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Recent increases in shale gas production provide an excellent opportunity for advancements in the energy-efficient separation of natural gas liquids because these are increasingly used as fuel sources and chemical feedstocks. Current fractionation schemes generally involve cryogenic distillation of C1-C4 hydrocarbons and are extremely energy-intensive. Here, we describe the first steps toward a lower-energy, kinetic pressure-swing-adsorption cycle for the separation of ethane, propane, propylene, and butane using ZIF-8 as a diffusionally selective adsorbent. Crystal engineering techniques were employed to control the diffusive time scale of the separation, allowing for multiple separations using the same adsorbent within reasonable process times. Equimolar separation of ethane/propane mixtures at 293 K exhibited separation factors of 2.7 in the gas phase under nonoptimized conditions, which enhances the concentration of the feed mixture to 75 mol % propane. The separation performance was shown to improve to 3.8 at lower temperatures (81 mol % propane), which is attributed to differences in the activation energy of permeation of the two components. Propane/butane mixtures demonstrated a lower diffusive selectivity and almost negligible enhancement, while propylene/propane showed enhancement beyond ethane/propane due to a strong diffusive selectivity and sorption selectivities closer to unity. Single-component adsorption and diffusion results were incorporated into a computational model of the system and shown to be in relatively good agreement with the experimental values. The model was used to predict the separation system performance and recovery at various temperatures. [ABSTRACT FROM AUTHOR]

Industrial separation processes comprise approximately 10 % of the global energy demand, driven largely by the utilization of thermal separation methods (e.g., distillation). Significant energy and cost savings can be realized using advanced separation techniques such as membranes and sorbents. One of the major barriers to acceptance of these techniques remains creating materials that are efficient and productive in the presence of aggressive industrial feeds. One promising class of emerging materials is zeolitic imidazolate frameworks (ZIFs), an important thermally and chemically stable subclass of metal organic frameworks (MOFs). The objectives of this paper are (i) to provide a current understanding of the synthetic methods that enable the immense tunability of ZIFs, (ii) to identify areas of success and areas for improvement when ZIFs are used as adsorbents, (iii) to identify areas of success and areas for improvement in ZIF membranes. A review is given of the state-of-the-art in ZIF synthesis procedures and novel ZIF formation pathways as well as their application in energy efficient separations. [ABSTRACT FROM AUTHOR]

A one-dimensional photonic crystal is prepared from porous silicon (pSi) and impregnated with a chemically specific colorimetric indicator dye to provide a self-referenced vapor sensor for the selective detection of hydrogen fluoride (HF), hydrogen cyanide (HCN), and the chemical nerve agent diisopropyl fluorophosphate (DFP). The photonic crystal is prepared with two stop bands: one that coincides with the optical absorbance of the relevant activated indicator dye and the other in a spectrally "clear" region, to provide a reference. The inner pore walls of the pSi sample are then modified with octadecylsilane to provide a hydrophobic interior, and the indicator dye of interest is then loaded into the mesoporous matrix. Remote analyte detection is achieved by measurement of the intensity ratio of the two stop bands in the white light reflectance spectrum, which provides a means to reliably detect colorimetric changes in the indicator dye. Indicator dyes were chosen for their specificity for the relevant agents: rhodamine-imidazole (RDI) for HF and DFP, and monocyanocobinamide (MCbi) for HCN. The ratiometric readout allows detection of HF and HCN at concentrations (14 and 5 ppm, respectively) that are below their respective IDLH (immediately dangerous to life and health) concentrations (30 ppm for HF; 50 ppm for HCN); detection of DFP at a concentration of 114 ppb is also demonstrated. The approach is insensitive to potential interferents such as ammonia, hydrogen chloride, octane, and the 43-component mixture of VOCs known as EPA TO-14A, and to variations in relative humidity (20-80% RH). Detection of HF and HCN spiked into the complex mixture EPA TO-14A is demonstrated. The approach provides a general means to construct robust remote detection systems for chemical agents.

The selective electrochemical reduction of CO 2 to CO in water by a Re(tBu-bpy)(CO) 3 Cl catalyst incorporated into multi-walled carbon nanotubes (MWCNT) was investigated. Current densities of ∼4 mA/cm 2 and selectivities (FE CO ) of 99% were achieved at -0.56 V vs RHE in CO 2 -saturated aqueous KHCO 3 solutions. The Re(tBu-bpy)(CO) 3 Cl catalyst has been widely studied as a homogeneous catalyst in organic solvents. Supporting Re(tBu-bpy)(CO) 3 Cl on MWCNTs increases current densities, decreases overpotential, retains selectivity for reduction of CO 2 to CO, and allows operation in water at pH = 7.3 compared to the molecular catalyst in acetonitrile solution. The Re/MWCNT electrocatalysts achieve TON > 5600 and TOF > 1.6 s -1 . This electrocatalyst material is efficient, robust, simple to prepare, and scalable.

This work presents the synthesis, characterization, and implementation of ZIF-8/cellulose acetate fiber sorbents for the cyclic kinetic adsorption separation of an equimolar propane/propylene feed. These fiber sorbents are packed as structured mass-transfer contactors and employed in a two-bed vacuum pressure swing adsorption cycle without propylene product purge. The unoptimized adsorption cycle process produces a high-pressure product of up to 81% propane purity at 31% recovery at 0 °C. The effects of adsorption step time, temperature, and feed rate are investigated and presented as a purity/recovery trade-off. This work represents the first successful demonstration of a metal-organic framework fiber sorbent in a pressure swing adsorption cycle and the first use of metal-organic frameworks in a kinetic separation cycle.