Process for the preparation of low haze, light color polyisocyanates
By separating and converting organic amine hydrochloride in crude isocyanate, the problems of high turbidity and dark color of polyisocyanate were solved, realizing the production of low-turbidity, light-colored polyisocyanate, and improving production efficiency and storage stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WANHUA CHEMICAL (NINGBO) CO LTD
- Filing Date
- 2022-03-23
- Publication Date
- 2026-05-19
AI Technical Summary
In existing polyisocyanate production processes, high turbidity and dark color result in poor optical performance of downstream products. Furthermore, organic amine hydrochloride catalyzes the isocyanate reaction, affecting storage stability and production efficiency.
By separating organic amine hydrochloride before high-temperature distillation of crude isocyanate and converting it into soluble urea compounds, the reaction between the urea and high-molecular isocyanate at high temperatures is avoided. The reaction is catalyzed by a solid acid catalyst, BiCl3/SiO2, to generate soluble urea compounds, thereby reducing turbidity and improving color.
It significantly reduces the turbidity and color depth of polyisocyanates, improves production and packaging efficiency, enhances the optical properties of downstream products, and improves storage stability, while preventing pipeline blockage and reactor contamination.
Smart Images
Figure CN116836351B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of isocyanates, and more specifically to a method for preparing a low-turbidity, light-colored polyisocyanate. Background Technology
[0002] Polyisocyanate, also known as "polymeric MDI", has the chemical name polyphenyl polymethylene polyisocyanate. Its molecular structure is shown below. It is the main raw material for the production of polyurethane foam and is mainly used in industries such as refrigerators, spraying, pipe insulation, boards, and solar energy.
[0003]
[0004] The turbidity and color of polyisocyanates both affect the optical properties of downstream polyurethane products. High turbidity can lead to pipeline blockage, reactor contamination, and other consequences, thus affecting the stability of downstream production processes. Typically, the color of polyisocyanates is characterized by their lightness (L*), with L* = 0 representing black and L* = 100 representing white. Therefore, a higher L* indicates a lighter polyisocyanate color. Consequently, obtaining polyisocyanate products with low turbidity and light color has become an urgent problem to be solved in the industry.
[0005] Chinese patent CN102257026B provides a method for preparing colorless polyisocyanates. By treating aliphatic or alicyclic polyisocyanates with light of wavelength 200-600 nm, the color number of polyisocyanates can be reduced without adding any additional substances to the system. The effect of this method on aromatic isocyanates is unknown, and the stability of the lightened color is poor.
[0006] Chinese patent CN101602859A describes a method of treating organic polyisocyanates with ozone-containing gas to lighten their color. The gas also contains at least one other inert and / or reactive gas, such as nitrogen oxides. The patent states that nitrogen oxides can better disperse ozone in polyisocyanates, and their high oxidizing properties can destroy colorants and promote color lightening. However, they are prone to leaving residues in polyisocyanate products, affecting their storage stability.
[0007] Currently, the main production process of polyisocyanate involves the condensation reaction of aniline and formaldehyde under the catalysis of Lewis acid to generate polyamines. The polyamines then react with phosgene in a solvent through a two-step cold and hot reaction to generate a photochemical liquid. This photochemical liquid undergoes a series of post-treatment processes to remove the solvent, yielding crude MDI. Crude MDI is then subjected to crude separation to obtain polyisocyanate and crude diphenylmethane diisocyanate. Because the diamine in the condensation stage does not completely react during the photochemical reaction, it forms organic amine hydrochloride under acidic conditions. This hydrochloride is slightly soluble in isocyanate and ultimately carries over into the crude MDI, thus entering the polyisocyanate product.
[0008] Under current processes, the turbidity of polyisocyanate (POI) products is typically above 5.0 NTU, and the filtration efficiency (L*) is usually between 50 and 65. High turbidity and low L* directly impact the optical properties of downstream products. During PIO production, to obtain low-turbidity products, small-pore filters are typically used, resulting in slow filtration rates and frequent filter replacements for packaging. The number of filter replacements per thousand tons is usually over 150, leading to a significant amount of manual labor and low production and packaging efficiency. Because the diamine does not fully react during the photochemical reaction in the condensation stage, the organic amine hydrochloride formed under acidic conditions is slightly soluble in isocyanate. Currently, PIO still contains trace amounts of organic amine hydrochloride, exceeding 50 ppm. However, the applicant has discovered that the presence of organic amine hydrochloride catalyzes the isocyanate reaction, causing an increase in PIO viscosity and affecting product storage stability. Furthermore, in downstream high-temperature applications, organic amine hydrochloride may react to form solid urea compounds, posing a risk of pipe blockage and reactor contamination, and also affecting the optical properties of the final product. Summary of the Invention
[0009] The purpose of this invention is to provide a method for preparing low-turbidity, light-colored polyisocyanate. This method involves separating organic amine hydrochloride from crude isocyanate before high-temperature distillation, and then using a catalytic reaction to generate soluble urea compounds from the organic amine hydrochloride. This avoids the reaction of organic amine hydrochloride with high-molecular-weight isocyanate at high temperatures to form solid urea compounds that clog pipes and contaminate the reactor, thereby reducing the turbidity of the polyisocyanate and making its color lighter. This, in turn, improves production and packaging efficiency and enhances the color of downstream products.
[0010] To achieve the above objectives, the present invention provides a low-turbidity, light-colored polyisocyanate comprising 10% to 80% by mass of diphenylmethane diisocyanate and 20% to 90% by mass of polyphenylmethylene polyisocyanate (a compound with three or more benzene rings, referred to as tricyclic or higher).
