FR2671338A1 - Process for obtaining a gaseous nitrogen/hydrogen mixture for the synthesis of ammonia - Google Patents

Abstract

The invention relates to a process for obtaining a nitrogen-hydrogen gas mixture for the synthesis of ammonia. According to the invention, a two-phase catalytic conversion of hydrocarbons is carried out in the presence of water vapor and an excess of compressed air, which provides a nitrogen-hydrogen mixture containing carbon monoxide and a conversion subsequent, by water vapor, from carbon monoxide to carbon dioxide and hydrogen; the process comprises, successively, the separation of carbon dioxide, methanization of the carbon monoxide residues, the separation of the excess nitrogen from the nitrogen-hydrogen mixture under a pressure close to that of the starting mixture and, simultaneously, the separation of hydrogen under a pressure the value of which is situated in the interval between the pressure substantially equal to that of the starting nitrogen-hydrogen mixture and the pressure at which the synthesis of ammonia, the final product, takes place. The invention will find applications in the chemical and petrochemical industries.

Description

The present invention relates to processes for obtaining mixtures

  The invention will find applications in the chemical and petrochemical industries. At present, a multitude of processes are known for obtaining a nitrogen-hydrogen mixture that can be used for the synthesis of ammonia. Thus, according to the process described in US Pat. No. 3,443,993, the starting mixture formed of a mixture of water vapor and hydrocarbons, is heated by the heat transferred by combustion products, a primary conversion is carried out by means of the steam, in the presence of a catalyst, at temperatures whose limits are lower and upper are respectively between 400 and 5400 C and between 750 and 8500 C, these temperatures being reached thanks to the heat ceded by the products of combustion, the primary conversion causing the reaction of 70% of the starting hydrocarbons; secondary conversion, also catalytic, is then carried out admitting air, the temperature of the products resulting from the secondary conversion being between 920 and 10500 C; then, at medium and low temperatures, a conversion of the carbon monoxide leading to the carbonic anhydride is carried out, this conversion being effected catalytically at temperatures of between 450 and 1900 ° C., and then the purification of the carbon monoxide is carried out. converted gas from its traces of oxide and carbon dioxide, with

methane formation.

  The resulting nitrogen-hydrogen mixture has an H 2 IN 2 ratio which is close to the ratio

stoichiometric equal to 3.

  The realization of the above process involves a considerable consumption of hydrocarbons and energy. In addition, the primary conversion is carried out

  in harsh technological conditions.

  A process for obtaining a nitrogen-hydrogen mixture is known, for the synthesis of ammonia (US Pat. No. 3442613), which comprises a heating of the vapor-hydrocarbon mixture by the heat yielded by the products of combustion. primary conversion by steam, carried out in the presence of a catalyst at a temperature, the lower and upper limits of which vary respectively between 400 and 5400 C and between 650 and 7500 C, this conversion taking place thanks to the contribution of heat supplied by the combustion products, the primary conversion reacting up to% of the starting hydrocarbons; a secondary conversion carried out admitting an excess amount of air, the temperature of the products resulting from the secondary conversion being between 820 and 10500 C; a conversion of carbon monoxide carried out at medium and low temperatures, which leads to carbon dioxide, this conversion being carried out in the presence of catalysts at temperatures ranging between 450 and 1900 C; a purification of the converted gas, ridding it of carbonic anhydride; a purification of the converted gas removing traces of carbon monoxide and carbon dioxide with methane formation, the converted gas then having a ratio H 2 / N 2 of between 2 and 2, 2, less than the required stoichiometric ratio for the synthesis of ammonia, and finally a low temperature separation of the converted gas to separate excess nitrogen and

inert methane.

  The advantages of the process described above for obtaining a nitrogen-hydrogen mixture, compared to the process according to US Pat. No. 3,443,993, are a reduction of 30% in the consumption of natural gas used for heating. a more efficient embodiment, compared with the method according to US, A, 3441393, of the primary conversion by the steam, which makes it possible to reduce the operating temperature from 100 to 1500 ° with respect to that described in US Pat. 3441393, obtaining a nitrogen-hydrogen mixture for the synthesis of ammonia containing a proportion of less than 80% of the inert gases such as Ar and CH 4, which allows a reduction of 5% of expenses for the compression of the mixture nitrogen-hydrogen at the pressure to be synthesized and a reduction in investment in equipment for the synthesis of ammonia. However, in the above process, all of the converted gas must be subjected to separation in order to obtain a stoichiometric composition required for the synthesis of ammonia, hence an expense.

considerable energy.

