In this dataset it means a patent family whose title, abstract or claims combine the term membrane reactor or catalytic membrane reactor with language addressing fouling resistance, thermal stability or chemical durability. That definition pulls in both hardware-focused separation claims and biological process claims run inside a membrane system, which is why the IPC spread here covers fermentation classes alongside separation-engineering classes. It does not capture every membrane patent, only the subset explicitly framed around durability under operating conditions.

Because a large share of catalytic membrane reactor applications run an enzymatic or fermentation process across the membrane, and durability claims in that context often describe the biological catalyst's stability alongside the membrane material's own resistance to fouling. The IPC data bears this out: C12N and C12P classes together outweigh the pure separation class B01D. Anyone searching this space purely from a materials-science angle should expect to find relevant prior art in enzyme engineering filings.

Filings grew from 26 in 2017 to a peak of 43 in 2022, then declined toward single digits by 2026. Because patent publication lags filing by roughly 18 months, the most recent one to two years in any such trend are undercounted and should not be read as a confirmed collapse. Taken together with the flat recent-year momentum across every tracked assignee, though, the multi-year decline before 2026 looks like a genuine slowdown rather than a data artefact.

The assignee ranking is led by enzyme and industrial gas technology companies, with the strongest co-filing relationships running through named individual inventors tied to a single enzyme-technology assignee. Research institutes also appear consistently, generally around catalytic membrane fundamentals rather than applied fermentation processes. None of the named leading assignees show any filings in the most recent tracked year, which is consistent with a claim landscape that has already been substantially staked out.

The thinner IPC pockets, C07C acyclic compound synthesis, H01M fuel-cell membranes and A23L food applications, carry far fewer records than the core C12N and B01D classes, which suggests less-crowded claim space around fuel-cell membrane durability under cyclic thermal load and food-grade chemical durability. A first claim in either branch should be drafted narrowly around the specific operating condition, such as cyclic thermal load or food-contact chemical exposure, rather than reusing the broad fouling-resistance language already dense in the core classes.