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Novel hybrid separation processes for solvent recovery based on positioning the extractive heterogeneous-azeotropic distillation
Chemical Engineering and Processing 43 (2004) 327–338
Novel hybrid separation processes for solvent recovery based on positioning the extractive heterogeneous-azeotropic distillation Agnes Szanyi, Peter Mizsey∗ , Zsolt Fonyo Chemical Engineering Department, Budapest University of Technology and Economics, Budapest, H-1521 Hungary Received 8 November 2002; received in revised form 14 March 2003; accepted 15 May 2003
Abstract The solvent recovery is often the separation of highly non-ideal mixtures. The separation and recovery of quaternary solvent mixtures coming from printing and medicine factories are investigated. The components of the six quaternary mixtures studied in form of heterogeneous and homogeneous azeotropes of minimum boiling point. The mixtures can be categorised into three groups according to their VLLE behaviours. After studying their behaviours, three novel hybrid separation processes based on the extractive heterogeneous-azeotropic distillation, a special kind of new distillation, are developed and recommended for each group of solvents. In the novel processes, beside the extractive heterogeneous-azeotropic distillation, ordinary distillations and phase separation units are also used utilising the fact that the combination of such units, the hybrid processes, offer a higher variety of the possibilities for the separation of highly non-ideal mixtures. The separation processes are verified experimentally and the agreements between the simulated and measured data prove to be rather favourable. A strategy is recommended for the use of the novel hybrid processes developed according to the VLLE behaviour of the non-ideal quaternary mixtures. © 2003 Elsevier B.V. All rights reserved. Keywords: Solvent recovery; Separation processes; Extractive heterogeneous-azeotropic distillation; Quaternary; Non-ideal mixtures
1. Introduction The solvent recovery is an important problem to minimise burden upon the environment with the off-site recycling and multiple use of solvents. The solvent recovery is also often economically beneficial but the saving always depends on the different, usually country specific, prices. The mixtures of solvents arising as waste streams in different companies, e.g. printing companies, medicine factories, consist of components which form usually highly non-ideal mixtures. The separation of such mixtures is always a challenge for chemical engineers and it has been being exhaustively and successfully studied by several authors on several levels. Some well known authors from the present are Schembecker and Simmrock [1], Blass [2], Biegler et al. [3], Stichlmair and Fair [4], and Doherty and Malone [5]. In spite of the several hundreds of publications and books about the separation of the non-ideal mixtures, the topic is still not exhausted and new problems and areas are arising day by day. ∗
Corresponding author. Tel.: +36-1-463-2174; fax: +36-1-463-3197. E-mail address: [email protected] (P. Mizsey).
0255-2701/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0255-2701(03)00132-6
A relatively new concept is the combination of different unit operations which results in the so-called hybrid separation technologies. There are in the literature comprehensive studies of the problem of the separation of the non-ideal mixtures (e.g. [1–5]), several hybrid separation processes are developed and different synthesis strategies have been recommended to give guideline for a systematic design of hybrid separation technologies (e.g. [5–7]). But, due to the complexity of this problem there is a permanent need for newer and newer separation processes which can give powerful solutions. Membrane separation technologies, e.g. pervaporation, are also involved in the research and practice usually with combination of distillation (e.g. [8–10]). A relatively less studied area of the separation of non-ideal mixtures is the separation of the non-ideal quaternary mixtures. In our previous research works, we have already successfully and solved the separation problem of highly non-ideal quaternary mixtures of different industrial solvents [6,7,11,12]. The mixtures studied have been the waste streams of printing companies and consist of ethanol (ETOH), ethyl acetate (ETAC), isopropyl acetate (IPAC), water (H2 O) and ethanol, ethyl acetate, methyl-ethylketone (MEK), and water. There are some accompanying
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Table 1 Azeotropes of water–ETOH–MEK–acetone mixture (mixture 1) Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
MEK (wt.%)
Acetone (wt.%)
Binary azeotropes Water–ETOH Water–MEK ETOH–MEK
78.2 73.7 74
4 12.7 0
96 0 39
0 87.3 61
0 0 0
Ternary azeotropes Water–ETOH–MEK
73.2
11
14
75
0
components in <5 wt.%, which are neglected in the study. The product purity specification is about 95 wt.%. The two quaternary mixtures studied in the earlier works are highly non-ideal ones and they form several binary and ternary azeotropes making the separation a quite complex problem. The azeotropes of the two mixtures found in the literature are collected in Tables 3 and 5 [13,14]. In other printing companies and medicine factories, other components can also be found in the waste streams of solvents to be recovered, e.g. acetone, iso-propanol (IPOH). While solving the separation problem it is our incentive to generalise the solutions for other non-ideal mixtures. For this sake, six mixtures are selected based on industrial problems for our study and hybrid separation process alternatives designed for their separation. In our solvent recovery problem, we are faced with the problems of this less studied area, namely, the separation of non-ideal quaternary mixtures with limited immiscibility. The six mixtures are classified according to their non-ideality, i.e. the number of binary and ternary azeotropes they form. In the literature not all ternary azeotropes are found but calculations prove that they do exist (not measured yet) and these azeotropes are also indicated in Tables 1–6 and they show the azeotropes of mixtures 1–6. Table 7 shows a summery of the six mixtures and the number of azeotropes they form. It is common in the six mixtures that they have limited immiscibility and they form both homogeneous and heterogeneous azeotropes of minimum boiling point.
