A recovery process for low concentration di(ethylene)propylene glycol as a by-product of carbonates

Abstract

The application belongs to the technical field of chemical industry and provides a recovery method of low-concentration di(ethyl(propyl)glycol by-produced in carbonate production, which comprises the following steps: step one, carbonization filtration; step two, di(ethyl(propyl)glycol salt concentration; step three, low-concentration di(ethyl(propyl)glycol circulation carbonization; and step four, di(ethyl(propyl)glycol circulation evaporation. In the application, a thin film evaporator is used to concentrate ethyl(propyl)glycol and sodium salt dissolved in di(ethyl(propyl)glycol, sodium salt in the material is removed by circulation carbonization, di(ethyl(propyl)glycol material is recovered, and low-concentration material emission is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, and in particular relates to a method for recovering low concentrations of diethylene (propylene) glycol, a byproduct of carbonate production. Background Technology

[0002] In the transesterification process for producing dimethyl carbonate, ethylene (propylene) carbonate reacts with methanol under the catalysis of sodium methoxide to produce dimethyl carbonate, while diethylene (propylene) glycol is also produced as a byproduct. Catalyst removal in the system typically employs carbonation filtration. Specifically, water and carbon dioxide are introduced into the reactor bottoms, where sodium methoxide reacts to produce sodium carbonate. Most of the sodium carbonate precipitates in the ethylene (propylene) glycol, and is removed by filtration. However, approximately 1% to 5% of the sodium salt remains dissolved in the ethylene (propylene) glycol and is ultimately discharged from the bottoms of either the propylene glycol or dipropylene glycol purification tower. This portion of the material is low-concentration diethylene (propylene) glycol, with high viscosity and strong alkalinity, making it difficult to process. In industrial production, it is treated as waste, posing a certain environmental risk.

[0003] Currently, there are very few research reports on the recovery of low-concentration diethylene (propylene) glycol from carbonate byproducts. Chinese patent application number 200910256079.3 discloses a new process for purifying high-quality propylene glycol during the production of dimethyl carbonate. This process recovers catalyst-containing materials through a second-step carbonization step. However, low-concentration diethylene (propylene) glycol waste still accounts for about 3.5 wt% of the main product, and the process is relatively long and complex.

[0004] Therefore, in view of the above situation, there is an urgent need to develop a method for recovering low-concentration diethylene (propylene) glycol from carbonate byproducts in order to overcome the shortcomings in current practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for recovering low-concentration diethylene (propylene) glycol from carbonate byproducts, aiming to solve the problems described in the background art.

[0006] The present invention is implemented as follows: a method for recovering low-concentration diethylene (propylene) glycol, a byproduct of carbonate production, includes the following steps:

[0007] Step 1, Carbonization and Filtration: The heavy components from the ethylene (propylene) glycol light component removal tower, along with the liquid phase outlet material from the thin-film evaporator, demineralized water, and carbon dioxide, enter the carbonization tank. The catalyst reacts with water and carbon dioxide to generate sodium carbonate crystals, which are then filtered out by a filter press. The filtrate enters the ethylene (propylene) glycol product tower. The heavy components entering the carbonization tank are the catalyst sodium methoxide, ethylene (propylene) glycol, and diethylene (propylene) glycol.

[0008] Step 2, Salt Concentration of Diethylene (Propylene) Glycol: The filtrate entering the ethylene (propane) glycol product tower is used to collect ethylene (propane) glycol through the ethylene (propane) glycol outlet on the side of the ethylene (propane) glycol product tower. The bottom of the ethylene (propane) glycol product tower contains salt-containing ethylene (propane) glycol and diethylene (propane) glycol concentrate.

[0009] Step 3: Low-concentration diethylene (propylene) glycol circulating carbonization: The bottom material of the ethylene (propylene) glycol product tower enters the thin film evaporator for evaporation and then enters the diethylene (propylene) glycol light component removal tower. The salt-containing liquid phase of the thin film evaporator enters the carbonization tank for circulating carbonization and desalination. At the same time, according to the content of heavy components, diethylene (propylene) glycol and sodium propylene glycol are intermittently discharged through the outlets of diethylene (propylene) glycol and sodium propylene glycol.

[0010] Step 4, Diethylene (Propane) Glycol Recirculation Evaporation: The bottom material of the diethylene (propane) glycol stripping tower enters the diethylene (propane) glycol product tower. The bottom material of the diethylene (propane) glycol product tower is returned to the thin-film evaporator for material recycling and evaporation. Diethylene (propane) glycol is collected through the diethylene (propane) glycol outlet on the side of the diethylene (propane) glycol product tower.

