Method for preparing green carbon-based catalyst by taking biomass waste as raw material and application of green carbon-based catalyst in preparation of synthesis gas by biomass gasification

Abstract

The invention discloses a method for preparing a green carbon-based catalyst by taking biomass waste as a raw material and application of the green carbon-based catalyst to preparation of synthesis gas by biomass gasification, biomass waste which is wide in source and low in price is used as a raw material of a carrier of the catalyst, and alkali (soil) metal and transition metal are used as active components for synergistic catalysis. When the catalyst is used for preparing hydrogen-rich synthesis gas through biomass catalytic cracking-steam gasification reforming, reducing gas does not need to be introduced again for high-temperature reduction before the catalyst is used, and resources and energy consumption are saved; meanwhile, the gasification reaction activation energy of synthesis gas produced by biomass can be effectively reduced, the gasification reaction temperature is reduced from 750 DEG C or above to 600 DEG C or below, the hydrogen yield is improved, the influence of biomass raw material types on gas products is reduced, unification of high activity, high stability and high selectivity is achieved, active metal can etch a carbon matrix to form a porous carbon structure, and the performance of the catalyst is improved. The tar yield can be further reduced.

Description

Technical field:

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a method for preparing a green carbon-based catalyst using biomass waste as a raw material and an application of the catalyst in preparing synthesis gas by biomass gasification. Background technology:

[0002] Synthetic Natural Gas (SNG) is an efficient and clean energy carrier, mainly composed of carbon monoxide (CO), carbon dioxide (CO2) and hydrogen (H2), which can be used to synthesize chemical products such as methanol, ethanol, and aromatics. At present, the main methods for preparing syngas are coal gasification, natural gas reforming, and biomass gasification technology. Among them, biomass gasification technology uses biomass with green properties as raw materials to obtain syngas through gasification reactions, which is particularly important for green carbon reduction in the chemical industry. However, the traditional biomass gasification method has problems such as high reaction temperature (above 750℃), low H2 content, high tar content, and the quality of syngas is easily affected by raw materials, which restricts its further promotion and application. Therefore, it is crucial to develop a catalyst that can reduce the activation energy of biomass gasification reaction, improve the quality of syngas, and reduce tar production for the preparation of hydrogen-rich syngas by biomass gasification.

[0003] At present, the catalysts commonly used in the preparation of biomass synthesis gas mainly include natural ore catalysts, precious metals, alkali metal catalysts and transition metal catalysts. Natural ore catalysts such as dolomite and olivine catalysts show good catalytic performance in the removal of tar during biomass pyrolysis, but they have problems such as low mechanical strength, easy wear, low service life and greater difficulty in recovery. Precious metal catalysts have high catalytic activity and good anti-carbon deposition performance, but they are expensive and difficult to achieve industrial application. Relatively cheap alkali metals can promote the cracking and conversion of tar into gas components by reducing the volatilization analysis temperature. For example, patent CN 113372934 A discloses a method for in-situ decarbonization and hydrogen production by potassium-calcium co-catalyzed biomass pyrolysis. It impregnates soybean straw powder with KOH-Ca(OH)2 mixed solution, obtains pyrolysis precursor raw material after dehydration and grinding, and then pyrolyzes it under Ar atmosphere to obtain hydrogen-rich gas product. This method directly mixes biomass with active components and then pyrolyzes them, so that biomass simultaneously assumes the functions of carbon carrier and raw material, and at the same time adjusts the potassium / calcium ratio to obtain synthesis gas with different H2 contents. However, this method requires that the biomass and metal salt solution be mixed and placed in a constant temperature shaker for shaking, and dehydration must be carried out in a blast drying oven at 100-120°C, and the catalyst cannot be recycled. Transition metal catalysts can reduce the reaction activation energy and adjust the composition of synthesis gas at the same time. For example, patent CN 115920937 A discloses the preparation of a biomass-based catalyst and its application in the methanol steam synthesis gas process. The catalyst uses waste biomass as raw material and loads copper and cobalt active metals. The preparation process is to first carbonize the dried biomass crushed material in an inert atmosphere, impregnate the copper-cobalt mixed solution to obtain a copper-cobalt / carbon mixture, and then roast it in a flowing nitrogen atmosphere to obtain a copper-cobalt / carbon catalyst. The synthesis gas obtained by this method has a high proportion of hydrogen, but it needs to undergo two high-temperature reactions under a nitrogen atmosphere, which has high energy consumption, and the catalyst needs to be reduced in a H2 / N2 atmosphere before use. The use process is cumbersome and has high requirements for equipment. Transition metals will also agglomerate due to high-temperature sintering during use, which greatly reduces the catalytic active sites, resulting in deactivation and reduced stability. Therefore, constructing a suitable catalyst carrier is also crucial to improving the dispersion and effective utilization of the catalyst active sites. Porous carriers can improve the dispersion of active components, effectively reduce metal agglomeration, facilitate the adsorption of macromolecular compounds such as tar, make it easier for the metal active sites in the pores to fully contact them, and improve the catalytic performance of the catalyst, but how to achieve this specifically requires further research. Summary of the invention:

[0004] The purpose of the present invention is to provide a method for preparing a green carbon-based catalyst using biomass waste as raw material and its application in preparing synthesis gas by biomass gasification.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing a green carbon-based catalyst using biomass waste as raw material, the method comprising the following steps:

[0007] (1) washing the biomass waste raw material with alkali solution, drying it, crushing it, and sieving it to obtain biomass particles with a mesh size of 10 to 60;

[0008] (2) mixing an alkali metal salt or an alkaline earth metal salt (compound A) with an acetic acid or nitrate of a transition metal (compound B) to obtain a mixture, then adding water to the mixture and mixing the mixture with biomass particles to uniformly stir, and standing for 1 to 3 hours to obtain a catalyst precursor;

[0009] (3) placing the catalyst precursor in a tubular furnace and calcining it in a water vapor atmosphere at a temperature of 300° C. to 550° C. for a time of 2 h to 12 h. After the reaction is completed, cooling is performed to obtain a green carbon-based catalyst.

[0010] Preferably, the biomass waste raw material in step (1) is selected from one or more of wheat straw, corn straw, rice straw, cotton straw, peanut straw, corn cobs, peanut shells, bran, rice husks, wood, sawdust, branches, bark, leaves, bamboo, and weeds.

[0011] Preferably, the mass concentration of the alkali solution in step (1) is 1% to 20%, more preferably 10% to 20%, the solid-liquid ratio of the biomass waste raw material to the alkali solution is 1:3 to 10 (raw material dry basis, by mass), more preferably 1:3 to 7, and the type of alkali in the alkali solution is selected from one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia water, mixed in any proportion.

[0012] Preferably, in step (2), the alkali metal salt or alkaline earth metal salt (compound A) is selected from one or more of sodium acetate, sodium nitrate, sodium carbonate, potassium acetate, potassium nitrate, potassium carbonate, calcium carbonate, calcium acetate, calcium nitrate, magnesium carbonate, magnesium acetate, magnesium nitrate, barium carbonate, barium chloride, barium acetate, and barium nitrate, and they are mixed in any proportion; the transition metal acetate or nitrate (compound B) is selected from one or more of ferric acetate, ferric nitrate, copper acetate, copper nitrate, zinc acetate, zinc nitrate, nickel acetate, nickel nitrate, cerium acetate, and cerium nitrate, and they are mixed in any proportion.

[0013] Preferably, in step (2), the mass ratio of the alkali metal salt or alkaline earth metal salt (compound A) to the acetic acid or nitrate of the transition metal (compound B) is 1:0.5-9, more preferably 1:0.5-4, and the mass ratio of the mixture (compound A and compound B) to the dry basis of the biomass particles is 1-20:1, more preferably 10-20:1.

[0014] Preferably, the water vapor flow rate in step (3) is 5 to 50 ml / min.

[0015] Another object of the present invention is to protect the use of the green carbon-based catalyst obtained by the above method in preparing synthesis gas by biomass gasification.

