DE4443452C2 - Device for carrying out chemical reactions - Google Patents

Description

The invention relates to a device for carrying out chemical reactions according to the first Pa entitlement.

A number of chemical reactions occur at overcritics conditions faster and with a higher yield because only there is a single phase. For example, by oxidation under supercritical conditions organic Destroy contaminants in an aqueous medium. In aqueous me supercritical conditions arise when the tem temperature is above 374 ° C and the pressure is more than 221 bar. Because the organic contaminants that are destroyed should mostly contain halogens, sulfur, boron etc., During the oxidation, corrosive substances are generally formed Fabrics. The oxidizing agent oxygen works under critical conditions conditions also corrosive. Oxidations under over critical conditions must therefore be in such devices be carried out under the high temperature and the high pressure against the corrosive attack. The Failure of such devices poses because of the high pressure represents a serious security risk.

A device of the type mentioned is from US-PS 5,167,930. This device, which is the implementation of Slurrying at high pressure, high temperature and corrosive loads conditions, has a double-shelled reaction chamber on, in which a pressure equalization between the reaction space and an interspace takes place. As a constructive means of Establishing pressure equalization becomes an elastic reaction onsraum, bellows on the reaction space or a telescope extendable part of the reaction space provided.

A further device for carrying out reactions under high temperatures and high pressure is known from the Journal of the American Chemical Society Vol. 78 (1956), pages 5983 to 5986, in particular from FIG. 1 and the associated description. This device contains a sealed ampoule, in which with increasing reaction temperature due to heating of the reactants, an external furnace generates a considerably increasing internal pressure, which is compensated for by a steel jacket enveloping the ampoule by means of nitrogen back pressure from a nitrogen bomb connected to the steel jacket space.

The US-PS 4,235,841 describes a double-walled high pressure furnace for gases. Dif. Can be found as a means of pressure equalization reference pressure detectors and overflow valves.

WO 92/18428 has proposed the supercritical Oxidation of organic compounds in a reaction room carry out, the walls of which contain a zirconium dioxide tend ceramic or made with such a ceramic are dressed. In the first case, the ceramic material must be in one such wall thickness can be used that the high pressure too is kept reliable. In the second case, the Kera is supported mic material against a metallic hollow body. The metal Lische hollow body can be made of a nickel alloy, in particular which consist of INCONEL. At one point in the publication (Page 15, lines 6-12) it is indicated that the lining also arranged at a distance from the metallic hollow body can be net, so that there is a space. By  an inert purge stream ("clean fluid purge "). The pressure of the flushing flow are in the Document contains no information. With the help of the flushing current are obviously supposed to be corrosive substances that the ceramic through penetrate and get into the space, be eliminated, so that the metallic hollow body is protected from these substances is.

Zirconia has a relatively low thermal conductivity ability coefficient. If a hollow body made of zirconium dioxide Ceramics have to be heated or cooled from outside, for one specified internal temperature significantly higher or lower Outside temperatures are generated. The temperature gradient in the wall of the hollow body runs because of the bad heat zirconia conduction very steep. This is particularly so problematic if a metallic hollow body with the Zirconia ceramic is lined because of the danger stands that the lining due to thermal expansion loosened from the metallic base or cracks form. Due to the high thermal conductivity of the metal tensions in the lining are additionally increased ken if the metallic hollow body is very different Exposed to temperatures. On the other hand, the danger ner crack formation in a hollow body, which consists exclusively of Ceramic does not exist under high internal pressure be closed, especially if additional mechani tensions are present.

The object of the invention is to avoid these disadvantages and in particular in the case of a device of the type mentioned at the outset, which contains a hollow body made of a ceramic, which the Reak enclosing space to arrange the hollow body in such a way that with temperature changes much lower voltages occur. The high pressure in the reaction chamber may cause the mechani Do not endanger the stability of the hollow body.  

The task is characterized by the features of claim 1 described features solved. Subject of further Claims are preferred configurations of the device.

