A method for pretreatment of biomass in oil bath assisted by microwave-coupled light waves

Abstract

The present invention belongs to the technical field of high-value conversion of biomass resources, and discloses a method for microwave-coupled light wave-assisted biomass oil bath pretreatment. The method comprises the following steps: using non-edible oils and fats as the biomass oil bath pretreatment medium, and performing oil bath pretreatment on the biomass based on microwave heating and light wave heating in alternating order, and the pretreated mixture can be used for processes such as pyrolysis and gasification. The present invention realizes the synergistic coupling of microwave heating and light wave heating, and by means of the advantages of bulk heating of microwave heating and the high dielectric properties of waste oils and fats, the raw materials are rapidly heated, the processing time is shortened, and energy consumption is reduced; as well as the advantages of high energy utilization efficiency and low energy consumption of light wave heating, the containers used are preheated and insulated, the heat exchange between the raw material system and the environment is reduced, and the rapid heating and constant insulation effect of the bio-oil oil bath process is achieved, which effectively improves the efficiency of the oil bath pretreatment, significantly improves the economy of the system, and has certain prospects for industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-value conversion of biomass resources, and in particular relates to a method for pretreatment of biomass in an oil bath assisted by microwave-coupled light waves. Background Art

[0002] In the context of the "dual carbon" initiative, we advocate a green, environmentally friendly, and low-carbon lifestyle, guide green technology innovation, adjust the energy structure, and vigorously develop renewable energy. As a plentiful renewable carbon source, the rational and efficient utilization of biomass contributes to green and low-carbon development. To achieve more efficient utilization, various technologies have been developed, with pyrolysis and gasification receiving significant attention. However, the low effective hydrogen-to-carbon ratio limits their efficient application through pyrolysis and gasification. Torrefaction of biomass prior to pyrolysis can effectively reduce the oxygenated compound and water content of bio-oil. Wet torrefaction removes oxygen and improves hydrogen retention. However, traditional wet torrefaction uses water as the medium, which consumes significant amounts of water resources and requires drying before subsequent pyrolysis. Using waste oils and fats as the wet torrefaction medium in oil bath torrefaction effectively addresses this issue, allowing the products to be directly subjected to subsequent pyrolysis or gasification processes. Furthermore, premixing biomass and waste oils in oil bath torrefaction enhances the interaction between the two, promoting the formation of hydrocarbons during pyrolysis. In 2021, Wu Qiuhao et al. published "Research Progress on Microwave-Assisted / Catalytic Pyrolysis of Waste Grease to Produce Hydrocarbon-Rich Bio-Oil," which documented the co-pyrolysis of waste grease and lignocellulosic biomass. In 2022, Dai Leilei published "Study on the Thermochemical Conversion of Lignocellulosic Biomass from Agricultural Product Processing Byproducts to Prepare Bio-Oil." Based on the properties of biomass after wet torrefaction, microwave wet torrefaction pretreatment was more effective than traditional wet torrefaction pretreatment in removing oxygen from biomass and acetyl groups from hemicellulose. However, this pretreatment method suffers from poor thermal insulation, unstable temperature fields, and high energy consumption.

[0003] Furthermore, to further exploit the advantages of waste oil and fat and fully utilize its high dielectric properties, microwave heating can be used to rapidly heat the raw material system. Combined with light wave heating and insulation, this maintains a stable temperature field in the system, reducing processing time and energy consumption. Currently, no relevant public information discloses this technology. Summary of the Invention

[0004] The present invention provides a method for microwave-coupled light wave-assisted biomass oil bath pretreatment. Microwave heating is introduced into the biomass oil bath pretreatment process, and waste oil with high dielectric properties is used as a baking medium. On the one hand, this method solves the defects of traditional hydrothermal baking process that requires large amounts of water resources and energy for drying. At the same time, microwave heating can quickly increase the temperature, save processing time, reduce energy consumption, and light wave heating and heat preservation can better maintain the temperature stability of the reaction system, which has the prospect of industrial production application.

