Isopropanol dehydration reaction rate kinetics measurement using H2O time histories

Abstract

AbstractH2O formation during thermal decomposition of isopropanol was measured behind reflected shock waves at temperatures ranging from 1127 to 1621 K at an average pressure of 1.42 atm using a laser absorption technique. Of the five modern chemical kinetics models used to compare the H2O time histories, the model from Li et al (Combust. Flame 2019;207:171‐185) showed the best overall agreement. Sensitivity and rate of production analyses using the Li et al model (as well as those from AramcoMech 3.0, CRECK, and Togbe et al (Energy Fuel. 2011;25:676‐683)) showed unimolecular dehydration of isopropanol, iC3H7OH ⇌ H2O + C3H6 (R1), is nearly the sole reaction controlling H2O production at early times, allowing for an a priori measurement of the forward rate constant k1. The Arrhenius expression k1 (s–1) = 2.60 × 1013 exp(−31 120 K/T) was determined to represent best the data from this study. According to the models and previous experimental investigations, the pressure investigated is well within the high‐pressure limit (HPL) for this reaction. Additional, higher‐pressure experiments also confirmed the HPL assumption. An uncertainty analysis was performed by varying secondary reactions within their uncertainties and examining their effect on the overall prediction, establishing an uncertainty within ±20% for all but the highest temperature cases, which have a maximum uncertainty of ±40%. Experiments conducted with a radical trapper, toluene, showed little influence from radical chemistry, suggesting this estimated uncertainty is fairly conservative. Experimental data from Heyne et al (Z Phys Chem. 2015;229:881‐907) were found to be in good agreement with the rate measurements from this study and, therefore, a second Arrhenius expression, k1 (s–1) = 2.11 × 1013 exp(−30 820 K/T), was found to represent both datasets well. This second expression has a larger temperature range of 976‐1621 K. The present study provides the first high‐temperature data collected for this reaction, adding to the limited data available for isopropanol in the literature.