Chemical Reaction Engineering-Houston

1 Design and Operation of a Novel Impinging Jet Infrared

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Cell-Recycle Reactor R.

LEUTE

and I. G .

DALLA

LANA

Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, Canada

In the study of chemisorbed species on catalyst surfaces, the application of infrared spectroscopic methods has developed from the early in situ studies of Eischens and Pliskin [1] to rather detailed surface kinetics measurements [5]. The variety of techniques which have been described [1,2,3,4,5,6,7,8] increase i n their effectiveness with their a b i l i t y to discriminate between the spectra of adsorbed species which are relevant to the reaction mechanism and spectra of spurious adsorbed species. These approaches may be c l a s s i f i e d using this c r i t e r i o n as follows: (i)

I n t r i n s i c Rates/Surface Spectra Transients Measured D i r e c t l y . Under reaction conditions where adsorbed reactants, intermediates, and products display significant IR absorption band i n t e n s i t i e s , the transient intensities may be quantita t i v e l y monitored. Considerable detailed studies are required to correlate these intensities with surface concen trations.

(ii)

Global Rates/Surface Spectra Static or Transient. By carrying out studies i n an IR cell - c i r c u l a t i o n flow reactor, a cause-and-effect r e l a t i o n between reactant concentration and specific band intensities may be discerned. Such mechanistic insights may be useful i n developing more r e l i a b l e forms of rate expressions.

(iii)

Indirect Studies of Adsorption and Surface Reactions. The observation of selected spectral band intensities attributed to chemisorbed species are assumed to be related to the surface reactions involved. I f the spectra are recorded at room temperature, the presence of spurious spectra may occur. Generally, additional experimental evidence is required to demonstrate the relevance of such observations to the kinetics of the c a t a l y t i c reaction.

©

0-8412-0401-2/78/47-065-003$05.00/0

Weekman and Luss; Chemical Reaction Engineering—Houston ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4

CHEMICAL REACTION ENGINEERING—HOUSTON

This paper d e s c r i b e s the development of an improved v e r s i o n of the IR cell-recycle r e a c t o r (type ( i i ) ) which is to be used to study the mechanism and kinetics of r e a c t i o n s of 2-propanol on v a r i o u s alumina c a t a l y s t s . While t h i s r e a c t i o n does not have direct commercial i m p l i c a t i o n s (dehydration or dehydrogenation), it e x h i b i t s many of the characteristics which make it very s u i t a b l e to demonstrate the usefulness of the IR technique. Design Factors The yin AAXU technique i n v o l v e s c a t a l y s t p e l l e t s i n the form of very t h i n wafers, about 40 mg/cm2 alumina content. The h i g h s u r f a c e area, about 4 