Adsorption of volatile organic compounds and microwave regeneration on self-prepared high-surface-area beaded activated carbon

Self-prepared beaded activated carbons (SBAC) were derived from carbonized phenolic formaldehyde (PF) resins through an optimal activation procedure (900 o C for 4 h) using CO 2 . A commercial BAC (termed KBAC) was adopted to compare with SBAC over physicochemical properties, adsorption performance against methyl ethyl ketone (MEK) and toluene (TOL), and the regenerability using microwave irradiation. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models showed good fitting results to explain the adsorption equilibrium. The isosteric heat of adsorption was calculated using the Clausius-Clapeyron equation; the parameters obtained from the D-R isotherm indicate that the interactions between adsorbate and adsorbent were mainly due to physisorption. Microwave heating was applied to the regeneration of saturated adsorbents to examine the effect of irradiation power and heating time on the desorption behavior of adsorbate. Within 12 min of microwave irradiation, excellent desorption efficiencies based on gravimetric method were shown, reaching 110.7 ± 14.4, 104.4 ± 2.6, 90.2 ± 2.3, and 85.5 ± 5.7% for MEK-SBAC, MEK-KBAC, TOL-SBAC, and TOL-KBAC, respectively. After an 8-cycle of adsorption/regeneration, the adsorption capacity for SBAC was significantly decreased when loaded with TOL, whereas it was more significant than the virgin sample as loaded with MEK. In contrast, KBAC was able to sustain the adsorption capacity after an 8-cycle of regeneration, proving its stability throughout the microwave heating. Kinetic models were further employed to illustrate the desorption of the adsorbates from BAC samples, showing that intraparticle diffusion in SBAC and KBAC was the rate-limiting step during microwave heating. The core kinetic parameters obtained could provide insights for lab-scale adsorbent beds or practical engineering scale design. In conclusion, this study demonstrates the excellent adsorption performance of SBAC and the feasibility of microwave regeneration of BACs.

An efficient method for removal of pentachlorophenol using adsorption and microwave regeneration with different magnetic carbon nanotubes

Various magnetic carbon nanotubes (CNTs) Co0.5M0.5Fe2O4-CNTs (M = Cu, Mn, Ni, Zn) were successfully prepared and applied for treatment of pentachlorophenol (PCP) with adsorption and microwave irradiation process. The Co0.5M0.5Fe2O4-CNTs were characterized by transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry, and microwave absorption spectroscopy. The adsorption experiment results showed the adsorption capacity for PCP was in the following order: Co0.5Cu0.5Fe2O4-CNTs > Co0.5Mn0.5Fe2O4-CNTs > Co0.5Ni0.5Fe2O4-CNTs > Co0.5Zn0.5Fe2O4-CNTs. After adsorption, the Co0.5M0.5Fe2O4-CNTs was separated by magnetic field and regenerated by microwave irradiation at 850 W for 180 s. It was confirmed that after six adsorption and microwave regeneration cycles, the regeneration efficiency maintained over 90%. In particular, Co0.5Cu0.5Fe2O4-CNTs exhibited excellent adsorption capacity and reusability. These results can open a new avenue for treatment of chlorinated organic compounds with efficiently and non-secondary pollution.

PARTICULARS OF ADSORBENT REGENERATION WITH THE USE OF MICROWAVE ENERGY

Energy conservation issues are acute in the world. Compressed air is widely used in the modern industrial production. The production of compressed air is a very energy-intensive process, since most of the energy, which is expended by the compressor, passes into the energy of heating. Compressed air cannot be used in modern production without a prior drying and cleaning. Industrial dryer’s air losses is up to 20% of compressed air additionally. Therefore, the issue of saving air during its drying stage is important. In the presented article, the thermal and aerodynamic processes that occur in the classical adsorption tower with the most modern design are considered. The processes that occur in the adsorption column with the microwave regeneration of the adsorbent are also considered. A comparative analysis of these constructions from the point of view of energy saving is made.