Process and system for the preparation of biuret polyisocyanate compositions

Abstract

The application provides a preparation method of biuret polyisocyanate composition, comprising the following steps: (1) biuret polyisocyanate composition is prepared by biuretization reaction of diisocyanate and water vapor in a reaction kettle, and tail gas is output; (2) the tail gas obtained in step (1) is first condensed, and condensate and non-condensable gas are output; (3) the condensate obtained in step (2) is sequentially subjected to water removal, preheating and breaking, and then is sent back to the reaction kettle for recycling; (4) the reaction liquid output from the reaction kettle is subjected to distillation separation, and unreacted diisocyanate in the reaction liquid is removed, so that biuret polyisocyanate composition product is obtained. A preparation system for the foregoing preparation method is also provided. The preparation method and the preparation system can avoid the problems of tail gas pipeline blockage and reaction kettle pollution caused by tail gas, and the turbidity of the obtained product is smaller.

Description

Technical Field

[0001] This invention belongs to the field of chemical equipment and chemical raw materials, specifically relating to a method and system for preparing biuret polyisocyanate compositions. Background Technology

[0002] Polyurethane synthetic materials are high-performance polymer compounds obtained by reacting isocyanates and polyols. Products prepared from biuret polyisocyanate compositions obtained from aliphatic or alicyclic isocyanates have been widely used in automotive original paints, automotive refinish paints, plastic coatings, anti-corrosion coatings, wood coatings, and industrial coatings due to their excellent mechanical wear resistance, good flexibility, strong adhesion, and excellent chemical resistance.

[0003] Biuret polyisocyanate compositions can be prepared by reacting polyisocyanates with water, amines, or water donors (such as tert-butanol, formic acid, hydrogen sulfide, crystalline hydrates, etc.), resulting in a mixture with a specific molecular weight distribution. Bayer's patent DE1101394, issued in 1958, disclosed a method for preparing biuret polyisocyanate compositions. Since then, the synthesis process for biuret polyisocyanate compositions has been continuously developed and improved. The published document "The Synthesis of Aliphatic Polyisocyanates Containing Biuret, Isocyanurate or Uretdione Backbones for Use in Coatings" (J. Prakt. Chem. 336, 1994, 185-200) discloses further possible preparation methods and discusses the advantages and disadvantages of these specific methods.

[0004] Previous research indicates that the industrial production of biuret polyisocyanates can be broadly divided into two methods: one is the so-called aqueous method, in which diisocyanate reacts with excess water or a water donor to produce urea, and the urea then reacts with excess diisocyanate to produce biuret; the second is the so-called amine method, in which diisocyanate and amine react to produce urea, and the urea then reacts with excess diisocyanate to produce biuret.

[0005] However, both methods currently have some obvious problems in the industrial production of biuret polyisocyanates. When preparing biuret polyisocyanate compositions by water method, a large amount of carbon dioxide gas is produced as a byproduct. When the exhaust gas is discharged, it carries HDI and water vapor. The two react in the exhaust gas pipeline to form polyurea. The polyurea produced will block the condenser and exhaust pipe. If it flows back to the reactor, it will cause reactor pollution, shorten the operating cycle, and cause the product to turn white and have high turbidity.

[0006] The preparation of biuret polyisocyanate compositions using the amine method typically involves high reaction temperatures. For example, US4264519 discloses a process for preparing biuret polyisocyanate compositions using the amine method, in which diamine is rapidly added to diisocyanate under high pressure through a specific nozzle, with a reaction temperature exceeding 180°C. This high reaction temperature leads to a higher color intensity in the final product. Because amines and isocyanates are highly reactive, their reaction is difficult to control. Therefore, the amine method heavily relies on high-intensity reaction mixers. A decrease in mixing efficiency results in frequent reactor contamination and clogging. Thus, improving the operational stability of the reaction system while maintaining product quality is a key research focus for those skilled in the art.

