Control of the Maximum-Boiling Acetone/Chloroform Azeotropic Distillation System

Atmospheric-Pressurized Process for Dimethyl Carbonate/Methanol Separation with and without Heat Integration: Design and Control

Process economy and dynamic controllability are critical for DMC/MeOH separation via the PSD process. In this paper, rigorous steady-state and dynamic simulations of atmospheric-pressurized process for DMC/MeOH separation with no, partial, and full heat integration have been carried out with Aspen Plus and Aspen Dynamics. Further investigations have been conducted into the economic design and dynamic controllability of the three neat systems. Simulation results indicated that: the separation process via full and partial heat integration provided TAC savings of 39.2 and 36.2%, respectively, compared to that of no heat integration; the non-heat-integrated system displays good dynamic performance, critical dynamic penalties were demonstrated for both partial and full heat integration processes, while the partial one exhibited a more robust control except for precisely maintaining X_B2(DMC); a PCTC scheme with a CC/TC cascade control was proposed to precisely maintain the product concentration for the fully heat-integrated PSD process. A comparison of the economy between atmospheric-pressurized and pressurized-atmospheric sequences indicated that the former is more energy efficient. Further, a comparison of the economy between atmospheric-pressurized and pressurized-atmospheric sequences indicated that the former is more energy efficient. This study will provide new insights into the energy efficiency and has some implications for design and control of DMC/MeOH separation in the industrialization process.

Effects of Energy Intensification of Pressure-Swing Distillation on Energy Consumption and Controllability

The aim of process integration is the efficient use of energy and natural resources. However, process integration can result in a more precise process operation, that is, it influences controllability. Pressure-swing distillation processes are designed for the separation of azeotropic mixtures, but their inherent heat integration option can be utilized to significantly reduce their energy consumption. One maximum-boiling and three minimum-boiling azeotropes are considered to study and compare the nonintegrated and integrated alternatives with the tool of mathematical modeling where ASPEN Plus and MATLAB software are used. The results show that the heat-integrated alternatives result in 32-45% energy savings that are proportional to the emission reduction and the consumption of natural resources. As far as the operability is concerned, the heat-integrated alternatives show worse controllability features than the nonintegrated base case. This can be due to the loss of one controllability degree of freedom. This recommends using more sophisticated control structures for the sake of safe operation if process integration is applied.

Optimal design of extractive dividing-wall column using an efficient equation-oriented approach

The extractive dividing-wall column (EDWC) is one of the most efficient technologies for separation of azeotropic or close boiling-point mixtures, but its design is fairly challenging. In this paper we extend the hybrid feasible path optimisation algorithm (Ma Y, McLaughlan M, Zhang N, Li J. Computers & Chemical Engineering, 2020, 143: 107058) for such optimal design. The tolerances-relaxation integration method is refined to allow for long enough integration time that can ensure the solution of the pseudo-transient continuation simulation close to the steady state before the required tolerance is used. To ensure the gradient and Jacobian information available for optimisation, we allow a relaxed tolerance for the simulation in the sensitivity analysis mode when the simulation diverges under small tolerance. In addition, valid lower bounds on purity of the recycled entrainer and the vapour flow rate in column sections are imposed to improve computational efficiency. The computational results demonstrate that the extended hybrid algorithm can achieve better design of the EDWC compared to those in literature. The energy consumption can be reduced by more than 20% compared with existing literature report. In addition, the optimal design of the heat pump assisted EDWC is achieved using the improved hybrid algorithm for the first time.

Effect of Ionic Liquids on the Isobaric Vapor-Liquid Equilibrium Behavior of Acetone-Chloroform

Isobaric vapor-liquid equilibrium (VLE) data of the ternary system acetone + chloroform + 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) or 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]) were obtained at 101.3 kPa. Results indicated that the addition of [MMIM][DMP] or [EMIM][DEP] could eliminate the azeotropic point of the binary system of acetone + chloroform when the mole fraction of ionic liquids (ILs) was above 0.15. Besides, the experimental data could be well correlated by the nonrandom two-liquid (NRTL) model. The structures as well as interactions between molecular solvents (acetone, chloroform) and the ion pairs ([MMIM][DMP], [EMIM][DEP]) were studied by quantum chemical calculations. The result indicated that the interaction energies (ΔE) follow the order of ΔE(acetone + [EMIM][DEP]) > ΔE(acetone + [MMIM][DMP]) > ΔE(chloroform + [EMIM][DEP]) ≈ ΔE(chloroform + [MMIM][DMP]), and chloroform had stronger affinity to ionic liquids than acetone.