The Study On Preparation Of Activated Carbon From Waste Tea And Its Adsorption Performance For SO₂, NO

One of the major effects of air pollution is acid rain caused by SO2and NO fromcoal-fired. Thus, the control of SO2and NO is important for the global environment.The removal of SO2and NO by activated carbon has been studied extensively, due tothe high adsorption efficiency of activated carbon. However, the costs and secondarypollution from raw material and modification of activated carbon are worthconsidering. Waste tea with a high carbon content and theophylline is a good precusorof activated carbon, which was used to remove acid gas. In this study, activatedcarbon was prepared from Tieguanyin waste tea, and its structure properties wereregulated by preparation process. The effects and mechanism of waste tea activatedcarbon on its desulfurization and denitrification performance were investigated.The activated carbon was prepared from waste tea by activation of steam andK2CO3, ZnCl2. And its structure properties and adsorption performance of activatedcarbon were investigated. The results showed that the activated carbon prepared fromwaste tea was mainly microporous. The adsorption of methylene blue and iodine ofactivated carbon obtained by K2CO3and ZnCl2activation were higher than the oneobtained by steam activation. Activation temperature has a significant impact onmesoporous of the activated carbon. Mesopores were donated on the activated carbonby ZnCl2activation at350℃, when the activation temperature increased from500℃to700℃, mesopore volume was decreased from0.55cm3/g to0.06cm3/g.Mesopores were developed on activated carbon obtained by K2CO3activation whenthe activation temperature was800℃. Micropore size of carbon activated by ZnCl2activation expanded from0.83nm to0.87nm when activation time increased from0.5h to1.5h, and shrunk at2h. Mesoporous of waste tea carbon activated by K2CO3began to appear when activation time up to2.5h. The biggest micropore volume ofwaste tea activated carbon was obtained when ZnCl2or K2CO3impregnation ratiowas1:1, and the micropore volume were48cm3/g、60cm3/g respectively.The effects of pore structure, graphite and surface structure of waste tea activated carbon on its desulfurization and denitrification performance were investigated,adsorption kinetics and adsorption process were also studied. The results showed thatless graphitization, less micropore size and more nitrogenous basic group ofadsorbent enhanced its desulfurization ability. When addition mesopores intoadsorbent, NO removal efficiency decreased, more nitrogenous basic groups promoteremoval rate of NO. When SO2and NO were removed together, competingadsorption were appeared. After oxygen and steam were introduced to flue gas,remove efficiency of SO2and NO was increased. The adsorptions of SO2and NO onthe adsorbent were physical adsorption without O2and H2O, and the regeneratedmaterials have maintained good adsorption properties for SO2and NO. While thevapor promoted chemical adsorption of SO2, and accelerated aging of the adsorbent.The reaction on surface and diffusion of particles affect the adsorption rate of SO2and NO. The adsorption process of the material can be described well by Banghamkinetic equation, and the value of R2was no less than0.989.The average pore size of waste tea activated carbon by pre-modified andpost-modified did not change significantly. The adsorbent pre-modified andpost-modified by KOH have added secondary amine basic nitrogen-containingfunctional groups. The secondary amides nitrogen-containing functional groups wereintroduced to the surface of adsorbent modified by NH3. The desulfurizationpenetration time was increased from30min to40min when post-modified by KOHand NH3.Desulfurization penetration time of the adsorbent pre-modified by KOH andNH3were prolonged to above60min and38min respectively. The denitrificationefficiency of the adsorbent pre-modified by KOH improved to above60%from40%in the first10min. The adsorbent modified by acetic acid increased the oxygenfunctional groups, however, the desulfurization and denitrification efficiencydecreased because of the reduced basic.