Spectroscopic Measurement of pH in Aqueous Sulfuric Acid and Ammonia from Sub- to Supercritical Conditions
Spectroscopic Measurement of pH in Aqueous Sulfuric Acid and Ammonia from Sub- to Supercritical Conditions
复制标题
亚临界至超临界条件下硫酸和氨水 pH 值的光谱测量
DOI：
10.1021/ie960368y
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发表时间：
1996
影响因子：
4.2
通讯作者：
E. Gloyna
中科院分区：
文献类型：
--
作者：
Tao Xiang;K. Johnston;W. T. Wofford;E. Gloyna
用光学指示剂吖啶测定了硫酸水溶液和硫酸-氨混合物的pH值，温度为200 ~ 400℃，压力为3500 ~ 6000 psia （41.3 MPa）。由于质子化吖啶在超临界水（SCW）中的pKa变化较大，可测pH范围从密度为0.60 g/cm3时的2−4变为密度为0.24 g/cm3时的4.5−7。在3500 psia时，随着温度的升高，H2SO4的第一解离常数（Ka1）在350℃以上急剧下降，这主要是由于密度的降低，从而导致硫酸氢离子和氢离子的溶剂化。在恒压下，H2SO4相对于HCl的酸度随着温度的升高而增加，直至纯水的临界点。用氨滴定硫酸溶液，在380°C和5000 psia （34.5 MPa）下观察到弱酸-弱碱行为。在这些条件下，H2SO4 - NH4HSO4体系可用作缓冲液，以保持pH在3.5±0.25范围内。
The pH of aqueous sulfuric acid and sulfuric acid−ammonia mixtures was measured using the optical indicator acridine at temperatures from 200 to 400 °C and pressures from 3500 (24.1) to 6000 psia (41.3 MPa). Because of large changes in the pKa of protonated acridine in supercritical water (SCW), the measurable pH range shifts from 2−4 at a density of 0.60 g/cm3 to 4.5−7 at a density of 0.24 g/cm3. At 3500 psia, the first dissociation constant (Ka1) of H2SO4 decreases sharply with increasing temperature above 350 °C, primarily due to a reduction in density and thus the solvation of the bisulfate and hydrogen ions. The acidity of H2SO4 relative to HCl increases with increasing temperature at constant pressure up to the critical point of pure water. Based on titrations of sulfuric acid solutions with ammonia, weak acid−weak base behavior is observed at 380 °C and 5000 psia (34.5 MPa). At these conditions the system H2SO4−NH4HSO4 may be used as a buffer to maintain pH in the range 3.5 ± 0.25.