RU2052376C1 - Method for production of synthesis gas and hydrogen for syntthesis of oxoalcohols - Google Patents

Abstract

FIELD: production of sysnthesis gas and hydrogen. SUBSTANCE: method for production of synthesis gas and hydrogen for synthesis of oxoalcohols consists in mixing of natural gas and/or light hydrocarbons with steam and carbon dioxide up to steam-to-carbon dioxide volumetric ratio of 0.1-0.2. Produced mixture is heated up to 300-400 C and mixed with oxygen containing a part of carbon dioxide. This mixture is supplied to layer of nickel catalyst for conversion. Temperature of converted gas is maintained at the outlet at the level of 800-950 C. Gas is cooled and cleaned by absorption until carbon dioxide content in gas amounts to 1-2 vol.%. Then, gas is divided into two flows. One flow is subjected to final cleaning from carbon dioxide with regenerated chemisorbent until its residual content is below 0.1 vol.% and directed to the stage of oxosynthesis. The other flow is subjected to final conversion of carbon monoxide with steam, and obtained flow of hydrogen is cleaned from carbon dioxide, first, partially by regenerated solution of chemisorbent down to carbon dioxide content of 1-2 vol.%, then from carbon dioxide and other impurities on molecular sieves and supplied to consumer. EFFECT: higher efficiency. 5 cl, 1 dwg, 1 tbl

Description

 The invention relates to a method for producing a mixture of synthesis gas and hydrogen, intended for organic syntheses, in particular for the synthesis of oxoalcohols.

 For the synthesis of oxo alcohols, a mixture of hydrogen and carbon monoxide is used, as well as hydrogen. The synthesis of oxo alcohols proceeds in two mutually independent phases. In the first phase, a reaction occurs between an unsaturated hydrocarbon, as well as carbon monoxide and hydrogen to form an aldehyde. In the second phase, the resulting aldehyde is hydrogenated to produce alcohol by reaction with hydrogen.

A prerequisite for high performance synthesis of oxo alcohols is the preparation of a mixture of hydrogen and carbon monoxide with a stable and constant composition. The ratio of H ₂ / CO in the gas for the synthesis of oxo alcohols should be maintained at a constant level, for example, about 1.07. The carbon dioxide content in said gas must not exceed 0.1 vol. Favorable conditions for the progress of the aldehyde hydrogenation reaction to obtain alcohol are created by the use of high frequency hydrogen and practically free of carbon monoxide and dioxide.

Synthesis gas (H ₂ + CO) is obtained mainly from hydrocarbons such as natural gas, light fractions of oil, oil and coal using the following processes: reforming of natural gas or light hydrocarbons; heavy oil conversion; gasification of coal and coke.

 Most often, steam reforming or autothermal steam-oxygen reforming of natural gas, or a combination of both processes, is used to produce synthesis gas.

The crude synthesis gas from steam or oxygen reforming, along with CO and H ₂ also contains impurities such as CO ₂ , H ₂ O, CH ₄ , Ar and N ₂ . Such gas is subject to purification, mainly from CO ₂ .

There are a number of factors that influence the choice of the process for producing and purifying synthesis gas. The most important of them are: the required ratio of H ₂ / WITH; required product purity; performance; availability of raw materials, including carbon monoxide and carbon dioxide; the possibility of using the resulting excess water vapor.

In the known process of methane reforming with water vapor, H ₂ and CO are produced by the reaction of CH ₄ + H ₂ O under conditions of elevated temperature and in the presence of a nickel catalyst placed in reaction tubes located in a stackable furnace providing heating for the implementation of the endothermic reforming reaction. Sweetened natural gas is mixed with steam and preheated to a temperature of about 500 ^{° C} before it is introduced into the tube. In pipes, the reaction occurs CH ₄ + H ₂ O - >> CO + 3H ₂ . The reaction of the conversion of part of CO with H ₂ O to CO ₂ and H ₂ also proceeds. The gas exits the tubes at a temperature ^of 850 900 C. The process may be carried out at elevated pressure, however due to the high temperature catalytic pipe pressure can not substantially exceed the values 1.05 of 2.0 MPa. To avoid the formation of soot, as well as to realize a high degree of methane conversion, a significant excess of water vapor is used, exceeding the stoichiometric need. This also causes a higher conversion of CO to CO ₂ , which leads to an increase in the H ₂ / CO ratio in the resulting gas. To reduce this ratio, part of the water vapor can be replaced with carbon dioxide, which should be returned to the reforming unit from the unit for gas purification from CO ₂ after it is compressed to the pressure of the reforming process.

Steam reforming is carried out under normal conditions with a minimum ratio of H ₂ O / C 2 and with the full return of CO ₂ . Under such conditions, it is possible to achieve a minimum H ₂ / CO 3.0 ratio in the synthesis gas. Reducing this ratio is possible in said process in the processing part of the synthesis gas in hydrogen and returning the total amount of CO obtained in the purification unit _2.

 The steam reforming process requires a high-volume plant to recover heat from the flue gases of a heated furnace, as well as heat from a cooled raw synthesis gas. It turns out excess water vapor, part of which can be used for other industries.

A more advantageous known method for producing synthesis gas of oxoalcohols is vapor-oxygen, i.e. autothermal reforming of gas (methane). In such a process, the reactions of incomplete combustion and semi-combustion of methane with oxygen are carried out along with the reforming reaction. First, part of the natural gas (light hydrocarbons) in the space above the catalyst is burned with the release of a significant amount of heat and a significant increase in temperature when using oxygen contained in the reaction mixture. Then, endothermic reactions of reforming the remaining methane with Н ₂ О and СО ₂ proceed to the release of CO and Н ₂ in the nickel catalyst layer, as well as partially the conversion of CO and Н ₂ О. Due to the fact that both processes take place in the same adiabatic reactor, the endothermic reactions is the result of exothermic hemisphere.

 The reformer (half-burning reactor) is a lined tank, in the upper part of which there is a burner, and in the lower layer of a nickel catalyst. The space between the burner and the catalyst bed is a combustion chamber. The burner provides intensive mixing of methane with oxygen and good combustion conditions in the space above the catalyst. The catalyst allows reforming reactions of partially oxidized gas.

The use of oxygen reduces the ratio of H ₂ O / C in the gas before reforming to a value of k1.5 vol. and excludes soot emissions. To ensure the preparation of respectively low ratio of H ₂ / CO and a high degree of methane conversion oxygen is fed in such quantities that the temperature of the gas exiting the reactor is 950-1000 ° ^C. The higher temperature creates favorable thermodynamic conditions for obtaining high concentrations of CO in the oxide with H ₂ , CO ₂ and H ₂ O. Compared with the methane reforming process with water vapor, under such conditions it is possible to obtain a minimum H ₂ / CO ratio of not 3.0, but 1.65. In this process, a smaller amount of excess water vapor and the absence of flue gases lead to the presence of a smaller amount of waste heat during the process. The use of a lined tank as a reactor also provides the possibility of conducting the process at a pressure higher than during the reforming process with water vapor. The disadvantage of this process is the need for oxygen. However, despite this, in connection with the use of simpler equipment, as well as with the possibility of producing synthesis gas with a correspondingly low H ₂ / CO ratio, this process is often used in practice.

In the synthesis of oxoalcohols, a gas with a H ₂ / CO ratio lower than what can be obtained in the reforming process is required provided that the CO _{2 is} completely returned from the regeneration of the solution used to wash the crude synthesis gas. Hydrogen is also required in the above synthesis. If there are no other sources of hydrogen to produce it, part of the synthesis gas is processed, which consists in dividing the synthesis gas stream into a hydrogen stream and a stream containing the remaining components of the synthesis gas. For this purpose, various known methods are used, in particular membrane separation or absorption of impurities from a gas, namely, CO ₂ , CH ₄ CO on molecular sieves operating on a variable pressure system (PSA). In the case of using (PSA), the regenerated gases are also sent back to the crude synthesis gas stream in front of the CO "purification unit to obtain the required H ₂ / CO ratio in the synthesis gas.

If the method of the autothermal reforming process, i.e. the process of oxidizing conversion, light hydrocarbons, mainly natural gas, so that after the burner, namely in the space above the catalyst, the mixture does not ignite spontaneously, then by processing the gas after this process it is possible to obtain directly synthesis gas with the ratio N ₂ / СО, which is required in the course of organic syntheses, in particular, a gas with a Н ₂ / СО ratio equal to or even slightly less than that required in the synthesis of oxoalcohols, and also, if necessary, obtain from this for hydrogen, in particular for the synthesis of oxo alcohols. This is provided by the method according to the invention.

According to the invention, synthesis gas and the required amount of hydrogen are obtained from natural gas and / or light hydrocarbons according to the following method. The feed is mixed with oxygen, carbon dioxide and water vapor and undergoes a process of autothermal, catalytic reforming. The resulting product is subjected to preliminary purification from CO ₂ to a content of 1-2 vol. CO ₂ by absorption in a partially regenerated chemisorbent solution. All pre-purified gas is divided into two streams.

