Mercury in petroleum

The understanding of the chemistry of geologic mercury has evolved due to t echnical 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 matr ices to better than 1 part in 10(10). Accurate determinations of total merc ury and speciation of mercury compounds depend on sophisticated sampling te chniques and rigorous analytical procedures. The mercury species that are p resent in crude oil and gas condensates include several that are seldom acc ounted for in routine analytical methodology. Although only limited amounts of data are presently available, it appears that the distribution of mercu ry compounds in petroleum samples varies widely. The amounts and relative d istribution of mercury compounds in liquid hydrocarbons depend on the sampl e source and history and include classes of compounds that have specific ne gative effects on people, equipment and catalysts. Crude oil and unprocesse d gas condensates contain significant amounts of suspended mercury compound s, mostly mercuric sulfide. The dominant dissolved species in petroleum are elemental mercury and ionic halides. Ionic mercury compounds have been fou nd in significant proportions in liquids but it is not known if they are ab undant naturally or if they exist due to post-collection conversion of othe r 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 cl ass of compounds as a potential health hazard to those exposed to gas conde nsate and oil, but hard evidence of exact concentrations is needed to suppo rt the hypothesis of possible risk. Mercury removal systems that employ sor bents to capture mercury in feeds to gas and liquid hydrocarbon processes d o not work effectively on all chemical forms of mercury. Suspended (colloid al) forms, such as mercuric sulfide, evade capture by sorbent beds and orga nic mercury compounds are captured to varying degrees depending upon sorben t chemistry, Understanding the reaction of chemisorbents with each of the v arious species that are present in feeds is essential to the design of merc ury removal systems. Mercury is universally detrimental to petroleum proces sing systems. In gas processing, mercury damages equipment and fouls cryoge nic heat exchangers. In chemical manufacturing and refining, mercury poison s catalysts and contaminates waste water, thus impacting regulatory complia nce. 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 indu stry can be at risk due to inhalation of mercury vapor and dermal absorptio n of organic mercury compounds unless proper precautions are implemented. ( C) 2000 Elsevier Science B.V. All rights reserved.