DE633294C - Process for the continuous production of concentrated NO-containing nitric acid - Google Patents

Description

Process for the continuous production of concentrated N204-containing Nitric acid It is known to produce nitrogen oxides from water or dilute nitric acid and oxygen under pressure and at elevated temperature, concentrated or highly concentrated To produce nitric acid. It is also known that there is an acceleration the course of the reaction can then be achieved if one for a fine distribution between liquid and gaseous phase takes care.

It has also already been proposed that this implementation be one with random packings equipped fractionation column in such a way that dilute nitric acid, Nitrogen tetroxide and oxygen introduced at the top of the column, with im upper part of the column the oxidation of nitrogen oxides with the formation of nitric acid takes place, while by heating the lower part of the column to 100 to z25 ° C a fractional distillation of the acid trickling down in. Such a way achieved becomes that a hydrous nitric acid is obtained at the lower end of the column, while at the point in the middle part of the column where the temperature is 86 to 9o ° C, anhydrous HN03 is present in vapor form, which is withdrawn there can.

In this known method, by regulating the temperature in such a way that this in the middle part of the column is the boiling point of the anhydrous HNOg (86 ° C) already exceeds and further down to 100 to 125 ° C increases, reaches that the acid mainly formed in the upper part of the column on their way down through the fractionation process along with the lower ones Nitrogen oxides, such as NO and N203, also the nitrogen tetroxide completely withdrawn is, so that the anhydrous nitric acid obtained in the middle part of the column is already free of nitrogen tetroxide while below this point. in the Column only a fractional distillation of water-containing nitric acid proceeds with the success that at the lower end of the column a weaker, completely Nitric acid freed from nitrogen oxides at one of the temperature prevailing there corresponding water content is obtained.

In contrast, it was found that when carrying out the reaction between water or dilute nitric acid, excess. Nitrogen oxides, such as B. nitrogen tetroxide, and oxygen at increased pressure of my column or a column-like apparatus with supply of heat to the lower part of the column and Condensation of the vapors formed in the upper part of the column z. B. by water or air cooling achieves considerable technical and economic advantages if man with the introduction of oxygen in the lower part of the column, the supply of heat regulates to the lower part of the column so that the boiling point there accumulating N204-containing nitric acid at the prevailing pressure, so that at none Place the Column, however, the boiling point is nitrogen oxide-free and anhydrous -Nitric acid can be achieved. In this case, the implementation process The lower nitrogen oxides formed are continuously discharged upwards, Stidk. "stofftetroxyd but in such a quantity in the -i # ';; Countercurrent to that introduced from below. oxygen Leave the liquid trickling down in the column, with constant new formation of H N 03 in the liquid trickling down at the lower end of the column liquid nitric acid with the desired maximum content of HN03 as well as with a z. B. 5 to. 2o o; o amount of N20, accrues.

This mode of operation is based on the following knowledge in the Column permissible reaction processes: The formation of concentrated nitric acid when nitrogen tetroxide is reacted with water and oxygen continues to run the following sum equation (gross equation) - 2N20, + 2H> .0 + Oz = 4HN03. Which here, however, there are chemical and physical processes that take place in detail extremely versatile and complicated, so that the implementation in detail does not follow of the above equation, especially since molecular oxygen does not even under pressure is able to oxidize N204 to N205 and the nitrous acid among the in question Is not oxidized directly to ENT under the following conditions.

The course of the various Processes can be identified by the following intermediate processes.

On the one hand, existing N "04 reacts with water or dilute nitric acid forming H N 02 + H N 03 according to N., 04 + HZ 0 - H N 02 + HN 03. (2) On the other hand decomposes under the prevailing reaction conditions that formed according to equation (2) HNO2 mainly in N203 and H20 according to the following equation: 2HN02-Nz03 + H20. (3) That, e.g. B. N2 03 resulting from this equation is, if more sufficient Oxygen is present, oxidizes to N204 Dach-2N203 + 01- = 2N - 104- (4) The rest But N203 reacts with already formed H N 03 according to N203 + SHN03 = 2N204 + H20, (5) The processes according to equations (2), (3) and (5) run essentially in the liquid phase, while the process according to equation (4) is essentially takes place in the gaseous phase.

.i` »The conversions according to equations and (5) have an effect on education from H hr 03 2. I oppose equation (2). It is essential that N @ O, 1 opposite strong nitric acid is indifferent, while ENT. and N203 of strong nitric acid are rapidly oxidized in terms of the reverse equation (2) and equation (5), so that with increasing HN 03 content of the acid already present, the decomposition occurs according to these equations, with the elimination of water, occurs increasingly faster.

Based on this knowledge, the aim of the present invention is made therein, the known reaction of water or dilute nitric acid with Nitrogen oxides and oxygen in a column or in a column-like apparatus to carry out under such conditions that all the way in the column trickling down liquid the new formation of H N 03 in the sense of equation (2) promoted, the decomposition of H N 03 formed in the sense of the reverse equation (2) and equation (5) is prevented as far as possible.

This is achieved according to the invention in that, in contrast to the afore-mentioned known method -on the one hand, the supply of heat to the lower part of the Column is so limited that there only the boiling temperature of the accumulating there N204-containing nitric acid and consequently the boiling point at no point in the column nitrogen-tetroxide-free and anhydrous (or even nitrogen-oxide-free hydrous nitric acid, as in the known method) is achieved (with the boiling temperatures on the prevailing pressure are related) and that on the other hand the oxygen in the lower Part of the column is introduced.

The latter measure achieves that all along the way that trickling down in the column in countercurrent to the rising gases and vapors Liquid in the gas phase, the new formation of N204 through oxidation of what is present N203 can take place through the oxygen supplied from below. Through the aforementioned Limitation of the heat supply is achieved that the trickling down liquid on their way through the column through the rising gases and vapors, namely with considerable participation of the oxygen flowing upwards from the bottom, to be sure those formed by the conversion processes according to the above equations (2) and (3) lower Nitrogen oxides, such as N20.3 and H N 02, as well as N O, are largely permanent be withdrawn, but that has not yet been converted to H N7 03 according to equation (z) Most of the nitrogen tetroxide remains in the liquid.

As a result of this measure, the trickling down is all along the way Liquid Opportunity for the formation of new nitric acid in terms of the gross equation above (i) given while by the continued removal of this according to the equations (z) and (g) primarily formed lower nitrogen oxides the reducing influence of the same on the already formed HN03 in the sense of the reverse equation (a) and the Equation (5) is largely eliminated. By working together. the aforementioned Factors and the associated promotion of acid formation and suppression of the processes counteracting the formation of acid, it is according to the invention enables the formation of concentrated acid in the shortest possible time and under to achieve the most advantageous economic conditions imaginable.

Another advantage of the new process is that it is even Pressure and temperature stress on the equipment material, causing shearing and swelling of the acid-resistant linings is largely avoided.

As is known, the exothermic reaction is caused by the temperature and affects the pressure in the sense that for the production of highly concentrated acids . Correspondingly higher temperatures and pressures are required. The reaction temperature can also through heat exchange z. B. between the discharged warm acid and the supplied oxygen regulated in known heat exchange devices will.

For the implementation of the method you can, for. B. a dividing element, use a distillation column containing sieve trays, Raschig rings or the like, which in its lower end part with a z. B. heatable by means of a steam jacket Liquid sump and is provided with a dephlegmator in its upper end part, with the water or the diluted nitric acid in the upper part and the oxygen is introduced in the lower part of the column. The nitrogen oxides can be in the upper Part or especially in the production of highly concentrated acids in the lower Part of the column are introduced.

The nitrogen oxides are used in excess, e.g. B. such that the Final acid contains about 5 to 20% N204. The final acid can then be removed after removal can be bleached in the apparatus using conventional methods. It is useful to use the Bleaching in a special distillation column directly connected to the reaction column to undertake, with the nitrogen oxides distilled off particularly condensed and then, together with fresh N20.1, to be fed back to the reaction column.

By suitable dimensioning of the arranged in the lower part of the column Liquid sump can be the residence time of the reaction liquid in the pressure apparatus be expanded and regulated according to the respective requirements. A Such a bottom can also be obtained through a sufficient number of suitable column trays replace or divide into smaller swamps.

The oxygen required for the process is in, the lower part the column either introduced above the liquid level or what is special - is expedient into the liquid itself or through the aforementioned liquid sump in fine distribution z. B. pressed in using fine-pored sieve plates.

The uniform supply of N204 and water or dilute nitric acid, which ensure that a constant ratio of the reaction components is maintained must, is expediently done by gear pumps. But it can also be supported by other funding, such as B. piston or rotating vane pumps are effected.

To an excessive impairment of the oxygen pressure as a result To avoid contamination of the sanitary material with nitrogen, argon, etc., one leaves expediently always in the upper part of the column some exhaust gas, z. B. about zo to 2o ojo of the compressed gases, escape.

For the successful implementation of the procedure, one is possible regular supply of the reaction components and a corresponding discharge of the finished crude acid is important. The continuous drainage of the acid is thereby most suitably guaranteed by sufficiently large float elements. For in the event of a swimmer malfunction, it is advisable to use electrical ones Provide safety devices or contacts that work in such a way that when excessive increase in the liquid level in the reaction apparatus of the gas and the flow of liquid is automatically interrupted.

In the case of low-pressure processes, such as those used for less highly concentrated acids come into use, you can also use the acid drain z. B. also by a liquid barrier actuate. For continuous outflow the exhaust fumes are voxfortable to provide the usual R.eguliex organs in high-pressure systems. The exhaust gases can What. especially with. Low-pressure process. Is. Expedient, also. If necessary, by a such liquid barrier can be discharged through it.

The parts of the apparatus exposed to the action of acid are expedient according to the acid concentration and composition in question made of ferrosilicon, clay, quartz, aluminum or similar corrosion-resistant material manufactured or disguised with such.

Claims (1)

PATENT CLAIM: Process for the continuous production of concentrated N2 04 -containing nitric acid by reacting water or dilute nitric acid with nitrogen oxides and oxygen, the liquid in intimate contact with the vaporous and gaseous reaction components in a column-like apparatus, one by supplying heat to the lower one Part of the column - and condensation of the vapors formed in the upper part of the column generated temperature gradient are passed through, characterized in that with the introduction of oxygen from below, the heat supply to the lower part of the column is regulated so that the boiling point there is N204-containing nitric acid is achieved at the prevailing pressure, but at any point of the column sfickstofftetroxyd- the boiling temperature and anhydrous nitric acid can be achieved at the prevailing pressure, that is, for example, at a pressure of o, 8 to i, z atm. a temperature of 3o to 35 ° C, so that although the lower nitrogen oxides formed in the reaction process are continuously discharged upwards, nitrogen tetroxide remains in the liquid trickling down in countercurrent to the oxygen introduced from below in the column in such an amount that under constant new formation of HNO3 in the falling liquid at the lower end of the column a liquid nitric acid with @ the desired. Maximum content of HN03 as well as with a z. B. 5 to 2o 0116 amount of N20 ¢ is obtained.