Boron‐substituted ZSM‐5 membranes: Preparation and separation performance

ZSM‐5 zeolite membranes with boron substituted into the framework for silicon were prepared on porous stainless‐steel and α‐alumina tubular supports. These membranes had higher n‐C4H10/i‐C4H10 separation selectivities, and effectively separated these isomer mixtures to higher temperatures than membranes with aluminum substituted into the framework. Membranes were prepared with Si/B ratios as low as 12, and the best membranes were prepared from alkali‐free gels. The highest n‐C4H10/i‐C4H10 permselectivity at 473 K was 60, and the highest at 527 K was 24. For most alkali‐free membranes, the n‐C4H10/i‐C4H10 permselectivities and separation selectivities increased with boron content, and membranes on α‐alumina supports had both higher permeances and separation selectivities. Membranes with the same permeances and selectivities can be reproducibly prepared, and they are stable at elevated temperatures.