[0011] In a further technical solution, in step one, the ethylene (propylene) glycol light-light removal tower is provided with a raw material inlet, and the material added to the ethylene (propylene) glycol light-light removal tower through the raw material inlet is a mixture of methanol, sodium methoxide, ethylene (propylene) glycol and diethylene (propylene) glycol from the bottom of the upstream reactive distillation tower; the top of the ethylene (propylene) glycol light-light removal tower is also provided with a methanol outlet.

[0012] In a further technical solution, in step one, the sodium methoxide content in the heavy component material is 1.5 wt% to 5 wt%.

[0013] In a further technical solution, in step one, the bottom and top of the carbonization tank are respectively provided with a carbon dioxide inlet and a demineralized water inlet; the operating temperature of the carbonization tank is 50-70℃, the pressure is 0-30Kpa, and the sodium methoxide content in the filtrate after the carbonization reaction is 0wt%.

[0014] In a further technical solution, in step one, the filter press is also provided with a sodium carbonate outlet for discharging sodium carbonate crystals; the top of the ethylene (propylene) glycol product tower is also connected to a carbonation tank for circulating distillation of ethylene (propylene) glycol containing a small amount of light component impurities.

[0015] In a further technical solution, in step one, the sodium salt content in the liquid phase outlet material of the thin-film evaporator is 5wt% to 15wt%.

[0016] In a further technical solution, in step two, the sodium salt content in the bottom liquid of the ethylene (propylene) glycol product tower is 3wt% to 8wt%, and the diethylene (propylene) glycol content is 40wt% to 70wt%.

[0017] In a further technical solution, in step three, the operating temperature of the thin-film evaporator is 120–150°C, and the pressure is -90–-60 kPa.

[0018] In a further technical solution, in step four, the top of the di(ethylene)propanediol product tower is also connected to the top of the di(ethylene)propanediol light component removal tower; the top of the di(ethylene)propanediol light component removal tower is also connected to a carbonization tank to recover the light component ethylene(propylene)diol from the material.

[0019] This invention provides a method for recovering low-concentration diethylene (propylene) glycol, a byproduct of carbonate production. The method uses a thin-film evaporator to concentrate the sodium salt dissolved in the ethylene (propylene) glycol and diethylene (propylene) glycol, and then uses cyclic carbonization to remove the sodium salt from the material, thereby recovering the diethylene (propylene) glycol material and significantly reducing the emission of low-concentration material. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a method for recovering low-concentration diethylene (propylene) glycol, a byproduct of carbonate production, provided in an embodiment of the present invention.

[0021] In the diagram: 1-Ethylene (propylene) glycol light component removal tower, 2-Carbonization tank, 3-Filter press, 4-Ethylene (propylene) glycol product tower, 5-Thin film evaporator, 6-Di(ethylene)propylene glycol light component removal tower, 7-Di(ethylene)propylene glycol product tower, 8-Raw material inlet, 9-Methanol outlet, 10-Carbon dioxide inlet, 11-Demineralized water inlet, 12-Sodium carbonate outlet, 13-Ethylene (propylene) glycol outlet, 14-Di(ethylene)propylene glycol and sodium propylene glycol outlet, 15-Diethylene (propylene) glycol outlet. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] This invention mainly targets two transesterification processes: one is the production of dimethyl carbonate from ethylene carbonate, with ethylene glycol and diethylene glycol as byproducts; the other is the production of dimethyl carbonate from propylene carbonate, with propylene glycol and dipropylene glycol as byproducts. That is, the diethylene (propylene) glycol described herein includes ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol, and so on. For example, ethylene (propylene) glycol represents ethylene glycol and propylene glycol.

[0024] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0025] like Figure 1 The image shows a method for recovering low-concentration diethylene (propylene) glycol, a byproduct of carbonate production, according to an embodiment of the present invention. The method includes the following steps:

[0026] Step 1, Carbonization and Filtration: The heavy component material from the ethylene (propylene) glycol light component removal tower 1, the liquid phase outlet material from the thin film evaporator 5, demineralized water, and carbon dioxide enter the carbonization tank 2. The catalyst reacts with water and carbon dioxide to generate sodium carbonate crystals, which are then filtered out by the filter press 3. The filtrate enters the ethylene (propylene) glycol product tower 4. The top of the ethylene (propylene) glycol product tower 4 is also connected to the carbonization tank 2 for circulating distillation of ethylene (propylene) glycol containing a small amount of light component impurities, thereby reducing material loss.

