A method for synthesizing phenolic resin

Abstract

The present invention discloses a method for synthesizing a phenolic resin. The method comprises heating a mixed solution containing phenol and formaldehyde to a temperature required for a polycondensation reaction under a protective atmosphere, dripping a catalyst solution into the mixed solution to carry out a catalytic polycondensation reaction, and after the polycondensation reaction is completed, removing the phenol by negative pressure to obtain the phenolic resin. The catalyst solution is dripped at a rate from slow to fast and in an amount from small to large. The method has simple steps and high reaction efficiency. The synthesized phenolic resin has a uniform molecular weight distribution, a light color, and high purity.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing a phenolic resin, and in particular to a method for synthesizing a phenolic resin with uniform molecular weight distribution quickly, efficiently and with high conversion rate by changing a catalyst addition method, belonging to the technical field of fine chemical synthesis. Background Art

[0002] Phenolic resin has excellent heat resistance, flame resistance, water resistance, insulation, machinability and bonding strength, and is widely used in the manufacture of molding compounds, honeycomb plastics, laminated plastic adhesives and other industries.

[0003] Currently, the production of thermoplastic phenolic resins primarily involves heating a phenol and formaldehyde solution under acidic catalysis, followed by reflux, dehydration, and dephenolization. Prior art synthesis methods typically involve adding the catalyst all at once, resulting in low efficiency and uneven molecular weight distribution of the resulting phenolic resin.

[0004] Chinese patent (CN111978499A) discloses a phenolic resin synthesis process. The resulting resin has a light color and a uniform molecular weight distribution. However, this method introduces a new solvent and requires high pressure control during the reaction process, which places high demands on equipment. Chinese patent (CN1850875) discloses a phenolic resin preparation method. The resulting resin has high purity and low free phenol and volatile content, but the process is long and involves washing and refining. Summary of the Invention

[0005] In view of the technical problems that the methods for synthesizing phenolic resins in the prior art have, such as a long process flow, low reaction efficiency, a high amount of residual monomers, and uneven molecular weight distribution of the synthesized phenolic resin, the object of the present invention is to provide a method for synthesizing phenolic resin, which has the characteristics of a short process flow, high reaction efficiency, uniform molecular weight distribution of the obtained phenolic resin, low free phenol content, etc., and is conducive to industrial large-scale production.

[0006] In order to achieve the above technical objectives, the present invention provides a method for synthesizing phenolic resin. The method comprises the following steps: heating a mixed solution containing phenol and formaldehyde to a temperature required for a polycondensation reaction under a protective atmosphere; dripping a catalyst solution into the mixed solution to carry out a catalytic polycondensation reaction; and after the polycondensation reaction is completed, removing the phenol by negative pressure to obtain the phenolic resin. The catalyst solution is dripped in a manner of gradually increasing the dripping rate from slow to fast and the dripping amount from small to large.

[0007] The technical solution of the present invention is key to controlling the polycondensation process of formaldehyde and phenol by controlling the addition mode of catalyst, in the polycondensation initial stage, due to the large concentration of raw materials in solution, the catalyst addition rate is too fast or the amount is too large, a large amount of exothermic explosive polyreactions will occur, thereby causing the phenolic resin molecular weight distribution to be wide, and by slowly dripping a small amount of catalyst, the reaction rate can be slowed down, the chain growth reaction of phenol and formaldehyde can be reduced, thereby reducing the generation of macromolecular phenolic resin, and in the polycondensation later stage, the rate of addition of the catalyst is accelerated and the amount is increased, which can reduce the polycondensation reaction time, improve monomer conversion production efficiency, thereby obtaining a phenolic resin molecular weight distribution uniform, conducive to the control of dephenolization reaction, and then making free phenol content low. Particularly, the rate of addition and the amount of the catalyst solution are controlled simultaneously, the rate of addition of the catalyst solution is from slow to fast, and the amount of the catalyst added is from less to more, which can ensure that the whole condensation reaction is continuously and evenly carried out, making the phenolic resin molecular weight distribution more uniform, and the monomer conversion rate is higher.

