Production method of 2, 3, 5-trimethylhydroquinone diester

Abstract

The invention provides a production method of 2, 3, 5-trimethylhydroquinone diester, which comprises the following steps: carrying out rearrangement reaction on 2, 6, 6-trimethyl-cyclohexyl-2-ene-1, 4-diketone and an acylating agent in a tubular reactor filled with a catalyst to obtain the 2, 3, 5-trimethylhydroquinone diester, all reaction parameters in the tubes of the tubular reactor meet the relationship shown in the formula 1. The production method has the advantages of high production efficiency, small corrosion to equipment and simple subsequent treatment process, and is suitable for wide popularization and application.

Description

Technical Field

[0001] This invention relates to the field of chemical product synthesis technology, and in particular to a method for producing 2,3,5-trimethylhydroquinone diester. Background Technology

[0002] Vitamins are a class of trace organic substances that the human body must obtain from the external environment to maintain normal physiological functions. Vitamin E, as one of the important vitamins, has received widespread attention for its antioxidant, anti-aging, and immune-boosting effects. 2,3,5-Trimethylhydroquinone diester (TMHQ-DA) is an important raw material for the synthesis of vitamin E and vitamin E acetate. Therefore, the production and preparation of TMHQ-DA through efficient and low-consumption methods is a key step in the artificial synthesis of vitamin E and is of great significance for meeting the increasing demand for synthetic nutritional products.

[0003] As shown in formula a, TMHQ-DA is currently mainly synthesized by rearrangement reaction of 2,6,6-trimethyl-cyclohexyl-2-ene-1,4-dione (oxoisophorone, KIP) with acid anhydride under the action of an acidic catalyst.

[0004]

[0005] Patents DE2149159A1, CN1165133A, and CN1241559A use protic acids or Lewis acids as catalysts to synthesize TMHQ-DA. However, this method often requires a large amount of acid, necessitating subsequent quenching treatment, making the process complex. Furthermore, the quenching process generates a large amount of waste salt, which is environmentally unfriendly. Additionally, using strong acids as catalysts places higher demands on the corrosion resistance of production equipment, resulting in high equipment investment costs.

[0006] To reduce the corrosive effect of strong acids on downstream equipment, CN101607896A proposed using acidic ionic liquids as catalysts to produce TMHQ-DA. However, this method significantly reduces the reaction rate, with the single-pass conversion rate decreasing to 21-66%. Furthermore, acidic ionic liquids are difficult to process and manufacture, resulting in high costs, which hinders their application in industrial production.

[0007] Patents CN111675612A and CN109970553A utilize supported solid acid catalysts to prepare TMHQ-DA. Although this can overcome the defects mentioned above and achieve a higher reaction rate, complex procedures such as filtration and backwashing or a large amount of manual operation are required to achieve catalyst recycling.

[0008] Therefore, it is necessary to provide a method for producing 2,3,5-trimethylhydroquinone diester that can improve the reaction rate, has low corrosiveness to equipment, and simplifies subsequent processing. Summary of the Invention

[0009] This invention provides a method for producing 2,3,5-trimethylhydroquinone diester. This method has high production efficiency, low corrosiveness to equipment, and simple subsequent processing, making it suitable for widespread application.

[0010] This invention provides a method for producing 2,3,5-trimethylhydroquinone diester, characterized by comprising the following steps:

[0011] 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione was rearranged with an acylating agent in a tubular reactor packed with a catalyst to obtain 2,3,5-trimethylhydroquinone diester.

[0012] The reaction parameters in the tubes of the tubular reactor satisfy the relationship shown in Equation 1;

[0013]

[0014] In Equation 1, A is the proportionality coefficient, and the value of A ranges from 11 to 15;

[0015] t is the time, in minutes, for the raw material to flow from the axial inlet of the tube to a certain point.

[0016] T represents the temperature at a certain point along the axial direction of the tubes, in °C.

[0017] c is the percentage (%) of the total amount of the catalyst loaded relative to the hourly feed mass of 2,6,6-trimethyl-cyclohexyl-2-ene-1,4-dione;

[0018] n is the exponential coefficient. When c < 5, n takes the value of 2; when c ≥ 5, n takes the value of 1.

[0019] x is the ratio of the amount of catalyst loaded at a certain point along the axial direction of the tube to the amount of catalyst loaded at the outlet of the tube.