m^/cm^- of IR beam c r o s s - s e c t i o n , enables s u f f i c i e n t adsorbed species to i n t e r a c t w i t h the IR beam even a t r e l a t i v e l y low s u r f a c e coverages (^ 10 ' molecules/cm2 IR beam) that s p e c t r a w i t h good r e s o l u t i o n may be obtained. I n s t u d y i n g s o l i d - c a t a l y z e d gas-phase r e a c t i o n s , the back ground s p e c t r a r e s u l t i n g from the gas-phase are u s u a l l y e l i m i n a t e d by use of a double-beam IR spectrophotometer, i n which the sample c e l l i s matched w i t h an " i d e n t i c a l " reference c e l l without c a t a l y s t i n i t . V a r i a t i o n s i n pressure and/or temperature between sample and reference c e l l s i n c r e a s e the d i f f i c u l t y of matching the two c e l l s . When the c a t a l y s t wafer i s placed t r a n s v e r s e t o the flow of gases through the IR c e l l - r e a c t o r , the flow p a t t e r n s w i t h i n the c e l l l e a d to c o n c e n t r a t i o n gradients along the a x i s of the IR beam, and between the f r o n t and r e a r s u r f a c e concentrations on the wafer. Under r e a c t i o n c o n d i t i o n s , these aspects l i m i t the s e n s i t i v i t y of the technique because of low s u r f a c e coverages a t r e a c t i o n temperatures. The new c e l l attempts t o e l i m i n a t e many of these o b j e c t i o n a b l e f e a t u r e s . Figure l a describes a t y p i c a l geometry f o r previous c e l l designs. I t should be evident that i t i s d i f f i c u l t to o b t a i n values of the i n t r i n s i c r e a c t i o n r a t e because of the uneven c o n t a c t i n g between the gas and wafer a t v a r i o u s p o i n t s on the wafer s u r f a c e . High r e c i r c u l a t i o n r a t e s w i t h i n such a steadys t a t e r e c y c l e r e a c t o r provide d i f f e r e n t i a l values of the r e a c t i o n r a t e , but these g l o b a l values are u n l i k e l y to equal i n t r i n s i c r a t e s ( n e g l e c t i n g , f o r the moment, i n t r a p a r t i c l e d i f f u s i o n ) . C o m p a t i b i l i t y of flow p a t t e r n s between the IR c e l l and an i d e a l continuous s t i r r e d - t a n k r e a c t o r are r e q u i r e d as a minimum c o n d i t i o n . Since the mode of h e a t i n g the wafer l i k e l y i n v o l v e s IR-transparent windows being a t temperatures lower than those of the wafer, compensation f o r temperature gradients may a l s o be required. Figure l b describes the proposed geometry of the improved IR c e l l - r e a c t o r . This r e c y c l e r e a c t o r i s t o be capable of being operated i n e i t h e r open (flow) o r c l o s e d (batch) modes of o p e r a t i o n . The r e a c t o r u n i t i s maintained a t the r e a c t i o n temper ature (up t o 400°C) and the pump and sampling system are maintained at a constant u s u a l l y lower temperature (220°C) t o ensure maximum



