Dynamic control of hybrid processes with liquid-liquid extraction for

Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

pubs.acs.org/IECR

Dynamic Control of Hybrid Processes with Liquid−Liquid Extraction for Propylene Glycol Methyl Ether Dehydration Kang Ma,† Xiangshuai Pan,† Tingran Zhao,† Jingwei Yang,† Zhaoyou Zhu,† Dongmei Xu,‡ and Yinglong Wang*,† †

College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao, 266590, China

‡

Downloaded via KAOHSIUNG MEDICAL UNIV on October 9, 2018 at 22:24:42 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: Dynamic control structures are significant for liquid−liquid extraction combined with heterogeneous azeotropic distillation (LEHAD) and liquid−liquid extraction combined with extractive distillation (LEED) processes, which were proposed in our previous work for the separation of the azeotrope of propylene glycol methyl ether and water. However, there may be complications regarding the dynamic controllability of the two hybrid processes, and this work investigates the dynamic control structures. For the LEHAD process, an improved composition−temperature cascade control structure using the ratio of the reboiler duty to feed flow (QR/F) can realize effective control when feed disturbances are added. For the LEED process, the improved dual temperature control structure with QR/F was able to handle the disturbances well. Moreover, a comparison between the two hybrid processes was made according to the dynamic controllability, and the integral of the squared errors was calculated. The results show that the LEHAD process has better dynamic controllability than the LEED process.

1. INTRODUCTION Dynamic control is critical and necessary for the separation processes of azeotropic mixtures, and it has received much research interest due to its practical application in industry.1−3 Some special separation methods, such as pressure-swing distillation,4−9 azeotropic distillation,10−15 extraction distillation,16−21 and liquid−liquid extraction,22−24 have been proposed and widely used to separate azeotropic mixtures. Recently, hybrid processes were explored and optimized to minimize energy consumption and CO2 emissions, which is a critical issue of global concern.25 Effective control schemes can ensure product purity when fresh feed disturbances are introduced for separation processes.26 In recent years, the dynamic control strategy of some special separation techniques has been widely investigated, such as pressure-swing distillation,27 extractive distillation,28,29 use of an extractive dividing wall column,30 and hybrid extraction− distillation.31 Luyben32 proposed a control strategy for a triplecolumn pressure-swing distillation process without heat integration using temperature controllers and pressure compensation. Chang and Chien33 studied the dynamic control strategy of an azeotropic distillation process with a decanter for separating an azeotropic mixture, and the products of methyl methacrylate and water were stabilized in initial purities when facing a fresh feed flow rate and composition variations via control of the temperature difference between two stages in the distillation column and the temperature of a single tray in the stripper. Qin et al.7 proposed two extractive distillation control structures for © XXXX American Chemical Society

the benzene and cyclohexane azeotropic system, and the temperature control trays in the control structures were chosen by singular value decomposition and slope criteria. Yang et al.34 investigated an improved control scheme with a fixed reflux-tofeed ratio (R/F), which was implemented based on the mass flow rate for an extractive distillation process and a dual temperature control structure to ensure robust control. Bao et al.35 proposed an improved control structure for reflux-to-feed ratios with a composition controller to maintain the purity of the products. Chen et al.22 studied a hybrid extraction−distillation process that showed better economics than heterogeneous azeotropic distillation. To achieve favorable controllability, closedloop dynamic simulations were adopted, and a trade-off between the economics and controllability was made by adjusting the amount of solvent. Chang and Chien31 explored a hybrid extraction−distillation process that can realize energy savings for n-propanol dehydration, and a novel control structure with an adjustable solvent flow rate during dynamic control was proposed to achieve effective control. In our previous study,36 the mixture of PM and water containing one binary minimum azeotrope was separated by the LEHAD and LEED processes. The minimal total annual costs (TACs) and CO2 emissions of the two hybrid processes were Received: Revised: Accepted: Published: A

June 27, 2018 September 18, 2018 September 19, 2018 September 20, 2018 DOI: 10.1021/acs.iecr.8b02894 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research

