Ethylene is an important petrochemical, but it may contain traces of acetylene that can destroy the catalysts used in downstream processes. The separation of ethylene and acetylene is difficult, and the main method, distillation, is energy intensive. A potential alternative is the use of regenerable, inexpensive materials that selectively separate acetylene from ethylene.
Although such materials are not yet available, professor Dan Zhao and his team at the Dept. of Chemical and Biomolecular Engineering, the National University of Singapore (www.nus.edu.sg) have developed a suitable metal organic framework (MOF) for acetylene capture. By combining small MOF pore sizes with open nickel sites and sites for preferential acetylene binding, the team has created a Ni-MOF called Ni(3)(pzdc)(2)(7Hade)(2) that can meet the demands of selectivity and robustness. The team has also adjusted the pore sizes of the MOF to allow entry only for very small gas molecules and filled the pore walls with chemical groups that would attract acetylene over ethylene.
According to the team, the Ni-MOF purified an ethylene stream by a factor of a thousand and maintained its high selectivity across a range of pressures and regeneration cycles. The Ni-MOF can be prepared in a standard hydrothermal procedure.