Siti Tasirin | Universiti Kebangsaan Malaysia (original) (raw)

Papers by Siti Tasirin

Selecting a proper support in the catalyst system plays an important role in hydrogen production ... more Selecting a proper support in the catalyst system plays an important role in hydrogen production via ethanol steam reforming. In this study, sol gel made alumina supports prepared for nickel (Ni) catalysts were calcined at different temperatures. A series of (Ni/Al S.G. ) catalysts were synthesized by an impregnation procedure. The influence of varying the calcination temperature of the sol gel made supports on catalyst activity was tested in ethanol reforming reaction. The characteristics of the sol gel alumina supports and Ni catalysts were affected by the calcination temperature of the supports. The structure of the sol gel made alumina supports was transformed in the order of γ → (γ + θ) → θ-alumina as the calcination temperature of the supports increased from 600 °C to 1000 °C. Both hydrogen yield and ethanol conversion presented a volcano-shaped behavior with maximum values of 4.3 mol/mol ethanol fed and 99.5%, respectively. The optimum values were exhibited over Ni/Al S.G800 (Ni catalyst supported on sol gel made alumina calcined at 800 °C). The high performance of the Ni/Al S.G800 catalyst may be attributed to the strong interaction of Ni species and sol gel made alumina which lead to high nickel dispersion and small particle size.

Procedia - Social and Behavioral Sciences

The objective of the study is to examine the effectiveness of learning and teaching techniques of... more The objective of the study is to examine the effectiveness of learning and teaching techniques of communication and teamwork skills of students in the learning process in the university. The study was based on a survey form and the examination results of students in courses selected by Department of Chemical and Process Engineering, which is Utilities Design and Integrated Projects (IP) with 75 and 43 respondents, respectively. The data analysis obtained shows that students are receptive to carrying out tasks in small group, satisfaction with the evaluation through presentations and receive new knowledge.

Deposition of amorphous particles, as a prevalent problem particularly in the spray drying of fru... more Deposition of amorphous particles, as a prevalent problem particularly in the spray drying of fruit and vegetable juices, is due to low-molecularweight sugars and is strongly dependent on the condition of the particles upon collision with the dryer wall. This paper investigates the condition of the amorphous particles impacting the wall at different drying conditions with the aim of elucidating the deposition mechanism and physical phenomena in the drying chamber. A model sucrose-maltodextrin solution was used to represent the low-molecular-weight sugar. Particle deposits were collected on sampling plates placed inside the dryer for analyses of moisture content, particle rigidity (using SEM) and size distribution. Moisture content was adopted as a general indicator of stickiness. Product particles collected at the bottom of the experimental dryer were found to have higher moisture than particle deposits on samplers inside the dryer. Moisture content profile in the dryer shows that apart from the atomizer region, where particles are relatively wet, particle deposits at other regions exhibit similar lower moisture content. At the highest temperature adopted in the experiments, particles became rubbery suggesting liquid-bridge formation as the dominant deposition mechanism. Further analysis on particles size distribution reveals a particle segregation mechanism whereby smaller particles follow preferentially to the central air stream while larger particles tend to re-circulate in the chamber, as predicted in past CFD simulation. The findings from this work will form the basis and provide validating data for further modeling of wall deposition of amorphous particles in spray drying using CFD.

Advanced Materials Research, 2014

ABSTRACT A high performance lateral silicon photodiode was designed on a Silicon–on-insulator (SO... more ABSTRACT A high performance lateral silicon photodiode was designed on a Silicon–on-insulator (SOI)-based substrate with SiGe/Si quantum dot technology. The device has the potential of being a serious candidate for applications in sensing applications as well as in optical fiber communications. Five device process parameters and two device noise factors were identified to make the virtual device design insensitive to variation in the selected fabrication parameters. An L9 array from Taguchi method was used to optimize the device design. The simulator of ATHENA and ATLAS were used for photodiode fabrication process and electrical characterization, respectively. The results obtained for responsivity and frequency response after the optimization approach were 0.36 A/W and 21.2 GHz respectively which correspond to the optimization value for the intrinsic region length of 6 μm, photo-absorption layer thickness of 0.505 μm, incident optical power of 0.5 mW/cm2 and bias voltage of 3.5 V. As a conclusion, the optimum solution in achieving the desired high speed photodiode was successfully predicted using Taguchi optimization method.

JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 2001

Batch experimental work on the fluidization hydrodynamic and entrainment phenomena of cohesive st... more Batch experimental work on the fluidization hydrodynamic and entrainment phenomena of cohesive starch powders was studied. Results show that fluidization can be realized as vibration break particleparticle bond in the bed. The higher U mf values compared to predictions indicate the formation of agglomerates in the bed. This has increased the residence time of fines to reduce material loss by entrainment. It was found that using starch powders as feed materials, entrainment was only in the range of 0.5-1.7% of the total fines (should be entrained) in the bed. As has also been found by other workers, the entrainment rate constants of group C decrease as particle size decreases. By adapting the criterion proposed by Rietema (1984) as well as Ma and Kato (1998), it was found in this case that the critical cohesion number, N coh * is 19.

Drying Technology, 2007

... Meng Wai Woo, Wan Ramli Wan Daud, Siti Masrinda Tasirin, and Meor Zainal Meor Talib Deparment... more ... Meng Wai Woo, Wan Ramli Wan Daud, Siti Masrinda Tasirin, and Meor Zainal Meor Talib Deparment of Chemical & Processing Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi ... The rig is held in place by pushing against the dryer wall using the stud rod and bolts. ...

Crystal Growth & Design, 2009

An examination of the aqueous solution solubility and batch crystallization kinetics of L-isoleuc... more An examination of the aqueous solution solubility and batch crystallization kinetics of L-isoleucine at the 250 mL scale size under a poly-and isothermal process condition is presented. Solubility data determined are consistent with the existence of two L-isoleucine polymorphic forms, in which both forms have different solubility and they are enantiotropically related. These polymorphs (A and B) can be recovered at different cooling rates of cooling crystallization. Crystal characterization using optical microscopy, differential scanning calorimetry, X-ray powder diffraction, and Fourier transform IR microscopy confirm this polymorphic behavior. Polythermal crystallization kinetic studies revealed the crystallization temperature increases with cooling rate and solute concentration, which results in a decrease of the metastable zone width (MSZW) with a decreasing cooling/heating rate. The study also revealed that cooling rates affect the polymorph formation, where at cooling rates of 0.25-0.75°C/min, form B is formed, while a more stable polymorph A can be recovered at a cooling rate of 0.10°C/min. Isothermal studies showed that the range of nucleation rate is between 1.79 × 10 -5 and 7.53 × 10 -4 kg/(m 3 min), and the interfacial surface free energy at high and low supersaturation system is 1.74 and 0.576 mJ/m 2 , respectively. For a high supersaturation system, the critical cluster radius r* is between 5-17 Å, associated with between 3-121 molecules (N*), and for a low supersaturation system, r* is between 3 and 14 Å and N* is between 1 and 64. For a pH range of 5.1-6.3 and a temperature range between 10 and 80°C, zwitterion species of L-isoleucine has remained as a dominating species in both solubility and crystallization studies. Thermodynamics properties generated from solubility data were also presented and discussed.

Catalysis Letters, 2007

Ethanol steam reforming has been studied over Ni/SiO 2 catalysts under a wide range of operating ... more Ethanol steam reforming has been studied over Ni/SiO 2 catalysts under a wide range of operating conditions, and the effect of Ni loading on catalyst properties and H 2 yield and selectivity has been analyzed. Surface area and pore volume significantly decrease with nickel content, but there is only a slight decrease in mean pore diameter. XRD patterns show peaks corresponding to NiO but no evidence of nickel silicate species has been found. Ni/SiO 2 catalysts are active for H 2 production by ethanol steam reforming over 400 ºC. Ethanol conversion and H 2 yield considerably increase with temperature and Ni loading. Up to 3.9 mol H2 /mol EtOH is obtained at 600 ºC and 8.3 g catalyst min/g EtOH , although lower temperatures (500 ºC) are more suitable for minimizing CO selectivity. An improvement in catalyst performance is observed for high values of time-on-stream, which is explained by coke deposition in the form of carbon fibers.

In this work, bamboo-shaped, multi-walled carbon nanotubes were synthesized via methane decomposi... more In this work, bamboo-shaped, multi-walled carbon nanotubes were synthesized via methane decomposition over a Ni–Co–Fe tri-metallic catalyst at 1000 °C. The nitrogen absorption (BET), X-ray diffraction (XRD), and particle size analysis results of the catalyst were used to demonstrate the surface area, size distribution, and crystallinity of the sample. The scanning electron microscopy (SEM) micrographs of the nanocarbons deposited via methane decomposition indicated that highly uniform carbon nanotubes were grown on the surface of the tri-metallic catalyst. The transmission electron microscopy (TEM) images showed that the carbon nanotubes were multi-walled and bamboo-shaped with a diameter of ~20 nm. Raman spectra revealed the graphitization degree of the CNTs with an I D /I G of 1.84, indicative of the crystallinity of CNTs with structural defects. The thermal analysis shows the high oxidation stability of the multi-walled carbon nanotubes.

