Ammonia Absorption in Room Temperature Ionic Liquids

Ionic liquids are relatively new generation solvents with low vapor pressure and high thermal stability. The solvency of the ionic liquids can be tuned by the variation in ion types, substitution and composition to provide unique properties to many industrial applications. In our research group, we have over 100 ionic liquids in our library.

Ammonia water vapor absorption system is an ancient heating/cooling system for large industrial applications. The physical properties of ammonia provide efficient, low cost cooling for large systems. The major drawback of the current system is the high cost of separation of water and ammonia in a separation unit. Ionic liquids with low vapor pressure offer an opportunity to overcome this problem and lower the operation costs.  Our research group’s goal is to utilize ionic liquids to provide a high efficiency and economic alternative to the current system.

Water Desalination via Gas Hydrate Technology

Global population continues to increase, consequently the demand for freshwater keeps rising. As a response to this pressing need, several desalination plants have developed during the past decades. Most of these utilize reverse osmosis (RO) or multi-stage flash distillation (MSF) as their separation technology. However, pumping large amounts of liquids to elevated pressures and the significant thermal heating requirement makes these technologies expensive. An alternative desalination technology is the use of clathrate hydrates.

A clathrate hydrate is a crystalline cage-like water structure which encloses a guest molecule. The conditions at which clathrate hydrates form are specific to the guest molecule. In past experiments, researchers have investigated several different refrigerants (HCFC-22, HFC-134A, HCFC-141b, etc.) as clathrate formers to separate brine from freshwater and have observed clathrates form at temperatures above the freezing point of water. This is an important benefit because it decreases the energy needed to cool the seawater to reach crystallization conditions. Nonetheless, due to the ozone depletion and global warming potentials related to CFCs, HFCs, and HCFCs, the clathrate formers investigated in the past are no longer environmentally viable.

The purpose of our research is to identify an optimum clathrate former. We will achieve our goal through fundamental studies on phase transition properties, hydrate formation kinetics, and solubility of refrigerants in saline water, while simultaneously sustaining a pragmatic approach to desalinating water by considering heat integration and technology coupling.

Designing Molecular Gate Adsorbents for Natural Gas Purification using PSA

The PSA system is used to study the separation of contaminants such as N2, CO2, CO, and H2S from natural gas (NG).  Shiflett lab group is currently working with Dr. David Corbin (Senior Scientist, CEBC) to develop new molecular sieves for the kinetic separation of N2, CO2, CO, and H2S from NG.

To remove contaminants, the natural gas is fed under pressure through a PSA column containing molecular sieve which can adsorb N2, CO2, CO, and H2S.  After the sieve is saturated with N2, CO2, CO, or H2S, the flow is redirected to the next column and the first column is depressurized to desorb the N2, CO2, CO, and H2S and regenerate the sieve. In some cases the desorption is slower than the adsorption step, so multiple columns are needed to allow time for complete column regeneration.  Development of a molecular sieve to remove N2, CO2, CO, and H2S from CH4 based on size difference is challenging because they only differ in size by 0.2 Angstroms (N2, CO2, CO, and H2S are about 3.4 to 3.6 Angstroms vs. CH4 is 3.8 Angstroms).  However, if a molecular sieve can be developed for this application, it will significantly reduce the cost of separating inert gases such as N2, CO2, CO, and H2S and possibly He from NG.  Current technologies, such as cryogenic plants for N2 removal, are complex and have high capital and operating costs compared to using a PSA system. The PSA technology is also field deployable, modular and can be scaled out to meet the capacity of the gas field.

Creating Cold-Chain Independent Vaccines with Inorganic Vehicles

Figure 1: Invasion Plasmid Antigen D conjugated with Gold Nano-particles in mesoporous silica.

The refrigeration of vaccine is critical to maintaining their efficacy. Vaccines are mainly composed of proteins, most of which are very sensitive to temperature changes. The cold chain cycle assures that vaccines are stored in controlled environments, between 2 to 8°C, to avoid conformational changes in protein structures. Keeping a constant environment that is optimal to the vaccine reduces changes to the protein’s secondary and tertiary structures while maintaining the vaccine’s potency. Any deviation from this range can result in significant waste and lead vaccination programs to a deficit. This is a common concern especially in developing countries where access to the necessary resources to store vaccines and a constant source of electricity are limited.

Figure 2: Zeolite and mesoporous material library donated by Dr. David Corbin to the Center for Environmentally Beneficial Catalysis (CEBC).

In the Shiflett group, we are currently trying to eliminate a vaccine’s dependency on refrigeration to reduce waste, cost, and increase the access of vaccines to those who need them. To accomplish this, we are currently working with Dr. David Corbin (Senior Scientist, CEBC) and Dr. William Picking (Distinguished Professor, KU) on selecting and developing vaccine specific inorganic vehicles that will act as thermal stabilizers and enhancers due to their adjuvant properties. Dr. William Picking, an expert in vaccines and pathogenic microbiology, completes our team by integrating his knowledge of pathogens, as we work to characterize the interactions between the inorganic vehicles and the Invasion Plasmid Antigen D. Together we are looking to apply our knowledge and resources to thermally stabilize vaccines in tailored inorganic materials.

Characterization of Melting Point Depression and Phase Change Behavior in Ionic Liquid + Compressed Gas Systems

Ionic liquids have become the subject of intense research due to their unique chemical properties including negligible vapor pressure and molecular tunability, with a theoretical quantity of 1018 unique cation/anion combinations. However, a significant proportion of ILs have high melting temperatures (>75°C) which prohibit using these novel salt molecules in processes that operate around room temperature (23°C). Previous studies have shown that the melting point of an ionic liquid can be lowered by absorption of a compressed gas. However, further research is needed to quantitatively characterize the depressed melting point.

Figure from Shiflett, Mark B., and Akimichi Yokozeki. “Phase Behaviour of Gases in Ionic Liquids.” Ionic Liquids Uncoiled: Critical Expert Overviews (2013): 349-386.

Our research group’s goal is to characterize the phase behavior around the solid liquid phase transition of ionic liquid and compressed gas binary systems. To reach this goal we will be using a Hiden Isochema Intelligent Gravimetric Analyzer (IGA), a gravimetric microbalance capable of measuring the weight of a sample suspended in a compressed gas environment with a precision of +/- 1 microgram. The sophisticated IGA software allows us to pressurize our sample to a desired pressure and slowly increase the temperature. Upon melting of the sample, a significant increase in sample weight can be observed, indicating absorption of our compressed gas into the ionic liquid sample. This is due to the differing solubilities of gas in the solid and liquid phases of the ionic liquid, and thus allows us to identify the temperature at which the sample melts under a given pressure.

These methods will be applied to a variety of ionic liquid and compressed gas systems. We will start with carbon dioxide as our compressed gas and move on to other potentially more soluble refrigerant gases. It is our aim to be able to completely customize the melting point of an ionic liquid species by manipulating the pressure of a compressed gas surrounding it. This could allow certain ionic liquids that were previously overlooked due to their high melting points to be investigated for practical applications.