Prof. Ir. Dr. Nor Aishah Saidina Amin

Abstract:

The aim of dynamic modeling of the tapioca starch hydrolysis process is to generate models for forecasting the future product concentration (glucose) from the initial conditions of available process measurements. This paper compares two methods of modeling the tapioca starch hydrolysis process: (1) The empirical approach and (2) the feed forward neural network (FFNN) approach. Experiments were conducted to obtain a set of data for the modeling purpose. The Gauss-Newton method was used for parameter estimation in the empirical analysis and a multilayer neural network with one hidden layer was utilized in the neural networks approach. This study indicates that the FFNN model of tapioca starch hydrolysis produces better predictive accuracy, that is simpler to develop and has a generalization capability compared with the empirical model.

1. Roslina Rashid, Hishamuddin Jamaluddin and Nor Aishah Saidina Amin (2006). Empirical and Feed Forward Neural Networks Models of Tapioca Starch Hydrolysis. Applied Artificial Intelligence, 20 (1), 79-96, Taylor & Francis.

Abstract:

The effects of operating temperature, inlet oxygen concentration, and F/W on ethylene production by oxidative coupling of methane (OCM) were studied over Li/MgO (Li/Mg = 0.1) catalyst. Central composite experimental design (CCD) and response surface methodology (RSM) were utilized to determine the best operating condition for maximum ethylene production. The design led to three surface responses describing the dependence of methane conversion, ethylene yield, and ethylene selectivity on operating temperature (737-913°C), inlet oxygen concentration (6.2-23.8 vol.%) and F/W (9280-35,720 ml/g h). The equation models were tested with analysis of variance with 5% level of significance. The results of the analysis revealed that the equation models fitted well with the experimental results for methane conversion and ethylene yield. Numerical results indicated the maximum ethylene yield was 8.14% at optimum operating temperature = 839.51°C, inlet oxygen concentration = 18.89 vol.% and F/W = 20264.34 ml/g h. Additional experiments were carried out at the optimum condition for verification.

1. Nor Aishah Saidina Amin and Soon Ee Pheng (2006). Influence of Process Variables and Optimization of Ethylene Yield in Oxidative Coupling of Methane over Li/MgO Catalyst. Chemical Engineering Journal, 116, 187-195, Elsevier.

Abstract:

Metal containing ZSM-5 can produce higher hydrocarbons in methane oxidation. Many researchers have studied the applicability of HZSM-5 and modify ZSM-5 for methane conversion to liquid hydrocarbons, but their research results still lead to low conversion, low selectivity and low heat resistance. The modified HZSM-5, by loading with tungsten (W), could enhance its heat resistant performance, and the high reaction temperature (800 °C) did not lead to a loss of the W component by sublimation. The loading of HZSM-5 with tungsten and copper (Cu) resulted in an increment in the methane conversion as well as CO2 and C5+ selectivities. In contrast, CO, C2–3 and H2O selectivities were reduced. The process of converting methane to liquid hydrocarbons (C5+) was dependent on the metal surface area and the acidity of the zeolite. High methane conversion and C5+ selectivity, and low H2O selectivity are obtained over W/3.0Cu/HZSM

1. Didi Dwi Anggoro and Nor Aishah Saidina Amin (2006). Methane Conversion to Liquid Hydrocarbons Over W-ZSM-5 and W-loaded Cu-HZSM-5. ASEAN Journal of Chemical Engineering, 6 (2), 58 – 65.

Abstract:

This paper deals with thermodynamic chemical equilibrium analysis using the method of direct minimization of Gibbs free energy for all possible CH4 and CO2 reactions. The effects of CO2/CH4 feed ratio, reaction temperature, and system pressure on equilibrium composition, conversion, selectivity and yield were studied. In addition, carbon and no carbon formation regions were also considered at various reaction temperatures and CO2/CH4 feed ratios in the reaction system at equilibrium. It was found that the reaction temperature above 1100 K and CO2/CH4 ratio=1 were favourable for synthesis gas production with H2/CO ratio unity, while carbon dioxide oxidative coupling of methane (CO2 OCM) reaction to produce ethane and ethylene is less favourable thermodynamically. Numerical results indicated that the no carbon formation region was at temperatures above 1000 K and CO2/CH4 ratio larger than 1

1. Istadi and Nor Aishah Saidina Amin (2005). Cogeneration of C₂ Hydrocarbons and Synthesis Gases from Methane and Carbon Dioxide: A Thermodynamic Analysis. Journal of Natural Gas Chemistry, 13 (3), 148-159, Science Press.

Abstract:

The catalytic activity of a series of CeO₂-ZrO₂ mixed oxides in the selective catalytic reduction (SCR) of NO by C₃H₆ at 400 °C has been investigated. The NO reduction activity of pure CeO₂ is enhanced in the presence of Zr, reaching a maximum NO conversion with CeO₂(75)-ZrO₂(25) catalyst. Then, the catalytic performances of Cu(4)/Ag(1)/CeO₂ and Cu(4)/Ag(1)/CeO₂(75)-ZrO₂(25) catalysts were compared and the latter showed better activity especially in the low temperature region (250–350 °C). The stronger metal-support interaction and higher reducibility shown by the Cu(4)/Ag(1)/CeO₂(75)-ZrO₂(25) catalyst were believed to enhance its performance compared to Cu(4)/Ag(1)/CeO₂ catalyst by activating more C₃H₆ to selectively reduce NO within this temperature region. Central composite response surface design methodology was employed to study the effect of operating variables such as temperature, NO and C₃H₆ concentrations on the SCR of NO by C₃H₆ over Cu(4)/Ag(1)/CeO₂(75)-ZrO₂(25) catalyst and to determine the optimum value of operating variables for maximum NO conversion. Numerical results indicated that the optimum NO conversion of 82.89% is attained at reaction temperature = 415.38 °C, NO concentration = 1827.16 ppm and C₃H₆ concentration = 1908.13 ppm. The addition of water vapor to the reactant significantly decreased the NO conversion over Cu(4)/Ag(1)/CeO₂ and Cu(4)/Ag(1)/CeO₂(75)-ZrO₂(25), but the inhibition was more pronounced over Cu(4)/Ag(1)/CeO₂ catalyst.

1. Nor Aishah Saidina Amin and Chong Chee Ming (2005). SCR of NO with C₃H₆ in the Presence of Excess O₂ over Cu/Ag/CeO₂ – ZrO₂   Chemical Engineering Journal, 113, 13-25, Elsevier.

Abstract:

The catalytic conversion of a methane and ethylene mixture to gasoline range hydrocarbons has been studied over W/HZSM-5 catalyst. The effect of process variables, such as temperature, percentage of volume of ethylene in the methane stream and catalyst loading on the distribution of hydrocarbons was studied. The reaction was conducted in a fixed-bed quartz-micro reactor in the temperature range of 300–500 °C using percentage of volume of ethylene in methane stream between 25 and 75% and catalyst loading of 0.2–0.4 g. The catalyst showed good catalytic performance yielding hydrocarbons consisting of gaseous products along with gasoline range liquid products. The mixed feed stream can be converted to higher hydrocarbons containing a high-liquid gasoline product selectivity (>42%). Non-aromatics C₅–C₁₀ hydrocarbons selectivity in the range of 12–53% was observed at the operating conditions studied. Design of experiment was employed to determine the optimum conditions for maximum liquid hydrocarbon products. The distribution of the gasoline range hydrocarbons (C₅–C₁₀ non-aromatics and aromatics hydrocarbons) was also determined for the optimum conditions.

1. Kusmiyati and Nor Aishah Saidina Amin (2005). Production Of Gasoline Range Hydrocarbons From Catalytic Reaction Of Methane In The Presence Of Ethylene Over W/HZSM-5. Catalysis Today, 106, 271-274, Elsevier.

