A method for separating methylcyclohexane and toluene

Abstract

The present invention discloses a method for separating methylcyclohexane and toluene. A bis(dimethoxytetra)arene crystal material is used to adsorb and separate a mixture containing toluene and methylcyclohexane. The bis(dimethoxytetra)arene crystal material selectively adsorbs and complexes with toluene to achieve the separation of toluene and methylcyclohexane. The chemical structural formula of the bis(dimethoxytetra)arene crystal material is as follows: The separation process of the present invention is simple in operation and has low equipment requirements; the separation process does not require rectification operation, has low energy consumption, saves energy, and reduces the production cost of methylcyclohexane; the crystal material used has high stability, high adsorption capacity and selectivity for toluene, good separation effect, and high purity of the toluene obtained by desorption.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorption separation, and particularly relates to a method for separating methylcyclohexane and toluene. Background Art

[0002] Methylcyclohexane (MCH) is an organic compound with high environmental protection properties, and has rich prospects whether as an organic solvent or a hydrogen storage material.

[0003] Since methylcyclohexane (oral LD50 in mice: 2250 mg / kg, inhalation in rats for 2 hours: LC50 41500 mg / m 3 ) belongs to low-toxic organic solvents, its inhalation toxicity is lower than that of toluene and its properties are similar to those of benzene and toluene. It can replace benzene-based and ketone solvents to a certain extent. However, the current situation is that the relatively low-cost toluene and xylene have not been replaced by the safer and more environmentally friendly methylcyclohexane.

[0004] However, with the increasing awareness of environmental protection, the market demand for methylcyclohexane is gradually increasing.

[0005] At present, methylcyclohexane is mainly used to replace benzene-based solvents such as benzene, toluene, and xylene in the fields of coatings, inks, and resin synthesis.

[0006] In addition, methylcyclohexane is also a hydrogen storage material that has received much attention. The liquid organic hydrogen carrier (LOHC) system composed of the methylcyclohexane-toluene system has characteristics such as a low melting point and a high boiling point compared with other organic hydrogen carriers. It can remain as a stable liquid with a low vapor pressure under normal conditions, which is convenient for transportation and not easily lost. In addition, compared with common high-pressure gaseous hydrogen storage and cryogenic liquid hydrogen storage, the liquid organic hydrogen carrier: (1) The hydrogenation process is reversible and has good repeatability; (2) It can be stored and transported at normal temperature and pressure, which is safe and suitable for long-distance transportation; (3) It can utilize existing infrastructure for storage and transportation, such as oil pipelines and gas stations.

[0007] In fact, the Hydrogen Energy Chain Technology Research Cooperation Group (AHEAD) composed of several Japanese companies has realized extracting hydrogen from methylcyclohexane to provide energy for the Mizue Power Plant.

[0008] At present, the main method for industrial production of methylcyclohexane is catalytic hydrogenation of toluene followed by separation and purification. Since the boiling points of methylcyclohexane (101.2 °C) and toluene (110.6 °C) are relatively close, separating methylcyclohexane from toluene by distillation usually involves huge energy consumption and high costs.

[0009] The patent specification with the publication number CN102675029A discloses a method for separating methylcyclohexane and toluene by differential pressure thermally coupled extractive distillation. This method uses phenol as the extractant, and the device employed includes a differential pressure thermally coupled extractive distillation column, an atmospheric column, a vacuum column, a phenol recovery column, a compressor, a main heat exchanger, an auxiliary condenser, a heat exchanger, a condenser, and a reboiler. Although this method improves the drawback of high energy consumption in traditional distillation processes, the equipment cost is high.

[0010] The patent specification with the publication number CN114085385A discloses a modified metal-organic framework capable of separating methylcyclohexane and impurity toluene. When the pressure is less than 0.2 kPa, the adsorption of toluene by this modified metal-organic framework takes precedence over that of methylcyclohexane, achieving the effect of separating toluene from methylcyclohexane under low pressure. Summary of the Invention

[0011] The present invention provides a method for separating methylcyclohexane and toluene, which uses bis(dimethoxytetrafluorophenyl)calix[5]arene crystal material to adsorb and separate the mixture containing toluene and methylcyclohexane. It has low energy consumption and a simple process, overcoming the defects of high energy consumption and cumbersome process existing in the separation technology of toluene and methylcyclohexane. The bis(dimethoxytetrafluorophenyl)calix[5]arene crystal material can adsorb toluene with high capacity and high selectivity from the mixture containing toluene and methylcyclohexane at normal temperature and pressure.

[0012] The specific technical solution is as follows:

[0013] A method for separating methylcyclohexane and toluene uses bis(dimethoxytetrafluorophenyl)calix[5]arene crystal material to adsorb and separate the mixture containing toluene and methylcyclohexane. The bis(dimethoxytetrafluorophenyl)calix[5]arene crystal material selectively adsorbs and complexes with toluene to achieve the separation of toluene and methylcyclohexane;

[0014] The chemical structural formula of the bis(dimethoxytetrafluorophenyl)calix[5]arene crystal material is as follows:

[0015]

[0016] Due to the difference in the molecular structures of toluene and methylcyclohexane, the bis(dimethoxytetrafluorophenyl)calix[5]arene crystal material can form a host-guest complex with toluene. This host-guest complex will gradually decomplex when heated, releasing the adsorbed toluene. The bis(dimethoxytetrafluorophenyl)calix[5]arene crystal material is chemically stable at the desorption temperature.

[0017] The bis(dimethoxytetra)arene crystal material can be obtained by recrystallization in a poor solvent followed by activation. Generally, the poor solvent used is methanol, but it is not limited thereto. The bis(dimethoxytetra)arene crystal material obtained by recrystallization can remove solvent molecules by heating and be activated under the condition of not less than 100 °C. The activation time can be not less than 2 hours. The activated bis(dimethoxytetra)arene crystal material can be directly used for the adsorption separation of a mixture containing toluene and methylcyclohexane.

[0018] In one embodiment, the separation method specifically includes: placing the bis(dimethoxytetra)arene crystal material in an atmosphere of mixed vapor containing toluene and methylcyclohexane. During the adsorption process, toluene in the mixed vapor will form a host-guest complex with the bis(dimethoxytetra)arene crystal material. The stoichiometric ratio of the host-guest complex is 1:2, that is, the bis(dimethoxytetra)arene crystal material has a high adsorption capacity for toluene.

[0019] In a preferred example, for the separation method of the present invention, the temperature of the adsorption separation is lower than 80 °C.

[0020] After the bis(dimethoxytetra)arene crystal material selectively adsorbs and complexes toluene to achieve the separation of toluene and methylcyclohexane, the mixture containing toluene and methylcyclohexane adsorbed on the surface of the bis(dimethoxytetra)arene crystal material can be removed by vacuum heating or reduced-pressure heating, and then the toluene adsorbed and complexed by the bis(dimethoxytetra)arene crystal material can be desorbed by heating to achieve the regeneration of the bis(dimethoxytetra)arene crystal material.

[0021] In a preferred example, the temperature of the vacuum heating or reduced-pressure heating is lower than 80 °C, for example, it can be 55 - 65 °C. Under the condition of lower than 80 °C, the host-guest complex still exists stably, while the mixture containing toluene and methylcyclohexane adsorbed on the surface can be volatilized and removed. By removing the mixture containing toluene and methylcyclohexane adsorbed on the surface, the purity of the separated toluene can be improved.

[0022] In a preferred example, the temperature of the thermal desorption is 100 - 120 °C. The desorption time can be adjusted according to the sample amount. At this temperature, the host-guest complex is unstable, and the adsorbed toluene molecules will be gradually released, while the bis(dimethoxytetra)arene crystal material is stable and only undergoes a change in crystal form during the desorption process.

[0023] As a general inventive concept, the present invention also provides the application of the bis(dimethoxytetra)arene crystal material in selectively adsorbing and complexing toluene in a mixture containing toluene and methylcyclohexane to achieve the separation of toluene and methylcyclohexane. The preferred technical solutions in the application can refer to the above separation method.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: the separation process is simple to operate and requires low equipment requirements; the separation process does not require rectification operation, has low energy consumption, saves energy, and reduces the production cost of methylcyclohexane; the crystal material used has high stability, high adsorption capacity and selectivity for toluene, good separation effect, and high purity of the desorbed toluene. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the powder X-ray diffraction (PXRD) pattern of the bis-dimethoxytetra[5]arene crystal material for Examples 1 to 3;

[0026] Figure 2 It is the gas chromatography characterization result diagram of the adsorption separation of methylcyclohexane and toluene by the bis-dimethoxytetra[5]arene crystal material in Example 3, where: the abscissa represents the retention time, with the unit of min; the ordinate represents the detector signal current intensity, with the unit of pA. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0028] For the operating methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0029] Example 1

[0030] Preparation of bis-dimethoxytetra[5]arene crystal material: Weigh 2 g of bis-dimethoxytetra[5]arene and place it in 20 mL of dichloromethane. Heat to boiling, add methanol dropwise until saturated, store the solution at 0 °C overnight, filter to collect the precipitated crystals, and vacuum dry the obtained crystals at 50 °C and activate them at 100 °C for 2 hours to obtain a yellow powder, which can be denoted as tetra[5]arene or T5.

[0031] The characterization data of the product prepared in this example are as follows:

[0032] T5, 1 H NMR (600 MHz, CD 2 Cl 2 , 298 K, ppm) δ 8.54 (s, 10H), 7.58 (d, 10H), 7.34 (d, 10H), 4.86 (s, 10H), 4.24 (s, 30H).

[0033] The PXRD detection result is as shown by line a in Figure 1 , and the obtained bis-dimethoxytetra[5]arene crystal material has good crystallinity.

[0034] Example 2

[0035] Adsorption of bis - dimethoxytac[5]arene crystal material on toluene or methylcyclohexane alone: Take 2 20 - mL culture bottles, add 1 mL of toluene and 1 mL of methylcyclohexane respectively, and name them T5 - toluene (or tac[5]arene + toluene) and T5 - methylcyclohexane (or tac[5]arene + methylcyclohexane). Take 10 mg of the bis - dimethoxytac[5]arene crystal material prepared in Example 1 and place it in two 5 - mL culture bottles. Place the two open 5 - mL culture bottles in two 20 - mL culture bottles, seal the 20 - mL culture bottles well, place them in a 25 °C water bath for 24 hours, and then place the obtained powder in a 60 °C vacuum oven for 30 minutes.

[0036] The characterization data of the product prepared in this example are as follows:

[0037] T5 - toluene, 1 H NMR(600 MHz, CD 2 Cl 2 , 298 K, ppm) δ8.54(s, 10H), 7.58(d, 10H), 7.34(d, 10H), 7.23(t, 4H), 7.34(d, 2H), 7.13(t, 4H), 4.86(s, 10H), 4.24(s, 30H), 2.33(s, 6H).

[0038] T5 - methylcyclohexane, 1 H NMR(600 MHz, CD 2 Cl 2 , 298 K, ppm) δ8.54(s, 10H), 7.58(d, 10H), 7.34(d, 10H), 4.86(s, 10H), 4.24(s, 30H).

[0039] 1 The H NMR results show that the bis - dimethoxytac[5]arene crystal material adsorbed toluene in a stoichiometric ratio of 1:2, and the adsorption amount of methylcyclohexane is very small.

[0040] As Figure 1 shown by the b - line in, relative to the PXRD pattern of the initially activated bis - dimethoxytac[5]arene crystal material, the PXRD pattern of the bis - dimethoxytac[5]arene crystal material after being placed in a toluene vapor atmosphere for some time has changed, indicating that its unit cell parameters have changed, meaning that toluene has been adsorbed into the bis - dimethoxytac[5]arene crystal material; as Figure 1As shown by the c line, compared with the PXRD pattern of the initial bis(dimethoxytetra)arene crystal material, the PXRD pattern of the bis(dimethoxytetra)arene crystal material after being placed in a methylcyclohexane vapor atmosphere for a period of time did not change, indicating that its unit cell parameters did not change, meaning that the bis(dimethoxytetra)arene crystal material has little adsorption capacity for methylcyclohexane.

[0041] Example 3

[0042] Adsorption of a 1:1 mixture of toluene and methylcyclohexane by the bis(dimethoxytetra)arene crystal material: Take a 20 mL culture bottle, add 0.50 mL of methylcyclohexane and 0.50 mL of toluene, and name it T5-mixture (or tetraarene + mixed sample). Take 10 mg of the bis(dimethoxytetra)arene crystal material prepared in Example 1 and place it in a 5 mL culture bottle. Place the open 5 mL culture bottle in the above 20 mL culture bottle, seal the 20 mL culture bottle, place it in a 25 °C water bath for 24 hours, and place the obtained powder in a 60 °C vacuum oven for 30 minutes.

[0043] The characterization data of the product prepared in this example are as follows:

[0044] T5-mixture, 1 H NMR (600 MHz, CD 2 Cl 2 , 298 K, ppm) δ 8.54 (s, 10H), 7.58 (d, 10H), 7.34 (d, 10H), 7.23 (t, 4H), 7.34 (d, 2H), 7.13 (t, 4H), 4.86 (s, 10H), 4.24 (s, 30H), 2.33 (s, 6H).

[0045] In 1 the H NMR spectrum, only the signals of the hydrogen atoms corresponding to toluene were found, indicating that the bis(dimethoxytetra)arene crystal material can selectively adsorb toluene with a high content ratio at room temperature and atmospheric pressure.

[0046] The PXRD test results are as Figure 1 shown by the d curve in. Compared with the PXRD pattern of the initially activated bis(dimethoxytetra)arene crystal material, the PXRD pattern of the bis(dimethoxytetra)arene crystal material after being placed in a mixed vapor of toluene and methylcyclohexane for a period of time changed, and the spectral change was similar to the PXRD pattern of the bis(dimethoxytetra)arene crystal material adsorbed with toluene alone, indicating that the bis(dimethoxytetra)arene crystal material can selectively adsorb toluene in a mixture of toluene and methylcyclohexane.

[0047] The results of headspace gas chromatography show that as Figure 2As shown, the bis-dimethoxytacn[5]arene crystal material can selectively adsorb toluene with a selectivity as high as 98.85%.

[0048] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for separating methylcyclohexane and toluene, characterized in that, a mixture containing toluene and methylcyclohexane is adsorbed and separated by using a bis(dimethoxytetra)arene crystal material, and the bis(dimethoxytetra)arene crystal material selectively adsorbs and complexes toluene to achieve the separation of toluene and methylcyclohexane; the chemical structural formula of the bis(dimethoxytetra)arene crystal material is as follows: the bis(dimethoxytetra)arene crystal material is obtained by recrystallization in a poor solvent and then activated; the activation temperature is not lower than 100 °C; the separation method specifically includes: placing the bis(dimethoxytetra)arene crystal material in an atmosphere of a mixed vapor containing toluene and methylcyclohexane; the temperature of the adsorption separation is lower than 80 °C.

2. The separation method according to claim 1, characterized in that, the poor solvent is methanol.

3. The separation method according to claim 1, characterized in that, after the bis(dimethoxytetra)arene crystal material selectively adsorbs and complexes toluene to achieve the separation of toluene and methylcyclohexane, vacuum heating or reduced-pressure heating is used to remove the mixture containing toluene and methylcyclohexane adsorbed on the surface of the bis(dimethoxytetra)arene crystal material, and then heating is used to desorb the toluene adsorbed and complexed by the bis(dimethoxytetra)arene crystal material to achieve the regeneration of the bis(dimethoxytetra)arene crystal material.

4. The separation method according to claim 3, characterized in that, the temperature of the vacuum heating or reduced-pressure heating is lower than 80 °C.

5. The separation method according to claim 3, characterized in that, the temperature of the heating desorption is 100-120 °C.

6. Application of the bis(dimethoxytetra)arene crystal material in selectively adsorbing and complexing toluene in a mixture containing toluene and methylcyclohexane to achieve the separation of toluene and methylcyclohexane, characterized in that, the chemical structural formula of the bis(dimethoxytetra)arene crystal material is as follows:

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