A block type enteromorpha polysaccharide derivative and preparation method thereof

Abstract

The present invention belongs to the field of marine polysaccharide extraction, and specifically relates to a block-type Enteromorpha polysaccharide derivative and a preparation method thereof. The method comprises the following specific steps: (1) extracting Enteromorpha polysaccharide: extracting Enteromorpha polysaccharide from fresh Enteromorpha as raw material; (2) grafting of hydrophobic chains: using Enteromorpha polysaccharide as an initiator and propylene oxide as a polymerization monomer, and utilizing the ring-opening polymerization reaction of propylene oxide to graft the polyoxypropylene ether hydrophobic chain segment onto Enteromorpha polysaccharide; (3) hydrophilic head group: grafting a hydrophilic head group at the end of the polyoxypropylene ether hydrophobic chain segment to prepare a block-type Enteromorpha polysaccharide derivative with surface activity. The method provided by the present invention imparts surface activity to Enteromorpha polysaccharide molecules, expands its application in the field of tertiary oil recovery, and can not only solve the problem of Enteromorpha flooding at the seaside, but also expand the biomass source of oil recovery agents.

Description

Technical Field

[0001] The invention belongs to the field of marine polysaccharide extraction, and particularly relates to a block type enteromorpha polysaccharide derivative and a preparation method thereof. Background Art

[0002] Although the outbreak of Enteromorpha has brought environmental problems, its rich biomass resources also provide the possibility for high-value utilization. Enteromorpha is rich in polysaccharides, proteins, vitamins and trace elements, and has a high development value. In recent years, research on the high-value utilization of Enteromorpha has continued to deepen, especially in the fields of bioactive substance extraction, feed additives, fertilizer processing and biomaterials, showing broad application prospects. Summary of the invention

[0003] In view of the above technical problems, the present invention provides a block-type Enteromorpha polysaccharide derivative and a preparation method thereof; based on the abundant hydroxyl groups in the molecular structure of Enteromorpha polysaccharide, a polyoxypropylene ether hydrophobic chain segment is grafted onto Enteromorpha polysaccharide by utilizing the propylene oxide ring-opening polymerization reaction, and finally a hydrophilic head group is grafted at the end of the hydrophobic chain segment to give the Enteromorpha polysaccharide molecule surface activity.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for preparing a block-type Enteromorpha polysaccharide derivative, the method comprising the following specific steps:

[0006] (1) Extraction of Enteromorpha polysaccharide: Extraction of Enteromorpha polysaccharide using fresh Enteromorpha as raw material;

[0007] (2) Grafting of hydrophobic chains: using the Enteromorpha polysaccharide as an initiator and propylene oxide as a polymerization monomer, the polyoxypropylene ether hydrophobic chain segments are grafted onto the Enteromorpha polysaccharide by utilizing the ring-opening polymerization reaction of propylene oxide;

[0008] (3) Hydrophilic head group: A hydrophilic head group is grafted onto the end of the polyoxypropylene ether hydrophobic segment to prepare a block-type Enteromorpha polysaccharide derivative with surface activity.

[0009] Furthermore, in step (1), the fresh enteromorpha is washed, dried, and ground before extracting enteromorpha polysaccharide. The method for extracting enteromorpha polysaccharide includes any one of hot water extraction, alkaline extraction, enzyme extraction, and microwave ultrasound-assisted extraction.

[0010] Furthermore, the hydroxyl content of the Enteromorpha polysaccharide extracted in step (1) is not less than 10% to ensure that the grafting rate of the hydrophobic segment is higher than 80%.

[0011] The Enteromorpha polysaccharide molecules used in the present invention contain abundant hydroxyl groups (content not less than 10%), which provide active hydrogen for the Enteromorpha polysaccharide molecules, so the Enteromorpha polysaccharide molecules can be used as initiators, and propylene oxide is grafted onto the polysaccharide molecules through a ring-opening polymerization reaction. By accurately controlling the polymerization number of the polyoxypropylene ether chain segment (i.e. controlling the length of the hydrophobic chain segment) through the feed amount of propylene oxide, and grafting the hydrophilic head group at the end of the molecule, the synthesis of Enteromorpha polysaccharide-based surfactants with different surface activities is achieved.

