A microalgae harvesting agent coupling in-situ flocculation and froth flotation and application thereof

Abstract

The application discloses a kind of in-situ flocculation and froth flotation coupling microalgae harvesting agent and application thereof, and relates to the technical field of microalgae harvesting.The microalgae harvesting agent is composed of cationic guar gum and sodium sulfosuccinate, and through the synergistic promotion of the two, the floc particle size and internal tightness are increased, the floc moisture content is reduced, and finally the microalgae collection efficiency and enrichment ratio are significantly improved, which is beneficial to the subsequent processing of microalgae biomass and improves the engineering application value of the coupling process for large-scale microalgae harvesting, providing technical guidance for efficient microalgae harvesting and enrichment.

Description

Technical Field

[0001] This invention relates to the field of microalgae harvesting technology, and in particular to microalgae harvesting agents coupled with in-situ flocculation and foam flotation and their applications. Background Technology

[0002] Microalgae, as a major source of third-generation biofuels, can not only replace traditional fossil fuels to address the energy crisis, but also have wide applications in wastewater treatment, pharmaceuticals, food, and cosmetics. Microalgae can fix atmospheric carbon dioxide through photosynthesis, helping to reduce greenhouse gas emissions. Besides extracting biofuels, microalgae can also produce other high-value-added products, such as crude protein, vitamins, and pigments.

[0003] However, harvesting is an unavoidable step in the practical application of microalgae and its biomass utilization. Microalgae harvesting is a crucial process for enriching and concentrating microalgae after they have been cultured to a certain biomass concentration. Due to their small particle size (2-30 μm), low biomass density (0.5-5.0 g / L), and negatively charged surface, microalgae are stably dispersed in the culture system; the polysaccharides and proteins secreted by microalgae give the entire culture system colloidal stability. These characteristics all increase the difficulty of microalgae harvesting. Related research results indicate that in practical applications, costs related to microalgae harvesting account for 20%–30% of the total cost, which significantly limits the progress of large-scale commercial applications of microalgae.

[0004] Currently, commonly used methods for microalgae harvesting include sedimentation, centrifugation, filtration, flocculation, flotation, and electrostatic extraction. Among these, sedimentation relies solely on the gravity of the microalgae to separate them from the water, which is time-consuming and has low harvesting efficiency. Centrifugation and filtration can achieve rapid microalgae harvesting, but they consume a lot of energy and are costly, making them unsuitable for large-scale production. Flocculation and flotation are considered two technologies suitable for large-scale microalgae harvesting, offering advantages such as ease of operation and high feasibility.

[0005] Flocculation utilizes the negatively charged surface of microalgae to induce the aggregation of microalgal cells into flocs. These flocs then settle easily under gravity to the bottom of the solution and separate from the water. Flotation, on the other hand, is a simple and low-cost harvesting method based on physicochemical gravity separation. When air bubbles pass through a liquid-solid suspension, microalgae adhere to the bubbles and float to the surface, then separate from the water through overflow or scraping.

[0006] Among existing microalgae harvesting technologies, Chinese patent application CN106701584A discloses a method using trivalent Fe 3+Chemical methods for harvesting microalgae have been developed, but the impact of metal ions on microalgal biomass is uncertain, hindering the reuse of harvested wastewater. Furthermore, the harvesting time is too long, requiring 12 hours of settling for complete harvesting, which is unsuitable for large-scale practical production. Chinese patent application CN103103125A uses microbial secretions to flocculate microalgae, followed by air flotation to harvest the microalgal flocs. However, this technology involves complex microbial flocculant extraction, low flocculant yield, and the impact of residual flocculants on microalgal biomass has not been fully assessed. Dissolved air flotation requires high energy consumption, demanding extremely high pressure and energy input, resulting in high harvesting costs. Summary of the Invention

[0007] This invention provides a microalgae harvesting agent coupled with in-situ flocculation and foam flotation, and its application. By preparing cationic guar gum and sodium sulfostearate, flocculation is first performed using cationic guar gum, followed by flotation using sodium sulfostearate. This achieves green, in-situ, short-range, and efficient harvesting of microalgae with low energy consumption, which is beneficial for subsequent processing of microalgae biomass. Specifically, this is achieved through the following techniques.

