Organic Radicals in Biomass Decomposition: Mechanisms & Dynamics

生物质分解中的有机自由基：机制和动力学巴尼·埃里森(有机化学家)和约翰·戴(工程师)提出了一套新的实验来研究生物质的热分解。A)基于Daily的流体动力学建模研究，Ellison将设计和制造一种新型设备，该设备使用高温喷嘴来分解简单的生物质材料，如糖、氧杂环和烷基芳基醚。高温、超音速喷嘴将专门为不挥发的生物质样品设计。利用真空紫外光电离质谱仪和红外吸收光谱仪对裂解产物进行同步监测。B)生物质气化产生稳定的有机自由基，如丙叉基和烯丙基，它们发生双分子反应形成芳环(C6H6)。该团队建议开发一种新的双共振测量方法来检查这些自由基的振动光谱。这项新颖的实验将使用一对红外和真空紫外光激光器。该团队还建议在高温超音速喷嘴中研究受控条件下小生物质样品的热分解。这项工作的目的是使用质谱仪和红外光谱来表征单糖和含氧杂环的分解反应。这样的实验可以洞察导致焦油(芳香化合物)形成的分子量增长反应。所有生物质气化方案中的一个主要问题是生物质气流中存在芳香化合物。模型有机化合物，如呋喃或呋喃甲醛，将在高温喷嘴中进行热解，产品将在新的实验中进行鉴定和表征。要最大限度地利用高温喷嘴作为流动反应器，需要详细描述气体流动和传热特性。Daily将对湍流气流进行建模，以确定热喷嘴的特性。喷嘴组件的设计是这样的：由于摩擦和热传递，流体在进口孔处堵塞，并在下游端再次堵塞。因此，喷嘴内的流动与下游条件隔离，在这种情况下，下游条件保持在真空条件下。当然，通过喷嘴的真实气体流动既不是绝热的，也不是无摩擦的，也不是均匀的，为了准确地模拟它，需要使用数值方法。在流动处于连续体域的情况下，应用Navier-Stokes方程，并且可以使用有限差分或有限元计算流体动力学方法来求解。喷嘴下游的流动不满足这一条件，需要采用直接模拟/蒙特卡罗方法。

Organic Radicals in Biomass Decomposition: Mechanisms & DynamicsBarney Ellison (an organic chemist) and John Daily (an engineer) propose a new set of experiments to study the thermal decomposition of biomass. A) Based on Daily's fluid-dynamical modeling studies, Ellison will design and build a novel apparatus that uses a high temperature nozzle to decompose simple biomass materials such as sugars, oxygen heterocycles, and alkylaryl ethers. The hyperthermal, supersonic nozzle will be especially designed for non-volatile, biomass samples. The cracking products will be monitored simultaneously by vacuum ultraviolet photoionization mass spectroscopy and infrared absorption spectroscopy. B) Biomass gasification produces stabilized organic radicals such as propargyl and allyl which undergo bimolecular reactions that form aryl rings (C6H6). The team proposes to develop a new double resonance measurement to examine the vibrational spectra of these radicals. This novel experiment will use a coupled pair of infrared and vacuum ultraviolet lasers. The team also proposes to study the thermal decomposition of small biomass samples under controlled conditions in a high temperature, supersonic nozzle. The objective of this work is to use a mass spectrometer and infrared spectroscopy to characterize the decomposition reactions of simple sugars and oxygen heterocycles. Such experiments could provide insight to the molecular weight growth reactions that lead to the formation of tars (aromatic compounds). A major problem in all biomass gasification schemes is the presence of aromatic compounds in the biomass gas stream. Model organic compounds, such as furan or furfural, will be pyrolyzed in a hyperthermal nozzle and products will be identified and characterized in the new experiment.To make maximum use of the hyperthermal nozzle as a flow reactor requires detailed characterization of the gas flow and heat transfer characteristics. Daily will model the turbulent gas flow to characterize the hot nozzle. The design of the nozzle assembly is such that the flow chokes at the inlet orifice and again chokes at the downstream end due to friction and heat transfer. Thus the flow within the nozzle is isolated from downstream conditions, which in this case is held at vacuum conditions. Of course, the real gas flow through the nozzle is neither adiabatic, frictionless, nor uniform, and to accurately model it requires a numerical approach. Where the flow is in the continuum domain, the Navier-Stokes equations apply and can be solved using finite difference or finite element Computational Fluid Dynamics approaches. The flow downstream of the nozzle does not meet this condition, and Direct Simulation/Monte Carlo approaches are required.