JPS5830301A - Separation of liquid mixture - Google Patents

Abstract

PURPOSE:To improve the efficiency of a separation process by connecting a distillation stage and a membrane separation stage with the concn. of the distillate of the distillation stage at which the sum of the energy functions required for both states attains a min. value. CONSTITUTION:When the concn. of one component of a mixture in the tower top distillate of a distillation tower 1 is defined as (x), the sum F(x) of the energies f(x) and g(x) required for a distillation stage and a membrane separation stage gives a curve having a min. value. For example, in a case in which an ethanol/water mixture is separated in the distillation tower 1 and the membrane separator 2, the F(x) gives a curve having a min. value. Therefore, the liquid mixture is separated advantageously in terms of energy by connecting the distillation stage and the membrane separation stage at the concn. of the distillate of the distillation stage at which the F(x) attains a min. value.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) The present invention relates to a method for separating liquid mixtures, and more particularly to an energy-efficient separation method that combines distillation and membrane separation means.

One of the most widely used techniques for separating liquid mixtures is the distillation method. However, the distillation method has the problem that an azeotrope may be formed depending on the liquid mixture system, making further separation impossible. Distillation is also not the preferred method for separating mixtures with low specific volatility or mixtures that contain substances that polymerize or modify when heated, and membrane separation using membranes is advantageous to solve these problems. It is said that there will be.

The process of separating liquid mixtures using polymer membranes has been studied for quite some time, and this separation process is known as the pervaporation process or R,O,(Reverse Osmosis).
It is broadly divided into processes. The former pervaporation method is a method in which the liquid to be treated is supplied to one side of the membrane, the other side is kept under reduced pressure, and substances that are easily permeable are preferentially permeated as vapor. The side is pressurized ((
2) This method maintains K (usually several thousand atmospheres) and allows permeable substances to pass through preferentially as a liquid.

There are also some proposals for technology for separating mixed liquids by combining distillation and membrane separation methods, for example,
As shown in No. 33279, it is limited to a combination technique in which an azeotrope is separated by a membrane, in order to solve the separation limitations in distillation means by membrane means.

The present inventors analyzed the distillation method in terms of the energy required, and found that in many liquid mixtures, it takes a large amount of energy to separate to the azeotrope concentration.
It has been found that the energy needed to separate the azeotrope concentration to the desired product concentration is relatively not large. We also analyzed the energy required for membrane separation and found that the situation differs depending on the liquid mixture and separation concentration, and that the membrane separation method is not simply more advantageous than the distillation method. Therefore, when combining a distillation method and a membrane separation method, the point at which to convert from the distillation method to the membrane separation method should be determined by considering (3), which is completely different from the conventional method. I found out that.

The purpose of the present invention is to perform separation with minimum energy consumption when using a combination of distillation method and membrane separation method, and to improve the efficiency of the separation process. Still other purposes will become apparent from the description below.

That is, the present invention provides a method for membrane-separating a liquid mixture consisting of at least two components by a combination of a distillation step and a membrane separation step, in which the energy function f (X) required for each of the above steps is
and g(x), and the sum F(x) −f(x) +
The concentration of distillate from the distillation process where g(x) is the minimum value Xm1n
This is a method for separating a liquid mixture characterized by connecting a distillation step and a membrane separation step.

Furthermore, the present invention provides a method for separating a liquid mixture consisting of at least two components by a combination of a first distillation step, a membrane separation step, and a second distillation step, in which the energy functions f(x) and g( x) and h(x), and calculate the first distillate at the concentration
(4) A method for separating a liquid mixture is provided, characterized in that (4) the distillation step and the membrane separation step are connected.

The liquid mixture treated in the present invention contains components that are relatively difficult to volatilize and have a large latent heat of vaporization. Separation is required by a combination of a separation step and a second distillation step. Liquid mixtures used in the present invention include ethanol/water, methanol/methyl acetate.

Acetic acid/water, methyl acetate/water, acetone/water, vinyl acetate/ethyl acetate, acetic acid/n-butyl acetate, methyl acetate/methanol/water, vinyl acetate/methanol/water, ethanol/water/benzene, etc. , especially ethanol/
Water, methanol/methyl acetate mixtures can be used advantageously. The following explanation will be given based on FIG. 1 using an ethanol/water mixture as an example. The ethanol/water mixture supplied to the distillation column 1 is separated in the distillation process, and water with a large latent heat of vaporization is distilled from the bottom of the column, and an ethanol/water mixture containing mainly ethanol with a small latent heat of vaporization is distilled from the top of the column. put out The ethanol/water mixture from the top of the column is then introduced (5) into a membrane separator 2 where it is fractionated so that mainly water passes through the membrane and ethanol is rejected. When a liquid mixture is separated using a membrane that transmits a component with a relatively large latent heat of vaporization and rejects a component with a small latent heat of vaporization, the problem of minimizing the required energy increases. The water passing through the membrane contains a small amount of ethanol, and it is disadvantageous to discard it, so it is usually desirable to return it to the feed line of the distillation column, as shown in FIG. Ethanol rejected by the membrane is recovered as a highly concentrated product.

