ethylbenzene mixture by

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Purification of styrene from a styrene/ ethylbenzene mixture by stripping crystallization Lie-Ding Shiau Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00647 • Publication Date (Web): 26 Apr 2018 Downloaded from http://pubs.acs.org on April 27, 2018

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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Industrial & Engineering Chemistry Research

Purification of styrene from a styrene/ethylbenzene mixture by stripping crystallization

Lie-Ding Shiaua,b a

Department of Chemical and Materials Engineering Chang Gung University, Taoyuan Taiwan R.O.C. b

Department of Urology

Chang Gung Memorial Hospital, Linko Taiwan R.O.C. (TEL) 011-886-3-2118800 EXT. 5291 (FAX) 011-886-3-2118700 (E-mail) [email protected] *Author to whom correspondence should be addressed.

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Stripping crystallization (SC) was used to purify styrene (ST) from a liquid mixture of ST and ethylbenzene (EB). This new separation technology combines vaporization and crystallization to yield a crystalline product and a vaporous mixture from a liquid feed via three-phase equilibrium transformations. The three-phase equilibrium conditions for a liquid mixture determined by the thermodynamic calculations were adopted to direct the SC experiments. An unique apparatus was designed for SC experiments at low temperatures and pressures for a series of three-phase equilibrium conditions (from −33℃ and 9.0Pa to −80℃ and 0.03Pa). The experiments indicate that SC can be applied to the purification of ST from a liquid mixture of ST and EB with an initial ST concentration of 0.80-0.95.

Keywords: Crystallization; Separation; Purification; Styrene; Ethylbenzene

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1. Introduction Styrene (ST) is among the most important aromatic compounds; it is used extensively in the manufacture of polystyrene. The separation of ST from ethylbenzene(EB) is encountered during ST production via the catalytic dehydrogenation of EB. Because their boiling points are similar and because ST tends to polymerize quickly, it is rather complicated and energy-intensive to separate the two by conventional distillation.1 Alternative separation techniques such as membrane permeation,2-5 extractive distillation,6-7 adsorption to nanoporous materials,8,9 and extraction using the ionic liquids10 have been proposed in the literature.

A new separation technology, stripping crystallization (SC), has been successfully developed to separate the mixed xylenes with similar boiling points.11-13 In principle, SC is performed at a triple-point condition where the liquid mixture is simultaneously vaporized and crystallized as a condition of the three-phase equilibrium. Thus, at completion, the liquid

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mixture becomes a crystalline form of the major component after the vapor is condensed and removed.

Unlike the solid-liquid equilibrium used in melt crystallization,14-23 SC uniquely requires no solid/liquid separation and no crystal washing, since no mother liquor is present with the crystals upon completion. The objective of this work was to investigate its feasibility in purifying ST from a liquid mixture of ST and EB.

2. The SC model Figure 1 illustrates the solid-liquid and vapor-liquid phase diagrams of ST (A-component) and EB (B-component) at normal pressure. The eutectic point for the solid-liquid phase diagram lies where T = −100°C and X = 0.16, implying that ST crystals can be produced when the temperature is between −100°C and −30.6°C when 0.16 < X < 1. Note that T, = −30.6°C. Generally, as pressure is reduced, the solid-liquid equilibrium temperature remains nearly constant, but the vapor-liquid

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equilibrium temperature decreases. Thus, for a given X within the range, as pressure decreases, the solid-liquid equilibrium temperature coincides with the vapor-liquid equilibrium temperature, leading to a three-phase equilibrium that yields pure ST crystals and liquid and vapor phases of the remaining mixture.

The SC process was simulated in a series of N equilibrium stage operations, as shown in Figure 2. Each stage was simulated under three-phase equilibrium conditions, requiring that several equations be satisfied. As the three-phase equilibrium is reached in each stage n, the solid-liquid equilibrium between the ST crystals and the liquid mixture is described by the van’t Hoff equation24-26 lnX γ =

∆,

"

! ,

!

