Both reactors process substrate (blue spheres) into product (green spheres) at the same time. The free enzyme (orange dots, drifting loose) reacts fastest — full flexibility, unobstructed access to every substrate molecule — so its vessel finishes each batch first. But once a batch drains, the free enzyme drains away with it: it's discarded, and the next batch needs a freshly bought charge plus resupply downtime.
The immobilized enzyme (cyan dots, pinned to a fixed support rack) reacts more slowly because the surface attachment restricts its motion and partly blocks substrate access — but when a batch drains, the beads stay put. There's nothing to re-buy: the same charge is filtered straight back in and starts the next batch almost immediately.
Track the live totals: free enzyme usually pulls ahead on total product early (it's faster per batch), while immobilized enzyme's cost curve flattens out after its one-time purchase — so its $/unit of product keeps falling and eventually undercuts free enzyme's $/unit, which stays roughly flat because a fresh cost is paid every single batch.
- Activity retention — how much catalytic speed immobilization costs the enzyme; higher = a more forgiving support chemistry.
- Free enzyme cost/batch — the recurring purchase cost every batch, since it can't be recovered.
- Immobilized cost (one-time) — the up-front cost of the support + attachment chemistry, amortized over every future batch.
- Resupply downtime — extra time the free-enzyme line loses sourcing and dissolving a new charge between batches.