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Kingsbury, Zhentao Wu and K. Zyryanov, A. Nemudry and V. Checchetto, R. Brusa, A. Miotello and A. Broglia, P. Pinacci and A. Galuszka and T. Malygin, A. Malkov, S. Mikhaylovskiy, S. Dubrovensky, N. Basov, M. Ermilova, N. Orekhova and G.
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The main characteristics of the reactors are reported in Table 4. Methane is supplied by cylinders, while process steam and sweep steam are generated by a dedicated electrical boiler. Thanks to the partial conversion carried out in R, syngas fed to R contained a certain amount of hydrogen, allowing the membrane to be active just at the entrance of the reactor. R is organized as a shell-and-tube configuration, where the molten salts mixture flows in the shell side supplying reaction heat, and the catalyst is installed inside the tubes. R is also arranged in a shell-and-tube configuration, with the molten salts flowing on the shell side.
Catalyst and membrane are arranged according to a tube-in-tube configuration, with the catalyst in the annular section around the membranes tube. The latter is equipped with an inner tube to allow the sweep gas to flow in the permeate side. The permeate stream collected from R was cooled down in order to easily separate the sweep gas as a condensate.
The nickel noble metal-based catalysts deposited on silicon carbide foam were shaped in the form of a cylinder and an annular cylinder for R and R, respectively. A total of 10 Pd-based membranes on ceramic supports were arranged in R, developing an overall area of about 0. Each membrane had an outside diameter of 14 mm and a length of 80 cm. To improve the separation efficiency, superheated steam was employed as sweep gas in a countercurrent configuration. The main operating conditions of the catalytic tests carried out with the integrated membrane reactor are reported in Table 6.
The process scheme of the pilot unit is reported in Figure 3 [ 28 , 29 , 30 ]. After desulphurization, the natural gas was mixed with the process steam and preheated in the convective section of the reformer.
The retentate, poor in hydrogen, was routed to the CPO reactor properly mixed inside the reactor with a stream of pure oxygen from the gas cylinders. The resulted retentate was a syngas, whose composition could be adjusted on the basis of the membrane hydrogen recovery factor. As reported in Figure 3 , the CPO reactor could be operated in a standalone mode with an external CH 4 stream or fully integrated with the membrane, accordingly fed with retentate, as described above. Structured catalysts in the forms of honeycomb monolith and pellets, both based on noble metals, were used in the CPO reactor.
The main characteristics of the CPO reactor are reported in Table 7. The membrane-based GTL process was operated at the operating conditions reported in Table 8. The overall concept was tested in open architecture at pilot level and at a capacity of 0. The process scheme of the pilot unit is reported in Figure 4 [ 31 , 32 , 33 , 34 ].
Propylene production membrane reactor a Process scheme; b Pilot unit assembly. The catalytic units consist of a catalytic reactor, characterized by a tubular shape and made of AISI stainless steel SS ; the reactor was loaded with a platinum—tin-based catalyst. The catalytic bed loading was also optimized with inters in order to minimize the undesired side reactions occurring in the homogeneous phase, both before and after the catalytic bed on reactants and products streams. The separation unit is constituted by a Pd-based membrane prepared on an SS porous tube and having an overall permeation surface of 0.
The temperature of the three process devices was controlled by means of electrical heaters, driven by a controller—programmer.
Membranes For Membrane Reactors Preparation Optimization And Selection 2011
The units were then wrapped in a thick layer of insulating mat to minimize heat losses. The behavior of the two-stages reaction and separation based configuration was deeply investigated.
The experimental results in terms of membrane stability and feed conversion confirmed, from a technical point of view, the feasibility of the proposed architecture. The development of proper start-up and shut-down procedures, especially with respect to the heating-up and cooling-down sequences, assured a stable operation for the three membrane modules.
The results clearly evidenced the effect of membrane separation on shifting the reaction towards the product, once hydrogen was removed from the syngas stream, and a second reaction stage was foreseen.
Figure 5 a reports the experimental data collected on a two-stage membrane reforming when the MA membrane was in operation. Hydrogen purity of at least Because of the modular concept characterizing the open architecture, the performance for a higher number of reaction and separation stages could be easily extrapolated, as shown in Figure 5 b. Starting from the experimental results, the behavior of the system for a higher membrane area per stage as well for different values of sweep gas flow rate and reaction pressure could be extrapolated.
An experimental campaign on closed-architecture membrane steam reforming was carried out in order to check the overall system performance. The reforming outlet temperature was regulated by adjusting the inlet molten salts temperature.
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Despite the low reaction temperature, a very high feed conversion was observed due to the effectiveness of hydrogen removal from the reaction environment. The latter plays a major role in the integrated configuration, where H 2 partial pressure on the reaction side is quite low because of continuous withdrawals. The low reaction temperatures combined with a high feed conversion achievable with the integrated configuration allows to minimize the CO content in the retentate side, thus avoiding any post-shift reaction and accounts for a final retentate stream reach in CO 2 and under pressure.
With respect to a conventional steam reformer where the overall produced CO 2 is available diluted and at atmospheric pressure in the flue gas stream, the proposed architecture allows for a less energy-intensive CO 2 capture, due to the fact that it is available at s higher partial pressure. Although more complex from a technologic point view, requiring a new reactor design with respect to conventional one, being able to house a catalyst, a membrane, and sweep gas, the integrated membrane configuration benefits from a higher effectiveness in equilibrium shifting.
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The contextual hydrogen removal and production allow for a higher hydrogen recovery factor characterizing the integrated membrane architecture, which definitively means a higher feed conversion. The most relevant results in this application are reported in Figure 7 a,b. Figure 7 a shows the product composition on a dry basis at steady-state conditions measured at the outlet of reformer, the membrane separation, and the CPO reactor, respectively. The oxygen to carbon ratio was evaluated by taking into account the carbon contribution of CO and CH 4 in the retentate stream.
A significant reduction in hydrogen content was observed in the retentate stream due to hydrogen recovery carried out by the first-stage membrane, whereas the concentration of other components increased, since the mixture became more concentrated. In addition, the performance of the membrane system resulted stable for more than h of continuous operation. Looking at the economics of the novel process for syngas production, it can be observed that the solution consisting of the CPO reactor integrated with the reformer and the membrane enables for a reduction in oxygen consumption, since a portion of feed conversion is achieved in the upstream reformer stage.
The removal of hydrogen in the first membrane module has the double role to favor both reactions of partial oxidation of methane and steam reforming inside the CPO reactor. In Figure 7 b, the comparison of oxygen consumption is reported, observed with both standalone and integrated configuration.
The oxygen consumption was referred to the natural gas available at the inlet of the reaction scheme in order to have a direct comparison. This can be translated into a lower operating temperature for the CPO section, accordingly with a difference in the outlet gas composition.