Process for the gasification of carbon-containing materials by means of thermal decomposition of methane and conversion of carbon dioxide

Abstract

Methods for gasifying a carbon-containing material, including: i) Reacting the carbon-containing material with steam in the presence of a catalyst containing a hydroxide, oxide or salt of an alkali metal, an alkaline earth metal or a mixture thereof, to produce a gas composition containing CO, CO2, CH4, H2O and H2, wherein the steam-to-carbon ratio is 1 to 2; ii) thermal decomposition of CH4 produced in gasification step i) into elemental carbon (C) and H2, wherein at least a part of the elemental carbon (C) produced in step ii) is recirculated into gasification step i); and iii) Converting CO2 produced in step i) into (a) CO using a process selected from reverse water-gas shift reaction and CO2 reforming reaction, wherein the product from step i) or ii) is used; and wherein 30 to 70 vol% of the total amount of H2 and CO contained in the gas product of step i) is recirculated into the gasification step i).

Description

Technical field

[0001] The present invention relates to a process for gasifying a carbonaceous material and in particular a process for gasifying a carbon-containing material which enables an increase in the utilization value of carbon and a reduction in the production of carbon dioxide. State of the art

[0002] With the profound societal developments since the 20th century, energy supply and demand have become unstable, and environmental problems such as global warming have moved to the forefront. Consequently, efforts continue to utilize a form of fossil energy that is environmentally friendly, and extensive research is being conducted into manufacturing processes for producing a fuel that does not cause any pollution. Instead of directly burning coal, which causes severe pollution, particular efforts are being made to convert coal into a gaseous fuel, such as synthesis gas (which is a mixture of hydrogen, carbon monoxide, etc.), a process called gasification.

[0003] This means that the term gasification refers to the reaction of a solid / liquid fuel containing carbon as a basic component, such as coal, coke, biomass, etc., with a gas, such as oxygen, water vapor, carbon dioxide, and hydrogen, producing combustible gases like CO, H₂, and CH₄. This process is primarily carried out under conditions of high temperature and high pressure to maximize gasification performance and efficiency. The resulting combustible gases are used as fuel for power generation or as raw materials for chemical products or synthetic oil via processes such as methanol synthesis, NH₃ synthesis, and Fischer-Tropsch synthesis. Alternatively, hydrogen is produced and used as a hydrogen source for the hydrodesulfurization and hydrocracking of crude oil.

[0004] A typical gasification system allows coal or other carbon-containing materials to react with water vapor and oxygen (or air) to produce a synthesis gas consisting mainly of hydrogen and carbon monoxide.

[0005] Fig. Figure 1 schematically shows a conventional gasification process. The following describes the CTL (coal-to-liquids) process, which uses the conventional gasification process.

[0006] Specifically, water vapor, oxygen, and coal are fed into a gasifier. The coal reacts with H₂O and oxygen in the gasifier, producing a product containing H₂, CO, CO₂, etc. The reactions in the gasifier are as follows. C + H2O → CO + H2 C + CO2 → 2CO C + O2 → CO2

[0007] The product generated in the gasifier undergoes the removal of suspended solids, Hg, and NOx, followed by the removal of acid gas to eliminate H2S and CO2. Subsequently, the generated gases are subjected to a targeted water-gas shift reaction, as shown below, so that they can be used for the FT synthesis reaction or the MeOH synthesis reaction, and the remaining hydrogen is used separately.

[0008] [Water-gas shift reaction] CO + H2O → H2 + CO2 [FT reaction] CO + 2H2 → -(CH2) n - + H2O [Methanol (MeOH) synthesis] CO + 2H2 → CH3OH

[0009] In the case where such a typical steam-oxygen gasifier is used, coal gasification (C + H₂O → H₂ + CO or C + CO₂ → 2CO) is highly endothermic, and consequently, the corresponding calorific value should be provided by the combustion reaction of the carbon (C + O₂ → CO₂). Therefore, a portion of the hydrocarbon used as feedstock is converted to carbon dioxide after combustion, either inside or outside the gasifier. After gasification, if the synthesis gas produced by the gasifier undergoes a water-gas shift process, such that the H₂ / CO ratio in the synthesis gas is stoichiometrically set to two, as required for FT synthesis or methanol production, the theoretical carbon utilization value of the entire process is less than 49.8%, and the CO₂ production is calculated to be 0.502 mol CO₂ / mol C or more.The following definition of carbon utility (carbon efficiency) is used here.

