Method for separating and recovering waste residues in production of carbonate solvents

Abstract

The present application belongs to the field of solid waste treatment, and discloses a separation and recovery method of waste residues in carbonate solvent production, which comprises the following steps: 1) separating the co-production after carbonization in the carbonate solvent production by using a filter, and obtaining waste residue filter cake and filtrate containing diols after filtration; 2) introducing an inhibitor into the filter, and washing the filter with desalted water and recovering the washing liquid; the inhibitor is a substance capable of reacting with alkali metal hydroxide to generate a water-soluble salt. In the present application, an inhibitor is added in the later stage of the filtration cycle to prevent the reaction of sodium carbonate into alkali under the action of propylene glycol in high-temperature filtration, thereby reducing the alkali corrosion and filter membrane fouling and plugging of the filter equipment, and prolonging the operation cycle of the equipment.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment, specifically relating to a method for recovering waste residue obtained in the production of carbonate solvents. Background Technology

[0002] Dimethyl carbonate is a carbonate solvent used as an electrolyte in lithium-ion batteries. Currently, the production method used by companies is transesterification, which involves exchanging ethylene carbonate or propylene carbonate with methanol to obtain dimethyl carbonate and the coproduct ethylene glycol or propylene glycol. Commonly used homogeneous catalysts for this reaction are sodium methoxide and potassium methoxide. Industrially, carbonation is often used to remove these strongly alkaline catalysts to avoid corrosion of metal materials at high temperatures. For example, adding water and CO2 to a glycol solution containing sodium methoxide converts the sodium methoxide into sparingly soluble sodium carbonate and / or sodium bicarbonate, which precipitate in the glycol solution, resulting in a mixture containing solid sodium salts. Filtration then separates the mixture into a solid filter residue containing sodium salts and an organic phase containing glycols. The resulting solid filter residue is generally treated as hazardous waste in the industry; however, the open discharge process often produces a strong, pungent odor, severely impacting the production environment.

[0003] CN114588909A discloses a process for recycling waste residue from dimethyl carbonate production, comprising: (1) mixing the waste residue with an organic solvent that can dissolve the organic matter in the waste residue, and using the sodium carbonate solid obtained by solid-liquid separation for later use; (2) mixing the sodium carbonate solid obtained in step (1) with a solution containing calcium ions, separating the calcium carbonate precipitate after the reaction is completed, and converting the waste residue into a high-value-added catalyst through a series of modification processes.

[0004] CN111762801A discloses a method for treating waste crystalline salt obtained from the co-production of dimethyl carbonate from ethylene glycol. The main components of the waste crystalline salt are sodium nitrate, sodium carbonate, sodium oxalate, sodium formate, and sodium nitrite. The waste crystalline salt is dissolved in water to obtain a waste crystalline salt mixture. The mixture is then subjected to the following treatments in sequence: adding nitric acid, blowing air into the mixture at 50-70°C, adjusting the pH of the mixture to neutral, adding calcium hydroxide, filtering to remove precipitate, evaporating the filtrate to crystallize, and drying to obtain sodium nitrate product.

[0005] CN101671038A discloses a method for comprehensive utilization of solid waste in dimethyl carbonate production. A solvent is added to the solid waste, and after thorough mixing at a volume ratio of 1:1.5, the mixture is filtered to obtain an organic phase solution and a sodium carbonate solid containing water of crystallization. The solid is then calcined to evaporate the water of crystallization, yielding 50% industrial-grade sodium carbonate by weight of the solid waste residue.

[0006] Although existing technologies disclose some methods for treating waste residue in carbonate solvent production and provide ideas for the recovery of by-product glycols and waste residue, the problem of irritating odors generated during the unloading process still exists.

[0007] In addition, when separating the filter cake and the organic phase in the filter, there is a situation where polymers encapsulate inorganic salts, causing scaling and clogging of the filter membrane, leading to unexpected shutdowns.

[0008] Therefore, it is necessary to improve the methods for separating and recovering waste residue in carbonate solvent production. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this invention provides a method for recovering waste residue and detergents, inhibiting alkaline corrosion of equipment, and extending equipment operating cycles in the production of carbonate solvents. The specific method is as follows:

[0010] This invention provides a method for separating and recovering waste residue in carbonate solvent production, the method comprising the following steps:

[0011] 1) The carbonized byproducts produced by carbonate solvent production are separated by a filter. Preferably, the carbonized byproducts are a suspension, including waste residue and an organic phase containing diol. After filtration, a waste residue filter cake and a filtrate containing diol are obtained.

