A method for dehydrating aqueous ethanol

Abstract

The present invention provides a method for dehydrating aqueous ethanol. The aqueous ethanol is first dehydrated through a permeable membrane and then dehydrated through dry adsorption, so that efficient dehydration of ethanol can be achieved to obtain high-purity anhydrous ethanol, wherein the mass content of water can be lower than 100 ppm, or even lower than 50 ppm, far exceeding the dehydration purity of ethanol in the prior art, achieving a technological breakthrough in the field, and permeable membrane dehydration and dry adsorption dehydration can be performed in a liquid phase state, thereby reducing equipment requirements and operating difficulty, reducing costs, and having low energy consumption, and having a prospect of large-scale application.

Description

Technical Field

[0001] The invention relates to the technical field of ethanol, in particular to a dehydration method of hydrous ethanol. Background Art

[0002] Ethanol, commonly known as alcohol, is a type of alcohol compound with a chemical formula of C2H6O. Ethanol is widely used in the chemical industry, medical and health care, food industry, agricultural production and other fields.

[0003] Industrial ethanol production methods mainly include fermentation and ethylene hydration. The ethanol produced by these methods is usually an azeotrope of ethanol and water. Anhydrous ethanol refers to an ethanol aqueous solution (hydrous ethanol) with a higher purity. Generally, an ethanol solution with a concentration of 99.5% (v / v) is called anhydrous ethanol. In some technical fields, such as the preparation of EMC electrolytes for new energy batteries, the ethanol concentration is required to be high, and the water content in anhydrous ethanol is expected to be as low as possible (<100ppm). In addition, in some format reaction systems, the water content of the raw ethanol is also required to be as low as possible.

[0004] Existing anhydrous ethanol is generally obtained by dehydrating industrial ethanol. The dehydration methods mainly include:

[0005] (1) Treating industrial ethanol with quicklime to convert water into calcium hydroxide, then distilling the ethanol and drying it with metallic sodium. This method is old and cumbersome;

[0006] (2) Azeotropic distillation dehydration, which is currently a commonly used method in industry;

[0007] (3) Dehydration with ion exchangers or molecular sieves followed by distillation. This method has high operating energy consumption and high cost.

[0008] However, the mass content of water in the anhydrous ethanol obtained by these methods is still higher than 1‰. How to further improve the purity of anhydrous ethanol and obtain high-purity ethanol is still one of the technical difficulties in the industry. Summary of the invention

[0009] In view of the above technical status, the present invention aims to obtain high-purity ethanol. To this end, the inventors have found after long-term scientific research in this field that by using hydrous ethanol, combining the permeable membrane dehydration technology with the dry adsorption dehydration technology, it is possible to achieve efficient dehydration of ethanol and obtain high-purity ethanol, wherein the mass content of water can be lower than 100ppm, or even lower than 30ppm. The high purity of the ethanol is unexpected by those skilled in the art. That is, the technical solution provided by the present invention is: a method for dehydrating hydrous ethanol, wherein the hydrous ethanol is first dehydrated by a permeable membrane and then dehydrated by dry adsorption.

[0010] In the present invention, the aqueous ethanol refers to a solution mainly comprising ethanol and water, wherein the mass percentage of ethanol is higher than 50%, further higher than 70%, higher than 90%, or even higher than 95%, for example, higher than 98%.

[0011] In the present invention, the permeable membrane has a selective water permeability function, that is, the ability of water molecules to permeate the permeable membrane is much higher than the ability of ethanol molecules to permeate the permeable membrane, so the permeable membrane can remove water from the hydrous ethanol. Preferably, the water content of the hydrous ethanol after dehydration through the permeable membrane is less than or equal to 1.0wt%, more preferably the water content is in the range of 0.5wt%-1.0wt%, and the ethanol content in the water permeating the permeable membrane is preferably less than 5wt%, and further preferably less than 1wt%.

[0012] In the present invention, taking into account the dehydration cost and reducing the difficulty of operation, it is preferred that the hydrous ethanol is dehydrated through the permeable membrane under liquid phase conditions, the operating temperature is preferably 70°C-105°C, the operating pressure is preferably 0.2kg-3.0kg, and the vacuum degree on the water permeable side is preferably 500Pa-3000Pa.

