Influence of the carrier on the catalytic performance of impregnated phosphoric acid in the hydration of ethylene

The hydration of ethylene was studied at 300 degrees C and 50 bar using pho sphoric acid impregnated silica, titania, mixed silica/titania, zinc oxide/ titania, tin oxide/titania, zirconia and niobic acid carriers. The time on stream of "solid phosphoric acid" i.e. phosphoric acid on silica is limited because of the crystallization of the silica carrier to beta-crystobalite. The addition of titania to the carrier of the well-known "solid phosphoric acid" catalyst results in a decrease of the catalytic activity in the hydr ation. The phosphoric acid is strongly bound to the surface of this carrier The activity of the "solid phosphoric acid" is related to the presence of the liquid form of the deposited phosphoric acid (SLP=supported liquid phas e catalyst). The determination of the amount of free phosphoric acid gives an indication of the state of phosphoric acid on different carrier material s. This amount was determined by measuring the acid which could be leached out by submerging the catalyst in water. The activity of carrier materials impregnated with phosphoric acid could not be correlated to the concentrati on of acid sites at strengths of -8.2<H(0)less than or equal to-3.0. (C) 19 99 Elsevier Science B.V, All rights reserved.