Browsing by Author "Simeonov E."
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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 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 Newly Synthesized Lignin Microparticles as Bioinspired Oral Drug-Delivery Vehicles: Flavonoid-Carrier Potential and In Vitro Radical-Scavenging Activity(2023-04-01) Ivanova D.; Toneva M.; Simeonov E.; Nikolova B.; Semkova S.; Antov G.; Yaneva Z.The aim of the present study was to synthesize lignin microparticles, to evaluate their physicochemical, spectral, morphological and structural characteristics, to examine their encapsulation and in vitro release potential and behaviour towards the flavonoid morin in simulated physiological medium and to assess the in vitro radical-scavenging potential of the morin-loaded lignin microcarrier systems. The physicochemical, structural and morphological characteristics of alkali lignin, lignin particles (LP) and morin-encapsulated lignin microparticles (LMP) were determined based on particle size distribution, SEM, UV/Vis spectrophotometric, FTIR and potentiometric titration analyses. The encapsulation efficiency of LMP was 98.1%. The FTIR analyses proved that morin was successfully encapsulated in the LP without unexpected chemical reactions between the flavonoid and the heteropolymer. The in vitro release performance of the microcarrier system was successfully mathematically described by Korsmeyer–Peppas and the sigmoidal models outlining the general role of diffusion during the initial stages of the in vitro release process in simulated gastric fluid (SGF), and the predominant contribution of biopolymer relaxation and erosion was determined in simulated intestinal medium (SIF). The higher radical-scavenging potential of LMP, as compared to that of LP, was proven via DPPH and ABTS assays. The synthesis of lignin microcarriers not only provides a facile approach for the utilization of the heteropolymer but also determines its potential for the design of drug-delivery matrices.Item Organic solvent nanofiltration - The efficient approach for natural products processing(2012-01-01) Koleva V.; Simeonov E.; Boam A.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 Solid liquid extraction of phenolic and flavonoid compounds from Cotinus coggygria and concentration by nanofiltration(2014-01-01) Koleva V.; Simeonov E.Extraction kinetics of polyphenols and flavonoids from plant material and their separation and concentration by nanofiltration were investigated. The kinetics experiments were carried out with Cotinus coggygria. The influence of the extraction solvent on the extraction rate was defined. Four different extraction solvents or mixtures were applied - methanol, azeotropic ethanol, 50/50 ethanol/water mixture, and pure water. The optimum extraction rate of flavonoids and polyphenols was achieved by using 50 % ethanol as a solvent for extraction. This solvent mixture was used for generating extracts for the nanofiltration experiments. Organic solvent nanofiltration membranes from DuraMem™ series with different pore sizes (200, 300 500 and 900 Da) were tested in dead-end and cross-flow filtration systems. Flux and rejection data were obtained for every membrane type. Very good separation and respectively concentration of the extracted useful compounds was achieved (rejection for polyphenols and flavonoids is 91 and 93 %, respectively). During a feed/extract concentration experiment, the constant polyphenols and flavonoids rejection was measured. The results suggest that the nanofiltration technology could be combined successfully with solid-liquid extraction for natural sourced valuable compounds enrichment.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.