Mother Liquor Recycle In The Low-cost Synthesis Of TS-1Molecular Sieve

TS-1is a titanium silicalite zeolite with MFI structure. It shows excellent performance on selective oxidation with the incorporation of Ti atoms into the framework. The catalytic system, which is composed of TS-1and dilute H2O2as oxidant under mild conditions, has been widely used in selective oxidation field. Relative to traditional oxidation system, it has the advantages such as energy-saving, economy and environmental friendly for operating easily and reducing environmental pollution. The classic method to synthesize TS-1uses tetrapropylammonium oxide (TPAOH) as the template, while a cheaper one is to use tetrapropylammonium bromide (TPABr). However, the use of template leads to a high cost of synthesis. Meanwhile, the discharging of synthesis mother liquor containing large amount of template and organic base would lead to serious environmental pollution which is unfavorable to industrial production.This paper investigates two different ways to decrease the cost of synthesis. One is reducing the amount of template in the synthesis system. The other is mother liquor recycle. The main research results are as follows:1. To optimize the synthesis of TS-1, the influence of different silicon sources and synthesis conditions were studied. It shows that alkaline silicon source (JN-30) is better than neutral (fumed silica) and acid ones (HP-20). Moreover, the addition of crystal seeds in synthesis system could accelerate crystallization.2. Reducing the amount of template added in initial gel would slow down the rate of crystallization. The addition of n-butylamine with proper amount would short the time of crystallization, which indicates that n-butylamine may play a role of structure-directing agent. In addition, seeds also show the structure-directing effect and accelerate the crystallization.3. The recycling experiments of mother liquor show that supplementing with a little amount of raw materials could synthesize high quality and steady TS-1.4. During the TS-1crystallization, the amount of TPABr in mother liquor decreased firstly and then kept at a certain value as time passed, while the amount of n-butylamine decreased at first and then increased rapidly to a maximum value. It means that, during the crystallization process of TS-1. TPA+in liquor is consumed and Ti enters into the zeolite framework gradually, which obey the liquid phase transformation mechanism raised by Kerr.