I see! While I believe it would be possible to derive the product in the earlier reactors from the volumetric flow data, that would require a highly specific calculation that in my view would only be possible using the advanced custom calculations feature (https://userguide.trendminer.com/en/tag-builder--custom-calculations.html).
In my experience, if it is in any way possible, it is better to have such tags for the other reactors created on a lower level in the data (DCS, Historian), than to calculate them later in TrendMiner.
Of course if the product type is really only determined at the last reactor, and there is no way of knowing the final product type in the upstream reactors, a calculation based on the volumetric flow (some sort of chain of backwards totalizing integrations of the volumetric flows to see where it matches the reactor volumes) becomes the only possibility.