Characterization of Surface Properties and Hydrocarbon Adsorption of Torrefied Cardboard via Inverse Gas Chromatography and Complementary Analytical Techniques

Inverse gas chromatography (IGC), atomic absorption spectroscopy (AAS), and Fourier-transform infrared spectroscopy (FTIR) were employed to investigate the surface properties of torrefied cardboard samples and their hydrocarbon adsorption. Three torrefied cardboard samples, TC-200, TC-250, and TC-300, were prepared at 200, 250, and 300 °C, respectively. A series of n-alkanes, BTX (benzene, toluene, and p-xylene), and several polar probes (dichloromethane, acetone, ethyl acetate, and tetrahydrofuran) were selected as molecular probes to measure the molar adsorption enthalpies ( $${\Delta H}_{\mathrm{m}}$$ ), dispersive surface energies, and acid–base properties of torrefied cardboard samples. The $${\Delta H}_{\mathrm{m}}$$ values of hydrocarbons measured on TC-300 and TC-250 were more exothermic than those measured for TC-200 by about 19 and 13%, respectively. The $${\Delta H}_{m}$$ values of benzene, toluene, and p-xylene on three torrefied cardboard samples became more negative than those of n-hexane, n-heptane, and n-octane by approximately 17–20%. Surface free energy analysis using molecular probes found that TC-300 exhibited higher dispersive and specific surface energy than TC-250 and TC-200 did. From FTIR spectra and elemental analysis via AAS, C=C moieties in the carbonaceous substances and inorganic mineral compositions are responsible for enhanced dispersive and specific surface energy of TC-300. BTX adsorption isotherms on torrefied cardboard samples were well-fitted using the Freundlich model. Fitted parameters of adsorption isotherms also found that TC-300 had a larger adsorption capacity toward BTX than TC-250, TC-200, and non-torrefied cardboard did.