2. Design of novel hybrid separation processes After studying the highly non-ideal VLLE nature of the six mixtures to be recovered, it becomes clear that the mix-
tures cannot be separated with the use of ordinary distillation techniques but a combination of different type of separation units, that is hybrid separation processes are needed. Each mixture contains water and heterogeneous azeotropes also exist. In earlier works, new separation processes have been designed: the so-called two-column system which consists of two coupled distillation columns with phase separation [11] and the so-called ternary-cut system which consists of nine unit operations [12,15]. The two-column system can cope with the problem of splitting the quaternary mixtures into two binary ones. The system is quite simple but its energy consumption is relatively high [15]. Fig. 1 shows the ternary-cut system designed for mixture 3. This system splits the quaternary mixture into two ternary ones which are processed independently but on a similar way. It can be seen that this system, however, is quite complex. Therefore, new, realistic, and simple hybrid separation systems with modest energy consumption and consisting of relatively less unit operation modules are to be designed. The possibility of generalisation of the separation technologies is also considered. During the system simulations the UNIQUAC thermodynamic property model with UNIFAC estimation for the non-measured data is used for the calculation of the VLLE equilibrium [16]. The six quaternary mixtures selected (Table 7) are classified in three groups according to the number of their binary and ternary azeotropes: • Group 1: mixtures 1 and 2; • Group 2: mixtures 3 and 4; • Group 3: mixtures 5 and 6. It can be also seen in Table 7 that the mixtures in each group have the same number of azeotropes, while the mixtures in Group 1 have three binary and one ternary
Table 2 Azeotropes of water–ETOH–ETAC–acetone mixture (mixture 2) Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
ETAC (wt.%)
Acetone (wt.%)
Binary azeotropes Water–ETOH Water–ETAC ETOH–ETAC
78.2 70.4 72.2
4 8.5 0
96 0 25.8
0 91.5 74.2
0 0 0
Ternary azeotropes Water–ETOH–ETAC
70.2
9
8.4
82.6
0
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Table 3 Azeotropes of water–ETOH–ETAC–IPAC mixture (mixture 3) Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
ETAC (wt.%)
IPAC (wt.%)
Binary azeotropes Water–ETOH Water–ETAC Water–IPAC ETOH–ETAC ETOH–IPAC
78.2 70.4 76.6 71.8 76.8
4 8.5 10.6 0 0
96 0 0 31 53
0 91.5 0 69 0.47
0 0 89.4 0
Ternary azeotropes Water–ETOH–ETAC Water–ETOH–IPAC
70.2 74.8
9 9.8
8.4 19.4
82.6 0
0 70.8
Table 4 Azeotropes of water–ETOH–MEK–IPAC mixture (mixture 4) Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
MEK (wt.%)
IPAC (wt.%)
Binary azeotropes Water–ETOH Water–MEK Water–IPAC ETOH–MEK ETOH–IPAC
78.2 73.3 76.6 74 76.8
4 12.7 10.6 0 0
96 0 0 39 53
0 87.3 0 61 0
0 0 89.4 0 47
Ternary azeotropes Water–ETOH–MEK Water–ETOH–IPAC
73.2 74.8
11 9.8
14 19.4
75 0
0 70.8
Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
ETAC (wt.%)
MEK (wt.%)
Binary azeotropes Water–ETAC ETOH–ETAC Water–MEK ETOH–MEK ETAC–MEK Water–ETOH
70.4 71.8 73.3 74.1 77 78.2
8.5 0 12.7 0 0 4
0 31 0 39 0 96
91.5 69 0 0 82 0
0 0 87.3 61 18 0
Ternary azeotropes Water–ETOH–ETACI Water–ETOH–MEK Water–ETAC–MEK
70.2 73.2 71.1
9 11 8.7
8.4 14 0
82.6 0 85
0 75 6.3
Table 5 Azeotropes of water–ETOH–ETAC–MEK mixture (mixture 5)
Table 6 Azeotropes of water–IPOH–ETAC–MEK mixture (mixture 6) Boiling temperature (◦ C)
Water (wt.%)
IPOH (wt.%)
ETAC (wt.%)
MEK (wt.%)
Binary azeotropes Water–ETAC IPOH–ETAC Water–MEK IPOH–MEK ETAC–MEK Water–IPOH
70.4 76.1 73.3 77.7 77 80.2
8.5 0 12.7 0 0 12.6
0 19.2 0 34.2 0 87.4
91.5 80.4 0 0 82 0
0 0 87.3 65.8 18 0
Ternary azeotropes MEK–IPOH–ETAC Water–IPOH–MEK Water–ETAC–MEK
75.9 72.8 71.1
0 11.2 8.7
16 2.8 0
68.6 0 85
15.4 86 6.3
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Table 7 Quaternary mixtures selected for the study Group 1
Group 2
Group 3
Mixture 1
Mixture 2
Mixture 3
Mixture 4
Mixture 5
Mixture 6
Water ETOH MEK Acetone
Water ETOH ETAC Acetone
Water ETOH ETAC IPAC
Water ETOH MEK IPAC
Water ETOH ETAC MEK
Water IPOH ETAC MEK
Binary azeotropes
3
3
5
5
6
6
Ternary azeotropes Literature [13,14] Calculated
1
1
2
2
3
1 2
Compound Compound Compound Compound
1 2 3 4
azeotropes, the mixtures in Group 2 form five binary and one ternary azeotropes, and then the mixtures of Group 3 form in each combination azeotropes and they have six binary and three ternary ones. Since water is originally present in the mixtures, the synthesised separation structures can exploit the advantage of heterogeneous azeotropy and immiscibility regions allowing the step over separation boundaries. This is quite typical for the so-called heterogeneous-azeotropic distillation but we can also utilise the effect of the extractive distillation if we use an entrainer. According to the classical definition [5], the extractive distillation is a method of separating minimum boiling binary azeotropes by use of an entrainer that is the heaviest species in the mixture, does not form any azeotropes with the original components, and is completely miscible with them in all proportions. Nowadays, we define extractive distillation in a wider manner, namely the entrainer can also be the lightest and the middle boiling component as well. If the entrainer is the lightest component we speak about the so-called “reverse extractive distillation” [17] that has been already used for successful separation. Extractive distillation of maximal azeotrope with middle boiling entrainer has been already reported [18]. All this indicates that in the area of the separation of the non-ideal mixtures we should not strictly insist on the classical definitions since due to complex nature of these kinds of separation problems always newer solutions are required. In our cases, we can utilise the fact that water is the heaviest component in each mixture and the mixtures form only minimum azeotropes. If additional amount of water is applied as an auto-entrainer to improve the separation of the heterogeneous-azeotropic distillation with the extractive distillation effect, one of the basic principles of the green chemistry is followed: no new material is added to the system [19]. This way we define a novel separation technique: the so-called “extractive heterogeneous-azeotropic distillation”, which is actually a heterogeneous-azeotropic distillation enhanced with extractive distillation effect. The additional amount of water added as entrainer leaves the distillation column in the bottom product. With the use of water as auto-entrainer a special separation technique is
enforced which can be considered as novel separation. According to our results and experience this novel technique, the extractive heterogeneous-azeotropic distillation with water as auto-entrainer allows more efficient separation than previous solutions. This combination of separation effects and its synonym are also used in other contributions [20,21]. The novel hybrid separation systems designed for the separation of the six highly non-ideal mixtures of industrial solvents integrate the distillation, the extractive effect, and/or the water addition in the phase-separator of the previously designed two-column or ternary-cut systems. These novel hybrid systems are based on extractive heterogeneous-azeotropic distillations defined above that prove to be a multifunctional unit and allow a simple solution of the solvent recovery that is the separation problem. 2.1. Novel hybrid separation systems for the mixtures of Group 1 In these mixtures there is one component (acetone) which is the most volatile component and forms no azeotropes with the other components. According to the well known separation heuristics it is recommended that in the first step this component should be separated with an ordinary distillation and then the separation of the ternary system follows (Fig. 2). This separation can be realised with extractive heterogeneous-azeotropic distillation adding water as auto-entrainer to the system. Figs. 3 and 4 show the VLLE data: the residue curve map, separation boundaries, the binary and ternary azeotropes, and the immiscibility region for mixtures 1 and 2, respectively, and the extractive heterogeneous-azeotropic distillation is also represented. The bottom product is the mixture of ethanol and water. The recovery of the ethanol from the water is a well known technique. In this study, since the product purity specification is about 95 wt.%, an ordinary distillation can be sufficient to recover the ethanol in a composition close to the azeotropic point. Another alternative for the separation is also designed: the mixtures can be also separated if the separation starts with
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Fig. 1. The ternary-cut separation system [12,15] (P1; W, water; P2, ETOH; P3, ETAC; P4, IPAC).
