Utilização da lignina alcalina como aditivo em pastas de cimento Portland classe G e sua influência no processo de carbonatação

Abstract

Portland cement is a binder used globally in oil wells, as well as carbon capture and storage (CCS) and Carbon Capture and Storage (CCS) wells. Portland cement is highly reactive with carbon dioxide, a substance found on a large scale in the most diverse types of oil reservoirs, including pre-salt formations. The reactions of the Portland cement with the CO2 result in the formation of carbonates and bicarbonates, causing the degradation of the cement and consequent loss of mechanical resistance. Alkaline lignin is a natural polymer that has a long three-dimensional chain with active functional groups that change the cement grains surface energies and interactions of certain cement phases with CO2. In this study, SIGMA alkaline lignin was added in formulations with Portland Class G, at concentrations of 0.3% and 0.5% by weight of cement (BWOC). The samples were divided into two groups, one group maintained in a bath without exposure to CO2 and, in the other, the samples were submerged in water and exposed for 90 days to the reactor under conditions of 15.7 MPa (2200 psi) CO2 and 70° C (158° F). Both groups were compared with samples of standard/reference formulation (cement and water). Results of pH, X-ray diffraction, infrared, scanning electron microscopy and thermogravimetric analyzes showed that the addition of lignin improved the cement resistance to reactions with CO2, reducing the advance of the carbonation front. Ettringite (AFt) and calcium silicate hydrate (C-S-H) presented significant interactions with the additive. The samples with 0.5% BWOC of additive presented in the area of longitudinal section an average of 87% preservation in the alkalinity and, the standard samples, average of 65% preservation of the alkalinity. The XRD results show a significant reduction in the formation of aragonite and carbonation of the hydrated calcium silicates in the samples with lignin. The additive does not appear to change the consumption of Ca(OH)2 in the carbonation process.