Selecting a proper support in the catalyst system plays an important role in hydrogen production ... more Selecting a proper support in the catalyst system plays an important role in hydrogen production via ethanol steam reforming. In this study, sol gel made alumina supports prepared for nickel (Ni) catalysts were calcined at different temperatures. A series of (Ni/Al S.G. ) catalysts were synthesized by an impregnation procedure. The influence of varying the calcination temperature of the sol gel made supports on catalyst activity was tested in ethanol reforming reaction. The characteristics of the sol gel alumina supports and Ni catalysts were affected by the calcination temperature of the supports. The structure of the sol gel made alumina supports was transformed in the order of γ → (γ + θ) → θ-alumina as the calcination temperature of the supports increased from 600 °C to 1000 °C. Both hydrogen yield and ethanol conversion presented a volcano-shaped behavior with maximum values of 4.3 mol/mol ethanol fed and 99.5%, respectively. The optimum values were exhibited over Ni/Al S.G800 (Ni catalyst supported on sol gel made alumina calcined at 800 °C). The high performance of the Ni/Al S.G800 catalyst may be attributed to the strong interaction of Ni species and sol gel made alumina which lead to high nickel dispersion and small particle size.

Procedia - Social and Behavioral Sciences

The objective of the study is to examine the effectiveness of learning and teaching techniques of... more The objective of the study is to examine the effectiveness of learning and teaching techniques of communication and teamwork skills of students in the learning process in the university. The study was based on a survey form and the examination results of students in courses selected by Department of Chemical and Process Engineering, which is Utilities Design and Integrated Projects (IP) with 75 and 43 respondents, respectively. The data analysis obtained shows that students are receptive to carrying out tasks in small group, satisfaction with the evaluation through presentations and receive new knowledge.

Deposition of amorphous particles, as a prevalent problem particularly in the spray drying of fru... more Deposition of amorphous particles, as a prevalent problem particularly in the spray drying of fruit and vegetable juices, is due to low-molecularweight sugars and is strongly dependent on the condition of the particles upon collision with the dryer wall. This paper investigates the condition of the amorphous particles impacting the wall at different drying conditions with the aim of elucidating the deposition mechanism and physical phenomena in the drying chamber. A model sucrose-maltodextrin solution was used to represent the low-molecular-weight sugar. Particle deposits were collected on sampling plates placed inside the dryer for analyses of moisture content, particle rigidity (using SEM) and size distribution. Moisture content was adopted as a general indicator of stickiness. Product particles collected at the bottom of the experimental dryer were found to have higher moisture than particle deposits on samplers inside the dryer. Moisture content profile in the dryer shows that apart from the atomizer region, where particles are relatively wet, particle deposits at other regions exhibit similar lower moisture content. At the highest temperature adopted in the experiments, particles became rubbery suggesting liquid-bridge formation as the dominant deposition mechanism. Further analysis on particles size distribution reveals a particle segregation mechanism whereby smaller particles follow preferentially to the central air stream while larger particles tend to re-circulate in the chamber, as predicted in past CFD simulation. The findings from this work will form the basis and provide validating data for further modeling of wall deposition of amorphous particles in spray drying using CFD.

Advanced Materials Research, 2014

ABSTRACT A high performance lateral silicon photodiode was designed on a Silicon–on-insulator (SO... more ABSTRACT A high performance lateral silicon photodiode was designed on a Silicon–on-insulator (SOI)-based substrate with SiGe/Si quantum dot technology. The device has the potential of being a serious candidate for applications in sensing applications as well as in optical fiber communications. Five device process parameters and two device noise factors were identified to make the virtual device design insensitive to variation in the selected fabrication parameters. An L9 array from Taguchi method was used to optimize the device design. The simulator of ATHENA and ATLAS were used for photodiode fabrication process and electrical characterization, respectively. The results obtained for responsivity and frequency response after the optimization approach were 0.36 A/W and 21.2 GHz respectively which correspond to the optimization value for the intrinsic region length of 6 μm, photo-absorption layer thickness of 0.505 μm, incident optical power of 0.5 mW/cm2 and bias voltage of 3.5 V. As a conclusion, the optimum solution in achieving the desired high speed photodiode was successfully predicted using Taguchi optimization method.

JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 2001

Batch experimental work on the fluidization hydrodynamic and entrainment phenomena of cohesive st... more Batch experimental work on the fluidization hydrodynamic and entrainment phenomena of cohesive starch powders was studied. Results show that fluidization can be realized as vibration break particleparticle bond in the bed. The higher U mf values compared to predictions indicate the formation of agglomerates in the bed. This has increased the residence time of fines to reduce material loss by entrainment. It was found that using starch powders as feed materials, entrainment was only in the range of 0.5-1.7% of the total fines (should be entrained) in the bed. As has also been found by other workers, the entrainment rate constants of group C decrease as particle size decreases. By adapting the criterion proposed by Rietema (1984) as well as Ma and Kato (1998), it was found in this case that the critical cohesion number, N coh * is 19.

Drying Technology, 2007

... Meng Wai Woo, Wan Ramli Wan Daud, Siti Masrinda Tasirin, and Meor Zainal Meor Talib Deparment... more ... Meng Wai Woo, Wan Ramli Wan Daud, Siti Masrinda Tasirin, and Meor Zainal Meor Talib Deparment of Chemical & Processing Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi ... The rig is held in place by pushing against the dryer wall using the stud rod and bolts. ...

Crystal Growth & Design, 2009

An examination of the aqueous solution solubility and batch crystallization kinetics of L-isoleuc... more An examination of the aqueous solution solubility and batch crystallization kinetics of L-isoleucine at the 250 mL scale size under a poly-and isothermal process condition is presented. Solubility data determined are consistent with the existence of two L-isoleucine polymorphic forms, in which both forms have different solubility and they are enantiotropically related. These polymorphs (A and B) can be recovered at different cooling rates of cooling crystallization. Crystal characterization using optical microscopy, differential scanning calorimetry, X-ray powder diffraction, and Fourier transform IR microscopy confirm this polymorphic behavior. Polythermal crystallization kinetic studies revealed the crystallization temperature increases with cooling rate and solute concentration, which results in a decrease of the metastable zone width (MSZW) with a decreasing cooling/heating rate. The study also revealed that cooling rates affect the polymorph formation, where at cooling rates of 0.25-0.75°C/min, form B is formed, while a more stable polymorph A can be recovered at a cooling rate of 0.10°C/min. Isothermal studies showed that the range of nucleation rate is between 1.79 × 10 -5 and 7.53 × 10 -4 kg/(m 3 min), and the interfacial surface free energy at high and low supersaturation system is 1.74 and 0.576 mJ/m 2 , respectively. For a high supersaturation system, the critical cluster radius r* is between 5-17 Å, associated with between 3-121 molecules (N*), and for a low supersaturation system, r* is between 3 and 14 Å and N* is between 1 and 64. For a pH range of 5.1-6.3 and a temperature range between 10 and 80°C, zwitterion species of L-isoleucine has remained as a dominating species in both solubility and crystallization studies. Thermodynamics properties generated from solubility data were also presented and discussed.

Catalysis Letters, 2007

Ethanol steam reforming has been studied over Ni/SiO 2 catalysts under a wide range of operating ... more Ethanol steam reforming has been studied over Ni/SiO 2 catalysts under a wide range of operating conditions, and the effect of Ni loading on catalyst properties and H 2 yield and selectivity has been analyzed. Surface area and pore volume significantly decrease with nickel content, but there is only a slight decrease in mean pore diameter. XRD patterns show peaks corresponding to NiO but no evidence of nickel silicate species has been found. Ni/SiO 2 catalysts are active for H 2 production by ethanol steam reforming over 400 ºC. Ethanol conversion and H 2 yield considerably increase with temperature and Ni loading. Up to 3.9 mol H2 /mol EtOH is obtained at 600 ºC and 8.3 g catalyst min/g EtOH , although lower temperatures (500 ºC) are more suitable for minimizing CO selectivity. An improvement in catalyst performance is observed for high values of time-on-stream, which is explained by coke deposition in the form of carbon fibers.

In this work, bamboo-shaped, multi-walled carbon nanotubes were synthesized via methane decomposi... more In this work, bamboo-shaped, multi-walled carbon nanotubes were synthesized via methane decomposition over a Ni–Co–Fe tri-metallic catalyst at 1000 °C. The nitrogen absorption (BET), X-ray diffraction (XRD), and particle size analysis results of the catalyst were used to demonstrate the surface area, size distribution, and crystallinity of the sample. The scanning electron microscopy (SEM) micrographs of the nanocarbons deposited via methane decomposition indicated that highly uniform carbon nanotubes were grown on the surface of the tri-metallic catalyst. The transmission electron microscopy (TEM) images showed that the carbon nanotubes were multi-walled and bamboo-shaped with a diameter of ~20 nm. Raman spectra revealed the graphitization degree of the CNTs with an I D /I G of 1.84, indicative of the crystallinity of CNTs with structural defects. The thermal analysis shows the high oxidation stability of the multi-walled carbon nanotubes.