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The Boudouard–Bell Reaction Analysis Under High Pressure Conditions

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The Boudouard–Bell Reaction Analysis Under High Pressure Conditions J Therm Anal Calorim (2012) 110:93–102 DOI 10.1007/s10973-012-2334-2 The Boudouard–Bell reaction analysis under high pressure conditions Andrzej Mianowski • Zbigniew Robak • Martyna Tomaszewicz • Sławomir Stelmach CEEC-TAC1 Conference Special Issue Ó The Author(s) 2012. This article is published with open access at Springerlink.com Abstract A new method for the measurement of solid b1, b2, b3 Constants in L–H Eq. 8 related with kinetic fuel reactivity towards carbon dioxide has been developed. constants This new method takes into account high-pressure and B, B1, B2 Constants in Eqs. 12–13, 15, dimensionless -1 -1 temperature effects. Three devolatilized carbonaceous C0 Constant in Eqs. 24, 25,K s materials have been used in experiments: chars derived C, C1, C2 Constants from lignite, bituminous coal and blast furnace coke. Pro- [CO2], [CO] Molar fractions of CO2 and CO, respec- cesses were carried out at temperatures of 800, 850 and tively, 0 B [CO2] B 1, 0 B [CO] B 1, 900 °C and pressures of 1.52, 2.5 and 3.4 MPa. Analysis of [CO]m Maximum obtained molar fraction of CO, the product gas composition was carried out with the 0 \ [CO] B 1 maximum degree of conversion of CO2 (am) proposed as a DFE Distance from thermodynamic equilibrium, representative reactivity parameter. Arrhenius and Eyring dimensionless relationships have been analyzed, and values of the acti- E Activation energy, J mol-1 vation energy and activation volume have been calculated. k Rate coefficient, s-1, indexed constants corresponds with adequate equations Keywords Boudouard–Bell reaction Á CO2 Á Gasification kg Rate coefficient acc. to [23] reactivity Á Kinetics Á Temperature Á Pressure K Equilibrium constant, calculated acc. to Eq. 34, dimensionless List of symbols Ka Approximated equilibrium constant, a Conversion degree of CO2,0\a\1 defined with (32), dimensionless am Maximum obtained conversion degree of m Mass of sample, g CO2 during process, 0\am 1 m0 Initial mass of sample, g as Conversion degree of solid phase of fuel, m_ Mass flow of CO2 in ambient temperature, -1 0 as 1 gs , A, A1, A2 Pre-exponential factor in Arrhenius g Thermodynamic yield of process/reaction, equation, s-1 or dimensionless 0 B g B 1 Dm Sum of stoichiometric coefficients of gaseous reactants P Pressure of CO2, MPa A. Mianowski Á Z. Robak Á S. Stelmach PH Standard pressure *0.1 MPa IChPW, Institute for Chemical Processing of Coal, -1 -1 Zamkowa 1 Street, 41-803 Zabrze, Poland R 8.314 J mol K , gas constant R_ Solid phase conversion rate, defined acc. to M. Tomaszewicz (&) (5), s-1 Department of Inorganic Chemistry, Technology and Fuels, r2 Determination coefficient, 0 B r2 B 1 Silesian University of Technology, Krzywoustego 6 Street, 44-100 Gliwice, Poland T0 Ambient temperature, K e-mail: [email protected] T Reaction/process temperature, K 123 94 A. Mianowski et al. V Volume of particular reactant, cm3 mol-1 oil as well as other chemical compounds and products like aldehydes and oxo alkohols obtained via V_ Volumetric flow of CO2 in ambient temperature, cm3 s-1, hydroformylation; D?V Volume of activation, cm3 mol-1 (3) the synthesis of methanol (1 mol CO ? 2.2 mol s Time, s H2 ? addition of CO2); (4) the synthesis of dimethyl ether; sm Time to obtain maximum conversion of (5) the synthesis of acetic acid; CO2,s, (6) the production of the chemical warfare agent phos- s0 Initial time in Eq. 12,h gene with chlorine participation, which is forbidden sz Equivalent time, s but necessary to produce polyurethane foams; Subscripts (7) the production of sodium formate by means of s, g Represents solid and gaseous phase, respectively reaction with sodium hydroxide; eq Equilibrium state (8) the production of the PHB (poly-3-hydroxybutyrate) biopolymer for use in the production of biodegradable packaging. Introduction Furthermore, carbon monoxide is used in the environ- A disproportionation reaction of carbon monoxide into mentally important catalytic processes of the reduction carbon dioxide and carbon black was investigated at the of nitrogen oxide according to the reaction: end of XIX century, first by Sainte-Claire Deville in 1864 NO ? CO = 1/2 N2 ? CO2 [9]. and then from 1869–1871 by the English metallurgist The optimal situation is when the measure of reactivity is Sir Isaac Lothian Bell [1]. As late as July 23rd, 1900, at strictly connected to the kinetic constant of reaction (1). Most a Paris conference, Octave Boudouard described and dis- often however, it is assumed that the reaction under consid- cussed his earlier published work [2] on the progress of the eration can be expressed by simplifying but technologically