JPH074485B2 - Batch distillation method and batch distillation apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses two components having different boiling points.
The present invention relates to a distillation method and a distillation apparatus for improving a product recovery rate or a product purity when a raw material contained above is separated by distillation in a batch system.

[0002]

2. Description of the Related Art Conventional apparatuses and methods are used to compare a raw material with a relatively high boiling point fraction (heavy fraction), an intermediate boiling point fraction (intermediate fraction) and a relatively low boiling point fraction. A case of (light fraction) will be described with reference to FIG. A conventional batch-type distillation apparatus is a means for heating a raw material, for example, a drum 2 provided with a reboiler 1, a rectification column 3 for vapor generated in the drum 2, a top vapor condensing / refluxing apparatus (condenser 4, rectification column 3) of the rectification column 3. A pipe for supplying the top vapor of the distillation column 3 to the condenser and a pipe for refluxing the condensate of the condenser 4 to the upper part of the rectification column 3, and a pipe for refluxing the condensate of the condenser 4 to the upper part of the rectification column 3. A reflux control valve V6 provided in
It has a product (middle distillate) withdrawal valve V5, a sample withdrawal valve V9, a light distillate withdrawal valve V7, a column bottom liquid (heavy fraction) withdrawal valve V8, and a column bottom liquid pump 5.

A drum 2 is filled with a raw material for distillation, a light distillate withdrawal valve V7 and a product (middle distillate) withdrawal valve V5
Closed and the recirculation control valve V6 opened, the reboiler 1
The raw material in the drum 2 is heated through steam. The raw material in the drum 2 becomes vapor and is totally refluxed from the upper part of the rectification column 3 to the upper part of the rectification column 3 via the condenser 4. When the inside of the rectification column has reached a steady state, V7 is opened, and the light fraction is withdrawn while performing reflux at a predetermined reflux ratio. Thereafter, sample from the valve V9 at any time, consider the distillate as a product when the light fraction in the distillate falls below the regulation, close the valve V7 and open the valve V5, and extract from the light fraction side to the product side. Switch to and collect. However, in this conventional method, a large amount of product (intermediate fraction) flows out together with the light fraction because the light fraction accumulated in the column is discharged.

[0004]

As described above, the product recovery rate is low in the conventional method. As a countermeasure for this, it is conceivable to increase the number of stages of the rectification column, but this is not a preferable means because it increases the equipment cost. The inventors of the present invention focused on that the light fraction in the drum and the lower part of the rectification column was below the specification before the light fraction in the distillate was below the specified value, improving the product recovery rate or the product. The present invention has made it possible to improve the purity of

[0005]

In the batch distillation method of the present invention, a vapor generated by heating a raw material composed of two or more components having different boiling points is introduced into a first rectification column and the top vapor is condensed. To a second rectification column equipped with a top vapor condensing / refluxing device, condensing the top vapor of the second rectification column and refluxing it to the second rectification column. While returning the bottom liquid to the upper part of the first rectification column, a distillation operation was performed without extracting the distillate to reach a steady state, and then a condensate of the top vapor of the second rectification column, if necessary. Intermittently withdraw a part of
When the purity of the liquid or vapor near the top of the rectification column exceeds a predetermined value, the flow of liquid and vapor between the first rectification column and the second rectification column is closed, It is characterized in that vapor or liquid is extracted from the first rectification column in a state where the distillate is contained in the second rectification column.

As a raw material for batch distillation, any material having two or more components having different boiling points may be used. Particularly, a component containing a target component and a component having a lower boiling point (light fraction) or a target component may be used. In addition to the component (intermediate fraction) and the light fraction, a component having a higher boiling point than the target component (heavy fraction) is suitable.

