64
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 17, No. E
Chemical Changes Occurring in Calcium CyanamideAcid Phosphate Mixtures‘ By K. D. Jacob and J. M. Braham FIXED
.
NITROGBN RESEARCHLABORATORY, WASHINGTON, D.
A limitation to the more extensive use of calcium cyanamide in mixed fertilizers is in its reaction with acid phosphate, resulting not only in the reversion of the phosphate but also in the conversion of a part of the cyanamide nitrogen into compounds which are objectionable in fertilizer mixtures. This paper presents t h e results of a study of the chemical changes occurring in simple mixtures of calcium cyanamide and acid phosphate as affected by t h e proportion of t h e constituents in t h e mixtures, by t h e moisture and free acid content of t h e phosphate, and by t h e temperature and duration of storage. The changes in calcium cyanamide in mixture with mono- and dicalcium phosphate and in dicyanodiamide and urea in mixture with acid phosphate were also studied. Urea, dicyanodiamide, guanylurea, and ammonia were found t o be the main nitrogen transformation products on storage of simple mixtures of calcium cyanamide and acid phosphate, and usually accounted for 80 to 85 per cent of t h e nitrogen added. I n mixtures containing 1 part of calcium cyanamide per
c.
20 parts of freshly manufactured acid phosphate, about 75
per cent of the nitrogen was transformed into urea and from 0 t o 13 per cent into guanylurea and dicyanodiamide. The decrease in available phosphate in such mixtures was almost negligible, even after 11 months’ storage. I n mixtures containing double this a m o u n t of cyanamide, urea constituted only about 40 per cent of t h e transformation products, dicyanodiamide and guanylurea representing most of t h e remainder. A considerable decrease in available phosphate also occurred in such mixtures. With airdried acid phosphate (low moisture and free-acid content) only about 15 per cent of t h e nitrogen was obtained a s urea and approximately 70 per cent as dicyanodiamide and guanylurea, even in mixtures containing only 1 part of calcium cyanamide to 20 parts of acid phosphate. Dicyanodiamide is hydrolyzed to guanylurea, not only by the free acid i n acid phosphate, but also by monocalcium phosphate. Urea is stable in mixture with acid phosphate a t ordinary storage temperatures, but a t 70’ C. or higher it is rapidly hydrolyzed to ammonia.
RACTICALLY all the calcium cyanamide t employed actions of caIcium cyanamide in fertilizer mixtures. Thus as a fertilizer in this country is used in mixtures in Harger,28 experimenting with complete fertilizers and simwhich acid phosphate is the main constituent. In ple mixtures in which calcium cyanamide was used in quansuch mixtures calcium cyanamide serves not only as source tities ranging from 25 to 100 parts per 1000 parts of acid of nitrogen, but also as a drier or “conditioner.” Poor phosphate, found that, even with 50 parts of the former, crop yieldsz6**from mixtures containing 100 kg. or more of considerable dicyanodiamide was formed. No analyses were calcium cyanamide per 500 kg. of acid phosphate or per ton reported for urea or guanylurea. I n the mixtures prepared by of mixed fertilizer were until quite recently attributed en- Harger the decrease in cyanamide nitrogen was much slower tirely to the reversion of the available phosphate by the where air-dried acid phosphate containing about 3 per cent alkaline calcium cyanamide. More recent investigations, moisture was used, than where the same phosphate was used however, have shown that calcium cyanamide may undergo but with sufficient water added to increase the moisture transformations in such mixtures, yielding some products content to 10 per cent. The decrease in cyanamide nitrogen which are harmful to plant growth, for example, dicyanodi- was largely due to the formation of dicyanodiamide. Landis,ag amide, and others, such as guanylurea, the value of which is in general criticism of Harger’s work, states that in factory still in doubt. mixtures containing 50 kg. of calcium cyanamide per 1000 A large number of investigations on the chemical changes kg. of acid phosphate, some dicyanodiamide is formed a t occurring in calcium cyanamide-acid phosphate mixtures first, but that it is later converted into guanylurea and other have been made, as shown by the accompanying bibliography, ureas. but most of them have dealt only with the changes in the I n this paper are reported the results of a study on the water-soluble and available phosphoric acid. Most of the chemical changes occurring in calcium cyanamide-acid phosmixtures studied contained a relatively large amount. of cal- phate mixtures with particular reference to the transformacium Cyanamide, and on storage the water-soluble phosphate tions of the nitrogen, although data on changes in the form of disappeared entirely and the available phosphate dimin- the phosphate were also obtained and are included. These ished considerably. changes, as affected by the proportions of calcium cyahamide With regard to changes in the cyanamide nitrogen, P r a n I ~ e ~and ~ acid phosphate in the mixtures, moisture and free acid states that, in a ton of mixed fertilizer containing 27.2 to of the acid phosphate, and temperature of storage, were 36.3 kg. (60 to 80 pounds) of calcium cyanamide and 454 kg. studied in laboratory mixtures of 45.4 kg. (100 pounds) (1000 pounds) of acid phosphate, the nitrogen originally and less over periods ranging from a few days to 11 months. present as cyanamide is ultimately converted into urea. Some of the mixtures contained calcium cyanamide in The Laboratory of Soil Fertility Investigations, Bureau of much larger proportions than are used in commercial Plant Industry, in its studies of the fertilizer value of calcium practice. The decomposition of calcium cyanamide in mixL cyanamide, has conducted some experiments on the inter- ture with mono- and dicalcium phosphate was studied, as well as the stability of urea and dicyanodiamide-the two 1 Received July 30, 1924. Presented before the Division of Fertilizer Chemistry a t the 68th Meeting of the American Chemical Society, Ithaca, primary decomposition products of cyanamide-in mixture N. Y., September 8 to 13, 1924. with acid phosphate. The investigation was confined to a t The term “calcium cyanamide” in this paper refers t o the coinmerciul study of the principal reactions occurring in simple mixhydrated and oiled calcium cyanamide unless otherwise stated. tures of calcium cyanamide and acid phosphate. Predic* Numbers in text refer t o bibliography a t end of article.
