Desorption properties of the R600, R134a and their mixtures in several MOF structures: A molecular dynamics study.

The efficiency of organic Rankine cycle is expected to be enhanced via using metal organic heat carriers. Thus, it is important to investigate the properties of organic working fluid in metal organic frameworks (MOFs). In this paper, molecular dynamics method was employed to study the desorption properties of R600, R134a, and their mixtures in MOF-5, IRMOF-16, and MOF-200 structures. The results show that the desorption capacity of pure working fluids are negatively correlated with their molecular size. In mixed refrigerant systems, the desorption of the working medium is competitive, and the higher the proportion of fluorine atoms in the system, the greater the desorption heat in IRMOF-16. It is noteworthy that the behavior of the desorption heat in the other two MOFs is diametrically opposed to this result. The desorption capacity is positively correlated with the average pore size, specific surface area, and porosity of the MOF. The self-diffusion coefficient of the working medium in MOF is inversely proportional to its molecular weight, but directly proportional to its molecular size and to the pore size of MOF.

Chemical profiling of Ziziphi spinosae semen using on-line comprehensive two-dimensional liquid chromatography-mass spectrometry based on a novel phthalic anhydride bonded stationary phase.

Ziziphi spinosae semen has been widely used to treat insomnia and anxiety. To profile its chemical components, an online comprehensive two-dimensional liquid chromatography-mass spectrometry was developed. In this two-dimensional liquid chromatography system, a novel phthalic anhydride-bonded stationary phase column was combined with a C18 column. As a result, this new stationary phase exhibited remarkable differences in separation selectivity from C18, achieving a good orthogonality of 83.3%. Moreover, this new stationary phase with weaker hydrophobicity than C18 realized solvent compatibility in the online configuration. Coupled with tandem MS, 154 compounds were identified, including 51 unreported compounds. Compared with one-dimensional liquid chromatography-mass spectrometry, this online two-dimensional liquid chromatography-mass spectrometry system exhibited a much higher resolving power in isomer separation. This work provided an effective separation and characterization method for the material basis of Ziziphi spinosae semen. This strategy provides ideas for the material basis research of other traditional Chinese medicines.