Composite oxidizing agent suitable for shale reservoir produced water treatment and application thereof

Abstract

The application discloses a composite oxidant suitable for shale reservoir produced water treatment and application thereof, and relates to the technical field of sewage treatment. The composite oxidant comprises an oxidant and a catalyst, and the preparation method of the catalyst comprises the following steps: taking iron salt, copper salt, manganese salt and water-soluble titanate to be dissolved in an aluminum sol solution, under the condition of continuous stirring, dropwise adding ammonia water and standing for a period of time, then taking the solid phase and washing several times with distilled water to obtain a precursor; taking the precursor, sintering under the condition of an oxygen-containing atmosphere and 400-550 DEG C for 2-5 hours, crushing and sieving, and the catalyst is obtained. The composite oxidant suitable for shale reservoir produced water treatment can effectively remove COD in shale gas produced water through the compounding of the oxidant and the catalyst, and has good reusability.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a composite oxidant suitable for treating produced water from shale reservoirs and its application. Background Technology

[0002] The development of shale gas and shale oil mainly generates three types of wastewater: waste drilling fluid, fracturing flowback fluid, and shale produced water. Shale produced water contains a large amount of minerals, and chemical additives such as corrosion inhibitors, foaming agents, and scale inhibitors are typically added during extraction and transportation. These chemical additives are usually polymers. Therefore, shale produced water is characterized by high salinity, high COD, and difficulty in biochemical treatment.

[0003] Therefore, advanced oxidants are typically used in the treatment of shale produced water to perform advanced oxidation treatment on the water after preliminary treatment (removal of large particulate impurities in sedimentation tanks). Existing advanced oxidation methods primarily utilize strong oxidants such as ozone, hydrogen peroxide, persulfate, and Fenton's reagent to treat COD. However, when applied to shale produced water, these oxidants not only have slow treatment rates but also relatively low final COD removal rates. Therefore, existing technologies also employ methods such as using multiple oxidants in combination or adding heterogeneous catalysts to assist oxidation. The problem with using multiple oxidants in combination is that costs rise rapidly, and although the treatment effect is improved to some extent, it is still not ideal. The problem with heterogeneous catalysts is that even if shale produced water has undergone preliminary treatment, it still contains a lot of small particles. After advanced oxidation and subsequent coagulation / flocculation, these small particles will co-sedimentate with the heterogeneous catalyst, making it difficult to separate some non-ferromagnetic catalysts in actual use and resulting in a high loss rate. At the same time, the existing heterogeneous catalysts can only be reused a few times, resulting in excessively high costs. Summary of the Invention

[0004] To address at least one of the aforementioned problems, this invention provides a composite oxidant suitable for shale reservoir produced water treatment and its application.

[0005] The technical solution of this invention to solve the above problems is as follows: A composite oxidant suitable for shale reservoir produced water treatment, comprising an oxidant and a catalyst, wherein the preparation method of the catalyst includes the following steps: On a molar basis, 2-3 parts of iron salt, 1 part of copper salt, 0.5-1 part of manganese salt, and 0.01-0.05 parts of water-soluble titanate were dissolved in an aluminum sol solution. Under continuous stirring, ammonia water was added dropwise to control the pH of the system to 10-11 and maintained for at least 30 minutes. After the addition was completed, the temperature was raised to 40-70°C and allowed to stand for 10-15 hours. The solid phase was then taken and washed several times with distilled water to obtain the precursor. The molar ratio of aluminum to copper salt was 0.1-0.3:1. Take the above precursor, sinter it in an oxygen-containing atmosphere at 400~550℃ for 2~5 hours, then crush and sieve it to obtain the final product.

[0006] In this invention, the oxidant can be selected from common oxidants in existing advanced oxidation methods, and the amount of oxidant added can also be calculated based on existing oxidant addition amounts: for example, based on the COD equivalent in water, the amount of oxidant added is 1.5 to 5 times the COD equivalent.

[0007] The catalyst of the present invention, through appropriate material ratio and appropriate process, can be obtained as a ferromagnetic catalyst. This catalyst has low solubility in water, can be reused multiple times, and has good catalytic effect.

