阅读说明：本技术 一种氯乙醇法制备乙二醇的反应系统及方法 (Reaction system and method for preparing ethylene glycol by chloroethanol method ) 是由 张志炳 周政 李磊 张锋 孟为民 王宝荣 杨高东 罗华勋 田洪舟 杨国强 曹宇 于 2020-12-16 设计创作，主要内容包括：一种氯乙醇法制备乙二醇的反应系统,包括：主物料反应器、回用反应器和结晶器；所述主物料反应器连接有碳酸氢钠存储罐和氯乙醇存储罐,所述主物料反应器反应后的产物进入到所述结晶器中,所述结晶器连接有所述回用反应器；所述回用反应器内设置有氨气微界面发生器、二氧化碳微界面发生器,所述氨气微界面发生器连接有氨气进气管道,所述二氧化碳微界面发生器连接有二氧化碳进气管道。本发明的反应系统降低了反应过程的成本,强化了反应的效率。(A reaction system for preparing ethylene glycol by a chlorohydrin method comprises: a main material reactor, a recycling reactor and a crystallizer; the main material reactor is connected with a sodium bicarbonate storage tank and a chlorohydrin storage tank, a product obtained after reaction of the main material reactor enters the crystallizer, and the crystallizer is connected with the recycling reactor; an ammonia gas micro-interface generator and a carbon dioxide micro-interface generator are arranged in the recycling reactor, the ammonia gas micro-interface generator is connected with an ammonia gas inlet pipeline, and the carbon dioxide micro-interface generator is connected with a carbon dioxide gas inlet pipeline. The reaction system of the invention reduces the cost of the reaction process and enhances the reaction efficiency.)

1. A reaction system for preparing ethylene glycol by a chlorohydrin method is characterized by comprising: a main material reactor, a recycling reactor and a crystallizer;

the main material reactor is connected with a sodium bicarbonate storage tank and a chlorohydrin storage tank, a product obtained after reaction of the main material reactor enters the crystallizer, and the crystallizer is connected with the recycling reactor;

an ammonia gas micro-interface generator and a carbon dioxide micro-interface generator are arranged in the recycling reactor, the ammonia gas micro-interface generator is connected with an ammonia gas inlet pipeline, and the carbon dioxide micro-interface generator is connected with a carbon dioxide gas inlet pipeline.

2. The reaction system of claim 1, wherein the ammonia gas micro-interface generator is disposed at the bottom of the recycling reactor and the carbon dioxide micro-interface generator is disposed at the middle of the recycling reactor.

3. The reaction system of claim 2, further comprising a gas distribution channel, wherein the gas distribution channel is vertically disposed between the ammonia gas micro-interface generator and the carbon dioxide micro-interface generator, an air outlet of the carbon dioxide micro-interface generator faces downward and is connected to the gas distribution channel, and an air outlet of the ammonia gas micro-interface generator faces upward and is connected to the gas distribution channel.

4. The reaction system of claim 3, wherein the gas distribution channel is provided with vent holes, and the vent holes are uniformly distributed on the side wall of the gas distribution channel.

5. The reaction system of claims 1-4, wherein a dissolver is arranged at the top of the recycling reactor for re-dissolving the solid sodium chloride separated out from the crystallizer into water.

6. The reaction system of claim 5 wherein a jet conduit is provided around the dissolver for injecting the dissolved sodium chloride solution into the recycling reactor.

7. The reaction system of claims 1-6 wherein the recycle reactor is coupled to the main feed reactor to provide sodium bicarbonate to the main feed reactor.

8. The method for preparing ethylene glycol from chloroethanol as claimed in any one of claims 1 to 7, comprising the steps of:

(A) reacting sodium bicarbonate, chlorohydrin and water to obtain ethylene glycol and a byproduct sodium chloride, and purifying the hexanediol;

(B) and (3) carrying out micro-interfacial dispersion and crushing on ammonia gas and carbon dioxide in advance, and reacting the byproduct sodium chloride with the ammonia gas and the carbon dioxide after the crushing and the dispersion to obtain sodium bicarbonate for reuse.