P
January, 1925
INDUJSTRIALA N D ENGINEERING CHEMISTRY
65
method.36 Ammonia in the mixtures was determined by treating with a sodium carbonate-chloride solution and aerating in the apparatus described by matt hew^.^^ Total, water-soluble, and available phosphoric acid were determined by the standard volumetric methods.37 Free acid was, in all cases, determined by extracting with ether and Experimental titrating with standard alkali, using sodium alizarin sulfonate MATERIALSUSED-AC~~Phosphate. Commercial acid 'indicator. Moisture was determined by heating a 2-gram phosphate containing a t least 16 per cent available P z O ~ sample a t 105" C. for 5 hours. It will be observed in the tables of results that in some cases was used in the experiments. The effect of moisture and free acid in the acid phosphate on the nature of the trans- there are inconsistencies in both the nitrogen and phosphate formation of cyanamide nitrogen was recognized early in analyses. These inconsistencies may be ascribed to nonthe investigation, and hence samples containing various uniformity of the mixtures, as well as to analytical error. amounts of moisture and free acid were obtained directly I n spite of the great care taken to obtain homogeneous from the factory and used a t once. For some of the mix- mixtures, some nonuniformity evidently existed. As for tures the acid phosphate was permitted to air-dry before use. the nitrogen determinations, it will be noted that in some The percentages of moisture and free acid are given in the cases the total nitrogen was as low as 0.43 per cent, and consequently even a small error in any of the several nitrogen tables of results. Calcium Cyanamide. This material was manufactured a t determinations produced a relatively large error in the perU. S. Nitrate Plant S o . 2, Muscle Shoals, Ala., and that used centage of total nitrogen present in any one form. in the majority of the experiments was hydrated and oiled a t Results this laboratory by properly adding about 6 to 7 per cent water and 2.5 to 3 per cent oil. I n all cases this material was pracMIXTURES CONTAINIKG 50 AND 100 PARTS CALCIUM CYANtically free from dicyanodiamide and urea. A typical AMIDE PER 1000 PARTS ACID PHOSPHATE-TWO mixtures of analysis of the freshly hydrated and oiled calcium cyanamide 45.4 kg. (100 pounds) each were prepared from calcium cyanis as follows : amide, acid phosphate, and sand, the sand being added as a Per cent Per cent filler to approximate roughly the dilution existing in some Total nitrogen 18 3 Dicyanodiamide nitrogen 0 0 mixed fertilizers. The calcium cyanamide had recently Water-soluble nitrogen 17.1 Urea nitrogen 0.0 Cyanamide nitrogen 17.0 Calcium 41.4 been hydrated and oiled. The mixtures were stored in heavy The other materials used are described in discussion of cloth bags in a storehouse and sampled a t intervals using an ordinary fertilizer sampling tube. mixtures containing them. The details of the experiments and the results are shown in PREPARATION A N D SAMPLINGOF MIXTURES-All mixtures were prepared by rotating in a ball mill until thoroughly Table I. The analytical data given in this and all subsemixed. I n sampling the small lots of bagged material, the quent tables have been corrected for changes in weight of the entire contents were first thoroughly mixed and then a 200- samples during storage. These mixtures were not analyzed to 300-gram sample taken. The samples were ground to for dicyanodiamide and guanylurea until the end of the pass 30 mesh. For the larger lots (45.4 kg.) samples from the storage period, owing to the lack of suitable methods until top, bottom, and three sides were obtained by means of a that time. sampling tube and the final