Measurement and Control Hardware for Laboratory-Scale Resin

Chapter 34

Measurement and Control Hardware for Laboratory-Scale Resin Preparations Chris Cassin

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Research Department, ICI Paints, Slough SL2 5DS, England

This paper describes work on equipment and instrument ation aimed at a computer-assisted lab-scale resin prep, f a c i l i t y . The approach has been to focus on hardware modules which could be developed and used incrementally on route to system integration. Thus, a primary split of process parameters was made into heat transfer and temperature control, and mass transfer and agitation. In the first of these the paper reports work on a range of temperature measurement, indicators and control units. On the mass transfer side most attention has been on liquid delivery systems with a little work on stirrer drives. Following a general analysis of different pump types the paper describes a programmable micro-computer multi-pump unit and gives results of its use.

The p r a c t i c e o f l a b - s c a l e r e s i n - m a k i n g i s an i m p o r t a n t element i n new p r o d u c t r e s e a r c h and p r o c e s s development f o r the c o a t i n g s i n d u s t r y . A t the I C I P a i n t s Research C e n t r e , where such e x p e r i m e n t a l work i s r e s t r i c t e d t o fume cupboards, the p o t e n t i a l number o f r e s i n p r e p , s t a t i o n s i s p r e s c r i b e d t o around 100-120. Assuming s i m i l a r numbers f o r o t h e r p a i n t and r e l a t e d c h e m i c a l companies, and n o t i n g the steady p r o g r e s s o f computerised d a t a l o g g i n g and c o n t r o l a t the p r o d u c t i o n s c a l e , i t i s s u r p r i s i n g t h a t l a b - s c a l e f a c i l i t i e s have changed so l i t t l e . The t r a d i t i o n a l arrangement of : s i m p l e s p h e r i c a l g l a s s w a r e and i s o m a n t l e s w i t h f u l l - p o w e r o n - o f f c o n t r o l l e r s monitored by mercury thermometers, would s t i l l be w i d e l y r e c o g n i s e d . So too would be t h e p l u g - s h o t p i s t o n pumps s e t up and m o n i t o r e d by use o f measuring c y l i n d e r s . A l t h o u g h t r i e d and t e s t e d t h i s hardware system r e q u i r e s c o n s t a n t a t t e n t i o n by a s k i l l e d l a b . t e c h n i c i a n t o a c h i e v e c o n t r o l and r e p r o d u c i b i l i t y o f even the f i r s t - o r d e r p r o c e s s parameters; manual d a t a c o l l e c t i o n i s h a r d l y f e a s i b l e a t b e t t e r than 10-15 minute i n t e r v a l s . 0097-6156/89/0404-0438$06.00/0 ο 1989 American Chemical Society

Provder; Computer Applications in Applied Polymer Science II ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Hardware for Laboratory-Scale Resin Preparations

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At I C I P a i n t s we have been t a c k l i n g some of those i s s u e s over the p a s t few y e a r s . Our approach, w h i l s t k e e p i n g i n mind t h e d i s t a n t u n i t a r y g o a l o f a c o m p u t e r - c o n t r o l l e d f a c i l i t y , has been to f o c u s on hardware modules w h i c h c o u l d be developed and used i n c r e m e n t a l l y on r o u t e t o system i n t e g r a t i o n . Thus, o u r work f o l l o w s t h e p r i m a r y s p l i t o f p r o c e s s parameters i n t o h e a t - t r a n s f e r and temperature c o n t r o l , and mass t r a n s f e r and a g i t a t i o n .