−"

(1)

#

where ∆H, = 1.10 ∗ 10' J/mol and T, = −30.6°C.27 Certain physical properties of ST and EB are shown in Table 1.

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Additionally, the vapor-liquid equilibrium is described by24-26 Y P = X γ P-./

(2)

Y0 P = X 0 γ0 P0-./

(3)

where P-./ and P0-./ are the temperature-dependent saturated pressures in stage n for ST and EB, respectively.27 As shown in Table 1, three-phase equilibrium occurs at −30.6°C and 10.6Pa for pure ST. When X0 < 1, the equilibrium temperature should be below −30.6°C, and the pressure should be below 10.6Pa. At low pressure, the assumption of ideal gases introduces little error. Aucejo et al.28 found that at 5kPa and 15kPa, this binary mixture exhibits very few deviations from ideal behavior, and no azeotrope exists. For simplicity, an ideal liquid solution is assumed (i.e., γ = 1 and γ0 = 1, given that the structures of ST and EB are similar). Therefore, X + X0 = 1

(4)

Y + Y0 = 1

(5)

6


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Because the three-phase equilibrium transformation occurs in each stage, eqs 1-5 were simultaneously solved to determine the three-phase equilibrium condition in each stage. By definition, the phase rule is24-26 F= C+2−π

(6)

where F is degree of freedom, C is number of component, and π is number of phases. For the binary ST/EB liquid mixture, F = 1 because C = 2 and π = 3 at three-phase equilibrium. Therefore, if T is specified in each stage, eqs 1-5 constitute a set of equations that can be simultaneously solved for five unknown variables, P , X , X0 , Y and Y0 for n = 1,2, … , N.

Figure 3 shows PT, X T and Y T solved using eqs 1-5 to determine the three-phase equilibrium conditions for the purification of ST from a liquid mixture of ST and EB. Thus, as the equilibrium temperature decreases, the corresponding pressure, PT, and the corresponding liquid composition of ST, X T, decreases. Similarly, Figure 3 reveals that, as the 7



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fraction of ST in the mixture decreases, the corresponding temperature and pressure for the three-phase equilibrium decreases.

As shown in Figure 2, the three-phase equilibrium transformation occurs in the liquid in each stage, leading to ST crystal formation amid vapors from the mixture and the remaining liquid phase. S and L represent the amount of crystalline ST and liquid mixture, respectively, remaining in stage n, and V represents the amount of vapor formed and removed in stage n. As the vapor formed in each stage is removed, the crystals and the liquid formed enter the next stage. The amount of liquid decreases, and the amount of the crystals increases; therefore, L9 > L! > L; … > L< , and S9 < S! < S; … < S< . In Figure 2, S=! + L=! represents the ST crystals and liquid entering stage n while S + L represents the ST crystals and liquid leaving stage n. The entire material balance in stage n is described by S=! + L=! = S + L + V

(7) 8


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Because V=! represents the vapor formed in stage n − 1 that is subsequently removed, it is not part of the equation for stage n.

It is assumed that pure ST crystals are formed at each stage without EB as an impurity and that EB exists only in the liquid and vapor phases. In stage n, the material balance for EB is described by L=! X>,0 =! = L X>,0 + V Y>,0

? A

(8)

C A

@ # @ @ # @ where X>,0 = ? # A B?@ #A@ and Y>,0 = C #A BC@ #A@. Notably,

X>,0 and Y>,0 can be calculated directly from X 0 and Y0 by simultaneously solving eqs 1-5.

The three-phase equilibrium transformation was seen to occur in the liquid very quickly in each stage, thus forming ST crystals, vapors, and the remaining liquid. Therefore, in each stage, the melting heat released upon forming ST crystals

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from the liquid was assumed to be quickly removed by the vaporization of some portion of the liquid. Therefore, in stage n, S − S=! ∆H, = L=! −L ∆HD,

(9)

where S − S=! represents the amount of ST crystals formed from the liquid in stage n, and L=! −L represents the amount of the liquid vaporized in stage n. For simplicity, the heat of vaporization for the liquid mixture is assumed to be close to ∆HD, because ∆HD, ≅ ∆HD,0 , as shown in Table 1.

