Membrane reactor technology for C5/C6 hydroisomerization.

In this paper, we propose an improved hydroisomerization process, making use of membrane reactor technology. Linear alkanes are selectively supplied from a hydrocarbon feed (consisting of branched and linear alkanes) through an inert tubular membrane to a packed bed of catalyst. The results indicate that n-, mono- and di-branched components in a gas mixture can be separated with a selectivity factor of greater than 20 with a zeolite membrane under dedicated parameter settings. The RON-value of the product was calculated to be as high as 90 in a single pass reactor, which is 50 points higher than the feed value. The flux through the membrane could be optimized to give a STY/ATY ratio for the reactor of 877 m-1, which falls within the limits of technical feasibility.

Molecular-dynamics analysis of the diffusion of molecular hydrogen in all-silica sodalite.

In order to investigate the technical feasibility of crystalline porous silicates as hydrogen storage materials, the self-diffusion of molecular hydrogen in all-silica sodalite is modeled using large-scale classical molecular-dynamics simulations employing full lattice flexibility. In the temperature range of 700-1200 K, the diffusion coefficient is found to range from 1.610(-10) to 1.810(-9) m(2)/s. The energy barrier for hydrogen diffusion is determined from the simulations allowing the application of transition state theory, which, together with the finding that the pre-exponential factor in the Arrhenius-type equation for the hopping rate is temperature-independent, enables extrapolation of our results to lower temperatures. Estimates based on mass penetration theory calculations indicate a promising hydrogen uptake rate at 573 K.

Fully coordinated silica nanoclusters: (SiO2)N molecular rings.

A new form of finite silica with edge-sharing SiO2 units connected in a ring is proposed. High-level density-functional calculations for (SiO2)(N), N=4-14, show the rings to be energetically more stable than the corresponding (SiO2)(N) linear chains for N>11. The rings display frequency modes in remarkable agreement with infrared bands measured on dehydrated silica surfaces indicating their potential as models of strained extended silica systems. Silica rings, if synthesized, may also be useful precursors for new bulk-silica polymorphs with tubular or porous morphologies.