Low halogen aliphatic cyclic hydrocarbon content polymeric mdi, and methods of making and using the same

Abstract

The application provides a low-halogen aliphatic cyclic hydrocarbon substance content polymeric MDI and a preparation method and application thereof. The low-halogen aliphatic cyclic hydrocarbon substance content polymeric MDI is applied to polyurethane adhesive, and the open time of the polyurethane adhesive can be improved. The halogen aliphatic cyclic hydrocarbon substance content of the low-halogen aliphatic cyclic hydrocarbon substance content polymeric MDI is less than or equal to 15 ppm, preferably less than or equal to 10 ppm, more preferably less than or equal to 5 ppm, and further preferably less than or equal to 1 ppm.

Description

Technical Field

[0001] This invention relates to the field of polymeric MDI technology, specifically to a polymeric MDI with low halogenated alicyclic hydrocarbon content, its preparation method, and its applications. Background Technology

[0002] Polymethylene polyphenyl polyisocyanate is one of the important raw materials for the preparation of polyurethane, mainly used in the production of rigid polyurethane foam, which is applied in home appliances, cold storage, containers, building insulation materials and other fields. As is well known, its production method generally involves first reacting aniline and formaldehyde with an acid catalyst to produce DAM (a mixture of diaminodiphenylmethane and polyphenyl polymethylene polyamine, abbreviated as polyamine). DAM is then reacted with phosgene in an inert solvent environment through liquid-phase phosgenation to obtain a reaction mixture. After phosgene removal, hydrogen chloride stripping, solvent removal and purification separation, the corresponding pure MDI (diphenylmethane series diisocyanate) and polymeric MDI products (a mixture of diphenylmethane diisocyanate and polyphenyl polymethylene polyisocyanate) can be obtained.

[0003] Currently, the methods disclosed in patents mainly focus on removing phenyl isocyanate impurities (PI) from polymerized MDI products. Many control schemes for reducing PI content have also been proposed in this field. For example, patent application CN114044746A proposes adding a special catalyst during the neutralization process of the DAM reaction solution to reduce the PI precursor impurity content in the final DAM, thereby obtaining isocyanates with low PI content. Patent application CN113474388A proposes adding a PI self-polymerization catalyst to the circulating solvent, catalyzing the self-polymerization of PI in the solvent to generate carbodiimide. The carbodiimide then reacts with MDI in the system to generate urea-ketimide, which ultimately enters the product without affecting its performance. Furthermore, to prevent the catalyst from circulating back into the system to catalyze MDI self-polymerization, a terminator is added to deactivate the catalyst before the solvent is reused. Patent US4405527 describes reducing the PI content in the system by reacting PI in the solvent with a stoichiometric excess of polyamines or glycols to convert it into carbamates or ureas.

[0004] Current methods for improving the quality of polymeric MDI products often require introducing new materials into the system, increasing operating costs and introducing new impurities, which can easily lead to new contamination. Secondly, changes to the existing process inevitably bring other adverse effects that are difficult to assess. Furthermore, none of the aforementioned existing technologies address the control of halogenated alicyclic hydrocarbon impurities in polymeric MDI, nor do they acknowledge the impact of halogenated alicyclic hydrocarbon impurities on the open time of polymeric MDI when used in polyurethane adhesives (e.g., potting compounds). Summary of the Invention

[0005] This invention provides a polymeric MDI with low halogenated alicyclic hydrocarbon content, its preparation method, and its application. This invention provides a polymeric MDI with controlled halogenated alicyclic hydrocarbon content, which, when applied to polyurethane adhesives, can improve the open time of the polyurethane adhesives.

[0006] To achieve its objective, the present invention provides the following technical solution:

[0007] In one aspect, the present invention provides a polymeric MDI with a low content of halogenated alicyclic hydrocarbons, wherein the content of halogenated alicyclic hydrocarbons in the polymeric MDI is ≤15ppm, preferably ≤10ppm, more preferably ≤5ppm, and even more preferably ≤1ppm.

[0008] The content of halogenated alicyclic hydrocarbons in the polymeric MDI is, for example, 0-15 ppm, such as 0 ppm, 0.05 ppm, 0.1 ppm, 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, 10 ppm, 11 ppm, 12 ppm, 13 ppm, 14 ppm or 15 ppm; preferably 0-10 ppm; more preferably 0-5 ppm; even more preferably 0-1 ppm, such as 0 ppm, 0.0001 ppm, 0.001 ppm, 0.01 ppm, 0.05 ppm, 0.1 ppm, 0.3 ppm, 0.5 ppm, 0.7 ppm, 1 ppm, etc.

[0009] In some embodiments, the content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤15 ppm, for example, 0.0001-15 ppm, 0.01-15 ppm, 0.1-15 ppm, 0.5-15 ppm, etc. In some embodiments, the content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤10 ppm, for example, 0.0001-10 ppm, 0.01-10 ppm, 0.1-10 ppm, 0.5-10 ppm, etc. In some embodiments, the content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤5 ppm, for example, 0.0001-5 ppm, 0.01-5 ppm, 0.1-5 ppm, 0.5-5 ppm, etc. In some embodiments, the content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤1 ppm, for example, 0.0001-1 ppm, 0.01-1 ppm, 0.1-1 ppm, 0.5-1 ppm, etc.

[0010] Furthermore, the halocyclic aliphatic hydrocarbon is one or more compounds having the following structural formulas (I) and (II):

[0011]

[0012] In both structural formulas (I) and (II), each R is independently hydrogen, methyl, halomethyl, or halogen, and at least one R in each of structural formulas (I) and (II) is a halogen or halomethyl; that is, the haloalicyclic hydrocarbon of structural formula (I) or (II) contains one or more halogen atoms. In this invention, the content of the haloalicyclic hydrocarbon refers to the sum of the mass percentages of compounds satisfying the above structural formulas (I) and (II) contained in the polymeric MDI.