Furthermore, ethanol/water mixtures can be separated more advantageously by the second method according to the invention. Separation by the second method will be explained based on FIG. 2.

The ethanol/water mixture supplied to the first distillation column 1 is separated in the distillation process, and water having a high heat of evaporation is distilled from the bottom of the column. An ethanol/water mixture consisting mainly of ethanol with a low latent heat of vaporization is distilled from the top of the column. The ethanol/water mixture (6) from the top of the column is then introduced into the membrane separator 2, where it is fractionated so that mainly water passes through the membrane and ethanol is rejected. The water that passes through the membrane still contains a small amount of ethanol, which cannot be discarded. Ethanol rejected by the membrane is recovered as a highly concentrated product.

The water/ethanol mixture that has passed through the membrane is further sent to the second distillation column 3, where water is distilled from the bottom of the column and a water/ethanol mixture with increased ethanol concentration is distilled from the top of the column.

This water/ethanol mixture is returned to the feed line to the first distillation column or to the membrane separator to increase ethanol recovery. Preferably, the mixture is returned to the membrane separator as shown in FIG. 2, and its concentration is preferably approximately equal to that of the mixture from the top of the first distillation column. In this way, components with a relatively low latent heat of vaporization are recovered from the rigid reactor of the membrane separation device, and components with a relatively large latent heat of vaporization are recovered from the bottoms of the first and second distillation columns. The circuit for separating the methanol/methyl acetate mixture shown in FIG. 3 may be similarly understood.

(7) In the separation method described above, the energy required for each step has not been studied so far. In order to analyze the separation of liquid mixtures from the energy point of view, we first
As a result of researching the energy required for each process, we found that when the concentration of one component of the mixture in the top distillate of the (first) distillation column is X, each process, that is, the (first) distillation process. , the membrane separation step, and the second distillation step are expressed as functions of X, f(x), g(x), and h(x), respectively. and the sum or total sum F(x)
−f(x)+g(x), F(x)=f(x)+g(x
)+h(x) was also found to be a curve with the minimum value. This fact was discovered for the first time by organizing and calculating data for each process, and was completely unexpected at first. Examples of POC) are shown in Figures 4 to 6, Figure 4.5 shows ethanol/water, and Figure 6 shows when the mixture is separated by the first method and second method of the present invention. This is the case when a methanol/methyl acetate mixture is separated by the second method.

The energy function will be explained in more detail (8). , total distillate amount at the top of the tower (concentration of component Latent heat of vaporization Ldlx of X component,
Since the latent heat of vaporization Ld1y of the y component can be determined as a constant, it can be expressed as follows.

f (x) = f (Fl (Fix), DI (
Cdlx) ) The amount of energy (conveniently converted as the amount of steam) due to each of these variables can be determined based on experiments. f(x) is the sum of energy amounts corresponding to each of these variables.

The energy function g (x) required for the membrane separation process has as a variable a factor related to the operation of the process: membrane permeation amount (X component concentration of the permeate) F2 (F21C), and the sensible heat of the feed liquid and The latent heat of vaporization Ld1x of the component and the latent heat of vaporization Ld1y of the y component can be determined as constants, so they can be expressed as follows: (9) g(x) = g (F2(F2K)) Here, depending on each variable The amount of energy is determined experimentally and then summed to obtain g(x).

The energy function h (x) required for the second distillation step is also the same as f (x) in the first distillation step, and each factor F a
(Fsx) and DB (Cd3x) as variables, the reflux ratio RRa is determined by D3//'F3, and F4
- The sensible heat of the liquid, the latent heat of vaporization Ld3x of the X component, and the latent heat of vaporization Ld3y of the y component can be determined as constants, so they can be expressed as (Cd8x))
h-(x) is the sum of energy amounts corresponding to each of these variables.

f (x), g(x), obtained by the above method,
With h(x), the sum is F (summer) - 3=.

