ie801286h

8/6/2019 ie801286h

1/8

Equilibrium and Kinetic Studies of in Situ Generation of Ammonia from Urea in

a Batch Reactor for Flue Gas Conditioning of Thermal Power Plants

J. N. Sahu, A. V. Patwardhan, and B. C. Meikap*

Department of Chemical Engineering, Indian Institute of Technology (IIT), Kharagpur, P.O. Kharagpur

Technology, West Bengal, 721302, India

Ammonia has long been known to be useful in the treatment of flue/tail/stack gases from industrial furnaces,incinerators, and electric power generation industries. In this study, urea hydrolysis for production of ammonia,in different application areas that require safe use of ammonia at in situ condition, was investigated in a batchreactor. The equilibrium and kinetic study of urea hydrolysis was done in a batch reactor at reaction pressureto investigate the effect of reaction temperature, initial feed concentration, and time on ammonia production.This study reveals that conversion increases exponentially with an increase in temperature but with increasesin initial feed concentration of urea the conversion decreases marginally. Further, the effect of time onconversion has also been studied; it was found that conversion increases with increase in time. Using collisiontheory, the temperature dependency of forward rate constant developed from which activation energy of thereaction and the frequency factor has been calculated. The activation energy and frequency factor of ureahydrolysis reaction at atmospheric pressure was found to be 73.6 kJ/mol and 2.89 107 min-1, respectively.

1. Introduction

Ammonia is a colorless gas with a pungent, suffocating odor.Ammonia is corrosive and exposure will result in a chemical-type burn. Since ammonia is extremely hygroscopic, it readilymigrates to moist areas of the body such as eyes, nose, throat,and moist skin areas. Exposure to liquid ammonia will also resultin frostbite since its temperature at atmospheric pressure is 2.2C. Specifically, upon sudden release to the atmosphere, as mightoccur in a train wreck or a traffic accident, the ammonia formsa cloud of aerosol fog of liquid ammonia droplets. Unlikegaseous ammonia, which, though toxic, is lighter than air andquickly dissipates to harmless concentrations, the cloud canpersist for a while before it disappears. The cloud is typicallyheavier than air and tends to drift along the surface of the earth,i.e., the ground or the surface of a body of water. The cloudmoves with the wind and can sweep over a total area, i.e., afootprint, much larger than the area covered by the cloud atany one moment. Contact with the cloud is instantly incapacitat-ing, and a single breath can be fatal.1

The Occupational Safety and Health Administration (OSHA)issues permissible exposure limits for ammonia of 50 ppm, or35 mg/m3, time-weighted average, and 35 ppm, or 27 mg/m3,short-term exposure, and also ammonia is a highly hazardouschemical under the Process Safety Management Standard.2,3

Many industrial plants require the supply of large quantitiesof ammonia, which frequently must be transported through andstored in populated areas. Important users among these areindustrial furnaces, incinerators, and electric power generationindustries.4 All of these are faced with a lowering of the amountof nitrogen oxides being discharged to the atmosphere in thecombustion gases being emitted from their operations, asrequired by environmental regulations.5 Another important useis for the so-called conditioning of flue gas by which animproved collection and removal of particles matter (fly ash) isobtained. 6,7

But, unfortunately, ammonia presents significant danger tohuman health as a hazardous chemical. Its transportation,storage, and handling triggers serious safety and environmentalregulatory requirements for risk management plans, accidentprevention programs, emergency response plans, and releaseanalysis. An alternative approach to ammonia supply suggestedin the late 1980s includes using urea feedstock to generateammonia on site.8 The method of urea to ammonia conversionis by hydrolysis process; urea is an ideal candidate for themanufacture of ammonia.4 Urea is an environmentally safematerial used primarily as fertilizer. Urea is a nontoxic chemicalcompound and presents essentially no danger to the environ-ment, animals, plants life, and human beings. It is solid under

ambient temperatures and pressures. Consequently, urea can besafely and inexpensively shipped in bulk and stored for longperiods of time until it is converted into ammonia. It will notleak, explode, be a source of toxic fumes, require pressurization,increase insurance premiums, require extensive safety programs,or be a concern to the plant, community, and individuals whomay be aware of the transportation and/or storage dangers ofammonia. It has been determined that using urea thermalhydrolysis is the preferred process for converting urea/watersolution into a gaseous mixture containing ammonia, carbondioxide, and water vapor.9

