PROCEDURE FOR THE TREATMENT OF REACTION GASES IN THE OXIDATION OF HYDROCHLORIC ACID
DESCRIPTION OF THE INVENTION The invention relates to a process for the treatment of reaction gases, consisting of chlorine, hydrogen chloride, water vapor and residual oxygen, generated in a reactor during the oxidation of hydrogen chloride to give chlorine and Water. The transformation of HC1 into chlorine has already been carried out with a series of procedures. In addition to the electrolysis of hydrochloric acid, there are two types of processes for the non-electrochemical transformation of HC1 into chlorine. This is the case of wet chemical processes and gas phase reactions. The wet chemical processes include the Kel-chlorine process [1] and the H202 procedure of Degussa [2]. In the case of gaseous phase procedures, the following are the most significant: The Shell procedure [3] The MTC procedure [4] and The USC procedure [5]. These processes work with a fluidized bed with copper chloride (USC, Shell) or with chromium oxide (MTC) as a catalyst on a reinforced support. The treatment of the reaction gases, consisting of Cl2, HC1, 02H20, is carried out according to various procedures. In the case of the USC process, the water is separated from the reaction in one stage of the reactor in two stages and discharged. Due to the high oxygen excess, which is required for the transport of the material of the fluidized bed from one stage to the other, the chlorine formed in the second stage is very rich in oxygen and can not be released from the inert gas, economically, -diante simple compression and liquefied. For this reason we work with a special absorption-entrainment system, in which CC14 is used as an adsorbent. The industrial-scale use of CC14 is questionable however for health reasons and in the future it will even be banned. Another disadvantage is the costly transport of large quantities of fluidized bed material between the two reactor stages, which must also be heated and cooled respectively. In this case the presence of the two stages is necessary only for the selective separation of the water from the reaction. On the contrary, the Shell procedure [3] works with a single stage, so that in the treatment the water of the reaction must also be separated concomitantly. In [6] a process is certainly described which makes possible, by means of an elegant working form of the columns in the sub-azeotropic or super-azeotropic range, the complete recycling to the reactor of the unconverted HCl gas; due to the large amount of inert gases, which are required for the work of the fluted bed reactor, of the chlorine content of the HCl and H20-free leaving gases, it is so low that the conditions for subsequent liquefying are quite unfavorable of chlorine. Therefore, an absorption / desorption of the non-liquefied chlorine on CC14 as absorbent has also been chosen in this case to separate the inert gases. Nor does the separation of the totality of the water from the reaction with the help of sulfuric acid, according to a variant of the Shell Oil Company [7], have changed the problem of inert gases little, so that in this case water must also be connected down an absorption-entrainment system with CC14 as absorber. Finally, the MTC process [4] is also worked with excess oxygen in the reactor, so that an absorption-desorption stage with CC14 as absorber must also be connected downstream. Also in [8] the realization of the proposed purification of chlorine m.H. of the adsorption process called Pressure Swing. The task of the invention is to develop a complete process for the treatment of the gases of - • + - reaction in the oxidation of hydrochloric acid for obtaining chlorine, which can be carried out without the previously described steps of absorption-desorption with foreign absorbers. In addition, the thermodynamic optimization in the hydrochloric acid / chlorine system should be exploited in the new procedure. This task is solved with the procedure indicated in the main claim. Further developments and preferred embodiments have been described in the dependent claims. The main advantage of the process is that, in the treatment of the gases produced, it can be de-sired from foreign media, with the exception of a small amount of sulfuric acid for the drying of the gaseous product. On the contrary, the thermodynamic possibilities of the hydrochloric acid / chlorine gas system are consequently used for the individual steps of the process. In this way, problematic solvents, such as for example CCl 4, can be dispensed with in order to recycle untreatable chlorine quantities to the process. When foreign water is given up for the separation of the HCl parts in the gaseous product, undesirable diluted acid will not be generated. The whole gas treatment system behind the reactor with the steps:
