以蜂巢狀光觸媒載體處理室內生物源揮發性有機物之研究

Abstract

本實驗將以光觸媒控制處理α-pinene。將嘗試以光觸媒披覆於蜂巢狀載體，藉由蜂巢狀載體增加反應面積，達到充分利用空間之目的，並且搭配光纖作為導光通道。實驗之光觸媒選用Degussa P25 TiO2商用化光觸媒，而紫外光燈管為8W，波長為254nm。實驗之影響因子包含α-pinene進流濃度、濕度、氣體流量，進行二重複實驗，取其平均值討論。 由實驗得知，氣體流量大於1,500ml/min時，可忽略氣相質傳效應，此時光催化反應速率決定步驟為觸媒表面反應所控制。因此將氣體流量控制1500ml/min下進行實驗，在進流濃度400ppb~2400ppb時，光觸媒轉化率不論在何種相對濕度下(30%、50%、70%)，皆能維持在90%~95%。而光觸媒反應速率皆隨進流濃度增加呈上升趨勢，然而在相對濕度50%時，光觸媒反應速率皆大於相對濕度30%及70%，因此適當的相對濕度(50%)有助於提升光觸媒反應速率。在相對濕度70%時，光觸媒轉化率與中間產物殘餘量隨進流濃度呈現下降的趨勢。光觸媒反應動力模式以雙分子競爭模式(Langmuir-Hinshelwood model)模擬，可得在相對濕度30%下，α-pinene與水分子之Langmuir吸附常數為0.17與0.01 ppm-1，α-pinene之反應速率常數為0.82 μmole/m2-s; 相對濕度50%下，α-pinene與水分子之Langmuir吸附常數為0.56與5.4×10-3 ppm-1，α-pinene之反應速率常數為0.24 μmole/m2-s; 相對濕度70%下，α-pinene與水分子之Langmuir吸附常數為1.74與9.6×10-3 ppm-1，α-pinene之反應速率常數為0.18 μmole/m2-s。 由於濕度對光觸媒催化反應具有生成氫氧自由基及與反應物產生競爭吸附之效果，由實驗而得，相對濕度的增加可降低約8%的中間產物產生，然而對光觸媒轉化率的影響較不明顯，因此濕度在本實驗中是具有增進氫氧自由基生成之正面效應。

Photocatalytic oxidation (PCO) was used to control α-pinene in indoor environment in this research. Effecient use the space for the photocatalystreaction with indoor VOCs is important. The objective of coating the photocatalyst on honeycomb support is to make the best of space by addition the area of reaction. The honeycomb support needs to be operated with optical fiber for UV light. In the experiment, Degussa P25 TiO2 was chosen as catalyst. The UV lamp is 254nm and 8W. The key factors including α-pinene concentration, relative humidity, gas flow rate and the experiment conducted twice for average. In the experiment, the effect of gas-phase transfer could be negligible when gas flow rate exceeded 1500ml/min. Therefore the rate-determaining step was related with the surface reaction of catalyst for photocatalysis. The gas flow rate is fixed at 1500ml/min to conduct the following experiment. The inlet concentration was from 400ppb to 2400ppb, the conversion of photocatalyst was maintained between 90% to 95% regardless of the relative humidity which is from 30% to 70%. PCO rate is increased with the inlet concentration. PCO rate at the relative humidity 50% is more than it at the relative humidity 30% and 70%. Therefore, the moderate relative humidity (50%) is helpful to PCO rate, others were not. At the relative humidity 70%, the conversion of photocatalyst and the residual intermediate were decrease with the inlet concentration. To fit the reaction rate of photocatalyst, it is to use the Langmuir-Hinshelwood model for bimolecular competitive adsorption form. The Langmuir adsorption constants of α-pinene and water at relative humidity 30% is 0.168 and 1×10-2 ppm-1. And the reaction rate constants of α-pinene at relative humidity 30% is 0.82 μmole/m2-s; The Langmuir adsorption constants of α-pinene and water at relative humidity 50% is 0.56 and 5.4×10-3 ppm-1. And the reaction rate constants of α-pinene at relative humidity 50% is 0.24 μmole/m2-s; The Langmuir adsorption constants of α-pinene and water at relative humidity 70% is 1.74 and 9.6×10-3 ppm-1. And the reaction rate constants of α-pinene at relative humidity 70% is 0.18 μmole/m2-s. Relative humidity may affect the production of hydroxyl radicals and the competitive adsorption in photocatalytic reaction. Results indicated that the increase of relative humidity could decrease the intermediates by about 8%. However, the increase of relative humidity had slightly effect on the conversion of photocatalyst. Consequently, relative humidity had an enhancement effect on production of the hydroxyl radicals in the experiment.