Dividing wall column (DWC) is a single shell, fully thermally coupled distillation column capable of separating mixtures of three or more components into high purity products. Compared to conventional columns-in-series and/or in-parallel configurations a DWC requires much less energy, capital and space. This makes DWC to something that corresponds with the present day idea of sustainable process technology. Based on published papers and patent literature this paper aims to give a complete overview of the work done so far on the research and implementation of DWCs, from early ideas on thermal coupling of distillation columns to practical issues that needed to be solved for their successful implementation. Approaches to short-cut and rigorous simulation, optimization, and control are highlighted, with particular focus on column internals and dimensioning, which is only conceptually considered in academic publications. A survey of relevant patents is included providing information on equipment innovations and application areas of industrial interest. Finally authors look at what is needed on research and engineering side to enable maximization of potential gains by building DWCs for obtaining four or even more products containing two or more partition walls in parallel, which is something not yet attempted in industrial practice.

Dividing wall column—A breakthrough towards sustainable distilling

Dividing wall columns in chemical process industry: A review on current activities

Most industrial scale reactive distillations (presently more than 150), operated worldwide today at capacities of 100–3000 ktonnes/y, and are reported in this paper. Most of these plants started up less than 15 years ago. The drivers, processes, systems, scale-up methods and partner collaborations for this rapid invasion of a new process intensified technique are explained in this paper. The business drivers are (a) economical (prosperity): variable cost, capital expenditure and energy requirement reduction. In all cases these are reduced by 20% or more, when compared to the classic set-up of a reactor followed by distillation. (b) Environmental (planet): lower emissions to the environment. In all cases carbon dioxide and diffusive emissions are reduced and (c) social (people): improvements on safely, health and society impact are obtained by lower reactive content, lower run away sensitivity and lower space occupation. These industrial reactive distillation systems comprise homogeneous and heterogeneous catalysed, irreversible and reversible reactions, covering large ranges of reactions, notably hydrogenations, hydrodesulfurisation, esterifications and etherification. Various commercial methods for packing heterogeneous catalyst in columns are now available. The systems comprise amongst others: multiple catalyst systems, gas and liquid internal recycle traffic over these catalyst systems, separation, mass flow, and enthalpy exchange. These are integrated optimally in a single vessel, a characteristic feature of process intensification. The scale-up methods applied from pilot plants to commercial scale are brute force and modelling. Technology providers CDTECH and Sulzer Chemtech have used these scale-up methods successfully. Barriers perceived and real have also been removed by these companies. Chemical manufacturing companies have also developed their own specific reactive distillations by their own research and development. These companies, both on their own and in consortia, also developed heuristic process synthesis rules and expert software to identify the attractiveness and technical feasibility of reactive distillation. Heuristic rules and expert software will be presented and supported by examples. Academic research also produced design methods to identify the feasibility of reactive distillation, to determine the feed locations, to select packing types, to sequence columns optimally and also produced methods to design, optimise and control the columns with steady state and dynamic simulation models. The rapid commercial scale implementation of reactive distillation by co-operation of partners in research, scale-up, design and reliable operation can also be seen as a model for rapid implementation of other process intensification techniques in the chemical industry.

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Reactive distillation: The front-runner of industrial process intensification - A full review of commercial applications, research, scale-up, design and operation

Different distillation sequences for the separation of near-ideal multicomponent mixtures have been proposed in the past. These sequences included both conventional and thermally coupled distillations. Investigations of these sequences based on thermodynamics and steady-state simulations aimed for identifying the economic and energetic favourable configuration. Dividing wall columns have shown to be superior to conventional distillation sequences in certain cases. For this reason dividing wall columns gained increasing application in the last years. More than 90 applications in production scale are known. The advantages are obvious. Depending on the case considered the energy and investment costs are reduced up to 30% compared to conventional technologies. The footprint is significantly smaller. Also advantageous is the higher flexibility of these systems in comparison to conventional column sequences. For temperature-sensitive products the thermal stress is reduced since the product is reboiled only once. Especially for high price products the product quality can be raised by simultaneously increasing the separation yield. An overview about fundamentals, applications, limitations and recent advances will be given in the paper.

Dividing wall columns: Fundamentals and recent advances

Answering to the challenges imposed by industrial growth, the distillation, which is the most mature among separations regarding the applications and technology development, still manages to improve and from time to time a technology breakthrough occurs which moves this proven technology to a higher level of sophistication. The purpose of this presentation is to address the recent distillation equipment developments, particularly those BASF, Montz, and TU Delft were involved with.

Equipment improvement trends in distillation

The combination of reactive distillation and a divided wall column leads to a reactive divided wall column. The first use of such a reactive divided wall column for the hydrolysis of methyl acetate is presented here. For the development of this system, kinetic data for the involved reactions was determined at the University of Stuttgart, mini plant experiments were performed at BASF and an industrial scale column with an inner diameter of 220 mm was run at Sulzer Chemtech. Results of one mini plant experiment and of one experiment in an industrial scale are shown.

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O. Ryll

Papers

Methyl Acetate Hydrolysis in a Reactive Divided Wall Column

Analysis of homogeneous distillation processes

Thermodynamic analysis of reaction-distillation processes based on piecewise linear models

Convex envelope method for the determination of fluid phase diagrams

Analysis of heterogeneous distillation processes