Simplification and Intensification of a C5 Separation Process

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Simplification and Intensification of a C5 Separation Process Hsiao-Ching Hsu, San-Jang Wang, John Di-Yi Ou, and David Shan Hill Wong Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b01705 • Publication Date (Web): 29 Sep 2015 Downloaded from http://pubs.acs.org on September 30, 2015

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Industrial & Engineering Chemistry Research

Simplification and Intensification of a C5 Separation Process Hsiao-Ching Hsu,† San-Jang Wang,*,‡ John Di-Yi Ou,† and David Shan Hill Wong*,†

†

Department of Chemical Engineering, National Tsing Hua University,Hsinchu 30013,

Taiwan ‡

Center for Energy and Environmental Research, National Tsing Hua University,

Hsinchu 30013, Taiwan

Corresponding authors *Tel.: +886-3-5715131 ext. 33624 or 33641. Fax: +886-3-5715408. E-mail: [email protected], [email protected]

1 ACS Paragon Plus Environment


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ABSTRACT: The C5 fraction, which accounts for 15–25% in naphtha, consists of molecules such as isoprene (IP), pentadiene (PD), cyclopentene (CP), and cyclopentadiene (CPD). The C5 fraction can be used to manufacture petroleum resin and other high value-added products. Yet it is often burned as fuel and not fully utilized because separation of these products with close boiling points is difficult. One common process is to react CPD with itself to form high boiling dicyclopentadiene (DCPD) that can then be separated from other C5 molecules. In addition, extractive distillation is also used to recover alkynes from light ends. Such a process involves the use of multiple separation columns and reaction zones. Furthermore, the reactor is highly coupled with one of the separation columns by two recycle streams, which may lead to a snowball effect and difficulty in controlling the process. Hence, many opportunities for process integration and intensification are available. We describe how the entire process with reaction and separation can be substantially simplified by reducing the number of reaction zones from two to one and the number of columns from eight to six. Such a simplification increases not only process operability but also product concentration of DCPD, while maintaining a high purity for the IP stream and a specified purity for the PD plus CP stream. Moreover, capital cost can be greatly decreased with the simplified process. This process can be further intensified by using thermal coupling and external heat integration. Large energy savings can be achieved


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for the intensified process. Simulation results demonstrate that the proposed simplified and intensified process for the separation of a C5 mixture can substantially reduce capital and operating costs as well as improve process operability and increase the main product purity of DCPD.

Keywords: Intensification,

steady-state

simulation,

plant-wide

integration, thermal coupling.


process,

heat


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1. INTRODUCTION Diolefins including cyclopentadiene (CPD), isoprene (IP), pentadiene (PD), and cyclopentene (CP) in the C5 fraction are a by-product of the ethylene industry. They are obtained from a naphtha cracking process by conventional distillation and extractive distillation. The rise of the shale gas industry, where light oil can be used for ethylene synthesis, has enabled ethylene to be obtained easily and lowered its production cost. Because of this reason, the current processes in the naphtha industry need to be improved for the recovery of high value-added products such as CPD, IP, PD, CP, etc. in order to increase their competitive strength. However, numerous units are used and much energy is consumed for the separation of close boiling-point components and azeotropes in the naphtha cracking process. Various strategies shown in Figure 1 can be used for treating hydrocarbon streams comprising CPD and other dienes. To obtain products that contain valuable materials, one of these strategies uses multiple dimerization of CPD and depolymerization of dicyclopentadiene (DCPD), as exemplified by the work of Nakamura et al.1 and Shen et al.2 They have shown that it is feasible to achieve high concentrations of DCPD by the use of 1) dimerization, 2) depolymerization and separation, and 3) dimerization and separation as given in Figure 1. However, there are some differences between their processes. Nakamura et al.1 used thermal cracking to depolymerize DCPD to CPD, but Shen et al.2 added acid


