US 2778733 A
Description (OCR text may contain errors)
APPARATUS FOR THE MANUFACTURE OF UREA, FGRWED OF ALUli IINUM BRONZE Jean Leon Maurice. Frejacques, Paris, France, assiguor to Pechiney, Compagnie de Protluits Chiiniques et Electrometallurgiqnes, Paris, France, a corporation of France Application December 7, 1953, SerialNo. 396,729.
Claims priority, application France December 13, 1952 4 Claims. (6]. 75-161) No Drawing.
The present invention, which is based upon the results of applicants researches, relates to materials employed in the construction of apparatus used in the synthetic manufacture of urea.
It. is known that one of the difficulties encountered in the industrial synthesis of urea from CO2 and NH3, carried out at temperatures above 130 C., resides in the corrosion of apparatus by the reaction medium. Lead, which is commonly employed, is suitable for use as lining only, because its mechanical properties render impossible its use in the. construction of the apparatus themselves, or of the valves, pipes, etc. Special nickel and/or chromium containing steels, as well as other alloysgenerally known as being corrosion-resistant, do not function in a satisfactory manner in the presence of the reaction medium under consideration here. Further, the costly use of silver does not yield results in proportion to the price of this metal.
The present invention makes it possible to carry out the production. of. urea with only insignificant corrosion, by the use of certain alloys of copper with aluminum.
Accordingto a first feature of the invention, the parts of apparatus, which are subjected to the attack by hot mixtures of urea-ammonium carbamate-water, are made of or are. protected with. alloys of special composition belonging to the so-called aluminum bronze group-of alloys. By this is meant copper alloys having 3 to 11% aluminum and, eventually, slight amounts of other metals such,v as Fe, Mn, Ni, Si, V, Cr, Pb, Ti, etc., the sum of which does not exceed 5%.
It is known that these bronzes resist reasonably well corrosion in acid media and atmospheric oxidation, but resist poorly corrosion in alkaline media, especially, at-a high temperature. Considering the fact that copper corrodes most readily in an ammoniacal medium, it was a 6 "ice 2 1 most unexpected discovery on the part of, applicant/that aluminum bronzes possess high corrosion resistance in the hot basic (ammoniacal) mixtures which urea forms with CO2, NH3 and water during its synthesis.
Since aluminum bronzes possessgood, mechanical characteristics, and are easily workable, they are used, according to the present invention, in the construction of the apparatus themselves, such as autoclaves, inlet pipes for CO and NH3, or any other pipes or parts terminatingv atthe autoclave or situated inside thereof, as well as in the manufacture of protecting linings for walls made or other metals.
However, not all aluminum bronzes behave in the; same manner with respect to the corrosive medium. Applicant has, therefore, as a result of his researches, discovered and selected those which possess the highest resistance to corrosion. Hence, according to another'feature of the present invention, the apparatus or parts thereof used in the synthesis of urea are madewith' the view of enhancing their resistance to corrosion-of aluminum bronze which contains manganese, and which hasan iron content lower than that of themanganese. The bronzeaccordiug to the invention should contain 0.1 to 4% Mn, while its iron content should not exceed that of the manganese.
Particularly satisfactory results are obtained when the alloy is composed, in addition to copper, of 8 to 10%- A1, 0.2 to 1% Mn, 0.02 to 0.4% Fe and less than 0.3% other elements, while the ratio- Percent Fe Percent Mn does not exceed 0.5. Preferably, said other elements should be, for example, Cr, V, Ti and/ or, especially, Si.
One of theimportant conditions to the obtainment of as high corrosion resistance'as possible is, that the aluminum bronze should be both poor in iron and that the ratio iron/ manganese below. However, commercial aluminum bronzes generally contain more than 0.5% Feand, most often, even more than 1%.; when-they contain manganese, the content of this element is lower than that of Fe. For example, most of commercial alloys have 1 to 4.25% Fe and those which also contain Mn, have less than 1.5% of the latter as against 2 to. 3.5% Fe. In substantiation ofthe foregoing, reference ismade to the followingtable which is reproduced from an article entitled: Aluminum Bronze by John L. Everhart, Materials, and Methods, December 1952, vol. 36, #6, pp. 119434, constituting-v Table I found at page 122 thereof.
Table 1.N0minal compositions of aluminum bronzes [The designations arearbitrary, as explained in the text] 1 Some of these alloys are alsoused in cast form.
I Ni+Mn+Sn 2 a max.
8 These compost ions are also used in wrought form, particularly for iorgings and extra? Accordingly, the carrying out of the present invention into practice under the best conditions required special aluminum bronzes. For this reason, there have been employed metals poor in iron and care was taken to avoid contamination with iron during the preparation of .the alloy. In this manner, a bronze was produced possessing outstanding resistance to corrosion when in contact with hot (150 "200 C.) mixtures of urea, ammonium carbamate and water, under pressure, and practically in the absence of oxygen. The said bronzereferred to as Special Bronze in the table given below, has the following composition:
Percent Cu 89.80 Al 9.54 Mn 0.45 Fe 0.17 Si 0.04
Apparatus made of this metallic composition have a very much longer life than when made of other alloys. In fact, it is found that, whereas the above identified bronze shows an increase in weight of about 2 gins. per square metre per annum in a hot urea-carbamate-water mixture, loss in weight amounting to 700 and 730 gms./ sq. mJyear are observed in the case of aluminum bronzes Ampco 8 and Ampco containing, respectively: 68% Al, 1.53% Fe, and, at most, 0.5 of other elements; and 910% Al, 2.75-3.75 Fe, and, at most, 0.5% of other elements.
