A green compound antiscalant for geothermal fluid and preparation method thereof

Abstract

The present invention provides a green compounded scale inhibitor for geothermal fluids. The compounded scale inhibitor comprises modified polyaspartic acid, highly hydrolyzed polymaleic anhydride, polyepoxysuccinic acid, and polyacrylic acid. The compounded scale inhibitor for geothermal fluids described herein exhibits excellent synergistic effects, inhibiting scale through chelation, solubilization, and lattice distortion. It exhibits significant scale inhibition advantages in actual geothermal water and has great practical application value.

Description

Technical Field

[0001] The present invention belongs to the field of geothermal energy, and in particular relates to a green compound scale inhibitor for geothermal fluid and a preparation method thereof. Background Art

[0002] Geothermal energy, a non-carbon, clean energy source, offers the advantage of stable and continuous output, making it crucial for achieving the development goals of carbon peak and carbon neutrality. However, geothermal water dissolves a rich variety of minerals during its formation. Highly mineralized geothermal water can cause scaling on geothermal well pipes, pumps, transmission lines, heat exchangers, and other equipment, impacting geothermal utilization.

[0003] The addition of chemical agents to geothermal water to prevent scale formation is a long-standing method, and the addition of scale inhibitors is generally considered the most direct and effective method for preventing scaling. Scale inhibitors can be divided into natural polymer scale inhibitors and synthetic polymer scale inhibitors based on their composition. Synthetic polymer scale inhibitors can be further divided into phosphorus-containing polymer scale inhibitors, carboxylic acid polymer scale inhibitors, sulfonic acid polymer scale inhibitors, and environmentally friendly scale inhibitors. Phosphorus-containing scale inhibitors have been the most widely used in the past few decades. However, these scale inhibitors can cause secondary pollution to the environment, requiring immediate recovery and disposal. This is especially true during geothermal water recharge, where they can contaminate groundwater and soil, posing a threat to the ecological environment.

[0004] At the same time, in practical applications, a single type of scale inhibitor is unlikely to achieve a comprehensive scale inhibition and dispersion effect in complex geothermal fluid systems composed of multiple ions. Current research on environmentally friendly compound scale inhibitors primarily focuses on scale inhibition for power plant circulating cooling water, boiler water, and other applications, while research on green scale inhibitors for geothermal water is limited. Summary of the Invention

[0005] In view of this, the present invention aims to overcome the defects in the prior art and proposes a green compound scale inhibitor for geothermal fluid and a preparation method thereof.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A green compound antiscalant for geothermal fluid, characterized in that the compound antiscalant comprises the following raw materials in parts by weight:

[0008]

[0009] Preferably, the compound scale inhibitor comprises the following raw materials in parts by weight:

[0010]

[0011] More preferably, the compound scale inhibitor comprises the following raw materials in parts by weight:

[0012]

[0013] Furthermore, the preparation method of the modified polyaspartic acid comprises the following steps: mixing dextran, polysuccinimide and a catalyst, reacting under heating conditions, and washing, filtering and drying the reaction product after the reaction is completed to obtain the modified polyaspartic acid.

[0014] Furthermore, the catalyst is prepared by mixing p-toluenesulfonic acid and dimethyl sulfoxide; the solid-liquid ratio of p-toluenesulfonic acid to dimethyl sulfoxide is 0.1-0.12 g:100-120 mL.

[0015] Furthermore, the mass ratio of the dextran, polysuccinimide and catalyst is 1-1.2 g: 2-2.5 g: 100-120 mL.

[0016] Furthermore, the temperature of the heating step is 120-125° C., the reaction time is 20-24 hours, and the molecular weight of the dextran is 1000.

[0017] Furthermore, the preparation method of the highly hydrolyzed polymaleic anhydride comprises the following steps: adding maleic anhydride, sodium hydroxide and ammonium ferric sulfate to deionized water, stirring until completely dissolved, adding hydrogen peroxide dropwise thereto under heating conditions, and cooling to room temperature after the reaction is completed to obtain the highly hydrolyzed polymaleic anhydride.

