Carbon Dioxide Utilization Coming of Age

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Microfabrication inside capillaries using multiphase laminar flow patterning

The reaction of species in solutions flowing laminarly (without turbulent mixing) inside capillaries was used as the basis for a broadly applicable method of microfabrication. In this method, patterning occurs as a result of transport of reactive species to interfaces within the capillary by laminar flow. A wide range of chemistries can be used to generate structures with feature sizes of less than 5 micrometers and with spatial localization to within 5 micrometers. The method is applicable to the patterning of metals, organic polymers, inorganic crystals, and ceramics on the inner walls of preformed capillaries, using both additive and subtractive processes

Experimental and theoretical scaling laws for transverse diffusive broadening in two-phase laminar flows in microchannels

This letter quantifies both experimentally and theoretically the diffusion of low-molecular-weight species across the interface between two aqueous solutions in pressure-driven laminar flow in microchannels at high Peclet numbers. Confocal fluorescent microscopy was used to visualize a fluorescent product formed by reaction between chemical species carried separately by the two solutions. At steady state, the width of the reaction-diffusion zone at the interface adjacent to the wall of the channel and transverse to the direction of flow scales as the one-third power of both the axial distance down the channel (from the point where the two streams join) and the average velocity of the flow, instead of the more familiar one- half power scaling which was measured in the middle of the channel. A quantitative description of reaction-diffusion processes near the walls of the channel, such as described in this letter, is required for the rational use of laminar flows for performing spatially resolved surface chemistry and biology inside microchannels and for understanding three-dimensional features of mass transport in shearing flows near surfaces

Optimization of a Nafion Membrane-Based System for Removal of Chloride and Fluoride from Lunar Regolith-Derived Water

A long-term human presence in space will require self-sustaining systems capable of producing oxygen and potable water from extraterrestrial sources. Oxygen can be extracted from lunar regolith, and water contaminated with hydrochloric and hydrofluoric acids is produced as an intermediate in this process. We investigated the ability of Nafion proton exchange membranes to remove hydrochloric and hydrofluoric acids from water. The effect of membrane thickness, product stream flow rate, and acid solution temperature and concentration on water flux, acid rejection, and water and acid activity were studied. The conditions that maximized water transport and acid rejection while minimizing resource usage were determined by calculating a figure of merit. Water permeation is highest at high solution temperature and product stream flow rate across thin membranes, while chloride and fluoride permeation are lowest at low acid solution temperature and concentration across thin membranes. The figure of merit varies depending on the starting acid concentration; at low concentration, the figure of merit is highest across a thin membrane, while at high concentration, the figure of merit is highest at low solution temperature. In all cases, the figure of merit increases with increasing product stream flow rate

Patterning electro-osmotic flow with patterned surface charge

This Letter reports the measurement of electro-osmotic flows (EOF) in microchannels with surface charge patterned on the 200 mu m scale. We have investigated two classes of patterns: (1) Those in which the surface charge varies along a direction perpendicular to the electric field used to drive the EOF; this type of pattern generates multidirectional flow along the direction of the field. (2) Those in which the surface charge pattern varies parallel to the field; this pattern generates recirculating cellular flew, and thus causes motion both parallel and perpendicular to the external field. Measurements of both of these flours agree well with theory in the Limit of thin double layers and low surface potential

Contaminant Removal from Oxygen Production Systems for In Situ Resource Utilization

The In Situ Resource Utilization (ISRU) project has been developing technologies to produce oxygen from lunar regolith to provide consumables to a lunar outpost. The processes developed reduce metal oxides in the regolith to produce water, which is then electrolyzed to produce oxygen. Hydrochloic and hydrofluoric acids are byproducts of the reduction processes, as halide minerals are also reduced at oxide reduction conditions. Because of the stringent water quality requirements for electrolysis, there is a need for a contaminant removal process. The Contaminant Removal from Oxygen Production Systems (CROPS) team has been developing a separation process to remove these contaminants in the gas and liquid phase that eliminates the need for consumables. CROPS has been using Nafion, a highly water selective polymeric proton exchange membrane, to recover pure water from the contaminated solution. Membrane thickness, product stream flow rate, and acid solution temperature and concentration were varied with the goal of maximizing water permeation and acid rejection. The results show that water permeation increases with increasing solution temperature and product stream flow rate, while acid rejection increases with decreasing solution temperature and concentration. Thinner membranes allowed for higher water flux and acid rejection than thicker ones. These results were used in the development of the hardware built for the most recent Mars ISRU demonstration project

Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO_2 Fixation

Two major energy-related problems confront the world in the next 50 years. First, increased worldwide competition for gradually depleting fossil fuel reserves (derived from past photosynthesis) will lead to higher costs, both monetarily and politically. Second, atmospheric CO_2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atmospheric CO2.1 Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand