Calcium oxide microcapsule as well as preparation method and application thereof

Abstract

The invention provides a calcium oxide microcapsule as well as a preparation method and application thereof. The calcium oxide microcapsule is obtained by sequentially wrapping the surface of a modified calcium oxide core with multi-aldehyde cellulose and chitosan, and the multi-aldehyde cellulose and the chitosan are respectively wrapped at least once and are mutually wrapped at intervals. The obtained calcium oxide microcapsule can obviously delay the heat release process of calcium oxide, and the preparation condition is mild.

Description

Technical Field

[0001] The invention belongs to the technical field of natural gas hydrate exploitation, and specifically relates to a calcium oxide microcapsule and a preparation method and application thereof. Background Art

[0002] Existing research on delaying the heat release rate of calcium oxide is mainly achieved by surface modification of calcium oxide. The hydration reaction of octadecyltrichlorosilane-modified calcium oxide is inhibited to a certain extent, and the time to reach the exothermic peak is extended from 25 minutes to 75 minutes. Patent CN105642360A discloses a method for preparing surface-modified nano calcium oxide, using a mixed solution of silane coupling agent KH570 and n-butyl bromide as a modifier. The prepared surface-modified calcium oxide with an average particle size of 30-50nm is mainly used as a catalyst in the preparation process of biodiesel. CN104893362B discloses a method for preparing surface hydrophobic modified calcium oxide for curing and stabilization treatment technology of soil contaminated by toxic organic matter. In an organic solvent ethanol, silane coupling agent KH570 and calcium oxide are stirred and modified in a ratio of 0.02ml / g to obtain a finished hydrophobic modified calcium oxide. Existing research on reducing the hydration reaction rate of calcium oxide uses surface modification methods, but the effect of surface modification in delaying the peak exothermicity of calcium oxide is difficult to meet the needs of hydrate pilot production projects, and research on the effect of modification on the exothermic performance of calcium oxide has not yet been carried out.

[0003] CN104840484A discloses a method for preparing calcium peroxide microcapsules, wherein calcium peroxide is dispersed in a dichloromethane solution of ethyl cellulose or polylactic acid, and a poor solvent petroleum ether is added to the reaction system to precipitate the polymer material on the surface of the calcium peroxide shell material, forming a continuous coating and solidifying. However, this method has not yet been applied to the preparation of calcium oxide microcapsules, and the delaying effect on the calcium oxide hydration reaction needs to be studied. Summary of the invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a calcium oxide microcapsule and a preparation method and application thereof. The calcium oxide microcapsule can significantly delay the heat release process of calcium oxide and the preparation conditions are mild.

[0005] In order to achieve the above object, the present invention provides a calcium oxide microcapsule, which is obtained by sequentially wrapping polyaldehyde cellulose and chitosan on the surface of a modified calcium oxide core, wherein the polyaldehyde cellulose and chitosan are respectively wrapped at least once and are wrapped at intervals from each other.

[0006] According to a specific embodiment of the present invention, preferably, the modified calcium oxide core is prepared by modifying calcium oxide with a silane coupling agent; and the polyaldehyde cellulose is prepared by reacting cellulose with sodium periodate.

[0007] According to a specific embodiment of the present invention, preferably, the particle size of the calcium oxide microcapsules is 2.99-91 μm, and the particle size of the modified calcium oxide core is 2.74-80 μm.

[0008] The present invention also provides a method for preparing the above calcium oxide microcapsules, which comprises the following steps:

[0009] (1) Preparation of polyaldehyde cellulose:

[0010] The cellulose aqueous solution is mixed with sodium periodate, and after the reaction is carried out in the dark, the reaction is terminated and a precipitate is precipitated to obtain the polyaldehyde cellulose;

[0011] (2) Preparation of modified calcium oxide core:

[0012] Dispersing calcium oxide in an alcohol solution of a silane coupling agent and stirring to obtain the modified calcium oxide core;

[0013] (3) Preparation of calcium oxide microcapsules:

[0014] The modified calcium oxide core is added to the alcohol dispersion of the polyaldehyde cellulose, stirred, centrifuged and dried to obtain a single-layer wrapped calcium oxide microcapsule, and then the single-layer wrapped calcium oxide microcapsule is added to the alcohol dispersion of chitosan, stirred, centrifuged and dried to obtain a double-layer wrapped calcium oxide microcapsule, and the above-mentioned wrapping operation is repeated to obtain the calcium oxide microcapsule wrapped with the target number of layers.

[0015] According to a specific embodiment of the present invention, preferably, in step (1), the concentration of the cellulose aqueous solution is 0.1-0.5 g / mL.

