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.