Method for separating substances with different physical-chemical properties

FIELD: physics.

SUBSTANCE: in the method, hard carrier with system of narrow pores and channels is kept under temperature below height of potential barriers for movement of at least one type of separated molecules.

EFFECT: higher efficiency.

4 dwg

 

The invention relates to physico-chemical methods of separation of substances and allows for separation of substances with different physical-chemical properties.

Known chromatographic column containing a cylindrical shell in which is inert solid carrier with the pores and channels [U.S. Patent N3319403, CL 55-386, 1968]. The disadvantage of this column is the low efficiency speakers and a sharp decrease when increasing the flow rate of the mobile phase and high pressure differential at the inlet and outlet of the column in a liquid version chromatography.

The known method and device is selected as the prototype for the separation of isotopes, in which there is an envelope filled with adsorbent containing porous powder or material with molecular sieves (pore diameter of 1-300 Å) [UK Patent GB N1162291, 1969]. When this is passed through the shell stream buffer gas, inert with respect to the adsorbent. Periodically in the gas stream is introduced in small portions to the mixture of the partial isotopes, which have different surface adsorption on the surface of the adsorbent. Thanks to the passion of the molecules of the isotope flowing buffer gas is provided directed physical movement of molecules shared isotopes from input to output shell filled with adsorbate At the exit from the shell isotopic composition of the mixture is recorded by a mass spectrometer, which allows to determine the time of maximum output of enriched detachable isotope mixture and sends a signal to open a channel through which displayed this enriched mixture.

The disadvantages of this method are the complexity of the design, not high enough coefficient of isotope separation and the need to use a buffer gas, which must subsequently be separated.

The technical result of the invention is to improve the degree of separation of substances with different physical-chemical properties on the surface of pores formed within a solid medium.

The technical result is achieved in that in the method for the separation of substances with different physical and chemical properties containing solid media system of narrow pores and channels, what's new is that for the separation of substances solid media support at a temperature below the height of the potential barriers to movement of at least one grade partial molecules.

This method does not use a buffer gas, and used the effect of strong differences of surface diffusion partial molecules over the surface of the pores of the solid carrier occurring under certain conditions.

Under certain conditions this refers to the use of specially selected combinations of the material of the carrier - shared is olekuly, as well as the selection of a specific temperature range.

The invention is illustrated by drawings. Figure 1 is given the profile of potential barriers (K) for the motion of hydrogen molecules inside narrow carbon nanotubes (6,0) along its axis, as well as modules of the wave functions of the first two lowest States of hydrogen molecules. Figure 2 shows the device setup for the separation of substances with different physical and chemical properties. Figure 3 shows the ratio of speeds of molecules of hydrogen isotopes (H2, D2, T2) inside carbon nanotubes (CNT) (6,0) and (3,3) depending on temperature. Figure 4 shows the effect of separating molecules of different chemical composition, namely, figure 4 shows the ratio of speeds of the partial molecules co and CO2inside CNT (6,0) depending on the temperature.

For the required combination of the partial molecules of the material of the solid carrier is selected on the basis of the height of the potential barriers and their thickness for the movement of the partial molecules over the surface of the pores of the solid media. Potential barriers are formed due to the presence of quantum-chemical (including correlation, i.e. van der Waals) interactions between adsorbed molecules and surface atoms in a solid medium, see figure 1, which shows the profile of a potential relief for the movement of hydrogen molecules inside narrow carbon nanotubes is IDA (6,0). Under the profile of the potential relief refers to the dependence of the potential energy of the molecule depending on the surface area over which it is located. The temperature in the system is maintained in this range, when the average kinetic energy of molecules (equal to 3/2 KinT, where Kinis the Boltzmann constant, T - temperature) 1.5 to 50 times smaller than the height of the potential barriers to movement of at least one grade partial molecules inside the pores. For example, the height of the potential barriers to the movement of hydrogen molecules inside carbon nanotubes of type (6,0) is ˜K (see figure 1), so the operating temperature is selected depending on the desired performance and the degree of separation in the range from liquid nitrogen temperature (77 K) to room. In these conditions it is likely that surface diffusion partial molecules above the surface of the pores of the solid media due to the presence of 2 mechanisms.

1) Podarennoe quantum tunneling through a potential barrier [see Llandow, E. Livshits "Quantum mechanics", M. 1963, Chapter 7, paragraph 50]. This mechanism works effectively to narrow the potential barriers and light molecular weight of the molecule is equal to 1-5 mass of the hydrogen molecule). When the partial molecules seep through the potential barriers to transparency coefficient D (E, m), a the following is vetelino, and with an average speed, which is very sensitive to the mass of the particle m and its average kinetic energy (temperature), [see formula 1]

Here U(x) - potential relief when tunneling of molecules through a potential barrier, but the limits of integration a and b are defined as the coordinates of the points on the one-dimensional trajectory of the molecule, where the energy E is compared with the potential energy U(x). The formula shows that even molecules of light isotopes (e.g., molecules of hydrogen and deuterium) are due to the difference in their mass, m, of different average speeds of diffusion, which is proportional to the probability of tunneling through the barrier. This method is chosen properly, the average kinetic energy of molecules E (equal to 3/2 KinT) so that the tunneling rate of all kinds of molecules is large enough for the desired performance of installation, but it varies significantly for different kinds of molecules due to the difference of their masses or differences of potential relief U(x), acting on them. For example, the average speed of diffusion of the light isotopes of hydrogen and deuterium at a temperature of 77 K inside carbon nanotubes of type (6,0) differ ˜200 time [see figure 3]. This mechanism is suitable for the separation of light molecules isotopes (hydrogen, helium, and others)