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

[0006] The method of the present invention for pretreatment of biomass oil bath by microwave-coupled light wave assistance comprises the following steps:

[0007] (1) The waste oil and biomass are stirred and mixed in a certain ratio and placed in a normal pressure reactor. The upper outlet of the reactor is connected to a mechanical stirrer, and the side outlet is connected to a condensation reflux device. The preferred ratio of waste oil and biomass is 10:1 to 2:1 by mass.

[0008] (2) Install the reactor, introduce inert gas to remove the air in the reactor and seal it.

[0009] (3) Adjust the ratio of microwave heating to light wave heating and the duration of each cycle, and alternately heat the mixture to the target temperature and maintain the temperature. Preferably, each cycle is 5-60 seconds; preferably, the microwave heating duration accounts for 60-75% of the total duration, and the light wave heating duration accounts for 25-40% of the total duration; and preferably, the target temperature is 180°C-270°C.

[0010] (4) After the oil bath treatment, the collected mixture can be used for pyrolysis, gasification and other processes.

[0011] The biomass described in the present invention is lignocellulosic biomass, including grasses, woody plants, litter, food processing waste, and the like, i.e., biomass raw materials primarily composed of one or more of cellulose, hemicellulose, and lignin. The waste oils and fats described in the present invention include swill oil, frying oil, soap stock and oil residues, byproducts of edible oil processing, inedible woody oils and fats, and crude glycerin, a byproduct of biodiesel production. The oil bath pretreatment involves oil bath baking of the waste oils and fats and the lignocellulosic biomass.

[0012] The present invention realizes the synergistic coupling of microwave heating and light wave heating, and takes advantage of the volume heating of microwave heating and the high dielectric properties of waste oil to achieve rapid heating of raw materials, shorten processing time, and reduce energy consumption; and the advantages of light wave heating such as high energy utilization efficiency and low energy consumption are used to preheat and insulate the containers used, reduce heat exchange between the raw material system and the environment, and achieve a rapid heating and constant insulation effect in the bio-oil oil bath process, effectively improving the efficiency of oil bath pretreatment, significantly improving the economy of the system, and having certain industrial application prospects.

[0013] Compared with the existing bio-oil pretreatment technology, the present invention has the following advantages.

[0014] (1) Microwave-coupled light wave heating is used to increase the heating rate of the reaction system through microwave heating, shorten the heating time, and maintain the temperature stability of the reaction system through light wave heating, thereby keeping the temperature insulated and reducing overall energy consumption.

[0015] (2) With the help of the high dielectric constant and high boiling point of waste oil, efficient microwave absorption and heat conversion are achieved. The high boiling point ensures that the system can operate normally under normal pressure, with low equipment requirements and reduced production costs.

[0016] (3) Select waste oil as the baking medium, simplify the technical process by changing the baking medium, reduce the steps of raw material processing before and after baking, and simplify the process flow. DETAILED DESCRIPTION

[0017] The present invention will be further illustrated by the following examples, which are intended to illustrate the present invention but not to limit it.

[0018] Example 1

[0019] According to the mass ratio of waste oil and fat: biomass = 5:2, 50g of waste oil and fat and 20g of walnut shell powder were weighed and mixed evenly, and placed in a normal pressure reactor. The outlet directly above the reactor was connected to a mechanical stirrer, and the side branch was connected to a condensation reflux device. After the reactor was installed, high-purity nitrogen was introduced to remove the air in the reactor and sealed, and continuous mechanical stirring was performed. The duration ratio of microwave heating and light wave heating was adjusted to 67:33, with each cycle being 15 seconds. After reaching the target temperature of 220°C, the temperature was kept warm for a total of 90 minutes, including the heating time, for oil bath pretreatment. During the oil bath treatment, the gases generated during the process were collected and measured. After the oil bath ended, the mixture was collected, and the pretreated walnut shells were collected by washing with dichloromethane, centrifugal separation, and low-temperature drying for elemental analysis. The results showed that the heating time was 12 minutes; gas analysis results showed that the CO2 production was 359.8 mL and the CO production was 155.7 mL; elemental analysis results showed that compared with the untreated walnut shell powder, the carbon content increased by 7.81 wt.%, the hydrogen content decreased by 0.36 wt.%, and the oxygen content decreased by 7.52 wt.%.

