Reforming sorption-enhanced

In the sorption-enhanced reforming (SER) process, one of the gaseous reaction products (C02) of the catalytic reforming reaction is separated from the reaction zone by sorption. As a result, the equilibrium of the reaction is shifted toward products according to the Le Chatelier s principle. Balasubramanian et al. [18] studied the SMR reaction in the presence of CaO as a C02 acceptor. Thus, in addition to reactions 2.4 and 2.6, the reaction of C02 with the C02 acceptor (CaO) takes place in the reaction zone ... 

Air Products and Chemicals pioneered the use of these potassium carbonate promoted hydrotalcite-based materials (K-HTC) for sorption-enhanced reforming of methane [26]. Mixing the K-HTC with a SMR catalyst in a 2 1 ratio gave high (90+%) conversions of methane at temperatures as low as 400 °C. In the first instance Ni-based catalysts were used, but they were not resistant to the environ-... 

Ordinary Methane Reforming Sorption-enhanced Reforming... 

Fig. 14.8 Schematic representation of sorption-enhanced reforming. The topmost reactor is in reforming mode, the bottom one is being regenerated using steam.

Ding and Alpay also studied sorption-enhanced reforming with K-HTC as sorbent [28], using a commercial Ni-based catalyst. They found that the SER process benefits from higher pressures and that lower steam to methane ratios can be used than in ordinary reforming. Reijers et al. [25] have shown that K-HTC is an effective sorbent between 400 and 500 °C, with an C02 uptake of approx. 0.2 mmol g 1. This capacity is low compared with calcium oxides and lithium zirconates. Above 500 °C, the C02 sorption capacity of K-HTC decreases rapidly to zero [36]. 

Fig. 14.9 Sorption-enhanced reforming experiment. (Originally published in Reijers et al., Ind. Eng. Chem. Res., 2006 [25] republished with permission from the American Chemical Society).

The following catalytic and material challenges can be extracted from an overview of the literature on membrane and sorption-enhanced reforming ... 

There is a need for low-cost methane steam reforming catalysts that are active at low temperature and resistant to coke formation under membrane reactor conditions. Low-cost (Ni-based) catalysts are also needed that can withstand regeneration conditions in a sorption-enhanced reformer. 

PBRs have been also investigated for sorption enhanced reforming by using Ca-based sorbent for CO2 combined with CuO to supply the heat of reaction during the regenerative stage [64, 65]. 

Among several enhanced fuel conversion processes, the most investigated are the Sorption-Enhanced Reforming (SER) process and Sorption-Enhanced Water Gas Shift (SEWGS). The first combines the separation of one product, typically CO2, within the reforming process, while the second applies it to the water-gas shift (WGS) reaction. 

Sorbents that are considered in the literature for sorption-enhanced reforming process are potassium promoted hydrotalcite (K-HTC), lithium orthosilicate (LiSi04), lithium zir-conate (LiZr03), sodium zirconate (Na2Zr03) and calcium oxide (CaO). The affinity of a sorbent to a molecule can be expressed by the equilibrium partial pressure at different temperatures. For example, the equilibrium partial pressure of carbon dioxide for different sorbents is shown in Figure 6.2. 

In sorption-enhanced reforming (SER) reactors, one of the products is extracted from the reaction zone, thus shifting the reaction equilibrium to the product side. In SER, the methane steam-reforming catalyst is mixed with a CO2 sorbent ( acceptor ). The CO2 produced during the reaction is adsorbed and the reverse... 

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