Interaction of polymers with liquids and gases

The processes of interaction of polymers with low molecular weight liquids play an important role in the processes of forming finished products (for example, fibers from a solution), modifying the properties (plasticization) of the material, and also in the operating conditions of these products in various liquid media. The interaction is expressed in the absorption of liquid by the polymer and is called sorption. If sorption proceeds in the volume polymer material, she is called absorption. If absorption occurs in the surface layers, then the process is called adsorption.

Sorption

The mechanism of adsorption is due to the presence of surface tension forces at the interfaces between media (Fig. 5.1) due to the difference in the forces of intermolecular interaction in them. This leads to the accumulation of excess energy on the surface of a substance that tends to draw in its surface molecules (molecules adsorbent) and weaker interacting molecules (molecules adsorptive) inside the volume. The amount of adsorption largely depends on the specific surface area of ​​the adsorbent. Numerically, adsorption is expressed by the number of moles of adsorbed substance per unit mass of the adsorbent - x/m.

The study of sorption makes it possible to obtain valuable information about the structure of a polymer and the degree of packing of its molecules.

Usually, sorption processes are described using curves of the dependence of the amount of adsorbed substance on its concentration (or pressure) in the gas phase at a constant temperature (sorption isotherms, Fig. 5.2.). Here the value R/R s is the ratio of the vapor pressure of the adsorbent to the elasticity of its saturated vapor at a given temperature.

In the region of low vapor pressures, Henry's linear law is fulfilled:

Where A- amount of adsorbed substance; a m- limiting adsorption proportional to the active surface of the adsorbent; p- sorbate pressure; k is the adsorption constant. On fig. 5.2 the completion of monomolecular adsorption is determined by the exit of the sorption isotherm to the shelf in the range of relative pressures 0.4 ÷ 0.5.

In the presence of polymolecular adsorption and condensation on the surface of a porous adsorbent ( R/R s > 0.6 in fig. 5.2) use the universal equation

(5.3)

Thermodynamics of the adsorption process

Since, as a rule, the intermolecular interaction of adsorbent molecules is less intense than that of the adsorbent, adsorption proceeds with a decrease in the free energy of the surface (Δ F < 0) и выделением тепла (уменьшением энтальпии ΔH < 0). При равновесии процессов адсорбции и десорбции ΔF= 0. The value calculated in the course of adsorption characterizes the number and activity of groups on the surface of the adsorbent capable of reacting with the absorbent. During adsorption, the entropy of the system also decreases (Δ S < 0), поскольку молекулы абсорбтива ограничивают подвижность молекул полимера, уменьшая возможное число конформаций: ΔS = k ln ( W 2 / W 1), where is the Boltzmann constant, W 2 and W 1 - thermodynamic probability of the final and initial state of the system.

"EDUCATIONAL AND METHODOLOGICAL MANUAL" THERMODYNAMICS OF ADSORPTION OF GASES, VAPOR AND SOLUTIONS (SPECIAL COURSE). A. M. TOLMACHEV 2012 Annotation The lectures analyze in detail the description of adsorption ...»

-- [ Page 1 ] --

Faculty of Chemistry of Moscow

state university

them. M. V. Lomonosov

EDUCATIONAL AND METHODOLOGICAL AID

«THERMODYNAMICS OF GAS ADSORPTION,

VAPOR AND SOLUTIONS

(SPECIAL COURSE).

A. M. TOLMACHEV

annotation

The lectures analyze in detail the description

adsorption equilibria on macro- and microporous

adsorbents both within the framework of the "Gibbs excess method" and within the framework of the "total content method". In the latter case, the consideration was carried out on the basis of the thermodynamic theory of stoichiometric adsorption of individual substances and binary and multicomponent solutions developed by the author.

The methods of theoretical (a priori) calculation of adsorption equilibria and the description of isotherms of "absolute" and "excessive" adsorption of gases, vapors and components of binary solutions of non-electrolytes by various equations obtained within the framework of phenomenological, lattice and empirical models are considered in detail.

The methods of quantitative description of adsorption isotherms and topological analysis of supramolecular structures of adsorbates on microporous active carbons by the method of molecular dynamics are considered.

Based on a comparison of numerical and physical experiments, the possibility of using the equations of the theory of volumetric filling of micropores (Dubinin Radushkevich, Dubinin-Astakhov), equations of lattice models, etc. at supercritical temperatures is proved.

A computer data bank on adsorption developed under the guidance of the author is presented.

This development is a presentation of the material of a special course of lectures, which the author has been reading for a number of years to students, graduate students and graduate students specializing in the field of adsorption. The author hopes that this teaching aid will fill the gap that exists in the scientific and educational literature on the topic under consideration, and will help novice researchers to get acquainted with the main problems and achievements of the science of adsorption, this most complex section of thermodynamics.

The proposed development option does not consider such important sections as adsorption on mesoporous adsorbents, accompanied by capillary condensation processes, and quantum chemical methods for analyzing adsorption phenomena. The author hopes to make the necessary additions in the future and will be grateful for all comments and suggestions for improving this manual.

Email: [email protected], [email protected] Honored Professor of Moscow State University A.M. Tolmachev Table of contents.

Lecture 1. Gibbs excess method

Lecture 2

Lecture 3. Thermodynamics of adsorption.

Stoichiometric theory of adsorption...............52 Lecture 4. Thermodynamics of adsorbed solutions

Lecture 5. Description of adsorption equilibria of solutions, gases and vapors on macro and microporous adsorbents

Lecture 7. Study of adsorption on microporous carbon adsorbents by numerical methods.

Adsorption isotherms and molecular nanostructures of sorbates ..........178 Lecture 8. Computer data bank on adsorption ......226.

–  –  –

Quantitative description of adsorption isotherms of individual substances and components of fluid mixtures on adsorbents various types and a priori calculation of adsorption equilibria in such systems, which are widely used in various processes of separation and deep purification of substances in chemical technology, medicine, in solving environmental problems, is one of the complex and, at the same time, important tasks of adsorption theory, since the experimental search for appropriate highly selective systems is quite time consuming.

The main difficulty in constructing a rigorous thermodynamic model of adsorption systems is the problem of dividing the system into two phases, more precisely, determining the coordinates of the surface separating the bulk and adsorption phases. Precise drawing of the separating surface is impossible, therefore, two approaches are considered in theoretical works: the thermodynamically rigorous, but little informative Gibbs excess method, which does not separate the system into bulk and adsorption phases and allows one to analyze only the properties of the system as a whole, and the Langmuir total content method, based on the chosen in one way or another, models (dimensions, capacity) of the adsorption phase and the use of real (absolute) concentrations of components in this phase. Although the latter method is less rigorous, it is significantly more informative, since

considers the adsorption system as a two-phase one and allows one to analyze the properties of each of the phases separately and, in particular, to compare the results obtained by thermodynamic and molecular-statistical (or based on molecular models) methods, since the latter always require specifying the “structure” of the adsorption phase. The term "full content" appeared in the literature in the last quarter of the last century, however, according to the author, its foundations were first formulated by Langmuir, although he did not use this terminology.

Indeed, the well-known classical Langmuir model of ideal adsorption was based on two defining principles: setting the capacity of the adsorption phase limited by the monolayer, considered precisely as a separate phase of the adsorption system, and considering the adsorbent as a component of this phase, the concentration of which changed during adsorption due to the transition of free adsorption surface centers into adsorption complexes adsorbate – adsorbent.

Adsorption is a thickening of a substance at the phase boundary, due to the unsaturation of the bonds of surface atoms or molecules and, as a consequence, the existence of an adsorption field that propagates, strictly speaking, to points infinitely distant from the surface of the adsorbent in the bulk phase. This circumstance leads to the need to take into account the following features of such systems:

1. The separation of the system into adsorption and bulk phases cannot be carried out strictly.

2. The adsorption phase isolated on the basis of some additional (always approximate) considerations will be energetically inhomogeneous (it will be in an inhomogeneous adsorption field) and, since this inhomogeneity cannot be taken into account within the framework of phenomenological thermodynamics, the description of the properties of the adsorption phase has to be carried out using phase-averaged parameter values ​​(concentrations, chemical potentials, etc.) .

Parameters of the adsorption phase: concentrations - c, x, activity coefficients -, chemical potentials - are marked either by a bar above the corresponding symbol, or by the subscript R.

3. The presence of the adsorption field must be taken into account in the expression for the chemical potential, i.e., use the full chemical potentials for the components of the adsorption phase:

For bulk gas or vapor phase:

–  –  –

where: surface (pore volume) of the adsorbent, W surface tension (internal pressure).

Using Maxwell's equations, we get:

–  –  –

It is useful to pay attention to two forms of the Gibbs-Duhem equation, which are widely used for adsorption solutions in the framework of the total content method. In older models, the adsorbent was often not considered as a component of the adsorption solution, but only as a source of the adsorption field (surface energy). In this case, for example, during the adsorption of a one-component vapor, the equation

Gibbs-Duhem has the form (P,T=const.):

c i d i Wd 0 (1.7) (W is the surface area of ​​the adsorbent, i is the total chemical potential of the adsorbate).

In modern models, the adsorbent (R) is a component of the adsorption solution. It is introduced either in the form of adsorption centers (as in the Langmuir and Tolmachev models) or in the form of vacancies (free voids of certain sizes in the adsorption solution).

