In-situ catalytic upgrading of pyrolysis vapor.

摘要

The rising fuel prices, environmental concerns over the emission of greenhouse gases, and the limited availability of fossil fuels led to the current focus on developing alternative fuel sources that are sustainable and environmentally benign. Lignocellulosic biomass, due to its high carbon value, abundance and for being greenhouse gas neutral, is a promising alternative energy resource. Fast pyrolysis of lignocellulosic biomass produces high energy density liquid fuel, called bio-oil, which has the potential as transportation fuel. But, crude bio-oils are chemically complex liquids with high oxygen contents (40 % oxygen content), high viscosity, low pH, low thermal stability, and poor heating values (20 MJ/Kg). Therefore, bio-oils must be substantially upgraded (de-oxygenated) to highly stable, non-corrosive, and high calorific value liquid fuels prior to their use as transportation fuels.;This research was conducted to investigate the efficiency of various acid catalysts in upgrading (cracking) the oxygenated pine wood pyrolysis vapors to high quality liquid fuel. Initial catalyst screening studies proved that zeolite acidity and pore structure is essential for effective cracking of pyrolysis vapors. Low space velocities and moderate temperatures were found to be favorable for the de-oxygenation of pyrolysis vapors. Various zeolites were tested, of which HZSM-5 with low Si/Al ratio was found to be an effective cracking catalyst. But the use of zeolites resulted in poor liquid yields. Zeolites were promoted with transition metal ions in order to inhibit the secondary cracking reactions occurring on Brönsted acid sites. The metal-promoted bi-functional catalysts were found to be the most effective catalysts, among all the catalysts employed in this research, in promoting hydrocarbon forming reactions without adversely affecting the liquid yields. Catalyst coking was unavoidable but the addition of metal ions to zeolites lowered the extent of coking. TG analysis of used catalysts indicated that the catalysts can be regenerated by calcining at 600–650 °C.