Preparation, Characterization And Properties Of The Novel Catalysts For The Hydrodeoxygenation Of Oxygenic Compounds In Bio-oil

With the continuing depletion of the reserves of non–renewable petroleum and the worsening environment pollution, bio–oil, as a renewable energy, has attracted much attention. However, the liquid bio–oil contains many oxygenic compounds including furans, phenols aldehydes, ketones, etc, leading to the high oxygen content of bio–crude (40–50 wt %), which contribute to some deleterious properties, such as low heating value, chemical instability, immiscibility with hydrocarbon fuels and corrosiveness. It is very necessary to selectively remove oxygen from the bio–oil via the hydrodeoxygenation (HDO) to improve the quality of the upgraded bio–oil. At present, the used HDO catalysts are mainly concentrated on noble metal catalysts, sulphide catalysts and phosphide catalysts. The noble metal catalysts have a good catalytic activity in the HDO of bio–oil, but their costs are very expensive. Although sulphide catalysts and phosphide catalysts have high activity, the dominant route in the HDO of phenols on them is direct deoxygenation, leading to the high content of aromatics in the products, which is very hard to meet the standards of clean fuel. Hence, decreasing the oxygen content and aromatics content and improving the H/C ratio are the key factors in the HDO of bio–oil. According to the above mentions, many kinds of catalysts were designed and prepared in this paper and their catalytic activities were tested using phenol, 4–methylphenol, benzaldehyde, acetophenone or cyclopentanone as the model oxygenic compound.The support used in the HDO catalysts is focused on Al₂O₃, and the reports concerned TiO₂–Al₂O₃ composite support was very few. Therefore, TiO₂–Al₂O₃ composite support was prepared by ultrasound–assisted precipitation method. The effects of aluminum sources and precipitants on the properties of TiO₂–Al₂O₃ composite supports and the effects of support properties on the HDO properties of Ni–Mo–S/TiO₂–Al₂O₃ catalysts were studied. The pore volume, the average pore diameter and the specific surface area of the composite support were high to 1.12 mL/g, 18 nm, and 295 m²/g, respectively. The primary factors of supports which affected the HDO properties of Ni–Mo–S/TiO₂–Al₂O₃ catalysts were the acidity and specific surface area of supports. In the HDO of phenol on Ni–Mo–S/TiO₂–Al₂O₃ catalyst under the conditions of 300℃and hydrogen pressure 4.0MPa, the conversion, the deoxygenation rate and the total oxygen–free compound were high to 81.9%, 79.4% and 100%, respectively. The main product was benzene and cyclohexane, and the benzene selectivity was high to 80%, which was very hard to meet the standards of clean fuel. Because amorphous catalyst have its interesting intrinsic properties such as the microstructure of short–range order and long–range disorder, unique isotropic and high concentration of coordinative unsaturated sites, leading to its excellent activity and selectivity in catalytic reaction. Ni or Co and Mo or W were selected as active components to prepared a serial of Ni–Mo–B, Co–Mo–B, Co–Ni–Mo–B, La–Ni–Mo–B, Ni–Co–W–B amorphous catalysts by chemical reduction method. These amorphous catalysts were applied into the HDO of bio–oil for the first time. The effects of active components mole ratio, the preparation conditions of the amorphous catalysts and the HDO reaction temperature on catalyst properties were optimized. Ni based amorphous catalysts had a higher hydrogenation activity while Co based amorphous catalyst exhibited a higher thermal stability. The HDO of phenol on Ni–Mo–B, Co–Mo–B, Co–Ni–Mo–B and La–Ni–Mo–B amorphous catalysts mainly proceeded with hydrogenation–dehydration route, which could decrease the aromatic content and improve the H/C atomic ratio of the products greatly. Hydrogenation–dehydration route was the only one route in the HDO of phenol on W based amorphous catalyst and the benzene selectivity was 0. The deoxygenation products in the HDO of benzaldehyde and acetophenone on La–Ni–Mo–B amorphous catalyst could be further hydrogenated to the corresponding alkane. The deoxygenation rate could be high to 100% in each HDO of oxygenic compound. The catalytic activity of amorphous catalyst in the HDO of bio–oil depended on its hydrogen–supplying ability, Br(?)nsted acid acidity and specific surface area. The main reason that the catalytic activity decreased obviously at high temperature was attributed to the destruction of amorphous structure. The oxygen content, the aromatics content and the H/C mole ratio in the upgraded bio–oil with these amorphous catalysts could fully meet the standards of clean fuel. However, the activity and the thermal stability of these amorphous catalysts need to be further improved.