9. The method according to claim 8, wherein the reaction temperature in the step (A) is 80 to 105 ℃ and the reaction temperature in the step (B) is 5 to 10 ℃.

Technical Field

The invention relates to the field of ethylene glycol preparation, and particularly relates to a reaction system and a method for preparing ethylene glycol by a chlorohydrin method.

Background

Ethylene Glycol (Ethylene Glycol), also known as Ethylene Glycol, is an important petrochemical organic raw material. The chemical reaction of the glycol is similar to that of the monohydric alcohol, and can perform typical reactions of many alcohols, such as esterification reaction, dehydration reaction, etherification reaction and the like, and the reaction product is mainly used for producing polyester fibers, polyester plastics and the like, is widely used for producing lubricants, plasticizers, nonionic surfactants, explosives and the like, and can be directly used as an antifreeze and a coolant for preparing engines. The traditional process utilizes the reaction of chloroethanol and alkali to generate cyclic chloroethane, and then the cyclic chloroethane is hydrolyzed to obtain ethylene glycol. The modern process is to react chloroethanol in weak alkali aqueous solution to directly synthesize glycol, and then to separate the glycol to obtain pure glycol. The modern process has higher requirement on the temperature during the reaction, and the preparation difficulty and the cost are improved.

Therefore, there is a need for improving the preparation of ethylene glycol by the chlorohydrin method, and increasing the purity and difficulty of ethylene glycol preparation by the chlorohydrin method by adding a new technology.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a reaction system for preparing ethylene glycol by a chlorohydrin method, which is characterized in that on one hand, sodium chloride is recycled to generate sodium bicarbonate by arranging a recycling reactor, the sodium bicarbonate is returned to a main material reactor to continue reaction, so that the cost is saved, on the other hand, a micro-interface generator is arranged in the recycling reactor to efficiently break an entering gas phase into micron-sized bubbles, and the micron-sized bubbles are dispersed to each part of the recycling reactor to form a micro-interface system, so that the gas-liquid phase interface area of the reaction is increased by tens of times, the mass transfer rate from the gas phase to the liquid phase is greatly increased, the sodium chloride can be fully recycled to generate the sodium bicarbonate serving as a raw material, the cost is saved, and the utilization rate of byproducts is increased.

The second purpose of the invention is to provide a method for preparing ethylene glycol by adopting the reaction system, the method is simple and convenient to operate, the obtained ethylene glycol has high purity and high product quality, and the method is widely popularized and applied.

In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

the invention provides a reaction system for preparing ethylene glycol by a chlorohydrin method, which comprises the following steps: a main material reactor, a recycling reactor and a crystallizer;

the main material reactor is connected with a sodium bicarbonate storage tank and a chlorohydrin storage tank, a product obtained after reaction of the main material reactor enters the crystallizer, and the crystallizer is connected with the recycling reactor;

an ammonia gas micro-interface generator and a carbon dioxide micro-interface generator are arranged in the recycling reactor, the ammonia gas micro-interface generator is connected with an ammonia gas inlet pipeline, and the carbon dioxide micro-interface generator is connected with a carbon dioxide gas inlet pipeline.

Preferably, the ammonia micro-interface generator is arranged at the bottom of the recycling reactor, and the carbon dioxide micro-interface generator is arranged in the middle of the recycling reactor.

Preferably, the reaction system further comprises a gas distribution channel, the gas distribution channel is vertically arranged between the ammonia gas micro-interface generator and the carbon dioxide micro-interface generator, a gas outlet of the carbon dioxide micro-interface generator faces downwards and is connected with the gas distribution channel, and a gas outlet of the ammonia gas micro-interface generator faces upwards and is connected with the gas distribution channel.

Preferably, the air distribution channel is provided with air exhaust holes, and the air exhaust holes are uniformly distributed on the side wall of the air distribution channel.

Preferably, a dissolver is arranged at the top of the recycling reactor and is used for re-dissolving the solid sodium chloride precipitated from the crystallizer into water.

