WO2022077429A1

WO2022077429A1 - Cyclic solvent in phosgenation reaction production and impurity removal method therefor

Info

Publication number: WO2022077429A1
Application number: PCT/CN2020/121465
Authority: WO
Inventors: 王振有; 陈良进; 徐丹; 文放; 吴雪峰; 马海洋; 张宏科
Original assignee: 万华化学集团股份有限公司; 万华化学（宁波）有限公司
Priority date: 2020-10-16
Filing date: 2020-10-16
Publication date: 2022-04-21

Abstract

The present invention relates to the technical field of impurity separation in a phosgenation reaction process, and specifically relates to a cyclic solvent in phosgenation reaction production and an impurity removal method therefor. The impurity removal method comprises: (1) rectifying a crude solvent; (2) extracting a gas-phase material flow I from a tower top, and performing gas-liquid separation after condensation, the obtained liquid-phase material flow II flowing back to the tower top, and the obtained gas-phase material flow II entering a tail gas treatment system; (3) dividing the liquid phase material flow I extracted by a tower into a liquid-phase material flow III to return to the tower and a liquid-phase material flow IV to be sent to a solvent reaction kettle; and (4) adding an amine compound to the solvent reaction kettle to react with the liquid-phase material flow IV, the obtained material being subjected to solid-liquid separation, and the liquid product being directly reused as a cyclic solvent. The impurity removal method of the present invention can ensure that the total amount of amine consumption substances in a cyclic solvent is reasonably controlled, reduce the generation of a solid by-product in a phosgenation reaction, and relieve the blockage of raw materials in transportation and storage, thereby prolonging the stable running time of a device, and improving product quality.

Description

Circulating solvent in phosgenation reaction production and method for removing impurities

technical field

The invention belongs to the technical field of impurity separation in a phosgenation reaction process, and in particular relates to a circulating solvent in the production of a phosgenation reaction and a method for removing impurities.

Background technique

In the process of producing diphenylmethane diisocyanate (MDI) by liquid phase phosgene method, in order to improve the mixing effect and reaction effect of phosgene and diaminodiphenylmethane (MDA), it is necessary to add a large amount of phosgene and MDA at the same time. Organic solvent, for example, chlorobenzene (MCB), ortho-dichlorobenzene (ODCB) etc., then after the reaction finishes, this organic solvent is separated from the isocyanate product by means such as distillation or rectification, and the solvent obtained from the separation can be reused to Phosgenation reaction system.

However, in this process, some impurities that can react with the amines as raw materials in the system will inevitably be brought in when the solvent is reused. Such impurities include: phosgene, hydrogen chloride, isocyanates, and acid chlorides. Wait. Therefore, in the process of using liquid phase phosgene method to produce MDI, it is necessary to purify the recovered solvent to remove impurities.

Patent document EP-A-1073628 discloses a two-step process for the production of diphenylmethane diisocyanate and polyphenyl polymethylene polyisocyanate (known as polyMDI) using a mixture of the corresponding amine and phosgene in the presence of a solvent. ) mixture method, after the two-step reaction, the excess phosgene, hydrogen chloride and solvent are separated from the obtained mixture product as a whole by means of distillation. The patent points out that after the excess phosgene is removed by distillation, the residual content of phosgene in the recovered solvent is less than 10 ppm, which is beneficial for obtaining good product quality. However, this patent only discusses the content of phosgene in the recovered solvent, and does not comprehensively limit the content of other impurities in the recovered solvent. Although the quality of MDI products can be improved to a certain extent, the improvement effect is limited. In addition, this patent only reflects the impact of phosgene content on product quality, and does not systematically and specifically target the possible adverse effects (for example, stable operation of the system, increased risk of equipment corrosion, etc.) after its content exceeds a certain value. sex research.

Chinese patent document CN 101302174A discloses a method for producing isocyanates, by reacting amines dissolved in a solvent with phosgene in the same solvent to produce corresponding isocyanates, and then distilling the crude isocyanate-containing solution Separation into isocyanate product and solvent, solvent recycling. It is mentioned in this patent that reducing the phosgene and isocyanate content in the recovered solvent is beneficial to improve the quality of the isocyanate product. Therefore, the recycled solvent is processed before being used to produce the solution containing amines, and the recycled solvent is The content of phosgene and diisocyanate is controlled within a certain range. Compared with the patent document EP-A-1073628, although this patent increases the control of the diisocyanate content, it still does not limit the content of other impurities in the recycled solvent. However, not only diisocyanates, but also a certain amount of polyisocyanates and acid chlorides may be present in the recycled solvent. These substances can also react with amines as raw materials for phosgenation to produce solid compounds such as urets and amides. , thereby affecting product quality, as well as problems that may cause system blockages.

It can be seen that the prior art has limited control on the content of impurities that can be reacted with amines as raw materials in the recovery solvent, generally only controls the content of several specific impurities such as phosgene and diisocyanate, and does not control all the impurities that can cause product quality to decline. The content of such impurities is comprehensively and systematically limited. Although this can improve the quality of the reaction products to a certain extent, it cannot completely solve the adverse effects of such impurities on the phosgenation reaction, especially for increasing the stable operation time of the system. less research.

