Design of thermally coupled reactive distillation schemes for triethyl citrate production using economic and controllability criteria

- Conceptual design of a triethyl citrate process was carried out.
- Reactive residue curve maps used for conceptual design of a multi-reaction system.
- Reactive dividing wall column used as intensification alternative.
- Optimization including controllability at early stages if conceptual design.
- Large energy savings using dividing wall columns with acceptable controllability.

This work describes a systematic process design for triethyl citrate production by direct esterification of citric acid with ethanol via simultaneous reaction-separation technologies. The design methodology includes simultaneous optimization of controllability and profitability criteria. With a novel approach, the conceptual feasibility analysis of the intensified processes was carried out by extending the reactive residue curve maps (RRCM) to mixtures with six components by implementing a substitution degree parameter. The RRCM have been also extended to the conceptual design of dividing wall columns. The configuration of both, traditional and dividing wall reactive distillation columns, were obtained from the conceptual analysis. The processes were simulated using experimentally validated models, and further optimized using a nature inspired multi-objective algorithm. A triethyl citrate production capacity of 10 kTon/yr was used as process specification. Final designs evidenced citric acid conversions above 99.9%, energy consumption from 3-5 MJ/kg, and a TEC production costs of c.a 1.5 USD/kg. Controllability assessment was performed by evaluating the condition number of the proposed operating schemes. Pareto diagrams indicate that the minimization of total annual costs and controllability are conflicting goals in both production schemes. Nevertheless, both alternatives withstand large perturbations over the main process variables. The reactive dividing wall column scheme results in large energy and cost savings over a traditional reactive distillation process.

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