A method for separating toluene and methylcyclohexane

Abstract

The present invention discloses a method for separating toluene and methylcyclohexane, which utilizes hetero[3]aromatic hydrocarbon crystal materials to absorb and separate a mixture of toluene and methylcyclohexane. The chemical structure of the hetero[3]aromatic hydrocarbon crystal materials is as follows: The separation process of the present invention is simple to operate and has low equipment requirements; the separation process does not require distillation operation, has low energy consumption, saves energy, and reduces the production cost of toluene; the crystal materials used are highly stable and can be recycled without reducing the separation effect.

Description

Technical Field

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

[0002] The separation of toluene and methylcyclohexane is of great importance in the chemical and petrochemical industries. Toluene is a key petrochemical product used not only as a chemical raw material, pesticides, dyes, and synthetic resins, but also as a key component of gasoline. Methylcyclohexane is widely used in the production of nylon, paints, varnishes, and pharmaceutical intermediates, but also as an excellent solvent for dissolving a variety of organic compounds. In the chemical industry, methylcyclohexane is primarily derived from the catalytic hydrogenation of toluene, and the removal of unreacted toluene from the reactor wastewater stream is crucial. However, the very close boiling points of toluene (383.75K) and methylcyclohexane (374.15K) make their separation virtually impossible via traditional distillation processes. Currently, the main industrial methods for separating toluene and methylcyclohexane mixtures are extractive distillation and azeotropic distillation. However, these methods require high energy, are complex, and have high operating costs. Therefore, the development of simpler and more energy-efficient methods for separating toluene and methylcyclohexane is necessary.

[0003] Patent specification CN 102675029 A discloses a method for separating toluene and methylcyclohexane by differential pressure thermally coupled extractive distillation. This method uses phenol as the extractant and employs a differential pressure thermally coupled extractive distillation tower, an atmospheric pressure tower, a vacuum tower, a phenol recovery tower, a compressor, a main heat exchanger, an auxiliary condenser, a heat exchanger, a condenser, and a reboiler. While this method can separate methylcyclohexane with a purity exceeding 99% and consumes over 30% less energy than conventional extractive distillation towers, the distillation process still consumes significant energy.

[0004] The patent specification with publication number CN 202983257 U discloses a toluene distillation separation device, comprising a distillation tower (1), a condenser (2), and a gas-liquid separator (3). The condenser (2) is arranged above the gas-liquid splitter (3). The top of the distillation tower (1) is connected to the upper part of the gas-liquid separator (3) through a pipeline; the liquid phase interface (3a) in the middle of the gas-liquid splitter is connected to the distillation tower to form an external reflux; and the liquid phase outlet (3b) at the bottom of the gas-liquid splitter is connected to a water separation device (4) through a pipeline. Although the structure is simple and reasonable, it has a high separation efficiency when removing toluene. However, the distillation device has cumbersome connections, occupies a large space, and the experimental safety is not guaranteed.

[0005] Patent specification CN 213652324 U discloses a toluene separation tank device, comprising a separation tank body, four sets of baffles mounted within the body, and mounting grooves matching one side of the baffles on the inner surface of the body. A motor is disposed on one side of the body, the output end of the motor being connected to a rotating shaft, and a strip groove matching the rotating shaft is disposed within the body, the strip groove communicating with the mounting groove. The rotating shaft is rotatably connected to the body via a bearing. Four sets of gears are fixedly sleeved on the surface of the rotating shaft, and the gears are located within the mounting grooves. A rack is meshed and connected to one side of the gear, and the rack is fixedly connected to the baffles. Compared with the prior art, this utility model achieves the following beneficial effects: the provision of gears effectively avoids the cumbersome disassembly process when the multiple baffles on the device become damaged after long-term use, facilitates convenient replacement of the baffles, and greatly improves the disassembly efficiency of the device. However, the separation tank device still suffers from drawbacks such as complex connections, large equipment size, and low separation efficiency.

[0006] Taking advantage of the differences in molecular size and geometry between toluene and methylcyclohexane, the use of ordered porous materials for adsorption separation is an effective separation method. For example, metal-organic frameworks (MOFs) have been experimentally studied for the adsorption separation of toluene and methylcyclohexane. However, due to their very close molecular sizes, the design and synthesis of suitable MOFs for the separation of toluene and methylcyclohexane is a challenge. In addition, MOFs composed of reversible metal-coordination bonds are not stable enough for practical recycling applications. Therefore, there is an urgent need to develop new stable and recyclable adsorbent materials for the effective separation of toluene and methylcyclohexane. Summary of the Invention

[0007] In view of the shortcomings in this field and the defects in the separation technology of toluene and methylcyclohexane, such as high energy consumption, complicated process and the need for high-purity desorbent, the present invention provides a method for separating toluene and methylcyclohexane, which utilizes hetero[3]aromatic crystal materials to adsorb and separate the mixture of toluene and methylcyclohexane, with low energy consumption and simple process.

[0008] A method for separating toluene and methylcyclohexane, wherein a mixture of toluene and methylcyclohexane is separated by adsorption using a hetero[3]aromatic hydrocarbon crystal material, wherein the chemical structure of the hetero[3]aromatic hydrocarbon crystal material is as follows:

[0009]

[0010] The toluene and methylcyclohexane mixture is a mixed vapor or mixed solution of methylcyclohexane and toluene. Preferably, the volume ratio of toluene to methylcyclohexane in the toluene and methylcyclohexane mixture is 1:1.

[0011] The hetero[3]arene crystalline material is an existing material, as disclosed by Jiong Zhou et al. in Chemical Communications, Vol. 52, 2016, pp. 1622-1624. Preferably, the hetero[3]arene crystalline material is activated after recrystallization in a poor solvent before use. The poor solvent may be acetone. The hetero[3]arene crystalline material obtained by recrystallization can be activated by heating to remove solvent molecules. Preferably, the activation temperature is not less than 150° C. and the activation time is not less than 2 hours. The activated hetero[3]arene crystalline material can be directly used for the adsorption separation of a mixture of toluene and methylcyclohexane.

[0012] The specific steps of using hetero[3]arene crystal material to adsorb and separate a mixture of toluene and methylcyclohexane are as follows: placing the hetero[3]arene crystal material in a mixed vapor atmosphere or mixed solution of methylcyclohexane and toluene at a temperature of less than 80°C. The adsorption time can be changed with factors such as the sample amount and the proportion of toluene in the mixture. During the adsorption process, the hetero[3]arene crystal material undergoes a change in crystal form. Due to the multiple non-covalent bond interactions between CH-π and CH-O, the toluene in the mixed vapor forms a host-guest complex with the hetero[3]arene, and the stoichiometric ratio of the host-guest complex is 1:1.

[0013] After the hetero[3]arene crystalline material is completely adsorbed in the mixed vapor atmosphere or mixed solution of toluene and methylcyclohexane, the hetero[3]arene crystalline material is removed, and then vacuum heating or reduced pressure heating is used to remove the toluene and methylcyclohexane mixture adsorbed on the surface of the hetero[3]arene crystalline material. Preferably, the temperature of the vacuum heating or reduced pressure heating is less than 80°C. The heating time can be adjusted according to the sample amount. Under conditions below 80°C, the host-guest complex still exists stably, and the toluene and methylcyclohexane mixture adsorbed on the surface can be gradually removed. By removing the mixed vapor or mixed solution adsorbed on the surface, the purity of the toluene separated by adsorption can be further improved.

[0014] Heating desorption can be used to remove the toluene adsorbed and complexed by the hetero[3]arene crystalline material, while simultaneously regenerating the hetero[3]arene crystalline material. The desorption time can be adjusted according to the sample amount. Preferably, the heating temperature is 80 to 100°C. At this temperature, the host-guest complex is unstable, and the adsorbed toluene molecules will gradually be released, while the hetero[3]arene crystalline material is stable, and only the crystal form changes during the desorption process. After desorption is completed, the regenerated hetero[3]arene crystalline material is obtained, which can be used to adsorb and separate toluene and methylcyclohexane for the next cycle.

[0015] Due to the difference in the molecular structures of toluene and methylcyclohexane, the hetero[3]arene crystalline material can form a host-guest complex with toluene in a stoichiometric ratio of 1:1. The host-guest complex gradually decomplexes upon heating, releasing the adsorbed toluene. The hetero[3]arene crystalline material is stable at the desorption temperature and can be reused after the desorption process is complete without loss of selectivity.

[0016] Beneficial effects of the present invention:

[0017] Compared with the prior art, the present invention has the following main advantages: the separation process is simple to operate and has low equipment requirements; the separation process does not require distillation operation, has low energy consumption, saves energy, and reduces the production cost of toluene; the crystal material used is highly stable and can be recycled without reducing the separation effect.

[0018] The use of hetero[3]aromatics enables the separation of toluene from a mixture of gaseous toluene and methylcyclohexane with a purity of 100% and the separation of toluene from a mixture of liquid toluene and methylcyclohexane with a purity close to 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 These are the X-ray diffraction (PXRD) data of hetero[3]arene after adsorption onto toluene and methylcyclohexane vapors.

[0020] Figure 2 Headspace gas chromatography of mixed vapor adsorption of hetero[3]aromatic hydrocarbons toluene and methylcyclohexane.

[0021] Figure 3 This is a cyclic performance diagram of the adsorption of mixed vapor of toluene and methylcyclohexane by hetero[3]aromatic hydrocarbons.

[0022] Figure 4 These are the PXRD data of hetero[3]arene after adsorption into toluene and methylcyclohexane solutions.

[0023] Figure 5 Headspace gas chromatography of a mixed solution of hetero[3]aromatic hydrocarbons adsorbed on toluene and methylcyclohexane. DETAILED DESCRIPTION

[0024] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0025] Example 1

[0026] Preparation of hetero[3]arene crystalline material: Weigh 2 g of hetero[3]arene and place it in 20 mL of acetone. Heat to boiling, add acetone dropwise until it is completely dissolved, store the solution at 0°C overnight, filter and collect the precipitated crystals, dry the obtained crystals in a vacuum at 50°C, and activate at 150°C for 2 hours to obtain a white powder, which is recorded as 1.

[0027] The product characterization data prepared in this example are as follows:

[0028] 1, 1 H NMR (600MHz, CDCl3, 293K, ppm) δ7.11 (d, J = 6Hz, 2H), 6.66 (d, J = 6Hz, 2H), 6.28 (s, 2H), 6.22 (s, 2H), 4.11-3.97(m,8H),3.83(s,6H),3.64(s,6H),3.57(s,6H),3.40(d,J=18Hz,2H),1.39(t,J=6Hz,6H).

[0029] The PXRD test results are as follows Figure 1 As shown, the obtained hetero[3]arene crystalline material has good crystallinity.

[0030] Example 2

[0031] Adsorption of hetero[3]aromatic hydrocarbon crystal materials on gaseous toluene or methylcyclohexane alone: ​​Take two 20 mL inoculum bottles, add 1 mL of toluene and 1 mL of methylcyclohexane respectively, and name them 1-Tol and 1-MCH. Take 20 mg of the hetero[3]aromatic hydrocarbon crystal material prepared in Example 1 and place them in two 4 mL open inoculum bottles respectively. Place the two open 4 mL inoculum bottles in two 20 mL inoculum bottles respectively. Seal the 20 mL inoculum bottles and place them in a 25°C water bath for 12 hours. Place the obtained powder in a 50°C vacuum oven for 30 minutes.

[0032] The product characterization data prepared in this example are as follows:

[0033] 1-Tol, 1 H NMR (600MHz, CDCl3, 293K, ppm) δ7.11-7.07(m,5H),7.11(d,J=6Hz,2H),6.66(d,J=6Hz,2H),6.28(s,2H),6.22(s,2H ), 4.11-3.97 (m, 8H), 3.83 (s, 6H), 3.64 (s, 6H), 3.57 (s, 6H), 3.40 (d, J = 18Hz, 2H), 2.29 (s, 3H), 1.39 (t, J = 6Hz, 6H).

[0034] 1-MCH,1 H NMR (600MHz, CDCl3, 293K, ppm) δ7.11 (d, J = 6Hz, 2H), 6.66 (d, J = 6Hz, 2H), 6.28 (s, 2H), 6.22 (s, 2H), 4.11-3.97(m,8H),3.83(s,6H),3.64(s,6H),3.57(s,6H),3.40(d,J=18Hz,2H),1.39(t,J=6Hz,6H).

[0035] 1 H NMR results showed that the hetero[3]arene crystalline material adsorbed toluene in a stoichiometric ratio of 1:1, but did not adsorb p-methylcyclohexane.

[0036] The PXRD test results are as follows Figure 1 As shown, compared with the PXRD spectrum of the initially activated hetero[3]aromatic hydrocarbon crystal material, the PXRD spectrum of the hetero[3]aromatic hydrocarbon crystal material after being placed in toluene vapor for a period of time changes, which indicates that its unit cell parameters have changed, meaning that toluene has been adsorbed into the hetero[3]aromatic hydrocarbon crystal material; the spectrum of the hetero[3]aromatic hydrocarbon crystal material after being placed in methylcyclohexane vapor for a period of time has almost no change, indicating that its unit cell parameters have almost no change, meaning that the hetero[3]aromatic hydrocarbon crystal material has no adsorption capacity for methylcyclohexane.

[0037] Example 3

[0038] Adsorption of 1:1 (v:v) mixed vapor of toluene and methylcyclohexane by hetero[3]aromatic crystalline material: Take a 20 mL inoculum bottle, add 1 mL of toluene and 1 mL of methylcyclohexane, and name it 1-Tol-MCH. Take 20 mg of the hetero[3]aromatic crystalline material prepared in Example 1 and place it in a 4 mL open inoculum bottle. Place the open 4 mL inoculum bottle in the above 20 mL inoculum bottle. Seal the 20 mL inoculum bottle and place it in a 25°C water bath for 24 hours. Place the obtained powder in a 50°C vacuum oven for 30 minutes.

[0039] The product characterization data prepared in this example are as follows:

[0040] 1-Tol-MCH, 1H NMR (600MHz, CDCl3, 293K, ppm) δ7.11-7.07(m,5H),7.11(d,J=6Hz,2H),6.66(d,J=6Hz,2H),6.28(s,2H),6.22(s,2H ), 4.11-3.97 (m, 8H), 3.83 (s, 6H), 3.64 (s, 6H), 3.57 (s, 6H), 3.40 (d, J = 18Hz, 2H), 2.29 (s, 3H), 1.39 (t, J = 6Hz, 6H).

[0041] exist 1 Only the signal of hydrogen atoms corresponding to toluene was found in the H NMR spectrum, which indicates that the hetero[3]arene crystal material can selectively adsorb toluene.

[0042] The PXRD test results are as follows Figure 1 As shown, compared with the PXRD spectrum of the initially activated hetero[3]arene crystal material, the PXRD spectrum of the hetero[3]arene crystal material after being placed in the mixed vapor of toluene and methylcyclohexane for a period of time changes, and the spectrum change is the same as that of 1-Tol, which indicates that the hetero[3]arene crystal material can selectively adsorb toluene.

[0043] The results of headspace gas chromatography are as follows Figure 2 As shown, the results indicate that hetero[3]arene crystalline materials can selectively adsorb toluene with a selectivity of 100%.

[0044] Example 4

[0045] Recycling of hetero[3]arene crystals: The hetero[3]arene crystals saturated with toluene were heated in a vacuum oven at 100°C for 2 hours. The toluene adsorbed and complexed by the hetero[3]arene crystals was removed by thermal desorption, thereby regenerating the hetero[3]arene crystals. The process of Examples 3 and 4 was repeated with 20 mg of the regenerated hetero[3]arene crystals.

[0046] The results of headspace gas chromatography are as follows Figure 3 As shown, it is shown that the hetero[3]arene crystal material can selectively adsorb toluene with a selectivity of up to 100%, and its selectivity does not decrease after being reused 5 times.

[0047] Example 5

[0048] Adsorption of hetero[3]aromatic hydrocarbon crystal materials on liquid toluene or methylcyclohexane alone: ​​Take two 5 mL inoculum bottles, add 1 mL of toluene and 1 mL of methylcyclohexane respectively, and name them 1+Tol and 1+MCH. Take 20 mg of the hetero[3]aromatic hydrocarbon crystal material prepared in Example 1 and place them in two 5 mL open inoculum bottles respectively. Seal the two open 5 mL inoculum bottles and place them in a 25°C water bath for 1 hour. Place the obtained powder in a 50°C vacuum oven for 30 minutes.

[0049] The product characterization data prepared in this example are as follows:

[0050] 1+Tol, 1 H NMR (600MHz, CDCl3, 293K, ppm) δ7.11-7.07(m,5H),7.11(d,J=6Hz,2H),6.66(d,J=6Hz,2H),6.28(s,2H),6.22(s,2H ), 4.11-3.97 (m, 8H), 3.83 (s, 6H), 3.64 (s, 6H), 3.57 (s, 6H), 3.40 (d, J = 18Hz, 2H), 2.29 (s, 3H), 1.39 (t, J = 6Hz, 6H).

[0051] 1+MCH, 1 H NMR (600MHz, CDCl3, 293K, ppm) δ7.11 (d, J = 6Hz, 2H), 6.66 (d, J = 6Hz, 2H), 6.28 (s, 2H), 6.22 (s, 2H), 4.11-3.97(m,8H),3.83(s,6H),3.64(s,6H),3.57(s,6H),3.40(d,J=18Hz,2H),1.39(t,J=6Hz,6H).

[0052] 1 H NMR results showed that the hetero[3]arene crystalline material adsorbed toluene in a stoichiometric ratio of 1:1, but did not adsorb p-methylcyclohexane.

[0053] The PXRD test results are as follows Figure 4 As shown, compared with the PXRD spectrum of the initially activated hetero[3]arene crystal material, the PXRD spectrum of the hetero[3]arene crystal material after being placed in the toluene solution for a period of time changes, which indicates that its unit cell parameters have changed, meaning that toluene has been adsorbed into the hetero[3]arene crystal material; the spectrum of the hetero[3]arene crystal material after being placed in the methylcyclohexane solution for a period of time changes very little, indicating that its unit cell parameters have almost no change, meaning that the hetero[3]arene crystal material has no adsorption capacity for methylcyclohexane.

[0054] Example 6

[0055] Adsorption of hetero[3]aromatic hydrocarbon crystalline materials on a 1:1 (v:v) mixed solution of toluene and methylcyclohexane: Take a 5 mL inoculum bottle, add 1 mL of toluene and 1 mL of methylcyclohexane, and name it 1+Tol+MCH. Take 20 mg of the hetero[3]aromatic hydrocarbon crystalline material prepared in Example 1 and place it in a 5 mL open inoculum bottle. Seal the 5 mL inoculum bottle and place it in a 25°C water bath for 2 hours. Place the resulting powder in a 50°C vacuum oven for 30 minutes.

[0056] The product characterization data prepared in this example are as follows:

[0057] 1+Tol+MCH, 1 H NMR (600MHz, CDCl3, 293K, ppm) δ7.11-7.07(m,5H),7.11(d,J=6Hz,2H),6.66(d,J=6Hz,2H),6.28(s,2H),6.22(s,2H ), 4.11-3.97 (m, 8H), 3.83 (s, 6H), 3.64 (s, 6H), 3.57 (s, 6H), 3.40 (d, J = 18Hz, 2H), 2.29 (s, 3H), 1.39 (t, J = 6Hz, 6H).

[0058] exist 1 Only the signal of hydrogen atoms corresponding to toluene was found in the H NMR spectrum, which indicates that the hetero[3]arene crystal material can selectively adsorb toluene.

[0059] The PXRD test results are as follows Figure 4 As shown, compared with the PXRD spectrum of the initially activated hetero[3]arene crystal material, the PXRD spectrum of the hetero[3]arene crystal material after being placed in a mixed solution of toluene and methylcyclohexane for a period of time changes, and the spectrum change is the same as that of 1+Tol, which indicates that the hetero[3]arene crystal material can selectively adsorb toluene.

[0060] The results of headspace gas chromatography are as follows Figure 5 As shown, the results indicate that hetero[3]arene crystalline materials can selectively adsorb toluene with a selectivity of 98.98%.

Claims

1. A method for separating toluene and methylcyclohexane, characterized in that, A mixture of toluene and methylcyclohexane is separated by adsorption using hetero[3]arene crystal materials, wherein the chemical structure of the hetero[3]arene crystal materials is as follows: The toluene and methylcyclohexane mixture is a mixed vapor or mixed solution of methylcyclohexane and toluene; The adsorption temperature is less than 80°C.

2. The method for separating toluene and methylcyclohexane according to claim 1, wherein After the adsorption is completed, vacuum heating or reduced pressure heating is used to remove the toluene and methylcyclohexane mixture adsorbed on the surface of the hetero[3]arene crystal material, and the temperature of the vacuum heating or reduced pressure heating is less than 80°C.

3. The method for separating toluene and methylcyclohexane according to claim 1, wherein The toluene adsorbed and complexed by the hetero[3] aromatic hydrocarbon crystal material is removed by heating and desorption, thereby achieving the regeneration of the hetero[3] aromatic hydrocarbon crystal material; the heating temperature is 80 to 100°C.

4. The method for separating toluene and methylcyclohexane according to claim 1, wherein The hetero[3]arene crystalline material is first recrystallized in a poor solvent and then activated before use.

5. The use according to claim 4, characterized in that The poor solvent is acetone.

6. The use according to claim 4, characterized in that The activation temperature is not lower than 150° C. and the activation time is not less than 2 hours.

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