Gas Absorption Rate Research Articles

E233 ミスト化ゼオライト粒子による炭酸ガス吸収の促進 : 続報 操作条件の影響

High efficiency of gas absorption may be one of the important techniques for protection of global environment. We have proposed the new method for Carbon Dioxide gas absorption, that is the condensate film method by utilizing condensation process and the solution condensate method. In present investigation, a new concept of the enhancement of gas absorption by utilizing zeolite particles with mist formation was proposed, and its proof experiment was conducted with regard to the gas absorption rate in vertical cooling tube. By comparing the present proposed method with falling liquid film method and our past-proposed methods, the effectiveness of the gas absorption through the zeolite particles and mist droplet was clarified. Furthermore, the effect of operating condition such as gas flow rate, gas concentration, temperature, vapor concentration and zeolite particle number density was examined.

Kinetics and chemical equilibrium of the hydration of formaldehyde

The reaction rate of the hydration of formaldehyde is obtained from the measured, chemically enhanced absorption rate of formaldehyde gas into water in a stirred cell with a plane gas–liquid interface, and mathematically modelling of the transfer processes. Experiments were performed at the conditions prevailing in industrial formaldehyde absorbers, i.e. at temperatures of 293– 333 K and at pH values between 5 and 7. The observed rate constants could be correlated as k h=2.04×10 5× e −2936/T s −1 . Using the results, and the dehydration reaction rate constant, obtained previously at similar conditions, the chemical equilibrium constant for the hydration is obtained as K h =e 3769/ T−5.494 .

The application of fine TiO 2 particles for enhanced gas absorption

The physical absorption of pure CO 2 in various liquids (water, hexadecane, and sunflower oil) containing micron sized TiO 2 particles has been investigated. Absorption studies were carried out in a batch stirred cell reactor at 298 K and initial pressures of 0.08 MPa. Solid loading and stirring intensities were varied systematically between 0–15 kg/m 3 and 3.3–12.5 s −1, respectively. Gas absorption rates are enhanced significantly in the presence of TiO 2 particles. Enhancement factors are a function of the solids loading and stirring intensity. Maximum enhancement factors of about 2 were observed for all solvents at low stirring intensities. The rate of gas absorption was theoretically analyzed using a heterogeneous unsteady state mass transfer model based on the Danckwerts surface renewal theory and a Langmuir-type of particle to interface adhesion isotherm. This model not only predicts the trends in the observed enhancement factors very well but also gives an accurate quantitative picture.

Gas Absorption with Instantaneous Irreversible Chemical Reaction in a Slurry Containing Sparingly Soluble Fine Reactant Particles

The problem of gas absorption followed by instantaneous irreversible chemical reaction in a slurry containing sparingly soluble fine reactant particles is considered. Models are developed for an infinitely deep quiescent liquid and, using the film theory, for an agitated liquid when the reactant particle dissolution in the liquid film next to the gas−liquid interface is nonnegligible. Simple analytical expressions for the rate of gas absorption are derived under the assumption of slow particle dissolution, and conditions are given for applicability of the models. A numerical example for the system SO2−Ca(OH)2 in water is discussed.

Absorption with instantaneous reaction in a droplet with sparingly soluble fines

AbstractThe problem of gas absorption followed by an instantaneous irreversible chemical reaction in a rigid droplet containing sparingly soluble fine reactant particles is discussed. A model was developed for the general case when the reactant particle dissolution near the gas–liquid interface is nonnegligible. Solids dissolution is treated taking into account the average spacing between the suspended particles. A simple analytical expression for the rate of gas absorption is derived under the assumption of slow particle dissolution, and conditions are given for applicability of the model. A numerical example, relevant for the spray‐dry desulfurization process, for the system SO2‐Ca(OH)2 in water is discussed.

