Synthesis and Catalytic Activity of Copper (II) Resorcylic Acid Nanoparticles*

CHEM. RES.

Available online at www.sciencedirect.com

CHINESE U.

2007, 2 3 ( 2 ) , 217-220

ScienceDirect

Article ID 1005-9040~2007', -02-217-04

Synthesis and Catalytic Activity of Copper( II ) Resorcylic Acid Nanoparticles* LI yu1,2**

and LIU You-zhi' 1. Institute of Chemical Engineering and Environment, North University of China, Research Center of Shanxi Province for High Gravity Engineering and Technology, Taiyuan 03005 1, P. R. China; 2. Institute of Chemical Engineering and Technology, T a i p n University of Technology, Taiyuun 030051, P. R. China Received Mar. 22, 2006 Copper( II ) resorcylic acid( CuRes) nanoparticles were synthesized by using reactive precipitation method with resorcylic acid and blue copperas as the raw material in a rotating packed bed. The sample obtained was characterized by using X-ray diffraction(XRD) , transmission electron microscopy( TEM) , Fourier transform infrared spectroscopy (FTIR) , thermo-gravimetric analyses (TG) , and element analysis. In addition, the catalytic activity of CuRes nanoparticles on the thermal decomposition of nitrocellulose-nitroglycerine( NC-NG) was also determined via DSC. The results show that the spherical nanoparticles with a diameter of 20 nm were obtained in ethanol solution. The peak temperature of the thermal decomposition of NC-NG-CuRes decreases by 3 't compared with that of normal CuRes , and the decomposition enthalpy is increased by 735 J/g, and therefore, it is reasonable to assume that CuRes nanoparticles have a better catalytic activity. Keywords Combustion catalyst; Resorcylic acid; Copper( II ) salt; Reactive precipitation; Rotating packed bed

Introduction Copper( I[ ) resorcylic acid is a type of conventional burning rate catalyst commonly used in solid propellant. Burning rate is considered as an important parameter in the performance of solid propellant. Recent literature has shown that the burning rate of solid propellant mainly depends on the diameter and the specific area of the burning rate catalyst. CuRes nanoparticles not only increase the burning rate but also lower the pressure exponent, and thereby improve the comprehensive properties of the solid propellant"'23. There are several methods for the synthesis of ordinary nano-sized particles, including physical vapor dep~sition'~] , chemical vapor depo~ition'~] , reactive precipitationr5], micro-emuIsion[61, supercritical chemical processing[71, hydrothermal synthesisL8], phase shift reaction''] , etc. Among those methods, the reactive precipitation is the most popular, and this is attributed to its ease of operation, low cost, and massive process. At present, the reactive precipitation process is often camed out in a stirred tank; the size and distribution of particles are difficult to be controlled, especially those reaction processes involving

the organic reactants with a high viscosity. Rotating packed bed has been proven to be very effective in extraction, preparation of liquid membrane, and other This article reports a novel method for the synthesis of CuRes nanoparticles via reactive precipitation in a rotating packed bed.

Experimental 1 Materials The raw materials used in this study were resorcylic acid from Haomei Chemical Engineering Co. (Shandong) and chemical grade blue copperas from Tongyuan Copper Co. (Shanxi). Analytical grade sodium hydroxide and deionized water were used throughout this study. 2 Methods The rotating packed bed employed in this study is shown in Fig. 1. The inner diameter of the shell is 400 mm; the dimensions of the rotor are 80 mm( i. d. ) ~ 3 0 mm( 0 0 . d. ) x 100 mm( axial depth). The type of packing is wire mesh, the inlet pipe is 6 mm, the bore diameter of the spraying nozzle is 1.5 mm , and the distance is 6 mm.

* Supported by the National Natural Science Foundation of China( No. 20576128) and partially supported by the Natural Science Foundation of Shanxi Province( No. 20051015). * * To whom correspondence should be addressed. E-mail: hgliyu@nuc. edu. cn

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reactions : OH

+

NaOH

+ cuso4

( 1 ) Spraying nozzle; ( 2 ) shell; ( 3 ) shaft;

( 4 ) motor; ( 5 ) reactant inlet; ( 6 ) packing.

