RU2202531C1 - Method of production of methanol - Google Patents

Abstract

FIELD: production of methanol from natural gas and hydrocarbon-containing tail gases of chemical and petrochemical processes. SUBSTANCE: proposed method includes stages of production of synthesis gas, catalytic conversion of obtained synthesis gas into methanol in several reaction at high temperatures and pressures , cooling of reaction products, separation of methanol and utilization of tail gases. Synthesis gas containing more than 20 vol-% of nitrogen at molar ratio of hydrogen to carbon oxide ranging from 1.2 : 1 to 4 : 1 is fed to inlet zones of reactors. Synthesis gas containing additionally oxygen in the amount not exceeding 0.9 vol-% is supplied periodically. As a rule, process is performed at temperature ranging from 160 to 300 C, pressure of 4.0 to 10.0 Mpa and volumetric flow rates of 500-10000 h^-1. As a rule, starting synthesis gas is divided into two flows: on flow is enriched with hydrogen in diaphragm-type mass- exchange unit and is fed to first catalytic reactor and second flow which is hydrogen deficient flow is mixed with gas flow escaping from last catalytic reactor after separation of methanol; mixture is fed to power plant as gas fuel. Proposed method ensures saving of energy at high productivity. EFFECT: increased productivity; improved quality of target product. 3 cl, 2 dwg, 4 ex

Description

 The invention relates to technologies for the synthesis of methanol from synthesis gas obtained by the partial oxidation of natural gas with air, oxygen-enriched air or in streams of oxygen-containing gas with a significant nitrogen content.

 More specifically, the invention relates to the field of chemical-technological, energy-saving processes for the production of methanol from natural gas or "tail" hydrocarbon-containing gases from chemical, petrochemical, gas processing and metallurgical industries.

In traditional industrial methanol production technologies, usually at the first stage of the process, synthesis gas is produced by steam conversion of natural gas hydrocarbons. At this stage, the complete conversion of gaseous hydrocarbons into synthesis gas is not achieved, and therefore, their additional conversion is carried out at the next stage - vapor-oxygen conversion. For its implementation, pure oxygen is usually used, the production of which is associated with significant energy costs. To increase the hydrogen content in the syngas, a steam reforming reaction of carbon monoxide is carried out, and in order to reduce the carbon dioxide content, it additionally organizes the processes of chemisorption of CO ₂ , in particular, solutions of ethanolamine or potassium carbonates.

 The cost of the resulting synthesis gas containing small amounts of nitrogen is high enough so that the produced synthesis gas can be used with high profitability in addition to the production of methanol in the production of olefins, motor fuels, dimethyl ether. The latter circumstance is due to the fact that the steam reforming reaction of light hydrocarbons is highly endothermic and, like the steam-oxygen reforming reaction of light hydrocarbons, it is implemented in expensive equipment with significant energy and operating costs.

 Known technologies for the production of methanol from natural gas (US 5245110), which provide for the production of synthesis gas as a result of catalytic oxidation of natural gas by air or oxygen-enriched air. Reducing the cost of synthesis gas is achieved by reducing the cost of producing oxygen-enriched air compared with the expensive production of pure oxygen, using simpler and less expensive equipment, and reducing operating costs.

 In a second methanol production step, high nitrogen synthesis gas is converted to methanol in four or six reactors connected in series with an intermediate output of methanol formed in the reactors after each catalytic reactor. The tail gases of methanol production have a rather high calorific value, which allows them to be used as fuel for gas turbines. Nitrogen in the system of catalytic reactors does not recycle and is discharged into the atmosphere with the exhaust gases of a gas turbine.

 Closest to the claimed method for the production of methanol, selected as a prototype, is the method described in patent RU 2152378. In the prototype method, synthesis gas with a high nitrogen content is converted in three series-connected catalytic reactors with an intermediate release of methanol formed in the reactors after each catalytic the reactor. Due to the organization of the thermal conditions of operation of each catalytic reactor, a high overall conversion of synthesis gas is achieved with high quality of the target product.

 The disadvantages of the known methods for the production of methanol based on synthesis gas with a significant nitrogen content (more than 20%) are: low conversion of synthesis gas with a hydrogen content of synthesis gas of less than 15 vol.%, Low volumetric load on raw materials when contained in synthesis gas nitrogen more than 70 vol.%, significant catalyst deactivation during prolonged operation of the reactor.