[0008] A microalgae harvesting agent coupled with in-situ flocculation and foam flotation comprises cationic guar gum and sodium sulfostearate, wherein the mass ratio of cationic guar gum to sodium sulfostearate is 1:(1-4).

[0009] The method for preparing the sodium sulfostearate includes the following steps:

[0010] Oleic acid, concentrated sulfuric acid and glacial acetic acid are stirred and mixed evenly. Hydrogen peroxide is added and the mixture is reacted at 40-90℃ for 1-3 h. The aqueous phase containing epoxy oleic acid is then separated.

[0011] Add sodium bisulfite solution to the aqueous phase containing the epoxy oleic acid, stir and mix evenly, react at 70-90℃ for 2-4 h, wash, and separate the organic phase containing sulfostearic acid;

[0012] Sodium hydroxide was added to the organic phase, and the reaction was carried out at 100-140°C for 4-7 h. The mixture was then purified with saturated sodium chloride solution, filtered, and dried to obtain the sodium sulfostearate.

[0013] Furthermore, the preparation method of the cationic guar gum includes the following steps:

[0014] Guar gum and sodium hydroxide solution were added to isopropanol and stirred until homogeneous to obtain a system containing alkalized guar gum.

[0015] Add 3-chloro-2-hydroxypropyltrimethylammonium chloride to the system, and then add sodium hydroxide solution and isopropanol again, stirring to mix thoroughly;

[0016] The mixture is heated to 50-80℃ and reacted for 2-4 hours. After filtration, washing, and drying, the cationic guar gum is obtained.

[0017] In the method for preparing cationic guar gum provided by this invention, the reaction system needs to maintain a stable alkaline environment, generally with a pH value ≥ 11. For this purpose, an appropriate amount of sodium hydroxide solution can be added before and after the reaction to maintain the alkaline environment. The washing process after the reaction is completed can generally be carried out using an 80% (v / v) isopropanol aqueous solution.

[0018] Optionally, in the method for preparing cationic guar gum, the mass ratio of guar gum to isopropanol is 1:(0.03-0.08):(4-7).

[0019] Furthermore, in the method for preparing cationic guar gum, the mass ratio of guar gum, 3-chloro-2-hydroxypropyltrimethylammonium chloride, and the added isopropanol is 1:(0.5-1.0):(4-7).

[0020] Furthermore, in the preparation method of the sodium sulfostearate, the mass ratio of oleic acid, concentrated sulfuric acid, hydrogen peroxide and glacial acetic acid is 1:(0.01-0.03):(0.17-0.24):(0.05-0.10).

[0021] Furthermore, in the preparation method of the sodium sulfostearate, the mass ratio of epoxy oleic acid to sodium bisulfite is 1:(0.05-0.1).

[0022] Furthermore, in the method for preparing sodium sulfostearate, the mass ratio of sulfostearic acid to sodium hydroxide is 1:(0.2-0.4).

[0023] In the preparation method of sodium sulfostearate, the concentration and amount of sodium bisulfite solution can be adjusted appropriately to ensure complete preparation of sulfostearate after the reaction. Generally, a saturated sodium bisulfite solution can be used.

[0024] After preparing an aqueous phase containing epoxy oleic acid, the epoxy oleic acid can be separated from the aqueous phase (by means of instruments such as a separatory funnel) after a short period of standing. This allows the epoxy oleic acid to be separated, washed, and its quality determined.

[0025] This invention provides the application of the microalgae harvesting agent coupled with in-situ flocculation and foam flotation as described in any one of the above-mentioned claims in the harvesting of microalgae.

[0026] The present invention also provides a method for harvesting microalgae, which uses the microalgae harvesting agent coupled with in-situ flocculation and foam flotation as described in any one of the above-mentioned methods. The cationic guar gum is added to the microalgae suspension and stirred; the sodium sulfostearate is added, and flotation stirring and foam scraping are carried out under aeration conditions to complete the microalgae harvesting.

[0027] Furthermore, the steps of the microalgae harvesting method include: using cationic guar gum at a concentration of 5-40 mg / L and sodium sulfostearate at a concentration of 30-90 mg / L.