In a typical synthesis process, a certain amount of resorcylic acid was added to sodium hydroxide solution, and the solution was heated until resorcylic acid was fully dissolved. The sodium resorcylate solution with a desired concentration was obtained. Blue copperas was added to de-ionized water to obtain a bluestone solution with a certain concentration. A certain amount of sodium resorcylate solution and bluestone solution were added to two different feed tanks and preheated up to 70-80 “c and were then introduced into spraying nozzle in the rotating packed bed via two high-pressured pumps, the two reactant streams impinge forward at a high rate and this resulted in the formation of an impinging section and are mixed together, reactive precipitation was carried out on the impinging section, and the part on the edge of the impinging section entered the rotating packing and the reaction was continued. The suspension discharged from the rotating packed bed was then filtered and rinsed thrice with deionized water to yield CuRes gel. The gel was redispersed into an ethanol solution and stirred for 30 min, filtered, rinsed, and dried at 100-105 T in a vacuum dryer for two hours to yield the sample.

3 Analysis and Measurements X-ray diffraction ( XRD) analysis of the catalyst was carried out by using a Rigaku D--2000 diflractometer (40 kV, 100 mA, Cu Kcu radiation). The morphology and size of the particle were examined by using a Hitachi-800 transmission electron microscope ( TEM ) . FTIR spectrum was recorded on a Hitachi 260-50 i&ared spectrophotometer. Thermo-gravimetric analysis( TG) was carried out in an instrument called Setaram TGA92. The samples were heated from 100 to 800 ‘I2 at a heating rate of 5 T / m i n in air.

Results and Discussion 1 Reactive Precipitation Process The syntheses process involves the following

OH NaOH

(1)

OH

OH

Fig. 1 Schematic diagram of the rotating packed bed

+ HzO

+

-

+ NaHS04 (2) OH HzO + Na2S04

(3) Reaction ( 2 ) is an instantaneous reactive precipitation process. To obtain CuRes nanoparticles, it is indispensable that a high degree of super-saturation leads to quickly nucleation. Micro mixing is the key factor for the formation of superfine particles during the reaction process. Rotating packed bed is one of the effective devices that can enhance the mass transfer and intensify the micro mixing between the phases, which assures that almost all the reactants are in the best micro mixture state. + NaHS04-

2 Effects of Operating Parameters To simplify the effects of structural factors of the rotating packed bed on CuRes particles size, Reynolds number Re was used as the grouping variable and this involves four factors : the distance ( 1 ) between the nozzles, initial jet velocity of the reactant( v ) , density ( p ) , and viscosity of the reactant(p) . Re = ( b v ) / p High-gravity number ( H) of rotating packed bed was employed as another grouping variable including the rotating speed( w ) and the mean value of the packing diameter( r ) . H = -w2r = - NZr g 900 The effects of Re and H on the particles size are shown in Fig. 2 , it is seen that particle size sharply decreases and then gradually reaches a plateau with the increase in the high-gravity number within the range of low Re values, whereas high-gravity number has only a negligible effect on particle size in the high Re region. The formation of superfine particles is because of the intensification of micro mixing of reactants in the rotating packing, this enhances nucleation in low R e , and H plays a significant role on the particle size. In high R e , most reactants react on the impinging section because of the impingement of high-velocity feed streams, and when Re is higher, the reaction during the impingement would be faster. To obtain most favorable micro mixture, H and Re should not be less than 200 and

LI Yu et al.

No. 2

219

12000, respectively.

1

120 1

80 E

3

60

t k=1840

40

20 200

400

600

H

800

1000

1200

Fig.4 “EM photograph of the sample

Fig. 2 Effect of operating parametem

I

I

Reative temperature : 50 ; reactant concentration :

1.0 moVL; final pH value: 5.

3 Effects of Reaction Conditions Under the conditions of Re = 12000 and H = 400, the effect of four reactant concentrations ( 0.5, 1.0, 1.2 and 1.5 moVL) on particle size was investigated at different reaction temperatures. The results shown in Fig. 3 indicate that particle size decreases with the increase of reactant concentration that resulted from the increase of super saturation as a result of the increase in reactant concentration. The nucleation rate ’ rapidly increases, which leads to the reduction of particle size because of the formation of more crystal nuclei. It can be observed that with the increase in temperature, the particle size decreases; however, when the reaction temperature is higher than 90 “c , the copper( II ) will be hydrolyzed.

10

0.6 0.8 1.0 1.2 1.4 Reactant concentration/(mo1.L-I)

1.6

Fig. 3 Effects of the concentration and temperature Reaction temperature: a. 25; b. 40; c. 65;

d. 75. R,=12000; H=400.

4 Characterization of the Sample 4. I TEM Analysis of the Sample

TEM photograph of the sample under the optimum conditions described previously is shown in Fig.4. It shows that the particles are fine and exhibit an even distribution, and the average size is 20-25 nm. 4.2 XRD Analysis of the Sample Fig. 5 shows the X-ray diffraction pattern of the

I

20

30

I

I

40 50 2810

I

I

60

70

80

Fig. 5 XRD patterns of the nanoparticle CURS Q.

