Tubular reactor for synthesizing polycarbonate polyether polyol

Abstract

The invention relates to the technical field of preparation of polycarbonate polyether polyol, and particularly discloses a tubular reactor for synthesizing polycarbonate polyether polyol. Through configuration of a specific solid-liquid mixing unit, a carbon dioxide-epoxy compound mixing heat transfer unit, a circulation control unit, a temperature control unit and a pressure control unit, high matching and overall synergistic effect of the internal structure of the tubular reactor, material circulation and reaction heat control are realized; and sufficient mixing, mass and heat transfer and precise temperature control conditions are provided for synthesis of the polycarbonate polyether polyol, a process for preparing the polycarbonate polyether polyol through one-time concentrated feeding is realized, and expanded industrial production of the polycarbonate polyether polyol is facilitated.

Description

Technical Field

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

[0002] Polycarbonate polyether polyols are a class of polyols with carbonate groups in the molecule and hydroxyl groups at the ends of the molecular chain. One of the raw materials, carbon dioxide, is cheap and easy to obtain, non-toxic and non-flammable, has a clear carbon dioxide chemical fixation effect, and the reaction requires low temperature and low energy consumption. The copolymerization of carbon dioxide and epoxide 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] in, is the average number of ether chain segments, It is the average number of ester chain segments. Chinese patent CN111378106A mentions that the activation energy of polymer generation is lower than that of cyclic carbonate generation, while the potential energy of cyclic carbonate is lower than that of polymer. Therefore, the reaction of generating cyclic carbonate is a thermodynamically favorable reaction, while the reaction of generating polycarbonate is a kinetically favorable reaction. If the temperature of the reaction process is too high, it will lead to low carbonate chain content, wide molecular weight distribution, and high proportion of by-product cyclic carbonate. Therefore, accurate reaction temperature control is the key to improving the main product - polycarbonate polyether polyol.

[0005] Another key factor affecting the yield of the main product is the action of the bimetallic complex (abbreviated as DMC) catalyst. If the activation is not smooth or the activation is instantaneous, there will be explosion and polymerization, which is easy to cause high temperature and high pressure safety accidents. Chinese patent CN115785435A summarizes the catalytic reaction mechanism of DMC into an induction activation period and a segment growth period. In the induction activation period, the reaction is exothermic, and the temperature peak should be paid attention to. The initial activation temperature should be controlled to avoid overheating, thereby affecting the pressure resistance of the equipment and the activity of the catalyst. In the segment growth period, after DMC is fully activated, the active center combines with the chain transfer agent, the epoxy compound is inserted into the polymerization, and the chain transfer agent undergoes a replacement reaction with the active structure of DMC and the epoxy compound. External heat is required at this stage to promote chain growth. Chinese patent CN106471042B defines the activation step of the DMC catalyst in the induction activation period, which refers to a step in which a partial amount of alkylene oxide is optionally added to the DMC catalyst in the presence of CO2, and then the addition of the alkylene oxide compound is stopped, wherein a temperature peak ("hot spot") and / or a pressure drop is observed in the reactor due to the subsequent exothermic chemical reaction. 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.

