Preparation method of low-color 3-isocyanate propyltrimethoxysilane

Abstract

The present invention provides a preparation method of 3-isocyanate propyl trimethoxysilane with low color, wherein raw material 3-trimethoxysilane methyl carbamate is introduced into the middle of a tower reactor equipped with a catalyst at the bottom, and the raw material reacts with the catalyst; after the reaction is completed, the top discharge of the reactor is an isocyanate silane product, and the bottom discharge of the reactor is a residual liquid, which can be mixed with fresh raw materials and re-enters the reactor for cracking reaction. The bottom discharge of the reactor of the present invention is substantially free of residue generation, and the bottom material can reach a raw material conversion rate of 100% through a cyclic reaction; the selected reaction raw materials are non-hazardous chemicals, the reaction is stable and controllable, and there is no dangerous operation. In particular, the reaction can be continuously operated; the use of solvents is avoided, solvent separation and recovery steps are omitted, and the concept of green environmental protection is met.

Description

Technical Field

[0001] The present invention relates to the field of organosilicon chemicals, and in particular to a method for preparing 3-isocyanatepropyltrimethoxysilane. Background Art

[0002] 3-Isocyanatepropyltrimethoxysilane is a silane coupling agent containing NCO groups. It is an excellent glass fiber treatment agent that can improve the mechanical strength, electrical properties and aging resistance of composite materials. It is widely used in the surface treatment of glass fibers in glass fiber reinforced plastics such as polyethylene cross-linking, unsaturated resins, polyethylene, and polypropylene resins. It can also be used as an adhesive for surface moisture-proof treatment of electronic components or surface treatment of inorganic silicon fillers.

[0003] Currently, the industrialized methods for preparing isocyanate silanes mainly include the phosgene (triphosgene) method, the isocyanate method and the thermal decomposition method.

[0004] Patent CN101307067 generates isocyanate groups by reacting phosgene with amines in an inert solvent, while Patent CN101492468 uses triphosgene to react with trialkoxysilaneamine under low temperature conditions to prepare trialkoxy isocyanates. The basic principles of the phosgene method and the triphosgene method are the same. The triphosgene method greatly improves the safety performance of the phosgene method. However, if solid phosgene comes into contact with water or heat during operation, phosgene will still be generated, posing a safety hazard. In addition, the reaction byproduct HCl is prone to causing significant corrosion to industrial equipment.

[0005] Patent CN104262384 uses NaNCO and chlorosilane as raw materials to directly produce isocyanate silane. This method has few reaction steps and is easy to operate. NaNCO is a solid and requires the addition of a polar solvent, but its solubility is poor, resulting in a long reaction time and low yield.

[0006] Patent CN101307067 uses carbamate silane as a raw material and produces isocyanate groups through high-temperature cracking of carbamate groups, with methanol as a by-product. This process is a one-pot high-temperature cracking method, which can greatly improve the safety of the preparation process. However, the process described in the patent does not use a catalyst. Relying solely on high-temperature and long-term heating can easily cause the raw material carbamate silane to self-polymerize, resulting in severe coking and low yield. Patent CN207259419 proposes using tubular heating instead of kettle heating to partially alleviate the raw material coking problem. However, due to the lack of a catalyst, it can only process gas-phase materials, resulting in low processing capacity and limited industrialization potential.

[0007] In summary, the thermal decomposition method has the advantages of high safety, short reaction time and no waste salt production, and has been widely used in industry. However, the main bottleneck of this method is how to quickly crack the raw material carbamate silane to avoid its polymerization and coking under long-term high-temperature heating, improve product yield and reduce residue production. Summary of the Invention

[0008] In view of the shortcomings of the existing thermal decomposition method for preparing isocyanate silane, the present invention provides a method for preparing 3-isocyanate propyltrimethoxysilane with a fast cracking rate, less residue and low color.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing low-color 3-isocyanate propyltrimethoxysilane, wherein the structural formula of the low-color 3-isocyanate propyltrimethoxysilane is:

[0011]

[0012] The preparation method comprises the following steps:

[0013] The raw material 3-trimethoxysilane methyl carbamate is introduced into the middle of a tower reactor with a catalyst at the bottom, and the raw material reacts with the catalyst;

[0014] After the reaction is completed, the material discharged from the top of the reactor is the isocyanate silane product, and the material discharged from the bottom of the reactor is the residual liquid, which can be mixed with fresh raw materials and re-entered into the reactor for re-cracking reaction.

