Continuous production of biodiesel with supercritical methanol: Optimization of a scale-up plug flow reactor by response surface methodology

A scale-up plug flow reactor was evaluated for the continuous production of biodiesel from refined palm kernel oil (PKO) with supercritical methanol and optimized by response surface methodology. The effects of the operating temperature (270–350 °C), pressure (15.0–20.0 MPa) and methanol:PKO molar ratio (20:1–42:1) were evaluated at a constant residence time of 20 ± 2 min by using a central composite design. Analysis of variance demonstrated that a modified quadratic regression model gave the best coefficient of determination (R² = 0.9615) and adjusted coefficient of determination (Adj. R² = 0.9273). The interaction terms in the regression model illustrated small synergistic effects of both temperature–pressure and temperature–methanol:PKO molar ratio. The optimal conditions were 325 ± 5 °C, 18.0 ± 0.5 MPa and a methanol:PKO molar ratio of 42 ± 2:1, attaining a maximum production rate of 18.0 ± 1.5 g biodiesel/min with a fatty acid methyl ester content of 93.7 ± 2.1%. The product obtained from the optimal conditions had high cetane number, and could be considered as a fuel additive for cetane number enhancement.     

Biodiesel production through transesterification over natural calciums

Transesterification of palm kernel oil (PKO) with methanol over various natural calciums, including limestone calcite, cuttlebone, dolomite, hydroxyapatite, and dicalcium phosphate, has been investigated at 60 °C and 1 atm. The study showed that dolomite, mainly consisting of CaCO₃ and MgCO₃, is the most active catalyst. The calcination temperature largely affected the physicochemical properties, as evidenced by N₂ adsorption-desorption measurement, TGA, SEM and XRD, and the transesterification performance of the resultant catalysts. It was found that the calcination of dolomite at 800 °C resulted in a highly active mixed oxide. CaO was suggested to be the catalytically active site responsible for the methyl ester formation. Under the suitable reaction conditions, the amount of dolomite calcined at 800 °C = 6 wt.% based on the weight of oil, the methanol/oil molar ratio = 30, and the reaction time = 3 h, the methyl ester content of 98.0% can be achieved. The calcined dolomite can be reused many times. The analyses of some important fuel properties indicated that the biodiesel produced had the properties that meet the standard of biodiesel and diesel fuel issued by the Department of Energy Business, Ministry of Energy, Thailand.     

CO2 gasification of Thai coal chars: Kinetics and reactivity studies

Two sized fractions (<75 μm and 150–250 μm) of Ban Pu lignite A and Lampang subbituminous B coals were pyrolyzed in a drop tube fixed bed reactor under nitrogen atmosphere at 500–900 °C. Gasification of coal chars with excess carbon dioxide was then performed at 900–1,100 °C. The result was analyzed in terms of reactivity index, reaction rate and activation energy. It was found that chars at lower pyrolysis temperature had highest carbon conversion, and for chars of the same sized fraction and at the same pyrolysis temperature, reactivity indices increased with gasification temperature. The lower rank Ban Pu lignite A had higher R _s values than higher rank Lampang subbituminous B coals. Smaller chars from both coals had higher R _s values, due to the higher ash content. At present, it can be concluded that, within the gasification temperature range studied, gasification rates of chars obtained at various pyrolysis temperatures showed a linear correlation with temperature. However, additional experiment is needed to verify the correlation.     

Al2O3-supported alkali and alkali earth metal oxides for transesterification of palm kernel oil and coconut oil

Transesterification of palm kernel oil (PKO) and coconut oil (CCO) with methanol was investigated under a heterogeneous catalysis system. Various Al₂O₃-supported alkali and alkali earth metal oxides prepared via an impregnation method were applied as solid catalysts. The supported alkali metal catalysts, LiNO₃/Al₂O₃, NaNO₃/Al₂O₃ and KNO₃/Al₂O₃, with active metal oxides formed at calcination temperatures of 450–550 °C, showed very high methyl ester (ME) content (>93%). XRF analysis suggests this is likely to be due to a homogeneous catalysis of dissoluted alkali oxides. On the other hand, Ca(NO₃)₂/Al₂O₃ calcined at 450 °C yielded the ME content as high as 94% with only a small loss of active oxides from the catalyst, whereas calcined Mg(NO₃)₂/Al₂O₃ catalyst possessed an inactive magnesium-aluminate phase, resulting in very low ME formation. At calcination temperatures of >650 °C, alkali metal- and alkali earth metal-aluminate compounds were formed. Whilst the water-soluble alkali metal aluminates formed over NaNO₃/Al₂O₃ and KNO₃/Al₂O₃ were catalytically active, the aluminate compounds on LiNO₃/Al₂O₃ and Ca(NO₃)₂/Al₂O₃ are less soluble, giving very low ME content. The suitable conditions for heterogeneously catalyzed transesterification of PKO and CCO over Ca(NO₃)₂/Al₂O₃ are the methanol/oil molar ratio of 65, temperature of 60 °C and reaction time of 3 h, with 10 and 15–20% (w/w) catalyst to oil ratio for PKO and CCO, respectively. Some important physical and fuel properties of the resultant biodiesel products meet the standards of diesel fuel and biodiesel issued by Department of Energy Business, Ministry of Energy, Thailand.     

Ca and Zn mixed oxide as a heterogeneous base catalyst for transesterification of palm kernel oil

Transesterification of palm kernel oil with methanol over mixed oxides of Ca and Zn has been investigated batchwise at 60 °C and 1 atm. CaO·ZnO catalysts were prepared via a conventional co-precipitation of the corresponding mixed metal nitrate solution in the presence of a soluble carbonate salt at near neutral conditions. The catalysts were characterized by using techniques of X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). The results indicated that the mixed oxides possess relatively small particle sizes and high surface areas, compared to pure CaO and ZnO. Moreover, the combination of Ca and Zn reduced the calcination temperature required for decomposition of metal carbonate precipitates to active oxides. Influences of Ca/Zn atomic ratio in the mixed oxide catalyst, catalyst amount, methanol/oil molar ratio, reaction time, and water amount on the methyl ester (ME) content were studied. Under the suitable transesterification conditions at 60 °C (catalyst amount = 10 wt.%, methanol/oil molar ratio = 30, reaction time = 1 h), the ME content of >94% can be achieved over CaO·ZnO catalyst with the Ca/Zn ratio of 0.25. The mixed oxide can be also applied to transesterification of palm olein, soybean, and sunflower oils. Furthermore, the effects of different regeneration methods on the reusability of CaO·ZnO catalyst were investigated.