[0013] Specifically, the halogenated alicyclic hydrocarbons include one or more alicyclic hydrocarbons with mono- or poly-substituted halogen elements. Further, the halogenated alicyclic hydrocarbons are, for example, halomethylcyclohexane, halomethylcyclohexene, or one or more of cyclohexane, cyclohexene, methylcyclohexane, methylcyclohexene, halomethylcyclohexane, and halomethylcyclohexene substituted with one or more halogen elements. Further, the halogen element is, for example, one or two of chlorine and bromine. Specifically, for example, the halogenated alicyclic hydrocarbons include one or more of mono- or poly-halogenated chlorocyclohexane, bromocyclohexane, chlorocyclohexene, and bromocyclohexene.

[0014] In this article, halogenated methyl groups include monohalogenated methyl groups and polyhalogenated methyl groups.

[0015] This invention provides a polymeric MDI with the content of halogenated alicyclic hydrocarbons controlled within a specific low range. The inventors have discovered that halogenated alicyclic hydrocarbons in polymeric MDI can affect its performance in polyurethane adhesives. If the content of halogenated alicyclic hydrocarbons in the polymeric MDI is too high, the open time of the polyurethane adhesive will be too long. By using the polymeric MDI with low halogenated alicyclic hydrocarbon content of this invention in polyurethane adhesives (e.g., potting compounds), the open time of the polyurethane adhesive can be improved. Specifically, it is beneficial to shorten the open time of the polyurethane adhesive; for example, in some embodiments, the open time can be shortened to between 25-36 minutes, thereby improving the application efficiency of the adhesive.

[0016] Currently, the known MDI production process in this field is mainly as follows: First, DAM (polyamine) and phosgene undergo a liquid-phase phosgenation reaction in a solvent to obtain a reaction mixture; then, phosgene is removed from the obtained reaction mixture; next, the phosgene-removed reaction mixture is subjected to stripping heat treatment with HCl gas; the stripped reaction mixture is then heated under negative pressure to remove the solvent; the solvent-removed liquid is further fed into a nitrogen stripping tower for nitrogen stripping treatment to obtain crude MDI; finally, the crude MDI is purified and separated to obtain the corresponding pure MDI and polymeric MDI products. In the prior art, the overhead condensate obtained after condensing the material collected from the top of the nitrogen stripping tower is directly combined with the reaction mixture obtained from the liquid-phase phosgenation reaction and enters the phosgene removal stage. The inventors have discovered that because the outlet temperatures of the phosgenation reaction, dephosgene, hydrogen chloride vaporization, and solvent removal processes are relatively low, only slightly higher than or lower than the boiling point of the solvent (e.g., chlorobenzene) at the operating pressure of the equipment, the components removed in these processes are mainly solvents and other light components, such as phosgene, hydrogen chloride, and carbon tetrachloride. However, the nitrogen stripping process operates at low pressure and high temperature, resulting in a large amount of MDI entrained in the top outlet material of the nitrogen stripping tower. Through research, the inventors have found that most of the halogenated alicyclic hydrocarbons (e.g., chlorocyclohexane, bromocyclohexane, chlorocyclohexene, bromocyclohexene, etc.) are removed during the nitrogen stripping process and subsequently condensed into the top condensate. Only a small amount of halogenated alicyclic hydrocarbons enter the crude MDI. Because the MDI in the top product of the nitrogen stripping tower is of high value, in traditional processes, this stream is directly condensed and recycled back into the system. The inventors have discovered that this will cause halogenated alicyclic hydrocarbon impurities to accumulate in the system during continuous operation of the polymeric MDI preparation process. Most of these impurities will eventually enter the crude MDI and then the polymeric MDI during the purification and separation process, thus affecting the polymeric MDI product and its subsequent applications.

[0017] In addition, since halogenated alicyclic hydrocarbon impurities are relatively stable, they cannot be removed by reaction conversion in existing processes. Furthermore, since the process for preparing polymeric MDI requires unavoidable high-temperature processes, these impurities cannot be eliminated at their source. Therefore, it is quite difficult to remove halogenated alicyclic hydrocarbon impurities using existing polymeric MDI processes.

[0018] This invention also provides a method for preparing polymeric MDI with low halogenated alicyclic hydrocarbon content as described above. Specifically, it is also a method for reducing the halogenated alicyclic hydrocarbon content in polymeric MDI. This method includes the following steps:

[0019] S1. The reaction mixture obtained by liquid-phase phosgenation of polyamine and phosgene in a solvent is subjected to phosgene removal treatment.

[0020] S2. The reaction mixture after step S1 is subjected to stripping heat treatment using hydrogen chloride gas.

[0021] S3. The reaction mixture after step S2 is subjected to solvent removal treatment to obtain a solvent-removed liquid.

[0022] S4. The liquid after solvent removal in step S3 is fed into a nitrogen stripping tower for stripping with nitrogen. The material collected from the top of the nitrogen stripping tower is condensed to obtain the top condensate. Crude MDI is obtained in the bottom of the nitrogen stripping tower. The crude MDI is purified and separated to obtain pure MDI and polymeric MDI.

[0023] S5. The condensate from the top of the column in step S4 is treated to remove halogenated alicyclic hydrocarbons and then sent to step S1 to be mixed with the reaction mixture.

[0024] In the preparation method of the present invention, the condensate at the top of the nitrogen stripping tower is treated to remove halogenated alicyclic hydrocarbons and then sent back to step S1 to be mixed with the reaction mixture before phosgene removal for subsequent processing. This can avoid the accumulation of halogenated alicyclic hydrocarbons in the system and finally obtain polymeric MDI with a low content of halogenated alicyclic hydrocarbons.

[0025] In a preferred embodiment, step S5, the removal treatment of the halogenated alicyclic hydrocarbons, includes the following steps:

[0026] S5a: The condensate from the top of the column is sent to a flash heat exchanger for treatment. The halogenated alicyclic hydrocarbons separated from the condensate enter the gas phase material of the flash heat exchanger. The liquid phase material obtained in the flash heat exchanger is rich in MDI and is sent to step S1 to be mixed with the reaction mixture before phosgene treatment, and then recycled into the process system. Through the above step S5a, the accumulation of toxic and harmful impurities (such as halogenated alicyclic hydrocarbons) in the system can be avoided, effectively reducing the content of halogenated alicyclic hydrocarbons in the final polymeric MDI product, which is beneficial to improving the application performance and application safety of the polymeric MDI product.