[0018] The molecular weight of the hydrolyzed polymaleic anhydride is 1500-2000.

[0019] Furthermore, the solid-liquid ratio of maleic anhydride, sodium hydroxide, ammonium ferric sulfate, hydrogen peroxide and deionized water is 400-500 g: 100-105 g: 0.04-0.06 g: 400-500 mL: 450-500 mL; and the mass concentration of the hydrogen peroxide is 30%.

[0020] Furthermore, the temperature of the heating step is 95-100° C.; the time of the reaction step is 3-4 hours; and the speed of the dropwise addition step is 50-60 drops / min.

[0021] Hydrolyzed polymaleic anhydride and polyacrylic acid are both highly effective, phosphorus-free, green scale inhibitors. Both belong to the carboxylic acid family of polymers. The carboxylic acid functional groups in the polymers form soluble chelates with calcium ions, thereby inhibiting the formation of calcium carbonate nuclei. Hydrolyzed polymaleic anhydride and polyacrylic acid exhibit a synergistic effect, and their copolymers exhibit significantly superior scale inhibition performance compared to either agent alone. However, the compound scale inhibitor of hydrolyzed polymaleic anhydride and polyacrylic acid has the following disadvantages: 1. Both hydrolyzed polymaleic anhydride and polyacrylic acid are biorefractory organic matter, and will still cause certain pollution to the ecological environment during the utilization and reinjection of geothermal water; 2. Commercially available hydrolyzed polymaleic anhydride is a partial hydrolysis product of polymaleic anhydride, with about 60-70% of the anhydride structure being hydrolyzed into carboxylic acid, which is not completely hydrolyzed, and has a low molecular weight, resulting in a large dosage problem; 3. The compound scale inhibitor of hydrolyzed polymaleic anhydride and polyacrylic acid has a general scale inhibition effect in high-alkalinity geothermal fluids; 4. In geothermal fluids with high mineralization, there are a large number of scale-forming ions and ions that interfere with scale inhibition, and the compound scale inhibitor of hydrolyzed polymaleic anhydride and polyacrylic acid has a general scale inhibition effect.

[0022] Therefore, the present invention adds biodegradable polyepoxysuccinic acid and modified polyaspartic acid suitable for high alkalinity water systems on the basis of a compound of hydrolyzed polymaleic anhydride and polyacrylic acid. On the one hand, the amount of hydrolyzed polymaleic anhydride and polyacrylic acid used can be reduced, the biodegradability of the compound scale inhibitor can be improved, and the pollution to the ecological environment caused by the compound scale inhibitor during the utilization and reinjection of geothermal water can be further reduced. On the other hand, the four scale inhibitors work synergistically, and the scale inhibition performance of the compound scale inhibitor is significantly improved. The number of active growth points for calcium carbonate scaling is limited. When the scale inhibitor molecules cover a certain active growth point, the activity of the point will be inhibited. Polyacrylic acid contains numerous carboxyl groups, hydrolyzed polymaleic anhydride contains numerous carboxyl and hydroxyl groups, modified polyaspartic acid contains numerous carboxyl, amino, hydroxyl, and glycosidic bonds, and polyepoxysuccinic acid contains numerous carboxyl, hydroxyl, and ether bonds. The compounded scale inhibitors cover the calcium ions that form calcium carbonate scale through the unpaired electrons of the nitrogen and oxygen atoms in these groups, and through hydrogen bonding, they cover the calcium carbonate ions that form calcium carbonate scale. The combination of these two strong non-bonding interactions results in a close attraction between the scale inhibitor molecules and the active sites on the calcium carbonate surface, enabling the four scale inhibitors to exert a synergistic scale inhibition effect. Furthermore, these groups embed or adsorb on the surface of the calcium carbonate nucleus, increasing the negative charge density on the nucleus surface, raising the nucleus potential, and increasing the Coulomb repulsion between nuclei, significantly hindering the formation and growth of the calcium carbonate nucleus. Furthermore, the four polymers have distinct spatial structures. Embedded or adsorbed on the surface of the calcium carbonate nucleus, they form a complex network structure that acts as a steric hindrance, significantly distorting the calcium carbonate crystal lattice and further hindering the growth of the calcium carbonate nucleus.

[0023] At the same time, the embedding or adsorption of hydrolyzed polymaleic anhydride on calcium carbonate crystals primarily relies on the double-bonded O atoms or -OH groups in maleic acid. Therefore, polymers with different degrees of hydrolysis approach calcium carbonate crystals to varying degrees, resulting in different energy changes. Studies have shown that as the degree of hydrolysis increases, polymer molecules approach calcium carbonate crystals more closely, the bond distances of active groups change more significantly, and the energy drop is greater, resulting in a more pronounced scale inhibition effect. Therefore, the present invention improves the hydrolysis degree of polymaleic anhydride by first neutralizing the maleic anhydride during the synthesis process, thereby enhancing the scale inhibition effect of the hydrolyzed polymaleic anhydride.

[0024] Furthermore, polyaspartic acid is not heat-resistant and is not suitable for high-temperature geothermal fluids, requiring modification. Given that glucan compounds have strong affinity and good water solubility, and contain a large number of hydroxyl groups in their molecular structure, the esterification reaction in which hydroxyl and carboxyl groups are dehydrated to form esters is one of the most common reactions in organic synthesis. Therefore, the present invention uses the nucleophilic attack of the CN bond of polysuccinimide by the nucleophilic reagent dimethyl sulfoxide to obtain polyaspartic acid monomers in both α and β configurations, and utilizes the hydroxyl groups in the glucan molecules to modify the carboxyl groups in the polyaspartic acid molecules, thereby achieving green modification of polyaspartic acid with glucan. Due to the large number of hydroxyl groups and hydrophobic carbon rings on its sugar chain, dextran exhibits a highly ordered helical structure in aqueous solution. After modification with dextran, hydroxyl groups and a helical structure are introduced into polyaspartic acid. The unpaired electrons carried by the O atoms in the hydroxyl groups are physically and chemically embedded or adsorbed on the surface of the calcium carbonate nucleus, increasing the negative charge density on the nucleus surface, raising the potential of the nucleus, and increasing the Coulomb repulsion between the nuclei, effectively hindering the formation of calcium carbonate nuclei. In addition, the helical structure of the modified polyaspartic acid further exacerbates the distortion of the calcium carbonate lattice, thereby significantly hindering the growth of the calcium carbonate nucleus. Therefore, the scale inhibition effect of the polyaspartic acid modified with dextran is significantly improved. In addition, dextran has good water solubility and biodegradability. Using dextran to modify polyaspartic acid can improve the effectiveness of the compound scale inhibitor while also ensuring the biodegradability of the modified polyaspartic acid.

[0025] The compound scale inhibitor of the present invention also shows good scale inhibition effect in high alkalinity geothermal water. - The ionization equilibrium of CO3 shifts to the right. 2-As the content increases, calcium carbonate precipitation tends to form, accompanied by the formation of calcium hydroxide precipitation, which reduces the scale inhibition effect of the scale inhibitor. However, as the pH increases, the dissociation of polyepoxysuccinic acid intensifies, the charge density on the molecular chain increases, and the ductility of the molecular chain increases, allowing it to expand from a coiled structure to an extended structure. The negatively charged groups are fully exposed, which is conducive to adsorption on the microcrystals of ionically bonded calcium carbonate scale, thereby inhibiting the further growth of calcium carbonate scale crystals. Polyaspartic acid, after being modified with dextran, has a helical structure. In high-alkalinity geothermal water, it can unwind to form a random coil state, exposing more negatively charged groups and better adsorbing on the microcrystals of ionically bonded calcium carbonate scale, exerting a good scale inhibition effect.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The green compound scale inhibitor for geothermal fluid described in the present invention is a compound of modified polyaspartic acid, highly hydrolyzed polymaleic anhydride, polyepoxysuccinic acid and polyacrylic acid, which has a good synergistic effect, and at the same time has a wide temperature adaptability and acid and alkali resistance. It achieves scale inhibition through chelation solubilization and lattice distortion, has obvious scale inhibition advantages in actual geothermal water, and has good practical promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The SEM images before and after use of the compound scale inhibitor described in Example 1 of the present invention are as follows: A is before adding the scale inhibitor, and B is after adding the scale inhibitor;

[0029] Figure 2 The XRD patterns of the compound scale inhibitor described in the embodiment of the present invention before and after use are shown in Figure 1. A is before adding the scale inhibitor, and B is after adding the scale inhibitor.

[0030] Figure 3 This is a bar graph showing the scale inhibition rates of the compound scale inhibitors described in Examples 1-2 and Comparative Examples 1-4 of the present invention;

[0031] Figure 4 This is a bar graph of the scale inhibition rate of the compound scale inhibitor described in Example 1 of the present invention and Comparative Example 1 at different temperatures;

[0032] Figure 5 This is a bar graph of the scale inhibition rate of the compound scale inhibitor described in Example 1 of the present invention at different pH values. DETAILED DESCRIPTION

[0033] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental methods described, unless otherwise specified, are conventional methods.

[0034] The present invention will be described in detail below with reference to the embodiments.

[0035] Example 1

[0036] A green compound scale inhibitor for geothermal fluid comprises the following raw materials in parts by weight: 4 parts of modified polyaspartic acid, 12 parts of highly hydrolyzed polymaleic anhydride, 4 parts of polyepoxysuccinic acid, and 4 parts of polyacrylic acid.

[0037] The preparation method of the modified polyaspartic acid comprises the following steps: mixing 1.0 g of dextran (molecular weight 1000), 2.0 g of polysuccinimide and a catalyst (the catalyst is a mixture of 0.1 g of p-toluenesulfonic acid and 100 mL of dimethyl sulfoxide), starting a stirrer, heating to 120° C., reacting for 24 hours, and after completion of the reaction, washing the reaction product with anhydrous ethanol, filtering, and drying to obtain the modified polyaspartic acid.

[0038] The preparation method of highly hydrolyzable polymaleic anhydride comprises the following steps: adding 500g of maleic anhydride, 102g of sodium hydroxide and 0.04g of ammonium ferric sulfate to 450mL of deionized water, turning on a stirrer, heating the water to 40-50°C, stirring the water until the water is completely dissolved, further heating the water to 95-100°C, dropwise adding 400mL of hydrogen peroxide (mass concentration 30%) at a dropping rate of 50-60 drops / min, starting a timer after all the hydrogen peroxide has been titrated, reacting the water for 3-4 hours, and cooling the water to room temperature after the reaction is complete to obtain the highly hydrolyzable polymaleic anhydride having a molecular weight of 1500-2000.

[0039] A method for preparing a green compound scale inhibitor for geothermal fluid comprises the following steps: weighing 0.5 g of highly hydrolyzed polymaleic anhydride and dissolving it in 100 mL of deionized water to prepare solution A; weighing 0.5 g of modified polyaspartic acid and dissolving it in 100 mL of deionized water to prepare solution B; weighing 0.55 g of polyepoxysuccinic acid (90%) and dissolving it in 100 mL of deionized water to prepare solution C; weighing 0.5 g of polyacrylic acid (molecular weight 5000) and dissolving it in 100 mL of deionized water to prepare solution D; and at room temperature, taking 1.2 mL of solution A, 0.4 mL of solution B, 0.4 mL of solution C, and 0.4 mL of solution D and mixing them to obtain a compound scale inhibitor, which can be used to effectively inhibit scale in 500-1000 mL of geothermal water.

