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How polymer additives reduce the pour point of hydrocarbon solvents containing wax crystals

Fletcher, Paul D. I.; Binks, Bernard P.; Fletcher, Paul D. I.; Roberts, Noel A.; Dunkerley, John; Greenfield, Hannah; Mastrangelo, Antonio; Trickett, Kieran

Authors

Paul D. I. Fletcher

Paul D. I. Fletcher

Noel A. Roberts

John Dunkerley

Hannah Greenfield

Antonio Mastrangelo

Kieran Trickett



Abstract

We have investigated how four different pour point depressant (PPD) polymers affect the pour point transition in mixtures of a single pure wax in a solvent. We used either n-eicosane (C20), CH3(CH2)18CH3, n-tetracosane (C24), CH3(CH2)22CH3 or n-hexatriacontane (C36), CH3(CH2)34CH3 as the wax component with either n-heptane or toluene as the solvent component. For all wax–solvent combinations, the measured variation of wax solubility with temperature is well predicted by ideal solution theory. The variation of pour point temperature as a function of the overall wax concentration is quantitatively modelled using the idea that, for each overall wax concentration, the pour point occurs at a temperature at which a critical volume fraction ϕ* of wax crystals has precipitated. Close to the pour point temperature, extraction and examination of the wax crystals show they consist of polydisperse, irregularly-shaped platelets with axial ratios (h/d, where h is the plate thickness and d is the plate long dimension) in the range 0.005–0.05. It is found that the measured ϕ* values corresponding to the pour point transitions are weakly correlated with the wax crystal axial ratios (h/d) for all wax–solvent–PPD polymer combinations. These results indicate that the pour point transition occurs at a volume fraction larger than the value at which the volumes of rotation of the platelet crystals overlap, i.e., 2.5(h/d) < ϕ* < 11(h/d). PPD polymers work, in part, by increasing the wax crystal axial ratio (h/d), thereby increasing ϕ* and reducing the pour point temperature. Since the PPD's ability to modify the wax crystal shape relies on its adsorption to the crystal-solution surface, it is anticipated and observed experimentally that optimum PPD efficacy is correlated with the difference between the wax and the polymer solubility boundary temperatures. This finding and the mechanistic insight gained here provide the basis for a simple and rapid screening test to identify candidate species likely to be effective PPDs for particular wax systems.

Journal Article Type Article
Publication Date Feb 14, 2015
Journal Physical chemistry chemical physics
Print ISSN 1463-9076
Electronic ISSN 1463-9084
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 17
Issue 6
Pages 4107-4117
APA6 Citation Binks, B. P., Fletcher, P. D. I., Roberts, N. A., Dunkerley, J., Greenfield, H., Mastrangelo, A., & Trickett, K. (2015). How polymer additives reduce the pour point of hydrocarbon solvents containing wax crystals. Physical chemistry chemical physics : PCCP, 17(6), 4107-4117. doi:10.1039/c4cp04329d
DOI https://doi.org/10.1039/c4cp04329d
Keywords Pour point depressant polymers; Pour point transition; Hydrocarbon solvents; Wax crystal shape
Publisher URL http://pubs.rsc.org/en/content/articlelanding/2015/cp/c4cp04329d#!divAbstract
Copyright Statement ©2015 University of Hull
Additional Information This is a description of an article which has been published in: Physical chemistry chemical physics, 2015, v.17 at http://pubs.rsc.org/en/...4cp04329d#!divAbstract.

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