[0007] US4028392A discloses the reaction of water with isocyanates in the presence of hydrophilic organic solvents (such as trialkyl phosphates and ethylene glycol methyl ether acetate). European patent EP0259233A2 discloses the addition of methyl and / or ethyl phosphates and alkoxyalkyl carboxylic acids as solubilizers during the reaction of water with isocyanates. A common drawback of these two patents is that the solvents or solvent mixtures used in the process can make the final product turbid, and a complex distillation process is required to remove the solvent, leading to a decrease in separation efficiency.

[0008] CN101072805B discloses a method for preparing colorless polyisocyanates containing biuret groups and which are stable in storage from di- or polyisocyanates using water and / or water vapor as biuretizing agents. This method solves the problem of water dispersion by using water vapor. However, although the loss of HDI is reduced to some extent by using cold HDI to wash the tail gas, the polyurea generated by the reaction of HDI with the moisture in the tail gas will still cause blockage of the tail gas pipeline and contamination of the reaction vessel. At the same time, it will also make the obtained product more turbid.

[0009] CN103709076B discloses a method for the continuous preparation of biuret polyisocyanate. In this method, a mixed solution of diisocyanate and catalyst, along with water vapor, reacts in a first reactor in the form of an aerosol. The reaction product then enters a second reactor for further reaction. The tail gas from the second reactor is condensed and refluxed, while the non-condensable gas enters a tail gas treatment unit. The reaction liquid in the second reactor then enters a third reactor for a ripening reaction to remove unconverted diisocyanate and obtain the product. This method suffers from high energy consumption in aerosol preparation and difficulty in industrialization. Furthermore, the reaction rate is low due to the reaction mechanism limitations caused by the mixed solution of diisocyanate and catalyst reacting with water vapor in the form of an aerosol, necessitating larger reaction equipment to ensure sufficient residence time, resulting in relatively low space-time efficiency.

[0010] CN107057012B discloses a method for preparing biuret polyisocyanate with low turbidity, no polyurea insolubles, and no blockage of the water vapor insertion tube. This method enhances the mixing of water vapor and diisocyanate by ultrasound to reduce blockage of the water vapor insertion tube. However, this method has the disadvantages of high energy consumption and difficulty in industrialization. At the same time, it does not solve the problem of blockage of the reaction vessel and tail gas pipeline caused by the reaction of water vapor and diisocyanate in the tail gas to form polyurea.

[0011] Existing methods for preparing biuret polyisocyanate compositions are difficult to overcome the problems of tail gas pipeline blockage and reactor contamination caused by reaction tail gas, and also lead to high turbidity of the prepared products. Summary of the Invention

[0012] The first objective of this invention is to provide a method for preparing a biuret polyisocyanate composition, which avoids the problems of tail gas pipeline blockage and reactor contamination caused by tail gas, and the resulting product has low turbidity.

[0013] A second objective of this invention is to provide a preparation system for the aforementioned preparation method, which avoids problems such as tail gas pipeline blockage and reactor contamination caused by tail gas, and produces a product with low turbidity.

[0014] To achieve the first objective of this invention, the following technical solution is adopted:

[0015] A method for preparing a biuret polyisocyanate composition includes the following steps:

[0016] (1) A biuret polyisocyanate composition is prepared by reacting diisocyanate with water vapor in a reaction vessel and then outputting tail gas;

[0017] (2) The tail gas obtained in step (1) is first condensed to output condensate and non-condensable gas;

[0018] (3) The condensate obtained in step (2) is dehydrated, preheated and broken down in sequence, and then returned to the reactor for recycling;

[0019] (4) The reaction liquid output from the reactor is distilled to remove unreacted diisocyanate to obtain a biuret polyisocyanate composition product.

[0020] In the preferred embodiment of the preparation method of the biuret polyisocyanate composition of the present invention, in step (2), the temperature of the condensate is 25-35°C.

[0021] In the preferred embodiment of the present invention, the preparation method of the biuret polyisocyanate composition is as follows: in step (3), the water content in the condensate is 0.1-0.5 wt% after removing water.