the extractive heterogeneous-azeotropic distillation and the recovery of the non-azeotropic component is the last step (Fig. 5). An economic investigation is carried out to determine which system is to be selected. The cost data are shown in Table 8. The capital cost is also estimated [22], the project life is 10 years. The acetone content of the feed is varied and the results are shown in Fig. 6. (The same tendency is found if the project life is 5 years). The economic comparison shows that the structure that separates the volatile non-azeotropic component with an
Table 8 Cost data Capital cost Marshall and Swift index Project life (years)
1056.8/280 10
Utility Steam (US$/t) Cooling water (US$/t) Electricity (US$/(kW h))
6.62 0.0067 0.06
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Fig. 2. Separation scheme starting with ordinary distillation for the mixtures of Group 1.
ordinary distillation in the first step proves to be always cheaper than the other alternative and the results correspond to the well known heuristics of the separation sequencing. 2.2. Novel hybrid separation system for the mixtures of Group 2 The components of the mixtures of this group form five binary and two ternary azeotropes (Tables 3 and 4). The mix-
tures of this group are more complicated than the ones of Group 1, so the VLLE data can be described already at the beginning in a tetrahedron and Fig. 7 shows the azeotropic points (square represents a binary and triangle represents a ternary azeotrope), separation boundaries, and the immiscibility region with the tie lines. For the sake of better overview the residue curves are not shown. In this case the VLLE data of the quaternary systems allows separating the quaternary mixtures with an
Fig. 3. Representation of VLLE data and the extractive heterogeneous-azeotropic distillations for mixture 1.
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Fig. 4. Representation of VLLE data and the extractive heterogeneous-azeotropic distillations for mixture 2.
extractive heterogeneous-azeotropic distillation, where water is the auto-entrainer, into two products (Fig. 8). The bottom product contains the component (ETOH) which is with water miscible and the distillate contains the components (ETAC, IPAC or MEK, IPAC) which are immiscible with water. However, the water appears also in the top product where phase separation is also used to enhance the separation. The operation of this extractive heterogeneous-azeotropic distillation is shown for mixture 4 in Fig. 7: F1 is the feed, R the recycled stream coming
from the subsequent ordinary distillation columns (binary azeotrope), F the mixtures of F1 and R, D1 and B1 are the products of the extractive heterogeneous-azeotropic distillation column. From the bottom product (ethanol and water) ethanol is recovered in a composition close to the azeotropic point with an ordinary distillation. The organic rich phase of the distillate of the extractive heterogeneous-azeotropic distillation (ETAC, IPAC, water or MEK, IPAC, water) is separated in two subsequent ordinary distillation columns. The top product (R) of the second
Fig. 5. Separation scheme starting with extractive heterogeneous-azeotropic distillation for the mixtures of Group 1.
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Fig. 6. Economic comparison of structures in Figs. 2 and 5.
ordinary distillation column (C3) is recycled into the extractive heterogeneous-azeotropic distillation column. This scheme can separate the mixtures of Group 2 that have five binary and two ternary azeotropes and water is also present forming heterogeneous and homogeneous minimum boiling azeotropes. 2.3. Novel hybrid separation system for the mixtures of Group 3 The mixtures of this group are the most complex ones in our assembly. In each combination, there is a binary and a ternary minimum boiling azeotrope (Tables 5 and 6). Fig. 9 shows the VLLE data of mixture 6: the azeotropic points (square represents a binary and triangle represents a ternary
Fig. 7. VLLE data of mixture 4 and representation of extractive heterogeneous-azeotropic distillation.
azeotrope), separation boundaries, and the immiscibility region with the tie lines. The study of the VLLE data results that with the use of extractive heterogeneous-azeotropic distillation, where water is the auto-entrainer again, it is possible to separate the organic components of these mixtures into two groups: with water miscible component (ETOH or IPOH), and with water immiscible components (ETAC, MEK). The water appears also in the top product of the extractive heterogeneous-azeotropic distillation column where phase separation is also used. The water rich phase is practically water. Fig. 9 shows that with the use of water as an auto-entrainer it is possible to cross separation boundary and get into the immiscibility region. The top and bottom products of the extractive heterogeneous-azeotropic distillation are also indicated, the top product (D1) is on the edge of the immiscibility region. The recovery of the ethanol or iso-propanol takes place in one ordinary distillation column, however, the azeotropic composition of the iso-propanol is still lower than the product purity prescription, so a different separation, maybe membrane separation, is needed. The elaboration of such a different separation is, however, neglected at this point of our study. On the contrary, it is rather interesting how to separate the top product of the extractive heterogeneous-azeotropic distillation column containing ethyl-acetate, methyl-ethylketone, and water. This ternary system forms also in every combination azeotropes. Fig. 10 shows the residue curve map, the separation boundaries, the binary and ternary azeotropes, and the immiscibility region for the MEK–ETOH–water mixture. After investigating these data a solution of the separation is designed and it is also shown in Fig. 11. The feed composition is out of the immiscibility region and for the separation the crossing of separation boundary would be necessary. The crossing of this boundary from this side is not possible [23], but it can be carried out if another
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Fig. 8. Separation scheme for the mixtures of Group 2.
extractive heterogeneous-azeotropic distillation is applied. The distillate of column 2 (C2) is in the immiscibility region and after a phase separation, that allows the crossing of the separation boundary, ethyl-acetate can be recovered in the prescribed purity. The bottom product is distilled in a common distillation column and its top product is in the immiscibility region again. After a phase separation crossing the separation boundary again, the methyl-ethyl-ketone is obtained in 93 wt.% purity. (The LLE allows only such purity but if higher purity of the methyl-ethyl-ketone were badly needed, further separation would be necessary.) This novel hybrid separation technology is also based on extractive heterogeneous-azeotropic distillation and allows the separation of the most complicated mixtures, i.e. mixtures 5 and 6.
