Adsorption of oxygen-containing aromatics used in petrochemical, pharmaceutical and food industries by means of lignin based active carbons

The adsorption processes of three aromatic chemicals onto activated carbons (ACs) from aqueous solutions have been studied. Eucalyptus kraft lignin obtained from cellulose industry as a residual biomass has been used to prepare activated carbons by physical activation with CO2. The influences of the activation time on the surface areas and pore volumes of the ACs were analyzed. The physicochemical properties and the surface chemical structure of the adsorbents have been studied by means of N-2 and CO2 adsorption, ultimate analysis, XPS, TPD and SEM. XPS and TPD spectra of the ACs have suggested the presence of aromatic rings and carbon-oxygen functional groups in the solid surfaces. The potential use of the ACs for the removal of acetaminophen (paracetamol), salicylic acid and benzoic acid has been investigated at different pH, temperature and contact time. The adsorption equilibrium data have been correlated to Langmuir isotherm model. The thermodynamic study has been developed, the values of Delta H, Delta G, and Delta S have been calculated and they indicated that the processes are endothermic for acetaminophen and exothermic for salicylic and benzoic acids. The analysis of the kinetic experiments showed that the effective diffusivities are low; 10(-12) to 10(-11) cm(2)/s, and they are the corresponding to intraparticle mass transfer, which appears as the controlling step for the net adsorption processes.