SUMMARY OF THE INVENTION

When the phosgenation reaction system is used for recycling of the circulating solvent, impurities such as phosgene, hydrogen chloride, isocyanates, acid chlorides, etc. will react gradually after contacting with the amines as raw materials, and finally generate urets, amides and amines Solid products such as hydrochloride. These solid products, on the one hand, will affect the quality of the products obtained from the phosgenation reaction and reduce the product purity; The blockage of the device, etc., will increase the operating cost of the equipment and reduce the stable operation time of the device. In addition, phosgene, hydrogen chloride and other substances in such impurities are acidic components, and their high content will not only cause the above two hazards, but also increase the risk of equipment corrosion. Therefore, in the process of producing MDI by liquid phase phosgene method, it is necessary to strictly control the content of such impurities in the recovered solvent.

In the present invention, all impurities in the circulating solvent that can react with the amines as raw materials are collectively referred to as "amine-consuming substances".

In view of the deficiencies of the solvent recovery process in the existing phosgenation reaction, the object of the present invention is to provide a circulating solvent in the production of the phosgenation reaction and an impurity removal method thereof, which can ensure the phosgenation reaction by the impurity removal method. The total amount of amine-consuming substances in the recycled solvent is controlled within a reasonable range, which greatly reduces the generation of solid by-products in the phosgenation reaction system, thereby reducing the risk of clogging of the reaction materials during transportation and storage, and prolonging the reaction. The stable operation time of the device, while improving the quality of the reaction product.

In order to achieve the above object, the present invention provides the following technical solutions:

In a first aspect, a circulating solvent in the production of phosgenation reaction is provided, including: amine consumption substances and organic solvent used in the production of phosgenation reaction;

The amine-consuming substances include: one or more of hydrogen chloride, phosgene, substances with NCO groups and substances with COCl groups;

In addition, amine-consuming substances may include other kinds of impurities;

Among them, substances with NCO groups, such as toluene isocyanate (PI), diphenylmethane diisocyanate (MDI) and other polyisocyanates; substances with COCl groups, such as carbamoyl chloride;

Based on the total weight of the recycled solvent, the content of the amine-consuming species is 0.2-5000 ppm (for example, 0.5 ppm, 1.5 ppm, 5 ppm, 8 ppm, 15 ppm, 30 ppm, 50 ppm, 80 ppm, 100 ppm, 200 ppm, 500 ppm, 1000 ppm) , 3000ppm), preferably 1-2000ppm, more preferably 10-300ppm. The content of amine-consuming substances mentioned herein may refer to the total amount of various types of amine-consuming substances contained in the circulating solvent.

According to the circulating solvent provided by the present invention, in some examples, the organic solvent is selected from one or more of ethyl isophthalate, benzene, toluene, xylene, chlorobenzene and o-dichlorobenzene, preferably chlorine Benzene and/or ortho-dichlorobenzene, more preferably chlorobenzene.

In a second aspect, a kind of impurity removal method of circulating solvent as above is provided, comprising the following steps:

(1) preheat the crude solvent obtained through preliminary distillation after the phosgenation reaction, then feed into solvent purification tower CO1 and carry out rectification treatment;

(2) the top of the solvent purification tower C01 is extracted gas-phase stream I, and after condensation, gas-liquid two-phase separation is carried out; the liquid phase stream II of the separation gained is all refluxed to the top of the solvent purification tower CO1; Stream II enters the tail gas treatment system for post-treatment;

(3) the column still of described solvent purification tower C01 draws out liquid-phase stream I and is divided into liquid-phase stream III and liquid-phase stream IV, wherein, liquid-phase stream III is refluxed to tower after reboiler heating Still, liquid phase stream IV is extracted and sent to solvent reactor R01;

(4) in described solvent reactor R01, add amine compound, react with described liquid-phase material stream IV; Carry out solid-liquid two-phase separation by the material after the reaction, isolate gained solid product (for example, comprise amine hydrochloric acid) Salts, urets, amides, etc.) are regularly extracted, and the liquid products obtained by separation are directly reused in the phosgenation reaction process as the circulating solvent.

In the present invention, the system after the phosgenation reaction contains the final isocyanate product, organic solvent, hydrogen chloride, unreacted residual phosgene and other impurities, and it is necessary to separate the isocyanate product from the system through a preliminary distillation process to obtain a higher purity High isocyanate product and crude solvent with various impurities. If such crude solvent is to be reused in the phosgenation reaction system, it needs to be purified. Amine-consuming substances exist as impurities in the crude solvent, which will affect the effect of recycling them to the phosgenation reaction system. Such amine-consuming species include, for example, one or more of hydrogen chloride, phosgene, NCO-bearing species, and COCl-bearing species.

According to the impurity removal method provided by the present invention, in some examples, the temperature of the preheating in step (1) is 80-125°C (eg, 90°C, 105°C), preferably 100-110°C.

In some examples, the feeding position of the crude solvent in step (1) into the solvent refining column C01 is above the first to fifth trays, preferably above the first to third trays.

In some examples, the top operating pressure of the solvent refining column CO1 is 100-200KPa (eg, 105KPa, 110KPa, 140KPa, 180KPa), preferably 120-160KPa.