[0028] Furthermore, in the microalgae harvesting method, after adding sodium sulfostearate, the flotation stirring method is to stir at 1400-2100 rpm for 5 min;

[0029] Furthermore, in the microalgae harvesting method, the aeration rate is 0.1-0.4 m / s. 3 / h.

[0030] Furthermore, in the microalgae harvesting method, the scraping time is 1-5 minutes.

[0031] The present invention also provides a method for culturing microalgae, which, in addition to the methods commonly used in the art for culturing microalgae, also includes the microalgae harvesting method described in any one of the above-mentioned methods.

[0032] Optionally, the microalgae cultivation method can be autotrophic, heterotrophic, or fascicative.

[0033] Alternatively, the culture medium used in the microalgae cultivation method can be BG-11 medium, synthetic wastewater, or pretreated actual wastewater.

[0034] Compared with existing technologies, the advantages of this invention are as follows: This invention uses guar gum and oleic acid, which are widely available raw materials, to prepare cationic guar gum and sodium sulfostearate, respectively, each with its own advantages. The combined use of these two materials forms a green, short-range, and efficient microalgae harvesting technology. This combined application is the first of its kind in the field of microalgae harvesting technology. Compared with using cationic guar gum alone or using flotation agents alone, the microalgae harvesting technology of this invention significantly improves the microalgae harvesting efficiency, significantly increases the floc particle size and internal compactness, and reduces the floc moisture content, which is beneficial for subsequent microalgae biomass processing. This enhances the engineering application value of this coupled process for large-scale microalgae harvesting. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the device structure for harvesting microalgae using the flocculation-flotation coupling process employed in the embodiments of this application; in the figure, 1 represents the introduced air, and 2 represents the obtained microalgae flocs.

[0036] Figure 2 The images show microalgal flocs obtained by the flocculation-only method (a) of Comparative Example 1 and the flocculation-flotation method (b) of Example 1, respectively. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In some embodiments of the present invention, the provided in-situ flocculation and foam flotation coupled microalgae harvesting agent comprises cationic guar gum and sodium sulfostearate.

[0039] The preparation method of the cationic guar gum includes the following steps:

[0040] Guar gum and sodium hydroxide solution were added to isopropanol and stirred until homogeneous to obtain a system containing alkalized guar gum.

[0041] Add 3-chloro-2-hydroxypropyltrimethylammonium chloride to the system, and then add sodium hydroxide solution and isopropanol again, and stir to mix evenly; optionally, the stirring and mixing method can be to stir at 20-40℃ for 0.5-2 h;

[0042] The mixture is heated to 50-80℃ and reacted for 2-4 hours. After filtration, washing, and drying, the cationic guar gum is obtained.

[0043] The method for preparing the sodium sulfostearate includes the following steps:

[0044] Oleic acid, concentrated sulfuric acid and glacial acetic acid are stirred and mixed evenly. Hydrogen peroxide is added and the mixture is reacted at 40-90℃ for 1-3 h. The aqueous phase containing epoxy oleic acid is then separated.

[0045] Add sodium bisulfite solution to the aqueous phase containing the epoxy oleic acid, stir and mix evenly, react at 70-90℃ for 2-4 h, wash, and separate the organic phase containing sulfostearic acid;

[0046] Sodium hydroxide was added to the organic phase, and the reaction was carried out at 100-140°C for 4-7 h. The mixture was then purified with saturated sodium chloride solution, filtered, and dried to obtain the sodium sulfostearate.

[0047] Optionally, in the above method for preparing cationic guar gum, the mass ratio of guar gum to isopropanol is 1:(4-7).

[0048] Optionally, in the above method for preparing cationic guar gum, the mass ratio of guar gum, 3-chloro-2-hydroxypropyltrimethylammonium chloride and the added isopropanol is 1:(0.5-1.0):(4-7).

[0049] Optionally, in the above method for preparing sodium sulfostearate, the mass ratio of oleic acid, concentrated sulfuric acid, hydrogen peroxide and glacial acetic acid is 1:(0.01-0.03):(0.17-0.24):(0.05-0.10).

