2.

3.

S. N. Sautin, Experiment Planning in Chemistry and Chemical Engineering [in Russian], Leningrad (1975). E. V. Markova, in: Experiment Planning [in Russian], Moscow (1966), pp. 225-231.

THERMORADIATION CHARACTERISTICS OF SOME MEDICINAL GRANULATES

N. B. Leus, M. A. Kropotkin, V. I. Leus, and G. N. Borisov

UDC 615.453.014.413

Drying of medicinal preparations is one of the most energy consuming processes in the pharmaceutical chemicals industry; therefore, improvement of drying methods is of great practical interest. The most promising method of heat treatment of various materials is infrared (IR) drying. The fraction of usable heat energy is in this case some 30-70 times higher than under conditions of convective drying, and thus the efficiency of the process is correspondingly higher. The widespread use of IR drying in the pharmaceutical chemicals industry requires the knowledge of the thermoradiation characteristics of medicinal granu- lates, i.e., of their absorption, reflection and transmission properties as a function of the moisture content and granulometric composition.

The present work has been carried out using the apparatus developed in V. I. Ul'yanov (Lenin) Leningrad Electrotechnical Institute.

The measurements of reflectance, K%, and transmittance, T%, of medicinal granulates with equilibrium moisture content were carried out (at 20 ~ and 50% relative air humidity) using a semispherical mirror attachment to a monochromatic IR spectrometer [i].

The dependence of the absorption coefficients on the moisture content and granulometric composition was studied by comparison of the given sample with a standard consisting of a similar granulate with the equilibrium moisture content whose characteristics had been previously determined using the spherical mirror attachment. This method was found to be valid owing to the lack of dependence of the form of the reflection indicatrix on the mois- ture content and composition of medicinal granulates. This has been established in a study of the spatial distribution of radiation reflected by medicinal granulates of various mois- ture content and granulometric composition, carried out using He, Ne and C02 lasers.

Measurements of the directional reflection coefficients were carried out using a mono- chromatic spectrometer adapted as follows (Fig. i). Radiation emerging from the spectrom- eter illuminator 1 was focused by means of a flat mirror 2 at the sample surface 3. A part of the radiation reflected by a spherical 4 and a flat 5 mirror was directed onto the monochromator entrance slit 6 (7 is the amplifier, 8, the recording arrangement).

The granulate reflectance was determined from

R~g = R~st I~ , 0

�9 /st

where RXs t and RXg a re r e f l e c t a n c e s o f t he s t a n d a r d and the g i v e n sample , r e s p e c t i v e l y ; I ~ t and I~ a r e t h e i n t e n s i t i e s o f r a d i a t i o n r e f l e c t e d by t h e s t a n d a r d and the g i v e n sample i n the dlrection ~ 0, respectively.

The reflection and transmission spectra were obtained for 0.1-1.25-mm granules of methionine, dibasol, dimedrol, calcium gluconate, glutamic acid, amidopyrine and rhubarb root as well as for the furacillin powder 0.I mm in diameter.

V. I. Ul'yanov (Lenin) Leningrad Electrotechnical Institute. Leningrad Institute of Pharmaceutical Chemistry. Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. i0, No. i0, pp. 100-103, October, 1976. Original article submitted March 9, 1976.

This material is protected by copyright registered in the name o f Plenum Publishing Corporation, 227 West 1 7th Street, New York, N. Y. 10011. No part o f this publication may he reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, wi thout written permission o f the publisher. A copy o f this article is available f rom the publisher for $ 7.50.

1382

o,8-

o,6

4

0,2 5

. Z . I I ,1 ! I I ~ I 1 ~ - - J _ . L . L - ~ . j j

0o,7 /,o f ,o a,o 5,0 7,o /o ~, #m

Fig. 1 Fig. 2

Fig. i. Optical scheme for measurements of directional reflection coef- ficients. Description in text.

Fig. 2. Absorbance A% of medicinal granulates as a function of the wavelength for granules of various sizes d. i) Rhubarb root, d = 0.28- 0.4; 2) dimedrol, d = 0.1-1.25; 3) calcium gluconate, d = 0.1-1.25; 4) dibasol, d = 0.1-1.25; 5) methionine, d = 0.1-1.25; 6) glutaminic acid, d = 0.1-1.25; 7) furacillin, d < 0.i; 8) amidopyrine, d = 0.28-0.4 mm.

The measured reflection, R%, and transmission coefficient, T~, were substituted into Kirchhof's law A% = 1 -- (R% + T%) to calculate the absorption coefficients, A~, of the granulates studied. Results of calculations are shown in Fig. 2.

