Influence of wax inhibitor molecular weight: Fractionation and effect on crystallization of polydisperse waxes

Abstract

The influence of wax inhibitor molecular weight on wax crystallization was investigated in three steps: (1) Wax inhibitor fractionation via stepwise precipitation or ultrasonic disintegration, (2) characterization of inhibitor and sub-fractions in terms of molecular weight distribution, hydrodynamic radius, and precipitation from pure solvent, and (3) inhibitor effect on wax appearance temperature (WAT), waxy gelling, and wax crystal morphology. Stepwise precipitation yielded narrower molecular weight distributions, whereas ultrasonic disintegration reduced the average molecular weight and increase the polydispersity index. Changes in inhibitor molecular weight could improve as well as diminish WAT depression. Waxy gelation temperature showed similar trends, but overall effects were more pronounced. It was concluded the wax inhibitor molecular weight is a parameter that can be used to fine-tune additives to a particular waxy oil, but only after an effective PPD type has been identified.

Graphical Abstract

KEYWORDS:

• Wax inhibitor
• pour point depressant
• wax crystallization
• waxy crude oil
• flow assurance

Acknowledgments

This work was carried out as a part of SUBPRO, a Research-based Innovation Center within Subsea Production and Processing. The authors gratefully acknowledge the financial support from SUBPRO, which is financed by the Research Council of Norway, major industry partners and NTNU. The authors would furthermore like to acknowledge Marcin Dudek for providing the SARA-analysis of the crude oil.

Disclosure statement

The authors declare that they have no conflict of interest.