In the method shown in Figure 1, F(X) = f(x) + g(x) In the method shown in Figures 2 and 3, F(x) = f(x) + g(x) + h(x)
It can be expressed as

(10) Each of these functions can be drawn in the form of a graph,
They can finally be shown as shown in FIGS. 4-6. Each function in the present invention cannot be expressed as a normal linear or quadratic function, etc., but is a relational expression obtained from numerical values obtained based on experiments.
) can be easily plotted on a graph. Figures 4 to 6 are examples. In either case, the curve has the minimum value. Referring to FIG. 5b, if the composition of the liquid supplied to the first distillation column differs, the curves of F(x) will differ as shown in a, b, and c. However, all curves are a', b', a'
has a minimum value as shown as . For example, regarding the curve, the F(x) value changes as shown in the curve depending on the concentration X of the top distillate (ethanol) of the first distillation column. Therefore, it is clear that connecting the first distillation step and the membrane separation step at ×mjn(b) corresponding to the minimum value b' of F(x) is advantageous in terms of energy.

For example, when compared with the F(X) value (b'') when the distillation process and membrane separation process are connected at an azeotropic concentration known as the conventional technology, it is recognized that the energy is reduced by about half. The reduction is commercially very significant.Also, one of the advantages of the process of the present invention is that X min is below the azeotropic concentration and that no azeotrope is formed. In the spirit of the invention, F(
The minimum value of Dew. The minimum value in the present invention is preferably a range up to 30% increase from the narrow minimum value, more preferably a range up to 10% increase, and X corresponding to the minimum value is defined as X mi
Let it be n.

As the distillation means and membrane separation means used in the present invention, any conventionally known means can be used. The membrane used in the membrane separation means is selected depending on the liquid mixture to be treated, but may be polyethylene,
Polypropylene, polybutadiene, polyacrylonitrile, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polymethacrylate, polyether,
Polycarbonate, polyester, polyamide, polyimide, fluororesin, silicone resin, cellulose polymer, and copolymers and graft copolymers thereof,
Block copolymers, blends, and coatings,
Also included are organic films made of modified products such as carboxylation, amination, sulfonation, etc., and films made of inorganic materials. Although the shape of the membrane may be arbitrary, it is advantageous to use the hollow fiber membrane as it is superior in terms of compactness and pressure resistance. Specifically, the membrane separation method is a so-called pervaporation method in which a liquid mixture is supplied to one side of the membrane and pressure is reduced on the other side to selectively separate one component of the liquid in a paper state, or a membrane separation method is used. One side is pressurized to tens of atmospheres to selectively permeate and separate components into the liquid.
The so-called reverse osmosis method can also be applied to any of the five stains.

1 to the separation coefficient α in the present invention is α~'B = (A2
Az)/ (”/'B 1 ), where A
t and Bt are the weight fractions (13) of components A and B in the mixed liquid before permeation through the membrane, respectively, and A2B□ is the weight fraction (14) of components A and B in the mixed liquid before passing through the membrane.
There is 7.' off the coast.

The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

Examples 1-6. Comparative Examples 1 to 4 Using the apparatus shown in the flow sheet of Fig. 1, the flow rate from A to 2 was
An aqueous solution of 07-21Ar with an ethanol concentration of 14.5% by weight is fed to a distillation column 1 with a plate number of 25R (however,
This feed liquid has an ethanol concentration of 1.3% by weight, which is condensed after passing through the membrane through pervaporation, which will be described later.
7.21 of the aqueous solution was added to the aqueous solution with an ethanol concentration of 155% by weight fed from A'). A liquid with a jetanol concentration of 80% by weight is distilled from the top of the column, and water with an ethanol content of 0.015% by weight or less is taken out from the bottom of the column. Water-containing ethanol distilled from the top of the column: 37.2 t/
hr is sent to the membrane separator 2 as shown in B, where it is treated by the pervaporation method, and vapor with an ethanol concentration of 1.3% by weight is taken out as a component permeated through the membrane, and it is condensed and liquefied in a heat exchanger. After that, it was fed from A to distillation column 1 as described above. Also, from the can bottom of the membrane separator 2 (14), ethanol with a concentration of 99% by weight was obtained as a membrane reject component. Energy function f (x
), g(x) are 5 Q kg/hr and l Q kg, respectively.
/hr, and the total required steam amount F(x) is 79 k1!
/hr.

Nao, the membrane used for pervaporation has a permeability of 0.
．． 3 kg/m, membrane area with % separation factor of 19 is 20
Using a hollow fiber type PVA membrane with a diameter of 100 m, the operating conditions are a pressure on the raw solution side of 1000-u-kb and a pressure on the steam side of 100 m2.
The temperature was 50°C.