Figure 1. Slope criterion and open-loop sensitivity analyses for the LEHAD process.

equipment, the pressure of the columns in the two processes was set at 1 atm. The initial feed setting of 1000 kmol/h with 7.8 mol % PM and 92.2 mol % water was the same as that used in the work of Zhao et al. and Chen et al.36,37 The product purities of the water and PM were identical to the specifications in our previous work. The tray pressure drop was assumed to be 0.0068 atm for the two strippers, and the major equipment sizing was specified according to recommendations by Luyben and Chien.3 The reflux drums and sump sizes were set to ensure a 10 min holdup with full liquid. To achieve effective separation of the aqueous and organic phases, the decanter was sized larger to ensure a 40 min holdup with the liquid half full. Then, the steady-state design was exported to an Aspen dynamic simulation. The liquid−liquid extractor model cannot be simulated as pressure-driven because it will cause overconstraint of the flow rates in the flowsheet (Aspen Dynamics 11.1 User Guide). The flow-driven simulation was selected. This is often a supposition, particularly when only liquid is contained in systems. The supposition of perfect flow control is usually accurate.31 The relative gain array method was not used to select the pairing of the closed loops due to the nonlinearity of these two processes. We used the methods developed by Luyben for selecting the pairing of the closed loops.38,39 For dynamic control, selecting the temperature sensitive tray is crucial. The slope criterion is the most common method and was used in this work.39,40 However, the slope criterion did not take into account the interaction with the possible manipulated variables available for the control loops. Therefore, we used three methods to select the temperature-sensitive tray for the two processes in this paper. For the LEHAD process, the slope criterion and open-loop sensitivity criterion methods were used to determine the tray temperature control point for the two columns.41 For open-loop sensitivity, the tray with a larger temperature difference should be selected. The slope criterion and open-loop sensitivity test results are shown in Figure 1. Stage 14 of the C1 column and stage 4 of the C2 column can be selected for temperature control. For the LEED process, the

obtained. Both processes were more attractive from the perspective of economics and environmental protection. However, the dynamic control structures were not studied in previous works, and the dynamic controllability is also an important evaluation index for the processes. It is important and significant to explore the feasible dynamic controllability to handle disturbances and maintain product purity. For the two hybrid processes, there are interactions and influences between the extraction columns and the distillation columns due to the presence of recycled streams, which increases the control difficulty. The aim of this work was to explore the dynamic controllability of the LEHAD and LEED processes for separating PM and water. A comparison between the two hybrid processes according to the dynamic controllability was also made. This work will contribute to developing a control scheme for the two energysaving hybrid processes.

2. STEADY-STATE DESIGN AND THE SELECTION OF TEMPERATURE-SENSITIVE TRAYS FOR TWO HYBRID PROCESSES The PM/water azeotrope with 80.45 mol % water and 19.55 mol % PM forms at 97.19 °C at atmospheric pressure, which is the homogeneous minimum-boiling azeotrope. In our previous work, two hybrid processes were proposed and optimized. For the LEHAD process, chloroform was selected as the solvent to extract PM from the feed and form a new heterogeneous azeotrope with water. For the LEED process, 2-ethylhexanoic acid was used as the solvent to extract PM from the feed and alter PM−water relative volatilities. For the thermodynamic model, we used the same model as Zhao et al.36 The NRTL thermodynamic model was selected to describe the phase behavior of the PM−water−solvent system. The UNIFAC group-contribution method was used to obtain the missing parameters for the PM and solvents, and the accuracy of the model selected is validated in the work of Zhao et al.36 To guarantee the use of cooling water in the condensers and avoid the use of vacuum B

DOI: 10.1021/acs.iecr.8b02894 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article


Figure 2. Slope criterion and singular value decomposition analysis for the LEED process.

slope criterion and SVD methods were used to select the temperature-sensitive tray. As shown in Figure 2, for SVD methods, the red line is associated with reflux, and the black line is associated with heat input. The results show that stage 12 can be controlled by heat input in the EDC column. For the RC column, stage 3 can be controlled by reflux and stage 11 by heat input. The results using SVD are similar to the slope criterion results. First, stage 11 was determined to be the temperaturesensitive tray by adjusting the reboiler duties in the RC.

