The Promotor and Poison Effects of the Inorganic Elements of Kraft Lignin during Hydrotreatment over NiMoS Catalyst

Abstract

One-pot deoxygenation of kraft lignin to aromatics and hydrocarbons of fuel-range quality is a promising way to improve its added value. Since most of the commercially resourced kraft lignins are impure (Na, S, K, Ca, etc., present as impurities), the effect of these impurities on the deoxygenation activity of a catalyst is critical and was scrutinized in this study using a NiMoS/Al2O3 catalyst. The removal of impurities from the lignin indicated that they obstructed the depolymerization. In addition, they deposited on the catalyst during depolymerization, of which the major element was the alkali metal Na which existed in kraft lignin as Na2S and single-site ionic Na+. Conditional experiments have shown that at lower loadings of impurities on the catalyst, their promotor effect was prevalent, and at their higher loadings, a poisoning effect. The number of moles of impurities, their strength, and the synergism among the impurity elements on the catalyst were the major critical factors responsible for the catalyst’s deactivation. The promotor effects of deposited impurities on the catalyst, however, could counteract the negative effects of impurities on the depolymerization.