Azeman Mustafa

The impact of ZIF-8 particle size and heat treatment on CO2/CH4 separation using asymmetric mixed matrix membrane

In this study, zeolitic imidazole framework 8 (ZIF-8) particles of different sizes were synthesized in aqueous media by varying the concentration of the base-type additive, triethylamine (TEA). ZIF-8 with particle sizes of ∼134 nm and ∼288 nm with surface areas of 418.44 m2 g−1 and 491.54 m2 g−1 were obtained without altering the crystalline structure. Synthesized ZIF-8 was further heat treated at 100 °C for a minimum of 12 hours, which led to an enhancement of its phase crystallinity and a surface area of 981.1 m2 g−1. Mixed matrix membranes (MMMs) were prepared via the dry–wet phase inversion method by dispersing as-synthesized ZIF-8s, heat-treated ZIF-8s and commercial ZIF-8 (∼493 nm) into a polysulfone (PSf) matrix. The thermal stability and mechanical strength of the membranes showed significant improvement after the incorporation of ZIF-8s. The MMMs were further subjected to the permeation experiments of CO2 and CH4. Although the majority of MMMs showed less selectivity than the neat PSf membrane, the incorporation of heat-treated ZIF-8 of the smallest size, exhibited CO2/CH4 selectivity of 28.5, which is significantly higher than the 19.43 obtained for the neat PSf membrane. Therefore, different ZIF-8 treatment protocols and particle sizes affect the MMMs performance significantly.

Aqueous room temperature synthesis of zeolitic imidazole framework 8 (ZIF-8) with various concentrations of triethylamine

In this study, a zeolitic imidazole framework (ZIF-8) was prepared, and physico-chemical characterizations were performed to investigate the influences of triethylamine (TEA) on the crystallinity, particle size, morphology, and defects of ZIF-8 synthesized via an aqueous room temperature approach with a relatively low molar ratio of ligands to metal salts. Increasing the concentration of TEA by raising the TEA/total molar ratio from 0.004 to 0.007 prompted the formation of pure phase ZIF-8, whereas a TEA/total molar ratio below 0.004 did not result in a yield of ZIF-8. The particle size of ZIF-8 decreased from approximately 288 to 133 nm with increasing TEA/total molar ratio, except at a TEA/total molar ratio of 0.007. However, an excessive TEA/total molar ratio alters the 2-MeIM chemistry, and partially forms hydroxylated 2-MeIM. Thus, this study shows that at relatively low molar ratios of ligands to metal salts, up to a maximum TEA/total molar ratio of 0.006, the TEA concentration plays an important role in assisting crystal formation and in controlling the particle size of ZIF-8. The proposed procedure enables pure phase nanoscale ZIF-8 to be synthesized with a high product yield and with minimal chemical usage.

Facile modification of ZIF-8 mixed matrix membrane for CO2/CH4 separation: synthesis and preparation

Metal–organic frameworks (MOFs) possess tunable characteristics that allow various modifications to be practiced and suitability for specific applications. In this study, zeolitic imidazole framework 8 (ZIF-8) was synthesized and subjected to ammonia modification under different temperatures and ammonia solution loading. The presence of the N–H group observed after the modification indicates the successful modification of ZIF-8. The modified ZIF-8 showed notable changes with increased phase crystallinity, micropore volume and BET surface area. The unmodified and modified ZIF-8s were then dispersed into a polysulfone (PSf) matrix, and the MMMs were prepared via dry/wet phase inversion. No apparent differences in the membrane’s morphology and thermal stability were noticed between the neat PSf membrane and the MMMs. The MMMs were further subjected to pure CO2 and CH4 gas permeation experiments. CO2 permeance decreased while CO2/CH4 selectivity increased as a result of ZIF-8 modification, due to the decrease in mesopore contribution and the increase in micropore contribution to the gas permeation path. The affinity of the N–H group in the modified ZIF-8 to CO2 also contributed to the increase of CO2 permeance. For example, when the ZIF-8 modified in 25 mL ammonia solution at 60 °C (Z25c) was dispersed in the PSf matrix, the CO2/CH4 selectivity increased to 72% and CO2 permeability to 43% compared to the neat PSf membrane.

Utilizing low ZIF-8 loading for an asymmetric PSf/ZIF-8 mixed matrix membrane for CO2/CH4 separation

Asymmetric mixed-matrix membranes (MMMs) were synthesized by incorporating zeolitic imidazole framework 8 (ZIF-8) into polysulfone (PSf) polymer matrix for CO2/CH4 separation. ZIF-8 was synthesized in aqueous media at room temperature with a base-type additive, triethylamine (TEA). The prepared ZIF-8 shows high crystallinity with a surface area of 1032 m2 g−1 and a particle size of ∼133 nm. MMMs were then prepared by incorporating the synthesized ZIF-8 up to 10 wt% (total solids) into PSf via a dry/wet phase inversion. The prepared MMMs exhibit significant improvement in thermal and mechanical stability even at a filler loading as low as 0.25 wt%. Uniform dispersion of ZIF-8 throughout the PSf matrix was evident via SEM, up to 1 wt% filler loading. The permeation behavior of MMMs varies with the ZIF-8 loading; i.e. insignificant change was observed at the low filler loading (0.25 wt%), while severe performance deterioration occurred at high filler loading (10 wt%). At an optimal ZIF-8 loading of 0.5 wt%, CO2 permeance was enhanced by 37% and CO2/CH4 selectivity was also enhanced by 19% as compared to that of neat PSf membrane.

