A method for separating a methanol-methylal mixture

Abstract

The present invention discloses a method for separating a methanol-methylal mixture, and relates to the field of chemical separation technology. The main contents of the method are as follows: NMP waste liquid is subjected to light removal treatment to remove light component impurities such as water; the extractant NMP light removal waste liquid is countercurrently contacted with the methanol-methylal mixed liquid in an extractive distillation tower, and the tower top obtains a purity higher than 99.9 wt% methylal; the extractive distillation tower kettle material enters a methanol refining tower, and the tower top obtains a purity higher than 99 wt% methanol; the methanol refining tower kettle material enters a weight removal tower, and high-purity NMP steam is obtained at the top of the weight removal tower, and the tower kettle obtains heavy component impurities. The present invention uses NMP light removal waste liquid as an extractant, utilizes the coupling enhancement of the separation process, realizes the separation of methanol and methylal azeotropic system, and reduces production material consumption and energy consumption costs.

Description

Technical Field

[0001] The invention relates to the technical field of chemical separation, and in particular to a method for separating a methanol-methylal mixture. Background Art

[0002] Methylal (dimethoxymethane) is a colorless, clear, volatile, flammable liquid with a chloroform-like and pungent odor. Methylal has stable chemical properties and is relatively stable to alkali, but it is easy to react with dilute hydrochloric acid to decompose into formaldehyde and methanol under heating conditions. Methylal has good solubility and is soluble in water and a variety of organic solvents.

[0003] Methylal has a wide range of uses in the industrial field. It can be used as a solvent in the production of cosmetics, pharmaceuticals, industrial automotive products, pesticides, rubber industry, paints, inks and other products. In addition, methylal has good degreasing ability and volatility. When used as a cleaning agent, it can replace chlorinated solvents and reduce the emission of volatile organic compounds (VOCs).

[0004] However, in the production process of methylal, due to the azeotropic phenomenon between methylal and methanol, it is difficult to obtain a high-purity methylal product that meets the needs of industrial production by a simple distillation separation method. Therefore, developing a method for efficiently separating methylal from methanol is of great practical significance for improving the purity and separation efficiency of methylal.

[0005] At present, there are two main separation methods for methanol-methylal mixed system, one is pressure swing distillation, that is, using pressure change to change the relative volatility of components, so as to separate the mixture. For example, Chinese invention patent application CN104761430A discloses a process for separating methylal and methanol by pressure swing heat coupling distillation, in which a mixed solution of methanol and methylal is pumped into a low-pressure tower, and a methanol product is obtained from the bottom of the low-pressure distillation tower by utilizing the azeotropic characteristics of methanol and methylal; while the azeotropic solution at the top of the tower enters a high-pressure distillation tower, and the methylal product is obtained from the tower kettle of the high-pressure distillation tower by utilizing the relative volatility change of the methanol-methylal mixed solution, and the azeotropic substance at the top of the tower is circulated to the low-pressure distillation tower. The process operation is relatively complicated, and the equipment cost and energy consumption cost are both high. The other is an extractive distillation method, which introduces an extractant to change the relative volatility between key components in the original solution, that is, to change the interaction force between the components of the original solution, to form a new non-ideal solution, thereby achieving effective separation of substances in the fractionation tower. For example, Chinese patent CN 108569952B discloses a method for separating methanol-methylal by ionic liquid extraction and distillation, in which 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid is mixed as an extractant, and an extractive distillation tower can obtain a methylal product with a mass fraction higher than 99.9% at the top of the tower under normal pressure. For example, Chinese invention patent application CN112225650 A discloses a method for refining industrial-grade methylal to obtain high-purity methylal, in which polymethoxy dimethyl ether polymer is used as an extractant to further purify methylal. For example, Chinese invention patent application CN 102627536 A discloses an intermittent extraction and distillation separation method for methylal-methanol azeotropic mixture, in which propanol, isopropanol, alcohol, tert-butyl alcohol, 1,3-propylene glycol or dimethyl sulfoxide is used as an extractant, and by controlling the operating conditions of the extractive distillation tower, methylal product, methylal-methanol transition section I, methanol product and methanol-extractant transition section II are obtained at one time. Although the above methods can achieve the separation of methanol and methylal, the high energy consumption of the extractive distillation process and the extractant regeneration process has always restricted the industrial application of these methods. Summary of the invention

[0006] In view of the technical problems of complex process operation, high equipment cost and high energy consumption cost in the above-mentioned separation method of methanol-methylal mixed system, the present invention provides a method for separating a methanol-methylal mixture. The method utilizes the principle of coupling enhancement of separation process to couple the NMP waste liquid refining process with the methanol / methylal separation process, utilizes the significant difference in boiling points between NMP light removal waste liquid and methanol and methylal, uses the NMP light removal waste liquid as an extractant, sequentially realizes the separation and refining of methylal and methanol in a methanol-methylal mixed liquid, realizes the cascade utilization of energy, and saves energy and reduces consumption.

