A system and method for continuous recovery of high-purity glycolic acid from exhaust gas.

Abstract

This invention belongs to the field of glycolic acid tail gas utilization, and discloses a system and method for continuous recovery of high-purity glycolic acid from tail gas. The system includes a recovery unit, an impurity removal unit, a reaction conversion unit, and a purification unit; the recovery unit includes a recovery tower, a circulating pump, and an adsorption tank; the impurity removal unit includes an impurity removal tower; the reaction conversion unit includes a mixer and a reaction converter connected in sequence; the purification unit includes a heat exchanger and a purifier connected in sequence. The system and method of this invention improve the utilization rate of glycolic acid-containing tail gas materials, resulting in significant economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of glycolic acid tail gas utilization, and more specifically, relates to a system and method for continuous recovery of high-purity glycolic acid from tail gas. Background Technology

[0002] For process materials such as glycolic acid, glycolide, and impurities in the exhaust gas, failure to recycle and discharge them will result in economic losses of the materials. At the same time, due to environmental protection requirements, the exhaust gas cannot be directly discharged into the atmosphere. Moreover, glycolide in the exhaust gas is easy to solidify and cannot be discharged into the flare. Therefore, a recycling system is needed to recover glycolic acid, hydrolyze glycolide into glycolic acid and then refine it to obtain glycolic acid for reuse. At the same time, impurities in the exhaust gas are removed to ensure that high-purity glycolic acid is obtained.

[0003] Existing research mainly focuses on the production of glycolic acid, as detailed in CN109694317A and CN107840790A. There are few reports on the recovery of glycolic acid-rich tail gas. Traditional tail gas recovery devices typically use water washing or other solvents to absorb the organic components in the tail gas. However, for glycolic acid-rich tail gas containing intermediate-boiling-point organic impurities, simple water washing is insufficient. Furthermore, the tail gas may contain glycolide, which requires hydrolysis to convert it into glycolic acid, necessitating improved recovery rates. Therefore, a new tail gas recovery system needs to be developed and designed to meet these requirements. Summary of the Invention

[0004] The purpose of this invention is to address the existing problem of utilizing glycolic acid-containing tail gas resources by providing a system and method for the continuous recovery of high-purity glycolic acid from tail gas. The system and method of this invention improve the utilization rate of glycolic acid-containing tail gas materials, resulting in significant economic and environmental benefits.

[0005] To achieve the above objectives, the present invention provides a system for continuous recovery of high-purity glycolic acid from exhaust gas, the system comprising a recovery unit, an impurity removal unit, a reaction conversion unit, and a purification unit;

[0006] The recovery unit includes a recovery tower, a circulation pump, and an adsorption tank;

[0007] The lower inlet of the recovery tower is connected to a tail gas feed pipeline; the upper inlet of the recovery tower is connected to a washing liquid feed pipeline; the top outlet of the recovery tower is connected to the adsorption tank; and the bottom outlet of the recovery tower is connected to the inlet of the circulation pump.

[0008] The impurity removal unit includes an impurity removal tower;

[0009] The bottom inlet of the impurity removal tower is connected to the middle outlet line of the packing of the recovery tower; the bottom outlet of the impurity removal tower is divided into two paths, one of which returns to the middle of the recovery tower.

[0010] The reaction conversion unit includes a mixer and a reaction converter connected in sequence;

[0011] The outlet pipeline of the circulating pump is divided into two lines: one line connects to the middle of the recovery tower, and the other line connects to the inlet of the mixer.

[0012] The mixer and the reaction converter are each independently connected to a steam heating input line;

[0013] The refining unit includes a heat exchanger and a refiner connected in sequence;

[0014] The outlet pipeline of the reaction converter is divided into two paths: one path circulates back to the inlet of the reaction converter through a reaction circulation pump, and the other path connects to the inlet of the heat exchanger.

[0015] According to the present invention, preferably, the top outlet of the adsorption tank is connected to a non-condensable gas output pipeline.

[0016] According to the present invention, preferably, the top inlet of the impurity removal tower is connected to an azeotropic agent input pipeline; the top outlet of the impurity removal tower is connected to a top material output pipeline.

