A continuous chromatographic reactor

Chem~cai~ngmeengSczenceVol 35,pp 74-81 PergamonPress Ltd ,1980, Pnntedm Great Bntaln

10 B.K

A

CONTINUOUS Cho,

Robert

CHROMATOGRAPHTC W.

Carr,

Jr.,

REACTOR and

R.

Arls

Department of Chemical Englneerlng and Materials Science Unlverslty of Mznnesota Mlnneapolls, Mxnnesota 55455

ABSTRACT

ReactIon chromatography has been done on a continuous basis in a reactor conflguratlon conslstlng of a packed cyllndrxcal annulus with a rotating feed port Chromaseparatxon of product streams emerging from the annutographlc actxon causes spatLa1 Thus has been demonstrated by an experImenta study of the acid catalyzed lar exit. hydrolysis of aqueous methyl formate Furthermore, separation of the products, suppresses the reverse reactzon causing conversIons to be formic acid and methanol, slgnlflcantly greater than equllxbrlum conversIons A mathematxcal model of the reactor has been developed and used for numerlcal slmulatlon of reactor behavior D,speradsorptlon Isotherms and react-Ion klnetlcs were all soon characterlstlcs of the bed, Comparedetermined 1x-a Independent experiments, and used as Input data for the model sons of numerlcally sxmulated reactor performance wLth experImenta results showed good agreement.

KEYWORDS Reactxon graphy,

chromatography, chemzcal reactor

continuous chromatography, continuous reactxon chromatodesign, numerical srmulatlon, hydrolyses of methyl formate

INTRODUCTION chemxcal reactlon and separation Chromatographlc reactors which simultaneously effect have been xnvestxgated since the 1960's (Gazxev, Fxllnovskll, and Yanovsklr, 1963, Gore, 1967, Langer, Yurchak and Patton, 1969, Magee, 1963, Matsen, Harding and These operate In a pulsed Yanovskll, 1964, Wetherold, Wlssler and Blschoff, 1974). stream of carrier fluld as It In which a reactant 1s InJected Into a continuous mode, It has also been demonstrated, following an flows through a chromatographlc column. that chromatography can be done on a contxnuous early suggestlon by Glddlngs (19621, Calhoun and Eglinton, 1969, Scott, basis In a rotatrng annular chromatograph (Fox, Mlddleton and Hudson, 1976) 1976, Wankat, Sussman and co-workers Spence and Slsson, in whxch two very (1972) extended this concept to a rotating disc ConfIguratIon, coated with a stationary phase, formed a chromatographxc closely spaced discs, This may be consldered a continuous analogue of capillary column chromatochannel. graphy In thrs work we explore the comblnatron of reactlon chromatography with continuous Contxnuous chemical reactlon chromatography has obvious advantages chromatography It also over a single pulsed mode reactor. in reactor throughput, or productlvlty, provides conslderably easxer handling of the reactant and the product streams over summIng to the same productlvlty Furthermore, for a battery of pulsed reactors of the products ~111 suppress the back reactIons of the type A z B + C, separation This would be of particular advantage reactlon and may lead to enhanced yields The reactor 1s a stationary, In cases where thermodynamxc equlllbrlum 1s unfavorable. A study of the acid catalyzed packed cyllndrlcal annulus with a rotating feed port and a mathematical model was developed formate was conducted, hydrolysis of methyl and used for numerIca slmulatlon of reacTor behavzor

74

A contmuous

B-10

chromatographlc

reactor

75

EXPERIMENTAL

Apparatus A cross-sectional consists of two

view of concentrlc

SAMPLING CORK TO

the reactor cylinders,

assembly an outer

IS shown in 8 Inch 0-D.

Fig 1. cylxnder

The and

maln body an znner 7

EED POSITION INDICATOR

P STOPPER

TO

RECEIVER

RECEIVER UPPORTING TEFLON

TEFLON FILTER

PAPER++-/ O-R

O-R FILTER

ING

ING

PAPER

OUTER

1

CYLINDER

ROTATING

I-j

SHAFT

ANNULAR REACTOR

INNER

CYLINDER

FILTER

PAPER

E

TEFLON

FLOW

SEAT

SEAT

&FEED

BAFFLE

CARRIER

INJECTION PORT FLUID RESERVOIR

THERMOMETER CARRIER

STATIONARY

SHAFT

REAc’TANT

Fig.

