Mercury can be present in trace amounts in all types of hydrocarbon streams such as crude oils. The amount can range from below the analytical detection limit to several thousand ppbw (parts per billion by weight) depending on the source.
Methods have been disclosed to remove mercury from liquid hydrocarbon feed, specifically volatile mercury. It has been reported that mercury in crude is primarily in the form of volatile species, e.g., 90% Hg0 and only 10% DMHg. See Wilhelm et al. Energy & Fuels 2006, 20, 180-186 (See Table 5 on page 184) http://pubs.acs.org/doi/pdf/10.1021/ef0501391. In contrast, Tao et al. J. Anal. At. Spectrom., 1998, 13, 1085-1093 http://pubs.rsc.org/en/content/articlepdf/1998/ja/a803369b show in Table 8 that dialkylmercury species out-proportion elemental Hg in condensates and natural gas liquids.
U.S. Pat. No. 4,915,818 discloses a method of removing mercury from liquid hydrocarbons (natural gas condensate) by contact with a dilute aqueous solution of alkali metal sulfide salt, for reaction of the sulfur component with the mercury, where the mercury sulfur compounds precipitate and settle for subsequent recovery as a solid waste. U.S. Pat. No. 6,268,543 discloses a method for removing elemental mercury with a sulfur compound where mercury is removed as a solid. U.S. Pat. No. 6,350,372 discloses the removal of mercury from a hydrocarbon feed upon contact with an oil soluble or oil miscible sulfur compound U.S. Pat. No. 4,474,896 discloses using polysulfide based absorbents to remove elemental mercury (Hg0) from gaseous and liquid hydrocarbon streams.
There are also a number of commercially available processes and products for the removal of (volatile) elemental mercury Hg0 from hydrocarbon streams including but not limited to ICI Synetix' Merespec™ fixed bed absorbents, UOP's HgSIV™ regenerative mercury removal adsorbents, and Johnson Matthey's Puraspec™ and Puracare™ granulated absorbents for the removal of mercury from naphtha and/or gaseous hydrocarbon streams. Adsorption technology does not work well for crude oils and condensates with low levels of mercury, and with primarily non-volatile mercury.
Production of oil and gas is usually accompanied by the production of water. This produced water in some cases is reinjected into the subsurface for disposal, to maintain pressure in the reservoir, or to achieve other beneficial effects. The produced water may consist of formation water (water present naturally in the reservoir), or water previously injected into the formation. As exploited reservoirs mature, the quantity of water produced increases. Produced water is the largest single fluid stream in exploration and production operations.
There is a need for methods for the removal of non-volatile mercury from liquid hydrocarbon streams, and particularly methods wherein produced water can be used/recycled.