Microalgae wall breaking method by coupling low-concentration acid with gas blasting

Abstract

The invention belongs to the technical field of microalgae processing, and particularly discloses a low-concentration acid coupled gas blasting microalgae wall breaking method which comprises the following steps: mixing microalgae and a low-concentration acid solution, putting the mixture into a pressure-resistant reactor, and sealing the reaction kettle; introducing gas into the reactor to increase the system pressure to a preset value; then heating the reaction system to a preset temperature, and carrying out a stirring reaction; after the reaction is finished, the reactor is subjected to rapid pressure relief, and the microalgae wall breaking process is completed through rapid expansion of dissolved gas. The method is used for microalgae wall breaking, conditions are mild, wall breaking efficiency is high, energy consumption is low, equipment requirements are simple, operation is safe, and the problems that in the prior art, wall breaking efficiency is low, conditions are harsh, and the method is not suitable for industrial production can be solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microalgae processing, and relates to a microalgae wall breaking method, in particular to a microalgae wall breaking method of low-concentration acid coupling gas explosion. BACKGROUND

[0002] Microalgae have the advantages of fast growth and reproduction, strong environmental adaptability, high photosynthetic efficiency, and high oil content, and the oil content accounts for 20%-50% of the dry weight of biomass, and the fatty acid composition is similar to that of plant oil. Therefore, sustainable development of oil resources from microalgae has become an important trend.

[0003] Microalgae oil is stored in the cell, and the cell wall structure is tight, often containing more than 45% of hemicellulose, cellulose and polysaccharide substances, which greatly increases the difficulty of breaking the wall and becomes the main bottleneck of microalgae industrialization. Therefore, developing an efficient and low-energy wall breaking technology is the key to realizing the extraction of microalgae oil.

[0004] The current wall breaking methods are mainly divided into mechanical methods (such as grinding method, high-pressure homogenization method, screw extrusion method) and non-mechanical methods (such as ultrasonic method, repeated freeze-thaw method, enzymatic method, acid heat method, steam explosion method, etc.). However, these methods usually have bottlenecks in energy consumption, wall breaking efficiency, equipment cost and operation safety, etc. For example, the ultrasonic breaking effect is good, but it is difficult to realize large-scale continuous production; the biological enzyme method has mild conditions and strong specificity, but the enzyme cost is high and the reaction time is long; the microwave method heats quickly, but the energy consumption is high.

[0005] Specifically, the screw extrusion method in the mechanical method has a fast processing speed, but it has extremely strict requirements for the dry matter concentration of the raw material, which greatly limits its application. For example, Chinese patent CN202010596528.5 discloses a screw extrusion wall breaking method, which clearly requires that the humidity of the microalgae material is 25-75% in claim 1, which means that the dry matter concentration of the microalgae is as high as 25% to 75%. This means that the microalgae cultivation liquid with a concentration usually less than 1% must be pretreated by high-energy concentration, dehydration or even semi-drying, which is very costly. In addition, this method still needs to be carried out at high temperature (the end point temperature of example 6 of the patent is as high as 190°C), which has the risk of high energy consumption and possible oxidation and denaturation of oil. Moreover, the extraction effect is still not as good as that of the traditional grinding method.

[0006] In the non-mechanical method, such as the acid heat method, the acid heat method can effectively acidify the cell wall, but often requires harsh process conditions. For example, the method disclosed in Chinese patent CN201310355221.6 clearly requires that the reaction temperature is as high as 120-400°C and the pressure is 0.65-3.5 MPa (corresponding to paragraph

[0025] of the specification), which requires extremely high energy consumption and equipment.