Figure 1.

(a)

OLDER TYPE IR REACTOR CELLS

Geometrical arrangement and flow patterns in typical and improved ir cell-reactors

(b)

NEW IR REACTOR C E L L

6


l o n g e v i t y of equipment. F i g u r e 2 d e s c r i b e s the i n f o r m a t i o n flow between the IR spectrophotometer and an IBM/1800 computer system which are i n t e r f a c e d . The s p e c t r a l data are monitored at wave number i n t e r v a l s as low as 0.2 cm over the complete s p e c t r a l scan range of the spectrophotometer (about 700 to 4000 cm"" , corresponding to a maximum of about 16,000 data p o i n t s ) . The "% t r a n s m i s s i o n " versus "wave number" p o i n t s are t r a n s m i t t e d i n d i g i t i z e d form to the computer from a b s o l u t e encoders. At p r e s e n t , the complete s p e c t r a l scan may be monitored and s t o r e d i n a d i s k f i l e and r e t r i e v e d at a l a t e r time. The coupled Model 621 spectrophoto meter w i t h IBM/1800-compatible i n t e r f a c e was purchased some time ago from Perkin-Elmer. The improved c e l l u t i l i z e s axisymmetric j e t s of feed gas impinging upon both s i d e s of the wafer to develop a h i g h l y turbu l e n t f i e l d over most of the wafer s u r f a c e . This enables g l o b a l r e a c t i o n r a t e s to approximate i n t r i n s i c r e a c t i o n r a t e s at h i g h f l o w - r a t e s and i n the absence of pore d i f f u s i o n . The new c o n f i g u r a t i o n shown i n F i g u r e 1 i s housed i n an oventype enclosure c o n t r o l l e d at the temperature, T 3 , by i n t e r n a l a i r c i r c u l a t i o n . I n a d d i t i o n to the oven h e a t e r , a second heater about the i n l e t s e c t i o n , packed w i t h g l a s s beads, r a i s e s the c i r c u l a t i n g gas temperature from the reduced temperature i n the pump compart ment to T j . Because of heat l o s s e s from the IR windows, the tem perature d i f f e r e n c e , T - T , could range as h i g h as 50°C This not only changes the d e n s i t y of the f l o w i n g gas but a l s o r e s u l t s i n a c o n s i d e r a b l e d e v i a t i o n of the t r u q temperature of the c a t a l y s t wafer from the measured values T . A d d i t i o n a l heaters p l a c e d around the ends of the two c y l i n d r i c a l s e c t i o n s compensated f o r the window heat l o s s e s . In t h i s way, the temperatures, T and T 3 , could be matched w i t h i n 0.5°C, and the w a l l temperature would be expected to d i f f e r from T (or T3) only i f the c a t a l y t i c r e a c t i o n e x h i b i t e d severe thermal e f f e c t s . With g r e a t l y improved mass t r a n s f e r r a t e s normal to the wafer s u r f a c e , one would a l s o expect from s i m i l a r i t y c o n s i d e r a t i o n s enhanced heat t r a n s f e r between the wafer s u r f a c e and the impinging gas j e t . Such adjustments among the three monitored temperatures enabled the r e f e r e n c e c e l l IR beam to compensate n e a r l y e x a c t l y f o r the sample c e l l gas phase absorption spectra. By changing the c o n f i g u r a t i o n of the two c e l l s i n the sample compartment of the IR spectrophotometer t h i s enables the d e t e r mination of e i t h e r r e c i r c u l a t i n g gas composition or p l o t t i n g of the b a s e l i n e spectrum f o r the c a t a l y s t wafer. With the two c e l l s i n the double-beam mode, the c a t a l y s t b a s e l i n e and surface s p e c t r a are recorded. I f the reference c e l l was p l a c e d i n the sample beam and an a i r gap i n the r e f e r e n c e beam, q u a n t i t a t i v e absorption s p e c t r o scopy was p o s s i b l e . The IR c e l l s thus provide i n f o r m a t i o n l e a d i n g to both r e a c t i o n r a t e s and m e c h a n i s t i c i n s i g h t s concerning adsorbed species at r e a c t i o n c o n d i t i o n s . When used as a r e c i r c u l a t i n g batch r e a c t o r , the spectrophotometer-computer i n t e r f a c e can monitor but not record the "% t r a n s -1

1

3

2

2

2

2


LEAUTE AND DALLA LANA

Infrared Cell-Recycle Reactor

X = Wave Length (abscissa) Y = Transmittance (ordinate) X

I

= analog signal, Wave Length, 5 digits

Y

1

= analog signal, Transmittance, 3 digits

Linear Encoder Shaft Encoder

X1

IR Spectra Source

Encoder Readout/ I nterf ace

Y1 I

~TT X| I

lY I

i_t

X-Y Recorder

Figure 2.

i

l X Display Y Display

Information flow between ir spectrophotometer and digital computer



8

m i s s i o n " at a f i x e d " s p e c t r a l frequency" ( u s u a l l y that of a s p e c i f i e d absorption band). At present, the drum chart on the IR recorder p l o t s the time - absorption band i n t e n s i t y r e l a t i o n c o r responding to t r a n s i e n t r e a c t i o n c o n d i t i o n s . The time constant of the spectrophotometer thermocouple sensor was s u f f i c i e n t l y s m a l l that the t r a n s i e n t r e a c t i o n r a t e s could be recorded. Experimental