  A process for the synthesis of ammonia according to US Pat. No. 4,289,888 is known, which comprises a heating of the vapor-hydrocarbon mixture by the heat transferred by the combustion products, a primary conversion by steam carried out under a pressure that can reach 40 bars in the presence of a catalyst, at a temperature

  the lower and upper limits are, respectively,

  This conversion is effected by the heat transferred by the combustion products, the primary conversion causing the reaction of the starting hydrocarbons up to 50%; a secondary conversion carried out with admission of an excess amount of air, the temperature of the products resulting from this secondary conversion being between 920 and 10500 C; a conversion at medium and low temperatures of carbon monoxide, leading to carbon dioxide, this conversion being carried out in the presence of catalysts, at temperatures ranging between 460 and 1900 C; purifying the converted gas to remove traces of carbon monoxide and carbon dioxide with methane formation; a compression of the nitrogen-hydrogen mixture having an H 2 / N 2 ratio of between 2 and 2.2, up to a pressure of 80 bars, and then the excess nitrogen remaining after condensation of the ammonia is removed at a low temperature and under a pressure of 0.5 bar. The advantage of the method described with respect to that according to US Pat. No. 3,442,613 lies in the reduction of the volume of the mixture to be separated at a low temperature, thus in a reduction of the energy expenditure due to a lower recovery of Cold and hot veins of the mixture to be separated However, the implementation of this method involves a considerable expenditure of energy for the compression of all the nitrogen-hydrogen starting mixture, which limits to 80 bar the pressure at which performs the synthesis; in addition, energy losses are caused by the circulation of the reaction mixture during the synthesis. The above method makes it possible to reduce the conversion temperatures by admitting an excess amount of air with respect to the stoichiometric proportion, and reduce the

  energy consumption for the synthesis of ammonia.

  There is also known a process for obtaining a gaseous mixture containing hydrogen according to EP, A, 106076, which comprises a mixture of the starting hydrocarbons with steam, the division of the two-part joint vein, one of which is subjected to a primary conversion by the steam in the presence of catalysts and is then brought to a secondary catalytic conversion by steam and air where the second part of the initial vein is also allowed. Hydrocarbons The conversion secondary supply a converted gas (nitrogen-hydrogen mixture) having, at the exit, a temperature of 920 to 10500 C, the heat of this product being subsequently used for the indirect heating of the joint vein of the starting hydrocarbon mixture at the stage The process also involves conversion at medium and low temperatures of the carbon monoxide contained in the resulting nitrogen-hydrogen mixture, conversion of which leads to carbon dioxide and which is carried out in the presence of a catalyst at a temperature between 450 and 1900 C; a purification of the converted gas which removes traces of carbon monoxide and carbon dioxide with formation of methane; a separation of the converted low temperature gas (1900 C), which provides a nitrogen-hydrogen mixture of a stoichiometric composition and a nitrogen fraction having a pressure of 0.5 atm and which is to be rejected; as well as a compression of the nitrogen-hydrogen mixture and the synthesis of ammonia To heat the air used for technological purposes, we put the heat of the fumes coming out of the gas turbine used as actuator of the compressor

from this air to contribution.

  The above process involves a considerable expenditure of energy at the stage of the separation at low temperature when obtaining the mixture

  nitrogen-hydrogen having a stoichiometric composition.

  The energy expenditure amounts to 0.77 GJ per tonne of NH 3. The purpose of the invention is to provide, by modifying the conditions at the stage of separation of the excess nitrogen and of the nitrogen-hydrogen mixture, to provide a process of obtaining a gaseous nitrogen-hydrogen mixture for the synthesis of ammonia, making it possible to reduce the expense

  of energy necessary for carrying out this process.

  The problem thus posed is solved with a process for obtaining a nitrogen-hydrogen gas mixture for the synthesis of ammonia, which comprises a catalytic conversion of hydrocarbons in two phases, carried out in the presence of steam and water. an excess of compressed air, this conversion providing a nitrogen-hydrogen mixture; a subsequent conversion, by steam, of the carbon monoxide contained in the mixture obtained, into carbon dioxide and hydrogen, and then separation of the carbon dioxide; a methanization of the carbon monoxide residues and a subsequent separation of the excess nitrogen and the nitrogen-hydrogen gas mixture obtained, in which, according to the invention, the separation of the excess nitrogen and the nitrogen-hydrogen malange is carried out under a pressure close to that of the starting nitrogen-hydrogen mixture and furthermore hydrogen is recovered under a pressure whose value is between the pressure substantially equal to that of the starting nitrogen-hydrogen mixture and the pressure at which is the synthesis

ammonia.

