KR100894761B1 - Preparation method of 2,6-naphthalene dicarboxylic acid with energy recovery and recycling - Google Patents

Abstract

The present invention relates to a method for producing 2,6-naphthalenedicarboxylic acid for recovering and recycling energy, and more particularly, to preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-dimethylnaphthalene. The method of claim 1, further comprising: generating steam by introducing exhaust gas discharged from a distillation tower installed above an oxidation reactor for oxidizing the 2,6-dimethylnaphthalene into a condenser; Supplying the generated steam to a steam turbine to convert it into energy; Heating the steam discharged after being converted into energy in the steam turbine in a heat exchanger in the upper part of the crystallization tank by heat generated by evaporating a part of the crystallization tank solvent; Recycling steam heated in the heat exchanger to the condenser; And the energy converted in the steam turbine is introduced into the oxidation reactor and the mixed dissolution tank and recycled. In addition, the present invention, the heat of the exhaust gas of the 2,6-dimethylnaphthalene oxidation reaction is transferred to the steam through the condenser, the heat of steam is converted into energy to initiate the oxidation reaction, the steam in the crystallization tank top heat exchanger By raising the temperature and recycling to the condenser, the energy recovery efficiency is high and economical, and the reaction process can be stably operated by removing corrosive substances of the solvent and unreacted materials.

2,6-naphthalenedicarboxylic acid, energy recovery, heat exchanger, condenser, exhaust gas

Description

Preparation method of 2,6-naphthalene dicarboxylic acid with energy recovery and recycling

The present invention relates to a method for producing 2,6-naphthalenedicarboxylic acid for recovering and recycling energy, and more particularly, to introduce a discharge gas discharged from a distillation column installed in an upper part of an oxidation reactor into a condenser to obtain steam from external water. After the production, the generated steam is supplied to a steam turbine to be converted into energy, and the steam discharged from the steam turbine is heated in a crystallization tank upper heat exchanger by heat generated by vaporizing a part of the crystallization tank solvent to the condenser. Recycling, and the energy generated in the steam turbine is introduced to the oxidation reactor and mixed dissolution tank, and relates to a method for producing 2,6-naphthalenedicarboxylic acid to recover and recycle the energy.

Generally 2,6-naphthalenedicarboxylic acid is prepared by oxidizing 2,6-dimethylnaphthalene in the gas phase or liquid phase. 2,6-naphthalenedicarboxylic acid is the main monomer used to produce polyethylene 2,6-naphthalate (PEN), one of high performance polyesters by condensation reaction with ethylene glycol. The PEN is used to manufacture films and fibers, and the films and fibers made from PEN have superior strength and thermal properties than films and fibers made from conventional polyethylene terephthalate (PET).

In addition, most of the liquid phase oxidation reactions are very exothermic. There are many ways to control the reaction temperature, but a common and convenient method is to remove heat by vaporizing part of the solvent during the reaction. This reaction gas and the vaporized solvent contain significant energy. The use of this energy efficiently is continually being improved.

In order to solve the above problems, a distillation column is installed on the upper part of the oxidation reactor to recover and recycle the oxidized exhaust gas discharged from the oxidizing reactor for liquid phase oxidation, distillation using heat of the exhaust gas and recover the solvent to recover the oxidation reactor. (US Pat. No. 5,463,113) is known. In this method, the exhaust gas from the distillation column is cooled with cooling water in the condenser to condense the water vapor in the exhaust gas, and the condensate is refluxed in the distillation column for use in distillation. However, the exhaust gas from the distillation column contains a large amount of acetic acid and corrosive substances, which causes a problem of corrosive air expanders and air compressors.

In addition, a method of recovering energy by heating or burning an exhaust gas of an oxidation reactor and supplying it to an air expander has been proposed (Korean Patent Publication No. 2000-0006106). The method connects the axis of rotation of the expander with the shafts of a power device and air compressor serving as a generator and a motor, and expands the oxidative exhaust to operate the power device and the compressor, whereby the power device recovers energy as power and air The compressor supplies an oxygen containing gas to the oxidation reactor. In this method, energy can be recovered by the expander and operated at low energy and low cost by operating the air compressor and the generator. However, since power must be supplied at the start of operation, considerable power is required when operating the air compressor directly connected to the expander and the power unit. This is necessary.

