Heavy bio-oil and biomass synergistic pyrolysis carbon sequestration method and bio-carbon

Abstract

The invention discloses a heavy bio-oil and biomass synergistic pyrolysis carbon sequestration method, which comprises the following steps: mixing crushed biomass and heavy bio-oil according to a mass ratio to obtain a mixture, the heavy bio-oil being bio-oil distillation residue; and pyrolyzing the mixture in an inert gas atmosphere to obtain the biochar. Therefore, the bio-oil distillation residues are used for assisting the moso bamboo pyrolysis to generate a carbon sequestration synergistic effect, the yield of the biochar is increased, and more carbon elements in the biomass are reserved in the biochar. The high retention rate of the carbon element in the biochar is also beneficial to improving the combustion heat value of the biochar as alternative fuel, enhancing the thermal stability of the biochar fuel, improving the fuel performance of the biochar, and enabling the biochar combustion process to approach to fossil fuel.

Description

Technical Field

[0001] The invention relates to the field of biochar production, and in particular to a method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass. Background Art

[0002] Excessive use of fossil fuels such as coal, oil and natural gas has caused environmental problems such as greenhouse effect, climate change and biodiversity degradation. Biomass energy is a widely distributed renewable energy source with carbon neutrality that can balance CO2 emission and absorption. Although biomass has the potential to be directly converted into fuel, its disadvantages such as high moisture content, low energy density, large volume, high fiber content, poor grindability and poor uniformity lead to a series of problems such as difficult biomass transportation, high cost and seasonal restrictions, which restrict its wider application.

[0003] As a biomass processing and fuel upgrading technology, pyrolysis can improve the characteristics of the raw materials themselves and produce energy and chemical products. Biomass is usually converted into three-phase products of gas, liquid and solid through pyrolysis technology, and the yield of the three-phase products is regulated by changing the pyrolysis process parameters, such as changing the pyrolysis temperature, heating rate and carrier gas flow rate. Among these three-phase products, biochar has the most potential to replace coal due to its good fuel properties (high energy density, high calorific value, high carbon content and low oxygen content).

[0004] However, traditional pyrolysis carbonization technology uses a single pyrolysis condition, resulting in low biochar yield. In addition, the traditional preparation process is not only complex and slow but also has poor economic efficiency. The generated biochar fuel yield, carbon retention rate and combustion performance have limitations. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass, which utilizes heavy bio-oil to fill part of the porous structure of biomass, restricts the escape of primary products of biomass pyrolysis, and thereby retains them in the carbon matrix. The free radicals in these primary pyrolysis products can cross-link with hemicellulose and cellulose, undergo further condensation polymerization reactions, and ultimately promote the formation of biochar with high yield and high carbon content.

[0006] According to a first aspect of an embodiment of the present invention, a method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass comprises the following steps:

[0007] The crushed biomass is mixed with heavy bio-oil in a mass ratio to obtain a mixture, wherein the heavy bio-oil is bio-oil distillation residue;

[0008] The mixture is pyrolyzed under an inert gas atmosphere to obtain biochar.

[0009] According to some embodiments of the present invention, the biomass is any one of bamboo, walnut shells, corn stalks and cotton stalks, or a combination of at least two of them.

[0010] According to some embodiments of the present invention, the method for obtaining heavy bio-oil comprises the following steps:

[0011] The pyrolysis gas after pyrolysis of biomass is separated and condensed to obtain bio-oil;

[0012] After the bio-oil is purified in a distillation tower, the bio-oil distillation residue at the bottom of the distillation tower is collected.

[0013] According to some embodiments of the present invention, the mass ratio of the heavy bio-oil to the biomass is in the range of 1:1-1:9. Preferably, the mass ratio of the heavy bio-oil to the biomass is 3:7.

[0014] According to some embodiments of the present invention, the temperature range of the mixture during pyrolysis under an inert gas atmosphere is 300° C. to 700° C.

[0015] Preferably, the mixture is pyrolyzed at a temperature of 300° C. under an inert gas atmosphere.

[0016] According to some embodiments of the present invention, the mixture is pyrolyzed under an inert gas atmosphere for a time ranging from 10 min to 50 min.

[0017] Preferably, the mixture is pyrolyzed under an inert gas atmosphere for 30 minutes.

[0018] According to some embodiments of the present invention, the inert gas is nitrogen.

[0019] Furthermore, the bio-oil will undergo further condensation and polycondensation reactions through processes such as distillation, rectification and catalytic hydrogenation, forming about 30 to 50% of heavy components at the bottom of the operating equipment. After cooling, this component appears as a black solid and releases an unpleasant pungent odor, which is usually called: heavy bio-oil or bio-oil distillation residue.