[0050] Optionally, in the above method for preparing sodium sulfostearate, the mass ratio of epoxy oleic acid to sodium bisulfite is 1:(0.05-0.1).

[0051] In the above method for preparing sodium sulfostearate, the mass ratio of sulfostearic acid to sodium hydroxide is 1:(0.2-0.4).

[0052] In other embodiments of the present invention, a method for harvesting microalgae using the microalgae harvesting agent coupled with the above-mentioned in-situ flocculation and foam flotation is provided. The specific steps include: adding the cationic guar gum to the microalgae suspension and stirring; adding the sodium sulfostearate, stirring and skimming the foam under aeration conditions to complete the microalgae harvesting.

[0053] Optionally, in the above-mentioned microalgae harvesting method, the amount of cationic guar gum used is 5-40 mg / L, and the amount of sodium sulfostearate flotation agent used is 30-90 mg / L.

[0054] Optionally, in the above microalgae harvesting method, the stirring method is to stir at 1400-2100 rpm for 5 min.

[0055] Optionally, in the above-mentioned microalgae harvesting method, the aeration rate is 0.1-0.4 m. 3 / h.

[0056] Optionally, in the above microalgae harvesting method, the skimming time is 1-5 minutes.

[0057] Example 1

[0058] The microalgae harvesting agent coupled with in-situ flocculation and foam flotation provided in this embodiment includes cationic guar gum and sodium sulfostearate.

[0059] The preparation method of cationic guar gum is as follows:

[0060] (1) Take 10 g of guar gum powder into a 250 ml three-necked flask, add 59 g of isopropanol and 1.44 g of 40% sodium hydroxide solution, stir at room temperature for 1 h to obtain a system containing alkalized guar gum;

[0061] (2) Add 7.7 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride solution and 1.44 g of 40% sodium hydroxide solution to the system containing alkalized guar gum in sequence;

[0062] (3) Heat the system to 55°C, stir for 3 h, and filter to separate the crude product of cationic guar gum.

[0063] (4) The crude cationic guar gum was filtered and then washed three times with 50 mL of isopropanol solution (isopropanol:water = 8:2, volume ratio); the washed and purified cationic guar gum was dried in a vacuum drying oven at 40℃ for 24 h to obtain the cationic guar gum product.

[0064] The preparation method of sodium sulfostearate is as follows:

[0065] (1) Preparation of epoxy oleic acid: 40 g of oleic acid was added to a 250 ml three-necked flask, and 0.8 g of concentrated sulfuric acid and 3.2 g of glacial acetic acid were added respectively. After stirring for 30 min, the system was heated to 55 °C and 25.5 g of hydrogen peroxide solution (hydrogen peroxide mass fraction 30%, analytical grade) was added dropwise. The reaction was continued to be stirred for 1.5 h, and the aqueous phase containing epoxy oleic acid was separated.

[0066] (2) The aqueous phase containing epoxy oleic acid was heated to 80°C for 4 h with 30.6 g sodium bisulfite solution (sodium bisulfite mass fraction 33%). After the reaction was completed, the organic phase was washed 3 times with pure water and transferred to a new three-necked flask.

[0067] (3) Add 47.5 g of NaOH solution (40% NaOH mass fraction) at 120℃ and react for 6 h. Filter the product, purify it with saturated sodium chloride solution, filter it, and dry it in a vacuum drying oven at 40℃ for 24 h to obtain the sodium sulfostearate.

[0068] Comparative Example 1

[0069] This comparative example directly used only the cationic guar gum prepared in Example 1 for microalgae collection. The collection process involved only stirring, without aeration. After flocculation, the solution was drawn from 2 / 3 of the liquid level, and the absorbance of the supernatant was measured to calculate the harvesting efficiency.

[0070] Comparative Example 2

[0071] This comparative example uses cationic guar gum prepared in Example 1 and phospho-based fatty acid soap (sodium phospho-based fatty acid) to collect microalgae.

[0072] The synthesis method of phosphostearic acid soap is similar to that of sodium sulfostearate in Example 1, except that sodium bisulfite is replaced with an equimolar amount of phosphorous acid H3PO3.

