Method for direct catalytic methanation of biomass

Abstract

The invention discloses a method for direct catalytic methanation of biomass. The method comprises the following steps: preparing a reaction raw material through one of a spraying method, an impregnation method, a ball milling method and a dry mixing combination method; the reaction raw materials and the gasifying agent react in a fixed bed or a fluidized bed, the reaction temperature is 650-950 DEG C, the pressure is 0.1-5 MPa, the flow velocity of the gasifying agent is 0.1-10 times of the minimum fluidization velocity of solid particles, and CH4 can be prepared. The method has the beneficial effects that the biomass is thoroughly converted within the minute-level particle retention time, and the methane selectivity is high; the dosage of the catalyst is greatly reduced; catalyst-containing biomass coke generated by direct catalytic methanation of biomass is used for in-situ catalytic volatilization splitting decomposition and methanation, the methane selectivity is improved, and the cracking degree of tar reaches 90% or above; the whole biomass catalytic methanation process is green and environment-friendly; and the catalyst of the residue is easy to recycle.

Description

Technical Field

[0001] The invention relates to the technical field of energy chemical industry, and in particular to a method for direct catalytic methanation of biomass. Background Art

[0002] As the only renewable energy source that can be converted into carbon-based oil and gas fuels, biomass energy is green, low-carbon and clean. However, the main form of biomass energy utilization in my country is power generation. How to convert it into oil and gas fuels has become an important issue related to the low-carbon development of my country's energy and industry.

[0003] There are three main methods for producing methane from biomass, namely anaerobic digestion, biomass gasification-methanation and catalytic hydrogenation pyrolysis. Anaerobic digestion is the use of anaerobic microorganisms to digest materials in a closed system. The required raw materials usually need to be easily digestible and contain a certain amount of water to increase the methane yield, such as biodegradable waste or feed such as mud, sewage and food waste. However, when considering commercial operation, the anaerobic digestion approach is difficult to apply on a large scale because the rate of methane production by anaerobic digestion is not high, and it is difficult for hard solid biomass such as lignocellulosic biomass and urban solid waste, which are abundant in reserves, to produce methane through anaerobic digestion. The biomass gasification-methanation method can be applied to biomass-based degradable waste, feed and abundant agricultural and forestry solid biomass. The process usually uses medium temperature (about 700℃-900℃) to gasify biomass in a fixed bed / fluidized bed, and the gases produced are CO, CO2, H2, light hydrocarbons (C2-C3), tar, sulfide, etc. Before the gas composition demethanization stage, the tar needs to be deeply removed and desulfurized, otherwise the tar will condense and block the subsequent pipelines, and the sulfide will poison the nickel-based catalyst for methanation. In addition, the H2 / CO ratio in the gas is often between 0.3 and 2. Before methanation, the gas composition in the synthesis gas needs to be adjusted by water gas shift reaction. Therefore, biomass gasification-methanization is a multi-step process consisting of biomass gasification, tar separation, desulfurization, shift, pre-reforming, CO2 separation, and subsequent methanation, resulting in a low thermal efficiency of 60-70% for the entire process. The 800kW pilot-scale device based on this has been put into operation at the Energy Technology Center of the Netherlands (ECN), with a processing capacity of about 160kg / h, and about 40% of the carbon can be converted into methane.

[0004] Biomass catalytic hydrogenation pyrolysis technology uses the acidic sites and hydrogen supply characteristics of supported catalysts (molecular sieves loaded with transition metals, porous oxides, etc.) to catalyze the pyrolysis of biomass volatiles for hydrogenation, generating methane and light liquid aromatics and other products in one step. This technology has the advantages of high hydrocarbon carbon yield (>35%), low oxygen content (<4%), and slow catalyst coking and deactivation. The 50kg / d demonstration of IH 2The process has initially verified that biomass catalytic hydrogenation pyrolysis technology has high thermal efficiency (~88%) and good economic performance, but the further development of this technology still faces the following problems: (1) Biomass char is difficult to be hydrogenated into CH4, and there is still 10-30% of residual char that needs to be post-processed; (2) The product gas still contains a large amount of by-products such as CO, CO2, and heavy aromatics, and it is difficult to obtain a high methane yield (<20wt.%) within a short particle residence time (<1.0h). Although Xiamen University and the Dalian Institute of Chemical Physics, Chinese Academy of Sciences reported that biomass catalytic hydrogenation pyrolysis can obtain a CH4 yield of more than 70%, the required particle residence time is as long as 5 hours (DOI: 10.1038 / s41467-021-27919-9). (3) The catalyst loading is large (the mass ratio to biomass is greater than 1:1), and it is difficult to completely regenerate after coking and deactivation.

