The current standards for refined naphthalene in various countries have acid washing colorimetric indicators, which are sensitive qualitative indicators for certain impurities in naphthalene; From the perspective of process principle, the refined naphthalene manufacturer believes that whether it uses static or dynamic crystallization for refining, it is separated by using the different crystallization points of Cai and impurities. Therefore, the remaining impurity components in Cai should also be similar, and the color tone after acid washing and colorimetry should be relatively similar.
The current use of crystallization method in the production of refined tea in China varies in color compared to acid washing, with various colors such as red, yellow, purple, and gray. Naphthalene refining, whether through chemical or physical methods, is mainly composed of sulfur indene as an impurity. If the chromogenic group is sulfhydrin, the color tone should be uniform, so that there will be no red, yellow, purple, or gray, indicating that there may be other chromogenic groups or impurities present. Perform acid washing colorimetric tests on certain impurities that may exist in refined naphthalene, with thionines as the main chromogenic group and the color after acidification being purple red. The higher the content of thionines, the darker the color of the sample after reaction, but thionines are not the only chromogenic group.
Thiindene is more prone to sulfonation than Gong, and reacts with concentrated sulfuric acid at 80C to produce a binary sulfonic acid mixture. Under the catalysis of acids, thionines themselves are prone to polymerization.
Although thioindene is the main impurity and color developing group in refined naphthalene, the unsaturated compound existing in tea also affects the color comparison and use performance of refined naphthalene in acid pickling. It is also a color developing group, mainly methylindene and methyloxyindene. For example, after the reaction of dimethyloxyindene with concentrated sulfuric acid, binary ternary quaternary polymers are generated, and after the reaction of dimethylindene with concentrated sulfuric acid, more than 1~50 monomers are polymerized.
The use of acid washing method for refining is based on this chemical principle. Due to the low content of unsaturated compound in refined naphthalene and the complex composition, it is difficult to directly determine them with conventional inspection methods, but their content can be determined by determining the "iodine value" of the unsaturated compounds in refined naphthalene.
The production practice of naphthol proves that the secondary refined naphthalene produced by acid washing method (the acid washing method is higher than the crystallization method, but the content of unsaturated compound is lower), and the content of thioindene is 1.2%~1.5%.
The production of naphthol is normal, but the production of naphthol with refined naphthalene with high unsaturated compound content (i.e. high iodine price) will produce resinous substances, affect filtration and even block pipes. This shows that unsaturated compound will have a great impact on the pickling colorimetry and use performance of refined tea. For more related content, come to our website http://www.chadtoddband.com Consult!