JP3069833B2 - Multicomponent mixture fractionation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fractional distillation (hereinafter referred to as "fractionation") of a mixture of a plurality of volatile substances having different boiling points, which are frequently used in the field of the chemical industry, to obtain each fraction having a predetermined purity. The present invention relates to a distillation operation for separation into minutes.

[0002]

2. Description of the Related Art Conventional techniques, for example, a, b,
FIG. 3 shows an example in which a standard continuous distillation column is used for fractionating a mixture of stock solutions consisting of the five components c, d, and e, and FIG. 4 shows an example in which a batch distillation column is used.

It is assumed that the components a, b, c, d, and e have higher boiling points in that order (ie, lower vapor pressure at the same temperature). This is usually defined as the order of volatility.

In FIG. 3, undiluted solutions a + b + c + d + e are:
First, it is sent to a supply stage appropriately determined in the middle stage of the tower 1 of the first tower, and the component a having the highest volatility from the top 4 (actually, it is not necessarily 100% a, (The fraction containing a as the main component is described as a for simplicity.)
Is distilled out, condensed in the condenser 5 and led to the distillate receiver 10 as a first fraction. On the other hand, another four-component mixture b + c + d + e having a lower volatility than a is collected in the bottom 3 and discharged as a still liquid. This effluent is subsequently supplied as a stock solution to the middle stage of the second column, where b is from the top and c is from the bottom.
+ D + e is discharged and becomes a feed solution for the third column. In this way, c and d are sequentially distilled from the tops of the third and fourth towers, respectively, and d + e and e are respectively obtained from the bottoms of the respective towers.
Is obtained as a kettle effluent.

The foregoing has described a case in which the five components are each separated and led to four fractions and a still liquid. However, depending on the purpose, each component may
It does not always correspond one-to-one. For example, the first fraction is a +
In some cases, b, the second fraction is c, and the pot liquid is d + e.

As described above, in order to fractionate a mixture consisting of five components into components a, b, c, d, and e, four components are required.
Requires a continuous distillation column. Generally, in order to fractionate a mixture consisting of M fractions, including the pot liquid, into M fractions in the order of volatility, a M-1 continuous column is required. However, these four or M-1 groups are the minimum number in theory, and in practice, it is not uncommon to need more groups due to design reasons or difficulty in controlling the operation.

FIG. 4 shows an example of a batch distillation column, in which a mixture of five fractions a, b, c, d and e is fractionated as in FIG. At this time, a certain amount of the undiluted solution a + b + c + d + e is charged into the bottom (kettle) 3 and the kettle liquid is heated by the reboiler-6. The generated steam is fractionated when passing through the inside of the tower 1, and the component a having the highest volatility is first distilled out from the tower top 4 and liquefied by the condenser 5 to become the first fraction. The liquid is guided to the liquid receiver 10. Eventually, a in the kettle
Disappears and changes to b + c + d + e, and then the vapor from the kettle 3 is fractionated inside the tower 1, and the next volatile component b is passed through the condenser 5 from the top 4 to the second fraction. And led to the distillate receiver 11. At that time, the pot liquid is c + d +
e, the fractionation is continued, and the component c is stored in the distillate receiver 12 from the top 4 as a third fraction, and the kettle liquid changes to d + e. Thus, in the final distilling stage of the batch distillation, the component d is distilled into the distillate receiver 13 as a fourth fraction,
The kettle liquid is collected outside the system as e. Also in this case, the relationship between each component and each fraction is the same as in the above continuous column, and each component is appropriately distributed to each fraction according to the purpose.

[0008]

As described in the above-mentioned conventional method, when a multi-component mixture is fractionated into a predetermined multiple fraction, at least M-1 columns corresponding to the fraction number M are required. Is considered to be inferior to a batch distillation column requiring only one column irrespective of the fraction M in terms of equipment cost.
In particular, in the case of small-lot multi-product production, which is one recent tendency, a batch distillation column that can be handled by one column is extremely advantageous. However, the fact that this batch system is not widely used is due to the following disadvantages of the batch column as compared with the continuous column.

(1) In a continuous column, the upper part is referred to as a concentrating step and the lower part is referred to as a recovering step from the stock solution supply stage. Also, it is larger for the recovery stage. The batch column is interpreted as lowering the position of the feed stage in the continuous column to the position of the still liquid, and there is no recovery stage. That is, from the viewpoint of the separation performance, the entire region of the tower body corresponds to the concentration stage. Therefore, if the total number of stages is the same, the effect on the separation performance of R cannot be expected in the continuous column.

