Non-reactive Columns Research Articles

Parallel column model for reactive dividing wall column simulation

Reactive Dividing Wall Column (RDWC) modelling has attracted significant attention in recent years because simulations of processes containing such columns have demonstrated the potential for significant savings in energy and capital cost. Most modelling of these columns involves decomposing RDWCs into a thermodynamically equivalent flowsheet of reactive and non-reactive column sections in a sequential modular process simulation package. Such simulations of (R)DWCs can be time consuming to create and difficult to converge. It has been suggested that equation-oriented solvers can have superior numerical performance. Here, we use a CAPE-OPEN compliant equation-based parallel column model (PCM) that enables the rapid modelling of an RDWC as a single self-contained unit. Some conventionally modelled RDWCs from the literature are reproduced with the PCM to demonstrate its validity and excellent numerical performance. The ease and rapidity with which different RDWC configurations can be created is a significant advantage of our PCM.

Design and analysis of an intensified column with side reactor configuration for ethylene glycol production from ethylene oxide

The side reactor concept (SRC), comprising a non-reactive column coupled with side reactors, is proposed for the synthesis of ethylene glycol (EG) by ethylene oxide (EO) hydration. Parallel isothermal continuous stirred tank reactors are employed and the combinations of the reactors and the column are cautiously examined. A preliminary analysis of the operating conditions for the reaction and separation and the detailed SRC configurations (such as the side stream rate, side stream location) are performed to generate the suggested values or ranges for their further optimization. The decisive variables are subsequently optimized by a sequential design procedure. The significant effects of the key decision variables on the trade-off between the reaction cost and the separation cost are well investigated. The reactor–separation unit, configured with a total liquid withdrawn and recycled back to the column stage below, demonstrates better system performance. Furthermore, the reaction at elevated temperature (150 °C) conductive for reaction and the separation occurring at the distillation temperature range of 106∼204 °C (124 kPa) gives out improved economic performance. Flexibility in the operating conditions in SRC makes it a competitive alternative to the RD process for EG production.

An Efficient Method of Constructing Pinch Point Curves and Locating Azeotropes in Nonideal Distillation Systems

An efficient, robust, ODE-based formulation of the continuation problem is presented for the automatic construction of all branches of the pinch point curves in any homogeneous distillation system (even highly nonideal ones) that can be represented using an activity coefficient model, with any number of components and for any adiabatic, nonreactive column configuration. Constant molar overflow is assumed. The curve is parametrized by reflux ratio, making it particularly applicable to distillation design and synthesis. Naturally, it can be used to find pinch point locations at a given finite reflux, as this is simply a subset of the pinch point curve. The method can also automatically locate all N-component azeotropes very efficiently (orders of magnitude faster than commercial process simulators). It has the additional advantage of being solvable using tools already available in typical mathematical software packages. A computer implementation of the proposed method is available.

Multiobjective optimization of reactive distillation with thermal coupling using non-dominated sorting genetic algorithm-II

In this study, the Multiobjective optimization of transesterification reactive distillation column with thermal coupling by using Non-Sorting Genetic Algorithm II (NSGA-II) is presented. A Visual C++ (VC++) code for real-parameter NSGA-II and HYSYS software for thermodynamic calculation of reactive distillation (RD) column have been linked to optimize the effective parameters of reactive distillation column. The 9 parameters, Feed ratio, Reflux ratio, Methyl acetate temperature, n-Butanol temperature, Tray number of n-butanol feed, Tray number of methyl acetate feed, tray number of side stream, Molar flow of side stream, and pressure of reactive distillation column, are selected as decision variables. The specification value for simulation of reactive and non-reactive columns is 0.995 for purity of n-butyl acetate and methanol respectively. The Non-Sorting Genetic Algorithm II was employed for minimization of reboiler energy cost, maximization of n-butyl acetate molar flow as reactive distillation productivity, and maximization of methanol molar flow as non-reactive distillation column productivity. The NSGA-II proposed multiple solutions set as optimal solutions, but from these results, three set give better results than the others.

Reactive pressure swing batch distillation by a new double column system

Ethyl-acetate is generally produced by the esterification reaction of ethanol with acetic-acid. Since the reaction is equilibrium-limited, the use of reactive distillation is an attractive option. A new double-column system is suggested for ethyl-acetate production by applying reactive pressure swing batch distillation. The system was investigated by a feasibility study based on the analysis of reactive and non-reactive residue curve maps. Two different process options were found to be feasible. In the first option, the reactive column operates at the lower pressure (1.01 bar), and the non-reactive column that removes ethyl-acetate from the system operates at the higher pressure (10 bar). The second option allows the reactive column to operate at the higher pressure (10 bar), and the non-reactive column removes water at the lower pressure (1.01 bar). The first process option was studied by rigorous simulation based on less simplifying assumptions using a professional dynamic simulator. The influence of the most important operation parameters was also studied.