1

Reactor

assembly

inch 0-D cylinder, both of whxch are k Inch thick and 16 Inches long. Both ends of the annular space are capped with blind flanges havlw 1 mm dlam. holes for the flow entrance and exxt to the annular reactor space. These were drilled LII 4 rows, totalxng 1560 holes on each flange. Both the statxonary and the rotating shafts were made from 1 l/16 Inch diameter Plexiglas rods. A small hole of l/16 Inch dzameter was drIlled through the center of the stationary shaft and at the bottom part of the rotatxng shaft. These serve as a flow path from the reactant feed tank to the Injectlon port. The drive shaft was connected to a l/2 HP DC motor through a 5-stage pulley system and a reducing gear box having a combined reduction ratio of l/31250. At the exit of the reactor 50 evenly spaced sampling posxtrons were provided around the annulus. The feed port rotates slowly while the annular region remains flxed ITI

76

ReactorModels

the laboratory coordinate annular, lagging the feed retentron by the stationary

Bed

system. port by phase.

a

Thus the distance

- Desrgn Studies

elucnt that

1s

"peaks" also prrmarrly a

B-10

travel around the functron of their

top

Characrerlstrcs

manufactured by Fisher Sclentrfrc Company Actrvated coconut charcoal (50 - 200 mesh) was sieved to select the szse range of 60 - 80 mesh, and then packed Into the annular reactor space by a dry free-falling technrque through a funnel rotatlng at 1 r-pm Every time the level of charcoal Increased 2 Inches, the rotation was stopped and the rnner and the outer wall of the reactor were gently tapped wrth a rubber hammer to The bed packing density and the expel arr pockets and obtain more uniform packrng. void fraction were measured at 0 543 gr charcoal/cc bed and 0.54 respectively. The checked by measuring the elutron proflle of a degree of unlformzty rn bed packrng was case methanol) at several different feed posltlons around trace component (In thus Peak shapes coming from drfferthe annular region keeprng the feed port statronary ent feed posltlons were rn reasonable agreement, lndicatlng that whrle the packrng rt 1s reasonably good. The average lateral Peclet number 1s not strrctly unrform, calculated from these elutron profiles 1s about 2700. The elutlon proflle of pure methanol was also determIned with the feedport rotatrng. The calculated axial Peclet Thus compares very well with publrshed data on number from thus proflle rs 560 1968, Levensprel, 19721, from which the drsperslon rn packed beds (Chung and Wen, axial Peclet number was estimated to be 915

Procedures Reactant and carrier fluid flow was drrven by a pressurrzed system connected to comFlow rates were measured by Fischer and Porter rotameters pressed air cylinders and that of the reactant The range of flow rates of the carrrer was 10 - 20 ml/mm The overall pressure drop through the system was was 0.03 of the carrier flow rate. The carrier The reactant port was rotated at 0.01 - 0 05 rad/mrn ca. 300 mm Hg flurd was fed along the whole annular area except the region where the reactant To mlnlmlze the mzxlng between the carrrer and the InJectron port was located. pressures at the reactant InJectIon port reactant before they enter the reactor bed, Product samples were taken from and the carrier fluid reservoir were kept the same. the fifty sampling positrons provided around the annular area at the exrt of the In one scheme samples were and two drfferent samplrng schemes were used reactor, from the rotatrng InJectIon port, which 1s essentaken at desired angular distances system whose orlgln is fixed at the trally a sampling method In a moving coordinate In the other scheme, samples were taken at a fixed pornt, rotating inlectlon port. wrth the angular distance between the samplrng pornt and the rotating InJectron port should grve the same elutron profrle rf varying with time Both sampling schemes It has already been noted that the the reactor bed packrng were everywhere unrform. so the elutron profrle obtarned by the rotating packing 1s not perfectly uniform, except for the scatter than the frxed-point scheme Hence, sampling scheme gave more The reagents used were the frxed-point samplrng scheme was used. frrst few runs, and Eastman Spectra Grade Hi-Pure chemicals electronic grade hydrochlorrc acid, chromatography on a 6 mm 0 D , 6 ft Samples were analyzed by gas methyl formate glass column packed with Porapak Q and operated at 13OoC