[0016] According to a specific embodiment of the present invention, preferably, in step (1), the molar ratio of the sodium periodate to the structural unit of the cellulose is 0.2-0.4:1.

[0017] According to a specific embodiment of the present invention, preferably, in step (1), the light-proof reaction condition is: stirring the reaction at room temperature for 4-10 hours under light-proof conditions.

[0018] According to a specific embodiment of the present invention, preferably, in step (1), after the reaction is carried out in the dark, ethylene glycol is added to terminate the reaction.

[0019] According to a specific embodiment of the present invention, preferably, in step (1), the precipitation conditions are: adding anhydrous ethanol in a volume ratio of 5-10:1 to the reaction solution.

[0020] According to a specific embodiment of the present invention, preferably, in step (1), after the precipitate is separated out, it is dried at 40-60° C. for 24-48 hours.

[0021] According to a specific embodiment of the present invention, preferably, in step (2), the silane coupling agent is 3-aminopropyltrimethoxysilane.

[0022] According to a specific embodiment of the present invention, preferably, in step (2), the alcohol solution of the silane coupling agent is a mixed solution of 3-aminopropyltrimethoxysilane and anhydrous ethanol in a volume ratio of 1:50-100.

[0023] According to a specific embodiment of the present invention, preferably, in step (2), the mass ratio of calcium oxide to silane coupling agent is 20:1.

[0024] According to a specific embodiment of the present invention, preferably, in step (2), the stirring temperature is 10-30° C., the stirring rate is 200-300 rpm, and the stirring time is 10-60 min.

[0025] According to a specific embodiment of the present invention, preferably, in step (2), centrifugation and drying are performed after stirring, and the drying conditions are drying at 70-80° C. for 0.5-2 h.

[0026] According to a specific embodiment of the present invention, preferably, in step (3), the concentrations of the alcohol dispersion of polyaldehyde cellulose and the alcohol dispersion of chitosan are both 2-6 mg / mL.

[0027] According to a specific embodiment of the present invention, preferably, in step (3), the mass ratio of the modified calcium oxide core to the single-wrapped polyaldehyde cellulose is 20-80:1, more preferably 50:1.

[0028] According to a specific embodiment of the present invention, preferably, in step (3), the mass ratio of the modified calcium oxide core to the single-wrapped chitosan is 20-80:1, more preferably 50:1.

[0029] According to a specific embodiment of the present invention, preferably, in step (3), the stirring temperature is room temperature, the stirring time is 10-20 min, and the stirring rate is 100-300 r / min, more preferably 200 r / min.

[0030] According to a specific embodiment of the present invention, preferably, in step (3), the drying temperature is 70-90° C., and the drying time is 5-30 minutes.

[0031] According to a specific embodiment of the present invention, the above preparation method comprises the following specific steps:

[0032] (1) Preparation of polyaldehyde cellulose:

[0033] Disperse an appropriate amount of cellulose in distilled water, add sodium periodate to start the reaction; after magnetic stirring at room temperature under light-proof conditions for a certain period of time, add an appropriate amount of ethylene glycol and stir for half an hour to terminate the oxidation reaction; add excess anhydrous ethanol to the reaction solution to precipitate, put it in an electric heating blast drying oven at a certain temperature and fully vacuum dry it to obtain polyaldehyde cellulose powder;

[0034] (2) Preparation of modified calcium oxide core:

[0035] 3-aminopropyltrimethoxysilane is mixed with anhydrous ethanol to obtain a silane coupling agent solution; a certain amount of calcium oxide is fully dispersed in the silane coupling agent solution and stirred for a certain period of time, and then the dispersion is centrifuged at 8000 rpm and placed in an electric heating blast drying oven for full vacuum drying to obtain a surface-modified calcium oxide core;

[0036] (3) Preparation of calcium oxide microcapsules:

[0037] Chitosan and polyaldehyde cellulose are stirred in anhydrous ethanol to prepare dispersions, modified calcium oxide cores are added to the polyaldehyde cellulose dispersions and stirred with magnetic force for a certain period of time, the resulting solution is centrifuged at 8000 rpm, and the collected products are fully dried at a suitable temperature to obtain a layer of calcium oxide microcapsules; thereafter, the obtained products are mixed and stirred in the chitosan dispersion for a certain period of time, the obtained solution is centrifuged, and the collected products are placed in a vacuum drying oven for full vacuum drying to obtain two layers of calcium oxide microcapsules. The same procedure is repeated until the target number of layers is reached.

[0038] The present invention also provides application of the calcium oxide microcapsules in natural gas hydrate exploitation.