[0020] Specifically, the preparation process of bio-oil distillation residue (heavy bio-oil) is as follows: walnut shells are pyrolyzed and liquefied in a self-heating biomass fluidized bed pyrolysis reactor with a maximum feed rate of 500 kg / h, and the resulting pyrolysis gas is successively purified and separated into bio-oil by a cyclone separator and a graded condensation system, and then the resulting bio-oil is subjected to a purification and quality improvement experiment in a distillation tower at 80°C. Since the distillation process promotes the polymerization of organic components in the bio-oil, the cooled bio-oil distillation residue is present in a solid form at the bottom of the distillation tower. After the distillation experiment is completed, the bio-oil distillation residue is recovered from the bottom of the tower.

[0021] When bamboo and heavy bio-oil are co-pyrolyzed, the three main components of bamboo will first decompose into pyrolysis intermediates (such as levoglucosan, furfural and aromatics) and volatile substances. The intermediate compounds and their ring structures are important sources and precursors of biochar. Then, as the temperature rises, the pyrolysis intermediates further decompose, resulting in the removal of heteroatoms and the formation of highly aromatic porous biochar. After severe destruction of functional groups such as -OH, -CH3, -CH2-, C=C, C=O, and CH3O- and deep removal of heteroatoms, a microcrystalline graphite structure is finally formed.

[0022] During the co-pyrolysis process, the presence of bio-oil distillation residue will fill part of the porous structure of biochar, thereby limiting the escape of the primary products of biomass pyrolysis and causing them to be retained in the carbon matrix. The free radicals in these primary pyrolysis products (such as phenoxy groups) can cross-link with hemicellulose and cellulose, undergoing further condensation polymerization reactions, and ultimately promoting the formation of stable biochar.

[0023] A biochar according to a second aspect of an embodiment of the present invention is biochar prepared by any of the above-mentioned preparation methods.

[0024] Beneficial effects:

[0025] The present invention utilizes bio-oil distillation residue to assist bamboo pyrolysis to produce a carbon fixation synergistic effect, thereby increasing the yield of biochar and retaining more carbon elements in the biomass into the biochar.

[0026] The high retention rate of carbon elements in biochar is also beneficial to improving the combustion calorific value of biochar as an alternative fuel, enhancing the thermal stability of biochar fuel, improving the fuel performance of biochar, and making the biochar combustion process closer to fossil fuels.

[0027] In addition, bio-oil distillation residue is a coal-like waste with high carbon content and high calorific value. It is polymerized from heavy components in bio-oil, mainly aromatic compounds. It accounts for 30-50% of the output and 15-25% of the carbon source in the bio-oil refining module. When this waste is mixed with biomass for pyrolysis, it produces the effect of a carbon fixer, thereby squeezing out its potential surplus value and turning waste into treasure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0029] Figure 1 is a disturbance diagram of the biochar yield by three variable parameters according to an embodiment of the present invention;

[0030] Figure 2 is a three-dimensional response surface diagram of pyrolysis temperature and mass ratio versus biochar yield according to an embodiment of the present invention;

[0031] Figure 3 is a three-dimensional response surface diagram of pyrolysis temperature and residence time on biochar yield according to an embodiment of the present invention;

[0032] Figure 4 It is a three-dimensional response surface diagram of mass ratio and residence time to biochar yield according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] Embodiments of the present invention are described in detail below, and the embodiments described with reference to the accompanying drawings are exemplary.

[0034] Example 1

[0035] In this example, the effects of co-pyrolysis of different biomasses with heavy bio-oil on the biochar yield and carbon content were studied, that is, bamboo, walnut shells, corn stalks and cotton stalks were co-pyrolyzed with heavy bio-oil to prepare biochar, and the specific steps were as follows:

[0036] A mass ratio of biomass to heavy bio-oil of 4:1 was adopted. The mixture was ground evenly and then pyrolyzed under pyrolysis conditions such as a pyrolysis temperature of 500°C, a residence time of 30 min, and a nitrogen flow rate of 200 mL / min. The yield and the experimental and theoretical content of carbon element of the solid product after pyrolysis were calculated according to the above method.

[0037] The results are shown in Table 1:

[0038] Table 1. Effects of co-pyrolysis of different biomasses and heavy bio-oil on biochar yield and carbon content

[0039] Biomass Experimental yield% Theoretical yield% Value Added % Experimental carbon content% Theoretical carbon content% Value Added % bamboo 29.30 28.34 0.97 84.90 84.39 0.51 Walnut Shells 32.30 30.82 1.49 86.63 83.37 3.26 Corn stalks 28.20 27.38 0.82 80.84 80.69 0.15 Cotton stalks 22.80 22.26 0.54 85.81 84.52 1.29

[0040] From the results shown in Table 1 above, it can be seen that the experimental values ​​of the yield and carbon content of biochar obtained by co-pyrolysis of different biomasses and heavy bio-oil are greater than the theoretical values, which indicates that heavy bio-oil does have a carbon fixation effect on the preparation of biochar by pyrolysis of biomass.

