A tubular reactor for synthesizing polycarbonate polyether polyols

Abstract

The present invention relates to the technical field of polycarbonate polyether polyol preparation, and specifically discloses a tubular reactor for synthesizing polycarbonate polyether polyol. By configuring a specific solid-liquid mixing unit, a carbon dioxide-epoxide compound mixing heat transfer unit, a circulation control unit, a temperature control unit, and a pressure control unit, a high degree of matching and overall synergy between the internal structure of the tubular reactor and material circulation and reaction heat control are achieved, sufficient mixing, mass transfer, heat transfer, and precise temperature control conditions are provided for the synthesis of polycarbonate polyether polyol, and a one-time centralized feeding process for preparing polycarbonate polyether polyol is achieved, which is conducive to the expanded industrial production of polycarbonate polyether polyol.

Description

Technical Field

[0001] The present invention relates to the technical field of polycarbonate polyether polyol preparation, and more particularly to a tubular reactor for synthesizing polycarbonate polyether polyol. Background Art

[0002] Polycarbonate polyether polyols are a class of polyols containing carbonate groups within the molecule and hydroxyl groups at the ends of the molecular chain. Carbon dioxide, one of the raw materials, is inexpensive, readily available, non-toxic, and non-flammable. It has a clear chemical fixation effect on carbon dioxide, and the reaction requires low temperatures and minimal energy. The regulated copolymerization of carbon dioxide with epoxides has broad application prospects and high industrial value.

[0003] The process for synthesizing polycarbonate polyether polyols is mainly synthesized by chain transfer agent, carbon dioxide and epoxy compound through zinc-cobalt bimetallic catalyst. Taking propylene oxide and succinic acid as chain transfer agent as an example, the synthesis route is as follows:

[0004]

[0005] in, is the average number of ether chain segments, is the average number of ester chain segments. Chinese patent CN111378106A mentions that the activation energy for polymer formation is lower than that for cyclic carbonate formation, while the potential energy of cyclic carbonate is lower than that of polymer formation. Therefore, the reaction to form cyclic carbonate is thermodynamically favorable, while the reaction to form polycarbonate is kinetically favorable. If the reaction temperature is too high, the carbonate chain content is low, the molecular weight distribution becomes wider, and the proportion of byproduct cyclic carbonate increases. Therefore, precise reaction temperature control is key to improving the main product—polycarbonate polyether polyol.

[0006] Another key factor affecting the yield of the main product is the action of the bimetallic complex (DMC) catalyst. Improper or instantaneous activation can lead to implosion, which can easily cause high-temperature and high-pressure safety hazards. Chinese Patent CN 115785435A summarizes the catalytic reaction mechanism of DMC as consisting of an induction activation phase and a chain growth phase. During the induction activation phase, the reaction is exothermic, and temperature peaks must be monitored. The initial activation temperature must be controlled to avoid overheating, which could affect the pressure resistance of the equipment and catalyst activity. During the chain growth phase, after DMC is fully activated, the active centers bind to the chain transfer agent, and the epoxy compound undergoes insertion polymerization. The chain transfer agent undergoes a displacement reaction with the active structures of the DMC and epoxy compound. During this phase, external heat is required to promote chain growth. Chinese Patent CN 106471042B defines the activation step of the DMC catalyst during the induction activation phase as a step in which a partial amount of alkylene oxide, optionally in the presence of CO2, is added to the DMC catalyst, followed by cessation of the addition of the alkylene oxide compound. The subsequent exothermic chemical reaction results in a temperature peak ("hot spot") and / or a pressure drop in the reactor. The activation period is the period from the addition of a partial amount of the alkylene oxide compound to the DMC catalyst, optionally in the presence of CO 2 , until the hot spot subsides.

[0007] To adapt to the aforementioned characteristics of the carbonate polyether polyol synthesis reaction and reduce the impact of thermal fluctuations on various reaction components, existing technologies require specialized catalyst design, process control, and / or independent reactor design for the induction activation stage. Specific existing technologies are as follows: 1. Existing technologies utilize specialized high-performance DMC catalysts, such as those described in Chinese patent CN115785435B. This utilizes a highly active and heat-resistant tri-ligand bimetallic complex catalyst, DMC, to produce polyether polyols through a single, centralized feed of the tri-ligand bimetallic complex catalyst, a chain transfer agent, and an epoxy compound at room temperature. 2. In terms of process improvements, Chinese patent CN116710504A uses a catalyst pre-activation technique, where the catalyst is pre-activated with a starting compound or the reaction product of the first, second, or third reaction. Specifically, a portion of the starting material is first used to activate the catalyst to initiate the reaction, and then the remaining starting material is added in batches or continuously. CN107108878A proposes a method for preparing polyether carbonate polyols, proposing that the DMC catalyst must be "pretreated at a temperature of 50 to 200°C and / or under a reduced pressure of 10 mbar to 800 mbar (absolute)." Furthermore, the method "continuously and at least intermittently metered a double metal cyanide catalyst, an alkylene oxide, a suspending agent, and / or an H-functional initiator compound into the first reactor" indicates that the process requires catalyst pre-activation and batch addition of reactants. 3. Regarding improvements to the reactor, Chinese patent CN116874759A proposes the use of an independent reactor for catalyst activation and maintenance of activity. To address the problems of DMC catalyst activation failure, explosive polymerization after instantaneous activation, and high safety risks, the technology involves a first reactor, a tubular reactor, and a second reactor, wherein the first reactor is used for DMC catalyst activation. Specifically, a chain transfer agent and DMC catalyst are added to the first reactor, the temperature is raised to 120-140°C, and epoxide is added for catalyst activation; after activation, epoxide is added to maintain activity and the temperature is lowered to 70-90°C; Chinese patent CN103403060B connects two tubular reactors of different inner diameters in series, and similarly controls the DMC induced activation period by introducing an independent reactor; Chinese patent CN106471042B uses a stirred tank main reactor and a tubular reactor in series, controlling the temperature of the tubular reactor to be 10-40°C higher than that of the main reactor, so that the DMC induced activation period occurs in the main reactor, while the chain segment growth period occurs in the tubular reactor.

