Method for extracting grease from microalgae dry powder by using azeotropic mixture

Abstract

The invention discloses a method for extracting grease from dry microalgae powder by using an azeotropic mixture, which comprises the following steps: S1, drying harvested fresh microalgae mud until the moisture content is less than or equal to 6% to prepare dry microalgae powder; s2, preparing an azeotropic mixture, wherein the azeotropic mixture comprises ethanol, ethyl acetate, acetone and hexane, and the volume ratio of the ethanol to the ethyl acetate to the acetone to the hexane is 2: (0-5): (0-3): (3-5); s3, adding the azeotropic mixture obtained in the step S2 into the dry algae powder obtained in the step S1, carrying out ultrasonic treatment at 20-50 kHz, and centrifuging to obtain a primary extracting solution; s4, the azeotropic mixture is added into the algae residues again, centrifugation is conducted after even mixing, a secondary extracting solution is obtained and mixed with the primary extracting solution, the azeotropic mixture is removed through evaporation, and the microalgae oil is obtained.The method is high in microalgae oil extraction efficiency and can be applied to edible microalgae oil processing.

Description

Technical Field

[0001] The present invention belongs to the technical field of microalgae deep processing, and particularly relates to a method for extracting oil from microalgae dry powder by using an azeotropic mixture. Background Art

[0002] Microalgae are a type of tiny eukaryotic or prokaryotic organisms with the ability of photosynthetic autotrophy. Due to their high oil content of up to 30%-70% (for some algal species), vigorous growth rate, and excellent carbon fixation ability, they provide a green and sustainable food source without occupying arable land. It is worth noting that the triglycerides rich in microalgae cells are similar in structure to vegetable oils, so they are widely regarded as an ideal choice to replace traditional edible oils. At the same time, microalgae also contain polar lipids represented by polyunsaturated fatty acids, which show great potential application value in the fields of food additives, nutritional fortification, and adjuvant therapy.

[0003] Since the cell volume of microalgae is extremely small, it is difficult to effectively extract oil by traditional mechanical methods such as extrusion or puffing. Therefore, solvent extraction method is usually used to obtain algal oil. Although the chloroform-methanol mixed solvent shows excellent extraction efficiency, it cannot be used for the production of food-grade algal oil due to the neurotoxicity of chloroform; while n-hexane can only extract neutral lipids and it is difficult to recover a large amount of polar lipids in it, resulting in high solvent consumption and incomplete extraction. In addition, the cell wall structure of microalgae is complex, and the penetration efficiency of the solvent into it is low. Even with the help of a mixed solvent (such as chloroform-methanol), the unbroken algal cells will still hinder the diffusion of the solvent, prolong the extraction time, and bring subsequent purification problems such as solvent residues. The ultrasonic cell disruption technology uses the cavitation effect induced by ultrasonic waves to generate high-speed microbubbles in the liquid phase environment and instantaneously collapse, forming a high-intensity impact force (local pressure can reach 1000 atm) and instant high temperature (about 5000 K), thereby directly destroying the microalgae cell wall and releasing the intracellular oil.

[0004] Chinese Patent CN104312720A discloses a method for extracting Chlorella oil, but this method needs to add cellulase and ultrasonically break the cells, and the cell disruption time is up to 1 hour; after the extraction, a strong alkali solution is needed to separate the oil and algal residue.

[0005] Chinese Patent CN104059773A discloses a method for wet extraction of microalgae oil. This method needs to dehydrate the cells with ethanol first, then add an alcohol organic solvent to break the cells, and then add n-hexane to extract the oil. The operation steps are cumbersome, the extraction temperature is high, the extraction time is long, and the energy consumption is too high.