[0017] According to the present invention, preferably, the impurity removal unit further includes a reboiler; another path of the bottom outlet of the impurity removal tower returns to the bottom of the impurity removal tower through the reboiler; the reboiler is provided with a steam heating input line and a reboiler condensate output line.

[0018] According to the present invention, preferably, the reaction converter is connected to a reaction converter condensate output line.

[0019] According to the present invention, preferably, the heat exchanger is connected to a condensate feed line and a condensate discharge line.

[0020] According to the present invention, preferably, the mixer is a jet mixer.

[0021] According to the present invention, preferably, the reaction converter is a tubular heated reactor.

[0022] According to the present invention, preferably, the impurity removal column is a distillation column, and more preferably an azeotropic distillation column.

[0023] According to the present invention, preferably, the purifier is a membrane separator and / or a centrifuge.

[0024] Another aspect of the present invention provides a method for continuously recovering high-purity glycolic acid from exhaust gas. This method utilizes the aforementioned system for continuously recovering high-purity glycolic acid from exhaust gas and includes the following steps:

[0025] S1: The tail gas containing glycolic acid is sent to the bottom of the recovery tower for water washing. The mixture of glycolic acid and glycolide in the tail gas enters the bottom of the recovery tower. The intermediate boiling point impurities in the tail gas containing glycolic acid enter the impurity removal tower through the middle outlet line of the packing. The non-condensable gas in the tail gas containing glycolic acid is discharged from the system after being adsorbed by the adsorption tank.

[0026] S2: The intermediate boiling point impurities are separated by distillation in the impurity removal tower to obtain the top impurity material and the reflux mixture. A portion of the reflux mixture is refluxed to the middle of the recovery tower.

[0027] S3: A portion of the mixture of glycolic acid and glycolide in the bottom of the recovery tower is returned to the middle of the recovery tower by the circulation pump, while the other portion enters the reaction conversion unit to react and obtain crude glycolic acid. A portion of the crude glycolic acid is returned to the reaction converter of the reaction conversion unit, while the other portion enters the purification unit for cooling and separation to obtain the glycolic acid product.

[0028] According to the present invention, preferably, based on the total weight of the glycolic acid-containing tail gas, the glycolic acid content in the tail gas is 5-55% wt, the glycolide content is 5-55% wt, the non-condensable gas content is 10-60% wt, and the intermediate boiling point impurity content is 5-30% wt.

[0029] According to the present invention, preferably, in the reaction conversion unit, the mixture of glycolic acid and glycolide is first mixed with high-temperature steam and heated in the mixer to obtain a first heated mixture; the first heated mixture is heated in the reaction converter by exchanging heat with high-temperature steam, so that glycolide and water in the first heated mixture react to generate glycolic acid.

[0030] According to the present invention, preferably, the temperature of the first heated mixture is 60-100°C.

[0031] According to the present invention, preferably, the reaction temperature inside the reaction converter is 100-150°C.

[0032] According to the present invention, preferably, the ratio of crude glycolic acid refluxed into the reactor to crude glycolic acid entering the purification unit is (1-20):1. The reactor outlet is recycled back to the reactor inlet to further improve the conversion rate of glycolide to glycolic acid.

[0033] According to the present invention, preferably, the distillation separation is azeotropic distillation separation; the azeotropic distillation separation includes adding an azeotropic agent to the top inlet of the impurity removal tower through the azeotropic agent input line, preferably, the azeotropic agent is water.

[0034] According to the present invention, preferably, other portions of the reflux mixture are refluxed to the impurity removal column for distillation circulation.

[0035] According to the present invention, preferably, the impurity material at the top of the tower is discharged from the system through the top material output pipeline.

[0036] According to the present invention, preferably, within the refining unit, the crude glycolic acid is cooled by exchanging heat with the condensing medium through the heat exchanger.

[0037] According to the present invention, preferably, the purifier is a membrane separator, and the crude glycolic acid is cooled to 20-60°C. If the purifier is a centrifuge, the crude glycolic acid is cooled to a temperature suitable for stable operation of the centrifuge.

[0038] According to the present invention, preferably, the purity of the glycolic acid product is 99-99.99%.