Heat T r a n s f e r and Temperature C o n t r o l

T r a d i t i o n a l Apparatus. The above r e f e r e n c e need o n l y be expanded t o i n c l u d e t h e common use o f c y l i n d r i c a l c u l t u r e v e s s e l s ( 1 ) , i n p l a c e o f t h e s p h e r i c a l r e a c t i o n f l a s k s , f o r shear s e n s i t i v e m a t e r i a l s and s i m p l e b o i l i n g w a t e r type b a t h s (2) as t h e i r h e a t i n g medium. E a r l y Moves. These i n c l u d e the use of n i c k e l - c h r o m i u m / n i c k e l aluminium (Type K) thermocouples f o r r e s o l u t i o n down t o ±0.1°C and ease o f c o n n e c t i o n t o d i g i t a l p a n e l meters (3) f o r r e l i a b l e temperature i n d i c a t i o n . A l s o t h e i n c o r p o r a t i o n o f meniscus d e t e c t i n g c o n t r o l l e r s w i t h mercury thermometers (4) w h i c h , a l t h o u g h d i f f i c u l t t o s e t up, can h o l d temperatures r e a s o n a b l y s t e a d y , as i l l u s t r a t e d by F i g u r e l a ; w i t h a mean some 0.4°C o f t a r g e t and a s t a n d a r d d e v i a t i o n of 0.5°C. However, they s t i l l r e q u i r e t h e o p e r a t o r t o g e t h i s f a c e h a z a r d o u s l y c l o s e t o t h e r e a c t o r t o read the a c t u a l temperature. On h e a t i n g d e v i c e s t h e m s e l v e s , t h e r e has been a move t o improved t h y r i s t o r e l e c t r o n i c c o n t r o l s (5) f o r i s o m a n t l e s and t h e i n t r o d u c t i o n o f h i g h e r performance w a t e r - b a t h s (6) w i t h f o r c e d c i r c u l a t i o n and i n - b u i l t feed-back c o n t r o l o f the h e a t - t r a n s f e r f l u i d (water o r o i l ) . Present S i t u a t i o n . F o r t h e most d i r e c t c o n t r o l of t h e r e s i n b a t c h temperature a couple o f t h e emerging l o w - c o s t s o l i d - s t a t e c o n t r o l l e r s (7) have been e v a l u a t e d . However, i n I C I P a i n t s t h e r e i s concern about i n t r o d u c t i o n of t h e thermocouple c i r c u i t i n t o t h e flammable atmosphere o f t h e r e a c t o r and thus none o f t h e growing number o f p r o p r i e t a r y u n i t s a r e a c c e p t a b l e . A c c o r d i n g l y we have developed an i n t r i n s i c a l l y s a f e d e v i c e w h i c h i n c o p o r a t e s an i s o l a t i o n b a r r i e r (8) w h i c h modulates t h e incoming thermocouple s i g n a l , and i n t h e event o f a f a u l t c o n d i t i o n l i m i t s e l e c t r i c a l energy t o t h e probe. The n o v e l IS u n i t (9) combines t h i s m i c r o t r a n s f o r m e r w i t h a v a r i a b l e p r o p o r t i o n a l - b a n d c o n t r o l l e r and an i n t e g r a l p a n e l meter r e a d i n g t o 1°C ( 1 0 ) . F o r more a c c u r a t e r e a d i n g s a s e p a r a t e o r d u a l thermocouple (11) p r o v i d e s f o r one of the r e c e n t h i g h r e s o l u t i o n (±0.5°C o r 0.1°C) (12-13) e l e c t r o n i c thermometers. On t h e output s i d e t h e c o n t r o l l e r has a s a f e s o l i d - s t a t e r e l a y capable o f 3kw w h i c h c o v e r s most i s o m a n t l e s and water-baths. Around 60 o f these c o n t r o l l e r s (9) (see F i g u r e 2) a r e a t work i n our l a b o r a t o r i e s b u t I C I P a i n t s has d e c i d e d a g a i n s t commercialisation.


Recorded p r o c e s s temperature u s i n g F i - M o n i t o r controller. Figure l a .

80 70 60 50 40

TIME IN MINUTES

30 20 10


controller/ Recorded p r o c e s s t e m p e r a t u r e u s i n g IS logger w i t h isomantle. Figure l b . Provder; Computer Applications in Applied Polymer Science II ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE Π

F i g u r e 2.

I S temperature C o n t r o l l e r w i t h d u a l and e l e c t r o n i c thermometer.

