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Biodiesel is a renewable alternative to “petro-diesel”. There is an established conventional production technology based on refined vegetable oils. However, this is always more expensive than petroleum-based diesel, mainly due to the feedstock cost, and the biodiesel market is based on subsidies. Use of a cheap non-edible feedstock, such as waste shark liver oil (WSLO), would reduce the biodiesel production cost and make the process more economically viable. In this study, production of fatty acid methyl ester (FAME) from WSLO using both acid (H2SO4) and base (NaOH) catalysts were investigated using a Design of Experiments approach (response surface methodology). Due to the high levels of FFA (free fatty acids) homogeneous alkali-catalysed transesterification of WSLO was less effective than the acid-catalysed process, resulting in WSLO to FAME conversion of 12% after 60 min, with maximum FAME conversion of about 40% after 15 min. Acid-catalysed WSLO transesterification achieved 99% FAME conversion at 10.3 M ratio of methanol to WSLO, 6.5 h reaction time, 60 °C temperature, and 5.9 wt % of H2SO4 catalyst. more...

Formation of styrene carbonate (SC) by the cycloaddition of CO2 to styrene oxide (SO) catalysed by pyrrolidinopyridinium iodide (PPI) in combination with zinc halides (ZnCl2, ZnBr2 and ZnI2) was investigated. Complete conversion of the SO to SC was achieved in 3 h with 100% selectivity using 1/0.5 molar (PPI/ZnI2) catalyst ratio under mild reaction conditions i.e., 100 °C and 10 bar CO2 pressure. The synergistic effect of ZnI2 and PPI resulted in more than 7-fold increase in reaction rate than using PPI alone. The cycloaddition reaction demonstrated the first-order dependence with respect to the epoxide, CO2 and catalyst concentrations. Moreover, the kinetic and thermodynamic activation parameters of SC formation were determined using the Arrhenius and Eyring equations. The positive values of ΔH‡ (42.8 kJ mol–1) and ΔG‡ (102.3 kJ mol–1) revealed endergonic and chemically controlled nature of the reaction, whereas the large negative values of ΔS‡ (–159.4 J mol–1 K–1) indicate a highly ordered activated complex at the transition state. The activation energy for SC formation catalyzed by PPI alone was found to be 73.2 kJ mol–1 over a temperature range of 100–140 °C, which was reduced to 46.1 kJ mol–1 when using PPI in combination with ZnI2 as a binary catalyst. Based on the kinetic study, a synergistic acid-based reaction mechanism was proposed. more...

Contamination of ground water and soil by arsenic poses serious environmental challenges globally. A possible solution to this problem is through phytoremediation using hyper-accumulating plants. This study investigates phytoremediation of soil containing 200 ± 3 mg kg−1 of arsenic using Pteris cretica ferns, and the strategies for arsenic extraction from the ferns biomass and subsequent conversions to valuable arsenic products. The Pteris cretica ferns achieved maximum arsenic accumulations of 4427 ± 79 to 4875 ± 96 mg of arsenic per kg dry biomass after 30 days. Extraction efficiencies of arsenic in the ferns fronds were 94.3 ± 2.1% for ethanol-water (1:1 v/v), 81.5 ± 3.2% for 1:1 (v/v) methanol-water, and 70.8 ± 2.9% for water alone. Molybdic acid process was used to recover 90.8 ± 5.3% of the arsenic, and 95.1 ± 4.6% of the phosphorus in the biomass extract. Quantitative precipitation of Mg3(AsO4)2 and Mg3(PO4)2 occurred on treatment of the aqueous solutions of arsenic and phosphorus after stripping at pH of 8–10. The efficiencies of Mg3(AsO4)2 and Mg3(PO4)2 precipitation were 96 ± 7.2% and 94 ± 3.4%, respectively. Arsenic nanoparticles produced from the recovered Mg3(AsO4)2, using two-stage reduction process, had average particle diameters of 45.5 ± 11.3 nm. These nanoparticles are potentially valuable for medical applications, while the Mg3(AsO4)2 could be converted to more valuable forms of arsenic or used as a pesticide, and the Mg3(PO4)2 in fertiliser. Recovery of these valuable products from phytoremediation biomass would incentivise and drive commercial industries' participation in remediation of contaminated lands. more...

