The conversion of green, cheap and renewable biomass materials into biofuels through thermochemical and biochemical methods is one of the key route to provide sustainable energy in future. The introduction of ultrasonic energy in biomass conversion could destroy the recalcitrance structure of lignocellulosic biomass at room temperature, facilitate the separation of complicated composition in raw materials, turn heterogeneous reactions into homogeneous or at least quasi- homogeneous reactions, and therefore essentially remove barriers that limited the efficiency and selectivity in biomass conversion.  Ultrasonic wave has some special physical properties. It can accumulate energy by acoustic cavitation, and then release them instantaneously by the collapse of cavitational bubbles within several microseconds. The intensity of released energy can be enough to break down any chemical linkage, destroy the limit in multiphase interface and enhance the mass transfer and heat transfer during the reactions. Therefore, sonochemical treatment could efficiently destroy biomass structure, improve the mixing and reactions of biomass materials, however, the selectivity of biomass reactions is not remarkably altered.

Although sonication had been used in many research fields related to biofuels, such as the pretreatment, saccharification, and fermentation of lignocellulose, biodiesel synthesis, pretreatment and chemical reactions of microalgae, but actually, not all processes using ultrasonic energy was economic or with high efficiency. The proper coupling of the energy from ultrasonic activation and that from biomass reactions, which could results in positive or even better benefit in energy output and process economics, is still the critical problem for the application of sonication in biofuel technologies.

Dr. Jia Luo and Professor Zhen Fang, from Research Group of Biomass Energy in Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, reviewed the progresses on the application of ultrasound in biofuels, with the main attentions on the progresses and trends in the fractionation and conversion of lignocellulose, biodiesel synthesis, as well as pretreatment and chemical reactions of microalgae, with low-frequency ultrasound at 20-50 kHz. It demonstrated that ultrasonic auxiliary did not substantially change the mechanism of chemical reactions, but could remarkably accelerate reactions, save reaction time, and even improve the efficiency and selectivity in biomass conversion by inhibiting secondary reactions. It was necessary to determine the way and the degree of incorporating sonication, change the design of novel sonochemical reactors, optimize the ultrasonic processing parameters, according to the energy demand for certain chemical processing. Sonication technology was also suggested to be combined with other methods such as solvents, catalysts and microwave to lessen the energy cost of using sonication, and achieve a greater benefit in energy output and process economics. At the last of the paper, the authors discussed the combination of sonication with solid catalysts and enzymes, discussed the problems related to the process economics in different biomass processing and reactions, and gave some constructive suggestions. The authors also gave some descriptions on the progresses on ultrasound-assisted emulsification of raw bio-oil and real time monitoring of biomass reactions with high-frequency ultrasound technologies.

The review paper (Jia Luo, Zhen Fang, Richard L. Smith Jr. Ultrasound-enhanced conversion of biomass to biofuels.) was accepted and already published on line.

URL: http://www.sciencedirect.com/science/article/pii/S036012851300052X

Mechanistic effects of ultrasonic energy in lignocellulose pretreatment and conversion

通过热化学和生物化学方法将绿色廉价、可再生的生物质原料转化为燃料是解决未来能源困境的重要途径。使用超声波能量实施过程强化，可以在室温条件下破坏顽抗的生物质结构，便利复杂化学组分的分离，将生物质的催化反应由非均相转变为均相或者准均相，从而在本质上改善制约生物质转化效率和选择性的因素。超声波具有特殊的物理特性，可以通过空化作用积累超声能量，然后通过空化气泡在微秒数量级的瞬间崩溃急剧释放能量。释放的能量强度足以破坏任何的化学键，打破多相体系的界面限制，强化反应过程的传质传热。因此，超声波处理既可以高效地破坏生物质结构，促进生物质原料的混合和反应，又不至于显著影响生物质反应的选择性，在生物燃料领域的研究中具有较大潜力。

尽管超声可以而且业已用于木质纤维素预处理和糖化发酵、生物柴油合成、微藻预处理和化学转化等多个生物燃料领域，但是并不是所有涉及超声的反应都是经济有效的。实际上，如何将超声活化的能量与生物质化学反应的能量耦合，获得最大的能量和经济收益，仍然是超声技术在生物燃料领域应用面临的首要问题。

版纳植物园生物能源组罗嘉博士和方真研究员，综述了超声在生物燃料领域的研究进展，重点介绍了20-50 kHz低频率超声在木质纤维素分级转化、生物柴油合成和微藻处理转化过程中的研究现状和趋势。综述表明，超声辅助强化并不能从实质上改变化学反应机理，但是可以显著地加快反应的进程，节约反应的时间，通过制约二次反应的发生来改善生物质转化反应的效率和选择性。需要针对特定化学反应的能量要求，设计超声辅助的方式和程度，改变超声反应器设计，优选超声处理参数。需要通过超声技术与溶剂、催化剂、微波等其它辅助技术的耦合来降低超声处理的能量成本，获取更大的能量和经济收益。作者在文末重点讨论了超声强化技术与固体催化剂、酶催化剂的结合问题，探讨了超声应用于不同生物质转化反应的经济性问题，并给出了合理的建议。作者还介绍了超声在生物燃油乳化、高频超声实时监控生物质转化过程等领域的研究进展。

该综述文章（Jia Luo, Zhen Fang, Richard L. Smith Jr. Ultrasound-enhanced conversion of biomass to biofuels.）已经被接收，并在线发表。

论文上网地址：http://www.sciencedirect.com/science/article/pii/S036012851300052X

超声能在木质纤维素预处理和转化中的作用机理

Progress in Energy and Combustion Science简介

Progress in Energy and Combustion Science （PECS）是能源与机械领域影响力最高的期刊（2013年IF为15.089），主要接受相关领域的综述类文章。PECS仅邀请和发表在国际上获得公认的作者（Internationally recognized authors）的文章，分为四个专题：Energy & Fuels; Engineering, Chemical; Engineering, Mechanical; Thermodynamics，各个专题分类在相关领域中排名第一。PECS 在2013年全年共有6期，发表文章20篇，中国大陆研究人员在PECS发表论文2篇。生物能源组郭峰博士和方真研究员曾于2012年在该期刊上发表论文1篇。