Ahmad Abdullah - Academia.edu (original) (raw)

Papers by Ahmad Abdullah

Journal of Plant Research, 1995

The morphological and phenological characteristics of leaf development ofDurio zibethinus Murray ... more The morphological and phenological characteristics of leaf development ofDurio zibethinus Murray were investigated at an experimental field of Universiti Pertanian Malaysia (UPM) in Selangor. Proportionality was observed in the relations of leaf length to leaf width and of leaf area to the product of leaf width and length. The proportionality was explained from the similarity of leaf shape. New leaves emerged continuously, but the number of new leaves fluctuated seasonally. The emergence of leaves was inhibited by the flower bud formation. In the survival curves of leaves, the relative fall rate was lower at the early stage of leaf development than at the late stage. Leaf longevity of 100 to 133 days was low and leaf expansion period of two weeks was short in comparison with the published data on tropical trees. From the ecophysiological viewpoint, the leaf survival strategy of the present species was discussed: the present species manages to set up a photosynthetic system in a short period by the rapid leaf growth; the lower leaf longevity is advantageous to reaching more frequently high photosynthetic production by newly emerged leaves.

Respirology, 2000

Observations have been made on the long-term trends of major air pollutants in Malaysia including... more Observations have been made on the long-term trends of major air pollutants in Malaysia including nitrogen dioxide, carbon monoxide, the ozone and total suspended particulate matter (particularly PM10), and sulfur dioxide, emitted from industrial and urban areas from early 1970s until late 1998. The data show that the status of atmospheric environment in Malaysia, in particular in highly industrialized areas such as Klang Valley, was determined both by local and transboundary emissions and could be described as haze and non-haze periods. During the non-haze periods, vehicular emissions accounted for more than 70% of the total emissions in the urban areas and have demonstrated two peaks in the diurnal variations of the aforementioned air pollutants, except ozone. The morning &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;rush-hour&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; peak was mainly due to vehicle emissions, while the late evening peak was mainly attributed to meteorological conditions, particularly atmospheric stability and wind speed. Total suspended particulate matter was the main pollutant with its concentrations at few sites often exceeding the Recommended Malaysia Air Quality Guidelines. The levels of other pollutants were generally within the guidelines. Since 1980, six major haze episodes were officially reported in Malaysia: April 1983, August 1990, June 1991, October 1991, August to October 1994, and July to October 1997. The 1997 haze episode was the worst ever experienced by the country. Short-term observations using continuous monitoring systems during the haze episodes during these periods clearly showed that suspended particulate matter (PM10) was the main cause of haze and was transboundary in nature. Large forest fires in parts of Sumatra and Kalimantan during the haze period, clearly evident in satellite images, were identified as the probable key sources of the widespread heavy haze that extended across Southeast Asia from Indonesia to Singapore, Malaysia and Brunei. The results of several studies have also provided strong evidence that biomass burning is the dominating source of particulate matter. The severity and extent of 1997&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s haze pollution was unprecedented, affecting some 300 million people across the region. The amount of economic costs suffered by Southeast Asian countries during this environmental disaster was enormous and is yet to be fully determined. Among the important sectors severely affected were air and land transport, shipping, construction, tourism and agro-based industries. The economic cost of the haze-related damage to Malaysia presented in this study include short-term health costs, production losses, tourism-related losses and the cost of avertive action. Although the cost reported here is likely to be underestimated, they are nevertheless significant (roughly RM1 billion). The general air quality of Malaysia since 1970 has deteriorated. Studies have shown that should no effective countermeasures be introduced, the emissions of sulfur dioxide, nitrogen oxides, particulate matter, hydrocarbons and carbon monoxide in the year 2005 would increase by 1.4, 2.12, 1.47 and 2.27 times, respectively, from the 1992 levels.

Journal of Plant Research, 2005

The daily variations in the in situ CO2 exchange of the reproductive organs of Durio zibethinus t... more The daily variations in the in situ CO2 exchange of the reproductive organs of Durio zibethinus trees, growing in an experimental field at University Putra Malaysia (UPM), were examined at different growth stages. Reproductive organs emerged on the leafless portions of branches inside the crown. The photon flux densities (PFD) in the chambers used for the measurements were less than 100 μmol m−2 s−1 and were 40% of the PFD outside of the crown. The daytime net respiration rate and the nighttime dark respiration rate were higher at the time of flower initiation and during the mixed stages, when flower buds, flowers, and fruit coexist, than at the flower bud stage. The net respiration rate was lower than the daytime dark respiration rate at given temperatures, especially at the flower bud and fruit stages. Conversely, the net respiration rate was similar to the daytime dark respiration rate at the mixed stage. Photosynthetic CO2 refixation reduced the daily respiratory loss by 17, 5, 0.3, and 24% at the flower bud, flower initiation, mixed, and fruit stages, respectively.

