II International Symposium on Carbon for Catalysis ABSTRACTS

KL-1
governed by the equation of the ideal reverse Carnot cycle: L/Q = (Т 0 - Т)/Т = (Т 0 /Т) – 1.
Estimations followed from this equation show that the hyperbolic type of this dependence
with the sharp increase of L/Q appears only in the region Т < 70 K, whilst at Т > 70 K the
required energy is virtually proportional to the temperature difference ΔТ. Correspondingly,
theoretical power inputs for obtaining one unit of cooling at the temperature decrease from
298 K down to ~20 K at the process of hydrogen liquefaction are five times of those required
for cooling to “nitrogen” temperature, which is about 77 K (actual power inputs are even one
order larger than the theoretical estimation). On the other hand, the cooling down to
“nitrogen” temperature creates the possibility of the use of the method based on physical
adsorption (C).
Physical condensation of Н 2 is impossible at room temperatures, as the kinetic energy
(that can be estimated as RT ~ 2.5 kJ/mol) is higher than the heat of condensation
(~0.9 kJ/mol). However, the heat of adsorption of Н 2 at the best carbonaceous nanostructural
adsorbents (CNA’s) of type АХ-21* 1 approaches 6.0-6.5 kJ/mol, which leads to sufficiently
large amounts adsorbed at additional decrease of the RT contribution. We have developed a
number of CNА’s having characteristics exceeding those of AX-21 (the formal specific
surface area A BET is greater than 3000 m 2 /g, the micropore volume V μ is larger than
1.5 cm 3 /g) that are able to reversibly adsorb hydrogen with a resulting capacity of more than
5wt% at 77 K and the pressure below 2-3 MPa. Estimated gravimetric density W f of the
adsorber with our CNA’s meets requirements of DOE 2 for 2007 (W f ≥ 4.5 wt %). We hope,
the optimization of the internal structure of our CNA’s will allow us to meet the requirements
of DOE on volumetric density (V f ≥ 36 kg Н 2 /м 2 ) and to increase specific amounts of H 2
adsorption per unit of mass. Our aim in the near future is to meet the requirements of DOE for
2010 (W f ≥ 6.0wt % and V f ≥ 60 kg Н 2 /м 2 ).
Our optimism rests on the observation that the heat of Н 2 adsorption in single-walled
carbon nanotubes (SWNT’s) approaches (from different sources) 12-20 kJ/mol, which leads
to a higher density of the adsorbed phase. Consequently, those SWNT’s have more optimal
pore sizes, but their total volume and surface are lower than CNA’s. For this reason
adsorption characteristics of SWNT’s are lower than those of CNA’s.
Manufacturing of SWNT’s is principally more complex and more expensive compared to
CNA’s. CNA’s can be obtained with the use of wide assortment of precursors, with all
* 1 manufactured by Anderson Develop. Co (USA); the same is Maxsorb-1 Kansai Coke and Chemical Co Ltd
(Japan)
* 2 DOE – US Department of Energy, generally accepted fashion legislator in the modern hydrogen technology.
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