SU1225810A1 - Method of preliminary preparation of zeolite,type nax - Google Patents

Description

1225810 .1

The invention relates to a chemical search plan for the optimal mode.

This method is also used in the preliminary preparation of the NaX adsorbent used for the deep drying and purification of gases and liquids in installations with a limited service life.

The purpose of the invention is to reduce and stabilize the adsorption capacity.

Example. Preliminary preparation of several samples of NaX adsorbent from different industrial batches is carried out. The mass of each sample is 5 rd- 0.5 kg. The sample is placed in a container, which is alternately transferred, from a cryostat to a thermostat and back with a constant duration of each cycle equal to 30 u. When performing thermal cycling, samples are taken from the samples in the amount of

thermocyclic processing of the NaX adsorbent is given in table. one; adsorbent capacity of the adsorbent

$ nitrogen at 77.4 K, depending on the thermal cycling mode, is given in Table. 2; nitrogen adsorption at 77.4 K and pressure 86.6 kPa - tab. 3

ten

Table

thermocyclic processing of the NaX adsorbent is given in table. one; adsorbent capacity of the adsorbent

nitrogen at 77.4 K, depending on the mode of thermal cycling treatment - in Table. 2; nitrogen adsorption at 77.4 K and pressure 86.6 kPa - tab. 3

Table

312258

Table 3

It follows from the above data that the adsorption capacity with approximately 80 thermal cycles begins to exceed the initial value obtained for adsorbelts of the NaX type, which did not undergo thermal cycling, and stabilized over 60 thermal cycles.

The rate of change in temperature during heat treatment is limited from above and is no more than ZO c / MHH on the basis of experimental data in the study of various batches of NaX zeolite taking into account thermal stability data for materials of similar structure. The lower limit of the rate of temperature change is associated with the occurrence of conditions for thermal buildup of the crystal lattice, leading to the migration of cations with partial destruction of bonds with bonding, which leads to an increase in the fraction of the free surface of NaX type crystals previously blocked by the binder and not available adsorbable substance. At low rates of temperature change, which are usually considered to be extremely affordable (up to 2.5 C / min), similar processes also occur. However, relaxation phenomena in the crystal lattice are so great that

five

about

0 5 Q 5

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there are only minor fluctuations in the zone of unstable initial position, which take place against the background of a general gradual destruction of the structure of the adsorbent with a constant drop in the initial adsorption capacity, which occur in practice in operational installations with an adsorbent like NaX.

Thermocyclic treatment with rates of temperature change less than 15-20 ° C / min is not economically feasible. This requires special installations for thermal cycling. With complex schemes for controlling the speed of both cooling and heating of the adsorbent, they cannot be solved only by moving the containers from the thermostat to the cryostat and back. Simultaneously with decreasing speed, the total time of one cooling cycle — heating — increases, which significantly increases the duration (by 3-4 times) of the required number of heat treatment cycles, without leading to qualitative changes in the NaX adsorbent structure.

The positive effect of an increase in the adsorption capacity and its stabilization at the achieved level, exceeding the initial one, is observed after at least 85 thermal cycles and is explained by a slow increase in changes in the crystal lattice associated with the migration of sodium cations and the destruction of the bonds between the crystallites and the original structure. .

The best results are achieved when thermal treatment is carried out in an atmosphere with a moisture content corresponding to a dew point of not more than -.

A decrease in the atmospheric moisture content (i.e., the partial pressure of water vapor in the pores) accelerates the restructuring of the lattice. This is due to the fact that due to the decrease in the number of water molecules in the pores, they are redistributed by type of interaction with a decrease in the proportion of molecules, localized by interaction with cations with high characteristic energies and inhibiting the process of lattice rearrangement.

In this method of preliminary preparation, conditions are created which allow an increase in the number 5 1225810 "

The adsorption capacity of the adsorbed pretreatment with moisture, such as NaX, before its accumulation in the content corresponding to the installation point by 2-6% and stabilizing the dews no more, allows an increase in the adsorption capacity of adsorbents to increase the value up to 60 drying cycles and cleaning in ad-5 ta type NaX by 5-10% and stabilization sorption unit. Use it for 80 working days in the gas medium during drying and cleaning cycles.

Claims (2)

1. METHOD FOR PRELIMINARY PREPARATION OF ZEOLITE TYPE NaX, including its heating and cooling, characterized in that, in order to increase and stabilize the adsorption capacity, heating is carried out to 250-450 * C, cooling to -100 * C, while the heating and cooling rate is 2.5-20 ° C / min, and the heating-cooling cycle is carried out at least 85 times. 2. The method of pop. 1, characterized in that the heating and cooling cycles are carried out at a moisture content corresponding to a dew point of q not more than -50 ⁱⁿ C. ® bn N3 SL 00