[0012] 2) After filtration, an inhibitor is introduced into the filter, followed by rinsing with demineralized water and recovering the rinsing solution. The inhibitor is a substance that can react with alkali metal hydroxides to form water-soluble salts. Demineralized water is a type of industrial water, mainly used to remove calcium, magnesium, and other ions from circulating water via resin exchange, and is a conventional water product in this field.

[0013] In a preferred embodiment, the inhibitor is a weakly acidic gas such as CO2 or SO2, more preferably CO2.

[0014] The inhibitor is introduced by using an aeration head for aeration, and the resulting water-soluble salts are dissolved in demineralized water and discharged into a dissolution tank.

[0015] Furthermore, the aeration time is less than the time interval between two filtration cycles, preferably 10 to 30 minutes; the aeration volume is 1 to 5 times the filter volume, preferably 2 to 4 times the filter volume.

[0016] The process of obtaining the co-products after carbonization of the carbonate solvent production is as follows: ethylene carbonate or propylene carbonate is subjected to transesterification with methanol, with an alkali metal methanol salt as the catalyst, to obtain dimethyl carbonate and a diol solution containing the alkali metal methanol salt; after separating the dimethyl carbonate, water and CO2 are added to the diol solution containing the alkali metal methanol salt to obtain the final product.

[0017] During filtration and separation, the filtration temperature is 80–160℃, preferably 120–140℃.

[0018] During filtration and separation, the filtration pressure is 0.1 to 0.8 MPa, preferably 0.2 to 0.4 MPa.

[0019] The filtration and separation process is stopped by monitoring the pressure difference between the filter inlet and outlet; filtration and separation stop when the pressure reaches 0.2 MPa.

[0020] Preferably, the waste residue contains alkali metal salts, more preferably alkali metal carbonates or bicarbonates.

[0021] Preferably, the alkali metal is sodium or potassium.

[0022] In a preferred embodiment, the diol is a byproduct of carbonate solvent production, mainly ethylene glycol or propylene glycol, determined by the raw materials used in carbonate solvent production; the organic components containing the diol include diol, diol monomethyl ether, water, sodium carbonate, sodium bicarbonate, methanol, etc.

[0023] The total content of carbonates and bicarbonates in the suspension is 0.1% to 5% (the percentage is the mass fraction, the same below).

[0024] In a preferred embodiment, the filter is a sealed horizontal blade filter with a filter cloth precision of 0.1–50 μm.

[0025] The interior of the filter mainly refers to the local dead zone, including the bottom drain outlet, and the inner wall where droplets are easily trapped, especially the local dead zone.

[0026] Furthermore, the local dead zone originates from the device's own structure, which prevents the liquid at the bottom drain port from draining and causes it to remain inside the filter.

[0027] Industrial production studies of existing carbonate solvents have revealed that during the separation of solid sodium salts, glycols at high temperatures convert alkali metal carbonates into more basic alkali metal hydroxides. As is known to those skilled in the art, alkali metal hydroxides can cause alkali embrittlement in carbon steel or alloy steel for several reasons: first, an alkali solution with a concentration greater than 10% is sufficient to induce alkali embrittlement; second, relatively high temperatures are required, although the temperature range for alkali embrittlement is wide, but the temperature most likely to cause embrittlement is near the boiling point of the solution; and third, tensile stress, which can be stress caused by external loads, residual stress, or a combination of both.

[0028] Inside the filter, residual alkali metal hydroxides can accumulate in localized dead zones, causing these areas to meet both high alkali concentrations and high temperatures during filtration. This increases the risk of stress corrosion cracking, leading to alkali corrosion of the filtration equipment. Simultaneously, the diols in the filtrate polymerize under the influence of alkali metal hydroxides. The resulting polymers encapsulate inorganic salts, causing scaling and clogging of the filter membrane at the filter disc, resulting in unexpected shutdowns.

[0029] Therefore, after the filter cake and filtrate are completely separated, by adding inhibitors to the aeration head, the alkali metal hydroxides produced by the filter during high-temperature filtration are transformed back into weakly alkaline alkali metal salts, thus removing the generated alkali metal hydroxides. This solves both the filter clogging problem and the instrument corrosion problem caused by alkali.

