Continuous Production of Oxamide by the Catalytic Oxidation of HCN

Europaisches Patentamt European Patent Office © Publication number: 0 571 041 A1 Office europeen des brevets

EUROPEAN PATENT APPLICATION

@ Date of filing: 18.05.93

® Priority: 22.05.92 IT MI921248 © Applicant: Enichem Anic S.r.l. Via Ruggero Settimo 55 @ Date of publication of application: 1-90139 Palermo(IT) 24.11.93 Bulletin 93/47 @ Inventor: Messina, Giuseppe © Designated Contracting States: Via Perpignan 27, AT BE CH DE DK ES FR GB GR IE IT LI LU MC 1-07041, Alghero (Sassari)(IT) NL PT SE Inventor: Sechi, Giovanni Matteo Via Alessandro Volta 4 1-07014, Ozieri (Sassari)(IT) Inventor: De Micheli, Silvio Via Roma 112 I-20024, Garbagnate Milanese (Milan)(IT)

© A continuous process for the production of ox- ng.3 amide is based on the catalytic oxidation of hydrogen cyanide with oxygen or air in a strong excess in a solution of copper nitrate in water-acetic acid. The process is carried out in a vertical tubular SR reactor, with continuous recycling of part of the V suspension of oxamides from the bottom to the top of the reactor. L5

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Rank Xerox (UK) Business Services (3. 10/3.6/3.3. 1) 1 EP 0 571 041 A1 2

The present invention relates to a procedure 2 HCN + 1/2 02 -> (CN)2 + H20 for the preparation in continuous of oxamide. (CN)2 + 2 H20 - ■> H2N-CO-CO-NH2 Oxamide is an organic compound which is used in the synthesis of the widest variety of pro- 2 HCN + 1/2 02 + H20 --> H2N-CO-CO-NH2 ducts ranging from esters, dialkylamides and 5 hydrazides of oxalic acid, to copolyoxamides or The scheme of the reaction zone of the copolymers of a bicarboxylic acid with the oxamide Hoechst process is shown in figure 1 . of an aliphatic or aromatic diamine; these com- The Hoechst process, as described in the pounds are described for example in Italian patent above patents and article, is carried out by feeding applications 20121 A/86, 20274 A/88 and 20276 10 in continuous, in the lower part of a tubolar bubble A/88 filed by the present applicant. reactor (T) containing the aqueous acid solution of The use of oxamide as a slow release fertilizer the catalyst, HCN together with oxygen. The ox- is just as well-known [Development in Plant and amide which is continuously formed precipitates in Soil Sci., 15, Fertilizer Manual, Ed. T.P. Higne; W. a crystalline form and is collected at the bottom of Junk Publishers (1985), page 279]; it is based on 15 the reactor (F), which has a conical shape, in the the slow release of nitrogen by the oxamide. so-called thickening zone, from which it is trans- In spite of the affirmed and increasing use of ferred as a suspension to a centrifuge, where the oxamide, this compound is still not produced on a oxamide is separated from the catalytic solution wide scale because of the relatively high costs and which is recycled to the tubular bubble reactor (T); complicated synthesis methods. There are basi- 20 the latter solution is regenerated by adding copper cally three of these methods: the Degussa process nitrate and the quantity of water consumed accord- (GB 1.251.721), which is based on the oxidation of ing to the stoichiometry of the reaction. The thick- HCN with hydrogen peroxide, the Sagami process ening zone of the solid (F) is situated below the (DE 2034208), which is based on the use of N02 inlet of the oxygen and HCN. instead of hydrogen peroxide, and the Hoechst 25 In the upper part of the reactor there is an process (DEO 2308941, DE 2403120) which is exchanger which cools the off-gases and con- based on the oxidation of HCN with oxygen and air. denses the vapours of water and acetic acid. Of the three above processes, the first two are The excess oxygen, hydrogen cyanide and un- rather expensive, both for the type of oxidant used converted cyanogen, nitrogen oxides (NyOx), CO, and for the necessity of isolating cyanogen (N=C- 30 C02, N2, deriving from the secondary reactions, C=N) as an intermediate product to be hydrolized leave the head of the tubolar reactor together with in a subsequent step. water and acetic acid. The Hoechst process on the other hand is The results of this process are still not satisfac- considered the most accessible and economical of tory however from the point of view of production the three, both for the low cost of the oxidant used 35 on an industrial scale because: (oxygen and air), and for the synthesis procedure - there is a heterogeneous distribution of the which consists of a single step; in addition all the reagents; in fact the oxygen tends to be products can be recycled, catalyst included. distributed preferentially in the upper part of The catalyst used is an aqueous solution of the reactor whereas the hydrogen cyanide, copper nitrate which is used in the presence of an 40 owing to its solubility in the catalyst, tends to aliphatic carboxylic acid (acetic acid). A subse- move both upwards and downwards with re- quent patent (DE 2402354) emphasizes, in the spect to the feeding point, economy of the process, the role of the oxidant - oxygen is never present in the suspension (oxygen or air), which must be advantageously taken from the thickening zone (F) of the used in great excess with respect to the 45 reactor whereas the gases contained therein stoichiometric quantity. are basically composed of N2, NO, CO and The relative reaction scheme as defined by the C02, authors (W. Riemenschneider, Chemtech., October - the recycled catalytic solution always con- 1976, pages 658-661) is specified below whereas tains reasonable quantities of formamide and the scheme of the Hoechst plant is specified in the 50 acetamide which are destroyed (by oxidation) same article. when re-fed into the reactor as such a quantity does not increase with time. 2 Cu(N03)2 + 4 HCN -- > (CN)2 + 2 CuCN + 4 The presence of NO in the suspension continu- HN03 ously removed from the thickening zone (F) of the 2 CuCN + 6 HNO3 - > 2 Cu(N03)2 + 2 HCN + 2 55 reactor, together with the lack of oxygen therein, H20 + 2 N02 indicates insufficient re-oxidation of this gas; infact, 2 N02 + 1/2 02 + H20 -- > 2 HNO3 in the oxidative process for the formation of oxamide, the nitrates can be reduced to products

