Dehydration of castor oil over H₆P₂W₁₈O₆₂@MCM-41

Abstract

The H₆P₂W₁₈O₆₂@MCM-41 catalyst (C-1) modified by dodecyltrimethoxysilane (DTMS) showed excellent catalytic performance during the dehydration of castor oil to produce dehydrated castor oil (DCO). The castor oil conversion and the DCO selectivity on H₆P₂W₁₈O₆₂-DTMS@Zr-MCM-41 (C-2) are higher than those of C-1. The dispersity of H₆P₂W₁₈O₆₂ is remarkably improved by an appropriate amount of DTMS modification on the C-2 because of the steric effect between the DTMS and H₆P₂W₁₈O₆₂. Therefore, the total acidic amount of C-2 is more than that of C-1, but the acidic intensity is weaker than that of C-1. The more total amount of acidity is good for improving the castor oil conversion, and the weaker acid strength leads to less carbon deposition. The amount of Brønsted acid sites is higher than that of C-1. However, the amount of Lewis acid sites is less than that of C-1, so the ration of B/(B + L) is higher than that of C-1, which is good for improving the DCO selectivity. The C-2 catalyst has proper hydrophobicity by grafting the silane group of DTMS on the surface of MCM-41, which can suppress the leaching of H₆P₂W₁₈O₆₂, because the water produced in reaction is not easily adsorbed on the surface of the catalyst. Proper lipophilicity is conducive to the absorption of castor oil to the surface of the catalyst, which can accelerate the reaction. The stability of C-2 is obviously higher than that of C-1, because the coke deposited and W elemental leaching on C-1 are more serious than those of C-2. Under the optimized reaction conditions: 220 °C, 2.8 wt% amount of C-2, H₆P₂W₁₈O₆₂ loading of 12 wt%, DTMS loading of 3.5 wt%, the iodine and hydroxyl value of product are 148.6 and 8.9, respectively.