FR2652073A1 - PROCESS FOR OBTAINING HYDROGEN GAS - Google Patents

Abstract

The invention relates to a process for obtaining a hydrogenated gas. According to the invention, the hydrocarbon raw material is mixed with water vapor, the catalytic vapor conversion of the vapor-gas mixture obtained is carried out beforehand, then the primary catalytic conversion and the catalytic conversion of secondary vapor-oxygen; the secondary conversion is carried out by admitting the oxygenated gas mixed with the coolant at the coolant / oxygen ratio equal to 0.5-30.0 and the temperature is brought to a temperature which does not exceed 900 ° C; the product obtained as a result of the secondary conversion is sent to the primary conversion on behalf of the heat of this product. The invention applies in particular to the production of ammonia, methanol or higher alcohols.

Description

The present invention relates to the conversion of a raw material

hydrocarbon, and more

  concretely, a process for obtaining a hydrogenated gas.

  The invention will find application in the production of ammonia, methanol, alcohols

  as well as in the production of hydrogen.

  Several processes for obtaining a hydrogenated gas are currently known, for example a process for obtaining an azohydrogenated mixture (US Pat. No. 3,414,993) comprises heating a steam-hydrocarbon mixture by means of the heat resulting from the combustion of products, a process of first-stage vapor conversion in the presence of a catalyst at a temperature of 400-540 ° C at 750-850 ° C for the heat of the products of combustion, o react 70% of the starting hydrocarbon raw material, and a conversion process in the second stage carried out on catalyst with air intake, the temperature of the conversion products at the outlet of the second conversion stage.

being 920-1050 C.

  There is also known a process for obtaining an azohydrogenated mixture (GB, A, 2082623) comprising: heating the starting vapor-hydrocarbon mixture with the heat of the stack gases; a catalytic conversion process of the first stage vapor, at which 50% of the initial hydrocarbon mixture is reacted and which is effected at temperatures of 400 C to 650-750 C for the heat of the combustion products heating gas; a second stage catalytic vapor conversion process in which 50 to 20% of the initial hydrocarbon mixture is reacted and which is carried out at a temperature of 650-750 C up to 750-850 C for indirect exchange of heat with the conversion products resulting from the third conversion stage carried out on catalyst during the admission of air, the temperature of the conversion products at the exit of the second stage

  conversion then being 920-1050 C.

  The advantages of the indicated method of obtaining an azohydrogen mixture in comparison with that described in US Pat. No. 3,443,993 are as follows: a 30% reduction in the consumption of natural gas used for heating, a more efficient embodiment of the conversion first stage vapor, which allows the process temperature to be reduced to 100-150 ° C compared with the first-stage vapor conversion temperature regime described in the US,

A, 3441393.

  However, for carrying out the indicated process, it is essential to use a large volume of the catalyst as a result of the inefficiency of the first stage steam conversion process and, moreover, there is a pressure drop between the reaction mixture. and combustion products, unstable conditions of the second stage steam conversion process due to temperature fluctuations of the third stage conversion products and significant consumption of the hydrocarbon raw material to maintain the temperature. process in the first stage of conversion because of the insufficient amount of heat brought by the technological airflow to the third

stage of conversion.

  A process for obtaining synthesis gas for ammonia from hydrocarbons (US, A, 4376758) comprising: heating the hydrocarbon raw material; separating the vapor-hydrocarbon mixture into two streams, one of which passes into the first stage of steam conversion on behalf of the heat of the heating gas and the second stage of the conversion process with an excess of air, obtaining a mixture of a non-stoichiometric composition for the synthesis of ammonia; the second stream of the starting hydrocarbon mixture passes through the steam conversion process at a conversion rate of 90-95% on behalf of an indirect heat exchange with the azohydrogenated mixture obtained as a result of the mixing of the first stream of the converted gas after the second stage and the second stream after the steam conversion process. The mixture of the two streams of the converted gas has a composition suitable for the synthesis of ammonia without

subsequent treatment.

