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Methanol as hydrate inhibitor and hydrate activator

Abstract

Water is always following hydrocarbon streams and appear as separate phase in contact with hydrocarbons during the transport to the processing plant. After the first separator water will, as a minimum, be dissolved into hydrocarbon phases. Changed conditions of temperature and pressure in the fluids during processing can lead to condensation of water and possible problems of ice and hydrate formation. Historically, methanol has been the dominating chemical to add for prevention of the formation of solid water phases. The polarity in methanol is concentrated on the hydroxyl group and the fairly limited charge on the large methyl group makes this molecule into a surfactant when exposed to non-polar hydrocarbon phases. Adding a small amount of methanol to free liquid water will therefore lead to its enhanced concentration in the interfacial region of aqueous phase facing the hydrocarbons. This will severely hinder the formation of a hydrate film which blocks mass transport across the water/hydrocarbon interface. The relatively high interface concentration of methanol will also reduce interfacial free energy, therefore increasing the transport rate of hydrocarbons into the aqueous phase. Yet another effect of the local high concentration is increased local solubility of methane due to methanol hydroxyl groups disrupting water hydrogen bonding. In this work, we applied Molecular Dynamics simulations to investigate and illustrate these effects. We have found that adding 5% of methanol will boost the diffusion of methane through the interface by more than 30% compared to the reference system. The amount of methane accumulated in the aqueous phase was also significantly higher. This will likely also result in a significant increase in homogeneous and heterogeneous hydrate formation in these regions in case of methanol-stimulated system, and necessitate the application of classical nucleation theory. In particular, our analysis emphasized the fact that several different hydrates may form in this scenario. In case of homogeneous hydrate formation, there will theoretically be an infinite number of hydrate phases corresponding to concentrations spanning the range between methane’s solubility and its hydrate stability limit.

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Publication details

The article was received on 17 Apr 2018, accepted on 06 Aug 2018 and first published on 07 Aug 2018


Article type: Paper
DOI: 10.1039/C8CP02447B
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Methanol as hydrate inhibitor and hydrate activator

    B. Kvamme, J. Selvåg, N. Saedi and T. Kuznetsova, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP02447B

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