Trees-structure and Function, 1995

We examined the in situ CO2 gas-exchange of fruits of a tropical tree, Durio zibethinus Murray, g... more We examined the in situ CO2 gas-exchange of fruits of a tropical tree, Durio zibethinus Murray, growing in an experimental field station of the Universiti Pertanian Malaysia. Day and night dark respiration rates were exponentially related to air temperature. The temperature dependent dark respiration rate showed a clockwise loop as time progressed from morning to night, and the rate was higher in the daytime than at night. The gross photosynthetic rate was estimated by summing the rates of daytime dark respiration and net photosynthesis. Photosynthetic CO2 refixation, which is defined as the ratio of gross photosynthetic rate to dark respiration rate in the daytime, ranged between 15 and 45%. The photosynthetic CO2 refixation increased rapidly as the temperature increased in the lower range of air temperature T c (T c T c ≥28.5 °C). Light dependence of photosynthetic CO2 refixation was approximated by a hyperbolic formula, where light saturation was achieved at 100 μmol m−2 s−1 and the asymptotic CO2 refixation was determined to be 37.4%. The estimated gross photosynthesis and dark respiration per day were 1.15 and 4.90 g CO2 fruit−1, respectively. Thus the CO2 refixation reduced the respiration loss per day by 23%. The effect of fruit size on night respiration rate satisfied a power function, where the exponent was larger than unity.

Bioresource Technology, 2010

In this study optimization of drying oil palm trunk core lumber (OPTCL) biomass using microwave r... more In this study optimization of drying oil palm trunk core lumber (OPTCL) biomass using microwave radiation was reported. Optimizing of the drying conditions using microwave, avoid burning, shrinkage and increasing the permeability of OPT was aimed to develop a new value added material. A set of experiments was designed by central composite design using response surface methodology (RSM) to statistically evaluate the findings. Three independent process variables including time (2-10 min), sample weight (300-1000 g) and input power (660-3300 W) were studied under the given conditions designed by Design Expert software. The results showed the effectiveness of microwave drying in reducing the time and better removal of moisture as compared to that of oven drying with no significant changes. Employing optimum conditions at 6.89 min of time with a microwave power set at 4 for a sample of 1000 g, predicting 14.62% of moisture content.

The construction of new service centers is very costly and the optimal site selection of these ce... more The construction of new service centers is very costly and the optimal site selection of these centers, one of the parameters for determining their degree of effectivencess, is of high importance. Public parkings are an example for these service centers. Population growth, sprawling of cities and increasing of vehicles result in heavy traffic and prolonged city trips.Utilizing public parkings can be regarded as an effective approach to abate traffic load in city centers, in that spaces designated for vehicles parking along the roads would be freed, and consequently the usable space of the roads would increase, which in turn would contribute to the smooth flow of traffic. In this paper, we describe an ideal method for parking site selection by the use of GIS, fuzzy logic and weighting criteria to determine proper parking sites. Suitable place for parking is selected for one of the high traffic regions of Esfahan city in Iran.

Chemcatchem, 2009

The mitigation and utilization of greenhouse gases, such as carbon dioxide and methane, are among... more The mitigation and utilization of greenhouse gases, such as carbon dioxide and methane, are among the most important challenges in the area of energy research. Dry reforming of CH4 (DRM), which uses both CO2 and CH4 as reactants, is a potential method to utilize the greenhouse gases in the atmosphere. Natural gas containing high concentrations of CO2 and CH4 could therefore be utilized for hydrogen and synthesis gas (syngas) production in the near future, without need for the removal of CO2 from the source gas. Thus, the DRM reaction is a suitable process to convert CH4 and CO2 to syngas, which is a raw material for liquid fuel production, through the Fischer–Tropsch process. Herein, the development of CO2 reforming for syngas production is reviewed, covering process chemistry, catalyst development, and process technologies as well as the potential future direction for this process.