[0006] In order to adapt to the above-mentioned characteristics of the reaction of synthesizing carbonate polyether polyols and reduce the influence of heat fluctuations on various components in the reaction, the existing technologies all require special catalyst design, process control and / or independent reactor design for the induced activation stage. The specific existing technologies are as follows: 1. The existing technology uses a special high-performance DMC catalyst, such as the Chinese patent CN115785435B, which uses a three-ligand bimetallic complex catalyst DMC with high activity and strong heat resistance to achieve a one-time centralized feeding of the three-ligand bimetallic complex catalyst DMC, a chain transfer agent and an epoxy compound at room temperature to prepare polyether polyols. 2. In terms of process improvement, Chinese patent CN116710504A adopts catalyst pre-activation technology, and pre-activates the catalyst with the starting compound or the reaction product of the first, second or third reaction, that is, first try to use part of the raw materials to activate the catalyst to start the reaction, and then add the remaining raw materials in batches or continuously; CN107108878A proposes a method for preparing polyether carbonate polyols, and proposes that the DMC catalyst needs to be "pre-treated at a temperature of 50 to 200°C and / or a reduced pressure (absolute) of 10 mbar to 800 mbar". At the same time, the method "adds the double metal cyanide catalyst, alkylene oxide, suspending agent and / or H-functional initiator compound to the first reactor at least intermittently in a continuous manner", which shows that the process needs to adopt catalyst pre-activation and batch addition of reactants. 3. Regarding the improvement of the reactor, Chinese patent CN116874759A proposes to use an independent reactor to activate the catalyst and maintain its activity. In order to solve the problem of unsmooth activation of the DMC catalyst, or easy explosion after instant activation and high safety risk, 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 a 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 the activity, and the temperature is reduced to 70-90°C; Chinese patent CN103403060B connects two tubular reactors with different inner diameters in series, and also controls the DMC induced activation period by introducing an independent reactor; Chinese patent CN106471042B uses a method of using a stirred tank main reactor and a tubular reactor in series, and controls the temperature of the tubular reactor to be 10°C to 40°C higher than the temperature of the main reactor, so that the DMC induced activation period occurs in the main reactor, and the segment growth period occurs in the tubular reactor.

[0007] However, from the perspective of reactor optimization, the technology of preparing carbonate polyether polyol by one-time centralized feeding in a reactor structure has not been described.

[0008] At present, the reactor for industrial production of polycarbonate polyether polyols can be divided into kettle reactors and pipeline reactors in terms of morphology. The surface area / volume ratio of the kettle reactor is low, the heat dissipation effect is poor, and it is not easy to handle high reaction heat. The pipeline reactor has controllable pressure and temperature during the reaction process, and has high monomer conversion efficiency, so it has attracted much attention in this field. Due to the small cross-sectional area of ​​the tubular reactor and limited production capacity, it is necessary to array it into a tube reactor for use. However, the general self-circulating tube reactor with an efficient mixer is described in CN109225114A, and the tube reactor is composed of a plurality of tubes, and the mixer outside the tube reactor is used to mix the materials. In the synthesis process of polycarbonate polyether polyols, there are higher requirements for material mixing and heat dissipation, and it is necessary to disperse the materials in time during the reaction and release the heat generated by the reaction at the same time to prevent explosion. Secondly, the head of multiple tubes in the tube reactor will cause solid catalyst accumulation, which is not conducive to the synthesis reaction. Therefore, the general tube reactor is not suitable for industrial production of polycarbonate polyether polyols.

[0009] In order to prolong the time that the materials stay in the reaction pipe and make the materials react fully, the tubular reactor specially used for preparing polycarbonate polyether polyols usually adopts a reaction pipe with a large aspect ratio. For example, Chinese patent CN103403060B proposes a method for preparing polyether carbonate polyols, which points out in the specification that "the tubular reactor within the meaning of the present invention usually has a ratio of tube length L to tube diameter dg of L / dg>50". However, the large aspect ratio (tube length L of the reaction pipe and tube diameter dg) R Ratio L / d R The shell-and-tube reactor with a diameter of more than 50 mm (0.177mm) inevitably brings about the problems of mixing and heat dissipation when preparing polycarbonate polyether polyols. With the increase of carbonate content, the viscosity of polycarbonate polyether polyols increases exponentially. The shell-and-tube reactor with a large aspect ratio divides the materials into slender shell-and-tube units, so that the mixed materials in the entire pipeline cannot be mixed evenly with each other. Moreover, after the synthesis of polycarbonate polyether polyols, the viscosity will increase sharply, and the fluidity of the materials will deteriorate. At this time, explosion points are easily generated in the pipeline, and it is impossible to dissipate heat and disperse the explosion points in a timely and effective manner, which will cause chain explosions and ultimately lead to the inability to synthesize the target product.

[0010] Another problem to be solved in the industrial production of polycarbonate polyether polyols is the scaling up effect. Chinese patent CN111484610A defines the scaling up effect, which refers to the research results obtained by using small equipment to conduct chemical process (i.e. small-scale) experiments (e.g. laboratory scale). Under the same operating conditions, the results obtained from large-scale production equipment (e.g. industrial scale) are often very different. The impact of these differences is called the scaling up effect. Since the viscosity of the materials increases during the synthesis of polycarbonate polyether polyols, the heat generated by the reaction is difficult to release. The heat generated increases the temperature, the reaction rate is accelerated, and more heat is generated. The scaling up effect is inevitable.

