碳酸乙烯酯合成过程的反应吸收多场协同分析及数值模拟

Multi-Field Synergy Analysis of Reaction-Absorption Coupling Process and Numerical Simulation for Ethylene Carbonate Synthesis

为提高尿素醇解法合成碳酸乙烯酯的收率,通过在酯化反应进行的同时吸收副产物氨气来实现全过程的强化.首先针对磷酸溶液中NH3鼓泡吸收的具体过程进行了多场协同分析,获得了反应吸收耦合过程强化的理论依据;进而运用流体体积函数多相流模型对单个NH3气泡的化学吸收过程进行了数值模拟.结果表明:受气膜传质控制的NH3化学吸收,实质上是气流速度场和压力梯度场共同作用的结果,传质效率直接受两场协同度的影响,该协同数不仅取决于两场标量值的大小,也取决于它们的矢量夹角,当夹角为0°时,场协同数最大,相应地对流传质系数就越大.在鼓泡吸收过程中,气液两相的流动促使NH3气泡内部气流形成由中心向四周发散的微小涡流,气流流场向着与相界面附近的压力梯度场达到最优协同度的方向发展,最大化了场协同数,有利于强化传质.

To improve the productivity of ethylene carbonate from the esterification of urea and ethylene glycol,the synthesis process is enhanced by removing by-product ammonia via bubbling in phosphoric acid solution.Multi-field synergy principle is employed to analyze the chemical absorption process,then numerical simulation is carried out for absorption of single ammonia bubble with the volume of fluid model.The results show that the chemical absorption of ammonia,which controlled by convective mass transfer,is essentially affected by the synergy of velocity and pressure gradient fields.The synergy is measured with mass transfer field synergy number,which is determined by scalar quantities of the two vector fields,and mostly,by their included angle.While the angle gets zero,the field synergy number reaches to the maximum,which leads to a larger mass transfer coefficient.During the bubbling absorption process,ammonia current inside the bubble facilitates forming tiny vortexes to give rise to the optimized ammonia velocity field and to optimize the synergy with pressure gradient field at gas-liquid interface,thus the field synergy number is maximized and the mass transfer efficiency of ammonia is consequently heightened.