[0008] In the catalyst preparation process, the base elements are iron, copper, and manganese. A composite oxide catalyst is prepared using a precipitation method. During the preparation process, titanate esters and aluminum sols are used to modify the aforementioned composite oxide catalyst. Furthermore, the titanate esters used in this invention exhibit better performance compared to conventionally used water-soluble titanium salts. The purpose of using aluminum and titanium is to reduce the solubility of iron, copper, and manganese, increasing their reusability and thus reducing costs.

[0009] The above-described raw material ratios and preparation process enable the catalyst prepared by this invention to possess a certain degree of ferromagnetism, making it relatively easy to separate and recover from wastewater for reuse.

[0010] The reason for allowing the precursor to stand at a certain temperature for 10-15 hours during precursor preparation is to consider the particle size of the precursor: if the temperature is too low or the standing time is too short, the final precursor size will be relatively small, making recovery in shale gas produced water more difficult, resulting in higher losses and higher metal dissolution. A longer standing time has less impact on particle size, and excessively large particles can also affect catalytic performance.

[0011] The purpose of washing the precursor several times with distilled water during the preparation process is to remove residual anions, cations and ammonia on the surface of the precursor, making the precursor purer.

[0012] Sintering in an oxygen-containing atmosphere mainly involves converting the hydroxide form of the precursor into a composite oxide form, which is a routine operation in this field.

[0013] The above-mentioned crushing and sieving operations can be performed by simple grinding, without the need for complex crushing. Secondly, sieving is mainly to remove large particles. In the actual sieving process, a 40-mesh sieve or a sieve with other aperture sizes can be used.

[0014] In one embodiment of the present invention, the oxidant is ozone or hydrogen peroxide. These are common oxidants in the art, and the catalyst of the present invention can effectively catalyze these two oxidants, thereby increasing their oxidation performance.

[0015] One embodiment of the present invention comprises: the iron salt being one of ferric sulfate, ferric nitrate, and ferric chloride; the copper salt being one of copper nitrate, copper sulfate, and copper chloride; the manganese salt being one of manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride; and the water-soluble titanate being diisopropyl di(triethanolamine)titanate. The aforementioned iron, copper, and manganese salts are common water-soluble metal salts in the art. Nitrates are more commonly used in the art because they are essentially non-corrosive. However, diisopropyl di(triethanolamine)titanate is more effective for water-soluble titanates.

[0016] One embodiment of the present invention involves the following method for preparing the aluminum sol: Boehmite is dispersed in water, acid is added dropwise to control the pH of the system to 2-4, and the mixture is continuously stirred at 40-60°C for 1-3 hours. The solid phase is then filtered off, and the remaining liquid phase is collected. Compared to aluminum sols prepared from water-soluble aluminum salts, such as aluminum nitrate, aluminum sols prepared from boehmite exhibit better performance in practical applications.

[0017] In one embodiment of the present invention, the stirring speed during the preparation of the precursor is 50-200 r / min. During the preparation of the precursor, the stirring speed should not be too fast, as this will result in a smaller particle size of the prepared precursor.

[0018] In one embodiment of the present invention, during the preparation of the precursor, the total concentration of iron salt, copper salt, and manganese salt in the aluminum sol solution is 0.3~0.8 mol / L. A suitable concentration allows the precursor to rapidly crystallize and grow to a larger size; if the concentration is too high, the final precursor will have a wide range of particle sizes, resulting in unstable catalyst performance; if the concentration is too low, the precursor will have a smaller particle size.

[0019] One embodiment of the present invention is that the oxygen-containing atmosphere refers to a gaseous atmosphere with an oxygen volume fraction of 15-80%.

[0020] In one embodiment of the present invention, during sintering, the temperature is raised to 400-500°C using a programmed heating method, with a heating rate of 80-120°C / h. If the heating rate is too fast, the precursor particle size will decrease, and the performance will deteriorate.