3. Experimental investigations The experimental investigation of a novel process is important to give confidence for the design methods applied and also for the results obtained. The core of the novel hybrid separation processes is an extractive heterogeneous-azeotropic distillation unit. These units are verified by laboratory experiments corresponding to the circumstances found by simulations. The internal diameter of the laboratory distillation column is 3 cm, the column height is about 2 m, and the column internal is structured packing. The height of the packing is varied according to the distillation investigated. Continuous distillation is Table 9 Measured and simulated data of column of separation scheme for mixture 3, Group 2 Feed (wt.%)
Water ETOH ETAC IPAC
21 32 26 21
Simulated data (wt.%)
Measured data (wt.%)
Distillate
Bottom
Distillate
Bottom
2.7 0 55.0 42.3
96.1 3.9 0 0
2.8 0 53.2 44.0
95.8 4.2 0 0
Table 10 Measured and simulated data of column 1 of separation scheme for mixture 5, Group 3 Feed (wt.%)
Fig. 9. VLLE data of mixture 6 and representation of extractive heterogeneous-azeotropic distillation.
Water ETOH ETAC MEK
13 24 34 29
Simulated data (wt.%)
Measured data (wt.%)
Distillate
Bottom
Distillate
Bottom
9.6 0 49.1 41.3
93 7 0 0
7 0 50.2 43
93.7 6.3 0 0
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Fig. 10. VLLE data and separation of MEK–ETAC–water mixture.
carried out for several hours, the top and bottom products are continuously analysed. The organic compounds are analysed by gaschromatograph, the water is analysed by the Karl–Fisher technique. The extractive heterogeneous-azeotropic distillation columns of the separation schemes designed for Groups 2 and 3 are tested. Tables 9 and 10 show the result of the
experiments and the comparisons with the simulated data as well. The comparisons show a good agreement which proves the accuracy of the selected UNIQUAC thermodynamic property model, the simulation procedure, and gives also confidence for the novel hybrid separation processes.
Fig. 11. Separation scheme for the mixtures of Group 3.
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Table 11 Suggested strategy for the separation of quaternary non-ideal mixtures Group
Component forming no azeotrope
Number of binary azeotropes
Number of ternary azeotropes
Recommended novel hybrid separation schemea
1
One component (volatile)
3
1
2
Two components in pair
5
2
3
–
6
3
Ordinary distillation followed by extractive heterogeneous-azeotropic distillation (Fig. 2) Extractive heterogeneous-azeotropic distillation followed by two ordinary distillation with recycle (Fig. 8) Two subsequent extractive heterogeneous-azeotropic distillation followed by one ordinary distillation (Fig. 11)
a
The separation of ethanol–water or iso-propanol–water is not included.
4. Conclusions The successful application of novel hybrid separation systems based on the combination of extractive heterogeneous-azeotropic distillation with water as autoentrainer, ordinary distillation, and phase separation allows significant simplification and improves economic features of the separation of quaternary non-ideal mixtures being typical for solvent recovery. The positioning of the extractive heterogeneous-azeotropic distillation in the hybrid systems plays an important role in these novel separation schemes. After studying the six mixtures of three groups a general guideline is suggested for a strategy to separate highly non-ideal quaternary mixtures forming binary and ternary, homogeneous and heterogeneous minimum boiling azeotropes. The strategy is based on the novel hybrid separation processes designed for the non-ideal quaternary mixtures studied. The novel processes can be successfully applied if water is present in the mixture to be separated and there is immiscibility region with heterogeneous azeotropes of minimum boiling points. These are quite common conditions because the behaviour of a lot of organic solvents with water corresponds to these. Table 11 shows the recommended strategy for the separation of quaternary non-ideal mixtures containing water as well. Economic comparison shows that it is recommended to separate first the component which is the most volatile and forms no azeotrope with the other three components and this separation can be carried out with an ordinary distillation. So, for the mixtures of Group 1 after the ordinary distillation the extractive heterogeneous-azeotropic distillation is applied to separate the azeotrope forming components. If there is a component pair which forms with each other no azeotrope but they do form azeotropes with the other components, an extractive heterogeneous-azeotropic distillation is applied, which is followed by two ordinary distillation columns with recycle. This technique is found to be suitable for the separation of the mixtures of Group 2. If in each combination a binary azeotrope exists (six pieces) and there are three ternary azeotropes, as well a separation scheme consisting of two subsequent extractive heterogeneous-azeotropic distillation columns followed
by one ordinary distillation is to be designed. Phase split effects due to the immiscibility are also utilised. This scheme is successfully investigated for the mixtures of Group 3. Experimental verifications show good agreement between the simulated and measured data that also supports the possible realisation of the synthesised novel solvent recovery processes. The developed solvent recovery processes based on the suggested strategy can realise significant saving and reduction of the burden upon the environment. References [1] G. Schembecker, K.H. Simmrock, Azeopert—a heuristic-numeric system for the prediction of azeotrope formation, Comput. Chem. Eng. 19 (1995) S253–S258. [2] E. Blass, Entwicklung Verfahrenstechnischer Prozesse, Springer, 1997. [3] L.T. Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall, Englewood Cliffs, NJ, 1997. [4] J.G. Stichlmair, J.R. Fair, Distillation, principles and practices, Wiley-VCH, USA, 1998. [5] M.F. Doherty, M.F. Malone, Conceptual Design of Distillation Systems, McGraw-Hill, New York, 2001. [6] E. Rev, P. Mizsey, Z. Fonyo, Framework for designing feasible schemes of multicomponent azeotropic distillation, Comput. Chem. Eng. 18 (1994) S43–S47. [7] P. Mizsey, E. Rev, Z. Fonyo, Systematic separation system synthesis of a highly non-ideal quaternary mixture, AIChE Spring National Mtg., Chicago, 1997, Paper 19f. [8] T. Raiser, H. Steinhauser, Azeotrope ausgetrickst, Chem. Tech. 23 (7) (1994) 44–46. [9] I. Wilson, Encyclopedia of Separation Science, Academic Press, New York, 2000. [10] A.M. Eliceche, M.C. Daviou, P.M. Hoch, I.O. Uribe, Optimisation of azeotropic distillation columns combined with pervaporation membranes, Comput. Chem. Eng. 26 (2002) 563–573. [11] P. Mizsey, A global approach to the synthesis of entire chemical processes, Ph.D. Thesis, No. 9563, Swiss Federal Institute of Technology, ETH Zürich, Germany, 1991. [12] A. Raab, Separation of highly non-ideal mixture for solvent recovery, Diploma work at Budapest University of Technology and Economics, 2001. [13] H.L. Horsley, Azeotropic data, American Chemical Society, Washington, DC, USA, 1973. [14] J. Gmehling, J. Menke, K. Fischer, J. Krafczyk, Azeotropic Data, VCH, Parts I, II, Weinheim, Germany, 1994.
