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 R2 of 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.

Two widely investigated methane hydrate promoters, tetra-n-butyl ammonium bromide (TBAB) and cyclopentane (CP), for methane hydrate formation and dissociation were comparatively investigated in the quiescent reactor at 2.5 °C and 8 MPa. The results indicated that the increase in the mass fraction TBAB decreased the induction time. However, it did not significantly affect the methane uptake. In the presence of CP, the increase in the CP concentration resulted in an increase in the induction time due to the increasing thicknesses of the CP layer in the unstirred reactor. Moreover, the methane uptake was varied proportionally with the CP concentration. The addition of TBAB resulted in a higher methane uptake than that of CP, since the presence of TBAB provided the cavities in the hydrate structure to accommodate the methane gas during the hydrate formation better than that of CP. On the contrary, the presence of CP significantly increased the induction time. Although the methane recovery remained relatively the same regardless of TBAB and CP concentrations, the recovery was higher in the presence of TBAB.

Comparative adsorption of methane and carbon dioxide on activated carbon and ZIF-8 (Zeolitic Imidazolate Framework) at 35 °C and up to 100 psi was made. In addition, different ratios of polyvinylidene fluoride (PVDF) with ZIF-8 were also investigated. The textural properties of adsorbents were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), and Quantachrom/Autosorb1-MP. All adsorbents were microporous materials. ZIF-8 has uniform crystalline structure, which is different from the amorphous structure of activated carbon. The result showed the increase in the methane and carbon dioxide adsorption when the pressure increased. ZIF-8 (pure) showed higher methane and carbon dioxide adsorption capacity than the activated carbon corresponding to its surface area, micropore volume, and average pore diameter. The addition of PVDF decreased the methane uptake. Furthermore, ZIF-8 (pure) and activated carbon adsorbed carbon dioxide more than methane, approximately twice due to its preferential adsorption towards carbon dioxide.

Natural gas hydrates are ice-like crystalline compounds and non-stoichiometric, and methane is trapped inside the water cages of the hydrates. In recent years, the hydrates have received much attention for natural gas storage and transportation. However, the use of methane hydrates has faced many challenges such as slow formation rate, low growth rate during hydrate formation, and low conversion ratio of gas to solid hydrates, leading to poor storage capacity. The addition of hydrate promoter is one of alternatives that may overcome these problems. In this work, porous materials, hollow silica (HSC) and activated carbon (AC), were investigated as the hydrate promoters at saturation condition, 1:10 HSC to water and 1:1 AC, to water on the hydrate formation and dissociation. The hydrate formation was conducted in a fix bed reactor at 8 MPa and 4 ºC. The results showed that the methane hydrate formation using the HSC enhanced the water conversion to hydrates and the methane consumption at a greater extent than the methane hydrate formation using the AC. The decomposition of hydrates was performed by thermal stimulation with 21 ºC temperature driving force. The results showed that the porous materials did not significantly affect the methane released and methane recovery from the hydrates.

Natural gas hydrates are ice-like crystalline and non-stoichiometric compounds formed by hydrogen bonds from water molecules when methane is trapped inside. Gas hydrates have received much attention not only as a new natural energy resource but also as a new means of natural gas storage and transportation. However, slow formation rate and stability of natural gas hydrates have been considered problems hindering the industrial applications. In this work, hydrate promoters, mixed MES and SDS, were investigated for hydrate formation and dissociation kinetic. The concentration of mixed surfactants were prepared at 0.5 mM MES/2 mMSDS, 1 mM MES/2mM SDS and 2mM MES/2mM SDS. The formation experiments were conducted in a batch reactor at 4 °C and 8 MPa. The results showed that all concentrations of mixed surfactant enhanced methane formation rate and methane consumption compared to pure water. The mixture of 0.5 mM MES and 2 mM SDS showed the highest methane consumption, while all concentrations of mixture showed the same rate of formation. The dissociation experiment was conducted after the formation with the driving force of 25 °C. The results showed that all promoters did not significantly affect the rate and methane recovery.

CO2 adsorption of polybenzoxazine-modified activated carbon prepared by grafting various polybenzoxazine (PBZ) via ring-opening polymerization of different amine precursors was investigated. Benzoxazine monomer (BZ) was synthesized from phenol, paraformaldehyde, and hexamethylenediamie (HMDA) or triethylenetetramine (TETA). The PBZ loading was varied by different benzoxazine monomer solution concentrations from 0.1 to 0.5 g/L. CO2 adsorption isotherms were obtained at 35 °C, 50 °C, and 75 °C. Adsorbents were characterized by TG-DTA, FT-IR, and surface area and pore size analyses. The amount of PBZ grafted on activated carbon was determined by UV-Vis spectroscopy. The results showed that the CO2 adsorption capacity of the PBZ grafted activated carbon was improved due to the synergistic effects between physical and chemical adsorption. When the adsorption temperature increased, the CO2 adsorption capacity of the grafted adsorbent decreased because the physisorption was more dominated than the chemisorption. The decrease in the capacity due to the temperature increase was more pronounced with the unmodified activated carbon. Using TETA resulted in high CO2 adsorption than using HMDA. It was likely that using TETA to synthesize PBZ contained secondary amine and tertiary amine whereas only tertiary amine was found in PBZ synthesized by HMDA. The secondary amine can directly react with CO2, but the tertiary amine has only van der Waals force to attract CO2. CO2 adsorbed onto PBZ/AC was completely desorbed by heating at 120 °C for 24 h. There was no significant change in the CO2 adsorption capacity of the regenerated adsorbents.

Adsorbed natural gas (ANG) is one of natural gas storage technologies, in which natural gas is adsorbed by a high porosity adsorbent material at relatively low pressure and room temperature with high methane capacity and low cost. Carbon-based materials, like activated carbons, are promising as an ANG storage adsorbent because of high surface area, high porosity, and high volumetric storage capacity. In this research, the adsorption capacity of single and binary component of CH4 and CO2 was investigated by using activated carbons including coconut shell activated carbon (CSAC), palm shell activated carbon (PSAC), and coal-based activated carbon (CBAC) in a packed bed column at room temperature. The composition ratio of single component of CH4 and CO2 was fixed at 20 vol% of the total feed gas, and the composition ratios of binary component of CH4 and CO2 were fixed at 14.6 : 5.4, 10.0 : 10.0, and 5.0 : 15.0 vol% of the total feed gases, respectively. The result of single component adsorption showed that all activated carbons exhibited preferential adsorption for CO2 in relation to CH4. It can be seen from binary component adsorption that the adsorbed amount increased with increased CO2 composition, while the amount of CH4 adsorbed decreased, indicating competition for adsorption sites and preferential adsorption of CO2 over CH4. In terms of the adsorption capacity of binary component, the methane selectivity was CSAC > PSAC > CBAC for the whole composition ratios of CH4 and CO2.

The slow formation rate and low conversion of water to hydrates hinder the production of gas hydrate storage and transportation of gas in industry. The presence of Tetrahydrofuran (THF) in the gas hydrate system was discovered that it could reduce the energy required for pressurization or cooling of hydrate drastically. Not only reducing the energy required was very important, but also increasing the rate formation of hydrates. cetyltrimethyl ammonium bromide (CTAB) was reported to increase hydrate formation rate because of reducing the interfacial surface tension between gas and water. The carbon dioxide hydrate formation in the presence of different THF and CTAB concentrations were investigated in terms of kinetic and thermodynamic. The formation experiment was conducted in the quiescent condition and closed system at 3.5 MPa and 4 °C. The dissociation experiment was carried out after the formation was completed at 2.5 MPa with the driving force of 21 °C. The results showed that the carbon dioxide hydrates formed in the presence of 10 mol% THF, while carbon dioxide hydrates did not form in the presence of CTAB in the quiescent closed system.

