Method for improving pyrolysis oil quality by straw pickling and catalytic pyrolysis

Abstract

The present application relates to the field of biomass pyrolysis oil upgrading, and specifically discloses a method for improving pyrolysis oil quality by straw pickling and catalytic pyrolysis, comprising the following steps: 1) performing acid pickling pretreatment on the straw to remove inorganic salts in the straw, inhibit the promoting effect of alkali metals and alkaline earth metals on the generation of water and acid substances, and realize straw deoxygenation and quality improvement; 2) using a high-efficiency catalyst for catalytic pyrolysis to promote the decomposition of pyrolysis volatile matter, improve the pyrolysis efficiency, significantly increase the content of phenolic compounds in the condensed oil, and reduce the content of ketone and acid compounds. The present application can improve the content of phenol in the pyrolysis oil, reduce the content of ketone and acid, increase the product quality of the pyrolysis oil, and realize harmless and green treatment of the straw and low-cost and high-value utilization.

Description

Technical Field

[0001] This invention relates to the field of biomass pyrolysis oil upgrading, and specifically discloses a method for improving the quality of pyrolysis oil through straw acid washing and catalytic pyrolysis. Background Technology

[0002] Biomass is a renewable green energy source, characterized by its renewability, abundant resources, low pollution, and carbon neutrality. Its main components are agricultural and forestry waste such as straw, rice husks, and sawdust. Straw is often not fully utilized and is instead left to rot in fields or discarded as waste, which not only easily breeds pests and diseases and increases plant protection costs but also causes environmental pollution. Pyrolysis is currently one of the more resource-efficient methods for processing biomass, converting it into high-calorific-value bio-oils that can serve as alternatives to fossil fuels. Phenolic compounds, due to their high reactivity of hydroxyl substitution and their ability to scavenge free radicals, have potential antioxidant activity and are of great use in the medical, environmental, and food fields. However, current pyrolysis technologies produce pyrolysis oils with high oxygen content, complex composition, and high acidity, making it difficult to produce high-quality, high-utilization-rate pyrolysis oils.

[0003] CN106928285B discloses a method for preparing L-glucanone by biomass catalytic pyrolysis. The method uses biomass-based phosphoric acid activated carbon as a catalyst, which is mechanically mixed with biomass and rapidly pyrolyzed at 250-470°C under inert and anaerobic conditions. After condensing the pyrolysis gas, a liquid product rich in L-glucanone is obtained. However, the L-glucanone content is only 7.1%-10.4%, and the catalytic yield improvement is not high.

[0004] CN109321290A discloses a liquid oil rich in furan compounds and its preparation method. The method involves acid washing biomass with hydrochloric acid solution, followed by rapid pyrolysis using Zr-Cu / SAPO-18 molecular sieve as a catalyst under an inert atmosphere at 400–700°C to obtain a liquid oil product rich in furan compounds. However, the liquid oil produced by this catalytic pyrolysis only contains 15%–30% furan compounds, the catalyst preparation process is cumbersome, and the catalytic enhancement effect is not significant.

[0005] This invention addresses the high-value utilization of straw by developing a method for improving the quality of pyrolysis oil through straw acid washing and catalytic pyrolysis. By combining acid washing pretreatment with an inexpensive and readily available hematite catalyst, the phenol content in the pyrolysis oil is increased while the ketone and acid content is reduced. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for improving the quality of pyrolysis oil by straw acid washing and catalytic pyrolysis.

[0007] A method for improving the quality of pyrolysis oil by straw acid washing and catalytic pyrolysis includes the following steps:

[0008] S1: Pulverize the straw raw material;

[0009] S2: Mix the acid solution with the crushed straw and soak it;

[0010] S3: Wash until pH 6.8-7.2;

[0011] S4: After drying, crush and sieve to obtain pretreated straw;

[0012] S5: Mix the hematite with the straw that has been pretreated in the above steps;

[0013] S6: Under inert and anaerobic conditions, a mixture of straw and hematite is heated to carry out a pyrolysis reaction, the pyrolysis volatiles are collected, and condensed to obtain phenol-rich pyrolysis oil.

[0014] The method wherein the straw in S1 includes at least one of chili straw, rice straw, corn straw, and cotton straw, and the crushed straw is passed through a 40-80 mesh sieve.

[0015] In the method described, the acid solution in S2 is a hydrochloric acid solution, the impregnation concentration is 0.1–2 mol / L, the impregnation temperature is 23–27°C, and the impregnation time is 0.5–3 h.