(2) In a continuous column, the composition of each part in the column does not change with time in principle, and it is easy to maintain a steady state. However, in a batch column, the composition changes every moment. In order to maintain the purity of the fraction at or above a certain limit, there is a problem of energy consumption such as setting R to be unnecessarily large, or a problem of control complexity such as increasing and changing R every moment. Further, in a batch column, the presence of the amount of retentate retained in the column leads to a delay in the change of the distillate composition, which hinders sharp separation when each fraction is switched. This tendency becomes more pronounced as the number of fractions increases. Further, as the amount of each fraction approaches the same level as the amount of distillate retained in the column, the purity of the obtained fraction must be reduced. In order to solve this, it is necessary that the column is constituted by a packing and a liquid distributor with a small amount of retained liquid.

(3) In order to obtain high separation performance in a batch column, a large number of theoretical plates (that is, a high column) and a large reflux ratio R (that is, a large amount of ascending steam inside the column) are higher than those of a continuous column. And descending liquid amount). Therefore, a large column cross-sectional area is inevitably required, which, together with a high column, leads to an increase in the volume of the column contents, that is, an increase in the amount of retentate, and conversely, a decrease in the separation performance. Therefore, in order to break this circulating contradiction, increase the amount of liquid in the bottom of the tower compared to the tower body, and compare the amount of each fraction generated at one time, especially the amount of small fractions, with the amount of liquid retained in the tower. There is no other way than to take it large enough. However, this increases the operating time for one batch. However, to plan a batch tower with a huge brewing kettle with several days of loading,
It will be a challenge in terms of regulations, installation locations, construction costs, etc.

(4) In addition to the above, a large amount of the charged liquid keeps the kettle liquid in a boiling state for a long time, and a batch liquid for separation of a raw liquid containing a component which may be thermally deteriorated exists. The use of a distillation column is inappropriate.

[0013] It is an object of the present invention to provide an economical single-column type multi-component mixture fractionation system which avoids the above-mentioned drawbacks of the batch distillation column and incorporates the merits thereof. .

[0014]

As a result of various searches, the inventor of the present application has come to think that one continuous distillation column, which has conventionally been used in large numbers depending on the fraction fraction, will be used semi-batch. The present invention has been completed.

That is, the present invention provides a method for fractionating a multi-component mixture using a continuous distillation column in which a concentration section and a recovery section are divided by a variable supply stage, wherein one continuous column comprises: Means for separating and obtaining each desired distillate associated therewith, using equipment equipped with at least two kettle liquid receivers for separating and containing the undiluted liquid and / or the kettle liquid discharged corresponding to each distillate, In the first stage, a certain amount of the undiluted solution is supplied to the continuous column, fractionated under predetermined operating conditions, and the first fraction obtained through the condenser and the reflux control valve from the top of the column is the first fraction. The first tank discharge obtained from the bottom of the column at the same time is sent to and stored in the first tank liquid receiver. The first tank effluent contained in the liquid receiver is sent to the continuous column and fractionated under operating conditions suitable for it. The second fraction obtained in the same manner as in the previous step is stored in the second separation means, and at the same time, the second tank discharge obtained from the bottom of the column is an empty kettle other than the receiver used in the immediately preceding step. By sending the liquid to a liquid receiver and storing the same, the same process is repeated as needed in accordance with the conditions for obtaining the desired fraction, so that the undiluted solution is finally separated according to a predetermined operation suitable for the purpose of each stage. The present invention relates to a method for fractionating a multi-component mixture, wherein each distillate is obtained from a separation and acquisition means thereof, and the final tank discharge is obtained as a tank liquid from a tank liquid receiver.

Further, in the above-mentioned fractionation method, the high-temperature kettle discharged from the bottom of the column to the kettle liquid receiver, and the column liquid from the stock solution tank or a kettle liquid receiver separate from the above-mentioned kettle liquid receiver. By providing a liquid-to-liquid heat exchanger between the supply liquid toward the body and performing heat exchange, the discharge liquid toward the liquid receiver is cooled to a predetermined low temperature, and the supply liquid toward the tower body is cooled. A multi-component system in which a part of the heat required for heating up to a predetermined high temperature is measured, and fractionation is performed while preventing deterioration of the thermally unstable fraction while also saving energy. The present invention relates to a method for fractionating a mixture.

