Activated carbon production from apple orchard woody waste using a fluidized bed reactor with freezing pretreatment to establish a local circular economy system

Abstract

Waste is always associated with all activities, and world population growth has caused a significant increase in its production ratio. Improper management of this material can have serious consequences for the environment and; consequently, human life. Agricultural activities are one of the major waste producers worldwide. Annually, in west Azerbaijan province of Iran 9,000 tons of woody waste is produced from apple orchards. Open burning is the primary method for managing this waste. Therefore, present research attempts to provide a comprehensive procedure for managing the generated waste. Converting woody waste into activated carbon (AC) with a fluidized bed reactor, and establishing a waste-based local circular economy system is the intended solution. Hence, to produce a high-porous adsorbent, freezing pretreatment is defined. To have an AC sample for further evaluations, a lab-scale fluidized bed reactor was manufactured. Carbonized granules were kept into a freezer at -30°C for 120 minutes, then the frozen granules were exposed to activating agent (water vapor) inside the reactor. Activation temperature and residence time were 500°C and 120 minutes, respectively. FT-IR, SEM, and eight standard tests were performed for revealing the produced AC characteristics. Findings demonstrated promising results; for instance, specific surface area and conversion ratio were 1240 m2/g and 1.2:1, respectively. Ultimately, the produced adsorbent was compared with similar products in market, and its selling price estimated. By considering the conversion ratio in carbonization and activation stages, converting the generated woody waste into AC can lead to produce 1,500 tons of this substance for 2.80 USD/kg.