T E C H N O L O G Y

C R I T I C A L V E L O C I T Y OF F L U I D I Z A T I O N

O F M E D I C I N A L G R A N U L A T E S

V. I . G o r o d n i c h e v , G. N. B o r i s o v , a n d V. I . E g o r o v a

UDC 615.253.3.014.21

The most important technological p a r a m e t e r determining the hydrodynamic conditions for the p rocess of drying medicinal granulates in the suspended state is the cr i t ical velocity of fluldization.

A la rge number of formulas have been proposed for calculating the cr i t ical velocity of fluidization of various loose mater ia ls [1-4], these having been obtained for d ry monodisperse products. Medicinal gran- ulates a re moist polydisperse multicomponent sys tems . The p resen t paper is devoted to a considerat ion of the possibi l i ty of using the available mathematical relat ionships for determining the cr i t ical velocity of fluidization of medicinal granulates .

The experimental investigations were pe r fo rmed according to a well-known method [2] in a cyl indri- cal column with a d iameter of 150 m m with the passage of a i r at room tempera ture through a l ayer of gran - ules. The a i r -d is t r ibut ing device consis ted of two layers of woven belting placed between two metal grids with 0 .8 -mm aper tures . The impulse tubes for measur ing the res i s t ance of the l ayer were located at its base (above the grid) and above the free surface [4]. The mater ia ls investigated were granules of urosal , sodium salicylate, rhubarb root, calcium gluconate, asphen, l iquorice root , amidopyrine, and sodium p- aminosalicylate. The cr i t ical velocity was determined f rom the fluldization curves. The main cha rac t e r - istics and the g ra in-s ize composit ions of the products mentioned are given in Table 1. The bulk density and the mean diameter of the polydisperse mixtures of granules were determined by the methods recommended for the evaluation of the proper t ies of medicinal granulates [5]. As an example, Fig. 1 gives the fluidization curves of dry granules of calcium gluconate with various amounts of mater ia l on the grid. An analysis of the curves shows that the cr i t ical velocity of fluidization under otherwise the same conditions is indepen- dent of the specific loading of mater ia l on the grid. Consequently, in subsequent investigations we used a constant specific charge of granules of 57 k g / m 2.

Table 2 shows the cr i t ical velocities of fluidization of dry medicinal granulates as a function of par t i - cle diameter . As can be seen f r o m Table 2, with an increase in the d iameter of the par t ic les the cr i t ical velocity of fluidization r i ses .

TABLE 1. Main Proper t i e s and Grain-Size Compositions of the Medic- inal Granulates

Mean diam. of particles of narrow fractions (ram) t . , l I I 1o,871 o.471 o,s31 o,241 o.lr[ o,12/o,o8 "~

Granulate ~ ~ ~-. ~.~" ~ e ~o ~ in the following amounts (wt. %) I~ ~ E

,~ o v

Sodium p-amino- salicylate

Asphen Calcium

gluconate Urosal Liquorice root Amidopyrine Soaium

salicylate Rhubarb root

1800 640 1360 620

1510 580 1400 550 ll0O 520 1200 500

1600 490 1050 440

3,28 4,6 8,7 5,2 5,3 ll,l

1,9 4,9 7,9 2,2 3,5 6,9 7,9 5,7 7,9 0,7 1,9 3,9

1,4 2,9 7,3 3,8 3,6 9,5

14,9 28,4 16,3 25,6

13,9 22,0 10,2 26,1 17,3 18,8 9,8 25,3

12,5 25,4 19,7 25,3

27,8 10,8 24,2 11,0

32,7 13,9 30,4 17,6 23,2 13,1 38,1 18,8

32,2 16,8 24,5 12,7

0,9 0,5 0,4 0,6

0,9 1,4 2,1 0,6 1,3 2,8 0,5 0,4

0,6 0,5 0,3 0,4

0,28 0,31

0,26 0,19 0,25 0,25

0,27 0,30

Leningrad Institute of Pharmaceut ica l Chemistry . Transla ted f r o m Khimiko-Farmatsevt icheski i Zhurnal, Vol. 8, No. 5, pp. 35-39, May, 1974.

�9 19 75 Plenum Publishing Corporation, 22 7 West 1 7th Street, New York, .IV. Y. 10011. No part o f this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy of this article is available from the publisher for $15.00.

