System and method for producing oligomer for polymerization through ester exchange

Abstract

The invention provides a system and method for producing oligomer for polymerization through ester exchange, and the system comprises a reboiler, a first ester exchange reactor, a first condenser, a heater, a second ester exchange reactor, a rectifying tower, a second condenser and a vacuum unit; the first ester exchange reactor is provided with a rectification separation area and a reaction area from top to bottom, and the second ester exchange reactor is provided with a multi-stage serial disc type reaction area and a falling film reaction area from top to bottom; an outlet of the reboiler is communicated with a vapor phase inlet of the reaction zone; a liquid phase discharge hole of the reaction area is communicated with an inlet of a first-stage reaction disc in the multi-stage serial disc type reaction area through a heater, and a vapor phase of a last-stage reaction disc in the multi-stage serial disc type reaction area is connected with an inlet of a rectifying tower through a pipeline; and the liquid phase of the last stage of reaction disc is communicated with the liquid phase outlet of the rectifying tower and the falling film reaction area through a pipeline. The system and the method are efficient and energy-saving, and the oligomer obtained by the system and the method is narrow in molecular weight distribution and good in chromaticity.

Description

Technical Field

[0001] The invention relates to a system and method for producing oligomers for polymerization through ester exchange, belonging to the technical field of fine chemicals. Background Art

[0002] High molecular polymer is an important synthetic material, and its molecular weight ranges from thousands to hundreds of thousands or even millions. Condensation polymerization is one of the important methods for synthesizing high molecular polymers. Condensation polymerization refers to the reaction in which one or more monomers condense with each other to form a high polymer, while other low molecular compounds (such as water, ammonia, alcohol, hydrogen halide or phenol, etc.) are precipitated. The initial stage of the reaction is generally called transesterification reaction or esterification reaction. For example, in the case of polyethylene terephthalate (PET), the esterification process produces small molecule water; in the case of polybutylene succinate (PBS), the transesterification process produces small molecule water and tetrahydrofuran, etc. At present, the field generally adopts multi-stage series vertical stirred tanks as transesterification (or esterification) reaction systems, etc. The main invention points are the type of stirring paddle, the type of coil (such as horizontal type, vertical type, etc.), and the location of the coil (such as inside the kettle, outside the kettle, etc.).

[0003] For the sake of clarity, the production of polycarbonate (PC) by the non-phosgene melt transesterification method is taken as an example.

[0004] The non-phosgene melt transesterification method uses bisphenol A (BPA) and diphenyl carbonate (DPC) as raw materials to produce polycarbonate through a series of reactions, including transesterification, pre-polycondensation, and final polycondensation. The by-product phenol can be recycled to the DPC unit and used as a raw material. The entire production process does not use phosgene, making it a green, safe, and clean process. It has gradually become the main method for PC production.

[0005] The transesterification reaction process involved in the production of PC by the non-phosgene melt transesterification method is as follows:

[0006]

[0007] The transesterification reaction involved in the production of polycarbonate by the non-phosgene melt transesterification method has the following main characteristics:

[0008] First, the transesterification reaction is the addition reaction process of BPA and DPC, and the actual reaction process is also accompanied by a small amount of polycondensation reaction. As the reaction proceeds, the molecular weight of the reactants gradually increases, and the viscosity also gradually increases. If the reaction process is uneven, it will lead to a broadening of the molecular weight distribution of the oligomers and uneven quality of the reactants.

[0009] Second, the transesterification reaction is a reversible thermodynamic equilibrium reaction process. The reaction produces phenol (i.e., a small molecule) as a by-product. For every 1 mol of reaction, 1 mol of phenol is produced. The amount of reaction by-products is large. If phenol is not removed from the reaction in a timely manner, it will affect the reaction's forward direction. To remove small molecules from the reaction system, it is often necessary to reduce the pressure, which will lead to an increase in the gas volume flow rate and a higher flow rate, inevitably entraining DPC and oligomers with relatively low boiling points. At the same time, the higher the vacuum, the higher the possibility of equipment leakage. For example, if air (oxygen, etc.) enters the reaction system, it will affect the color of the final product.

[0010] Third: BPA has low reactivity. In order to increase the BPA conversion rate, the actual reaction molar ratio (DPC:BPA) will be higher than the theoretical molar ratio, and the transesterification reaction temperature will also be higher. However, the raw materials and products are heat-sensitive to a certain extent, which will lead to the thermal decomposition of the materials and accelerate side reactions such as cross-linking and branching.

[0011] Fourth: BPA, DPC and phenol have high freezing points, and the corresponding equipment and pipelines require heating and insulation, which results in high investment costs. In addition, phenol is highly corrosive, requiring the use of high-temperature and acid-resistant materials. If the system contains water and continues to accumulate, the corrosiveness of the material will increase, further increasing material costs.

[0012] At present, the existing non-phosgene melt transesterification reaction system for producing polycarbonate basically adopts a multi-stage series fully mixed kettle process to obtain oligomers with a narrow molecular weight distribution. The main equipment basically adopts a vertical reactor, such as CN101448872A using three vertical reactors connected in series, CN102153739A using more than two vertical reactors connected in series, CN108948341A using two high-pressure vertical reactors connected in series, and CN104411738A using at least one vertical reactor.

[0013] This type of technology has at least the following problems:

[0014] 1) The reaction is carried out under high vacuum, and the by-product vapor-phase phenol has a large flow rate and high flow velocity, which can carry DPC out of the reaction system, resulting in an imbalance in the reaction molar ratio, affecting the transesterification reaction rate and reducing the product yield. To ensure the reaction molar ratio, additional DPC is added during production to adjust it. Due to the special physical properties of DPC, this not only increases costs but also increases the risk of pipeline blockage.