[0013] In the present invention, the permeable membrane is not limited, and any permeable membrane that can achieve the above-mentioned selective water permeability function can be used in the present invention. As an implementation method, the permeable membrane adopts the T / NaY zeolite molecular sieve composite membrane described in patent CN 112705053 A, and the preparation method of the composite membrane includes the following steps:

[0014] (1) dispersing NaY zeolite molecular sieve in deionized water to obtain a NaY zeolite molecular sieve dispersion; contacting the NaY zeolite molecular sieve dispersion with a porous carrier, introducing the NaY zeolite molecular sieve as a seed crystal on the porous carrier, and then removing impurities, drying, and calcining;

[0015] (2) placing the porous carrier treated in step (1) in a NaY zeolite molecular sieve synthesis solution, and growing NaY zeolite molecular sieve seed crystals by a hydrothermal method to obtain a carrier modified with a NaY zeolite molecular sieve coating;

[0016] (3) placing the carrier treated in step (2) in a T-type zeolite molecular sieve synthesis solution, and obtaining a T / NaY zeolite molecular sieve composite membrane using a hydrothermal method.

[0017] The T / NaY zeolite molecular sieve composite membrane can make the water content in the hydrous ethanol less than or equal to 1.0wt%, preferably in the range of 0.5wt%-1.0wt%, and the ethanol content in the water passing through the permeable membrane is preferably less than 5wt%.

[0018] In the present invention, the dry adsorption dehydration is performed by an adsorbent, and the adsorbent is not limited. Preferably, the adsorbent has high hydrophilicity and nanopores, for example, a highly hydrophilic zeolite molecular sieve, a highly hydrophilic membrane tube, etc. can be selected. Figure 1 This is a schematic diagram of water-containing ethanol passing through a highly hydrophilic membrane tube, where the small-diameter spheres refer to water molecules, the large-diameter spheres refer to ethanol, the micropores refer to the nanopores of the membrane tube, and the permeation of water refers to the water that passes through the membrane. Figure 1 As shown, due to the confinement effect, water molecules can be preferentially adsorbed on the adsorbent surface and then penetrate into the adsorbent pores, while ethanol macromolecules are difficult to adsorb on the adsorbent surface and cannot penetrate into the adsorbent pores, thereby achieving deep removal of water from ethanol.

[0019] The highly hydrophilic zeolite molecular sieve is not limited, and may be, for example, one or more of 3A, NaA, NaX, SSZ-13, etc.

[0020] The pore size of the nanopore is preferably less than 0.5 nm.

[0021] In the present invention, the method of using adsorbent for dehydration is not limited. For example, the hydrous ethanol is dehydrated through a permeable membrane to obtain a dehydrated product, which mainly contains ethanol and a small amount of water. The dehydrated product is recorded as crude ethanol, and the crude ethanol is transported to a drying adsorption tower filled with the adsorbent for dehydration.

[0022] In the present invention, the mass content of water in the crude ethanol after drying, adsorption and dehydration can be lower than 100 ppm, or even lower than 50 ppm.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention uses hydrous ethanol and combines the osmotic membrane dehydration technology with the dry adsorption dehydration technology to achieve efficient dehydration of ethanol and obtain high-purity ethanol, wherein the mass content of water can be lower than 100 ppm, or even lower than 50 ppm, far exceeding the purity of ethanol in the prior art, and achieving a technological breakthrough in this field.

[0025] (2) In the present invention, the aqueous ethanol can be dehydrated by osmotic membrane and dry adsorption in the liquid phase. Compared with vaporization dehydration, the requirements for equipment and the difficulty of operation are reduced, the cost is reduced, and it has the prospect of large-scale application.

[0026] (3) The present invention uses aqueous ethanol. Both osmotic membrane dehydration and dry adsorption dehydration belong to physical dehydration technology. No other substances need to be added, no new pollution is generated, and no subsequent additional treatment is required. In addition, the osmotic membrane can be operated continuously, has high dehydration efficiency and low energy consumption, thereby greatly reducing the energy consumption of ethanol purification, thereby reducing the purification cost.

[0027] (4) The dehydration and purification method of the present invention has great application prospects in the fields of preparing high-purity ethanol and recycling waste ethanol. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of aqueous ethanol passing through a highly hydrophilic membrane tube.

[0029] Figure 2 This is the test result of the micro-moisture analyzer on the crude ethanol side after the aqueous ethanol in Example 1 is dehydrated through the permeable membrane.

