Chemical Pumping Research Articles

New sealless design for chemical applications

Chemical pumping applications are highly demanding. For years, sealless magnetic drive centrifugal pumps have been doing the job, serving as the workhorses of many chemical plants. As environmental regulations get tighter and applications become even more demanding, sealless pump manufacturers must respond with reliable, rugged pumps. Daniel Roll , of Finish Thompson, describes the company's latest offering.

Char-Supported Nano Iron Catalyst for Water-Gas-Shift Reaction: Hydrogen Production from Coal/Biomass Gasification

This paper reports a novel char-supported nano iron catalyst prepared from the pyrolysis and gasification of iron-loaded Victorian brown coal. The catalyst samples were examined using X-ray diffraction and TEM. Iron is highly dispersed in the char matrix as magnetite with a particle size smaller than 50 nm. The catalyst is found experimentally to be very active for the water–gas-shift reaction at temperatures as low as 300°C. A conceptual process is proposed for the integrated catalytic production of hydrogen based on the gasification of solid fuels such as coal and biomass. Within the proposed process, the char-supported nano Fe catalyst in a moving-bed reactor has the potential to carry out integrated functions of chemical heat pumping, hot gas cleaning, pollutant (particularly NH3 and H2S) abatement and water–gas-shift reaction catalysis.

A Concept of Chemical Potential Pumping Effect of Nonstoichiometric Oxides and the NOx Sensing Mechanism of the Perovskite-Type La0.5Sr0.5FeO3

A concept of chemical potential pumping effect was introduced to describe the NOx sensing mechanism of oxide catalysts with high electronic conductivity and large carrier density. When NOx gas in a gas-stream decomposed on the surface of the catalyst oxides continuously, the high oxygen potential released by the decomposition of NOx stationarily covered the whole surface of the oxide. Then, the bulk oxide was equilibrated with the steady-state high oxygen potential of the surface, which was much larger than that determined by the oxygen pressure of the surrounding gas-phase. This effect was confirmed by the conductivity enhancement of La2CuO4 and La0.5Sr0.5FeO3 with NO2 as well as nonstoichiometry variation of La0.5Sr0.5CoO3 and EMF of galvanic cell with La0.6Sr0.4CoO3−d. It was shown that the chemical potential pumping effect appears essentially on dense materials while the effect is hardly observed on porous material with large surface relative. On La0.5Sr0.5FeO3 as well as on La2CuO4, NO2 was found to decompose into NO and O2, while NO was almost inactive on these oxides.

Reactor and Technical Feasibility Aspects of a CO2 Decomposition-Based Power Generation Cycle, Utilizing a High-Temperature Membrane Reactor

The technical feasibility of separating and decomposing CO2 in the context of a novel energy generation cycle during the operation of a glass furnace was investigated. The concept envisions CO2 decomposition to take place in a membrane reactor utilizing high-temperature solid-oxide membranes with the aid of oxygen chemical pumping. The glass furnace environment is well suited for such an application because it provides the high-temperature conditions needed for the operation of these membranes. As part of this effort, solid-oxide membranes were prepared and their oxygen permeation was measured in a membrane reactor system. The O2 permeabilities in the presence of a reactive sweep were significantly higher than the corresponding permeabilities measured in the presence of He as a sweep gas. These membranes were utilized for CO2 decomposition in a membrane reactor. Conversions significantly higher than the expected thermodynamic equilibrium values were attained. Engineering calculations of the overall glass furnace efficiency were also carried out, and the conditions for optimal performance were determined. The effects of the application of this novel cycle on glass furnace operation in terms of combustion stability (quantified by the extinction strain rates of the relevant combustion mixtures) and pollutant (NOx) emissions were also determined. Generally, improvements in combustion intensity and stability can be achieved but at a cost of increased NOx emissions and vice versa. A range of conditions also exists for which the cycle allows for effective waste heat utilization without undue impact on pollutant emissions.

