Method for producing liquefied natural gas by methanation of coke oven gas

Abstract

The invention belongs to the technical field of waste gas recycling, and discloses a method for producing liquefied natural gas by methanation of coke oven gas. The method specifically comprises the following steps: (1) pretreatment; (2) performing fine desulfurization and impurity removal on coke oven gas under the action of a modified adsorbent, and then separating desorption gas and methane synthesis raw material gas by utilizing a molecular sieve membrane; (3) producing methane under the action of a methanation catalyst; and (4) feeding into a cryogenic liquefaction separation tower to obtain liquefied natural gas (LNG) and hydrogen-rich tail gas. The method can be used for efficiently removing sulfur-containing components and impurities in the coke oven gas, high methane yield is obtained, high-purity liquefied natural gas (LNG) is obtained at low cost and energy consumption, the resource utilization rate of the coke oven gas is increased while the technological process is shortened, and finally efficient liquefied natural gas production through coke oven gas methanation is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of waste gas resource utilization, and more specifically to a method for producing liquefied natural gas by methanation of coke oven gas. Background Art

[0002] As a clean energy source with high economic benefits and environmental friendliness, natural gas is gradually becoming an effective way to transition from fossil fuels to renewable resource utilization. The use of fossil fuels such as coal will cause a large amount of toxic and greenhouse gas emissions such as carbon monoxide (CO), nitrogen oxides (NO x ), carbon dioxide (CO 2 ). Coke oven gas, as a by-product of the coking industry, is one of the common industrial exhaust gases, and its main components are CH 4 , H 2 , CO, CO 2 , etc. By hydrogenating CO and CO 2 in coke oven gas to methane and further processing to obtain the industrial product liquefied natural gas (LNG), not only the added value of the product is increased, but also the resource utilization of coke oven gas provides a practical and effective method for supplementing the gap between natural gas and chemical products in China.

[0003] The typical composition of coke oven gas is as follows in Table 1:

[0004] Table 1 is the typical composition of coke oven gas

[0005] Composition <![CDATA[H 2 > <![CDATA[CH 4 > CO <![CDATA[CO 2 > <![CDATA[N 2 > <![CDATA[O 2 > <![CDATA[C m H n > Content (volume fraction) / % 54-59 24-28 5.5-7 1-3 3-5 0.3-0.7 2-3

[0006] The "hydrogen-rich gas reduction and condensation compression" process is generally used for the methanation of coke oven gas to produce liquefied natural gas. The main existing problems include: the presence of sulfur-containing gases in the methanation process of coke oven gas is likely to cause catalyst deactivation; the catalytic efficiency of the methanation catalyst is low, resulting in low CH 4 production; the production temperature of CH 4 is generally high, resulting in high energy consumption and cost; the problem of resource utilization of the catalyst after the reaction is not considered; there are still impurities in the prepared liquefied natural gas (LNG), and it is difficult to meet the purity requirements as a chemical product; the resource utilization cost of the hydrogen-rich tail gas is high.

[0007] Therefore, solving the above problems to achieve efficient methanation of coke oven gas to produce liquefied natural gas is the research focus in this field. Summary of the Invention

[0008] In view of this, the present invention provides a method for producing liquefied natural gas by methanation of coke oven gas to solve the deficiencies in the current technology.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] (1) Impurity removal and desulfurization pretreatment of coke oven gas: In the activated carbon filter, the alkali-modified activated carbon adsorbent is used to filter and pretreat the coke oven gas, mainly for the preliminary removal of sulfur, tar, dust, naphthalene, benzene and other impurities in the coke oven gas. The naphthalene and tar content at the outlet ≤ 1mg / Nm 3 ;

[0011] (2) Fine desulfurization, impurity removal and molecular sieve membrane separation of coke oven gas: Using a composite bed, first under high temperature and low pressure, a soluble metal salt-impregnated modified adsorbent is used for fine desulfurization and impurity treatment, and the total sulfur content at the outlet ≤ 0.1ppm; after cooling and boosting pressure, a molecular sieve membrane is used to separate the analysis gas from the methane synthesis raw gas;

[0012] (3) Methanation reaction of coke oven gas: The methane synthesis raw gas and part of the analysis gas are used in an adiabatic fixed bed with a quartz window and a ternary solid solution catalyst modified by metal oxides to synthesize a methane mixture;

[0013] (4) Cryogenic liquefaction separation: The methane mixture is subjected to cryogenic liquefaction treatment, and liquefied natural gas (LNG) is obtained at the bottom of the cryogenic liquefaction tower.

[0014] Preferably, in step (1), the alkali-modified activated carbon is bituminous coal activated carbon, fruit shell activated carbon or bagasse activated carbon, preferably fruit shell activated carbon or bagasse activated carbon.

[0015] Furthermore, the preparation method of the alkali-modified activated carbon is as follows:

[0016] A 1 . Weigh bituminous coal activated carbon, fruit shell activated carbon or bagasse activated carbon with a specific surface area of 2000 - 3000m 2 / g as the carrier;

[0017] B 1 . Prepare an alkaline solution of potassium hydroxide, sodium bicarbonate or sodium hydroxide with a concentration of 0.01 - 0.05mol / L;

[0018] C 1 . Put the carrier into the alkaline solution at a mass ratio of 1:(10 - 15), stir at room temperature for 12h - 24h, filter, dry for 12 - 20h, and calcine in a muffle furnace at 400℃ - 550℃ for 4 - 12h to obtain the alkali-modified activated carbon.