According to the invention, the hollow body which surrounds the reaction space consists of a non-porous ceramic. In principle, any ceramic can be used which has no continuous pores and is resistant to the corrosive substances present during the implementation of the reaction, e.g. B. also the zirconium dioxide mentioned at the beginning. However, the ceramic preferably consists of at least 99% by weight of aluminum oxide. Sapphire can also be used for maximum corrosion resistance. Alumina is resistant to most chemical substances; it also has the relatively high coefficient of thermal conductivity α = 30 W / mK at 100 ° C (for _comparison : α _INCONEL = 10 W / mK at room temperature; α _{zirconium dioxide} = 2.5 W / mK at 100 ° C). With aluminum oxide, heating up to high temperatures results in significantly lower voltages because the temperature gradient is flat.

In principle, the hollow body can have any shape; because of the high pressures in supercritical conditions the hollow body is preferably a tube. Tubes made of aluminum Umoxid are commercially available. The wall thickness of the pipe is of minor importance because inside and outside side of the pipe not exposed to different pressures becomes.

The hollow body is inserted into a container that consists of a Metal alloy is made to withstand the high pressure and the high Temperature is stable in supercritical conditions. Before preferably a nickel alloy, especially INCONEL, preferably INCONEL-625, used as a metal alloy. The The dimensions of the hollow body and container are thus one on top of the other matched that a space between the two components arises. The container comes with the corrosive substances  at most in cold places. It therefore takes not to attack the corrosive substances at high temperatures to be interpreted.

The inner shape of the container is preferably in the Matched to the outer dimension of the hollow body that between the outer wall of the hollow body and the inner wall of the Container only a narrow gap (less than 1 mm, at e.g. 0.1 mm) remains. This will make the volume of the Zwi space is kept as low as possible. By this arrangement convections in the space are prevented and the thermi cal efficiency improved.

According to the invention can be in the space with the help of a set the same pressure as in the reaction chamber prevails. The hollow body made of ceramic is therefore not a Druckbe exposed to stress because in its cavity and on its There is the same pressure on the outside. He needs alone against the corrosive attack designed at high temperatures his; a ceramic material that is also high pressure withstands is not necessary. In the simplest case there is the device from two coupled pumps, one of which the reactants in the reaction space and the other at same chem pressure conveys an inert fluid into the intermediate space. Instead of the pumps, two pressure accumulators are also possible, in who are under the same pressure, and one of which is the Reak tanden and the other an inert fluid, e.g. B. pure water, contains.

However, preference is given as a device for setting the same a pressure transmitter is used in the intermediate space. Of the Pressure transmitter is preferably made of a tough metal alloy tion, for example made of INCONEL or a stainless steel does. It can consist of a tube that has an interior Diffusion barrier contains the pipe interior in two areas che shares. The first area is via a first pipeline  with the reaction space and the second area via a second Pipeline connected to the space. In the first pipe the reactants are conveyed with the help of a pump, while the second area, the second pipe and the Gap are filled with an inert fluid. With help the diffusion barrier, the pressures between the first and the second area in the pressure transmitter and thus between Re action space and space balanced. The diffusions Can lock a movable, the areas against each other be a sealing piston. As material for the sliding Piston comes in particular polytetrafluoroethylene (PTFE) dress. PTFE slides easily on metal surfaces and is ge inert to most aggressive substances.

The pressure transmitter with ion exchange also appears possible shear to fill, so that from the first to the second area flowing fluid containing the reactants the reactants especially the corrosive substances are removed. As a result this measure is the gap only with an inert Fluid filled, so that the metallic container does not contain the kor exposed to rosy substances.

With the help of a pressure transmitter, the chemical reac continuously. He does come in his he most area in contact with the corrosive substances and stands under high pressure; however, it can be at room temperature are held so that the corrosive attack is greatly reduced is. A suitable material for the pressure transmitter is INCONEL or stainless steel. Preferably, the volume of the Pressure transmitter 10 to 100 times as large as the volume of the Space.

