Carbon dioxide removal with water

Carbon dioxide reacts with water to form the weak acid H2CO3 which would cause the blood acidity to become dangerously high if it were not promptly removed as it is excreted by the cells. This is accomplished by combining it with carbonate ion through the reaction... 

In equations (3.1) and (3.2) we saw how carbon dioxide reacts with water to form carbonic acid which then reacts with calcium hydroxide to form calcium carbonate. This removes the hydroxyl ions from solutions and the pH drops so that the passive layer is no longer maintained and corrosion can be initiated. 

In carbon dioxide removal, the water wash was very early replaced with more efficient systems using MEA or hot potassium carbonate as the absorbent. Later, the efficiency of these processes was gradually improved, and also new processes based on physical or combined physical and chemical absorption were developed. See also Sect. 6.3.4. 

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. 

It is estimated that photosynthesis is a sink for around 60 billion tons of carbon every year, by far the strongest mechanism for carbon dioxide removal from the atmosphere. (This removal is almost exactly balanced by the respiration of animals, which combines oxygen with hydrocarbons to produce carbon dioxide and water vapor.)... 

SCE with carbon dioxide removes organic contaminants and leaves much of the original soil organic matrix in place. The contaminants are then collected on activated carbon in a contaminant collection vessel and transported in an aqueous stream to the WAO reactor for destruction. The concentration of the organic contaminants on activated carbon in water provides a suitable matrix for the WAO feed stream and allows for a smaller reactor size. The activated carbon is then regenerated in the WAO reactor with minimal carbon loss and can be recycled to the contaminant collection vessel. 

LNG is simple to re-gasify in order to deliver almost pure methane at the end users. In contrast to natural gas that contains typically around 90% methane, and some ethane, propane and heavier hydrocarbons, the liquefaction process involves pre-treatment of the gas in order to remove carbon dioxide, sulphur compounds, water, and petroleum gases with carbon number higher than one (butane, propane etc.). This is done in order to avoid formation of solids in the cold heat exchangers. The presence of nitrogen is usually limited at about 1% (refer Table 2 on page 81). 

Referring to point a, in desalination the content of oxygen and carbon dioxide in the water affects the material life of the plant (because of corrosion problems), as well as the pH and the conductivity of water. Usually, these gases are removed by stripping in a packed column and the final water p H is adjusted by means of caustic soda. By using membrane contactors, there is no need for chemicals, with a consequent reduction of the environmental impact. 

When only potassium carbonate or organic solvents are used, the effects are less important. Potassium carbonate blocks the catalyst pores, and can be removed by washing with water to restore normal performance. Methanation catalysts can be protected from poisons by installing a guard bed of zinc oxide absorbent. This will remove traces of sulfur and droplets of liquid from the carbon dioxide removal system70. 

Phenylgermanic acid anhydride, (CgHsGeOjaO.—Equimolecular proportions of mercury diphenyl and germanium tetrachloride in dry xylene are heated in a sealed Pyrex bulb for two days, then diluted with dry ether and filtered. The solid residue is pure phenylmercuric chloride, and the filtrate is treated with benzene, and finally with water containing a few drops of ammonium hydroxide. The granular precipitate which separates at the liquid interface is removed and dried at 115° C. The anhydride is a white, fluffy, amorphous solid, with no definite melting-point, soluble in excess of alkali, and reprecipitated by carbon dioxide, insoluble in water and organic solvents. 

Acetone should be colourless and completely miscible with water. Its specific gravity should not exceed 0 800 at 15 It should give no turbidity on mixing with twenty times its volume of carbon disulphide, and no residue on evaporation. It should be free from acidity, except for traces of dissolved carbon dioxide (approximately o oi per cent,). To test acidity the acetone is boiled to remove carbon dioxide, diluted with an equal volume of water (free from carbon dioxide) and titrated with alkali, using phenol phthalein as indicator. Alkalinity should be absent, as it indicates the presence of amines it is tested for by diluting... 

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