[0019] The beneficial effect of adopting the above further technical solution is that: after pretreatment, the impurities in the coke oven gas are effectively removed, and part of the sulfides can be adsorbed in the pores of the activated carbon, improving the subsequent gas treatment efficiency and the purity of liquefied natural gas; the advantages of using fruit shell activated carbon or bagasse activated carbon are high carbon content, easy availability of raw materials, large output, low price and stable properties.

[0020] Preferably, in step (2), the composite bed is a continuously operating system composed of two temperature swing adsorption beds, which can be heated, purged, pressurized, depressurized, and filled with adsorbent. The operating temperature of the upper temperature swing adsorption bed is 250°C to 300°C, the operating pressure is 1.0 to 2.0 MPa, the total sulfur content at the outlet is ≤0.1 ppm, and the adsorbent is one or a combination of two of inert alumina, molecular sieve, or pressure swing adsorption silica gel impregnated and modified with soluble metal salts; the operating temperature of the lower temperature swing adsorption bed is 25°C to 80°C, the operating pressure is 2.0 MPa to 3.0 MPa, and the molecular sieve membrane is DD3R, ZSM-11, SSZ-13, or ZSM-15 molecular sieve membrane, preferably DD3R or SSZ-13 molecular sieve membrane, which is used to separate the desorbed gas and the methane synthesis feed gas. The methane content in the desorbed gas is 43 to 50%, and part of the desorbed gas is discharged as supplied fuel.

[0021] Furthermore, in step (2), the preparation method of the soluble metal salt-impregnated and modified adsorbent is as follows:

[0022] A 2 . Weigh one or a combination of two of inert alumina, molecular sieve, or pressure swing adsorption silica gel as the carrier;

[0023] B 2 . Prepare a soluble cerium salt, nickel salt, lanthanum salt, or iron salt solution with a concentration of 0.5 to 1.0 mol / L;

[0024] C 2 . Put the carrier into the metal salt solution at a mass ratio of 1:(5 to 10), stir at room temperature for 12 h to 24 h, filter, dry for 10 to 14 h, and calcine in a muffle furnace at 400°C to 600°C for 2 to 10 h to obtain the soluble metal salt-impregnated and modified adsorbent.

[0025] The beneficial effects of adopting the above further technical solution are as follows: After multi-stage impurity removal and desulfurization, the impurities and sulfides in the coke oven gas are almost completely removed, improving the subsequent gas treatment efficiency and the purity of liquefied natural gas; the metal salt-impregnated and modified adsorbent can selectively adsorb sulfides to achieve fine desulfurization; the molecular sieve membrane can selectively separate the desorbed gas and the methane synthesis feed gas to obtain a high proportion of methane components. Part of it used as fuel can reduce costs and energy consumption, and most of the remaining desorbed gas replenishes carbon for the subsequent methanation process, increasing methane production. At the same time, without additional major equipment, the process flow is shortened.

[0026] Furthermore, in step (3), the preparation method of the metal oxide-modified ternary solid solution catalyst is as follows:

[0027] A 3.Dissolve any three combinations of soluble transition metal salts, such as zirconium salts, cerium salts, nickel salts, iron salts, aluminum salts, cobalt salts, zinc salts or copper salts, in deionized water and organic solvents according to the metal molar ratio of 2∶(1 - x)∶x, and stir at room temperature for 10 min to 40 min. Among them,

[0028] the molar ratio of the total metal ions to the organic solvent is 1:20 to 90;

[0029] the volume ratio of deionized water to the organic solvent is V 水 ∶V 有机溶剂 =1∶1 to 1∶7;

[0030] B 3 .Then add the alkalizing agent urea CO(NH 2 ) 2 , and adjust the molar ratio of the alkalizing agent to the total added metal cations, M(M + )∶M(CO(NH 2 ) 2 )=1∶1 to 1∶5, and stir at room temperature for 10 min to 40 min;

[0031] C 3 .Then add the metal oxide MeO to the metal salt solution at a mass concentration of 5% to 40%, stir at room temperature for 30 min to 60 min, then heat at 150 °C to 240 °C for 1 to 7 h, filter the obtained solid by suction, and dry it at 70 °C to 100 °C for 12 to 20 h;

[0032] D 3 .Place the dried solid in a muffle furnace and calcine it at 250 °C to 500 °C for 1 to 5 h, and then pretreat it under hydrogen at 350 °C to 550 °C for 1 h to 5 h to obtain the catalyst for the methanation of coke oven gas.

[0033] Preferably, in step A 3 , the value of x is 0.2, 0.4, 0.6, 0.8; the organic solvent is selected from one or more of ethanol, ethylene glycol, polyethylene glycol, and acetone organic solvents.

[0034] More preferably, in step A 3 , the value of x is 0.4; the soluble transition metal salt with a metal molar ratio of 2 is selected as the metal nickel salt, and the other two are any combinations of soluble metal cerium salts, aluminum salts, zirconium salts, zinc salts, and iron salts.

