The method of analysis of the composition of liquid nitrogen fertilizers based on urea and ammonium nitrate

 

(57) Abstract:

The inventive determine the density of the mixed aqueous solution of urea and ammonium nitrate at 25oAnd titrimetric method set the concentration of ammonium nitrate in the same solution, and then calculate the index of composition of the solution, for example, the total mass fraction of nitrogen, equation with constant coefficients. However, when used in agriculture mixed aqueous solutions of urea and ammonium nitrate as liquid nitrogen fertilizer added to them in a relatively small doses of other components depending on the objectives pursued, for example, ammonium phosphates, as a corrosion inhibitor (0.2% of P2O5) or trace elements (from a few hundredths of a percent to several percent). This method takes into account the possible influence of impurities on the density of the mixed aqueous solution of urea and ammonium nitrate, resulting in the complex task of analyzing the composition of the liquid nitrogen fertilizers with various impurities is reduced to a more simple and already solved the problem of analysis of net mixed aqueous solution of urea and ammonium nitrate. At the same time analyze the fertilizer is to be derived from fertilizer, if the last impurities related substances to replace the equivalent mass quantities of water. The density of the thus obtained pure mixed aqueous solution can easily be calculated depending on the impurity content in the fertilizer and the temperature at which the measured density of the fertilizer in the range of 20 - 30oC. the result can be calculated not only the ratio of total nitrogen, and mass fraction of urea in the fertilizer with impurities related substances. 2 C.p. f-crystals, 3 tables.

The invention relates to analytical chemistry, in particular, to methods of analysis of liquid nitrogen fertilizers containing urea and ammonium nitrate in the form of their mixed aqueous solution.

These fertilizers are known under the name "Cam" or "Cam solutions". They contain from 28 to 34 wt.% of nitrogen.

There is a method of analysis of the composition of the mixture of nitrogen fertilizers (including liquid nitrogen fertilizers based on urea and ammonium nitrate) with the subsequent calculation of the indicator composition [1].

As an indicator of the composition of the calculated total mass fraction of nitrogen in the mixture. The essence of the method consists in the reduction of nitrate nitrogen to ammonia chromium powder in hydrochloric acid medium, the ammonium concentrated sulfuric acid in the presence of a catalyst, the Stripping of ammonia from the alkaline solution, the absorption of ammonia excess titrated solution of sulfuric acid, the reverse titration of the excess acid is titrated with a solution of sodium hydroxide and subsequent calculation of the mass fraction of nitrogen depending on the volume of titrated solutions of sulfuric acid and sodium hydroxide.

The disadvantages of this method are its complexity, duration, complexity and poor reproducibility of the analysis results. In addition, the method determines only the total percentage of nitrogen contained in all the substances of the sample. In the analysis of liquid nitrogen fertilizers based on urea and ammonium nitrate in this way it is impossible to determine the proportions in which these substances are among themselves, although it depends on the crystallization temperature of the fertilizer.

The closest set of features and technical essence is a method of analysis of the composition of liquid nitrogen fertilizers based on urea and ammonium nitrate, including determination of mass fraction of ammonium nitrate (xAND) titrimetric method, the density measurement fertilizers (dbeats) and the calculation of the composition of the fertilizer (p) with uhA+a5x2A+a6d

where xN- total mass fraction of nitrogen in the fertilizer, %;

xAND- mass fraction of ammonium nitrate fertilizer, %.

Since this method ignores the impurities related substances in fertilizers, in equation take d = dbeatswhile the density of the fertilizer dbeatsmeasured at 25oC.

For use in agriculture mixed aqueous solutions of urea and ammonium nitrate as liquid nitrogen fertilizer UAN added to them in a relatively small doses of other components depending on the objectives pursued. For example, in Cam solutions to reduce their corrosive add the ammonium phosphates in amounts of 0.2 - 0.5 wt.% in terms of P2O5and up to 0.5 wt.% free ammonia. Sometimes Cam solutions saturated with trace elements such as molybdenum, cobalt, boric acid, zinc, copper, manganese in the form of their salts, of complexions or chelate compounds to increase crop yields, and concentrations of these compounds in a mixed aqueous solution of urea and ammonium nitrate can take values in the range from a few hundredths of a percent to several procento etc. (0.5 to 1.5 wt.%) to extend the validity period on plants of nitrogen contained in the fertilizer.

