[0004] In industrial production, when citric acid is used as the initiator to prepare polycarbonate polyether polyol, the characteristics of citric acid will cause the DMC catalyst to be deactivated, resulting in the functionality of the polycarbonate polyether polyol being much lower than the theoretical value. It will also cause the molecular weight to decrease and the number of by-products to increase. The higher the functionality, the better the processing performance, the greater the foam density, the higher the Tg, and the better the mechanical properties. On the contrary, the lower the functionality, the poorer the mechanical properties of the foam. (Zhang Fei, Zhang Zinan, Zhang Hongbin. Effect of PAPI functionality and isocyanate index on the performance of HFC-365mfc / H2O mixed foaming system RPUF [J]. Polyurethane Industry, 2010, 25(5): 24-27. DOI: 10.3969 / j.issn.1005-1902.2010.05.007. CN105473638B) Therefore, the polycarbonate polyether polyol prepared by the deactivation of the DMC catalyst has a problem of poor mechanical strength in the subsequent polyurethane foaming application. The specific reasons why citric acid deactivates the DMC catalyst are as follows: (1) Citric acid releases water at high temperatures, deactivating the DMC catalyst and affecting the polymerization process and product performance. Citric acid will melt and lose its crystal water and partially evaporate at high temperatures of 137-178 °C (Zhou Shun, Xu Yingbo, Wang Chenghui, et al. Pyrolysis characteristics of citric acid [J]. Tobacco Science and Technology, 2011(9):45-49. DOI:10.3969 / j.issn.1002-0861.2011.09.011.), propylene oxide has a low boiling point and high activity. It is easy to undergo random self-polymerization at room temperature to generate a large amount of heat, especially in the polymerization reaction of industrial polycarbonate polyether polyols. Due to the large amount of raw materials such as propylene oxide, carbon dioxide, citric acid and DMC catalyst, propylene oxide will release a large amount of heat during the catalyst activation process and the polymerization reaction. The whole system is in a high temperature and high pressure state with poor controllability. The huge heat released by the reaction cannot be transferred in time and dispersed in the material to form multiple high temperature points, that is, local overheating causes the citric acid to lose water, and the water evaporated from this part of the citric acid deactivates part of the DMC in the reaction system. The contact between each other in the production pipeline causes the DMC catalyst to deactivate, making the polymerization reaction slow or even unable to proceed, resulting in a decrease in the conversion rate of epoxy compounds. As a result, the polycarbonate polyether polyols prepared in large quantities will have problems such as low functionality, decreased molecular weight, and increased by-products. For example, Hu Bing et al. recorded in their study on the effect of impurities in initiators on DMC catalytic polymerization that when the initiator and catalyst were added to the autoclave at the same time, with 0.4% and 0.9% of the mass of the initiator in water, after vacuuming, it was found that no induced reaction could be carried out. This shows that water has a great influence on the polymerization reaction and it will deactivate the DMC catalyst in the reaction (Hu Bing, Qi Weixin, Ding Guolai, et al. Effect of impurities in initiator on DMC catalytic polymerization to prepare polyether [J]. Polyurethane Industry, 2004, 19(3): 29-31. DOI: 10.3969 / j.issn.1005-1902.2004.03.008.).

[0005] (2) Adding citric acid together with DMC catalyst will reduce or inactivate the catalyst. In the synthesis process of polycarbonate polyether polyol, the initiator can adjust the chain length of polycarbonate polyether polyol, narrow the molecular weight distribution, and obtain the target molecular weight product. In Chinese patent CN115785435B, the order of adding initiators will affect the overall reaction time and product weight of the process. If the initiator is added before activation, the catalyst activity will be reduced or inactivated. For the DMC active center, it will produce a "passivation" effect. The "passivation" effect means that the initiator covers the surface of DMC, which reduces or inactivates the catalyst activity. Therefore, the initiator cannot be added together with the catalyst and epoxy compound. For most types of catalysts such as carboxylic acids, phenols, etc., it is easy to passivate the catalytic active center and is suitable for addition after activation.

[0006] Based on the above situation that citric acid deactivates the DMC catalyst, there are 3 primary hydroxyl groups and 1 tertiary hydroxyl group in citric acid. When the reaction starts, the primary hydroxyl group takes priority to participate in the reaction due to its strong reaction activity. However, due to the deactivation of the DMC catalyst, the 3 primary hydroxyl groups cannot react completely in the actual reaction, and the reaction activity of the tertiary hydroxyl group is very weak, and it is difficult for the -OH bond to break. Only in the later stage of the reaction does the reaction start to partially occur. However, in the later stage of the reaction, the reaction rate becomes lower, and the catalytic activity is greatly reduced due to the deactivation of the catalyst. It is difficult for the tertiary hydroxyl group to participate in the reaction, so that the functionality of most citric acid polyol products can only reach 3 or less than 3 at most.

