Temperature-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification as well as preparation method and application of temperature-resistant and salt-resistant welan gum

Abstract

The invention relates to the technical field of biopolymer materials, in particular to temperature-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification as well as a preparation method and application of the temperature-resistant and salt-resistant welan gum. The preparation method comprises the following steps: dissolving welan gum powder in a system containing NaOH and DMSO, adding 3-chloro-2-hydroxypropyl trimethyl ammonium chloride and 1-bromohexadecane, adding ethanol, centrifuging to obtain a reaction solution, and finally centrifuging and freeze-drying the solid to obtain the welan gum. The salt-resistant and temperature-resistant tackifier can be used in oilfield exploitation, realizes dynamic salt-resistant and temperature-resistant tackifying in an extreme salt temperature environment, has higher viscosity, can maintain stable viscosity along with the increase of salt concentration, and is suitable for tertiary oil recovery of a high-salt stratum; the compound can be used as a seed coating agent, a soil conditioner, a pesticide slow-release carrier and a fertilizer synergist in agriculture; the product can be used as a thickening agent, a stabilizing agent and a gelling agent in the food industry; the product can be used as a humectant and a rheology modifier in the cosmetic industry; the product can be used as a cement additive in the field of building materials, and can be used in tile glue and putty powder.

Description

Technical Field

[0001] The invention belongs to the technical field of biopolymer modification, and particularly relates to a temperature-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification, and a preparation method and application thereof. Background Art

[0002] In modern industry and scientific research, the functional modification of polymer materials has always been a key direction for promoting technological innovation. Welan Gum, a natural polysaccharide polymer synthesized by microbial fermentation, has excellent rheological properties due to its unique pentasaccharide repeating unit structure (containing glucose, mannose, glucuronic acid, etc.). This main chain composed of alternating β-(1-4) linked glucuronic acid residues and β-(1-4) linked glucose residues, combined with the rhamnose and mannose groups on the side chains, makes it exhibit typical pseudoplastic fluid behavior in aqueous solution.

[0003] Welan gum's molecular structure contains a variety of functional groups, which give it excellent basic properties such as thickening, suspending, and emulsifying. This unique structure enables welan gum to demonstrate excellent thickening stability in the food industry, allowing ice cream to maintain a smooth texture even after three months of storage at -18°C. In oil drilling fluid systems, a 0.3% concentration of welan gum solution can increase the base fluid viscosity to over 80 mPa·s, effectively suspending weighting materials such as barite. In the pharmaceutical field, its excellent biocompatibility and degradability make it an ideal material for applications such as drug carriers. The presence of reactive groups such as hydroxyl and carboxyl groups along its molecular chain provides ideal sites for chemical modification.

[0004] However, as the application scenarios extend to extreme environments, the inherent defects of Welan gum gradually become prominent. In a simulation experiment of ultra-deep wells in the Tarim Oilfield (well depth > 7000m), when the temperature rose to 120°C, the viscosity of the unmodified Welan gum solution dropped sharply from 500mPa·s to below 30mPa·s, which could not meet the rock carrying requirements. In the high-salt formation water environment (total mineralization > 200,000mg / L) of the Bohai Bay Oilfield, its molecular chains curled up due to the salting-out effect, resulting in a loss of 92% in the apparent viscosity of the solution. In a high-salt environment, such as some marine oil and gas production areas or high-mineralization formation water conditions, the functional groups on the unmodified Welan gum molecular chains may interact with the salt ions, causing the molecular chains to curl up, thereby reducing the viscosity of the solution and worsening the thickening effect. This greatly limits the application of Welan gum in these high-salt environments and cannot meet actual engineering needs. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and to provide a heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification, and a preparation method and application thereof.