[0015] 2) The transesterification process is accompanied by a small amount of polycondensation reaction. In a continuous production device, in order to achieve a good molecular weight distribution effect, multiple reactors are often required to be connected in series. The more reactors connected in series, the narrower the molecular weight distribution of the reactants and the more uniform the oligomer quality, but the corresponding investment cost is also higher;

[0016] 3) The reaction temperature is increased by inputting heat energy by arranging a coil in the reactor, and a large amount of heat energy needs to be input through the coil to vaporize phenol to remove the reaction by-product phenol, thereby promoting the reaction. Due to the low heat transfer coefficient of the coil, the coil area is large, and the coil will take up a large space in the reactor, which reduces the volume utilization of the reactor and further increases the investment cost;

[0017] 4) When using a traditional stirred tank reactor to prepare polycarbonate oligomers, a high stirring intensity is required to achieve uniform mixing of the materials in the reactor, resulting in high power consumption;

[0018] 5) In order to achieve low oxygen or oxygen-free reaction system, the agitator shaft seal needs to use a mechanical seal with better performance, that is, a mechanical seal, and be equipped with a flushing and cooling system to ensure continuous and stable operation of the mechanical seal. However, lowering the temperature will increase the risk of solidification of the reaction materials and damage the mechanical seal, which will lead to higher investment and maintenance costs.

[0019] Therefore, providing a new system and method for producing oligomers for polymerization by ester exchange has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0020] To address the above shortcomings and deficiencies, the present invention provides a system and method for producing oligomers for polymerization by transesterification. The system and method provided by the present invention are highly efficient and energy-efficient, and the oligomers obtained by the system and method have a narrow molecular weight distribution and good color.

[0021] To achieve the above objectives, in one aspect, the present invention provides a system for producing oligomers for polymerization by transesterification, wherein the system comprises a reboiler, a first transesterification reactor, a first condenser, a heater, a second transesterification reactor, a distillation column, a second condenser, and a vacuum unit; the first transesterification reactor is provided with a distillation separation zone and a reaction zone (or reaction section) from top to bottom, and the second transesterification reactor is provided with a multi-stage series-connected disc reaction zone and a falling film reaction zone from top to bottom;

[0022] The liquid phase discharge port of the reaction zone is connected to the inlet of the reboiler through a pipeline, and the outlet of the reboiler is connected to the vapor phase inlet of the reaction zone through a pipeline; the vapor phase outlet of the distillation and separation zone is connected to the inlet of the first condenser through a pipeline, and the non-condensable gas outlet and condensate outlet of the first condenser are connected to the reflux port of the vacuum unit and the distillation and separation zone through pipelines respectively;

[0023] The liquid phase discharge port of the reaction zone is also connected to the inlet of the first-stage reaction disk in the multi-stage series disk reaction zone through a pipeline via a heater. The vapor phase of the last-stage reaction disk in the multi-stage series disk reaction zone is connected to the inlet of the distillation tower by a pipeline. The liquid phase of the last-stage reaction disk and the liquid phase outlet of the distillation tower are connected to the falling film reaction zone through a pipeline; the vapor phase outlet of the distillation tower is connected to the inlet of the second condenser through a pipeline, and the non-condensable gas outlet and condensate outlet of the second condenser are respectively connected to the reflux port of the vacuum unit and the distillation tower through pipelines.

[0024] As a specific embodiment of the above-mentioned system of the present invention, the system also includes a third condenser and a circulating liquid cooler, the vapor phase extraction outlet of the falling film reaction zone is connected to the inlet of the third condenser through a pipeline, and the non-condensable gas outlet of the third condenser is connected to the vacuum unit through a pipeline; the condensate outlet of the third condenser is connected to the circulating liquid inlet of the third condenser through a pipeline via the circulating liquid cooler.

[0025] When the present invention uses diphenyl carbonate and bisphenol A as raw materials to produce polycarbonate, as a specific embodiment of the above system of the present invention, the condensate outlet of the third condenser is further connected to the diphenyl carbonate device through a pipeline, so that part of the condensate of the third condenser is used as a raw material for producing diphenyl carbonate;

[0026] And / or the condensate outlet of the second condenser is also connected to the diphenyl carbonate device through a pipeline, so that part of the condensate of the second condenser is used as a raw material for producing diphenyl carbonate.

[0027] As a specific embodiment of the above system of the present invention, the system further includes an aqueous waste liquid storage tank, and the condensate outlet of the first condenser is further connected to the aqueous waste liquid storage tank through a pipeline.

[0028] As a specific embodiment of the above system of the present invention, the internals of the distillation separation zone include plate-type internals or fillers, preferably high-efficiency anti-clogging fillers.

[0029] When the present invention uses diphenyl carbonate and bisphenol A as raw materials to produce polycarbonate, as a specific embodiment of the above-mentioned system of the present invention, the upper and middle extraction port of the distillation separation zone is connected to the diphenyl carbonate device through a pipeline, so that the extracted small molecular compound by-product, namely phenol, can be used as a raw material for producing diphenyl carbonate.

[0030] As a specific embodiment of the above system of the present invention, the liquid phase pipeline of the last stage reaction disk and the liquid phase outlet of the distillation tower are combined outside the second transesterification reactor through a pipeline and then connected to the falling film reaction zone.

[0031] In the system described above, the first transesterification reactor adopts the concept of reactive distillation, and is provided with functional zones such as a distillation separation zone and a reaction zone from top to bottom. The lower reactor and reboiler circulation system, namely the reaction zone and reboiler, serve as the main reaction zone. The reaction zone has a good vapor-liquid reaction interface and high circulation flow intensity, thus replacing mechanical stirring. The upper portion serves as the distillation separation zone. The distillation separation zone and the reaction zone are directly connected, and low-boiling point reactants and oligomers obtained by the reaction can be directly refluxed, thereby achieving reaction molar ratio fidelity and high yield. The organic combination of the two zones ensures that small molecule compound byproducts produced by the reaction, such as phenol produced when producing polycarbonate using DPC and BPA as raw materials, are promptly removed from the reaction system, thereby driving the reaction in the positive direction.