[0007] In summary, the production process of preparing polycarbonate polyether polyols using citric acid as an initiator has the problem that citric acid reduces the activity of the DMC catalyst, slows down the polymerization reaction rate or even makes it impossible, resulting in low actual functionality and low molecular weight of the polycarbonate polyether polyol products, which affects the subsequent mechanical properties in polyurethane foaming applications. This problem is more prominent in industrial-scale production, greatly affecting production efficiency and product quality. Summary of the invention

[0008] In view of the deficiencies of the prior art, the present invention provides a production process for citric acid type polycarbonate polyether polyol. According to the raw materials and product characteristics of citric acid type polycarbonate polyether polyol, the production process parameters and the corresponding tubular reaction device are designed in a targeted manner. The premixing unit adopts a partitioned premixing form to prevent the passivation of the catalyst activation center by citric acid. A gas-liquid mass transfer zone with a specific ratio is provided in the tubular reactor of the reaction unit, a gas-liquid dual circulation mode is adopted, a double-flow atomizing nozzle with a specific structure is designed, a static mixer is arranged in the reaction zone, and the material circulation flow rate and range are accurately controlled. The prepared citric acid type polycarbonate polyether polyol has a functionality of 3-4, a molecular weight in the range of 3000-6000, and a propylene oxide conversion rate of more than 90%, which effectively improves the propylene oxide conversion rate and the functionality of the citric acid type polycarbonate polyether polyol, prevents local overheating and explosion, solves the problem of low actual functionality and low molecular weight of the product obtained by using citric acid as an initiator in production, improves the mechanical properties of the citric acid type polycarbonate polyether polyol in polyurethane foaming applications, and can significantly improve production efficiency and product quality in industrial production.

[0009] The technical solution of the present invention is as follows: The present invention provides a production process of citric acid type polycarbonate polyether polyol, which is carried out in a tube-in-tube reaction device and specifically comprises: Step 1: premixing unit: 90% of propylene oxide and all citric acid are fully premixed in a first premixing tank (1), and 10% of propylene oxide and all DMC catalyst are fully premixed in a second premixing tank; Step 2: Reaction unit: the premixed raw materials enter the tubular reactor (2) for reaction, the volume of the materials accounts for ≤70% of the reaction pipeline (212), and the rest is the gas-liquid mass transfer zone (208). The tubular reactor adopts a gas-liquid dual circulation method to carry out a cyclic reaction of the materials, and the reaction temperature is 80°C±5°C. A double-flow atomizing nozzle (207) is provided at one end of the feed inlet of the tubular reactor for mixing and atomizing the circulated gas and liquid materials and dispersing them in the gas-liquid mass transfer zone (208) for mass transfer and heat transfer. A static mixer (210) is provided in the reaction pipeline (212). The reaction flow rate is 5-10 minutes to complete a cycle, and the reaction endpoint is judged by density. Step three post-processing unit: after the reaction is completed, the material is discharged and sequentially passed through a primary separation device to remove carbon dioxide and propylene oxide, a catalyst separation device to separate the catalyst, and a secondary separation device to remove by-products to obtain the citric acid type polycarbonate polyether polyol.

[0010] The invention specifically designs production process parameters and corresponding tube-in-tube reaction devices according to the raw materials and product characteristics of citric acid type polycarbonate polyether polyol, and achieves synergistic effect through matching of the process and the device, thereby solving the problem of low actual functionality of products obtained by using citric acid as an initiator in production, improving the mechanical properties of citric acid type polycarbonate polyether polyol in polyurethane foaming applications, and significantly improving production efficiency and product quality in industrial production. In the production process of the present invention, the premixing unit is only for physical mixing, which ensures that the reactants are fully dissolved and mixed, and no polymerization reaction or catalyst activation reaction occurs. The citric acid and the DMC catalyst are premixed with a portion of propylene oxide respectively, which can ensure that the raw materials are fully mixed and can effectively prevent the citric acid from covering the catalyst, effectively avoiding the passivation effect of the citric acid on the catalyst before the catalyst is activated, and will not affect the activity of the catalyst. In the reaction unit, a gas-liquid mass transfer zone of a specific ratio is set in the reaction pipeline, and a gas-liquid dual circulation mode is adopted. A static mixer and a double-flow atomizing nozzle are used to complete material mixing and heat conduction during the reaction process, increase the uniformity of the materials and disperse the high-temperature points caused by the generated heat, and at the same time, a double-flow atomizing nozzle is used above the reaction pipeline. A spray nozzle is used, a compression pump is used to compress and circulate the gas above the pipeline, a circulating pump is used to circulate the reaction materials to the top and pass them into the double-flow atomizing nozzle together, the materials are fully dispersed after atomization, so that the materials are dispersed in the carbon dioxide gas cavity, the liquid surface area is increased, and the materials can be fully transferred and heat transferred in the gas-liquid mass transfer area, and the temperature of citric acid in the system is reduced to prevent thermal decomposition. Then, after the materials enter the reaction zone, the local high heat center is dispersed by a static mixer, and the appropriate material flow rate ensures the mixing degree of the static mixer and the materials will have a certain temperature and time to react during the process of flowing down in the pipeline, and then through the circulation, the double-flow atomizing nozzle is atomized into droplets with suitable particle size in the carbon dioxide cavity, releasing heat, and thus performing multiple cycles to complete high-quality polymerization reactions. Therefore, the combination of multiple features of the process and device of the present invention prevents the occurrence of local heat centers in the reaction system, thereby improving the product quality. After the reaction is completed, the unreacted raw materials, catalysts and by-products are separated and removed in sequence to obtain the high-quality citric acid type polycarbonate polyether polyol of the present invention.

[0011] Furthermore, the structural formula of the citric acid type polycarbonate polyether polyol prepared by the production process of the present invention and the corresponding device is as follows: , Among them, 1≤m1,m2,m3≤34, 1≤n1,n2,n3≤48, 0≤m4≤37, 0≤n4≤58; The functionality of the citric acid type polycarbonate polyether polyol is 3-4; preferably, the functionality is 3.2-4; The molecular weight of the citric acid type polycarbonate polyether polyol is in the range of 2500-6500; The PO conversion rate of the citric acid type polycarbonate polyether polyol is above 90%; Furthermore, in the production process of the present invention, a step of purifying raw materials is also included before the premixing unit; In one embodiment, the feed ratio of propylene oxide and citric acid is propylene oxide:succinic acid=45:1-95:1, and the DMC catalyst is 500-1000ppm.

