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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 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.

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%.

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.

The goal of this study was to prepare a CaO·ZnO catalyst containing a small amount of K2CO3 and analyze its activity for biodiesel synthesis. The catalyst was prepared using the following procedure: CaO and ZnO (mole ratio of 1:2), water and K2CO3 (in various amounts) were mechanochemically treated and after milling heated at 700°C in air atmosphere for obtaining mixed CaO·ZnO/xK2CO3 oxides (x = 0, 1, 2 and 4 mol of K2CO3 per 10 mol of CaO). All the samples were characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), scanning electron microscopy/ energy-dispersive spectroscopy (SEM/EDS), particle size laser diffraction (PSLD) distribution, solubility measurement of Ca, Zn and K ions in methanol as well as by determination of their alkalinity (Hammett indicator method). Prepared CaO·ZnO/xK2CO3 composite powders were tested as catalysts for methanolysis of sunflower oil at 70 °C using mole ratio of sunflower oil to methanol of 1:10 and with 2 mass% of catalyst based on oil weight. The presence of K2CO3 in prepared samples was found to increase the activity of catalyst, and that such effect is caused by homogeneous-heterogeneous catalysis of biodiesel synthesis., Cilj ovih istraživanja bio je da se pripremi CaO·ZnO katalizator koji sadrži malu količinu K2CO3 i analizira njegova aktivnost u sintezi biodizela. Katalizator je pripremljen prema sledećoj proceduri: CaO i ZnO (molski odnos 1:2), voda i K2CO3 (u različitoj količini) su tretirani mehanohemijski i nakon mlevenja zagrevani na 700 °C u atmosferi vazduha da bi se dobila smeša oksida CaO·ZnO/xK2CO3 (x = 0, 1, 2 i 4 mol K2CO3 na 10 mol CaO). Karakterizacija pripremljenih katalizatora izvršena je metodama rendgenske difrakcije (XRD), indukovane kuplovane plazme (ICP), spektroskopije fotoelektrona dobijenih X-zracima (XPS), termogravimetrijske analize (TGA), infracrvene spektroskopije (FTIR), skenirajuće elektronske mikroskopije i energetske disperzione spektroskopije (SEM/EDS), raspodele veličine čestica (PSLD), merenjem rastvorljivosti katalizatora odnosno Ca, Zn i K jona u metanolu, kao i određivanjem njihove baznosti (metodom Hametovih indikatora). Pripremljeni CaO·ZnO/xK2CO3 kompozitni prahovi testirani su kao katalizatori u reakciji metanolize suncokretovog ulja na 70 °C, pri molarnom odnosu suncokretovog ulja i metanola od 1:10 i sa 2 mas.% katalizatora u odnosu na masu ulja. Pokazano je da prisustvo K2CO3 u pripremljenim uzorcima povećava aktivnost katalizatora i da je takav efekat posledica homogeno-heterogene katalize u sintezi biodizela.

The kinetics of heterogeneous methanolysis of sunflower oil was studied at 60 °C using mechanochemically synthesized CaO·ZnO as catalyst. The influence of agitation speed, catalyst amount, and methanol-to-oil molar ratio on the rate of reaction was analyzed. The rate of the process depends on the two resistances - mass transfer of triglycerides to the catalyst surface and chemical reaction on the catalyst surface, which are defined as the values of the overall triglyceride volumetric mass transfer coefficient, kmt,TG, and the effective pseudo first-order reaction rate constant, k, respectively. These kinetic parameters actually determine the value of the apparent reaction rate constant, kapp, the time dependence of which is defined by the change of triglyceride (TG) conversion. A kinetic model is proposed and the model parameters are determined., Kinetika heterogene metanolize suncokretovog ulja je ispitivana na 60 °C korišćenjem CaO·ZnO katalizatora koji je sintetizovan mehanohemijskim putem. Analiziran je uticaj intenziteta mešanja, mase korišćenog katalizatora u sintezi i različitog molskog odnosa metanola i ulja na brzinu metanolize. Brzina procesa metanolize zavisi od dva otpora - otpora prenosu mase triglicerida do površine katalizatora i otpora brzini hemijske reakcije na površini katalizatora. Oba otpora određuju vrednost ukupnog zapreminskog koeficijenta prenosa mase triglicerida, kmt,TG, odnosno efektivne vrednosti konstante brzine hemijske reakcije pseudo-prvog reda, k. Ovi kinetički parametri određuju vrednost prividne konstante brzine procesa metanolize, kapp, koja se menja sa vremenom u zavisnosti od ostvareneog stepena konverzije triglicerida (TG). Predložen je odgovarajući model kojim je moguće definisati brzinu metanolize i određeni su odgovarajući parametri ovog modela.