Further, the exhaust gas discharged from the oxidation reactor is condensed at 50 to 150 ° C. in the condenser, a portion of the condensate is refluxed to the distillation column, a part is supplied to the purification process, and the exhaust gas is washed with washing water after condensation to lower carboxyl. After recovering acid, a method of recovering energy from an air expander by burning in a combustor (International Patent No. 1996-011899) is disclosed. However, even when recovering lower carboxylic acid with washing water, lower carboxylic acid accumulates in the oxidation reactor. As a result, only the lower carboxylic acid concentration in the exhaust gas rises, and eventually, the combustion cost is exhausted to the combustor and the manufacturing cost increases.

The present invention is to solve the problems of the prior art to efficiently recover the energy of the exhaust gas to start the oxidation reaction with less energy, increase the efficiency of energy recovery after the oxidation reaction is started, the steam discharged from the steam turbine To provide a method for producing 2,6-naphthalenedicarboxylic acid, which recovers and recycles energy which further increases energy recovery efficiency by raising the temperature by heat generated by vaporizing a part of the crystallization tank solvent, recycling it to a condenser and recycling the reaction. The purpose is.

The object of the present invention is to oxidize 2,6-dimethylnaphthalene in the process for producing 2,6-naphthalenedicarboxylic acid, which is discharged from the distillation column installed above the oxidation reactor for oxidizing the 2,6-dimethylnaphthalene Introducing exhaust gas into the condenser to produce steam; Supplying the generated steam to a steam turbine to convert it into energy; Heating the steam discharged after being converted into energy in the steam turbine in a heat exchanger in the upper part of the crystallization tank by heat generated by evaporating a part of the crystallization tank solvent; Recycling steam heated in the heat exchanger to the condenser; And the energy converted from the steam turbine is introduced into the mixing reactor and the mixed dissolution tank and recycled. The energy can be achieved by providing a 2,6-naphthalenedicarboxylic acid manufacturing method for recovering and recycling energy. .

The present invention provides a method for producing 2,6-naphthalenedicarboxylic acid for recovering and recycling energy, the method for producing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-dimethylnaphthalene. The method of claim 1, further comprising: generating steam by introducing exhaust gas discharged from a distillation tower installed above an oxidation reactor for oxidizing the 2,6-dimethylnaphthalene into a condenser; Supplying the generated steam to a steam turbine to convert it into energy; Heating the steam discharged after being converted into energy in the steam turbine in a heat exchanger in the upper part of the crystallization tank by heat generated by evaporating a part of the crystallization tank solvent; Recycling steam heated in the heat exchanger to the condenser; And the energy converted in the steam turbine is introduced into the oxidation reactor and the mixed dissolution tank and recycled.

The method for producing 2,6-naphthalenedicarboxylic acid for recovering and recycling the energy of the present invention is a step of producing 2,6-naphthalenedicarboxylic acid by liquid phase oxidation of 2,6-dimethylnaphthalene with an oxygen-containing gas. The present invention relates to a method for producing 2,6-naphthalenedicarboxylic acid that enables efficient use of energy by recovering and recycling high enthalpy discarded in exothermic liquid phase oxidation.

Specifically, 2,6-naphthalenedicarboxylic acid production method for recovering and recycling the energy of the present invention, the oxidation step of 2,6-dimethylnaphthalene, the distillation step of the exhaust gas discharged after oxidation, condensation of distillation gas and In the method for producing 2,6-naphthalenedicarboxylic acid comprising the step of recovering energy from steam and combustion exhaust gas, and purification of 2,6-naphthalenedicarboxylic acid, discharged from a distillation column installed above the oxidation reactor Condensing in a first condenser condensing the off-gas; Gas-liquid separating the discharge gas and the liquid discharged from the first condenser in a gas-liquid separator; Refluxing a portion of the separated liquid to a reactor top distillation column; Condensing in a second condenser condensing the exhaust gas discharged from the gas-liquid separator; Removing unreacted 2,6-dimethylnaphthalene and an oxidized solvent through an absorber after passing the exhaust gas and the liquid discharged from the second condenser through a gas-liquid separator; The steam generated in each condenser is supplied to steam turbines and converted into energy, and the exhaust steam from the steam turbine is heated by heat generated by vaporizing a part of the crystallization tank solvent in the heat exchanger at the top of the crystallization tank, and supplied to each condenser. step; And the energy generated from the steam turbine is introduced into the oxidation reactor and the mixed dissolution tank and recycled.

