Simultaneous absorption of two gases accompanied by reversible instantaneous chemical reactions

The problem of simultaneous absorption of two gases accompanied by reversible instantaneous chemical reactions is considered. Analytical equations are derived for the rates of absortion of the two gases. The solution is valid when the diffusivities of all species are assumed to be the same. The theoretical aspects of the problem of simultaneous absorption of hydrogen sulphide and carbon dioxide in amine solutions under equilibrium reaction conditions are also considered.     

Simultaneous absorption with reaction in a slurry containing fine particles

The simultaneous absorption of two gases accompanied by chemical reaction into a slurry of fine suspended particles was numerically analysed using the model obtained with some extension of the corresponding single gas absorption.Experiments were performed for the simultaneous absorption of sulfur dioxide and carbon dioxide with a plane gas—liquid type stirred tank absorber. The experimental results were satisfactorily elucidated by the proposed model and it is suggested that when accompanied by sulfur dioxide absorption, carbon dioxide may almost be regarded as an inert gas.     

Rate-based modelling of SO2 absorption into aqueous NaHCO3/Na2CO3 solutions accompanied by the desorption of CO2

A rate-based model of a counter-current reactive absorption/desorption process has been developed for the absorption of SO₂ into NaHCO₃/Na₂CO₃ in a packed column. The model adopts the film theory, includes diffusion and reaction processes, and assumes that thermodynamic equilibrium among the reacting species exists in the bulk liquid. Model predictions were compared to experimental data from literature. For the calculation of the absorption rate of SO₂ into NaHCO₃/Na₂CO₃ solutions and concomitant CO₂-desorption, it is important to take into account all reversible reactions simultaneously. It is clear that the approximate analytical based model cannot be expected to predict the absorption rates under practical conditions because of the complicated nature of the reactive absorption processes. The rigorous numerical approach described here only requires definition of the individual reactions in the system, and subsequent solution is independent of specific assumptions made, or operational variables like pH or compound concentrations. As an example of the flexibility of this approach, additional calculations were conducted for SO₂ absorption in a phosphate-based buffer system.     

燃煤烟气中细颗粒物与共存气态组分对膜吸收CO2的影响

由于燃煤烟气中细颗粒物和气态污染物难以完全脱除,同时经湿法脱硫后烟气中水汽接近饱和状态,因此,有必要揭示细颗粒物及共存气态组分对膜吸收CO₂的影响。采用燃煤热态试验装置,考察了燃煤烟气中细颗粒物、SO₂、水汽对膜吸收CO₂性能的影响,并进行了实际燃煤湿法脱硫净烟气环境下的膜吸收CO₂试验。结果表明:细颗粒物随烟气通过膜组件后,部分细颗粒物可被膜截留,沉积于膜表面,导致膜吸收CO₂效率下降,其影响程度随细颗粒物浓度的降低而减弱,与细颗粒物物性有一定关系,通过有效降低烟气中细颗粒物浓度,可显著延长膜的稳定运行时间;SO₂的存在会与CO₂产生竞争吸收现象,但因烟气中SO₂含量远低于CO₂,对CO₂吸收效率影响不明显;对于水汽,只需在运行一段时间后对膜组件作气体干燥反吹,可基本维持膜组件的稳定运行。     

An analysis of simultaneous absorption of two gases reacting between themselves in a semi-batch reactor

The problem of simultaneous absorption of two gases reacting between themselves in a semi-batch reactor has been analysed. An exact analytical solution for the enhancement factor has been obtained which requires neither a prior knowledge of the regime of absorption nor arbitrary choice of bulk liquid phase concentrations of gaseous reactants. The methodology developed here can easily be extended to a continuous flow reactor.     