[0005] Based on the above analysis, it is still necessary to develop suitable catalysts and design catalytic reaction processes. In particular, how to achieve high methane yield and thermal efficiency within a short particle residence time under the action of low-cost catalysts and realize the large-scale application of direct methanation of biomass is an urgent problem to be solved. Summary of the invention

[0006] In order to solve the above problems, especially the shortcomings of the prior art, the present invention provides a method for direct catalytic methanation of biomass to solve the above problems. The present invention applies the catalytic hydrogenation methanation process of biomass to a fixed bed or fluidized bed reactor, achieving a biomass conversion rate of more than 95% within a minute-level solid particle residence time, high methane selectivity and yield, and the catalyst loading in the process is lower than that of existing research. The entire catalytic reaction process is green and environmentally friendly, with no NO x , HCN, SO x And other pollutants are produced.

[0007] To achieve the above purpose, the present invention adopts the following technical means:

[0008] A method for direct catalytic methanation of biomass comprises the following steps:

[0009] Step 1: Preparation of reaction materials

[0010] Prepare the reaction raw material by one of the methods of spraying, impregnation, ball milling and dry mixing, wherein the reaction raw material consists of biomass and catalyst, and the catalyst is anchored in the biomass solid phase structure in the form of physical embedding or chemical dispersion;

[0011] Step 2: Preparation of CH4

[0012] Based on the reaction raw materials in step one, the reaction with the gasifying agent is carried out in a fixed bed or a fluidized bed, the reaction temperature is 650-950°C, the pressure is 0.1-5MPa, and the flow rate of the gasifying agent is 0.1-10 times the minimum fluidization velocity of the solid particles, so as to produce CH4.

[0013] A further embodiment of the present invention is that the dry mixing combination method is a method of combining one of the following methods: an immersion method, a spraying method or a ball milling method with a dry mixing method.

[0014] A further embodiment of the present invention is that the reaction raw material is biomass loaded with catalyst or a mixture of biomass loaded with catalyst and biomass coke containing catalyst, and the ratio of biomass loaded with catalyst to biomass coke containing catalyst in the mixture is 0.1-10.

[0015] A further embodiment of the present invention is that the biomass is biomass, raw materials containing biomass and / or derived from biomass, and has a particle size range of 0.3-50 mm.

[0016] A further embodiment of the present invention is that the catalyst is one or two of alkali metal species, alkaline earth metal species and transition metal species.

[0017] A further embodiment of the present invention is that, in the catalyst, the mass ratio of metal atoms to biomass is 0.001-0.05, calculated by atomic mass ratio.

[0018] A further embodiment of the present invention is that the elements of the catalyst include Fe, Na, K, Ca, Ba, Mg, or Al, and the parent of the catalyst species is carbonate, nitrate, acetate, or oxide.

[0019] A further embodiment of the present invention is that the catalyst is a binary catalyst composed of Fe and Na / K / Ca elements.

[0020] A further solution of the present invention is that the gasifying agent is pure hydrogen, or a mixture of hydrogen and CO, or a mixture of hydrogen and CO2, and the volume fraction of hydrogen in the mixture is not less than 60%.

[0021] A further solution of the present invention is that the catalyst in the reaction residue in step 2 can be recycled after being recovered by acid dissolution, or recycled by mixing with biomass raw materials and ball milling.

[0022] Beneficial effects of the present invention:

[0023] 1. The present invention achieves complete biomass conversion within the minute-level particle residence time, and high methane selectivity. By loading a suitable catalyst, biomass methanation can achieve a stable conversion rate of more than 95% within a relatively short particle residence time of 20 minutes, and the methane yield can reach more than 80%;

[0024] 2. The amount of catalyst used in the present invention is greatly reduced. The present invention directly loads the catalyst onto the biomass particles in the form of nano-scale dispersion, and a low catalyst amount of 0.1-5wt.% can exert a good catalytic methanation effect.