[0027] More preferably, the process further includes step S5b: feeding the gaseous material from step S5a into a distillation column for processing to separate the solvent from the gaseous material, obtaining a gaseous solvent portion at the top of the column, and obtaining an impurity portion containing the halogenated alicyclic hydrocarbons at the bottom of the column. This impurity portion also contains some solvent and may contain other impurities. The impurity portion containing the halogenated alicyclic hydrocarbons can be directly sealed for subsequent incineration, avoiding secondary hazards caused by other treatment methods.

[0028] More preferably, in step S5b, the gaseous solvent portion is condensed to obtain condensate. Part of this condensate is sent to a solvent storage tank, where it can be further purified and reused as a solvent in the liquid-phase phosgenation reaction. The remaining condensate from the gaseous solvent portion is returned to the distillation column in step S5b. Through the processing in step S5b, a portion of the solvent can be separated and recovered, reducing solvent loss and lowering production costs.

[0029] In some embodiments, in step S5a, the flash heat exchanger is a rising film evaporator or a falling film evaporator;

[0030] Preferably, when the flash heat exchanger is a rising film evaporator, the operating pressure of the rising film evaporator is 20-60 kPa, for example, 20, 25, 30, 35, 40, 45, 50, 55, or 60 kPa, preferably 30-60 kPa, and more preferably 40-50 kPa; the operating temperature is 80-150℃, for example, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, or 150℃, preferably 90-150℃, and more preferably 110-130℃. Using these preferred process conditions facilitates a more thorough separation of halogenated alicyclic hydrocarbons from the overhead condensate, further reducing the content of halogenated alicyclic hydrocarbons in the polymerized MDI product.

[0031] In a preferred embodiment, in step S5b, the distillation column is a packed column with a theoretical number of 20-50 plates, preferably 25-50 plates, such as 25, 30, 35, 40, 45, 50 plates, etc., more preferably 30-40 plates; the reflux ratio is controlled at 0.2-0.6, such as 0.2, 0.3, 0.4, 0.5, 0.6, etc., preferably 0.4-0.5. Using these preferred process conditions facilitates a more thorough separation of halogenated alicyclic hydrocarbons from the gaseous material obtained in step S5a, further reducing the content of halogenated alicyclic hydrocarbons in the recovered solvent. When the solvent is subsequently recycled into the system, this helps reduce the content of halogenated alicyclic hydrocarbons in the polymerized MDI. In some embodiments, in step S5b, the content of halogenated alicyclic hydrocarbons in the condensate obtained after condensing the gaseous solvent portion can be controlled to <5 ppm. In step S5b, the packing in the distillation column can be the packing conventionally used in the art, such as structured metal packing (M500Y, M452Y, M252Y, etc.) or random metal packing (IR, IMTP, Raschig rings, rectangular saddle rings, Pall rings, etc.), and there are no particular restrictions on this.

[0032] In some embodiments, in step S5b, the distillation column is equipped with a reboiler at the bottom and a condenser at the top.

[0033] In some embodiments, the gas phase fraction at the reboiler outlet is controlled to be between 10-20%, such as 10%, 12%, 15%, 17%, 20%, etc., preferably 10-16%, such as 12-16%.

[0034] In some embodiments, the operating pressure at the top of the distillation column is 25-50 kPa, such as 20 kPa, 25 kPa, 30 kPa, 35 kPa, 40 kPa, 45 kPa, 50 kPa, etc., preferably 30-50 kPa, and more preferably 35-40 kPa; adopting the preferred operating conditions is beneficial to more thoroughly separating the halogenated alicyclic hydrocarbons.

[0035] In some embodiments, the operating temperature of the distillation column reboiler is 100-140°C, such as 100°C, 110°C, 120°C, 130°C, 140°C, etc., preferably 110-130°C; adopting the preferred operating conditions is beneficial to more thoroughly separating the halogenated alicyclic hydrocarbons.

[0036] In some embodiments, the operating temperature of the condenser at the top of the distillation column is 30°C-70°C, preferably 40-50°C.

[0037] In this invention, polyamine refers to a mixture of diaminodiphenylmethane and polyphenylmethylene polyamine (DAM), also known as diphenylmethane series diamines and polyamines. The preparation of the reaction mixture by liquid-phase phosgenation of polyamines and phosgene in a solvent can be carried out using conventional processes in this technical field, and this invention does not impose any particular limitations on this. Numerous documents describe in detail the preparation of polymeric MDI by liquid-phase phosgenation of polyamines and phosgene in a solvent, such as CN116217439A, CN111961185B, CN108147979B, CN116034102A, CN104755458B, CN111170891B, etc. In some embodiments, the solvent used for the liquid-phase phosgenation reaction is, for example, one or more of chlorobenzene, dichlorobenzene, diethyl carbonate, and cyclohexanone, preferably chlorobenzene. In some embodiments, for reference, the conditions for carrying out the liquid-phase phosgenation reaction include: a reaction temperature of 60-160°C, a reaction pressure of 2-30 bar, a mass ratio of polyamine to solvent of 1:(1.1-5), and a mass ratio of polyamine to phosgene of 1:(1.1-5).

[0038] The main improvement in the preparation method of this invention lies in the fact that, in step S5, the overhead condensate obtained from the condensation of the material collected from the top of the nitrogen stripping tower is treated to separate the halogenated alicyclic hydrocarbons therein. After the halogenated alicyclic hydrocarbons are separated, the material is returned to step S1, thereby entering the process system. The corresponding process operations and conditions in steps S1-S4 of the preparation method of this invention can all be carried out using conventional process operations and conditions in the art, and there are no particular limitations.

