Feed Flow Rate Ratio Research Articles

A Microfluidic Concentration Gradient Maker with Tunable Concentration Profiles by Changing Feed Flow Rate Ratios.

Microfluidic chips—in which chemical or biological fluid samples are mixed into linear or nonlinear concentration distribution profiles—have generated enormous enthusiasm of their ability to develop patterns for drug release and their potential toxicology applications. These microfluidic devices have untapped potential for varying concentration patterns by the use of one single device or by easy-to-operate procedures. To address this challenge, we developed a soft-lithography-fabricated microfluidic platform that enabled one single device to be used as a concentration maker, which could generate linear, bell-type, or even S-type concentration profiles by tuning the feed flow rate ratios of each independent inlet. Here, we present an FFRR (feed flow rate ratio) adjustment approach to generate tens of types of concentration gradient profiles with one single device. To demonstrate the advantages of this approach, we used a Christmas-tree-like microfluidic chip as the demo. Its performance was analyzed using numerical simulation models and experimental investigations, and it showed an excellent time response (~10 s). With on-demand flow rate ratios, the FFRR microfluidic device could be used for many lab-on-a-chip applications where flexible concentration profiles are required for analysis.

CONCEPTUAL DESIGN OF NON-IDEAL MIXTURE SEPARATION WITH LIGHT ENTRAINERS

A method is proposed to study the separation of minimum-, maximum-boiling azeotropic, and low volatility mixtures with a light entrainer, to investigate feasible regions of the key operating parameters reboil ratio (S) and entrainer - feed flowrate ratio (FE/F) for continuous processes. The thermodynamic topological predictions are carried out for 1.0–2, 1.0–1a, and 0.0–1 Serafimov’s class diagrams. It relies upon the knowledge of residue curve maps, along with the univolatility line, and it enables the prediction of possible products at the bottom of the column and limiting values of FE/F. The profiles of the stripping, extractive, and rectifying sections are calculated by equations considering S and FE/F, and they bring information about the location of singular points and possible composition profile separatrices that could impair process feasibility. Providing specified product composition and recovery, the approximate calculations are compared with rigorous simulations of extractive distillation processes. Separating non-ideal mixtures using a light entrainer provides more opportunities for the case when it is not easy to find an appropriate heavy or intermediate entrainer

Performance Research on a Methane Compact Reformer Integrated with Catalytic Combustion

AbstractA multichannel reformer integrated with catalytic combustion was investigated for methane steam reforming to produce hydrogen. In this system, the main portion of the required heat was supplied by methane oxidation in the catalytic combustor located on two sides of the reformer. In the compact multichannel reactor, the methane conversion rate is high enough compared to the equilibrium values at different temperatures. The performance of the multichannel reformer was investigated under various operating conditions, such as the reformer temperature and the feed stream ratios in both the reformer and the catalytic combustor. The best feed flow rate ratio of reforming to combustion ranged from 1.3 to 1.5, with > 95 % methane conversion. It is anticipated that this multichannel reformer can generate enough hydrogen for a 30‐W fuel cell system, due to its small volume.

Standing wave design of a four-zone thermal SMB fractionator and concentrator (4-zone TSMB-FC) for linear systems

For a dilute feed, a four-zone SMB with temperature gradient (4-zone TSMB-FC) can fractionate and simultaneously concentrate two solutes. Optimization of the operating parameters for this system, which include four zone flow rates and port switching time, is a major challenge because of the five variables. Initial choice of the variables using the triangle theory followed by a systematic search using rate model simulations is time-consuming. In this study, the SWD developed previously for isothermal systems is modified for the first time for a 4-zone TSMB-FC. The optimum operating parameters are determined with the new method. Only linear isotherm systems with significant mass transfer resistances are considered. For a dilute feed, a 4-zone SMB-FC can produce pure desorbent, in addition to extract and raffinate products with high purities. For the separation of p-xylene and toluene with silica gel in the temperature range from 0 to 80 °C, the enrichment factor in the linear region can be as high as 80 fold for an extract purity of 99.99 % and tenfold for raffinate purity of 99.8 %, while withdrawing the desorbent at a desorbent to feed flow rate ratio of 0.53 and 0.78, respectively.

Spiral-Wound Water-Gas-Shift Membrane Reactor for Hydrogen Purification

Water-gas-shift (WGS) membrane reactor is a promising approach to purify hydrogen produced by hydrocarbon or biomass reforming to fuel cell grade (<10 ppm CO). CO2-selective polymer membranes suitable for the above operation can potentially be fabricated into spiral-wound modules with catalyst packed on the feed side and sweep gas flowing on the permeate side. This paper presents a detailed model based on both mass and enthalpy balances as well as pressure drop to study this intricate reactive separation system. The kinetics of the WGS reaction was incorporated using a published rate expression for the commercial CuO/ZnO/Al2O3 catalyst. The resulting 1-D (cocurrent or countercurrent flow of feed and sweep streams) or 2-D (crossflow) system of differential equations was solved using COMSOL Multiphysics. The model was validated by comparing the predicted CO results with previously published experimental data for a lab-scale flat rectangular membrane reactor. The effects of the type of flow mode on concentration and temperature profiles within the membrane reactor were predicted. Also, a sensitivity study was carried out to quantify the effects of operating parameters like feed pressure, sweep to feed flow rate ratio, and steam/CO ratio on membrane area and hydrogen recovery. Results show that although the countercurrent flow mode is the most efficient in terms of CO reduction, the crossflow mode might provide a better trade-off between CO reduction and heat management. For the countercurrent mode, it was also shown that it is important to enhance both the CO2 permeance as well as the catalyst activity to reduce the membrane reactor size.

