DE2344918A1 - IMPROVED PROCESS FOR THE RECOVERY OF HYDROGEN CYAN - Google Patents

Description

PATENT LAWYERS j O / / Q -1 Q

Dipl .-! Ng. P. WIRTH Dr. V. SCHMIED-KOWARZ1K Dfpt.-Ing. G. DANNENBERG Dr. P. WEINHOLD Dr. D. GUDEL

281134 6 FRANKFURT AM MAIN

TELEPHONE C061I)

287014 GR. ESCHENHEIMER STRASSE 3Θ

SK / SK

MAHLER ET AL PID-38-R

EGG. DuPont de Nemours and Company Wilmington, Del. /UNITED STATES

Improved process for the recovery of hydrogen cyanide

The production of hydrogen cyanide is known, in particular by the Andrussow process (cf. US Pat. No. 1,934,838); this takes place through the reaction of methane with ammonia and air over a platinum metal catalyst at an elevated temperature (about 100O ⁰ C). This process produces a mixture of products including the desired hydrogen cyanide and water, unreacted ammonia and methane, nitrogen, argon, hydrogen and carbon oxides. An improvement on the Andrussow process, in which the reactants are mixed with steam prior to reaction, is described in US Pat. No. 3,667,907.

Such a product mixture serves as a frequently used source of hydrogen cyanide, especially where this is in the form of an alkaline one Solution such as one made of an alkali or alkaline earth metal can be used.

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For purposes where practically anhydrous hydrogen cyanide required, complicated and costly rectification and isolation procedures were required to create a satisfactory one Product necessary. Furthermore, there has also been a more efficient utilization of hydrogen cyanide in the production of Cyanohydrinan, such as acetone cyanohydrin, which is an important intermediate in the manufacture of methacrylate resins, is the target an essential research. Therefore, improved methods of utilizing the hydrogen cyanide contained in gaseous mixtures have been developed sought in the manufacture of ketone cyanohydrins and the creation of hydrogen cyanide in a practically anhydrous form.

The present invention now provides a method for obtaining the enthafenen in a gaseous mixture hydrogen cyanide, which is characterized in that (a) the gaseous mixture with an aqueous solution containing about 1 wt -.% Up to the time required for a saturated solution Contains amount of an alkali metal carbonate, at a temperature between about 15-150 C. and a pressure of at least 0.5 at to absorb the hydrogen cyanide and to form an aqueous product solution containing alkali metal cyanide and alkali metal bicarbonate, while at the same time expelling the unabsorbed gas from the Product solution treated; (b) the aqueous product solution from (a) with a ketone having 3-15 carbon atoms at a temperature between 10-150 C. ^D under a pressure of at least 0.5 at the formation of a cyanohydrin-ketone mixture, and for regenerating the alkali metal carbonate in the aqueous solution in

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stirs, the concentration of the alkali metal carbonate in the aqueous solution from step (a) being such that the cyanohydrin-ketone mixture formed in step (b) is practically immiscible with the aqueous solution containing the regenerated alkali metal carbonate; separating the aqueous alkali metal carbonate solution from the cyanohydrin-ketone mixture and recycling the carbonate solution to the gas absorption stage (a); and the cyanohydride-ketone mixture wins. The gaseous mixture in step (a) preferably with an aqueous solution having a Kaliumcarbonatgehalt of 25-45 wt -% treated and a pH of at least 9.0, and the product solution obtained in step (b) to form. corresponding cyanohydrin-acetone mixture brought into contact with acetone. The cyanohydrin ketone mixture obtained in step (b) is preferably subjected to at step (c) a temperature of between 50-160 ^C and a pressure of 0.1-5 C. to give the corresponding ketone and hydrogen cyanide

