Search

An explainable supervised machine learning was used to inspect the insight into the former selection for methane hydrate forming systems in the presence of water-soluble organic molecules. The former is an important ingredient that allows methane hydrate formation at conditions closer to the ambient in solidified natural gas technology (SNG). Over 800 samples were collected from literatures and experiments and utilized for supervised modeling. The data were split into train and test sets with an 80:20 ratio, preprocessed, and used to build predictive models, which are linear regression-based and tree-based models. Categorical Boosting Machine Regressor (CatBoost) performed the best on the equilibrium temperature prediction using 10 relevant attributes on the unseen data set with R2of 0.973, RMSE of 1.375, and MAPE of 0.269 %. Feature selection suggested that only 7 necessary attributes are adequate to make a model, which is comparable to the full model. The model was then explained via Shapley Additive Explanations (SHAP) analyses. Cyclic molecules without hydrogen bond donors, with low polarity, at a mole fraction in the range of 0.02 – 0.07 were suggested to be effective formers that can shift the equilibrium temperature to higher levels.

The hydrate morphology pattern plays a critical role in the reactor design for hydrate-based gas storage/separation technology. This work investigated the morphology of mixed methane–THF hydrate formation using salt water (3.5 wt % NaCl) instead of pure water at 288.2 K and 8 MPa. The result indicated that the nucleation occurred at the gas/liquid interface and then the hydrates grew along the wall of the crystallizer column. After a specific time interval, the hydrates gradually grew downward until they completely covered the bulk solution. This work applied 500 ppm of co-promoters, including sodium dodecyl sulfate (SDS) and three amino acids─valine, leucine, and methionine to improve the kinetics of mixed hydrate formation. The presence of SDS in the system resulted in distinct mixed hydrate formation patterns. After hydrate nucleation at the gas/liquid interface, most of the hydrates predominantly grew downward and enveloped the solution within a few minutes. Moreover, the mushy hydrates gradually transformed into stiff hydrates over time. Three amino acids resulted in the same hydrate patterns as those formed in the absence of a co-promoter, but the formation was completed more rapidly. The kinetic data indicated that using salt water for the formation of mixed methane–THF hydrates resulted in low hydrate formation kinetics. The presence of SDS significantly enhanced the kinetics of hydrate formation but decreased the final gas uptake by about one-half. Additionally, it was discovered that the presence of amino acids accelerated the hydrate formation kinetics while having a negligible effect on the final methane uptake.

The solidified natural gas (SNG) technology via hydrates is a promising and potential method for storing natural gas. It offers a compact mode of natural gas storage with high degree of safety. In this work, we present the synergistic effects of tetrahydrofuran (THF), hollow silica (HS), and sodium dodecyl sulfate (SDS) in enhancing the kinetics of mixed methane–THF hydrate formation at 6 MPa and 293.2 K in an unstirred reactor configuration. HS at the low loading of 0.5% w HS/v in 5.56 mol % THF solution used in the current study is an innovative approach to improve the surface contact area resulting in kinetic enhancement at moderate conditions (low driving force). However, the mixture of 0.5% w HS/v in 5.56 mol % THF solution resulted in a long induction time (about 400 min), which is not favorable for the SNG technology. Addition of SDS decreased the induction time and increased the hydrate formation rate under similar experimental conditions. The induction time significantly decreased with the increase in the SDS concentration. Additionally, the presence of SDS played a key role in influencing the temperature profile and the hydrate morphology during mixed hydrate formation. The methane gas uptake was 0.0591 (±0.0007) and 0.0615 (±0.0023) mol of methane/mol of water without and with SDS, respectively. Thermal stimulation with ΔT= 15 K was employed to recover methane from hydrates. A recovery of 96–98% of the stored methane gas from the hydrates formed with and without SDS was demonstrated. Interestingly, the presence of HS was effective in preventing the foam generation during hydrate dissociation in the presence of SDS.

This paper examines the effect of metal loading (Zr-, V-, Ti-, and K-compounds) on the hydrogen storage property of mechanically milled graphite. The hydrogen adsorption took place at room temperature and 11 MPa measured by thermal volumetric analysis. The results showed that the graphite loaded with ZrCl4 provided a maximum hydrogen storage capacity of 0.6 wt%. Moreover, a milling time of 2 h seems to be the best, offering the highest hydrogen adsorption capacity due to the high specific surface area and the appropriate pore diameter created after the milling. In addition, it was found that the transition metals (ZrCl4 and VCl3) could stabilize the graphite structure and enlarge the gap between the grapheme layers to be suitable trapping sites for hydrogen adsorption. On the other hand, the K2CO3 and TiO2 loaded graphite did not show any improvement for hydrogen adsorption.

