CONCENTRATION THERMOLABILE

OF

SOLUTIONS

AND

FOAMING

CONTAINING SUBSTANCES

A. V. Viter, V . M. Z a i c h e n k o , A. N. Marchenko, and V. P. Plavnik

UDC 615.451.16

The concentration of aqueous alcoholic e x t r a c t s containing t h e r m o l a b i l e and foaming s u b s t a n c e s in the production of phytochemical medicinal p r e p a r a t i o n s is often c a r r i e d out in stills o r tubular v a c c u m e v a p o r a t o r s . In these c a s e s the product being c o n c e n t r a t e d is in the elevated t e m p e r a t u r e zone f o r a p r o longed t i m e ; this inevitably leads to a loss of the labile substance. During the concentration of foaming e x t r a c t s in these a p p a r a t u s , in spite of the use of complex m e c h a n i c a l antifoaming agents, l o s s e s of the p r o duct with the f o a m and the f o r m a t i o n of deposits and c r u s t s which, in t h e i r turn, also lead to spoilage and l o s s e s of product, a r e frequent. F o r a m o r e complete p r e s e r v a t i o n of a valuable t h e r m o l a b i l e or foaming s u b s t a n c e , t h e concentration of such e x t r a c t s a r e b e t t e r c a r r i e d out in a thin f i l m centrifugal e v a p o r a t o r . The main advantage of this a p p a r a t u s is the extremely" s h o r t contact t i m e of the product being c o n c e n t r a t e d with the heated s u r f a c e of the a p p a r a t u s . Thus, if the duration of the c o n c e n t r a t i o n of solutions in stills is usually 7-8 h and in tubular e v a p o r a t o r s with r e c i r c u l a t i o n of the product being c o n c e n t r a t e d is 3-5 h, then the duration of contact of the product being concentrated with the heated s u r f a c e in a thin film centrifugal e v a p o r a t o r does not exceed 3-5 sec and the r e q u i r e d concentration is attained in one pass [1-3]. A s c h e m e f o r an e x p e r i m e n t a l a r r a n g e m e n t for a thin f i l m centrifugal e v a p o r a t o r is given in Fig. 1. The e x t r a c t intended f o r concentration is fed by the pump (1) via the r o t a m e t e r (2) through the feed tube (3) onto the u p p e r portion of a rapidly rotating t a p e r e d r o t o r (4) and under the influence of the c e n t r i f ugal f o r c e is u n i f o r m l y s p r e a d as a thin l a y e r (of thickness 0.1 to 0.5 mm) o v e r the total heating s u r f a c e . The e v a p o r a t e d concentrate is collected in the lower wide p a r t of the t a p e r e d r o t o r and spun by the c e n t r i f ugal f o r c e through the d i s c h a r g e pipe (5) to one of the r e c e i v e r s (9). The s e c o n d a r y v a p o r is r e m o v e d through the c e n t r a l tube, condensed in the tubular c o n d e n s e r (8) and collected in one of the r e c e i v e r s (10). Through the r e g u l a t i n g valve (16) s t e a m is admitted to heat the housing of the c e n t r i f u g a l e v a p o r a t o r (6), the condensate f r o m the heating v a p o r is expelled by the e j e c t o r (14) into the overflow line. With the vacuum pump (11) and the end packing (7) the inside of the a p p a r a t u s is maintained at a set reduced p r e s s u r e which g u a r a n t e e s a low boiling t e m p e r a t u r e (40-45~ for the aqueous e x t r a c t s . S t e a m can be admitted to heat the a p p a r a t u s at a p r e s s u r e below a t m o s p h e r i c and a t e m p e r a t u r e b e low 100 ~ using the regulating valve (16); this in connection with the low boiling t e m p e r a t u r e of the e x t r a c t being concentrated and its s h o r t contact time with the heating s u r f a c e provides m o r e c o m p l e t e p r e s e r v a tion of the t h e r m o l a b i l e substance. Foam, which is inevitably f o r m e d on boiling solutions which contain foaming s u b s t a n c e s , is quenched by the c e n t r i f u g a l f o r c e of the rotating heating s u r f a c e . As a t e s t substance, a s t r o n g l y foaming saponin containing aqueous alcoholic e x t r a c t of leaves of Digitalis purpurea, used f o r the p r e p a r a t i o n of digitoxin and gitexin, was c o n c e n t r a t e d in the d e s c r i b e d apparatus. T e m p e r a t u r e of e x t r a c t fed to e v a p o r a t o r Heating v a p o r t e m p e r a t u r e T e m p e r a t u r e of exiting c o n c e n t r a t e Unit efficiency T i m e of contact of e x t r a c t with heated s u r f a c e P r e s s u r e in a p p a r a t u s

