利用衝擊波管研究乙醛及異丁烷高溫熱解的反應動力學

Abstract

本研究利用活塞型衝擊波管‐原子共振吸收技術在高溫研究乙醛 (1395至1800 K) 及異丁烷 (1297 K 至1804 K) 的熱解動力學。使用動力學模擬軟體 Chemkin 及 senkin 來適解由實驗測得的氫原子濃度變化，進而得到在該反應條件下的速率常數與反應分枝比。我們利用在高溫1698 K 到1800 K 的氫原子濃度變化來得到乙醛熱解兩主要途徑之分枝比: CH3CHO → CH3 + CHO 途徑：ϕ = 0.67 CH3CHO → CH4 + CO 途徑：ϕ = 0.33 並將適解得到的k值以Arrhenius方程式表示如下

k (2 atm)=(8.24±3.50)×〖10〗^12 exp((-33310±1330)⁄T)（s-1）

本研究也得到異丁烷在1297-1503 K 間之反應速率常數值如下:

k (2 atm)=4.44×〖10〗^15 exp((-39213)⁄T)（s-1）

同時我們也發現在溫度高於1600 K 時，[H]/[i-C4H10]之比值大於1，推斷其熱解產物 (C3H6) 會進一步熱解釋放氫原子。詳細之後續反應機制仍有待進一步探討。

Abstract A diaphramless shock tube coupled with atomic resonance absorption spectroscopy was employed to study the kinetics of the decomposition of acetaldehyde between 1395 and 1800 K and isobutene at 1297 K-1804 K. Kinetics software Chemkin & Senkin were used to fit the experiment data to obtain the reaction rate constants and branching ratios. The branching ratio for CH3CHO decomposition were obtained by the observed [H] plateu at 1698 – 1800 K. CH3CHO → CH3 + CHO channel：ϕ = 0.67 CH3CHO → CH4 + CO channel：ϕ = 0.33 The decomposition rate of acetaldehyde, yielded by fitting the [H] temporal profile between 1395 – 1606 K, can be expressed by Arrhenius equation as:

k(2 atm)=(8.24±3.50)×〖10〗^12 exp((-33310±1330)⁄T)（s-1）

The rate constant for the thermal decomposition of isobutene between 1297 and 1503 K can be expressed as: k (2 atm)=4.44×〖10〗^15 exp((-39213)⁄T)（s-1） The value of [H]/[i-C4H10] were larger than unity at temperature above 1600 K. Subsequent rapid decomposition of the product C3H6 may attribute to this observation. Further investigation is needed and has been studied in this laboratory.