Effect of the vibrational nonequilibrium on the characteristics of a gas flow of a reacting N 2O+CO+(H 2) mixtures

The problem of the calculation of chemical and vibrational nonequilibrium flow of a multicomponent gas mixture through a nozzle is formulated. Coupling of the chemical and vibrational kinetic processes was taken into account. The coefficient of optical amplification and/or inversion for the transition CO 2(001) → CO 2 (100) has been used as one of the principal characteristics calculated. The nonequilibrium behaviour of the reacting N 2O+CO+He mixture has been considered in the subsonic, transonic, and supersonic regions of flow. The possibility of the superequilibrium chemical pumping in the supersonic region, as a result of the effect of fast bimolecular reactions, was examined for different initial conditions and different nozzle characteristic dimensions; the influence of small concentrations of the substances containing hydrogen was considered also.

A self-consistent fluid model for radio-frequency discharges in SiH4–H2 compared to experiments

A one-dimensional fluid model for radio-frequency glow discharges is presented which describes silane/hydrogen discharges that are used for the deposition of amorphous silicon (a-Si:H). The model is used to investigate the relation between the external settings (such as pressure, gas inlet, applied power, and frequency) and the resulting composition of the gas and the deposition rate. In the model, discharge quantities such as the electric field, densities, and fluxes of the particles are calculated self-consistently. Look-up tables of the rates of the electron impact collisions as a function of the average electron energy are obtained by solving the Boltzmann equation in a two term approximation for a sequence of values of the reduced electric field. These tables are updated as the composition of the background neutral gas evolves under the influence of chemical reactions and pumping. Pumping configuration and gas inlet are taken into account by adding source terms in the density balance equations. The effect of pumping is represented by an average residence time. The gas inlet is represented by uniformly distributed particle sources. Also the radial transport of neutrals from the discharge volume into the discharge-free volume is important. As the fluid model is one dimensional, this radial transport is taken into account by an additional source term in the density balance equations. Plasma–wall interaction of the radicals (i.e., the growth of a-Si:H) is included through the use of sticking coefficients. A sensitivity study has been used to find a minimum set of different particles and reactions needed to describe the discharge adequately and to reduce the computational effort. This study has also been used to identify the most important plasma-chemical processes and resulted in a minimum set of 24 species, 15 electron-neutral reactions, and 22 chemical reactions. In order to verify the model, including the chemistry used, the results are compared with data from experiments. The partial pressures of silane, hydrogen, disilane, and the growth rate of amorphous silicon are compared for various combinations of the operating pressure (10–50 Pa), the power (2.5–10 W), and the frequency (13.56–65 MHz). The model shows good agreement with the experimental data in the dust free α regime. Discharges in the γ′ regime, where dust has a significant influence, could not be used to validate the model.

Selective separation and concentration of vanadium(V) by a chemical pumping hollow-fiber supported liquid membrane

A hollow fiber supported liquid membrane (HFSLM) system for the separation and concentration of vanadium (V) has been developed and characterized by using tricaprylylmethylammonium chloride (Aliquat 336®) dissolved in dodecane as carrier. The transport of vanadium through the liquid membrane is based on a pH gradient between feed and stripping solutions to provide an appropriate change on the chemical species of aqueous vanadate, i.e., aqueous metavanadate, VO 2(OH) 2 −1 (4.0 < pH < 7.0) is extracted by Aliquat 336 and VO 3OH 2− (pH > 8.0) is not extracted. Selective separation and concentration experiments were carried out at low vanadium(V) concentration (mg 1 −1 level). The study of the HFSLM includes the influence of hydrodynamic, physical and chemical conditions, i.e., flow rate of feed solution through the fibers, number and length of fibers, lifetime of the system, initial vanadium concentration in the feed solution, and pH of aqueous phases. Transport of V(V) increases with the flow rate of the feed solution through the fibers until a ‘plateau’ is reached (> 0.2 ml min −1 in a single fiber). It has been shown that in a HFSLM module, the membrane area increases with the number of fibers but also there is an increase of the sterical hindrance between the fibers which reduces the expected increase of vanadium transport. On the other hand, the length of the fibers has a scarce influence on the transport process. The effect of the acidity of the feed solution on the vanadium transport shows a similar behavior to that obtained previously for liquid-liquid distribution and laminar SLM studies. The results obtained indicate that vanadium(V) can be effectively concentrated and selectively separated by hollow fiber SLM containing Aliquat 336® as carrier.

