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Biodiesel, a mixture of fatty acid methyl esters (FAME), is an excellent non-toxic, and biodegradable substitute for mineral diesel fuels produced from crude oil. It is made from renewable sources by transesterification of triglycerides with methanol, or by a reaction usually defined as methanolysis. Usage of low-quality feedstock, such as waste cooking oil (WCO), is challenging due to the undesirable side reactions as a result of the presence of free fatty acids (FFA), and water, thus a pretreatment stage before subjecting it to the transesterification process is usually required. In the present study, a two-step approach based on an adsorptive pretreatment with quicklime in order to remove FFA from WCO, followed by methanolysis using CaO∙ZnO as a heterogeneous catalyst was proposed. The first step was analyzed with the goal to define the optimal temperature of adsorption, the adsorbent particle size, calcination procedure, as well as the necessary amount of quicklime used. The analysis of adsorption kinetics was performed using pseudo-first and pseudo-second order kinetic models, and the efficiency of quicklime in the FFA removal from the WCO was also determined. The results showed that FFA from WCO could be successfully removed using quicklime as adsorbent at 30 °C for 1 h, with a removal efficiency of 72% and an adsorption capacity of 910 mg/g. The amount of Ca2+ ion present in the oil after the pretreatment was determined to be 12.64 mg/kg, showing that a very small amount of calcium from CaO was dissolved in treated WCO. The FTIR analysis of quicklime after the adsorption of FFA confirmed the interaction of the carboxyl group in FFA with the active site of the adsorbent. Adsorptive pretreatment had a positive effect on the rate of transesterification reaction with CaO∙ZnO as a catalyst, enabling the achievement of over 96% of FAME yield in only 15 min at 60 °C. The present study showed that quicklime, being cheap, available, and efficient, has considerable pot

The high potential of industrial hemp (Cannabis sativa), mainly due to the high-quality fibers and bioactive compounds, coupled with the decriminalization and/or legalization in some regions of the world, led to the steady growth of scientific research over the past couple of decades [1, 2]. From an industrial point of view, cannabinoids, primarily non-psychotropic cannabidiol (CBD), are considered the most valuable compounds, as they possess a broad range of therapeutic properties, such as anxiolytic, neuroprotective, antibiotic, antiinflammatory activity, and anti-oxidant. The hemp industry has already adopted supercritical carbon dioxide scCO2 extraction as a well-established process since it is a promising ‘green’ alternative to conventional extraction methods, selective, with short processing time, and low impact on the environment. In the present study, the preliminary analysis was performed to determine the influence of different scCO2 densities based on the different combinations of process pressure and temperature on the kinetics of supercritical extraction of Cannabis sativa, extract yield and the chemical composition of obtained extracts. Experiments were performed at temperatures ranging from 40 to 60 °C and pressures ranging from 10 to 30 MPa. Prior to extraction, the plant material was grounded and submitted to decarboxylation process at 120 °C for 1 h, in order to transform cannabidiolic acid, which is the precursor present in the plant material, to CBD. Experimental design for optimization plays an important role both in science and industry, because it allows evaluation of the effects of multiple factors and their interactions on one or more response variables. The present work was focused on the further optimization of scCO2 extraction with the aim to maximize the yield of extracts with high recoveries of CBD, by means of response surface methodology (RSM), based on a central composite design (CCD) using Design of Experiment software (Stat-Ease, De

Synthesis of biodiesel from various plant oils is realized by the transesterification of triglycerides with methanol or by a reaction usually defined as methanolysis. The usage of low-quality oils, such as waste cooking oil (WCO), is followed by undesirable side reactions as a result of the increased content of free fatty acids (FFA), and water. The presence of FFA in WCO usually requires a pretreatment stage before subjecting it to methanolysis. In the present work, heterogeneously catalyzed methanolysis of WCO with and without pretreatment was investigated. Removal of FFA from WCO was conducted by using only quicklime or with the addition of a small amount of methanol (FFA to methanol = 1:3 molar ratio). The obtained results showed that pretreatment of WCO with quicklime at 30 °C after 1 h reduces the FFA content by 72 %, while the adsorption capacity was determined to be 910 mg g-1. The adsorptive pretreatment, as a simple operation, using low-cost quicklime under mild conditions, had a positive effect on the transesterification rate with CaO∙ZnO as a catalyst, enabling the achievement of over 96 % of biodiesel yield in only 15 min, compared to 1 h without the pretreatment. Furthermore, pretreated WCO allows an increase in repeated catalyst use and overall savings in the necessary amount of catalyst. The present study showed that quicklime is an economic, environmental-friendly, and sustainable material for FFA removal from WCO.

Cannabis sativa is one of the oldest plant cultures, which has been used for centuries as a source of textile fibres, for paper production, as well as a source of bioactive compounds used in medicine. Although being restrained for a long time, its high potential, coupled with the progress in legislation and/or legalization in some regions of the world, led to the significant increase of scientific research towards isolation of cannabinoids, primarily a non-psychotropic cannabidiol (CBD), over the past couple decades. Beside cannabinoids, found only in cannabis plants, Cannabis sativa is characterized by very complex chemical composition with almost 500 constituents, including terpenes, flavonoids, phenolic compounds and fatty acids [2]. The co-presence of these numerous molecules in preparations obtained from Cannabis sativa may lead to a greater biological activity due to the “entourage” or synergistic effect [3]. CBD has attracted considerable interest due to its numerous therapeutic properties and pharmacological activities [1]. However, cannabinoids are characterized by a low solubility in aqueous media and, as a consequence, a relatively poor bioavailability. Therefore, improvement of their stability, shelf-life and bioavailability, by incorporation into biocompatible carriers is still a challenge. As an answer to this issue, integrated process of supercritical fluid extraction (SFE) from Cannabis sativa and supercritical solvent impregnation (SSI) of obtained extract into starch aerogel was tested. Starch gels were prepared starting from hydrogel formed from an aqueous solution of cornstarch (1:10 w/v). During replacement of water with acetone, by successive increase of its concentration until 100%, acetogel was formed and further subjected to drying using supercritical CO2 (scCO2) at 45 °C and 8-10 MPa to obtain aerogel. For comparison, a part of acetogel was dried in the oven at 60 °C to obtain xerogel. Textural properties and morphology of prepared material

