phosphrus modified zeolites heteropoly acids and various sulfonated resins the use of a sulfonated solid resin catalyst is preferred these resin type catalysts include the reaction products of phenolformaldehyde resins and sulfuric acid and sulfonated polystyrene resins including those crosslinked with divinylbenzene further information on suitable etherification catalysts may be obtained by reference to u s pat nos 2 480 940 2 922 822 and 4 270 929 and the previously cited etherification references a broad range of suitable etherification conditions includes a superatmospheric pressure sufficient to maintain the reactants as a liquid phase generally below about 200 bars and a temperature between about 30 u00b0 c 85 u00b0 f and about 100 u00b0 c 210 u00b0 f due to the presence of additional light materials pressures in the range of 10 to 40 bars are preferred a preferred temperature range is from 50 u00b0 c 120 u00b0 f to 100 u00b0 c 210 u00b0 f the reaction rate is normally faster at higher temperatures but conversion is more complete at lower temperatures high conversion in a moderate volume reaction zone can therefore be obtained if the initial section of the reaction zone e g the first two thirds is maintained above 70 u00b0 c 160 u00b0 f and the remainder of the reaction zone is maintained below 50 u00b0 c 120 u00b0 f this may be accomplished most easily with two reactors the ratio of feed alcohol to isoolefin should normally be maintained in the broad range of 1 1 to 2 1 with the.