Application Of Nanocomposites For CO2 Gas Barrier Properties In Gas Pipelines

Abstract

Corrosion is a major problem facing humanity both at industrial level as well as in domestic applications. This problem has particularly plagued the oil and gas industry since the large-scale production of fossil fuels began after the Industrial Revolution. Majority of the corrosion-related damages in the oil and gas industry are in longdistance natural gas transmission pipelines, as natural gas inherently contains acid gases (mainly CO2 and H2S) as impurities. These gases can combine with moisture in the atmosphere to form acids which accelerate the corrosion rate. Corrosion has led to both financial losses as well as threat to human health and safety due to the failure of material and ensuing accidents due to failure. To overcome this menace, different strategies have been employed. Two of the most important strategies include protective coatings and cathodic protection. Cathodic protection strategy has been largely discontinued in oil and gas industry due to the high operational and maintenance costs. On the other hand, protective coatings are a much cost-effective and long-lasting corrosion prevention strategy. Different types of coatings have historically been used; some of them include coal tar asphalt, three-layer polyethylene, fusion-bonded epoxy coatings. More recently, two-dimensional (2D) materials based polymer nanocomposites have emerged as an even less costly and more long-lasting alternative to the conventional protective coatings. The mechanism by which these coatings prevent corrosion is by avoiding intimate contact between acid gases and pipeline material. This is achieved by the inclusion of 2D materials; which due to their high aspect ratio act as impermeable barriers to gas flow, thus greatly reducing the rate of corrosion. Hexagonal boron nitride (h-BN) nanosheets have proven to be an advanced nanofiller for use in gas barrier enhancement of polymer matrices for a variety of applications. Although the use of h-BN nanosheets has not been explored for corrosion protection in particular, but the excellent gas barrier properties imparted by incorporating very low loading of the nanosheets in polymers makes them ideal candidates for this application. However, nanosheets have historically been synthesized by using toxic solvents including N-methyl-2-pyrrolidone (NMP) and only limited work has been done on using green solvent. Moreover, cellulose acetate has been utilized for the fabrication of membranes for different applications. xviii However, CA-based nanocomposites have not been widely used for corrosion protection. Therefore, the objective of this PhD dissertation is to fabricate CA-based polymer nanocomposite membranes using solution casting method. Moreover, h-BN nanosheets are prepared using conventional solvent such as NMP as well as a green solvent, i.e. isopropanol (IPA). This is done to enhance the gas barrier and corrosion protection properties of cellulose acetate and its application for prevention of corrosion of mild steel. Of all the nanocomposite samples prepared in this work, optimum corrosion protection performance and highest CO2 gas barrier enhancement of 91.67% and 99.84% respectively was observed with CA-based nanocomposite membranes containing 0.01% by weight h-BN nanofiller with the nanosheets being prepared using NMP as the exfoliation medium. Furthermore, these samples also demonstrated high corrosion protection efficiency of up to 82.14% even after six weeks of immersion in corrosive media. On the other hand, nanosheets prepared using green solvents provided high gas barrier performance of 99.91%, but the corrosion protection efficiency was significantly lower (91.35% as compared to uncoated steel) than that of nanocomposites containing NMP-based h-BN nanosheets. This is exemplified by the contact angle measurements which show that nanocomposites based on h-BN nanosheets prepared by green solvents have higher hydrophilicity and will therefore be less viable for use in humid environments as may be encountered in natural gas pipelines. Nevertheless, the results obtained are exceptional and unprecedented, and these results coupled with the extensive research data provided in this research work serves as a roadmap for the development of advanced, long-lasting and more efficient corrosion protective coating materials. Furthermore, these results also aid in fulfilling the United Nations Sustainable Development Goals (SDG), specifically SDG9 which emphasizes the need for durable infrastructure with sustainable industrialization using innovation. In this regard, this work is pertinent to the societal needs and demands of industry