A method for preparing CO by pyrolysis of biomass

Abstract

The present invention discloses a method for preparing CO by pyrolyzing biomass. The pyrolysis method utilizes the dual functions of calcium oxide (CaO) and an oxygen carrier to increase the yield and purity of CO. The specific method is as follows: (1) Raise the temperatures of the biomass, CaO, and the oxygen carrier to 550 °C. CaO will react with the generated CO2 to form CaCO3. This process is beneficial for the pyrolysis of biomass to produce high-purity hydrogen (H2), and the generated H2 can reduce the oxygen carrier; (2) When the reaction temperature is further raised to 700 °C, CaCO3 will decompose and release CO2 again. The released CO2 can react with the carbon (C) in the remaining solid substances, so that a part of the solid C is gasified to form CO; in addition, the reduced oxygen carrier will react with CO2 at 700 °C to form CO. Therefore, this method can effectively promote the directional conversion of CO2 to CO, thus avoiding the problem of waste of a large amount of C elements in biomass and realizing the recycling of resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass pyrolysis, and particularly relates to a method for preparing CO by pyrolyzing biomass. Background Art

[0002] In recent years, extreme weather has occurred frequently in many parts of the world, seriously threatening the sustainable development of humanity. Controlling carbon dioxide emissions has become one of the great challenges currently faced globally. In the long run, the development and utilization of renewable energy are the only way to achieve the carbon emission reduction goal. Biomass energy is the only renewable energy that can be directly converted into solid, liquid, and gaseous products that are convenient for storage and transportation, which can effectively make up for the randomness and uncertainty of renewable energies such as wind energy and solar energy. Therefore, the development of biomass energy is of great significance for establishing a continuous, reliable, and safe renewable energy system.

[0003] So far, thermochemical treatment is an effective method for treating biomass. Incineration for power generation is the most common thermochemical treatment technology at present, and other emerging technologies mainly include pyrolysis and gasification. Different from incineration that directly recovers heat from sludge, pyrolysis and gasification can produce value-added chemicals or fuels, such as biochar, liquid fuels, and syngas. Among these products, syngas, mainly composed of hydrogen and carbon monoxide, has received extensive attention and research because it is the raw material for producing high-value-added chemicals and liquid fuels in chemical processes such as Fischer-Tropsch synthesis. Preparing syngas using biomass energy can provide a sustainable, green, and low-carbon approach for the synthesis of value-added chemicals and liquid fuels, and accelerate the carbon emission reduction process.

[0004] Since H 2 has both high calorific value and clean energy attributes, traditional pyrolysis / gasification processes mostly focus on the preparation of H 2 so that the purity can reach 70 - 80 vol%. However, compared with the content of the C element, the content of the hydrogen (H) element in organic solid waste is relatively low (5.0 - 7.8 wt%, see Table 1), only about 10 - 15% of the content of the C element. And the traditional sorption-enhanced gasification process only recovers the H element therein and does not pay attention to the C element, which is undoubtedly a huge waste of organic solid waste resources.

[0005] Table 1 Elemental composition of organic solid waste (wt%, ash-free dry basis)

[0006]

[0007] Based on the problems existing in the current biomass pyrolysis / gasification, it is necessary to improve it. Summary of the Invention

[0008] The present invention provides a method for preparing CO by pyrolyzing biomass to solve or at least partially solve the problem of waste of the C element existing in the prior art.

[0009] The present invention provides a biomass pyrolysis method, comprising the following steps:

[0010] Dry and crush the biomass to obtain small-sized biomass solids;

[0011] Mix the biomass solids with an additive, granulate, and screen to obtain a mixture;

[0012] Place the mixture in a quartz tube, and place an oxygen carrier (LaCo 0.6 Fe 0.4 O 3 / CeO 2 ) on the upper layer;

[0013] Place the quartz tube in a tube furnace and pyrolyze it in an inert gas;

[0014] Wherein, the additive comprises CaO with different masses.

[0015] Preferably, the biomass is naturally dried and crushed to obtain biomass solids.

[0016] Preferably, the particle size of the mixture is 0.5 - 0.85 mm.

