Аннотация и ключевые слова
Аннотация (русский):
Melanoidins are widely used in food and pharmaceutical industries. Melanoidins, which get in water bodies with wastewater of plants, pollute them, which subsequently can have a negative impact on the population health. Wastewater treatment of plants is an important condition to preserve the integrity of aquatic ecosystems. Sorption filtration is the most effective way of removing organic substances among the methods, used for wastewater treatment. To study the adsorption kinetics, the carbonic sorbents of the brands ABG and Purolat-Standard were used, which differ with a raw material, a surface chemistry state and a porous structure. The study of the adsorption kinetics allows to determine the mechanism of mass transfer in the system adsorbent-adsorbate and to obtain the parameters, necessary for engineering evaluation of adsorption processes in practice. It is shown that the time of reaching equilibrium in the sorption system varies in the range of 150-250 minutes. The degree of reaching the adsorption equilibrium () and the dimensionless kinetic parameters T have been calculated, which are proportional to the time of the process (t). It is found that the melanoidin adsorption rate is controlled by external mass transfer, necessary for calculation of optimum parameters and modes of the adsorption process. Experimental research allows to determine that the granules of the used carbonic sorbents interact with the dissolved substance in the full volume and throughout the particle is in the reaction zone; such interaction relates to a quasi-homogeneous model. It is shown that at the melanoidin adsorption, the rate of the internal diffusive mass transfer depends on the porous structure of the carbonic adsorbents. A high value of the external mass transfer coefficient for the carbonic sorbent Purolat-Standard suggests a high degree of melanoidin extraction from aqueous solutions.

Ключевые слова:
Melanoidin, kinetics, adsorption, active carbon
INTRODUCTION With the development of the industrial sector, the issue of industrial wastewater treatment and recycling arises increasingly. The deteriorating environmental situation forces to tighten the requirements for discharge of waste and wastewater. As it is known, almost no plant can work without waste. The treatment of wastewater, appearing during the production of medicines and food, is an important condition for preserving the purity of water bodies. Adsorption is one of the effective methods of removing small amounts of organic substances from aqueous solutions, which allows to use the adsorbent repeatedly and to create a resource-saving and ecologically safe production. Melanoidins are widely used in food industry not only as antioxidants, but also as biostimulants in cattle breeding and veterinary, as well as in medicine as drugs of anticoagulant and wound-healing action. Furthermore, there is an immunostimulating effect of melanoidins. In this regard, there is a high level of environmental pollution, which has a negative impact on the population health and the ecosystem as a whole. Melanoidins (Greek melanos - dark) are a product of melanoid formation, obtained from the interaction of reducing sugars (monosaccharides and reducing disaccharides, contained both in the product itself and formed during the hydrolysis of more complex carbohydrates) with amino acids, peptides and proteins, which usually have a dark colour (from red-brown to dark-brown) (Fig.1) [1, 2]. Melanoidins, formed as waste of food production, can lead to serious pollution. In particular, because of their dark colour, they block the sunlight penetration and reduce photosynthesis and oxygen levels in rivers. To prevent a serious pollution, it is necessary to conduct a special treatment of industrial wastewater before its draining into a waste body. A method of adsorption treatment with active carbons is the most advantageous. To understand the mechanism of adsorption of organic substances, it is necessary to know the limiting stage of this process. The study of the adsorption kinetics allows to determine time, necessary for reaching adsorption equilibrium adsorbent-adsorbate, and to obtain the parameters, necessary for engineering evaluation of adsorption processes in practice. Fig. 1. Structure of melanoidin polymer fragment (glc - residue of D-glucose). Please cite this article in press as: Zelenaya K.V., Golubeva N.S., and Khlopova A.V. Research on the mechanism of melanoidin adsorption kinetics from aqueous solutions by carbonic adsorbents. Science Evolution, 2017, vol. 2, no. 2, pp. 40-43. DOI: 10.21603/2500-1418-2017-2-2-40-43. Copyright © 2017, Zelenaya et al. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://, allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license. This article is published with open access at http:// science- The object of the present paper is the study of the mechanism of kinetics of melanoidin adsorption on carbonic sorbents for determination of the kinetic parameters of the process, necessary for calculation of the optimum parameters of the adsorption column and the modes of the continuous adsorption cleaning. MATERIALS AND METHODS Active carbons ABG and Purolat-Standard were used as sorbents, which differ with a raw material, a surface chemistry state and a porous structure [3, 4]. ABG and Purolat-Standard carbonic sorbents are semi-cokes, produced according to the new technology. The distinctive feature of this technology lies in the replacement of the traditional two-stage raw material carbonization process in RESULTS AND DISCUSSION Research on the melanoidin adsorption kinetics (Fig. 2) indicates that when removing melanoidin on the ABG activated carbon in the sorption system, equilibrium is achieved within 250 min, and on the Purolat-Standard active carbon it is achieved within 150 min. To determine the limiting stage of diffusion and to establish the porous structure model of the studied active carbons, dependence was studied of the degree of reaching the adsorption equilibrium () and the dimensionless kinetic parameters (T) on the duration of mixing the solutions (t) (Fig. 3, 4). 10 the inert atmosphere with the following activation by a 8 1 a. mg/g*103 single-stage auto-thermal gasification process. This allows to reduce the sorbent end price due to the reduction of energy, consumed for its production. 