Performance

1. Mass Transfer Performance t e s t s were designed to t e s t f o r micromixing or f o r mass t r a n s f e r performance and thus, to f a c i l i t a t e d e f i n i t i o n of the c e l l design s p e c i f i c a t i o n s . L i m i t e d reac t i o n data had been recorded f o r the 2-proposal r e a c t i o n over alumina. Figure 3 summarizes the mass t r a n s f e r c h a r a c t e r i s t i c s which were observed i n a protptype c e l l w i t h naphthalene used f o r the wafer m a t e r i a l . A i r flows between 10 and 50 t/m±n were passed through the c e l l and the corresponding s u b l i m a t i o n r a t e s , mg/min, were recorded. Since the c e l l geometry was h e l d constant f o r a s e r i e s of flow r a t e s and the temperatures were always at room temperature, the coordinates of Figure 3 show the measured s u b l i mation r a t e s versus flow r a t e r a t h e r than Reynolds number. The exponent of the flow parameter (given by the slope of the l i n e ) i s seen to remain n e a r l y constant over a wide range of c o n d i t i o n s v e r i f y i n g that the t u r b u l e n t flow regime i s maintained. The i n f l u e n c e of changing the o r i f i c e s i z e used to create the j e t s , and of the spacing between the o r i f i c e and the wafer upon mass t r a n s f e r r a t e s are a l s o shown. In a d d i t i o n to the above t e s t s w i t h the new design, mass t r a n s f e r r a t e s were a l s o observed f o r c e l l - r e a c t o r s of the o l d type, w i t h wafers p o s i t i o n e d both p a r a l l e l and transverse to flows. These t e s t s suggest t h a t i n such geometries much of the stream bypasses the wafer surface making i t d i f f i c u l t to o b t a i n i n t r i n s i c r a t e s of r e a c t i o n . Furthermore, c o n t a c t i n g of the gas flow w i t h l o c a l i z e d p o r t i o n s of the periphery of the wafer r e s u l t e d i n abnormally h i g h l o c a l mass t r a n s f e r r a t e s . F i g u r e 3 demonstrates that o l d type c e l l designs provide mass t r a n s f e r performance i n f e r i o r to that observed w i t h the impinging j e t s . By c a l c u l a t i n g mass t r a n s f e r c o e f f i c i e n t s from the u s u a l equation f o r the r a t e of s u b l i m a t i o n , gmol/(min)(g c a t a l y s t ) . r

s

=

k

g

a

(C

. surface

-C) o

and using the bulk gas phase c o n c e n t r a t i o n , C =0, and e x t e r n a l area, a=10 cm , some experimental c o e f f i c i e n t s could be compared to values estimated from p u b l i s h e d c o r r e l a t i o n s . Table 1 shows these r e s u l t s . 2


Table 1 Comparison of Mass Transfer C o e f f i c i e n t s (cm/sec) Model Flat plate i n perpendicular flow Sphere of equal area i n a packed bed Experimental wafer, c o n v e n t i o n a l geometry Experimental wafer, new geometry

Flow = 10 l/min 1.3 cm/sec

Flow = 50 l / m i n 2.9 cm/sec

2.1

5.4

1.6

3.0

3.7

9.2

Table 1 and F i g u r e 3 both i l l u s t r a t e the marked s u p e r i o r i t y of the new IR c e l l - r e a c t o r design i n promoting mass t r a n s f e r at the wafer s u r f a c e . However, i t s t i l l remains to be demonstrated t h a t under r e a c t i o n c o n d i t i o n s , i n t r i n s i c r a t e s of r e a c t i o n may be obtained at the flow r a t e s mentioned.



