帶電濾材對室內懸浮微粒去除效能之研究

Abstract

靜電濾材是近年來最常被用來去除室內懸浮微粒之濾材，本研究是以界面活性劑處理不帶電濾材使，其成為帶有表面電荷之帶電濾材（Surfactant Pretreated Filters, SPFs），本研究選取三型界面活性劑來處理聚丙烯濾材，其分別為sodium dodecyl sulfate（SDS）與sodium oleate（SO）陰離子界面活性劑及dimethyl dioctadecylammonium bromide（DDAB）陽離子界面活性劑。更針對不同之實驗變因探討濾材之微粒穿透率，包含氣膠大小（0.05-0.5 µm）、表面風速（0.1-1.0 m/s）、氣膠種類，同時求得三種界面活性劑前處理濾材之表面電荷與建立靜電力單一纖維效率半經驗式，更進一步評估此類SPFs之微粒載負特性以及其對生物氣膠之過濾特性。 三種界面活性劑（0.05 M DDAB、SO及SDS）前處理濾材在0.3 µm中性帶電微粒之穿透率分別為37%、45%、60%，未處理濾材之0.3 µm中性帶電微粒穿透率為76%，同時利用表面電場計量測三種SPFs，發現DDAB前處理濾材之表面電場最大，其次為SO前處理濾材，SDS前處理濾材最低。由兩部分實驗結果可知界面活性劑前處理程序的確會使不帶電濾材之表面帶有電荷。越高調理濃度之SPFs其表面電場越高，其微粒穿透率也越低。當表面風速由0.1 m/s增加至1.0 m/s時，氣膠微粒的穿透率隨之上升。比較SPFs對固體氣膠與油滴氣膠之過濾特性，發現SPFs對於固體氣膠微粒有較佳的過濾效率。當氣膠微粒之介電常數越大，過濾效率越佳。相對濕度對SPFs之微粒穿透率影響並不明顯。三種界面活性劑前處理濾材之庫倫力與介電力單一纖維過濾效率之半經驗式已建立。 SPFs之微粒載負過程可分為兩個階段，第一階段微粒穿透率會先開始上升，待上升至最大值後，在開始下降，直到穿透率下降至零。0.05 M DDAB前處理之濾材之阻塞點約在30 g/m2附近，而0.05 M SO前處理之濾材之阻塞點約在28g/m2附近，然未處理濾材之阻塞點在18 g/m2，整體結果顯示當濾材以界面活性劑處理後除使得其穿透率下降外，載負量也大幅之提升。比較不同濃度之界面活性劑前處理濾材，發現濃度越高，其阻塞點越大，可以發現越小之微粒，其阻塞點越小，當表面風速越大時，其阻塞點越小。 E-Coli生物氣膠在未處理、0.05 M SO與0.05 M DDAB前處理濾材上之穿透率分別為66%、28%及22%，Candida famata var. flareri生物氣膠在未處理、0.05 M SO與0.05 M DDAB前處理濾材上之穿透率分別為60%、21%及15%，可知SPFs對於生物氣膠有較佳之過濾效率。SPFs表面上之界面活性劑對於生物氣膠滋生有明顯抑制作用。面風速由0.05 m/s增加至0.2 m/s時，生物氣膠微粒之穿透率隨之上升。

This study elucidates the effects of using a surfactant-pretreated filter (SPF) as an electret filter on the aerosol penetration. Surfactants (dimethyl dioctadecyl ammonium bromide, DDAB; sodium oleate, SO; sodium dodecyl sulfate, SDS) were used to pretreat polypropylene fibrous filters to make them charged. Various factors, including the particle size (0.05 to 0.5 μm), the aerosol charge state (Boltzmann-equilibrium charge, neutral and singly charge), the face velocity (0.1, 0.3, 0.5 and 1.0 m/s), the species of aerosol, the relative humidity (RH 30% and RH 70%) and the concentration of surfactant (0.01 M, 0.05 M and 0.08M) were considered to evaluate their effects on the aerosol collection characteristics. The Loading behaviors of these SPFs were also evaluated in this study. Furthermore, this study investigated the collection characteristics of the SPFs for bioaerosols. Experimental results from our study demonstrate that the aerosol penetrations through SPFs were lower than through the untreated filter. The 0.3 μm-aerosol penetrations through an untreated, 0.05 M DDAB, SO and SDS-pretreated filters with Boltzmann-equilibrium charged aerosol were about 76%, 37%, 45% and 60%. Pretreating the filter with anionic surfactant did not change the structure of the filter and the mechanical capture force. The electric field measured by an electrofieldmeter of the SPFs was larger than that of untreated filter obviously. These findings imply that pretreatment with surfactant made the filters charged. The surface charge of the SPFs increased with the surfactant concentration. Aerosol penetrations through the SPFs increased with the face velocity. SPFs performed better against solid aerosol than against liquid aerosol. SPFs performed better when the tested aerosol had a larger dielectric constant. Relative humidity has no effect on the aerosol penetration through the SPFs. Regression equations for Coulombic and dielectrophoretic single-fiber efficiencies in terms of the dimensionless parameters could be fitted by the experimental measurements of SPFs in this work. The results also demonstrate pretreatment of the filter with surfactant increases its particle-loading capacity. The clogging points of the 0.05 M DDAB and SO pretreated filters and untreated filter are 30, 28 and 18 g/m2. When a filter pretreated with a higher concentration of surfactant has a larger loading capacity, and a filter cake is formed as more mass is deposited. Additionally the loading behavior of the SPFs also depended on the size of the particle. The smaller particle more seriously clogs the SPFs. The loading capacity of the SPFs is lower at a higher face velocity. Results of this study indicate that the bioaerosol penetrations through SPFs were lower than that through the untreated filter. Penetrations through an untreated, 0.05 M SO and DDAB-pretreated filters with E-Coli bioaerosol were about 66%, 28% and 22%, and Candida famata var. flareri bioaerosol penetration through an untreated, 0.05 M SO and DDAB-pretreated filters were about 60%, 21% and 21%. The data also imply that the surfactant on the SPFs has the restraint on bioaerosols. The penetrations through the SPFs with bioaerosol increased with the face velocity.