[0027] The ethylene (propylene) glycol light-light removal tower 1 is equipped with a feed inlet 8. The material added to the ethylene (propylene) glycol light-light removal tower 1 through the feed inlet 8 is a mixture of methanol, sodium methoxide, ethylene (propylene) glycol, and diethylene (propylene) glycol from the bottom of the upstream reactive distillation tower. Additionally, the top of the ethylene (propylene) glycol light-light removal tower 1 is equipped with a methanol outlet 9. The heavy component material from the ethylene (propylene) glycol light-light removal tower 1 is sodium methoxide catalyst, ethylene (propylene) glycol, and diethylene (propylene) glycol, with the sodium methoxide content in the heavy component material ranging from 1.5 wt% to 5 wt%.

[0028] The carbonization tank 2 is provided with a carbon dioxide inlet 10 at the bottom and a demineralized water inlet 11 at the top, which are used to add demineralized water and carbon dioxide into the carbonization tank 2, respectively; the operating temperature of the carbonization tank 2 is 50-70℃ and the pressure is 0-30KPa.

[0029] The sodium salt content in the liquid phase outlet material of the thin film evaporator 5 is 5wt% to 15wt%.

[0030] The filter press 3 is also equipped with a sodium carbonate outlet 12 for discharging sodium carbonate crystals.

[0031] Step 2, Concentration of diethylene (propylene) glycol with salt: The filtrate entering the ethylene (propylene) glycol product tower 4 is used to collect ethylene (propylene) glycol through the ethylene (propylene) glycol outlet 13 on the side of the ethylene (propylene) glycol product tower 4. The bottom of the ethylene (propylene) glycol product tower 4 contains concentrated ethylene (propylene) glycol and diethylene (propylene) glycol with salt. The sodium salt content in the bottom liquid is 3wt% to 8wt%, and the diethylene (propylene) glycol content is 40wt% to 70wt%.

[0032] Step 3, Low-concentration diethylene (propylene) glycol circulating carbonization: The bottom material of the ethylene (propylene) glycol product tower 4 enters the thin film evaporator 5 for evaporation and then enters the diethylene (propylene) glycol light component removal tower 6. The salt-containing liquid phase of the thin film evaporator 5 enters the carbonization tank 2 for circulating carbonization and desalination. At the same time, according to the content of heavy components, diethylene (propylene) glycol and sodium propylene glycol are intermittently discharged through the diethylene (propylene) glycol and sodium propylene glycol outlet 14.

[0033] The thin-film evaporator 5 operates at a temperature of 120–150°C and a pressure of -90–-60 kPa.

[0034] Step 4: Diethylene (propylene) glycol recycling evaporation: The bottom material of the diethylene (propylene) glycol light component removal tower 6 enters the diethylene (propylene) glycol product tower 7. The bottom material of the diethylene (propylene) glycol product tower 7 is returned to the thin-film evaporator 5 for material recycling evaporation, reducing material discharge. Diethylene (propylene) glycol is collected through the diethylene (propylene) glycol outlet 15 on the side of the diethylene (propylene) glycol product tower 7. The top of the diethylene (propylene) glycol product tower 7 is also connected to the top of the diethylene (propylene) glycol light component removal tower 6, and the top of the diethylene (propylene) glycol light component removal tower 6 is also connected to the carbonization tank 2 to recover the light component ethylene (propylene) glycol in the material.

[0035] According to the above description, the top of the ethylene (propylene) glycol light residue removal tower 1 is methanol output, and the bottom of the tower contains ethylene (propylene) glycol and di(ethylene) propylene glycol containing the catalyst sodium methoxide, which is connected to the inlet of carbonization tank 2. The bottom of carbonization tank 2 is connected to the CO2 pipeline inlet, and the top is connected to the demineralized water inlet 11. The outlet of carbonization tank 2 is connected to the inlet of filter press 3, and the liquid phase outlet of filter press 3 is connected to ethylene (propylene) glycol product tower 4. Solid sodium carbonate is filtered by filter press 3 and then sent out of the unit. The top of ethylene (propylene) glycol product tower 4 is connected to carbonization tank 2, and ethylene (propylene) glycol exits via a side stream. The diethanol product corresponds to ethylene (propylene) glycol outlet 13. The bottom of the column is connected to the inlet of thin film evaporator 5. The vapor phase outlet of the thin film evaporator 5 is connected to the di(ethylene) propylene glycol light removal column 6. The liquid phase low-concentration diethylene (propylene) glycol containing salt is connected to the inlet of carbonization tank 2. The top of the di(ethylene) propylene glycol light removal column 6 is connected to carbonization tank 2. The bottom of the column is connected to the di(ethylene) propylene glycol product column 7. The top of the di(ethylene) propylene glycol product column 7 is connected to the di(ethylene) propylene glycol light removal column 6. The bottom of the column is connected to the thin film evaporator 5, and the diethylene (propylene) glycol product is produced by the side stream.