(5) The organic phase level of the decanter is controlled by operating the solvent makeup flow rate. (6) The aqueous phase level of the decanter is controlled by operating the aqueous phase stream outlet flow rate. (7) The temperatures of stage 14 in C1 and stage 4 in C2 are controlled by operating the corresponding reboiler duty. (8) The temperature of the mixed stream leaving the cooler is controlled by operating the corresponding cooler heat removal. Proportional-integral (PI) controllers were used for the flow, pressure, and temperature controllers. For the level loops in the two strippers, proportional-only (P-only) controllers were used, and the gain (KC) and integral time (τI) were set as 2 and 9999 min, respectively. For the decanter organic level-control loops, the gain was set to 10 to ensure the adjustment of the import and export of the organic phase without delay because the level is controlled via the small solvent makeup flow rate. For the flow controllers and pressure controllers, KC was 0.5 and 20, respectively, and τI was 0.3 and 12, respectively. Each temperature controller is inserted with a 1 min dead-time block. In this work, relay-feedback tests are conducted, and the closed loop is selected as the test method for all temperature controllers to obtain the ultimate gain (KU) and period (PU). Then, the

3. DYNAMIC CONTROL FOR THE LEHAD PROCESS 3.1. Basic Control Structure for the LEHAD Process. Based on the optimal TAC flowsheet, a basic control strategy is proposed for the LEHAD process. The basic controllers are used, and the related settings for the basic control are as follows: (1) The fresh feed flow rate is controlled via flow controllers. (2) The solvent flow rate is controlled via flow controllers, and there is a constant ratio with the fresh feed flow rate. Meanwhile, the flow controller is in cascade mode. (3) The operating pressures in the two strippers are controlled by operating the top vapor flow rates. (4) The sump levels in the two strippers are controlled by operating the bottom flow rates. C


Article


Figure 3. Basic control structure for the LEHAD process.

Figure 4. Dynamic responses of the basic control structure for the LEHAD process after introducing the ±20% feed rate disturbance.

Figure 5. Dynamic responses of the basic control structure for the LEHAD process after introducing the ±20% feed composition disturbance.

corresponding tuning parameters for the temperature controllers are calculated using the Tyreus−Luybe rule and are shown in Table S1. Figure 3 shows the basic control strategy of the LEHAD process. The ±20% feed flow rate and ±20% feed composition disturbances were added to evaluate the control performance of the basic control strategy of the LEHAD process. All disturbances are set to be introduced at 0.5 h and finished at 20 h. The corresponding dynamic responses for the LEHAD process in the case of adding ±20% feed rate disturbances are shown in Figure 4. The purity of PM is stabilized at 99.9 mol %, which is almost the initial specification, and water is stabilized at 99.8 mol %, which deviates from the initial value. All controlled temperatures of C1 and C2 can also stabilize at the initial value.

The controlled temperature in C2 has a transient deviation of more than 30 °C after fresh feed flow rate disturbances are added, which leads to a large transient deviation in PM purity. This result is due to a lag in the response signal of the temperature controller when the temperature changes in stage 4 in C2. Therefore, the reboiler duty lags behind the variation in tray temperature. Figure 5 shows the dynamic responses for the LEHAD process after the ±20% feed composition disturbance. For the +20% disturbance, the fresh feed contains 9.36% PM and 90.64% water, whereas that for the −20% disturbance consists of 6.24% PM and 93.76% water. As shown in Figure 5, the PM and water purities can be near the initial values within 3 h after the composition disturbances and maintain a steady state. D


Article


Figure 6. Composition−temperature cascade control structure with QRC2/F for the LEHAD process.

Figure 8. Dynamic responses of the improved control structure for the LEHAD process after introducing the ±20% feed composition disturbance.

Figure 7. Dynamic responses of the improved control structure for the LEHAD process after introducing the ±20% feed rate disturbance.

