Method for producing a synthesis gas mixture

Abstract

A method for producing a synthesis gas mixture containing hydrogen and carbon monoxide by non-catalytic partial oxidation of a hydrocarbon in the presence of oxygen and carbon dioxide, comprising: supplying at least one reactant gas containing a hydrocarbon, a reactant gas containing oxygen, and a reactant gas containing carbon dioxide to a partial oxidation reactor and reacting them at a temperature in the range of 1200 to 1550°C; separating at least a portion of the carbon dioxide from the product gas mixture and recycling it to the partial oxidation reactor, thereby obtaining a product gas mixture containing water, carbon monoxide, and carbon dioxide; the carbon dioxide supplied to the partial oxidation reactor includes additional carbon dioxide introduced; and obtaining a product gas mixture in the partial oxidation reactor having a hydrogen to carbon monoxide molar ratio in the range of 0.8:1 to 1.6:1.

Description

[Technical field]

[0001] The present invention relates to a process for producing a synthesis gas mixture. [Background technology]

[0002] Many chemical syntheses carried out on an industrial scale not only produce valuable products, but also carbon-containing by-products. These are used only by thermal means, for example to preheat reaction materials or to generate steam. When combusted, the by-products release CO2. If the energy demand previously supplied by thermal use of the by-products can be made available through the use of renewable energy sources, then the physical use of the by-products can reduce the formation of the greenhouse gas CO2.

[0003] The physical utilization of the by-product streams can be made possible by specific gasification technologies, in which the by-product streams are reacted with gasification means, such as pure oxygen, steam and / or CO2, to obtain a synthesis gas containing carbon monoxide (CO) and hydrogen (H2) as valuable components. In known gasification methods, fossil energy carriers, such as coal, refinery residues (HVR - heavy vacuum residues) or natural gas, or biogenic materials, such as wood or straw, are converted into synthesis gas in a gasifier. A drawback is that this conversion is achieved with the formation of CO2.

[0004] However, it is possible to recycle the CO2 formed by gasification after separation, which at the same time affects the H2 / CO ratio of the resulting product syngas.

[0005] Carbon-containing feedstocks such as coal, refinery residues, or gaseous substances such as natural gas are partially oxidized in a non-catalytic hydrothermal high-temperature and high-pressure process in a gasifier (POX process). This converts most of the carbon present into carbon monoxide and carbon dioxide. Carbon dioxide is one valuable product, hydrogen is the other. The amount produced depends on the amount of combined hydrogen in the feedstock and the amount of steam added. The refined product gas stream, consisting essentially of hydrogen and carbon monoxide, is called synthesis gas. The H2 / CO ratio can vary. It depends on the feedstock used and the gasification method chosen, and can be 0.6-0.8 for coal, 0.8-1.0 for HVR, and 1.5-1.9 for natural gas.

[0006] Industrially relevant H2 / CO ratios are, for example, H2 / CO=1.0:1 for the oxo process (hydroformylation) and H2 / CO=2.1:1 for methanol synthesis. If the gasifier needs to produce synthesis gas with H2 / CO < 1.0:1, the ratio can be increased by a downstream CO shift process (CO+H2O → CO2+H2). This produces significant amounts of additional CO2. If the gasifier needs to produce a higher H2 / CO ratio than necessary, the excess H2 can be separated by cryogenic distillation separation, pressure swing adsorption or membranes.

[0007] In the gasification of refinery residues (HVR), the liquid feedstock is atomized with steam and partially oxidized with pure oxygen to form synthesis gas with approximately H2 / CO=1:1. The by-product formed is about 0.3 tonnes of CO2 per tonne of synthesis gas, which is released as exhaust. Partial oxidation under these conditions reaches temperatures of 1200-1550 °C, e.g. 1300-1500 °C, at the reactor outlet, resulting in complete methane conversion with a methane content of less than 1.5 vol.% at the reactor outlet. This low methane concentration is an essential quality characteristic of the synthesis gas, since an excessively high methane content can cause difficulties in downstream processes.

[0008] In natural gas (NG) gasification, natural gas is partially oxidized with pure oxygen and flame moderated with water steam to form synthesis gas with a H2 / CO ratio of about 1.9:1. This also forms about 0.2 tonnes of CO2 per tonne of synthesis gas, which is released as CO2 emissions. This partial oxidation also reaches reactor outlet temperatures of 1200-1550°C, resulting in virtually complete methane conversion with a methane content of less than 1.5% by volume at the reactor outlet.