[0020] In the production method described above, the diameter of the tubes in the tubular reactor gradually increases from the inlet to the outlet.

[0021] In the production method described above, the tubes are variable diameter tubes with an outer diameter of 10-57 mm;

[0022] Preferably, the variable diameter tube is formed by combining at least two of the heat exchange tubes with outer diameters of 10mm, 14mm, 19mm, 25mm, 38mm, 45mm, and 57mm.

[0023] In the production method described above, the amount of catalyst loaded in the tubular reactor gradually increases from the inlet to the outlet.

[0024] In the production method described above, the ratio of the amount of catalyst loaded at the inlet of the tube to the amount of catalyst loaded at the outlet of the tube is 0.05-0.8.

[0025] In the production method described above, the temperature in the tubular reactor gradually increases from the inlet to the outlet.

[0026] In the production method described above, the inlet temperature of the tubular reactor is 20-60°C; and / or,

[0027] The outlet temperature of the tubular reactor is 70-100℃;

[0028] Preferably, the inlet temperature of the tubular reactor is 25-55°C; and / or,

[0029] The outlet temperature of the tubular reactor is 75-95℃.

[0030] The production method described above, wherein c% is 2-15%; and / or,

[0031] The total residence time of the raw material from the inlet to the outlet of the tube is 40-240 min; and / or,

[0032] In the rearrangement reaction, the molar ratio of 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione to the acylating agent is 1:(2-20);

[0033] Preferably, c% is 2.5-10%; and / or,

[0034] The total residence time of the raw material from the inlet to the outlet of the tube is 60-150 min; and / or,

[0035] In the rearrangement reaction, the molar ratio of 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione to the acylating agent is 1:(3-10).

[0036] The production method described above further includes preheating 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione with an acylating agent at a temperature of 25-40°C.

[0037] In the production method described above, the acylating agent is selected from at least one of acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, and benzoic anhydride;

[0038] Preferably, the acylating agent is acetic anhydride; and / or,

[0039] The catalyst includes a support and an active acid anion supported on the support;

[0040] Preferably, the active acid anion is at least one selected from sulfate, sulfonate, nitrate, and phosphate.

[0041] The method for producing 2,3,5-trimethylhydroquinone diester of the present invention involves a rearrangement reaction of 2,6,6-trimethyl-cyclohexyl-2-ene-1,4-dione with an acylation agent in a tubular reactor packed with a catalyst to obtain 2,3,5-trimethylhydroquinone diester. Compared with a stirred reactor, the tubular reactor is closer to a plug flow reactor, which can reduce backmixing in the rearrangement reaction and increase the reaction rate. Furthermore, the present invention ensures that the parameters in the tubular reactor satisfy the relationship shown in Equation 1, which can promote the formation of the main product and suppress the formation of byproducts such as 2,4,5-trimethylhydroquinone diester and 3,4,5-trimethylhydroquinone diester while ensuring the reaction rate of the rearrangement reaction and the conversion rate of the raw materials, thereby improving reaction selectivity and product yield. Furthermore, the catalyst of this invention is packed in a tubular reactor, which can reduce the requirements for equipment materials, reduce equipment investment, simplify the subsequent processing flow, eliminate the catalyst quenching process, avoid the generation of wastewater, waste salt and other "three wastes", simplify the post-treatment process, save energy and protect the environment, and does not involve complex operations such as catalyst recycling and regeneration, which is conducive to large-scale industrial production. Detailed Implementation

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0043] This invention provides a method for producing 2,3,5-trimethylhydroquinone diester, comprising the following steps:

[0044] 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione was rearranged with an acylating agent in a tubular reactor packed with a catalyst to obtain 2,3,5-trimethylhydroquinone diester.

[0045] The reaction parameters in the tubes of the tubular reactor satisfy the relationship shown in Equation 1;

[0046]

[0047] In Equation 1, A is the proportionality coefficient, and the value of A ranges from 11 to 15;

[0048] t is the time, in minutes, for the raw material to flow from the axial inlet of the tube to a certain point.

[0049] T represents the temperature at a certain point along the axial direction of the tube, in °C.

[0050] c represents the percentage of the total catalyst charge in the hourly feed mass flow rate of 2,6,6-trimethyl-cyclohexyl-2-ene-1,4-dione, c%;

[0051] n is the exponential coefficient. When c < 5, n takes the value of 2; when c ≥ 5, n takes the value of 1.