Journal of Membrane Science, 2009

The process optimization of p-xylene separation from p-/o-xylene binary mixture through silicalit... more The process optimization of p-xylene separation from p-/o-xylene binary mixture through silicalite-1 membrane using statistical design of experiments (DoE) is reported in the present study. The silicalite-1 membrane was synthesized and characterized using different analytical techniques. The effect of three important process variables, temperature (150-250 • C), p-xylene feed partial pressure (0.04-0.50 kPa) and p-xylene feed composition (0.20-0.80) on the separation performance of the membrane was studied. The response surface methodology (RSM) coupled with central composite design (CCD) was used to develop three models to correlate the effect of process variables to three responses: (i) p-xylene flux, (ii) o-xylene flux and (iii) p-/o-xylene separation factor. The most influential factor on each of the response was identified using the analysis of variance (ANOVA). The interaction between the three variables was systematically investigated based on three-dimensional response surface plots. The optimum operating condition for the process was determined by setting the optimization criteria to maximize the p-xylene flux and p-/o-xylene separation factor, and to minimize the o-xylene flux. The optimum p-xylene flux of 3.83 × 10 −6 mol/m 2 s and p-/o-xylene separation factor of 46 were obtained at a temperature of 198 • C, p-xylene feed partial pressure of 0.15 kPa and p-xylene feed composition of 0.80. The simulated values obtained from the statistical model were in agreement with the experimental results within an average error of ±2.70%. The mass transport of xylene isomers and its separation in the silicalite-1 membrane was related with the characteristics of the membrane.

Journal of Hazardous Materials, 2006

The paper reports on the performance of chromium or/and copper supported on H-ZSM-5 (Si/Al = 240)... more The paper reports on the performance of chromium or/and copper supported on H-ZSM-5 (Si/Al = 240) modified with silicon tetrachloride (Cr 1.5 /SiCl 4 -Z, Cu 1.5 /SiCl 4 -Z and Cr 1.0 Cu 0.5 /SiCl 4 -Z) as catalysts in the combustion of chlorinated VOCs (Cl-VOCs). A reactor operated at a gas hourly space velocity (GHSV) of 32,000 h −1 , a temperature between 100 and 500 • C with 2500 ppm of dichloromethane (DCM), trichloromethane (TCM) and trichloroethylene (TCE) is used for activity studies. The deactivation study is conducted at a GHSV of 3800 h −1 , at 400 • C for up to 12 h with a feed concentration of 35,000 ppm. Treatment with silicon tetrachloride improves the chemical resistance of H-ZSM-5 against hydrogen chloride. TCM is more reactive compared to DCM but it produces more by-products due to its high chlorine content. The stabilization of TCE is attributed to resonance effects. Water vapor increases the carbon dioxide yield through its role as hydrolysis agent forming reactive carbocations and acting as hydrogen-supplying agent to suppress chlorine-transfer reactions. The deactivation of Cr 1.0 Cu 0.5 /SiCl 4 -Z is mainly due to the chlorination of its metal species, especially with higher Cl/H feed. Coking is limited, particularly with DCM and TCM. In accordance with the Mars-van Krevelen model, the weakening of overall metal reducibility due to chlorination leads to a loss of catalytic activity.

Journal of Hazardous Materials, 2008

The performance of silver-loaded zeolite (HY and HZSM-5) catalysts in the oxidation of butyl acet... more The performance of silver-loaded zeolite (HY and HZSM-5) catalysts in the oxidation of butyl acetate as a model volatile organic compound (VOC) was studied. The objective was to find a catalyst with superior activity, selectivity towards deep oxidation product and stability. The catalyst activity was measured under excess oxygen condition in a packed bed reactor operated at gas hourly space velocity (GHSV)=15,000-32,000 h(-1), reaction temperature between 150 and 500 degrees C and butyl acetate inlet concentration of 1000-4000 ppm. Both AgY and AgZSM-5 catalysts exhibited high activity in the oxidation of butyl acetate. Despite lower silver content, AgY showed better activity, attributed to better metal dispersion, surface characteristics and acidity, and its pore system. Total conversion of butyl acetate was achieved at above 400 degrees C. The oxidation of butyl acetate followed a simple power law model. The reaction orders, n and m were evaluated under differential mode by varying the VOC partial pressure between 0.004 and 0.018 atm and partial pressure of oxygen between 0.05 and 0.20 atm. The reaction rate was independent of oxygen concentration and single order with respect to VOC concentration. The activation energies were 19.78 kJ/mol for AgY and 32.26 kJ/mol for AgZSM-5, respectively.