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regenerate substance from / cyanohydrin and hydrogen cyanide and Gain ketone; and the gaseous mixture is in step (a) in particular with an aqueous solution containing Alkali metal carbonate of 10-45 wt .- ^ and a pH of min 9.0 at a temperature between 40-100 C. and a pressure between 0.5-5.0 at, while the aqueous product solution with the ketone in stage (b), in particular at a temperature between 25-10 ° C. and a pressure between 0.5-5 at is brought into contact. The ketcn in stage (b) is preferably methyl ethyl ketone, cyclohexanone or 3-methylcyclohexanone, and the alkali metal carbonate is preferably sodium or potassium carbonate. The gaseous one containing the hydrogen cyanide

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Mixture in stage (a) is preferably from the reaction of Ammonia, methane and oxygen over a platinum metal catalyst obtained at elevated temperature. The cyanamide and the ketone that result from the cracking of the cyanohydrine in stage (c) are formed, are subjected to an acid wash and then distilled to practically anhydrous hydrogen cyanide and to deliver the corresponding ketone from the cyanohydrin.

The ketone cyanohydrin together with unreacted or excess Ketone should be mixed with the aqueous, the alkali metal carbonate containing phase be practically immiscible, so that it can be obtained as a cyanohydrin or cyanohydrin-ketone mixture can be easily separated. The cyanohydrin phase can also be thermally decomposed (b) to add ketone and hydrogen cyanide regenerate.

The stages shown above are represented by the following equations with sodium being given as a typical alkali metal and methyl ethyl ketone being given as a typical ketone.

Andrussow—
(a) converter

HO,

HO, CII ₄ ,
HCN, Ar,
CO, CO,

ΜΗ-

HaCN + NaHCO +

HO, Ar,
IiH-, CO,

^C0 2> ^N 2
H ₂ , CH4

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(b) MaC »+ NaHCO ₃ +

OH

Na CO + CH-C-2 3 ^ CN

_(c) CH ₃ J-CH-γ * OH ₃ -CC ₂ H ₅ + HCH CN

As shown above, the HCN contained in the gaseous products from an Andrussow reactor is absorbed in an aqueous solution of an alkali metal carbonate. Aqueous carbonate solutions from approximately 1-strength solutions to saturated solutions can be used. As cautioned, it is essential that the cyanohydrin formed in step (b) or the cyanohydrin-ketone mixture is practically immiscible with the aqueous phase in order to allow the reaction products to be easily separated off in this step. If the ketone is acetone, then the alkali metal carbonate preferably potassium carbonate in concentrations of 25-45 weight used in step (a) -.% Of the aqueous solution. If ketones with more than 3 and up to 15 carbon atoms are used, the alkali metal carbonates preferred in step (a) are sodium or potassium carbonate in concentrations of 10-25% by weight . In any case, the concentration of the alkali metal carbonate used in step (a) is such that the cyanohydrin-ketone mixture formed in step (b) is practically immiscible with the aqueous phase.

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The molar ratio of carbonate to hydrogen cyanide should exceed the value 1 before absorption and should also do so in particular after absorption. The pH of the absorbent solution should be above 9. The absorption temperature is usually preferably between 40-100 ⁰ C maintained between about 15-150 ⁰ C,. The pressures can vary from sub-atmospheric to super-atmospheric pressure. Usually the experience takes place at a pressure of at least 0.5 at, preferably between 0.5-5 at.

After the absorption stage, the aqueous, alkali metal cyanide and containing bicarbonate and unused carbonate Solution as mentioned above brought into contact with a ketone, a cyanohydrin ^ or a cyanohydrin-ketone mixture formed and the alkali metal carbonate is regenerated. The ketone can contain 3-15 carbon atoms and can be aliphatic or alicyclic and contain aromatic substituents. Typical ketones include acetone, methyl ethyl ketone, methyl butyl ketone » Methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, 3-methylcyclohexanone and cyclododecanone. Methyl ethyl ketone, Cyclohexanone and 3-methylcyclohexanone are particularly preferred if a practically anhydrous cyanogen is desired as the product will. The amount of ketone used should usually be over the stoichiometric amount, the excess not being critical and usually by economic considerations is determined.

