Integrated process and solvent design for C0 2 removal from natural gas

Carbon dioxide (C02) capture is of crucial importance for the environment. A large number of countries agreed on the fact that greenhouse gases, especially C02 can have harmful effects leading to major climate changes; in particular, since the ratification of the Kyoto Protocol in 1997 it is apparent that action should be taken. In this context, new solutions are necessary to reduce carbon dioxide emissions. In this work, we present the new challenge that the Kyoto Protocol represents for the petroleum industry, especially considering that large amount of C02, which would be captured from large C02 emissions sources, could be reinjected in oil and gas reservoirs. Re-injection will lead to increased productions of oil and gas, which can compensate the cost of C02 capture. Unfortunately, the oil and gas produced will be increasingly richer in C02 and specific absorption processes must be designed to address this problem. Such processes should show flexibility with respect to the feed C02 content. Physical absorption processes are currently the most promising option, as they are more economical for removing large quantities of C02. A cryogenic absorption process (Ryan-Holmes) using n-butane as a solvent demonstrated the advantages of using alkane-based solvents. The adaptation of the Ryan-Holmes process to high temperatures offers real potential. This requires the identification of the optimal alkane solvent. Integrated process and solvent design using state of the art thermodynamics, process modelling and optimisation can bring significant new benefits. Advanced thermodynamic models such as SAFT-VR can be used advantageously in this study as they have proven successful for predicting the phase behaviour (VLE) of a large range of n-alkane/C02 mixtures [A. Galindo and F.J. Bias, J. Phys. Chern. B, .2002, 106, 4503], and for a large range of pressure and temperature. The SAFT-VR equation of state has been used to study mixtures of C02 and methane in detail, and it is found that it describes accurately both supercritical and coexistence states. This equation of state has been implemented within gPROMS software, allowing its use for process modelling. The units used in a separation have been modelled with mass and energy balance equations. The dimensioning of the units has also been performed as the sizes of the units are required to estimate their cost. A complete cost estimation has been carried out in order to estimate the capital and operating expenses of the plant. We have applied this new integrated approach to process and solvent design to identify the most appropriate flowsheet to perform profitable capture of C02 for feed C02 contents from 10% to 70%. We have also carried out a sensitivity study which shows that changes in the thermodynamic model parameters has a limited impact on the optimal process. The effect of the presence of small quantities of ethane in the feed has also been evaluated on the optimal flowsheet, and we find that ethane is co-absorbed with C02. Finally, we show that it is possible to design a process that covers the full range of feed C02 contents [10%, 70%], and we give the values of the control variables and the economics performance as a function of the feed C02 content.Imperial Users onl

Phase behaviour studies related to biodiesel production using supercritical methanol

