Determination of formal kinetic constants of thermal decomposition of aqueous hydrogen peroxide solution in a mixture of magnetic powder, based on experimental thermogram, obtained in adiabatic conditions

Process of thermal decomposition of hydrogen peroxide aqueous solution with the addition of magnetic powder in the form of toner for printers and lanthanum manganite were considered. Obtained resulting from an experiment in the Dewar container conducted thermogram analyzed using mass balance equations and heat. Formal kinetic parameters determined, and conclude that the magnetic powder in the mixture does not have catalytic properties. The described technique is recommended as a rapid analysis of the kinetics of the various reactions to substances having predefined thermal and thermodynamic properties. Recently, it has been suggested to use fluids mixed with a fine powder to change the thermophysical features of coolants in order to increase the heat exchanger efficiency. Application of magnetic powders allows for additional control over unit operation using the magnetic field. An aqueous hydrogen peroxide solution is often suggested to be used as a coolant in a variety of heat exchangers (such as solar collectors). The aqueous hydrogen peroxide solution with additives of fine magnetic powder can significantly improve the efficiency of heat exchangers. To study the kinetics of thermal decomposition of hydrogen peroxide aqueous solution with added magnetic powder, series of experiments were done to determine the process thermogram in adiabatic conditions of Dewar vessels. Dynamic heat balance equation for the reaction of thermal decomposition of hydrogen peroxide aqueous solution, considering the presence of magnetic powder particles and the reaction of hydrogen peroxide thermal decomposition are recorded under the assumption of the process equilibrium within the entire time interval . During experiments the mixture temperature variations from the initial to final did not exceed 8.5 K, which allows, according to the Hess’s law, heat of reaction (qd,, J/mol) to be taken as constant. The thermodynamic system is a colloidal solution of hydrogen peroxide, oxygen in water (with current masses, respectively, mH2O2 , mO2 , mH2O) and fine magnetic powder, consisting of toner for printers and lanthanum manganite (LaySrMnO3−X(y < x)) of the total mass mmp. Specific heat components, respectively, cH2O2 , cO2 , cH2O & cmp are temperature functions for a general case. Heat from the a Corresponding author: bvborisov@tpu.ru This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/20147601032 EPJ Web of Conferences hydrogen peroxide decomposition reaction Q = −qr dmH2O2 d goes to change the system’s internal energy U : dU d = (cH2O2mH2O2 + cO2mO2 + cH2OmH2O + cmpmmp) dT d . In terms of the above assumptions, the heat balance equation is set down as follows: ( cH2O2mH2O2 + cO2mO2 + cH2OmH2O+ cmpmmp ) dT d = −qr dmH2O2 d · (1) Mass of the system is assumed the same: m = mH2O2 + mO2 + mH2O + mmp. According to H2O2 = H2O + 2 O2 + qr mass balance equation system is complemented by the balance equation of individual components: − dmH2O2 d = dmH2O d + dmO2 d . Under the Arrhenius theory, the rate of hydrogen peroxide thermal decomposition (loss) H2O2 reaction is described by the following ratio: dc d = −cnA exp ( − Ea RT ) , (2) where c–concentration of H2O2, [c] = kmol/m; n – the reaction order, Ea – activation energy [Ea] = kmol/kJ; R – universal gas constant R = 8314 J/(kmol · K). Dewar volume V , and consequently, of the working fluid remains unchanged. As a result, dc d = 1 V · MH2O2 dmH2O2 d ⇒ dmH2O2 d = V · MH2O2 dc d · (3) From (1) with consideration for (2) and (3): dT d = qr ( V · MH2O2 )1−n cH2O2mH2O2 + cO2mO2 + cH2OmH2O + cmpmmp mnH2O2A exp ( − Ea RT ) · (4) Equation (4) is closed by ratios for current values of component masses: mH2O2 = mH2O2 ∣∣ = 0 + ∫ 0 dmH2O2 d d mH2O2 = mH2O ∣∣ = 0 − MH2O MH2O2 ∫

Recently, it has been suggested to use fluids mixed with a fine powder to change the thermophysical features of coolants in order to increase the heat exchanger efficiency.Application of magnetic powders allows for additional control over unit operation using the magnetic field.An aqueous hydrogen peroxide solution is often suggested to be used as a coolant in a variety of heat exchangers (such as solar collectors).The aqueous hydrogen peroxide solution with additives of fine magnetic powder can significantly improve the efficiency of heat exchangers.To study the kinetics of thermal decomposition of hydrogen peroxide aqueous solution with added magnetic powder, series of experiments were done to determine the process thermogram in adiabatic conditions of Dewar vessels.
