Journal of Thermal Analysis, Vol. 18 (1980) 501--508

T H E R M A L D E C O M P O S I T I O N OF THE A D D I T I O N C O M P O U N D

OF POTASSIUM CARBONATE W I T H H Y D R O G E N P E R O X I D E

T. NAGAISHI, J. YOSHIMURA, M. MATSUMOTO and S. YOSHINAGA

Department of Industrial Chemistry, Kyushu Sangyo University, 2-327, MatsugadaL Higashi-ku, Fukuoka, Japan

(Received July 23, 1979)

The kinetics of the thermal decomposition of the addition compound of potassium carbonate with hydrogen peroxide was carried out using a fixed bed flow reactor with gas-chromatography. The experimental results can be best represented over the whole range of the decomposition, by the equation -- In (1 -- ~) = kt, where e = degree of decomposition, t = time (min.), and k = rate constant (min. -~). The activation energy and the pre-exponential factor for 0 < c~ < 0.8, are 74.3 kJ/mol and 7.8 �9 10 ~, and for the decay period (0.8 < c~ < 1.0), 77.3 kJ/mol and 1.38 �9 101~ respectively.

There are many addition compounds of carbonates with hydrogen peroxide [1 ]. Those of sodium or potassium carbonate with hydrogen peroxide are widely used as detergents in industry.

Nevertheless, the thermal analysis of these substances has been little studied, although the thermal decomposition of the addition compound of sodium carbon- ate with hydrogen peroxide was studied and discussed by this author [2]. In previous papers [2, 3] a fixed bed flow reactor with gas-chromatography was shown to be very useful for the accurate determination of the thermal decomposition pro- cess of a solid. This flow method can eliminate the effects of heat of reaction and catalytic action of product gas(es) on thermal decomposition.

This paper discusses the kinetics of the thermal decomposition of the addition compound of potas'sium carbonate with hydrogen peroxide by means of the DTA, TG, X-ray diffraction analysis, mass-spectrometry and gas-chromatography.

Experimental

Material used in the experiment

The sample was prepared from "Special" grade reagents. The addition com- pound of potassium carbonate with hydrogen peroxide was synthesized at room temperature [1]. It was crystallized with 150 ml methanol f rom a solution mixed with 10 ml of 6.5M potassium carbonate solution and 40 ml of 30 w t ~ hydrogen peroxide. The precipitate was washed with methanol till free f rom potassium ions, carbonate ions and hydrogen peroxide, and dried at 35 ~ for 24hrs.

7 d. Thermal AnaL 18, 1980

502 NAGAISHI et al.: THERM AL DECOMPOSITION OF ADDITION COMPOUND

Thermal analysis

The fixed bed flow reactor with gas-chromatography (Toyo Instruments Co. Lttd., colum packing material: molecular sieve 5A, carrier gas: Helium) was used to obtain the decomposition curves for the determination of kinetic parameters under isothermal conditions in the temperature range of 65 to 80 ~ and in helium gas flow (flow velocity = 77 ml/min).

A set of runs was devised for powders. The D T A and T G data for the sample were obtained simultaneously in a Shi-

mazu Thermal Analyzer, DT-2B apparatus under the following conditions: sample weight = 100 rag, heating rate = 10 deg/min, sensitivity of D T A = +50 #V, that o f T G = 0.33 mg/division, atmosphere = air.

X-ray diffraction analysis was carried out at variable temperatures in air with a AD-1 apparatus.

Mass spectra were recorded on a Shimazu GC-MS analyzer at variable tempera- tures under a highly reduced atmosphere.

Results and discussion

DTA and T G curves of K2CO3 �9 1/2 H20 " 2 H202 are shown in Fig. 1. The curves are characterized by an exothermic peak and sharp weight loss at ca.

70 ~ In the 120-150 ~ region, a small broad endothermic rise and similar weight loss occur.

The probable mode of the decomposition of K2CO 3 �9 1/2 H20 " 2 H202 would be,

K2COz �9 1/2 H20 " 2 H202 = K2CO3 " 1/2 H~O + 02 + 2H20 (1)

K2CO3 " 1/2 H20 = K2COz + 1/2 HzO (2)

tIOTA T 10--

20--

30

4 0 , I 20 40

o

I I 1 I I 60 80 100 120 11,0 160

Tenaper~ture~ ~

Fig. 1. DTA and TG curves of KzCOa " I[2 H~O " 2 H202

J. Thermal AnaL 18, 1980

NAGAISHI et al.: THERMAL DECOMPOSITION OF ADDITION COMPOUND 503

The observed weight losses were 21 ~ at 102 ~ and 35.3 ~ at 200 ~ which are in close agreement with the calculated ones corresponding to 23.3 ~o for the reaction (1) and to 35.8 ~ for the reaction (1) + (2), respectively.

i

1.0 f 0.5

o r~' i, 20

I'0 I 05

li

a) Room temperature

I ~ t j~ ~ lid ~ 40 60

20 b) 60 ~

o t f , , , ~ ' r

o 1,0 2Q c) 80 ~

z~ 05

::n 40 1.0 20

d) 90 =C c

0.5 [

0 ~ , t ] i l I LD,.. 20 40 60

e) 200 ~ 0.5

20 40 60

20

Fig. 2. X-ray diffraction patterns at various temperatures. �9 K2CO3 �9 1/2 H20"2 H20~; O: K2CO8 " I/2 H~O; o: K2COs

Figure 2 shows X-ray diffraction patterns at various temperatures, which indicate the formation of K2CO~ �9 1/2 HzO and K~COa, and confirm the above interpreta- tion of the DTA and TG curves.