[0017]

Next, the present invention will be described in more detail with reference to FIG. 1 which shows an outline of one embodiment of the present invention.

FIG. 1 shows an apparatus for separating a stock solution containing five components of a + b + c + d + e into fractions for each component, as one example as in the description of the prior art. Reference numeral 1 denotes a tower having a required number of theoretical stages, and a flow control valve CV1
Is a continuous rectification column that feeds a stock solution to a variable supply stage by selecting the flow opening / closing valves V2, 3, 4 and the like. The major difference from a general continuous distillation column is that it has at least two tank liquid receivers 7 and 8 for temporarily storing the tank liquid corresponding to the fraction of each predetermined desired component. Means for separating and obtaining distillate, in which distillate receivers 10, 11, 1
2 and 13. The number of the receivers needs to be a number corresponding to the fraction number M. In this example, 5-1 = 4 receivers are provided. However, the means for receiving the distillate need not necessarily be fixed by piping as shown in FIG.

First, as a first step, the undiluted solution is stored in the undiluted solution tank 9 from the undiluted solution pipe 14, and the flow rate switching valve
1 through a liquid feed pump 15, adjusted by a flow control valve CV1, and subsequently supplied through a flow opening / closing valve from a predetermined preferred stock solution supply stage into the distillation column. The undiluted solution is continuously distilled under a reflux ratio R determined by distillation theory or experience. First, a fraction containing a as a main component passes through a condenser 5, a reflux valve CV4, and a distillate through a flow opening / closing valve V5. It is stored in the receiver 10. During this time, the liquid level in the bottom of the tower 3 is adjusted by LC, and the entire amount is received as a liquid composed of b + c + d + e in one of the empty tank liquid receivers 7 and 8 (the receiver 7 in this example).
Note that the stock tank for the stock solution in the first stage does not necessarily need to be the stock solution tank 9 and may be either the pot solution receiver 7 or 8 (if the receiver 7 is used instead of the stock solution tank, the stock solution is used). The receiver will of course be the empty receiver 8). Thus, when the stock solution is exhausted, the first stage ends. When the undiluted solution is supplied from the undiluted solution tank 9, the capacity of the receiver that can be received in the first stage is:
Needless to say, the amount is substantially equal to b + c + d + e excluding a from the maximum amount of the stock solution.

Next, as a second step, the mixed liquid stored in the kettle liquid receiver 7 is converted from the contained b + c + d + e components into
b is again supplied to the same distillation column from an optimal supply stage for fractionation as a main fraction under operating conditions such as a reflux ratio suitable for obtaining a target purity. Is stored in the distillate receiver 11, which is a receiving means, via the flow rate on-off valve V7. On the other hand, c + d which lost b component and flowed down to the bottom 3
The + e component is stored in the now empty kettle liquid receiver 8 while being controlled by the LC.

Similarly, as a third step, c is fractionated as a main fraction from the c + d + e component stored in the kettle liquid receiver 8 into the distillate receiver 12, and the d + e fraction that has become the kettle liquid is emptied. In the liquid receiver 7.

As a final fourth stage, d +
The component e is subjected to fractional distillation in substantially the same manner as in the previous stage, the component d is obtained as a main fraction in the distillate receiver 13, and the component e remaining as the bottom is stored in the tank liquid receiver 8.

In this way, the five components a + b + c + d + e can be obtained by using only one continuous column per batch.
It is separated into four distillate components a, b, c, and d and a kettle liquid of e with almost the same separation efficiency as when four continuous columns are used.

It is sufficient that at least two kettle liquid receivers are used irrespective of the number of components. However, it is acceptable to use three or more kettles to provide a margin for cleaning or the like. It is also possible to increase the thermal efficiency by exchanging heat (not shown) between the overhead vapor and the stock solution (supply liquid).

In the tank liquid receivers 7 and 8, the tank liquid discharged at a high temperature from the column bottom 3 during the entire distillation time stays. If there is a risk that the components may undergo thermal alteration during that time,
A cooler (not shown) is provided between the kettle liquid receivers 7 and 8 and
It is a reasonable measure to store the liquid at low temperature and to place a heater (not shown) in the meantime before sending it to the column 1 again.

