Semicontinuous Distillation of Quintenary and N-ary Mixtures

Semicontinuous distillation (SCD) is a process intensification technique for separating N-component (N ≥ 3) mixtures. Its feature is forced circulation in three distinct operation modes: separating, discharging, and charging. To explore better control methods, a cascade model predictive control (MPC) strategy is proposed with a proportional-integral (PI) control loop, utilizing a multiple-input multiple-output transfer function (MIMOTF) matrix as the MPC prediction model. The MIMOTF matrix precisely represents the system’s dynamic behavior across the complete cycle. This method proves to be highly effective in controlling the entire SCD process while successfully meeting both product purity requirements and hydraulic constraints. A simulative economic comparison is conducted to assess the applicability of semicontinuous and conventional continuous systems in terms of the annual yield. The superiority of the cascade MPC strategy is demonstrated with remarkable reductions of 9.1% in separation cost (SC) and 8.9% in cycle time compared to the PI-only configuration.

Section: Introductionmentioning

confidence: 99%

Optimal Control Framework for Alkane Separation in Semicontinuous Distillation

Qu,

Zhang,

Shen

et al. 2023

“…Despite these limitations, in this study, the brute force approach was chosen because it offers a practical way to approach a cycle (startup), and it features a simple computational method. All previous studies 5,[10][11][12]17,18 that used the brute force method determined the arbitrary initial state by designing a continuous distillation process (referred to as continuous middle vessel-column system in this study) which comprises of a distillation column with a side draw (Figure 1, top left). The continuous distillation process is designed to meet the top and bottoms product purities that is desired in the semicontinuous distillation process.…”

Section: ■ Introductionmentioning

confidence: 99%

Finding Better Limit Cycles of Semicontinuous Distillation. 1. Back Stepping Design Methodology

Madabhushi

Adams

2019

Semicontinuous ternary zeotropic distillation is a periodic process that is carried out in a single distillation column and a tightly integrated external middle vessel. In the state-of-the-art design procedure of this process, a continuous distillation process that separates the top and bottom products to the desired purity is used to generate an arbitrary initial state for simulating the dynamics of the semicontinuous distillation process. Although this method is useful in estimating the limit cycle, it was later found that the operation of the process in this limit cycle was economically suboptimal. In this study, a new algorithmic design procedure, called the back-stepping design methodology, is proposed to find better limit cycles for zeotropic ternary semicontinuous distillation using the aspenONE Engineering suite. The proposed methodology was applied to two different case studies using feed mixtures with different chemical components. A comparison with the current design procedure for the two case studies indicates that the new method outperforms the state-of-the-art by finding limit cycles that were 4−16% lower in separating cost, which was the chosen measure of cycle performance.

“…Espada et al conducted the extraction of waxes from different crude oils by using the sequential chromatographic method. Besides, distillation, membrane separation, , and the urea-adduct process have also been reported to apply for n -alkanes separation. Among these processes, adsorption has the advantages of low energy consumption, high selectivity, and good product purity .…”

Section: Introductionmentioning

confidence: 99%

Tuning n-Alkane Adsorption on Mixed-Linker Zeolitic Imidazolate Framework-8-90 via Controllable Ligand Hybridization: Insight into the Confinement from an Energetics Perspective

Sun

Jiang

Kong

et al. 2019

Linker hybridization provides enormous tunability of structures and properties of zeolitic imidazolate frameworks (ZIFs). We synthesized hybrid ZIF-8-90 structures by using binary organic ligands and examined their compositional and structural evolution using multiple techniques including field emission scanning electron microscopy (FESEM), Raman, X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), N 2 adsorption, and 1 H NMR analyses. Well-designed ligand compositions of ZIF structures contribute to the continuously switchable pore structures. The average micropore diameter shrinks from 0.72 to 0.65 nm, while the mesopore width monotonically increases from 2.18 to 3.29 nm as the carboxaldehyde-2-imidazole (OHC-IM) proportion rises from 0.31 for ZIF-8-90-S1 to 0.88 for ZIF-8-90-S5. An increase in framework polarity can lead to the strengthened guest−host interaction and therefore energetically exerts a positive effect on the adsorption affinity of n-hexane on hybrid ZIF-8-90 structures. The highest n-hexane adsorption capacity is found on the ZIF-8-90-S4 sample (having OHC-IM proportion of 0.82). At a close OHC-IM proportion of 0.792, the simulation result exhibits the strongest guest−host interaction (with the largest van der Waals interaction energy).