The controlled temperatures in the two strippers are stable at the initial set points. Overall, a corresponding improved control strategy should be proposed to maintain the water purity and eliminate the lag effect. 3.2. Composition−Temperature Cascade Control Structure with QRC2/F for the LEHAD Process. An improved control structure for the LEHAD process was explored. The composition−temperature cascade control structure was used to maintain the water purity of stream B1 when introducing a ± 20% feed rate disturbance. The dead time for the composition controller is usually larger than the temperature controller, which was set as 3 min. The input signal was the water purity of stream B1, and it was in cascade with the temperature controller to ensure the water purity and quick response. To reduce the lag time, a feed forward control structure was added. The reboiler duty in C2 and the feed flow rate are proportional to each other,

and a multiplier that represents the ratio of reboiler duty to mole feed flow rate (QRC2/F) was added. For the QRC2/F control structure, one input signal is the ratio that is controlled via the temperature controller of stage 14 in C2, and the other is the fresh feed mole flow rate. After the relay-feedback test, the ultimate KU and PU of the two temperature controllers for the two strippers and the composition controller were calculated via Tyreus−Luybe tuning. The tuning parameters are shown in Table S2. Figure 6 shows the final control strategy for the LEHAD process, and the dynamic responses are shown in Figures 7 and 8. The water purity stabilized at approximately 99.9 mol % for the ±20% feed rate disturbance. The transient deviation of the stage 4 temperature in C2 is below 12 °C when fresh feed flow rate disturbances are introduced. Thus, the composition−temperature cascade control structure with E


Article


Figure 9. Basic control structure for the LEED process.

Figure 10. Dynamic responses of the basic control structure for the LEED process after introducing the ±20% feed rate disturbance.

Figure 11. Dynamic responses of the basic control structure for the LEED process after introducing the ±20% feed composition disturbance.

QRC2/F shows good controllability for corresponding feed disturbances.

(4) The reflux ratios in the ERC and RC are fixed. (5) The temperatures of stage 12 in the EDC and stage 11 in the RC are controlled by operating the reboiler duty. (6) The temperature of the recycled solvent is controlled by operating the heat removal rate of the cooler.

4. DYNAMIC CONTROL FOR THE LEED PROCESS 4.1. Basic Control Structure for the LEED Process. For the LEED process, the initial control structure is shown in Figure 9. The settings for some controllers were different from those of the LEHAD process, and the detailed differences are as follows: (1) The operating pressures in the ERC and RC are controlled by operating the heat removal rate of the corresponding condensers. (2) The reflux drum levels in the ERC and RC are controlled by operating the flow rate of the distillates. (3) The sump level in the RC is controlled by operating the flow rate of the solvent makeup.

For the three temperature controllers in the ERC and RC, the tuning parameters calculated using the Tyreus−Luybe rule are listed in Table S3. The corresponding dynamic responses for the LEED process from adding the ±20% feed rate and ±20% composition disturbances are shown in Figure 10 and Figure 11, respectively. The water purity in the bottom stream of LED2 (R) and the top stream of EDC (D1) can approach the initial purity when achieving a new stability. However, the PM purity is 98.63 mol %, which has a large deviation from the initial purity F


Article


Figure 12. Improved dual temperature control structure with QRRC/F for the LEED process.

when a −20% feed composition disturbance is encountered. Moreover, the transient deviation for the controlled temperature of stage 11 in the RC is more than 20 °C when fresh feed disturbances are introduced. Therefore, the basic control structure cannot handle the disturbances efficiently, and a corresponding improved control structure should be studied. 4.2. Improved Dual Temperature Control Structure with QRRC/F for the LEED Process. In the RC, it is not easy to achieve light and heavy component purity control in the top and bottom parts using only one control tray due to the large temperature difference. Thus, the temperature of stage 3 was controlled via the reflux ratio to prevent much 2-ethylhexanoic acid from rising to the top by enlarging the reflux when the temperature of stage 3 increases. This is because there is a lag in the response of the temperature controller when the temperature changes in stage 11. Therefore, the reboiler duty lags behind the variation in tray temperature. Thus, the ratio of reboiler duty to mole feed flow rate (QRRC/F) can reduce the lag time. The two temperature controllers in the RC were tuned individually. For these temperature controllers, the temperature controller for stage 11 was tuned primarily, and the temperature controller for stage 3 was tuned afterward. For the four temperature controllers in the ERC and RC, the tuning parameters are listed in Table S4. The improved dual temperature control structure with QRRC/F is shown in Figure 12 and was evaluated via the feed flow rate and the feed composition disturbances. Figure 13 and Figure 14 provide the dynamic responses of the improved control structure with dual temperature and QRRC/F for the LEED process by adding the ±20% feed disturbance. The PM product composition is maintained at 99.84%, which is near the initial values. The fluctuations of controlled temperature in the RC were greatly improved compared to the basic control structure performance when fresh feed disturbances were introduced. Hence, the improved dual temperature control structure with QRRC/F can handle the disturbances well.