[0052] x is the ratio of the amount of catalyst loaded at a certain point along the axial direction of the tube to the amount of catalyst loaded at the outlet of the tube.

[0053] In this invention, the catalyst is packed in the tubes of a tubular reactor. The reactants 2,6,6-dimethyl-cyclohex-2-ene-1,4-dione and the acylating agent flow through the tube side and pass through the catalyst. Under the catalysis of the catalyst, a rearrangement reaction occurs to generate 2,3,5-trimethylhydroquinone diester (TMHQ-DA).

[0054] The tubular reactor of this invention can be arranged vertically. The reactants enter the reactor from the bottom, and the resulting 2,3,5-trimethylhydroquinone diester reaction solution flows out from the top. Compared to stirred reactors, the tubular reactor is closer to a plug flow reactor, which can reduce backmixing in rearrangement reactions and increase the reaction rate. Furthermore, the catalyst of this invention is packed into the tubular reactor, which reduces the requirements for equipment materials, decreases equipment investment, simplifies subsequent processing, eliminates the catalyst quenching process, avoids the generation of wastewater, waste salt, and other "three wastes," simplifies post-treatment processes, saves energy and is environmentally friendly, and avoids complex operations such as catalyst recycling, which is beneficial for large-scale industrial production.

[0055] The reaction parameters in the tubes of the tubular reactor satisfy the relationship shown in Equation 1. Here, x refers to the ratio of the amount of catalyst loaded from the inlet to the outlet of the tube to the amount of catalyst loaded infinitely close to the outlet of the tube.

[0056] In some implementations, the heat transfer cooling water can enter in the shell side, exchange heat with the reactants in the tubes in a co-current manner, control the heat transfer temperature difference, and adjust the temperature inside the tubes, so that the temperature distribution in the tubes of the tubular reactor satisfies Equation 1.

[0057] This invention adjusts the catalyst loading, the number of acidic sites in the tubular reactor, and the residence time of the raw materials in the tubular reactor to ensure that the reaction parameters in the tubular reactor can satisfy Equation 1. This can promote the formation of the main product and inhibit the formation of byproducts such as 2,4,5-trimethylhydroquinone diester and 3,4,5-trimethylhydroquinone diester while ensuring the reaction rate of the rearrangement reaction and the conversion rate of the raw materials, thereby improving the reaction selectivity and product yield.

[0058] Therefore, the production method of 2,3,5-trimethylhydroquinone diester of the present invention not only has excellent high production efficiency and low corrosivity to equipment, but also has simple subsequent processing technology, making it suitable for widespread application.

[0059] In some embodiments of the present invention, the diameter of the tubes in the tubular reactor gradually increases from the inlet to the outlet.

[0060] It is understood that the diameter of the tubes in this invention can increase in an ordered manner (e.g., in a functional relationship) or in a random manner from the inlet to the outlet.

[0061] In a tubular reactor, the feedstock enters from the tube side. When the inlet diameter of the tubes in the tubular reactor is small, it is beneficial to improve the heat transfer efficiency, achieve precise temperature control, and accurately control the catalyst loading. When the outlet diameter of the tubes is increased, the amount of catalyst that can be accommodated can be increased. At the same time, it is beneficial to increase the residence time of the feedstock in the tubular reactor, thereby improving the efficiency of the rearrangement reaction.

[0062] In some embodiments of the present invention, the tubes are variable diameter tubes with an outer diameter of 10-57 mm.

[0063] Furthermore, the reducing tube is formed by combining at least two of the heat exchange tubes with outer diameters of 10mm, 14mm, 19mm, 25mm, 38mm, 45mm, and 57mm.

[0064] For example, the tube is a reducing tube formed by combining heat exchange tubes with an outer diameter of 19 mm and heat exchange tubes with an outer diameter of 25 mm. That is, the inlet diameter of the tube is 19 mm and the outlet diameter is 25 mm.

[0065] In some embodiments of the present invention, the amount of catalyst loaded in the tubular reactor gradually increases from the inlet to the outlet.

[0066] It is understood that in the tubular reactor of the present invention, the amount of catalyst loaded gradually increases from the inlet to the outlet, and the increase follows the pattern of Equation 1. The amount of catalyst loaded at the outlet of the tubular reactor is greater than the amount loaded at the inlet, which can further improve the reaction rate.