Chemical pumping of rhodium by a supported liquid membrane containing Aliquat 336 as carrier

The mass transfer of Rh(III) from aqueous feed chloride solutions containing SCN − through a solid-supported liquid membrane (SSLM) consisting of Aliquat 336 dissolved in dodecane has been studied. The influence of hydrodynamic conditions as well as the chemical composition of the system on the permeation rate was investigated. Among the reagents tested as carriers, quaternary amines have been shown to be the most effective for the metal transport. Aliphatic organic diluents were chosen to avoid the degradation of the polymeric support, and 1-dodecanol was used as a modifier to increase the solubility of the extractant. The presence of thiocyanate in the feed solution was essential for the extraction of Rh(III). Furthermore, previous heating of the feed solution was necessary in order to form the extractable complex Rh(SCN) 6 3. Different reducing compounds were tested as stripping agents, and 1.0 M NaHSO 3 solution was found to be the most effective to strip Rh(III) from the organic phase. Under these conditions, transport of Rh(III) through the membrane against its concentration gradient was achieved. The transport behavior of palladium and platinum in the proposed liquid membrane system was also studied. The obtained results reveal the possibility of exploiting the kinetic differences in the chemistry of the platinum group metals in the design of a process for the separation of these three metals.

Chemical pumping in vacuum technology

Chemical pumping in vacuum technology has gained an ever increasing importance during the last two decades. It is based on the capability of metals, such as Zr, Ti, Ba and others, in pure or (more usually) alloy forms, to chemisorb the active residual gases present in vacuum devices or systems. These metals, used in powder form or in many different configurations, are known as getters; their role is to improve and maintain the required vacuum in many kinds of vacuum devices working in the range of 1–10 −11 Pa. They are often used, particularly in sealed-off devices, as in situ pumps to speed up the manufacturing process and make it more cost effective. Their application is performed in an evaporated or non-evaporated mode and spans from CRTs to big particle accelerators and even to gas purifiers used in the semiconductor industry. This broad range of applications has required a continuous enhancement in the study of getters from both the technical and the scientific point of view. The most relevant achievements in this field will be here reviewed and discussed.

The possibility of “long” population inversion in active media for IR chemical lasers

Theoretical investigation shows that during the chemical pumping of high vibrational levels of diatomic molecules partial population inversion between these levels can exist much longer than that for the vibrational transition 1-0. In case of fast VV exchange the “long” inversion appears long after finishing of the inversion for the 1→0 transition. It lasts up to completion of the chemical pumping reaction. The calculations are made for a number of mixtures used as active media for available lasers: H 2/F 2, CS 2/O 2.

Calculation of infrared limb emission by ozone in the terrestrial middle atmosphere: 1. Source functions

Two statistical equilibrium models are compared to analyze the departure from local thermodynamic equilibrium (LTE) in the vibration‐rotation bands of ozone in the middle atmosphere. The bands that emit in the 9–11 μm spectral interval depart from LTE due to chemical pumping, spontaneous emission, radiative absorption, and photochemical reaction. The diurnal variation in the ν1 and ν3 fundamental band source functions is determined by the diurnal changes in the rate of photolysis of ozone by solar radiation. The hot band source functions (υ &gt; 2) are invariant above 85 km due to the diurnal invariance in the chemical pumping process. The magnitude of the hot‐band source functions is uncertain because of the lack of understanding of the chemical pumping process. Collisional quenching of vibrationally excited ozone by atomic oxygen may reduce the magnitude of the ν3 and ν1 fundamental source functions by 10% near 100 km.