[0032] As a specific embodiment of the system described above, in the multi-stage series-connected disc reaction zone, the number of stages of the series-connected reaction discs is 2-6, preferably 2-4. In some embodiments of the present invention, the number of stages of the series-connected reaction discs can be, for example, 2, 3, 4, 5, or 6.

[0033] As a specific embodiment of the above-mentioned system of the present invention, in the falling film reaction zone, the number of stages of the falling film reactor is 1-4, preferably 2-3.

[0034] In the above-described system of the present invention, the reboiler can be a forced circulation reboiler, preferably a thermosyphon circulation reboiler. The reboiler can be a shell-and-tube type, preferably a spiral tube type, a high-throughput tube type, or the like. In some embodiments of the present invention, the reboiler circulation rate or reboil ratio is theoretically calculated to meet the heat demand and to calculate the flow and mixing requirements of the reaction liquid phase.

[0035] In the above-mentioned system of the present invention, the non-condensable gas outlet of the first condenser is connected to the vacuum unit through a pipeline, so as to generate the vacuum required for the reaction in the first transesterification reactor.

[0036] In the system described above, the vacuum unit can be an independent system, that is, a separate vacuum unit is designed for each of the first condenser, the second condenser, and the third condenser, or only one vacuum unit can be used. The vacuum unit is preferably a liquid ring pump, a mechanical vacuum pump (such as a Roots pump, a screw pump), or a combination thereof.

[0037] The equipment and pipelines used in the above-mentioned system of the present invention are all insulated by jacketed pipes, half-pipe heating, etc.

[0038] On the other hand, the present invention also provides a method for producing oligomers for polymerization by transesterification, wherein the method is implemented using the above-mentioned system for producing oligomers for polymerization by transesterification, and comprises the following steps:

[0039] Step (1): a mixture of diol or dihydric phenol, carbonic acid diester or dibasic acid and catalyst is passed through a reboiler into the reaction zone of a first transesterification reactor, and the first transesterification reaction is completed under high temperature and vacuum conditions;

[0040] Step (2): the vapor phase obtained after the first transesterification reaction enters the distillation separation zone of the first transesterification reactor for distillation separation, the liquid phase separated in the distillation separation zone returns to the reaction zone of the first transesterification reactor to continue to participate in the reaction, the vapor phase separated in the distillation separation zone enters the first condenser for condensation to obtain a first condensate and a first non-condensable gas, the first condensate is refluxed back to the distillation separation zone, and the first non-condensable gas is allowed to enter the vacuum unit;

[0041] Step (3): the liquid phase obtained after the first transesterification reaction is preheated by a heater and then sent to the multi-stage series disc reaction zone of the second transesterification reactor for reaction. After the reaction is completed, the vapor phase obtained from the last stage reaction disc enters the distillation tower for distillation separation, and the separated vapor phase enters the second condenser for condensation to obtain a second condensate and a second non-condensable gas, and the second condensate is refluxed back to the distillation tower and the second non-condensable gas enters the vacuum unit; the liquid phase obtained from the last stage reaction disc and the liquid phase separated from the distillation tower enter the falling film reaction zone to continue the falling film reaction, and oligomers are obtained after the falling film reaction is completed.

[0042] As a specific embodiment of the above method of the present invention, in step (1), a mixed solution of diol or dihydric phenol, carbonate diester or dibasic acid and catalyst is added from the inlet of the reboiler and / or the bottom liquid phase pipeline of the first transesterification reactor.

[0043] In the above method of the present invention, the carbonic acid diester includes any one or a combination of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, dioctyl carbonate, diphenyl carbonate, etc.; the dibasic acid includes any one or two of terephthalic acid, succinic acid, etc.; the diol includes any one or a combination of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, etc.; the dihydric phenol includes bisphenol A, etc.; the catalyst can be a conventional catalyst used in the art and can be reasonably selected as needed. When carbonic acid diester and dihydric alcohol or dihydric phenol are used as raw materials, the system and method provided by the present invention can be used to produce polycarbonate. When terephthalic acid in the dibasic acid and ethylene glycol in the dihydric alcohol are used as raw materials, the system and method provided by the present invention can be used to produce polyethylene terephthalate (PET). When succinic acid in the dibasic acid and 1,4-butanediol in the diol are used as raw materials, the system and method provided by the present invention can be used to produce polybutylene succinate (PBS).

[0044] As a specific embodiment of the above method of the present invention, in step (1), when the reaction raw materials are diols or dihydric phenols and carbonic acid diesters, such as bisphenol A and diphenyl carbonate, the temperature of the first transesterification reaction is 190-220° C. and the pressure is 30-60 kPaA;

[0045] When the reaction raw materials are diols or dihydric phenols and dibasic acids, such as 1,4-butanediol and succinic acid or ethylene glycol and terephthalic acid, the temperature of the first step of the transesterification reaction is 250-265° C. and the pressure is 60-150 KPaG.

[0046] As a specific embodiment of the above-described method of the present invention, step (2) further includes extracting the small molecule compound by-product from the upper-middle extraction port of the distillation and separation zone and recycling it. For example, when the present invention uses diphenyl carbonate and bisphenol A as raw materials to produce polycarbonate, phenol is extracted from the upper-middle extraction port of the distillation and separation zone and sent to a diphenyl carbonate unit to be used as a raw material for producing diphenyl carbonate.