The analysis of results shows that all granulates absorb to a very slight extent in the short wavelength part of the spectrum (% = 0.75-1.8 ~m)~ The absoprtion sharply increases for wavelengths exceeding 2 pm. The selective absorption bands at 2.7-3.0 and 6.0-7.0 pm correspond to the resonance absorption bands of water molecules. The granulate based on the plant powder shows a higher absorption within the entire investigated range (Fig. 2, curve i), probably owing to the porous-capillary structure of this sample and its content of com- plex organic compounds.

The absorbance of methionine and dibasol at various wavelengths is plotted in Fig. 3 as a function of the moisture content W. The results show that the absorbance increases with increasing moisture content, particularly within the short wavelength part of the spectrum and in the region of the water resonance absorption bands. The effect of moisture on the thermoradiation characteristics differs for various granulates, and for the given granulate depends on the type of binding between the moisture and material. According to [2], in the region of hygroscopic moistening, the moisture content in methionine is below 4.55% and in dibasol less than 3%. The absorption coefficients depend here more strongly on the moisture content than in the 5 < W < 15% region. Also, at high moisture content (W > 15%) absorbance increases with increasing W (Fig. 3, curve 2). Apparently, at higher moisture content, pores and cavities inside and between the granules fill up with moisture, bringing about a decrease of the "back scattered" radiation. At low transmittance this is equivalent to an increase of the sample absorbance [3, 4].

The absorbance of methionine and dibasol of various granulometric composition is plot- ted in Fig. 4 as a function of the wavelength. It can be seen that the granulates' absor- bance increases with increasing granule size, particularly within the short wavelength part of the spectrum. This is connected with decreased losses due to the reflection from the gran- ule's surface and the increase of the fraction of radiation interacting with the granule material.

The transmission study showed that medicinal granulates have little transparency. A 2.5-mm-thick layer is transparent in a very narrow range only (% < 1.8 pm) and even here the transmission coefficient does not exceed 4%. We were unable to study thinner layers owing to the rather large particle size of the materials studied, preventing the possibility of obtaining homogeneous structures in thin layers.

The R% and T% values obtained for methionine, dibasol and amidopyrine were used to cal- culate the mean absorption coefficients K~ and "back scattering" coefficients S~. The

1383

6a

#,G

#,4

0,2

0 . . . . . . .

! 2

S/

o,z

o.4

o,~

0,8

I t Io 15 w %

Fig. 3

i

0,8

O,G

O,4

O,2

q8

o,6

j-- I 2

I l i I I i I ] ] I 1 I I ] ~ I L l l i l l l l

5 G

6" 0,7 I,.0 ZO a,O ~0 7,0 7,0.~,l~m

Fig. 4

Fig. 3. Absorbance A% of polydispersed medicinal granulates vs mois- ture content W for various wavelengths, i) Dibasol, % = i ~m; 2) methionine, % = i pm; 3)dibasol, % = 2.9 pm; 4) methionine, % = 2.9 pm; 5) dibasol, ~ = 8 pm; 6) methionine, ~ = 8 ~m.

Fig. 4. Absorbance of methionine and dibasol granulates as a function of the wavelength for various granule sizes, i) methionine, d = 0.i- 0.14; 2)methionine, d = 0.1-1.25; 3)methionine, d = 0.28-0.4; 4) methionine, d = 0.8-1.25; 5) dibasol, d = 0.1-1.14; 6) dibasol, d = 0.i- 1.25; 7) dibasol, d--0.28-0.4; 8) dibasol, d = 0.8-1.25 mm.

obtained values (K% = 3000-5000, S% = 100-200) show that in the 0.75-1.8 pm range the granu- lates scatter strongly and absorb weakly [4].

The accuracy of measurements was limited by the experimental errors and the irreproduc- ibility of the sample surface to 9% (probability coefficient 0.95).

The reported study indicates the possibility of the efficient IR drying of medicinal granulates using wavelengths exceeding 1.8 pm.

.

2.

3.

4.

LITERATURE CITED

M. A. Kropotkin, N. B. Kutilina, and T. Yu. Sheveleva, Izv. Leningr. Elektrotekh. Inst., No. 161, 110-114.* V. I. Gorodnichev, V. I. Egorova, and G. N. Borisov, Khim. Farm. Zh., No. 7, 47-50 (1972). S. G. ll'yasov and V. V. Krasnikov, Methods of Determination of Optical and Thermoradia- tion Characteristics of Food Products [in Russian], Moscow (1972). E. V. Zhidkova, Zh. Eksp. Teor. Fiz., 27, 458-466 (1954).

*Date omitted in Russian original -- Consultants Bureau.

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