[0012] Furthermore, step (2) specifically includes:

[0013] (2.1) Adding Enteromorpha polysaccharide and catalyst into a reaction kettle;

[0014] (2.2) Close the reactor, set the temperature at 70°C - 120°C, and remove water under reduced pressure. The vacuum degree in the reactor is 4mm -20 mm Hg column, and the dehydration time is 0.5 h to 2 h. This step can remove trace moisture in Enteromorpha polysaccharide to prevent water from participating in the subsequent polymerization reaction.

[0015] (2.3) Set the kettle temperature to 110℃ - 145℃, replace nitrogen 3-5 times, and finally fill the kettle with nitrogen pressure to -0.02 MPa - 0.05 MPa to remove oxygen in the reactor. The purpose of this step is to remove trace oxygen in the reactor to ensure the smooth progress of the subsequent polymerization reaction.

[0016] (2.4) Add propylene oxide to the reactor and control the feed rate of propylene oxide to 6 mL / min - 12 mL / min; set the reaction temperature to 110°C - 145°C and control the reaction temperature within ±2°C of the set reaction temperature; continue the reaction for another half an hour until the addition of propylene oxide is complete, then discharge the material to complete the grafting of the hydrophobic chain.

[0017] Furthermore, in step (2.1), the catalyst includes any one of potassium hydroxide, sodium hydroxide and a double metal cyanide catalyst;

[0018] The mass of the added catalyst is 0.05wt% - 3wt% of the total mass of the product.

[0019] Furthermore, the length of the hydrophobic segment is controlled by controlling the feed amount of propylene oxide, and in the prepared segmented Enteromorpha polysaccharide derivative, the number of ethylene oxide in each hydrophobic segment ranges from 3 to 30.

[0020] Furthermore, in step (3), the end of the hydrophobic segment is carboxylated, sulfonated or phosphorylated to achieve the grafting of a hydrophilic head group at the end of the polyoxypropylene ether hydrophobic segment.

[0021] A block type Enteromorpha polysaccharide derivative is prepared by using Enteromorpha polysaccharide as a raw material, grafting a polyoxypropylene ether hydrophobic chain segment onto Enteromorpha polysaccharide by using a propylene oxide ring-opening polymerization reaction, and then grafting a hydrophilic head group at the end of the polyoxypropylene ether hydrophobic chain segment. The block type Enteromorpha polysaccharide derivative has surface activity.

[0022] Furthermore, in the segmented Enteromorpha polysaccharide derivative, the number of ethylene oxides in each hydrophobic segment ranges from 3 to 30; and the hydrophilic head groups grafted at the ends of the polyoxypropylene ether hydrophobic segments include sodium carboxylate groups, sodium sulfonate groups, and sodium phosphate groups.

[0023] The invention discloses an application of a block type Enteromorpha polysaccharide derivative, wherein the block type Enteromorpha polysaccharide derivative is used as an oil displacing agent.

[0024] Beneficial technical effects of the present invention:

[0025] The present invention proposes a method for preparing a block-type Enteromorpha polysaccharide derivative. Based on the abundant hydroxyl groups in the molecular structure of Enteromorpha polysaccharide, a polyoxypropylene ether hydrophobic segment is grafted onto Enteromorpha polysaccharide by using a propylene oxide ring-opening polymerization reaction, and finally a hydrophilic head group is grafted at the end of the hydrophobic segment to give Enteromorpha polysaccharide molecules surface activity and expand its application in the field of tertiary oil recovery. It can not only solve the problem of Enteromorpha flooding at the seaside, but also expand the biomass source of oil recovery agents. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of a method for preparing a block-type Enteromorpha polysaccharide derivative in an embodiment of the present invention.