[0012] In one embodiment, in step 1, the pressure of the premixing unit is 0.3 MPa by introducing CO2; In one embodiment, in step 1, the temperature of the premixing unit is 0-60°C; In one embodiment, in step 1, the premixing time is 1-4 hours; In one embodiment, in step 2, the premixed raw materials enter the tubular reactor (2) from the feed port (205) through a metering pump, at which time the temperature in the reaction pipe (212) is 40° C. and the carbon dioxide pressure is 0.5 MPa; when 10% by weight of the raw materials enter, the circulation pump (214) is turned on to ensure that the flow rate is 5-10 minutes to complete one cycle, and at the same time, the compression pump (206) is turned on to circulate the carbon dioxide gas; In one embodiment, in step 2, after the feeding is completed, the feed port (205) is closed, and the reaction pressure is adjusted to 2-6 MPa and maintained through the carbon dioxide gas supply port (203) according to the data of the pressure sensor (202), and the reaction temperature in the reaction pipe is adjusted to 80°C ± 5°C by adjusting the temperature of the heating medium (211) of the insulation layer (209); more preferably, the reaction temperature is 80°C; the reaction is continued until the flow / density meter (213) data reaches 1.1 ± 0.005 g / cm 3 The reaction is then considered complete.

[0013] In one embodiment, in step 2, liquid material enters the double-flow atomizing nozzle (207) from the liquid material atomizing feed port (2071), CO2 enters from the carbon dioxide circulation air inlet (2072), and then enters the mixing chamber (2074) through the mixing chamber air injection hole (2073) in the double-flow atomizing nozzle (207) to be fully mixed, and then droplets are sprayed out from the double-flow atomizing nozzle (2075); preferably, the length of the mixing chamber (2074) is 5mm-25mm; preferably, the ratio of the diameter of the double-flow atomizing nozzle (2075) to the diameter of the reaction pipe (212) is 1:1000; more preferably, the diameter of the double-flow atomizing nozzle (2075) is 0.1-2.5mm. Preferably, the gas-liquid ratio of the droplets sprayed by the double-flow atomizing nozzle (2075) is 2%-10%, and the gas-liquid ratio is the ratio of the mass of gas and liquid passing through the mixing chamber (2074) per unit time; the gas-liquid ratio is controlled by the flow rates of gas circulation and liquid circulation and the gas injection hole of the mixing chamber; the specific double-flow atomizing nozzle described in the present invention uses gas to inject bubbles into the liquid material through the gas injection hole (2073) of the mixing chamber, and uses the bubbles to break the liquid, thereby atomizing the liquid; the present invention cools the CO2 through external circulation and disperses the material in the liquid circulation into droplets with a particle size of ≤30μm through the double-flow atomizing nozzle, and the proportion of gas during atomization is 2%-10%, so that the material completes deep mass transfer and heat transfer in the gas-liquid mass transfer zone, solves the mass transfer and heat transfer problem of insufficient CO2 dissolution and heat generation during the reaction process, and no local overheating center will appear in the reaction pipeline, and the reaction is uniform, so that the properties of citric acid type polycarbonate polyether polyol are stable, and the product has a higher conversion rate and functionality.

[0014] In one embodiment, in step 2, the volume of the material accounts for 50%-70% of the reaction pipe (212); In one embodiment, the center distance between the nearest neighboring pipes of the reaction pipe is less than or equal to twice the pipe diameter; In one embodiment, the ratio of the length L to the diameter d of the reaction pipe (212) is 10≤L:d≤40. The heating time of the industrial production of polycarbonate polyether polyol has particularity. In the polycarbonate polyether polyol tubular reactor, when the flow rate is constant, the heating time per unit volume of material is short, and the reaction conversion rate per unit time will be greatly reduced. While a longer reaction time is required, a longer heating time will cause the polyester chain segments to decompose, and the product will turn yellow, that is, the length of the reaction pipe cannot be too long. At the same time, the reaction process continues to generate heat, which will increase the temperature of the reaction system. The reactor needs to release the heat generated in the material in time. When the flow rate is constant, the liquid needs to complete the circulation through the gas-liquid heat transfer zone within the specified time, and there is enough area to disperse to complete the heat release and gas-liquid mass transfer, that is, the length of the pipe cannot be too slender. The synthetic polyester polyether polyol reaction pipe (212) should have a special length-to-diameter ratio to ensure that the product has sufficient heating reaction time and meets the requirements of gas-liquid mass transfer and heat release at the same time.

[0015] In one embodiment, the DMC catalyst is a zinc-cobalt double metal cyanide catalyst modified by a mixed acid, wherein the metal elements of the catalyst are only two metal elements, zinc and cobalt, except for impurities; the catalyst is obtained by reacting water-soluble metal salts of zinc and cobalt in a water-soluble solvent, wherein the water-soluble metal salt of cobalt is a cyanide salt of cobalt; the catalyst is modified by a mixed acid during synthesis, wherein the mixed acid comprises at least one organic acid and at least one water-soluble inorganic acid, wherein: The water-soluble inorganic acid is selected from dilute sulfuric acid and dilute hydrochloric acid, and the pH value is between 0 and 5; The organic acid is selected from any one or more of succinic acid, glutaric acid, phthalic acid, iminodiacetic acid, pyromellitic acid, butanetetracarboxylic acid, and the molar ratio of the water-soluble inorganic acid to the organic acid is 1:10 to 10:1.