[0016] In the method described above, in step S3, the straw is washed with deionized water.

[0017] In the method described above, in step S4, the straw is dried at a temperature of 90-120℃ for 24-48 hours to remove free moisture, and then crushed through a 40-80 mesh sieve to obtain the pretreated straw.

[0018] The acid washing method of this invention mainly increases the phenols in straw pyrolysis oil, with relatively little impact on acids and ketones. Through the synergistic catalytic treatment of acid washing and hematite, the effects on improving the quality of bio-oil are complementary.

[0019] In the method described above, in step S5, hematite and pretreated straw are mixed at a mass ratio of (5:1) to (1:5); preferably 2:1 to 1:1.

[0020] In the method described, the hematite in S5 is a powder of 1000-2000 mesh.

[0021] In the method described above, the inert oxygen-free condition in step S6 is a nitrogen atmosphere or an argon atmosphere, and the gas flow rate during the pyrolysis process is 50–200 mL / min.

[0022] In the method described, the pyrolysis temperature in step S6 is 550–870°C, the heating rate during the pyrolysis process is 5–20°C / min, and the holding time at the highest temperature is 0.5–3 h.

[0023] This invention is the first to use hematite as a catalyst. When this catalyst is used alone to treat straw, it cannot achieve the desired effect of reducing ketone and acid content. Only when it works in synergy with acid washing can it effectively reduce ketone and acid content. This further demonstrates the complementary effect of acid washing and hematite catalysis, which can both increase the phenol content in pyrolysis oil and reduce its ketone and acid content.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention uses hydrochloric acid as a straw pretreatment solution, which effectively reduces the impact of inorganic salts in straw on the quality of pyrolysis oil and lowers the activation energy of the pyrolysis reaction to a certain extent, thus facilitating the pyrolysis process. Furthermore, this invention uses hematite as a catalyst, enabling efficient catalytic cracking of volatiles from biomass pyrolysis. This catalyst breaks down long-chain substances into shorter-chain substances to a certain extent, promoting the pyrolysis reaction rate of the raw materials and improving the quality of bio-pyrolysis products. Hematite is a common ore rich in Fe2O3, abundant in resources, and inexpensive. During the catalytic cracking of biomass, some of the Fe2O3 on the surface of the hematite can be reduced by the pyrolysis gas to magnetic Fe3O4, allowing for catalyst recovery and reuse. In addition, its main catalytic component, Fe2O3, has a dehydroxylation effect, which can reduce the content of ketones and acids in the pyrolysis oil, improving its quality.

[0026] This invention utilizes the synergistic effect of acid washing pretreatment and catalyst on straw pyrolysis to increase the phenol content in pyrolysis oil while reducing the content of ketones and acids, effectively improving the quality of pyrolysis oil and providing some exploration and reference for the high-value utilization of straw. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0028] This invention provides a method for improving the quality of pyrolysis oil by straw acid washing and catalytic pyrolysis. To make the purpose, technical solution and effects of this invention clearer, the following examples further illustrate the solution.

[0029] Unless otherwise specified, all percentages in the following examples are by mass. A comparison of the pyrolysis oil content and the contents of phenols, ketones, and acids in Examples 1-8 is shown in Table 1.

[0030] Example 1

[0031] Blank experiment: 10.00g of 60-mesh chili straw powder was placed in a quartz boat for pyrolysis. N2 was used as a protective gas, and the flow rate was 100mL / min with leak checks. Aeration continued for 10 minutes to completely purge the air from the passageway, ensuring no leaks. Subsequently, the temperature was increased from 30℃ to over 150℃ at a rate of 10℃ / min, and a gas collection bag was connected. The temperature was further increased to 700℃ and held for 1 hour. The yield of the liquid product was 17.50%. Gas chromatography-mass spectrometry analysis revealed the contents of phenols, ketones, and acids to be 60.80%, 11.68%, and 2.31%, respectively.

[0032] Example 2

[0033] Weigh 30.00g of 60-mesh chili straw powder and add it to a beaker containing 600mL of distilled water. Place the beaker on a magnetic stirrer and stir continuously for 2 hours. After stirring, filter the sample to obtain the pretreated sample and wash it repeatedly with deionized water until the pH of the filtrate is close to neutral. Then place the sample in an oven at 105℃ and dry for 24 hours to remove moisture.