[0047] As a specific embodiment of the above-described method of the present invention, in step (2), aqueous waste liquid is extracted from the bottom of the first condenser. The main purpose is to separate water introduced into the raw materials and water leaked into the system under vacuum conditions, reduce the corrosiveness of the materials, and ensure that the water content of the separated small molecule compound by-products, such as phenol produced when polycarbonate is produced using DPC and BPA as raw materials, meets the recycling requirements. Qualified small molecule compound by-products, such as phenol produced when polycarbonate is produced using DPC and BPA as raw materials, are extracted from the middle and upper part of the distillation separation zone and sent to the diphenyl carbonate device for use as raw materials for the production of diphenyl carbonate; the liquid phase at the bottom of the distillation separation zone (such as when BPA and DPC are used as raw materials to produce polycarbonate, the liquid phase contains DPC and oligomers) is returned to the reaction zone of the first transesterification reactor, that is, the lower bottom of the tower, to continue participating in the reaction.

[0048] In the above-described method of the present invention, the heat required for vaporizing the reaction carried out in the first transesterification reactor and the small molecular compound by-products, such as phenol generated when producing polycarbonate using DPC and BPA as raw materials, is introduced through the reboiler of the tower.

[0049] When the present invention uses diphenyl carbonate and bisphenol A as raw materials to produce polycarbonate, in step (2) of the above-mentioned method of the present invention, a qualified small molecule compound by-product, i.e., phenol, is extracted from the middle and upper outlet of the distillation and separation zone and sent to the diphenyl carbonate device for use as a raw material for producing diphenyl carbonate. In step (3), part of the second condensate is sent to the diphenyl carbonate device alone or together with the qualified small molecule compound by-product extracted from the middle and upper outlet of the distillation and separation zone for use as a raw material for producing diphenyl carbonate.

[0050] As a specific embodiment of the above-described method of the present invention, in step (3), the preheating is performed to 230-250°C. The preheating is performed in a heater, which is a feed heater, for heating the first transesterification reaction product, thereby reducing the coil area of ​​the multi-stage series disc reaction zone above the second transesterification reactor and reducing the effective volume of the reaction zone. The heater can be a shell-and-tube heat exchanger or a welded plate heat exchanger; when a shell-and-tube heat exchanger is used, a spiral tube type or a high-throughput tube type is preferred.

[0051] In step (3) of the method described above, the reaction product obtained after the first transesterification reaction is pumped into the second transesterification reaction section, where the reaction continues under vacuum at a higher temperature to increase the molecular weight. The second transesterification reactor used in the second transesterification reaction section adopts a gravity-fed multi-stage series reaction concept, including a multi-stage series disc reaction zone and a falling film reaction zone. Both types of reaction zones have high surface reaction rates, thereby replacing mechanical stirring. The multi-stage series disc reaction zone at the top and the falling film reaction zone at the bottom of the second transesterification reactor are relatively independent, and different reaction temperatures, reaction vacuums, etc. can be achieved in their respective zones.

[0052] In step (3) of the method described above, the vapor phase obtained from the last stage reaction disk enters a distillation tower for distillation separation, and the separated vapor phase enters a second condenser for condensation to obtain a second condensate and a second non-condensable gas, and the second non-condensable gas enters a vacuum unit to generate the vacuum required in the multi-stage series disk reaction zone at the top of the second transesterification reactor.

[0053] In step (3) of the above-described method of the present invention, the liquid phase obtained after the first transesterification reaction is preheated by a heater and then fed into the multi-stage series disc reaction zone of the second transesterification reactor for gradient reaction, that is, the vacuum of each stage of the series reaction disc gradually increases from top to bottom, and the vacuum of each stage of the series reaction disc is determined by calculation based on the set reaction conversion rate, etc., and the vacuum gradient is determined by the resistance drop of the vapor phase from the upper stage reaction disc into the lower stage reaction disc; alternatively, the vapor phase pipes at each stage can also be designed to pass through the outside of the second transesterification reactor and then return to the inside of the second transesterification reactor, and automatic valves can be set on the extended pipes to adjust the vacuum degree.

[0054] The temperature of each stage of the series-connected trays increases gradually from top to bottom. The temperature of each stage is determined by the set reaction conversion rate and the amount of small molecule compound byproduct vaporization, and is adjusted by varying the flow rate of the heat transfer medium within the coils. A gradient reaction, where the reaction temperature and pressure of each stage increase as needed from top to bottom, minimizes the residence time of reactants at high temperatures, reduces side reactions, and achieves optimal oligomer color.

[0055] As a specific embodiment of the above method of the present invention, in step (3), when the reaction raw materials are diols or dihydric phenols and carbonic acid diesters, such as bisphenol A and diphenyl carbonate, in the multi-stage series disk reaction zone, the reaction temperature and reaction pressure of the first stage reaction disk are 230-250° C. and 20-30 kPaA, respectively, and from top to bottom, the reaction temperature and reaction pressure of each stage reaction disk increase by 3-6° C. and 2-7 kPaA, respectively;

[0056] When the reaction raw materials are diols or dihydric phenols and dibasic acids, such as 1,4-butanediol and succinic acid or ethylene glycol and terephthalic acid, in the multi-stage series disc reaction zone, the reaction temperature and reaction pressure of the first stage reaction disc are 265-275°C and 5-10 kPaG, respectively. From top to bottom, the reaction temperature and reaction pressure of each stage reaction disc increase by 3-6°C and 2-7 kPaG, respectively.

[0057] As a specific embodiment of the above-described method of the present invention, in step (3), the liquid phase obtained from the last stage reaction disk and the liquid phase separated from the distillation tower are mixed outside the second transesterification reactor and then enter the falling film reaction zone to continue the falling film reaction.