Figure 13. Dynamic responses of the improved dual temperature control structure with QRRC/F for the LEED process after introducing the ±20% feed rate disturbance.

where ysp is the set value of purity, y is the actual value of purity, t0 is the initial time, and t is the terminal time. Figure 15 compares the dynamic responses between the two processes, and Table S5 shows the ISE values for the two control structures (for ease of comparison, two water streams in the LEED process were combined through calculation in Figure 15). As observed in Figure 15, the transient deviations in water and PM purity were slightly larger in the LEHAD process after introducing a ± 20% feed rate disturbance. This can be explained by the response to the changing of the feed in a column. The bottoms product is more affected than the distillation if the feed is liquid.43 The water and PM were obtained from the bottom of the column in the LEHAD process and from the top of the column in the LEED process. Thus, the water and PM purity were affected more in the LEHAD process than in the LEED process. Although

5. COMPARISONS AND DISCUSSION A comparison between the LEHAD and LEED processes in terms of improved dynamic control structures is made in this section. Normally, the integral of squared error (ISE) or the integral of absolute error (IAE) is used to evaluate controllability.42 In this work, the dynamic controllability for the control structures was evaluated via ISE, and the related formula was expressed by eq 1. ISE =

∫t

t 0

(y − y sp )2 dt

(1) G


Article


Figure 14. Dynamic responses of the improved dual temperature control structure with QRRC/F for the LEED process after introducing the ±20% feed composition disturbance.

Figure 15. Comparison between the dynamic controllability of the LEHAD and LEED processes.

the transient deviations for the LEHAD process are larger, the final deviation relative to the initial product purity is relatively small for both processes. This is easily observed from the ISE values in Table S5. The average ISE values for the LEHAD process were close to those of the LEED process. When introducing a ±20% composition disturbance, the transient deviations are quite similar for the two processes. However, the final deviations relative to the initial product purity were much larger in the LEED process. The average ISE values were 101.8 × 10−6 and 46.0 × 10−6 for the LEED process, which were much larger than the values of 11.76 × 10−6 and 10.42 × 10−6 for the LEHAD process. Overall, the LEHAD process shows better dynamic controllability. The LEED process showed better economics, whereas the LEHAD process showed better dynamic controllability.

whereas the LEHAD process showed better dynamic controllability. For the hybrid processes with liquid−liquid extraction for propylene glycol methyl ether dehydration with high control requirements, the LEHAD process should be selected. Otherwise, the LEED process can be adopted in the propylene glycol methyl ether dehydration process.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.8b02894. Tuning parameters of basic control structure for LEHAD process (Table S1); tuning parameters of improved control structure for LEHAD process (Table S2); tuning parameters of basic control structure for LEED process (Table S3); tuning parameters of improved control structure for LEED process (Table S4); ISE index for dynamic controllability between LEHAD and LEED process (Table S5) (DOCX)

