Simultaneous absorption and reaction of two gases: absorption of CO2 and NH3 in water and aqueous solutions of alkanolamines

Some aspects of simultaneous absorption and reaction of two gases in an inert medium, and a medium containing species which react with one of the dissolved gases have been considered. Experiments were made on simultaneous absorption of carbon dioxide and ammonia in water and aqueous solutions of mono- and di-ethanolamine in a 5 cm i.d. continuous glass bubble column. A good agreement between the experimental and predicted values was observed.     

Simultaneous Absorption of H2S and Co2 Into Aqueous Methyldiethanolamine

Abstract

The tertiary araine methyldiethanolamine (MDEA) is finding increasing application as a chemical solvent for selective absorption of hydrogen sulfide from gases containing hydrogen sulfide and carbon dioxide. Gas streams of this type include some natural gases, synthetic gases from coal and heavy oil gasification and tail gases from sulfur plants. Selectivity for H2S is needed either to enrich Glaus sulfur plant feed in H2S or to remove only H₂S when CO₂ removal is not necessary or economic. For the absorption of hydrogen sulfide into MDEA, the reaction which occurs can be considered to be instantaneous while carbon dioxide undergoes a second-order reaction with MDEA.

In this work, the simultaneous absorption of two gases into a liquid containing a reactant with which both gases react is modelled using the film theory. Physical properties and kinetic rate parameters used in the model have been measured in our laboratory. The model is used to study the effect of process variables on the selectivity of MDEA for H₂S over C0₂. The simultaneous absorption of H₂S and CO₂ gases into aqueous MDEA is studied experimentally using a continuous stirred tank absorber. Experimental absorption rates are compared to predictions based on a multicomponent mass transfer model. The average deviations of the theoretical calculations from the experimental results are 10.2% and 12.9% for C0₂ and H₂S, respectively.     

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.     

Simultaneous absorption of two gases accompanied by a complex chemical reaction: approximate solutions

Approximate solutions to the problem of simultaneous absorption of two gases in a liquid accompanied by a complex chemical reaction have been presented based on the film theory. Two approximate profiles, a nonlinear exponential profile and a trigonometric profile, for the concentration of each of the gaseous species in the film have been used in analysing the problem. The complex scheme considered is:

For the exponential case two approximations have been considered: [1] in which the higher order terms are included, and [2] in which the higher order terms are neglected.The results obtained using the two profiles have been compared with numerical solutions for the film theory in the range of

from 1 to 3. The results show that both the approximations yield solutions close to the numerical, in particular case [1] of the exponential approximation. Some special cases have then been considered followed by a discussion of an industrially important system: simultaneous absorption of ethylene and chlorine in water to give ethylene chlorohydrin.     

Selective Removal of Hydrogen Sulfide from Gases Containing Hydrogen Sulfide and Carbon Dioxide Using Diethanolamine

Abstract

It is sometimes necessary to selectively remove hydrogen sulfide from gases containing carbon dioxide. This may be the case for example in the production of sulfur using the Claus process. When two gases are simultaneously absorbed into a solution containing a reactant with which each gas can react, the rate of absorption of each component is affected by the presence of the other gas. For the absorption of hydrogen sulfide into primary and secondary amines, the reaction which occurs can usually be considered to be instantaneous. An instantaneous reaction is diffusion-limited since the reaction occurs so rapidly that the liquid phase reactant and the absorbed gas cannot coexist in the same region of the liquid. For primary and secondary amines used for gas treatment, the reaction with carbon dioxide is much slower than for hydrogen sulfide and can often be considered to be second order.

In this work the simultaneous absorption of two gases into a liquid containing a reactant with which both gases can react is modeled using penetration theory. It is assumed that one gas reacts instantaneously and the other gas undergoes a second order reaction. Parameters used in the calculations are those available in the literature corresponding to the absorption of hydrogen sulfide and carbon dioxide in diethanolamine.     

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.     

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.     

Absorption of Inorganic Gases by Aqueous Solutions of Salts,Primary Amines,and Ammonia

The kinetics of absorption of inorganic gases by aqueous solutions of some salts, primary amines, and ammonia in a number of practically important cases is reduced to the kinetics observed during absorption of these gases by solutions of acids and bases. Problems of unsteady-state absorption and release of inorganic gases from the aforementioned aqueous solutions are considered using the example of two stagnant media (a liquid and a gas).__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 4, 2005, pp. 390–400.Original Russian Text Copyright © 2005 by Babak.     

