Valorization of Grass Lignins: Swift and Selective Recovery of Pendant Aromatic Groups with Ozone

Abstract

The lack of a simple process for valorizing the lignin produced during cellulosic ethanol manufacture is a major hurdle preventing such biorefineries from becoming economically sustainable. Here, we demonstrate a facile ozonolysis process in a continuous stirred tank reactor (CSTR) to generate a value-added product stream from lignin dissolved in either acetic acid (as in acetosolv lignin) or formic acid. At ambient pressure, relatively mild temperature (70 °C), and short residence times (few minutes), ozone is bubbled through the solution to selectively cleave the C═C bonds associated with specific pendant groups present in corn stover and wheat straw lignins. The resulting products, mainly vanillin and 4-hydroxybenzaldehyde, constitute approximately 7 wt % of the lignin and command high value with established applications in the flavoring, pharmaceutical, and electronics industries. These products are easily separated from the remaining lignin via membrane nanofiltration of the product mixture. The lign...