Method for desalinating seawater by using perfluorohexanone

Abstract

The invention discloses a method for desalinating seawater by using perfluorohexanone. The method comprises the following steps: preparing a gas hydrate by using seawater in a high-pressure reaction kettle; unreacted seawater in the gas hydrate system is discharged; injecting a certain amount of perfluorohexanone into the autoclave; the solid-phase hydrate is immersed in the perfluorohexanone by adopting a proper method; slowly decomposing the gas hydrate at a proper temperature, wherein water generated by decomposition and saline water contaminated on the surface float on the upper part of the liquid phase of the perfluorohexanone; removing decomposition water in the beginning period of time; completely decomposing the hydrate, and then separating the perfluorohexanone from the water by using a phase splitter to obtain desalted water. According to the method provided by the invention, seawater contaminated on the surface of the hydrate can be removed, the seawater desalination effect is effectively improved, a large amount of precious pure water is not wasted, and the method has very important application value.

Description

Technical Field

[0001] The invention belongs to the field of seawater desalination methods, and in particular relates to a method for desalinating seawater by utilizing perfluorohexanone. Background Art

[0002] Water is an essential substance for the survival of all living things on Earth. It is a natural resource that humans rely on for daily life and industrial production. However, fresh water resources only account for 2% of all water resources, and 87% of fresh water resources are sealed in ice and glaciers at the poles and high mountains, making them difficult to develop and utilize. With the rapid development of the industrial economy and the increasing environmental pollution, the shortage of fresh water resources has become a global problem.

[0003] Seawater desalination is a method of obtaining pure water by removing salt from seawater. Currently, the more commonly used desalination methods include: distillation, freezing, semi-permeable membrane, etc. However, although these desalination methods are mature and have reached industrial application, they still have some defects. Distillation desalination is a method of heating seawater to boil and evaporate, and then condensing the steam into the required fresh water. Among them, multi-effect evaporation is composed of multiple groups of single-effect evaporators in series. The heat utilization rate is high and it is known as one of the methods with the lowest energy consumption in seawater desalination. However, multi-effect evaporation has problems with container structure and equipment corrosion, which greatly affects the market development of this method. The membrane method separates salt water from fresh water based on the selective permeability of the membrane, including electrodialysis and reverse osmosis. Among them, reverse osmosis is the most competitive method with thermal distillation. Reverse osmosis can remove a large amount of inorganic salts in water, and can also remove suspended matter, colloids, viruses and other substances. However, the low life of the semi-permeable membrane, the pretreatment requirements for removing impurities, the limited operating pressure, and the instability of fresh water quality caused by the easy contamination of the osmotic membrane have become the main problems restricting the large-scale application of the reverse osmosis method.

[0004] The use of hydrate method for seawater desalination is a new method developed this year. The hydrate desalination method is to react molecules that are easy to form hydrates (gas molecules or liquid molecules) with seawater to form hydrate crystals. Since the structure of hydrates only contains water molecules and guest molecules, salt and other impurities will be excluded from the hydrate structure during the hydrate formation process and remain in the residual brine. The hydrate desalination method has the advantages of low energy consumption, simple generation equipment, and no pollution to the environment in the desalination process and products. However, the efficiency of desalination using the hydrate method is generally low (up to about 84%), which is much lower than the conventional chemical method (evaporation method, reverse osmosis method), and cannot be used directly as pure water. This is caused by two aspects. First, a certain amount of salt water will be wrapped between the hydrate crystals; second, the salt water contaminated on the surface of the hydrate crystals will contaminate the final purified water. Among them, factor two has a more significant impact on the desalination effect of seawater. At present, the solution to this problem is to rinse the surface with pure water to wash away the salt water contaminated on the surface, but this method will waste a large amount of precious fresh water.

[0005] In the process of seawater desalination using the gas hydrate method, the surface of the solid hydrate will inevitably be contaminated with salt water, affecting the desalination effect of seawater. In order to solve this problem, the present invention proposes a method for removing salt water from the surface of solid hydrate using perfluorohexanone, which can remove the seawater contaminated on the surface of the hydrate and effectively improve the desalination effect of seawater without wasting a large amount of precious pure water, and has very important application value. Summary of the invention

[0006] The purpose of the present invention is to solve the problem that the salt water on the surface of solid hydrates will affect the desalination effect in the current hydrate method desalination process, and to invent a new method for removing the salt water on the surface of hydrates using perfluorohexanone. The method can effectively remove the salt water on the surface of hydrates and improve the desalination effect.