[0039] In some embodiments, in step S1, the phosgene removal process is to heat-treat the reaction mixture to remove phosgene; preferably, the temperature of the heat treatment is 100-150°C, such as 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, etc.

[0040] In some embodiments, in step S2, the temperature for stripping heat treatment with hydrogen chloride gas is 100-200°C, such as 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, etc., and the residence time is preferably 1-20 min, such as 1 min, 5 min, 10 min, 15 min, 20 min. The mass ratio of hydrogen chloride to the reaction mixture is 0.01-0.1, such as 0.01, 0.05, 0.1, etc.

[0041] In some embodiments, in step S3, the solvent removal process is to remove the solvent by heating under negative pressure, preferably under operating pressure of 20-50 kPa (e.g., 20 kPa, 30 kPa, 40 kPa, 50 kPa, etc.) and temperature of 120-240°C (e.g., 120°C, 150°C, 200°C, 240°C, etc.).

[0042] In some embodiments, in step S4, the operating pressure of the nitrogen stripping tower is 20-60 kPa, for example, 20 kPa, 30 kPa, 40 kPa, 50 kPa, or 60 kPa; the temperature is 150-230°C, for example, 150°C, 180°C, 200°C, or 230°C; the mass ratio of nitrogen to the liquid after solvent removal (stripping mass ratio) is 0.005-0.1, for example, 0.005, 0.01, 0.05, or 0.1. The temperature at which the overhead gas phase at the top of the nitrogen stripping tower condenses is 20-60°C, for example, 20°C, 30°C, 40°C, 50°C, or 60°C.

[0043] Unless otherwise specified, all pressures mentioned in this invention refer to absolute pressure.

[0044] In some embodiments, the purification and separation of crude MDI in step S4 is carried out in a distillation column. The process conditions of the distillation column include, for example, controlling the bottom temperature at 180-250°C, such as 180°C, 200°C, 230°C, 250°C, etc., and controlling the top pressure at 10-1000Pa, such as 10Pa, 50Pa, 100Pa, 1000Pa, etc., and obtaining polymerized MDI product in the bottom of the column.

[0045] In some embodiments, in step S4, the content of the halogenated alicyclic hydrocarbon in the overhead condensate is between 10 and 10,000 ppm.

[0046] By using the above-described preparation method of the present invention, the content of halogenated alicyclic hydrocarbons in polymeric MDI can be reduced, and polymeric MDI with a halogenated alicyclic hydrocarbon content that meets the required requirements can be obtained.

[0047] As mentioned earlier, some impurities are inevitably generated during the DAM production process. After phosgenation, hydrogen chloride vaporization, and high-temperature treatment during the solvent removal stage, halogenated alicyclic hydrocarbons (HALs) are generated. The inventors have discovered that because some substances have boiling points higher than or close to those of the solvent (e.g., chlorobenzene), complete removal during solvent removal is not possible, resulting in a small amount of HALs entering the polymeric MDI product. On the one hand, these substances are generally volatile; therefore, in downstream applications, if the temperature is too high, they will volatilize into the environment, posing a potential safety risk. On the other hand, the inventors have found that these substances affect the product's application performance, particularly the open time (operable time) after the reaction of polymeric MDI with white materials (polyether polyols, etc.) in downstream potting compounds. Excessive content of these impurities leads to an excessively long open time, affecting process operation and reducing construction efficiency. Therefore, reducing the content of HALs in polymeric MDI products is beneficial for improving the downstream application performance and safety of polymeric MDI products and reducing their environmental impact.

[0048] This invention also provides a method for improving the open time of a polyurethane adhesive, wherein the raw material used in the polyurethane adhesive includes polymeric MDI, and the content of halogenated alicyclic hydrocarbons in the polymeric MDI is controlled to be ≤15ppm, preferably ≤10ppm, more preferably ≤5ppm, and even more preferably ≤1ppm. The inventors have found that by controlling the content of halogenated alicyclic hydrocarbons in the polymeric MDI used in the polyurethane adhesive to meet the above requirements, it is beneficial to improve the open time of the polyurethane adhesive. Specifically, for example, it can prevent the open time from becoming too long. Compared with polymeric MDI whose halogenated alicyclic hydrocarbon content does not meet the above requirements, the open time can be shortened, improving construction efficiency, for example, reducing the open time to between 25-36 minutes.

[0049] Furthermore, the halocyclic aliphatic hydrocarbon is one or more compounds having the following structural formulas (I) and (II):

[0050]

[0051] In both structural formulas (I) and (II), each R is independently hydrogen, methyl, halomethyl or halogen, and at least one R in each of structural formulas (I) or (II) is a halogen or halomethyl.

[0052] Specifically, for example, the haloallicyclic hydrocarbon is halomethylcyclohexane, halomethylcyclohexene, or one or more of cyclohexane, cyclohexene, methylcyclohexane, methylcyclohexene, halomethylcyclohexane, and halomethylcyclohexene that are substituted by one or more halogen elements.

[0053] For example, the halogen element is one or both of chlorine and bromine.

[0054] Specifically, for example, in some embodiments, the halogenated alicyclic hydrocarbon includes one or more of monohalogenated or polyhalogenated chlorocyclohexane, bromocyclohexane, chlorocyclohexene, bromocyclohexene, etc.

[0055] In some embodiments, in the method for improving the open time of the polyurethane adhesive, the content of halogenated alicyclic hydrocarbons in the polymeric MDI used is controlled to be 0-15 ppm, for example, 0 ppm, 0.05 ppm, 0.1 ppm, 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, 10 ppm, 11 ppm, 12 ppm, 13 ppm, 14 ppm, or 15 ppm; preferably 0-10 ppm; more preferably 0-5 ppm; and even more preferably 0-1 ppm, for example, 0 ppm, 0.0001 ppm, 0.001 ppm, 0.01 ppm, 0.05 ppm, 0.1 ppm, 0.3 ppm, 0.5 ppm, 0.7 ppm, 1 ppm, etc.