Cannabis sativa is one of the oldest plant cultures with multiple purposes. It has been used for centuries as a source of textile fibers, for paper production, as a medicine due to its therapeutic properties, but also as a psychoactive drug. This valuable plant is characterized by very complex chemical composition with almost 500 constituents, including terpenes, flavonoids, phenolic compounds, fatty acids and the highly specific family of C21 terpenophenolic compounds named cannabinoids, found only in cannabis plants [1, 2]. These compounds have been proven to have high antioxidant, analgetic, anxiolytic, anti-inflammatory and neuroprotective activity, which made them potentially useful for various applications, mainly in the field of medicine [3]. Expectedly, the scientific research aimed toward isolating cannabinoids, primarily cannabidiol (CBD), has been in steady growth for the past couple of decades. In this study, the supercritical carbon dioxide (SC CO2) extraction was investigated as a method for isolating the extract of Cannabis sativa. Compared to conventional extraction methods, such as hydrodistillation and organic solvent extraction, utilizing SC CO2 has several advantages: 1) extractions are performed at mild temperatures, enabling preservation of thermally labile compounds; 2) there is no need for subsequent separation of the solvent as CO2 is easily completely removed by reducing pressure to atmospheric; 3) properties of CO2 are easily manipulated by the choice of operating pressure and temperature, which enables selective extraction (extraction of specific group(s) of compounds); 4) CO2 is non-toxic, non-flammable, abundant, recyclable and relatively cheap. Experiments were performed at temperatures ranging from 40 to 60 °C and pressures ranging from 10 to 30 MPa, with the goal of optimizing the yield of the obtained extract based on the composition. Prior to extraction, the plant material was grounded and submitted to decarboxylation process at 12

Supercritical CO2 extraction was applied on fenugreek (Trigonella foenum-graecum L., Fabaceae) seeds with the aim to define optimal process conditions to obtain the maximal extract yields content of steroidal sapogenins. Central composite rotatable design (CCRD) combined with response surface methodology (RSM) was applied to determine optimal process conditions defined by the influence and interaction of pressure, temperature and time of extraction through consumption of SC CO2. Optimization experiments revealed that the pressure of 24.73 MPa, the temperature of 38.2 degrees C and the consumption of SC CO2 of 19.24 g/g(DM) were the best process conditions enabling the maximal yield of extract and gain of the highest content of sapogenins. The optimal values of pressure and temperature defined SC CO2 density of 885.47 kg/m(3), which provided the maximal yield of the extract with the highest content of steroidal sapogenins. The achieved yield of extract at these conditions was 0.073g/g(DM), with 0.774 mg/g(DM) diosgenin, 0.477 mg/g(DM) protodioscin, 0.713 mg/g(DM) sarsapogenin and 0.205 mg/g(DM) oleanolic and ursolic acid with a significant quantity of 2.475 mg/g(DM) in the obtained extract.

Supercritical CO2 extraction was applied on fenugreek (Trigonella foenum-graecum L., Fabaceae) seeds with the aim to define optimal process conditions to obtain the maximal extract yields content of steroidal sapogenins. Central composite rotatable design (CCRD) combined with response surface methodology (RSM) was applied to determine optimal process conditions defined by the influence and interaction of pressure, temperature and time of extraction through consumption of SC CO2. Optimization experiments revealed that the pressure of 24.73 MPa, the temperature of 38.2 degrees C and the consumption of SC CO2 of 19.24 g/g(DM) were the best process conditions enabling the maximal yield of extract and gain of the highest content of sapogenins. The optimal values of pressure and temperature defined SC CO2 density of 885.47 kg/m(3), which provided the maximal yield of the extract with the highest content of steroidal sapogenins. The achieved yield of extract at these conditions was 0.073g/g(DM), with 0.774 mg/g(DM) diosgenin, 0.477 mg/g(DM) protodioscin, 0.713 mg/g(DM) sarsapogenin and 0.205 mg/g(DM) oleanolic and ursolic acid with a significant quantity of 2.475 mg/g(DM) in the obtained extract.

The powder mixtures of calcium oxide (CaO) and silica gel (SiO2) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO3, Ca3Si2O7, Ca2SiO4 compounds and CaO/Ca2SiO4 two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV-vis diffuse reflectance spectroscopy (DRS), N-2 adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO center dot SiO2 and 3CaO center dot SiO2 calcined at 700 degrees C, and 3CaO center dot SiO2 calcined at 900 degrees C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca2SiO4 complex mixture. The effect of different amount of catalyst used for transesterification (0.2-2 wt%) was analyzed using the most active catalyst i.e. 3CaO center dot SiO2 calcined at 700 degrees C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO3, Ca3Si2O7 and Ca2SiO4, phases did not possess catalytic activity.

The powder mixtures of calcium oxide (CaO) and silica gel (SiO2) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO3, Ca3Si2O7, Ca2SiO4 compounds and CaO/Ca2SiO4 two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV–vis diffuse reflectance spectroscopy (DRS), N2 adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO·SiO2 and 3CaO·SiO2 calcined at 700 °C, and 3CaO·SiO2 calcined at 900 °C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca2SiO4 complex mixture. The effect of different amount of catalyst used for transesterification (0.2–2 wt%) was analyzed using the most active catalyst i.e. 3CaO·SiO2 calcined at 700 °C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO3, Ca3Si2O7 and Ca2SiO4, phases did not possess catalytic activity.

The powder mixtures of calcium oxide (CaO) and silica gel (SiO2) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO3, Ca3Si2O7, Ca2SiO4 compounds and CaO/Ca2SiO4 two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV–vis diffuse reflectance spectroscopy (DRS), N2 adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO·SiO2 and 3CaO·SiO2 calcined at 700 °C, and 3CaO·SiO2 calcined at 900 °C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca2SiO4 complex mixture. The effect of different amount of catalyst used for transesterification (0.2–2 wt%) was analyzed using the most active catalyst i.e. 3CaO·SiO2 calcined at 700 °C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO3, Ca3Si2O7 and Ca2SiO4, phases did not possess catalytic activity.

The UV–vis diffuse reflectance (DRS) spectra and Kubelka-Munk transformed reflectance spectra of the samples calcined at 700 and 900 oC along with starting CaO and SiO2 powders used for the synthesis

The powder mixtures of calcium oxide (CaO) and silica gel (SiO2) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO3, Ca3Si2O7, Ca2SiO4 compounds and CaO/Ca2SiO4 two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV–vis diffuse reflectance spectroscopy (DRS), N2 adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO·SiO2 and 3CaO·SiO2 calcined at 700 °C, and 3CaO·SiO2 calcined at 900 °C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca2SiO4 complex mixture. The effect of different amount of catalyst used for transesterification (0.2–2 wt%) was analyzed using the most active catalyst i.e. 3CaO·SiO2 calcined at 700 °C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO3, Ca3Si2O7 and Ca2SiO4, phases did not possess catalytic activity.