Integrated adsorption and absorption process for post-combustion CO2 capture

This study explored the feasibility of integrating an adsorption and solvent scrubbing process for post-combustion CO₂ capture from a coal-fired power plant. This integrated process has two stages: the first is a vacuum swing adsorption (VSA) process using activated carbon as the adsorbent, and the second stage is a solvent scrubber/stripper system using monoethanolamine (30 wt-%) as the solvent. The results showed that the adsorption process could enrich CO₂ in the flue gas from 12 to 50 mol-% with a CO₂ recovery of >90%, and the concentrated CO₂ stream fed to the solvent scrubber had a significantly lower volumetric flowrate. The increased CO₂ concentration and reduced feed flow to the absorption section resulted in significant reduction in the diameter of the solvent absorber, bringing the size of the absorber from uneconomically large to readily achievable domain. In addition, the VSA process could also remove most of the oxygen initially existed in the feed gas, alleviating the downstream corrosion and degradation problems in the absorption section. The findings in this work will reduce the technical risks associated with the state-of-the art solvent absorption technology for CO₂ capture and thus accelerate the deployment of such technologies to reduce carbon emissions.     

Experimental measurement of gas permeability through bitumen: results for H2, N2 and O2

This study reports experimental results concerning the transport of permanent gases (H₂, O₂, N₂) through bitumen between 15 and 25 °C. A pressure differential technique, already used in membrane science in order to determine the permeability of gases through dense polymeric films, has been attempted with bitumen samples. It is shown that reproducible permeability data can be obtained thanks to this strategy, providing that bitumen mechanical resistance is improved by a support paper and a low leak module is used. Experimental results are analyzed in terms of permeability value and temperature dependency (activation energy) in comparison with other dense and permeable organic solids (polymers). The limitations of the technique as well as its potential extension to diffusion coefficient determination are discussed.     

The absorption of CO2 by amine-potash solutions

CO₂ has been absorbed in a stirred vessel into aqueous solutions of MEA and DEA containing K₂CO₃, K₂SO₄ and Na₂SO₄ at 25° and 11°C. While electrolytes in general appear to increase the rate of reaction between CO₂ and both MEA and DEA, K₂CO₃ increases the rate of reaction of DEA much more than that of MEA. The addition of K₂CO₃ to solutions of DEA increases the absorption rate, in spite of the decrease in the solubility and diffusivity of CO₂. The observations help to explain why DEA is an effective promoter for the absorption and desorption of CO₂ by hot, concentrated potash solutions.     

UV/H2O2氧化联合CaO吸收脱除NO的传质-反应动力学

在实验室规模的光化学反应器中,基于实验研究﹑动力学理论以及双膜理论,研究了UV/H₂O₂氧化联合CaO吸收(UV/H₂O₂-CaO工艺)脱除燃煤烟气中NO的传质-反应动力学。分析了NO吸收的传质-反应过程,明确了NO吸收过程的主要控制步骤和强化措施,测定了关键的动力学参数,推导了NO吸收过程的理论模型。结果表明:在实验范围内,NO吸收速率随着NO浓度的增加几乎呈线性增加。随着H₂O₂浓度和CaO浓度的增加,NO的吸收速率均呈现先增加后变缓的趋势。UV/H₂O₂-CaO工艺脱除NO是一个拟一级快速反应过程,强化气相主体扰动﹑增加气液接触面积和提高NO分压可有效提高NO的吸收速率。NO吸收速率方程的计算值和实验值具有较好的一致性。     

CO2 absorption and regeneration of alkali metal-based solid sorbents

Potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property were measured in the presence of H₂O in a fixed-bed reactor, during multiple cycles at various temperature conditions (CO₂ capture at 60 °C and regeneration at 130–400 °C). Sorbents such as K₂CO₃/AC, K₂CO₃/TiO₂, K₂CO₃/MgO, and K₂CO₃/Al₂O₃, which showed excellent CO₂ capture capacity, could be completely regenerated above 130, 130, 350, and 400 °C, respectively. The decrease in the CO₂ capture capacity of K₂CO₃/Al₂O₃ and K₂CO₃/MgO, after regeneration at temperatures of less than 200 °C, could be explained through the formation of KAl(CO₃)₂(OH)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely converted to the original K₂CO₃ phase. In the case of K₂CO₃/AC and K₂CO₃/TiO₂, a KHCO₃ crystal structure was formed during CO₂ absorption, unlike K₂CO₃/Al₂O₃ and K₂CO₃/MgO. This phase could be easily converted into the original phase during regeneration, even at a low temperature (130 °C). Therefore, the formation of the KHCO₃ crystal structure after CO₂ absorption is an important factor for regeneration, even at the low temperature. The nature of support plays an important role for CO₂ absorption and regeneration capacities. In particular, the K₂CO₃/TiO₂ sorbent showed excellent characteristics in CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (mg CO₂/g sorbent) and fast and complete regeneration at a low temperature condition (1 atm, 150 °C).     

