Biomass aerogel and preparation method and application thereof

Abstract

The application discloses biomass aerogel and a preparation method and application thereof, and adopts kitchen garbage as raw material, and after gelatinization, aging forming, freeze drying and heat treatment, biomass aerogel is obtained, the preparation method is simple in operation, low in cost, green and environment-friendly, and can realize resource utilization of biomass waste; the obtained biomass aerogel is porous and light, has good lipophilicity and hydrophobicity, stability and reusability, and can realize large-scale preparation, and is applied to treatment of marine pollution, river pollution and the like.

Description

Technical Field

[0001] This invention belongs to the field of porous material preparation technology, and particularly relates to a biomass aerogel, its preparation method and application. Background Technology

[0002] In recent years, the large-scale discharge of industrial oily wastewater and the frequent occurrence of oil spills have had a serious negative impact on aquatic ecosystems. Marine pollution and river pollution threaten the survival of humans and other organisms, thus attracting widespread social attention.

[0003] Currently, the main methods for treating oil pollution are physical, chemical, biological, and adsorption methods. Physical methods primarily use oil booms and skimmers, but their treatment efficiency is low. Chemical methods typically involve treating oil-water mixtures with chemical dispersants and solidifying agents or through direct in-situ combustion, but this can cause serious secondary pollution problems, such as dioxin emissions from combustion and the biotoxicity of dispersants. Biological methods generally utilize highly efficient microbial strains to specifically degrade oil pollutants; while there is no secondary pollution, the treatment cycle is long and environmental requirements are stringent. Adsorption methods mainly utilize superhydrophobic / superoleophilic materials such as membranes, foams, sponges, and aerogels for oil-water separation. Due to their advantages of simple operation, cost-effectiveness, and easy recycling, they have become a focus of attention. However, these materials still suffer from high preparation costs and secondary pollution, thus affecting their practical application.

[0004] Aerogels are porous nanoscale materials with extremely low density and unique porous structures. In recent years, aerogels have become a research hotspot in oil-water separation materials due to their considerable specific surface area and excellent adsorption properties. For example, invention patent application CN 114437399 A discloses a method for preparing a starch-biomass cellulose composite aerogel. The preparation method includes the following steps: weighing biomass fibers and dispersing them in an alkaline solution, adding ammonia and mechanically stirring, then adding starch and continuing to stir until the starch is completely dissolved to obtain a homogeneous solution; pouring the obtained homogeneous solution into a mold and heat-treating it in an oven, followed by freeze-drying to obtain the starch-biomass cellulose composite aerogel. However, when using the starch-biomass cellulose composite aerogel for oil-water separation, the composite aerogel structure is easily deformed and damaged, and its performance deteriorates rapidly, making it unsuitable for long-term use. In addition, the preparation process of the above-mentioned composite aerogel uses a large amount of chemical raw materials such as alkaline solution and ammonia, which is environmentally unfriendly. Summary of the Invention

[0005] To address the above problems, this invention provides a biomass aerogel and its preparation method, which enables the low-cost and environmentally friendly large-scale preparation of biomass aerogel and its application in oil-water separation.

[0006] The technical solution of the present invention to solve the above problems is as follows:

[0007] A method for preparing biomass aerogel includes the following steps:

[0008] S1. Mix kitchen waste with water and heat it to gelatinize it, thus obtaining a paste.

[0009] S2. Let the paste stand to age and solidify, and you will get a hydrogel.

[0010] S3. Freeze-dry the hydrogel to obtain a porous body, and then heat-treat the porous body to carbonize it to obtain a biomass aerogel.

[0011] Preferably, in step S1, the kitchen waste includes at least vegetables and rice / noodles.

[0012] As is common knowledge in this field, biomimetic loofah sponges are lightweight, porous, and highly resistant to pressure. Based on this, the applicant used kitchen waste, including at least vegetable and rice / noodle waste, as raw materials. The cellulose in the vegetable waste served as the framework, and the starch in the rice / noodle waste served as the cross-linking agent, forming a complete gel network structure similar to a biomimetic loofah sponge.

[0013] Preferably, in step S1, the mass ratio of rice / noodles to vegetables is (0.01~5):(0.01~5).

[0014] Preferably, in step S1, the mass ratio of kitchen waste to water is (0.5~2):(4~6).

[0015] Preferably, in step S1, the gelatinization temperature is 85~100℃ and the gelatinization time is 30~50min.