[0010] Carbon utilization value (%) = (mol CO in synthesis gas with an H2 / CO ratio of 2 to 2.1) x 100 / mol carbon of the gasification feed gasification 1.0C + 1.0H2O → 1.0H2 + 1.0CO combustion 0.34C + 0.34O2 → 0.34CO2 Water-gas shift 0.33CO + 0.33H2O → 0.33H2 + 0.33CO2 entire reaction 1.34C + 1.33H2O + 0.34O2 → 1.33H2 + 0.67CO + 0.67CO2

[0011] Such a low carbon utilization value reduces the profitability of CTL (coal liquefaction). Furthermore, reducing the formation of the greenhouse gas CO2 requires an additional and very expensive facility to capture and store the CO2, making it difficult to establish a profitable, commercially viable plant.

[0012] Korean patent publication KR 10 2008 0 041 635 A discloses an alkali metal catalytic steam gasification process that uses a CO2 separator material and / or a mineral binder material in a gas generator. To increase the catalyst activity in the patent, the CO2 separator material is used to convert the CO2 into solid carbonate or bicarbonate; however, the CO2 cannot be converted into a usable material such as CO or similar. Furthermore, the patent is problematic because it uses a specific catalyst and requires an additional CO2 separator material, such as CaO or similar.

[0013] German patent DE 10 2008 002 963 A1 (General Electric Company) discloses a so-called polygeneration system consisting of several components within a single plant, namely, among others, a synthesis gas generator for producing synthesis gas containing carbon monoxide and water, a synthesis gas enrichment unit in which unwanted components are separated from the synthesis gas, and a synthesis gas utilization system intended for the production of useful chemical products. The polygeneration system may also include other components, such as a power generation unit and other parts.

[0014] Austrian patent AT 504 188 A2 (Electrovac AG) discloses a device for the production of a hydrogen-containing gas, in which a hydrocarbon-containing feed gas is converted to hydrogen and solid carbon (elemental carbon) using a cracking catalyst. Methane or biogas is used as the feed gas. The production of hydrogen as a fuel is central to the process. The carbon is preferably obtained in the form of nanocarbon, high-quality technical carbon black, nanofibers, or nanotubes. Revelation Technical Problem

[0015] The present invention is the culmination of intensive and extensive research aimed at solving the problems in the prior art, with the result that, after a gasification step using a catalyst, a thermal decomposition of methane is additionally carried out, and some or all of the carbon produced thereby is fed back into the gasification step, thereby increasing the carbon utilization value in the gasification, and a CO2 conversion is also additionally carried out to reduce the formation of CO2.

[0016] Accordingly, the object of the present invention is to provide a method for gasifying a carbon-containing material, comprising decomposing methane and converting CO2 in order to achieve a high carbon utility value and reduce the formation of CO2. Technical solution

[0017] To accomplish the above task, the present invention provides a method for gasifying a carbon-containing material with the features of claim 1.

[0018] Furthermore, the process includes the recycling of the carbon produced in ii) to i), in which the carbon-containing material is converted into gas. Beneficial effects

[0019] According to the present invention, the gasification process can achieve a high carbon utilization value of 63 to 73% and produce a remarkably reduced proportion of CO2 on the order of 0.4 mol CO2 / mol C or less.

[0020] Furthermore, no additional facilities and equipment are required for capturing and storing CO2, which makes the process simple and inexpensive. Character description Fig.Figure 1 is a schematic representation showing a conventional gasification process using steam-oxygen gasification; Fig. Figure 2 is a schematic representation showing a gasification process according to the present invention; Fig. Figure 3 is a schematic representation showing a gasification process according to the present invention, which uses a carbon-carbon dioxide gasification reaction for carbon dioxide conversion; Fig. Figure 4 is a schematic representation showing a gasification process according to the present invention which uses a reverse water-gas shift reaction for carbon dioxide conversion; Fig. Figure 5 is a schematic representation showing a gasification process according to the present invention, which uses a CO2 hydrogenation reaction for carbon dioxide conversion; and Fig.Figure 6 is a schematic representation showing a gasification process according to the present invention which uses a CO2 reforming reaction for carbon dioxide conversion. Preferred (best) version

[0021] A detailed description of the present invention is given below with reference to the accompanying figures.