Dynamic heat balance equation for the reaction of thermal decomposition of hydrogen peroxide aqueous solution, considering the presence of magnetic powder particles and the reaction of hydrogen peroxide thermal decomposition are recorded under the assumption of the process equilibrium within the entire time interval .
During experiments the mixture temperature variations from the initial to final did not exceed 8.5 K, which allows, according to the Hess's law, heat of reaction (q d, , J/mol) to be taken as constant.The thermodynamic system is a colloidal solution of hydrogen peroxide, oxygen in water (with current masses, respectively, m H 2 O 2 , m O 2 , m H 2 O ) and fine magnetic powder, consisting of toner for printers and lanthanum manganite (La y SrMnO 3−X (y < x)) of the total mass m mp .Specific heat components, respectively, c goes to change the system's internal energy In terms of the above assumptions, the heat balance equation is set down as follows: Mass of the system is assumed the same: mass balance equation system is complemented by the balance equation of individual components: d .Under the Arrhenius theory, the rate of hydrogen peroxide thermal decomposition (loss) H 2 O 2 reaction is described by the following ratio: where c-concentration of H 2 O 2 , [c] = kmol/m 3 ; n -the reaction order, E a -activation energy [E a ] = kmol/kJ; R -universal gas constant R = 8314 J/(kmol • K).Dewar volume V , and consequently, of the working fluid remains unchanged.As a result, From ( 1) with consideration for ( 2) and (3): Equation ( 4) is closed by ratios for current values of component masses: where M H 2 O , M H 2 O 2 and M O 2 , respectively, the molecular masses of water, hydrogen peroxide and oxygen.To solve the system (4) and (5) temperatures and masses of components at the initial moment of time ( = 0) are involved as the initial conditions.
Tabulated values of the specific heats of hydrogen peroxide, oxygen and water were used for the numerical implementation.Their mean values were, respectively: The magnetic powder heat capacity, determined in separate independent experiments, was Thermal effect of the thermal decomposition reaction q r = 98 kJ/kmol is the minimal of those mentioned in references, and that allows evaluating the upper limit for the thermal decomposition reaction rate.The experimental results processing, the equation numerical solution (4) to determine the kinetics constants of the reaction under investigation were carried out by means of MS EXEL.
Using this program, the results of experiments were smoothed, for that reason the trend lines were determined.The obtained lines were used to determine the dynamics of temperature derivatives in the Dewar in time, and which values in the selected time interval served as input parameters for the regression analysis, which was used to determine the sought data on the formal kinetics constants.
Analysis of the experimental data, obtained by J.A. Zaripov, indicates that the thermal decomposition reaction of hydrogen peroxide has two periods of time, which are significantly different from each other (Fig. 1).This is noted by other authors [1][2][3].For the numerical analysis of the experimental results, the best approximation of trend line for the reaction's initial period are thirddegree polynomials for cases under study (Fig. 2).Here the approximation error is not greater than 1.8÷2.0%.Power function was the best overall trend line function for the obtained thermograms.Here the approximation error did not exceed 6.5 ÷7.0% (Fig. 3).
The regression analysis has revealed that the closest description of kinetics of thermal decomposition of hydrogen peroxide in the initial portion is a second-order response (to be exact, it is closer to the second: n = 1.8÷2.1)with an activation energy within the range of 78÷87 MJ/kmol.Subsequently, the reaction order reduced to zero fairly quickly (the reaction rate is practically independent of concentration) and activation energy increases to 120÷240 MJ/kmol.Depth value of hydrogen peroxide H 2 O 2 , c O 2 , c H 2 O & c mp are temperature functions for a general case.Heat from the a Corresponding author: bvborisov@tpu.ruThis is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.EPJ Web of Conferences hydrogen peroxide decomposition reaction Q = −q r dm H 2 O 2 d