[0025] 3. The present invention uses the in-situ catalytic volatilization and methanation of biomass coke containing catalyst produced by direct catalytic methanation of biomass to improve methane selectivity and make the degree of tar cracking reach more than 90%. The residual liquid phase product is mainly light liquid aromatics, reducing the risk of tar condensation blocking subsequent pipelines.

[0026] 4. The entire biomass catalytic methanogenesis process of the present invention is green and environmentally friendly, with no NO x 、SO x , HCN and other pollutants are produced.

[0027] 5. The catalyst of the residue of the present invention is easy to recycle. The catalyst of the residue after the reaction can be recovered by a simple acid dissolution method, and the catalyst can be reloaded into biomass by a simple ball milling method for recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, a method for direct catalytic methanogenesis of biomass comprises the following steps:

[0031] Step 1: Preparation of reaction materials

[0032] The reaction raw material is prepared by a method selected from the group consisting of a spraying method, an impregnation method, a ball milling method, and a dry mixing method. The reaction raw material consists of biomass and a catalyst, and the catalyst is anchored in the solid phase structure of the biomass in the form of physical embedding or chemical dispersion;

[0033] Step 2: Preparation of CH4

[0034] Based on the reaction raw materials in step one, the reaction with the gasifying agent is carried out in a fixed bed or a fluidized bed, the reaction temperature is 650-950°C, the pressure is 0.1-5MPa, and the flow rate of the gasifying agent is 0.1-10 times the minimum fluidization velocity of the solid particles, so as to produce CH4.

[0035] The reaction raw material in step 1 is biomass loaded with catalyst or a mixture of biomass loaded with catalyst and biomass coke containing catalyst, and the ratio of biomass loaded with catalyst to biomass coke containing catalyst in the mixture is 0.1-10.

[0036] The biomass in step 1 is biomass, raw materials containing biomass and / or biomass-derived materials, and has a particle size range of 0.3-50 mm.

[0037] The catalyst in step 1 is one or two of alkali metal species, alkaline earth metal species, and transition metal species; the atomic mass ratio of the catalyst is 0.001-0.05; the elements of the catalyst include Fe, Na, K, Ca, Ba, Mg, or Al, and the parent of the catalyst species is carbonate, nitrate, acetate or oxide.

[0038] The catalyst in step 1 is preferably a binary catalyst composed of Fe and Na / K / Ca elements.

[0039] The spraying method in step 1 specifically includes the following steps:

[0040] A. Measure the volume of water required to completely wet 100 g of dry biomass sample;

[0041] B. Weigh the catalyst according to the proportion of catalyst metal atoms in the dry biomass sample of 0.1%-5%, and dissolve it in deionized water, the volume of which is less than the volume of A; sprinkle the catalyst-containing solution evenly on the surface of the biomass with a shower, let it stand for 2-24 hours, and then vacuum dry the sample at 60-100° C. for 2-24 hours to obtain a biomass sample loaded with the catalyst.

[0042] The impregnation method in step 1 specifically comprises the following steps:

[0043] A. Measure the volume of water required to completely wet 100 g of dry biomass sample;

[0044] B. Weigh the catalyst according to the ratio of catalyst metal atoms to 0.1%-5% of the dry biomass sample, and dissolve it in deionized water. The volume of deionized water can be measured according to step A. Pour the biomass sample into the solution containing the catalyst, stir it in ultrasound for 0.1-20h, and then keep the sample in a water bath at 30-60℃ and vacuum dry at 60-100℃ for 2-24h to obtain a biomass sample loaded with the catalyst.

[0045] The ball milling method in step 1 specifically includes the following steps:

[0046] The catalyst is weighed according to the catalyst metal atoms accounting for 0.1%-5% of the dry biomass sample, the catalyst and biomass are evenly mixed, and then the sample is placed in a ball mill for collision for 2-60s. After taking out and sieving to the target particle size, the sample is vacuum dried at 60-100°C for 2-24h to obtain a biomass sample loaded with the catalyst.

