حذف تولوئن از جريان هواي آلوده در فرايند ازنزني كاتاليستي با استفاده از كاتاليستهاي MnO/GAC و MgO/GAC

Toluene Removal from Waste Air Stream in Catalytic Ozonation Process Using MgO/GAC and MnO/GAC Catalysts

مهمترين پارامتر براي حذف آلاينده هاي آلي در روش ازن زني كاتاليستي بكارگيري كاتاليست مناسب است. در اين تحقيق كارائي كاتاليست هاي MnO/GAC و MgO/GAC براي حذف تولوئن از هوا در حضور ازن در مقياس آزمايشگاهي مورد مطالعه قرار گرفت. كاتاليست هاي MnO/GAC و MgO/GAC با روش سل ژل توليد و با آناليزهاي BET، XRD و SEM تعيين مشخصات شدند. متغيرهاي زمان ماند (0/5، 1، 1/5، 2و Sec 4)، غلظت تولوئن (100، 200، 300 و ppmv 400) و دماي هواي ورودي (25، 50، 75 و ˚C100) بعنوان پارامترهاي عملكردي موثر در فرايند ازن زني كاتاليستي مورد مطالعه قرار گرفتند. دوز ازن ورودي معادل g/h 0/1 در كليه آزمايشات ازن زني كاتاليستي ثابت نگه داشته شد. كارائي كاتاليست هاي MgO/GAC و MnO/GAC در حذف تولوئن در حضور ازن بر اساس زمان نقطه شكست و ظرفيت حذف تعيين و از نظر آماري مقايسه شدند. نتايج نشان داد افزايش زمان ماند از 0/5 به Sec4 زمان شكست ستون MgO/GAC و MnO/GAC را به ترتيب 11/3 و 13/9 برابر افزايش داد. افزايش غلظت تولوئن (ppmv 100-400) باعث كاهش زمان نقطه شكست و افزايش ظرفيت حذف به ترتيب به ميزان 65% و 39/1% براي MgO/GAC و 62/2% و 50/4% براي MnO/GAC شد. كارائي كاتاليستMgO/GAC و MnO/GAC با افزايش دما از 25 به ˚C100 به ترتيب 78/3% و 31/5% افزايش يافت. يافته هاي تحقيق نشان داد كاتاليست هاي MgO/GAC و MnO/GAC پتانسيل بالايي براي حذف تركيبات آلي فرار از جريان هوا در حضور ازن دارند. كاتاليست MgO/GAC نسبت به MnO/GAC پتانسيل بالاتري در حذف تولوئن از جريان هوا در حضور ازن داشت (0.05 ≥ P).

Toluene, as one of the volatile organic compounds, is extensively used in industrial processes. Because of the harmful effects of toluene on environment and human health, removal of toluene from contaminated air stream is necessary. Catalytic ozonation process (COP) is one of the emergent technologies for removal of volatile compounds from air streams. Catalytic ozonation process is efficient, cost-effective and easy to operate for elimination of organic compounds. Type of the catalyst is one of the main factors directly affecting the VOC removal efficiency and ozone destruction rate. In this study potential of MnO/GAC and MgO/GAC catalysts is investigated for the elimination of toluene content of air stream in the presence of ozone, in lab scale. The MnO/GAC and MgO/GAC catalysts are prepared by Sol-gel method and then characterized by BET, XRD and SEM analysis. Specific concentrations of toluene in air are produced by using an air pump and a syringe pump. Phocheck is used to measure the concentration of toluene in gas phase. The effect of retention time (0.5-4 Sec), inlet toluene concentration (100-400 ppmv) and air temperature (25-100˚C) are investigated on catalysts efficiency in the presence of ozone. Ozone dosage (0.1 g/h) is kept constant in all experiments. Efficiency of the presence of MnO/GAC and MgO/GAC are determined from the breakthrough time and removal capacity and the results are compared statistically. The BET surface area derived from N2 adsorption-desorption isotherms. From the results the BET surface area of MnO/GAC (1103 m2/g) is greater than that of MgO/GAC catalyst (1082 m2/g). XRD patterns clearly illustrate the formation of MgO and MnO crystals on GAC surface. From XRD patterns the peaks at 2θ degrees of 50.3° and 73.8° were related to the MgO crystals. The peaks at 2θ degrees of 42.1°, 51.8° and 70.9° reveal the formation of Mn3O4. The crystallite phase of MgO and MnO was hexagonal and tetragonal, respectively. The average sizes of MgO and MnO crystals were 10 and 12 nm, respectively, calculated by Debby-Scherrer equation. Results of experiments in different retention times showes that breakthrough time of MnO/GAC and MgO/GAC catalysts increased by 11.3 and 13.9 times, respectively, by increasing retention time from 0.5 to 4 seconds. When inlet toluene concentration is increased from 100 to 400 ppmv, the breakthrough time of MgO/GAC and MnO/GAC columns decreased by 65% and 62.2%, respectively. In contrast, removal capacity of MgO/GAC and MnO/GAC increased by 39.1% and 50.4% by increasing inlet toluene concentration from 100 to 400 ppmv, respectively. The efficiency of MgO/GAC and MnO/GAC catalysts increased by 78.3% and 31.5% by increasing air temperature from 25 to 100 ˚C, respectively. These results demonstrates that increase of retention time and bed temperature could positively affect the performance of MgO/GAC and MnO/GAC catalysts in toluene removal from waste air stream in the presence of ozone. It can be concluded that MgO/GAC and MnO/GAC catalysts have high potential in VOCs removal from air stream in the presence of ozone. The difference between the efficiency of MgO/GAC and MnO/GAC catalysts was significant (P ≤ 0.05) and MgO/GAC catalyst has higher efficiency than MnO/GAC for toluene removal from waste air in the presence of ozone.