[0030] In a preferred embodiment, the waste filter cake obtained in step 1) is washed with washing liquid and discharged into a dissolving tank. Then, demineralized water is used to dissolve the waste filter cake. The resulting salt solution is used in the water treatment unit to adjust the pH value of the acidic wastewater in the carbonate solvent production process.

[0031] The washing process involves washing the filter cake with a washing solution to remove filtrate components other than sodium salts from the filter cake. After washing, the filtrate content in the filter cake is reduced to below 5%, preferably below 1%.

[0032] The washing liquid is a solvent that cannot dissolve alkali metal salt waste residue, preferably a low-boiling-point solvent such as alcohol, ether, or ester, and more preferably methanol.

[0033] Furthermore, the amount of washing liquid used is 1 to 5 times the filter volume, preferably 2 to 3 times.

[0034] Prior to washing, to prevent the low-boiling-point solvent from vaporizing, the filter cake is preferably cooled to 40–100°C, more preferably to 50–60°C. Furthermore, the solvent used for cooling is the most abundant component in the co-products, preferably a diol.

[0035] The amount of demineralized water is 5 to 20 times the mass of the filter cake.

[0036] In a preferred embodiment, the filtrate and washing liquid are recovered by distillation and / or rectification, preferably by rectification.

[0037] The distillation process involves obtaining a low-boiling-point solvent from the top of the separation column, which is recycled as filter cake washing liquid; and obtaining a crude diol product from the bottom of the column, which is then separated and purified in a refining column inside the carbonate solvent production unit.

[0038] The method provided by this invention has the following advantages compared with the prior art:

[0039] In the later stages of the filtration cycle in a closed-loop filter, an inhibitor is introduced into the filter to suppress alkali corrosion and polymerization clogging caused by strong alkalis at high temperatures, thus extending the operating cycle of the filtration equipment. Simultaneously, this allows waste residue to be separated and recovered within the filtration system, significantly reducing the irritating odor problem associated with open-loop sludge discharge. Attached Figure Description

[0040] Figure 1 This is a schematic flowchart of a waste residue recovery method in the production of carbonate solvents according to the present invention. Detailed Implementation

[0041] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but it is not limited to these embodiments.

[0042] Unless otherwise specified, all percentages used in the embodiments of the present invention are mass percentages.

[0043] Example 1

[0044] In the laboratory, a 100ml Erlenmeyer flask was used as the reaction vessel. 0.625g of water, 0.1125g of sodium carbonate, and 24.26g of ethylene glycol (i.e., a mass content of 2.5% water, 0.45% sodium carbonate, and 97.05% ethylene glycol) were added to simulate the co-products of carbonate solvent production followed by carbonation. A magnetic stir bar was then added, and the flask was placed on a single-point magnetic stirrer for heating and stirring. During this process, the temperature of the materials in the Erlenmeyer flask was monitored with a thermometer, and the temperature setting of the single-point magnetic stirrer was continuously adjusted until the material temperature stabilized at around 140℃. After stirring openly for 0.5 hours, a sample of the material in the Erlenmeyer flask was titrated. The determined forms were sodium hydroxide and sodium carbonate, with a sodium carbonate conversion rate of 49.83%.

[0045] Example 2

[0046] In the laboratory, a 100ml Erlenmeyer flask was used as the reaction vessel. 0.75g of water, 0.5g of sodium carbonate, and 23.76g of propylene glycol (i.e., 3% water, 2% sodium carbonate, and 95% propylene glycol by mass) were added to simulate the co-products of carbonate solvent production followed by carbonation. A magnetic stir bar was then added, and the flask was placed on a single-point magnetic stirrer for heating and stirring. During this process, the temperature of the materials in the Erlenmeyer flask was monitored with a thermometer, and the temperature setting of the single-point magnetic stirrer was continuously adjusted until the material temperature stabilized at around 140℃. After stirring openly for 0.5 hours, a sample of the material in the Erlenmeyer flask was titrated. The results showed that the substances present were sodium hydroxide and sodium carbonate, with a sodium carbonate conversion rate of 43%.

[0047] Comparative Example 1

[0048] In the laboratory, a 100ml Erlenmeyer flask was used as the reaction vessel. 0.625g of water, 0.1125g of sodium carbonate, and 24.26g of DMSO (i.e., a mass content of 2.5% water, 0.45% sodium carbonate, and 97.05% DMSO) were added. A magnetic stir bar was then added, and the flask was placed on a single-point magnetic stirrer for heating and stirring. During this process, the temperature of the materials in the Erlenmeyer flask was monitored with a thermometer, and the temperature setting of the single-point magnetic stirrer was continuously adjusted until the temperature stabilized at approximately 140℃. After stirring openly for 0.5 hours, a sample of the material in the Erlenmeyer flask was titrated. The determined form was sodium carbonate, indicating that the sodium carbonate was not converted.