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to catalyze the depolymerization reaction of DCPD. Other processes also exist like the one used by Cheng et al.3 who separated the DCPD product from crude C5 components after using only a single step of CPD dimerization to get DCPD and obtained a DCPD product of 94 wt%. In contrast to the process of Cheng et al.,3 Anzick et al.4 stated that CPD can be pre-separated from crude C5 components and then converted into DCPD by reactors while assuring high conversion efficiencies for CPD and achieving a DCPD product of 90 wt%. In addition, Li et al.5 used numerous reactors proceeding only dimerization of CPD to obtain DCPD with high recoveries but moderate concentrations. In crude C5 oil, besides CPD and its derivative materials, IP is also an important component and it is mixed with close boiling-point components. Some azeotropes can be found among them. Extractive distillation is commonly used in the industry to separate these azeotropes. Three solvents can be used in extraction distillation for the purification of IP. These solvents include acetonitrile (ACN), dimethylformamide (DMF), and n-methyl-2-pyrrolidone (NMP).6–8 In this study, DMF, used by Zeon Cooperation of Japan, was chosen as the solvent for the separation of IP because the DMF-based extractive distillation process is cheap and non-corrosive, and DMF can be constantly reused.8 Process intensification is a design philosophy that integrates distinct processes



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into a single unit. It represents an important trend in chemical engineering and has attracted much attention in the research and industrial communities. Intensification technologies can reduce energy consumption and capital investments, as well as achieve environmental and safety benefits. In the chemical process industry, the process of distillation, which consumes approximately 3% of the energy used around the world,9 is undoubtedly the most energy-intensive separation one utilized in practice. Motivated by the large energy requirements for distillation, much research has been devoted to improvements in the thermal coupling between the distillation columns in series for the separation of multi-component mixtures. In comparison with conventional distillation trains, thermally coupled distillation techniques can supply potential energy savings of around 30% by implementing the interchange of liquid and vapor between two columns. Capital cost can be further reduced if two columns with thermal coupling are integrated into one shell. This alternative to a conventional column train is termed a dividing wall column (DWC), which is thermodynamically equivalent to a Petlyuk column. Recently, Dejanović et al.10 comprehensively surveyed DWCs in both theoretical studies and the patent area. Yildirim et al.11 gave a review of the current industrial applications for DWCs and related research activities. According to Schultz et al.,12 DWCs will become a standard distillation tool in the next 50 years.


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In addition to exploring the issues discussed above, this research investigates the intensification of distillation processes through external heat integration. External heat integration implies heat integration between a rectifying section and a stripping section (i.e., a heat sink and a heat source) of different distillation columns. Pinch analysis was used in this study to achieve energy saving. The C5 separation processes involving multiple reactors and distillation units are rather complicated. The aforementioned literature discusses various methods for process improvement. However, to the best of our knowledge, a unified benchmark for various processes and a systematic approach to improving these processes have not been found in the open literature. The objective of this study is to not only simplify but also intensify the C5 separation process for the recovery of high purity DCPD, high purity IP, and concentrated PD mixed with CP by the technologies of thermal coupling and external heat integration.

2. THERMODYNAMICS AND KINETIC MODELS The crude C5 separation process involves various components like CPD, IP, C4 components,

1,4-pentadiene,

2-methyl-butane,

3-methyl-1-butene,

isopentane,

1-pentene, n-pentane, trans-2-pentene, cis-2-pentene, trans-PD, cis-PD, CP, 1-pentyne, 1,2-pentadiene, cyclopentane, C6 components, DCPD, etc. A rigorous model



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RADFRAC from the Aspen Plus software with version 8.4 was used in this study to conduct the simulation of the crude C5 separation process. The vapor-liquid equilibrium relationship was described by NRTL activity coefficient model.13 The phase-equilibrium relationships for the pairs not built in the Aspen data bank were determined by UNIFAC model.14 The relative volatilities of IP and the other components in the crude C5 in the presence of the solvent (DMF), which was used in the extractive distillation process, were provided from the literature.15 These experimental data were obtained under the condition of 50 °C and 1 bar and are shown in Figure 2. The predictions from the NRTL plus UNIFAC model were found to agree well with the experimental data. There are dimerization, trimerization, and depolymerization reactions occurring in the studied system. The main reactions considered included 1) self-dimerization of CPD, IP, and PD; 2) co-dimerization between CPD and IP and between CPD and PD; and 3) depolymerization of the DCPD. Very few trimerization reactions occur, and these were ignored in this study. Table 1 gives the kinetic parameters of the frequency factor and activation energy for the reactions involved in the system.16–18 A series of experimental reaction data given by Szekeres et al.19 and shown in Figure 3 were used to check the accuracy of the simulation results for the main reactions of CPD self-dimerization and DCPD depolymerization. There was excellent fit between the


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experiment and simulation data for these reactions. From the frequency factor and activation energy values given in Table 1, the best selectivity for DCPD can be achieved at 40 °C on the basis of our calculations. However, this reaction temperature would result in a slow reaction rate during the production of DCPD by the self-dimerization of CPD. Increasing the reaction temperature up to 110 °C would result in a higher reaction rate, but there would be high amounts of by-products due to side reactions. Considering the trade-off between the reaction rate and side product production, the reaction temperature is suggested to be operated between 75 °C and 110 °C.

3. CONVENTIONAL PROCESS The main purpose for the crude C5 separation process is to recover high value-added components such as DCPD, IP, and PD/CP. In this study, the conventional plant-wide process of crude C5 separation was simulated. A flowsheet of this process is shown in Figure 4, and it is based on the U.S. patent20 and the Chinese patent.21 The process descriptions are given in the following. The mixture fed to column 101 (C101) mainly contains C4, C5, and C6 components. C101 is used for the separation of C4 materials. Low boiling-point C5 components are distillated at the column top and the remaining ones are obtained at



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the column bottom. The product withdrawn from the column bottom is fed into the first reaction zone, which includes three adiabatic plug-flow reactors (R1-1 to R1-3). In these reactors, the main reactions that proceed between the C5 diolefins are CPD self-dimerization, IP self-dimerization,

PD self-dimerization,

CPD

and

IP

co-dimerization, and CPD and PD co-dimerization. These reactions are exothermic ones and can automatically occur without catalysts. Therefore, no catalysts were present in the process. The products from the first reaction zone are fed into column 102 (C102). This column is used for the separation of IP and CPD that are obtained mainly from the column top and bottom, respectively. It should be noted that some traces of CPD will still be found at the column top because of azeotropes formed between CPD and some components such as pentane, trans-2-pentene, cis-2-pentene, and 1-pentyne. In addition to CPD, small amounts of IP, PD, and CP will also be found at the column bottom. The distillate products from the column are then introduced into the IP extraction zone (C103, C104, and C105), while the bottom ones from the column are fed into the IP, PD/CP, and DCPD recovery zone, which includes C106, C107, C108, and the second reaction zone that contains only one plug-flow reactor (R2). The second reaction zone is mainly used for DCPD production by CPD self-dimerization. In the IP extraction zone, an extractive distillation process with column 103 (C103) and column 104 (C104) is used to extract IP by using DMF as the


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solvent. Alkanes and alkenes of C5 are obtained from the top of the extractive distillation column C103, while dienes, alkynes, and DMF from the column bottom are fed into the solvent recovery column C104. The DMF with a high purity of 99.98 wt% is recovered from the bottom of C104 and then recycled to C103. Dienes and alkynes withdrawn from the top of C104 are introduced into column 105 (C105) for further separation of IP and some amounts of CPD and DCPD produced from CPD self-dimerization. High purity IP can be distillated from the top of C105, while most of CPD and DCPD are collected in the bottom stream. The bottom products of C102 and C105 are together fed into column 106 (C106). The products, which contain CPD, PD, and CP along with small amounts of IP, from the top of C106 are fed into the second reaction zone. The output products from the reaction zone are then separated in column 107 (C107), which has three outlet streams that include the products of IP along with a small amount of unreacted CPD in distillate, the PD/CP mixture at side-draw, and the DCPD along with by-products at the bottom. The distillate and bottoms streams are recycled to mixer 1 and mixer 2, respectively. The bottom product of column 106 is introduced into column 108 (C108) to obtain the C6 to C9 components at the top and the main product DCPD with purities between 85 and 92 wt% at the bottom. In the conventional process, the second reaction zone is added because unreacted CPD can be fed into this zone and dimerized to DCPD. The use of



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the second reaction zone raises the reaction conversion of CPD and results in a higher production rate of DCPD. In the crude C5 separation process, the target specifications commonly used in the industry are given in Table 2. The product purity and recovery from our simulation results for the conventional process are also given in this table. For the mixture with 75,000 ton per annum fed to column 101, the total reboiler duty required is 34.5 MW. With an 8-year payback period, the annual capital cost was found to be 2,316,000 USD/yr. The annual operating cost was found to be 2,856,000 USD/yr, and the total annual cost (TAC) equaled 5,172,000 USD/yr. The above costs were calculated by using the method described in Douglas.22 In general, the conventional process can provide an effective way to recover valuable materials in crude C5. However, the main issue of the complexity in the design remains unsolved because a few recycle streams and many units are involved in the process. At times, recycle streams can result in a snowball effect and Luyben23, 24

has shown the control difficulties from the snowball effect. The whole process

containing eight columns and two reaction zones with a total length of 216 m requires high capital and operating costs. In the following work, the complexity problems mentioned above are solved by simplifying the conventional process.


