Membranas compósitas de poli(uretano-ureia) com sistemas de Ag NP/ativador e AgBF4/BMImBF4 para separação de olefinas/parafinas leves

Abstract

Light olefins are mainly produced by the naphtha steam cracking, which is among the more energy intensive processes in the petrochemical industry. To save energy, some alternatives have been proposed to partially replace or combine with cryogenic distillation, the conventional technology to separate olefins and paraffins. Within this aim, facilitated transport membranes, mainly with Ag+ cations as selective carriers, have received great attention owing to the high selectivity and permeance provided. However, the undesirable instability associated to the Ag+ cation should be considered. Poisonous agents and polymer membrane materials are sources of Ag+ deactivation. In recent years, great achievements on the separation performance have been reported, but the current challenge is to maintain the selectivity in long-term separation processes. Among alternatives that have been proposed to overcome the potential causes of Ag+ deactivation, this Thesis focuses on the use of Ag NP as carrier and IL for Ag+ stabilization. The polymer matrix investigated as membrane material are waterborne poly(urethane urea)s (WPUU). The general goal of the work is to prepare membranes with Ag NP/activator and AgBF4/BMImBF4 systems for light olefins/paraffins separation. It was possible to prepare successfully WPUU/Ag NP membranes up to 50 wt% of silver content. The facilitated transport of olefin was not reached, even with the use of activators, BMImBF4 and p-Bq. WPUU/AgBF4 membranes with more than 50 wt% of AgBF4 provided facilitated transport of olefin. However, the olefin flux decreased due to the moisture loss during the experiments with dried gases and the intensive Ag+/ether interaction in WPUU matrix. IL (BMImBF4) was introduced to the electrolyte membranes prepared. IL was able to smooth Ag+/ether interaction leading to an increase of the final selectivity when compared with membrane without IL. Before the olefin flux drop, the maximum olefin permeance (13.94 GPU) and selectivity (97.5) was achieved in 1 WPUU: 2 AgBF4: 0.5 IL (weight ratio) membrane. This result reached the minimum performance required to replace C3 splitters. It was possible to recovery (84%) the olefin flux when the moisture level of the membrane was recovered. This result suggests that the initial source of olefin flux decline was not the Ag+ reduction problem, but the moisture loss, which led to Ag+ cations unfeasibility for olefin interaction