Novel Simulated Moving-Bed Cascades with a Total of Five Zones for

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Novel Simulated Moving-Bed Cascades with a Total of Five Zones for Ternary Separations Feng Wei,* Bo Shen, Mingjie Chen, and Yingxian Zhao Ningbo Institute of Technology, Zhejiang University, Ningbo, China 315100 ABSTRACT: Two simulated moving-bed (SMB) cascades are proposed for the separation of a ternary mixture containing the least, medium-, and most retained solutes (A, B, and C). Each cascade has a total of five zones. The first cascade combines two three-zone SMBs sharing zone III: the one SMB with zones I to III separates (A+B+C) into A and (B+C), and the other threezone SMB with zones III to V separates (B+C) into B and C. The second cascade combines a four-zone SMB consisting of zones I to IV and a three-zone SMB comprising zones IV, V and I: the former separates (A+B+C) into (A+B) and C, and the latter separates (A+B) into A and B. Analysis of the concentration band movement together with a modeling study confirms the feasibilities of the two cascades, suggesting that the first cascade should be adopted if the separation of (A+B) and C is easier than that of A and (B+C), and otherwise, the second cascade should be used.

1. INTRODUCTION As a continuous chromatographic separation technique,1−4 the simulated moving bed (SMB) consists of many columns connected end-to-end and is divided into four zones by the feed, raffinate, desorbent, and extract ports (Figure 1). A feed

biomolecules with the adsorption to be highly sensitive to the liquid composition. In the fourth, a semicontinuous two-zone SMB/chromatography hybrid system18,19 was designed for ternary separations. In the last, a cascade of two four-zone SMBs in a series was suggested, which might either be separated20,21 or combined in a single device.22,23 The two SMB cascades could operate continuously, but often required many columns and an additional separation unit to remove excess liquid between the trains. In the present work, we propose two schemes for ternary separations by combining two SMBs in a single device with a total of five zones as shown in Figure 2, where letters A, B, and C denote the least, medium, and most retained solutes in a ternary mixture, respectively. The first cascade is a combination of two three-zone SMBs in tandem (Figure 2a). Zones I to III constitute a three-zone SMB without the liquid regeneration zone to separate (A+B+C) into A and (B+C), and zones III to V constitute another three-zone SMB to separate (B+C) into B and C. Zone III is shared by the two SMBs, and thus, the total number of zones is reduced to five. In comparison, the second cascade is a combination of a special four-zone SMB (zones I to IV) and a three-zone SMB (zones IV, V, and I) sharing zones I and V. The four-zone SMB first separates (A+B+C) into (A+B) and C, and then the three-zone SMB separates (A+B) into A and B. To minimize confusion, the SMB cascade in Figure 2a is called (3 + 3)-SMB, whereas the cascade in Figure 2b is termed (4 + 3)-SMB. The following sections will discuss the feasibility of the two cascades in detail. The movement of the concentration band is first investigated to reveal the separation principle. Model simulations are then conducted to demonstrate the separation performances such as the purity, productivity, solvent consumption, and recovery.

Figure 1. Scheme of a standard four-zone SMB.

mixture is continuously separated into two fractions, flowing out of the raffinate and the extract port. The “simulated” counter-current movement of the solid against the liquid caused by the periodic switches of the four ports in the liquid flow direction confers unique advantages for the SMB over batch chromatography in terms of the productivity and solvent consumption. However, a single standard four-zone SMB cannot purify a target product from a mixture by eliminating impurities eluted before and after it. Some modifications have to be made. In the first, a five-zone SMB was adopted to collect the mediumretained solute from a side stream.5−8 This modification requires that the medium- and most retained solutes should be easy to separate so that the latter could be temporarily captured in the column without leaking from the side stream. The idea could also be actualized in a four-zone SMB, in which zone I is disconnected from zone II and the medium- and most retained solutes successively flow out of zone I.9−11 In the second, two types of pseudo-SMBs12−15 were developed, but they are not continuous, thereby losing the advantage of the SMB. In the third, Morbidelli’s group developed a continuous multicolumn countercurrent solvent gradient purification (MCSGP) process,16,17 which was slightly similar to the first modification. However, the MCSGP could modify the liquid composition in most columns, and be very suitable for separating valuable © 2012 American Chemical Society

Received: Revised: Accepted: Published: 5805

October 20, 2011 March 24, 2012 April 2, 2012 April 2, 2012 dx.doi.org/10.1021/ie2024189 | Ind. Eng. Chem. Res. 2012, 51, 5805−5812