298

T A B L E 2. Cr i t i ca l Veloc i tes of F h i d i z a t i o n of Medicinal Granu la tes as Func t ions of P a r t i c l e Size

Granulate

Asphen Urosal Calcium gluconate Rhubarb root Sodium p-aminosalicylate Liquorice root Amidopyrine Sodium salicylate

Particle size (ram) 0,08 [0 ,12 [0,17 ] 0,24 ]0 ,33 [0,47 [ 0,67

critical velocity of fluidization (m/sec)

0,008 0,014 0,012 0,018 0,009 0,014 0,010 0,015

0,015 0,025 0,025 I 0,045 0,022 ] 0,036 0,035 [ 0,057 0,015 [ 0,024 0,026 0,050 0,018 0,030 0,028 0,050

I 0,044 ] 0,082 0,084 0,142 0,056 I 0,108 0,100 [ 0,188 0,046 0,078 0,090 0,164 0,068 0,104 0,084 0,150

0,138 0,220 0,183 0,334 0,138 0,304 0,182 0,264

0,247 0,450 0,324 0,616 0,258 0,564 0,338 0,446

0,475 0,945 0,596 1,25 0,475 1,19 0,655 0,946

,~p, mm water 70

60

4 O

f o

V I o

) �9

e

A

x

- o u

i

�9 7 �9

6"e

o 5 J ~

D J a

9 1 9

I

J 0,O3 0,O5" O,08 0,r

m/sec

Fig. 1

I( Ar

<L

?,5

' G 0,8 1,6

log Recr

Fig. 2

z,4

Fig. 1. C u r v e s of the f lu id iza t ion of g r a n u l e s of c a l c i u m g luco - nate . Weight of g ranu les on the g r id (in kg): 1) 0.5; 2) 0.6; 3) 0.7; 4) 0.8; 5) 0.9; 6) 1; 7) 1.2.

Fig. 2. Dependence of log A r on log Recr . roo t ; 3) asphen; 4) r h u b a r b root .

1) Urosa l ; 2) l i quor i ce

T A B L E 3. Values of the Coeff ic ients e a n d f in Eq. (1)

Granulate [ c.10 8 f

Sodium p-aminosalicylate I Asphen [ 1,9 2,5 CaIcium gluconate / 3,5 Urosal 3,6 Liquorice root 3,8 Amidopyrine 4,5 Sodium salicylate 5,0 Rhubarb root 6,0

0 ,84 0,87 0,85 0,89 0,92 0,86 0,88 0,90

In a plot of log R e c r v e r s u s log A r (Fig. 2), the e x p e r i - menta l points f o r the va r ious g ranu la tes lee on s t r a igh t l ines that a r e a l m o s t p a r a l l e l and can be r e p r e s e n t e d by equat ions of the f o r m :

Reor --- cArJ, (1)

w h e r e R e c r and A r a r e the Reynolds and A r c h i m e d e s n u m b e r s c o r r e s p o n d i n g to the c r i t i ca l ve loc i ty of f lu id iza t ion and c and f a r e the coef f ic ien ts that depend on the p r o p e r t i e s of the gTan- ula tes .

The values of the magni tudes R e c r and A r w e r e d e t e r - mined f r o m the f o r m u l a s

eecr = Vc#Pa , (2)

A r - - dspa (p -- pa) g ~, , (3)

299

c . I d a 6

4

3

2

! 4oo

\ \

VCD m/see 0,5

? /

o,1

/

50O 600 7OO 0 0.1 O,2 0,8 O,4

Pb �9 kg/ms W, kg of moisture/kg of drymateriaI

Fig. 3 Fig. 4

Fig. 3. Dependence of the coefficient c in Eq. (1) on the bulk den- s i ty of the granules Pb"

Fig. 4. Dependence of the c r i t i ca l veloci ty of fluidization Ver of medicinal granula tes on the moi s tu re content W. 1) Asphen; 2) Urosal ; 3) ca lc ium gluconate; 4) sodium p-aminosa l i cy la te ; 5) amidopyr ine ; 6) sodium sa l icyla te .