Since the present invention circulates and recycles the energy required for the reaction after the start of the oxidation reaction, it is possible to minimize additional energy requirements.

1 is a manufacturing process chart of 2,6-naphthalenedicarboxylic acid according to the present invention.

As shown in FIG. 1, heavy metal complex catalyst compound (1) of 2,6-dimethylnaphthalene, cobalt component, manganese component, and bromine component is added to a mixed dissolution tank (2) with a solvent to dissolve therein, and is supplied with energy to receive an oxidation reactor. The 2,6-dimethylnaphthalene is oxidized in (3). Above the oxidation reactor 3, there is a distillation column for dividing the product. The distillation column is provided with a solid adsorption tray at the bottom to remove the solids contained in the oxidized exhaust gas.

The exhaust gas generated in the distillation column is condensed by water in an external tube through the first condenser 13 to generate high pressure steam and high temperature condensed water, and the high pressure steam is heated at the top of the first condenser 13. The exhaust gas and the hot condensate remaining without being condensed are discharged to the turbine 22 and are condensed through the first gas-liquid separator 14.

The exhaust gas discharged from the first gas-liquid separator 14 is supplied to the second condenser 15 again, and the second condenser 15 generates medium pressure high pressure steam and high temperature condensed water.

The medium temperature high pressure submersible is discharged to the steam turbine 22 above the second condenser 15 to be converted into energy, and the remaining exhaust gas and the high temperature condensed water which remain uncondensed form the second gas-liquid separator 16. Separated through.

Here, a plurality of condensers including a first condenser or a second condenser for condensing the exhaust gas discharged from the distillation column installed above the oxidation reactor are used.

In the present invention, two stages of condensers are used, but the number of condensers is not limited, and multiple stages of condensers can be used.

In addition, the high pressure steam generated in the condenser is supplied to the steam turbine 22 is converted into energy, the gas containing oxygen is supplied to the oxidation reactor (3) at a high temperature and high pressure through an air compressor (24), The power used for the air compressor is supplied through the steam turbine 22 and the motor 21 of the air expander 19.

Here, the energy generated in the steam turbine 22 is introduced into the oxidation reactor 3 and the mixed dissolution tank 2 and recycled. Therefore, when the reaction is initiated, the energy can be recovered and used, thereby reducing additional energy usage.

The steam discharged from the steam turbine 22 is heated up by heat generated by vaporizing a part of the crystallization tank solvent in the heat exchanger 26 located above the crystallization tank via the cooler 23 to the first condenser 13 and the It is supplied to the second condenser 15.

When the steam is heated to the heat exchanger, heat generated by vaporizing a part of the solvent in a crystallization tank is used. Therefore, no additional supply of energy is necessary.

The discharge temperature of the first condenser 13 should maintain the discharge temperature of the first condenser 13 at 120 to 250 ° C., depending on the efficiency of the reaction and the solvent to be condensed.

And, if the second condenser 15 or more condenser, the discharge temperature of the final condenser should be maintained at 30 to 100 ℃. If the temperature is 100 ° C. or higher, the energy recovered is significantly reduced, and below 30 ° C., hot condensate cannot be obtained, and a large number of condensers are required.

The method may further include a step of refluxing the exhaust gas discharged from the first condenser and refluxing a part of the separated liquid to a distillation column installed above the oxidation reactor.

Here, since the high temperature condensed water including the solvent condensed in the first condenser 13 is recycled to the upper part of the distillation column above the oxidation reactor 3, the reaction temperature of the oxidation reactor 3 may be affected, and thus recycled. It is necessary to adjust the temperature and the amount of the solvent to be. For this purpose, the capacity of the condenser must be constant.