[0067] Furthermore, when the ratio of the amount of catalyst loaded at the inlet of the tubular reactor to the amount of catalyst loaded at the outlet of the tubular reactor is 0.05-0.8, the distribution of catalyst in the tubular reactor can be more closely matched with the distribution of feed concentration, which can further improve the reaction rate.

[0068] In some embodiments of the present invention, the temperature in the tubular reactor gradually increases from the inlet to the outlet.

[0069] It can be understood that the temperature in the tubular reactor of the present invention gradually increases from the inlet to the outlet, and the increase follows the law of Equation 1.

[0070] Typically, the feed concentration at the inlet of a tubular reactor is high, while the feed concentration at the outlet is low. This invention ensures that the inlet temperature of the tubular reactor is lower than the outlet temperature, creating an inverse distribution of temperature gradient and feed concentration within the reactor. The high feed concentration at the reactor inlet guarantees the reaction rate, and the corresponding low reaction temperature can suppress the formation of byproducts such as 2,4,5-trimethylhydroquinone diester, thus improving reaction selectivity. The reduced feed concentration at the reactor outlet lowers the reaction rate, but by controlling the temperature at this outlet, the reaction rate can be accelerated, ensuring the reaction conversion rate.

[0071] Furthermore, the inlet temperature of the tubular reactor is 20-60℃; and / or,

[0072] When the outlet temperature of a tubular reactor is 70-100℃, the temperature distribution in the tubular reactor can be more closely matched with the feed concentration distribution, thereby improving the reaction rate, reaction conversion rate, and reaction selectivity.

[0073] Furthermore, the inlet temperature of the tubular reactor is 25-55°C; and / or, the outlet temperature of the tubular reactor is 75-95°C.

[0074] In some embodiments, the inlet of the tubular reactor has a high feed concentration, low temperature, small tube diameter, and low catalyst content; while the outlet of the tubular reactor has a low feed concentration, high temperature, large tube diameter, and high catalyst content. This can maximize the suppression of the formation of byproducts such as 2,4,5-trimethylhydroquinone diester while ensuring the reaction rate of the rearrangement reaction, thereby improving the selectivity of the reaction and extending the residence time of the feed in the tubular reactor, thus ensuring the reaction conversion rate of the rearrangement reaction.

[0075] The inventors also discovered in their research that when c% is 2-15%, the catalyst loading in the tubular reactor can be better matched with the mass flow rate of the feedstock, thereby improving the reaction rate and selectivity of the rearrangement reaction. Further, c% is 2.5-10%.

[0076] In some embodiments of the present invention, when the total residence time of the raw material from the inlet to the outlet of the tube is 40-240 min, the raw material can react more fully, thereby improving the conversion rate. Further, the total residence time of the raw material from the inlet to the outlet of the tube is 60-150 min.

[0077] In some embodiments of the present invention, the 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione and the acylating agent are further subjected to a preheating treatment at a temperature of 25-40°C.

[0078] Specifically, 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione and the acylating agent can be preheated to a temperature of 25-40°C. Then, 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione and the acylating agent can be introduced into a tubular reactor for a rearrangement reaction.

[0079] This invention preheats the raw materials, which facilitates faster initiation of rearrangement reactions in the tubular reactor, thereby improving reaction efficiency and conversion rate.

[0080] This invention involves a rearrangement reaction of 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione with an acylating agent in a tubular reactor packed with a catalyst to yield 2,3,5-trimethylhydroquinone diester. Therefore, it is understood that the amounts of 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione and the acylating agent are crucial to the reaction efficiency of the rearrangement reaction. Consequently, this invention further selects the molar ratio of 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione to the acylating agent in the rearrangement reaction to ensure a more complete reaction, thereby improving reaction efficiency, conversion rate, and selectivity. Exemplarily, in some embodiments of this invention, the molar ratio of 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione to the acylating agent in the rearrangement reaction is 1:(2-20). Furthermore, in the rearrangement reaction, the molar ratio of 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione to the acylating agent is 1:(3-10); even further, in the rearrangement reaction, the molar ratio of 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione to the acylating agent is 1:(3-5).

[0081] The present invention does not particularly limit the acylating agent, and it can be any acylating agent commonly used in the art. For example, the acylating agent can be one or more of acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, and benzoic anhydride. Further, the acylating agent can be acetic anhydride.