[0008] However, from the perspective of reactor optimization, there is no description of a technology for preparing carbonate polyether polyols by centralized feeding in a single reactor structure.

[0009] Currently, reactors used in the industrial production of polycarbonate-polyether polyols can be categorized by their morphology into tank reactors and pipeline reactors. Tank reactors have a low surface area-to-volume ratio, poor heat dissipation, and difficulty handling high reaction heat. Pipeline reactors, on the other hand, offer controllable pressure and temperature during the reaction process and high monomer conversion efficiency, thus attracting considerable attention in this field. Due to the small cross-sectional area and limited production capacity of tubular reactors, they must be arrayed as tube reactors. However, a common self-circulating tube reactor with a high-efficiency mixer, such as that described in CN 109225114A, consists of a plurality of tubes within the tube reactor, with a mixer external to the tube reactor used for material mixing. However, the synthesis process of polycarbonate-polyether polyols places higher demands on material mixing and heat dissipation, requiring timely dispersal of the materials during the reaction while simultaneously releasing the heat generated by the reaction to prevent implosion. Furthermore, solid catalyst accumulation can occur at the top caps of the multiple tubes in a tube reactor, hindering the synthesis reaction. Therefore, common tube reactors are not suitable for the industrial production of polycarbonate-polyether polyols.

[0010] Tubular reactors specifically used for the preparation of polycarbonate polyether polyols typically employ reaction tubes with large aspect ratios in order to prolong the residence time of the materials in the reaction tubes and ensure sufficient reaction. For example, Chinese patent CN103403060B proposes a method for preparing polyether carbonate polyols, which states in its specification that "a tubular reactor within the meaning of the present invention typically has a tube length L to tube diameter dg ratio of L / dg > 50." However, a large aspect ratio (tube length L to tube diameter dg) is not suitable for the preparation of polycarbonate polyols. R Ratio L / d R The use of tubular reactors with a diameter greater than 50 mm inevitably leads to mixing and heat dissipation problems when preparing polycarbonate polyether polyols. As the carbonate content increases, the viscosity of the polycarbonate polyether polyol increases exponentially. The large aspect ratio of the tubular reactor divides the material into slender tubular units, preventing uniform mixing of the mixed materials throughout the entire pipeline. Furthermore, after the polycarbonate polyether polyol is synthesized, the viscosity increases dramatically, and the material fluidity deteriorates. At this time, explosive points are easily generated in the pipeline. The inability to dissipate heat and disperse the explosive points in a timely and effective manner will cause chain explosions, ultimately preventing the synthesis of the target product.

[0011] Another issue to be addressed in the industrial production of polycarbonate polyether polyols is the scaling-up effect. Chinese Patent CN111484610A defines the scaling-up effect as "the effect of increasing the viscosity of the materials during the synthesis of polycarbonate polyether polyols, making it difficult to release the heat generated by the reaction. This heat, when heated, accelerates the reaction rate, generating more heat. More materials generate more heat, making the scaling-up effect unavoidable."

[0012] Therefore, in the technical field of polycarbonate polyether polyol preparation, there is no technology that can realize one-time centralized feeding to prepare carbonate polyether polyol, ensure gas-liquid mass transfer of materials, uniform solid-liquid-gas mixing, sufficient heating and heat dissipation, and a tubular reactor without an amplification effect. Summary of the Invention

[0013] In response to the deficiencies in the prior art, the present invention discloses a tubular reactor specifically for the synthesis of polycarbonate polyether polyols. The reactor employs a reaction pipe with a small aspect ratio and is configured with a specific carbon dioxide-epoxide compound mixed heat transfer unit, a solid-liquid mixing unit, a circulation control unit, a temperature control unit, and a pressure control unit. This achieves a high degree of matching and overall synergy between the internal structure of the tubular reactor and material circulation and reaction heat control, making the reactor particularly suitable for the large-scale industrial production of polycarbonate polyether polyols.

[0014] The technical solution of the present invention is as follows: A tubular reactor for synthesizing polycarbonate polyether polyols, comprising a reaction pipe and:

[0015] A carbon dioxide-epoxide mixing heat transfer unit is arranged on the upper part of the reaction pipe, and is used to reduce the material temperature;

[0016] a solid-liquid mixing unit disposed in the reaction pipe and located below the carbon dioxide-epoxide mixing heat transfer unit;

[0017] A circulation control unit for driving the circulation flow of materials in the reaction pipe;

[0018] A temperature control unit for controlling the temperature in the reaction pipe;

[0019] A pressure control unit for controlling the pressure in the reaction pipe;

[0020] The circulation control unit, temperature control unit, and pressure control unit work together to control the entire reaction process; the specific process is as follows:

[0021] After the epoxy compound, chain transfer agent, and catalyst are fed into the reaction pipe in a centralized manner at one time, only carbon dioxide is added during the reaction process, the circulation control unit transports the material in the solid-liquid mixing unit to the carbon dioxide-epoxide mixed heat transfer unit, and the material returns to the solid-liquid mixing unit after the temperature is reduced, and the circulation control unit adjusts the material circulation speed, and simultaneously adjusts the temperature control unit and the pressure control unit to maintain the material temperature in the upper part of the reaction pipe lower than the material temperature in the lower part of the reaction pipe, the temperature difference between the material in the middle part of the reaction pipe and the material in the lower part of the reaction pipe does not exceed 5° C., and the temperature of the material in the reaction pipe increases gradually in the flow direction;

[0022] The length-to-diameter ratio L:d of the reaction pipe is less than 50;

[0023] The material is a mixture of reaction raw materials and reaction products, including but not limited to epoxy compounds, chain transfer agents, catalysts and polycarbonate polyether polyols.

[0024] The reaction is carried out in a reaction pipe. During the reaction, the epoxy compound and the chain transfer agent are continuously consumed. Under the action of the DMC catalyst, the reaction continues to generate polycarbonate polyether polyol, which increases the overall viscosity and density of the material.