Methyl esters of fatty acids are widely used as biodiesel, a sustainable replacement for petro-diesel. The conventional biodiesel process produces crude glycerol, which constitutes about 10 wt% of the total products. This has led to a surplus of crude glycerol due to global increase in biodiesel use, necessitating increased research into sustainable processes that could convert the crude glycerol into higher value-added products. This study investigates biodiesel processes for continuous transesterification of triglycerides to methyl esters, coupled to conversion of the glycerol by-product into solketal, a value-added product, via reaction with acetone in situ. The study was carried out using one-stage and two-stage catalytic transesterification of triacetin and methanol in mesoscale oscillatory baffled reactors (meso-OBRs). The two-stage process involved two meso-OBRs in series packed with AmberlystTM resin catalysts: a basic AmberlystTM A26-OH in the first stage to catalyse transesterfication of triacetin with methanol, and an acidic AmberlystTM 70-SO3H in the second stage to catalyse the coupling of glycerol and acetone to form solketal. One-stage triacetin transesterification and glycerol coupling with acetone was carried out in a meso-OBR packed with the acidic AmberlystTM 70-SO3H resin. In the two-stage process, the triacetin was converted to 99.1 ± 2.0% methyl acetate and 98.0 ± 1.3% glycerol after 25 min residence time in the first reactor and the glycerol was reacted with acetone in the second reactor to achieve 76.5 ± 2.8% solketal conversions after 35 min. The single-stage process achieved 48.5 ± 2.7% solketal conversion after 30 min. The meso-OBR was operated continuously to achieve high quality steady states and consistent triacetin conversions. The triglyceride transesterification with reactive coupling of glycerol with acetone produces less crude glycerol by-product. This process strategy could be optimised for future biodiesel production. more...

A simple and robust microalgae kinetic model has been developed for application in the prediction and control of algae cultivations in wastewater. The microalgae kinetic model was calibrated using experimental cultivation data from Desmodesmus sp. to determine specific microalgae growth rates (μmax and μmaxNO3), microalgae death rates (μd), and the NH4+ to NO3− oxidation rate (μB). Model parameters obtained were: μmax = 0.17 day−1, μd = 0.004 day−1, and μB = 0.14 day−1. Microalgae specific growth rate based on NO3− alone (μmaxNO3 = 0.1 day−1) was lower than the overall growth rate (μmax). The kinetic model was validated using additional experimental data for the Desmodesmus sp. and Scenedesmus obliquus cultivation in wastewater containing 0% and 7% landfill leachate, with accuracy above 98% in all cases. These results demonstrated the kinetic model was accurate in predicting microalgae growth, wastewater nutrient removal, and changes in the culture media pH. Biomass productivity of the algae culture was associated with an exponential increase in the media pH, which led to ammonia volatilisation and decreased carbon intake. Between 28.8 and 29.7% of the initial NH4+ was lost to ammonia volatilisation in wastewater containing 7% landfill leachate. Hence, loss of ammonium nitrogen contained in domestic wastewater must be avoided to ensure steady and efficient inorganic carbon utilisation which inherently maximises biomass production efficiency. The optimal pH for the microalgae culture was 8.1, at which point microalgae could achieve about 99% carbon fixation efficiency. To ensure constant pH in the microalgae growing system, immediate removal of the OH− generated is needed, which could be facilitated by injections of 1.14 g CO2 and 0.067 g OH− per gram of produced algae when using NH4+ nutrient, and 1.54 g of CO2 per gram of produced algae when using NO3− nutrient. This could be done in a wastewater pond by using an optical density-controlled smart CO2 injection system. more...

Homogenous alkali-catalysed biodiesel production from waste cooking oil (WCO) requires acid-catalysed pre-treatment steps due to high free fatty acid (FFA) contents. This study investigated strategies to obtain high yields of fatty acid methyl esters (FAME) from one-step base-catalysed transesterification of WCO containing high levels of free fatty acids (up to 5.5 wt%) and 3 wt% of water by altering operating conditions. About 98% FAME yield in homogeneous NaOCH3-catalysed transesterification was obtained within 5 min reaction time at methanol to WCO molar ratios of 12:1–18:1 and 3 wt% catalyst loading for WCO containing 1.53% FFA and 0.12 wt% water. It was found that high molar ratios of methanol to oil (>6:1) could prevent saponification. At 5.5 wt% FFA and 3 wt% water contents, ≥96.5% FAME yield was achieved at 18:1 M ratio of methanol to WCO within 5 min compared to only 62.8 ± 1.2% for a molar ratio of 6:1. Mathematical modelling (MATLAB) was used to predict FAME yields at various conditions and validated using experimental data. Sets of conditions identified in this study can be used to rapidly produce biodiesel from low quality triglyceride sources in a single step base-catalysed process. more...

