Chemical Engineering
Effect of Reaction Temperature on The performance of Thermal Swing Sorption Enhanced Reaction Process for Simultaneous Production of Fuel Cell Grade H2 and Compressed CO2 from Synthesis Gas
A novel cyclic thermal swing sorption enhanced reaction (TSSER) process concept was recently proposed for simultaneous production of fuel-cell grade H2 and compressed CO2 from a synthesis gas containing CO and H2O. The process carried out the catalytic water gas shift (WGS) reaction (CO + H2O ↔ CO2 + H2) with simultaneous removal of CO2 from the reaction zone by a reversible, hydrophobic, CO2 selective chemisorbent in order to circumvent the thermodynamic limitation of the WGS reaction and enhance the rate of the forward reaction. The chemisorbent was periodically regenerated using the principles of thermal swing adsorption by purging the sorber-reactor with super heated steam at different pressures and temperatures. Several intermediate process steps were employed to produce a pure and compressed CO2 by-product during the thermal desorption process.
New experimental data are reported to demonstrate that high purity H2 can be directly produced by sorption-enhanced water gas shift (WGS) reaction using synthesis gas (CO + H2O) as sorber-reactor feed gas. An admixture of a commercial WGS catalyst and a proprietary CO2 chemisorbent (K2CO3 promoted hydrotalcite or Na2O promoted alumina) was used in the sorber-reactor for removal of CO2, the WGS reaction by-product, from the reaction zone. The promoted alumina was found to be a superior CO2 chemisorbent for this application because (a) it could directly produce a fuel-cell grade H2 product (<10-20 ppm CO) at reaction temperatures of 200 and 400 oC, and (b) it produced ~ 45.6% more high purity H2 product per unit amount of sorbent than the promoted hydrotalcite at 400 oC. Furthermore, the specific fuel-cell grade H2 productivity by the promoted alumina at a reaction temperature of 200 oC was ~ 3.6 times larger than that at 400 oC. These striking differences in the performance of the two CO2 chemisorbents were caused by the differences in their CO2 sorption equilibria and kinetics.
Study of Monomer Droplets in Miniemulsions
The droplet size distribution (DSD) of miniemulsions can be successfully characterized using, with adaptation, particle sizing techniques such as capillary hydrodynamic fractionation (CHDF), acoustic attenuation spectroscopy (AAS), surfactant titration, and microscopy. Because these techniques vary in size range suitability, a combination should be utilized to fully observe the DSD, which can range from tens of nanometers to several microns. The DSDs of a styrene miniemulsion were measured via different techniques. Although the measurement ranges of the techniques differ, there is good agreement between the distributions. The DSD obtained from AAS shows the presence of micron-scale droplets, observable via optical microscopy.
Seeded Dispersion Polymerization
The effect of reaction parameters on the seeded dispersion polymerization of methyl methacrylate (MMA) using submicron PMMA latex particles as seed was studied in detail. Monodisperse particles were only obtained when the methanol content was between 60% and 80%; the final particle number (N(final)) decreased with increasing methanol content. Maximum values of N(final) were found at 0.3 wt% AIBN (on MMA), 11.7 wt% MMA (on total), and 25 wt% PVP K30 (on MMA) when those parameters were varied using a constant initial seed number (N(initial) = 201012 L-1). N(final) increased linearly with N(initial) when N(initial) was greater than N(ab initio), which is the particle number obtained from the ab initio dispersion polymerization. When N(initial) was less than N(ab initio), N(final) was equal to N(ab initio). Poorer monomer swellability of the seed particles resulted in lower values of N(final) (<N(initial)) in seeded dispersion polymerizations of MMA.
Study of Monomer Droplets in Miniemulsions
Miniemulsion technology offers possible applications such as encapsulation of pigments, oils, and polymers, and polymerization of highly water-insoluble monomers not possible via conventional emulsion polymerization. Fundamental understanding of miniemulsions has been hindered by ignorance of their droplet size distribution (DSD). In this work, the droplet size and size distribution of miniemulsions have been characterized using, with adaptation, particle sizing techniques such as capillary hydrodynamic fractionation (CHDF), acoustic attenuation spectroscopy (AAS), surfactant titration, dynamic light scattering (DLS), and microscopy. › Continue reading
Deposition and meniscus alignment of DNA-CNT on a substrate
We present a study of deposition and meniscus alignment of DNA-carbon nanotube (DNA-CNT) hybrids on a silicon wafer coated with an alkyl-silane monolayer. We show that this process occurs in two stages: adsorption of DNA-CNT onto the hydrophobic surface and subsequent alignment by a passing meniscus. In our work we study how the pH, ionic strength, and time affect the density of nanotubes deposited on the surface. We also study how surface density of nanotubes and the speed of the meniscus motion affect alignment of nanotubes. Experimental results are interpreted using models for the kinetics of deposition and for forces that affect alignment by the meniscus. We show that this deposition and alignment process can be used to generate spatially varying surface patterns that may be useful for applications that require targeted placement of nanotubes on a surface.