Steam adsorption on molecular sieve 3A for sorption enhanced reaction processes
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Steam adsorption on molecular sieve 3A for sorption enhanced reaction processes Jasper van Kampen1,2 · Jurriaan Boon1,2 · Martin van Sint Annaland2 Received: 14 August 2020 / Revised: 26 October 2020 / Accepted: 3 November 2020 © The Author(s) 2020
Abstract Steam adsorption enhanced reaction processes are a promising process intensification for many types of reactions, where water is formed as a byproduct. To assess the potential of these processes, adequate models are required that accurately describe water adsorption, particularly under the desired elevated temperatures and pressures. In this work, an adsorption isotherm is presented for H2O adsorption at 200–350 °C and 0.05–4.5 bar partial pressure on molecular sieve (LTA) 3A. The isotherm has been developed on the basis of experimental data obtained from a thermogravimetric analysis and integrated breakthrough curves. The experimental data at lower steam partial pressures can be described with a Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm, whereas at higher steam partial pressures the experimental data can be adequately captured by capillary condensation. Based on the characteristics of the adsorbent particles, a linear driving force relation has been derived for the adsorption mass transfer rate and the apparent micropore diffusivity is determined. The isotherm and mass transport model presented here prove to be adequate for modelling and improved evaluation of steam adsorption enhanced reaction processes.
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Adsorption
Keywords Capillary condensation · H2O adsorption · Linear driving force · LTA · Molecular sieve · Sorption enhanced reaction Nomenclature ap Particle interfacial area (m2 m−3) b Isotherm equilibrium constant (bar−1) dc Crystal diameter (m) dm Macropore diameter (m) dp Particle diameter (m) Dc Micropore diffusion coefficient (m2 s−1) Dk Knudsen diffusion coefficient (m2 s−1) Dm Molecular diffusion coefficient (m2 s−1) Dp Macropore diffusion coefficient (m2 s−1) Ea Activation energy (kJ mol−1) Fi Molar flow of component i (mol s−1) kf External film mass transfer coefficient (m s−1) kLDF Linear driving force rate constant (s−1) KL Equilibrium constant of the multi-site Langmuir model Kn Equilibrium constant of the GSTA model (–) m Number of equilibrium parameters in the GSTA model mads Mass of adsorbent (kg) Mi Molecular weight of component i (kg mol−1) n Index number of parameters and adsorption sites in the GSTA model P Pressure (bara) P0 Standard pressure (bara) Pi Partial pressure of component i (bara) qi Adsorbent loading (mol kg−1) or (kg kg−1) qmax Maximum adsorption capacity (kg kg−1) qs Saturation capacity (kg kg−1) R Ideal gas constant (J mol−1 K−1) Rc Crystal radius (m) Rp Particle radius (m) Re Reynolds number (–) Sc Schmidt number (–) Sh Sherwood number (–) t Time (s) T Temperature (K) u Superficial gas velocity (m s−1) v Interstitial gas velocity (m s−1) Vg Gas vo
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