[0016] In one embodiment, in the post-processing unit, the material includes product polycarbonate polyether polyol, by-product cyclic carbonate and unreacted propylene oxide, and the primary separation device purifies and recovers unreacted carbon dioxide and propylene oxide by vacuum distillation; the catalyst separation device adds a refining agent to the material and then separates and removes the residual catalyst using a solid-liquid separation device; the secondary separation device includes a distillation tower, which separates the product citric acid type polycarbonate polyether polyol and the by-product propylene carbonate by distillation.

[0017] It can be seen from the above technical solution that the beneficial effects of the present invention are: The invention specifically designs production process parameters and a corresponding tube-in-tube reaction device according to the raw materials and product characteristics of citric acid type polycarbonate polyether polyol, and prepares high-quality citric acid type polycarbonate polyether polyol by synergistic effect through matching of the process and the device. The invention mainly comprises: a premixing unit adopts a partitioned premixing form to prevent citric acid from passivating the activation center of the catalyst; a gas-liquid mass transfer zone with a specific ratio is provided in the tubular reactor of the reaction unit; a gas-liquid dual circulation mode is adopted; a double-flow atomizing nozzle with a specific structure is designed; a static mixer is arranged in the reaction zone; and the circulation flow rate and the range temperature of the material are precisely controlled. The functionality of the prepared citric acid type polycarbonate polyether polyol is 3-4, the molecular weight range is 3000-6000, and the propylene oxide conversion rate is above 90%. The conversion rate of propylene oxide and the functionality of the citric acid type polycarbonate polyether polyol are effectively improved, the by-product content is reduced, and local overheating and explosion are prevented. The problem that the product obtained by using citric acid as an initiator in production has low actual functionality, low molecular weight and high by-products is solved, the mechanical properties of the citric acid type polycarbonate polyether polyol in polyurethane foaming applications are improved, and the production efficiency and product quality can be significantly improved in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the production process of citric acid type polycarbonate polyether polyols.

[0019] Figure 2 It is a front view schematic diagram of the first premixing kettle and the second premixing kettle in the tube-in-tube reaction device. The second premixing kettle has the same structure as the first premixing kettle.

[0020] Figure 3 It is a front view schematic diagram of the tube-in-tube reactor of the tube-in-tube reaction device.

[0021] Figure 4 The schematic diagram of the top view of the tube-in-tube reactor of the tube-in-tube reaction device is shown in FIG. Figure 4 (a) is a top view of a tube reactor with 8 reaction pipes connected in parallel. Figure 4 (b) is a top view schematic diagram of a tube-in-tube reactor with four reaction pipes connected in parallel.

[0022] Figure 5 This is a schematic diagram of the structure of a double-flow atomizing nozzle on a tube reactor.

[0023] In the figure: 1, first premixing kettle; 11, carbon dioxide raw material inlet; 12 propylene oxide feeding port; 13, catalyst / initiator feeding port; 2, tubular reactor; 201, temperature sensor; 202, pressure sensor; 203, carbon dioxide gas supply port; 204, liquid distributor; 205, feed port; 206, compression pump; 207, double-flow atomizing nozzle; 208, gas-liquid mass transfer zone; 209, insulation layer; 210, SL static mixer; 211, heating medium; 212, reaction pipeline; 213, flow / density meter; 214, circulation pump; 215, discharge port; 216, connecting pipeline; 2071, liquid material atomization feed port; 2072, carbon dioxide circulation air inlet; 2073, mixing chamber air injection hole; 2074, mixing chamber; 2075, double-flow atomizing nozzle. DETAILED DESCRIPTION

[0024] In the description of the present invention, it should be noted that the terms "up", "down", "left", "right", "vertical", "parallel", "inside", "outside", "front", "back", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0025] The DMC catalyst described in the examples and comparative examples of the present invention is a zinc-cobalt double metal cyanide catalyst modified by a mixed acid; the specific preparation is as follows: i) at least one water-soluble zinc salt and at least one water-soluble cobalt salt, wherein the water-soluble cobalt salt is a cobalt cyanide salt, react in an aqueous solvent in the presence of a mixed acid, wherein the mixed acid comprises at least one organic acid and at least one water-soluble inorganic acid, wherein: the water-soluble inorganic acid is selected from dilute sulfuric acid and dilute hydrochloric acid, and the pH value is between 0 and 5; the organic acid is selected from any one or more of succinic acid, glutaric acid, phthalic acid, iminodiacetic acid, pyromellitic acid, and butanetetracarboxylic acid; the molar ratio of the water-soluble inorganic acid to the organic acid is 1:10 to 10:1; ii) The catalyst obtained in step i) is separated, washed and dried for multiple times until the pH of the washing liquid is 6-7 to obtain a mixed acid-modified zinc-cobalt double metal cyanide catalyst.

[0026] The present invention provides a synthesis process for synthesizing citric acid type polycarbonate polyether polyol, and the specific implementation method is as follows: The purified raw materials are premixed in different proportions. 90% of the total weight of propylene oxide is added to the first premixing kettle (1) through the propylene oxide feeding port (12) and citric acid is added to the catalyst / initiator feeding port (13). The remaining 10% of the total weight of propylene oxide is added to the second premixing kettle through the propylene oxide feeding port (12) and DMC catalyst is added to the catalyst / initiator feeding port (13). The premixing temperature is 0-60°C. The CO2 pressure in the premixing kettle is 0.3Mpa through the carbon dioxide raw material inlet (11). The premixing time is 1-4h. The DMC catalyst is prepared by the method described in Chinese patent CN115785435B.