Injection coolant, apparatus for phase separation, drying, liquefied / recovery chlorine distillation, purification of purge gas with hydrochloric acid by means of an absorption-entrainment system and recovery of useful gases by oxygen used as drag gas, represents a procedure that saves a lot of energy and easy to control. Next, the individual stages with their advantages will be explained successively. In the case of the optimal solution of the procedure all the stages will be used. In the case of less demanding requirements, individual stages may be discontinued. The refrigerant by injection works with direct introduction by means of nozzles of refrigerated concentrated hydrochloric acid. The excesses of this hydrochloric acid, which can also be charged with traces of catalytic saline fusion from the reactor, are enriched, according to an additional development of the process, in a proper cooling-extinguishing circuit in relation to the entrained quantities of catalyst. and they are sent to a pre-extinction arranged in the head part of the reactor. They can also be used for the dissolution of the solidified fusions in the reactor after cold stops. In this way, a recycling of the expelled amounts of the catalyst is achieved. The reaction water is separated in the phase separation apparatus, which is formed as a counter-flow column, by direct condensation over concentrated, cooled hydrochloric acid in circulation. This has two advantages: a) The gaseous product, released from the water of the reaction, has only a small residual moisture, due to the small partial pressure of the water vapor on the concentrated hydrochloric acid, which has a positive effect on the consumption of acid for drying (for example sulfuric acid) in the drying of the reaction gases. b) The saline, saturated, concentrated hydrochloric acid has absorbed an amount of the unconverted gas HCl corresponding to the amount of the reaction water, and can be used for other process steps. It intentionally desists from the complete separation of the HCl parts in the gaseous product, since extraneous water would be required for this. In the later stages of processing these parts of HCl behave similarly to that of inert gases. For the separation of the inerts and the rest of the HCl, the chlorine must be liquefied. The cooling power in the chlorine bleach is in this case taken from the chlorine itself. Liquid chlorine is used as a refining agent. To do this, decompose on the secondary side, in the chlorine liquefier, the liquid chlorine that comes out under liquefaction pressure, up to the supply pressure to the consumer. In this case it is cooled correspondingly to the decrease in pressure and takes, in its evaporation, the condensing heats of the chlorine offered on the primary side under pressure, it produces its liquefaction and in this case it separates the inert gases and the gaseous HCl. In this process form, considerable savings in external cold for the chlorine bleach as well as in external cold for the chlorine removal are advantageous. A small cold installation simply serves to re-chlorinate the chlorine at lower temperatures. For this, the proportion of chlorine in the waste gas will be reduced in such a way that, during its recycling to the reactor, the equilibrium of the reaction is not disturbed in a remarkable manner. During the bleaching of chlorine, a part of the gaseous HCl is physically dissolved. In the case where the HCl parts impair the subsequent reactions, a separation is offered by means of a simple distillation column. The cost is low since the chlorine and HCl lines are separated by approximately 50 ° C. Chlorine distillation can be carried out at relatively lower temperatures with residual heats, since the boiling temperature of the chlorine is approximately 20 ° C at the liquefaction pressure. Advantageously, the HCl-rich overhead gas from the distillation is recycled back to the suction side of the chlorine compressor. In this way, the proportion of HCl in chlorine increases before liquefaction; however, the physical solubility of HCl in the liquid chlorine increases considerably less, so that, in this way, the gaseous HCl can be almost completely recycled to the reactor with untransformed oxygen and chlorine residues. in the recycle stream. A special problem during the treatment of the gaseous product is the control of the level of foreign gases in the gaseous product stream. The foreign gases are fed with the gases of the educt, especially with gaseous HCl from the previous stages of production. By recycling the unconverted parts of the reactant gases into the reactor, the level would be permanently increased in extraneous gases and finally would significantly disturb the development of the process. Therefore, a partial quantity of the recycle gases has to be discharged, which means a non-negligible loss in chlorine and in gaseous HCl. In addition, these gases would have to be charged through an absorption facility, where they would have to be neutralized, with consumption of chemical products, for