In this case, the Gibbs-Duhem equation can be represented in two equivalent forms (single-component vapor, P,T=const.):

with i d i c R d R Wd 0 (1.8) and since s(st.), then within the framework of the “hard” solution model (the molar areas of the components - s=const., s i +sR=W) (1.8) reduces to the form:

c i d i c R d R (si sR)d Wd c i d iR c R d R 0 .

The above features of adsorption systems led to the development of two versions of their thermodynamic description:

1. The Gibbs excess method - a thermodynamically rigorous description of the change in the properties of the entire system during adsorption on the basis of experimentally determined excess adsorption values ​​(see below) without its separation into two phases. This method, obviously, does not allow obtaining any information about the properties of the adsorption phase and, therefore, is not informative enough, especially when solving practical problems, since it does not provide information about the capacity of the adsorbent with respect to the components of the bulk phase, about its structure, properties, and etc..

2. Total content method, based on the separation of the system into two phases (see below) and the description of its properties as a heterogeneous system using the absolute concentrations of the components in each of the equilibrium phases. Thermodynamically, this method is less rigorous, because it is based on a model approximation that determines the interface between the bulk and adsorption phases, but it is obviously much more informative, because

allows one to obtain the characteristics of the adsorption phase, which is extremely important from a practical point of view, and, in addition, allows one to compare them with those calculated on the basis of various molecular models, which are necessarily associated with specifying a specific arrangement of molecules near the surface of the adsorbent.

In this regard, a significant part of modern information on adsorption is presented within the framework of the total content method, and the excess method is used to obtain primary information and as a criterion (see below) when choosing a model for switching to the total content method. For a long time, the attention of researchers was drawn to the study of the adsorption of gases and vapors at relatively low pressures, at which the values ​​of excess and absolute adsorption practically coincided, and the problem of choosing a method for the thermodynamic analysis of adsorption phenomena was not actively discussed.

Interest in this problem reappeared in the last quarter of the last century in connection with the active use in industry of adsorption processes at high pressures. During this period, a significant number of works appeared devoted to the experimental and theoretical study of adsorption equilibria in wide ranges of temperature and pressure changes and a detailed analysis of the ways of converting experimentally determined values ​​of excess adsorption into absolute ones.

Since our task does not include a detailed analysis of various options for the thermodynamic consideration of adsorption phenomena, we will restrict ourselves to a brief comparison of the two approaches noted above, focusing on the problems of the total content method, within the framework of which almost all methods for describing and a priori calculation of adsorption equilibria have been developed.

Gibbs excess method.

A brief summary of the fundamentals of the "Gibbs Excess Method" will begin with two quotations that fairly fully set out the main idea of ​​the method and reflect two approaches to assessing the significance of this method in the modern theory of adsorption phenomena:

“A feature of Gibbs' approach is that he immediately abandoned the attempt to characterize adsorption by any absolute values, i.e., to consider the interfacial layer as some physical object, which has natural boundaries and, therefore, contains a certain amount of substance in a certain volume, which could be equated with the measured adsorption value. Such a consideration would be contrary to the principles of adsorption measurement. The advantage of excess quantities is that they are directly measured in the experiment and therefore are not associated with any models. With their help, it is possible to construct a thermodynamic theory that will include only experimental quantities”;

“Some features of the thermodynamic formalism proposed in the description of adsorption phenomena are, it seems to us, in sharp discrepancy with state of the art theory of adsorption. Excess value adsorption is determined directly from the adsorption experiment, and in any equation of the Gibbs adsorption theory it is allowed to use only this value.

From our point of view, the use of only excess adsorption in all cases brought the Gibbs method into irreconcilable contradiction with adsorption science at the end of the 20th century. Indeed, any equation of the adsorption isotherm (for example, the Langmuir equation) or the equation of state of the adsorption phase, based on molecular kinetic concepts, includes not the number of excess molecules, but the total number of real molecules in the region of inhomogeneity. The heats of adsorption determined experimentally are associated with a change in enthalpy when all, and not just excess, molecules enter the adsorbent field. Not only excess, but all adsorbed molecules participate in two-dimensional phase transitions. Finally, when applying the method of statistical thermodynamics to describe adsorption phenomena, it should be remembered that in statistical physics there are no "excess" molecules at all. Thus, in almost any modern study of adsorption, it is necessary to take into account all the molecules of the adsorbate, while in the Gibbs thermodynamic equations, in the name of ephemeral "strictness", only excess adsorption should be taken into account.

Sharing, in the main, the point of view stated in the second quote, we note that the Gibbs method has retained its significance for the analysis of surface phenomena at the gas-liquid and liquid-liquid interfaces, for which it was originally developed, since in these cases the surface tension () , which is included in the famous Gibbs adsorption equation, is an experimentally measured quantity.

Let us first consider the essence of this method using the adsorption of a one-component gas as an example.

We introduce into three (I, II, III) identical vessels (Fig. 1.1) with volumes V0 the same number of moles of gas n0. Let the walls of vessel I absolutely do not adsorb this gas - then its pressure in vessel I will be Р0, molar density 0, and the number of moles n0=0V0. Let the lower wall in vessel II be an adsorbing surface. Then, near the surface, the density of the gas will increase, and away from the surface in the volume of the vessel, it will decrease to.

–  –  –

Since the adsorption phase is not released, the volume of the vessel does not change, and the amount of gas in this volume decreases to V0, if we assume that the density extends up to the lower adsorbing surface (the adsorption phase is identified with the geometric surface located on the lower wall of the vessel II).

Change in the amount of gas in the volume of vessel II compared to vessel I:

ne V00 V0 (1.10),

–  –  –

Since at low (up to several atmospheres) pressures, the last terms on the right-hand sides of equations (1.13) and (1.14) are vanishingly small compared to excess adsorption, when describing the adsorption of gases and vapors, there is often no distinction between absolute and excess values. Only in experiments with high pressures of adsorptives do these differences become noticeable.

Indeed, the absolute values ​​of adsorption increase with increasing pressure, tending to a certain limit:

–  –  –

where v is the molar volume of the adsorbate in the adsorption phase (usually it is taken equal to the molar volume of a pure liquid adsorptive). At the same time, excess adsorption passes through a maximum with increasing pressure and then decreases to zero, since the density of the bulk phase becomes the same , as well as near the surface.

Rice. 1.2. Isotherms of excessive adsorption of methane on activated carbon at different temperatures.

In some cases, the density in the bulk phase may even exceed the density near the surface due to the limitation of the mobility of molecules near the surface and, as a consequence, their less compact packing (excess adsorption will be negative in this case). Examples of excess adsorption isotherms are shown in Figs. 1.2, while total content isotherms in fig. 1.3:

–  –  –

Rice. 1.3. Adsorption isotherms of hydrocarbons and CO2 on Nuxit activated carbon at 293K. Designations: - methane, - ethylene, - ethane, - propylene, - propane, - CO2.

Let us now consider the adsorption of one of the components of a binary liquid solution:

If the excess adsorption of a solution component is determined similarly to the excess adsorption of a gas, then it is necessary to take into account the change in the volume of the solution due to its compression in the adsorption field (without dividing the volume of the system into

–  –  –

Based on (1.24), the Gibbs adsorption equation, which is the basis of the thermodynamic description of adsorption systems in the framework of the excess method, can be, taking into account (1.17) and (1.18), as well as the relations obviously following from the Gibbs-Duhem equation written for a bulk solution with using molar concentrations or mole fractions:

–  –  –

The lower integration limits in (1.25) and (1.26) are determined by the choice of adsorption values ​​at which the surface tension is assumed to be 0. For example,

–  –  –

surface active) is an important characteristic of such systems.

Since a change in surface tension during adsorption leads to a change in the total chemical potentials of adsorbates and, therefore, thermodynamic functions, from (1.25) and (1.26) one can obtain (we will not consider the corresponding conclusions) relations for calculating the excess thermodynamic functions of adsorption (Ge, He, Se), characterizing the change in the corresponding properties of the entire system as a whole as a result of the adsorption process compared to the corresponding comparison system. It is important to emphasize that these calculations are carried out using experimentally determined excess adsorption values ​​and are not related to the choice of any model of the adsorption phase.

As applied to adsorption on solid adsorbents, equations (1.25) and (1.26) are not widely used, and the Gibbs excess method is used mainly as a criterion when choosing a thermodynamically permissible volume of the adsorption phase in the total content method.

The most useful in this sense were the equations describing the dependences of the excess thermodynamic functions for the adsorption system as a whole on the composition of two-component bulk (mainly liquid) phases. If we choose an adsorbent wetted with a pure second component as a reference state, then the corresponding equation for changing the excess isobaric potential

Gibbs (G e) has the form:

–  –  –

If there are experimental data on the temperature dependence of adsorption, then equations for the corresponding dependences of the excess enthalpies and entropies of the system can be easily obtained from (1.27).

Attempts to represent the dependences of the corresponding “isosteric” thermodynamic functions on the values ​​of andexcess adsorption clearly demonstrate the difficulties of their physical interpretation, which is clearly seen in the example of the corresponding dependence for the differential isosteric excess heats of methane adsorption on Rho zeolite on the filling and adsorption temperature shown in Fig. 1.3.