 The above-mentioned disadvantages of the technologies considered complicate their direct use in the organization of small-tonnage methanol production in gas fields and medium-tonnage methanol production in chemical, petrochemical and gas processing enterprises.

 In the present invention, the following tasks are set: achieving a high productivity of the synthesis gas-based methanol production process with a simultaneous high degree of utilization of the feedstock, reducing the degree of catalyst deactivation during the long-term operation of an industrial plant, and obtaining the high-quality methanol target product.

 The objectives are achieved by a method for producing methanol, including a stage for producing synthesis gas, a stage for regulating the oxygen content in it, a stage for catalytic conversion of synthesis gas to methanol in several reactors, including heating and conversion of synthesis gas, cooling of reaction products and methanol evolution, utilization of tail gases, in which synthesis gas containing more than 20 vol.% nitrogen at a molar ratio of hydrogen and carbon monoxide from 1.2: 1 to 4: 1 at a higher GOVERNMENTAL temperatures and pressures.

The methanol synthesis process is preferably carried out in the temperature range 160-300 ^o C, pressure 4.0-10.0 MPa, volumetric flow rates of 500-10000 hour ^-1 .

 As the catalyst activity decreases, synthesis gas is periodically fed to the reactors, additionally containing oxygen in an amount not exceeding 0.9% vol.

 In order to reduce energy consumption, the initial synthesis gas can be divided into two streams, one of which is enriched with hydrogen in a membrane-type mass transfer unit and fed to the first catalytic reactor, and the second stream, depleted in hydrogen, is mixed with the gas stream leaving, after methanol evolution, the last a catalytic reactor, and the mixture is supplied to the power plant as gas fuel.

 In FIG. 1 illustrates the essence of the invention, which involves the use of a plant consisting of series-connected reactors oriented, firstly, to regulate the oxygen content in the synthesis gas, and secondly, to synthesize methanol from synthesis gas with an intermediate methanol outlet after each catalytic the reactor.

 The synthesis gas obtained in energy machines as a result of the reaction of homogeneous partial oxidation of natural gas contains 1.2-1.5 vol.% Oxygen. The latter has a concentration higher than the permissible concentration in the input streams of methanol synthesis reactors. Its decrease to values of 0-0.9 vol. % is achieved in an oxygen reactor 1, in which oxygen is oxidized by carbon monoxide to carbon dioxide in synthesis gas pre-heated to a predetermined temperature in a heat exchanger 5. Methanol is produced in catalytic reactors 2, 3, 4 loaded with a promoted copper-zinc catalyst, each of which has an input zone 7 and the main zone of the catalytic reaction 8. Zones 8 are connected to heat exchangers-condensers 9, 12, 15, and the latter to separators 10, 13, 16. Before entering the synthesizer -gaz passes through the compressor and enters the heat exchanger 5.

 Figure 2 schematically shows an energy-technological installation for the production of methanol in accordance with paragraph 4 of the claims. The installation further comprises a membrane element 17, a steam turbine 20, a furnace for heating gas-vapor streams 19, a gas turbine 18.

 The energy-chemical method for producing methanol is implemented on the installation shown in figure 1, 2, as follows.

The feedstock is synthesis gas (obtained by partial oxidation of natural gas in internal combustion engines, gas turbines or catalytic reactors) is supplied with a space velocity of 500-10000 h ^-1 in compressor 5, where it is compressed to a pressure of, for example, 5.0-7, 0 MPa. Then it is sent to the reactor 1, in which the catalytic process of oxidizing part of the carbon monoxide of the synthesis gas by the residual oxygen of the exhaust gases of the internal combustion engine is carried out. Next, the synthesis gas with a given oxygen concentration is fed into the heat exchanger 6, where it is heated by the product flows of the reactor 2 to a temperature close to the temperature at which the methanol production reaction begins. After the heat exchanger 6, the synthesis gas is sent to the reactor 2, in the inlet zone 7 of which it is heated to the reaction temperature. Then, synthesis gas passes through zone 8, in which the main conversion of synthesis gas to methanol takes place. In zone 7, the initial reactants are heated by the coolant boiling in the jacket of the catalytic reactor, and in zone 8 due to heat release due to chemical reactions. From the reactor 1, a gas stream passes through a heat exchanger 6, where it heats the feedstock to a temperature close to the temperature at which the reaction began. Next, the gas stream through the refrigerator-condenser 9 is sent to the separator 10, where methanol is condensed, and non-condensing gases are sent to the heat exchanger 11 and then to the inlet zone 7 of the reactor 3.