[0021] One embodiment of the present invention includes the following steps after sintering: cooling the sintered body to 250-300°C and holding it in a weak reducing atmosphere for 30-60 minutes; the weak reducing atmosphere refers to a gaseous atmosphere with a carbon monoxide volume fraction of 5-15%. Through short-term treatment in a low-temperature, weak reducing atmosphere, the catalytic performance of the catalyst can be further improved. During the replacement with a weak reducing atmosphere, similar to conventional operations in the art, after sintering, the furnace body is purged with an inert atmosphere (such as nitrogen), and the oxygen content inside the furnace is monitored in real time. When the oxygen content decreases to a certain threshold (such as 100 ppm or 500 ppm), and the furnace body is cooled to 250-300°C, carbon monoxide gas is slowly introduced until the carbon monoxide concentration inside the furnace reaches the target concentration. In fact, hydrogen can also be used as the reducing gas; however, hydrogen has poor safety and requires a high oxygen content inside the furnace, therefore carbon monoxide is usually used.

[0022] Another object of the present invention is to provide an application of the above-mentioned composite oxidant, comprising the following steps: adding a catalyst to shale gas produced water at a dosage of 300-2000 ppm, followed by adding an oxidant at a COD equivalent of 1.3-3 times that of the shale gas produced water, and catalytic oxidation for at least 10 minutes. The dosage of the oxidant is that of conventional oxidants in the art; regarding the dosage of the catalyst, the higher the COD, the higher the polymer content, and the higher the content of aromatic compounds in the produced water, the greater the dosage.

[0023] The beneficial effects of the present invention are as follows: the composite oxidant of the present invention, which is suitable for the treatment of shale reservoir produced water, can effectively remove COD from shale gas produced water through the combination of oxidant and catalyst, and has good reusability. Attached Figure Description

[0024] Figure 1 The performance test results are shown in the graph for reuse. Detailed Implementation

[0025] The specific embodiments of the present invention will be clearly and completely described below with reference to examples. Obviously, the described examples are only some embodiments of the present invention, and not all embodiments.

[0026] Unless otherwise specified, all operations used in the following embodiments are conventional operations in the art.

[0027] Unless otherwise specified, all products used in the following embodiments are conventional commercial products in the art.

[0028] In the following examples, the concentration of ammonia water used was 0.1 mol / L.

[0029] In the following embodiments, the first aluminum sol was prepared by the following method: Boehmite was dispersed in water, hydrochloric acid was added dropwise to control the pH of the system to 3, and the mixture was stirred continuously at 50°C for 2 hours. The solid phase was then filtered off to obtain the aluminum sol. The aluminum concentration of the aluminum sol was determined to be 3.2 mol / L by EDTA displacement titration (GB 15892-2009).

[0030] In the following embodiments, the second aluminum sol was prepared by the following method: aluminum nitrate was dissolved in water, ammonia was added to precipitate it, the precipitate was washed several times with deionized water, the precipitate was dispersed in water, nitric acid was added and stirred rapidly at 65°C, the pH of the system was controlled at 3.5, and then the system was kept at 65°C for 3 hours to obtain the sol. The concentration of aluminum was determined to be 2.6 mol / L by EDTA displacement titration.

[0031] Example 1: A composite oxidant suitable for shale reservoir produced water treatment, comprising hydrogen peroxide and a catalyst, wherein the catalyst is prepared as follows: Preparation of the precursor: Take the first aluminum sol mentioned above and dilute it 80 times with water and stir evenly. Take 1000 ml of the diluted aluminum sol and add 0.25 mol of ferric nitrate nonahydrate, 0.1 mol of copper nitrate, 0.08 mol of manganese nitrate hexahydrate, and 0.004 mol of diisopropyl di(triethanolamine)titanate. Stir to dissolve it. Then, under stirring conditions of 100 r / min, add ammonia dropwise and maintain the pH of the system at about 10.5. The ammonia dropwise addition time is controlled at 30 min. After the addition is completed, heat to 60℃ and let stand for 12 h. After standing, filter to take the solid phase and wash the solid phase three times with distilled water to obtain the precursor.

[0032] Sintering process: Take the above precursor and place it in a muffle furnace with an air atmosphere. Heat it to 480℃ at a rate of 100℃ / h and hold it for 3 hours. After sintering, cool it down to 260℃ and replace the atmosphere in the muffle furnace with a weak reducing atmosphere (composed of carbon monoxide and nitrogen, of which carbon monoxide has a volume fraction of 12%). Hold it for 45 minutes. After the holding period, let it cool to room temperature, grind it, and take the particles that pass through a 40-mesh sieve.