As follows from the figure, under "isosteric" conditions, with increasing temperature, the differential excess heats of adsorption are at first constant (curves 1,2,3), and then sharply increase, fanning out due to the imperfection of the gas phase. The heat value reaches values ​​exceeding 150 kJ/mol.

Fig.1.4. Temperature dependence of the isosteric excess heat of methane adsorption on Rho zeolite at Г 1 (mmol/g): 0.5 (1.4); 0.535 (2.5); 0.645 (3.6).

x The further course of the heats of adsorption is due to the presence of a maximum on the excess adsorption isotherms and the manifestation of a break in the derivative to the isostere when passing through this point. The heats acquire a negative sign and in the region of high pressures gradually approach the abscissa axis.

It is clear that a comparison of these results with the experimentally observed calorimetric heats of adsorption, which depend on the total amount of adsorbed molecules, is at least difficult.

However, despite these difficulties, the Gibbs excess method has been repeatedly analyzed and refined. "Geometric"

Gibbs' formalism was developed by Guggenheim and Adam, later Hansen and Goodrich developed an "algebraic" formalism that did not explicitly require the introduction of a geometric interface for the liquid-liquid boundary. An important stage in the development of the Gibbs method was the work of Tikodi and, especially, Shai, in which adsorption on solid adsorbents was considered. The result of these many years of research was summed up in the fundamental monograph by Lopatkin, who analyzed in detail and clarified all the problems of applying the "excess method" to the analysis of adsorption equilibria on solid adsorbents of various structures.

Literature.

1. Gibbs J.W. //Thermodynamics. Statistical mechanics.

The science. Moscow,.

2. Lopatkin A.A. // Theoretical foundations of physical adsorption, Publishing House of Moscow State University, 1983.

3. Tolmachev A.M.// Langmuir, 1991, No. 7, p.1400;

Tolmachev A.M. // Vestn.Mosk. University. Series 2. Chemistry, 1990, vol. 31, no. 6, p. 529; Tolmachev A.M. //Vestn. Moscow University.

Ser. 2. Chemistry, 1994, vol. 35, no. 2, p. 115.

4. Larionov O.G. /Dis. dr. chem. Sciences. Institute of Chemistry of the Academy of Sciences of the USSR, Moscow, 1975.

5. V. V. Serpinsky and T. S. Yakubov, Izv. Academy of Sciences of the USSR. Ser.chem., 1985, p.12.

6. Fomkin A.A. //Dis. dr. physics and mathematics Sciences. IPC RAS, Moscow, 1993.

7. A. A. Pribylov, T. S. Yakubov, G. F. Stekli, L. Curry, I. A. Kalinnikova, and L. G. Shekhovtsova, Russ. //Izv. AN. Ser.chem.

8. Szepesy L., Illes V.// Acta Chim. Hung., 1963, vol. 35, pp. 37, 54, 245, 373.

9. Guggengeim E.A.// Modern Thermodynamics Stated According to Gibbs Method), Moscow-Leningrad: GNTI, 1941.

10 Guggenheim E.A., Adam N.K. //Proc. Roy. Soc., 1933, vol.

11. Hansen R.S. // J. Phys. Chem., 1962, vol. 66, p. 410.

12. Goodrich F.C. // Trans. Faraday Soc., 1968, vol. 64, p. 3403.

13. Tykodi R.J. // J. Chem. Phys., 1954, vol. 22, p. 1647.

14. Shay G.A. // Pure Apple. Chem., 1976, vol. 48, p. 393.

Lecture 2. Full content method.

Introduction.

Insufficient information content of the Gibbs excess method, difficulties in interpreting the thermodynamic characteristics of adsorption systems obtained on its basis, the practical need to analyze the properties of the region of inhomogeneity (adsorption phase) led to the emergence of a series of studies in which the mathematical Gibbs interface was replaced by a real phase with its own physical and thermodynamic characteristics .

Initially, these studies were developed within the framework of the finite thickness layer method, and later developed within the framework of the total content method.

Consideration of the transition region of inhomogeneity as a certain layer of finite thickness, separated from homogeneous bulk phases by two surfaces, i.e. as a separate phase with its own energy, entropy, mass and volume, with real, "absolute" concentrations of components, was started in the works, and also in .

A detailed development and detailed analysis of this approach was carried out in the works of A.I. Rusanov, who, following mainly the Gibbs method, derived all the necessary relationships for the thermodynamic analysis of surface phenomena and properties of a layer of finite thickness (both with flat and curved surfaces) using not excess, but total concentrations of components in the layer. So for the adsorption of a binary liquid solution on a flat surface of a solid adsorbent, a strict thermodynamic equation (2.1) was obtained:

–  –  –

where: x 1, x 1 - equilibrium mole fractions of the first component in a layer of finite thickness and in a bulk solution; i, i corresponding chemical potentials of components in equilibrium phases; A is the interface per mole of the mixture.

Integration (2.1) for the simplest case, when both phases are assumed to be ideal, and A is an additive function of the areas of each of the components (s 0 i), leads to an equilibrium equation like the law of mass action:

x 1 (1 x 1) K (2.2), x 1 (1 x 1) s 01 where: K is a constant; - stoichiometric coefficient s 02 mutual displacement of components.

As part of the finite thickness layer method, the most stringent and accurate methods for determining its thickness (capacity) have not been developed. In addition, it has been developed mainly for binary (and multicomponent) bulk phases and analysis of the properties of surface phases. Therefore, for the analysis of adsorption equilibria proper, the total content method is widely used, which does not fundamentally differ from the finite thickness layer method, but relies on the developed methods for determining the “sizes” (capacity) of the adsorption phase and the use of the chemical potential apparatus, which makes it possible to obtain the ratios in a simpler way similar to (2.2), including those for adsorption from one-component bulk phases. Within the framework of the total content method, almost all known equations of adsorption isotherms from single- and multi-component bulk phases were obtained; therefore, we will consider the main features of this method in more detail.

full content method.

The first work in which the full content method was introduced is, as already noted, the work of Langmuir. However, the consideration of the problem in general terms and the thermodynamic justification of the method were carried out in the second half of the last century in a series of studies that considered methods for determining the "dimensions"

(volume, capacity) of the adsorption phase and methods for converting excess adsorption values ​​into total (absolute), as well as adsorption thermodynamics within the framework of the total content method.

To calculate the absolute values ​​of adsorption in the total content method, it is necessary to choose the volume or limiting capacity of the adsorption phase.

The very possibility of such a choice was called into question on the basis of the following reasoning:

Since the adsorption potential tends to zero at an infinite distance from the surface, the total content of individual gases during adsorption should be defined as a definite integral:

–  –  –

converges.

However, one can always choose the distance from the surface (z0) at which the increase in fluid density due to the adsorption field is compensated by the equilibrium fluctuation of the fluid density, i.e. adsorption is zero. Taking this circumstance into account, the total content should be defined in the form of a convergent integral

–  –  –

Since the choice of the size of the adsorption phase in the transition to the total content method is different for different types of adsorbents, let us consider the main types of adsorbents:

–  –  –

In accordance with the widely used classification of adsorbent types proposed by M.M. Dubinin, all adsorbents are divided into three groups:

microporous adsorbents with a narrow size distribution of micropores (0.5 - 1.5 nm): active carbons, zeolites.

microporous adsorbents with a bimodal micropore size distribution (0.5 - 1.5 and 1.5 - 2.0 nm.): some types of active carbons.

mesoporous adsorbents (2.0 - 20 nm.): silica gels, oxides of aluminum, iron, etc.

macroporous adsorbents (r 20 nm.): graphite soot, silica gels, surfaces of single crystals, etc.

In accordance with the theory of volumetric filling of micropores (TOSM), adsorbate molecules at any point in a micropore are in the zone of action of the adsorption potential of the pore walls and, therefore, unlike mesopores, phase transitions of the first order (liquid adsorbate - vapor) are impossible in them. In this regard, we note that quantum chemical calculations show that the adsorption potential sharply decreases with distance from the adsorbing surface and, as is clearly seen from Fig. 2.1, noticeably manifests itself at distances up to 0.8–1 nm, which corresponds to the accepted maximum micropore sizes of 1.6–2.0 nm. In classical thermodynamics, it is usually assumed that the adsorbate-adsorbent interaction potential decreases with the adsorption layer number (n) in accordance with the formula:

–  –  –

4.0 Fig. 2.1. Interaction energy profiles between propene (0), benzene (1), and methanol (2) molecules with a carbon surface, calculated by the quantum chemical method (DFT PBE0/6 311G).

Before considering the problem of determining the volume of the adsorption phase, we obtain relations similar to (1.13, 1.14) for adsorption from binary liquid solutions.

The corresponding calculation formulas can easily be obtained on the basis of balance ratios.

–  –  –

Various choices of values ​​V or c i are discussed in detail in the literature. We will briefly consider the most widely used methods in relation to adsorption on adsorbents of various structures.

Adsorption on smooth surfaces (macroporous and mesoporous adsorbents).

