Saeed M. Al-Zahrani

A framework for visible-light water splitting

This review article reports the most significant advances made in H2 production via water-splitting and the challenges that need to be addressed over the coming years to verify the feasibility of H2 production by both inorganic semiconductors and living microorganisms as a competitive process in the hydrogen economy.

A method of predicting effective solvent extraction parameters for recycling of used lubricating oils

Solvent extraction technique is one of the cheapest and most efficient processes experienced in recycling of used lubricating oils. In this paper, the performance of three extracting solvents (2-propanol, 1-butanol, and methyl-ethyl-ketone (MEK) in recycling used oil was evaluated experimentally. The effect of the most critical parameters (type of solvent, solvent to oil ratio, and extraction temperature) was investigated. The results show that MEK achieved the best performance with the lowest percent oil losses, followed by 2-propanol and 1-butanol, and as the extraction temperature increases the percent oil losses decreases. The anti-solvency energy (Es), which originates from the solubility parameters difference between the solvent and oil was related to the solvent to oil ratio. It was found that the critical clarifying ratio predicted from such relations for the three solvents reasonably agrees with that measured experimentally. Relations between Es and solvent to oil ratio give a proper guideline for preliminary evaluation of the extracting solvent. It also can be used to predict the optimum solvent:oil ratio and extraction temperature based on the solvent ability to dissolve the base oil in used motor oil.

Combined organic―inorganic fouling of forward osmosis hollow fiber membranes

This research focused on combined organic-inorganic fouling and cleaning studies of forward osmosis (FO) membranes. Various organic/inorganic model foulants such as sodium alginate, bovine serum albumin (BSA) and silica nanoparticles were applied to polyamide-polyethersulfone FO hollow fiber membranes fabricated in our laboratory. In order to understand all possible interactions, experiments were performed with a single foulant as well as combinations of foulants. Experimental results suggested that the degree of FO membrane fouling could be promoted by synergistic effect of organic foulants, the presence of divalent cations, low cross-flow velocity and high permeation drag force. The water flux of fouled FO hollow fibers could be fully restored by simple physical cleaning. It was also found that hydrodynamic regime played an important role in combined organic-inorganic fouling of FO membranes.

A general model for the viscosity of waxy oils

A generalized viscosity model suitable for describing the non-Newtonian behaviour of waxy crudes has been developed. The model, which has the following expression predicts the viscosity as a function of shear rate, temperature, and wax concentration: m B 1 g [( gA1 A 1 ) n 1] (1:n) e (C:T D W) where m is the viscosity, g is the shear rate, T is the temperature, and W is the percentage of wax. The viscosity measurements were performed by measuring the rheological properties of the waxy oil at four different concentrations and five different temperatures. A reduced form of the model may be used to predict the viscosity of Newtonian and non-Newtonian fluids with or without yield stress. The proposed model was found to fit the experimental data well as demonstrated by a high coefficient of correlation (97.5%). The nonlinear regression analysis was used to determine the model parameters A, B, C, and n.

A generalized rheological model for shear thinning fluids

Abstract A generalized rheological model for shear thinning fluids has been developed. The new model relates shear stress to shear rate for this type of fluids and predicts the behaviour of hyperbolic, parabolic, elliptic, and Newtonian fluids with or without yield stress at one or both extremes of the shear rate. It correlates the shear stress to the shear rate for a variety of drilling fluids better than both the power-law and Hershel—Bulkley model. It can also predict the viscosity of these fluids. The shear stress and viscosity are required for pressure drop calculations of flow in pipes, annuli, and packed beds.

Ethanesulfonic acid-based esterification of industrial acidic crude palm oil for biodiesel production.

An industrial grade acidic crude palm oil (ACPO) pre-treatment process was carried out using ethanesulfonic acid (ESA) as a catalyst in the esterification reaction. ESA was used in different dosages to reduce free fatty acid (FFA) to a minimum level for the second stage of biodiesel production via alkaline transesterification reaction. Different process operating conditions were optimized such as ESA dosage (0.25-3.5% wt/wt), methanol to ACPO molar ratio (1:1-20:1), reaction temperature (40-70 °C), and reaction time (3-150 min). This study revealed the potential use of abundant quantities of ACPO from oil palm mills for biodiesel production. The lab scale results showed the effectiveness of the pre-treatment process using ESA catalyst. Three consecutive catalyst recycling runs were achieved without significant degradation in its performance. Second and third reuse runs needed more reaction time to achieve the target level of FFA content. Esterification and transesterification using ESA and KOH respectively is proposed for biodiesel industrial scale production. The produced biodiesel meets the international standards specifications for biodiesel fuel (EN 14214 and ASTM D6751).