Norm CuRes; b. nano CuRes.

nanoparticle CuRes, the 28 values and the half-height widths of the highest peaks of the samples were mea-. sured using X-ray broadening analysis. The average particle size was calculated via the Scherer equation : D = KA/(pcos8) where D ( nm) is the average particle size, K is the Scherer’s constant, also called the shape factor, K = 0. 89, A ( nm) is the wavelength of the X-ray used,

p( rad)

0.4

I

is the width of the line at the half-maximum intensity, and 8 is the B r a g angle ( ’) The calculated result shows that the average particle size is 20 nm. 4.3 TG and DTA Analyses of the Sample The thermal stability of the sample was investigated by using Setaram TGA92. The sample was heated to 800 T in air at a constant heating rate of 5 T/min. TG and DTA analysis curves are shown in Fig. 6. From the TG curve, it can be seen that the first variation is asso-ciated with a weight loss of 6.98% , the second one with a weight loss of 7.4% , and the last one with a weight loss of 61.7% over 210 “c , which agrees with the theoretical weight loss of 62%, and the final remainder is CuO. In the second stage of weight loss (over 165 “c ) , CuRes loses two molecules of water of crystallization, so the final drying temperature of the particles should be controlled, and it should not be higher than 165 T .

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16

-

5 12

-

~

DTA

-

-

8 -

TG

2

4 0

shown in Fig. 7 . There is no obvious variation near the benzenoid skeleton C-C stretch vibration band ( 1500 cm - I ) , inner bending vibration band( 1093.56 em ) , and external bending vibration band ( 694.33 cm - 1 ) , but they all showed a red-shift. The stretching vibrations vC* ( 1639.38 cm-' ) and vc- ( 1232.43 cm ) , and inner bending stretching vibration ( 400620 c m - ' ) assigned to -COOH have disappeared in

0.00 0.05

- 0.10 5 E - 0.15

m

.-gI

- 0.20 -

,

4000

I

l

I

3500

3000

I

2500

Fig.7

-

0.25

2000

1750

Catalytic Activity of the Sample DSC curve of the thermal decomposition of NC-NG-CuRes is shown in Fig. 8. The peak temperature of the thermal decomposition of NC-NG-Nan0 CuRes is decreased by 3 "r: compared with the molar ratio of 5: 1 of NC-NG to CuRes, and the decomposition enthalpy is increased by 735 J/g in comparison with that of pure NC-NG. By comparing the uses of nanometer CuRes particles in the catalytic assistance of thermal decomposition of NC-NG nanometer, it is proved that CuRes exhibits a better catalytic activity than the normal. This is attributed to smaller size,

t

n(NC-NG): n(CuResF5 :11

t

LNC-NG 160

1 180

200 220 Temperature/%

Fig.8 DSC cww

Of

1500

1250

1000

750

500

c1crn-l E"IIR spectra of CuRes(a) and IiRes(b)

5

20

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NC-NG-CuRe

larger specific area, and several defect dot inside the catalyst, which forms more catalytic active centers to enhance the complete decomposition of NC-NG.

References Armstmng R. W. , Baschung B . , Booth D. W . , et al.

, Nano

Le-rs, 2000, 3 ( 2 ) , 253 Li Shu-fen, Wang Jin, Zhao Feng-qi , et al. , Journal of Propul-

sion Technology, 2001, 22( 2 ) , 165 h i s F. E. , Fissan H. , Peled A. , A Revim J. Aerosol Sci. , 1998, 29, 511 Hang L. S. , Lai H. T., Id.Eng. Chem. Res. , 1999, 38,

950 Chen Jian-feng, Wang Yu-hong, Guo Fen, Ind. Ens. Chem. Res. , 2000, 3 9 , 948 Lopez Perez J. A. , Lopez Quintela M. A. , Mira J. , J. Phys. Chem. B , 1997, 101, 8045 Reverchon E. , Porta D. G. , Trolio D. A. , et al. , Id.Eng. Chem. Res. , 1998, 37, 952 Shi Wei , Liu Hai-yan, Ren Dong-mei , Chem. Res. Chinese Universities, u)o6, 2 2 ( 3 ) , 364 Lian Hong-lei , Jia Ming-jun, Pan Wei-cheng, Chem. Res. ChineseUniverSities,2006,22(1),99 Bums J. R. , Jamil J. N. , Ramshaw C. , Chemical Engineering science, m , 55,2401 Wang M., Zou H. K. , Shao L. , et al. , Powder Technology, 2004, 142, 166