The operating pressure here is absolute pressure.

In some examples, the operating temperature of the column kettle of the solvent refining column C01 is 120-200°C (eg, 140°C, 150°C, 180°C), preferably 130-160°C.

In some examples, the solvent refining column C01 adopts valve trays, and the theoretical plate number is 10-50 (eg, 15, 30, 45), preferably 20-40.

After the crude solvent is subjected to rectification treatment through the operation process of step (1), a large part of the light components in the amine-consuming substances can be removed. For example, in the obtained liquid-phase stream I after the rectification treatment, the content of impurities such as hydrogen chloride and phosgene is significantly reduced.

According to the impurity removal method provided by the present invention, a certain amount of low-boiling amine-consumed substances (for example, light components in the amine-consumed substances) will be contained in the gas-phase stream I drawn from the top of the column. In the step (2), the gas-phase stream I is condensed to carry out gas-liquid separation, and the content of low-boiling amine consumption substances in the obtained liquid-phase stream II is relatively low, and all of them can be refluxed to the top of the solvent purification tower C01. The remaining low-boiling amine-consuming substances are in gaseous form as components of the gas-phase stream II, and can enter the tail gas treatment system for post-treatment. In some examples, the condensation process in this step can be implemented by using a conventional condenser, and the operation process thereof is a conventional choice in the field, and details are not described herein again.

According to the impurity removal method provided by the invention, step (3) divides the liquid phase stream I drawn from the tower still, and a part (that is, the liquid phase stream III) is heated by the reboiler and is refluxed to the tower still, and the other part (ie, liquid phase stream IV) is sent to the solvent reactor.

In some examples, the mass ratio of the reboiler recycle to the column still output is 1:1-1:5 (eg, 1:1.5, 1:2, 1:2.5, 1:3.5, 1:4), It is preferably 1:1-1:3. The mass ratio of the reboiler recycle amount to the tower bottom production amount mentioned here refers to the mass ratio of the liquid phase stream III to the liquid phase stream IV. The purpose of controlling the reboiler circulation volume and the extraction volume of the tower reactor is to: (1) optimize the effect of rectification to remove light components and prepare for the subsequent treatment in the solvent reactor; (2) on the basis of ensuring the separation effect Reduce energy consumption as much as possible.

According to the impurity removal method provided by the present invention, the liquid-phase material stream IV is sent to the solvent reactor, and it reacts with the added amine compound for further impurity removal.

The amine compound is preferably the same as the amine material used as the raw material in the phosgenation reaction process; these amine compounds can be, but are not limited to, 1,4-diaminobutane, 1,6-diaminohexane, 1 ,5-naphthalenediamine, 1,4-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,2-diaminodicyclohexylmethane, 2,4-diaminodicyclohexylmethane , one or more of 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane and 2,2-diaminodiphenylmethane. In a preferred embodiment, the amine compound in step (4) is selected from 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane and 2,2-diaminodiphenylmethane one or more of.

After step (4) adding the amine compound, the principle of reacting some components in the amine consumption substance with the amine compound is as follows:

①Reaction formula of hydrogen chloride and amine compounds:

HCl+R- _NH2 →R- _NH2 ·HCl (amine hydrochloride);

②Reaction formula of phosgene and amine compounds:

COCl ₂ +R-NH ₂ →R-NCO;

③ Reaction formula of substances with NCO groups and amine compounds:

④Reaction formula of substances with COCl groups and amine compounds:

The substances generated by the above four reactions are solid products, which can be extracted regularly; for example, separation and extraction can be realized in a settling tank.

In order to ensure the viscosity of the recovered solvent and reduce the total amount of amine consumption substances contained therein, it is necessary to strictly control the consumption of the amine compound added in the solvent reactor R01, that is, by controlling the mass flow of the amine compound and the liquid phase stream IV. than realized. In a preferred embodiment, the mass flow ratio of the amine compound in step (4) to the liquid phase stream IV is 0.001-0.1:1 (for example, 0.005:1, 0.008:1, 0.012:1, 0.018:1, 0.025:1, 0.04:1, 0.06:1, 0.08:1), preferably 0.01-0.05:1, more preferably 0.02-0.03:1.

At the same time, the reaction time of step (4) also has an important influence on the viscosity of the recovered solvent and the total amount of amine-consuming substances contained in the recovered solvent. In some examples, the residence time of the amine compound and the liquid phase stream IV in the solvent reactor R01 is 10-60min (for example, 12min, 15min, 25min, 30min, 40min), preferably 10-50min, more preferably 10 to 20 minutes.

Through the above-mentioned impurity removal method, the circulating solvent used in the production of phosgenation reaction can be efficiently removed, which can not only reduce the content of a certain low-boiling point impurity or reduce the content of a certain heavy component impurity, but also Ensure that the total amount of amine-consuming substances contained in it is reduced to a level that meets the requirements. Based on the total weight of the circulating solvent, the content of the amine-consuming substances is 0.2-5000 ppm, preferably 1-2000 ppm, more preferably 10-300 ppm. Here, the content of amine-consuming substances may refer to the total content of each impurity contained in the amine-consuming substances.