The published information in the literature about hydrolysisof urea for production of ammonia is very little detailed and is

patented.

4,5,8-14

However, there is no information available inthe literature regarding the equilibrium and kinetic study of ureahydrolysis for production of ammonia in a batch reactor, andalso in our early study in semibatch reactor at atmosphericpressure it shows very slow rate of reaction.15,16 Therefore, wedecided to study more thoroughly the phenomenon of ureahydrolysis for production of ammonia in situ in a batch reactorfor different applications.

2. Method of Experiment

2.1. Process. The schematic of experimental setup is shownin Figure 1 and a photographic view is shown in Figure 2. Theexperimental setup mainly consists of a high-pressure (100 kg/

* Corresponding author. Tel.: +91 3222 283958(O)/2283959 (R).Fax: +91-3222-282250. E-mail: [email protected],[email protected].

Ind. Eng. Chem. Res. 2009, 48, 27052712 2705

10.1021/ie801286h CCC: $40.75 2009 American Chemical SocietyPublished on Web 02/09/2009

8/6/2019 ie801286h

2/8

cm2) reactor, heat exchanger, condenser, metering pump, feedtank, control panel, and product storage tank. The reactor is of2000 mL capacity and is made of stainless steel-316 to preventcorrosion. A metering pump was used to feed the urea solution

to the reactor at high pressure at controlled flow rate against apositive differential head between pump suction and discharge.

The shell and tube type condenser was used to exchange heatbetween the products (NH3, CO2, H2O(V)) and cooling water.The system has a heat exchanger to cool the unreacted urea forrecycle to the reactor where tap water at room temperaturewithout any pressure is used for cooling purpose. Apart fromabove, it also has two storage vessels, one for urea solutionand another for product storage. The reactor has two openings:one is for feeding urea solution and the other for withdrawingthe product to condense the gaseous product from the reactor

where tap water is used for the purpose of condensation. Tomeasure the temperature and pressure of the reactor, a thermo-couple and pressure gauge were attached to the reactor throughthe control panel. Cooling coil was placed inside the reactor tocool the reactor when required; tap water was used here also asa coolant. There is a control panel to control the requiredtemperature and speed of the stirrer. To supply the necessaryheat, electrical heating by coil outside the reactor wall wasprovided at a controlled rate by means of control panel. Thecontrol panel consists of several controllers and instruments.The control panel consists of indicators that are connected byelectrical wire, mains on/off switch, stirring motor on/off switchwith variable speed inverter drive and speed indicator, electrical

heater on/off switch, alarm system, fuses, and PID temperaturecontroller. The whole setup is placed on a stand with movingarrangement.

2.2. Experimental Technique. IFFCO make urea samplewas used to conduct the experiment which has been collectedfrom market. First, urea solutions of different concentration (10,20, 30, and 40 wt %) were prepared. In each case the volumeof water was taken as 450 mL. Then the solution of particularconcentration was fed into the feed tank. A metering pump wasused to feed the urea solution to the reactor at high pressure atcontrolled flow rate against a positive differential between pumpsuction and discharge. The experiments are conducted withoutstirrer. Heat was supplied by heating electrical coil outside of

