Alkanolamine solutions

Primary alkanolamine solutions require a relatively high heat of regeneration. Also excessive temperatures or localized overheating in reboilers cause the MEA to decompose and form corrosive compounds. An inhibitor system, such as the Amine Guard system developed by Union Carbide, is an effective method of corrosion control (52). Inhibitors permit the use of higher (25—35%) concentration MEA solutions, thus allowing lower circulation rates and subsequendy lower regeneration duty. 

Surfactants are also prepared by the reaction of glycerol derivatives RC02 [CH2CH(0H)CH20] H (R = C6 16 alkyl, n = 1-5) with P4O10 at 60-80°C with subsequent neutralization of the resulting phosphate ester acids with aqueous alkali or alkanolamine solution at 50-70°C [10]. 

Many of the undesirable substances present in gaseous or liquid streams form volatile weak electrolytes in aqueous solution. These compounds include ammonia, hydrogen sulfide, carbon dioxide and sulfur dioxide. The design and analysis of separation processes involving aqueous solutions of these materials require accurate representation of the phase equilibria between the solution and the vapor phase. Relatively few studies of these types of systems have been published concerning solutions of weak electrolytes. This paper will review the methods that have been used for such solutions and, as an example, consider the alkanolamine solutions used for the removal of the acid gases (H2S and C02) from gas streams. 

Dankwerts and McNeil ( 3) have employed the method of Van Krevelen et al. to predict the partial pressure of carbon dioxide over carbonated alkanolamine solutions. The central feature of this model is the use of pseudo-equilibrium constants and their dependence on ionic strength. The ratio of the pseudo-equilibrium constant at a certain ionic strength to that at zero ionic strength has been termed the "ionic characterization factor". However, ionic strength alone is insufficient to determine the ionic characterization factors. As well the ionic characterization factors are sometimes not a simple linear function of ionic strength. 

Application to Alkanolamine Solutions Aqueous alkanolamine solutions are widely used for the removal of H2S and C02 from gaseous streams, because they can reduce the concentration of H2S and C02 to low levels, even if the gas stream is at a low total pressure. The most commonly used alkanolamines are monethanolamine (MEA) and diethanolamine. However, diisopropanolamine... 

Deshmukh and Mather ( 1 8) have recently presented a model for the equilibria in alkanolamine solutions using the ideas of Edwards et al. (6) for calculation of the activity coefficients. Here only the salient features of this model will be presented. The main reactions occuring in the C02+H2S+alkanolamine+H20... 

The application of this model to alkanolamine solutions is not possible directly since the specific interaction parameters (B s) for alkanolammonium ions and carbamate ions are not available. Also the dissociation constant for the simplest amines (MEA, DEA,... 

Versteeg, G.F. andvanSwaaij, P.M. Solubility and diffusivity of acid gases (CO2, N2O) in aqueous alkanolamine solutions, / Chem. Eng. Data, 33(l) 29-34, 1988. 

Solvent UCARSOL Alkanolamine Solution with Metal-Passivating Corrosion Inhibitors... 

In this case, carbon dioxide reacts reversibly in the adsorber with aqueous alkaline solutions to form a carbonate adduct (configuration 1). This adduct decomposes in the stripper upon heating. In early ammonia plants, an aqueous solution of 15-20 wt % monoethanolamine (MEA) was always standard for removing CO2. Primary alkanolamine solutions, however, require a relatively high heat of regeneration so that, nowadays, secondary and tertiary ethanol amines are mainly used. 

The removal of the acid components H2S and CO2 from gases by means of alkanolamine solutions is a well-established process. The description of the H2S and CO2 mass transfer fluxes in this process, however, is very complicated due to reversible and, moreover, interactive liquid-phase reactions hence the relevant penetration model based equations cannot be solved analytically [6], Recently we, therefore, developed a numerical technique in order to calculate H2S and CO2 mass transfer rates from the model equations [6]. 

Hoff KA, Juliassen O, Falk-Pedersen O, and Svendsen HF, Modeling and experimental study of carbon dioxide absorption in aqueous alkanolamine solutions using a membrane contactor. Industrial and Engineering Chemistry Research 2004, 43(16), 4908 921. 

Alkanolamine solutions are generally used as chemical absorbent for the recovery of acid compounds from flue gases. Although the reaction between carbon dioxide and a variety of amino compounds, represented by monoethanolamines, has been widely studied , there is still a great need to develop more effective and chemically more stable absorbents. In the present study, we have prepared several different types of amino compounds and compared their capacity for the reversible absorption of carbon dioxide at different temperatures and under different pressures of carbon dioxide. 