Absorption of hydrogen sulfide into aqueous solutions of ferric nitrilotriacetic acid: local auto-catalytic effects

The rates of reactive absorption of H 2S into aqueous solutions of ferric nitrilotriacetic acid, at T=303 K and pH=4.5, studied in a flat-interface stirred cell, appear to be auto-catalyzed by freshly precipitated sulfur particles. These auto-catalytic effects, which are more prominent at higher ferric chelate concentration, seem to involve particle-to-interface adhesion phenomena. A model based on Higbie's penetration theory, which incorporates particle-to-interface adhesion, as well as a growing particle coverage during a liquid element's contact time at the interface, is used to analyze the experimental data. This model gives a reasonable description of the local auto-catalytic effects on the gas absorption rate.

Investigation of Enhanced Gas Absorption by Adsorptive Bucky Balls in a Multiphase Slurry Reactor in the Presence and Absence of Ultrasound

Fullerenes (e.g., bucky balls) constitute a fascinating class of novel materials, which have shown very high adsorption capacities for hydrogen (5-10 wt% at pressures of less than 1 bar near room temperature by the single-wall nanotubes) under gas-solid conditions. In this work, hydrogen absorption in aqueous slurries of bucky balls has been investigated in a flat stirred cell under slurry conditions at different solid loadings in the presence and in the absence of ultrasound. Enhancements in the gas absorption up to 2.4 were observed using suspended bucky balls. Further enhancements could be obtained by application of ultrasound during the experiment or by presonication of the slurry. Gas absorption rates are a strong function of the solid loading and the stirrer speed. The performance of the bucky balls was compared to that of activated carbon. Bucky balls showed a higher adsorption capacity for H 2 than activated carbon. The increase in the gas absorption in the presence and in the absence of ultrasound was theoretically analyzed using the enhanced gas absorption model. Good agreement between observed and theoretical enhancement factors was obtained.

Simultaneous Removal of Naphthalene and Sulfur Dioxide using Surfactant

Anionic surfactant was added during absorption to investigate the solubility of vapor phase naphthalene and SO\d2 in water. Anionic surfactant employed was sodium dodecyl sulfate. Lower than critical micelle concentration (CMC), the apparent solubility and absorption rates of SO\d2 or naphthalene apparent solubility increased linearly in proportion to the surfactant concentrations. The solubilization effect of micelles resulted in the increase. Because the micelle solubilization effect was greater than that of the decrease of the mass transfer coefficient, the gas absorption rate increased. When surfactant concentration was 0.1 M, the enrichment factor (EF) value of naphthalene with SO\d2 was 4.54, which was only half of its value without SO\d2. When surfactant concentration was 0.2 M, the SO\d2 EF values increased to 2.24. These empirical findings confirm that to increase the removal efficiency of simultaneous absorption of hydrophobic organic compounds and SO\d2 via a spray or packed tower, an anionic surfactant can be employed.

1524 ミスト化ゼオライト粒子による炭酸ガス吸収の促進

High efficiency of gas absorption may be one of the important techniques for protection of global environment. We have proposed the new method for Carbon Dioxide gas absorption, that is the condensate film method by utilizing condensation process and the solution condensate method. In present investigation, a new concept of the enhancement of gas absorption by utilizing Zeolite particles with mist formation was proposed, and its proof experiment was conducted with regard to the gas absorption rate in vertical cooling tube. Comparing the present proposed method with falling liquid film method and our past-proposed methods, the effectiveness of the gas absorption through the Zeolite particle and mist droplets was clarified.