[0047] The dry mixing method in step 1 is a combination of one of the dipping method, the spraying method or the ball milling method and the dry mixing method, and specifically comprises the following steps:

[0048] A. Prepare a biomass sample loaded with a catalyst according to the steps described in the impregnation method, spraying method or ball milling method;

[0049] B. Obtaining pyrolysis semi-coke of the biomass sample loaded with the catalyst under actual reaction conditions, with the pyrolysis time being 0-5 min;

[0050] C. The pyrolysis semi-coke containing the catalyst is mixed with the biomass sample loaded with the catalyst in a ratio of 0.1-10 by a dry mixing method, and the sample is vacuum dried at 60-100° C. for 2-24 hours to obtain a reaction raw material.

[0051] The feeding method of the reaction raw materials in step 2 into the fixed bed or fluidized bed is intermittent feeding or continuous feeding.

[0052] When the reactor in step 2 is a fixed bed, the method for preparing the reaction raw materials is preferably a dry mixing combination method combining ball milling and dry mixing; when the reactor is a fluidized bed, the method for preparing the reaction raw materials is preferably a dry mixing combination method combining immersion or spraying with dry mixing.

[0053] When the reactor in step 2 is a fluidized bed reactor, no additional fluidizing medium is required.

[0054] The gasifying agent in step 2 is pure hydrogen, or a mixture of hydrogen and CO, or a mixture of hydrogen and CO2, and the volume fraction of hydrogen in the mixture is not less than 60%.

[0055] The catalyst in the reaction residue in step 2 can be recycled after being recovered by acid dissolution, or recycled by mixing with biomass raw materials and ball milling.

[0056] The acid used in the catalyst recovery and recycling is dilute hydrochloric acid, dilute nitric acid or dilute acetic acid.

[0057] The method of recycling the catalyst by mixing and ball milling the catalyst with the biomass raw material specifically comprises the following steps:

[0058] A. Mixing the gasified residue with the biomass raw material in a ratio of 0.1-10;

[0059] B. The catalyst in the residue is embedded into the biomass by ball milling, and the obtained sample is vacuum dried at 60-100° C. for 2-24 h to obtain the biomass loaded with the catalyst.

[0060] The biomass direct catalytic methanation process involved in the present invention in the same reaction system is as follows:

[0061] Step 1: Rapid catalytic hydropyrolysis

[0062] 1.1 Biomass devolatilization → CO, CO2, Tar, CH4, C + , C - ;

[0063] 1.2 Catalytic hydrogenation of volatile matter → CH4, C2-C3, H2O, light tar;

[0064] Step 2: Rapid reaction in the intermediate phase

[0065] 2.1 Rapid catalytic hydromethanation of C + +H→CH4;

[0066] 2.2 Rapid polycondensation of biochar C + +C + →C-;

[0067] Step 3: Slow catalytic hydrogenation and methanation of biomass char - +H→CH4;C + : activated carbon; C - : Inert carbon.

[0068] The design of the biomass direct catalytic methanation process is mainly to solve the problems of low methanation degree of volatile components such as CO, CO2, and tar in the first step and slow methanation rate of biomass coke in the third step. In the biomass hydrogenation process, a one-way catalyst composed of alkali metal / alkaline earth metal / transition metal or a two-way catalyst composed of alkali metal / alkaline earth metal and transition metal is introduced, and a certain proportion of biomass coke containing the catalyst is mixed. Through the catalyst's provision of active hydrogen and breaking of CO / CC / C=C bonds, it can not only catalyze the deeper hydrogenation and methanation of step 1.2 and inhibit the condensation of activated carbon in step 2.2, but also accelerate the methanation of inert biomass coke in the third step, thereby promoting the selectivity of methane and biomass conversion rate in the biomass hydrogenation conversion process.

[0069] Alkali metals / alkaline earth metals can promote the dispersion of transition metal catalysts and can also combine with sulfur in biomass to prevent sulfur poisoning of transition metal catalysts and inhibit the emission of sulfur-containing harmful gases.

[0070] After the catalyst is loaded in the biomass, it can also play a role in catalytic depolymerization in the 1.1 pyrolysis process of the biomass. Under the reaction conditions of 650-950℃ and pressure of 0.1-5MPa, the biomass pyrolysis can produce more volatiles and C + , thereby regulating the distribution of pyrolysis products and promoting the reactivity of biomass char methanogenesis in the later stage.