TABLE 4. Exper imenta l and Calculated Values of the Cr i t i ca l Velocity of the Fluldizat ion of Po lyd i spe r se Mixtures of Medicinal Granula tes

Granulate

Sodium p-aminosalicylam Asphen Calcium gluoonate Urosal Liquorice root Amidopyrine Sodium salicylate Rhubarb root

~ean . ]Critical am. or t e mixt. mini :m l exp a"

0,28 0,31 0,26 0,19 0,25 0,25 0,27 0,30

0,064 0,075 0,089 0,072 0.107 0,085 0,104 0,165

velocity of fluidization (Vcr, in m/sec) calculated from formulas

(1) (2) (3)

0,040 0,044 0,294 0,045 0,049 0,216 0,036 0,039 0,316 0,018 0,020 0,060 0,025 0,027 0,131 0,026 0,030 0,161 0,040 0,045 0,304 0,033 0,036 0,274

(5)

0,074 0,080 0,074 0,055 0,085 0,093 0,136 0,134

where Vcr is the cr i t ica l ve loci ty of fluldization (in m / s e e ) , d is the mean d i ame te r of the granules (in m), Pa is the densi ty of the a i r (in kg/ma), # is the v i scos i ty of a i r (in N" sec/m2), p i s t he dens i tyo f the g r a n u l e s (in kg/m3), and g is the acce le ra t ion due to g rav i ty (9.81 see/m2) .

The values of the coeff icients c a n d f in Eq. (1) calcula ted by the method of l ea s t squares [6] a re given in Table 3.

It can be seen f r o m Table 3 that the value of the c o e f f t c i e n t f in Eq. (1) changes insignificantly and its mean value may be taken as Sm=0.88.

A considera t ion of the f igures of Tables 1 and 3 together shows that with an inc rease in the bulk den- s i ty of the granules the value of the coefficient c d e c r e a s e s . As can be seen f r o m Fig. 3, between the co- efficient c and the bulk density of the granules there is a l i nea r re la t ionship of the f o r m

c = n - . % (4)

F o r the medicinal g ranula tes invest igated, n =0.015 and m = 2 . 1 0 -5 ma/kg.

On the bas i s of this , Eq. (1) for de termining the c r i t i ca l ve loci ty of f iuidization of d ry medicinal g r an - ulates has the f o r m

Recr = (0.015--2 �9 10-s Pb)Ar~ (5)

300

TABLE 5. Cr i t i ca l and Limi t ing Moisture Contents of Medicinal Granula tes

Moisture content (in kg of moisture/kg of

Granulate dry material

Asphen Amidopyrine Calcium gluconate Sodium p-amino-

salicylate Sodium salicylate Liquorice root Rhubarb root Urosal

, Wcr

0,032 0,01 0,032

0,16 0,09 0,18 0,21 0,025

Wlim

0,23 0,28 0,35

0,31 0,21 0,28 0,30 0,21

TABLE 6. Values of the Co- eff icient K in Eq. (7)

Granulate K(mX kgof dry materi~ al/iec • kg of moisture)

Asphen 0,72 Amidopyrine 0,63 C alcium glucon~tte 1,11 Sodium p-aminosalicylate 3,18 Sodium saticylate 2,12 Liquorice root 3,55 Rhubarb root 5,77 Urosal 0,83

m x kg of du material ~e of moisture

I

4 !

0 ! 2~., 3 , . , 4 5 G Wma+Wpa

Wcap

Fig. 5. Dependence of the co- efficient K in Eq, (7) on the ra t io (Wma +Wpa)/Wcapo

granules is imposs ib le . The values of given in Table 5.

Table 4 gives the values of the c r i t i ca l ve loc i ty of fluidization for po lyd i spe r se mix tu res of granula tes obtained exper imenta l ly and calcula ted f r o m the fo rmulas given above (1, 2, 3), and also f r o m Eq. (5). As can be seen f r o m Table 4, Eq. (5) gives the bes t a g r e e - ment of the calcula ted and exper imen ta l f igures . It is known [4] that the c r i t i ca l veloci t ies of the fluidization of dry and moi s t d i s - p e r s e m a t e r i a l s a r e different .

