Wensheng Lin

Temperature-dependent state of hydrogen molecules within the nanopore of multi-walled carbon nanotubes

Abstract In observation of the state of hydrogen molecules within the carbon nanopore, the excess adsorption amounts of hydrogen on the multi-walled carbon nanotubes (MWCNTs) were measured at equilibrium pressure–temperatures from 0.1 to 12.3 MPa and 123 to 310 K . The principles of thermodynamic equilibrium and a higher order Virial adsorption coefficient were applied to determining the maximum surface coverage of hydrogen molecules on the adsorbent surface. The thermodynamic equilibrium-based adsorption model was linearized to estimate the interaction energy among the adsorbed hydrogen molecules at each adsorption equilibrium state. The results demonstrate that the interaction energies among adsorbed hydrogen molecules are positive in the lower temperature region ( K ) and reach the maximum value around a temperature from 160 to 180 K . However, it will gradually be negative when the temperature is approaching 230 K . In other words, the confined hydrogen molecules repulse each other in the low-temperature environment while they attract each other at the ambient temperature. It implies that the dissociativeness of hydrogen occurred in the experimental pressure–temperature range, and it is also suggested that the temperature between 160 and 180 K could be a preferable condition to make full use of physical and chemical adsorption of hydrogen molecules on the adsorbent.

CBM Nitrogen Expansion Liquefaction Processes Using Residue Pressure of Nitrogen From Adsorption Separation

Coalbed methane (CBM) is a kind of important energy resources in the world. Liquefaction is a good option for recovery of CBM. Generally, CBM consists of a lot of nitrogen besides methane, which is usually required to be separated by adsorption before liquefaction, or by distillation after liquefaction. For the CBM adsorption-liquefaction processes, two novel processes are proposed, which integrate the two parts of adsorption and liquefaction together by utilizing the residue pressure of the waste nitrogen: the released nitrogen expanded directly to precool CBM or further compressed and then expanded to liquefy CBM. Taking the unit product liquefaction power consumption as the major index and the nitrogen content of CBM feed gas together with the residue pressure of waste nitrogen as variables, the system performance of these two integrated processes is studied and compared with that of the nitrogen expansion liquefaction process without integration. By simulation and calculation with HYSYS , it is confirmed that system power consumption can be reduced by both methods to utilize the residue pressure, and for CBM with high nitrogen content, the energy conservation effect is considerable; furthermore, it is better to use waste nitrogen to precool CBM than to liquefy it.

A Transcritical CO

A novel transcritical Rankine cycle is presented in this paper. This cycle adopts CO2 as its working fluid, with exhaust from a gas turbine as its heat source and LNG as its cold sink. With CO2 working transcritically, large temperature difference for the Rankine cycle is realized. Moreover, the CO2 in the gas turbine exhaust is further cooled and liquefied by LNG after transferring heat to the Rankine cycle. In this way, not only the cold energy is utilized, but also a large part of the CO2 from burning of the vaporized LNG is recovered. In this paper, the system performance of this transcritical cycle is calculated. The influences of the highest cycle temperature and pressure to system specific work, exergy efficiency and liquefied CO2 mass flow rate are analyzed. The exergy loss in each of the heat exchangers is also discussed. It turns out that this kind of CO2 cycle is energy-conservative and environment-friendly.Copyright

A study of the optimum temperature for hydrogen storage on Carbon Nanostructures

Publisher Summary This chapter studies the temperature dependent state of hydrogen molecules on multi-walled carbon nanotubes (MWCNTs) at a temperature range from 123–310 K. The energy of intermolecular interaction is used to probe into the optimum temperature for hydrogen storage by adsorption on carbon nanostructures. Thermodynamic analysis is undertaken based on the lattice theory to the adsorption data of hydrogen on MWCNTs over a temperature range of 123–310 K and pressure up to 12.5 MPa. The isosteric heat of hydrogen adsorption in low limit of the surface concentration on the MWCNTs is smaller than that on the graphitized carbon black. The hydrogen–hydrogen interaction energy shows characteristics of physical adsorptions of supercritical gases, the optimum adsorption temperature has not been revealed by the determined results and should still be in researching. Results show that the hydrogen–hydrogen interaction energy captures characteristics of physical adsorptions of supercritical gases; almost linearly increases with increases of adsorption temperatures and surface loadings.