Abstract:

The screening of a series of W-based catalysts on different supports i.e. HZSM-5, Hβ, USY and Al₂O₃ for the dehydroaromatization of methane (DHAM) revealed that HZSM-5 emerged as the best support. Next, the performance of W/HZSM-5 and W-H₂SO₄/HZSM-5 catalysts for the DHAM reaction was compared to study the effect of acidic treatment in the impregnation method. The results showed that the optimum activity of W-H₂SO₄/HZSM-5 catalyst exceeded that of W/HZSM-5 catalyst. Finally, the influence of Si/Al ratio in the W-H₂SO₄/HZSM-5 catalyst was studied and the catalyst with Si/Al ratio = 30 was found to be the most promising for the DHAM reaction. The remarkable activity of the catalyst is attributed to the presence of dual effects: suitable content of octahedral polymeric and tetrahedral monomeric tungstate species accompanied by proper amount and strength of acid sites in the catalyst.

1. Kusmiyati and Nor Aishah Saidina Amin (2005). Dual effect of Supported W Catalyst for Dehydroaromatization of Methane in the Absence of Oxygen. Catalysis Letters, 102 (1-2), 69-78, Springer.

Abstract:

A new hybrid numerical approach, using Weighted Sum of Squared Objective Functions (WSSOF) algorithm, was developed for multi-responses optimization of carbon dioxide oxidative coupling of methane (CO₂ OCM). The optimization was aimed to obtain optimal process parameters and catalyst compositions with high catalytic performances. The hybrid numerical approach combined the single-response modeling and optimization using Response Surface Methodology (RSM) and WSSOF technique of multi-responses optimization. The hybrid algorithm resulted in Pareto-optimal solutions and an additional criterion was proposed over the solutions to obtain a final unique optimal solution. The simultaneous maximum responses of C₂selectivity and yield were obtained at the corresponding optimal independent variables. The results of the multi-response optimization could be used to facilitate in recommending the suitable operating conditions and catalyst compositions for the CO₂ OCM process.

1. Istadi and Nor Aishah Saidina Amin (2005). A Hybrid Numerical Approach for Multi-Responses Optimization of Process Parameters and Catalyst Compositions in CO₂ OCM Process over CaO-MnO/CeO₂ Chemical Engineering Journal, 106, 213-227, Elsevier.

Abstract:

The dehydroaromatization of CH₄ over W-supported ZSM-5 with varying degrees of Li⁺ ion-exchanged catalysts was studied with and without oxygen at 1073 K and 1 atm. The activity and stability of the catalysts for the conversion of CH₄ to aromatics over W supported HZSM-5 could be improved by replacing H⁺ proton associated with Brönsted acid with a suitable Li content on the ZSM-5 support and be further improved by adding oxygen in the feed. The 3WHLi-Z (5:1) catalyst with 74% of the original HZSM-5 strong acid sites displayed maximum activity and stability with and without oxygen addition in the feed gas.

1. Nor Aishah Saidina Amin and Kusmiyati (2004). Improved Performance Of W/HZSM-5 Catalysts For Dehydroaromatization Of Methane. Journal of Natural Gas Chemistry, 13 (3), 148-159, Science Press.

Abstract:

The catalyst screening tests for CO₂ oxidative coupling of methane (CO₂-OCM) were studied over ternary and binary metal oxide catalysts. The catalysts were prepared by doping MgO- and CeO₂-based solids with oxides from alkali (Li₂O), alkaline earth (CaO), and transition metal groups (WO₃ or MnO). The high reducibility of the CeO₂ catalyst, an important factor in the CO₂-OCM catalyst activity, could be enhanced by the presence of manganese oxide species. These species increased oxygen mobility and oxygen vacancies in the CeO₂ catalyst. The performance of 5%/MnO/15%CaO/CeO₂ catalyst was the most potential among the CeO₂-based catalysts. The 2%Li₂O/MgO catalyst showed the most promising C₂₊ hydrocarbons selectivity and yield at 98 and 5.7%, respectively. Carbon in CO₂ was only converted into CO. Carbon and/or hydrogen in methane were only converted into ethane, ethylene acetylene, and CO and/or hydrogen and water, respectively.

1. Istadi and Nor Aishah Saidina Amin (2004). Screening of MgO- and CeO₂– Based Catalysts for Carbon Dioxide Oxidative Coupling of Methane to C₂₊ Journal of Natural Gas Chemistry, 13 (1), 23-35, Science Press.