[0082] This invention does not impose any particular limitation on the catalyst; the catalyst can be any catalyst commonly used in the art that can be packed in a tubular reactor for rearrangement reactions. In some embodiments of this invention, the catalyst includes a support and an active acid anion supported on the support.

[0083] It is understandable that in a catalyst, active acid radicals can be supported on at least part of the surface of the support, or they can be supported inside the support.

[0084] The present invention does not impose any particular limitation on the carrier. For example, the carrier may be one or more of ion exchange resin, silicon dioxide, silicon carbide, titanium dioxide and zirconium oxide. Further, the carrier may be one or more of ion exchange resin, zirconium oxide and silicon dioxide.

[0085] The present invention does not specifically limit the active acid radical. For example, the active acid radical can be any one or more of the acid radicals such as sulfate, sulfonate, nitrate and phosphate.

[0086] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0087] Unless otherwise specified, the raw materials used in the following examples and comparative examples of this invention were obtained from commercial sources. Specifically, 2,6,6-trimethyl-cyclohexane-2-ene-1,4-dione (KIP) was purchased from Sigma-Aldrich; and the solid acid catalyst was purchased from DuPont's Amberlyst series.

[0088] Example 1

[0089] The method for producing 2,3,5-trimethylhydroquinone diester in this embodiment includes the following steps:

[0090] Trimethyl-cyclohexyl-2-en-1,4-dione (KIP) and acetic anhydride were mixed in a molar ratio of 1:3 and then fed into a feed preheater to be preheated to 40°C. The mixture was then continuously fed into the tubular reactor from the inlet at a total flow rate of 3.22 ml / min. Samples were taken at the outlet of the tubular reactor to test the reaction.

[0091] The axial temperature distribution inside the tubes of the tubular reactor is adjusted by using shell-side heat transfer cooling water to ensure that the axial temperature distribution of the tubes in the tubular reactor satisfies Equation 1. The inlet temperature of the tubular reactor is 43℃, the outlet temperature is 82℃, the inlet tube diameter is 19mm, the outlet tube diameter is 25mm, and the tube length is 500mm.

[0092] The tubular reactor is filled with a sulfate solid acid catalyst from the Amberlyst series of DuPont. The total catalyst content is 3.5% of the KIP feed mass per hour. The catalyst content in the tubes increases along the axial direction. The proportion of the catalyst loading at the tube inlet to the catalyst loading at the tube outlet is 0.4. The total residence time of the feed from the tube inlet to the tube outlet in the tubular reactor is 60 min.

[0093] The loading amount and temperature distribution of the axial catalyst in the tube are shown in Table 1.

[0094] Table 1

[0095] Tube position 1 / 4 1 / 2 3 / 4 Exit t-min 15 30 45 60 T-℃ 52 62 77 82 x 0.54 0.72 0.87 1

[0096] The reaction conversion rate of this embodiment was 99.9% and the selectivity was 99.9% as tested.

[0097] Example 2

[0098] The production method of 2,3,5-trimethylhydroquinone diester in this embodiment is basically the same as that in Example 1, except that:

[0099] Butyric anhydride was used instead of acetic anhydride, and the total flow rate was 2.76 mL / min;

[0100] The total catalyst content in the tubular reactor is 3.8% of the KIP feed mass per hour, and the residence time of the feed in the tubular reactor is 70 min.

[0101] The inlet temperature of the tubular reactor is 43℃, and the outlet temperature is 88℃.

[0102] Table 2 shows the loading amount and temperature distribution of the axial catalyst in the tube;

[0103] Table 2

[0104] Tube position 1 / 4 1 / 2 3 / 4 Exit t-min 17 35 52 70 T-℃ 55 65 80 88 x 0.57 0.69 0.84 1

[0105] The reaction conversion rate of this embodiment was 99.9% and the selectivity was 99.8% as tested.

[0106] Example 3

[0107] The production method of 2,3,5-trimethylhydroquinone diester in this embodiment is basically the same as that in Example 1, except that:

[0108] The molar ratio of KIP to acetic anhydride is 1:10, and the total flow rate is 2.42 mL / min;

[0109] The tubular reactor is filled with a nitrate solid acid catalyst from the Amberlyst series of DuPont. The total catalyst content in the tubular reactor is 2.8% of the KIP feed mass per hour. The proportion of the catalyst loading at the inlet of the tubular reactor to the catalyst loading at the outlet of the tubular reactor is 0.5. The residence time of the raw material in the tubular reactor is 80 min.

