The adsorbed species on ZrO, and CeO, during CO hydrogenation forming branched carbon chains, especially isobutene, (over ZrO,), have been investigated by chemical trapping, in situ IR, and solid-state NMR methods.These indicated that methoxide and formate were present as the surface species on ZrO, . CO hydrogenation on ZrO, with pre-adsorbed methoxide or formate showed that the pre-adsorption of methoxide promotes the formation of the higher hydrocarbons containing mainly isobutene but that formate retards the reaction. Chemical trapping experiments on CeO, after CO hydrogenation at 523 and 673 K led to the formation of methane together with methanol, indicating the presence of methyl, p-methylene, or carbene as a surface species. q2-Formaldehyde was suggested to be the precursor of the methyl, p-methylene, or carbene species, the latter of which in turn gives C, species by insertion of CO. Following the products of CO hydrogenation and chemical trapping on CeO, at 523 K with time indicated that an aldol-condensation-type reaction leads to C, and branchedchain C, products from C, oxyhydrocarbon.
The CO–H2 reaction over ZrO2 was studied in detail. Methanol and isobutene were selectively formed at 473–523 and 623–673 K, respectively. The activation energies for C2, C3, and linear C4 hydrocarbon formation are 79, 84, and 96 kJ mol−1 (523–723 K), while that for branched-chain C4 hydrocarbons is about 210 kJ mol−1 (523–623 K). At 673 K the rate of C4 hydrocarbon formation is as follows: r=kPH2·Pco2, while those of C1, C2, and C3 are written by the functions having the maximum values regarding CO pressure. C4 hydrocarbons consist mostly of isobutene at the temperature. From these results it was concluded that isobutene is formed via different path from those of C1, C2, C3, and linear C4 hydrocarbons. The addition of high electronegative oxides such as SiO2 and Nb2O5 resulted in the decrease of isobutene and the increase of methane. The selective formation of isobutene proceeds over pure ZrO2 and ZrO2 modified with 3a Group and basic metal oxides. The nature of active site for isobutene formation was discussed.
Pressure swing adsorption (PSA) is one practical process for CO 2 separation from the exhaust gases in various industries, such as blast furnace gas in steel works. For optimum design of the PSA process, precise estimation of the adsorption equilibrium of mixed gases is desired. The ideal adsorbed solution (IAS) model is a reliable model for this estimation. However, the IAS model requires convergent calculations, which significantly increase the calculation load, especially in dynamic PSA simulations. An analytical formula such as the extended Langmuir (EX-LM) equation is more useful for calculation of the equilibrium adsorption amounts of mixed gases. A drawback of this equation, however, is the uncertainty of the thermodynamic consistency and consequently the accuracy of the calculation results. In order to clarify the necessary conditions for application of the EX-LM equation as an approximation of the IAS model with Langmuir equation (IAS-LM model), both the analytical features and the estimation accuracy of these different methods were evaluated. To evaluate the accuracy of the equations, the equilibrium adsorption amount of mixed gases consisting of CO 2 , N 2 , and CO, which are the major gas components of blast furnace gas in steel works, on 13X zeolite were measured experimentally. The results confirmed that the accuracy of the EX-LM equation varies depending on the gas pressure and also the affinities of the adsorbates. Under higher gas pressure conditions, more reliable calculation results were obtained by the IAS-LM model.
PSA system for the recovery of carbon dioxide from blast furnace is examined. From the results of bench plant experimental operation, it was revealed that recovery cost of carbon dioxide was below 2,000 yen per ton. Further experimental operation to assure the commercial PSA system is ongoing.
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