Compared with the operation method of first reacting and then rectifying, the present invention first removes most of the low-boiling amine consumption substances in the recovery solvent through the rectifying process, and then adopts the amine substances corresponding to the phosgenation reaction to effectively remove the amine substances. Residual amine-consuming substances can be removed in layers by removing various types of amine-consuming substances. Such a process operation can avoid incomplete reaction of light components during the reaction process, and reduce the operational complexity and fineness of rectification and impurity removal. At the same time, the consumption of added amine compounds can also be reduced, and raw materials, costs and energy consumption can be saved.

Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

(1) the present invention has increased the purification process that reacts with corresponding amine substances on the basis of traditional rectification process, can make the total content of amine consumption substances in the gained recovery solvent to decline obviously, the removal effect is better, and the obtained after treatment The mixed solution formed by the amine compound and the recovered solvent can be directly used in the phosgenation reaction, eliminating the subsequent treatment process and reducing the solvent refining cost;

(2) Through the optimization of the parameters in the rectification process and the selection of the amine compound reaction process parameters corresponding to the phosgenation reaction (for example, the type and amount of the amine compound, the reaction time), the amine in the recovered solvent can be recovered. The total amount of consumable substances is controlled within a reasonable range, which greatly avoids the occurrence of side reactions when the recovered solvent is reused to the phosgenation reaction system, thereby reducing the risk of corrosion and blockage of the reaction materials during transportation and storage. The stable operation time of the reaction device is prolonged, and the quality of the isocyanate product is improved at the same time.

Description of drawings

FIG. 1 is a process flow diagram of an embodiment of the impurity removal method of the present invention.

The symbols in the figure are explained as follows:

D01-top gas-liquid separator, C01-solvent refining tower, R01-solvent reactor, T01-solvent settling tank, E01-coarse solvent preheater, E02-tower still reboiler, E03-tower top condenser;

1- preheater feed pipe, 2- solvent refining tower feed pipe, 3- tower kettle reboiler feed pipe, 4- tower kettle draw pipe, 5- tower kettle reboiler discharge pipe, 6- Column top gas phase outlet pipe, 7- condenser material outlet pipe, 8- gas-liquid separator gas phase extraction pipe, 9- tower top reflux pipe, 10- amine compound feed pipe; 11- sedimentation tank feed pipe; 12 - Sedimentation tank impurity extraction pipe; 13- Refined solvent outlet pipe.

Detailed ways

In order to be able to understand the technical features and contents of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. While preferred embodiments of the present invention have been described in the examples, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.

In a specific embodiment, as shown in Figure 1, the impurity removal method of circulating solvent in the production of phosgenation reaction comprises the following steps:

(1) the crude solvent obtained through preliminary distillation after the phosgenation reaction is passed into the crude solvent preheater E01 through the preheater feed pipe 1 and preheated, for example, the preheated temperature is 80-125 ° C; Passing the preheated crude solvent into the solvent refining tower C01 through the solvent refining tower feed pipe 2 to carry out rectification treatment; Tower C01 adopts valve tray, and its theoretical plate number is 10-50;

(2) the tower top of described solvent purification tower C01 draws out gas-phase stream 1 by tower top gas phase outlet pipe 6, enters tower top gas-liquid separator D01 through condenser material outlet pipe 7 after being condensed by tower top condenser E03 In, the gas-liquid two-phase is separated out; The separated gained liquid phase stream II is all refluxed to the top of the solvent refining tower C01 through the tower top reflux pipe 9, and the separated gained gas phase stream II enters the tail gas through the gas-liquid separator gas phase extraction pipe 8 post-processing by the processing system;

(3) the tower still of described solvent refining tower C01 draws out liquid-phase stream I, then is divided into liquid-phase stream III and liquid-phase stream IV, wherein, liquid-phase stream III is fed by the tower kettle reboiler After the pipe 3 enters the reboiler E02 heating, it is refluxed to the tower still of the solvent refining tower C01 through the tower still reboiler discharge pipe 5, and the liquid phase stream IV is extracted by the tower still extraction pipe 4 and sent to the solvent reaction In still R01; For example, the mass ratio of reboiler circulation and tower still output is 1:1-1:5;

(4) adding amine compound into the solvent reactor R01 through the amine compound feed pipe 10, and reacting with the liquid phase stream IV; for example, the mass flow ratio of the amine compound to the liquid phase stream IV is 0.001 -0.1:1, the residence time is 10-60min; the reacted material is passed into the solvent sedimentation tank T01 through the sedimentation tank feed pipe 11 for sedimentation and solid-liquid separation, and the solid product obtained from the separation passes through the sedimentation tank impurity extraction pipe 12 Periodically extracted, the upper liquid phase (ie, the circulating solvent) of the solvent settling tank T01 can be directly reused in the phosgenation reaction process through the purified solvent outlet pipe 13 .