Removal of carbon dioxide (natural gas sweetening) increases the calorific value and transportability of the natural gas stream. Carbon dioxide content in the natural gas obtained from the gas or oil well can vary from 4% to 50%. It has to be reduced down to ca. 2%-5%. This goal is typically achieved by means of absorption with an aqueous alkanolamine solution that has as main drawback the tendency to corrode equipment and to lose amine properties by... 

In this section, we review the characterization of photoetching patterns evolved on the surface of polycrystalUne CdX(X = S, Se), which are one of the most extensively studied semiconductors as photoelectrodes in photoelectrochemical cells, photoconductors, and other optoelectronic usages. Anodic photocurrent flowing through the electrode-electrolyte interface is entirely due to the oxidative dissolution of the semiconductors themselves to form Cd " " ion and elemental chalco-gen, except in certain redox solutions, such as aqueous polysulfide, polyselenide, and alkanolamine solutions. For example, in an aqueous NaCl solution, CdSe is photoanodically decomposed to form Cd + ion and elemental Se. After the photoelectrolysis of a CdSe electrode under potentiostatic conditions and a subsequent... 

Desorption of CO and H-S from carbonated potash and alkanolamine solutions... 

Aqueous alkanolamine solutions are frequently used for removal of acidic gases such as carbon dioxide and hydrogen sulfide from gas streams in the natural gas, synthetic, and refinery industries. Several options are available for removing acid gases, but by far the most popular is the absorption by amine based solvents such as monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), di-isopropanolamine (DIPA), triethanolamine (TEA), N-methyldiethanolamine (MDEA), 2-amino-2-methyl-l-propanol (AMP), and 2-piperidineethanol (2-PE) in reversible absorption-regeneration processes [1]. 

Aliabad,H and Mirzaei,S. Removal of CO2 and H2S using Aqueous Alkanolamine Solutions, World Academy of Science, Engineering and Technology, Issue. 25, pp. 194 - 203, January 2009. 

A number of reviews are available discussing the application of membrane contactors for acid gas removal (Li and Chen, 2005 Mansourizadeh and Ismail, 2009) [4] [7]. Most research activities described in the literature deal with use of membrane contactor for the removal of carbon dioxide. Most of the time alkanolamine solutions have been used for the selective removal of CO2 from various gas streams (Jamal et al. 2006 Wang et al. 2004) [2] [10]. The effect of the amine solvent, the operating conditions, and the membrane characteristies on the removal of CO2 has been studied by (Wang et al, 2004) [10]. Results for the kinetics for both the absorption and desorption rate of CO2 for different amine absorption liquids (MEA, DEA, MDEA) and AMP and mixtures of these absorption liquids have been reported by (Jamal et al., 2006) [2]. Also, the use of other types of absorption liquids has been studied. Results for different amino acid salt solutions as CO2 absorbent have been described by (Lu et al., 2009) [6]. The use of membrane contactors is not limited to the removal of CO2. Membrane contactors have also been applied to remove H2S and SO2 from different gas streams (Li et al. 2000) [5]. 

The absorption in alkanolamine solutions (MEA, DEA, ADIP, DGA, etc.) is the commercially most important process for the removal of CO2 from synthesis gas for ammonia and methanol production, for the production of hydrogen, in natural gas purification, coal liquefaction, and the like. In the present example a gas containing 13.55 mole-% of CO2 is to be purified by absorption into an aqueous solution of 13.6 wt-% MEA. The column, filled with 0.05 m steel Pall rings, has a diameter of 1.05 m and is operating at a temperature of 315 K and a pressure of 14.3 bars. The inlet flow rates of gas and liquid are 497 kmol/h and 76.9 mVh, respectively. Determine the packed column height necessary to reduce the mole fraction of CO2 to 5 x 10 at the top of the column. 

Approximate Integral Heats of Solution for Absorption of H2S and CO2 fo Alkanolamine Solutions... 

Figure 2-63. Specific gravity of aqueous alkanolamine solutions. (GPSA 1994 ... 

Deshmukh, R. D., and Mather, A. E., 1981, A Mathematical Model for Equilibrium Solubility of Hydrogen Sulfide and Carbon Dioxide in Aqueous Alkanolamine Solutions, Chemical Engineering Science, Vol. 36, pp. 355-362. 

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