[0006] An azeotrope refers to a mixture formed by two or more liquids in a specific ratio that has a fixed boiling point. Its vapor phase and liquid phase have the same composition. There are non-ideal interactions between components such as hydrogen bonds and van der Waals forces, and the total vapor pressure after mixing deviates from Raoult's law. The azeotropic point of an azeotrope is usually lower or higher than that of the pure components. By designing the composition and ratio of organic solvents with different polarities to regulate the azeotropic point of the mixed solvent, energy consumption can be reduced, and at the same time, the extraction rate of total microalgal lipids can be increased. Moreover, when the azeotrope is distilled and recovered, the operation is simple. Only single distillation is required, and the solvent recovery rate can reach more than 85%.

[0007] To overcome the limitations such as large solvent consumption, high energy consumption, and lipid loss, this study proposed and explored a new path for low-temperature and high-efficiency extraction of microalgal lipids using "ultrasonic cavitation-assisted mixed solvents" based on the characteristics of azeotropes. By utilizing the ultrasonic cavitation effect to enhance the cell wall breaking efficiency and combining with an appropriate solvent system, efficient and low-loss recovery of neutral lipids and polar lipids can be achieved, providing an innovative and feasible technical solution for the large-scale extraction and functional development of microalgal lipids. Summary of the Invention

[0008] The purpose of the present invention is to design a method for extracting lipids from microalgal dry powder using an azeotrope, which has a high extraction efficiency for microalgal lipids and can be applied to the processing of edible microalgal oil.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for extracting lipids from microalgal dry powder using an azeotrope, characterized in that the method is as follows: S1: Dry the harvested fresh microalgal sludge until the moisture content ≤ 6% to obtain microalgal dry powder; S2: Prepare an azeotrope, which includes ethanol, ethyl acetate, acetone, and hexane, and the volume ratio of each mixture is 2:0 - 5:0 - 3:3 - 5; S3: Add the azeotrope obtained in S2 to the dry powder obtained in step S1, assisted by ultrasonic treatment at 20 - 50 kHz, and centrifuge to obtain a primary extract; S4: Add the azeotrope to the algal residue again, mix well and centrifuge to obtain a secondary extract, mix it with the primary extract, and evaporate to remove the azeotrope to obtain microalgal lipids.

[0010] Furthermore, in step S1, the fresh algal sludge can be the sludge obtained by autotrophic, heterotrophic, or autotrophic-heterotrophic mixed cultivation; the drying methods include one or more combinations of drying, spray drying, and freeze drying; the microalgae are one of Chlorella, Scenedesmus, Nannochloropsis, Phaeodactylum, Chrysophyceae, Schizochytrium, and Dunaliella; the microalgal dry powder includes one or more microalgae.

[0011] Further, in step S2, the azeotropic mixture can be replaced with a ternary system of ethanol, ethyl acetate, and hexane with a volume ratio of 2:2 - 5:3, and the azeotropic point of this ternary system is about 50 - 54 °C; or a ternary system of ethanol, acetone, and hexane with a volume ratio of 1 - 3:3 - 4:4 - 5, and the azeotropic point of this ternary system is about 50 - 55 °C.

[0012] Further, in step S3, the solvent ratio of the azeotropic mixture to the dry algal powder is 3 - 10 mL of solvent volume: 1 g of algal powder mass, and ultrasonic treatment is carried out for 3 - 15 min at an ultrasonic power of 400 - 600 W.

[0013] Further, in step S4, the composition and solvent ratio of the azeotropic mixture added again are exactly the same as those of the azeotropic mixture described in step S2. The pressure of the evaporation condition is 100 - 200 mBar, the evaporation temperature is 30 - 50 °C, and the evaporated azeotropic mixture is condensed and recycled.

