Preparation Of Novel Composite Activated Carbon With High Applicability To Microwave And Its Regeneration Properties Under Microwave Radiation

Microwave regeneration technology is recognized as a high-efficiency and energy-saving regeneration technology, due to its special heating and capability of heating materials in molecular level. However, the industrial application of microwave regeneration technology is still limited because the poor applicability of the traditional adsorbents to microwave. Under microwave raduation, the great temperature gradients will occur in the traditional adsorbent bed, such as the traditional activated carbon bed, and the heat in the adsorbent bed can′t be moved quickly due to the low thermal conductivity of the traditional adsorbent. This kind of temperature gradient not only may lower the efficiency, uniformity of microwave regeneration, but also may induce the adsorbent bed spontaneously combust in oxygen atmosphere. In order to eliminate this kind of temperature gradient created in traditional activated carbon bed under microwave radiation, a novel composite activated carbon with high thermal conductivity by adding expanded nature graphite was prepared in this paper.In this paper, a kind of new composite activated carbon with high thermal conductivity is prepared from walnut shells and expanded nature graphite by adding chemical activation agent ZnCl2.The results shown that the best composite activated carbon with high thermal conductivity was obtained under activation temperature of 600℃, activation time of 5h, the content of expanded graphite of 25(wt)%, the ratio of ZnCl2 to walnut shells of 3:1, the thermal conductivity of composite activated carbons is measured to be 6 times higher than those of activated carbons without adding expanded nature graphite, with surface area of 947 m2/g and micropore volume of 0.318 cm3/g.In this paper, the isotherms of toluene, methanol on composite activated carbon with high applicability to microwave (AC-ENG) were measured with IGA003 at 25℃. The Langmuir, Freundlich, Langmuir-Freundlich and Toth adsorption equations were used to simulate the isotherms. The results shown that AC-ENG had a high adsorption capacity for these two VOCs, toluene and methanol adsorption value 500mg/g. The agreement between the Langmuir-Freundlich and Toth model fitting and the experimental data was very good. The desorption experiments under microwave radiation were carried out with adsorbatesof toluene, benzene and methanol as adsorbates and the composite activated carbon with high applicability to microwave (AC-ENG-25), Lab-prepared activated carbon (AC) and commercial activated carbon (SY-6) as adsorbenrs. Then the desorption curves, temperature-raising curves of fixed beds under microwave radiation were measured, and then the activation energies for desorption under the microwave radiation were estimated. The results shown that the temperature-raising range of AC-ENG-25 fixed bed is smaller than that of AC and SY-6, due to the thermal conductivity of AC-ENG-25 is higher than that of AC and SY-6, and the activation energy for desorption of VOCs on the composite activated carbon with high applicability to microwave is smaller than that on the activated carbons without expanded graphite. The activation energy for desorption of toluene on AC-ENG is 18.08kJ/mol, 25 percent lower than that on the commercial activated carbons (24.84 kJ/mol), the activation energy for desorption of benzene on AC-ENG is 28.79kJ/mol, 18 percent lower than that on the industrial activated carbons (35.50 kJ/mol). For AC-ENG-25, the specific surface area and pore volume almost have no variation after microwave regeneration. So it is concluded that the prepared composite activated carbon with high thermal conductivity not only has good adsorption properties, but also has good applicability to microwave radiation.