reactor wall at a controlled rate by means of the control panel.The decomposition of urea takes place slowly starting aroundat 110 C. As the reaction starts, the product, which is a gaseousmixture of ammonia, carbon dioxide, and water vapor, goesthrough the condenser. In the condenser the gaseous productmixture gets condensed where tap water at room temperaturewithout any pressure was circulated through the condenser. Thenthe product was stored in the product storage tank and wascollected in a beaker with boric acid solution as it is an absorbingmaterial for ammonia solution. Boric acid solution is preparedby dissolving 4 g of boric acid in 100 mL of warm distilledwater. Then the absorbing ammonia solution was taken out andits volume was measured. After it gets absorbed with boric acid,three samples each of 10 mL volume were taken for titration.Three drops of methyl orange indicator is mixed in each sample.Then it is titrated with hydrochloric acid. Boric acid is so weakthat it does not interfere with acidimetric titration. Then bycomparing the initial concentration and final concentration theequilibrium conversion was found out. Finally, the rate ofreaction was found out from the slope of the line in the graphwhich was plotted between time versus concentration data. Agraph was plotted between ln(CA) and ln(rA). The slope andintercept give the values of order of the reaction and rateconstant, respectively.

2.3. Characterization of Urea. Urea and biuret weredetected and quantified using HPLC (high performance liquidchromatography).The HPLC equipment consisting of a Perki-

nElmer chromatograph series 200 UV/vis LC detector (Perki-nElmer, USA) equipped with an isocratic pump series 200 and

Figure 1. Schematic of the experimental setup for urea hydrolysis.

Figure 2. Photograph of the experimental setup of a high-pressure reactor.

2706 Ind. Eng. Chem. Res., Vol. 48, No. 5, 2009

8/6/2019 ie801286h

3/8

a rheodyne injector with a 20 L loop with variable-wavelengthultraviolet /visible detector was used. The equipment wascontrolled by Total chrome software that controlled the solventgradient, data acquisition, and data processing. The column wasa reversed-phase Agilent column. Separation was in a C-18column (250 mm 4.6 mm dia.), 5 m pore size, and a UVdetector set at a wavelength of 199 nm. The mobile phase usedhere 0.1 M phosphate buffer pH 6.7 at flow rate 1 mL/min, andthe column temperature was 25 ( 1 C. HPLC provides the

following features: high resolving power, speedy separation,continuous monitoring of the column effluent, accurate quantita-tive measurement, repetitive and reproducible analysis using thesame column, and automation of the analytical procedure anddata handling.

2.4. Reagents. All the chemicals used in the study were fromMerck (India) Ltd. and Qualigens Glaxo (India) Ltd. analyticalgrade.

3. Results and Discussion

3.1. Reaction Pathway. The basic chemistry employed inthe hydrolysis of urea is a reverse of that employed in theindustrial production of urea from ammonia and carbon dioxide

and employs two reaction steps, as follows:17

The reaction in eq 1 where urea hydrolyzes to form am-monium carbamate is mildly exothermic, while eq 2, in whichammonia and carbon dioxide are produced, is strongly endo-thermic, with the result that the reaction to release ammoniaand carbon dioxide requires heat and quickly stops when thesupply of heat is withdrawn. Excess water promotes thehydrolysis reaction, the overall reaction for which is as follows:

3.2. Physical and Chemical Characterization of the

Urea Samples. IFFCO make urea samples were collected fromnear the local market in Kharagpur, India. It is a commonnitrogen fertilizer used by Indian farmers. The physical appear-ance is of granular structure, white in color, and it is highlysoluble in water. The pH of the urea solution of 10 wt % ureato water was 7.84. The urea sample was characterized to theknown purity before conducting the experiment. Urea sampleswere characterized by HPLC to find out the impurities. TheHPLC analysis of the feed urea sample is shown in Figure 3.The chromatographs show the presence of urea and biuret in

the inlet feed solution of urea. It has been observed that IFFCOurea contains 2.05% biuret and its purity is 91.21.3. 3. Study of Equilibrium Conversion. Experiment was

conducted for hydrolysis of urea at high pressures in a batchreactor at different temperatures, pressures, and concentrations;both equilibrium and kinetic studies were done. From the initialconcentration and final concentration, the conversion was foundout and the equilibrium study of hydrolysis reaction withoutstirring was studied. Here the effect of equilibrium conversionon temperatures, pressures, and concentrations was studied.