[0025] The carbon dioxide-epoxide compound mixed heat transfer unit includes a gas-liquid mass transfer and heat transfer zone, and realizes gas-liquid mass transfer and heat transfer by epoxide compound absorbing carbon dioxide and carbon dioxide absorbing liquid heat, thereby reducing the material temperature.

[0026] The one-time centralized feeding means that the epoxy compound, chain transfer agent and catalyst are fed into the tubular reactor at one time for reaction, and only carbon dioxide is added during the reaction without adding these three raw materials.

[0027] The tubular reactor described herein provides sufficient mixing, mass and heat transfer, and precise temperature control for the synthesis of polycarbonate polyether polyols. This eliminates the need for catalysts with specialized structures and preactivation. The catalyst induction activation phase and the chain growth phase can occur within the same reaction tube, enabling a single, centralized feed process for preparing polycarbonate polyether polyols. This allows for the synthesis of high-quality polycarbonate polyether polyols without scale-up effects, making it suitable for industrial, large-scale production. The technical solution of the present invention utilizes a reaction tube with a low aspect ratio (L:d ratio of the reaction tube <50) and is equipped with a specific carbon dioxide-epoxide mixing and heat transfer unit, a solid-liquid mixing unit, a circulation control unit, a temperature control unit, and a pressure control unit. These units work synergistically with the reaction tube to achieve material mixing, heat and mass transfer, and precise temperature control at specific locations in the reaction tube, effectively dissipating heat from the material and preventing implosion.

[0028] In one embodiment, the temperature control unit includes temperature sensors indicating the temperature of materials in three different areas of the reaction pipe: the upper, middle, and lower areas; a jacket for heating or cooling the reaction pipe; and a heat transfer medium filled between the jacket and the reaction pipe.

[0029] In one embodiment, when the temperature in the middle area of ​​the reaction pipe is higher than the reaction temperature threshold, the temperature control unit is adjusted to lower the temperature inside the reaction pipe, and the material circulation speed and the speed of replenishing carbon dioxide gas are increased until the temperature in the middle of the reaction pipe is maintained within the reaction temperature threshold range; when the temperature difference between the middle and lower areas of the reaction pipe is greater than the temperature difference threshold, the material circulation speed and the speed of replenishing carbon dioxide gas are increased until the temperature difference does not exceed the temperature difference threshold.

[0030] In one embodiment, a density sensor indicating the material density is provided at the outlet of the reaction pipe, and the reaction process is controlled according to the rate of change of the material density.

[0031] In one embodiment, the process of controlling the entire reaction process also includes, when the density change of the material per minute is greater than the density change rate threshold, increasing the material circulation speed and the speed of replenishing carbon dioxide gas until the density change rate does not exceed the threshold.

[0032] In one embodiment, the carbon dioxide-epoxide mixed heat transfer unit is located in the gas-liquid mass transfer heat transfer zone, which is the upper space of the reaction pipe. The volume of the gas-liquid mass transfer heat transfer zone is greater than or equal to 20% of the volume of the reaction pipe.

[0033] In one embodiment, the carbon dioxide-epoxide mixed heat transfer unit includes a gas distributor located 10 to 50 mm from the top of the reaction tube. The gas distributor is a porous structure. Preferably, the porous structure is elliptical, with a major axis of 2 mm and a minor axis of 1 mm. Preferably, the porous structure is arranged in a rectangular pattern. Preferably, the porous structure has a 3 mm pore spacing.

[0034] In one embodiment, the solid-liquid mixing unit comprises a mixer. Preferably, the mixer is a static mixer.

[0035] In one embodiment, the inner diameter of the reaction pipe is 100 to 1500 mm.

[0036] In one embodiment, the length-to-diameter ratio of the reaction pipe satisfies 10≤L:d≤40.

[0037] In one embodiment, the number of the reaction pipes is 2 to 8.

[0038] In one embodiment, the reaction tubes are connected in parallel, and the center distance between the nearest neighboring tubes is less than or equal to twice the diameter of the tubes.

[0039] In one embodiment, the reaction pipes are independent of each other and are closed and isolated by valves.

[0040] In one embodiment, the material circulation paths formed between the reaction pipes and the circulation units are the same.

[0041] In one embodiment, the circulation speed of the circulation unit is 10-20 min / cycle.

[0042] Compared with the prior art, the tubular reactor provided by the present invention uses a reaction pipe with a small aspect ratio and is designed with a specific carbon dioxide-epoxide compound mixing heat transfer unit, a solid-liquid mixing unit, a circulation control unit, a temperature control unit, and a pressure control unit. The carbon dioxide-epoxide compound mixing heat transfer unit, the solid-liquid mixing unit, the circulation control unit, the temperature control unit, and the pressure control unit work synergistically with the reaction pipe to provide sufficient mixing, mass transfer, heat transfer, and precise temperature control conditions for the synthesis of polycarbonate polyether polyols, thereby achieving the following beneficial effects:

[0043] (1) The reaction process is coordinated by the temperature, pressure and material density in the reaction pipeline, and the circulation flow of the material is used to achieve efficient material mixing, effective mass and heat transfer and precise temperature control to synthesize high-quality polycarbonate polyether polyols.

[0044] (2) Only conventional catalysts are used and the catalysts do not need to be pre-activated. The catalyst induction activation period and the chain segment growth period can be carried out in the same reaction pipeline, realizing a one-time centralized feeding process for preparing polycarbonate polyether polyols.

[0045] (3) There is no amplification effect, which is conducive to the expanded industrial production of polycarbonate polyether polyols. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0047] Figure 1 Schematic side view of a shell and tube reactor according to an embodiment of the present invention.

[0048] Figure 2 Schematic top view of a shell and tube reactor according to an embodiment of the present invention.

[0049] Figure 3 This is a comparison diagram of the density change curves of the polycarbonate polyether polyols of Example 1 and Comparative Examples 1-7.