[0008] As a preferred solution, the molar ratio of phenol to formaldehyde is 1:0.5 to 0.9. This preferred ratio range is beneficial for improving the conversion rate of phenol.

[0009] As a preferred solution, the mixed solution containing phenol and formaldehyde is heated to 80-100° C. The preferred temperature condition is conducive to the polycondensation reaction between phenol and formaldehyde.

[0010] As a preferred solution, the mass percentage concentration of the catalyst solution is 5 to 15%.

[0011] As a preferred solution, the catalyst solution is a common acidic solution, specifically at least one of a sulfuric acid solution, a phosphoric acid solution, a p-toluenesulfonic acid solution, a hydrochloric acid solution, and an oxalic acid solution.

[0012] As a preferred embodiment, the catalyst solution is added dropwise by uniformly adding 25-30% of the total mass of the catalyst solution to the mixed solution over 2-3 hours, and then uniformly adding 70-75% of the total mass of the catalyst solution to the mixed solution over 1-2 hours. Based on the characteristics of the condensation reaction between phenol and formaldehyde, controlling the catalyst addition method can improve the mass and heat transfer efficiency of the reaction system, making the entire condensation reaction more uniform and efficient, thereby increasing the phenol conversion rate and obtaining a phenolic resin with a uniform molecular weight distribution.

[0013] As a preferred solution, the mass of the catalyst in the catalyst solution accounts for 0.5% to 4% of the mass of phenol.

[0014] As a preferred solution, after the catalyst solution is added dropwise, the temperature is maintained at 80-100° C. and the polycondensation reaction is continued for 1-3 hours.

[0015] As a preferred solution, the negative pressure dephenolization conditions are: temperature controlled at 90°C to 280°C, and pressure controlled at -0.09 to 0.1 MPa. Generally speaking, the lower the dephenolization pressure, the better.

[0016] The protective atmosphere involved in the present invention can be nitrogen or an inert gas such as argon.

[0017] The present invention provides a method for synthesizing a phenolic resin. The key improvement of the method is that the method of adding a catalyst to the reaction system is different from the prior art. The catalyst is added to the reaction system in a special gradient manner to change the polymerization reaction process of phenol and formaldehyde to achieve a better reaction effect. The method specifically comprises the following steps:

[0018] Step 1: First, fill the reactor with inert gas to keep the reactor free of oxygen;

[0019] Step 2: heating phenol to a liquid state and keeping the temperature for later use; mixing phenol and a 37% formaldehyde aqueous solution at a molar ratio of 1:0.5 to 0.9 to obtain a mixed liquid;

[0020] Step 3: Weigh a certain amount of catalyst solution, where the catalyst accounts for 0.5% to 4% of the mass of phenol, and set it aside for later use;

[0021] Step 4: Heat the mixed liquid obtained in step 2 to 80-100°C; after the temperature stabilizes, weigh 25%-30% of the total mass of the catalyst solution obtained in step 3 and evenly add it dropwise into the reactor. The addition time is controlled within 2-3 hours;

[0022] Step 5: Continue to dropwise add the remaining catalyst solution to the material obtained in step 4, and control the dropwise addition time to be 1 to 2 hours; after the catalyst dropwise addition is completed, maintain the reaction for 1 to 3 hours;

[0023] Step 6: The material obtained in step 5 is subjected to negative pressure dephenolization by controlling the temperature at 90° C. to 280° C. and the pressure at −0.09 to 0.1 MPa using steam azeotropy or inert gas partial pressure; after dephenolization, phenol novolac resin is obtained.

[0024] Compared with the prior art, the advantages of the technical solution of the present invention are:

[0025] In the prior art, when preparing resol, generally phenol, formalin and catalyst are added in advance to reactor, because reaction process is that phenol and formaldehyde carry out addition, polycondensation reaction under the condition of catalyst, so along with the carrying out of reaction, reaction generates phenolic prepolymer, and its viscosity is larger, and molecular diffusion slows down in whipping process, reduces the mass transfer and heat transfer rate of reaction, and material reaction is insufficient, thereby causes long reaction time, low efficiency. And technical solution of the present invention is first mixed with molten phenol and formalin, after reaching reaction required condition, in system, catalyst solution is dripped by different masses and different speeds in stages, this mode is simple to operate, and catalyst just starts dropping speed and addition amount is small, mainly solves the problem that polycondensation reaction is early stage because raw material concentration is large, easily causes implosion, when catalyst is slowly dripped, raw material can react more fully, can reduce the generation of macromolecular substance in system, material viscosity is low in system, mass transfer and heat transfer effect of material is better, and raw material concentration reduces in reaction later stage, accelerates the speed and consumption of dripping catalyst, can reduce reaction time, improves production efficiency, improves monomer conversion. The reaction efficiency of the entire process is thereby improved, and the obtained phenolic resin has uniform molecular weight distribution and low free phenol content. DETAILED DESCRIPTION

[0026] Below in conjunction with specific embodiment, the present invention is described in further detail, and described embodiment is only a part of embodiment of the present invention, rather than all embodiments. All embodiments have inert gas protection system in reaction process. Based on the embodiment among the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the scope of protection of the present invention. Unless otherwise specified, each raw material used in the following embodiment is commercially available product.

[0027] Example 1

[0028] Add 100g of molten phenol and 43.8g of formaldehyde solution to a four-necked flask equipped with a stirrer and condenser and mix. Raise the temperature to 80°C and begin adding 2g of 10% oxalic acid solution dropwise over 2 hours. Raise the temperature to 95°C and begin adding the remaining 6g of 10% oxalic acid solution dropwise over 1 hour, maintaining the temperature for 1 hour after the addition is complete. Then, increase the temperature to 270°C and the pressure to -0.09 to 0.1 MPa to obtain phenol-formaldehyde resin.

[0029] The phenolic resin has a number average molecular weight of 415, a weight average molecular weight of 653, a PD of 1.57, a softening point of 52° C., a free phenol content of 0.03%, and a chromaticity (Gardner) of 0.28.

[0030] Example 2

[0031] Add 105g of molten phenol and 54g of formaldehyde solution to a four-necked flask equipped with a stirrer and condenser and mix. Raise the temperature to 85°C and begin adding 3g of 10% phosphoric acid dropwise over 3 hours. Then, begin adding the remaining 9g of 10% phosphoric acid dropwise over 1 hour, maintaining the temperature for 1 hour after the addition is complete. Continue heating the flask for dephenolization, maintaining the temperature at 280°C and the pressure at -0.09 to 0.095 MPa. Once dephenolization is complete, phenol-formaldehyde resin is obtained.

[0032] The resin has a number average molecular weight of 470, a weight average molecular weight of 759, a PD of 1.61, a softening point of 60° C., a free phenol content of 0.02%, and a chromaticity (Gardner) of 0.3.

[0033] Example 3

[0034] Add 115g of molten phenol and 70g of formaldehyde solution to a four-necked flask equipped with a stirrer and condenser and mix. Raise the temperature to 90°C and begin adding 3g of 8% hydrochloric acid dropwise over 2.5 hours. Then, begin adding the remaining 7g of hydrochloric acid dropwise over 1.5 hours, maintaining the temperature for 1.5 hours after the addition is complete. Continue heating the phenolization process, maintaining the temperature at 275°C and the pressure at -0.095 to 0.1 MPa. Once the phenolization is complete, phenol-formaldehyde resin is obtained.

[0035] The resin has a number average molecular weight of 531, a weight average molecular weight of 869, a PD of 1.63, a softening point of 71° C., a free phenol content of 0.03%, and a color (Gardner) of 0.25.

[0036] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection claimed by the present invention.

[0037] Compared with similar products at home and abroad, the product of the present invention has the following performance:

[0038]

[0039] GPC: Test conditions: 39-42 bar, 35°C, tetrahydrofuran as mobile phase, injection volume 20 μl, flow rate 1 ml / min. Instrument: Agilent Gel Chromatograph LC-1260.

[0040] Gardner: Test conditions: Dissolve the sample in a solvent at a certain ratio, pour into a cuvette, and then place it in the test instrument. Instrument: Fully automatic spectrophotometer CM-5.

