Abstract

The United States Environmental Protection Agency (U.S. EPA), in cooperation with the American Petroleum Institute (API) and the National Petrochemical and Refiners Association (NPRA), has initiated a project to determine the mercury content of crude oil processed in the United States. The focus of the project is to determine the mean concentration and range of concentrations of mercury (total) in crude oil in a statistical fashion. Data generated in the course of the project will be used to estimate an upper limit to the contribution of mercury in crude oil to anthropogenic mercury emissions in the United States. Portions of the project are examining analytical issues, determining concentration variance in crude oil streams and building a database on total mercury concentrations in crude oils processed in the United States.

Limited data are reported that compare three analytical methods used to measure total mercury content in crude oils. The data demonstrate expected analytical method variance, detection limits and mercury species sensitivities. Aspects of the work in progress address questions concerning sampling methods, sample stability and mercury concentration variability in crude oils having a generic market identity. The plan for statistical sampling of crude oils processed in the U.S. is described in general terms.

In addition to the environmental issues, mercury in crude oil has an impact on its market quality (price). Measuring mercury concentrations in crude oil is now becoming more important as mercury's impact on production and processing systems becomes better understood. The EPA/API/NPRA project should assist development of sampling and analysis methods for crude oil and also will assist researchers to study the distribution of mercury in produced fluids throughout production and processing systems.

Introduction

U.S. EPA is under Congressional mandate (Clean Air Act) to investigate and take appropriate actions to minimize emissions of mercury to the atmosphere. Over the past several years, considerable resources have been devoted to understanding the sources of these emissions and the fate of mercury in the environment. Table 1 compiles the accounting of mercury emissions contained in the EPA Mercury Report to Congress issued in 19981. The tabulation identifies coal combustion and waste incineration as major sources of atmospheric mercury emissions in the United States. The report also admitted that there were, at that time, insufficient data and information to estimate the magnitude of mercury emissions that derive from combustion of liquid fossil fuels. Understanding the range and mean concentration of mercury in crude oil processed in the United States is fundamental to this question in that total mercury in crude oils serves as an upper limit to mercury emissions attributable to petroleum.

In 2000, U.S. EPA Office of Research and Development (EPA ORD) began to gather information on this subject starting with a literature review and preliminary estimate2,3. In 2002, EPA ORD initiated a study of mercury in crude oil so as to be able in the future to estimate atmospheric emissions that derive from liquid fossil fuel use. Parallel to this effort, EPA's Air Toxics initiative monitors mercury emissions from utility oil- and coke-fired boilers thus providing information on specific fuel streams.

The American Petroleum Institute and the National Petrochemical and Refiners Association have offered industry cooperation and support to the U.S. EPA effort. Understanding and measuring mercury in hydrocarbons is important to the industry's pollution prevention efforts on a variety of fronts and the study of mercury in crude oil is seen as a way to advance the science needed to understand mercury's impact on production and processing systems. Aside from the environmental issues, mercury in processed crude oil has a detrimental impact on refining by poisoning catalysts, degrading materials and reducing product quality, especially refined products used as feedstocks for petrochemical manufacture.

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