The analysis method for the content of various impurities (amine-consuming substances) in the circulating solvent is as follows:

1. Content detection of toluene isocyanate (PI) and diphenylmethane diisocyanate (MDI): use the chromatographic model Agilent GC7890B, the chromatographic column is HP-5, and the external standard quantification method is used, and the spectrum is normalized to obtain PI and MDI content;

2. Content detection of phosgene + hydrogen chloride: use methanol to dissolve the sample to be tested, then react with sodium hydroxide, and finally titrate with silver nitrate to obtain the content of phosgene and hydrogen chloride;

3. Detection of the total content of amine-consuming substances: n-butylamine is used to react with the sample to be tested, and then back-titration with hydrochloric acid is used to obtain the total amount of amine-consuming substances.

In the crude chlorobenzene (for example, the flow rate is 300kg/h) produced during the preparation of diphenylmethane diisocyanate, the total amount of amine-consuming substances is 15,000-40,000 ppm. in,

The content ranges of various types of impurities are as follows:

The content of toluene isocyanate (PI) is 300-1000ppm,

The content of diphenylmethane diisocyanate (MDI) is 250-1000ppm,

The content of phosgene + hydrogen chloride is 500-5000ppm,

The balance is the content of other types of impurities.

The operating pressures presented in the following examples and comparative examples are absolute pressures.

Example 1

Adopt the process flow diagram shown in Fig. 1, the 300kg/h crude chlorobenzene that produces in the preparation process of diphenylmethane diisocyanate is carried out impurity removal treatment, comprises the following steps:

(1) 300kg/h of crude chlorobenzene is passed into the crude solvent preheater E01 through the preheater feed pipe 1 and preheated; then the preheated crude solvent is passed into the solvent through the solvent purification tower feed pipe 2 Rectification treatment is carried out in the refining tower CO1; the main parameters are controlled as follows:

The outlet temperature of the crude solvent preheater E01 is 100°C; the solvent purification tower C01 adopts a floating valve tray, and the number of theoretical trays is 25; the feed position of the crude chlorobenzene is above the first tray of the solvent purification tower C01, and the solvent The top operating pressure of the refining tower C01 is 150kpa, and the tower still operating temperature is 140°C;

(2) the tower top of solvent purification tower C01 draws out gas-phase stream 1 by tower top gas phase outlet pipe 6, enters in tower top gas-liquid separator D01 after being condensed by condenser material outlet pipe 7 through tower top condenser E03, The gas-liquid two phases are separated; the separated gained liquid phase stream II is all refluxed to the top of the solvent refining tower C01 by the top reflux pipe 9, and the separated gained gas phase stream II enters the tail gas treatment system through the gas-liquid separator gas phase extraction pipe 8 post-processing;

(3) the tower still of solvent refining tower C01 draws out liquid-phase stream I and is divided into liquid-phase stream III and liquid-phase stream IV, wherein, liquid-phase stream III enters by tower-still reboiler feed pipe 3 After the reboiler E02 is heated, it is refluxed to the tower still of the solvent refining tower C01 through the tower still reboiler discharge pipe 5; the liquid phase stream IV is extracted through the tower still extraction pipe 4 and sent to the solvent reactor R01 ; The mass ratio of reboiler E02 circulation and tower still output is 1:1;

(4) adding the amine compound into the solvent reactor R01 through the amine compound feed pipe 10, and reacting with the liquid phase stream IV;

The amine compound entering the solvent reactor R01 adopts the mixture of 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane and 2,2-diaminodiphenylmethane. The mass flow ratio of liquid phase stream IV is 0.005:1, and the residence time of the two in the reactor is 15min;

The reacted material is passed into the solvent settling tank T01 through the settling tank feed pipe 11 to settle and carry out solid-liquid separation, and the solid product obtained from the separation is regularly extracted through the settling tank impurity extraction pipe 12, and the upper liquid phase of the solvent settling tank T01 (That is, the recovered chlorobenzene) can be directly reused in the phosgenation reaction process through the purified solvent outlet pipe 13 .

Based on the total weight of the recovered chlorobenzene, the total amount of amine-consuming substances in the recovered chlorobenzene was 1425 ppm. Among them, the content of toluene isocyanate (PI) is 102ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 107ppm, the content of phosgene+hydrogen chloride is 168ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to operate in the phosgenation reaction process, and in the crude product of diphenylmethane diisocyanate in the production gained, based on the gross weight of the crude product of diphenylmethane diisocyanate, the content of the NCO group is 30.1% , the cleaning cycle of the inlet filter of the crude isocyanate product tank is 30 days.

Example 2

(1) 300kg/h of thick chlorobenzene is passed into the crude solvent preheater E01 by the preheater feed pipe 1 and preheated; then the preheated thick solvent is passed into the solvent by the solvent purification tower feed pipe 2 Rectification treatment is carried out in the refining tower CO1; the main parameters are controlled as follows:

The outlet temperature of the crude solvent preheater E01 is 100°C; the solvent purification tower C01 adopts a floating valve tray, and the number of theoretical trays is 25; the feed position of the crude chlorobenzene is above the first tray of the solvent purification tower C01, and the solvent The operating pressure of the tower top of the refining tower C01 is 140kpa, and the operating temperature of the tower kettle is 140°C;

Based on the total weight of the recovered chlorobenzene, the total amount of amine-consuming substances in the recovered chlorobenzene was 1234 ppm. Among them, the content of toluene isocyanate (PI) is 100ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 104ppm, the content of phosgene+hydrogen chloride is 105ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to run in phosgenation reaction operation, in the crude product of production gained diphenylmethane diisocyanate, based on the weight of the crude product of diphenylmethane diisocyanate, the content of NCO group is 30.3%, The cleaning cycle of the crude isocyanate product tank inlet filter is 35 days.