The advantage of the invention is that the requirements regarding the pressure and temperature resistance and the Un sensitivity to corrosive substances at high temperatures temperature according to the prior art cited at the beginning  from a single component to multiple construction parts are divided. The hollow body made of ceramic needs only resist the corrosive attack at high temperature to be dig. The pressure resistance requirement is taken from the metallic container. This can the wall thickness of the ceramic is thin (e.g. in the area of some mm) are kept so that the temperature gradient is flat remains. Opposite metallic Be lined with ceramics ratios, the invention has the advantage that the individual Components are commercially available and not under correspond high costs must be manufactured. Furthermore, it does not apply the risk of the lining flaking off and the metallic Container material is released. A possible failure of the The device according to the invention can also be operated with the aid of pressure measuring devices can be easily determined.

The invention is explained in more detail below with reference to figures purifies.

Fig. 1 illustrates an embodiment of the invention;

Fig. 2 shows a plant for the oxidation of organic substances in an aqueous medium, in which the device according to the invention is integrated.

In Fig. 1 an embodiment of the device according to the invention is shown. The reaction space is formed by the inner space of a tube 1 made of aluminum oxide as a hollow body. The tube 1 is enclosed by a second tube 2 , which consists of INCONEL. The tube 2 is tightly connected to the ceramic tube 1 by pressure and temperature-resistant glue or solders and is heatable in its central area by an outside heater. To compensate for thermal expansion, the tube 2 holds a metal bellows. Alternatively, the tube 2 can be connected to the tube 1 made of aluminum oxide in the cold area by O-ring seals. There is a space 3 between the aluminum oxide tube 1 and the INCONEL tube 2 .

Furthermore, a pressure transmitter 4 in the form of a tube 7 made of a stainless steel is provided, in the interior of which a displaceable piston 10 made of PTFE is arranged. The piston 10 divides the interior of the tube 7 into two areas 8 , 9 . The second region 9 , the intermediate space 3 and the connecting pipeline are filled with an inert fluid.

The required reaction pressure is applied by a high pressure pump 5 , which is connected via a pipeline 6 to the reaction space. A branch of the pipeline 6 connects the high pressure pump 5 to the first area 8 of the pressure transmitter 4 . The movable piston 10 ensures that the pressure prevailing in the reaction space occurs in the intermediate space 3 . The reaction space is thus hydraulically coupled to the inter mediate space 3 .

In Fig. 2 is a plant for the oxidation of organic substances fen in an aqueous medium at supercritical conditions Darge presents. The system and the operating procedure are described in the following. The reference symbols used in FIG. 1 have the same meaning in FIG. 2.

The reaction solution is placed in a storage container 16 with a vent line which can be flushed with nitrogen via a further line. To simulate a reaction under supercritical conditions, the reaction solution consists of an aqueous solution of approx. 0.5 mol hydrogen peroxide / l (3% by weight) and 0.05 mol hydrochloric acid / l. This solution is compressed with the high pressure pump 5 to 250 to 500 bar. The flow can be set between 0.5 and 5 ml / min. The line 17 through which this compressed but still cold solution is conveyed branches to the reaction space and to the pressure transmitter 4 . For the introduction of the aqueous fluid with the reactants into the reaction space and for the removal of the fluid loaded with the reaction products, two lines 6 ', 15 are provided.

The pressure transmitter consists of a tube 7 made of stainless steel 1.4401 with 14.3 mm outside diameter, 8 mm inside diameter and 500 mm length. Approximately in the middle of the tube interior, a movable piston 10 made of PTFE is positioned, which divides the tube interior into two areas 8 and 9 . The entire tube 7 is flooded with water before the experiment is carried out. The first area 8 is connected to the high-pressure pump 5 via the lines 13 and 6 . The second region 9 is connected to the intermediate space 3 via the line 14 . Lines 6 , 13 and 14 are capillary tubes with an inner diameter of 0.5 mm. The pressure transmitter 4 has room temperature during the experiment.