[0035] Preferably, in step C 3 , the MeO is selected from Al 2 O 3 , CuO, ZnO, TiO 2 , MnO 2 , CeO2 , Co 3 O 4 . The mass concentration of the MeO in the metal salt solution is preferably 30% - 40%.

[0036] More preferably, the ternary solid solution catalyst modified by metal oxide is: CeO 2 / NiZrFeO 3 , TiO 2 / NiCeAlO 3 or ZnO / NiZrAlO 3 .

[0037] The further beneficial effects of adopting the above are as follows: for the ternary solid solution modified by metal oxide synthesized in the present invention, the high content of Ni existing in the ternary solid solution can significantly improve the methane selectivity, and the additional doping of two metal elements improves the dispersion of Ni, avoiding deactivation due to high-temperature effects; the confinement effect of the metal oxide inhibits the agglomeration of the catalyst, and at the same time, the heterojunction formed between the ternary solid solutions modified by metal oxide synthesized by the hydrothermal method endows it with certain photocatalytic activity. Using a single band or continuous band (200nm - 780nm) in the ultraviolet band (200nm - 400nm) and visible light band (400nm - 780nm), methane selectivity of 99.5% - 100% and methane production rate of 350 - 450 mmol / (g·h) can be achieved at a low temperature of 180°C - 240°C, significantly reducing the reaction energy consumption and maintaining long-term catalytic stability; when there is no external light source, it still has strong thermal catalytic activity, and methane selectivity of 99.3% - 99.7% and methane production rate of 300 - 400 mmol / (g·h) can be achieved at a low temperature of 240°C - 280°C; the synthesized ternary solid solution modified by metal oxide can synthesize methane products at a lower treatment temperature, avoiding the problem of sintering deactivation of the catalyst active components and the occurrence of methane reforming side reactions, and reducing the reaction energy consumption.

[0038] Preferably, in step (3), the reaction pressure of the adiabatic fixed bed is 0.2 MPa - 0.5 MPa, the reaction temperature is 180°C - 280°C, and the volume space velocity is 10000h -1 -50000h -1 .

[0039] More preferably, in step (3), the reaction temperature is 220°C - 280°C.

[0040] Furthermore, in step (3), the adiabatic fixed bed further includes an external light source;

[0041] The external light source is an ultraviolet light band, visible light band, single band or continuous band of 200nm - 780nm.

[0042] Preferably, in step (3), the methane content in the analysis gas is 3-12%, and the volume ratio of the methane synthesis raw gas to the analysis gas is 1:1-5.

[0043] Preferably, in step (4), the cryogenic liquefaction separation uses one or a combination of refrigerants such as isobutane, propane, and ethane. Through cryogenic liquefaction separation, liquefied natural gas (LNG) is obtained at the bottom of the cryogenic separation column, and hydrogen-rich tail gas is obtained at the top of the column. The purity of the liquefied natural gas product can reach more than 89%, and the yield can reach about 95%.

[0044] The beneficial effects of adopting the above technical solution are as follows: Through cryogenic liquefaction separation treatment, the yield and purity of liquefied natural gas can be effectively improved; the hydrogen-rich tail gas can be returned to the coke oven gas pipeline as regeneration gas, replacing part of the coke oven gas raw material, increasing the proportion of the raw material gas, increasing the production of liquefied natural gas, reducing costs, or compressing and liquefying it for power supply in a thermal power plant.

[0045] Furthermore, the above method for producing liquefied natural gas by methanation of coke oven gas further includes: using the deactivated methanation catalyst for selective denitrification of industrial waste gas.

[0046] The beneficial effect of adopting the above further technical solution is that due to the methoxy intermediate formed on the surface during the methanation process, the deactivated methanation catalyst can combine with nitrate species to generate N 2 , removing nitrogen oxides in industrial waste gas, realizing the resource utilization of the catalyst and denitrification of industrial waste gas, and the denitrification efficiency is greater than 90%.

[0047] It can be seen from the above technical solutions that compared with the prior art, the beneficial effects obtained by the present invention are as follows:

[0048] 1. After multi-stage impurity removal and desulfurization, tar, dust, naphthalene, benzene, and sulfides are effectively removed, avoiding the deactivation of the catalyst affected by sulfides, and at the same time meeting the purity requirements as a chemical product;

[0049] 2. Part of the analysis gas obtained after treatment with the molecular sieve membrane is used as fuel, which can reduce costs and energy consumption, and most of the remaining analysis gas supplies carbon for the subsequent methanation process, promoting methane production and simplifying the process flow;

[0050] 3. The methanation catalyst synthesized in the present invention has photocatalytic activity, with high methane selectivity and methane yield at low temperatures and long-term catalytic stability. It effectively reduces energy consumption while avoiding the occurrence of methane reforming side reactions, playing a positive promoting role in the methanation reaction. When there is no external light source, it still has strong thermal catalytic activity at low temperatures. Using the deactivated methanation catalyst for selective denitrification of industrial waste gas helps reduce industrial waste gas emissions, effectively improves resource utilization efficiency, and achieves the goal of "treating waste with waste".

