I. Field of the Invention

The invention refers to the field of batch type gas purification equipment, in particular, to rotating autoclaves with mechanochemical activation of the sorption material.

II. Background

The production of high purity and ultra pure gases is an expensive process, the final stage of which is passing the treating gas through the sorption column with porous adsorbent or reactant. Here we mainly mean purification of gases like Ar, N ₂ , ¾, He, Xe and some other.

The efficiency of the final stage of purification can be estimated by the ratio Qlm, where Q is the quantity of captured gas impurity and m is the quantity of sorbent. The value Qlm has the meaning of the specific sorption capacity of the purification material and the problem of the current technologies is that this value is small.

In the case of adsorbents, the smallness of the value Qlm is explained by the fact that the process of capturing the impurity gases continues only until the moment when the available for gases material surface is saturated. In the case of reactants, where the value Qlm is usually by two orders of magnitude higher than that of adsorbents

[K.Chuntonov, J.Setina, G. Douglass. The Newest Getter Technologies: Materials, Processes, Equipment. Journal of Materials Science and Chemical Engineering, 2015, 3, 57-67; K. Chuntonov, J. Setina. Reactive getters for MEMS applications. Vacuum, 123 (2016) 42-48; K. Chuntonov, A.O. Ivanov, B. Verbitsky, J. Setina. Getters for vacuum insulated glazing. Vacuum, 155 (2018) 300-306.], and where not only the surface but also the volume of the material participates in gas capturing, the specific sorption capacity does not achieve its theoretical limit either. The reason of such behavior of reactants is clear: while the reaction front moves into the depth of the material sorption rate regularly decreases going down with time to such an extent that the process becomes economically unviable and must be stopped. A significant part of the reactant by that moment has not been consumed [K. Chuntonov, A.O. Ivanov, B. Verbitsky, V.L. Kozhevnikov. Gas Purification and Quality Control of the End Gas Product. Journal of Materials Science and Chemical Engineering, 2017, 5, 44-58; K. Chuntonov, B. Verbitsky, A.O. Ivanov, V.L. Kozhevnikov. Mechanochemical Methods in the Production of High Purity Gases. Materials Sciences and

Applications, 2018, 9, 489-501].

Thus, the purification technology based on capturing gas impurities in sorption columns with motionless porous or powder material exhausted its potential. Radical changes in the ways of organizing the sorption process targeted at elimination of the kinetic restrictions, which impede the reactant in current production conditions completely fulfill its sorption potential, are required. One of the steps in this direction is the development of gas purification equipment functioning as mechanochemical reactors.

At the present time, two variants of this kind of equipment has been created: mechanochemical sorption apparatuses [K. Chuntonov. Sorption Apparatus for the Production of Pure Gases. US Patent No. 9095805] and reactive sorbers [K. Chuntonov, B. Verbitsky, A.O. Ivanov, V.L. Kozhevnikov. Mechanochemical Methods in the Production of High Purity Gases. Materials Sciences and Applications, 2018, 9, 489-501]. The first ones are sorption columns containing an ingot of reactive alloy, which is turned by the cutting tool into powder saturated with defects inside the column in the flow of the treated gas. The cutting tool is set into motion by the outside actuator transmitting the effort via a hermetical feedthrough. The rate of milling the ingot is regulated according to production needs. The second ones, i.e. reactive sorbers, are flow high pressure reactors, in which the granules of the reactant are stirred by the blades of a magnetic stirrer in the flow of the treated gas. In the process of mutual rubbing of the reactant granules their surface is continuously renewed, which maintains the rate of capturing the impurity at the required high level. Like in the case of the mechanochemical sorption apparatus the work of the sorber can be controlled by changing the rotation rate of the stirrer.

Below one more method of increasing the efficiency of gas purification processes is described, where the reactant serves as the sorption material and where mechanical activation of the consumed sorbent is used to stimulate the reactions in the system gas/reactant.

III. Summary.

The given invention contains a number of distinctions from those solutions, which are the basis of the

mechanochemical sorption apparatus and of the reactive sorber. These innovations widen the frames of using reactants in the gas industry and reduce the expenses for manufacturing gas equipment and production of gas purification material.

The essence of the new method is that gas purification takes place not in a flow column but in an isolated high pressure vessel, in an autoclave, having a shape of an elongated cylinder. This cylinder with gas and a certain amount of reactant, consisting of pieces of cast material or monolithic granules, is rotated with moderate rate in a horizontal position around its axis. During the rotation of the cylinder, pieces of the reactant come into motion and, start colliding with each other, shaving surface layers, which are the products of the reaction between the gas impurity and the reactive metal.