The mass spectrometer run is presented in Fig. 3. The data indicate a noticeable shift of the decomposition toward lower tempera-

ture probably due to the accuracy with which the temperature in the pyrolyzer is measured. It is, however, important to notice in the mass spectra that hydrogen peroxide molecules were detected in addition to oxygen and water molecules.

It is revealed from the mass spectra result that the reaction (1) can be replaced

7* J. Thermal AnaL 18, 1980

504 NAGAISHI et a l . : THERMAL DECOMPOSITION OF ADDITION COMPOUND

by the fo l lowing sequence o f reactions:

KzCO z �9 1/2 H 2 0 �9 2 H202 = K2COz " 1/2 HzO + 2 HzOz ( la)

H202 = H 2 0 + 1/2 02 ( lb)

That the D T A curve has only one exothermic peak at ca. 70 ~ suggests that either the rate of reaction ( la ) or that of reaction ( lb) is faster than the other.

A 1 .0 _|_

0 . 5

0

1.0 |

0.5

1 o 20

2 t (7.4) j

| 20

c - - 1 . 0 - - _ 1 -

13.5

o I 20

a) Room te~nperatu~e (HzO) (1.57) (O2)

_ |_

(N2) [(HIO2)

I ~ [ , 11 20 30

b) .3O*C (1.6)

_1_

[ i L i

3O c} 50 ~ (2.5)

1

i , r S0

d) 80 ~

4O role

40 role

4O m/e

, L [ i I ~.. 30 40

m/e

Fig. 3. Mass spectra record at variable temperatures

The rate of 02 gas evolution, d(Oz)/dt (ml/min) is plotted versus time at various temperatures measured with the fixed bed flow reactor with gas-chromatography (Fig. 4). These curves were integrated graphically to obtain the decomposition curves. The rate of the reaction obeys the first-order equation in the whole range of decomposition,

- I n (1 - 7) = kt (3)

The applicability of Eq. (3) is shown in Figs 5 and 6, where In (1 - c 0 is plotted vs. time, t.

& Thermal Anal. 18, 1980

N A G A I S H I et al . : T H E R M A L D E C O M P O S I T I O N O F A D D I T I O N C O M P O U N D 5 0 5

For 0 < c~ < 0.8, this equation assumes both random nucleation and the reac- tion ending at different times in different crystals [5].

In the decay period (0.8 < e < 1.0), the equation can be derived on the basis that the rate of reaction is simply proportional to the amount of substance un-

O~ 80~

2 0 ~ 750C

~ 70~

0 50 100 1.0i I Time, min

80oc 75~

0 . 5 ~ I b)

0 50 100 Time~ min

Fig. 4. (a) The rate of O~ gas evolution vs. time and (b) the decomposition curves

decomposed, if each molecule possesses an equal probabili ty for decomposi t ion [611.

The Arrhenius plots are shown in Fig. 6, f rom which the activation energy and pre-exponential factor are computed as follows:

k = 7.82 �9 109 exp ( - 7 4 . 3 (kJ/mol)/RT) for 0 < e < 0.8 and

k = 1.38 �9 101~ ( - 7 7 . 3 (kJ/mol)/RT) for 0.8 < c~ < 1.0.

,iT. Thermal AnaL 18, 1980

506 N A G A I S H I et al . : T H E R M A L D E C O M P O S I T I O N O F A D D I T I O N C O M P O U N D

2 i

i

I ime, mm

0 10 20 30 40

1 ~ N 65 ~

2

Fig. 5. The first-order plot for 0 < c~ < 0.8

Time,rain

I 20 50 100 p..

" ,~ o

2

i

Fig. 6. The f irst-order p lot for 0.8 < cr <: 1.0

s Thermal Anal. 18, 1980

NAGAISHI et al.: THERMAL DECOMPOSITION OF ADDITION COMPOUND 507

The reaction scheme of the thermal decomposition of Na2CO a �9 2 H202 which is the same as that of potassium, is expressed by the equations:

Na2COz �9 2 H202 = Na2CO3 + 2 H202 (4)

H202 = H 2 0 + 1/2 02 (lb)

at higher temperature (at ca. 120 ~ than K2CO 3 �9 The decomposition occurs �9 1/2 H20 " 2 H202.

7

1/T.103 K -1 2.B 2.9 3.0 2 ! I

o <0.8

4 -- 0.8<oc<1.0" ~ ~

Fig. 7. The Arrhenius plot

The decomposition process of Na2CO3 �9 2 H202 is described by three stages which are nucleation, growth period of nuclei and the decay period�9 The kinetic laws obey the first-order equation for the nucleation, the Avrami-Erofeev equa- tion for the growth period and the first-order equation for the decay period.