thermocouple


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443

C u r r e n t Developments. A number of l o w - c o s t p r o p r i e t a r y temperature l o g g e r s are b e i n g t r i a l l e d i n c o n j u n c t i o n w i t h the above IS C o n t r o l l e r . I n one form (14) these produce o n l y a s t r i p c h a r t d a t a t a b l e . A l t h o u g h c o n v e n i e n t f o r s t a t i s t i c a l a n a l y s i s these r e q u i r e k e y i n g i n t o a f u r t h e r microcomputer p l o t t e r t o draw a complete p r o c e s s temperature p r o f i l e , as shown i n F i g u r e l b . As an i l l u s t r a t i o n of the IS C o n t r o l l e r s performance, s t a t i s t i c s f o r the 150 minutes a f t e r e x o t h e r m i c overshoot i n d i c a t e a mean temperature w i t h i n 0.1°C of the s e t p o i n t and a s t a n d a r d d e v i a t i o n of 0.4°C. I n t h e i r o t h e r form ( 1 5 ) , temperature l o g g e r s s t o r e the d a t a f o r down-loading onto an IBM PC. T h i s g i v e s e x t e n s i v e m a n i p u l a t i o n and p r i n t i n g c a p a b i l i t i e s , as i l l u s t r a t e d by F i g u r e 3. However, t h i s o n l y becomes a v a i l a b l e a f t e r p o l y m e r i s a t i o n i s complete. Design s t u d i e s are i n hand to e s t a b l i s h how b e s t to i n t e g r a t e such f a c i l i t i e s as a r e a l time p l o t i n t o a s i n g l e microcomputer c a p a b l e of f u l l system d u t i e s - a s , f o r i n s t a n c e , the IBM AT s p e c i f i e d f o r the I n t e l l i g e n t Pump U n i t d e s c r i b e d below. As a p o t e n t i a l l y more s i g n i f i c a n t change we are examining the u t i l i t y of s i n g l e and double j a c k e t e d v e s s e l s f o r t h e i r comprehensive heat t r a n s f e r c a p a b i l i t i e s , i n c l u d i n g p r o c e s s and c r a s h c o o l i n g . I n t h i s work the two d i f f e r e n t forms of w a t e r - b a t h are b e i n g t r i a l l e d as p r i m a r y , but p h y s i c a l l y s e p a r a t e heat s o u r c e s . I n the case of the b o i l i n g w a t e r - b a t h , c o n t r o l i s p r o v i d e d by one of the l a t e s t a d a p t i v e s e l f - t u n i n g t h r e e - t e r m c o n t r o l l e r s ( 1 6 ) . P r e l i m i n a r y p r o c e s s s i m u l a t i o n r e s u l t s , see F i g u r e 4, are p r o m i s i n g and the apparatus i s b e i n g worked up f o r p r o p e r l a b o r a t o r y t r i a l s . Agitation. A s s o c i a t e d w i t h the s p e c i a l j a c k e t e d v e s s e l s mentioned above some attempt i s b e i n g made t o s i m u l a t e p r o d u c t i o n p l a n t geometries f o r b e t t e r c o r r e l a t e d d i s p e r s i o n and n u c l e a t i o n . A l t h o u g h no a t t e n t i o n has been g i v e n t o the a c t u a l s t i r r i n g p r o c e s s , v a r i o u s d r i v e systems have been e v a l u a t e d from the s i m p l e mains e l e c t r i c (17) and pneumatic u n i t s (18) a v a i l a b l e c o m m e r c i a l l y , through s t e p p e r motors t o the s m a l l modern DC u n i t s . Although e x t r e m e l y a c c u r a t e the former were found to be somewhat s h o r t of power, r a t h e r prone to s t a l l and t h e n , v e r y d i f f i c u l t t o r e - s t a r t . I n c o n t r a s t , the l a t e s t DC motors are v e r y p o w e r f u l and w i t h i n t e g r a l feedback they a l s o e x h i b i t c l o s e speed c o n t r o l to ±2 rpm w i t h i n range 50-700; s i m p l e i n d i c a t i o n s of speed and motor l o a d are a l s o p o s s i b l e . The t r i a l s of two such home-made u n i t s around the l a b o r a t o r i e s have met w i t h e n t h u s i a s t i c and u n i v e r s a l welcome, a c l e a r s i g n of i n c i p i e n t demand f o r t h e i r c o m m e r c i a l i s a t i o n . Mass T r a n s f e r . T r a d i t i o n a l Apparatus. As i n d i c a t e d e a r l i e r , l i q u i d d e l i v e r y systems f o r c o n t r o l l e d r a t e a d d i t i o n of monomers and i n i t i a t o r s have tended to r e l y upon c o n s t a n t speed p i s t o n pumps (19) i n which v o l u m e t r i c c o n t r o l i s a c h i e v e d by manual adjustment of s t r o k e l e n g t h , and m o n i t o r i n g i s by d i s c h a r g e from measuring c y l i n d e r s .


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COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE II

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&

F i g u r e 3.

78.

71.

Logged d a t a a n a l y s e d by PC.



0

F i g u r e 4.

10

ADDITION STARTS

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40

50

TIME IN MINUTES

80

70

Θ0

Temperature s t a b i l i t y o f c o n t r o l l e d r e a c t o r w i t h simulated feed.

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ADDI TON ENDS

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COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE II

E a r l y Moves. The p o s s i b l e move t o r e c i p r o c a t i n g diaphragm pumps (20) f o r t h e i r improved c o n t r o l o f p u l s e s t r o k e and frequency gained o n l y l i m i t e d acceptance, a l t h o u g h a few a r e s t i l l p r e f e r r e d f o r c o r r o s i v e o r h i g h l y t o x i c chemicals. The t r a n s i t i o n which gained the most widespread and d r a m a t i c acceptance w i t h r e s i n chemists was to p e r i s t a l t i c pumps (21) . A f t e r thorough e v a l u a t i o n the type s e l e c t e d was o f t h e f i x e d t r a c k , a d j u s t a b l e s p r i n g - l o a d e d r o l l e r head. W i t h v a r i o u s s i z e s o f t u b i n g two models o f pump c a n span the d e s i r e d range o f 0.04-700ml/min. w i t h h i g h p r e c i s i o n and r e p r o d u c i b i l i t y ; a comparison o f t y p i c a l f l o w p a t t e r n s f o r t h e t h r e e b a s i c types o f pump i s g i v e n i n F i g u r e 5. T h i s i l l u s t r a t e s the s u p e r i o r i t y o f p e r i s t a l t i c pumps, and i n as l i t t l e as two y e a r s up t o 100 o f these pumps have come i n t o r e g u l a r use i n o u r l a b o r a t o r i e s . I n a growing number o f cases they a r e b e i n g combined w i t h l o w - c o s t e l e c t r o n i c b a l a n c e s (22) t o a c h i e v e d i r e c t c o n v e r s i o n t o g r a v i m e t r i c set-up and m o n i t o r i n g . T y p i c a l r e s u l t s as i n F i g u r e 6 a , over t h r e e hours w i t h manual adjustments a t 20-minute i n t e r v a l s i n d i c a t e mean feed r a t e s w i t h i n 1-2% o f s e t p o i n t and s t a n d a r d d e v i a t i o n o f 4-10%. Present S i t u a t i o n . To complete t h e c o n v e r s i o n t o g r a v i m e t r i c a d d i t i o n s w i t h f u l l feed-back c o n t r o l , two o f t h e p e r i s t a l t i c pump heads (23) were f i t t e d w i t h s t e p p e r motor d r i v e s , each b e i n g l i n k e d to a h i g h performance e l e c t r o n i c b a l a n c e (24) and t h e whole i n t e r f a c e d t o a cheap microcomputer (25) t o form a t r u l y I n t e l l i g e n t Pump U n i t ( I P U ) . T h i s has been e x t e n s i v e l y t r i a l l e d and found t o have p o t e n t i a l i n two q u i t e d i f f e r e n t ways. I n t h e f i r s t , i t s v e r y h i g h r e p r o d u c i b i l i t y a s s i s t s c l o s e o p t i m i s a t i o n o f known p r o c e s s e s , and t h e o t h e r i t s programmable c a p a b i l i t i e s a r e used f o r ramped o r mixed p r o f i l e feeds i n s p e c u l a t i v e new system e x p e r i m e n t s , as i l l u s t r a t e d by F i g u r e 6b. S t a t i s t i c s f o r t h e u n i f o r m phase i n d i c a t e f e e d r a t e c o n t r o l w i t h i n 0.1% o f the s e t p o i n t a t s t a n d a r d d e v i a t i o n of 3%. C u r r e n t Development. F o l l o w i n g success o f t h e p r o t o t y p e IPU a second more comprehensive f a c i l i t y was commissioned. T h i s i s capable o f up t o f o u r pumps o f mixed p e r i s t a l i t i c o r diaphragm t y p e s , each l i n k e d t o s p e c i f i c feed v e s s e l s on i n d i v i d u a l b a l a n c e s . The whole i s i n t e r f a c e d t o an IBM AT computer (see F i g u r e 7) w h i c h i n a d d i t i o n t o i n t e l l i g e n t l i q u i d a d d i t i o n s , has t h e c a p a c i t y t o absorb modules from t h e work on temperature c o n t r o l and s t i r r i n g i n a f u l l m u l t i - t a s k i n g c o m p u t e r - a s s i s t e d system, as mentioned above. A t t h e c u r r e n t stage o f development, the m u l t i p l e pump c a p a b i l i t i e s o f t h e Mk.II u n i t p e r m i t s f u l l programming o f a l l f o u r l i q u i d f e e d s . I n a d d i t i o n t o t h e r o l e s i l l u s t r a t e d by F i g u r e 5b f o r two, t h r e e o r f o u r mixed monomers and i n i t i a t o r s , where o n l y the normal d u a l feeds a r e r e q u i r e d , t h e e x t r a two pumps may be used f o r c o n t r o l l e d a d d i t i o n s over a few minutes a t t h e s t a r t and end o f the p r o c e s s , as i l l u s t r a t e d i n F i g u r e 8.


34.

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Measurement and Control Hardware for Laboratory-Scale Resin

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