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4. SIMPLIFIED PROCESS In this study, the simplified process shown in Figure 5 was designed by deleting the first reaction zone, C106 and C108, and two recycle streams from C107 in the conventional process shown earlier in Figure 4. The first reaction zone was not used because the presence of IP in the reaction zone can cause chemical reactions to produce some high boiling-point by-products that can reduce the purity of the final recovered DCPD product. According to the design, the IP and CPD are separated by C102 in the simplified process before being fed into the reaction zone. With IP removed from the top of C102, the IP recovery can be improved because of the reduction of the IP self- and co-dimerizations that occur in the first reaction zone of the conventional process. The main purpose of C106 in the conventional process is to separate the DCPD and heavy materials formed in the first reaction zone at the bottom and provide higher concentrations of CPD that are then fed into the second reaction zone. In the simplified process, the bottom product, which includes mostly CPD, PD, and CP, of C102, is directly fed into the reaction zone without the use of C106. The length of the reaction zone is thus reduced from 72 m, as shown in Figure 4, to 30 m, as shown in Figure 5. In addition, C107 and C108 in the conventional process are integrated into C107, which has three outlet streams in the simplified process once C106 is omitted. The PD plus CP product is obtained from the top of C106, heavy C5



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components and C6 by-products are withdrawn from the side stream, and DCPD is recovered from the column bottom. The RE1 stream in Figure 4, which contains only tiny amounts of IP and CPD, is ignored in the simplified process. This modification might cause small losses of IP; however, higher overall recovery of IP can still be achieved because of the removal of the first reaction zone. Table 2 also gives the product recovery and product concentration achieved in the simplified process. This table indicates that the simplified process can provide not only high purity products but also much improved recovery in comparison with the conventional process. The DCPD product with increased purity of 98.84 wt% thus makes the simplified process more competitive. The recoveries of IP, PD/CP, and DCPD were raised by 7.1%, 1.2%, and 4.9%, respectively, in the simplified process. Table 3 provides the total reboiler duty, annual operating cost, annual capital cost, and TAC for various design strategies given in this study. In comparison with the conventional process, the capital cost is substantially reduced by 35.4% for the simplified process because of the removal of some columns and reactors.

5. INTENSIFIED PROCESS The simplified process given in Figure 5 still consists of six distillation columns for IP removal and C5 recovery. In this study, the simplified process is intensified by


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the use of thermal coupling and external heat integration for further reduction of energy consumption. C103 is operated at higher pressure than the other columns, and its bottom stream at higher temperature can be used for external heat integration with other heat sources with lower temperatures. Hence, a logical choice to implement thermal coupling would be between columns C104 and C105 and between columns C101 and C102. Figure 6 shows the configuration of thermal coupling. C104 and C105 are integrated into the DWC (referred to as C104&105) by sharing a condenser. One condenser can be deleted by the vapor and liquid interchange between these two columns. The number of trays in the DWC is kept the same as the total number of trays in C104 and C105. In the DWC, the bottom product (on the left side) containing enriched DMF at 99.98 wt% is recycled to mixer 1, while that (on the right side) containing mixed C5s is sent to mixer 2. The distillate of the DWC is an IP product with high purity above 99.75 wt%. The DWC configuration can reduce 30% of the total reboiler duty of C104 and C105. In addition to C104&105, C101 and C102 are further integrated into the DWC (referred to as C101&102) by sharing a reboiler. One reboiler can be omitted by implementing the thermal coupling between these two columns. The number of trays in the DWC is also kept the same as the total number of trays in C101 and C102. The DWC configuration can reduce 13% of the total reboiler



