Rapid dissolution of cinnabar in crude oils at reservoir temperatures facilitated by reduced Sulfur Ligands

• Mercury (Hg) is present in petrochemical samples, including crude oils, and the processing and use of petroleum products contribute to global Hg emissions. We present a refined theory on geochemical processes controlling Hg concentrations in crude oil by studying dissolution kinetics and solubility thermodynamics of cinnabar (α-HgS(s)) in different crude oils held at reservoir temperatures. In a black light crude oil, α-HgS(s) dissolved in an apparent zero-order reaction with a rate of 0.14−0.58 μmoles m−2 s −1 at 170−230 °C and an estimated activation energy of 43 kJ mol−1 . For crude oil samples with a total sulfur concentration spanning 0.15− 2.38% (w/w), the measured dissolution rate varied between 0.05 and 0.24 μmoles m−2 s−1 at 200 °C. Separate tests showed that thiols and, to a lesser extent, organic sulfides increased the solubility of α-HgS(s) in isooctane at room temperature compared to thiophenes, disulfides, and elemental sulfur. Long-term (14 days) α-HgS(s) solubility tests in a crude oil at 200 °C generated dissolved Hg concentrations in the 0.3% (w/w) range. The high α-HgS(s) dissolving capacity of the crude oils was more than 2 orders of magnitude greater than the highest reported Hg concentration in crude oils globally. On the basis of the kinetic and solubility data, it was further concluded that α-HgS(s) is not stable under typical petroleum reservoir conditions and would decompose to elemental mercury (Hg0 ). Our results suggest that source/reservoir temperature, abundance of reduced sulfur compounds in the crude oil, and dissolved Hg0 evasion processes are principal factors controlling the ultimate Hg concentration in a specific crude oil deposit.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

Nyckelord

mercury

crude oil

cinnabar

dissolution kinetics

thiol compounds

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)