[0041] Reversed-phase liquid chromatography method: Test conditions: YWG C18 column, methanol-water as mobile phase, flow rate of 1.0 ml / min, UV detection wavelength of 216 nm. Instrument: LC-6A high performance liquid chromatograph.

[0042] Comparative Example 1

[0043] Add 100g of melted phenol, 43.8g of aqueous formaldehyde solution, and 10g of 10% oxalic acid solution to a four-necked flask equipped with a stirrer and condenser. Heat to 80°C and react for 4 hours. Then, remove the phenol by heating at 270°C and pressure between -0.09 and 0.1 MPa. After removal of the phenol, a phenol-formaldehyde resin is obtained.

[0044] During the reaction, the temperature was difficult to control, soaring from 80°C to 95°C. Furthermore, the viscosity of the material increased, requiring increased stirring speed. The resulting resin had an uneven molecular distribution.

[0045] The phenolic resin has a number average molecular weight of 503, a weight average molecular weight of 881, a PD of 1.75, a softening point of 75° C., a free phenol content of 0.03%, and a chromaticity (Gardner) of 0.29.

[0046] Comparative Example 2

[0047] Add 100g of melted phenol and 43.8g of formaldehyde solution to a four-necked flask equipped with a stirrer and condenser and mix. Raise the temperature to 80°C and begin adding 10g of a 10% oxalic acid solution dropwise for 3 hours. Maintain the temperature for 1 hour after the addition is complete. Then, increase the temperature to 270°C and control the pressure between -0.09 and 0.1 MPa to obtain phenol-formaldehyde resin.

[0048] During the reaction, the temperature fluctuated between 80°C and 90°C. With the addition of the catalyst, the viscosity of the material increased, necessitating increased stirring speed. Furthermore, as the raw material concentration decreased and the system viscosity increased, the reaction slowed down, while the catalyst addition rate remained constant, increasing production time and reducing efficiency. The resulting resin exhibited uneven molecular weight distribution.

[0049] The phenolic resin has a number average molecular weight of 450, a weight average molecular weight of 765, a PD of 1.70, a softening point of 66° C., a free phenol content of 0.03%, and a chromaticity (Gardner) of 0.3.

Claims

1. A method for synthesizing a phenolic resin, characterized in that: Under a protective atmosphere, a mixed solution containing phenol and formaldehyde is heated to a temperature required for a polycondensation reaction, a catalyst solution is added dropwise to the mixed solution to carry out a catalytic polycondensation reaction, and after the polycondensation reaction is completed, phenol removal is performed under negative pressure to obtain a phenolic resin; the catalyst solution is added dropwise at a rate from slow to fast and in a gradient amount from small to large; The catalyst solution is at least one of a sulfuric acid solution, a phosphoric acid solution, a p-toluenesulfonic acid solution, a hydrochloric acid solution, and an oxalic acid solution; The catalyst solution is added dropwise as follows: first, 25-30% of the total mass of the catalyst solution is evenly added dropwise to the mixed solution within 2-3 hours, and then 70-75% of the total mass of the catalyst solution is evenly added dropwise to the mixed solution within 1-2 hours.

2. A method for synthesizing a phenolic resin according to claim 1, characterized in that: The molar ratio of phenol to formaldehyde is 1:0.5~0.

9.

3. The method for synthesizing a phenolic resin according to claim 1, wherein: The mixed solution containing phenol and formaldehyde is heated to 80~100℃.

4. The method for synthesizing a phenolic resin according to claim 1, wherein: The mass percentage concentration of the catalyst solution is 5-15%.

5. The method for synthesizing a phenolic resin according to claim 1, wherein: The mass of the catalyst in the catalyst solution accounts for 0.5% to 4% of the mass of phenol.

6. The method for synthesizing a phenolic resin according to claim 1, wherein: After the catalyst solution is added dropwise, the temperature is maintained at 80-100°C and the polycondensation reaction is continued for 1-3 hours.

7. The method for synthesizing a phenolic resin according to claim 1, wherein: The negative pressure dephenolization conditions are: the temperature is controlled at 90° C. to 280° C., and the pressure is controlled at -0.09 to 0.1 MPa.

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