Predicting molecular composition of primary product derived from fast pyrolysis of lignin with semi-detailed kinetic model

A numerical approach is presented for predicting the yields of char and volatile components obtained from fast pyrolysis of three types of lignin (enzymatic hydrolysis lignin, EHL; organic extracted lignin, OEL; and Klason lignin, KL) in a two-stage tubular reactor (TS-TR) at 773–1223 K. The heating rate of lignin particle in the TS-TR was estimated at 10²–10⁴ K/s by solving the heat transfer equation. The pyrolytic behavior of lignin and the formation of products in the temperature rising process were predicted using a semi-detailed kinetic model consisting of 93 species and 406 reactions, and the predicted yields of 8 primary products (i.e., char, tar, CO, CO₂, H₂O, CH₃OH, C₂H₆, and C₃H₆) were compared with experimental data for the critical evaluation. For EHL, the predicted yields of char and H₂O were in good agreement with the experimental results at all temperatures. However, the numerical simulation overestimated tar yield and underestimated CO yield at high temperature probably due to a lack of the kinetic model of the tar cracking reaction. The predicted yields of CH₃OH, C₂H₆, and C₃H₆ were close to the experimental values at high temperature by adding the detailed chemical kinetic model of the secondary vapor-phase reaction. Moreover, the model reproduced the experimental observation that among the three types of lignin the char yield increased in the order of EHL < OEL < KL, whereas the tar yield decreased.