[0006] In order to achieve the above and other purposes, the present invention is implemented through the following technical solutions:

[0007] The present invention provides a preparation method of a heat-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification, comprising: taking Welan gum as the main body, simultaneously introducing a quaternary ammonium salt group and an alkyl long chain into the Welan gum molecule for double modification, thereby obtaining the heat-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification; wherein the quaternary ammonium salt group is introduced by reacting 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) with a hydroxyl group on the Welan gum molecule, and the alkyl long chain is introduced by reacting 1-bromohexadecane with a hydroxyl group on the Welan gum molecule. In this preparation method, the Welan gum is double-modified by synergistically enhancing the electrostatic repulsion of the cationic group and the hydrophobic association, thereby obtaining a Welan gum that is dynamically salt-resistant, temperature-resistant, and thickening in an extreme salt and temperature environment.

[0008] Furthermore, the method comprises the following steps: step S1, dispersing welan gum powder in dimethyl sulfoxide (DMSO) to obtain a welan gum solution, then adding a sodium hydroxide (NaOH) aqueous solution to the welan gum solution, stirring at 25-35° C. for 1-3 hours to obtain an alkalized welan gum solution; step S2, simultaneously adding 3-chloro-2-hydroxypropyltrimethylammonium chloride and 1-bromohexadecane to the alkalized welan gum solution, stirring and reacting at 60-80° C. for 16-18 hours to obtain a reaction system; this step is set to allow the hydroxyl groups on the welan gum molecules to undergo a quaternization reaction with CHPTAC and an alkylation reaction with 1-bromohexadecane; step S3, after the reaction is completed, wait for the reaction system to cool to room temperature, add ethanol to promote product precipitation, then collect the precipitate by centrifugation, vacuum freeze-dry the precipitate for 12-24 hours, and then grind it to obtain the temperature-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification (hereinafter referred to as double-modified welan gum).

[0009] Furthermore, the amounts of the components are used in the following proportions. Step S1 specifically includes: dispersing 5 g of welan gum powder in 120 mL of DMSO to form the welan gum solution.

[0010] Furthermore, in step S1, the concentration of the sodium hydroxide aqueous solution is 40 wt %, and the amount used is 1 mL.

[0011] Furthermore, in step S2, the amount of 1-bromohexadecane added is 0.05 g, 0.1 g, 0.25 g, 0.5 g, 0.75 g or 1 g.

[0012] Furthermore, in step S3, the amount of ethanol added is such that the ethanol content in the reaction system reaches 50% to 70%; the vacuum freezing method is to use a refrigerated centrifuge with a rotation speed of 8000 rpm and a centrifugation time of 7 minutes.

[0013] The present invention also provides the heat-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification prepared by the above-mentioned preparation method of the heat-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification.

[0014] Furthermore, in the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification, the molar ratio of the quaternary ammonium salt group to the hexadecyl group in the alkyl long chain is 1:(50-1000). The quaternary ammonium salt group delays salt-induced curling by enhancing the electrostatic repulsion of the molecular chain, while the hexadecyl group constructs a three-dimensional dynamic network through association.

[0015] The present invention also provides applications of the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification in the fields of agriculture, food industry, cosmetics industry and building materials.

[0016] The present invention also provides the above-mentioned heat-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification with a total mineralization degree of>1×10 5 mg / L and its application in oil field exploitation with temperature>85℃.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects:

[0018] The present invention provides a heat-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification and its preparation method and application, which is suitable for the total mineralization degree>1×10 5 mg / L and a temperature >85°C for tertiary oil recovery in high-salinity reservoirs, achieving salt-thickening flooding with synergistic cation-hydrophobic enhancement. It can also be used in a variety of fields, including agriculture, the food industry, the cosmetics industry, and building materials. Its preparation method is to first dissolve welan gum powder in a system containing NaOH and DMSO, then add 3-chloro-2-hydroxypropyltrimethylammonium chloride and 1-bromohexadecane, then add ethanol and centrifuge to obtain a reaction solution. Finally, centrifuge and freeze-dry the solid to obtain a modified sample. This technology uses a double modification technology of Welan gum that synergistically enhances the electrostatic repulsion of cationic groups and hydrophobic association. It can be used in oil field exploitation to achieve dynamic salt-resistant and temperature-resistant viscosity increase in extreme salt temperature environments. Compared with the original Welan gum and the separate quaternized ammonium-modified Welan gum, it has higher viscosity. As the salt concentration (sodium chloride, calcium chloride, magnesium chloride) increases, the viscosity can remain stable, making it suitable for tertiary oil recovery in high-salt formations. In agriculture, it can be used as a seed coating agent, soil conditioner, pesticide slow-release carrier and fertilizer synergist; in the food industry, it can be used as a thickener, stabilizer and gelling agent; in the cosmetics industry, it can be used as a moisturizer and rheology regulator; in the field of building materials, it can be used as a cement additive and used in tile adhesives and putty powders. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1The shear rate-viscosity curve of 1% (w / v) Weilan gum solution at 25°C;

[0020] Figure 2 The shear rate-viscosity curve of 1% (w / v) Weilan gum and 0.18% (w / v) polyacrylamide (HPAM) at 85°C;

[0021] Figure 3 The temperature-viscosity curve of 1% (w / v) Weilan gum and 0.18% (w / v) HPAM at 25-85°C;

[0022] Figure 4 1% (w / v) Weilan gum and 0.18% (w / v) HPAM at a shear rate of 100s -1 , NaCl concentration-viscosity curve at a temperature of 85°C;

[0023] Figure 5 1% (w / v) Weilan gum and 0.18% (w / v) HPAM at a shear rate of 100s -1 , CaCl2 concentration-viscosity curve at a temperature of 85℃;

[0024] Figure 6 1% (w / v) Weilan gum and 0.18% (w / v) HPAM at a shear rate of 100s -1 , MgCl2 concentration-viscosity curve at a temperature of 85℃. DETAILED DESCRIPTION

[0025] In response to the technical bottlenecks in the existing technology, researchers have carried out various modification explorations. Conventional carboxymethylation modification can improve salt tolerance, but it will lead to a decrease in temperature resistance; although cationic modification enhances the charge repulsion effect, it lacks stability in a divalent salt environment. The present invention creatively proposes a synergistic modification strategy of quaternization and hydrophobic alkylation. By simultaneously introducing quaternary ammonium salt cationic groups and C16 long-chain alkyl groups on the molecular chain, a "charge barrier-hydrophobic association" dual action mechanism is constructed, aiming to significantly improve the comprehensive performance of Welan gum, meet the needs of different fields for high-performance polymer materials, broaden the application range of Welan gum, and modify Welan gum to improve its performance. It is of great significance. This synergistic effect enables the modified Welan gum to maintain a stable three-dimensional network structure at 85°C, and the viscosity retention rate in 100,000 mg / L NaCl solution is more than 85%, breaking through the performance boundaries of traditional single modification methods.

[0026] In the following specific embodiments, if no specific experimental steps or conditions are specified, the operation or conditions of the conventional experimental steps described in the literature in this field can be carried out. If the manufacturer of the reagents or instruments used is not specified, they are all conventional reagent products that can be obtained commercially. The term "comprising" is intended to be open-ended and can be replaced with "consisting of..." where appropriate. In this article, unless otherwise indicated, percentages refer to weight / weight percentages. Except in the examples, or otherwise clearly stated, all numbers indicating the mass of substances, physical properties, etc. in the specification and claims should be understood to be modified by "about".

[0027] The present invention provides a technology for preparing heat- and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification. Welan gum powder is dissolved in a system containing NaOH and DMSO, and then CHPTAC and 1-bromohexadecane are added. Through a double modification of Welan gum that synergistically enhances the electrostatic repulsion of cationic groups and hydrophobic association, dynamic salt resistance and temperature-resistant viscosity enhancement in extreme salt and temperature environments are achieved. Specifically, Welan gum can be subjected to cationic-hydrophobic synergistic modification by the following method:

[0028] Example 1

[0029] Step S1: raw material preparation;

[0030] Prepare Welan gum powder, CHPTAC, 1-bromohexadecane, NaOH, ethanol, and DMSO.

[0031] Step S2: solution preparation and alkalization;

[0032] 5 g of welan gum powder was dispersed in about 120 mL of DMSO to prepare a welan gum solution of a certain concentration, and then 1 mL of a 40 wt % NaOH aqueous solution was added, and the mixture was stirred at 30° C. for 2 h to alkalize the welan gum solution.

[0033] Step S3: double modification reaction;

[0034] 0.001 g of CHPTAC and 0.05 g of 1-bromohexadecane were added simultaneously to the alkalized welan gum solution, and the mixture was stirred at 60° C. for 16 to 18 hours to cause the hydroxyl groups on the welan gum molecules to undergo quaternization reaction with CHPTAC and alkylation reaction with 1-bromohexadecane.

[0035] Step S4: Collection of modified products;

[0036] After the reaction is completed, the mixture is cooled to room temperature and ethanol is added to promote product precipitation. The amount of ethanol added is such that the ethanol content in the system reaches 50% to 70%. The precipitate is then collected by centrifugation. The collected precipitate is vacuum freeze-dried for 12 to 24 hours and then ground to obtain double-modified welan gum powder.

[0037] Example 2

[0038] Based on Example 1, the only difference from Example 1 is that in step S3, the amount of 1-bromohexadecane added is 0.1 g.

[0039] Example 3

[0040] Based on Example 1, the only difference from Example 1 is that in step S3, the amount of 1-bromohexadecane added is 0.25 g.

[0041] Example 4

[0042] Based on Example 1, the only difference from Example 1 is that in step S3, the amount of 1-bromohexadecane added is 0.5 g.

[0043] Example 5

[0044] Based on Example 1, the only difference from Example 1 is that in step S3, the amount of 1-bromohexadecane added is 0.75 g.

[0045] Example 6

[0046] Based on Example 1, the only difference from Example 1 is that in step S3, the amount of 1-bromohexadecane added is 1 g.

[0047] Comparative Example 1

[0048] 1% (w / v) original Weilan gum

[0049] Comparative Example 2

[0050] 0.18% (w / v) HPAM

[0051] Comparative Example 3

[0052] Based on Example 1, the only difference from Example 1 is that in step S3, the amount of 1-bromohexadecane added is 0 g.

[0053] Evaluation of product performance of Examples 1 to 6 and Comparative Examples 1 to 3:

[0054] (1) Evaluation of the viscosity-increasing properties of modified Weilan gum

[0055] The determination method is as follows: Examples 1 to 6 are stirred at 80°C and dispersed in water to prepare 20 mL of a 1% (w / v) solution. The solution is then measured using a rotational rheometer (Anton Paar MCR 302) at a temperature of 25°C and a shear rate of 0.01-1000 s. -1 The apparent viscosity of Figure 1 .

[0056] In order to more clearly analyze the viscosity of different modified welan gums, the cross equation was used to fit the rheological data. The cross equation (1) was then used to fit the data to obtain the rheological properties. The viscosity data obtained by fitting are shown in Table 1.

[0057]

[0058] Where η α is the apparent viscosity; η0 and η ∞ are the zero shear viscosity and the limiting viscosity at infinite shear rate, respectively; τ is the time constant; γ is the shear rate; and m is a dimensionless constant.