In accordance with (2.6), in the adsorption of gases, the adsorption phase always represents a monolayer. However, to determine the limiting adsorption (capacity of the monolayer c i a m mol.cm-2), it is necessary to know the surface area of ​​the adsorbent (A) and the area per adsorbate molecule ():

am A / Na (2.11) At the same time, equation (2.11) is used to determine the surface area from the “experimental” values ​​of a m found as a parameter of the equations describing the isotherms of polymolecular vapor adsorption (we will consider these equations in detail below), while no satisfactory equations have yet been proposed to describe gas adsorption isotherms (the classical Langmuir equation is inapplicable in real systems). Further, based on various estimates (quantum chemical calculations, van der Waals radii, etc.), taking into account possible orientations of molecules near the surface, values ​​are found and a m is calculated for gas adsorption. Thus, in the thermodynamic analysis of gas adsorption on macroporous adsorbents within the framework of the total content method, one should take into account the difficulties of accurately determining a m, as well as the possibility of changing the orientation of molecules during the adsorption of gas mixtures.

In the case of polymolecular adsorption of vapors on macroporous adsorbents, the volume of the sorption phase is variable, since the condensation of the adsorbent in the second and subsequent layers due to the presence of an adsorption field (although sharply decreasing with distance from the surface) occurs at pressures lower than the saturation vapor pressure (Ps). In this regard, thermodynamic analysis in the framework of the total content method for such systems is difficult and is limited to using the equations of excess adsorption isotherms (mainly for determining the surface of adsorbents) in cases where the values ​​of Ps are small and excess adsorption can be equated to absolute:

The two-parameter BET and Aranovich equations are most widely used (see Lecture 5 for details), one of the parameters of which is a m. It should be emphasized that during the adsorption of gases, it is not the volume of the adsorption phase that is determined, but the volume of the monolayer, which, during the adsorption of gas mixtures, can be a variable value due to the difference effective radii molecules, and a thermodynamically more important quantity is the capacitance of a monolayer at a constant surface area (see lecture 3), i.e.

a two-dimensional problem is considered.

In the case of adsorption of liquid solutions on macroporous adsorbents, the adsorption phase, as a rule, is also limited to a monolayer; it is much less often necessary to consider it as a two-layer one. In this case, two methods are used to determine the volume (capacity) of the adsorption phase:

1. Universal thermodynamic method O. G.

Larionova,

2. A method based on the Aranovich-Tolmachev equation.

The first one is based on the comparison of changes

–  –  –

and, in the presence of the corresponding data for different temperatures, H e, S e during the transition from the adsorbent wetted with pure component 2 to solutions of composition x 1, for the adsorption system as a whole, i.e. within the framework of the Gibbs excess method, with similar dependences calculated within the framework of the total content method. Since in the latter case, the change in the thermodynamic functions of the system as a whole will depend on the separation of the system into two phases (into the volume of the adsorption phase V and the volume of the solution phase V-V):

G(x 1) (VG ads. (V V)G vol.)(x 1) (2.13), then by varying the values ​​of V, one can find the volume (capacity) of the adsorption phase, at which the corresponding dependences in the excess method and in the total content method will match.

Analysis of a large number of adsorption systems by this method showed that the adsorption phase, as a rule, is a monolayer and, relatively rarely, two layers (for example, in the case of alcohols characterized by a strong adsorbate–adsorbate interaction).

The second method, based on the use of the Ono-Kondo lattice model and the Aranovich-Tolmachev equation obtained within the framework of this model, was proposed in .

In this work, it is shown that a quantitative description of the isotherms of excess adsorption of components of nonelectrolyte solutions on macroporous adsorbents with physically reliable values ​​of parameters (interaction energies, monolayer capacity, layer composition) can be obtained based on the system of Aranovich Tolmachev equations.

The corresponding equations will be presented in Lecture 5.

The parameters of the equations (a1,m, / kT, B) are found by a numerical method (by minimizing the deviations of the calculated and experimental values ​​of Г1). Then, using a special program, the compositions of the first two layers of the adsorbate are calculated. The results are presented in table 2.1. It can be seen from the table that for systems with / kT, which characterize the differences in the interaction energies of identical and different solution molecules, less than 0.04 (the majority of such systems!) the composition of only the first layer X1(n=1) differs from the composition of the bulk phase X1(oo), those. the adsorption phase is monolayer, which agrees with the conclusions obtained by the Larionov method.

Table 2.1 Dependence of X1(n) on X1() at 303K for systems:

I-CCl4-iso-C8H18-graphite. carbon black (/kT theor.=0.01), II- C6H5CH3C6H5Cl-silica gel (/kT theor.=0.04), III- c-C6H12-С6H5NO2Al2O3 (/kT theor.=0.16) –  –  –

Adsorption on microporous adsorbents (activated carbons, zeolites) has been studied and continues to be intensively studied, since the widespread use of adsorption technologies for the separation and deep purification of substances, protection environment, in various catalytic processes is based on the use of precisely microporous adsorbents.

On the other hand, microporous adsorbents are a convenient object for various theoretical studies. Thus, the interests of fundamental science and practice are successfully combined.

In particular, the total content method is most strictly and successfully used specifically for studying adsorption on microporous adsorbents, since the volume (capacity) of the adsorption phase in this case is determined quite strictly.

Determination of the volume (capacity) of the adsorption phase:

The simplest is the "limiting" capacity of adsorption 1.

phase, which it is natural to take the volume of micropores, is determined using equations describing the vapor adsorption isotherms, of which it is a parameter.

These are, first of all, the equations of the theory of volumetric filling of micropores (TOZM): Dubinin - Radushkevich (microporous coals) and Dubinin - Astakhov (zeolites) and the Tolmachev-Aranovich equation (microporous coals and zeolites), one of the parameters of which is the limiting capacity of the adsorption phase at adsorbate pressure equal to the pressure of its saturated vapor (Ps). Of course, it is necessary to use adsorptives having saturated vapor pressures less than one atmosphere at the temperature of the experiment, so that the excess and absolute adsorption coincide. A detailed analysis of these and other equations will be considered in Chapter 5.

2. When adsorbing solutions, the volume (capacity) of the adsorption phase can be determined by the Larionov method described above. The application of this method in all cases leads to the volume (capacity) of the adsorption phase, which practically coincides with the volume (capacity) of micropores, determined by vapor adsorption.

3. An interesting way to determine absolute adsorption in the framework of the total content method was proposed by Fomkin. This method, which requires special equipment for the experimental determination of excess liquid and vapor adsorption at a pressure equal to Ps, shows the possibility of a fairly accurate determination of absolute adsorption without determining the volume of micropores.

–  –  –

Rice. 2.2. Scheme for determining absolute adsorption.

At the first stage, a sample of a microporous adsorbent is placed in an adsorption vessel of volume V (the scheme is shown in Fig. 2.2) and the usual calibration is carried out using helium at high temperature(400-500K), when its adsorption can be neglected. In this case, it is not the true volume of the adsorbent with micropores that is determined, but a somewhat larger volume V (shown by a dotted line in the figure), since helium atoms have their own volume.

At the second stage, the determination of excess adsorption from saturated vapor and liquid is carried out. Obviously, the absolute adsorption is the same in both cases, and therefore

–  –  –

which makes it possible to calculate the absolute adsorption without determining the true volume of micropores. Estimates that can be made in the case of zeolites, for which the geometric micropore volume can be calculated from X-ray analysis data, show that the available micropore volume is 20-30% less than the geometric one.

In connection with the consideration of this method, we emphasize that in the total content method, it is the capacity (limiting capacity) of the adsorption phase, which can be calculated quite accurately, that is the main characteristic used in thermodynamic analysis. The constancy of the volume of micropores or the surface in the case of macroporous adsorbents is an important condition that makes it possible to characterize the adsorption phase as a phase of limited capacity with respect to the components of the system. In this case, it is often not necessary to accurately determine the volume of micropores or the surface.

In conclusion, we note that the absolute adsorption of vapor or pure liquid at saturated vapor pressure is usually taken as the limiting capacity or limiting filling of the adsorption phase.

However, in accordance with the Langmuir-Tolmachev quasi-chemical model, the limiting saturation of the adsorption phase can be achieved only at a pressure tending to infinity. In addition, it has been experimentally shown that with an increase in the hydrostatic pressure on a liquid, the limiting adsorption in micropores can increase by 10-15% due to the rearrangement of the adsorbate structure.

Therefore, in the thermodynamic analysis of adsorption systems, it is necessary to accurately define the concept of the limiting capacity of the adsorption phase.

The change in the limiting adsorption with a change in the composition of the adsorbed solution during the adsorption of liquid solutions is calculated using the "hard" solution model.

As already noted, this is a forced approximation, since there are practically no data on partial molar volumes.

However, if we assume that the volume of the adsorption phase during adsorption on zeolites is equal to the volume of the cavities, then the “absolute” adsorption in the total content method can be found not by calculation using equations (2.10), but experimentally during adsorption from solutions (by the pycnometric method) as for pure adsorptives, and for solutions.

Obviously, the rigid solution model should lead to a linear dependence of the absolute total adsorption

–  –  –

Of the five systems studied so far, the corresponding linear dependences with a good approximation are fulfilled for four (see, for example, Fig.