The hydrogen desorption/absorption behaviors of LiAlH4/LiBH4 with a focus on the effects of catalysts, namely TiCl3, TiO2, VCl3, and ZrCl4, were investigated using a thermal-volumetric apparatus. The hydrogen desorption was performed from room temperature to 300 °C with a heating rate of 2 °C min−1. The LiAlH4–LiBH4 mixture with a molar ratio of 2:1 decomposed between 100 and 220 °C, and the hydrogen desorption capacity reached up to 6.6 wt %. Doping 1 mol % of a catalyst to the mixture resulted in the two-step decomposition and a decrease in the hydrogen desorption temperature. All the doped samples provided lower amountz of desorbed hydrogen than that obtained from the undoped one. No hydrogen absorption was observed under 8.5 MPa of hydrogen pressure and 300 °C for 6 h. Despite the fact each of the catalysts may affect the hydrogen storage behaviors of the mixture differently, none resulted in a change in the sample reversibility.

A thorough investigation on hydrogen desorption of MgH2 and its reversibility with the focus on effects of a catalyst (TiCl3, TiO2, ZrCl4, and ZrO2) were reported. The experiments were carried out using a Sievert’s type apparatus. The reaction kinetics and the phase transformation behaviours were examined using a differential scanning calorimeter (DSC) and an X-ray diffractometer (XRD). It was found that the catalysts play an important role in facilitating smaller MgH2 crystallite size formation during ball-milling and accelerating hydride formation during the subsequent hydrogen absorption cycles resulting in the hydrogen desorption and reversibility enhancement of MgH2. Doping with ZrCl4 resulted in the smallest MgH2 crystallite size. That, in turn, resulted in the lowest hydrogen desorption temperature and the highest amount of released hydrogen in the first desorption. However, TiO2 was identified as the best catalyst because doping with TiO2 provided the highest amount of reversible hydrogen (~10% capacity drop from initial cycle).

This work studied the effects of activated carbon and tetrathydrofuran (5.56 mol % THF) on methane hydrate phase equilibrium and hydrate dissociation. The hydrate formation was carried out in the quiescent condition and close system at 4 °C. After completion of hydrate formation, the hydrate dissociation was observed by thermal stimulation. The pressure was adjusted to the desired experimental pressure, and then the temperature was increased. When the temperature and pressure in the system crosses the phase boundary, methane gas will release. The results showed that the presence of activated carbon in the system had no effect on hydrate phase boundary, while 5.56 mol % THF affected the thermodynamic methane hydrate phase boundary. Moreover, it indicated that the rate of released gas depended on the experimental pressure, and the methane recovery was in the ranges of 70.0 - 94.9 % in all experiments.

Effects of microaeration on the anaerobic digestion of cassava wastewater with added cassava residue in the continuous stirred tank reactor (CSTR) system were studied. The CSTR system was operated at ambient temperature. The biogas was analysed for the production rate and compositions by a gas meter and gas chromatography (GC), respectively. In addition, the overflown liquid effluent was collected and analysed for chemical characteristics. Operating parameters were varied to achieve the optimum chemical oxygen demand (COD) loading rate, the maximum content of added cassava residue, and the optimum oxygen dosing on the degradation of the cellulosic fraction. The COD loading rate was varied from 0.604to 2.500 kg/m3 d to determine the optimum COD loading rate without oxygen supply. The results showedthat with the optimum COD loading rate of 1.710 kg/m3 d, the generated gas mainly composed of 74.42 % CH4 and 18.43 % CO2 with negligible amounts of nitrogen and oxygen. The addition of a small amount of oxygen played an important role in the methane production.

This study compared the methane adsorption on activated carbon with and without the treatment with sulphuric acid (H2SO4) and potassium hydroxide (KOH) and metal organic frameworks (MOFs)–Basolite C300 and Basolite Z1200. In the experiment, methane gas was pressurized up to 500 psia and the temperature was set at 303 K. The results showed that, gravimetrically, Basolite C300 had the highest methane adsorption capacity of 8.95 mmol/g. The chemical treatments of activated carbon, both H2SO4 and KOH, resulted in the increase in the surface area and pore structure of the activated carbon. Moreover, based on a 70 L storage tank, the addition of H2SO4 treated-activated carbon increased the amount of methane gas in the tank up to 51.7%.