[0059] Table 1. Cross equation fitting of various examples and comparative examples at 25°C and shear rate of 0.01-1000s -1 Parameters obtained from the shear rate-viscosity curve

[0060]

[0061] Analysis: Table 1 shows the viscosity of Comparative Examples 1 to 3 and Examples 1 to 6 at 25°C. From Table 1, it can be seen that the zero shear viscosity (η0) of Comparative Example 1 is 331.48±0.32 mPa.s,

[0062] The data show that the η0 of all example samples is higher than that of Comparative Example 3. Among them, the η0 values of Example 1 and Example 6 reached 3025.26±0.68mPa.s and 2653.02±0.57mPa.s, respectively, which are approximately 3 times and 2.5 times higher than those of Comparative Example 3. This phenomenon shows that the introduction of the hydrophobic group 1-bromohexadecane on the basis of quaternary ammonium modification can further enhance the viscosity-increasing effect. The mechanism is that the long hydrophobic chains form a dynamic physical cross-linked network through intermolecular association, thereby increasing the viscosity of the solution. In contrast, single quaternary ammonium modification mainly relies on charge interactions and lacks the contribution of hydrophobic interactions to the viscosity-enhancing effect.

[0063] Figure 1 The shear rate-viscosity curves of 1% (w / v) original Welan gum, quaternized modified Welan gum and double modified Welan gum solutions at 25°C are shown. Figure 1 As shown, all samples exhibit typical non-Newtonian fluid properties, with apparent viscosity decreasing as the logarithm of shear rate increases, demonstrating shear thinning. This phenomenon is primarily due to the fact that polysaccharide molecules form a relatively stable structure through intermolecular interactions at low shear rates. As the shear rate increases, these intermolecular interactions are disrupted, leading to the disintegration of the polysaccharide structure and a decrease in viscosity.

[0064] Comparing the curve of Comparative Example 3 and Examples 1 to 6, it can be found that the apparent viscosity of Examples 1 to 6 under identical shear rates is significantly higher than that of Comparative Example 3, and shows better stability under high shear rates. This may be because the introduction of 1-bromohexadecane increases the hydrophobic interaction between molecules. This hydrophobic interaction can effectively maintain the expanded state of the molecular chain in solution, making the molecular chain more difficult to shrink when subjected to shearing, thereby maintaining higher viscosity. In addition, the rigidity of the molecular chain may also be increased in the double modification process, further enhancing the stability of the solution. Therefore, Examples 1 to 6 have better shear stability compared to Comparative Example 3.

[0065] (2) Evaluation of heat resistance of modified Weilan gum

[0066] The heat resistance of Examples 1 to 6 was evaluated and compared with Comparative Examples 1 to 3.

[0067] The determination method is as follows: Examples 1 to 6 were stirred at 80°C and dispersed in water to prepare 20 mL of a 1% (w / v) solution. A rotational rheometer (Anton Paar MCR 302) was then used to measure the solution at a temperature of 85°C and a shear rate ranging from 0.01 to 1000 s. -1 The apparent viscosity of Figure 2 ,Depend on Figure 2 It can be seen that Comparative Example 2 has the highest viscosity at low shear rates, but as the increase in shear rate, the viscosity decreases rapidly, and the shear resistance is poor. The viscosity of Comparative Example 1 is relatively stable over the entire shear rate range, but the initial viscosity is the lowest. The viscosity of Comparative Example 3 is slightly higher than Comparative Example 1, and the viscosity of Examples 1 to 6 is significantly higher than Comparative Example 3, and as the increase in shear rate, the viscosity decreases less, and the shear stability is better. This shows that the introduction of 1-bromohexadecane enhances the rigidity and temperature resistance of the molecular chain.

[0068] The rheological properties were obtained by fitting the data using the cross equation (1). The viscosity data obtained by fitting are shown in Table 2.