2) Periodically the Kai adsorption and partial desorption of molecules on the surface of the pores. As is known, the frequency of desorption νdesorbmolecules from the surface is calculated as:

where ν1- frequency normal to the surface of the pores of the vibrations of the molecule, and Ec- the value of the potential barrier for desorption (separation) of this molecule adsorbed on the surface [see P.A.Redhead, Vacuum 12 (1962), p.203]. As ν1and Ecdepend on the nature of the molecule, therefore, different molecules will have different speeds desorption from the surface. This difference in the rate of desorption of different molecules (with different values of Ewith) increases with decreasing temperature due to the difference of the exponential multiplier (when KinT≪Fwith). This effect is emitted from the surface of the particle crosses the season in diameter and again adsorbed on the pore surface at a different point. Further, the process of diffusion through the process of adsorption-desorption is repeated several times. It should be noted that the pore diameter of D must be small (D≪ the average free path length of the partial molecules in a gas at a given temperature and pressure. Otherwise uncontrolled diffusion partial molecules on the surface of pores (i.e. the movement of molecules in the form of free gas flow) will prevail. This mechanism can be applied for the separation of molecules of different chemical SOS is ava.

For both mechanisms the height of the potential barriers for each pair shared the molecule - surface of the solid carrier can be calculated by quantum chemistry methods, for example, using a pseudo-potential method [J.R.Chelikowsky, "The Pseudopotential Density Functional Method (PDFM) Applied to Nanostructures," Journal of Physics D33, R33 (2000)]. This method is implemented in Kant-chemical program VASP 4.4.5 [see http://cms.mpi.univie.ac.at/vasp/)/], which allows to calculate the potential barriers to any combination of the surface of a solid carrier is adsorbed molecule.

Additionally, we consider it necessary to clarify some moments.

1) the Adsorbent should be selected based on the following conditions: adsorbent must not form chemical bonds with adsorbed molecules, as such links are too hard to break under the action of temperature.

2) When using the first mechanism for isotope separation distance between adjacent local minima of the potential barriers should be small (for tunneling), so the period of the unit cell of the adsorbent L may not be large (L˜3-7 Å). The mass share of the molecules should not exceed 1-30 mass of the proton, or the probability of tunneling is negligible.

Based on the above requirements, the adsorbent can serve as carbon nanotubes (as one who tennie, and multi wall), surface oxides, sulphides, halides of metals and other

The proposed method of separation of substances for separation: (a) isotopes of hydrogen and (b) a gas consisting of a mixture of molecules of CO and CO2implemented in the following way.

a) Solid shell 1, having an inlet 2 and outlet 3 [see figure 2] filled with solid media 4 (zeolite powder AlPO4-5, super-narrow channels which fabricated carbon nanotubes with a diameter of 4-5 And [see N. Wang, Z. Tang, K., Li, G.D. and J.S. Chen, Nature, 408 (2000), p.51]. The shell is cooled by liquid nitrogen to a temperature of 77 K. Through the inlet under pressure ˜10 ATM mixture of hydrogen and deuterium is served in the shell. These gases due to their different molecular weight diffuse internal surfaces of carbon nanotubes within the pores of the zeolite with a different speed (see the first diffusion mechanism and formula 1)). Molecules of protium (light isotope of hydrogen H2) have a significantly greater rate of diffusion (see Fig. 3, which shows the ratio of speeds of the different tunneling of hydrogen isotopes inside the carbon nanotubes of the two species ((3,3) and (6,0)) compared with the diffusion rate of the isotope deuterium, and especially tritium. Therefore, the gas mixture is enriched with a light isotope of hydrogen at the outlet of 3. Heavy hydrogen is collected at the entrance of the socket 2, where he PE eticheski pumped.

b) Solid shell 1, having an inlet 2 and outlet 3 [see figure 2], filled with the same carrier 4, as in case (a). The shell is cooled to a temperature of 220K. Through the inlet under pressure ˜10 ATM mixture of carbon dioxide (CO2) and carbon monoxide (CO) is fed into the shell. These gases due to their different chemical properties diffuse inside carbon nanotubes with different speed (see the second mechanism of diffusion and the formula 2). Molecules of CO2have several times greater rate of diffusion (see figure 4, which shows the relationship of the speed of diffusion of the molecules CO and CO2inside nanotubes (6,0)). Therefore, the gas mixture enriched in carbon dioxide at the outlet of 3. Molecules WITH remain mostly in the input pipe 2, where the gas is periodically pumped out.

The advantage of this method of separation is a significant increase (up to tens of thousands of times) the coefficient of separation of substances. While it is possible to separate even molecules isotopes, despite their chemical identity. Another advantage is no need to use a buffer gas, which dramatically simplifies design, installation and eliminates the need for additional separation of the gas from the shared substances.

Method for the separation of substances with different physico-chemical the ski properties based on the use of solid media system of narrow pores and channels, characterized in that for the separation of substances solid media support at a temperature below the height of the potential barriers to movement of at least one grade partial molecules.



 

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