Extractive distillation dehydration separation method of isopropanol and water azeotropic system

Abstract

The invention discloses an extractive distillation dehydration separation method of an isopropanol and water azeotropic system, and relates to the field of distillation dehydration. According to the method, an azeotropic entrainer methyl cyclohexane is added into a rectifying tower, the azeotropic entrainer methyl cyclohexane can be mixed with raw materials and can also be added at a position higher than a feeding position in the tower, and the azeotropic entrainer methyl cyclohexane and water form a new low-boiling-point azeotrope. According to the characteristics that an azeotrope formed by methylcyclohexane and water is an unstable azeotrope and the intersolubility of methylcyclohexane and water is low at normal temperature, a tower top reflux tank can be set as an oil-water separator to separate oil-phase methylcyclohexane and water in a water phase, the oil-phase methylcyclohexane is used as an azeotropic entrainer to flow back into the tower, the water is discharged as waste liquid, and the azeotrope is recycled. Therefore, the isopropanol is separated from the water to obtain the high-purity isopropanol. The method has the advantages of simple process, low energy consumption, high product purity, environment-friendly azeotropic entrainer and the like, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention relates to the field of distillation and dehydration, and in particular to an extraction distillation and dehydration separation method of an azeotropic system of isopropanol and water. Background Art

[0002] Isopropyl Alcohol (IPA), an important and common solvent, has a boiling point of 82.5°C. It is often used as an excellent solvent and cleaning agent in ink printing, optoelectronics, semiconductors, chemicals, energy, and medical and pharmaceutical industries. In industrial applications, the purity of isopropyl alcohol, especially the water content, is high, but isopropyl alcohol forms an azeotrope with water, and its boiling point is 80.0°C and the water content is 11.7wt%. The industrial preparation of isopropyl alcohol mainly adopts the propylene hydration method to obtain a water-containing isopropyl alcohol product, which needs to be refined and dehydrated to obtain a high-quality product. In addition, the isopropyl alcohol waste liquid in the printing industry, optoelectronics and semiconductor industries also contains a certain amount of water, and the waste liquid recycling and regeneration also requires refined dehydration. Due to the existence of the azeotropic phenomenon and the small difference between the boiling point of the azeotrope and the boiling point of isopropyl alcohol, it is difficult to obtain high-purity isopropyl alcohol by ordinary distillation operations.

[0003] The commonly used treatment methods in industry are as follows: azeotropic distillation, extractive distillation, adsorption separation, etc. Azeotropic distillation requires benzene as an azeotropic agent, but benzene is not very friendly to human health. Chinese patent CN117362156A uses n-butane, isobutane, n-pentane or isopentane as a stripping agent to separate isopropanol and water, but the operating temperature is higher than 140°C. Although it can remove water from isopropanol, it has high energy consumption. Extractive distillation also uses ethylene glycol, ethylene glycol methyl ether, anisole, propyl butyrate, isobutyl ester, diethylene glycol, etc. as extractants, which also have problems such as high energy consumption and low recovery rate of extractants. Adsorption separation method utilizes the difference in diameter size between isopropanol and water molecules, and uses solid adsorbent to selectively adsorb water without introducing third component impurities, such as Chinese patent CN107021872B uses 3A molecular sieve or 4A molecular sieve or lime particles or crushed corn kernels. However, the operation process of adsorption and desorption is non-steady-state, and the desorption liquid produces a large amount of isopropanol-containing wastewater, and the comprehensive treatment performance is poor. Chinese patent CN111848348 believes that the above method has the disadvantages of high energy consumption or discontinuous operation or complicated operation, and proposes a method for molecular sieve membrane pervaporation dehydration, but the technology provided by the patent requires preheating the raw liquid of isopropanol and water and then entering the membrane separation component for dehydration under the operating conditions of 100~130℃. In fact, there is also the problem of high energy consumption, and the membrane has a certain life limit, and the difficulty of membrane regeneration also creates the problem of high cost. Chinese patent CN117919747A introduces a method for azeotropic distillation of separation demembrane water and isopropanol. The corresponding process adopts a double-tower series distillation process, in which cyclohexane is used as an azeotropic agent. The process method is relatively complicated, and the operating temperature and operating pressure are both high, resulting in high energy consumption in the operation process. Therefore, it is very necessary to develop a simple process, economical and energy-saving isopropanol dehydration process. Summary of the invention