[0073] Comparative Example 3

[0074] This comparative example uses cationic guar gum prepared in Example 1 and hydroxy fatty acid soap (sodium hydroxy fatty acid) to collect microalgae.

[0075] The synthesis method of phosphostearic acid soap is similar to that of sodium sulfostearate in Example 1, except that sodium bisulfite is replaced with an equimolar amount of deionized water.

[0076] Comparative Example 4

[0077] This comparative example uses cationic guar gum prepared in Example 1 and hexadecyltrimethylammonium bromide (CTAB, purchased from Sinopharm Group, analytical grade, concentration 10 g / L) to collect microalgae.

[0078] The synthesis method of phosphostearic acid soap is similar to that of sodium sulfostearate in Example 1, except that sodium bisulfite is replaced with an equimolar amount of deionized water.

[0079] Application Example 1: Microalgae were harvested using the formulations from the above examples and comparative examples.

[0080] To verify the technical effect of Example 1, this application example selected Chlorella sorokinina as the algal species and adopted a multi-trophic culture method with BG-11 medium as the culture medium.

[0081] The specific method of combined breeding is as follows:

[0082] (1) Chlorella sorokiniana was inoculated into a conical flask containing 100 mL of BG-11 medium and placed in a light incubator for culture;

[0083] The temperature was 301±1 K, and the light intensity was 200 μmol / (m²). 2 ·s), with a light-to-dark ratio of 12 h:12 h.

[0084] (2) After the microalgae have grown to the stationary phase, the Chlorella in the conical flask is transferred to an 8L cylindrical photobioreactor (S=113 cm) containing 5L of BG-11 medium. 2 In the same light culture conditions (h=70 cm), the culture continued.

[0085] During cultivation, air is pumped into the reactor at a flow rate of 0.1 m³ / s. 3 / h of compressed air (reference "Structural insights into mechanisms of rapid harvesting of microalgae with pH regulation by magnetic chitosan composites: A study based on E-DLVO model and component fluorescence analysis", Dian Dai, Mingxiang Qv, Dongyang Liu, Chunming Tang, Wei Wang, Qirui Wu, Zhihong Yin, Liandong Zhu, https: / / doi.org / 10.1016 / j.cej.2022.141071). The culture medium was BG-11 medium (purchased from Qingdao High-tech Industrial Park Haibo Biotechnology Co., Ltd., product number: HB8793).

[0086] The apparatus and method for collecting microalgae from the above-mentioned microalgae suspension are as follows: Figure 2 As shown, Figure 2 In the diagram, 1 represents the introduced air, and 2 represents the obtained microalgal flocs. The specific method is as follows:

[0087] (1) Add 660 ml of microalgae suspension with a biomass concentration of 0.5 g / L to the flotation cell and stir at 1800 rpm for 1.5 min.

[0088] (2) Add 1.98 ml of 10 g / L cationic guar gum aqueous solution (19.8 mg cationic guar gum) and stir for 5 min.

[0089] (3) Add 1.98 ml of 20 g / L sodium sulfostearate aqueous solution (or phospho fatty acid soap of Comparative Example 2, or hydroxy fatty acid soap of Comparative Example 3, or CTAB of Comparative Example 4) (sodium sulfostearate / phospho fatty acid soap / hydroxy fatty acid soap / CTAB) 39.6 mg, and continue stirring for 5 min.

[0090] (4) Turn on the aeration at 0.1 m 3 Flotation and foaming were performed at an air blowing rate of / h for 5 minutes.

[0091] When using cationic guar gum as in Comparative Example 1, only steps (1) and (2) above are required to complete the microalgae collection.

[0092] When using cationic guar gum and phospho fatty acid soap in Comparative Example 2, cationic guar gum and hydroxy fatty acid soap in Comparative Example 3, and cationic guar gum and CTAB in Comparative Example 4, only steps (1), (2), (3) and (4) above are used to complete the microalgae collection.

