JPH0568801A - Separation system for nonideal multicomponent liquid mixtures - Google Patents

Abstract

PURPOSE:To obtian a separation system for nonideal multicomponent mixtures by dividing components in a nonideal multicomponent liquid mixture into the prescribed groups of ternary systems and getting a total reflux elemental separation diagram for each system to confirm separation ability, etc. CONSTITUTION:For the combination of components, that of those with about <=2 deg.C difference in boiling pt., from each other, that of those forming azeotrope, and that of those consisting of isomers or compounds having a similar functional group are selected. A total reflux elemental separation diagram is obtained by 'ASOG and UNIFAC', a system for giving the vapor-liquid equilibrium relationship of nonideal three components. For example, total reflux distillation curves for the methanil-ethanol- water system are obtained by ASOG, changing the feed composition and the number of stages. Each diagram represents an elemental separation diagram indicating the ratio of components when they are in vapor-liquid equilibrium in total reflux distrillation for each number of stages. Namely, ethanol and water are hard to separate because of having an azeotropic point at 351.32 deg.K. It is concluded, however, that methanol and water can be separated by distillation. Thereby the behavior of each component on distillation is confirmed in advance and a separation system is synthesized.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a system for separating each component from a non-ideal multi-component system. Specifically, it relates to a separation system obtained from each elemental separation diagram relating to a predetermined three-component system contained in a non-ideal multi-component liquid mixture.

[0002]

2. Description of the Prior Art Various methods are conventionally used for separating each component from a liquid mixture containing multiple components. For example, the separation of multicomponent liquid mixtures by distillation has already been practiced for a long time. Separation of multi-component liquid mixture is mainly continuous distillation in a rectification column, an industrial distillation separation system starts from the design of the distillation column, depending on the type and composition ratio of the constituent components of the liquid mixture to be separated, It is necessary to determine various distillation conditions such as the reflux ratio, the number of stages calculation, the raw material charging stage and the like in advance. For so-called ideal multi-component mixtures,
Conventionally, various separation systems have been proposed, and it is easy to determine distillation separation conditions using these systems.

[0003]

However, in the distillative separation of a non-ideal multi-component mixture, there are already established separation systems for the components in the mixture, and it seems that an extraction medium is specified. Under the conditions, it is only possible to establish a distillation separation system with reference to them. Therefore, in the distillation separation of any non-ideal multi-component mixture, trial and error, and relying on the experience and intuition of a skilled technician, it is necessary to perform a flurry of condition determination while performing enormous calculations with a computer. The current situation is that it will not happen. Therefore, for the component separation of an arbitrary non-ideal multi-component mixture, the development of a method for constructing a separation system in advance is extremely useful and desired in the design of each separation process. An object of the present invention is to provide a separation system for a non-ideal multi-component mixture whose method has not yet been established as described above.

[0004]

According to the present invention, a plurality of predetermined three-component system groups contained in a non-ideal multi-component liquid mixture are selected, and based on the total reflux element separation diagram of each three-component system. A non-ideal multi-component liquid mixture separation system characterized by being synthesized is provided. In the present invention, the total reflux elemental separation line is a distillation curve and refers to a tie line locus at any liquid composition and number of stages, and the elemental separation system is a region where the total reflux elemental separation line has the same pattern. Say.

[0005]

The present invention is configured as described above, and by dividing the components in the non-ideal multi-component liquid mixture into predetermined three-component system groups, their behaviors can be expressed on the drawing, and the groups are configured. By obtaining the total reflux element separation diagram of each of the three-component system, the component separation ability and the like in the three-component system can be confirmed, and the component separation system can be synthesized through a predetermined simple simulation.