FIG. 2 shows that the above-described cooler and heater are combined into one liquid-liquid heat exchanger 20 in order to use it advantageously when there is a large amount of a stock solution containing components susceptible to thermal deterioration as described above. And the effect of preserving unstable components and saving energy at the same time. The temperature is controlled by the TIC and the flow control valve CV5, and the preheater 19 connected to the steam pipe 18 is provided.
Is intended to heat the supply liquid, which is insufficient in the liquid-to-liquid heat exchange, to reach the temperature of the supply stage. By such means, even when thermally unstable components are present in the stock solution,
The time of exposure to high temperature during the distillation depends on the contents of the column 2 and the bottom 3 of the column.
The short time corresponding to the amount of retentate can be eliminated, and the drawbacks of the ordinary batch distillation column can be eliminated.

[0027]

Since the present invention is configured as described above, it has the following effects.

(1) Only one distillation column is required for fractionation of multiple components, and the equipment cost is significantly reduced as compared with the conventional continuous distillation system. In addition, since a continuous distillation method is employed for the fractionation, a disadvantage relating to the separation efficiency of the batch distillation column is avoided.

(2) Since the fractional distillation in each stage is a continuous operation, the working conditions are constant, the operation is easy to be stable, and the thermal efficiency is good, which is superior to the batch distillation.

(3) Despite enjoying the advantages associated with continuous distillation, it is easy to cope with a relatively small amount of diversified stock solution.

(4) Since it is not necessary to expose the kettle liquid to a high temperature for a long whole distillation time as in the batch distillation, it is necessary to wait at a low temperature except for a short time corresponding to a slight liquid retention in the column. It can also advantageously cope with distillation of a stock solution containing a component having a problem in thermal stability.

[Brief description of the drawings]

FIG. 1 shows a flowchart illustrating one embodiment of the present invention.

FIG. 2 shows a flow chart illustrating another embodiment of the present invention.

FIG. 3 shows a flowchart of one embodiment of a conventional continuous distillation apparatus.

FIG. 4 shows a flow chart of one embodiment of a conventional batch distillation apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 tower body 2 tower body contents 3 tower bottom 4 tower top 5 condenser 6 reboiler 7, 8 kettle liquid receiver 9 raw liquid tank 10, 11, 12, 13 distillate receiver 14 raw liquid pipe 15 liquid feed pump 16 , 18 Steam piping 17 Cooling water piping 19 Preheater 20 Liquid-to-liquid heat exchanger V1 to V17 Flow control valves CV1 to CV5 Flow control valves

Claims (2)

(57) [Claims] 1. A method for fractionating a multi-component mixture using a continuous distillation column in which a concentration section and a recovery section are divided by a variable feed stage, wherein one continuous column and its associated Means for separating and obtaining each distillate, using equipment equipped with at least two kettle liquid receivers for separating and accommodating the kettle effluent discharged corresponding to each distillate, in the first stage, a certain amount of The undiluted solution is supplied to the continuous column, fractionated under predetermined operating conditions, and the first fraction obtained through the condenser and the reflux control valve from the top of the column is stored in the first fractionation obtaining means. At the same time, the first kettle effluent obtained from the bottom of the tower is sent to and contained in the first kettle liquid receiver, and in the second stage following the end of the first stage,
The first tank discharge contained in the tank liquid receiver is sent to the continuous column and fractionated under operating conditions suitable for the same, and the second fraction obtained in the same manner as in the previous step is the second fraction. And the second tank discharge obtained from the bottom of the column at the same time is sent to and stored in an empty pot liquid receiver other than the pot liquid receiver used in the immediately preceding step, and then stored as necessary. By repeating the same process as in the second step according to the conditions for obtaining the desired distillate, the undiluted solution is finally fractionated according to a predetermined operation suitable for the purpose of each stage, and each distillate is A method for fractionating a multi-component mixture, characterized in that a final tank discharge is obtained as a tank liquid from a tank liquid receiver by each of these separation and acquisition means. 2. A high temperature kettle discharged from a bottom of the tower toward a kettle liquid receiver, and a raw liquid tank or a kettle liquid receiver separate from the above-mentioned kettle liquid receiver. A liquid-to-liquid heat exchanger is provided between the liquid and the incoming liquid to perform heat exchange, so that the liquid discharged to the liquid receiver is cooled to a predetermined low temperature and the liquid supplied to the tower is cooled to a predetermined temperature. A method for fractionating a multi-component mixture, comprising recovering a part of the heat required for heating to a high temperature.