[0016] Preferably, the green carbon-based catalyst is used for catalytic cracking-steam gasification reforming of agricultural, forestry and animal husbandry organic waste to prepare hydrogen-rich synthesis gas, the reaction temperature is 570-590° C., and the hydrogen gas volume fraction in the obtained synthesis gas is ≥55%.

[0017] Preferably, the green carbon-based catalyst can be recycled multiple times and the catalytic efficiency remains stable.

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) The present invention uniformly mixes biomass particles and active metal components and then calcines them in one step. During the carbonization process, the active metal components can be evenly distributed in the carbon skeleton structure and form stable structures such as metal carbides and metal nitrides with elements such as C and N in the biomass waste;

[0020] (2) The synergistic catalytic system constructed by the combined action of alkaline (earth) metals, transition metals and carbon-based carriers in the present invention can inhibit the generation of by-products in the synthesis gas preparation process and improve the yield and quality of synthesis gas. The coupled synergistic effect not only reduces the activation energy of the gasification process, but also can etch the carbonization of biomass waste to form a porous structure, which has a good adsorption capacity for macromolecules such as tar, is beneficial to the catalytic conversion of tar, and can further increase the hydrogen content in biomass synthesis gas;

[0021] (3) In the calcination process of the present invention, inexpensive water is used as the atmosphere source, and no additional inert gas is required, which not only saves costs, but also the reducing gases H2 and CO generated by the reaction of biomass particles with water vapor during the carbonization process can directly reduce the transition metal to a low-valent or zero-valent metal, which has the following advantages: First, there is no need to introduce reducing gas again before use to reduce the catalyst at high temperature, which not only simplifies the use process, but also greatly saves resources and energy consumption; second, the reduction of transition metals to low-valent or zero-valent metals can effectively reduce the activation energy of the biomass gasification reaction to produce synthesis gas, and the gasification reaction temperature is reduced from more than 750°C to less than 600°C, thereby increasing the hydrogen yield and reducing the influence of the type of biomass raw materials on the gaseous products, thereby achieving the unity of high activity, high stability and high selectivity.

[0022] (4) The green carbon-based catalyst of the present invention can be reused multiple times, and the catalytic effect is maintained well, thereby reducing the cost of using the catalyst;

[0023] (5) The present invention utilizes biomass waste, which is widely available and inexpensive, as the raw material of the catalyst carrier, thereby realizing the resource utilization of biomass waste. The active metal is also relatively cheap, which reduces the production cost of the catalyst. In addition, the preparation process of the catalyst is simple, and it has good application prospects in the industrial preparation of hydrogen-rich synthesis gas.

[0024] In summary, the present invention utilizes biomass waste, which is widely available and inexpensive, as the raw material of the catalyst carrier, and uses alkaline (earth) metals and transition metals as active components of synergistic catalysis. A green carbon-based catalyst is directly synthesized through a process with simple procedures, low operating difficulty, and low energy consumption. The active catalytic metal in the catalyst is highly uniformly dispersed on the skeleton structure of the biomass waste carbon-based carrier, and forms stable structures such as metal carbides and metal nitrides with the C and N elements in the biomass waste, and has good catalytic activity and stability for biomass gasification conversion; when the catalyst is used for biomass catalytic cracking-steam gasification reforming to prepare hydrogen-rich synthesis gas, since during the catalyst preparation process, the biomass Waste is calcined in a water vapor atmosphere so that H2 and CO generated during the calcination process can reduce transition metals to low-valent or zero-valent metals. The catalyst does not need to be introduced into the reducing gas for high-temperature reduction before use, thus saving resources and energy consumption. At the same time, it can effectively reduce the activation energy of the biomass gasification reaction to produce synthesis gas, and the gasification reaction temperature is reduced from above 750°C to below 600°C, thereby increasing the hydrogen yield and reducing the influence of the type of biomass raw materials on the gaseous products, thus achieving the unity of high activity, high stability and high selectivity. In addition, the active metal can etch the carbon matrix to form a porous carbon structure, which is beneficial to the adsorption of macromolecular substances such as tar, further reducing the tar yield and promoting the process of preparing hydrogen-rich synthesis gas by biomass gasification. Description of the drawings:

[0025] Figure 1 This is a comparison chart of the catalytic performance of 1-1# green carbon-based catalyst synthesized in Example 1 after 10 cycles. Specific implementation method:

[0026] The following is a further description of the present invention, rather than a limitation of the present invention.