Preferably, a jet flow pipeline is arranged around the dissolver for spraying the dissolved sodium chloride solution into the recycling reactor.

In a reaction system for preparing ethylene glycol from chloroethanol in the prior art, chloroethanol and sodium bicarbonate are subjected to hydrolysis reaction to generate ethylene glycol and sodium chloride, and the sodium chloride is filtered out after being precipitated in a crystallizer, so that waste of raw materials is caused; and when sodium chloride is used for generating sodium bicarbonate, the sodium bicarbonate generating efficiency is low because the phase boundary mass transfer area between ammonia gas and carbon dioxide and the sodium chloride solution is small, and the contact time is short. The present invention has been made to solve the above problems, and an object of the present invention is to provide a reaction system in which a recycle reactor is disposed below a crystallizer to collect sodium chloride precipitate discharged from the recycle crystallizer, and a micro-interface generator is added to the recycle reactor to improve reaction efficiency.

The main material reactor is connected with a sodium bicarbonate storage tank and a chlorohydrin storage tank, the sodium bicarbonate and the chlorohydrin react in the main material reactor to generate ethylene glycol and sodium chloride and are conveyed to a crystallizer, sodium chloride crystals are separated out after the crystallizer is cooled, and the sodium chloride crystals are discharged from the crystallizer and then enter a recycling reactor.

The recycling reactor is internally provided with an ammonia micro-interface generator for crushing and dispersing ammonia conveyed by an ammonia inlet pipeline into ammonia micro-bubbles, and the recycling reactor is internally provided with a carbon dioxide micro-interface generator for crushing and dispersing carbon dioxide conveyed by a carbon dioxide inlet pipeline into carbon dioxide micro-bubbles. The ammonia gas and the carbon dioxide are broken and dispersed into micro bubbles by the micro-interface generator, so that the mass transfer area of phase boundaries among the ammonia gas, the carbon dioxide and the sodium chloride solution is increased, and the reaction efficiency of the generation of the ethylene glycol is improved.

The ammonia gas micro-interface generator is arranged at the bottom of the recycling reactor, and the carbon dioxide micro-interface generator is arranged in the middle of the recycling reactor, because the density of the ammonia gas is less than that of the carbon dioxide, and the rising speed of the ammonia gas in the solution is faster than that of the carbon dioxide in the solution. Therefore, the ammonia micro-interface generator is arranged at the bottom of the recycling reactor, and the carbon dioxide micro-interface generator is arranged in the middle of the recycling reactor, so that the reaction time of ammonia and carbon dioxide is prolonged in the reaction process, and the reaction efficiency of sodium bicarbonate is improved.

An air distribution channel is also arranged between the ammonia gas micro-interface generator and the carbon dioxide micro-interface generator, an air outlet of the carbon dioxide micro-interface generator faces downwards and is connected with the air distribution channel, and an air outlet of the ammonia gas micro-interface generator faces upwards and is connected with the air distribution channel. The gas distribution channel is arranged between the two micro-interface generators, the gas distribution channel is provided with exhaust holes, and the exhaust holes are uniformly distributed on the side wall of the gas distribution channel and used for uniformly dispersing micro-bubbles discharged from the micro-interface generators into the recycling reactor, so that the fusion degree between the dispersed and crushed carbon dioxide and ammonia gas can be improved. The gas outlet of the carbon dioxide micro-interface generator faces downwards to be connected with the gas distribution channel, and the gas outlet of the ammonia micro-interface generator faces upwards to be connected with the gas distribution channel, so that carbon dioxide micro-bubbles are easier to react with ammonia micro-bubbles downwards because the density of carbon dioxide is higher than that of ammonia.

