In general, total concentration of metals in hydrocarbons and other matrices is usually determined by spectroscopic methods after sample dissolution. For matrix digestion, many methods have been proposed in the literature. They are essentially based on wet digestion procedures often using nitric and hydrochloric acids combined with hydrogen peroxide, to solubilize metals prior analysis by inductively coupled plasma-atomic emission spectroscopy or inductively coupled plasma-mass spectrometry (ICP-AES and ICP-MS). These methods differ not only on the reagents selected but also for the completely different experimental conditions like temperature, digestion time and use of open or closed systems; these differences could obviously lead to different results. Conventional ashing and air-refluxing methods have been widely used in the Petroleum industry's analytical laboratories for many years. These traditional methods are always time consuming, labor-intensive, and tedious. Additionally, contamination is very likely to occur from the acids (especially sulfuric acid) and/or vessels used during sample preparation. The use of closed microwave (MW) oven systems overcome the timing problem and has become a quite popular method in the last few years. Utilizing a high pressure microwave system, many innovative and rapid analytical methods were developed and applied particularly to heavy feedstocks. The high operating temperature and pressure attainable in microwave digestion systems ensure total decomposition of complex petroleum crude oils and petrochemical products, with no residual organic content. Sample preparation time has been reduced from days to hours.  The method presented here has improvements in terms of time, and effectiveness of metal extraction, such as tungsten from heavy feedstocks, by using a mixture of HNO3-H3PO4 under MW procedures which reduce the tendency to precipitate insoluble tungstate species, commonly occurring during acid digestion.In this article, 3 metals commonly used for the preparation of ultradispersed catalysts for hydroprocessing heavy crude oils were selected as analytes. Cobalt incorporation as internal standard for monitoring the digestion efficiency is also presented. The evaluation of different feedstocks starting from VGO up to petroleum coke is also presented.

Microwave assisted procedure for metal extraction in heavy hydrocarbon feedstocks and emulsions

244th National Meeting (2012)

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