Emulsion Polymers and Emulsion Polymerization - American

31 On-Line Monitoring of Emulsion Polymerization Reactor Dynamics

Downloaded by PENNSYLVANIA STATE UNIV on June 15, 2013 | http://pubs.acs.org Publication Date: October 7, 1981 | doi: 10.1021/bk-1981-0165.ch031

F. J. SCHORK and W. H. RAY Department of Chemical Engineering, University of Wisconsin, Madison, WI 53706 The available data from emulsion polymerization systems have been obtained almost exclusively through manual, off-line analysis of monomer conversion, emulsifier concentration, particle size, molecular weight, etc. For batch systems this results in a large expenditure of time in order to sample with sufficient frequency to accurately observe the system kinetics. In continuous systems a large number of samples are required to observe interesting system dynamics such as multiple steady states or limit cycles. In addition, feedback control of any process variable other than temperature or pressure is impossible without specialized on-line sensors. This note describes the initial stages of development of two such sensors, (one for the monitoring of reactor conversion and the other for the continuous measurement of surface tension), and their implementation as part of a computer data acquisition system for the emulsion polymerization of methyl methacrylate. Emulsion Density and Monomer Conversion Monomer conversion has traditionally been determined gravitimetrically by drying emulsion samples to constant weight. The procedure is slow, requiring several hours for analysis, and precludes automated data acquisition. A new method has been developed based on the DMA-series digital densitometers manufactured by Anton Paar of Austria, and marketed in the United States by Mettler Instrument Corporation. (Very recently Dr. Kirk Abbey made us aware of his parallel work in these directions and of some initial data reported from his laboratory [1,2]). This instrument is capable of immediate determination of the density of any test fluid, and, if equipped with a flow cell, can continuously monitor the density of a process stream. Results are displayed locally and can be transmitted digitally to a data acquisition computer.

0097-6156/81/0165-0505$05.00/0 © 1981 American Chemical Society

In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

506

EMULSION POLYMERS

AND

EMULSION POLYMERIZATION

D e n s i t y measurement i s a c c o m p l i s h e d b y i n t r o d u c i n g a t e s t f l u i d i n t o a g l a s s U-shaped sample t u b e w h i c h i s r i g i d l y s u p p o r t e d a t i t s open e n d s . The t u b e i s e l e c t r o n i c a l l y e x c i t e d t o v i b r a t e a t i t s n a t u r a l f r e q u e n c y . The f r e q u e n c y o f o s c i l l a t i o n i s c o n t i n u o u s l y m o n i t o r e d e l e c t r o n i c a l l y , a n d f r o m t h e change o f frequency caused by t h e t e s t f l u i d w i t h i n t h e t u b e , t h e d e n s i t y of t h e t e s t f l u i d c a n b e d e t e r m i n e d f r o m t h e f o r m u l a

(p - ρs )

2

(1)

where ρ a n d Τ a r e t h e d e n s i t y a n d p e r i o d o f o s c i l l a t i o n f o r t h e t e s t f l u i d and p and T a r e t h e d e n s i t y and p e r i o d f o r a s t a n dard. O s c i l l a t i o n i s c o n t i n u o u s and t h e p e r i o d o f o s c i l l a t i o n i s u p d a t e d e v e r y two s e c o n d s , m a k i n g t h e i n s t r u m e n t e s s e n t i a l l y c o n tinuous. The c a v i t y s u r r o u n d i n g t h e sample t u b e i s f i l l e d w i t h gas o f h i g h t h e r m a l c o n d u c t i v i t y ; t h i s i n t u r n , i s s u r r o u n d e d b y t h e r m o s t a t e d l i q u i d f o r a c c u r a t e sample t e m p e r a t u r e c o n t r o l . An a c c e s s o r y f l o w a d a p t e r may b e added t o m o n i t o r t h e d e n s i t y o f p r o c e s s streams. Output o f e i t h e r p e r i o d o f o s c i l l a t i o n o r actual density i s possible. Models a r e a v a i l a b l e w i t h f o u r , five, or s i x place precision. The i n s t r u m e n t i s n o r m a l l y c a l i b r a t e d a g a i n s t d i s t i l l e d water and a i r by r e a r r a n g i n g E q u a t i o n (1) a s f o l l o w s : g