The powder mixtures of calcium oxide (CaO) and silica gel (SiO2) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO3, Ca3Si2O7, Ca2SiO4 compounds and CaO/Ca2SiO4 two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV-vis diffuse reflectance spectroscopy (DRS), N-2 adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO center dot SiO2 and 3CaO center dot SiO2 calcined at 700 degrees C, and 3CaO center dot SiO2 calcined at 900 degrees C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca2SiO4 complex mixture. The effect of different amount of catalyst used for transesterification (0.2-2 wt%) was analyzed using the most active catalyst i.e. 3CaO center dot SiO2 calcined at 700 degrees C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO3, Ca3Si2O7 and Ca2SiO4, phases did not possess catalytic activity.

Тhe MnCO3/Na silicate (Mn/Na/Si mole ratio of 4.65:1:1.65) catalyst in the form of solid particles with diameter of 0.99–1.99 mm was used as a catalyst for transesterification of soybean oil in batch autoclave at different conditions: 388–468 K, methanol-to-oil mole ratio 12:1–30:1, catalyst amount based on the mass of oil 0–12.5 %. The complete triacylglycerols (TAG) conversion and high yield of fatty acid methyl ester (FAME) was obtained after 1 h at 458 K, methanol-to-oil mole ratio 30:1 and 10 % of catalyst. Kinetics of transesterification process was analyzed by three models: the simple first order irreversible reaction rate, as well as two more complex models recently reported in literature. The catalyst reuse in transesterification process was tested and the average values of 99.0 % of TAG conversion and 97.5 % of FAME yield were obtained after 8 consecutive runs. Different techniques were used to characterize fresh and used MnCO3/Na silicate catalyst. The determined amounts of leached Na (<500 ppm) and Mn (<20 ppm) in biodiesel phase implied that the homogeneous-heterogeneous process influences the catalyst selectivity, whereby leached Na enables the complete transformation of TAG to FAME.

In this work, synthesis of several types of calcium oxide based catalysts by mechanochemical treatment and subsequent calcination is presented. Prepared nanocomposite CaO·ZnO, calcium containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5, a series of CaO·SiO2 mixed oxides and calcium diglyceroxide (CaDG) were characterized and tested in the methanolysis of sunflower oil under different working conditions: catalyst amount, agitation speed, temperature and methanol to oil molar ratio.

The manganese carbonate catalyst, prepared by precipitation method, was used in transesterification of soybean oil under subcritical condition of methanol. Catalyst samples were characterized by X-ray diffraction (XRD), Fourier trans-form infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The triacylglycerol (TAG) conversion and fatty acid methyl esters (FAME) yield were determined using high performance liquid chromatography (HPLC). The transesterification was realized for 1 h using various working conditions: 0-3 wt.% of catalyst (based on the mass of oil), the mole ratio of methanol to oil from 13:1 to 27:1 and temperature ranging from 393 to 473 K. A maximum TAG conversion of 98.1% could be obtained at the optimal reaction conditions: 2 wt.% of catalyst, methanol/oil mole ratio of 21:1, for 1 h in a batch reactor at 453 K. Kinetic analysis showed that the model based on mass transfer and chemical reaction at the catalyst surface confirmed the experimental data. Using that kinetic expression, the effect of continuous transesterification was proposed and verified by a 360-h long realized experiment in a laboratory packed-bed reactor (PBR). Slow deactivation of the catalyst was caused by leaching of Mn in both biodiesel and glycerol phases and by blocking the active sites of the catalyst with organic compounds.

The MnCO3/Na silicate (Mn/Na/Si mole ratio of 4.65:1:1.65) catalyst in the form of solid particles with diameter of 0.99-1.99 mm was used as a catalyst for transesterification of soybean oil in batch autoclave at different conditions: 388-468 K, methanol-to-oil mole ratio 12:1-30:1, catalyst amount based on the mass of oil 0-12.5 %. The complete triacylglycerols (TAG) conversion and high yield of fatty acid methyl ester (FAME) was obtained after 1 h at 458 K, methanol-to-oil mole ratio 30:1 and 10 % of catalyst. Kinetics of transesterification process was analyzed by three models: the simple first order irreversible reaction rate, as well as two more complex models recently reported in literature. The catalyst reuse in transesterification process was tested and the average values of 99.0 % of TAG conversion and 97.5 % of FAME yield were obtained after 8 consecutive runs. Different techniques were used to characterize fresh and used MnCO3/Na silicate catalyst. The determined amounts of leached Na ( lt 500 ppm) and Mn ( lt 20 ppm) in biodiesel phase implied that the homogeneous-heterogeneous process influences the catalyst selectivity, whereby leached Na enables the complete transformation of TAG to FAME.

The continuous biodiesel production from soybean oil was carried out under the subcritical condition of methanol with MnCO3/Na-silicate as a heterogeneous catalyst. The transesterification rate was first investigated in a set of experiments performed in a batch autoclave at 448 K using methanol-to-oil molar ratio of 18:1 and various catalyst loadings (5, 10 and 20 wt% based on the oil mass). The results from these experiments, as well as the experimental data and the appropriate kinetic model recently reported in the literature were used for designing a packed bed tubular reactor (PBTR), a main unit of the pilot plant with the capacity of 100 L of biodiesel per day. The pilot plant was constructed and tested under various operating conditions. The first 11 h of the pilot-plant operation was realized in the tubular reactor packed with inert glass beads (i.e. without the catalyst) in order to analyze the effect of the non-catalyzed subcritical biodiesel (fatty acid methyl esters, FAME) production. Then, glass beads were replaced with a mix of MnCO3/Na-silicate catalyst particles and glass beads, and the catalytic biodiesel production was continuously run under the subcritical methanol condition for 85 h. Two mass balance tests during the continuous pilot plant operation were performed.

The continuous biodiesel production from soybean oil was carried out under the subcritical condition of methanol with MnCO3/Na-silicate as a heterogeneous catalyst. The transesterification rate was first investigated in a set of experiments performed in a batch autoclave at 448 K using methanol-to-oil molar ratio of 18:1 and various catalyst loadings (5, 10 and 20 wt% based on the oil mass). The results from these experiments, as well as the experimental data and the appropriate kinetic model recently reported in the literature were used for designing a packed bed tubular reactor (PBTR), a main unit of the pilot plant with the capacity of 100 L of biodiesel per day. The pilot plant was constructed and tested under various operating conditions. The first 11 h of the pilot-plant operation was realized in the tubular reactor packed with inert glass beads (i.e. without the catalyst) in order to analyze the effect of the non-catalyzed subcritical biodiesel (fatty acid methyl esters, FAME) production. Then, glass beads were replaced with a mix of MnCO3/Na-silicate catalyst particles and glass beads, and the catalytic biodiesel production was continuously run under the subcritical methanol condition for 85 h. Two mass balance tests during the continuous pilot plant operation were performed. © 2018 Elsevier Ltd

In this work, synthesis of several types of calcium oxide based catalysts by mechanochemical treatment and subsequent calcination is presented. Prepared nanocomposite CaO·ZnO, calcium containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5, a series of CaO·SiO2 mixed oxides and calcium diglyceroxide (CaDG) were characterized and tested in the methanolysis of sunflower oil under different working conditions: catalyst amount, agitation speed, temperature and methanol to oil molar ratio.

