Process for producing a synthesis gas mixture

Abstract

A process for the production of a synthesis gas mixture comprising hydrogen and carbon monoxide by non-catalytic partial oxidation of hydrocarbons in the presence of oxygen and carbon dioxide, which process feeds at least one reactant gas comprising hydrocarbons, a reactant gas comprising oxygen and a reactant gas comprising carbon dioxide to a partial oxidation reactor and reacts at a temperature in the range of from 1200 to 1550°C to obtain a product gas mixture comprising hydrogen, carbon monoxide and carbon dioxide, separates at least a portion of the carbon dioxide from the product gas mixture and recycles it to the partial oxidation reactor. The process is characterized in that the carbon dioxide fed to the partial oxidation reactor comprises additionally inputted carbon dioxide to obtain in the partial oxidation reactor a product gas mixture having a hydrogen / carbon monoxide molar ratio in the range of from 0.8:1 to 1.6:1.

Description

[0001] This invention relates to a method for producing a synthesis gas mixture.

[0002] In many chemical synthesis processes conducted on an industrial scale, not only are valuable products obtained, but also carbon-containing byproducts, which are utilized only by thermal means, such as preheating reactants or generating steam. Combustion of these byproducts produces CO2. If the energy demand previously met through the thermal utilization of byproducts can be met using renewable energy sources, the physical utilization of these byproducts can reduce the formation of the greenhouse gas CO2.

[0003] The physical utilization of byproduct streams can be achieved through specific gasification technologies, in which the byproduct streams react with gasifying agents such as pure oxygen, steam, and / or CO2 to produce syngas 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 residue), or natural gas, or biomass such as wood or straw, are converted into syngas in a gasifier. A drawback is that this conversion is accompanied by the formation of CO2.

[0004] However, it is possible to recycle the generated CO2 back into the gasification process after separation. This also affects the H2 / CO ratio of the resulting syngas.

[0005] Carbonaceous feedstocks such as coal, refinery residues, or gaseous substances such as natural gas are partially oxidized in a gasifier using a non-catalytic hydrothermal high-temperature and high-pressure method (POX method). This converts most of the carbon present into carbon monoxide and carbon dioxide. Carbon monoxide is one valuable product, and the other is hydrogen. The amount produced depends on the amount of hydrogen bound to the feedstock and the amount of steam added. The purified product gas stream, consisting primarily of hydrogen and carbon monoxide, is called syngas. The H2 / CO ratio can vary. It depends on the feedstock used and the gasification method chosen; it 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, 1.0:1 for carbonyl synthesis processes (hydroformylation) or 2.1:1 for methanol synthesis. If the gasifier produces syngas with an H2 / CO ratio < 1.0:1, this ratio can be increased through a downstream CO shift process (CO + H2O → CO2 + H2). This generates a considerable amount of additional CO2. If the gasifier produces an H2 / CO ratio higher than required, excess H2 can be separated by cryogenic distillation, pressure swing adsorption, or membrane separation.

[0007] In the gasification of refinery residue (HVR), the liquid feedstock is atomized with steam and partially oxidized with pure oxygen to form syngas with an H2 / CO ratio of approximately 1:1. The byproduct is approximately 0.3 tons of CO2 per ton of syngas, which is released as emissions. Partial oxidation under these conditions raises the reactor outlet temperature to 1200–1550°C, for example, 1300–1500°C, achieving complete methane conversion with a methane content of <1.5% by volume at the reactor outlet. This low methane concentration is a fundamental quality characteristic of syngas, as excessive methane content can cause difficulties in downstream processes.

[0008] In the gasification of natural gas (NG), the natural gas is partially oxidized along with pure oxygen, with the flame moderated by steam to form syngas with an H2 / CO ratio of approximately 1.9:1. This also produces 0.2 tons of CO2 per ton of syngas, which is released as CO2 emissions. This partial oxidation also raises the temperature at the reactor outlet to 1200 to 1550°C, achieving almost complete conversion of methane, with the methane content at the reactor outlet being <1.5% by volume.

[0009] In the gasification of natural gas, all CO2 formed as a byproduct may also be recycled, thus releasing no CO2 emissions. This provides syngas with an H2 / CO ratio of 1.5:1 at the reactor outlet. Subsequent H2 removal may establish the desired H2 / CO ratio and thus obtain syngas with, for example, an H2 / CO ratio of 1:1.

