CN109748790B - Method for producing dimethyl adipate - Google Patents
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Abstract
The object of the present invention is a process for the production of dimethyl adipate, comprising: (1) adding fresh methanol and molten adipic acid into a primary esterification reactor; (2) the tube pass discharge of the first-stage esterification reactor enters the upper part of the reaction section of the esterification rectifying tower, the vaporized methanol enters the lower part of the reaction section, a product containing dimethyl adipate is extracted from the tower bottom, and the top gas containing dimethyl ether is extracted from the tower top and is directly sent into a methanol recovery tower without cooling; (3) non-condensable gas containing dimethyl ether and liquid phase containing light components are extracted from the top of the methanol recovery tower, methanol is extracted and recovered from the side line liquid phase, the methanol is circulated to the first-stage esterification reactor without cooling and is used as a heat removing medium, and heavy components containing water are extracted from the bottom of the tower; (4) fresh methanol is used as reflux liquid of the esterification rectifying tower, and esters are absorbed from the rising gas phase. The method has the advantages of small device occupied area, high reaction conversion rate, low unit consumption, high product purity and low energy consumption, and can be used for industrial production of dimethyl adipate.
Description
Technical Field
The invention relates to a method for producing dimethyl adipate, in particular to a method for producing dimethyl adipate by combining primary esterification and secondary esterification.
Background
Dimethyl adipate is a high boiling, colorless, transparent liquid, readily soluble in alcohols and ethers, but insoluble in water. It is an important solvent which is difficult to volatilize, and is widely used in products such as high-grade paint, synthetic resin, cleaning agent, printing ink and the like. As an excellent cold-resistant plasticizer, the low-temperature soft rubber can endow the product with excellent low-temperature soft performance, and has certain photo-thermal stability and water resistance. Has wide application in solvent, medicine and perfume synthesis, paper making and cellulose resin production. In addition, dimethyl adipate is also an intermediate for synthesizing 1, 6-hexanediol.
Because concentrated sulfuric acid has dehydration and oxidation effects, the traditional process for synthesizing dimethyl adipate adopts concentrated sulfuric acid as a catalyst, but causes the problems of more side reactions, equipment corrosion and three-waste pollution, which cause high equipment investment and three-waste treatment cost. In order to overcome the defects of the concentrated sulfuric acid method, researches on using hydrated sodium bisulfate, p-toluenesulfonic acid, heteropoly acid, solid superacid and the like as esterification catalysts are reported in recent years, and a better esterification effect is obtained; but also has the defects of difficult recovery and reuse of the catalyst, difficult preparation, difficult purification of the product, great industrialization difficulty and the like. The strong acid cation exchange resin has the advantages of small volume affected by solvent, easy realization of continuous production and the like, and simultaneously has mild reaction conditions, and is easy to separate and reuse from a reaction system, thereby having better industrial application prospect.
At present, the demand for dimethyl adipate in foreign countries is continuously rising, and the demand in domestic is not very large, but has a certain rising trend.
