Browsing by Author "Chilev C."
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Item A COMPUTER SIMULATION OF A BIOMASS GASIFICATION PROCESS(2020-01-01) Chilev C.; Simeonov E.; Stoyanov V.; Chaushev S.The biomass is one of the promising energy sources of the future. It is possible to use its energy potential through thermo-chemical conversion processes of pyrolysis and gasification. A particular attention has been recently paid to biomass gasification. Several models have been advanced to describe this complex process. The present communication suggests a flowsheet simulating a wood biomass gasifier. The simulations are carried out by ASPEN PLUS V.8.0 commercial software. The thermo-chemical models assume that the reactants reach a chemical equilibrium. The flowsheet includes three stages: raw biomass drying, a gasification process and a products separation. The simulations provide to predict the final composition of the gas mixture produced by biomass gasification. Sensitivity analyses are performed to determine the effect of the pressure, the air flow, the moisture content, and the air stream enthalpy on the amounts of the gases produced.Item Carbon dioxide capture by adsorption (review)(2016-01-01) Hinkov I.; Lamari F.D.; Langlois P.; Dicko M.; Chilev C.; Pentchev I.The present paper reviews the different types of adsorbents that could be used for CO2 capture from flue gases. They include carbon-based adsorbents, zeolites, molecular sieves, metal-organic frameworks, hydrotalcite-like compounds and advanced adsorbents. Their possibilities are described and confronted. In particular, it has been demonstrated that classical adsorbent materials need further functionalization or impregnation with different nitrogen-containing species in order to become suitable for CO2 capture. The different methods for CO2 capture by adsorption cyclic processes such as Pressure Swing Adsorption (PSA), Vacuum Swing Adsorption (PSA), Thermal Swing Adsorption (TSA), Electric Swing Adsorption (ESA) as well as the combination of TSA and chemical reaction, known as Thermal Swing Sorption-Enhanced Reaction (TSSER), are also mentioned in the cited literature.Item Flavonoids Extraction Kinetics, Antimicrobial Activity and Radical Scavenging Potential of Bulgarian Woundwort (Solidago virgaurea L.)(2022-02-01) Yaneva Z.; Simeonov E.; Rusenova N.; Ivanova D.; Nikolova G.; Karamalakova Y.; Chilev C.; Beev G.The medicinal plant woundwort (Solidago virgaurea L.) characterizes by diuretic, antimutagenic, anti-inflammatory activity and it has been applied for urinary tract, nephrolithiasis and prostate disorders treatment. The aim of the present study was to analyze the extraction kinetics of catechin, epigallocatechin and quercetin from Bulgarian woundwort extracts, to assess the antibacterial potential of the medicinal plant extracts against four bacterial strains (Staphylococcus aureus ATCC25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Bacillus cereus), their antioxidant capacity and radical scavenging potential. The concentrations of the flavonoids in the extracts obtained at different extraction conditions (solvent, temperature, extraction time) were determined by newly-developed by the scientific team RP-HPLC-PDA methodologies. The agar well diffusion method was applied to evaluate the antibacterial activity of the plant extracts. The 70% EtOH extracts at 20◦C displayed significantly higher antibacterial activity against the foodborne pathogenic bacteria S. aureus and P. aeruginosa as compared to the 70% and 98% EtOH extracts at 30◦C and 20◦C, respectively. The medicinal plant exhibited satisfactory antioxidant potential and radical-scavenging activity.Item Investigation of acetic acid dehydration by various methods(2016-01-01) Chilev C.; Lamari F.D.; Dicko M.; Simeonov E.Some separation methods for acetic acid dehydration, such as azeotropic distillation, extractive distillation and hybrid extraction/distillation process (HEDP) are investigated and further analyzed. In order to optimize the separation process, different separation agents were investigated. The phase equilibria (vapor-liquid and vapor-liquid-liquid) of the ternary system acetic acid/water/separating agent are analyzed in order to choose an appropriate thermodynamic model suitable for the simulation of the system. The results show that the azeotropic distillation is the most undesirable dehydration method among the three separation processes investigated. Almost similar results are obtained using the extractive distillation and HEDP. The latter is energetically more favorable, but the extractive distillation requires less equipment and control operations costs. Therefore, HEDP using methyl tert-butyl ether as an extraction agent is the most promising separation method for the system studied.Item Kinetics of green solid-liquid extraction of useful compounds from plant materials: Kinetics coefficients and modeling(2018-02-23) Simeonov E.; Yaneva Z.; Chilev C.A mathematical model for modeling solid-liquid extraction from plants was developed. Two extraction systems, System I Nicotiana tabacum L.-water and System II Geranium sanguineum L.-water, were investigated. The effect of agitation rate on the mode of the extraction process was studied, as the limit values in the case of internal diffusion for System I and System II were determined. The kinetics of extraction for both systems at determined technological parameters (temperature and solid/liquid ratio) was experimentally investigated. The values of the partial mass transfer coefficient, k, were determined by the Regular regime method. A four-parameter empirical model for prediction of the effective diffusivity, Deff, was also presented. The model adequacy is verified with the experimental data and shows very good coincidence.Item Modeling and kinetics study of solid-liquid extraction from leaves of nicotiana tabacum L.