[0007] Traditional steam explosion method usually requires special steam generator and pressure-resistant steam explosion tank to achieve effective "instant explosion", and the operating temperature is often as high as 150-250℃ or even higher, and the pressure is several to tens of megapascal, so as to ensure strong steam explosion force. For example, Chinese patent CN02153296.6 discloses a steam explosion method for breaking the wall of large economic seaweed (such as kelp and laver). Although this method attempts to use relatively mild conditions (80-100℃, 0.8-1.5MPa), it relies on "instantaneous pressure release", which usually requires a special explosion tank with quick door opening, and the equipment is complex and expensive. At the same time, the millisecond instantaneous explosion will produce a huge impact force, which has safety risks such as equipment impact and material splashing and difficult to collect, and this patent does not provide specific microalgae oil extraction rate data to prove its effectiveness. In actual operation, due to the toughness of the microalgae cell wall, under the above working conditions, the steam explosion force is limited, and it is difficult to get good wall breaking effect.

[0008] Chinese patent CN200810240949.3 attempts to use steam to break the wall under alkaline conditions (pH 7.5-12) with a temperature of 110-140℃. However, this method requires the algae liquid and high-temperature steam to be atomized and sprayed into the reaction kettle, which increases the complexity and cost of the equipment. In addition, this method does not clearly disclose the key reaction pressure parameter, and the final oil extraction amount obtained is limited (45g of oil is obtained from 2000g of wet algae mud in Example 1), and there is still a lot of room for improvement.

[0009] In summary, the existing microalgae wall breaking technology cannot be compatible with high efficiency, low energy consumption / cost and simple process / operation safety. The mechanical method is limited by the concentration of raw materials; the strong acid / strong base method requires high temperature and high pressure; and the steam explosion method is limited by expensive special equipment and safety risks. Therefore, there is an urgent need in the art to develop a new wall breaking method that can achieve high efficiency under mild conditions (low temperature, low pressure), can use conventional equipment, is safe and simple to operate, and can directly process low concentration microalgae culture solution. SUMMARY

[0010] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a microalgae wall breaking and oil extraction method with mild conditions, high wall breaking efficiency, low energy consumption, simple equipment requirements and safe operation, so as to solve the problems of low wall breaking efficiency, harsh conditions and unsuitability for industrial production in the prior art.

[0011] To achieve the above object, the present application provides a low-concentration acid and gas explosion coupled microalgae cell wall breaking method. The core mechanism is as follows: under mild heating conditions, low-concentration acid catalyzes the hydrolysis of hemicellulose and other components in the microalgae cell wall, making it fragile and producing microcracks; at the same time, before the hydrolysis reaction, a proper amount of gas is filled and dissolved in the aqueous phase under pressure, and then permeates into the cell with the aqueous phase; finally, through rapid pressure relief, the dissolved gas in the cell expands sharply due to the sudden drop in pressure, which completely destroys the cell wall that has been weakened by acid, thereby achieving efficient and mild cell wall breaking effect. Thus, the microalgae oil spills out, facilitating oil extraction.

[0012] The present application does not require high-energy consumption deep concentration of microalgae culture solution, nor does it rely on high-temperature and high-pressure steam or special instantaneous explosion device. Only a pressure-resistant reactor equipped with a conventional pressure relief valve is needed to complete the controllable rapid pressure relief within a few seconds to a few minutes, which greatly reduces the special requirements and investment cost of the core equipment, and avoids the equipment impact and safety hazards caused by instantaneous explosion, making the process safer and more easily industrialized.

[0013] Specifically, the technical scheme provided by the present application is as follows:

[0014] A low-concentration acid and gas explosion coupled microalgae cell wall breaking method, comprising the following steps: mixing microalgae (which can be in the form of algal powder, algal mud or algal liquid) with a low-concentration acid solution and placing it in a pressure-resistant reactor, and sealing the reactor; introducing gas into the reactor to increase the system pressure to a preset value; then heating the reaction system to a preset temperature and stirring the reaction; after the reaction is completed, the reactor is rapidly depressurized to complete the microalgae cell wall breaking process by using the rapid expansion of dissolved gas.

[0015] Further, the microalgae is a microalgae containing hemicellulose in the cell wall, preferably selected from Chlorella vulgaris, Nannochloropsis, and Schizochytrium.

[0016] Further, the acid is an organic acid or an inorganic acid, wherein the organic acid is, for example, formic acid, acetic acid, etc., and the inorganic acid is, for example, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc.