[0004] The object of the present invention is to solve the above-mentioned problems in the prior art and provide an extractive distillation dehydration separation method of an azeotropic system of isopropanol and water, for an isopropanol raw material with a water content of 1 wt% to 15wt% or an isopropanol waste liquid generated in the printing and cleaning industries, to obtain an isopropanol product with a water content of less than 0.5wt% by refining, dehydrating and purifying.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] The invention discloses an extractive distillation dehydration separation method for an azeotropic system of isopropanol and water, which adopts methylcyclohexane as an azeotropic entrainer to carry out distillation separation on a water-containing isopropanol raw material liquid.

[0007] The methylcyclohexane is mixed with the raw material liquid and then enters the distillation tower, or the methylcyclohexane and the raw material liquid enter the distillation tower at different feed ports, and the feed position of the methylcyclohexane is higher than the feed position of the raw material liquid.

[0008] The mass feed ratio of the raw material liquid to methylcyclohexane is raw material liquid: methylcyclohexane = 1: 0.1-0.5.

[0009] The top of the distillation tower is provided with a top condenser and an oil-water separation tank in sequence, and azeotropic distillation is performed in the distillation tower. The azeotrope of methylcyclohexane and water is evaporated from the top of the tower, and enters the oil-water separation tank for stratification after condensation. A part of the upper oil phase rich in methylcyclohexane is refluxed to the distillation tower, and the other part is mixed with the raw material liquid and sent to the distillation tower or directly to the azeotropic entrainer feed port of the distillation tower, and the lower water phase is discharged as waste liquid; and isopropyl alcohol is obtained as a product at the bottom of the distillation tower.

[0010] If the discharged wastewater contains isopropanol, it is sent to a dehydration tower for treatment. The binary azeotrope of isopropanol and water is evaporated from the top of the dehydration tower and returned to the distillation tower as feed after condensation.

[0011] The operating temperature of the oil-water separator is room temperature. At this temperature, the mutual solubility of the azeotropic entrainer and water is low, thus forming oil-water phase separation. A partition is designed from the bottom of the oil-water separator to two-thirds of the height from the top. The density of the azeotropic entrainer methylcyclohexane is smaller than that of water. Therefore, the azeotropic entrainer after phase separation is located in the upper layer, while the water is in the lower layer. The upper layer after phase separation overflows to the other side of the oil-water separator through the top of the partition, and the water remains on the feed side of the oil-water separator. The azeotropic entrainer methylcyclohexane on the oil side returns to the distillation tower as reflux liquid to continue to carry water as an entrainer, and the water on the water side is discharged, and isopropanol is obtained in the bottom of the tower.

[0012] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0013] The azeotropic entrainer methylcyclohexane of the present invention forms an azeotrope with water at normal pressure, and the azeotropic temperature is 61.7°C, which is lower than the boiling point of isopropanol (82.5°C), the boiling point of methylcyclohexane (101.1°C) and the boiling point of water (100°C) at normal pressure. Therefore, during azeotropic distillation, the azeotrope is extracted from the top of the distillation tower, and the operating temperature of the tower bottom is relatively low, and low-temperature distillation separation can significantly reduce energy consumption. Since the azeotropic entrainer methylcyclohexane and water form an azeotrope that is unstable, and the miscibility of methylcyclohexane and water is low at normal temperature, after the azeotropic product at the top of the distillation tower is condensed by a condenser, water and methylcyclohexane are stratified due to immiscibility.

