Enhanced liquid–solid mass transfer by carbon nanofibers on solid foam as catalyst support

Abstract

This paper presents the liquid–solid mass transfer characteristics for Pd-catalyst on carbon nanofiber (CNF) covered reticulated vitreous carbon (RVC) foam (hairy foam). RVC foam was used with 20, 45, and 60 pores per linear inch (PPI), covered with CNFs synthesized at 773, 873, and 973 K. The effects of superficial liquid velocity ( u l = 4.3 × 10 - 3 to 77 × 10 - 3 m l 3 m r - 2 s - 1 ) and reaction temperature (323 and 343 K) are studied using the fast liquid phase oxidation of sodium formate. The overall reaction rate coefficient ( k ov ) increases with decreasing PPI number. k ov for 20 PPI CNF/RVC foam is significantly higher than for regular foam packings and random packings, ranging from 0.15 to 0.90 m l 3 m r - 3 s - 1 . k ov 's for 45 and 60 PPI CNF/RVC foams are higher than for regular foam packings and approximately equal to random packings, ranging from 0.075 to 0.36 m l 3 m r - 3 s - 1 . k ov 's for CNF/RVC foam with CNFs synthesized at 773 and 873 K are approximately equal, ranging from 0.07 to 0.4 m l 3 m r - 3 s - 1 . For CNFs synthesized at 973 K, k ov is significantly higher, ranging from 0.18 to 0.57 m l 3 m r - 3 s - 1 . The high liquid–solid mass transfer rates of CNFs on solid foam with respect to regular foam is attributed to the hydrodynamic accessibility of the CNFs. The pressure drop of the CNF/RVC foam ( < 4000 Pa m - 1 ) is significantly lower than for random packings ( 5.2 × 10 3 to 1.2 × 10 6 Pa m - 1 ). This shows that higher or at least equivalent mass transfer rates can be obtained, but at a considerably lower pressure drop than for random packings.