Etherification of n-butanol to di-n-butyl ether over Keggin-, Wells-Dawson-, and Preyssler-type heteropolyacid catalysts.

Etherification of n-butanol to di-n-butyl ether was carried out over various structural classes of heteropolyacid (HPA) catalysts, including Keggin- (H3PW12O40), Wells-Dawson- (H6P2W18O62), and Preyssler-type (H14[NaP5W30O110]) HPA catalysts. Successful formation of HPA catalysts was well confirmed by FT-IR, 31P NMR, and ICP-AES analyses. Acid properties of HPA catalysts were determined by NH3-TPD (temperature-programmed desorption) measurements. Acid strength of the catalysts increased in the order of H14[NaP5W30O110] < H6P2W18O62 < H3PW12O40. The catalytic performance of HPA catalysts was closely related to the acid strength of the catalysts. In the etherification of n-butanol to di-n-butyl ether over various structural classes of HPA catalysts, Conversion of n-butanol and yield for di-n-butyl ether increased with increasing acid strength of HPA catalysts. Among the catalysts tested, Keggin-type (H3PW12O40) HPA catalyst with the strongest acid strength showed the best catalytic performance. Acid strength of HPAs served as an important factor determining the catalytic performance in the etherification of n-butanol to di-n-butyl ether.