Some Engineering Technical Problems And Solutions Of Several Organic Pigments

Flocculation phenomena might happen in some of C.I. Pigment Orange34, when it was used to make ink, in the storage of the ink. This problem had confused ink-maker for20years at least. The present study investigated the flocculation by means of Laser particle size analyzer, electrophoretic test, Micromeritics ASAP2020M surface areas, Zeta analyzer and XRD. The XRD results indicated that the differences of crystal modification among various samples were not the key factor of causing flocculation. The distribution of particle size of the untreated pigment was broad. After treatment with organic solvents, the distributions of particle size became much narrow, which would not cause flocculation during the storage of the ink, when it was used to make ink. The fact showed that the broad distribution of particle size of C.I. Pigment Orange34was the major factor of causing flocculation during the storage of the ink. The further study indicated the mechanism of forming flocculation is the smaller particles were more soluble in the ink than the larger particles. The dissolution and precipitation of the smaller particles generate larger particles during storage, which led to the flocculation phenomena.C.I. Pigment Yellow191possesses of polymorphism. The commodity of the pigment made by Clariant is a mixture of α-modification and (β-modification with the content of α-modification in65%, which is in the protecting region of their patent. The commodities of the pigment made by some local pigment-makers were also the mixture of α-modification and (β-modification with the content of α-modification between70%and80%, which is in the protecting region of Clariant patent as well. The wet C.I. Pigment Yellow191samples are (β-modification, and they will turn into α-modification after drying. When the moisture content of α-modification was higher than1.5%, part of α-modifications would turn into (β-modification. To control the drying conditions for wet C.I. Pigment Yellow191samples or the storage conditions of α-modification could make the samples keep in a-modification or mixture with α-modification content less than10%, which can be out of the claims of Clariant’patent.N-ethyl carbazole reacts with nitric acid in chlorobenzene to form N-ethyl-3-nitrocarbazole. which dissolves well in chlorobenzene. So after removing chlorobenzene in filtrate, the residue contains N-ethyl-3-nitrocarbazole as high as80%. To extract the residue with ethanol. N-ethyl-3-nitrocarbazole could be recovered, whose purity could be increased to97%. The purified N-ethyl-3-nitrocarbazole could be used to synthesize C.I. Pigment Violet23crude, which would turn into C.I. Pigment Violet23, whose performance was the same as the commodity of the pigment both in hue and strength. To recovery N-ethyl-3-nitrocarbazole from the residue is equal to increase the yield of the nitration of N-ethyl carbazole. By doing so, the waste discharge from the reaction would be reduced.