SIMULATION STUDIES OF GAS-SOLID IN THE RISER OF A CIRCULATING FLUIDIZED BED

A numerical parametric study was performed on the influence of various riser exit geometries on the hydrodynamics of gas-solid twophase flow in the riser of a Circulating Fluidized Bed (CFB). A Eulerian continuum formulation was applied to both phases. A two fluid framework has been used to simulate fully developed gas-solid flows in vertical riser. A two dimensional Computational Fluid Dynamics (CFD) model of gas-particle flow in the CFB has been investigated using the code FLUENT. The turbulence was modeled by a k-e turbulence model in the gas phase. The simulations were done using the geometrical configuration of a CFB test rig at the Universiti Teknologi Malaysia (UTM). The CFB riser column has 265 mm (width), 72 mm (depth) and 2.7 m height. The riser is made up of interchangeable Plexiglas columns. The computational model was used to simulate the riser over a wide range of operating and design parameters. In addition, several numerical experiments were carried out to understand the influence of riser end effects, particle size, gas solid velocity and solid volume fraction on the simulated flow characteristics. The CFD model with a k-e turbulence model for the gas phase and a fixed particle viscosity in the solids phase showed good mixing behaviour. These results were found to be useful in further development of modeling of gas solid flow in the riser. However, computational fluid dynamics (CFD) is emerging as a very promising new tool in modeling hydrodynamics. While it is now a standard tool for single-phase flows, it is at the development stage for multiphase systems, such as fluidized beds [3]. Many researchers have used commercial CFD codes for simulating multiphase problems and similar simulations were performed by Taghipour [4] in fluidized bed with the presence of air and sand using FLUENT 4.56. The research was carried out at various velocities. The performance of the code was better at higher gas velocities. Many researchers have simulated three-dimensional two fluids CFD model of gas particle flow in the CFB using the code CFX4.3. The turbulence was modeled by k-e turbulence model in the gas phase and a fixed particle viscosity model in the solid phase. This CFD model showed good agreement with the experiments [5]. A similar study of gas/particle flow behavior in the riser section of a circulating fluidized bed (CFB) was done using FLUENT 4.4. Fluid Catalytic Cracking (FCC) particles and air were used as the solid and gas phases, respectively. The computational results showed that the inlet and outlet design have significant effects on the overall gas and solid flow patterns and cluster formations in the riser [6].

Increasing the Performance of PES-CNTs Mixed Matrix Membrane using Carbon Nanotubes (CNTs) Functionalization

A new type of mixed matrix membrane consisting of functionalized carbon nanotubes (CNTs) and polyethersulfone (PES) is prepared for biogas purification. PES mixed matrix membrane with and without modification of carbon nanotubes were prepared by a dry/wet phase inversion technique using a pneumatically flat sheet membrane casting machine system. The modified carbon nanotubes were prepared by treating the carbon nanotubes with chemical modification using Dynasylan Ameo (DA) silane agent to allow PES chains to be grafted on carbon nanotubes surface. The results from the FESEM, DSC and FTIR analysis confirmed that chemical modification on carbon nanotubes surface had taken place. Meanwhile, the nanogaps in the interface of polymer and carbon nanotubes were appeared in the PES mixed matrix membrane with unmodified of carbon nanotubes. The modified carbon nanotubes mixed matrix membrane increases the mechanical properties, the productivity and purity of biogas. For PES-modified carbon nanotubes mixed matrix membrane the maximum selectivity achieved for CO2/CH4 is 36.78

Enhanced carbon dioxide separation by polyethersulfone (PES) mixed matrix membranes deposited with clay

Abstract Asymmetric mixed matrix membranes (MMMs) incorporating Cloisite15A (C15A) clay particles were prepared using solvent evaporation and phase inversion with polyethersulfone (PES) as the membrane matrix. C15A loadings varied at 1 wt% and 5 wt%. Membrane morphological and thermal properties were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Addition of the C15A favorably altered the microscopic structure of membranes from finger-like to homogeneous sponge-like structure as the loading increased. While the amorphous nature of MMMs was retained, the thermal stability was also found to be improved with a slight decrease in glass transition temperature (Tg). PES/C15A1 MMM showed the best gas transport properties, with 37% and 65% improvement in CO2 permeance and CO2/CH4 selectivity, respectively. Unlike 1 wt%, the loss in selectivity shown by 5 wt% clay loadings suggested that the interphase voids and extent of silicate layers dispersion play a significant role in the overall performance of MMMs.

Effect of venom from Bitis nasicornis (rhinoceros horned viper) on isolated rabbit aortic strips

Venom from B. nasicornis, but not from Bitis arietans, Echis carinatus or Cerastes cerastes, produced an irreversible contraction of the isolated aortic strip that was slow in onset, increased with time, and reached maximum in about 10-15 min. The contraction was not inhibited by pretreatment with atropine, yohimbine, phentolamine, cyproheptadine or indomethacin, however, it was blocked by incubation in a Ca2+-free solution and was partially blocked by incubation with the Ca2+ channel blockers verapamil and nifedipine. It is concluded that B. nasicornis venom may act by increasing the Ca2+ influx into smooth cells, thus causing an increase in intracellular Ca2+ concentration and hence a contraction of the aortic strip.