[0020] Application to rapid pyrolysis to prepare hydrocarbon compounds: The oil-bath mixture obtained in Example 1 (roasted walnut shell powder and waste oil) was subjected to rapid pyrolysis. 0.5 mg of the mixture was placed in a micro-cracker and heated to 650°C at a heating rate of 20°C / ms for 60 seconds. The pyrolysis gas was directly fed into a gas chromatography-mass spectrometer connected in series with the micro-cracker without condensation for component analysis. The results showed that the hydrocarbon compound content in the pyrolysis product was 97.48%, including 4.69% alkanes, 32.19% alkenes, 2.32% alkynes, 54.24% monocyclic aromatic hydrocarbons, and 4.04% polycyclic aromatic hydrocarbons.

[0021] Comparative Example 1 (microwave heating only)

[0022] 50g of waste oil and 20g of walnut shell powder were weighed and mixed in a ratio of 5:2. The mixture was then placed in a normal pressure reactor. A mechanical stirrer was connected to the reactor's top outlet, and a condenser reflux device was connected to the side outlet. After the reactor was installed, high-purity nitrogen was introduced to expel air from the reactor, and the reactor was sealed. Mechanical stirring was maintained throughout. Microwave heating was performed to a target temperature of 220°C, followed by a 90-minute oil bath pretreatment. During the oil bath treatment, the gases generated were collected and analyzed. After the oil bath, the mixture was collected, washed with dichloromethane, centrifuged, and dried at low temperature. The pretreated walnut shells were then collected for elemental analysis. The results showed a heating time of 6.5 minutes. Gas analysis revealed a CO2 production of 247.9mL and a CO production of 86.3mL. Elemental analysis revealed a 5.09wt.% increase in carbon content, a 0.49wt.% decrease in hydrogen content, and a 4.65wt.% decrease in oxygen content compared to untreated walnut shell powder.

[0023] Application to rapid pyrolysis to prepare hydrocarbon compounds: The mixture obtained after the oil bath in Comparative Example 1 (roasted walnut shell powder and waste oil) was used for rapid pyrolysis. 0.5 mg of the mixture was placed in a micro-cracker and heated to 650°C at a heating rate of 20°C / ms and maintained for 60 seconds. The pyrolysis gas was directly fed into a gas chromatography-mass spectrometer connected in series with the micro-cracker without condensation for component analysis. The results showed that the hydrocarbon compound content in the pyrolysis product was 92.51%, including 4.28% alkanes, 27.68% alkenes, 2.56% alkynes, 52.74% monocyclic aromatic hydrocarbons, and 5.25% polycyclic aromatic hydrocarbons.

[0024] Comparative Example 2 (Light Wave Heating Only)

[0025] 50g of waste oil and 20g of walnut shell powder were weighed and mixed in a ratio of 5:2. The mixture was then placed in a normal pressure reactor. A mechanical stirrer was connected to the reactor's top outlet, and a condenser reflux device was connected to the side outlet. After the reactor was installed, high-purity nitrogen was introduced to expel air from the reactor, and the reactor was sealed. Mechanical stirring was maintained throughout. Heat was applied by light wave heating to a target temperature of 220°C, which was then maintained for a total of 90 minutes, including the ramp time, for oil bath pretreatment. During the oil bath treatment, the gases generated were collected and analyzed. After the oil bath ended, the mixture was collected, washed with dichloromethane, centrifuged, and dried at low temperature. The pretreated walnut shells were then collected for elemental analysis. The ramp time was 25 minutes. Gas analysis revealed a CO2 production of 150.9mL and a CO production of 46.4mL. Elemental analysis revealed a 3.09wt.% increase in carbon content, a 0.48wt.% decrease in hydrogen content, and a 2.72wt.% decrease in oxygen content compared to untreated walnut shell powder.

[0026] Application to rapid pyrolysis to prepare hydrocarbon compounds: The mixture obtained after the oil bath in Comparative Example 2 (roasted walnut shell powder and waste oil) was used for rapid pyrolysis. 0.5 mg of the mixture was placed in a micro-cracker and heated to 650°C at a heating rate of 20°C / ms and maintained for 60 seconds. The pyrolysis gas was directly fed into a gas chromatography-mass spectrometer connected in series with the micro-cracker without condensation for component analysis. The results showed that the hydrocarbon compound content in the pyrolysis product was 89.41%, including 6.21% alkanes, 28.05% alkenes, 3.47% alkynes, 46.80% monocyclic aromatic hydrocarbons, and 4.88% polycyclic aromatic hydrocarbons.

[0027] Compared with Comparative Examples 1 and 2, it can be seen that the heating strategy described in Example 1 shows a significant advantage in terms of heating time compared to light wave heating alone. From the perspective of CO2 and CO gas production, it is significantly higher than the results in the two comparative examples. At the same time, the results of elemental analysis also show that the heating strategy described in Example 1 has the best effect on walnut shell oil bath deoxygenation, which is specifically reflected in a significant increase in carbon elements and a significant decrease in oxygen elements. From the perspective of application in the preparation of hydrocarbon compounds by rapid pyrolysis, the content of hydrocarbon compounds in Example 1 is significantly higher than that in Comparative Examples 1 and 2, and the content of high-value compound monocyclic aromatic hydrocarbons in Example 1 is also significantly higher than that in Comparative Examples 1 and 2.

[0028] Example 2 (the duration ratio of microwave heating to light wave heating is 67:33)

[0029] According to the mass ratio of waste oil: biomass = 5:3, 50g of waste oil and 30g of southern jujube kernel powder were weighed and mixed evenly, and placed in a normal pressure reactor. The outlet directly above the reactor was connected to a mechanical stirrer, and the side branch was connected to a condensation reflux device. After the reactor was installed, high-purity nitrogen was introduced to remove the air in the reactor and sealed, and continuous mechanical stirring was performed. The duration ratio of microwave heating and light wave heating was adjusted to 67:33, with each cycle being 15 seconds. After reaching the target temperature of 220°C, the temperature was kept warm for a total of 90 minutes, including the heating time, for oil bath pretreatment. During the oil bath treatment, the gases generated during the process were collected and measured. After the oil bath ended, the mixture was collected, and the pretreated walnut shells were collected by washing with dichloromethane, centrifugal separation, and low-temperature drying for elemental analysis. The results showed that the heating time was 14 minutes; gas analysis results showed that the CO2 production was 516.9 mL and the CO production was 224.9 mL; elemental analysis results showed that compared with the untreated Axillaris jujuba kernel powder, the carbon content increased by 8.34 wt.%, the hydrogen content decreased by 0.24 wt.%, and the oxygen content decreased by 8.10 wt.%.

[0030] Comparative Example 3 (the duration ratio of microwave heating to light wave heating is 51:49)

[0031] According to the mass ratio of waste oil and fat: biomass = 5:3, 50g of waste oil and fat and 30g of southern jujube kernel powder were weighed and mixed evenly, and placed in a normal pressure reactor. The outlet directly above the reactor was connected to a mechanical stirrer, and the side branch was connected to a condensation reflux device. After the reactor was installed, high-purity nitrogen was introduced to remove the air in the reactor and sealed, and continuous mechanical stirring was performed. The duration ratio of microwave heating and light wave heating was adjusted to 51:49, with each cycle being 15 seconds. After reaching the target temperature of 220°C, the temperature was kept warm for a total of 90 minutes, including the heating time, for oil bath pretreatment. During the oil bath treatment, the gases generated during the process were collected and measured. After the oil bath ended, the mixture was collected, and the pretreated walnut shells were collected by washing with dichloromethane, centrifugal separation, and low-temperature drying for elemental analysis. The results showed that the heating time was 17 minutes; gas analysis results showed that the CO2 production was 308.4 mL and the CO production was 94.7 mL; elemental analysis results showed that compared with the untreated walnut shell powder, the carbon content increased by 4.71 wt.%, the hydrogen content decreased by 0.46 wt.%, and the oxygen content decreased by 4.39 wt.%.

