Molecular characterization of wax isolated from a variety of crude oils

Petroleum waxes from sixteen different crude oils were analyzed after isolation from the crude in a two-step process. These waxes were characterized molecularly to aid in the investigation of the effect of wax type and quantity on water-in-crude oil emulsion stability. The techniques used to gather information about the waxes included elemental analysis, FTIR spectroscopy, field desorption mass spectroscopy, (1)H NMR spectroscopy, (13)C NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. ?two distinctly different types of petroleum waxes were discerned, microcrystalline and paraffinic. Microcrystalline waxes are aliphatic hydrocarbon compounds containing a substantial amount of branches and rings. They have large molecular weight ranges from 300 to 2500 amu and are gel-like in appearance. The rings give rise to a decreased WC ratio relative to paraffinic waxes, often as low as 1.85. Because of the large number of different compounds and the lack of large-scale crystallinity, a distinct melting regime is not observed. FTIR spectroscopy determined that these waxes contained approximately 55% straight chain methylene, that is, methylene groups directly attached to each other. Five waxes exhibited these characteristics and thus were considered typical microcrystalline waxes. Paraffin waxes are hydrocarbon chains with few or no branches and WC ratios between 1.96 and 2.05. They have distinct melting regions and narrow molecular weight ranges between 350 and 600 amu. They contained 63-78% straight chain methylene as gauged by FTIR spectroscopy. Six of the remaining eleven waxes exhibited all the characteristics of this paraffin category while the other five were mixtures of microcrystalline and paraffinic wax.