[0039] The present invention also provides a method for calculating the decomposition amount of natural gas hydrates produced by using the above calcium oxide microcapsules, which is calculated by the following formula:

[0040] n=Q / ΔH, where n is the amount of hydrate decomposition during calcium oxide heating, mol; Q is the heat release value of calcium oxide microcapsules, m; ΔH is the dissociation heat of natural gas hydrate, KJ / mol.

[0041] The present invention has the following beneficial effects:

[0042] (1) To address the problem of too fast heat release rate in the reaction between calcium oxide and water, a preparation method for calcium oxide microcapsules was proposed by combining surface modification and covalent layer-by-layer self-assembly method. The method can adjust the time of calcium oxide heat release peak by different numbers of encapsulation layers, reduce the heat loss of calcium oxide in the wellbore during injection, and control the hydrate decomposition rate under the influence of calcium oxide microcapsules;

[0043] (2) Modifying calcium oxide with the hydrolysis product of aminosilane coupling agent increases the surface hydrophobicity and provides amino functional group reaction sites for the subsequent covalent self-assembly coating process, thereby improving the encapsulation efficiency of the layer-by-layer self-assembly process, significantly reducing the contact rate between calcium oxide and water, and delaying the process of calcium oxide exothermicity caused by external water intrusion;

[0044] (3) Polyaldehyde cellulose was prepared by sodium periodate oxidation method, chitosan and polyaldehyde cellulose were selected as layer-by-layer self-assembly encapsulation materials, and the Schiff base reaction between the aldehyde group on polyaldehyde cellulose and the amino group on 3-aminopropyltrimethoxysilane and the amino group in chitosan was used to achieve the connection and encapsulation between the modified calcium oxide core and the shell, thus preparing a polysaccharide self-assembled membrane with stable structure and tight and orderly arrangement;

[0045] (4) The calcium oxide microcapsules proposed in the present invention have mild reaction conditions, a wide range of raw material sources, low cost, and can significantly delay the exothermic process of calcium oxide. They have the prospect of large-scale industrial production and are of great significance for the exploitation of natural gas hydrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the cumulative particle size distribution diagram of the samples obtained in Example 1, Comparative Example 6 and Comparative Example 1;

[0047] Figure 2 The exothermic curves of modified calcium oxide prepared with different amounts of coupling agent;

[0048] Figure 3 This is a cumulative particle size distribution diagram of the samples obtained in Example 1, Comparative Example 6 and Comparative Example 1 after the simulated seawater test;

[0049] Figure 4 The exothermic curves of the products obtained in Example 1, Comparative Example 6 and Comparative Example 1;

[0050] Figure 5 This is the prediction curve of methane release from the decomposition of natural gas hydrate under the action of calcium oxide and calcium oxide microcapsules. DETAILED DESCRIPTION

[0051] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0052] Example 1

[0053] This embodiment provides a calcium oxide microcapsule, which is prepared by the following steps:

[0054] (1) Preparation of polyaldehyde cellulose:

[0055] Disperse 10 g of cellulose in 100 ml of distilled water, add sodium periodate to start the reaction, adjust the pH to 4, heat in a constant temperature water bath, the heating temperature is 40°C, and the unit molar ratio of sodium periodate to cellulose is 1:5; after magnetic stirring at room temperature in the dark for 6 hours, add 3.5 mL of ethylene glycol and stir for 30 minutes to terminate the oxidation reaction; add 5 times the volume of anhydrous ethanol to the reaction solution to precipitate, and place it in an electric heating blast drying oven at 40°C for vacuum drying for 48 hours to obtain polyaldehyde cellulose powder;

[0056] (2) Preparation of modified calcium oxide core:

[0057] 1 ml of 3-aminopropyltrimethoxysilane was mixed with 100 ml of anhydrous ethanol to obtain a silane coupling agent solution, the mass ratio of calcium oxide to the silane coupling agent was maintained at 20:1, 20 g of calcium oxide was fully dispersed in the silane coupling agent solution and stirred for 40 minutes at a stirring rate of 200 rpm, and then the dispersion was centrifuged at 8000 rpm for 10 minutes, and placed in an electric heating blast drying oven at 70° C. for vacuum drying for one hour to obtain a surface-modified calcium oxide core having a particle size of 2.74-80 μm, the same below;

[0058] (3) Preparation of calcium oxide microcapsules:

[0059] Chitosan and polyaldehyde cellulose are separately prepared into dispersions in 100 ml of anhydrous ethanol (the concentration of chitosan solution is 0.1wt%, and the concentration of polyaldehyde cellulose solution is 5wt%), and the mass ratio of modified calcium oxide core to polyaldehyde cellulose / chitosan is 50:1 (the ratio of a single package); firstly, the modified calcium oxide core is added to the polyaldehyde cellulose dispersion, and magnetic stirring is performed for 20 minutes at a stirring rate of 200rpm, and ultrasonic dispersion is performed for 10 minutes. The obtained solution is centrifuged at 8000rpm for 10 minutes, and filtered and washed for multiple times. The collected product is dried at 70°C for 30 minutes to obtain a layer of wrapped calcium oxide microcapsules; then, it is mixed and stirred in the chitosan dispersion for 20 minutes at a stirring rate of 200rpm. The rate is 200rpm, and ultrasonic dispersion is performed for 10 minutes. The resulting solution is centrifuged at 8000rpm for 30 minutes, filtered and washed multiple times, and the collected product is placed in a vacuum drying oven at 70°C and vacuum dried for 30 minutes to obtain two-layer wrapped calcium oxide microcapsules; the obtained two-layer wrapped calcium oxide microcapsule product is added to a polyaldehyde cellulose dispersion (the concentration and volume of the dispersion during wrapping are the same as those during the first wrapping, the same below), and magnetic stirring is performed for 20 minutes at a stirring rate of 200rpm. The resulting solution is centrifuged at 8000rpm for 10 minutes, and the collected product is dried at 70°C for 30 minutes to obtain three-layer wrapped calcium oxide microcapsules, recorded as mCaO3x, and dried at 70°C before use.

[0060] Example 2

[0061] This embodiment provides a calcium oxide microcapsule, which is prepared by the following steps:

[0062] (1) Preparation of polyaldehyde cellulose:

[0063] Disperse 10g of cellulose in 100ml of distilled water, add sodium periodate to start the reaction, adjust the pH to 4, heat in a constant temperature water bath, the heating temperature is 40°C, and the unit molar ratio of sodium periodate to cellulose is 1:5; after magnetic stirring at room temperature in the dark for 6 hours, add 3.5ml of ethylene glycol and stir for 30 minutes to terminate the oxidation reaction; add 5 times the volume of anhydrous ethanol to the reaction solution, precipitate, and place in an electric heating blast drying oven at 40°C for vacuum drying for 48 hours to obtain polyaldehyde cellulose powder;

[0064] (2) Preparation of modified calcium oxide core:

[0065] 1 ml of 3-aminopropyltrimethoxysilane was mixed with 100 ml of anhydrous ethanol to obtain a silane coupling agent solution, the mass ratio of calcium oxide to the silane coupling agent was maintained at 20:1, 20 g of calcium oxide was fully dispersed in the silane coupling agent solution and stirred for 40 minutes at a stirring rate of 200 rpm, and then the dispersion was centrifuged at 8000 rpm for 10 minutes and placed in an electric heating blast drying oven at 70° C. for vacuum drying for one hour to obtain a surface-modified calcium oxide core;

[0066] (3) Preparation of calcium oxide microcapsules:

[0067] Chitosan and polyaldehyde cellulose were prepared into dispersions in 100 ml of anhydrous ethanol (chitosan solution concentration was 0.1 wt %, polyaldehyde cellulose solution concentration was 5 wt %), and the mass ratio of modified calcium oxide core to polyaldehyde cellulose / chitosan was 50:1; firstly, the modified calcium oxide core was added to the polyaldehyde cellulose dispersion, stirred magnetically for 20 minutes at a stirring rate of 200 rpm, and dispersed by ultrasonic for 10 minutes. The resulting solution was centrifuged at 8000 rpm for 10 minutes and filtered multiple times. Wash, and dry the collected product at 70°C for 30 minutes to obtain a layer of wrapped calcium oxide microcapsules; then, mix and stir it in a chitosan dispersion for 20 minutes at a stirring rate of 200r / min, and disperse it by ultrasonic wave for 10 minutes. The obtained solution is centrifuged at 8000rpm for 30 minutes, filtered and washed several times, and the collected product is placed in a vacuum drying oven at 70°C and vacuum dried for 30 minutes to obtain two layers of wrapped calcium oxide microcapsules, recorded as mCaO2x, and dried at 70°C before use.

[0068] Example 3

[0069] This embodiment provides a calcium oxide microcapsule, which is prepared by the following steps:

[0070] (1) Preparation of polyaldehyde cellulose:

[0071] Disperse 10g of cellulose in 100ml of distilled water, add sodium periodate to start the reaction, adjust the pH to acidic, heat in a constant temperature water bath, the heating temperature is 40°C, and the unit molar ratio of sodium periodate to cellulose is 1:5; after magnetic stirring at room temperature in the dark for 6 hours, add 3.5ml of ethylene glycol and stir for 30 minutes to terminate the oxidation reaction; add 5 times the volume of anhydrous ethanol to the reaction solution, precipitate, and place in an electric heating blast drying oven at 40°C for vacuum drying for 48 hours to obtain polyaldehyde cellulose powder;