Alloys having a composition approximating that of applicants outstanding aluminum bronze, the Special Bronze, described above, can also be successfully used. This applies especially to bronzes containing Percent Al 9 to 10 Mn 0.2 to 0.6 Fe 0.05 to 0.25
The ratio Percent Fe Percent Mn preferably ranging between 0.1 and 0.45. These alloys may preferably contain 0.01 to 0.1% Si, this silicon being partially or completely replaceable by V, Cr or Ti. Alloys within this range have a loss by corrosion in the presence of urea amounting to less than 100 grs. per square metre per year.
Applicant is aware that it has previously been suggested to use aluminum bronzes in the construction of apparatus intended for use in the synthetic manufacture of urea. Thus, in French Patent 826,281, issued to the same assignee as of the present applicationformerly known as Compagnie de Produits Chimiques et Electromtallurgiques Alais, Froges et Camargueit is proposed to use for this "purpose apparatus constructed of steel provided with lining of tin or lead, nickel and various alloys having a low or high content of aluminum. In a later French patent, viz 958,503, likewise issued to applicants assignee, it is stated that chromium-nickel containing stainless steel, copper alloys such as aluminum bronzes, Monel metal, and copper alloys can be used with urea. Further, in an article by Bolotov in the Russian periodical: Zhurnal Khimicheskoi Promyshlennosti (Journal of Chemical Industry, Moscow), Number 10, May, 1937, there are given the results of corrosion tests in 4 the presence of urea, carried out with various metallic substances and, among others, with B. A. J. M. bronze (Correx Metal) having the following composition:
It is clear from the data set forth in the article that thi aluminum bronze has a resistance to corrosion distinctly less than that of the aluminum bronzes of the present invention. That is, whereas, the bronzes described in the Bolotov article suffered a loss in weight of 1290 grammes per square metre per year, applicants aluminum bronze of the composition set out above i. e. Special Bronze actually shows an increase of 2 grammes per square metre per year.
In comparison with the aluminum bronzes proposed in the prior art discussed above, applicants aluminum bronzes are characterized by a critical relationship of the proportions of the constituents used, particularly, as regards the actual and relative proportions of Fe and Mn, when both of these are used in formulating the alloy. As indicated earlier in the present specification, applicant has discovered that it is of critical importance that the aluminum bronze-for the purpose in viewhave a very low iron content, that the total Fe and Mn content not exceed 5%, and that the ratio of iron to manganese not exceed 3/4; applicant has also disclosed preferred compositions for his alloys. When aluminum bronze is formulated with due regard to the critical relationships taught by applicant, then, the resultant product possesses to an exceptional degree resistance to corrosion when in presence of a hot-urea-ammonium carbamatewater mixture.
As disclosed above, the preferred alloys of applicants invention, i. e. those possessing the most outstanding characteristics as regards resistance to corrosion, contain both Fe and Mn within the proportions specified. However, in the course of applicants researches, it was further established that aluminum bronzes which are free of manganese, but which have a very low iron content, also possess valuable properties as regards resistance to corrosion. This is particularly true of a bronze-identified as bronze A on the table set out belowhaving the following composition:
Percent Cu 90.99
A1 8.96 Fe 0.048
1 By difference.
This alloy shows a loss of 109 grammes per square metre per year in the presence of urea. Bronzes of which applicants bronze A is one example, belong to the group of aluminum bronzes comprehended within applicants invention and which have the following composition:
Metals other than copper, less than 0.3%. Balance copper.
Aluminum bronzes which are free of manganese but contain a small but effective amount iron, in general show a loss less than 700 grammes per square metre per year and, hence, are more valuable in this regard than the commonly available aluminum bronzesas will be apparent from the following tabulation which compre- 4. Apparatus for use in the synthesis of urea from ammonia and carbon dioxide, characterized in that the Loss of weight calculated in grammes per square metre per year Composition Corrosion Percent Percent Percent Percent Al Cu Fe Mn (by difierence) Applicants Bronze A 90. 99 0. 048 none 8.96 109 Applicant's Bronze C 88. 54 0. 048 9.49 126 Applicant's Special Bronze 89. 8 0.17 0. 45 9.54 (+81 0.04) +2 AmpcoS 88. 5-921) 1.5-3.0 6-? I(oth(e)ar51)netalsless -700 Ampco 86.2-87.7 2. 75-3. 76 9-10 (other metals -730 less than 0.5). B. A. .T. M. (Russia) (Metal Cortex) 84.5 3.2 0.7 11.6 -1,300
Norm-Minus sign indicates loss of weight; plus sign indicates gain of weight.
1. Apparatus for use in the synthesis of urea from ammonia and carbon dioxide, characterized in that the parts of the apparatus in contact with the hot reaction medium are formed of aluminum bronze, containing Percent Aluminum 8 to 10 Manganese 0.2 to 1 Iron 0.02 to 0.4 Constituents other than copper less than 0.3
the ratio of iron to manganese being less than 0.5.
2. Apparatus according to claim 1 which includes silicon as one of said constituents.
3. Apparatus for use in the synthesis of urea from ammonia and carbon dioxide, characterized in that the parts of the apparatus in contact with the hot reaction medium are formed of aluminum bronze, containing Percent Aluminum 9 to 10 Manganese 0.2 to 0.6 Iron 0.05 to 0.25
the ratio of iron to manganese ranging from 0.1 to 0.45.
parts of the apparatus in contact with the hot reaction medium are formed of aluminum bronze, which consists of (24th ed., 1940), page 1237.
Louis Cassier Co. Ltd., Metals and Alloys 1941 edition), page 13.