Cenospheres are plausible intermediates in entrained flow gasification (EFG) of biogenic suspension fuels. However, their structure and reactivity remain poorly understood, limiting the accuracy of numerical simulations of entrained flow gasifiers.

The present study characterizes cenospheres from two experiments in a technical entrained flow gasifier using beech wood pyrolysis oil (PO) and char suspensions (slurry; POC) under intentionally low air ratios (0.35). Structural features and CO2 gasification kinetics are investigated, and mass transport effects under technically relevant conditions (1000 – 1500 °C, 10 bar CO2) are evaluated.

A broad particle size distribution of the cenospheres (100 – 800 µm) is identified. Micro computer tomography reveals internal macro-structures ranging from uniformly distributed porosity to a porous shell, with embedded char particles in POC cenospheres.

Micro- and mesoporosity are analyzed via argon physisorption. Only POC cenospheres show microporosity, which is assigned to the char particles. Structural ordering determined by X-ray diffraction (XRD) is stronger for smaller cenospheres. The evolution with increasing particle diameter differs between POC and PO cenospheres, with radial expansion of the graphene layers prevailing in POC cenospheres, while both radial expansion and graphene stacking vary in the structured domains in PO cenospheres.

Reaction kinetics in CO2 (5 – 20 bar, 810 – 850 °C) are determined in the differential fixed bed reactor for 200 – 400 and 600 – 800 µm fractions. The reaction rate increases with increasing temperature and CO2 partial pressure as described by the Arrhenius and the power law model (activation energy: 210 – 242 kJ/mol; reaction order: 0.2 – 0.3). Especially the mantle area-to-volume ratio of the stacked graphene layers derived from XRD and the mesopore surface area are found to impact the reaction rate.