If the feed is a liquid mixture only, L9 , with a known X F,0 9 , enters the first stage in Figure 2, leading to S9 = 0. Equations 7-9 constitute a set of equations that can be solved simultaneously for three unknown variables, S! , L! and V!. Subsequently, S , L and V can be solved for n = 2,3, … , N using a similar approach. Because S< and L< represent the final amount of crystalline ST and the remaining liquid, respectively, upon completion, the total amount vapor formed and removed is ∑< H! V . 10


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3. Experimental The experimental assembly consists of a sample container in a large chamber as shown in Figure 4. The entire chamber was fitted with a cooling jacket in which liquid nitrogen was injected to lower the chamber temperature. A mechanical vacuum pump and turbo molecular pump were used in series to lower the pressure in the chamber. A temperature probe was positioned at the center of the liquid feed, and a pressure gauge was connected to the chamber. Thus, the operating temperature and pressure could be adjusted mid-experiment. Crystallization and vaporization of the liquid sample during the three-phase transformation were observed in the chamber via transparent cover.

At the beginning of each experiment, 50 g liquid feed mixture with a known composition, X 9 , prepared by mixing ST (Acros, >99% purity) and EB (Tedia, >99.7% purity), was injected into the sample container. Because liquid nitrogen was used to cool

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the jacket, the temperature of the liquid feed decreased gradually over time. Generally, the cooling rate began at 0.4 ℃/min and gradually slowed in later stages. As temperature decreased, pressure was adjusted downward based on Figure 3. Thus, a series of three-phase equilibrium transformations occurred in the liquid feed, leading to ST crystal formation amid vapors from the mixture and the remaining liquid. The experiments were ended when vaporization was no longer observed in the chamber. Upon completion, the ST crystals and the remaining liquid in the sample container were weighed, and the latter was analyzed by gas chromatography.

A batch experiment was performed based on Figure 4 and is illustrated in Figure 5. Each stage corresponded to a three-phase equilibrium condition at a given time, t , during the batch experiment. The liquid mixture was injected into the sample container at t = 0. Once the initial three-phase equilibrium condition T! , P! was reached for the initial liquid feed at t! , the three-phase equilibrium transformation occurred 12


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in the liquid, leading to the formation of ST crystals, vapor, and the remaining liquid. A new three-phase equilibrium condition T; , P; was then reached for the remaining liquid at t ; , and the three-phase equilibrium transformation occurred again in the remaining liquid. Subsequently, a series of three-phase equilibrium transformations occurred in the liquid feed at 0 < L < t M . At the conclusion of the batch experiment t M , only the produced crystals and the remaining liquid could be found in the sample container. Thus, a batch experiment performed based on Figure 4 is consistent with the scheme illustrated in Figure 2, where the vapor formed in each stage was removed, and the produced crystals and remaining liquid in the sample container in each stage entered the next stage.

4. Results and discussion In this work, ST was purified from a 50 g binary liquid mixture of ST and EB. The fraction of ST was X >, 9 = 0.95 for Feed 1, X >, 9 = 0.90 for Feed 2, X>, 9 = 0.85 for Feed 3, and X>, 9 = 0.80 for Feed 4. The temperature was determined using 13



eq 1, for example, T9 = −33℃ for Feed 1. As shown in Table 2, T was specified in each stage by T=! − T = ∆T, and ∆T = 2℃. Then, P , X , X 0 , Y , and Y0 were determined in each stage by simultaneously solving eqs 1-5 for the three-phase equilibrium conditions. Subsequently, S , L and V were determined in each stage by simultaneously solving eqs 7-9 for L9 = 50 g and S9 = 0. Results are shown in Table 2. Thus, the batch experiments for Feed 1 were performed based on the corresponding T and P in each stage shown in Table 2, where the final T and P were at N = 4, determined when vaporization was no longer observed. It should be noted in Table 2 that, as T decreased during an experiment, the corresponding P and X for three-phase equilibrium decreased.