[0011] Preferably, the polyisocyanate has a turbidity <1.0 NTU, L*>70, and an organic amine hydrochloride content <1 ppm; more preferably, the turbidity <0.8 NTU, L*>72, and the organic amine hydrochloride content <0.5 ppm, wherein the structural formula of the organic amine hydrochloride is as follows:
[0012]
[0013] Furthermore, the polyisocyanate comprises 0-5 wt% of 2,2-MDI, 0.1 wt%-20 wt% of 2,4-MDI, 5 wt%-80 wt% of 4,4-MDI, 10 wt%-50 wt% of polyphenyl polymethylene polyisocyanate (a compound with three benzene rings, referred to as a tricyclic mixture), 5 wt%-30 wt% of polyphenyl polymethylene polyisocyanate (a compound with four benzene rings, referred to as a tetracyclic mixture), 5 wt%-50 wt% of polyphenyl polymethylene polyisocyanate (a compound with five or more benzene rings, referred to as a pentacyclic and above mixture), and <1 ppm of organic amine hydrochloride.
[0014] Preferably, the polyisocyanate comprises 0-1 wt% of 2,2-MDI, 0.5 wt%-10 wt% of 2,4-MDI, 10 wt%-50 wt% of 4,4-MDI, 15 wt%-40 wt% of polyphenyl polymethylene polyisocyanate (tricyclic mixture), 5 wt%-20 wt% of polyphenyl polymethylene polyisocyanate (tetracyclic mixture), 10 wt%-40 wt% of polyphenyl polymethylene polyisocyanate (pentacyclic and above mixture), and <0.5 ppm of organic amine hydrochloride.
[0015] This invention also provides a method for preparing a low-turbidity, light-colored polyisocyanate, the method comprising the following steps:
[0016] (1) After the crude isocyanate (A) is rapidly cooled and filtered, the filtrate is crude isocyanate (C);
[0017] (2) The crude isocyanate (C) is fed into the crystallization device, and the crystallization product is crude diphenylmethane diisocyanate (G) containing organic amine hydrochloride, and the crystallization residue is crude isocyanate (D).
[0018] (3) The crude isocyanate (D) was sent to a distillation column to separate polyisocyanate (E) and crude diphenylmethane diisocyanate (F);
[0019] (4) Crude diphenylmethane diisocyanate (G) containing organic amine hydrochloride is reacted with a catalyst to obtain crude diphenylmethane diisocyanate (H);
[0020] (5) Crude diphenylmethane diisocyanate (H) and polyisocyanate (E) are mixed and rapidly cooled, and then cured, viscosity adjusted and filtered to obtain polyisocyanate (K).
[0021] In this invention, the crude isocyanate (A) comprises 0-5 wt% of 2,2-MDI, 0.5 wt%-30 wt% of 2,4-MDI, 30 wt%-80 wt% of 4,4-MDI, 5 wt%-30 wt% of polyphenyl polymethylene polyisocyanate (tricyclic mixture), 3 wt%-20 wt% of polyphenyl polymethylene polyisocyanate (tetracyclic mixture), 5 wt%-30 wt% of polyphenyl polymethylene polyisocyanate (pentacyclic and above mixture), and 100-2000 ppm of organic amine hydrochloride.
[0022] Preferably, the crude isocyanate (A) comprises 0-3 wt% of 2,2-MDI, 0.5 wt%-20 wt% of 2,4-MDI, 40 wt%-70 wt% of 4,4-MDI, 10 wt%-25 wt% of polyphenyl polymethylene polyisocyanate (tricyclic mixture), 5 wt%-15 wt% of polyphenyl polymethylene polyisocyanate (tetracyclic mixture), 10 wt%-25 wt% of polyphenyl polymethylene polyisocyanate (pentacyclic and above mixture), and 200-1000 ppm of organic amine hydrochloride.
[0023] Further, crude isocyanate (A) is obtained through the following steps: aniline and formaldehyde undergo a condensation reaction under the catalysis of Lewis acid to generate a polyamine, the polyamine reacts with phosgene in a solvent in two steps of cold and hot reaction to generate a photochemical solution, and the photochemical solution is post-treated to remove the solvent to obtain crude isocyanate (A).
[0024] In this invention, the Lewis acid is hydrochloric acid, the mass ratio of formaldehyde to aniline is 0.3–0.8, the mass ratio of hydrochloric acid to aniline is 0.1–0.5, the temperature of the condensation reaction is 40–100°C, the mass ratio of phosgene to polyamine reaction is 1–5, the cold reaction temperature is 60–120°C, the hot reaction temperature is 100–150°C, and the post-treatment process specifically includes phosgene removal and benzene removal treatment. The phosgene removal treatment temperature is 110–170°C, and the pressure is controlled at 10–50 kPaG; the benzene removal treatment temperature is 130–220°C, and the pressure is controlled at 10–60 kPaA.
[0025] In this invention, the crude isocyanate (A) quenching process involves directly mixing crude isocyanate (A) with cooled crude isocyanate, then cooling the mixture through a heat exchanger before partially collecting and partially recycling the mixture, with the recycling rate remaining constant at 30–80 m³ / h. 3 / h, the outflow rate is the same as the feed flow rate of crude isocyanate (A), the composition of crude isocyanate remains unchanged in the entire quench system, and crude isocyanate (B) is obtained after quenching, with the temperature controlled at 20-100℃, preferably 30-50℃.
[0026] In this invention, the crude isocyanate (A) filtration is a two-stage filtration process. The first-stage filter has a pore size of 100–500 μm, preferably 150–300 μm, and the second-stage filter has a pore size of 1–100 μm, preferably 30–60 μm.
[0027] In this invention, the operating conditions for the crystallization process of crude isocyanate (C) include controlling the crystallization endpoint temperature at 2 to 20°C, preferably 3 to 10°C, controlling the cooling rate at -0.1 to -1.0°C / min, preferably -0.3 to -0.6°C / min, and controlling the perspiration amount to raw material mass ratio at 2% to 10%, preferably 3% to 6%.
[0028] In this invention, the operating conditions for the distillation process of crude isocyanate (D) include controlling the bottom temperature of the column at 170–270°C, preferably 190–230°C; the top temperature of the column at 60–130°C, preferably 90–110°C; the top pressure of the column at 0.3–2.5 kPa, preferably 0.4–0.8 kPa; and the side stream reflux ratio at 35%–85%, preferably 45%–65%.
