SU823286A1 - Method of isolating ammonia from industrial gases - Google Patents

Description

(54) METHOD FOR ISOLATION OF AMMONIA FROM HOSE

GAS

one -. The invention relates to coke-chemical, petrochemical, and nitrogen-gas production and can be used to extract ammonia from WASTE gases containing ammonia and acid gas impurities (, HCN, CQjL, etc.). There is a known method for trapping ammonia from the gas phase with water 1. A disadvantage of the known method is the small ammonia capacity of the sorbent, the ammonia water obtained is contaminated with acidic impurities contained in the gas. There is a known method for trapping ammonia from the gas phase with sulfuric acid G2. The disadvantage of this method is the production of large quantities of sulphate and mmonium, the value of which as a fertilizer is insignificant and which needs further processing. The closest to the invention according to the technical essence and the achieved result is the method of extracting ammonia from industrial gases containing acidic impurities, including treatment of the gas with a solution of phosphate salts to form a suspension of ammonium crystals. phosphate salts, thermal decomposition of the salts formed to produce ammonia. The solution obtained after absorption of ammonia, having the NH: HjPO ratio. (1.9-2) :, is fed to the regeneration which is carried out using water from a steam bath. When this occurs, the dissociation of diammonium phosphate to ammonia and a solution of ammonium phosphate with a molar ratio of 1.1-1.3. The vapor-ammonia mixture obtained during regeneration is condensed and subjected to distillation under a pressure of 15 atm to obtain anhydrous ammonia L3J. The disadvantage of this method is the need for additional purification of concentrated ammonia vapors from acidic impurities, which, when distilling ammonia from the suspension in the regeneration column, popg in the gas phase. The removal of acidic impurities is carried out with an alkali solution, which results in the formation of a significant amount of wastewater. Since the absorption solution is saturated with ammonia only before the formation of diammonium phosphate, i.e. molar ratios MNZ: H P04 - (1.9-2): 1 in solution after absorption, the ammonia capacity of the absorbent is relatively small (about 55-60 g / l), regeneration of aqueous solutions of diammonium phosphate requires large consumption of water vapor. The purpose of the invention is to reduce energy costs, increase the purity of ammonia and prevent the formation of alkaline waste. This goal is achieved by the fact that, according to the method of isolating ammonia I5 of industrial gases containing acidic impurities, including treating the gas with a solution of phosphate salts to form a suspension of crystals of ammonium phosphate salts, thermal decomposition of the salts formed to produce ammonia, and treating the gas with a solution lead to the ratio in ammonia to phosphoric acid from 2.8: 1 to 3: 1 / and the crystals of ammonium phosphate salts, previously isolated from the suspension, are subjected to thermal decomposition. The thermal decomposition of salt crystals is carried out at 100-200s. In the known methods, saturation by the swallowing solution leads to a molar ratio of no higher than 2.0, which leads to the formation of 1 | 1% of well soluble phosphates, and upon thermal decomposition - contaminates amPaccinating solution

Regenerated solution

Ammonia capacity of the absorption solution, g / dm

The degree of gas purification from ammonia,%

Irrigation density when the content of ammonia in the gas is 10 g / dm,

Steam consumption for regeneration, t / t of 100% ammonia Example. 60 at, containing 0.1 g / dm ammonia. 0.005 g / dm of hydrogen sulphide, 0.03 g / dm of carbon dioxide, is fed to a bubble column filled with a 2 molar solution of monoammonium phosphate in the amount of OD00 dm. The saturation of the solution with ammonia ends when the molar ratio is reached. 3: 1 The triammonium phosphate crystals are separated by filtration. Solid salt yield

Mono - and diammonium phosphate with

NH: HgPO 1.1: 1.2

Triammonium phosphate 2): 1 MNZ: H P04 3: 1

130 98.6

0.078 3.9 miac acidic impurities. To avoid this, it is necessary to desorb ammonia from salt crystals with the formation of slightly soluble sodium or triammonium phosphates at a molar ratio of ammonia to phosphoric acid from 2.8: 1 to 3: 1. When the MH: HzRO ratio is 2.8: 1, a small amount of triammonium phosphate salt crystals is obtained in suspension, therefore, the saturation of the absorption solution with ammonia below this ratio is impractical. Achieving the ratio NH ,, above 3: 1 is impossible due to the tribasic nature of phosphoric acid. The temperature range of decomposition of ammonium phosphate salt crystals 100-200 0 was chosen based on the fact that at below 100 ° C the rate of ammonia release from salt is so small that it is impractical to conduct the process at these temperatures. Thermal dissociation of phosphates with higher is undesirable, since irreversible changes in salt occur with the formation of pyrophosphates. Recycling of the regenerated salt in this case becomes impossible. Data for comparing the effectiveness of the proposed and known methods are given in the table. 36 g / h HCN and C0 impurities, are removed by filtration with a mother liquor. The solid salt decomposes at 140 ° C. The yield of pure ammonia is 5.5 g. The proposed method of separating ammonia from industrial gases has the following advantages: a significant simplification of the process of ammonia liberation, achieved by eliminating the alkaline washing of concentrated ammonia vapors from acidic impurities ;

reduction of the volume of the absorption solution in the cycle due to an increase in the degree of saturation of the absorbent to the molar ratio of NH. “- (2.8-3): 1; 334

elimination of heat consumption by reducing the quantities of reagents processed.

Claims (3)

Invention Formula A method for ammonia conversion of non-propellant gases containing acidic impurities, including treating the gas with a solution of phosphoric acid salts to form a suspension of crystals of ammonium phosphate salts, thermal decomposition of the salts formed to produce semiaxia, about l and h, and that, in order to reduce energy costs, increase the purity of ammonia and prevent the formation of alkaline wastewaters, gas treatment with a solution is reduced to a ratio in the ammonia solution to phosphoric acid from 2.8: 1 to 3: 1, and the thermal decomposition is subjected to crystals of ammonium phosphate salts / previously isolated from the suspension. 2. The method according to claim 1, characterized in that the thermal desorption of salt crystals is carried out at 100-2OO C. Sources of information taken into account in the examination 1. Antipova V.V. Combined cleaning of coke oven gas from ammonia and hydrogen sulfide. - Express Information Inchermeta USSR, 1974, no. 7, series 10. 2..Lazorin S.N., Stetsenko E.O. Production of ammonium sulfate at coke-chemical plants. M., Metallurgists, 1965. 3. Rice R.O. and HamMton C.W. The coks oven.managers year-book. 1976, p. 161-177 (irotype).