Effect of Temperature, Pressure, and Residence Time on Pyrolysis of Pine in an Entrained Flow Reactor

High-pressure biomass gasification is poorly understood at heating rates of practical significance. This paper addresses this knowledge gap by performing pyrolysis of pine at high temperatures (600-1000°C) and high pressures (5-20 bar) in an entrained flow reactor. Heating rates of 10³-10 ⁴°C/s are achieved with solids residence time ranging from 4 to 28 s. The pyrolysis chars, gases, and tars are characterized using several techniques: N₂ and CO₂ physisorption, elemental analyses, SEM, XRD, micro-GC, FTIR-MS, and GCxGC-TOF-MS. The evolution of gases at high pressure is studied by pyrolyzing pine in PTGA at 800°C between 5 and 30 bar. Pyrolysis pressure, temperature, heating rate, and residence time dramatically influence the physical and chemical properties of char, mainly through differences in the release of volatiles, evolution of char morphology, and carbonization of the char skeleton. The surface area and pore properties of chars correlate with the development of graphite-like structures in the carbon matrix. The gas composition from both the PTGA and PEFR shows that CO, CO ₂, H₂, and CH₄ are the major light gases evolved, whereas C₂-C₄ hydrocarbons, oxygenates, and benzene are the minor light gas species observed. The formation of polynuclear aromatic tars at the longest residence times appears to occur via gas phase molecular weight growth reactions. The knowledge of char structure evolution developed in this paper will help us better understand char gasification kinetics which is important for the design of gasifiers.