[0032] Comparative Example 4 (the duration ratio of microwave heating to light wave heating is 30:70)

[0033] According to the mass ratio of waste oil and fat: biomass = 5:3, 50g of waste oil and fat and 30g of southern jujube kernel powder were weighed and mixed evenly, and placed in a normal pressure reactor. The outlet directly above the reactor was connected to a mechanical stirrer, and the side branch was connected to a condensation reflux device. After the reactor was installed, high-purity nitrogen was introduced to remove the air in the reactor and sealed, and continuous mechanical stirring was performed. The duration ratio of microwave heating and light wave heating was adjusted to 30:70, with each cycle being 15 seconds. After reaching the target temperature of 220°C, the temperature was kept warm for a total of 90 minutes, including the heating time, for oil bath pretreatment. During the oil bath treatment, the gases generated during the process were collected and measured. After the oil bath ended, the mixture was collected, and the pretreated walnut shells were collected by washing with dichloromethane, centrifugal separation, and low-temperature drying for elemental analysis. The results showed that the heating time was 18.5 minutes; gas analysis results showed that the CO2 production was 279.3 mL and the CO production was 84.7 mL; elemental analysis results showed that compared with the untreated walnut shell powder, the carbon content increased by 4.56 wt.%, the hydrogen content decreased by 0.51 wt.%, and the oxygen content decreased by 4.18 wt.%.

[0034] Comparative Example 5 (Microwave Heating and Light Wave Heating)

[0035] According to the mass ratio of waste oil and fat: biomass = 5:3, 50g of waste oil and fat and 30g of southern jujube kernel powder were weighed and mixed evenly, and placed in a normal pressure reactor. The outlet directly above the reactor was connected to a mechanical stirrer, and the side branch was connected to a condensation reflux device. After the reactor was installed, high-purity nitrogen was introduced to remove the air in the reactor and sealed, and continuous mechanical stirring was performed. Microwave heating was used to heat the material to the target temperature. After reaching the target temperature of 220°C, light wave heating was used to keep the temperature for a total of 90 minutes, including the heating time, for oil bath pretreatment. During the oil bath treatment, the gases generated during the process were collected and measured. After the oil bath ended, the mixture was collected, and the pretreated walnut shells were collected by washing with dichloromethane, centrifugal separation, and low-temperature drying for elemental analysis. The results showed that the heating time was 8 minutes; gas analysis results showed that the CO2 production was 220.4 mL and the CO production was 67.1 mL; elemental analysis results showed that compared with the untreated walnut shell powder, the carbon content increased by 5.22 wt.%, the hydrogen content decreased by 0.31 wt.%, and the oxygen content decreased by 4.80 wt.%.

[0036] Compared with Comparative Examples 3, 4 and 5, it can be seen that Example 2 has a significant advantage in heating time over Comparative Examples 3 and 4. From the perspective of CO2 and CO gas production, it is significantly higher than the results in the three comparative examples. At the same time, the results of elemental analysis also reflect that the heating strategy described in Example 2 has the best effect on the oil bath deoxidation of the jujube kernel, which is specifically reflected in the significant increase of C element and the significant decrease of oxygen element.

[0037] Example 3 (15 seconds for one heating cycle)

[0038] According to the mass ratio of waste oil and fat: biomass = 5:2, 50g of waste oil and fat and 20g of corn cob powder were weighed and mixed evenly, and placed in a normal pressure reactor. The outlet directly above the reactor was connected to a mechanical stirrer, and the side branch was connected to a condensation reflux device. After the reactor was installed, high-purity nitrogen was introduced to remove the air in the reactor and sealed, and continuous mechanical stirring was performed. The duration ratio of microwave heating and light wave heating was adjusted to 67:33, with each cycle being 15 seconds. After reaching the target temperature of 220°C, the temperature was kept warm for a total of 90 minutes, including the heating time, for oil bath pretreatment. During the oil bath treatment, the gases generated during the process were collected and measured. After the oil bath ended, the mixture was collected, and the pretreated walnut shells were collected by washing with dichloromethane, centrifugal separation, and low-temperature drying for elemental analysis. The results showed that the heating time was 13 minutes; gas analysis results showed that the CO2 production was 415.3 mL and the CO production was 113.6 mL; elemental analysis results showed that compared with the untreated Axillaris jujuba kernel powder, the carbon content increased by 16.66 wt.%, the hydrogen content decreased by 0.11 wt.%, and the oxygen content decreased by 18.79 wt.%.

