Adsorption performance of standard biochar materials against volatile organic compounds in air: A case study using benzene and methyl ethyl ketone

Recently, biochars have been proposed as highly efficient and low-cost media for the adsorptive removal of various hazardous compounds. However, there is a dearth of literature focusing on adsorption performance of biochars against gaseous volatile organic compounds (VOCs). In light of this limitation, the adsorption performances of 12 standard biochars made of six different raw materials (i.e., Miscanthus straw pellets, oil seed rape straw pellets, rice husk, sewage sludge, soft wood pellets, and wheat straw pellets) at two pyrolysis temperature conditions (i.e., 550 °C and 700 °C) were investigated against two model gaseous VOCs (i.e., benzene and methyl ethyl ketone (MEK)) at 1 Pa each. The breakthrough volume (BTV) and partition coefficient (PC) of benzene at 10% BTV, when measured for all these biochars, varied from 1.4 to 10 L atm g⁻¹ and 6.E-04 to 1.4E-02 mol kg⁻¹ Pa⁻¹, respectively. Similarly, their counterpart values for MEK were 1.8 to 40 L atm g⁻¹ and 1.E-03 to 2.E-03 mol kg⁻¹ Pa⁻¹, respectively. The largest adsorption capacity values for benzene (2.9 mg g⁻¹) and MEK (43 mg g⁻¹) were observed from the soft wood pellet biochar prepared at 700 °C (SWP700) and rice husk biochar prepared at 550 °C (RH550), respectively. The results indicate that most biochars adsorbed MEK preferentially over benzene. The adsorption of MEK appeared to be primarily influenced by surface features and composition of each specific biochar, while that of benzene was proportionate to their surface area. Overall, the results of this investigation are expected to help establish technical standards for effective removal of gaseous VOCs by biochars.