Biogas Membrane Upgrading (2D): Purity vs Recovery Trade-off

This is the 2D counterpart to the 3D biogas-upgrading membrane simulator, computing the identical solution-diffusion separation through the Weller-Steiner cross-flow equations and showing it as a schematic membrane cross-section plus a live purity-vs-recovery trade-off curve instead of a rendered 3D module. Tune the feed CH₄ fraction, membrane selectivity, pressure ratio and membrane area (or turn on the 2-stage cascade) and watch CO₂ molecules cross the membrane wall while the trade-off curve reshapes and the operating point slides along it — the same fundamental purity-versus-recovery limit every real biomethane plant has to balance.