Adipic acid reacts with methanol to produce dimethyl adipate and water, which is a reversible reaction. And when the reaction reaches the equilibrium, the conversion rate of the acid is not changed, and the conversion rate of the adipic acid batch esterification reaction is far lower than 100 percent. In addition, in large-scale industrial production, the intermittent operation is discontinuous in material feeding and discharging, and technological parameters are continuously fluctuated in the production process. In order to greatly increase the conversion rate of acid, the main operation schemes are as follows: and continuously replenishing methanol to the system to increase the ratio of alcohol to acid and promote the conversion of acid. However, the method has the disadvantages of large methanol circulation amount, large loss, high energy consumption of subsequent separation and low economy. In another scheme, the water in the reaction solution is continuously discharged to promote the reaction to proceed to the right, so that the reaction is completed. At present, the scheme has more researches and various means. Water is taken out by a water-carrying agent (cyclohexane, toluene and the like) through a water separator, and methanol and the water-carrying agent flow back to the reactor. The method is more applied in general laboratory scientific research, but the industrial high-purity product obtained still needs to face the separation problem of a large amount of water-carrying agents, and the energy consumption is higher. Patent GB143069 discloses a more primitive process using concentrated sulfuric acid as catalyst and a tank reactor reactive distillation to remove water. The dimethyl adipate is produced by taking sulfuric acid or other inorganic liquid acid as a catalyst, and the inorganic liquid acid is taken as the catalyst, so that the problems of corrosion of the inorganic liquid acid to equipment, three-waste treatment of reaction products and the like, and environmental pollution exist. The patent W09008127 discloses the inside of a tubular reactor divided into a plurality of beds, a solid catalyst is loosely arranged in the beds, alcohol vapor is contacted with acid and the solid catalyst in an acid solution in a bubbling mode, and the reaction is carried out under certain pressure. The reactor is divided into a plurality of beds, and the catalyst is loosely arranged in the beds, so that the catalyst is inconvenient to fill. Patent CN200410020789.3 discloses a method for producing 1, 6-hexanediol, which involves the synthesis of dimethyl adipate. Adipic acid and methanol are introduced from the lower end of a tower-type esterification reactor according to a certain weight ratio, a self-made catalyst loaded with activated carbon is filled in the reactor, and dimethyl adipate, water and a mixture of the unreacted adipic acid and the methanol which are generated by the reaction flow out from the upper end of the esterification reactor; then the effluent is rectified to obtain high-purity adipic acid dimethyl ester. The process flow is complex, the catalyst preparation cost is high, and the method is not suitable for industrial production. Patent CN200920110006.9 discloses a device for producing dimethyl adipate by pervaporation-reaction coupling. The device consists of a reactor, a pervaporation membrane, a delivery pump and a cold trap. The top of the reactor is provided with a raw material inlet, a methanol inlet and a reaction liquid outlet. The reaction liquid outlet is connected with a delivery pump to the feed liquid inlet of the pervaporation membrane, and the side outlet of the pervaporation membrane is connected with the methanol inlet. The permeation side of the pervaporation membrane is connected with the input end of a U-shaped pipe in the cold well and is connected with a vacuum pump. Although the device can improve the conversion rate and reduce the energy consumption, the used membrane component has higher cost. CN103342642 adopts three reaction kettles connected in parallel and a rectifying tower combined, methanol and water in the reaction system are evaporated out while the reaction is carried out, steam is separated and purified by the rectifying tower, moisture is discharged from the tower kettle, methanol returns to the reaction kettle from the tower top, the moisture is continuously carried out of the reaction system, and the esterification reaction finally tends to be complete. The method has the advantages of long reaction time, difficult control and high energy consumption. CN102311342 adopts the combination of pre-esterification and continuous esterification rectification, the pre-esterification does not need a catalyst, but does not fully utilize reaction heat, the continuous esterification rectification adopts a packed tower, the reaction residence time is limited, the catalyst replacement time is long, the cost is high, the gas phase at the tower top is condensed and recovered, and the energy consumption is high.
Disclosure of Invention
The invention aims to provide a method for producing dimethyl adipate, which solves the problems of low acid conversion rate, high energy consumption, low productivity, serious pollution and the like in the prior art. The process of the invention enables the production process of dimethyl adipate to be simpler, the conversion rate to be high, the yield to be high and the pollution to be less. In order to ensure that the conversion rate of the adipic acid is close to 100 percent, the conversion rate of the adipic acid limited by thermodynamic equilibrium in the batch esterification technology is greatly improved by combining the pre-esterification technology and the continuous esterification technology.
The invention can solve the problems in the prior art by generating a primary esterification reaction in a primary esterification reactor, leading the product of the primary esterification reaction to be in countercurrent contact with methanol on a tower plate carrying a catalyst in an esterification rectifying tower to generate a secondary esterification reaction, leading the dimethyl adipate product to be capable of carrying out hydrogenation reaction without purification to obtain 1, 6-hexanediol, and leading the gas phase at the top of the esterification rectifying tower containing dimethyl ether to directly enter a methanol recovery tower.
