Synthesis and Characterisation of Water Soluble Polymer Drag Reducing Agents

Abstract

Dilute solutions of high molecular weight (HMW) polymers can reduce friction experienced by a fluid in turbulent pipe flow, greatly decreasing energy required for transfer of the solution. These polymers are known as drag reducing agents (DRA). Polyacrylamide (PAM), synthesised using free-radical inverse-emulsion polymerisation, is most commonly used in commercial aqueous applications. Restrictions on the acrylamide monomer have recently been imposed due to its carcinogenicity, furthermore, the use of inverse-emulsions, containing oil and surfactant, has a negative impact on the environment. The susceptibility of HMW polymers to mechanical degradation in turbulent flow quickly decreases their drag reducing efficiency (DRE), a major problem for current systems.

The aim of this project was to produce an effective water soluble polymer DRA with the following properties; 1) acrylamide free; 2) environmentally friendly; 3) oil/surfactant free; 4) mechanically stable; 5) economically viable. It was proposed that by the synthesis of HMW, acrylamide free, star polymers using Cu(0)-mediated polymerisation, effective water soluble drag reducing polymers with enhanced mechanical stability could be produced. An aqueous polymerisation method at ambient temperature would greatly reduce the environmental impact of the process.

In Chapter 1, a general background of the drag reduction phenomenon, potential mechanisms of action and key properties for effective drag reducing polymers is given. This chapter also introduces branched polymers and controlled radical polymerisation methods; in particular, Cu(0)-mediated techniques.

Chapter 2 focusses on the synthesis of water-soluble, poly(ethylene glycol) (PEG) containing macro-initiators (I4-S, I4-T and I2-S) for use in Cu(0)-mediated polymerisation reactions. By coupling a branching unit containing two potential initiation sites to each end of a PEG chain, multi-functional initiators for the synthesis of star polymers were produced and fully characterised using 1H and 13C NMR spectroscopy as well as MALDI-ToF mass spectrometry.

In Chapter 3, the polymerisation of tert-butyl acrylate (tBA) is conducted in DMSO utilising a several initiators; 4,4’-oxybis(3,3-bis(2-bromopropionate)butane (4AE), I4-S, I4-T and I2-S, and a simple catalyst system (Cu(0)/TREN). The reactions proceeded as a self-generating bi-phasic system due to the insolubility of PtBA in the solvent. A model initiator, methyl 2-bromopropionate (MBP), was also used to investigate the polymerisation of tBA further by introducing several changes in reaction conditions. The initiators were used to prepare polymer samples for drag reduction testing.

Chapter 4 describes the aqueous Cu(0)-mediated polymerisation of sodium acrylate (NaA) using the I4-S and I4-T macro-initiators. Kinetics study of the reaction using I4-T demonstrated the polymerisation proceeded via a free-radical mechanism. Although complete control over the reaction was not observed, a branched polymer was synthesised by the incorporation of the multi-functional macro-initiator in to the final product and HMW samples were generated for drag reduction testing.

The drag reducing properties of the PtBA and PNaA samples are tested in Chapter 5 using a pipe flow test rig. The PtBA samples were first hydrolysed using trifluoroacetic acid (TFA) to provide water soluble poly(acrylic acid) (PAA). For comparison, several commercially available HMW PAM (Praestol, PAM-6M), poly(ethylene oxide) (PEO-8M) and PAA (PAA-1M) samples were also measured. The results demonstrated that the branched PAA/PNaA samples were effective as DRAs. Furthermore, by cycling the polymer solution through the test rig the mechanical stability of the polymer samples was investigated. An increased resistance to mechanical degradation was observed for the star polymers when compared to linear analogues.

In Chapter 6 general conclusions and future perspectives for the work are discussed.