5. What is effect of reducing impurities like so2- , s- and fe3- (if not removed) affect the Do determination?
Answers
Explanation:
Some industrial CO2 streams stored geologically may contain impurities including SO2, O2, and NOX. The impacts of these reactive gases in CO2-water-rock interactions have received limited attention relative to pure CO2 studies. An experimental and geochemical modelling study of reservoir and cap-rock core samples from a potential CO2 storage site in the Surat Basin, Queensland, Australia is described. Reservoir and cap-rock samples were reacted with low salinity fluid saturated with an impure CO2 stream containing 0.16% SO2 at reservoir simulated in situ conditions. This study is relevant to the storage of impure CO2 streams from industrial sources in sandstone reservoirs.
Answer:
Several wet flue gas desulfurization (FGD) processes are based on the absorption of sulfur dioxide in caustic suspension or absorption liquor. The dissolved sulfur dioxide, which we will refer to as S(IV), is neutralized by the additive, commonly lime or limestone [1].
In aqueous phase several species of S(IV), hydrated sulfur dioxide, bisulfite and sulfite are formed according to the dissociation properties of S(IV)-oxides in aqueous solution. The distribution among the protonated and non protonated species is determined by the pH-value.
Parallel to dissolution and neutralization, S(IV) is oxidized by residual oxygen, absorbed from flue gas. This oxidation implies the addition of dissolvedi oxygen to an S(IV) species to produce
This reaction is of great interest in the study of wet flue gas desulfurization processes. In the case of the normally used absorption additive lime, the oxidation of S(IV) is an essential step in quantitatively producing the final product, gypsum (CaSO4- 2H2O). Beside detoxication of S(IV) the dewatering properties of gypsum are improved when a high oxidation yield is achieved. The conditions of improved oxidation are realized by bubbling air into the sulfurous suspension downstream the absorber [1]. Thus S(IV) oxidation takes place in the spray of the scrubber as well as in the downstream part.
It is well known that the rate of S(IV) oxidation is strongly influenced by the pH-value, which determines the sulfite/bisulfite-equilibrium [2,3]. Gmelin [3] reports the mavimnm oxidation rate to be in the pH-range of 8 - 10. Another major parameter is the presence of catalysts, even in traces. Literature reports the catalytic activity of several transition metals (Co2 +, Cu2 +, Mn2 +, Fe3 +) [1,4,5]. Sulfite concentration and oxygen concentration, temperature of operation and presence of inhibitors have to be considered [3]. The reaction type of S(IV) oxidation is supposed to be a radical type reaction, involving several steps, according to general agreement in literature [3,5–9].
Many researchers have studied S(IV) oxidation, yet the published data is sometimes inconsistent or not reproducible. The reason for that is supposed to originate in the sensitivity of oxidation kinetics to operation conditions [1] and catalytic activity or inhibiting trace impurities [6].
Concerning the catalytic effect of the metal ions mentioned above, research has been focused on Co2 +, Mn2 + or Cu2 + [1,5]. Little and contradictory data is available about the effect of Fe2 + [2,3,6,7,9]. Target of the present project has been, to examine the role of Fe2 + and the role of Fe2 + combined with Mn2 +, as well as the influence of the pH-value in sulfite/bisulfite oxidation. Provided a better understanding of this subject, the performance of S(IV) oxidation in FGD could be optimised by choosing absorption additives with appropriate catalyst concentration or by adding catalyst, to achieve the optimum concentration for maximum oxidation yield, as already suggested by Gmelin [3].
Literature data indicate catalytic activity of Fe3 + and synergism of iron/manganese. Ulrich et al. [6] investigated, among other metal ions, the effect of iron(m) and manganese(II) under FGD conditions (T = 50°C, pH = 4 - 6). Manganese showed almost no catalytic activity for concentration below 10- 3 mol/L and steadily increasing enhancement of mass transfer for higher concentrations up to 10- 1 mol/L. Iron(III), however, yielded distinct enhancement for the whole concentration range (10- 4 - 10- 1 mol/L), with a slightly decreasing tendency for increasing concentration. For catalyst concentration below 3- 10- 3 mol/L iron seemed to be more active than manganese (and all the other metal ions under investigation). Increasing the pH-value led to higher enhancement. When adding manganese(II) to sulfite solution with constant iron(m) content, a distinct increase in activity could be remarked for Mn2 + concentrations above equimolarity to iron.
Trzepierczynska et al. [7] put forward a kinetic model for iron catalysis of sulfite oxidation, assuming a multistep radical mechanism, and he determined the reaction order of sulfite oxidation. Martin [2] reports a literature survey of the atmospheric chemistry approach to S(IV) oxidation and experimental data, indicating a distinct synergism of iron/manganese. Reda [9] observed a steadily increasing oxidation rate for higher iron(III) content (concentration range 10- 4 - 10- 1 mol/L) and a synergistic effect of iron/manganese. Gmelin [3] gives a survey of a great amount of data up to 1963, implying several contradictions and inconsistencies