Calculation of infrared limb emission by ozone in the terrestrial middle atmosphere: 2. Emission calculations

The spectrally integrated limb radiance is calculated for ozone and for carbon dioxide in the 9–11 μm spectral interval for tangent heights between 30 and 100 km for noon and midnight conditions using a high‐resolution, line‐by‐line radiative transfer model that incorporates nonlocal thermodynamic equilibrium (NLTE) energy level populations in the transmittance calculations and NLTE source functions. The radiances assuming local thermodynamic equilibrium (LTE) are compared to the NLTE radiances. The NLTE ozone limb radiance is equal to the LTE radiance below 55 km at noon and below 70 km at midnight. The largest difference between the LTE and NLTE spectrally integrated ozone radiances occurs near 96 km in tangent height at noon and near 93 km at midnight. The difference between radiances decreases significantly from noon to midnight and is dependent on the portion of the spectral interval that is observed. Because of the uncertainty in the chemical pumping process, limb radiances utilizing two statistical equilibrium models of ozone are compared, yielding a maximum 32% difference in the spectrally integrated radiance at a tangent height of 84 km. Overlap of ozone spectral lines from bands possessing different source functions is not significant in calculating the infrared limb emission from the mesosphere and lower thermosphere. Finally, carbon dioxide is predicted to be responsible for a significant fraction of the total limb radiance in the 9–11 μm spectral interval in the daytime upper mesosphere and lower thermosphere. The implications of NLTE radiative transfer on the remote sensing of ozone are discussed.

Carbon Dioxide Transport by Ocean Currents at 25°N Latitude in the Atlantic Ocean

Measured concentrations of CO(2), O(2), and related chemical species in a section across the Florida Straits and in the open Atlantic Ocean at approximately 25 degrees N, have been combined with estimates of oceanic mass transport to estimate both the gross transport of CO(2) by the ocean at this latitude and the net CO(2) flux from exchange with the atmosphere. The northward flux was 63.9 x 10(6) moles per second(mol/s); the southward flux was 64.6 x 10(6) mol/s. These values yield a net CO(2) flux of 0.7 x 10(6) mol/s (0.26 +/- 0.03 gigaton of C per year) southward. The North Atlantic Ocean has been considered to be a strong sink for atmospheric CO(2), yet these results show that the net flux in 1988 across 25 degrees N was small. For O(2) the equivalent signal is 4.89 x 10(6) mol/s northward and 6.97 x 10(6) mol/s southward, and the net transport is 2.08 x 10(6) mol/s or three times the net CO(2) flux. These data suggest that the North Atlantic Ocean is today a relatively small sink for atmospheric CO(2), in spite of its large heat loss, but a larger sink for O(2) because of the additive effects of chemical and thermal pumping on the CO(2) cycle but their near equal and opposite effects on the CO(2) cycle.

Time structure of iodine laser pulse in the free running mode of operation

Time structure of iodine laser pulse in the free running mode of operation was studied using the power amplifier of laser system PERUN as the laser oscillator. Two characteristic shapes of laser pulse correspond to different regimes of laser operation, the existence of which is ascribed to the critical concentration of I2 molecules. Simultaneously an additional chemical pumping was proved at least in the initial phase of photodissociation and in a late-time lasing after the end of flashlamps pumping light.

Effects of translational and rotational nonequilibrium on cw chemical laser performance

A previous model used to describe cw chemical laser performance is generalized to include rotational as well as translational nonequilibria. The resultant equations are simplified by the realistic assumption that translational and rotational relaxation rates are fast compared with convection, chemical pumping, and collisional deactivation rates. As a consequence, translational and rotational relaxation are in equilibrium with stimulated emission. A further simplification is introduced by the assumption |1-(R(t)/R(r))|(Delta nu (h)/Delta nu (d) << 1, where R(t)/R(r) is the ratio of translational to rotational relaxation rates, and Delta nu (h)/Delta nu (d) is the ratio of homogeneous to Doppler widths. The resultant system of equations is independent of rotational relaxation. An amplifier solution is presented that predicts saturation effects in accord with experiments. Fabry-Perot oscillator solutions are also presented for a multiline saturated laser and a partly saturated single-line laser. The present results provide a basis for simplification of numerical codes. It is concluded that a reasonable first estimate for cw chemical laser performance can be obtained by assuming rotational equilibrium and translational nonequilibrium.

