A method for recycling the residue after distillation of desolvated dioxane

Abstract

This invention provides a method for recovering and utilizing distillation residue after solvent removal from homohydric anhydride, relating to the field of fine chemical technology. The method includes anhydride treatment, vaporization and sublimation, dissolution and recrystallization, distillation, and water washing. In this invention, the distillation residue is anhydride-treated under high temperature and negative pressure, followed by vaporization and sublimation under vacuum to separate mechanical impurities and high-boiling substances. Then, through dissolution and recrystallization, the difference in solubility between homohydric anhydride and metahydric anhydride in polar solvents is utilized to preferentially crystallize out the homohydric anhydride. The mother liquor is distilled to remove the solvent, and then colored impurities are removed by hot water washing and activated carbon adsorption. Finally, it is cooled and crystallized to obtain trimellitic acid. The homohydric anhydride obtained by this invention has a purity ≥95% and a yield of 84-89%, and the trimellitic acid has a purity ≥97% and a yield of 81-86%. This method achieves effective recovery of high-value-added components from distillation residue, demonstrating significant economic and environmental benefits and promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, and in particular to a method for recycling distillation residue after solvent removal from homogenizing anhydride. Background Technology

[0002] The distillation residue after solvent removal from homogenizing anhydride originates from the refining process waste in the homogenizing anhydride workshop. The main process involves oxidizing mesitylene and air under the action of a catalyst. The reaction gas is collected by a trap to obtain crude anhydride, which is then sent to the refining workshop to be refined into high-purity homogenizing anhydride. A small amount of residue is generated during the evaporation and crystallization refining process. This distillation residue contains trimellitic anhydride and its acidic variant trimellitic acid, pyromellitic anhydride and its acidic variant pyromellitic acid, as well as small amounts of 2-formylbenzoic acid, 2,4-diformylbenzoic acid, 2-formyl-4,5-dimethylbenzoic acid, phthalic anhydride, 4,5-dicarboxyphthalide, and small amounts of mechanical impurities. Among these, trimellitic anhydride and pyromellitic anhydride have higher added value.

[0003] Currently, the distillation residue after solvent removal from homogeneous anhydride is disposed of as hazardous waste generated during the production process by qualified environmental protection companies. This method not only results in extremely high production costs but also leads to significant resource waste, and poses high risks during storage, transportation, and disposal. Furthermore, some similar companies incinerate the distillation residue on their own premises. This method carries storage risks, involves large volumes of homogeneous and partial anhydride that are not properly utilized and are lost as waste. Incineration also generates pollutants such as dioxins and particulate matter, resulting in significant environmental risks.

[0004] From a technical perspective, homohydric anhydride and partial anhydride have very high boiling points at atmospheric pressure, and they are prone to decomposition or cross-linking reactions when heated. This leads to product deterioration, generating light volatile organic compounds or cross-linking to form impurities such as yellow polymers. Therefore, effective separation cannot be achieved at atmospheric pressure using simple methods. Furthermore, their extremely high boiling points at atmospheric pressure require very high temperatures to vaporize, which is highly uneconomical in practice, and high temperatures accelerate the formation of polymer impurities, affecting product purity.

[0005] Therefore, how to efficiently recover homogenate and acid from distillation residue is one of the technical problems that needs to be solved in this field. Summary of the Invention

[0006] In view of this, the present invention provides a method for recycling distillation residue after solvent removal of homohydric anhydride. The present invention extracts and purifies homohydric anhydride and metaacid from the distillation residue through steps such as acid anhydride formation, vacuum vaporization and sublimation, dissolution and recrystallization, distillation, and water washing followed by cooling and crystallization. This method solves the problems of high cost and serious resource waste associated with treating distillation residue as hazardous waste in existing technologies, as well as the high environmental risks caused by the generation of dioxins and other pollutants from incineration. It has promising application prospects.

[0007] The present invention provides a method for recovering and utilizing distillation residue after solvent removal from homogenate, comprising the following steps: S1. Anhydration: The distillation residue is heated under high temperature and negative pressure to completely anhydrate the carboxyl groups in the distillation residue. The small amount of water produced by the dehydration and anhydration of free carboxyl groups in the distillation residue is completely removed through the isothermal process, and anhydrated distillation residue is obtained. S2, vaporization and deposition: The distillation residue of S1 anhydride is distilled under high temperature and vacuum, so that the homogenous anhydride and the partial anhydride are vaporized and deposited, thereby completely separating a small amount of mechanical impurities and high-boiling substances to obtain a deposited solid; since the boiling points of the partial anhydride and homogenous anhydride are very high under normal pressure, a high degree of vacuum is required in the system. S3, Dissolution and Recrystallization: Dissolve the sublimated solid of S2 in 2-5 times its volume of solvent to obtain an acid anhydride solution. Remove 60-90% of the solvent from the acid anhydride solution by atmospheric distillation. The solubility of homogeneous anhydride in solvent is much lower than that of partial anhydride. Prepare a supersaturated solution of homogeneous anhydride and an unsaturated solution of partial anhydride from the acid anhydride solution. The homogeneous anhydride crystallizes out from the supersaturated solution. Because homogeneous anhydride has lower polarity, it first forms a saturated solution in polar solvents. However, partial anhydride has higher polarity due to the presence of carboxyl groups, making it more difficult to form a saturated solution in polar solvents. Therefore, homogeneous anhydride recrystallizes out from the solution first to form solid crystals and precipitate out from the solution. However, partial anhydride is unsaturated, so only homogeneous anhydride precipitates out at this time. Filter the saturated solution under negative pressure to obtain the homogeneous anhydride solid. S4. Distillation: The mother liquor from S3 is distilled under normal pressure, and then distilled under reduced pressure to ensure that the solvent is removed as much as possible, and the bottom of the distillation vessel is obtained. S5. Washing: Add 3-5 times the amount of deionized water and activated carbon to the distillation residue from S4. After adsorption by heating, wash with water, filter while hot, cool to crystallize, and vacuum dry to obtain trimellitic acid. The distillation residue after complete solvent removal contains a small amount of anhydride, colored impurities, etc., which need to be removed by hot water washing and activated carbon adsorption. The distillation residue contains benzene-containing organic compounds, and a small number of hydrogen atoms on the benzene ring are replaced by aldehyde groups. Uneven heating may cause oxidative cross-linking between the aldehyde groups of the benzene ring, generating delocalized large π bonds. These bonds allow electrons to pass through the aldehyde groups. It can move freely within a relatively large range and easily absorbs blue-violet light to become excited, which manifests as colored impurities with yellow groups. These colored impurities have large molecular weights and are easily adsorbed by activated carbon. Since the previous recrystallization operation has separated most of the anhydride, a high-concentration trimellitic acid solution will be obtained after water washing. The concentration of trimellitic acid in cold aqueous solution is extremely low. During the water washing and cooling crystallization process, trimellitic acid precipitates out due to supersaturation, while trimellitic acid remains in the aqueous solution because it is unsaturated in water and is thus separated, yielding trimellitic acid.

[0008] Preferably, the distillation residue includes trimellitic anhydride, trimellitic acid, pyromellitic anhydride, and pyromellitic acid.

[0009] Preferably, in step S1, the vacuum degree is 0.075~0.090 MPa, the heating temperature is 210℃~230℃, and the heating time is 30 min. The drying process uses a relatively low vacuum, and maintaining the temperature at 210℃~230℃ is sufficient for anhydride formation and dehydration. More preferably, the heating temperature is 215℃~225℃.

[0010] Preferably, in step S2, the vacuum degree is 0.098~0.10 MPa, the distillation temperature is 230℃~280℃, and the distillation time is 60 min.

[0011] At atmospheric pressure, homohydric and partial anhydrides have very high boiling points and are prone to decomposition or cross-linking reactions when heated. This leads to product deterioration, generating light volatile organic compounds or cross-linking to form impurities such as yellow polymers. Therefore, effective separation cannot be achieved at atmospheric pressure using simple methods. Furthermore, their extremely high boiling points at atmospheric pressure require very high temperatures to vaporize, which is highly uneconomical in practice. High temperatures also accelerate the formation of polymer impurities, affecting product purity. The acid anhydration and sublimation processes are mainly distinguished by controlling the drying time of acid anhydration (30 min) and the acid anhydration temperature to be below 230℃.

[0012] Preferably, in step S3, the solvent is one or a mixture of acetone, methanol, ethanol, formamide, and acetonitrile; the volume of the solvent is 3 to 4 times the mass of the sublimated solid; the purity of the homogenizing anhydride is ≥95%, and the yield is 84 to 89%. More preferably, the volume of the distilled solvent is 60% to 80% of the total volume.

[0013] Preferably, in step S4, the atmospheric distillation temperature is 60~75℃ and the time is 30 min, while the vacuum distillation pressure is 0~300 Pa, the temperature is 130℃~150℃, and the time is 30 min. More preferably, the vacuum distillation pressure is 50~150 Pa.

[0014] Preferably, in step S5, the amount of activated carbon used is 0.1% to 0.5% of the distillation vessel bottoms, and the temperature after heating is 80 to 99°C to increase the solubility of trimellitic acid; the temperature for cooling and crystallization is -10 to 10°C, and the cooling and crystallization time is 6 to 48 hours. More preferably, the temperature after heating is 85 to 95°C, and the cooling and crystallization time is 18 to 36 hours.

[0015] Preferably, the method for recovering and utilizing the distillation residue after solvent removal from the homogenate yields trimellitic acid with a purity ≥97% and a yield of 81-86%.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention extracts the high-value-added components of homogeneous anhydride and trimellitic acid from the distillation residue after desolventizing homogeneous anhydride through steps such as acid anhydride conversion, vaporization and sublimation, dissolution and recrystallization, distillation, and water washing. The homogeneous anhydride is purified to a high purity and can be sold as a product or reused after further purification. The purity of homogeneous anhydride can reach more than 95% with a yield of 84-89%, and the purity of trimellitic acid can reach more than 97% with a yield of 81-86%.

[0017] This invention avoids the high costs associated with disposing of distillation residue as hazardous waste to environmental protection companies, as well as the risks involved in storage, transportation, and disposal. It also avoids the resource waste and environmental risks associated with direct incineration, such as dioxins and particulate matter.

[0018] This invention employs vacuum conditions for vaporization and sublimation, effectively reducing the vaporization temperature of homohydric anhydride and partial anhydride, avoiding decomposition and cross-linking reactions at normal pressure and high temperature, and ensuring product purity. By using the methods of dissolution-recrystallization and water washing-cooling crystallization, the difference in solubility of homohydric anhydride and partial anhydride in polar solvents and water is utilized to achieve effective separation of the two. The overall process is simple and feasible, with significant economic and environmental benefits, and has good application prospects. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 This is a process flow diagram of the method for recycling distillation residue after solvent removal of homogenate according to the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.

[0023] Example 1: A method for recovering and utilizing distillation residue after solvent removal from homogenizing anhydride, comprising the following steps: S1. Anhydride formation: The distillation residue is heated and distilled under high temperature and negative pressure. The system vacuum degree is 0.090 MPa and the temperature is 230℃, so that the carboxyl groups in the distillation residue can be completely anhydrinated. The anhydride formation time is 30 min. The distillation residue contains trimellitic anhydride, trimellitic acid, pyromellitic anhydride, and pyromellitic acid in a mass ratio of 54.5:18.2:17.6:7.5. S2, vaporization and sublimation: The distillation residue of S1 anhydride is distilled under high temperature vacuum. The system vacuum degree is 0.10MPa. The heating voltage of the heating jacket is adjusted to continuously heat the vacuum distillation vessel and keep the bottom temperature of the vessel at 280℃. The target components such as homoanhydride and partial anhydride in the distillation residue in the distillation vessel are distilled out as completely as possible to obtain a sublimated crystallized solid. The vaporization and sublimation time is 60 min. S3, Dissolution and Recrystallization: Add the solid crystallized from S2 to a three-necked flask and dissolve it in 3 times its volume of solvent to obtain an anhydride solution. Stir and completely dissolve the crystalline solid in the solvent. Then, perform simple atmospheric distillation on the target solution in a three-necked flask, keeping the solvent in the crystallized solution in the distillation vessel slowly distilling out. Distill out 65% of the total solvent mass. Pour the solution into a vacuum filter funnel for filtration. Dry the obtained solid in a vacuum drying oven at 80°C to obtain the homogeneous anhydride product. S4. Distillation: The mother liquor obtained from S3 is distilled under normal pressure to ensure that the solvent in the mother liquor in the distillation kettle is completely distilled out, and the system vacuum degree is 300 Pa. The vacuum distillation kettle is continuously heated and the bottom temperature is 140℃ to ensure that the solvent in the bottom material in the distillation kettle is sublimated as completely as possible. The system vacuum degree is 150 Pa. S5. Washing: Add 3 times the amount of deionized water and 0.1% of the amount of activated carbon to the distillation residue from S4. Activated carbon can adsorb a small amount of aldehyde genes on the benzene ring in the solution, which locally cause yellow polymers and other colored substances. Increase the water temperature to 95℃ to increase the solubility of trimellitic acid. After adsorption and washing, filter the activated carbon while it is hot, cool and crystallize, filter after 24 hours, and vacuum dry in an 80℃ vacuum drying oven to obtain trimellitic acid.

[0024] The purity of the anhydride was 96% and the yield was 85.6%; the purity of trimellitic acid was 97% and the yield was 84.6%.

[0025] Comparative Example 1 The difference from Example 1 is that the S1 anhydride treatment is not performed, and the distillation residue is directly subjected to the S2 vaporization and sublimation treatment.

[0026] The purity of the anhydride was 95.2% and the yield was 80.4%; the purity of trimellitic acid was 95.7% and the yield was 79.6%.

[0027] Comparative Example 2 The difference from Example 1 is that the S3 dissolution and recrystallization step is not performed, and the condensed solid obtained in S2 is directly subjected to S4 distillation and S5 water washing treatment.

[0028] Testing revealed no homogenate material was generated; the purity of trimellitic acid was 71.6%, and the yield was 85.9%.

[0029] Comparative Example 3 The difference from Example 1 is that activated carbon is not added in the S5 water washing step.

[0030] The purity of the anhydride was 96% and the yield was 85.6%; the purity of trimellitic acid was 96.2% and the yield was 84.2%.

[0031] Comparative Example 4 The difference from Example 1 is that the vaporization and sublimation step S2 is carried out at atmospheric pressure and the temperature is 395°C.

[0032] The purity of the anhydride was 93.5%, with a yield of 26.5%; the purity of trimellitic acid was 97.5%, with a yield of 42.3%.

[0033] Comparative Example 5 The difference from Example 1 is that the vacuum degree in the S2 vaporization and sublimation step is 0.050 MPa.

[0034] The purity of the anhydride was 95.8%, and the yield was 74.3%; the purity of trimellitic acid was 97.7%, and the yield was 76.4%.

[0035] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. 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 all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for recovering and utilizing distillation residue after solvent removal from homogenizing anhydride, characterized in that, Includes the following steps: S1. Anhydride formation: The distillation residue is heated under high temperature and negative pressure to completely anhydride the carboxyl groups in the distillation residue, thus obtaining anhydride-formed distillation residue. S2, vaporization and deposition: The distillation residue of S1 anhydride is distilled under high temperature and vacuum to vaporize the homoanhydride and partial anhydride, which are then collected by deposition to obtain the deposition solid. S3, Dissolution and recrystallization: Dissolve the condensed solid in 2 to 5 times its volume of solvent to obtain an acid anhydride solution. Remove 60 to 90% of the solvent from the acid anhydride solution by atmospheric distillation to obtain a saturated solution. Filter the solution and dry the solid to obtain homogeneous anhydride. S4. Distillation: The mother liquor obtained from S3 is subjected to atmospheric distillation, followed by vacuum distillation to obtain the bottom product of the distillation vessel. S5. Washing with water: Add 3 to 5 times the amount of deionized water and activated carbon to the bottom of the distillation vessel in S4. After heating and adsorption, wash with water, filter while hot, cool and crystallize, and vacuum dry to obtain trimellitic acid.

2. The method for recycling distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, The distillation residue includes trimellitic anhydride, trimellitic acid, pyromellitic anhydride, and pyromellitic acid.

3. The method for recycling distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, In step S1, the vacuum degree is 0.075~0.090 MPa, the heating temperature is 210℃~230℃, and the heating time is 30min. The vacuum in the drying process is relatively low, and the temperature is maintained at 210℃~230℃ to achieve anhydride formation and thus complete dehydration.

4. The method for recycling distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, In step S2, the vacuum degree is 0.098~0.10 MPa, the distillation temperature is 230℃~280℃, and the distillation time is 60 min.

5. The method for recycling distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, In step S3, the solvent is one or a mixture of acetone, methanol, ethanol, formamide, and acetonitrile.

6. The method for recycling distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, In step S3, the volume of the solvent is 3 to 4 times the mass of the sublimated solid, and the volume of the evaporated solvent is 60% to 80% of the total volume.

7. The method for recycling distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, In step S4, the atmospheric distillation temperature is 60~75℃ and the time is 30 min, while the vacuum distillation pressure is 0~300 Pa, the temperature is 130℃~150℃, and the time is 30 min.

8. The method for recycling distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, In step S5, the amount of activated carbon used is 0.1% to 0.5% of the bottom material of the distillation vessel, and the temperature after heating is 80 to 99°C to increase the solubility of trimellitic acid; the temperature for cooling and crystallization is -10 to 10°C, and the cooling and crystallization time is 6 to 48 hours.

9. The method for recycling distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, In step S3, the purity of the homogenate is ≥95%, and the yield is 84~89%.

10. The method for recovering and utilizing distillation residue after solvent removal from homogenizing anhydride according to claim 1, characterized in that, In step S5, the trimellitic acid has a purity of ≥97% and a yield of 81~86%.

Images