  The total reduction in energy expenditure compared to the known process (EP, A, 106076) amounts to

0.82 GJ per tonne of NH 3 approximately.

  According to the invention, it is advantageous to perform the recovery of hydrogen from the nitrogen-hydrogen mixture using intermetallic compounds, which is explained by the presence, in the technological scheme, of a free heat to low potential (60 to 800 C) which is sufficient for the recovery of the largest

possible amount of hydrogen.

  Since the technological scheme provides for the presence of water vapor under a pressure equal to or greater than that of the starting nitrogen-hydrogen mixture, it is advantageous, according to the invention, to carry out the recovery of hydrogen from its mixture.

  nitrogen-hydrogen using diffusion elements.

  Other features and advantages of the invention will be better understood when reading the

  detailed description which will follow of a process

  obtaining a nitrogen-hydrogen gas mixture for the synthesis of ammonia, as well as detailed non-ammonia

limiting its realization.

  The process according to the invention for obtaining a nitrogen-hydrogen gas mixture for the synthesis of ammonia is based on the separation of the excess nitrogen and the nitrogen-hydrogen mixture, separation carried out under a pressure of between 5 and 50 bar. , and additional recovery of hydrogen operating under a pressure close to or greater than that

  starting nitrogen-hydrogen mixture.

  The process according to the invention provides for the use, as raw materials, of crude hydrocarbons such as methane, ethane, propane and their mixtures, higher hydrocarbons which are, in the

  normal conditions, in the gaseous or liquid state.

  According to the invention, the starting hydrocarbons mentioned above, preferably compressed under a pressure of between 10 and 100 bar, are mixed with water vapor in a ratio ratio ratio

equal to 2.52.

  The resulting steam-gas mixture is heated, after mixing, to a temperature of 4500 C and then subjected to a primary catalytic conversion by steam, increasing the temperature of the reaction mixture to 621-790 ° C. the steam is carried out, in this case, as an endothermic reaction in the presence, in particular, of a nickel catalyst. The gaseous reaction mixture, at a temperature of between 621 and 7490 ° C., undergoes a secondary catalytic conversion by steam carried out in presence of air brought to a temperature not exceeding 9000 C. At the end of the secondary catalytic conversion by steam and air, a nitrogen-hydrogen mixture is obtained whose temperature is between 980 and 10100 C, which is recycled at the primary conversion stage where it is cooled to a temperature of 520 to 8000 C, giving up its heat to the endothermic conversion of methane by steam,

  conversion taking place at this stage.

  The resulting nitrogen-hydrogen mixture is cooled to 3600 C and the carbon monoxide it contains is subjected to conversion by steam, which provides

  carbon dioxide and hydrogen.

  The carbon dioxide thus formed is separated from the nitrogen-hydrogen mixture by any of the known processes, in particular using absorbents. The residual carbon monoxide (0.5%) undergoes anaerobic digestion at a temperature of 200.degree. to 4000 C. In doing so, we can purify the nitrogen-hydrogen mixture of carbon dioxide and carbon monoxide until their rate in the

mixture does not exceed 50 ppm.

  To obtain, from this product, a nitrogen-hydrogen mixture that can be used for the synthesis of ammonia, the excess nitrogen is removed from this product, which is under a pressure of 5 to 90 bar; in addition, according to the invention, hydrogen is also recovered at pressures ranging from 5 to

500 bars.

  According to the invention, the recovery of hydrogen is carried out either with the aid of intermetallic compounds, in particular Ni 5, Fe Ti, Fe Ti Mn, or by diffusion through metal membranes, in particular through membranes containing palladium The depleted mixture which remains after recovery of hydrogen (in an amount up to 92% by weight) is divided into two veins, one of which is removed from the technological cycle (with subsequent use of its energy) and whose other, reduced nitrogen content, is mixed with the previously recovered hydrogen to obtain a gaseous nitrogen gas hydrogen used for the synthesis of ammonia The division of the nitrogen-hydrogen mixture into two veins can be carried out before separation of hydrogen excess is then recovered from one of the veins, hydrogen, and mixed with the other vein obtaining a gas mixture nitrogen-hydrogen for the synthesis of ammonia a when the excess nitrogen vein remaining after recovery of hydrogen is removed from the technological cycle with

  subsequent use of its energy.