[0017] Preferably, the mass ratio of biomass solids to CaO is 6:4, 7:3, 8:2, and 9:1.

[0018] Preferably, a certain amount of LaCo 0.6 Fe 0.4 O 3 / CeO 2 is added.

[0019] Preferably, the pyrolysis temperature is greater than 500 °C.

[0020] Preferably, the pyrolysis temperature is 550 and 700 °C.

[0021] Preferably, the step of placing the mixture in a tube furnace and pyrolyzing it in an inert gas is specifically: place the mixture in a tube furnace, then purge it with an inert gas at a rate of 30 mL / min for 30 - 40 min, and then carry out pyrolysis.

[0022] Preferably, the heating rate of the tube furnace is 30 °C / min, and the pyrolysis time is 100 min.

[0023] Preferably, the inert gas includes helium or nitrogen, etc.

[0024] The biomass pyrolysis method of the present invention has the following beneficial effects compared with the prior art:

[0025] The biomass pyrolysis method of the present invention uses a metal oxide (CaO) as an additive and also adds an oxygen carrier (LaCo 0.6 Fe 0.4 O 3 / CeO 2 ). At 550 °C, CaO reacts with the generated CO 2 to form CaCO 3 , which is beneficial for the pyrolysis of biomass to produce high-purity hydrogen (H 2 ). The generated H 2 can reduce the oxygen carrier; when the reaction temperature further rises to 700 °C, CaCO 3 will decompose and release CO 2 again. The released CO 2 can react with the carbon (C) in the remaining solid substances, causing a part of the solid C to gasify into CO; in addition, the reduced oxygen carrier reacts with CO 2 to form CO at 700 °C. Therefore, this method can effectively promote the directional conversion of CO 2 to CO, avoiding the waste of a large amount of C elements in biomass and realizing the recycling of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for the description of the embodiments or the prior art.

[0027] Figure 1 Shows the yields of pyrolysis gas after pyrolysis at 550 °C for the pyrolysis methods in Examples 1-4 and Comparative Example 1 of the present invention;

[0028] Figure 2 Shows the yields of pyrolysis gas after pyrolysis at 700 °C for the pyrolysis methods in Examples 1-4 and Comparative Example 1 of the present invention;

[0029] Figure 3 Shows the purity of CO in the pyrolysis gas after pyrolysis at 700 °C for the pyrolysis methods in Examples 1-4 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with 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 them. 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.

[0031] The embodiments of the present application provide a biomass pyrolysis method, including the following steps:

[0032] S1. Dry and crush the biomass to obtain biomass solids with a small particle size;

[0033] S2. Mix the biomass solids with an additive, granulate, and screen to obtain a mixture;

[0034] S3. Place the mixture in a quartz tube and place an oxygen carrier (LaCo 0.6 Fe 0.4 O 3 / CeO 2 ) on the upper layer;

[0035] S4. Place the quartz tube in a tube furnace and pyrolyze it in an inert gas;

[0036] Wherein, the additive includes CaO with different masses.

[0037] The biomass pyrolysis method of the present application is used to prepare CO in the pyrolysis gas obtained after biomass pyrolysis; in the biomass pyrolysis method of the present application, the additive is a metal oxide (CaO), and at the same time, an oxygen carrier (LaCo 0.6 Fe 0.4 O 3 / CeO 2 ) is added. At 550 °C, CaO will react with the generated CO 2 to form CaCO 3 , this process is beneficial to the generation of high-purity hydrogen (H 2 ) during biomass pyrolysis, and the generated H 2 can reduce the oxygen carrier; when the reaction temperature further rises to 700 °C, CaCO 3 will decompose and release CO 2 again, and the released CO 2 can react with the carbon (C) in the remaining solid substances, so that a part of the solid C is gasified to generate CO; in addition, the reduced oxygen carrier will react with CO 2 to generate CO at 700 °C. Therefore, this method can effectively promote the directional conversion of CO 2 to CO, thus avoiding the problem of waste of a large amount of C elements in biomass and realizing the recycling of resources.

[0038] In some embodiments, the biomass is dried and crushed to obtain biomass solids with a small particle size.

