Design and Synthesis of Low Molecular Weight and Polymeric Surfactants for Enhanced Oil Recovery

Surfactants are defined as molecules able to lower the surface (or interfacial)tension at the gas/liquid, liquid/liquid, and liquid/solid interfaces. Due totheir properties, they are typically employed as detergents, emulsifiers, dispersants,wetting and foaming agents. In chemical enhanced oil recovery (cEOR), surfactantsare used as flooding agents, alone or in combination with polymers, alkali, and morerecently nanoparticles, to increase the microscopic displacement efficiency. Froma chemical point of view, surfactants are amphiphiles, meaning that they bear intheir structure both hydrophilic and hydrophobic moieties. Some naturally occurringsurfactants exists, but the majority are synthetic. The availability of syntheticsurfactants, allows a big variety of structures and properties. In this chapter, the mainclasses of surfactants will be reviewed, with focus on those used or proposed foruse for chemical enhanced oil recovery. After a general introduction about surfactantsand their main structural and physico-chemical properties, specific aspects ofdesign and synthesis will be discussed. Particular emphasis will be given to the mostrecent developments, which includes zwitterionic, gemini and polymeric surfactants.Own work of the author of this chapter in the field of polymeric surfactants will behighlighted

Simulation of the carbon dioxide hydrate-water interfacial energy

Hypothesis: Carbon dioxide hydrates are ice-like nonstoichiometric inclusion solid compounds with importance to global climate change, and gas transportation and storage. The thermodynamic and kinetic mechanisms that control carbon dioxide nucleation critically depend on hydrate-water interfacial free energy. Only two independent indirect experiments are available in the literature. Interfacial energies show large uncertainties due to the conditions at which experiments are performed. Under these circumstances, we hypothesize that accurate molecular models for water and carbon dioxide combined with computer simulation tools can offer an alternative but complementary way to estimate interfacial energies at coexistence conditions from a molecular perspective. Calculations: We have evaluated the interfacial free energy of carbon dioxide hydrates at coexistence conditions (three-phase equilibrium or dissociation line) implementing advanced computational methodologies, including the novel Mold Integration methodology. Our calculations are based on the definition of the interfacial free energy, standard statistical thermodynamic techniques, and the use of the most reliable and used molecular models for water (TIP4P/Ice) and carbon dioxide (TraPPE) available in the literature. Findings: We find that simulations provide an interfacial energy value, at coexistence conditions, consistent with the experiments from its thermodynamic definition. Our calculations are reliable since are based on the use of two molecular models that accurately predict: (1) The ice-water interfacial free energy; and (2) the dissociation line of carbon dioxide hydrates. Computer simulation predictions provide alternative but reliable estimates of the carbon dioxide interfacial energy. Our pioneering work demonstrates that is possible to predict interfacial energies of hydrates from a truly computational molecular perspective and opens a new door to the determination of free energies of hydrates.We thank Pedro J. Pérez for the critical reading of the manuscript. We also acknowledge Centro de Supercomputación de Galicia (CESGA, Santiago de Compostela, Spain) and MCIA (Mésocentre de Calcul Intensif Aquitain) of the Universités de Bordeaux and Pau et Pays de l’Adour (France) for providing access to computing facilities. We thank financial support from the Ministerio de Economía, Industria y Competitividad (FIS2017- 89361-C3-1-P), Junta de Andalucía (P20-00363), and Universidad de Huelva (P.O. FEDER UHU-1255522), all three cofinanced by EU FEDER funds. J.A. acknowledges Contrato Predoctoral de Investigación from XIX Plan Propio de Investigación de la Universidad de Huelva and a FPU Grant (Ref. FPU15/03754) from Ministerio de Educación, Cultura y Deporte. J. A., J. M. M., and F. J. B. thankfully acknowledge the computer resources at Magerit and the technical support provided by the Spanish Supercomputing Network (RES) (Project QCM- 2018–2- 0042). Funding for open access charge: Universidad de Huelva / CBU

Xenon hydrate as an analog of methane hydrate in geologic systems out of thermodynamic equilibrium

