CN111253219B

CN111253219B - Preparation method of 3, 5-dimethylphenol

Info

Publication number: CN111253219B
Application number: CN202010176695.4A
Authority: CN
Inventors: 殷飞; 曹忠; 魏一帆; 刘小棒; 张敏敏
Original assignee: Zhejiang Jinke Household Chemical Materials Co ltd
Current assignee: Zhejiang Jinke Daily Chemical New Materials Co ltd
Priority date: 2020-03-13
Filing date: 2020-03-13
Publication date: 2022-05-27
Anticipated expiration: 2040-03-13
Also published as: CN111253219A

Abstract

The invention discloses a preparation method of 3, 5-dimethylphenol, which takes isophorone as a raw material to carry out cracking reaction under the action of a catalyst, and specifically comprises the following steps: carrying out water removal treatment on isophorone by using a water absorbent until the water content of isophorone is less than or equal to 0.2%, adding a catalyst into isophorone after water removal, and uniformly mixing to obtain a raw material mixture; under the protection of inert gas, the raw material mixture is pumped into the tubular reactor from the top of the tubular reactor, and the retention time of the raw material mixture in the tubular reactor is 40-48 s; the reaction temperature is 480-520 ℃; the reaction pressure is normal pressure; the product is withdrawn from the bottom of the tubular reactor. The method for preparing the 3, 5-dimethylphenol has the characteristics of high reaction conversion rate, high selectivity, low catalyst price and the like.

Description

Preparation method of 3, 5-dimethylphenol

Technical Field

The invention belongs to the field of organic synthesis, and particularly relates to a preparation method of 3, 5-dimethylphenol.

Background

3, 5-dimethylphenol of the formula C₈H₁₀O, molecular weight is 122, the structural formula is shown as formula 1, and the compound is an important industrial intermediate and is mainly used for preparing antioxidants, antibiotics, resin adhesives, vitamin E and the like.

From the domestic and foreign documents reported at present, the main preparation method of 3, 5-dimethylphenol is isophorone catalytic cracking, and the method is mainly divided into the following types according to different selected catalysts:

the patent (CN101348421A) proposes that under the conditions that the reaction temperature is 550 ℃, the reaction pressure is 2atm and the catalyst dosage is 0.8 percent, the conversion rate of isophorone is 96 percent and the selectivity of 3, 5-dimethylphenol is 89 percent by using n-bromobutane as a catalyst; the catalyst can not make the raw material completely react, and has low selectivity. The method uses methyl iodide as a catalyst, under the conditions that the reaction temperature is 550 ℃, the reaction pressure is 2atm, and the catalyst dosage is 0.5%, the conversion rate of isophorone is 100%, the selectivity of 3, 5-dimethylphenol is 95%, and the methyl iodide has a good catalytic effect, but the methyl iodide is expensive, belongs to a highly toxic medicine, and has a certain safety problem.

The patent (CN105061155A) proposes that the conversion rate of isophorone is 89% and the selectivity of 3, 5-dimethylphenol is 89% under the conditions of reaction temperature of 570 ℃ and reaction pressure of 2.5MPa by using iron-nickel-chromium oxide mixture as a catalyst, the reaction needs high temperature and high pressure, the requirement on equipment is high, and the conversion rate and the selectivity are not high.

In the above prior art, if the reaction is carried out under normal pressure instead, the conversion rate of isophorone is greatly reduced, and the selectivity of 3, 5-dimethylphenol is greatly reduced.

Disclosure of Invention

The invention aims to solve the technical problem of providing a preparation method of 3, 5-dimethylphenol, which has the characteristics of high reaction conversion rate, high selectivity, low catalyst price and the like.

In order to solve the technical problems, the invention provides a preparation method of 3, 5-dimethylphenol, which takes isophorone as a raw material to carry out a cracking reaction under the action of a catalyst, and comprises the following steps:

1) and dewatering:

carrying out water removal treatment on isophorone by using a water absorbent until the water content of isophorone is less than or equal to 0.2% (mass%), so as to obtain dehydrated isophorone;

2) adding a catalyst (bromine hydrocarbon catalyst) into the dehydrated isophorone, and uniformly mixing to obtain a raw material mixture; the mass ratio of the catalyst to the dehydrated isophorone is 0.8% -1%;

under the protection of inert gas (nitrogen), the raw material mixture is pumped into the tubular reactor from the top of the tubular reactor, and the retention time of the raw material mixture in the tubular reactor is 40-48 s; the reaction temperature is 480-520 ℃ (preferably 500-520 ℃); the reaction pressure is normal pressure;

the product is withdrawn from the bottom of the tubular reactor.

