Study on two-step pyrolysis of soybean stalk by TG-FTIR and Py-GC/MS

Two-step pyrolysis (TSP) of soybean stalk (SS) was investigated by Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and Thermogravimetric analyzer coupled with FTIR spectrophotometer (TG-FTIR) to obtain high value chemicals and high quality bio-oil. The hemicellulose and cellulose in SS were almost decomposed from 200 degrees C to 400 degrees C in TG process, while little lignin was decomposed in this stage. Then the first step temperature (T1) was set from 250 degrees C to 450 degrees C, and the second step temperature was set as 650 degrees C to compare with the one-step pyrolysis at 650 degrees C (OSP). The yields of volatiles of TSP were lower than that of OSP, but the yields of solid products were similar to each other approximately. T1 of 250 degrees C and 300 degrees C torrified the SS, but had little influence on the product distribution of the second step. T1 of 350 degrees C enhanced poly condensation reaction of SS and reached minimum volatile yield. For optimum conditions at T1 of 400 degrees C and 450 degrees C, higher contents of oxygenous products (acids, furans, alcohols, ketones and phenols with methoxyl) and nitrogen compounds were achieved in the first step to increase the selectivities toward high value chemicals, and high quality bio-oil with high contents of hydrocarbons could be obtained in the second step.