RESULTS

Reactron

Klnetrcs

The klnetlcs of the catalytic hydrolysis Newling Dawdrng and Noble, 1955, (Bell, 1974) and can be Wlssler and Blschoff, dCA -dt where [II+] 1s the hydrogen Ion IS Itself autocatalytic because

=

kEh+]

of methyl formate by HCl 1s and Hlnshelwood, 1936, Salml, expressed as

(CA

concentration of the hydrogen

-

well establrshed 1939, Wetherold,

CBCC/Ke) the uncatalyzed However, ions from formic acid.

reactlon The auto-

B-10

catalytrc

reactlon

rates

were k'

wxth

a

klnetlc

=

Acontinuous

chromatographlc reactor

measured

XT) a

2.157

batch

K' e

= 11 290

k'C

05 C

reactor -0

10 -3(mole/l)

x

77

at

5 ,,n-1

25OC

to

obtain

and

mole/l

model dC --

A

dt

=

(CA

-

CBCC/Ke'>

Though the autocatalytlc reactlon rate was negllglble compared to the 25OC catalytic reactxon rate (k = 0 176 m~n-l and K, = 6.94 at 1N HCl), these data were necessary Isotherms in the uncatalyzed reactlon mixture study multlcomponent

AdsorptIon

to

Measurements

Measurements of multlcomponent adsorptlon xsotherms were not sufflclently accurate to give reliable constants when fatted by Langmulr Isotherms Thus binary adsorptlon Isotherms were obtaxned for CH30H-H20, HCOOCH3-H20, HCOOH-H20 and CHxOH-LN HCl systems 2 gave good frts to by the static method (Klpllng, 1965) The experlmental data III Fig

01

001

I 002

FLUID

2

I

I 005

,,,I

PHASE

01

I 02

I1

I,I,,l 05

IO

CONCENTRATION,

I 20

I

I

,111 50

II

MOLE/LITER

Binary adsorptlon Isotherm on activated coconut charcoal. l HCOOH-H20, A CHxOHFresh adsorbent, a HCOOCH3-H20, A CH30H-1N HCl. Aged adsorbent, o CH3OH-H20, H20, 0 CH30K-1N HCl.

Freundllch Isotherms It was observed that after long use, approximately 100 hours, in the 1N HCl environment, the adsorptive capacxty of charcoal for CH30H decreased, possibly because of deactlvatlon or xmpurlty contamrnatlon. This was not observed for other components for the first 200 hours of operation.

MATHEMATICAL In derrvlng the reactor bed has annular reactor

MODEL

model equations for our present reactor a uniform packrng and can be treated as space 1s so thin compared to the diameter

system It 1s assumed that the a homogeneous contrnuum The of the Inner and the outer

Reactor

78

Models

- Desrgn Studzes

B-IO

cylinders that Its curvature 1s unimportant AdsorptIon equillbrlum 1s maintalned throughout the reactor, which 1s also Isothermal. This assumption ~~11 be a good appronlmatlon when the absorbent particle srze and the fluld flow velocity are very small, as =n this system. The effect of pressure drop along the reactor and dlsperslve effects In the fluld phase are negllglble. The fluid velocity dlstrlbutlon 1s assumed to be uniform across the reactor bed Mass balances for each component over the reactor result in the following dImensIonless equations In vector form

au

with

the

Inlet

and

boundary

condltrons =(0,9)

uts,e>

ocece -

=

u.

=

9,

=

sts,etl)

'

-

D<0<1

(4)

Here, g refers to the concentration, f(u) the bed-Isotherm vector, and -R(u) the reac-tlon rate vector. The axial and the lateral coordinate are represented by 5 and e . Various numerlcal schemes (Lax, 1957, Lax and Wendroff, 1964, Emery, 1968, Rusanov, 1970) were tested on equations (3) and (4), and Lax' method was found to be the most accurate In generatzng the posItIon of the sharp profIle while avoldlng osclllatlon phenomena near the shock layer In formulating the flnlte difference scheme based upon Lax' method, the number of mesh points both In the axial and In the lateral dIrectIon was determined In such a way that dlsperslon effects neglected in the above ideal model could be approximately accounted for. This was accomplished by using second moments obtalned from a model contalnlng dispersion effects to determine mesh The simulated peak shapes were nearly the same size for use *n Lax' formulation. since the drspersron effect was very small here. for small changes of mesh sizes The parameters used are llsted below. KA mA k PB

N

8

=

3

4813

x

10 -3

mole/gr,

KB

=

1 4043

=

0

7213

=

0.336

,

mFi

=

0.176

mln-1

’

Ke = 6 94

=

0

gr/cc

,

L

=

100.

