Membranas de alginato com adição de poliéteres para a permeação de gases

Abstract

Polymer membrane gas separation technology has been used for carbon dioxide (CO2) removal from natural gas or flue gases. Poly(ethylene glycol) (PEG) has been used as an additive in polymer membranes for this purpose, because of its affinity towards CO2, which increases its sorption in the membrane. In this context, this work aims to develop a novel polymeric material made of PEG or its copolymers with poly(propylene glycol) (EG-b-PG) in a matrix of alginate (Alg) for CO2 separation. The objective will be to analyze the influence of the addition of low molar mass PEG and its copolymers on the thermal and gas transport properties of sodium and calcium alginate films. Sodium alginate (NaAlg) and calcium alginate (CaAlg) films were prepared with PEG of molecular mass of 1450, 4000 and 6000 Daltons in the mass ratio of Alg:PEG of 7:3. At the mass ratio of 9:1, CaAlg films were prepared with PEG 6000 and with EG-b-PG copolymers with EG contents of 7 and 17% by mass. The films were characterized by scanning electron microscopy (MEV), hermogravimetric analysis (TGA), differential scanning calorimetry (DSC), infrared spectroscopy (FTIR) and permeability to CO2, CH4 and N2. It was observed that the molar mas and the amount of PEG influenced in the structure of the films, as well as the pre-crosslinking and the crosslinking steps. The films with 30% of PEG that weren t crosslinked, and the crosslinked ones weren homogeneous, showing white regions, that were attributed to denser regions rich in PEG. In the pre-crosslinked films, there was an increase in the homogeneity of the film with the increase of molar mass. MEV images appointed the formation of defects in these films, showing that they weren t a selective barrier for gases. However, the crosslinked films with 10% in mass of PEG 6000, EG-b-PG with 7% or 17% of EG exhibited the gas barrier property this property, presenting a CO2/CH4 selectivity of 99, 15 and 113 for CO2 permeabilities of 38, 13 and 67 barrer, respectively. Comparing with the literature, the membranes containing PEG 6000 and EG-b-PG with 17% of EG are promising. Comparing to the bare CaAlg, whose CO2/CH4 selectivity was 5 with CO2 permeability of 30 barrer, it is observed an increase in selectivity for all additives. These results weren t constant in long tests, indicating that possibly the films lost humidity, decreasing selectivity. These membranes seem promising for the separation of humid gases, however some modifications in the experimental apparatus are necessary to confirm this observation.