Effects of different polyethyleneimine (PEI) molecular weights on CO2 adsorption on activated carbon (AC) were investigated. The PEI loading was varied using different PEI initial concentrations from 1 to 5 g/L. CO2 adsorption isotherms were investigated at 30 and 75 °C. Adsorbents were characterized by TG-DTA, FTIR, and surface area and pore size analysis. The results showed that PEI impregnated on activated carbon improved the CO2 adsorption capacity due to the synergistic effects between physical and chemical adsorption. AC impregnated with low molecular weight PEI showed improvement in the CO2 adsorption capacity at a low temperature. Higher PEI molecular weights showed higher adsorption capacity at a high temperature. An optimum amount of PEI loading and appropriate PEI molecular weight are needed to increase the CO2 adsorption capacity.

Advanced oxidation processes (AOPs) are effective techniques used to efficiently degrade non-biodegradable organic contaminants present in wastewater. Photocatalysis is an AOP that is very promising in the use of solar energy to initiate degradation reactions. The most interesting photocatalyst is SrTiO3 since it is chemically stable, non-toxic, and highly active in hydrogen production. In this work, mesoporous-assembled SrTixZn1-xO3 nanostructure photocatalysts were synthesized by a sol-gel method with the aid of a structure-directing surfactant. The Ag, Cu, and Pt loadings on SrTixZn1-xO3 were carried out by the photochemical deposition method. The synthesized photocatalysts without and with different metal loadings were tested for the degradation of phenol, which was used as a model contaminant in water. The effects of various synthesis parameters, such as the ratio of Ti:Zn, calcination temperature, and metal loading content, on photocatalytic phenol degradation performance were investigated. The mesoporous-assemble photocatalyst SrTixZn1-xO3 nanostructure photocatalyst with a Ti-to-Zn molar ratio of 0.97:0.03 calcined at 700 °C provided the highest phenol degradation rate constant (k) of 0.80 h-1. Among the studied loaded metals, Pt provided the highest photocatalytic activity toward phenol degradation.

Solidified natural gas (SNG) via clathrate hydrates has been proposed as an alternative approach for natural gas storage and transportation. In this work, the roles of 5.56 mol% pyrrolidine were investigated for the methane hydrate formation in terms of thermodynamics and kinetics along with morphology. The results showed that pyrrolidine generally improved the thermodynamic stability of mixed methane hydrates, enhancing the formation at milder conditions than those of pure methane hydrates. To demonstrate the kinetic performance of pyrrolidine, the experiments were performed at 8 MPa and 285.2 K in a quiescent configuration. The results showed that a very short induction time and a rapid rate of hydrate formation with desirable methane uptake were achieved. In addition, a distinct methane bubble with breathing effect, assisting methane gas to interact with the bulk solution, was observed during the hydrate formation morphology. The comparative kinetic study with 5.56 mol% tetrahydrofuran (THF) was also carried out under the same driving force and the same experimental condition. Surprisingly, although THF gave a high methane uptake, pyrrolidine could give more than 10 times higher rate of hydrate formation at the same driving force; moreover, it provided a competitive rate with THF at the similar formation condition. Figure G1 Thermodynamics, kinetics, and morphology of the mixed methane hydrate formation in the presence of 5.56 mol% pyrrolidine. [Display omitted] • Up to ten-time increase in the rate of methane hydrate formation with pyrrolidine compared to tetrahydrofuran (THF). • A new insight on the roles of pyrrolidine in methane hydrate formation through morphology investigation. • A shift in the methane hydrate phase equilibrium in the presence of pyrrolidine. • A clear comparison on the roles of pyrrolidine and THF in the methane hydrate formation. [ABSTRACT FROM AUTHOR]