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duty of C101 and C102. In comparison with the conventional process, the results in Table 3 indicate that the total reboiler duty and TAC can be reduced by 21.6% and 27.0%, respectively, for the simplified + intensified process with thermal coupling (denoted by S+ITC). Apart from the thermal coupling between the two columns to reduce reboiler duty, energy consumption can also be decreased by external heat integration. To effectively extract IP, C103 is operated at a high pressure, thus resulting in a high temperature around 220 °C at the column bottom. The bottom stream of C103 must be cooled down to 50 °C before it is fed into C104 for better separation efficiency. In addition, the DMF recycle stream, on the left side of C104&105, should be cooled down to 50 °C before it is fed into C103 in order to satisfy the high purity requirement of the product at the top of C103. These two streams with higher temperatures are the main sources of energy supply for external heat integration. In general, the heat exchanger needs a certain temperature difference for heat transport. Here, we choose 10 °C for the heat transfer between hot and cold streams. Figure 7 shows the relationship between TAC and number of heat exchangers for external heat integration. There may be some different configurations even if the same number of heat exchangers is used. The use of a higher number of heat exchangers can lead to a decrease in energy utilization through external heat integration but to an increase in investment costs.


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TAC is minimized when nine heat exchangers are used for external heat integration. Figure 8 shows the grid diagram for the analysis of external heat integration. The heat of the hot streams represented by red lines can be recovered by the cold streams represented by blue lines. The pinch line represented by a vertical dash points out the limitation of temperature exchange. Figure 9 gives the intensified process with DWCs and external heat integration. The bottom stream in C103 is used to provide reboiler duties of C104&105, C107, and C101&102 via heat exchangers E1, E3, E2, and E4, respectively. The DMF recycle stream supplies partial reboiler duties of C104&105 and C101&102 via heat exchangers E5 and E6, respectively. In addition, the partial reboiler duty of C101&102 is given by the bottom stream of C107 via heat exchanger E8. It is also used to preheat the feed stream of the reactor by the heat exchanger E7. The reaction temperature is then raised from 58.9 °C to 72.0 °C, which results in faster reaction rates. At the same time, the reactor length can be reduced from 30 to 15 m under the same CPD conversion and by-product amounts. Furthermore, the top vapor of the C103 can be used as the heat input of the heat exchanger E9 in C101&102. The design results for the simplified + intensified process with thermal coupling and external heat integration, represented by S+ITC+EHI, are also given in Table 3. The total reboiler duty of the conventional process can be substantially decreased by



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46.1% for this S+ITC+EHI process. The contribution towards the energy reduction was the greatest for external heat integration (24.5%) followed by thermal coupling (13.7%) and process simplification (7.9%). Thus, external heat integration provides the most energy saving method among these design strategies in the studied process. The annual capital cost of the conventional process is reduced by 36.6% for the S+ITC+EHI process. The simplification technique provided the most contribution in regards to this reduction. The S+ITC+EHI process needs slightly higher capital cost than the S+ITC process because of the addition of some auxiliary reboilers for external heat integration. Overall, however, the simulation results reveal that much economic benefit can be achieved from the 36.3% reduction of the TAC for the proposed S+ITC+EHI process.

6. CONCLUSIONS In this study, the conventional process applied to crude C5 for the separation of IP, PD/CP, and DCPD can be substantially simplified by separating the low boiling materials and IP first before CPD dimerization and by using a side-draw column in the final separation. Only 64.6% of the original capital cost is necessary for the simplified process. The recovery and purity of the main product, DCPD, can be increased by reducing the number of reaction zones and columns and rearranging the


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position of the reaction zone. The intensified process designed by the use of thermal coupling and external heat integration technologies can further reduce 41.5% of the heat duty and 31.8% of the operating costs in the simplified process. Simulation results demonstrate that the economic benefit of the crude C5 conventional process can be remarkably enhanced by the simplification procedures and intensification technologies of thermal coupling and external heat integration.

ACKNOWLEDGMENTS This work was financially supported by the Ministry of Science and Technology of Taiwan under grant no. MOST 102-2622-E-007-029-CC1.