In order to keep the reaction temperature constant, the temperature of the solvent to be condensed must be maintained at 120 to 250 ° C. When the temperature of the solvent exceeds 250 ℃, the amount of solvent to be condensed is small and the amount of energy recovered is small, and if the temperature of the solvent is less than 120 ℃ to reduce the oxidation reaction temperature adversely affects the reaction. Therefore, the discharge temperature of the first condenser 13 should be maintained at 120 to 250 ° C.

After gas-liquid separation of the exhaust gas discharged from the second condenser further comprises the step of removing the unreacted 2,6-dimethylnaphthalene or oxidation solvent through the absorber.

Here, the exhaust gas discharged from the second gas-liquid separator 16 is supplied to the lower part of the absorber 17. The absorber 17 is divided into an upper part and a lower part. In the lower part, the unreacted 2,6-dimethylnaphthalene and lower carboxylic acid ester in the exhaust gas are absorbed by the solvent, and the discharged solvent and the unreacted 2,6-unreacted. The liquid containing dimethyl naphthalene and lower carboxylic acid ester is supplied to the mixed dissolution tank 2 and recycled. Therefore, the corrosive solvent and the unreacted substance are separated alone and do not cause corrosion.

The upper end of the absorber 17 absorbs the corrosive solvent in the exhaust gas with water. The process is more stable by removing the corrosive solvent.

Exhaust gas discharged from the absorber 17 is supplied to the air expander 19, and the energy is recovered from the air expander 19 and sent to the steam turbine 22 through the motor 21, and then the oxidation reactor Recycle in (3).

In addition, a part of the exhaust gas discharged from the absorber 17 is supplied to the regenerated pyrolyzer 20, treated and discharged.

The solvent discharged from the lower portion of the second gas-liquid separator 16 contains methyl acetate and water generated in the oxidation reaction, thereby affecting the reaction when recycled to the oxidation reactor 3. To remove this, the discharge solvent is condensed through the third condenser 27 and introduced into the water solvent separation distillation column 18 to be separated. In the water solvent separation distillation column 18, water and solvent separation may be facilitated by using a heat exchanger 28. Then, the separated solvent is introduced into the mixed dissolution tank 2 and recycled.

In addition, the remaining solvent except for the solvent classified in the water solvent separation distillation column 18 passes through the fourth condenser 29 above the water solvent distillation column 18 and is introduced into the water and methyl acetate separation distillation unit 25. It is separated into water and methyl acetate.

Next, the slurry including the high temperature and high pressure 2,6-naphthalenedicarboxylic acid produced by the oxidation reactor 3 is decompressed in the first crystallization tank 4, and the steam generated at this time is the upper heat exchanger 26. ) And flows into the second crystallization tank 5.

The slurry from the first crystallization tank 4 is supplied to the second crystallization tank 5 which is operated at atmospheric pressure, and then to the first solid-liquid separator 6.

In this case, the method may further include using the high temperature condensed water generated in the second condenser to raise the temperature of the 2,6-naphthalenedicarboxylic acid purification solvent.

Here, the 2,6-naphthalenedicarboxylic acid solid coming out of the first solid-liquid separator 6 is supplied to the purification mixing tank 7 and purified, and the second gas-liquid separator ( The 2,6-naphthalenedicarboxylic acid is purified by supplying and mixing a solvent in which a portion of the hot condensate discharged from 16) is purified.

Here, in the purification mixing tank 7, 2,6-formylnaphthoic acid (2,6-FNA), methylnaphthoic acid (MNA), naphthoic acid (NA) generated during the oxidation of 2,6-dimethylnaphthalene. Impurities such as tricarboxylic acid (TMLA), etc. are present. Some of the impurities are removed through the solvent in which the high temperature condensed water discharged from the second gas-liquid separator 16 in the purification mixing tank 7 is purified. do.

Subsequently, the slurry from the purification mixing tank 7 is supplied to the second solid-liquid separator 8 again, and the separated solid 2,6-naphthalenedicarboxylic acid is supplied to the dryer 9 and dried. The dried 2,6-naphthalenedicarboxylic acid is transferred to the reservoir 10 and stored.