example sodium hydroxide solution and discharged as waste water loaded with salts. For the recycling of the parts of useful gases constituted by chlorine and by HCl from the recycle stream from the additional refrigeration stage after the bleaching of the chlorine (hereinafter referred to as "purge gas") to the reactor, it will be used particularly advantageous is the concentrated, saturated hydrochloric acid, which comes from the separation of the water from the reaction (apparatus for phase separation or countercurrent column). For this purpose, the concentrated hydrochloric acid, which exits the entrainment column, will be cooled and brought into contact in a falling film with the purge gases which are under the compression pressure, in the absorber column under pressure to counter-pressure. current. By taking advantage of the good solubility of chlorine in the concentrated hydrochloric acid and of the good absorption capacity of a concentrated hydrochloric acid and cooled below the saturation temperature, for additional amounts of HCl, this hydrochloric acid will be further concentrated and It will be charged with chlorine. In this case it is heated due to the heats of solvation. This hydrochloric acid is decompressed to normal pressure, combined with the hydrochloric acid-water of the reaction, hot discharged and introduced into the drag column. Hydrochloric acid is released from the load of chlorine and excess amounts of HCl, with the oxygen used as the entraining gas, which is fed in the lower part countercurrently, cooling with dissipation of the heats of solvation. The cooled hydrochloric acid is fed again under pressure into the absorption column and the charging cycle can be repeated. The purge gas stream can thus be released from chlorine and gaseous HCl to small debris. Neither are strange means required for this. The charged oxygen is fed to the reactor. The hydrochloric acid, corresponding to the water of reaction, can be discharged to the desired concentration and represents a valuable by-product. In this way they must finally execute almost all the currents of the side of the educt and the product, a thermodynamic work in addition to its proper function and in this case they help to avoid the use of strange means. In a particularly advantageous variant of the described process, the hydrochloric acid-water stream of the reaction proceeding from the phase separation apparatus will not be directly cooled and fed back into the upper part, with only the corresponding amount being discharged from the drag column. water of the reaction. On the contrary, all the circulating hydrochloric acid stream will be carried to the trailing column, there it will be enriched with the oxygen used and, if necessary, with additional heat input, it is cooled and fed back to the phase separation apparatus. In this way, gaseous HCl from the gaseous product stream will additionally be bound, blown again through the tow column and recycled back to the reactor directly with the oxygen used. By correspondingly increasing this circulation of hydrochloric acid, the total amount of HCl in the gaseous product stream will finally be reduced so that the distillation of the liquid chlorine can be desisted for the separation of the dissolved amounts of HCl. The reduction of the proportion of inert gases in the gaseous product stream also improves the conditions for the bleaching of chlorine so that the proportion of external colds for the chlorine relining is clearly reduced and, in the same way, the non-condensed quantity of chlorine decreases considerably. chlorine, which has to be recycled to the reactor.
In the following, embodiments of the invention will be explained in greater detail by means of the drawings. They show FIG. 1 shows a complete flow chart of the process for the treatment process; and FIG. 2 shows a diagram of the process for a variant, in which the total amount of the hydrochloric water is conducted in a closed circuit through the trailing column. present in the water separation of the reaction. In reactor 1, to which the gaseous HCl and oxygen feed are fed, direct oxidation of HCl is carried out to give free chlorine according to the equation
4 HCl + 02 = > 2 Cl2 + 2 H20