Oxidative dehydrogenation of isobutane over pyrophosphates catalytic systems

The catalytic effect of metal pyrophosphates (i.e., Mn2P2O7, Ni2P2O7, CeP2O7, Mg2P2O7, ZrP2O7, Ba2P2O7, V4(P2O7)3 and Cr4(P2O7)3) on the oxidative dehydrogenation of isobutane to isobutene in the reaction temperature range of 400–600 °C has been investigated. CeP2O7 gives the highest isobutene yield and selectivity (71%), however, V4(P2O7)3 is the most active catalyst with an isobutane conversion of 33.5% at 500 °C. Increasing the reaction temperature results in higher isobutane conversions and lower isobutene selectivity. Reaction by-products are propylene, CO, CO2 and traces of methane and ethylene. No oxygenate products are formed under the used reaction conditions. The sum of selectivities of CO, CO2 and methane is approximately equal to that of propylene, indicating their formation from total oxidation of C1 species accompanying the isobutane crack reactions. Working at temperatures higher than 550 °C, the homogeneous gas phase reactions become significant and the oxygen conversion reaches 100%.

Alumina-supported chromium-based mixed-oxide catalysts in oxidative dehydrogenation of isobutane to isobutene

The effect of various metal additives on the catalytic performance of a chromium-based alumina-supported catalyst in oxidative dehydrogenation of isobutane was investigated in the low reaction temperature range 200 � /350 8C and at atmospheric pressure. Various parameters such as Cr wt.% in Cr � /M � /O system, different i C4H10:O2 ratios at a total flow rate of 75 cm 3 /min, and contact time on the activity and selectivity of the catalysts were varied in this study. For the binary catalysts, the addition of Co and Ni enhanced the overall activity while W and Mo improved the catalyst selectivity to i C4H8. The presence of V and Li deteriorated significantly the catalyst activity and selectivity. Increasing the percent of Cr in Cr � /M � /O increased i C4H10 and O2 conversion at the expense of selectivity. Tertiary systems such as Cr � /W � /Co � /O, Cr � /W � /Ni � /O and Cr � /Ni � /Co � / Og ave a much better overall performance compared with Cr � /O alone. In particular, Cr � /W � /Co � /O improved the overall activity of Cr � /O catalyst by 17% while its i C4H8 selectivity improved by 15%. The low temperature activity of these catalysts makes them important candidates for further investigations. # 2002 Elsevier Science B.V. All rights reserved.

Catalysts for Hydrogen Production from Heavy Hydrocarbons

Sustainable hydrogen production is a key target in the development of future alternative energy systems for providing a clean and affordable energy supply. Nowadays, the lack of widely available sources of H2 dictates the use of logistic fuels, multicomponent mixtures containing a large number of hydrocarbons, in the near term as a way to facilitate the introduction of hydrogen in energy systems, as this option entails no extra capital cost for developing the infrastructure and so relieves the economic pressure on moving to a hydrogen economy. A further advantage is that developments in the field of hydrogen generation from conventional fuels could be applied to the extraction of hydrogen from other liquid fuels that contain heavy hydrocarbons produced from biomass, thereby providing a bridge for the transition of hydrogen production from fossil fuels to renewable production from biomass. Catalysts for hydrogen production from heavy hydrocarbons have made remarkable progress in recent years, but there are various technical challenges, mainly low activity and durability, that need to be addressed for future improvement. This Review provides an overview of the research progress on hydrogen production from logistic hydrocarbons. The challenges for catalysts applied to the reforming of logistic hydrocarbons are discussed in detail to reveal the specific needs for each of the main reforming processes used with such hydrocarbons: Steam reforming, partial oxidation, and autothermal reforming. The four challenges for each process are activity, sulfur poisoning, carbon formation, and sintering. An overview is provided of the research strategies and approaches adopted in search of catalysts that respond to the above challenges; that is, selection of active phase, promoters, and supports and control of the synthesis of materials for customizing the crystallinity, electronic structure and morphology of catalysts at the nanoscale.

Studies on crystallization kinetics, microstructure and mechanical properties of different short carbon fiber reinforced polypropylene (SCF/PP) composites

Carbon fiber reinforced thermoplastics provide light weight materials with high mechanical, electrical and thermal properties required for aircraft, automobile and fuel cell and other high-end applications. In this study, short carbon fibers (SCF) of varying length were incorporated into polypropylene (PP) matrix to obtain short carbon fiber reinforced polypropylene (SCF/PP) composites by melt blending and injection molding techniques. The thermo-mechanical properties of SCF/PP composites were studied to investigate the effect of fiber length on their functionality. The crystallization behavior and the microstructure of SCF/PP were studied using several techniques such as differential scanning calorimeter (DSC), rheology and scanning electron microscopy (SEM). The thermo-mechanical stability of SCF/PP composites was shown to be improved with increase in fiber length. The isothermal crystallization kinetics of neat PP and SCF/PP composites were studied using Avrami equation. The results suggested the formation of two-dimensional growth of crystallites from instantaneous nucleation for neat PP as well as SCF/PP composites.