The continuous biodiesel production from soybean oil was carried out under the subcritical condition of methanol with MnCO3/Na-silicate as a heterogeneous catalyst. The transesterification rate was first investigated in a set of experiments performed in a batch autoclave at 448 K using methanol-to-oil molar ratio of 18:1 and various catalyst loadings (5, 10 and 20 wt% based on the oil mass). The results from these experiments, as well as the experimental data and the appropriate kinetic model recently reported in the literature were used for designing a packed bed tubular reactor (PBTR), a main unit of the pilot plant with the capacity of 100 L of biodiesel per day. The pilot plant was constructed and tested under various operating conditions. The first 11 h of the pilot-plant operation was realized in the tubular reactor packed with inert glass beads (i.e. without the catalyst) in order to analyze the effect of the non-catalyzed subcritical biodiesel (fatty acid methyl esters, FAME) production. Then, glass beads were replaced with a mix of MnCO3/Na-silicate catalyst particles and glass beads, and the catalytic biodiesel production was continuously run under the subcritical methanol condition for 85 h. Two mass balance tests during the continuous pilot plant operation were performed. © 2018 Elsevier Ltd

The continuous biodiesel production from soybean oil was carried out under the subcritical condition of methanol with MnCO3/Na-silicate as a heterogeneous catalyst. The transesterification rate was first investigated in a set of experiments performed in a batch autoclave at 448 K using methanol-to-oil molar ratio of 18:1 and various catalyst loadings (5, 10 and 20 wt% based on the oil mass). The results from these experiments, as well as the experimental data and the appropriate kinetic model recently reported in the literature were used for designing a packed bed tubular reactor (PBTR), a main unit of the pilot plant with the capacity of 100 L of biodiesel per day. The pilot plant was constructed and tested under various operating conditions. The first 11 h of the pilot-plant operation was realized in the tubular reactor packed with inert glass beads (i.e. without the catalyst) in order to analyze the effect of the non-catalyzed subcritical biodiesel (fatty acid methyl esters, FAME) production. Then, glass beads were replaced with a mix of MnCO3/Na-silicate catalyst particles and glass beads, and the catalytic biodiesel production was continuously run under the subcritical methanol condition for 85 h. Two mass balance tests during the continuous pilot plant operation were performed. © 2018 Elsevier Ltd

The manganese carbonate catalyst, prepared by precipitation method, was used in transesterification of soybean oil under subcritical condition of methanol. Catalyst samples were characterized by X-ray diffraction (XRD), Fourier trans-form infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The triacylglycerol (TAG) conversion and fatty acid methyl esters (FAME) yield were determined using high performance liquid chromatography (HPLC). The transesterification was realized for 1 h using various working conditions: 0-3 wt.% of catalyst (based on the mass of oil), the mole ratio of methanol to oil from 13:1 to 27:1 and temperature ranging from 393 to 473 K. A maximum TAG conversion of 98.1% could be obtained at the optimal reaction conditions: 2 wt.% of catalyst, methanol/oil mole ratio of 21:1, for 1 h in a batch reactor at 453 K. Kinetic analysis showed that the model based on mass transfer and chemical reaction at the catalyst surface confirmed the experimental data. Using that kinetic expression, the effect of continuous transesterification was proposed and verified by a 360-h long realized experiment in a laboratory packed-bed reactor (PBR). Slow deactivation of the catalyst was caused by leaching of Mn in both biodiesel and glycerol phases and by blocking the active sites of the catalyst with organic compounds.

The MnCO3/Na silicate (Mn/Na/Si mole ratio of 4.65:1:1.65) catalyst in the form of solid particles with diameter of 0.99-1.99 mm was used as a catalyst for transesterification of soybean oil in batch autoclave at different conditions: 388-468 K, methanol-to-oil mole ratio 12:1-30:1, catalyst amount based on the mass of oil 0-12.5 %. The complete triacylglycerols (TAG) conversion and high yield of fatty acid methyl ester (FAME) was obtained after 1 h at 458 K, methanol-to-oil mole ratio 30:1 and 10 % of catalyst. Kinetics of transesterification process was analyzed by three models: the simple first order irreversible reaction rate, as well as two more complex models recently reported in literature. The catalyst reuse in transesterification process was tested and the average values of 99.0 % of TAG conversion and 97.5 % of FAME yield were obtained after 8 consecutive runs. Different techniques were used to characterize fresh and used MnCO3/Na silicate catalyst. The determined amounts of leached Na ( lt 500 ppm) and Mn ( lt 20 ppm) in biodiesel phase implied that the homogeneous-heterogeneous process influences the catalyst selectivity, whereby leached Na enables the complete transformation of TAG to FAME.

The continuous biodiesel production from soybean oil was carried out under the subcritical condition of methanol with MnCO3/Na-silicate as a heterogeneous catalyst. The transesterification rate was first investigated in a set of experiments performed in a batch autoclave at 448 K using methanol-to-oil molar ratio of 18:1 and various catalyst loadings (5, 10 and 20 wt% based on the oil mass). The results from these experiments, as well as the experimental data and the appropriate kinetic model recently reported in the literature were used for designing a packed bed tubular reactor (PBTR), a main unit of the pilot plant with the capacity of 100 L of biodiesel per day. The pilot plant was constructed and tested under various operating conditions. The first 11 h of the pilot-plant operation was realized in the tubular reactor packed with inert glass beads (i.e. without the catalyst) in order to analyze the effect of the non-catalyzed subcritical biodiesel (fatty acid methyl esters, FAME) production. Then, glass beads were replaced with a mix of MnCO3/Na-silicate catalyst particles and glass beads, and the catalytic biodiesel production was continuously run under the subcritical methanol condition for 85 h. Two mass balance tests during the continuous pilot plant operation were performed.

Helichrysum italicum presents a valuable source of natural bioactive compounds. In this work, a literature review of terpenes, phenolic compounds, and other less common phytochemicals from H. italicum with regard to application of different separation methods is presented. Data including extraction/separation methods and experimental conditions applied, obtained yields, number of identified compounds, content of different compound groups, and analytical techniques applied are shown as corresponding tables. Numerous biological activities of both isolates and individual compounds are emphasized. In addition, the data reported are discussed, and the directions for further investigations are proposed.

