Abstract
2,6-Dimethylnaphthalene (2,6-DMN) is a commercially important chemical for the production of polyethylenenaphthalate and polybutylene naphthalate. However, its complex synthesis procedure and high production cost significantly reduce the use of 2,6-DMN. In this study, the synthesis of 2,6-DMN was investigated with methylation of 2-methylnaphthalene (2-MN) over metal-loaded beta zeolite catalysts including beta zeolite, Cu-impregnated beta zeolite and Zr-impregnated beta zeolite. The experiments were performed in a fixed-bed reactor at atmospheric pressure under a nitrogen atmosphere. The reactor was operated at a temperature range of 400–500 °C and varying weight hourly space velocity between 1 and 3 h−1. The results demonstrated that 2,6-DMN can be synthesized by methylation of 2-MN over beta type zeolite catalysts. Besides 2,6-DMN, the product stream also contained other DMN isomers such as 2,7-DMN, 1,3-DMN, 1,2-DMN and 2,3-DMN. The activity and selectivity of beta zeolite catalyst were remarkably enhanced by Zr impregnation, whereas Cu modification of beta zeolite catalyst had an insignificant effect on its selectivity. The highest conversion of 2-MN reached 81%, the highest ratio of 2,6-DMN/2,7-DMN reached 2.6 and the highest selectivity of 2,6-DMN was found to be 20% by using Zr-modified beta zeolite catalyst.
Highlights
2,6-Dimethylnaphthalene (2,6-DMN) is a commercially important chemical for the production of polyethylenenaphthalate and polybutylene naphthalate
The results demonstrated that 2,6-DMN can be synthesized by methylation of 2-MN over beta type zeolite catalysts
The effects of Cu- and Zr-impregnated beta zeolite catalysts on the methylation of 2-MN were experimentally investigated. 2-MN conversion increases with an increase in the temperature and decreases with an increase in the weight hourly space velocity (WHSV) for BZ, Cu-impregnated beta zeolite (CuBZ) and ZrBZ
Summary
2,6-Dimethylnaphthalene (2,6-DMN) is a crucial chemical as a feedstock material for the production of high-performance polyester resins such as polyethylenenaphthalate (PEN) and polybutylene naphthalate (PBN). Jin et al (2008) investigated the methylation of 2-MN over modified ZSM-5 type zeolite catalyst in a fixed-bed micro-reactor at 400 °C with a reactant mixture of 2-MN, methanol and mesitylene having a molar ratio of 1:5:3, respectively. Both catalytic activity and lifetime of ZSM-5 zeolite catalyst were improved by NaOH treatment. The catalysts used in the methylation reaction play an important role in the synthesis procedure to achieve high 2,6-DMN selectivity A catalyst such as beta zeolite can be used in both methylation (Park et al 2002; Van der Mynsbrugge et al 2012) and isomerization (Wang et al 1997; Motoyuki et al 2000) processes and could give higher selectivity for specific DMN isomers. The conversion of 2-MN, the ratio of 2,6DMN/2,7-DMN and the selectivity of 2,6-DMN are investigated to demonstrate the activity of the beta type zeolite catalysts
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