Assessment of the apparent activation energies for gas/solid reactions-carbonate decomposition

Journal of Universiry of Science and Technology BeyingVolume 10, Number 2, April 2003, Page 25MetallurgyAssessment of the apparent activation energies for gas/ solid reactionscarbonate decompositionJianhua Li.d and Jiayun ZhangMetallurgical Engineering School. University of Science and Technology Beijing. Beijing 100083. ChinaReceived 2001-08-20)Abstract: T 1e guidelines for assessing the apparent activation energies of gas/solid reactions have been proposed based on the ex-perimental n:sults from literatures In CO, free inlet gas flow, CacO, decomposition between 950 and 1250 K with thin sample layercould be controlled by the interfacial chemical reaction with apparent activation energy E=(215#10)kJ/mol and E=(200+10)kJ/mol at T=813 to 1020K, respectively. With relatively thick sample layer between 793 and 1273 K, the CacO, decompositioncould be controlled by one or more steps involving self-cooling, nucleation, intrinsic diffusion and heat transfer of gases, and e couldeary betwee 1 147 and190 kJ/mol In CO contaning in let gas flow (5%0-100%of CO. ) E was determined to be varied from 949to697 kJ/moL. For SrCO, and BaCO, decompositions controlled by the interfacial chemical reaction, E was(213+15kJ/mol (10001350 K)an I(30.5+15)kJ/mol (1260-1400 K), respectivelyKey words: assessment: activation energy: decomposition: carbonate(This work i as financially supported by the National Natural Science Foundation of China(No 59774023To apply the reported apparent activation energy(4)Nucleationdata to the: kinetic evaluations and process optimiza(5) The heat transfer.ions, the assessments of these data are quite necessaryand favorable. As a part of the work in developing theThe complexity of the reaction kinetics may indiintellectualized database management system on ki- cate the necessity to correlate the apparent activationnetics of metallurgy (IDMSKM) involving kinetic energy and other kinetic parameters with the experiprediction of gas/solid reactions(KinPreGSR)| 1-31, mental conditions mentioned above. The variation ofthe assessment of apparent activation energies were the experimental conditions may be the most impor-carried ou: for some gas/solid reactions. In this paper. tant reason resulting in the diverse of the kinetic pathe guidelines of the assessment are introduced and rameters. The other reason could be the difficulties inthe assessment for some decomposition reactions of the dynamic measurements at high temperature. Thecarbonate: is describedpreceding discussion suggests that this assessmentmust be based on an extensive data accumulation from1 Guidelines of the assessment of gas/solid kinetic literature, and the work must proceed underreaction:reasonable scientific guidelines. According to theauthors' practice, the following guidelines should beA gas/ olid reaction often involves some of the obeyedfollowing steps(I) The kinetic data should be published in the(l)The external mass transfer of the gaseous reac- worldwide acknowledged scientific journals or welltant or product to or from the surface of the solid par- known Chinese journalsticle(2)The internal diffusion of the gaseous reactant or a/ysks, experimental results(and the mechanism(2)If t中国煤化工 essary experIproduct through the pores in the solid matrixCNMHG not becomethe data3) The interfacial chemical reaction at the interface(3)The kinetic data should be measured usingJ. Univ Sci. Technol. Beijing, VoL 10, No 2, Apr 200curate techniques with better reproducibility.values of (200+10)kJ/mol. The temperature eftect can(4) Grouping the apparent activation energy datathe slightly higher CO2 partial prshould be based on the reaction mechanism(rate con-caused by high decomposition temperature. This willincrease the activation energy significantly. The con-trolling step(s)). Since the influences of the experi-mental conditions, the corresponding experimental SIderation is further confirmed by the data given inparaineters should also be grouped accordinglyGroup Ill. The partial overlap in activation energyvalues and experimental conditions for the two sub-2 As sessments of the apparent activation en- groups is considered to be reasonableTable 1 The samples for CaCO, decompositionThe present authors took the decomposition of alNo. m/mg Geometry of particle(s)aline earth carbonates as the first attempt. In the rePellets, D=20-60 um. d=l 6 umtion, the carbonates decompose to produce the al-Powder, d= 20-44 umkaline oxides and carbon dioxide40-65 Single crystal. a= 0.5-1 mmSingle crystal. a= 1. 4-1. mm2.1 The decomposition of CacO3B:sed on guidelines(1)-(3), thirteen references [4.16] have been selected from more than thirty paperson the CacO, decomposition kinetics, The apparent6789activ ation energy data with the corresponding mechaPowdernism descriptions(the rate controlling step(s))and key10429&315 Pellet,D=4.5or3.8mmexperimental parameters are listed in tables 1 and 2PelloAccording to the rate controlling step(s), the data have234Powderbeen divided into three groups. groups I to Ill. Group IPellet or powdinvolves the data at lines 1-8. The common features inPowder, d=20-44 umthose experiments were as follows: the relativelyPowder, d=20-44 ummall(1-100 mg) sample mass resulting in thin sam2-32Powderple layer; CO, free in inlet gas flow, interfacial chemiPowdercal reaction controlling(CR). Group Il consists of thePellet, D=4.0 mmdata at lines -13 in tables I and 2. In the relevant experiments, all sample mass (2290 mg)and Co2 free inGreater apparent activation energy values, 564-inlet gas flow were used. The overall rates in those 3824 kJ/mol, in group Ill show that the CO, contentproce sses may be controlled by the steps: the self- significantly affects the activation energy. With thecooling, internal diffusion of gaseous species. heat extracted activation energy values from the decompo-trans er(HT) from the surface of solid particles to thents (lines 14-16), it can be concludedchemical reaction interface. the nucleation as wellthat the activation energy for the calcium carbonatethe interfacial chemical reaction jointly. Group Ill decompositions in COz containing gas(5%)rangescomprises some data obtained in the decomposition from 950 to 3000 kJ/mol. More experiments are reexperiments carried out in CO, containing inlet gas quired to quantify how the apparent activation energyflow(see lines 14 to 18). For the sake of brevity, the varies with the COz content in the inlet gas. The actirate-controlling steps and experimental conditions are vation energy data listed in lines 17 and 18 fall fardenoted using a couple of alphabets in the tables ofyond this range. The NTGa technique with just athis F aper, which are listed in table 3. Also the adjec- single rising temperature run and unclear descriptionLive apparent' will be removed from now on in the of experimental conditions may rise doubt on the pretextcision and accuracy. For this reason, those results haveIn group I, the activation energy values are rangednot been taken into considerationfrom 190 to 230 kJ/mol when the reaction is con- The mechanisms listed in lines 14-16 were regatrolled by the interfacial chemical reaction stepby the authors [5, 16 as to be heat transfer step con-lines 1-3, the exal temperature is somewhat trolling. The experimental basis was that the rates oflower than that at lines 4-8. Therefore, the activation the中国煤化工 ferent gases wereenergy values in Group I are classified into two sub- progroups to improve the precision. In the temperatureCNMHG,hat they were de-range of 950-1250 K, the values vary within(215+10) termined by mass transfer of the evolved CO,.ItkJ/mol, while between 813 and 1020 K, it takes the seems that further studies are needed to identify theJ.H. Liu et ai., Assessment of the apparent activation energies for gas/solid reactions- carbonate decompositionsmechanismTable 2 The kinetic data for CacO, decorT/KITGA880-981190208ITAITGA934-10l34TGA910-1110 Vacuum209±12.5NTGA1063-1250210.21210 K/m6NTGA0-115010-20K/minDTA950-1150213-228993-1053 Vaccu147-176c10ITGA987-1090121023-1173GIDNTGA793-127314NTGA873-173180-195%CO,+TGA813-105394995%ArITA813-lHT16ITA1173-1223NTGA564-382416NTGA181000-1040CO210mm167120.58 K/minTable 3 List of symbolsnterfacial chemical reactionGaseous intermal diffusionSIDSolid ion diffusionHeat flow in solidITGa Isothermal thermogravimetric analysisNtGa Non-isothermal thermogravimetric analysisDTADifferential thermal analysisThe data have not been found in the literatureApparent