The reaction temperature may be between 10-150 ⁰ C., preferably between 25-100 ⁰ C. lie. As in the absorption stage you can

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the pressures vary with sub-atmospheric and super-atmospheric pressure. Usually this step is carried out at a pressure of at least 0.5, with a range between 0.5-5 atm being preferred. In the cyanohydrin reaction, the regenerated alkali metal carbonate can be used containing solution are returned to the absorption stage after separation from the cyanohydrin phase.

After the step of contacting an aqueous solution containing alkali metal cyanide and bicarbonate with a corresponding ketone to form the corresponding cyanohydrin or the cyanohydrin-ketone mixture, the cyanohydrin-ketone mixture can be separated from the aqueous phase and obtained by known methods; or it can optionally be thermally decomposed together with hydrogen cyanide to regenerate the ketone. For this step to a temperature between 50-160 ⁰ C. and a pressure of between 0.1-5 usually is used at. The hydrogen cyanide is usually subjected to an acid wash and, if necessary, can be further treated to form the practically anhydrous product. The ketone can easily be separated from the more volatile hydrogen cyanide and recycled to the process.

In addition to the extraction of HCN from the well-known Andrussow conversion reactors this improved process can also be used for the recovery of HCN from other HCN processes, such as e.g. Degussa process, as well as from other gaseous streams -a mixture of HCN with any or all of the following materials are used: ammonia, nitrogen, hydrogen, Hydrocarbons, oxygen, carbon oxides, argon, nitriles

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and water. The method according to the invention is particularly suitable for the extraction of hydrogen cyanide in the form of the extremely valuable Cyanohydrin intermediates for the manufacture of the important methacrylate resins as well as for the production of hydrogen cyanide in practical anhydrous form, as it is suitable for large-scale syntheses, e.g. the hydrocyanation of olefins.

The operation of the method according to the invention is shown in FIG shown diagrammatically in the accompanying drawing.

As mentioned, the preferred alkali metal carbonate is sodium or sodium Potassium carbonate. The preferred ketones in the process are acetone, methyl ethyl ketone, cyclohexanone and 3-methylcyclohexanone. The general method described below is illustrated with sodium carbonate, and of course also the other alkali metal carbonates mentioned in the examples can be used. Similarly, others can Ketones are used as the preferred.

With reference to Figure 1, hydrogen cyanide is optionally produced by reaction of ammonia, methane and oxygen as in the Andrussow process over a platinum metal catalyst at elevated temperature (about 1000 C.) - in a gaseous stream of ammonia, hydrogen, methane, carbon oxides, oxygen, Nitrogen, argon and water, through line 10 x near the The bottom of the absorption column 11 'introduced, preferably at a pressure of 0.5-3 at. Aqueous sodium carbonate is introduced to the top of the column through line 12, optionally containing sodium cyanide and sodium bicarbonate, and

with the HCN to form sodium cyanide and sodium bicarbonate -. - 8th -

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reacted. The exhaust gases, ie all incoming gases minus the absorbed hydrogen cyanide and a small amount of ammonia and carbon dioxide, which may have been absorbed at the same time, pass the column 11 ', exit through line 14 and are then burned or optionally further _{treated to obtain NH 3.}

The aqueous sodium cyanide, sodium bicarbonate and sodium carbonate solution is introduced through line 13 into a reactor for the formation of cyanohydrin 33, where it is mixed with a line introduced ketone, eg methyl ethyketone, which can form a cyanohydrin. The reactor is preferably operated at 25-100 ° C. and operated at 0.5-3 at pressure with a residence time of ketone and aqueous material in the reactor of 0.1-20 minutes; the reaction can be carried out in more than one stage. Part of the ketone reacts with the sodium cyanide and sodium bicarbonate present in the aqueous phase to form the ketone cyanohydrin. The aqueous carbonate-cyanohydrin mixture leaves the reactor through line 16 and is fed to the decanter 17, where the cyanohydrin and aqueous phase are separated. The decanter is operated preferably at 25-100 ⁰ C. and 0.5-3 atm pressure with an average l / erweilzeit of organic and aqueous material from 1-20 minutes. Reaction and dean

even
animals can optionally / be carried out in the same vessel.

