Novel preparation method and application of oxygen carrier for preparing synthesis gas through chemical chain gasification of jute pear wood semicoke

Abstract

The invention belongs to the technical field of energy and chemical industry, and provides a novel preparation method and application of an oxygen carrier for preparing synthesis gas through chemical chain gasification of jute pear wood semicoke. The method comprises the following steps: firstly, preparing a MgO-NiFeO4 / SiO2 oxygen carrier by using a sol-gel method, then mixing the jute pear semicoke and the NiFeO4 oxygen carrier, loading the mixture into a fixed bed reactor, and carrying out chemical chain gasification to prepare the synthesis gas, so that the problems of low carbon conversion rate, low synthesis gas selectivity and especially low CO selectivity when the NiFeO4 oxygen carrier is used for chemical chain gasification are solved. Meanwhile, SiO2 is used for dispersing the oxygen carrier, MgO is used for modifying the oxygen carrier, the gasification performance is improved, and the high application value is achieved. The CO-rich synthesis gas prepared by the method has a wide application prospect when being used for preparing fuels or deeply processing chemicals.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy chemical engineering, and relates to a new method for preparing an oxygen carrier for the chemical looping gasification of pear wood semicoke to produce syngas and its application. Background Art

[0002] Fossil energy is a non-renewable resource. Especially for China, the energy consumption is huge. Therefore, it is of great significance to use renewable energy to replace fossil energy for China's energy security. Biomass, as a renewable energy, has a very rich reserve in China. The theoretical resource amount of biomass energy in China exceeds 4.4 billion tons of standard coal. And in the application of biomass energy in China, the application proportion of forestry waste is relatively small. Therefore, converting it into energy can promote the utilization of biomass resources in China.

[0003] Chemical looping gasification technology is one of the clean and efficient resource utilization methods. Developing biomass chemical looping gasification technology is of great significance for solving problems such as China's energy supply and environmental pollution. It transfers oxygen to biomass semicoke through an oxygen carrier as an intermediate medium, enabling it to decompose into small molecules such as H2, CH4, CO, and CO2 that can be captured. Among them, H2 and CO are the target products of gasification. The oxygen carrier releases heat during the oxygen release process, which can provide heat for subsequent technological processes and also play the role of a heat carrier. The reduced oxygen carrier can remove carbon deposition through air calcination and also realize the regeneration of the oxygen carrier. Compared with traditional gasification systems, chemical looping gasification is conducive to CO2 collection and treatment, without the need to additionally increase too many CO2 separation devices, saving costs and protecting the environment. Secondly, the oxygen carrier used eliminates the process of preparing pure oxygen, saving costs and improving the energy utilization efficiency.

[0004] In the prior art, research has been carried out on composite metal oxygen carriers prepared from two or more metals. Among them, the NiFe2O4 oxygen carrier has relatively low activity during chemical looping gasification, cannot make the materials react fully, and cannot obtain high syngas selectivity and high carbon conversion rate. Based on the problems existing in the above NiFe2O4 oxygen carrier, it is necessary to modify it to obtain an oxygen carrier with higher CO selectivity. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention proposes a new preparation method for an oxygen carrier used in chemical-looping gasification to produce syngas. The NiFe2O4 oxygen carrier prepared by the sol-gel method can be dispersed with SiO2, making the oxygen carrier more stable and extending its service life. Modifying the NiFe2O4 oxygen carrier with metallic magnesium can further improve the selectivity of the oxygen carrier for CO. The prepared MgO-NiFe2O4 / SiO2 oxygen carrier not only effectively improves the CO selectivity of the NiFe2O4 oxygen carrier, but also increases the carbon conversion rate.