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[20] Lelkes, Z., Rodriguez-Donis, I., Lovász, A., Papp, K., Gerbaud, V., Rev, E., Feasibility studies of heterogeneous extractive distillation process, in: Proceedings of the Days of Chemical Engineering’03, KE MÜKKI, Veszprem, Hungary, 8–10 April 2003, pp. 208–213. [21] I. Rodriguez-Donis, V. Gerbaud, Z. Lelkes, J. Acosta Esquijarosa, K. Papp, E. Rev, X. Joulia, Z. Fonyo, Separation of an azeotropic mixture by heterogeneous-extractive continuous distillation, in: Proceedings of the Sixth Italian Conference on Chemical and Process Engineering on Oral Presentation at ICheaP 6, Paper no. 314, 8–11 June 2003, Pisa, Italy. [22] J.M. Douglas, Conceptual Design of Chemical Processes, McGrawHill, New York, 1989. [23] B.J. Bossen, S.B. Jorgensen, R. Gani, Simulation, design, and analysis of azeotropic distilktion operations, Ind. Eng. Chem. Res. 32 (1993) 620–630.
Novel hybrid separation processes for solvent recovery based on positioning the extractive heterogeneous-azeotropic distillation Agnes Szanyi, Peter Mizsey∗ , Zsolt Fonyo Chemical Engineering Department, Budapest University of Technology and Economics, Budapest, H-1521 Hungary Received 8 November 2002; received in revised form 14 March 2003; accepted 15 May 2003
Abstract The solvent recovery is often the separation of highly non-ideal mixtures. The separation and recovery of quaternary solvent mixtures coming from printing and medicine factories are investigated. The components of the six quaternary mixtures studied in form of heterogeneous and homogeneous azeotropes of minimum boiling point. The mixtures can be categorised into three groups according to their VLLE behaviours. After studying their behaviours, three novel hybrid separation processes based on the extractive heterogeneous-azeotropic distillation, a special kind of new distillation, are developed and recommended for each group of solvents. In the novel processes, beside the extractive heterogeneous-azeotropic distillation, ordinary distillations and phase separation units are also used utilising the fact that the combination of such units, the hybrid processes, offer a higher variety of the possibilities for the separation of highly non-ideal mixtures. The separation processes are verified experimentally and the agreements between the simulated and measured data prove to be rather favourable. A strategy is recommended for the use of the novel hybrid processes developed according to the VLLE behaviour of the non-ideal quaternary mixtures. © 2003 Elsevier B.V. All rights reserved. Keywords: Solvent recovery; Separation processes; Extractive heterogeneous-azeotropic distillation; Quaternary; Non-ideal mixtures
1. Introduction The solvent recovery is an important problem to minimise burden upon the environment with the off-site recycling and multiple use of solvents. The solvent recovery is also often economically beneficial but the saving always depends on the different, usually country specific, prices. The mixtures of solvents arising as waste streams in different companies, e.g. printing companies, medicine factories, consist of components which form usually highly non-ideal mixtures. The separation of such mixtures is always a challenge for chemical engineers and it has been being exhaustively and successfully studied by several authors on several levels. Some well known authors from the present are Schembecker and Simmrock [1], Blass [2], Biegler et al. [3], Stichlmair and Fair [4], and Doherty and Malone [5]. In spite of the several hundreds of publications and books about the separation of the non-ideal mixtures, the topic is still not exhausted and new problems and areas are arising day by day. ∗
Corresponding author. Tel.: +36-1-463-2174; fax: +36-1-463-3197. E-mail address: [email protected] (P. Mizsey).
0255-2701/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0255-2701(03)00132-6
A relatively new concept is the combination of different unit operations which results in the so-called hybrid separation technologies. There are in the literature comprehensive studies of the problem of the separation of the non-ideal mixtures (e.g. [1–5]), several hybrid separation processes are developed and different synthesis strategies have been recommended to give guideline for a systematic design of hybrid separation technologies (e.g. [5–7]). But, due to the complexity of this problem there is a permanent need for newer and newer separation processes which can give powerful solutions. Membrane separation technologies, e.g. pervaporation, are also involved in the research and practice usually with combination of distillation (e.g. [8–10]). A relatively less studied area of the separation of non-ideal mixtures is the separation of the non-ideal quaternary mixtures. In our previous research works, we have already successfully and solved the separation problem of highly non-ideal quaternary mixtures of different industrial solvents [6,7,11,12]. The mixtures studied have been the waste streams of printing companies and consist of ethanol (ETOH), ethyl acetate (ETAC), isopropyl acetate (IPAC), water (H2 O) and ethanol, ethyl acetate, methyl-ethylketone (MEK), and water. There are some accompanying
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Table 1 Azeotropes of water–ETOH–MEK–acetone mixture (mixture 1) Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
MEK (wt.%)
Acetone (wt.%)
Binary azeotropes Water–ETOH Water–MEK ETOH–MEK
78.2 73.7 74
4 12.7 0
96 0 39
0 87.3 61
0 0 0
Ternary azeotropes Water–ETOH–MEK
73.2
11
14
75
0
components in <5 wt.%, which are neglected in the study. The product purity specification is about 95 wt.%. The two quaternary mixtures studied in the earlier works are highly non-ideal ones and they form several binary and ternary azeotropes making the separation a quite complex problem. The azeotropes of the two mixtures found in the literature are collected in Tables 3 and 5 [13,14]. In other printing companies and medicine factories, other components can also be found in the waste streams of solvents to be recovered, e.g. acetone, iso-propanol (IPOH). While solving the separation problem it is our incentive to generalise the solutions for other non-ideal mixtures. For this sake, six mixtures are selected based on industrial problems for our study and hybrid separation process alternatives designed for their separation. In our solvent recovery problem, we are faced with the problems of this less studied area, namely, the separation of non-ideal quaternary mixtures with limited immiscibility. The six mixtures are classified according to their non-ideality, i.e. the number of binary and ternary azeotropes they form. In the literature not all ternary azeotropes are found but calculations prove that they do exist (not measured yet) and these azeotropes are also indicated in Tables 1–6 and they show the azeotropes of mixtures 1–6. Table 7 shows a summery of the six mixtures and the number of azeotropes they form. It is common in the six mixtures that they have limited immiscibility and they form both homogeneous and heterogeneous azeotropes of minimum boiling point.
