Membrane Fouling Mechanism of Phenol Hydroxylation Over Ultrafine TS-1 in a Side-Stream Membrane Reactor

Membrane fouling mechanism of phenol hydroxylation over ultrafine TS-1 in a side-stream membrane reactor

Xiulong Jiang, Fei she, Hong Jiang, Rizhi Chen*, Weihong Xing, Wanqin Jin

State Key Laboratory of Materials-Oriented Chemical Engineering, Jiangsu Key Laboratory of Industrial water-Conservation & Emission Reduction, Nanjing University of Technology, Nanjing 210009, P.R. China

*Corresponding author. E-mail address: rizhichen@163.com

Abstract: Titanium silicalites-1 (TS-1), as a new catalytic material first synthesized in 1983, has been investigated extensively for their high catalytic activity and selectivity in the selective oxidation of organic compounds [1]. Phenol hydroxylation over ultrafine TS-1 with H₂O₂ as the oxidant is a typical case. A major difficulty is the separation of TS-1 catalysts because the traditional methods cannot effectively recover the particles from the slurry due to the ultrafine size. One of the promising methods to solve the problem is to couple the heterogeneous catalytic reaction with the membrane separation to structure a membrane reactor, in which the membrane facilitates the in situ separation of ultrafine catalysts from the reaction mixture [2].

The membrane fouling is a key factor affecting the membrane lifetime and commercial viability of a membrane system. According to the definition provided by IUPAC, the membrane fouling is the process resulting in the loss of performance of a membrane due to the deposition of suspended or dissolved substances on its external surfaces, as its pore opening or within its pores [3]. Membrane fouling leads to the permeate flux decline, and thus more frequent membrane cleaning and replacement are necessary which increase the operating cost and energy consumption [4]. The membrane fouling mechanisms are complex and dependent on the physical and chemical characteristics of foulant and membrane.

Our previous works have demonstrated the feasibility of continuous phenol hydroxylation over ultrafine TS-1 in a side-stream membrane reactor. However, the membrane fouling mechanism is not clear, which are critical for membrane permeability and cleaning strategies. In this study, some special experiments were designed and carried out to investigate the membrane fouling mechanism of this process in the membrane reactor system and the corresponding cleaning method was developed.

Keywords: TS-1; phenol hydroxylation; membrane reactor; membrane fouling

References:

[1]       A. Corma, J. Catal., 216, 298-312 (2003).

[2]       R.Z. Chen, Z. Bu, Z.H. Li, et al., Chem. Eng. J., 156, 418-422 (2010).

[3]       W.J. Koros, Y.H. Ma, T. Shimidzu, J. Membr. Sci., 120, 149-159 (1996).

[4]       I. Chang, P. Le Clech, B. Jefferson, et al., J. Environ. Eng., 128, 1018-1029 (2002).

Acknowledgments

Financial supports from the National Key Science and Technology Program (2011BAE07B05), the National High Technology Research and Development Program (2012AA03A606) and the National Natural Science Foundation (20990222, 21106061) of China are gratefully acknowledged.