Carbon dot catalyst and method for applying carbon dot catalyst to preparation of ethylene glycol diacetate

Abstract

The invention discloses a carbon dot catalyst and a method for applying the same to preparation of ethylene glycol diacetate, and the carbon dot catalyst is prepared by the following steps: mixing urea, citric acid and taurine according to a molar ratio of 1: 0.3: (0.01-0.1), dissolving in water, heating and distilling to remove most moisture, and drying at 70-80 DEG C to obtain a dry mixture A; putting the dry mixture A into a high-temperature tubular furnace, heating to 240-260 DEG C under the protection of inert gas, and pyrolyzing for 2-3 hours to obtain a pyrolysis product B; washing and centrifugally separating the pyrolysis product B until supernatant liquid is neutral, collecting a lower-layer solid C, and drying the lower-layer solid C to obtain the carbon dot catalyst. The catalytic esterification effect of the carbon dot catalyst provided by the invention is superior to that of traditional cationic resin, and the catalytic efficiency of the carbon dot catalyst is far higher than that of a traditional solid catalyst due to the extremely high specific surface characteristic; and secondly, the prepared carbon dot catalyst has no obvious corrosion to equipment, and can be directly dispersed and used in a kettle.

Description

Technical Field

[0001] The invention relates to the technical field of ethylene glycol diacetic acid preparation process, and in particular to a carbon dot catalyst and a method for applying the carbon dot catalyst to prepare ethylene glycol diacetate. Background Art

[0002] Ethylene glycol diacetate is the abbreviation of 1,2-ethylene glycol diacetate (also known as ethylene glycol diacetate, Ethyleneglycol diacetate, EGDA), which is a high-boiling point environmentally friendly solvent with excellent solubility properties. It can be used to make paints, inks, adhesives and paint removers.

[0003] Industrially, EGDA can be prepared by esterification reaction of ethylene glycol and acetic acid. The preparation method generally used in industry is to use sulfuric acid, sulfonic acid or sulfonic acid type cationic resin as catalyst. Sulfuric acid has ideal catalytic activity as catalyst and is cheap, but it is highly corrosive and easily causes side reactions such as oxidation, carbonization, polymerization, and dehydration. Therefore, in order to avoid corrosion to equipment, cationic resin is usually used as catalyst, and the catalyst is filled in a fixed bed reactor for catalytic reaction. For example, patent (publication number CN104045554 A) discloses a method for preparing EGDA using a fixed bed continuous esterification process, but this scheme increases equipment investment cost and process complexity.

[0004] Therefore, in order to avoid the problem of catalyst corrosion on the kettle body during the batch process of producing EGDA, ethylene glycol and methyl acetate / butyl acetate can be used as raw materials to carry out ester exchange to obtain EGDA. This solution does not require the use of corrosive strong acid catalysts, but the catalytic efficiency of this reaction is still low, the by-products are not easy to separate, and the overall process energy consumption is high.

[0005] In view of this, it is necessary to provide a carbon dot catalyst and a method for applying the same to the preparation of ethylene glycol diacetate to overcome the above-mentioned defects. Summary of the invention

[0006] The purpose of the present invention is to provide a carbon dot catalyst and a method for applying the same to the preparation of ethylene glycol diacetate, aiming to improve the problems of strong catalyst corrosion or low catalytic efficiency in the existing EGDA preparation process, facilitate the recovery of by-products and catalysts, and have low overall process energy consumption.

[0007] In order to achieve the above object, the present invention provides a method for preparing a carbon dot catalyst, comprising:

[0008] Step S11: dissolving urea, citric acid and taurine in water at a molar ratio of 1:0.3:(0.01-0.1), heating and distilling to remove most of the water, and drying at 70° C.-80° C. to obtain a dry mixture A;

[0009] Step S12: placing the dry mixture A into a high-temperature tube furnace, heating to 240° C.-260° C. under inert gas protection for pyrolysis for 2 h-3 h to obtain a pyrolysis product B;

[0010] Step S13: washing the pyrolysis product B with water and centrifuging until the upper clear liquid is neutral, collecting the lower solid matter C, and drying the lower solid matter C to obtain the carbon dot catalyst.

[0011] In a preferred embodiment, in the step S12, the pyrolysis temperature of the dry mixture in a high temperature tube furnace is 250°C.

[0012] In a preferred embodiment, in the step S12, the inert gas is N2.