[0011] Therefore, in the technical field of polycarbonate polyether polyol preparation, there is no tube reactor 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 has no amplification effect. Summary of the invention

[0012] In view of the deficiencies in the prior art, the present invention discloses a tubular reactor specially used for synthesizing polycarbonate polyether polyols. The invention adopts 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 to achieve a high degree of matching and overall synergy between the internal structure of the tubular reactor and material circulation and reaction heat control. The tubular reactor is particularly suitable for large-scale industrial production of polycarbonate polyether polyols.

[0013] The technical solution of the present invention is as follows: A tubular reactor for synthesizing polycarbonate polyether polyols, comprising a reaction pipeline, and also comprising: 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, 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 compound mixed heat transfer unit, and the material temperature is lowered and then returned to the solid-liquid mixing unit, and the circulation speed of the material is adjusted by the circulation control unit, and the temperature control unit and the pressure control unit are adjusted at the same time, so that the material temperature at the upper part of the reaction pipe is maintained 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 length-to-diameter ratio L:d of the reaction pipe is less than 50; 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.

[0014] The reaction is carried out in a reaction pipeline, during which the epoxy compound and the chain transfer agent are continuously consumed, and the reaction continues under the action of the DMC catalyst to generate polycarbonate polyether polyol, thereby increasing the overall viscosity and density of the material.

[0015] The carbon dioxide-epoxide compound mixed heat transfer unit comprises a gas-liquid mass transfer and heat transfer zone, and the carbon dioxide absorbs liquid heat through the epoxy compound absorbing carbon dioxide, thereby achieving gas-liquid mass transfer and heat transfer, thereby reducing the material temperature.

[0016] The one-time centralized feeding means that the epoxide compound, the chain transfer agent and the catalyst are fed into the tubular reactor at one time for reaction, and only carbon dioxide is added during the reaction without adding the three raw materials.

[0017] The tubular reactor of the present invention can provide sufficient mixing, mass transfer, heat transfer and precise temperature control conditions for the synthesis of polycarbonate polyether polyols, without the need to use a catalyst with a special structure, and the catalyst does not need to be preactivated. The catalyst induction activation period and the segment growth period can be carried out in the same reaction pipeline, realizing a one-time centralized feeding process for preparing polycarbonate polyether polyols, synthesizing high-quality polycarbonate polyether polyols, without amplification effect, and suitable for industrial large-scale production. The technical solution of the present invention adopts a reaction pipeline with a small aspect ratio (the aspect ratio of the reaction pipeline L:d<50), and is equipped 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 units and the reaction pipeline work together to achieve material mixing and heat and mass transfer, and achieve precise temperature control at a specific position of the reaction pipeline, so as to achieve effective heat dissipation of the material and prevent implosion.

[0018] In one embodiment, the temperature control unit includes a temperature sensor indicating the temperature of materials in three different areas of the reaction pipe: the upper, middle and lower parts; a jacket for heating or cooling the reaction pipe; and a heat transfer medium filled between the jacket and the reaction pipe.

[0019] 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 supplementing 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 supplementing carbon dioxide gas are increased until the temperature difference does not exceed the temperature difference threshold.

[0020] In one embodiment, a density sensor indicating the density of the material is disposed at the outlet of the reaction pipeline, and the reaction process is controlled according to the rate of change of the material density.

[0021] In one embodiment, the process of controlling the entire reaction progress 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.

[0022] 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, 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 pipe.

[0023] In one embodiment, the carbon dioxide-epoxide mixed heat transfer unit includes a gas distributor, which 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. 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.

[0024] In one embodiment, the solid-liquid mixing unit comprises a mixer. Preferably, the mixer is a static mixer.

[0025] In one embodiment, the inner diameter of the reaction pipe is 100 to 1500 mm.

[0026] In one embodiment, the aspect ratio of the reaction pipe satisfies 10≤L﹕d≤40.

[0027] In one embodiment, the number of the reaction pipes is 2 to 8.