[0058] In step (3) of the method described above, the liquid phase obtained from the last stage reaction tray and the liquid phase separated from the distillation column are mixed to obtain a mixed liquid, which is then distributed by a liquid distributor provided above the falling film reaction zone and then enters the falling film reactor in the falling film reaction zone to continue the falling film reaction. After the falling film reaction is completed, oligomers are obtained. The falling film reactor used in the present invention can have a structure such as a tubular falling film or an umbrella-cap falling film. The falling film reactor completes the reaction at a higher reaction temperature and under a reaction vacuum to achieve a predetermined oligomer molecular weight.

[0059] As a specific embodiment of the above method of the present invention, in step (3), when the reaction raw materials are diols or dihydric phenols and carbonic acid diesters, such as bisphenol A and diphenyl carbonate, the reaction temperature of the falling film reaction is 255-285° C., and the reaction pressure is 2-10 kPaA;

[0060] When the reaction raw materials are diols or dihydric phenols and dibasic acids, such as 1,4-butanediol and succinic acid or ethylene glycol and terephthalic acid, the reaction temperature of the falling film reaction is 270-278° C. and the reaction pressure is 1-5 KPaG.

[0061] As a specific embodiment of the method described above of the present invention, the method further includes: extracting a vapor phase from between the last two falling film reactors in the falling film reaction zone, allowing the extracted vapor phase to enter a third condenser for condensation to obtain a third condensate and a third non-condensable gas, allowing the third non-condensable gas to enter a vacuum unit, and allowing the third condensate to be cooled by a circulating liquid cooler and then circulated back to the third condenser for spray cooling. In step (3), the third non-condensable gas generated by the third condenser enters a vacuum unit to generate the vacuum required for the reaction in the falling film reaction zone at the bottom of the second transesterification reactor. The third condenser is a vapor phase condenser, preferably a dedicated vapor phase treatment device, such as the pretreatment device disclosed in CN110962033A.

[0062] As a specific embodiment of the above-described method of the present invention, the method further includes: recycling a portion of the condensate from the third condenser and / or a portion of the condensate from the second condenser. For example, when the present invention uses diphenyl carbonate and bisphenol A as raw materials to produce polycarbonate, the portion of the condensate from the third condenser and / or the portion of the condensate from the second condenser can be sent to a diphenyl carbonate unit to be used as a raw material for producing diphenyl carbonate.

[0063] Compared with the prior art, the technical solution provided by the present invention can achieve the following beneficial technical effects:

[0064] First: Compared with the existing multi-stage series vertical kettle process, the two-kettle process provided by the present invention has a short process flow, reduces the corresponding automatic valves and connecting pipes, etc., reduces the risk of high-freezing point materials clogging the pipeline, and is conducive to the continuous and stable operation of the device.

[0065] Second: The first transesterification reactor used in the present invention is provided with a distillation separation zone and a reaction zone from top to bottom, which organically couples the reaction and distillation, can replace the agitator, and can promptly remove the small molecule compound by-products from the reaction system, thereby promoting the reaction in the positive direction; the raw materials (such as DPC, etc.), oligomers, etc. entrained in the reaction vapor phase can also be directly returned to the reaction zone, thereby ensuring the reaction molar ratio and reducing material loss; the upper distillation separation zone has a water extraction function, which reduces the corrosiveness of the reactants at high temperatures; the external reboiler serves as the main heat input zone, and has a large heat transfer coefficient, which effectively improves the reaction space utilization rate of the bottom of the first transesterification reactor.

[0066] Third: The second transesterification reactor used in the present invention is provided with a multi-stage series disc reaction zone and a falling film reaction zone from top to bottom, that is, it adopts a disc + membrane multi-stage series reaction coupling, and both types of internal parts have a high surface reaction rate, thereby being able to replace mechanical stirring; the plug flow of the material is realized to the greatest extent, thereby achieving a narrow molecular weight distribution.

[0067] Fourth, the present invention utilizes neither the first nor the second transesterification reactor without an agitator, significantly reducing power consumption and achieving inherent energy efficiency in the production process. The absence of a shaft seal eliminates the risk of oxygen-induced degradation of oligomer color due to air leakage into the reaction system during vacuum reactions. For example, in some embodiments of the present invention, using a 100,000-ton polycarbonate production plant as an example, with an oligomer molecular weight of 2,000-5,000, the system and method provided by the present invention can save 120-150 kW·h / h of agitator power consumption compared to a prior art transesterification process using three to four vertical reactors connected in series, improve the molecular weight distribution of the resulting oligomers by 0.3-0.5, and enhance oligomer color. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] 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 describing the embodiments. Obviously, the drawings described below are 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.

[0069] Figure 1 This is a schematic structural diagram of a system for producing oligomers for polymerization by ester exchange provided in an embodiment of the present invention.

[0070] Description of main figures:

[0071] 4-1, thermosyphon reboiler; 4-2, first transesterification reactor; 4-3, first condenser; 4-4, first reflux pump; 4-5, first discharge pump; 4-6, second discharge pump; 4-7, feed heater;

[0072] 4-9, second transesterification reactor; 4-10, distillation tower; 4-11, third condenser; 4-12, third discharge pump; 4-13, second condenser; 4-14, second reflux pump; 4-15, circulating liquid cooler; 4-16, circulating pump; 4-17, vacuum unit. DETAILED DESCRIPTION

[0073] It should be noted that the term "comprise" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or apparatus.

[0074] In the present invention, terms such as "upper," "lower," "inner," "outer," "center," "left," "right," "top," and "bottom" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe the present invention and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0075] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to indicate a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0076] Furthermore, the terms "disposed" and "connected" should be interpreted broadly. For example, "connected" can mean a fixed connection, a removable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediary, or it can be internal communication between two devices, elements, or components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0077] The "range" disclosed in the present invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4, and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0078] In the present invention, unless otherwise specified, the numerical range "ab" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed in this invention, and "0-5" is merely an abbreviation for these numerical combinations.