In order to solve the technical problems, the technical scheme of the invention is as follows: a process for producing dimethyl adipate comprising the steps of:
(1) adding fresh methanol and molten adipic acid into a primary esterification reactor, wherein the reactor is a shell-and-tube heat exchanger, the reaction material passes through a tube pass, the circulating methanol is used as a heat removing medium and passes through a shell pass, and the circulating methanol is pressurized to react without adding a catalyst; the shell-and-tube heat exchanger can be any one of a spiral coil heat exchanger and a screwed pipe wound heat exchanger;
(2) the tube pass discharge enters the upper part of the reaction section of the esterification rectifying tower, the vaporized methanol enters the lower part of the reaction section to carry out secondary esterification, the tower bottom liquid is a product containing dimethyl adipate, can be directly used as a product without purification or sent into a hydrogenation unit to produce 1, 6-hexanediol, and the gas phase at the top of the tower containing dimethyl ether directly enters a methanol recovery tower;
(3) non-condensable gas containing dimethyl ether and liquid phase containing light components are extracted from the top of the methanol recovery tower, methanol (dehydrated and removed of light component impurities) is extracted from the side line liquid phase, the methanol is circulated to a first-stage esterification reactor without being cooled and is used as a heat removing medium, and heavy components containing water are extracted from the bottom of the tower;
(4) fresh methanol is used as reflux liquid of the esterification rectifying tower, and esters are absorbed from the rising gas phase.
The reaction pressure of the first-stage esterification reactor is 0.3-1.5 MPaG, preferably 0.5-1 MPaG; the reaction temperature is 90-150 ℃, preferably 100-120 ℃.
The molar ratio of methanol to adipic acid in the first-stage esterification reactor is 2-8: 1, and preferably 3-6: 1.
The upper parts of the esterification rectifying tower and the methanol recovery tower both adopt high-efficiency low-resistance fillers, and the lower parts thereof are plate towers. Wherein, the lower part of the esterification rectifying tower is a plate tower, which is beneficial to increasing the liquid holdup of the plate tower, thereby increasing the reaction residence time and being convenient for replacing the catalyst. If the lower reaction section adopts a packed tower, the catalyst is inconvenient to replace, and the device must be stopped when the catalyst is replaced.
The catalyst at the reaction section of the esterification rectifying tower is suspended in a layer on a plate, and any layer of catalyst can be taken out and replaced without influencing the operation of the esterification rectifying tower.
The rectifying section at the upper part of the esterification rectifying tower is filled with filler, catalyst particles can be packaged in a metal filler cage, and a small amount of adipic acid carried by methanol and monomethyl adipate can be reacted again to be converted into dimethyl adipate. The purpose that the rectification section adopts the filler can also prevent that lower part catalyst particle from rising to mix into gaseous phase and block up equipment and pipeline, and catalyst particle encapsulation can also prevent that resin catalyst from rising to mix into gaseous phase and block up equipment and pipeline in the metal packing cage, can reduce bed pressure drop simultaneously, intercepts the monoester that smugglies in the gaseous phase and takes place the reaction, because of the gaseous phase smugglies monoester volume lowly, catalyst long service life.
The tower top pressure of the esterification rectifying tower is 0.02-0.6 MPaG, and preferably 0.04-0.2 MPaG; the components in the tower bottom are mainly dimethyl adipate, and in order to prevent the dimethyl adipate from high-temperature coking or decomposition, the temperature in the tower bottom is 120-195 ℃ and preferably 165-195 ℃.
The liquid volume space-time rate of the esterification rectifying tower is 0.2-0.6 h-1。
The purity of the adipic acid dimethyl ester product at the bottom of the esterification rectifying tower is more than or equal to 99.5 percent, the acid value of the adipic acid dimethyl ester is less than or equal to 0.5mgKOH/g, the adipic acid dimethyl ester can be directly sold as a product, and a 1, 6-hexanediol product can be produced by hydrogenation.