[0014] The invention has the advantages of simple process, low energy consumption, high product purity, environmental friendliness of azeotropic entrainer, etc., and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the process flow of Example 1 of the present invention;

[0016] Figure 2This is a schematic diagram of the process flow of Example 2 of the present invention. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0018] See also Figure 1~2 The azeotropic entrainment distillation separation process of the present invention comprises a distillation tower, a mixer, a reboiler, a condenser, an oil-water separation tank, and auxiliary equipment such as pumps, valves, and decanters. The distillation tower of the present invention can be a packed tower or a plate tower, and the operating pressure of the distillation tower can be atmospheric pressure or negative pressure operation. The top reflux can be bubble point reflux or cold liquid reflux. The cold liquid reflux effect is better than the bubble point reflux separation effect, but the cold liquid reflux energy consumption is slightly higher, which can be weighed according to the specific situation, and other operating conditions can be adjusted according to the actual situation.

[0019] Example 1

[0020] Isopropanol containing 8% water (mass fraction) was used as the raw material. A plate distillation tower with 40 theoretical plates was used. The feed position of the raw material liquid was the 27th plate, the feed position of the azeotropic entrainer methylcyclohexane was the 2nd plate, the feed rate of the raw material liquid was 100 kg / hr, the feed rate of the azeotropic entrainer methylcyclohexane was about 38.5 kg / hr, and considering the reuse of methylcyclohexane, the water content of the azeotropic entrainer methylcyclohexane was about 0.013% (mass fraction). The top of the tower was bubbled and refluxed, and the reflux ratio was 9.53. Considering the loss of methylcyclohexane, the amount of supplementary azeotropic entrainer was 0.381 kg / hr, the top temperature was controlled at about 67°C, and the bottom temperature was controlled at about 82°C. After the azeotropic product is evaporated from the top of the tower and condensed and separated, part of the oil phase is directly refluxed to the distillation tower, and the other part is used as an azeotropic entrainer and mixed with the supplemented fresh azeotropic entrainer methylcyclohexane and then enters the tower from the second tower plate at the top of the tower. The water in the oil-water separation tank is discharged as waste water, and the product with an isopropyl alcohol content of 99.5% (mass fraction) is obtained in the bottom of the tower. The isopropyl alcohol recovery rate of the whole process is more than 99.5%. Figure 1 The logistics composition information corresponding to the process diagram is shown in Table 1.

[0021] Table 1

[0022]

[0023] Example 2

[0024] Using isopropanol containing 8% water (mass fraction) as raw material, a plate distillation tower with a theoretical plate number of 40 plates is used. The azeotropic entrainer methylcyclohexane is mixed with the raw material liquid and then fed. The feeding position is the 27th plate, and the total feed amount is 138.5 kg / hr. The azeotropic entrainer methylcyclohexane is mainly the circulation amount. The composition (mass fraction) of the circulating azeotropic entrainer methylcyclohexane stream is 98% methylcyclohexane, 1.9% isopropanol and 0.1% water. Considering the loss of methylcyclohexane, the fresh methylcyclohexane supplement amount is 0.5 kg / hr. The top of the tower is bubbled and refluxed, and the reflux ratio is 4.4. The top temperature is controlled at about 67°C, and the bottom temperature is controlled at about 82°C. After the azeotropic product is evaporated from the top of the tower and condensed and separated, part of the oil phase is directly refluxed to the distillation tower, and the other part is used as an azeotropic entrainer and mixed with the fresh azeotropic entrainer methylcyclohexane supplemented with the raw material liquid and then enters the tower from the 27th tower plate. The water in the oil-water separation tank is discharged as waste water, and the product with an isopropyl alcohol content of 99.5% (mass fraction) is obtained in the bottom of the tower. The isopropyl alcohol recovery rate of the whole process is more than 99.5%. This embodiment Figure 2 The logistics composition information corresponding to the process diagram is shown in Table 2.