[0036] Example 1

[0037] like Figure 1 The image shows a method for recovering low-concentration diethylene (propylene) glycol, a byproduct of carbonate production, according to an embodiment of the present invention. The method includes the following steps:

[0038] Step 1, Carbonization and Filtration: The heavy component material from the ethylene (propylene) glycol light component removal tower 1, the liquid phase outlet material from the thin film evaporator 5, demineralized water, and carbon dioxide enter the carbonization tank 2. The catalyst reacts with water and carbon dioxide to generate sodium carbonate crystals, which are then filtered out by the filter press 3. The filtrate enters the ethylene (propylene) glycol product tower 4. The top of the ethylene (propylene) glycol product tower 4 is also connected to the carbonization tank 2 for circulating distillation of ethylene (propylene) glycol containing a small amount of light component impurities, thereby reducing material loss.

[0039] The ethylene (propylene) glycol light-light removal tower 1 is equipped with a feed inlet 8. The material added to the ethylene (propylene) glycol light-light removal tower 1 through the feed inlet 8 is a mixture of methanol, sodium methoxide, ethylene (propylene) glycol, and diethylene (propylene) glycol from the bottom of the upstream reactive distillation tower. Additionally, the top of the ethylene (propylene) glycol light-light removal tower 1 is equipped with a methanol outlet 9. The heavy component material from the ethylene (propylene) glycol light-light removal tower 1 is sodium methoxide catalyst, ethylene (propylene) glycol, and diethylene (propylene) glycol, with the sodium methoxide content in the heavy component material being 1.5 wt%.

[0040] The carbonization tank 2 is provided with a carbon dioxide inlet 10 at the bottom and a demineralized water inlet 11 at the top, which are used to add demineralized water and carbon dioxide into the carbonization tank 2, respectively; the operating temperature of the carbonization tank 2 is 50℃ and the pressure is 0KPa.

[0041] The sodium salt content in the liquid phase outlet material of the thin-film evaporator 5 is 5 wt%.

[0042] The filter press 3 is also equipped with a sodium carbonate outlet 12 for discharging sodium carbonate crystals.

[0043] In addition, the sodium methoxide content in the carbonized filtrate is 0 wt%.

[0044] The carbonization reaction is: 2CH3ONa + CO2 + H2O = 2CH3OH + Na2CO3↓;

[0045] The reaction when carbon dioxide is in excess is: Na₂CO₃ + CO₂ + H₂O = 2NaHCO₃↓.

[0046] Step 2, Concentration of diethylene (propylene) glycol with salt: The filtrate entering the ethylene (propylene) glycol product tower 4 is used to collect ethylene (propylene) glycol through the ethylene (propylene) glycol outlet 13 on the side of the ethylene (propylene) glycol product tower 4. The bottom of the ethylene (propylene) glycol product tower 4 contains concentrated ethylene (propylene) glycol and diethylene (propylene) glycol with salt, wherein the sodium salt content in the bottom liquid is 3wt% and the diethylene (propylene) glycol content is 40wt%.

[0047] Step 3, Low-concentration diethylene (propylene) glycol circulating carbonization: The bottom material of the ethylene (propylene) glycol product tower 4 enters the thin film evaporator 5 for evaporation and then enters the diethylene (propylene) glycol light component removal tower 6. The salt-containing liquid phase of the thin film evaporator 5 enters the carbonization tank 2 for circulating carbonization and desalination. At the same time, according to the content of heavy components, diethylene (propylene) glycol and sodium propylene glycol are intermittently discharged through the diethylene (propylene) glycol and sodium propylene glycol outlet 14.

[0048] The thin-film evaporator 5 operates at a temperature of 120℃ and a pressure of -90KPa.