[0039] The beneficial effects of the technical solution of the present invention are as follows:

[0040] 1) The system and method of the present invention improve the utilization rate of glycolic acid-containing tail gas materials, resulting in significant economic and environmental benefits;

[0041] 2) This invention improves the heat and mass transfer efficiency between glycolide and water by setting up a jet mixer;

[0042] 3) This invention increases the residence time of the reaction conversion and improves the hydrolysis conversion rate of glycolide by setting up a tubular reactor and material circulation;

[0043] 4) By setting up a purification unit, this invention can remove impurities such as oligomers generated during the reaction process, thus ensuring the quality of the recovered high-purity glycolic acid as a raw material.

[0044] 5) By setting up an impurity removal tower, this invention can reduce the content of intermediate boiling point impurities in glycolic acid tail gas, prevent side reactions in downstream reaction conversion units, and ensure the quality of high-purity glycolic acid recovered as raw material.

[0045] 6) The present invention has an adsorption tank at the top of the recovery tower to ensure that the exhaust gas emissions meet environmental protection requirements.

[0046] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0047] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0048] Figure 1 A schematic diagram of a system for continuous recovery of high-purity glycolic acid from exhaust gas provided in Embodiment 1 of the present invention is shown.

[0049] The annotations in the attached figures are explained as follows:

[0050] 1-Recovery tower, 2-Circulation pump, 3-Impurification tower, 4-Reboiler, 5-Adsorption tank, 6-Mixer, 7-Reaction converter, 8-Heat exchanger, 9-Refiner, 10-Reaction circulation pump, 11-Tail gas feed line, 12-Washing liquid feed line, 13-Non-condensable gas output line, 14-Azeotropic agent input line, 15-Top material output line, 16-Steam heating input line, 17-Reboiler condensate output line, 18-Condensate discharge line, 19-Condensate feed line, 20-Ethanolic acid product output line, 21-Packaging intermediate outlet line, 22-Circulation middle line, 23-Reaction converter condensate output line, 24-Circulation bottom line. Detailed Implementation

[0051] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0052] Example 1

[0053] This embodiment provides a system for the continuous recovery of high-purity glycolic acid from exhaust gas, such as... Figure 1 As shown, the system includes a recovery unit, a deimpuration unit, a reaction conversion unit, and a purification unit;

[0054] The recovery unit includes a recovery tower 1, a circulation pump 2, and an adsorption tank 5;

[0055] The lower inlet of the recovery tower 1 is connected to the exhaust gas feed pipeline 11; the upper inlet of the recovery tower 1 is connected to the washing liquid feed pipeline 12; the top outlet of the recovery tower 1 is connected to the adsorption tank 5; and the bottom outlet of the recovery tower 1 is connected to the inlet of the circulation pump 2.

[0056] The top outlet of the adsorption tank 5 is connected to a non-condensable gas output pipeline 13.

[0057] The impurity removal unit includes an impurity removal tower 3 and a reboiler 4;

[0058] The top inlet of the impurity removal tower 3 is connected to an azeotropic agent input pipeline 14; the top outlet of the impurity removal tower is connected to a top material output pipeline 15.

[0059] The bottom inlet of the impurity removal tower 3 is connected to the intermediate outlet line 21 of the packing of the recovery tower; the bottom outlet of the impurity removal tower is divided into two paths, one path returns to the middle of the recovery tower through the central circulation pipeline 22, and the other path returns to the bottom of the impurity removal tower 3 through the reboiler 4.

[0060] The reboiler 4 is equipped with a steam heating input line 16 and a reboiler condensate output line 17.

[0061] The reaction conversion unit includes a mixer 6 and a reaction converter 7 connected in sequence;

[0062] The outlet pipeline of the circulating pump 2 is divided into two lines: one line is connected to the middle of the recovery tower through the bottom circulating pipeline 24, and the other line is connected to the inlet of the mixer 6.

[0063] The mixer 6 and the reaction converter 7 are each independently connected to a steam heating input line 16; the reaction converter is connected to a reaction converter condensate output line 23.

[0064] The refining unit includes a heat exchanger 8 and a refiner 9 connected in sequence;

[0065] The outlet pipeline of the reaction converter 7 is divided into two paths: one path circulates back to the inlet of the reaction converter 7 through the reaction circulation pump 10, and the other path connects to the inlet of the heat exchanger 8.