Effect of Temperatures on Conversion. It can be seen fromFigure 4 that the conversion is a function of temperature. Itincreases exponentially with increase in temperature. For 10%urea solution, the conversion increases from 3% to 30% when

temperature increases from 110 to 160 C in 10 C intervals.Similar trend has been observed for 20, 30, and 40% feed

solution and the conversions are 27, 25, and 23%, respectively,

at 160 C. It was observed that the initially conversion is slowerat lower temperature and it becomes rapid at around 130 C.

NH2CONH2 + H2O f NH2COONH4 (1)

NH2COONH4 f 2NH3 + CO2 (2)

xH2O + NH2CONH2 f 2NH3 + CO2 + (x - 1)H2O (3)

Figure 3. HPLC analysis of the urea feed solution.

Figure 4. Effect of temperature on conversion at different concentrations.

Ind. Eng. Chem. Res., Vol. 48, No. 5, 2009 2707

8/6/2019 ie801286h

4/8

At this temperature the production of ammonia is higher thanthat at lower temperature.

Effect of Initial Concentration on Conversion. The conver-sion was slightly affected by the initial concentration of ureathat is feed to the reactor. It can be seen from Figure 5 thatwith increases in initial concentration of urea the conversiondecreases marginally. For each initial concentration the tem-

perature was varied from 110 to 160 C. Keeping temperatureconstant at 160 C, the conversion decreases from 30% to 23%when concentration varies from 10% to 40%. Similarly for 120,130, 140, and 150 C the equilibrium conversion decreases from7% to 2.5%, 9% to 4%, 11% to 7%, and 20% to 11%,respectively, when the initial concentration of urea increasesfrom 10% to 40%. This is due to the fact that higher weight %of urea possesses less pressure in comparison to the lower weight% urea solution as shown in Figure 8. Hence, during thedecomposition the solution, this has less urea content and willgive more ammonia, carbon dioxide, and water vapor asproducts from the reactor.

3.4. Vapor-Liquid equilibrium. The operating temperature

and pressure of the reaction of the reaction vessel along withthe excess water added (over the stoichiometric amount neededto hydrolyze urea) will determine the concentration of water inthe mixture at equilibrium. The gas discharging from the reactorwill leave saturated with water vapor. Figure 6 depicts themeasured concentration of product composition (moles ofproduct/total moles of products) obtained from the reactor with40 wt % of urea to water feed inlet solution at differenttemperatures. It can be seen from the figure that the productionof ammonia and carbon dioxide increases markedly as thetemperature increased and the production of excess waterdecreased.

Figure 7 depicts the measured reaction pressure of the ureahydrolysis reaction mixture at steady state for various temper-

atures at different initial feed concentrations of urea. It can beseen from the figure that reaction pressure increases from 50 to

900 kPa and 100 to 950 kPa with temperature increases from110 to 160 C, when 10 and 40 wt % urea solution, respectively,is feed to the reactor. The benefits of operating at a pressureuniquely related to the operating temperature for a specifiedconcentration of aqueous urea feed can be seen from Figures 7and 8. From Figure 8 we can seen that with increase in reactionpressure the conversion increases from 2.5 to 22.5% and 4 to30% with increase pressure from 50 to 900 kPa and 100 to 950kPa, respectively, when at 10 and 40 wt % urea solution,respectively, is feed to the reactor.

At an operating temperature of 110-160 C and operatingpressure in the 50-950 kPa range, the concentrations ofammonia and carbon dioxide held in the reactor liquid solutionare relatively low. Assuming ideal gas behavior, we can make

use of Raoults law and Daltons law to understand theequilibrium of the solution.