[0029] In this invention, the quenching process for polyisocyanate (E) involves directly mixing polyisocyanate (E), crude diphenylmethane diisocyanate (H), and cooled polyisocyanate, then cooling the mixture through a heat exchanger before partially collecting and partially recycling the mixture, with the recycling rate maintained at 30–80 m³ / h. 3 / h, the outflow rate is the same as the feed flow rate of polyisocyanate (E), the composition of polyisocyanate remains unchanged in the entire quenching system, and crude isocyanate (I) is obtained after quenching, with the temperature controlled at 20-60℃, preferably 30-50℃.
[0030] In this invention, the curing temperature of polyisocyanate (I) is controlled at 40-80°C, preferably 50-70°C, and the curing time is controlled at 8-48h, preferably 12-24h, and polyisocyanate (J) is obtained after curing.
[0031] In this invention, the polyisocyanate (J) filtration is a two-stage filtration. The first-stage filter has a pore size of 100-500 μm, preferably 150-300 μm, and the second-stage filter has a pore size of 1-100 μm, preferably 60-80 μm.
[0032] In this invention, the crude diphenylmethane diisocyanate (G) catalytic reaction device in step (4) is a fixed bed, the reaction temperature is controlled at 100-180℃, preferably 130-150℃, the absolute pressure is controlled at 1-2 bar, preferably 1-1.5 bar, and the mass hourly space velocity is controlled at 1-20 h⁻¹. -1 8-10 hours is preferred. -1 .
[0033] Preferably, the fixed-bed catalyst is a solid acid catalyst BiCl3 / SiO2, prepared through the following steps:
[0034] (1) Place powdered BiCl3 and SiO2 into a reaction vessel and purge with nitrogen to replace the air.
[0035] (2) Under closed conditions, the reactor is heated to 500-700℃ and reacted for 2-5 hours. Then nitrogen gas is introduced to purge and cool down.
[0036] (3) The solid catalyst after the reaction is mixed with powdered Al2O3 and extruded into shape.
[0037] Preferably, the mass ratio of BiCl3 to SiO2 is (1-10):100, more preferably (2-5):100, and the ratio of solid catalyst to powdered Al2O3 after reaction is (1-5):1, more preferably (2-3):1.
[0038] In this invention, the content of organic amine hydrochloride in crude isocyanate (D) is 0-5 ppm, preferably 0-2 ppm, and more preferably 0-0.5 ppm.
[0039] Furthermore, the crude isocyanate (D) also includes 0–5.5 wt% of 2,2-MDI, 0.5 wt%–32 wt% of 2,4-MDI, 28 wt%–76 wt% of 4,4-MDI, 5.5 wt%–32 wt% of polyphenyl polymethylene polyisocyanate (tricyclic mixture), 3.5 wt%–21 wt% of polyphenyl polymethylene polyisocyanate (tetracyclic mixture), and 5.5 wt%–32 wt% of polyphenyl polymethylene polyisocyanate (pentacyclic and above mixture). More preferably, it includes 0 to 3.5 wt% of 2,2-MDI, 0.5 wt% to 21 wt% of 2,4-MDI, 38 wt% to 67 wt% of 4,4-MDI, 10.5 wt% to 26.5 wt% of polyphenyl polymethylene polyisocyanate (tricyclic mixture), 5.5 wt% to 16 wt% of polyphenyl polymethylene polyisocyanate (tetracyclic mixture), and 10.5 wt% to 26.5 wt% of polyphenyl polymethylene polyisocyanate (pentacyclic and above mixture).
[0040] In this invention, the content of organic amine hydrochloride in crude diphenylmethane diisocyanate (G) is 0.1 wt% to 10 wt%, preferably 0.4 wt% to 5 wt%.
[0041] Furthermore, the crude diphenylmethane diisocyanate (G) further includes 0-0.5 wt% of 2,2-MDI, 0-1 wt% of 2,4-MDI, 90 wt%-99.8 wt% of 4,4-MDI, and 0 wt%-1 wt% of polyphenylmethylene polyisocyanate (a mixture of tricyclic and above compounds); more preferably, it includes 0-0.1 wt% of 2,2-MDI, 0-0.5 wt% of 2,4-MDI, 95 wt%-99.5 wt% of 4,4-MDI, and 0 wt%-0.5 wt% of polyphenylmethylene polyisocyanate (a mixture of tricyclic and above compounds).
[0042] In this invention, the content of organic amine hydrochloride in crude diphenylmethane diisocyanate (H) is 0-10 ppm, preferably 0-5 ppm.
[0043] Furthermore, the crude diphenylmethane diisocyanate (H) also includes 0-0.5 wt% of 2,2-MDI, 0-1 wt% of 2,4-MDI, 50 wt%-99.5 wt% of 4,4-MDI, and 0.5 wt%-50 wt% of polyphenylmethylene polyisocyanate (a mixture of tricyclic and above compounds); more preferably, it includes 0-0.1 wt% of 2,2-MDI, 0-0.5 wt% of 2,4-MDI, 70 wt%-98 wt% of 4,4-MDI, and 2 wt%-30 wt% of polyphenylmethylene polyisocyanate (a mixture of tricyclic and above compounds).
[0044] All pressures described in this invention are absolute pressures.
[0045] The polyisocyanate product prepared by this invention has a turbidity of <1.0 NTU, L*>70, and organic amine hydrochloride content of <1 ppm, preferably a turbidity of <0.8 NTU, L*>72, and organic amine hydrochloride content of <0.5 ppm. It has low turbidity and light color, which is beneficial to the color of downstream products. At the same time, the organic amine hydrochloride content in the polyisocyanate is very low, which has excellent storage stability and no risk of solid impurity generation during downstream application.
