JPH0521601B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for separating, purifying, and recovering high-boiling components by rectifying a raw material containing high-boiling components, low-boiling components, and dissolved gases. [Prior Art] Generally, a rectification method is used to separate high-boiling components and low-boiling components. The rectification columns used in the rectification method can be roughly divided into tray type and packed type. In general, when it is carried out industrially on a large scale, a plate rectification column is advantageous in terms of operational stability. [Problems to be solved by the invention] In industrial implementation, in addition to high-boiling components and low-boiling components, systems containing dissolved gas components in the raw materials, such as formaldehyde-methanol-ammonia systems, are used. , N,N-dimethylformaldehyde-methanol-dimethylamine type and trioxane-benzene-formaldehyde type are surprisingly common. When high-boiling components are separated and recovered from raw materials containing dissolved gas components using a rectification method using a plate rectification column, an unexpectedly large amount of gas components dissolves and contaminates the high-boiling components. An unexpected phenomenon may occur in which it is not possible to obtain an object of desired quality, or in other words, only an object of undesirable quality is obtained. Considering the boiling point of the pure substance in question, the boiling point of the mixed gas component is much lower than the boiling point of the low-boiling component, but the gas component cannot be removed from the target high-boiling component. What you say happens. That is, such a phenomenon is particularly likely to occur in the above-mentioned systems, such as trioxane (high-boiling component; boiling point: 114.5°C/757mmHg).
Benzene (low boiling component; boiling point 80.1℃/760mmHg) -
Formaldehyde (gas component; boiling point -19.3℃/
760mmHg) system. Therefore, in general, in order to remove gas components from high-boiling components, a degassing step is usually performed, if necessary.
Alternatively, an extraction process is provided. [Means for Solving the Problems] The present inventors have developed a tray-type method for separating and recovering such high-boiling components, low-boiling components, and high-boiling components by rectification of raw materials containing dissolved gases. Surprisingly, the present inventors have discovered that the removal efficiency of gas components can be dramatically increased when a part of the rectification column is of a packed type, leading to the completion of the present invention. In other words, the present invention provides deaeration,
This is a method for separating and recovering high-purity high-boiling components in the above-mentioned system, using only rectification without using any other means such as extraction, and while taking advantage of the industrial advantages of the plate rectification column. be. That is, the present invention provides a method for separating a mixture containing one or more types of high-boiling components, low-boiling components, and dissolved gas components into high-boiling components, low-boiling components, and dissolved gas components by distillation. This is a rectification method characterized by using a rectification column in which a part of the rectification column is a packed type rectification column. There are no particular restrictions on the diameter and overall height of the rectification column, the height of the tray-type section, and the number of plates, and they can be selected as appropriate depending on the raw material and the purpose of the rectification operation. Designed. Furthermore, there are no particular restrictions on the type of shelf or the type of filling material. Commonly used types of shelves include bubble bell shelves, valve trays, and perforated plates. As a filling, Raschig ring, Lessing ring, saddle mold, Stedman, etc.
There are many different types, such as Patzking, Dickson Tamaki, McMahon Patzking, etc. The rectification operation, ie, the mode of operation of the rectification column, may be either batchwise or continuous, but in large-scale industrial implementation, continuous mode is preferred. When carrying out the present invention, the detailed design of the rectification column and rectification operating conditions such as pressure, temperature, reflux ratio, etc.
Depending on the purpose of the rectification operation, chemical engineering studies based on basic data such as physical property values and actual measured values of the compounds that make up the raw material (feed liquid), as well as the results of demonstration experiments using pilot plants, are used. It is determined by performing an optimization study. [Effects of the Invention] The height of the packed bed portion of the rectification column at which the effects of the present invention can be fully exhibited varies depending on the raw material and the purpose of the rectification operation, but in general, the height of the tray-type portion In other words, it is 5% or more of the total tower height, and usually 10 to 30% is sufficient. When the height ratio of the packed bed portion exceeds 50%, the stability of the distillation operation, that is, the operability, decreases, and the effect of the present invention, in which the packed bed portion is disposed in a part of the tray distillation column, diminishes. In addition, it is disadvantageous in terms of economic efficiency in equipment design and construction, and the advantage of the plate distillation column is reduced. Systems in which the effects of the present invention are noticeable (systems in which it is difficult to remove gas components from high-boiling components) generally include:
This is a system in which the affinity between the gas component and the high-boiling component is stronger than the affinity between the gas component and the low-boiling component. In such a system, in order to separate and recover high-purity high-boiling components from which gas components have been sufficiently removed, it is preferable that the packed section of the rectification column is located in the lower half of the column, and the continuous section is In this case, it is preferable to locate it below the raw material supply port [stage]. At this time, the positional relationship between the tiered part and the filling part is such that the filling part is installed below the tiered part. In addition, if desired, a filling type part may be inserted in the middle of the shelf type part, or in other words, the shelf type part may be installed above and below the filling type part. Generally, the purpose can be sufficiently achieved by installing a packed part below the tiered part, or in other words, by installing a tiered layer above the packed layer. As mentioned above, there are many systems from which high-purity high-boiling components can be obtained according to the present invention, such as trioxane,
High purity trioxane with a sufficiently low formaldehyde content can be separated and recovered from a raw material (supply liquid) containing benzene and formaldehyde. Hereinafter, the effects and embodiments of the present invention will be specifically explained by showing Examples and Comparative Examples. They are not intended to limit the scope of the embodiments or specifications. Example 1 A batch rectification operation was carried out using a rectification column in which a packed distillation column was connected in series under a plate-type distillation column with a column diameter of 50 mm. The tiered part is a so-called older tower equipped with perforated plates with a tier interval of 50 mm. A packed column with a height of 500 mm filled with stainless steel Raschig rings [1 liter] with a diameter of 6 mm and a length of 6 mm was used for the filling type part. A flask with a capacity of 2 liters was connected to the bottom of the column to form an evaporator. In the evaporator, trioxane 74.8% by weight, benzene
Raw materials containing 25.0% by weight of formaldehyde, 0.16% by weight of formaldehyde, and a trace amount of low-boiling components such as methanol were charged. According to a conventional method, the reactor was operated at normal pressure and a reflux ratio of 3, and a distillate containing benzene and formaldehyde was taken out from the top of the column, and trioxane was recovered from the evaporator. The temperature inside the evaporator reached 116℃ 45 minutes after heating started.
reached. The solution [trioxane] was collected from the evaporator as an analysis sample, and the amount of formaldehyde in the trioxane was determined by the sulfite addition method. The analysis results are shown in Table 1. Comparative Example 1 The plate distillation column used in Example 1, that is, the column diameter
A batch rectification operation was carried out using only an Olders column equipped with perforated plates of 50 mm and stage spacing of 50 mm. Trioxane used in Example 1 was added to the evaporator.
Raw materials containing 74.8% by weight, 25.0% by weight of benzene, 0.16% by weight of formaldehyde, and a trace amount of low-boiling components such as methanol were charged. It was treated in the same manner as in Example 1, and the results shown in Table 1 were obtained.

