Mercury in petroleum

Abstract

The understanding of the chemistry of geologic mercury has evolved due to technical advances that allow differentiation of the various chemical forms of mercury in hydrocarbon matrices. Newly developed techniques can measure the concentration of mercury and mercury compounds in some hydrocarbon matrices to better than 1 part in 10 10. Accurate determinations of total mercury and speciation of mercury compounds depend on sophisticated sampling techniques and rigorous analytical procedures. The mercury species that are present in crude oil and gas condensates include several that are seldom accounted for in routine analytical methodology. Although only limited amounts of data are presently available, it appears that the distribution of mercury compounds in petroleum samples varies widely. The amounts and relative distribution of mercury compounds in liquid hydrocarbons depend on the sample source and history and include classes of compounds that have specific negative effects on people, equipment and catalysts. Crude oil and unprocessed gas condensates contain significant amounts of suspended mercury compounds, mostly mercuric sulfide. The dominant dissolved species in petroleum are elemental mercury and ionic halides. Ionic mercury compounds have been found in significant proportions in liquids but it is not known if they are abundant naturally or if they exist due to post-collection conversion of other mercury species. Detection and quantification of dialkylmercury in liquid hydrocarbons have been accomplished analytically but only limited data are available concerning its prevalence in petroleum and processed fuels. The recent understanding of the toxicology of dialkylmercury identifies this class of compounds as a potential health hazard to those exposed to gas condensate and oil, but hard evidence of exact concentrations is needed to support the hypothesis of possible risk. Mercury removal systems that employ sorbents to capture mercury in feeds to gas and liquid hydrocarbon processes do not work effectively on all chemical forms of mercury. Suspended (colloidal) forms, such as mercuric sulfide, evade capture by sorbent beds and organic mercury compounds are captured to varying degrees depending upon sorbent chemistry. Understanding the reaction of chemisorbents with each of the various species that are present in feeds is essential to the design of mercury removal systems. Mercury is universally detrimental to petroleum processing systems. In gas processing, mercury damages equipment and fouls cryogenic heat exchangers. In chemical manufacturing and refining, mercury poisons catalysts and contaminates waste water, thus impacting regulatory compliance. Contamination of primary gas treatment systems (amine and glycol) and accumulation of toxic sludge deposits in separators generate waste streams that are difficult to dispose of. Maintenance workers in the petroleum industry can be at risk due to inhalation of mercury vapor and dermal absorption of organic mercury compounds unless proper precautions are implemented.