Online Simulations depends on physically-sound first principal models. Unlike conventional approaches, they are executed live and thus simultaneously with production. This presentation will provide insights into two typical use cases of Online Simulation at Covestro as well as technical background information on their infrastructure: (1) The usage of an Online Model by our in-house simulator VtPlan in connection with the PI system for reactor catalyst performance monitoring is discussed. (2) A prototype of an APS Online Model for reactor fouling monitoring is in development. (3) Major aspects of our current and planned Online Simulation infrastructure are presented. In conclusion, Online Simulations show great potential for KPI monitoring and process insight. New tools such as APS and PI-AF can help to improve the workflow for Online Model building and maintenance. But infrastructure for Online Simulation, (PI) data integration and accessibility remain a challenge to overcome.