Industrial & Engineering Chemistry Research

Article

rather than during one switch interval, making inequality 4 different from inequality 1. Substituting inequality 3 into inequality 4 gives ε mIV ≥ HC − HB − (4a) 1−ε Inequalities 2 and 3, together with mIII > mII, define a triangle in the (mII−mIII) plane for separating (A+B+C) into A and (B +C), and inequality 4a or 5 and inequality 6, along with mV > mIV, define another triangle in the (mIV−mV) plane for separating (B+C) into B and C. The (3 + 3)-SMB can separate the medium-retained solute from a ternary mixture if inequalities 1−6 are simultaneously satisfied. However, a mass balance constraint exists as follows: FI − FII = FV − FIV

Under the operating conditions defined by inequalities 1−6, (3 + 3)-SMB has to be modified if (FI−FII) > (FV−FIV). For example, the side-stream of (FI−FII) is concentrated using evaporation before it flows into zone V, reducing the flow rate of the side-stream to (FV−FIV):

Figure 2. Scheme of the novel SMB cascades for continuous ternary separations. (a) (3 + 3)-SMB is combination of two three-zone SMBs, one of which consists of zones I to III while the other consists of zones III to V. (b) (4 + 3)-SMB is a combination of a four-zone SMB (zones I to IV) and a three-zone SMB (zones IV, V, and I).

α(FI − FII) = FV − FIV

FIIΔt − Vcol ε ≥ HA Vcol(1 − ε)

(2)

mIII =

FIIIΔt − Vcol ε ≤ HB Vcol(1 − ε)

(3)

Second, solutes B and C coming out of zone I partially flow into zone V and form a new concentration band in zones IV and V, respectively. To distinguish the new bands, only those moving in zones I to III are called the original bands, which directly stem from the feed. For the two new bands, the Triangle Theory gives (FIV Δt − Vcol ε) + (FIIIΔt − Vcol ε) Vcol(1 − ε) ε ≥ HC − 1−ε

FIV Δt − Vcol ε ≥ HB Vcol(1 − ε)

F Δt − Vcol ε mV = V ≤ HC Vcol(1 − ε)

mII ≥ HB

(10)

mIII ≤ HC

(11)

mIV ≤ HA

(12)

mIV + mV ≥ HB −

mIV + mIII =

mIV =

(8)

where α is an enrichment factor smaller than 1. The enrichment operation is very similar to that of the enriched extract (EE)SMB,27 in which the stream leaving zone I is concentrated, partially collected as the extract, and partially reinjected into the system at the inlet of zone II. Also, the enrichment can be either continuous or batchwise, which should not affect the separation performance because the side-stream is actually the feed of the second SMB. In this work, the side-stream is assumed to be concentrated continuously. 2.2. (4 + 3)-SMB. Similar to (3 + 3)-SMB, (4 + 3)-SMB has the following constraints: ε mII + mI ≥ HC − (9) 1−ε

2. DESIGNING THE SMB CASCADES 2.1. (3 + 3)-SMB. Some constraints are incorporated in the concentration bands to achieve an effective separation. First, zones I to III constitute a three-zone SMB to separate (A+B +C) into A and (B+C). Hence, inequalities 1−3 are easily obtained following the Triangle Theory.24−26 F Δt − Vcol ε mI = I ≥ HC Vcol(1 − ε) (1) mII =

(7)

(4)

(5)

(6)

ε 1−ε

(13)

mV ≥ HA

(14)

mI ≤ HB

(15)

Substituting inequality 15 into inequality 9 gives ε mII ≥ HC − HB − 1−ε

(9a)

Substituting inequality 12 into inequality 13 gives ε mV ≥ HB − HA − 1−ε

(13a)

Inequalities 9−12 define the movement of the original tails of C and B and the original fronts of C and A in the four-zone SMB consisting of zones I to IV, whereas inequalities 13−15 give the requirements on the new tails of B and A and the new front of B in the three-zone SMB consisting of zones IV, V, and I, respectively.