[0049] Step 4: Diethylene (propylene) glycol recycling evaporation: The bottom material of the diethylene (propylene) glycol light component removal tower 6 enters the diethylene (propylene) glycol product tower 7. The bottom material of the diethylene (propylene) glycol product tower 7 is returned to the thin-film evaporator 5 for material recycling evaporation, reducing material discharge. Diethylene (propylene) glycol is collected through the diethylene (propylene) glycol outlet 15 on the side of the diethylene (propylene) glycol product tower 7. The top of the diethylene (propylene) glycol product tower 7 is also connected to the top of the diethylene (propylene) glycol light component removal tower 6, and the top of the diethylene (propylene) glycol light component removal tower 6 is also connected to the carbonization tank 2 to recover the light component ethylene (propylene) glycol in the material.

[0050] Table 1. Comparison of the cyclic carbonization method and the non-cyclic carbonization method in Example 1

[0051] Low concentration diethylene (propylene) glycol as a percentage of the product (wt%) Example 1 - Cyclic Carbonization Method 0.27％ Non-cyclic carbonization method 3.5％

[0052] Example 2

[0053] like Figure 1 The image shows a method for recovering low-concentration diethylene (propylene) glycol, a byproduct of carbonate production, according to an embodiment of the present invention. The method includes the following steps:

[0054] Step 1, Carbonization and Filtration: The heavy component material from the ethylene (propylene) glycol light component removal tower 1, the liquid phase outlet material from the thin film evaporator 5, demineralized water, and carbon dioxide enter the carbonization tank 2. The catalyst reacts with water and carbon dioxide to generate sodium carbonate crystals, which are then filtered out by the filter press 3. The filtrate enters the ethylene (propylene) glycol product tower 4. The top of the ethylene (propylene) glycol product tower 4 is also connected to the carbonization tank 2 for circulating distillation of ethylene (propylene) glycol containing a small amount of light component impurities, thereby reducing material loss.

[0055] The ethylene (propylene) glycol light-light removal tower 1 is equipped with a feed inlet 8. The material added to the ethylene (propylene) glycol light-light removal tower 1 through the feed inlet 8 is a mixture of methanol, sodium methoxide, ethylene (propylene) glycol, and diethylene (propylene) glycol from the bottom of the upstream reactive distillation tower. Additionally, the top of the ethylene (propylene) glycol light-light removal tower 1 is equipped with a methanol outlet 9. The heavy component material from the ethylene (propylene) glycol light-light removal tower 1 is sodium methoxide catalyst, ethylene (propylene) glycol, and diethylene (propylene) glycol, with the sodium methoxide content in the heavy component material being 3 wt%.

[0056] The carbonization tank 2 is provided with a carbon dioxide inlet 10 at the bottom and a demineralized water inlet 11 at the top, which are used to add demineralized water and carbon dioxide into the carbonization tank 2, respectively; the operating temperature of the carbonization tank 2 is 60℃ and the pressure is 0KPa.

[0057] The sodium salt content in the liquid phase outlet material of the thin-film evaporator 5 is 8 wt%.

[0058] The filter press 3 is also equipped with a sodium carbonate outlet 12 for discharging sodium carbonate crystals.

[0059] In addition, the sodium methoxide content in the carbonized filtrate is 0 wt%.

[0060] The carbonization reaction is: 2CH3ONa + CO2 + H2O = 2CH3OH + Na2CO3↓;

[0061] The reaction when carbon dioxide is in excess is: Na₂CO₃ + CO₂ + H₂O = 2NaHCO₃↓.

[0062] Step 2, Concentration of diethylene (propylene) glycol with salt: The filtrate entering the ethylene (propylene) glycol product tower 4 is used to collect ethylene (propylene) glycol through the ethylene (propylene) glycol outlet 13 on the side of the ethylene (propylene) glycol product tower 4. The bottom of the ethylene (propylene) glycol product tower 4 contains concentrated ethylene (propylene) glycol and diethylene (propylene) glycol with salt. The sodium salt content in the bottom liquid is 5 wt%, and the diethylene (propylene) glycol content is 55 wt%.

[0063] Step 3, Low-concentration diethylene (propylene) glycol circulating carbonization: The bottom material of the ethylene (propylene) glycol product tower 4 enters the thin film evaporator 5 for evaporation and then enters the diethylene (propylene) glycol light component removal tower 6. The salt-containing liquid phase of the thin film evaporator 5 enters the carbonization tank 2 for circulating carbonization and desalination. At the same time, according to the content of heavy components, diethylene (propylene) glycol and sodium propylene glycol are intermittently discharged through the diethylene (propylene) glycol and sodium propylene glycol outlet 14.

[0064] The thin-film evaporator 5 operates at a temperature of 130℃ and a pressure of -90KPa.