[0009] In the gasification of natural gas, it is also possible to recycle all the CO2 formed as a by-product so that no CO2 emissions are released. This results in a synthesis gas with H2 / CO=1.5:1 at the reactor outlet. Subsequent removal of H2 allows the desired H2 / CO ratio to be established, thus obtaining, for example, a synthesis gas with H2 / CO=1:1.

[0010] In addition to CO2 recycling, in natural gas gasification, it is also possible to introduce additional CO2 via the so-called ATR (autothermal reforming) process. Here, it is possible to set the H2 / CO ratio in the range of 0.9-1.5:1 without releasing CO2 emissions. In the ATR mode of operation, a catalyst bed is used to assist the conversion. However, the temperature of the catalyst bed can only be up to 1000 °C, otherwise the catalyst would be damaged. Lower temperatures would result in incomplete methane conversion and 2-4 vol.% methane still being present in the reactor outlet gas. Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to provide a method for producing synthesis gas, which results in a synthesis gas with a H2 / CO ratio suitable for the OXO process. A further object of the present invention is to physically utilize carbon-containing material streams obtained as by-products that would otherwise be utilized for heat, thus reducing CO2 emissions overall. Furthermore, it is an object of the present invention to provide a method for producing synthesis gas that can act as a CO2 sink. [Means for solving the problem]

[0012] This object is achieved by a method for producing a synthesis gas mixture comprising hydrogen and carbon monoxide by non-catalytic partial oxidation of a hydrocarbon in the presence of oxygen and carbon dioxide, in which at least one reactant gas comprising a hydrocarbon, a reactant gas comprising oxygen and a reactant gas comprising carbon dioxide are fed to a partial oxidation reactor and reacted at a temperature in the range of 1200-1550°C, at least a portion of the carbon dioxide is separated from the product gas mixture which is recycled to the partial oxidation reactor to obtain a product gas mixture comprising water, carbon monoxide and carbon dioxide, the carbon dioxide fed to the partial oxidation reactor comprising additional carbon dioxide introduced, and a product gas mixture having a hydrogen to carbon monoxide molar ratio in the range of 0.8:1 to 1.6:1 is obtained in the partial oxidation reactor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the context of the present invention, hydrocarbons are compounds containing carbon and hydrogen, and may also include oxygenates such as methanol, ethanol and dimethyl ether. These are often present as secondary components in the hydrocarbon-containing reactant stream. Generally, the reactant hydrocarbons contain at least 80% by volume of hydrocarbons containing only C and H, such as alkanes, cycloalkanes, alkenes and aromatic hydrocarbons. They preferably contain at least 80% by weight of alkanes (linear, branched and possibly cyclic alkanes), generally having 1 to 6 carbon atoms.

[0014] This novel method allows for the production of synthesis gas while consuming CO2.

[0015] The additional introduction of further CO2 from an external source makes it possible to optimize the H2 / CO ratio. It is even possible to set the H2 / CO ratio of about 1:1 required for the OXO process directly in the synthesis gas production stage without downstream enrichment or reduction steps. With the non-catalytic implementation of this process at temperatures in the range of 1200-1550°C, preferably 1250-1400°C, practically complete methane conversion is achieved. The methane content at the outlet from the synthesis gas reactor is generally less than 1.5% by volume, preferably less than 0.2% by volume and even less than 0.05% by volume.

[0016] The method of the present invention allows for the physical utilization of carbon-containing by-product streams and CO2 released in any other production process, which binds the maximum amount of carbon in the synthesis gas. If the required process heat or mechanical process energy is provided by a renewable energy source, the thermally utilized carbon-containing by-product stream is released for physical utilization. Carbon-containing material streams that would otherwise be incinerated with the release of CO2 for the production of heat or steam can be used as feedstock for synthesis gas production according to the present invention. A high hydrogen to carbon ratio is advantageous in the reaction feedstock hydrocarbons, because a large amount of carbon dioxide is introduced into the process and can be physically utilized. The optimal reaction feedstock hydrocarbon is methane with a hydrogen to carbon ratio of 4:1.

[0017] The gaseous or liquid hydrocarbon-containing reactant feedstock and the gasifying agents oxygen and carbon dioxide as further reactant feedstocks flow through the high-temperature partial oxidation reactor used according to the invention. The reaction is generally carried out under high pressure in order to carry out a high throughput, generally at pressures between 1 and 100 bar, preferably between 10 and 60 bar, more preferably between 20 and 60 bar. The interior of the partial oxidation reactor is generally cylindrical, with one or more burners present on the outer surface. In the region of the oxygen input (flame), local temperatures of more than 2000°C are possible.

