利用表面損失揮發模式估算純有機物質揮發之研究

目前對於純物質的揮發並無有效的估算方式，若要估算純物質的揮發量，經常需依靠經驗式進行估算，但此方法在不同環境下即無法準確估算，在本研究將以表面損失揮發模式( Surface depletion rate-limiting , SDRL )為基礎，測量純物質之揮發量，並應用實驗所得之結果，討論在表面損失揮發模式中的氣相參數(β )的變化。應用此模式可以解決傳統的二層膜理論算複雜的缺點，且能夠更合理的解釋氣相和液相擾動對於有機物揮發之影響。在本研究中選擇具備揮發性之有機物，包括了正癸烷、正辛烷、四氯乙烯、鄰二甲苯、對二甲苯、1,2,4-偏三甲苯、甲苯、1,1,2-三氯乙烷、正丙苯、二氯苯和丙酮等11種有機物進行測試，環境條件設定除了靜止外，尚包括0~250 rpm之液相攪拌，以及0~6 m/s風速。在指定的時間內測量在不同環境條件下之重量損失，並以表面損失揮發模式中的液相參數 α 等於1之條件下估算氣相參數( β )值，理論上在相同的環境條件下不同有機物可以獲得固定的β值，同時β值將隨攪拌強度增加與風速增加而增加。研究結果發現純物質的揮發速率呈現零階反應。靜止時的平均β值為2.14×10-5；風速的條件下則是0.2 m/s 時為3.09 × 10-4 至 3.19 × 10-4，風速6m/s 為9.95 × 10-4 至 10.14 × 10-4，風速與靜止時相差約14至47倍；而轉速最低為50rpm 的平均β值0.34 × 10-4 至 0.46 × 10-4 ，最高轉速250rpm 為2.00 × 10-4 至 2.25 × 10-4 ，與靜止時則相差2到10倍。可見在本研究中風速對揮發的影響遠大於轉速，另外本研究所估算的揮發量數據可由各時段的β值變化來討論量測可能產生誤差之原因。

關鍵字

揮發；表面損失揮發模式；二層膜理論；揮發量

並列摘要

This study is focused on estimation of volatile amount for volatile organic compounds (VOCs) through a surface depletion rate-limiting (SDRL) model. The model was derived gas kinetic. The parameters α relative to the solution concentration and β relative to gas conditions were added in the gas kinetic. The model can effectively estimate the volatile amount of pure organic compounds, comparing with the traditional two-film model. In this study, theαvalue is the concentration ratio of organic compounds in interface to those in bulk phase. The αvalue is equal to1.0 for volatilization of pure substance. The β values for various compounds are a constant under the given conditions. Moreover, the β values increase with the increasing liquid mixing intensities and wind speeds. In this study, 11 organic compounds including n-decane, n-octane, o-xylene, tetrachloroethylene, p-xylene, 1,2,4-trimethylbenzene, toluene, 1,1,2-trichloroethane, propylbenzene, dichlorobenzene, acetone were selected to examine the volatile amounts under liquid mixing (0 ~ 250 rpm) and wind speed (0 ~ 6 m / s). The volatilization rates of organic compounds based on mass loss were estimated ih the given periods. The obtained volatile amounts of organic compounds were applied to calculated β values. The characteristics of β can be applied to explain the behavior of emission for an organic compound. The volatilization rates of the test VOCs can be regarded as the zero order reaction. As expected, the β values approach a constant under the given conditions. The average β value is 2.14×10-5 without liquid mixing and wind. The β values for wind speed at 0.2 m/s is ranged from 3.09 × 10-4 to 3.19 × 10-4 , and for wind speed at 6 m/s is ranged from 9.95 × 10-4 to 10.14 × 10-4. The wind speed can highly enhance the β value. The β values at 50 rpm are ranged from 0.34 × 10-4 to 0.46 × 10-4 , and the at 250 rpm are ranged from 2.00 × 10-4 to 2.25 × 10-4. The liquid mixing only slightly enhanced β values.