[0022] In the preparation method of the biuret polyisocyanate composition of the present invention, preferably, in step (3), the dehydration medium used for dehydration is a water-absorbing filler, which includes an inert inorganic water absorbent and an inert organic water absorbent;

[0023] Preferably, the inert inorganic desiccant includes any one or more combinations of CaCl2, silica gel, and molecular sieves;

[0024] Preferably, the inert organic desiccant includes SAP.

[0025] In the preferred embodiment of the present invention, the preparation method of the biuret polyisocyanate composition involves preheating the condensate to a temperature of 70-90°C in step (3).

[0026] In the preferred embodiment of the present invention, the preparation method of the biuret polyisocyanate composition involves step (3) breaking down the solid particles in the condensate to a particle size of 10-200 μm.

[0027] In the preferred embodiment of the present invention, the preparation method of the biuret polyisocyanate composition is as follows: in step (1), the mass ratio of diisocyanate to water vapor is (20-200):1.

[0028] In the method for preparing the biuret polyisocyanate composition of the present invention, preferably, in step (1), the diisocyanate is an aliphatic diisocyanate and / or an alicyclic diisocyanate.

[0029] In the preparation method of the biuret polyisocyanate composition of the present invention, in step (1), the reaction temperature is 80-200℃ and the reaction time is 30-400min.

[0030] To achieve the second objective of the present invention, the present invention also provides a preparation system for the aforementioned preparation method.

[0031] In one embodiment, the preparation system includes a reaction vessel, a tail gas treatment unit, a return pipeline, and a distillation apparatus;

[0032] The exhaust gas treatment unit includes a condenser, a water separator, a preheater, and a decomposer connected in sequence via pipelines.

[0033] The condenser is connected to the gas phase outlet of the reactor and is used to condense the tail gas from the reactor to obtain condensate and non-condensable gas.

[0034] The water remover, the preheater, and the decomposer are used to sequentially remove water, preheat, and decompose the condensate from the condenser.

[0035] One end of the return pipeline is connected to the liquid phase outlet of the breaker 5, and the other end is connected to the liquid phase inlet of the reactor, for returning the material obtained after being treated by the tail gas treatment unit to the reactor.

[0036] The distillation apparatus is connected to the liquid phase outlet of the reactor and is used to distill and separate the reaction liquid from the reactor to remove unreacted diisocyanate and obtain a biuret polyisocyanate composition product.

[0037] The beneficial effects of this invention are as follows:

[0038] The preparation method and system of the biuret polyisocyanate composition of the present invention can treat the exhaust gas, avoid the problems of exhaust gas pipeline blockage and reaction vessel pollution caused by the exhaust gas, and the stable operation cycle of the reaction vessel and exhaust gas pipeline can reach more than 18 months; and the obtained product has a clear and bright appearance without whitening, and the turbidity is less than 0.4 NTU. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the preparation system for the biuret polyisocyanate composition of the present invention in one embodiment. Detailed Implementation

[0040] The technical solution and effects of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only, and the invention is not limited to the described embodiments or examples. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0041] A method for preparing a biuret polyisocyanate composition includes the following steps:

[0042] (1) A biuret polyisocyanate composition is prepared by reacting diisocyanate with water vapor in a reaction vessel and then outputting tail gas;

[0043] (2) The tail gas obtained in step (1) is first condensed to output condensate and non-condensable gas;

[0044] (3) The condensate obtained in step (2) is dehydrated, preheated and broken down in sequence, and then returned to the reactor for recycling;

[0045] (4) The reaction liquid output from the reactor is distilled to remove unreacted diisocyanate to obtain a biuret polyisocyanate composition product.

[0046] Those skilled in the art will understand that the biuretization reaction in step (1) is an oxygen-free process, and nitrogen gas is introduced into the reactor as an inert gas for nitrogen sealing protection, that is, the biuretization reaction is carried out under nitrogen protection.

[0047] Those skilled in the art will understand that the tail gas obtained in step (1) includes unreacted diisocyanate, water vapor, carbon dioxide (a byproduct of the reaction) and nitrogen (from the nitrogen sealing process); after condensation, the non-condensable gas obtained mainly includes carbon dioxide and nitrogen, and the condensate obtained mainly includes diisocyanate and water.