[0050] Explanation of the accompanying numbers: 1-gas supply port, 2-first temperature sensor, 3-second temperature sensor, 4-third temperature sensor, 5-liquid distributor, 6-gas distributor, 7-jacket, 8-mixer, 9-reaction pipe, 10-density sensor, 11-circulation device, 12-connecting pipe, 13-heat transfer medium. DETAILED DESCRIPTION

[0051] To further clarify the objectives, technical solutions, and advantages of the present invention, embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. It should be understood that the described embodiments represent only a portion of the present invention, and not all of the embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein. In the description of the present invention, it should be noted that terms such as "upper," "lower," "left," "right," "perpendicular," "parallel," "inner," "outer," "front," and "rear" indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings. These terms are used solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the present invention.

[0052] Figure 1 Schematic side view of a shell and tube reactor according to an embodiment of the present invention. Figure 2 Schematic diagram of a top view of a tubular reactor according to an embodiment of the present invention. Figure 1 and Figure 2 As shown, the shell and tube reactor of the embodiment of the present invention includes: a reaction pipe 9; a carbon dioxide-epoxide compound mixing heat transfer unit, including a gas distributor 6 arranged at the upper part of the reaction pipe; a solid-liquid mixing unit, including a mixer 8 arranged in the reaction pipe and located below the gas distributor 6; a temperature control unit, including a first temperature sensor 2 arranged at the upper part of the reaction pipe, a second temperature sensor 3 arranged in the middle part of the reaction pipe, and a third temperature sensor 4 arranged at the lower part of the reaction pipe, a jacket 7 covering the outside of the reaction pipe, and a heat transfer medium 13 filled between the reaction pipe and the jacket; a circulation control unit, including a density sensor 10 and a circulation device 11 located at the outlet of the lower end of the reaction pipe; a pressure control unit, including a gas supply port 1 at the inlet of the upper end of the reaction pipe; multiple reaction pipes are connected in parallel, and the reaction raw materials are respectively transported to the multiple reaction pipes through the liquid distributor 5 and the connecting pipe 12.

[0053] In order to ensure sufficient mixing of the raw materials and prevent uneven reactions from causing excessively wide molecular weight distribution or explosion, a reaction preparation stage is required before the solid-liquid reactants are passed into the tubular reactor. In a 0.1-0.5MPa carbon dioxide environment, the raw epoxide is purified by the system and added from the storage tank to the raw material mixing device. Subsequently, the chain transfer agent and catalyst are added to fully mix with the raw epoxide. The premixing temperature range is 0-60°C, the pressure range is 0.1-2Mpa, and the premixing time is 1-4 hours. The raw material mixing device includes but is not limited to premixing kettles, venturi tubes and other devices. At this time, only physical mixing is performed in the raw material mixing device to ensure sufficient dissolution and mixing of the reactants, no polymerization reaction occurs, and no catalyst activation reaction occurs.

[0054] After premixing, the raw materials are fed through a metering pump from the feed port into a reaction pipe with a temperature of 40°C and a carbon dioxide pressure of 0.1-2MPa. When a fixed amount of raw materials enters the reaction pipe, the feeding is stopped, carbon dioxide is introduced through the air supply port 1, and the circulation device is turned on. The initial flow rate of the circulation device 11 is based on a cycle of 10-20 minutes. The carbon dioxide in the raw materials is provided by the carbon dioxide pipeline. The pressure in the raw material mixing zone is adjusted to 2-6MPa and maintained by adding carbon dioxide. The jacket 7 is used to adjust the temperature of the heat transfer medium 13 and control the temperature of the material in the reaction pipe at 70-90°C. During the reaction, the material flows from top to bottom in the reaction pipe, first flowing through the carbon dioxide-epoxide mixed heat transfer unit, then flowing through the solid-liquid mixing unit, and then flowing out of the reaction pipe. It is transported to the liquid distributor through the circulation device, and then dispersed into each reaction pipe and flows down from top to bottom to complete the cycle. Observe the data of the density sensor 10 and reach 1.12g / cm 3The reaction is then considered complete. Figure 1 As shown, the upper part of the reaction pipe 9 is a carbon dioxide-epoxide compound mixed heat transfer unit, and the lower part is a solid-liquid mixing unit. The gas distributor 6 in the carbon dioxide-epoxide compound mixed heat transfer unit increases the contact area between the epoxy compound and the carbon dioxide and prolongs the contact time, so that the epoxy compound absorbs carbon dioxide and releases heat, thereby reducing the temperature of the material. After the carbon dioxide is consumed, the pressure in the reaction pipe decreases, and carbon dioxide gas is replenished from the gas replenishment port 1. At the same time, the newly replenished carbon dioxide gas reduces the temperature of this area. The circulation device 11 continuously transports the material from the solid-liquid mixing unit to the carbon dioxide-epoxide compound mixed heat transfer unit. After the temperature of the material is reduced, it returns to the solid-liquid mixing unit again, so that the reaction raw materials and reaction products are evenly mixed during the circulation process, avoiding explosions caused during the reaction process. The viscosity of the material increases after the reaction, and the flow rate in the solid-liquid mixing unit decreases, while the unreacted material will preferentially flow downward, so that the unreacted material can reach the gas-liquid mixing zone again in time for mass transfer and heat transfer. The material circulation flow direction is as follows Figure 1 As shown by the arrow in . In the reaction pipe, the temperature of the material increases gradually along the direction of material flow, that is, the closer to the bottom, the higher the reaction temperature and the faster the reaction process. The faster the reaction process, the faster the material density change rate. Therefore, the material density change rate is used as one of the judgment bases for circulation control. During the reaction process, when the temperature of the second temperature sensor 3, that is, the temperature of the material in the middle area of ​​the reaction pipe is higher than 85°C, the jacket is controlled to lower the temperature inside the reaction pipe and at the same time increase the circulation speed until the temperature inside the reaction pipe is maintained at 70-90°C; when the temperature difference between the middle and lower areas of the material in the reaction pipe, that is, the temperature difference between the second temperature sensor 3 and the third temperature sensor 4, is greater than 5°C, the circulation speed is increased until the temperature difference does not exceed 5°C. When the density change of the liquid material is greater than 0.06g / cm per minute 3 When it occurs, it means that the reaction rate is too fast, and carbon dioxide is added to maintain the pressure in the reaction pipe. At the same time, the material circulation speed is increased to speed up the mixing process and the heat dissipation process to prevent the local temperature from being too high. Through the synergistic effect of the circulation control unit, the temperature control unit, and the pressure control unit, and in conjunction with the cooling function of the carbon dioxide-epoxide mixed heat transfer unit, the temperature of the material in the upper area of ​​the reaction pipe is maintained lower than the temperature of the material in the lower area of ​​the reaction pipe, that is, the temperature of the first temperature sensor 2 is always lower than the temperature of the third temperature sensor 4; the temperature difference between the material in the middle of the reaction pipe and the material in the lower part of the reaction pipe does not exceed 5°C, that is, the temperature difference between the second temperature sensor 3 and the third temperature sensor 4 does not exceed 5°C; the temperature of the material in the reaction pipe increases gradually in the flow direction. The arrangement of the reaction pipes 9 inside the shell and tube reactor is as follows: Figure 2 As shown, but not limited to this arrangement.

