Optimization of Nonideal Separation Structures Based on Extractive Heterogeneous Azeotropic Distillation

Coarse-grained (CG) simulation models of condensed-phase systems can be derived with well-established methods that perform coarse-graining in space and provide an effective Hamiltonian with which some of the structural and thermodynamic properties of the underlying fine-grained (FG) reference system can be represented. Coarse-graining in time potentially provides CG models that furthermore represent dynamic properties. However, systematic efforts in this direction have so far been limited, especially for moderately coarse-grained, chemistry-specific systems with complicated conservative interactions. With the aim of representing structural, thermodynamic, and dynamic properties in CG simulations of multi-component molecular systems, we investigated a recently introduced method in which the force on a CG particle originates from conservative interactions with surrounding particles and non-Markovian dissipative interactions, the latter introduced by means of a colored-noise thermostat. We examined two different methods to derive isotropic memory kernels required for integrating the corresponding generalized Langevin equation (GLE) of motion, based on the orthogonal dynamics of the FG forces and on an iterative optimization scheme. As a proof of concept, we coarse-grain single-component molecular liquids (cyclohexane, tetrachloromethane) and ideal and non-ideal binary mixtures of cyclohexane/tetrachloromethane and ethanol/tetrachloromethane, respectively. We find that for all systems, the FG single particle velocity auto-correlation functions and, consequently, both the short time and long time diffusion coefficients can be quantitatively reproduced with the CG-GLE models. We furthermore demonstrate that the present GLE-approach leads to an improved description of the rate with which the spatial correlations decay, which is artificially accelerated in the absence of dissipation.

The Doong-Yang model, which is used for predicting gas mixture adsorption equilibrium from pure-component isotherms of the Dubinin type, is modified by incorporating the Lewis relationship. The modified model is tested against experimental data for four binary systems, including a like-component (or nearly ideal) mixture, CH(4) + C(2)H(6), a moderately nonideal mixture, CO(2) + C(2)H(4), and two highly nonideal mixtures, CO(2) + C(3)H(8) and CO(2) + H(2)O. Comparisons are made with the ideal adsorbed solution (IAS) theory and the Bering model. Results show that the proposed model is the best for the like-component mixture and the moderately nonideal mixture. In contrast, for the highly nonideal mixtures, the original Doong-Yang model is the only one among the four models that can predict CO(2) + C(3)H(8) adsorption correctly. The IAS theory and the Bering model have similar predictions and are suitable only for like-component mixtures. The new model requires a simple numerical iteration but is easy to use; no new parameters are required. Theoretical reasons are given for the fact that the original Doong-Yang model is best for nonideal mixtures, whereas the modified Doong-Yang model is best for ideal mixtures.

Modelling of Organophilic and Hydrophilic Pervaporations for Separation of Ethyl Acetate – water Mixture

Separation sequence optimization is an energy-saving strategy for improving the process economy. This work introduces a rigorous simulation-based method to identify the best separation sequence for the separation of N-component mixture, aiming to reduce the total operating cost. Through data interaction between Aspen HYSYS and MATLAB, a separation sequence matrix and an operating cost matrix for the N-component mixture are established. Based on this, the optimal separation sequence with the lowest total operating cost is automatically identified. The separation of 5-component hydrocarbon mixture is studied to illustrate the feasibility of the proposed method. This work also evaluates separation sequences for variant feed compositions, and shows the effects of feed compositions on the best separation sequences. This method is also applicable for separation of the other mixture, giving a new solution for identification of the optimal separation sequence.

Equilibrium properties and surface transfer coefficients from molecular dynamics simulations of two-component fluids

The conceptual design and process intensification of the separation of ternary azeotropic mixture with heterogeneous characteristic

6 - Diffusion

Hybrid separation processes combining simulated moving bed chromatography and crystallization have been known to reduce the capital cost for enantiomer separation, but past studies have been limited to systems of single-component pure solvent. In this study, a model-based design strategy using a binary solvent is presented. Separation of d- and l-phenylalanine in a mixture of methanol and water was employed as a case study. Experimental data for solid–liquid equilibrium as well as chromatographic separation were obtained at various compositions of the solvent mixture to model the process. The experimental data were used to model and optimize the design of the hybrid separation process. The trade-offs between the solubility, temperature, chromatographic separation, and eutectic compositions were analyzed using the model-based optimization approach. In a case study, it was found that the productivity can be increased by over 18% when the temperature is increased from 10 to 50 °C because of the lower eutectic purity.

In this study, the task is to develop a heuristic procedure for the synthesis of systems for the separation of multicomponent mixtures, which would take into account the uncertainty of the factors of the separation processes and the multivariance of the solution.
 The authors reviewed the current state of the existing methods for the separation of mixtures. Many works devoted to the synthesis of effective systems for the separation of multicomponent mixtures leave unsolved the problem of taking into account the uncertainty of many factors of the separation processes. In the presented work, it is proposed that a heuristic approach is applied using fuzzy logic.
 The proposed procedure is based on the choice of a separation sequence that takes into account the value of the separation coefficient and the difference in boiling points of two adjacent key components. The proposed strategy is based on an estimate of the likelihood of each rule for each possible separation. The search for solutions has five stages. First, the mixture to be separated and the available equipment are determined. After that, an ordered list of all separation options is drawn up with possible values of the economic costs of their implementation. Next, the mass load of possible separation is estimated and the separation with the minimum value of the separation ratio is selected. The heuristic is that the heavy separation is done last. And, at the last step, the most economical separation scheme is selected.
 The above strategy at the stage of quantitative assessment is subject to the value of the threshold S (boiling point difference). This point can be used to determine the quasi-optimal solutions to the problem of sequencing according to the rules of relaxation of separation. 
 For this fuzzy heuristic method for determining cost-effective separation sequences for mixtures, appropriate software has been developed. In addition, since the procedure uses the theory of fuzzy sets, the Fuzzy Logic Toolbox package of the Matlab was also used to solve the problem of synthesizing schemes for separating hydrocarbon mixtures. The proposed procedure was successfully tested in both software implementations using the example of separating a five-component mixture. 
 The main difference between the proposed approach and other approaches based on fuzzy logic for the synthesis of separation systems is the gradation of working rules and possible quantification of a set of rules, which eliminates conflicts between the rules.