[0048] The preparation method of the biuret polyisocyanate composition of the present invention can treat the exhaust gas, avoid the problems of exhaust gas pipeline blockage and reaction vessel pollution caused by the exhaust gas, and the reaction vessel and exhaust gas pipeline have a long stable operation cycle; and the obtained product has a clear and bright appearance without whitening and low turbidity.

[0049] Through long-term research, the inventors have discovered that during the process of preparing biuret polyisocyanate composition by reacting diisocyanate with water vapor, the main component carried in the exhaust gas is diisocyanate. Under suitable conditions, the diisocyanate carried in the exhaust gas reacts with water vapor to generate insoluble substances such as polyurea. This is a key factor in the blockage of the exhaust gas pipeline, contamination of the reaction vessel, and ultimately a decrease in the operational stability of the reaction system. It is also a key factor leading to high turbidity in the product.

[0050] In one embodiment, in step (2), the temperature at which the condensate is cooled is 25-35°C, such as 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, and 34°C. At this temperature, aliphatic diisocyanates and / or alicyclic diisocyanates hardly react with water for a short period of time, thus minimizing the generation of pollutants such as polyurea and preventing tail gas pipeline blockage and reactor contamination at the source.

[0051] In this invention, the condensation equipment can be a condenser commonly used in the art, such as an industrially common heat exchanger, such as a shell-and-tube heat exchanger and a plate heat exchanger, preferably a shell-and-tube heat exchanger. The cooling medium used for condensation is water or brine. In one embodiment, the temperature of the cooling medium is 5-10°C, such as 6°C, 7°C, 8°C, and 9°C.

[0052] Through long-term research, the inventors discovered that during the preparation of biuret polyisocyanate compositions by reacting diisocyanate with water vapor, the exhaust gas contains 1-10 wt% water in addition to diisocyanate. High concentrations of water typically cause phase separation with diisocyanate, and the two readily react upon heating to generate large amounts of polyurea blockages. The method of this invention solves this problem by removing water from the condensate.

[0053] In this invention, the equipment used for water removal can be commonly used in the field, such as industrial filters, which are filled with absorbent packing material.

[0054] In one embodiment, in step (3), the dewatering medium used is a water-absorbing filler, which includes an inert inorganic water absorbent and an inert organic water absorbent.

[0055] In one embodiment, the inert inorganic desiccant includes any one or more combinations of CaCl2, silica gel, and molecular sieves (such as 5A molecular sieve).

[0056] In one embodiment, the inert organic absorbent includes SAP (superabsorbent polymer).

[0057] In one embodiment, in step (3), the temperature of the condensate is preheated to 70-90°C, such as 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C and 88°C.

[0058] The inventors discovered through research that, when the water content in the condensate after dehydration is 0.1-0.5 wt%, at 70-90℃, water reacts rapidly with aliphatic and / or alicyclic diisocyanates to form small molecule ureas, thus quickly removing the water. Taking hexamethylene diisocyanate and water as an example, the reaction formula is as follows:

[0059] Wherein, R = (CH2)6.

[0060] Therefore, in step (3), the water content in the preheated condensate is very low, and its main components are diisocyanate and a small amount of small molecule urea (solid particles).

[0061] In this invention, the equipment used for preheating can be commonly used equipment in the field, such as industrial heat exchangers, such as shell-and-tube heat exchangers and plate heat exchangers, with shell-and-tube heat exchangers being preferred.

[0062] Through in-depth research, the inventors discovered that if small molecule urea is not broken down and dispersed in time, it is very easy to agglomerate and form polyurea, leading to the formation of solid pollutants. In one embodiment, in step (3), the particle size of the solid particles in the condensate is broken down to 10-200 μm, such as 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm and 180 μm, thereby significantly reducing the tendency and possibility of deep polymerization of small molecule urea to form polyurea. However, if the small molecule urea is further broken down to a particle size below 10 μm, the energy consumption of the breaking down process is too high, and further reducing the particle size of small molecule urea does not have a more significant effect on reducing polyurea formation.