Biodiesel is a promising renewable and sustainable fuel that can replace fossil fuels. Among the different techniques used to produce biodiesel, the transesterification process is currently the preferred method. The conventional transesterification process is based on acid-base catalysis, but this technique has many drawbacks including a requirement for high-purity feedstocks, and costly pre-treatment and downstream processes. A recent alternative process, using a supercritical alcohol (preferably methanol) without a catalyst, may offer some advantages. This process can utilise a wide range of potential feedstocks (especially wastes), shows high production efficiency, and requires only simple post-processing. However, this technique requires conditions of high temperature and high pressure which increase the utility costs and may restrict the economic feasibility and sustainability of the process. In order to fully explore these issues and to optimise the process conditions, better understanding of the phase behaviour of the mixtures involved in the biodiesel process is required. The components of interest include fatty acids, esters alcohols and co-solvent such as carbon dioxide and the conditions include high pressures and wide ranges of temperature. Phase equilibrium studies on systems relevant to biodiesel production with supercritical methanol available in the literature are very limited. The principal focus of this project is the experimental investigation of the phase behaviour of representative mixtures with small molecular chains, which exist during biodiesel production, over wide ranges of temperatures and pressures. In addition to the experimental work, the research will include both modelling works on the mixtures of interest supported by a simulation for the process using gPROMS, a simulation tool developed by Process Systems Enterprise (PSE) company. In this project, new fluid-phase equilibrium measurements have been carried out on two relevant representative binary systems: (methyl propanoate + carbon dioxide) and (butanoic acid + carbon dioxide) using a high-pressure quasi-static analytical apparatus with compositional analysis using a gas chromatography. The measurements for the (methyl propanoate + carbon dioxide) mixture were made along six isotherms at temperatures from (298.15 to 423.15) K and at pressures up to near the mixture critical pressure at each temperature while for the mixture (butanoic acid + carbon dioxide) the measurements were made along eight isotherms at temperatures from (323.13 to 423.2) K and pressures up to the mixture critical pressures. Vapour-liquid equilibrium (VLE) data obtained for the mixtures have been compared with the predictions of SAFT- Mie model, a group-contribution version of the Statistical Associating Fluid Theory (SAFT). The group interaction parameters in SAFT- Mie reported in literature have been revised by fitting to the new experimental VLE data. After parameters optimisation, the model was found to be in a good agreement with the measured VLE data for both bubble and dew points. The experimental data were also compared with the description of Peng Robinson equation of state (PR EoS) combined with the classical one-fluid mixing rules integrating one temperature-independent binary interaction parameter for (methyl propanoate + carbon dioxide) system and two temperature-independent binary interaction parameters for (butanoic acid + carbon dioxide) system. The results after tuning show that the PR EoS can also predict well the system measured data, except in the critical regions in which PR EoS shows overprediction. Furthermore, the phase equilibria of (methyl propanoate + propionic acid + carbon dioxide), (tert-butanol + water + carbon dioxide) and (toluene + water + carbon dioxide) ternary systems were studied by the means of the high-pressure quasi-static analytical apparatus. Compositions of present phases coexisting in vapour-liquid equilibrium (VLE) for (methyl propanoate + propionic acid + carbon dioxide) mixture were measured along six isotherms at temperatures from (323.12 to 423.11) K and pressures from (1 to 20) MPa at equal feed molar ratio of (methyl propanoate + propionic acid). Phase behaviour measurements were also collected at different compositions of the mixture (methyl propanoate + propionic acid) at fixed temperatures and pressures. Compositions of coexisting phases of the ternary system (tert-butanol + carbon dioxide + water) have been obtained along five isotherms at temperatures of (283.2, 298.18, 323.13, 373.10 and 423.17) K and at pressures of (4.0, 8.0, 12.0 and 18.0) MPa with different known feed compositions of (tert-butanol + water) while the phase behaviour of the system (toluene + water + carbon dioxide) was investigated along four isotherms at temperatures from (338.15 to 413.15) K and pressures up to the upper critical end point (UCEP). The data obtained for the ternary mixtures have been compared with the descriptions of SAFT- Mie and PR equation of states. Other cross interactions available in biodiesel systems such as (COOH - CH3OH), (OH_Gl - CH3OH), (CO2 - CH=), (CH3OH - CH=), (COOH - CH=) and (H2O - CH=) were estimated in this work by regression to fluid-phase behaviour data published in literature. The comparison between the predictions of SAFT- Mie reported in literature and those of SAFT- Mie after refining the parameters were shown. Preliminary designs of one-step process (transesterification) and two-step processes (hydrolysis and esterification) for biodiesel production under supercritical conditions were suggested and simulated using gPROMS ProcessBuilder software. The CO2 co-solvent effect on the one-step process based on literature data was also examined by a process flowsheet. The research including new phase behaviour measurements, modelling and gPROMS simulation is expected to contribute to optimisation of biodiesel production processes.Open Acces

Physical Solubility of Carbon Dioxide in Decane (C10H22) Solvent from a CO2/CH4 System

An investigation of the potential removal of Carbon Dioxide (CO2) from a gas stream containing CO2 and methane (CH4) using n-decane (C10H22) as the physical solvent is presented. Physical absorption has been identified as one of the most effective ways to capture CO2 from natural gas streams as it can handle high pressures and high concentrations of CO2. The study is divided into two parts – the solubility experiment, and a simulation of the process in Aspen HYSYS. The solubility experiments were conducted to predict the solubility of CO2/CH4 at different temperatures and pressures using a high pressure gas solubility cell. The simulation was carried out at different pressures up to 60 bar, for various gas compositions. Two thermodynamic models were selected and analyzed, the PR-EOS and the SRK-EOS. Subsequently, the data obtained was used to estimate Henry’s constant for CO2. The simulation results for n-decane showed an increase in CO2 capturing capacity at lower temperatures and at higher pressures, which is in agreement with Henry’s law, and the absorption capacity was found to be selectively higher for CO2 than for CH4. Based on the experiment results; there was more absorption of CO2 and CH4 at lower temperatures and at a higher pressure, and that the absorption was selectively higher for CO2 than it was for CH4. Therefore, the simulation and the solubility experiment findings show that n-decane is a potential candidate as a physical solvent for the application of the removal of CO2 from natural gas