In the batch distillation method of the present invention, two rectification columns, a first rectification column and a second rectification column, are provided,
A raw material is supplied to the first rectification column, and an apparatus connected so that vapor generated from the raw material by heating passes through the first rectification column and the second rectification column in sequence is used. The second rectification column is equipped with a top vapor condensing / refluxing device, condenses the top vapor of the second rectification column and totally recirculates it to the second rectification column, and if necessary, of the second rectification column. A part of the condensate of the top vapor is intermittently withdrawn and the light fraction is concentrated in the second rectification column until the purity of the liquid or vapor near the top of the first rectification column reaches a predetermined value or higher. When the purity of the liquid or vapor in the vicinity of the top of the first rectification column exceeds a predetermined value, the flow of liquid and vapor between the first rectification column and the second rectification column is closed, and the light fraction is removed. The target fraction is extracted from the first rectification column while being contained in the second rectification column.

By the above batch distillation method, the target component is extracted from the first rectification column while the vapor containing a large amount of the light fraction is contained in the second rectification column.
A product with a light fraction below the specified value can be obtained.

Further, the batch distillation apparatus of the present invention comprises a first rectification column having means for heating the raw materials and having a top vapor condensing / refluxing apparatus, and a second rectification column having a top vapor condensing / refluxing apparatus. ,
Pipe for supplying the top vapor of the first rectification column to the lower part of the second rectification column, pipe for supplying the bottom liquid of the second rectification column to the upper part of the first rectification column, second rectification The first rectification has a pipe for extracting the condensate of the vapor condensing / refluxing device at the top of the distillation column, a pipe for extracting the vapor or the liquid from the first rectification column, and a pipe for extracting the residual liquid of the first rectification column. A device in which vapor generated from the raw material supplied to the column is connected so as to sequentially pass through the first rectification column and the second rectification column, and the top vapor of the first rectification column is 2 is a pipe for supplying the lower part of the rectification column and a pipe for supplying the bottom liquid of the second rectification column to the upper part of the first rectification column, each of which is provided with an opening / closing means. .

The first rectification column and the second rectification column may be installed one above the other as shown in FIG. 1 or may be installed individually as shown in FIG. Both are functionally independent rectification towers.

More specifically, referring to FIG. 1, the batch distillation apparatus of the present invention is provided with a reboiler 1 as a means for heating a raw material to a drum 2 to which the raw material is supplied. A first rectification column 3A equipped with a pipe for supplying the top vapor of the distillation column 3A to the condenser 4A and a pipe for refluxing the condensate of the condenser 4A to the upper part of the rectification column 3A, a top vapor condensing / refluxing device (condenser) 4B, a pipe for supplying the top vapor of the rectification column 3B to the condenser 4B, and a pipe for refluxing the condensate of the condenser 4B to the upper part of the rectification column 3B). A pipe for supplying the top vapor of the distillation column 3A to the lower part of the second rectification column 3B, a pipe for supplying the bottom liquid of the second rectification column 3B to the upper part of the first rectification column 3A, the second rectification Top vapor condensing / refluxing device of distillation column 3B A pipe for withdrawing the condensate through the valve V7, a pipe for withdrawing the condensate from the top vapor condensing / refluxing device through the valve V5 as a pipe for withdrawing vapor or liquid from the first rectification column 3A, and a pipe for the first rectification column 3A. It has a pipe for extracting the residual liquid from the drum 2 through the valve V8,
Is a device connected so that the vapor generated from the raw material supplied to the rectification column 3A of FIG. 1 sequentially passes through the first rectification column 3A and the second rectification column 3B. A valve V is provided in a pipe for supplying the top vapor of the tower 3A to the lower part of the second rectification tower 3B.
2. A valve V3 is provided in the pipe for supplying the bottom liquid of the second rectification column to the upper part of the first rectification column. As the top vapor condensing / refluxing device in the second rectification column, a condensate receiver may be provided at the outlet of the condenser 4B, and the condensate may be recirculated to the upper part of the rectification column 3B via this receiver. The pipe for withdrawing vapor or liquid from the first rectification column is not limited to the condensate withdrawal pipe of the top vapor condensing / refluxing device, but is provided so as to withdraw the top vapor of the first rectification column without condensing. Alternatively, the internal reflux liquid of the first rectification column, particularly the internal reflux liquid near the top, may be provided so as to be extracted. The heating means for the raw material may be provided inside the first rectification column as shown in FIG. 1, but may be provided separately from the rectification column as shown in FIG. 2, for example. Reference numeral 5 is a pump for withdrawing the bottom liquid from the drum 2, and valve V9 is a sample withdrawal valve. Note that the valve V1 is a valve that closes the supply of steam to the first condenser 4A, the valve V4 is a valve that controls the reflux liquid from the first condenser 4A, and the valve V6 is the second condenser 4A.
This is a valve for controlling the reflux liquid from B.