[0065] Step 4: Diethylene (propylene) glycol recycling evaporation: The bottom material of the diethylene (propylene) glycol light component removal tower 6 enters the diethylene (propylene) glycol product tower 7. The bottom material of the diethylene (propylene) glycol product tower 7 is returned to the thin-film evaporator 5 for material recycling evaporation, reducing material discharge. Diethylene (propylene) glycol is collected through the diethylene (propylene) glycol outlet 15 on the side of the diethylene (propylene) glycol product tower 7. The top of the diethylene (propylene) glycol product tower 7 is also connected to the top of the diethylene (propylene) glycol light component removal tower 6, and the top of the diethylene (propylene) glycol light component removal tower 6 is also connected to the carbonization tank 2 to recover the light component ethylene (propylene) glycol in the material.

[0066] Table 2 Comparison results of the cyclic carbonization method and the non-cyclic carbonization method in Example 2

[0067] Low concentration diethylene (propylene) glycol as a percentage of the product (wt%) Example 2 - Cyclic Carbonization Method 0.29％ Non-cyclic carbonization method 3.5％

[0068] Example 3

[0069] like Figure 1 The image shows a method for recovering low-concentration diethylene (propylene) glycol, a byproduct of carbonate production, according to an embodiment of the present invention. The method includes the following steps:

[0070] Step 1, Carbonization and Filtration: The heavy component material from the ethylene (propylene) glycol light component removal tower 1, the liquid phase outlet material from the thin film evaporator 5, demineralized water, and carbon dioxide enter the carbonization tank 2. The catalyst reacts with water and carbon dioxide to generate sodium carbonate crystals, which are then filtered out by the filter press 3. The filtrate enters the ethylene (propylene) glycol product tower 4. The top of the ethylene (propylene) glycol product tower 4 is also connected to the carbonization tank 2 for circulating distillation of ethylene (propylene) glycol containing a small amount of light component impurities, thereby reducing material loss.

[0071] The ethylene (propylene) glycol light-light removal tower 1 is equipped with a feed inlet 8. The material added to the ethylene (propylene) glycol light-light removal tower 1 through the feed inlet 8 is a mixture of methanol, sodium methoxide, ethylene (propylene) glycol, and diethylene (propylene) glycol from the bottom of the upstream reactive distillation tower. Additionally, the top of the ethylene (propylene) glycol light-light removal tower 1 is equipped with a methanol outlet 9. The heavy component material from the ethylene (propylene) glycol light-light removal tower 1 is sodium methoxide catalyst, ethylene (propylene) glycol, and diethylene (propylene) glycol, with the sodium methoxide content in the heavy component material being 5 wt%.

[0072] The carbonization tank 2 is provided with a carbon dioxide inlet 10 at the bottom and a demineralized water inlet 11 at the top, which are used to add demineralized water and carbon dioxide into the carbonization tank 2, respectively; the operating temperature of the carbonization tank 2 is 70℃ and the pressure is 0KPa.

[0073] The sodium salt content in the liquid phase outlet material of the thin film evaporator 5 is 15 wt%.

[0074] The filter press 3 is also equipped with a sodium carbonate outlet 12 for discharging sodium carbonate crystals.

[0075] In addition, the sodium methoxide content in the carbonized filtrate is 0 wt%.

[0076] The carbonization reaction is: 2CH3ONa + CO2 + H2O = 2CH3OH + Na2CO3↓;

[0077] The reaction when carbon dioxide is in excess is: Na₂CO₃ + CO₂ + H₂O = 2NaHCO₃↓.

[0078] Step 2, Concentration of diethylene (propylene) glycol with salt: The filtrate entering the ethylene (propylene) glycol product tower 4 is used to collect ethylene (propylene) glycol through the ethylene (propylene) glycol outlet 13 on the side of the ethylene (propylene) glycol product tower 4. The bottom of the ethylene (propylene) glycol product tower 4 contains concentrated ethylene (propylene) glycol and diethylene (propylene) glycol with salt, wherein the sodium salt content in the bottom liquid is 8 wt% and the diethylene (propylene) glycol content is 70 wt%.

[0079] Step 3, Low-concentration diethylene (propylene) glycol circulating carbonization: The bottom material of the ethylene (propylene) glycol product tower 4 enters the thin film evaporator 5 for evaporation and then enters the diethylene (propylene) glycol light component removal tower 6. The salt-containing liquid phase of the thin film evaporator 5 enters the carbonization tank 2 for circulating carbonization and desalination. At the same time, according to the content of heavy components, diethylene (propylene) glycol and sodium propylene glycol are intermittently discharged through the diethylene (propylene) glycol and sodium propylene glycol outlet 14.