In addition, a part of the solvent separated in the first solid-liquid separator 6 and the second solid-liquid separator 8 is transferred to a purification process to remove impurities, and part of the solvent is mixed to dissolve the 2,6-dimethylnaphthalene. It is supplied to the dissolution tank 2.

Here, as a catalyst used to oxidize the 2,6-dimethylnaphthalene to the 2,6-naphthalenedicarboxylic acid, a complex catalyst system composed of a combination of a cobalt component, a manganese component and a bromine component is used. Compounds which can be used are cobalt acetate, cobalt naphthalate, cobalt carbonate and the like, and compounds which can be used as manganese components are manganese acetate, manganese phthalate, manganese carbonate, manganese bromide, and manganese bromide, cobalt bromide, One or more compounds selected from the group consisting of sodium bromide, ammonium bromide and tetrabroethane can be used.

In addition, as the oxidation reaction solvent, a weak acid including acetic acid, phosphoric acid, or carbonic acid may be used, and a mixed acid of the weak acid may be used.

The 2,6-dimethylnaphthalene oxidation reaction temperature is 130 to 350 ℃, the pressure is preferably maintained at 10 to 40kg / ㎠ by oxygen-containing air and diluent gas. If the temperature is lower than 130 ° C., the amount of reaction intermediates such as 2,6-formylnaphthoic acid and by-product trimellitic acid increases, and if it exceeds 350 ° C., the amount of trimellitic acid does not decrease any more, but more acetic acid Weak acid solvent, including the combustion is consumed. In addition, if the pressure is outside the above range, the reactants cannot maintain the liquid phase.

In the present invention, the exhaust gas from the distillation column above the oxidation reactor 3 is condensed using a condenser, and the flow rate of the liquid returned to the distillation column is minimized to increase the generation of high pressure steam to improve energy recovery efficiency. In addition, the exhaust gas from the steam turbine 22 is not directly supplied to the first condenser 13 and the second condenser 15 through the cooler 23, but the crystallization tank upper heat exchanger 26. Since it is supplied after being preheated through), the amount of steam generated is increased.

As described above, 2,6-naphthalenedicarboxylic acid production method for recovering and recycling energy according to the present invention, the heat of the exhaust gas of the 2,6-dimethylnaphthalene oxidation reaction is transferred to the steam generated through the condenser Afterwards, the heat of steam is converted into energy in the steam turbine, the energy initiates an oxidation reaction, and the steam is heated in a crystallization tank upper heat exchanger by heat generated by vaporizing a part of the crystallization tank solvent and recycled to the condenser. It is economical because of high energy recovery efficiency. In addition, the present invention has the advantage that the reaction process can be stably operated by removing the corrosive material of the solvent and unreacted material.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited by the following examples.

Example  One

In the mixed dissolution tank, acetic acid as a solvent was supplied at 80 kg / hr and 4 kg / hr of 2,6-dimethylnaphthalene to dissolve 2,6-dimethylnaphthalene in acetic acid, and the temperature of the reactant mixed dissolution tank was maintained at 80 ° C. It was. At this time, the catalyst was mixed in the composition ratio as shown in Table 1. The mixture was fed to a 300 L titanium oxidation reactor equipped with a heater, a distillation column and a stirrer, the temperature of the oxidation reactor was adjusted to 200 ° C., the reaction pressure was set to 18 kg / cm 2, and the stirrer speed was set to 700 rpm. The reactor injected into the furnace was properly dispersed. Oxygen was reacted with 4 moles of oxygen per mole of dimethylnaphthalene, and air containing oxygen was used.

Cobalt acetate 0.78wt% Manganese Acetate 0.12wt% 48% bromic acid 0.13wt%

The oxidation reactor upper distillation column used a total of 24 high-efficiency distillation column, the first condenser discharge temperature was maintained at 160 ℃, the second condenser discharge temperature was maintained at 50 ℃. In addition, a method of supplying the gas discharged from the steam turbine to the condenser again through a heat exchanger in the upper part of the crystallization tank. The total amount of heat recovered at this time is shown in Table 2.