[0071] After the reaction is completed, the transition metal in the catalyst exists in the form of a metal element, and the alkali metal / alkaline earth metal exists in the form of an oxide. They can be recovered by a simple acid dissolution method, or they can be re-loaded and embedded into biomass particles by ball milling.

[0072] Example 1

[0073] Weigh 50g of 0.3-1mm biomass that was vacuum dried at 80℃ for 2.0h, add deionized water to the biomass, and measure that the volume of water required to completely soak 50g of biomass is 120ml. Weigh 3.6g Fe(NO3)3·9H2O and dissolve it in 120ml of deionized water. Slowly pour 50g of dry biomass into the impregnation mother liquor. Place the impregnation mother liquor containing biomass in an ultrasonic environment at 50℃ and stir for 2h, then turn off the ultrasound and evaporate it at a constant temperature in a 60℃ water bath for 12h. Take out the mixture and place it in a vacuum environment at 80℃ to dry for 12h, then sieve it to 0.3-1mm and dry it for use.

[0074] The fluidized bed reactor system was pre-displaced with N2 for 1.0h. After the reactor was controlled to 850℃ by a three-stage temperature-controlled furnace, the reactor was pressurized to 3.0MPa with a mixed atmosphere of H2+CO2. 50.0g of biomass loaded with catalyst was added to the feeder, and the feeder was pressurized to 3.5MPa before the reaction started. The flow rates of H2 and CO2 were controlled by mass flow meters respectively. The volume fraction of H2 used was 90%, and the volume fraction of CO2 was 10%. After the outlet gas composition was stable, the valve of the feeder was opened, the materials were added to the fluidized bed reactor at one time, and then the feed valve was closed. Gas-liquid-solid three-phase products were generated during the reaction. The gas phase products could be collected and the gas composition could be measured through the air bag, the liquid phase products could be collected by condensation of the two-stage cold trap, and the solid phase residue could be poured out from the bottom of the reactor after the reaction was completed and the reactor was cooled. Quartz wool was laid at the gas outlet on the top of the reactor to prevent solid fine powder from being taken out of the reactor and blocking the system.

[0075] Take out the residue after the reaction, dissolve the Fe in the residue with enough 0.5 mol / L dilute hydrochloric acid, stir while dissolving in a 60°C water bath, filter while hot after 1.0h and wash the filter cake to neutrality. Repeat this three times, and finally combine the filtrate, evaporate and concentrate to 500ml. Use an ion concentration detector (ICP) to measure the concentration of Fe in the concentrate and calculate the recovery rate of Fe.

[0076] Example 2

[0077] Weigh 50g of 0.3-1mm biomass that was vacuum dried at 80℃ for 2.0h, add deionized water to the biomass, and measure that the volume of water required to completely soak 50g of biomass is 120ml. Weigh 3.6g Fe(NO3)3·9H2O and 3.0gCa(NO3)2·4H2O and dissolve them in 120ml of deionized water. Slowly pour 50g of dry biomass into the impregnation mother liquor. Place the impregnation mother liquor containing biomass in an ultrasonic environment at 50℃ and stir for 2h, then turn off the ultrasound and evaporate it at a constant temperature in a 60℃ water bath for 12h. Take out the mixture and dry it in a vacuum environment at 80℃ for 12h, then sieve it to 0.3-1mm and dry it for use.

[0078] The fluidized bed reactor system was pre-displaced with N2 for 1.0h. After the reactor was controlled to 850℃ by a three-stage temperature-controlled furnace, the reactor was pressurized to 3.0MPa with a mixed atmosphere of H2+CO2. 50.0g of biomass loaded with catalyst was added to the feeder, and the feeder was pressurized to 3.5MPa before the reaction started. The flow rates of H2 and CO2 were controlled by mass flow meters respectively. The volume fraction of H2 used was 100%, and the volume fraction of CO2 was 0%. After the outlet gas composition was stable, the valve of the feeder was opened, the materials were added to the fluidized bed reactor at one time, and then the feed valve was closed. Gas-liquid-solid three-phase products were generated during the reaction. The gas phase products could be collected and the gas composition could be measured through the air bag, the liquid phase products could be collected by condensation of the two-stage cold trap, and the solid phase residue could be poured out from the bottom of the reactor after the reaction was completed and the reactor was cooled. Quartz wool was laid at the gas outlet on the top of the reactor to prevent solid fine powder from being taken out of the reactor and blocking the system.

