The influence of alkane class-types on crude oil wax crystallization and inhibitors efficiency

The effect of paraffin class-types on the wax crystallization tendency in oils and the activity of paraffin inhibitors was studied for waxy crude oils. Oils enrichment with isolated paraffin fractions allowed the assessment of the influence of their molecular weight on the cloud point and the behavior of crystal modifiers. An insensitive crude oil without response to wax inhibitors was separated into its (normal/cyclo + branched) paraffin fractions. Reduced pressure distillation, n-heptane asphaltenes precipitation from the residue, high performance liquid chromatography (HPLC) of maltenes, and molecular sieves inclusion of the saturates were the separation techniques used for the isolation of the (cyclo + branched) paraffin fraction. (Cyclo + branched) paraffins, also known as (naphthwne + iso) alkane isomers, were added to the selected crude, in order to investigate their effect on the cloud point. These fractions have no significant impact in the inhibitors effect for concentrations lower than 40 wt%, but they increase the crude oil cloud point when their amount was greater than 50 wt%. This increment in the cloud point was believed to arise as a consequence of the higher average molecular weight introduced by these components. The effect of cyclic and branched alkanes on the activity of a commercial crystal modifier was studied and observed to be a complex one. At low-medium concentrations, the effect was antagonistic and believed to be controlled by the average molecular mass of the added fractions. High concentrations of cycle + branched alkanes (> 50 wt%) enhanced the activity of the crystal modifier. This result was believed to be caused by an structural effect, i.e., loose packing of crystals fi om the steric effect of naphthenic and branched structures. (C) 2000 Elsevier Science B.V. All rights reserved.