activation energyFractional conversionThe activation energy values in group ll(at lines 9- be assessed between 145 and 190 k/mol with13)of tables I and 2 are between 147-190 kJ/mol mass of 290-1000 mg for the process performed inlower than those in group I. The relatively large acti- standard commercial general thermogravimetric ana-vation energy variation could be due to the thicker and lysis unitsvarying layer of the solid samples in group Il. 290- Linghai et al. [181 compared the decomposition ki-1000 mg. which would rise resistances for thenetics of nano-particles of CaCO3(40 nm in diameter)sion,heat transfer of the gaseous species(including with the powder containing particles of 5-20 um inself-coolirg effect). and perhaps of nucleation. As diameter in N2 inlet gas flow using non-isothermalseparating the effects of the above steps is sometimes DTA tecl中国煤化工vation edifficult, ve may simply regard that the overall Caco, for the fower than thatdecompos tion with the thick sample layer in CO, free of the latCN MH Gnce could beinlet flow is controlled by mixed steps mentioned due to the higher surface free energy the stress andabove. And the corresponding activation energy could distortion on the nano-particles. This indicates that theJ. Univ. Sci. Technol. Beiing, voL 10. No. 2, Apr 2003above assessed activation energies for groups l, II and has been reported that two phase transformations mayIll may not be used for the nano-particle calciteoccur during the decomposition of BacO,[21],thetransformation of orthorhombic to hexagonal at 10793.2The decomposition of SrCO, and BacO3K, hexagonal to cubic at 1273 K. The eutectic reactionThe kinetic data of SrCO, and BacO, decomposi- may proceed at high temperature. According to theions reported in the previous investigations are re- phase diagram [23] for BaCO, decomposition, thespectively listed in tables 4 and 5[19, 22]. Compared eutectic point is at 1333 K and 0.661 kPa. So in thewith the data for CaCO, there are much less publica- BaCO, decomposition studies, the phase transforma-tions that make our assessment difficult. In addition it tions and eutectic reaction must be taken into accountTable 4 The kinetic data for SrCO, decompositionControllingExperimental Technology T/K Atmosphere (k/mol) step(s)Reference10 mgNTGA,10-20Kmin1000-1350203-21813 2 mg pressed flakes withNTGA1000-1350thickness less than 0.5 m9904 200-1000 mg powderITGA1173-1273288SIDTable 5 The kinetic data for BaCO, decompositionNOExperimental T/K Atmosphere E/(J/mol) Controlling steps) Reference10 mg, powderNTGA 7-15 K/minX<0.15,CR200-1000 mg, powderTGA1443230Single crystal with INTGASID or desorptionmm in thickness2591220From tables 4 and 5, the following viewpoints very little, were used to extract the activation energiescould be drawnto ensure the reaction was controlled by the interfacial(I) The activation energy data in lines I and 2 ofchemical reaction. The non-isothermal experimentstable 4 are close. In the relevant experiments, the arwere formed with very strictly controlled parametergon flow and internal diffusion rates were high, and 50, the reported activation energy for the decomposihe consequent interfacial chemical reaction was ratetion controlled by interfacial chemical reaction step atcontiolling. For the better reproducibility, the activa1260-1400 K could be confirmed to be(305+15tion energy could be recommended to be (213+15) k /mol. Some relevant ITGA measurements at similarkJ/mal under conditions of interfacial chemical reacticondition are expected to complete the assessmenon controlling between 1000 and 1350 K(4)The sample mass used for the BacO, decompo-sition experiment listed in line 2 of table 5, 200-1000(2)Corresponding to line 3 of table 4, a higher ac- mg, was higher and varied considerably. The meas-tivation energy of 288 kJ/mol was attained. whichement was carried out at 1323-1443 K. During themay suggest a solid-diffusion step controlling mecha- course, eutectic reaction would happen influencing onnism. However, as the large sample mass adopted, the the mechanism. However, the activation energy wassitua ion could be complex. To quantify resistances of extracted and the mechanism was evaluated by fitingtransport steps on the rate of the decomposition, more the experimental data from