Example 3

The outlet temperature of the crude solvent preheater E01 is 100°C; the solvent purification tower C01 adopts a floating valve tray, and the number of theoretical trays is 25; the feed position of the crude chlorobenzene is above the first tray of the solvent purification tower C01, and the solvent The top operating pressure of the refining tower C01 is 120kpa, and the tower still operating temperature is 140°C;

Based on the total weight of the recovered chlorobenzene, the total amount of amine-consuming substances in the recovered chlorobenzene was 1302 ppm. Among them, the content of toluene isocyanate (PI) is 105ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 111ppm, and the content of phosgene+hydrogen chloride is 70ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to operate in the phosgenation reaction process, and in the crude product of the diphenylmethane diisocyanate produced, based on the gross weight of the crude product of diphenylmethane diisocyanate, the content of the NCO group is 30.2%. , the cleaning cycle of the inlet filter of the crude isocyanate product tank is 33 days.

Example 4

The outlet temperature of the crude solvent preheater E01 is 100°C, and the solvent purification tower C01 adopts a valve tray, and its theoretical plate number is 25; the feed position of the crude chlorobenzene is above the first tray of the solvent purification tower C01, and the solvent The top operating pressure of the refining tower C01 is 120kpa, and the tower still operating temperature is 140°C;

The amine compound entering the solvent reactor R01 adopts the mixture of 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane and 2,2-diaminodiphenylmethane. The mass flow ratio of liquid phase stream IV is 0.015:1, and the residence time of the two in the reactor is 15min;

Based on the total weight of recovered chlorobenzene, in the recovered chlorobenzene, the total amount of amine-consuming substances was 662 ppm. Among them, the content of toluene isocyanate (PI) is 65ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 59ppm, and the content of phosgene+hydrogen chloride is 57ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to run in the phosgenation reaction process, and in the crude product of the diphenylmethane diisocyanate produced, based on the gross weight of the crude product of diphenylmethane diisocyanate, the content of the NCO group is 31.0%. , the cleaning cycle of the inlet filter of the crude isocyanate product tank is 60 days.

Example 5

(3) the tower still of solvent refining tower C01 draws out liquid-phase stream I and is divided into liquid-phase stream III and liquid-phase stream IV, wherein, liquid-phase stream III enters by tower-still reboiler feed pipe 3 After the reboiler E02 is heated, reflux to the tower still of the solvent refining tower C01 through the reboiler discharge pipe 5 of the tower still; Liquid phase stream IV is extracted through the tower still extraction pipe 4 and sent to the solvent reactor R01 ; The ratio of reboiler E02 circulation and tower still production is 1:1;

The amine compound entering the solvent reactor R01 adopts the mixture of 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane and 2,2-diaminodiphenylmethane. The mass flow ratio of liquid phase stream IV is 0.025:1, and the residence time of the two in the reactor is 15min;

Based on the total weight of the recovered chlorobenzene, the total amount of amine-consuming substances in the recovered chlorobenzene was 125 ppm. Wherein, the content of toluene isocyanate (PI) is 9ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 12ppm, the content of phosgene+hydrogen chloride is 5ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to run in the phosgenation reaction process, in the production of gained diphenylmethane diisocyanate crude product, based on the gross weight of diphenylmethane diisocyanate crude product, the content of NCO group is 32.9% , the cleaning cycle of the inlet filter of the crude isocyanate product tank is 180 days.

Example 6

The amine compound entering the solvent reactor R01 adopts the mixture of 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane and 2,2-diaminodiphenylmethane. The mass flow ratio of liquid phase stream IV is 0.035:1, and the residence time of the two in the reactor is 15min;

Based on the total weight of the recovered chlorobenzene, the total amount of amine-consuming substances in the recovered chlorobenzene was 226 ppm. Among them, the content of toluene isocyanate (PI) is 35ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 42ppm, the content of phosgene+hydrogen chloride is 15ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to run in the phosgenation reaction process, and in the crude product of diphenylmethane diisocyanate produced, based on the gross weight of the crude product of diphenylmethane diisocyanate, the content of NCO group is 32.1% , the cleaning cycle of the inlet filter of the crude isocyanate product tank is 120 days.

Example 7

The amine compound entering the solvent reactor R01 adopts the mixture of 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane and 2,2-diaminodiphenylmethane. The mass flow ratio of liquid phase stream IV is 0.045:1, and the residence time of the two in the reactor is 15min;

Based on the total weight of the recovered chlorobenzene, the total amount of amine-consuming substances in the recovered chlorobenzene was 351 ppm. Among them, the content of toluene isocyanate (PI) is 74ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 81ppm, and the content of phosgene+hydrogen chloride is 32ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to operate in the phosgenation reaction process, in the production of the gained diphenylmethane diisocyanate crude product, based on the gross weight of the diphenylmethane diisocyanate crude product, the content of the NCO group is 31.6% , the cleaning cycle of the inlet filter of the crude isocyanate product tank is 95 days.