Inequalities 4−6 have the same meanings as inequalities 1−3. However, the new tail of C formed in the first column of zone IV during the (n − 1)th switch interval is switched into zone III and proceeds toward the column outlet during the nth switch interval. Therefore, the new tail should move a distance longer than one column length during two successive switch intervals 5806

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Inequality 9a or 10 and inequality 11, together with mIII > mII, define a triangle in the (mII−mIII) plane for separating (A +B+C) into (A+B) and C, and inequality 13a or 14 and inequality 15, along with mI > mV, define another triangle in the (mV−mI) plane for separating (A+B) into A and B. A mass balance constraint similar to equality 8 is described as follows: α(FIII − FIV ) = FI − FV

PuB =

PrB = SCB =

(16)

Inequalities 9−15, together with equality 16, can give a rough estimation of the operating conditions, which should be further screened using the subsequent model study.

ReB =

3. SMB CASCADE SEPARATION PROCESS MODEL The separations by the SMB cascades are investigated using a rigorous SMB model with periodic switches of the four ports.28−30 The change of component i in column j during each switch interval is described by the transport−dispersive equations as follows: ∂Ci , j ∂t

∂qi , j ∂t

+

∂ 2Ci , j ∂Ci , j 1 − ε ∂qi , j + DL , i = −uj ∂Z ε ∂t ∂Z2

(17)

(18)

(i = A, B, C)

(19)

To solve the model, the boundary and initial conditions for each column should be given. Zones I and IV in (3 + 3)-SMB and zones II and V in (4 + 3)-SMB have zero inlet concentrations:

Ci , j(t , 0) = 0 Cfeed, iFfeed + Ci ,II(t , L)FII FIII

(21)

The inlet concentrations of zone V in (3 + 3)-SMB is Ci ,I(FI − FII) + Ci ,IV(t , L)FIV FV

(22)

α=

The inlet concentration of zone I in (4 + 3)-SMB is Ci , j(t , 0) =

Cproduct,BFproduct VcolN

(25)

Fdesorbent1 + Fdesorbent2 + Ffeed Cproduct,BFproduct

(26)

Cproduct,BFproduct Cfeed,BFfeed

(27)

value 0.75 10 cm 1.0 cm 10 5 g/L 2 4 6 60 min−1 0.01 cm2/min

FV − FIV = 0.47 FI − FII

(28)

This means that after an enrichment by 53%, the flow rate of the side-stream is identical to (FV−FIV). The simulation result shows that (3 + 3)-SMB can separate the medium-retained solute from the ternary mixture to give a very high purity and recovery as listed in Table 2 (case 1). After reaching a cyclic steady state, C and A successively flow out of zone III during a switch interval, whereas B flows out of zone V, as shown in parts a and b in Figure 3. All the values of mI to mV are close to the lower limit or upper limit, and the corresponding operation points in the planes of mII−mIII and mIV−mV are also close to the vertexes of the two triangles as shown in Figure 4. Meanwhile, the separation is still effective as listed in Table 2. Thereby, the operation conditions should have approached the optimal

Ci ,III(FIII − FIV ) + Ci ,V(t , L)FV FI

parameters ε L d N Cfeed,A(= Cfeed,B = Cfeed,C) HA HB HC kf,A(= kf,B = kf,C) DL,A(= DL,B = DL,C)

4.1.1. Separations by (3 + 3)-SMB. The initial conditions of separation to meet inequalities 1−6 define two triangles respectively in the planes of mII−mIII and mIV−mV as shown in Figure 4. Model simulations are used to screen and tune the initial conditions, giving the feasible operation conditions (see case1 listed in Table 2) when taking into account the nonideal cases. Since (FI−FII) is larger than (FV−FIV), the side-stream of (FI−FII) has to be concentrated before flowing into zone V. The enrichment factor is

(20)

For the two SMB cascades, the inlet concentration of zone III is

Ci , j(t , 0) =

(24)

4. RESULTS AND DISCUSSION 4.1. Feasibility of the Cascade of SMBs. The separation performance of the SMB systems can be accurately predicted using a proper model if the mass transfer coefficients, axial dispersion coefficients, and adsorption isotherms are appropriately estimated in advance. The model parameters are listed in Table 1. Each zone consists of two columns in tandem, and the switch interval is 4 min.

where qi* is the solid concentration in equilibrium with the liquid concentration Ci, and j is the serial number of the column starting from the first column in zone I. The adsorption equilibrium follows Henry’s law as follows:

Ci , j(t , 0) =

Cproduct,A + Cproduct,B + Cproduct,C

Table 1. Model Parameters

= k f , i(qi*, j − qi , j)

qi* = HiCi

Cproduct,B

(23)