endothermic and reversible reaction: sensible approximations, by the three kinetic constants: C þ CO 2CO DH ¼ 172:5 kJ molÀ1 ð1Þ k1 2 298 C þ CO2 $ CO "þCsO ð3Þ kÀ1 which, in terminology of coal technology, is defined as k2 carboxy reactivity. CsO ! CO "ð4Þ Reaction (1) has seen many elaborations of its multi-subject In this article, a new conception of Boudouard–Bell reac- aspects. In practice, a high carboxy reactivity results in unde- tion analysis is proposed, using both our own and literature sirable characteristics of coke. This is because, when used in the derived data, as well as a specially designed high-pressure blast furnace process and in the manufacturing of coal-graphite experimental set-up. For reaction (1), from both a ther- products, fuel consumption increases, its mechanical strength modynamic point of view and from the Le Chatelier– deteriorates, and the temperature of the process is reduced (the Brauns principle (Dm = 2 - 1 =?1), an increase in so-called ‘‘cooling down’’). This detrimental effect (the pressure results in a shift of the reaction equilibrium to the excessively high carboxy reactivity) is also known and left (in the direction of the reactants); however, because of described in the processes of the industrial combustion of solid mechanism (3) and (4) as well as the different character- fuels, especially for coal. The reaction capacity of solid fuels istics of the different carriers of carbon as compared to dictates the possibility and method of their utilization. It is graphite, increased pressure sometimes aids the reaction. obvious that the low reactivity of blast furnaces and foundry cokes is desirable, while a higher reactivity of the fuel supplied to the gasification systems is preferred. The kinetics of the Boudouard–Bell reaction/process Carbon monoxide can be applied in many chemical synthesis reactions [3–8] including the following: The course of the heterophase reaction (1) is limited by many factors, including: (1) the production of hydrogen in a homogenous Water– Gas Shift reaction: (1) thermodynamic parameters (T, P, V); (2) the quality of the carbon carrier that is dependent ðgÞ À1 CO þ H2O ! CO2 þ H2 DH298 ¼41:1 kJ mol ; ð2Þ upon what fuel is used, which may include biomass (including waste), coal that has undergone either low or high levels of metamorphosis, chars, cokes and (2) the synthesis of liquid motor fuels by the Fischer– graphite only for cognitive purposes, as well as on the Tropsch process, both to produce gasoline and diesel presence of mineral substances; and. 123 The Boudouard–Bell reaction analysis 95 (3) the means of the solid sample preparation (particle ½CO2þ½CO¼1: ð8Þ size reduction, porosity) and the type of process employed (stationary process, once-through process, A final expression for the kinetic equation is: fluidized process). m T gðaÞ¼k 0 0 ð9Þ g _ As a result, many kinetic equations for the reaction in VT question have been proposed; herein, only the most popular where the mass integral g(a) is expressed by: are presented. They can be grouped according to the presence gðaÞ¼a À 2lnð1 À aÞð10Þ of the solid phase, gas phase or of both phases. It is known that the factor hampering an explicit quantification of the reaction The right side of the Eq. 10 is a linear combination of both kinetics is a complex of carbon (C) with the product (CO), the Ist (F1) and 0th (R1) kinetic orders using symbolic written in the mechanism reaction Eqs. 3 and 4 as CsO. notation for the (2F1-R1) mechanisms. Equation (9) can be written in a general form: Solid phase analysis gðaÞ¼ksz ð11Þ The entire group of equations takes into account a loss of Based on the method described above, Słomska [24] has the solid phase, i.e., a loss of weight of the sample, rep- proposed another empirical formulation under the resented by the level of conversion. By using the Arrhenius assumption of condition (8) that is comprised of 5 equation, the following expression can be derived [10–19]: constants: das E ½¼CO B1 exp½k1ðs À s0Þ þ B2 exp½k2ðs À s0Þ; so R_ ¼ ¼ A Á exp À ðÞ1 À as ds RT ð5Þ ¼ 0:28 h ¼ const: T ¼ const; P ¼ 0:1 MPa ¼ const ð12Þ Solving Eq. 5 for the condition s = 0, as = 0 gives the Analyses conducted by the authors (based on detailed data typical first-order kinetic relationship: of Słomska given in [24]) have proved that, for the condition E (s - so) = 0and[CO]= 0, B1 = B2, the resulting equation gðÞ¼a A Á exp À Á s where gða Þ¼Àlnð1 À a Þ s RT s s has the characteristic form of the consecutive reactions comprising the kinetic constants k ik: ð6Þ 1 2 ½¼CO B½expðk1sÞexpðk2sÞ; k2 [ k1: ð13Þ The other form of the mass integral most often encountered 1/3 is the g(as) = 1- (1 - as) expression, according to the The maximum amount of the [CO]m created derives simplified Shrinking Core Model [20, 21].
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