2.3a), however, in one system, deviations from linearity are noticeable (see Fig. 2.3b)

–  –  –

In thermodynamic analysis, such deviations from the rigid solution model are formally taken into account in the activity coefficients of the components of the adsorbed solution, which, according to the apt expression of V.S. Soldatov, in this case become "the coefficients of our ignorance".

In conclusion, we note that the total content method turns out to be necessary and very fruitful in the analysis of the adsorption of gases, vapors, and liquids on microporous adsorbents in wide temperature and pressure ranges.

Peculiarities of adsorption in micropores.

Physical adsorption of gases, vapors, and liquids on microporous adsorbents differs significantly from adsorption on an open surface. In micropores, the adsorption potential greatly increases due to the superimposition of adsorption fields of opposite walls. These features of the microporous system of the adsorbent dramatically change the properties of the substance in the adsorbed state. The adsorption field of a microporous adsorbent imposes its structure and disperses the substance in such a way that there are no first-order phase transitions of the condensation type in the adsorbate. However, with an increase in adsorption in it, processes of restructuring similar to second-order phase transitions become possible.

Adsorption Interaction of Adsorbate Molecules with a Surface solid body in the general case, it always leads to a change in the state of the rigid body itself. This change can be more or less significant, depending on how strongly the surface of the solid body is developed, whether it has high-energy adsorption centers that exhibit specific interaction, and whether the energies of intermolecular bonds of atoms or molecules that make up the solid body are high. When adsorbed on microporous adsorbents, the adsorbent and adsorbate are equal participants in the adsorption process.

Features of the properties of adsorption systems and the adsorbate in microporous adsorbents are especially noticeable in the behavior of adsorption isotherms and isosteres, adsorption deformation of the adsorbent, and thermodynamic functions of adsorption systems when studied in wide ranges of pressures and temperatures.

A detailed study of these processes was carried out in the works of A.A. Fomkin and colleagues. .In these works it was shown:

The adsorption of gases, vapors, and liquids in microporous adsorbents increases smoothly with increasing pressure when passing through the critical temperature and during phase transitions in the adsorbent.

Rice. 2.4. Adsorption isotherms of water (1-3) and benzene (4.5) on NaX zeolite at T (K): 1-303; 2-313; 3-323; 4-303, 5-323.

–  –  –

hydrostatic pressure up to 100 MPa), and in fig. 2.5 isotherms of methane at temperatures lower and higher Tcr.

As follows from Fig. 2.5, the adsorption isotherms change symbatically with increasing temperature when passing through the temperature of the critical point of the adsorptive: Tcrit. = 190.55 K, which indicates the absence of condensation effects in the adsorbate.

a[mmol.g-1]

1 0 1 2 3 4 5 6 logP(P[ Pa]) 2.5. CH4 adsorption isotherms on the microporous carbon adsorbent PAU-10, at T, K: 1 - 120; 2 - 130; 3 Adsorption isosteres in the coordinates lnP=f(1/T)a remain linear in wide ranges of pressures and temperatures and do not change their slope when passing through the critical temperature of the gas phase. This is clearly seen from the data shown in Fig. 2.6.

From fig. It can be seen from Fig. 2.6 that isosteres remain linear over the entire studied pressure and temperature range, and, what is especially important, isosteres that terminate at the saturated vapor pressure line continue linearly in the supercritical region, and adsorption isosteres that begin in the vapor region continue linearly in the region state of compressed fluid.

Rice. 2.6. Xe adsorption isosteres on NaX zeolite during adsorption, mmol/g: 1 – 0.1; 2 - 0.2; 3-0.4; 4 - 1.0; 5 - 2.5; 6 - 3.5;

7 - 4.0; 8-4.5:9-4.7; 10-4.9; 11-5.15; 12-5.3; 13 - 5.5; 14 - 5.8. ln Ps

– saturated steam pressure line.

The linearity of adsorption isosteres in the region where gases have significant deviations from ideality, their linear continuation in the region of the liquid state of the adsorbent and in the supercritical region - all this indicates that the adsorbate in the microporous adsorbent is a special state of matter.

This position is also confirmed by studies of the adsorption of various liquids on NaX zeolite along the saturated vapor pressure line, carried out by M.M. Dubinin et al. С9Н20, СF3Cl) and inert gases (Xe, Kr, Ar) at low temperatures - less, and near the critical temperature - more liquid adsorptive density. The temperature at which they are equal is approximately 0.8 Tcr. The average densities of adsorbed polar substances (H2O, C6H6, C2H5OH) in the studied temperature range of 273–473 K are higher than the liquid density and change much more slowly with temperature. It is significant that the density curve for adsorbed water does not have a maximum at 277.15 K, which is characteristic of ordinary water.

The differential molar isosteric heat of adsorption at high pressures depends on temperature both due to the nonideality of the gas phase and the noninertness of the adsorbent, i.e. the intensity of its temperature and adsorption deformation (Fig. 2.7.). Similar results were also obtained for other systems.

Differential molar isosteric heat capacities of adsorption systems (Fig. 2.8.) at high adsorption values ​​have maxima, indicating the presence of structural rearrangement processes (second-order phase transitions) in the adsorbate.

Similar dependences of the isosteric heat capacity have also been obtained for other adsorption systems. The main reason for the appearance of maxima on the curves of isosteric heat capacity, apparently, is the properties of the adsorbed substance in the micropores of adsorbents. This is indicated, first of all, by the temperature intervals in which extreme phenomena develop. From fig. 2.8 it follows that the maxima begin to appear in the temperature range approximately 100–200K higher than the critical temperature of the sorbed gas. Similar dependences were also obtained for other studied systems. With an increase in adsorption and, consequently, the average number of molecules in the cavities of microporous adsorbents, the maxima of the isosteric heat capacity become more pronounced and shift to the region of low temperatures.

Rice. 2.7. Dependence of the differential molar heat of Xe adsorption on NaX zeolite, taking into account the adsorption deformation, on the adsorption value at T(K): 1-150; 2–210; 3 The dashes show the shape of the curves without regard to adsorption deformation).

Fig.2.8. Temperature dependencies differential molar isosteric heat capacity of the adsorption system "Xe - zeolite NaX" at different adsorption values, mmol/g: 1-1.0; 2 - 2.0; 3 - 4.0; 4 - 4.5; 5 - 4.7; 6 - 4.9; 7 - 5.0; 8 - 5.15; 9 – 5.30 a.m.

At low fillings, according to the calculations of the potential energy maps of interaction in the pores of the adsorbent, the molecules are in deep potential "wells". However, with an increase in temperature under isosteric conditions at medium and high fillings, due to an increase in the kinetic energy of molecules, the process of transition of molecules from adsorption centers to the volume of micropores with the formation of associates becomes more and more likely. In particular, such an adsorption mechanism, that is, the transition from partially localized to delocalized adsorption, was discovered by A.A. Fomkin et al. in the analysis of helium adsorption in NaX zeolite.

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Adsorption takes place at the phase boundary. Therefore, it is reasonable to consider the thermodynamic description of surface phenomena as special case thermodynamics of heterogeneous systems.

Rice. 3.4. Gibbs adsorption: 1- two-phase reference system, 2- real two-phase system with inhomogeneous region

The thermodynamics of heterogeneous systems uses additivity principle, which is as follows: all the extensive properties of a heterogeneous system are equal to the sum of the corresponding extensive properties that the phases would have had before they were brought into contact. Let us denote the phases by α and β (Fig. 4). Then for an ideal system, such that the properties of the phases near the interface coincide with their bulk properties, for the internal energy U, volume V, mass (number of moles) n, entropy S after equilibrium is established in a heterogeneous system, the relations are valid:

U = U α + U β , V = V α + V β , n = n α + n β , S = S α + S β

This assumes that the temperature and pressure in both phases are the same.

For real heterogeneous systems, the transition region at the interface between two phases makes an additional contribution to the extensive properties of the system. If surface phenomena occur, one should take into account the difference between the extensive properties of a real heterogeneous system and the extensive properties of a model system in which there are no surface phenomena. Such a system is called a comparison system. The comparison system has the same intensive parameters (T, P, C i …) and the same volume V as the real system (Fig. 4).

From a thermodynamic point of view, the adsorption value G is understood as the excess amount of substance n s, expressed in moles or grams, which a real heterogeneous system has in comparison with the reference system, related to the surface area of ​​the phase separation or to the surface area of ​​the adsorbent A. It is assumed that the comparison system has the same intensive parameters (T, P, C i) and the same volume (V = V α + V β) as the real system (Fig. 4).

G \u003d (n - n α - n β) / A \u003d n s / A 3.11

Excess thermodynamic functions of the transition region of a real system (denoted by the index s) can be written as

U s = U - U α - U β , n s = n - n α - n β , S s ​​= S - S α - S β etc.