Helichrysum italicum presents a valuable source of natural bioactive compounds. In this work, a literature review of terpenes, phenolic compounds, and other less common phytochemicals from H. italicum with regard to application of different separation methods is presented. Data including extraction/separation methods and experimental conditions applied, obtained yields, number of identified compounds, content of different compound groups, and analytical techniques applied are shown as corresponding tables. Numerous biological activities of both isolates and individual compounds are emphasized. In addition, the data reported are discussed, and the directions for further investigations are proposed.

In the present work, calcium diglyceroxide (CaDG) was synthesized by mechanochemical treatment of CaO dispersed in glycerol, and characterized by X-ray diffraction (XRD), thermal analysis (TGA/DTA), infrared spectroscopy (FTIR), and Hammett indicator method for base strength determination. The obtained CaDG was tested as a catalyst in the methanolysis of sunflower oil under different working conditions: catalyst amount, agitation speed, temperature and methanol to oil molar ratio. The main advantage of CaDG used as a catalyst in methanolysis is related to the initial rate of methanolysis. According to many previously reported data in literature the mass transfer resistance controls the overall rate of methanolysis, but it is not observed with CaDG used as catalyst. Recently developed kinetic model that describes the complex methanolysis process was successfully applied for this system and model parameters were determined, supporting the explanation of the physical effect of the CaDG catalyst on the reduction of mass transfer resistance and increasing the rate of methanolysis. The absence of mass transfer rate at the beginning of process is a consequence of the nature of the CaDG, which is adsorbed at the droplet interfaces between methanol and oil leading to the formation of fine dispersion of these two immiscible liquids.

Calcium-containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 were synthesized by calcination of mechanochemically treated stoichiometric mixtures of CaCO3 and either TiO2, MnO2, ZrO2 or Fe2O3 powders. X-ray diffraction analysis revealed a pure single perovskite phase for all four samples after calcination. This study proved that the pure perovskite phase exhibited low or no catalytic activity at 60 °C for the methanolysis of sunflower oil. However, at 165 °C FAME yield of more than 90% was reached after 2 h using CaTiO3, CaMnO3 and CaZrO3 as catalyst. Contrary to inactive pure perovskites at 60 °C, the CaTiO3 and Ca2Fe2O5 samples containing a very small amount of “free” CaO also showed methanolysis activity at 60 °C. This fact can be used to explain some contradictory statements reported in literature related to the perovskites as catalyst for biodiesel synthesis at mild temperatures.

Currently, the catalytic efficiency and reusability of the solid base catalysts cannot meet the demand of industrial biodiesel production under low temperature. The purpose of this study is to define the kinetics of heterogeneous transesterification process that could be used for the prediction of the biodiesel synthesis at high temperature and pressure. The focus in this study was paid to recently repotted data obtained with different catalysts used for biodiesel synthesis in a batch reactor at high temperatures. It was shown that three kinetic models, including: a) irreversible first order reaction, b) reaction with changeable order and c) resistances of mass transfer and chemical reaction at active sites of the catalyst, could be applied for predicting the effect of high temperature of the transesterification. The apparent reaction rate constant of the irreversible first order reaction was determined, as well as the parameters of the other two, more complicated kinetic. models. The best agreement was obtained with the more complicated models and the mean relative percent deviation between calculated and experimentally determined triacylglycerols conversion for these kinetic models is between 3 and 10%.

Supercritical CO2 (SC-CO2) extraction of fenugreek seeds (Trigonella foenum-graecum L, Fabaceae) was analyzed using different pressure and temperature (16.6-33.4 MPa and, 30-50 degrees C), which corresponded to SC-CO2 density between 779 and 957 kg/m(3). The yield of extract as well as its composition were determined and analyzed for different solvent consumption defined as mass of used CO2 for extraction per mass of dry fenugreek seeds. A central composite design (CCD) combined with response surface methodology (RSM) was used to study the best extraction conditions which determined that 27.0 MPa, 42.6 degrees C, and 24.6 gCO(2)/g(dm), were the optimal conditions for isolation of total extract. The calculated yield of extract at these conditions defined by SC-CO2 density of 890 kg/m3 could be 2.57% based on fenugreek seed. Moreover, the best extraction conditions for obtaining extract which contains the maximal amount of sterols, or maximal amount of vitamin E or vitamin D were also analyzed. These RSM optimizations showed that at slightly lower pressure (22.8-24.8 MPa), temperature (39.9-42.0 degrees C) and consumption of SC-CO2 (19.0-19.7 gCO(2)/g(dm)) is followed by smaller amount of isolated extract but with maximum content of sterols (16.28%), or vitamin E or vitamin D (1.44% and 0.71%, respectively) at these conditions. Calculation of molar solubility of total extract, and apparent solubility of sterols, vitamin E and D in SC-CO2 was performed at different pressure and temperature. They were correlated to density of SC-CO2, temperature at which extractions were performed and Hildebrand solubility parameter of solvent and solubility parameter of compounds which are the main constituents of extract. These calculations also show that the highest molar solubility of total extract and apparent molar solubility of its constituents could be obtained using optimal density of SC-CO2 (830-890 kg/m(3)) defined by corresponding values of temperature and pressure (310-320

In the present work, calcium diglyceroxide (CaDG) was synthesized by mechanochemical treatment of CaO dispersed in glycerol, and characterized by X-ray diffraction (XRD), thermal analysis (TGA/DTA), infrared spectroscopy (FTIR), and Hammett indicator method for base strength determination. The obtained CaDG was tested as a catalyst in the methanolysis of sunflower oil under different working conditions: catalyst amount, agitation speed, temperature and methanol to oil molar ratio. The main advantage of CaDG used as a catalyst in methanolysis is related to the initial rate of methanolysis. According to many previously reported data in literature the mass transfer resistance controls the overall rate of methanolysis, but it is not observed with CaDG used as catalyst. Recently developed kinetic model that describes the complex methanolysis process was successfully applied for this system and model parameters were determined, supporting the explanation of the physical effect of the CaDG catalyst on the reduction of mass transfer resistance and increasing the rate of methanolysis. The absence of mass transfer rate at the beginning of process is a consequence of the nature of the CaDG, which is adsorbed at the droplet interfaces between methanol and oil leading to the formation of fine dispersion of these two immiscible liquids.