The initial and other boundary conditions are identical to those in conventional SMBs.28,29 The convective term ∂C/∂Z is approximated using the five-point biased upwind finite difference scheme, and the dispersive item ∂2C/∂Z2 is approximated using the five-point centered scheme.31 Thus, the model is discrete to ordinary differential equations, which are solved using the ODE15s solver in Matlab. The purity (Pu), productivity (Pr), solvent consumption (SC), and recovery (Re) of the main product B are calculated using the average concentrations in the product stream coming out of zone V in (3 + 3)-SMB or out of zone IV in (4 + 3)-SMB as follows: 5807



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Table 2. Simulating Separation Results for Novel Five-Zone SMBs case 1 SMB configuration flow rates without change m-value without change changeable flow rate changeable m-value concentrated factor purity (%) concentration(g/L) recovery (%) solvent consumption(L/g) productivity(g·h−1·L−1)

case 2

case 3

(3 + 3)-SMB FI/FII/ FIII/ FV = 4.45/2.48/3.41/4.38 mI/mII/ mIII/ mV = 6.07/2.05/3.95/5.92 FIV = 3.46 FIV = 2.85 mIV = 4.05 mIV = 2.81 0.47 0.78 99.75 99.80 1.06 1.05 99.85 98.83 1.90 1.80 3.55 3.51

FIV = 2.41 mIV = 1.91 1 99.81 0.97 91.37 1.83 3.25

case 4

case 5

case 6

(4 + 3)-SMB FII/FIII/ FIV/ FV = 3.46/4.38/2.44/2.48 mII/mIII/ mIV/ mV = 4.05/5.92/1.97/2.05 FI = 3.41 FI = 4.00 FI = 4.42 mI = 3.95 mI = 5.15 mI = 6.01 0.48 0.78 1 99.83 99.83 99.82 1.88 1.87 1.74 99.92 99.07 92.31 1.49 1.50 1.62 3.51 3.48 3.25

concentration of B in the side-stream of (FI−FII) is high at the beginning and then reduces to zero about 2.8 min later in each switch interval as shown in Figure 6. Consequently, solute B always forms a new tail at the head of the first column in zone V around at the 2.8 minute in each switch interval. In the next 1.2 min, the new tail moves forward and away from the head of the column at the end of the switch. In the next switch interval, the tail will be shifted into zone IV and continue to move forward, merging with the new tail formed in the next switch interval finally. Consequently, the tail always appears at the middle of the last column of zone IV at the beginning of each switch interval, and may be completely eluted out of zone IV even, reducing FIV. Thus, FIV is reduced from 3.46 mL/min (case 1) to 2.85 mL/ min (case 2), so that the corresponding operation point in the (mIV−mV) plane has been out of the triangle defined by the Triangle Theory as shown in Figure 4. The purity and the solvent consumption can be improved. As the new tail of B in zone IV is stretched a little (Figure 5b), an insignificant loss of B occurs in the stream from zone III (Figure 3c), causing a slight reduction in the recovery and productivity. It seems that FIV can be further reduced from the new tail of B at the end of the switch as shown in Figure 5b. In case 3, FIV reduces to 2.41 mL/min so that the enrichment factor is 1. The stretching of the new tail of B can be observed very clearly in Figure 5c, and the loss of B in the stream out of zone III is relatively large as shown in Figure 3e. Thus, all the concentration, recovery, and productivity are decreased, while the purity changes very insignificantly (see Table 2). Furthermore, it is unnecessary to concentrate the side-stream of (FI−FII) by an additional operation since the enrichment factor has been 1, making the operation very convenient. From this point of view, the operation conditions in case 3 should be adopted, as the recovery of 91.37% is still high enough. 4.1.2. Separations by (4 + 3)-SMB. The values of FI to FV are set as 3.41, 3.46, 4.38, 2.44, and 2.48 mL/min respectively, as listed in Table 2 (case 4). Similar to case 1, since (FIII−FIV) is larger than (FI−FV), the side-stream of (FIII−FIV) has to be concentrated before flowing into zone I. The medium-retained solute flows out of zone IV (Figure 7a), whereas the least and most retained solutes flow out of zone I successively (Figure 7b). Except for the concentration and solvent consumption, the purity, recovery, and productivity are close to those by (3 + 3)SMB (Table 2). Similar to case 1, all the values of mI to mV in case 4 are close to their lower limit or upper limit, and the corresponding operation points in the planes of mII−mIII and mV−mI are also near the vertexes of the two triangles in Figure 8, meaning that

Figure 3. Evolution of solute concentrations in the streams from zone III (left) and zone V (right) during a switch interval in cases 1 (a, b), 2 (c, d) and 3 (e, f).

