Phase Behavior of Binary Ionic Liquid Systems: Ionic Liquids with Ammonia, Carbon dioxide, and Dihydroxy Alcohols

Solvents play a crucial role in industrial processes, which might directly or indirectly have a bearing on the environment. As engineers and scientists, our goal is to advance or develop more sustainable chemicals to overcome the environmental challenges of the 21st century. Therefore, ionic liquids (ILs) might offer a unique solution. Ionic liquids are low melting point salts composed entirely of ions. The characteristics of ILs can be designed by varying both the cation, anion, and substituents. Therefore, ILs can be designed to be non-volatile, non-toxic, and environmentally benign. ILs are soluble with a wide range of compounds, allowing the use in various applications such as catalysis, separation, and solvents, to name a few. In order to develop these processes, fundamental phase behavior knowledge is required. The main objective of this thesis is to investigate the phase behavior of ionic liquids with gases (ammonia and carbon dioxide) and organic solvents (diols) over a wide temperature and pressure range. ILs are relatively viscous compared to traditional solvents like water; therefore, in addition to the thermodynamic measurements and modeling, the kinetics of gas dissolution in the ILs were also explored. Nuclear Magnetic Resonance (NMR) spectroscopy was utilized to further advance the understanding of the interaction in binary ionic liquid mixtures (i.e., NH3+ILs). In the investigation of the ionic liquid and ammonia system, vapor-liquid equilibrium (VLE) measurements for the binary systems of ammonia (NH3) with aprotic and protic ionic liquids have been successfully measured using a new Hiden XEMIS gravimetric microbalance. This study reports the first gravimetric measurements conducted for the solubility of NH3 in ionic liquids and provides the most accurate data to date. The NH3 sorption measurements were conducted at temperatures of 283.15, 298.15, 323.15, and 348.15 K and at pressures up to 0.7 MPa. The VLE data were correlated using the Peng-Robinson equation of state, the Non-Random Two Liquid (NRTL), and the Flory-Huggins model. All models are in excellent agreement with the experimental data. The Flory-Huggins model demonstrated that the non-idealities in NH3 solubility in the imidazolium-based ILs are due to both entropic and enthalpic impacts. The Fickian diffusivities of NH3 in imidazolium-based ILs were obtained by fitting experimental concentration to the one-dimensional (1D) mass diffusion equation and found to be about 3 to 5 times slower than the diffusion of NH3 in water. The semi-theoretical Stokes-Einstein equation was used to model diffusivities and to obtain the diffusing radius of NH3 in imidazolium-based ILs. NMR spectroscopy is utilized to investigate the interaction between NH3 and imidazolium-based ILs. NMR spectra of the NH3 systems revealed that the NH3 interacts with all protons in the cation while interacting with the most acidic hydrogen more profoundly. One exception is the system of ammonia and 1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate where NH3 interacts with all hydrogens in a similar manner. In the investigation of IL and carbon dioxide system, the high-pressure vapor-liquid equilibrium for the binary systems of carbon dioxide and a series of 1-alkyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids ([CnC1pyr][NTf2] (n = 3,4,6)) are measured at 298.15, 318.15, and 338.15 K and at pressures up to 20 MPa. Experiments were conducted using gravimetric (IGA and XEMIS microbalances) and volumetric (high-pressure view cell) methods. In this study, the solubility of CO2 in pyrrolidinium ionic liquids increases with increasing pressure and decreasing temperature. However, the high-pressure behavior (above 10 MPa) approaches almost a vertical slope, which indicates the CO2 solubility only slightly increases despite large increases in pressure. The CO2 solubility is found to be slightly dependent on the alkyl chain length on the pyrrolidinium cation, which is potentially due to the steric impacts. Molar volume and volume expansion of CO2 + IL mixtures at high pressures were also measured and reported. The Fickian diffusion of CO2 in pyrrolidinium-based ionic liquids (~10-10 m2·s) was calculated at pressures up to 2 MPa and found to be slightly lower than the diffusivity of CO2 in an imidazolium-based ionic liquid with the [NTf2] anion. In the investigation of ionic liquids and dihydroxy alcohols system, liquid-liquid equilibria (LLE) for the mixtures with three imidazolium-based ionic liquids were measured. The dihydroxy alcohols were 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol and the ionic liquids were 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2C1im][BF4]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2C1im][NTf2]), and 1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate ([C2C1im][TFES]). The experimental LLE data were well correlated using the NRTL activity coefficient model, which allows quantification of the the miscibility gaps. All binary diol systems with [C2C1im][BF4] or [C2C1im][NTf2] demonstrated an upper critical solution temperature (UCST) between 310 to 360 K. An equimolar mixture of diols and [C2C1im][TFES] showed complete miscibility between 293.15 to 373.15 K. An increase in alkyl chain length of the dihydroxy alcohols and/or changing the anion from [BF4] to [NTf2] for a given [C2C1im] cation results in an increase in the UCST. The excess molar volume of diols with ILs was, in most cases, larger than those of ordinary solutions

