The combination of 1-octyl-3-methylimidazolium tetrafluorborate with TBAB or THF on CO2 hydrate formation and CH4 separation from biogas

[C_8min] BF_4 was used in this work to combine with TBAB or THF for the investigation about thermodynamic and kinetic additives on CO_2 and CH_4/CO_2 hydrates. The results show that [C_8min] BF_4 has the inhibition effect on the equilibrium of hydrate formation. About the kinetic study, [C_8 min] BF_4 could improve the rate of CO_2 hydrate formation and increase the gas uptake in hydrate phase. At the same time, the combination of TBAB and [C8 min] BF_4 could increase the mole friction of CH_4 in residual gas comparing with the data in THF solution. CH_4 separation efficiency was strongly enhanced. Since that the size of CO_2 and CH_4 molecules are similar, CH_4 and CO_2 could form the similar hydrate, so the recovery of CH_4 from biogas decreases lightly. The CH_4 content in biogas can purified from 67 mol% to 77 mol% after one-stage hydrate formation. In addition, the combination of THF and[C_8 min] BF_4 do not have obvious promoting effect on CH_4 separation comparing with the gas separation results in pure THF solution.

Boosting of reversible capacity delivered at a low voltage below 0.5 V in mildly expanded graphitized needle coke anode for a high-energy lithium ion battery

The rate performance and cycle stability of graphitized needle coke(GNC)as anode are still limited by the sluggish kinetics and volume expansion during the Li ions intercalation and de-intercalation process.Especially,the output of energy density for lithium ion batteries(LIBs)is directly affected by the delithiation capacity below 0.5 V.Here,the mildly expanded graphitized needle coke(MEGNC)with the enlarged interlayer spacing from 0.346 to 0.352 nm is obtained by the two-step mild oxidation intercalation modification.The voltage plateau of MEGNC anode below 0.5 V is obviously broadened as compared to the initial GNC anode,contributing to the enhancement of Li storage below the low voltage plateau.Moreover,the coin full cell and pouch full cell configured with MEGNC anode exhibit much enhanced Li storage ability,energy density and better cycling stability than those full cells configured with GNC and commercial graphite anodes,demonstrating the practical application value of MEGNC.The superior anode behaviors of MEGNC including the increased effective capacity at low voltage and superior cyclic stability are mainly benefited from the enlarged interlayer spacing,which not only accelerates the Li ions diffusion rate,but also effectively alleviates the volume expansion and fragmentation during the Li ions intercalation process.In addition,the above result is further confirmed by the density functional theory simulation.This work provides an effective modification strategy for the NC-based graphite to enhance the delithiation capacity at a low voltage plateau,dedicated to improving the energy density and durability of LIBs.

Experimental investigation on the effective thermal conductivities of different hydrate-bearing sediments

The natural gas hydrate has been regarded as an important future green energy.Significant progress on the hydrate exploitation has been made,but some challenges are still remaining.In order to enhance the hydrate exploitation efficiency,a significant understanding of the effective thermal conductivity(ETC)of the hydrate-bearing sediment has become essential,since it directly controls the heat and mass transfer behaviors,and thereby determines the stability of hydrate reservoir and production rate.In this study,the effective thermal conductivities of various hydrate-bearing sediments were in-situ measured and studied.The impacts of temperature,particle size and type of sediment were investigated.The effective thermal conductivities of the quartz sand sediments before and after hydrate formation were in-situ measured.The results show the weak negative correlation of effective thermal conductivity of the quartz sand sediment on the temperature before and after the hydrate formation.The effective thermal conductivity of the hydrate-bearing sediment decreases with the increase of particle size of the sediment.The dominant effect of the type of porous medium on the characteristics of the effective thermal conductivity of hydrate-bearing sediment was highlighted.The results indicate that both the effective thermal conductivities of hydrate-bearing quartz sand sediment and hydrate-bearing silicon carbide sediment are weakly negatively correlated with temperature,but the effective thermal conductivity of hydrate-bearing clay sediment is weakly positively dependent on the temperature.In addition,the values of the effective thermal conductivities of various hydrate-bearing sediments are in the order of hydrate-bearing silicon carbide sediment>hydrate-bearing quartz sand sediment>hydrate-bearing clay sediment.These findings could suggest that the intrinsic thermal conductivity of porous medium could control the characteristics of effective thermal conductivity of hydrate-bearing sediment.