Removal and recovery of nitrogen compounds in crude methylnaphthalene oil using aluminium sulfate supported on silica gel

Abstract

Removal of nitrogen compounds from a crude methylnaphthalene oil (CMNO) obtained from coal tar was studied using Al 2(SO 4) 3 supported on silica gel (MB-4B and MB-3A), to obtain highly denitrogenated CMNO as well as quinoline bases. An adsorbent of 5 wt% sulfate on MB-4B reduced the nitrogen content of CMNO from 2.07 to 0.83 wt% at a recovery rate of 86 wt% at CMNO/adsorbent and solvent (hexane)/CMNO weight ratios of 5/3 and 1/1, respectively. The major portion of adsorbed nitrogen compounds was recovered by extraction with benzene, in a Soxhlet apparatus, the nitrogen content in the recovered fraction being enriched to 9.41 wt% at a yield of 9.0 wt% CMNO. MB-4B with larger pores appeared to be the better support. The adsorbed nitrogen per Al (atomic ratio) decreased from 7.90 to 1.06 with increasing sulfate load from 3 to 20 wt%. The optimum load of sulfate appeared to be ca. 5 wt% to balance the nitrogen content of recovered CMNO and the adsorbed nitrogen per Al. The ratios of CMNO/adsorbent and hexane/CMNO were found to be optimum at 2–3 and 2, respectively. Seventy-five percent of basic nitrogen and half of the pyrrolic nitrogen compounds, such as indole and its alkylated derivatives, were removed under optimum conditions. Repeated adsorption using fresh adsorbent removed the rest of the basic nitrogen compounds and another 30 wt% of pyrrolic nitrogen compounds.