Analysis of yield and composition profile of Melissa officinalis (Lemon balm) extract obtained by two-step CO2 extraction at high pressure was analyzed. The first or essential oil fraction, collected at 10 MPa and 40 degrees C, contained mostly the high volatile and aromatic compounds. The second fraction was consenquently extracted at 30 MPa using different temperature: 25 degrees C (higher pressure than critical pressure but at temperature below the critical; HPCP-CO2), 40 degrees C or 100 degrees C (supercritical CO2; SC-CO2). Obtained yield of essential oil fraction was 0.45% at 10 MPa, while depending on applied extraction temperature (HPCP-CO2 or SC-CO2), the yields of the second fractions collected at 30 MPa varied from 0.44% to 0.94%. Within the study, the content of active substances in obtained extracts was analyzed, too. For comparison with CO2 extracts (HPCP or SC) the yield and characterization of essential oil obtained by hydrodistillation was accomplished, as well. A significant difference was noted not only between the essential oil isolated by hydrodistillation and SC-CO2 extraction (40 degrees C, 10 MPa) but also between total extracts obtained by HPCP-CO2 and SC-CO2 extraction. The pseudo kinetic model was applied to define SC-CO2 extraction of Lemon balm to describe the relation between the yield of extraction and CO2 consumption. Antioxidant activity of obtained extracts was determined by free radical scavenging capacity (RSC) and significant correlation of antioxidant capacity and composition profile between obtained extracts was observed.

A heterogeneous cerium-manganese oxide catalyst was synthesized by a co-precipitation method, characterized and tested in soybean oil transesterification with methanol under subcritical condition for methanol. Conversion of triglycerides after 40 min of transesterification in a batch process was over 99% with a fatty acid methyl ester (FAME) yield of 91.6% when 3 wt.% of catalyst based on oil, and 18:1 methanol/oil molar ratio were applied. The same amount of catalyst was used in 12 cycles of transesterification with catalyst regeneration performed only after the 7th cycle. The catalyst exhibited good tolerance toward soybean oil containing below 1.5 wt.% of water or 4 wt.% of free fatty acids. The mechanisms of Ce/Mn catalytic activity and its deactivation were discussed according to the characterization of the fresh and used catalyst according to results of different analytical methods: the Hammett titration, BET surface area, scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), FTIR, X-ray diffraction (XRD), ICP-MS and TG-DSC. It was assumed that deactivation of catalyst was mainly a consequence of manganese solubility in methanol and glycerol.

Pretreatment of fenugreek (Trigonella foenum-graecum L, Fabaceae) seeds was achieved using the step of defatting and acid hydrolysis. The obtained hydro-isolate (HI) was used as initial feed for diosgenin isolation by supercritical CO2 extraction (SC-CO2). Preliminary tests performed at conditions resulting in SC-CO2 density ranging from 800 to 920 kg/m(3) indicated that at some pressure, temperature as well as consumption of supercritical fluids the optimal working conditions for diosgenin isolation could be determined. For this purpose, the following range of working conditions of SC-CO2 were tested by using Central Composite Rotatable Design (CCRD) and Response Surface Methodology (RSM): pressure from 16.6 to 33.4 MPa, temperature from 30 to 50 degrees C and consumption of SC-CO2 from 11.6 to 28.4 g(co2)/g(dm). The result of this investigation indicated that maximum yield of 0.81 mg diosgenin from 1 g of fenugreek seeds on dry basis (about 1.3% of total extract) at 24.6 MPa, 43.5 degrees C, and 20.87 g(co2)/g(dm) could be obtained.

Increased environmental concern and awareness of limited reserves of fossil fuels gave a great importance to alternative and renewable energy sources over the past couple decades. An excellent substitute for mineral diesel fuels is biodiesel, a mixture of fatty acid methyl esters (FAME), made by alcoholysis of different triacylglycerols (TAG) from various renewable sources (vegetable oils or animal fats) in the presence of a homogeneous or heterogeneous catalyst. Drawbacks of homogeneously catalyzed alcoholysis, to-day the most commonly used commercial biodiesel production process, have shifted the research focus on technologies based on utilization of solid catalyst. Heterogeneously catalyzed alcoholysis is more environmentally friendly, offers simplified production and improved process efficiency, allowing the possibility of catalyst’s regeneration, too. This technology of biodiesel synthesis is also the base for the continuous process development. Although great attention has been paid to the development of a catalyst that will have good activity and stability, followed by cheap method of synthesis, this task is still a challenge and needs further intensive research. Solid base catalysts have been characterized by high activity under mild reaction conditions and short reaction times, however, due to their sensitivity to the presence of impurities in the oil, primary the presence of free fatty acids (FFA) and water, they were not suitable, according to results of many investigations, for transesterification of lower-cost feedstock, such as non-edible plant oils and the waste cooking oils. For these feedstocks heterogeneous biodiesel synthesis should be performed applying solid acid catalyst. Despite the generally lower activity compared to solid base catalysts and higher reaction temperatures required for transesterification of oils into biodiesel, the main advantage of solid acids is their ability to simultaneously carry out esterification of FFA and transesterif

Limited reserves of fossil fuels as well as the growing concern for the environment, has led to a worldwide search for renewable energy sources, among which biodiesel, a mixture of fatty acid methyl esters (FAME), is one of the most perspective alternative fuels since it is a non-toxic and can be produced from different renewable sources through simple cost-effective alcoholysis, while being compatible with existing infrastructures. Vegetable oils, as renewable in nature and environmentally friendly, with a possibility to be produced on a large scale, represent a promising feedstock for biodiesel production. In this chapter, a comprehensive review of different vegetable oils as a feedstock for biodiesel synthesis is reported, including edible and non-edible oils, as well as waste vegetable oils. Selection of feedstock for biodiesel production mainly depends on the specific conditions and circumstances in some region (climate, presence of certain crops, the economic development of a country, etc.). Various fatty acid compositions of triacylglycerols directly determine the quality and fulfillment of the standards of biodiesel. One of the crucial points which determine technology route for biodiesel synthesis is content of free fatty acids (FFA) which might be present in vegetable oils, as well as the presence of water and other compounds. Also, many analysis performed in the past have shown that the production cost of biodiesel is mainly determined by the price of used feedstock, which represents 70-80% of total production costs of biodiesel. Currently more than 95% of feedstock comes from edible oils since they are easily accessible, consists mainly of triacylglycerols, whereby the properties of biodiesel produced from these oils are suitable to be used as diesel fuel substitute. Most commonly used edible oils for biodiesel production are rapeseed, soybean, sunflower and palm. However, for economic and social reasons, in recent years research and development of biodi

Vegetable oils are mainly esters of fatty acids and glycerol, which can be converted to fatty acid methyl esters (FAME), also known as biodiesel, by the transesterification reaction with methanol. In order to attain environmental benignity, much attention has been focused in the last decades on utilizing heterogeneous catalysts for biodiesel production instead the homogenously catalyzed transesterification of vegetable oil. The pure CaO or CaO mixed with some other metal oxide due to its low solubility in methanol, FAME and glycerol, low cost and availability, is one of the most promising among the proposed heterogeneous catalysts. Solid catalysts containing CaO usually fulfill a number of important requirements, such as high activity at mild temperature, marginal leaching of Ca cations, long life activity, reusability in transesterification of vegetable oil and easy recovery from the final products of trancesterification (FAME and glycerol). This review is focused on the recent application of pure CaO or CaO in complex catalyst structure and their use as heterogeneous base catalysts for biodiesel synthesis and suitability for industrial application.

