Crude oil wax crystallization. The effect of heavy n-paraffins and flocculated asphaltenes

The influence of heavy linear alkanes concentration on the wax crystallizat ion tendency or wax appearance temperature (WAT) of a paraffinic crude oil and on a paraffin inhibitor effectiveness was evaluated by means of polariz ed light microscopy. A crude oil insensitive to the addition of wax inhibit ors was fractionated into its hydrocarbon class fractions. Virgin crude oil distillation, deasphaltation of the 385 degrees C+ residue, HPLC separatio n of the heavy saturated hydrocarbons, and molecular sieves adduction enabl ed us to isolate the linear paraffins fraction with a carbon distribution o f more than 24 atoms (nC24+- paraffins). A synthetic crude was prepared by mixing all separated fractions, except nC24+ paraffins, and the effect of t his fraction concentration was evaluated by its controlled addition to the synthetic crude followed by cloud point measurements of all doped samples. The influence of this hydrocarbon class family concentration on a maleic an hydride copolymer derivative paraffin inhibitor (MAC) efficiency was also e valuated in all doped synthetic crudes. Abundance of these large linear alk anes increases the crude oil tendency to wax crystallization, a fact that w as demonstrated by a linear correlation between the concentration of this h ydrocarbon family and the crude oil cloud point. nC24+ paraffins proved to be deleterious for the efficiency of the selected paraffin inhibitor, affor ding an asymptotic curve which tends to a zero activity value at 30 wt % co ncentration of this fraction. Additionally, it was demonstrated that the fl occulated asphaltenes provide wax crystallization sites whose presence incr eases the cloud point of the crude oil and also interferes with the crystal inhibition mechanism.