The fresh surface of the reactant sorbs impurities contained in the gas by orders of magnitude faster than the surface covered with the products of reaction and this is just what is required in the given case. The process is continued until the entire active impurity is removed from the gas phase of the vessel. Following the removal of the impurities, the vessel is connected via filters that stop the solid waste particles, to the gas line for filling an intermediate gas tank for storage of purified gas or for distributing the pure gas to standard high pressure cylinders for further delivery to the end user. The vessel itself is then again filled with the next portion of the initial gas repeating the procedures and alternating this periodically with the refilling the vessel with sorption material.

Below there is a list of constructional and technological differences between the present invention and Prior Art, to which the mechanochemical sorption apparatus and the reactive sorber refer.

Therefore, the new gas purification method occurs by chemical reactions between the gas impurity and reactant particles, which are activated due to tribochemical effects while rotating the high pressure cylinder around its axis (autoclave). These tribochemical effects are responsible for the high sorption kinetics and high sorption efficiency of the given gas purification method. The distinctions of this method to Prior Art are significant.

IV. Brief Description of the Drawings.

Fig.l . Tribochemical principle of gas purification.

Fig.2. Sequence of technological operations.

Fig.3. Rotation of the autoclave.

Fig.4. Two-stage procedure.

Fig.5. Gas inlet and outlet.

V. Description of the Invention.

Any cylindrical high pressure vessel can be turned into a reactor for chemical purification of gas from impurities species if this cylinder is charged with a certain quantity of metallic chemisorbent, e.g. reactant, filled with gas to be purified, closed hermetically, being disconnected from the gas line, and then set into rotation around its axis in a horizontal position. Under the reactant we understand here an alloy of alkali and/or alkali-earth metals in a form of cast granules or pieces of a monolithic ingot produced by its grinding.

Figure 1 discloses the mechanism of a stimulating impact produced by rotation of the cylinder 1 on the sorption process. Reactant 3, located in the gas medium 2, reacts with the gas impurity as the result of which a layer of products of the given reaction grows on the surface of the reactant. In sorption technologies with motionless reactant this layer of products is responsible for the abrupt decrease of sorption kinetics and for the decrease of the efficiency of the gas purification process. However in the described here invention this problem is overcome due to one more, the third, method of mechanochemical activation of the sorption material. This is the method of“soft” autogenous milling, the target of which is not so much the grinding of the material, as its surface peeling, thus removing the surface layer, which has already reacted with the impurity.

The similar renewal of the reactant surface takes place at rotation of cylinder 1 (Fig.l), which sets into motion the entire mass of the reactant 3. Pieces or granules of the reactive alloy slide, roll, and collide with one another getting rid of the outside exhausted layers, which detach from the metal core in a form of dust-like particles 4 (Fig.l,b). The fresh metallic regions on the reactant surface, which appear as the result of such peeling, are characterized with high chemical activity and sorption kinetics. For more intensive stirring, cylinders with shoulders can be used (Fig. l,c).

For any gas impurity Y except noble gases it is possible to select such a reactant Me, which in the described above tribochemical conditions by the end of the production process completely turns into a solid product of the approximate composition Me: Y = 1: 1, where for each metal atom there is one atom of the retained gas. This is an exceptionally high result and so it is important to show how it is achieved in this new variant of mechanochemical sorption equipment.

In autogenous milling technologies usually the ration between the volume of the solid charge and the volume of the gas atmosphere in a rotating vessel is 1:2 taking into account the voids between the granules. In other words, it is the case when the“geometrical” boundary between the charge and the free space divides the inner volume into two approximately equal parts. Let us take the mentioned ratio and let us analyze what steps can increase the efficiency of the purification process in a corresponding technology. Let us assume that the volume of the vessel is V, the density and the molar mass of the reactant are accordingly p and A, the gas pressure in the vessel is P, and the temperature is T. Then the total quantity of the reactant is m = pV / _> A and the total quantity Q of the impurity, which is contained in the treated gas is Q = 2 cPV /3RT, where c is the initial concentration of the impurity, and R is a universal gas constant. If the product of the reaction between the impurity and the reactant has a composition MeY then the consumption of the reactant Me in capturing of the impurity Y will be Am = 2cPV/3RT. From here we get that the ratio Am/m = 2cAP / pRT determines the share of the reactant, which is consumed at complete removal of gas species Y from the vessel.