Calcium-containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 were synthesized by calcination of mechanochemically treated stoichiometric mixtures of CaCO3 and either TiO2, MnO2, ZrO2 or Fe2O3 powders. X-ray diffraction analysis revealed a pure single perovskite phase for all four samples after calcination. This study proved that the pure perovskite phase exhibited low or no catalytic activity at 60 degrees C for the methanolysis of sunflower oil. However, at 165 degrees C FAME yield of more than 90% was reached after 2 h using CaTiO3, CaMnO3 and CaZrO3 as catalyst. Contrary to inactive pure perovskites at 60 degrees C, the CaTiO3 and Ca2Fe2O5 samples containing a very small amount of "free" CaO also showed methanolysis activity at 60 degrees C. This fact can be used to explain some contradictory statements reported in literature related to the perovskites as catalyst for biodiesel synthesis at mild temperatures.

In the present work, calcium diglyceroxide (CaDG) was synthesized by mechanochemical treatment of CaO dispersed in glycerol, and characterized by X-ray diffraction (XRD), thermal analysis (TGA/DTA), infrared spectroscopy (FTIR), and Hammett indicator method for base strength determination. The obtained CaDG was tested as a catalyst in the methanolysis of sunflower oil under different working conditions: catalyst amount, agitation speed, temperature and methanol to oil molar ratio. The main advantage of CaDG used as a catalyst in methanolysis is related to the initial rate of methanolysis. According to many previously reported data in literature the mass transfer resistance controls the overall rate of methanolysis, but it is not observed with CaDG used as catalyst. Recently developed kinetic model that describes the complex methanolysis process was successfully applied for this system and model parameters were determined, supporting the explanation of the physical effect of the CaDG catalyst on the reduction of mass transfer resistance and increasing the rate of methanolysis. The absence of mass transfer rate at the beginning of process is a consequence of the nature of the CaDG, which is adsorbed at the droplet interfaces between methanol and oil leading to the formation of fine dispersion of these two immiscible liquids.

Calcium-containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 were synthesized by calcination of mechanochemically treated stoichiometric mixtures of CaCO3 and either TiO2, MnO2, ZrO2 or Fe2O3 powders. X-ray diffraction analysis revealed a pure single perovskite phase for all four samples after calcination. This study proved that the pure perovskite phase exhibited low or no catalytic activity at 60 °C for the methanolysis of sunflower oil. However, at 165 °C FAME yield of more than 90% was reached after 2 h using CaTiO3, CaMnO3 and CaZrO3 as catalyst. Contrary to inactive pure perovskites at 60 °C, the CaTiO3 and Ca2Fe2O5 samples containing a very small amount of “free” CaO also showed methanolysis activity at 60 °C. This fact can be used to explain some contradictory statements reported in literature related to the perovskites as catalyst for biodiesel synthesis at mild temperatures.

Supercritical CO2 (SC-CO2) extraction of fenugreek seeds (Trigonella foenum-graecum L, Fabaceae) was analyzed using different pressure and temperature (16.6-33.4 MPa and, 30-50 degrees C), which corresponded to SC-CO2 density between 779 and 957 kg/m(3). The yield of extract as well as its composition were determined and analyzed for different solvent consumption defined as mass of used CO2 for extraction per mass of dry fenugreek seeds. A central composite design (CCD) combined with response surface methodology (RSM) was used to study the best extraction conditions which determined that 27.0 MPa, 42.6 degrees C, and 24.6 gCO(2)/g(dm), were the optimal conditions for isolation of total extract. The calculated yield of extract at these conditions defined by SC-CO2 density of 890 kg/m3 could be 2.57% based on fenugreek seed. Moreover, the best extraction conditions for obtaining extract which contains the maximal amount of sterols, or maximal amount of vitamin E or vitamin D were also analyzed. These RSM optimizations showed that at slightly lower pressure (22.8-24.8 MPa), temperature (39.9-42.0 degrees C) and consumption of SC-CO2 (19.0-19.7 gCO(2)/g(dm)) is followed by smaller amount of isolated extract but with maximum content of sterols (16.28%), or vitamin E or vitamin D (1.44% and 0.71%, respectively) at these conditions. Calculation of molar solubility of total extract, and apparent solubility of sterols, vitamin E and D in SC-CO2 was performed at different pressure and temperature. They were correlated to density of SC-CO2, temperature at which extractions were performed and Hildebrand solubility parameter of solvent and solubility parameter of compounds which are the main constituents of extract. These calculations also show that the highest molar solubility of total extract and apparent molar solubility of its constituents could be obtained using optimal density of SC-CO2 (830-890 kg/m(3)) defined by corresponding values of temperature and pressure (310-320

Analysis of yield and composition profile of Melissa officinalis (Lemon balm) extract obtained by two-step CO2 extraction at high pressure was analyzed. The first or essential oil fraction, collected at 10 MPa and 40 degrees C, contained mostly the high volatile and aromatic compounds. The second fraction was consenquently extracted at 30 MPa using different temperature: 25 degrees C (higher pressure than critical pressure but at temperature below the critical; HPCP-CO2), 40 degrees C or 100 degrees C (supercritical CO2; SC-CO2). Obtained yield of essential oil fraction was 0.45% at 10 MPa, while depending on applied extraction temperature (HPCP-CO2 or SC-CO2), the yields of the second fractions collected at 30 MPa varied from 0.44% to 0.94%. Within the study, the content of active substances in obtained extracts was analyzed, too. For comparison with CO2 extracts (HPCP or SC) the yield and characterization of essential oil obtained by hydrodistillation was accomplished, as well. A significant difference was noted not only between the essential oil isolated by hydrodistillation and SC-CO2 extraction (40 degrees C, 10 MPa) but also between total extracts obtained by HPCP-CO2 and SC-CO2 extraction. The pseudo kinetic model was applied to define SC-CO2 extraction of Lemon balm to describe the relation between the yield of extraction and CO2 consumption. Antioxidant activity of obtained extracts was determined by free radical scavenging capacity (RSC) and significant correlation of antioxidant capacity and composition profile between obtained extracts was observed.