Separation and Purification Technology, 2011

Sonocatalytic degradation of Rhodamine B was investigated using titanium dioxide (TiO2) powder an... more Sonocatalytic degradation of Rhodamine B was investigated using titanium dioxide (TiO2) powder and titanium dioxide nanotubes (TiO2 NTs) which were synthesized using sol–gel and hydrothermal method, respectively. Structural and crystalline information for both types of catalyst were characterized using transmission electron microscope (TEM), X-ray diffractometer (XRD) and surface analyzer. Remarkable improvement in the sonocatalytic activity of TiO2 NTs was achieved

Chemical Engineering Journal, 2010

a b s t r a c t m-Xylene isomerization kinetics has been studied using acid-functionalized silica... more a b s t r a c t m-Xylene isomerization kinetics has been studied using acid-functionalized silicalite-1 catalytic membrane in the temperature range of 355-450 • C. Two types of catalytic membranes: (1) propylsulfonic acid-functionalized silicalite-1 membrane and (2) arenesulfonic acid-functionalized silicalite-1 membrane were synthesized on ␣-alumina support via one-step in situ hydrothermal crystallization and subsequent post-synthesis modifications. The membranes were characterized by scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH 3 -TPD) and Fourier transform infrared spectroscopy (FT-IR). Arenesulfonic acid-functionalized silicalite-1 membrane with its higher acidity gave better catalytic activity as compared to propylsulfonic acid-functionalized silicalite-1 membrane. The continuous removal of reaction products over the membrane contributed in the higher p-xylene yield. A triangular reaction scheme based on time on stream (TOS) model was used to analyze the experimental data. The simulated results were in good agreement with the experimental results, within an error less than ±5%. The estimated activation energies indicated that conversion of m-xylene to p-xylene in both acid-functionalized silicalite-1 membranes is affected by the mass transfer rate through the membrane, while conversion of m-xylene to o-xylene is controlled by the reaction rate.

Chemical Engineering Journal, 2008

Zeolite membranes are relatively new class of advanced materials where its characteristics have o... more Zeolite membranes are relatively new class of advanced materials where its characteristics have opened up the new opportunities of their application in separator, sensitive chemical sensors, and catalytic membrane reactor. The present review focuses on the development ...

Microporous and Mesoporous Materials, 2009

A series of partially crystalline silicalite-1 based materials were synthesized by varying the mo... more A series of partially crystalline silicalite-1 based materials were synthesized by varying the molar ratio of organosilane source, phenethyltrimethoxysilane (PE) to tetraethylorthosilicate (TEOS) in the range of 0.05-0.50, using one step co-condensation hydrothermal synthesis method. The phenethyl group was subsequently sulfonated to arenesulfonic acid group following strong acid treatment. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and desorption and elemental analysis. The structure of these materials was determined by Fourier transform infrared spectroscopy (FTIR), 29 Si and 13 C solid state NMR. The % crystallinity of the partially crystalline silicalite-1 as determined from XRD was in the range of 33-73%. The average crystallite size decreased with the increase of PE concentration in the synthesis mixture. The thermogravimetric analysis shows that the structures were thermally stable up to 550°C after elimination of the structure directing agents (SDAs) by calcination at 420°C. The acid capacities of these materials ranged from 2.52 to 6.63 mmol H + /g.

Industrial & Engineering Chemistry Research, 2003

Kinetic modeling of catalytic combustion of ethyl acetate and benzene over Cr-ZSM-5 (Si/Al ) 240)... more Kinetic modeling of catalytic combustion of ethyl acetate and benzene over Cr-ZSM-5 (Si/Al ) 240) is reported. Ethyl acetate was more reactive than benzene and could suppress benzene conversion in the binary mixture while water vapor retarded the conversion of both organics. Kinetic data obtained in the differential reactor at GHSV 78 900 h -1 were best fitted by the Mars-van Krevelen model. In binary mixtures, a competitive model based on the Mars-van Krevelen mechanism satisfactorily predicted the ethyl acetate reaction rate. Ethyl acetate was more favorably adsorbed on the oxidized catalytic sites and could stabilize benzene by inducing an electron cloud from the aromatic ring. The inhibition effect by water was modeled by a competitive adsorption mechanism. Deviation in reaction rates at a feedwater concentration of 9000 ppm was attributed to the formation of water clusters that blocked the internal diffusion of VOC molecules. The oxidation/reoxidation steps of the active sites appeared to be the ratelimiting steps in the catalytic combustion of VOC over Cr-ZSM-5 catalyst.