The apparatus shown in FIG. 2 comprises a first rectification column and a second rectification column.
The rectification pump has the same configuration as that shown in FIG. 1 except that the rectification towers are separately installed, and the bottom liquid of the second rectification tower is supplied to the upper part of the first rectification tower. 6 is provided.

Using the above apparatus, a raw material composed of two or more components having different boiling points, for example, a relatively high boiling fraction (heavy fraction), an intermediate boiling fraction (intermediate fraction) and A method of batch-distilling a raw material composed of a relatively low boiling point fraction (light fraction) to obtain an intermediate fraction as a product will be described with reference to FIGS. 1 and 2.

A drum 2 provided with a reboiler 1 containing the above raw materials.
In the top vapor condensing / refluxing device (condenser 4A, a pipe for supplying the top vapor of the rectification column 3A to the condenser 4A and a pipe for refluxing the condensate of the condenser 4A to the upper part of the rectification column 3A). To the first rectification column 3A. Without condensing the top vapor of the first rectification column 3A (that is, with the valves V1 and V4 leading to the condenser 4A closed), through the valve V2 (open), the top vapor condensing / reflux device (condenser 4B, refinement). Pipe for supplying top vapor of distillation column 3B to condenser 4B and condenser 4B
Of the condensate to the upper part of the rectification column 3B), and the top vapor thereof is condensed and refluxed to the second rectification column 3B. While returning the bottom liquid of the second rectification column 3B to the upper part of the first rectification column 3A via the valve V3 (open), the fraction is not extracted, that is, the valves V7, V5 and V8 are Distillation is performed in the closed state. After reaching the steady state, the valve V7 is opened as necessary (when the purity of the liquid or vapor near the top of the first rectification column 3A does not reach a predetermined value in the steady state), and the second rectification column is opened. A portion of the condensate of the top vapor of 3B is withdrawn intermittently. When the condensate (light fraction) is withdrawn, it may be withdrawn under reflux, or may be withdrawn without reflux. Whether or not the purity of the liquid or vapor near the top of the first rectification column 3A has reached a predetermined value is determined by, for example, determining whether the bottom liquid of the second rectification column 3B is
This can be confirmed by extracting the sample from the valve V9 connected to the pipe returning to the upper part of the rectification column 3A and analyzing it. Further, a sample may be extracted from a pipe for supplying the top vapor of the first rectification column 3A to the lower part of the second rectification column 3B to check whether or not the vapor purity has reached a predetermined value. The concentration of vapor or internal reflux liquid at a predetermined position inside the first rectification column 3A can also be used as an index.

When the purity of the liquid or vapor near the top of the first rectification column 3A, that is, the bottom liquid of the second rectification column 3B in the figure becomes a predetermined value or higher, the valves V2 and V3 are closed. The flow of liquid and vapor between the first rectification column 3A and the second rectification column 3B is closed, and the light fraction is contained inside the second rectification column 3B. With the light distillate thus contained, the valves V1 and V4 are opened to operate the top vapor condensing / refluxing device of the first rectification column to condense the top vapor of the first rectification column to
The condensate of the top vapor of the first rectification column 3A is withdrawn as a product while refluxing to the rectification column. For the product, the valve V5 may be opened to withdraw the condensate from the condenser 4A, or the vapor may be withdrawn directly from the top of the rectification column 3A. Also the first
The internal reflux liquid, for example, can be directly withdrawn as a product from the rectification column 3A. In that case, it is preferable to carry out the withdrawal near the top of the tower. The product can be collected in a gaseous state and can be appropriately selected depending on the purpose. After the product is recovered, the distillation is completed, the valve V8 is opened, and the heavy fraction is extracted by the column bottom liquid pump 5. The light fraction confined inside the second rectification column 3B is withdrawn from the top of the second rectification column 3B in the next distillation operation.