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having a lower oxidation level (NO and NO2) which however, if there is a strong excess of oxygen, as 2 HCN + 1/2 02 + H20 -- > H2N-OC-CO-NH2 is also recommended in German patent application DE 2402354, should be reoxidized to nitric acid. and including the following operations: In addition, the lack of oxygen in the thickening 5 - feeding in continuous into a tubular vertical zone (F) of the reactor favours the accumulation of reactor: reduced products (e.g. HNO2) which can attack the i) the catalytic solution of copper nitrate Cu- oxamide, oxidizing it exhaustively with the forma- (N03)2, which also contains acetic acid, nitric tion of gaseous products such as those specified acid and the stoichiometric quantity of water above, in the suspension at the bottom; for exam- 10 consumed in the reaction, ple: ii) hydrogen cyanide (HCN), iii) oxygen or air which, bubbling through the H2N-CO-CO-NH2 + 2HN02 -- > 2 N2 + CO + tubular reactor, causes the stirring of the sus- C02 + 3 H20 pension of oxamide inside, 15 - continuously removing the suspension of ox- The carbon monoxide which is formed accord- amide from the bottom of the tubular reactor ing to this reaction, as it is also flammable, in- and the quantity of oxygen in excess of the creases the concentration of combustible products stoichiometric quantity from the head of the (hydrogen cyanide, acetic acid, cyanogen) in the reactor together with any other gases pro- gaseous phase and makes more critical the control 20 duced in secondary reactions, of the explosivity of the gaseous mixture both in - continuously separating the oxamide from a the head of the reactor and in the bubbling-bed. part of the suspension removed from the The present invention therefore relates to a bottom of the reactor, process for the production of oxamide which, al- - recycling the catalyst solution, containing though using the same reagents and same catalytic 25 copper nitrate, acetic acid and nitric acid, system of the Hoechst process mentioned above, after adding the stoichiometric quantity of wa- overcomes the above disadvantages of the known ter consumed in the synthesis reaction, art. this process being characterized in that: In fact, as mentioned before, the applicant has a) the suspension of oxamide is continuously discovered that the disadvantages of the known art 30 removed from the lowest point of the reactor, can mainly be attributed to the bad distribution of b) a great quantity of the suspension of oxamide the reagents and, among these, above all oxygen, removed from the lowest point of the reactor is both inside the reactor where the synthesis of the recycled, re-introducing it into the highest part oxamide takes place and on the bottom (thickening of the reactor, after cooling it in a heat ex- zone F) and outside the reactor before the oxamide 35 changer at a temperature which is sufficient to in suspension is separated from the catalytic solu- maintain the established reaction temperature tion. inside the reactor, In fact, the relatively long period of residence c) an amount of the suspension of oxamide of the oxamide precipitated in the thickening zone continuously removed from the lowest point of (F) of the reactor, before being removed, i.e. in a 40 the reactor, is not recycled but is rapidly treated zone which, as said before, has no oxygen, favours in a battery with two cyclones placed in series, the oxidative demolition of the oxamide as already to separate the oxamide from the majority of the specified. The same parasitic reaction and also acid catalyst solution, others (formation of formamide and acetamide by d) the oxygen or air in an excess of 40 to 60% the action of acetic acid) occur in the interval 45 of the stoichiometric quantity is fed to the base between the depositing of the oxamide on the of the reactor, bottom (F) of the reactor, its removal and separa- e) the HCN under pressure and in a liquid phase tion from the solution by centrifugal treatment. is fed into the highest part of the tubular reactor, All these disadvantages have been overcome at a height which is never less than 4/9 of the with the synthesis process of oxamide of the ap- 50 height of the aereated liquid inside the column plicant. and never more than 8/9 of the same height, In accordance with this, a first aspect of the f) the catalytic solution, before being charged present invention relates to a process for the prep- into the reactor, is added to the recycled sus- aration in continuous of oxamide, by the oxidation pension of oxamide, and is then introduced with of HCN with oxygen or air in the presence of an 55 the same suspension into the upper part of the aqueous solution of copper nitrate [ Cu(N03)2 ] tubular reactor, and at a height which is never containing acetic acid and nitric acid, basically ac- lower than that at which the HCN is introduced. cording to the following scheme:

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An important characteristic of the synthesis suspension of oxamide taken from the recycled procedure of oxamide according to the present amount (through line L4; see fig. 2), are made by invention is that the removal, both of the amount of Alfa Laval. suspension to be recycled and the amount to be The main operating parameters of the process separated in the cyclones, is carried out in a single 5 of the present invention are: point situated in the lowest part of the reactor. - the concentration of aqueous catalyst solution Figure 2 shows the scheme of the reaction which contains: from 10 to 15 g/l of copper zone of the synthesis process of oxamide accord- nitrate and preferably 12.5 g/l; from 3000 to ing to the present invention, whereas figure 1, as 6000 ppm of HN03 and from 65% to 70% by already specified, shows the scheme of the reac- 10 weight of acetic acid; tion zone of the synthesis process according to - the total quantity of suspension which is con- Hoechst. tinuously removed from the bottom of the Figure 2 clearly shows the reactor (R) from the reactor and which is between twice and 6 bottom whereof the suspension of oxamide, most times the volume of liquid of the reactor per of which is recycled through line L3, is continu- 15 hour; preferably the hourly quantity is 4 times ously removed; a quantity of the removed suspen- the volume of the reactor; sion is not recycled, but is sent through line L4 to a - the part of suspension taken from the bottom battery (I) of two cyclones placed in series where of the reactor which is not recycled but sent the suspension of oxamide is rapidly thickened and to the cyclones for the separation of the sent to the centrifuge; from here, after squeezing 20 oxamide, which is between 25 and 40% in the slurry, the catalytic solution is re-fed to the volume; this quantity is preferably 33% of the productive cycle through line L6, after being re- total volume of suspension taken from the integrated with a new aqueous acid solution of bottom of the reactor; copper nitrate; the catalytic solution separated by - the temperature inside the reactor which is the thickening treatment effected by the battery 25 between 45 and 65 °C and is preferably with hydrocyclones (I), is, instead, refed to the 55 °C; productive cycle through line L5. - the pressure in the roof of the reactor, which Figure 2 also shows the bottom of the tubular is between 1 and 2*1 05 Pa and preferably (for reactor (R) which is narrowed towards the bottom T = 55°C) 1 .5*1 05 Pa. starting from the inlet point of the oxygen which 30 Operating with the synthesis procedure of the comes from line L2. present invention conversions of hydrogen cyanide Another important characteristic of the present of more than 99.5% are obtained whereas the invention lies in the introduction of oxygen and selectivity to oxamide is higher than 98.5%. hydrogen cyanide in two separate and clearly dis- The description of the preferred operating pro- tinct points of the reactor; the oxygen, in great 35 cedure in the synthesis process of oxamide ac- excess with respect to the stoichiometric quantity, cording to the present invention refers to figure 3, is admitted to the bottom of the reactor by means enclosed with the present description, which shows of a torus and in the form of small bubbles uni- the operating scheme of the production plant. formly distributed on the transversal section of the The reactor is a vertical reaction column (R), column of liquid, whereas the HCN is introduced in 40 wherein the oxygen forms a bubbling-bed inside the upper part of the reactor, in an area situated the catalytic solution, having a volume of 38.5 m3 between 4/9 and 8/9 of the height of the aereated and having a ratio between the height of the liquid inside the reactor and preferably at 2/3 of the aereated liquid (catalytic solution) contained therein height. and the internal diameter of 5.7. The section for the All the above elements guarantee the most 45 thickening of the solid, which in the Hoechst uniform distribution possible of oxygen in the reac- scheme was situated at the bottom of the reactor, tion mixture and not only inside the reactor but also is now separated from the reactor and is composed in the so-called "dead points" (where the oxygen of the battery with 2 hydrocyclones in series (I), does not bubble) such as the zone in the reactor which separates the majority of the catalytic solu- which is below the feeding point of the oxygen; the 50 tion from the solid treated suspension. volume of this zone, in the synthesis process of the On the bottom of the reactor, which does not present invention, is infact very small as the two have a thickening zone but is narrowed imme- hydrocyclones, which have a negligible volume, diately after the oxygen inlet, a reasonable amount substitute the thickening zone of the reactor (F in (160 ton/hr) of suspension is continuously removed, figure 1) which, being no longer necessary, has 55 the majority of which (107 ton/hr) is recycled, been eliminated. through line L3, in the higher part of the reactor; The two cyclones placed in series and used for this is cooled along the way by exchanger S1 to a the concentration (thickening) of the quantity of temperature which is sufficient to maintain a tem-