[0040] The morphological evolution of calcium carbonate scale after adding the compound scale inhibitor described in Example 1 and without adding the scale inhibitor is as follows: Figure 1 As shown. Figure 1As shown in Figure A, when no compound scale inhibitor is added, the crystals are regular cubes with a tight and orderly arrangement, which is the typical appearance of calcite. The compound scale inhibitor contains a large number of N, O atoms and hydrogen bonds with unpaired electrons. The scale inhibitor molecules cover the calcium ions of calcium carbonate scale through these N and O atoms, and cover the calcium carbonate ions of calcium carbonate scale through hydrogen bonds. The combination of these two strong non-bonding interactions will cause the scale inhibitor molecules to be tightly attracted to the active sites on the surface of calcium carbonate, allowing the four scale inhibitors to exert a good synergistic scale inhibition effect. In addition, these groups are embedded in or adsorbed on the surface of the calcium carbonate crystal nucleus, which increases the negative charge density on the surface of the crystal nucleus, increases the potential of the crystal nucleus, and increases the Coulomb repulsion between the crystal nuclei, thereby significantly hindering the formation and growth of the calcium carbonate crystal nucleus. Moreover, the spatial structures of the four polymers are different. They are embedded in or adsorbed on the surface of the calcium carbonate crystal nucleus to form a complex network structure, which plays a role of steric hindrance, resulting in obvious distortion of the calcium carbonate crystal lattice, further hindering the growth of the calcium carbonate crystal nucleus. By Figure 1 As shown in Figure B, after the addition of the compound scale inhibitor, defects appeared on the edge of the crystal, the growth pattern gradually became irregular, broken or relatively loose, with different shapes and small size, indicating that the composite scale inhibitor affected the nucleation and growth process of the calcium carbonate crystal. This may be because the composite scale inhibitor is embedded or adsorbed on the surface of the calcium carbonate crystal, making it unable to grow in a normal way, resulting in its structure being relatively loose, small, with different appearances and easy to break.

[0041] The crystal structure of calcium carbonate formed without and with antiscalant was analyzed by XRD. The results are as follows: Figure 2 As shown. When no scale inhibitor is added, the calcium carbonate crystals produced after constant temperature for 10 hours have characteristic peaks of calcite at diffraction angles of 2θ at 23.02°, 29.47°, 31.42°, 35.97°, 39.40°, etc., indicating that the crystal form of calcium carbonate is basically the most stable calcite. After adding the scale inhibitor and keeping the temperature for 10 hours, the intensity of the characteristic absorption peak of calcite is significantly reduced, and the characteristic peaks of metastable vaterite and aragonite appear at 2θ at 26.21°, 27.21°, 32.74° and 45.85°, etc., and its crystal form is calcite, vaterite and aragonite structure. Since the characteristic absorption peak of calcite is significantly reduced, it can be inferred that after the addition of the scale inhibitor, the calcium carbonate crystals are transformed from stable calcite to unstable vaterite and aragonite, indicating that the addition of the scale inhibitor causes the calcium carbonate lattice to be distorted.

[0042] Furthermore, static scale inhibition experiments revealed that the calcium carbonate crystals at the bottom of the flask without the addition of a scale inhibitor were dense white precipitates that were difficult to wash off, whereas the calcium carbonate precipitates at the bottom of the beaker with the addition of a scale inhibitor were soft and flocculent and could be washed off with a slight shake. Combining static scale inhibition experiments, electron microscopy images of scale samples, and theories related to scale inhibition mechanisms, we analyzed that the scale inhibition mechanism primarily involves chelation solubilization and lattice distortion.

[0043] Example 2

[0044] The only difference from Example 1 is that the following raw materials are included in parts by weight: 4 parts of modified polyaspartic acid, 10 parts of highly hydrolyzed polymaleic anhydride, 4 parts of polyepoxysuccinic acid, and 5 parts of polyacrylic acid.