[0079] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0080] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0081] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b) and (c), or may comprise steps (a), (c) and (b), or may comprise steps (c), (a) and (b), etc.

[0082] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and Examples. The following embodiments are part of the present invention, rather than all of the embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0083] Example 1

[0084] This embodiment provides a system for producing oligomers for polymerization by transesterification, and its structural diagram is shown in FIG. Figure 1 As shown, from Figure 1 It can be seen that the system includes: a thermosyphon reboiler 4-1, a first transesterification reactor 4-2, a first condenser 4-3, a feed heater 4-7, a second transesterification reactor 4-9, a distillation column 4-10, a second condenser 4-13, a third condenser 4-11, a circulating liquid cooler 4-15 and a vacuum unit 4-17;

[0085] The first transesterification reactor 4-2 is provided with a distillation separation zone and a reaction zone from top to bottom, that is, the bottom of the first transesterification reactor 4-2 is the reaction zone, and the reaction zone adopts a partition structure without a partition, and the second transesterification reactor 4-9 is provided with a multi-stage series disc reaction zone and a falling film reaction zone from top to bottom;

[0086] The liquid phase discharge port of the tower bottom of the reaction zone is connected to the inlet of the thermosyphon reboiler 4-1 through a pipeline, and the outlet of the thermosyphon reboiler 4-1 is connected to the vapor phase inlet of the reaction zone, that is, the vapor phase inlet of the tower bottom, through a pipeline; the top vapor phase outlet of the distillation and separation zone is connected to the inlet of the first condenser 4-3 through a pipeline, the non-condensable gas outlet of the first condenser 4-3 is connected to the vacuum unit 4-17 through a pipeline, and the condensate outlet of the first condenser 4-3 is connected to the reflux port of the distillation and separation zone and the aqueous waste liquid storage tank through a pipeline via a first reflux pump.

[0087] The liquid phase discharge port of the tower bottom of the reaction zone is also connected to the inlet of the first stage reaction disk in the multi-stage series disk reaction zone through a pipeline via a second discharge pump 4-6, a feed heater 4-7 and through the side wall of the second ester exchange reactor 4-9. The vapor phase of the last stage reaction disk in the multi-stage series disk reaction zone is connected to the inlet of the distillation tower 4-10 by a pipeline. The liquid phase of the last stage reaction disk is combined with the liquid phase outlet of the tower bottom of the distillation tower 4-10 through a pipeline outside the second ester exchange reactor 4-9 and then connected to the falling film reaction zone through a liquid distributor provided on the upper part of the falling film reaction zone; the vapor phase outlet of the top of the distillation tower 4-10 is connected to the inlet of the second condenser 4-13 through a pipeline, the non-condensable gas outlet of the second condenser 4-13 is connected to the vacuum unit 4-17 through a pipeline, and the condensate outlet of the second condenser 4-13 is connected to the reflux port of the distillation tower 4-10 through a pipeline via a second reflux pump 4-14;

[0088] The vapor phase extraction outlet of the falling film reaction zone in the second transesterification reactor 4-9 is connected to the inlet of the third condenser 4-11 through a pipeline, and the non-condensable gas outlet of the third condenser 4-11 is connected to the vacuum unit 4-17 through a pipeline; the condensate outlet of the third condenser 4-11 is connected to the circulating liquid inlet of the third condenser 4-11 through a pipeline via a circulating pump 4-16 and a circulating liquid cooler 4-15;

[0089] The bottom of the second ester exchange reactor 4-9 is a conical structure (i.e., a cone), and the bottom outlet of the conical structure is connected to the downstream polycondensation reaction device through a pipeline via the third discharge pump 4-12 to send the produced oligomer to the downstream polycondensation reaction device as a polycondensation reaction raw material.

[0090] Example 2

[0091] This example uses DPC and BPA as raw materials, utilizes the system for producing oligomers for polymerization by transesterification provided in Example 1, produces oligomers for polymerization through a non-phosgene melt transesterification reaction, and uses the oligomers to produce polycarbonate through a polymerization reaction, including the following specific steps:

[0092] Step (1): a mixed solution of bisphenol A, diphenyl carbonate, and an alkali metal catalyst (based on 1 ton of oligomers, the amount of bisphenol A is 0.9 ton, the amount of diphenyl carbonate is 0.88 ton, and the amount of the alkali metal catalyst is 600 ppm) is introduced into the inlet pipeline of a thermosiphon reboiler 4-1, heated to 220° C. in the thermosiphon reboiler 4-1, and the vapor-liquid two-phase flow in the thermosiphon reboiler 4-1 enters the reaction zone of the first transesterification reactor 4-2 through the vapor phase inlet of the reaction zone of the first transesterification reactor 4-2, and the first transesterification reaction is completed under high temperature vacuum conditions;

[0093] The bottom temperature of the first transesterification reactor is 220° C. and the reaction pressure is 60 KPaA.

[0094] Step (2): The vapor phase (containing phenol, DPC, and oligomers, etc.) obtained after the first transesterification reaction enters the distillation separation zone of the first transesterification reactor 4-2 for distillation separation, wherein the distillation separation zone is provided with two sections of packing from top to bottom, the upper first section of packing is used to enrich water, and the lower second section of packing is used to enrich phenol; the first discharge pump 4-5 is used to extract qualified phenol from the liquid collection tray between the two sections of packing in the distillation separation zone, and pump it to the diphenyl carbonate device as a raw material for producing diphenyl carbonate;

[0095] The liquid phase (mainly DPC, oligomers, etc.) separated at the bottom of the distillation separation zone returns to the reaction zone of the first transesterification reactor 4-2, that is, the bottom of the tower continues to participate in the reaction. The vapor phase separated at the top of the distillation separation zone enters the first condenser 4-3 and is cooled to the saturation temperature, preferably 10°C subcooled to obtain the first condensate (the main components are water, phenol, etc.) and the first non-condensable gas. The first non-condensable gas enters the vacuum unit 4-17, and the first reflux pump 4-4 is used to pressurize the first condensate. Most of it is refluxed to the distillation separation zone, and a small part is extracted and stored in the aqueous waste liquid storage tank.

