Effect of Pressure on the Crystallization of Crude Oil Waxes. II. Evaluation of Crude Oils and Condensate

Abstract

Laboratory analyses of the formation of wax deposits in crude oil are generally performed at atmospheric pressure on stabilized samples without the presence of light components. Therefore, the effects of two important factors that influence the solubility of waxes, namely, light fractions and pressure, are not considered. As a consequence, the results may not reflect what really happens in production lines and equipment. In this work, we evaluated five Brazilian crude oil samples and one condensate, recombined with different gases and under varying pressures, using the high-pressure microcalorimetry technique (HPμDSC). The samples were characterized with regard to the distribution of waxes by the number or carbon atoms to correlate with the results for wax appearance temperature (WAT) and crystallization enthalpy. The results indicate that rising pressure causes the WAT to rise as well and the recombination with gases composed mainly of light hydrocarbons reduces the WAT. Methane has the greatest influence on the oils containing higher amounts of macrocrystalline waxes, an effect that is stronger at higher pressures. Nitrogen does not act as a solvent of the paraffins present, whether of the macro- or microcrystalline type. Fractions lighter than C3, contained in the saturation gas mixtures, are more efficient in the solubilization of waxes, mainly those with lower molar masses. Variations in temperature and enthalpy of crystallization depend upon the pressure, composition of the gas (or mixture of gases), and composition of each crude oil.

A study of asphaltene-resin interactions

“…So, the use of calorimetric or microcalorimetric methods to determine enthalpy, entropy or free energy can be insightful to infer the nature and magnitude of forces associated with the phenomenon(a) under investigation. [28][29][30][31][32] Different volumes of asphaltene-in-toluene solutions, resin-in-n-heptane solutions and also pure solvents were mixed in this experimental work. Although, it is indisputable that the changes in the solubility parameter affect the interaction between solutes from different solvents, our aim here was to force the asphaltenes (from the toluene solution) to come out of solution, by adding a bad solvent (resins containing n-heptane), thus generating large specific surface area of asphaltene particles (colloidal ones) with which resins (in n-heptane solution) could promptly interact.…”

Wax Deposition and Fouling

“…The crystals are thermoplastic in nature and could exist as solid or liquid in solution depending on the temperature and pressure condition of the crude oil (Vieira et al, 2010). The temperature at which all the wax crystals dissolve back into oil (wax dissolution temperature, WDT) is generally higher than the WAT.…”

Liquid-Solid Phase Equilibria of Paraffinic Systems by DSC Measurements

“…The paraffin crystallization process can be influenced by many factors such as paraffin composition, solvent nature, polidispersity, rate of cooling, pressure, kinetics and presence of impurities [1,9,14,28,30,[35][36], so that a better knowledge of factors affecting wax solubility will also improve the understanding of the wax precipitation phenomena in the petroleum industry described above. The studies about the effect of solvent on solubility of waxes reported in literature [1] have shown that waxes do not exhibit ideal solution behavior when crystallizing and that their solubility in a solvent increases as both the solvent molecular size and solvent solubility parameter decrease.…”