[0063] In this invention, the equipment used for breaking down the material can be any breaking down equipment commonly used in the field, such as a breaking down device, or a breaking down device commonly used in the coatings industry, such as a high-speed disperser.

[0064] Those skilled in the art will understand that the biuretization reaction in step (1) is a routine reaction of this technique.

[0065] In one embodiment, in step (1), the mass ratio of diisocyanate to water vapor is (20-200):1, such as 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 110:1, 120:1, 130:1, 140:1, 150:1, 160:1, 170:1, 180:1 and 190:1.

[0066] In one embodiment, in step (1), the diisocyanate is an aliphatic diisocyanate and / or an alicyclic diisocyanate.

[0067] In one embodiment, in step (1), the diisocyanate includes any one or a combination of pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (HMDI), 1,4-cyclohexane diisocyanate, methylcyclohexyl diisocyanate, and cyclohexanedimethylene diisocyanate.

[0068] In one embodiment, in step (1), the reaction temperature is 80-200°C, such as 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, and 190°C; and the reaction time is 30-400 min, such as 50 min, 70 min, 90 min, 110 min, 130 min, 150 min, 170 min, 190 min, 210 min, 230 min, 250 min, 270 min, 290 min, 310 min, 330 min, 350 min, 370 min, and 390 min.

[0069] In step (1) of this invention, the reactor for the reaction of diisocyanate with water vapor can be a stirred tank reactor, and the reaction in step (1) can be carried out in a batch manner, or multiple reactors can be connected in series in a continuous manner, or other reactor types commonly used in industrial applications can be used. In one embodiment, the flow rate of water vapor is 0.1-5 kg / min, such as 0.2 kg / min, 0.3 kg / min, 0.5 kg / min, 1 kg / min, 2 kg / min, 3 kg / min, 4 kg / min, and 5 kg / min. In one embodiment, the reactor in step (1) is a stirred tank reactor, and the reaction in step (1) is carried out in a batch manner. In one embodiment, the reaction in step (1) is carried out under an inert gas atmosphere (such as nitrogen). In one embodiment, a catalyst is also added during the reaction in step (1); preferably, the amount of catalyst added is 0.01-5 wt%, such as 0.02 wt%, 0.03 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, and 4.5 wt%, based on the amount of diisocyanate used. In one embodiment, the catalyst is a carboxylic acid catalyst, preferably a combination of one or more of formic acid, acetic acid, propionic acid, pentylene acid, oxalic acid, and malonic acid.

[0070] According to the preparation method of the present invention, the prepared biuret polyisocyanate composition product is clear and bright in appearance without whitening, and the turbidity is less than 0.4 NTU; at the same time, it fundamentally inhibits the pollution of the reactor and tail gas pipeline, and the stable operation cycle of the reactor and tail gas pipeline can reach more than 18 months.

[0071] The present invention also provides a preparation system for the aforementioned preparation method.

[0072] In one implementation, such as Figure 1 As shown, the preparation system includes a reaction vessel 1, a tail gas treatment unit, a return pipeline 6, and a distillation device 8;

[0073] The exhaust gas treatment unit includes a condenser 2, a water separator 3, a preheater 4, and a decomposer 5 connected in sequence by pipelines.

[0074] The condenser 2 is connected to the gas phase outlet of the reactor 1 and is used to condense the tail gas from the reactor 1 to obtain condensate and non-condensable gas.

[0075] The water remover 3, the preheater 4, and the dewatering device 5 are used to sequentially remove water, preheat, and dewater the condensate from the condenser.

[0076] One end of the return pipeline 6 is connected to the liquid phase outlet of the breaker 5, and the other end is connected to the liquid phase inlet of the reactor 1, for returning the material obtained after being treated by the tail gas treatment unit to the reactor 1.

[0077] The distillation apparatus 8 is connected to the liquid phase outlet of the reactor 1 and is used to distill and separate the reaction liquid from the reactor 1 to remove unreacted diisocyanate and obtain a biuret polyisocyanate composition product.