[0006] The technical solution of the present invention:

[0007] A new preparation method for an oxygen carrier used in the chemical-looping gasification of pear-wood semi-coke to produce syngas, the steps are as follows:

[0008] Prepare the MgO-NiFe2O4 / SiO2 oxygen carrier using the sol-gel method

[0009] First, prepare a mixed solution of Fe(NO3)3·9H2O and Ni(NO3)2·6H2O, wherein the molar ratio of Ni to Fe is 1:2 and the total cation concentration is 1 mol / L; according to the molar ratio of citric acid to cations being 1.5:1, add citric acid to the mixed solution, stir well at room temperature until evenly mixed, then add Zn(NO3)2 and continue stirring until completely dissolved to obtain solution A; the molar ratios of Zn(NO3)2 and Ni(NO3)2·6H2O in solution A are 0.05 - 0.25 respectively; prepare an ethanol solution of TEOS, wherein the volume ratio of TEOS to ethanol is 1:2 to obtain solution B, and the SiO2 after hydrolysis of TEOS in solution B accounts for 60% of the total mass of the oxygen carrier, and drop solution B into solution A; at a temperature of 65 °C, continue stirring for 5 - 6 h to form a wet gel; place the wet gel in a constant-temperature vacuum drying oven and dry at 120 °C for 10 h to obtain a dry gel; pre-calcine the dry gel at a temperature of 200 °C for 30 min; then set the heating program as: rise to 500 °C at 5 °C / min, keep the temperature constant for 1 h, continue to rise to 1000 °C at 5 °C / min and keep the temperature constant for 5 h, and naturally cool to room temperature and then grind and sieve to obtain the MgO-NiFe2O4 / SiO2 oxygen carrier. Among them, the loading amount of MgO in the MgO-NiFe2O4 / SiO2 oxygen carrier is 5% - 25%, and the mass of SiO2 is 60% of the total mass.

[0010] A method for realizing fixed-bed chemical-looping gasification to produce syngas using an oxygen carrier, the steps are as follows:

[0011] Mix the semi-coke of Pyrus serrulata with the MgO-NiFe₂O₄ / SiO₂ oxygen carrier evenly and then fill it into the reactor to conduct a fixed-bed experiment to prepare syngas. The fixed-bed experiment refers to heating the reactor to 900 °C at a heating rate of 40 °C / min in an N₂ atmosphere and maintaining it for 60 minutes to obtain a gas product rich in syngas.

[0012] The semi-coke of Pyrus serrulata refers to the semi-coke obtained after pyrolyzing Pyrus serrulata in a tubular furnace at 450 °C for 1 hour and crushing it to less than 80 mesh.

[0013] The oxygen-to-carbon ratio of the semi-coke of Pyrus serrulata to the MgO-NiFe₂O₄ / SiO₂ oxygen carrier is 1:1.

[0014] Advantages of the present invention:

[0015] (1) Adding TEOS to SiO₂ can increase the proportion of syngas in the gas product after gasification, especially the content of CO. Compared with the unmodified parent NiFe₂O₄ oxygen carrier, the relative content of syngas has increased. The CO yield reaches up to 0.71 m 3 / kg, an increase of 21.4% compared with the parent NiFe₂O₄ oxygen carrier; the selectivity of CO reaches 64%, an increase of 7% compared with the parent NiFe₂O₄ oxygen carrier. The modified oxygen carrier has better gasification performance compared with the parent.

[0016] (2) Adding MgO can increase the proportion of syngas in the gas product after gasification. Compared with the NiFe₂O₄ / SiO₂ oxygen carrier, the carbon conversion rate changes less. The relative content of syngas has increased. The CO yield reaches up to 0.79 m 3 / kg, an increase of 11.4% compared with the NiFe₂O₄ / SiO₂ oxygen carrier; the selectivity of CO reaches 70%, an increase of 7% compared with the parent NiFe₂O₄ oxygen carrier. The oxygen carrier after adding MgO has better gasification performance compared with NiFe₂O₄ / SiO₂. Description of the drawings

[0017] Figure 1 Schematic diagram of the influence of different MgO-loaded NiFe₂O₄ / SiO₂ oxygen carriers on different gas contents;

[0018] Figure 2 Schematic diagram of the influence of the semi-coke chemical looping gasification cycle performance of the NiFe₂O₄ oxygen carrier under the condition of 900 °C;

