Browsing by Author "Ivanov T."

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    A spherical cavity model for quadrupolar dielectrics
    (2016-03-21) Dimitrova I.; Slavchov R.; Ivanov T.; Mosbach S.
    The dielectric properties of a fluid composed of molecules possessing both dipole and quadrupole moments are studied based on a model of the Onsager type (molecule in the centre of a spherical cavity). The dielectric permittivity ε and the macroscopic quadrupole polarizability αQ of the fluid are related to the basic molecular characteristics (molecular dipole, polarizability, quadrupole, quadrupolarizability). The effect of αQ is to increase the reaction field, to bring forth reaction field gradient, to decrease the cavity field, and to bring forth cavity field gradient. The effects from the quadrupole terms are significant in the case of small cavity size in a non-polar liquid. The quadrupoles in the medium are shown to have a small but measurable effect on the dielectric permittivity of several liquids (Ar, Kr, Xe, CH4, N2, CO2, CS2, C6H6, H2O, CH3OH). The theory is used to calculate the macroscopic quadrupolarizabilities of these fluids as functions of pressure and temperature. The cavity radii are also determined for these liquids, and it is shown that they are functions of density only. This extension of Onsager's theory will be important for non-polar solutions (fuel, crude oil, liquid CO2), especially at increased pressures.
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    Comment on “A spherical cavity model for quadrupolar dielectrics” [J. Chem. Phys. 144, 114502 (2016)]
    (2017-05-14) Dimitrova I.; Slavchov R.; Ivanov T.; Mosbach S.
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    DEVELOPMENT OF SIMPLIFIED MODELS FOR OPTIMIZATION OF BIOCHEMICAL METHANE POTENTIAL PROCEDURE
    (2022-01-01) Velichkova P.; Ivanov T.; Lalov I.
    Anaerobic digestion (AD) can be used to convert biomass materials into methane for energy recovery and achieve waste stabilization and environment stress reduction. The effect of substrate/inoculum ratio, temperature and trace elements on the biochemical methane potential (BMP) was evaluated through the calculation of performance parameters by using three simplified mathematical models. The Modified Gompertz equation, the Logistic equation and Reaction curve (Transference) models were all used with experimental data from the BMP determination. The substrate was vinasse with COD 216 g O2 L-1, obtained as by-product in wine distillation process. The lag time phase, maximum rate of biogas production and maximal potential biogas production was estimated in each experiment by application of mathematical models. The obtained results indicate that the use of models allow accurate determination of parameters in BMP determination. In case with vinasse the modified Gompertz model fits better than others.
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    ESTIMATION OF BIOCHEMICAL METHANE POTENTIAL OF HIGH PROTEIN SPIRULINA BIOMASS
    (2023-01-01) Ivanov T.; Lalov I.
    Biomass from microalgae is a promising feedstock for energy production through anaerobic digestion. The aim of this study was to determine the biochemical methane potential of Spirulina biomass. Тhe investigated biomass is characterized by a high protein content and a low carbon/nitrogen ratio. In order to improve the biodegradability of the biomass, the fresh biomass was pre-treated by thermolysis. Although a yield of 0.295 L CH4 g-1 VSS was obtained in the initial experiments, subsequent batch processes showed a drop in yield, slowing until the complete cessation of the methanation process. The main reason for the problems is the inhibition from high concentration of ammonium ions. After regeneration of the methanogenic consortium with vinasse substrate, an increase in yield to 0.445 L CH4 g-1 VSS was observed. The use of pretreated biomass resulted in an unexpected yield reduction effect. Application of vinasse as a co-substrate for methanation showed an increase in yield to 0.529 L CH4 g-1 VSS and stabilization of the process
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    RYEGRASS AS A FEEDSTOCK FOR BIOETHANOL PRODUCTION
    (2023-01-01) Ivanov T.; Petrin S.; Lalov I.
    In current paper a comparative study of bioethanol yields from ryegrass biomass by different type of pretreatment and enzyme hydrolysis is done. Acidic and alkali hydrolysis was used as a pretreatment of this feedstock. Cellulase blend 10 FPU g-1 dry matter was used for enzyme hydrolysis. The pre-treatment was conducted by autoclaving for 20 minutes at 121°C. Best results were obtained by pretreatment with 1 % HCl and 1 % NaOH. Hydrolysate obtained by pretreatment with hydrochloric acid contained 33.6 mg mL-1 reducing sugars, and that obtained by pretreatment with base - 29.0 mg mL-1. Both hydrolysates were found to be suitable substrates for bioethanol generation, where 5.55 g ethanol/100 g dry matter was produced from grass hydrolysate obtained by acidic hydrolysis followed by enzyme hydrolysis and from alkali pretreated hydrolysate-4.73 g ethanol/100 g dry matter. The results demonstrated that ryegrass biomass is suitable feedstock for bioethanol production.
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    The polarized interface between quadrupolar insulators: Maxwell stress tensor, surface tension, and potential
    (2015-10-21) Slavchov R.I.; Dimitrova I.M.; Ivanov T.
    The quadrupolar Maxwell electrostatic equations predict several qualitatively different results compared to Poisson's classical equation in their description of the properties of a dielectric interface. All interfaces between dielectrics possess surface dipole moment which results in a measurable surface potential jump. The surface dipole moment is conjugated to the bulk quadrupole moment density (the quadrupolarization) similarly to Gauss's relation between surface charge and bulk polarization. However, the classical macroscopic Maxwell equations completely neglect the quadrupolarization of the medium. Therefore, the electrostatic potential distribution near an interface of intrinsic dipole moment can be correctly described only within the quadrupolar macroscopic equations of electrostatics. They predict that near the polarized interface a diffuse dipole layer exists, which bears many similarities to the diffuse charge layer near a charged surface, in agreement with existing molecular dynamics simulation data. It turns out that when the quadrupole terms are kept in the multipole expansion of the laws of electrostatics, the solutions for the potential and the electric field are continuous functions at the surface. A well-defined surface electric field exists, interacting with the adsorbed dipoles. This allows for a macroscopic description of the surface dipole-surface dipole and the surface dipole-bulk quadrupole interactions. They are shown to have considerable contribution to the interfacial tension - of the order of tens of mN/m! To evaluate it, the Maxwell stress tensor in quadrupolar medium is deduced, including the electric field gradient action on the quadrupoles, as well as quadrupolar image force and quadrupolar electrostriction. The dependence of the interfacial tension on the external normal electric field (the dielectrocapillary curve) is predicted and the dielectric susceptibility of the dipolar double layer is related to the quadrupolarizabilities of the bulk phases and the intrinsic polarization of the interface. The coefficient of the dielectro-Marangoni effect (surface flow due to gradient of the normal electric field) is found. A model of the Langevin type for the surface dipole moment and the intrinsic surface polarizability is presented.