[0078] The preparation system of the present invention, used in the aforementioned preparation method, can treat the exhaust gas, avoiding the problems of exhaust gas pipeline blockage and reactor contamination caused by the exhaust gas. The stable operation cycle of the reactor and exhaust gas pipeline can reach more than 18 months. Moreover, the obtained product has a clear and bright appearance without whitening, and the turbidity is less than 0.4 NTU.

[0079] In this invention, the condenser 2 is a heat exchanger commonly used in industry, such as a shell-and-tube heat exchanger and a plate heat exchanger, with a shell-and-tube heat exchanger being preferred.

[0080] In this invention, the water separator 3 is a commonly used industrial filter, filled with a water-absorbing medium, i.e., a water-absorbing packing material with water-absorbing properties. In one embodiment, the water separator 3 is filled with water-absorbing packing material, which includes an inert inorganic water-absorbing agent and an inert organic water-absorbing agent; preferably, the inert inorganic water-absorbing agent includes any one or more combinations of CaCl2, silica gel, and molecular sieves (such as 5A molecular sieve), and the inert organic water-absorbing agent includes SAP (superabsorbent polymer).

[0081] In one embodiment, there are at least two water separators 3 arranged in parallel to divert and remove water from the condensate from the condenser 2, thereby increasing the water removal efficiency and avoiding the situation where the water removal effect is affected by the water absorption packing inside the single water separator 3 becoming saturated.

[0082] To ensure continuous and stable operation of the system, the at least two water separators 3 connected in parallel can be configured with at least one in operation and at least one in standby mode. Once the absorbent packing in the water separator 3 in operation is saturated with water, the standby water separator 3 can be switched on and the absorbent packing can be refilled.

[0083] In one embodiment, there are at least two water separators 3 arranged in series to remove water from the condensate from the condenser 2 in stages, thereby improving the water removal effect and avoiding the situation where the water removal effect is affected by the water absorption packing inside the single water separator 3 becoming saturated.

[0084] In this invention, the preheater 4 is a commonly used industrial heat exchanger, such as a shell-and-tube heat exchanger and a plate heat exchanger, preferably a shell-and-tube heat exchanger. In one embodiment, the heat medium of the preheater 4 is hot oil or steam, preferably the temperature of the heat medium is 150-180°C, such as 155°C, 160°C, 165°C, 170°C, and 175°C.

[0085] In this invention, the breaker 5 is a common breaking device in the coatings industry, such as a high-speed disperser.

[0086] The reaction liquid output from the reactor includes unreacted diisocyanate and the biuret polyisocyanate composition prepared by the reaction, both of which are liquids. Those skilled in the art will understand that the distillation apparatus 8 can be a commonly used distillation apparatus in the art, such as a thin-film evaporator, used to remove unreacted diisocyanate from the reaction liquid output from the reactor to obtain a biuret polyisocyanate composition with higher purity.

[0087] In one embodiment, the preparation system further includes an exhaust line 7, one end of which is connected to the gas phase outlet of the condenser 2 and the other end is connected to the fan inlet, for conveying the non-condensable gas from the condenser 2 to the fan for exhaust.

[0088] like Figure 1 As shown, in one embodiment, the preparation system of the present invention operates as follows:

[0089] 1) Diisocyanate reacts with water vapor in the reactor 1, and exhaust gas is output from the gas phase outlet of the reactor 1;

[0090] 2) The exhaust gas obtained in step 1) is sent to the condenser 2 of the exhaust gas treatment unit for condensation, and condensate and non-condensable gas are output; the obtained non-condensable gas is sent to the fan for exhaust through the exhaust pipeline 7.

[0091] 3) The condensate obtained in step 2) is transported to the dewatering device 3 for dewatering to obtain dewatered condensate;

[0092] 4) The dehydrated condensate obtained in step 3) is transported to the preheater 4 for preheating to obtain preheated condensate;

[0093] 5) The preheated condensate obtained in step 4) is transported to the breaker 5 for breaking to obtain broken condensate;

[0094] 6) The condensate obtained in step 5) is returned to the reactor 1 via the return pipeline 6 for circulation;

[0095] 7) The reaction liquid output from the liquid phase outlet of the reactor 1 is transported to the distillation equipment 8 for distillation separation to remove unreacted diisocyanate and obtain biuret polyisocyanate composition product.

