Alkylation of naphthalene with isopropanol over a novel catalyst UDCaT-4: Insight into selectivity to 2,6-diisopropylnaphthalene and its kinetics

Numerous routes to 2,6-naphthalenedicarboxylic acid, a feedstock for high performance polyester polyethylene naphthalate, exist starting with the alkylation of an aromatic ring. However, the route beginning with naphthalenic compounds has an economic advantage because of reduction in the number of reaction steps to build the naphthalene ring. This has spurred a lot of interest in the shape selective dialkylation of naphthalene. Mono alkylation of naphthalene is simple, but its further shape selective dialkylation to 2,6-dialkylnaphthalene (2-DAN), is challenging. A variety of solid acid catalysts especially zeolites have been reported in studies to investigate the effect of acidity, pore geometry and shape selectivity in this reaction. However, the activity of most catalysts is susceptible to coke formation within a few hours of time on stream. It is in this perspective that we report the novelties of UDCaT-4, a synergistic combination of persulfated alumina and zirconia with hexagonal mesoporous silica, which exhibits tremendous stability, activity and selectivity in the vapour-phase isopropylation of naphthalene with isopropanol to 2,6-diisopropylnaphthalene (DIPN). It leads to better yields and selectivity in comparison with other catalysts reported in literature. A systematic investigation of the effects of various operating parameters was accomplished. Furthermore, a mathematical model was developed to describe the reaction pathway and the model validated with experimental results.