Alumina-coated, silicon carbide monoliths were used as supports for B-ZSM-5 zeolite membranes, which were synthesized by in situ hydrothermal crystallization. Both 2 turn x 2 mm (66 channels) and 4 mm x 4 mm (22 channels) monoliths with effective membrane area/volume ratios of 10.6 and 7.2 cm(2)/cm(3), respectively, were used. The membranes separated C-4 and C-6 hydrocarbon isomer vapor mixtures with high selectivities. The selectivities and permeances were comparable to tubular ZSM-5 membranes for butane isomers. The highest ideal selectivities at 473 K were 34 for n-C4H10/i-C4H10 and 77 for H-2/i-C4H10. The highest n-C4H10/i-C4H10 separation selectivity was 35 at 373 K, and the highest n-hexane/2,2-dimethylbutane separation selectivity was 247 at 436 K. (C) 2002 Elsevier Science B.V. All rights reserved.