Experimental measurements of adsorption always give adsorption precisely as an excess of a component in real system compared to the chosen comparison system. For example, when adsorbing a gas on a solid adsorbent or when adsorbing components on a solid phase, to find the adsorption values, the change in the initial concentrations of the adsorbate is determined after the contact of the phases α and β

n i s = V(C i o - C i),

Where C i o– initial concentration of the i-th component, C i is the concentration of the i-th component after the establishment of equilibrium between the contiguous phases. It is assumed that the volume V does not change. However, the concentration i-th component C i, obtained experimentally, is determined in the volume V' above the interface without taking into account the volume of the inhomogeneous region of the transition layer Vα at the interface where the concentration is C i α. Thus, due to the existence of an inhomogeneous region in a real system, the total volume of the system can be represented as V = V' + Vα. Whole quantity i-th component C i o distributed between these two volumes:

V C i o = V' C i + V α C i α ,

and the number of moles of the component i, adsorbed on the interface, will be equal to

n i s = (V’C i + V α C i α) – (V’ + V α)C i = V α (C i α – C i) 3.12

Those. adsorption determined experimentally is an excess of the i-th component in the volume V α in comparison with the amount of this component in the same volume far from the interface. This type of adsorption is called Gibbs adsorption. .

V α C i α called full content i- th component in the adsorption layer. In the region of very low concentrations C i in volume V' amendment V α C i equation (3.2) can be neglected and the measured value can be considered V α C i α full content i- th component in the adsorption layer, for example, in the adsorption of gas on a solid adsorbent at low pressures.

REFERENCES

1. Pope M.T, Müller A. Polyoxometalate Chemistry: An Old Field with New Dimensions in Several Disciplines // Angew. Chem. Int. Ed. English - 1991. - V. 30. - P. 34-48.

2. Pop M.S. Heteropoly- and isopolymetallates. - Novosibirsk: Nauka, 1990. - 232 p.

3. Maksimov G.M. Achievements in the field of synthesis of polyoxometalates and the study of heteropolyacids // Uspekhi khimii. - 1995. - T 64. - No. 5. - S. 480-493.

4. Dobrynina N.A. Isopoly and heteropoly compounds // Journal of Inorganic Chemistry. - 2002. - T. 47. - No. 4. - S. 577-587.

5. Cartmell E., Fowles G.W.A. Valency and structure of molecules. -M.: Chemistry, 1979. - S. 272.

6. Fedotov M.A., Samokhvalova E.P., Kazansky L.P. 17O and 183W NMR diamagnetic and paramagnetic shifts in heterodecatungstates XW10O36- (X=Ln, Th, U) in aqueous solitions // Polyhedron. -1996. - V. 15. - No. 19. - P. 3341-3351.

7. Shiozaki R., Inagaki A., Ozaki A., Kominami H., Yamaguchi S., Ichiha-ra J., Kera Y. Catalytic behavior of series of lanthanide decatungstates for H2O2 - oxidations of alcohols and olefins. Some chemical effects ofthe 4fn - electron in the lanthanide(III) ion on the catalyses // J. Alloys Compounds. -1997. - V. 261. - P. 132-139.

8. Kazansky L.P., Golubev A.M., Baburina I.I., Torchenko-va E.A., Spitsyn V.I. Vibrational spectra of heteropoly-

anions XW10O36n- // Izvestiya AN SSSR. Ser. chem. - 1978. - No. 10. - S. 2215-2219.

9. Kolenkova M.A., Krein O.E. Metallurgy of scattered and light rare metals. - M.: Metallurgy, 1977. - S. 12.

10. Kaziev G.Z., Dutov A.A., Olgin K.S., Belsky V.K., Zavod-nik V.E., Hernandez-Peres T., Kanaev A.A. Synthesis and X-ray diffraction study of potassium decamolybdenodicobaltate(III) // Journal of Inorganic Chemistry. - 2004. - T. 49. - No. 5.

11. Chemistry and Technology of Rare and Trace Elements, Ed. K.A. Bolshakov. - M.: Higher School, 1976. - Part 2. -S. 166, 174; Part 3. - S. 176, 233, 170, 171, 228.

12. Zagrebin P.A., Borzenko M.I., Vasiliev S.Yu., Tsirlina G.A. Kinetics of electroreduction of the central ion in cerium(GU)-decatungstate // Elektrokhimiya. - 2004. - T. 40. - No. 5. - S. 565-575.

13. Safronov, S.M., Berezina, E.M., Terent’eva, G.A., Chernov, E.B., and Filimoshkin, A.G., Nonlinear extrapolation of the concentration dependences of the reduced viscosity and the structure of polymer solutions, Vysokomoleklyar. -2001. - ser. B. - T. 43. - No. 4. - S. 751-754.

14. Romanova T.A., Krasnov P.O., Kachin S.V., Avramov P.V. Theory and practice of computer modeling of nanoobjects.

Krasnoyarsk: IPTs KSTU, 2002. - 223 p.

UDC 544.3:622.331

THERMODYNAMICS OF THE ADSORPTION OF COMPOUNDS ON HUMIC ACIDS

S.G. Maslov, L.I. Tarnovskaya

Tomsk Polytechnic University E-mail: [email protected]

Abstract—The process of adsorption of organic compounds (n-alkanes, cycloalkanes, alkenes, ethers, esters, and cyclic ethers, ketones, alcohols, aromatic and chlorine-substituted hydrocarbons) on humic acids of the original and heat-treated peat was studied by the gas chromatographic method in order to determine the adsorption and thermodynamic parameters. The characterization of humic acids is given by methods generally accepted in the chemistry of solid fossil fuels using NMR spectroscopy.

Relationships between physicochemical characteristics and retention parameters on the adsorbent are revealed. Differences in the processes of adsorption on humic acids of the original and heat-treated peat due to the increased content of oxygen-containing groups and aromatic fragments in the heat-treated samples were established. The relationship between the thermodynamic probability of the process of adsorption on humic acids and the polarity of adsorbates is shown.

Introduction

Literature information on the adsorption properties of humic acids (HA) is clearly insufficient. The traditional point of view that the adsorption process, on the one hand, is of a volumetric nature, and, on the other hand, is specific due to the presence of various functional groups, does not give a clear idea of ​​the mechanism of this phenomenon. There is evidence that condensed aromatic nuclei can also be carriers of adsorption properties. It should be noted that most authors have studied the process of adsorption of metal ions and inorganic substances. There are very few works devoted to the study of the adsorption capacity of HA with respect to organic compounds and they are not systematic.

The purpose of this work is to study the adsorption capacity of HA with respect to a number of organic compounds.

Experiment and Method

Sedge peat with a degree of decomposition of 35% of the Tagansky deposit of the Tomsk region was used as the object of study.

HA was obtained according to the prescription of the Peat Institute and characterized both by the methods generally accepted in the chemistry of solid fossil fuels and by the method of NMR spectroscopy. The adsorption properties of HA were studied by a modified gas chromatographic method.

The study was carried out on a Tsvet-100 chromatograph with a thermal conductivity detector at

use of helium as a carrier gas. The chromatograph is equipped with a reference pressure gauge to measure the column pressure gradient and correct for compressibility. The HA samples were ground in an agate mortar and the fraction

0.5...0.25 mm. A steel column 1 m long and 4.2 mm in diameter was filled with prepared HAs in an amount of 6.7 g at a pressure of 10–3 Pa. The samples were heated in a linear mode from 333 to 363 K at a rate of 2 deg/min. Organic compounds were used as adsorbates: alkanes, cycloalkanes, chlorine-substituted alkanes, arenes, alcohols, alkenes, ketones, simple, complex and cyclic ethers. The analyzed samples were injected into the chromatograph using a microsyringe.

Table 1. Characteristics of sedge peat, wt. %

Technical and elemental composition Group composition per organic mass

Noe Aa V1e "S^e" H1e" LG B VRV LGV GK FK C NO

6,7 7,9 68,4 53,4 5,9 2,1 38,5 2,6 1,8 30,9 35,1 11,2 2,1 15,5

Note: № - analytical humidity; A1 - ash content for dry fuel; V11 "- volatile content on the combustible mass; B - bitumen; VRV and LGV - water-soluble and easily hydrolysable substances; FA - fulvic acids; C - cellulose; HO - non-hydrolyzable residue

Table 2. Characteristics of peat humic acids

Peat HA Elemental composition, % Content, mg.eq./g

Weight Atomic Atomic ratios □= o o C COOH, OH,

S1e" N1e" KOLZ" S N O/S n/s

Baseline 54.84 6.66 35.60 35.28 48.41 15.84 0.45 1.37 2.56 6.00

Heat-treated 60.09 5.22 34.69 40.48 41.90 17.01 0.42 1.03 3.06 6.89

Table 3. Content of HA structural fragments according to NMR spectroscopy data, %

Peat HA s and □= C 1 1 0 1 Chp □= 1 0 and □= C 1 1 0 1 o< □= 1 о < о < 1 0 1 о Г си 1? 1 1? 1

Initial 25.0 5.3 8.1 3.0 21.4 19.8 4.8 3.6 3.0 6.0 0.275

Heat-treated 22.0 3.2 4.1 3.3 19.5 33.3 3.3 2.4 2.4 6.5 0.456

Note: " - aromaticity

From the chromatograms, the retention times (T), s, and the values ​​of the corrected retention volumes were calculated:

where I is the distance on the chromatogram from the moment the sample is injected into the column to the moment the peak maximum exits, m; U - chart tape speed, m/s.