Foam generation from the presence of sodium dodecyl sulfate (SDS) as a kinetic promoter in methane hydrate formation can be potentially reduced by using mixed surfactants. Mixtures of SDS with nonionic surfactants were proposed to solve this problem. Polyoxyethylene (n) lauryl ether (EO 3 and EO 5) and alkyl poly glycol ether (APG) were chosen to mix with SDS in different concentrations at 8 MPa and 4 °C in the quiescent system for both kinetics and morphology studies. The result showed that the addition of EO 3 resulted in the slight increase for the induction time but no change in the formation rate. Adding EO 5 showed the stochastic phenomenon on hydrate formation kinetics. In the presence of APG, the induction time increased up to ten times and lowered the hydrate formation rate compared to only 0.25 wt% SDS. The methane uptakes were about the same with all conditions. The morphology showed similar hydrate formation and dissociation patterns with all investigated solutions. Interestingly, the mixture of nonionic surfactants with SDS decreased the foam formation compared with the system with only SDS. The addition EO 3 showed the gradual decrease in the foam height with the higher concentration of EO 3. Adding the highest EO 5 concentration showed the optimum foam reduction compared with all conditions. Moreover, the presence of APG showed the similar effects of foam reduction with EO 5. • Kinetics and morphology during the methane hydrate formation and dissociation in the presence of mixed surfactants. • A large amount of foam generated during gas recovery from the presence of sodium dodecyl sulfate. • The foam formation decreased with the addition of nonionic surfactant. • The formation kinetics hardly affected in the presence of mixed surfactants. [ABSTRACT FROM AUTHOR]

Photocatalytic degradation of 4-chlorophenol was studied using TiO2, Pt/TiO2, TiO2-SiO2, and Pt/TiO2-SiO2 prepared by the sol-gel method. The addition of Pt in TiO2 improved the catalytic activity and the highest activity was obtained with 1% Pt/TiO2. For TiO2-SiO2, the highest activity was achieved with 10%SiO2TiO2 because of its highest adsorption capacity. Although 1% Pt or 10% Si in TiO2 improved the catalyst activity, the synergistic effect of adding both 1% Pt and 10% Si was not observed. [ABSTRACT FROM AUTHOR]

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 LiAlH4 with a catalyst decreased the desorption temperature and desorption kinetics of the hydride. [ABSTRACT FROM AUTHOR]

The kinetics of methane hydrate formation in the presence of methyl ester sulfonate (MES), a bio-based anionic surfactant, was evaluated in an unstirred reactor. MES concentration was varied from 1 mM to 8 mM (0.029 wt% to 0.232 wt%) and its effect on the kinetics of the methane hydrate formation was observed at 277.2 K and 8 MPa. MES drastically improved the kinetics of methane hydrate formation and methane consumption. The increase in the MES concentration dramatically decreased the induction time as well. In addition, the morphology of methane hydrate formation observed with the different MES concentrations was presented. Hydrate nucleation was observed at the gas/liquid interface followed by the hydrate growth in the upward direction into the gas phase and then downward direction into the liquid phase, respectively. Dissociation characteristics and methane recovery were not significantly different for different MES concentrations. Image 1 • Biodegradable MES surfactant significantly enhanced the kinetics of methane hydrate formation in an unstirred tank reactor • Increase in MES concentration reduced the induction time and increased the gas uptake. • Morphology observations during the methane hydrate formation and dissociation in presence of MES are presented [ABSTRACT FROM AUTHOR]

Effects of tetrahydrofuran (THF) concentration on the mixed methane hydrate formation, dissociation, and stability were investigated. The experiment was conducted at 286.2 K and 6 MPa in a quiescent reactor. The presence of THF below 2.5 mol% did not show the evidence of hydrate formation. However, the concentration above 2.5 mol% enhanced the methane formation rate and the methane consumption. Increasing the THF concentration decreased the induction time as the result of the decrease in the surface tension. Moreover, the methane uptake and formation rate increased with the THF concentration due to the higher degree of hydrate nucleation. The methane recovery after the dissociation experiment showed up to 96%. Furthermore, the hydrate stability increased, and the hydrate dissociation kinetics decreased with the increase in the THF concentration. The optimum THF concentration to enhance and improve the hydrate formation kinetics and stability is its stoichiometric concentration.