Comparative Example 1

The 300kg/h crude chlorobenzene produced in the preparation process of p-diphenylmethane diisocyanate is treated with impurity removal, including the following steps:

(3) the tower still of solvent refining tower C01 draws out liquid-phase stream I and is divided into liquid-phase stream III and liquid-phase stream IV, wherein, liquid-phase stream III enters by tower-still reboiler feed pipe 3 After the reboiler E02 is heated, it is refluxed to the tower still of the solvent refining tower C01 through the tower still reboiler discharge pipe 5; the liquid phase stream IV is extracted through the tower still extraction pipe 4, that is, the recovered chlorobenzene is obtained; The mass ratio of the reboiler E02 circulating capacity and the output of the tower still is 1:1;

Based on the total weight of the recovered chlorobenzene, the total amount of amine-consuming substances in the recovered chlorobenzene was 10325 ppm. Wherein, the content of toluene isocyanate (PI) is 214ppm, the content of diphenylmethane diisocyanate (MDI) is 176ppm, the content of phosgene+hydrogen chloride is 219ppm, and the balance is the content of other impurities.

Adopt this recovered chlorobenzene to operate in phosgenation reaction operation, in the crude product of production gained diphenylmethane diisocyanate, based on the gross weight of the crude product, the content of NCO group is 28.5%, and the crude isocyanate product tank imports The filter cleaning cycle is 5 days.

Comparative Example 2

The 300kg/h thick chlorobenzene produced in the preparation process of p-diphenylmethane diisocyanate is treated with impurity removal, and its operation steps are carried out with reference to Example 5, the difference is: the preheated thick solvent is first passed into the solvent reactor In R01, react with the added amine compound; then pass the material obtained from the reaction into the solvent purification tower C01 for rectification treatment.

Based on the total weight of the recovered chlorobenzene, in the recovered chlorobenzene, the total amount of amine-consuming substances was 7832 ppm. Among them, the content of toluene isocyanate (PI) is 232ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 186ppm, the content of phosgene+hydrogen chloride is 45ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to operate in phosgenation reaction operation, in the crude product of production gained diphenylmethane diisocyanate, based on the gross weight of the crude product, the content of NCO group is 28.8%, and the crude isocyanate product tank imports The filter cleaning cycle is 10 days.

Comparative Example 3

Adopt the process flow diagram shown in Fig. 1, the 300kg/h thick chlorobenzene that produces in the preparation process of diphenylmethane diisocyanate carries out the removal of impurities, and its operation procedure is carried out with reference to embodiment 5, and difference is: step (4 ), the mass flow ratio of the amine compound to the liquid phase stream IV is 0.0005:1.

Based on the total weight of the recovered chlorobenzene, in the recovered chlorobenzene, the total amount of amine-consuming substances was 6738 ppm. Among them, the content of toluene isocyanate (PI) is 192ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 165ppm, the content of phosgene+hydrogen chloride is 68ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to operate in phosgenation reaction operation, in the crude product of production gained diphenylmethane diisocyanate, based on the gross weight of the crude product, the content of NCO group is 29.1%, and the crude isocyanate product tank imports The filter cleaning cycle is 12 days.

Comparative Example 4

Adopt the process flow diagram shown in Fig. 1, the 300kg/h thick chlorobenzene that produces in the preparation process of diphenylmethane diisocyanate carries out the removal of impurities, and its operation procedure is carried out with reference to embodiment 5, and difference is: step (4 ), the mass flow ratio of the amine compound to the liquid stream IV is 0.15:1.

Based on the total weight of the recovered chlorobenzene, the total amount of amine-consuming substances in the recovered chlorobenzene was 120 ppm. Wherein, the content of toluene isocyanate (PI) is 8ppm, the content of 4,4-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate (MDI) is 12ppm, the content of phosgene+hydrogen chloride is 5ppm, The balance is the content of other impurities.

Adopt this recovered chlorobenzene to operate in phosgenation reaction operation, in the crude product of production gained diphenylmethane diisocyanate, based on the gross weight of the crude product, the content of NCO group is 28.6%, and the crude isocyanate product tank imports The filter cleaning cycle is 10 days.

The content of each impurity in each comparative example and embodiment gained recovery solvent, as shown in table 1:

Table 1 Summary table of the contents of various impurities in the recovered solvent

As can be seen from the experimental results in Table 1, the method for removing impurities provided by the invention can reasonably control the content of impurities in the recovered solvent, effectively reducing the total content of amine-consuming substances in the recovered chlorobenzene, thereby reducing the amount of light The formation of by-products in the gasification reaction reduces the risk of clogging of the reaction device in the system, prolongs its stable operation time, and improves product quality at the same time.

In addition, the impurity removal method provided by the present invention can reduce the content of acid gases such as phosgene and hydrogen chloride in the recovered solvent to less than 10 ppm, effectively reducing the risk of equipment corrosion that may be caused after the recovered solvent is returned to the system.