The method is also suitable for producing diethyl adipate, diisooctyl adipate, dibutyl adipate and dimethyl succinate.
Due to the adoption of the technical scheme, the method has the following technical effects:
(1) the primary esterification reaction process is combined with the secondary esterification reaction rectification process, and the esterification reaction with equivalent conversion rate is carried out in the primary esterification reaction process, so that the reaction load in the secondary esterification reaction rectification process is reduced, the consumption of a strong acid resin catalyst is reduced, and the operation cost is reduced while the conversion rate of adipic acid is improved.
(2) The shell-and-tube reactor with an internal component is used as a primary esterification reactor, so that the problem that the primary esterification reaction cannot be continuous is solved. At low temperature, adipic acid is slightly soluble in methanol, a pasty mixture of adipic acid and methanol is directly used as esterification rectification feeding, the service life of a second-level esterification rectification catalyst can be shortened, a first-level esterification reactor is a shell-and-tube heat exchanger, the shell-and-tube heat exchanger can be any one of a spiral coil tube type heat exchanger and a threaded tube wound type heat exchanger, the residence time of reaction materials can be controlled by adjusting the length of a tube, the reaction degree can be better controlled, and therefore continuous production of the first-level esterification reactor is realized.
(3) The first-stage esterification reactor serves as an intermediate reboiler of the esterification rectifying tower. The esterification reaction is exothermic reaction, the temperature of the first-stage esterification material is above 100 ℃, the circulating methanol raw material is used as a heat removing medium, the circulating methanol is discharged from a top side line liquid phase of the esterification rectifying tower, and the first-stage esterification material is used as a second-stage esterification raw material, so that the energy consumption can be fully reduced, and the equipment utilization rate is improved.
By adopting the technical scheme of the invention, the reaction pressure of the primary esterification reactor is 0.3-1.5 MPaG, preferably 0.5-1 MPaG; the reaction temperature is 90-150 ℃, and preferably 100-120 ℃; the molar ratio of methanol to adipic acid in the first-stage esterification reactor is 2-8: 1, preferably 3-E6: 1; the tower top pressure of the esterification rectifying tower is 0.02-0.6 MPaG, and preferably 0.04-0.2 MPaG; the components in the tower bottom are mainly dimethyl adipate, the temperature in the tower bottom is 120-210 ℃, and preferably 165-195 ℃; the liquid volume space-time rate of the esterification rectifying tower is 0.2-0.6 h-1(ii) a The purity of the adipic acid dimethyl ester product at the bottom of the esterification rectifying tower is more than or equal to 99.5 percent, the acid value of the adipic acid dimethyl ester is less than or equal to 0.5mgKOH/g, the adipic acid dimethyl ester product can be directly sold for external use, and 1, 6-hexanediol products can be produced by hydrogenation, so that a good technical effect is obtained.
Drawings
FIG. 1 is a schematic process flow diagram of the present invention.
In the figure: r1 is a first-stage esterification reactor, T1 is an esterification rectifying tower, T2 is a methanol recovery tower, E1 is a T1 tower bottom discharge cooler, E2 is a T1 tower reboiler, E3 is a T2 tower top condenser, F1 is a T1 tower bottom discharge filter, and D1 is a T2 tower top reflux tank.
The method comprises the following steps of (1) dividing fresh methanol 1 into two parts, adding one part 2 and molten adipic acid 4 into a first-stage esterification reactor R1, wherein a reactor R1 is a shell-and-tube heat exchanger, feeding reaction materials into a tube pass without adding a catalyst, and feeding circulating methanol 11 serving as a heat removal medium into a shell pass;
the tube pass discharge is fed from the upper part of a reaction section of an esterification rectifying tower T1, the vaporized methanol 6 is fed from the lower part of the reaction section, secondary esterification reaction occurs, tower bottom liquid 9 is mainly a product containing dimethyl adipate, the product is cooled by a tower bottom discharge cooler E1, the product enters a T1 tower bottom discharge filter F1 for filtration, the product can be directly used as a product without purification or sent to a hydrogenation unit for producing 1, 6-hexanediol, and a tower top gas phase 8 containing dimethyl ether directly enters a methanol recovery tower T2;
e2 is T1 tower reboiler, for the supplementary heat of esterification reaction rectifying column.