[0030] Figure 3 This is a gas chromatograph test chart of the membrane permeation side after the aqueous ethanol in Example 1 is dehydrated through the permeation membrane.

[0031] Figure 4 This is the test result of the micro-moisture analyzer on the crude ethanol side after the crude ethanol in Example 1 is dried, adsorbed and dehydrated by the adsorbent. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with the embodiments and drawings. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0033] Embodiment 1:

[0034] High-purity ethanol is obtained by using aqueous ethanol.

[0035] Hydrous ethanol is composed of ethanol and water, with ethanol accounting for 70% and water accounting for 30% by mass.

[0036] The aqueous ethanol is used to obtain high-purity ethanol, as follows:

[0037] (1) Dehydration of aqueous ethanol through a permeable membrane

[0038] The permeable membrane is a silicon dioxide membrane.

[0039] 100 kg of hydrous ethanol was separated and dehydrated through a permeable membrane at a flow rate of 5 kg / h, with an operating temperature of 90°C and a pressure of 1.8 kg.

[0040] The test method for the water content of the crude ethanol side after dehydration is as follows: a total of 1g of crude ethanol is tested in a moisture meter. Figure 2As shown, the water content is 4720.2ug. After calculation, the water content of the crude ethanol side is 4720.2 / 10 6 ×100%=4720.2ppm=0.47202%.

[0041] like Figure 3 As shown, the water content in the permeate side of the membrane was 99.1 wt % as measured by gas chromatography.

[0042] (2) Crude ethanol is dried, adsorbed and dehydrated by adsorbent

[0043] The adsorbent used was 3A spherical zeolite molecular sieve adsorbent, which has strong water absorption and a pore size of 0.3 nm, and is recorded as 3A adsorbent.

[0044] The crude ethanol is transported to a drying adsorption column filled with 3A adsorbent for dehydration. The crude ethanol flows in from the bottom of the drying column. As the inflow increases, the dehydrated ethanol flows out from the top of the drying column. In this process, since the 3A adsorbent has strong water absorption and a smaller pore size than the ethanol molecule, water is selectively adsorbed into the pores of the 3A adsorbent, while ethanol is not adsorbed and flows out from the top of the column.

[0045] The test method for the water content of the crude ethanol side after dehydration is as follows: a total of 1g of crude ethanol is tested in a moisture meter. Figure 4 As shown, the water content is 45.9ug. After calculation, the water content of the crude ethanol side is 45.9 / 10 6 ×100%=45.9ppm=0.00459%.

[0046] Embodiment 2:

[0047] High-purity ethanol is obtained by using aqueous ethanol.

[0048] Hydrous ethanol is composed of ethanol and water, with ethanol accounting for 60% and water accounting for 40% by mass.

[0049] The aqueous ethanol is used to obtain high-purity ethanol, as follows:

[0050] (1) Dehydration of aqueous ethanol through a permeable membrane

[0051] The permeable membrane is a T / NaY zeolite molecular sieve composite membrane described in patent CN 112705053 A. A porous α-Al2O3 hollow ceramic fiber tube is used as a support carrier, with a diameter of 12 mm and an average pore size of 2 μm. The T / NaY zeolite molecular sieve composite membrane is prepared on the porous carrier.

[0052] 100 kg of hydrous ethanol was separated and dehydrated through the permeable membrane at a flow rate of 5 kg / h. The testing method for the water content on the crude ethanol side after dehydration and the testing method for the water content on the membrane permeation side were the same as those in Example 1. The water content in the crude ethanol was measured to be 0.5 wt%, and the water content on the membrane permeation side was 99.4 wt%.

[0053] (2) Crude ethanol is dried and adsorbed by an adsorbent to remove water

[0054] The adsorbent used was 3A spherical zeolite molecular sieve adsorbent, which has strong water absorption and a pore size of 0.3 nm, and is recorded as 3A adsorbent.

[0055] The crude ethanol is transported to a drying adsorption column filled with 3A adsorbent for dehydration. The crude ethanol flows in from the bottom of the drying column. As the inflow increases, the dehydrated ethanol flows out from the top of the drying column. In this process, since the 3A adsorbent has strong water absorption and a smaller pore size than the ethanol molecule, water is selectively adsorbed into the pores of the 3A adsorbent, while ethanol is not adsorbed and flows out from the top of the column.