[0046] This may be because the organic amine hydrochloride in polyisocyanate slowly decomposes and reacts with isocyanate-like substances during storage, leading to a decrease in the NCO content and L* of polyisocyanate, an increase in viscosity, and affecting the product's shelf life. Simultaneously, during the high-temperature downstream reaction of polyisocyanate, the organic amine hydrochloride also decomposes and reacts with isocyanate-like substances to generate solid urea compounds, causing problems such as downstream pipeline blockage and reactor contamination, and also affecting the optical properties of downstream products.
[0047] The inventors unexpectedly discovered that the organic amine hydrochloride in crude isocyanate is unstable under high temperature conditions and decomposes into organic amine and hydrogen chloride. The organic amine preferentially reacts with macromolecular polyisocyanate to generate macromolecular solid urea substances, and at the same time, it continues to catalyze the self-polymerization reaction of isocyanate, making the color of PM darker. Therefore, the presence of organic amine hydrochloride in crude isocyanate is an important reason for the high turbidity and dark color of polyisocyanate. The inventors also discovered that in the presence of only small-molecule isocyanates (such as diphenylmethane diisocyanate), organic amine hydrochloride reacts with the small-molecule isocyanate. The resulting small-molecule solid urea can continue to react rapidly to form small-molecule urea compounds under the action of the solid acid catalyst BiCl3 / SiO2. Small-molecule urea compounds have high solubility in the isocyanate system. Due to the low temperature and short residence time, the small-molecule urea compounds will not continue to react to form large-molecule urea compounds and precipitate out. Therefore, in this invention, diphenylmethane diisocyanate containing organic amine hydrochloride is separated, and the organic amine hydrochloride is reacted into soluble small-molecule urea compounds under the action of a catalyst. This is then formulated into polyisocyanate, which can effectively solve the problems of increased turbidity and darkening of polyisocyanate caused by organic amine hydrochloride. It also avoids the potential impact of residual organic amine hydrochloride in polyisocyanate on downstream applications, such as reactor contamination and pipeline blockage.
[0048] The method described in this invention does not introduce exogenous substances, significantly reduces the turbidity of intermediates and finished products during polyisocyanate production, improves production and packaging efficiency, and simultaneously increases the L* of polyisocyanate, thus improving the color of downstream products. The polyisocyanate prepared by this method exhibits high storage stability and poses no risk of solid impurity formation during downstream applications. Attached Figure Description
[0049] Figure 1 This is a flow chart of the production process of the polyisocyanate of the present invention. Detailed Implementation
[0050] The specific implementation scheme of this method is further illustrated below with examples. However, the present invention is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims of the present invention.
[0051] Preparation of crude isocyanate (A): Aniline, formaldehyde, and hydrochloric acid were mixed and reacted. The reaction mixture was then subjected to vacuum to remove aniline and water, yielding a diphenylmethane diamine / polyamine mixture. Chlorobenzene solvent was mixed with the diphenylmethane diamine / polyamine mixture at a mass ratio of 4:1 in a static mixer to generate a mixed solution. Phosgene and the mixed solution were mixed in a dynamic mixer at a phosgene to diamine / polyamine mass ratio of 4:1. The mixture was then subjected to a cold-hot phosgenation reaction. The cold reaction temperature was controlled at 75°C and the pressure at 270 kPaG, while the hot reactor temperature was controlled at 125°C and the pressure at 270 kPaG. The hot reaction solution was then passed through a dephosgene tower at 140°C and 30 kPaG to remove phosgene and hydrogen chloride. After further solvent removal in a desolventizing tower at 150°C and 30 kPaA, crude isocyanate (A), a mixture of diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanate, was obtained. By controlling the molar ratio of aniline, formaldehyde, and hydrochloric acid, crude isocyanate (A) with different component contents can be obtained. However, fluctuations in the raw material components such as aniline, formaldehyde, hydrochloric acid, and phosgene, as well as the process parameters for preparing crude isocyanate (A), will cause changes in the content of components such as organic amine hydrochloride in crude isocyanate (A).
[0052] Preparation of solid acid catalyst: Powdered BiCl3 and SiO2 were placed in a reactor at a mass ratio of 3.5:100. After purging with nitrogen to remove air, the reactor was heated to 600℃ and reacted for 3.5 hours under sealed conditions. After the reaction, nitrogen was purged to cool the reactor. The reacted solid catalyst was then thoroughly mixed with powdered Al2O3 at a mass ratio of 2.5:1. After extrusion molding and drying, the solid acid catalyst BiCl3 / SiO2 was obtained.
[0053] In this invention, the analysis of organic amine hydrochloride was performed using an Agilent LC1260 liquid chromatography system. 0.12 g of crude isocyanate or polyisocyanate sample, 1 g of dichloromethane, and 4 g of methanol were mixed thoroughly and derivatized at 70°C for 60 min. 1.5 ml of the mixture was then injected into a vial for chromatographic analysis. The chromatographic column was a TC C18 column, with a column temperature of 40°C and a flow rate of 1 mL / min. The peak position at 7 min in the chromatogram represents the organic amine hydrochloride.
[0054] In this invention, the turbidity of isocyanate was analyzed using a Hach 2100Q portable turbidimeter, and L* was measured using an integrating sphere spectrophotometer Color Eye 7000A.
[0055] Comparative Example 1:
[0056] Crude isocyanate (A) containing 55 wt% polyphenylene polymethylene polyisocyanate (bicyclic mixture), 13 wt% polyphenylene polymethylene polyisocyanate (tricyclic mixture), 14 wt% polyphenylene polymethylene polyisocyanate (tetracyclic mixture), and 18 wt% polyphenylene polymethylene polyisocyanate (pentacyclic and above mixture) at 205℃ was quenched with a circulation rate of 50 m³ / min. 3 / h, the outlet temperature of the quench heat exchanger is 40℃; after quenching, the crude isocyanate (B) is filtered in two stages, with the first filter screen having a pore size of 180um and the second filter screen having a pore size of 45um. The turbidity of the crude isocyanate (C) in the filtrate after filtration is 0.8NTU, the L* is 82, and the organic amine hydrochloride content is 1801ppm.