Chemical heat pumping—A rapid experimental procedure for investigating the suitability of salt hydrates under dynamic conditions

A rapid experimental procedure of interest in determining the suitability of salt hydrates to be used in chemical heat pumping is described. Thermogravimetry under controlled water vapour pressure is utilized as the key diagnostic method. The test procedure relies largely on two critical tests: a cycling and an inhibition test. The former gives information on the stoichiometric reversibility and hysteresis between the dehydration and rehydration branches, while the inhibition test yields more quantitative information about the extent of inhibition. The latter represents a source of irreversibility inherent to the salt hydrate system. The test procedure is discussed and illustrated using four different salt hydrates: barium chloride, sodium sulphide, magnesium chloride and lithium hydroxide.

On hot atom non-equilibrium processes in laser chemistry and chemical lasers

Hot atom reactions in laser chemistry and in the pumping of some kinds of chemical lasers are treated by the method of the non-equilibrium chemical kinetics proposed in previous works of the author. This method is based on the use of the multigroup approximation for the description of hot atom slowing down. The three-group approximation is applied to the kinetics of two hot H atom reactions with N 2O having different activation energies. The hot atoms are supposed to be produced by 248 nm excimer laser photolysis of HI and to have initial kinetic energies of 1.8907 and 0.95400 eV. The kinetics of these reactions and the dependence of the product yields on the rare gas concentration in the system are obtained. It was shown how the same formulae (with a change of symbols) can be applied to the description of the vibrotational level populations of product molecules. Some kinetic experiments are suggested to obtain the data necessary for the determination of the group constants. The hot atom kinetics of the chemical laser pumping made by the light of a flash-lamp (or of a laser) or by the particle beam is studied by use of the two-group approximation. A two-level model of the lasing molecule is employed. Lasing molecules are supposed to be produced by a hot atom reaction with the bulk molecules. The inverse population and its dependence on the rare gas concentration in the system are obtained. The possibility and usefulness of more complicated models (more energy groups and more molecular levels) are discussed.

Feasibility of construction of a chemical laser utilizing theB→Xelectronic transition in the IF molecule

A model is proposed of chemical pumping of the B3Π0+ state of the IF molecules in F–H2–NF2– IF mixtures. This model is used in numerical calculations of the kinetics of the relevant reactions. It is shown that the B→X transition in IF can ensure a high small-signal gain which should be sufficient for lasing. The processes which limit the rate of pumping of the upper active level are identified. Methods for removing such limitations are suggested.

Bromine photodissociation chemical laser

The development of a photodissociation chemical laser utilizing the 2P1/2–2P3/2 transition between components of the fine structure of the bromine atom (λ = 2.714 μ) is reported. The laser utilizes an i-C3F7I–IBr mixture. As a result of pulsed photoinitiation of this mixture, both photodissociative pumping IBr + hν → Br(2P1/2) + I, typical of an IBr molecular photodissociation laser, and chemical pumping RI + hν → R + I(2P1/2); I(2P1/2) + IBr → I2 + Br(2P1/2), similar to that found in a chemical laser utilizing an RI + Br2 mixture, are achieved simultaneously. The maximum output energy of a photodissociation chemical laser is 3.9 and 1.6 times higher than the values for photodissociation and chemical lasers, respectively. The degree of excitation of bromine atoms in the second reaction, determined by laser resonance spectroscopy, is e 5 = [Br(2P1/2)] / [Br (2P1/2)] + [Br(2P3/2)] = 0.5 ± 0.1.

An updated review of getters and gettering

A brief review of present day getter materials is made with reference to the two principal families, i.e., evaporable and nonevaporable getters. The main physicochemical processes involved in the gettering process are reviewed in order to establish the concept of gettering-selective chemical pumping. Examples of practical getter devices are described in connection with a brief overview of some of the most common applications. However, most emphasis will be placed in describing some of the most advanced and more unusual applications of getters which may not always be in widespread use but which indicate the versatility of gettering in widely differing fields.