Co-pyrolysis characteristics of petrochemical wastewater sludge and Huolinhe lignite were investigated using thermogravimetric analyzer and packed-bed reactor coupled with Fourier transform infrared spectrometer and gas chromatography. The pyrolysis characteristics of the blends at various sludge blending ratios were compared with those of the individual materials. Thermogravimetric experiments showed that the interactions between the blends were beneficial to generate more residues. In packed-bed reactor, synergetic effects promoted the release of gas products and left less liquid and solid products than those calculated by additive manner. Fourier transform infrared spectrometer analysis showed that main functional groups in chars gradually disappeared with pyrolysis temperatures increasing, and H2O, CH4, CO, and CO2 appeared in volatiles during pyrolysis. Gas compositions analysis indicated that, the yields of H-2 and CO clearly increased as the pyrolysis temperature and sludge blending ratio increasing, while the changes of CH4 and CO2 yields were relatively complex. (C) 2016 Elsevier Ltd. All rights reserved.