The first stream is subjected to further purification from CO ₂ to a content below 0.1 vol. CO ₂ by absorption in a fully regenerated solution of chemisorbent and then, after a possible adjustment of the ratio of H ₂ / CO using a stream of hydrogen is sent in the form of synthesis gas for organic synthesis.

The second stream is subjected to catalytic conversion of CO with water vapor, purified from CO ₂ to a content of 1-2 vol. CO ₂ by absorption in a partially regenerated chemisorbent solution and sent to the installation of molecular sieves operating on the PSA system. At a molecular sieve plant, the gas is cleaned of residues of CO ₂ and other impurities (CO, CH ₄ and N ₂ ) to the desired concentration level. Pure hydrogen after the installation of molecular sieves is sent to organic synthesis. Solutions of chemisorbent saturated with CO _{2 are} regenerated, and the extracted CO _{2 is} sent back to reforming.

The stream of natural gas and / or light hydrocarbons directed to reforming is mixed with the stream of CO ₂ or part thereof returned to the process, as well as with the stream of water vapor supplied in an amount providing a H ₂ O / C ratio of 0.1-0.2. The mixture was heated to 300-400 ^C. The second directed into the reformer stream is oxygen or oxygen mixed with a portion recycled to the CO ₂ process.

Both flows are mixed, and this mixture at a temperature below its spontaneous combustion temperature is fed into the reforming catalyst bed to carry out an exothermic reaction of the combustion of part of the hydrocarbon with oxygen, an endothermic reaction of the conversion of hydrocarbon residues with CO ₂ and H ₂ O, as well as the accompanying exothermic reaction of CO conversion and H ₂ O to H ₂ and CO ₂ . Oxygen is supplied in such an amount that the reaction mixture leaving the reactor reforming had a temperature of ^about 800-950 C and therefore a low content of CH _4.

Reforming process can be carried out with a ratio H ₂ O / C in the feedstock 0.1-0.2 without fear of separation of soot with the proviso that the reaction mixture temperature will not exceed the self-ignition temperature, and thus the process of mixing the hydrocarbon with oxygen, CO _2, and water vapor flows without ignition over the catalyst bed.

A low H ₂ O / C ratio makes it possible to achieve a correspondingly low H ₂ / CO ratio at lower temperatures of the autothermal reforming process. As a result, the consumption of raw materials is reduced, i.e. natural gas and / or light hydrocarbons, oxygen and water vapor, creates milder conditions for the operation of the catalyst and reactor and leads to the fact that the amount of utilized heat of the reaction gas is less and practically corresponds to the needs of reforming and purification of synthesis gas and hydrogen.

In order to prevent spontaneous combustion, it is important to thoroughly mix the flows in such a way that the oxygen concentration in the reaction mixture is equalized in almost every point. All amounts of CO ₂ returned from the regeneration process of the absorption solution can be introduced into the stream of natural gas and / or hydrocarbons, but to create more efficient mixing conditions, it is also possible to introduce part of the returned CO ₂ into the gas and mix the rest with oxygen and only then mix both flows .

Mixing a stream containing hydrocarbons with a stream of oxygen previously diluted with CO ₂ reduces the likelihood of local higher oxygen concentrations that can cause spontaneous combustion of the mixture at the outlet of the mixer. The distribution of the returned CO ₂ between the two streams is carried out in such a way that both streams at the mixer outlet have the most similar kinetic energies, since this circumstance is one of the conditions for good mixing of the streams. Mentioned separation depends on the design of the mixer.

 The conversion process is carried out at a pressure lower than the gas purification process, preferably at a pressure of 0.12-0.2 MPa. The gas purification process is carried out similarly to known processes under pressure equal to or greater than the pressure of organic synthesis, in particular the synthesis of oxoalcohols.

Purification of synthesis gas by the CO ₂ may be carried out using any hemisorbenta solution, but it is recommended to clean the gas from the CO ₂ gas ppomyvkoy hot potassium carbonate solution. The regeneration of the postabsorption solution should be carried out under a pressure slightly higher than the pressure of the autothermal reforming process in order to simplify the process of returning the required amount of CO ₂ to a stream containing hydrocarbons and, depending on circumstances, to an oxygen stream.