[0049] Comparative Example 2

[0050] In the laboratory, a 100ml Erlenmeyer flask was used as the reaction vessel. 0.625g of water, 0.1125g of sodium carbonate, and 24.26g of 1,4-dioxane (i.e., mass content of 2.5% water, 0.45% sodium carbonate, and 97.05% 1,4-dioxane) were added. A magnetic stir bar was then added, and the flask was placed on a single-point magnetic stirrer for heating and stirring. During this process, the temperature of the materials in the Erlenmeyer flask was monitored with a thermometer, and the temperature setting of the single-point magnetic stirrer was continuously adjusted until the temperature stabilized at around 140℃. After stirring openly for 0.5 hours, a sample of the material in the Erlenmeyer flask was titrated. The determined form was sodium carbonate, indicating that the sodium carbonate was not converted.

[0051] Examples 1-2 and Comparative Examples 1-2 show that ethylene glycol and propylene glycol can convert sodium carbonate into sodium hydroxide at high temperatures. However, under the same conditions, DMSO and 1,4-dioxane cannot convert sodium carbonate into sodium hydroxide. This demonstrates that in the industrial production of carbonate solvents, alkali corrosion and polymerization blockage occur because ethylene glycol or propylene glycol in sodium-containing materials convert sodium carbonate into sodium hydroxide, leading to alkali embrittlement and polymerization reactions.

[0052] Example 3

[0053] like Figure 1As shown, a small horizontal blade filter with a volume of 1L and a filter cloth precision of 10μm was used. The propylene glycol solution (140℃) contained 3% sodium carbonate, 0.01% sodium bicarbonate, 96% propylene glycol, and 0.99% other organic impurities. 5L of material was pumped to the filter inlet using an air pump. After filtration at 0.4MPa and 120℃ for 15 minutes, the filtrate became clear, forming an effective filter cake. Filtration was stopped when the pressure difference between the filter inlet and outlet reached 0.2MPa. A draining operation was then performed. After the filter was emptied, low-temperature propylene glycol was pumped to the filter to cool the filter cake to 60℃. The amount of propylene glycol was twice the filter volume. A second draining operation was performed using nitrogen (N2). After the filter was emptied, methanol was pumped to the filter to wash the filter cake. The amount of methanol was twice the filter volume. After the methanol is emptied, the demineralized water is pumped to a filter, and the waste residue is dissolved and discharged into a dissolving tank to prepare a 15% (w / w) solution. The conversion rate of sodium carbonate to sodium hydroxide is 44%. The propylene glycol content in the methanol washing liquid is 5%, which is purified using a distillation column. Methanol with a purity of 99.5% is obtained at the top of the column, and propylene glycol with a purity of 99% is obtained at the bottom.

[0054] At room temperature, the inside of the filter was rinsed with distilled water of 1 volume, and CO2 gas of 3 volumes was introduced into the filter system at a rate of 0.2 kg / h for 20 min. No sodium hydroxide was detected in the collected aqueous solution.

[0055] Example 4

[0056] like Figure 1 As shown, a small horizontal blade filter with a volume of 1L and a filter cloth precision of 10μm was used. The ethylene glycol solution (140℃) contained 2% sodium carbonate, 0.01% sodium bicarbonate, 97% ethylene glycol, and 0.99% other organic impurities. 5L of material was pumped to the filter inlet using an air pump. After filtration at 0.2MPa and 100℃ for 15 minutes, the filtrate became clear, forming an effective filter cake. Filtration was stopped when the pressure difference between the filter inlet and outlet reached 0.2MPa. A draining operation was then performed. After the filter was emptied, low-temperature ethylene glycol was pumped to the filter to cool the filter cake to 50℃. The amount of ethylene glycol was twice the filter volume. A second draining operation was performed using nitrogen (N2). After the filter was emptied, methanol was pumped to the filter to wash the filter cake. The amount of methanol was twice the filter volume. After the methanol is emptied, the demineralized water is pumped to a filter to dissolve the waste residue and discharge it into a dissolving tank to prepare a 5% (w / w) solution. The conversion rate of sodium carbonate to sodium hydroxide was tested to be 49%. The ethylene glycol content in the methanol washing liquid was 4.5%, which was purified using a distillation column. Methanol with a purity of 99.5% was obtained at the top of the column, and ethylene glycol with a purity of 99% was obtained at the bottom.