REFERENCES (1) Nakamura, T.; Kawakita, M.; Minomiya, K. Process for the Vapor-Phase Thermal Cracking of Dicyclopentadiene and a Process for the Manufacture of High Purity Dicyclopentadiene. United States patent US5321177, 1994. (2) Shen, L.; Jiang, H.; Huang, Y. H.; Gao, J. H. A High-Purity Dicyclopentadiene Production Technology. Chinese patent CN1781887 A, 2006. (3) Cheng, J. M.; Liu, Z. X.; Liang, G.; Li, D. F. Method for Preparing



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Dicyclopentadiene by Carbon 5 Fraction. Chinese patent CN101450886 A, 2009. (4) Anzick, R. K.; Blackbourn, R. L.; Nayarajan, S. K. Method of Treating a Hydrocarbon Stream Comprising Cyclopentadiene and One or More Diolefins. United States patent US20110178349 Al, 2011. (5) Li, Z. X.; Liao, L. H.; Li, D. F.; Peng, D. C.; Jing, W.; Cheng, J. M.; Guo, L. Method for Separating Carbon 5 Fraction by One-Stage Extraction and Rectification. Chinese patents CN101450885 A, CN101450885 B, 2012. (6) Shu, Q. J.; Wang, F. H.; Zhao, X. W.; Lui, H. G.; Lui, L. J.; Wu, S. C. Domestic Technological Advances Separate. China Elastomerics 2009, 19, 71. (7) Liu, Z. X.; Li, D. F.; Cheng, J. M.; Liao, L. H.; Li, S. F.; Luo, S. J. A C5 Segregation Based Mixed Ionic Liquid Solvent. Chinese patents CN102452882 A, CN102452882 B, 2014. (8) Takao, S.; Shi, C.; Hokari, H. Method for Separation of Conjugated Diolefin by Back Wash in Extractive Distillation. United States patent US3436436 A, 1969. (9) Khalifa, M.; Emtir, M. Rigorous Optimization of Heat-Integrated and Petlyuk Column Distillation Configurations Based on Feed Conditions. Clean Technol. Environ. Policy 2009, 11, 107. (10) Dejanović, I.; Matijašević, Lj.; Olujić, Ž. Dividing Wall Column - A Breakthrough towards Sustainable Distilling. Chem. Eng. Process. 2010, 49, 559.


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(11) Yildirim, Ö.; Kiss, A. A.; Kenig, E. Y. Dividing Wall Columns in Chemical Process Industry: A Review on Current Activities. Pur. Technol. 2011, 80, 403. (12) Schultz, M. A.; Stewart, D. G.; Harris, J. M.; Rosenblum, S. P.; Shakur, M. S.; O’Brien, D. E. Reduce Costs with Dividing-Wall Columns. Chem. Eng. Prog. 2002, 98, 64. (13) Renon, H.; Prausnitz, J. M. Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures. AIChE J. 1968, 14, 135. (14) Hansen, H. K.; Rasmussen, P.; Fredenslund, A.; Schiller, M.; Gmehling, J. Vapor-Liquid Equilibria by UNIFAC Group Contribution. 5 Revision and Extension. Ind. Eng. Chem. Res. 1991, 30, 2352. (15) Weitz, H. M.; Loser, E. Isoprene. Ullmann’s Encyclopedia of Industrial Chemistry; Wiley, 2000. (16) Liu, J.; Wang, X.; Zhang, Z.; Li, J. Formation of Dicyclopentadiene by Thermal Dimerization from C5 Fractions. Petrochemical Technology 1996, 25, 248 (in Chinese). (17) Sun, S.; Dong, L.; Hao, X.; Wang, Y.; Lu, A. Studies on Cyclopentadiene Removal from Pyrolysis C5 Distillates with Thermal Polymerization. Qilu Petrochemical Technology 2007, 35, 6 (in Chinese). (18) Walling, C.; Peisach, J. Organic Reactions under High Pressure. IV. The



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Dimerization of Isoprene. J. Am. Chem. Soc. 1958, 80. 5819. (19) Szekeres, G.; Siklos, P.; Nagy, L. Thermal Dimerization of Cyclopentadiene and its Reaction with Isoprene. Chem. Eng. 1977, 21, 13. (20) Tian, B.; Li, P.; Du, C.; Xu, H.; Feng, H.; Hu, J.; Gao, J.; Ma, M. Process for Separating C5 Cuts Obtained from a Petroleum Cracking Process. United States patent US6958426 B2, 2003. (21) Sun, C.; Fu, F. S.; Yao, B. T.; Yang, Z. S.; Yao, Y. J.; Wang, J. Y.; Wu, Z. P.; Zhang, D. M. Separation Method of C5 Fraction. Chinese patent CN102951989 A, 2013. (22) Douglas, J. M. Conceptual Design of Chemical Processes; McGraw Hill: New York, 1988. (23) Luyben, W. L. Dynamics and Control of Recycle Systems. 3. Alternative Process Designs in a Ternary System. Ind. Eng. Chem. Res. 1993, 32, 1142. (24) Luyben, W. L. Snowball Effects in Reactor/Separator Processes with Recycle. Ind. Eng. Chem. Res. 1994, 33, 299.