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 20(5), (2019):2462-2472, doi:10.1029/2019GC008250.Methane hydrate occurs naturally under pressure and temperature conditions that are not straightforward to replicate experimentally. Xenon has emerged as an attractive laboratory alternative to methane for studying hydrate formation and dissociation in multiphase systems, given that it forms hydrates under milder conditions. However, building reliable analogies between the two hydrates requires systematic comparisons, which are currently lacking. We address this gap by developing a theoretical and computational model of gas hydrates under equilibrium and nonequilibrium conditions. We first compare equilibrium phase behaviors of the Xe·H2O and CH4·H2O systems by calculating their isobaric phase diagram, and then study the nonequilibrium kinetics of interfacial hydrate growth using a phase field model. Our results show that Xe·H2O is a good experimental analog to CH4·H2O, but there are key differences to consider. In particular, the aqueous solubility of xenon is altered by the presence of hydrate, similar to what is observed for methane; but xenon is consistently less soluble than methane. Xenon hydrate has a wider nonstoichiometry region, which could lead to a thicker hydrate layer at the gas‐liquid interface when grown under similar kinetic forcing conditions. For both systems, our numerical calculations reveal that hydrate nonstoichiometry coupled with hydrate formation dynamics leads to a compositional gradient across the hydrate layer, where the stoichiometric ratio increases from the gas‐facing side to the liquid‐facing side. Our analysis suggests that accurate composition measurements could be used to infer the kinetic history of hydrate formation in natural settings where gas is abundant.This work was funded in part by the U.S. Department of Energy, DOE [awards DE‐FE0013999 and DE‐SC0018357 (to R. J.) and DOE Interagency Agreement DE‐FE0023495 (to W. F. W.)]. X. F. acknowledges support by the Miller Research Fellowship at the University of California Berkeley. W. F. W. acknowledges support from the U.S. Geological Survey's Gas Hydrate Project and the Survey's Coastal, Marine Hazards and Resources Program. L. C. F. acknowledges funding from the Spanish Ministry of Economy and Competitiveness (grants RYC‐2012‐11704 and CTM2014‐54312‐P). L. C. F. and R. J. acknowledge funding from the MIT International Science and Technology Initiatives, through a Seed Fund grant. The simulation data are available on the UC Berkeley Dash repository at https://doi.org/10.6078/D1G67B.2019-11-0

Xenon Hydrate as an Analog of Methane Hydrate in Geologic Systems Out of Thermodynamic Equilibrium

Methane hydrate occurs naturally under pressure and temperature conditions that are not straightforward to replicate experimentally. Xenon has emerged as an attractive laboratory alternative to methane for studying hydrate formation and dissociation in multiphase systems, given that it forms hydrates under milder conditions. However, building reliable analogies between the two hydrates requires systematic comparisons, which are currently lacking. We address this gap by developing a theoretical and computational model of gas hydrates under equilibrium and nonequilibrium conditions. We first compare equilibrium phase behaviors of the Xe·H₂O and CH₄·H₂O systems by calculating their isobaric phase diagram, and then study the nonequilibrium kinetics of interfacial hydrate growth using a phase field model. Our results show that Xe·H₂O is a good experimental analog to CH₄·H₂O, but there are key differences to consider. In particular, the aqueous solubility of xenon is altered by the presence of hydrate, similar to what is observed for methane; but xenon is consistently less soluble than methane. Xenon hydrate has a wider nonstoichiometry region, which could lead to a thicker hydrate layer at the gas‐liquid interface when grown under similar kinetic forcing conditions. For both systems, our numerical calculations reveal that hydrate nonstoichiometry coupled with hydrate formation dynamics leads to a compositional gradient across the hydrate layer, where the stoichiometric ratio increases from the gas‐facing side to the liquid‐facing side. Our analysis suggests that accurate composition measurements could be used to infer the kinetic history of hydrate formation in natural settings where gas is abundant

Molecular Mechanisms by which Tetrahydrofuran Affects CO₂ Hydrate Growth: Implications for Carbon Storage

Gas hydrates have attracted siginifcant fundamental and applied interests due to their important role in various technological and enviromental processes. More recently, gas hydrates have shown potential applications for greenhouse gas capture and storage. To facilitate the latter application, introducing chemical additives into clathrate hydrates could help to enhance hydrate formation/growth rates, provided the gas storage capacity is not reduced. Employing equilibrium molecular dynamics, we study the impact of tetrahydrofuran (THF) on the kinetics of carbon dioxide (CO₂) hydrate growth/dissociation and on the CO₂ storage capacity of hydrates. Our simulations reproduce experimental data for CO₂ and CO₂+THF hydrates at selected operating conditions. The simulated results confirm that THF in stoichiometric concentration does reduce CO₂ storage capacity. This is not only due to the shortage of CO₂ trapping in sII hydrate 5^{12} cages, but also because of the favored THF occupancy in hydrate cages due to preferential THF−water hydrogen bonds. An analysis of the dynamical properties for CO₂ and THF at the hydrate-liquid interface reveals that THF can expedite CO₂ diffusion yielding a shift in the conditions conducive to CO₂ hydrate growth and stability to lower pressures and higher temperatures compared to systems without THF. These simulation results augment literature experimental observations, as they provide needed insights into the molecular mechanisms that can be adjusted to achieve optimal CO₂ storage in hydrates