[0056] In some embodiments, the method for improving the open time of the polyurethane adhesive controls the content of halogenated alicyclic hydrocarbons in the polymeric MDI used to be >0 and ≤15 ppm, for example, 0.0001-15 ppm, 0.01-15 ppm, 0.1-15 ppm, 0.5-15 ppm, etc. In some embodiments, the content of halogenated alicyclic hydrocarbons in the polymeric MDI used to be >0 and ≤10 ppm, for example, 0.0001-10 ppm, 0.01-10 ppm, 0.1-10 ppm, 0.5-10 ppm, etc. In some embodiments, the content of halogenated alicyclic hydrocarbons in the polymeric MDI used to be >0 and ≤5 ppm, for example, 0.0001-5 ppm, 0.01-5 ppm, 0.1-5 ppm, 0.5-5 ppm, etc. In some embodiments, the content of halogenated alicyclic hydrocarbons in the polymeric MDI used is controlled to be >0 and ≤1ppm, for example 0.0001-1ppm, 0.01-1ppm, 0.1-1ppm, 0.5-1ppm, etc.

[0057] In the method for improving the open time of polyurethane adhesives provided by the present invention, the polymeric MDI used can be prepared by the method for preparing polymeric MDI with low halogenated alicyclic hydrocarbon content described above.

[0058] Specifically, the raw materials of the polyurethane adhesive include component A (black component) and component B (white component), wherein component A includes at least the polymeric MDI as the black component; and component B includes at least a polyether polyol as the white component. The formulation of the polymeric MDI-based polyurethane adhesive (including but not limited to the selection and dosage of each component) can adopt conventional compositions in the art and is not particularly limited thereto. The key to this invention is to control the content of halogenated alicyclic hydrocarbons in the polymeric MDI used in this type of polyurethane adhesive to meet the specific requirements of this invention, thereby achieving the purpose of improving open time.

[0059] In some implementations, as an example, the mass ratio of component A to component B is 1:(1-10), such as 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0060] In some implementations, as an example, in addition to polyether polyols, other components permitted in the field of polyurethane adhesives may be added to component B, such as, but not limited to, flame retardants, plasticizers, antioxidants, modifiers, defoamers, grafting agents, etc. The amount of these components may be determined according to the application requirements. In some examples, for instance, the mass percentage of these components in component B is less than 0.5%.

[0061] The polyether polyol used in polyurethane adhesives can be any type of polyether polyol commonly used in the art, and there are no particular limitations. For example, the polyether polyol in component B can be one or more of polyethylene oxide polyol, polypropylene oxide polyol, polytetrahydrofuran and its coether polyols, etc., and the molar mass of the polyether polyol can be, for example, 200-10000 g / mol.

[0062] As those skilled in the art will know, the above-mentioned polyurethane adhesives can be applied, for example, in the fields of electronics and electrical appliances, aerospace equipment, medical industry, and construction.

[0063] In this text, "open time" refers to the time interval from when the polyurethane adhesive is applied to the surface of the bonded object until the adhesive can no longer be used for effective application. Effective application includes brushing, rolling, or transferring the adhesive to another bonded object. The effective time for these operations is called open time. In other words, open time can also be understood as the maximum time that the polyurethane adhesive can be left in the air after being applied to the bonded object before the bonded object is bonded.

[0064] In another aspect, the present invention provides a polyurethane adhesive comprising component A and component B, wherein component A comprises at least the polymeric MDI described above, and component B comprises at least a polyether polyol. Preferably, the mass ratio of component A to component B is 1:1-10. Further descriptions of the polyurethane adhesive can be found in the corresponding descriptions in the preceding description of the method for improving the open time of polyurethane adhesives, and will not be repeated here.

[0065] The technical solution provided by this invention has the following beneficial effects:

[0066] 1) This invention provides a polymeric MDI with controlled content of low-halogenated alicyclic hydrocarbons. When using the polymeric MDI provided by this invention in polyurethane adhesives, compared with using polymeric MDI without controlled content of low-halogenated alicyclic hydrocarbons, the open time can be significantly improved, the excessively long open time can be shortened, and the construction efficiency can be improved.

[0067] 2) The method for preparing polymeric MDI with low halogenated alicyclic hydrocarbon content provided by this invention involves separately treating the overhead condensate of the nitrogen stripping tower during the polymeric MDI production process to separate MDI, solvent, and halogenated alicyclic hydrocarbon impurities. The separated MDI-rich stream is recycled back to the system, while the solvent can be stored in a solvent storage tank for subsequent reuse. The concentrated portion containing halogenated alicyclic hydrocarbon impurities is not reintroduced into the process system. The solution proposed in this invention features a simple process flow and operation, minimal modifications to existing processes, low modification difficulty, and no adverse effects on existing processes. Furthermore, this solution avoids the accumulation of halogenated alicyclic hydrocarbon impurities in the system, effectively reducing the content of halogenated alicyclic hydrocarbon impurities in the produced polymeric MDI. This allows the content of halogenated alicyclic hydrocarbon impurities in the polymeric MDI to be controlled within the required range, improving the application performance of the polymeric MDI product and the safety of downstream applications.

[0068] 3) The method for preparing polymeric MDI with low halogenated alicyclic hydrocarbon content provided by the present invention has the characteristics of simple process, low operating cost and easy operation. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of a process for removing halogenated alicyclic hydrocarbon impurities in one embodiment.