The invention is provided with a dissolver at the top of the recycling reactor for dissolving the solid sodium chloride precipitated from the crystallizer into water again. And a jet flow pipeline is arranged around the dissolver and used for jetting the dissolved sodium chloride solution into the recycling reactor, and the ammonia gas microbubbles and the carbon dioxide microbubbles which are originally gathered at the top return to the middle part or the bottom of the recycling reactor along with the jetting of the sodium chloride solution, so that the ammonia gas microbubbles and the carbon dioxide microbubbles fully react with the sodium chloride solution, and the reaction efficiency is enhanced.

In a word, a recycling reactor is added into the reaction system, and waste sodium chloride is recycled to generate sodium bicarbonate, so that the cost is saved; the micro-interface generator, the dissolver and the gas distribution channel are arranged in the recycling reactor, so that the mass transfer area of the phase boundary between ammonia gas, carbon dioxide and sodium chloride solution is increased, the ammonia gas, the carbon dioxide and the sodium chloride solution are fully contacted, the reaction efficiency is improved, and the reaction time is shortened.

It will be appreciated by those skilled in the art that the micro-interface generator used in the present invention is described in the prior patents of the present inventor, such as the patents of application numbers CN201610641119.6, CN201610641251.7, CN201710766435.0, CN106187660, CN105903425A, CN109437390A, CN205833127U and CN 207581700U. The detailed structure and operation principle of the micro bubble generator (i.e. micro interface generator) is described in detail in the prior patent CN201610641119.6, which describes that "the micro bubble generator comprises a body and a secondary crushing member, wherein the body is provided with a cavity, the body is provided with an inlet communicated with the cavity, the opposite first end and second end of the cavity are both open, and the cross-sectional area of the cavity decreases from the middle of the cavity to the first end and second end of the cavity; the secondary crushing member is disposed at least one of the first end and the second end of the cavity, a portion of the secondary crushing member is disposed within the cavity, and an annular passage is formed between the secondary crushing member and the through holes open at both ends of the cavity. The micron bubble generator also comprises an air inlet pipe and a liquid inlet pipe. "the specific working principle of the structure disclosed in the application document is as follows: liquid enters the micro-bubble generator tangentially through the liquid inlet pipe, and gas is rotated at a super high speed and cut to break gas bubbles into micro-bubbles at a micron level, so that the mass transfer area between a liquid phase and a gas phase is increased, and the micro-bubble generator in the patent belongs to a pneumatic micro-interface generator.

In addition, the first patent 201610641251.7 describes that the primary bubble breaker has a circulation liquid inlet, a circulation gas inlet and a gas-liquid mixture outlet, and the secondary bubble breaker communicates the feed inlet with the gas-liquid mixture outlet, which indicates that the bubble breakers all need to be mixed with gas and liquid, and in addition, as can be seen from the following drawings, the primary bubble breaker mainly uses the circulation liquid as power, so that the primary bubble breaker belongs to a hydraulic micro-interface generator, and the secondary bubble breaker simultaneously introduces the gas-liquid mixture into an elliptical rotating ball for rotation, thereby realizing bubble breaking in the rotating process, so that the secondary bubble breaker actually belongs to a gas-liquid linkage micro-interface generator. In fact, the micro-interface generator is a specific form of the micro-interface generator, whether it is a hydraulic micro-interface generator or a gas-liquid linkage micro-interface generator, however, the micro-interface generator adopted in the present invention is not limited to the above forms, and the specific structure of the bubble breaker described in the prior patent is only one of the forms that the micro-interface generator of the present invention can adopt.

Furthermore, the prior patent 201710766435.0 states that the principle of the bubble breaker is that high-speed jet flows are used to achieve mutual collision of gases, and also states that the bubble breaker can be used in a micro-interface strengthening reactor to verify the correlation between the bubble breaker and the micro-interface generator; moreover, in the prior patent CN106187660, there is a related description on the specific structure of the bubble breaker, see paragraphs [0031] to [0041] in the specification, and the accompanying drawings, which illustrate the specific working principle of the bubble breaker S-2 in detail, the top of the bubble breaker is a liquid phase inlet, and the side of the bubble breaker is a gas phase inlet, and the liquid phase coming from the top provides the entrainment power, so as to achieve the effect of breaking into ultra-fine bubbles, and in the accompanying drawings, the bubble breaker is also seen to be of a tapered structure, and the diameter of the upper part is larger than that of the lower part, and also for better providing the entrainment power for the liquid phase.