Similarly, Tables 3-5 list the calculated results for three different feeds. These experiments were stopped when vaporization was no longer observed, which was 60 min for Feed 1, 130 min for Feed 2, 190 min for Feed 3, and 250 min for Feed 4. As shown in Tables 2-5, no vaporization was observed from

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−33℃ and 8.9Pa to −41℃ and 5.3Pa within 60 min for Feed 1. This was also the case from −40℃ and 4.7Pa to −80℃ and 0.03Pa for 250 min for Feed 4. Thus, lower values for T and P were required with longer experimental times when X>, 9 was lower.

For each feed, when the T and P values for the three-phase equilibrium (Tables 2-5) were reached for the first stage, the transformation occurred very quickly, a phenomenon consistent with the assumption developed for eq 9. Therefore, eqs 1-5 and eqs 7-9, developed based on the scheme in Figure 2, can be adopted to study three-phase equilibrium transformations for the batch experiments performed in Figure 4.

The experimental recovery ratio of ST is defined as RR =

>S ?T, S

(10)

UV ?T, V

where L9 is the initial weight of the mixed liquid feed, XF,9 denotes the initial purity of ST in the feed, WM refers to the final weight of the product, including the crystals and the

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remaining liquid obtained at the end of the experiment, and XF, M represents the experimental purity of the post-experimental ST.

As shown in Tables 2-5, some liquid remained with the crystals at the end of each calculation. The calculated purity of ST in the final product, including the final crystals and the remaining liquid, is defined as X>, =

XY BUY ?T, Y

(11)

XY BUY

The calculated recovery ratio of ST is defined as RZ =

XY BUY ?T, Y

(12)

UV ?T, V

where S< , L< and [XF, \< denote the crystal, liquid, and weight fraction of ST in the final stage based on the thermodynamic calculations. For example, Feed 1 yielded S< = 38.2 g, L< = 0.6 g, and X>, < = 0.78 in the last stage N = 4, leading to X>, = 0.997 and R Z = 81% using eqs 11 and 12.

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Figure 6 and 7 show the calculated final product purity plotted against final operating temperature, X>, T. The starting point for each curve represents feed purity and initial SC operating temperature; the ending point represents the calculated product purity and final SC operating temperature. The number in the parenthesis next to the ending point of each curve represents R Z . Also shown in Figures 6 and 7 are comparisons with experimental results. Each data point represents the experimental final purity of the product versus the final operating temperature for a given batch experiment as well as the operating pressure PT for the three-phase equilibrium.

As shown in Figure 6, the thermodynamic calculations suggest that Feed 1 can yield X>, = 0.997 and R Z = 81% performing SC from −33℃ and 8.9Pa to −41℃ and 5.3Pa. Two batch experiments yielded X>, = 0.970 − 0.976 and R R = 71% − 74%. The thermodynamic calculations suggest that Feed 2 can yield X>, = 0.97 and R Z = 83% performing SC from −35℃ and 7.2Pa to −55℃ and 0.93Pa. 17



Two batch experiments yielded X>, = 0.951 − 0.961 and R R = 71% − 73%. As shown in Figure 7, the thermodynamic calculations suggest that Feed 3 can yield X>, = 0.967 and R Z = 83% performing SC from −38℃ and 5.9Pa to −74℃ and 0.09Pa. Two batch experiments yielded X>, = 0.945 − 0.953 and R R = 66% − 70%. The thermodynamic calculations suggest that Feed 4 can yield X>, = 0.931 and R Z = 85% performing SC from −40℃ and 4.7Pa to −80℃ and 0.03Pa. Two batch experiments yielded X>, = 0.916 − 0.922 and R R = 66% − 69%. Final experimental purities were generally slightly lower than those predicted using the thermodynamic calculations, and R R is slightly lower than R Z .

