Co-pyrolysis of wastes mixtures obtained from rice production: upgrading of produced liquids

摘要

The increasing need to find alternative fuels to decrease the dependency on fossil fuels and to reduce the negative environmental impact of wastes accumulation has led to the idea of studying the energetic valorisation of different types of wastes by co-pyrolysis. Rice production process generates rice husk together with polyethylene (PE) bags that are used for rice packaging and to transport seeds and fertilizers used for rice culture. In Portugal, most of these plastic bags waste usually end up in landfills, since the amount of dirt and dust does not allow their recycling. Bio-oils produced by rice wastes pyrolysis present some undesirable properties: chemical instability, high solids content, ashes, oxygenated compounds and water, which prevent its direct use in conventional engines. On the other hand, PE pyrolysis produces around 80% w/w of liquid hydrocarbons (bio-oils) composed by a complex mixture of hydrocarbons from C5 to C20 (without the mentioned undesirable properties), 10% w/w of gases and almost no solids. Co-pyrolysis of rice husk blended with plastic wastes leads to the production of bio-oils that may be used as bio-fuels or as raw materials. These bio-oils quality can be improved by the optimisation of co-pyrolysis experimental conditions, including the use of suitable catalysts. Otherwise, liquids may be thermally upgraded to convert heavier liquid molecules into smaller ones with lower molecular weight and better fuel properties. The capability of these bio-fuels for energy production to be used during rice milling processes was analysed. Different approaches: pyrolysis, hydrogenation and pyrolysis followed by hydrogenation were analysed, considering the technical, economical and environmental viability of each process.