CO₂ capture using ionic liquids: thermodynamic modeling and molecular dynamics simulation

Global climate change is happening now, and the average temperature of Earth is rising. Several evidences show that one of the main reasons for global warming is the increased concentration of greenhouse gases (GHGs) in the atmosphere, particularly carbon dioxide (CO₂). CO₂ is mostly producing from burning fossil fuels. One of the effective strategies to reduce CO₂ emissions is implementing carbon capture in fossil fuel power plants. Current post-combustion carbon capture techniques typically employ amine-based solvents, such as monoethanolamine (MEA), for the absorption of CO₂. Although alkanol amines have an acceptable absorption capacity, their high vapor pressure, solvent loss during desorption, and high corrosion rate make amines absorption plants energy-intensive. In recent years, Ionic Liquids (ILs) have been emerged as promising alternative solvents for physisorption and chemisorption of acid gases due to their unique physiochemical properties, including negligible vapor pressure, high thermal stability, tunability, and being environmentally safe. ILs require to be screened based on technical, economical, and environmental aspects. The main challenges of using ILs are increasing CO₂ capture capacity of ILs, and detailed understanding of the diffusivity of CO₂ in ILs, the effect of additives in solubility, selectivity features of ILs, phase behavior of gas-IL systems, and absorption mechanism. These challenges can be addressed using either experiment, thermodynamic modeling, and/or molecular simulations. In this study, the potential of the screened imidazolium-based ILs is investigated using thermodynamic modeling. The extended Peng–Robinson (PR) and Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) EOSs are implemented to evaluate the solubility and selectivity of CO₂ in pure ILs and their mixture with water and toluene. The effects of water and toluene on solubility and viscosity of ILs are investigated. Low concentrations of water (< 1 wt%) do not affect solubility; however, with increasing water concentration, the solubility of CO2 is decreased. On the other hand, with increasing water content, the IL viscosity significantly decreases, which is in the favor of using viscous ILs for CO₂ separation. In this thesis, Molecular Dynamics (MD) simulation is performed to determine the properties of ILs ([Bmim][BF₄] and [Bmim][Ac]), their structures, and molecular dynamics. A great agreement is noticed between the density and viscosity of the studied ILs from MD simulations and experimental data, indicating the accuracy of our simulation runs. This study also includes the effect of temperature and anion type on the structuring of ions and their self-diffusivities. Bulk systems of ILs and CO₂ are studied to evaluate the influence of temperature and types of ions on the diffusivity of CO₂ in the solvent as well as structural characteristics. A comprehensive analysis of the characteristics of the interface of IL/CO₂ is performed to explore species distribution, gas behavior at the interface, and molecule orientation. At the interface, CO₂ creates a dense layer which interrupts the association of cations and anions, leading to a decrease in the surface tension. In addition, a comprehensive study on hydrophilic IL, 1-Butyl-3-methylimidazolium acetate or [Bmim][Ac], is conducted to evaluate the thermophysical properties, excess energy, structure, and dynamic characteristics of IL/Water and IL/Water/CO2 systems, using MD simulation approach. The effect of water on radial distribution functions, coordination numbers, water clusters, hydrogen bonding, and diffusivity coefficients of the ions is assessed. The presence of water in IL mixture, even at high concentrations of water (>0.8 mole fraction), increases the diffusivity of cation, anion, water, and CO2 molecules in the mixture due to hydrophilicity of [Bmim][Ac] IL. MD simulations generate reliable and accurate results while dealing with systems including water, CO₂, and IL for carbon capture. In this thesis, novel and robust computational approaches are also introduced to estimate the solubility of CO₂ in a large number of ILs within a wide range of temperatures and pressures. Four connectionist tools- Least Square Support Vector Machine (LSSVM), Decision Tree (DT), Random Forest (RF), and Multilinear Regression (MLR)- are employed to obtain CO₂ solubility in a variety of ILs based on thermodynamic properties and Quantitative Structure-Activity Relationship (QSPR) model. Among different types of descriptors, the most important input variables (e.g., Chi_G/D 3D and Homo/Lumo fraction (anion); SpMax_RG and Disps (cation)) are selected using Genetic Algorithm (GA)-MLR method. A great agreement between the predicted values and experimental measurements is attained while using RF and DT techniques developed based on descriptors and thermodynamics properties. The structural descriptors-based models are more accurate and robust than those built on critical properties