[0033] Example 2: A composite oxidant suitable for shale reservoir produced water treatment, comprising ozone and a catalyst, wherein the catalyst is prepared as follows: Preparation of the precursor: Take the above-mentioned second aluminum sol and dilute it 40 times with water and stir evenly. Take 1000 ml of the diluted aluminum sol and add 0.28 mol of ferric nitrate nonahydrate, 0.1 mol of copper nitrate, 0.06 mol of manganese nitrate hexahydrate, and 0.002 mol of diisopropyl di(triethanolamine)titanate. Stir to dissolve it. Then, under the stirring condition of 100 r / min, ammonia water is added dropwise, and the pH of the system is maintained at about 10.5. The ammonia water is added dropwise over a period of 30 min. After the addition is complete, the temperature is raised to 50℃ and allowed to stand for 14 h. After standing, the solid phase is filtered and washed three times with distilled water to obtain the precursor.

[0034] Sintering process: Take the above precursor and place it in a muffle furnace with an air atmosphere. Heat it to 420℃ at a rate of 90℃ / h and hold it for sintering for 5 hours. After sintering, cool it down to 280℃ and replace the atmosphere in the muffle furnace with a weak reducing atmosphere (composed of carbon monoxide and nitrogen, of which carbon monoxide has a volume fraction of 8%). Hold it for 50 minutes. After holding it for 50 minutes, let it cool to room temperature, grind it, and take the particles that pass through a 40-mesh sieve.

[0035] Example 3: A composite oxidant suitable for shale reservoir produced water treatment, comprising hydrogen peroxide and a catalyst, wherein the catalyst is prepared as follows: Preparation of precursor: Compared with Example 1, the difference is that after holding at 480°C, it was directly cooled to room temperature, and then ground to obtain particles that passed through a 40-mesh sieve. The rest are the same.

[0036] The sintering process is the same as in Example 1.

[0037] Example 4: A composite oxidant suitable for shale reservoir produced water treatment, comprising hydrogen peroxide and a catalyst, wherein the catalyst is prepared as follows: Preparation of precursor: Compared with Example 1, the difference is that the stirring speed is 300 r / min, and all other aspects are the same.

[0038] The sintering process differs from that in Example 1 in that the sintering temperature is 450°C and the sintering time is 4 hours, while all other aspects are the same.

[0039] Example 5: A composite oxidant suitable for shale reservoir produced water treatment, comprising hydrogen peroxide and a catalyst, wherein the catalyst is prepared as follows: Preparation of precursor: Compared with Example 1, the difference is that the amount of aluminum sol added is 400 ml, and all other aspects are the same.

[0040] The sintering process differs from that in Example 1 in that the programmed heating rate is 200℃ / h, while all other processes are the same.

[0041] Comparative Example 1 differs from Example 1 in that diisopropyl di(triethanolamine)titanate was not added during the preparation of the precursor, while all other aspects were the same.

[0042] Comparative Example 2 differs from Example 1 in that, during the preparation of the precursor, the amount of ferric nitrate nonahydrate added is 0.1 mol, and the amount of manganese nitrate hexahydrate added is 0.25 mol, while the rest are the same.

[0043] Comparative Example 3 differs from Example 1 in that water was used instead of aluminum sol in the preparation of the precursor, while the rest were the same.

[0044] Comparative Example 4 differs from Example 1 in that the sintering temperature is 650°C, while all other conditions are the same.

[0045] To further illustrate the performance of the composite oxidant prepared in the embodiments and comparative examples of the present invention, tests were conducted on it below.

[0046] A sample of produced water from a shale gas plant was coarsely filtered to remove large particles and silt. The mineralization was measured to be 33,000 mg / L and the COD was 2,200 mg / L. The main source of COD was high-molecular additives, such as polyacrylamide thickeners, shale inhibitors, and filtration loss reducers, which are difficult to biochemically analyze.

[0047] COD removal rate test: The composite oxidant from the above examples and comparative examples was added to 1L of shale gas produced water, with a catalyst dosage of 800ppm. Condition 1: Hydrogen peroxide dosage was 3300mg / L, treatment time was 12min; ozone flow rate was 0.25L / min, and the inlet time was 12min19s. Condition 2: Hydrogen peroxide dosage was 3300mg / L, treatment time was 30min; ozone flow rate was 0.1L / min, and the inlet time was 30min48s.

