Pyrolysis of Lignite with Internal Recycling and Conversion of Oil

The present authors studied pyrolysis of lignite with internal recycling of a heavier portion of the liquid product (oil), employing a reactor that experimentally simulated continuous pyrolysis in a gassolid countercurrent moving-bed reactor. The lignite particles traveled through the isothermal section at the temperature (T-iso) of 140 or 180 degrees C and then the non-isothermal section from T-iso to the peak pyrolysis temperature (T-p) of 600 degrees C. Among the volatile products, a lighter portion of the oil (LO) with a normal boiling point of <360 degrees C was allowed to escape from the reactor together with steam and non-condensable gas, while the heavier portion of the oil was sorbed by the moving particles in both sections, recycled to the pyrolysis and then converted into char, water, and non-condensable gases inside the reactor. The oil recycling increased the char yield by up to 6 wt % dry lignite. LO consisted mainly of alkanes/alkenes (3749 wt %), lower oxygenates (acids, ketones, esters, and ethers; 17 wt %), phenols (626 wt %), and monoaromatic hydrocarbons (1221 wt %), but it contained no triaromatics. LO was evaporated completely upon heating to 200 degrees C, leaving no residue. T-iso influenced the composition of LO. The heaviest compounds varied from C-17 to C-21 paraffins for T-iso of 140180 degrees C, respectively.