[0055] In one embodiment, the carbon dioxide-epoxide mixed heat transfer unit is located in the gas-liquid mass transfer heat transfer zone, which is the upper space of the reaction pipe. The volume of the gas-liquid mass transfer heat transfer zone is greater than or equal to 20% of the volume of the reaction pipe.

[0056] In one embodiment, the gas distributor 6 is located at a position of 10 to 50 mm near the top of the reaction pipe 9, and the gas distributor 6 is a porous structure; preferably, the porous structure is elliptical, with a major axis of 2 mm and a minor axis of 1 mm; preferably, the porous structure is arranged in a rectangular shape; preferably, the porous structure has a pore spacing of 3 mm.

[0057] In one embodiment, the inner diameter of the reaction pipe is 100 to 1500 mm. In the process of industrial production of polycarbonate polyether polyol, if the inner diameter is too small, the efficiency of gas-liquid mass transfer is directly affected. When the liquid passes through the carbon dioxide gas area, the gas-liquid contact area is small, the mass transfer efficiency is low, and the required polyester polyether polyol cannot be obtained. Not only does it lead to a too small carbonate chain segment ratio (as defined in Example 1), but there is also a high probability of implosion due to the lack of carbon dioxide participation. If the inner diameter is too large, the efficiency of internal heat transfer is directly affected. The excessively large inner diameter causes the solid-liquid mixing unit to be unable to mix the material heat evenly in time, and the temperature difference between the central area and the outer area of ​​the raw material in the pipe is too large, resulting in an overly wide molecular weight distribution of the product, affecting the performance of the product.

[0058] In one embodiment, the ratio of the length L to the diameter d of the reaction tube is 10 ≤ L: d ≤ 40. The heating time for industrial production of polycarbonate polyether polyols is unique. In a polycarbonate polyether polyol tubular reactor, if the flow rate is constant and the heating time per unit volume of material is short, the reaction conversion rate per unit time will be significantly reduced, requiring a longer reaction time. This longer heating time will lead to decomposition of the polyester chain segments and yellowing of the product. Therefore, the reaction tube length cannot be too long. Furthermore, the reaction process continuously generates heat, which increases the temperature of the reaction system. The reactor needs to promptly release the heat generated in the material. When the flow rate is constant, the liquid must circulate through the gas-liquid heat transfer zone within a specified time to complete heat release and gas-liquid mass transfer. Therefore, the tube length cannot be too long. The reaction tube for synthesizing polyester polyether polyols should have a specific length-to-diameter ratio to ensure sufficient heating reaction time for the product while meeting the gas-liquid mass transfer and heat release requirements.

[0059] In one embodiment, the number of the reaction pipes is 2 to 8.

[0060] In one embodiment, the reaction pipes are connected in parallel, and the center distance between the nearest neighbor pipes is less than or equal to twice the pipe diameter.

[0061] In one embodiment, the reaction pipes are independent of each other and are closed and isolated by valves; and the liquid circulation paths formed between the reaction pipes and the circulation control unit are the same.

[0062] In one embodiment, the circulation speed of the circulation unit is 10-20 min / cycle.

[0063] The reaction products contain polycarbonate polyol, polyether polyol, cyclic carbonate, and unreacted epoxide. Next, the liquid product passes through a catalyst filter to recover the catalyst. The filtrate then flows into a distillation unit, which combines a falling film tower with a scraped-surface evaporator. The filtrate first passes through the falling film tower to distill the epoxide into a buffer tank for recovery. The filtrate then flows into a scraped-surface evaporator or a distillation tower to separate the main product, polycarbonate polyether polyol, from the byproduct, cyclic carbonate. The separation rate for polyols and cyclic carbonate is 98%. After complete separation, the two products are canned separately for later use.

[0064] The tubular reactor of the present invention will be further described below with reference to specific embodiments.

[0065] Example 1:

[0066] 8L of propylene oxide, 4g of DMC catalyst, and a chain transfer agent at a molar ratio (epoxide to chain transfer agent) of 55:1 were added to a premix kettle. 0.4MPa of carbon dioxide was introduced and the mixture was stirred at 40°C. After stirring for 1 hour, the mixture was pressurized into an 8L x 2 reactor array. Each reaction channel had a diameter of 100mm and a length of 1000mm. After the mixture was fully introduced, carbon dioxide was introduced into the reaction channels to a pressure of 3MPa and maintained at that pressure. A circulation system was started with a flow rate of 600g / min. Using temperature sensor 2 as the reaction temperature, the reaction was maintained at 80°C for 3 hours. After the density uniformly increased to 1.12g / cm³ and stabilized, the reaction was completed and the temperature was lowered to remove the product. After the catalyst was removed through a catalyst filtration device, the main and by-products were separated using a scraper evaporator.

