Chemistry of inorganic compounds – Nitrogen or compound thereof – Ammonia or ammonium hydroxide
Patent
1986-01-31
1987-10-13
Doll, John
Chemistry of inorganic compounds
Nitrogen or compound thereof
Ammonia or ammonium hydroxide
252376, C01C 104
Patent
active
046997725
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for preparing ammonia.
In current processes for the preparation of ammonia the synthesis gas is usually prepared by steam-reforming or partial oxidation of a hydrocarbon feed stock, which can be a liquid or a gaseous hydrocarbon or mixture of hydrocarbons, e.g. naphta or natural gas. A process of the type wherein the synthesis gas is obtained by partial oxidation is known from P. H. Brook: Ammonia Plant Revamping, Proceedings of the Fertilizer International Conference 1983, p. 159-175. In this process natural gas is partially oxidized with air in a Texaco gasifier and the quantity of nitrogen introduced in the process with the air, in excess of the quantity stoichiometrically required for the conversion of the hydrogen formed to ammonia, which excess may be about 200%, is removed in a cryogenic separation section. The feed gas and the process air are preheated to about 590.degree. C. and about 815.degree. C., respectively, in a separate furnace by combusting a suitable fuel, such as natural gas expanded to atmospheric pressure. The quantity of oxygen must be sufficient to attain the required degree of hydrocarbon conversion and the feeding thereof as air at the reaction pressure to the partial oxidation zone involves the compression and the heating of the excess introgen and other components of the air, which heating occurs by combustion of natural gas in the preheating and the partial oxidation zones. However, the compression energy and the heat required therefor can be recovered only partially. Moreover, the non catalytic partial oxidation process used necessitates a carbon removal step to remove the solid carbon formed in the partial oxidation zone and entrained in the gaseous effluent therefrom. The temperatures in the partial oxidation reactor are high so that at the exit the temperature is about 1260.degree. C.
The principal object of the present invention is to provide a process for preparing ammonia the energy consumption of which is lower than the energy consumption of the known process referred to. More particularly the present invention is aimed at a process for preparing ammonia in which the presence of a large excess of nitrogen in the ammonia synthesis gas is obviated so that a cryogenic removal of excess nitrogen can be dispensed with. A still further particular object is to provide a process in which the heat generated in the partial oxidation zone is used in an efficient manner.
These, and other objects which will become clear from the detailed description below, are attained in a process for the preparation of ammonia from hydrogen and nitrogen comprising the steps of:
(a) feeding to a first reaction zone, at a suitable pressure, a stream of air and a stream of hydrocarbon or a mixture of hydrocarbons to form by partial oxidation a gas mixture comprising hydrogen, nitrogen, carbon oxides, water and unconverted hydrocarbon material;
(b) shift conversion of carbon monoxide contained in the gas mixture obtained in step (a) into carbon dioxide and hydrogen and removing carbon dioxide and water from the gas mixture resulting from said shift conversion,
(c) feeding the synthesis gas mixture resulting from step (b) to a second reaction zone to partially convert hydrogen and nitrogen contained in said synthesis gas mixture to ammonia;
(d) separating ammonia from the gaseous effluent from said second reaction zone;
(e) recycling at least a portion of the gas mixture remaining after the separation of ammonia in step (d), in which process, according to the invention, suitable catalyst at a pressure of from 35 to 150 bar, and temperatures of from 850.degree.-1200.degree. C. at the exit of the first reaction zone, the quantity of air fed to the first reaction zone is such that the molar ratio of hydrogen to nitrogen in the gas mixture resulting from step (b) is between 2.5 and 3 to 1 and an additional quantity of oxygen is fed to the first reaction which oxygen together with the oxygen contained in the said quantity of air is sufficient to effect the required degree
REFERENCES:
patent: 4296085 (1981-10-01), Banquy
patent: 4383982 (1983-05-01), Pinto
patent: 4409196 (1983-10-01), Skinner et al.
patent: 4524056 (1985-06-01), Banquy
P. H. Brook: Ammonia Plant Revamping, Proceedings of the Fertilizer International Conference, 1983, pp. 159-175.
Doll John
Langel Wayne A.
Stamicarbon B.V.
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