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Revista ION

versão impressa ISSN 0120-100X

Rev. ion vol.29 no.2 Bucaramanga jul./dez. 2016

http://dx.doi.org/10.18273/revion.v29n2-2016010 

Artículos de Investigación Científica y Tecnológica

Solubility of Urea in ethanol-water mixtures and pure ethanol from 278.1K to 333.1K

Solubilidad de Urea en mezclas de etanol-agua y etanol puro a temperaturas de 278,1K a 333,1K

Solubilidade da Ureia em misturas de etanol-água e em etanol puro em temperaturas de 278,1K a 333,1K

Ana Paula Silva Capuci1  , Noemy D. de Carvalho1  , Moilton R Franco Jr2  , Ricardo A Malagoni1 

1University of Uberlândia Chemical Engineering Faculty Brazil

2 PPG - Biocombustíveis - IQUFU Federal University of Uberlândia, Av. João Naves de Ávila, 2121, Bloco 1 K, Campus Santa Mônica, Uberlândia - MG, Zip Code: 38.408-144, Brazil

Abstract

This paper deals with the solubility of urea in ethanol-water mixtures in mole fractions of ethanol between 0.0901 and 1.000 at temperatures ranging from 278.1 to 333.1K. The investigation of solubility contributes to research in many others fields of study in chemical engineering, since there are several studies where the solubility of urea and its behavior in solution influence the system. The experiment was carried out at constant temperature, stirring for 2h and then leaving the solution at rest for 2h. After collecting the data, the solubility of urea was calculated based on the gravimetric method. The experimental results obtained were correlated with the temperature of the solvents using three equations based on the literature. The three models demonstrated results in line with the experimental data. It was observed that adding ethanol to the water decreased urea solubility in all cases. The differences between the predicted and the experimental values were on average 4.7%.

Key words: urea; ethanol; gravimetric method; solubility

Resumen

Este artículo trata de la solubilidad de la urea en mezclas de etanol-agua en fracciones molares de etanol entre 0,0901 y 1,000 a temperaturas de 278,2 a 333,2K. La investigación de la solubilidad contribuye en muchos estudios en muchos otros campos de estudio en ingeniería química, ya que hay varios estudios en que la solubilidad de la urea y su comportamiento en solución influyen en el sistema. El experimento se llevó a cabo a temperatura constante, se agitó durante 2h y en seguida la solución se dejó en reposo también por 2h. Después de recoger los datos, la solubilidad de la urea se calculó basándose en el método gravimétrico. Los resultados experimentales obtenidos se correlacionaron con la temperatura de los disolventes usando tres ecuaciones basadas en la literatura. Los modelos han demostrado resultados en línea con los datos experimentales. Se observó que la adición de etanol al agua disminuye la solubilidad de la urea en todos los casos. Las diferencias entre los predichos y los valores experimentales fueron en promedio de 4,7%.

Palabras-clave: etanol; método gravimétrico; solubilidad

Resumo

Este artigo trata da solubilidade de uréia em misturas de etanol-água em frações molares de etanol entre 0,0901 e 1,000 e temperaturas que variam de 278,1 a 333,1K. A investigação de solubilidade contribui para a pesquisa em muitos outros campos de estudo em engenharia química, uma vez que há vários estudos em que a solubilidade da ureia e o seu comportamento em solução influenciam o sistema. O experimento foi realizado a uma temperatura constante com agitação de 2h e, em seguida, deixando a solução em repouso durante 2h. Depois de recolher os dados, a solubilidade da ureia foi calculada com base no método gravimétrico. Os resultados experimentais obtidos foram correlacionados com a temperatura dos solventes utilizando três equações com base na literatura. Os três modelos demonstraram resultados condizentes com os dados experimentais. Observou-se que a adição de etanol na mistura provoca diminuição na solubilidade ureia em todos os casos. As diferenças entre os valores previsto e os experimentais foram, em média, 4,7%.

Palavras-Chave: uréia; etanol; método gravimétrico; solubilidade.

Introduction

Urea (NH2-CO-NH2) is the most commonly used nitrogen fertilizer in the world, due to their low value and high nitrogen content 1,2. Urea has also many uses in chemical industries such as the manufacture of resins, medicines, cosmetics and cleaning products 1,2,3,4,5,6. Besides, it has great biological importance, since it is the final metabolite of nitrogenous compounds in mammals 1,3,5. The study of the solubility is important in the process of nucleation and crystallization 7,8,9,10,11,12. The solubility of urea is not fully explored and the process has not been studied over wide ranges of temperature and solvents 13-14.

Since ancient times, some natural and industrial processes require information of mixtures in equilibrium phases containing, or not, electrolytes. Some examples are: precipitation and crystallization processes; water desalination; control of water pollution; extraction and distillation; food processing, production of fertilizer among others 15.

Data regarding chemical compounds solubility in water and solvent mixtures are fundamental in designing of industrial separation equipment such as crystallizers, extractors, evaporators and absorption units.