Table 4. Retention times of organic compounds on HA during linear heating from 333 to 363 K

Adsorbates Molecular weight Boiling point, °С Dipole moment Polarizability, А3 Adsorbent HA Retention times, s

Pentane 72.2 36.1 0 10.0 ref. 16.7

Hexane 86.2 68.7 0 11.9 ref. 21.9

Heptane 100.2 93.6 0 13.7 ref. 29.7

Isooctane 114.2 99.3 0 ref. 34.9

Cycloalkanes

Cyclohexane 84.2 81 0 11.0 ref. 28.1

Heptene 98.2 93.6 ref. 29.5

Ethers

Diethyl ether 74.1 35.6 1.18 10.0 ref. 18.5

Dipropyl ether 102.2 91.0 13.7 ref. 21.5

Esters

Ethyl acetate 88.1 77.2 1.81 9.0 ref. 37.7

Butylformate ref. 43.6

Cyclic ethers

Dioxane 88.1 101.3 0 9.6 ref. 39.9

Acetone 58.1 56.2 1.66 6.6 ref. 21.1

Methyl ethyl ketone 72.1 79.6 ref. 20.2

Butanol-2 74.1 99.5 1.65 9.5 ref. 47.2

aromatic

Benzene 78.1 80.1 0 10.4 ref. 29.1

Toluene 92.1 110.6 0.36 12.4 ref. 34.2

Chlorine-substituted

Carbon tetrachloride 153.8 76.8 11.2 ref. 14.3

V \u003d Schyarglt P0t,

where W1 is the volumetric velocity of the carrier gas, m/s; P1, T1 - pressure and temperature in the carrier gas flow meter, Pa and K; P0 - gas pressure at the outlet of the column, Pa; T - column temperature, K; ] - correction for pressure drop in the column; t is the weight of the adsorbent, kg.

] = 3[(P/P0)2 -1]/2[(P/P0)3-1], where P1 is the gas pressure at the column inlet, Pa.

The study of the thermodynamic characteristics of adsorption was based on the fulfillment of the following condition: the gas-adsorbent equilibrium should be established in no more than 60 s. The equilibrium chromatography condition for HA, as studies have shown, corresponds to symmetrical peaks. These authors found that carrier gas velocity and adsorbate sample size had no effect on retention volumes, i.e. thermodynamic equilibrium is reached in the system.

The calculated retention volumes at different temperatures made it possible to calculate the heats of adsorption and other thermodynamic characteristics under equilibrium conditions.

The gas chromatographic method is based on the idea of ​​establishing a gas-condensed phase equilibrium for an adsorbate characterized by a distribution coefficient K:

The heat of adsorption (enthalpy) was determined by the formula:

AN \u003d R e 1n (Kd / T), kJ / mol.

The entropy of adsorption was determined by the equation А5=(АА-АО)/T, J/moleK, where АS - free energy adsorption (Gibbs energy) -AO=JT 1pK, kJ/mol.

Results and discussion

From the point of view of the molecular-statistical theory of adsorption of HA due to the presence of carboxyl groups, phenolic hydroxyls, quinoid, carbonyl groups, ketones, carbonyl groups, aldehydes, and others, apparently, can be attributed to a weakly specific adsorbent. In the solid state, planar HA molecules are “packed” into packs of several layers, which is a local manifestation of partial ordering. The polyconjugation system, due to the delocalization of x-electrons, leads to an increase in the mutual influence of atoms, but the presence of different groups still creates a chemical inhomogeneity of the surface, which is associated with weak specificity.

As can be seen from the data given in table. 4, the retention times for almost all adsorbates on HA from heat-treated peat are shorter than those on HA from the original peat.

The largest retained volumes are observed in alcohols, cyclic and esters, aromatic; the smallest - in alkanes, chlorine-substituted, ketones and ethers.

The molecular statistical theory of adsorption relates retention times and retention volumes to intermolecular electrostatic interactions of dipoles. Therefore,

The native picture for different classes of organic compounds is determined by the presence or absence of dipole moments in molecules. As is known, the molecules of alcohols, esters and aromatics have a significant dipole moment, and alkanes have a zero dipole moment. However, it is impossible to unambiguously relate the retention times to the dipole moment of substances. For example, acetone has a dipole moment of 1.66 and toluene 0.36, while the retention time of acetone is much shorter than that of toluene.

Probably, in this case, not only intermolecular, but also electrostatic interactions play a role in the adsorption interaction, but a large contribution is made by the nonspecific interaction of the adsorbent with the adsorbate, which is determined by the values ​​of the van der Waals radii and the values ​​of the polarizability, which for toluene ( Table 4) is almost 2 times higher compared to acetone. This is explained by the inhomogeneous porous structure of HA. Studies have shown that the pore radius of HA varies within 10.70 Å with the predominance of small pores of 10.15 Å, which is commensurate with the linear dimensions of the “primary” fragment of the HA structure. For toluene, the diameter of the molecule is much smaller; therefore, its molecules easily penetrate into the pores of the adsorbent.

From Table. 4 it can be seen that there is no regular change in the values ​​of retained volumes from the boiling point of organic compounds. This is explained by the fact that the boiling point is associated with the interaction of molecules with each other in the liquid, and in the case of adsorption, the interaction occurs with the adsorbent.

Judging by the data obtained, alkanes exhibit, on average, a low adsorption capacity, which is noticeably higher for the HAs of heat-treated peat. Among alkanes, isooctane has slightly higher retention volumes. Alkanes having st-bonds interact nonspecifically with adsorbents. The values ​​of electronic polarizabilities in the series of alkanes from pentane to hexane increase linearly, and the retention volumes (RV) also increase.

The cyclization of the alkane chain leads to a decrease in the volumes of cyclohexane due to a decrease in the number of hydrogen atoms and a deviation in the arrangement of carbon atoms from coplanarity. The links of the carbon skeleton probably cannot simultaneously touch the basal face of the adsorbent.

Very high SVs are observed for aromatic hydrocarbons, toluene to a greater extent. Moreover, the values ​​are equally high for both types of HA. This behavior of toluene can be explained by the presence of a methyl group, which, due to the manifestation of a positive inductive electronic effect and the effect of overconjugation, increases the electron density in the benzene ring and reduces it on the methyl group.

Alcohols with a large dipole moment have large SV values, which especially increase during adsorption on heat-treated peat HA.

Ketones and ethers, as substances with weaker polarity, have lower SV. This is due to the smaller contribution of the hydrogen bond energy to the retention of ketones and ethers, although the dipole moment, for example, of acetone is equal to the dipole moment of butyl alcohol.

Cyclic esters are characterized by the highest SV, due to a more pronounced polarization of bonds in oxygen-containing fragments compared to ethers, and as a result, a greater ability to form hydrogen bonds.

However, in all these cases, the chemical identity of the molecule is preserved, i.e. the interaction has a “molecular” rather than a “chemical” character.

As noted above, the adsorption properties of heat-treated peat HA are higher than those of the original HA, which is most pronounced for the case of polar adsorbates. This nature of the properties can be fully explained by the changes that occur with HA in the process of low-temperature thermolysis of peat. According to the data of chemical analyzes and NMR spectroscopy, a slight increase in oxygen-containing groups (carboxyl, phenolic hydroxyls) and glucose fragments is observed.

As can be seen from the data in Table. 5, the heats of adsorption for dipole molecules (ethers, ketones) and for weakly dipole molecules (aromatic hydrocarbons and alcohols) are higher than the heats of adsorption of n-alkanes, which have a zero dipole moment and are incapable of a specific molecular interaction. It should be noted, as the authors pointed out, that the total heat of adsorption of any organic molecules consists of two components: the heat of adsorption due to interaction with the active centers of the adsorbent and the heat of interaction of adsorbed molecules with each other. However, it is not possible to separate and calculate the heats from these results.

It can be seen from the experimental data that, in the n-alkanes series, an increase in the length of the carbon chain leads to an increase in the heat of adsorption and their polarizability. The value of the heat of adsorption for n-al-kanes is commensurate with the values ​​of the van der Waals interaction energy (<5 кДж/моль), вероятно, взаимодействие между ГК и н-алканами осуществляется за счет ван-дер-ваальсовых сил.

From the data in Table. Figure 5 shows that the heats of adsorption of ethers, alcohols, ketones, and aromatic compounds on HA lie within 5 kJ/mol, which are typical for the energies of typical hydrogen bonds; therefore, adsorption proceeds through the formation of hydrogen bonds.

