Crude oil producers have used pour point depressants with great success for several decades. However, chemical wax control packages can be plagued by crude oil specificity, large package treat rates, and waxy components that can be hard to apply.
This paper discusses what factors affect the performance of crude oil wax control additives and what contributes to crude oil specificity. This study investigated the effects of the wax control additives’ polymer backbone, pendant chains, and molecular weight on cold flow performance. The impact of the solvents used, the extent of the packages’ dilution and the effect of proper additive dosing is addressed.
Introduction
Handling and transporting crude represents a major challenge for crude oil producers. Transporting crude from its source to the refinery can involve sub-sea umbilicals, pipelines, intermediate storage tanks, and transportation vessels, all of which depend on the crude oil remaining liquid in the various environments and conditions of transportation.
Oil producers use several methods to ensure a liquid product and an uninterrupted flow of crude. These methods include heating, dilution with lighter stocks, and the preferred method, additizing with pour point depressants.
Pour point depressants have been used with great success for several decades. However, they can be plagued by crude oil specificity, large package treat rates, and waxy components that can be hard to apply1. This paper discusses what factors affect the performance of crude oil wax control additives and what contributes to crude oil specificity.
Crude Oil Pour Point Depressants.
The pour point of crude oil is the lowest temperature at which movement of the crude is observed. In this test, after preliminary heating, the crude is cooled at a specific rate and examined at intervals for movement. The lowest temperature at which movement of the specimen is observed is recorded as the pour point.
When the crude reaches its pour point, the sample is not frozen solid. What actually happens is that the paraffins in the crude crystallize and form a matrix of wax crystals. The wax crystal matrix holds the bulk of the liquid portion of the crude within it. By trapping the liquid portion within the wax crystal matrix, the wax crystals prevent the liquid in the crude from flowing and the sample no longer moves. Anything that disrupts the formation or the properties of the wax crystal matrix, such as pour point depressants, will affect the pour point of the crude.
Wax control additives, which include crude oil pour point depressants, are polymers with pendant hydrocarbon chains that interact with the paraffins in the crude and thus inhibit the formation of large wax crystal matrices, (Figure 1). The interaction retards wax crystal formation and growth, alters the paraffin's heat of crystallization and subsequently depresses the crude's pour point while affecting the size and shape of the wax crystals2.
Examples of the types of chemistries used as crude oil pour point depressants include ethylene vinyl acetate copolymers, vinyl acetate olefin copolymers, alkyl esters of styrene maleic anhydride copolymers, alkylesters of unsaturated carboxylic acids, polyalkylacrylates, polyalkylmethacrylates, alkyl phenols, and alpha olefin copolymers.
Crude Oil Specificity.
Wax control additives for crude oil are plagued by "specificity". Specificity is exhibited when a cold flow package will work only for a specific crude oil. Even slight changes in the crude oil wax composition can cause a reduction or a total loss of performance.