[0041] Example 2

[0042] In this example, the effects of different pyrolysis temperatures on the biochar yield and carbon content of co-pyrolysis of bamboo and heavy bio-oil were studied, that is, co-pyrolysis biochar was prepared at pyrolysis temperatures of 300°C, 500°C and 700°C, respectively. The specific steps are as follows:

[0043] A mass ratio of bamboo to heavy bio-oil of 7:3 was adopted. The mixture was ground evenly and then pyrolyzed at 300°C, 500°C and 700°C, with a residence time of 30 min and a nitrogen flow rate of 200 mL / min. The yield and actual and theoretical contents of carbon element of the solid product after pyrolysis were calculated according to the above method.

[0044] The results are shown in Table 2:

[0045] Table 2 Effects of different pyrolysis temperatures on biochar yield and carbon content from co-pyrolysis of bamboo and heavy bio-oil

[0046] Pyrolysis temperature / ℃ Experimental yield% Theoretical yield% Value Added % Experimental carbon content% Theoretical carbon content% Value Added % 300 44.62 41.87 2.74 75.39 74.25 1.14 500 31.94 29.55 2.38 85.04 84.51 0.53 700 29.87 26.07 3.79 88.26 87.83 0.43

[0047] From the results shown in Table 2 above, it can be seen that at low temperature pyrolysis temperature, it is beneficial to improve the charcoal yield of biochar, and at high temperature pyrolysis temperature, it is beneficial to improve the carbon content of biochar.

[0048] Example 3

[0049] In this example, the effects of different residence times on the yield and carbon content of biochar from the co-pyrolysis of bamboo and heavy bio-oil were studied, that is, co-pyrolysis biochar was prepared using residence times of 10 min, 30 min, and 50 min, respectively. The specific steps are as follows:

[0050] A mass ratio of bamboo to heavy bio-oil of 7:3 was adopted. The mixture was ground evenly and then pyrolyzed at a pyrolysis temperature of 500°C, residence times of 10 min, 30 min and 50 min, and a nitrogen flow rate of 200 mL / min. The yield and actual and theoretical contents of carbon in the solid product after pyrolysis were calculated according to the above method.

[0051] The results are shown in Table 3:

[0052] Table 3. Effects of different residence times on biochar yield and carbon content from co-pyrolysis of bamboo and heavy bio-oil

[0053] Stay time min Experimental yield% Theoretical yield% Value Added % Experimental carbon content% Theoretical carbon content% Value Added % 10 31.97 28.84 3.13 84.12 84.55 -0.43 30 31.90 29.55 2.35 85.01 84.51 0.50 50 30.16 29.27 0.89 85.07 84.13 0.94

[0054] From the results shown in Table 3 above, it can be seen that a long residence time is beneficial to the carbon content of biochar, but is not beneficial to the biochar yield.

[0055] Example 4

[0056] In this example, the effects of different mass ratios of heavy bio-oil to biomass on the yield and carbon content of co-pyrolysis biochar were studied, that is, 10%, 30% and 50% of heavy bio-oil were added to bamboo to prepare co-pyrolysis biochar, and the specific steps were as follows:

[0057] Heavy bio-oil was used in mass ratios of 10%, 30% and 50% respectively. The mixture was ground evenly and then pyrolyzed under pyrolysis conditions such as pyrolysis temperature of 500°C, residence time of 30 min, and nitrogen flow rate of 200 mL / min. The yield and actual and theoretical content of carbon element in the solid product after pyrolysis were calculated according to the above method.

[0058] The results are shown in Table 4:

[0059] Table 4 Effects of different mass ratios on biochar yield and carbon content from co-pyrolysis of bamboo and heavy bio-oil

[0060] Addition ratio% Experimental yield% Theoretical yield% Value Added % Experimental carbon content% Theoretical carbon content% Value Added % 10 28.69 27.18 1.51 84.63 84.41 0.22 30 31.67 29.55 2.11 85.04 84.51 0.53 50 31.82 31.93 -0.11 82.91 84.61 -1.70

[0061] From the results shown in Table 4 above, it can be seen that the carbon content effect is best when the addition mass ratio is 30%, which means that the addition ratio of the heavy bio-oil should be appropriate.

[0062] According to the contents of the above embodiments, the bio-oil distillation residue has potential surplus value as a high-quality solid waste. Its carbon fixation effect on the pyrolysis of bamboo biomass can increase the yield of biochar by 25.34% on the basis of the theoretical value, and increase the carbon content, fixed carbon content and calorific value by 2.3%, 4.6% and 3.7%, respectively.