[0039] Comparative Example 6 (45 seconds for one heating cycle)

[0040] According to the mass ratio of waste oil and fat: biomass = 5:2, 50g of waste oil and fat and 20g of corn cob powder were weighed and mixed evenly, and placed in a normal pressure reactor. The outlet directly above the reactor was connected to a mechanical stirrer, and the side branch was connected to a condensation reflux device. After the reactor was installed, high-purity nitrogen was introduced to remove the air in the reactor and sealed, and continuous mechanical stirring was performed. The duration ratio of microwave heating and light wave heating was adjusted to 67:33, with each cycle being 45 seconds. After reaching the target temperature of 220°C, the temperature was kept warm for a total of 90 minutes, including the heating time, for oil bath pretreatment. During the oil bath treatment, the gases generated during the process were collected and measured. After the oil bath ended, the mixture was collected, and the pretreated walnut shells were collected by washing with dichloromethane, centrifugal separation, and low-temperature drying for elemental analysis. The results showed that the heating time was 14 minutes; gas analysis results showed that the CO2 production was 369.1 mL and the CO production was 79.6 mL; elemental analysis results showed that compared with the untreated walnut shell powder, the carbon content increased by 15.32 wt.%, the hydrogen content decreased by 0.35 wt.%, and the oxygen content decreased by 17.14 wt.%.

[0041] Comparative Example 7 (60 seconds for one heating cycle)

[0042] According to the mass ratio of waste oil and fat: biomass = 5:2, 50g of waste oil and fat and 20g of corn cob powder were weighed and mixed evenly, and placed in a normal pressure reactor. The outlet directly above the reactor was connected to a mechanical stirrer, and the side branch was connected to a condensation reflux device. After the reactor was installed, high-purity nitrogen was introduced to remove the air in the reactor and sealed, and continuous mechanical stirring was performed. The duration ratio of microwave heating and light wave heating was adjusted to 67:33, with each cycle being 60 seconds. After reaching the target temperature of 220°C, the temperature was kept warm for a total of 90 minutes, including the heating time, for oil bath pretreatment. During the oil bath treatment, the gases generated during the process were collected and measured. After the oil bath ended, the mixture was collected, and the pretreated walnut shells were collected by washing with dichloromethane, centrifugal separation, and low-temperature drying for elemental analysis. The results showed that the heating time was 14.5 minutes; gas analysis results showed that the CO2 production was 349.3 mL and the CO production was 61.7 mL; elemental analysis results showed that compared with the untreated walnut shell powder, the carbon content increased by 14.91 wt.%, the hydrogen content decreased by 0.41 wt.%, and the oxygen content decreased by 16.83 wt.%.

[0043] Compared with Comparative Examples 6 and 7, Example 3 demonstrates a significant advantage in heating time. The CO2 and CO production rates are significantly higher than those in the two comparative examples. Elemental analysis also demonstrates that the heating strategy described in Example 3 is the most effective for deoxygenating corncob oil baths, as evidenced by a significant increase in carbon and a significant decrease in oxygen.

[0044] The above description merely represents the preferred embodiments of the present invention, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications, improvements, and substitutions without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for pretreatment of biomass in an oil bath assisted by microwave-coupled light waves, characterized in that: The method comprises the following steps: (1) The waste oil and biomass are stirred and mixed in a certain proportion and placed in a normal pressure reactor. The outlet directly above the reactor is connected to a mechanical stirrer, and the side branch outlet is connected to a condensation reflux device; (2) Install the reactor, introduce inert gas to remove the air in the reactor and seal it; (3) Adjust the ratio of microwave heating to light wave heating and the duration of each cycle, and alternately heat the sample to the target temperature and keep it warm; (4) After the oil bath pretreatment, the mixture is collected for pyrolysis and gasification processes; The duration of each cycle in step (3) is 5-60 seconds; the microwave heating duration accounts for 60-75% of the total duration, and the light wave heating duration accounts for 25-40% of the total duration; the target temperature is 180°C-270°C.

2. The method of microwave-coupled light wave assisted biomass oil bath pretreatment according to claim 1, characterized in that: The mass ratio of the waste oil and fat to the biomass is 10:1 to 10:

7.

3. The method for microwave-coupled light wave-assisted biomass oil bath pretreatment according to claim 1 or 2, characterized in that: The biomass is lignocellulose biomass.