[0027] The premixed raw materials enter the reaction pipe (212) with a temperature of 40°C and a carbon dioxide pressure of 0.5 MPa through the feed port (205). After 10% of the mass of the materials enter, the circulation pump (214) is turned on. The flow rate of the circulation device is based on 5-10 minutes to complete one cycle. At the same time, the compression pump (206) is turned on to allow both CO2 gas and liquid materials to pass through the double-flow atomizing nozzle (207). The liquid material enters from the liquid material atomizing feed port (2071), and the CO2 enters from the carbon dioxide circulation air inlet (2072). Then, the CO2 enters the mixing chamber through the mixing chamber injection hole (2073) in the double-flow atomizing nozzle (207). (2074) is fully mixed, and then droplets are sprayed out by the double-flow atomizing nozzle (2075), so that the material undergoes gas-liquid mass transfer and heat conduction in the gas-liquid mass transfer zone (208) in the form of droplets. The feed volume should be less than 70% of the pipeline volume, preferably 50%-70%; after the feeding is completed, the feed port (205) is closed, and after the reaction starts, 20°C CO2 is continuously and slowly supplemented through the carbon dioxide replenishment port (203) according to the data of the pressure sensor (202), and the reaction pressure is maintained at 2-6Mpa. By adjusting the temperature of the heating medium (211) in the insulation layer (209) of the reaction pipeline, the temperature of the reactants in the reaction pipeline is kept at 80°C±5°C.

[0028] The raw materials are circulated and reacted in the tubular reactor in a gas-liquid dual circulation mode. The circulating pump (214) allows the materials to complete a cycle in 5-10 minutes to ensure that the reaction is carried out and the heat is dissipated in time. At the same time, an SL static mixer (210) is provided in the reaction pipeline (212) to evenly disperse the solid catalyst into the epoxy compound and disperse the generated reaction heat, thereby reducing the points where the temperature is concentrated and high temperature is generated, and reducing the temperature difference between the center temperature in the pipeline and the wall of the pipeline. The reaction pipeline (212) is provided with a liquid distributor (204), a connecting pipeline (216), a compression pump (206), and a double-flow atomizing nozzle (207) at the feed inlet (205) end, so that the materials with higher temperature and consumed carbon dioxide are returned to the gas-liquid mass transfer zone (208). ) dissolves CO2 so that there is sufficient CO2 to participate in the reaction. At the same time, heat exchange is carried out in the gas-liquid mass transfer zone (208), which ensures that the material that generates heat during the synthesis process can release the heat in time. Furthermore, the material in the reaction will not generate more polyether products due to the decrease in carbon dioxide content. After sufficient mass transfer and heat transfer in the gas-liquid mass transfer zone (208) and the static mixer (210), the risk of explosion of the reaction system is further reduced. The reaction process will continue to consume carbon dioxide. After the carbon dioxide is consumed, carbon dioxide is continuously replenished through the carbon dioxide replenishment port (203) to maintain the reaction pressure. The addition of low-temperature carbon dioxide allows the heat of reaction to be effectively released here, thereby making the reaction system more stable. At the same time, during the reaction process, it is necessary to observe the data of the temperature sensor (201) and dynamically adjust the temperature to maintain at 80°C ± 5°C to maintain the stability of the reaction. For example, when the material temperature exceeds 85°C, the temperature of the heating medium (211) in the insulation layer (209) is adjusted to 70°C. When the material temperature is lower than 83°C, it is gradually restored to 80°C and the reaction is continued until the flow / density meter (213) data reaches 1.1g / cm 3 After that, the fluctuation range was observed to be within 0.005g / cm within 5 minutes. 3 The reaction is considered to be complete and the liquid flows out through the discharge port (215).

[0029] The outflowing mixture containing polycarbonate polyether polyol, cyclic carbonate and unreacted raw material propylene oxide is passed into the next-stage separation device, and the first-stage separation device separates the propylene oxide and dissolved CO2 in the mixture to obtain a crude product, and adjusts the viscosity of the crude product at the same time; the crude product is passed into a catalyst separation device, and a refining agent is added for adsorption treatment, and a crude product with a catalyst metal content of less than 5 ppm is obtained after filtration; the refined crude product is passed into a secondary separation device to separate the main product polycarbonate polyether polyol and the by-product cyclic propylene carbonate, that is, a citric acid type polycarbonate polyether polyol product is obtained, and then filled.

[0030] The specific implementation of the present invention is further described below. The parameters of different reaction devices are shown in Table 1.

[0031] Table 1 Parameters of citric acid type polycarbonate polyether polyol reaction device

[0032] Embodiment 1: 7.2L (90%) propylene oxide and 439.6g citric acid were added to the first premixing kettle (1) and fully premixed. 0.8L (10%) propylene oxide and 4g DMC catalyst were added to the second premixing kettle and fully premixed. 0.3Mpa of carbon dioxide was introduced into both premixing kettles and mixed and stirred at 40°C. After stirring for 1h, the mixture was pumped into an 8L×2 tubular reactor with a metering pump. The diameter of a single reaction pipe was 100mm, the length of the reaction pipe was 1000mm, the temperature in the reaction pipe was 40°C, and the carbon dioxide pressure was 0.5MPa. After all the mixture was pumped in, carbon dioxide was introduced into the reaction pipe to 3Mpa and the pressure was maintained. The circulation pump was turned on, the flow rate was controlled at 800g / min, and the gas-liquid ratio of the atomizing nozzle was controlled at 5%. After reacting at 80°C±5°C for 3h, the density was uniformly increased to 1.102g / cm 3 The reaction is complete and the product is taken out after cooling down. Unreacted carbon dioxide and propylene oxide are recovered by vacuum distillation in the primary separation device, and then a refining agent is added to the catalyst separation device to remove the residual catalyst by solid-liquid separation equipment, and then the main and side products are separated by a distillation tower in the secondary separation device to obtain a purified citric acid type polycarbonate polyether polyol product.

