High surface area biocarbon monoliths for methane storage

New energy sources that reduce the volume of harmful gases such as SO_(x)and NO_(x)released into the atmosphere are in constant development.Natural gas,primarily made up of methane,is being widely used as one reliable energy source for heating and electricity generation due to its high combustion value.Currently,natural gas accounts for a large portion of electricity generation and chemical feedstock in manufacturing plastics and other commercially important organic chemicals.In the near future,natural gas will be widely used as a fuel for vehicles.Therefore,a practical storage device for its storage and transportation is very beneficial to the deployment of natural gas as an energy source for new technologies.In this tutorial review,biomaterials-based carbon monoliths(CMs),one kind of carbonaceous material,was reviewed as an adsorbent for natural gas(methane)adsorption and storage.

Improving methane storage on wet activated carbons at various amounts of water

Different mesoporous activated carbons were prepared by both chemical and physical activation processes and were examined for methane uptake in the presence of water.Methane isotherms were obtained at wet condition by wetting samples with water at mass ratio of water/carbon(R) close to 1.0.To compare,the amount of methane storage were also measured at dry situation.The maximum amount of methane stored was attained as 237 V/V at R=1.0 by hydrate formation at the methane critical pressure.In the next step,mass ratios of water/carbon were changed to investigate various amount of water for methane storage enhancement.Two other values of mass ratio of water/carbon(R=0.8 and 1.4) were selected and methane isotherms were obtained at the same conditions.Maximum values of 210 and 248 V/V were reached for methane storage,respectively.It was also observed that,in the pressure range lower than hydrate pressure,by increasing water ratio the hydrate formation pressure was decreased and methane uptake was much less than that of dry condition due to pore filling by water.

Accelerated methane storage in clathrate hydrates using surfactantstabilized suspension with graphite nanoparticles

In this study,enhanced kinetics of methane hydrate formation in the sodium dodecyl sulfate(SDS)solution with different concentrations of suspended graphite nanoparticles(GNPs)were investigated at 6.1-9.0 MPa and 274.15 K.The GNPs with rough surfaces and excellent thermal conductivity not only provided a considerable number of microsites for hydrate nucleation but also facilitated the fast hydrate heat transfer in the suspension system.At a relatively low pressure of 6.1 MPa,the suspension with 0.4 wt%of GNPs exhibited the minimum induction time of 22 min and maximum methane uptake of 126.1 cm3·cm-3.However,the methane storage performances of the suspensions with higher and lower concentrations of GNPs were not satisfactory.At the applied pressure,the temperature increase arising from the hydrate heat in the suspension system with the optimized concentration(0.4 wt%)of GNPs was more significant than that in the traditional SDS solution.Furthermore,compared with those of the system without GNPs,enhanced hydration rate and storage capacity were achieved in the suspensions with GNPs,and the storage capacities were increased by 3.9%-17.0%.The promotion effect of GNPs on gas hydrate formation at low pressure is much more obvious than that at high pressure.

Preparation of activated carbon with high surface area for high-capacity methane storage

Activated carbon （AC） was fabricated from corncob, which is cheap and abundant. Experimental parameters such as particle size of corncob, KOHlchar weight ratio, and activation temperature and time were optimized to generate AC, which shows high methane sorption capacity. AC has high specific surface area （3227 m^2/g）, with pore volume and pore size distribution equal to 1.829 cm^3/g and ca. 1.7-2.2 nm, respectively. Under the condition of 2℃ and less than 7.8 MPa, methane sorption in the presence of water （Rw = 1.4） was as high as 43.7 wt% methane per unit mass of dry AC. The result is significantly higher than those of coconut-derived AC （32 wt%） and ordered mesoporous carbon （41.2 wt%, Rw = 4.07） under the same condition. The physical properties and amorphous chaotic structure of AC were characterized by N2 adsorption isotherms, XRD, SEM and HRTEM. Hence, the corncob-derived AC can be considered as a competitive methane-storage material for vehicles, which are run by natural gas. Key words

Synthesis of nanoporous copper terephthalate [MIL-53(Cu)] as a novel methane-storage adsorbent

Copper （II） dicarboxylate, MIL-53, metal-organic framework synthesized hydrothermally has been used for the first time as an adsorbent for methane gas adsorption. Methane adsorption capacity of MIL-53（Cu） was increased to about 8.52 mmol·g-1 at 298 K and 35 bar for methane storage. The adsorbent was characterized by X-ray diffraction （XRD）, Brunauer-Emmet-Teller （BET） method, Fourier transform infrared （FT-IR）, thermo gravimetric analysis （TGA） and scanning electron microscopy （SEM）. The adsorption property of CH4, on MIL-53（Cu） was investigated by volumetric measurement. The enhancement of CH4 adsorption capacity of MIL-53（Cu） is attributed to the increase of micropore volume of MIL-53（Cu）.

A robust soc-MOF platform exhibiting high gravimetric uptake and volumetric deliverable capacity for on-board methane storage

Emerging as an outperformed class of metal-organic frameworks(MOFs),square-octahedron(soc)topology MOFs(soc-MOFs)feature superior properties of high porosity,large gas storage capacity,and excellent thermal/chemical stability.We report here an iron based soc-MOF,denoted as Fe-pbpta(H4pbpta=4,4',4'',4'''-(1,4-phenylenbis(pyridine-4,2-6-triyl))-tetrabenzoic acid)possessing a very high Brunauer,Emmett and Teller(BET)surface area of 4,937 m2/g and a large pore volume of 2.15 cm3/g.The MOF demonstrates by far the highest gravimetric uptake of 369 cm3(STP)/g under the DOE operational storage conditions(35 bar and 298 K)and a high volumetric deliverable capacity of 192 cc/cc at 298 K and 65 bar.Furthermore,Fe-pbpta exhibits high thermal and aqueous stability making it a promising candidate for on-board methane storage.

