Isopropanol dehydration reaction rate kinetics measurement using H₂O time histories

Abstract

H 2 O 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 H 2 O 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, iC 3 H 7 OH ⇌ H 2 O + C 3 H 6 (R1), is nearly the sole reaction controlling H 2 O production at early times, allowing for an a priori measurement of the forward rate constant k 1. The Arrhenius expression k 1 (s-1) = 2.60 × 10 13 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, k 1 (s-1) = 2.11 × 10 13 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.

An Experimental Study of 2-Propanol Pyrolysis Chemistry

“…None of the species show significant sensitivity to pressure, which indicates pressure-dependent reactions important in the 2-propanol pyrolysis system are at the high-pressure limit at the conditions studied. As noted earlier, this is consistent with the work by Cooper et al 19 who found, for the H 2 O elimination reaction, (R1a) was in the high-pressure limit for P > 1.4 atm. All the stable intermediate species measured in the current work were also observed in the propanol isomer pyrolysis study by Li et al 25 Their flow reactor study covered a broad range of temperatures and nearly 2 orders of magnitude of pressures.…”

“…Even more recently, Cooper et al 19 used shock tube studies and laser absorption to measure H 2 O production during 2propanol pyrolysis at a pressure of 1.42 atm and in the temperature range of 1127−1621 K. The authors found the data agreed well with the reaction mechanism created by Li et al 13 and that 2-propanol consumption was dominated by the dehydration channel (R1a) at the conditions studied. Because the water elimination channel was well-isolated in the study, Cooper et al 19 combined their results with the data from Heyne et al 17 and provided a further updated recommendation for the rate coefficient of the dehydration reaction that was in good agreement with measurements from 976 to 1621 K. Notably, Cooper et al 19 determined the dehydration reaction was within the high-pressure limit for pressures at and above 1.4 atm.…”

“…Even more recently, Cooper et al . used shock tube studies and laser absorption to measure H 2 O production during 2-propanol pyrolysis at a pressure of 1.42 atm and in the temperature range of 1127–1621 K. The authors found the data agreed well with the reaction mechanism created by Li et al .…”

“…However, at low temperatures methyl recombination is negligible and is dramatically underpredicted. This could indicate the C−C scission reaction (R1b) producing methyl is underpredicted, but this is considered unlikely given the current experimental conditions and prior studies of the R1 reaction by Cooper et al 19 and Li et al 13 The reaction mechanism by Saggese et al 24 was developed to model combustion of C3−C4 alcohols and 2-propanol, in particular. The kinetics were validated over a broad range of oxidizing conditions including the temperatures and pressures considered in the current work.…”

“…The objective of the current work was to provide new understanding on the fundamental chemistry of 2-propanol pyrolysis, specifically focusing on gaps in the literature for temperatures below 1200 K and at pressures above 1 atm. Based on the prior work by Cooper et al 19 and others, the H 2 O elimination reaction (R1a) was expected to be in the high-pressure limit for this study, although pressure effects were considered to confirm this expectation. The technical approach used measurements of key stable intermediate species expected as direct products of propanol thermal decomposition and as direct products of radical + propanol reactions.…”