Similarly, the ethanol concentration and membrane area in each of A', A, and B were changed, and the concentration was adjusted to 99% using the same method as in Example 1.
The total amount of steam required to obtain ethanol was determined, and the results are shown in Examples 2 to 6 in Table 1. Furthermore, in Comparative Example 1, the ethanol concentration at points A', A, and B was 50 + 4.
It was shown that the total required steam amount to obtain 99% ethanol at 95% by weight is 127.4 #/hr, which is 81% compared to the minimum required steam amount defined in the present invention. % excess steam was required. Comparative Examples 2 to 4 were also shown in the same manner.

(15) Examples 7 to 12. Comparative Examples 5 to 8 Using the apparatus shown in sheet 70 of FIG. 2, an aqueous solution with a jetanol concentration of 15% by weight was prepared at a flow rate of 200 t/b.
The mixture is fed into a distillation column 1 having 24 plates at a ratio of y, and a liquid having a jetanol concentration of 80% by weight is distilled from the top of the column, and water having a jetanol content of 0ff15% by weight or less is taken out from the bottom of the column. The concentration of water-containing ethanol distilled from the top of column 1 and the concentration distilled from the top of distillation column 3, which has 22 plates as described below, is 8.
Water-containing ethanol containing 0% by weight was sent from B to the membrane separator 2 at a rate of 37.5 t/br (0.21 of this is the aqueous ethanol solution distilled from the top of the distillation column 3). , processed by pervaporation method to extract vapor with an ethanol concentration of 1.3% by weight as a membrane-permeable component,
Ethanol with a concentration of 99% by weight was obtained as a film reject component from the bottom of the can. After condensing the vapor distilled from the top of the can using a heat exchanger, it is fed to the distillation column 3 to distill water-containing ethanol with a concentration of 80% by weight from the top of the column.
It was re-fed to the membrane separator 2. From the bottom of the distillation column 3, water containing less than 0.005 ml of shetanol (17) was taken out.

Energy functions f(x), g(x) in this example,
h(x) are each 45 kv'br, l Q k@/hr
, 9 k@/hr, and the total required steam amount F(x) is 54 kg/by.

Nao, the membrane used for pervaporation has a permeability of 0.31 hr, a separation coefficient of 19, and a membrane area of 20.2 m.
A hollow 7 eyeper type PVA membrane was used, and the operating conditions were: the pressure on the raw solution side was 10001 HP, the pressure on the steam side was 100 HP,
The temperature was 50°C.

Similarly, by changing the ethanol concentration and membrane area in each of A and B, the total amount of steam required to obtain ethanol with a concentration of 99% was determined using the same method as in Example 7, and the results are shown in Table 2. 8 to 12. In addition, in Comparative Example 5, it was shown that the total amount of steam required to obtain 99% ethanol when the ethanol 11 degree at points A and B is 50.95% by weight is 212 ky/hr, but this is not the case in this book. A 74% excess amount of steam was required compared to the minimum required amount of steam defined in the invention. Similarly, Comparative Examples 6 to 8
Also shown.

(18) Examples 13-16. Comparative Examples 9 to 12 Using the apparatus shown in the flow sheet of Figure 3, a methanol solution with a concentration of methyl acetate of 15% was prepared from A at a flow rate of 20%.
The liquid is fed to a distillation column 1 having 48 plates at a rate of 0 t/hr, and a liquid with a methyl cyacetate concentration of 70% by weight is distilled from the top of the column, and a liquid with a methyl cyacetate concentration of 0.015% by weight is distilled from the bottom of the column. Remove the methanol.

A mixed solution of methyl acetate/methanol distilled from the top of column 1 and a methanol solution with a methyl acetate concentration of 80% by weight distilled from the top of distillation column 3 having 22 plates, which will be described later, were mixed into 4
3.21/br (out of which, 0.41 is the methyl acetate solution distilled from the top of the distillation column 3), which is in excess of the membrane separator 2, treated by the pervaporation method, Methyl acetate concentration is 2.2% by weight as a membrane-permeable component.
The vapor was taken out, and methyl acetate with a concentration of 99% was obtained as a membrane reject component from the bottom of the can. The vapor distilled from the top of the tank is condensed by a heat exchanger and then fed to the distillation column 3. From the top of the column, a methanol solution with a concentration of methyl acetate of 70% by weight is distilled out. It was re-fed to the membrane separator 2 (20). Methanol having a methyl acetate content of 0.005% by weight or less was taken out from the bottom of the distillation column 3.