[0067] The DMC catalyst described in this example is a zinc-cobalt double metal cyanide complex catalyst obtained by reacting water-soluble metal salts of zinc and cobalt in an aqueous solvent. The catalyst is prepared as follows: a certain amount of cobalt salt and zinc salt, specifically sodium thiocyanatocobaltate and zinc bromide, are weighed in a molar ratio of 1:4, dissolved in an aqueous solvent containing water and tert-butyl alcohol, and continuously stirred. The aqueous solvent is composed of water and tert-butyl alcohol, and the total mass ratio of the metal salts (i.e., the cobalt and zinc salts) to the aqueous solvent is 1:5. An inorganic acid and an organic acid are added. The inorganic acid is dilute hydrochloric acid at a pH of 2, and the organic acid is glutaric acid. The molar ratio of the inorganic acid to the organic acid is 5:1, and the total molar ratio of the metal salt to the acid is 4:1. The mixture is stirred at 10-100°C for several hours until a precipitate is continuously formed. The turbid solution is filtered and dried to obtain a filter cake. The filter cake is re-slurried and washed with an aqueous solvent at a temperature of 10-100°C, specifically at 100°C for 3 minutes. After stirring for several hours, the filter cake is filtered and dried to obtain a filter cake. The slurrying, washing, and drying steps are repeated multiple times at 10-100°C until the liquid pH of the system reaches 6-7, specifically at 60°C for 6 minutes each time. The solid product is further dried under vacuum at 80-100°C to obtain the final catalyst. The catalyst is processed into powder particles by mechanical grinding under anhydrous drying conditions before use.

[0068] The chain transfer agent described in this embodiment is selected from any one or more of ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, glycerol, trimethylolpropane, trimethylolethane, 1,2,4-butanetriol, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, phthalic acid, trimesic acid, pyromellitic acid, catechol, resorcinol, and hydroquinone.

[0069] The epoxide described in this embodiment is selected from at least one of ethylene oxide, propylene oxide, butylene oxide, and epichlorohydrin. Specifically, the epoxide is propylene oxide (PO).

[0070] To meet downstream polyurethane synthesis applications, synthesized polycarbonate polyether polyols must meet certain quality requirements. Quality is primarily evaluated based on molecular weight distribution and ester content. Molecular weight distribution is measured by the polymer polydispersity index (PDI), while ester content is measured by the carbonate linkage ratio. A narrower molecular weight distribution (i.e., a lower PDI) indicates fewer small molecules and minimizes their impact on the reaction rate in downstream polyurethane synthesis. A higher lipid content (i.e., a higher carbonate linkage ratio) improves carbon dioxide fixation, but it should be kept within certain limits, as this will affect the soft and hard segment requirements in polyurethane synthesis. Polycarbonate polyether polyols are graded based on the PDI and carbonate linkage ratio. A PDI below 2 and a carbonate linkage ratio of 50-65% are considered acceptable, while a PDI below 1.5 and a carbonate linkage ratio of 55-60% are considered superior.

[0071] The purified product is sampled and analyzed. Specifically, the polymerization reaction product (polycarbonate-polyether polyol and cyclic propylene carbonate and unreacted epoxide) is sampled and collected in a container. The polymerization reaction product stream sample is characterized by nuclear magnetic resonance (NMR) spectroscopy to calculate the ratio of polymer to cyclic small molecules in the crude product. After purification, the polymer is tested by nuclear magnetic resonance (NMR) spectroscopy to calculate the ratio of polycarbonate chain segments to polyether chain segments on the polymer main chain (i.e., the carbonate chain segment ratio). The calculation method is polycarbonate chain segment / polyether chain segment. 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%.

[0072] With the help of 1 The amount of incorporated carbon dioxide (carbonate segment content) and the ratio of propylene carbonate (cyclic carbonate) to polycarbonate polyether polyol in the resulting polycarbonate polyether polyol were determined by H-NMR (Bruker, DPX400, 400 MHz; pulse program zg30, wait 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:

[0073] Among them, 5.0ppm and 4.2ppm belong to the proton peaks of the methine and methylene groups on the polycarbonate chain, 4.9ppm, 4.5ppm and 4.1ppm belong to the proton peaks of the methine and methylene groups in the five-membered ring carbonate, and 3.5-3.8ppm belong to the proton peaks 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 It represents the integrated area of ​​the peak at 5.0 ppm. 1The integrated area of ​​the H-NMR spectrum and its related proton peaks, the ratio of carbonate chain segments 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:

[0074] 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%;

[0075] W PC =102×A 1.5 / [102×(A 5.0 +A 4.2 -2×A 4.6 +A 1.5 )+58×A 3.5 ]×100%;

[0076] M CO2 =44×F CO2 / [102×F CO2 +58×(1-F CO2 )]×100%;

[0077] Here, 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 PO (molar mass 58 g / mol).

[0078] The formula for calculating product conversion rate is n=m×(1-M CO2 ) / (Mm×M CO2 ); wherein m is the mass of the product after removing propylene oxide, and M is the total sample containing propylene oxide.

[0079] The polymer number average molecular weight (Mn) and the polymer polydispersity index (PDI) were determined by gel permeation chromatography (GPC).

[0080] The data are shown in Table 1:

[0081]

[0082] The data from Example 1 demonstrates that the tubular reactor of the present invention allows for full reaction of the raw materials at 80°C, resulting in a polycarbonate-polyether polyol with a narrower molecular weight distribution and a PDI of 1.13. It also boasts an optimal carbonate segment ratio, ranging from 55% to 60%, resulting in a high carbon dioxide fixation rate while meeting the application requirements. Furthermore, the reaction time is very short, reaching the desired conversion rate in just 3 hours. With a single, centralized feed, the tubular reactor can synthesize high-quality polycarbonate-polyether polyols with a conversion exceeding 95%, a PDI below 1.5 (i.e., a narrow molecular weight distribution), and a carbonate segment ratio between 55% and 60%.