[0010] In natural gas gasification, in addition to CO2 recirculation, additional CO2 may be introduced via a process known as ATR (Autothermal Reforming). Here, it is possible to set the H2 / CO ratio in the range of 0.9-1.5:1 without releasing CO2 emissions. In ATR operation, a catalyst bed is used to assist the conversion. However, this only allows temperatures up to 1000°C in the catalyst bed; otherwise, the catalyst will be damaged. In contrast, lower temperatures result in incomplete methane conversion, leaving 2-4% by volume of methane in the reactor outlet gas.

[0011] One object of the present invention is to provide a method for producing syngas, wherein syngas with an H2 / CO ratio suitable for carbonyl synthesis processes is obtained. A further object of the present invention is to physically utilize the carbonaceous material stream obtained as a byproduct and which would otherwise be thermally utilized, thereby reducing CO2 emissions overall. Additionally, an object of the present invention is to provide a method for producing syngas that can act as a CO2 sink.

[0012] This objective is achieved by a method for producing a syngas mixture containing hydrogen and carbon monoxide through the non-catalytic partial oxidation of hydrocarbons in the presence of oxygen and carbon dioxide, wherein at least one reactant gas containing hydrocarbons, a reactant gas containing oxygen, and a reactant gas containing carbon dioxide are fed into a partial oxidation reactor and reacted at a temperature of 1200 to 1550°C to obtain a product gas mixture containing water, carbon monoxide, and carbon dioxide, wherein at least a portion of carbon dioxide is separated from the product gas mixture and recycled back to the partial oxidation reactor, wherein the carbon dioxide fed into the partial oxidation reactor includes additionally input carbon dioxide to obtain a product gas mixture in the partial oxidation reactor with a hydrogen / carbon monoxide molar ratio in the range of 0.8:1 to 1.6:1.

[0013] Hydrocarbons in this invention are compounds containing carbon and hydrogen, and may also include oxygenates such as methanol, ethanol, and dimethyl ether. These are typically present as minor components in hydrocarbon-containing reactant streams. Generally, the reactant hydrocarbons comprise at least 80% by volume of hydrocarbons containing only C and H, such as alkanes, cycloalkanes, alkenes, and aromatics; they preferably comprise at least 80% by weight of alkanes (straight-chain, branched-chain, and optionally cyclic alkanes) typically having 1 to 6 carbon atoms.

[0014] This novel method can generate syngas while consuming CO2.

[0015] Additional external input of CO2 from external sources enables optimization of the H2 / CO ratio. It is even possible to set the approximately 1:1 H2 / CO ratio required for the carbonyl synthesis process directly during the syngas generation stage, without downstream enrichment or depletion stages. Non-catalytic implementation of this method at temperatures between 1200 and 1550 °C, preferably between 1250 and 1400 °C, achieves near-complete methane conversion. The methane content at the syngas reactor outlet is typically <1.5 vol%, preferably <0.2 vol% or even <0.05 vol%.

[0016] The method of this invention enables the physical utilization of carbon-containing byproduct streams and CO2 released in any other production process, which binds the maximum amount of carbon within the syngas. If the required process heat or mechanical energy is provided by renewable energy sources, carbon-containing byproduct streams that would otherwise be thermally utilized can be released for physical utilization. Carbon-containing streams that would otherwise be incinerated to generate heat or steam, releasing CO2 in the process, can be used as feedstock for syngas production according to this invention. A high hydrogen / carbon ratio is advantageous in reactant hydrocarbons because a large amount of carbon dioxide is subsequently input into the method and physically utilized. The optimal reactant hydrocarbon is methane with a hydrogen / carbon ratio of 4:1.

[0017] Gaseous or liquid hydrocarbon-containing reactants and oxygen and carbon dioxide, which act as vaporizing agents for other reactants, flow through a high-temperature partial oxidation reactor used according to the invention. To achieve high throughput, the reaction is typically carried out under high pressure, typically 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 typically cylindrical, with one or more burners present on the outer surface. Local temperatures exceeding 2000°C are possible in the oxygen input (flame) region.

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

[0019] In the gasifier (partial oxidation reactor, syngas reactor), the carbon dioxide generated during partial oxidation is subsequently separated from the crude syngas by gas scrubbing and recycled back to the gasifier. Gas scrubbing can be performed according to existing technology. The crude syngas is countercurrently scrubbed in a scrubbing tower with an amine-containing scrubbing agent, where the CO2 present in the crude syngas is almost completely absorbed by the amine. For this purpose, the crude syngas is cooled to 30-70°C before entering the scrubbing tower to avoid thermal stress on the amine. The CO2-enriched scrubbing agent is then regenerated in a desorption tower under heating. The regenerated scrubbing agent can be reused in the scrubbing tower in a recycle mode. CO2 typically exits the desorption tower at ambient pressure at the top. To recycle the CO2 back to the partial oxidation reactor, it is pre-pressurized in a compressor to the system pressure.