A pressure meter (PIRCA S) is attached to line 13 and is connected to a computer. The pressure gauge is used for documentation, the control of the pressure regulator 19 in the line 15 and the alarm monitoring; it controls the pressure to within ± 2 bar. The line 15 opens into a sample container 18 . A second pressure gauge (PIRA) is integrated in the line 14 . This pressure meter is also connected to the computer and is used for pressure monitoring in the pressure transmitter 4th

The reactor chamber is closed by a hollow body in the form of a ceramic tube 1 made of aluminum oxide without continuous pores. The ceramic tube 1 has an outer diameter of 8 mm, an inner diameter of 5 mm and a length of 710 mm. It is surrounded by a container in the form of a tube 2 made of INCONEL-625 with an outside diameter of 14.4 mm, an inside diameter of 8.1 mm and a length of 700 mm. INCONEL pipe 2 is designed for a pressure of 830 bar at 630 ° C. The outside of the INCONEL tube 2 is heated in the middle area by a heating coil 11 with an output of 400 W. The heated zone is 400 mm long and surrounded by insulation with a total length of 420 mm. The temperature is measured by three thermocouples (TIR, TIRC, TIR) and recorded by the computer. The heating is regulated by a pulse packet control from the computer. This ensures that the temperature is kept constant in the heated area at 450 ° C who can.

At the entrance and exit of the insulation, two 50 or 100 mm long heat sinks are attached at a distance of 30 mm each, which consist of copper and are flowed through by a cooling unit 12 (cooling capacity 200 W) with water at 20 ° C.

The open ends of the ceramic tube 1 and the INCONEL tube 2 are connected to each other with the help of a pressure-tight adapter (SF 562 CX from Schmidt and Kranz, straight reducing screw connection 9/16 '' to 1/16 ''). The adapters are shown schematically by triangles in the figure. Within the adapter, the two pipes 1 , 2 each end in a common room that is filled with water before the start of the experiment. The gap 3 is closed against the two common spaces at the ends of the tubes 1 , 2 by two angeord Nete in the cold area, in milled grooves in the tube 2 O-rings 20 , the gap 3 still at a pressure difference up to 20th seal reliably. The O-rings do not need to withstand a high differential pressure because the same pressure prevails in the common spaces and in the intermediate space 3 ; however, they prevent the reaction solution from entering the intermediate space 3 .

The system described was operated for about 500 hours in experimental operation with the above reaction solution (0.5 mol H₂O₂ / l, 0.05 mol HCl / l) at 450 ° C and 250 bar. In the heating zone, hydrogen peroxide decomposes to water and oxygen. To a small extent, the hydrochloric acid is oxidized to elemental chlorine. Furthermore, the Kera mikrohr 1 is loaded by the high temperature gradient between the heat sinks and the heating coil 11 , where the temperature rises from 20 ° C to 450 ° C. Nevertheless, no macroscopic signs of corrosion could be found on the ceramic tube 1 after the test operation. The concentration of the aluminum released from the ceramic tube 1 in the sample collection container 18 was approximately 1 ppm.

Claims (4)

1. Device for carrying out chemical reactions which take place under a high pressure and a high temperature and in which corrosive substances are reacted and / or released, with

• a) a tubular hollow body ( 1 ), the cavity of which represents a reaction chamber enclosing the corrosive substances and which consists of a non-porous ceramic which is resistant to the corrosive substances at the high temperature,
• b) a tubular container ( 2 ) from a metal against the ho hen pressure and high temperature resistant metal, which encloses the tubular hollow body ( 1 ) in such a way that between the tubular hollow body by ( 1 ) and the tubular container ( 2nd ) there is an intermediate space ( 3 ),
• c) a high-pressure pump ( 5 ) which is connected to the reaction space via a pipeline ( 6 ),
• d) means by means of which the prevailing pressure in the reaction space can be adjusted in the space ( 3 ) so that the same pressure prevails in both the reaction space and in the space ( 3 ),

characterized in that
as such means a pressure transmitter ( 4 ) consisting of a tube ( 7 ) with an arranged in the interior of the tube ( 7 ) on arranged movable piston ( 10 ) which divides the interior of the tube ( 7 ) into two areas ( 8 , 9 ), is provided, the first region ( 8 ) of the interior being connected to the pipeline ( 6 ) and the second region ( 9 ) of the interior being connected to the intermediate space ( 3 ). 2. Device according to claim 1 with a ceramic of at least 99 wt .-% aluminum oxide as the material for the tubular shaped body ( 1 ). 3. Device according to claim 1 or 2 with a nickel alloy as alloy material for the tubular container ( 2 ).