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perature of 55 °C in the reactor; a part of suspen- - feeding in continuous into a vertical tubu- sion (53 ton/hr) is continuously removed from the lar reactor: recycling line L3 and is sent through L4, as already i) an aqueous solution containing acetic specified, to the battery with 2 hydrocyclones (I); acid, nitric acid and copper nitrate [ the catalyst solution which is separated from the 5 (CuN03)2 ], suspension (50 ton/hr), is added to the recycled ii) hydrogen cyanide (HCN), suspension through line L5, whereas the suspen- iii) oxygen or air sion concentrated with oxamide is sent along line - continuously removing the suspension of L6 to the accumulator (A) and from here to the oxamide from the bottom of the tubular centrifuge where the solid oxamide is separated 10 reactor and the quantity of oxygen in from the residuous part of the catalyst solution; the excess of the stoichiometric quantity latter is sent, through line L7, to the re-integrating from the head of the reactor together tank SR. with any other gases produced in secon- In the re-integrating tank (SR), the solution is dary reactions, restored to the concentration values of copper ni- is - continuously separating the oxamide trate (12.5 g/l), water (30%) and acetic acid (70%) from a part of the suspension removed existing in the tubular reactor by adding a solution from the bottom of the reactor, of the three ingredients and is then sent to the - recycling the catalyst solution, containing reactor by line L8. copper nitrate, acetic acid and nitric acid, The optimum concentration of nitric acid, (4000 20 after adding the stoichiometric quantity of ppm) is kept constant by re-integrating it through water consumed in the synthesis reac- line L9. tion, Other parameters used in the synthesis pro- this process being characterized in that: cess are: concentration of oxamide in the reactor a) the suspension of oxamide is continu- under standard conditions of about 2.4% by weight; 25 ously removed from the lowest point of the temperature in the tubular reactor of 55 °C; pres- reactor, sure of 1 .5*105 Pa. b) a great quantity of the suspension of The hydrogen cyanide (775 Kg/hr) is fed, in a oxamide removed from the lowest point of liquid phase and at a temperature lower than 10 °C, the reactor is recycled, re-introducing it into into the upper part of the reactor through line L1; 30 the highest part of the reactor, after cooling the inlet in the reactor is situated at 2/3 of the it in a heat exchanger at a temperature height of the aereated liquid. which is sufficient to maintain the estab- The flow rate of oxygen, which is fed through lished reaction temperature inside the reac- line L2 into the lower part of the reactor and tor, precisely in the narrowed point of the reactor, is in 35 c) an amount of the suspension of oxamide an excess of 50% with respect to stoichiometric continuously removed from the lowest point quantity; the excess of oxygen, after being bubbled of the reactor, is not recycled but is rapidly into the reactor and in countercurrent with respect treated in a battery with two cyclones to the solution of reagents, leaves the head of the placed in series, to separate the oxamide reactor and is sent to the incinerator, through line 40 from the majority of the acid catalyst solu- L10. With the reactor under steady conditions, and tion, under the operating conditions used, 1250 Kg/hr of d) the oxygen or air in an excess of 40 to oxamide are produced with a conversion of the 60% of the stoichiometric quantity is fed to hydrogen cyanide of 99.8% and selectivity of the base of the reactor, 99.7%. 45 e) the HCN under pressure and in a liquid phase is fed into the highest part of the Claims tubular reactor, at a height which is never less than 4/9 of the height of the aereated 1. Process for the preparation in continuous of liquid inside the column and never more oxamide, by the oxidation of HCN with oxygen so than 8/9 of the same height, or air in the presence of an acid aqueous f) the catalytic solution, before being solution of copper nitrate [ Cu(N03)2 ], ba- charged into the reactor, is added to the sically according to the following scheme: recycled suspension of oxamide, and is then introduced with the same suspension 2 HCN + 1/2 02 + H20 -- > H2N-OC-CO-NH2 55 into the upper part of the tubular reactor, and at a height which is never lower than and including the following operations: that at which the HCN is introduced.

