CATALYTIC CONVERSION OF LIGNIN TO PRODUCE
AROMATIC ALDEHYDES AND ORGANIC ACIDS
ABREU, Cesar A. M., CALDAS, Raphael and LIMA FILHO, Nelson M.
Federal University of Pernambuco, 50.740-521 Recife, PE, Brazil
cesar@ufpe.br, raphael@ufpe.br, nelel@uol.com.br
Abstract
The catalytic oxidation using air and supported catalysts indicated to be an
attractive method for effluents treatment and by-product of the biomass industry. Many
heterogeneous catalysts have been studied for the oxidation of phenol, carboxylic acids
and effluents from pulp and paper mills. Metal oxide and noble metal catalyst supported
on alumina were effective for lignin conversions of black liquor. In the lignin oxidation
process the reactions lead to the production of a great variety of intermediary products.
In general, it is considered that oxidation proceeds in two or more steps, where lignin, a
macromolecule of complex structure, is hydrolyzed breaking up into fragments
producing aromatic aldehydes and other products of lower molecular weight and
smaller molecules such as carbon dioxide and water.
Wet air oxidation process has been used as an alternative technology for treatment of
organic compounds that are converted into carbon dioxide and carboxylic acid.
Intending to valorize the lignocellulosic materials, the catalytic wet air oxidation
(CWAO) of lignin, obtained from sugar-cane bagasse, was evaluated through kinetic
studies, to produce aromatic aldehydes and organic acids. The reaction conditions were
selected in order to obtain intermediate oxidation products or final acids. The oxidations
were carried out in a slurry reactor with a palladium catalyst, in a temperature range of
373-413 K, under an oxygen partial pressure range of 2-10 bar. Experimental evidences
obtained lead to the proposition of a mechanism, assuming that the lignin was
depolymerized in an oxidant medium with the productions of aldehydes, acids and other
products of low molecular weights. The aromatic aldehydes were submitted to
subsequent oxidations forming other products, such as organic acids that can degrade
into carbon dioxide.