Monoethanolamine solutions

In monoethanolamine solutions the unknown interaction parameters and equilibrium constants were determined by fitting the model to data for the three component systems CC +MEA+ O and H2S+MEA+H2O. The agreement of the fitted model with Che data was found to be good. The parameters obtained in this way were then used to predict the partial pressures of mixtures of HoS and CO2 over aqueous MEA solutions. The predictions were in good agreement with experimental data, except at the higher partial pressures. 

The acid gases, usually CO2 and H2S, are removed by scrubbing with diethanolamine or monoethanolamine solutions and possibly an additional caustic treatment. Older processes used caustic solutions of 5-15 wt% NaOH followed by a water wash. Of course, the spent caustic creates a disposal problem it must be neutralized with acid and then properly disposed of according to prevailing pollution and hazard waste standards. Different column configurations have been proposed, but usually large scrubber towers with well over 30 valve-type trays are used. 

Monoethanolamine is very hygroscopic and is unstable when exposed to light. Aqueous monoethanolamine solutions may be sterilized by autoclaving. 

When handling concentrated solutions of monoethanolamine, personal protective equipment such as an appropriate respirator, chemically resistant gloves, safety goggles, and other protective clothing should be worn. Transfer or prepare monoethanolamine solutions only in a chemical fume hood. 

The research locally developed on a CO2 removal pilot plant currently in use for research aims, revealed the high efficiency of CO2 recovery from flue gas, high carrying capacity of the monoethanolamine solution and satisfactory regeneration with low energy consumption. 

A comprehensive study or the stripping of carbon dioxide from monoethanolamine solutions in a packed coluntu is described by Weiland et at-40 These investigntors developed a design approach that uses only fundamental physicochemical data and tested the approach against 173 experiments on the mass transfer performance or a pilot scale stripping column. Predicted mass transfer coefficients agreed with observed values within 23%. 

Repeat the calculations of Problem 3.23, but using a 2 N monoethanolamine solution as absorbent. 

This process lends itself to portable units. The reaction takes place at about 260 C and can be carried out in ordinary steel. The carbon dioxide can be scrubbed out with monoethanolamine solution. 

After the water-gas diift reaction, the CO2 is scrubbed from the gas with aqueous monoethanolamine solution followed by NaOH solution. Hie purified gas is compressed from about 0.6 to 1,000 atm (15,000 psi), and residual CO, about 1.5 per cent, is catalytically hydrogenated to methane and water. Methane does not poison the ammonia synthesis catalyst, but as previously explained, it must be purged from the system with other inerts in order to maintain the optimum partial pressure of the reactants. 

Bolling Points and Condensation Temperatures of Aqueous Monoethanolamine Solutions at 25 pal Absoluts... 

Weight per Gallon of Aqueous Monoethanolamine Solutions at Various Temperatures... 

Table 14.64 Bolling Point Composition Curves for Aqueous Monoethanolamine Solutions (19)...

Reversible Reaction. This type of absorption is characterized by the occurrence of a chemical reaction between the gaseous component being absorbed and a component in the liquid phase to form a compound that exerts a significant vapor pressure of the absorbed component. An example is the absorption of carbon dioxide into a monoethanolamine solution. This type of system is quite difficult to analyze because the vapor-liquid equilibrium curve is not linear and the rate of absorption may be affected by chemical reaction rates. 

Figure 5.59 Experimental solubilities [3] of CO2 in methanol (A) and aqueous monoethanolamine solution (30 mass%) ( ) at 7 = 313.15 K.

Figure 5.60 Chemical reactions which have to be considered besides the gas solubility for the absorption of CO2 in aqueous monoethanolamine solutions.

DeMontigny, D., Tontiwachwuthikul, P., Chakma, A., 2001, Parametric Studies of Carbon Dioxide Absorption into ffighly Concentrated Monoethanolamine Solutions, Can. J. Chem. Eng., 79,137-142. 

In chemical engineering it is often neeessary to make estimates using incomplete data. Estimate the relative effective capacity of the following two liquids for absorbing carbon dioxide (a) monoethanolamine solution (20 per cent by weight), and (b) water at various pressures. The MEA absorptive capacity is in practice limited to 0.35 moles of carbon dioxide per mole of amine. The solubility of carbon dioxide in water at 20°C is about 0.039 mol litre" bar. 

Marking tests—utilizing various solvent and corrosive mixtures in heated beakers on hot plates. The provisions for local exhaust ventilation (LEV) in the form of a metal hood with adequate face velocities are needed to control fugitive emissions. Monoethanolamine solutions can results in exposures in excess of the PEL/TLV P 1... 

A 7-ft 0-in. ID CO2 absorber in an ammonia plant presentiy is equipped with 20 valve trays on 24-in. spacing. The gas to the absorber is 79,400 Ib/h at 130°F with a density of 0.792 Ib/ft. The inlet gas contains 18.2 mol % CO2, which must be reduced down to 90 mol ppm CO2 in the outlet gas stream. The absorber operates at a top pressure of 325 psia. The liquid feed is 30.2 wt % monoethanolamine solution at a temperature of 110°E This lean solution flow is 575,000 Ib/h, which contains 0.12 mol CO2 per mol MEA. It is desired to increase the rates by 35%, which the present trays will not accommodate. Can the existing column handle these higher rates with tower packing ... 

Hikita H, Asai S, Katsu Y, Ikuno S (1979) Absorption of carbon-dioxide into aqueous monoethanolamine solutions. AIChE J 25 793-800... 

Figure 2-19. Effect of dissolved hydrogen sulfide on vapor pressure of CO2 over 2.5 N monoethanolamine solution at 25°C. Data ofllluhlbaueranillilhm ian (1957)...

Figure 2-81. Calculated plate diagram for stripping of CO2 from aqueous monoethanolamine solutions.

Lai, D., Isaacs, E. E., Mather, A. E., and Otto, F. D., 1980, Equilibrium Solubility of Acid Gases in Diethanolamine and Monoethanolamine Solutions at Low Partial Pressures, Proceedings of the 1980 Gas Conditioning Confa-ence, University of Oklahoma, Norman, OK... 

---