Energy functions f(x), g(x) in this example,
h(x) are 50.8 kg/hr and 9.2 kIl, respectively.
/hr, 4.0kg/hr, and the total required steam amount F(x) was 64.0yu/11r.The membrane used for pervaporation had a permeability of 0.0kg/hr.
2 #/m・hr, separation coefficient is 19, membrane area is 51.2
The hollow fiber type ethylene vinyl alcohol copolymer membrane of I was used, and the operating conditions were that the pressure on the raw solution side was 1000 W.
HF, the steam side pressure was loOmH, and the temperature was 50°C.

In the same manner as in Example 13, by changing the methyl acetate concentration and membrane area in each AB, find the required amount of steam to obtain 99% methyl acetate when 99% acetic acid is 60.70% by weight. It was shown that the total amount of steam required to obtain methyl is 143'ii/hr, which is 30% excess steam compared to the minimum required amount (21) defined in the present invention. did. Comparative Examples 10 to 12 were also shown in the same manner.

outer bottom margin (22)

[Brief explanation of the drawing]

1 to 3 are flow sheets showing examples of an apparatus for implementing the present invention, and FIGS. 4 to 6 are graphs showing examples of the required energy function F(x) in the present invention. Patent applicant RiRa Shi Co., Ltd. Agent Ken Kinoshita
Megnol Point B Ethanol Concentration (WL%) Figure 4 Point B Ethanol Concentration (WL%) Figure 5 O Figure 6 Procedure Amendment 1- (Spontaneous) Mu October 1980 Kasuga Patent Application No. 127429/1982 2, Invention Name of method for separating liquid mixtures 3, relationship with the case of the person making the amendment Patent applicant: 1621 Sakazu, Kurashiki City (108) Rira Shi Co., Ltd. Representative director Tsugu Oka Hayashi 4, agent (Tokyo contact information) Co., Ltd. Kuraray Patent Department (within Tokyo Branch) Telephone: Tokyo 03 (277) 3182 6. Details of the amendment 1) Delete "and" in the 4th line of page 9 of the specification. 2) Insert [reflux ratio RRI J] after [Dt(Cdtx) J on the 4th line of page 9. 3) "The reflux ratio RRt is Dl/Fl" on page 9, line 5.
Delete "Requested". 4) On page 9, line 10, [f(Fl(Ftx),
DI(Qllx)) J as [f(Fl(Fix), Dl(
Cdix), RRt). 5) “Da(Cdax)J (
6) Insert ", RRa j" after D. 6) "The reflux ratio RRs is D3/F" on the 7th line of page 10.
Delete "I'm asked for it." 7) 1h(F3(F3x, D
a(Cd3x))J [h(F3(F3x), DB(C
d3x), RR3]”. 8) “1.3” on page 10, lines 6 and 18 of the detailed letter
Correct "60 weight" to "60 weight" respectively. 9) Replace “19” on page 15, line 6 with “156J (1
) to be corrected. 10) Table 1 on page 16 of the same page is corrected as shown in the attached sheet. (The corrected part is the "value in the section of permeated vapor composition.") 11) "1.3% by weight" on page 17, line 14 of the same page has been changed to "60M amount%."
” is corrected. 12) Correct "19" in the 6th line of page 18 to "156". 13) Table 2 on page 19 of the same page is corrected as shown in the attached sheet. (The corrected area is [numerical value in the permeated vapor composition section]) 14) Correct "2.2% by weight" on page 20, line 15 of the same to "26.9% by weight." 15) Page 21, line 8 d, f) [0.2 kg/n
! , hr J, [19J and 1-51.2J,
-Respectively "o, 1kti/r! - Uji,
16) Table 6 on page 26 of the same page is corrected as shown in the attached sheet. (The correction location is [Numbers in the section of permeated vapor composition]) 17) No. 2
Replace the figure and Figure 5 with the attached sheet. Above (4) (5) Figure 2 Water/Ethanol Figure 3

Claims (1)

[Claims] 1. In a method for separating a liquid mixture consisting of at least two components by a combination of a distillation step and a membrane separation step, the energy functions f(x) and g(x) required for each of the above steps are determined, A method for separating a liquid mixture, characterized in that the distillation step and the membrane separation step are connected at a concentration Xmin of the distillate from the distillation step such that the sum F(x) = f(x) + g(x) is the minimum value. . 2. In a method of separating a liquid mixture consisting of at least two components by a combination of a first distillation step, a membrane separation step, and a second distillation step, the energy functions f (X), g( x) and h(x), and calculate the concentration of the distillate in the first distillation process x min, where the sum F(x) = f(x) + g(x) + h(x) is the minimum value. A method for separating a liquid mixture, characterized in that a distillation step and a membrane separation step are connected.