F igure 4 shows the resu l t s of invest igat ions cha rac te r i z ing the influence of the mois tu re content of the granules on the cr i t ica l ve loci ty of fluldization. As can be seen f r o m Fig. 4, there is a def- inite value of the cr i t ica l mo i s tu re content of the granules Wet be - low which the veloci ty of fluidization does not depend on the m o i s - tu re content of the granules . At a moi s tu re content of the granules higher than Wcr the tendency of the pa r t i c l e s to agglutinate and aggrega te i nc r ea se s . In these c i r c u m s t a n c e s , the cr i t ica l veloci ty of fluidization r i s e s considerably . At some l imit ing moi s tu re con- tent of the granules Wcr channel fo rmat ion and the caking of the l a y e r is obse rved , and under these conditions the fluidization of the

the c r i t i ca l and l imi t ing moi s tu re contents for different granules a re

By compar ing the f igures of Table 5 with the indices that we have obtained p rev ious ly [7] on the d is - t r ibut ion of the total amount of hygroscopic mo i s tu re over the var ious ways in which it is bound to the m a - t e r i a l , it may be concluded that the c r i t i ca l mo i s tu r e content of the granules Wcr r e p r e s e n t s the phys ico- chemica l ly bound moi s tu re (in Academic ian P. A. Reb tnde r ' s c lass i f icat ion) . Accordingly, we may wr i te :

Wcr = Wma-+- ~a, (6)

where Wma and Wpa a re the moi s tu re contents of the granules due, r e spec t ive ly , to monomolecu la r and po lymolecu la r adsorpt ion (in k i log rams of moi s tu re p e r kg of d ry mater ia l ) .

It follows f r o m Fig. 4 that the c r i t i ca l ve loci ty of f lutdization of mois t medicinal granula tes in the range of moi s tu re contents f r o m Wcr to Wli m (see Table 5) can be e x p r e s s e d by the equation:

vor, m= Vor + K (W--Wor), (7)

where Ve t is the c r i t i ca l ve loci ty of fluidization of the d ry granules in m / s e e ) ; K is an exper imenta l coeff i - cient (m • kg of dry m a t e r i a l / s e c x kg of mois tu re ; Table 6); andW is the instantaneous mois tu re content of the granules (in kg of moi s tu re p e r kg of d ry mate r ia l ) . As can be seen f r o m Table 6, the value of the co- eff icient K in Eq. (7) va r i e s f r o m 0.63 to 5.77. The cons iderable d i f ferences in the values of the coefficient K a re due to fea tu res of the dis t r ibut ion of the total amount of hygroscopic mo i s tu re of the granules ove r the f o r m s of its binding with the ma te r i a l .

F igure 5 shows the dependence of the coeff icient K on the ra t io of the amount of phys icochemica l ly bound moi s tu re (Wma +Wpa) and the amount of phys icomechan ica l ly bound (capillary) w a t e r (Wcap) in the

301

granules . As can be seen f r o m Fig. 5, the exper imenta l points l ie sa t i s fac tor i ly on a s t ra ight line which passes through the origin and is descr ibed by an equation of the fo rm

K = a ( Wma }- w'pa Wcap ), (8)

where a = 1.14 m x kg of d ry m a t e r i a l / s e e x kg of moi s tu re (proport ional i ty factor) .

Taking into account Eqs. (6) and (8), Eq. (7) assumes the fo rm

Vcr. n~ Vcr -1-1.14 (l~n~7~ WPa ][W-- (Wma-t- Wpa)]. x cap /

(9)

An exper imental check of Eq. (9) has shown that the g rea tes t difference between the exper imental and cal- culated values of the cr i t ica l veloci ty of fluidization of important medicinal granulates does not exceed 20%. Consequently we r e c o m m e n d formulas (5) and (9) for determining the cr i t ica l veloci ty of fluldization of d ry and moist medicinal granulates in tablet ing prac t ice .

1.

2. 3. 4.

5, 6.

7.

L I T E R A T U R E C I T E D

V. D. Goroshko, R. B. Rozenbaum, and O. M. Todes, Izv. Vysshykh Uchebn. Zaved. Neft' t Gaz, No. 1, 125 (1958). M. Leva, Fluidization [in Russian], Moscow (1961). I. M. Fedorov, The Theory and Calculation of the Drying Process [in Russian], Moscow (1955). N. I. Gel'perin, V. G. Ainshtein, and V. B. Kvasha, Principles of Fluidization Technology [[rt Russian], Moscow (1967). V. I. Egorova, Med. Prom. SSSR, No. 1, 35 (1964). O. N. Kassandrova and V. V. Lebedev, Treatment of the Results of Observations [in Russian], Mos- cow (1970). V. I. Gorodniehev, V. I. Egorova, and G. N. Borisov, Khim.-Farmatso Zh., No. 7, 47 (1972).

302