[0018] The endothermic gas reforming reaction (dry reforming, empirical formula: CH4+CO2→2CO+2H2) cools the gas phase, and the reactor outlet temperature reaches 1200-1550°C. This gas reforming reaction at 1200-1550°C, preferably 1250-1400°C, achieves high synthesis gas yields and substantially complete hydrocarbon conversion (especially methane conversion).

[0019] The carbon dioxide generated in the gasifier (partial oxidation reactor, syngas reactor) during partial oxidation is then separated from the crude syngas by gas scrubbing and recycled to the gasifier. Gas scrubbing can be carried out according to conventional techniques. The crude syngas is scrubbed in countercurrent with an amine-containing scrubbing agent in a scrubbing tower, and the CO2 present in the crude syngas is practically completely absorbed by the amine. For this purpose, the crude syngas is cooled to 30-70 ° C before entering the scrubbing tower in order to avoid thermal stress to the amine. The CO2-enriched scrubbing agent is then regenerated in a desorption tower while supplying heat. The regenerated scrubbing agent can be used again in the scrubbing tower in circulation mode. At the top of the desorption tower, the CO2 leaves the tower generally at ambient pressure. To recycle (recycle) the CO2 to the partial oxidation reactor, the CO2 is pre-brought to system pressure in a compressor.

[0020] According to the invention, depending on the required H2 / CO ratio, additional CO2 is introduced from an external source. The more CO-rich the desired synthesis gas is, i.e., the lower the desired H2 / CO ratio, the more CO2 can be used and physically utilized from an external source. The more hydrogen in the hydrocarbon-containing by-product stream used, the more CO2 can be introduced from an external source to establish a specific H2 / CO ratio.

[0021] Generally, the C fed to the partial oxidation process depends on the H / C ratio in the reactant hydrocarbon stream. x H yThe molar ratios of CxHy / CO2 / O2 reactants (including recycled CO2) are 0.19-0.57 / 0.02-0.30 / 0.31-0.70 depending on the desired H2 / CO ratio in the crude syngas. Exemplary molar ratios of CxHy / CO2 / O2 (mol / Σmol; total 1.0) are shown in Tables 1-9 below for various reactant hydrocarbons and various H2 / CO ratios, reactor outlet temperatures from 1250°C to 1450°C, and pressures of 10, 46, and 100 bar(a).

[0022] [Table 1]

[0023] [Table 2]

[0024] [Table 3]

[0025] [Table 4]

[0026] [Table 5]

[0027] [Table 6]

[0028] [Table 7]

[0029] [Table 8]

[0030] [Table 9]

[0031] According to the present invention, the molar ratio of hydrogen to carbon monoxide in the product gas mixture by partial oxidation is in the range of 0.8:1 to 1.6:1. The molar ratio of hydrogen to carbon monoxide is preferably 0.8:1 to 1.2:1, more preferably 0.9:1 to 1.1:1.

[0032] C x H y The following Tables 10 to 18 showing the molar ratios of CO2 / O2 (mol / Σmol; total 1.0) only consider the amount of CO2 introduced into the partial oxidation process (recycled CO2 is not included). The higher the H / C ratio in the reaction feed hydrocarbon, the lower the set reaction outlet temperature and the lower the system pressure, the more CO2 can be introduced into the process from an external source.

[0033] The carbon-containing component is preferably methane. For example, the molar ratio of CH4 / CO2 / O2 reactants fed to the partial oxidation process without recycled CO2 is 0.50 / 0.13 / 0.37. Methane is the reactant hydrocarbon and therefore allows the maximum CO2 introduction at a H2 / CO ratio of 1:1 in the synthesis gas. It can be used directly, i.e. without further concentration or reduction steps, in downstream syntheses (Oxo process, hydroformylation). With pure methane as the reactant hydrocarbon, it is possible to physically utilize 0.30 tonnes of introduced CO2 per tonne of synthesis gas (H2:CO = 1:1). This amount decreases with increasing chain length of the reactant hydrocarbon and is still 0.20 t CO2 / t for ethane, 0.13 t CO2 / t for propane, 0.10 t CO2 / t for butane and 0.08 t CO2 / t for pentane.

