Upgrading of raw biogas using membranes based on the ultrapermeable polymer of intrinsic microporosity PIM-TMN-Trip

Abstract

The potential of an ultrapermeable benzotriptycene-based polymer of intrinsic microporosity (PIM-TMN-Trip) for the upgrading of biogas is investigated. Permeation experiments were performed using an in-house bespoke permeation unit for pure gases and gas mixtures, and included tests with model mixtures as well as real biogas from a sewage treatment plant, under dry and humid conditions. Permeability and CO2/CH4 selectivity for either pure gases or for real biogas were high and lie close to or on the recently defined 2019 Robeson upper bound based on ideal permselectivities. In addition, a remarkable increase in CO2/CH4 selectivity was observed after two weeks of continuous exposure to CO2 due to a significant decrease of CH4 permeability. The constant CO2 permeability and increased selectivity upon ageing suggest that ageing in the presence of CO2 causes a rearrangement, rather than a reduction of the fractional free volume. The mixed gas permeability experiments were performed with high stage-cut in order to mimic a real separation process, and the results confirmed the potential of PIM-TMN-Trip membranes for biogas upgrading.

PEEK–WC-Based Mixed Matrix Membranes Containing Polyimine Cages for Gas Separation

“…The obtained results are shown in Table 1. 1 H-NMR spectra were recorded on a Bruker ADVANCE 400 spectrometer (operating at 9.37 T, 400 MHz). Chemical shifts are reported in ppm with the residual solvent as internal reference.…”

“…The following are available, Figure S1: 1 H-NMR spectrum of Fura in CDCl 3, , Figure S2: 1 H-NMR spectrum of m-xy in CDCl 3 , Figure S3: 1…”

“…Gas separation by membranes is an application in continuous growth. Because of low operating costs compared to traditional techniques, it has spread its use in several processes, including biogas [ 1 ] and natural gas separation [ 2 ], H 2 recovery [ 3 ], post-combustion CO 2 capture, and oxygen enriched air production [ 4 , 5 ]. The development of new materials that can improve separation performances represents a continuous request for the research field.…”

Ultrapermeable Polymers of Intrinsic Microporosity Containing Spirocyclic Units with Fused Triptycenes

“…For both polymers, the CO 2 /N 2 mixed gas permeability data lie in a more favorable position of the Robeson plot as compared to the single gas data (Figure 4b), and for PIM‐SBI‐Trip they are even above the 2019 upper bound. Remarkably, the mixed gas performance of PIM‐SBI‐Trip and PIM‐1/SBI‐Trip shows systematically higher selectivities than aged PIM‐TMN‐Trip and with similar CO 2 permeability (Figure S20, Supporting Information), demonstrating the potential of these ultrapermeable PIMs for biogas upgrading [ 32 ] and CO 2 capture from flue gases. [ 34 ] Previous work with benchmark polymer PIM‐1 shows significantly improved selectivity in hollow fiber membranes, [ 35 ] suggesting that also for the present polymers even better separation performance may be expected when prepared in the form of asymmetric or thin film composite membranes.…”

“…[ 31 ] Ultrapermeable polymers easily lead to a high stage‐cut, where the separation factor depends on the process conditions as much as the material properties. [ 32 ] The experiments in this work were therefore carried out at low stage‐cut (<<1%, see Figure S18, Supporting Information), using a small membrane area, a high feed flow rate and a relatively high sweep flow rate, in order to focus mainly on the materials properties. The gas permeability in both PIM‐SBI‐Trip‐based films shows a modest feed pressure dependence, similarly to that prepared from PIM‐SBF‐1.…”