6 Kinetic studies were carried out in melanoidin aqueous solutions with the concentration of the studied 4 2 component of 100 mg/dm3 from the limited volume by shaking the adsorbent weighed amount with the solution 2 and by the following determination of the concentration of remaining substances. The contact time of the 0 melanoidin solution with the active carbon samples varied from 1 min to 7 h. The concentration of melanoidin in solutions was monitored with spectrophotometric method by characteristic adsorption. The optical density was measured with spectophotometer PE-5300 V (thickness of the light-adsorbing layer was 10 mm and the wavelength was 400nm). 1 0.8 0.6 γ 0.4 0.2 0 0 100 200 300 400 500 0 100 200 300 400 500 min Fig. 2. Kinetic curves of melanoidin adsorption from aqueous solutions by active carbons of the brands ABG (1) and Purolat-Standard (2). 0.16 0.14 0.12 0.1 T 0.08 0.06 0.04 0.02 0 0 5 10 15 20 min t. min (b) Fig. 3. Kinetic curves of melanoidin adsorption by active carbon of the brand ABG in coordinates γ - t (a) and T - t (b). 1.2 1 0.8 γ 0.6 0.4 0.2 0 0 50 100 150 200 250 300 1.2 1 0.8 T 0.6 0.4 0.2 0 0 10 20 30 40 min t. min (b) Fig. 4. Kinetic curves of melanoidin adsorption by active carbon of the brand Pulorat-Standard in coordinates γ - t (a) and T - t (b). 1.2 1 0.8 γ 0.6 0.4 0.2 0 T 0 1 2 3 4 5 2 1 T 0 1 2 3 1 0.8 0.7 0.6 0.5 0.4 0.3 0.9 2 γ 1 0.2 0.1 0 0 100 200 300 400 0 100 200 300 400 500 min t. min (b) Fig. 5. Kinetic curves of melanoidin adsorption by active carbons of the brands ABG (a) and Purolat-Standard (b) in coordinates γ - t: measured (1) and experimental (2). Melanoidin adsorption on ABG active carbon, according to the linear dependence of T on t, is limited by external mass transfer during the first 10 minutes, and on the Purolat-Standard active carbon - during 15 minutes. After that, the role of the external diffusive transfer became to influence clearly the overall adsorption rate. The analysis of the curves, obtained experimentally (Fig. 3a, 4a), allows to determine the porous structure type of the studied active carbons. Dependence of the degree of reaching the adsorption equilibrium on time has a rectilinear character up to γ = 0.9-0.95, which suggests that the granules of the used sorbents correspond with the quasi-homogeneous model of porous structure, as well as allows to calculate the kinetics with this model [4, 5]. The quasi-homogeneous model is based on the idea that a solute, upon penetrating into the adsorbent, interacts with it in the full volume and throughout the particle is in the reaction zone. A sorbent grain can be considered as a system, formed by irregular interlacement of pores. The results of the comparison of experimental and theoretical kinetic curves are indicated in Fig. 5. In the area of small values of γ, the experimental and moments of time, which is true only in case of a linear adsorption isotherm [10, 11]. The method of determining β is resolved into comparison of the theoretical kinetic curve γ(T), given by equation (1 and 1.1) and the experimental kinetic curve γ(T), under the identical values of γ. By plotting the dependence diagram T(t), we can find β according to the formula (2). y = 1 - e-T, (1) Т = А ∙ f3 ∙ t (1.1) f3 tga, (2) A where A is the coefficient, which was found according to the formula: А = Vz +К , (2.1) Vр 1 where Vz is the specific total volume of the sorbent mass, cm3/g; Vp is the volume of the solution in contact with the sorbent, cm3; K1 is the equation constant, governing the internal diffusive kinetics of absorption of a solute, is calculated according to the formula: 1 theoretically calculated kinetic curves are fairly close to each other, which indicates a quick flow of the limiting К1 = , (2.2) Кg external diffusion in terms of the experiment. Further discrepancy between the theoretical and experimental curves can be explained by the role of internal diffusion, as the path of diffusion within the grain increases [6, 7]. The external mass transfer coefficient during adsorption from solutions can be found from the overall mass transfer coefficient if the experiment is carried out in conditions, where the limiting stage of the process is the external diffusion. Herewith, the area of the prevailing influence of the external mass transfer becomes apparent by indirect indicators [8, 9]. The overall mass transfer coefficient is calculated from the basic mass transfer equation, in which the driving force of the process is calculated as an average logarithmic value from the driving forces in the first and final where Kg is the adsorption coefficient, on the linear part of the isotherm: Kg=ap/Cp (where ap is the equilibrium amount of the adsorbed substance with a concentration of Cp, mg/g; Cp is the equilibrium concentration of the adsorbed substance in a solution, mg/dm3). The melanoidin external diffusive mass transfer coefficients are indicated in Table 1. Brand of carbonic sorbent External mass transfer coefficient, ß, min-1 ABG 0.000164 Pulorat-Standard 0.000821 Table 1. Melanoidin external diffusive mass transfer coefficients Table 2. Active carbon structural characteristics Active carbon brand Vmicro, cm3/g Vmeso, cm3/g Vmacro, cm3/g Vz, cm3/g ABG 0.02 0.24 0.73 0.99 Pulorat- Standard 0.07 - 0.43 0.5 The values of the external diffusive mass transfer coefficient during adsorption from melanoidin solutions show that the mass transfer rate depends on the sorbent structural characteristics (Table 2). The structural characteristics (volume of micro-, meso- and macropores) were studied with the method of low-temperature nitrogen adsorption at 77°C with Sorbtometr M. A high coefficient value, when extracting on semi-coke Pulorat-Standard, is due to the absence of mesopores in contrast to ABG [12, 13, 14]. A higher value of mass transfer coefficient for the semi-coke Purolat-Standard allows to expect a higher degree of extraction of melanoidin products, which is consistent with the earlier studies of melanoidin adsorption in static conditions [15, 16]. CONCLUSIONS The adsorption parameters, obtained during the research on kinetics, can be used for a calculation of the parameters of the adsorption column, as well as for optimization of modes of continuous wastewater treatment from melanoidin with the studied semi-cokes.
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