Abstract
Hierarchical HZSM-5 membranes were prepared on the inner wall of stainless steel tubes, using amphiphilic organosilane (TPOAC) and mesitylene (TMB) as a meso-porogen and a swelling agent, respectively. The mesoporosity of the HZSM-5 membranes were tailored via formulating the TPOAC/Tetraethylorthosilicate (TPOAC/TEOS) ratio and TMB/TPOAC ratio, in synthesis gel, and the prepared membranes were systematically characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption–desorption, N2 permeation, inductively coupled plasma (ICP), in situ fourier transform infrared (FT-IR), ammonia temperature-programmed desorption (NH3-TPD), etc. It was found that the increase of the TPOAC/TEOS ratio promoted a specific surface area and diffusivity of the HZSM-5 membranes, as well as decreased acidity; the increase of the TMB/TPOAC ratios led to an enlargement of the mesopore size and diffusivity of the membranes, but with constant acid properties. The catalytic performance of the prepared HZSM-5 membranes was tested using the catalytic cracking of supercritical n-dodecane (500 °C, 4 MPa) as a model reaction. The hierarchical membrane with the TPOAC/TEOS ratio of 0.1 and TMB/TPOAC ratio of 2, exhibited superior catalytic performances with the highest activity of up to 13% improvement and the lowest deactivation rate (nearly a half), compared with the microporous HZSM-5 membrane, due to the benefits of suitable acidity, together with enhanced diffusivity of n-dodecane and cracking products.
Highlights
Over the last few decades, catalytic cracking of liquid hydrocarbons has been well-established for thermal management system of hypersonic aircrafts [1,2]
With the TPOAC/TEOS ratios in the synthesis gel growing from 0 to 0.15, the relative crystallinities of the HZSM-5 membranes decreased gradually, which was in line with the observation of Peng et al [24] and Cho et al [31]
Wang et al observed that the increase in thickness of the zeolite membranes would reduce the intensity of the stainless steel support signals [20]
Summary
Over the last few decades, catalytic cracking of liquid hydrocarbons has been well-established for thermal management system of hypersonic aircrafts [1,2]. Zhang et al prepared hierarchical coating membranes with desilication-treated HZSM-5 zeolites, and found that the catalytic cracking performance was significantly improved, due to the enhanced diffusion properties of the coatings [13]. We synthesized wall-coated meso-HZSM-5@MCM-41 zeolites, and found that the hierarchical structure facilitated acid site accessibility and, improved the catalytic cracking activity [15]. An important concern for further improving the catalytic cracking performances of zeolite membranes, is to prepare a membrane with a high mesoporosity. The texture properties, diffusivity, and acidities of the synthesized membranes were characterized by various instrumental methods These membranes were employed as catalysts for catalytic cracking of the supercritical n-dodecane
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