Solving the problem: Organic vapor causes the dissolution of molecular salts

Researchers at the Institute of Industrial Sciences, University of Tokyo, discover that organic vapors can induce the dissolution of molecular salts (ie, organic liquefaction), similar to water vapor-induced liquefaction. Credit: Institute of Industrial Sciences, University of Tokyo

It has long been known that when salt is stored in a humid environment, it absorbs water, dissolves some of the salt and causes it to clump. Now researchers from Japan have discovered that water vapor is not the only means that can do this.

In a study appearing in RSC Progressresearchers at the Institute of Industrial Science, The University of Tokyo, have revealed that organic vapors can cause the dissolution of molecular salts in a manner similar to water vapor.

This finding could have applications for cleaning up indoor pollutants. Volatile Organic Compounds (VOCs) are organic chemicals that exist as vapors at room temperature. The highest concentrations of VOCs are found indoors and some are harmful to human health and the environment. These compounds can be removed in a number of ways, but to date, removal has been through a phenomenon known as organic liquefaction has not been investigated.

“Liquidation has been used to collect atmospheric water vapor, but to our knowledge, organic vapor liquefaction has not yet occurred,” said lead author of the study, Kazuyuki Ishii. “We investigated this phenomenon using several solid molecular salts that react to organic vapors by undergoing solid to liquid changes.”

Liquefaction is the process by which a solid becomes liquid as a result of absorbing enough moisture from the air to dissolve in an aqueous solution. This has been reported for a number of chemicals, including: calcium chloride (CaCl2), which spontaneously create aqueous solutions in moist conditions. Simply increasing the ambient humidity can cause liquefaction (perceived as the change from solid to liquid) for some water-soluble chemicals, without heating or adding liquid. CaCl2for example, has been used as a chemical desiccant (ie, a water-absorbent substance used to induce or maintain dryness).

Credit: University of Tokyo

“We used CaCl2 powder in a typical control experiment, in which it clearly turned into a aqueous solution via water vapor-induced liquefaction,” explains senior author Kyoko Enomoto. “The changes we observed in molecular salts in the presence of an organic vapor were similar to the results of that control experiment under equivalent conditions.”

The researchers noted that the molecular salts changed from solid to liquid when chemicals such as chloroform (CHCl3) were used as organic solvents.

“We found that organic liquefaction is not rare – instead, appropriate organic liquefaction reactions to VOCs can be designed based on the general rule ‘as dissolves as’,” explains Ishii.

There is an urgent need to remove VOCs from indoor environments using organic solvents, especially industrial facilities that use large amounts. Based on the efficacy of CaCl2 as a chemical desiccant for capturing atmospheric water vapor, the results of this study provide a promising method for developing means to capture VOCs.

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More information:
Organic Liquefaction: Organic vapor induced solution of molecular salts, RSC Progress (2022). DOI: 10.1039/D2RA03390A

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