[0007] In order to solve the above problems, the present invention is achieved by the following methods:

[0008] A method for desalinating seawater using perfluorohexanone comprises the following steps:

[0009] (1) Preparing gas hydrates using seawater in a high-pressure reactor;

[0010] (2) draining the unreacted seawater from the gas hydrate system;

[0011] (3) injecting a certain amount of perfluorohexanone into the autoclave;

[0012] (4) immersing the solid hydrate in perfluorohexanone by a suitable method;

[0013] (5) Decomposing the gas hydrate slowly at a suitable temperature, the water produced by the decomposition and the salt water contaminated on the surface will float on the upper part of the liquid phase of perfluorohexanone;

[0014] (6) Remove the decomposed water in the initial period of time, because these are a mixture of brine and decomposed water on the hydrate surface;

[0015] (7) The gas hydrate is completely decomposed, and then perfluorohexanone and water are separated by a phase separator to obtain desalinated water.

[0016] Furthermore, the gas hydrates in step (1) are used to synthesize gas hydrates, including but not limited to: methane, ethane, propane, carbon dioxide, and nitrogen.

[0017] Furthermore, the minimum amount of perfluorohexanone in step (3) should be enough to completely immerse the solid phase hydrate, and the maximum amount should be enough to fill the entire autoclave.

[0018] Furthermore, the suitable method in step (4) includes: using a partition (with or without holes), gauze, etc. to press the solid hydrate to the bottom of the reactor; gas hydrate can also be directly produced in porous media such as sand, glass beads, and ceramsite.

[0019] Furthermore, the suitable temperature in step (5) is 1 to 5° C. higher than the phase equilibrium temperature of the gas hydrate.

[0020] Furthermore, the initial period of time in step (6) refers to 10% to 90% of the entire decomposition cycle.

[0021] The beneficial effects of the present invention are:

[0022] Desalination of seawater using the gas hydrate method is a widely studied technology and will have great industrial application value in the future. However, the unfrozen concentrated brine on the surface of the solid particles of the gas hydrate is an important factor affecting the final desalination effect. The present invention utilizes the density difference between perfluorohexanone and water to more effectively remove the brine on the surface of the gas hydrate particles, thereby improving the implementation effect of desalination using the gas hydrate method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the method scheme of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary method personnel in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1This is a typical schematic diagram of seawater desalination using the hydrate method. First, gas hydrates are formed in the reactor, as shown in Figure (a); second, the water in the reactor is drained from the bottom, as shown in Figure (b); third, perfluorohexanone is injected into the reactor, and the temperature and pressure are adjusted to carry out the hydrate decomposition process, as shown in Figure (c); finally, the liquid at the top of perfluorohexanone in different time periods is continuously collected for analysis to evaluate the desalination effect, as shown in Figure (d);

[0025] Figure 2 The time comparison of desalinating seawater by different methods in Example 1;

[0026] Figure 3 The time comparison of desalinating seawater by different methods in Example 2;

[0027] Figure 4 The time comparison of desalinating seawater by different methods in Example 3 is shown. DETAILED DESCRIPTION

[0028] The above description is only an overview of the method scheme of the present invention. In order to more clearly understand the method means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following specifically cites the preferred embodiments and describes them in detail with the accompanying drawings.

[0029] Example 1

[0030] Add 100mL of seawater (replaced with 3.5% NaCl solution) into a 500mL sapphire reactor; close the autoclave, and introduce CO2 gas to 4.0MPa; turn on the agitator, turn on the water bath, and start generating gas hydrates. When the gas hydrates are prepared, discharge the unreacted liquid from the bottom of the reactor, and accurately weigh the volume of the discharged water; use a porous plate in the reactor to press the solid phase hydrate to the bottom of the reactor; inject 250mL of pre-cooled perfluorohexanone; adjust the reactor temperature to 2°C above the CO2 phase equilibrium temperature to promote the decomposition of gas hydrates. At different times, take the liquid water from the upper part of the perfluorohexanone and discharge it for salt content analysis to determine the optimal time for taking pure water, and draw a graph for analysis. The experimental results are as follows: Figure 2 As shown, according to Figure 2 The results show that when perfluorohexanone immersion method is used for seawater desalination, the time for desalinated water to reach the standard is reduced from 50 hours to less than 4 hours, which has a very obvious strengthening effect.

