Thermodynamic analysis and optimization of isoprene/n-pentane separation process

doi:10.11949/0438-1157.20241115

Abstract

Abstract:

For the isoprene-pentane azeotropic system commonly found in C₅ fractions, this paper proposes a method to evaluate the extractive distillation process with the help of an intelligent optimization algorithm and to design it based on thermodynamic principles. First, a conceptual design is developed based on the residue curve map, followed by closed-loop global optimization of process parameters using an improved genetic algorithm. The optimization is carried out with economic performance, energy efficiency, and extractive section separation efficiency (unique to extractive distillation) as evaluation criteria. Subsequently, the TOPSIS (technique for order preference by similarity to ideal solution) method is employed to select the optimal design scheme from the Pareto front solutions, followed by an analysis of the optimization results from the thermodynamic perspective. The results indicate that the best scheme excels in separation efficiency, economic viability, and energy utilization; reducing the amount of extraction agent, appropriately increasing the number of trays, and optimizing the reflux ratio can effectively enhance separation efficiency while lowering costs. This research provides theoretical foundations and design guidance for the efficient separation of isoprene and pentane in industrial applications.

Key words: azeotrope, global optimization, extraction distillation, improved genetic algorithm, thermodynamics

摘要：

针对C₅馏分中常见的异戊二烯-正戊烷共沸体系，提出了一种借助智能优化算法评估萃取精馏工艺，并从热力学原理进行设计的方法。首先，基于残余曲线图进行概念设计，并利用改进的遗传算法对工艺参数进行闭环全局优化，以经济性、能源效率及萃取段分离效率（萃取精馏所特有）为评价指标来进行综合优化。接着，结合TOPSIS方法从Pareto前沿解中筛选出最佳设计方案，并基于热力学原理对优化结果进行分析。研究结果表明，最佳方案在分离效率、经济性和能量利用率上均表现优异；通过减少萃取剂用量、适当增加塔板数和优化回流比，可有效提高分离效率并降低成本。研究结果为工业上异戊二烯与正戊烷的高效分离提供了理论依据和设计指导。

关键词: 共沸物, 整体优化, 萃取精馏, 改进的遗传算法, 热力学

CLC Number:

TQ 028.3

Lin LI, Mingmei WANG, Erwei SONG, Wenwen WANG, Yaochang ZHANG, Erqiang WANG. Thermodynamic analysis and optimization of isoprene/n-pentane separation process[J]. CIESC Journal, 2025, 76(6): 2549-2558.

李琳, 王明媚, 宋二伟, 王雯雯, 张耀昌, 王二强. 异戊二烯-正戊烷分离工艺的热力学分析及优化[J]. 化工学报, 2025, 76(6): 2549-2558.

Figures/Tables 11

Fig.1 Comparison of experimental data and VLE data simulated by different thermodynamic models

Fig.2 RCMs of the IP/n-Pen/DMF system at 1bar

Fig.3 Extractive distillation process flow diagram for isoprene and n-pentane

Fig.4 Variation of liquid vapor pressure with temperature for isopentane and n-pentane

Fig.5 The optimization process of extractive distillation based on improved genetic algorithm

Fig.6 Multi-objective optimization result for the extraction distillation process used in the separation of the IP/n-Pen/DMF system

Table 1 Design parameters of five optimized schemes for the extractive distillation of isoprene/n-pentane separation

Item	S1	S2	S3	S4	S5
N_EDC	77	127	116	78	90
N_E	8	7	9	9	12
N_{F, EDC}	27	35	50	23	33
D_EDC/(kmol/h)	14.97	15.00	14.98	15.01	15.00
F_E/(kmol/h)	130.52	87.26	86.11	216.68	112.94
R_EDC	9.422	10.53	14.95	14.31	11.01
N_SRC	19	49	24	52	27
N_{F, SRC}	7	10	8	30	7
D_SRC/(kmol/h)	60.04	60.05	60.05	60.04	60.05
R_SRC	0.202	0.204	1.225	0.274	0.226
TOC/(10⁵ USD)	5.52	5.26	7.34	8.13	5.72
TCC/(10⁵ USD)	3.60	5.92	5.23	5.09	4.05
TAC/(10⁵USD)	9.12	11.19	12.57	13.22	9.77
Ex_loss/kW	240.71	228.62	366.20	339.55	245.63
E_ext	0.432	0.524	0.611	0.381	0.484
e_ext✕10^-1	0.240	0.194	0.153	0.293	0.242

Fig.7 The influence of key design parameters FE and REDC of the EDC column on the objective functions Eext and TAC

Fig.8 Distribution of distillate flow rates at the top of the column on the Pareto front

Fig.9 Composition profiles in the EDC column for design schemes S1—S5

Fig.10 Relative volatility of n-Pen/IP in the EDC column for design schemes S1—S5

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