(301b) Batch-to-Continuous Protocol – a Guideline for Lab-Scale Chemistry

M. Padaro, M. A. Liauw, ITMC - RWTH Aachen University,

Aachen, Germany

Introduction

Traditional lab-scale syntheses are typically developed by chemists, and carried out as batch reactions. When an industrial application becomes interesting, there often is a move towards continuous operation, be it because of higher productivities, more constant product quality, or higher safety. The transition batch-to-continuous is particularly difficult if crucial aspects were not considered during batch optimization.

A systematic protocol, based on a sound understanding of the reactive system, is desirable that will facilitate the implementation of a continuous operation. This would also resolve many scale-up issues.

Approach

In the project SusChemSys at RWTH Aachen, a systematic protocol is developed as a guideline to lab-scale chemistry.  For a given reaction system, the batch protocol is assessed. Individual steps of the protocol, such as dosing, mixing, heating or reacting, are depicted as a material flow through spatially separated elements (see e.g. [1], [2]). This structure is now evaluated against selected criteria outlined below. Where a potential problem is identified, the guideline gives suggestions (many taken from literature) for solving this problem. After their implementation, the evaluation is resumed.

Results

The list of criteria encompasses issues like solids handling, corrosion, order of reactant addition, heat management and phase behavior. As an example, the solids issue may be resolved by varying the temperature or the solvent, by adding a co-solvent or an immiscible second liquid phase that sweeps up precursors to solids formation. All these points are backed by references where this approach has been successfully applied. Obviously, the corrosionissue will strongly benefit from including a corresponding material database in the protocol environment. Of course, many other criteria have to be addressed: mixing, viscosity, pressure dependences and pressure drop, separation.

It is crucial to acknowledge that all elements in the synthesis structure are closely related to one another. If e.g. an undesired reaction is identified, it may be decided to avoid it by adding an inhibitor to the reactants. That inhibitor may however lead to corrosion upstream of the reaction, or to solids formation downstream. Ideally, the synthesis chemist is assisted in taking the decisions by an expert system that reconciliates all these cross-correlations efficiently. As a limiting case, the protocol yields the insight that a given synthesis cannot be run continuously in an economically viable manner.

As a case study, the approach is demonstrated for one or two examples (e.g. [3]). It is finally discussed how process development engineers may be interested in supporting the development of this protocol that promises a smoother transition from lab-scale batch syntheses into continuous operation.

Acknowledgment

Financial support by SusChemSys is gratefully acknowledged. The project "Sustainable Chemical Synthesis (SusChemSys)" is co‐financed by the European Regional Development Fund (ERDF) and the state of North Rhine‐Westphalia, Germany, under the Operational Programme "Regional Competitiveness and Employment" 2007 - 2013.

References

[1]   J. A. Arizmendi-Sánchez, P. N. Sharratt, “Multilevel Phenomenological Modelling Approach to Support the Evaluation and Generation of Intensified Processes”, European Symposium on Computer Aided Process Engineering – 15, Eds. L. Puigjaner, A. Espuña (2005).

[2]   H. Freund, K. Sundmacher, “Towards a methodology for the systematic analysis and design of efficient chemical processes: Part 1. From unit operations to elementary process functions”, Chem. Eng. Process 47(2008) 2051-2060.

[3]   C. B. Minnich, L. Greiner, C. Reimers, M. Uerdingen, M. A. Liauw, “Bridging the gap: A nested-pipe reactor for slow reactions in continuous flow chemical synthesis”, Chem. Eng. J. 168 (2011) 759-764.