[0072] (2) Preparation of modified calcium oxide core:

[0073] 1 ml of 3-aminopropyltrimethoxysilane was mixed with 100 ml of anhydrous ethanol to obtain a silane coupling agent solution, the mass ratio of calcium oxide to the silane coupling agent was maintained at 20:1, 20 g of calcium oxide was fully dispersed in the silane coupling agent solution and stirred for 40 minutes at a stirring rate of 200 rpm, and then the dispersion was centrifuged at 8000 rpm for 10 minutes and vacuum dried at 70° C. for one hour to obtain a surface-modified calcium oxide core;

[0074] (3) Preparation of calcium oxide microcapsules:

[0075] Chitosan and polyaldehyde cellulose are prepared into dispersions in 100 ml of anhydrous ethanol (the concentration of chitosan solution is 0.1 wt %, and the concentration of polyaldehyde cellulose solution is 5 wt %), and the mass ratio of modified calcium oxide core to polyaldehyde cellulose / chitosan is 50:1 (the ratio of single encapsulation); firstly, the modified calcium oxide core is added to the polyaldehyde cellulose dispersion, and stirred with a magnetic force for 20 minutes at a stirring rate of 200 rpm, and ultrasonically dispersed for 10 minutes. The obtained solution is centrifuged at 8000 rpm for 10 minutes, filtered and washed for multiple times, and the collected product is dried at 70° C. for 30 minutes to obtain a layer of encapsulated calcium oxide microcapsules; then, it is dispersed in chitosan dispersion The mixture was mixed and stirred in the liquid for 20 minutes at a stirring rate of 200r / min, ultrasonically dispersed for 10 minutes, the obtained solution was centrifuged at 8000rpm for 30 minutes, filtered and washed multiple times, and the collected product was placed in a vacuum drying oven at 70°C for vacuum drying for 30 minutes to obtain two-layer wrapped calcium oxide microcapsules; the obtained two-layer wrapped calcium oxide microcapsule product was added to the polyaldehyde cellulose dispersion liquid and stirred with magnetic force for 20 minutes at a stirring rate of 200rpm, ultrasonically dispersed for 10 minutes, the obtained solution was centrifuged at 8000rpm for 10 minutes, filtered and washed multiple times, and the collected product was dried at 70°C for 30 minutes to obtain three-layer wrapped calcium oxide microcapsules. After that, it was mixed and stirred in the chitosan dispersion liquid for 20 minutes at a stirring rate of 200rpm, ultrasonically dispersed for 10 minutes, the obtained solution was centrifuged at 8000rpm for 30 minutes, and the collected product was placed in a vacuum drying oven at 70°C for vacuum drying for 30 minutes to obtain four-layer wrapped calcium oxide microcapsules. The obtained four-layer wrapped calcium oxide microcapsule product was added to a polyaldehyde cellulose dispersion and stirred magnetically for 20 minutes at a stirring rate of 200 rpm. The obtained solution was centrifuged at 8000 rpm for 10 minutes. The collected product was dried at 70°C for 30 minutes to obtain five-layer wrapped calcium oxide microcapsules, recorded as mCaO5x, which were dried at 70°C before use.

[0076] Comparative Example 1

[0077] This comparative example provides an untreated calcium oxide material, which is a product provided by Aladdin Company and is denoted as CaO.

[0078] Comparative Example 2

[0079] This comparative example provides a modified calcium oxide core, which is prepared by the following steps:

[0080] The modified calcium oxide core was prepared in the same manner as in Example 1, except that no polysaccharide material was used for coating, and was recorded as mCaO (mCaO1.0).

[0081] Comparative Example 3

[0082] This comparative example provides a modified calcium oxide core, which is prepared by the same method as comparative example 2, except that the mass ratio of calcium oxide to silane coupling agent is maintained at 20:0.5, denoted as mCaO0.5.

[0083] Comparative Example 4

[0084] This comparative example provides a modified calcium oxide core, which is prepared by the same method as comparative example 2, except that the mass ratio of calcium oxide to silane coupling agent is maintained at 20:1.5, denoted as mCaO1.5.

[0085] Comparative Example 5

[0086] This comparative example provides a modified calcium oxide core, which is prepared by the same method as comparative example 2, except that the mass ratio of calcium oxide to silane coupling agent is maintained at 20:2.0, denoted as mCaO2.0.