2

= k(T - T ) s

s

ρ =

2

c ( T - D)

(2)

The v a l u e s o f C a n d D a r e d e t e r m i n e d f r o m t h e known d e n s i t i e s o f water and a i r . Once c a l i b r a t e d , t h e i n s t r u m e n t s h o u l d n o t n e e d r e c a l i b r a t i o n u n l e s s t h e sample t u b e i s r e p l a c e d . S i n c e monomer c o n v e r s i o n i s a l i n e a r f u n c t i o n o f e m u l s i o n s p e c i f i c v o l u m e , t h e f r a c t i o n a l c o n v e r s i o n , x , may b e c a l c u l a t e d as

(v° - v )

(i/p° - i/P )

e

Λ

"

e

(3)

( v j - v j ) " (1/P°-1/Pe>

where t h e s p e c i f i c volumes a t 0 and 100% c o n v e r s i o n , and v \ may b e a p p r o x i m a t e d a s w e i g h t e d a v e r a g e s o f t h e component s p e c i f i c volumes: V° = X V e mm V

1

e

+ X v Aw

(4)

= X V + X.V m ρ Aw

(5)

A

w h e r e X a n d X a r e t h e i n i t i a l w e i g h t f r a c t i o n s o f monomer a n d aqueous p h a s e r e s p e c t i v e l y . F o r b a t c h systems, and f o r a con t i n u o u s s y s t e m w i t h s t a r t - u p f r o m a n empty r e a c t o r , t h e w e i g h t f r a c t i o n t o t a l monomer i n t h e sample s t r e a m , X ( i n c l u d i n g mono mer i n c o r p o r a t e d i n p o l y m e r c h a i n s ) , r e m a i n s c o n s t a n t a n d e q u a l m

A

m


31.

SCHORK AND RAY

Emulsion

Polymerization

Reactor

Dynamics

507

to the i n i t i a l o r i n l e t value. I f s t a r t - u p i s from a f u l l con tinuous r e a c t o r (water o r emulsion f i l l e d ) , i n t h e sample stream approaches t h e v a l u e o f t h e feed a s f o l l o w s : X

m " V


feed

+ < V " V > ι feed

e

x

P ι r

t t t » Jι ι ι ?Jt ι ι f { ι ι ι ? j ι ι t ι j

400

TOO

iOO

701?

500

900

MINUTE

Figure 6. Example data acquisition for the continuous emulsion polymerization of MM A showing conversion and surface tension oscillations (Run 15, Recipe 8; Τ = 40°C; initiator (ammonium persulfate) =0.01 gmol/L H 0; emulsifier (SLS) = 0.02 gmol/L H 0;wt.ratio monomer/water = 0.43) 2

2



SCHORK AND RAY

Emulsion

β Of

ι

ΙΟΙ

ι

1—I

fι

ι

Polymerization

ι

tι

1

1—ι—\

!

1

Reactor

ll|

1

3 0

0

0.01

Figure 7.

.

• . . ...I

I

ι

0.1 10 CONCENTRATION S L S (qms/l)

»

Dynamics

513

Γ

•

I

10.0

Wilhelmy plate measurements of surface tension for SLS solutions: (A) no Μ Μ A; (Β) saturated with MM A


514

EMULSION POLYMERS AND EMULSION POLYMERIZATION

Acknowledgements The authors are indebted to the National Science Foundation and the Mobil Foundation for research support and to the Rohm & Haas Company for contributing the MMA monomer. Literature Cited


1. 2. 3. 4. 5.

Abbey, K. J., personal communication, February (1980). Abbey, K. J., paper presented at the 1979 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. Ley, G., and H. Gerrens, Makromol. Chem. 1974, 175, 563. Padday, J. F., in "Surface and Colloid Science 1", E. Matijevic, Ed., Wiley, N.Y., 1969. Schork, F. J., Ph.D. Thesis, University of Wisconsin, (1981).

RECEIVED

April 6, 1981.


Emulsion Polymers and Emulsion Polymerization - American

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