[0051] 4. The deep cryogenic liquefaction separation technology effectively improves the yield and purity of liquefied natural gas. The separated hydrogen-rich tail gas can be used as the raw material gas for coke oven gas, increasing the production of liquefied natural gas and reducing costs, or used for power generation in thermal power plants to maximize resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the provided drawings.

[0053] Figure 1 Schematic diagram of the adsorption treatment capacity of shell activated carbon and bagasse activated carbon with different specific surface areas and different potassium hydroxide impregnation concentrations provided by the present invention for naphthalene and tar (reaction conditions: normal temperature and pressure, total naphthalene and tar amount 10mg / Nm 3 )

[0054] Figure 2 Schematic diagram of the adsorption treatment capacity of inert alumina, molecular sieve, alumina and molecular sieve combination provided by the present invention for sulfide (H 2 S) (reaction conditions: 250°C, 1.5MPa, total sulfide amount 150ppm)

[0055] Figure 3 Schematic diagram of the adsorption treatment capacity of the combination of alumina and molecular sieve impregnated with different metal salts (nickel nitrate, cerium nitrate, lanthanum nitrate) with the same concentration and different concentrations of cerium salt impregnation provided by the present invention for sulfide (H 2 S) (reaction conditions: 250°C, 1.5MPa, total sulfide amount 150ppm)

[0056] Figure 4 Schematic diagram of 30% CeO 2 / NiZrFeO 3 、30% TiO 2 / NiCeAlO 3, 30% ZnO / NiZrAlO 3 Methane production rate of the methanation catalyst (Reaction conditions: continuous band of visible light and ultraviolet light from 380 nm to 600 nm, reaction pressure 0.3 MPa, reaction temperature 200 °C, space velocity 40,000 h -1 ) Schematic diagram.

[0057] Figure 5 30% CeO provided by the present invention 2 / NiZrFeO 3 , 30% TiO 2 / NiCeAlO 3 , 30% ZnO / NiZrAlO 3 UV-visible spectrum of the methanation catalyst.

[0058] Figure 6 30% TiO provided by the present invention 2 / NiCeAlO 3 Long-term stability test (methane selectivity, methane production rate) schematic diagram of the methanation catalyst in the continuous band of visible light and ultraviolet light from 380 nm to 600 nm, reaction pressure 0.3 MPa, reaction temperature 200 °C, space velocity 40,000 h -1 . Detailed implementation method

[0059] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0060] Embodiment 1

[0061] A method for producing liquefied natural gas by methanation of coke oven gas specifically includes the following steps:

[0062] (1) Pretreat the coke oven gas with an activated carbon filter, and the adsorbent is alkali-modified fruit shell activated carbon, and the naphthalene and tar content at the outlet ≤ 0.08 mg / Nm 3 ;

[0063] Among them, the preparation method of the alkali-modified fruit shell activated carbon is:

[0064] a. Weigh fruit shell activated carbon with a specific surface area of 2000 m 2 / g as the carrier;

[0065] b. Prepare a potassium hydroxide alkaline solution with a concentration of 0.02 mol / L;

[0066] c. Put the activated carbon from fruit shells carrier into a potassium hydroxide alkaline solution at a mass ratio of 1:10, stir at room temperature for 14 h, filter, dry for 12 h, and calcine in a muffle furnace at 400 °C for 4 h to obtain potassium hydroxide-modified activated carbon from fruit shells.

[0067] (2) Feed the pretreated coke oven gas into a composite bed for impurity removal and fine desulfurization first. The operating temperature is 250 °C, the operating pressure is 1.0 MPa, the adsorbent is inert alumina impregnated and modified with ferric chloride, and the total sulfur content at the outlet is 0.06 ppm. Then use the SSZ-13 molecular sieve membrane to separate the desorbed gas from the methane synthesis feed gas. The methane content in the desorbed gas is 8%, and the volume ratio of the methane synthesis feed gas to the desorbed gas is 1:1. The operating temperature is 25 °C, and the operating pressure is 2.0 MPa;

[0068] The preparation method of the inert alumina impregnated and modified with ferric chloride is as follows:

[0069] a. Weigh the inert alumina as the carrier;

[0070] b. Prepare a ferric chloride solution with a concentration of 0.5 mol / L;

[0071] c. Put the inert alumina carrier into the ferric chloride solution at a mass ratio of 1:5, stir at room temperature for 12 h, filter, dry for 12 h, and calcine in a muffle furnace at 450 °C for 2 h to obtain the inert alumina impregnated and modified with ferric chloride.

[0072] (3) Feed the separated coke oven gas into an adiabatic fixed bed with a quartz window, use a single band of 395 nm ultraviolet light, and carry out the methanation reaction under the CeO 2 / NiZrFeO 3 methanation catalyst. The reaction pressure is 0.2 MPa, the reaction temperature is 240 °C, the volume space velocity is 10000 h -1 , the methane selectivity is 99.5%, and the methane yield is 355.6 mmol / (g·h) and maintains long-term catalytic stability;

[0073] Without an external light source, a methane selectivity of 99.4% and a methane yield of 310.3 mmol / (g·h) are obtained at 260 °C.

