A new technique was proposed for estimating the pH of concentrated aqueous solutions in equilibrium with high pressure H2S and CO2 from ambient to elevated temperatures. The effects of co-existing anions (carbonate and sulfate) and cations (alkali and alkali-earth metal ions) were taken into consideration through their influence on dissociation equilibria as well as on activity coefficients.

The physico-chemical parameters were obtained by thermodynamic estimation; the H2S and CO2 solubility constants were calculated by a Correspondence principle, and the dissociation constants of H2S, CO2 and HSO4- by a PBILC (Principle of balance of identical-like charges) method. It was found that the presence of carbonate ion raises the pH value even at a fairly small content of 10-4 to 10-3 mol/kg. Sulfate also raised the pH value when its concentration is over approximately 3 x 10-2 mol/kg.

The validity of estimation was confirmed by the fact that the experimentally measured pH values were in good agreement with the thermodynamically calculated ones. The calculation of the pH of the sour and sweet environments, from low to high pressures of H2S and CO2 and from ambient to elevated temperatures, was thus facilitated by the newly proposed technique.

Subject
Anions, Marine environments, Thermodynamics, Hydrogen concentration, Sour environments, Sulfates, Sodium chloride, Bicarbonates, Aqueous solutions, Acidity, Constants, Sodium chloride solution, Cations
Keywords:
sour gas, pH, thermodynamics, activity, hydrogen ion, hydrogen sulfide, carbon dioxide, activity coefficients
© 1992 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1992
Association for Materials Protection and Performance (AMPP)
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