2. Design of novel hybrid separation processes After studying the highly non-ideal VLLE nature of the six mixtures to be recovered, it becomes clear that the mix-
tures cannot be separated with the use of ordinary distillation techniques but a combination of different type of separation units, that is hybrid separation processes are needed. Each mixture contains water and heterogeneous azeotropes also exist. In earlier works, new separation processes have been designed: the so-called two-column system which consists of two coupled distillation columns with phase separation [11] and the so-called ternary-cut system which consists of nine unit operations [12,15]. The two-column system can cope with the problem of splitting the quaternary mixtures into two binary ones. The system is quite simple but its energy consumption is relatively high [15]. Fig. 1 shows the ternary-cut system designed for mixture 3. This system splits the quaternary mixture into two ternary ones which are processed independently but on a similar way. It can be seen that this system, however, is quite complex. Therefore, new, realistic, and simple hybrid separation systems with modest energy consumption and consisting of relatively less unit operation modules are to be designed. The possibility of generalisation of the separation technologies is also considered. During the system simulations the UNIQUAC thermodynamic property model with UNIFAC estimation for the non-measured data is used for the calculation of the VLLE equilibrium [16]. The six quaternary mixtures selected (Table 7) are classified in three groups according to the number of their binary and ternary azeotropes: • Group 1: mixtures 1 and 2; • Group 2: mixtures 3 and 4; • Group 3: mixtures 5 and 6. It can be also seen in Table 7 that the mixtures in each group have the same number of azeotropes, while the mixtures in Group 1 have three binary and one ternary
Table 2 Azeotropes of water–ETOH–ETAC–acetone mixture (mixture 2) Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
ETAC (wt.%)
Acetone (wt.%)
Binary azeotropes Water–ETOH Water–ETAC ETOH–ETAC
78.2 70.4 72.2
4 8.5 0
96 0 25.8
0 91.5 74.2
0 0 0
Ternary azeotropes Water–ETOH–ETAC
70.2
9
8.4
82.6
0
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Table 3 Azeotropes of water–ETOH–ETAC–IPAC mixture (mixture 3) Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
ETAC (wt.%)
IPAC (wt.%)
Binary azeotropes Water–ETOH Water–ETAC Water–IPAC ETOH–ETAC ETOH–IPAC
78.2 70.4 76.6 71.8 76.8
4 8.5 10.6 0 0
96 0 0 31 53
0 91.5 0 69 0.47
0 0 89.4 0
Ternary azeotropes Water–ETOH–ETAC Water–ETOH–IPAC
70.2 74.8
9 9.8
8.4 19.4
82.6 0
0 70.8
Table 4 Azeotropes of water–ETOH–MEK–IPAC mixture (mixture 4) Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
MEK (wt.%)
IPAC (wt.%)
Binary azeotropes Water–ETOH Water–MEK Water–IPAC ETOH–MEK ETOH–IPAC
78.2 73.3 76.6 74 76.8
4 12.7 10.6 0 0
96 0 0 39 53
0 87.3 0 61 0
0 0 89.4 0 47
Ternary azeotropes Water–ETOH–MEK Water–ETOH–IPAC
73.2 74.8
11 9.8
14 19.4
75 0
0 70.8
Boiling temperature (◦ C)
Water (wt.%)
ETOH (wt.%)
ETAC (wt.%)
MEK (wt.%)
Binary azeotropes Water–ETAC ETOH–ETAC Water–MEK ETOH–MEK ETAC–MEK Water–ETOH
70.4 71.8 73.3 74.1 77 78.2
8.5 0 12.7 0 0 4
0 31 0 39 0 96
91.5 69 0 0 82 0
0 0 87.3 61 18 0
Ternary azeotropes Water–ETOH–ETACI Water–ETOH–MEK Water–ETAC–MEK
70.2 73.2 71.1
9 11 8.7
8.4 14 0
82.6 0 85
0 75 6.3
Table 5 Azeotropes of water–ETOH–ETAC–MEK mixture (mixture 5)
Table 6 Azeotropes of water–IPOH–ETAC–MEK mixture (mixture 6) Boiling temperature (◦ C)
Water (wt.%)
IPOH (wt.%)
ETAC (wt.%)
MEK (wt.%)
Binary azeotropes Water–ETAC IPOH–ETAC Water–MEK IPOH–MEK ETAC–MEK Water–IPOH
70.4 76.1 73.3 77.7 77 80.2
8.5 0 12.7 0 0 12.6
0 19.2 0 34.2 0 87.4
91.5 80.4 0 0 82 0
0 0 87.3 65.8 18 0
Ternary azeotropes MEK–IPOH–ETAC Water–IPOH–MEK Water–ETAC–MEK
75.9 72.8 71.1
0 11.2 8.7
16 2.8 0
68.6 0 85
15.4 86 6.3
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Table 7 Quaternary mixtures selected for the study Group 1
Group 2
Group 3
Mixture 1
Mixture 2
Mixture 3
Mixture 4
Mixture 5
Mixture 6
Water ETOH MEK Acetone
Water ETOH ETAC Acetone
Water ETOH ETAC IPAC
Water ETOH MEK IPAC
Water ETOH ETAC MEK
Water IPOH ETAC MEK
Binary azeotropes
3
3
5
5
6
6
Ternary azeotropes Literature [13,14] Calculated
1
1
2
2
3
1 2
Compound Compound Compound Compound
1 2 3 4
azeotropes, the mixtures in Group 2 form five binary and one ternary azeotropes, and then the mixtures of Group 3 form in each combination azeotropes and they have six binary and three ternary ones. Since water is originally present in the mixtures, the synthesised separation structures can exploit the advantage of heterogeneous azeotropy and immiscibility regions allowing the step over separation boundaries. This is quite typical for the so-called heterogeneous-azeotropic distillation but we can also utilise the effect of the extractive distillation if we use an entrainer. According to the classical definition [5], the extractive distillation is a method of separating minimum boiling binary azeotropes by use of an entrainer that is the heaviest species in the mixture, does not form any azeotropes with the original components, and is completely miscible with them in all proportions. Nowadays, we define extractive distillation in a wider manner, namely the entrainer can also be the lightest and the middle boiling component as well. If the entrainer is the lightest component we speak about the so-called “reverse extractive distillation” [17] that has been already used for successful separation. Extractive distillation of maximal azeotrope with middle boiling entrainer has been already reported [18]. All this indicates that in the area of the separation of the non-ideal mixtures we should not strictly insist on the classical definitions since due to complex nature of these kinds of separation problems always newer solutions are required. In our cases, we can utilise the fact that water is the heaviest component in each mixture and the mixtures form only minimum azeotropes. If additional amount of water is applied as an auto-entrainer to improve the separation of the heterogeneous-azeotropic distillation with the extractive distillation effect, one of the basic principles of the green chemistry is followed: no new material is added to the system [19]. This way we define a novel separation technique: the so-called “extractive heterogeneous-azeotropic distillation”, which is actually a heterogeneous-azeotropic distillation enhanced with extractive distillation effect. The additional amount of water added as entrainer leaves the distillation column in the bottom product. With the use of water as auto-entrainer a special separation technique is
enforced which can be considered as novel separation. According to our results and experience this novel technique, the extractive heterogeneous-azeotropic distillation with water as auto-entrainer allows more efficient separation than previous solutions. This combination of separation effects and its synonym are also used in other contributions [20,21]. The novel hybrid separation systems designed for the separation of the six highly non-ideal mixtures of industrial solvents integrate the distillation, the extractive effect, and/or the water addition in the phase-separator of the previously designed two-column or ternary-cut systems. These novel hybrid systems are based on extractive heterogeneous-azeotropic distillations defined above that prove to be a multifunctional unit and allow a simple solution of the solvent recovery that is the separation problem. 2.1. Novel hybrid separation systems for the mixtures of Group 1 In these mixtures there is one component (acetone) which is the most volatile component and forms no azeotropes with the other components. According to the well known separation heuristics it is recommended that in the first step this component should be separated with an ordinary distillation and then the separation of the ternary system follows (Fig. 2). This separation can be realised with extractive heterogeneous-azeotropic distillation adding water as auto-entrainer to the system. Figs. 3 and 4 show the VLLE data: the residue curve map, separation boundaries, the binary and ternary azeotropes, and the immiscibility region for mixtures 1 and 2, respectively, and the extractive heterogeneous-azeotropic distillation is also represented. The bottom product is the mixture of ethanol and water. The recovery of the ethanol from the water is a well known technique. In this study, since the product purity specification is about 95 wt.%, an ordinary distillation can be sufficient to recover the ethanol in a composition close to the azeotropic point. Another alternative for the separation is also designed: the mixtures can be also separated if the separation starts with
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Fig. 1. The ternary-cut separation system [12,15] (P1; W, water; P2, ETOH; P3, ETAC; P4, IPAC).