[0079] Take out the residue after 20 minutes of reaction, dissolve the Fe in the residue with enough 0.5 mol / L dilute hydrochloric acid, dissolve in a 60°C water bath while stirring, filter while hot after 1.0h and wash the filter cake to neutrality. Repeat this three times, and finally combine the filtrate, evaporate and concentrate to 500ml. Use an ion concentration detector (ICP) to measure the concentration of Fe in the concentrate and calculate the recovery rate of Fe.

[0080] Example 3

[0081] Weigh 50g of 0.3-1mm biomass that was vacuum dried at 80℃ for 2.0h, add deionized water to the biomass, and measure that the volume of water required to completely soak 50g of biomass is 120ml. Weigh 3.6g Fe(NO3)3·9H2O and 3.0gCa(NO3)2·4H2O and dissolve them in 120ml of deionized water. Slowly pour 50g of dry biomass into the impregnation mother liquor. Place the impregnation mother liquor containing biomass in an ultrasonic environment at 50℃ and stir for 2h, then turn off the ultrasound and evaporate it at a constant temperature in a 60℃ water bath for 12h. Take out the mixture and dry it in a vacuum environment at 80℃ for 12h, then sieve it to 0.3-1mm and dry it for use.

[0082] The fluidized bed reactor system was pre-displaced with N2 for 1.0h. After the reactor was controlled to 850℃ by a three-stage temperature-controlled furnace, the reactor was pressurized to 3.0MPa with a mixed atmosphere of H2+CO2. 50.0g of biomass loaded with catalyst was added to the feeder, and the feeder was pressurized to 3.5MPa before the reaction started. The flow rates of H2 and CO2 were controlled by mass flow meters respectively. The volume fraction of H2 used was 100%, and the volume fraction of CO2 was 0%. After the outlet gas composition was stable, the valve of the feeder was opened, the materials were added to the fluidized bed reactor at one time, and then the feed valve was closed. Gas-liquid-solid three-phase products were generated during the reaction. The gas phase products could be collected and the gas composition could be measured through the air bag, the liquid phase products could be collected by condensation of the two-stage cold trap, and the solid phase residue could be poured out from the bottom of the reactor after the reaction was completed and the reactor was cooled. Quartz wool was laid at the gas outlet on the top of the reactor to prevent solid fine powder from being taken out of the reactor and blocking the system.

[0083] The residue (biomass char containing catalyst) after 5 minutes of reaction was taken out and mixed with the same mass of biomass containing catalyst, stirred mechanically for 0.5 hours to make the two materials evenly mixed, and then dried in a vacuum environment at 80°C for 2.0 hours. After obtaining the dry raw materials, the steps in the previous paragraph were repeated to carry out the direct catalytic methanation reaction of biomass in a pressurized fluidized bed and analyze the products.

[0084] Take out the residue after 20 minutes of reaction, dissolve the Fe in the residue with enough 0.5 mol / L dilute hydrochloric acid, dissolve in a 60°C water bath while stirring, filter while hot after 1.0h and wash the filter cake to neutrality. Repeat this three times, and finally combine the filtrate, evaporate and concentrate to 500ml. Use an ion concentration detector (ICP) to measure the concentration of Fe in the concentrate and calculate the recovery rate of Fe.

[0085] Example 4

[0086] Weigh 50g of 0.3-1mm biomass that was vacuum dried at 80℃ for 2.0h, add deionized water to the biomass, and measure that the volume of water required to completely soak 50g of biomass is 120ml. Weigh 2.5g Co(NO3)2·6H2O and 3.0gCa(NO3)2·4H2O and dissolve them in 120ml of deionized water. Slowly pour 50g of dry biomass into the impregnation mother liquor. Place the impregnation mother liquor containing biomass in an ultrasonic environment at 50℃ and stir for 2h, then turn off the ultrasound and evaporate it at a constant temperature in a 60℃ water bath for 12h. Take out the mixture and dry it in a vacuum environment at 80℃ for 12h, then sieve it to 0.3-1mm and dry it for use.