That is, from the total reflux element separation diagram of the three-component system group selected from the non-ideal multi-component liquid mixture, it is possible to separate relatively easily from a plurality of three-component systems including two components which are difficult to separate. A three-component system is selected, and the target composition of the components to be separated in the selected three-component system is obtained as an overhead distillate or bottom product in the steady state of total reflux distillation. Find a solution. As a result, from the obtained charge composition and overhead distillate or bottom product, the target composition of other components to be separated is similarly sequentially solved so as to become the top distillate or bottom product. Obtained, according to the number of components to be separated, appropriately select the charge composition, the top outflow composition, the bottom composition and the number of stages in each distillation step of the required number of up to the distillation column charging the multi-component liquid mixture as a raw material. The separation system can be synthesized by simulating the material balance in the steady state under total reflux so as to match the composition ratio of the raw material non-ideal multi-component liquid mixture.

The present invention will be described in more detail below. In the present invention, four or more components contained in the non-ideal multi-component liquid mixture are combined into a predetermined three-component system and divided into a plurality of three-component system groups. In this case, the ternary combination in the n-component mixture (provided n ≧ 4) is generally n! / [(N-3)!・ 3! ], For example, if n = 5, 5! / (2! ・ 3!) = Only 10 combinations are possible. However, in the present invention, it is preferable to reduce the number of ternary systems constituting the ternary system group as much as possible. The combination of components that make up this three-component system is
The three-component system group can be selected based on the following criteria.

That is, (1) Boiling point is similar, usually about 2 ° C.
The following combinations of boiling point differences, (2) combinations that form an azeotropic system, and (3) combinations of isomers or compounds having similar functional groups are selected from the ternary system group. Any of these combinations of components can be easily selected based on ordinary knowledge in the technical field of the present invention, and the three-component system of the combination of (1) and (2) described above is generally difficult to separate. It is clear that the isomers (3) and the like above are difficult to separate by distillation, and thus remain as two components in any of the methods, and it is necessary to finally superfractionate. is there. In addition, (4) a component or a component system whose boiling point difference is remarkably different from other components and can be reliably separated can be excluded in advance from the selection of the three-component system group. According to the above selection criteria (1) to (4), the number of three-component systems forming the three-component system group selected from the multi-component system does not become an enormous number but is naturally limited. Therefore, the distillation simulation, which will be described later, is not enormous and can be performed by a relatively simple calculation.

Next, according to the present invention, a total reflux element separation diagram is obtained for each of the three-component systems constituting the three-component system group selected as described above. The total reflux element separation diagram of the present invention is
System "ASOG and UNIFAC" developed by the inventors for determining the gas-liquid equilibrium relationship of a non-ideal three-component system
(Kojima, Tochigi, "ASOG and UNIFAC" 198
6-year Chemical Industry Co., Ltd.). For example, a total reflux distillation line of methanol / ethanol / water
When the raw material composition and the number of stages are changed to obtain by ASOG, it becomes as shown in FIG. The respective diagrams displayed in FIG. 1 represent elementary separation diagrams showing the component ratios of the three-component system in vapor-liquid equilibrium in the total reflux distillation of each number of stages. From the elementary separation diagram of FIG. 1, it can be determined that ethanol and water have an azeotropic point of 351.32 K and separation is difficult, but methanol and water can be separated by distillation. In the present invention, a non-ideal multi-component system is a group of three-component systems that can be displayed in a graph, and regarding the selected three-component system, the behavior of each component at the time of distillation is obtained by obtaining the total reflux element separation diagram as described above. Is confirmed in advance and the separation system is synthesized.