sample taken after mixing these TABLE I-CHEMICAL CHANGES IN MIXTURES O B CALCIUM CYANAMIDE, ACID PHOSPHATE, AND SAND IN BAGSIN STOREHOUSE portions. At the end of the storage test the entire contents PER CENT TOTAL of the bags were thoroughly mixed and sampled. PER CBNT TOTAL NITROGEN PeOo PRESENT AS Total PRESENT AS WaterAvailaSTORAGE OF MIXTURES-Mixtures were stored (1) in an nitrogen Cyanamide Urea Undetersoluble able TIME Per cent nitrogen nitrogen mined PzOs PZOK unheated, well-ventilated storehouse under usual atmospheric conditions (duiing the period of this investigation the Mixture A-Calcium cyanamide, 50; acid phosphafe, 1000; sand, 950 $arts average temperature was 15' C. and the relative humidity 73 (Calrulated values)' 0.46 91.3 0.0 8.7 75.5 96.8 per cent as recorded by a Friez hygrothermograph); ( 2 ) in Beginning of espt. 0.43 88.4 0.0 11.6 49.7 97.1 closed containers a t laboratory temperature; and (3) in 1 week 0.46 17.4 3 0 . 4 (?) ... 46.7 97.0 0.0 73.9 26.1 49.5 96.2 4 weeks 0.46 sealed containers in an electric oven a t 72' to 75" C. 11 months 0.46 0.0 75.3 21.7b 42.1 93.7 AKALYTICAL METHODS-TOta1 nitrogen was determined Mixture B-Calcium cyanamide, 100; acid phosphate, 1000: sand, 900 p a d s by the Gunning method32and cyanamide nitrogen by Caro's (Calculated values) 0.92 91.3 0.0 8.7 78.5 96.6 meth0d,~3ammoniacal silver nitrate being used instead of the acetate as a precipitant. All the values for dicyanodi- Beginning 1 9 . 4 9 7.2 0 . 0 3 2 . 6 67.4 of expt. 0.92 91.7 76.9 22.0 7.7 15.4 1 week 0.91 amide were determined by the nickel method34except those 9 1.5 7 8 . 5 1 9 . 2 0.0 21.5 4 weeks 0.88 0.0 22.2 77.80 20.3 88.9 for Mixtures C and D, for which Brioux's m ~ d i f i c a t i o nof~ ~ 11 months 0 . 9 0 Caro's method was used. Guanylurea was not present in Mixture A . Total weight 45.4 kg.; 4t (temperature increase on mix17' C.; moisture in acid phosphate 7.7 per cent, free acid (PiOs)0.8 these two mixtures and the urea content was sufficiently ing) per cent. low for quite accurate results for dicyanodiamide to be in A .Mixture B. Total weightr45.4 kg.; At 25' C.: acid phosphate same as obtained with Brioux's modification. The method is not a Calculated values in this and subsequent tables are based on analyses before mixing. reliable, however, if guanylurea or considerable urea is pres- of constituents b Dicyanodiamide and guanylurea absent; 3 . 3 per cent of the total ent. Dicyanodiamide and guanylurea were not determined nitrogen as ammonia nitrogen. Of the total nitrogen, 27.8 per cent present as dicyanodiamide nitrogen, in several of the mixtures, owing to the lack of a suitable 32.2 cper cent as guanylurea nitrogen, and 3.3 per cent as ammonia nitrogen. method a t the time this investigation was started. The It is to be noted, in particular, that in Mixture A urea innickel method for dicyanodiamide consists in extracting the latter with acetone (guanylurea is not dissolved), hydrolyzing creased up to 78.3 per cent of the total nitrogen a t the end of to guanylurea in nitric acid solution, and weighing as the 11 months, and that no dicyanodiamide or guanylurea was nickel compound. Guanylurea present in the mixtures was present a t that time. I n Mixture B only 22.2 per cent of the total nitrogen was determined in an aqueous extract of the sample as the nickel compound. Urea was determined as ammonia by the urease in the form of urea, while 60 per cent was in the form of
tions as to the transformations of cyanamide nitrogen in commercial mixtures, such as those containing ammoniated base, other organic material, etc., together with acid phosphate, cannot safely be made on the basis of the results from the simple mixtures here studied.
66
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 17, No. 1
dicyanodiamide and guanylurea. It is seen also that, while either mixture a t any time during the storage. This was the water-soluble P2Os in Mixture A decreased markedly, expected, since in both Mixtures C and D monocalcium phosthe decrease in available (ammonium citrate-soluble) PzOs phate and other acid salts which are capable of causing the was negligible. I n Mixture B, however, an appreciable hydrolysis of dicyanodiamide to guanylurea were absent. decrease even in the citrate-soluble PzOsoccurred. MIXTURES CONTAINING UNTREATED CALCIUM CYANAMIDE MIXTURESCOWAININO250 AND 900 PARTSCALCIUM --For use as fertilizer, calcium cyanamide is usually treated CYANAMIDE PER 1000 PARTSACID PHOSPHATE-TO deter- with 6 to 7 per cent of water to decompose any unnitrified carmine the effect of greatly increasing the proportion of cal- bide and to hydrate the free lime, and 2 to 3 per cent of oil cium cyanamide in mixtures with acid phosphate, two to reduce the dustiness of the material. It seemed desirable, mixtures of 5.9 kg. each were prepared in the proportions however, to make some experiments in which untreated given above using partially air-dried acid phosphate. To calcium cyanamide was mixed with acid phosphate. The eliminate the action of atmospheric moisture and to confine calcium cyanamide contained 20.4 per cent total nitrogen. the chemical changes to reactions between the two ingredients, Two mixtures of 5.4 kg. each were prepared and analyzed over both of the mixtures were stored in air-tight jars a t laboratory a period of 4 weeks. The data are given in Table I11 and pretemperature. The results are shown in Table 11. sented graphically in Figs. 1 and 2. TABLE 11-CHEMICAL
CHANGES IN nIlXTURES O F CAI,CIUM CYANAMIDE AND ACID PHOSPHATE CONTAINING RELATIVELY LARGEPROPORTIONS OR CALCIUM CYANAMIDE PER CENT To-PER CENT TOTAL NITROGEN-TAL PzOa PRESPRESRNT AS ENT A S Total Cyan- Dicyano- Urea Undeter- Water- Availnitrogen amide diamide nitro- mined soluble able PgOa TIME Percent nitrogen nitrogen gen nitrogen pzos Mixture C. Calcium cyanamide. 250: acid phosphate. 1000 parts ~~. (Calculated values) 3.40 92.4 0.9 0.9 5.8 76.9 95.4 6 days 3.40 61.2 29.4 3.2 6.2 0.1 95.2 1 month 3.43 50.1 37.3 S.5 4.1 0.0 82.7 5month.s 3.42 29.8 50.0 10.5 4.7 0.0 79.1 10 months 3.38 16.6 57.1 21.9 4.4' 0.0 Mixfure D. Calcium cyanamide, 900: acid phosphate. 1000 parts (CVagTZzd 8.70 92.3 0.8 0.8 6.1 77.0 95.4 6days 8.45 89.5 2.1 1.0 7.4 0.0 88.8 1 month 8.50 90.1(?) 3.9 3.2 0.0 82.8 5months 8.47 85.5 5.7 1.5 7.3' 0.0 86.5 Mixture C . Total weight 5.9 kg.: At 40.5' C.; partially air-dried acid phosphate. Mixture D. Total weight 5.9 kg.; At 19.5' C . : partially air-dried acid phosphate. a No test obtained for guanylurea in either mixture at any time.
...
...
The reactions which are here shown to occur in such mixtures are in the main deleterious from the standpoint of fertilizers. It will be noticed in particular that dicyanodiamide is the chief decomposition product of calcium cyanamide and that there is a marked decrease in available phosphate. Transformations of unhydrdfed and unoiled csfcium cyanamide in rnixfure wifh acid ph0sph.de /n proporfions of 22 7 kq [ 5 0 l b s ) cs/cium cyanamide t o 454 kg (/OOO/bz) a c i d phosphete (Correspondinq/y comp/ef c dsfs for hydrafed 8od o//ed msferm/ nof sva//abie)
TABLE111-CHEMICAL CHANGESIN MIXTURESOF UNTREATED CALCIUM CYANAMIDE AND ACIDPHOSPHATS
-PER CENT TOTAL N I T R O G E N PRESENT AS-Total Cyan- Dicyano- GuanylUndenitrogen amide diamide urea Urea termined TIME Per cent nitrogen nitrogen nitrogen nitrogen nitrogen Mixture E . Calcium cyanamide, 50; acid phosphate, 1000 parts (Calculated values) 0.99 92.4 0.2 0.0 0 9 6.5 Beginning 0.0 3.9 25.1 2°A,",","t' 0 ' ' .09°8 4 67 0 .' 5 0 11.5 0.0 16.3 25.2 1 week 0.98 29.2 6.3 15.9 36.7 11.9 2 weeks 1.00 10.8 1.9 23.1 53.8 10.4 4weeks 1.00 1.5 2.7 23.2 62.0 10.6 Mixture F . Calcium cyanamide, 100; acid phosphate, 1000 parts (Calculated values) 1.87 93.2 0.2 0.0 0.9 5.7 ~ ~ ~ i ~ ~ i ~ ~ of expt. 1.85 54.7 17.8 5.4 7.0 15.1 2 days 1.83 40.6 26.7 2.9 10.0 19.8 1 week 1.83 28.9 29.8 7.7 18.3 15.3 2 weeks 1.83 17.1 31.2 12.1 26.8 12.8 4 weeks 1.82 7.5 30.5 14.7 35.9 11.4 Mixture E . Total weight 5.4 kg.; A t 39' C.; moisture in acid phosphate 9.9 per cent, free acid 1.7 per cent; storage in bags in storehouse. Mixture F . Total weight 5.4 kg.; A t 69' C.; acid phosphate and storage same as in Mixture E.
The outstanding fact shown by these data, particularly from Mixture E, is that a greater percentage of the cyanamide nitrogen is converted to dicyanodiamide and guanylurea when using untreated calcium cyanamide, than when using the treated material. The higher content of reactive lime and lower content of moisture in the mixture, and also the higher temperature reached on mixing, probably all contributed to the greater formation of dicyanodiamide. It is also seen that in Mixture E practically all the dicyanodiamide was hydrolyzed to guanylurea within a month. Substitution of untreated calcium cyanamide for the treated material in mixtures in the proportions 100 parts calcium cyanamide pef 1000 parts acid phosphate does not to any great extent alter the nature or rate of changes in the calcium cyanamide. Effect of Temperature on Decomposition of Calcium Cyanamide-Acid Phosphate Mixtures
It should be pointed out that the quantity of calcium cyanamide used in these mixtures is far above that employed in commercial practice. Exposure of such mixtures to atmospheric moisture would hasten the reactions. Guanylurea could not be detected in
When small quantities of calcium cyanamide and acid phosphate are mixed in the proportions of 50 to 100 parts of the former per 1000 parts of the latter, the temperature of the mix usually rises to 50" to 90" C . , but the heat of reaction is dissipated so rapidly that it apparently has no very pronounced influence upon the nature or rate of decomposition of the calcium cyanamide. On the other hand, in mixtures of several tons or more the outer layers of the mix, if left undisturbed, serve to retain the heat in the interior, and the centei of the pile may remain a t a comparatively high temperature for several days. Hill and Landis20 found that in preparing 10 tons of a mixed fertilizer, containing 454 kg. (1000 pounds) of acid phosphate and 56.7 kg. (125 pounds) of granulated calcium cyanamide per ton, the temperature in the center of the pile rose to 70" C. within 4 days after mixing and then slowly cooled off. To determine the effect of
IND UXTRIAL AND EATGINEERISG CHEMISTRY
January, 1925
elevated temperatures on the chemical reactions occurring in mixtures of calcium cyanamide and acid phosphate, two mixtures of 6.8 kg. (15 pounds) each were prepared in the proportions of 50 and 100 parts of calcium cyanamide to 1000 parts of acid phosphate, and 1.36 kg. (3 pounds) of each mix/w so
60 I
2
P@2r Pensforinefions of unhydrated and unoi/ed cdcium cyunamide in mixfure w i t h ucd phosphete. /nproporhons o f 4 5 4 ky. //OO/b$ ce/cium yanemide to 454 49 f/OOO/bs) acid . phosphate. (Correspondnqk cornp/ete dm'n f i r hydrsted end oded material n o f svui/ab/e;)
-
x 70
s
1
h0 .
67
Effect of Free Acid and Moisture in Acid Phosphate on the Decomposition of Calcium Cyanamide
Samples of acid phosphate containing different percentages of free acid and moisture were mixed with calcium cyanamide in proportions of 1000 parts acid phosphate to 50 parts calcium cyanamide. The phosphate was used directly as obtained from the factory, without attempting to modify in any way its free acid and moisture content. The phosphate used in Mixture K was permitted to air-dry. The conditions under which the experiments were made and the results obtained are shown in Table V. Dicyanodiamide and guanylurea were not determined until the end of the storage period.
OF FREE ACIDAND MOISTURE IN ACIDPHOSPHATE ON THE CHEMICAL CHANGES I N MIXTCRES CONTAINING 50 PARTSCALCIUM CYANAMIDE PER 1000 PARTS ACID PHOSPHATE, WHEN STORED IN BAGSIN STOREHOt'SE NITROGEN PRESINT A s Total PBR CBNT TOTAL nitrogen Cyanamide Urea UndeterTIME Per cent nitrogen nitrogen mined Mixture I . Moisture content of acid phosphate, 11.4 per cent; free acid (PaOs), 2.0 per cent; A t , 30' C. 0.0 8.1 0.87 91.9 (Calculated values) 0.0 18.6 0.86 81.4 Beginning of expt. 29.4 25.1 0.85 45.5 1 week 4 weeks 0.87 11.5 12 weeks 0.89 0.0 74.1 2:5:9 40 weeks 0.89 0.0 74.1 25.9' Mixture J . Moisture content of acid phosphate 10.3 per cent; free acid, 1.35 per cent; A t , 32' 'c. 11.1 82.2 6.7 Beginning of expt. 0.90 I I I I I 1 O b i 23.7 54.7 21.6 0.86 1 week 26.5 33.3 40.2 0.87 4 weeks 3 Weeks 4 Weeks IWeeh 2 Weeks ZL%ys 0.88 9 1 65.9 25.0 12 weeks 0.88 0.0 71.6 28.4) 40 weeks Moisture content of acid phosphate, 3.6 per cent; free acid, 0.31 Mixture K . ture were placed in sealed glass jars in an electric oven a t per cent; A t , 3' C . 72" to 75" C., the remainder being stored in cloth bags in Beginning of expt. 0.89 71.9 2.2 25.9 1 week 0.89 46.1 6.7 47.2 the storehouse. The results are shown in Table IV. 4 weeks 0.89 27.0 4.5 68.5 12 weeks 0.90 12.2 7.8 80.0 16 weeks 0 . 9 0 8 . 9 ... TABLEIV-EFFECT OF TEMPERATURE ON THE CHEMICAL CHANGESIN 40 weeks 0.89 0.0 14.6 85.40 CALCIUM CYANAMIDE-ACID PHOSPHATE MIXTURES Weight of each mixture, 4.54 kg. - - P E R CENT TOTAL NITR.OGEN PRESENTASPER CENT T O T A ~ Cyan- Dicyano- GuanylAmploPros PRESENT AS a Dicyanodiamide absent; 12.4 per cent of total nitrogen present as amide diamide urea Urea nia Unde- Water- Availguanylurea nitrogen. nitronitro- nitro- nitro- nitro- tersoluble able b Dicyanodiamide absent; 12.5 per cent of total nitrogen present a s TIME gen gen gen gen gen mined Pa06 PzOr guanylurea nitrogen. c Of the total nitrogen, 16.9 per cent present as dicyanodiamide nitrogen; Mixture G. Calcium cyanamide, 50; acid phosphate, 1000 pavts 55.1 per cent as guanylurea nitrogen. Weight of (1) Storage in bag in storehouse a t atmospheric temperature. sample, 5.4 kg. (Calculated It is seen from the results in Table V that the quantity of 0.0 0.0 1.2 0.0 4.7 80.3 92.8 values) 9 4 . 1 26 days 18.8 0.9 0.0 60.0 5.2 15.1 46.8 91.8 urea produced in mixtures containing 50 parts of calcium (2) Storage in closed container at 72' t o 75' C. Weight of sample, 1.36 kg. cyanamide per 1000 parts of acid phosphate is dependent upon 7days 0.0 0.0 0.0 37.033.7 29.3 34.4 88.1 the quantity of free acid and of moisture in the original Mixture € I . Calcium cyanamide, 100; acid phosphate, 1000 pavls acid phosphate. The acid phosphate used in Mixtures A , (1) Storage in bag in storehouse at atmospheric temperature. Weight of sample 5.4 kg. B, I , and J contained from 0.8 to 2 per cent free acid and (Calculated 0.0 0.0 1.2 0.0 4.7 80.3 92.8 7.7 to 11.4 per cent moisture, and in all cases more than 70 values) 9 4 . 1 26days 19.7 54.2 0.0 18.5 3 . 1 4.5 15.4 91.0 per cent of the total nitrogen was converted into urea. On (2) Storage in closed container at 72' t o 75' C. Weight of sample, 1.36 kg. the other hand, when air-dried phosphate is used, as in Mix7days 0.0 3.4 50.6 22.9 11.2 11.9 15.6 72.8 iMoisture content of acid phosphate in each case, 11.25 per cent; free acid ture K , the rate of decomposition is considerably slower and (Pa03 0.41 per cent. 1
1
TABLE V-EFFECT
...
...
Table IV shows that the rate of decomposition of calcium cyanamide-acid phosphate mixtures is greatly accelerated by elevating the temperature. Dicyanodiamide is rapidly hydrolyzed to guanylurea and the urea largely converted into ammonia, the latter reaction being particularly noticeable in Mixture G, containing 50 parts of calcium cyanamide per 1000 parts of acid phosphate. Nit,rogen compounds other than those determined were also produced in greater quantity in the mixtures stored a t 72" to 75" C., than in those stored a t atmospheric temperature. The rapid hydrolysis of dicyanodiamide to guanylurea in Mixture H stored at 72" to 75" C. explains the observations reported by Landis129that in a large fertilizer mixture containing calcium cyanamide and acid phosphate no dicyanodiamide could be found within a few days after the mixture was prepared, although the calcium cyanamide itself originally contained considerable dicyanodiamide,
the proportions of the decomposition products are practically reversed, about 70 per cent of the total nitrogen being present as dicyanodiamide and guanylurea and only about 15 per cent as urea. Mixtures I, J, and K were prepared and stored under identical conditions, and hence any differences in the rate or nature of the chemical changes may be safely attributed to differences in the free acid and moisture content of the original acid phosphate.
Chemical Changes Occurring i n Mixtures of Calcium Cyanamide with Mono- and Dicalcium Phosphate
Calcium cyanamide was mixed with mono- and dicalcium phosphate and stored to determine the effect of these two phosphates on the decomposition of calcium cyanamide. The monocalcium phosphate was carefully prepared from calcium carbonate and orthophosphoric acid. It contained about 5.5 per cent moisture and no free acid, the latter having been completely removed by repeated extraction with ether. The
INDUSTRIAL A N D ENGINEERING CHEMISTRY
68
dicalcium phosphate contained about 5.5 per cent moisture and no free acid or monocalcium phosphate. Mixtures of calcium cyanamide with the two phosphates were prepared in the proportions of 50 parts of the former to 1000 parts of the latter and stored in bags in the storehouse for 32 weeks. The rate of calcium cyanamide decomposition was found to be very much slower in both cases than in mixture with acid phosphate, the rate in the mixture containing dicalcium phosphate being nearly as slow as for calcium cyanamide alone. Urea, dicyanodiamide, and guanylurea were the identified transformation products in the mixture containing monocalcium phosphate, and the results showed conclusively that this phosphate is capable of causing the hydrolysis of dicyanodiamide to guanylurea. Urea and dicyanodiamide were formed in the mixture containing dicalcium phosphate. Guanylurea was not present in a detectable amount. , Stability of Dicyanodiamide and Urea in Mixture with Acid Phosphate
To determine the stability of the two principal decomposition products of calcium cyanamide-namely, dicyanodiamide and urea-in mixture with acid phosphate, three mixtures (2.27 kg. each) of C. P. dicyanodiamide and acid phosphate were prepared and stored in cloth bags. Before mixing with the dicyanodiamide, sufficient calcium oxide was added to the acid phosphate used in Mixture N to approximate the acid conditions existing in mixtures containing 50 parts of calcium cyanamide per 1000 parts of acid phosphate.
-
Vol. 17, N o . 1
HzCNz f HZO-CO(NHZ)~
(4)
I n large quantities of such mixtures, where a relatively high temperature persists for some time, considerable ammonia may be formed by hydrolysis of the urea. CO(NH2)z
+ Hz0-2”~
+ COz
(6)
When calcium cyanamide is mixed with acid phosphate containing what may be termed a normal amount of free acid, in the ratio of 1 to 10, or with air-dried acid phosphate in the ratio of 1to 20, the mixtures usually contain no free acid and comparatively little monocalcium phosphate, and hence the free cyanamide formed is largely polymerized to dicyanodiamide. 2HzCNz-
(HzCNdz
(6)
The dicyanodiamide formed in the mixtures is hydrolyzed to guanylurea, slowly at atmospheric temperatures and rapidly a t elevated temperatures such as might exist for some time when large quantities of the mixtures are prepared. (HzCNz)z
+ HzO+NHzC(NH)NHCONHz
(7)
Some unidentified nitrogen compound or compounds are evidently formed also in calcium cyanamide-acid phosphate mixtures. Acknowledgment
The authors are indebted to E. J. Fox, L. A. Pinck, M. A. Kelly, K. S. Love, M. S. Sherman, J. H. McCormick, W. Rosett, and L. Smith for the analytical data presented in this paper. Bibliography
1-Soderbaum, K g l . Landtbruks-Akad. Handl. T i d . , 46, 201 (1907). 2-Immendorf and Kempski, Centr. Bakt. Parasitenk. I I Abt., 20, TABLEVI-STABILITY OP DICYANODIAMIDE IN MIXTURE WITH ACID PHOSPHATE 304 (1908). PER CENT PRESENT PER CEXT ORIGINAl, 3-Anon., L’Engrais, 28, 159 (1908). IMMEDIATELY AFTER MIXING DICYANODIAMIDE 4-Anon., A m . Fertilizer, 29, No. 5 , 18 (1908). Period of Hydrolyzed Dicyano5-Namba and Kanomata, Bull. Coll. Agr. I m p . Univ. Tokyo, 7, 631 Free storage to diamide Present guanylurea PzOs Weeks nitrogen Mixture (1908); J . Chem. SOC.(London), 94, 623 (1908). 32.6 49 66.5 6-Hall, J . Board Agr., 14, 652 (1908). 0.46 0 006 N 58.2 27.3 32 1.45 NA 1 10 7-Pluvinage, Bull. SOC. encour. i n d . nut., 111, 549 (1909). 28.0 32 73.5 1.94 1.45 NB 8-Masson-Polet, J . soc. agy. Brabant el Hainaut, 64, 626 (1909). 9-Frear, Pa. Dept. Agr., Bull. 177, 78 (1909). It is seen that in mixture with acid phosphate, dicyanodi10-Schneidewind and Myer, Landw. Jahrb., 89, Erg 3, 236 (1910). 11-KBnig, Deut. Landw. Presse, 57, 375 (1910). amide is converted pirncipally into guanylurea. No change 12-Ampola, A n n . r . slaz. chim. agrar. sper. Roma, [2] 4, 73 (1910). could be detected in the urea content of mixtures containing 13-Hendrick, J . Soc. Chem. I n d . , SO, 522 (1911). urea and acid phosphate stored in cloth bags for 6 months. 14-Mil0, Arch. Suzkerind., a0, 1039 (1912). lt5-Christensen, Ugeskr. Landm., 58, 51 (1913). Discussion of Chemical Reaction Involved 16-De Wildt and Berkhout, Arch. Suikerind., 21, 717 (1913). 17--Brackett, J. I n d . Eng. Chem., 6, 933 (1913). The reactions occurring in mixtures of calcium cyanamide 18-Koppen, Illus. Landw. Z l g . , 54, 181(1914). 19-Pranke, American Pertiher Handbook, 1914, p. 67. and acid phosphate may be summarized as follows: 20-Hill and Landis, J . I n d . Eng. Chem., 6 , 20 (1914). Calcium cyanamide reacts with any moisture present in 21-Abr, Mztt. deut. Landw.-ges., S O , 732 (1915). acid phosphate to give free cyanamide and calcium hydroxide, 22-Malpeaux, V i e agr. el rurale, 6, 28 (1915). calcium acid cyanamide being formed as an intermediate 23--Hals, Tids. Novske Landbr., 2 2 , 332 (1915). 24--Pranke, Commercial Fertzlizer, 10, No. 2, 15 (1915). product. 25--King, Ibrd , 10, No. 1, 14 (1915). 2CaCNz 2Hz0-+Ca(HCNz)z f Ca(0H)z (1) 26-Haselhoff, Fdhling’s Landw. Ztg., 66, 105 (1917). Ca(HCN& 2H20c;LLH?CNz Ca(OH)p (2) 27-Pranke, Chem. Met. Eng., 23, 1102 (1920), Calcium cyanamide reacts with monocalcium phosphate to 28--Harger, J . I n d . Ens. Chem., 12, 1111 (1920). 29-I,andis, A m . Feutzlizer, 64, No. 2, 49 (1921); J . I n d . Eng. Chem., 14, produce free cyanamide, dicalcium phosphate, and some tricalcium phosphate if the calcium cyanamide is present in 143 (1922). 3O--Breckenridge, Ibid., 14, 145 (1922). sufficient quantity. Calcium acid Cyanamide is formed as an 31-Aston, New Zealand Dept. A g r . , Annual Report 17, 187 (1909). intermediate product. 32-Assoc. Official Agr. Chem., Methods, 1920. p. 7. 33--Pranke, “Cyanamide,” 1915, p. 20. The Chemical Publishing Co., CaCNz Ca(HZPO&AHzCN2 2CaHPOd (3) Esston, Pa. The reaction with free phosphoric acid, and possibly with 34-The details and applications of this method will be published later. dicalcium phosphate, takes place in a similar manner. Mono3 6 F o x and Geldard, I n d . Eng Chem., 16, 743 (1923). 3&Matthews, J. Agr. Sci., 10, Part I, 72 (1920). calcium phosphate and free phosphoric acid also react with 37-Assoc. Official Agr. Chem., Methods, lSa0, p. 3.
++
+
+
+
the calcium hydroxide present in calcium cyanamide liberating water, which may be partially used up in Reactions 4; 5, and 7. I n mixtures containing considerable free acid or monocalcium phosphate, the free cyanamide produced principally by Reactions 2 and 3 is largely hydrolyzed within a short time to urea.
Production of Cyanamide in France-Cyanamide was produced in France in 1923 by three plants at Bellegrade, Marignac, and Brignoud. During the present year other cyanamide factories have been established, and it is anticipated that the total output of the French cyanamide factories in 1924 will reach 90,000 tons, representing 18,000 tons of nitrogen.
