Scotognella, Vincenzo (2025) Transportation of hydrocarbons in pipelines: polyolefin additives for reducing turbulent flow. [Tesi di dottorato]

Documento PDF Scotognella_Vincenzo_PhD_XXXVIII_Thesis_FINAL.pdf Visibile a [TBR] Amministratori dell'archivio Download (2MB) | Richiedi una copia

Abstract

‘Drag-Reducing Agents’ (DRAs) are additives which decrease the turbulence of fluids in pipelines. A most important specific application concerns the long-distance transport of crude oil, for which preferred DRAs are Ultra-High Molecular Weight Higher Poly(Alpha-Olefin)s (UHMW-HPAOs) such as, e.g. poly(1-hexene), poly(1-octene) or poly(1-decene), neat or in mixtures. The addition of one such UHMW-HPAO already at the level of few parts per million (ppm) changes the flow from turbulent to laminar up to high flow rates, thus allowing to enhance the flow while decreasing the pumping power, with significant energy and cost savings. Intriguingly, the UHMW-HPAO materials currently on the market for DRA applications are mainly produced with 2nd-generation TiCl3-based Ziegler-Natta Catalysts (ZNC), likely due to delayed innovation in a compartment that represents a small niche of the overall polyolefin industry. The general aim of this PhD Thesis, that was carried out in collaboration with the Research Center of Lamberti S.p.A. (Albizzate, VA), was to explore the scope and opportunities offered by modern MgCl2-supported ZNC formulations. In particular, fourth generation MgCl2/TiCl4/DBP precatalysts (DBP = Dibutylphthalate) with or without particle morphology control were activated with a variety of trialkyl-Al cocatalysts and screened in a state-of-the-art High-Throughput Experimentation platform to explore all relevant physical and chemical polymerization variables. 1-Hexene and 1-Decene were used as representative higher alpha-olefin (HAO) monomers. The first important goal was to design and implement a catalyst preparation protocol suited to a slurry technology in which polymerization necessarily occurs in non-agitated batch reactors. By applying an original prepolymerization step entailing a smart combination of precatalyst and alkyl-Al activator in the presence of proper modifiers, a catalyst slurry featuring a negligible tendency to undergo sedimentation for several hours in the liquid HAO was obtained. This slurry could be dispensed similarly to a truly homogeneous catalyst, and maintained its productivity for a long time likely due to the lack of Ti-Alkyl bonds amenable to Beta-H elimination processes initiating catalyst decomposition. The next objective was to identify the best combination of catalyst system and polymerization conditions to produce UHMW-HPAO samples with high DR efficiency. A thorough molecular kinetic screening led to conclude that optimal results require a controlled morphology precatalyst and a trialkyl-Al cocatalyst modified with an alkoxysilane with modest steric demand. When tested at Lamberti, the thus prepared UHMW-HPAO samples demonstrated excellent DRA properties, outperforming the commercial benchmarks. Finally, in a research stage carried out at the Department of Material Analytics and Characterization at the Fraunhofer Institute for Structural Durability and System Reliability (LBF) in Darmstadt (Germany), advanced HT-GPC methods were utilized to measure the average values of Mn and Mw for selected UHMWHPAO samples and correlate the results to the observed DRA performance. The conclusion was that values of Mn in excess to 1 MDa, in combination with low Mw/Mn ratios (<2.5, indicatively), correspond to optimum DR behavior. The PhD project was a sophisticated and challenging piece of scientific and technological work, combining fundamental and applied concepts of heterogeneous organometallic catalysis, polymer reaction engineering and polymer science and technology. Notwithstanding the difficulties, the work was highly successful, and laid the foundations for the subsequent step of pre-industrial upscaling at Lamberti.

Downloads

Actions (login required)

Modifica documento