Liquid absorption purification

Conventional Hydrogen Production Using Liquid Absorption Purification... 

Product purification. In a liquid absorption system, carbon dioxide is removed. The product gas undergoes a methanation step to remove the residual traces of carbon oxides. Recent SMR plants use a pressure swing absorption (PSA) unit instead, producing 99.99% pure hydrogen. 

Natural gas is processed mainly for the recovery of liquid hydrocarbons useful in gasoline, pure hydrocarbons as butane, propane, ethane, or mixtures of them, hydrogen sulfide (and sulfur or sulfuric acid), and carbon black but significant amounts of gas are also converted into ammonia, synthesized by the Fischer-Tropsch reaction, or oxidized into chemical products such as formaldehyde. Conventional operations, however, consist of mainly two operations, viz., recovery of liquids (absorption, etc.), and purification of the liquid. 

The application of liquid dispersion reac tors to the absorption of fluorine gases is described by Kohl and Riesenfeld (G .s Purification, Gulf, 1985, pp. 268-288). 

Absorption is a commonly applied operation in chemical processing. It is used as a raw material or a product recovery technique in separation and purification of gaseous streams containing high concentrations of organics (e.g., in natural gas purification and coke by-product recovery operations). In absorption, the organics in the gas stream are dissolved in a liquid solvent. The contact between the absorbing liquid and the vent gas is accomplished in countercurrent spray towers, scrubbers, or packed or plate columns. 

Purification of Synthesis Gas. This involves the removal of carbon oxides to prevent poisoning of the NIT3 catalyst. An absorption process is used to remove the bulk of the C02, followed by methanation of the residual carbon oxides in the methanator, Modern ammonia plants use a variety of C02-removal processes with effective absorbent solutions. The principal absorbent solutions currently in use are hot carbonates and cthanolamincs. Other solutions used include methanol, acetone, liquid nitrogen, glycols, and other organic solvents. 

Numerous industrial operations involve a heat transfer between a liquid phase and a gaseous phase, with an important mass transfer effect, either as desorption-evaporation or as absorption-condensation. Here are some examples reconcentration, by evaporation, of solvents, toxic industrial effluents production, by absorption, of industrial aqueous acid solutions reversible or irreversible chemical reactions (oxidation, hydrogenation, sulfonation) purification of permanent gases (air, smoke) by scrubbing of soluble vapors desorbers and absorbers for heat pumps, where these two operations occur simultaneously. 

Similar to the case of coke gas purification (see Section 9.5.2), this complex reactive absorption problem is solved by a purely numerical method. The liquid film is... 

In liquid ejectors or aspirators, the liquid is the motive fluid, so the gas pressure drop is low. Flow of slurries in the nozzle may be erosive. Otherwise, the design is as simple as that of the venturi. Kohl and Riesenfeld (Gas Purification, Gulf, 1985, pp. 268-288) describe the application of liquid dispersion reactors to the absorption of fluorine gases. 

In a 500-cc. round-bottomed flask fitted with a reflux condenser carrying at the top a tube leading to a gas absorption trap (Org. Syn. 14, 2) are placed 32.8 g. (0.2 mole) of 7-phenyl-butyric acid (p. 64) and 20 cc. (32 g., 0.27 mole) of thiony] chloride (Note 1). The mixture is carefully heated on a steam bath until the acid is melted and then the reaction is allowed to proceed without the application of external heat. After twenty-five to thirty minutes hydrogen chloride is no longer evolved and the mixture is warmed on the steam bath for ten minutes. The flask is then connected to the water pump, evacuated, and heated for ten minutes on the steam bath and finally for two or three minutes over a small flame in order to remove the excess thionyl chloride. The acid chloride thus obtained is a nearly colorless liquid and needs no further purification. The flask is cooled, 175 cc. of carbon disulfide is added, and the solution cooled in an ice bath. Thirty grams (0.23 mole) of... 

The considerations developed so far allows setting up the final conceptual flowsheet, as displayed in Figure 11.9. After reaction and quench the off-gas is submitted to a first separation of acrylonitrile by low-temperature cooling, at 10 °C. In the decanter the liquid splits into two phases. If the acetonitrile concentration is negligible, the organic phase containing acrylonitrile can be sent directly to the first purification column (Heads). The aqueous phase is sent to the acrylonitrile recovery. The off-gas from flash is compressed at 4.5 bar and submitted to absorption in cold water of 5 °C. In this way higher acrylonitrile recovery may be achieved (over 99.8%) with reduced water consumption. 

The extract is then flashed to liberate, the dissolved olefins and. after recompression, to return them to the extractive distillation step. The liquid fraction rich in butadiene and acetylenic compounds is preheated and sent to a regeneration column with 20 trays operating at about 0.2.10 Pa, at 90°C at the top and 150°C at the bottom. The solvent drawn off is recycled, possibly after purification if required. The distillate is partly condensed. The liquid fraction sei es as a reflux, and that in the gas phase is recompressed and partly returned to the absorption step. The crude butadiene remaining is rid of methyiacetylene and heavier compounds in two simple distillation columns, with about 40 and 110 trays respectively, in the presence of r-butylpyrocatechol. 

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