  An alternative embodiment of the process consists in dividing the nitrogen-hydrogen mixture at a temperature of not less than 1700 C, in two veins, after recovery of the hydrogen With this method, the vein which is mixed with the hydrogen beforehand recovered to form the gaseous mixture nitrogen-hydrogen for the synthesis of the ammonia is evacuated under a pressure close to that of the starting nitrogen-hydrogen mixture while the second vein is

evacuated at a reduced pressure.

  The particularity of the recovery of hydrogen using intermetallic compounds or diffusion metal membranes offers the possibility of simultaneous compression up to a pressure at which the synthesis takes place, which ensures

  mechanical energy saving compression.

  The choice of the excess nitrogen separation variant with additional recovery of hydrogen in the presence of intermetallic compounds is determined by the balance of excess heat at low potential at a temperature level of between 1300 C and 1300 C, heat available in the technological scheme, or by the general balance of veins of energy vehicles such as steam under a pressure of 5 to 100 bar. The invention will be better understood by means of

  non-limiting examples of embodiments that will follow.

EXAMPLE 1

  A hydrocarbon natural gas having the following composition, where the parts are by volume: 82.2% of CH 4; 4.47% C 2 H 6; 1.36% C 3 H 8; 0.49% C H; 0.29% of C H 6.98% of N 2; 0.03% of

410 512 '2

  Ar; 0.03% C 02; 4.2% of H 2, is mixed under a pressure of 4.3 M Pa, with steam at a vapor: carbon ratio equal to 2, 52: 1, then it is heated to 4500 C and then is brought to the primary conversion stage by steam, which provides a reaction mixture at a temperature of 7270 C and having a

  of CH 4 in the converted dry gas equal to 28.08% by volume.

  The converted gas resulting from the primary conversion stage by the steam is brought to the secondary conversion stage by steam and air. A vapor-air mixture is also allowed at 8000 C, the H 0 / air ratio being equal to 0 1. The temperature of the nitrogen-hydrogen mixture at the exit of the secondary conversion stage by steam and air is 10100 C; the methane level is 0.33% in

  volume and the ratio H 2 + CO / N is equal to 1.85%.

  At the end of the secondary conversion, the nitrogen-hydrogen mixture is returned to the primary conversion stage where it is cooled to 5800 C, yielding its heat to the endothermic conversion of methane by the

  steam, which takes place at this stage.

  The nitrogen-hydrogen mixture obtained is cooled to 3600 ° C. and is then converted to carbon monoxide by steam in order to obtain carbon dioxide in an amount of 16.88% by volume. hydrogen in an amount of 53.02% by volume. Carbon dioxide and carbon monoxide are extracted from the nitrogen-hydrogen mixture until

  their residual rate in the mixture does not exceed 5 ppm.

  From the purified nitrogen-hydrogen mixture having the following volume composition: 62.95% H 2; 35% N 2, 0.42% Ar; 3.04% of CH 4 under a pressure of 2.99 M Pa, 85% by volume of hydrogen are separated in the presence of an intermetallic compound, La Ni 5 The separation of hydrogen is carried out under

a pressure of 2.95 M Pa.

  The nitrogen-enriched mixture, remaining after separation of the hydrogen, is divided into two veins at a ratio of 0.58: 0.42, the first of which is mixed with the separated hydrogen to obtain the nitrogen-hydrogen gas mixture for the synthesis of ammonia having the following composition, by volume: 74.22% H 2; 24.72% N 2, 0.29% Ar; 0.7% of CH with a stoichiometric ratio between hydrogen and nitrogen equal to 3: 1 The second vein, with excess nitrogen, having the following composition, by volume: 76.55% of N 2, 31% H 2, 0.91% Ar; 2.23% of CH 4 under a pressure of 2.87 M Pa is removed from the technological scheme

using his energy.

EXAMPLE 2

  A hydrocarbon natural gas of the following composition by volume: 82.11% of CH 4; 4.47% C 2 H 6; 38%, 48% C H; 0.25% C H; 0.03% 1, 3% e CH 3 0.48% C 5 12 CO 2; 4.20% H 2; 7.07% N 2; 0.03% of Ar, under a pressure of 4.3 M Pa, is mixed with steam at the steam / carbon ratio equal to 2.52: 1, then is heated to 4500 C and is brought to the stage primary conversion by steam, which provides a reaction mixture at a temperature of 729.10 C The rate of CH 4 in the converted dry gas is 27.80% by volume the converted gas from the primary conversion stage by the steam is brought to the secondary conversion stage by steam and air It is also allowed a vapor-air mixture heated to a temperature of 7000 C, the ratio H 20 / air

being equal to 0.1.