[0017] Further, the concentration of the acid solution is 0.5% to 2% (w / w).

[0018] Further, the gas is a gas that has a certain solubility in the reaction system, such as air, oxygen, nitrogen, carbon dioxide, etc.

[0019] Further, the preset pressure of the reactor is 0.5 to 2.0 MPa, preferably 1.0 to 1.5 MPa.

[0020] Further, the stirring reaction time is 15-45 minutes.

[0021] Further, the preset temperature of the reactor is 80-150°C, preferably 100-120°C.

[0022] Further, the microalgae dry weight concentration (microalgae dry weight / low concentration acid solution volume) is 5-50 g / L.

[0023] Further, the rapid pressure relief is to reduce the system pressure to normal pressure within 30 seconds to 5 minutes.

[0024] Further, the method further comprises the step of extracting algal oil from the broken cell microalgae solution, including but not limited to one or more conventional separation and purification methods in the art, such as extraction, centrifugation, demulsification, standing and layering, dehydration, etc.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] 1) High breaking efficiency: coupling acid catalyzed hydrolysis and gas expansion explosion two mechanisms, synergistic effect, breaking effect is significantly better than single acid hydrolysis or physical breaking method.

[0027] 2) Mild conditions: the operating temperature and pressure are significantly lower than those of traditional acid heat method and steam explosion method, which reduces energy consumption and is beneficial to protect active ingredients such as oil. And the gas used for pressurization is cheap and easy to obtain.

[0028] 3) Simple equipment, high safety: no need for expensive special instantaneous explosion device or steam atomization equipment, it can be realized by using conventional reaction kettle, the investment cost is low; controllable rapid pressure relief process avoids the safety risk of violent explosion, and the operation is safer.

[0029] 4) Wide adaptability of raw materials, low pretreatment cost: low concentration microalgae solution or algal mud can be directly treated, without the need for high energy consumption deep drying or concentration pretreatment, reducing the overall cost.

[0030] 5) Environmentally friendly: low acid concentration, small amount, waste liquid can be neutralized and treated, with little environmental pollution. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The oil extraction rates obtained by the method of the present application for Chlorella vulgaris and Nannochloropsis gaditana in the examples are compared.

[0032] Figure 2 The oil extraction rates obtained by the traditional freeze-thaw method, acid heat method, etc. for the same batch of Chlorella vulgaris powder in the examples 1, 2 and comparative examples of the present application are compared. DETAILED DESCRIPTION

[0033] The application is further illustrated by the following examples, but the scope of the application is not limited to these examples.

[0034] The pressure-resistant reaction kettle used in the following examples is a general-purpose quick-opening mechanical stirring kettle, which is purchased from Anhui Kepu Instrument Co., Ltd., and the model is MSG100-P5-T3-SS1-SV-R-BS; the organic solvent used for extraction is a chloroform-methanol (v:v=2:1) solution.

[0035] In the application, the oil extraction rate is calculated according to the following formula:

[0036] Oil extraction amount = mass of extracted oil / mass of dry microalgae (mg / g DW), wherein DW (Dry Weight) represents the dry weight of microalgae.

[0037] Example 1: verification of the effect of oxygen (Chlorella)

[0038] A 30 mL Chlorella solution with a concentration of 10 g / L is prepared using 1% sulfuric acid aqueous solution, and is placed in a 100 mL pressure-resistant reaction kettle. After being sealed, 1 MPa oxygen is filled into the reaction kettle. The reaction system is heated to 120°C, and is stirred at this temperature for 30 minutes. After the reaction is completed, the pressure relief valve is immediately opened, and the pressure of the reaction kettle is reduced to normal pressure within 30 seconds. After the reaction, the algal solution is extracted with an organic solvent, centrifuged and dried to obtain microalgae oil. The oil extraction rate calculated by weighing is 286.0 mg / g DW.

[0039] Example 2: verification of the effect of air (Chlorella)

[0040] The operation method is the same as that in Example 1, and the only difference is that 1.0 MPa air is filled. The calculated oil extraction rate is 158.5 mg / g DW.