[0014] The following beneficial effects can be obtained through the above technical solutions: The method of this application utilizes ultrasonic cavitation effect to assist the azeotropic mixture in breaking the cell wall and dissolving microalgae cells. While significantly reducing the dosage of the azeotropic mixture, it significantly improves the extraction efficiency and yield of microalgae oil. The polarity gradient of the ethanol - ethyl acetate - n - hexane mixed solvent and the ethanol - acetone - n - hexane azeotropic mixture covers a wide range, which can not only fully extract the neutral lipids in microalgae cells but also efficiently extract polar lipids; the boiling point is further reduced by 5 - 8 °C compared with the ethanol - n - hexane system, reducing the risk of lipid oxidation, especially suitable for the extraction of polyunsaturated fatty acids, thus obtaining a microalgae oil product with more comprehensive nutritional components and stronger functionality. Compared with traditional methods, the present invention can not only reduce production costs, reduce solvent residues and environmental burdens, but also show greater application potential in the fields of food, health products, and biofuels, providing a new technical path for the comprehensive utilization of microalgae resources. Specific Embodiments

[0015] The following further illustrates the present invention in conjunction with embodiments: Example 1

[0016] Fresh Nannochloropsis Nannochloropsis sp.) algal sludge was spray - dried to obtain algal powder with a moisture content of about 6%. According to a solvent ratio of 4:1, an azeotropic mixture composed of ethanol, ethyl acetate, and n - hexane (volume ratio of 2:3:5) was added to the dry algal powder, and ultrasonic treatment was carried out at 600 W for 6 min. After ultrasonic treatment, centrifugation was carried out at 4000 r / min for 5 min, and the upper - layer organic solvent was taken as the primary extraction solution. The azeotropic mixture was added to the algal residue again, mixed well and centrifuged, and the upper - layer secondary extraction solution was mixed with the primary extraction solution. Microalgae oil was separated by rotary evaporation under the conditions of 150 mBar and 35 °C, and the extraction rate of microalgae oil was 98%. Example

[0017] Fresh Scenedesmus ( Scenedesmus sp.) algae mud was spray dried to obtain algae powder with a moisture content of about 6%. An azeotropic mixture consisting of ethanol, acetone and n-hexane (volume ratio of 1:1:2) was added to the dry algae powder at a solvent ratio of 3:1, and ultrasonicated at 500 W for 5 min. After ultrasonication, centrifuged at 4000 r / min for 5 min, and the upper organic solvent was taken as the primary extract. The azeotropic mixture was added to the algae residue again, mixed and centrifuged, and the upper secondary extract was mixed with the primary extract. Microalgae oil was separated by rotary evaporation at 150 mBar and 40°C. The extraction rate of microalgae oil was 97%. Example 2

[0018] Fresh triangular kelp ( Phaeodactylum sp) Algae mud was spray dried to obtain algae powder with a moisture content of about 6%. An azeotropic mixture consisting of ethanol, acetone and n-hexane (volume ratio of 1:1:2) was added to the dry algae powder at a solvent ratio of 4:1, and ultrasonicated at 400 W for 3 min. After ultrasonication, the mixture was centrifuged at 4000 r / min for 5 min, and the upper organic solvent was taken as the primary extract. The azeotropic mixture was added to the algae residue again, mixed and centrifuged, and the upper secondary extract was mixed with the primary extract. Microalgae oil was separated by rotary evaporation at 150 mBar and 40°C. The extraction rate of microalgae oil was 98%. Example 3

[0019] Fresh Chlorella ( Chlorella sp.) algae mud was spray dried to obtain algae powder with a moisture content of about 6%. An azeotropic mixture consisting of ethanol, acetone and n-hexane (volume ratio of 3:3:4) was added to the dry algae powder at a solvent ratio of 5:1, and ultrasonicated at 400W for 5 min. After ultrasonication, centrifuged at 4000 r / min for 5 min, and the upper organic solvent was taken as the primary extract. The azeotropic mixture was added to the algae residue again, mixed and centrifuged, and the upper secondary extract was mixed with the primary extract. Microalgae oil was separated by rotary evaporation at 150 mBar and 40°C. The microalgae oil extraction rate was 93%.