[0028] 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.

[0029] In one embodiment, the reaction pipes are independent of each other and are closed and isolated by valves.

[0030] In one embodiment, the material circulation paths formed between each reaction pipe and the circulation unit are the same.

[0031] In one embodiment, the circulation speed of the circulation unit is 10-20 min / cycle.

[0032] Compared with the prior art, the tubular reactor provided by the present invention adopts a reaction pipe with a small aspect ratio, and designs 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. The carbon dioxide-epoxide compound mixed 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 as a whole to provide sufficient mixing, mass transfer, heat transfer, and precise temperature control conditions for the synthesis of polycarbonate polyether polyols, and has the following beneficial effects: (1) The reaction process is coordinated and controlled according to the temperature, pressure and material density in the reaction pipeline. The circulation flow of materials is used to achieve efficient material mixing, effective mass and heat transfer and precise temperature control to synthesize high-quality polycarbonate polyether polyols.

[0033] (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.

[0034] (3) There is no amplification effect, which is conducive to the large-scale industrial production of polycarbonate polyether polyols. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. 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 creative labor.

[0036] Figure 1 Schematic side view of a tube-in-tube reactor according to an embodiment of the present invention.

[0037] Figure 2 Schematic diagram of a top view of a tube reactor according to an embodiment of the present invention.

[0038] Figure 3It is a comparison diagram of the density change curves of the polycarbonate polyether polyols of Example 1 and Comparative Examples 1-7.

[0039] Explanation of the accompanying drawings: 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 pipeline, 10-density sensor, 11-circulation device, 12-connecting pipeline, 13-heat transfer medium. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention clearer, the embodiments of the present invention will be described in more detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments of the present invention, and 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 the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "vertical", "parallel", "inner", "outer", "front", "back" and the like is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0041] Figure 1 Schematic side view of a tube-in-tube reactor according to an embodiment of the present invention. Figure 2 Schematic diagram of a top view of a tube reactor according to an embodiment of the present invention. Figure 1 and Figure 2 As shown, the tubular reactor of the embodiment of the present invention comprises: a reaction pipe 9; a carbon dioxide-epoxide compound mixing heat transfer unit, comprising a gas distributor 6 arranged at the upper part of the reaction pipe; a solid-liquid mixing unit, comprising a mixer 8 arranged in the reaction pipe and located below the gas distributor 6; a temperature control unit, comprising 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, a third temperature sensor 4 arranged at the lower part of the reaction pipe, a jacket 7 coated on the outside of the reaction pipe, and a heat transfer medium 13 filled between the reaction pipe and the jacket; a circulation control unit, comprising 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, comprising a gas replenishing port 1 at the inlet of the upper end of the reaction pipe; a plurality of reaction pipes are connected in parallel, and the reaction raw materials are respectively transported to the plurality of reaction pipes through the liquid distributor 5 and the connecting pipe 12.

[0042] In order to ensure sufficient mixing of the raw materials and prevent uneven reactions from causing excessively wide molecular weight distribution or implosion, 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 to the raw material mixing device from the storage tank, and then 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.

[0043] The premixed raw materials are pumped through 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, and 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 10-20 minutes to complete a cycle. 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 to control the material temperature in the reaction pipe at 70-90°C. During the reaction, the material flows from top to bottom in the reaction pipe, first flows through the carbon dioxide-epoxide mixed heat transfer unit, then flows through the solid-liquid mixing unit, and then flows 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, reaching 1.12g / cm 3 The 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 after the reaction increases, and the flow rate in the solid-liquid mixing unit decreases, while the unreacted material will flow downward first, 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 shown in FIG. Figure 1As 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 progress. The faster the reaction progress, 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 internal temperature of the reaction pipe, and at the same time, the circulation speed is increased until the internal temperature of 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 per minute is greater than 0.06g / cm 3 When it is too fast, 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 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 tube reactor is as follows: Figure 2 As shown, but not limited to this arrangement.

[0044] 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, 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 pipe.

[0045] 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.