[0093] The efficiency and enrichment ratio of microalgae harvesting using the formulations in the examples and comparative examples were calculated separately. For reference, see the literature “Gemini surfactant: A novel flotation collector for harvesting of microalgaeby froth flotation” (Zhiqiang Huang, Chen Cheng, Zuwen Liu, Wuhui Luo, Hong Zhong, Guichun He, Changli Liang, Liqing Li, Lanqing Deng, Weng Fu, https: / / doi.org / 10.1016 / j.biortech.2018.12.106).

[0094] Harvesting efficiency and enrichment ratio are calculated using the following formulas:

[0095] Microalgae recovery rate R during flotation:

[0096] ;

[0097] Water recovery rate (WR) during flotation:

[0098] ;

[0099] Enrichment ratio (ER) is defined as the ratio of microalgal biomass concentration to the initial biomass concentration during the feeding process, and is calculated using the following formula:

[0100] ;

[0101] In the above formula, X is the volume of the microalgae solution remaining in the flotation cell (L), F is the volume of algae solution added during the feeding process (L), x is the biomass concentration of microalgae in the flotation cell (g / L), f is the biomass concentration of microalgae added during the feeding process (g / L), and R is the recovery rate of microalgae after flotation.

[0102] The results are shown in Table 1 below.

[0103] Table 1. Efficiency and enrichment ratio of microalgae harvesting in each example and comparative example.

[0104]

[0105] The calculation results of microalgae harvesting efficiency and enrichment ratio in Table 1 show that cationic guar gum has excellent charge neutralization properties, rapidly capturing microalgae in the system, altering the surface properties of microalgae, reducing electrostatic repulsion between microalgae, and increasing the operability of microalgae harvesting in subsequent flotation processes. When sodium sulfostearate is replaced with sodium phosphonate or sodium hydroxystearate, both the microalgae harvesting efficiency and enrichment ratio decrease. This indicates that sulfonation modification is superior to phosphonate and hydroxyl modification, and cationic guar gum and sodium sulfostearate have a significant synergistic promoting effect on microalgae harvesting and enrichment. Furthermore, higher harvesting efficiency was achieved when cationic guar gum and CTAB were used in synergistic harvesting; however, CTAB contains bromide ions, and its pollution and harm to biomass and the environment have not been systematically evaluated. Simultaneously, CTAB has bactericidal and algicidal properties, and its effects on microalgae cell structure have been reported in the literature, leading to cell disruption and release of intracellular substances during harvesting, thus affecting the quality of microalgae biomass. Cationic guar gum and sodium sulfostearate are derived from renewable bio-based materials, which reduce the potential threat to microalgal biomass from the use of chemical agents while maintaining high harvesting efficiency and enrichment ratio.

[0106] Application Example 2: Determination of morphology, median particle size, and water content of microalgal flocs collected using the microalgal harvesting agent of Example 1.

[0107] This application example measures the morphology, particle size, and water content of microalgal flocs from Example 1 (flocculation-flotation) and Comparative Example 1 (flocculation only).

[0108] The floc morphology of Example 1 (flocculation-flotation) and Comparative Example 1 (flocculation using cationic guar gum only) is as follows: Figure 2 As shown, the floc structure obtained by using only cationic guar gum flocculation in Comparative Example 1 is relatively loose. Due to the high-speed stirring of the flotation machine, granular flocs still exist in the flocculated system. In contrast, the microalgae floc structure obtained by flocculation-flotation harvesting in Example 1 is more compact, with the flocs agglomerating into clumps, and the number of granular flocs in the system is significantly reduced.

[0109] This application example also determined the microalgae harvesting agents collected using Example 1 (flocculation-flotation) and Comparative Example 1 (flocculation only). Specifically, sulfostearic acid soap (OA-1) with cationic guar gum at concentrations of 20 mg / L, 40 mg / L, 60 mg / L, 80 mg / L and 100 mg / L were used in synergistic effects. The median particle size in the resulting microalgae systems is shown in Table 2 below.