In its turn the inverse relation m/ Am = pRT /2 cAP is the maximal number of three-stage cycles of purification of the type“filling of the autoclave with gas to be purified / purification of the gas by rotating the autoclave / outletting the gas into a special receiver”, which can be performed on the basis of one charge of reactant of the quantity m. Here we are talking about a three-stage production cycle, which will be further mentioned for short as“gas introduction / gas purification / gas outlet” and which in the conditions of the described above surface rubbing of the granules can be repeated m/ Am times. The state of a complete exhaustion of the charge Me corresponds to the end of the series of cycles of this kind.

In the processes of achieving gas purification, the concentration c of impurity species is small and the number m/ Am is big and corresponds to the theoretical limit of sorption capacity of the reactant. In respect to such an important parameter as the coefficient of consumption of the reactant the method of a rotating autoclave is not inferior to the mechanochemical apparatus or the reactive sorber, surpassing at this both of them in the production scale, i.e. in the volume of the treated gas.

In fact, there is no comparison between the sorber or the mechanochemical apparatus and the autoclave: the latter looks against then as a giant with regard to the size of the vessel and the mass of participating in the sorption process reactant and the amount of purified per unit of time gas. In any of the mentioned parameters the autoclave exceeds its mechanochemical predecessors by orders of magnitude, i.e. by hundreds, thousands and more times, which puts it on a par with big industrial manufactures of high - and super pure gases.

The basic variant of the new method of gas purification looks like an elementary alternation of three-stage cycles “gas introduction / gas purification / gas outlet”, the characteristic feature of which is continuously increasing the duration of the middle stage of these cycles goes under the name of“gas purification”. This prolongation of the purification time takes place due to two reasons: firstly, due to the decrease of the total surface area of the granules in the course of their rubbing and secondly, due to the decrease of the rubbing rate with time. As the resulting time expenditure for purification of the set quantity of gas with the increasing number of cycles, inevitably the moment comes, when the process must be terminated as furthering it would become uneconomical. The main drawback of the described variant of gas purification is that by the end of the process the share of the consumed reactant does not to exceed one half of its initial mass. That is, the basic technology needs to be improved.

From the two mechanisms of slowing down the rate of gas purification, which can be formally defined as Qlt, the limiting one is the second mechanism, namely, slowing of the rate of the surface rubbing due to the accumulation of the waste formed as the result of sorption and rotation of the cylindrical vessel. Here t is the duration of the middle stage,“gas purification”, which is understood as the time of the removal of the entire impurity from the gas phase of the vessel at constant rate of its rotation.

The process of the surface rubbing (peeling) runs normally as long as the granules contact each other directly. With time the voids between the granules are filled with powder particles MeY and then peeling slows down and the rate of capturing the gas impurity by the reactant slows down as well. The turning point of the sorption process comes at the stage when the share of the consumed reactant reaches 25±5% of its initial mass. The need for increasing gas purification rate appears in the vicinity of this event. The task of improving the basic technology in the given invention is solved with the help of periodical blowing the autoclave with inert or treated gas for removing the powder particles MeY, which hinder the peeling (rubbing) of the granules. Instead of blowing the vessel with gas vacuum removal of particles MeY can be used. This procedure is started when rotation of the vessel is terminated and this termination is used also to refill (additionally charge) the vessel with the reactant. The mentioned refill compensates the losses of the reactant in the processes of its reactions with the impurity gas and besides, which is also important, restores the volume of the rubbing material to the initial level, measured as an apparent or“geometrical” half of the vessel volume.

So, the new gas purification technology in its improved form represents by itself an alternate change of two operations, the main one and the auxiliary one. The main operation consists of a chain of three-stage cycles“gas introduction / gas purification / gas outlet” following one another until 25±5% of the initial mass of the reactant has been used. Then the time comes for the auxiliary operation, consisting of the two-stage procedure“blowing the vessel / refill of the vessel” at the completion of which the main operation is restarted. These operations are repeated further as many times as it is necessary to satisfy the production need.

Figure 2 schematically discloses the essence of the method of a rotating autoclave. It is seen that three-stage production cycles“gas introduction / gas purification / gas outlet” follow each other n times, where n ~

0.25 m/Am, i.e. till the consumption of the reactant Me reaches 20-30% of its initial quantity m. By that moment the rate of purification decreases to the critical value, which makes it necessary to switch to the auxiliary procedure “blowing the vessel / refill of the vessel”, which restores the kinetic characteristics of the process and raises the sorption potential of the purification material to its initial level.