Infrared absorption spectra of adsorbed dinitrogen on RuAl2O3K below 2000 cm−1

A new dinitrogen species is found by ir absorption at 1935 cm^?1 (Type B) when a dinitrogen species at 2020 cm^?1 (Type A) prepared from N₂ on RuAl₂O₃K is treated with H₂ above 170 °C or with NH₃ at 25 °C, or when H₂-treated catalyst is treated with N₂ at 250 °C. The Type B species is more reactive to H₂ or O₂ than the Type A species. Another ir band is found at around 1870 cm^?1 (Type C) when Type B species is evacuated at 200 °C. Both species, B and C, are likely located on the surface, while the Type A species is in an absorbed state. The Type C species is removed rapidly on introduction of H₂ or NH₃ at 25 °C, probably by displacement. The very low wavenumber, the high sensitivity to gases, and the high stability to evacuation disclose the unique character of the Type C species.     

Thermal effects of condensation on absorption of gases in growing droplets

Absorption of gases by a stationary droplet growing in a stagnant supersaturated medium is analyzed by solving the coupled unsteady state mass and energy balance equations for the gas and droplet phases. By means of a parametric study the effects of droplet surface temperature, growth, heat of condensation and solubility-temperature relationship on absorption are elucidated. The results indicate that for low heats of condensation the absorption rate can increase significantly due to growth. For high heats of condensation, the rapid increase in surface temperature, induced by high growth rates, can significantly lower absorption rates.     

Adsorption of CO2 from dry gases on MCM-41 silica at ambient temperature and high pressure. 2: Adsorption of CO2/N2, CO2/CH4 and CO2/H2 binary mixtures

Adsorption equilibrium capacity of CO₂, CH₄, N₂, H₂ and O₂ on periodic mesoporous MCM-41 silica was measured gravimetrically at room temperature and pressure up to 25 bar. The ideal adsorption solution theory (IAST) was validated and used for the prediction of CO₂/N₂, CO₂/CH₄, CO₂/H₂ binary mixture adsorption equilibria on MCM-41 using single components adsorption data. In all cases, MCM-41 showed preferential CO₂ adsorption in comparison to the other gases, in agreement with CO₂/N₂, CO₂/CH₄, CO₂/H₂ selectivity determined using IAST. In comparison to well known benchmark CO₂ adsorbents like activated carbons, zeolites and metal-organic frameworks (MOFs), MCM-41 showed good CO₂ separation performances from CO₂/N₂, CO₂/CH₄ and CO₂/H₂ binary mixtures at high pressure, via pressure swing adsorption by utilizing a medium pressure desorption process (PSA-H/M). The working CO₂ capacity of MCM-41 in the aforementioned binary mixtures using PSA-H/M is generally higher than 13X zeolite and comparable to different activated carbons.     

Mass transfer with complex chemical reactions: Simultaneous absorption of H2S and CO2 in solutions of alkanolamines

An absorption model has been developed which is able to calculate the simultaneous absorption rates (and corresponding enhancement factors) of two gaseous components into a reactive liquid. In the liquid phase multiple complex parallel reversible reactions may take place. This model, for example, can be used for design and development of gas-treating processes for the selective removal of hydrogen sulphide. Due to the implementation of an additional transformation of the spatial coordinate, the required computational time could be reduced substantially without loss of accuracy. The present model can be incorporated into an overall absorption module for column design and simulation. Experimentally determined simultaneous absorption rates of H₂S and CO₂ in aqueous solutions of alkanolamines and mixtures of alkanolamines can be predicted satisfactorily well for the conditions where both gases have a mutual interaction on the respective rates. The experiments were carried out in a stirred vessel with a flat surface over a wide range of process conditions.     

Characterization of Ni-Mo/Al2O3 catalysts prepared by simltaneous impregnation of the active components

Three Ni-Mo/Al₂O₃, catalysts were prepared, containing similar amounts of NiO (2.8%) and MoO₃ (13.5%), by simultaneous impregnation of the active components, varying the nature of the solubilizing agent (ammonia, citric acid and phosphoric acid). The catalysts were characterized with respect to texture (surface area and pore volume), presence of crystalline phases (XRD), distribution of active components (EPMA) and nature of the active phases (DRS). Catalytic activity was measured using thiophene hydrogenolysis as a model reaction. A commercial Ni-Mo catalyst of similar composition was characterized by the same methods.