Figure 4. Separation regions in the (mII−mIII) and (mIV−mV) planes for (3 + 3)-SMB.

values. At the beginning of each switch interval, the original tails of C and A and the new tail of B should always appear at the head of the first column in zones I, II, and IV, whereas the original front of B and the new front of C should always appear at the head of the last column in zones III and V, respectively. Nevertheless, the new tail of B is at the middle of the last column in zone IV rather than the head of the first column in zone IV as shown in Figure 5, indicating that FIV is not optimized at all. The main reason for that is because the 5808



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Figure 5. Concentration profiles in the (3 + 3)-SMB in cases 1 (top), 2 (middle), and 3 (bottom).

Figure 6. Evolution of solute concentrations in the side-stream from zone I to zone V in case 1.

Figure 8. Separation regions in the (mII−mIII) and (mV−mI) planes for (4 + 3)-SMB.

Figure 7. Evolution of solute concentrations in the streams from zone IV (left) and zone I (right) during a switch interval in cases 4 (a,b), 5 (c,d), and 6 (e,f).

the operation should have been optimized. From the concentration profiles at the beginning of a switch (Figure 9a), FII, FIII, FIV, and FV are surely very close to their optimal values as the original tail of B, the original fronts of C and A, and the new tail of B are at the head of the first column in zone II, the last column in zone III, the last column in zone IV, and the first column in zone V, respectively. However, FI is far away from its optimal value as the new front of B is not at the head of the last column in zone I. A similar phenomenon occurs in zone IV in case 1. The main reason is because the side-stream of (FIII−FIV) does not contain B until 1.5 min after the beginning of the switch as shown in Figure 10. Accordingly, solute B always starts to form a new front at the head of the first column of zone I at the 1.5 min in each switch interval. The front does not reach the outlet of the column at the end of the switch. It will be switched into the last column in zone V and continue to move forward, finally embedding into the end portion of the new front just formed in the next switch interval. Thereby, there are several ridges on the concentration plateau of B in the 5809



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Figure 9. Concentration profiles in the (4 + 3)-SMB in cases 4 (top), 5 (middle), and 6 (bottom).

first column of zone V at the beginning of each switch interval as shown in Figure 9a. On the basis of the analysis of the new front of B, FI is increased to 4.00 mL/min in case 5, corresponding to a change of the enrichment factor from 0.22 to 0.73. Compared with that of case 4, the height of the new concentration band of A decreases. Similar to the new tail of B in case 2, the new front of B in case 4 is also stretched in zone I (Figure 9b), causing minor reductions in the concentration, recovery, and productivity. As the recovery of 99.07% in case 4 is still very high, FI is further enhanced to 4.48 mL/min so as to make (FIII−FIV) identical to (FI−FV), meaning that the side-stream of (FIII−FIV) can directly flow into zone V without the prior enrichment. Similar to the new tail of B in case 3, the new front of B is stretched very obviously, and the loss of B in the stream out of zone I increases accordingly, causing the reductions in the concentration, recovery, and productivity (see Table 2). Nevertheless, the purity changes little. Furthermore, the recovery of 92.31% can be accepted in general. Thus, the

Figure 10. Evolution of solute concentrations in the side-stream from zone III to zone I in case 4.

Table 3. Effect of the Henry’s Constant on the Separations by Five-Zone SMBs case 7 Henry’s constant SMB configuration flow rates without change m-value without change changeable flow rate changeable m-value concentrated factor purity (%) concentration (g/L) recovery (%) solvent consumption (L/g) productivity (g·h−1·L−1)

case 8

HA = 2, HB = 3, HC = 6 (3 + 3)-SMB FI/FII/ FIII/ FIV/FV = 4.45/2.48/2.92/4.38 mI/mII/ mIII/ mV = 6.07/2.05/2.95/5.92 FIV = 2.97 FIV = 2.41 mIV = 3.05 mIV = 1.91 0.72 1 99.80 99.82 0.50 0.50 99.84 99.84 3.58 3.58 1.68 1.68

case 9

case 10

(4 + 3)-SMB FII/FIII/ FIV/ FV = 2.97/4.38/2.44/2.48 mII/ mIII/ mIV/ mV = 3.05/5.92/1.97/2.05 FI = 2.92 FI = 4.42 mI = 2.95 mI = 6.00 0.23 1 99.87 99.61 2.89 0.93 99.98 32.28 0.97 3.00 5.38 1.74 5810