  The advantage of the process given, in comparison with the US, A, 3441393, lies in the reduction of about 30% of the hydrocarbon consumption for

heating.

  However, the indicated process is characterized by inefficient use of the catalyst in the steam conversion process of the two vapor-hydrocarbon mixture streams, considerable hydrocarbon consumption for heating, and a high inert methane content in the azohydrogenated mixture of second current as a result of the realization of the single-stage conversion in

  severe temperature conditions.

  A process for obtaining a synthesis gas (US Pat. No. 4,631,1182) is also known which consists in using, in the first stage, the conversion of a prior adiabatic vapor of the vapor-hydrocarbon mixture to a temperature of 440-510. C up to 400-500 ° C at a pressure between 1 and 30 bar, to use, in the second stage a steam reforming process on behalf of the heat of the heating gas at a temperature of 400-500 C up to at 750-850 C and, at a third stage, a conversion with air at a temperature of the converted gas at the exit of the third

stage of 920-1050 C.

  The advantage of the indicated method lies in the increase of the efficiency of use of the primary reforming catalyst, which leads to a

  volume reduction (primary conversion stage).

  However, this process is carried out at the stage of prior adiabatic steam conversion in a temperature range which is not optimal, in particular, in the case of the use, as a hydrocarbon raw material, of natural gas, which causes a low conversion rate of methane in the starting hydrocarbon mixture and a high volume of the catalyst

at the primary conversion stage.

  There is known a process for obtaining hydrogenated gas (EP, A, 106076) which comprises mixing the hydrocarbon raw material and steam, separating the general stream into two parts, one of which passes through the first stage of the process. catalytic conversion of the vapor and is accepted in the second stage of catalytic conversion of steam with air, or is allowed

  second part of the starting vapor-hydrocarbon stream.

  The second stage conversion process is carried out with the obtaining of the target product at a temperature of 920 to 1050 C, using subsequently the heat of the product obtained for the indirect heating of the part of the general stream of the starting hydrocarbon mixture at the stage of the

steam conversion.

  In the process mentioned, the steam conversion of the hydrocarbon raw material between 25 and 50 bar and at a temperature at the beginning of the process of 450 to 700 ° C. at a ratio by weight of steam / carbon of 2.5 is expected. and 4.5 on a nickel catalyst (temperature at the end of the steam conversion from 680 to 790 C). The secondary conversion is carried out during the admission of a technological air stream heated to 700-900 C in an amount ensuring, at the exit of the second secondary stage, a temperature of 850 to 1000 C. The process indicated allows to obtain a gas

H + CO

  hydrogen at a ratio of 1.9, which is related to a considerable energy consumption for the compression of excess air and a loss of a portion of the hydrocarbon raw material due to the reaction with the oxygen from the excess amount of air. It has therefore been proposed, by modifying the conditions for carrying out the secondary vapor conversion, to develop a process for obtaining a hydrogenated gas, making it possible to reduce the energy expenditure for its production as well as to reduce the consumption of reagents to obtain the product

  targeted, while ensuring a stable gas composition.

  The solution lies in the fact that, in a process for obtaining hydrogenated gas comprising mixing the hydrocarbon raw material with water vapor, the catalytic conversion of the preliminary steam of the mixture obtained, the catalytic conversion of the steam primary and secondary catalytic conversion secondary vapor-oxygen, admitting the oxygenated gas at a temperature not exceeding 900 C, and the shipment of the product referred to the primary conversion for carrying out the steam conversion on behalf of the heat of the product referred to, according to the invention, the oxygenated gas admitted to the secondary conversion, before heating, is mixed with the coolant at a ratio of

  heat transfer volume / oxygen which is equal to 0.5 - 30.0.

  With the present invention, it is possible to reduce the consumption of oxygenated gas and consequently the expenditure of electrical energy for obtaining it and to reduce the consumption of hydrocarbons that react with the oxygenated gas.

  at the stage of secondary steam-oxygen conversion.