Mass transfer with chemical reaction—I. A second-order irreversible reaction

The process of simultaneous absorption of two gases which react between themselves in an inert liquid is examined in the realistic limit of fast reaction. In this limit the nonlinear mass balance equations based on film theory are solved analytically using the method of matched asymptotic expansions. Explicit analytical expressions for the enhancement factors and concentration profiles of the gaseous solutes are derived. Results are given for the case where the two gases undergo an irreversible chemical reaction and the reaction rate is first order with respect to each of the solute concentrations. The nonlinear mass-transfer equations are also solved numerically using a shooting technique. When the dimensionless reaction rate constant is large, the analytical solution for the enhancement factor is found to be in excellent agreement with the numerical solution, with an error of less than 0.2% (better than any previously achieved).     

SIMULATION OF AEROSOL FORMATION IN GAS-LIQUID CONTACT DEVICES

In gas-liquid contact devices like absorbers, quench coolers, or condensers, aerosols can be formed by spontaneous phase transitions, initiated by homogeneous or heterogeneous nucleation, if a supersaturated gas phase emerges due to simultaneous heat and mass transfer processes or chemical reactions. Typical examples are the absorption of acid gases, like HCl or SO₃, the condensation of solvents in the presence of inert gases, and the humidification of cold gases by hot liquids.

In this article the basic principles of aerosol formation in contact devices are briefly described. A strategy for modeling and simulation of aerosol formation and particle dynamics is discussed. Simulation results generated with the process tool AerCoDe for the countercurrent absorption of HCl and the humidification of air are presented.     

SIMULATION OF AEROSOL FORMATION IN GAS-LIQUID CONTACT DEVICES

In gas-liquid contact devices like absorbers, quench coolers, or condensers, aerosols can be formed by spontaneous phase transitions, initiated by homogeneous or heterogeneous nucleation, if a supersaturated gas phase emerges due to simultaneous heat and mass transfer processes or chemical reactions. Typical examples are the absorption of acid gases, like HCl or SO₃, the condensation of solvents in the presence of inert gases, and the humidification of cold gases by hot liquids.

In this article the basic principles of aerosol formation in contact devices are briefly described. A strategy for modeling and simulation of aerosol formation and particle dynamics is discussed. Simulation results generated with the process tool AerCoDe for the countercurrent absorption of HCl and the humidification of air are presented.     

A GENERALIZED PERTURBATION APPROACH TO THE ANALYSIS OF MASS TRANSFER WITH CHEMICAL REACTION

A generalized perturbation approach is presented for the analysis of the simultaneous absorption of two gases in a liquid accompanied by a chemical reaction. The main objective is to derive approximate analytical solutions for the enhancement factors of the solute gases, for all reaction rates. The method consists of constructing a regular perturbation solution for slow reaction, whose convergence is accelerated by means of an Euler transformation, thereby extending its range of utility for larger reaction rates. Convergence is further improved by suppressing the leading singularity of the Euler-transformed series. The accelerated solution is found to predict the enhancement factors very accurately in the slow, intermediate and fast reaction regimes, and in particular, approach the boundary layer limit associated with fast reaction.     

Energy optimization of bioethanol production via gasification of switchgrass

In this article, we address the conceptual design of the bioethanol process from switchgrass via gasification. A superstructure is postulated for optimizing energy use that embeds direct or indirect gasification, followed by steam reforming or partial oxidation. Next, the gas composition is adjusted with membrane‐PSA or water gas shift. Membrane separation, absorption with ethanol‐amines and PSA are considered for the removal of sour gases. Finally, two synthetic paths are considered, high alcohols catalytic process with two possible distillation sequences, and syngas fermentation with distillation, corn grits, molecular sieves and pervaporation as alternative dehydration processes. The optimization of the superstructure is formulated as an mixed‐integer nonlinear programming problem using short‐cut models, and solved through a special decomposition scheme that is followed by heat integration. The optimal process consists of direct gasification followed by steam reforming, removal of the excess of hydrogen and catalytic synthesis, yielding a potential operating cost of $0.41/gal. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

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.     

Simultaneous absorption of two gases which react between themselves in a liquid medium: An approximate solution

An approximate solution for the simultaneous absorption and reaction of two gases in a liquid has been presented based on the film theory, assuming a nonlinear (exponential) profile for the concentration of each of the gaseous species in the film. The solution obtained has been compared with the numerical solution of Roper, Hatch and Pigford and found to be in good agreement, thus proving the validity of the approximations.     