case 11

case 12

HA = 2, HB = 5, HC = 6 (3 + 3)-SMB FI/FII/ FIII/ FV = 4.45/2.48/3.90/4.38 mI/mII/ mIII/ mV = 6.07/2.05/4.95/5.92 FIV = 3.95 FIV = 2.41 mIV = 5.05 mIV = 1.91 0.22 1 99.64 99.45 1.62 0.51 99.81 31.44 1.39 4.41 5.42 1.71

case 13

case 14

(4 + 3)-SMB FII/FIII/ FIV/ FV = 3.95/4.38/2.44/2.48 mII/ mIII/ mIV/ mV = 5.05/5.92/1.97/2.05 FI = 3.90 FI = 4.42 mI = 4.95 mI = 6.00 0.73 1 99.73 99.73 0.88 0.88 99.68 99.68 3.20 3.20 1.64 1.64



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and C is easier than that of A and (B+C), i.e. (HB − HC) is larger than (HA − HB), the first cascade performs better than the second cascade in terms of the productivity, solvent consumption, and recovery. Conversely, the latter is preferable to the former. Before flowing into the second SMB in each preferable cascade, the side-stream should be concentrated. Otherwise, the large loss of B will significantly reduce the separation performance. However, the two cascades have the similar performance when the difference of (HB − HC) and (HA − HB) is not so significant. The side-stream can directly flow into the corresponding port without the additional enrichment as the reduction in the separation performance is not large.

operation conditions should be adopted since the additional operation to concentrate the side-stream of (FIII−FIV) could be canceled. 4.2. Effect of the Henry’s Constant on the Separations. The data in Table 3 show the effect of the Henry’s constant on the separations. In cases 7, 9, 11, and 13, before flowing into the corresponding port, the side-stream, (FI−FII) in (3 + 3)-SMB or (FIII−FIV) in (4 + 3)-SMB, is concentrated with an additional treatment. It should be noted that the four operations have been screened very carefully so that all the mvalues in the four cases approach their lower limit or upper limit. The simulation results are in accord with the heuristics for designing separation sequences that easy separations should be conducted as early as possible. For example, in cases 7 and 9 the Henry’s constants of A, B, and C are 2, 3, and 6, and thus separating (A+B) and C is easier than separating A and (B+C). (4 + 3)-SMB has precedence over (3 + 3)-SMB as the former first separates (A+B) and C, whereas the latter first separates A and (B+C). On the other hand, (3 + 3)-SMB (case 11) is superior to (4 + 3)-SMB (case 13) when Henry’s constant of A, B and C are 2, 5, and 6, respectively. In cases 8, 10, 12, and 14, the side-stream flows directly into the corresponding port without an additional enrichment. It is found that high separation performance and convenient operation cannot be achieved simultaneously. When the separation of (A+B) and C is easier than the separation of A and (B+C), canceling the additional enrichment does not affect the separation by (3 + 3)-SMB (case 8), but does reduce largely the separation performance of (4 + 3)-SMB. Conversely, when the separation of A and (B+C) is easier in cases 12 and 14, the separation of (3 + 3)-SMB becomes bad, for example, the recovery reduces from 99.81% to 31.44%, whereas the separation by (4 + 3)-SMB does not change. From the above analysis, the enrichment of the side-stream cannot be removed if the separation of A and (B+C) is more difficult than the separation of (A+B) and C, and vice versa. Otherwise, the loss of B will be larger, reducing the concentration and productivity even if the purity does not change.

■

AUTHOR INFORMATION

Corresponding Author

*Tel: +86-574-88229075. Email: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This research was supported by grants from NSF of Ningbo, China (No. 2009A610153) and Education Bureau of Ningbo,China (Jd090222).

■

5. CONCLUSIONS Two SMB cascades with a total of five zones are proposed for the separation of the medium-retained solute from a ternary mixture. The first cascade of SMBs is a combination of two three-zone SMBs without the liquid regeneration zone. Considering the two SMBs to share zone III, a total of five zones can achieve ternary separations. The first three-zone SMB consisting of zones I to III separates the mixture into A and (B+C). The side-stream containing (B+C) from zone I is introduced into the second three-zone SMB consisting of zones III and V, in where solutes B and C are separated and flow out of zones V and III, respectively. The second cascade of SMBs is a combination of a four-zone SMB and a three-zone SMB. The four-zone SMB consisting of zones I to IV separates (A+B+C) into (A+B) and C. The sidestream flowing out of zone III is introduced into the node between zones V and I. Zones IV, V, and I constitute a threezone SMB without the liquid regeneration zone and separate (A+B) into A and B. The feasibility of the two SMB cascades was confirmed via the analysis of the movement of the concentration bands as well as through model simulations. If the separation of (A+B)

LIST OF SYMBOLS C = liquid phase concentration (g/L) CFeed = feed concentration(g/L) d = chromatographic column diameter (cm) DL = axial dispersion coefficient (cm2/min) F = flow rate (mL/min) u = flow velocity (cm/min) H = Henry’s constant kf = overall mass-transfer coefficient (1/min) L = chromatographic column length (cm) m = flow-rate ratio in Triangle Theory N = the number of columns in SMB Pu = purity (%) Pr = productivity (g/(L·h)) q = solid phase concentration (g/L) q* = solid phase concentration in equilibrium with C (g/L) Re = recovery (%) SC = solvent consumption (L/g) t = time (min) Δt = switch interval (min) Vcol = column volume (mL) Z = axial coordinate of column (cm)

Subscripts

i = component A, B, C I...IV = zone of the SMB cascades j = column number desorbent = desorbent stream feed = feed stream product = product stream Greek Symbols

■

α = enrichment factor ε = column voidage

REFERENCES

(1) Broughton, D. B.; Gerhold, C. G. Continuous Sorption Process Employing Fixed Bed of Sorbent and Moving Inlets and Outlets, U.S. Patent 2985589, 1961.

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(2) Rajendran, A.; Paredes, G.; Mazzotti, M. Simulated Moving Bed Chromatography for the Separation of Enantiomers. J. Chromatogr. A 2009, 1216, 709. (3) Seidel-Morgenstern, A.; Keβler, L. C.; Kaspereit, M. New Developments in Simulated Moving Bed Chromatography. Chem. Eng. Technol. 2008, 31, 826. (4) Chin, C. Y.; Wang, L.N-H. Simulated Moving Bed Equipment Designs. Sep. Purif. Rev. 2004, 33, 77. (5) Beste, Y. A.; Arlt, W. Side-Stream Simulated Moving-Bed Chromatography for Multicomponent Separation. Chem. Eng. Technol. 2002, 25, 956. (6) Wang, X.; Ching, C. B. Chiral Separation of β-Blocker Drug(Nadolol) by Five-Zone Simulated Moving Bed Chromatography. Chem. Eng. Sci. 2005, 60, 1337. (7) Paredes, G.; Abel, S.; Mazzotti, M.; Morbidelli, M.; Stadler, J. Analysis of a Simulated Moving Bed Operation for Three-Fraction Separations(3F-SMB). Ind. Eng. Chem. Res. 2004, 43, 6157. (8) Abel, S.; Bäbler, M.; Arpagaus, U. C.; Mazzotti, M.; Stadler, J. Two-Fraction and Three-Fraction Continuous Simulated Moving Bed Separation of Nucleosides. J. Chromatogr. A 2004, 1043, 201. (9) Jo, S.-H.; Nam, H.-G.; Mun, S. Optimal Design and Experimental Validation of a Modified Four-Zone SMB Process for the Separation of a Ternary Amino Acid Mixture. Process Biochem. 2010, 45, 1288. (10) Kim, J. K.; Zang, Y.; Wankat, P. C. Single-Cascade Simulated Moving Bed Systems for the Separation of Ternary Mixtures. Ind. Eng. Chem. Res. 2003, 42, 4849. (11) Kurup, A. S.; Hidajat, K.; Ray, A. K. Comparative Study of Modified Simulated Moving Bed Systems at Optimal Conditions for the Separation of Ternary Mixtures under Nonideal Conditions. Ind. Eng. Chem. Res. 2006, 45, 3902. (12) Kurup, A. S.; Hidajat, K.; Ray, A. K. Optimal Operation of a Pseudo-SMB Process for Ternary Separation under Non-ideal Conditions. Sep. Purif. Technol. 2006, 51, 387. (13) Borges da Silva, E. A.; Rodrigues, A. E. Design Methodology and Performance Analysis of a Pseudo-Simulated Moving Bed for Ternary Separation. Sep. Sci. Technol. 2008, 43, 533. (14) Wei, F.; Li, M.; Huang, F.; Chen, M.; Jiang, H.; Zhao, Y. A Novel Pseudo-simulated Moving Bed for Ternary Separations. J. Chromatogr. A 2011, 1218, 2906. (15) Wei, F. Method for Separating a Mixture Comprising Three Components by Simulated Moving Bed Chromatography, CN Patent 101961565A, 2011. (16) Müller-Späth, T.; Aumann, L.; Ströhlein, G.; Kornmann, H.; Valax, P.; Delegrange, L.; Charbaut, E.; Baer, G.; Lamproye, A.; Jöhnck, M.; Schulte, M.; Morbidelli, M. Biotech. Two Step Capture and Purification of IgG2 Using Multicolumn Countercurrent Solvent Gradient Purification (MCSGP). Bitotechnol. Bioeng. 2010, 107, 974. (17) Müller-Späth, T.; Krattli, M.; Aumann, L.; Ströhlein, G.; Morbidelli, M. Increasing the Activity of Monoclonal Antibody Therapeutics by Continuous Chromatography (MCSGP). Biotechnol. Bioeng. 2010, 107, 652. (18) Hur, J. S.; Wankat, P. C. New Design of Simulated Moving Bed(SMB) for Ternary Separations. Ind. Eng. Chem. Res. 2005, 44, 1906. (19) Hur, J. S.; Wankat, P. C. Two-Zone SMB/Chromatography for Center-Cut Separation from Ternary Mixtures: Linear Isotherm Systems. Ind. Eng. Chem. Res. 2006, 45, 1426. (20) Nicolaos, A.; Mubr, L.; Gotteland, P.; Nicoud, R.-M.; Bailly, M. Application of Equilibrium Theory to Ternary Moving Bed Configurations (Four+Four, Five+Five, Eight and Nine Zones) I. Linear Case. J. Chromatogr. A 2001, 908, 71. (21) Wankat, P. C. Simulated Moving Bed Cascades for Ternary Separations. Ind. Eng. Chem. Res. 2001, 40, 6185. (22) Wooley, R.; Ma, Z.; Wang, L.N-H. A Nine-Zone Simulated Moving Bed for the Recovery of Glucose and Xylose from Biomass Hydrolyzate. Ind. Eng. Chem. Res. 1998, 37, 3699. (23) Chiang, A. S. T. Continuous Chromatographic Process Based on SMB Technology. AIChE J. 1998, 44, 1930.

(24) Storti, G.; Baciocchi, R.; Mazzotti, M.; Morbidelli, M. Design of Operating Conditions of Simulated Moving Bed Adsorptive Separation Units. Ind. Eng. Chem. Res. 1995, 34, 288. (25) Migliorini, C.; Mazzotti, M.; Morbidelli, M. Continuous Chromatographic Separation through Simulated Moving Beds under Linear and Nonlinear Conditions. J. Chromatogr. A 1998, 827, 161. (26) Mazzotti, M. Design of Simulated Moving Bed Separations: Generalized Langmuir Isotherm. Ind. Eng. Chem. Res. 2006, 45, 6311. (27) Paredes, G.; Rhee, H.-K.; Mazzotti, M. Design of SimulatedMoving-Bed Chromatography with Enriched Extract Operation (EESMB): Langmuir Isotherms. Ind. Eng. Chem. Res. 2006, 45, 6289. (28) Wei, F.; Zhao, Y. Modeling Comparison between Novel and Traditional Feed Modes of Simulated Moving Bed. Ind. Eng. Chem. Res. 2008, 47, 3200. (29) Wei, F.; Shen, B.; Chen., M. From Analytical Chromatography to Simulated Moving Bed Chromatography: Resolution of Omeprazole Enantiomers. Ind. Eng. Chem. Res. 2006, 45, 1420. (30) Haag, J.; Vande Wouwer, A.; Lehoucq, S.; Saucez, P. Modeling and Simulation of a SMB Chromatographic Process Designed for Enantioseparation. Control Eng. Pract. 2001, 9, 921. (31) Vande Wouwer, A.; Saucez, P.; Schinesser, W. E. Simulation of Distributed Parameter Systems Using a Matlab-Based Method of Lines Toolbox: Chemical Engineering Applications. Ind. Eng. Chem. Res. 2004, 43, 3469.

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Novel Simulated Moving-Bed Cascades with a Total of Five Zones for

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