SIMULTANEOUS ABSORPTION OF VAPOR PHASE POLYCYCLIC AROMATIC HYDROCARBON AND CARBON DIOXIDE IN ANIONIC SURFACTANT SOLUTIONS

The goal of this work was to investigate whether the solubility of vapor phase polycyclic aromatic compounds (PAHs) and CO2 in water could be enhanced by adding anionic surfactant during the absorption process. Naphthalene was the PAH surrogate and sodium dodecyl sulfate (SDS) was the anionic surfactant. A series of batch experiments in an absorption cell were performed at 50°C with the surfactant concentration both lower than and higher than the critical micelle concentration (CMC). The experimental findings indicate that the CMC was not a function of pH at values of 3, 5 and 7. Furthermore, at surfactant concentrations less than the CMC, naphthalene apparent solubility increased slightly. On the other hand, the equilibrium naphthalene or CO2 apparent solubility increased linearly, in proportion to the surfactant concentration at concentrations greater than the CMC. This is due to the solubilization effect of micelles, which were formed by the surfactant at concentrations above the CMC. During simultaneous absorption of the two, the presence of CO2 only slightly decreased naphthalene apparent solubility, while the apparent solubility of CO2 was drastically reduced in the presence of naphthalene. As the magnitude of the micelle solubilization effect was greater than the reduction of the mass transfer coefficient in the presence of the surfactant, the total gas absorption rate increased. When the surfactant concentration was 0.1 M, the enrichment factor (the ratio of the solubility in surfactant solution to that in water) values of naphthalene both with and without CO2 increased to 9.05 and 8.60, respectively. These experimental findings demonstrate that anionic surfactant may be applied to increase the removal efficiency of hydrophobic compounds and CO2 through either a spray or packed tower.

Gas absorption into aqueous reactive slurries of calcium and magnesium hydroxide in a multiphase reactor

Investigation of absorption of SO 2 into aqueous slurries of fine and reactive hydroxide particle of calcium and magnesium was carried out in a stirred vessel at 298 K at realistically high mass transfer coefficients. Enhancement in the rate of gas absorption was measured at different solid loadings and speed of agitation. The absorption process is theoretically analyzed using two different models. For the SO 2–Ca(OH) 2 system, a single reaction plane model was used and for the SO 2–Mg(OH) 2 system, a two reaction plane model incorporating the solids dissolution promoted by the reactions with the absorbed SO 2 in the liquid film was employed. A correct procedure was adopted to estimate the contribution of the suspended particles in the enhancement of gas absorption. Theoretical enhancement factors thus obtained compared well with the experimental data. The extra enhancement observed for the SO 2–Mg(OH) 2 system could be explained from the reaction between SO 2 and the dissolved [SO 3] 2−.

Gas absorption in an agitated gas–liquid–liquid system

Gas–liquid–liquid systems have gained interest in the past decade and are encountered in several important industrial applications. In these systems an immiscible liquid phase may affect the gas absorption rate significantly. This phenomenon, however, is not completely understood and underlying mechanisms need further study. In this work the well-known Danckwerts-plot technique is used to determine the liquid side mass transfer coefficient k L and the gas–liquid interfacial area a simultaneously in this type of systems. As absorption/reaction system CO 2 absorption in a 0.5 M K 2 CO 3 0.5 M KHCO 3 buffer solution catalysed by sodium hypochlorite was chosen. Toluene, n-dodecane, n-heptane and 1-octanol were applied as dispersed liquid phases. The Danckwerts-plot could be well used in gas–liquid–liquid systems and from the results it appeared that two types of systems exist; systems that enhance mass transfer and systems that do not enhance mass transfer. Effects at low dispersed phase hold-up were observed to be very strong and are thus important, but were not taken into account in further analysis of the effect of dispersed phase hold-up on mass transfer. In systems where dodecane and heptane were added to the buffer solutions no enhancement of mass transfer was observed. However, the addition of toluene and 1-octanol caused an enhancement of mass transfer that could be well described using a homogeneous model of the shuttle mechanism.