[0110] Table 2

[0111] As can be seen, using different amounts of sulfostearic acid soap (OA-1) and cationic guar gum for flocculation and flotation, the median particle size D 50 The median particle sizes were 12.7±0.24, 18.44±0.26, 22.23±0.45 μm, 25.63±1.45, and 23.51±1.66 μm, respectively. Only cationic guar gum from Comparative Example 1 was used for flocculation, and the median particle size D... 50 The particle size was only 7.19 μm, and the water content was 53.6% and 59.3%, respectively. This indicates that compared with the single flocculation method in Comparative Example 1, the flocculation-flotation coupling process in Example 1 further increases the floc particle size and internal compactness, and reduces the floc water content, which is beneficial to the subsequent processing of microalgae biomass.

[0112] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A microalgae harvesting agent coupling in-situ flocculation and foam flotation, characterized in that, It includes cationic guar gum and sodium sulfostearate, wherein the mass ratio of cationic guar gum to sodium sulfostearate is 1:(1-4); when harvesting microalgae, cationic guar gum is first used for flocculation, and then sodium sulfostearate is used for flotation. The method for preparing the sodium sulfostearate includes the following steps: Oleic acid, concentrated sulfuric acid and glacial acetic acid are stirred and mixed evenly. Hydrogen peroxide is added and the mixture is reacted at 40-90℃ for 1-3 h. The aqueous phase containing epoxy oleic acid is then separated. Add sodium bisulfite solution to the aqueous phase containing the epoxy oleic acid, stir and mix evenly, react at 70-90℃ for 2-4 hours, wash, and separate the organic phase containing sulfostearic acid. Sodium hydroxide was added to the organic phase, and the reaction was carried out at 100-140°C for 4-7 h. The mixture was then purified with saturated sodium chloride solution, filtered, and dried to obtain the sodium sulfostearate.

2. The microalgae harvesting agent coupled with in-situ flocculation and foam flotation according to claim 1, characterized in that, The preparation method of the cationic guar gum includes the following steps: Guar gum and sodium hydroxide solution were added to isopropanol and stirred until homogeneous to obtain a system containing alkalized guar gum. Add 3-chloro-2-hydroxypropyltrimethylammonium chloride to the system, and then add sodium hydroxide solution and isopropanol again, stirring to mix thoroughly; The mixture is heated to 50-80℃ and reacted for 2-4 hours. After filtration, washing, and drying, the cationic guar gum is obtained.

3. The microalgae harvesting agent coupled with in-situ flocculation and foam flotation according to claim 2, characterized in that, In the preparation method of the cationic guar gum, the mass ratio of the guar gum, 3-chloro-2-hydroxypropyltrimethylammonium chloride and the added isopropanol is 1:(0.5-1.0):(4-7).

4. The microalgae harvesting agent coupled with in-situ flocculation and foam flotation according to claim 1, characterized in that, In the preparation method of sodium sulfostearate, the mass ratio of oleic acid, concentrated sulfuric acid, hydrogen peroxide and glacial acetic acid is 1:(0.01-0.03):(0.17-0.24):(0.05-0.10).

5. The microalgae harvesting agent coupled with in-situ flocculation and foam flotation according to claim 1, characterized in that, In the preparation method of sodium sulfostearate, the mass ratio of epoxy oleic acid to sodium bisulfite is 1:(0.05-0.1).

6. The microalgae harvesting agent coupled with in-situ flocculation and foam flotation according to claim 1, characterized in that, In the preparation method of sodium sulfostearate, the mass ratio of sulfostearic acid to sodium hydroxide is 1:(0.2-0.4).

7. The application of a microalgae harvesting agent coupled with in-situ flocculation and foam flotation as described in any one of claims 1-6 in the harvesting of microalgae.

8. A method for harvesting microalgae, characterized in that, Using the microalgae harvesting agent coupled with in-situ flocculation and foam flotation as described in any one of claims 1-6, the cationic guar gum is added to the microalgae suspension and stirred; the sodium sulfostearate is added, and flotation stirring and foam scraping are performed under aeration conditions to complete the microalgae harvesting.

9. The microalgae harvesting method according to claim 8, characterized in that, The steps include: using 5-40 mg / L of cationic guar gum and 30-90 mg / L of sodium sulfostearate.

10. The microalgae harvesting method according to claim 9, characterized in that, The flotation stirring method is 1400-2100 rpm for 5 min; the aeration rate is 0.1-0.4 m / s. 3 / h, the foaming time is 1-5 min.

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