[0027] Figure 2 It is the nuclear magnetic hydrogen spectrum of the block type Enteromorpha polysaccharide derivative in the embodiment of the present invention.

[0028] Figure 3 This is a comparison chart of the effects of the block-type Enteromorpha polysaccharide derivative used as an oil-displacing agent in the examples of the present invention and the traditional petroleum sulfonate oil-displacing agent. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] On the contrary, the present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the detailed description of the present invention below. Those skilled in the art can fully understand the present invention without the description of these details.

[0031] Enteromorpha polysaccharide mainly includes rhamnose, galactose, xylose, glucuronic acid, arabinose and galactose, and contains rich hydroxyl groups. The present invention develops a block type Enteromorpha polysaccharide derivative and a preparation method thereof, and realizes the sustainable utilization of Enteromorpha resources and the improvement of economic value by utilizing Enteromorpha polysaccharide in a high value manner.

[0032] The present invention provides a method for preparing a block-type Enteromorpha polysaccharide derivative, which comprises the following specific steps:

[0033] (1) Extraction of Enteromorpha polysaccharide: Extraction of Enteromorpha polysaccharide using fresh Enteromorpha as raw material;

[0034] (2) Grafting of hydrophobic chains: using the Enteromorpha polysaccharide as an initiator and propylene oxide as a polymerization monomer, the polyoxypropylene ether hydrophobic chain segments are grafted onto the Enteromorpha polysaccharide by utilizing the ring-opening polymerization reaction of propylene oxide;

[0035] (3) Hydrophilic head group: A hydrophilic head group is grafted onto the end of the polyoxypropylene ether hydrophobic segment to prepare a block-type Enteromorpha polysaccharide derivative with surface activity.

[0036] Specifically, in step (1), the fresh enteromorpha is washed, dried, and ground before extracting enteromorpha polysaccharide. The method for extracting enteromorpha polysaccharide includes any one of hot water extraction, alkaline extraction, enzyme extraction, and microwave ultrasound assisted extraction.

[0037] The Enteromorpha polysaccharide extracted in this step has abundant hydroxyl groups, wherein the hydroxyl content is obtained by dividing the molecular weight of the hydroxyl group by the molecular weight of the polysaccharide, and the hydroxyl content is determined by the hydroxyl value. The average molecular weight range of the Enteromorpha polysaccharide used in the present invention is: 3*10 3 – 5*10 6 Da;

[0038] In order to more efficiently extract Enteromorpha polysaccharide, the present invention provides a preferred method for extracting Enteromorpha polysaccharide, specifically:

[0039] (1) Collection and pretreatment: Collect fresh Enteromorpha, wash it thoroughly to remove surface salt and impurities, dry it in a cool and ventilated place or through a low-temperature dryer, and after drying, crush it into powder to increase the extraction efficiency.

[0040] (2) Extraction process: Place Enteromorpha powder in distilled water at a ratio of 1:10 – 1:30 (mass / volume), heat the mixture to 65°C - 90°C, maintain the temperature and stir for 1-3 hours to dissolve the polysaccharide, and add a small amount of dilute acid (such as 0.1 M - 0.5 M hydrochloric acid) to accelerate the release of the polysaccharide;

[0041] (3) Crude extraction and precipitation: Filter the mixture to remove insoluble solids, collect the filtrate, gradually add 2-6 volumes of cold ethanol to the filtrate, stir gently to avoid polysaccharide degradation, let the mixture stand overnight to allow the polysaccharide to completely precipitate, and use filter cloth or centrifuge to separate the precipitated polysaccharide.

[0042] Washing and purification: The collected polysaccharide precipitate is washed with a small amount of ethanol to remove impurities, dissolved in a small amount of distilled water, and the ethanol precipitation step is repeated for further purification. The polysaccharide solution is dialyzed in distilled water for 24 hours using a dialysis bag to remove small molecule impurities and salts.

[0043] (4) Determination of molecular weight of Enteromorpha polysaccharide: The molecular weight is determined by gel permeation chromatography or multi-angle light scattering, and the hydroxyl content in the molecule is determined by hydroxyl value.