the extractive heterogeneous-azeotropic distillation and the recovery of the non-azeotropic component is the last step (Fig. 5). An economic investigation is carried out to determine which system is to be selected. The cost data are shown in Table 8. The capital cost is also estimated [22], the project life is 10 years. The acetone content of the feed is varied and the results are shown in Fig. 6. (The same tendency is found if the project life is 5 years). The economic comparison shows that the structure that separates the volatile non-azeotropic component with an
Table 8 Cost data Capital cost Marshall and Swift index Project life (years)
1056.8/280 10
Utility Steam (US$/t) Cooling water (US$/t) Electricity (US$/(kW h))
6.62 0.0067 0.06
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Fig. 2. Separation scheme starting with ordinary distillation for the mixtures of Group 1.
ordinary distillation in the first step proves to be always cheaper than the other alternative and the results correspond to the well known heuristics of the separation sequencing. 2.2. Novel hybrid separation system for the mixtures of Group 2 The components of the mixtures of this group form five binary and two ternary azeotropes (Tables 3 and 4). The mix-
tures of this group are more complicated than the ones of Group 1, so the VLLE data can be described already at the beginning in a tetrahedron and Fig. 7 shows the azeotropic points (square represents a binary and triangle represents a ternary azeotrope), separation boundaries, and the immiscibility region with the tie lines. For the sake of better overview the residue curves are not shown. In this case the VLLE data of the quaternary systems allows separating the quaternary mixtures with an
Fig. 3. Representation of VLLE data and the extractive heterogeneous-azeotropic distillations for mixture 1.
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Fig. 4. Representation of VLLE data and the extractive heterogeneous-azeotropic distillations for mixture 2.
extractive heterogeneous-azeotropic distillation, where water is the auto-entrainer, into two products (Fig. 8). The bottom product contains the component (ETOH) which is with water miscible and the distillate contains the components (ETAC, IPAC or MEK, IPAC) which are immiscible with water. However, the water appears also in the top product where phase separation is also used to enhance the separation. The operation of this extractive heterogeneous-azeotropic distillation is shown for mixture 4 in Fig. 7: F1 is the feed, R the recycled stream coming
from the subsequent ordinary distillation columns (binary azeotrope), F the mixtures of F1 and R, D1 and B1 are the products of the extractive heterogeneous-azeotropic distillation column. From the bottom product (ethanol and water) ethanol is recovered in a composition close to the azeotropic point with an ordinary distillation. The organic rich phase of the distillate of the extractive heterogeneous-azeotropic distillation (ETAC, IPAC, water or MEK, IPAC, water) is separated in two subsequent ordinary distillation columns. The top product (R) of the second
Fig. 5. Separation scheme starting with extractive heterogeneous-azeotropic distillation for the mixtures of Group 1.
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Fig. 6. Economic comparison of structures in Figs. 2 and 5.
ordinary distillation column (C3) is recycled into the extractive heterogeneous-azeotropic distillation column. This scheme can separate the mixtures of Group 2 that have five binary and two ternary azeotropes and water is also present forming heterogeneous and homogeneous minimum boiling azeotropes. 2.3. Novel hybrid separation system for the mixtures of Group 3 The mixtures of this group are the most complex ones in our assembly. In each combination, there is a binary and a ternary minimum boiling azeotrope (Tables 5 and 6). Fig. 9 shows the VLLE data of mixture 6: the azeotropic points (square represents a binary and triangle represents a ternary
Fig. 7. VLLE data of mixture 4 and representation of extractive heterogeneous-azeotropic distillation.
azeotrope), separation boundaries, and the immiscibility region with the tie lines. The study of the VLLE data results that with the use of extractive heterogeneous-azeotropic distillation, where water is the auto-entrainer again, it is possible to separate the organic components of these mixtures into two groups: with water miscible component (ETOH or IPOH), and with water immiscible components (ETAC, MEK). The water appears also in the top product of the extractive heterogeneous-azeotropic distillation column where phase separation is also used. The water rich phase is practically water. Fig. 9 shows that with the use of water as an auto-entrainer it is possible to cross separation boundary and get into the immiscibility region. The top and bottom products of the extractive heterogeneous-azeotropic distillation are also indicated, the top product (D1) is on the edge of the immiscibility region. The recovery of the ethanol or iso-propanol takes place in one ordinary distillation column, however, the azeotropic composition of the iso-propanol is still lower than the product purity prescription, so a different separation, maybe membrane separation, is needed. The elaboration of such a different separation is, however, neglected at this point of our study. On the contrary, it is rather interesting how to separate the top product of the extractive heterogeneous-azeotropic distillation column containing ethyl-acetate, methyl-ethylketone, and water. This ternary system forms also in every combination azeotropes. Fig. 10 shows the residue curve map, the separation boundaries, the binary and ternary azeotropes, and the immiscibility region for the MEK–ETOH–water mixture. After investigating these data a solution of the separation is designed and it is also shown in Fig. 11. The feed composition is out of the immiscibility region and for the separation the crossing of separation boundary would be necessary. The crossing of this boundary from this side is not possible [23], but it can be carried out if another
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Fig. 8. Separation scheme for the mixtures of Group 2.
extractive heterogeneous-azeotropic distillation is applied. The distillate of column 2 (C2) is in the immiscibility region and after a phase separation, that allows the crossing of the separation boundary, ethyl-acetate can be recovered in the prescribed purity. The bottom product is distilled in a common distillation column and its top product is in the immiscibility region again. After a phase separation crossing the separation boundary again, the methyl-ethyl-ketone is obtained in 93 wt.% purity. (The LLE allows only such purity but if higher purity of the methyl-ethyl-ketone were badly needed, further separation would be necessary.) This novel hybrid separation technology is also based on extractive heterogeneous-azeotropic distillation and allows the separation of the most complicated mixtures, i.e. mixtures 5 and 6.