[0087] Comparative Example 6

[0088] This comparative example provides a calcium oxide microcapsule, which is prepared by the following steps:

[0089] (1) Preparation of polyaldehyde cellulose:

[0090] Disperse 10g of cellulose in 100ml of distilled water, add sodium periodate to start the reaction, adjust the pH to 4, heat in a constant temperature water bath, the heating temperature is 40°C, and the unit molar ratio of sodium periodate to cellulose is 1:5; after magnetic stirring at room temperature in the dark for 6 hours, add 3.5ml of ethylene glycol and stir for 30 minutes to terminate the oxidation reaction; add 5 times the volume of anhydrous ethanol to the reaction solution, precipitate, and place in an electric heating blast drying oven at 40°C for vacuum drying for 48 hours to obtain polyaldehyde cellulose powder;

[0091] (2) Preparation of modified calcium oxide core:

[0092] 1 ml of 3-aminopropyltrimethoxysilane was mixed with 100 ml of anhydrous ethanol to obtain a silane coupling agent solution, the mass ratio of calcium oxide to the silane coupling agent was maintained at 20:1, 20 g of calcium oxide was fully dispersed in the silane coupling agent solution and stirred for 40 minutes at a stirring rate of 200 rpm, and then the dispersion was centrifuged at 8000 rpm for 10 minutes and placed in an electric heating blast drying oven at 70° C. for vacuum drying for one hour to obtain a surface-modified calcium oxide core;

[0093] (3) Preparation of calcium oxide microcapsules:

[0094] Polyaldehyde cellulose is prepared into a dispersion in 100 ml of anhydrous ethanol (the concentration of the polyaldehyde cellulose solution is 5wt%), and the mass ratio of the modified calcium oxide core to the polyaldehyde cellulose is 50:1; first, the modified calcium oxide core is added to the polyaldehyde cellulose dispersion and stirred magnetically for 20 minutes at a stirring rate of 200rpm. The resulting solution is centrifuged at 8000rpm for 10 minutes. The collected product is dried at 70°C for 30 minutes to obtain a layer of wrapped calcium oxide microcapsules, recorded as mCaO1x, which are dried at 70°C before use.

[0095] Test Example 1

[0096] The particle size distribution curves of the products obtained in Example 1, Comparative Example 6 and Comparative Example 1 were tested in anhydrous ethanol by Malvern Mastersizer 3000. The results are as follows: Figure 1 Compared with calcium oxide, the overall particle size of calcium oxide microcapsules increased significantly. When the cumulative volume coefficient was 50%, the particle size of the microcapsules changed slightly, and the particle size of the particles with a cumulative volume coefficient of 90% increased from 56.2μm to 91μm. The above results show that the covalent layer-by-layer self-assembly method can effectively cover calcium oxide particles.

[0097] Test Example 2

[0098] In this experiment, modified calcium oxide prepared from 0.5g to 2.0g of coupling agent was prepared according to a gradient of 0.5g, and the exothermic performance of Comparative Examples 2, 3, 4 and 5 was tested. 6g of sample was added to 3.5% sodium chloride aqueous solution, and the temperature change was tested with a temperature sensitive meter in a vacuum insulation instrument. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the exothermic peak time of the modified calcium oxide prepared using 1.0g of coupling agent is about 1.1h, which is longer than the peak time of the 0.5g group and the 1.5g group. Although the 2.0g group doubled the amount of coupling agent, its exothermic peak time was only slightly longer than that of the 1.0g group, and its peak temperature was also lower than that of the 1.0g group. Considering the cost and effect factors comprehensively, it is obviously most appropriate to use 1.0g of coupling agent to prepare modified calcium oxide.

[0099] Test Example 3

[0100] Similarly, the particle size of Example 1, Comparative Example 6 and Comparative Example 1 was tested after sufficient reaction in simulated seawater. 6 g of the sample was added to a 3.5% sodium chloride solution and the particle size was tested by a laser particle size analyzer. The results are as follows: Figure 3As shown in the figure, since calcium oxide expands during the hydration process, both the calcium oxide sample and the modified calcium oxide microcapsules expand significantly. According to previous studies, the pore sizes in hydrate-bearing sediments are mainly distributed between 10 μm and 100 μm. The size of the modified calcium oxide microcapsules is highly consistent with the pore size of the formation, and can expand the scope of influence through long-distance transportation of water in the formation, and generate calcium hydroxide after the reaction to achieve the role of supporting the rock matrix.