[0034] 10.00g of 60-mesh chili straw powder was placed in a quartz boat, which was then placed in a horizontal tube furnace. A condenser was connected to collect the liquid product, and a gas bag was used to collect the gaseous product. N2 was used as the protective gas in the experiment. N2 was purged at a flow rate of 100mL / min, and leak checks were performed. The purging was continued for 10 minutes to completely remove air from the passage, ensuring no leaks. Subsequently, the temperature was increased from 30℃ to over 150℃ at a rate of 10℃ / min, and then connected to the gas bag. The temperature was further increased to 700℃ and held for 1 hour. The yield of the liquid product was 17.63%. Gas chromatography-mass spectrometry analysis revealed the contents of phenols, ketones, and acids to be 62.98%, 7.16%, and 1.31%, respectively.

[0035] Example 3

[0036] Weigh 30.00g of 60-mesh chili straw powder and add it to a beaker containing 600mL of 0.1mol / L HCl. The sample is then processed according to the pretreatment method in Example 2.

[0037] 10.00 g of 60-mesh chili straw powder pretreated with 0.1 mol / L HCl was pyrolyzed. N2 was used as a protective gas for pyrolysis, with a flow rate of 100 mL / min during the pyrolysis process. The flow was maintained for 10 minutes to ensure complete air removal from the pyrolysis path, provided there were no leaks. The temperature was then increased from 30°C to above 150°C at a rate of 10°C / min, and a gas collection bag was connected. The temperature was further increased to 700°C and held for 1 hour. The yield of the liquid product was 20.50%. Gas chromatography-mass spectrometry (GC-MS) analysis revealed the contents of phenols, ketones, and acids to be 73.37%, 11.04%, and 1.56%, respectively.

[0038] Example 4

[0039] Weigh 30.00g of 60-mesh chili straw powder and add it to a beaker containing 600mL of 0.5mol / L HCl. The sample is then processed according to the pretreatment method in Example 2.

[0040] 10.00 g of 60-mesh chili straw powder pretreated with 0.5 mol / L HCl was pyrolyzed. N2 was used as a protective gas for pyrolysis, with a flow rate of 100 mL / min during the pyrolysis process. After leak testing, the flow was maintained for 10 minutes to completely purge the air from the pyrolysis path. The temperature was then increased from 30 °C to above 150 °C at a rate of 10 °C / min, and a gas collection bag was connected. The temperature was further increased to 700 °C and held at this temperature for 1 hour. The yield of the liquid product was 25.73%. Gas chromatography-mass spectrometry (GC-MS) analysis revealed the contents of phenols, ketones, and acids to be 73.49%, 12.39%, and 0.77%, respectively.

[0041] Example 5

[0042] Weigh 30.00g of 60-mesh chili straw powder and add it to a beaker containing 600mL of 0.9mol / L HCl. The sample is then processed according to the pretreatment method in Example 2.

[0043] 10.00 g of 60-mesh chili straw powder pretreated with 0.9 mol / L HCl was pyrolyzed. N2 was used as a protective gas for pyrolysis, with a flow rate of 100 mL / min during the pyrolysis process. The flow was maintained for 10 minutes to ensure complete air removal from the pyrolysis path, provided there were no leaks. The temperature was then increased from 30°C to above 150°C at a rate of 10°C / min, and a gas collection bag was connected. The temperature was further increased to 700°C and held at this temperature for 1 hour. The yield of the liquid product was 22.94%. Gas chromatography-mass spectrometry (GC-MS) analysis revealed the contents of phenols, ketones, and acids to be 74.73%, 9.75%, and 1.54%, respectively.

[0044] Example 6

[0045] 10.00g of 60-mesh chili straw and 10.00g of 1250-mesh hematite powder were mechanically mixed at a mass ratio of 1:1. The mixture was then pyrolyzed at 700℃, a heating rate of 10℃ / min, and a N2 atmosphere for 1h, yielding a liquid product with a yield of 27.23%. The contents of phenols, ketones, and acids were analyzed by gas chromatography-mass spectrometry, and the yields of phenols, ketones, and acids were calculated to be 60.51%, 10.93%, and 4.42%, respectively.

