Paolo Davini

Adsorption and desorption of SO2 on active carbon : the effect of surface basic groups

Abstract The adsorption and the desorption of SO2 on active carbons is studied in relation to the surface characteristics of the carbons. Surface basic groups (with pyronic or pyronic-like structure) greatly increase the adsorption of SO2, that can be divided into two forms, one weakly and the other strongly bonded to the carbon, referred to in this paper SO2 (a) and SO2 (b), respectively. The surface area of the carbon and the temperature of the process are the fundamental parameters of the desorption process of SO2.

Effect of surface acidity of activated carbon on hydrogen storage

Hydrogen adsorption studies at 78 K and pressures up to 40 atmosphere were conducted on nine commercial activated carbon samples. The amount of hydrogen adsorbed increased with increasing surface area. Surface modification consisting of controlled high-temperature reduction and oxidation revealed that BET surface area was not affected by these treatments. The surface acidity, however, increased with increasing oxygen treatment. The amount of hydrogen adsorbed also increased as the surface acidity of the activated carbons increased.

Adsorption of sulphur dioxide on thermally treated active carbon

Abstract An active, commercial-grade carbon, washed with boiling 1 M HCl, to eliminate ash from its surface, was thermally treated in the presence of oxygen at temperatures between 400 and 750 °C, to produce carbon samples whose capacity to adsorb SO2 was investigated. The amount of SO2 adsorbed appears to be closely connected to the basic surface properties of the carbons, measured in terms of benzoic acid adsorption.

Investigation of the SO2 adsorption properties of Ca(OH)2-fly ash systems

The desulfurization activity of the sorbent obtained by a suitable mixture of calcium hydroxide and fly ash from coal combustion was studied. This sorbent is of pozzolanic nature and shows a better reactivity towards SO2 than the calcium hydroxide itself. This behaviour is closely related to the nature of the products formed and to the greater surface area. The influence of parameters such as the fly ash/Ca(OH)2 and water/solid ratios, time and temperature of sorbent preparation, temperature and relative humidity in the adsorption step on the reactivity of the sorbent was particularly studied. The possibility of a recycling process for large amounts of fly ash is pointed out.

SO2 and NOx adsorption properties of activated carbons obtained from a pitch containing iron derivatives

Abstract Activated carbons derived from a petroleum pitch impregnated with certain iron derivatives by pyrolysis and subsequent activation with CO2 show good SO2 and NOx sorbent characteristics. These characteristics are better than those of similarly activated carbons impregnated with iron after the activation process. This behaviour is basically attributed to the more favourable surface properties obtained in the pyrolysis step and to a more homogeneous distribution of the iron (responsible for a high catalytic activity) on the carbonaceous matrices. Moreover, activated carbons with better sorbent properties are less sensitive to the loss of sorbent activity after some adsorption–desorption cycles that simulate their use in the treatment of industrial flue gases.

SO2 adsorption by activated carbons with various burnoffs obtained from a bituminous coal

Activated carbons, obtained from pyrolysis and CO2 activation of both a bituminous coal and its reduced ash content derivative produced by HCl and HF treatment, were used to show that SO2 sorbent characteristics are improved by increasing their degree of burnoff and are related to their content of surface sites with acidic and basic features, their surface area, and their pore size distribution. Active carbons with reduced ash content also show better SO2 sorption properties at lower burnoff values and a better retention of their initial SO2 sorbent activity after ten adsorption–desorption cycles. Their improved behaviour is related to the presence of pores with larger dimensions and to a redistribution of the metals in the original mineral matter on the carbonaceous matrices induced by acid washing.

The effect of certain metallic derivatives on the adsorption of sulphur dioxide on active carbon

Abstract The SO2 adsorption characteristics of low ash active carbons are strongly influenced by the presence of certain transition metal derivatives and by the composition of the gaseous sorption mixture; in particular, the effect of oxygen and water vapour is very important. In the SO2 sorption–desorption cycles on these supported carbons (simulating their application in a real desulphurisation process) the decrease of sorption activity of the carbon matrix appears to be strongly reduced in the presence of SO2, especially when H2O is also present. Moreover, the presence of vanadium and iron particularly enhances this effect. This is probably related to the catalytic activity of these elements in the SO2 oxidation process.

An investigation of the influence of sodium chloride on the desulphurization properties of limestone

Abstract This investigation shows how sodium chloride adsorbed on particles of limestone can influence certain surface characteristics of the calcium oxide obtained by the calcination process and its capability for flue-gas desulphurization. About 2 wt% of NaCl was found to favour the formation of CaO with a porous texture and also with a better size distribution, which is related both to a higher degree of conversion to CaSO 4 of the sorbent and to a higher rate of conversion. This effect reaches a maximum activity at a temperature of about 850 °C and markedly decreases with increase in the sorbent particle size. KCl behaves in a similar way, but other metallic chlorides examined led to a decrease of the sorption activity of the CaO.

Properties and reactivity of reactivated calcium-based sorbents ☆

Calcium-based sorbents used in the process of high temperature desulfurisation of flue gases are partly regenerable by hydration with steam; the best results are obtained for treatment temperatures of approximately 300 °C. The regeneration process, and the consequent increase in the sorbent consumption can be correlated to the surface characteristics (BET surface area, porosity and pore size distribution) of the sorbents themselves. In particular, the presence of suitable pore structure, also having pores large enough to let molecules easily penetrate the inner part of the sorbent particles, is very important.

Adsorption and desorption of sulphur dioxide from simulated flue gas on active carbon: The effect of the ash content

Abstract Samples of active carbon with different ash contents were prepared from two commercial active carbons. They were submitted to a cyclic process of SO2 adsorption at 150°C from a gaseous mixture with a composition similar to that of flue gases, followed by subsequent desorption at 360°C with N2. If ashes are present in the carbons in significant quantities, they can markedly decrease the amount of SO2 adsorbed, in close relation to an oxidation of the carbonaceous matrix that causes a progressive loss of surface area and the formation of surface acidic functions. The presence of certain metals, such as iron, in the ashes increases the effects described above.