[0016] Preferably, in step S2, the aging and molding temperature is 1~6℃ and the time is 20~28h.

[0017] Preferably, in step S3, the hydrogel is pre-frozen at -4~0℃ for 5~9h before freeze-drying, and the freeze-drying temperature is -60~-20℃ for 35~45h.

[0018] Preferably, in step S3, the heat treatment temperature is 260~300℃ and the time is 1~3h.

[0019] The present invention also provides a biomass aerogel, which is obtained by the above-described preparation method.

[0020] The present invention also provides the application of the above-mentioned biomass aerogel in the field of oil-water separation, including the treatment of marine pollution, river pollution, etc.

[0021] The present invention has the following beneficial effects:

[0022] This invention provides a method for preparing biomass aerogel. Using kitchen waste as raw material, the aerogel is obtained through gelatinization, aging, freeze-drying, and heat treatment. This preparation method is simple to operate, low in cost, and environmentally friendly, and enables the resource utilization of biomass waste. The resulting biomass aerogel is porous, lightweight, and possesses good oleophilic and hydrophobic properties, stability, and reusability. It can be prepared on a large scale and applied to the treatment of marine and river pollution. Attached Figure Description

[0023] Figure 1 SEM images of Example 1, Example 3 and Comparative Example 1;

[0024] Figure 2 EDS plots for Examples 1, 3, and Comparative Example 1;

[0025] Figure 3 The XRD patterns are of Examples 1-4 and Comparative Examples 1-2;

[0026] Figure 4 The FT-IR plots are for Examples 1-4 and Comparative Examples 1-2;

[0027] Figure 5 The figures show the contact angle test results of Examples 1-4 and Comparative Examples 1-2;

[0028] Figure 6 This is a graph showing the oil-water separation performance test results of Example 2;

[0029] Figure 7 The results of oil absorption and oil retention tests are for Examples 1-4 and Comparative Examples 1-2.

[0030] Figure 8 The graph shows the repeatability test results of Examples 1-4 and Comparative Examples 1-2. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0032] Example 1

[0033] S1. Weigh 40.0761g of rice and flour kitchen waste and 10.0230g of vegetable kitchen waste and add them to 250mL of deionized water. Place them in a 95℃ water bath for 40min to gelatinize and obtain a paste.

[0034] S2. Pour the paste into the mold and cover it with plastic wrap to prevent moisture evaporation. After the paste in the mold cools to room temperature, transfer it to a refrigerator at 4°C for aging and molding for 24 hours to obtain a hydrogel.

[0035] S3. Transfer the hydrogel to a low-temperature freezer at -4℃ for 7 hours to pre-freeze. Demold the frozen hydrogel and place it in a freeze dryer at -40℃ for 40 hours. Then, heat-treat it in a muffle furnace at 280℃ for 2 hours to obtain biomass aerogel, denoted as C-02.

[0036] Example 2

[0037] S1. Weigh 37.5612g of rice and flour kitchen waste and 12.6584g of vegetable kitchen waste and add them to 250mL of deionized water. Place them in a 95℃ water bath for 40min to gelatinize and obtain a paste.

[0038] S2. Pour the paste into the mold and cover it with plastic wrap to prevent moisture evaporation. After the paste in the mold cools to room temperature, transfer it to a refrigerator at 4°C for aging and molding for 24 hours to obtain a hydrogel.

[0039] S3. Transfer the hydrogel to a low-temperature freezer at -4℃ for 7 hours to pre-freeze. Demold the frozen hydrogel and place it in a freeze dryer at -40℃ for 40 hours. Then, heat-treat it in a muffle furnace at 280℃ for 2 hours to obtain biomass aerogel, denoted as C-03.

[0040] Example 3

[0041] S1. Weigh 33.2939g of rice and flour kitchen waste and 16.7708g of vegetable kitchen waste and add them to 250mL of deionized water. Place them in a 95℃ water bath for 40min to gelatinize and obtain a paste.

[0042] S2. Pour the paste into the mold and cover it with plastic wrap to prevent moisture evaporation. After the paste in the mold cools to room temperature, transfer it to a refrigerator at 4°C for aging and molding for 24 hours to obtain a hydrogel.

[0043] S3. Transfer the hydrogel to a low-temperature freezer at -4℃ for 7 hours to pre-freeze. Demold the frozen hydrogel and place it in a freeze dryer at -40℃ for 40 hours. Then, heat-treat it in a muffle furnace at 280℃ for 2 hours to obtain biomass aerogel, denoted as C-04.