[0033] The crude product after the catalyst is removed is sampled and analyzed. At this time, the crude product contains the main product polycarbonate polyether polyol and the by-product cyclic propylene carbonate. Specifically, the crude product is sampled and collected in a container, and the crude product logistics sample is characterized by nuclear magnetic resonance hydrogen spectrum to calculate the ratio of polymer to cyclic small molecules in the crude product. After the polymer is purified, the nuclear magnetic resonance hydrogen spectrum test is performed again to calculate the ratio of polycarbonate chain segments to polyether chain segments on the polymer main chain. There are only two structures, polycarbonate chain segments and polyether chain segments, on the polymer main chain, and the sum of the two percentages is 100%.

[0034] With the help of 1 The amount of carbon dioxide introduced in the obtained polycarbonate polyether polyol (carbonate segment content) and the ratio of propylene carbonate (cyclic carbonate) to polycarbonate polyether polyol were determined by H-NMR (Bruker, DPX400, 400 MHz; pulse program zg30, waiting time d1:10 s, 64 scans). In each case, the sample was dissolved in deuterated chloroform. 1 The relevant resonances in H-NMR (based on TMS = 0 ppm) are as follows: Among them, 5.0ppm and 4.2ppm belong to the proton peaks of the methine and methylene on the polycarbonate chain, 4.9ppm, 4.5ppm and 4.1ppm belong to the proton peaks of the methine and methylene in the five-membered ring carbonate, and 3.5-3.8ppm belong to the proton peak of the ether chain. The capital letter A plus a number subscript represents the integrated area of ​​the peak at a certain ppm on the nuclear magnetic resonance hydrogen spectrum. A is the abbreviation of Area in English, for example, A 5.0 represents the integrated area of ​​the peak at 5.0 ppm. 1 The integrated area of ​​the H-NMR spectrum and its related proton peaks, the ratio of carbonate chains in the copolymerization reaction (molar ratio) (F CO2 ) and the mass fraction of cyclic carbonate content (W PC ), the amount of carbon dioxide embedded (M CO2 ) is calculated as follows: in, F CO2 =(A 5.0 +A 4.2 -2×A 4.6 ) / [(A 5.0 +A 4.2 -2×A 4.6 )+A 3.5 ]×100%; W PC =102×A 1.5 / [102×(A 5.0 +A 4.2 -2×A 4.6 +A1.5)+58×A 3.5 ]×100%; M CO2 =44×F CO2 / [102×F CO2 +58×(1-F CO2 )]×100%; The coefficient 44 is the molar mass of carbon dioxide, the coefficient 58 is the molar mass of PO, and the coefficient 102 is the sum of the molar masses of carbon dioxide (molar mass 44 g / mol) and the molar masses of PO (molar mass 58 g / mol).

[0035] The PO (propylene oxide) conversion rate is the product taken out by cooling, and the unreacted propylene oxide is separated by distillation in a primary separation device and the conversion rate is calculated. The calculation formula is n=m×(1-M CO2 ) / (Mm×M CO2 ); wherein m is the mass of the product after removing unreacted propylene oxide, and M is the total sample containing propylene oxide.

[0036] The polymer number average molecular weight (Mn) and polymer molecular weight polydispersity index (PDI) were determined by gel permeation chromatography (GPC).

[0037] Average functionality:

[0038] in is the number average molecular weight, which is determined by gel permeation chromatography (GPC). The hydroxyl value (OHV) is obtained by testing in accordance with GB / T12008.3-2009 Plastic polyether polyols Part 3: Determination of hydroxyl value.

[0039] Example 2-Example 14 refers to the preparation method and detection method of Example 1, the material parameters and process parameters are shown in Table 2 and Table 3, and the performance test table is shown in Table 4.

[0040] Table 2 Input material parameters of citric acid type polycarbonate polyether polyol

[0041] Table 3 Process parameters of citric acid type polycarbonate polyether polyol polymerization reaction

[0042] Table 4 Performance parameters of citric acid type polycarbonate polyether polyols of Examples 1-14

[0043] It can be seen from the data in Tables 2 to 4 that Examples 1 and 2 are for adjusting the volume proportion of the material in the pipeline. After the adjustment in the range of 50%-70%, the ester content of the polyol does not change much, and the product remains basically stable; Examples 3, 4, 5, and 6 are for enlarging the pipeline reactor for reaction. It can be seen that the molecular weight distribution is still very low, and the molecular weight does not fluctuate much. The production process of the present invention has an extremely low scale-up effect. Examples 7 and 8 are parallel structures with added pipeline reactors. It can be seen that when adding pipeline reactors for expansion, the molecular weight distribution does not increase due to the addition of multiple reactors, and the molecular weight is basically within the control range; Examples 9 and 10 adjust the pressure during the reaction. The reaction pressure affects the amount of CO2 dissolved in the material from another aspect. The method solves the problem of CO2 dissolution through liquid circulation and a double-flow atomizing nozzle, so within a wider pressure range, the properties such as the product ester-ether ratio remain basically unchanged; Examples 11 and 12 adjust the initiator ratio to adjust the molecular weight of the polycarbonate polyether polyol. When adjusting the initiator ratio, it is not necessary to adjust the process parameters to cope with the impact of changes in the material input ratio; Examples 13 and 14 adjust the gas-liquid ratio of the double-flow atomizing nozzle. The gas-liquid ratio affects the atomization effect and thus affects the mass transfer and heat transfer of the material in the upper CO2 space. When the gas-liquid ratio is between 2% and 10%, the properties of the product are basically stable.

