ABSTRACT
The residual catalyst (CR) from Fluid Catalytic Cracking (FCC) in petroleum refineries has been studied as pozzolan in cementitious materials to evaluate the development of mechanical properties and durability. However, studies on the degradation of these materials with supercritical carbon dioxide (scCO2) are recent. This article evaluates the degradation of hardened pastes with replacement of cement mass by CR (0%, 15% and 30% CR) exposed for 7 h to scCO2, in the temperature and pressure condition estimated at 760 m depth (53,55 °C / 12,41 MPa). The density of the slurries was set at 1.89 g/cm3 and curing time of 28 days. The formulation of the slurries and supercritical condition aimed to simulate the application in the structure of an onshore well in the northeast of Brazil, considering that the contact with scCO2 happens after the hardening of the slurries. The microstructure was evaluated by X-ray diffraction (XRD) and Thermal Analysis (TG / DTG and DTA), hardness measured by Rockwell surface hardness (HR15T) and carbonated areas calculated after the pH indicator solution was sprayed. The slurries containing CR had reduced surface hardness and higher free water content, indicating a higher porosity in relation to pure cement slurries. The pozzolanic reactions of CR caused partial reduction of calcium hydroxide [Ca(OH)2] content and formation of cementitious compounds [C-S-H, C-A-S-H, C-A-H and Af(t)]. After exposure to scCO2, the pastes with CR had a larger area/depth of carbonation than the 0% CR paste. The formation of CaCO3 resulted in an increase in surface hardness mainly in the pastes with CR. Due to the reactions with scCO2, the CR-containing pastes had partially decalcified cementitious compounds but remained equivalent to or higher than those found in the 0% CR paste whose carbonatation caused a partial reduction of Ca(OH)2.
Keywords
Residual Catalysts; FCC; Supercritical carbon dioxide; Cement paste