10

2. Mixing W i t h i n C e l l The a n a l y s i s of performance w i t h i n a d i f f e r e n t i a l bed-recycle r e a c t o r i s u s u a l l y compared to t h a t of a continuous s t i r r e d - t a n k r e a c t o r . By operating the r e a c t o r w i t h an i n e r t wafer and by i n t r o d u c i n g a l c o h o l to the feed as a step change i n c o n c e n t r a t i o n , the mixing performance of t h i s r e a c t o r may be compared to t h a t p r e d i c t e d f o r an i d e a l CSTR of comparable volume. Figure 4 i l l u s t r a t e s such a comparison and i n d i c a t e s s u b s t a n t i a l agreement w i t h the i d e a l behaviour. I t may be expected that c h a n n e l l i n g , s t a g n a t i o n of some f l o w , e t c . are absent from the r e c y c l e r e a c t o r w i t h i n the range of performance of the pump. 3. Double-beam Compensation f o r Gas Phase A b s o r p t i o n When r e c o r d i n g IR s p e c t r a at r e a c t i o n temperature, the IR beams are attenuated by the number of molecules i n the beam path. Since the gas phase p o p u l a t i o n i s l i k e l y only one or two orders of magnitude g r e a t e r than the number of s i m i l a r molecules adsorbed on the wafer s u r f a c e , i t i s important t h a t the gas phase beam a t t e n u a t i o n i n the two c e l l s be balanced as w e l l as p o s s i b l e . For example, a pressure drop between the two c e l l s n e c e s s i t a t e s h e a t i n g the upstream c e l l to reduce i t s gas d e n s i t y to that i n the down stream c e l l . S i m i l a r l y , d i f f e r e n c e s i n temperature between the c e l l s must a l s o be compensated. Such inbalances between reference and sample c e l l gas phases r e q u i r e d c a l i b r a t i o n s ^ t o determine the values of T^ r e q u i r e d , f o r a f i x e d value of T (= T3) and given c i r c u l a t i o n r a t e at v a r i o u s i s o p r o p a n o l concentrations i n the gas-phase, to blank out gas phase absorption s p e c t r a . F i g u r e 5 shows how s p e c t r a l bands i n the 1200-1500 cm r e g i o n from gas phase i s o p r o p a n o l can be a l t e r e d be changing T j . Curve B represents n e a r - e x t i n c t i o n of the back ground whereas curves A and B represent under- and over-compensa tion, respectively. 4. Dehydration of 2-Propanol over Alumina The p r e l i m i n a r y measurements of s p e c t r a f o r adsorbed species w i l l be used to i l l u s t r a t e how the mechanism of r e a c t i o n may be c l a r i f i e d . The main f e a t u r e of the IR c e l l - f l o w r e a c t o r i s i t s c a p a b i l i t y of determining s p e c t r a at r e a c t i o n c o n d i t i o n s . Most published work on the dehydration of i s o p r o p a n o l by alumina describes Zn A^Lta s t u d i e s w i t h s p e c t r a recorded w i t h the c e l l at room temperature. Figure 6 r e v e a l s a b s o r p t i o n bands i n s e l e c t e d regions of the spectrum f o r s e v e r a l c o n c e n t r a t i o n l e v e l s of i s o p r o p a n o l vapour. Each curve, A, B, or C, represents a s p e c t r a l scan at steady-state r e a c t i o n c o n d i t i o n s w i t h a l l r e a c t i o n parameters except feed composition of i s o p r o p a n o l being kept constant. I f d i f f e r e n t curves (A, B, and C) r e s u l t , the adsorbed species a s s o c i a t e d w i t h the s p e c t r a are considered to be germane to the r e a c t i o n mechanism. In the event that the s p e c t r a l bands do not change the adsorbed species are considered to be spurious. Subsequently, the r e a c t o r may be operated i n a batch mode and the questionable band moni tored c o n t i n u o u s l y . The f a i l u r e of t h i s band to change w i t h the extent of r e a c t i o n would provide e x t r a support to the view that the band i s a s s o c i a t e d w i t h a by product species not i n v o l v e d i n the dehydration mechanism. 2

-1


LEAUTE AND DALLA LANA


Figure 4. Comparison between ideal CSTR and improved cell-reactor to step change in input concentration


12

CHEMICAL REACTION ENGINEERING—HOUSTON 1

1

1

1

110

1

1

T 2 = 2 8 7 . 8 ° C - A l c o h o l 5.5% A: T1 = 2 2 6 . 5 ° C B: T1=251.5°C C: T1 = 2 7 3 . 5 ° C

100

c | 80 (0

-4

70

60

\J

u 1

1

1500

1400

1

1300

I

I

1200

1100

Frequency, cm"

I

1000

1

Figure 5. Compensation of gas-phase adsorbance between reference and sample cells

Baseline without alcohol Alcohol Partial Pressure = 2.1 cmHg Alcohol Partial Pressure = 3.2 cmHg

Catalyst Weight = 0.151 g Temperature = 246.1°C

Free O H Groups

3800

3600

CH

3

3000

Stretching

2800

Low Frequency Region

1600

Frequency, c m "

1400 1

Figure 6. Steady-state spectral scans for dehydration of isopropanol at reaction conditions


1.