[0057] Crude isocyanate (C) was fed into a distillation unit and separated under the following process conditions: bottom temperature 223°C, top temperature 86°C, top pressure 1.1 kPa, and side-stream reflux ratio 65%. Crude diphenylmethane diisocyanate (F) and polyisocyanate (E) were obtained. Polyisocyanate (E) was then quenched, with a quench system circulation rate of 40 m³ / h. 3 / h, the outlet temperature of the quench heat exchanger is 45℃; the quenched polyisocyanate (I) is cured at 60℃ for 24h and then subjected to two-stage filtration. The first-stage filter screen has a pore size of 180um and the second-stage filter screen has a pore size of 75um. The filtrate (K) after filtration is the final polyisocyanate product, with a turbidity of 12.8NTU, an L* of 62, an organic amine hydrochloride content of 162ppm, and a per-thousand-ton screen replacement number of 237 for the polyisocyanate product packaging.
[0058] Storage stability of polyisocyanate products was investigated. After 30 days of storage at 45°C, the viscosity increased by 93 cp.
[0059] Comparative Example 2:
[0060] Crude isocyanate (A) containing 46 wt% polyphenylene polymethylene polyisocyanate (bicyclic mixture), 18 wt% polyphenylene polymethylene polyisocyanate (tricyclic mixture), 21 wt% polyphenylene polymethylene polyisocyanate (tetracyclic mixture), and 15 wt% polyphenylene polymethylene polyisocyanate (pentacyclic and above mixture) at 217℃ was quenched with a circulation rate of 78 m³ / min. 3 / h, the outlet temperature of the quench heat exchanger is 95℃; after quenching, the crude isocyanate (B) is filtered in two stages, with the first filter having a pore size of 500um and the second filter having a pore size of 90um. The turbidity of the crude isocyanate (C) in the filtrate after filtration is 6.1NTU, L* is 79, and the organic amine hydrochloride content is 193ppm.
[0061] Crude isocyanate (C) was fed into a distillation unit and separated under the following process conditions: bottom temperature 178°C, top temperature 62°C, top pressure 0.3 kPa, and side-stream reflux ratio 40%. Crude diphenylmethane diisocyanate (F) and polyisocyanate (E) were obtained. Polyisocyanate (E) was then quenched, with a quench system circulation rate of 35 m³ / h. 3 / h, the outlet temperature of the quench heat exchanger is 25℃; the quenched polyisocyanate (I) is cured at 40℃ for 48h and then subjected to two-stage filtration. The first-stage filter screen has a pore size of 106um and the second-stage filter screen has a pore size of 5um. The filtrate (K) after filtration is the final polyisocyanate product with a turbidity of 8.7NTU, an L* of 65, an organic amine hydrochloride content of 65ppm, and a per-thousand-ton screen replacement number of 294 for the polyisocyanate product packaging.
[0062] Storage stability of polyisocyanate products was investigated. After storage at 45°C for 30 days, the viscosity increased by 62 cp.
[0063] Comparative Example 3:
[0064] Crude isocyanate (A) containing 64 wt% polyphenylene polymethylene polyisocyanate (bicyclic mixture), 10 wt% polyphenylene polymethylene polyisocyanate (tricyclic mixture), 12 wt% polyphenylene polymethylene polyisocyanate (tetracyclic mixture), and 14 wt% polyphenylene polymethylene polyisocyanate (pentacyclic and above mixture) was quenched at 134℃. The circulation rate of the quenching system was 30 m³ / min. 3 / h, the outlet temperature of the quench heat exchanger is 22℃; after quenching, the crude isocyanate (B) is filtered in two stages, with the first filter screen having a pore size of 106um and the second filter screen having a pore size of 5um. The turbidity of the crude isocyanate (C) in the filtrate after filtration is 0.5NTU, L* is 80, and the organic amine hydrochloride content is 591ppm.
[0065] Crude isocyanate (C) was fed into a distillation unit and separated under the following process conditions: bottom temperature 255°C, top temperature 117°C, top pressure 1.9 kPa, and side-stream reflux ratio 80%. This yielded crude diphenylmethane diisocyanate (F) and polyisocyanate (E). Polyisocyanate (E) was then quenched, with a quench system circulation rate of 80 m³ / h. 3 / h, the outlet temperature of the quench heat exchanger is 60℃; the quenched polyisocyanate (I) is cured at 80℃ for 8h and then subjected to two-stage filtration. The first-stage filter screen has a pore size of 500um and the second-stage filter screen has a pore size of 90um. The filtrate (K) after filtration is the final polyisocyanate product with a turbidity of 10.5NTU, an L* of 64, an organic amine hydrochloride content of 51ppm, and a per-thousand-ton screen replacement number of 162 for the polyisocyanate product packaging.
[0066] Storage stability of polyisocyanate products was investigated. After 30 days of storage at 45°C, the viscosity increased by 58 cp.
[0067] Example 1:
[0068] Crude isocyanate (A) containing 55 wt% polyphenylene polymethylene polyisocyanate (bicyclic mixture), 13 wt% polyphenylene polymethylene polyisocyanate (tricyclic mixture), 14 wt% polyphenylene polymethylene polyisocyanate (tetracyclic mixture), and 18 wt% polyphenylene polymethylene polyisocyanate (pentacyclic and above mixture) at 205℃ was quenched with a circulation rate of 50 m³ / min. 3 / h, the outlet temperature of the quench heat exchanger is 40℃; after quenching, the crude isocyanate (B) is filtered in two stages, with the first filter screen having a pore size of 180um and the second filter screen having a pore size of 45um. The turbidity of the crude isocyanate (C) in the filtrate after filtration is 0.8NTU, the L* is 82, and the organic amine hydrochloride content is 1801ppm.
