Elemental mercury and several mercury compounds occur naturally in geologic hydrocarbons including petroleum and gas condensates. Recent advances in analytical chemistry are assisting our understanding of the chemistry of mercury in petroleum and its fate in petrochemical processes. Analytical techniques now are capable of measuring the concentration of mercury and mercury compounds in most hydrocarbon matrices to better than 1 part in 1010. A recently developed model proposes that the mean amount of mercury in crude oil is no more than 10 ppb.
The various chemical forms of mercury exhibit significantly different chemical and physical behavior and thus partition to fuels, products and effluents in a complex fashion. Speciation of compounds and accurate determination of species concentrations assists accounting for mercury in petrochemical processes and prediction of the magnitude of its occurrence in water and air emissions. From knowledge of the solubilities and partition factors of the mercury compounds in petroleum, one can predict concentrations in separations and distillations. The developing understanding of mercury concentrations in crude oil suggest that mercury discharges to the environment from petroleum are small as compared to those that originate from coal combustion.
Although it is generally recognized that reductions in anthropomorphic mercury emissions are beneficial to reducing mercury in the global cycle, the strategies to achieve this goal should be carefully constructed and based on the known amounts of mercury in industrial emissions. Regulations, both existing and anticipated, are major factors driving the development of mercury sequestration strategies. Emissions of mercury from petroleum production and processing are regulated by water, sediment and air criteria that are based on estimates of mercury concentrations in liquid fuels that may be in error by at least an order of magnitude.
Aside from environmental concerns, mercury also is problematic to both gas processors and refiners from the standpoint of operations. The issues relate to catalyst poisoning, health and safety and occasionally precipitation/condensation of mercury in cryogenic processes. Although mercury removal systems are applied to gas and gas liquids processing, such systems are ineffective for application to crude oil.