[0044] This method is a preferred method, and Enteromorpha polysaccharide extracted by other conventional methods can also be used for the subsequent preparation of block-type Enteromorpha polysaccharide derivatives.

[0045] The hydroxyl content of the Enteromorpha polysaccharide extracted in step (1) is not less than 10% to ensure that the grafting rate of the hydrophobic segment is higher than 80%.

[0046] Step (2) specifically includes:

[0047] (2.1) Adding Enteromorpha polysaccharide and catalyst into a reaction kettle;

[0048] (2.2) Close the reactor, set the temperature at 70°C - 120°C, and remove water under reduced pressure. The vacuum degree in the reactor is 4mm -20 mm Hg column, and the water removal time is 0.5 h to 2 h. This step can remove trace water in Enteromorpha polysaccharide.

[0049] (2.3) Set the kettle temperature to 110℃ - 145℃, replace nitrogen 3-5 times, and finally fill the kettle with nitrogen pressure to -0.02 MPa - 0.05 MPa to remove oxygen in the reactor. The purpose of this step is to remove trace oxygen in the reactor to ensure the smooth progress of the subsequent polymerization reaction.

[0050] (2.4) Add propylene oxide to the reactor and control the feed rate of propylene oxide to 6 mL / min - 12 mL / min; set the reaction temperature to 110°C - 145°C and control the reaction temperature within ±2°C of the set reaction temperature; continue the reaction for another half an hour until the addition of propylene oxide is complete, then discharge the material to complete the grafting of the hydrophobic chain.

[0051] Specifically, in step (2.1), the catalyst includes any one of potassium hydroxide, sodium hydroxide and a double metal cyanide catalyst; the mass of the added catalyst is 0.05wt% - 3wt% of the total mass of the product.

[0052] Specifically, the length of the hydrophobic segment is controlled by controlling the feed amount of propylene oxide, and in the prepared segmented Enteromorpha polysaccharide derivative, the number of ethylene oxide in each hydrophobic segment ranges from 3 to 30.

[0053] Specifically, the amount of propylene oxide added in step (2.4) depends on the molecular weight of Enteromorpha polysaccharide, the hydroxyl content and the amount of propylene oxide to be polymerized in each hydrophobic segment; the specific amount added can be obtained by simple calculation; the amount of propylene oxide added = molecular weight of Enteromorpha polysaccharide * hydroxyl content * grafting rate of hydrophobic segment * amount of propylene oxide to be polymerized in each hydrophobic segment.

[0054] Specifically, in step (3), the end of the hydrophobic segment is carboxylated, sulfonated or phosphorylated to achieve the grafting of a hydrophilic head group at the end of the polyoxypropylene ether hydrophobic segment. The method of grafting a sulfonic acid group includes but is not limited to the aminosulfonic acid method, the chlorosulfonic acid method and the sulfur trioxide direct sulfonation method.

[0055] Preferably, the present invention provides a method for grafting sulfonic acid groups, comprising the following steps:

[0056] (1) 0.05 mol - 0.5 mol of the polyether intermediate and an equal molar amount of 1, 2-dichloroethane are added to a four-necked flask for dissolution;

[0057] (2) In an ice-water bath, under mechanical stirring, reflux and an HCl absorption device, slowly dropwise add 1.1-1.5 times the molar amount of chlorosulfonic acid relative to the molar amount of the polyether intermediate, at a temperature not exceeding 10°C, for a dropwise addition time of more than 30-100 minutes;

[0058] (3) After the addition is completed and the reaction is allowed to react for 3 hours, the reaction mixture is neutralized with 10 wt% - 50 wt% NaOH solution to a pH of about 8, and a portion of the water and all of the solvent are removed by rotary evaporation to obtain a product (i.e., a segmented Enteromorpha polysaccharide derivative having surface activity). The product is sampled and the content of anionic active substances in the product is measured by a mixed indicator two-phase titration method, and the content is 50% - 90%.