[0069] Table 2. Cross equation fitting of various examples and comparative examples at 85°C and shear rate of 0.01-1000s -1 Parameters obtained from the shear rate-viscosity curve

[0070]

[0071] Table 2 shows the viscosity of Comparative Examples 1 to 3 and Examples 1 to 6 at 85°C. The data show that the η0 values of Examples 1 to 6 are all higher than those of Comparative Example 3. Among them, the η0 values of Example 1 and Example 6 reached 513.84±3.15mPa.s and 423.71±0.93mPa.s, respectively, which are about 5 times and 4.5 times higher than those of Comparative Example 3 (77.79±0.37mPa.s). This is because the introduction of 1-bromohexadecane enhances the rigidity and hydrophobic association of the molecular chain. The above data show that the double modification can further improve the heat resistance of Weilan gum compared to the single quaternization modification, but there is still a significant gap compared to HPAM.

[0072] After studying the viscosity of each sample at 85°C, the effect of temperature on solution viscosity was further investigated. Figure 3 1% (w / v) Weilan gum and 0.18% (w / v) HPAM at a shear rate of 7.34s -1 , temperature-viscosity curve at temperature 25~85℃. Figure 3 It is shown that as the temperature rises, the viscosity of the three solutions of Comparative Example 1, Comparative Example 3 and Examples 1 to 6 all show a downward trend. This is mainly due to the inherent characteristics of Welan gum and its modified products as polysaccharide polymers: the increase in temperature leads to the intensification of the thermal motion of the molecular chains, the weakening of the interactions such as intermolecular hydrogen bonds, and the transformation of the polymer chains from a curled conformation to a stretched conformation, thereby reducing the apparent viscosity of the solution. For the double-modified products of Examples 1 to 6, their viscosity values at each temperature point are higher than that of the solution of Comparative Example 3, and as the temperature rises, the decrease in the viscosity of Examples 1 to 6 is smaller than that of Comparative Example 3. This phenomenon can be attributed to the dual synergistic mechanism brought about by the long hexadecyl chain: on the one hand, the hydrophobic association can still maintain partial intermolecular association at high temperature to form a dynamic physical cross-linking network; on the other hand, the introduction of rigid hydrophobic groups limits the conformational freedom of the molecular chains and improves the thermal stability of the polymer chains.

[0073] exist Figure 3 The temperature resistance of Examples 1 to 6 is also compared with that of HPAM (Comparative Example 2), a commonly used oil-displacing agent in industry. At 25°C, the initial viscosity of Examples 1 to 6 is about 1.5 to 2.8 times that of Comparative Example 2. However, in the range of 25 to 35°C, as the temperature increases, the viscosity of the solution of Comparative Example 2 increases slightly, which may be related to the conformational transition of its molecular chain at the critical temperature. When the temperature exceeds 35°C, the viscosity of the solution of Comparative Example 2 tends to stabilize, while the viscosity of Examples 1 to 6 continues to decrease. At 85°C, the viscosity of Comparative Example 2 is about 20% higher than its initial viscosity, which is higher than the residual viscosity of Examples 1 to 6, indicating that the temperature resistance of the double-modified polysaccharide is still somewhat lower than that of Comparative Example 2.

[0074] (3) Evaluation of salt resistance of modified Weilan gum

[0075] The viscosity of Examples 1 to 6 and Comparative Examples 1 to 3 at different concentrations of NaCl, CaCl2 and MgCl2 was measured (the shear rate was constant at 100s -1 , the temperature is constant at 85℃), the results are shown in Figure 4 、 Figure 5 and Figure 6 .

[0076] like Figures 4 to 6 As shown in Figure 2, with the increase of the concentration of chlorinated inorganic salts, the viscosity of the solutions of Comparative Example 1 and Comparative Example 2 showed a continuous downward trend. This phenomenon is mainly attributed to the charge shielding effect in the solution. In addition, divalent cations (Ca 2+ and Mg 2 + ) exhibits a more significant viscosity-reducing effect than monovalent cations. This is because divalent ions carry a larger charge and their stronger charge shielding ability leads to a greater weakening of the electrostatic repulsion of polymer molecular chains, thereby exacerbating the reduction in solution viscosity.