This is based, for example, on the Deacon method, in which the two gas-generating educts are brought into contact in the reactor 1, constituted by a phase contact apparatus, with a hot salt fusion of CuCl 2 as a catalyst. As an apparatus for phase contact, a falling film reactor, for example a column of filling bodies, is particularly suitable. The hot reaction gases, consisting of Cl2, HCl, 02, and H20 in the form of steam (crude gas) are cooled immediately after leaving the reactor 1 in an injection coolant 2 (extinguisher). In the extinguisher 2, refrigerated hydrochloric acid is injected from the treatment. The gases thus cooled enter, together with the evaporated hydrochloric acid, at the bottom in the phase separation column 3 for the separation of the water from the reaction. In this case, the phase separation column is constituted by a countercurrent column with, for example, impact plates, in which direct condensation takes place with the cooled hydrochloric acid, which is released at the top of the column 3. In this case the mixture of the reaction gases, which penetrate through the lower part, passes countercurrently through the descending cooled hydrochloric acid, whereby practically all the water vapor is condensed together with the amount of gaseous HCl , corresponding to the thermodynamic equilibrium at the set temperatures, as water of the reaction. From column 3, therefore, always fully saturated hydrochloric acid is pumped through pump 4 and recycled in a partial stream (approximately 92%) to the head of column 3. Other partial flow of hydrochloric acid (approximately 3%) is diverted at the head of column 3 and pumped to injection coolant 2. In the heat exchanger 5 of the hydrochloric acid closed circuit, the hydrochloric acid pumped is cooled. The partial part (approximately 5%) of the hydrochloric acid formed in column 3, which corresponds to the amount of the reaction water, is discharged and sent to a treatment of the entrainment and purge gases, which describe later. The reaction gas remaining in the countercurrent column, which consists of Cl, 02, and N2, as well as a remaining part of water vapor and gaseous HCl, is sent to a washing tower with hydrochloric acid 6 for its drying The joint condensation of the water of the reaction and of the HCl, which leads to the formation of thermally saturated hydrochloric acid in the column in countercurrent 3, results in a very low partial pressure of water vapor in the gas of the conducted reaction subsequently to the final drying, so that very small consumption can be maintained in drying agents (in this case sulfuric acid). After the run through the final drying, the mixture of the reaction gases, released from the water, is compressed in a compressor 7 to a pressure of 1 to 30 bar, preferably 2 to 10 bar, and cooled in a heat recovery unit. chlorine 8, configured as a decompression cooler, in a proportion such that the chlorine is liquified except for a small residual part (approximately 10 to 20%). In this case the cooling power is made available, necessary for the chlorine reclaimer 8, by decompression and evaporation of liquefied chlorine, which leaves the chlorine recuperator, on the secondary side of the recuperator 8. The liquid chlorine obtained is therefore simultaneously used as a cooling agent. In this way, temperatures of -10 ° C to -15 ° C can be established without problems in the chlorine recuperator. The liquid chlorine main stream, separated in the chlorine reclaimer 8, can be further conveyed until the final purification in a distillation column 9, in which the chlorine is released from the dissolved residual HCl, oxygen and, if necessary, from the chlorine. other inert gases, for example nitrogen. The gas, withdrawn at the top of the distillation column, consisting essentially of HCl, chlorine, oxygen and other inert gases, is recycled to the suction part of the compressor 7. The purified liquid chlorine is removed as a product of the process by the bottom of the distillation column 9 and stored in a tank 10. From tank 10 chlorine gas is removed and decompressed in the chlorine reclaimer 8, as described above, and evaporated and, thus, It is used as a cooling agent. The gaseous chlorine, which leaves the chlorine recuperator 8 through the outlet branch pipe 23, is sent to consumers, who use chlorine in chemical processes as raw material. The non-condensed reaction components in the chlorine recovery unit 8, including the residual part of chlorine, are removed at the top and at least partially liquefied in the subsequent cooling stage 11, whose working temperature, with a value from -20 ° C to -30 ° C, it is clearly lower than the temperature in the chlorine reclaimer 8. The chlorinated bleach is combined with the main stream of chlorine from the chlorine reclaimer 8. The remaining residual gases then contain only proportions relatively small chlorine, unconverted HCl, unconverted oxygen, as well as parts of inert gases of other impurities. This gaseous stream is recirculated through a decompression valve 12 and a preheating stage 13 to the reactor 1. In order that the level of the impurities does not increase constantly in the system from one cycle to the other, it has that a partial quantity of the recycled gas is discharged from the system to the reactor 1. This discharge is carried out at the branch point 14. For the use of the HCl and chlorine parts in the discharged gas stream, the hydrochloric acid present will be used in the system. With this finality the gas discharged will be conducted to an absorption column 15, which is made to work with cooled, aqueous hydrochloric acid, coming from the