[0059] The following are specific embodiments:

[0060] Embodiment 1: A method for preparing a block-type Enteromorpha polysaccharide derivative, comprising:

[0061] (1) In this example, Enteromorpha was collected from Shilaoren Sea in Qingdao. The extraction process was as follows: Enteromorpha mass: water volume was 1:20, heated to 65°C, stirred for 1.5 hours, and 0.1 M dilute hydrochloric acid was added;

[0062] (2) During the crude extraction and precipitation process, 2 volumes of cold ethanol are used to separate the precipitated polysaccharides using filter cloth or centrifuge.

[0063] (3) The molecular weight of Enteromorpha polysaccharide was determined by the hydroxyl value determination method, which was 130,000 g / mol and the hydroxyl content was 15%.

[0064] (4) Take the calculated amount of Enteromorpha polysaccharide, add potassium hydroxide catalyst to make the total mass of the product 3.5 wt%, set the reduced pressure dehydration temperature to about 80 °C, and perform dehydration with a vacuum degree of 8 mm Hg column;

[0065] (5) The kettle temperature was set to 120 °C, and nitrogen was replaced again three times. Finally, the nitrogen pressure was filled to 0.02 MPa, the feed rate was 10 mL / min, and the number of propylene oxides to be polymerized in each hydrophobic segment was 3. After the feeding was completed, the reaction was continued for 30 minutes to obtain a polyether intermediate product;

[0066] (6) Put 0.05 mol of the polyether intermediate and an equal molar amount of 1,2-dichloroethane into a four-necked flask to dissolve, and slowly add 1.1 times (relative to the polyether intermediate) molar amount of chlorosulfonic acid (temperature not exceeding 10°C) for 30 minutes;

[0067] (7) After the addition was completed and the reaction was allowed to react for 3 hours, the reaction mixture was neutralized with a 10 wt% NaOH solution to a pH of about 8, and part of the water and all the solvent were removed by rotary evaporation. The anionic active matter content was measured to be 70%. The novel Enteromorpha polysaccharide-based surfactant a was obtained. When the usage amount was 1.0 wt%, the oil recovery efficiency was increased by 5% compared with the traditional petroleum sulfonate surfactant.

[0068] Figure 2 : is the H NMR spectrum of the product synthesized in this example, which proves that the present invention successfully synthesized the block-type Enteromorpha polysaccharide derivative.

[0069] Figure 3 This is a comparison chart of the effects of the block-type Enteromorpha polysaccharide derivative as an oil-displacing agent and the traditional petroleum sulfonate oil-displacing agent in the embodiment of the present invention. Figure 3 It can be seen that the oil displacement effect of using the block-type Enteromorpha polysaccharide derivative provided by the present invention as an oil displacement agent is much better than that of the traditional petroleum sulfonate oil displacement agent.

[0070] Embodiment 2: A method for preparing a block-type Enteromorpha polysaccharide derivative, comprising:

[0071] (1) In this example, Enteromorpha was collected from the Jinshatan sea area of ​​Huangdao District, Qingdao. The extraction process was as follows: Enteromorpha mass: water volume was 1:15, heated to 85°C, stirred for 2 hours, and 0.3 M dilute hydrochloric acid was added;

[0072] (2) In the crude extraction and precipitation process, 5 volumes of cold ethanol are used to separate the precipitated polysaccharides using filter cloth or centrifuge.

[0073] (3) The molecular weight of Enteromorpha polysaccharide was determined by the hydroxyl value determination method, which was 230,000 g / mol and the hydroxyl content was 20%.