Figure 5. Effect of initial feed concentration on conversion at differenttemperatures.

Figure 6. Temperature evolution of reactor products for initial feedconcentration of 40 wt % urea to water.

Figure 7. Effect of temperature on reaction pressure at different concentrations.


8/6/2019 ie801286h

5/8

Raoults law is written as follows:

and Daltons law is

where pi is defined as the partial pressure of the component i,Pi is defined as the vapor pressure of component i at theoperating temperature of the system, xi is the mole fraction ofcomponent i in the liquid phase, yi is the mole fraction ofcomponent i in the vapor phase, and P is the total pressure,which is equal to the sum of the partial pressures of allcomponents in the vapor phase.

Theoretically determined reaction pressures by using Raoultslaw and Daltons law based on vapor pressure of water in the

same range of temperatures are presented for comparison withexperimental data in Figure 9.3.5. Study of Reaction Kinetics. Experiments were con-

ducted for hydrolysis of urea in a batch reactor at differenttemperatures, reaction pressures, and concentrations and kineticstudy was done. From the initial feed concentration and finalconcentration, the conversion was found out and the kineticstudy of hydrolysis reaction was studied. Assuming no backwardreaction, the rate constant for forward reaction was calculated.As in the reaction excess water is used, the concentration ofwater is neglected. Let -rA be the rate of reaction, CA0 the initialconcentration, and CA the concentration at any time. The rateof reaction for forward reaction can be written as

Multiplying ln on both sides in eq 6 we have

Hence if a graph is plotted taking ln(CA) on the abscissa andln(-rA) on the ordinate, a straight line will be obtained whose

y-intercept represents the rate constant.EffectofTimesonConcentration.Fromtheconcentration-time

data, a kinetic study was done. Figure 10 depicts that theconcentration of urea decrease as time increases at a constanttemperature, and also it depicts that the higher temperaturepossesses less concentration of urea compared to the lowertemperature. It is observed from Figure 11 that the conversionincreases with time. For 10 wt % initial concentrations, theconversion reaches from 0% to 88% at a constant temperature140 C when time increases from 0 to 90 min. So 90 min is

required for achieving 90% conversion for 10 wt % solution,but the time will be high for higher concentration solution asshown in Figure 11. From Figure 12 it is seen that the timetaken to achieve higher conversion is more at 120 C and lessat 150 C temperature.

The effect of rate on concentration at a fixed temperature isshown in Figure 13. From the figure it is observed that the slopeof the plot is approximately 1. This indicates that the forwardreaction is first-order type. Further, the intercept of the above-mentioned figure gives the value of forward rate constant whichis a function of temperature. It is observed from the figure thatwith increase in temperature from 140 to 150 C the forwardrate constant increases from 0.013 to 0.22 min-1. The variationwith temperature is very small because of the fact that there

was no stirring and catalyst. Table 1 shows the values of rateconstant with temperature.

Figure 8. Effect of reaction pressure on conversion at different initial feedconcentrations.

pi ) Pixi (4)

pi ) Pyi (5)

-rA )-dCA

dt) k(CA)

n (6)

Figure 9. Comparison of experimental and theoretically determined reactionpressures at different temperatures.

ln(-rA) ) ln(k) + n ln(CA) (7)


8/6/2019 ie801286h

6/8

From the above result it is observed that the order of the

forward reaction is close to 1 and with increase in temperaturethe rate constant increases. So finally the temperature depen-dency of forward rate constant was explained by Arrheniustheory. The rate equation can be written as follows:

where -rA is the reaction rate, k forward rate constant, and CAconcentration of urea solution.

According to Arrhenius theory, the temperature dependencyof forward rate constant can be written as

where A is frequency factor and E is activation energy.From the Figure 14 the activation energy and frequency factorwas found out as 73.6 kJ/mol and 2.89 107 min-1, respec-tively. These values are compared with the values reported byAoki et al.18 They reported the activation energy and frequencyfactor as 87.78 kJ/mol and 3.753 107 min-1, respectively.

