AbstractKinetic modeling of lignin removal under conditions of high-boiling solvent (HBS, i.e. 1,4-butanediol) auto-catalyzed pulping of bagasse has been studied. The experimental data were collected based on the absorption of dissolved lignin in black liquor at a wavelength of 320 nm, which can eliminate the interferences arising from furfural (F) and 5-hydroxymethyl furfural (HMF) generated during pulping. The results indicated that the delignification process consists of two distinct phases. The initial phase, involving a very fast reaction, is followed by a rather slow second phase. The delignification equation was determined as: D=87.71×C0.8982× (1-e-1.757t) ×100%, which is valid within an HBS concentration range of 50% to 80% and can be used for predict the lignin removal from bagasse by HBS pulping.