[0096] Step (3): Use the second discharge pump 4-6 to pressurize the liquid phase obtained after the first transesterification reaction, i.e., the reactor reactants, and then send it to the feed heater 4-7 to be preheated to 250°C, and then send the material preheated to 250°C into the multi-stage series disc reaction zone in the second transesterification reactor 4-9 for reaction, wherein the multi-stage series disc reaction zone includes three series reaction discs from top to bottom, the reaction temperature of the first reaction disc is 250°C, and the temperature of each reaction disc increases by ~5°C from top to bottom; the reaction pressure of the first reaction disc is 30KPaA, and the vacuum of each reaction disc increases by ~5KPaA from top to bottom. The reaction disc adopts central feeding, and the liquid and gas on the reaction disc enter the next reaction disc in parallel through their respective vapor phase pipes and liquid phase pipes;

[0097] After the reaction is completed, the vapor phase obtained from the third-stage reaction disk enters the distillation tower 4-10 for distillation separation, wherein the distillation tower 4-10 is provided with a section of filler, which is mainly used to enrich phenol, and the operating pressure is 20KPaA. The top vapor phase after separation in the distillation tower 4-10 enters the second condenser 4-13 for condensation to obtain a second condensate and a second non-condensable gas, and the second non-condensable gas enters the vacuum unit 4-17. After the second condensate is pressurized by the second reflux pump 4-14, a part of it is refluxed to the distillation tower 4-10, and a part is extracted and mixed with the qualified phenol extracted in step (2) and then pumped to the diphenyl carbonate device as a raw material for producing diphenyl carbonate;

[0098] The liquid phase extracted from the third stage reaction disk and the bottom flow of the distillation tower 4-10 (mainly containing DPC, oligomers, etc.) are mixed outside the second transesterification reactor 4-9 (specifically, the liquid phase extracted from the third stage reaction disk enters the mixing device outside the second transesterification reactor 4-9 through an automatic valve, and is mixed with the bottom flow of the distillation tower 4-10 in the mixing device) and then enters the distributor of the falling film reaction zone. After being evenly distributed by the distributor, it enters the falling film reaction zone to continue the falling film reaction. Among them, the material flows downward in the form of a film in the tube, and the surface is continuously renewed during the gravity self-flow process. The heat required for the reaction is provided by the heat transfer medium outside the tube. Provide, strictly control the inlet and outlet temperature difference of the heat transfer medium; wherein, the falling film reaction zone is provided with two stages of falling film reactors from top to bottom, namely, the first stage falling film reactor and the second stage falling film reactor, the reaction temperature is 285°C, and the reaction pressure is 10KPaA; the oligomers that have completed the first stage falling film reaction enter the second stage falling film reactor through the liquid collector and distribution umbrella cap at the bottom of the first stage falling film reactor, and the oligomers that have undergone the second falling film reaction enter the cone of the second transesterification reactor 4-9 to further remove residual small molecules, etc., and the produced oligomers are pressurized by the third discharge pump 4-12 and sent downstream as raw materials for the polycondensation reaction;

[0099] The vapor phase is extracted from the middle of the liquid collector and the distribution umbrella cap, and the vapor phase is made to enter the third condenser 4-11 from the lower part of the third condenser 4-11. The third condenser 4-11 is cooled by circulating liquid spraying, and the cooling capacity is provided by the circulating liquid cooler 4-15. Preferably, the temperature of the refrigerant needs to be considered to prevent the circulating liquid from solidifying at low temperatures. The circulation power is provided by the circulating pump 4-16. A small amount of circulating liquid is extracted and sent to the diphenyl carbonate device.

[0100] Taking a 100,000-ton polycarbonate plant as an example, with an oligomer molecular weight of 2000-5000 as the benchmark, compared with the transesterification process using three vertical reactors connected in series in Example 1 of CN101448872A, the above-mentioned process in Example 2 of the present invention can save 140 kW·h / h of agitator power consumption, improve the molecular weight distribution of the obtained oligomer by 0.35, and improve the oligomer color.

[0101] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of patent protection, should still fall within the scope of this patent. Furthermore, the technical features of this invention may be freely combined with one another, with other technical inventions, and with other technical inventions.

Claims

1. A system for producing oligomers for polymerization by transesterification, characterized in that: The system includes a reboiler, a first transesterification reactor, a first condenser, a heater, a second transesterification reactor, a distillation tower, a second condenser and a vacuum unit; the first transesterification reactor is provided with a distillation separation zone and a reaction zone from top to bottom, and the second transesterification reactor is provided with a multi-stage series disk reaction zone and a falling film reaction zone from top to bottom; The liquid phase discharge port of the reaction zone is connected to the inlet of the reboiler through a pipeline, and the outlet of the reboiler is connected to the vapor phase inlet of the reaction zone through a pipeline; the vapor phase outlet of the distillation and separation zone is connected to the inlet of the first condenser through a pipeline, and the non-condensable gas outlet and condensate outlet of the first condenser are connected to the reflux port of the vacuum unit and the distillation and separation zone through pipelines respectively; The liquid phase discharge port of the reaction zone is also connected to the inlet of the first-stage reaction disk in the multi-stage series disk reaction zone through a pipeline via a heater. The vapor phase of the last-stage reaction disk in the multi-stage series disk reaction zone is connected to the inlet of the distillation tower by a pipeline. The liquid phase of the last-stage reaction disk and the liquid phase outlet of the distillation tower are connected to the falling film reaction zone through a pipeline; the vapor phase outlet of the distillation tower is connected to the inlet of the second condenser through a pipeline, and the non-condensable gas outlet and condensate outlet of the second condenser are respectively connected to the reflux port of the vacuum unit and the distillation tower through pipelines.