[0031] Example 2

[0032] Add 100mL of seawater (replaced with 3.5% NaCl solution) into a 500mL high-pressure stainless steel reactor; close the autoclave, and introduce CH4 gas to 4.0MPa; turn on the agitator, turn on the water bath, and start generating gas hydrates. When the gas hydrates are prepared, discharge the unreacted liquid from the bottom of the reactor, and accurately weigh the volume of the discharged water; use a porous plate in the reactor to press the solid phase hydrate to the bottom of the reactor; inject 250mL of pre-cooled perfluorohexanone; adjust the reactor temperature to 2°C above the CH4 phase equilibrium temperature to promote the decomposition of the hydrate. At different times, take the liquid water from the upper part of the perfluorohexanone and discharge it for salt content analysis to determine the optimal time for taking pure water, and draw a graph for analysis. The experimental results are as follows: Figure 3 As shown, according to Figure 3 The results show that when perfluorohexanone immersion method is used for seawater desalination, the time for desalinated water to reach the standard is reduced from 50 hours to less than 4 hours, which has a very obvious strengthening effect.

[0033] Example 3

[0034] Add 200mL of quartz sand (60-80 mesh) with a brine saturation of 50% into a 500mL sapphire reactor; close the autoclave, and introduce CO2 gas to 4.0MPa into the autoclave; turn on the water bath to start generating gas hydrates. When the gas hydrate is prepared, discharge the unreacted liquid from the bottom of the reactor, and accurately weigh the volume of the discharged water; use a porous plate in the reactor to press the solid phase hydrate to the bottom of the reactor; inject 250mL of pre-cooled perfluorohexanone; adjust the reactor temperature to 2°C above the CO2 phase equilibrium temperature to promote the decomposition of the hydrate. At different times, take the liquid water from the upper part of the perfluorohexanone and discharge it for salt content analysis to determine the optimal time for taking pure water, and draw a graph for analysis. The experimental results are as follows: Figure 4 As shown, according to Figure 4 The results show that when perfluorohexanone immersion method is used for seawater desalination, the time for desalinated water to reach the standard is reduced from 50 hours to less than 4 hours, which has a very obvious strengthening effect.

[0035] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any method personnel familiar with the field of the method within the scope of the method disclosed in the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for desalinating seawater using perfluorohexanone, comprising: (1) Preparing gas hydrates using seawater in a high-pressure reactor; (2) draining the unreacted seawater from the gas hydrate system; (3) injecting a certain amount of perfluorohexanone into the autoclave; (4) immersing the solid hydrate in perfluorohexanone by a suitable method; (5) using appropriate temperature to decompose gas hydrates; (6) removing the decomposed water within a certain period of time; (7) The gas hydrate is completely decomposed, and then perfluorohexanone and water are separated by a phase separator to obtain desalinated water.

2. The method according to claim 1, wherein: The gas hydrate in step (1) includes one or more of methane, ethane, propane, carbon dioxide and nitrogen.

3. The method according to claim 1, wherein: The minimum amount of perfluorohexanone in step (3) should be enough to completely immerse the solid phase hydrate, and the maximum amount should be enough to fill the entire autoclave.

4. The method according to claim 1, wherein: The suitable method for step (4) includes: using a partition or gauze to press the solid hydrate to the bottom of the reactor; or directly producing gas hydrate in a porous medium.

5. The method according to claim 4, wherein: The porous medium includes: sand, glass beads and ceramsite.

6. The method according to claim 1, wherein: The suitable temperature in step (5) is 1 to 5° C. higher than the phase equilibrium temperature of the gas hydrate.

7. The method according to claim 1, wherein: The initial period of time in step (6) refers to 10% to 90% of the entire decomposition cycle.

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