[0077] Results from studies of different chlorinated inorganic salt systems show that, compared to the solutions in Comparative Examples 1 and 2, Comparative Example 3 and Examples 1 to 6 exhibit superior salt tolerance. Both exhibit a significant salt-thickening effect with increasing NaCl concentration, and maintain good viscosity stability in both MgCl2 and CaCl2 systems. Furthermore, the dual-modified solutions of Examples 1 to 6 exhibit superior salt tolerance compared to the single-modified Comparative Example 3. When the NaCl addition level is 100,000 mg / L, the viscosity of the solutions of Examples 1 to 6 is approximately 2 to 7 times that of Comparative Example 3; when the MgCl2 addition level is 10,000 mg / L, the viscosity of the solutions of Examples 1 to 6 is approximately 1.6 to 5 times that of Comparative Example 3; and when the CaCl2 addition level is 5,000 mg / L, the viscosity of the solutions of Examples 1 to 6 is approximately 1.4 to 4 times that of Comparative Example 3. This can be attributed to the following factors: First, while Comparative Example 3 increases its charge density and improves salt tolerance through the introduction of quaternary ammonium groups, the dual-modified solutions of Examples 1 to 6 further integrate the hydrophobic association effect. The long-chain alkyl group introduced by 1-bromohexadecane is hydrophobic and forms a layered structure around the polysaccharide molecules. This structure can reduce direct contact between salt ions and polysaccharide molecules, reducing the shielding effect of salt ions on charge repulsion, allowing the polysaccharide molecules to maintain a relatively good dispersion state at higher salt concentrations. At the same time, as a long-chain hydrophobic alkyl group, 1-bromohexadecane produces hydrophobic interactions in salt solutions that can, to a certain extent, resist the effects of salt ions on polysaccharides, allowing the polysaccharides to maintain a certain molecular conformation and stability through hydrophobic interactions. Secondly, the long-chain alkyl group of 1-bromohexadecane has a large steric hindrance effect, which can prevent the polysaccharide molecular chains from approaching and aggregating with each other, allowing the polysaccharide molecules to maintain their molecular form and dispersion state in high-salt solutions, thereby maintaining the viscosity stability of the polysaccharide solution under high temperature and high salt conditions.

[0078] In summary: Double modification of Welan gum has the following advantages:

[0079] Charge repulsion and hydrophobic association work synergistically. The quaternary ammonium salt group maintains the extension of the molecular chain through electrostatic repulsion, and the hexadecyl long chain forms a dynamic cross-linked network through hydrophobic interaction. The two work together to improve the solution viscosity and salt resistance stability.

[0080] The modified wellan gum exhibits excellent viscosity-enhancing properties. Compared to the original wellan gum, the double-modified wellan gum increases viscosity by approximately 175% to 812%. Compared to quaternization alone, the double-modified wellan gum increases viscosity by approximately 64% to 302%.

[0081] The double-modified welan gum exhibits improved heat resistance. Compared to pristine welan gum, the double-modified welan gum's temperature tolerance increases by approximately 200% to 704%. Compared to quaternization alone, the double-modified welan gum's temperature tolerance increases by approximately 146% to 560%.

[0082] Salt tolerance is significantly enhanced after double modification. Regarding NaCl tolerance, the original Welan gum's viscosity decreases by 85% at a NaCl concentration of 100,000 mg / L; the double-modified Welan gum's viscosity increases by 128% to 145% at this concentration, representing a 280% increase in tolerance compared to the original Welan gum and a 166% increase compared to the quaternization alone. Regarding CaCl2 tolerance, the original Welan gum's viscosity decreases by 90% at a CaCl2 concentration of 5,000 mg / L; the double-modified Welan gum's viscosity increases by 5% to 18% at this concentration, representing a 200% increase in tolerance compared to the original Welan gum and a 50% increase compared to the quaternization alone. Regarding MgCl2 tolerance, the original Welan gum's viscosity decreases by 95% at a MgCl2 concentration of 10,000 mg / L; the double-modified Welan gum's viscosity increases by 3% to 6% at this concentration, representing a 100% increase in tolerance compared to the original Welan gum and a 20% increase compared to the quaternization alone.