[0039] In some embodiments, the particle size of the mixture is 0.5 - 0.85 mm. The biomass solids and the additive are mixed, granulated, and screened according to a certain mass ratio to obtain a mixture with a particle size of 0.5 - 0.85 mm.

[0040] In some embodiments, the pyrolysis temperature is 550 - 700 °C, preferably 550 °C and 700 °C. In the present application, CaO adsorbs the CO generated during the pyrolysis process. 2 When adsorbing CO, the pyrolysis temperature is crucial. By adjusting the pyrolysis temperature to 550 °C, a large amount of CO can be adsorbed by CaO at this temperature. 2 Thereby, the yield and purity of CO at 700 °C are improved.

[0041] In some embodiments, the pyrolysis of the mixture in an inert gas in a tubular furnace is specifically as follows: Place the mixture in a tubular furnace, then introduce an inert gas at a rate of 30 mL / min for purging for 30 - 40 min, and then carry out pyrolysis.

[0042] In some embodiments, the pyrolysis time is 100 min.

[0043] In some embodiments, the inert gas includes helium or nitrogen, etc.

[0044] The following further illustrates the biomass pyrolysis method of the present application with specific examples. The biomass used in the following examples is from wheat straw waste in a certain farmland. The moisture content of the straw is 5.60%, the volatile matter content is 83.48%, the ash content is 6.23%, and the fixed carbon content is 4.69%. In the following examples and comparative examples, the composition and relative content of the pyrolysis gas are measured by a gas chromatograph (GC); CaO is purchased from Shanghai Macklin Biochemical Co., Ltd.

[0045] Example 1

[0046] The embodiment of the present application provides a biomass pyrolysis method, including the following steps:

[0047] S1. Naturally dry and crush the biomass to obtain small - sized biomass solids;

[0048] S2. Mix 0.18 g of biomass solids and 0.02 g of CaO evenly, granulate, and screen to obtain a mixture;

[0049] S3. Place the mixture in a quartz tube, and put 0.06 g of oxygen carrier on the upper layer. Separate the mixture and the oxygen carrier with quartz wool in the middle;

[0050] S4. Place the quartz tube in a tubular furnace, introduce helium into the tubular furnace at 30 mL / min, and purge for 30 min to create an anaerobic condition;

[0051] S5. Heat the tubular furnace from room temperature to 550 °C at a heating rate of 30 °C / min, and keep it at a constant temperature for 50 min for pyrolysis. Then, heat it to 700 °C at the same heating rate and keep it at a constant temperature for 50 min. During the pyrolysis process, the content and purity of the pyrolysis gas are measured in real - time.

[0052] The yields of CO, CH 4 , CO 2 and H 2 in the pyrolysis gas measured at 550 °C are 9.00, 6.02, 53.37, 12.98 mL / g dry sample respectively; the yields of CO, CH 4 , CO 2 and H 2 in the pyrolysis gas measured at 700 °C

[0053] are 105.07, 0, 17.58, 3.21 mL / g dry sample respectively, and the CO purity is 83.48%.

[0054] Example 2

[0055] An embodiment of the present application provides a biomass pyrolysis method, including the following steps:

[0056] S1. Naturally dry and crush the biomass to obtain biomass solids with a small particle size;

[0057] S2. Mix 0.16 g of biomass solids and 0.04 g of CaO evenly, granulate and screen to obtain a mixture;

[0058] S3. Place the mixture in a quartz tube, and put 0.06 g of oxygen carrier on the upper layer. Separate the mixture and the oxygen carrier with quartz wool;

[0059] S4. Place the quartz tube in a tube furnace, and introduce helium into the tube furnace at a rate of 30 mL / min, and purge for 30 min to create an anaerobic condition;

[0060] S5. Heat the tube furnace from room temperature to 550 °C at a heating rate of 30 °C / min, and keep it at a constant temperature for 50 min for pyrolysis. Then, heat it to 700 °C at the same heating rate and keep it at a constant temperature for 50 min. During the pyrolysis process, the content and purity of the pyrolysis gas are measured in real time.