[0015] The catalyst is a metal-supported catalyst, which is prepared by loading an active component onto a carrier. The active component is a metal oxide, and the carrier is selected from one of molecular sieves, γ-Al2O3 or activated carbon. The amount of the active component added is: the mass ratio of the active component to the mass ratio of the carrier is 8-15%.

[0016] The active component is any one of zinc oxide, magnesium oxide, titanium oxide or zirconium oxide or a combination of several of them.

[0017] The preferred catalyst carrier is a silica-alumina molecular sieve.

[0018] In the above method, the reaction temperature is controlled at 220-260° C., and the raw material space velocity is 0.05-1 g / h / g / cat.

[0019] Furthermore, as a preference, the reaction temperature is more preferably 220-240° C., and the raw material space velocity is more preferably 0.15-0.25 g / h / g / cat.

[0020] The reactor described in the above steps is divided into two sections: the upper section is used to place the distillation filler, and the lower section is used to place the catalyst. The raw materials enter from the middle of the reactor and are cracked through the catalyst bed. The product vapor is refined upward through the distillation layer to obtain the product and methanol. The boiling point difference can be used to remove the methanol to obtain the refined product.

[0021] The raw material, methyl 3-trimethoxysilylcarbamate, is introduced into the center of the tower reactor containing the catalyst. Specifically, the raw material is pumped through a feed pump and precisely controlled by a mass flow controller. The flow rate range is determined by the space velocity, which ranges from 0.05 to 1 g / h / g / cat. Once the catalyst weight is determined, the raw material flow rate is determined.

[0022] The structural formula of the 3-trimethoxysilane methyl carbamate is:

[0023]

[0024] The preparation method of the catalyst is as follows:

[0025] Using the carrier as a matrix, metal nitrate is mixed with an appropriate amount of deionized water to form a solution, stirred until the solution is completely impregnated, and then allowed to stand for aging;

[0026] Then filter and wash the filter cake with deionized water, repeat the above steps until there is no nitrate ion, dry the filter cake and crush it, mix it evenly with the binder and nitric acid aqueous solution, adjust it into a mud, squeeze it into strips, dry it and place it in a muffle furnace for roasting to obtain the required catalyst.

[0027] Specifically, the carrier is a silicon-aluminum molecular sieve with a silicon-aluminum ratio of 25 to 40 and a specific surface area of ​​300 to 500 m 2 / g, pore volume 0.2~0.4ml / g.

[0028] The metal nitrate is one or more of zinc nitrate, magnesium nitrate, titanium nitrate and zirconium nitrate.

[0029] The filter cake is dried in an oven at 120-140°C, crushed, and evenly mixed with a binder and a nitric acid aqueous solution to form a slurry. The mixture is then extruded into cylindrical strips using an extruder. The strips are then dried in an oven at 120-140°C and calcined in a muffle furnace at 400-600°C to obtain the catalyst. The catalyst is then cut into 2-5 mm pieces for later use. The binder is γ-Al2O3 powder, the mass ratio of the γ-Al2O3 powder to the mass ratio of the carrier being 10-25%, and the nitric acid aqueous solution is a 5% by mass dilute nitric acid aqueous solution.