Solidified natural gas is an appealing option for storing natural gas in the form of clathrate hydrates. However, it has some limitations, particularly the slow rate of hydrate formation and the requirement for severe operating conditions. To overcome these constraints, one approach is to introduce promoters into the system to enhance the hydrate formation rate. Amino acids have been reported as kinetic promoters with the potential to improve the methane hydrate formation. In this work, the effect of three different side-chain amino acids (l-methionine, l-leucine, and l-valine) on methane hydrate formation and dissociation was investigated in terms of kinetics and morphology. The experiments were conducted at 8 MPa and 277.2 K using a hybrid combinatorial reactor approach at various amino acid concentrations (0.10 to 1.00). The results showed that the presence of amino acids significantly decreased the induction time and increased the rate of methane hydrate formation. In addition, l-methionine was shown to be the most effective as a kinetic promoter in this work. However, the final methane uptake and the water to hydrate conversion were the same in all experiments. For all the investigated experiments, the morphology of methane hydrate formation exhibited a similar pattern, including methane bubbles and capillary channels. In terms of hydrate dissociation, methane recovery was greater than 95% in all studies, and no foam was generated during hydrate dissociation, which is favorable for large-scale applications.

Abstract: Adsorption of the equilibrium mixture of 1,5-, 1,6- and 2,6-dimethylnaphthalene (DMN) was investigated on a series of alkaline and alkaline earth ion-exchanged faujasite zeolites using pulse test and breakthrough techniques. It was found that the adsorption of the DMNs would proceed through a complex mechanism governing by at least molecular diffusion, acid-base interaction, preferential interaction with cation and molecular displacement. All ion-exchanged faujasite zeolites only provided rejective systems for 2,6-DMN and some of them were potential adsorbents for the 2,6-DMN purification.

The polymer–zeolite mixed matrix membranes were fabricated by incorporating nanosized or microsized zeolite 4A into polyethersulfone. A comparison of zeolite 4A nanocrystals and microcrystals was made by using SEM, XRD, N2 adsorption–desorption measurements. Zeolite particles were well‐distributed in the polymer phase, as reflected by the SEM images. The effects of the zeolite 4A particle size on the gas permeation performance were studied. Experimental results demonstrate that mixed matrix membranes exhibit decreased gas permeabilities due to the barrier effect of zeolite particles. The obtained permselectivity is greatly enhanced for He/N2, H2/N2, He/CO2, and H2/CO2 gas pairs, especially for nanosized zeolite 4A mixed matrix membranes. The gas permeation performance difference is observed between the nanostructured and microstructured membranes, which is attributed to a combined effect of different zeolite composition and different particle size. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3800–3805, 2006

Two types of mixed matrix membranes were developed by UOP in the late 1980s. The first type includes adsorbent polymers, such as silicalite-cellulose acetate (CA), NaX-CA, and AgX-CA mixed matrix membranes. The silicalite-CA has a CO2H2selectivity of 5.15 ± 2.2. In contrast, the CA membrane has a CO2H2selectivity of 0.77 ± 0.06. The second type of mixed matrix membrane is PEG-silicone rubber. The PEG-silicone rubber mixed matrix membrane has high selectivity for polar gases, such as SO2, NH3, and H2S.

Among the tested carbons, only carbon aerogels (CAs) had significant effects on the hydrogen desorption behavior of LiAlH4. Adding 15 wt % CAs decreased the desorption temperature, while, with 5 wt % CAs, the desorption temperature was still the same. The desorption kinetics of the hydride with 15 wt % CAs, however, did not improve but adding 5 wt % CAs resulted in desorption kinetics improvement. In addition, mixing LiAlH4with a catalyst decreased the desorption temperature and desorption kinetics of the hydride.

Without Abstract:

New bimetallic framework and non-framework titanium and tin silicalite have been investigated for phenol hydroxylation with H2O2in different solvents, and the optimized catalyst composition showed 26 higher initial rate than reference TS-1.

New bimetallic framework and non-framework titanium and tin silicalite have been investigated for phenol hydroxylation with H₂O₂ in different solvents, and the optimized catalyst composition showed 26% higher initial rate than reference TS-1.