Synthesis Of 1,1,3,3-Tetramethylguandium Acrylate-based Polymers And The SO₂ Absorption Behaviors

Environmental pollution has become one of the most vital problems for the human beings. Room temperature ionic liquids is a novel kind of benign solvents with high potential in replacing the Volatile Organic Compounds (VOCs) in chemical process. Furthermore, polymerizable ionic liquids can also be used as novel polymer materials such as polyelectrolyte and gas separation materials. In this paper, we synthesized new ionic polymers containing 1,1,3,3- tetramethylguanidinium cation for the first time and studied its SO₂ absorption and desorption behaviors.Firstly, 1,1,3,3-tetramethylguanidine-based ionic liquids including polymerizable one such as acrylate (TMGA) were synthesized via direct neutralization of TMG and vinyl acids under nitrogen atmospherewhich. TMGA is a colorless, transparent and hygroscopic liquid with a melting point of-20.1℃. TMGA exhibited certain capability for SO₂ absorption, but it was not very stable. It would lose its weight just at temperature over 100℃.Then, the linear poly(l,l,3,3-Tetramethylguandium acrylate) (PTMGA) was synthesized via free radical solution polymerization of TMGA in aqueous medium. PTMGA is a kind of amorphous polymer. It does not decompose until 170℃ and therefore, is much more thermally stable than TMGA. The obvious weight loss after 170℃ is attributed to the cleavage of the ionic bond between the carboxyl anion and the 1,1,3,3-tetramethylguandium cation and pyrolysis of the polymer backbone, respectively. It has been found that PTMGA is able to adsorb SO₂ with high selectivity, high capacity and rapid rate, and its absorption capacity and rate is obviously higher than the monomer and other TMG-based ionic liquids. The SO₂ absorbed at relatively low temperature can be desorbed effectively at high temperature and/or under vacuum. The absorption and desorption process can be circularly operated and thus the polymer can be reused. Under typical operation conditions, about 0.25-0.5 gram SO₂ per gram polymer can be separated in each cycle.In addition, for the first time, we prepared cross-linked copolymers (PTMGA-CL)of TMGA with water-soluble crosslinker (CL) by inverse suspension polymerization with non-polar solvent as oil phase and Span as dispersant. The copolymers appear porous particles and the porosity is of about 40%. The particles are composed of smaller spherical particles distributed in random way. The porous crosslinked PTMGA-CL particles possess higher absorption capacity of SO2 than the linear PTMGA while the absorption velocity almost kept unchanged. And unlike PTMGA, the morphology of PTMGA-CL kept unchanged during SO2 absorption. This polymer can also be reused for several circles. Under typical operation conditions, namely, absorption at 50 °C under atmospheric pressure and desorption at 90 °C and under vacuum, about 0.284 gram SO2 per gram polymer can be separated in each cycle.The high selectivity, strong absorption capability, quick absorption speed and the reusability make the tetramethylguanidinium-containing ionic polymers, especially the crosslinked PTMGA-CLs very promising solid-state SO2 absorbents for potential applications in fuel gas desulfurization (FGD) and other fields for purification of SO2-containing gases.