Co-current and counter-current configurations for ethanol steam reforming in a dense Pd–Ag membrane reactor

The ethanol steam-reforming reaction to produce pure hydrogen has been studied theoretically. A mathematical model has been formulated for a traditional system and a palladium membrane reactor packed with a Co-based catalyst and the simulation results related to the membrane reactor for both co-current and counter-current modes are presented in terms of ethanol conversion and molar fraction versus temperature, pressure, the molar feed flow rate ratio and axial co-ordinate. Although the counter-current mode does not always give an ethanol conversion higher than the one obtained in membrane reactor operated in co-current mode, in the first case it is always possible to extract more hydrogen from the reaction zone. With this theoretical analysis, different values of the operating parameters that allow to have a CO-free hydrogen stream and a complete recovery of the hydrogen from the lumen side of the reactor are investigated.

Co-current and counter-current modes for methanol steam reforming membrane reactor

In this simulation study, methanol steam reforming reaction to produce synthesis gas has been studied in a membrane reactor when shell side and lumen side streams are in co-current mode or in counter-current mode. The simulation results for both co-current and counter-current modes are presented in terms of methanol conversion and molar fraction versus temperature, pressure, H 2 O / CH 3 OH molar feed flow rate ratio and axial co-ordinate. Although the methanol conversion is sometimes higher in the membrane reactor operated in co-current mode than in the counter-current one, in the last case it is possible to extract more hydrogen from the reaction zone. With this theoretical analysis, we present a set of parameters which permit to have a CO-free hydrogen stream and a complete recovery of the hydrogen from the lumen side of the reactor.

A novel route to produce phthalic anhydride by oxidation of o-xylene with air over mesoporous V-Mo-MCM-41 molecular sieves

Mesoporous V-Mo-MCM-41 with Si/(V + Mo) ratio equal to 46, 92, 184 and 230 were synthesized using cetyltrimethylammonium bromide surfactant as template under hydrothermal conditions while the mesoporous materials were characterized using several techniques e.g., ICP-AES, XRD, N 2-adsorption, FTIR, TG/DTA, 51V-MAS-NMR, 95Mo-MCM-41, 29Si-MAS-NMR, SEM and TEM. The d-spacing value and unitcell parameter in the V-Mo-MCM-41 increases by increasing the metal ions content. FTIR studies showed that V- and Mo-ions were incorporated into the hexagonal mesoporous MCM-41 materials, however, the wavenumber of the anti-symmetric Si–O–Si vibration bands (1097 cm −1) in V-Mo-MCM-41 are higher than those in Si-MCM-41 (1081 cm −1). These bands should be due to the increase of the mean Si–O distance in the wall caused by the substitution of the small ionic radii of silicon by the larger ionic radii of vanadium and molybdenum. The surface area, pore diameter, pore volume, hydrothermal stability and acid sites in the V-Mo-MCM-41 decreases by increasing the metal ions content. The incorporated metal ions as V 5+ and Mo 6+ in V-Mo-MCM-41 are coordinated to Si(IV) by tetrahedral environments. The synthesized V-Mo-MCM-41 materials were found to be effective as catalysts in the oxidation of alkyl aromatics, e.g., in the oxidation of o-xylene using O 2 gas as the oxidizing agent for the production of phthalic anhydride. The effect of reaction temperature, feed flow rate ratio ( o-xylene:O 2 gas), contact time and recyclability on the selectivity of phthalic anhydride were studied. Thus, the selectivity of phthalic anhydride in the presence of V-Mo-MCM-41(46) catalyst was higher than that of other V-Mo-MCM-41 catalysts due to increasing the catalytic activity on the inner side pores of silica surface.

PETEOS simulation using EVOLVE, a deposition simulator

In this paper, we compare simulated and experimental silicon dioxide film profiles deposited over metal lines on a silicon substrate using plasma enhanced deposition from a mixture of tetraethoxysilane (TEOS) and oxygen. The deposition was performed in an Applied Materials Precision CVD 5000 at 673 K, 9 Torr, a 9:5 TEOS to oxygen feed flow rate ratio, and a power density of 10 W cm −2. We use EVOLVE, a physically based low pressure deposition simulator, to simulate this deposition using the structure of a set of constitutive relationships developed for this deposition process at very different deposition conditions. These constitutive models include (1) a plasma model, (2) a plasma sheath model and (3) the kinetics of the deposition reactions. By adjusting two independent parameters of the constitutive models, good agreement between simulated and experimental profiles is found. We also discuss a few common obstacles encountered while trying to match the details of simulated and deposited film profiles. We do not consider the simulations discussed in this paper to be completely physically based, because the constitutive relationships required for completely physically based simulations are not available. Regardless, process development can be guided by the results obtained through these simulations. In addition, comparisons between simulated and experimental profiles can provide information with which to design experiments to improve the constitutive relationships for a given deposition process.