Beneficial Use of Ash and Char From Biomass Gasification

Biomass is likely to be a significant energy resource in the future. A common way to recover energy from biomass is through gasification where synthesis gas is produced; by-products of this process are tar and ash/char. This research investigates the potential to use the ash/char as a catalyst by understanding the properties of char generated under different gasification conditions. Specifically, it is desired to produce a porous char which could be used as a catalyst or as a support for more catalytically active metals. In this work, poplar wood was gasified under CO₂, steam, and air at different reaction temperatures. Experiments were done in a fluidized bed reactor at temperatures of 500°C, 750°C and 920°C and char was recovered. BET-surface area measurements showed that gasification under CO₂ has the potential to produce char with a higher surface area than char produced from steam gasification. Higher temperature or longer gasification times resulted in the production of a more porous char. TGA experiments showed that gasification under CO₂ resulted in a higher mass loss compared to gasification with steam. Gasification with steam/CO₂ mixtures yielded a mass loss similar to that of steam only which could be indicative of competitive reactions between steam and CO₂. Experiments done in an ESEM allowed for visual observation of the changes in physical properties of the biomass during gasification. With CO₂, physical changes were observed at temperatures as low as 400°C whereas physical changes were not observed under steam at this temperature.