Reactor

543

=

x

41.15

10s3

mole/gr,

KC ,

mC

,c cm

,

x

10

-3

=

3

4553

=

0

2636

,

=

0

54

,

=

30

mole/gr,

NC

Performance

3andFlg 4. Typlcal experImenta results are given In Fig These experiments were with a flow veloczty of 1.04 cmjmln, and an inJectIon port speed of done at 2S°C, 3 are for a 3.0 N aqueous methyl formate feed with 0 0302 rad/mln. The data In Fig and the product stream was sampled by the fixed point a 1.0 N aqueous HCl carrier, sampling method Figure 4 reports data for a feedstream conslstlng of an equlllbrlum mixture, and sampled by the rotating sampling method The data points show more we attribute to nonuniformity of bed packing. scatter than those of Fig. 3, which This is not a factor In stationary sampling Figures 3 and 4 lndlcate the absence We have been unable to detect methyl of methyl formate In the reactor effluent formate in any experiments by our routine analytical procedure, which 1s capable Thus the reaction IS driven vrrtually to completion of detectzng 2 x 10m3 mole/lThe 25oC equlllbrlum conversIon of due to the separation occurlng In the bed. methyl formate having an initial concentration of 3.0 N is 75% Separation of Both components methanol and formic acid is also evident from Fig. 3 and Fig. 4 show tailing of the peaks due to their polarity. This is particularly so for formic which comes off in a broad peak havrng a long tall which stretches nearly acid, completely around the reactor Talllng could be reduced by use of a different 4 are the results of numerlThe lines in Fig. 3 and Fig. chromatographlc material These were calculated from the model equations using literature cal simulation and experrmantally measured adsorptlon data as input values of rate coefflclents, It can be seen that the slmulatlon gives good agreement with experiment, parameters. It should also be noted that the both with respect to peak shape and posltlon. In agreement with experiment slmulatlon predicts greater than 98% conversion,

I

B-10

Acontu~uouschromatograpluc

79

reactor

06

05-

04-

03-

0

45

90

135

180

ANGULAR

F1g.

3

l

/Y

Elutlon profile, 0 ExperImental, slmulatlon

DISTANCE,

Feed, CH30H,

CAO 0

061

= 3 0, HCOOH.

01’

0

0

0

0

0

a

r-0.

IZ;r

315

360

DEGREES

CB~ = CCQ = TheoretIcal,

0

0 -

mole/liter NumerIcal

45

I \ l

-

.O OOG

l I

I

90

135

ANGULAR

4.

270

l

mm

Fig.

225

Feed, Elutlon proflle Experimental, mole/liter. Numerzcal slmulatlon.

3_

DISTANCE,

l

Q*krnv. --

,OOP

180

CAoa

l

0.3219, CH30H,

w

225

0 270

DEGREES C

I

cI 315

360

Reactor Models

80

- Desgn Studies

B--IO

SUMMARY 1

A continuous chromatographic reactor has been deslgned acid catalyzed hydrolyses of methylformate. aqueous, methanol and formic acid, gave reasonably well defined No reactant peak was detected, lndrcatlng that larger was obtaIned.

2.

An 1s

3.

In the numerical slmulatxon the Freundllch adsorptxon Isotherm was used Binary component adsorptron Isotherm data are capable of glvlng good agreement between the srmulatlon results and the experlmental data. Thus seems to be due to the concentration of methylformate a short drstance quack disappearance of the hrgh from the reactor inlet and almost no competrtlve adsorptron between methanol and formrc acid.

4

To reduce necessary

Ideal chromatographlc model, capable of gxvrng excellent

the scatter to Improve

modified predIctIon

and constructed for the The reactron products, chromatographlc peaks than equrllbrlum conversIon

by slmulatxng small of the experImenta

dlspersron results

effects,

of data points In the rotating sampling scheme or develop a more effective packing technology.