After that the next series of the three-stage cycle (Fig.2) starts, after it the two-stage procedure is performed, etc., in accordance with the production target. Theoretically this is an endless process with alternate operations, the main one, producing the finished gas product and an auxiliary one, creating the necessary starting conditions for the main operation.

Let us for example consider purification of Ar of purity grade 99.99% with the help of a small autoclave of a cylindrical shape of the volume of V = 1.5 m ³ . Let us charge it with granules of a ternary alloy CaLiMg c p = 1.25 g/cm ³ , A = 24g with the total mass of the reactant of 600kg. The pressure of the argon to be purified in the autoclave is equal to 220 bar and the ambient temperature is 298K. The mentioned alloy in the conditions of mechanical activation of granules at rotation of the autoclave is able to remove all atmospheric impurities 0 ₂ , H ₂ 0, CO, C0 ₂ ,

H ₂ , N2 , etc. from Ar like to the level of“nondetectable”.

However, for the estimation of profitability of the technology it is necessary to know how the three-stage and the two-stage procedures will correlate to each other (Fig.2). In other words, it is necessary to define the number n = 0.25 m/Am, which shows how many production three-stage cycles are contained between two restoring procedures“blowing the vessel / refill of the vessel”. Substituting into the expression for n the numerical values, which define m and Am, we get that n ~ 1750.

This is a perfect result, which means that in the new technology it is necessary to spend only 150kg of ternary alloy CaLiMg for the production of ultra pure gas of the quantity (1750m ³ x 220bar). For the better understanding of the situation let us mention that this quantity of gas is equal to the amount of gas, which is contained in 35000 standard high pressure cylinders with the capacity of 50L each at the pressure of 220bar. If we compare the consumption of purification material for the production of the given quantity of ultra pure gas in modern rectification technologies and in the method of autoclave rotation, then the first value appears to be -1000 times larger than the second one. Analogous ratio is observed in the case reactive sorbers, where also the use of reactants in sorption processes with dominating tribochemical contribution provides an equally strong production effect. A big advantage of the method of a rotating autoclave is the simplicity of those practical steps, which constitute the gas purification process (Fig.2). In the essence this is a chain of elementary operations, performed using known equipment, where only the purpose of this equipment is new. For this reason the industry transition to new technology will not require big efforts and the new technology itself can be easily adjusted to the existing production infrastructure. Let us also mention that the described method can take different forms and can be embodied in different modifications depending on the nature of the concrete application.

There is freedom in the choice of gas purification system with a rotating autoclave from the very beginning, i.e. still at the selection of the type of the cylinder and means for its rotation. The size of the high pressure cylinder can be varied in a wide range from tens of liters to tens of cubic meters and the pressure - from several bars to hundreds of bars. The same can be said about the mechanisms setting the autoclave into motion: these can be simple conveyer belts, where a number of small cylinders is placed, these can be more powerful mechanisms with gear drives (Fig.3, a, b, c), or some other kinds of solutions targeted at big autoclaves.

In the given method the preference is given to cylinders with two gas ports, one at each end as shown in Fig. 4, which discloses the work of the autoclave during the two-stage procedure. Although the sorption function is fulfilled by the autoclave at its rotation in the horizontal position it is more convenient to perform the release of the end gas product as well as the removal of the solid waste and refill of the vessel with the reactant in the vertical position of the cylinder.

Position I in Fig.4 corresponds to the state of the autoclave directly after the end of the n-th three-stage cycle, when the share of the exhausted reactant reaches approximately 25% from its preliminary value. Further the auxiliary operation is started; first cylinder 2 is released from particles MeY (positions II - IV) and then the operation is completed by the refill of the cylinder with reactant Me (positions V - VIII).

For this purpose, in position II with the help of the top and bottom valves 1 a weak upwardly moving gas flow 4 is created due to a small excess of the inside pressure over the atmospheric. This allows to disconnect the upper flange 5 (position III) in the flow of outlet inert or treated gas and to connect a trap of particles MeY, which contains a number of filters 7, to the cylinder (position IV). After that the rate of the gas flow 6 is abruptly increased passing over to the regime of blowing the cylinder. Small particles of the solid waste go to the trap and collect there in a form of powder column 8 and the gas exits through the valve in the upper zone of the trap.

