Polyethyleneimine-coated magnetic iron oxide nanoparticles for improvement of flow assurance
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This thesis aims to gain further insight into how the naphthenic acids(NA), which cause different problems with respect to flow assurance, canbe removed from the water phase. The main objective has been to testhow effective the polyethyleneimine functionalized magnetic iron oxidenanoparticles are to remove phenylacetic acid, which functioned as modelnaphthenic acid from water. The first part of the experimental work was concerned with the adsorp-tion of polyethyleneimine onto the nanoparticle surface. The zeta potentialsas function of pH were determined for both the iron oxide nanoparticlesand the polymer. From superimposing the isoelectric points for both syn-thesised and purchased iron oxide nanoparticles and comparing them to thezeta potentials for polyethyleneimine, pH 8 was chosen. Since the confidence for the true mean of the zeta potential was lowfor the functionalized iron (II, III) oxide core, using shaking overnight, thefunctionalization was done again with iron (III) oxide as core. In a newapproach the polyethyleneimine was added to the supernatant of iron (III)oxide after centrifugation followed by sonication. The new functionalized nanoparticles gave a high confidence for thezeta potentials and were attracted to an external magnetic field. The spe-cific surface area for the functionalized iron (III) oxide nanoparticles wasiiidetermined to be 62.5 ± 0.2 with 95% confidence, using gas adsorption.The composition with respect to mass was determined to be 6 wt% fromrunning a thermogravimetric analysis. Hence, the surface excess of poly-ethyleneimine was calculated to be 0.9 mg/m 2 . In the second part of the experiments, test adsorptions of the modelacid were conducted using the polyethyleneimine coated iron (III) oxidenanoparticles. At pH 8 the adsorption of the phenylacetic acid was negli-gible. A new calibration curve was made at pH 4.5. Two different valuesfor the surface excess were obtained. When concentration of the bulk acidprior to the adsorption was estimated from the calibration curve, the surfaceexcess was calculated to be 0.16 mg/m 2 , whereas 0.28 mg/m 2 was procuredusing the value from the balance. Since previous research has indicated that the chain length of the poly-mer determines the adsorption and the surface excess is independent of thechain length, it was concluded to continue using polyethyleneimine in thefunctionalization of iron (III) oxide, but with a lower average molecularweight.