Development of coarse-grained force fields from a molecular based equation of state for thermodynamic and structural properties of complex fluids

In spite of the vast array of modelling techniques and force fields available, the study of the phase behaviour, structure, microstructure, and dynamics of mixtures remains a challenging task. A systematic coarse-graining (CG) methodology is employed in this thesis involving the parameterisation of force fields using a top-down approach, by effectively describing a large number of target macroscopic thermodynamic states with a rigorous molecular-based equation of state. A recent incarnation of the Statistical Associating Fluid Theory (SAFT-gamma) is used. The underlying force field is based on the Mie intermolecular potential, which is a generalised form of the Lennard-Jones potential with a variable and versatile form of the repulsive and attractive interactions. The coarse-grained force fields developed in this manner are used directly in Molecular Dynamics simulations in order to explore the dynamical, structural, and interfacial properties, which can not be directly accessed by the equation of state (unless a suitable treatment of the inhomogenous properties of the system is made). The goal of any coarse-graining procedure is to derive simple, but accurate, robust, and transferable force fields. By aiming for the simplicity, the coarse-grained models developed in our work are typically based on the three-to-one mapping, i.e., one bead containing approximately three heavy atoms, or one-to-one mapping for the small spherical molecules, with the polar, directional, and long-ranged interactions between the beads treated implicitly using the effective spherically-symmetric Mie potentials. The SAFT-gamma Mie coarse-graining methodology is exemplified for a number of fluid systems of different complexities, including pure component systems, such as: the homologous series of n-alkanes, n-perfluoroalkanes, semifluorinated alkanes, ethers and water; binary and ternary mixtures, comprising the carbon dioxide, n-alkanes, and water; and finally the aqueous mixtures of alkyl polyoxyethylene glycol non-ionic surfactants. An accurate representation of the vapour-liquid properties with both, the equation of state and molecular simulation, is obtained for the molecules of different size and chemical nature. Describing the properties of water is, however, a much more difficult task. The CG model suffers from issues associated with the transferability and representability of the various properties for different thermodynamic conditions, as a consequence of the aggressive averaging of the strongly directional and polar forces into an effective spherically symmetrical potential. It has been shown that an isotropic single-site CG model based on a spherically symmetrical potential cannot capture all of the thermodynamic properties of water simultaneously (the issue of representability). Two different CG models of water are proposed: the first is designed to accurately reproduce the saturation liquid density and vapour pressure, and the second to capture the saturation liquid density and surface tension with high precision. Both models benefit from an accurate parameterisation of temperature dependence following the target properties over the entire temperature range of the fluid. An additional model is developed based on the two-to-one mapping, enabling more efficient large scale simulations in, for example, biomolecular systems. The models of the binary mixtures are developed by using the corresponding pure component models with an additional adjustable parameter to account for the unlike interactions; the latter are obtained by considering appropriate properties of the mixtures such as the fluid-phase equilibria or the thermodynamic properties of mixing. The unlike interactions are shown to be transferable for a quantitative description of the phase behaviour over a wide range of conditions and for the systems of related components. We are able to obtain an accurate prediction of the azeotropic point, critical loci, tree phase line, global density, and the shape of phase envelopes for studied mixtures. The quality of predictions is found comparable to the results from the atomistic models and other equations of state. The aqueous mixtures of alkyl polyoxyethylene glycol non-ionic surfactants are a key final goal of the research presented in this thesis. The CG models of the surfactants are developed within the SAFT-gamma group-contribution framework, where each functional group is derived from an accurate representation of the corresponding chemical moiety. By capturing a delicate interplay of the repulsive and attractive intermolecular interactions and obtaining the right balance between energetic and entropic effects, the various phase morphologies at ambient conditions can be reproduced in agreement with the experimental findings over the entire concentration range. The force fields developed in the current work allow for a prediction of key structural and interfacial properties. The Molecular Dynamics simulations reveal the spontaneous formation of micelles at low surfactant concentrations and a self-assembly into a bilayer at high surfactant concentrations. The aggregation numbers, the critical micelle concentration, area per molecule, the surface excess properties, and bilayer thickness are found in very good agreement with experimental data. This is very encouraging considering that only macroscopic thermophysical properties are used to develop the underlying force fields that describe the fine interactions between the molecules in the system. Despite the simplicity, coarse-grained force fields are shown to be robust and transferable; they can be applied to predict the properties which were not used in the original parameterisation procedure, with an accuracy comparable to the more sophisticated and computationally demanding models.Open Acces