[0083] Application value:

[0084] This invention, through cationic-hydrophobic synergistic modification, achieves breakthrough improvements in the viscosity-increasing, temperature-resistance, and salt-resistance properties of welan gum. In high-temperature (85°C) and high-salt (100,000 mg / L NaCl) reservoirs, the salt-thickening effect and shear resistance of the double-modified welan gum significantly outperform those of the traditional oil displacement agent HPAM, thereby improving oil recovery. This provides technical support for its application in extreme environments and has significant economic and social benefits.

Claims

1. A method for preparing a heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification, characterized in that: include: With Welan gum as the main component, quaternary ammonium salt groups and alkyl long chains are simultaneously introduced into the Welan gum molecules for double modification, thereby obtaining the heat-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification; The quaternary ammonium salt group is introduced by reacting 3-chloro-2-hydroxypropyltrimethylammonium chloride with the hydroxyl group on the welan gum molecule, and the alkyl long chain is introduced by reacting 1-bromohexadecane with the hydroxyl group on the welan gum molecule.

2. The method for preparing the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification according to claim 1, wherein The steps include: Step S1, dispersing welan gum powder in dimethyl sulfoxide to obtain a welan gum solution, then adding a sodium hydroxide aqueous solution to the welan gum solution, stirring at 25-35° C. for 1-3 hours, to obtain an alkalized welan gum solution; Step S2, adding 3-chloro-2-hydroxypropyltrimethylammonium chloride and 1-bromohexadecane to the alkalized welan gum solution simultaneously, stirring and reacting at 60-80° C. for 16-18 hours to obtain a reaction system; Step S3: After the reaction is completed, wait for the reaction system to cool to room temperature, add ethanol to promote product precipitation, then collect the precipitate by centrifugation, vacuum freeze-dry the precipitate for 12 to 24 hours, and then grind it to obtain the temperature-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification.

3. The preparation method of the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification according to claim 2, characterized in that, The amounts of the components are used in the following proportions. Step S1 specifically includes: dispersing 5 g of welan gum powder in 120 mL of DMSO to form the welan gum solution.

4. The method for preparing the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification according to claim 3, wherein In step S1, the concentration of the sodium hydroxide aqueous solution is 40 wt %, and the amount used is 1 mL.

5. The method for preparing the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification according to claim 4, wherein In step S2, the amount of 1-bromohexadecane added is 0.05 g, 0.1 g, 0.25 g, 0.5 g, 0.75 g or 1 g.

6. The method for preparing the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification according to claim 5, characterized in that: In step S3, the amount of ethanol added is such that the ethanol content in the reaction system reaches 50% to 70%; the vacuum freezing method is to use a refrigerated centrifuge with a rotation speed of 8000 rpm and a centrifugation time of 7 minutes.

7. The heat-resistant and salt-resistant Welan gum based on cation-hydrophobic synergistic modification obtained by the method for preparing the heat-resistant and salt-resistant Welan gum based on cation-hydrophobic synergistic modification according to any one of claims 1 to 6.

8. The heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification according to claim 7, characterized in that: In the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification, the molar ratio of the quaternary ammonium salt group to the hexadecyl group in the alkyl long chain is 1:(50-1000).

9. Application of the heat-resistant and salt-resistant welan gum based on cationic-hydrophobic synergistic modification as claimed in claim 7 in the fields of agriculture, food industry, cosmetics industry and building materials.

10. The heat-resistant and salt-resistant Welan gum based on cationic-hydrophobic synergistic modification according to claim 7 has a total mineralization degree of >1×10 5 mg / L and its application in oil field exploitation with temperature>85℃.

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