Gray-box surrogate models for flash, distillation and compression units of chemical processes

Fabian Zapf, Thomas Wallek*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Surrogate models of chemical processes can substitute rigorous models that are computationally expensive or of limited stability by simplified and typically solely data-driven models. In this work, gray-box surrogate models of classical process engineering unit operations comprising flash, distillation and compression units are developed to provide accurate models that allow for fast and stable predictions in view of later optimization of coupled models. The gray-box surrogates are first tested as individual models and then applied to model the cracked-gas compression of an ethylene plant, including a recycle stream. The process streams are hydrocarbon mixtures containing 50 components, which typically leads to significant convergence issues with rigorous approaches. A concluding comparison of the proposed surrogate models’ accuracies proves their robustness and computational efficiency and highlights the advantages of the proposed modeling methodology that complements and extends simple but physically meaningful white-box models with black-box models from the field of machine learning.

Original languageEnglish
Article number107510
JournalComputers and Chemical Engineering
Publication statusPublished - Dec 2021


  • Cracked-gas compression
  • Distillation column
  • Gray-box models
  • Hybrid semi-parametric models
  • Isothermal flash
  • Surrogate models

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Computer Science Applications

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