Nombre: HAYANE AMORIM FERNANDES
Tipo: MSc dissertation
Fecha de publicación: 03/04/2020
Supervisor:
Nombre |
Rol |
|---|---|
| MARIA DE FATIMA PEREIRA DOS SANTOS | Advisor * |
| MARISTELA DE ARAUJO VICENTE | Co-advisor * |
Junta de examinadores:
| Nombre |
Rol |
|---|---|
| ÉRICO MARLON DE MORAES FLORES | External Examiner * |
| MARIA DE FATIMA PEREIRA DOS SANTOS | Advisor * |
| MARISTELA DE ARAUJO VICENTE | Co advisor * |
Resumen: The standard method for determination of the total acid number (TAN) crude oil is the
ASTM D664, which uses potentiometric titration in non-aqueous solvents. In this paper,
the interference of the salts NaCl, CaCl2, MgCl2, and SrCl2, in the TAN determination
method, was evaluated and quantified. The interference of the salts in the titration
solvent (test blank), and in two samples of crude oil, classified as light and extra-heavy
oil, was evaluated. Salt was added in the titration solvent (test blank) of the ASTM
D664 method individually and mixed. For the crude oil samples, it was evaluated the
mixed effect of the salts. Salt was added to the titration solvent and crude oil samples
in proportions simulating brine compositions of the pre-salt (76% NaCl, 14% CaCl2, 7%
MgCl2 and 3% SrCl2) and post-salt (70% % NaCl, 10% CaCl2 and 20% MgCl2) oil
reservoirs. When added individually to the titration solvent, it was observed that the
presence of NaCl in up to 8000 mg.kg-1 does not affect TAN. For the remaining salts,
the presence of 50 mg.kg-1 of salt in the titration solvent was enough to overestimate
the value of TAN. Among the evaluated salts, MgCl2 and CaCl2 are responsible for the
largest interference in TAN. The increase in TAN due to the presence of SrCl2 is less
pronounced, approximately 1.3 times. The interference of salts in TAN is ranked in the
following order MgCl2> CaCl2 >> SrCl2; the presence of these salts can increase the
TAN value by up to 9.59 mg KOH/g, 5.77 mg of KOH/g, and 0.22 mg KOH/g,
respectively. Additionally, it was observed that the presence of salts in the titration
solvent (test blank) in the pre-salt and post-salt proportions overestimates the TAN
value by up to 1.68 mg KOH/g and 2.7 mg KOH/g, respectively. Similar behavior was
observed in crude oil, the presence of the mixture of salts CaCl2, MgCl2, and SrCl2, in
both light and extra-heavy oil samples, overestimates the NAT value by up to 1.62 mg
KOH/g, and 2.19 mg KOH/g for the pre-salt and post-salt proportions, respectively.
solvent, it was noted the formation of a precipitate
when the salts CaCl2, MgCl2, and SrCl2 were present, which suggests an interaction
mechanism between the titrant and alkaline earth metals. To better understand the
influence of the alkaline earth metals in the potentiometric titration, the precipitates
formed during the were characterized using gravimetry, X-ray powder diffraction,
thermogravimetry, Scanning Electron Microscopy with Energy Dispersive
Spectroscopy, Fourier transform infrared spectroscopy, chromatography, and
potentiometry. Using the techniques cited above, the precipitate was characterized;
the compounds KCl, magnesium, and calcium hydroxide were identified. It was not
possible to identify strontium hydroxide; it was identified that the precipitate, formed
when SrCl2 was present, was composed mainly of the SrCl2 deposited before the
titration started, which explains why Sr(OH)2 was not identified. The identification of
KCl and hydroxides in the precipitates suggests that the reaction mechanism
responsible for the increase in TAN is the reaction between alcoholic KOH and the
salts CaCl2, MgCl2 and SrCl2 salts forming calcium, magnesium and strontium
hydroxides.
