Partial Oxidation of Ethanol in Supercritical Water

Abstract

Ethanol is partially oxidized in a continuous supercritical water reactor at temperatures from 500 to 530 °C, constant pressure of 25 MPa, initial ethanol concentration of 5 wt %, residence times of 3−8 s, and oxidant-to-fuel stoichiometric equivalence ratios of 5, 7.5, and 10%. The experimental conditions are selected to study the regime where ethanol oxidation happens rapidly but below the temperature necessary to initiate hydrolysis reactions. The reactions and interactions of intermediate species can be analyzed, leveraging previous experimental results and the existing body of literature on ethanol hydrolysis, pyrolysis, and oxidation. Higher oxidant concentration increases ethanol destruction and gasification efficiency, although significant coke/char buildup is qualitatively observed within the reactor. Product yields from the experiments are used to infer significant reaction mechanisms, and a pathway is postulated for the counterintuitive formation of char under the studied conditions.

High Performance Generation of H2O2under Piezophototronic Effect with Multi‐Layer In2S3Nanosheets Modified by Spherical ZnS and BaTiO3Nanopiezoelectrics

“…This means that pure water cannot act as scavenger, while with absolute ethanol there is no enough water to form a considerable number of H 2 O 2 ; only ethanol in water can act as a hole scavenger, inhibiting the recombination of photoexcited electrons and holes and thus allowing to generate H 2 O 2 . On the other hand, the Raman spectra show the generation of acetaldehyde in ethanol‐water solution [ 28 ] (Figure S13, Supporting Information), giving a proof that ethanol has been partly oxidized by photoexcited holes in the present reaction system in agreement with mechanism (1.4) below. Usually, the amount of generated acetaldehyde can be quantified by a gas chromatography method, [ 29 ] but the qualitative analysis is chosen here mainly because the generation of H 2 O 2 is the main objective of this study.…”

Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling

“…Fortunately, properties of the most abundant compounds in the SCWO process, such as H 2 O, CO 2 , N 2 , and O 2, are available from the NIST database . Properties of fuels (e.g., ethanol) and intermediate species (e.g., formic acid) are available for a limited temperature range as these compounds undergo decomposition (hydrolysis) in a high-temperature, high-pressure environment. − Most properties can be modeled using a piecewise polynomial fit based on the NIST data. For accurate predictions near the transition region, an accurate estimation of water properties presents the most significant challenge.…”

“…Several researchers have reported kinetic rates for SCWO of ethanol ,− and methanol. − Rice and Croisset first provided a detailed mechanism for ethanol oxidation in supercritical water, which was later updated by Hayashi et al based on their experimental and modeling analysis. Simulating a detailed chemical kinetic mechanism coupled with detailed fluid mechanics is computationally expensive but may be required for resolving high-gradient kinetically controlled environments.…”

Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling and Validation

“…Several researchers have reported kinetic rates for SCWO of ethanol 21,[24][25][26][27] and methanol. [28][29][30] Rice and Croisset 26 first provided a detailed mechanism for ethanol oxidation in supercritical water which was later updated by Hong et al 27 based on their experimental and modeling analysis.…”