(90e) Improved Carbon Coatings for Nitrogen Production and Upgrading Pyrolysis Oils

Improved
carbon coatings for nitrogen production and upgrading pyrolysis oils

Charles
G. Coe

 Chemical
Engineering Department, Villanova University, PA

The structural variability of carbons provides a means
for controlling many coating features necessary to build a selective carbon
adsorbent or a hydrothermally stable coating on a metal oxide.  After defining
the motivation for exploring improvements for two important applications of
carbon coatings, the talk will review progress made in both of these areas.

Carbon molecular sieves (CMS) are a subgroup of
activated carbon which allow separation of nitrogen from oxygen on a kinetic
basis.  The effective micropore size of the CMS can be controlled by selective
hydrocarbon cracking to narrow only the pore mouth preserving the usable O₂
uptake rate.  Remarkably, deposition of only 0.1% (by weight) of carbon
can convert an unselective CMS to a CMS with O₂/N₂
selectivity of >20.  In addition to the pore mouth structure, the overall pellet
density and porosity are important.  The improved understanding of carbon
composite microstructures led to realizing superior carbons for use in N₂
PSA.    

Bio-oils derived from the fast pyrolysis of woody
biomass are hydrogenated to improve the stability and heating value of the
liquid hydrocarbon products.  Since pyrolysis produces bio-oils having up to 30
vol% water, HDO catalysts must be stable under hydrothermal conditions associated
with hydrodeoxygenation (HDO) processes.  We investigated the effect of carbon
coatings on a variety of silica, mixed zirconia-silica oxides and alumina.  Systematic
studies of the effects of the composition and structure of the carbon
precursor, the inclusion of a zirconium modifier, the carbon loading and
carbonization conditions led to the development of highly stable carbon
modified zirconium silicate and mesoporous alumina supports that substantially
maintain pore size distribution and surface area under HDO process conditions.