[0027] Example 1: A method for preparing green carbon-based catalyst from biomass waste

[0028] The following steps are involved:

[0029] (1) 10 g of wheat straw (dry basis weight) was taken as a raw material, soaked in a 20% mass concentration alkali solution prepared by 6 g of potassium hydroxide and 24 g of water, washed, dried, crushed, and sieved to obtain wheat straw particles of 10 to 60 meshes;

[0030] (2) 0.3 g of the wheat straw particles obtained in step (1), 4 g of an alkali (earth) metal salt mixture A (3 g of potassium carbonate, 1 g of calcium acetate), 2 g of a transition metal salt mixture B (1.5 g of ferric nitrate, 0.5 g of cerium acetate) and 6 g of water were placed in a beaker and stirred to mix evenly, and allowed to stand for 1 hour to obtain a catalyst precursor;

[0031] (3) The catalyst precursor in step (2) is placed in a tubular furnace and calcined in a water vapor atmosphere at a flow rate of 20 ml / min, heated to 550° C. and calcined for 2 h. After natural cooling, the solid product is collected, which is the 1-1# green carbon-based catalyst.

[0032] Example 2

[0033] The same as Example 1, except that: in step (1), the mass concentration of potassium hydroxide is 10%, and the solid-liquid ratio of wheat straw to alkali solution is 1:7; in step (2), the ratio of alkali (earth) metal salt mixture A and transition metal salt mixture B is 1:4, and the ratio of wheat straw to metal mixture is 1:10, to obtain 1-2# green carbon-based catalyst.

[0034] Example 3

[0035] The same as Example 1, except that: in step (1), the mass concentration of potassium hydroxide is 1%, and the solid-liquid ratio of wheat straw to alkali solution is 1:10; in step (2), the ratio of alkali (earth) metal salt mixture A and transition metal salt mixture B is 1:9, and the ratio of wheat straw to metal mixture is 1:1, to obtain 1-3# green carbon-based catalyst.

[0036] Comparative Example 1:

[0037] Refer to Example 1, except that no transition metal salt mixture B is added in step (2), and the resulting catalyst is recorded as 1-A.

[0038] Comparative Example 2:

[0039] Referring to Example 1, the difference is that no alkaline (earth) metal salt mixture A is added in step (2), and the obtained catalyst is recorded as 1-B.

[0040] Example 4

[0041] A method for preparing a green carbon-based catalyst from biomass waste comprises the following steps:

[0042] (1) taking 100 g corn cob (dry basis weight) as a raw material, soaking it in a 10% mass concentration alkali solution prepared by 60 g sodium hydroxide, 10 g calcium hydroxide and 630 g water, washing, drying, crushing and sieving to obtain corn cob particles of 10 to 60 meshes;

[0043] (2) 1 g of the corncob particles obtained in step (1), 2 g of an alkali (earth) metal salt mixture A (1.6 g of sodium acetate, 0.2 g of potassium nitrate, and 0.2 g of barium carbonate), 8 g of a transition metal salt B (nickel nitrate), and 15 g of water were placed in a beaker, stirred to mix evenly, and allowed to stand for 2 h to obtain a catalyst precursor;

[0044] (3) The catalyst precursor in step (2) is placed in a tubular furnace and calcined in a water vapor atmosphere at a flow rate of 5 ml / min, heated to 450° C. and calcined for 6 h. After natural cooling, the solid product is collected, which is the 2# green carbon-based catalyst.