[0044] Comparative Example 1 The only difference between Comparative Example 1 and the device 1 of Example 1 is that a dispersion sheet is used at the top of the pipeline reactor instead of a double-flow atomizing nozzle combined with a atomizing nozzle and a gas circulation nozzle. The rest is based on the preparation method and detection method of Example 1. The obtained product is recorded as CK1, and the performance parameters are shown in Table 5.

[0045] Comparative Example 2 Compared with the production process of Example 1, the only difference in Comparative Example 2 is that in Comparative Example 2, all propylene oxide, catalyst, and citric acid are premixed in a premixing kettle instead of premixing in different zones. For the rest, the preparation method and detection method of Example 1 are referred to. The obtained product is recorded as CK2, and the performance parameters are shown in Table 5.

[0046] Comparative Example 3 The only difference between the production process of Comparative Example 3 and that of Example 1 is that the gas-liquid dual circulation method is not adopted, that is, the carbon dioxide gas does not enter the reaction channel through the gas-liquid atomizing nozzle, but a circulating pump is used to compress CO2 and then pass it from the bottom. The rest is based on the preparation method and detection method of Example 2. The obtained product is recorded as CK3, and the performance parameters are shown in Table 5.

[0047] Comparative Example 4 The only difference between the production process of Example 2 and Comparative Example 4 is that the volume of the material in the reaction pipe (212) accounts for 80%. The rest is based on the preparation method and detection method of Example 2. The obtained product is recorded as CK4, and the performance parameters are shown in Table 5.

[0048] Comparative Example 5 Compared with the production process of Example 1, the only difference is that the circulation flow rate of the material is 15 min / circulation. The rest is based on the preparation method and detection method of Example 1. The obtained product is recorded as CK5, and the performance parameters are shown in Table 5.

[0049] Table 5 Parameters of Comparative Examples 1-5 Citric Acid Polycarbonate Polyether Polyol Products

[0050] It can be seen from the data in Table 5 that in Comparative Example 1, the double-flow atomizing nozzle is not used, resulting in low mass transfer and heat transfer efficiency in the upper CO2 area. When the reaction is intense, there is not enough capacity to release heat and dissolve more CO2. Part of the initiator decomposes to generate a small amount of water, resulting in a decrease in conversion rate. The insufficient amount of CO2 dissolved reduces the ester content. In Comparative Example 2, all materials are mixed in a premixing kettle for premixing. The early addition of the initiator leads to a decrease in catalyst activity, which reduces the conversion rate. At the same time, due to the decrease in catalyst activity, a longer reaction time is required when the same amount is added, resulting in a wider molecular weight distribution. In Comparative Example 3, since the gas-liquid dual circulation method is not adopted, the mixing uniformity of the materials during the reaction is reduced, and the solid raw materials tend to accumulate downward, making the reaction unbalanced and prone to high-temperature zones. The domain makes the initiator decompose and inhibit the reaction, which reduces the conversion rate, and because the points that are prone to high temperature are more likely to implode; Comparative Example 4 reduces the volume proportion of the CO2 area, compresses the size of the heat and mass transfer area, and also causes insufficient ability to release heat and integrate more CO2 when the reaction is violent. Part of the initiator produces a small amount of water, which causes the conversion rate to decrease, and the amount of CO2 dissolved is not enough to reduce the ester content; Comparative Example 5 reduces the circulation rate, and the mixing effect in the pipeline is reduced at this time. At the same time, the time for the material to flow and heat in the pipeline is long, and it cannot reach the upper CO2 space in time through the circulation after the reaction consumes CO2 to generate heat for mass transfer and heat transfer. At this time, the reaction will implode, causing the temperature to rise sharply in a short time, resulting in a very low ester content, and the molecular weight distribution becomes wide, and the molecular weight is unstable. The average functionality of the citric acid type polycarbonate polyether polyol prepared in the embodiment of the present invention is increased by 17%-45%, which significantly improves the product performance in subsequent applications.

[0051] Application examples: The polycarbonate polyether polyols of Examples 1-14 and Comparative Examples 1-5 were applied in a polyurethane foaming process, and the polyurethane foaming process was as follows: 70 g of citric acid polycarbonate polyether polyol, 70 g of PPG2000, 70 of 300N, 8 g of ultrapure water, 1.5 g of L-580, 0.3 g of A33, and 0.24 g of TP were sequentially added into a beaker, and premixed by stirring at 2000 r / min for 3 min using a stirring motor, and 95 g of TDI was added and stirred at 3000 r / min for 10 s, and then poured into a 20×20×20 cm container for foaming, and cut into suitable sizes for testing after aging for 24 h.

[0052] The physical properties of the tested polyurethane products are shown in Table 6, where the test methods for each index are as follows: Density: GB / T 6343-2009 "Determination of apparent density of cellular plastics and rubber"; Tensile strength (Kpa): GB / T 6344-2008 Determination of tensile strength and elongation at break of soft foam polymer materials; Elongation at break (%): GB / T 6344-2008 Determination of tensile strength and elongation at break of flexible foam polymeric materials; Compression set (50%): GB / T 6669-2008 Determination of compression set of soft foam polymeric materials; Compression set (70%): GB / T 6669-2008 Determination of compression set of soft foam polymer materials; Table 6 Performance parameters of polyurethane products

[0053] From Table 6, we can see the performance of polyurethane foaming. Compared with the citric acid type polycarbonate polyether polyol produced in the example, the mechanical properties such as tensile strength and elongation at break of the low functionality and wide molecular weight distribution citric acid polyol in the comparative example are greatly reduced after the foam is synthesized, and it has great limitations in use and application.