[0074] The preparation method of the CeO 2 / NiZrFeO 3 methanation catalyst is as follows:

[0075] a. Dissolve 1.091 g of Fe(NO 3 ) 3 ·9H 2O, 0.773 g of Zr(NO 3 ) 2 ·5H 2 O and 2.597 g of Ni(NO 3 ) 2 ·6H 2 O, according to the molar ratio of total metal ions to ethanol of 1:50, V 水 ∶V 乙醇 = 1:1 volume ratio, dissolved in 38 mL of deionized water and 38 mL of ethanol, stirred at room temperature for 20 min;

[0076] b. According to the molar ratio of M(M + )∶M(CO(NH 2 ) 2 ) = 1∶1, 0.78 g of urea was added to the solution and stirred at room temperature for 20 min;

[0077] c. CeO 2 was added to the solution according to a mass concentration of 35%, stirred at room temperature for 30 min, then heated by hydrothermal method at 240 °C for 3 h, and then the obtained precipitate was filtered by suction and dried at 70 °C for 12 h;

[0078] d. The dried solid was calcined in a muffle furnace at 500 °C for 1 h and pretreated under hydrogen at 550 °C for 1 h, then the CeO 2 / NiZrFeO 3 coke oven gas methanation catalyst was prepared.

[0079] The deactivated CeO 2 / NiZrFeO 3 methanation catalyst was used for selective denitrification of industrial waste gas, and the denitrification efficiency was 95%;

[0080] (4) The obtained methane mixed gas was subjected to cryogenic liquefaction treatment, and propane was used as the refrigerant. Liquefied natural gas (LNG) was obtained at the bottom of the cryogenic separation tower, and hydrogen-rich tail gas was obtained at the top. The obtained hydrogen-rich tail gas could be returned to the coke oven gas pipeline as regenerated gas or compressed and liquefied for power supply in a thermal power plant. The purity of the liquefied natural gas product could reach 90%, and the yield could reach 95%.

[0081] Example 2

[0082] A method for producing liquefied natural gas by methanation of coke oven gas specifically includes the following steps:

[0083] (1) The coke oven gas was pretreated with an activated carbon filter, and the adsorbent was alkali-modified bagasse activated carbon. The naphthalene and tar content at the outlet was ≤ 0.03 mg / Nm 3 ;

[0084] The preparation method of the alkali-modified bagasse activated carbon is as follows:

[0085] a. Weigh bagasse activated carbon with a specific surface area of 2500 m 2 / g as the carrier;

[0086] b. Prepare a potassium hydroxide alkaline solution with a concentration of 0.03 mol / L;

[0087] c. Put the shell activated carbon carrier into the potassium hydroxide alkaline solution at a mass ratio of 1:13, stir at room temperature for 15 h, filter, dry for 14 h, and calcine in a muffle furnace at 450 °C for 6 h to obtain the potassium hydroxide-modified bagasse activated carbon.

[0088] (2) Feed the pretreated coke oven gas into the composite bed for impurity removal and fine desulfurization first. The operating temperature is 250 °C, the operating pressure is 1.5 MPa, the adsorbent is inert alumina and molecular sieve impregnated with cerium nitrate, and the total sulfur content at the outlet is 0.01 ppm. Then use the DD3R molecular sieve membrane to separate the analyzed gas and the methane synthesis raw gas. The methane content in the analyzed gas is 12%, the volume ratio of the methane synthesis raw gas to the analyzed gas is 1:3, the operating temperature is 30 °C, and the operating pressure is 2.5 MPa;

[0089] The preparation method of the inert alumina and molecular sieve impregnated with cerium nitrate is as follows:

[0090] a. Weigh inert alumina and molecular sieve as the carrier, with a mass ratio of 1:1;

[0091] b. Prepare a cerium nitrate solution with a concentration of 0.5 mol / L;

[0092] c. Put the inert alumina and molecular sieve carrier into the cerium nitrate solution at a mass ratio of 1:7, stir at room temperature for 14 h, filter, dry for 14 h, and calcine in a muffle furnace at 500 °C for 4 h to obtain the inert alumina and molecular sieve impregnated with cerium nitrate.

[0093] (3) Feed the separated coke oven gas into an adiabatic fixed bed with a quartz window, and carry out the methanation reaction under a continuous band of visible light and ultraviolet light with wavelengths of 380 nm - 600 nm, over the TiO 2 / NiCeAlO 3 methanation catalyst. The reaction pressure is 0.3 MPa, the reaction temperature is 200 °C, the volume space velocity is 40000 h -1 , the methane selectivity is 100%, and the methane yield is 439.8 mmol / (g·h) and maintains long-term catalytic stability;

[0094] When there is no external light source, a methane selectivity of 99.7% and a methane production rate of 393.6 mmol / (g·h) are obtained at a low temperature of 240 °C.