[0070] Among them, E1 is the flash heat exchanger, E2 is the top condenser, E3 is the bottom reboiler, C1 is the distillation column, P1 is the reboiler circulation and collection pump, and D1 is the storage tank for halogenated alicyclic hydrocarbon impurities. Detailed Implementation

[0071] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0072] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0073] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0074] Method for detecting the content of halogenated alicyclic hydrocarbons: The sample to be tested is diluted 10 times by mass with dichloromethane and then analyzed directly by gas chromatography. The determination conditions are as follows:

[0075] Gas chromatograph: Agilent 7890A, column HP-5 (30m × 0.25um × 320μm). Chromatographic conditions: Column temperature: 50℃ for 0.5min, ramp up to 80℃ at 5℃ / min and hold for 1min; ramp up to 280℃ at 10℃ / min and hold for 10min; Injector temperature: 280℃, detector temperature: 295℃; Septum purge gas flow rate: 3.0mL / min; Carrier gas (nitrogen) flow rate: 3mL / min; Air flow rate: 350mL / min; Hydrogen flow rate: 35mL / min; Make-up gas (nitrogen) flow rate: 25mL / min; Split injection, split ratio 1:10, injection volume 0.5μL.

[0076] In the following examples, the content of halogenated alicyclic hydrocarbons refers to the sum of the mass contents of chlorocyclohexane, bromocyclohexane, chlorocyclohexene, and bromocyclohexene, wherein the halogenated alicyclic hydrocarbons include corresponding compounds of monohalogenated and polyhalogenated forms.

[0077] Open time test method for potting compound: Measured using an Ecori GT-2 gel time tester. After mixing components A and B, add the mixture to a test tube immediately and perform the following operations: Immerse the test tube in a constant temperature dish; insert a stirring glass rod into the test tube, connecting the rod to a torsion wire driven by a synchronous motor at a rotation speed of 1 rpm. Start timing, and the gel time tester monitors the test process until the gel point is reached; the displayed gel time is the open time.

[0078] Raw material description:

[0079] Diphenylmethane series diamines and polyamines (DAM): Wanhua Chemical (Ningbo) Co., Ltd., purity >99.99%; Specifically, the DAM preparation method is as follows: Aniline and 32wt% hydrochloric acid are mixed at a molar ratio of 1:0.3 at 60℃ and 1 bar to generate aniline hydrochloride. Then, it is reacted with formaldehyde (molar ratio of formaldehyde to aniline is 0.4:1) at 120℃ for 2 hours. After condensation and transposition, the transposition liquid is obtained, which is neutralized with 32wt% sodium hydroxide aqueous solution. After washing with water, the polyamine is obtained. DAM is obtained by distillation stripping at 200℃ and 10 kPa.

[0080] Chlorobenzene: Wanhua Chemical (Ningbo) Co., Ltd., purity >99.9%.

[0081] Phosgene: Wanhua Chemical (Ningbo) Co., Ltd., purity >95.0%.

[0082] Polyether polyol: Hydrophobic polyether polyol D3201, manufactured by Dow Chemical.

[0083] Example 1

[0084] A mixture of diphenylmethane-based diamines and polyamines (DAM) with chlorobenzene was prepared to obtain a 30 wt% amine concentration. A 60 wt% phosgene-chlorobenzene solution (DAM to phosgene mass ratio of 1:2.4) was added to the mixture, and the reaction was carried out at 3 barg and 100 °C for 1 h to obtain a reaction mixture. Phosgene was then removed from the reaction mixture at 0.1 MPa and 135 °C. Following this, the mixture was stripped with hydrogen chloride at 180 °C, with a HCl to HCl mass ratio of 0.05 and a residence time of 5 min. The stripped reaction mixture was then subjected to dechlorobenzene treatment at 35 kPa and 205 °C. The dechlorobenzene-treated MDI (i.e., the reaction solution after solvent removal) was then fed into a nitrogen stripping tower at 40 kPa and 200 °C, with the nitrogen to desolventized reaction solution mass ratio controlled at 0.03.

[0085] The material collected from the top of the nitrogen stripping column is condensed to obtain the top condensate, which contains 1000 ppm of halogenated alicyclic hydrocarbons. This top condensate is sent to a rising film evaporator E1 for processing at an operating pressure of 40 kPa and a temperature of 120 °C. The liquid phase is then fed into a phosgene removal stage to mix with the reaction mixture obtained before phosgene removal. The gaseous material obtained from the rising film evaporator E1 is then fed into a distillation column C1. This distillation column C1 is a packed column using Sulzer M452Y structured metal packing with 40 theoretical plates and a reflux ratio of 0.5. The column C1 has a reboiler E3 at the bottom and a condenser E2 at the top. The operating pressure at the top of the distillation column C1 is 35 kPa, the bottom temperature is 120 °C, the vapor fraction at the outlet of the reboiler E3 is 10%, and the operating temperature of the condenser E2 is 45 °C. The top of distillation column C1 produces vaporous chlorobenzene. This vaporous chlorobenzene is condensed at 45°C, and a portion of the resulting chlorobenzene condensate is sent to a crude chlorobenzene storage tank, while the remainder is refluxed back into distillation column C1. The chlorobenzene condensate contains 0.5 ppm of halogenated alicyclic hydrocarbons. The portion of the chlorobenzene condensate containing these halogenated alicyclic hydrocarbons, collected from the bottom of distillation column C1, enters a halogenated alicyclic hydrocarbon impurity storage tank D1.

[0086] The crude MDI (chlorobenzene content of 800 ppm) obtained from the bottom of the nitrogen stripping column is sent to the downstream distillation column for purification. The process conditions of the distillation column are a top pressure of 20 Pa and a bottom temperature of 200 °C. Polymerized MDI product is obtained from the bottom of the distillation column.

[0087] The content of halogenated alicyclic hydrocarbons in the polymeric MDI product prepared by the process in Example 1 is 1 ppm.

[0088] The polymeric MDI prepared in Example 1 was used to formulate a potting compound, wherein component A (black component) was the polymeric MDI prepared in Example 1, and component B (white component) was a polyether polyol. Component A and component B were mixed at a mass ratio of 1:5, and the open time of the potting compound was measured to be 30 min.

[0089] Example 2

[0090] The procedure was carried out in accordance with Example 1, except that some process conditions were changed. Specifically, the operating pressure of the rising film evaporator was adjusted to 20 kPa and the temperature to 80°C; the number of theoretical plates in the distillation column used to process the gaseous material from the rising film evaporator was 20, the reflux ratio was 0.2, the operating pressure at the top of the distillation column was 25 kPa, and the bottom temperature was 130°C. All other operations were the same as in Example 1.