Absorption of Ozone and Seven Organic Pollutants by Populus nigra and Camellia sasanqua

Foliar absorption of seven organic pollutants (acetone, acetonitrile, acrolein, methyl ethyl ketone (MEK), isobutyl methyl ketone (IBMK), chloroform, and benzene), and ozone was examined. Two woody species (Populus nigra and Camellia sasanqua ) were exposed to each pollutant at a concentration of 0.5 or 1.0 ppmv (Imol mol -1 ), and gas absorption and transpiration rates were measured simultaneously. Ozone and acrolein were effectively absorbed by both species. MEK was absorbed by C. sasanqua only. A model analysis of gas exchange rates revealed that foliar absorption of the three pollutants was predominantly through the stomata, and cuticular contribution on gas removal is, if any, very small. The plant leaves showed no detectable absorption of the other five organic pollutants. We conclude that plant leaves act as an effective sink for some organic pollutants but not for others. The factor that determines whether plant leaves can effectively absorb pollutants in this study seems to be whether the pollutant is effectively metabolized in the leaf cells.

Heterogeneous mass transfer models for gas absorption in multiphase systems

Heterogeneous, instationary 2-D and 3-D mass transfer models were developed to study the effect of dispersed liquid-phase droplets near the gas–liquid interface on the local gas absorption rate. It was found among other things that droplets (or particles) influence local mass transfer rates over an area exceeding largely the projection of the droplets on the gas–liquid interface. For a specific application particle–particle interaction was studied and could be described by a single parameter, depending only on the minimum interparticle distance. For gas absorption flux prediction an unit cell must be defined. The sensitivity of the absorption flux to the definition of the unit cell was investigated. Finally, a complete strategy to arrive at gas absorption flux prediction from single particle simulations has been proposed.

Measurement of gas diffusivity in heavy oils

Molecular diffusion of gases in oil plays a role in several heavy oil recovery processes. In solution gas drive, the gas diffusion coefficient has a direct impact on the amount of gas that is released and the level of supersaturation that exists during pressure depletion. In the Vapex process, molecular diffusion controls the rate at which the solvent vapour is absorbed by the oil. Molecular diffusion is also important in supercritical fluid extraction of heavy oils and in recovery of residual oil by miscible displacement. Unfortunately experimental data on gas diffusion coefficient in heavy oils are relatively scarce due to the tedious nature of diffusivity measurements. The main objective of this work was to develop a simple experimental technique for measuring gas diffusion coefficients in heavy oils. Diffusion coefficients of carbon dioxide and methane were measured by measuring the rate of gas absorption in a high-pressure windowed cell. The diffusion equation, coupled with the gas material balance equation, was used to history match the gas absorption data using the diffusion coefficient as an adjustable parameter. The diffusion coefficients calculated by this history match technique are compared with the reported values of diffusion coefficients in similar systems.

Oxidation of Ferrous Nitrilotriacetic Acid with Oxygen: A Model for Oxygen Mass Transfer Parallel to Reaction Kinetics

The kinetics of the reaction of ferrous chelate of nitrilotriacetic acid (NTA) and gaseous oxygen were studied in a stirred-cell reactor. The initial concentration of ferrous chelate was 0.100 kmol/m(3). Other reaction conditions include 293 <T <333 K, 2 <pH <10, and 20 <p(O2) <90 kPa. The structure of ferrous chelates as a function of temperature and pH was studied by potentiometric titrations. Under the conditions applied, the reaction rate appeared to proceed according to R-O2 = k(1,2)C(O2)C(Fe(II))(2) with k(1,2)(infinity) = (1.4 +/- 0.35) x 10(7) m(6)/mol(2) s and E-a = 52.5 +/- 1.4 kJ/mol for no excess NTA. In the presence of excess NTA, a double-coordinated ferrous species is produced, whose reactivity appears to depend on pH and NTA concentration. Due to undesired side reactions with ligand NTA, more oxygen disappears than expected from the conversion of ferrous chelate. If no excess ligand is present, the gas absorption rate is pH-dependent for pH less than or equal to 4. Excess ligand results in a pH-dependence over the entire pH-range studied. The observed regeneration rate as a function of pH can be explained from a more comprehensive model, accounting for complex chemical reaction, in parallel with interfacial mass-transfer limitations.

Bubble Behaviour and Absorption Rate in Gas Injection through Rotary Lances.