[0069] Crude isocyanate (C) was fed into a crystallization unit. Under conditions of a final crystallization temperature of 2°C, a cooling rate of -0.1°C / min, and a perspiration-to-raw material mass ratio of 10%, crude diphenylmethane diisocyanate (G) and crude isocyanate (D) were obtained, wherein the crude isocyanate (D) contained 8 ppm of organic amine hydrochloride. Crude isocyanate (D) was fed into a distillation unit and separated under process conditions of a bottom temperature of 235°C, a top temperature of 94°C, a top pressure of 1.3 kPa, and a side stream reflux ratio of 65%, to obtain crude diphenylmethane diisocyanate (F) and polyisocyanate (E).
[0070] The crude diphenylmethane diisocyanate (G) obtained by crystallization separation was fed into a fixed bed and subjected to a temperature of 170°C, a pressure of 2 bar, and a mass hourly space velocity of 2 h⁻¹. -1 After reaction under certain conditions, the mixture is combined with the polyisocyanate (E) collected from the bottom of the distillation column and then fed into the quench system. The circulation rate of the quench system is 40 m³ / s. 3 / h, the outlet temperature of the quench heat exchanger is 45℃. The quenched polyisocyanate (I) is cured at 60℃ for 24h and then subjected to two-stage filtration. The first-stage filter has a pore size of 180um and the second-stage filter has a pore size of 75um. The filtrate (K) after filtration is the final polyisocyanate product, with a turbidity of 0.8NTU, an L* of 73, and an organic amine hydrochloride content of 0.8ppm. The number of screen replacements per thousand tons of polyisocyanate product packaging is 25.
[0071] Storage stability of polyisocyanate products was investigated. After storage at 45°C for 30 days, the viscosity increased by 23 cp.
[0072] Example 2:
[0073] Crude isocyanate (A) containing 46 wt% polyphenylene polymethylene polyisocyanate (bicyclic mixture), 18 wt% polyphenylene polymethylene polyisocyanate (tricyclic mixture), 21 wt% polyphenylene polymethylene polyisocyanate (tetracyclic mixture), and 15 wt% polyphenylene polymethylene polyisocyanate (pentacyclic and above mixture) at 217℃ was quenched with a circulation rate of 78 m³ / min. 3 / h, the outlet temperature of the quench heat exchanger is 95℃; after quenching, the crude isocyanate (B) is filtered in two stages, with the first filter having a pore size of 500um and the second filter having a pore size of 90um. The turbidity of the crude isocyanate (C) in the filtrate after filtration is 6.1NTU, L* is 79, and the organic amine hydrochloride content is 193ppm.
[0074] Crude isocyanate (C) was fed into a crystallization unit. Under the conditions of a final crystallization temperature of 18°C, a cooling rate of -1.0°C / min, and a perspiration-to-raw material mass ratio of 2%, crude diphenylmethane diisocyanate (G) and crude isocyanate (D) were obtained, wherein the crude isocyanate (D) contained 6 ppm of organic amine hydrochloride. Crude isocyanate (D) was fed into a distillation unit and separated under the process conditions of a bottom temperature of 189°C, a top temperature of 71°C, a top pressure of 0.4 kPa, and a side stream reflux ratio of 45%, to obtain crude diphenylmethane diisocyanate (F) and polyisocyanate (E).
[0075] The crude diphenylmethane diisocyanate (G) obtained by crystallization separation was fed into a fixed bed and subjected to a temperature of 105℃, a pressure of 1 bar, and a mass hourly space velocity of 18 h⁻¹. -1 After reaction under certain conditions, the mixture is combined with the polyisocyanate (E) collected from the bottom of the distillation column and then fed into the quench system. The circulation rate of the quench system is 35m³. 3 / h, the outlet temperature of the quench heat exchanger is 25℃. The quenched polyisocyanate (I) is cured at 40℃ for 48h and then subjected to two-stage filtration. The first-stage filter has a pore size of 106um and the second-stage filter has a pore size of 5um. The filtrate (K) after filtration is the final polyisocyanate product, with a turbidity of 0.7NTU, an L* of 71, and an organic amine hydrochloride content of 0.4ppm. The number of screen replacements per thousand tons of polyisocyanate product packaging is 65.
[0076] Storage stability of polyisocyanate products was investigated. After storage at 45°C for 30 days, the viscosity increased by 21 cp.
[0077] Example 3:
[0078] Crude isocyanate (A) containing 64 wt% polyphenylene polymethylene polyisocyanate (bicyclic mixture), 10 wt% polyphenylene polymethylene polyisocyanate (tricyclic mixture), 12 wt% polyphenylene polymethylene polyisocyanate (tetracyclic mixture), and 14 wt% polyphenylene polymethylene polyisocyanate (pentacyclic and above mixture) was quenched at 134℃. The circulation rate of the quenching system was 30 m³ / min. 3 / h, the outlet temperature of the quench heat exchanger is 22℃; after quenching, the crude isocyanate (B) is filtered in two stages, with the first filter screen having a pore size of 106um and the second filter screen having a pore size of 5um. The turbidity of the crude isocyanate (C) in the filtrate after filtration is 0.5NTU, L* is 80, and the organic amine hydrochloride content is 591ppm.
[0079] Crude isocyanate (C) was fed into a crystallization unit. Under the conditions of a final crystallization temperature of 8°C, a cooling rate of -0.4°C / min, and a perspiration-to-raw material mass ratio of 5%, crude diphenylmethane diisocyanate (G) and crude isocyanate (D) were obtained, wherein the crude isocyanate (D) contained 5 ppm of organic amine hydrochloride. Crude isocyanate (D) was fed into a distillation unit and separated under the process conditions of a bottom temperature of 265°C, a top temperature of 128°C, a top pressure of 2.3 kPa, and a side stream reflux ratio of 80%, to obtain crude diphenylmethane diisocyanate (F) and polyisocyanate (E).