At the beginning of the synthesis of the separation system, the total reflux element separation diagrams obtained for each of the three components constituting the selected three-component system group were compared and examined. As a result, the separation was most difficult and the final distillation was completed. Select a ternary system consisting of the combined components to be separated in stages. Then, the material balance is calculated as the overhead distillate or bottom product in the steady state of the total reflux distillation in which the components to be separated in the selected three-component system have a predetermined concentration and the number of plates is appropriately selected. .. As a result, the charge composition of the obtained distillation column is similarly solved by the mass balance equation so that it becomes a top distillate or bottom product in the steady state of the total reflux distillation of the distillation column of the previous step. Ask for. Similarly calculate the material balance for the required number of distillation steps, and to the composition obtained after the required distillation steps,
A composition obtained by adding a small amount of components to be separated from the remaining components other than the initially selected three-component system in the same manner as overhead distillate or bottom product in the steady state of total reflux distillation As the above, the material balance is calculated in the same manner as above, and then the charged composition in which a small amount of the component to be separated is added is determined. As described above, the charge composition, the overhead outflow composition, the bottom composition and the number of plates in each distillation step are appropriately selected, and the calculation of the steady state mass balance under total reflux is performed according to the number of components to be separated. The process is repeated until the distillation column is charged with the raw material multi-component liquid mixture, and the final composition is simulated so that the composition ratio of the raw material non-ideal multi-component liquid mixture matches.

As described above, the material balance in the steady state under total reflux is sequentially simulated to calculate the bottom composition and the overhead distillation composition, and the multi-component mixture is withdrawn from the raw material charging distillation column to the next step distillation. You can define the steps. The separation system of the non-ideal multi-component liquid mixture of the present invention is based on the simulation result finally obtained as described above, and the multi-component liquid mixture-prepared distillation column is adapted to the operating conditions, material balance and other necessary conditions. Then, it is resimulated in the reverse order from the first step to the next step distillation to establish the synthesis. Regarding the above-mentioned steady state material balance under total reflux, it can be performed by the following mathematical formulas 1 and 2. These solutions can be found, for example, in Newton-Raphson.
It can be obtained by iteratively calculating by using the method until the objective functions represented by the formulas 3 and 4 become 1 × 10 ⁻⁸ or less.

[0012]

[Equation 1]

[0013]

[Equation 2]

[0014]

[Equation 3]

[0015]

[Equation 4]

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples. Acetone: Ethanol: n-Propanol: t-
Butanol: water = 7.9: 9.9: 36.6: 31.
Acetone-ethanol-n-propanol-t-butanol-of a non-ideal five-component liquid mixture with a ratio of 6: 14.0
The synthesis of a separation system for a water (AE-Pr-B-W) mixture is described. In the non-ideal five-component system, the three-component system group originally has 10 combinations as described above, but from the above principle (4), acetone (A) has a boiling point of 56.5 ° C. and other components. However, since it is obvious that it is separable first, it is excluded from the selection of the ternary system group. Therefore, the remaining four components ethanol (E), n-
A combination of three components is selected from propanol (Pr), t-butanol (B) and water (W). These four to three component systems are E-Pr-B, E-Pr-W, Pr-B.
There are four types of combinations of -W and B-W-E, but E-
Pr-B ternary system is excluded from the principle of (4) above,
Three-component system group (i) E-Pr-W, (ii) Pr-B-W and (i
ii) A total reflux element separation diagram is obtained for each of the three kinds of three-component systems B-W-E.

2 to 4 are each a three-component system group (i) E
It is a total reflux element separation diagram of -Pr-W, (ii) Pr-B-W, and (iii) B-W-E. In FIGS. 2 to 4, each separation line a to f represents the gas-liquid equilibrium relationship at the time of total reflux distillation obtained by the “ASOG” system with the composition of the charged raw materials and the number of stages described at the bottom of each drawing. It was done. Considering each of the diagrams shown in FIGS.
(Iii) The combination of the three-component system B-W-E, which is the most difficult to separate in distillation, is suitable as the starting system for the synthesis of the system, and the separation ability between t-butanol and ethanol. It turns out that is good. FIG. 5 shows (iii) of FIG.
Separation of t-butanol and ethanol is more clearly displayed in the separation diagram when the number of stages is 200 in the raw material composition in the separation diagram d of B-WE. As described above, in the four-component system in which acetone is removed from the five-component system of the A-E-Pr-B-W liquid mixture, first, in the final step, the three components of t-butanol-ethanol-water are changed to t-butanol. It became clear that it could be separated from ethanol. Based on this result, a five-component liquid mixture separation system is then synthesized.