[0061] The yields of CO, CH 4 , CO 2 and H 2 in the pyrolysis gas measured at 550 °C are 8.84, 2.93, 38.10, 15.42 mL / g dry sample respectively; the yields of CO, CH 4 , CO 2 and H 2 in the pyrolysis gas measured at 700 °C are 137.36, 0, 24.42, 1.16 mL / g dry sample respectively, and the CO purity is 84.30%.

[0062] Example 3

[0063] An embodiment of the present application provides a biomass pyrolysis method, including the following steps:

[0064] S1. Naturally dry and crush the biomass to obtain small-particle-size biomass solids;

[0065] S2. Mix 0.14 g of biomass solids and 0.06 g of CaO evenly, granulate, and screen to obtain a mixture;

[0066] S3. Place the mixture in a quartz tube, put 0.06 g of oxygen carrier on the upper layer, and separate the mixture and the oxygen carrier with quartz wool in the middle;

[0067] S4. Place the quartz tube in a tube furnace, introduce helium into the tube furnace at a rate of 30 mL / min, and purge for 30 min to create an anaerobic condition;

[0068] S5. Heat the tube furnace from room temperature to 550 °C at a heating rate of 30 °C / min, keep it at a constant temperature for 50 min for pyrolysis, then heat it to 700 °C at the same heating rate, and keep it at a constant temperature for 50 min. During the pyrolysis process, measure the content and purity of the pyrolysis gas in real time.

[0069] Measure the yields of CO, CH 4 , CO 2 and H 2 in the pyrolysis gas at 550 °C are 11.07, 6.21, 36.47, 18.49 mL / g dry sample respectively; measure the yields of CO, CH 4 , CO 2 and H 2 in the pyrolysis gas at 700 °C are 154.38, 0, 33.94, 0.66 mL / g dry sample , and the purity of CO is 81.70%.

[0070] Example 4

[0071] An embodiment of the present application provides a biomass pyrolysis method, including the following steps:

[0072] S1. Naturally dry and crush the biomass to obtain small-particle-size biomass solids;

[0073] S2. Mix 0.12 g of biomass solids and 0.08 g of CaO evenly, granulate, and screen to obtain a mixture;

[0074] S3. Place the mixture in a quartz tube, put 0.06 g of oxygen carrier on the upper layer, and separate the mixture and the oxygen carrier with quartz wool in the middle;

[0075] S4. Place the quartz tube in a tube furnace, introduce helium into the tube furnace at a rate of 30 mL / min, and purge for 30 min to create an anaerobic condition;

[0076] S5. Heat the tube furnace from room temperature to 550 °C at a heating rate of 30 °C / min, and keep it at a constant temperature for 50 min for pyrolysis. Then, heat it to 700 °C at the same heating rate and keep it at a constant temperature for 50 min. During the pyrolysis process, measure the content and purity of the pyrolysis gas in real time.

[0077] At 550 °C, the yields of CO, CH 4 , CO 2 and H 2 are 10.18, 8.21, 17.56, and 20.87 mL / g respectively dry sample ; at 700 °C, the yields of CO, CH 4 , CO 2 and H 2 are 167.57, 0, 49.07, and 1.89 mL / g respectively dry sample , and the purity of CO is 76.68%.

[0078] Comparative Example 1

[0079] This comparative example provides a biomass pyrolysis method, including the following steps:

[0080] S1. Naturally dry and crush the biomass to obtain small-sized biomass solids;

[0081] S2. Place 0.20 g of biomass solids in a tube furnace, introduce helium into the tube furnace at a rate of 30 mL / min, and purge for 30 min to create an anaerobic condition;

[0082] S3. Heat the tube furnace from room temperature to 550 °C at a heating rate of 30 °C / min, and keep it at a constant temperature for 50 min for pyrolysis. Then, heat it to 700 °C at the same heating rate and keep it at a constant temperature for 50 min. During the pyrolysis process, measure the content and purity of the pyrolysis gas in real time.

[0083] At 550 °C, the yields of CO, CH 4 , CO 2 and H 2 are 8.55, 6.87, 72.01, and 15.67 mL / g respectively dry sample ; at 700 °C, the yields of CO, CH 4 , CO 2 and H 2The yields are 34.58, 0, 11.82, and 2.27 mL / g respectively dry sample , and the CO purity is 71.05%.