3.6. Characterization of the Reactor Liquor Samples. Thedetailed analysis of reactor liquid sample was done at 160 Cand with inlet feed concentration of 10 wt % of urea to water.The pH of the reactor liquid sample solution was 9.02. Thereactor liquid typically contains 3-4% urea, 0-5% higher ureaderivatives, and 1-2% ammonia. At temperature above 120 C,any ammonium carbamate in the liquid formed immediatelydecomposes to ammonia and carbon dioxide and hence very

small concentrations (1-2%) of ammonium carbamate will bepresent in the reactor liquor, and the rest is water. The HPLC

analysis of the reactor liquor sample is shown in Figure 15.The HPLC analysis of reactor liquor samples shows the presenceof urea, biuret, and other new products also observed. The

presence of urea in reactor liquor decreases compared to inletfeed urea solution, but the biuret percentage increases, maybe

Figure 10. Effect of time on concentration at different temperatures.

-rA ) kCA (8)

k) Ae-E/RT (9)

Figure 11. Effect of time on conversion at different weight percent solutionsfor constant temperature 140 C.

Figure 12. Effect of time on conversion at different temperatures for constantinitial feed concentration 10 wt % solution.


8/6/2019 ie801286h

7/8

due to the formation of higher urea derivatives as new peaksalso observed.

4. Conclusions

The objective of this work was to study the hydrolysis ofurea for generation of ammonia in a batch reactor. A number

of experiments were carried out in a batch reactor at differenttemperatures taking different concentrations of urea solutionfrom 10 to 40% by weight, and both equilibrium and kineticstudies were done. From equilibrium study it is concluded thatwith increase in temperature and pressure the equilibriumconversion increases and a maximum conversion of 30% ispossible with 10% concentration and at 160 C temperature and896.32 kPa reaction pressure. The equilibrium conversiondecreases with increase in concentration. It has also been foundthat the forward reaction is a pseudo-first-order reaction withrate constant varying from 0. 013 to 0.035 min-1 within thetemperature range of 140 and 160 C, respectively. Theactivation energy and frequency factor of urea hydrolysisreaction are found to be 73.6 kJ/mol and 2.89 107 min-1,

respectively. Finally, it can be concluded that the hydrolysis ofurea to form ammonia and carbon dioxide behaves as a first-

order reaction with respect to urea. Also it can be concluded

that the initial reaction rate is slower and it becomes rapid ataround 130 C. At this temperature the production of ammonia

Figure 13. Effect of concentration on reaction rate at different temperatures.

Table 1. Kinetic Data for Urea Hydrolysis in a Batch Reactor

temp (C) k (min-1

) n(calcd) n(av) R2

140 0.0134 0.947 0.947145 0.0198 1.120 0.979150 0.0220 1.110 1.0 0.970155 0.0344 1.058 0.893160 0.0350 0.913 0.935

Figure 14. Effect of temperature on rate constant.

Figure 15. HPLC analysis of the precipitated solids from the reactorsolution.


8/6/2019 ie801286h

8/8

is higher than that at lower temperature. Further the reactionrate constant is function of temperature.

Acknowledgment

The authors gratefully acknowledge the financial support tothe National Thermal Power Corp. (NTPC), New Delhi, India,has extended toward them for this work.

Nomenclature

A ) frequency factor (min-1)

CA ) final concentration of urea solution (mol/L)

CA0 ) initial concentration of urea solution (mol/L)

E) activation energy (kJ/mol)

k) forward rate constant (min-1)

n ) order of forward reaction

P ) total pressure (Pa)

pi ) partial pressure of the component i at the operating temperature

of the system (Pa)

Pi ) vapor pressure of component i at the operating temperature

of the system (Pa)

R)

ideal law gas constant (kJ/kgmolK)Ra ) rate of reaction

T) reaction temperature (K)

t) reaction time (min)

xi ) mole fraction of component i in the liquid phase

yi ) mole fraction of component i in the vapor phase

Literature Cited

(1) Spokoyny, F. E.Method and apparatus for the production of gaseousammonia from a urea solution US Patent application no. US2006/0147361A1, 2006.