The catalyst prepared in the phosphoric acid medium (catalyst P) had a significantly lower surface area. In phosphorus-containing catalysts there was a marked tendency of this element to be deposited on the external region of the catalyst extrudates. The DRS spectra showed that Mo was present predominantly as polymolybdate species in all cases. In the industrial catalyst (catalyst I) the presence of nickel spinel was clearly observed. Catalyst P had an absorption minimum in the visible region displaced to higher wavelength compared to the catalysts prepared in ammonia (catalyst A) and citric acid (catalyst C) media. The observed order of activity was P > C > A > I.     

On boundary conditions to the film model of mass transfer in chemical absorption

The problem of appropriate boundary conditions for mass transfer within the liquid film in chemical absorption ih reconsidered. It has been shown that the most general solution to the problem of mass transfer in the liquid film can be obtained if a fixed bulk composition is taken as a film-bulk boundary condition to the differential balance equations of the film. This method leads to solutions which can be incorporated into absorber balance equations of any type. As an illustrative example, the simultaneous absorption of two gases which react together in a semi-batch absorber is discussed. A new, approximate but very simple and accurate solution to this problem is proposed.     

XPS investigation of the reaction of carbon with NO, O2, N2 and H2O plasmas

The interaction of graphite with plasmas of pure gases (O₂, N₂ or H₂O), air or mixtures of gases containing NO has been studied by XPS “in situ” analysis. Depending on the type of plasma, different species of nitrogen, oxygen and carbon have been detected on the surface of graphite. The nitrogen containing species have been attributed to pyridinic, pyrrol, quartenary and oxidized groups adsorbed on the surface. The evolution with the treatment time of the relative intensity of the different nitrogen bands for Ar + NO, N₂ + NO, air or N₂ plasmas has served to propose a model accounting for the reactions of graphite with plasmas of NO containing gases. The model explains why carbon materials (in the form of graphite, soot particles, etc.) can be very effective for the removal of the NO present in exhaust combustion gases excited by a plasma. The analysis of the C1s and O1s photoemission peaks reveals the formation of C/O adsorbed species up to a maximum concentration on the surface of around 10% atomic oxygen. A general evolution is the progressive formation of C/O species where the carbon is sp³ hybridized. This tendency is enhanced when graphite is treated with the plasma of water.     

Experimental study of CO2 absorption/stripping via PVDF hollow fiber membrane contactor

Gas–liquid hollow fiber membrane contactor can be a promising alternative for the CO₂ absorption/stripping due to the advantages over traditional contacting devices. In this study, the structurally developed hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared via a wet spinning method. The membranes were characterized in terms of morphology, permeability, wetting resistance, overall porosity and mass transfer resistance. From the morphology analysis, the membranes demonstrated a thin outer finger-like layer with ultra thin skin and a thick inner sponge-like layer without skin. The characterization results indicated that the membranes possess a mean pore size of 9.6 nm with high permeability and wetting resistance and low mass transfer resistance (1.2 × 10⁴ s/m). Physical CO₂ absorption/stripping were conducted through the fabricated gas–liquid membrane contactor modules, where distilled water was used as the liquid absorbent. The liquid phase resistance was dominant due to significant change in the absorption/stripping flux with the liquid velocity. The CO₂ absorption flux was approximately 10 times higher than the CO₂ stripping flux at the same operating condition due to high solubility of CO₂ in water as confirmed with the effect of liquid phase pressure and temperature on the absorption/stripping flux.     

Effect of As2O3 and NaNO3 on the Solution of O2 in Soda-Lime Glass

The rate at which soda-lime glass absorbed oxygen increased with the addition of arsenious oxide to the batch; the absorption rate increased further when sodium nitrate was substituted for part of the sodium carbonate in the batch. There was little difference, however, between the rate of absorption in melts in a gas furnace and melts in an electric furnace. The rate of absorption increased in all cases as the temperature increased in the range 1065° to 1280°C.