[0022] The present invention provides a method for gasifying a carbon-containing material, which, in addition to conventional catalytic gasification, includes methane substitution and carbon dioxide conversion.

[0023] The present invention provides a method for gasifying a carbon-containing material, comprising: i) reacting the carbon-containing material with steam in the presence of a catalyst, thereby producing a gas composition containing CO, CO2, CH4, H2O and H2; ii) thermally decomposing CH4 produced in i) into C and H2; and iii) converting CO2 produced in i) into CO using the product of i) or ii).

[0024] Fig. Figure 2 schematically shows the method according to the present invention.

[0025] Specifically, the carbon-containing material, along with H₂O and a catalyst, is subjected to a gasification step. The catalyst can be a conventional catalyst for the gasification of carbon-containing materials, but it is preferably a catalyst containing an alkali metal or an alkaline earth metal. Typical examples of alkali metal components include Li, Na, K, Cs, Mg, Ca, etc., and alkaline earth metals include Mg, Ca, etc. The catalyst can be a hydroxide, oxide, or salt of the aforementioned single metal, but it can also be used in a mixture of two or more metals. Such a metal component can be combined with a conventional gasification catalyst.

[0026] The following reactions take place during the gasification step, resulting in the production of H2, CO, CH4, CO2, etc. Gasification: C + H2O → H2 + CO, C + CO2 → 2CO Water gas shift: CO + H2O → H2 + CO2 Methanation: CO + 3H2 → CH4 + H2O Overall reaction: C + H2O → 0.5CH4 + 0.5CO2

[0027] The product of the gasification step is H₂, CO, CH₄, and CO₂, including H₂O. Except for H₂O, the product contains 20 to 25 vol% CH₄, 20 to 25 vol% CO₂, and a remainder of H₂ and CO. The ratio of H₂ to CO can vary depending on the amount of steam supplied to the gasifier. If the steam-to-carbon ratio in the gasifier is 1, the H₂ / CO ratio can be approximately 1, and if the steam-to-carbon ratio is 2, the H₂ / CO ratio can be approximately 4. More specifically, according to the operating results of the pilot plant provided by Exxon, the CH4 content of the product can be approximately 21 vol% once the H2O / C ratio is 1.65, and the H2 / CO ratio can be approximately 3 to 4 [Science.215 (4529), 1982, DOE Report, 1987 (DOE / ER-0326)].

[0028] In the case where the ratio of CO to H2 in the gasification product is 3, the composition of the gasification product includes, except for H2O, 43.5 vol% H2, 14.5 vol% CO, 21 vol% CH4 and 21 vol% CO2.

[0029] As a product of the gasification step, H₂ and CO can be recirculated into the gasification process. Although the proportion of recirculated H₂ and CO is not specifically limited, it can range from 30% to 70% of the total amount. If the amount recirculated is too large, the efficiency improvements according to the present invention may be reduced. Conversely, if the amount recirculated is too small, the gasifier may not function properly.

[0030] The process may include i) catalytic gasification, however the present invention is not limited thereto, and a gasification process may be used in which 10 vol% or more methane is present in the gasification product.

[0031] The gasification process according to the present invention comprises the decomposition of CH4 produced in the gasification step described above. The decomposition of CH4 includes any process, including thermal decomposition and catalytic cracking. Some or all of the carbon formed during the thermal decomposition of CH4 can be recycled back into the gasification step.

[0032] If the carbon produced during the thermal decomposition of CH4 is recycled and used as input, the carbon utility value in the gasification reaction can be increased.

[0033] H2 produced during CH4 decomposition can increase the H2 content of the synthesis gas, which is the gasification product, and C formed during CH4 decomposition can be used as a reactant for the conversion of CO2 or as a fuel to provide the heat of reaction required for gasification.

[0034] The CH4 decomposition reaction is endothermic, and the heat of reaction required for this can be obtained by using carbon as fuel that was formed in the same process. CH4 → C + 2H2 (ΔH = 18.0Kcal / mol) C + O2 → CO2 (ΔH = -93.8Kcal / mol)

[0035] The gasification process according to the present invention further comprises converting the CO2 formed in the gasification step or the like, in particular into CO or -(CH2)-containing FT products or methanol. The reaction for converting the CO2 can be any reaction for converting CO2, including a C-CO2 gasification reaction (C + CO2 → 2CO), a reverse water-gas shift reaction (H2 + CO2 → CO + H2O), a CO2 hydrogenation reaction (nCO2 + 3nH2 → -(CH2)) n - + 2nH2O, CO2 + 3H2 → CH3OH + H2O) and a CO2 reforming reaction (CO2 + CH4 → 2CO + 2H2). The reactant used to convert the CO2 can be the product obtained from any of steps i) to iii).