The gas phase at the top of the methanol recovery tower enters a T2 overhead condenser E3 for condensation, the gas phase 15 containing dimethyl ether is taken as non-condensable gas for extraction, a small amount of light components 17 are extracted at the top of the tower, methanol (dehydrated and removed of light component impurities) 11 is extracted from a side line liquid phase, the methanol is circulated to a first-stage esterification reactor R1 without cooling and is taken as a heat removing medium, and a heavy component 12 mainly containing water is extracted from the bottom of the tower;
The invention is further illustrated by the following examples.
Detailed Description
[ example 1 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.5 MPaG; the reaction temperature was 100 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 3: 1.
The tower top pressure of the esterification rectifying tower is 0.04 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 175 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time rate of the esterification rectifying tower is 0.3h-1。
The retention time of the first-stage esterification reactor is 2 hours, the conversion rate of adipic acid is 92 percent, wherein the content of dimethyl adipate in the generated ester is 60 percent, the monomethyl adipate is 40 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.50 percent, and the acid value of the dimethyl adipate is 0.5mgKOH/g, and the dimethyl adipate can be directly sold as a product and can also be hydrogenated to produce a 1, 6-hexanediol product.
[ example 2 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.6 MPaG; the reaction temperature was 100 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 3: 1.
The tower top pressure of the esterification rectifying tower is 0.04 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 175 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time velocity of the esterification rectifying tower is 0.3h-1。
The retention time of the first-stage esterification reactor is 2 hours, the conversion rate of adipic acid is 92 percent, wherein the content of dimethyl adipate in the generated ester is 62 percent, the monomethyl adipate is 38 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.52 percent, and the acid value of the dimethyl adipate is 0.5mgKOH/g, and the dimethyl adipate can be directly sold as a product and can also be hydrogenated to produce a 1, 6-hexanediol product.
[ example 3 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.8 MPaG; the reaction temperature was 120 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 4: 1.
The top pressure of the esterification rectifying tower is 0.06 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 182 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time velocity of the esterification rectifying tower is 0.4h-1。
The retention time of the first-stage esterification reactor is 4 hours, the conversion rate of adipic acid is 94 percent, wherein the content of dimethyl adipate in the generated ester is 68 percent, the monomethyl adipate is 32 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.65 percent, and the acid value of the dimethyl adipate is 0.4mgKOH/g, so that the dimethyl adipate can be directly sold as a product and can also be hydrogenated to produce a 1, 6-hexanediol product.
[ example 4 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.10 MPaG; the reaction temperature was 120 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 4: 1.
The tower top pressure of the esterification rectifying tower is 0.08 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 188 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time velocity of the esterification rectifying tower is 0.5h-1。
The retention time of the first-stage esterification reactor is 4 hours, the conversion rate of adipic acid is 95 percent, wherein the content of dimethyl adipate in the generated ester is 72 percent, the monomethyl adipate is 28 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.70 percent, and the acid value of the dimethyl adipate is 0.3mgKOH/g, so that the dimethyl adipate can be directly sold as a product and can also be hydrogenated to produce a 1, 6-hexanediol product.
[ example 5 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.10 MPaG; the reaction temperature was 120 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 4: 1.
The tower top pressure of the esterification rectifying tower is 0.08 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 188 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time velocity of the esterification rectifying tower is 0.5h-1。
The retention time of the first-stage esterification reactor is 5 hours, the conversion rate of adipic acid is 95.5 percent, wherein the content of dimethyl adipate in the generated ester is 75 percent, the monomethyl adipate is 25 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.70 percent, and the acid value of the dimethyl adipate is 0.3mgKOH/g, and the dimethyl adipate can be directly sold as a product and can also be hydrogenated to produce a 1, 6-hexanediol product.