[0080] The crude diphenylmethane diisocyanate (G) obtained by crystallization separation was fed into a fixed bed and subjected to a temperature of 140°C, a pressure of 1.5 bar, and a mass hourly space velocity of 7 h⁻¹. -1 After reaction under certain conditions, the mixture is combined with the polyisocyanate (E) collected from the bottom of the distillation column and then fed into the quench system. The circulation rate of the quench system is 80 m³ / s. 3 / h, the outlet temperature of the quench heat exchanger is 60℃. The quenched polyisocyanate (I) is cured at 80℃ for 8h and then subjected to two-stage filtration. The first-stage filter has a pore size of 500um and the second-stage filter has a pore size of 90um. The filtrate (K) after filtration is the final polyisocyanate product, with a turbidity of 0.6NTU, an L* of 73, and an organic amine hydrochloride content of 0.3ppm. The number of screen replacements per thousand tons of polyisocyanate product packaging is 14.
[0081] Storage stability of polyisocyanate products was investigated. After storage at 45°C for 30 days, the viscosity increased by 20 cp.
[0082] Example 4:
[0083] Crude isocyanate (A) containing 46 wt% polyphenylene polymethylene polyisocyanate (bicyclic mixture), 18 wt% polyphenylene polymethylene polyisocyanate (tricyclic mixture), 21 wt% polyphenylene polymethylene polyisocyanate (tetracyclic mixture), and 15 wt% polyphenylene polymethylene polyisocyanate (pentacyclic and above mixture) at 217℃ was quenched with a circulation rate of 78 m³ / min. 3 / h, the outlet temperature of the quench heat exchanger is 95℃; after quenching, the crude isocyanate (B) is filtered in two stages, with the first filter screen having a pore size of 180um and the second filter screen having a pore size of 25um. The turbidity of the crude isocyanate (C) in the filtrate after filtration is 0.6NTU, the L* is 79, and the organic amine hydrochloride content is 198ppm.
[0084] Crude isocyanate (C) was fed into a crystallization unit. Under conditions of a final crystallization temperature of 10°C, a cooling rate of -0.5°C / min, and a perspiration-to-raw material mass ratio of 6%, crude diphenylmethane diisocyanate (G) and crude isocyanate (D) were obtained, wherein the crude isocyanate (D) contained 3 ppm of organic amine hydrochloride. Crude isocyanate (D) was fed into a distillation unit and separated under process conditions of a bottom temperature of 190°C, a top temperature of 71°C, a top pressure of 0.4 kPa, and a side stream reflux ratio of 45%, to obtain crude diphenylmethane diisocyanate (F) and polyisocyanate (E).
[0085] The crude diphenylmethane diisocyanate (G) obtained by crystallization separation was fed into a fixed bed and subjected to a temperature of 105℃, a pressure of 1 bar, and a mass hourly space velocity of 18 h⁻¹. -1 After reaction under certain conditions, the mixture is combined with the polyisocyanate (E) collected from the bottom of the distillation column and then fed into the quench system. The circulation rate of the quench system is 35m³. 3 / h, the outlet temperature of the quench heat exchanger is 25℃. The quenched polyisocyanate (I) is cured at 40℃ for 48h and then subjected to two-stage filtration. The first-stage filter has a pore size of 106um and the second-stage filter has a pore size of 5um. The filtrate (K) after filtration is the final polyisocyanate product, with a turbidity of 0.4NTU, an L* of 72, and an organic amine hydrochloride content of 0.2ppm. The number of screen replacements per thousand tons of polyisocyanate product packaging is 21.
[0086] Storage stability of polyisocyanate products was investigated. After storage at 45°C for 30 days, the viscosity increased by 18 cp.
[0087] Example 5:
[0088] Crude isocyanate (A) containing 71 wt% polyphenylene polymethylene polyisocyanate (bicyclic mixture), 8 wt% polyphenylene polymethylene polyisocyanate (tricyclic mixture), 9 wt% polyphenylene polymethylene polyisocyanate (tetracyclic mixture), and 12 wt% polyphenylene polymethylene polyisocyanate (pentacyclic and above mixture) at 176℃ was quenched with a circulation rate of 40 m³ / min. 3 / h, the outlet temperature of the quench heat exchanger is 40℃; after quenching, the crude isocyanate (B) is filtered in two stages, with the first filter screen having a pore size of 300um and the second filter screen having a pore size of 75um. The turbidity of the crude isocyanate (C) in the filtrate after filtration is 1.0NTU, the L* is 84, and the organic amine hydrochloride content is 1214ppm.
[0089] Crude isocyanate (C) was fed into a crystallization unit. Under the conditions of a final crystallization temperature of 5°C, a cooling rate of -0.2°C / min, and a perspiration-to-raw material mass ratio of 8%, crude diphenylmethane diisocyanate (G) and crude isocyanate (D) were obtained, wherein the crude isocyanate (D) contained 8 ppm of organic amine hydrochloride. Crude isocyanate (D) was fed into a distillation unit and separated under the process conditions of a bottom temperature of 210°C, a top temperature of 80°C, a top pressure of 0.8 kPa, and a side stream reflux ratio of 50%, to obtain crude diphenylmethane diisocyanate (F) and polyisocyanate (E).
[0090] The crude diphenylmethane diisocyanate (G) obtained by crystallization separation was fed into a fixed bed and subjected to a temperature of 160°C, a pressure of 1.8 bar, and a mass hourly space velocity of 5 h⁻¹. -1 After reaction under certain conditions, the mixture is combined with the polyisocyanate (E) collected from the bottom of the distillation column and then fed into the quench system. The circulation rate of the quench system is 60 m³ / s. 3 / h, the outlet temperature of the quench heat exchanger is 40℃. The quenched polyisocyanate (I) is cured at 40℃ for 48h and then subjected to two-stage filtration. The first-stage filter has a pore size of 125um and the second-stage filter has a pore size of 20um. The filtrate (K) after filtration is the final polyisocyanate product, with a turbidity of 0.6NTU, an L* of 75, and an organic amine hydrochloride content of 0.6ppm. The number of screen replacements per thousand tons of polyisocyanate product packaging is 28.
[0091] Storage stability of polyisocyanate products was investigated. After storage at 45°C for 30 days, the viscosity increased by 21 cp.