(2015-01-01) Simeonov E.; Chilev C.Experimental kinetics has been obtained by extraction from leaves of Nicotiana tabacum L. at periodical conditions in a stirred vessel. The influence of the liquid-solid ratio and the kind of the solvent have been determined. A four parameters model for calculating the values of Deffhas been found using non-linear regression of the experimental results. The diffusion model have been solved using variable Deff. There is a very good coincidence between the numerical and experimental data.Item Modelling of Single-Gas Adsorption Isotherms(2022-10-01) Chilev C.; Dicko M.; Langlois P.; Lamari F.The present paper reviews and analyses different models that could be used to describe the adsorption equilibrium of pure gases. The adsorption equilibrium of hydrogen, nitrogen and methane is characterised and modelled. Several thermodynamic conceptions have been selected and tested for the calculation of physico-chemical parameters. The model of Dubinin has been selected to estimate the pseudo-saturation vapour pressure. The best results for the molar volume of the adsorbate have been obtained by using Do’s equation. Eight models, namely Langmuir, Freundlich, Sips, Toth, Jovanovic, UNILAN, OBMR and Potential Theory, describing the adsorption equilibrium of pure gases, have been tested and compared with experimental data obtained from the literature at three different temperatures (283 K, 298 K and 313 K). In order to determine the best fit, the correlation coefficient and the standard errors for each parameter have been used to evaluate the data. All the models used in this study, except for Freundlich’s equation in the case of nitrogen or methane adsorption, are in good agreement between experiment and modelling for the adsorption isotherms.Item Multi-Compound H2, CH4, and N2 Adsorption Analysis(2022-11-01) Chilev C.; Langlois P.; Lamari F.In order to study the purification of hydrogen and its separation from gas mixtures by adsorption, different models describing the adsorption equilibrium of gas mixtures have been tested; seven of them have been compared with experimental multi-component data obtained from the literature. The measurements include three-component mixtures of hydrogen, nitrogen, and methane. All the models used in this study are purely predictive; such models are competitive isotherm models which use only the previously obtained coefficients of the single-component isotherms. A mathematical description of each model is developed and discussed. Based on the results of numerical experiments, an analysis of how best to apply the Sips multi-component approach and the Ideal Adsorbed Solution theory is developed. A discussion on the ability and accuracy of the different models to describe the multi-component adsorption equilibria is developed. Based on this research, the Jovanovic model, which best reproduces the experimental results of the adsorption equilibrium in all cases, can be recommended as the most appropriate to use.Item Numerical Simulation of a Valorisation-Oriented Hybrid Process for the Bio-Oil-Related Separation of Acetol and Acetic Acid(2024-02-01) Chilev C.; Lamari F.; Langlois P.Biomass as a whole offers a more diverse potential for valorisation than any other renewable energy source. As one of the stages in the separation of bio-oil involves a liquid mixture of acetol and acetic acid, and as both components are particularly well suited for valorisation, a hybrid method was developed for their separation with a high purity level through an approach combining liquid–liquid extraction and distillation. In order to design and simulate the flowsheet, the ChemCAD 7.0 simulation software was used. Sensitivity analyses were carried out to investigate the influence of the different parameters in the distillation columns, such as the reflux ratio, the feed stage location, and the vapour/bottom molar flow ratio. The effect of different extractants and of their excess on the separation process, as well as the possibility of regenerating the extractant, was also studied. Tri-n-octylamine was accordingly selected as a separating agent that was fully recycled. The end result for separating an initial 48/52 wt% acetol/acetic acid liquid mixture was acetol with a purity of 99.4 wt% and acetic acid with a purity of 100 wt%.Item Simulation of biodiesel production by transesterification of vegetable oils(2014-01-01) Chilev C.; Simeonov E.This work presents an ChemCAD 6.0 Simulation study for biodiesel production. The simulation illustrates the production of biofuel from pure vegetable oil with an alkaline catalyst. The main areas are transesterification, methanol separation, water washing, FAME purification, catalyst neutralization and glycerol purification. The equipment used includes in particular reactors, distillation and extraction columns and components splitters. As a result of the simulation, the two final target products - biodiesel and glycerol, are obtained with purity 98% and 99%, respectively. The suggested technological scheme provides a possibility for recuperation of the heat streams.Item VALORIZATION OF WASTE LAVENDER RESIDUE FROM THE ESSENTIAL OIL INDUSTRY FOR PRODUCTION OF ROSMARINIC ACID -A STUDY ON THE SOLID-LIQUID EXTRACTION(2022-01-01) Chilev C.; Simeonov E.; Dimitrova B.; Yonkova V.; Pietsch S.; Heinrich S.; Peshev D.The possibility for valorization of the waste lavender residue from the essential oil industry via solvent extraction was studied. The plant residue of Lavandula angustifolia, from which the lavender oil is extracted through steam distillation, contains Key Biologically Active Components (KBAC) such as: rosmarinic acid, caffeic acid, luteolin. The feasibility of the solvent extraction for their isolation was assessed by comparison of the kinetics and equilibrium of extraction of KBAC from spent and raw plant material (collected from the same batch before the steam distillation) using different solvent compositions. The parameters of the extraction process were experimentally and numerically optimized. To determine the most efficient solvent, two pure and two mixed solvents were tested: pure water, 99.9 % ethanol and their mixtures - (40 % and 60 % ethanol). Using 40 % ethanol as extraction solvent resulted in maximum recovery of KBAC. A mathematical model for the solid-liquid extraction from lavender materials was developed. The values of the model parameters were determined using the Regular regime method. A four-parameter empirical model for prediction of the effective diffusivity, Deff, was also applied. The model adequacy was experimentally verified. Based on the theoretical and experimental results KBAC recovery the following extraction conditions were recommended: extraction time - 30 min, temperature - 30 °C, liquid-solid ratio - 0,01 m3 kg- and 40 % ethanol as an extraction solvent.