The solubility of organic compounds in water is an important data in chemical, pharmaceutical, food industries, and environmental applications 16. The lack of experimental solubility data of solutes in solvents limits the development of predictive models 17.

The study of the water-organic phase behavior is essential in the design of separation process and operation of separation units in the chemical industry and in related industries 11. In many cases a complete equilibrium data is practically impossible due to the long time taken to get them and also by the high cost of analysis. Thus, models and parameters are obtained by a minimum number of experiments 18. Data on the solubility of urea in aqueous ethanol solution are essential for industrial design and further theoretical studies 10,11. In this paper, the solubility of urea in pure ethanol and in ethanol and water mixtures (0.0901; 0.2096 and 0.3757 of ethanol) at temperatures ranging from 278.2 to 333.2K was systematically measured by gravimetric method. The results were correlated using different equations available in the literature.

Experimental

Materials

Urea with 99.5% (in mass) purity and ethanol with a purity of 99.8% (in mass) were purchased from Nuclear and Vetec, respectively. Deionized (E. J. Krieger & Cia. Ltd., model Permution) and distilled (Quimis, model G.341.25) water was used in the experiments. All chemicals were used without further purification.

Experimental apparatus

The solubility of urea was measured using an equilibrium cell similar to that reported in the literature 10,11,12,13,14. The solubility of urea was determined in a temperature range from 278.2 to 333.2K at atmospheric pressure (92654.3Pa), in pure ethanol and mixtures of water and ethanol with ethanol mole fractions of 0.0901, 0.2096 and 0.3757, in a previously prepared solution using analytical balance (Gehaka, AY-220± 0.0001g). A jacketed borosilicate glass cell with capacity of

40.0mL and with sampling points at the side was used in this work. Urea was added in excess to the solution, which was stirred for two hours using a magnetic stirrer (Marconi, MA-089).

Subsequently, the system was left decanting for two hours, keeping the temperature control of the cell through a thermostatic bath (Marconi, MA-184). A thermocouple (Full-Gauge, TIC-17RGTi ± 0.1K), which was calibrated using an Incoterm standard thermometer (± 0.1K), was used to measure the temperature inside the cell. The experimental apparatus can be seen in Figure 1.

Figure 1 The experimental apparatus: (A) Equilibrium cell; (B) Magnetic stirrer; (C) Latex hose; (D) Thermocouple; (E) Thermostatic bath. 

For each temperature, four samples were drawn using a glass syringe (10mL, Artiglass) to check the reproducibility of the procedure. The samples were quantified by gravimetric analysis, remaining 48h in a stove (Medicate, MD-1.3) at 338.2K.

After the drying period, the samples containing crystallized urea was placed in a desiccator with silica for 30min, then the molar fraction of dry urea was quantified to determinate the value of solubility. Four solubility values ( xexp ) were determined for each temperature. Afterwards, the average of those four measurements was computed. Equation 1 was used to calculate the mole fraction solubility 10:

where m1, m2 and m3 represent the mass of the solute (urea), solvent (water, ethanol) and ethanol only, respectively. M 1, M 2 and M 3 are the respective molecular weights.

Results and Discussion

Experimental data

Table 1 contains solubility data experimentally obtained for the urea in a mixture of ethanol and water with ethanol mole fraction of 0.0901; 0.2096 and 0.3757 and in pure ethanol. This table also reports standard deviations (δ) of the value of solubility for each temperature and shows data available in the Lee and Lahti’s 13 work for urea in ethanol and water mixtures in compositions of 0.1242 and 0.3095 (mole fraction) and in pure ethanol. These results were used for comparison and validation of the data found on this paper.

Table 1 Experimental solubility of urea in ethanol-water mixtures and in pure ethanol at different temperatures along with the solubility of urea in Lee and Lahti 13

It is noticeable that the solubility of urea in a mixture of ethanol and water increases with increasing temperature and decreases with increasing ethanol concentration to the mixture. The fact that the solubility decreases with decreasing temperature at low pressures is attributed to the reduction in density 19. Figure 2 shows the decrease in solubility of urea with increasing mole fraction of ethanol in the solution.

We can also observe that the standard deviation was low in all cases (about 4.7%). Figure 3 shows solubility data for urea in mixture of ethanol and water obtained in this study, along with the data of Lee and Lahti 13. Comparing the data obtained in this study with the data provided by literature, the results were consistent.

Figure 2 Solubility of urea (in mole fraction) in all temperaturas 

Figure 3 Solubility of urea: (○), 20.2% ethanol; (●), 26.64% ethanol (Lee and Lahti); (◊), 40.4% ethanol; (♦),53.36% ethanol (Lee and Lahti); (□), 60.6% ethanol; (+), 100% ethanol; (▲), 100% ethanol (Lee and Lahti). 

Adjustments of solubility

Literature (13, 20, 21, 22) reports several equations or models to correlate solubility data. In this paper, we can cite the useful correlations proposed by Lee and Lahti 13, Yaws et al.20, Buchowski et al.22. The solubility of urea in mixture of solvents was correlated by Eqs. (2), (3) and (4).

where xc1 represents the solubility calculated using the Lee and Lahti equation; A and B represent the parameters of the equation and T represents the temperature measured in Kelvin.

where xc2 represents the solubility calculated using the Yaws equation; A’, B’ and C’ represent the parameters of the equation and T represents the temperature measured in Kelvin.

where x c3 is the solubility of urea calculated using the Buschowski equation; λ and h are the model parameters, T and Tm are the experimental and the standard melting point of urea in Kelvin, respectively.

The correlations of experimental data and data calculated using the thermodynamic models obtained from the relative deviation (RD) expressed by Equation 5 are listed in Table 2. The parameters of models obtained from linear and nonlinear regressions and their values are listed in Tables 3−4. The relative average deviation (RAD) and the corresponding root mean square deviation (RMSD) along with the R2 as expressed by eqs 5, 6, 7 are shown in Tables 3−5.

Table 2 shows the experimental and calculated results of solubility for urea in ethanol+water and in pure ethanol using the Equations 2 - 4. It is important to comment that to calculate the values in Table 2 it was follow the same experimental temperatures showed in Table 1.

According to the above-mentioned correlations of experimental data obtained at different temperatures in various mixtures of ethanol and water and in pure ethanol together with the calculated data (Tables 2−5), it was indicated that the solubility of urea calculated from the studied models showed good agreement. Taking the solubility data in the selected solvents fitted by the Yaws et al. model as an illustration, the relative average deviations are 0.01%, 0.06%, 0.16%, and 0.62%, respectively; which indicate that the modified Yaws et al. equation is suitable for correlating the solubility data of urea in the mixtures of ethanol and water and in pure ethanol. The same conclusion can be drawn after analyzing the solubility data and the parameters that fitted by the Lee and Lahti equation and the Buchowski λh equation.

However, we can see that the RAD values of Lee and Lahti equation, the Yaws et al. equation and the Buchowski−Ksiazaczak λh equation are 4.84%, 0.86%, and 0.97%.

This result indicates that the Yaws et al. model proved to be more accurate and suitable for the description of dissolution of urea in the studied solvents at various temperatures.

Figure 4 shows the solubility of urea in a mixture of ethanol and water and in pure ethanol correlated with Equation (3). Analyzing Figure 4, it can be noted that the equation proposed by Yaws et al. (Equation 3) correlates the solubility of urea data well.

Table 2 Experimental and calculated (Eq. 2 - 4) solubility of urea in pure ethanol and ethanol+water mixtures. 

Table 3 Parameters of the Lee and Lahti model for Urea in pure ethanol and ethanol+water mixtures 

Table 4 Parameters of the Yaws model for Urea in pure ethanol and ethanol+water mixtures. 

Figure 4 Mole fraction solubility of urea: (○), 20.2% ethanol; (□), 40.4% ethanol; (◊), 60.6% ethanol; (▲), 100% ethanol; (-) correlated data with Equation (3) 

Table 5 Parameters of the Bucchowski λh model for Urea in pure ethanol and ethanol+water mixtures. 

Conclusion

The solubility of urea in ethanol-water mixtures and in pure ethanol within the temperature range 278.1 to 333.1K was measured. The authors got the following conclusions: (1) The solubility of urea increased when temperature increased. (2) The addition of ethanol in the mixture resulted in a decreasing of urea solubility which can be verified by analyzing the experimental data of this paper and the literature data. (3) The solubility phenomena of urea were evaluated using the thermodynamics models. The data calculated from the Yaws et al. model was in good agreement with the experiment. This model was the most suitable for the description of the dissolution of urea.

Also, the experimental apparatus proved to be efficient in determining the data solubility using the gravimetric method, since the standard deviations of the samples were low.

The solubility data obtained in this paper is important because it may also contribute to other scientific research, since there are references where the solubility of urea in solution and it behavior influence and modify the system under study.

List of symbols

A Parameter of Equation 2

A’ Parameter of Equation 3

B Parameter of Equation 2

B’ Parameter of Equation 2

C’ Parameter of Equation 3

h Parameter of Equation 4

λ Parameter of Equation 4

mi Mass

Mi Molecular weight

N Number of experiments in Equation 6

T Temperature (K)

xexp Experimental urea solubility (mole fraction)

xc1 Calculated solubility using Equation 2

xc2 Calculated solubility using Equation 3

xc3 Calculated solubility using Equation 4

Δ Standard deviation

Acknowledgments

This work was financially supported by FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais)

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0Cita: Silva AP, de Carvalho ND, Franco Jr MR, Malagoni RA. Solubility of Urea in ethanol-water mixtures and pure ethanol from 278.1K to 333.1 K. rev.ion. 2016;29(2):125-133

Received: 2015; Accepted: 2016

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