DE2015781B2 - PROCESS FOR OBTAINING AN UNREACTED REACTION PARTICIPANTS FREE UREA SOLUTION - Google Patents

Description

The invention relates to a method of extraction a \ on unreacted reaction participants of the a ° ] -larnslofiV \ nthese free 1 [arnstoff solution by distillation in several stages with known temperature and pressure conditions and recirculation of the unconverted raw materials.

The products emerging from the synthesis device during the 1 larnslofisvniliese of carbon dioxide and ammonia, such as. B. Carbaniat. Ammonia or Oarbonal need to achieve complete conversion of the starting materials introduced into the orrichumg Synthesev and to obtain an aqueous i ^i> solution \ on virtually pure urea as a finished product in the device can be recycled.

It is known that the separation of urea of those emerging from the synhesy reserve Products normally takes place in several stages at different pressures. In the first stages one works with pressures within a range from 15 to 40 kg cm-, while one works in the end pins at much lower pressures close to atmospheric pressure. In the valley only at 5> If the push button is very low, the process content of the remaining ammonia and carbon dioxide in the uric acid solution for an insignificantly short period of time are reduced, and this is because the distillation of the remaining compounds of the Urinary dissolution cannot be carried out at temperatures that are too high, which would result in the risk of that see the urea with the formation of by-products, e.g. Pj. Biuret or Tntiret, decomposed.

The ammonia Co obtained in the distillation and carbon dioxide-containing vapors must be used to achieve a complete conversion of the starting materials in urea can normally be recovered (process with a closed Cycle). The stages of distillation are generally in the known processes either with distillation towers or with shell and tube heat exchangers and following it

Separators to separate the gaseous phase

carried out.

The "use of distillation towers is most expedient from the point of view of process technology, since it results in the greatest separation of X ^: " less valuable "components (NH ₃ and CO ..). and the regulation of the distillation of the less volatile components (H ₂ O) enables which should be the lowest. In fact, Cs is erfnrdc: - borrowed. daLWlie obtained from the distillation stages., üasföriTiiiier. Mixtures only in the depressurizing valve! - rich ar. Water are where its presence is essential to ih: _: ■ complete condensation without the addition of \, - fahreiivv.as-ei.

The presence of this water is especially important in the case of the Deslillation steps. <eiesinit De- '! lalioiiskulo-inen or with 1 ■ ilmwärmeauslaiische:. which work at low pressures: precisely here de ν lier'i a certain amount of water and allows s ··, '_ condensate -'. rion of the gaseous products without ... · of process water. On this·? It is wise to determine the amount of water in the synthesis process; ■ _ to limit the current to be returned to values. . '■ are useful for the Hanistoffsyniliese. In the ^; higher pushers, working levels are located. _:: .. the: ibz.uireniiende: '.' I components from almost ^ chlie · . in the szasiformc-n state, while in the last Sv: also an amount of L-criu ^ e Wa-scr is distilled. v. . · ■. the other gaseous components with gcii, i_ ■. Portion i :; the liquid are present.

In one of the processes described in the French patent document 1 2Ov - - _{: the W 11} - men-'e should / was also low in the return in the circulation. However, there the urine · .. · is left there. s \ ni! reading device coming solution in e;, ...: Sepaialor expand and so separates off the ammonia present in the L ber - c. I3ies.es in the over ·. '., Existing ammonia is mixed with water. in order to separate the small amounts of carbon contained therein as ammonium c:; rbanial. !; ■ _ ■ F-fiinding is now running a method to t _iL · :. .-staiuL in which washing with the help of Wa., .. i klt-me.i part of the water obtained by the reaction of the harm; · ■; ": 'formation.

Also, according to the French patent specification 1 30ίΊ i <\ is as feedback ^ .Power an aqueous Ammoiiüir.icarbainatlösiing erhallen. In addition, there is in the gases that are obtained by heating and expansion with subsequent condensation. Water available.

Like eiwähni. are generally used in Destillaiinns-Üirnie /v.·: application, the use of which is, however, extraordinarily expensive. process parts must also be bought, since their operation is critical because of the formation of solid phases such as carbamate or carbonate.

Carrying out the distillation using shell and tube heat exchangers with Adjacent separators eliminate the above disadvantages, but these are procedural Unsatisfactory from the point of view. The reason is that the final weight obtained. if the gaseous phase itself in its formation in the distillation device in the Is conducted cocurrent and in the presence of the liquid phase along the entire heat exchanger, if not the separation of the gaseous phase

takes place in a suitable separator, determined to be negative in relation to donations obtained when using a distillation tower. So is. The distillation of the more volatile components is much more effective and a difficult-to-control younger distillation of the less volatile components (M ₂ O) occurs. The liquid flowing through these heat exchangers thus occupies the entire cross-section of the tube; In: during the flow, the liquid is heated by heat exchange with a gentle solvent which flows on the mania cord of the heat exchanger.

Due to this warming, the ammonium arbamai contained in the i Tüssigkcil is split off or / erset / t. The gaseous / erset / iuigsi ud'ikt attempt η / UMmmuii with all in the In the liquid, the clans, themselves \ on the liquid ; 'u separate: however, this separation is not allowed on the basis of the fact. dai.i the liquid den entire Rohrquerseh.niii occupies, so dall one Separation just / u expect is. when the mixture is out the v \ iirmausaus.tier enters a C '.as-1 li, - fluid wedge separate entry. This separation due to continuous conact, the two phases along the entire heat exchanger tube is not the best.

In every heat exchanger is due to the Direct current \ of liquid and gases the an / alil the equilibrium stages attainable between liquid and gas are small, guided liquids and gases.

From NOrsteliendem it follows that only in the For mares with low pressure it becomes possible to achieve a near / u complete separation of animal more volatile components carry out, the resulting gaseous mixtures no longer the / u their complete Condensation can contain sufficient amount of water, as the mineral solution in the preceding ! Hole and media pressure desililation stages considerably under high pressure of water is.

W-rgufen with the known measures should now the separation h / w. Cleaning ir. With better efficiency and in simpler, i. ii. fewer costly ways.

This is achieved according to the invention by that in a process of the type mentioned, the stepwise distillation in I ilmvvürmeaustauschcrn at temperature and pressure conditions from 50 to 25 <> C or 0.1 to 250 at is carried out.

/ Weekly is used in distillation an inert gas with, in particular that in the llarnstoffsynthese generated gas mixture, as a so-called Strippermiltel.

Due to the in itself unusual in this process Use of film heat exchangers will help entire device simpler compared to distillation columns and more effective compared to conventional heat exchangers. One must keep in mind that distillation columns are very expensive devices, their use out of proportion to the success to be achieved.

By the measure according to the invention In addition, the disadvantages of the distillation columns that occur in certain but possible cases \ Avoided in which testes ammonium carbamate may form, causing pipes and plates clog.

The separation of the gaseous components is thus carried out in a simple manner with the help of devices, which are particularly cheap compared to destination columns, which is a fuel solution with a degree of purity can be expected, and with water almost completely separated in the final stages and in small amounts.

Enter a film heat exchanger is an exchanger of any shape including those using tubes in which the

ίο the liquid to be treated in the form of a film . is shared. the top down on a heated one Surface falls that provides the required heat. The 1 lei / riedium can either steam (water vapor) or any other heating means. The mn

ι ;, HiHe Desii'uiiiiMissiLifen carried out by FiUnwärmeauslauseliern may self-stripping effects due to ties be carried out without the introduction of any stripping agent: if desired, it is however possible, a Sirippermiuel on the ground

yo em / iilüien.

In this lalle the Mitiel can consist of an or order multiple components. The inertgassiroir.i of the plant, tier usually at different Pressing vented into the air may vary depending on the applied procedures can be used appropriately for this purpose. Viii help aes according to the invention applied substitute, the following results can be obtained:

1. Immediate separation of a large part of the volatile components Phase in the. upper separator of the air reservoir itself. This separation is a consequence of the so-called Flash 'phenomenon. the one prevailing at the transition of the mineral solution from the height pressure animal Level occurs at a lower pressure.

2. A self-ripping effect, as there is a film of liquid flowing from top to bottom in the exchanger runs, meets an upward gaseous stream, which is more of lighter components and more impoverished.

Iniols lie in the end point of the dropout primarily the less dense components in the gaseous phase; this fact restricts the distillation of this component from the liquid phase.

The following examples illustrate the invention.

example 1

5 "from one at a pressure of 16 atm and 153 C operated still. with no stripping agent was introduced from the outside, the experimental data given in Table I below were obtained α halls compared with those.

obtained with normal jacket and tube stills.

From these data it can be seen that the residual NEE ₁ and CO ..

in the Elarnslofflösimg was considerably lower than normally with the help of shell and tube heat exchangers obtained content operated under the same temperature and pressure conditions while the residual water content was higher. Also: ci pointed out that these values are absolutely comparable with the values obtainable using distillation towers was.

Table I.

CO.,
H ₂ O
urea

Composition of
Soil fraction
of the distillation tower
in percent by weight

6.2

K3

27.5

65.0

Composition of the soil fraction in the FiIm distillation in percent by weight

1.1 27.9 65.0

Composition in the separator of the jacket and pipe style

lators

in percent by weight

8.5

2.2 22J 67.0 dates obtained with the corresponding dates obtained with normal jacket and tube stills. Besides, be it should be noted that these values correspond to the values obtained for distillation towers were absolutely veralichbar.

Table 11

In particular, the components emerging from the film desillators were compared to the Values observed with the shell and tube heat exchangers normally used have made the following changes in percent by weight:

NH., - content reduced by 29%, COo content reduced by 50%. HoO content increased by 20%.

Example 2

In a distillation stage operated at a pressure of 4 atm and 132 ° C., in which no stripping agent was supplied from the outside, the experimental NH _{3 indicated in Table II below were obtained}
COo
H ₂ O
urea

Composition of
Soil fraction
of the distillation tower
in percent by weight

Composition of the odenfraklion in FiImi! Estillation in percent by weight

Composition in Jem separator of the Vlanicl

and R destilUi in percent by weight

> hrturs

2.4

0.5

27.2

69.9

1.5

0.7

26.8

70.0

3.5

1.5

22.0

73.0

In detail, the following changes to the components in percent by weight were made in the Film stills leaking solutions compared to the values with those normally used Shell and tube heat exchangers were obtained.

NH ₃ content reduced by 28.5%, COo content reduced by 53.5%,

H ₂ O content increased 18%.

Claims (2)

Patent claims: 1. Procedure for obtaining a \ un niclit converted reaction parts of urea synthesis free urine solubilization by distillation in several stages at liier for known temperature and pressure conditions and recycling of the unreacted starting materials, d a J u r c h g e k e η η ζ e i c h net. that one gradually Distillation in Filmsvürmea.! Static at temperature and pressure conditions from 50 to 250 C b / w. () .l to 250 al. 2. The method according to claim 1, characterized in that that an inert gas is used in the distillation, especially that of the! urea thesis generated Gas mixture, as a so-called Siripperniiuel with- \ erw ends.