Effects of drying pretreatment on microwave pyrolysis characteristics of tobacco stems

In this work, the effect of volumetric drying and surface drying pretreatment on microwave pyrolytic characteristics of tobacco stems was investigated. The microwave oven was used for volumetric drying with different power outputs, while the electric oven was used for surface drying at 105celcius. The biomass dried using microwave drying was compared with the dried using oven drying, and the yields and properties of solids, liquids, and gases were determined. Besides, the decomposition mechanism of nicotine was preliminarily expounded. The results showed that the drying rate of microwave could reach up to 1.093 g m(-2) s(-1), which was approximately 5 times the maximum drying rate of oven. There was little change in the yield of biochar, and the yield of bio-oil increased, while the yield of non-condensable gas decreased by microwave compared to oven. When microwave drying was used, the concentration of CO2 in the pyrolysis gas was higher, but the yields of H-2, CO and CH4 were lower. The preliminary analysis of pyrolytic bio-oil revealed that the relative content of alcohols, acids, aldehydes, and ketones increased to 6.46%, 3.39%, 18.59%, and 18.18%, and the relative content of phenols decreased to 8.74% by microwave. After oven drying, the residence time of volatiles in the reaction zone increased during the pyrolytic process, and nicotine was thermally decomposed at high temperatures and combined with other free radicals; the relative contents of nicotine in the bio-oil have decreased from 11.78 to 6.55%. Microwave drying decreased the water content of bio-oil. At the same time, the stability of bio-oil improved. Therefore, microwave drying is an economical pretreatment method for biomass fast pyrolysis.

Automated summary

This study investigates the effect of volumetric drying and surface drying pretreatment on the microwave pyrolytic characteristics of tobacco stems. The results show that microwave drying has a higher drying rate, resulting in higher yields of bio-oil and solids, and lower yield of non-condensable gases. Microwave drying also reduces the water content of bio-oil and improves its stability.