Simultaneous Photoacoustic Spectroscopy of Aerosol and Oxygen A-Band Absorption for the Calibration of Aerosol Light Absorption Measurements

ABSTRACT

The calibration of photoacoustic aerosol optical absorption measurements through simultaneous photoacoustic spectroscopy of the oxygen A-band absorption is demonstrated. While aerosol absorption shows no sharp spectral structures for size-distributed aerosols, the molecular oxygen A-band has sharp absorption lines in the near-infrared (i.e., 760–770 nm) spectral region. Line-strength, shape, and broadening of these lines are well known and molecular oxygen is ubiquitous with a constant concentration in the troposphere. Simultaneous photoacoustic spectroscopy of aerosol and molecular oxygen A-band absorption with a tunable, external cavity diode laser yields a convenient calibration for the photoacoustic measurement of aerosol absorption coefficients without the need for pressurized and potentially toxic calibration gases.     

Numerical calculation of the simultaneous absorption of two gases with reversible chemical reactions

We present here a general model for the numerical computation of mass-transfer rates for the simultaneous absorption of two gases in the presence of reversible chemical reactions. We use the computed mass-transfer rates to calculate the concentration of the gases and their products in a holding tank (mixing tank) over time. These concentration values could be correlated with experimental data. The numerical technique involves the use of DISPL, a software package for the solution of partial differential equations by the method of lines. This model and the numerical technique may be used to simulate selective gas removal and other industrial systems.

Scope—This paper is concerned with the numerical simulation of a simple gas scrubber. The mathematical model is described and the relationship to a laboratory-type scrubber is given. The method of computationally separating the gas absorber and the holding tank is described. This is shown to be equivalent to solving the time-dependent reaction-diffusion (absorber) model for the absorber and the time-dependent kinetics (holding tank) model separately. Of course, the two submodels are connected through mass-transfer rates, which are recalculated, as required. Computationally this allows us to push the holding tank equations to steady state. Some computational results are given, along with a schematic diagram of a laboratory apparatus.

Calculations and Significance—The numerical simulation of a gas scrubber for long time periods can be computationally prohibitive. This is attributable to the stiffness of the mathematical model and the need for good resolution. We have demonstrated a technique for separating the absorber from the holding tank in the simulations. This has resulted in a computationally tractable problem for which we have obtained reasonable results.     

Absorption with simultaneous complex reactions in both phases, demonstrated by the modeling and calculation of a counter-current flow column for the production of nitric acid

Separation processes with simultaneous chemical reactions play an important part in large-scale production. The calculation of the proper devices, usually plate columns, has not been satisfactorily solved in a general form. We present here an adequate model and a numerical method of calculation, with a corresponding computer program which allows the calculation of plate columns for absorption occurring with simultaneous reaction in both phases. The number of the reactant species and the number of the corresponding reactions is not limited. A column has been calculated rigorously for the most important industrial example of this kind of reaction, the absorption of nitrous gases in the production of nitric acid.     

Absorption of gases by aqueous solutions of acids and alkalis

Unsteady-state absorption of inorganic gases by aqueous solutions of acids and alkalis is considered using the example of two stagnant media (a liquid and a gas). It is shown that, in the general case, only two absorption modes are possible. In one of the modes, the resistance to mass transfer is concentrated in the gas phase, and, in the other, there is an instantaneous chemical reaction, in which the acceleration of two-phase physical absorption is constant. Conditions for each of these modes are found.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 2, 2005, pp. 152–162.Original Russian Text Copyright © 2005 by Babak.     

Solvent selection for CO<Subscript>2</Subscript> capture from gases with high carbon dioxide concentration

Amine absorption processes are widely used to purify both refinery and process gases and natural gas. Recently, amine absorption has also been considered for application to CO₂ removal from flue gases. It has a number of advantages, but there is one major disadvantage-high energy consumption. This can be solved by using an appropriate solvent. From a group of several dozen solutions, seven amine solvents based on primary amine, tertiary amine and sterically hindered amine were selected. For the selected solutions research was conducted on CO₂ absorption capacity, an absorption rate and finally a solvent vapor pressure. Furthermore, tests on an absorber-desorber system were also performed. In this study the most appropriate solvent for capturing CO₂ from flue gases with higher carbon dioxide concentrations was selected.