110th Anniversary: The First Thermodynamic and Kinetic Analysis of Ammonia in Imidazolium-Based Ionic Liquids Using a Gravimetric Microbalance

The first vapor liquid equilibrium (VLE) measurements for the binary systems of ammonia (NH3) and three imidazolium-based ionic liquids (ILs) have been successfully measured using a gravimetric microbalance. ILs 1-butyl-3-methylimidazolium hexafluorophosphate ([C4C1im][PF6]), 1-butyl-3-methylimidazolium tetrafluoroborate ([C4C1im][BF4]), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2C1im][NTf2]) were measured at temperatures of 283.15, 298.15, 323.15, and 348.15 K and at pressures up to 0.7 MPa using the new Hiden XEMIS gravimetric microbalance. The VLE data were correlated using the Peng–Robinson equation of state and the Non-Random Two Liquid (NRTL) activity coefficient models. Both models are in excellent agreement with the experimental data. The Fickian diffusivities of NH3 in imidazolium-based ILs were obtained fitting experimental concentration to the one-dimensional (1D) mass diffusion equation, and found to be about 3 to 5 times lower than the diffusion of NH3 in water (H2O). The semitheoretical Stokes–Einstein equation was used to model diffusivities and to obtain the diffusing radius of NH3 in imidazolium-based ILs

Air Dehumidification using Ionic Liquid-Based Fiber Bundle Membrane Contactor

Air dehumidification is essential since excess moisture in the buildings causes discomfort to the occupants, encourages the production of air pathogens such as mold or mildew, and causes corrosion and rotting that degrade building materials. Existing moisture removal processes are mainly focused on condensation and desiccant (liquid or solid) techniques with direct contact between air and desiccant. However, these methods are energy-intensive, or desiccant might be lost or cause corrosion in the process. The main objective of this study is to investigate an ionic liquid-based liquid desiccant absorber based on a membrane fiber bundle. A novel membrane contactor system was fabricated with a bundle of 10,000 polypropylene fibers. Each fiber has 0.3 micron outer diameter, with ionic liquid flowing inside, and air flowing outside. The fibers provide a high contact area among phases: 1.4 m2 contact surface area in a 0.00015 m3 volume (9,333 m2/m3 ratio of surface area to volume). The ionic liquid as a sorbent has selectivity for water vapor (i.e., the ionic liquid has higher affinity for water vapor) prevents the loss of solvent in the operation due to negligible volatility, provides fast diffusion due to low viscosity compared to common ionic liquids, and has high affinity and solubility in water. The dehumidification capacity of the prototype membrane system was experimentally investigated using six modules with 10,000 fibers each. The experimental results show that the ionic-liquid based membrane system can effectively remove excess moisture from the air. The novel fiber bundle dehumidification system has a total system volume of 0.00798 m3 (7.98 L) and active heat and mass transfer surface area of 8.4 m2. It achieved an average dehumidification of 320 ± 25 W with a volumetric air flowrate of 3.1 m3/min (108 ft3/min)

Review Article: Gas and vapor sorption measurements using electronic beam balances

The beam balance is one of the oldest known measuring instruments. Until the 20th century, balances had been the most sensitive and precise instruments used for scientific measurements. The original balances used a beam supported at the center with pans hung from cords on both ends. The modern electronic beam balances still resemble those original designs; however, the resolution, accuracy, and capabilities have been significantly improved. This review provides a short introduction to the history of beam balances followed by a detailed description of three gravimetric microbalances manufactured by Hiden Isochema for measuring gas and vapor sorption in a variety of materials

Measurements Of Evaporation And Condensation Mass Transfer Resistances For Surfaces In Residential Dishwashers