Table 5. Thermodynamic characteristics of adsorption and retention volumes

Adsorbates Adsorbents, HA Retention volume at 333.363 K, ^■103, m3/kg -AN, kJ/mol -A5, J/mol -AG, kJ/mol

Pentane ref. 4.8 1.9 10.1 5.3

ter. 9.3 3.8 19.5 10.2

Hexane ref. 6.2 2.5 13.0 6.8

ter. 11.2 4.5 23.5 12.2

Heptane ref. 9.0 3.6 18.9 9.9

ter. 13.2 5.3 27.7 14.5

Isooctane ref. 11.5 4.6 24.1 12.6

ter. 16.7 6.7 35.0 18.3

Cycloalkanes

Cyclohexane ref. 2.3 1.0 4.8 2.5

ter. 9.3 3.8 19.5 10.2

Heptene ref. 8.4 3.4 17.6 9.2

ter. 10.1 4.1 21.2 11.1

Ethers

Diethyl ether ref. 6.8 2.7 14.3 7.5

ter. 13.5 5.4 28.3 14.8

Dipropyl ether ref. 11.5 4.6 24.1 12.6

ter. 17.4 7.0 36.5 19.1

Esters

Ethyl acetate ref. 19.7 8.0 41.3 21.6

ter. 28.2 11.4 59.1 30.9

Butylformate ref. 24.3 9.8 51.0 26.7

ter. 30.5 12.3 64.0 33.5

Cyclic ethers

Dioxane ref. 26.5 10.7 55.6 29.1

ter. 27.8 11.2 58.3 30.5

Acetone ref. 10.1 4.1 21.2 11.1

ter. 14.3 5.8 30.0 15.7

Methyl ethyl ketone ref. 9.7 3.9 20.3 10.6

ter. 10.1 4.0 21.1 11.0

Butanol-2 ref. 39.2 15.8 82.2 43.0

ter. 40.2 16.2 84.3 44.1

aromatic

Benzene ref. 18.4 7.4 38.6 20.2

ter. 19.2 7.7 40.3 21.1

Toluene ref. 20.2 8.1 42 .4 22.2

ter. 25.4 10.2 53.3 27.9

Chlorine-substituted

Carbon tetrachloride ref. 4.2 1.7 8.8 4.6

ter. 8.4 3 , 4 17.6 9.2

Diethyl ether is characterized by a low heat of adsorption comparable to that of hexane. Probably, the manifestation of a strong specific interaction of the functional groups of HA with diethyl ether is hindered by the location in

oxygen in the middle of the hydrocarbon chain, which makes it difficult to contact with the adsorbent. For ester molecules, the heats of adsorption are higher compared to simple ethers due to the presence of C=0 groups, which give increased polarity, and there is closer contact with the functional groups of the adsorbent. On the surface of HAs, probably, the electron density is locally concentrated on the periphery of functional groups, which ensures the high specificity of the adsorption of molecules of alcohols, complex and cyclic ethers, and aromatic compounds. As the authors note, it is necessary to take into account the effect of hydrogen bonding on the heat of adsorption of the adsorbate-adsorbent. The heat of adsorption of substances forming hydrogen bonds will always be greater than the heat of adsorption of substances of similar structure, but not forming it. For example, dipropyl ether has a higher heat of adsorption than diethyl ether due to a stronger hydrogen bond. HA molecules act as a proton donor (electron acceptor due to OH-, and to a lesser extent COOH groups), and ether and ester molecules act as an electron donor (proton acceptor), due to an ether bond (-O-) with the formation of an associate, but the complete transition of the proton does not occur in this case. The electron donor properties of the ether bond of dipropyl ether are higher than those of diethyl ether. Therefore, the contribution to the heat of adsorption due to hydrogen bonding is higher for dipropyl ether. It should be noted that heat-treated peat HAs are probably characterized by increased electron density at the periphery of functional groups and electron-withdrawing properties compared to HAs from the original peat.

It is known that the calculation of the entropy of adsorption is carried out in order to establish the degree of mobility of adsorbed molecules. The change in entropy includes the entropy of the translational, rotational and vibrational motion of molecules.

According to the data (Table 5), there is a relationship between |-AN| and |-A6| for different substances: aliphatic, aromatic hydrocarbons, alcohols, ethers and ketones. It can be assumed that the interaction of the listed adsorbates with HA has the same picture. Large negative values ​​are typical for alcohols, complex and cyclic ethers, which is associated with the pronounced polarity of the molecules. For heat-treated peat HA, the negative entropy characteristic is lower compared to the original peat. Probably, in the structure of heat-treated peat HA there is a wider distribution in terms of displacement, rotation, and vibration of adsorbate molecules. According to the data, the closer the molar volume of the adsorbate is to the limiting volume of the sorption space of the adsorbent, the more inhibited is the translational, rotational motion of the adsorbate molecule, the greater the absolute value of the negative values ​​of Ae

For humic acids, the value of the sorption volume is 4.0.10-4 m3/kg, which is close to the molar volumes of butanol-2, ethyl acetate, dioxane, benzene and toluene, ranging from 2.5 to 3.0.10-4 m3/ kg, therefore, they are characterized by low A£ values. For n-alkanes, alkenes and chlorine-substituted hydrocarbons, the molar volumes are below 2.5.10-4 m3/kg, for which the A£ values ​​are higher.

The values ​​of the Gibbs energy indicate the possibility of the adsorption process, as well as the equilibrium state of the system. The highest AO values ​​were obtained for alcohol, cyclic esters, and aromatic hydrocarbons. If we compare the AO values ​​for the HAs of the original and heat-treated peat, then the latter value is somewhat higher. It is likely that the process of adsorption on the HAs of the original peat is more shifted towards desorption compared to heat-treated peat.

An analysis of the thermodynamic characteristics of adsorption suggests that adsorbates can be arranged in a row as their adsorption capacity decreases: alcohols > esters > cyclic ethers > aromatic ketones > ethers, alkenes, alkanes

1. It has been shown that active adsorption centers in HA are functional groups: carboxyl, phenolic hydroxyls, glucosidic and aromatic fragments. Since HAs from heat-treated peat have a high content of the above groups, they have an increased adsorption capacity.

2. It has been shown that the adsorption capacity of HA with respect to polar compounds (alcohols, complex and cyclic ethers, aromatics, ketones) is higher than for non-polar adsorbates (alkanes, alkenes).

3. Relationships between some physicochemical characteristics (polarizability, dipole moment) of adsorbates and retention parameters are obtained.

4. It has been proven that the increased adsorption capacity of heat-treated peat HA is due to the increased content of oxygen-containing groups (carboxyl, phenolic hydroxyls), glucoside and aromatic fragments in the structure compared to the original HA.

5. It was revealed that the thermodynamic characteristics (-AD-A^Ab) for the HAs of the original and heat-treated peat are interconnected for all the studied adsorbates.

6. It has been established that the thermodynamic probability of adsorption on HA occurs in the following order: alcohols > esters > cyclic ethers > aromatic ketones > ethers, alkenes, alkanes.

BIBLIOGRAPHY

1. Komissarov I.D., Loginov L.F. Humic substances in the biosphere. - M.: Nauka, 1993. - 352 p.

2. Lishtvan I.I., Kruglitsky N.N., Tretinnik V.Yu. Physicochemical mechanics of humic substances. - Minsk: Science and technology, 1976. - 264 p.

3. Pal U.K., Chakravarti S.K. Volume absorption of the ethyldiamino complex Co on soil and peat humic acids // Journal of Indian Chemical Society. - 1986. - V. 63. - No. 10. - P. 883-889.

4. Pilipenko A.T., Vasiliev N.G., Buntova M.A., Savkin A.G. Mechanism and strength of sorption of transition metal cations by humic acids // Doklady AN UkrSSR. - 1986. - No. 7. - S. 42-45.

5. Gamayunov N.I., Maslennikov B.I., Shulman Yu.A. Ion exchange in humic acids // Chemistry solid fuel. -1991. - No. 3. - S. 32-39.

6. Alexandrov I.V., Kandelaki G.I., Kulikova I.P. Zeolite-humic sorbents for wastewater treatment // Solid Fuel Chemistry. - 1994. - No. 4-5. - S. 136-142.

7. Bratasevszskij A., Gaidarob O., Gordienko Sz. Study of the process of complex formation of humic acids by the potentiometric method // Agrochem. es tobaj. - 1971. - V. 2. - No. 2.

8. Parkhomenko V.V., Kudra A.A. On the calculation of thermodynamic functions of the process of adsorption of methyl alcohol by humic acids and humates according to one isotherm // Surface phenomena in dispersed systems. - Kyiv: Naukova Dumka, 1974.

Issue. 3. - S. 35-43.

9. Tarnovskaya L.I., Maslov S.G., Smolyaninov S.I. Chemical composition of organic substances of solid residues of peat pyrolysis // Chemistry of solid fuels. - 1988. - No. 3. - S. 26-29.

10. Lishtvan I.I., Korol N.T. Basic properties of peat and methods for their determination. - Minsk: Science and technology, 1975. - 320 p.

11. Bazin E.T., Kopenkin V.D., Kosov V.I. etc. Technical analysis of peat. - M.: Nedra, 1992. - 431 p.

12. Tarnovskaya L.I., Maslov S.G. Change chemical composition humic acids in the process of peat thermolysis // Chemistry of solid fuels. - 1994. - No. 4-5. - S. 33-39.

13. Kiselev A.V., Yashin Ya.I. Physical and chemical application of gas chromatography. - M.: Chemistry, 1973. - 214 p.

14. Wigdergauz M.S., Izmailov R.I. Application of gas chromatography to determine the physicochemical properties of substances.

M.: Nauka, 1970. - 159 p.

15. Stall D., Westram E., Zinke G. Chemical thermodynamics of organic compounds. - M.: Mir, 1971. - 807 p.

INCREASING THE EFFICIENCY OF INDUSTRIAL OPERATION OF LCH-35-11/1000 AND LG-35-8/300B REFORMING UNIT AT KINEF ON THE BASIS OF A CATALYST OPERATION CONTROL SYSTEM

DI. Melnik, S.A. Galushin, A.V. Kravtsov, E.D. Ivanchina, V.N. Fetisova

Tomsk Polytechnic University E-mail: [email protected]

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