<p>The degradative solvent extraction (DSE) method has been proven effective in simultaneous deoxygenation and deashing of lignocellulosic biomass. However, the effects of K, the most abundant metallic element in biomasses, still remain unclear. Therefore, this study experimentally investigated the effects of K on biomass DSE process using cellulose as the model compound, and correlated kinetic parameters are demonstrated using a lumped reaction model. Results show that K prohibits the degradation and deoxygenation of residue while suppressing the formation of well-aromatized extract. Kinetic studies further revealed that the dominant reaction of cellulose during DSE process was the conversion from residue to liquid (<i>k</i> = 0.0772&#xa0;min⁻¹) and from liquid to extract (<i>k</i> = 0.0189&#xa0;min⁻¹) at 300&#xa0;°C and 350&#xa0;°C, respectively. When K is added, the dominant reactions accordingly become the conversion from residue to liquid and the conversion from residue to extract. This is because the presence of K should not only enhance the intermolecular condensation reactions which impede the depolymerization of residue, but also inhibit the aromatization of small organic molecules concerning extract formation. Consequently, it is recommended to de-ash biomasses before DSE process so as to maximize the production of valuable and well-aromatized extract. This study provides theoretical guidance to biomass DSE mechanism incorporating nutritious elements and sheds light on the mechanism development of other thermochemical processes.</p> Graphical Abstract <p></p>