[0044] Example 4

[0045] S1. Weigh 25.1352g of rice and flour kitchen waste and 25.0703g of vegetable kitchen waste and add them to 250mL of deionized water. Place them in a 95℃ water bath for 40min to gelatinize and obtain a paste.

[0046] S2. Pour the paste into the mold and cover it with plastic wrap to prevent moisture evaporation. After the paste in the mold cools to room temperature, transfer it to a refrigerator at 4°C for aging and molding for 24 hours to obtain a hydrogel.

[0047] S3. Transfer the hydrogel to a low-temperature freezer at -4℃ for 7 hours to pre-freeze. Demold the frozen hydrogel and place it in a freeze dryer at -40℃ for 40 hours. Then, heat-treat it in a muffle furnace at 280℃ for 2 hours to obtain biomass aerogel, denoted as C-05.

[0048] Comparative Example 1

[0049] S1. Weigh 50.0480g of rice and flour kitchen waste and add it to 250mL of deionized water. Place it in a 95℃ water bath for 40min to gelatinize and obtain a paste.

[0050] S2. Pour the paste into the mold and cover it with plastic wrap to prevent moisture evaporation. After the paste in the mold cools to room temperature, transfer it to a refrigerator at 4°C for aging and molding for 24 hours to obtain a hydrogel.

[0051] S3. Transfer the hydrogel to a low-temperature freezer at -4℃ for 7 hours to pre-freeze. Demold the frozen hydrogel and place it in a freeze dryer at -40℃ for 40 hours. Then, heat-treat it in a muffle furnace at 280℃ for 2 hours to obtain biomass aerogel, denoted as C-01.

[0052] Comparative Example 2

[0053] S1. Weigh 50.8675g of vegetable kitchen waste and add it to 250mL of deionized water. Place it in a 95℃ water bath for 40min to gelatinize and obtain a paste.

[0054] S2. Pour the paste into the mold and cover it with plastic wrap to prevent moisture evaporation. After the paste in the mold cools to room temperature, transfer it to a refrigerator at 4°C for aging and molding for 24 hours to obtain a hydrogel.

[0055] S3. Transfer the hydrogel to a low-temperature freezer at -4℃ for 7 hours to pre-freeze. Demold the frozen hydrogel and place it in a freeze dryer at -40℃ for 40 hours. Then, heat-treat it in a muffle furnace at 280℃ for 2 hours to obtain biomass aerogel, denoted as C-06.

[0056] The morphology and structure of the above-mentioned examples and comparative examples were characterized using SEM, XRD, EDS, and FT-IR. The hydrophobic properties of Examples 1-4 and Comparative Examples 1-2 were tested using a contact angle meter, and the results are as follows. Figures 1-5 As shown.

[0057] Figure 1 SEM images of Example 1, Example 3, and Comparative Example 1, from... Figure 1 It can be seen that Comparative Example 1 (C-01) has a very large number of obvious pore structures, and the pore structures are densely distributed and large in size, but the pore thickness is relatively thin. Compared with Comparative Example 1, after increasing the proportion of vegetable waste in the aerogel, Examples 1 (C-02) and 3 (C-04) also showed an increase in pore thickness while maintaining the porous and macroporous structure, which enhanced the oil absorption performance of the aerogel. However, after further increasing the proportion of vegetable waste in the aerogel, it can be seen that with the increase of the proportion of vegetable waste, the salt content remaining in the aerogel also increases, the overall structure begins to become brittle, and the mechanical strength of the aerogel begins to deteriorate.

[0058] Figure 2 EDS plots for Examples 1, 3, and Comparative Example 1, from... Figure 2 It can be seen that the main elements of aerogel are N and C, indicating that the aerogel of this application belongs to green and pollution-free devices;

[0059] Figure 3 The XRD patterns are of Examples 1-4 and Comparative Examples 1-2. Figure 3 It can be seen that the obtained diffraction peaks are consistent with the JCPDS 99-0059 standard card corresponding to NaCl, indicating that as the amount of vegetable waste in the aerogel preparation process increases, NaCl will remain in the biomass aerogel. Judging from the intensity of the diffraction peaks, as the proportion of vegetable waste increases, the amount of NaCl remaining in the aerogel also gradually increases, which corresponds to the phenomenon observed in the above SEM image.