[0020] According to the present invention, additional CO2 is introduced from an external source, depending on the desired H2 / CO ratio. The more CO-rich the required syngas, i.e., the lower the required H2 / CO ratio, the more CO2 from external sources can be used and physically utilized. The more hydrogen-rich the hydrocarbon byproduct feedstock used, the more CO2 can be introduced from external sources to establish the specific H2 / CO ratio.

[0021] Generally speaking, C is supplied to the partial oxidation method. x H yThe molar ratios of the CO2 / O2 reactants (including recycled CO2, depending on the H / C ratio in the reactant hydrocarbon feed stream) 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 CxHy / CO2 / O2 molar ratios (mol / ∑mol; total 1.0) are shown in Tables 1 through 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: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1250 °C and at 46 bar (a).

[0023]

[0024]

[0025] Table 2: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1350 °C and at 46 bar (a).

[0026]

[0027]

[0028] Table 3: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1450 °C and at 46 bar (a).

[0029]

[0030] Table 4: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1250 °C and at 10 bar (a).

[0031]

[0032]

[0033] Table 5: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1350 °C and at 10 bar (a).

[0034]

[0035]

[0036] Table 6: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1450 °C and at 10 bar (a).

[0037]

[0038] Table 7: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1250 °C and at 100 bar (a).

[0039]

[0040]

[0041] Table 8: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1350 °C and at 100 bar (a).

[0042]

[0043]

[0044] Table 9: Reactant composition of the gasifier, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1450 °C and at 100 bar (a).

[0045]

[0046] According to the present invention, the hydrogen / carbon monoxide molar ratio in the partially oxidized product gas mixture is in the range of 0.8:1 to 1.6:1. The hydrogen / carbon monoxide molar ratio is preferably 0.8:1 to 1.2:1, more preferably 0.9:1 to 1.1:1.

[0047] Tables 10 to 18 below show C x H y The molar ratio of CO2 / O2 (mol / ∑mol; total 1.0) only considers the amount of CO2 input during the partial oxidation process (CO2 without recycling). The higher the H / C ratio in the reactant hydrocarbons, the lower the set reactor outlet temperature, and the lower the system pressure, the more CO2 can be input into this method from external sources.

[0048] The preferred carbon-containing component is methane. For example, the molar ratio of CH4 / CO2 / O2 reactants (excluding recycled CO2) supplied to the partial oxidation process is 0.50 / 0.13 / 0.37. Therefore, methane is the reactant hydrocarbon that allows the maximum CO2 input at a 1:1 H2 / CO ratio in the syngas. This can be directly used in downstream synthesis (carbonyl synthesis processes, hydroformylation), i.e., without further enrichment or depletion stages. Using pure methane as the reactant hydrocarbon, it is possible to physically utilize 0.30 tons of input CO2 per ton (t) of syngas (H2:CO = 1:1). This amount decreases with increasing reactant hydrocarbon chain length, and remains at 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.

[0049] Table 10: Reactant composition for partial oxidation methods, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1250 °C and at 46 bar (a).

[0050]

[0051] Table 11: Reactant composition for partial oxidation methods, in mol / mol, for various H2 / CO ratios at a reactor outlet temperature of 1350 °C and at 46 bar (a).

[0052]

[0053] Table 12: Reactant composition for partial oxidation methods at reactor outlet temperature of 1450 °C and at 46 bar (a) for various H2 / CO ratios, in mol / mol.

[0054]

[0055]

[0056] Table 13: Reactant composition for partial oxidation methods at reactor outlet temperature of 1250 °C and at 10 bar (a) for various H2 / CO ratios, in mol / mol.

[0057]

[0058] Table 14: Reactant composition for partial oxidation methods at reactor outlet temperature of 1350 °C and at 10 bar (a) for various H2 / CO ratios, in mol / mol.

[0059]

[0060]

[0061] Table 15: Reactant composition for partial oxidation methods at reactor outlet temperature of 1450 °C and at 10 bar (a) for various H2 / CO ratios, in mol / mol.

[0062]

[0063]

[0064] Table 16: Reactant composition for partial oxidation methods at reactor outlet temperature of 1250 °C and at 100 bar (a) for various H2 / CO ratios, in mol / mol.

[0065]

[0066] Table 17: Reactant composition for partial oxidation methods at reactor outlet temperature of 1350 °C and at 100 bar (a) for various H2 / CO ratios, in mol / mol.

[0067]

[0068]

[0069] Table 18: Reactant composition for partial oxidation methods at reactor outlet temperature of 1450 °C and at 100 bar (a) for various H2 / CO ratios, in mol / mol.