Example  2

It carried out similarly to Example 1 except having advanced the 1st condenser discharge temperature at 150 degreeC and the 2nd condenser discharge temperature at 80 degreeC. The total amount of heat recovered is shown in Table 2.

Comparative example

It carried out similarly to Example 1 except having advanced without using the heat exchanger of a crystallization tank upper part. The total amount of heat recovered is shown in Table 2.

Example 1 Example 2 Comparative Example 1 First condenser 4271.4 kcal / hr 3476.2 kcal / hr 4271.4 kcal / hr Second condenser 2723.8 kcal / hr 3004.8 kcal / hr 2723.8 kcal / hr Crystallizer Top Heat Exchanger 2021.7 kcal / hr 2021.7 kcal / hr - Gas inflator 849.8 kcal / hr 654.8 kcal / hr 849.8 kcal / hr Recoverable calories 7400.0 kcal / hr 6868.0 kcal / hr 5883.8 kcal / hr

Comparing Example 1 and Example 2 with the comparative example, it appears that there is a difference of about 20% of the amount of heat that can be recovered depending on the presence or absence of an upper heat exchanger. In addition, the difference also occurs depending on the discharge temperature of the condenser. In the present invention, the discharge temperature of the first condenser is high, and therefore, Example 1, which recovers as much heat as possible from the exhaust gas, is more advantageous for energy recovery than Example 2.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a manufacturing process chart of 2,6-naphthalenedicarboxylic acid according to the present invention.

Explanation of symbols on the main parts of the drawings

1: 2,6-dimethylnaphthalene, heavy metal complex catalyst 2: mixed dissolution tank

3: oxidation reactor 4: first crystallization tank

5: second crystallization tank 6: first solid-liquid separator

7: tablet mixing tank 8: second solid-liquid separator

9: dryer 10: reservoir

11a, 11b: solvent reprocessing 12: retreated solvent

13: first condenser 14: first gas-liquid separator

15 second condenser 16 second gas-liquid separator

17: absorber 18: water, solvent separation distillation column

19: air expander 20: regeneration pyrolysis

21: motor 22: steam turbine

23: cooler 24: air compressor

25: water, methyl acetate separation stills 26: crystallization tank heat exchanger

27: third condenser 28: heat exchanger

29: fourth condenser

Claims (5)

In the step of oxidizing 2,6-dimethylnaphthalene to produce 2,6-naphthalenedicarboxylic acid, Generating steam by introducing exhaust gas discharged from a distillation tower installed above an oxidation reactor for oxidizing the 2,6-dimethylnaphthalene into a condenser; Supplying the generated steam to a steam turbine to convert it into energy; Heating the steam discharged after being converted into energy in the steam turbine in a heat exchanger in the upper part of the crystallization tank by heat generated by evaporating a part of the crystallization tank solvent; Recycling steam heated in the heat exchanger to the condenser; And The energy converted in the steam turbine is introduced into the mixed reaction tank and the oxidation reactor and recycled; comprising, 2,6-naphthalenedicarboxylic acid manufacturing method for recovering and recycling the energy. The method of claim 1, wherein a plurality of condensers including a first condenser or a second condenser for condensing the exhaust gas discharged from the distillation column installed above the oxidation reactor is used 2,6 for recovering and recycling energy -Naphthalenedicarboxylic acid production method. The energy of claim 1 or 2, further comprising gas-separating the exhaust gas discharged from the first condenser and refluxing a part of the separated liquid to a distillation column installed above the oxidation reactor. 2,6-naphthalenedicarboxylic acid production method for recovering and recycling. The method of claim 1 or 2, further comprising removing unreacted 2,6-dimethylnaphthalene or an oxidizing solvent through an absorber after gas-liquid separation of the exhaust gas discharged from the second condenser. 2,6-naphthalenedicarboxylic acid production method for recovering and recycling the energy. The method of claim 1 or claim 2, further comprising the step of using the high temperature condensate water generated in the second condenser to increase the temperature of the 2,6-naphthalenedicarboxylic acid purification solvent. And 2,6-naphthalenedicarboxylic acid production method for recycling.

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