A PROCESS FOR CONTACTING LIQUID AND GASEOUS REACTANTS WITH TWO DIFFERENT PARTICULATE CONTACT SOLIDS, EACH HAVING A DIFFERENT SPECIFIC PHYSIOCHEMICAL FUNCTION RELATIVE TO SAID REACTANTS. THE REACTANTS ARE PASSED UPWARDLY THROUGH A BED OF ONE OF THE SOLIDS WHICH IS COMPOSED OF PARTICLES HAVING SIZES GREATER THAN 40 MESH, U.S., AT VELOCITIES WHEREBY THE BED IS EXPANDED AND DESIGNATED AS EBULLATED. THE SECOND SOLID IS A POWDER, THE PARTICLES OF WHICH ARE IN A SIZE RANGE LESS THAN 40 MESH, U.S., AND HAS A TRANSPORT VELOCITY EQUIVALENT TO THAT REQUIRED FOR 20 TO 100% EXPANSION OF THE LARGER SOLIDS WHICH CONSTITUTE THE EBULLATED BED. THE POWDER IS INTRODUCED TO THE LIQUID FEDD PRIOR TO ITS ENTERING THE CONTACT ZONE AND THE POWDER TRANSVERSES THROUGH AND IS REMOVED FROM THE CONTACT ZONE ALONG WITH THE REACTION PRODUCTS, WHILE THE LARGER CONTACT SOLIDS ARE RETAINED IN THE ZONE.