(352c) Utilization of Solid Residual Wastes Arising from Woody Biomass Gasification

Biomass Gasification usually generates significant amount of solid residues i.e. char and ashes as by-products, which usually contains high concentration of harmful compounds and heavy metals. As a result, disposal of these solid residual wastes is creating grave risks to human health. Majority of them is dumped or used in low-valued methods such as using as a land-fill material. However, the cost of landfilling is now dramatically increasing due to the presence of harmful compounds, strict environmental regulations and limited availability of landfill space. From those points of view, it is essential to develop beneficial uses of these solid residual wastes to solve the concerns associated with their disposal.

In this work, ashesarising from woody biomass gasification have been successfully refined into the active CaO catalyst for biodiesel production. Calcium carbonate was found to be the main component in woody biomass gasification bottom ash, which can be completely transformed into the active CaO catalyst after calcination under air at 800 °C or above. The obtained CaO catalyst exhibits high biodiesel production activity, over 90% yield of biodiesel can be achieved at the optimum reaction condition (methanol-to-oil molar ratio, 20:1; catalyst, 5 wt. %; temperature, 65 °C).

Moreover, it was found that ashes arising from woody biomass gasification also have high contents of potassium (1.92 g/kg), phosphate (0.47 g/kg) and other elements which are in the desired range for planting. Therefore, in this work, ashes have also been used as agricultural fertilizer by mixing it with soil in different ratios and used for planting of water spinach (Ipomea aquatica) which can be fully grown within 6 weeks. Performance of the ashes-derived fertilizer was investigated by a growth rate (i.e. height and weight) and heavy metal accumulation of the water spinach.

On the other hand, char (another by-product from woody biomass gasification) has been employed as a precursor of activated carbon (one of the most important microporous adsorbents), due to its highly porous structure, its higher surface area and larger pore volume. In this work, activated carbon has been developed from char by chemical activation using potassium hydroxide as an activating agent. The effects of operating conditions of activation process, such as temperature, activating agent to char mass ratio, and nitrogen flow rate, on the textural and chemical properties of the activated carbon product were investigated. From BET analysis, the surface area of char was less than 10 m²/g and increased to more than 500 m²/g after the activation process.

The utilization of solid residues arising from woody biomass gasification as a source of above materials not only provides a cost-effective and environmental friendly way of recycling those solid residual wastes, reducing its negative environmental effects, but also produces highly-valuable products, offering the economic benefits for biomass gasification process.