The cyanohydrin phase is removed from the decanter through line 18 and stored in 19. The aqueous phase from the decanter is removed through line 20, with any dissolved Ketone thereof in Binem Ketonblitzverdarnpfer 21 at 10-760 Torr

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Flash evaporated and the ketone through lines 22 and 15 to the cyanohydrin reactor returned u / ird. The water becomes from the aqueous Recycle stream (ketone flash vaporizer runs) by withdrawing a side stream through line 23 into a purge vaporizer ("purge evaporator") 25 out. The salt concentrate obtained by removing the water is removed through line 24 and this mainly aqueous material is passed through line 26 to the absorption column. Additional sodium carbonate or Base (lye) is fed to the HgO circulation system as required 27 added. The by-products are withdrawn through line 28 as needed.

Ici of the Cyanhydrinbehälter 19 held, cyanhydrinhaltige stream may be withdrawn, or for recovering the cyanohydrin performed as required through line 29 to the cracking unit 30 where it at to temperatures of 50-150 ⁰ C. and pressures of 0.1-5 at \ / dwell times of one second to 10 minutes heated u / ird, so that the cyanohydrin is partially or completely dissoci

and evaporated to ketone and free HCN. The heavy ends from the cracking unit to be removed through line 31, mixed in line 32 and finally -by from d _em H ₉ 0-circulation system remote ketone in line 15 with the heavy ends from the distillation column 41 and recycled to the Cyanhydrinreaktor 33rd These recycle ketone streams can also be used for their. Return to the cyanohydrin reactor can be stored. The HCN-containing gas, which is distilled off overhead in the cracking plant, is passed without condensation through line 34 to the acid scrubber 35, where the HCN-containing gas with an acid or an acidic solution dissolved in water

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is brought into contact without condensation to remove traces of the volatile basic materials formed in the cracking unit or in the cracking feed. Any acid or acid salt with the exception of those formed by weak acids can be used in the washing process. Examples are sulfuric acid or sodium hydrogen sulfate, between 5-70 wt -% dissolved in water.. The acid wash system takes place at 50-100 ° C. under a pressure of 0.1-5 at. The acid solution enters the acid scrubber near the top through line 36 and leaves it through line 37 near the scrubber bottom. Additional acid can be added to the acid recycle system through line 38, while the spent acid is removed through line 39 as needed. The acid-stabilized, HCN-containing gas is removed from the acid scrubber near the top through line 40 and can be passed to the HCN enrichment column 41 without condensation. Traces of acid in an amount of 0.1-100 ppm acid per part HCN feed are introduced in the middle or at the top of the HCN enrichment column 41 through line 42 to stabilize the HCN. The enrichment column should be constructed in such a way that it allows the HCN to be separated from the ketone and the water fed to the column. The tailings of the enrichment column largely contain ketone, water and residual ketone cyanohydrin and are passed through line 43 and returned to the cyanohydrin reactor. The overhead material from the enrichment column is practically anhydrous HCN. It is withdrawn from the enrichment column after condensation through line 44 and can be used immediately or, if necessary, stabilized with acid and stored until it is consumed.

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be stored. The enrichment column itself can be a multi-stage Be distillation column.

Organic Ketone A small part of the circulating in the system is / is carried out by conduction 45 withdrawn and passed to vaporizer 46 where the ketone is recovered and returned through line 47 to the ketone system ujird. The tailings from the evaporation are passed through line 48 deducted. Additional ketone can be added to the organic system through line 49 and ground as needed.

The following examples illustrate the various stages in the process of the invention. The temperatures of Example 1-5 are, unless indicated otherwise, between 25-30 ⁰ C. Example 1

Reaction of NaCIM and NaHCO-j (excess Na ₇ CO ₃ present) with methyl ethyl ketone (FlEK) to form methyl ethyl ketone cyanohydrin and Na2CCL

42.7 g (0.403 mol) sodium carbonate Na ₃ CO ₃ , 17.0 g (0.202 mol) sodium bicarbonate NaHCO, and 10.0 g (0.204 mol) sodium cyanide NaCN were dissolved in 254 g water to form a solution containing 13 21 wt% NaCO ₃ , 5.26 wt% NaHCO ₃ and 3.09 wt % NaCN. There were 43.0 g (0.598 mol) of wet Methyläthyketon (47.8 g of a 10 wt -.% Water-containing solution) is added to the aqueous solution and the two phases were mixed 25 minutes and then separate gaLassen. 321.2 g of the aqueous phase were analyzed for NaCN and contained 0.90 wt .- / ° 2.89 g (0.059 mol). 47.6 g of the organic phase contained 29.8 wt .- ^ methyl ethyl ketone cyanohydrin (MEK-HCN, 14.18 g, 0.143 mol)

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and a trace of free HCN. The total cyanide was 99 % with 29 % in the aqueous phase as NaCN and 70 % in the organic phase as cyanohydrin. The weight percent of other salts in addition to the present in the aqueous phase after the reaction NaCfJ was 17.90 wt -.% Na ₃ CO ₃ and 1.54 wt .- # NaHCO _3.

example 2

Production of cyclohexanone cyanohydrin

30.0 g (0.283 mol) of sodium carbonate were dissolved in 200.2 g of water, the system was sealed, and 3.46 g (0.128 mol) of anhydrous liquid HCN were added to the solution. Little or no heat was given off in the reaction and the product solution was clear. 32.05 g (0.327 mol) of cyclohexanone were introduced into the system with good mixing, the mixture immediately heated to 10 ° C. and the organic and aqueous phases were mixed for a further 15 minutes and then allowed to separate. 35.9 g of the organic layer was analyzed for free HCN and showed no result; a subsequent analysis for combined and free HCN gave a value of 3.19 g (0.118 mol) or 92 % of the originally introduced HCN as cyanohydrin in the organic phase.

Example 3

Production of cyclohexanone cyanohydrin
Use of potassium carbonate

121.7 g (0.882 mol) of potassium carbonate were dissolved in 100 g of water, the system was sealed, then 7.12 g (0.264 mol) introduced liquid anhydrous HCN, which was then stirred for a few minutes. After this time, something in the water

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rigen phase of suspended solids found. Then 45.4 g (0.464 mol) of cyclohexanone was introduced into the system, the phases were mixed for a few minutes and then allowed to separate. The aqueous phase contained no excessive solids and weighed 218.5 g. The 51.32 g of the organic layer was analyzed for free HCN and showed no result. Analysis of the organic layer for total, ie combined and free HCN, found 5.37 g (0.199 moles) or 75.5 % of the initial amount in the carbonate introduced HCN as cyclohexanone cyanohydrin.

Example 4

Production of 3-methylcyclohexanone cyanohydrin

400 grams of sodium carbonate (3.77 moles) was dissolved in 1600 grams of water to form a 20 weight percent sodium carbonate solution. The system was sealed, then 21 g (0.778 mol) of anhydrous liquid HCN was introduced into the solution, which was then stirred for a few minutes. 255.4 g (2.28 mol) of 3-methylcyclohexanone were added to the aqueous solution and mixed in, an immediate temperature rise being observed in the solution. The organic and aqueous mixture was stirred for 5 minutes and then allowed to separate into an organic and aqueous phase overnight. The 1981.3 g of the aqueous phase showed, according to analysis, 5.08 g (0.104 mol) or 0.26% by weight of NaCN. The 281.4 g of the organic phase were analyzed for total HCN as cyanohydrin and free HCN and gave a value of 0.675 mol HCN. The analysis for free HCN in the organic phase showed no result. The total HCN found was 100 % with % in the aqueous and 87 % in the organic phase.

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example

Production of cyanohydrin from methyl ethyl ketone

118.6 g (1.117 mol) of sodium carbonate were dissolved in 406.9 g of water, the system was sealed, and 17.90 g of 99% gas liquid HCN (17.72 g of HCN; 0.656 mol) were added. Then 75.2 g (1.043 mol) of methyl ethyl ketone were added, the aqueous and organic phases were stirred for 1 hour, then heated to about 80 ° C. for 30 minutes and left to stand overnight. The aqueous and organic layers were separated; the aqueous layer weighed 509.8 g, the organic 96.6 g. Analysis of the organic layer for total HCN, ie combined and free, gave a value of 13.5 g HCN (0.50 mol). According to the subsequent !!. · Analysis for free HCN, 0.66 g were present in the organic layer. 67 % of the total HCN originally introduced into the aqueous phase was recovered in the organic phase as free and combined HCN.

Example 6_

Comparative experiment - reaction of a sodium cyanide solution (MaCN) with methyl ethyl ketone (MEK)

19.79 g (0.404 mol) of sodium cyanide were dissolved in 102.2 g of water to form a 16.2% strength by weight NaCN solution at 25 ^° C. 100.18 g (1.27 mol) of wet methyl ethyl ketone (with an H ^ O content of 10 % by weight and 91.7 g of methyl ethyl ketone) were mixed with the aqueous phase for 25 minutes and then allowed to separate. The aqueous phase weighed 138 g, the organic 82.3 g. Analysis of the organic phase on total HCN, combined and free, gave a value of 0.71 g HCN (0.0264 mol) of which 3.17 wt -.% MEK.HCN corresponded. The analysis for free HCN in the organic layer

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mar negative. . The percentage of NaCN originally present in the aqueous phase and transferred into the organic phase was 6.5 %.

Example 7

Semi-continuous decomposition (cracking) of methyl ethyl ketone cyanohydrin

Two water jacketed reactors connected in series to the same hot water source were connected together in such a way that the exhaust gas from the first could be sprayed into a liquid in the second reactor without condensation of the gas, followed by the washed one from the second reactor escaping gas was condensed in a dry ice trap. 120 grams of sodium hydrogen sulfate monohydrate was added to the second reactor along with 33 grams of water. A mixture of methyl ethyl ketone and methyl ethyl ketone cyanohydrin (334.6 g with a methyl ethyl ketone cyanohydrin content of 53% by weight * 177.4 g 1.793 mol) were added to the first reactor; the first and second reactor were heated to 82 ⁰ C.. At this point there was a violent boiling in the first reactor and the gas flowed through the second reactor. After 2 hours, 60.2 g of liquid had been removed from the dry ice trap. The analysis of this liquid for free HCN gave a value of 12.6% by weight (7.57 g, 0.28 mol); the value on the total HCN, or combined and free, was 14.1 wt -.% (8.5 g total HCN, 0.315 mol). While the above overhead sample was being collected, 127 grams of tailings were withdrawn from the cracker (with no new addition of cyanohydrin to the cracker). The analysis of these tailings for total HCN gave a value of 13.8% by weight , while the analysis for free

HCN indicated the presence of 0.43 % by weight. The assemblies - 16 -

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of the HCN in the overhead material from the cracking plant at the The above composition of the cyanohydrin feed was almost exactly the same as that of the cyanohydrin feed, which was practical indicates stabilization of the HCN formed in the cracking unit by the above acidic washing process.

For s ρ ie 1 8

Cracking of cyelohexanone cyanohydrin

Cyclohexanone with cyclohexanone cyanohydrin content (290.74 g with 71.6 g = 24.6 % by weight of cyclohexanone cyanohydrin) were added to a 500 cc distillation still equipped with a thermometer and a long distillation column made of glass filled with glass spirals was provided with a diameter of 1.25 cm; the distillation column was provided with a microcooler and a hood with a dry ice cold trap to take up HCN. A catalytic amount of sodium cyanide (0.05 g) was added to the bladder, and the bladder containing cyanohydrin was heated to 154 ° C. At this point the contents of the bubble boiled. HCN distilled at the distillation head at 26 ° C. overhead. The cracking (distillation) was continued for 1.5 hours after which the bubble was cooled. The overhead condensate was 7.3 g of "free" HCN (0.270 mol). Analysis of the bubble contents (281 g) showed that 7.54 g of HCN (0.280 mol) were still present.

Example 9
Continuous attempt

To illustrate a continuous process, the following operations were carried out in a system as shown in FIG. II.

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80 ccm / min of an aqueous solution containing 1.2% sodium cyanide, 16.1 % sodium carbonate and 2.0 7 ° sodium bicarbonate were introduced into a 1-1 stirred reactor (Α) through line 2. Also in (A), 0.75 g / min of liquid HCN was introduced through line 1. The product stream from (A) then flowed through line 3 to reactor (B), specifically at practically the same rate of 80 ecm / min. In (B), through line 4, 36 ccm / min of a stream with 63.1 % methyl ethyl ketone, 27 % methyl ethyl ketone cyanohydrin and 9.9 5S H ₂ O were introduced. The residence time in reactor (B) was 12 minutes. The mixed phases exiting (B) enter the decanter (c) through line 5, where the two phases are allowed to separate. The heavier aqueous phase emerged through line 2 and was returned to (A). The above compositions were equilibrated after charging the system with approximately the same compositions and running for 4 hours. The lighter oil phase left the decanter through line 6 and entered a cracking plant (D); this was heated to 80-85 ⁰ C., so that a follower (line 7) 15.5 cc / min showed the remainder was evaporated overhead. The composition of the tailings was 38 % methyl ethyl ketone cyanohydrin, 8.0 % H ₂ O and 54 % methyl ethyl ketone. The steam was passed through line 8 through a sieve plate washer (E) into which an aqueous solution of sodium bisulfate was introduced through line 12 and discharged through line 13 and used to remove traces of base. The washed vapor entered a 20 tray distillation column (F) through line 9 and HCN was withdrawn overhead through line 11 at a rate of 0.5 g / min. The follow-up "from the

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Column (line 10) was combined with that from line 7 and returned through line 4 to reactor (B). The system was run in this manner for 4.75 hours; During this time, a total of 214 g of HCN was added to the system. A total of 175 g was recovered overhead from the distillation column. The concentration of methyl ethyl ketone cyanohydrin increased by 5% in the 2800 g of the organic phase, and 38 g of HCN, ie the remainder.

Example J [O

Production of cyanohydrin from acetone

80.0 g (0.579 mol) of potassium carbonate were dissolved in 120.0 g of water, the system was sealed and about 10.0 g of 99% liquid HCN (6.93 g, 0.257 mol) were added; the mixture was equilibrated at 5O ⁰ C., then poured acetone were 29.0 g 99,5- ^. (0.544 mol with 0.5 % H ₂ O) was added. The phases were mixed for 15 minutes at 50 ° C. and then separated; the aqueous layer weighed 200 g, the organic 34 g. Analysis of the organic layer for HCN as acetone cyanohydrin indicated that 45 % of the total HCN originally introduced into the aqueous phase was recovered as cyanohydrin in the organic phase.

Example Vj_

Continuous attempt

To further illustrate the recovery section of the process in a continuous manner, especially when using acetone in the cyanohydrin formation, in a system according to Fig. II worked as follows.

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56 g / min of an aqueous solution containing 2.9% potassium cyanide, 33.9 % potassium carbonate and 4.4 % potassium bicarbonate were introduced through line 2 into a 1-1 stirred reactor (Α). Also through line 1, 0.63 g / min of liquid HCN were introduced into (A) to simulate absorption from HCN synthesis gas in a large-scale process. The product stream from (A) then flowed through line 3 to a reactor (B) at 56.5 g / min. Also in (B) u / are introduced through line 4 31.8 g / min of a stream of 56.5 % acetone, 25.4 % acetone cyanohydrin and 18.1 % H ₂ O. The residence time in reactor (B) was 12 minutes. The mixed phases exiting (B) entered the decanter (C) through line 5 where the two phases were allowed to separate. The heavier aqueous phase emerged through line 2 and was returned to (a). The compositions given above were the equilibrium values after charging the system with approximately the same compositions and running for 4 hours. The lighter oil phase left the decanter through line 6 at 32.4 g / min. It contained 31 % acetone cyanohydrin, ie a net production rate of 1.98 g / min acetone cyanohydrin.

If the recovery of pure HCN was desired, the oil phase was passed through line 6 to the cracking unit (D). This was heated to 80-85 ° C., so that a tail (line 7) of 16.2 g / min resulted, the remainder being evaporated overhead. The tailings had a composition of 32.2 % acetone cyanohydrin, 22.7 % water and 45.1 % acetone. The steam was passed by pipe through a sieve plate washer (E), an aqueous one

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Sodium bisulphate solution to remove traces of base was used. The mixed steam entered a distillation column (F) at 20 trays through line 9 and HCN was withdrawn overhead at a rate of 0.63 g / min.

The tailings from column (F) were combined via line 10 with that from line 7 and through line 4 to the reactor (B) returned. The system was on for 3.5 hours in this way operated. However, the oil phase could also be withdrawn from (C) to obtain acetone cyanohydrin.

40981 1/0993

Claims (6)

- 22 claims 1, - l / experienced for the recovery of hydrogen cyanide in a gaseous mixture by treating the same with an aqueous solution containing an alkaline material and subsequent formation of a ketone cyanohydrin by reaction with a ketone, characterized in that (a) the gaseous mixture with a aqueous solution containing from 1 wt .- ^ to the amount of an alkali metal carbonate required for a saturated solution, at a temperature between about 15-150 C. and a pressure of at least 0.5 at for the absorption of hydrogen cyanide and formation of a treated aqueous, alkali metal cyanide and alkali metal bicarbonate containing product solution, wherein the unabsorbed gases are driven off from the product solution, (b) the aqueous product solution from (a) with a ketone with 3-15 carbon atoms at a temperature between 10-150 ⁰ C. and a Pressure υοη at least 0.5 at for the formation of a cyanohydrin-ketone mixture and for the regeneration of the alka brings limetallcarbonates in the aqueous solution into contact, the concentration of the alkali metal carbonate in the aqueous solution in step (a) is such that the cyanohydrin-ketone mixture formed in step (b) practically not with the aqueous solution containing the regenerated alkali metal carbonate is miscible, the aqueous alkali metal carbonate solution is separated from the cyanohydrin-ketone mixture and the carbonate solution is returned to the gas absorption stage (a); and the cyanohydrin-ketone mixture wins. - 22 - 4098 1 1/0993 2.- The method according to claim 1, characterized in that the gaseous mixture in step (a) with an aqueous solution a potassium carbonate content of 25-45 Gem .- ^ and a pH value of at least 9.0 and treated the product solution obtained in step (b) with acetone to form the corresponding cyanohydrin-acetone mixture is brought into contact. 3.- The method according to claim 1, characterized in that the cyanohydrin-ketone mixture obtained in step (b) then in a stage (c) a temperature between 50-160 C. and a Pressure of 0.1-5 at to regenerate the corresponding ketone to the and hydrogen cyanide from / cyanohydrin and recovery of hydrogen cyanide and is subjected to ketone. 4.- The method according to claim 3, characterized in that the gaseous mixture in step (a) with an aqueous solution with an alkali metal carbonate content of 10-45 wt .- / b and a pH of at least 9.0 at a temperature zii / ischen 40-100 ^D C. and a pressure between 0.5-5.0 at. 5.- The method according to claim 4, characterized in that the aqueous product solution ^{is brought into contact with a ketone in step (b) at a temperature between 25-10O 0} C. and a pressure between 0.5-5 atm. 6.- The method according to claim 5, characterized in that as Ketone in stage (b) methyl ethyl ketone, cyclohexanone or 3-methylcyclohexanone and sodium or potassium carbonate can be used as the alkali metal carbonate. .. ", The patent attorney: 40981 1/0993