Siti Zubaidah Sulaiman

The Influence of 90 Degree Bends in Closed Pipe System on the Explosion Properties Using Hydrogen-Enriched Methane

This work sought to evaluate the explosion severity on hydrogen enrichment in methane-air mixture explosion. For this purpose, different hydrogen mixture compositions ranges between 4 to 8% v/v were considered. This work was performed using CFD tool FLACS that has been well validated for safety studies on both natural gas/methane and hydrogen system. FLACS is used to validate the maximum pressure and flame speed predicted by the CFD tool for combustion of premixed mixtures of methane and hydrogen against the experimental data. Experimental work was carried out in a closed pipe containing 90- degree bends with a volume of 0.41 m3, operating at ambient conditions. From the experiment observation, it shown that the coupling effect of bending and thermal diffusivity gave the dramatic influent on explosion severity in hydrogen-methane/air at very lean concentration. However, simulation results showed that FLACs is under-predicting the overpressure at very lean concentration of hydrogen in methane/air mixtures. It can be said that lower hydrogen content in methane/air mixture limits the hydrogen diffusivity, leading to the decrease of the burning rate and flame speeds. It is also demonstrated that the presence of 90-degree bend in closed pipe system increases the simulated flame speeds to the factor of 2-3, as compared to the experimental data. There are significant discrepancies between experimental and simulation, however, the results seem conservative in general.

Stability and reusability of cyclodextrin glucanotransferase immobilized on hollow fiber membrane

Cyclodextrin glucanotransferase (CGTase) is a starch degrading enzyme to produce cyclodextrin (CD), which can encapsulate compounds to remove flavors and aroma. However, the use of the enzyme is often limited due to the instability of the enzyme resulting in low production of CD. Immobilization technique has greatly improved the characteristics of the enzyme during the reaction. In this study, CGTase was immobilized on polyvinylidene difluoride (PVDF) hollow fiber membrane by adsorption method. The stability and reusability of the immobilized CGTase were studied and compared with free form of the CGTase. Thermal stability of the immobilized CGTase able to retain 50% of the initial residual activity at temperature up to 70°C. While there was an improvement in pH stability with a wider pH range from pH 5 to pH 8. The reusability of the immobilized CGTase was able to retain up to 40% of the initial CD production after repeatedly used for 10 cycles. Hence, the immobilization of CGTase shows a good physical and chemical resistance, which may be advantageous to be applied in industry.

Effect of Cooling Rates on Shape and Crystal Size Distributions of Mefenamic Acid Polymorph in Ethyl Acetate

This study investigate the effect of cooling rates on mefenamic acid crystallisation in ethyl acetate. The cooling rate was varied from 0.2 to 5 °C/min. The in-line conductivity system and turbidity system were employed to detect the onset of the crystallization process. The crystals produced were analysed using optical microscopy and Fourier transform infrared spectroscopy (FTIR). It was found that the crystals produced at different cooling rates were needle-like and exhibit polymorphic form type I. However, the aspect ratio and crystal size distributions were varied with the increased of cooling rate. A high crystals aspect ratio and narrower CSD (100–900 μm) was obtained at cooling rate of 0.5 °C/min. Thus, can be suggested as the most suitable cooling rate for crystallization of mefenamic acid in ethyl acetate.