  The total reduction in energy consumption compared with the method of EP, A, GJ 106076 is 0.6 gJ tNH3. In accordance with the present invention, it is rational to use, as coolant, steam. water and / or carbon dioxide which is explained by the economic utility as well as by the fact that the carbon dioxide promotes the displacement of the thermodyamic equilibrium of the secondary conversion on the side of the formation of the carbon monoxide and improves the quality of the intended product for the production of alcohols

whose index is the ratio H2 / C0.

  In order to stabilize the temperature regime during the primary conversion and thereby to ensure the stability of the secondary conversion, it is advantageous, according to the invention, before mixing with the coolant, to take the oxygenated gas at a rate of 0, 1-2.0% by volume of its total amount and mix with the target product, before sending it to the primary conversion. In order to reduce the consumption of the oxygenated gas for the secondary conversion and to increase the efficiency of the catalyst, it is rational, according to the invention, to carry out the catalytic conversion of the prior vapor

  at an initial temperature of 540-570C.

  Other objects and advantages of the present invention will be better understood on subsequent reading

  of the description of the process for obtaining the hydrogenated gas

  which will follow and practical examples of non-limiting embodiments of this method. The process for obtaining hydrogenated gas according to the invention is based on a conversion method

  catalytic vapor-oxygen in two steps.

  The process according to the invention is intended for the use, as initial hydrocarbon feedstock, of methane, ethane, propane and their mixtures: the higher hydrocarbons which, under normal conditions, are in the gaseous state or liquid state. According to the process of the invention, the hydrocarbonaceous material, preferably compressed at a pressure of 100 bar and at a temperature of 400.degree. C., is mixed with water vapor in an amount ensuring a ratio H.sub.2 O equal to at 2.5-4. the temperature of the water vapor is preferably C 380 C. The vapor-gas mixture is obtained

  after brewing is at a temperature of about 390 C.

  According to the present invention, the vapor-gas mixture obtained is brought to a temperature between 480 and 570 C, preferably between 540 and 570 C and is subjected to a catalytic conversion of prior vapor using, for example, a catalyst

nickel or nickel-cobalt.

  The pre-steam conversion process is adiabatic and is carried out on behalf of the physical heat of the vapor-gas mixture with hydrogen being obtained and with a simultaneous cooling of the vapor-gas mixture at a temperature of 440 to 570 C,

preferably between 470 and 480 C.

  The heating of the initial steam-gas mixture to a temperature, preferably between 540 and 570 C is explained by the fact that at a temperature below 540 C, under the conditions of the adiabatic process, it becomes necessary to turn up the volume

catalyst.

  Introduction to the pre-steam conversion of a steam gas mixture having a temperature greater than 570 C causes a cracking process of the higher hydrocarbons, leading to the release of

carbon black.

  The use, for the prior conversion of the vapor-gas mixture, of a temperature of 540-570 ° C makes it possible to increase the degree of interaction and thus to reduce the temperature of the converted gas after carrying out the prior conversion, which subsequently, when carrying out the primary catalytic conversion, will reduce the composition of the oxygenated gas. A higher conversion rate of the initial hydrocarbon feedstock makes it possible to direct the product to a high hydrogen content towards the following primary catalytic conversion, which increases the efficiency of the catalyst and allows

reduce its volume.

  After the pre-conversion, the partially converted gas at a temperature of 440-510 C undergoes a primary vapor catalytic conversion, increasing its temperature to 650-850 C. The steam conversion, in this case, is carried out according to an endothermic reaction with use of a conventional catalyst such as a nickel catalyst. The reaction gas at a temperature of 650-850 C undergoes a catalytic conversion of secondary vapor which is carried out in the presence of oxygenated gas. The oxygenated gas admitted to the secondary conversion is at a temperature which does not exceed 900 C. According to the present invention, the oxygenated gas, before heating to the indicated temperature, is mixed with the coolant at a heat transfer volume / oxygen ratio which is equal to

0.5 - 30.0.