[0110] The inlet temperature of the tubular reactor is 44℃, and the outlet temperature is 76℃.

[0111] The catalyst loading and temperature distribution along the axial direction of the tube are shown in Table 3.

[0112] Table 3

[0113] Tube position 1 / 4 1 / 2 3 / 4 Exit t-min 20 40 60 80 T-℃ 50 60 69 76 x 0.61 0.75 0.88 1

[0114] The reaction conversion rate of this embodiment was 99.6% and the selectivity was 99.9% as tested.

[0115] Example 4

[0116] The production method of 2,3,5-trimethylhydroquinone diester in this embodiment is basically the same as that in Example 1, except that:

[0117] The molar ratio of KIP to acetic anhydride is 1:2, and the total flow rate is 1.42 mL / min;

[0118] The tubular reactor is filled with sulfonate solid acid catalyst. The proportion of the catalyst loading at the inlet of the tubular reactor to the catalyst loading at the outlet of the tubular reactor is 0.6. The residence time of the raw material in the tubular reactor is 100 min.

[0119] The inlet temperature of the tubular reactor is 50℃, and the outlet temperature is 85℃.

[0120] The loading amount and temperature distribution of the axial catalyst in the tube are shown in Table 4.

[0121] Table 4

[0122] Tube position 1 / 4 1 / 2 3 / 4 Exit t-min 25 50 75 100 T-℃ 61 69 81 85 x 0.65 0.76 0.89 1

[0123] The reaction conversion rate of this embodiment was 99.6% and the selectivity was 99.7% as tested.

[0124] Example 5

[0125] The production method of 2,3,5-trimethylhydroquinone diester in this embodiment is basically the same as that in Example 1, except that:

[0126] Propionic anhydride was used instead of acetic anhydride, with a total flow rate of 3.06 mL / min;

[0127] The tube diameter of the tubular reactor is 25 mm.

[0128] The tubular reactor is filled with sulfonate solid acid catalyst. The total catalyst content is 3.2% of the KIP feed mass per hour. The proportion of the catalyst loading at the inlet of the tubular reactor to the catalyst loading at the outlet of the tubular reactor is 0.8. The residence time of the raw material in the tubular reactor is 90 min.

[0129] The inlet temperature of the tubular reactor is 55℃, and the outlet temperature is 80℃.

[0130] The loading amount and temperature distribution of the axial catalyst in the tube are shown in Table 5.

[0131] Table 5

[0132] Tube position 1 / 4 1 / 2 3 / 4 Exit t-min 23 45 67 90 T-℃ 63 70 75 80 x 0.83 0.91 0.95 1

[0133] The reaction conversion rate of this embodiment was 99.7% and the selectivity was 99.7% as tested.

[0134] Example 6

[0135] The production method of 2,3,5-trimethylhydroquinone diester in this embodiment is basically the same as that in Example 1, except that:

[0136] The total catalyst content in the tubular reactor is 10% of the KIP hourly feed mass. The catalyst content in the tubes increases along the axial direction. The proportion of the catalyst loading at the tube inlet to the catalyst loading at the tube outlet is 0.05. The residence time of the raw material in the tubular reactor is 60 min.

[0137] The inlet temperature of the tubular reactor is 22℃, and the outlet temperature is 78℃.

[0138] Table 6 shows the loading amount and temperature distribution of the axial catalyst in the tube;

[0139] Table 6

[0140] Tube position 1 / 4 1 / 2 3 / 4 Exit t-min 15 30 45 60 T-℃ 41 53 65 78 x 0.30 0.54 0.78 1

[0141] The reaction conversion rate of this embodiment was 99.7% and the selectivity was 99.8% as tested.

[0142] Comparative Example 1

[0143] The production method of 2,3,5-trimethylhydroquinone diester in this comparative example includes the following steps:

[0144] KIP and acetic anhydride undergo a rearrangement reaction in a batch reactor under the catalysis of concentrated sulfuric acid catalyst.

[0145] The catalyst dosage was 5% of the KIP mass, and the molar ratio of KIP to acetic anhydride was 1:3. The reaction temperature was 90℃, the operation was at atmospheric pressure, and the reaction time was 120 min.