The separation in a batch vacuum column of the essential oil of common juniper berries (Juniperus communis L., from the southern part of Serbia) was analyzed. The main goal of the analyzed separation process was to isolate several fractions from the essential oil which mainly contained á-pinene, sabinene and myrcene. These compounds contain about 65 mass% of the essential oil produced by hydrodistillation from the juniper berries originated from the southern part of Serbia. The results of experimental work in a laboratory column with 36 theoretical stages under vacuum (8.0-3.35 kPa) was simulated using Aspen software, and a proposed mathematical model was used to analyze some other operating conditions for fractionation of juniper berry's oil (number of plates: 25, 36 and 45 and reflux ratio: 2-10). According to the results of performed simulations, the most acceptable separation procedure which takes into account the prices of raw materials and distillate (á-pinene) as well as consumed energy was proposed., U ovom radu je ispitivana separacija etarskog ulja iz bobica kleke (Juniperus communis L. sa podneblja južne Srbije) postupkom šaržne vakuum destilacije. Glavni cilj laboratorijskih ispitivanja je usmeren ka izdvajanju pojedinih frakcija iz etarskog ulja kleke koje sadrže u većem procentu á-pinen, sabinen i mircen, a čine 65 mas% etarskog ulja dobijenog hidrodestilacijom bobica kleke. Rezultati eksperimentalnih ispitivanja sprovedenih šaržnom destilacijom pod vakuumom (8,0-3,35 kPa) u koloni sa 36 teorijskih podova su bili osnova za definisanje odgovarajućeg matematičkog modela i njegovog rešavanja primenom softverskog paketa Aspen. Dobijeno je dobro slaganje između eksperimentalnih vrednosti i vrednosti izračunatih na osnovu ovog modela. Potvrđena korektnost modela iskorišćena je za analizu uticaja različitih operativnih parametara (refluksni odnos od 2 do 10) i konstrukcionih karakteristika kolone (broj podova: 25, 36 i 45) na efekte separacije etarskog ulja kleke. Rezultati su pokazali, na osnovu analize uticaja cene ulazne sirovine, cene izdvojenih frakcija (á-pinen; smeše á-pinena sabinena, mircena) i ukupno utrošene energije za separaciju, da je u laboratorijskim uslovima izvedeno frakcionisanje etarskog ulja kleke najprihvatljivije.

The present study was aimed to investigate and compare the efficiency of different methods for the isolation extract from a plant material. Extracts from dried leaves of Aloe vera (A. barbadensis Mill.) and Sweet Bay (Laurus nobilis L.) were obtained applying the following techniques: supercritical carbon dioxide (SC CO2) extraction at 30 MPa and 100°C, a combined ultrasonic extraction and pre-treatment using SC CO2 (US-SCCO2), and a conventional ultrasonic extraction (US) with 96% ethanol. US-SCCO2 resulted in much higher yields of extracts of aloe and bay compared to SC CO2 extraction. Determined extract's yield was used for calculating the maximum useful work and exergy loss as a measure of irreversibility of the extraction process. Calculated maximum useful work per 1 kg of the extract was ranged from 0.7 to 226 kJ while estimated values of the exergy loss were from 48 to 416 kJ per 1 kg of the extract. The maximum useful work and exergy loss have the largest value for SCE much more than for other processes of extraction (US and US-SCCO2). The pre-treatment of the plant material with SC CO2 before an ultrasound-assisted extraction or the decrease of a particle size used for ultrasound-assisted extraction of Aloe vera has led to the decrease of maximum useful work and exergy loss. Unlike, pre-treatment with SC CO2 followed by ultrasound-assisted extraction increased the exergy loss when bay was used as the plant material.

Almost complete methanolysis of triglycerides is usually not enough to fulfil the strict standards of biodiesel quality. A key step in this process is neutralization of alkali (catalyst) followed by the washing procedure necessary for removing different impurities such as traces of catalyst and methanol and removal of soaps and glycerol from esters phase. The washing with hot water is still widely used in many industrial units for the biodiesel production. In this study, different procedures of biodiesel washing using hot water were investigated. The orto-phosphoric acid was suggested as the best compound for alkali catalyst (sodium hydroxide) neutralization. The main goal of the performed analysis was to minimize the water usage in the washing-neutralization step during the biodiesel production. Such solution would make the process of biodiesel synthesis more economical taking into account the decrease of energy consumed for evaporation of water during the final product purification, as well as more acceptable procedure related to the impact on environment (minimal waste water release). Results of the performed simulation of the washing process supported by original experimental data suggested that neutralization after the optimized washing process of the methyl ester layer could be the best solution. The proposed washing procedure significantly decreases the amount of waste water giving at the same time the desired purity of final products (biodiesel and glycerol). The simulation of the process was performed using ASPEN plus software supported by ELCANTREL and UNIQUAC procedure of required properties calculation.