[ example 6 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.10 MPaG; the reaction temperature was 120 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 4: 1.
The tower top pressure of the esterification rectifying tower is 0.08 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 188 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time velocity of the esterification rectifying tower is 0.55h-1。
The retention time of the first-stage esterification reactor is 5 hours, the conversion rate of adipic acid is 95.5 percent, wherein the content of dimethyl adipate in the generated ester is 75 percent, the monomethyl adipate is 25 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.72 percent, the acid value of the dimethyl adipate is 0.3mgKOH/g, the dimethyl adipate can be directly sold as a product, and the 1, 6-hexanediol product can also be produced by hydrogenation.
[ example 7 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.10 MPaG; the reaction temperature was 120 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 4: 1.
The tower top pressure of the esterification rectifying tower is 0.08 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 188 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time velocity of the esterification rectifying tower is 0.6h-1。
The retention time of the first-stage esterification reactor is 5 hours, the conversion rate of adipic acid is 95.5 percent, wherein the content of dimethyl adipate in the generated ester is 75 percent, the monomethyl adipate is 25 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.68 percent, and the acid value of the dimethyl adipate is 0.35mgKOH/g, and the dimethyl adipate can be directly sold as a product and can also be hydrogenated to produce a 1, 6-hexanediol product.
[ example 8 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.10 MPaG; the reaction temperature was 120 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 4: 1.
The tower top pressure of the esterification rectifying tower is 0.08 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 188 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time velocity of the esterification rectifying tower is 0.7h-1。
The retention time of the first-stage esterification reactor is 5 hours, the conversion rate of adipic acid is 95.5 percent, wherein the content of dimethyl adipate in the generated ester is 75 percent, the monomethyl adipate is 25 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.50 percent, and the acid value of the dimethyl adipate is 0.5mgKOH/g, and the dimethyl adipate can be directly sold as a product and can also be hydrogenated to produce a 1, 6-hexanediol product.
[ example 9 ]
This embodiment is described with reference to fig. 1 and the drawings.
The reaction pressure of the first-stage esterification reactor is 0.10 MPaG; the reaction temperature was 120 ℃.
The molar ratio of methanol to adipic acid in the first esterification reactor was 4: 1.
The tower top pressure of the esterification rectifying tower is 0.08 MPaG; the tower bottom component is mainly dimethyl adipate, and the temperature of the tower bottom is 188 ℃ in order to prevent the dimethyl adipate from coking or decomposing at high temperature.
The liquid volume space-time velocity of the esterification rectifying tower is 0.75h-1。
The retention time of the first-stage esterification reactor is 5 hours, the conversion rate of adipic acid is 95.5 percent, wherein the content of dimethyl adipate in the generated ester is 75 percent, the monomethyl adipate is 25 percent, the purity of dimethyl adipate in the esterification rectifying tower is 99.20 percent, the acid value of the dimethyl adipate is 0.6mgKOH/g, and the 1, 6-hexanediol product can be produced by hydrogenation.
[ COMPARATIVE EXAMPLE ]
Different from the embodiment 5, the method does not adopt the design and the energy-saving measure, the first-stage esterification reactor adopts a continuous stirring type reaction kettle, the jacket of the reactor adopts circulating cooling water for heat removal, after the gas phase at the top of the esterification rectifying tower is condensed, one part of the gas phase is used as reflux, one part of the methanol removing recovery tower is used as feeding material, and other conditions are the same.
The retention time of the first-stage esterification reactor is 5 hours, the conversion rate of adipic acid is 95.5 percent, wherein the content of dimethyl adipate in the generated ester is 75 percent, the monomethyl adipate is 25 percent, the purity of the dimethyl adipate product at the bottom of the esterification rectifying tower is 99.70 percent, and the acid value of the dimethyl adipate is 0.6mgKOH/g, and the dimethyl adipate can be directly sold as a product and can also be hydrogenated to produce a 1, 6-hexanediol product.