 The operating conditions of the reactors 3, 4 are similar to those of the reactor 1. From the reactor 4, the product gas stream is fed through the refrigerator-condenser 15 to the separator 16, where methanol is condensed, and non-condensable gases are fed to the tail gas recovery unit (shown in Fig. 2 ) The system of gas transport communications of the installation is organized in such a way that periodically synthesis gas with a higher oxygen concentration can be supplied to each of the reactors 2, 3, 4.

 A variant of the methods corresponding to claim 4 is as follows.

 Raw materials - synthesis gas with a high nitrogen content exceeding 20 vol.%, Is fed to the compressor, the permeate stream from the membrane apparatus 17 enters the first stage suction line. The smaller part of the synthesis gas stream from compressor 5 enters the membrane apparatus 17, the gas stream is divided into two streams. The first - the permeate stream is enriched with hydrogen, the second - the retentate stream is depleted in hydrogen and enriched in nitrogen.

 The hydrogen-rich feed stream, compressed in compressor 5, passes through three series-connected reactors 2, 3, 4 with the formation of methanol in each of them. In separators 10, 13, 16, the methanol produced is separated from the gas stream, collected in a common tank and removed from the installation. The unreacted, non-condensing synthesis gas after the separator 16 is combined with the retant flow of the membrane element 17 and sent to the gas turbine 18 to generate electricity. The flue gases of the turbine 18 enter the furnace 19 to superheat the steam coming from the reactors 2, 3, 4. The superheated steam enters the steam turbine 20 to generate electricity.

 The above examples do not exhaust all possible implementations of the methanol production process.

 Therefore, the physicochemical meaning of the invention lies in the fact that the synthesis of methanol in the medium of synthesis gas and nitrogen (with a content of more than 20 vol.%) On promoted copper-zinc catalysts is carried out in the presence of oxygen, the concentration of which varies in a certain way over time, which allows you to adjust the degree of reduction of the surface of the catalyst, which ensures its increased operational characteristics.

 The invention is illustrated by the following specific examples of embodiments of the method.

Example 1. 1002 m ³ / h of methane and an oxidizing agent (air) are supplied to an energy machine (diesel). The excess ratio of the oxidizing agent is 0.34. 5400 m ³ / h of synthesis gas is formed, vol.%: H ₂ 27, CO 14, N ₂ 52, CO ₂ 2.5, O ₂ 0.9. Upon receipt of 1000 m ^{3 of} pure synthesis gas (without nitrogen), more than 0.35 MW of electricity is generated.

The generated synthesis gas (Fig. 2) is supplied to the oxygen purification catalytic reactor 1. In the feedstock, the oxygen content of 0.0% at the outlet of the reactor 1, the volumetric rate of the feedstock 2500 hours ^-1 . After the catalytic reactor 1, the feed at a pressure of 6.0 MPa and a temperature of 195 ^o C (the feed is heated by the product streams of the reactor 2) is supplied for 120 hours to the reactor 2, in which 495 kg / h of methanol is formed. The reaction mixture at the outlet of the reactor 2 is cooled in the heat exchanger 9 and from the separator 10 non-condensable gases enter the reactor 3, in which 195 kg / h of catalysis is formed. The product mixture at the outlet of the reactor 3 enters the heat exchanger 12 and the separator 13. Non-condensable gas components are fed after heating by the product flows of the reactor 4 into the reactor 4, in which 97 kg / h of methanol is formed. After cooling the gas mixture in the heat exchanger 15 is separated in the separator 16. "Tail" gases are sent to a gas turbine to generate electricity.