counter-runner column 3, as a working medium. Since the hydrochloric acid leaving the countercurrent column 3 is saturated, it has to be pre-depleted. The depletion is carried out in an HCl blowing column or drag column 16, which uses as the entraining gas the oxygen that is fed into reactor 1 as an educt. The driving column 16 can be heated if necessary. The entrained gases, consisting of chlorine, HCl and oxygen, are removed from the head and cooled to reactor l. The depleted hydrochloric acid is withdrawn at the bottom of the trailing column 16 and is fed through the upper part of the absorption column 15 by means of the pump 17 through a cooler 18. The absorption column works particularly advantageously under the pressure of the compressed gas product. The recycle gas stream from the subsequent cooling stage 11 (gaseous purge stream) is charged thereto countercurrently through the absorption column 15. The hydrochloric acid absorbs in this case the HCl part of the gas stream of recycling, with which it concentrates. At the same time this guarantees the good solubility of the chlorine in the concentrated hydrochloric acid so that - ß - the purge gas stream is also liberated from the chlorine in addition to being liberated from the HCl. The inert gases released from chlorine and HCl are discharged through the head of the absorption column 15. The hydrochloric acid enriched again by the absorption of HCl from the purge gas stream, and charged with chlorine, is then decompressed through the throttle 20 to the pressure level of the stripping column 16 and combined with the hydrochloric acid stream, coming from the countercurrent column 3, before its penetration into the column. the drag column 16. Oxygen, used as entrainment gas in the entrainment column 16, thus absorbs, in addition to the gaseous HCl, also the chlorine from the recycled partial stream of hydrochloric acid, which is recycled to the reactor 1 together with the other entrained gases, as indicated above. The hydrochloric acid, obtained as a by-product (at the bottom of the drag column 16), is therefore free of chlorine. According to a variant of the method shown in FIG. 2, the parts of gaseous HCl which could not be separated in the process according to FIG. 1 under the saturation conditions in column a have been removed directly from the countercurrent column 3. -current 3 and which therefore had to be further processed in the subsequent steps of the process (washing tower with sulfuric acid 6, liquefied chlorine 8, 11, distillation of chlorine 9, absorption column 15) and then recycled to the reactor 1. The advantage is that, in this way, the load is reduced with inert gases in the following stages, especially in the bleaching of chlorine 8, 11 in the not insignificant proportion of gaseous HCl. For this purpose, the installation will be modified in such a way that a further recirculation of the cooled, depleted hydrochloric acid is carried out in the countercurrent column 3. This modification is carried out by means of a recycling conduit 21, which leads from the hydrochloric acid refrigerant 18 directly to the head of the countercurrent column 3 (see Figure 2). The depleted, cooled hydrochloric acid necessary for the operation of the absorption column 15, which works under pressure, is diverted into the recycling conduit 21. By recycling the depleted hydrochloric acid, cooled, in the trailing column 16, it is it will achieve a higher absorption capacity for HCl in the countercurrent column 3. In the countercurrent column 3 a complementary solution of gaseous HCl takes place, since depleted hydrochloric acid and therefore the binding with the recirculated, cooled and depleted hydrochloric acid, additionally made available, is offered. In this way it is achieved that the amount of gaseous HCl leaving the countercurrent column 3 and circulating through the system, is 10% less than in the first variant of the process. Therefore, in this variant of the process, the distillation of the chlorine (distillation column 9) can be dispensed with. The best possible embodiments of the invention have been described by means of FIGS. 1 and 2. As a consequence of a simplified procedure, also within the scope of the invention, the subsequent liquefaction of chlorine 11, the treatment of gases in the absorption column 15 and the hydrochloric acid treatment in the drag 16, when lower requirements are required in relation to yield and purity. Exemplary embodiments Example 1. They are used in the direct oxidation process of hydrogen chloride to give chlorine, per hour, 3,750 kg of HCl and 823 kg of oxygen. Additionally, approximately 80 kg of extraneous gases are dragged (see Figure 1). The gaseous product stream, after leaving reactor 1, contains 3,800 kg / h of chlorine, 1,825 kg / h of unconverted HCl, 187 kg / h of converted oxygen, 828 kg / h of reaction water and 165 kg / of inerts, feed to the reactor, in addition to the starting