Desenvolvimento de membranas de poliuretano com carbonato de cálcio nanométrico e pó de ostras obtidas por inversão de fases visando a separação de gases

Abstract

Human actions over the years have aroused concern due to their polluting potential, causing an increase in the emission of greenhouse gases into the atmosphere. To separate these gases, polymeric membranes have been used, as this technology has shown to be promising and presents a lower energy consumption when compared to other separation processes. In this study, the effect of calcium carbonate (CaCO3) and oyster powder additives was evaluated on polymeric polyurethane (PU) membranes. The membranes were prepared with membranes with different concentrations of CaCO3 and oyster powder [0.05 and 0.10% (m/m)], and were obtained by the phase inversion technique using two different techniques, immersion-precipitation and solvent evaporation, with membrane thickness ranging from 51 micrometers to 83.7 micrometers. The membranes obtained were tested in the separation of pure methane (CH4) and carbon dioxide (CO2) gases and mixtures (40% CO2/60% CH4 e 30% CO2/70% CH4 - m/m), which are the main contributors to the increase in the greenhouse effect. Scanning microscopy (SEM), infrared spectrometry with Fourier transform (FTIR), differential scanning calorimetry (DSC), permeability and selectivity tests were used to characterize the tested membranes. The permeability and selectivity of gas mixtures (CO2 and CH4) were quantified by gas chromatography (CG). The SEM results showed a dense membrane morphology with an increase in free volume when adding additives to the PU structure. According to the FTIR results, the membranes obtained did not change the structure of the PU. In the DSC analyzes there was a change in the crystalline structure of the polymer, identified in the melting event and conformed by the change in crystallization in cooling. In the permeability and selectivity tests for pure gases, the CC5-10IP membrane showed greater permeability (1407 Barrer for CH4 and 852 Barrer for CO2). The PO5-10EV and PO10-5EV membranes showed the best selectivity results, when tested at a pressure of 200, 250 and 300 kPa, they did not present a permeate flow for CO2, showing affinity to the passage of CH4. For gas mixtures, the permeability decreased with increasing pressure applied, in the gas mixture with 70% CH4 and 30% CO2, the PU-5EV membrane permeability was 2044 Barrer at an applied pressure of 200 kPa and it dropped to 1446 Barrer when a pressure of 600 kPa was applied. The CC5-10IP membrane showed a permeability of 272 Barrer at 200 kPa and dropped to 211 Barrer when a pressure of 600 kPa was applied. In general, the membranes showed greater permeability for CH4 gas, due to a greater affinity of the gas with the polymeric matrix. The addition of CaCO3 and oyster powder to the composition of the polymeric membrane contributes to the increased permeability of the gases tested, due to the increase in free volume. [resumo fornecido pelo autor]