Small Phenolic Compounds Production from Kraft Black Liquor by Lignin Depolymerization with Different Catalytic Agents

Abstract

This work is aimed to produce small phenolic compounds from Kraft black liquor. For this purpose, depolymerization reaction is directly carried out over the liquor, without a previous isolation of lignin. In this sense, the intensification of lignin valorization is carried out by the reduction of the total stages of the whole process. Due to the alkali degree of Kraft liquors, base catalyzed depolymerization is proposed for the lignin cleaved reaction. In addition, two facilitating agents (phenol and hydrogen peroxide) were used to reduce the amount of undesirable reaction products, such as residual lignin and coke.
High yield of phenolic oil was recovered after treatment of the Kraft liquor in blank reaction (~30 %). However, high amount of undesirable products (residual lignin and coke) was also obtained (~65 % between both). The addition of phenol as capping agent reduced coke formation (almost to the half); and monomer phenolic compounds in oil were increased four times. The use of hydrogen peroxide reduces the phenolic oil yield (lower than 20 %). Catechol derivatives were the most plentiful products in the phenolic oil (92.44 % of total phenolic monomers) and a decreased of coke formation was similar to that in phenol. As summary it can be established that the intensification of the lignin depolymerization can be accomplished with high yields of phenolic oil production by avoiding the isolation of lignin and its further solubilization.