[0070]

[0071]

[0072] The reactant gas containing hydrocarbons used for partial oxidation preferably contains methane. The hydrogen / carbon monoxide molar ratio in the syngas is preferably from 0.8:1 to 1.2:1, more preferably from 0.9:1 to 1.1:1. With the aid of pure methane, it is possible to combine 0.30 tons of input, i.e., non-recycled, CO2 per ton of syngas (H2:CO = 1:1).

[0073] If a hydrocarbon reactant gas mainly composed of methane is used, preferably at least 80% by weight, more preferably at least 90% by weight, the total molar ratio of methane:oxygen:carbon dioxide in the reaction gas (i.e., including input CO2 and recycled CO2) used throughout the method is preferably 0.39 to 0.57:0.30 to 0.40:0.05 to 0.30, more preferably 0.39 to 0.57:0.31 to 0.38:0.05 to 0.30.

[0074] The methane present in the reactant gas used for partial oxidation is preferably obtained in a steam cracker.

[0075] The reactant mixture used in steam cracking processes is typically naphtha obtained from mineral oil refineries. The actual cracker is a tubular reactor with coils made of chromium / nickel alloy and located in a flame-heated furnace. The reactant mixture is preheated to 550-600°C, for example, at approximately 12 bar in the convection zone of the furnace. Process steam at 180-200°C is also added in this zone. This reduces the partial pressure of the individual reactants and further prevents polymerization of the reaction products. After the convection zone, the fully gaseous reactant mixture reaches the radiation zone. Here, it is cracked, for example, at 1050°C, to yield low molecular weight hydrocarbons. The residence time is, for example, approximately 0.2-0.4 seconds. This produces ethylene, propylene, 1,2- and 1,3-butadiene, n-butene and isobutene, benzene, toluene, and xylene. It also forms significant amounts of hydrogen and methane, such as approximately 16% by weight, as well as other byproducts, some of which are interfering, such as acetylene, propyne (trace amounts), propadiene (trace amounts), and as components of pyrolytic gasoline, n-, iso-, and cycloalkanes and alkenes, C9 and C6 hydrocarbons. 10 Aromatic compounds. The heaviest fraction is the so-called ethylene cracker residue, with a boiling range of, for example, 210-500°C.

[0076] To prevent oligomerization of the reaction products, the thermal cracking gas is rapidly cooled to approximately 350 to 400°C in a heat transfer unit. Subsequently, the thermal cracking gas is further cooled to 150 to 170°C with quenching oil for subsequent fractionation.

[0077] The product stream at the furnace outlet contains many substances, which are then separated from each other. Valuable products, ethylene and propylene, are typically obtained at extremely high purity. Substances not desired as products are partially recycled back to the cracker and partially incinerated.

[0078] Post-treatment begins with oil and water washing, in which the still-hot gas is further cooled and heavy impurities such as coke and tar are separated. The cracked gas is then gradually cooled and subjected to a series of applications, in which the hydrocarbon mixture is separated into fractions with different carbon numbers. Each fraction is further separated into saturated and unsaturated hydrocarbons in further distillation. Separation of light hydrocarbons requires cryogenic distillation under high pressure. For this purpose, the cracked gas is first gradually compressed to, for example, approximately 30 bar. Acidic gases are absorbed in an alkaline wash. Water is removed using an adsorption dryer.

[0079] Using electricity from renewable energy sources to drive compressors previously powered by steam eliminates the need to burn hydrocarbon-containing byproducts to generate steam. These hydrocarbon-containing byproducts can therefore be used as feedstocks for syngas production according to the invention.

[0080] The removal of trace amounts of acetylene is extremely difficult, therefore acetylene is catalytically hydrogenated to ethylene. Similarly, after the C3 fraction has been separated and before propane-propylene separation, propyne and propadiene fractions are selectively hydrogenated to propylene and propane, respectively.

[0081] Methane can be separated from acetylene, ethylene, and ethane, for example, at 13 bar and -115°C.

[0082] The main products, especially ethylene and propylene, are obtained in pure form. Butene isomers can be used in various petrochemical processes; for example, isobutene is used to produce MTBE and ETBE, and n-butene is used to produce alkylates. Pyrolysis gasoline is a raw material used to obtain benzene and toluene.

[0083] Fractions not intended as products, especially alkanes, can be recycled back to the cracker. Fractions unsuitable for cracking, especially hydrogen and methane, have traditionally been incinerated in cracking furnaces to meet the process's energy requirements. Tar-like residues are incinerated at power plants, sold as binders for graphite electrode production, or used in the production of industrial carbon black.