The given procedure is completed by charging of a new portion of the reactant of the quantity of ~ 0.25 m instead of the spent during n three-stage cycles material. For this in the regime of weak gas flow the trap is disconnected (position V) and a charging chamber 10 with closed valve 11 is connected to the upper flange. After charging the granules (position VI) flange 5 with the valve and filter is returned to its working place (positions VII - VIII). The autoclave is ready for the next series of the n three-stage cycles.

One of the possible schemes of exiting the pure gas from the cylinder and filling it with a new portion of the treated gas is shown in Fig.5, which does not require special explanations. The first step is to define the purity of the treated in the autoclave gas, for which at closed valves 2 and 5 a sample of gas product is taken from the cylinder along the line valve 1 - valve 3 - a filter - valve 4. After the analysis of gas at closed filters 2 and 4 the gas flow is directed to cylinders for storage or transportation of pure gas. The remaining part of the purified product is transferred through valve 6 to the special tank (for further usage) lowering the gas pressure to the value, which is slightly higher than the outside pressure. The completion of the operation is filling the autoclave with the next portion of the treated gas trough valves 2 and 1 at closed valve 3.

For a more complete description of the method of a rotating autoclave let us touch the question about the reactants. Their material basis is alloys of calcium with magnesium, which depending on the chemical nature of the gas impurity can be alloyed with lithium, strontium, barium or even sodium. In the given technology, the suitability for practical use of reactant is represented by either small ingots e.g., granules, or products of grinding of larger ingots. From the economical view point this is much more profitable than to use traditional high porosity getters, which are the products of 4 - or even 5 - stage treatment of the initial alloys based on Ti, V, Zr. Moreover, the requirement of the monolithic structure of the initial pieces of or granules of the reactant is obligatory. Let us also mention that Ca and Mg are widely spread in the Earth crust, have low melting temperatures and their alloys are apt to surface rubbing.

The requirements to size d _T of the pieces of the charged reactant are the following: d _T should be smaller than the diameter d of the entry channel and much smaller than diameter D of the cylinder itself (Fig.5,b). These are the obvious conditions both for charging the consumable material and for its rubbing (peeling) during rotation of the cylinder. Taking into account the current needs and possibilities in the considered technical field it is possible to point out for the value d _T the range 5mm < d _T < 100mm as preferable although the process can be carried out at other values of d _T .

Summarizing the above said we should point out that the method of rotating autoclave is technically simple and effective in sorption with respect to approximating in the process kinetics and in the product yield, to the theoretical limit of both. This is the consequence of combining in the given technology two innovations: using reactants as purification material and stimulating reactions gas / solid with the help of the tribochemical technique. The application field of this method is rather wide; it is not limited only to the production of high purity and ultrapure gases but includes other processes as well, like recycling of used rare gases (e.g. He, Xe, etc.), capturing of toxic vapors or gases (e.g. Hg, CO, S- or N- containing volatile substances), etc.

VI. Detailed Description of the Drawings.

Fig.l . Tribochemical principle of gas purification.

(a) the starting state, (b) the regime of“soft” self-grinding (autogenous milling), (c) the cylinder with shoulders;

1 - the cylinder wall, 2 -treated gas, 3 - reactant Me, 4 - small particles MeY, 5 - shoulders.

Fig.2. Sequence of technological operations.

Each block of n three-stage cycles producing the purified gas is followed by two-stage restoring procedure, which returns the initial kinetic characteristics to the charge of reactant Me.

Fig.3. Rotation of the autoclave.

(a) a conveyer belt, 1 - a cylinder, 2 - a belt; (b) a roll mechanism, 1 - a cylinder, 2 -a roll; (c) a gear mechanism, 1 - a cylinder, 2 - a gear.

Fig.4. Two-stage procedure.

Positions I - IV answer the actions for removal of small particles MeY from the autoclave, positions V - VIII answer the actions for additional charge of the autoclave with reactant Me. Here 1 is a gas valve, 2 is a cylinder, 3 is reactant, 4 is upstream gas flow at a small excess of pressure over the outside pressure, 5 is an upper flange with a valve and a filter, 6 is gas flow at the pressure, which is sufficient for capturing and taking away particles MeY, 7 is filter, 8 is waste MeY, 9 is a hermetic stop-cock, 10 is a chamber with granules Me, 11 is a hermetic stop-cock in the position“closed”, 11 * is a hermetic stop-cock in the position“open”.

Fig.5. Gas inlet and outlet. (a) 1, 2, 3, 4, 5 and 6 are valves regulating gas flows in the operation of filling the cylinder with feed gas and exiting the gas into containers for collecting the pure product;

(b) d is diameter of the charging channel, D is diameter of the cylinder.