It

may

be

ACKNOWLEDGEMENT This 2945.

work

was

supported

by

the

U.S.

Department

of

Energy

under

Contract

No

Ey-76-OZ-

NOMENCLATURE fluId

C

phase

concentratxon,

mole/l m,-1

r

a

k

forward

K

adsorptlon

Ke L

vector

of

reactron

reactron total

drmenslonless rate

bed constant,

equrllbrlum

constant,

length,

the

exponentral

factor

n

solrd

concentration,

N

number

r

mean

II

reactron

rate,

u

a

of

V

lnterstltlal

z

axral

Greek E 8 d 5 PB 9 =s + W

of

mesh

value

of

vector

distance

pornts the

f,=ur+p

K u Brtl

mole/gr-adsorbent mole/l m

Freundlrch

adsorptron

Isotherm,

mole/gr-adsorbent

In

reactor

the

Lax'

radius,

formulatron cm

mole/mln

drmensronless flow in

concentration

velocrty the

m UI1/E

cm

m

phase

In

with

rn=n-L

constant,

equrllbrrum reactor

Isotherm

In

reactor,

the

axial

cm

Symbols void fractron of the bed drmensronless angular distance, 4/2x drmensionless feed port width, 0.03 drmensronless axral distance, Z/L reactor bed density, gr-adsorbent/cc-bed residence trme ratlo, Lw/ZnV reactron time, L/Ve angular distance, radian angular velocrty, rad/mln

with

uI=C1/GAo

dIrectIon,

cm/mln

nl=KIG

1

B-10

A continuous chromatographx

reactor

81

SubscrIpts A B C 1

methyl formate methanol formic acid component A, B

5 e 0

or

axxal component lateral component Inlet feed condltlon

C

REFERENCES Arls, R andN R Amundson (1973). Mathematical Methods I" Chemical Enp~Lneerlng, --Vol 2 Prentice-Hall, Englewood Cliffs, N .J Bell,R P,A L DowdIng and J. A Noble (1955). J Chem sot. 3106 Chung, S F and C Y Wen (1968) AIChE J 14(6), 857 -Emery, A F (1968) J. Comput Phys , 2, 366. Fox, J B.Jr,R C Calhoun and W J Egllnton (1969). .J Chromatoq. )P 43 48 Gazlev, G A , V Yu Flllnovskll, and M I Yanovskll (1963). Krnet. Katal , 4, 688. Glddlngs, J C (1962) Anal . Chem., 34, 37 Gore, F E. (1967). I & EC Proc Deslg" & Devel., 6, 10. Klpllng, .I J (1965). AdsorptIon from Solutions of Non--electrolytes, Academic Press, New York Langer, S H , J Y Yurchak and J E. Patton (1969). I & EC, 61, 11. Lax, P D (1957). Commun. Pure & Appl. Math., 10, 537. Lax, P D and B Wendroff (1964) Commun. Pure & Appl Math., 17, 381. -Levensplel, 0 Chemical Reactlon EnglneerLnq, 2nd ed John Wiley & Sons, (1972).* New York. Magee, E M (1963) I & EC Fundam" , 2, 32 Matsen, J M , J W Harding and E M. Magee (1965) J. Phys. Chem , 69, 522 and C N Newllng, W B S Hlnshelwood (1936) J. Chz. Sot 1357 Roglnskll, S Z , M I Yanovskll, and G , 3, A. Gazxev (1962) K:net Katal 529 Rusanov, V V (1970). J Comput. Phys 5, 507 Bexchte , 72B, 17;7 Salml, E J (1939). Scott, D D , R/D Spence and W G Slsson (1976) J Chromatog 126, 381 Roglnskll, and M I Semenenko, E I , S 2 Yanovskll (1964). KxAet Katal , 5, 490 N Sussman, M AstIll, R. Rombach, A Cerullo, and S. S Chen (1972) V., K I & EC Fundam , 11(2), 182 Adv Chem Vlswanathan, S and R Arls (1974) Ser , 133, 191 Wankat, P C , A R MIddleton and B L Hudson (1976) I & EC Fundam , 150, 309 Wetherold, R G , E H Wlssler and K. B. Bxschoff (1974) Adv. Chem. Ser., 133, 181