[0056] The testing method for the water content of the crude ethanol after dehydration was the same as that in Example 1, and the water content of the crude ethanol after dehydration was measured to be 50 ppm.

[0057] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for dehydrating aqueous ethanol, characterized in that: The aqueous ethanol is first dehydrated by passing through a permeable membrane and then by dry adsorption.

2. The dehydration method according to claim 1, wherein: The aqueous ethanol is a solution comprising ethanol and water, wherein the mass percentage of ethanol is higher than 50%; Preferably, the mass percentage of ethanol is higher than 70%; Preferably, the mass percentage of ethanol is higher than 90%, more preferably higher than 95%, and most preferably higher than 98%.

3. The dehydration method according to claim 1, wherein: The water content of the hydrous ethanol after dehydration through the permeable membrane is less than or equal to 1.0wt%; Preferably, the water content of the hydrous ethanol after dehydration through the permeable membrane is in the range of 0.5wt%-1.0wt%; Preferably, the water content of the hydrous ethanol after dehydration through the permeable membrane is in the range of 0.5wt%-1.0wt%, and the ethanol content in the water permeating the permeable membrane is less than 5wt%, more preferably less than 1wt%.

4. The dehydration method according to claim 1, wherein: The aqueous ethanol is dehydrated by passing through the permeable membrane under liquid phase conditions; Preferably, the hydrous ethanol is dehydrated by passing through the permeable membrane at a temperature of 70°C to 105°C under liquid phase conditions; Preferably, the hydrous ethanol is dehydrated by passing through the permeable membrane under a pressure of 0.2kg-3.0kg and liquid phase conditions; Preferably, the hydrous ethanol is dehydrated through the permeable membrane under liquid phase conditions, and the vacuum degree on the water permeable side is 500Pa-3000Pa.

5. The dehydration method according to claim 1, characterized in that: The permeable membrane adopts a T / NaY zeolite molecular sieve composite membrane, and the preparation method of the T / NaY zeolite molecular sieve composite membrane comprises the following steps: (1) dispersing NaY zeolite molecular sieve in deionized water to obtain a NaY zeolite molecular sieve dispersion; contacting the NaY zeolite molecular sieve dispersion with a porous carrier, introducing the NaY zeolite molecular sieve as a seed crystal on the porous carrier, and then removing impurities, drying, and calcining; (2) placing the porous carrier treated in step (1) in a NaY zeolite molecular sieve synthesis solution, and growing NaY zeolite molecular sieve seed crystals by a hydrothermal method to obtain a carrier modified with a NaY zeolite molecular sieve coating; (3) placing the carrier treated in step (2) in a T-type zeolite molecular sieve synthesis solution, and obtaining a T / NaY zeolite molecular sieve composite membrane using a hydrothermal method.

6. The dehydration method according to claim 1, characterized in that: The drying adsorption dehydration is performed by an adsorbent, wherein the adsorbent has high hydrophilicity and nanopores; Preferably, the adsorbent is a highly hydrophilic zeolite molecular sieve; Preferably, the highly hydrophilic zeolite molecular sieve is one or more of 3A, NaA, NaX, and SSZ-13; Preferably, the pore diameter of the nanopore is less than or equal to 0.5 nm.

7. The dehydration method according to claim 1, characterized in that: The hydrous ethanol is dehydrated through a permeable membrane to obtain a dehydrated product, which is referred to as crude ethanol. The crude ethanol is transported to a drying adsorption tower filled with the adsorbent for dehydration.

8. The dehydration method according to claim 1, characterized in that: The hydrous ethanol is dehydrated through the drying tower under liquid phase conditions; Preferably, the hydrous ethanol is dehydrated by passing through the drying tower at a temperature of 50°C to 70°C under liquid phase conditions; Preferably, the hydrous ethanol is dehydrated by passing through the drying tower under a pressure of 0.2kg-3.0kg and liquid phase conditions.

9. The dehydration method according to any one of claims 1 to 8, characterized in that: The mass content of water in the hydrous ethanol after dehydration by the adsorbent is less than 100 ppm.

10. The dehydration method according to claim 9, characterized in that: The mass content of water in the hydrous ethanol after dehydration by the adsorbent is less than 100 ppm, preferably less than 50 ppm.

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