3. Experimental investigations The experimental investigation of a novel process is important to give confidence for the design methods applied and also for the results obtained. The core of the novel hybrid separation processes is an extractive heterogeneous-azeotropic distillation unit. These units are verified by laboratory experiments corresponding to the circumstances found by simulations. The internal diameter of the laboratory distillation column is 3 cm, the column height is about 2 m, and the column internal is structured packing. The height of the packing is varied according to the distillation investigated. Continuous distillation is Table 9 Measured and simulated data of column of separation scheme for mixture 3, Group 2 Feed (wt.%)
Water ETOH ETAC IPAC
21 32 26 21
Simulated data (wt.%)
Measured data (wt.%)
Distillate
Bottom
Distillate
Bottom
2.7 0 55.0 42.3
96.1 3.9 0 0
2.8 0 53.2 44.0
95.8 4.2 0 0
Table 10 Measured and simulated data of column 1 of separation scheme for mixture 5, Group 3 Feed (wt.%)
Fig. 9. VLLE data of mixture 6 and representation of extractive heterogeneous-azeotropic distillation.
Water ETOH ETAC MEK
13 24 34 29
Simulated data (wt.%)
Measured data (wt.%)
Distillate
Bottom
Distillate
Bottom
9.6 0 49.1 41.3
93 7 0 0
7 0 50.2 43
93.7 6.3 0 0
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Fig. 10. VLLE data and separation of MEK–ETAC–water mixture.
carried out for several hours, the top and bottom products are continuously analysed. The organic compounds are analysed by gaschromatograph, the water is analysed by the Karl–Fisher technique. The extractive heterogeneous-azeotropic distillation columns of the separation schemes designed for Groups 2 and 3 are tested. Tables 9 and 10 show the result of the
experiments and the comparisons with the simulated data as well. The comparisons show a good agreement which proves the accuracy of the selected UNIQUAC thermodynamic property model, the simulation procedure, and gives also confidence for the novel hybrid separation processes.
Fig. 11. Separation scheme for the mixtures of Group 3.
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Table 11 Suggested strategy for the separation of quaternary non-ideal mixtures Group
Component forming no azeotrope
Number of binary azeotropes
Number of ternary azeotropes
Recommended novel hybrid separation schemea
1
One component (volatile)
3
1
2
Two components in pair
5
2
3
–
6
3
Ordinary distillation followed by extractive heterogeneous-azeotropic distillation (Fig. 2) Extractive heterogeneous-azeotropic distillation followed by two ordinary distillation with recycle (Fig. 8) Two subsequent extractive heterogeneous-azeotropic distillation followed by one ordinary distillation (Fig. 11)
a
The separation of ethanol–water or iso-propanol–water is not included.
4. Conclusions The successful application of novel hybrid separation systems based on the combination of extractive heterogeneous-azeotropic distillation with water as autoentrainer, ordinary distillation, and phase separation allows significant simplification and improves economic features of the separation of quaternary non-ideal mixtures being typical for solvent recovery. The positioning of the extractive heterogeneous-azeotropic distillation in the hybrid systems plays an important role in these novel separation schemes. After studying the six mixtures of three groups a general guideline is suggested for a strategy to separate highly non-ideal quaternary mixtures forming binary and ternary, homogeneous and heterogeneous minimum boiling azeotropes. The strategy is based on the novel hybrid separation processes designed for the non-ideal quaternary mixtures studied. The novel processes can be successfully applied if water is present in the mixture to be separated and there is immiscibility region with heterogeneous azeotropes of minimum boiling points. These are quite common conditions because the behaviour of a lot of organic solvents with water corresponds to these. Table 11 shows the recommended strategy for the separation of quaternary non-ideal mixtures containing water as well. Economic comparison shows that it is recommended to separate first the component which is the most volatile and forms no azeotrope with the other three components and this separation can be carried out with an ordinary distillation. So, for the mixtures of Group 1 after the ordinary distillation the extractive heterogeneous-azeotropic distillation is applied to separate the azeotrope forming components. If there is a component pair which forms with each other no azeotrope but they do form azeotropes with the other components, an extractive heterogeneous-azeotropic distillation is applied, which is followed by two ordinary distillation columns with recycle. This technique is found to be suitable for the separation of the mixtures of Group 2. If in each combination a binary azeotrope exists (six pieces) and there are three ternary azeotropes, as well a separation scheme consisting of two subsequent extractive heterogeneous-azeotropic distillation columns followed
by one ordinary distillation is to be designed. Phase split effects due to the immiscibility are also utilised. This scheme is successfully investigated for the mixtures of Group 3. Experimental verifications show good agreement between the simulated and measured data that also supports the possible realisation of the synthesised novel solvent recovery processes. The developed solvent recovery processes based on the suggested strategy can realise significant saving and reduction of the burden upon the environment. References [1] G. Schembecker, K.H. Simmrock, Azeopert—a heuristic-numeric system for the prediction of azeotrope formation, Comput. Chem. Eng. 19 (1995) S253–S258. [2] E. Blass, Entwicklung Verfahrenstechnischer Prozesse, Springer, 1997. [3] L.T. Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall, Englewood Cliffs, NJ, 1997. [4] J.G. Stichlmair, J.R. Fair, Distillation, principles and practices, Wiley-VCH, USA, 1998. [5] M.F. Doherty, M.F. Malone, Conceptual Design of Distillation Systems, McGraw-Hill, New York, 2001. [6] E. Rev, P. Mizsey, Z. Fonyo, Framework for designing feasible schemes of multicomponent azeotropic distillation, Comput. Chem. Eng. 18 (1994) S43–S47. [7] P. Mizsey, E. Rev, Z. Fonyo, Systematic separation system synthesis of a highly non-ideal quaternary mixture, AIChE Spring National Mtg., Chicago, 1997, Paper 19f. [8] T. Raiser, H. Steinhauser, Azeotrope ausgetrickst, Chem. Tech. 23 (7) (1994) 44–46. [9] I. Wilson, Encyclopedia of Separation Science, Academic Press, New York, 2000. [10] A.M. Eliceche, M.C. Daviou, P.M. Hoch, I.O. Uribe, Optimisation of azeotropic distillation columns combined with pervaporation membranes, Comput. Chem. Eng. 26 (2002) 563–573. [11] P. Mizsey, A global approach to the synthesis of entire chemical processes, Ph.D. Thesis, No. 9563, Swiss Federal Institute of Technology, ETH Zürich, Germany, 1991. [12] A. Raab, Separation of highly non-ideal mixture for solvent recovery, Diploma work at Budapest University of Technology and Economics, 2001. [13] H.L. Horsley, Azeotropic data, American Chemical Society, Washington, DC, USA, 1973. [14] J. Gmehling, J. Menke, K. Fischer, J. Krafczyk, Azeotropic Data, VCH, Parts I, II, Weinheim, Germany, 1994.
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