[0030] Reaction equation of the present invention is as follows:

[0031]

[0032] The beneficial effects of the present invention are as follows:

[0033] (1) The tower reactor of the present invention is divided into two sections. The reaction is carried out in the lower section, and the separation and purification is carried out in the upper section. The product can be obtained by discharging the material from the top. The reaction conversion rate and selectivity are high, and the obtained product is light in color. The material discharged from the bottom of the reactor is basically free of residue. The bottom material is recycled and the raw material conversion rate can reach 100%;

[0034] (2) The reaction raw materials selected in the present invention are non-hazardous chemicals, the reaction is stable and controllable, and there is no dangerous operation. In particular, the reaction can be operated continuously;

[0035] (3) The present invention avoids the use of solvents, omitting the solvent separation and recovery steps, and is in line with the concept of green environmental protection. DETAILED DESCRIPTION

[0036] Example 1: Effect of different catalyst systems

[0037] Weigh 100g of γ-Al2O3 (5 parts) as a benchmark, 15g of γ-Al2O3 (5 parts) as a binder, and weigh different weights of metal salts (see Table 1) according to 4 different mass ratios. The metal salts (zinc nitrate and magnesium nitrate, titanium nitrate, and zirconium nitrate) are respectively configured into solutions with an appropriate amount of deionized water, stirred until the impregnation is complete, and allowed to stand for aging; then filter and wash the filter cake with deionized water, repeat the above steps until there is no nitrate ion, dry the filter cake in an oven at 120-140°C, crush it, mix it evenly with the binder γ-Al2O3 powder and 5%wtHNO3 aqueous solution, adjust it into a muddy state, extrude it into cylindrical strips with an extruder, dry it in an oven at 120-140°C, and then place it in a muffle furnace at 400-600°C for calcination to obtain the desired catalyst, and finally cut it into 2-5mm pieces to make the catalyst for standby use.

[0038] The raw material 3-trimethoxysilylcarbamate was fed into the middle of the tower reactor via a metering pump to control the flow rate. The raw material space velocity was 0.4 g / h / g / cat, the reaction temperature was 220°C, and the bottom of the reactor was discharged as residual liquid, which could be mixed with fresh raw materials and re-entered the reactor for cracking reaction. The specific results are shown in the following table:

[0039] Table 1 Effects of different catalysts on the reaction results.

[0040]

[0041] As can be seen from Table 1, the catalyst systems of the present invention achieved yields exceeding 76% under the initial reaction conditions, indicating that the prepared catalysts possessed relatively good catalytic activity. The catalysts whose active components were zinc oxide, titanium oxide, and combinations thereof exhibited relatively good activity, while the catalyst whose active component was zirconium oxide exhibited slightly poorer activity. Furthermore, it can be seen that the reaction conditions were not optimal and require further optimization.

[0042] Example 2: Effect of reaction temperature

[0043] The catalyst preparation process and working principle of this example are the same as those of Example 1, except that the reaction temperature is different. The results are shown in Table 2. Other conditions: The catalyst # of Example 5 was used, and the feed space velocity was 0.4 g / h / g / cat.

[0044] Table 2 Effect of different reaction temperatures on reaction results.

[0045]

[0046] Reaction temperature significantly affects the activity of the raw materials and the reaction rate. When the temperature is too low, the reaction generally cannot proceed rapidly. Higher temperatures can cause the product to polymerize into dimers and polymers, significantly increasing the number of byproducts. While conversion rates increase consistently within this temperature range of 220°C to 260°C, yield peaks at 230°C. Further increases in temperature result in a decreasing yield. Therefore, considering both conversion and yield, a temperature between 220°C and 260°C is optimal, with 230°C being the most preferred.

[0047] Example 3: Effect of feed space velocity

[0048] The catalyst preparation process and working principle of this embodiment are the same as those of embodiment 1, except that the reaction was carried out at different feed space velocities. The results are shown in Table 3. Other conditions: the catalyst # of embodiment 5 was used, and the reaction temperature was 230°C.

[0049] Table 3 Effect of different feed space velocities on reaction performance.

