Fe-Modified ZSM-5 Shape Selective Catalysts for the Synthesis of 2, 6-Dimethylnaphthalene

Open Access
Author:
Dhar, Vasudha Gudimella
Graduate Program:
Energy and Geo-Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 13, 2007
Committee Members:
  • Chunshan Song, Thesis Advisor
  • Sarma V Pisupati, Thesis Advisor
  • Andre Louis Boehman, Thesis Advisor
Keywords:
  • zeolites
  • Shape Selective catalysis
  • naphthalene alkylation
Abstract:
ABSTRACT This work is a part of the DOE refinery Integration project at the Pennsylvania State University which involved the production of organic chemicals from coal blends and petroleum derived middle distillates as well as the production of advanced liquid fuels including diesel fuel, jet fuel and gasoline. The main objective of this work is to study metal modified zeolite catalysts to selectively improve the yield of 2, 6-dimethylnaphthalene during the alkylation of naphthalenes and methylnaphthalenes isolated from the coal blends and by products from petroleum refining operations like Light Cycle Oil (LCO) from the catalytic cracking unit. The major task in this application is to focus on the methylation of methylnaphthalene to get a higher selectivity of 2, 6-dimethylnapthalene, an important feedstock for the 2, 6-naphthalenedicarboxylic acid, a precursor for the polymer polyethylene naphthalene (PEN). Since the key step is to achieve higher ¥â- selectivity during the alkylation, 2-methylnaphthalene (2-MN) was taken as the model feed for the methylation in this work. Medium pore zeolites were modified by the isomorphous substitution of Fe into the framework of the zeolites. The relative change in acidity based on the amount of Fe substitution in the zeolites was studied and its effect on the catalyst performance during the methylation reaction was studied. The changes in the catalyst properties after modification were studied using various characterization techniques. The reaction system was a fixed bed down flow reactor at 300¨¬C at a WHSV of 6 h-1. Prior to the experiments, the catalysts were pretreated in-situ at 450¨¬C for one hour at atmospheric pressure under a nitrogen flow rate of 20 mL/min. Several conclusions were drawn based on the methylation experiments on various catalysts and their characterization studies. The medium pore zeolite was found to exhibit ¥â selectivity for this reaction but the conversion of 2-MN was reported to be very low for the catalyst. Also, a lot of secondary isomerization as well as non selective surface reactions were being carried out. The catalyst acidity also played a significant role in the selective formation of 2, 6-DMN. Based on the acidity studies using NH3-TPD and microcalorimetry, it was confirmed that the acidity of the catalysts was significantly lowered after modification. Based on the methylation reaction results, it was determined that the moderate acidity range gave the best 2, 6-DMN /2, 7-DMN ratio. Also it was found that the surface reactions were inhibited and this increased the overall 2, 6-DMN in the products. The X-Ray diffraction studies revealed increase in the crystallinity of the modified samples confirming dealumination and a slight increase in the lattice parameters of the modified samples concurring with the Framework IR studies and 27Al MAS NMR studies. However, no significant pore size changes were observed during modification with Fe. Further study is recommended do determine the effects of slight pore size alteration on the shape selective formation of the 2, 6-DMN.