Silica membrane reactors

Nomura, M., Seshimo, M., Aida, H., Nakatani, K., Gopalakrishnan, S., Sugawara, T., Ishikawa, T., Kawamura, M., and Nakao, S. Preparation of a catalyst composite silica membrane reactor for steam reforming reaction by using a counter-diffusion CVD method. Industrial Engineering Chemistry Research, 2006, 45 (11), 3950. 

Giessler, S., Jordan, L., Diniz da Costa, J.C., and Lu, G.Q. Performance of hydrophobic and hydrophilic silica membrane reactors for the water gas shift reaction. Separation and Purification Technology, 2003, 32, 255. 

T. loannides and G.R. Gavalas, Catalytic isobutane dehydrogenation in a dense silica membrane reactor. /. Membr. Sci., 77 (1993) 207. 

Battersby et al. [35] investigated hydrostable cobalt-doped silica membrane reactors for WGS reaction. They used metal for hydro stabilizes the membrane. The H2/CO separation increases three times when reaction temperature increased from 150 to 250 °C. However, the reaction temperature has less influence on H2/CO2 separation. And also, increases in steam to CO ratio decrease the H2/CO and H2/CO2 separations. However, they observed the maximum CO conversion of 95%. 

S. Giessler, L. Jordan, J. C. Dinizda Costa, G. Q. Lu, PerfOTmance of hydrophobic and hydrophilic silica membrane reactors for the water gas shift reactitm, Sep. Purif. Technol. 32 (2003) 255-264. 

Battersby S, Duke MC, Liu S, Rudolph V, da Diniz Costa JC (2008) Metal doped silica membrane reactor operational effects of reaction and permeation for the water gas shift reaction. J Membr Sci 316 46... 

Even if the results are better than the ones obtained with a traditional packed bed reactor, there are many variables that can be used for optimizing the performance of a silica membrane reactor. One of these is the operative mean pressure that creates obstacles for the thermodynamic, but help for the permeation (Lee, Hacarlioglu, Oyama, 2004). This explains why a maximum can be found in the hydrogen and carbon monoxide yield as a function of pressure (Lee et al., 2004), as visible in Figure 4.5. 

Figure 4.5 Effect of pressure on the performance of a silica membrane reactor for dry reforming.

Table 5.4 WGS reaction conditions and performance using silica membrane reactors... 

Ghasemzadeh, K., Morrone, P., lulianelli. A., Liguori, S., Babaluo, A. A., Basile, A. (2013). H2 production in silica membrane reactor via methanol steam reforming modeling and HAZOP analysis. International Journal of Hydrogen Energy, 38, 10315—10326. 

Koutsonikolas, D., Kaldis, S., Zaspalis, V. T., Sakellaropoulos, G. P. (2012). Potential application of a microporous silica membrane reactor for cyclohexane dehydrogenation. International Journal of Hydrogen Energy, 37, 16302—16307. 

Nomura M., S. Kasahara, and S.-I. Nakao, Silica membrane reactor for the thermochemical iodine-sulphur process to produce hydrogen. Industrial and Engineering Chemistry Research, 2004.43 5874-5879. 

Key words microporous silica, membrane reactors, water-gas shift reaction, autothermal reforming, steam reforming. 

A silica membrane reactor will be efficient and effective therefore, when the membrane, working at full capacity, is able to process all the H2 produced by the reaction. This situation arises when the DaPe = 1 and simulations for silica membrane reactors for the water gas shift (WGS) reaction have indeed demonstrated that maximum CO conversion was achieved at DaPe close to 1 (Battersby et al., 2006 Ikuhara et al, 2007). Thus the DaPe number is a valuable metric to evaluate the potential performance of a membrane reactor and a valuable, yet simple, design tool to ensure that both the reactor and membrane components work together for maximum efficacy. However, the DaPe number does not take into account the selectivity of the membrane which obviously does affect the membrane reactor performance. Both experimental and simulation studies have shown that higher permeation results in higher conversion and product yield enhancements (Battersby et al., 2006 Boutikos and Nikolakis, 2010 Lim et al., 2010).That is not to say that a membrane with a low selectivity cannot be successfully utilized in a membrane reactor set-up. Provided the membrane has nominal selectivity for the desired products over reactants, the conversion of equilibrium-limited reactions will be enhanced in a membrane reactor system. However, the product purity will remain dilute and thus additional operational and capital expenditure will be required for further downstream processing. If the membrane is unable to separate gases then the system behaves as a packed bed reactor. 

The largest knowledge gap in the use of silica membrane reactor for the WGS is that all but a Umited number of published studies have focussed their investigations on the LT-WGS reaction. However, the LT-WGS reaction is already more thermodynamically favoured to high CO conversions and so the benefits of employing a membrane reactor are limited. The HT-WGS reaction on the other hand has a lower CO conversion and so there is a greater potential enhancement if a silica membrane reactor is employed. In the only study published so far, Galuszka et al. employed a... 

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