In this research, the separate production of hydrogen (H 2 ) and methane (CH 4 ) from cassava wastewater with added cassava residue was investigated using a two-stage upflow anaerobic sludge blanket (UASB) system under thermophilic temperature (55 °C) in a continuous mode of operation and steady state condition. The two-stage UASB system was operated under an optimum chemical oxygen demand (COD) loading rate of 10.29 kg/m 3 d (based on the total volume of both bioreactors) of the cassava wastewater with different concentrations of added cassava residue. The recycle ratio of the effluent from the second bioreactor to the feed flow rate was fixed at 1:1 (v/v). In addition, the solution pH in the first bioreactor was controlled at 5.5, while that in the second bioreactor was not controlled. Under the optimum cassava residue concentration of 1200 mg/L, the produced gas from the first bioreactor contained 42.3% H 2 , 55% carbon dioxide (CO 2 ) and 2.70% CH 4 , while that from the second bioreactor contained 70.5% CH 4 , 28% CO 2 and 1.5% H 2 . Apart from a high H 2 and CH 4 production performance (45.2 and 150% improvement, respectively, as compared to the system without added cassava residue) under the optimum cassava residue concentration (1200 mg/L) and the controlled COD loading rate (10.29 kg/m 3 d) of the cassava wastewater, the degradation performance of cellulose and hemicellulose were 41% and 22%, respectively, for the first bioreactor and 23% and 11%, respectively, for the second bioreactor. The digestibility of the cassava residue at thermophilic operation was higher than that at mesophilic temperature., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Sodium dodecyl sulfate (SDS) markedly improved tetrahydrofuran (THF) - assisted methane hydrate formation. Firstly, methane hydrate formation with different THF amount, 1, 3, and 5.56 mol%, was studied. SDS with 1, 4, and 8 mM was then investigated for its roles on the methane hydrate formation with and without THF. The experiments were conducted in a quiescent condition in a fixed volume crystallizer at 8 MPa and 4°C. The results showed that almost all studied THF and SDS concentrations enhanced the methane hydrate formation kinetics and methane consumption compared to that without the promoters, except 1 mol% THF. Although, with 1 mol% THF, there were no hydrates formed for 48 hours, the addition of just 1 mM SDS surprisingly promoted the hydrate formation with a significant increased in the kinetics. This prompts the use of methane hydrate technology for natural gas storage application with minimal promoters.

The in vitro metabolism of (-)-cis- and (-)-trans-rose oxide was investigated using human liver microsomes and recombinant cytochrome P450 (P450 or CYP) enzymes for the first time. Both isomers of rose oxide were incubated with human liver microsomes, and the formation of the respective 9-oxidized metabolite were determined using gas chromatography-mass spectrometry (GC-MS). Of 11 different recombinant human P450 enzymes used, CYP2B6 and CYP2C19 were the primary enzymes catalysing the metabolism of (-)-cis- and (-)-trans-rose oxide. CYP1A2 also efficiently oxidized (-)-cis-rose oxide at the 9-position but not (-)-trans-rose oxide. α-Naphthoflavone (a selective CYP1A2 inhibitor), thioTEPA (a CYP2B6 inhibitor) and anti-CYP2B6 antibody inhibited (-)-cis-rose oxide 9-hydroxylation catalysed by human liver microsomes. On the other hand, the metabolism of (-)-trans-rose oxide was suppressed by thioTEPA and anti-CYP2B6 at a significant level in human liver microsomes. However, omeprazole (a CYP2C19 inhibitor) had no significant effects on the metabolism of both isomers of rose oxide. Using microsomal preparations from nine different human liver samples, (-)-9-hydroxy-cis- and (-)-9-hydroxy-trans-rose oxide formations correlated with (S)-mephenytoin N-demethylase activity (CYP2B6 marker activity). These results suggest that CYP2B6 plays important roles in the metabolism of (-)-cis- and (-)-trans-rose oxide in human liver microsomes., (Copyright © 2015 John Wiley & Sons, Ltd.)