[0080] The thin-film evaporator 5 operates at a temperature of 150℃ and a pressure of -90KPa.

[0081] Step 4: Diethylene (propylene) glycol recycling evaporation: The bottom material of the diethylene (propylene) glycol light component removal tower 6 enters the diethylene (propylene) glycol product tower 7. The bottom material of the diethylene (propylene) glycol product tower 7 is returned to the thin-film evaporator 5 for material recycling evaporation, reducing material discharge. Diethylene (propylene) glycol is collected through the diethylene (propylene) glycol outlet 15 on the side of the diethylene (propylene) glycol product tower 7. The top of the diethylene (propylene) glycol product tower 7 is also connected to the top of the diethylene (propylene) glycol light component removal tower 6, and the top of the diethylene (propylene) glycol light component removal tower 6 is also connected to the carbonization tank 2 to recover the light component ethylene (propylene) glycol in the material.

[0082] Table 3. Comparison results of the cyclic carbonization method and the non-cyclic carbonization method in Example 3.

[0083] Low concentration diethylene (propylene) glycol as a percentage of the product (wt%) Example 3 - Cyclic Carbonization Method 0.33％ Non-cyclic carbonization method 3.5％

[0084] The above embodiments of the present invention provide a method for recovering low-concentration diethylene (propylene) glycol, a byproduct of carbonate production, with the following main advantages:

[0085] 1) The sodium salt dissolved in ethylene (propylene) glycol and diethylene (propylene) glycol is concentrated using a thin-film evaporator 5;

[0086] 2) Utilize cyclic carbonization to remove sodium salts from materials and recover diethylene (propylene) glycol materials, significantly reducing the emission of low-concentration materials.

[0087] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for recovering low-concentration diethylene glycol as a byproduct of carbonate production, characterized in that, Includes the following steps: Step 1, Carbonization and Filtration: The heavy components from the ethylene glycol light component removal tower, along with the liquid phase outlet material from the thin-film evaporator, demineralized water, and carbon dioxide, enter the carbonization tank. The catalyst reacts with water and carbon dioxide to generate sodium carbonate crystals, which are then filtered out by a filter press. The filtrate enters the ethylene glycol product tower. The heavy components entering the carbonization tank are the catalyst sodium methoxide, ethylene glycol, and diethylene glycol. Step 2, Salt Concentration of Diethylene Glycol: The filtrate entering the ethylene glycol product column is used to collect ethylene glycol through the ethylene glycol outlet on the side of the column. The bottom of the ethylene glycol product column contains salt-containing ethylene glycol and diethylene glycol concentrate. Step 3, Low-concentration diethylene glycol circulating carbonization: The bottom material of the ethylene glycol product tower enters the thin film evaporator for evaporation and then enters the diethylene glycol light component removal tower. The salt-containing liquid phase of the thin film evaporator enters the carbonization tank for circulating carbonization and desalting. At the same time, diethylene glycol is intermittently discharged through the diethylene glycol outlet according to the content of heavy components. Step 4, Diethylene Glycol Recirculation Evaporation: The bottom material of the diethylene glycol light residue removal tower enters the diethylene glycol product tower. The bottom material of the diethylene glycol product tower is returned to the thin-film evaporator for material recycling and evaporation. Diethylene glycol is collected through the diethylene glycol outlet on the side of the diethylene glycol product tower. In step one, the ethylene glycol light-removal tower is provided with a raw material inlet. The material added to the ethylene glycol light-removal tower through the raw material inlet is a mixture of methanol, sodium methoxide, ethylene glycol and diethylene glycol from the bottom of the upstream reactive distillation tower. The top of the ethylene glycol light component removal tower is also equipped with a methanol outlet; The carbonization tank is provided with a carbon dioxide inlet and a demineralized water inlet at the bottom and top, respectively; The filter press is also equipped with a sodium carbonate outlet for discharging sodium carbonate crystals; The top of the ethylene glycol product column is also connected to a carbonization tank for circulating distillation of ethylene glycol containing a small amount of light component impurities. In step four, the top of the diethylene glycol product column is also connected to the top of the diethylene glycol light component removal column; The top of the diethylene glycol light component removal tower is also connected to a carbonization tank to recover the light component ethylene glycol from the material.

2. The method for recovering low-concentration diethylene glycol as a carbonate byproduct according to claim 1, characterized in that, In step one, the sodium methoxide content in the heavy component material is 1.5 wt% to 5 wt%. The carbonization tank operates at a temperature of 50–70°C and a pressure of 0–30 kPa. The sodium methoxide content in the filtrate after carbonization is 0 wt%.

3. The method for recovering low-concentration diethylene glycol as a carbonate byproduct according to claim 1, characterized in that, In step one, the sodium salt content in the liquid phase outlet material of the thin film evaporator is 5wt% to 15wt%.

4. The method for recovering low-concentration diethylene glycol as a carbonate byproduct according to claim 3, characterized in that, In step two, the sodium salt content in the bottom liquid of the ethylene glycol product column is 3wt% to 8wt%, and the diethylene glycol content is 40wt% to 70wt%.

5. The method for recovering low-concentration diethylene glycol as a carbonate byproduct according to any one of claims 1-4, characterized in that, In step three, the operating temperature of the thin-film evaporator is 120–150°C, and the pressure is -90–-60 kPa.

6. A method for recovering low-concentration dipropylene glycol as a byproduct of carbonate production, characterized in that, Includes the following steps: Step 1, Carbonization and Filtration: The heavy components from the propylene glycol light component removal tower, along with the liquid phase outlet material from the thin-film evaporator, demineralized water, and carbon dioxide, enter the carbonization tank. The catalyst reacts with water and carbon dioxide to generate sodium carbonate crystals, which are then filtered out by a filter press. The filtrate enters the propylene glycol product tower. The heavy components entering the carbonization tank are the catalyst sodium methoxide, propylene glycol, and dipropylene glycol. Step 2, Salt Concentration of Dipropylene Glycol: The filtrate entering the propylene glycol product column is used to collect propylene glycol through the propylene glycol outlet on the side of the propylene glycol product column. The bottom of the propylene glycol product column contains salt-containing propylene glycol and dipropylene glycol concentrate. Step 3, Low-concentration dipropylene glycol circulating carbonization: The bottom material of the propylene glycol product tower enters the thin film evaporator for evaporation and then enters the dipropylene glycol light component removal tower. The salt-containing liquid phase of the thin film evaporator enters the carbonization tank for circulating carbonization and desalination. At the same time, according to the content of heavy components, dipropylene glycol and sodium propylene glycol are intermittently discharged through the outlets of dipropylene glycol and sodium propylene glycol. Step 4, Dipropylene Glycol Recirculation Evaporation: The bottom material of the dipropylene glycol light removal tower enters the dipropylene glycol product tower. The bottom material of the dipropylene glycol product tower is returned to the thin film evaporator for material recycling and evaporation. Dipropylene glycol is collected through the dipropylene glycol outlet on the side of the dipropylene glycol product tower. In step one, the propylene glycol light-removal tower is provided with a raw material inlet. The material added to the propylene glycol light-removal tower through the raw material inlet is a mixture of methanol, sodium methoxide, propylene glycol and dipropylene glycol from the bottom of the upstream reactive distillation tower. The propylene glycol light removal tower is also equipped with a methanol outlet at the top; The carbonization tank is provided with a carbon dioxide inlet and a demineralized water inlet at the bottom and top, respectively; The filter press is also equipped with a sodium carbonate outlet for discharging sodium carbonate crystals; The top of the propylene glycol product column is also connected to a carbonization tank for circulating distillation of propylene glycol containing a small amount of light component impurities. In step four, the top of the dipropylene glycol product column is also connected to the top of the dipropylene glycol light component removal column. The top of the dipropylene glycol light component removal tower is also connected to a carbonization tank to recover the light component propylene glycol from the material.

7. The method for recovering low-concentration dipropylene glycol as a carbonate byproduct according to claim 6, characterized in that, In step one, the sodium methoxide content in the heavy component material is 1.5 wt% to 5 wt%. The carbonization tank operates at a temperature of 50–70°C and a pressure of 0–30 kPa. The sodium methoxide content in the filtrate after carbonization is 0 wt%.

8. The method for recovering low-concentration dipropylene glycol as a carbonate byproduct according to claim 6, characterized in that, In step one, the sodium salt content in the liquid phase outlet material of the thin film evaporator is 5wt% to 15wt%.

9. The method for recovering low-concentration dipropylene glycol as a carbonate byproduct according to claim 8, characterized in that, In step two, the sodium salt content in the bottom liquid of the propylene glycol product column is 3wt% to 8wt%, and the dipropylene glycol content is 40wt% to 70wt%.

10. The method for recovering low-concentration dipropylene glycol as a carbonate byproduct according to any one of claims 6-9, characterized in that, In step three, the operating temperature of the thin-film evaporator is 120–150°C, and the pressure is -90–-60 kPa.

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