[0096] Those skilled in the art will understand that step 7) is performed after the loop of step 6).

[0097] The present invention will be further described below through specific embodiments.

[0098] In the following examples and comparative examples, the sources of raw materials and equipment are as follows:

[0099] Hexamethylene diisocyanate, Wannate HDI, Wanhua Chemical, purity 99.5%.

[0100] Pteropenic acid, Sigma-Aldrich, 99% purity.

[0101] Isophorone diisocyanate, Wannate IPDI, Wanhua Chemical, purity 99.5%;

[0102] Dicyclohexylmethane diisocyanate, Wannate HMDI, Wanhua Chemical, purity 99.5%;

[0103] Acetic acid, Sigma-Aldrich, 99% purity;

[0104] Propionic acid, Sigma-Aldrich, purity 99.5%;

[0105] The reactor, condenser, dehydrator, preheater, and crusher were all designed and manufactured by Wanhua Kimura Machinery Processing Co., Ltd.

[0106] The testing method is as follows:

[0107] The turbidity of the biuret polyisocyanate composition was tested using a Hach 2100N turbidity meter, and calibrated with a standard solution before testing.

[0108] The particle size of solid particles in the condensate was determined using a Fritsch A22 MicroTec Plus laser particle size analyzer.

[0109] Example 1 (S1)

[0110] Utilize Figure 1 The preparation system shown, according to the aforementioned preparation method of the present invention, prepares a biuret polyisocyanate composition, comprising the following steps:

[0111] 1) Under nitrogen protection, 4000 kg of hexamethylene diisocyanate (HDI) and 0.4 kg of tervalic acid were added to the reactor 1. The reactor 1 was heated to 120°C. Then, 20 kg of water vapor was introduced into the reactor 1 at a flow rate of 0.2 kg / min. The mixture was stirred and reacted for 120 min to prepare a biuret polyisocyanate composition. The tail gas was then discharged.

[0112] 2) The exhaust gas obtained in step 1) is transported to the condenser 2 of the exhaust gas treatment unit for condensation, and condensate 1' and non-condensable gas are output at a temperature of 25°C; the obtained non-condensable gas is transported to the fan for exhaust through the exhaust pipeline 7; wherein, the condenser 2 uses water at 5°C as the cooling medium.

[0113] 3) The condensate 1' obtained in step 2) is transported to the dewatering device 3 for dewatering until its water content is 0.1 wt%, to obtain dewatered condensate 2'; wherein, the water-absorbing packing material in the dewatering device 3 is 5A molecular sieve;

[0114] 4) The dehydrated condensate 2' obtained in step 3) is transported to the preheater 4 for preheating to a temperature of 70°C to obtain preheated condensate 3';

[0115] 5) The preheated condensate 3' obtained in step 4) is transported to the breaker 5 for breaking until the particle size of the solid particles therein is 10μm, to obtain the broken condensate 4';

[0116] 6) The condensate 4' obtained in step 5) is returned to the reactor 1 via the return pipeline 6 for circulation;

[0117] 7) The reaction liquid output from the liquid phase outlet of the reactor 1 is transported to the distillation equipment 8 for distillation separation to remove unreacted diisocyanate, yielding biuret polyisocyanate composition product A1; wherein,

[0118] The distillation equipment 8 is a thin-film evaporator.

[0119] Example 2-6 (S2-6)

[0120] Biuret polyisocyanate composition A2-6 was prepared according to the preparation method of Example 1. The only difference between A2-6 and the preparation method in Example 1 is the preparation conditions, as shown in Table 1.