[0034] [Table 10]

[0035] [Table 11]

[0036] [Table 12]

[0037] [Table 13]

[0038] [Table 14]

[0039] [Table 15]

[0040] [Table 16]

[0041] [Table 17]

[0042] [Table 18]

[0043] The reactant gas containing hydrocarbons for partial oxidation preferably contains methane. The molar ratio of hydrogen to carbon monoxide in the synthesis gas here is preferably 0.8:1 to 1.2:1, more preferably 0.9:1 to 1.1:1. With pure methane, it is possible to combine 0.30 tons of introduced, i.e. non-recycled, CO2 per ton of synthesis gas (H2:CO = 1:1).

[0044] When a hydrocarbon reaction feed gas consisting mainly of methane, preferably consisting of at least about 80% by weight, more preferably at least about 90% by weight, of methane is used, the total molar ratio of methane:oxygen:carbon dioxide in the entire process, i.e., in the reaction gas containing introduced CO2 and recycled CO2, is preferably 0.39-0.57:0.30-0.40:0.05-0.30, more preferably 0.39-0.57:0.31-0.38:0.05-0.30.

[0045] The methane present in the reactant gas for the partial oxidation is preferably obtained in a steam cracker.

[0046] The reactant mixture used in the steam cracking process is often naphtha obtained in mineral oil refineries. The actual cracking unit is a tubular reactor with pipe coils made of chromium / nickel alloy and is located in a furnace heated by a flame. The reactant mixture is preheated to 550-600 °C in the convection zone of the furnace, for example at about 12 bar. In this zone, process steam at 180-200 °C is also added. This reduces the partial pressure of the individual reaction participants and further prevents polymerization of the reaction products. After the convection zone, the completely gaseous reactant mixture reaches the radiant zone. There it is cracked, for example at 1050 °C, to obtain low molecular weight hydrocarbons. The residence time is, for example, about 0.2-0.4 seconds. This produces ethene, propene, 1,2- and 1,3-butadiene, n- and i-butenes, benzene, toluene and xylenes. Hydrogen and methane are also formed in significant amounts, e.g., about 16% by weight, as well as other by-products, such as ethyne, propyne (trace amounts), propylene (trace amounts), and n-, i- and cyclo-paraffins and -olefins, C9 and C10 as components of pyrolysis gasoline. 10 Aromatic compounds are also formed. The heaviest fractions are the so-called ethylene cracker residues and have a boiling range of, for example, 210-500°C.

[0047] To prevent the reaction products from oligomerizing, the hot cracked gas is rapidly cooled to about 350-400°C by heat transfer. The hot cracked gas is then further cooled to 150-170°C by quench oil for subsequent fractionation.

[0048] The product stream at the outlet of the furnace contains a number of substances which are then separated from one another. The valuable products ethene and propene are generally obtained in very high purity. The substances which are not desired to be obtained as products are partly recycled to the cracker and partly incinerated.

[0049] The post-treatment starts with oil and water scrubbing, where the still hot gas is further cooled and heavy impurities such as coke and tar are separated. This is followed by a series of treatments that gradually cool the cracked gas and split the hydrocarbon mixture into fractions with different carbon numbers. The individual fractions are separated into saturated and unsaturated hydrocarbons in a further distillation. Separation of the lighter hydrocarbons requires low-temperature rectification at high pressure. For this purpose, the cracked gas is first compressed in stages, for example to about 30 bar. The acid gases are absorbed in an alkaline scrub. An adsorption dryer removes the water.

[0050] The use of electrical energy from renewable energy sources to drive a compressor that was previously steam-driven allows for the elimination of the combustion of hydrocarbon-containing by-products to generate steam, which can then be utilized as a feedstock for the synthesis gas production of the present invention.

[0051] Since it can be very difficult to remove traces of ethyne, it is instead catalytically hydrogenated to ethene. Similarly, after the C3 fraction is separated, the propyne and arene fractions are converted to propene and propane, respectively, by selective hydrogenation before the propane-propene separation.

[0052] Methane can be separated from ethyne, ethene and ethane, for example at 13 bar and -115°C.

[0053] The main products, especially ethene and propene, are obtained in pure form. The butene isomers can be used in various petrochemical processes, for example iso-butenes for the production of MTBE and ETBE, and n-butenes for the production of alkylates. Pyrolysis gasoline is the starting material for obtaining benzene and toluene.

[0054] The fractions not desired as products, especially alkanes, can be recycled to the cracker. The fractions not suitable for cracking, especially hydrogen and methane, have traditionally had to be incinerated in the cracker to meet the energy demands of the process. The tar-like residues are either incinerated in power plants, sold as binders for the production of graphite electrodes, or used to produce industrial carbon black.