As an improvement of the process for producing 3, 5-dimethylphenol of the present invention: the catalyst is bromobutane, bromopropane, bromoethane, dibromoethane and tetrabromoethane.

As a further improvement of the process for producing 3, 5-dimethylphenol of the present invention, step 1): the mass ratio of the water absorbent to the isophorone is 5-15%; the water absorbent is molecular sieve, anhydrous sodium sulfate, and anhydrous magnesium sulfate.

As a further improvement of the preparation method of 3, 5-dimethylphenol of the invention, step 1) is molecular sieve dehydration: taking a 3A molecular sieve, activating at 400 ℃ for 8h, cooling to 130-170 ℃, adding into an isophorone raw material, sealing, standing and dehydrating for 24 h.

The invention has the following technical advantages:

1. water is removed from isophorone raw material by using water absorbents such as molecular sieve, the water content in the raw material is reduced to be less than or equal to 0.2%, side reaction between isophorone and water is avoided, and the selectivity of the reaction is improved.

2. Avoids the hydrolysis reaction between the bromohydrocarbon catalysts such as dibromoethane and the like and water, reduces the consumption of the catalysts and ensures that the conversion rate of the raw materials reaches 100 percent.

3. By the water removal operation, a bromine hydrocarbon catalyst can be used instead of an expensive catalyst such as methyl iodide, and the same catalytic effect can be achieved.

Drawings

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

FIG. 1 is a schematic view of the structure of a reaction apparatus used in the present invention.

Detailed Description

The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto:

the reaction device adopted by the invention is shown in figure 1 and comprises a tubular reactor; the tubular reactor is provided with a thermocouple for controlling the reaction temperature in a matching way and a matched temperature display;

the tubular reactor is provided with a transformer 1 and a transformer 2 which are used for heating the tubular reactor; the top of the tubular reactor is provided with a nitrogen inlet and a material inlet, so that the material can enter the tubular reactor from the top of the tubular reactor under the protection of nitrogen.

The bottom of the tubular reactor is provided with a product collecting device, such as a three-neck flask.

The length of a main body pipe of the tubular reactor is 120cm, and the inner diameter of the main body pipe of the tubular reactor is 6 cm; therefore, when the feeding speed is 1-1.2 ml/min, the retention time of the corresponding material in the tubular reactor is 40-48 s.

Example 1, a method of preparing 3, 5-dimethylphenol, sequentially performing the following steps:

1) and molecular sieve dewatering:

weighing 20g of 3A molecular sieve, activating at 400 ℃ for 8h, cooling to about 150 ℃, adding into 200g of isophorone, sealing, and standing for 24 h; and obtaining the dehydrated isophorone.

Using a karl fischer moisture meter, the following results were measured: before water removal, the water content of isophorone is about 1.5%, after water removal, the water content of isophorone is 0.2%. The above% is by mass.

2) Weighing 100g of dehydrated isophorone, adding 1g of dibromoethane, and uniformly mixing to obtain a raw material mixture;

when the temperature of the tubular reactor is raised to 500 ℃, the raw material mixture is pumped into the tubular reactor under the protection of nitrogen, the feeding speed is 1.1ml/min (namely, the retention time of the raw material mixture in the tubular reactor is 44s), the reaction is carried out under normal pressure, and a three-neck flask is used for receiving a product below the reactor.

(3) And after the reaction is finished, taking a proper amount of product, diluting the product with ethanol, and carrying out gas phase detection. The detection conditions comprise hydrogen flame ionization detection, capillary column chromatographic column with specification of 66m × 0.25mm × 1.0um, vaporization chamber temperature of 260 deg.C, column temperature of 120 deg.C, and detector temperature of 260 deg.C. The detection result shows that the conversion rate of the isophorone is 100%, and the selectivity of the 3, 5-dimethyl (MX) is 96%.