Modeling and Control of Post-Combustion CO2 Capture Process Integrated with a 550MWe Supercritical Coal-fired Power Plant

This work focuses on the development of both steady-state and dynamic models for an monoethanolamine (MEA)-based CO2 capture process for a commercial-scale supercritical pulverized coal (PC) power plant, using Aspen PlusRTM and Aspen Plus DynamicsRTM. The dynamic model also facilitates the design of controllers for both traditional proportional-integral-derivative (PID) and advanced controllers, such as linear model predictive control (LMPC), nonlinear model predictive control (NMPC) and H? robust control.;A steady-state MEA-based CO2 capture process is developed in Aspen PlusRTM. The key process units, CO2 absorber and stripper columns, are simulated using the rate-based method. The steady-state simulation results are validated using experimental data from a CO2 capture pilot plant. The process parameters are optimized with the goal of minimizing the energy penalty. Subsequently, the optimized rate-based, steady-state model with appropriate modifications, such as the inclusion of the size and metal mass of the equipment, is exported into Aspen Plus DynamicsRTM to study transient characteristics and to design the control system. Since Aspen Plus DynamicsRTM does not support the rate-based model, modifications to the Murphree efficiencies in the columns and a rigorous pressure drop calculation method are implemented in the dynamic model to ensure consistency between the design and off-design results from the steady-state and dynamic models. The results from the steady-state model indicate that between three and six parallel trains of CO2 capture processes are required to capture 90% CO2 from a 550MWe supercritical PC plant depending on the maximum column diameter used and the approach to flooding at the design condition. However, in this work, only two parallel trains of CO2 capture process are modeled and integrated with a 550MWe post-combustion, supercritical PC plant in the dynamic simulation due to the high calculation expense of simulating more than two trains.;In the control studies, the performance of PID-based, LMPC-based, and NMPC-based approaches are evaluated for maintaining the overall CO2 capture rate and the CO2 stripper reboiler temperature at the desired level in the face of typical input and output disturbances in flue gas flow rate and composition as well as change in the power plant load and variable CO2 capture rate. Scenarios considered include cases using different efficiencies to mimic different conditions between parallel trains in real industrial processes. MPC-based approaches are found to provide superior performance compared to a PID-based one. Especially for parallel trains of CO2 capture processes, the advantage of MPC is observed as the overall extent of CO2 capture for the process is maintained by adjusting the extent of capture for each train based on the absorber efficiencies. The NMPC-based approach is preferred since the optimization problem that must be solved for model predictive control of CO2 capture process is highly nonlinear due to tight performance specifications, environmental and safety constraints, and inherent nonlinearity in the chemical process. In addition, model uncertainties are unavoidable in real industrial processes and can affect the plant performance. Therefore, a robust controller is designed for the CO2 capture process based on ?-synthesis with a DK-iteration algorithm. Effects of uncertainties due to measurement noise and model mismatches are evaluated for both the NMPC and robust controller. The simulation results show that the tradeoff between the fast tracking performance of the NMPC and the superior robust performance of the robust controller must be considered while designing the control system for the CO2 capture units. Different flooding control strategies for the situation when the flue gas flow rate increases are also covered in this work

Applications of fluorocarbons for supercritical extraction in the petroleum industry.

