Carbon dioxide aqueous amine solutions

AMINEX A process for removing hydrogen sulfide and carbon dioxide from gas and LPG streams, by circulating an aqueous amine solution through bundles of hollow fibers immersed in them. Developed in 1991 by the Merichem Company, Houston, TX. 

The absorption of carbon dioxide into aqueous amine solutions has been investigated by Danckwerts and McNeil(42) using a stirred cell. It was found that the reaction proceeded... 

Danckwerts, P. V. and McNeil, K. M. Trans. Inst. Chem. Eng. 45 (1967) 32. The absorption of carbon dioxide into aqueous amine solutions and the effects of catalysis. 

Teramoto, M. Nakai, K. Ohnishi, N. Huang, Q. Watari, T. Matsuyama, H. 1996, Facilitated Transport of Carbon Dioxide through Supported Liquid Membranes of Aqueous Amine Solutions. Ind.Eng.Chem.Res. 35. 

Facilitated Transport of Carbon Dioxide Through Supported Liquid Membranes of Aqueous Amine Solutions... 

Stress corrosion cracking of carbon steel by aqueous amine solutions, which are used to remove hydrogen sulfide and carbon dioxide from refinery and petrochemical plant streams, has been a recurring problem for number of years. 

Chill the concentrated solution of the amine hydrochloride in ice-water, and then cautiously with stirring add an excess of 20% aqueous sodium hydroxide solution to liberate the amine. Pour the mixture into a separating-funnel, and rinse out the flask or basin with ether into the funnel. Extract the mixture twice with ether (2 X25 ml.). Dry the united ether extracts over flake or powdered sodium hydroxide, preferably overnight. Distil the dry filtered extract from an apparatus similar to that used for the oxime when the ether has been removed, distil the amine slowly under water-pump pressure, using a capillary tube having a soda-lime guard - tube to ensure that only dry air free from carbon dioxide passes through the liquid. Collect the amine, b.p. 59-61°/12 mm. at atmospheric pressure it has b.p. 163-164°. Yield, 18 g. 

Experience in air separation plant operations and other ciyogenic processing plants has shown that local freeze-out of impurities such as carbon dioxide can occur at concentrations well below the solubihty limit. For this reason, the carbon dioxide content of the feed gas sub-jec t to the minimum operating temperature is usually kept below 50 ppm. The amine process and the molecular sieve adsorption process are the most widely used methods for carbon dioxide removal. The amine process involves adsorption of the impurity by a lean aqueous organic amine solution. With sufficient amine recirculation rate, the carbon dioxide in the treated gas can be reduced to less than 25 ppm. Oxygen is removed by a catalytic reaction with hydrogen to form water. 

Methylkasugaminide (5) from C9-Amine (3). An aqueous solution (30 ml.) saturated with barium hydroxide was added to a solution of Co-amine hydrochloride (250 mg., 0.93 mmole) dissolved in water (3 ml.) free from carbon dioxide. The solution was refluxed for 10 hours on a steam bath. By the similar treatment of the reaction mixture as described in the case of cold alkaline hydrolysis, ammonia (0.91 mmole), barium... 

NOTE In simple filming amine formulations ODA is the most widely employed ingredient. Formulations are typically available as 100% concentrated flakes, 2 to 5% strength aqueous solutions, or 5 to 10% strength emulsions. Solid ODA should be stored without exposure to air because it gradually reacts with carbon dioxide to form ODA carbonate, which is white and crumbly in composition. 

More recently Hand et al. (ref. 9) have studied the decomposition reaction of N-chloro-a-amino acid anions in neutral aqueous solution, where the main reaction products are carbon dioxide, chloride ion and imines (which hydrolyze rapidly to amine and carbonyl products). They found that the reaction rate constant of decarboxylation was independent of pH, so they ruled out a proton assisted decarboxylation mechanism, and the one proposed consists of a concerted decarboxylation. For N-bromoamino acids decomposition in the pH interval 9-11 a similar concerted mechanism was proposed by Antelo et al. (ref. 10), where the formation of a nitrenium ion (ref. 11) can be ruled out because it is not consistent with the experimental results. Antelo et al. have also established that when the decomposition reaction takes place at pH < 9, the disproportionation reaction of the N-Br-amino acid becomes important, and the decomposition goes through the N,N-dibromoamino acid. This reaction is also important for N-chloroamino compounds but at more acidic pH values, because the disproportionation reaction... 

Many investigations of the molecular structure of thin films formed by y-APS deposited onto inorganic substrates from aqueous solutions have been carried out. Ondrus and Boerio [2] used reflection-absorption infrared spectroscopy (RAIR) to determine the structure of y-APS films deposited on iron, 1100 aluminum, 2024 aluminum, and copper substrates from aqueous solutions at pH 10.4. They found that the as-formed films absorbed carbon dioxide and water vapor to form amine bicarbonate salts which were characterized by absorption bands near 1330, 1470, 1570, and 1640 cm-1. y-APS films had to be heated to temperatures above about 90°C in order to dissociate the bicarbonates, presumably to free amine, carbon dioxide, and water. Since the amine bicarbonates failed to react with epoxies, the strength of adhesive joints prepared... 

Carbon dioxide removal by reactive absorption in amine solutions is also applied on the commercial scale, for instance, in the treatment of flue gas (see later in this chapter). Another possible application field of the technique is gas desulfurization, in which H2S is removed and converted to sulfur by means of reactive absorption. Aqueous solutions of ferric chelates (160-162) as well as tetramethylene sulfone, pyridine, quinoline, and polyglycol ether solutions of S02 (163,164) have been proposed as solvents. Reactive absorption can also be used for NOx reduction and removal from flue or exhaust gases (165,166). The separation of light olefins and paraffins by means of a reversible chemical com-plexation of olefins with Ag(I) or Cu(I) compounds in aqueous and nonaqueous solutions is another very interesting example of reactive absorption, one that could possibly replace the conventional cryogenic distillation technology (167). 

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. 

Total carbon dioxide (CO2) content of plasma consists of carbon dioxide dissolved in an aqueous solution (dCOa), CO2 loosely bound to amine groups in proteins (carbamino compounds), HCO3 and vanishingly small amounts of CO ions, and carbonic acid (H2CO3). Bicarbonate ions make up ail but 2 mmol/L of the total carbon dioxide of plasma (22 to 31 mmol/L). Measurement of the tota CO2 as part of an electrolyte profile is useful chiefly to evaluate HCO3 concentration in assessment of acid-base disorders. 

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