LEAUTE AND DALLA LAN A


13

The s t e a d y - s t a t e s p e c t r a l scans when recorded on the IBM/1000 may be processed. ( i ) t o s u b t r a c t the b a s e l i n e of the c a t a l y s t wafer from each s p e c t r a l scan at v a r y i n g p a r t i a l pressures of the i s o p r o panol; ( i i ) to s u b t r a c t one s p e c t r a l scan at (P - , - ) i from another s p e c t r a l scan a t of the change i n band i n t e n s i t i e s at given band f r e q u e n c i e s . A p r e l i m i n a r y i n t e r p r e t a t i o n of the s p e c t r a shown i n Figure 6 would suggest the f o l l o w i n g o b s e r v a t i o n s . The f r e e h y d r o x y l groups on the surface of alumina p r o g r e s s i v e l y disappear, A to B to C, w i t h i n c r e a s i n g reactant c o n c e n t r a t i o n , i s o p r o p a n o l . This i m p l i e s that the a l c o h o l hydrogen bonds to these hydroxyl s i t e s but i t i s not c l e a r whether the a l c o h o l 0 o r H atom i n i t s h y d r o x y l group i s i n v o l v e d . The s t r e t c h i n g v i b r a t i o n s from the methyl groups i n i s o p r o panol a l s o d i s p l a y d i r e c t correspondence between t h e i r surface c o n c e n t r a t i o n and that of the i s o p r o p a n o l vapour c o n c e n t r a t i o n . This i n f o r m a t i o n suggests that isopropanol adsorption on y a l u m i n a i n v o l v e s more than one adsorption band, i . e . both hydroxyl and emthyl groups are bonded and l i k e l y to d i f f e r e n t s i t e s on the surface of alumina. In the low frequency r e g i o n , region I r e l a t e s t o carbon chain s k e l e t a l v i b r a t i o n s and r e g i o n I I to symmetrical C-H deformation v i b r a t i o n s i n the methyl group. Both of these observations are i n accord w i t h a m u l t i - s i t e a d s o r p t i o n model. Region I I I shows the s t r e t c h i n g v i b r a t i o n f o r a carboxylate species formed on the s u r f a c e . Since the band i n t e n s i t i e s i n region I I I do not change w i t h i s o p r o p a n o l vapour c o n c e n t r a t i o n , the s p e c t r a are considered i n c i d e n t a l to the r e a c t i o n mechanism. With J C Q a d d i t i o n a l experiments, i t should be p o s s i b l e to d i s t i n g u i s h which surface s i t e s on the alumina are s p e c i f i c a l l y i n v o l v e d and thus t o propose a r e a c t i o n mechanism compatible w i t h such chemical evidence. During the above s p e c t r a l measurements, steady-state r e a c t i o n r a t e s i n the r e c i r c u l a t i o n r e a c t o r were a l s o determined. These r a t e s may then be used to t e s t the k i n e t i c model r e s u l t i n g from observations o f the s p e c t r a of adsorbed s p e c i e s . Comments 1.

11

The use of a " s i n g l e - w a f e r c a t a l y t i c r e c y c l e r e a c t o r system r e q u i r e s s t r i c t a t t e n t i o n to o p e r a t i n g parameters, i f one a s p i r e s to o b t a i n i n t r i n s i c r a t e s of r e a c t i o n . By modifying the flow past the wafer to ensure h i g h l y t u r b u l e n t c o n d i t i o n s on both s i d e s of the wafer, mass t r a n s f e r r a t e s may be more than doubled over those observed i n the o l d design of c e l l s i n which flow i s transverse t o the wafer s u r f a c e . This i n d i c a t e s that the u t i l i z a t i o n of both s i d e s of the wafer i s g r e a t l y improved and that the average mass t r a n s f e r r a t e s are a l s o enhanced.