[0063] Further, the effect of the synergistic effect of the three components on the biochar yield was explored. As shown in the figure, the curve shows the independent effects of the three experimental variables (pyrolysis temperature, mass ratio and residence time) on the biochar yield, and the gradient represents the sensitivity of the biochar yield to the experimental variables. In the figure, A represents the pyrolysis temperature; B represents the mass ratio, and C represents the residence time.

[0064] Specifically, Figure 1 As shown, it can be determined that factor A has the greatest impact on the biochar yield obtained by carbon fixation. As the pyrolysis temperature increases, the biochar yield decreases significantly and then fluctuates slightly.

[0065] During pyrolysis carbon fixation, the main reason for the decrease in biochar yield is the degradation of (hemi)cellulose in bamboo in the low temperature range, while the bio-oil distillation residue also volatilizes a large amount of organic matter in the sub-high temperature range. The two synergistically induce a decrease in biochar yield.

[0066] When the temperature rises further, the degradation of lignin is limited by temperature changes, the aromatic substances in the bio-oil distillation residue gradually form an aromatic matrix, and the decomposition of macromolecular organic matter is difficult to precipitate volatile fractions. At this time, the biochar yield tends to be stable.

[0067] With the increase of mass ratio, the biochar yield showed a continuous upward trend. At the same time, with the increase of residence time, the biochar yield showed an insignificant downward trend. This is because the breaking time of macromolecular chemical bonds during low-temperature pyrolysis is longer, resulting in a decrease in biochar yield.

[0068] Furthermore, the interaction between the two experimental variables was investigated to investigate the effect of bio-oil distillation residue on the biochar yield of bamboo pyrolysis carbon fixation.

[0069] like Figure 2As shown in the figure, when the residence time is fixed at 30 min, the biochar yield increases with the increase of mass ratio, which is due to the formation of coke when the bio-oil distillation residue is heated. At the same time, the biochar yield decreases with the increase of pyrolysis temperature, mainly because the volatile matter undergoes secondary decomposition at high temperature, producing non-condensable gases.

[0070] like Figure 3 As shown in the figure, when the mass ratio is 30%, the interaction between residence time and pyrolysis temperature affects the biochar yield. Since the extension of residence time mainly changes the surface and internal structure of biochar, the effect on biochar yield is small. Therefore, with the extension of residence time, the biochar yield increases slightly. However, when the pyrolysis temperature increases from 300℃ to 500℃, the biochar yield decreases sharply, and when it increases from 500℃ to 700℃, the biochar yield increases slightly. This is because the free radical fragments generated by the bond breaking of the bio-oil distillation residue components at high temperature may recombine to form ultra-large molecules and coke.

[0071] like Figure 4 As shown in the figure, when the pyrolysis temperature is 500 ° C, the effect of residence time and mass ratio on biochar yield. It can be seen that increasing the mass ratio is beneficial to biochar yield, which is related to the decomposition of organic compounds. However, with the increase of residence time, the increase of mass ratio hinders the increase of biochar yield, which may be because the increase of residence time leads to the re-decomposition of unstable components in biochar.

[0072] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0073] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0074] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass, characterized in that: The method comprises the following steps: The crushed biomass is mixed with heavy bio-oil in a mass ratio to obtain a mixture, wherein the heavy bio-oil is bio-oil distillation residue; The mixture is pyrolyzed under an inert gas atmosphere to obtain biochar.

2. The method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass according to claim 1, characterized in that: The biomass is any one of bamboo, walnut shell, corn stalk and cotton stalk, or a combination of at least two of them.

3. The method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass according to claim 1, characterized in that: The method for obtaining the heavy bio-oil comprises the following steps: The pyrolysis gas after pyrolysis of biomass is separated and condensed to obtain bio-oil; After the bio-oil is purified in a distillation tower, the bio-oil distillation residue at the bottom of the distillation tower is collected.

4. The method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass according to claim 1, characterized in that: The mass ratio of the heavy bio-oil to the biomass is in the range of 1:1 to 1:

9.

5. The method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass according to claim 4, characterized in that: The mass ratio of the heavy bio-oil to the biomass is 3:

7.

6. The method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass according to claim 1, characterized in that: The mixture is pyrolyzed in an inert gas atmosphere at a temperature ranging from 300° C. to 700° C.

7. The method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass according to claim 1, characterized in that: The mixture is pyrolyzed under an inert gas atmosphere for a time ranging from 10 min to 50 min.

8. The method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass according to claim 1, characterized in that: The inert gas is nitrogen.

9. A biochar, characterized in that: Biochar prepared by the method for synergistic pyrolysis and carbon fixation of heavy bio-oil and biomass according to any one of claims 1 to 8.

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