[0083] The conditions of Example 2 are the same as those of Example 1, with the only difference being that the amount of propylene oxide added is 12.8 L, i.e., the gas-liquid volume ratio is 1:4.

[0084] The conditions of Example 3 are the same as those of Example 1, the only difference being that device 2 is used and the inner diameter of the pipe is 220 mm.

[0085] The conditions of Example 4 are the same as those of Example 1, with the only difference being that device 3 is used and the inner diameter of the pipe is 1500 mm.

[0086] The conditions of Example 5 are the same as those of Example 1, with the only difference being that apparatus 4 is used, there are four reaction pipes, and the amount of propylene oxide added is 16 L.

[0087] The conditions of Example 6 are the same as those of Example 1, with the only difference being that apparatus 5 is used, there are 8 reaction pipes, and the amount of propylene oxide added is 32 L.

[0088] The conditions of Example 7 are the same as those of Example 1, the only difference being that device 6 is used and the length-to-diameter ratio of the pipeline is 20:1.

[0089] The conditions of Example 8 are the same as those of Example 1, the only difference being that device 7 is used and the length-to-diameter ratio of the pipeline is 40:1.

[0090] The conditions of Example 9 are the same as those of Example 1, with the only difference being that the reaction temperature is 70°C.

[0091] The conditions of Example 10 are the same as those of Example 1, the only difference being that the reaction temperature is 90°C.

[0092] The conditions of Example 11 are the same as those of Example 1, with the only difference being that the initial circulation flow rate is maintained at 10 min / cycle.

[0093] The conditions of Example 12 are the same as those of Example 1, with the only difference being that the initial circulation flow rate is maintained at 15 min / cycle.

[0094] The reaction apparatus and reaction conditions involved in each embodiment are shown in Table A and Table B, where Temperature 1, Temperature 2, and Temperature 3 are the temperatures of the materials in the upper, middle, and lower parts of the reaction pipe, respectively.

[0095]

[0096]

[0097] The products obtained in Examples 2-12 were tested according to the method in Example 1. The test results are shown in Table C.

[0098]

[0099] The reaction results of each embodiment are shown in Table C. In Examples 1 and 3-12, the gas-liquid ratio is 1:1, i.e., the volume of the gas-liquid mass transfer and heat transfer zone accounts for 50% of the volume of the reaction pipe. In Example 2, the volume of the CO2 is reduced, i.e., the volume of the gas-liquid mass transfer and heat transfer zone is reduced to 20%. It can be seen that the product molecular weight, molecular weight distribution, and ester-ether ratio do not change much. Therefore, the volume of the gas-liquid mass transfer and heat transfer zone in the tubular reactor provided by the present invention is greater than or equal to 20% of the volume of the reaction pipe. Compared with Example 1, Examples 3 and 4 increase the diameter of the reaction pipe, Examples 5 and 6 increase the number of reaction pipes, and Examples 7 and 8 use reaction pipes with a larger aspect ratio. Examples 3-8 all industrialize the tubular reactor. From the perspective of the reaction process and product results, there is no significant fluctuation in indicators such as the molecular weight, molecular weight distribution, and conversion rate of the polymer. The molecular weight difference index is small and the molecular weight distribution is narrow, and products of comparable quality are obtained, indicating that the tubular reactor of the present invention has no amplification effect. Therefore, when we amplify the reaction, we only need to increase the number of parallel reaction pipes and the circulation pump flow rate needs to be opened accordingly. No process adjustments need to be made, and it is suitable for industrial production. Moreover, the parallel reaction pipes in the present invention can share a set of heating equipment, which can reduce energy consumption while amplifying. It can be seen from the data of Examples 9 and 10 and Example 1 that the shell and tube reactor provided by the present invention can synthesize high-quality products at 70-90°C. In Examples 1-10, during the reaction process, the temperature of the upper material of the temperature reaction pipe is maintained lower than the temperature of the lower material, and the temperature difference between the material in the middle of the reaction pipe and the material in the lower part of the reaction pipe does not exceed 5°C, and high-quality products can be synthesized. It can be seen from the data of Examples 11 and 12 and Example 1 that the shell and tube reactor provided by the present invention can synthesize high-quality products when the circulation speed is maintained at 10-20min / cycle.

[0100] The conditions of Comparative Example 1 are the same as those of Example 1, with the only difference being that the amount of propylene oxide added is 13.3 L, i.e., the gas-liquid volume ratio is 1:5.

[0101] The conditions of Comparative Example 2 are the same as those of Example 1, with the only difference being that the initial flow rate is 5 min / cycle.

[0102] The conditions of Comparative Example 3 are the same as those of Example 1, with the only difference being that the initial flow rate is 25 min / cycle.

[0103] The conditions of Comparative Example 4 are the same as those of Example 1, the only difference being that the device 8 is used and the diameter of the reaction pipe is 50 mm.

[0104] The conditions of Comparative Example 5 are the same as those of Example 1, the only difference being that Device 9 is used and the length-to-diameter ratio of the reaction pipe is 50:1.

[0105] The conditions of Comparative Example 6 are the same as those of Example 1, with the only difference being that device 10 is used, the number of reaction pipes is 10, and the amount of propylene oxide added is 40 L.

[0106] The conditions of Comparative Example 7 are the same as those of Example 1, with the only difference being that the temperature difference between Temperature 2 and Temperature 3 during the reaction is greater than 5°C.

[0107] The reaction apparatus and reaction conditions involved in each comparative example are shown in Table D and Table E.

[0108]

[0109]

[0110] The products obtained in Comparative Examples 1-7 were tested according to the method in Example 1. The test results are shown in Table F.