[Table] Examples 2 to 5 Continuous distillation experiments were conducted using a continuous rectification apparatus in which a raw material supply port was provided in the same rectification column as that used in Example 1. In addition, the filling layer part has a 6mm
A packed column filled with ×7 mm McMahon packing was used. According to a conventional method, raw materials containing 29.5% by weight of trioxane, 70.0% by weight of benzene, 0.45% by weight of formaldehyde, and trace amounts of low-boiling components such as methanol are continuously fed from the raw material supply port at normal pressure and a reflux ratio of 2. The distillate was fed at a feed rate of 500 g/hr, and the continuous distillation operation was continued while a distillate containing benzene and formaldehyde was taken out from the top of the column. After 16 hours of operation, the liquid level in the evaporator reaches 2.
Since the amount was reduced to a little, continuous extraction of the bottom liquid was started, and trioxane was obtained as the bottom liquid. The average withdrawal rate of bottoms liquid was 147 g/hr. 24 hours after the start of operation, it was confirmed that the distillation system was in a stable state, an analysis sample was collected from the bottoms flow, and the amount of formaldehyde in trioxane was determined in the same manner as in Example 1. , the results shown in Table 2 were obtained. Comparative Examples 2 to 3 Continuous distillation experiments were conducted in the same manner as in Example 2 using a continuous rectification apparatus in which a raw material supply port was provided in the same rectification column as that used in Comparative Example 1. It was treated in the same manner as in Example 2, and the results shown in Table 2 were obtained.

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Claims (1)

[Scope of Claims] 1. When separating a mixture containing one or more of each of high-boiling components, low-boiling components, and dissolved gas components into high-boiling components, low-boiling components, and dissolved gas components by distillation, A rectification method characterized by using a rectification column consisting of a type part and a packed type part. 2. The rectification according to claim 1 using a rectification column in which the height of the packed section is in the range of 5% to 50% of the sum of the height of the tray section and the height of the packed section. Method. 3. The rectification according to claim 1 using a rectification column in which the height of the packed section is in the range of 10% to 30% of the sum of the height of the tray section and the height of the packed section. Method. 4. The rectification method according to claim 1, which uses a rectification column in which the packed portion is located in the lower half of the column. 5. The rectification method according to claim 1, which uses a continuous rectification column in which the packed section is located below the raw material supply port of the column. 6. The rectification method according to claim 1, wherein the raw material contains trioxane as a main component of high-boiling components, benzene as a main component of low-boiling components, and formaldehyde as a dissolved gas component.