Further, as a distillation apparatus in the case where the raw material consists of a fraction having a relatively high boiling point and a fraction having a relatively low boiling point, the first rectification column having means for heating the raw material, top vapor condensation A second rectification column equipped with a reflux device, a pipe for supplying the top vapor of the first rectification column to the lower part of the second rectification column, and the first rectification of the bottom liquid of the second rectification column. Piping to supply to the top of the tower,
Vapor generated from the raw material supplied to the first rectification column, having a pipe for extracting the condensate of the top vapor condensing / refluxing device of the second rectification column and a pipe for extracting the residual liquid of the first rectification column Is a device connected so as to sequentially pass through the first rectification column and the second rectification column, and the top vapor of the first rectification column is supplied to the lower part of the second rectification column. An opening / closing means is provided in each of the pipe and the pipe for supplying the bottom liquid of the second rectification column to the upper part of the first rectification column, that is, the first rectification column is provided with a top vapor condensation reflux device. Alternatively, the high-boiling fraction (product) may be extracted from the bottom of the first rectification column. Referring to FIGS. 1 and 2, the capacitor 4
A, the valve V1, the valve V4, and the valve V5 are not provided, and the valve V8 is a product withdrawal valve.

The distillation method in the case where the raw material consists only of a relatively high-boiling fraction (product) and a relatively low-boiling fraction (light fraction) is as follows. The steam generated by heating is introduced into the first rectification column 3A, and the top vapor thereof is passed through the valve V2 (open) to the top vapor condensing / refluxing device (condenser 4B, top vapor of the rectification column 3B to the condenser 4B). To the second rectification column 3B). The top vapor of the second rectification column 3B is condensed and refluxed to the second rectification column 3B,
While returning the bottom liquid of B through the valve V3 (open) to the upper part of the first rectification column 3A, without extracting the fraction, that is, the valve V
The distillation operation is performed with 7 and the valve V8 closed. After reaching the steady state, if necessary (in the steady state, the purity of the liquid or vapor near the top of the first rectification column 3A does not reach a predetermined value), the valve V7 is opened to perform the second rectification. Part of the condensate of the top vapor of column 3B is withdrawn intermittently. When the condensate (light fraction) is withdrawn, it may be withdrawn under reflux, or may be withdrawn without reflux. Whether the purity of the liquid or vapor near the top of the first rectification column 3A has reached a predetermined value is determined by, for example, returning the bottom liquid of the second rectification column 3B to the upper part of the first rectification column 3A. This can be confirmed by extracting the sample from the valve V9 connected to the pipe and analyzing it.

When the purity of the liquid or vapor in the vicinity of the top of the first rectification column 3A, that is, the bottom liquid of the second rectification column 3B in the figure exceeds a predetermined value, the valves V2 and V3 are closed, The flow of liquid and vapor between the first rectification column 3A and the second rectification column 3B is closed, and the valve V8 is opened with the light distillate contained in the second rectification column 3B. The bottom liquid of the rectification column 1 is withdrawn as a product. The confirmation of the purity of the liquid or vapor in the vicinity of the top of the first rectification column 3A is performed by checking the top vapor of the first rectification column 3A or the first rectification column in addition to the bottom liquid of the second rectification column 3B. 3A
It is also possible to target the concentration of the vapor or the internal reflux liquid at a predetermined position inside.

The present invention will be specifically described below with reference to examples (results of computer simulation).
The present invention is not limited to the examples below.