Doctor of Philosophy in Chemical Engineering. University of KwaZulu-Natal, Howard College 2016The majority of supercritical processes utilise carbon dioxide (CO2) as the principal solvent, because CO2 has many attributes that make it an ideal supercritical fluid (SCF) solvent. This study investigates the possibility of replacing CO2 with trifluoromethane or hexafluoroethane, because of the poor performance of CO2 in cases where more polar and heavier molecular weight solutes must be extracted. Several applications in the petroleum industry, such as oil sludge treatment and the treatment of contaminated soils, are discussed. Due to the large number hydrocarbons present in such applications, a selection of solutes that could be used to simulate a simplified stream were chosen for these investigations. These selected solutes were n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, 1-hexene, 3-methylpentane, methylcyclohexane, toluene and water. High-pressure vapour-liquid equilibria and vapour-liquidliquid equilibria for binary systems containing either trifluoromethane or hexafluoroethane, with these solutes were measured using a static-analytic apparatus at temperatures of between (272.9 and 313.2) K. For several systems, the phase equilibria data were verified using bubble-point pressures measured with a static-synthetic, variable-volume cell. Parameters for thermodynamic models were obtained by regression of the experimental data for the binary systems. The models provide a good representation of the majority of the systems investigated, and were therefore also used to estimate portions of the critical locus curves. These critical locus curves were compared to the critical loci that were extrapolated from the sub-critical coexistence data as well as critical loci that were measured with a critical point determination apparatus. There is satisfactory agreement between the calculated, the extrapolated and the measured critical loci. The thermodynamic models were used to simulate the separation of several hydrocarbon-water emulsions using either CO2, trifluoromethane, hexafluoroethane or mixtures thereof. The simulations confirmed that trifluoromethane, hexafluoroethane as well as mixtures thereof, provide improved performances (recoveries and yields) when used as alternative solvents in the SCF extraction of these systems. An economic analysis of a SCF extraction process was performed to investigate the performance of the solvents, and if such SCF extraction processes, using a mixture of trifluoromethane and hexafluoroethane, would provide an economically competitive treatment process for hydrocarbon-water emulsions

Application of the truncated perturbed chain-polar statistical associating fluid theory (tPC-PSAFT) to alcohol/alkane mixtures at high pressures.

Masters Degree. University of KwaZulu-Natal, Durban.Constitutive equations, such as equations of state (EoS) characterize mathematical relationships between state functions under set physical conditions and are imperative for the accurate design of chemical processes (Devilliers, 2011; Al-Malah, 2015). Most models, however, fail to accurately predict thermophysical properties of complex mixtures such as those exhibiting molecular association and hydrogen bonding. The Statistical Associating Fluid Theory (SAFT), based on thermodynamic perturbation theory, explicitly accounts for molecular association, hence, providing a more suitable prediction of thermophysical properties (Devilliers, 2011). This work investigates the performance of the truncated Perturbed Chain-Polar Statistical Associating Fluid Theory (tPC-PSAFT) model in accurately accounting for the effect of molecular association on compressed liquid density in liquid alkane-alcohol mixtures at elevated pressures. This was achieved by comparing the density predictions calculated by the tPC-PSAFT model to novel experimental density data. Isothermal measurements were conducted utilizing an Anton Paar DMA HP densimeter with a upplier stated uncertainty ranging between 0.1 and 1 kg.m-3. Measurements were conducted in the temperature and pressure ranges of 313.15 to 353.15 K and 0.1 to 20 MPa, respectively, over the entire composition range. Furthermore, a test system consisting of ethanol (1) + n-heptane (2) was used to confirm the reliability of the experimental setup and procedure. The density data obtained for the test system was compared to literature and demonstrate excellent correlation of the data, with a maximum relative difference of 0.0005, confirming the reliability of the procedure utilized in this study. The density data of six novel binary systems namely, butan-1-ol/butan-2-ol/2-methylpropan-1-ol (1) + n-octane/n-decane (2) are presented in this work. The maximum expanded combined uncertainties for pressure, temperature, composition and density were 0.032 MPa, 0.02 K, 0.0002 mole fraction, and between 1.10 to 1.12 kg.m-3, respectively. Density data obtained experimentally for all six binary systems comply with the general trend regarding temperature and pressure in that the density of the liquid mixtures decreased with an increase in temperature and increase with an increase in pressure. Furthermore, derived thermodynamic properties namely, the excess molar volume, thermal expansivity and isothermal compressibility were computed for each of the binary systems. Large positive deviations from ideality were noted for the excess volumes for all systems. This is attributed to the different shapes and sizes of the molecules as well as the attractive mixture interactions when compared to those of the individual pure components. In addition, the thermal expansivity and isothermal compressibility demonstrate highly non-linear behaviour which is indicative of systems comprising complex mixtures. The experimental data were compared to correlations/predictions resulting from five models namely, the Modified Toscani-Szwarc (MTS) equation of state (EoS), the Benedict-Webb-Rubin-Starling (BWRS) EoS, Peng-Robinson (PR) EoS, Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) model and the truncated Perturbed Chain-Polar Statistical Associating Fluid Theory (tPC-PSAFT) model. Both the MTS and BWRS EoS demonstrated excellent correlation of the data for all six of the binary systems attributed to the empirical nature of the model and the significant number of fitting parameters employed. The maximum root mean square deviation (RMSD) was found in the butan-2-ol (1) + n-octane (2) binary system at RMSD = 4.72 x 10-4. In addition, improvements in model performance were noted for the BWRS EoS at higher temperatures and pressures. The PR EoS demonstrated poor correlation of the density data of the mixtures (exceeding RMSD = 0.024), attributed to the poor prediction of the pure component data by the model and the use of a single binary interaction fitting parameter in the cases of the mixtures. Density predictions from the PC-SAFT model demonstrated significant deviation from experimental data (exceeding RMSD = 0.011) in that the PC-SAFT model underpredicts densities for the binary systems. Furthermore, a progressive deterioration in the model’s performance was noted as the respective alcohol concentration increases. Accurate prediction of the density was however noted for the 2-methylpropan-1-ol binary systems in the alcohol dilute region. In addition, some improvement in model performance was observed at higher pressures and temperatures for the butan-2-ol and 2-methylpropan-1-ol binary systems. The tPC-PSAFT model demonstrated improvement in accurately predicting the density data, for all six systems, when compared to those obtained via the PC-SAFT model, with an improvement in excess of 72% in some cases. In addition, the model performs well in the alcohol dilute region and at high pressures and temperatures. However, a progressive deterioration in the model’s performance is noted as the concentration of the alcohol in solution is increased. This was unexpected as both the PC-SAFT and tPC-PSAFT models explicitly account for molecular association and were theorized to perform well in predicting the alcohol mixture behaviour. The model’s poor performance can be attributed to the lack of high precision pure component parameters currently available in the literature that do not effectively characterize the density of the systems under high pressure. All five models exhibit similar trends to that of the experimental data despite their individual merits and shortcomings