[0013] The present invention also provides a carbon dot catalyst, which is applied to the EGDA preparation process and is prepared by the preparation method of the carbon dot catalyst described in any one of the above embodiments.

[0014] The present invention also provides a method for preparing ethylene glycol diacetate, using the carbon dot catalyst described in the above embodiment as an esterification catalyst.

[0015] In a preferred embodiment, the method comprises:

[0016] Step S21: adding ethylene glycol and acetic acid in a molar ratio of 1:(2.5-3.5) into a reaction kettle for mixing, and then adding a carbon dot catalyst accounting for 1% to 5% by mass of the total amount and a water-carrying agent accounting for 1% to 5% by mass of the total amount;

[0017] Step S22: heating the reactor to 80° C. to 130° C. for reaction, collecting the water generated by the reaction by the water-carrying agent through a water separator, until the amount of water collected by the water separator reaches more than 95% of the theoretical amount of water, and then dehydrating the product in the reactor to obtain a crude product of ethylene glycol diacetate;

[0018] Step S23: distilling the crude ethylene glycol diacetate product through a distillation column, and collecting product fractions to obtain a finished ethylene glycol diacetate product;

[0019] Step S24: washing the residual liquid collected after distillation with water and centrifuging for multiple times to remove the upper clear liquid, collecting the lower solid matter and drying it to obtain the recovered carbon dot catalyst.

[0020] In a preferred embodiment, in step S21, the water-carrying agent is toluene or cyclohexane.

[0021] In a preferred embodiment, in the step S22, the reaction temperature of the reactor is 110°C to 120°C.

[0022] In a preferred embodiment, in step S24, the residual liquid collected after distillation is washed with water and centrifuged three times.

[0023] The carbon dot catalyst provided by the present invention and the method for applying the same to the preparation of ethylene glycol diacetate have the following beneficial effects: the carbon dot catalyst is an efficient solid catalyst, and its catalytic esterification effect is better than that of the traditional cationic resin, which is manifested in that on the one hand, the carbon dot particle size is small, and the primary particle size can reach less than 10nm, which is a nano-scale catalyst, and the extremely high specific surface characteristics make its catalytic efficiency much higher than that of the traditional solid catalyst; on the other hand, when preparing the carbon dot, only a very small amount of sulfonic acid precursor needs to be added to make the prepared carbon dot catalyst show a good catalytic effect, so the prepared carbon dot catalyst has no obvious corrosion to the equipment, and can be directly dispersed in the kettle for use without the need for a fixed bed fluidized process. In addition, the use of the carbon dot catalyst can react under higher temperature conditions (120-130°C or even higher), while the temperature conditions of the use of the cationic resin are generally controlled at 80-100°C. Reacting under higher temperature conditions can increase the reaction rate and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A flow chart of a method for preparing a carbon dot catalyst provided by the present invention;

[0026] Figure 2 The present invention provides a flow chart of the method for preparing ethylene glycol diacetate. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be understood that the specific implementation methods described in this specification are only for explaining the present invention, not for limiting the present invention.

[0028] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0029] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0030] In an embodiment of the present invention, a carbon dot catalyst is provided for use in the EGDA preparation process, so that it can be carried out in a reactor and has no obvious corrosiveness to equipment such as the reactor. It can be directly dispersed and used in the reactor without the need for a fixed bed fluidized bed process.

[0031] like Figure 1 As shown, the method for preparing the carbon dot catalyst includes steps S11-S13.

[0032] Step S11: Dissolve urea, citric acid and taurine in water at a molar ratio of 1:0.3:(0.01-0.1), heat and distill to remove most of the water, and then dry at 70°C-80°C to obtain a dry mixture A. For example, heat and distill to remove more than 80% of the theoretical water content and then dry. The amount of dissolved water is controlled to be sufficient to completely dissolve urea, citric acid and taurine.

[0033] Step S12: Place the dry mixture A in a high-temperature tube furnace, heat it to 240°C-260°C under the protection of inert gas, and pyrolyze it for 2h-3h to obtain a pyrolysis product B. In this embodiment, the inert gas can be a rare gas or N2. The pyrolysis temperature of the dry mixture is preferably 250°C.

[0034] Step S13: The pyrolysis product B is washed with water and centrifuged until the upper clear liquid is neutral, and then the lower solid matter C is collected and dried to obtain a carbon dot catalyst.

[0035] The present invention also provides a carbon dot catalyst, which is applied to the EGDA preparation process and is prepared by the preparation method of the carbon dot catalyst described in any one of the above embodiments.