[0066] The heat exchanger is connected to a condensate feed line 19 and a condensate discharge line 18.

[0067] The mixer 6 is a jet mixer; the reaction converter 7 is a tubular heating reactor; the impurity removal tower 3 is an azeotropic distillation tower; and the purifier 9 is a membrane separator.

[0068] The method for continuous recovery of high-purity glycolic acid using the above system includes the following steps:

[0069] S1: Based on the total weight of the glycolic acid-containing tail gas, the glycolic acid content in the tail gas is 33% wt, the glycolide content is 29% wt, the non-condensable gas content such as nitrogen is 28% wt, and the intermediate boiling point impurity content is 10% wt. The glycolic acid-containing tail gas is sent to the bottom of the recovery tower 1 for water washing. The glycolic acid and glycolide mixture in the glycolic acid-containing tail gas enters the bottom of the recovery tower 1. The intermediate boiling point impurities in the glycolic acid-containing tail gas enter the impurity removal tower 3 through the intermediate outlet line 21 of the packing. The non-condensable gases in the glycolic acid-containing tail gas are adsorbed and treated by the adsorption tank 5 and then discharged from the system through the non-condensable gas output pipeline 13.

[0070] S2: Intermediate boiling point impurities are separated by azeotropic distillation in the impurity removal tower 3 to obtain top impurity material and reflux mixture. A portion of the reflux mixture is refluxed back to the middle of the recovery tower 1 through the central circulation pipeline 22, and the other portion is refluxed back to the impurity removal tower 3 for distillation circulation. The top impurity material is discharged from the system through the top material output pipeline.

[0071] The azeotropic distillation separation includes adding an azeotropic agent, which is water, to the top inlet of the impurity removal tower through the azeotropic agent input line 14.

[0072] S3: A portion of the glycolic acid and glycolide mixture in the bottom of the recovery tower 1 is returned to the middle of the recovery tower 1 via the circulation pump 2, while the remainder enters the reaction conversion unit.

[0073] Within the reaction conversion unit, the mixture of glycolic acid and glycolide is first mixed with high-temperature steam in mixer 6 and heated to 90°C to obtain a first heated mixture. This first heated mixture is then heated to 130°C in reaction converter 7 through heat exchange with high-temperature steam, causing the glycolide and water in the first heated mixture to react and generate glycolic acid, yielding crude glycolic acid. A portion of the crude glycolic acid is returned to reaction converter 7 of the reaction conversion unit via reaction circulation pump 10, while the remaining portion enters the purification unit. The ratio of crude glycolic acid returned to the reaction converter to crude glycolic acid entering the purification unit is 5:1.

[0074] In the refining unit, the crude glycolic acid is cooled to room temperature by exchanging heat with the condensing medium through the heat exchanger 8, and then separated by the refining unit 9 (membrane separator) to obtain glycolic acid product with a purity of 99%.

[0075] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A system for continuous recovery of high-purity glycolic acid from exhaust gas, characterized in that, The system includes a recovery unit, a de-impurity unit, a reaction conversion unit, and a purification unit; The recovery unit includes a recovery tower, a circulation pump, and an adsorption tank; The lower inlet of the recovery tower is connected to a tail gas feed pipeline; the upper inlet of the recovery tower is connected to a washing liquid feed pipeline; the top outlet of the recovery tower is connected to the adsorption tank; and the bottom outlet of the recovery tower is connected to the inlet of the circulation pump. The top outlet of the adsorption tank is connected to a non-condensable gas output pipeline. The impurity removal unit includes an impurity removal tower; The top inlet of the impurity removal tower is connected to an azeotropic agent input pipeline; the top outlet of the impurity removal tower is connected to a top material output pipeline. The bottom inlet of the impurity removal tower is connected to the intermediate outlet line of the packing of the recovery tower; the bottom outlet of the impurity removal tower is divided into two paths, one of which returns to the middle of the recovery tower; the impurity removal unit also includes a reboiler; the other path of the bottom outlet of the impurity removal tower returns to the bottom of the impurity removal tower through the reboiler; the reboiler is equipped with a steam heating input line and a reboiler condensate output line. The reaction conversion unit includes a mixer and a reaction converter connected in sequence; The outlet pipeline of the circulating pump is divided into two lines: one line connects to the middle of the recovery tower, and the other line connects to the inlet of the mixer. The mixer and the reactor are each independently connected to a steam heating input line; the reactor is connected to a reactor condensate output line. The refining unit includes a heat exchanger and a refiner connected in sequence; The outlet pipeline of the reaction converter is divided into two paths: one path circulates back to the inlet of the reaction converter through a reaction circulation pump, and the other path connects to the inlet of the heat exchanger. The heat exchanger is connected to a condensate feed line and a condensate discharge line.

