Pore–Scale Study of Effects of Hydrate Morphologies on Dissociation Evolutions Using Lattice–Boltzmann Method

The natural gas hydrate, plentifully distributed in ocean floor sediments and permafrost regions, is considered a promising unconventional energy resource. The investigation of hydrate dissociation mechanisms in porous media is essential to optimize current production methods. To provide a microscopic insight in the hydrate dissociation process, we developed a Lattice Boltzmann (LB) model to investigate this multi–physicochemical process, including mass transfer, conjugate heat transfer, and gas transport. The methane hydrate dissociation is regarded as the reactive transport process coupled with heat transfer. The methane transport in porous media is modelled by the generalized LB method with the Bhatnagar-Gross-Krook (BGK) collision model. The mass transfer from hydrate to fluid phase is described by the hydrate kinetic and thermodynamic models. Finally, the conjugate heat transfer LB-model for heterogeneous media is added for solving the energy equation. In the numerical experiments, we primarily investigated the effects of different hydrate distribution morphologies such as pore–filling, grain–coating, and dispersed on the hydrate dissociation process. From simulations, we found that in general, the dissociation rate and the methane average density rapidly approached the maximum value and then decreased with fluctuation during the dissociation process. This trend is due to that the endothermic reaction heat decreased the temperature, resulting in decelerating the dissociation. The average temperature decreased to minimum value instantaneously as hydrate started to dissociate. After the minimum value, the average temperature would increase slowly, accompanied by the thermal stimulation and hydrate consumption, displaying a valley shape of the temperature curve. We also found that the whole dissociation process and permeability–saturation relations are significantly affected by the hydrate morphologies. Under the same hydrate saturation, the dispersed case dissolves the fastest, whereas the grain–coating case is the slowest. Furthermore, we proposed a general permeability–saturation relation applicable for three cases, filling the gap in the current relative permeability models. The LB model proposed in this study is capable to simulate the complex physicochemical hydrate dissociation process. Considering the impacts of thermodynamic conditions (P,T), we investigated their influences on the coupled interaction between dissociation and seepage under three different morphologies and proposed a general permeability–saturation relationship. The results can be applied as input to adjust parameters in the continuum model, and provide instructions for exploring clean energy with environmental considerations.

Methane Dissociation Over the Rh-Decorated Ni(100) Surface: A Density Functional Theory Investigation

The mechanism of methane dissociation on an Rh-decorated Ni(100) surface has been investigated Using density functional theory. The study includes the determination of the most stable adsorbate/adsorbent configurations of the species associated with subsequent reactions and generating the energy surface for 𝐶𝐻4 dissociation process. The Rhdecorated Ni(100) surface was found to be more favorable for the process than the NiRh(111) configuration, mainly due to lower the activation energy of 𝐶𝐻 decomposition reaction by 48.5%, leading to a higher conversion of 𝐶𝐻4 to carbon and hydrogen

Antiradical Activity of Beetroot (Beta vulgaris L.) Betalains

Flavonoids, phenolic acids, and anthocyanidins are widely studied polyphenolics owing to their antiradical activity. Recently, beetroot dyes have drawn an attention as possible radical scavengers, but scant information can be found on this topic. In this study selected compounds were investigated using computational chemistry methods. Implicit water at physiological pH was chosen as the environment of interest. Betalains’ dissociation process and electronic structure were examined, as well as the reactivity in six pathways against some common radicals, such as hydroxyl, hydroperoxide, superoxide, and nitric oxide. The study showed that all carboxyl groups are dissociated in the given conditions. The dissociation process impacts the electronic structure, which has consequences for the overall activity. Highly stabilized conjugated structures favor the electron–accepting type of scavenging reactions, primarily by a radical adduct formation mechanism. Betanidin and indicaxanthin were found to be the most promising of the compounds studied. Nevertheless, the study established the role of betalains as powerful antiradical dietary agents.