Discrepancies between calculated and experimental results are attributed to: (a) The assumption in the thermodynamic calculations that each stage is operated at the three-phase equilibrium; however, experimentally, this might not always be achieved; (b)liquid inclusion might occur during crystal growth experimentally; (c)some amount of liquid might not have been removed from the crystals when experiments were ended; and (d)

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the current three-phase equilibrium conditions are calculated based on the thermodynamic data at normal temperature and pressure, which might cause deviations in determination of the actual three-phase equilibrium conditions; if more reliable thermodynamic data at low temperatures and pressures are available, more accurate three-phase equilibrium conditions can be determined in the thermodynamic calculations to reduce discrepancies between calculated and experimental results.

5. Conclusions SC was successfully used to purify ST from a liquid mixture of ST and EB. The three-phase equilibrium conditions for the liquid mixture determined by the thermodynamic calculations are adopted to direct the SC experiments. Based on the thermodynamic calculations, a series of three-phase equilibrium conditions were achieved in SC experiments by lowering the temperature and pressure of the liquid mixture initially containing ST at a concentration of 0.80-0.95, leading to the formation of ST crystals, vapors of the mixture, and remaining liquid. An unique

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apparatus was designed for SC experiments, and it was operated at low temperature and pressure for a series of three-phase equilibrium conditions (from −33℃ and 9.0Pa to −80℃ and 0.03Pa). Experimental results indicate that when the initial ST concentration was lower, the final temperature and pressure had to be lower, and operating time had to be longer for purification. Experimental purity of ST ranged from 0.916 to 0.976, and the recovery ratio was 66% to 74%. Both are slightly lower than predicted by the thermodynamic calculations. The major concern for the SC operation is a portion of ST is lost through the vapor stream of each stage. To minimize the loss of ST in the vapor, the vaporized mixture can be recycled for continuous operation or mixed with the feed in next batch for batch operation.

Because no chemicals need to be added, SC is a clean separation technology. In essence, it can be continued until the liquid phase is completely eliminated, and only pure crystals remain. Compared to conventional crystallization, neither a solid/liquid separation nor crystal washing is required because

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no mother liquor adheres to the crystal surfaces upon completion. Therefore, SC is a potential method for purifying ST from a liquid mixture of ST and EB. In spite of the advantages of SC described above, the major difficulty for industrial operation lies in the costly requirements of SC operated under the extremely low temperatures and pressures. It is the current research task in our laboratory to improve the recovery ratio and the final purity of ST without the extremely operating conditions.

Acknowledgments The author would like to thank Chang Gung Memorial Hospital (CMRPD2F0081) and Ministry of Science and Technology of Taiwan (MOST103-2221-E-182-067-MY3) for financial support of this research. The author also expresses his gratitude to Tze-Chi Liu and Keng-Fu Liu for their experimental work.

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Notation ∆H,^ = heat of melting for component-i (>0), J / mol ∆HD,^ = heat of vaporization for component-i (>0), J / mol L = mass of the liquid phase out of stage n, g M^ = molecular weight of component-i, g / mol P = pressure, Pa P^-./ = saturated pressure for the liquid of component-i, Pa R = ideal gas constant, 8.314 J / mol − K RZ

= calculated recovery ratio, dimensionless

RR

= experimental recovery ratio, dimensionless

S

= mass of the solid phase out of stage

T

n, g

= temperature, K

Tab

= eutectic temperature, K

T,^

= melting temperature of component-i, K

T/c^,^ = triple-point temperature of component-i, K V X^

= mass of the vapor phase out of stage n, g = mole fraction of component-i in liquid phase, dimensionless

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XF,^ = weight fraction of component-i in liquid phase, dimensionless Y^

= mole fraction of component-i in vapor phase, dimensionless

YF,^

= weight fraction of component-i in vapor phase, dimensionless

Greek letters γ^ = activity coefficient of component-i in liquid phase, dimensionless

