Kraft lignin generated as a byproduct in the paper manufacturing process is typically disposed of by direct combustion. A two-step process for converting this waste, which amounts to about 50 million tons annually, into value-added nylon precursors has been devised at the U.S. Department of Energy’s Ames Laboratory.

The first step entails depolymerization of the waste lignin under alkaline conditions with aqueous sodium hydroxide at 200° C to produce guaiacol, an aromatic oil that is then converted into ketone-alcohol oil, an industrial precursor for nylon, using a ruthenium/carbon catalyst at 150° C in a second step.

Maintaining low hydrogen pressure conditions ensured full selectivity to ketone-alcohol oil and prevented catalyst deactivation. The use of low hydrogen pressure also prevented the formation of undesired methoxy-cyclohexanol byproduct. Eliminating the need for organic solvents and high pressure hydrogen required in other depolymerization techniques offers benefits in terms of both safety and cost.

The research published in Green Chemistry may represent a new low-energy method for lignin utilization in the production of high-demand value-added chemicals.

A two-step process converts Kraft waste into value-added nylon precursors. Source: U.S. Department of Energy’s Ames Laboratory