  The upper limit (30.0) of the stated volume ratio is determined by the process for obtaining the affected product used in the production of ammonia

  when using air as an oxygen gas.

  In this case, the product concerned is obtained at a ratio

stoichiometric H2 / N = 3.

  The lower limit (0.5) of the indicated ratio is determined by the safe conditions of realization of the technological process where the discontinuity is excluded.

possible oxygen.

  The oxygenated gas contains, as an inert heat carrier, for example, steam,

  carbon dioxide, nitrogen or argon.

  According to the present invention, it is preferable to use, as coolant,

  water vapor and / or carbon dioxide.

  The use of water vapor makes it possible to reduce the energy consumption for the compression of the inert coolant since, in this case, heat is used at low temperature and the introduction of the coolant is carried out by saturation. oxygenated gas. The use of water vapor as coolant makes it possible to use, in the process, oxygen heated to 900 ° C, while in the absence of a coolant due to a high temperature in the zone of Oxygen interaction with the gas, after primary conversion, the process is practically unachievable. The use of carbon dioxide makes it possible, in the case of obtaining a hydrogenated gas for the production of methanol or higher alcohols, to improve the H2 / CO ratio in the target product which is

  the important index of the quality of the product concerned.

  According to an alternative embodiment of the invention, before mixing with the mentioned heat transfer medium, oxygenated gas (oxygen or air) is taken at a rate of 0.1 to 2.0% by volume of its total quantity and mixed with the target product resulting from the secondary catalytic conversion of the reaction gas at a temperature of 950-1050 C. Most of the oxygenated gas is directed, after mixing with the coolant, to the secondary catalytic conversion as

been indicated above.

  The oxygenated gas mixed with the product concerned is admitted to the primary conversion for the realization of the steam conversion on behalf of the heat of the

product concerned.

  The temperature of the product under consideration for the intake of oxygenated gas in the product concerned is kept constant at 20-30 C beyond that reached after the secondary conversion. The product referred to the indicated temperature is admitted to the primary conversion where it is cooled to a temperature of 500 to 700 C,

preferably from 500 to 6000 C.

  As a result of the admission of the oxygenated gas into the target product resulting from the secondary conversion, it is possible to stabilize the temperature regime for the realization of the conversion at the first stage and, thereby, to ensure the stability of the work and the secondary conversion process, the composition of the gas after the primary conversion then being stabilized at

  the input of the secondary conversion.

  The process according to the invention for obtaining a hydrogenated gas makes it possible to obtain an azohydrogenated mixture as a mixture that is directly suitable for the synthesis of ammonia, as well as an azohydrogenated mixture of a stoichiometric composition used in the synthesis. ammonia in the case of temperature-based separation or release of excess nitrogen at the most economically advantageous technological regime. The process according to the invention also makes it possible to obtain a synthesis gas for the production of alcohols of large composition with an optimum H2 / CO ratio. The method according to the invention makes it possible to reduce the expenses

  of energy for the production of ammonia from 0.5 to 5.0%.

  Below will be given concrete examples

  embodiment of the method according to the invention.

EXAMPLE 1

  Natural gas having the following composition: 92.8% CH4, 3.9% C2H6, 1.1% C3H8, 0.5% C4H10, 1.6% N2, 0.1% CO2, is mixed at a pressure of 4.3 MPa with steam at a steam / carbon ratio of 3: 1 and then heated to a temperature of 570 C and admitted to the stage of primary steam conversion o the conversion of methane at the primary conversion stage is 32% at a CH 4 content of 26.6% dry converted gas at a temperature of 713 ° C. The converted gas after the primary vapor conversion stage is admitted to the secondary vapor-oxygen conversion stage. It also admits the steam-air mixture

  brought to 900 C at the ratio H20 / 02 = 0.5.