[0045] Example 5

[0046] A method for preparing a green carbon-based catalyst from biomass waste comprises the following steps:

[0047] (1) 10 g of sawdust (dry basis weight) was taken as a raw material, soaked in a 1% mass concentration alkali solution prepared by 4 g of concentrated ammonia water (25% mass concentration) and 96 g of water, washed, dried, crushed, and sieved to obtain sawdust particles of 10 to 60 meshes;

[0048] (2) 4 g of the wood pellets obtained in step (1), 0.4 g of alkaline earth metal salt A (magnesium nitrate), 3.6 g of transition metal salt mixture B (3 g of copper nitrate, 0.6 g of cerium nitrate) and 8 g of water were placed in a beaker and stirred to mix evenly, and allowed to stand for 3 h to obtain a catalyst precursor;

[0049] (3) The catalyst precursor in step (2) is placed in a tubular furnace and calcined in a water vapor atmosphere at a flow rate of 50 ml / min, heated to 300° C. and calcined for 12 h. After natural cooling, the solid product is collected, which is the 3# green carbon-based catalyst.

[0050] Example 6

[0051] An application of a green carbon-based catalyst in the field of synthesis gas production comprises the following steps:

[0052] In order to verify the catalytic effect of green carbon-based catalysts on the preparation of hydrogen-rich synthesis gas, the effect evaluation was carried out on a gasification reactor device. 4.5g of the catalyst prepared in Example 1-5 and Comparative Example 1-2 was mixed evenly with 15g of sawdust (dry basis mass) (total weight 19.5g), and sent to a gasification reactor for gasification reaction, using water vapor as a gasifying agent, a gasification temperature of 580°C, a gasification time of 6h, and the gasification reaction conditions were the same. At the same time, a comparative experiment without catalyst active ingredients (the catalyst did not add alkali (earth) metal salt mixture A, nor did it add transition metal salt mixture B) under the same gasification conditions was carried out. The gas output was recorded by a gas flowmeter, and the gas composition was analyzed by a gas chromatograph. The tar content in the gas was tested in accordance with the national standard GB / T40508-2021 "Determination of tar and dust content in biomass gas". The catalytic effects are shown in Table 1. The yields of hydrogen-rich synthesis gas produced by the five catalysts are much higher than the catalytic effect of no catalyst, and the hydrogen content in the synthesis gas is higher than 60%, and the tar yield is also greatly reduced compared with no catalyst. From the comparison of the catalytic effects of the catalyst (1-1#) prepared in Example 1, the catalyst prepared in Comparative Example 1 (Comparative 1-A), the catalyst prepared in Comparative Example 2 (Comparative 1-B), and the catalyst without adding the alkali (earth) metal salt mixture A and the transition metal salt mixture B (catalyst-free, as a blank control) in Table 1, it can be seen that the alkali (earth) metal and transition metal in Example 1 of the present invention, as active components of synergistic catalysis, significantly increase the yield of hydrogen-rich synthesis gas.

[0053] Table 1 Catalytic gas production effects of five carbon-based catalysts and reactions without catalysts

[0054]

[0055] The term "catalyst-free" in Table 1 means that neither the alkaline (earth) metal salt mixture A nor the transition metal salt mixture B is added to the catalyst.

[0056] Example 7

[0057] In order to verify the recycling ability of carbon-based catalysts, the following cycle test can be carried out. The specific experimental steps are as follows:

[0058] The experiment was conducted using 1-1# carbon-based catalyst, and the gasification reaction conditions were the same as those in Example 6. After each gasification reaction, the bottom residue (containing the catalyst) was collected, weighed after drying, and supplemented with sawdust to a total weight of 19.5 g, and loaded into a gasification reactor device for effect evaluation. The effect of the catalyst recycling is shown in the following table. After 10 cycles, the gas production can maintain 97% of the initial gas production, the volume ratio of the hydrogen component is maintained at more than 61%, and the proportion of each gas component is also basically stable. The tar content increases slightly with the increase in the number of cycles, but the increase is not large.