[0048] The COD of the treated shale gas produced water was measured using the potassium dichromate method, and the final results are shown in Table 1.

[0049] As shown in Table 1, the COD in shale gas produced water can be effectively removed after treatment with the composite oxidant of this embodiment of the invention.

[0050] Reusability performance test: The composite oxidants from Examples 1, 4, Comparative Example 1, and Comparative Example 3 were used for repeated testing 10 times under condition 2 of the COD removal rate test procedure. After each test, the catalyst was recovered using an external magnetic field. After recovery, the catalyst was washed several times with clean water and dried for reuse. No new catalyst was added during the test. The final test results are shown in Table 2 and... Figure 1 As shown.

[0051] Table 2 Reuse Test Results From Table 2 and Figure 1 It can be seen that the catalyst prepared in the embodiments of the present invention can be reused, and its performance remains good after multiple reuses. Referring to Examples 1 and 4, it can be seen that higher stirring speeds lead to decreased reusability.

[0052] The present invention has been disclosed above through preferred embodiments; however, those skilled in the art should understand that these embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Further modifications can be made without departing from the principles of the invention, and these modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite oxidant suitable for treating produced water from shale reservoirs, characterized in that, It includes an oxidant and a catalyst, wherein the oxidant is ozone or hydrogen peroxide, and the method for preparing the catalyst includes the following steps: In molar amounts, 2-3 parts of iron salt, 1 part of copper salt, 0.5-1 part of manganese salt, and 0.01-0.05 parts of water-soluble titanate were dissolved in an aluminum sol solution. Under continuous stirring, ammonia water was added dropwise to control the pH of the system to 10-11 and maintained for at least 30 minutes. After the addition was complete, the temperature was raised to 40-70°C and allowed to stand for 10-15 hours. The solid phase was then collected and washed several times with distilled water to obtain the precursor. The molar ratio of aluminum to copper salt was 0.1-0.3:

1. The water-soluble titanate was diisopropyl di(triethanolamine) titanate. Take the above precursor, sinter it in an oxygen-containing atmosphere at 400~550℃ for 2~5 hours, then crush and sieve it to obtain the final product.

2. The composite oxidant for shale reservoir produced water treatment according to claim 1, characterized in that, The iron salt is one of ferric sulfate, ferric nitrate, and ferric chloride; the copper salt is one of copper nitrate, copper sulfate, and copper chloride; and the manganese salt is one of manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride.

3. The composite oxidant for shale reservoir produced water treatment according to claim 1, characterized in that, The aluminum sol is prepared as follows: Boehmite is dispersed in water, acid is added dropwise to control the pH of the system to 2-4, and the mixture is stirred continuously at 40-60℃ for 1-3 hours. The solid phase is then filtered off, and the remaining liquid phase is collected.

4. The composite oxidant for shale reservoir produced water treatment according to claim 1, characterized in that, During the preparation of the precursor, the stirring speed is 50~200 r / min.

5. The composite oxidant for shale reservoir produced water treatment according to claim 1, characterized in that, During the preparation of the precursor, the total concentration of iron salt, copper salt and manganese salt in the aluminum sol solution is 0.3~0.8 mol / L.

6. The composite oxidant for shale reservoir produced water treatment according to claim 1, characterized in that, The oxygen-containing atmosphere refers to a gaseous atmosphere with an oxygen volume fraction of 15-80%.

7. The composite oxidant for shale reservoir produced water treatment according to claim 1, characterized in that, During sintering, the temperature is raised to 400~500℃ using a programmed heating method, with a heating rate of 80~120℃ / h.

8. The composite oxidant for shale reservoir produced water treatment according to claim 1, characterized in that, After sintering, the following steps are also included: the sintered body is cooled to 250~300℃ and kept at that temperature for 30~60 minutes in a weak reducing atmosphere; the weak reducing atmosphere refers to a gaseous atmosphere with a carbon monoxide volume fraction of 5~15%.

9. The application of the composite oxidant for shale reservoir produced water treatment as described in any one of claims 1 to 8, comprising the following steps: Add the catalyst to the shale gas produced water at a dosage of 300-2000 ppm, followed by an oxidant with a COD equivalent of 1.3-3 times that of the shale gas produced water, and catalytic oxidation for at least 10 minutes.

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