the initial to the laterexperimental work is requiredstages using different kinetic equations [20]. From the(3, The experimental data in line I of table 5 were viewpoint of the present authors, more experimentalobtained with shallow bed powder and a high argon data are desirableflow rate. Thus the resistances of the mass transfer of(5)The decomposition described at line 3 in table 4COz, the heat transfer from the gas stream to the reac- was performed bellow the temperatures of the phasetion interface were neglected. The decomposition tran中国煤化工eon. Accordingwere carried out at 1260-1400 K. the influences of the to-on of BaCO, with aphase transformations could also be avoided. The ex- thiCNMH Ge gas flow may beperinental data at the earlier stages(X <0. 15). when controlled by solid phase diffusion or a surface stepthe amount of liquid due to the eutectic reaction was prior to desorption. This conclusion should be testifiedJ.H. Liu et ai., Assessment of the apparent activation energies for gas/solid reactions-carbonate decompositionsby further i: othermal TGA measurementsChem. Soc. Faruday Trans, 70(1974), No 12. p 2145[7 E.K. Powell and A w. Searcy, The rate and activationIt should be pointed out that the above condenthalpy of decomposition of CaCO, J]. Metallurgicalgarding the SrCO, and BaCO, decompositions areTransactions B, 11B(1980), p. 427.tentative. for the less relevant data in literatures. More (81 C Guler D. Dollimore and G.R. Heal. The investigationexperiment i are required to provide more accurate as-of the decomposition kinetics of calcium carbonate alonesessment on the activation energies of the decompoand in the presence of some clays using the rising tem-perature technique IJ]. Thermochimica Actu. 54(1982),p191 A.W. Coats and J. P. Redfern, Kinetic parameters from(1)The decomposition of small amount of CacOthermogravimetric data [J]. Nature, 201(1964).p 68powder in CO, free inlet gas flow from 813 to 1250 K [101 X Xiao S Du H.Y. Sohn, and S.Seetharaman, Determi-nation of kinetic parameters using differential thermalcould be controlled by interfacial chemical reactionanalysis-application to the decomposition of CacO, JIand the ac ivation energy could be (215+10)kJ/molMetallurgical and Materials Transactions B. 28B(1997).pbetween 9 0 and 1250 K, and(200+10) kJ/mol from813 to 102)K. The decomposition with thicker sam- [11] H.T.S. Britton. J. Gregg, and G.w. winsor, The calcinaple layer in CO, free atmosphere ranging from 793 totion of dolomite, part 1- The kinetics of the thermal de-1273 K might be controlled by one or the mixed stepscomposition of calcite and of magnesite J]. Trans. faraof the interfacial chemical reaction, self-cooling, nu-day Soc.48(1952). p6cleaton, ir termal diffusion and heat transfer of gas-12] A L. Draper and L K Sveum, The Analysis of ThermalData [J]. Thermochimica Acta, I( 1970), P. 345eous species jointly. The apparent activation energy [131 T.R. Ingraham and P. Marier. Kinetic studies on the therfrom 147 to 190 kJ/mol. The activationmal decomposition of calcium carbonate [] The canadiergy of the decomposition in CO2 containing gas (5%an Journal of Chemical Engineering, 41( 1963). p 170100%)could be very high, 564-3824 kJ/mol[14 E.S. Freeman and B. Carroll. The application of thermo-(2) The activation energy of SrCO, decompositionanalytical techniques to reaction kinetics. The thermogra-vimetric evaluation of the kinetics of the decomposition ofcontrolled by the interfacial chemical reaction be-calcium oxalate monohydrate [J]. J. Phys. Chem. 62tween 1000 -1350 K could be in a range of 203-233(1958),p.394kJ/mol. For the decomposition controlled by diffusion [151 J. H. Sharp and S. A. Went worth, Kinetic analysis ofin solid reactants between1 173-1273K. it could be asthermogravimetric data [JI. Analytical Chemistry, 41much as(2 8+15 ) k/mol1969).p.2060[16 P K. Gallagher and D w. Johnso, Kinetics of the thermal(3)Between 1260-1400 K, the E value of BacO3decomposition of CaCO, in CO, and some observationscomposition under interfacial chemical reactionon the kinetic compensation effect !J], Therochimica Actacontrolling mechanism could be as much as(305+15)14(1976),p.255J/mol. Under solid-state diffusion or desorption con- [I7] J.w. 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