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LIST OF FIGURES Figure 1. Available strategies for crude C5 separation. Figure 2. Comparison of relative volatility data between the experiment and simulation. Figure 3. Comparison of reaction data between the experiment and simulation at different temperatures. Figure 4. Conventional process flowsheet. Figure 5. Simplified process flowsheet. Figure 6. Flowsheet of the simplified + intensified process with thermal coupling. Figure 7. The relationship between TAC and number of heat exchangers for external heat integration. Figure 8. Grid diagram for the analysis of external heat integration. Figure 9. Flowsheet of the simplified + intensified process with thermal coupling and external heat integration.



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LIST OF TABLES Table 1. The Frequency Factor and Activation Energy of Various Reactions Table 2. Target Specifications of Conventional and Simplified Processes Table 3. Comparison of the Total Reboiler Duty, Annual Operating Cost, Annual Capital Cost, and TAC for Various Design Strategies


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Figure 1. Available strategies for crude C5 separation.



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Figure 2. Comparison of relative volatility data between the experiment and simulation.


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Figure 3. Comparison of reaction data between the experiment and simulation at different temperatures.



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Figure 4. Conventional process flowsheet.


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Figure 5. Simplified process flowsheet.



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Figure 6. Flowsheet of the simplified + intensified process with thermal coupling.


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Figure 7. The relationship between TAC and number of heat exchangers for external heat integration.



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Pinch line 67.4 С 204.9 С 156.5 С 130.7 С 71.2 С 71.2 С

166.5 С 140.7 С H1

94.5 С

67.4 С

50.0 С

94.5 С

50.0 С

H2

97.7 С

25.0 С

DCPD streams 71.2 С

C103-condenser

25.0 С

L2 streams 42.4 С 28.9 С 25.8 С 18.5 С 2.3 С

204.7 С

C103-reboiler

156.5 С

C104-reboiler

130.7 С

C107-reboiler

84.5 С

C105-reboiler

72.0 С

E7

C102-condenser L3 streams C105-condenser C101-condenser C107-condenser 204.7 С 156.5 С 130.7 С 84.5 С 58.9 С

57.4 С C102-reboiler 57.4 С Pinch line

57.4 С

Figure 8. Grid diagram for the analysis of external heat integration.


42.4 С 25.0 С 25.8 С 18.5 С 2.3 С

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Figure 9. Flowsheet of the simplified + intensified process with thermal coupling and external heat integration.



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Table 1. Frequency Factor and Activation Energy of Various Reactions Reactions

ko (L/mol/s)

E (kJ/kmol)

2CPD → DCPD

2,590,000

72,523

2IP → X2-1

79,000,000

104,082

2PD → X2-2

599,600

93,632

CPD + IP → X3-1

94,500

72,368

CPD + PD → X3-2

2.22E+13

147,136

DCPD → 2CPD

7.41E+12

147,236


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Table 2. Target Specifications of Conventional and Simplified Processes

Target

Conventional process

Simplified process

IP product concentration (wt%)

99.75

99.82

99.78

IP product recovery (%)

>90

90.52

97.62

PD+CP product concentration (wt%)

89.81

90.79

90.34

PD+CP product recovery (%)

-

92.84

94.04

DCPD product concentration (wt%)

83.27

86.73

98.84

DCPD total recovery (%)

-

89.30

94.16



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Table 3. Comparison of the Total Reboiler Duty, Annual Operating Cost, Annual Capital Cost, and TAC for Various Design Strategies Total reboiler duty (MW)

Annual operating cost ($103/yr)

Annual capital cost ($103/yr)

TAC ($103/yr)

34.50

2,856

2,316

5,172

Simplified

31.76

2,677

1,496

4,173

process

(7.9%)

(6.3%)

(35.4%)

(19.3%)

S+ITC

27.04

2,365

1,413

3,777

process

(21.6%)

(17.2%)

(39.0%)

(27.0%)

S+ITC+EHI

18.60

1,825

1,469

3,294

process

(46.1%)

(36.1%)

(36.6%)

(36.3%)

Designed process Conventional process


Simplification and Intensification of a C5 Separation Process

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