Since the micro-interface generator was just developed in the early stage of the prior patent application, the micro-interface generator was named as a micro-bubble generator (CN201610641119.6), a bubble breaker (201710766435.0) and the like in the early stage, and is named as a micro-interface generator in the later stage along with the continuous technical improvement, and the micro-interface generator in the present invention is equivalent to the micro-bubble generator, the bubble breaker and the like in the prior art, and has different names.

In summary, the micro-interface generator of the present invention belongs to the prior art, although some micro-interface generators belong to the pneumatic type micro-interface generator, some micro-interface generators belong to the hydraulic type micro-interface generator, and some micro-interface generators belong to the gas-liquid linkage type micro-interface generator, the difference between the types is mainly selected according to the different specific working conditions, and the connection between the micro-interface generator and the reactor and other devices, including the connection structure and the connection position, is determined according to the structure of the micro-interface generator, which is not limited.

Preferably, the recycle reactor is connected with the main material reactor to provide sodium bicarbonate to the main material reactor.

In addition, the invention also provides a reaction method for preparing ethylene glycol from chloroethanol, which comprises the following steps:

(A) reacting sodium bicarbonate, chlorohydrin and water to obtain ethylene glycol and a byproduct sodium chloride, and purifying hexanediol;

(B) and (3) carrying out micro-interfacial dispersion and crushing on ammonia gas and carbon dioxide in advance, and reacting the byproduct sodium chloride with the ammonia gas and the carbon dioxide after the crushing and the dispersion to obtain sodium bicarbonate for reuse.

Preferably, the reaction temperature of the step (A) is 80-105 ℃, and the reaction temperature of the step (B) is 5-10 ℃.

Compared with the method for preparing the ethylene glycol by using the chloroethanol in the prior art, the method disclosed by the invention can be used for collecting and recycling the waste sodium chloride, and the production efficiency of the sodium bicarbonate is improved, so that the production efficiency of the ethylene glycol is improved.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention recycles the waste sodium chloride by arranging the recycling reactor, thereby saving the cost;

(2) the reaction system of the invention efficiently crushes and disperses the entered gas phase into micron-sized bubbles through the micro-interface generator arranged in the recycling reactor, and disperses the micron-sized bubbles into the solvent to form a micro-interface system, thereby greatly improving the mass transfer rate from the gas phase to the liquid phase;

drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

fig. 1 is a schematic structural diagram of a reaction system for preparing ethylene glycol by a chlorohydrin method according to an embodiment of the present invention.

Wherein:

101-a sodium bicarbonate storage tank; 102-a chlorohydrin storage tank;

103-a carbon dioxide inlet duct; 104-ammonia gas inlet pipe;

20-main feed reactor; 30-a crystallizer;

40-recycling reactor; 41-carbon dioxide micro-interface generator;

42-ammonia micro-interface generator; 43-gas distribution channel;

431-exhaust hole; 44-a dissolver;

441-jet flow duct; 50-a distillation column;

60-a filter; 70-a rectifying tower;

80-ethylene glycol storage tank.

Detailed Description

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and the detailed description, but those skilled in the art will understand that the following described embodiments are some, not all, of the embodiments of the present invention, and are only used for illustrating the present invention, and should not be construed as limiting the scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In order to more clearly illustrate the technical solution of the present invention, the following description is made in the form of specific embodiments

