Effect of Alkali Vapor Exposure on Ni-MgO/γ-Al₂O₃/Cordierite Monolithic Catalyst for Biomass Fuel Gas Reforming

Abstract

Fly ash compounds, such as alkali salts, in the raw biomass fuel gas can contaminate and deposit on traditional granular Ni-based catalysts, which resulted in catalyst deactivation and pressure increase of the downstream reformer. The impact of alkali salt exposure (KCl, K 2 SO 4 , K 2 CO 3 , by evaporation at about 7.8 mg/L for 6 h) on dry CH 4 /CO 2 reforming of model biomass fuel gas (H 2 /CO/C 2 H 4 /CH 4 /CO 2 / N 2) 15.8/12.1/2.51/ 15.0/22.1/32.6 vol %) over Ni-MgO/γ-Al 2 O 3 /cordierite monolithic catalyst (MC) was investigated and studied. The results showed that CH 4 and CO 2 conversions and CO and H 2 yields increased at 700-850°C for undeposited and deposited MC. Compared with undeposited MC, the deposited catalysts show lower CH 4 conversion but higher CO 2 conversion and CO yield at 750-830°C. The stability tests also show that CH 4 conversion and H 2 content in the tail gas decreased dramatically from 87.2% to 32.0% and from 35.1% to 26.7%, respectively, after 17 h time on stream (TOS) for the deposited MC, while CH 4 conversion kept steady of above 90% after 60 h TOS for undeposited MC at 750°C. Characterization by N 2-physisorption, XRD, ICP-AES, SEM-EDS, and XPS of MC indicate that alkali salt aerosol covering the catalyst surface or blocking mesopore channels was the main reason for the decreased reforming performance and MC deactivation, which occurred mainly at the top part of monolithic catalyst (K) 1.39 wt % by EDS), vicinal to the alkali source. The reforming of real biomass fuel gas (H 2 /CO/C 2 H 4 /CH 4 /CO 2 /N 2) 10.2/16.8/0.5/6.4/15.2/51.0 vol %) from air gasification of pine sawdust in the pilot plant (200-250 kg/h) by the reformer packed with MCP, larger in size than MC, exhibits pressure drop of less than 700 Pa, CH 4 conversion of about 84%, and tar content from 4.8-5.3 g/m 3 to 0.12-0.14 g/m 3 during 60 h TOS at 600°C. The porosity structure of MCP catalytic bed and relatively low alkali (K, Na) 0.03-0.07 wt %) deposition by fly ash from real biomass fuel gas were the main reasons for the excellent reformer performance.

Reforming of Syngas from Biomass Gasification: Deactivation by Tar and Potassium Species

“…Ethene was completely converted in all cases (not shown), probably reflecting the fate of other reactive components at these conditions, as also found by Li et al [15]. For all temperatures and catalysts a higher CH 4 conversion is achieved at elevated S/C ratios.…”

“…Albertazzi et al [33] exposed a Ni-based catalyst to gas from a lab-scale gasifier and observed loss in the reforming activity, but also reported that the activity was regained during the reforming process, presumably the alkali was washed off the catalyst surface. Li et al [15] exposed a monolithic Ni-based catalyst to alkali salt vapors (KCl, K 2 SO 4 , K 2 CO 3 ) and found a general deactivation of the reforming reaction. Physical characterization revealed severe loss of surface area of the catalyst.…”

Hydrogen production from pyrolysis catalytic reforming of cellulose in the presence of K alkali metal

“…Addition of potassium to a Ni-based catalyst resulted in the increase of hydrogen production from biomass thermo-chemical conversion [34,35]. The negative effect of the presence of alkali metal on hydrogen production from biomass thermo-chemical conversion has been reported by Wu et al [36] who found that H2 content decreased from 35.1 to 26.7% when alkali metal vapors exposed over catalyst for 17 hours during the catalytic reforming of biomass fuel gas.…”

Progresses in the Preparation of Coke Resistant Ni‐based Catalyst for Steam and CO2 Reforming of Methane

“…The many related reports of alkali or alkaline earth metal promoted catalysts in the literature have been summarized by Hu and Ruckenstein. [28][29][30][31][32] CO 2 adsorption can be significantly enhanced over Ni catalysts that incorporate basic metal oxides, which is very helpful for the inhibition of carbon formation. [28][29][30][31][32] CO 2 adsorption can be significantly enhanced over Ni catalysts that incorporate basic metal oxides, which is very helpful for the inhibition of carbon formation.…”