[0087] The fluidized bed reactor system was pre-displaced with N2 for 1.0h. After the reactor was controlled to 850℃ by a three-stage temperature-controlled furnace, the reactor was pressurized to 3.0MPa with a mixed atmosphere of H2+CO. 50.0g of biomass loaded with catalyst was added to the feeder, and the feeder was pressurized to 3.5MPa before the reaction started. The flow rates of H2 and CO were controlled by mass flow meters respectively. The volume fraction of H2 used was 80%, and the volume fraction of CO was 20%. After the outlet gas composition was stable, the valve of the feeder was opened, the materials were added to the fluidized bed reactor at one time, and then the feed valve was closed. Gas-liquid-solid three-phase products were generated during the reaction. The gas phase products could be collected and the gas composition could be measured through the air bag, the liquid phase products could be collected by condensation of the two-stage cold trap, and the solid phase residue could be poured out from the bottom of the reactor after the reaction was completed and the reactor was cooled. Quartz wool was laid at the gas outlet on the top of the reactor to prevent solid fine powder from being taken out of the reactor and blocking the system.

[0088] The residue after 20 minutes of reaction was taken out, mixed with 50.0 g of dry biomass, stirred mechanically for 0.5 h to make the two materials evenly mixed, then placed in a ball mill for 30 s, the sample was taken out and sieved to 0.3-1 mm, and then dried in a vacuum environment at 80°C for 2.0 h. After obtaining the dry raw material, the steps in the previous section were repeated to carry out the direct catalytic methanation reaction of pressurized fluidized bed biomass and analyze the product.

[0089] Take out the reaction residue, dissolve the Co in the residue with enough 0.5 mol / L dilute hydrochloric acid, dissolve in a 60°C water bath while stirring, filter while hot after 1.0h and wash the filter cake to neutrality. Repeat this three times, and finally combine the filtrate, evaporate and concentrate to 500ml. Use an ion concentration detector (ICP) to measure the concentration of Co in the concentrate and calculate the recovery rate of Co.

[0090] Comparative Example 1

[0091] Weigh 50g of 0.3-1mm biomass that was vacuum dried at 80℃ for 2.0h for later use. Replace the fluidized bed reactor system with N2 for 1.0h in advance. After the reactor is controlled to 850℃ by a three-stage temperature-controlled furnace, the reactor is pressurized to 3.0MPa with a mixed atmosphere of H2+CO2. Add 50.0g of biomass to the feeder, and pressurize the feeder to 3.5MPa before the reaction starts. The flow rates of H2 and CO2 are controlled separately by a mass flowmeter. The volume fraction of H2 used is 100%, and the volume fraction of CO2 is 0%. After the outlet gas composition is stable, open the valve of the feeder, add the material to the fluidized bed reactor at one time, and then close the feed valve. Gas-liquid-solid three-phase products are generated during the reaction. The gas phase product can be collected and the gas composition can be measured through the air bag, and the liquid phase product can be collected by condensation of the two-stage cold trap. The solid phase residue can be poured out from the bottom of the reactor after the reaction is completed and the reactor is cooled. The gas outlet on the top of the reactor is paved with quartz wool to prevent solid fine powder from being carried out of the reactor and clogging the rear system.

[0092] The biomass-based analysis data used in the four embodiments of the present invention and Comparative Example 1 are shown in Table 1.

[0093] The gasification results of the four embodiments of the present invention and comparative example 1 after the sample injection was completed and run for 20 minutes are shown in Table 2.

[0094] The catalyst recovery results of the present invention are shown in Table 3.