[0055] In a further embodiment of the invention, methane is obtained as a by-product in propane dehydrogenation.

[0056] In a further preferred embodiment of the invention, the carbon dioxide present in at least one reactant gas stream is obtained in ammonia synthesis. The production of ammonia takes place by the equilibrium reaction of hydrogen with nitrogen (N2+3H2→2NH3). Hydrogen is produced on an industrial scale by steam reforming of natural gas, which in a first step produces a synthesis gas mixture of H2 and CO. In the subsequent water-gas shift step (CO+H2O→H2+CO2), CO is converted with water into hydrogen and carbon dioxide. The hydrogen produced by this route produces about 10 tonnes of carbon dioxide per tonne of hydrogen. The CO2 is removed by acid gas scrubbing and, after a compression step, is available in pure form as a reactant for the partial oxidation process described herein.

[0057] In a further preferred embodiment of the invention, the carbon dioxide introduced into the partial oxidation reactor is obtained in the synthesis of ethylene oxide.

[0058] Ethylene oxide is produced on an industrial scale by catalytic oxidation of ethene with oxygen at temperatures between 230 and 270 °C and pressures between 10 and 20 bar. The catalyst used is finely divided silver powder applied to an oxide support, preferably alumina. The reaction takes place in a shell-and-tube reactor, in which the considerable heat of reaction is removed with the aid of molten salts and utilized to generate superheated high-pressure steam. The yield of pure ethylene oxide is, for example, 85%. A side reaction that occurs is the complete oxidation of ethene to carbon dioxide and water.

Claims

1. A process for producing a synthesis gas mixture comprising hydrogen and carbon monoxide by non-catalytic partial oxidation of a hydrocarbon in the presence of oxygen and carbon dioxide, comprising: feeding at least one reactant gas comprising a hydrocarbon, a reactant gas comprising oxygen, and a reactant gas comprising carbon dioxide to a partial oxidation reactor and reacting at a temperature in the range of 1200 to 1550°C, preferably separating a portion of the carbon dioxide from the product gas mixture and recycling it to the partial oxidation reactor to obtain a product gas mixture comprising water, carbon monoxide, and carbon dioxide, wherein the carbon dioxide fed to the partial oxidation reactor comprises additional carbon dioxide introduced, and the total molar ratio of hydrocarbon:oxygen:carbon dioxide in the reactant gas is 0.19 to 0.57:0.31 to 0.70:0.02 to 0.30; the hydrocarbon-containing reactant gas from the partial oxidation contains 80 wt % methane, and the total molar ratio of hydrocarbon:oxygen:carbon dioxide in the reactant gas is 0.39-0.57:0.30-0.40:0.05-0.30; A product gas mixture having a hydrogen to carbon monoxide molar ratio in the range of 0.8:1 to 1.2:1 is obtained in said partial oxidation reactor.

2. 10. The method of claim 1, wherein the hydrocarbons are obtained as a by-product in a manufacturing process and are typically utilized for thermal purposes.

3. The method of claim 2 , wherein the hydrocarbons are typically incinerated to generate steam.

4. 4. The method according to claim 1, wherein the introduced carbon dioxide is obtained in a manufacturing process or is separated from air.

5. The method of any one of claims 1 to 4, wherein the hydrocarbons may further comprise oxygenates.

6. A process according to any one of claims 1 to 5, wherein the molar ratio of hydrogen to carbon monoxide in the product gas mixture is in the range of 0.9:1 to 1.1:

1.

7. 7. The process according to claim 1, wherein the total molar ratio of methane:oxygen:carbon dioxide in the reactant gas from the partial oxidation is 0.39-0.57:0.31-0.38:0.05-0.

30.

8. A reaction feed gas containing hydrocarbons is obtained in a steam cracker, and preferably contains CO ２ Emission-free power or reduced CO ２ The method according to any one of claims 1 to 7, obtained in a steam cracker, the emissions of which are replaced by the use of electricity, and made available for physical utilization.

9. The process according to any one of claims 1 to 8, wherein the hydrocarbon-containing reactant gas is obtained as a by-product in the dehydrogenation of propane.

10. The process according to any one of claims 1 to 9, wherein the introduced carbon dioxide is obtained in ammonia synthesis.

11. 10. The process according to claim 1, wherein the introduced carbon dioxide is obtained in the synthesis of ethylene oxide.