A novel catalytic filter for tar removal from biomass gasification gas: Improvement of the catalytic activity in presence of H2S

A 1 wt%/0.5 wt% nickel–calcium catalyst was co-precipitated inside porous filter discs using the urea method to develop a gas cleaning technique involving the combined removal of tars and particles from hot biomass gasification gas. Special attention was paid to the improvement of the resistance of the catalyst against sulphur poisoning by the H2S present in the gasification gas. Deactivation tests were performed on catalytic filter discs using either benzene, naphthalene or a mixture of benzene and naphthalene as tar model compounds in a simulated gasification gas containing up to 200 ppmH2S. At 900(degree)C and at a filtration velocity of 2.5 cm/s, the developed catalyst formulation shows a benzene conversion of 93% (50 ppmH2S), 78% (100 ppmH2S) and 57% (200 ppmH2S). However, benzene is not a problematic compound concerning the utilization of biomass gasification. More important is the removal capacity of this catalytic filter disc for the problematic heavy tars like naphthalene. Subsequent deactivation tests with naphthalene and with a mixture of benzene and naphthalene as tar model compounds showed that for simulated gasification gas containing up to 100 ppmH2S and for a filtration velocity of 2.5 cm/s (typical value in real gas) the naphthalene conversion is 98% in both cases. As a result, the target tar conversion (>95%) was achieved in typical hot gas filtration conditions. The significant improvement over a pure nickel based catalyst by adding the appropriate amount of CaO is encouraging towards the further improvement of the sulphur tolerance of this catalyst.