[0111]

[0112] Figure 3The density change curve comparison of polycarbonate polyether polyol in Example 1 and Comparative Examples 1-7 is shown. Compared with Example 1, Comparative Example 1 has a different gas-liquid ratio, which reduces the volume of the gas-liquid mass transfer and heat transfer zone, resulting in the inability of the material to effectively transfer mass and heat, a wider molecular weight distribution, and a lower ester content. Compared with Example 1, Comparative Example 2 has a different initial circulation flow rate. When the circulation flow rate is faster, the temperature of the material in the pipeline is maintained in a lower range, the reaction rate is lowered, resulting in a longer reaction time, which leads to a wider molecular weight distribution. Similarly, when the flow rate slows down in Comparative Example 3, the temperature of the material in the pipeline will be maintained in a higher range, the reaction rate will be faster, the CO2 participation level will be lower, the ester content will be reduced, and it is easy to cause explosion. In Example 4, the diameter of the reaction tube is 50 mm, which is less than 100 mm, resulting in low polyol ester content, wide molecular weight distribution, and low conversion rate; in Comparative Example 5, the aspect ratio of the reaction tube is 50, which leads to problems such as uneven material mixing and poor gas-liquid mass transfer and heat transfer efficiency, resulting in low polyol ester content and wide molecular weight distribution; in Comparative Example 7, the temperature difference is not controlled to be less than 5°C, and the temperature at the lower part of the reaction tube is 8°C higher than the temperature in the middle of the reaction tube. The reaction implodes, the temperature rises sharply, and the temperature in the middle of the reaction tube reaches 95°C. Therefore, high-quality polycarbonate polyether polyols with a PDI of less than 2 cannot be synthesized. As can be seen from the density growth curve, when synthesizing polycarbonate polyether polyols in Comparative Examples 1-7, the density increases too quickly, resulting in large changes in the internal temperature, which also leads to poor performance of the synthesized polyols. The density increases too slowly, which prolongs the reaction time and causes the molecular weight distribution to become wider. The reason why the density change in Comparative Example 6 is the same as that in Example 1 is because the reaction conditions are the same, but the number of reaction tubes is 10. Excessive reaction tubes will cause the molecular weight gap between each tube to widen and the molecular weight distribution to become wider. Therefore, the preferred number of reaction tubes provided by the present invention is 2 to 8.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A tubular reactor for synthesizing polycarbonate polyether polyols, comprising a reaction pipeline; characterized in that: Also includes: A carbon dioxide-epoxide mixed heat transfer unit disposed on the upper portion of the reaction pipeline is used to reduce the material temperature; a solid-liquid mixing unit disposed in the reaction pipe and located below the carbon dioxide-epoxide mixing heat transfer unit; A circulation control unit for driving the circulation flow of materials in the reaction pipeline; A temperature control unit for controlling the temperature in the reaction pipe; A pressure control unit for controlling the pressure in the reaction pipeline; The circulation control unit, temperature control unit, and pressure control unit work together to control the entire reaction process; the specific process is as follows: After the epoxy compound, the chain transfer agent and the catalyst are fed into the reaction pipe in a one-time centralized manner, the circulation control unit transports the material in the solid-liquid mixing unit to the carbon dioxide-epoxide compound mixed heat transfer unit, and the material temperature is lowered and then returned to the solid-liquid mixing unit again, and the circulation control unit adjusts the material circulation speed, and adjusts the temperature control unit and the pressure control unit to maintain the material temperature at the upper part of the reaction pipe lower than the material temperature at the lower part of the reaction pipe, and the temperature difference between the material in the middle part of the reaction pipe and the material in the lower part of the reaction pipe does not exceed 5° C., and the temperature of the material in the reaction pipe increases gradually in the flow direction; The carbon dioxide-epoxide mixed heat transfer unit is located in the gas-liquid mass transfer heat transfer zone, which is the upper space of the reaction pipeline, and the volume of the gas-liquid mass transfer heat transfer zone is greater than or equal to 20% of the volume of the reaction pipeline; The carbon dioxide-epoxide mixed heat transfer unit includes a gas distributor; The length-to-diameter ratio L:d of the reaction pipe is less than 50.

2. The tubular reactor according to claim 1, characterized in that: The temperature control unit includes a temperature sensor indicating the temperature of materials in three different regions, namely, the upper, middle and lower regions in the reaction pipeline, a jacket for heating or cooling the reaction pipeline, and a heat transfer medium filled between the jacket and the reaction pipeline.

3. The tubular reactor according to claim 1, characterized in that: When the temperature in the middle area of ​​the reaction pipeline is higher than the reaction temperature threshold, the temperature control unit is adjusted to lower the internal temperature of the reaction pipeline, and the material circulation speed and the speed of replenishing carbon dioxide gas are increased until the temperature in the middle of the reaction pipeline is maintained within the reaction temperature threshold range; when the temperature difference between the middle and lower areas of the reaction pipeline is greater than the temperature difference threshold, the circulation speed and gas replenishment speed are increased until the temperature difference does not exceed the temperature difference threshold.

4. The tubular reactor according to claim 1, characterized in that: The process of controlling the entire reaction process also includes, when the density change of the material per minute is greater than the density change rate threshold, increasing the material circulation speed and the speed of replenishing carbon dioxide gas until the density change rate does not exceed the threshold.

5. The tubular reactor according to claim 1, characterized in that: The gas distributor is located at a position of 10 to 50 mm near the top of the reaction pipe, and the gas distributor is a porous structure.

6. The tubular reactor according to claim 1, characterized in that: The inner diameter of the reaction pipe is 100 to 1500 mm.

7. The tubular reactor according to claim 1, characterized in that: The length-to-diameter ratio of the reaction pipe satisfies 10≤L﹕d≤40.

8. The tubular reactor according to claim 1, characterized in that: The number of the reaction pipes is 2 to 8.

9. The tube-in-tube reactor according to claim 8, characterized in that: The reaction pipes are connected in parallel, and the center distance between the nearest neighbor pipes is less than or equal to twice the pipe diameter.

10. The tube-in-tube reactor according to claim 9, characterized in that: The reaction pipelines are independent of each other and are closed and isolated by valves.

11. The tubular reactor according to claim 10, characterized in that: The material circulation paths formed between each reaction pipeline and the circulation unit are the same.

12. The tubular reactor according to claim 1, characterized in that: The circulation speed of the circulation control unit is 10-20 min / circulation.

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