[0036] In this case, the type of CO2 conversion reaction used can be selected appropriately depending on the amount of carbon to be converted or the process conditions under which the above reaction is applied. For example, if all the carbon produced during CH4 decomposition is recycled back into the gasification step, the CO2 can be converted via a reverse water-gas shift reaction or a hydrogenation reaction.

[0037] Furthermore, the H2 and CO formed during the CO2 conversion can be recycled back into the gasification step.

[0038] The H2 and CO formed by the gasification process according to the present invention can be used in Fischer-Tropsch synthesis or methanol synthesis, and H2 itself can be formed as a product.

[0039] Furthermore, the gasification process according to the present invention can additionally include carrying out a water-gas shift reaction (CO + H2O → H2 + CO2) which uses the H2 and CO formed in the respective steps after the CO2 conversion.

[0040] The carbon-containing material used for the gasification process according to the present invention can include coal, biomass, waste, heavy oil, oil coke, etc., and the present invention is not limited thereto. Example

[0041] The process according to the present invention was carried out at 650 to 700 °C under a pressure of 35 atm and using an alkali metal catalyst. Furthermore, the H₂ / CO ratio in the final product was adjusted to 2, so that the final product was suitable for a Fischer-Tropsch reaction and a methanol production reaction. Comparative example

[0042] In a conventional gasification process according to Fig. In step 1, a carbon-containing material reacted with H₂O and O₂ in a gasification step, forming CO, H₂, CO₂, etc. Subsequently, Hg, NOx, etc., were removed from the gas product generated in the gasification step, followed by the removal of the sour gas (i.e., CO₂ and sulfurous sour gas, etc.). The gas product, free of Hg, NOx, and sour gas, was allowed to react with steam (CO + H₂O → H₂ + CO₂). In the case where the H₂ / CO ratio is adjusted to step 2 via the water-gas shift reaction, the carbon mass balance in the comparative example is approximately as shown below. C (+ H2O + O2) → H2 + 0.5CO + 0.5CO2

[0043] In this case, the carbon utilization value was 49.8%, and the amount of CO2 produced was 0.502 mol / mol C. Example 1

[0044] In the present example, which is in Fig.As shown in Figure 3, 50% of the H₂ and CO in the gas product obtained in i) were recycled back to i). None of the carbon produced in ii) was recycled back to i), and all of the carbon was used as a heat source for the CH₄ decomposition in ii) or was added to iii). In the present example, C-CO₂ gasification (C + CO₂ → 2CO) was carried out in iii). The gas produced in ii) and added to iii) was reacted with the CO₂ formed in i), producing CO.

[0045] In particular, in i) H2, CO and CO2 were formed, in ii) H2 was formed, and in iii) CO was formed. The present example is shown schematically in Fig. 3 shown.

[0046] The carbon mass balance in the present example is given below. 1.00C (+ H2O) → 1.29H2 + 0.63CO + 0.37CO2

[0047] If the ratio of H2 and CO ultimately formed in the present example was approximately 2.1, the carbon utilization value was approximately 62.7%, and the amount of CO2 produced was approximately 0.374 mol / mol C, which is a significant improvement compared to the conventional steam-oxygen gasification process used. Example 2

[0048] In this example, which is in Fig. As shown in Figure 4, a reverse water-gas shift reaction (H2 + CO2 → CO + H2O) was used for the CO2 conversion. Accordingly, 50% of the H2 and CO of the gas product obtained in i) were recycled back to i). 80.8% of the carbon produced in ii) was recycled back to i), the remainder was used as a heat source for the CH4 decomposition, and some of the produced H2 was fed into iii).

[0049] The hydrogen produced in step ii) and fed into step iii) was reacted with the CO2 produced in step i), yielding CO and H2O. Finally, the H2, CO, and CO2 produced in step i), the H2 produced in step ii), and the CO produced in step iii) yielded a synthesis gas in which the H2 / CO ratio was 2.