To reduce the energy intensity of the cleaning process, as well as to obtain additional amounts of CO ₂ to return to the conversion process, the hydrogen stream is removed from CO ₂ in two stages. First, a purification using a partially regenerated potassium carbonate solution is carried out previously similarly to the crude synthesis gas, and then from already small amounts of CO ₂ and impurities contained in the hydrogen stream on molecular sieves. The use of hydrogen purification with a small amount of impurities on molecular sieves using the PSA system allows one to achieve a high degree of purification, mainly from CO and CO ₂ , i.e. to a concentration below 10 ppm by volume, and also to provide a high yield of hydrogen contained in the gas before purification. The use of a partially regenerated potassium carbonate solution for the purification of two different gas streams allows the regeneration of both postabsorption solutions in one common regenerator. Part of such a solution is regenerated deeper with the consumption of additional heat for regeneration. Said solution is used for the final purification of synthesis gas from CO ₂ to a level below 0.1 vol. The regeneration of a chemisorbent solution is recommended to be carried out under a pressure slightly higher than the pressure of autothermal reforming.

It is effective to carry out the conversion process at a pressure slightly higher than atmospheric, and the process of gas purification from CO ₂ and a hydrogen stream at a pressure equal to or higher than that required in the synthesis of oxoalcohols. The use of low pressure in the half-burning process allows one to obtain very pure synthesis gas, i.e. with a low methane content, at relatively low temperatures. The use of pressure below the pressure of the regeneration of the potassium carbonate solution, namely 0.15-0.2 MPa, does not require additional compression of CO ₂ returned from the purification unit of the crude gas and hydrogen stream. The use of low pressure in the conversion process also creates more favorable conditions for the compression of oxygen and allows you to get the minimum consumption of energy raw materials, namely: natural gas, oxygen and water vapor. The process for producing synthesis gas according to the method according to the invention, i.e. when applying a low H ₂ O / C ratio, it is possible to obtain synthesis gas with a H ₂ / CO ratio slightly lower than that required for the synthesis of oxo alcohols, and then by directing a portion of the obtained hydrogen into the synthesis gas stream, the ratio required for this can be established synthesis.

 The drawing shows the installation for producing from natural gas (methane) synthesis gas and hydrogen for the synthesis of oxoalcohols.

Natural gas (methane) is supplied via line 1, after mixing with part of the returned CO ₂ is supplied via line 2, heated to a temperature of 400 ^{° C} in preheater 10 and then supplemented with steam via line 3 for the ratio H ₂ O / CH ₄ 0.1. Such a mixture through pipeline 4 is supplied to a mixer 5 located in the converter 6, operating at a pressure of 0.15 MPa. Oxygen mixed with the rest of the returning CO ₂ is also supplied to the mixer 5 through pipeline 7. A stream of carefully mixed raw materials is fed to a nickel catalyst layer, on which the exothermic reaction of methane oxidation, as well as the endothermic reforming reaction of unoxidized methane with carbon dioxide and water vapor, and the reaction of the conversion of carbon monoxide with water vapor to H ₂ and CO ₂ occur simultaneously. As a result of the above reactions set temperature of the reaction mixture at the outlet 830 ^{° C,} wherein the crude synthesis gas with a desired ratio of H ₂ / CO exits the reactor 6 through line 8. The gas is then cooled in steam boiler 9, feed preheater 10, and water heater feeding a steam boiler 1.1. The produced steam is used for the process, as well as for the regeneration of solutions that clean the gas from CO ₂ . The cooled gas is compressed in the compressor 12 to a pressure of 3.5 MPa and is subjected to a CO ₂ purification process in the absorber 13. In the lower part of the absorber using a partially regenerated potassium carbonate solution supplied to the middle part of the absorber through line 14, the crude gas is purified to a concentration of 1 -2 vol. The gas thus purified is divided into two streams. One, intended for the production of hydrogen, is discharged from the middle of the absorber through line 15. The second stream in the upper part of the absorber is purified to a final concentration of CO ₂ , i.e. below 0.1 vol. when using a regenerated and partially chilled solution of potassium carbonate, brought through the pipe 16 to the upper part of the absorber 13. The purified gas is discharged from the upper part of the absorber and after cooling in the refrigerator 17 is directed to the oxoalcohol plant through the pipe 18. The hydrogen stream leaving the absorber through the pipe 15 , after mixing with water vapor, is sent to the reactor 19 to carry out the conversion of carbon monoxide with water vapor into hydrogen. The resulting hydrogen stream through a pipe 20 is fed into the absorber 21, fed through a pipe 22 partially regenerated solution of potassium carbonate. Here the gas is purified from CO ₂ to a concentration of about 1.5 vol. Used postabsorption solutions through pipelines 23 and 24, after expanding to the regeneration pressure, are discharged to the regenerator 25, operating at a pressure of 0.16 MPa. The carbon dioxide released during the regeneration process exits the regenerator through the pipeline 26 and, after cooling and condensation of the water vapor in the refrigerator 27 and separation in the separator 28, partially returns via the pipeline 2 to the converter. From the middle part of the regenerator, part of the partially regenerated potassium carbonate solution is discharged through the pipe 29 to the pump 30. The pump 30 pumps the partially regenerated solution to the middle part of the absorber 13 through the pipe 14 and to the absorber 21 through the pipe 22. The rest of the solution flows into the lower part of the regenerator 25, where it is carefully regenerated using heat and water vapor. A stream of water vapor from the middle of the regenerator enters the upper part of the regenerator to regenerate postabsorption solutions to the extent that the gas is purified from CO ₂ to a concentration of about 1.5 vol.