17~ 93~ 45~ 325 I / m 2 . h 3 sec 150 m m Hg

Ukrainian Scientific R e s e a r c h and Design Institute of C h e m i c a l Engineering, Pilot Plant of the Kharkov Scientific R e s e a r c h P h a r m a c e u t i c a l Chemistry- Institute. T r a n s l a t e d f r o m K h i m i k o - F a r m a t s e v t i c h e s k i i Zhurnal, No. 12, pp. 45-47, D e c e m b e r , 1968. Original a r t i c l e submitted August 5, 1968.

692

,J Fig. 1. Scheme of an a r r a n g e m e n t for a thin film e v a p o r a t o r . 1) Feed pump; 2 ) r o t o m e t e r 3) feed tube; 4) e v a p o r a t o r r o t o r ; 5) d i s charge pipe; 6) e v a p o r a t o r housing; 7) packi/lg; 8) tubular condens e r ; 9) c o n c e n t r a t e r e c e i v e r ; 10) distillate r e c e i v e r ; 11) vacuum pump; 12) vacuum gage; 13) t h e r m o m e t e r ; 14) e j e c t o r ; 15) e l e c t r i c m o t o r ; 16) regulating valve. Ratio of volume of c o n c e n t r a t e and original e x t r a c t L o s s of product with distillate

1:20 trace

During the concentration of this e x t r a c t the t e m p e r a t u r e of the e v a p o r a t o r was i n c r e a s e d somewhat to guarantee flow of the viscous c o n c e n t r a t e . L a b o r a t o r y analysis of the obtained c o n c e n t r a t e showed a 25% i n c r e a s e in the glycosides in c o m p a r i son to the still r e s i d u e s f r o m the e v a p o r a t i o n of the s a m e e x t r a c t in the stills at the pilot plant of the Kharkov Scientific R e s e a r c h C h e m i c o - P h a r m a c e u t i c a l Institute,and the absence of heat denaturing i m p r o v e d the conditions f o r f u r t h e r t r e a t m e n t of the raw m a t e r i a l and enabled a m o r e c o m p l e t e s e p a r a t i o n of the end product. The thin f i l m of liquid being concentrated and the s m a l l amount on the heated s u r f a c e (less than 0.5 1 per m 2) m a k e s it possible to rapidly d i s c h a r g e in a given operation, to modify during operation, and to shut down the a p p a r a t u s without loss of t h e r m o l a b i l e substance. Only the e x t r a c t feed and the t e m p e r a t u r e of the heating vapor a r e controlled during the operation of theplant; this in conjunction with continuous o p e r a t i o n of the p r o c e s s facilitates automation of the whole production. Owing to the high heat t r a n s f e r p r o p e r t i e s of the rotating heated s u r f a c e it is possible to e v a p o r a t e w a t e r at 800 k g / h in a c o m m e r c i a l centrifugal e v a p o r a t o r plant with a heat t r a n s f e r s u r f a c e of 2.4 m 2. The c l e a r reduction in loss of a f o a m i n g therm01abile substance during evaporation, the concentration without loss of foaming e x t r a c t s , and the possibility of automation of the whole p r o c e s s open a broad channel for the introduction of centrifugal e v a p o r a t o r s into the p h a r m a c e u t i c a l industry. LITERATURE I. 2. 3.

CITED

A. N. Marchenko, V. M. Bespyatov, V. I. Polstyanoi, et al., M a s l o z h i r o v a y a P r o m . , No. 1, 27 (1968). A. Skocylas, Brit. Chem. Eng., 12, 1235 (1967). Y. N~lkki and I. Veldstra, Food Technol., 21, 15 (1967).

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