ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Estimation and Measurements of pH in High Temperature and High Pressure Sour Environments
Akihiro MiyasakaKozo DenpoHiroyuki Ogawa
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1989 Volume 29 Issue 1 Pages 85-91


A new technique for estimating the pH of concentrated aqueous solutions in equilibrium with high pressure H2S and CO2 at elevated temperature was proposed. Based on the thermodynamic investigation for solution properties, the following equation was obtained.pH=-logγH+{(K1, H, KH, H, PH2S2±H2S)1/2+(K1, C, KH, C, PCO22±CO2)1/2}The physico-chemical parameters in the equation were calculated by PBILC (Principle of Balance of Identical-Like Charges) proposed by Cobble et al. or assumed to be identical with those for HCl+NaCl aqueous solutions. The calculation of the pH of high temperature and high pressure sour environments was facilitated by the of this equation.
A Nb-doped TiO2 semiconductor electrode of n-type was found to be suitable for the measurement of the pH of the environments; no interference from NaCl, H2S and CO2 occurred. The measured pH values agreed well with those estimated by the newly proposed technique at the temperatures up to 473 K and at partial pressures of H2S and CO2 up to 4 MPa. It was ascertained by pH measurements for HCl+NaCl aqueous solutions at elevated temperatures that the assumption made for physico-chemical parameters in the pH estimation was valid.

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