[0092] In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the invention. Therefore, the specification and drawings should be considered illustrative rather than restrictive.
Claims
1. A method for preparing a low-turbidity, light-colored polyisocyanate, the method comprising the following steps: (1) After the crude isocyanate (A) is subjected to rapid cooling and filtration, the filtrate is crude isocyanate (C); (2) The crude isocyanate (C) is fed into the crystallization device, and the crystallization product is crude diphenylmethane diisocyanate (G) containing organic amine hydrochloride, and the crystallization residue is crude isocyanate (D). (3) The crude isocyanate (D) was sent to a distillation column to separate polyisocyanate (E) and crude diphenylmethane diisocyanate (F); (4) Crude diphenylmethane diisocyanate (G) containing organic amine hydrochloride is reacted with a catalyst to obtain crude diphenylmethane diisocyanate (H); (5) Crude diphenylmethane diisocyanate (H) and polyisocyanate (E) are mixed and rapidly cooled, and then cured, viscosity adjusted and filtered to obtain polyisocyanate (K); The crude isocyanate (A) comprises 0–5 wt% 2,2-MDI, 0.5 wt%–30 wt% 2,4-MDI, 30 wt%–80 wt% 4,4-MDI, 5 wt%–30 wt% tricyclic mixture polyphenyl polymethylene polyisocyanate, 3 wt%–20 wt% tetracyclic mixture polyphenyl polymethylene polyisocyanate, 5 wt%–30 wt% pentacyclic and above mixture polyphenyl polymethylene polyisocyanate, and 100–2000 ppm organic amine hydrochloride; In step (4), the crude diphenylmethane diisocyanate (G) catalytic reaction device is a fixed bed, the fixed bed catalyst is a solid acid catalyst BiCl3 / SiO2, the reaction temperature is controlled at 100-180℃, the absolute pressure is controlled at 1-2 bar, and the mass hourly space velocity is controlled at 1-20 h⁻¹.
2. The method as described in claim 1, characterized in that, The crude isocyanate (A) is obtained through the following steps: aniline and formaldehyde undergo a condensation reaction under the catalysis of Lewis acid to generate a polyamine; the polyamine and phosgene react in a solvent in two steps, cold and hot, to generate a photochemical solution; the photochemical solution is then post-treated to remove the solvent, and crude isocyanate (A) is obtained.
3. The method as described in claim 1, characterized in that, In step (1), the rapid cooling process involves directly mixing crude isocyanate (A) with cooled crude isocyanate, then cooling it through a heat exchanger before partially collecting and partially recycling the mixture, with the recycling rate remaining constant at 30–80 m³ / h. 3 / h, the output flow rate is the same as the feed flow rate of crude isocyanate (A), the composition of crude isocyanate remains unchanged in the entire quench system, and crude isocyanate (B) is obtained after quenching, with the temperature controlled between 20 and 100℃.
4. The method as described in claim 3, characterized in that, In step (1), the temperature is controlled at 30-50℃.
5. The method according to any one of claims 1-4, characterized in that, In step (1), the filtration is a two-stage filtration, with the first-stage filter having a pore size of 100-500um and the second-stage filter having a pore size of 1-100um.
6. The method as described in claim 5, characterized in that, In step (1), the filtration is a two-stage filtration, with the first-stage filter having a pore size of 150-300 μm and the second-stage filter having a pore size of 30-60 μm.
7. The method according to any one of claims 1-4, characterized in that, The operating conditions for the crystallization process in step (2) include controlling the crystallization endpoint temperature between 2 and 20°C, controlling the cooling rate between -0.1 and -1.0°C / min, and controlling the ratio of sweating amount to raw material mass between 2% and 10%.
8. The method as described in claim 7, characterized in that, The operating conditions for the crystallization process in step (2) include controlling the crystallization endpoint temperature at 3 to 10°C, controlling the cooling rate at -0.3 to -0.6°C / min, and controlling the perspiration amount to raw material mass ratio at 3% to 6%.
9. The method according to any one of claims 1-4, characterized in that, The operating conditions for the distillation process in step (3) include controlling the bottom temperature of the column at 170-270℃; the top temperature of the column at 60-130℃; the top pressure of the column at 0.3-2.5kPa; and the side stream reflux ratio at 35%-85%.
10. The method according to any one of claims 1-4, characterized in that, The operating conditions for the distillation process in step (3) include controlling the bottom temperature of the column at 190-230℃; the top temperature of the column at 90-110℃; the top pressure of the column at 0.4-0.8 kPa; and the side stream reflux ratio at 45%-65%.
11. The method according to any one of claims 1-4, characterized in that, In step (4), the rapid cooling process involves directly mixing polyisocyanate (E), crude diphenylmethane diisocyanate (H), and cooled polyisocyanate, then cooling the mixture through a heat exchanger before partially collecting and partially circulating the mixture, with the circulation rate remaining constant at 30–80 m³ / h. 3 / h, the outflow rate is the same as the feed flow rate of polyisocyanate (E), the composition of polyisocyanate remains unchanged in the entire quench system, and crude isocyanate (I) is obtained after quenching, with the temperature controlled at 20-60℃.
12. The method according to any one of claims 1-4, characterized in that, In step (5), the curing temperature of polyisocyanate (I) is controlled at 40-80℃ and the curing time is controlled at 8-48h, and polyisocyanate (J) is obtained after curing; and / or, the polyisocyanate (J) is filtered in two stages, with the first stage filter having a pore size of 100-500um and the second stage filter having a pore size of 1-100um.
13. The method according to any one of claims 1-4, characterized in that, In step (5), the curing temperature of polyisocyanate (I) is controlled at 50-70°C and the curing time is controlled at 12-24h. After curing, polyisocyanate (J) is obtained. And / or, the polyisocyanate (J) filtration is a two-stage filtration, with the first-stage filter having a pore size of 150–300 μm and the second-stage filter having a pore size of 60–80 μm.