[0057] At room temperature, the inside of the filter was rinsed with distilled water of 1 volume, and SO2 gas of 2 volumes was introduced into the filter system at a rate of 0.3 kg / h for 20 min. No sodium hydroxide was detected in the collected aqueous solution.

[0058] The above examples and comparative examples demonstrate that adding an inhibitor to the filter during the later stages of the filtration cycle can inhibit the conversion of sodium carbonate to sodium hydroxide. The presence of sodium hydroxide catalyzes the polymerization of glycols into polyglycols, and the combination of poorly soluble macromolecules with the salt leads to filter clogging. Eliminating sodium hydroxide inhibits polymer formation, thereby reducing polymerization clogging caused by sodium hydroxide, and also reduces alkaline corrosion.

[0059] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0060] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. A method for separating and recovering waste residue in the production of carbonates via transesterification, the method comprising the following steps: 1) The carbonized byproducts produced by carbonate solvent production are separated using a filter, and the filtered product is a waste filter cake and a filtrate containing glycol; the carbonized byproducts are a suspension, including waste residue containing alkali metal salts and an organic phase containing glycol; 2) Inhibitors are introduced into the filter and the filter is rinsed with demineralized water and the rinsing solution is recovered; the inhibitor is a substance that can react with alkali metal hydroxides to form water-soluble salts; In step 1), the filtration temperature is 80~160℃ and the filtration pressure is 0.1~0.8 MPa.

2. The method according to claim 1, characterized in that, The inhibitor is a weakly acidic gas.

3. The method according to claim 2, characterized in that, The inhibitor is CO2 gas or SO2 gas.

4. The method according to claim 2 or 3, characterized in that, The inhibitor is introduced by aeration, with the aeration volume being 1 to 5 times the filter volume; the aeration time is less than the time interval between two filtration cycles.

5. The method according to claim 4, characterized in that, The aeration rate is 2 to 4 times the filter volume; the aeration time is 10 to 30 minutes.

6. The method according to claim 1, characterized in that, The process for obtaining the co-products of the carbonate solvent production after carbonization is as follows: ethylene carbonate or propylene carbonate is subjected to transesterification with methanol, with an alkali metal methanol salt as the catalyst, to obtain dimethyl carbonate and a diol solution containing the alkali metal methanol salt; after separating the dimethyl carbonate, water and CO2 are added to the diol solution containing the alkali metal methanol salt to obtain the final product.

7. The method according to claim 6, characterized in that, In step 1), the filtration temperature is 120~140℃ and the filtration pressure is 0.2~0.4 MPa.

8. The method according to claim 1, characterized in that, The alkali metal salt is an alkali metal carbonate or bicarbonate; The organic phase containing diol includes diol, diol monomethyl ether, water, sodium carbonate, sodium bicarbonate, and methanol; The total mass content of carbonates and bicarbonates in the suspension is 0.1% to 5%.

9. The method according to claim 8, characterized in that, The alkali metal is sodium or potassium.

10. The method according to any one of claims 1-3 and 5-9, characterized in that, The waste filter cake obtained in step 1) is washed with washing liquid and discharged into a dissolving tank. Then, demineralized water is used to dissolve the waste filter cake to obtain a salt solution, which is used in the water treatment unit.

11. The method according to claim 10, characterized in that, The washing liquid is a solvent that cannot dissolve alkali metal salt waste residue.

12. The method according to claim 11, characterized in that, The washing solution is a low-boiling-point alcohol, ether, or ester solvent.

13. The method according to claim 12, characterized in that, The washing solution is methanol.

14. The method according to any one of claims 11-13, characterized in that, The amount of washing liquid used is 1 to 5 times the filter volume.

15. The method according to claim 14, characterized in that, The amount of washing liquid used is 2 to 3 times the filter volume.

16. The method according to any one of claims 11-13 and 15, characterized in that, Before washing, the filter cake is cooled to 40-100°C; the solvent used for cooling is the most abundant component in the co-products.

17. The method according to claim 16, characterized in that, Before washing, cool the filter cake to 50-60℃.

18. The method according to claim 16, characterized in that, The solvent used for cooling is glycol.

19. The method according to claim 10, characterized in that, The amount of water used for desalination is 5 to 20 times the mass of the filter cake.

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