[0041] Example 3: verification of the effect of nitrogen (Chlorella)

[0042] The operation method is the same as that in Example 1, and the only difference is that 1.0 MPa nitrogen is filled. The calculated oil extraction rate is 101.5 mg / g DW.

[0043] Example 4: verification of the effect of different algae (Nannochloropsis)

[0044] The operation method is the same as that in Example 2, and the only difference is that the microalgae is replaced by Nannochloropsis. The calculated oil extraction rate is 126.1 mg / g DW.

[0045] Example 5: verification of the effect of different algae (Schizochytrium)

[0046] The operation method is the same as Example 2, the only difference is that the microalgae is replaced by Schizochytrium sp. The calculated oil extraction rate is 305.6 mg / g DW.

[0047] Example 6: Verify the effect of lower pressure

[0048] The operation method is the same as Example 2, the only difference is that the gas filled is 0.5 MPa air. The calculated oil extraction rate is 86.5 mg / g DW.

[0049] Example 7: Verify the effect of lower temperature

[0050] The operation method is the same as Example 2, the only difference is that the reaction temperature is 100℃. The calculated oil extraction rate is 112.1 mg / g DW.

[0051] Example 8: Verify the effect of slower pressure relief time

[0052] The operation method is the same as Example 2, the only difference is that: after the reaction is completed, the pressure is slowly reduced to atmospheric pressure within 4 minutes. After the algae solution after the reaction is extracted by an organic solvent, centrifuged and dried, the microalgae oil is obtained, and the calculated oil extraction rate is 129.4 mg / g DW.

[0053] Comparative Example 1: Freeze-thaw method

[0054] Prepare 30 mL of Chlorella solution with a concentration of 10 g / L with 1% sulfuric acid aqueous solution, freeze at -20℃ for 12 h, then take out to room temperature to melt, this freeze-thaw cycle is repeated 5 times, and the subsequent oil extraction and calculation method is the same as Example 1. The calculated oil extraction rate is 103.5 mg / g DW.

[0055] Comparative Example 2: Acid heat method (no gas pressurization)

[0056] The operation method is the same as Example 1, the only difference is that: before the reaction, no gas is filled (i.e. only under atmospheric pressure, the acid heat reaction is carried out). The calculated oil extraction rate is 74.2 mg / g DW.

[0057] Comparative Example 3: Ordinary hydrothermal method (no acid, no gas)

[0058] A 30 mL Chlorella solution with a concentration of 10 g / L was prepared using deionized water, placed in a 100 mL pressure-resistant reaction kettle, sealed, and not filled with gas. The reaction system was heated to 120 DEG C, stirred at this temperature for 30 minutes, and immediately opened after the reaction was completed. The gas valve was opened within 30 seconds to reduce the pressure of the reaction kettle to normal pressure. After the reaction, the algae liquid was extracted with an organic solvent, centrifuged and dried to obtain microalgae oil, and the oil extraction rate was calculated to be 12.7 mg / g DW.

[0059] Comparative Example 4: Gas explosion method (without acid)

[0060] The operation method is the same as that of Comparative Example 3, except that the prepared 10 g / L Chlorella solution is placed in the reaction kettle, sealed, and filled with 1 MPa air for reaction. The calculated oil extraction rate is 54.9 mg / g DW.

[0061] The oil extraction rates obtained by the method of the present application on Chlorella, Nannochloropsis, and Schizochytrium are compared as shown in Table 1. Figure 1 The oil extraction rates obtained by the traditional freeze-thaw method, acid heat method, etc. on the same batch of Chlorella algae powder in Examples 1, 2 and Comparative Examples are compared as shown in Table 2. Figure 2

