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

- Two-step pyrolysis of soybean stalk (SS) was studied by Py-GC/MS.
- The effects of the first step temperatures on the two-step pyrolysis were studied.
- Two-step pyrolysis mechanism was analyzed by using TG-FTIR of SS and FTIR of chars.
- High selectivities toward high value chemicals were achieved in the first step.
- High quality bio-oil was obtained in the second step.

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 °C to 400 °C in TG process, while little lignin was decomposed in this stage. Then the first step temperature (T1) was set from 250 °C to 450 °C, and the second step temperature was set as 650 °C to compare with the one-step pyrolysis at 650 °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 °C and 300 °C torrified the SS, but had little influence on the product distribution of the second step. T1 of 350 °C enhanced polycondensation reaction of SS and reached minimum volatile yield. For optimum conditions at T1 of 400 °C and 450 °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.