Two-Stage Gasification of Sewage Sludge for Enhanced Hydrogen Production: Alkaline Pyrolysis Coupled with Catalytic Reforming Using Waste-Supported Ni Catalysts

Abstract

Sewage sludge is a potential source of H2-rich fuel via a catalytic thermo-chemical reaction, which can facilitate the economical disposal of this hazardous waste. In this study, dry sludge is subject to a two-stage gasification process, i.e., the alkaline pyrolysis (P-stage) and the catalytic reforming (R-stage). The evolved volatiles from the P-stage are reformed in the R-stage with significant enhancement in both yield and concentration of H2. The Ni-doped catalysts are supported on dental wastes (DWs), with both significant environmental and cost benefits. The optimized H2 production (29.03 mmol g–1 sludge, dry basis) is observed when the R-stage temperature is 800 °C with the sludge/catalyst mass ratio at 1:1 (Ni loading of 10 wt % in the catalyst, specific surface area of 9.1 m2 g–1). The synergy between P- and R-stages is investigated through GC-MS analysis, indicating that the presence of NaOH in the P-stage eliminates the fatty acids in the tar with production of intermediates (e.g., alkane) which most likely contributes to easier R-stage reactions and enrichment of the H2 fraction.

Obtaining High Yield Hydrogen from Sewage Sludge by Two-Stage Gasification: Alkaline Pyrolysis Coupled with Catalytic Reforming

“…The results of proximate analysis and ultimate analysis of sludge can be found in a previous study . The same Ni/DW catalysts employed in previous studies were used here, , and a catalyst with a theoretical Ni loading of 10% was selected for conducting the reaction in this study.…”

“…Experimental Methods. An injection pump device (HK-400, China) was added to a two-stage reactor 13 to provide steam required for the reaction (Figure 1). The twoway connector upper ventilation port of the two-stage reactor was changed to a three-way connector to enable the steam and nitrogen carriers from the injection pump to simultaneously enter the reactor.…”

“…H 2 production has been increased from 2.81 mmol g –1 to 29.03 mmol g –1 sludge, dry basis, using this process. 13 …”

“…Therefore, the demand for an increase in H 2 production can be met through the use of alkaline pyrolysis coupled with ex-situ catalytic gasification. H 2 production has been increased from 2.81 mmol g –1 to 29.03 mmol g –1 sludge, dry basis, using this process …”

“…H 2 production has been increased from 2.81 mmol g −1 to 29.03 mmol g −1 sludge, dry basis, using this process. 13 Studies have shown that H 2 production can be further improved by employing steam gasification. In the study of pyrolysis gas production from sludge in a fixed-bed reactor, the production of H 2 was increased by approximately 60% when steam was added.…”