Converting Tobacco Stalk Wastes into Value-Added Products via Sequential Hydrothermal and Pyrolysis Treatments

With the increasing concerns of human health and the ecological environment, tobacco stalks from the cigarette industry have been recognized as hazardous wastes requiring cautious treatment. However, there is still a lack of a simple and efficient route for full utilization of tobacco stalks. Herein, we attempted to convert tobacco stalk waste to value-added carbohydrates, bio-oil, and biochar through sequential hydrothermal and pyrolysis treatments. The results showed a high carbohydrate yield under the optimized condition using a microwave reaction system. The subsequent pyrolysis of residual solids at high temperatures could produce unexpected high-level aromatic chemicals including phenols and even benzenes—difficult to form without the facilitation of catalysts or salts. The obtained by-product biochar showed rapid absorption of tetracycline in 5 min and gradual introparticle diffusion from 30 to 240 min. The isotherm result had the characteristics of the Langmuir model, displaying homogeneous active sites on the biochar surface. Probably due to the hydrothermal pretreatment before pyrolysis, the obtained biochar exhibited a high adsorption capacity toward tetracycline without introducing the activation chemicals. These results illustrate that the proposed strategy may pave the way for dealing with tobacco wastes in the agricultural field.