(2) Bhattacharya, S.; Peters, H. J.; Fisher, J.; Spencer, H. W. Urea-to-Ammonia (U2A) Systems: operation and process chemistry. Proc. 2003

Mega Symp., 2003.(3) Salib, R.; Keeth, R. Optimization of Ammonia Source for SCR

Applications. Proc. 2003 Mega Symp., 2003.

(4) Cooper, H. B. H.; Spencer, H. W.Methods for the production ofammonia from urea and/or biuret, and uses for NOx and/or particulate matterremoval US Patent application no. US 6,730,280 B2, 2004.

(5) Spencer, H. W.; Peters, H. J.Method for controlling the productionof ammonia from urea for NOx scrubbing US Patent application no. US6,436,359 B1, 2002.

(6) Baxter, W. A. Recent electrostatic precipitator experience withammonia conditioning of power boiler flue gases. J. Air Pollut. Control

Assoc. 1968, 18, 817.(7) Dismukes, E. B. Conditioning of fly ash with ammonia. J. Air Pollut.

Control Assoc. 1975, 25, 152.

(8) Brooks, B.; Jessup, W. A.; Macarthur, B. W.Method of quantita-tively producing ammonia from urea US Patent application no. US6,887,449 B2, 2005.

(9) Jacob, E.; Kafer, S.; Muller, W.; Lacroix, A.; Herr, A.Method andapparatus for producing ammonia (NH3) US Patent application no. US6,928,807 B2, 2005.

(10) Glesmann, R. T.; Titus, J. J.; Walker JR. H.G.Process andapparatus for conditioning of combustion flue gases with ammonia fromhydrolyzed urea US Patent application no. 2003/0118494 A1, 2003.

(11) Hofmann, L.; Rusch, K.Process for converting urea into ammoniaUS Patent application no. US 6,471,927 B2, 2002.

(12) Jacob, E.; Stiermann, E.Device and method for producing ammoniafrom solid urea US Patent application no. US0045835 A1, 2006.

(13) Wojichowski, D. L.Methods of converting urea to ammonia forSCR, SNCR and flue gas conditioning US Patent application no.US0211024 A1, 2003.

(14) Young, D. C.Transporting urea for quantitative conversion intoammonia US Patent application no. US 5,252,308, 1993.

(15) Sahu, J. N.; Mahalik, K.; Patwardhan, A. V.; Meikap, B. C.Equilibrium and kinetic studies on the hydrolysis of urea for ammoniageneration in a semi-batch reactor. Ind. Eng. Chem. Res. 2008, 47, 4696.

(16) Sahu, J. N.; Mahalik, K.; Meikap, B. C.; Patwardhan, A. V.Equilibrium studies on hydrolysis of urea in a semi-batch reactor forproduction of ammonia to reduce hazardous pollutants from flue gas. J.

Hazard. Mater. 2008, in press. DOI: 10.1016/j.jhazmat.2008.08.063.(17) Rahimpur, M. R. A non-ideal rate-based model for industrial urea

thermal hydrolyser. Chem. Eng. Process. 2004, 43, 1299.(18) Aoki, H.; Fujiwara, T.; Morozumi, Y.; Miura, T. Proceedings of

the Fifth International Conference on Technologies and Combustion for aClean Environment, Lisbon, 1999.

ReceiVed for reView August 24, 2008ReVised manuscript receiVed September 22, 2008

Accepted November 21, 2008IE801286H


ie801286h

Documents

Transcript of ie801286h