Modeling and Data Analysis of a Palladium Membrane Reactor for Tritiated Impurities Cleanup

A Palladium Membrane Reactor (PMR) is under consideration for the tritium plant for the International Thermonuclear Experimental Reactor (ITER). The ITER reactor exhaust will contain tritiated impurities such as water and methane. Tritium will need to be recovered from these impurities for environmental and economic reasons. For this purpose a promising device, PMR, has been proposed. The PMR is a combined permeator and catalytic reactor. Shift catalysts are used to foster reactions such as water-gas shift, H{sub 2}O + CO {yields} H{sub 2} + CO{sub 2}, and methane steam reforming, CH{sub 4} + H{sub 2}O {yields} 3H{sub 2} + CO. Due to thermodynamic limitations these reactions only proceed to partial completion. Thus, a Pd/Ag membrane, which is exclusively permeable to hydrogen isotopes, is incorporated into the reactor. By maintaining a vacuum on the permeate, product hydrogen isotopes are removed, enabling the reactions to proceed to completion. A model has been developed to study the complex interactions in a PMR so that the optimal design can be determined. The model accounts for the coupled effects of transport-limited permeation of hydrogen isotopes and chemical reactions. The permeation model is an extension of previous models that include the effects of temperature, wall thickness, reaction-side pressure, and permeate-side pressure. Reaction rates for methane steam reforming and the water-gas shift reaction are incorporated into the model along with the respective reverse reactions. The model is compared to PMR data and used to investigate the concentration and pressure profiles in the reactor. Due to the interactions of permeation and reaction complex profiles can be produced in a PMR. For example, the water concentration often increases after the inlet to the PMR to a maximum value, and then decreases to the low values expected with a PMR. Detailed information like this is required for the design and optimization of PMRs for the ITER tritium plant

Enhanced hydrogen production from thermochemical processes

To alleviate the pressing problem of greenhouse gas emissions, the development and deployment of sustainable energy technologies is necessary. One potentially viable approach for replacing fossil fuels is the development of a H2 economy. Not only can H2 be used to produce heat and electricity, it is also utilised in ammonia synthesis and hydrocracking. H2 is traditionally generated from thermochemical processes such as steam reforming of hydrocarbons and the water-gas-shift (WGS) reaction. However, these processes suffer from low H2 yields owing to their reversible nature. Removing H2 with membranes and/or extracting CO2 with solid sorbents in situ can overcome these issues by shifting the component equilibrium towards enhanced H2 production via Le Chatelier's principle. This can potentially result in reduced energy consumption, smaller reactor sizes and, therefore, lower capital costs. In light of this, a significant amount of work has been conducted over the past few decades to refine these processes through the development of novel materials and complex models. Here, we critically review the most recent developments in these studies, identify possible research gaps, and offer recommendations for future research

A comparison of estimation methods for computational fluid dynamics outflow boundary conditions using patient-specific carotid artery

Computational fluid dynamics simulations can provide important hemodynamic insights for investigating the effectiveness of carotid artery stenting, but its accuracy is dependent on the boundary conditions such as the outflow pressure, which is difficult to obtain by measurements. Many computational fluid dynamics simulations assume that the outflow pressure is constant (P = 0), but this method is likely to produce different results compared to clinical measurements. We have developed an alternative estimation method called the minimum energy loss method based on the concept of energy loss minimization at flow bifurcation. This new method has been tested on computational fluid dynamics simulation of two patients treated with carotid artery stenting, and its flow ratio at internal carotid artery and wall shear stress distribution was compared with the constant zero outlet pressure method. Three different procedure stages (prestent, poststent, and follow-up) were analyzed. The internal carotid artery flow ratio using the minimum energy loss method generally matched well with ultrasound measurements, but the internal carotid artery flow ratio based on zero outlet pressure method showed a large difference. Wall shear stress distributions varied between methods in response to the change in internal carotid artery flow rate. This study demonstrates the importance of accurate outlet boundary condition for assessing the long-term efficacy of carotid artery stenting and the risk of restenosis in treated patients

Adjuvant activities of quinonyl-N-acetyl muramyl dipeptides in mice and guinea pigs.

The adjuvant and tumor-suppressive activities of the quinonyl [2,3-dimethoxy-5-methyl-6-(9'-carboxynonyl)-1,4-benzoquinone (QS-10)] derivatives of N-acetyl muramyl dipeptides were examined. N-Acetyl muramyl-L-valyl-D-isoglutamine (MurNac-L-Val-D-isoGln), QS-10-MurNAc-L-Val-D-isoGln, and their methyl esters were shown to have potent adjuvant activity on the induction of delayed-type hypersensitivity to monoazobenzenarsonate-N-acetyl-L-tyrosine in guinea pigs and on the primary immune response against sheep erythrocytes in vitro; however, only QS-10-MurNAc-L-Val-D-isoGln methyl ester, i.e., QS-10-MurNAc-L-Val-D-Glu(OCH3)NH2 (quinonyl-MDP-66), was shown to be an active adjuvant for the induction of allogeneic killer T cells in mice and the suppression of tumor growth in syngeneic mice when it was administered as a suspension in phosphate-buffered saline. The effectiveness of the chain length of the quinonyl moiety in quinonyl-MDP-66 and the replacement of the L-valine residue with L-serine or L-threonine were also examined in comparison with the adjuvant and tumor-suppressive activities of quinonyl-MDP-66