The activation energies of each process are 154�9 115.9 and 75.2 kJ/mol, re- spectively, which is different from the decomposition of K2CO 3 �9 1/2 H20 " 2 H202 except for the decay period.

It is concluded from the activation energy and the decomposition temperature that the bond strength between carbonate and hydrogen peroxide is larger in Na2CO a �9 2 H.,O2 than in K2COz ' I /2 H . ,O '2H202 , and K2C03"1/2 H20" �9 2 H20~ is less stable towards heat than Na2COz �9 2 H202.

The authors wish to express their appreciation to Dr. D. Dollimore for his valuable com- ments and thank Mr. H. Nakamura, Research Fellow, Department of Environmental Engi- neering, Kyushu Institute of Technology, for his advise.

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508 NAGAISHI et al.: THERMAL DECOMPOSITION OF ADDITION COMPOUND

References

1. Gmelins Handbuch der anorg. Chemie, Verlag Chemie GmbH. Weinheim, 1969, System No. 21, p. 1364, System No. 22, p. 869, System No. 24, p. 225, System No. 25, p. 237.

2. T. NAGAISHI, T. KANEDA, M. MATSUMUTO and S. YOSHINAGA, J. Industrial Explosives Society, Japan, 37 (1976) 84.

3. H. NAKAMURA, S. NAKAMURA and I. NAKAMORI, ibid., 36 (1975) 27. 4. M. ISHIBASHI, Experimental Quantitative Analysis, Fuzanbo, Kyoto 1963, p. 452 (in Japa-

nese). 5. C. H. BAMFORD and C. F. H. TII'PER, Comprehensive Chemical Kinetics, Elsevier Publica-

tion Corp. 1969, vol. 2, p. 390 6. W. E. GARNER, Chemistry of the Solid State, Butterworth Science Corp., 1955, p. 211.

R s -- On a 6tudi6, par chromatographie en phase gazeuse, la cin4tiquede lad6composition thermique du compos6 d'addition du carbonate de potassium avec de l'eau oxyg6n6e, en se servant d 'un r6acteur h 6coulement, type lit fixe.

Les r6sultats exp6rimentaux peuvent 6tre d6crits avec un bon ajustement dans tout l'inter- valle de d6composition, par l'6quation (I) - -In (1 -- e ) = kt; c~ = degr6 de d6composition, t = temps (rain) et k = constante de vitesse (min-1).

L'dnergie d'activation et le facteur pr6exponentiel sont pour 0 < c~ < 0.8, respectivement 6gaux A 74.3 et 7.8 �9 109 kJ/mole, et pour la p6riode d'amortissement (0.8 < e < 1.0) ~ 77.3 et 1.38 �9 101~ kJ/mole.

ZUSAMMENFASSUNG - - Die Kinetik der thermischen Zersetzung der Additionsverbindung von Kaliumcarbonat mit Wasserstoffperoxid wurde unter Anwendung eines Fixbett-DurchfluB- reaktors durch Gaschromatographie untersucht.

Die Versuchsergebnisse kSnnen im ganzen Bereich der Zersetzung am besten durch die Gleichung (I) - -In (1 -- ~) ---- kt beschrieben werden; a = Zersetzungsgrad, t ---- Zeit (rain) und k = Geschwindigkeitskonstante (min-1).

Die Aktivierungsenergie und der prfiexponentielle Faktor betragen, ffir 0 < c~ < 0.8, 74.3 kJ/Mol, bzw. 7.8 �9 109 und ffir die Periode des Abklingens (0.8 < ~ < 1.0) 77.3 kJ/Mol, bzw. 1.38 �9 101~

Pe3ioMe - - I/Iccne)loBaHa FatHeTm(a Tepivl!4~ecKoro pa3~o~eHan npo~lyKTa npKcoe~nnenn~ Kap- 60rlaTa xanrl~ ri nepeKHcrI Bo~opo~a, rlcnonl~3y~t ynopI~bli~ peai~Top )IJIa HenpepLiBHoro npolIecca COBMeCTHO C Fa3OBSIM XpOMaTorpaqboM. BO Bce~ O62IaCT~I pa3aoxearI~ 3KcnepnMeHTanbH~Ie pe3y~lLTaT~,I garlnymle MOFyT 6I,ITB rlpejIcTaBJieHl, i ypaBHemleM -- ln(1--c 0 = m, rJIe c~-crelierm paanoxeHI, I,q, t-BpeMJI (MICH.) rI K-KOHCTaHTa CKOpOCTII (M!IH.--1). ~Heprri~ aKTIIBaILIIH M npe~- 3I~ClIO}ienunanl~m, ii~ qbaKTop ~tJI~ 0 < ~ < 0.8, COOTBeTCTBeI-mo,paBrlLI 74.3 Ir 1~ 7.8. 109, a ~IJI~ ueprlo~a pacna~Ia (0.8 < e < 1.0) - - 77.3 KJlX]MOJII~ rI 1.38. 10 l~

d. Thermal AnaL 18, 1980