[0060] Figure 4 The FT-IR plots for Examples 1-4 and Comparative Examples 1-2 are shown below. Figure 4 It can be seen that 3432cm -1 The peak at 1632 cm⁻¹ represents the stretching vibration of the OH group. -1 The peak at 1400 cm⁻¹ represents the stretching vibration of the NH group. -1 The corresponding peaks are C=C vibration peaks, and the infrared spectra of biomass aerogels prepared from different proportions of rice and flour-based kitchen waste remain almost unchanged, proving that the internal composition of biomass aerogels is almost unchanged and contains C and N elements, which corresponds to the SEM and EDS images.

[0061] Figure 5The graph shows the contact angle test results of Examples 1-4 and Comparative Examples 1-2. From C-01 to C-06, as the amount of vegetable waste added increases, the contact angle of the aerogel shows an overall trend of first increasing and then decreasing. Among them, Example 2 (C-03) has the largest contact angle at 124.6°. When the biomass aerogel contains only vegetable waste and no rice or flour waste, Comparative Example 2 (C-06) has the smallest contact angle at only 103.1°. The contact angle changes are small in the early stage. The applicant believes that this is because its main component is still starch and there is not much fiber added. Therefore, the contact angle does not change much in the early stage. However, in Comparative Example 2 (C-06), the aerogel contains almost no starch and the fibers are randomly distributed. The prepared aerogel has many gaps and will absorb water. Therefore, the contact angle begins to decrease.

[0062] The oil-water separation performance of the aerogel obtained in Example 2 was tested. The oil used in the test was from ARAMCO, with an API specific gravity between 20 and 35 (the specific gravity of oil fluid relative to water) and a viscosity of 4 to 6 cSt at 40°C.

[0063] The testing method is as follows:

[0064] (a) The aerogel obtained in Example 2 is placed in the middle of the vacuum filtration device;

[0065] (b) Mark the oil red with oil red and the deionized water blue with methylene blue;

[0066] (c) Shake the oil and deionized water well;

[0067] (d) Pour the oil-water mixture into the vacuum filter and observe the oil-water separation.

[0068] The results are as follows Figure 6 As shown, after the oil-water mixture is poured into the filter device, the aqueous phase flows into the receiving bottle through the aerogel, while the oil phase is adsorbed and fixed.

[0069] The oil absorption and oil retention properties of the above embodiments and comparative examples were tested. The test methods are as follows. The oil used in the test was from ARAMCO, with an API specific gravity between 20 and 35 (the specific gravity of petroleum fluid relative to water) and a viscosity of 4 to 6 cSt at 40°C.

[0070] Oil absorption capacity test:

[0071] After weighing the aerogels obtained in the examples and comparative examples, immerse them in a beaker containing 50 ml of oil and soak at room temperature for 5 minutes. Hang the beaker until no oil droplets remain, then weigh the aerogels using an electronic analytical balance to calculate the oil absorption. Each sample was measured three times, and the average value was taken.

[0072] The amount of oil absorbed can be obtained from (1).

[0073] W = (Mt - M0) / M0 (1)

[0074] In the formula: W is the oil absorption amount, g / g;

[0075] M0 is the initial aerogel mass, in g;

[0076] Mt is the total mass after oil absorption, in grams.

[0077] Oil retention capacity test:

[0078] The oil retention properties of the aerogels obtained in the examples and comparative examples were evaluated by comparing the changes in the initial mass (M0) of the aerogels after 5 min of adsorption (M1), the mass after 30 min of adsorption, and the mass after 12 h of adsorption (M2).

[0079] The oil retention capacity can be obtained from (2).

[0080] R=(M2-M0) / (M1-M0)×100% (2)

[0081] In the formula: R is the oil retention capacity, g / g;

[0082] M0 is the initial mass of the high-temperature carbonized aerogel, in g;

[0083] M1 is the total mass after 5 minutes of oil absorption, in grams;

[0084] M2 is the total mass after 30 min / 12 h of oil absorption, in grams.

