Evaluation of Paraffin Wax Inhibitors: An Experimental Comparison of Bench-Top Test Results and Small-Scale Deposition Rigs for Model Waxy Oils

Abstract

The performance of paraffin inhibitors from several chemical families was evaluated using two model waxy oils in bench-top tests such as cloud point and pour point, and in small-scale deposition rigs using a cold finger and a flow loop. In addition, rheological characterization of the inhibited systems was conducted to provide additional insights into the function of the paraffin inhibitors. Similarities and differences in the response of the model oils to the paraffin inhibitors are discussed along with the correlations between the results from bench-top tests and the observed wax deposit inhibition performance.The model waxy-oils were formulated using blends of commercially available waxes dissolved in a paraffinic solvent or a mixture of paraffinic and aromatic solvents. The wax blends were chosen to represent a broad range of carbon number distributions including one highly polydisperse distribution with an extended distribution of high carbon number waxes exceeding C50. Candidate paraffin inhibitors were initially evaluated for their impact on cloud point and pour point in these model oils. Subsequent testing of the inhibited systems included rheological characterization over a range of temperatures, cold finger deposition tests and flow loop deposition tests in a pipe-in-pipe geometry. All results are compared to the baseline results for the uninhibited model waxy oils.While changes in cloud point and pour point gave a good indication that a particular paraffin inhibitor was impacting the wax crystallization process, this did not guarantee a significant reduction in deposits of the inhibited system. Moreover, the experimental conditions used in the small-scale deposition tests also affected the observed performance of paraffin inhibitors, indicating that temperature gradients (i.e., oil temperature and coolant temperature) must be optimized to achieve the highest discriminating power. This study highlights the degree of correlation and the areas of departure between bench-top test results and the main objectives of deposit reduction, and yield stress reduction in flowing systems. It also discusses the advantages and risks of using only the bench-top test results for the selection of paraffin inhibitors.

Mitigating Wax Deposition From Crude Oils: Correlations Between Physical-Chemical Properties of Crude Oils and the Performance of Wax Inhibitors

“…The performance of these commercially-available additives has been previously evaluated using model waxy oils [1]. Table 1 indicates the chemical type for each additive studied.…”

“…Figure 1 shows the broad carbon number distribution of the paraffin wax mixture used to formulate the oils, which comprise hydrocarbons from C 18 to C 50 , where normal alkanes are major constituents (~80 % by weight). Additional details of the formulation were reported in a previous work [1].…”

“…For these studies, a mixture of paraffin waxes was dissolved in three types of crude oils and their low temperature crystallization behavior was characterized in terms of the wax appearance temperature (WAT), pour point, steady shear viscosity and yield stress. The observed behavior was compared to that observed for a model waxy fluid, formulated by dissolving the same paraffin wax mixture in a blend of industrial solvents [1]. Some properties that reflect the differences in physical and chemical properties of the crude oils with respect to the model fluid solvent are presented in Table 4.…”

“…The pour point was also determined, using the robotic tilt method specified by the method ASTM D6892 [15]. Letter codes of additives were made to match those used in our previous paper [1]. (7) crude oils were selected to study the effects of the chemical and physical properties of crude oils on the crystallization behavior of refined paraffin waxes in the presence of wax inhibitors.…”

“…First, the effects of the type of fluid was studied by dissolving refined paraffin waxes in non-waxy crude oils-here termed ЉdoctoredЉ crude oils-of different properties and comparing the wax appearance temperature and pour point of the doctored crude oils to those determined for a model waxy fluid used in previous studies [1]. After treating the doctored crude oils with wax inhibitors, the ability of the chemicals to depress pour point was examined.…”