Thus, the product is mainly 3, 5-dimethylphenol with a content of 96%, and the remainder is toluene, m-xylene, mesitylene, etc., as by-products, which can be separated by conventional distillation methods.

Examples 2 to 7

The catalyst amount, the feeding speed and the reaction temperature in example 1 were changed and the rest was the same as example 1, the following examples 2 to 7 were obtained, respectively, and the conversion rate of isophorone and the selectivity of MX are shown in Table 1 below.

TABLE 1

Description of the drawings:

the feeding speed is 1.0ml/min, and the retention time of the corresponding materials in the tubular reactor is 48 s;

the feed rate was 1.2ml/min, corresponding to a residence time of 40s of the material in the tubular reactor.

Examples 8 to 9, step 1) was modified to: respectively adding anhydrous sodium sulfate and anhydrous magnesium sulfate solid into the raw materials, wherein the adding amount is 10 percent of the mass of the isophorone, sealing, standing for 24 hours, and the rest is identical to example 1, and the results are shown in the following table 2:

TABLE 2

Examples 10 to 13, the kind of the catalyst was changed and the amount of the catalyst was kept constant; the rest is equivalent to example 1, and the results are shown in the following table 3:

TABLE 3

	Catalyst and process for preparing same	Conversion of isophorone	Selectivity to MX
				Example 10	Bromobutane	100％	95％
Example 11	Bromopropane	100％	95％
				Example 12	Bromoethane	100％	95％
Example 13	Tetrabromoethane	100％	96％

Comparative examples 1 to 5, example 1, and examples 10 to 13 were each treated as follows:

the molecular sieve dehydration in the step 1) is cancelled; in the step 2), 101.3g of isophorone is directly used for replacing 100g of isophorone after water removal, so that the actual effective using amount of isophorone is kept unchanged; thus comparative examples 1 to 5 were obtained correspondingly. The results are given in table 4 below:

TABLE 4

It can be seen from the above examples and comparative examples that when the water content in the raw material is reduced to 0.2%, the conversion rate of isophorone reaches 100%, and the selectivity of MX is above 95%, if the raw material is not subjected to water removal, the reaction of isophorone raw material is incomplete, and the selectivity is low, so that the water removal of raw material is beneficial to improving the selectivity and conversion rate of the reaction.

Finally, it is also noted that the above-mentioned lists merely illustrate a few specific embodiments of the invention. It is obvious that the invention is not limited to the above embodiments, but that many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.

Claims

The preparation method of the 1, 5-dimethylphenol is characterized by comprising the following steps: the method takes isophorone as a raw material, and carries out cracking reaction under the action of a catalyst, and comprises the following steps:

1) and dewatering:

carrying out water removal treatment on isophorone by using a water absorbent until the water content of isophorone is less than or equal to 0.2%, so as to obtain dehydrated isophorone;

2) adding a catalyst into the dehydrated isophorone, and uniformly mixing to obtain a raw material mixture; the mass ratio of the catalyst to the dehydrated isophorone is 0.8% -1%; the catalyst is bromobutane, bromopropane, bromoethane, dibromoethane or tetrabromoethane;

under the protection of inert gas, pumping the raw material mixture into the tubular reactor from the top of the tubular reactor, wherein the retention time of the raw material mixture in the tubular reactor is 40-48 s; the reaction temperature is 480-520 ℃; the reaction pressure is normal pressure;

the product is withdrawn from the bottom of the tubular reactor.
2. The process for producing 3, 5-dimethylphenol according to claim 1, characterized in that the step 1):

the mass ratio of the water absorbent to the isophorone is 5-15%;

the water absorbent is molecular sieve, anhydrous sodium sulfate, and anhydrous magnesium sulfate.
3. The process for preparing 3, 5-dimethylphenol according to claim 2, characterized in that step 1) comprises molecular sieve dehydration: taking a 3A molecular sieve, activating at 400 ℃ for 8h, cooling to 130-170 ℃, adding into isophorone serving as a raw material, sealing, standing and dehydrating for 24 h.