14


2.

I d e a l mixing (CSTR) i s obtained w i t h the r e c i r c u l a t i n g rates a v a i l a b l e from the bellows pump used to t h i s system. The corresponding residence time d i s t r i b u t i o n f u n c t i o n i s not of value i n the a n a l y s i s of the k i n e t i c s s i n c e i t i s a n t i c i p a t e d that n o n - l i n e a r r a t e expressions w i l l be encountered. The usefulness of a combined I R - k i n e t i c s study i n e s t a b l i s h i n g a more r e l i a b l e k i n e t i c model i s apparent. The processing of such data to a s c e r t a i n which s p e c t r a l bands are s i g n i f i c a n t i s u s u a l l y a very tedious chore. By i n t e r f a c i n g the IR spectrophotometer to a d i g i t a l computer, a number of data processing s i m p l i f i c a t i o n s are e v i d e n t . F u l l use of t h i s s i t u a t i o n has not yet been a t t a i n e d i n t h i s program. Whether or not improved r e s o l u t i o n of minor s p e c t r a l bands r e s u l t s from an o n l i n e computer f a c i l i t y s t i l l remains to be demon s t r a t e d f o r t h i s r e a c t i o n system. The problem of i s o l a t i n g i n t r i n s i c rates of r e a c t i o n from r e a c t i o n r a t e s measured i n a single-wafer r e a c t o r appears to have been reduced but not n e c e s s a r i l y s o l v e d . If r e l a t i v e i n t e n s i t i e s of absorption bands e x h i b i t e d by reactants or r e a c t i o n intermediates can be a s c e r t a i n e d as a f u n c t i o n of time, i t may be p o s s i b l e to check r a t e expressions based upon a s i n g l e step being r a t e - c o n t r o l l i n g . Many extensions of t h i s technique (using the new r e a c t o r ) are evident i n the study of c a t a l y t i c k i n e t i c s . Some aspects worth pursuing i n c l u d e : ( i ) a study of pore d i f f u s i o n under c o n t r o l l e d c o n d i t i o n s ; v a r y i n g wafer thickness at constant p o r o s i t y should provide a d i r e c t means of c a l c u l a t i n g the e f f e c t i v e n e s s f a c t o r as a f u n c t i o n of wafer t h i c k n e s s . ( i i ) the r o l e of t r a c e amounts of c a t a l y s t promoters or i n h i b i t o r s may be examined using IR techniques and c o r r e l a t e d d i r e c t l y w i t h steady-state r e a c t i o n r a t e s .

3.

4.

5.

Acknowledgements F i n a n c i a l support of t h i s p r o j e c t by the N a t i o n a l Research C o u n c i l of Canada i s g r a t e f u l l y acknowledged. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8.

Eiechens, R.P., Pliskin, W.A., Advan. Cata., (1957), 9, 662. Heyne, H., Tompkins, F.G., Proc. Roy. Soc., (1966), A292, 460. Baddour, R.F., M o d e l l , M., and Goldsmith, R.L., J . Phys. Chem. (1968), 72, 3621. Dent, A.L., and Kokes, R.J., J . Phys. Chem, (1970), 74, 3653. Tamaru, K., O n i s h i , T., Fukada, K., Noto, Y., Trans. Faraday Cos., (1967), 63, 2300. Thornton, R., Ph.D. t h e s i s , U n i v e r s i t y of Delaware 1973, Shih, Stuart Shan San, Ph.D. t h e s i s , Purdue U n i v e r s i t y , 1975. London, J.W., B e l l , A.T., J . Cat., (1973), 31, 36-109.


Chemical Reaction Engineering-Houston

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