 After 300 hours of operation of the installation according to the above scheme, the operation of reactor 1 is organized in such a way that the oxygen content in the feedstock entering the second reactor is 0.2 vol.%. The duration of the installation with this composition of raw materials is 20 hours. Then, for 150 hours, the installation is re-operated in the absence of oxygen in the feed synthesis gas. Further, the oxygen supply cycle is repeated with a specified time interval.

 After every 720 hours of operation of the installation, the feedstock feed circuit switches to the reactor. For the first 720 hours of operation, the reactors operate in the sequence 1 -> 2 -> 3, the next 720 hours in the sequence 2 -> 3 -> 1, the next 720 hours in the sequence 3 -> 1 -> 2 and finally, after 720 hours - again according to scheme 1 -> 2 -> 3.

 The total average productivity of the installation according to the above scheme for methanol per year is 787 kg / hour, according to the process organization scheme according to the patent prototype - less than 747 kg / hour. The composition of methanol produced by the new technology: methanol - 98.8 wt.%, Water - 1.2 wt.%. The content of organic compounds (ethanol, propanol, formates, dimethyl ether) in trace amounts.

Example 2. In the energy machine due to the partial oxidation of 1005 m ³ / h of natural gas, 5400 m ³ / h of synthesis gas of the composition, vol.%: Hydrogen 37.2, carbon monoxide 18.5, carbon dioxide 2.5, methane 1 , 5, the rest is nitrogen.

The resulting synthesis gas with an oxygen content of 0.0 vol.% From the reactor 1 is fed after heating with the product gases of the reactor 2 to the reactor 2, in which at a pressure of 7.0 MPa, a temperature of 210 ^o C, a volumetric flow rate of 4000 h ^-1 the synthesis methanol. After cooling in the heat exchanger 9 and condensation in the separator 10 from raw methanol gas and water, non-condensable gas components are fed after pre-heating with the product flows of the reactor 3 to the reactor 3. The pressure in the reactor 3 is 7.0 MPa, the temperature is 220 ^o C. After cooling in the heat exchanger 12 and condensation in the raw methanol separator 13, non-condensable gas components are heated by the product gases of reactor 4 and enter reactor 4, in which methanol is synthesized at a pressure of 6.9 MPa and a temperature of 220 ^{° C.} At the outlet of the reactor 4 after cooling the product mixture in the heat exchanger 15 and condensation of the crude methanol in the separator 16, non-condensable gases are sent to the gas turbine to generate electricity.

 When carrying out the process in the absence of oxygen in the synthesis gas and without switching the input stream of the synthesis gas to reactors 3 and 4, the average productivity of each reactor for 1600 hours of its operation is: 2 - 749.4 kg / h, 3 - 336.5 kg / hour, 4 - 137.3 kg / hour. The total average productivity of the installation is 1223.2 kg / h.

 When operating modes of the unit operation are implemented (at an oxygen concentration of 0.4 vol% and a catalyst treatment time of 10 hours) with a periodic oxygen supply scheme, the average productivity of the first reactor in the three-reactor methanol synthesis unit is 810.0 kg / h, and the second 362.2 kg / hour, the third - 163.3 kg / hour. The total average productivity of the installation is 1335.5 kg / h. After 8000 hours of operation of the reactor unit, its total average productivity with a periodic oxygen supply scheme was 1175.24 kg / h (88%). The average productivity of reactor 2 is 696.6 kg / hr (86%), reactor 3 is 332.4 kg / hr (89%), and reactor 4 is 146.24 kg / hr (89.5%).

Example 3. In an energy machine, a partial oxidation of 1020 m ³ / h of natural gas is carried out. The composition of the obtained synthesis gas, vol.%: Hydrogen 29, carbon monoxide 16, carbon dioxide 3, the rest are inert components (nitrogen and methane). The flow of synthesis gas is directed to the membrane element, in which it is divided into two streams - permeate (4640 m ³ / h) and retant (760 m ³ / h). The permeate stream, enriched in hydrogen to a concentration of 33 vol.%, Is sent through reactor 1 to reactor 2, in which at a pressure of 7.0 MPa, a temperature of 205 ^o C and a volumetric flow rate of 3200 h ^-1 at an oxygen concentration of 0.0 vol. % formed 489 kg / h of methanol. In reactor 3 at 7.0 MPa and 205 ^° C, 158.5 kg / h of methanol was obtained, in reactor 4 at 7.0 MPa and 210 ^° C, 83.4 kg / h of methanol. The average productivity of the plant for 1500 hours of operation is 730.9 kg / h of methanol.

