Preparation of Pine Char Sulfonic Acids with High Acid Capacity Using Phosphoric Acid as a Dehydration Catalyst

A series of pine char sulfonic acids were prepared via a two-step procedure involving phosphoric acid catalytic charring of pine sawdusts and successively sulfonation of the charred precursors. Solid sulfonic acid material prepared in this new route possessed high sulfonic acid loading with 2.36 mmol g-1 at the optimal charring conditions of phosphoric acid being 85%, ratio of pine sawdusts and phosphoric acid being 1: 10, charring time being 3 h, charring temperature being 140 °C. Pine char sulfonic acids showed excellent activity in the esterification of n-butanol and acetic acid.