Proton concentration of supercritical water and high-concentrated carbon dioxide mixture using UV-vis spectroscopy

Kimitaka Minami, Takashi Suzuki, Takafumi Aizawa, Kiwamu Sue, Kunio Arai, Richard L. Smith

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

High-temperature and high-pressure UV-vis spectroscopy was applied to evaluate the proton concentration in supercritical water (SCW)-CO2 (3 and 7 mol%) mixture at 380 °C and a water density of 400 kg m-3 using 4-nitrophenol as a probe molecule. From the absorption spectra measured at various NaOH concentrations, the first dissociation constant of aqueous carbon dioxide (CO2,aq + H2O = H+ + HCO3 -) was determined to be 3.3 × 10-13. The determined dissociation constant was one order of magnitude smaller than that estimated from the revised HKF equation of state (2.5 × 10-12). Using the determined dissociation constant, proton concentration in SCW-CO2 mixture was estimated at various CO2 concentrations (1-7 mol%) and was shown to be 6-19 times higher than that in pure SCW. The compound, 4-nitrophenol, was found to be a reliable probe for estimating proton concentrations in supercritical aqueous solutions. The estimated proton concentration in SCW-CO2 mixture can be used for detailed analysis of SCW reactions, especially for acid-catalyzed ones.

Original languageEnglish
Pages (from-to)177-182
Number of pages6
JournalFluid Phase Equilibria
Volume257
Issue number2
DOIs
Publication statusPublished - 2007 Aug 25

Keywords

  • Carbon dioxide
  • Proton concentration
  • Supercritical water
  • UV-vis spectroscopy

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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