Experimental investigation of the interface and wetting characteristics of rock-H2-brine systems for H2 geological storage

The projected rise in demand for hydrogen (H2) production is a response to several factors, including greenhouse gas emissions caused by burning fossil fuels, depletion of fossil fuel reserves, and their uneven distribution around the earth. Thus, increased requirement for large-scale hydrogen storage solutions is anticipated to overcome imbalance between energy demand and supply. Deep underground formations such as salt caverns and porous reservoir rocks (e.g., depleted hydrocarbon reservoirs and deep saline aquifers) are necessary to achieve such volumes in practice. This process is known as underground hydrogen storage (UHS) which is technically very similar to underground natural gas storage. Although these two gas types have similar storage mechanisms, their behavior underground differs significantly, and this divergence could affect the efficiency, sustainability, safety, and commercial feasibility of deploying and operating gas storage systems. The interface and wetting characteristics of the various rock/H2/brine systems are significant physicochemical factors in controlling containment security and storage capacity. These factors demand a thorough assessment. Nevertheless, there exists a literature gap concerning these aspects under diverse geological conditions, encompassing variations in pressure, temperature, organic matter, and salinity. This study presents experimental data on interfacial tension (IFT) values between H2 and brine as well as the wettability of different rock/H2/brine systems under reservoir conditions. The wettability measurements are taken by directly observing the advancing and receding contact angles of water using the pendant drop tilted-plate technique. The experiments are conducted at high pressures (up to 20 MPa), elevated temperatures (up to 353 K) and brine salinities (up to 4.95 mol.kg-1 ) to simulate subsurface conditions commonly encountered in such systems. For the investigation of wettability, various rocks were selected: calcite and Indiana limestone (which are representative of carbonate rocks); shales and evaporate (which are representative of caprocks), and basalt (which is representative of volcanic rocks). The effects of other rock surface properties such as surface roughness by atomic force microscopy (AFM) and organic matter concentration of shale by total organic content (TOC) analyzer on wettability were also investigated in this study. The study employed several other methods to characterize the composition of the rock and fluid samples, which included: 1) energy dispersive spectroscopy (EDS) to determine the elemental composition of the rock surface, 2) x-ray diffraction (XRD) to identify the mineral composition of the rock sample, and 3) inductively coupled plasma (ICP) to determine the elemental composition of the brine sample. The obtained IFT and contact angle data were utilized to theoretically calculate the IFT of various rock-hydrogen and rock-water systems by the combination of Young’s equation and Neumann’s equation of state. Additionally, the electrochemical mechanisms controlling the wetting behavior of basalt under various geological conditions were investigated via streaming zeta potential core flooding system. The results of H2-brine interfacial tension indicate a linear decrease with increasing pressure and temperature, but a linear increase with increasing salinity over the entire range studied. The findings of the study reveal that in the majority of the rock/H2/brine systems analyzed, the water advancing and receding contact angles exhibited an increase (more H2-wet) with increasing pressure, salinity, and organic matter concentration but a decrease (more water-wet) with increasing temperature. Moreover, the samples with a high organic acid concentration showed a decrease in hydrophobicity following treatment with the nanofluid. The rock-hydrogen interfacial tension in shale, evaporite and basaltic rocks decreased with increasing pressure, temperature, and organic matter concentration. Also, the rock-water interfacial tension in these rocks decreased with increasing temperature but increased with increasing organic matter concentration. On the other hand, the calcite-hydrogen interfacial tension decreased with increasing pressure, salinity, and organic acid concentration, while it increased with increasing temperature. The calcite-water interfacial tension showed only minor variations with these parameters. Additionally, according to the findings, the zeta potential of basalt remained stable in response to pressure but showed an increase (less negative) trend as temperature and salinity increased. Conversely, the zeta potential of basalt exhibited a decrease (more negative) trend as the pH level increased. This thesis offers valuable insights for evaluating the potential of different minerals composing the geological formations as H2 storage options. The outcomes of this study are especially useful for analyzing the capillary sealing efficiency of caprocks, which can help in identifying the factors that contribute to the leakage of H2. Furthermore, the information presented can be utilized as a valuable input in the development of H2/brine flow simulations, which have the potential to provide more accurate predictions and, therefore, reduce the uncertainty associated with H2 geostorage projects