[0007] The invention provides a method for separating a methanol-methylal mixture. NMP waste liquid is preheated to obtain NMP hot waste liquid, the NMP hot waste liquid enters a light-removal device, light component impurities in the NMP waste liquid are removed, and NMP light-removal waste liquid is obtained; the NMP light-removal waste liquid is used as an extractant, the NMP light-removal waste liquid enters an extractive distillation tower to countercurrently contact with a methanol-methylal mixed liquid, and methylal with a purity higher than 99.9 wt % is obtained at the top of the extractive distillation device; the mixed liquid obtained at the bottom of the extractive distillation device enters a methanol refining device, methanol with a purity higher than 99.0 wt % is obtained at the top of the methanol refining device, and NMP primary light-removal waste liquid is obtained at the bottom; the NMP primary light-removal waste liquid enters a heavy-removal device, the NMP steam obtained at the top of the heavy-removal device is circulated for heat exchange with the NMP waste liquid, and heavy component impurities are removed at the bottom of the heavy-removal device.

[0008] Furthermore, the preheating of the NMP waste liquid is achieved by heat exchange with NMP steam through a preheating device, recovering most of the sensible heat and latent heat in the NMP steam, and obtaining NMP hot waste liquid. The feed temperature of the NMP waste liquid is room temperature, and the feed temperature of the NMP steam is 200°C-300°C.

[0009] Furthermore, the light component impurities removed from the NMP waste liquid are substances with a normal pressure boiling point lower than that of NMP, including at least two of water, methanol, isopropanol, acetone, propylene glycol methyl ether, propylene glycol monobutyl ether, propylene glycol methyl ether acetate, propylene glycol monobutyl ether acetate, ethyl lactate, butyl acetate, and dimethylacetamide.

[0010] Furthermore, the top temperature of the light removal unit is 40°C-200°C, the bottom temperature is 150°C-250°C, the operating pressure is 0.4 atm ~ 3.0 atm, the number of theoretical plates is 15 - 40, and the reflux ratio is 0.5 - 5.

[0011] Furthermore, the NMP content in the NMP light removal waste liquid is 80.0 wt% - 99.0 wt%.

[0012] Furthermore, in the extractive distillation device, the feed temperature of the NMP light waste liquid is 150°C-250°C, the feed mass flow rate ratio of the NMP light waste liquid to the methanol-methylal mixed liquid is 0.2~10:1, the operating pressure of the extractive distillation device is 0.4atm~3.0atm, the top temperature of the extractive distillation device is 30-60°C, the bottom temperature is 80-150°C, and the reflux ratio is 2-10.

[0013] Furthermore, the top temperature of the methanol refining unit is 30°C-90°C, the bottom temperature is 150°C-250°C, the operating pressure is 0.4 atm~3.0 atm, and the reflux ratio is 1-10.

[0014] Furthermore, the top temperature of the deweighting device is 170°C - 250°C, the bottom temperature is 200°C - 300°C, and the operating pressure is normal pressure.

[0015] The above-mentioned reflux ratio refers to the ratio of the mass flow rate of the reflux liquid returning to the device from the top of the distillation or refining device to the mass flow rate of the product at the top of the device.

[0016] The beneficial effects of the present invention are:

[0017] The invention uses NMP light waste liquid as an extractant and utilizes coupling enhancement of the separation process to realize azeotropic separation of methanol and methylal, which can not only make the mass concentrations of methylal and methanol as high as 99wt% or more, but also significantly reduce production material consumption and energy consumption costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0020] The process flow diagram of the present invention is as follows Figure 1 As shown, the specific embodiments are as follows: Example 1

[0021] After the NMP waste liquid with a mass flow rate of 3500 kg / h is heat exchanged with NMP steam in the preheating device, the obtained NMP hot waste liquid enters the light removal device. The top temperature of the light removal device is 100℃, the bottom temperature is 250℃, the operating pressure is 2.0 atm, the number of theoretical plates is 25, the reflux ratio is 2, and the bottom of the light removal device obtains a light removal waste liquid with a mass flow rate of 2834 kg / h and a temperature of 202℃. The light removal waste liquid enters the upper section of the extractive distillation device, and the methanol-methylal mixed liquid with a mass flow rate of 1000 kg / h enters the middle section of the extractive distillation device. The operating pressure of the extractive distillation device is 2.0 atm, the top temperature of the extractive distillation device is 50℃, the bottom temperature is 150℃, the reflux ratio is 3, the top of the extractive distillation device obtains a mass flow rate of 750 kg / h, the mass purity is 99.9 wt% methylal, and the bottom of the extractive distillation device obtains a mixed liquid with a mass flow rate of 3084 kg / h and a temperature of 115℃. The mixed liquid is pumped into the middle section of the methanol refining unit. The top temperature of the methanol refining unit is 70°C, the bottom temperature is 200°C, the operating pressure is 1.0 atm, the reflux ratio is 4, and the methanol with a temperature of 64°C, a mass flow rate of 250 kg / h, and a mass purity of 99.0 wt% is obtained from the top of the methanol refining unit. The NMP primary light-removal waste liquid obtained at the bottom of the methanol refining unit enters the de-heavy unit, and the NMP steam obtained at the top of the de-heavy unit enters the preheating unit and is circulated for preheating of the NMP waste liquid. Example 2