[0059] Table 21-1# Effect of catalytic gas production by recycling carbon-based catalyst

[0060]

[0061] Example 8

[0062] Referring to Example 6, 1-1# carbon-based catalyst was selected, except that various organic wastes of agriculture, forestry and animal husbandry, including wheat straw, corn straw, eucalyptus branches, eucalyptus bark, grapevine, bamboo powder, cow dung and sugarcane bagasse, were used as cracking and gasification raw materials. The catalytic gas production effect is shown in Table 3. Different raw material components result in different syngas production and tar content, but the volume ratio of hydrogen component in syngas is higher than 57%.

[0063] Table 31-1# Carbon-based catalyst catalytic gas production effect on different agricultural, forestry and animal husbandry organic waste raw materials

[0064]

[0065] The description of the above embodiments is only used to help understand the technical solution and core ideas of the present invention. It should be pointed out that for technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a green carbon-based catalyst using biomass waste as raw material, characterized in that: The method comprises the following steps: (1) washing the biomass waste raw material with alkali solution, drying it, crushing it, and sieving it to obtain biomass particles with a mesh size of 10 to 60; (2) mixing an alkali metal salt or an alkaline earth metal salt with an acetic acid or a nitrate of a transition metal to obtain a mixture, then adding water to the mixture and mixing it with biomass particles to uniformly stir, and letting it stand for 1 to 3 hours to obtain a catalyst precursor; (3) placing the catalyst precursor in a tubular furnace and calcining it in a water vapor atmosphere at a temperature of 300° C. to 550° C. for a time of 2 h to 12 h. After the reaction is completed, cooling is performed to obtain a green carbon-based catalyst.

2. The method according to claim 1, characterized in that In step (1), the biomass waste raw material is selected from one or more of wheat straw, corn straw, rice straw, cotton straw, peanut straw, corn cob, peanut shell, bran, rice husk, wood, sawdust, branches, bark, leaves, bamboo and weeds.

3. The method according to claim 1, characterized in that The mass concentration of the alkali solution in step (1) is 1% to 20%; the solid-liquid ratio of the biomass waste raw material to the alkali solution is 1:3 to 10 based on the dry weight of the raw materials; the type of alkali in the alkali solution is selected from one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia water, and mixed in any proportion.

4. The method according to claim 3, characterized in that: The mass concentration of the alkali solution in step (1) is 10% to 20%; Calculated on the dry basis weight of the raw materials, the solid-liquid ratio of the biomass waste raw materials to the alkali solution is 1:3-7.

5. The method according to claim 1, characterized in that: In step (2), the alkali metal salt or alkaline earth metal salt is selected from one or more of sodium acetate, sodium nitrate, sodium carbonate, potassium acetate, potassium nitrate, potassium carbonate, calcium carbonate, calcium acetate, calcium nitrate, magnesium carbonate, magnesium acetate, magnesium nitrate, barium carbonate, barium chloride, barium acetate, and barium nitrate, and they are mixed in any proportion; the transition metal acetate or nitrate is selected from one or more of ferric acetate, ferric nitrate, copper acetate, copper nitrate, zinc acetate, zinc nitrate, nickel acetate, nickel nitrate, cerium acetate, and cerium nitrate, and they are mixed in any proportion.

6. The method according to claim 1, characterized in that In step (2), the mass ratio of the alkali metal salt or alkaline earth metal salt to the acetic acid or nitrate of the transition metal is 1:0.5-9, and the mass ratio of the mixture to the dry basis of the biomass particles is 1-20:

1.

7. The method according to claim 1, characterized in that In step (2), the mass ratio of the alkali metal salt or alkaline earth metal salt to the acetic acid or nitrate of the transition metal is 1:0.5-4, and the mass ratio of the mixture to the dry basis of the biomass particles is 10-20:

1.

8. The method according to claim 1, characterized in that: In step (3), the water vapor flow rate is 5 to 50 ml / min.

9. Use of the green carbon-based catalyst obtained by the method of claim 1 in preparing synthesis gas by biomass gasification.

10. The use according to claim 9, characterized in that: The green carbon-based catalyst is used for catalytic cracking-steam gasification reforming of agricultural, forestry and animal husbandry organic waste to prepare hydrogen-rich synthesis gas, and the reaction temperature is 570-590°C.

Images