Molecular Characterization of Wax Isolated from a Variety of Crude Oils

Abstract

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, 1H NMR spectroscopy, 13C 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 H/C 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 H/C 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.

The thermal properties of beeswaxes: unexpected findings

“…The clear advantage of DSC analysis lies in the ability to quantify thermal characteristics that are not apparent in capillary melting point tests or other less precise methods. To this end, Fourier transform infrared (FTIR) spectroscopy may also be a promising method for investigating wax thermal characteristics (Musser and Kilpatrick, 1998).…”

Waxes in asphaltenes of crude oils and wax deposits

“…Waxes, which consist primarily of the higher molecular weight n-alkanes within C 30 -C 60 , with a high share of iso-paraffins and naphthenes, and have much higher melting point ranges (above 60-90°C), are referred to as microcrystalline waxes. According to Musser and Kilpatrick (1998), paraffinic and microcrystalline waxes have molecular weight ranges of 350-600 and 300-2500, respectively.…”

“…The ratio of paraffinic to microcrystalline waxes in oils depends on origin of oils (Tissot and Welte 1978;Musser and Kilpatrick 1998;Philp 2004;Fazeelat and Saleem 2007). However, in most cases, the higher molecular weight paraffin hydrocarbons (microcrystalline type) are present in very low concentrations or are absent in produced oils.…”

Influence of Waxes on Bitumen and Asphalt Concrete Mixture Performance

“…Much of this wax comes from petroleum, which is the largest single source of hydrocarbon waxes (Musser et al, 1998). Petroleum wax is a by-product in the petroleum industry.…”