The
environmental problems in Peru are rooted in the waste management
of the residual agricultural biomass. Via our cooperative international
research, nine different agricultural wastes from Peru were used as
renewable sources to produce activated carbons that were tested in
gas-phase xylene adsorption. The special properties of agro-waste
activated carbons are the very large mesopore surface area, the narrow
pore size distribution within the microporous–mesoporous region,
and the slightly acidic character in the presence of oxygen-containing
surface groups. The textural, structural, and surface properties of
nine agro-waste activated carbons were correlated with their adsorption
capacities in xylene adsorption and compared with those of a commercial
activated carbon made of black coal. Adsorption capacities of agro-waste
activated carbons were in the range of 371–115 mgxylene/gAC, whereas the adsorption capacity was 214 mgxylene/gAC for black coal-activated carbon. Higher adsorption
capacities of ACs can be assigned to the synergism of their textural
properties (larger mesopore surface area and larger micropore volume
related to total pore volume) and their surface properties (lower
content of surface oxygen functional groups related to their less
acidic character and higher π–π* transitions in
aromatic rings resulting in fewer defects within the graphitic structure).
Ashes were prepared by annealing selected types of solid fuels (biomass: corn cobs, sunflower husks, olive pomace, hay pellets and rice husks; coal: lignite and bituminous; and alternative fuel: paper sludge) at different temperatures (550°C, 815°C and 975°C). Based on X-ray fluorescence spectra, the slagging/fouling indexes were used to study the effects of the type of ash and the ashing temperature on the ash fouling and slagging properties. Slagging indexes were compared with the ash fusion temperatures. Ash fusion temperatures were measured by a LECO AF-700. The lowest deformation temperature (below 1000°C) was seen for the ashes prepared from hay pellets and corn cobs. On the other hand, the deformation temperature exceeded 1500°C for ashes prepared from paper sludge, sunflower husks and rice husks. By calculating the different slagging/fouling indexes, all the ashes exhibited slagging/fouling problems of varying degrees.
Adsorption experiments of nitric oxide in nitrogen carrier gas were held on activated carbon in a fixed bed flow system. Breakthrough curves describing the dependence of exit concentrations of nitric oxide on time were matched with theoretical response curves calculated from the linear driving force model (LDF). The model assumes Langmuir adsorption isotherm for the description of non-linear equilibrium and overall mass transfer coefficient for mass transfer mechanism. Overall mass transfer coefficients were obtained by the method of least squares for fitting numerically modelled breakthrough curves with experimental breakthrough curves. It was found that LDF model fits all the breakthrough curves and it is a useful tool for modelling purposes.
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