[0046] In one embodiment, the inner diameter of the reaction pipe is 100 to 1500 mm. In the process of industrial production of polycarbonate polyether polyols, 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, which not only leads to a carbonate chain segment ratio (as defined in Example 1) that is too small, but also has a higher probability of causing explosion due to lack of carbon dioxide participation. When 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 pipeline is too large, resulting in a wide molecular weight distribution of the product, affecting the performance of the product.

[0047] In one embodiment, the ratio of the length L to the diameter d of the reaction pipe 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, the reaction conversion rate per unit time will be greatly reduced, and a longer reaction time is required. The 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 cycle through the gas-liquid heat transfer zone within the specified time to complete the heat release and gas-liquid mass transfer, that is, the length of the pipe cannot be too long. The synthetic polyester polyether polyol reaction pipe should have a special aspect 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.

[0048] In one embodiment, the number of the reaction pipes is 2 to 8.

[0049] 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.

[0050] 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 each reaction pipe and the circulation control unit are the same.

[0051] In one embodiment, the circulation speed of the circulation unit is 10-20 min / cycle.

[0052] The product after the reaction contains polycarbonate polyol, polyether polyol, cyclic carbonate and unreacted raw material epoxide. Next, the liquid product is passed through a catalyst filter to filter and recover the catalyst, and the filtrate flows into a distillation device, which is a falling film tower and a scraper evaporator. The filtrate first passes through the falling film tower to distill the epoxide into a buffer tank for recovery and application, and then flows into a scraper evaporator or a distillation tower to separate the main product polycarbonate polyether polyol and the by-product cyclic carbonate. The separation rate of polyol and cyclic carbonate is 98%. After the two are completely separated, they are canned separately for standby use.

[0053] The tubular reactor of the present invention will be further described below in conjunction with specific embodiments.

[0054] Embodiment 1: 8L propylene oxide, 4g DMC catalyst, and chain transfer agent with a feed ratio (molar ratio of epoxide and chain transfer agent) of 55:1 were added to the premixing kettle respectively, and 0.4Mpa of carbon dioxide was introduced and mixed and stirred at a temperature of 40°C. After stirring for 1h, the mixture was pressed into an 8L×2 reactor array, and the diameter of a single reaction pipe was 100mm and the length of the reaction pipe was 1000mm. After all the mixture was pressed in, carbon dioxide was introduced into the reaction pipe to 3Mpa and the pressure was maintained. The circulation device was turned on, and the flow rate was controlled at 600g / min. The temperature sensor 2 was used as the material reaction temperature. After the material was controlled to react at a temperature of 80°C for 3h, the density was uniformly increased to 1.12g / cm3 and stabilized. At this time, the reaction was completed, and the temperature was lowered to take out the product. After removing the catalyst through the catalyst filtration device, a scraper evaporator was used to separate the main and by-products.

[0055] The DMC catalyst described in this embodiment is a zinc-cobalt double metal cyanide complex catalyst obtained by reacting water-soluble metal salts of zinc and cobalt in a water-soluble solvent; the specific preparation is as follows: weigh a certain mass of cobalt salt and zinc salt, specifically, sodium thiocyanate cobaltate and zinc bromide, the molar ratio is 1:4, dissolve in an aqueous solvent and continue to stir, the aqueous solvent includes water and tert-butyl alcohol, and the total mass of the metal salt (i.e., cobalt salt and zinc salt) and the mass ratio of the aqueous solvent is 1:5. Add inorganic acid and organic acid, the inorganic acid is dilute hydrochloric acid, the pH value is 2, the organic acid is glutaric acid, the molar ratio of inorganic acid to organic acid is 5:1, the total mole number of metal salts and the mole number of acid are 4:1, stir at a temperature of 10-100°C for several hours, and continue to generate precipitation. The above turbid liquid 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 a temperature of 100°C, washed for 3 minutes, stirred for several hours, and then filtered and dried to obtain a filter cake. The slurrying, washing, and drying steps are repeated for multiple times at a temperature of 10-100°C until the pH value of the liquid in the system is 6-7, specifically, at a temperature of 60°C, for 6 minutes each time. The solid product is further dried under vacuum conditions at 80-100°C to obtain the final catalyst, which is processed into powder particles by mechanical grinding under anhydrous drying conditions before use.

[0056] 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.