[0036] The present invention also provides a method for preparing ethylene glycol diacetate, which is used to apply the carbon dot catalyst prepared in the above embodiment to the catalytic process of ethylene glycol diacetate (EGDA). That is, the carbon dot catalyst described in the above embodiment is used as an esterification catalyst.

[0037] Specifically, Figure 2As shown, the method for preparing ethylene glycol diacetate includes steps S21-S24.

[0038] Step S21: Ethylene glycol and acetic acid are added to a reactor in a molar ratio of 1:(2.5-3.5) and mixed, and then 1%-5% by mass of a carbon dot catalyst and 20%-50% by mass of a water-carrying agent are added.

[0039] In this embodiment, the water-carrying agent is toluene or cyclohexane. It should be noted that the water-carrying agent, also known as the entrainer, is a chemical substance used to change the azeotropic point of the mixture in the industrial distillation process to achieve separation. They are often used in the azeotropic distillation process. By adding a third component, it forms a new azeotrope with a component in the original mixture. The boiling point of this new azeotrope is lower than the boiling point of any component in the original mixture. In this way, during the distillation process, the new azeotrope can be distilled from the top of the tower, leaving a purer component at the bottom of the tower.

[0040] Step S22: The reactor is heated to 80°C to 130°C for reaction, and the water generated by the reaction is taken out by the water separator until the amount of water collected by the water separator reaches more than 95% of the theoretical amount of water, and then the product in the reactor is dehydrated to obtain a crude product of ethylene glycol diacetate. Furthermore, the reaction temperature of the reactor is preferably 110°C to 120°C.

[0041] Step S23: distilling the crude ethylene glycol diacetate through a distillation column, and collecting product fractions to obtain the finished ethylene glycol diacetate.

[0042] Step S24: The collected kettle residue after distillation is washed with water and centrifuged for multiple times (for example, three times), the upper clear liquid is removed, and the lower solid is collected and dried to obtain the recovered carbon dot catalyst.

[0043] The present invention also provides ethylene glycol diacetate, which is prepared by the preparation method of ethylene glycol diacetate described in any of the above embodiments.

[0044] In an exemplary embodiment and its comparative example, a specific case will be used to assist in illustrating the beneficial effects of the present invention.

[0045] Embodiment 1:

[0046] 6.0g urea, 5.8g citric acid and 2.5g taurine were added to 30g water and dissolved completely. The mixture was distilled in an evaporating dish until salt began to precipitate and then dried in an oven at 70-80℃ for 1h. The dried mixture was placed in a high-temperature tube furnace and heated to 250℃ for pyrolysis for 2h under N2 protection. The obtained product was washed with water and centrifuged until the upper clear liquid was neutral. The lower solid was collected and dried to obtain a carbon dot catalyst.

[0047] In a four-necked flask with a water separator, 124g of ethylene glycol, 300g of glacial acetic acid, 150g of cyclohexane, and 5g of carbon point catalyst were added. The temperature was raised to 90°C to 100°C for reaction (this temperature range is the reflux temperature of the system), and the water separation was stopped after the water in the receiving water separator reached 69g. The temperature was raised to 130°C to remove most of the unreacted acetic acid and cyclohexane to obtain 304g of crude ethylene glycol diacetic acid. The main fraction 288g was collected by rectification, which was the finished product of ethylene glycol diacetate. The residual liquid of about 15g was washed with water and centrifuged three times, and the lower solid matter after centrifugation was collected as the recovered carbon point catalyst. It should be noted that in other embodiments, if toluene is used as the water-carrying agent, the reflux temperature will reach 110°C to 120°C.

[0048] Comparison example:

[0049] A 732 cationic resin catalyst (a cation exchange resin with sulfonic acid groups (-SO3H) on a 7% cross-linked styrene-diethylene copolymer) was used as a replacement control for the carbon dot catalyst, and the remaining reaction parameters and raw materials were the same as those in Example 1 above.

[0050] Through the above two comparative tests, it is found that: under the same temperature (90℃~100℃) and the same dosage conditions, when about 95% of the water is collected, the scheme using carbon dots as catalysts requires about 5.5 hours, while the scheme using cationic resins as catalysts requires about 23.5 hours. It is obvious that the catalytic efficiency of the scheme using carbon dots is significantly improved. It should be noted that the optimal catalytic temperature of the carbon dot catalyst is 110℃~120℃, and the temperature condition of the cationic resin is generally controlled at 80℃~100℃. Therefore, in order to make the temperature conditions of Example 1 consistent with those of the control example, the temperature conditions of the carbon dot catalyst in Example 1 are reduced. That is, if the catalytic temperature is optimized on the basis of Example 1, the catalytic efficiency can be further improved (that is, the time required to collect about 95% of the water is less than 5.5 hours).

