Open Structured Cobalt Catalyst for Fischer-Tropsch Synthesis and Reactor Design

JOHN VAN DER SHAAF; J.C. SCHOUTEN; FERNANDA NEIRA D ANGELO; ALEJO AGUIRRE

Noordwijkerhout

Conferencia; XIX Netherlands' Catalysis and Chemistry Conference; 2018

NCCC

The Fischer-Tropsch (FT) process is widely applied to convert synthesis gas to liquid fuels andchemical intermediates. The products are mostly saturated aliphatic hydrocarbons with adistribution that generally follows the Anderson Schulz Flory (ASF) distribution, which establishes adependence of the length of the hydrocarbons on the H /CO ratio in the feed. [1].A challenge in FT, is that the reaction is fast and easily affected by mass transport limitations. As aresult, the process is not optimally operated and the product composition deviate to the expectedone. In particular, internal mass transport limitations cause gradient concentrations in the catalyticparticle, resulting in a deviation of the product distribution. This effect is well described in thecalculations performed by van Ommen et al. [2]. For this reason, it is necessary to develop a newgeneration of optimized catalysts with optimized transport properties.One attractive solution is the use of structured solid foam catalyst. A solid foam is made ofinterconnected solid struts forming a network with relative high geometric surface area andporosity. A main advantages of these structures is that they can be used as substrate to deposit awash-coat layer of a porous catalyst with high dispersion of the active phase. The thickness of thewash-coated layer can be easily tuned to prevent internal mass transfer limitations, thus resultingin optimal catalyst utilization. This work presents the design of a new catalytic reactor with ahighly accessible structured solid foam catalyst. We investigate the effect of intra-particle diffusionlimitations on the selectivity and productivity of foam catalysts in FT reaction.Aluminum foams of 10, 20 and 40 pores per linear inch (ppi) were coated with layers of Co(15%)/γ-Al O of thickness from 5 to 30 µm. The details of the employed wash-coating method can befound elsewhere [3]. The obtained foams were characterized by TPR, S and SEM and tested inFT at reaction conditions: 20 bar, 210-250ºC and H /CO = 2,1.The results show that the obtained wash-coated catalyst foam have a high surface area, aremechanically stable and are active for the FT reaction. Moreover, the products distribution followsthe ASF tendency and the reactor performance is influenced by the thickness of the wash-coatedlayer. Finally, a reactor model considering the external and internal mass transport processes hasbeen developed in order to interpret the experimental observations.