Purification of raw biogas using membranes made of ultra-permeable polymer with intrinsic microporosity
Separation of gas mixtures is one of the priority directions of the Department of Membrane Separation Processes of the Institute. The research focuses primarily on the application potential of membrane materials and processes for the purification of flue gases or raw biogas. The purification of biogas using a new type of polymer membranes with so-called intrinsic microporosity (PIM), which are highly permeable for CO2, is discussed in a new paper published by a team led by Dr. Izak in collaboration with the University of Edinburgh and the Institute of Membrane Technology in Italy. The work was published in the prestigious scientific journal Journal of Membrane Science.
The work describes the separation capabilities of the PIM-TMN-Trip polymer membrane, which consists of tetramethyltetrahydronaphthalene units attached to a triptycene chain. The permeation properties of the membrane were studied using a unique apparatus at ICPF, which can simulate real processes of separation of various gas mixtures. The tested membranes showed excellent separation properties, both for binary mixtures of CO2 and CH4 and for real biogas from the wastewater treatment plant, even at a small pressure difference, when the energy consumption for compressing of the purified gas is minimal. The separation characteristics of the membranes exceeded the upper bounds from 2008 and reached the recently defined limits for pure gases from 2019. Increasing inlet pressure resulted in reduced CO2 permeability and mixed-gas selectivity, while ideal selectivity, defined as the ratio of clean gases permeabilities, remained practically unchanged. An interesting finding is also that during the longer exposure to pure CO2 at 5 bar, the ideal selectivity of the membrane increased 2.5 times, without reducing the CO2 permeability usually caused by aging of the membrane in a swollen state. This phenomenon may indicate the behavior of the membrane during long-term operation at high-pressure separation. It has been also shown that the presence of more than 400 ppm H2S in the raw biogas does not significantly affect the transport and separation capabilities of the membrane, which opens interesting prospects for using this membrane in the separation of raw biogas without the need of pre-treatment.
Stanovsky, M. Karaszova, Z. Petrusova, M. Monteleone, J.C. Jansen, B. Comesaña‑Gándara, N.B. McKeown, P. Izak Upgrading of raw biogas using membranes based on the ultrapermeable polymer of intrinsic microporosity PIM-TMN-Trip J. Membr. Sci. 2021, 618, 118694. DOI: 10.1016/j.memsci.2020.118694
Diagram of selectivity, i.e. the ratio of permeability of individual gases, vs. CO2 permeability for various forms of PIM-TMN-Trip membrane