高效脫硝觸媒蜂巢式載體覆膜技術開發及活性測試

Abstract

NOx是氮氧化物的統稱主要包含一氧化氮(NO)和二氧化氮(NO2)，此種氣體是一種法定的空氣汙染物，會導致臭氧層的破壞、酸雨、霧霾以及誘導光化學煙霧的形成，同時也對人體健康造成危害。為此，各個國家制定了NOx的排放標準，所以工廠需要將煙氣中的NOx去除，以達到法定標準。使用氨氣(NH3)作為還原劑的選擇性觸媒還原法(selective catalytic reduction, SCR)是目前工業界最廣泛使用的脫硝方法，而在脫硝的反應器中經常使用的是蜂巢式觸媒，因其有高機械強度和低壓降的優點。 本研究將探討覆膜的蜂巢式觸媒，主要分成兩個部分，一是蜂巢式載體的覆膜技術；二是脫硝的活性測試。 在蜂巢式載體的覆膜技術中，使用材質為堇青石(cordierite)的蜂巢式載體作為骨架，然後使用浸漬覆膜法(dip coating)將二氧化鈦(TiO2)覆膜至蜂巢式載體表面。最後使用溼式含浸法(wet impregnation)將活性金屬擔載至二氧化鈦覆膜的蜂巢式載體上，從而得到覆膜的蜂巢式觸媒。從結果可看出，蜂巢式載體的TiO2覆膜具有穩固的附著力。除此之外，本研究也證實在金屬含浸溶液中加入PEG(Polyethylene glycol)，能有效讓金屬離子留在蜂巢式載體的孔洞中，並達到更均勻的活性金屬分布。另外，增加金屬含浸溶液的濃度也能限制溶液在乾燥過程的流動。 在活性測試中，測試蜂巢式觸媒MnPVMo/TiO2/HC的脫硝反應活性，並且會加入二氧化硫(SO2)和水氣到反應器，測試此觸媒的抗硫抗水能力。結果顯示在溫度250℃、GHSV=1910h-1、100 ppm SO2和13% H2O的條件下，能表現超過90%的一氧化氮(NO)轉化率。除此之外，也進行長時間穩定性測試，發現沒有明顯的活性下降，表示此觸媒具有非常良好的穩定性以及抗硫抗水的能力，是符合我們期望的觸媒。除此之外，透過測試實驗，也證實水的吸附為主要造成活性下降的原因。

NOx generally contains NO and NO2. It’s one of the legal air pollutants, and it causes ozone depletion, acid rain and photochemical smog. NOx is also harmful to human health. Many countries regulate NOx emission regulations, so industries need to remove NOx from the flue gas. The NH3-SCR(selective catalytic reduction) is most widely used de-Nox process in the industry. Honeycomb catalyst is used in the reactor because it has the advantages of high mechanical strength and low-pressure drop. In this thesis, there are two parts, including the honeycomb coating of catalysts and the de-NOx activity test. In the coating process, start with cordierite as the honeycomb framework, and a TiO2 layer was covered on the honeycomb support by dip coating. Then, the active metals on the TiO2 layer on the honeycomb was deposited by the wet impregnation method. As a result, the TiO2 coating layer had stable and sturdy adhesion. Besides, our result confirmed that adding PEG (Polyethylene glycol) to the metal solution could keep metal ions in the channels of the honeycomb during the drying step, thus obtaining uniform metal distribution. Increasing the concentration of the metal solution can also restrict the metal solution from moving to outer surface during the drying process. In de-NOx activity evaluation, the best honeycomb catalyst, MnPVMo/TiO2/HC, was performed. In order to test the honeycomb catalyst’s resistance to SO2 and water, SO2 and water vapor were added to the reaction stream. As a result, this catalyst demonstrated over 90% NO conversion under the condition at 250℃, GHSV=1910h-1 with 100 ppm SO2 and 13% water. In addition, a long-term stability test showed no significant decrease of NO conversion in 60 hours. In summary, this catalyst maintained very good stability and resisted SO2 and water. The honeycomb catalyst reached our expectations. Besides, through experiments, it was also confirmed that water adsorption is the main reason for the decrease in activity.