[0095] Table 1 Biomass basic analysis data

[0096]

[0097] Table 2 Results of biomass-based product yield (carbon yield) after 20 min of operation after sample injection for five embodiments

[0098]

[0099] Table 3 Catalyst recovery rate investigation results

[0100]

[0101] Comparing Example 1 and Comparative Example 1 in Table 2, it is found that the biomass loaded with Fe catalyst is applied to the fixed bed / fluidized bed direct catalytic methanation, which can significantly improve the methane yield within a short particle residence time; Comparing Example 1 and Example 2, it can be found that adding a certain promoter to the Fe catalyst to form a binary catalyst can greatly improve the catalytic effect; Comparing Example 2 and Example 3, it can be found that the biomass gasification residue is recovered and simply dry mixed with the biomass raw material loaded with the catalyst, and a high degree of removal of byproducts such as CO, CO2, and tar in the biomass pyrolysis-gasification product can be achieved, and a substantial increase in the CH4 yield can be achieved simultaneously. Comparing Example 3 and Example 4, it can be found that the low-cost Fe-based catalyst has similar activity to the expensive Co-based catalyst for direct catalytic methanation of biomass, especially within a particle residence time of 20 minutes, the biomass converter can reach 94.8%, the CH4 yield is as high as 75.2%, and the methane yield is 2.1 times that of the catalyst-free condition, which reflects the high activity of the low-cost Fe-based catalyst in the direct methanation process of biomass. The data in Table 3 prove that more than 98.5% of the catalyst can be recovered by a simple acid dissolution method, and the catalyst loss cost is relatively small.

[0102] The above results show that the method of the present invention effectively solves the problems that biomass coke is difficult to be hydrogenated into CH4 during biomass hydrogenation conversion; the product gas contains many byproducts such as CO, CO2, and heavy aromatics. This provides a practical reference basis and ideas for further expansion and application of the technical route of direct conversion of biomass to methane. The present invention is a new technical route for biomass to produce natural gas that is efficient, economical, and environmentally friendly and suitable for fixed bed / fluidized bed gasifiers.

[0103] The examples given in the present invention are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here, and the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for direct catalytic methanation of biomass, characterized in that: The steps include: Step 1: Preparation of reaction materials Prepare the reaction raw material by one of the methods of spraying, impregnation, ball milling and dry mixing, wherein the reaction raw material consists of biomass and catalyst, and the catalyst is anchored in the biomass solid phase structure in the form of physical embedding or chemical dispersion; Step 2: Preparation of CH4 Based on the reaction raw materials in step one, the reaction with the gasifying agent is carried out in a fixed bed or a fluidized bed, the reaction temperature is 650-950°C, the pressure is 0.1-5MPa, and the flow rate of the gasifying agent is 0.1-10 times the minimum fluidization velocity of the solid particles, so as to produce CH4.

2. The method for direct catalytic methanation of biomass according to claim 1, characterized in that: The dry mixing combination method is a method of combining one of an immersion method, a spraying method or a ball milling method with a dry mixing method.

3. The method for direct catalytic methanation of biomass according to claim 1, characterized in that: The reaction raw material is biomass loaded with catalyst or a mixture of biomass loaded with catalyst and biomass coke containing catalyst, and the ratio of biomass loaded with catalyst to biomass coke containing catalyst in the mixture is 0.1-10.

4. The method for direct catalytic methanation of biomass according to claim 1, characterized in that: The biomass is biomass, raw materials containing biomass and / or biomass-derived, and has a particle size range of 0.3-50 mm.

5. The method for direct catalytic methanation of biomass according to claim 1, characterized in that: The catalyst is one or two of alkali metal species, alkaline earth metal species and transition metal species.

6. The method for direct catalytic methanation of biomass according to claim 5, characterized in that: In the catalyst, the mass ratio of metal atoms to biomass is 0.001-0.05, calculated by atomic mass ratio.

7. The method for direct catalytic methanation of biomass according to claim 6, characterized in that: The elements of the catalyst include Fe, Na, K, Ca, Ba, Mg, or Al, and the parent of the catalyst species is carbonate, nitrate, acetate, or oxide.

8. The method for direct catalytic methanation of biomass according to claim 7, characterized in that: The catalyst is a binary catalyst composed of Fe and Na / K / Ca elements.

9. The method for direct catalytic methanation of biomass according to claim 1, characterized in that: The gasifying agent is pure hydrogen, or a mixed gas consisting of hydrogen and CO, or a mixed gas consisting of hydrogen and CO2, and the volume fraction of hydrogen in the mixed gas is not less than 60%.

10. The method for direct catalytic methanation of biomass according to claim 1, characterized in that: The catalyst in the reaction residue in step 2 can be recycled after being recovered by acid dissolution, or recycled by mixing with biomass raw materials and ball milling.

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