[0057] 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).

[0058] In order to meet the downstream polyurethane synthesis application, the synthesized polycarbonate polyether polyol needs to meet certain quality requirements. The quality is mainly evaluated from two aspects: molecular weight distribution and ester content. The molecular weight distribution is expressed by the polymer molecular weight polydispersity index (PDI), and the ester content is expressed by the carbonate chain segment ratio. The narrower the molecular weight distribution, the smaller the PDI, the fewer small molecules, and the less impact on the reaction rate in the downstream synthesis of polyurethane; the higher the lipid content, the higher the carbonate chain segment ratio, the better the effect of fixing carbon dioxide, but it cannot be too high, otherwise it will affect the requirements for soft and hard segments in polyurethane synthesis. The quality grade of polycarbonate polyether polyols is divided by the evaluation indicators PDI and carbonate connection ratio. Those with PDI below 2 and carbonate chain segment ratio of 50-65% are qualified products, and those with PDI below 1.5 and carbonate chain segment ratio of 55-60% are superior products.

[0059] The purified product is sampled and analyzed. Specifically, the polymerization reaction products (polycarbonate-polyether polyols and cyclic propylene carbonate and unreacted epoxide) are sampled and collected in a container, and the polymerization reaction product logistics samples are characterized by nuclear magnetic resonance spectroscopy to calculate the ratio of polymer to cyclic small molecules in the crude product. After the polymer is purified, nuclear magnetic resonance spectroscopy is performed again 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%.

[0060] 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 HNMR spectrum and its related proton peaks, the ratio of carbonate chains in the copolymerization reaction (molar ratio) (FCO2 ) and the mass fraction of cyclic carbonate content (W PC ), the amount of carbon dioxide embedded (M CO2 ) is calculated as follows: 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%; Among them, coefficient 44 is the molar mass of carbon dioxide, coefficient 58 is the molar mass of PO, and coefficient 102 is the sum of the molar mass of carbon dioxide (molar mass 44 g / mol) and the molar mass of PO (molar mass 58 g / mol).

[0061] The product conversion rate is calculated as follows: 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.

[0062] The polymer number average molecular weight (Mn) and polymer molecular weight polydispersity index (PDI) were determined by gel permeation chromatography (GPC).

[0063] The data are shown in Table 1:

[0064] From the data of Example 1, it can be known that the tubular reactor of the present invention can fully react the raw materials at 80°C, and the prepared polycarbonate polyether polyol has a narrower molecular weight distribution and a PDI of 1.13; the carbonate segment ratio is better, within 55%-60%, that is, the carbon dioxide fixation rate is high while meeting the application requirements; and the reaction time is very short, and it only takes 3 hours to reach a given conversion rate. After a one-time centralized feeding, the tubular reactor can synthesize high-quality polycarbonate polyether polyols with a conversion rate higher than 95%, a PDI lower than 1.5, that is, a narrow molecular weight distribution, and a carbonate segment ratio between 55-60%.

[0065] 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.

[0066] 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.

[0067] The conditions of Example 4 are the same as those of Example 1, the only difference being that device 3 is used and the inner diameter of the pipe is 1500 mm.

[0068] The conditions of Example 5 are the same as those of Example 1, the only difference being that device 4 is used, there are 4 reaction pipes, and the amount of propylene oxide added is 16 L.

[0069] The conditions of Example 6 are the same as those of Example 1, the only difference being that device 5 is used, there are 8 reaction pipes, and the amount of propylene oxide added is 32 L.

[0070] 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.

[0071] 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.

[0072] The conditions of Example 9 are the same as those of Example 1, the only difference being that the reaction temperature is 70°C.

[0073] The conditions of Example 10 are the same as those of Example 1, the only difference being that the reaction temperature is 90°C.

[0074] 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.

[0075] 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.

[0076] The reaction devices and reaction conditions involved in each embodiment are shown in Table A and Table B, wherein 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.

[0077]

[0078]

[0079] The products obtained in Examples 2-12 were tested according to the method in Example 1. The test results are shown in Table C below.