[0101] Test Example 4

[0102] Figure 4 The exothermic effects of Example 1, Comparative Example 6, and Comparative Example 1 are demonstrated (6 g of sample is added to a 3.5% sodium chloride solution, and the temperature change during the reaction is recorded in a vacuum insulated container). Compared with CaO, the peak temperature corresponding time of mCaO1x and mCaO3x is extended from 10 minutes to 1 hour and 10 minutes and 6 hours and 51 minutes, respectively. It can be seen that the exothermic time of the calcium oxide microcapsules after the layer-by-layer self-assembly wrapping film is significantly delayed. Therefore, the reaction heat is gradually released throughout the process, and the delay effect of the surface-modified calcium oxide increases with the increase of the assembly layer. By combining the synergistic effect of surface modification and layer-by-layer self-assembly, the polysaccharide coating greatly reduces the direct contact between water and the modified calcium oxide surface. The Schiff base film also has self-healing properties. When the outer layer of the calcium oxide coating is destroyed, it can maintain the balance between the rupture and regeneration of the valence bond to prevent the continuous invasion of water.

[0103] Test Example 5

[0104] The heat dissipation of calcium oxide and microcapsule products was calculated based on the environment and measuring instrument parameters. The actual heat release of Example 1, Comparative Example 6 and Comparative Example 1 was close to the theoretical heat release, so it can be used to predict the decomposition amount of natural gas hydrate.

[0105] The heat released by calcium oxide in the reactor satisfies Formula I:

[0106]

[0107] In Formula I, Q CaO ——The heat released by the reaction of calcium oxide with water, J; Q out ——The amount of heat dissipated by the system, J; Q 水 ——heat absorbed by water, J;

[0108] The heat absorbed by water can be calculated using the specific heat capacity formula (Formula II):

[0109]

[0110] In formula II, c is the specific heat capacity of the salt water, J / (g·℃); m is the mass of water, g; T 1——Temperature of water at the beginning of the reaction, °C; T 2 ——Water temperature at the end of the reaction, °C;

[0111] The exothermic reaction formula of calcium oxide is:

[0112] CaO(s)+H 2 O(l)=Ca(OH) 2 (s)Δ r H m =-64.9 kJ / mol

[0113] Calculations show that theoretically, the heat required for 6g of calcium oxide to fully react is Q CaO =6944J.

[0114] The heat dissipation of the entire system is calculated as:

[0115]

[0116]

[0117] Φ 1 =k 1 A 1 (T f2 -T f1 ) Formula V,

[0118] Q 环空 =Φ 1 (t end -t begin ) Formula VI,

[0119] In formula III to formula VI, k i ——Comprehensive heat transfer coefficient, W / (m 2 ℃), i=1,2,…,n;

[0120] A i ——The area of ​​the contact surface during heat transfer, m 2 ;

[0121] Φ 1 ——comprehensive heat transfer power of the annulus, W;

[0122] T f1 ——Temperature measured by the thermometer inside the reactor, °C;

[0123] T f2 ——Indoor air temperature, °C;

[0124] t——time, s;

[0125] h 1 ——Heat transfer coefficient of the solution inside the reactor, W / (m 2 ℃);

[0126] h 2 ——Heat transfer coefficient of the vacuum part of the reactor, W / (m 2 ℃);

[0127] h 3 ——Heat transfer coefficient between the air outside the reactor and the outer wall, W / (m 2 ℃);

[0128] λ——Thermal conductivity of reactor material, W / (m·℃);

[0129] d 1 ——diameter of the inner wall of the inner cylinder, m;

[0130] d 2 ——Diameter of the outer wall of the inner cylinder, m;

[0131] d 3 ——diameter of the inner wall of the outer cylinder, m;

[0132] d 4 ——Diameter of the outer wall of the outer cylinder, m;

[0133] l——the height of the reactor, m.

[0134] Calculation of natural gas hydrate decomposition amount:

[0135]

[0136] n=Q / ΔH Formula VII,

[0137] In formula VII, n is the amount of hydrate decomposed during the heating of calcium oxide, mol; Q is the heat release value of calcium oxide microcapsules, m; ΔH is the dissociation heat of natural gas hydrate, KJ / mol.

[0138] The prediction results are as follows Figure 5 As shown, 6g of calcium oxide is expected to decompose 127mmol of natural gas hydrate. The decomposition rates of natural gas hydrate under the influence of 6g of CaO, mCaO1x or mCaO3x are 36.2mmol / h, 17.7mmol / h and 11.1mmol / h, respectively. This shows that the modified calcium oxide microcapsules can effectively slow down the reaction rate and heat release rate of calcium oxide and water, achieve the effect of delaying reaction and heat release, and can penetrate deep into the reservoir with high utilization efficiency, which is conducive to solving the problem of unstable reservoir temperature and pressure during hydrate decomposition.

[0139] In summary, the present invention provides a polysaccharide-coated calcium oxide microcapsule that can be applied to hydrate formations based on a covalent bond layer-by-layer self-assembly method. By performing layer-by-layer self-assembly after surface modification, a series of microcapsule products are obtained, the exothermic peak of which can be extended from 0.16 hours to 1 hour 10 minutes and 6 hours 51 minutes or more. The median particle size of the calcium oxide microcapsule is 56.2 μm, the encapsulation effect is good, and the particles expand after the reaction, which can achieve the function of supporting the formation.