  The temperature of the product aimed at the exit of the secondary vaporoxygen conversion is 970 C, the methane content is 0.53%, the H2 + CO ratio is N2 of 2.08. The target product after the secondary conversion stage is admitted to the primary conversion stage where it is cooled to a temperature of 620 ° C, giving up its heat for the conversion of endothermic methane vapor that takes place at the indicated stage.

EXAMPLE 2

  A natural gas having the following composition: 92.8% CH4, 3.9% C2H6, 1.1% C3H8, 0.5% C4H10, 1.6% N2, 0.1% CO2, is mixed with steam at a pressure of 4.3 MPa and at a ratio of 3.5: 1, heated to a temperature of 570 C and admitted to the primary steam conversion stage of at a temperature of 840 ° C, with a methane content of 9.0%, the conversion rate of methane at the primary conversion stage is 67%. The converted gas, after the primary steam conversion stage, is brought to the secondary vapor-oxygen conversion stage. The vapor-air mixture heated to 800 ° C. is introduced at the ratio H 2 O / O 2 equal to 30. The temperature of the product at the outlet

  the secondary steam-oxygen conversion is 940 C.

  The ratio (H 2 O + CO) / N 2 is 3.1. The affected product, after the secondary steam conversion stage, is directed to the primary vapor conversion stage where it is cooled to a temperature of 620 C, giving up its heat to the endothermic vapor conversion of the reactor.

  methane that takes place at the indicated stage.

EXAMPLE 3

  A mixture of propane and butane at a ratio of 2: 1, at a pressure of 8.0 MPa, is kneaded with water vapor at a ratio of H 0 / C equal to 3: 1 and at a temperature of 500 C is then admitted to the stage of primary steam conversion where it is discharged at a temperature of 826 C, the methane content being 17.8%. The converted gas, after the primary steam conversion stage, is brought to the secondary steam-oxygen conversion stage. The oxygen / carbon dioxide mixture is introduced at the CO 2 / O 2 ratio of 6: 1 and is heated to 540 ° C. However, insignificant variations in the parameters of the technological currents lead to temperature fluctuations of 970 to 950 ° C. secondary conversion, the value of the residual methane being from 0.49 to 0.70%. With fluctuations in the target product temperature from 970 to 950 C after the secondary conversion, the residual methane content and the temperature values after the conversion of the primary vapor change: the CH4 content varies between

  17.8 and 19.7% and the temperature varies between 826 and 810 C.

  In the case of admitting the 0.1 to 2.0% by volume oxygenated mixture into the product concerned, after the secondary vapor conversion stage, the temperature before the primary conversion, and therefore the composition after the primary conversion,

are stabilized.

  The average temperature of the product concerned, before introduction into it, of the very small portion of oxygenated gas, is 960 C, that after introduction is 970 C. The residual methane content of the product concerned is 0 , 5% by volume. The affected product, after the secondary steam conversion stage, is sent to the primary steam conversion stage where it is cooled to 570 C, giving up its heat to the steam conversion

  endothermic methane that takes place at this stage.

EXAMPLE 4

  Natural gas having the following composition: 92.8% CH4, 3.9% C2H6, 1.1% C3H8, 0.5% C4H10, 1.6% N2, 0.1% CO2, at a pressure of 4.3 MPa, is mixed with steam at the steam / carbon ratio of 3: 1, then is warmed to a temperature of 570 C and is admitted to the adiabatic precarversion stage o occurs the conversion of steam on behalf of the physical heat of the vapor-gas malfunction and the cooling of the reaction mixture at 490 C. The composition of the gas after the pre-conversion is as follows: 0.07% CO, 2.50% CO 2 , 9.32% H2, 22.21% CH4, 65.00% H2O and 0.90%

of N2.