[0045] Comparative Example 1

[0046] The only difference from Example 1 is that the modified polyaspartic acid is replaced by conventional commercially available polyaspartic acid.

[0047] Comparative Example 2

[0048] The only difference from Example 1 is that the highly hydrolyzed polymaleic anhydride is replaced by conventional commercially available hydrolyzed polymaleic anhydride.

[0049] Comparative Example 3

[0050] The only difference from Example 1 is that the modified polyaspartic acid is replaced by conventional commercially available polyaspartic acid, and the highly hydrolyzed polymaleic anhydride is replaced by conventional commercially available hydrolyzed polymaleic anhydride.

[0051] Comparative Example 4

[0052] The only difference from Example 1 is that the added amount of modified polyaspartic acid is 7 parts, the added amount of highly hydrolyzed polymaleic anhydride is 7 parts, the added amount of polyepoxysuccinic acid is 7 parts, and the added amount of polyacrylic acid is 7 parts.

[0053] The scale inhibitors obtained in Examples 1-2 and Comparative Examples 1-4 were subjected to the following experiments:

[0054] 1. The scale inhibition rate of the compound scale inhibitor was determined according to the national standard "Determination of scale inhibition performance of water treatment agents: calcium carbonate precipitation method" (GB / T 16632-2019). The geothermal fluid from a geothermal well in Tianjin was used as the background water. Table 1 shows the main chemical components and contents of the geothermal fluid. 240 mg / L CaCl2 (in the form of CaCl2) was added to the geothermal water. 2+ ), 732mg / L NaHCO3 and the scale inhibitors of each embodiment and each comparative example, the scale inhibition rate is as follows Figure 3 As shown, the reaction temperature is 80°C and the reaction time is 10 h.

[0055] Table 1 Contents of main chemical components of geothermal fluid from a geothermal well in Tianjin

[0056] Analysis Project Concentration (mg / L) Analysis Project Concentration (mg / L) Analysis Project Concentration (mg / L) <![CDATA[Na + ]]> 228 <![CDATA[SO4 2- ]]> 163 Total alkalinity 263 K+ 56.6 <![CDATA[HCO3 - ]]> 317 Total hardness 89.1 <![CDATA[Ca 2+ ]]> 25.3 <![CDATA[CO3 2- ]]> 1.8 Mineralization 1020 <![CDATA[Mg 2+ ]]> 6.37 Cl 137 solid matter 861.5 <![CDATA[Fe 2+ ]]> 0.24 <![CDATA[NO3 - ]]> 0.27 <![CDATA[SiO2]]> 85.6 <![CDATA[Free CO2]]> 0 <![CDATA[P04 3- ]]> 0.02 pH 8.33 F 7.77

[0057] like Figure 3As shown, the scale inhibition rate of the compound scale inhibitor prepared in Example 1 is significantly higher than that of the compound scale inhibitors prepared in Comparative Examples 1, 2, and 3, indicating that the modified polyaspartic acid and highly hydrolyzed polymaleic anhydride significantly enhance the scale inhibition effect of the compound scale inhibitor. The scale inhibition rates of the compound scale inhibitors prepared in Examples 1 and 2 are significantly higher than that of the compound scale inhibitor prepared in Comparative Example 4, indicating that optimizing the dosage and ratio of the four scale inhibitors can significantly enhance the scale inhibition effect of the compound scale inhibitor.

[0058] 2. The scale inhibition rate of the compound scale inhibitor was determined according to the national standard "Determination of scale inhibition performance of water treatment agents: calcium carbonate precipitation method" (GB / T 16632-2019). The geothermal fluid from a geothermal well in Tianjin was used as the background water. The main chemical components and contents of the geothermal fluid are shown in Table 1. 240 mg / L CaCl2 (in the form of CaCl2) was added to the geothermal water. 2+ ), 732mg / LNaHCO3 and the scale inhibitors of Example 1 and Comparative Example 1, other reaction conditions remain unchanged, and the reaction temperatures are 40℃, 60℃, 80℃, 100℃, and 120℃. The scale inhibition rate is as follows Figure 4 shown.