A partially heat integrated reactive distillation: Feasibility and analysis

Published studies have been focused mainly on the internal heat integration of nonreactive columns. In this contribution, a novel partially heat integrated reactive column configuration is proposed. The representative reactive column is originally a unit of the two-column sequence used for the production of high-purity ethyl acetate. The present study identifies the thermodynamic feasibility of the reactive process and explores an economically interesting partially heat integrated reactive distillation column (HIRDC). Sensitivity tests have been conducted to tune the design and operating variables. An economic comparison between the proposed two-column scheme consisting of HIRDC followed by a recovery column and its conventional counterpart is also performed. Due to the internal energy integration, better performance is achieved with more than 20% energy saving and a payback time of 3.58 years is obtained.

Reactive Distillation in a Dividing Wall Column: Rate-Based Modeling and Simulation

In this paper, a novel rate-based description of nonreactive and reactive dividing wall columns is presented. These highly integrated units promise advantages in the context of process intensification. Until now, published studies have been focused on the nonreactive columns, based on equilibrium stage models, whereas the modeling of both dividing wall columns and reactive dividing wall columns, using the rate-based approach, has not been done yet. In the presented model, special attention is given to phenomena that have not been considered in previous publications (e.g., heat transfer through the dividing wall). The model has been applied to a nonreactive, ternary alcohol mixture and successfully validated. The transesterification of carbonates has been identified as an interesting system for the reactive dividing wall column. This reaction system is equilibrium limited and characterized by high conversion, yet low selectivity. Initial simulation studies demonstrate that the selectivity can be significan...

Predicting Multiple Steady States in Equilibrium Reactive Distillation. 2. Analysis of Hybrid Systems

Guttinger and Morari (Ind. Eng. Chem. Res. 1998, 38, 1633−1648) developed graphical methods for the prediction of output multiplicities caused by the reactive vapor−liquid equilibrium in reactive distillation. These methods rest upon the limiting case of reactive columns of infinite length operated at infinite internal flows (∞/∞ analysis) and are directly applicable to systems where the reactions take place in the entire column (“nonhybrid” columns). In this work, the reactive ∞/∞ analysis is extended to columns with a reactive core (“hybrid” columns) by introduction of two new procedures. First, necessary and sufficient feasibility conditions for hybrid column profiles are derived under the assumption that each of the reactive and nonreactive column sections has infinite length. Using these conditions, an “exact” method is formulated where all possible products of such an ∞/∞ hybrid column can be located in the composition space (by a continuation of solutions). The existence of multiple steady states a...

Predicting Multiple Steady States in Equilibrium Reactive Distillation

This paper presents graphical methods for the prediction of output multiplicities caused by the reactive vapor-liquid equilibrium in equilibrium reactive distillation. The methods rest upon the limiting case of reactive columns with infinite length operated at infinite internal flows (∞/∞ analysis) and are directly applicable to systems where the reactions take place in the entire column (“non-hybrid” columns). Applying a necessary and sufficient condition for the existence of output multiplicities, the region of all feed locations leading to multiple steady states can be constructed. Since many industrial reactive systems are “hybrid” (non-reactive columns with a reactive core), the prediction methods are extended to cover hybrid columns where analogous results can be obtained as for non-hybrid systems. The methods will be applied to the well-known MTBE reactive distillation process and the physical phenomena which cause multiplicities in this process are determined by analytical investigations and compared to the available literature results.

Preparation and Gas Chromatography of the Trimethylsilyl Derivatives of Resin Acids and the Corresponding Alcohols

Trimethylsilyl esters of resin and fatty acids and trimethylsilyl ethers of the corresponding alcohols can be prepared readily and quantitatively using hexamethyldisilazane and trimethylsilyl chloride in hydrocarbon solvent. Pyridine was found to be detrimental to formation of the esters. Polyester liquid phases cannot be used for the analysis of the trimethylsilyl esters. However, because the silyl esters are very rapidly hydrolyzed, a simple means is thus available to recover the free acids after preparative gas chromatographic separation with other, nonreactive column packings.