Yan Dai

Application of poly(phthalazinone ether sulfone ketone)s to gas membrane separation

A series of poly(phthalazinone ether sulfone ketone) (PPESK) copolymers containing different component ratios of bis(4-fluorodiphenyl) ketone and bis(4-chlorodiphenyl)sulfone with respect to a certain amount of 4-(4-hydroxyphenyl)-2,3-phthalazin-1-one were synthesized by polycondensation. Glass transition temperatures ofthese polymers were adjusted from 263°C to 305°C by changing the ratios of reactants. Gas permeability and selectivity of the dense membranes of the polymers for three kinds of gases (CO 2 , O 2 , and N 2 ) were determined at different temperatures. The result indicated that the membrane of PPESK (S/K = 1/1, mol ratio) had an excellent gas separation property. Permeability of the polymer membranes for CO 2 , O 2 , and N 2 was P CO2 = 4.121 barrier, P O2 = 0.674 barrier, and P N2 = 0.0891 barrier, respectively. Separation factors of α O2 /N and α CO2 /N 2 were 7.6 and 46, respectively. New material was made into a composite membrane with silicone rubber for blocking up leaks and defects on the surface of its nonsymmetrical membrane. As a result of the test, permeability of the composite membrane was J O2 = 7.2 × 10 -6 cm 3 (STP) cm -2 S -1 cm-1 Hg and J N2 = 0.99 × 10 -6 cm 3 (STP) cm -2 S -1 cm -1 Hg, whereas the α O2 /N 2 was still higher than 7. These showed that PPESKs had a bright prospect as the potential membrane material for high-temperature gas separation.

An integrally thin skinned asymmetric architecture design for advanced anion exchange membranes for vanadium flow batteries

A novel integrally thin skinned asymmetric anion exchange membrane (ISAAEM) with sufficiently low ion exchange capacity (IEC) was proposed to improve the chemical stability of AEMs for vanadium flow batteries (VFBs). The ISAAEM with an IEC of 0.72 meq. g−1 showed low area resistance, slight VO2+ crossover and good electrochemical performance in VFBs.

Pressure swing adsorption/membrane hybrid processes for hydrogen purification with a high recovery

Hydrogen was recovered and purified from coal gasification-produced syngas using two kinds of hybrid processes: a pressure swing adsorption (PSA)-membrane system (a PSA unit followed by a membrane separation unit) and a membrane-PSA system (a membrane separation unit followed by a PSA unit). The PSA operational parameters were adjusted to control the product purity and the membrane operational parameters were adjusted to control the hydrogen recovery so that both a pure hydrogen product (>99.9%) and a high recovery (>90%) were obtained simultaneously. The hybrid hydrogen purification processes were simulated using HYSYS and the processes were evaluated in terms of hydrogen product purity and hydrogen recovery. For comparison, a PSA process and a membrane separation process were also used individually for hydrogen purification. Neither process alone produced high purity hydrogen with a high recovery. The PSA-membrane hybrid process produced hydrogen that was 99.98% pure with a recovery of 91.71%, whereas the membrane-PSA hybrid process produced hydrogen that was 99.99% pure with a recovery of 91.71%. The PSA-membrane hybrid process achieved higher total H2 recoveries than the membrane-PSA hybrid process under the same H2 recovery of membrane separation unit. Meanwhile, the membrane-PSA hybrid process achieved a higher total H2 recovery (97.06%) than PSA-membrane hybrid process (94.35%) at the same H2 concentration of PSA feed gas (62.57%).

Interpenetrated Networks between Graphitic Carbon Infilling and Ultrafine TiO2 Nanocrystals with Patterned Macroporous Structure for High-Performance Lithium Ion Batteries

Interpenetrated networks between graphitic carbon infilling and ultrafine TiO2 nanocrystals with patterned macropores (100-200 nm) were successfully synthesized. Polypyrrole layer was conformably coated on the primary TiO2 nanoparticles (∼8 nm) by a photosensitive reaction and was then transformed into carbon infilling in the interparticle mesopores of the TiO2 nanoparticles. Compared to the carbon/graphene supported TiO2 nanoparticles or carbon coated TiO2 nanostructures, the carbon infilling would provide a conductive medium and buffer layer for volume expansion of the encapsulated TiO2 nanoparticles, thus enhancing conductivity and cycle stability of the C-TiO2 anode materials for lithium ion batteries (LIBs). In addition, the macropores with diameters of 100-200 nm in the C-TiO2 anode and the mesopores in carbon infilling could improve electrolyte transportation in the electrodes and shorten the lithium ion diffusion length. The C-TiO2 electrode can provide a large capacity of 192.8 mA h g-1 after 100 cycles at 200 mA g-1, which is higher than those of the pure macroporous TiO2 electrode (144.8 mA h g-1), C-TiO2 composite electrode without macroporous structure (128 mA h g-1), and most of the TiO2 based electrodes in the literature. Importantly, the C-TiO2 electrode exhibits a high rate performance and still delivers a high capacity of ∼140 mA h g-1 after 1000 cycles at 1000 mA g-1 (∼5.88 C), suggesting good lithium storage properties of the macroporous C-TiO2 composites with high capacity, cycle stability, and rate capability. This work would be instructive for designing hierarchical porous TiO2 based anodes for high-performance LIBs.