[0121] Table 1 Preparation conditions of S1-6

[0122]

[0123]

[0124] Comparative Example 1 (D1)

[0125] The biuret polyisocyanate composition A1' was prepared according to the preparation method of Example 1, the only difference being that:

[0126] Steps 3)-6) are omitted, and only steps 1), 2) and 7) are performed. After step 2), the resulting condensate 1' is directly returned to the reactor 1 for circulation, and then step 7) is performed.

[0127] The biuret polyisocyanate composition products A1-6 and A1' obtained in Examples 1-6 (S1-6) and Comparative Example 1 (D1) were tested respectively. Their turbidity was tested, their appearance was observed, and the stable operation cycle of the corresponding reaction vessel 1 and tail gas pipeline was tested. See Table 2 for details.

[0128] Table 2. Relevant information for S1-6 and D1

[0129]

[0130]

[0131] Based on the comparison of Examples 1-6 and Comparative Example 1 and the contents of Tables 1-2, it can be seen that when the biuret polyisocyanate composition is prepared using the preparation method of the present invention, the turbidity of the obtained product is below 0.4 NTU, the product appearance is clear and bright without whitening, and the pollution of the reaction vessel and tail gas pipeline is greatly reduced. The stable operation cycle of the reaction vessel and tail gas pipeline can reach more than 18 months.

Claims

1. A method for preparing a biuret polyisocyanate composition, characterized in that, The preparation method includes the following steps: (1) A biuret polyisocyanate composition is prepared by reacting diisocyanate with water vapor in a reactor and then outputting tail gas; (2) The tail gas obtained in step (1) is first condensed to output condensate and non-condensable gas; (3) After the condensate obtained in step (2) is dehydrated, preheated and broken down in sequence, it is returned to the reactor for recycling; (4) The reaction liquid output from the reactor is distilled to remove unreacted diisocyanate, yielding a biuret polyisocyanate composition product; wherein, In step (2), the temperature of the condensate is 25-35 ℃; In step (3), the water content in the condensate is reduced to 0.1-0.5 wt% after water removal. In step (3), the condensate is preheated to a temperature of 70-90 ℃; In step (3), the particle size of the solid particles in the condensate is 10-200 μm.

2. The preparation method according to claim 1, characterized in that, In step (3), the water removal medium used during water removal is a water-absorbing filler, which includes an inert inorganic water absorbent and an inert organic water absorbent.

3. The preparation method according to claim 2, characterized in that, The inert inorganic water absorbent includes any one or more combinations of CaCl2, silica gel, and molecular sieves.

4. The preparation method according to claim 2, characterized in that, The inert organic absorbent includes SAP.

5. The preparation method according to any one of claims 1-4, characterized in that, In step (1), the mass ratio of diisocyanate to water vapor is (20-200):

1.

6. The preparation method according to claim 1, characterized in that, In step (1), the diisocyanate is an aliphatic diisocyanate and / or an alicyclic diisocyanate.

7. The preparation method according to any one of claims 1-4 and 6, characterized in that, In step (1), the reaction temperature is 80-200 ℃ and the reaction time is 30-400 min.

8. A preparation system for the preparation method according to any one of claims 1-7, characterized in that, The preparation system includes a reaction vessel (1), a tail gas treatment unit, a return pipeline (6), and a distillation device (8). The exhaust gas treatment unit includes a condenser (2), a water separator (3), a preheater (4), and a decomposer (5) connected in sequence by pipelines. The condenser (2) is connected to the gas phase outlet of the reactor (1) and is used to condense the tail gas from the reactor (1) to obtain condensate and non-condensable gas. The dewatering device (3), the preheater (4), and the dewatering device (5) are used to sequentially dewater, preheat, and dewater the condensate from the condenser; One end of the return pipeline (6) is connected to the liquid phase outlet of the breaker (5), and the other end is connected to the liquid phase inlet of the reactor (1), for returning the material obtained after being treated by the tail gas treatment unit to the reactor (1). The distillation apparatus (8) is connected to the liquid outlet of the reactor (1) for distilling and separating the reaction liquid from the reactor (1) to remove unreacted diisocyanate and obtain a biuret polyisocyanate composition product.

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