[0046] Example 7

[0047] 10.00g of 60-mesh chili straw (pretreated with water, the same as in Example 2) and 10.00g of 1100-1400 mesh hematite powder were mechanically mixed at a mass ratio of 1:1. The mixture was then pyrolyzed at 700℃, a heating rate of 10℃ / min, and a N2 atmosphere for 1h, yielding a liquid product with a yield of 22.68%. The contents of phenols, ketones, and acids were analyzed by gas chromatography-mass spectrometry, and the yields of phenols, ketones, and acids were calculated to be 65.50%, 12.47%, and 1.54%, respectively.

[0048] Example 8

[0049] 10.00g of 60-mesh chili straw pretreated with 0.5mol / L HCl (same pretreatment as in Example 4) was mechanically mixed with 10.00g of 1100-1400-mesh hematite powder at a mass ratio of 1:1. The mixture was then pyrolyzed at 700℃, a heating rate of 10℃ / min, and a N2 atmosphere for 1h, yielding a liquid product with a yield of 34.01%. The contents of phenols and ketones were analyzed by gas chromatography-mass spectrometry, and the yields of phenols, ketones, and acids were calculated to be 74.40%, 3.08%, and 0.30%, respectively.

[0050] Example 9

[0051] 10.00g of 60-mesh chili straw pretreated with 0.5mol / L HCl (same pretreatment as in Example 4) was mechanically mixed with 10.00g of 1100-1400-mesh hematite powder at a mass ratio of 2:1. The mixture was then pyrolyzed at 700℃, a heating rate of 10℃ / min, and a N2 atmosphere for 1h, yielding a liquid product with a yield of 28.98%. The contents of phenols and ketones were analyzed by gas chromatography-mass spectrometry, and the yields of phenols, ketones, and acids were calculated to be 50.67%, 4.73%, and 0.67%, respectively.

[0052] Example 10

[0053] 10.00g of 60-mesh chili straw pretreated with 0.5mol / L HCl (same pretreatment as in Example 4) was mechanically mixed with 10.00g of 1100-1400-mesh hematite powder at a mass ratio of 1:2. The mixture was then pyrolyzed at 700℃, a heating rate of 10℃ / min, and a N2 atmosphere for 1h, yielding a liquid product with a yield of 33.43%. The contents of phenols and ketones were analyzed by gas chromatography-mass spectrometry, and the yields of phenols, ketones, and acids were calculated to be 73.23%, 6.98%, and 0.89%, respectively.

[0054] Table 1. Content of phenol, ketone, and acid in chili straw pyrolysis oil after pretreatment with different concentrations of hydrochloric acid and catalytic pyrolysis with hematite.

[0055]

[0056]

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the present invention.

Claims

1. A method for improving the quality of pyrolysis oil by straw acid washing and catalytic pyrolysis, characterized in that, Includes the following steps: S1: Pulverize the straw raw material; S2: Mix the acid solution with the crushed straw and soak it; S3: Wash until pH 6.8-7.2; S4: After drying, crush and sieve to obtain pretreated straw; S5: Mix the hematite with the straw that has been pretreated in the above steps; S6: Under inert and anaerobic conditions, the mixture of straw and hematite is heated to carry out a pyrolysis reaction, the pyrolysis volatiles are collected, and condensed to obtain phenol-rich pyrolysis oil; The straw in S1 includes at least one of chili straw, rice straw, corn straw, and cotton straw; The acid solution in S2 is hydrochloric acid solution, and the concentration of the impregnation treatment is 0.1~2 mol / L; the impregnation temperature is 23~27℃, and the impregnation time is 0.5~3 h; In step S5, hematite is mixed with pretreated straw at a mass ratio of (2:1) to (1:1); The pyrolysis temperature in S6 is 550~870 ℃, the heating rate of the pyrolysis process is 5~20 ℃ / min, and the holding time at the highest temperature is 0.5~3 h.

2. The method according to claim 1, characterized in that, The crushed straw in S1 is passed through a 40-80 mesh sieve.

3. The method according to claim 1, characterized in that, In step S3, the straw is washed with deionized water.

4. The method according to claim 1 or 3, characterized in that, In step S4, the straw is dried at a temperature of 90-120℃ for 24-48 hours to remove free moisture. After drying, it is crushed and passed through a 40-80 mesh sieve to obtain the pretreated straw.

5. The method according to claim 1, characterized in that, The hematite in S5 is a powder with a mesh size of 1000-2000.

6. The method according to claim 1, characterized in that, The inert oxygen-free condition in S6 is a nitrogen atmosphere or an argon atmosphere, and the gas flow rate during the pyrolysis process is 50~200 mL / min.

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