Some substances in liquid nitrogen fertilizer in the production of impurities along with the original solutions coming onto the mixture in the preparation of fertilizers. For example, an aqueous urea solution contains ammonia (0.3 to 0.8 wt.%), carbon dioxide (0.5%), biuret (0.4%), the resulting net thermal decomposition of urea.

There is also information about applying as a liquid nitrogen fertilizer mixed aqueous solutions of urea, ammonium nitrate and ammonium sulphate.

In light of the above, the main disadvantage of the prototype method is ignoring admixtures of other substances in addition to urea and ammonium nitrate. Impurities affect the density of the fertilizer and cause an additional error in the calculation of the composition of the fertilizer by the equation obtained for pure mixed aqueous solution of urea and ammonium nitrate.

Another disadvantage of the prototype method is that its application must be fixed at the level of the 25oC sample temperature equation. This requires the use of components of the prosperity of the prototype method is after calculation of the indicator composition of the fertilizer, in this case, the total content of nitrogen in the fertilizer, it is necessary amendments to the value, since it only takes into account the nitrogen contained in the urea and ammonium nitrate, and ignores the nitrogen introduced in the fertilizer together with impurities.

The objective of the invention is to provide a method of analysis of the composition of liquid nitrogen fertilizers based on urea and ammonium nitrate containing significant impurities of various other substances.

An additional object of the invention is to simplify and reduce the complexity of the method of analysis of fertilizers due facilitate the determination of the density of fertilizer.

In addition, the invention aims to expand the range of the calculated indicators of the composition of the fertilizer.

This problem solved by the fact that in the known method of analysis of the composition of liquid nitrogen fertilizers based on urea and ammonium nitrate, including determination of mass fraction of ammonium nitrate (xAND) titrimetric method, the density measurement fertilizers (dbeats) and the subsequent calculation of the composition of the fertilizer (p) using equations with constant coefficients A+a6d

where n is the number of considered impurities;

Bi- empirical constant, pre-selected for each of the i-th impurity and defined by the formula

< / BR>
where d0- density at 25oC sample aqueous solution not containing impurities;

Di- density at 25oC sample aqueous solution with exactly the same content of urea and ammonium nitrate, as in the first sample, but additionally including only one of the i-th impurity related substance with a mass fraction Yi.

In addition, according to the invention as a calculated measure of the composition of the fertilizer accept ratio

< / BR>
where xTO- mass fraction of urea;

xAND- mass fraction of ammonium nitrate,

in the case of the expression of the density in kg/m3and the mass fraction of ammonium nitrate in percent using the following values of the constant coefficients: a1= 7,60667; a2= -1,53776 10-2; a3= 8,22779 10-6; a4= 8,34644 10-2; a5= 1,55006 10-4; a6= -8,87473 10-5.

Another difference is that as a calculated parameter of the composition of liquid nitrogen fertilizer (p) take the mass fraction of urea (xauzentech use the following values of the constant coefficients: a1= -3,10303 102; a2= 2,93498 10-1: a3= 1,87906 10-5; a4= 1,07516 10-1; a5= 1,31491 10-4; a6= -1,33328 10-3.

Due to the fact that the method of analysis of liquid nitrogen fertilizer according to the invention takes into account the influence of particles of foreign substances on the density of the mixed aqueous solution of urea and ammonium nitrate, a difficult task analysis fertilizers containing any number of impurities is reduced to a simpler problem - the analysis of a mixed aqueous solution containing no impurities. Ultimately increases the accuracy of the analysis of the composition of the fertilizer.

By expanding the scope of permissible temperatures when measuring the density of the fertilizer to 20-30oC (instead of a fixed temperature of 25oC) there is no need to use a thermostat and additional time to stabilize the temperature of the sample at 25oC. it simplifies and eases the way of analysis of fertilizers in General.

