1. Introduction - Firenze University Press

Even if the dolomite shows a larger uptake when compared to that of synthetic sorbent, a decay in
the capacity to retain carbon during the first few cycles was found for Bianchi dolomite whereas the
synthetic sorbent shows higher uptake while the material is cycled during CO2 capture tests. As
shown in Fig 3, the self reactivation was observed also for the 85% CaO sorbent. Interestingly,
during the first cycles the uptake of CO2 for the 85% CaO sorbent is greater to that of 75% CaO
sorbent because there is more active phase (CaO). But as the cycling runs the pore plugging occurs
likely due to the reduced amount (15%) of binder leading to more CaO being less dispersed and
thus more inaccessible to CO2.
Uptake [g-CO2/g-sor]
0,20
0,15
0,10
0,05
0,00
0 20 40 60 80
Cycle number [-]
Fig. 3. Effect of CaO load: increasing the load of active phase a decreasing of capacity was
observed
In fact during repeated cycling the grains grow and sinter together via formed 'necks' as reported in
Fig 4. You can see the genesis of a neck structure for a 75% CaO sorbent. The circle (a) focuses the
neck between two different bodies, at a later stage the neck increases its cross section (b) and when
the neck reaches at its maximum size the two bodies merge together in a single body (c). This
structural alteration could lead the blockage of pores and the formation of isolated volumes
throughout the particle and it is likely an important factor leading to reduced uptake kinetics and
capacity.
Fig. 4. Micrograph of sorbent after 60 carbonation/regeneration cycle
75% CaO
sorbent
Improvement of sorbent activity was also observed for the sorbent obtained by chemical
pretreatment of the sorbent precursor. By adding water after the second grinding (see Sec 2.1) the
obtained sorbent shows greater uptake when compared with the sorbent whose precursor was dry
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