New route to naphthalenedicarboxylic acids through dichromate oxidation of HS and HI/BS fractions of SRC from akabira coal.

Abstract

FD-MS analysis and pyrolytic study of lighter portions of Solvent Refined Coal (SRC) showed abundance of dimethylnaphthalene derivatives in the fraction or its pyrogram, which fact suggested that these compounds are involved in a unit structure of relatively high-molecular-weight fraction, such as hexane-insoluble and benzene-soluble fraction (HI/BS) of SRC. Oxidation of hexane-soluble fraction (HS) and HI/BS of SRC at 250°C by Na2Cr2O7 produces several aromatic carboxylic acids in which naphthalenedicarboxylic acids are most abundant as expected. This result shows that many alkylaromatic compounds in the HS and HI/BS of SRC were selectively oxidized to corresponding aromatic carboxylic acids, notably yields of naphthalenedicarboxylic acids reached 9.5wt% with HS and 2.4% with HI/BS (HS and HI/BS basis, respectively). Oxidation of original coal and its extract at the same reaction conditions afforded 20% and 30% of acids products, respectively. However, naphthalenedicarboxylic acids along with other aromatic carboxylic acids as observed with the run of SRC fraction could be observed only on a slight extent. Oxidation of lighter fractions of SRC, therefore, is a promising method to directly produce naphthalenedicarboxylic acids.