Desulfurization of Biomass Syngas Using ZnO-Based Adsorbents: Long-Term Hydrogen Sulfide Breakthrough Experiments

Area of Science:

• Chemical Engineering
• Environmental Science
• Materials Science

Background:

• Biomass gasification produces syngas, a valuable fuel, but requires sulfur removal.
• Conventional wet scrubbing for syngas desulfurization has limitations.
• Dry-bed adsorption using metal oxides offers a potential alternative.

Purpose of the Study:

• To investigate the technical feasibility of zinc oxide (ZnO) for dry-bed adsorptive desulfurization of biomass-based syngas.
• To evaluate ZnO performance under realistic gasification conditions, including steam-rich and tar-rich syngas.
• To identify factors limiting ZnO desulfurization efficiency and develop a predictive model.

Main Methods:

• Laboratory-scale H2S breakthrough experiments were conducted using a steam-rich model biosyngas.
• Experiments simulated realistic H2S concentrations and employed varying conditions (space velocity, particle size).
• An empirical deactivation model was fitted to experimental data to predict breakthrough curves.

Main Results:

• Apparent ZnO utilization rates ranged from 10% to 50% under tested conditions.
• Intraparticle mass-transfer resistances and product-layer resistances were identified as limiting factors.
• ZnO performance was not significantly impacted by hydrocarbons in tar-rich syngas, despite carbon deposition.

Conclusions:

• ZnO is a technically feasible adsorbent for dry-bed desulfurization of low-to-medium sulfur biomass syngas.
• Optimizing particle size and space velocity is crucial to mitigate mass-transfer limitations.
• ZnO demonstrates robustness against hydrocarbons, making it suitable for tar-containing syngas applications.