[0020] Comparative Example 1 Fresh Nannochloropsis algae ( NannochloropsisThe algal sludge of [sp.] was spray-dried to obtain algal powder with a moisture content of about 6%. Hexane was added to the dry algal powder at a solvent ratio of 10:1, and ultrasonic treatment was carried out at 600 W for 20 min. After ultrasonic treatment, centrifugation was carried out at 4000 r / min for 5 min, and the upper organic solvent was taken as the primary extraction solution. The extraction solvent was added to the algal residue again, and after mixing, centrifugation was carried out. The upper secondary extraction solution was mixed with the primary extraction solution. Microalgal oil was separated by rotary evaporation under the conditions of 150 mBar and 40 °C. The extraction rate of microalgal oil was 75%.

[0021] Comparative Example 2 Fresh Chlorella vulgaris Chlorella The algal sludge of [sp.] was spray-dried to obtain algal powder with a moisture content of about 5%. An extraction solvent composed of 98% ethanol solution was added to the dry algal powder at a solvent ratio of 8:1, and ultrasonic treatment was carried out at 600 W for 30 min. After ultrasonic treatment, centrifugation was carried out at 4000 r / min for 5 min, and the upper organic solvent was taken as the primary extraction solution. The extraction solvent was added to the algal residue again, and after mixing, centrifugation was carried out. The upper secondary extraction solution was mixed with the primary extraction solution. Microalgal oil was separated by rotary evaporation under the conditions of 150 mBar and 40 °C. The extraction rate of microalgal oil was 86%.

[0022] The above are all preferred embodiments of the present invention. For those of ordinary skill in the art of the present technology, without departing from the principle of the present invention, modifications of various equivalent forms of the present invention all fall within the protection scope of the appended claims of this application.

Claims

1. A method for extracting oil from microalgae dry powder using an azeotropic mixture, characterized in that: The method is as follows: S1: Drying the harvested fresh microalgae mud to a moisture content of ≤6% to obtain dry microalgae powder; S2: preparing an azeotropic mixture, the azeotropic mixture comprising ethanol, ethyl acetate, acetone, and hexane, and the volume ratio of each mixture is 2:0-5:0-3:3-5; S3: adding the azeotropic mixture of S2 to the dry algae powder obtained in step S1, assisted by 20-50 kHz ultrasonic treatment, and centrifuging to obtain a primary extract; S4: adding the azeotropic mixture to the algae residue again, mixing and centrifuging to obtain a secondary extract, mixing the secondary extract with the primary extract, removing the azeotropic mixture by evaporation, and obtaining microalgae oil.

2. The method for extracting oil from microalgae dry powder using an azeotropic mixture according to claim 1, characterized in that: The fresh algae mud in step S1 can be algae mud obtained by autotrophic, heterotrophic or autotrophic-heterotrophic mixed culture; the drying method includes one or more combinations of drying, spray drying and freeze drying; the microalgae is one of Chlorella, Scenedesmus, Nannochloropsis, Brown Finger Algae, Chrysophyte, Schizochytrium, and Dunaliella; the dry microalgae powder includes one or more microalgae.

3. The method for extracting oil from microalgae dry powder using an azeotropic mixture according to claim 1, characterized in that: The azeotropic mixture in step S2 can be replaced by ethanol, ethyl acetate and hexane in a volume ratio of 2:2-5:3, and the azeotropic point of the ternary system is about 50-54°C; or ethanol, acetone and hexane in a volume ratio of 1-3:3-4:4-5, and the azeotropic point of the ternary system is about 50-55°C.

4. A method for extracting oil from microalgae dry powder using an azeotropic mixture according to claim 1 or 3, characterized in that: In step S3, the solvent ratio of the azeotropic mixture to the dry algae powder is 3-10:1 in terms of solvent volume mL:algae powder mass g, and ultrasonication is performed at an ultrasonic power of 400-600 W for 3-15 min.

5. The method for extracting oil from microalgae dry powder using an azeotropic mixture according to claim 1, characterized in that: The azeotropic mixture added again in step S4 has the same composition and solvent ratio as the azeotropic mixture in step S2. The pressure of the evaporation conditions is 100-200 mBar, the evaporation temperature is 30-50°C, and the evaporated azeotropic mixture is condensed, recovered and recycled.