Green and efficient preparation of hollow titanium silicalite-1 by using recycled mother liquid

Abstract

A green and efficient preparation of hollow titanium silicalite-1 (TS-1) has been developed by using recycled mother liquid in the post-synthesis treatment. The parent TS-1 was hydrothermally treated with different bases, and hollows appeared in the crystals, due to the controlled desilication from framework. In the presence of tetrapropylammonium cation (TPA+) during post-synthesis treatment, more hollows were generated, and higher concentration of Ti inside crystals was obtained. The reaction substrates could get sufficient contact with the active centers, and this hollow TS-1 exhibited superior catalytic activity in the propylene epoxidation compared to that of parent sample. When the sample was prepared by using ethanolamine and TPABr as desilication medium, the obtained mother liquid can be reused in the next post-synthesis treatment. In the recycling process, the added amount of ethanolamine and TPABr was only 50% and 25% of the amount for the first post-synthesis treatment, respectively. Even the mother liquid was recycled eight times, all obtained hollow TS-1 showed similar catalytic activity in the propylene epoxidation to that of the sample prepared by using TPAOH as desilication medium. This process can almost eliminate the discharge of waste liquid to achieve a sustainable development, and save the cost of hollow TS-1 production.