Competitive multi-component bio-syngas separation for hydrogen production: breakthrough dynamics, thermal effects, and adsorbent stability analysis under practical operating conditions

Abstract

The present work experimentally investigates the ability of zeolite 13X to purify H2 from a multi-component bio-syngas feed [composition (mol%): H2/CH4/CO/CO2 – 51.7/3.4/13.2/31.7] in a bench scale, glass wool insulated column simulating a near-industrial adiabatic environment. The column breakthrough dynamics and thermodynamic interactions are studied as a function of total pressure and feed flow rate. The adsorbent showed excellent separation characteristics with the highest affinity for CO2 followed by CO and CH4, and completely restricts their propagation for pure H2 production. The non-isothermal operation results in forming two distinct temperature fronts and manifests itself by broadening the mass transfer zone, decreasing loadings, and causing an early breakthrough of various adsorbates. The competitive adsorption is confirmed through the presence of roll-ups with a slowly moving CO2 concentration front displacing pre-adsorbed CH4 and CO over the duration of the experiment. Further, dynamic adsorption and desorption (sweep gas: He and CO2) experiments are respectively employed to measure competitive equilibrium loadings of heavy (CO2) and light components (CH4, CO). Additionally, the variation in breakthrough time, adsorbate propagation rate, column peak temperature, breakthrough and effective loading, and competitive selectivities are analyzed and discussed. Finally, a novel methodology to design H2 purification systems is proposed and put to practical use by developing and long duration (∼1500 cycles) testing a pilot scale (feed flow rate: 100 Nm3/h) vacuum pressure swing adsorption system. The cyclic separation unit while generating fuel-cell grade H2, displayed complete operational repeatability, with minimal deviation (<6 %) in adsorbent textural properties and crystalline structure.