2. The system for continuous recovery of high-purity glycolic acid from tail gas according to claim 1, wherein, The mixer is a jet mixer; The reaction converter is a tubular heated reactor; The impurity removal column is an azeotropic distillation column; The purifier is a membrane separator and / or a centrifuge.

3. A method for continuous recovery of high-purity glycolic acid from exhaust gas, characterized in that, This method employs the system for continuous recovery of high-purity glycolic acid from tail gas as described in claim 1 or 2, and includes the following steps: S1: The tail gas containing glycolic acid is sent to the bottom of the recovery tower for water washing. The mixture of glycolic acid and glycolide in the tail gas enters the bottom of the recovery tower. The intermediate boiling point impurities in the tail gas containing glycolic acid enter the impurity removal tower through the middle outlet line of the packing. The non-condensable gas in the tail gas containing glycolic acid is discharged from the system after being adsorbed by the adsorption tank. S2: The intermediate boiling point impurities are separated by distillation in the impurity removal tower to obtain the top impurity material and the reflux mixture. A portion of the reflux mixture is refluxed to the middle of the recovery tower. S3: A portion of the mixture of glycolic acid and glycolide in the bottom of the recovery tower is returned to the middle of the recovery tower by the circulation pump, while the other portion enters the reaction conversion unit to react and obtain crude glycolic acid. A portion of the crude glycolic acid is returned to the reaction converter of the reaction conversion unit, while the other portion enters the purification unit for cooling and separation to obtain the glycolic acid product.

4. The method for continuous recovery of high-purity glycolic acid from tail gas according to claim 3, wherein, Based on the total weight of the glycolic acid-containing tail gas, the glycolic acid content in the tail gas is 5-55 wt%, the glycolide content is 5-55 wt%, the non-condensable gas content is 10-60 wt%, and the intermediate boiling point impurity content is 5-30 wt%.

5. The method for continuous recovery of high-purity glycolic acid from tail gas according to claim 3, wherein, Within the reaction conversion unit, the mixture of glycolic acid and glycolide is first mixed with and heated by high-temperature steam in the mixer to obtain a first heated mixture. The first heated mixture is then heated in the reaction converter by exchanging heat with high-temperature steam, causing glycolide and water in the first heated mixture to react and generate glycolic acid.

6. The method for continuous recovery of high-purity glycolic acid from tail gas according to claim 5, wherein, The temperature of the first heated mixture is 60-100℃; The reaction temperature inside the reactor is 100-150℃; The ratio of crude glycolic acid refluxed to the reactor to crude glycolic acid entering the purification unit is (1-20):

1.

7. The method for continuous recovery of high-purity glycolic acid from tail gas according to claim 3, wherein, The distillation separation is an azeotropic distillation separation; the azeotropic distillation separation includes adding an azeotropic agent, which is water, to the top inlet of the impurity removal tower through the azeotropic agent input pipeline; The remaining portion of the reflux mixture is refluxed to the impurity removal column for distillation circulation; The impurities at the top of the tower are discharged from the system through the top material output pipeline.

8. The method for continuous recovery of high-purity glycolic acid from tail gas according to claim 3, wherein, Within the refining unit, the crude glycolic acid is cooled by exchanging heat with the condensing medium through the heat exchanger. When the purifier is a membrane separator, the crude glycolic acid is cooled to 20-60°C.

9. The method for continuous recovery of high-purity glycolic acid from tail gas according to claim 3, wherein, The purity of the glycolic acid product is 99-99.99%.

Images