A process for making an ethylated polycyclic aromatic compound in a mixed aromatic fluid, the process comprising contacting the mixed aromatic fluid containing a polycyclic aromatic compound and a monocyclic aromatic compound having an ethyl substituent in the presence of an acid catalyst under conditions sufficient to effect transalkylation to form the ethylated polycyclic compound and a de-ethylated monocyclic aromatic compound and removal of the de-ethylated monocyclic aromatic compound. A process for decreasing naphthalene concentration in a naphthalene-containing aromatic fluid by acid catalyzed transalkylation of an alkylbenzene and naphthalene to form benzene and an alkylnaphthalene.