[0091] Results: In Example 2, the content of halogenated alicyclic hydrocarbons in the chlorobenzene condensate was 50 ppm, and the content of halogenated alicyclic hydrocarbons in the final polymeric MDI product was 12 ppm.

[0092] The polymeric MDI prepared in Example 2 was used to prepare potting compound according to the procedure in Example 1, and the open time of the resulting potting compound was measured to be 36 min.

[0093] Example 3

[0094] The procedure was carried out in accordance with Example 1, except that some process conditions were modified. Specifically, the operating pressure of the rising film evaporator was adjusted to 35 kPa and the temperature to 105°C; the number of theoretical plates in the distillation column used to process the gaseous material from the rising film evaporator was 30, the reflux ratio was 0.3, the operating pressure at the top of the distillation column was 25 kPa, and the bottom temperature was 130°C. All other operations were the same as in Example 1.

[0095] Results: In Example 3, the content of halogenated alicyclic hydrocarbons in the chlorobenzene condensate was 30 ppm, and the content of halogenated alicyclic hydrocarbons in the final polymeric MDI product was 8 ppm.

[0096] The polymeric MDI prepared in Example 3 was used to prepare potting compound according to the procedure in Example 1, and the open time of the resulting potting compound was measured to be 34 min.

[0097] Example 4

[0098] The procedure was carried out in accordance with Example 1, except that some process conditions were changed. Specifically, the operating pressure of the rising film evaporator was adjusted to 35 kPa and the temperature was adjusted to 110°C; the theoretical plate number of the distillation column used to process the gaseous material from the rising film evaporator was 35, and the reflux ratio was 0.4. All other operations were the same as in Example 1.

[0099] Results: In Example 4, the content of halogenated alicyclic hydrocarbons in the chlorobenzene condensate was 5 ppm, and the content of halogenated alicyclic hydrocarbons in the final polymeric MDI product was 2 ppm.

[0100] The polymeric MDI prepared in Example 4 was used to prepare potting compound according to the procedure in Example 1, and the open time of the resulting potting compound was measured to be 32 min.

[0101] Comparative Example 1

[0102] A mixture of diphenylmethane-based diamines and polyamines (DAM) with chlorobenzene was prepared to obtain a 30 wt% amine concentration. A 60 wt% phosgene-chlorobenzene solution (DAM to phosgene mass ratio 1:2.4) was added to the mixture, and the reaction was carried out at 3 barg and 100 °C for 1 h to obtain a reaction mixture. Phosgene was then removed from the reaction mixture at 0.1 MPa and 135 °C, followed by stripping with hydrogen chloride at 180 °C (HCl to reaction mixture mass ratio 0.05, residence time 5 min). The stripped reaction mixture was then subjected to further treatment at 35 kPa and 205 °C. The MDI after dechlorobenzene treatment (i.e., the reaction liquid after solvent removal) is sent to a nitrogen stripping tower for treatment at 40 kPa and 200°C, with the mass ratio of nitrogen to the reaction liquid after solvent removal controlled at 0.03. The material collected from the top of the nitrogen stripping tower is condensed to obtain the top condensate, which is directly sent to the phosgene removal stage to be mixed with the reaction mixture before phosgene removal. The crude MDI (chlorobenzene content of 800 ppm) obtained from the bottom of the nitrogen stripping tower is sent to a distillation tower for purification. The process conditions of the distillation tower are a top pressure of 20 Pa and a bottom temperature of 200°C. Polymerized MDI product is obtained from the bottom of the distillation tower.

[0103] Results: The content of halogenated alicyclic hydrocarbons in the obtained polymeric MDI product was 20 ppm. The polymeric MDI obtained in Comparative Example 1 was used to prepare potting compound according to the procedure in Example 1, and the open time of the resulting potting compound was measured to be 40 min.

[0104] As can be seen from the above experimental results, in the embodiments of the present invention, the content of halogenated alicyclic hydrocarbons in the obtained polymeric MDI is controlled to be below 15 ppm. Compared with Comparative Example 1, its application in potting compound can shorten the open time from 40 min in Comparative Example 1 to between 25-36 min, achieving both good workability and construction efficiency. Preferably, in Examples 1-4, the content of halogenated alicyclic hydrocarbons in the polymeric MDI is 1, 12, 8, and 2 ppm, respectively, and the open times of the resulting potting compounds are 30, 36, 34, and 32 min, respectively, all around 30 minutes. It can be seen that the lower the content of halogenated alicyclic hydrocarbons, the more significant the reduction in open time, which is still within the range of 25-36 min.

[0105] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing polymeric MDI with low halogenated alicyclic hydrocarbon content, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is ≤15ppm; the halogenated alicyclic hydrocarbons are one or more compounds having the following structural formulas (I) and (II): (AND), (II); In both structural formulas (I) and (II), each R is independently hydrogen, methyl, halomethyl or halogen, and at least one R in each structural formula (I) or (II) is a halogen or halomethyl. The preparation method includes the following steps: S1. The reaction mixture obtained by liquid-phase phosgenation of polyamine and phosgene in a solvent is subjected to phosgene removal treatment. S2. The reaction mixture after step S1 is subjected to stripping heat treatment using hydrogen chloride gas. S3. The reaction mixture after step S2 is subjected to solvent removal treatment to obtain a solvent-removed liquid. S4. The liquid after solvent removal in step S3 is fed into a nitrogen stripping tower for stripping with nitrogen. The material collected from the top of the nitrogen stripping tower is condensed to obtain the top condensate. Crude MDI is obtained in the bottom of the nitrogen stripping tower. The crude MDI is purified and separated to obtain pure MDI and polymeric MDI. S5. The condensate from the top of the column in step S4 is treated to remove halogenated alicyclic hydrocarbons before being sent to step S1 to be mixed with the reaction mixture; the removal of halogenated alicyclic hydrocarbons includes the following steps: S5a. The condensate from the top of the column is sent to a flash heat exchanger for processing. The halogenated alicyclic hydrocarbons separated from the condensate from the top of the column enter the gas phase material. The liquid phase material obtained from the flash heat exchanger is sent to step S1 to be mixed with the reaction mixture. The flash heat exchanger is a rising film evaporator, and the operating pressure of the rising film evaporator is 20-60 kPa, and the operating temperature is 80-150℃.