  The temperature of the hydrogen nitrogen mixture at the outlet of the secondary conversion by steam and air is 10100 C, the methane level is 0.31% by volume,

the ratio H 2 + CO / N 2 is 1.77.

  At the end of the secondary conversion stage, the nitrogen-hydrogen mixture is brought to the primary conversion stage where it is cooled to a temperature of 5800 C, giving up its heat to the endothermic conversion of the

  methane by steam, which takes place at this stage.

  The nitrogen-hydrogen mixture obtained is cooled to 3600 ° C. and is converted to carbon monoxide by steam in order to obtain carbon dioxide in an amount of 16.8% by volume.

  and hydrogen in an amount of 52.29% by volume.

  From the nitrogen-hydrogen mixture, carbon dioxide and carbon monoxide are separated until their residual rate in the mixture is not

greater than 5 ppm.

  The purified nitrogen-hydrogen mixture having the following composition, by volume: 62.02% H 2; 36.55% N 2, 0.44% Ar; 0.99% of CH 4, at a pressure of 2.99 M Pa, is divided into two veins at a ratio equal to 0.55: 0.45 From the second vein, in the presence of Fe Ti, hydrogen at a pressure of 12.00 M Pa in an amount of 85% by volume, which is mixed with the first vein separated from the nitrogen-hydrogen mixture, to obtain a gaseous nitrogen-hydrogen mixture for the synthesis of ammonia having the following composition, by volume: 75.5% H 2; 24.55% N 2, 0.29% Ar; 0.66% of CH 4 with a stoichiometric ratio of hydrogen to nitrogen equal to 3: 1 The vein remaining after separation of hydrogen, containing excess nitrogen and having the following composition, by volume: 3% of N 2; 19.68% H 2, 0.92% Ar; 2.10% of CH 4 under a pressure of 2.81 M Pa, is removed from the diagram

  technological, with recovery of its energy.

EXAMPLE 3

  A hydrocarbonaceous natural gas having the following composition, by volume: 82.36% of CH 4; 4.49% C H; 1.37% C 3 H 8; 0.49% C H; 0.24% of

26 8410

  C 5 H 12; 4.2% H 2; 6.80% of N 2; 0.03% of Ar; 0.03% of C 02, under a pressure of 4.3 M Pa, is mixed with steam at a steam: carbon ratio of 2.52: 1, then is heated to 4500 C and is heated to stage of the primary steam conversion, which provides a reaction mixture at a temperature of 748.70 C The CH 4 content in the dry converted gas is 25.04% by volume The converted gas at the end of the conversion stage primary steam is carried to the secondary conversion stage by steam and air A vapor-air mixture is also admitted, which is heated to a temperature of 8000 C, its

ratio H 20 / air being 0.1.

  The temperature of the nitrogen-hydrogen mixture at the outlet of the secondary conversion by the vapor and the air and of 10100 C, the rate of methane being of 0.38% in

volume.

  At the end of the secondary conversion stage, the nitrogen-hydrogen mixture is brought to the primary conversion stage where it is cooled to 5200 C, yielding its heat to the endothermic conversion of methane by steam, which takes place at this stage . The nitrogen-hydrogen mixture obtained is cooled to 3600 C. It is sent to the conversion, by the steam of the carbon monoxide, in order to obtain carbon dioxide in a quantity of 16.99% by volume and of

  hydrogen in an amount of 54.39% by volume.

  Carbon dioxide and crone oxide are separated from the nitrogen-hydrogen mixture until their residual level in the mixture does not exceed 5 ppm. From the purified nitrogen-hydrogen mixture having the following composition, by volume: 64.67% H 2; 33.79% N 2 90, 40% Ar; 1.17% of CH 4 under a pressure of 2.99 M Pa, is separated, using diffusion membranes containing palladium and in the presence of steam under a pressure of 30 M Pa, the hydrogen in an amount of 90% by volume, this hydrogen associating with the vapor The vapor is condensed, the condensation heat being used for technological purposes, while the hydrogen thus released, under a pressure of 3.0 M Pa, is mixed with one of the parts of the mixture previously divided into two parts at a ratio of 0.6: 0.4, namely the part which has remained after recovery of the hydrogen and which has the following composition, by volume: 15.47% H 2; 80.8% of N 2; 0.96% of Ar; 2.72% of CH 4 is thus obtained a nitrogen-hydrogen gas mixture for the synthesis of ammonia, this mixture having the following composition, by volume: 74.09% H 12; 24.78% of N 2, 0.29% of Ar 0.84% of CH 4, the stoichiometric ratio between

  the hydrogen and the nitrogen being equal to 3.