  The gas after the pre-conversion is sent to the primary steam conversion stage where it is discharged at a temperature of 754 C and a CH4 content of the dry converted gas of 21.20%. The converted gas, after the primary steam conversion stage, is admitted to the secondary vapor-oxygen conversion stage. It also admits the vapor-air mixture which is heated to 500 C with the H20 / 02 ratio of 0.5. the target product temperature at the outlet of the secondary steam-oxygen conversion is 970 ° C., the methane content is 0.5% and the ratio (H2 + CO) / N2 is 2.08. The desired product after the secondary conversion stage is sent to the primary vapor conversion stage where the gas is cooled to a temperature of 540 C, giving up its heat to the

  endothermic vapor conversion of methane.

EXAMPLE 5

  The starting steam-hydrocarbon mixture, described in Example 4, is heated and is admitted to the adiabatic preconversion stage where a vapor conversion process occurs on behalf of the physical heat of the vapor-gas mixture with cooling. of the reaction mixture at 470 C. The heating temperature of the steam-air mixture at an H 2 O / O 2 ratio of 0.5 is 60000 C. The temperature of the product concerned, after cooling to the primary conversion stage, is

  5400C, the ratio (H2C0) / N2 is 2.08.

EXAMPLE 6

  A natural gas of the following composition: 92.8% CH4, 3.9% C2H6, 1.1% C3H8, 0.5% C4H10, 1.6% N2, 0.1% CO, at a pressure of 4.3 MPa, is mixed with steam at the steam / carbon ratio of 4: 1, brought to 570 C and is admitted to the adiabatic preconditioning stage where the steam conversion process is carried out on behalf of the physical heat of the steam-gas mixture

  with a cooling of the reaction mixture at 485 C.

  The composition of the gas after the conversion is then as follows: 0.05% CO, 2.35% CO 2, 8.86% H 2, 17.55% CH 4, 70.5% H 2 O and 0.69%. % of N2. The gas, after preconversion, is directed to the stage of primary vapor conversion where it leaves at a temperature of 760 C.

  and a CH4 content of the converted dry gas is 15.38%.

  The converted gas, after the primary conversion stage, is

  admitted to the secondary steam-oxygen conversion stage.

  The vapor-oxygen-nitrogen mixture is brought to 750 C at the ratio (N 2 + H 2 O) / O 2 of 5.47, with H 2 O / O 0.59. In the case of the presence of pressurized nitrogen, it is used as an additive to technological air. The target product temperature at the exit of the steam-oxygenate conversion is 940 C, the methane content

  is 0.6%, the ratio (H2 + CO / N2 is 2.08.

  The affected product is allowed, after the secondary conversion stage at the stage of primary vapor conversion, where it is cooled to a temperature of 540 C, giving up its heat to the endothermic vapor conversion of methane.

Claims (4)

CLAIMS CATIONS   1. Process for obtaining a hydrogenated gas, of the type comprising the mixture of the hydrocarbon raw material with steam, the catalytic conversion of prior vapor of the mixture obtained, the catalytic conversion of primary steam and the catalytic conversion subsequent secondary oxygen-vapor with admission of oxygenated gas to it at a temperature not exceeding 900 ° C and obtaining the intended product, the admission of the product referred to the primary conversion for the purpose of carrying out the process of conversion of vapor on behalf of the heat of the product concerned, characterized in that the oxygenated gas admitted to the secondary conversion, before heating, is mixed with a coolant at a ratio of heat transfer volume / oxygen equal to 0.5-30.0.   2. Method according to claim 1, characterized in that, as coolant,   water vapor and / or carbon dioxide.   3. Process according to any one of   claims 1 or 2, characterized in that before the   mixture with the coolant, the oxygenated gas is removed at a rate of 0.1 to 2.0% by volume of its total quantity and is mixed with the product concerned before directing it to the primary conversion.   4. Process according to any one of   preceding claims, characterized in that the   catalytic conversion of pre-steam is carried out at   a starting temperature of between 540 and 570 C.