Pulverization Control by Confining Fe3O4 Nanoparticles Individually into Macropores of Hollow Carbon Spheres for High-Performance Li-Ion Batteries

In this article, double carbon shell hollow spheres which provide macropores (mC) for ultrasmall Fe3O4 nanoparticle (10-20 nm) encapsulation individually were first prepared (Fe3O4@mC). The well-constructed Fe3O4@mC electrode materials offer the feasibility to study the volume change, aggregation, and pulverization process of the active Fe3O4 nanoparticles for Li-ion storage in a confined space. Fe3O4@mC exhibits excellent electrochemical performances and delivers a high capacity of 645 mA h g-1 at 2 A g-1 after 1000 cycles. Even at 10 A g-1 or after 1000 cycles at 2 A g-1, the porous carbon structure was well maintained and no obvious aggregation and pulverization of the Fe3O4 nanoparticles was observed, although the volume of the active Fe3O4 particles was expanded to 40-60 nm compared to that of the original particles (10-20 nm). This can be due to the in situ embedment of one Fe3O4 nanoparticle into one macropore individually. The uniform dispersion and confinement of the Fe3O4 nanoparticles in the macropores of the carbon shell could effectively accommodate severe volume variations upon cycling and prevent self-aggregation and spreading out from the carbon shell during the expansion process of the nanoscale Fe3O4 particles, leading to improved capacity retention. Our work confirms the effectiveness for pulverization control by confining Fe3O4 nanoparticles individually into macropores to improve its Li-ion storage properties, providing a novel strategy for the design of new-structured anode materials for Li-ion batteries.

Integration of molecular dynamic simulation and free volume theory for modeling membrane VOC/gas separation

Gas membrane separation process is highly unpredictable due to interacting non-ideal factors, such as composition/pressure-dependent permeabilities and real gas behavior. Although molecular dynamic (MD) simulation can mimic those complex effects, it cannot precisely predict bulk properties due to scale limitations of calculation algorithm. This work proposes a method for modeling a membrane separation process for volatile organic compounds by combining the MD simulation with the free volume theory. This method can avoid the scale-up problems of the MD method and accurately simulate the performance of membranes. Small scale MD simulation and pure gas permeation data are employed to correlate pressure-irrelevant parameters for the free volume theory; by this approach, the microscopic effects can be directly linked to bulk properties (non-ideal permeability), instead of being fitted by a statistical approach. A lab-scale hollow fiber membrane module was prepared for the model validation and evaluation. The comparison of model predictions with experimental results shows that the deviations of product purity are reduced from 10% to less than 1%, and the deviations of the permeate and residue flow rates are significantly reduced from 40% to 4%, indicating the reliability of the model. The proposed method provides an efficient tool for process engineering to simulate the membrane recovery process.

Amphiprotic Side-Chain Functionalization Constructing Highly Proton/Vanadium-Selective Transport Channels for High-Performance Membranes in Vanadium Redox Flow Batteries

A novel amphiprotic side-chain-functionalized membrane was for the first time designed for vanadium redox flow battery (VFB). Different from frequently used blending amphiprotic membranes, the one proposed here is allowed to possess high anion-exchange capacity (IECa) without sacrificing the cation-exchange capacity (IECc) because both IECa and IECc increased with the grafting degree of side chains. Having a high IECa, the membrane prepared here exhibits an ultralow vanadium permeability (<10-8 cm2 s-1), which leads to very high Coulombic efficiencies (97-98% at 40-200 mA cm-2) of VFB and good cell self-discharge durability. Moreover, the high IECc contributes to a decent ionic conductivity (area resistance: 0.5 Ω cm-2), which ensures a high-voltage efficiency of the cell. On the basis of these good properties, the VFB single cell with this membrane achieves a high energy efficiency (e.g., 77.4% at 200 mA cm-2) that is higher than those of Nafion 212 and other reported amphiprotic membranes. These results indicate that the approach proposed here is an ideal option to prepare amphiprotic membranes for VFBs with high efficiency and good durability.