Określenie rozpuszczalności głównych składników biogazu w membranie polisulfonowej

Przeprowadzono badania rozpuszczalności głównych składników biogazu w membranie polisulfonowej. Otrzymane metodą grawimetryczną izotermy adsorpcji opisano za pomocą modelu sorpcji dualnej. Stwierdzono bardzo dobrą zgodność modelu z wynikami eksperymentalnymi. Określono również udział rozpuszczalności poszczególnych gazów zarówno w matrycy polimerowej, jak i w objętości swobodnej szklistego polimeru.

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The biomethane sector should become much more visible in the face of global challenges such as reducing greenhouse gas emissions and replacing fossil fuels with renewable sources. Especially in the overall changes in the field of energy production, decarbonization of industry, and the circular economy. The value chain of biomethane produced by methane fermentation is shown in Figure 1. Based on the literature data and results of our research, it was found that the model has to include the multi-component nature of mass transport through the membrane in case of biogas separation. There is a high probability that for the CH 4-CO 2-membrane system, competitive sorption of those components occurs in the empty spaces of the glassy polymer. Including this phenomenon in the model should result in good agreement between numerical calculations and experimental data. This is particularly important in the case of the design and optimization of the biogas separation process into bioCH 4 and bioCO 2 streams. In this work, the total solubility (in the matrix and the free volume of the glassy polymer) was experimentally determined. The tested samples were taken from Air Products' commercial membrane module. The sorption isotherms of carbon dioxide, methane, nitrogen, and oxygen on a polysulfone membrane sample were determined by a gravimetric analyzer (Figure 3). Based on the results of the equilibrium concentrations and the corresponding pressures, gas solubilities in pressure function were determined. Adsorption isotherms of gases were determined at a temperature of 293 K and the pressure in the range from 0 to 10 bar. The measurement of a given isotherm point was ended when the measured change in the sample mass reached 99.8% of the predicted asymptotic value or the measurement time for a given point exceeded 120 minutes. For each isotherm, one cycle of pressure increasing and one cycle of pressure decreasing were performed. The obtained results are presented in Figures 6-7. It has been found that in the case of carbon dioxide, sorption/desorption hysteresis occurs, which may lead to changes in the transport properties of the membrane. The obtained adsorption isotherms of individual gases were described by the dual-mode sorption (DMS). The individual coefficients of this model (k D, CˈH , b), existing in equation (2), were determined using the least squares method. The values of these coefficients are presented in Table 1. Very good agreement of the DMS model with the experimental results is shown in Figure 8. In addition, the work also determines the share of solubility of individual gases both in the polymer matrix and in the free volume of the glassy polymer (Figures 9 and 10). It was found that Langmuir sorption has to be included for both carbon dioxide and methane, in contrast to oxygen and nitrogen.