[0054] Based on the above embodiments and comparative examples, the present invention specifically designs production process parameters and corresponding tube-in-tube reaction devices according to the raw materials and product characteristics of citric acid type polycarbonate polyether polyol, and prepares high-quality citric acid type polycarbonate polyether polyol through the synergistic effect of matching the process and the device. The invention mainly comprises: a premixing unit adopts a partitioned premixing form to prevent citric acid from passivating the catalyst activation center; a gas-liquid mass transfer zone with a specific ratio is provided in the tubular reactor of the reaction unit; a gas-liquid dual circulation mode is adopted; a dual-flow atomizing nozzle with a specific structure is designed; a static mixer is arranged in the reaction zone; and the material circulation flow rate and range temperature are accurately controlled. The prepared citric acid type polycarbonate polyether polyol has a functionality of 3-4, a molecular weight range of 2500-6500, and a propylene oxide conversion rate of more than 90%, effectively improving the conversion rate of propylene oxide and the functionality of the citric acid type polycarbonate polyether polyol, preventing local overheating and explosion, solving the problem that the product obtained by using citric acid as an initiator in production has low actual functionality and low molecular weight, improving the mechanical properties of the citric acid type polycarbonate polyether polyol in polyurethane foaming applications, and significantly improving production efficiency and product quality in industrial production.

Claims

1. A production process of citric acid type polycarbonate polyether polyol, It is characterized in that The production process of the citric acid type polycarbonate polyether polyol is carried out in a tube-in-tube reaction device, and specifically comprises: Step 1: premixing unit: 90% of propylene oxide and all citric acid are fully premixed in a first premixing tank (1), and 10% of propylene oxide and all DMC catalyst are fully premixed in a second premixing tank; Step 2: Reaction unit: the premixed raw materials enter the tubular reactor (2) for reaction, the volume of the materials accounts for ≤70% of the reaction pipeline (212), and the rest is the gas-liquid mass transfer zone (208). The tubular reactor adopts a gas-liquid dual circulation method to carry out a cyclic reaction of the materials, and the reaction temperature is 80°C±5°C. One end of the tubular reactor feed port is provided with one or more dual-flow atomizing nozzles (207) for mixing and atomizing the circulated gas and liquid materials and dispersing them in the gas-liquid mass transfer zone (208) for mass transfer and heat transfer. A static mixer (210) is provided in the reaction pipeline (212). The reaction flow rate is 5-10 minutes to complete a cycle, and the reaction endpoint is judged by density. Step three post-processing unit: after the reaction is completed, the material is discharged and sequentially passed through a primary separation device to remove carbon dioxide and propylene oxide, a catalyst separation device to separate the catalyst, and a secondary separation device to remove by-products to obtain the citric acid type polycarbonate polyether polyol.

2. The production process according to claim 1, It is characterized in that The liquid material of the double-flow atomizing nozzle (207) enters from the liquid material atomizing feed port (2071), and CO 2 The carbon dioxide enters from the carbon dioxide circulation air inlet (2072), then enters the mixing chamber (2074) through the mixing chamber air injection hole (2073) in the double-flow atomizing nozzle (207) to be fully mixed, and then is sprayed out as droplets by the double-flow atomizing nozzle (2075).

3. The production process according to claim 2, It is characterized in that The double-flow atomizing nozzle (2075) sprays droplets with a gas-liquid ratio of 2%-10%.

4. The production process according to claim 3, It is characterized in that The particle size of the droplets is ≤30 μm.

5. The production process according to claim 2, It is characterized in that The ratio of the diameter of the dual-flow atomizing nozzle (2075) to the diameter of the reaction pipe (212) is 1:1000.

6. The production process according to claim 1, It is characterized in that The feed ratio of propylene oxide and citric acid is propylene oxide:succinic acid=45:1-95:1, and the DMC catalyst is 500-1000ppm.

7. The production process according to claim 1, It is characterized in that In step 2, the premixed raw materials enter the tubular reactor (2) from the feed port (205) through a metering pump. At this time, the temperature in the reaction pipe (212) is 40° C. and the carbon dioxide pressure is 0.5 MPa. When 10% by weight of the raw materials enter, the circulation pump (214) is turned on to ensure that the flow rate is 5-10 minutes to complete a cycle, and at the same time, the compression pump (206) is turned on to circulate the carbon dioxide gas.

8. The production process according to claim 1, It is characterized in that In step 2, the volume of the material accounts for 50%-70% of the reaction pipeline (212).

9. The production process according to claim 1, It is characterized in that In step 2, after the feeding is completed, the feeding port (205) is closed, and the reaction pressure is adjusted to 2-6 MPa and maintained through the carbon dioxide gas supply port (203) according to the data of the pressure sensor (202), and the reaction temperature in the reaction pipe is adjusted to 80°C ± 5°C by adjusting the temperature of the heating medium (211) of the insulation layer (209); the reaction is continued until the flow / density meter (213) data reaches 1.1 ± 0.005 g / cm 3 The reaction is then considered complete.

10. A citric acid type polycarbonate polyether polyol prepared by the production process according to any one of claims 1 to 9, It is characterized in that The structural formula is as follows: ， wherein 1≤m1, m2, m3≤34, 1≤n1, n2, n3≤48, 0≤m4≤37, 0≤n4≤58, and the functionality of the citric acid type polycarbonate polyether polyol is 3-4; The molecular weight of the citric acid type polycarbonate polyether polyol is in the range of 2500-6500; The PO conversion rate of the citric acid type polycarbonate polyether polyol is above 90%.

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