During the drying phase of a dishwasher, water evaporation and condensation phenomena take place. Some wet surfaces inside the dishwasher are above the local air dewpoint and will experience evaporation, while other surfaces are below the local air dewpoint and will experience condensation. In this study, the evaporation mass transfer resistance of a standard load used in a household dishwasher was experimentally measured. The standardized load measurements were taken in situ during a regular drying phase after the ordinary washing was complete. To determine the mass transfer resistance of condensation, a tub wall sample was cut from the interior of a commercially available dishwasher. The wall samples were tested ex-situ in a benchtop psychrometric chamber to determine the condensation heat and mass transfer coefficient. The wall samples were locally cooled using a thermoelectric module. The experimental results were compared to those from a heat and mass transfer resistance correlation. The measured evaporation and condensation mass transfer coefficients can be used to model the drying process in a humid and stagnated environment

Review of Low-Cost Organic and Inorganic Phase Change Materials with Phase Change Temperature between 0°C and 65°C

Phase change materials (PCMs) that undergo a phase transition may be used to provide a nearly isothermal latent heat storage at the phase change temperature. This work reports the energy storage material cost ($/kWh) of various PCMs with phase change between 0 – 65°C. Four PCM classes are analyzed for their potential use in building systems: 1) inorganic salt hydrates, 2) organic fatty acids, 3) organic fatty alcohols, and 4) organic paraffin waxes. Many salt hydrates have low material costs (0.09 – 2.53$/kg), high latent heat of fusion (100 – 290 J/g), and high densities (1.3 – 2.6 g/cm3), leading to favorable volumetric storage density and low energy storage costs, 50 – 130 kWh/m3 and 0.90 – 40 $/kWh, respectively. Some salts are notably more expensive due to their scarcity or pressures from competing industries such as lithium-based salts. Fatty acids have the lowest energy storage cost in the temperature range 8 – 17°C at 6.50 – 40$/kWh. Despite favorable latent heat (125 – 250 J/g) their low density gives (0.9 g/cm3) gives poor volumetric storage capacity, 32 – 80 kWh/m3. Fatty alcohols generally have high material costs 2.50 – 200 $/kg which leads to high energy storage costs, 40 – 3000$/kWh. With latent heat and density similar to fatty acids, fatty alcohols have poor volumetric energy storage, 43 – 55 kWh/m3. Paraffin waxes containing only a single length carbon chain have a higher energy cost (15 – 500 $/kWh) than generic paraffin waxes containing many lengths of carbon chains (7 – 30$/kWh). Pure waxes have a discrete phase change temperature due to their homogeneity. In contrast, a less refined generic wax with several carbon chain lengths is more likely to have a pronounced temperature glide during its phase change. Pure single carbon chain waxes are generally required for applications \u3c45°C as generic paraffin waxes melt between 45 – 70°C. For many waxes, a solid-solid transition occurs at temperatures below the solid-liquid phase change. For pure paraffins with carbon content ≥22 C atoms, these transitions may appear near the same temperature resembling a temperature glide. The challenges with fatty acids, fatty alcohols, and waxes are low thermal conductivity, low density, some flammability concerns, and compatibility issues with some common engineering materials such as polymers. Challenges with salt hydrates are pronounced supercooling (\u3e5°C), incongruent melting, and corrosiveness. All PCMs may degrade if exposed to ambient conditions and therefore require proper sealing

Novel Dishwasher with Thermal Storage and Thermoelectric Heat Recovery

Residential dishwashers typically consume domestic hot water, heat it further with electric resistance heating elements, and drain the soiled heated water before each subsequent water fill. During the final rinse, the water is heated to a temperature of approximately 54.5–57.2°C (130–135°F) to heat the load and promote passive drying after the final drain event. In this work, the energy consumption, water consumption, and drying performance of a conventional dishwasher were measured under test conditions similar to U.S. energy efficiency test standards but with an unsoiled load. These measurements were considered baseline performance metrics. The dishwasher was then experimentally modified to recover heat from the drain water utilizing thermoelectric (TE) heat pump modules and a thermal storage component. The TEs were also used during the drying phase to improve the drying of the load. The novel dishwasher was operated in the laboratory under the same conditions as the baseline unit, and its energy consumption, water consumption, and drying performance were measured. The results demonstrated a 14.5% reduction in energy consumption, with the same amount of water consumption, and improved drying by 60% compared to the baseline