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[求助]
请高手指点芳香族异氰酸酯类化合物脱色的问题？
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脱色的问题：芳香族异氰酸酯类化合物 不想过柱，活性炭、硅藻土试过了，重结晶也不行！ 只能从黄色变为乳白色（略带黄色），纯品白色！ 进一步脱色不行！ 请高手指点！ |
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EP 561225 Polyisocyanates contg. no discoloring components are prepd. by treatment, after phosgenation, with H at 100-180°/3-150 bar for 15-240 min in the presence of catalysts. Treating MDI with H at 160°/30 bar in the presence of a Co-Mn-Ag-Ru/Al2O3 catalyst for 3 h gave MDI with extinction coeff. at 430 and 520 nm 0.21 and 0.020, resp., and transparency at 450, 500, 550, and 600 nm 13, 50, 72, and 78%, resp.; vs. 0.28, 0.046, 10, 42, 63, and 74, resp., without hydrogenation. GB 1417075 Tolylene diisocyanate (I) [26471-62-5] and 4,4'-diphenylmethane diisocyanate [101-68-8] were decolorized by treatment of the liq. with 1/16 in. 5A mol. sieve pellets in the dark. Further yellowing was reduced by this treatment. Thus, 25 vol. parts of a 6-month old 80:20 mixt. of the 2,4 and 2,6 isomers of I was stored over 2 wt. parts mol. sieve pellets. Coloration was 30 and 20 Hazen units after 24 and 94 hr, resp., over the mol. sieve compared with 40 Hazen units for untreated liq. DE4215761 The title mixts. are decolorized by treatment with radical-forming azo compds. after removal of excess COCl2 and solvents. Stirring 200 g crude MDI (oligomer content 39.5%) with 0.6 g AIBN at 90° for 3 h gave a product with I color no. 32; vs. 50 before AIBN treatment. |
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