[0019] Figure 3 Schematic diagram of the influence of the semi-coke chemical looping gasification cycle performance of the NiFe₂O₄ / SiO₂ oxygen carrier under the condition of 900 °C;

[0020] Figure 4Schematic diagram of the influence of the cyclic performance of char chemical looping gasification with a 20% MgO-loaded NiFe2O4 / SiO2 oxygen carrier at 900 °C;

[0021] Figure 5 Schematic diagram for the preparation of the MgO-NiFe2O4 / SiO2 oxygen carrier. Specific implementation manners

[0022] The following further illustrates the specific implementation manners of the present invention in combination with the attached drawings and technical solutions.

[0023] Using the above-mentioned novel oxygen carrier for chemical looping gasification to produce syngas, the percentages involved in the following examples are all mass percentages (%), and the proximate analysis and ultimate analysis of Chinese pear tree wood and its char are shown in Table 1.

[0024] Table 1 Proximate analysis and ultimate analysis of Chinese pear tree wood and its char

[0025]

[0026] Note: * Obtained by the difference method.

[0027] Example 1

[0028] First step, using the parent NiFe2O4 oxygen carrier, mix Chinese pear tree wood char and the parent NiFe2O4 oxygen carrier in a ratio of oxygen to carbon of 1:1, and then load them into a fixed-bed reactor for chemical looping gasification.

[0029] Second step, under a N2 atmosphere, heat the fixed-bed reactor to 900 °C at a heating rate of 40 °C / min and hold for 60 minutes to produce syngas.

[0030] Example 2

[0031] First step, prepare a mixed solution of Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and Mg(NO3)2. Add citric acid to the above mixed solution according to a molar ratio of citric acid to cations of 1.5:1, and then continue to add an ethanol solution of TEOS, with the addition amount of MgO being 5%;

[0032] Second step, mix Chinese pear tree wood char and the 5% MgO-NiFe2O4 / SiO2 oxygen carrier evenly in a ratio of oxygen to carbon of 1:1, and then load them into a fixed-bed reactor for chemical looping gasification.

[0033] Third step, under a N2 atmosphere, heat the fixed-bed reactor to 900 °C at a heating rate of 40 °C / min and hold for 60 minutes to produce syngas.

[0034] Example 3

[0035] The difference from Example 2 is only that the addition amount of MgO is 10%.

[0036] Example 4

[0037] The difference from Example 2 is only that the addition amount of MgO is 15%.

[0038] Example 5

[0039] The difference from Example 2 is only that the addition amount of MgO is 15%.

[0040] Example 6

[0041] The difference from Example 2 is only that the addition amount of MgO is 25%.

[0042] Comparative Example 1

[0043] First step: Using the parent NiFe2O4 oxygen carrier, mix the jujube wood semicoke and the parent NiFe2O4 oxygen carrier in a ratio of oxygen to carbon of 1:1 and load them into a fixed-bed reactor for chemical-looping gasification.

[0044] Second step: Under an N2 atmosphere, heat the fixed-bed reactor to 900 °C at a heating rate of 40 °C / min and hold for 60 minutes to prepare syngas.

[0045] Third step: Put the reacted oxygen carrier into a muffle furnace and calcine it in air for 60 minutes, then repeat the above first step and second step until five cycles.

[0046] Comparative Example 2

[0047] The difference from Comparative Example 1 is only that the oxygen carrier is replaced with NiFe2O4 / SiO2.

[0048] Comparative Example 3

[0049] The difference from Comparative Example 1 is only that the oxygen carrier is replaced with MgO-NiFe2O4 / SiO2.

[0050] The gas-phase products of the above examples and comparative examples were uniformly analyzed by gas chromatography, and the contents and conversion rates of the gas-phase products prepared under different conditions are summarized in Table 1.

