PEER-REVIEWED ARTICLE bioresources.com Shao et al. (2017). “Catalytic lignin pyrolysis,” BioResources 12(3), 4639-4651. 4639 Catalytic Stepwise Pyrolysis of Technical Lignin Lupeng Shao, a Tingting You, a Chao Wang, a Guihua Yang, b Feng Xu, a,b, * and Lucian A. Lucia c The stepwise pyrolysis of technical lignin with and without a catalyst was investigated by pyrolysis-gas chromatography/mass spectrometry (Py- GC/MS). Lignin was first pyrolyzed at 260 or 360 °C, and then the residue was subsequently pyrolyzed at 650 °C. It was found that stepwise pyrolysis of lignin concentrated the phenolic compounds in lignin-derived bio-oil. In a stepwise 260 to 650 °C process, the maximum total phenolic compounds were 86.2%. Among the phenolic compounds, guaiacol-type and phenol-type phenolic compounds were predominant. Further addition of a catalyst (HZSM-5) in the stepwise pyrolysis process enhanced control over the product distribution through conversion of phenolic compounds into aromatic hydrocarbon products. The aromatic hydrocarbons achieved the highest yield of 30.4% in the catalytic stepwise 260 to 650 °C process. Keywords: Lignin; Catalyst; Pyrolysis; Stepwise; Py-GC/MS Contact information: a: Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, China; b: Shandong Key Laboratory of Paper Science & Technology, Qilu University of Technology, Jinan 250353, China; c: Department of Forest Biomaterials, North Carolina State University, Box 8005, Raleigh, NC27695-8005 USA; *Corresponding author: xfx315@bjfu.edu.cn INTRODUCTION Lignocellulose, which includes forest materials, agricultural residues, or energy crops, is the cheapest and most abundant form of biomass. Biomass is a promising alternative to petroleum for the production of fuels and chemicals (Brebu et al. 2013). It consists of approximately 35% to 45% cellulose, 25% to 30% hemicellulose, and 20% to 35% lignin (Custodis et al. 2015). Lignin, nature’s dominant aromatic polymer, is found in most terrestrial plants and provides structural integrity (Ragauskas et al. 2014). Lignin is a complex amorphous copolymer in which guaiacyl (G), p-hydroxyphenyl (H), and syringyl (S) units are interconnected by various ether bonds and carbon-carbon linkages (Shen et al. 2015). The majority of interunit linkages are β-O-4, β-5, and β–β (Yue et al. 2017). β-O-4 bonds especially are the most frequent coupling linkage and comprise 50% to 60% of the total linkages (Chu et al. 2013). Lignin as a by-product of the pulp and paper industry and the bioethanol industry is very underutilized because of its inherent heterogeneity, low reactivity, and recalcitrance. Most lignin has been traditionally employed for heat and power purposes through combustion (Xu et al. 2014). However, lignin is a potential source for fuel and chemical production because of its rich aromatic structures. The use of lignin as a substitute for crude oil to produce petrochemicals can reduce the reliance on fossil fuel resources or replace it to some extent in the future. Therefore, efficient transformation of lignin is necessary. Pyrolysis has been identified as one of the primary thermochemical conversion technologies for lignin transformation (Liu et al. 2016). During pyrolysis, lignin can be rapidly converted into gaseous products, volatiles, and solid residue, in which the