[0084] In a further embodiment of the invention, methane is obtained as a byproduct of propane dehydrogenation.

[0085] In a further preferred embodiment of the invention, carbon dioxide present in the at least one reactant gas stream is obtained in ammonia synthesis. Ammonia production is achieved through a balance reaction of hydrogen and nitrogen (N₂ + 3H₂ → 2NH₃). Hydrogen is produced on an industrial scale by steam reforming of natural gas, which produces a syngas mixture of H₂ and CO in a first step. In a subsequent water-gas shift stage (CO + H₂O → H₂ + CO₂), CO is converted to hydrogen and carbon dioxide by water. The hydrogen produced via this route yields approximately 10 tonnes of carbon dioxide per tonne of hydrogen. CO₂ is removed by acid gas scrubbing and, after a compression stage, can be used in pure form as a reactant in the partial oxidation method described herein.

[0086] In a further preferred embodiment of the invention, carbon dioxide fed into a partial oxidation reactor is obtained during ethylene oxide synthesis.

[0087] Ethylene oxide is produced on an industrial scale by the catalytic oxidation of ethylene with oxygen at a temperature of 230-270°C and a pressure of 10-20 bar. The catalyst used is finely dispersed silver powder applied to an oxidation support, preferably alumina. The reaction is carried out in a shell-and-tube reactor, where a significant amount of heat of reaction is removed by means of a salt melt and used 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 ethylene to carbon dioxide and water.

Claims

1. A method for producing a syngas mixture comprising hydrogen and carbon monoxide by non-catalytic partial oxidation of hydrocarbons in the presence of oxygen and carbon dioxide, wherein at least one reactant gas comprising hydrocarbons, a reactant gas comprising oxygen, and a reactant gas comprising carbon dioxide are fed into a partial oxidation reactor and reacted at a temperature of 1200 to 1550°C to obtain a product gas mixture comprising water, carbon monoxide, and carbon dioxide, wherein the carbon dioxide fed into the partial oxidation reactor comprises additionally introduced carbon dioxide, and wherein the total molar ratio of hydrocarbons:oxygen:carbon dioxide in the reactant gas is 0.19 to 0.57: 0.31 to 0.70: 0.02 to 0.30, wherein the reactant gas comprising hydrocarbons from the partial oxidation comprises at least 80% by weight of methane, and the total molar ratio of methane:oxygen:carbon dioxide in the reactant gas is 0.39 to 0.57: 0.30 to 0.40: 0.05 to 0.30, and wherein a product gas mixture in which a hydrogen / carbon monoxide molar ratio is in the range of 0.8:1 to 1.2:1 is obtained in a partial oxidation reactor.

2. The method of claim 1, wherein the hydrocarbon is obtained as a co-product in the production process and is thermally utilized.

3. The method of claim 2, wherein the hydrocarbon is burned to generate steam.

4. The method according to any one of claims 1 to 3, wherein at least one reactant gas containing hydrocarbons, a reactant gas containing oxygen and a reactant gas containing carbon dioxide are fed into a partial oxidation reactor and reacted at a temperature of 1200 to 1550°C to obtain a product gas mixture containing water, carbon monoxide and carbon dioxide, wherein a portion of the carbon dioxide is separated from the product gas mixture and recycled back to the partial oxidation reactor.

5. The method according to any one of claims 1 to 4, wherein the input carbon dioxide has been obtained in the production process or separated from the air.

6. The method according to any one of claims 1 to 5, wherein the hydrocarbon further comprises an oxygen-containing compound.

7. The method according to any one of claims 1 to 6, wherein the hydrogen / carbon monoxide molar ratio in the product gas mixture is in the range of 0.9:1 to 1.1:

1.

8. The method according to any one of claims 1 to 7, wherein the total molar ratio of methane:oxygen:carbon dioxide from the partially oxidized reactant gas is 0.39 to 0.57 : 0.31 to 0.38 : 0.05 to 0.

30.

9. The method according to any one of claims 1 to 8, wherein the hydrocarbon-containing reactant gas is obtained in a steam cracker.

10. The method according to any one of claims 1 to 8, wherein the hydrocarbon-containing reactant gas is obtained in a steam cracker, where it is replaced by a power source with no CO2 footprint or a reduced CO2 footprint and is thus available for physical utilization.

11. The method according to any one of claims 1 to 10, wherein the reactant gas containing hydrocarbons is obtained as a byproduct of propane dehydrogenation.

12. The method according to any one of claims 1 to 11, wherein the input carbon dioxide is obtained in ammonia synthesis.

13. The method according to any one of claims 1 to 11, wherein the input carbon dioxide is obtained in the synthesis of ethylene oxide.

Images