Electrochemical sensor for the detection of scaling ions in formation water

Crapnell, Robert David

Abstract

This thesis aims to develop appropriate sensing chemistry for the electrochemical detection of alkaline-earth metal ions in formation water. Accordingly, the first chapter outlines the relevance of this work and gives an overview of the methods currently used for the determination of alkaline-earth metals in aqueous conditions. The second chapter then details the electrochemical concepts that underpin the subsequent results and the third chapter outlines the experimental techniques used throughout this work.
The reliable measurement of peak potentials in non-aqueous conditions is challenging. IUPAC recommends the use of an internal standard, typically the ferrocene | ferricinium redox couple. Chapter 4 investigates the reliability of this system and finds that chloride ions present in the system interfere with the ferrocene. This chapter shows that the ferrocene | ferricinium redox couple can be used as an internal standard in non-aqueous environments alongside a quasi-reference electrode; however, the exact solution composition and conditions must be considered. Therefore, any result obtained must be thought of in terms of the system, where each component must be scrutinised.
Chapter 5 focusses on the interaction of chlorquinaldol and broquinaldol with alkaline-earth metals as a route for detection. Firstly, the voltammetric response of the two quinaldols is characterised in equimolar DMSO/H2O with a DISP2 reaction process proposed for both due to the decrease in apparent diffusion coefficients with increasing concentrations. Both ligands produced an increase in the Neff values in the presence of barium ions above 10 mM. It is also demonstrated that chlorquinaldol is more sensitive to barium ions over strontium and calcium ions.
The use of compounds soluble in aqueous conditions allows for the use of a reliable commercial Ag | AgCl reference electrode. Ferrocenemethanol is a water-soluble derivative of ferrocene that interacts with thiols. Chapter 6 explores the EC’ electrode mechanism that is present for ferrocenemethanol and tiopronin. It shows how the turnover number can be manipulated by changing the solution pH in order to increase the reactivity of the tiopronin. The introduction of barium ions to the system (above 10 mM) is shown to reduce the turnover number; this allows for their determination but not to levels low enough for the desired application of this work.
The first two sensing methodologies explored utilised amperometric changes to determine the presence of alkaline-earth metal cations. Chapter 7 utilises an entirely novel approach to ion sensing by using changes in both the peak potential and current to successfully determine the concentration of alkaline-earth metal ions. It looks at the voltammetric response of disodium rhodizonate which is a water soluble compound that can bind with barium to produce a solid precipitate. This complexation is shown to produce an oxidative shift in the reductive peak potentials and a decrease in the peak current. The system exhibits the ability to detect alkaline-earth metal cations in this way at pH 8.5 (sea water), pH 7 (formation water) and at 35 % salinity (sea water). A 3-Dimensional model is produced that allowed for the prediction of barium ion concentrationn in samples containing strontium ions as an interfering substance. This model produced good results with every test sample producing a peak potential within 5 mV of the true value.

Citation

Crapnell, R. D. (2018). Electrochemical sensor for the detection of scaling ions in formation water. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4628886

• Thesis Type: Thesis
• Deposit Date: Apr 22, 2024
• Publicly Available Date: Apr 22, 2024
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4628886
• Award Date: Feb 1, 2018