[0095] Among them, TiO 2 / NiCeAlO 3 The preparation method of the methanation catalyst is as follows:

[0096] a. Dissolve 0.736 g of Al(NO 3 ) 3 ·9H 2 O, 0.328 g of Ce(NO 3 ) 2 ·6H 2 O and 2.597 g of Ni(NO 3 ) 2 ·6H 2 O in 10 mL of deionized water and 60 mL of ethylene glycol according to the molar ratio of total metal ions to ethylene glycol of 1:90 and the volume ratio of V 水 ∶V 乙二醇 =1∶6, and stir at room temperature for 30 min;

[0097] b. According to the molar ratio of M(M + )∶M(CO(NH 2 ) 2 )=1∶5, add 3.397 g of urea to the solution and stir at room temperature for 30 min;

[0098] c. Add TiO 2 to the solution at a mass concentration of 30%, stir at room temperature for 60 min, then heat at 180 °C for 3 h using the hydrothermal method, and then filter the obtained precipitate and dry it at 90 °C for 14 h;

[0099] d. Place the dried solid in a muffle furnace and calcine it at 250 °C for 1 h, and pretreat it under hydrogen at 500 °C for 4 h to obtain the TiO 2 / NiCeAlO 3 coke oven gas methanation catalyst.

[0100] Use the deactivated TiO 2 / NiCeAlO 3 methanation catalyst for selective denitrification of industrial waste gas, and the denitrification efficiency is 98%;

[0101] (4) The obtained methane mixed gas is subjected to cryogenic liquefaction treatment, and the refrigerant uses a combined refrigerant of propane, ethane and isobutane. Liquefied natural gas (LNG) is obtained at the bottom of the cryogenic separation tower, and hydrogen-rich tail gas is obtained at the top of the tower. The obtained hydrogen-rich tail gas can be returned to the coke oven gas pipeline as regenerated gas or compressed and liquefied for power supply in a thermal power plant. The purity of the liquefied natural gas product can reach 93%, and the yield can reach 97%.

[0102] Example 3

[0103] A method for producing liquefied natural gas by methanation of coke oven gas specifically includes the following steps:

[0104] (1) The coke oven gas is pretreated with an activated carbon filter, and the adsorbent uses alkali-modified bagasse activated carbon. The content of naphthalene and tar at the outlet is ≤ 0.04 mg / Nm 3 ;

[0105] The preparation method of the alkali-modified bagasse activated carbon is as follows:

[0106] a. Weigh bagasse activated carbon with a specific surface area of 3000 m 2 / g as the carrier;

[0107] b. Prepare a sodium hydroxide alkaline solution with a concentration of 0.05 mol / L;

[0108] c. Put the shell activated carbon carrier into the sodium hydroxide alkaline solution at a mass ratio of 1:15, stir at room temperature for 18 h, filter, dry for 16 h, and calcine in a muffle furnace at 500 °C for 8 h to obtain sodium hydroxide-modified bagasse activated carbon.

[0109] (2) The pretreated coke oven gas is sent to a composite bed for impurity removal and fine desulfurization first. The operating temperature is 260 °C, the operating pressure is 2.0 MPa, and the adsorbent uses a molecular sieve impregnated and modified with lanthanum nitrate. The total sulfur content at the outlet is 0.01 ppm. Then, a DD3R molecular sieve membrane is used to separate the analyzed gas from the methane synthesis raw gas. The methane content in the analyzed gas is 10%, and the usage ratio of the methane synthesis raw gas to the analyzed gas is 1:5 (volume ratio). The operating temperature is 50 °C, and the operating pressure is 3.0 MPa;

[0110] The preparation method of the molecular sieve impregnated and modified with lanthanum nitrate is as follows:

[0111] a. Weigh the molecular sieve as the carrier;

[0112] b. Prepare a lanthanum nitrate solution with a concentration of 1.0 mol / L;

[0113] c. The molecular sieve support was put into a lanthanum nitrate solution at a mass ratio of 1:9, stirred at room temperature for 20 h, filtered, dried for 12 h, and calcined in a muffle furnace at 550 °C for 8 h to obtain a lanthanum nitrate-impregnated modified molecular sieve.

[0114] (3) The separated coke oven gas was introduced into an adiabatic fixed bed with a quartz window, and a single band of visible light with a wavelength of 400 nm - 600 nm was used. The methanation reaction was carried out over a ZnO / NiZrAlO 3 methanation catalyst. The reaction pressure was 0.3 MPa, the reaction temperature was 230 °C, and the volume space velocity was 50000 h -1 . The methane selectivity was 99.6%, and the methane yield was 360.4 mmol / (g·h), and long-term catalytic stability was maintained.

[0115] When there was no external light source, a methane selectivity of 99.3% and a methane yield of 338.7 mmol / (g·h) were obtained at a low temperature of 270 °C.

[0116] Among them, the preparation method of the ZnO / NiZrAlO 3 methanation catalyst was as follows:

[0117] a. 0.736 g of Al(NO 3 ) 3 ·9H 2 O, 0.773 g of Zr(NO 3 ) 2 ·5H 2 O and 2.597 g of Ni(NO 3 ) 2 ·6H 2 O were dissolved in 9 mL of deionized water and 45 mL of polyethylene glycol according to the molar ratio of total metal ions to polyethylene glycol of 1:20 and the volume ratio of V 水 ∶V 聚乙二醇 =1∶5, and stirred at room temperature for 40 min.

[0118] b. According to the molar ratio of M(M + )∶M(CO(NH 2 ) 2 )=1∶5, 3.397 g of urea was added to the solution and stirred at room temperature for 40 min.