[0080]

[0081] The reaction results of each embodiment are shown in Table C. In Embodiment 1 and Embodiment 3-12, the gas-liquid ratio is 1:1, that is, the volume of the gas-liquid mass transfer and heat transfer zone accounts for 50% of the volume of the reaction pipeline. Embodiment 2 is to reduce the volume proportion of CO2, that is, to reduce the volume proportion of the gas-liquid mass transfer and heat transfer zone 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 pipeline. Compared with Embodiment 1, Embodiments 3 and 4 increase the diameter of the reaction pipeline, Embodiments 5 and 6 increase the number of reaction pipelines, and Embodiments 7 and 8 use a reaction pipeline with a larger aspect ratio. Embodiments 3-8 are all industrialized to the tubular reactor. From the perspective of the reaction process and product results, the molecular weight, molecular weight distribution, and conversion rate of the polymer have no obvious fluctuations, the molecular weight difference index is small, and the molecular weight distribution is narrow, and a product of comparable quality is 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 pipelines, and the circulation pump flow rate needs to be opened accordingly, and no process adjustment is required, which 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 expanding. 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 while maintaining a circulation speed of 10-20min / cycle.

[0082] The conditions of Comparative Example 1 and Example 1 are the same, the only difference is that the amount of propylene oxide added is 13.3 L, that is, the gas-liquid volume ratio is 1:5.

[0083] The conditions of Comparative Example 2 and Example 1 are the same, the only difference being that the initial flow rate is 5 min / cycle.

[0084] The conditions of Comparative Example 3 and Example 1 are the same, the only difference being that the initial flow rate is 25 min / cycle.

[0085] The conditions of Comparative Example 4 are the same as those of Example 1, the only difference being that device 8 is used and the diameter of the reaction pipe is 50 mm.

[0086] 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.

[0087] The conditions of Comparative Example 6 are the same as those of Example 1, 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.

[0088] The conditions of Comparative Example 7 are the same as those of Example 1, the only difference being that the temperature difference between Temperature 2 and Temperature 3 during the reaction is greater than 5°C.

[0089] The reaction apparatus and reaction conditions involved in each comparative example are shown in Table D and Table E.

[0090]

[0091]

[0092] 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 below.

[0093]

[0094] Figure 3The density change curve comparison diagram 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 to effectively transfer mass and heat of the material, 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 material temperature in the pipeline is maintained in a lower range, the reaction rate is lowered, resulting in a longer reaction time, thereby causing the molecular weight distribution to become wider; similarly, when the flow rate in Comparative Example 3 is slowed down, the material temperature in the pipeline will be maintained in a higher range, the reaction rate will be faster, the CO2 participation degree will be lower, the ester content will be reduced, and it is easy to cause explosion; Comparative Example 3 In Example 4, the diameter of the reaction pipe is 50 mm, which is less than 100 mm, resulting in low polyol ester content, wide molecular weight distribution, and reduced conversion rate; in Comparative Example 5, the aspect ratio of the reaction pipe 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, the temperature at the lower part of the reaction pipe is 8°C higher than the temperature in the middle part of the reaction pipe, the reaction occurs implosion, the temperature rises sharply, and the temperature in the middle part of the reaction pipe reaches 95°C, so high-quality polycarbonate polyether polyols with a PDI below 2 cannot be synthesized. It can be seen from the density growth curve that when synthesizing polycarbonate polyether polyols in Comparative Examples 1-7, the density increases too fast, which will cause a large change in the internal temperature, which will also lead to poor effects of the synthesized polyols. The density increases too slowly, which will prolong the reaction time and cause the molecular weight distribution to become wider. Among them, the density change of Comparative Example 6 is the same as that of Example 1 because the reaction conditions of the two are the same, but the number of reaction pipes is 10. Too many reaction pipes will cause the molecular weight gap between each pipe to widen and the molecular weight distribution to become wider. Therefore, the preferred number of reaction pipes provided by the present invention is 2 to 8.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution 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 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 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.

6. The tubular reactor according to claim 1, characterized in that: The carbon dioxide-epoxide mixed heat transfer unit comprises a gas distributor, which is located at a position of 10 to 50 mm near the top of the reaction pipe and is a porous structure.

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

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

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

10. The tube-in-tube reactor according to claim 9, 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.

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

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

13. 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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