Intensified production of carboxylic acid esters has been investigated using a mesoscale oscillatory baffled reactor (meso-OBR), operated in continuous multi-steady states, dynamic and multi-dimensional modes. This study was performed to investigate the suitability of the reactor for solid-liquid reactions, capacity for quality steady states and rapid process development. A heterogeneously catalysed hexanoic acid esterification with methanol was studied in a meso-OBR packed with Amberlyst™ 70 resin as an acid catalyst. The esterification conditions investigated were feed molar ratios in the range of 1.5:1–30:1 and residence times in the range of 1 min–20 min. The meso-OBR was operated at oscillatory conditions of 4.5 Hz frequency and 8 mm amplitude (centre-to-peak) and reaction temperature of 60 °C. Clear steady states were achieved at all the residence times used, with maximum hexanoic acid to methyl hexanoate conversion of 95.4 ± 1.0% obtained at 20 min residence time and 30:1 methanol to acid molar ratio. Methyl ester conversions were 98.5 ± 1.5% at 20 min residence time and 30:1 methanol to acid molar ratio for dynamic screening, and 98.2 ± 1.1% at 14 min residence time and 21:1 methanol to acid molar ratio for the multi-dimensional mode. Use of dynamic screening required 16% less time and reactant compared to the multi-steady states approach. A more significant reduction in the process development time and reactants requirement, approximately 30% compared to the multi-steady states approach, was achieved using the multi-dimensional approach. This demonstrates a substantial reduction in process development time, another major advantage of the meso-OBR platform as the choice reactor in process development for multiphase reactions. The Amberlyst™ 70 entirely regained its catalytic activity after water spiking, and was not permanently deactivated by water. more...

Naturally occurring terpenes have been identified as key starting materials for bio-based polymers such as non-isocyanate polyurethanes (NIPUs), having a broad range of applications such as thermoset materials, elastomers, or thermoplastics, etc. In this study, synthesis of trans-limonene bis-epoxide (trans-LBE) was carried out via stereoselective di-bromohydration of both the exocyclic and endocyclic double bonds of (R)-(+)-limonene. The effects of various parameters such as reaction temperature, (R)-(+)-limonene:N-bromosuccinimide (NBS) molar ratio and reaction time were investigated. As a result, a 97 % yield of trans-LBE was achieved using 1:2 (R)-(+)-limonene: NBS molar ratio at 60 °C after 5 min of reaction time. more...

Reaction kinetics for heterogeneous catalysis of styrene carbonate (SC) synthesis via CO2 cycloaddition to styrene oxide (SO) using silica-supported pyrrolidinopyridinium iodide (SiO2-PPI) catalyst has been investigated. The results obtained from the mixing study and theoretical analysis based on Thiele modulus ( more...

The research focused mainly on kinetics of the side reactions occurring during homogeneous base-catalysed transesterification processes, which were not studied previously. The rates of fatty acid methyl esters (FAME) saponification with sodium and potassium hydroxides were investigated in methanol and ethanol (commonly used in biodiesel production) at temperatures of 40, 50 and 60 °C. The effect of water on the rate of FAME saponification in the alcoholic hydroxide solutions was also studied (at 60 °C). The apparent rate constants of FAME saponification were strongly influenced by the types of alcohol, but little affected by variation of the metal hydroxides. The apparent rate constants for FAME saponification using the ethanol hydroxides were 5–7 times higher than for methanol hydroxides. This was due to the lower acidity of ethanol, leading to a higher concentration of hydroxide ions in the ethanol–hydroxide solutions. The rate constant of the FAME saponification increased with temperature. For example, it was 1.31 L mol −1 min −1 at 40 °C, but 3.08 and 5.63 L mol −1 min −1 at 50 and 60 °C in the methanol–NaOH solution. Arrhenius activation energies for the FAME saponification in the alcoholic hydroxides were in the range of 60.3–64.0 kJ mol −1 . It was found that the FAME saponification rate in ethanol–hydroxides was 3.5 times higher than that in methanol–hydroxides in the presence of water. This indicates that use of methanol should be preferred over ethanol in alkali-catalysed transesterification, as the amount of soap produced by saponification of triglycerides and alkyl esters will be lower. more...

A more robust kinetic model of base-catalysed transesterification than the conventional reaction scheme has been developed. All the relevant reactions in the base-catalysed transesterification of rapeseed oil (RSO) to fatty acid methyl ester (FAME) were investigated experimentally, and validated numerically in a model implemented using MATLAB. It was found that including the saponification of RSO and FAME side reactions and hydroxide–methoxide equilibrium data explained various effects that are not captured by simpler conventional models. Both the experiment and modelling showed that the “biodiesel reaction” can reach the desired level of conversion (>95%) in less than 2 min. Given the right set of conditions, the transesterification can reach over 95% conversion, before the saponification losses become significant. This means that the reaction must be performed in a reactor exhibiting good mixing and good control of residence time, and the reaction mixture must be quenched rapidly as it leaves the reactor. more...