The reduction of energy consumption in the supercritical carbon dioxide extraction of essential oils from leaves of species of the Lamiaceae family due to the optimal pretreatment of herbaceous material was studied in the present work. Essential oils of species of the Lamiaceae family are stored in peltate glandular trichomes on the leaf surface, and the optimal pretreatment for this type of secretory structure should include grinding followed by supercritical carbon dioxide batch (non-flow) pretreatment under extraction conditions prior to continuous flow extraction. Supercritical fluid extractions of peppermint (Mentha piperita), wild thyme (Thymus serpyllum) and hyssop (Hyssopus officinalis) leaves were performed including only grinding pretreatment as well as optimal pretreatment. The experimentally determined reductions of supercritical carbon dioxide consumption, for the observed extraction yields, ranged from 0.250 to 0.889 kg CO2 per gram of produced essential oil extract, while the corresponding reductions of energy consumption were in the range 48-170.7 kJ per gram of produced essential oil extract., U radu je ispitana mogućnost uštede energije u procesima ekstrakcije etarskih ulja biljaka familije Lamiaceae natkritičnim ugljen dioksidom, usled optimalnog predtretmana biljnog materijala. Kod biljaka ove familije, etarska ulja se nalaze u peltate glandularnim trihomima na samoj površini lista. Optimalan predtretman za ovaj tip sekrecione strukture uključuje, pored procesa mlevenja, i izlaganje mlevenog biljnog materijala kao šarže natkritičnom ugljen dioksidu na radnim uslovima, pre početka kontinualne ekstrakcije. Natkritične ekstrakcije etarskih ulja lista mente (Mentha piperita), majčine dušice (Thymus serpyllum) i izopa (Hyssopus officinalis) izvedene su sa optimalnim predtretmanom biljnog materijala, kao i sa predtretmanom koji je uključio samo mlevenje. Eksperimentalno određene vrednosti uštede natkritičnog rastvarača, za postizanje određenog prinosa, se nalaze u opsegu 0.250-0.889 kg CO2 po gramu proizvedenog ekstrakta, dok se odgovarajuće vrednosti uštede energije nalaze u opsegu 48-170.7 kJ po gramu proizvedenog ekstrakta. Pošto procese pod visokim pritiscima karakterišu visoki operativni troškovi, ostvarene uštede energije optimalnim predtretmanom biljnog materijala su bitne na industrijskom nivou.

The performed investigations were directed toward the analysis of the performance and activity of the fresh and regenerated Cyanamid HDS 20C catalyst in a laboratory batch reactor (2 dm3) for the HDS of the diesel fraction (light gas oil, LGO). Testing of the regenerated catalyst was performed with light gas oil (LGO) of different characteristics. The determined values of the reaction rate constant were compared to some published data in the literature for the HDS of specific sulfur compounds as well as the values of the activation energy. The rates of deactivation of the fresh and regenerated catalyst actually existed compared to some other results recently published in the literature. However, such an observed differences were not sufficient to derive a relation which could be used for the determination of the rate of catalyst deactivation.

Sol-gel synthesis, and the resulting materials (xerogels and aerogels) are finding increasing application in the synthesis of catalysts, due to their unique characteristics. The most important features of the sol-gel process are: the ability to achieve homogeneity at the molecular level, the introduction of several species in only one step and the ability to stabilize metastable phases. The supercritical drying process produces aerogels with structural features quite different to conventional materials. Some of these characteristics of aerogels can make them very effective catalysts.

The most complex step in the production of aerogels is the supercritical drying step, and it is therefore important to study its dynamics using mathematical models. Alumina/silica aerogel was obtained using a one step sol-gel synthesis and subsequent drying with supercritical carbon dioxide. The wet gel weight change with time was monitored. The dry aerogel sample porous structure was determined using the BET method and nitrogen adsorption/desorption. Supercritical drying of the wet gel sample was represented as the unsteady and one dimensional diffusion of 1-butanol through aerogel pores filled with supercritical carbon dioxide. Different mathematical models describing supercritical drying of the wet gel cylindrical sample were developed. Shrinking core models used one value of the effective diffusivity for the whole material, and they failed to describe the drying experiment correctly. Parallel pore models used different effective diffusivity values for each pore size. The best simulation results were obtained using the parallel pore model with local porosity or tortuosity values for each pore size.