Separation system synthesis will be further described with reference to the block flow sheet of FIG. In FIG. 6, in each of the distillation columns 1 to 5, the theoretical plate number N = 30, the total charge amount S _T = 32 mol, the bottom liquid amount S = 1 mol, the distillation amount P = 1 mol, and the liquid holdup H _j = 1 mol was set.
First, in order to obtain t-butanol to be separated in the distillation column 5,
A: E: Pr: as a bottom composition (mol%, the same applies below)
B: W = 0.0: 0.1: 0.0: 99.8: 0.1 is set, and the substances in the steady state under total reflux distillation are included in the formulas 1 and 2 together with the above conditions. Make a balance calculation,
As the overhead distillation composition, A: E: Pr: B: W = 0.0:
1.8: 0.0: 63.2: 35.6 and the charged composition were calculated, and the calculation was repeated until each of the obtained charged compositions corresponded to the bottom composition of the distillation column in the previous step.
In this case, the same calculation was sequentially performed up to the distillation column 3, and after reaching about 5 distillation steps, it reached the distillation column 3 which is the step of starting the separation of t-butanol and ethanol.

The number of steps required for this predetermined distillation column 3 is calculated by the mass balance calculation in the steady state under total reflux in the distillation step in which the distillation composition of the distillation column 3 and the following steps are used as the charge composition. Performed sequentially, and after the required number of steps, in the distillation column 4
The concentration of ethanol separated from t-butanol is 8
The distillation column 3 was simulated to have a top distillate composition and a bottom composition so that the content was 9.7 mol%. in this case,
It is also possible to set the respective compositional concentrations of ethanol and t-butanol to be separated, and similarly calculate and simulate from both values. Then, the distillation column 3 set as described above
Was calculated, and the obtained composition was almost the same as the top distillate composition of the distillation column 2 in the first stage, and the Pr content of n-propanol was very small (about 1 × 10 ⁻⁷ mol%). As the added composition, the bottom composition and the charging composition in the distillation column 2 were obtained in the same manner, and the composition in which the A component of acetone was added in a small amount (about 1 × 10 ⁻⁷ mol%) in the same manner as in the obtained charging composition was It was confirmed that it was obtained as an intermediate stage composition of the distillation column 1, the overhead distillation composition was A as a main component, the bottom composition was Pr as a main component, and that the charged composition matched the predetermined raw material composition.

The simulation according to the above method was performed by calculating from the downstream distillation column to the raw material charging distillation column so that the simulation would match a predetermined raw material composition for each simulation in each distillation column. The results are shown in FIG.
The charged composition, the overhead distillation composition and the bottom composition of Nos. 5 to 5 are shown in the line portions.

[0021]

INDUSTRIAL APPLICABILITY In the present invention, a separation system for a non-ideal multi-component liquid mixture, which has been conventionally sought by a skilled engineer using a computer, is a three-component system total reflux element separation line which can be displayed on a graph. Using the figure, a separation system can be synthesized by a simple simulation, which is industrially useful.

[Brief description of drawings]

FIG. 1 is an example of a total reflux element separation diagram of a ternary mixture of the present invention.

FIG. 2 is a total reflux element separation diagram of a ternary mixture according to an embodiment of the present invention.

FIG. 3 is a total reflux element separation diagram of a ternary mixture according to an embodiment of the present invention.

FIG. 4 is a total reflux element separation diagram of a ternary mixture according to an embodiment of the present invention.

FIG. 5: Total reflux element separation line used for synthesis of separation system from total reflux element separation line diagram of ternary mixture of one embodiment of the present invention

FIG. 6 is a block flow sheet of an embodiment of the present invention.

Claims (1)

[Claims] 1. A non-ideal, characterized in that a plurality of predetermined three-component system groups included in a non-ideal multi-component liquid mixture are selected and synthesized based on a total reflux element separation diagram of each of the three-component systems. Separation system for multi-component liquid mixtures.