[0051] Table 1

[0052]

[0053] With the increase of the MgO addition amount, the carbon conversion rate increases, and the synthesis gas selectivity and CO selectivity increase. The carbon conversion rate increases from 66.18% to 71.88%, the synthesis gas selectivity increases from 60.97% to 75.17%, and the CO selectivity increases from 57.00% to 71.47%. In addition, the MgO-NiFe2O4 / SiO2 oxygen carrier after five cycles has a higher carbon conversion rate, synthesis gas selectivity and CO selectivity than the NiFe2O4 oxygen carrier. Therefore, it is considered that the MgO-NiFe2O4 / SiO2 oxygen carrier with 20% MgO addition amount under the condition of 900 °C is the appropriate addition amount in the chemical looping gasification experiment of biomass semicoke. The application of the present invention in the chemical looping gasification process of biomass semicoke can realize the utilization of biomass semicoke, and still maintain good performance after multiple cycles, greatly improving the selectivity of synthesis gas, and at the same time greatly improving the utilization rate of semicoke, which has far-reaching significance for the production of high-value-added chemical products.

[0054] Although the present invention has been described with reference to exemplary embodiments, it should be understood that the present invention is not limited to the exemplary embodiments. The scope of the appended claims should also be given a broader interpretation so as to cover equivalent modifications, variations, and equivalent ratios and substances that are consistent with the spirit of the present invention.

Claims

1. A novel method for preparing an oxygen carrier for preparing synthesis gas by chemical chain gasification of schisandra semi-coke, characterized in that: Here are the steps: Preparation of MgO-NiFe2O4 / SiO2 oxygen carrier using sol-gel method First, a mixed solution of Fe(NO3)3·9H2O and Ni(NO3)2·6H2O was prepared, wherein the molar ratio of Ni to Fe was 1:2 and the total cation concentration was 1 mol / L; citric acid was added to the mixed solution at a molar ratio of citric acid to cation of 1.5:1, and the mixture was stirred thoroughly at room temperature until it was uniformly mixed, and then Zn(NO3)2 was added and stirred continuously until it was completely dissolved to obtain solution A; the molar ratios of Zn(NO3)2 and Ni(NO3)2·6H2O in solution A were 0.05-0.25, respectively; an ethanol solution of TEOS was prepared, wherein the volume ratio of TEOS to ethanol was 1:

1. The ratio of TEOS to oxygen carrier is 1:2 to obtain solution B, in which SiO2 after hydrolysis of TEOS accounts for 60% of the total mass of the oxygen carrier. Solution B is dropped into solution A; at a temperature of 65°C, stirring is continued for 5-6 hours to form a wet gel; the wet gel is placed in a constant temperature vacuum drying oven and dried at 120°C for 10 hours to obtain a dry gel; the dry gel is pre-calcined at a temperature of 200°C for 30 minutes; the temperature rising program is set as follows: rise to 500°C at 5°C / min, keep the temperature for 1 hour, continue to rise to 1000°C at 5°C / min and keep the temperature for 5 hours, naturally cool to room temperature, grind and sieve to obtain MgO-NiFe2O4 / SiO2 oxygen carrier.

2. The novel preparation method according to claim 1, characterized in that: The loading amount of MgO in the MgO-NiFe2O4 / SiO2 oxygen carrier is 5%-25%, and the mass of SiO2 is 60% of the total mass.

3. A method for preparing synthesis gas by fixed bed chemical chaining gasification using an oxygen carrier, characterized in that: Here are the steps: The hemp wood semi-coke is mixed evenly with the MgO-NiFe2O4 / SiO2 oxygen carrier and then filled into a reactor to carry out a fixed bed experiment to prepare synthesis gas. The fixed bed experiment refers to heating the reactor to 900°C at a heating rate of 40°C / min under a N2 atmosphere and maintaining it for 60 minutes to obtain a gas product rich in synthesis gas.

4. The method according to claim 3, characterized in that The hemp wood semi-coke refers to the semi-coke obtained after the hemp wood is pyrolyzed in a tube furnace at a temperature of 450° C. for 1 hour, which is crushed to less than 80 meshes.

5. The method according to claim 3, characterized in that: The oxygen-carbon ratio of the hemp wood semi-coke and the MgO-NiFe2O4 / SiO2 oxygen carrier is 1:1.

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