Intermolecular Transalkylation of Isopropylnaphthalene and Its Application in the Production of 2,6-Diisopropylnaphthalene1

Isopropylation of naphthalene with propene resulted in a variety of isomers having different alkylation levels. The most important isomer is 2,6-DIPN, which is the precursor of important monomer 2,6-naphthalene dicarboxylic acid used for making liquid crystal polymers. In order to increase the yield of 2,6-DIPN, the intermolecular transalkylation with naphthalene was applied to the mixture of other DIPNs and PIPN to obtain MIPN enriched product, which underwent isopropylation with propene to produce 2,6-DIPN in a higher yield. The experimental study showed that the preferable conditions for transalkylation were reaction temperature of 325°C, the molar ratio of isopropyl group to naphthyl group (1P/N) of 0.8: 1–0.9: 1, reaction time of 4h and 5% of amorphous silica-alumina by mass. The conversions of DIPN and PIPN in its mixture were 62%–69% and 87%–88% respectively and the yield of MIPN was greater than 40%. The mixture of MIPN enriched product and recovered MIPN from rectification was subject to isopropylation with propene at 275°C over a shape-selective catalyst to produce 2,6-DIPN in a yield up to 38%. A recycled process of recovered components was established, through one cycle the yield of 2,6-DIPN based on naphthalene may be 2.8 times higher than before, and the utilization ratio of raw naphthalene was increased by 46%.