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51315-5646-Structure and Stoichiometry of Mixed Divalent Metal (Ca²+/Mg²?+Sr²+/Ba²+) Phosphonate Scale Inhibitor Complexes

Previously, precipitation of SI and Ca2+ was investigated. Similar work has also been performed by other researchers. The current paper presents corresponding experimental results where the binding of divalent cations Ca2+ and Sr2+ to 9 phosphonate SIs at pH 8.5, 95oC is investigated.

Product Number: 51315-5646-SG
ISBN: 5646 2015 CP
Author: Scott Shaw
Publication Date: 2015
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In oilfield applications, various divalent cations are present in field produced waters, e.g. Ca2+, Mg2+, Sr2+ and Ba2+. 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” Ca2+/M2+ phosphonate SI complexes formed by 9 common phosphonate species are investigated, where M2+ may be Mg2+, Sr2+, or Ba2+. These 2 and 3 metal ion complexes with SI are of the form and , where the stoichiometry , and , are the respective (M2+/SI) molar ratios. Static precipitation tests were performed varying the amounts of Ca2+ and M2+ present in the system (at a constant ionic strength), at 95oC, 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 Ca2+, M2+, 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 M2+ binding sites per molecule, solution pH, the relative SI binding constants to Ca2+ and M2+ at the test pH, and the solution molar ratio of M2+/Ca2+.

 

Key words: conference papers, 2015 conference papers, downloadable, scale inhibitor, phosphonate, complexes, calcium, magnesium, strontium, barium, binding, precipitation, stoichiometry

 


precipitation stoichiometry

In oilfield applications, various divalent cations are present in field produced waters, e.g. Ca2+, Mg2+, Sr2+ and Ba2+. 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” Ca2+/M2+ phosphonate SI complexes formed by 9 common phosphonate species are investigated, where M2+ may be Mg2+, Sr2+, or Ba2+. These 2 and 3 metal ion complexes with SI are of the form and , where the stoichiometry , and , are the respective (M2+/SI) molar ratios. Static precipitation tests were performed varying the amounts of Ca2+ and M2+ present in the system (at a constant ionic strength), at 95oC, 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 Ca2+, M2+, 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 M2+ binding sites per molecule, solution pH, the relative SI binding constants to Ca2+ and M2+ at the test pH, and the solution molar ratio of M2+/Ca2+.

 

Key words: conference papers, 2015 conference papers, downloadable, scale inhibitor, phosphonate, complexes, calcium, magnesium, strontium, barium, binding, precipitation, stoichiometry

 


precipitation stoichiometry

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