Synthesis and characterization of sustainable Zinc Oxide nanoparticles for waxy crude flow assurance application

Wax precipitation in crude oil pipelines is a challenge to production. Current inhibitors raise concerns about toxicity and environmental impact. Hence, the need for sustainable alternatives arises. This study aims to explore the Vitex doniana-assisted synthesis, characterization, and application of zinc oxide nanoparticles as crude oil wax inhibitors. The nanomaterial was characterized using Fourier Transform Infrared Spectroscopy, Gas Chromatography-Mass Spectrometry, X-Ray Diffraction, Field Emission Scanning Electron Microscopy, Energy-Dispersive X-Ray Spectroscopy, and Thermogravimetric Analysis. The application of 0.04 wt% zinc oxide was evaluated based on wax appearance temperature, rheological properties, and wax-inhibition efficiency. Fourier Transform Infrared Spectroscopy analysis on the ethanolic Vitex doniana leaf extract confirmed the presence of alcohols, phenolics, carbonyls, aromatics, proteins, and polyphenols responsible for nanoparticle reduction and stabilization of the nanoparticle. Gas Chromatography-Mass Spectrometry of the extracts identified 18 distinct peaks in the organic profile, revealing a mixture of esters, aldehydes, acids, and heterocycles. The dominance of n‑hexane (34.9%) and glycidyl oleate (21.2%) highlights hydrocarbon and ester fractions as major components. X-Ray Diffraction analysis confirmed zinc oxide nanocrystals in a pure hexagonal wurtzite phase (a = 3.243 Å, c = 5.195 Å) with an average crystallite size of 36.1 nm and microstrain of 1.4 × 10 - ⁴, evidencing high crystallinity and suitability for optoelectronic and photocatalytic applications. Field Emission Scanning Electron Microscopy-Energy-Dispersive X-Ray Spectroscopy confirmed elemental composition of 64.3 wt% Zn, 20.6 wt% O, 15.1 wt% residual C, and trace N, evidencing high purity. Thermogravimetric Analysis indicated high thermal stability with minimal mass loss (1.308% at ~118.7 °C, 3.340% at ~227.9 °C, and 7.427% at ~391.8 °C; total mass loss < 12.1% up to ~800 °C). Rheological analysis showed a reduction in viscosity of up to 56.2% at 23 °C when crude oil was blended with zinc oxide nanoparticles. The Cross-Polarized Microscopy test showed that zinc oxide modified the wax structure, resulting in clustered morphology, suggesting a cocrystallization mechanism. The Arrhenius plot of viscosity showed that zinc oxide reduced the flow activation energy from 213.6 kJ mol - ¹ to 207.6 kJ mol - ¹, confirming the effectiveness of zinc oxide nanoparticles in improving crude oil flow by disrupting wax-crystal networks. These findings confirm the successful production of high-quality, thermally stable, and surface-functionalized zinc oxide nanoparticles, suitable for various industrial applications, especially waxy crude flow assurance.