Amine Solution Purification

As previously discussed, amine solutions are degraded by reaction with CO2, oxygm, organic sulfur compounds, and other gas impurities to form heat-stable salts and amine degradation products. These contaminants cause corrosion and lower the treating capacity of the amine solution. In corrunercial plant operations, the concentration of amine decomposition products should not be allowed to exceed about 10% of the active antine concentratiotL Once amine contamination has reached this level, contaminants should be removed by solution purging, solution change-out, or amine solution purification. 

Table 3-6 Compaitoon of Amine Solution Purification Techniqiies ... 

Amide-amine solutions react vigorously with water and oxygenous impurities in syngas and form insoluble products. Hence, scrupulous purification of feed gas becomes inevitable. At high pressures, hydrogen reacts with methylamide catalyst [potassium methyla-mide (PMA) ] to form potassium hydride (KH), which is insoluble in amine. To circumvent this hydride precipitation and obtain a reasonable rate, an equimolar mixture of lithium methylamide (LMA) and PMA, called PLMA, was developed by Canadian workers. ... 

Matsumiya N, Teramoto M, Kitada S, Matsuyam H. Evaluation of energy consumption for separation of CO2 in flue gas by hollow fiber facilitated transport membrane module with permeation of amine solution. Sep Purif Technol 2005 46 26-32. 

Hot potash processes have been very much superseded by alkanolamine processes. This is partly due to the much greater adaptability of amine solutions to different gas purification jobs, and partly to the fact that the additives used. 

The simultaneous absorption of two gases that react with the solvent at different rates has been studied by Ouwerkerk. The specific system which he selected for analysis was the selective absorption of HjS in the presence of CO2 into amine solutions. This operation is a feature of several commercially important gas purification processes. Bench scale experiments were conducted to collect the necessary pi sico-chemical data. An absorption rate equation was developed for H2S based on the assumption of instantaneous reaction. For CO2 it was found that the rate of absorption into diisopropanolamine (DIPA) solution at low CO2 partial pressures can best be correlated on the l is of a fast pseudo-first-order reaction. A computer program was developed which took into account the competition between H2S and CC>2 when absorbed simultaneously, and the computer predictions were verified by experiments in a pilot scale absorber. Finally, the methodology was employed successfully to design a large commercial plant absorber. 

There is an added advantage to having a hindered amine. For gas purification by absorption in an aqueous amine solution in a continuous process with a fixed absorbent, the amine solution has to be regenerated by heating and CO2 is stripped from the solution. Reactions... 

A flow modification which has been proposed for aqueous amine solutions to reduce the steam requirement is shown in Figure 2-11. The split-stream scheme, in which only a portion of the solution is stripped to a low acid-gas concentration, has been applied to several gas-purification processes, including the Shell iripotassium phosphate process and the hot... 

After the initial charging of the reclaimer kettle with amine solution, fresh solution diluted with water is led at a slow rate on level control, and steam is added on flow control. At steady state, the amine solution is brought to a concentration where the equilibrium vapor leaving the reclaimer has the same amine content as the feed. As shown in Figure 3-29, if the solution fed to the purification kettle contains 20% (by weight) MEA in water, at atmospheric pressure the solution in the kettle has to be concentrated to an MEA content of 68% (by weight) in order to obtain an MEA concentration of 20% (by weight) in the vapor. At steady state, the reclaimer... 

Purification as their N-acetyl derivatives is satisfactory for primary, and to a limited extent secondary, amines. The base is refluxed with slightly more than one equivalent of acetic anhydride for half to one hour, cooled and poured into ice-cold water. The insoluble derivative is filtered off, dried, and recrystallised from water, ethanol, aqueous ethanol or benzene (CAUTION toxic ). The derivative can be hydrolysed to the parent amine by refluxing with 70% sulfuric acid for a half to one hour. The solution is cooled, poured onto ice, and made alkaline. The amine is steam distilled or extracted as above. Alkaline hydrolysis is very slow. 

The following are some of the typical industrial applications for liquid-phase carbon adsorption. Generally liquid-phase carbon adsorbents are used to decolorize or purify liquids, solutions, and liquefiable materials such as waxes. Specific industrial applications include the decolorization of sugar syrups the removal of sulfurous, phenolic, and hydrocarbon contaminants from wastewater the purification of various aqueous solutions of acids, alkalies, amines, glycols, salts, gelatin, vinegar, fruit juices, pectin, glycerol, and alcoholic spirits dechlorination the removal of... 

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