Examples

Referring to fig. 1, a reaction system for preparing ethylene glycol from chlorohydrin according to an embodiment of the present invention mainly includes a sodium bicarbonate storage tank 101, a chlorohydrin storage tank 102, a main material reactor 20, a crystallizer 30, a recycling reactor 40, a carbon dioxide gas inlet pipeline 103, an ammonia gas inlet pipeline 104, a distillation tower 50, a filter 60, a rectification tower 70, and an ethylene glycol storage tank 80. The sodium bicarbonate storage tank 101 and the chlorohydrin storage tank 102 are connected with the main material reactor 20 for delivering raw materials of sodium bicarbonate and chlorohydrin to the main material reactor 20, wherein the sodium bicarbonate and the chlorohydrin react in the main material reactor 20 to generate ethylene glycol and byproduct sodium chloride, and the reaction temperature is 100 ℃. The ethylene glycol and sodium chloride generated by the reaction are conveyed to a crystallizer 30, the solution is cooled in the crystallizer 30 to separate out sodium chloride crystals, and the purified ethylene glycol enters a distillation tower 50. The discharged sodium chloride crystals enter a dissolver 44 at the top of the recycling reactor 40 for dissolution and become a sodium chloride solution. A jet pipe 441 is further provided around the dissolver 44, and the sodium chloride solution is injected into the recycling reactor 40 through the jet pipe 441.

The recycling reactor 40 is also provided with a carbon dioxide micro-interface generator 41 and an ammonia gas micro-interface generator 42, and the recycling reactor 40 is also provided with a carbon dioxide gas inlet pipeline 103 and an ammonia gas inlet pipeline 104. The carbon dioxide gas inlet pipe 103 passes through the side wall of the recycling reactor 40 and is connected with the carbon dioxide micro-interface generator 41 to deliver oxygen to the carbon dioxide micro-interface generator 41, and the ammonia gas inlet pipe 104 passes through the side wall of the recycling reactor 40 and is connected with the ammonia gas micro-interface generator 42 to deliver ammonia gas to the ammonia gas micro-interface generator 42. The carbon dioxide micro-interface generator 41 is arranged in the middle of the recycling reactor 40, the ammonia gas micro-interface generator 42 is arranged at the bottom of the recycling reactor 40, and the gas distribution channel 43 is vertically arranged between the carbon dioxide micro-interface generator 41 and the ammonia gas micro-interface generator 42.

The upper end of the gas distribution channel 43 is connected with the gas outlet of the carbon dioxide micro-interface generator 41, and the lower end is connected with the gas outlet of the ammonia micro-interface generator 42. The carbon dioxide micro bubbles from the carbon dioxide micro interface generator 41 and the ammonia micro bubbles from the ammonia micro interface generator 42 are fully mixed in the gas distribution channel 43, and then are discharged from the gas outlet 431 to enter the recycling reactor 40. Since the gas exhaust holes 431 are uniformly distributed on the gas distribution channel 43, the ammonia microbubbles and the carbon dioxide microbubbles are uniformly dispersed into the recycling reactor 40. The ammonia gas, the carbon dioxide and the sodium chloride solution are fully reacted in the recycling reactor 40 to generate sodium bicarbonate, and the sodium bicarbonate is returned to the main material reactor 20 to react with the chloroethanol again.

The ethylene glycol generated in the main material reactor 20 is purified by the crystallizer 30 and then enters the distillation tower 50, the distillation tower 50 distills water, the saturation degree of the ethylene glycol is reduced to separate out ethylene glycol crystals, and the precipitated ethylene glycol crystals are collected and then conveyed to the filter 60.

The filter 60 is filled with an acetone solution, and since the ethylene glycol crystals are easily dissolved in the acetone solution, the ethylene glycol crystals collected from the distillation column 50 are all dissolved in the acetone solution. After the ethylene glycol is dissolved in the acetone solution, the acetone solution carries the ethylene glycol into the rectifying tower 70, the rectifying tower 70 converts the acetone into a gas phase by utilizing the fact that the components of the mixture have different volatility, the gas phase is discharged from the top of the tower, the unreacted ethylene chlorohydrin is discharged from the bottom of the tower, and the residual ethylene glycol is conveyed to an ethylene glycol storage tank 80 for storage.

In addition, in the specific reaction process, the reaction temperature in the main material reactor 20 is 100 ℃, and the reaction temperature in the recycling reactor 40 is 5 ℃.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.