 The retant stream combined with the product gas stream of the reactor 4 is directed to a gas turbine to generate electricity.

 With additional dosing of oxygen into the synthesis gas to a concentration of 0.6 vol. % and the duration of activation of the catalysts in each reactor for 10 hours, the average productivity of the installation for 1500 hours of operation is 752.0 kg / hour (under the process conditions defined in example 3).

 When dosing oxygen to synthesis gas to a concentration of 0.8 vol% and a catalyst activation time of 10 hours in each reactor, the average plant productivity for 1500 hours of operation is 732.0 kg / hour (under the process conditions defined in Example 3). When dosing oxygen into synthesis gas, the quality of the target product, methanol, does not deteriorate.

Example 4. In an energy machine, a partial oxidation of 1234 nm ³ / h of natural gas is carried out. Get 4100 nm ³ / hour of synthesis gas composition, vol.%: Hydrogen 47.2, carbon monoxide 25.1, carbon dioxide 5.0, nitrogen 22.0, the rest is methane.

The resulting synthesis gas with an oxygen content of 0.0 vol.% From the reactor 1 is fed after heating with the product gases of the reactor 2 to the reactor 2, in which at a pressure of 10.0 MPa, a temperature of 240 ^o C, a volumetric flow rate of 10,000 h ^-1 synthesis methanol. After cooling in the heat exchanger 9 and condensation from raw methanol gas and water, non-condensable gas components are fed after pre-heating with the product flows of the reactor 3 to the reactor 3. The pressure in the reactor 3 is 9.9 MPa, a temperature of 230 ^o C. After cooling in the heat exchanger 12 and condensation in the raw methanol separator 13, non-condensable gas components are heated with the product gases of reactor 4 and fed to reactor 4, in which methanol synthesis is carried out at a pressure of 9.9 MPa and a temperature of 220 ^{° C.} At the outlet of the reactor 4 after cooling the product mixture in the heat exchanger 15 and condensation of the crude methanol in the separator 16, non-condensable gases are sent to a gas turbine to generate electricity.

 When carrying out the process in the absence of oxygen in the synthesis gas, the average productivity of each reactor for 200 hours of its operation is: 2 - 630.0 kg / h, 3 - 270.2 kg / h, 4 - 92.4 kg / h. The total average productivity of the installation is 992.6 kg / h.

 When implementing plant operation modes (at an oxygen concentration of 0.6 vol.% And a catalyst treatment time of 10 hours) with a periodic oxygen supply scheme, the average productivity of the first reactor in the three-reactor methanol synthesis unit is 676.2 kg / hour, and the second - 301.8 kg / hour, of the third - 137.9 kg / hour. The total productivity of the installation is 1115.9 kg / h. When dosing oxygen into synthesis gas, the quality of the target product, methanol, does not deteriorate.

Claims (3)

 1. A method for producing methanol, including the steps of producing synthesis gas, catalytically converting the resulting synthesis gas to methanol in several reactors at elevated temperatures and pressures, cooling the reaction products, recovering methanol and utilizing tail gases, characterized in that in the input zones reactors supply synthesis gas containing more than 20 vol. % nitrogen, with a molar ratio of hydrogen to carbon monoxide in the range from 1.2: 1 to 4: 1, with a periodic supply of synthesis gas containing additional oxygen in an amount not exceeding 0.9 vol.%. 2. The method of producing methanol according to claim 1, characterized in that the methanol synthesis process is carried out in the temperature range 160-300 ^o C, a pressure of 4.0-10.0 MPa, volumetric flow rates of 500-10000 h ^-1 .  3. A method for producing methanol according to claims 1 and 2, characterized in that the initial synthesis gas is divided into two streams, one of which is enriched with hydrogen in a membrane-type mass transfer unit and fed into the first catalytic reactor, and the second stream depleted in hydrogen is mixed with a gas stream leaving the last catalytic reactor after methanol is isolated, and the mixture is supplied to the power plant as gas fuel.

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