2. The method for preparing polymeric MDI according to claim 1, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is ≤10ppm.

3. The method for preparing polymeric MDI according to claim 2, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is ≤5ppm.

4. The method for preparing polymeric MDI according to claim 3, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is ≤1 ppm.

5. The method for preparing polymeric MDI according to claim 1, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤15ppm.

6. The method for preparing polymeric MDI according to claim 5, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤10ppm.

7. The method for preparing polymeric MDI according to claim 6, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤5ppm.

8. The method for preparing polymeric MDI according to claim 7, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤1ppm.

9. The method for preparing polymeric MDI according to claim 1, characterized in that, The halogen element is one or both of chlorine and bromine.

10. The preparation method according to claim 1, characterized in that, It also includes step S5b: feeding the gaseous material from step S5a into a distillation column for processing to separate the solvent from the gaseous material, obtaining the gaseous solvent portion at the top of the column, and obtaining the impurity portion containing the halogenated alicyclic hydrocarbons at the bottom of the column.

11. The preparation method according to claim 10, characterized in that, In step S5b, the gaseous solvent is partially condensed to obtain condensate, and a portion of the condensate is sent to a solvent storage tank.

12. The preparation method according to claim 1, characterized in that, In step S5a, the operating pressure of the rising film evaporator is 30-60 kPa and the operating temperature is 90-150 °C.

13. The preparation method according to claim 12, characterized in that, In step S5a, the operating pressure of the rising film evaporator is 40-50 kPa and the operating temperature is 110-130℃.

14. The preparation method according to claim 10, characterized in that, In step S5b, the distillation column is a packed column with a theoretical number of 20-50 packing plates; the reflux ratio is controlled at 0.2-0.

6.

15. The preparation method according to claim 14, characterized in that, In step S5b, the distillation column is a packed column with a theoretical number of 25-50 packing plates and a reflux ratio controlled at 0.4-0.

5.

16. The preparation method according to claim 15, characterized in that, In step S5b, the distillation column is a packed column with a theoretical number of 30-40 packing plates.

17. The preparation method according to claim 14, characterized in that, In step S5b, the distillation column is equipped with a reboiler at the bottom and a condenser at the top.

18. The preparation method according to claim 17, characterized in that, The gas phase fraction at the reboiler outlet is controlled to be between 10-20%; The operating pressure at the top of the distillation column is 25-50 kPa; The operating temperature of the distillation column reboiler is 100-140℃; The operating temperature of the condenser at the top of the distillation column is 30℃-70℃.

19. The preparation method according to claim 18, characterized in that, The gas phase fraction at the reboiler outlet is controlled to be between 10% and 16%. The operating pressure at the top of the distillation column is 30-50 kPa; The operating temperature of the distillation column reboiler is 110-130℃; The operating temperature of the condenser at the top of the distillation column is 40-50℃.

20. The preparation method according to claim 19, characterized in that, The operating pressure at the top of the distillation column is 35-40 kPa.

21. The preparation method according to claim 1, characterized in that, In step S1, the phosgene removal process involves heat-treating the reaction mixture to remove phosgene, and the heat treatment temperature is 100-150℃. In step S2, the temperature for stripping heat treatment with hydrogen chloride gas is 100-200℃, and the mass ratio of hydrogen chloride to the reaction mixture is 0.01-0.

1. In step S3, the solvent removal process is carried out under operating conditions of 20-50 kPa pressure and 120-240°C temperature; In step S4, the operating pressure of the nitrogen stripping tower is 20-60 kPa, the temperature is 150-230℃, and the mass ratio of nitrogen to the liquid after solvent removal is 0.005-0.

1. The solvent used for the liquid-phase phosgenation reaction is one or more of chlorobenzene, dichlorobenzene, diethyl carbonate, and cyclohexanone.

22. The preparation method according to claim 21, characterized in that, In step S2, the residence time for the stripping heat treatment with hydrogen chloride gas is 1-20 min.

23. The preparation method according to claim 10, characterized in that, In step S4, the content of the haloallocyclic hydrocarbon in the condensate at the top of the column is between 10 and 10,000 ppm. And / or, in step S5b, the content of the haloallocyclic hydrocarbon in the condensate obtained after the gaseous solvent is condensed is <5 ppm.

24. A method for improving the open time of a polyurethane adhesive, wherein the raw material used in the polyurethane adhesive includes polymeric MDI, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymerized MDI is controlled to be ≤15ppm; The halocyclic alicyclic hydrocarbon is one or more compounds having the following structural formulas (I) and (II): (AND), (II); In both structural formulas (I) and (II), each R is independently hydrogen, methyl, halomethyl or halogen, and at least one R in each of structural formulas (I) or (II) is a halogen or halomethyl.

25. The method according to claim 24, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is controlled to be ≤10ppm.

26. The method according to claim 25, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is controlled to be ≤5ppm.

27. The method according to claim 26, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is controlled to be ≤1ppm.

28. The method according to claim 24, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤15ppm.

29. The method according to claim 28, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤10ppm.

30. The method according to claim 29, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤5ppm.

31. The method according to claim 29, characterized in that, The content of halogenated alicyclic hydrocarbons in the polymeric MDI is >0 and ≤1ppm.

32. The method according to claim 24, characterized in that, The halogen element is one or both of chlorine and bromine.

33. The method according to claim 24, characterized in that, The raw materials of the polyurethane adhesive include component A and component B, wherein component A includes at least the polymeric MDI; component B includes at least the polyether polyol; and the mass ratio of component A to component B is 1:1-10.

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