[0119] c. ZnO was added to the solution at a mass concentration of 40%, stirred at room temperature for 40 min, then heated at 220 °C for 5 h by the hydrothermal method, and then the obtained precipitate was filtered by suction and dried at 100 °C for 12 h.

[0120] d. The dried solid was calcined in a muffle furnace at 350 °C for 1 h and pretreated under hydrogen at 450 °C for 2 h to obtain ZnO / NiZrAlO3 Coke oven gas methanation catalyst.

[0121] The deactivated ZnO / NiZrAlO 3 methanation catalyst is used for selective denitrification of industrial waste gas, and the denitrification efficiency is 95%;

[0122] (4) The obtained methane mixed gas is subjected to cryogenic liquefaction treatment, and the refrigerant uses a combined refrigerant of propane and ethane. Liquefied natural gas (LNG) is obtained at the bottom of the cryogenic separation tower, and hydrogen-rich tail gas is obtained at the top of the tower. The obtained hydrogen-rich tail gas can be returned to the coke oven gas pipeline as regenerated gas or compressed and liquefied for power supply in a thermal power plant. The purity of the liquefied natural gas product can reach 92%, and the yield can reach 96%.

[0123] As shown in the appendix Figure 1 , at normal temperature and pressure, when the total naphthalene and tar content is 10 mg / Nm 3 , the adsorption treatment capabilities of shell activated carbon and bagasse activated carbon with different specific surface areas and different potassium hydroxide impregnation concentrations for naphthalene and tar are analyzed. When the specific surface area of bagasse activated carbon is 2000 m 2 / g, the performance of bagasse activated carbon impregnated with 0.1 mol / L potassium hydroxide (0.03 mg / Nm 3 ) is higher than that impregnated with 0.2 mol / L potassium hydroxide (0.07 mg / Nm 3 ); when bagasse activated carbon is impregnated with 0.1 mol / L potassium hydroxide, the performance of bagasse activated carbon with a specific surface area of 2000 m 2 / g (0.03 mg / Nm 3 ) is higher than that with a specific surface area of 2500 m 2 / g (0.09 mg / Nm 3 ); when the specific surface areas of shell activated carbon and bagasse activated carbon are both 2000 m 2 / g and impregnated with 0.1 mol / L potassium hydroxide of the same concentration, the treatment performance of bagasse activated carbon is better than that of shell activated carbon.

[0124] As shown in the appendix Figure 2 , at 250 °C, 1.5 MPa, and a total sulfide (H 2 S) content of 150 ppm, the adsorption treatment capabilities of inert alumina, molecular sieve, and the combination of alumina and molecular sieve for sulfide (H 2 S) are analyzed. Among them, the combination of alumina and molecular sieve has a stronger adsorption treatment ability for sulfide (H 2 S), reducing the total sulfide content to 1.7 ppm.

[0125] As shown in the appendix Figure 3 , at 250 °C, 1.5 MPa, and total sulfide (H2 When the amount of S is 150 ppm, the adsorption treatment ability of the combination of alumina and molecular sieve impregnated with different metal salts (nickel nitrate, cerium nitrate, lanthanum nitrate) at the same concentration and cerium metal salts at different concentrations for sulfide (H 2 S) was analyzed. The combination of alumina and molecular sieve was impregnated with metal nickel salts, cerium salts, and lanthanum salts at the same concentration respectively. Among them, the combination of alumina and molecular sieve after being impregnated with cerium metal salts had a stronger adsorption treatment ability for sulfide (H 2 S), reducing the total sulfide amount to 0.8 ppm. The combination of alumina and molecular sieve was impregnated with cerium salts at different concentrations respectively. Among them, the combination of alumina and molecular sieve after being impregnated with 0.5 mol / L cerium metal salts had a stronger adsorption treatment ability for sulfide (H 2 S), reducing the total sulfide amount to 0.1 ppm.

[0126] As shown in the appendix Figure 4 As shown, in the continuous band of visible light and ultraviolet light from 380 nm to 600 nm, the reaction pressure was 0.3 MPa, the reaction temperature was 200 °C, and the volume space velocity was 40,000 h -1 -1, the methanation performance of 30% CeO 2 / NiZrFeO 3 、30% TiO 2 / NiCeAlO 3 、30% ZnO / NiZrAlO 3 methanation catalysts was analyzed. Among them, 30% TiO 2 / NiCeAlO 3 showed the best methanation performance, with a methane production rate as high as 439.8 mmol / (g·h).

[0127] As shown in the appendix Figure 5 As shown, the ultraviolet-visible spectrogram of the 30% CeO 2 / NiZrFeO 3 、30% TiO 2 / NiCeAlO 3 、30% ZnO / NiZrAlO 3 methanation catalysts provided by the present invention. Among them, the 30% TiO 2 / NiCeAlO 3 methanation catalyst showed stronger light absorption ability in the ultraviolet-visible continuous band of 365-700 nm.

[0128] As shown in the appendix Figure 6 As shown, the 30% TiO 2 / NiCeAlO 3In the continuous band of visible light and ultraviolet light from 380 nm to 600 nm, the reaction pressure is 0.3 MPa, the reaction temperature is 200 °C, and the volume space velocity is 40,000 h -1 for the long-term stability test. The results show that 30% TiO 2 / NiCeAlO 3 methanation catalyst has long-term catalytic stability, the methane production rate is maintained at 439.2 mmol / (g·h), and the methane selectivity is maintained at 99.7%.

