Structure and stoichiometry of mixed divalent metal (Ca2+/Mg2+/Sr2+/Ba2+) phosphonate scale inhibitor complexes for application in precipitation squeeze processes

S. S. Shaw, K. S. Sorbie

Research output: Contribution to conferencePaper

Abstract

In oilfield applications, various divalent cations are present in field produced waters, e.g. Ca<sup>2+</sup>, Mg<sup>2+</sup>, Sr<sup>2+</sup> and Ba<sup>2+</sup>. The interaction of these cations with phosphonate scale inhibitors (SI) is important both for scale inhibition and inhibitor retention mechanisms. In this paper, the properties of precipitated "mixed" Ca<sup>2+</sup>/M<sup>2+</sup> phosphonate SI complexes formed by 9 common phosphonate species are investigated, where M<sup>2+</sup> may be Mg<sup>2+</sup>, Sr<sup>2+</sup>, or Ba<sup>2+</sup>. These 2 and 3 metal ion complexes with SI are of the form SI-Ca<inf>N1</inf>-Sr<inf>N2</inf> and SI-Ca<inf>N1</inf>-Mg<inf>N2</inf>-Ba<inf>N3</inf>, where the stoichiometry N<inf>1</inf>, N<inf>2</inf> and N<inf>3</inf>, are the respective (M<sup>2+</sup>/SI) molar ratios. Static precipitation tests were performed varying the amounts of Ca<sup>2+</sup> and M<sup>2+</sup> present in the system (at a constant ionic strength), at 95°C, pH 8.5, and fixed [SI]= 2,000ppm. The stoichiometries of the solid precipitates were determined by re-dissolving the precipitated deposits in acidified distilled water (DW/HCl), and then assaying for Ca<sup>2+</sup>, M<sup>2+</sup>, and P directly, under each test condition, by Inductively Coupled Plasma (ICP) spectroscopy. It is shown experimentally that, for all 9 phosphonates tested, these stoichiometries depend on the number of M<sup>2+</sup> binding sites per molecule, solution pH, the relative SI binding constants to Ca<sup>2+</sup> and M<sup>2+</sup> at the test pH, and the solution molar ratio of M<sup>2+</sup>/Ca<sup>2+</sup>.

Original languageEnglish
Publication statusPublished - Jan 2015
EventCorrosion 2015 - Dallas, United States
Duration: 15 Mar 201519 Mar 2015

Conference

ConferenceCorrosion 2015
CountryUnited States
CityDallas
Period15/03/1519/03/15

Keywords

  • Scale inhibitor phosphonate complexes calcium magnesium strontium barium binding precipitation stoichiometry

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Chemistry(all)
  • Materials Science(all)

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