When calculating an indicator composition ratio xTO/(xTO+ xANDor the mass fraction of urea xTOthere is no need to amend the indicator composition, because the impurities carabodidae to determine the empirical constants Biwith regard to phosphates of different nature, added to the mixed aqueous solution of urea and ammonium nitrate as corrosion inhibitors.

As ammonium phosphates used:

1) liquid complex fertilizers HCS 10:34:0, containing a mixture of ammonium phosphates (ortho-, pyro-, Tripoli, Metropolitanate) 34 wt.% in terms of P2O5;

2) diammonium phosphate;

3) monoammonium phosphate (map).

In experiments 1 to 20 weight method were samples of mixed aqueous solutions of urea and ammonium nitrate containing and not containing (experiments 1, 6, 9, 12, 15, 17) impurities phosphates. For example, in experiment 1 determined the density (d0) at 25oC net mixed aqueous solution of urea (37,81 wt.%) and ammonium nitrate (36,81 wt.%), as in experiments 2 - 5 the influence of the additive phosphates in the form of HUS density of sample (Dicontaining the same amount of urea (37,81%) and ammonium nitrate (36,81%) at different values of the mass fraction Yithe accompanying substances. In column 8 of table. 1 the calculated values of Bifor phosphates in the measurement of their mass fraction in percent P2O5. The value of Bivary in the interval from 0,00390 to 0,00418 that nahoditsya difference values Biin the interval 0,00387 - 0,00469, which is in satisfactory agreement with the results for utility services, given that the concentrations of various ammonium phosphates having different molecular weight, reduced to the common database - mass fraction P2O5.

Experiments 21 and 22 show an example of monoammonium phosphate (LFA) as a companion substances saline nature that the constant Biit is possible to determine, without conducting additional studies (such as experiments 1 to 20), but only by using already published data on the density of aqueous solutions of this concomitant substances.

In the experience of 22 mass fraction of the LFA is given in terms of P2O5that helped lead to the result of this experience (Bi= 0,00432) in accordance with the previous experiments. Thus, the last value of Bi= 0,00432 can be used for ammonium phosphates with different chemical structures subject to a recalculation of their concentration in % P2ABOUT5.

Example 2. In table. 2 shows the experimental results set to determine the empirical constants Biwith respect to ammonium sulfate which may be present in liquid nitrogen fertilizer as an additional cue empirical constants Biwith difference from 0,00193 to 0,00225, which is quite acceptable and due to unavoidable experimental errors. You can take B = 0,002.

It should be noted that experiments 7 and 8 confirm established in example 1, the fact that the impurity salt nature increase the density of the liquid sample by the same law, regardless of the content of urea and ammonium nitrate Therefore, when determining the empirical constants Bithere is no need to compare the density of the mixed aqueous solution of urea and ammonium nitrate; it is enough to compare the density of an aqueous solution of the salt of Diwith the density of pure water d0at 25oC.

Example 3. In the process of cooking liquid nitrogen fertilizer from aqueous solutions of urea and ammonium nitrate in a mixture of nitric acid to neutralize the excess of ammonia introduced into the mixture together with the urea solution, and bringing the final amount in the mixture up to 0.02 - 0.05 wt.%. In this respect, it may be necessary to control the composition of the mixture in the content of major nutrients in the background impurities of ammonia or nitric acid.

In table. 3 shows the results of experimental research of the influence of impurities it is ity, the corresponding solutions without additives, are not included in table 3.

Adding ammonia to the solution while maintaining the concentration of urea and ammonium nitrate) reduces the density of the solution. For ammonia accept the averaged value of the empirical constant Bi= -0,0035.

Adding nitric acid to the liquid nitrogen fertilizer in excess of 2 wt.%, leads to the formation of the sludge solution of nitrate of urea. Relatively small differences in the value of the empirical constant Bicalculated for nitric acid when it is added to water (0,00247) and to the solution of fertilizer (0,00276), indicate that the acid influence on the density behaves as salt and substances of nature. Therefore, nitric acid, you can take Bi= 0,0025, focusing on the experience of 8.

