Hydrogen Production via Photolytic Oxidation of Aqueous Sodium Sulfite Solutions

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• 作者：Cunping Huang ; Clovis A. Linkous ; Olawale Adebiyi ; Ali T-Raissi
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：July 1, 2010
• 年：2010
• 卷：44
• 期：13
• 页码：5283-5288
• 全文大小：191K
• 年卷期：v.44,no.13(July 1, 2010)
• ISSN：1520-5851

文摘

Sulfur dioxide (SO₂) emission from coal-burning power plants and refinery operations has been implicated as a cause of acid rain and other air pollution related problems. The conventional treatment of SO₂−contaminated air consists of two steps: SO₂ absorption using an aqueous sodium hydroxide solution, forming aqueous sodium sulfite (Na₂SO₃), and Na₂SO₃ oxidation via air purging to produce sodium sulfate (Na₂SO₄). In this process, the potential energy of SO₂ is lost. This paper presents a novel ultraviolet (UV) photolytic process for production of hydrogen from aqueous Na₂SO₃ solutions. The results show that the quantum efficiency of hydrogen production can reach 14.4% under illumination from a low pressure mercury lamp. The mechanism occurs via two competing reaction pathways that involve oxidation of SO₃²⁻ to SO₄²⁻ directly and through the dithionate (S₂O₆²⁻) ion intermediate. The first route becomes dominant once a photostationary state for S₂O₆²⁻ is established. The initial pH of Na₂SO₃ solution plays an important role in determining both the hydrogen production rate and the final products of the photolytic oxidation. At initial solution pH of 9.80 Na₂SO₃ photo-oxidation generates Na₂SO₄ as the final reaction product, while Na₂S₂O₆ is merely a reaction intermediate. The highest hydrogen production rate occurs when the initial solution pH is 7.55. Reduction in the initial solution pH to 5.93 results in disproportionation of HSO₃⁻ to elemental sulfur and SO₄²⁻ but no hydrogen production.