Zsm-5 made from siliceous ash

Abstract

The present invention relates in general to a method of making ZSM-5 zeolite. More specifically, the present invention relates to using plant waste material such as rice hull ash or any siliceous waste containing amorphous SiO as a source for SiO in making ZSM-5, thus producing a ZSM-5 that is lower cost than prior art methods. The method comprises providing siliceous ash having a carbon content between about 0 percent and 10 percent by weight of total rice hull ash, wherein the SiO content is greater than 90 percent by weight of total siliceous ash, and wherein the SiO and carbon are substantially amorphous. The synthesis of the ZSM-5 of the invention involves first suspending the siliceous ash in water. Next, a source of alumina is added to the suspension of siliceous ash. The source of alumina and siliceous ash are added such that the molar ratio of SiO to Al O in the ZSM-5 is in the range from approximately 15 to 150, thus forming a second suspension. Sodium Hydroxide is then added to the second suspension a quantity of NaOH, wherein the quantity added is such that the molar ratio of Na O to Al O in the ZSM-5 is between about 2 and 10, thus forming a third suspension. In order to precipitate the ZSM-5, the third suspension is seeded with silicalite and heated in a closed system at 150° C. to 220° C., thus yielding the ZSM-5.