[0074] (4) Take the calculated amount of Enteromorpha polysaccharide, add sodium hydroxide catalyst to 3 wt% of the total mass of the product, set the reduced pressure dehydration temperature to about 70 °C, and perform dehydration with a vacuum degree of 4 mm Hg column;

[0075] (5) The kettle temperature was set to 125 °C, and nitrogen was replaced again three times. Finally, the nitrogen pressure was filled to -0.02 MPa, the feed rate was 8 mL / min, and the number of propylene oxides to be polymerized in each hydrophobic segment was 6. After the feeding was completed, the reaction was continued for 30 minutes to obtain a polyether intermediate product;

[0076] (6) Put 0.1 mol of the polyether intermediate and an equal molar amount of 1,2-dichloroethane into a four-necked flask to dissolve, and slowly add 1.5 times (relative to the polyether intermediate) molar amount of chlorosulfonic acid (temperature not exceeding 10°C) for 50 minutes;

[0077] (7) After the addition was completed and the reaction was allowed to react for 3 hours, the reaction mixture was neutralized with a 20 wt% NaOH solution to a pH of about 8, and part of the water and all the solvent were removed by rotary evaporation. The anionic active matter content was measured to be 89%;

[0078] (8) The novel Enteromorpha polysaccharide-based surfactant b was obtained. When used in an amount of 0.5 wt%, the oil recovery efficiency was increased by 10% compared with the traditional water-soluble polyacrylamide.

[0079] Embodiment 3: A method for preparing a block-type Enteromorpha polysaccharide derivative, comprising:

[0080] (1) In this example, Enteromorpha was collected from Shazikou Sea in Qingdao. During the extraction process, Enteromorpha mass: water volume ratio was 1:20, heated to 90°C, stirred for 3 hours, and 0.5 M dilute hydrochloric acid was added;

[0081] (2) Crude extraction and precipitation process: Use 4 times the volume of cold ethanol to separate the precipitated polysaccharides using filter cloth or centrifuge.

[0082] (3) The molecular weight of Enteromorpha polysaccharide was determined by the hydroxyl value determination method. The molecular weight was 100,000 g / mol and the hydroxyl content was 25%.

[0083] (4) Take the calculated amount of Enteromorpha polysaccharide, add a metal cyanide catalyst to a total mass of 0.05 wt% of the product, set the reduced pressure dehydration temperature at about 100 °C, and perform dehydration with a vacuum degree of 8 mm Hg column;

[0084] (5) The kettle temperature was set to 135 °C, and nitrogen was replaced three times again. Finally, the nitrogen pressure was filled to 0.05 MPa, the feed rate was 12 mL / min, and the number of propylene oxides to be polymerized in each hydrophobic segment was 9. After the feeding was completed, the reaction was continued for 30 minutes to obtain a polyether intermediate product;

[0085] (6) Put 0.3 mol of the polyether intermediate and an equal molar amount of 1,2-dichloroethane into a four-necked flask to dissolve, and slowly add 1.3 times (relative to the polyether intermediate) molar amount of chlorosulfonic acid (temperature not exceeding 10°C) for 60 minutes;

[0086] (7) After the addition was completed and the reaction was allowed to react for 3 hours, the reaction mixture was neutralized with a 30 wt% NaOH solution to a pH of about 8, and part of the water and all the solvent were removed by rotary evaporation. The anionic active matter content was measured to be 79%;

[0087] (8) A novel Enteromorpha polysaccharide-based surfactant c was obtained. When used in an amount of 1.5 wt%, the oil recovery efficiency was increased by 20% compared with the traditional alkylbenzene sulfonate.

[0088] Example 4: A block-type Enteromorpha polysaccharide derivative, which is prepared by using Enteromorpha polysaccharide as raw material, grafting polyoxypropylene ether hydrophobic chain segments onto Enteromorpha polysaccharide by propylene oxide ring-opening polymerization, and then grafting hydrophilic head groups at the ends of the polyoxypropylene ether hydrophobic chain segments. The block-type Enteromorpha polysaccharide derivative has surface activity.

[0089] Specifically, in the segmented Enteromorpha polysaccharide derivative, the number of ethylene oxides in each hydrophobic segment ranges from 3 to 30; the hydrophilic head groups grafted at the ends of the polyoxypropylene ether hydrophobic segments include sodium carboxylate groups, sodium sulfonate groups, and sodium phosphate groups.