Highly structured metal-organic framework nanofibers for methane storage

Porous materials such as metal-organic frameworks(MOFs)with high theoretical volumetric gas uptake capacity are promising materials for gas storage and separation,but the structuring for practical applications is challenging.Herein,we report a general and feasible strategy to combine electrospinning with a phase conversion method to decorate polyacrylonitrile nanofibers(PAN NFs)with CuMOF(HKUST-1).The strategy is based on the combination of surface pretreatment of the NFs with Cu(OH)_(2) and a subsequent phase conversion into HKUST-1 crystals(PCHKUST-1).A significant higher loading of HKUST-1 in the PAN NF matrix was achieved by the phase conversion method compared with direct electrospinning of MOF slurries or insitu growth of MOF crystals on NFs.As a result,the hierarchical structured PC(phase conversion)-HKUST-1 NFs revealed the highest gravimetric storage capacity of 86 cm^(3) g^(-1)(STP)at 3500 kPa and 298 K for methane(CH_(4)),which is higher than other HKUST-1 NFs reported previously.The improved CH_(4) uptake can be explained by the high loading of HKUST-1 due to the high availability of Cu-ions localized on the surface of the NFs during the phase conversion process,resulting in high surface area and excellent gas access of the phase converted HKUST-1.Thus,the developed strategy of structuring MOFs could be of interest for the fabrication of tailor-made MOF NF architectures for other energy and environmental applications.

A novel pillared-layer-type porous coordination polymer featuring three-dimensional pore system and high methane storage capacity

Solvothermal reaction of Zn（NO3）2, 4-（1H-pyrazol-4-yl）pyridine （Hpypz） and 1,3,5-benzenetricarboxylic acid （H3btc） in N,N-dimethylacetamide （DMA） produced a new porous coordination polymer [Zns（pypz）4（btc）2] （1）. Single-crystal X-ray diffraction study of 1 showed that deprotonated pypz^- ligands served as 1,2,4-triazolate-like ligands, linking Zn（II） ^＋ ions to form porous two-dimensional （2-D） sql-a layers {Zn（pypz）} , which were further connected by eight-legged pillars {Zn2（btc）4（H2O）2}8- based on the typical paddlewheel dinuclear Zn2（RCOO）4（H20）2 cluster to form a novel type of non-interpenetrated pillared-layer framework with 3-D intersecting pore system and large pore volume. Gas sorption measurements revealed that 1 possesses large BET surface area of 2061 m^2g^-1 and very high methane total uptake of 245 cm^3（STP） cm^-3 at 298 K and 65 bar.

Turning gas hydrate nucleation with oxygen-containing groups on size-selected graphene oxide flakes

Gas hydrate is a promising alternative for gas capture and storage due to its high gas storage capacity achieved with only structured water molecules.Nucleation is the critical controlling step in gas hydrate formation.Adding an alien solid surface is an effective approach to regulate gas hydrate nucleation.However,how the solid surface compositions control the gas hydrate nucleation remains unclear.Benefiting from the fact that the surface compositions of graphene oxide(GO)can be finely tuned,we report the effect of functional groups of size-selected GO flakes on methane hydrate nucleation.The carbonyl and carboxyl of GO flakes showed a more prominent promotion for methane hydrate nucleation than the hydroxyl of GO flakes.Surface energy,zeta potential,Raman spectra,and molecular dynamics simulation analysis were used to reveal the regulation mechanism of the functional groups of size-selected GO flakes on methane hydrate nucleation.The GO flakes with abundant carbonyl and carboxyl exhibited higher charge density than those enriched in hydroxyl.The negatively charged GO flakes can induce water molecules to form an ordered hydrogen-bonded arrangement via charge-dipole interactions.Therefore,the water molecules surrounding the carboxyl and carbonyl showed a more ordered hydrogen-bonded structure than those around the hydroxyl of GO flakes.The ordered water arrangement,similar to methane hydrate cages,significantly accelerated methane hydrate nucleation.Our study shows how the surface chemistry of solids control gas hydrate nucleation and sheds light on the design of effective heterogeneous nucleators for gas hydrate.

Importance of storage time in mesophilic anaerobic digestion of food waste

Storage was used as a pretreatment to enhance the methanization performance of mesophilic anaerobic digestion of food waste. Food wastes were separately stored for 0, 1,2, 3, 4, 5, 7, and 12 days, and then fed into a methanogenic reactor for a biochemical methane potential（BMP） test lasting up to 60 days. Relative to the methane production of food waste stored for 0–1 day（285–308 m L/g-added volatile solids（VSadded））, that after2–4 days and after 5–12 days of storage increased to 418–530 and 618–696 m L/g-VSadded,respectively. The efficiency of hydrolysis and acidification of pre-stored food waste in the methanization reactors increased with storage time. The characteristics of stored waste suggest that methane production was not correlated with the total hydrolysis efficiency of organics in pre-stored food waste but was positively correlated with the storage time and acidification level of the waste. From the results, we recommend 5–7 days of storage of food waste in anaerobic digestion treatment plants.