[0025] Table 2

[0026]

[0027] Example 3

[0028] To compare the method of separating isopropanol and water using cyclohexane as an azeotropic entrainer in Chinese patent CN117919747A and the method proposed in the present invention, the raw material is the raw material in CN117919747A, the mass fraction of isopropanol in the raw material is 85.3%, and the mass fraction of water is 14.7%. When the process parameters of CN117919747A are used for separation and the process parameters of the present invention are used for separation to obtain the same product quality and recovery rate, the feed rate of the raw material liquid is 100 kg / h, and the energy consumption of the tower bottom reboiler when cyclohexane is used as the azeotropic entrainer is 11.9 kW higher than that of the present process, and the heat load of the tower bottom reboiler when cyclohexane is the azeotropic entrainer is 61.2 kW, while the heat load of the tower bottom reboiler when the process parameters of the present invention are 49.2 kW.

[0029] Example 4

[0030] In order to optimize different azeotropic entrainers, isopropanol containing 8% (mass fraction) of water is used as raw material, and the method proposed in this process is adopted. When the azeotropic entrainers are methylcyclohexane (azeotropic entrainer A), cyclohexane (azeotropic entrainer B), 1,1-dimethylcyclohexane (azeotropic entrainer C), 1,2-dimethylcyclohexane (azeotropic entrainer D), 1,3-dimethylcyclohexane (azeotropic entrainer E), and 1,4-dimethylcyclohexane (azeotropic entrainer F), the corresponding heat load data of the top condenser and the bottom reboiler are shown in Table 3 below. It can be seen from the data in the table that methylcyclohexane is the preferred azeotropic entrainer.

[0031] Table 3

[0032]

[0033] The invention has the advantages of simple process, low energy consumption, high product purity, environmental friendliness of azeotropic entrainer, etc., and is suitable for large-scale industrial production.

Claims

1. An extractive distillation dehydration separation method of an azeotropic system of isopropanol and water, characterized in that: Methylcyclohexane was used as an azeotropic entrainer to carry out distillation separation of aqueous isopropanol raw material liquid.

2. The extractive distillation dehydration separation method of an azeotropic system of isopropanol and water as claimed in claim 1, characterized in that: The methylcyclohexane is mixed with the raw material liquid and then enters the distillation tower.

3. The extractive distillation dehydration separation method of an azeotropic system of isopropanol and water as claimed in claim 1, characterized in that: The methylcyclohexane and the raw material liquid enter the distillation tower at different feed inlets, and the feed position of the methylcyclohexane is higher than the feed position of the raw material liquid.

4. The extractive distillation dehydration separation method of an azeotropic system of isopropanol and water as claimed in claim 1, characterized in that: The mass feed ratio of the raw material liquid to methylcyclohexane is raw material liquid: methylcyclohexane = 1: 0.1-0.

5.

5. The extractive distillation dehydration separation method of an azeotropic system of isopropanol and water as claimed in claim 1, characterized in that: A top condenser and an oil-water separation tank are arranged at the top of the distillation tower in sequence, and azeotropic distillation is carried out in the distillation tower. The azeotrope of methylcyclohexane and water is evaporated from the top of the tower, and enters the oil-water separation tank for stratification after condensation. A part of the upper oil phase rich in methylcyclohexane is refluxed to the distillation tower, and the other part is mixed with the raw material liquid and sent to the distillation tower or directly sent to the distillation tower, and the lower water phase is discharged as waste liquid; isopropyl alcohol is obtained at the bottom of the distillation tower.

6. The extractive distillation dehydration separation method of an azeotropic system of isopropanol and water as claimed in claim 1, characterized in that: If the wastewater contains isopropanol, it is sent to a dehydration tower for treatment. The binary azeotrope of isopropanol and water is evaporated from the top of the dehydration tower and returned to the distillation tower as feed after condensation.

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