Effect of impurities on CO2 stream properties

CO2 obtained by capture process (such as post combustion, pre combustion and oxy-fuel combustion) is not 100% pure and may contain impurities such as H2, Ar, CO, H2S and water. The presence of such impurities in CO2 stream can lead to challenging flow assurance and processing issues. The gaseous CO2-rich stream is generally compressed to be transported as liquid in order to avoid two-phase flow and increase the density of the system. One aim of this work is to evaluate the effect of impurities on the physical properties of CO2 such as density, viscosity, speed of sound and on the phase behaviour of such systems. Speed of sound and isothermal compressibility of CO2/impurities mixtures were measured at condition above the saturation curve and temperature from 268.15 to 301.15 K. A new volume correction was implemented to the Peng-Robinson equation of state in order to minimise the error associated with the isothermal compressibility prediction. Moreover, density and viscosity are two of the most important properties in transport properties. Therefore, the effect of impurities on density and viscosity were experimentally and theoretically investigated in liquid CO2 and liquid CO2/impurities systems. The viscosity measurements were performed using in-house capillary tube apparatus in the range from 280 to 343.15 K and pressure up to 40 MPa. Two viscosity models, LBC and Pedersen, were modified in order to predict the viscosity of both pure and impure CO2. The density measurements were carried-out using an Anton Paar densitometer in both liquid and supercritical regions from 283.15 to 423.15 K. In order to improve the accuracy of EOSs in density of CO/impurities systems, a new modification was developed based on mixing the volume obtained from EOSs (SRK, PR and VPT) and the volume obtained from CO2-MBWR. The presence of water may result in ice and/or gas hydrate formation and cause blockage of pipelines. Several measurements were also conducted to evaluate the hydrate stability zone of pure and rich CO2 systems in free water. A thermodynamic model based on the VPT EOS was adopted to predict the hydrate phase of the systems. In addition, few saturation measurements of synthetic alkane mixture plus pure or impure CO2 were performed at 344.3 K in order to investigate the effect of impurities on the saturation pressure of CO2/alkane system. IFT and swelling factor properties on CO2/n-decane mixture were investigated at 310.95 K from ambient to near the minimum miscibility pressure of the mixture. The experiments were extended to cover the presence of impurities on the properties at the same range of pressure. Minimum miscibility pressure of the systems was estimated by both Vanishing Interfacial Tension method and multiple-mixing-cell calculation

Gas hydrates in sustainable chemistry

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hassanpouryouzband, A., Joonaki, E., Farahani, M. V., Takeya, S., Ruppel, C., Yang, J., English, N. J., Schicks, J. M., Edlmann, K., Mehrabian, H., Aman, Z. M., & Tohidi, B. Gas hydrates in sustainable chemistry. Chemical Society Reviews, 49(15), (2020): 5225-5309, doi:10.1039/c8cs00989a.Gas hydrates have received considerable attention due to their important role in flow assurance for the oil and gas industry, their extensive natural occurrence on Earth and extraterrestrial planets, and their significant applications in sustainable technologies including but not limited to gas and energy storage, gas separation, and water desalination. Given not only their inherent structural flexibility depending on the type of guest gas molecules and formation conditions, but also the synthetic effects of a wide range of chemical additives on their properties, these variabilities could be exploited to optimise the role of gas hydrates. This includes increasing their industrial applications, understanding and utilising their role in Nature, identifying potential methods for safely extracting natural gases stored in naturally occurring hydrates within the Earth, and for developing green technologies. This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade. Challenges, limitations, and future perspectives of each field are briefly discussed. The overall objective of this review is to provide readers with an extensive overview of gas hydrates that we hope will stimulate further work on this riveting field.A. H. and K. E. were partially supported by funding from UKRI-EPSRC (grant number EP/S027815/1). C. R. was partially supported by DOE-USGS Interagency agreement DE-FE0023495. C. R. thanks L. Stern and W. Waite for insights that improved her contributions. E. J. is partially supported by Flow Programme project sponsored by Department for Business, Energy and Industrial Strategy (BEIS), UK. Any use of trade, firm or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government

Investigation of Formation and Dissociation Mechanisms of Pure and Mixed CO2 Hydrates in the Presence of Thermodynamic and Kinetic Promoters using Molecular Dynamics Simulation

CO2 hydrates as non-flammable solid compounds would contribute to many industrial processes. Toward developing substantial applications of CO2 hydrates, molecular dynamics (MD) simulations can aid to understand their characteristics and mechanisms involved so that complete the laboratory experimental results at a macroscopic level. In this regard, understanding the promotion mechanisms of promoters on the hydrate formation and dissociation at the molecular level would assist in either establishing feasible processes or finding more efficient promoters