[0090] Example 5: Application of a block-type Enteromorpha polysaccharide derivative, wherein the block-type Enteromorpha polysaccharide derivative is used as an oil-displacing agent. Specifically, when used as an oil-displacing agent, the amount of the block-type Enteromorpha polysaccharide derivative is in the range of 0.5 wt% - 1.5 wt%.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a block-type Enteromorpha polysaccharide derivative, characterized in that: The method comprises the following specific steps: (1) Extracting Enteromorpha polysaccharide: Extracting Enteromorpha polysaccharide from fresh Enteromorpha; (2) Grafting of hydrophobic chains: using the Enteromorpha polysaccharide as an initiator and propylene oxide as a polymerization monomer, the polyoxypropylene ether hydrophobic chain segments are grafted onto the Enteromorpha polysaccharide by means of a ring-opening polymerization reaction of propylene oxide; (3) Hydrophilic head group: Grafting a hydrophilic head group at the end of the polyoxypropylene ether hydrophobic segment to prepare a block-type Enteromorpha polysaccharide derivative with surface activity; Step (2) specifically includes: (2.1) Adding Enteromorpha polysaccharide and catalyst into a reaction kettle; (2.2) Close the reactor, set the temperature at 70°C-120°C, and remove water under reduced pressure. The vacuum degree in the reactor is 4mm-20mmHg column, and the water removal time is 0.5h to 2h; (2.3) Set the kettle temperature to 110°C-145°C, replace nitrogen 3-5 times, and finally fill the nitrogen pressure to -0.02MPa-0.05MPa to remove oxygen in the reactor; (2.4) Add propylene oxide to the reactor, control the feed rate of propylene oxide to 6 mL / min-12 mL / min; set the reaction temperature to 110° C.-145° C., and control the reaction temperature within ±2° C. of the set reaction temperature; until the addition of propylene oxide is completed, react for another half an hour, discharge the material, and complete the grafting of the hydrophobic chain; In step (2.1), the catalyst comprises any one of potassium hydroxide, sodium hydroxide and a double metal cyanide catalyst; the mass of the added catalyst is 0.05wt%-3wt% of the total mass of the product; In step (3), the end of the hydrophobic segment is carboxylated, sulfonated or phosphorylated to achieve the grafting of a hydrophilic head group at the end of the polyoxypropylene ether hydrophobic segment.

2. The method for preparing a block-type Enteromorpha polysaccharide derivative according to claim 1, characterized in that: In step (1), the fresh enteromorpha is washed, dried, ground and then enteromorpha polysaccharide is extracted. The method for extracting enteromorpha polysaccharide includes any one of hot water extraction, alkaline extraction, enzyme extraction and microwave ultrasound assisted extraction.

3. The method for preparing a block-type Enteromorpha polysaccharide derivative according to claim 1, characterized in that: The hydroxyl content of the Enteromorpha polysaccharide extracted in step (1) is not less than 10% to ensure that the grafting rate of the hydrophobic segment is higher than 80%.

4. The method for preparing a block-type Enteromorpha polysaccharide derivative according to claim 1, characterized in that: The length of the hydrophobic segment is controlled by controlling the feed amount of propylene oxide, and the number of propylene oxide in each hydrophobic segment of the prepared segmented Enteromorpha polysaccharide derivative is in the range of 3-30.

5. A block-type Enteromorpha polysaccharide derivative, prepared by the method according to any one of claims 1 to 4, characterized in that: The block type Enteromorpha polysaccharide derivative is prepared by using Enteromorpha polysaccharide as a raw material, grafting a polyoxypropylene ether hydrophobic chain segment onto Enteromorpha polysaccharide by using a propylene oxide ring-opening polymerization reaction, and then grafting a hydrophilic head group at the end of the polyoxypropylene ether hydrophobic chain segment. The block type Enteromorpha polysaccharide derivative has surface activity.

6. The use of a block-type Enteromorpha polysaccharide derivative according to claim 5, characterized in that: The block-type Enteromorpha polysaccharide derivative is used as an oil-displacing agent.

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