生物油酯化-加氢提质制备醇酯类燃料

Esterification-hydrogenation of bio-oil to generate alcohol & ester fuels

作为清洁可再生的化石燃料取代燃料,生物油的酸性及不稳定性是阻碍其规模化应用的主要障碍之一。该文基于生物油高酮、醛及酸类含量,研究了生物油轻质组分分步酯化加氢(SHE,separated esterification and hydrogenation)、一步酯化加氢(OEH,one step esterification-hydrogenation)及一步酯化加氢后二次加氢(OEH plus,one step esterification-hydrogenation plus second hydrogenation process)的提质过程,考察了钼改性雷尼镍催化剂(Mo-RN,Mo-Raney Ni)及Ru/C催化剂催化生物油制备醇类燃料的重复使用性能,并研究了酯化-加氢反应过程及反应路径。结果表明,生物油经不同酯化-加氢方法处理后,饱和醇酯含量均显著提高,生物油品质得到改善。其中以OEH plus提质处理后的生物油产物中,饱和醇、酯含量最高,分别达74.21%和9.96%。此外,提质后的生物油p H值及酸量下降最为显著,生物油的p H值由反应前的3.67提高到5.88,酸量由111.52 mg/g降至11.75 mg/g。Mo-RN及Ru/C催化剂在酯化-加氢路径下的重复使用性能良好,催化活性均无明显降低。试验证明利用酯化-加氢提质生物油为生物油精制制备含氧燃料提供有效途径。

As a clean sustainable substitute for fossil fuel, bio-oil has properties of acidity and instability, which affected its large scale application. Based on its high acid, ketone, aldehyde and phenol content, three processes for the bio oil upgrading were investigated： Separated esterification and hydrogenation（SHE）, one step esterification-hydrogenation（OEH）, and one step esterification-hydrogenation plus second hydrogenation process（OEH plus）. The studies were conducted over Mo modified Raney Ni catalyst（Mo-RN） and Ru/C catalyst with the light fraction of sawdust fast pyrolysis oil as feedstock. The catalysts reuse performance and the reaction pathways of the typical components during the bio-oil upgrading process were also studied. For the SEH process, esterification reaction was conducted without catalysts, and the hydrogenation reaction of the produced esterification bio-oil were carried out over Mo-RN and Ru/C respectively. For the OEH process, methanol and the raw bio-oil were reacted over Mo-RN and Ru/C directly. Based on OEH-Ni, second hydrogenation over Ru/C catalyst under mild condition（120℃） was conducted after the OEH-Ni process. Over all, the oil properties were improved significantly through the different upgrading process. Through the separate esterification process, oil acidity decreased substantially, showing the acid content decreased from 39.41% of the raw oil to 12.40% of the ES-oil. Accordingly, the total acid value decreased from 55.76 to 16.11 mg/g. In the following hydrogenation process, esters converted to corresponding alcohols under H2 atmosphere over Mo-RN and Ru/C catalyst, resulted in an alcohol content of 56.61% and 43.06%, respectively. Mo-RN showed better catalytic performance on the hydrogenation of phenol and ketone compounds. In the one step hydrogenation reaction process, Ru/C showed better performance for acid and ester converting to corresponding alcohols, showing the acid and ester content of 8.12% and 8.01% for OEH-Ru and 11.43% and 17.15% for OEH-Ni process. Mo-RN better improved the ketone and phenol conversion, showing the content of 1.56% and 6.60%. Through the OEH process, saturated alcohol ester content increased from 9.99% in the raw oil to 58.31% and 71.95% for Ru/C and Mo-RN, respectively. For the one step hydrogenation over Mo-RN catalyst along with its following second hydrogenation process, acid, phenol and ester in OEH-Ni oil got more thoroughly conversion to alcohol compounds, leading to obtaining an OEH plus upgraded oil of 84.20% saturated alcohol and ester content. Meanwhile, through the second hydrogenation, oil properties showed great improvement for the total acid value decreasing from 111.52 to 11.75 mg/g and pH value from 3.67 increased to 5.88. Besides, even in the second use of Mo-RN and Ru/C catalyst, no significant deactivation was observed. The saturated alcohol and ester content was still kept at 68.37% and 75.84% degree for the OEH –Ni＊ and OEH plus process, respectively. Through esterification hydrogenation process, oil properties showed great improvement in the acidity and stability. This esterification hydrogenation method is proved to be a promising routine for efficient upgrading bio-oil to oxygenated fuel.