Claims

1. A calcium oxide microcapsule, which is obtained by sequentially wrapping polyaldehyde cellulose and chitosan on the surface of a modified calcium oxide core, wherein the polyaldehyde cellulose and chitosan are wrapped at least once respectively and are wrapped at intervals from each other.

2. The calcium oxide microcapsule according to claim 1, in, The modified calcium oxide core is prepared by modifying calcium oxide with a silane coupling agent; The polyaldehyde cellulose is prepared by reacting cellulose with sodium periodate.

3. The calcium oxide microcapsule according to claim 1, in, The particle size of the calcium oxide microcapsule is 2.99-91 μm, and the particle size of the modified calcium oxide core is 2.74-80 μm.

4. The method for preparing the calcium oxide microcapsules according to any one of claims 1 to 3, wherein The following steps are involved: (1) Preparation of polyaldehyde cellulose: The cellulose aqueous solution is mixed with sodium periodate, and after the reaction is carried out in the dark, the reaction is terminated and a precipitate is precipitated to obtain the polyaldehyde cellulose; (2) Preparation of modified calcium oxide core: Dispersing calcium oxide in an alcohol solution of a silane coupling agent and stirring to obtain the modified calcium oxide core; (3) Preparation of calcium oxide microcapsules: The modified calcium oxide core is added to the alcohol dispersion of the polyaldehyde cellulose, stirred, centrifuged and dried to obtain a single-layer wrapped calcium oxide microcapsule, and then the single-layer wrapped calcium oxide microcapsule is added to the alcohol dispersion of chitosan, stirred, centrifuged and dried to obtain a double-layer wrapped calcium oxide microcapsule, and the above-mentioned wrapping operation is repeated to obtain the calcium oxide microcapsule wrapped with the target number of layers.

5. The preparation method according to claim 4, in, In step (1), the concentration of the cellulose aqueous solution is 0.1-0.5 g / mL; Preferably, in step (1), the molar ratio of the sodium periodate to the structural unit of the cellulose is 0.2-0.4:1; Preferably, in step (1), the light-proof reaction condition is: stirring the reaction at room temperature for 4-10 hours under light-proof conditions; Preferably, in step (1), after the reaction is carried out in the dark, ethylene glycol is added to terminate the reaction; Preferably, in step (1), the precipitation conditions are: adding anhydrous ethanol in a volume ratio of 5-10:1 to the reaction solution; Preferably, in step (1), after the precipitate is separated out, it is dried at 40-60° C. for 24-48 hours.

6. The preparation method according to claim 4, in, In step (2), the silane coupling agent is 3-aminopropyltrimethoxysilane; Preferably, in step (2), the alcohol solution of the silane coupling agent is a mixture of 3-aminopropyltrimethoxysilane and anhydrous ethanol in a volume ratio of 1:50-100; Preferably, in step (2), the mass ratio of calcium oxide to silane coupling agent is 20:1; Preferably, in step (2), the stirring temperature is 10-30°C, the stirring rate is 200-300 rpm, and the stirring time is 10-60 min; Preferably, in step (2), the stirring is followed by centrifugation and drying, and the drying conditions are drying at 70-80° C. for 0.5-2 h.

7. The preparation method according to claim 4, in, In step (3), the concentrations of the alcohol dispersion of polyaldehyde cellulose and the alcohol dispersion of chitosan are both 2-6 mg / mL; Preferably, in step (3), the mass ratio of the modified calcium oxide core to the single-wrapped polyaldehyde cellulose is 20-80:1, more preferably 50:1; Preferably, in step (3), the mass ratio of the modified calcium oxide core to the chitosan wrapped once is 20-80:1, more preferably 50:1; Preferably, in step (3), the stirring temperature is room temperature, the stirring time is 10-20 min, and the stirring rate is 100-300 r / min, more preferably 200 r / min; Preferably, in step (3), the drying temperature is 70-90° C. and the drying time is 5-30 minutes.

8. Use of the calcium oxide microcapsules according to any one of claims 1 to 3 in natural gas hydrate exploitation.

9. A method for calculating the decomposition amount of natural gas hydrates produced by using the calcium oxide microcapsules described in any one of claims 1 to 3, which is calculated by the following formula: n=Q / ΔH, Wherein, n is the amount of hydrate decomposition during calcium oxide heating, mol; Q is the heat release value of calcium oxide microcapsules, m; ΔH is the dissociation heat of natural gas hydrate, KJ / mol.

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