6. CONCLUSION In this work, the dynamic control structures of liquid−liquid extraction combined with heterogeneous azeotropic distillation (LEHAD) and liquid−liquid extraction combined with extractive distillation (LEED) processes for separating propylene glycol methyl ether (PM) and water were explored. For the LEHAD process, the composition−temperature cascade control structure with a ratio of reboiler duty to mole feed flow (QR/F) was proposed, and the purities of PM and water can come very close to the initial values at the new steady state after approximately 3 h when a ±20% feed disturbance was introduced. For the LEED process, an improved dual temperature control structure with QR/F was proposed. The results show that the system could reach a new steady state within 4 h after ±20% feed composition disturbances. Compared with the dynamic performances of the LEED process using the integral of squared error method, the LEHAD process shows better dynamic controllability. Overall, the LEED process showed good economics,

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Dongmei Xu: 0000-0002-5770-0513 Yinglong Wang: 0000-0002-3043-0891 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial support from the National Natural Science Foundation of China (Project 21776145 and Project 21676152) is gratefully acknowledged. H


Article


■

ternary azeotropic mixture via adjusting the solvent content. Sep. Purif. Technol. 2018, 191, 8−26. (18) Zhao, Y.; Zhao, T.; Jia, H.; Li, X.; Zhu, Z.; Wang, Y. Optimization of the composition of mixed entrainer for economic extractive distillation process in view of the separation of tetrahydrofuran/ ethanol/water ternary azeotrope. J. Chem. Technol. Biotechnol. 2017, 92 (9), 2433−2444. (19) Han, J.; Lei, Z.; Dong, Y.; Dai, C.; Chen, B. Process intensification on the separation of benzene and thiophene by extractive distillation. AIChE J. 2015, 61 (12), 4470−4480. (20) Wang, Y.; Cui, P.; Ma, Y.; Zhang, Z. Extractive distillation and pressure-swing distillation for THF/ethanol separation. J. Chem. Technol. Biotechnol. 2015, 90 (8), 1463−1472. (21) Zhao, Y.; Ma, K.; Bai, W.; Du, D.; Zhu, Z.; Wang, Y.; Gao, J. Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary mixture containing bioethanol. Energy 2018, 148, 296−308. (22) Chen, Y.-C.; Li, K.-L.; Chen, C.-L.; Chien, I. L. Design and Control of a Hybrid Extraction−Distillation System for the Separation of Pyridine and Water. Ind. Eng. Chem. Res. 2015, 54 (31), 7715−7727. (23) Neves, C. M. S. S.; Granjo, J. F. O.; Freire, M. G.; Robertson, A.; Oliveira, N. M. C.; Coutinho, J. A. P. Separation of ethanol-water mixtures by liquid-liquid extraction using phosphonium-based ionic liquids. Green Chem. 2011, 13, 1517−1526. (24) Harvianto, G. R.; Kang, K. J.; Lee, M. Process Design and Optimization of an Acetic Acid Recovery System in Terephthalic Acid Production via Hybrid Extraction−Distillation Using a Novel Mixed Solvent. Ind. Eng. Chem. Res. 2017, 56 (8), 2168−2176. (25) Xia, H.; Ye, Q.; Feng, S.; Li, R.; Suo, X. A novel energy-saving pressure swing distillation process based on self-heat recuperation technology. Energy 2017, 141, 770−781. (26) Luo, H.; Liang, K.; Li, W.; Li, Y.; Xia, M.; Xu, C. Comparison of Pressure-Swing Distillation and Extractive Distillation Methods for Isopropyl Alcohol/Diisopropyl Ether Separation. Ind. Eng. Chem. Res. 2014, 53 (39), 15167−15182. (27) Wang, Y.; Zhang, Z.; Xu, D.; Liu, W.; Zhu, Z. Design and control of pressure-swing distillation for azeotropes with different types of boiling behavior at different pressures. J. Process Control 2016, 42, 59− 76. (28) Wang, Y.; Liang, S.; Bu, G.; Liu, W.; Zhang, Z.; Zhu, Z. Effect of Solvent Flow Rates on Controllability of Extractive Distillation for Separating Binary Azeotropic Mixture. Ind. Eng. Chem. Res. 2015, 54 (51), 12908−12919. (29) Luyben, W. L. Control comparison of conventional and thermally coupled ternary extractive distillation processes. Chem. Eng. Res. Des. 2016, 106, 253−262. (30) Sun, L.; Wang, Q.; Li, L.; Zhai, J.; Liu, Y. Design and Control of Extractive Dividing Wall Column for Separating Benzene/Cyclohexane Mixtures. Ind. Eng. Chem. Res. 2014, 53 (19), 8120−8131. (31) Chang, W.-L.; Chien, I. L. Potential for Significant Energy-Saving via Hybrid Extraction−Distillation System: Design and Control of Separation Process for n-Propanol Dehydration. Ind. Eng. Chem. Res. 2016, 55 (43), 11291−11304. (32) Luyben, W. L. Control of a triple-column pressure-swing distillation process. Sep. Purif. Technol. 2017, 174, 232−244. (33) Chang, W.-L.; Chien, I. L. Energy-Saving Design and Control of a Methyl Methacrylate Separation Process. Ind. Eng. Chem. Res. 2016, 55 (11), 3064−3074. (34) Yang, S.; Wang, Y.; Bai, G.; Zhu, Y. Design and Control of an Extractive Distillation System for Benzene/Acetonitrile Separation Using Dimethyl Sulfoxide as an Entrainer. Ind. Eng. Chem. Res. 2013, 52 (36), 13102−13112. (35) Bao, Z.; Zhang, W.; Cui, X.; Xu, J. Design, Optimization and Control of Extractive Distillation for the Separation of Trimethyl Borate−Methanol. Ind. Eng. Chem. Res. 2014, 53 (38), 14802−14814. (36) Zhao, T.; Geng, X.; Qi, P.; Zhu, Z.; Gao, J.; Wang, Y. Optimization of liquid−liquid extraction combined with either heterogeneous azeotropic distillation or extractive distillation processes

SYMBOLS USED PM = propylene glycol methyl ether; TAC = total annual cost; LEHAD = liquid−liquid extraction combined with heterogeneous azeotropic distillation; LEED = liquid−liquid extraction combined with extractive distillation; C1 = stripper 1; C2 = stripper 2; EDC = extractive distillation column; RC = solvent recovery column; PI = proportional-integral; KC = gain of the controller; τI = integral time of the controller (min); Q/F = the ratio of reboiler duty to mole feed flow rate; QC1 = the reboiler duty of stripper C1; QC2 = the reboiler duty of stripper C2; QEDC = the reboiler duty of the extractive distillation column; QRC = the reboiler duty of the solvent recovery column; ISE = the integral of squared error; IAE = the integral of absolute error

■

REFERENCES

(1) Skogestad, S. Control structure design for complete chemical plants. Comput. Chem. Eng. 2004, 28 (1−2), 219−234. (2) Wang, Q.; Yu, B.; Xu, C. Design and Control of Distillation System for Methylal/Methanol Separation. Part 1: Extractive Distillation Using DMF as an Entrainer. Ind. Eng. Chem. Res. 2012, 51 (3), 1281−1292. (3) Luyben, W. L.; Chien, I. L. Design and Control of Distillation Systems for Separating Azeotropes; Wiley: Hoboken, NJ, 2011. (4) Liang, S.; Cao, Y.; Liu, X.; Li, X.; Zhao, Y.; Wang, Y.; Wang, Y. Insight into pressure-swing distillation from azeotropic phenomenon to dynamic control. Chem. Eng. Res. Des. 2017, 117, 318−335. (5) Zhu, Z.; Xu, D.; Liu, X.; Zhang, Z.; Wang, Y. Separation of acetonitrile/methanol/benzene ternary azeotrope via triple column pressure-swing distillation. Sep. Purif. Technol. 2016, 169, 66−77. (6) Li, W.; Shi, L.; Yu, B.; Xia, M.; Luo, J.; Shi, H.; Xu, C. New Pressure-Swing Distillation for Separating Pressure-Insensitive Maximum Boiling Azeotrope via Introducing a Heavy Entrainer: Design and Control. Ind. Eng. Chem. Res. 2013, 52 (23), 7836−7853. (7) Qin, J.; Ye, Q.; Xiong, X.; Li, N. Control of Benzene−Cyclohexane Separation System via Extractive Distillation Using Sulfolane as Entrainer. Ind. Eng. Chem. Res. 2013, 52 (31), 10754−10766. (8) Zhu, Z.; Wang, L.; Ma, Y.; Wang, W.; Wang, Y. Separating an azeotropic mixture of toluene and ethanol via heat integration pressure swing distillation. Comput. Chem. Eng. 2015, 76, 137−149. (9) Modla, G.; Lang, P.; Denes, F. Feasibility of separation of ternary mixtures by pressure swing batch distillation. Chem. Eng. Sci. 2010, 65 (2), 870−881. (10) Janakey Devi, V. K. P.; Sai, P. S. T.; Balakrishnan, A. R. Heterogeneous azeotropic distillation for the separation of n-propanol + water mixture using n-propyl acetate as entrainer. Fluid Phase Equilib. 2017, 447, 1−11. (11) Shi, L.; Huang, K.; Wang, S.-J.; Yu, J.; Yuan, Y.; Chen, H.; Wong, D. S. H. Application of Vapor Recompression to Heterogeneous Azeotropic Dividing-Wall Distillation Columns. Ind. Eng. Chem. Res. 2015, 54 (46), 11592−11609. (12) Le, Q.-K.; Halvorsen, I. J.; Pajalic, O.; Skogestad, S. Dividing wall columns for heterogeneous azeotropic distillation. Chem. Eng. Res. Des. 2015, 99, 111−119. (13) Franke, M. B. MINLP optimization of a heterogeneous azeotropic distillation process: Separation of ethanol and water with cyclohexane as an entrainer. Comput. Chem. Eng. 2016, 89, 204−221. (14) Pla-Franco, J.; Lladosa, E.; Loras, S.; Montón , J. B. Thermodynamic Analysis and Process Simulation of Ethanol Dehydration via Heterogeneous Azeotropic Distillation. Ind. Eng. Chem. Res. 2014, 53 (14), 6084−6093. (15) Tabari, A.; Ahmad, A. A semicontinuous approach for heterogeneous azeotropic distillation processes. Comput. Chem. Eng. 2015, 73, 183−190. (16) Luyben, W. L. Improved design of an extractive distillation system with an intermediate-boiling solvent. Sep. Purif. Technol. 2015, 156, 336−347. (17) Wang, Y.; Zhang, X.; Liu, X.; Bai, W.; Zhu, Z.; Wang, Y.; Gao, J. Control of extractive distillation process for separating heterogenerous I


Article

Industrial & Engineering Chemistry Research to reduce energy consumption and carbon dioxide emissions. Chem. Eng. Res. Des. 2018, 132, 399−408. (37) Chen, Y. C.; Yu, B. Y.; Hsu, C. C.; Chien, I. L. Comparison of heteroazeotropic and extractive distillation for the dehydration of propylene glycol methyl ether. Chem. Eng. Res. Des. 2016, 111, 184− 195. (38) Bristol, E. H. On a new measure of interactions for multivariable process control. IEEE Trans. Autom. Control 1966, 11, 133−134. (39) Luyben, W. L. Distillation Design and Control Using Aspen Simulation; John Wiley & Sons: New York, 2013. (40) Luyben, W. L. Evaluation of criteria for selecting temperature control trays in distillation columns. J. Process Control 2006, 16 (2), 115−134. (41) Tututi-Avila, S.; Jiménez-Gutiérrez, A.; Hahn, J. Control analysis of an extractive dividing-wall column used for ethanol dehydration. Chem. Eng. Process. 2014, 82, 88−100. (42) Segovia-Hernández, J. G.; Hernández, S.; Jiménez, A. Control Behaviour of Thermally Coupled Distillation Sequences. Chem. Eng. Res. Des. 2002, 80 (7), 783−789. (43) Luyben, W. L. Comparison of Extractive Distillation and Pressure-Swing Distillation for Acetone-Methanol Separation. Ind. Eng. Chem. Res. 2008, 47, 2696−2707.

J


Dynamic control of hybrid processes with liquid-liquid extraction for

Recommend Documents