gases, also recycle gases from the treatment. After leaving the column in countercurrent 3, the water content in the gaseous product stream has decreased to 41 kg / h and the HCl ratio to 1475 kg / h. The other parts remain practically unchanged in the gaseous product. After drying in the drying tower with sulfuric acid 6, the gaseous product stream in the compressor 7 is compressed to 7 bar, it is liquefied in the chlorine recuperator 8 and flows in the form of crude liquid chlorine through the distillation column 9 and from there in the form of pure liquid chlorine to the chlorine tank 10. The chlorine stream discharged from the network for the consumer it is withdrawn in the form of liquid chlorine from the tank 10, decompressed in a throttle 22, refrigerated in this case correspondingly to the supply pressure of 1.5 bar to 25 ° C, dissipates the condensation heats during its evaporation of the chlorine compressed by the compression side of the chlorine reclaimer 8 and liquefies it at approximately -10 ° C. The overhead gas stream from the chlorine reclaimer 8 still contains chlorine parts, which are subsequently liquefied at lower temperatures (-25 ° C) in the subsequent cooling stage 11. The crude liquid chlorine which is discharged in this case it is combined with the main stream and released from the HCl parts in the chlorine distillation column 9. Of the 581 kg / h of HCl dissolved in the crude chlorine, only 30 kg / h reaches the liquid chlorine stream. The exhaust gases from the additional cooling stage 11 are recycled in this example in equal parts as recycle gas to reactor 1 or else they are charged as purge gas stream, coming from the chlorine compression, in the column of absorption 15 of the absorption-entrainment system. At this point it contains 723 kg / h of HCl, 302 kg / h of chlorine, 94 kg / h of oxygen as well as 83 kg / h of inert gases and is exchanged in the absorption column 15 countercurrent with concentrated hydrochloric acid, descending , which has been clearly cooled below its saturation conditions. This hydrochloric acid has a high absorbent capacity for gaseous HCl and offers a good solubility for gaseous chlorine. In these loads of the purge gas stream, an amount of hydrochloric acid in recirculation is sufficient through the absorption-drag system of 15,000 kg / h to purify the stream of purge gases up to 0.2 kg / h of chlorine and 8.3 kg / h of HCl and for discharge as waste gas stream.
The hydrochloric acid charged and heated by about 10 K by means of the heats of solvation, is reduced to 1.3 bar and is fed, together with the hot hydrochloric acid leaving the column in countercurrent 3, to the column of drag 16. The oxygen used with an amount of 823 kg / h absorbs, in the manner of dragging gels, dissolved chlorine with 303 kg / h and excess HCl with an amount of 638 kg / h and combines with the recycle gas upstream of a preheating stage before it enters the reactor 1. The hydrochloric acid is cooled in this case by means of the dissipation of the heats of solution and is re-puffed up to the absorption column 15. The amount of hydrochloric acid, corresponding to Water of the reaction is discharged in the form of 35% hydrochloric acid. In this case, an impoverishment with recycling was discontinued until the HCl parts process. E emolo 2. In a variant of the process (see FIG. 2), the entire hydrochloric acid stream, which circulates through the column in countercurrent 3, is charged through the entrainment column 6, is cooled in the coolant 18 and fed back into the countercurrent column 3. It is further heated before it enters the entrainment column 16 to recycle more gaseous HCl from the countercurrent column 3 directly to reactor 1, in the entrainment process with the starting oxygen with impoverishment of the hydrochloric acid. This modified procedure has as a consequence that the gaseous product contains, after leaving the column in countercurrent 3, in addition to 3,457 kg / h of chlorine, 18 kg / h of water, unconverted oxygen, as well as inerts, still 55 kg / h of HCl gaseous, of which only 31 kg / h remain in the liquid chlorine stream after the chlorine bleach (8) so that in this case the distillation of the chlorine (9 in Figure 1) can be desisted. The external cold requirements for the reli-cuado is, in this example, less than a third of those of Example 1 due to the lower charge with HCl of the gaseous product stream. The amount of hydrochloric acid corresponding to the reaction water of 29% hydrochloric acid is discharged from the system as an accompanying product at the bottom of the trailing column 16. Literary appointments. [1] Che. Eng. Okt. 11, 1976, pages 86-87. [2] DE-OS 1963946. [3] The Chemical Engineer, March 1968, pages EC 41-45. [4] EP 0233 773 [5] PCT Application WO 90/15017 [6 ] DE-OS 1467142 [7] US 4394367 [8] EP 0 517 427. It is noted that with regard to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property: