초록 ▼

A solvent refining method for isocyanate prepared by the phosgene method and multistage absorbing towers used in same. Solvent to be refined which contains water, iron, and/or phosgene, hydrogen chloride and other materials with color is dealt by the present method and multistage absorbing towers, w

A solvent refining method for isocyanate prepared by the phosgene method and multistage absorbing towers used in same. Solvent to be refined which contains water, iron, and/or phosgene, hydrogen chloride and other materials with color is dealt by the present method and multistage absorbing towers, which can effectively prevent a drying agent from absorbing water and hardening, partial overheating in the tower and generating channeling. Meanwhile, the pressure drop is effectively lowered. In addition, the content of water is ≦50 ppm, the content of iron is ≦5 ppm, the content of phosgene and hydrogen chloride is ≦20 ppm, Pt—Co chroma is ≦20 in the refined solvent. Therefore, the refined solvent can be used as the solvent for preparing isocyanate in the phosgene method and remarkably improve an L color of isocyanate.

대표청구항 ▼

1. A method for refining solvents generated in the preparation of isocyanates by the phosgene method, comprising treating the solvents to be refined with a multistage absorption tower comprising a support packing section at the bottom, a packing absorbing section in the middle and a support packing

1. A method for refining solvents generated in the preparation of isocyanates by the phosgene method, comprising treating the solvents to be refined with a multistage absorption tower comprising a support packing section at the bottom, a packing absorbing section in the middle and a support packing section on the top from bottom to top, wherein the packing absorption section in the middle comprises N absorbing layers, and N is an integer from 3 to 8; from the first absorbing layer to the Nth absorbing layer, the layers are arranged from bottom to top; from the first absorbing layer to the (N−1)th absorbing layer, each layer of these layers is composed of an upper liquid distributing device that connects an external feeding pipe and a lower absorbing packing layer; and the absorbing packing layer of every of the absorbing layers is formed by the uniform mixing of desiccants and adsorbents. 2. The method according to claim 1, wherein the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of the first absorbing layer is 1:1-5:1, and the desiccants represent 4-15% of the weight of all the desiccants in the multistage absorption tower; the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of the Nth absorbing layer is 5:1-12:1, and the desiccants represent 4-15% of the weight of all the desiccants in the multistage absorption tower; and the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of every of the second absorbing layer to the (N−1)th absorbing layer is 5:1-15:1, and the desiccants of every of the absorbing packing layers represent 15-92% of the weight of all the desiccants in the multistage absorption tower. 3. The method according to claim 1, wherein the desiccants are alkaline desiccants, which are selected from the group consisting of calcium oxide, sodium hydroxide, potassium hydroxide, and a mixture of two or more thereof; the BET specific surface area of the desiccants is 1500-4500 m2/g; the average particle size is 0.5-10 μm; and the mechanical strength is 85-99%. 4. The method according to claim 1, wherein the adsorbents are macroporous resin adsorbents or activated carbon; the macroporous resin adsorbents are selected from the group consisting of nonpolar macroporous adsorption resins of styrene polymer, nonpolar macroporous adsorption resins of divinylbenzene polymer, and a mixture of two or more thereof the BET specific surface area of the adsorbents is 2500-5000 m2/g; the pore size of mesoporous is 2-10 nm; and the mechanical strength is 85-98%. 5. The method according to claim 1, wherein the support packings of the support packing section on top and the support packing section at the bottom are selected from the group consisting of gravels, molecular sieves, activated carbon, and a mixture of two or more thereof; the weight of the support packings in the support packing section on top and the weight of the support packings in the support packing section at the bottom are the same; and the weight ratio of the support packings in the support packing section on top to all the desiccants in the multistage absorption tower is 1:20-1:3. 6. The method according to claim 1, wherein the ratio of the volume flow rate of the total feed rate of the solvents to be refined to the total weight of all the desiccants and the adsorbents in the multistage absorption tower is 1:200-1:600 m3/kg/h. 7. The method according to claim 6, wherein the feeding volume of the external feeding pipe of the first absorbing layer represents 1/15-⅓ of, the total feeding volume of the solvents to be refined, the feeding amount of the external feeding pipe of the (N−1)th absorbing layer represents 1/15-⅓ of the total feeding volume of the solvents to be refined, and the feeding amount of the external feeding pipe of every of the absorbing layers, from the second absorbing layer to the (N−2)th absorbing layer, represents 1/15-⅘of the total feeding amount of the solvents to be refined. 8. The method according to claim 7, wherein the residence time of the solvents to be refined in the multistage absorption tower is 0.25-8 hrs. 9. The method according to claim 6, wherein the refined solvents partially reflux and enter into the multistage absorption tower after mixing with the solvents to be refined, and the reflux ratio is 0.5-4; and the pressure drop between the external feeding pipe of the first absorbing layer of the multistage absorption tower and the outlet on top of the tower is 5-40 kPa. 10. The method according to claim 1, wherein the solvents to be refined are the waste solvents that contains impurities generated during the preparation of isocyanates by the phosgene method or the fresh solvents that should be added to the reaction system during preparation of isocyanates because of the consumption of solvents, and the content of water, iron and the color number in the fresh solvents fail to reach standards; the solvents are selected from the group consisting of o-dichlorobenzene, chlorobenzene, toluene, and a mixture of two or more thereof; the content of water in the solvents to be refined is 150-600 ppm; the content of iron component is 40-300 ppm; the content of phosgene and hydrogen chloride is 0-10000 ppm; the Pt—Co color number is 30-100; the content of water in the refined solvents is ≦50 ppm; the content of iron component is ≦5 ppm; the content of phosgene and hydrogen chloride is ≦20 ppm; and Pt—Co color number is ≦20. 