From the results of each example, it can be seen that with the increase of the mass flow ratio of the amine compound to the solvent, the impurity removal effect changes accordingly, and the properties (for example, the viscosity) of the recovered solvent also change accordingly, and the obtained recovered solvent is used for the preparation of During the production of isocyanate, the cleaning cycle of the crude isocyanate product tank inlet filter shows a trend of first increasing and then decreasing. Therefore, the dosage of amine compounds needs to be controlled within a certain range to reduce the risk of system blockage and prolong its stable operation time.

From the results of Comparative Example 1, it can be seen that only a part of low-boiling amine-consuming substances can be removed by rectification treatment, and the impurity removal effect is not good. The total amount of amine-consuming substances in the recovered solvent is very large, which is returned to the system. Afterwards, the risk of equipment blockage may increase, and it is not conducive to the phosgenation reaction.

From the results of Comparative Example 2, it can be seen that the crude solvent is first reacted with amine compounds and then subjected to rectification treatment. Under the condition of the same amount of amine compounds, low-boiling amine consumption substances (for example, phosgene, hydrogen chloride) are due to Without pre-removal, a certain amount of amine compounds will be consumed, which will affect the removal effect of heavy components in amine-consuming substances, and also lead to poor impurity removal effect of amine-consuming substances.

It can be seen from the results of Comparative Example 3 that when the amount of amine compound added is too small, it will also affect the removal effect of heavy components in amine-consuming substances, and also lead to poor removal of impurities from amine-consuming substances.

It can be seen from the results of Comparative Example 4 that when the amount of amine compounds added is too large, although the removal capacity of amine-consuming substances reaches the limit (for example, around 120 ppm), the viscosity of the recovered solvent after treatment increases, As a result, the mixing effect of the materials reused in the phosgenation reaction becomes poor, resulting in an increase in the amount of by-products generated, which in turn leads to a shorter cleaning cycle of the filter.

While some embodiments of the present invention have been described above, the foregoing description is exemplary, not exhaustive, and not limiting of the disclosed embodiments. Numerous modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

A kind of circulating solvent in phosgenation reaction production is characterized in that, comprises: amine consumption class material and the organic solvent used for phosgenation reaction production;

The amine-consuming substances include: one or more of hydrogen chloride, phosgene, substances with NCO groups and substances with COCl groups;

Based on the total weight of the circulating solvent, the content of the amine-consuming substances is 0.2-5000 ppm, preferably 1-2000 ppm, more preferably 10-300 ppm.
Circulating solvent according to claim 1, is characterized in that, described organic solvent is selected from one or more in ethyl isophthalate, benzene, toluene, xylene, chlorobenzene and o-dichlorobenzene, preferably is chlorobenzene and/or o-dichlorobenzene, more preferably chlorobenzene.
A kind of impurity removal method of circulating solvent as claimed in claim 1 and 2, is characterized in that, comprises the following steps:

(1) preheat the crude solvent obtained through preliminary distillation after the phosgenation reaction, then feed into a solvent purification tower (CO1) and carry out rectification treatment;

(2) the top of the solvent purification tower (C01) extracts the gas-phase stream I, and carries out gas-liquid two-phase separation after condensation; the separated gained liquid-phase stream II is all refluxed to the top of the solvent purification tower (CO1) ;

(3) the column still of described solvent refining tower (CO1) extracts liquid-phase stream I and is divided into liquid-phase stream III and liquid-phase stream IV, wherein, liquid-phase stream III is refluxed after reboiler heating To tower still, liquid phase stream IV is extracted and sent to solvent reactor (R01);

(4) in described solvent reactor (R01), add amine compound, react with described liquid-phase material flow IV; Carry out solid-liquid two-phase separation with the material after the reaction, separate gained solid product extraction, separate gained The liquid product is directly reused in the phosgenation reaction process as the circulating solvent.
The method for removing impurities according to claim 3, wherein the temperature of the preheating in step (1) is 80-125°C, preferably 100-110°C.
impurity removal method according to claim 3 or 4, is characterized in that, the feeding position that the described crude solvent of step (1) enters solvent refining tower (C01) is above the first to fifth trays, preferably Above the first to third trays; and/or

The top operating pressure of the solvent purification tower (C01) is 100-200KPa, preferably 120-160KPa; and/or

The operating temperature of the tower kettle of the solvent purification tower (C01) is 120-200°C, preferably 130-160°C; and/or

The solvent purification tower (C01) adopts valve trays, and the number of theoretical plates is 10-50, preferably 20-40.
The method for removing impurities according to any one of claims 3-5, is characterized in that, in step (3), the mass ratio of reboiler circulating capacity and tower still output is 1:1-1:5, It is preferably 1:1-1:3.
The method for removing impurities according to any one of claims 3-6, wherein the amine compound in step (4) is selected from 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane One or more of phenylmethane and 2,2-diaminodiphenylmethane.
The method for removing impurities according to any one of claims 3-7, wherein in step (4), the mass flow ratio of the amine compound to the liquid phase stream IV is 0.001-0.1:1, preferably It is 0.01-0.05:1, more preferably 0.02-0.03:1.
The method for removing impurities according to any one of claims 3-8, characterized in that, in step (4), the residence time of described amine compound and liquid phase stream IV in solvent reactor (R01) is 10 to 60 minutes, preferably 10 to 50 minutes, more preferably 10 to 20 minutes.