[0050]

[0051]

[0052] The space velocity reflects the residence time of the material in the reactor. Different catalyst systems have their own matching material space velocity. As can be seen from Table 3, the most suitable space velocity for catalyst #5 in Example 1 is 0.3 g / h / g / cat.

[0053] The tower reactor used in the embodiment of the present invention includes an upper section and a lower section that are connected, and a middle section between the upper section and the lower section. A distillation filler is placed in the upper section, a catalyst is placed in the lower section, and the middle section is provided with a feed port. The middle section and the lower section are connected, so that the raw material 3-trimethoxysilane methyl carbamate can enter the lower section from the middle section. The middle section and the upper section are connected, and are specifically set to a structure that can circulate gas but cannot pass through solids, such as: a baffle structure with multiple micropores, which can make the product vapor of the lower section reach the distillation layer upward, and the distillation filler in the upper section will not fall. The raw material 3-trimethoxysilane methyl carbamate enters from the middle section of the tower reactor and reaches the lower section of the tower reactor. The top of the upper section of the tower reactor is used to discharge the isocyanate silane product and methanol. The product 3-isocyanate propyltrimethoxysilane is obtained by a primary condenser connected to the top of the upper section of the tower reactor, and methanol is obtained by a secondary condenser connected to the primary condenser.

[0054] The operating pressure of the tower reactor is normal pressure or slightly negative pressure: -0.05 to -0.03 MPa. The operating temperature of the catalyst layer in the lower section of the tower reactor is 220 to 260°C, and the operating temperature of the distillation layer in the upper section is 120 to 150°C.

[0055] The above content is a further detailed description of the technical solution provided in combination with the preferred implementation methods of the present invention. It cannot be determined that the specific implementation of the present invention is limited to the above descriptions. For technicians in the technical field of the present invention, simple deductions and replacements made without departing from the concept of the present invention should be deemed to fall within the scope of protection of the present invention.

Claims

1. A method for preparing low-color 3-isocyanate propyltrimethoxysilane, wherein the structural formula of the low-color 3-isocyanate propyltrimethoxysilane is: The preparation method comprises the following steps: The raw material 3-trimethoxysilane methyl carbamate is introduced into the middle of a tower reactor with a catalyst at the bottom, and the raw material reacts with the catalyst; After the reaction is completed, the material discharged from the top of the reactor is the isocyanate silane product, and the material discharged from the bottom of the reactor is the residual liquid, which can be mixed with fresh raw materials and re-entered into the reactor for cracking reaction; The catalyst is a metal-supported catalyst, which is prepared by loading an active component onto a carrier, wherein the mass ratio of the active component to the carrier is 12%, the active components are zinc oxide and titanium oxide, and the mass ratio of zinc oxide to titanium oxide is 1:1; and the carrier is γ-Al2O3; The preparation method of the catalyst comprises the following steps: S1. Using the carrier as a matrix, prepare a solution of metal nitrate and deionized water, stir until the solution is completely immersed, and allow to stand for aging; S2, filtering and washing the filter cake with deionized water; S3, repeat S2 until there are no nitrate ions, then dry the filter cake and crush it, mix it evenly with the binder and nitric acid aqueous solution, adjust it into a mud, dry it and place it in a muffle furnace for calcination to obtain the desired catalyst; The reactor is divided into two sections: the upper section is used to place the distillation filler, and the lower section is used to place the catalyst. The raw material enters the middle of the reactor and is cracked through the catalyst bed. The product vapor is refined upward through the distillation layer to obtain the product and methanol. The methanol is removed by using the boiling point difference to obtain the refined product. The operating pressure of the tower reactor is atmospheric pressure or slightly negative pressure: -0.05~-0.03MPa, the operating temperature of the catalyst layer in the lower section of the tower reactor is 220~240°C, and the operating temperature of the distillation layer in the upper section is 120~150°C; the feed space velocity is 0.1~0.4g / h / g / cat; The structural formula of the 3-trimethoxysilane methyl carbamate is: 。

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