Bubble behaviour and absorption rate of gas injected into a liquid bath through rotary L-shaped lances were studied by cold models. A high-speed video recording system was used to measure the bubble diameter and the rising velocity. The absorption rate of injected CO2 gas in aqueous NaOH solution was measured by using a pH meter. It is found that the lance rotation leads to a decrease in the bubble diameter and the rising velocity as compared with the stationary lance. The bubbles produced by a multi-hole lance are smaller than those produced by a single-hole lance. The reduction in the bubble rising velocity is connected with the decrease in the bubble diameter, distribution of bubbles over the liquid bath and distortion of the bubble rising path due to the lance rotation. The gas absorption rate for the rotary lances is larger than that for the stationary lance. The effect of the rotation speed on volumetric mass transfer coefficient is larger at lower gas flow rate. The multi-hole lance can increase the volumetric mass transfer coefficient by about three times larger than the single-hole lance.The results are discussed in terms of the bubble coalescence, mass transfer coefficient and total interfacial area between bubbles and liquid

Gas absorption in reactive slurries: Particle dissolution near gas-liquid interface

The rates of gas absorption into reactive slurries constituted by “fine” particles of a sparingly soluble reactant are known to be enhanced when the particle size is smaller than the characteristic diffusional lengths of the reactive species. This study examines the process of particle dissolution and the consequent change in particle size(s) near the gas-liquid interface, in the presence of diffusional gradients, using Higbie's extended theory of mass transfer with chemical (instantaneous) reaction. The effect of changing particle size (including complete dissolution of the particles in this “film” zone) on the mechanism and extent of enhancement in the specific rate of absorption has been assessed using a population balance approach to track the interaction of the dissolution process with the evolving particle size distributions. It has been shown that the rates predicted from the proposed theory differ considerably from those computed using models available in the literature, for particles which are “small” enough. A variety of initial particle size distributions of different spreads have been used to show that for a given mean particle size, wide distributions produce lower enhancements in the specific rate than narrow ones. The specific rate-batch time trajectories for a typical batch slurry reactor have been generated along with the evolution of the particle size distributions in the bulk slurry phase in order to track the solid conversion as a function of batch time. Such conversions computed from theories available in the literature are likely to be gross overestimates in relation to the actual scenario. Some of the reported experimental absorption data have been reinterpreted in the light of the models developed here.

Modeling of gas absorption into turbulent films with chemical reaction

A mathematical model has been developed to predict the rates of gas absorption in turbulent falling liquid films with and without the first order homogeneous reaction and external gas phase mass transfer resistance. The eddy viscosity model used to describe the flow distribution is the van Driest model, modified in the outer region of the film by the use of an eddy diffusivity deduced from gas absorption measurements. The results are given for special cases to illustrate the effects of turbulence, reaction rate and gas phase resistances on the concentration profiles and the rates of gas absorption.

Modelling and experimental study of key parameters of absorption on wetted sphere contactor

Liquid spray curtains can be used to contain the effect of accidental release of toxic gases; they work by a combination of dilution and absorption. In this work, we have investigated the possibility of adding chemicals to the liquid spray which may react with the toxic gases and enhance the absorption capacity of the spray. The work is aimed at a fundamental understanding of the chemistry and the mass transfer behavior of toxic gas — reactive liquid systems. We have performed continuous mass transfer rate experiments on one sphere absorber (the model systems considered being CO 2 Na 2CO 3 and O 2 Na 2SO 3 ), and we have interpreted these in terms of mass transfer with chemical reaction theory. The system was modelled as a series of a sphere gas-liquid reactor (SGLR) and a continuous-stirred tank (CST). A numerical technique was used to predict both the unsteady state liquid reactant concentration and the specific absorption rate of gas in the system. A systemic approach was employed to determine values of key parameters that quantify a given mechanism. The results obtained, together with pilot plant results on the hydrodynamics of liquid sprays, may form the basis for a predictive model of chemical liquid spray behavior in environmental control.