[0146] After the reaction was completed, the conversion rate was measured to be 99.9%, and the selectivity was 91.9%. The reaction solution needed to be quenched with an alkaline solution before entering the downstream separation system to obtain the pure product.

[0147] Comparative Example 2

[0148] The production method of 2,3,5-trimethylhydroquinone diester in this comparative example is basically the same as that in Example 1, except that:

[0149] The temperature inside the tubes of the tubular reactor is adjusted to 60℃ by cooling water transferred from the shell side (this does not satisfy Equation 1).

[0150] The reaction conversion rate of this comparative example was 99.6%, and the selectivity was 93.4%.

[0151] As can be seen from the examples and comparative examples, the present invention prepares 2,3,5-trimethylhydroquinone diester by rearranging 2,6,6-trimethyl-cyclohexyl-2-ene-1,4-dione with an acylating agent in a tubular reactor packed with a catalyst. Furthermore, by selecting the relationship between the various parameters in the tubular reactor, the conversion rate and selectivity of the reaction can be improved.

[0152] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for producing 2,3,5-trimethylhydroquinone diester, characterized in that, Includes the following steps: 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione was rearranged with an acylating agent in a tubular reactor packed with a catalyst to obtain 2,3,5-trimethylhydroquinone diester. The reaction parameters in the tubes of the tubular reactor satisfy the relationship shown in Equation 1; In Equation 1, A is the proportionality coefficient, and the value of A ranges from 11 to 15; t is the time, in minutes, for the raw material to flow from the axial inlet of the tube to a certain point. T represents the temperature at a certain point along the axial direction of the tubes, in °C. c is the percentage of the total amount of the catalyst loaded to the hourly feed mass of 2,6,6-trimethyl-cyclohexyl-2-ene-1,4-dione, c%; n is the exponential coefficient. When c < 5, n takes the value of 2; when c ≥ 5, n takes the value of 1. x is the ratio of the amount of catalyst loaded at a certain point along the axial direction of the tube to the amount of catalyst loaded at the outlet of the tube.

2. The production method according to claim 1, characterized in that, The diameter of the tubes in the tubular reactor gradually increases from the inlet to the outlet.

3. The production method according to claim 2, characterized in that, The tubes are variable diameter tubes with an outer diameter of 10-57 mm; Preferably, the variable diameter tube is formed by combining at least two of the heat exchange tubes with outer diameters of 10mm, 14mm, 19mm, 25mm, 38mm, 45mm, and 57mm.

4. The production method according to any one of claims 1-3, characterized in that, The amount of catalyst loaded in the tubular reactor gradually increases from the inlet to the outlet.

5. The production method according to claim 4, characterized in that, The ratio of the catalyst loading at the inlet of the tube to the catalyst loading at the outlet of the tube is 0.05-0.

8.

6. The production method according to any one of claims 1-5, characterized in that, The temperature in the tubular reactor gradually increases from the inlet to the outlet.

7. The production method according to claim 6, characterized in that, The inlet temperature of the tubular reactor is 20-60℃; and / or, The outlet temperature of the tubular reactor is 70-100℃; Preferably, the inlet temperature of the tubular reactor is 25-55°C; and / or, The outlet temperature of the tubular reactor is 75-95℃.

8. The production method according to any one of claims 1-7, characterized in that, c% is 2-15%; and / or, The total residence time of the raw material from the inlet to the outlet of the tube is 40-240 min; and / or, In the rearrangement reaction, the molar ratio of 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione to the acylating agent is 1:(2-20); Preferably, c% is 2.5-10%; and / or, The total residence time of the raw material from the inlet to the outlet of the tube is 60-150 min; and / or, In the rearrangement reaction, the molar ratio of 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione to the acylating agent is 1:(3-10).

9. The production method according to any one of claims 1-8, characterized in that, It also includes preheating 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione with an acylation agent at a temperature of 25-40°C.

10. The production method according to any one of claims 1-9, characterized in that, The acylating agent is selected from at least one of acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, and benzoic anhydride; Preferably, the acylating agent is acetic anhydride; and / or, The catalyst includes a support and an active acid anion supported on the support; Preferably, the active acid anion is at least one selected from sulfate, sulfonate, nitrate, and phosphate.

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