[0020]

Example 1 Paraxylene (light fraction) 1000 p
pm, orthoxylene (light fraction) 1000 weight pp
m, propylbenzene (middle distillate) 99.75% by weight,
A case where propylbenzene having a purity of 99.96 wt% is recovered from a raw material containing 500 wt ppm of dodecane (heavy fraction) will be described (see FIG. 1 or 2). The operating conditions were that the pressure was normal pressure and the temperature was 160 to 170 ° C. As the rectification column, a first rectification column 3A having 15 plates and a second rectification column 3B having 5 plates were used. The raw material was charged into a drum 2 and steam was passed through a reboiler 1 to heat it. Drum 2
The liquid inside becomes vapor and passes through the first rectification column 3A and the second rectification column 3B and is condensed by the upper condenser 4B,
Return to the upper part of the second rectification column 3B. At this time, the valves V1 to V9
Among them, the open valves were V2, V3, and V6, and there was no distillation of the product (propylbenzene) and the light fractions (paraxylene and orthoxylene), so it was in the state of total reflux. After the temperature and flow rate inside the tower were stabilized by the operation of total reflux, the second
The bottom liquid of the rectification column 3B is sampled from a valve V9 provided in a pipe for supplying the upper part of the first rectification column 3A, and a light distillate withdrawal valve V7 is used until the propylbenzene content becomes 99.96% by weight or more. The light fraction was extracted by intermittently opening and closing.
Propylbenzene is 99.96 by sampling of valve V9.
Valves V1, V4, V5, V at the point where the weight is over
6 was opened, and valves V2, V3, V7, V8 and V9 were operated to be closed, and the product was recovered from the condenser 4A while keeping the fluid in the second rectification column 3B. . In the subsequent operation, the steam supply to the reboiler 1 was stopped and the distillation was stopped when the temperature in the first rectification column reached a predetermined value or higher, as in the conventional method. After the distillation was completed, the valve V8 was opened and the column bottom liquid pump 5 extracted the heavy fraction.

From the examples, the following was found. 1 raw material
Purity of 99.96% by weight when charged to 0 m ³ drum 2
The amount of product recovered from 8.3m ³ in the conventional method is 9.8m ^3.
improved to m ³ . Therefore, the product recovery rate improved from 83% to 98%. Furthermore, the distillation time was shortened from 8 hours to 7 hours because the outflow amount of the light fraction was reduced. When the product recovery rate is set to 83% as before, the product purity is improved from 99.96% by weight to 99.976% by weight, and the content of impurities is 400 to 240 ppm.
Decrease to.

[0022]

The effects of the present invention are as follows from the above examples. (1) The recovery amount of products is improved, and the product recovery rate can be improved. (2) The distillation amount of the light fraction is reduced, and the distillation time can be shortened. (3) The purity of the product can be improved. (4) Due to the above (1) and (2), the size of the device can be reduced. Specifically, the capacities of the light distillate distillate receiving tank and the drum can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an example of a batch distillation apparatus and a distillation method of the present invention.

FIG. 2 is a diagram for explaining another example of the batch distillation apparatus and the distillation method of the present invention.

FIG. 3 is a diagram for explaining a conventional batch distillation apparatus and distillation method.

Claims (7)