[0062] Numbering Method description Algae Pressure (MPa) Temperature (°C) Pressure release time Oil extraction rate (mg / g DW) Example 1 Invention (oxygen) Chlorella vulgaris 1.0 120 30 seconds 286.0 Example 2 Invention (air) Chlorella vulgaris 1.0 120 30 seconds 158.5 Example 3 Invention (nitrogen) Chlorella vulgaris 1.0 120 30 seconds 101.5 Example 4 Invention (air) Nannochloropsis sp. 1.0 120 30 seconds 126.1 Example 5 Invention (air) Schizochytrium sp. 1.0 120 30 seconds 305.6 Example 6 Invention (air) Chlorella vulgaris 0.5 120 30 seconds 86.5 Example 7 Invention (air) Chlorella vulgaris 1.0 100 30 seconds 112.1 Example 8 Invention (air) Chlorella vulgaris 1.0 120 4 minutes 129.4 Comparative Example 1 Freeze-thaw method Chlorella vulgaris — -20℃ 103.5 Comparative Example 2 Acid heat method (without gas) Chlorella vulgaris — 120 30 seconds 74.2 Comparative Example 3 Hydrothermal method (without acid, without gas) Chlorella vulgaris — 120 30 seconds 12.7 Comparative Example 4 Gas explosion method (without acid) Chlorella vulgaris 1.0 120 30 seconds 54.9

[0063] From the above results, it can be seen that:

[0064] The oil extraction rate of the wall breaking method (Examples 1-8) of the present application is significantly higher than that of all comparative examples, which proves the synergistic effect of low concentration acid and gas explosion (comparing Comparative Examples 2, 3 and 4).

[0065] Oxygen is the best, air is the second, nitrogen is relatively poor but still better than the traditional method, which shows that the solubility and chemical properties of the gas affect the wall breaking effect.

[0066] Even under milder conditions (0.5 MPa / 120 DEG C, 1.0 MPa / 100 DEG C) and longer pressure relief time (4 minutes), the method of the present application still maintains excellent wall breaking effect (Examples 6, 7 and 8), which proves the wide operation window and industrialization potential of the method.

[0067] The method of the present application has a significant wall breaking effect on different algae species (Chlorella, Nannochloropsis, and Schizochytrium), and has good universality.

[0068] ​The preferred embodiments of the application have been described above with particularity and detail, but the application is not limited to such preferred embodiments. All equivalent or alternative modifications and variations of the preferred embodiments that fall within the spirit and scope of the application are intended to be included. No exhaustive list of all embodiments is required or possible. Changes or alterations to the preferred embodiments that are obvious to a person of ordinary skill in the art are intended to be within the scope of the present application.

Claims

1. A method for disrupting microalgae cell walls using low-concentration acid-coupled gas explosion, characterized in that: Microalgae are mixed with a low-concentration acid solution and placed in a pressure-resistant reactor, which is then sealed. Gas is introduced into the reactor to raise the system pressure to a preset value. The reaction system is then heated to a preset temperature and stirred. After the reaction is completed, the reactor is rapidly depressurized, and the microalgae cell wall breaking process is completed by the rapid expansion of the dissolved gas.

2. The method according to claim 1, characterized in that, The acid is an inorganic acid or an organic acid. The inorganic acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and the organic acid includes at least one of formic acid and acetic acid. The concentration of the acid solution is 0.5% to 2% (w / w).

3. The method according to claim 1, characterized in that, The gas is at least one of air, oxygen, nitrogen, and carbon dioxide; the preset pressure of the reactor is 0.5~2 MPa, and the preset temperature is 80~150℃.

4. The method according to claim 1, characterized in that, The rapid depressurization is to reduce the system pressure to atmospheric pressure within 30 seconds to 5 minutes.

5. The method according to claim 1, characterized in that, The stirring reaction time is 15 to 45 minutes.

6. The method according to claim 1, characterized in that, The microalgae mentioned are those whose cell walls contain hemicellulose.

7. The method according to claim 6, characterized in that, The microalgae are Chlorella vulgaris, Nannochloropsis, or Schizochytrium.

8. The method according to claim 1, characterized in that, The dry weight of the microalgae is 5~50 g / L.

9. The method according to claim 1, characterized in that, The method also includes a step of extracting algal oil from the microalgae solution after cell wall disruption.

10. The method of claim 9, wherein the step of collecting algal oil comprises one or more of extraction, centrifugation, demulsification, separation, and dehydration.

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