Subscript 0

= in the feed

n

= in stage n

f

=

in the final stage

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[25] Smith, J.M.; Van Ness, H.C.; Abbott, M.M. Introduction to Chemical Engineering Thermodynamics, McGraw-Hill Book Co., Singapore, 2001. [26] Sandler, S.I. Chemical, Biochemical, and Engineering Thermodynamics, John Wiley & Sons, Asia, 2006. [27] NIST Standard Reference Database 11：DIPPR data compilation of pure compound properties.”Version 5.0, sponsored by The Design Institute for Physical Property Data (DIPPR) of the American Institute of Chemical Engineers, copyright by The American Institute of Chemical Engineers, 1985. [28] Aucejo, A.; Loras, S.; Martinez-Soria, V.; Becht, N.; Del Rio, G. Isobaric vapor-Liquid equilibria for the binary mixtures of styrene with ethylbenzene, o-xylene, m-xylene, and p-xylene. J. Chem. Eng. Data 2006, 51, 1051-1055.

29


Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Page 30 of 45

Table 1. Certain physical properties of styrene and ethylbenzene.1,27

property

styrene

ethylbenzene

molecular weight

104.2

106.2

boiling point,℃

145.2

136.2

melting point,℃

-30.6

-95.0

10.6

4.01*10-3

1.10*107

9.18*106

4.71*107

4.78*107

triple point pressure, 2

Pa(N/m ) heat of melting, J/mol heat of vaporization, J/mol

30


Page 31 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


Table 2. The results based on the thermodynamic calculations for 50 g Feed 1 with X>,9 = 0.95 (T9 = −33℃, ∆T = 2℃)

n

T(℃)

P(Pa)

XA(-)

YA(-)

L(g)

S(g)

V(g)

0

-33

8.93

0.949

0.880

50

0

0

1

-35

7.60

0.908

0.811

13.3

29.4

7.27

2

-37

6.40

0.866

0.745

6.28

34.9

1.60

3

-39

5.33

0.826

0.680

3.48

36.9

0.78

4

-41

5.33

0.787

0.619

0.60

38.2

1.57

31



Page 32 of 45


n

T(℃)

P(Pa)

XA(-)

YA(-)

L(g)

S(g)

V(g)

0

-35

7.20

0.890

0.810

50

0

0

1

-39

4.93

0.820

0.680

18.3

25.0

6.72

2

-43

3.33

0.744

0.562

9.94

31.2

2.08

3

-47

2.27

0.673

0.467

6.14

33.9

1.19

4

-51

1.47

0.607

0.393

3.95

35.2

0.86

5

-55

0.93

0.546

0.329

2.50

36.0

0.70

32


Page 33 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47



n

T(℃)

P(Pa)

XA(-)

YA(-)

L(g)

S(g)

V(g)

0

-38

5.87

0.848

0.710

50

0

0

1

-44

3.33

0.737

0.536

19.5

23.7

6.83

2

-50

1.73

0.633

0.407

10.9

29.9

2.34

3

-56

0.91

0.541

0.315

6.90

32.5

1.44

4

-62

0.44

0.460

0.239

4.53

33.8

1.06

5

-68

0.20

0.390

0.180

2.95

34.5

0.86

6

-74

0.09

0.330

0.137

1.82

34.9

0.73

33



Page 34 of 45


n

T(℃)

P(Pa)

XA(-)

YA(-)

L(g)

S(g)

V(g)