Partial molal volumes in aqueous mixed-micellar and solubilized systems

Rate Based Modelling and Simulation Studies of Hybrid Processes consisting of Distillation, Vapour Permeation and Adsorption for the dehydration of ethanol

A method is reported to estimate the batch sizes, operating times, equipment sizes, utility loads, and costs for the batch distillation of nonideal multicomponent mixtures. The method provides an estimate for both the design and the operating policy for the reflux or reboil ratio without the need to integrate the full column model numerically. This operating policy approximates the constant product composition policy for high purities and high fractional recoveries and shows a substantial cost savings over the constant reflux or reboil policies, primarily on account of a substantial reduction in the vapor rate. The approach provides a good approximation to the results of a detailed optimization in an example for a binary mixture. A more interesting application is illustrated for the separation of a quaternary azeotropic mixture arising from the transesterification of ethyl acetate with methanol to produce ethanol and methyl acetate.

This paper considers the problem of finding minimum energy requirements of a single-feed adiabatic distillation column for a given separation task. Over the years, many attempts to understand this problem have been made. This paper presents an approach which is at the intersection of the thermodynamic and geometric points of view. In it, an analysis of multicomponent distillation is carried out via the notion of power of separation, which is akin to compositional exergy. It is shown mathematically that this concept, although taking its roots in thermodynamics, has a strong link with the geometry of liquid composition trajectories in multicomponent distillation and is also related to the traditional McCabe−Thiele diagram for binary distillation. By considering pinch-point curves for adiabatic column sections and their link with reversible column profiles, a characterization of minimal energy requirements of the single-feed adiabatic distillation process is proposed. As a consequence, a shortcut method to determine minimal energy requirements of multicomponent distillation is introduced. Examples validating this approach for multicomponent distillation of ideal, nonideal, zeotropic, and azeotropic mixtures with up to six components are presented. These examples indicate that the new method can, in principle, treat any number of mixture components. All types of pinch behavior are covered, that is, the method can find minimal energy designs associated to feed, saddle, or tangent pinch points. Case studies where pinched minimum energy solutions exist, where pinched solutions can be reduced to nonpinched solutions, and where no pinched solutions exist are presented. In all these cases, the new method can find, if they exist, pinched and nonpinched solutions.

The adiabatic temperature rise in catalytic pellets is predicted from a modified version of the Prater equation. Onsager reciprocal relations for coupled heat and mass transfer are violated in an analysis of thermal diffusion in macroporous catalysts with exothermic chemical reaction when Dufour conduction (i.e., the diffusion‐thermo effect) is neglected. In this contribution, Dufour conduction is analyzed for both ideal and non‐ideal pseudo‐binary gas mixtures that simulate the production of methanol from carbon monoxide and hydrogen. In the diffusion‐controlled regime at large intrapellet Damköhler numbers where intermolecular collisions provide the dominant resistance to mass transfer within the catalytic pores, temperatures in the catalytic core could be much greater than predictions based on the original Prater equation when the Prater number exceeds 0.30. The molecular flux of thermal energy includes Fourier's law, the interdiffusional flux, and Dufour conduction. Diffusional mass flux includes Fick's law and the Soret effect. All physicochemical properties of the reactive gas mixture exhibit temperature dependence. There is essentially no difference between maximum intrapellet temperature predictions that include or neglect ideal Dufour conduction when external catalytic surface temperatures range from 300‐400 K and thermal diffusion enhances the flux of “smaller” reactants toward the centre of the catalyst. For “large‐molecule reactants” that participate in exothermic reactions, thermal diffusion opposes Fick's law and Dufour conduction opposes Fourier's law. Under these conditions, it is demonstrated that core temperatures are overestimated by neglecting both off‐diagonal coupling mechanisms (i.e., Soret diffusion and Dufour conduction). Prater numbers greater than unity and unrealistically high gas pressures are required to distinguish between maximum intrapellet temperatures for ideal and real gas simulations, where the latter consider two‐body interactions for Lennard‐Jones molecules in the virial equation of state.

The results obtained by using derived equations prove to be equally accurate and more economic to simulate if applied to the olefinic and some selected members of the alkylbenzene series as they were for the paraffinic series. A large number of mixtures with a temperature span of 5.9 to 30.5°C are involved in this study. Satisfactory results are also obtained when these equations, slightly modified by appropriate pressure correction factors, are applied to hydrocarbon mixtures at nonatmospheric pressures. The proposed approach is, however, not recommended for nonideal hydrocarbon mixtures. The statistical approach can save up to 60% of computer CPU time for mixtures containing up to 10 components. Computed bubble and dew points are compared with both the conventional iterative method and some VLE experimental data.