[0084] Figure 1 Shows the yields of H 2 , CO, and CO 2 and CH 4 during the pyrolysis process at 550 °C for the pyrolysis methods in Examples 1-4 and Comparative Example 1. Among them, 0% CaO represents Comparative Example 1, 10% CaO represents Example 1, 20% CaO represents Example 2, 30% CaO represents Example 3, and 40% CaO represents Example 4.

[0085] Figure 2 Shows the yields of H 2 , CO, and CO 2 during the pyrolysis process at 700 °C for the pyrolysis methods in Examples 1-4 and Comparative Example 1. Among them, 0% CaO represents Comparative Example 1, 10% CaO represents Example 1, 20% CaO represents Example 2, 30% CaO represents Example 3, and 40% CaO represents Example 4.

[0086] Figure 3 Shows the purity of CO after pyrolysis at 700 °C for the pyrolysis methods in Examples 1-4 and Comparative Example 1.

[0087] From the data of the above Examples 1-4 and the comparative examples, it can be seen that at 550 °C, as the CaO content increases, the CO 2 yield continuously decreases because CaO reacts with the generated CO 2 to form CaCO 3 (Eq.1). At the same time, this process is beneficial to the pyrolysis of biomass to produce high-purity hydrogen (H 2 ), and the generated H 2 can reduce the oxygen carrier (Eq.2). When the reaction temperature is further increased to 700 °C, for the CO purity, it is the highest at 20% CaO, reaching 84.30%. At the same time, it can be seen that the CO yield increases significantly with the increase of the CaO content. The highest yield increases from 34.58 mL / g dry sample to 167.57 mL / g dry sample , which is 3.8 times higher. The increase in the CO yield is due to the dual action of CaO and the oxygen carrier. At 700 °C, CaCO 3 will decompose and release CO 2 again (Eq.3), and the released CO 2It can react with carbon (C) in the remaining solid substances, causing a part of the solid C to gasify to form CO (Eq. 4); in addition, the reduced oxygen carrier will react with CO at 700 °C 2 to form CO (Eq. 5).

[0088] CaO + CO 2 CaCO 3 (Eq. 1)

[0089] MeO y + H 2 MeO y-1 + H 2 O (Eq. 2)

[0090] CaCO 3 CaO + CO 2 (Eq. 3)

[0091] CO 2 + C 2CO (Eq. 4)

[0092] MeO y-1 + CO 2 CO + MeO y (Eq. 5)

[0093] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing CO by pyrolyzing biomass, characterized in that it comprises the following steps: (1) Drying and crushing the biomass to obtain a biomass solid; (2) Mixing the biomass solid with an additive, granulating, and screening to obtain a mixture; (3) Placing the mixture in a quartz tube and placing an oxygen carrier on the upper layer; placing the quartz tube in a tube furnace and pyrolyzing it in an inert gas; Among them, the additive includes CaO with different masses, and the mass ratio of the biomass solid to the additive is 6:4, 7:3, 8:2, and 9:1; the oxygen carrier is LaCo 0.6 Fe 0.4 O 3 / CeO 2 ; for the pyrolysis, first pyrolyze at 550 °C and keep the temperature constant for 50 min, then raise the temperature to 700 °C and keep the temperature constant for 50 min.

2. The method for preparing CO by pyrolyzing biomass according to claim 1, characterized in that the particle size of the mixture in step (2) is 0.5 - 0.85 mm.

3. The method for preparing CO by pyrolyzing biomass according to claim 1, characterized in that pyrolyzing the mixture in a tube furnace in an inert gas specifically means: placing the quartz tube in a tube furnace, then purging with an inert gas at a rate of 30 mL / min for 30 - 40 min, and then performing pyrolysis.

4. The method for preparing CO by pyrolyzing biomass according to claim 3, characterized in that the heating rate of the tube furnace is 30 °C / min and the pyrolysis time is 100 min.

5. The method for preparing CO by pyrolyzing biomass according to claim 1, characterized in that the inert gas includes helium or nitrogen.

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