  The second part of the divided mixture after recovery of hydrogen, part containing excess nitrogen, is removed from the technological cycle, with

recovery of his energy.

EXAMPLE 4

  A starting mixture having the following composition, by volume: 82.28% CH 4; 4.48% C 2 H 6 1.36% C H 0.49% C 4 H 10; 0.24% C H; O 03% 38 e '512 from Ar; 6.89% of N 2; 4.20% H 2, at a pressure of 4.3 M Pa, is mixed with steam at a steam: carbon ratio equal to 25.2: 1, then is heated to a temperature of 4500 C. and is brought to the primary conversion stage by steam, which provides a reaction mixture at a temperature of 725.40 C and a dry converted gas CH 4 content of 28.37% by volume. The converted gas from the primary conversion by steam is carried to the secondary conversion stage by steam and air. A vapor-air mixture

  9000 C, the ratio H 0 / air being 0.1.

  The temperature of the nitrogen-hydrogen mixture at the exit of the secondary conversion stage by steam and air is 10100 C, the methane level is 0.32% in

  volume, the ratio (H 2 + CO) / N 2 is 1.92.

  At the end of the secondary conversion stage, the nitrogen-hydrogen mixture is brought to the primary conversion stage where it is cooled to 5800 C, yielding its heat to the endothermic conversion of methane by the steam, which

takes place at this stage.

  The nitrogen-hydrogen mixture obtained is cooled to 3600 C and then sent to the conversion of carbon monoxide by the steam to obtain carbon dioxide in an amount of 16.93% by volume and

  of hydrogen in an amount of 53.72% by volume.

  Carbon dioxide and carbon monoxide are separated from the nitrogen-hydrogen mixture until

  their residual rate in the mixture does not exceed 10 ppm.

  From the purified nitrogen-hydrogen mixture having the following composition, by volume: 63.83% H 2; 34.67% N 2; 0.41% of Ar; 1.09% of CH 4 under a pressure of 2.99 M Pa, the hydrogen is separated in an amount of 90% by volume in the presence of a compound

intermetallic, Fe Ti Mn. The separation of hydrogen is carried out under

a pressure of 30.0 M Pa.

  From the nitrogen-hydrogen mixture remaining after the recovery of hydrogen, the following volume composition is separated: 14.99% H 2; 81, 49% of N 2; 0.97% of Ar; 2.55% of CH 4, at a temperature of minus 1800 ° C., the excess nitrogen with an impurity content of H 2 of 1.13% by volume, Ar of 2.51% by volume, CH 4 of 7.18% by volume, operating under a pressure of 0.7 M Pa and then removed from the technological cycle, with recovery of energy The technological nitrogen present in the nitrogen-hydrogen mixture having the following volume composition: 77.25% N 2; 22.61% H 2 y 0.13% Ar; 0.01% of CH 4 is mixed with the separated hydrogen, thus obtaining a nitrogen-hydrogen gas mixture for the synthesis of ammonia whose volume composition is as follows: 74.96% of H 2; 24.989% of N 2 '0.04% of Ar 0.07% of CH 4, with a stoichiometric ratio between

hydrogen and nitrogen equal to 3.

Claims (3)

R E V E N D I C A T IO N S   1 Process for obtaining a nitrogen-hydrogen gas mixture for the synthesis of ammonia, of the type comprising a catalytic conversion into two hydrocarbon phases, carried out in the presence of water vapor and an excess of air compressed, and providing a nitrogen-hydrogen mixture, a subsequent conversion, by water vapor, carbon monoxide in the mixture thus obtained, carbon dioxide and hydrogen, the separation of carbon dioxide, the methanization of the residual carbon monoxide, and finally the separation of the excess nitrogen, of the gaseous nitrogen-hydrogen mixture obtained, characterized in that the separation of the excess nitrogen from the nitrogen-hydrogen mixture is carried out under a pressure close to that of the starting nitrogen-hydrogen mixture, the hydrogen being separated from this mixture under a pressure whose value is between a pressure substantially equal to that of the starting nitrogen-hydrogen mixture and a pressure at which the synthesis takes place ammonia.   Process according to Claim 1, characterized in that the separation of hydrogen is   performed using intermetallic compounds.   3. Process according to claim 1, characterized in that the separation of hydrogen is   performed using broadcast elements.