[0129] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing liquefied natural gas by methanation of coke oven gas, characterized in that: The following steps are involved: (1) Pretreatment: Use alkali-modified activated carbon adsorbent to filter and pre-treat the coke oven gas. The naphthalene and tar content at the outlet is ≤1mg / Nm 3 ; (2) Molecular sieve membrane separation: First, a soluble metal salt is used to impregnate the modified adsorbent for fine desulfurization and impurity treatment at a temperature of 250°C to 300°C and a pressure of 1.0 to 2.0 MPa, and the total sulfur content at the outlet is ≤0.1 ppm; then, a molecular sieve membrane is used to separate the analytical gas and the methane synthesis feed gas at a temperature of 25°C to 80°C and a pressure of 2.0 to 3.0 MPa; (3) Methanation reaction: methane synthesis feed gas and part of the desorption gas are synthesized into a methane mixed gas using a ternary solid solution catalyst modified by metal oxides in an adiabatic fixed bed; (4) Cryogenic liquefaction separation: The methane mixed gas is subjected to cryogenic liquefaction treatment to obtain liquefied natural gas at the bottom of the cryogenic liquefaction tower.

2. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 1, characterized in that: In step (1), the preparation method of the alkali-modified activated carbon is: A1. Weigh the specific surface area of ​​2000~3000m 2 / g bituminous coal activated carbon, fruit shell activated carbon or bagasse activated carbon as a carrier; B1. Prepare an alkaline solution of potassium hydroxide, sodium bicarbonate or sodium hydroxide with a concentration of 0.01-0.05 mol / L; C1. Place the carrier in an alkaline solution at a mass ratio of 1: (10-15), stir at room temperature for 12h-24h, filter, dry for 12-20h, and calcine in a muffle furnace at 400°C-550°C for 4-12h to obtain alkali-modified activated carbon.

3. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 1, characterized in that: In step (2), the preparation method of the soluble metal salt impregnated modified adsorbent is: A2. Weigh one or two of inert alumina, molecular sieve or pressure swing adsorption silica gel as a carrier; B2. Prepare a soluble cerium salt, nickel salt, lanthanum salt or iron salt solution with a concentration of 0.5 to 1.0 mol / L; C2. Place the carrier in a metal salt solution at a mass ratio of 1:(5-10), stir at room temperature for 12h-24h, filter, dry for 10-14h, and calcine in a muffle furnace at 400°C-600°C for 2-10h to obtain a soluble metal salt impregnated modified adsorbent.

4. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 1, characterized in that: In step (3), the preparation method of the metal oxide modified ternary solid solution catalyst is: A3. Any three combinations of soluble transition metal zirconium salts, cerium salts, nickel salts, iron salts, aluminum salts, cobalt salts, zinc salts or copper salts are dissolved in deionized water and an organic solvent at a metal molar ratio of 2:(1-x):x, and stirred at room temperature for 10 min to 40 min, wherein: The molar ratio of total metal ions to organic solvent is 1:20-90; The volume ratio of the deionized water to the organic solvent is V 水 :V 有机溶剂 =1:1~1:7; B3. Then add urea CO(NH2)2, an alkalizing agent, to adjust the molar ratio of the alkalizing agent to the total metal cations added, M(M + ): M(CO(NH2)2) = 1:1-1:5, stirring at room temperature for 10-40 min; C3. Then add the metal oxide MeO to the metal salt solution at a mass concentration of 5% to 40%, stir at room temperature for 30min to 60min, then heat at 150°C to 240°C for 1 to 7h, filter, and dry at 70°C to 100°C for 12 to 20h; D3. The dried solid was placed in a muffle furnace and calcined at 250°C to 500°C for 1 to 5 hours, and then pretreated at 350°C to 550°C under hydrogen for 1 to 5 hours to obtain a coke oven gas methanation catalyst.

5. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 4, characterized in that: In step A3, the organic solvent is selected from one or more of ethanol, ethylene glycol, polyethylene glycol, and acetone organic solvents.

6. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 4, characterized in that: In step C3, the MeO is selected from Al2O3, CuO, ZnO, TiO2, MnO2, CeO2, and Co3O4.

7. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 1, characterized in that: In step (3), the reaction pressure of the adiabatic fixed bed is 0.2MPa-0.5MPa, the reaction temperature is 180°C-280°C, and the volume space velocity is 10000h -1 ~50000h -1 .

8. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 7, characterized in that: The adiabatic fixed bed also includes an external light source; The external light source is an ultraviolet light band, a visible light band, a single band or a continuous band in the range of 200nm to 780nm.

9. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 1, characterized in that: In step (3), the methane content in the desorption gas is 3-12%, and the volume ratio of the methane synthesis raw gas to the desorption gas is 1:1-5.

10. The method for producing liquefied natural gas by methanation of coke oven gas according to claim 1, characterized in that: The method further comprises a step (5) of using the metal oxide-modified ternary solid solution catalyst deactivated in step (3) for selective denitration of industrial waste gas.

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