[0059] Depend on Figure 4 As can be seen, the scale inhibition rate of the compound scale inhibitor prepared in Example 1 is above 90% within the range of 40-120°C, indicating that the compound scale inhibitor has a wide temperature range of application. At temperatures of 80°C, 100°C, and 120°C, the scale inhibition rate of the compound scale inhibitor prepared in Example 1 is significantly higher than that of Comparative Example 1, indicating that the temperature resistance of the compound scale inhibitor is significantly improved after modification with polyaspartic acid.

[0060] 3. The scale inhibition rate of the compound scale inhibitor was determined according to the national standard "Determination of scale inhibition performance of water treatment agents: calcium carbonate precipitation method" (GB / T 16632-2019). The geothermal fluid taken from a geothermal well in Tianjin was used as the background water. The main chemical components and contents of the geothermal fluid are shown in Table 1. 240 mg / L CaCl2 (in the form of CaCl2) was added to the geothermal water. 2+ ), 732mg / LNaHCO3 and the scale inhibitor of Example 1, the reaction conditions remain unchanged, and the pH of the test solution is adjusted to 7, 8, 9, and 10 with sodium hydroxide solution. The scale inhibition rate is as follows Figure 5 shown.

[0061] Depend on Figure 5 It can be seen that in alkaline geothermal water with a pH of 7-10, the scale inhibition rate of the compound scale inhibitor prepared in Example 1 is above 85%, and the scale inhibition effect is obvious, indicating that the compound scale inhibitor has good acid and alkali resistance.

[0062] 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 principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A green compound scale inhibitor for geothermal fluid, characterized by: The compound scale inhibitor comprises the following raw materials in parts by weight: 3-4 parts of modified polyaspartic acid, Highly hydrolyzed polymaleic anhydride 10-12 parts, 1-4 parts of polyepoxysuccinic acid, 4-5 parts of polyacrylic acid; The preparation method of the modified polyaspartic acid comprises the following steps: mixing dextran, polysuccinimide and a catalyst, reacting under heating conditions, and washing, filtering and drying the reaction product after the reaction is completed to obtain the modified polyaspartic acid; The catalyst is prepared by mixing p-toluenesulfonic acid and dimethyl sulfoxide; the solid-liquid ratio of p-toluenesulfonic acid to dimethyl sulfoxide is 0.1-0.12 g:100-120 mL; The mass ratio of the dextran, polysuccinimide and catalyst is 1-1.2 g: 2-2.5 g: 100-120 mL; The preparation method of the highly hydrolyzed polymaleic anhydride comprises the following steps: adding maleic anhydride, sodium hydroxide and ammonium ferric sulfate into deionized water, stirring until completely dissolved, adding hydrogen peroxide dropwise thereto under heating conditions, and cooling to room temperature after the reaction is completed to obtain the highly hydrolyzed polymaleic anhydride.

2. The green compound antiscalant for geothermal fluid according to claim 1, characterized in that: In the preparation method of the modified polyaspartic acid, the temperature of the heating step is 120-125° C., the reaction time is 20-24 hours, and the molecular weight of the dextran is 1000.

3. The green compound antiscalant for geothermal fluid according to claim 1, characterized in that: In the preparation method of highly hydrolyzed polymaleic anhydride, the solid-liquid ratio of maleic anhydride, sodium hydroxide, ammonium ferric sulfate, hydrogen peroxide and deionized water is 400-500 g:100-105 g:0.04-0.06 g:400-500 mL:450-500 mL; and the mass concentration of the hydrogen peroxide is 30%.

4. The green compound antiscalant for geothermal fluid according to claim 1, characterized in that: In the method for preparing highly hydrolyzed polymaleic anhydride, the temperature of the heating step is 95-100° C.; the time of the reaction step is 3-4 hours; and the speed of the dropwise addition step is 50-60 drops / min.

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