11. A multistage absorption tower used for refining solvents generated in the preparation of isocyanates by the phosgene method, comprising: a support packing section at the bottom;a packing absorbing section in the middle; anda support packing section on top from bottom to top;wherein the packing absorbing section in the middle comprises N absorbing layers, and N is an integer from 3 to 8; from the first absorbing layer to the Nth absorbing layer, the layers are arranged from bottom to top; from the first layer to the (N−1)th absorbing layer, each layer of these layers is composed of an upper liquid distributing device that connects an external feeding pipe and a lower absorbing packing layer; and the absorbing packing layer of every of the absorbing layers is formed by the uniform mixing of desiccants and adsorbents. 12. The multistage absorption tower according to claim 11, wherein the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of the first absorbing layer is 1:1-5:1, and the desiccants represent 4-15% of the weight of all the desiccants in the multistage absorption tower; the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of the Nth absorbing layer is 5:1-12:1, and the desiccants represent 4-15% of the weight of all the desiccants in the multistage absorption tower; and the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of every of the second absorbing layer to the (N−1)th absorbing layer is 5:1-15:1, and the desiccants of every of the absorbing packing layers represent 15-92% of the weight of all the desiccants in the multistage absorption tower. 13. The multistage absorbing tower according to claim 11, wherein the desiccants are alkaline desiccant, which are selected from the group consisting of calcium oxide, sodium hydroxide, potassium hydroxide, and a mixture of two or more thereof; the BET specific surface area of the desiccants is 1500-4500 m2/g; the average particle size is 0.5-10μm; and the mechanical strength is 85-99%. 14. The multistage absorbing tower according to claim 11, wherein the adsorbents are macroporous resin adsorbents or activated carbon; the macroporous resin adsorbents are selected from the group consisting of nonpolar macroporous adsorption resins of styrene polymer, nonpolar macroporous adsorption resins of divinylbenzene polymer, and a mixture of two or more thereof; the BET specific surface area of the adsorbents is 2500-5000 m2/g; the pore size of mesoporous is 2-10 nm, and the mechanical strength is 85-98%. 15. The multistage absorbing tower according to claim 11, wherein the support packings of the support packing section on top and the support packing section at the bottom are selected from the group consisting of gravels, molecular sieves, activated carbon, and a mixture of two or more thereof; the weight of the support packings in the support packing section on top and the weight of the support packing in the support packing section at the bottom are the same; and the weight ratio of the support packing in the support packing section on top to all the desiccants in the multistage absorption tower is 1:20-1:3. 16. The method according to claim 1, where N is an integer from 4-6. 17. The method according to claim 2, wherein the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of the first absorbing layer is 2:1-4:1, and the desiccants represent 5-10% of the weight of all the desiccants in the multistage absorption tower; the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of the Nth absorbing layer is 6:1-10:1, and the desiccants represent 5-10% of the weight of all the desiccants in the multistage absorption tower; and the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of every of the second absorbing layer to the (N−1)th absorbing layer is 6:1-10:1, and the desiccants of every of the absorbing packing layers represent 20-45% of the weight of all the desiccants in the multistage absorption tower. 18. The method according to claim 6, wherein the ratio of the volume flow rate of the total feed rate of the solvents to be refined to the total weight of all the desiccants and the adsorbents in the multistage absorption tower is 1:300-1:500 m3/kg/h. 19. The method according to claim 7, wherein the feeding volume of the external feeding pipe of the first absorbing layer represents 1/10-⅕of the total feeding volume of the solvents to be refined, the feeding amount of the external feeding pipe of the (N−1)th absorbing layer represents 1/10-⅕of the total feeding volume of the solvents to be refined, and the feeding amount of the external feeding pipe of every of the absorbing layers, from the second absorbing layer to the (N−2)th absorbing layer, represents 1/10- 7/10of the total feeding amount of the solvents to be refined. 20. The method according to claim 9, wherein the reflux ratio is 1-3; and the pressure drop between the external feeding pipe of the first absorbing layer of the multistage absorption tower and the outlet on top of the tower is 10-25 kPa. 21. The multistage absorption tower according to claim 11, wherein N is an integer from 4 to 6. 22. The multistage absorption tower according to claim 12, wherein the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of the first absorbing layer is 2:1-4:1, and the desiccants represent 5-10% of the weight of all the desiccants in the multistage absorption tower; the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of the Nth absorbing layer is 6:1-10:1, and the desiccants represent 5-10% of the weight of all the desiccants in the multistage absorption tower; and the weight ratio of the desiccants to the adsorbents of the absorbing packing layer of every of the second absorbing layer to the (N−1)th absorbing layer is 6:1-10:1, and the desiccants of every of the absorbing packing layers represent 20-45% of the weight of all the desiccants in the multistage absorption tower.