Modelagem computacional da interação entre o íon de cálcio (II) e espécies inibidores de incrustação: compreendendo a reação anti-incrustação
The deposition of scaling salts, such as calcium carbonates (CaCO3), in production pipelines is a very challenging problem for the oil and gas industry, occurring as a consequence of the physicochemical conditions in oil wells. In order to remedy the oil industries, use chemical species as scale...
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| Formato: | doctoralThesis |
| Idioma: | pt_BR |
| Publicado em: |
Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/50057 |
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| Resumo: | The deposition of scaling salts, such as calcium carbonates (CaCO3), in production
pipelines is a very challenging problem for the oil and gas industry, occurring as a
consequence of the physicochemical conditions in oil wells. In order to remedy the
oil industries, use chemical species as scale inhibitors to prevent deposition. The
understanding of the molecular mechanism of action of inhibitors is not very clear.
Therefore, this thesis presents a computational modeling of the interaction
between scale inhibitors and calcium cations (Ca2+), in order to provide details at
the molecular level about the mechanistic action of anti-scalants. The
computational results shown in this thesis are based on calculations that combine
density functional methods with the implicit solvation model. The thesis was
divided into three different studies, involving the calculation of the interaction
energy between the Ca2+ ion(s) and inhibitory species, namely: (i) the
hexametaphosphate (HMF) anion; (ii) the monomer of the poly(4-styrene-sulfonicacid-co-maleic-acid) [P(SSMA)] copolymer and the surfactant sodium dodecyl
sulfate (DSS); and (iii) monomers of the carboxymethylcellulose (CMC) and
hydroxyethylcellulose (HEC) polymers. In all studies, the interaction energies
between the inhibitor species and the Ca2+ ion were compared with those formed
by Ca2+ with the carbonate (CO32–) and bicarbonate (HCO3–) anions. In (i) the
complexes formed by the interaction between the Ca2+ ions and the HMF
coordination sites are thermodynamically favorable. Furthermore, the pKa values
of the (de)protonation process for hexametaphosphoric acid (HPO3)6 were
calculated, namely: pKa_1 = –1.2; pKa_2 = –1.0; pKa_3 = +3.7; pKa_4 = +5.6;
pKa_5 = +10.4; and pKa_6 = +12.0. The values obtained by the theoretical
calculations show good agreement with values of +6.2 and +9.2 obtained
experimentally. In (ii) the theoretical results suggest that the interaction energies
between the monomeric species of P(SSMA) and Ca2+ ions are thermodynamically
favorable if the coordination occurs through the carboxylate groups. However, the
interaction energy between SDS and Ca2+ ion is unfavorable in terms of Gibbs
energy. Furthermore, the cooperative interaction of the surfactant DSS and
P(SSMA) with the Ca2+ ion(s) can result in an exergonic complex. Finally, in (iii)
the results of the calculations of interaction energy between Ca2+ and CMC and
HEC monomers suggest that the Ca2+ cation interacts more strongly with CMC than with HEC. This is because while the CMC monomer has carboxylate groups
to interact with the cation, the HEC has only polar (non-anionic) groups.
Furthermore, for this system, the interaction energy of the monomers with a CaCO3
cluster was calculated. Theoretical results suggest that the CMC monomer can
replace the position of a CO32–ion in the cluster, but the HEC monomer does not have this ability. |
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