[0050] The carbon mass balance in the present example is shown below. 1.00C (+ H2O) → 1.47H2 + 0.73CO + 0.27CO2

[0051] In this case, the carbon utilization value was approximately 73.3%, and the amount of CO2 produced was approximately 0.267 mol / mol C, which were significant improvements compared to the conventional hydrogen-oxygen gasification process used. Example 3

[0052] This example, which is in Fig.The process shown in Figure 5 was carried out by repeating Example 2, except that a CO2 hydrogenation (CO2 + 3H2 → -(CH2)- + 2H2O, CO2 + 3H2 → CH2OH + H2O) was used for the CO2 conversion. Example 4

[0053] In the present example, a CO2 reforming reaction was used for the CO2 conversion (CO2 + CH4 → 2CO + 2H2).

[0054] Example 4 is shown schematically in Fig.Figure 6 shows that H2 and CO formed in a gasification step of the carbonaceous material (i)) were recirculated at a rate of 50%, as in the example above. A portion of the methane formed during the gasification of the carbonaceous material was fed to a thermal decomposition step of CH4 (ii)), and a portion of the carbon consequently formed was used as fuel to provide the heat required for the CH4 decomposition, while the remainder was used as fuel to provide the heat required for the CO2 reforming in iii).

[0055] The remaining CH4 formed in the gasification step of the carbon-containing material was fed into the CO2 conversion step to be used for CO2 conversion. In the CO2 conversion, the CO2 was allowed to react with CH4 to form CO and H2. The mass balance of the carbon in this example is shown below. 1.00C (+ H2O) → 1.29H2 + 0.63CO + 0.37CO2

[0056] In the present example, the carbon utilization value, once the synthesis gas, in which the H2 / CO ratio was 2.1, was finally formed, was approximately 62.8%, and the amount of CO2 produced was 0.372 mol / mol C. The carbon utilization value had increased significantly compared to the use of conventional steam-oxygen gasification, and CO2 production had decreased remarkably.

[0057] The comparative example of conventional gasification and examples 1 to 4 according to the present invention are shown in Table 1 below. Table 1 Comparative example Example 1 Example 2 Example 3 Example 4 C-utility value (%) 49.8 62.7 73.3 73.3 62.8 CO2 production (CO2 mol / mol C) 0.502 0.374 0.267 0.267 0.372 CO2 conversion no C-CO2 gasification reverse water-gas shift Hydrogenation CO2 reform

[0058] As can be seen from Table 1, in examples 1 to 4, the carbon utilization value was much higher and the CO2 production was remarkably lower when using the methods according to the present invention, compared to the comparison example where conventional gasification was used.

[0059] In the respective examples, the H2 / CO ratio was set to 2 to 2.1, although the present invention is not necessarily limited to this. For example, if the H2 / CO ratio is 4, hydrogen is in excess and then the hydrogen remaining after the Fischer-Tropsch synthesis or the methanol synthesis can be formed on its own as a product, and this does not limit the present invention.

[0060] Furthermore, a variety of materials can be used, and the carbon mass balance was applied only in the interest of expediency, but even taking into account any original composition CxHyOz of the material, it turns out that the carbon utility is further increased and the production of CO2 is further reduced.

Claims

[1] Method for gasifying a carbon-containing material comprising: i) Reacting the carbon-containing material with steam in the presence of a catalyst containing a hydroxide, oxide or salt of an alkali metal, an alkaline earth metal or a mixture thereof, to produce a gas composition containing CO, CO2, CH4, H2O and H2, wherein the steam-to-carbon ratio is 1 to 2; ii) thermal decomposition of CH4 produced in gasification step i) into elemental carbon (C) and H2, wherein at least a part of the elemental carbon (C) produced in step ii) is recirculated into gasification step i); and iii) Converting CO2 produced in step i) into (a) CO using a process selected from reverse water-gas shift reaction and CO2 reforming reaction, wherein the product from step i) or ii) is used; and wherein 30 to 70 vol% of the total amount of H2 and CO contained in the gas product of step i) is recirculated into the gasification step i). [2] The method of claim 1, further comprising recycling H2 and CO produced in step i) to step iii). [3] Method according to claim 1 or 2, further comprising a gas separation according to step i) which converts the carbon-containing material into gas. [4] Method according to claim 1 or 2, further comprising carrying out a water-gas shift reaction according to step iii). [5] Method according to claim 1 or 2, wherein the carbon-containing material is coal, biomass, waste, heavy oil or oil coke.

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