[0022] The NMP waste liquid was directly subjected to light removal treatment without preheating, and the other parameters were consistent with those in Example 1. Example 3

[0023] Without preheating, and without removing light treatment from the NMP waste liquid, the other parameters are consistent with those in Example 1. Example 4

[0024] The NMP waste liquid is not subjected to light removal treatment, and light component impurities with a boiling point lower than that of NMP are removed in a methanol refining device. The remaining parameters are consistent with those in Example 1.

[0025] The treatment effects of Examples 1 to 4 are shown in the following table.

[0026]

[0027] By comparing Example 1 and Example 2, it can be seen that without preheating, the total energy consumption of separating methanol-methylal mixed solution with NMP waste liquid will be significantly improved. By comparing Example 1 and Example 3, it can be seen that if the NMP waste liquid is not removed in advance, the light components in the NMP waste liquid will interfere, and the quality of the final obtained methylal and methanol products will be significantly reduced. By comparing Example 1 and Example 4, it can be seen that although the removal of light components can also be carried out in the methanol refining device, the mass concentration of the final obtained methylal is more obviously reduced, and the decline in the methanol mass concentration is close to 50%. Therefore, it can be seen from the above-mentioned embodiment that using NMP light-removing waste liquid as an extractant can not only achieve efficient separation of methanol-methylal mixed solution; and by recovering the NMP waste liquid regeneration treatment energy, the NMP light-removing process and the methanol-methylal separation process energy consumption can be significantly reduced, and the energy cascade utilization is realized.

Claims

1. A method for separating a methanol-methylal mixture, characterized in that: The NMP waste liquid is preheated to obtain NMP hot waste liquid, and the NMP hot waste liquid enters a light removal device to remove light component impurities in the NMP waste liquid to obtain NMP light removal waste liquid; the NMP light removal waste liquid is used as an extractant, and the NMP light removal waste liquid enters an extractive distillation tower to countercurrently contact with a methanol-methylal mixed liquid, and methylal with a purity higher than 99.9 wt% is obtained at the top of the extractive distillation device; the mixed liquid obtained at the bottom of the extractive distillation device enters a methanol refining device, and methanol with a purity higher than 99.0 wt% is obtained at the top of the methanol refining device, and NMP primary light removal waste liquid is obtained at the bottom; the NMP primary light removal waste liquid enters a heavy removal device, and the NMP steam obtained at the top of the heavy removal device is circulated for heat exchange with the NMP waste liquid, and heavy component impurities are removed at the bottom of the heavy removal device; The light component impurities include at least two of water, methanol, isopropanol, acetone, propylene glycol methyl ether, propylene glycol monobutyl ether, propylene glycol methyl ether acetate, propylene glycol monobutyl ether acetate, ethyl lactate, butyl acetate, and dimethylacetamide; The NMP content in the NMP light waste liquid is 80.0 wt% - 99.0 wt%; The preheating of NMP waste liquid is achieved by heat exchange with NMP steam through a preheating device. The feed temperature of NMP waste liquid is room temperature, and the feed temperature of NMP steam is 200°C-300°C. The top temperature of the light removal unit is 40℃-200℃, the bottom temperature is 150℃-250℃, the operating pressure is 0.4 atm ~3.0 atm, the number of theoretical plates is 15 - 40, and the reflux ratio is 0.5 - 5; In the extractive distillation device, the feed temperature of the NMP light waste liquid is 150°C-250°C, the feed mass flow rate ratio of the NMP light waste liquid to the methanol-methylal mixed liquid is 0.2-10:1, the operating pressure of the extractive distillation device is 0.4 atm-3.0atm, the top temperature of the extractive distillation device is 30-60°C, the bottom temperature is 80-150°C, and the reflux ratio is 2-10.

2. The method for separating a methanol-methylal mixture according to claim 1, characterized in that: The top temperature of the methanol refining device is 30°C-90°C, the bottom temperature is 150°C-250°C, the operating pressure is 0.4 atm~3.0atm, and the reflux ratio is 1-10.

3. The method for separating a methanol-methylal mixture according to claim 1, characterized in that: The top temperature of the deweighting device is 170°C - 250°C, the bottom temperature is 200°C - 300°C, and the operating pressure is normal pressure.

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