0

-40

4.67

0.797

0.644

50

0

0

1

-48

2.13

0.666

0.446

21.1

22.1

6.79

2

-56

0.89

0.536

0.315

11.8

28.7

2.74

3

-64

0.35

0.433

0.218

7.69

31.2

1.59

4

-72

0.12

0.347

0.151

5.22

32.4

1.22

5

-80

0.03

0.275

0.102

3.49

33.1

1.04

34


Page 35 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure captions Figure 1. The solid-liquid and vapor-liquid phase diagrams of styrene (ST, A-component) and ethylbenzene (EB, B-component) at normal pressure. Figure 2. Simulated SC operation where each stage is operated at a three-phase equilibrium condition. Figure 3. The three-phase equilibrium conditions for purifying ST from a liquid mixture of ST and EB. Figure 4. Schematic diagram of the experimental apparatus for SC with the features: (1) magnetic-driven motor, (2) rotating scraper, (3) sample container, (4) sample, (5) coolant jacket, (6) insulation wall, (7) turbo molecular pump, (8)mechanical pump, (9) thermocouple, (10) pressure gauge, (11) transparent cover, (12) liquid nitrogen. Figure 5. Schematic diagram of a batch experiment, where each stage corresponds to a three-phase equilibrium condition at a given time: at t = 0, only a liquid mixture feed in the sample container; at 0 < L < t M, the 33



three-phase equilibrium of ST crystals, vapors of the mixture, and remaining liquid; at t M , only ST crystals in the sample container. Figure 6. Comparison of experimental and calculated results for Feed 1 with X>, 9 = 0.95 and Feed 2 with X>, 9 = 0.90 ( represents the initial purity for Feed 1, represents the calculated final purity for Feed 1, represents the experimental final purity for Feed 1; represents the initial purity for Feed 2, represents the calculated final purity for Feed 2, represents the experimental final purity for Feed 2; the number in the parenthesis next to each data point represents the recovery ratio). Figure 7. Comparison of experimental and calculated results for Feed 3 with X>, 9 = 0.85 and Feed 4 with X>, 9 = 0.80 ( represents the initial purity for Feed 3, represents the calculated final purity for Feed 3, represents the experimental final purity for Feed 3; represents the initial purity for Feed 36


Page 36 of 45

Page 37 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4, represents the calculated final purity for Feed 4, represents the experimental final purity for feed 4; the number in the parenthesis next to each data point represents the recovery ratio).

37



160 P=1.013*105 Pa

V

140

120

V+L L

T(oC)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 45

-40

-60 B+L -80

-100 A+L 0.0

EB(B)

A+B 0.2

0.4

0.6

XA(-)

Figure 1

38


0.8

1.0

ST(A)

Page 39 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


V1

S0 L0 (XA)0 (XB)0

Vn-1

1

n-1

T1 P1

Tn-1 Pn-1

Vn

Sn-1 Ln-1 (XA)n-1 (XB)n-1

n Tn Pn

Vn+1

Sn Ln (XA)n (XB)n

VN

n+1

N

Tn+1 Pn+1

TN PN

T0 P0

Figure 2

39


SN

Page 40 of 45

1.0

10

0.8

8 Teu 6

0.6 XA

P(Pa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

XA(-),YA(-)


4

0.4 YA

0.2

0.0 -110 -100

2

P

-90

-80

-70

-60

-50

T(oC)

Figure 3

40


-40

0 -30

Page 41 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9 10

11 7 2

12 4

3

5 8

6 1

Figure 4

41



vapor

vapor

Page 42 of 45

vapor

at t=0

at t1

at t2

at t3

at tf

T0,P0

T1,P1

T2,P2

T3,P3

Tf,Pf

Figure 5

42


Page 43 of 45

1.00

0.95

10

(81%) (71%) (74%)

(83%) (71%) (73%)

8

XW,A(-)

Feed 1

0.90

Feed 2

6

P(Pa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.85

4

0.80

2

0.75 -60

-50

-40

T(oC)

Figure 6

43


0 -30


10

1.00

(83%)

0.95

(70%) (66%)

8

XW,A(-)

(85%) (66%) (69%)

6

0.90

P(Pa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 45

0.85

Feed 3

0.80

0.75 -90

Feed 4

-80

-70

-60

-50

T(oC)

Figure 7

44


-40

4

2

0 -30

Page 45 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC graphic:

vapor

vapor

vapor

at t=0

at t1

at t2

at t3

at tf

T0,P0

T1,P1

T2,P2

T3,P3

Tf,Pf

45


ethylbenzene mixture by

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