Example 4. The analysis of the composition of liquid nitrogen fertilizers based on urea, ammonium nitrate and water, containing as impurities related substances ammonium phosphates, ammonium sulfate and ammonia.

Measure the density of samples of fertilizers: dbeats= 1293 kg/m3. When measuring the density of the sample temperature was equal to t = 20,6oC, i.e., not coming out of every 20 - 30oC.

Using traditional techniques, establish mass fraction Yirelated substances, numbered in the order listed, - ammonium phosphate (1), ammonium sulphate (2) and ammonia (3): Y1= 0,33 wt.% P2O5; Y2= 9.5 wt.% (NH4)2SO4; Y3= 0.09 wt.% NH3.

The number of impurities is n = 3.

Accept the following values of empirical constants Bi: B1= 0,0043 (from table. 1, column 8, line 22); B2= 0,0022 (from table. 2, column 8, line 8); B3= 0,0035 (from table. 3, column 8, line 6).

We calculate the density:

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The dimension of density kg/m3.

Next, the calculated parameters of the composition of the fertilizer equation with constant coefficients.

The total mass fraction of nitrogen present in the urea and ammonium nitrate:

xN= -1,34579 102+ 1,17876 10-11226,2 + 1,75870 10-51226,22+ 5,00661 10-134,1 + 2,21304 10-434,12- 7,10431 10-41226,2 34,1 = -134,579 + 144,53955 + 26,443223 + 17,07254 + 0,2573345 - 29,705549 = 24,028 wt.%.

Mass fraction of urea in the fertilizer:

xTO= -3,10303 102+ 2,93498 10-11226,2 + 1,87906 10-51226,22+ 1,07516 10-134,1 + 1,31491 10-434,12- 1,33328 10-3the ia for less impurities related substances:

xTO/xTO+ xAND= 7,60667

-1,53776 10-21226,2 + 8,22779 10-61226,22+ 8,34644 10-234,1 + 1,55006 10-434,12- 8,87473 10-51226,2 34,1 = 7,60667 - 18,856013 + 12,371028 + 2,846136 + 0,1802425 - 3,7108281 = 0,437.

Here we find another equation: xTO/xAND= 0,437 / (1 - 0,437) = 0,777.

1. The method of analysis of the composition of liquid nitrogen fertilizers based on urea and ammonium nitrate, including determination of mass fraction of ammonium nitrate (xand) titrimetric method, the density measurement fertilizers (dyd) and the subsequent calculation of the composition of the fertilizer (p) using equations with constant coefficients a1- a6:

p = a1+a2d+a3d2+a4xA+a5x2A+a6d

where n is the number of considered impurities;

Bi- empirical constant, pre-selected for each of the i-th impurity and defined by the formula

< / BR>
where dabout- density at 25oWith an aqueous solution not containing impurities;

Di- density at 25oWith samples of an aqueous solution containing urea and ammonium nitrate equal to the content of these substances in the first sample, optionally including the i-th impurity e calculated indicator of the composition of the fertilizer accept ratio

< / BR>
where xtoand xAND- mass fraction of urea and ammonium nitrate, in the case of the expression of the density in kg/m3and the mass fraction of ammonium nitrate in percent using the following values of the constant coefficients: a1= 7,60667; a2= -1,53776 10-2; a3= 8,22779 10-6; a4= 8,34644 10-2; a5= 1,55006 10-4; a6= -8,87473 10-5.

3. The method according to p. 1, characterized in that as a calculated parameter composition of fertilizers take mass fraction of urea, in the case of the expression of the density in kg/m3and mass fraction of urea and ammonium nitrate in percent using the following values of the constant coefficients: a1= -3,10303 102; a2= 2,93498 10-1; a3= 1,87906 10-5; a4= 1,07516 10-1; a5= 1,31491 10-4; a6= -1,33328 10-3.

 

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