Dynamic control and performance comparison of conventional and dividing wall extractive distillation for benzene / isopropanol / water separation

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BACKGROUND The triple‐column extractive distillation (TCED) process for the ternary multi‐azeotropic mixture of N‐hexane/acetone/chloroform is a significant step in waste recovery and purification. Given the common occurrence of feed disturbances in practical industrial production, a feasible dynamic control scheme should effectively resist feed disturbances and ensure product quality, enabling the process to run steadily and safely with a high efficiency. However, it is challenging to design a robust control scheme for separation processes accompanied by side‐stream capability. In this work, dynamic control schemes were designed for four separation processes: conventional and double side‐stream TCED processes with single and double entrainers. A multipoint temperature control scheme, composition‐temperature cascade control scheme and variable ratio control were combined to improve the dynamic performance of the control schemes. RESULTS The results showed that the control schemes designed for the four extractive distillation processes are highly robust, resisting ±20% feed flow and composition disturbances. A variable ratio control combined with composition‐temperature cascade was found to be vital for double side‐stream TCED schemes. CONCLUSION The conventional TCED with a single entrainer (CS‐TCED) is an optimal process for N‐hexane/acetone/chloroform separation both from control and economic perspectives. The designed control scheme is simple, low‐cost and easy‐to‐implement with a superior dynamic performance over other separation schemes. This study has a certain theoretical guidance for N‐hexane/acetone/chloroform separation in terms of economic benefits and practical production. © 2022 Society of Chemical Industry (SCI).

‐ 1 / \ln ((), ISE) goodbreak= goodbreak- 1 / \ln \int_{t_{o}}^{t} {(y - y^{italicsp})}^{2} italicdt

Figure 10 shows the average value of the −1/ln(ISE) under different feed disturbances, where the FD and CD represent the flow disturbances and composition disturbances, respectively.…”

Section: Steady‐state Analysismentioning

confidence: 98%

“…However, instead, the −1/ln(ISE) can reduce the exponential difference in the ISE values in the figure, which can clearly reflect the magnitude relationship of the ISE without distortion, as commonly adopted in other studies. 29,30 The calculation equation is as follows:…”

Section: Control Performance Comparison and Analysismentioning

confidence: 99%

Dynamic control design and performance evaluation of extractive distillation for N‐hexane/acetone/chloroform

Guo

et al. 2022

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“…Recovery of valuable products from waste liquids by separation and purification is a crucial way to achieve green and sustainable development. 1,2 High-efficiency separation technology of multiple azeotropic systems has received extensive research and attention by special distillation, including pressure-swing distillation (PSD), [3][4][5] extractive distillation, [6][7][8] azeotropic distillation [9][10][11] and reactive distillation. [12][13][14] Compared with other separation methods, PSD separation of azeotropes has the advantages of no need to add other impurities, and being an energy-saving, simple process, especially for material systems where the composition of azeotrope mixture changes with the change of pressure.…”

Section: Introductionmentioning

confidence: 99%

Economic optimization and dynamic control of pressure‐swing distillation for separating the ternary azeotrope of butanone/n‐heptane/isopropanol

Sun

Zhang

et al. 2022

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BACKGROUND Economic optimization and dynamic control of the separation process for recovering the ternary mixture of butanone (MEK)/n‐heptane/isopropanol (IPA) from industrial wastewater is a significant topic. In this work, the optimal pressure‐swing distillation (PSD) sequence, heat integration and dynamic control for separating MEK/n‐heptane/IPA were investigated systematically. The optimal separation sequence was determined by combining the minimum total annual cost (TAC) with the residual curves map (RCM). Pressure‐swing distillation with non‐heat integration, partial heat integration or full heat integration was compared in terms of TAC. Dynamic control schemes were designed for optimal processes of two separation sequences with and without heat integration. RESULTS The results demonstrate that the TAC of optimal PSD with non‐heat integration process can be reduced by 31.11%, whereas the TAC of optimal partial heat integration and full heat integration schemes can be reduced by 39.73% and 40.96%, respectively. The dynamic performance of all control schemes that can resist ±20% feed flow disturbances and composition disturbances are compared with the integral of squared error. CONCLUSION It is demonstrated that PSD with full integration process (FHIPSD) for separating MEK/n‐heptane/IPA has optimal economic performance, whereas PSD with non‐heat integration process (NTIPSD) has the optimal dynamic performance and robust stability. This work provides a significant reference for industrial separation of MEK/n‐heptane/IPA. © 2022 Society of Chemical Industry (SCI).

“…However, under normal temperature and pressure, the mixture of n-hexane and chloroform forms a minimum azeotrope, making it difficult to separate high-purity products from the waste liquid. Therefore, special distillation methods must be used, such as pressure swing distillation, 2,3 extractive distillation [4][5][6] and azeotropic distillation. 7,8 Extractive distillation(ED) is a typical technology for separating azeotropic compounds.…”

Section: Introductionmentioning

confidence: 99%

“…Extractive distillation(ED) is a typical technology for separating azeotropic compounds 9,10 . However, the remixing effect of intermediate components in multicomponent mixtures results in high energy consumption for the extractive distillation process 6,11 . Therefore, it is urgent to develop an alternative process with more energy competitiveness.…”

Section: Introductionmentioning

confidence: 99%

Comparison of different extractive distillation processes for chloroform/n‐hexane separation: design and control

Zeng

Jianting²,

Zhu

et al. 2022

Background When extracting total glycosides from Panax notoginseng, a waste liquid containing chloroform and n‐hexane will be produced. These waste liquids are not separated and recycled in time, which will not only waste resources but also cause environmental pollution. Chloroform and n‐hexane form an azeotrope which cannot be separated by ordinary distillation methods. This study proposes three extractive distillation processes to separate the chloroform/n‐hexane azeotrope: conventional extractive distillation (ED), side‐stream extractive distillation (SSED) and extractive dividing wall column (EDWC). The total annual cost (TAC) and carbon dioxide (CO2) emissions of the three options were compared, and the optimal process was selected. Furthermore, this research developed dynamic control of the optimal process. Results Compared with ED, from the perspective of economic indicators, the SSED process showed 18.9% reduction in TAC yet the EDWC process showed 33.2% reduction in TAC. In terms of CO2 emission indicators, the EDWC process also is more advantageous. Three control structures thus were developed for EDWC: applying ±5% or ±10% feed flow disturbance, and feed composition disturbance. The results show that CS3 with temperature composition cascade control structure can perfectly control all disturbances. Conclusion This paper designs an economical, environmentally friendly and controllable chloroform/n‐hexane azeotropic separation process, which can provide a reference for the industrial application of chloroform/n‐hexane separation. © 2022 Society of Chemical Industry (SCI).