Integrated process and solvent design for CO₂ removal from natural gas

Carbon dioxide (C02) capture is of crucial importance for the environment. A large number of countries agreed on the fact that greenhouse gases, especially C02 can have harmful effects leading to major climate changes; in particular, since the ratification of the Kyoto Protocol in 1997 it is apparent that action should be taken. In this context, new solutions are necessary to reduce carbon dioxide emissions. In this work, we present the new challenge that the Kyoto Protocol represents for the petroleum industry, especially considering that large amount of C02, which would be captured from large C02 emissions sources, could be reinjected in oil and gas reservoirs. Re-injection will lead to increased productions of oil and gas, which can compensate the cost of C02 capture. Unfortunately, the oil and gas produced will be increasingly richer in C02 and specific absorption processes must be designed to address this problem. Such processes should show flexibility with respect to the feed C02 content. Physical absorption processes are currently the most promising option, as they are more economical for removing large quantities of C02. A cryogenic absorption process (Ryan-Holmes) using n-butane as a solvent demonstrated the advantages of using alkanebased solvents. The adaptation of the Ryan-Holmes process to high temperatures offers real potential. This requires the identification of the optimal alkane solvent. Integrated process and solvent design using state of the art thermodynamics, process modelling and optimisation can bring significant new benefits. Advanced thermodynamic models such as SAFT-VR can be used advantageously in this study as they have proven successful for predicting the phase behaviour (VLE) of a large range of n-alkane/C02 mixtures [A. Galindo and F.J. Bias, J. Phys. Chern. B, .2002, 106, 4503], and for a large range of pressure and temperature. The SAFT-VR equation of state has been used to study mixtures of C02 and methane in detail, and it is found that it describes accurately both supercritical and coexistence states. This equation of state has been implemented within gPROMS software, allowing its use for process modelling. The units used in a separation have been modelled with mass and energy balance equations. The dimensioning of the units has also been performed as the sizes of the units are required to estimate their cost. A complete cost estimation has been carried out in order to estimate the capital and operating expenses of the plant. We have applied this new integrated approach to process and solvent design to identify the most appropriate flowsheet to perform profitable capture of C02 for feed C02 contents from 10% to 70%. We have also carried out a sensitivity study which shows that changes in the thermodynamic model parameters has a limited impact on the optimal process. The effect of the presence of small quantities of ethane in the feed has also been evaluated on the optimal flowsheet, and we find that ethane is co-absorbed with C02. Finally, we show that it is possible to design a process that covers the full range of feed C02 contents [10%, 70%], and we give the values of the control variables and the economics performance as a function of the feed C02 content.EThOS - Electronic Theses Online ServiceGBUnited Kingdo