The completely regenerated solution from the lower part of the regenerator by means of a pump 31 and with partial cooling is sent via line 16 to the upper part of the absorber 13. The hydrogen stream purified in the absorber 21 also contains insignificant amounts of impurities such as CO, CH ₄ , Ar and N ₂ , after cooling, it is fed to the refrigerator 32 for final purification on molecular sieves in the PSA 33 assembly. Hydrogen, purified from CO and CO ₂ to a concentration not exceeding 10 ppm by volume, is discharged through a pipe 34 to the oxoalcohol plant. A small portion of hydrogen via line 35 can be fed into the synthesis gas stream (line 18) to accurately establish the H ₂ / CO ratio required in the synthesis of oxo alcohols. Molecular sieves are regenerated by a portion of purified hydrogen, and post-regeneration gases are discharged through line 36 for use, for example, for heating.

 The table presents the results of a comparison of the method of producing synthesis gas and hydrogen for the synthesis of oxoalcohols according to the invention and by a known method.

The table shows that the method according to the invention enables the production of synthesis gas for the synthesis of oxo alcohols converter under less stringent operating conditions (the gas temperature at the outlet 830 ^{° C)} and at low flow rates of natural gas and oxygen. The total energy consumption for producing synthesis gas and hydrogen in terms of 1000 Nm ³ СО + Н _{2 is} less by about 10%

Claims (5)

1. METHOD FOR PRODUCING SYNTHESIS-GAS AND HYDROGEN FOR SYNTHESIS OF OXO-ALCOHOLS, including mixing natural gas and / or light hydrocarbons with water vapor and carbon dioxide, heating the mixture with heat of converted gas, mixing it with oxygen, conversion in a nickel catalyst layer at elevated temperature, purification of the converted gas from carbon dioxide by absorption by a chemisorbent under a pressure equal to or lower than the pressure of the synthesis stage of oxo alcohols, regeneration of chemisorbent and return of chemisorbent released during regeneration and carbon dioxide in the process, characterized in that the mixture of gases with steam is carried out until the volume ratio steam: carbon of 0.1 - 0.2, heating the mixture is carried out up to 300 - 400 ^o C and then it is mixed with oxygen containing part dioxide carbon obtained in the regeneration stage, and this mixture at a temperature below its autoignition temperature is fed into the bed of the nickel catalyst for the conversion, the converted gas outlet temperature is maintained at 800 - 950 ^o C, after which the gas is cooled and cleaned of carbon dioxide are part but the regenerated chemisorbent to its content in the gas 1 - 2 vol.%, then the gas is divided into two streams, one of which is subjected to purification of carbon dioxide with the regenerated chemosorbent to its residual content below 0.1 vol.% and sent to the stage of oxosynthesis, and the second stream is subjected to carbon monoxide conversion with water vapor and the resulting hydrogen stream is purified from carbon dioxide, first with a partially regenerated chemisorbent solution to a carbon dioxide content of 1 - 2 vol.%, then from carbon dioxide and other molecular impurities sieves and are given to the consumer, and the saturated chemisorbent solution is regenerated and the released carbon dioxide is returned to the process.  2. The method according to claim 1, characterized in that the conversion of natural gas and / or light hydrocarbons is carried out under a pressure of 0.15 - 0.20 MPa.  3. The method according to PP. 1 and 2, characterized in that the potassium carbonate solution is used as a chemisorbent.  4. The method according to claims 1 to 3, characterized in that the hydrogen stream is subjected to purification on molecular sieves to a residual carbon dioxide content of not more than 10 ppm by volume.  5. The method according to PP. 1 to 4, characterized in that the solutions of the chemisorbent potassium carbonate after absorption of carbon dioxide from two purified gas streams regenerate together.

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