[0085] The oil absorption and oil retention performance test results of the examples and comparative examples are as follows: Figure 7 As shown:

[0086] The bar chart represents the oil absorption performance test analysis. The oil absorption of aerogels generally shows a pattern of high absorption in the middle and low absorption at both ends. The oil absorption of aerogels is as follows: C-01 is 5.45 g / g, C-02 is 5.49 g / g, C-03 is 6.22 g / g, C-04 is 5.60 g / g, C-05 is 5.72 g / g, and C-06 is 5.47 g / g. The oil absorption capacity was highest in C-03, reaching 6.22 g / g, while it was lowest in C-01, at only 5.45 g / g. The oil absorption capacity of C-06 was only 0.02 g / g higher than that of C-01. This is because, in the preparation of the aerogel, there was no vegetable waste in Comparative Example 1, resulting in fewer pores in the aerogel and weaker oil absorption capacity. In Comparative Example 2, the proportion of vegetable waste was too high, and the increase in NaCl residue would also affect the oil absorption performance. This is consistent with the detection results of the SEM image.

[0087] The line graph shows the oil retention performance test analysis of the aerogel, indicating that the oil retention capacity of the aerogel decreases with increasing time. The specific oil retention rates of the aerogels obtained in the above examples and comparative examples are as follows: After 30 minutes, the oil retention rates were 99.65% for C-01, 99.01% for C-02, 98.55% for C-03, 97.86% for C-04, 99.09% for C-05, and 95.47% for C-06. The highest oil retention rate was 99.65% for C-01, and the lowest was 95.47% for C-06. After 12 hours... The oil retention rates were 97.49% for C-01, 96.73% for C-02, 95.46% for C-03, 95.44% for C-04, 98.05% for C-05, and 92.81% for C-06. The highest oil retention rate was observed for C-05, and the lowest was 92.81% for C-06. Although the aerogels with the highest oil retention rates after 30 min and 12 h were different, it was observed that the lowest and most unstable C-06 still had an oil retention rate as high as 92.81% after 12 h, indicating that the aerogels prepared by the method of this invention have excellent oil retention properties.

[0088] To test the reproducibility of the aerogel of this application, the aerogels prepared in the above examples and comparative examples were subjected to 10 oil-water separation cycles. The results are as follows: Figure 8 As shown: C-01 decreased from 99.65% to 89.5%, C-02 from 96.73% to 79.85%, C-03 from 98.55% to 89.49%, C-04 from 97.86% to 77.44%, C-05 from 99.09% to 71.47%, and C-06 from 95.47% to 61.13%. Among them, C-01 and C-03 decreased by about 10%, C-02 and C-04 by about 20%, and C-06 experienced the most severe decrease, at about 34%. Overall, this indicates that only biomass aerogels made from vegetable waste may have high oil absorption capacity in the early stages, but their recyclability is low; while C-01 and C-03, although decreasing after repeated adsorption, show little change, demonstrating good reusability.

[0089] However, considering the overall pore structure, contact angle test, oil absorption capacity test, and oil retention performance test results of the aerogel, the aerogel (C-01) prepared in Comparative Example 1 showed poor overall performance and could not be used for oil-water separation. In contrast, the biomass aerogels (C-02, C-03, C-04, C-05) prepared using the method of this invention are porous, lightweight, and possess good oleophilic and hydrophobic properties, stability, and reusability, making them suitable for oil-water separation, especially for treating marine and river pollution.

Claims

1. A method for preparing biomass aerogel, comprising the following steps: S1. Mix kitchen waste with water and heat it to gelatinize it, thus obtaining a paste. S2. Let the paste stand to age and solidify, and you will get a hydrogel. S3. Freeze-dry the hydrogel to obtain a porous body, and then heat-treat the porous body to carbonize it to obtain a biomass aerogel; wherein, in step S3, the heat treatment temperature is 260~300℃ and the time is 1~3h; the kitchen waste includes at least vegetables and rice.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of rice and flour to vegetables is (0.01~5):(0.01~5).

3. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of kitchen waste to water is (0.5~2):(4~6).

4. The preparation method according to claim 1, characterized in that, In step S1, the gelatinization temperature is 85~100℃ and the gelatinization time is 30~50min.

5. The preparation method according to claim 1, characterized in that, In step S2, the aging molding temperature is 1~6℃ and the time is 20~28h.

6. The preparation method according to claim 1, characterized in that, In step S3, the hydrogel is pre-frozen at -4~0℃ for 5~9h before freeze-drying, and the freeze-drying temperature is -40~-20℃ for 35~45h.

7. A biomass aerogel, characterized in that, The biomass aerogel is obtained by the preparation method according to any one of claims 1 to 6.

8. The application of the biomass aerogel according to claim 7 in the field of oil-water separation.

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