2. The system according to claim 1, wherein: The system also includes a third condenser and a circulating liquid cooler. The vapor phase extraction outlet of the falling film reaction zone is connected to the inlet of the third condenser through a pipeline, and the non-condensable gas outlet of the third condenser is connected to the vacuum unit through a pipeline; the condensate outlet of the third condenser is connected to the circulating liquid inlet of the third condenser through a pipeline via the circulating liquid cooler.

3. The system according to claim 1 or 2, characterized in that The system further includes an aqueous waste liquid storage tank, and the condensate outlet of the first condenser is further connected to the aqueous waste liquid storage tank through a pipeline.

4. The system according to claim 1 or 2, characterized in that The internals of the rectification and separation zone include plate internals or packing.

5. The system according to claim 1 or 2, characterized in that The liquid phase of the last stage reaction tray is connected to the liquid phase outlet of the distillation tower through a pipeline outside the second transesterification reactor and then connected to the falling film reaction zone.

6. The system according to claim 1 or 2, characterized in that In the multi-stage series disk reaction zone, the number of stages of the series reaction disks is 2-6, preferably 2-4.

7. The system according to claim 1 or 2, characterized in that In the falling film reaction zone, the number of stages of the falling film reactor is 1-4, preferably 2-3.

8. A method for producing oligomers for polymerization by transesterification, characterized in that: The method is achieved by utilizing the system for producing oligomers for polymerization by transesterification according to any one of claims 1 to 7, and comprises the following steps: Step (1): a mixture of diol or dihydric phenol, carbonic acid diester or dibasic acid and catalyst is passed through a reboiler into the reaction zone of a first transesterification reactor, and the first transesterification reaction is completed under high temperature and vacuum conditions; Step (2): the vapor phase obtained after the first transesterification reaction enters the distillation separation zone of the first transesterification reactor for distillation separation, the liquid phase separated in the distillation separation zone returns to the reaction zone of the first transesterification reactor to continue to participate in the reaction, the vapor phase separated in the distillation separation zone enters the first condenser for condensation to obtain a first condensate and a first non-condensable gas, the first condensate is refluxed back to the distillation separation zone, and the first non-condensable gas is allowed to enter the vacuum unit; Step (3): the liquid phase obtained after the first transesterification reaction is preheated by a heater and then sent to the multi-stage series disc reaction zone of the second transesterification reactor for reaction. After the reaction is completed, the vapor phase obtained from the last stage reaction disc enters the distillation tower for distillation separation, and the separated vapor phase enters the second condenser for condensation to obtain a second condensate and a second non-condensable gas, and the second condensate is refluxed back to the distillation tower and the second non-condensable gas enters the vacuum unit; the liquid phase obtained from the last stage reaction disc and the liquid phase separated from the distillation tower enter the falling film reaction zone to continue the falling film reaction, and oligomers are obtained after the falling film reaction is completed.

9. The method according to claim 8, characterized in that In step (1), when the reaction raw materials are diol or dihydric phenol and carbonic acid diester, the temperature of the first transesterification reaction is 190-220° C. and the pressure is 30-60 KPaA; When the reaction raw materials are diols or dihydric phenols and dibasic acids, the temperature of the first step of the transesterification reaction is 250-265° C. and the pressure is 60-150 KPaG.

10. The method according to claim 8, characterized in that Step (2) also includes taking out the small molecule compound by-product from the middle and upper outlet of the distillation separation zone and recycling it.

11. The method according to claim 8, characterized in that In step (3), the preheating is preheating to 230-250°C.

12. The method according to any one of claims 8 to 11, characterized in that In step (3), when the reaction raw materials are diols or dihydric phenols and carbonate diesters, in the multi-stage series disk reaction zone, the reaction temperature and reaction pressure of the first stage reaction disk are 230-250° C. and 20-30 kPaA, respectively, and the reaction temperature and reaction pressure of each stage reaction disk increase by 3-6° C. and 2-7 kPaA, respectively, from top to bottom; When the reaction raw materials are diols or diphenols and dibasic acids, in the multi-stage series disk reaction zone, the reaction temperature and reaction pressure of the first stage reaction disk are 265-275°C and 5-10KPaG respectively. From top to bottom, the reaction temperature and reaction pressure of each stage reaction disk increase by 3-6°C and 2-7KPaG respectively.

13. The method according to any one of claims 8 to 11, characterized in that: In step (3), the liquid phase obtained from the last stage reaction tray and the liquid phase separated from the distillation tower are mixed outside the second transesterification reactor and then enter the falling film reaction zone to continue the falling film reaction.

14. The method according to any one of claims 8 to 11, characterized in that In step (3), when the reaction raw materials are diols or dihydric phenols and carbonate diesters, the reaction temperature of the falling film reaction is 255-285° C., and the reaction pressure is 2-10 KPaA; When the reaction raw materials are diols or dihydric phenols and dibasic acids, the reaction temperature of the falling film reaction is 270-278° C. and the reaction pressure is 1-5 KPaG.

15. The method according to any one of claims 8 to 11, characterized in that: The method further includes: extracting a vapor phase from between the last two falling film reactors in the falling film reaction zone, allowing the extracted vapor phase to enter a third condenser for condensation to obtain a third condensate and a third non-condensable gas, allowing the third non-condensable gas to enter a vacuum unit, and allowing the third condensate to be cooled by a circulating liquid cooler and then circulated back to the third condenser for spray cooling.

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