Uptake of Gas-Phase Nitrous Acid by pH-Controlled Aqueous Solution Studied by a Wetted Wall Flow Tube
Uptake of Gas-Phase Nitrous Acid by pH-Controlled Aqueous Solution Studied by a Wetted Wall Flow Tube
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DOI：
10.1021/jp8051483
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发表时间：
2008-11-27
影响因子：
2.9
通讯作者：
Mafune, Fumitaka
中科院分区：
文献类型：
--
作者：
Hirokawa, Jun;Kato, Takehiro;Mafune, Fumitaka
采用湿壁流动管研究了气相亚硝酸（HONO）在pH控制的水溶液中的吸收动力学。通过化学电离质谱仪以高灵敏度的方式选择性地测量暴露于水溶液后HONO的气相浓度。发现气态HONO的吸收速率取决于溶液的pH。对于中性和碱性溶液的吸收，观察到气相浓度呈指数衰减，表明吸收完全受气相扩散的限制。另一方面，被酸性溶液的吸收被发现是由气相扩散和液相过程，如物理吸收和可逆的酸解离反应。衰减进行了分析的速率方程使用的时间依赖性的吸收系数涉及的液体表面的饱和度。虽然使用原液报告的物理和化学参数计算的吸收过程很好地描述了pH = 2-3时溶液的吸收过程，但4 < pH < 7时溶液的吸收速率偏离计算值。目前的结果可以表明，在液体表面的pH值低于在本体液体，这是负责从气相到液相的传质的附加阻力。
Uptake kinetics of gas phase nitrous acid (HONO) by a pH-controlled aqueous solution was investigated by using a wetted wall flow tube. The gas phase concentration of HONO after exposure to the aqueous solution was measured selectively by the chemical ionization mass spectrometer in a high sensitive manner. The uptake rate of the gaseous HONO was found to depend on the pH of the solution. For the uptake by neutral and alkaline solutions, the gas phase concentration was observed to decay exponentially, suggesting that the uptake was fully limited by the gas phase diffusion. On the other hand, the uptake by the acidic solution was found to be determined by both the gas phase diffusion and the liquid phase processes such as physical absorption and reversible acid dissociation reaction. The decay was analyzed by the rate equations using the time dependent uptake coefficient involving the saturation of the liquid surface. While the uptake processes by the solution at pH = 2-3 were well described by those calculated using the physical and chemical parameters reported for the bulk, the uptake rates by the solution at 4 < pH < 7 deviate from the calculated ones. The present result can suggest that the pH at the liquid surface is lower than that in the bulk liquid, which is responsible for the additional resistance of mass transfer from the gas to the liquid phase.