Catalytic dehydration of 1,2-butanediol to n-butyraldehyde in sub- and supercritical water

The change of the raw material basis to alternative sources, especially biomass, is advisable because of both the continuous shortage of fossile resources and the advancing change in world climate. Carbohydrates have the highest share in biomass. However, as they are overfunctionalized with chemically almost equal hydroxy groups, the high-scale industrial use of carbohydrates is restrained. In addition, the diversity and the high amount of functional groups of carbohydrates complicate the prediction of possible reaction pathways. This is the reason why monoalcohols and polyols are used as model compounds. One interesting reaction is the dehydration of 1,2-butanediol to n-butyraldehyde, an important chemical intermediate. Supercritical water is an appropriate reaction medium for dehydrations because of its special physical and chemical properties. The addition of acids enhances the reaction rate but at the same time intensifies corrosion. Sulfate salts, especially zinc sulfate, can have similar positive effects without increasing the corrosion potential. The experimental results of the catalytic influence of different metal sulfate salts on the dehydration of 1,2-butanediol to n-butyraldehyde are presented in this paper.