Study On Technical Conditions For Preparing 2,6-diisopropyl Naphthalene From Refined Naphthalene

2,6-Diisopropylnaphthalene (2,6-DIPN) is the precursor of 2,6-naphthalene dicarboxylic acid, which is an important monomer for synthesizing new polyester, poly (ethylene naphthalate), and thermotropic liquid crystalline polymers. In this study, the shape-selective isopropylation of naphthalene with propylene has been processed in 0.5L autoclave with steam-dealuminated mordenite (SDHM) as the catalyst to produce 2,6-DIPN instead of the conventional Friedel—Crafts catalyst.The nitrogen content in refined naphthalene showed great impact on the activity of catalyst. Results showed that the lower the nitrogen content in refined naphthalene, the better the results of isopropylation. Hydroisopropylation could effectively slow down the deactivation rate of catalyst. When the reaction conditions were at reaction temperature 275℃, hydrogen pressure 0.4MPa, reaction time 7h and 7% SDHM by mass, the average conversion rate of naphthalene could be maintained at approximate 90%, the average yield of target product, 2,6-DIPN,≮35 %, and selectivity close to 65% showing good practicability.When modified with rare earths, the acid sites on external surface of SDHM were partly covered, the selectivity in isopropylation of naphthalene could be improved. The selectivity of 2,6-DIPN, 2,6-/DIPN (%), and 2,6-/2,7-DIPN mol ratio could be significantly raised, and the yield of 2,6-DIPN increased, so that the product could be more easily separated and purified. The catalyst modified with mixed rare earths (La, Ce, and Pr) was better than that modified with single rare earth La in its reaction effectiveness; furthermore, after regeneration it could still keep its good activity.A product of 2,6-DIPN with purity≥99% was produced through static fractional crystallization. By repeated crystallization of melts with different concentration levels, the yield of pure 2,6-DIPN was enhanced to 87%. It is significant in its applicability in manufacturing. The eutectic temperature and the composition of eutectic point of 2,6 DIPN～2,7-DIPN binary system were determined to plot corresponding solid liquid phase diagram, which could be taken as guidance in controlling crystallization temperature.The isomerization within DIPN molecules was not easy-to-occur, however, was subject to transalkylation with naphthalene to obtain a product rich in monoisopropylnaphthalene, which would be beneficial in utilization of by-products. The conversion rate of DIPN reached 77%. The amorphous silica-alumina LXC-11 was the suitable catalyst.