[0051] In summary, the carbon dot catalyst provided by the present invention and the method for applying the same to the preparation of ethylene glycol diacetate have the following beneficial effects: the carbon dot catalyst is an efficient solid catalyst, and its catalytic esterification effect is better than that of the traditional cationic resin, which is manifested in that the carbon dot particle size is small, and the primary particle size can reach less than 10nm, which is a nano-scale catalyst, and the extremely high specific surface area makes its catalytic efficiency much higher than that of the traditional solid catalyst; on the other hand, when preparing the carbon dot, only a very small amount of sulfonic acid precursor needs to be added to make the prepared carbon dot catalyst show a good catalytic effect, so the prepared carbon dot catalyst has no obvious corrosion to the equipment, and can be directly dispersed in the kettle for use without the need for a fixed bed fluidized process. In addition, the use of the carbon dot catalyst can react under higher temperature conditions (120°C to 130°C or even higher), while the temperature conditions of the use of the cationic resin are generally controlled at 80°C to 100°C. Moreover, the reaction under higher temperature conditions can increase the reaction rate and improve production efficiency.

[0052] The present invention is not limited to what is described in the specification and implementation modes, and therefore additional advantages and modifications can be easily realized by those skilled in the art. Therefore, without departing from the spirit and scope of the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details, representative devices, and illustrative examples shown and described herein.

Claims

1. A method for preparing a carbon dot catalyst, characterized in that: include: Step S11: dissolving urea, citric acid and taurine in water at a molar ratio of 1:0.3:(0.01-0.1), heating and distilling to remove most of the water, and drying at 70° C.-80° C. to obtain a dry mixture A; Step S12: placing the dry mixture A into a high-temperature tube furnace, heating to 240° C.-260° C. under inert gas protection for pyrolysis for 2 h-3 h to obtain a pyrolysis product B; Step S13: washing the pyrolysis product B with water and centrifuging until the upper clear liquid is neutral, collecting the lower solid matter C, and drying the lower solid matter C to obtain the carbon dot catalyst.

2. The method for preparing a carbon dot catalyst according to claim 1, characterized in that: In the step S12, the pyrolysis temperature of the dry mixture in a high temperature tube furnace is 250°C.

3. The method for preparing a carbon dot catalyst according to claim 1, characterized in that: In the step S12, the inert gas is N2.

4. A carbon dot catalyst used in the EGDA preparation process, characterized in that: The carbon dot catalyst is prepared by the preparation method of any one of claims 1 to 3.

5. A method for preparing ethylene glycol diacetate, characterized in that: The carbon dot catalyst as claimed in claim 4 is used as an esterification catalyst.

6. The method for preparing ethylene glycol diacetate according to claim 5, characterized in that: include: Step S21: adding ethylene glycol and acetic acid in a molar ratio of 1:(2.5-3.5) into a reaction kettle for mixing, and then adding a carbon dot catalyst accounting for 1% to 5% by mass of the total amount and a water-carrying agent accounting for 1% to 5% by mass of the total amount; Step S22: heating the reactor to 80° C. to 130° C. for reaction, collecting the water generated by the reaction by the water-carrying agent through a water separator, until the amount of water collected by the water separator reaches more than 95% of the theoretical amount of water, and then dehydrating the product in the reactor to obtain a crude product of ethylene glycol diacetate; Step S23: distilling the crude ethylene glycol diacetate product through a distillation column, and collecting product fractions to obtain a finished ethylene glycol diacetate product; Step S24: washing the residual liquid collected after distillation with water and centrifuging for multiple times to remove the upper clear liquid, collecting the lower solid matter and drying it to obtain the recovered carbon dot catalyst.

7. The method for preparing ethylene glycol diacetate according to claim 6, characterized in that: In the step S21, the water-carrying agent is toluene or cyclohexane.

8. The method for preparing ethylene glycol diacetate according to claim 6, characterized in that: In the step S22, the reaction temperature of the reactor is 110°C to 120°C.

9. The method for preparing ethylene glycol diacetate according to claim 6, characterized in that: In the step S24, the residual liquid collected after distillation is washed with water and centrifuged three times.

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