Vegetable oils are mainly esters of fatty acids and glycerol, which can be converted to fatty acid methyl esters (FAME), also known as biodiesel, by the transesterification reaction with methanol. In order to attain environmental benignity, much attention has been focused in the last decades on utilizing heterogeneous catalysts for biodiesel production instead the homogenously catalyzed transesterification of vegetable oil. The pure CaO or CaO mixed with some other metal oxide due to its low solubility in methanol, FAME and glycerol, low cost and availability, is one of the most promising among the proposed heterogeneous catalysts. Solid catalysts containing CaO usually fulfill a number of important requirements, such as high activity at mild temperature, marginal leaching of Ca cations, long life activity, reusability in transesterification of vegetable oil and easy recovery from the final products of trancesterification (FAME and glycerol). This review is focused on the recent application of pure CaO or CaO in complex catalyst structure and their use as heterogeneous base catalysts for biodiesel synthesis and suitability for industrial application.

Calcium-containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 were synthesized by calcination of mechanochemically treated stoichiometric mixtures of CaCO3 and either TiO2, MnO2, ZrO2 or Fe2O3 powders. X-ray diffraction analysis revealed a pure single perovskite phase for all four samples after calcination. This study proved that the pure perovskite phase exhibited low or no catalytic activity at 60 degrees C for the methanolysis of sunflower oil. However, at 165 degrees C FAME yield of more than 90% was reached after 2 h using CaTiO3, CaMnO3 and CaZrO3 as catalyst. Contrary to inactive pure perovskites at 60 degrees C, the CaTiO3 and Ca2Fe2O5 samples containing a very small amount of "free" CaO also showed methanolysis activity at 60 degrees C. This fact can be used to explain some contradictory statements reported in literature related to the perovskites as catalyst for biodiesel synthesis at mild temperatures.

Pretreatment of fenugreek (Trigonella foenum-graecum L, Fabaceae) seeds was achieved using the step of defatting and acid hydrolysis. The obtained hydro-isolate (HI) was used as initial feed for diosgenin isolation by supercritical CO2 extraction (SC-CO2). Preliminary tests performed at conditions resulting in SC-CO2 density ranging from 800 to 920 kg/m(3) indicated that at some pressure, temperature as well as consumption of supercritical fluids the optimal working conditions for diosgenin isolation could be determined. For this purpose, the following range of working conditions of SC-CO2 were tested by using Central Composite Rotatable Design (CCRD) and Response Surface Methodology (RSM): pressure from 16.6 to 33.4 MPa, temperature from 30 to 50 degrees C and consumption of SC-CO2 from 11.6 to 28.4 g(co2)/g(dm). The result of this investigation indicated that maximum yield of 0.81 mg diosgenin from 1 g of fenugreek seeds on dry basis (about 1.3% of total extract) at 24.6 MPa, 43.5 degrees C, and 20.87 g(co2)/g(dm) could be obtained.

Currently, the catalytic efficiency and reusability of the solid base catalysts cannot meet the demand of industrial biodiesel production under low temperature. The purpose of this study is to define the kinetics of heterogeneous transesterification process that could be used for the prediction of the biodiesel synthesis at high temperature and pressure. The focus in this study was paid to recently repotted data obtained with different catalysts used for biodiesel synthesis in a batch reactor at high temperatures. It was shown that three kinetic models, including: a) irreversible first order reaction, b) reaction with changeable order and c) resistances of mass transfer and chemical reaction at active sites of the catalyst, could be applied for predicting the effect of high temperature of the transesterification. The apparent reaction rate constant of the irreversible first order reaction was determined, as well as the parameters of the other two, more complicated kinetic. models. The best agreement was obtained with the more complicated models and the mean relative percent deviation between calculated and experimentally determined triacylglycerols conversion for these kinetic models is between 3 and 10%.

Limited reserves of fossil fuels as well as the growing concern for the environment, has led to a worldwide search for renewable energy sources, among which biodiesel, a mixture of fatty acid methyl esters (FAME), is one of the most perspective alternative fuels since it is a non-toxic and can be produced from different renewable sources through simple cost-effective alcoholysis, while being compatible with existing infrastructures. Vegetable oils, as renewable in nature and environmentally friendly, with a possibility to be produced on a large scale, represent a promising feedstock for biodiesel production. In this chapter, a comprehensive review of different vegetable oils as a feedstock for biodiesel synthesis is reported, including edible and non-edible oils, as well as waste vegetable oils. Selection of feedstock for biodiesel production mainly depends on the specific conditions and circumstances in some region (climate, presence of certain crops, the economic development of a country, etc.). Various fatty acid compositions of triacylglycerols directly determine the quality and fulfillment of the standards of biodiesel. One of the crucial points which determine technology route for biodiesel synthesis is content of free fatty acids (FFA) which might be present in vegetable oils, as well as the presence of water and other compounds. Also, many analysis performed in the past have shown that the production cost of biodiesel is mainly determined by the price of used feedstock, which represents 70-80% of total production costs of biodiesel. Currently more than 95% of feedstock comes from edible oils since they are easily accessible, consists mainly of triacylglycerols, whereby the properties of biodiesel produced from these oils are suitable to be used as diesel fuel substitute. Most commonly used edible oils for biodiesel production are rapeseed, soybean, sunflower and palm. However, for economic and social reasons, in recent years research and development of biodi

Increased environmental concern and awareness of limited reserves of fossil fuels gave a great importance to alternative and renewable energy sources over the past couple decades. An excellent substitute for mineral diesel fuels is biodiesel, a mixture of fatty acid methyl esters (FAME), made by alcoholysis of different triacylglycerols (TAG) from various renewable sources (vegetable oils or animal fats) in the presence of a homogeneous or heterogeneous catalyst. Drawbacks of homogeneously catalyzed alcoholysis, to-day the most commonly used commercial biodiesel production process, have shifted the research focus on technologies based on utilization of solid catalyst. Heterogeneously catalyzed alcoholysis is more environmentally friendly, offers simplified production and improved process efficiency, allowing the possibility of catalyst’s regeneration, too. This technology of biodiesel synthesis is also the base for the continuous process development. Although great attention has been paid to the development of a catalyst that will have good activity and stability, followed by cheap method of synthesis, this task is still a challenge and needs further intensive research. Solid base catalysts have been characterized by high activity under mild reaction conditions and short reaction times, however, due to their sensitivity to the presence of impurities in the oil, primary the presence of free fatty acids (FFA) and water, they were not suitable, according to results of many investigations, for transesterification of lower-cost feedstock, such as non-edible plant oils and the waste cooking oils. For these feedstocks heterogeneous biodiesel synthesis should be performed applying solid acid catalyst. Despite the generally lower activity compared to solid base catalysts and higher reaction temperatures required for transesterification of oils into biodiesel, the main advantage of solid acids is their ability to simultaneously carry out esterification of FFA and transesterif