Two-step pyrolysis characteristic of cellulose: effects of pyrolysis temperature and residence time

Two-step pyrolysis (TSP) of cellulose was conducted by Py-GC/MS to investigate the pyrolytic behavior of cellulose. The effects of the first step pyrolysis temperature (T1) and residence time (RT1) on the products distribution were studied. The pyrolytic mechanism was also analyzed detailedly. T1 was set from 250 degrees C to 650 degrees C with an interval of 50 degrees C and RT1 was set as 10, 20, and 40 s. The contents of anhydrosugar and their derivatives decreased in the first step and increased in the second step with T1 increasing, reaching maximum higher than 80.00% at T1 of 350(o)C in the first step and at T1 higher than 500(o)C in the second step. RT1 had little influence on the contents of anhydrosugar and their derivatives in the second step and at T1 lower than 500 degrees C in the first step. With T1 increasing, the content of furans increased firstly and then became stable at RT1 of 10 and 20 s in the first step, reaching higher than 25.00% at T1 higher than 550 degrees C with RT1 less than 20 s. In the second step, the content of furans kept stable at T1 lower than 350 degrees C and then decreased with T1 and RT1 elevated. The increased T1 facilitated the generation of light linear compounds in the first step. In the second step, the contents of aromatic compounds increased firstly and then decreased with T1 increasing. Besides, some value-added chemicals, namely levoglucosan (LG) 5-hydroxymethyl-furfural (HMF) and furfural (FF) levoglucosenone (LGO) could be obviously enriched. T1 of 450-500 degrees C with RT1 about 20 s was the optimum pyrolysis condition for improving the selectivities of the value-added chemicals in TSP, which was conducive to the practical application of TSP of cellulose.