Process for Hydrogen Production from Sodium Sulfite Solutions Resulting from Capture of SO2 from Coal Flue Gas
Researchers at the University of Central Florida have developed a novel ultraviolet (UV) photolytic process for the production of hydrogen from aqueous Na2SO3 (sodium sulfite) solutions created by the absorption of SO2 using an aqueous sodium hydroxide solution as a mechanism to treat SO2 emissions from sources such as coal-fired power plants and refineries.
A paper on their work was published 1 June in the ACS journal Environmental Science & Technology.
A number of technologies have been employed for the capture and disposal of SO2 from a flue gas stream. Those processes consist mainly of an absorption step and an oxidation step. A typical example is the use of a dilute aqueous sodium hydroxide (NaOH) solution to absorb SO2 from flue gas, forming an aqueous Na2SO3 solution. Before disposal the solution must be purged with air to oxidize Na2SO3 into Na2SO4. Alternatively, oxidation of an aqueous Na2SO3 solution can be carried out for the production of high purity clean hydrogen fuel.
—Huang et al.
Results from using the ultraviolet (UV) photolytic process for production of hydrogen from aqueous Na2SO3 solutions showed 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...The highest hydrogen production rate occurs when the initial solution pH is 7.55.
—Huang et al.
Cunping Huang, Clovis A. Linkous, Olawale Adebiyi and Ali T-Raissi (2010) Hydrogen Production via Photolytic Oxidation of Aqueous Sodium Sulfite Solutions. Environ. Sci. Technol., Article ASAP doi: 10.1021/es903766w