Amines absorber solution

Scrubbing andDesliming. Sylvinite ores in North America contain 1—6 wt % water-insoluble clays. A significant portion of these clays is less than 0.002 mm in diameter. If not removed or controUed in some manner, clay bodies that are dispersed in the flotation solution, ie, brine saturated with KCl and NaCl, absorb the amine coUector, which is added to effect flotation separation, and the coUector is rendered ineffective. Clay is the most troublesome impurity encountered in the processing of sylvinite ore. 

The gas mixture from the converter is cooled and passed to a hydrogen purifying system where carbon dioxide is absorbed into amine solutions and later driven off to the atmosphere by heating the rich amine solution in the reactivator. 

The problem of the interactions between membrane and absorbent solution interests, for instance, the removal of CO2. Reactive absorption liquids, such as amines, that are used for this type of removal, usually wet polyolefin membranes. Wettability depends on the surface tension of the liquid, membrane material, contact angle, and pore properties of the membrane. Possible solutions to this problem are to employ more resistant membrane materials, to use different absorbent liquids, and to deposit a nonporous layer on the membrane surface that prevents any passage of the liquid through pores. In order to do not increase too much the resistance to the mass transport, the layer has to be thin and highly permeable to the gaseous species. The dense skin can be useful also for avoiding any possible contamination of the feed gas by the absorbent (Figure 38.4). 

Diazotization involves drawing a known volume of atmospheric air through an absorbent solution, hydrolyzing the isocyanate to amine, diazotization and coupling this amine, and comparison of colour formation with a range of standards. The method varies in detail with the specific isocyanate being determined. 

Absorption may be either physical or chemical (or a combination of both). Physical absorption involves the solubility and the vapor-pressure relationships. Chemical absorption involves a reaction of the primarily physically absorbed solute with the absorbing medium. Thus, chemical absorption always combines with physical absorption, as visualized in Figure 3.3.23 for the chemical absorption of CO2 and H2S in an amine solution. 

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... 

Ammonia is a common mqruiity in gases derived from coal. It is not an acid, but is readily absorbed by amine solutions because of its extremely high solubility in water. It does not react chemically with any of the amines, and is generally expelled in the stripper. However, its presence can cause operating problems such as corrosion in the stripper overhead systnn (see prior section on wet acid gas corrosion). 

Capture processes were developed in the past to remove acid gases such as carbon dioxide and hydrogen sulfide (H2S) from natural gas. They are mainly based on chemical and physical dissolution of the acid gas in aqueous solutions of amines. The technique is considered as mature enough to be adapted in next future to the treatment of post combustion effluents. The new processes should take into account difference from natural gas treatment such as temperature, pressure or composition of the effluent. However one major barrier for the integration into industrial sites in the few coming years is the economical cost of the so called ton of CO2 avoided. Specific researches are then carried out on both the technology and the choice of the absorbent solutions. 

Future absorbent solutions have to combine high carbon dioxide loading charges (moles of dissolved carbon dioxide per mole of amine) with low energies of regeneration. Characterization of new absorbent solution can be performed by calorimetric studies of gas dissolution. The experimental data collected are essential to develop thermodynamic models representative of the C02-absorbent solution systems that will be used to design the future capture units. The dissolution properties required are the mainly the gas solubility and the enthalpy of solution. However some other properties also have to be studied, such as heat capacity, vapor pressure, chemical and thermal degradations. Then specific calorimetric techniques were set up to provide the essential experimental data. 

Aqueous solutions of amine are considered as promising solvent but the selection of the best adapted molecule is still open. Then important experimental work will be necessary to characterize and test the dissolution of carbon dioxide. In this domain, determination of calorimetric properties such as enthalpy of solution of carbon dioxide in absorbent solutions will be essential. The enthalpies of solution are particularly important for the estimation of the energy required for the solvent regeneration step of an industrial process. For theoretical point of view, this thermodynamic property participates to the development of thermodynamic models representative of gas-absorbent systems. This chapter has focused on mixing calorimetric techniques used to investigate gas dissolution in liquid absorbents. The presented techniques can be adapted, in studies of CO2 dissolution in aqueous solution of amines, to investigate for example each chemical reaction involved such as amine protonation or carbamate formation. 

Ammonium fluorosulfate is produced from ammonium fluoride by reaction with sulfur trioxide, oleum, or potassium pyrosulfate, 1 2820 (48). Solutions of ammonium fluorosulfate show Htfle evidence of hydrolysis and the salt may be recrystallized from hot water. Ammonium fluorosulfate absorbs anhydrous ammonia to form a series of Hquid amines that contain 2.5—6 moles of ammonia per mole of salt (77). 

The Cansolv process, Hcensed by Union Carbide Corporation, features an aqueous solution of a proprietary amine to absorb the sulfur dioxide. 

Choline Chloride. This compound [67-48-17 is a crystalline dehquescent salt, usually with a slight odor of trimethyl amine (6). It is very soluble in water, freely soluble in alcohol, slightly soluble in acetone and chloroform, and practically insoluble in ether, benzene, and ligroin. Its aqueous solutions ate neutral to litmus and are stable (4). The specific gravity of these solutions is a straight-line function between pure water and the value of 1.10 for the 80% solution, which represents the approximate limit of solubiUty. Choline chloride absorbs moisture from the atmosphere at relative humidities greater than 20% at 25.5°C. 

The temperature of the lean amine solution entering the absorber should be about 10°F higher than the inlet gas temperature to prevent hydrocarbon condensation and subsequent foaming. 

If I ever have to design an amine plant I will know, for example, that the temperature of the lean amine solution entering the absorber should be about 10°F higher than the inlet gas temperature to prevent hydrocarbon condensation and subsequent foaming, that the reboiler tube bundle should be placed on a slide about six inches above the bottom of the shell to provide good circulation, that about two percent of the total circulating flow should pass through the carbon towers, and many other necessary requirements. 

A typical amine system is shown in Figure 7-4. The sour gas enters the system through an inlet separator to remove any entrained water or hydrocarbon liquids. Then the gas enters the bottom of the amine absorber and flows counter-current to the amine solution. The absorber can be either a trayed or packed tower. Conventional packing is usually used for 20-in. or smaller diameter towers, and trays or structured packing for larger towers. An optional outlet separator may be included to recover entrained amines from the sweet gas. 

Commonly, amine absorbers include an integral gas. scrubber section in the bottom of the tower. This scrubber would be the same diameter as required for the tower. The gas entering the tower would have to pass through a mist eliminator and then a chimney tray. The purpose of this scrubber is to remove entrained water and hydrocarbon liquids from the gas to protect the amine solution from contamination. 

The rich amine solution from the absorber is flashed to a separator to remove any hydrocarbons. A small percentage of acid gases will also flash when the pressure is reduced. The dissolved hydrocarbons should flash to the vapor phase and be removed. Flowever, a small amount of hydrocarbon liquid may begin to collect in this separator. Therefore, a provision should be made to remove these liquid hydrocarbons. 

Figure 3-14. Absorbance-time plots for the reaction of carbon suboxide and triethylamine in ether solution in the presence of acetic anhydride. The initial C3O2 concentration was 2.03 X I0 - M the amine concentrations were 3 X lO " M, 5 x 10 M, and 7 X lO " M.

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