Compared with example 4, 2 continuous stirring type reaction kettles and 1 condenser are required, the cooling load is increased by 28.5%, and the heating load is increased by 21.5%.
Claims (11)
1. A process for producing dimethyl adipate comprising the steps of:
(1) adding fresh methanol and molten adipic acid into a primary esterification reactor, wherein the reactor is a shell-and-tube heat exchanger, the reaction material passes through a tube pass, the circulating methanol is used as a heat removing medium and passes through a shell pass, and the circulating methanol is pressurized to react without adding a catalyst; the shell-and-tube heat exchanger is any one of a spiral coil heat exchanger and a screwed pipe wound heat exchanger;
(2) the tube pass discharge enters the upper part of the reaction section of the esterification rectifying tower, the vaporized methanol enters the lower part of the reaction section to carry out secondary esterification, the tower bottom liquid is a product containing dimethyl adipate, the product is directly used as a product or sent into a hydrogenation unit to produce 1, 6-hexanediol without purification, and the tower top gas containing dimethyl ether directly enters a methanol recovery tower;
(3) non-condensable gas containing dimethyl ether and a liquid phase containing light components are extracted from the top of the methanol recovery tower, methanol is extracted and recovered from the side line liquid phase, namely, the methanol is dehydrated and the light component impurities are removed, the methanol is circulated to a first-stage esterification reactor without being cooled and is used as a heat removing medium, and heavy components containing water are extracted from the bottom of the tower;
(4) fresh methanol is used as reflux liquid of the esterification rectifying tower, and esters are absorbed from rising gas phase;
wherein the reaction pressure of the primary esterification reactor is 0.3-1.5 MPaG, the reaction temperature is 90-150 ℃, and the molar ratio of methanol to adipic acid is 2-8: 1.
2. The method for producing dimethyl adipate as claimed in claim 1, wherein the reaction pressure of the primary esterification reactor is 0.5-1 MPaG; the reaction temperature is 100-120 ℃.
3. The method for producing the adipic acid dimethyl ester according to claim 1, wherein the molar ratio of the methanol to the adipic acid in the primary esterification reactor is 3-6: 1.
4. The method for producing the dimethyl adipate as claimed in claim 1, wherein the esterification rectifying tower and the methanol recovery tower adopt high-efficiency low-resistance packing at the upper parts and adopt plate towers at the lower parts.
5. The method for producing the dimethyl adipate as claimed in claim 1, wherein the catalyst of the reaction section of the esterification rectifying tower is suspended in a liquid layer on a plate, and any layer of the catalyst can be taken out and replaced without influencing the operation of the esterification rectifying tower.
6. The method for producing dimethyl adipate as claimed in claim 1, wherein the upper rectifying section of the esterification rectifying tower adopts a filler, and catalyst particles are encapsulated in a metal filler cage.
7. The method for producing dimethyl adipate as claimed in claim 1, wherein the top pressure of the rectifying tower of the esterification reaction is 0.02 to 0.6 MPaG; the temperature of the tower kettle is 120-210 ℃.
8. The method for producing dimethyl adipate as claimed in claim 1, wherein the overhead pressure of the rectifying tower of the esterification reaction is 0.04 to 0.2 MPaG; the temperature of the tower kettle is 165-195 ℃.
9. The method for producing dimethyl adipate as claimed in claim 1, wherein the liquid volume hourly space velocity of the esterification rectifying tower is 0.2-0.6 h-1。
10. The method for producing the dimethyl adipate as claimed in claim 1, wherein the purity of the dimethyl adipate product at the tower bottom of the esterification rectifying tower is more than or equal to 99.5 percent, and the acid value of the dimethyl adipate product is less than or equal to 0.5 mgKOH/g.
11. The method for producing adipic acid dimethyl ester according to claim 1, wherein the method is suitable for producing diethyl adipate, diisooctyl adipate, dibutyl adipate and dimethyl succinate.
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