選擇性催化還原脫硝蜂巢式觸媒的製備和鑑定

Preparation and Characterization of Honeycomb Catalyst for Selective Catalytic Reduction of NO

白立旻(Limin Pai)

指導教授 ： 吳紀聖

國立臺灣大學/工學院/化學工程學系/碩士(2023年)

https://doi.org/10.6342/NTU202303246

摘要

隨著工業的發展，氮氧化物的排放量日益增加，為了降低氮氧化物對人類和環境的危害，各國制定了更嚴格的法規限制氮氧化物(NOx)的排放。工廠尾氣處理中最常使用的脫硝技術為選擇性催化還原法(Selective Catalytic Reduction, SCR)，利用NH3與NO反應成無害的N2。由於尾氣流速高、含有飛灰，需使用蜂巢式觸媒(honeycomb)降低壓降及增加機械強度。本研究旨在探討SCR蜂巢式觸媒的製備與鑑定。將SCR觸媒的載體TiO2覆膜於蜂巢式載體上，接著含浸活性金屬上去。TiO2覆膜溶液組成最適化，並探討乾燥方法和蜂巢前處理對覆膜附著力的影響，發現NaOH前處理和慢速乾燥能大幅提升覆膜的附著力符合工業上的標準。
TiO2本身沒有脫硝活性，本研究以Mn為活性基，運用含浸法負載20%Mn於已覆膜TiO2的蜂巢式載體上。測試並比較五種不同乾燥方法對金屬分布的影響，分別為烘箱乾燥、室溫乾燥、強制對流乾燥、冷凍乾燥和覆膜溶液加polyethylene glycol(PEG)乾燥。結果發現烘箱乾燥、室溫乾燥、強制對流乾燥金屬分布不均，冷凍乾燥金屬分布均勻但觸媒附著力變差，而PEG乾燥金屬分布均勻且保有附著力。脫硝活性結果顯示經PEG乾燥的蜂巢式觸媒比起烘箱乾燥擁有更高的活性。本研究也比較了蜂巢式觸媒和粉末觸媒的活性差異，發現在相同Gas Hourly Space Velocity (GHSV)的反應條件下，蜂巢式觸媒因為大部分皆為無活性的材質，活性很低。然而若在相同Weight Hourly Space Velocity(WHSV)的反應條件下，蜂巢式觸媒擁有與粉末觸媒近似的活性。蜂巢式觸媒的元素組成亦與粉末觸媒有些不同，蜂巢式觸媒的Mn負載量及Mn4+含量較少。
工業中常用的觸媒之一為耐硫抗水的釩鈦觸媒，因此本研究也製備並測試MnPVMo/TiO2/蜂巢，結果在200 ℃、[NO] = 200 ppm、[NH3] = 200 ppm、[SO2] = 100 ppm、[H2O] = 13%的反應條件下能達到45%的NO轉化率。

關鍵字

氮氧化物 ； 選擇性觸媒還原 ； 蜂巢式反應器 ； 二氧化鈦 ； 脫硝 ； 浸漬覆膜

並列摘要

The emission of nitrogen oxides (NOx) increases gradually due to the development of industry. In order to reduce harmful NOx, most countries have enacted stricter laws to limit the emission of NO. Selective Catalytic Reduction (SCR) is the most commonly used denitrification unit in the industry for tail gas treatment. NH3 is applied to reduce NO to harmless N2 selectively. Due to the high gas flow rate and fly ash in the exhaust, a honeycomb catalyst is needed to decrease the pressure drop and improve the mechanical strength. This study aims to investigate the preparation and characterization of SCR honeycomb catalysts. The SCR catalysts with active metals were impregnated on the layer of TiO2 which was coated on the honeycomb. The composition of the TiO2 coating solution was optimized, and the influence of the drying procedures and honeycomb pretreatments on the adhesion of the coating was studied. NaOH pretreatment of honeycomb and slow drying rate can greatly improve the adhesion of the coating to meet the requirement of the industry standard.
Pure TiO2 shows no de-NOx activity. In this study, Mn was used as the active component. 20% Mn was loaded on the honeycomb carrier, which was covered with TiO2 layer by the impregnation method. Influence of five different drying methods on metal distribution was evaluated and compared, that is, drying in an oven, drying under room temperature, drying by forced flow, drying by freeze drying, and drying with additional polyethylene glycol (PEG) in coating solution. We found that metals were unevenly distributed by drying in an oven, drying under room temperature, and drying by forced flow. Freeze drying showed even metal distribution but the adhesion of catalyst is poor. The catalyst on the honeycomb by drying with additional PEG gave evenly distributed metal and maintained strong adhesion. The result of de-NOx activity showed that the honeycomb catalyst by additional PEG drying procedure had higher activity than that by oven drying. This study also compared the activity difference between the honeycomb and the powder catalyst and found that under the same Gas Hourly Space Velocity (GHSV) conditions, the honeycomb catalyst showed much lower activity because the honeycomb consists of inactive materials. If the reaction is based on the same Weight Hourly Space Velocity (WHSV) conditions, the honeycomb catalyst gave similar activity to the powder catalyst. The element composition of the honeycomb catalyst was slightly different from that of the powder catalyst. The Mn loading and Mn4+ content on the honeycomb catalyst was less than that of the powder catalyst.
One of the catalysts commonly used in industry is sulfur and water resistant vanadium-titanium catalyst. This study also prepared and tested MnPVMo/TiO2/honeycomb and found that NO conversion achieved 45% under the reaction conditions on 200°C, [NO] = 200 ppm, [NH3] = 200 ppm, [SO2] = 100 ppm, and [H2O] = 13%.

並列關鍵字

NOx ； selective catalytic reduction ； honeycomb reactor ； TiO2 ； de-NOx ； dip coating

參考文獻

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