5 EP 0 571 041 A1 10

2. Process according to claim 1, characterized in that the reactor is a vertical column in which the ratio between the height of the liquid suspension and the internal diameter is between the values of 5 and 6. 5

3. Process according to claim 1, characterized in that the concentration of the aqueous catalyst solution contains: from 10 to 15 g/l of copper nitrate and preferably 12.5 g/l; from 3000 to 10 6000 ppm of nitric acid and from 65 to 70% of acetic acid.

4. Process according to claim 1, characterized in that the total quantity of suspension which is is continuously removed from the bottom of the reactor is between twice and 6 times the volume of the liquid in the reactor for each hour.

5. Process according to claim 1, characterized in 20 that the total quantity of suspension which is continuously removed from the bottom of the reactor is 4 times the volume of the reactor for each hour. 25 6. Process according to claim 1, characterized in that the part of suspension removed from the reactor which is not recycled but sent to the cyclones for the separation of the oxamide, is between 25 and 40% by volume and prefer- 30 ably 33% by volume.

7. Process according to claim 1, characterized in that the temperature inside the reactor is between 45 and 65 0 C and preferably 55 0 C. 35

8. Process according to claim 1, characterized in that the pressure inside the reactor is between 1 and 2*1 05 Pa and preferably (for T = 55°C) 1 .5*1 05 Pa. 40

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OFF-GAS

CATALYST RECYCLING HCN

DRYER

CENTRIFUGE H20

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9 European Patent EUROPEAN SEARCH REPORT Application Number Office EP 93 20 1408

DOCUMENTS CONSIDERED TO BE RELEVANT Category Citation of document with indication, where appropriate, Relevant CLASSIFICATION OF THE of relevant passages to claim APPLICATION (Int. Cl.S ) A FR-A-2 219 153 (FARBWERKE HOECHST AG) 1 C07C231/00 * the whole document * C07C233/56 D & DE-A-2 403 120

A DE-A-2 423 538 (HOECHST AG) 1 * page 4 - page 6 *

A DE-A-2 427 269 (HOECHST AG) 1 * the whole document *

A SOVIET PATENTS ABSTRACTS 1 Section Ch, Week 9148, 22 January 1992 Derwent Publications Ltd., London, GB; Class C, AN 91-351568/48 & SU-A-1 616 897 (EREMEEV V S) 30 December 1990 * abstract *

A,P SOVIET PATENTS ABSTRACTS 1 Section Ch, Week 9234, 7 October 1992 Derwent Publications Ltd., London, GB; technical fields Class C, AN 92-282991/34 searched (int. ci.s > & SU-A-1 691 362 (EREMEEV V S) 15 November 1991 C07C * abstract *

A PATENT ABSTRACTS OF JAPAN 1 vol. 8, no. 130 (C-229)1984 & JP-A-59 039 858 ( ASAHI KASEI K0GY0 KK ) * abstract *

The present search report has been drawn up for all claims Place of ftcarcii Date of conpletioi of the March BERLIN 30 JUNE 1993 RUFET J. CAIEUUKY UK UILU UUCUMENTS T : theory or principle underlying the invention E : earlier patent document, but published on, or X : particularly relevant if taken alone after the filing date Y : particularly relevant if combined with another D : document cited in the application document of the same category L : document cited for other reasons A : technological background O : non-written disclosure & : member of the same patent family, corresponding P : intermediate document document