[Claims] 1. A vapor generated by heating a raw material composed of two or more components having different boiling points is introduced into a first rectification column, and a top vapor condensing / refluxing device is provided without condensing the top vapor. To the second rectification column, condense the top vapor of the second rectification column and return to the second rectification column, and return the bottom liquid of the second rectification column to the upper part of the first rectification column. However, after the distillation operation was performed without extracting the distillate fraction to reach a steady state, a part of the condensate of the top vapor of the second rectification column was intermittently withdrawn as needed to remove the first fraction. When the purity of the liquid or vapor in the vicinity of the top of the distillation column exceeds a specified value, the flow of the liquid and vapor between the first and second rectification columns is closed, and the fraction with a relatively low boiling point A batch distillation method, wherein vapor or liquid is extracted from the first rectification column in a state where the is contained in the second rectification column. 2. A vapor generated by heating a raw material composed of two or more components having different boiling points, a fraction having a relatively high boiling point, a fraction having an intermediate boiling point and a fraction having a relatively low boiling point. To a first rectification column equipped with a top vapor condensing / refluxing device, and without condensing the top vapor to a second rectification column equipped with a top vapor condensing / refluxing device, The top vapor is condensed and refluxed to the second rectification column, the bottom liquid of the second rectification column is returned to the upper part of the first rectification column, and the distillation operation is performed without extracting the fraction. After reaching a steady state, if necessary, a part of the condensate of the top vapor of the second rectification column is intermittently withdrawn, and the purity of the liquid or vapor in the vicinity of the top of the first rectification column is above a prescribed value. The first rectification tower and the second
The liquid and vapor flows between the rectifying towers are closed, and the top vapor of the first rectifying tower is condensed while the relatively low-boiling fraction is contained inside the second rectifying tower. The batch distillation method according to claim 1, wherein vapor or liquid of a fraction having an intermediate boiling point is extracted from the first rectification column while refluxing to the first rectification column. 3. A raw material composed of two or more components having different boiling points is composed of a fraction having a relatively high boiling point and a fraction having a relatively low boiling point, and steam generated by heating this is first rectified. 2nd equipped with top vapor condensing and refluxing device
To the second rectification column, condense the top vapor of the second rectification column and return to the second rectification column, and return the bottom liquid of the second rectification column to the upper part of the first rectification column. However, after performing a distillation operation without extracting the fraction to reach a steady state, if necessary, a part of the condensate of the top vapor of the second rectification column is intermittently withdrawn,
When the purity of the liquid or vapor near the top of the first rectification column exceeds a predetermined value, the flow of the liquid and vapor between the first rectification column and the second rectification column is closed, and the relative low The batch having a relatively high boiling point is withdrawn from the bottom of the first rectification column in a state where the boiling point fraction is contained in the second rectification column. Formula distillation method. 4. The purity of the liquid or vapor in the vicinity of the top of the first rectification column is the liquid or vapor between the first rectification column and the second rectification column, or in the first rectification column. The batch distillation method according to claim 1, 2 or 3, wherein the purity is vapor or internal reflux liquid. 5. A first rectification column having a means for heating a raw material and having a top vapor condensing / refluxing device, a second rectification column having a top vapor condensing / refluxing device, and a first rectification column. Second top steam
Pipe for supplying the bottom liquid of the second rectification column to the upper part of the first rectification column, and the condensate for the top vapor condensation reflux device of the second rectification column. It has a pipe for withdrawing, a pipe for withdrawing vapor or liquid from the first rectification column, and a pipe for withdrawing residual liquid of the first rectification column, and the vapor generated from the raw material supplied to the first rectification column is sequentially A device connected to pass through a first rectification column and a second rectification column,
Opening / closing means for each of the pipe for supplying the top vapor of the first rectification column to the lower part of the second rectification column and the pipe for supplying the bottom liquid of the second rectification column to the upper part of the first rectification column A batch-type distillation apparatus characterized by being provided with. 6. The pipe for withdrawing vapor or liquid from the first rectification column is a pipe for withdrawing either vapor at the top of the first rectification column, internal reflux liquid or condensate of the top vapor condensation reflux device. The batch distillation apparatus according to claim 5. 7. A first rectification column having means for heating a raw material, a second rectification column having a top vapor condensing / refluxing device, and a first rectification column.
For supplying the top vapor of the rectification column to the lower part of the second rectification column, the pipe for supplying the bottom liquid of the second rectification column to the upper part of the first rectification column, the second rectification column Has a pipe for extracting the condensate of the top vapor condensing / refluxing device and a pipe for extracting the residual liquid of the first rectification column, and the vapor generated from the raw material supplied to the first rectification column is sequentially supplied to the first rectification column. An apparatus connected so as to pass through the distillation column and the second rectification column, which is a pipe for supplying the top vapor of the first rectification column to the lower part of the second rectification column and the second rectification column. A batch distillation apparatus, characterized in that an opening / closing means is provided in each of the pipes for supplying the bottom liquid of the distillation column to the upper part of the first rectification column.