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A SINGLE-STAGE, LIQUID-PHASE DIMETHYL ETHERSYNTHESIS PROCESS FROM SYNGAS III. DUAL CATALYSTCRYSTAL GROWTH, DEACTIVATION, AND ACTIVITYCONSERVATION STUDIESMakarand R. Gogate a , Annabelle Foos a , Sunggyu Lee a & Conrad J. Kulik ba Department of Chemical Engineering , The University of Akron Akron , Ohio, 44325b Fuel Science Program , Electric Power Research Institute , Palo Alto, California, 94304Published online: 27 Apr 2007.

To cite this article: Makarand R. Gogate , Annabelle Foos , Sunggyu Lee & Conrad J. Kulik (1991) A SINGLE-STAGE, LIQUID-PHASE DIMETHYL ETHER SYNTHESIS PROCESS FROM SYNGAS III. DUAL CATALYST CRYSTAL GROWTH, DEACTIVATION, ANDACTIVITY CONSERVATION STUDIES, Fuel Science and Technology International, 9:8, 949-975, DOI: 10.1080/08843759108942306

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FUEL SCIENCE AND TECHNOLOGY INT'L., 9(8), 949-975 (1991)

A SINGLE-STAGE, LIQUID-PHASE DIMETHYL ETHER SYNTHESIS PROCESS FROM SYNGAS

111. DUAL CATALYST CRYSTAL GROWTH, DEACTIVATION, AND ACTIVITY CONSERVATION STUDIES

Makarand R. Gogate, Annabelle Foos*, Sunggyu ~ee+, and Conrad J. ~ulik#

Department of Chemical Engineering The University of Akron

Akron, Ohio 4 4 3 2 5

#Fuel Science Program Electric Power Research Institute

Palo Alto, California 94304

ABSTRACT

In the liquid phase dimethyl ether (DME) synthesis process, both the methanol synthesis catalyst (composed of CuO, ZnO, and A1203) and the methanol dehydration catalyst (composed of gamma-alumina) are slurried in the inert oil phase. Various long-term activity checks were conducted on these dual catalysts to characterize the crystal growth and the thermal aging behavior. X-ray powder diffraction, X-ray fluorescence and elemental intensity compositions, and the crystallite size distributions of the aged catalysts were examined. Based on the current investigation, it was established that the crystal growth and the catalyst deactivation problems in the methanol synthesis catalyst are less severe when it is used along with the methanol dehydration catalyst.

I

+TO whom all correspondence should be directed. *currently with the Department of Geology.

Copyright O 1991 by Marcel Dekker, Inc

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GOGATE ET AL.

INTRODUCTION

In the liquid phase methanol synthesis process, the

synthesis catalyst is slurried in an inert hydrocarbon

oil such as Witco-40, Witco-70, or Freezene-100 oil.

Syngas which is typically a mixture of Hz, CO, C02, and

some inert (Ar or CH4), reacts over the active catalyst

dispersed in the oil. This process was first developed

by Chem Systems, Inc. in 1975 and since then, various

process development studies have been carried out (Lee,

1986, 1988a, 1990a; Air Products and Chemicals, Inc.,

1986).

The problem of crystal size growth in the liquid

phase methanol synthesis catalyst has also been studied

in some detail (Sawant, 1987; Sawant et al., 1988).

Some major causes of catalyst deactivation and

structural degradation have been identified as follows

(Lee, l99Ob) :

(1) Presence of trace metal carbonyls and sulfur compounds in the feed syngas.

(2) Structural breakdown due to mechanical stress. I

(3) Carbon deposition on the catalyst surface.

(4) Hydrothermal catalyst crystal growth.

(5) Water accumulation in the catalyst pores.

(6) Interaction of the metal ingredients of the catalyst with in-situ produced water.

It should be noted that the first two causes of the

catalyst deactivation have been well investigated (Lee,

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DIMETHYL ETHER SYNTHESIS PROCESS. 111 951

1990b), and can almost entirely be eliminated. The

presence of carbon deposition on the catalyst surface is

very difficult to envisage when the methanol synthesis

catalyst is immersed in oil, as in the liquid phase

methanol synthesis process. Further, although very much

suspected, this fact has never been corroborated with

concrete experimental evidence before. The remaining

three causes are, however, very much present in the

liquid phase methanol synthesis process, and all of

these focus on the role of water in promoting the

crystal growth and mineral leaching from the synthesis

catalyst.

In the liquid phase methanol synthesis process,

water is inevitably produced along with methanol,

although the overall selectivity towards methanol is

always kept very high by the forward water gas shift

reaction. The reactions which occur in the liquid phase

methanol synthesis process under normal CO-rich syngas

conditions are (Lee, 1990b):

When this reaction system is modified to co-produce

methanol and DME (Lee et al., 1988b, 1990~). the

reaction chemistry includes the DME synthesis reaction

via methanol dehydration and is represented by:

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GOGATE ET AL.

Thus, this system has one more source of water

generation. However, again, since the water gas shift

reaction (4) proceeds faster than the methanol synthesis

reaction (3) and the methano1,dehydration reaction .(5),

the selectivity towards methanol and DME is always

maintained very high (Lee et al., 1990~). ~x~eriments

also show that very little water is produced in net

amount.

Although the selectivity towards the products (DME

and methanol) is very high, it is generally realized

that the presence of water is very important in

modifying the reaction environment and in increasing the

rate of methanol synthesis. However, at the same time,

water can damage the catalyst by any of the causes (d)

through (f) listed above. Since the co-production of

DME and methanol has two sources of water generation,

the effect of these causes can be more critical and

significant. Thus, the crystal growth and deactivation

problems have to be extensively reexamined in this

process. The current study attempts to clarify some of

these important issues relating to catalyst life and

activity conservation.

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DIMETHYL ETHER SYNTHESIS PROCESS. I11 953

EXPERIMENTAL

A laboratory scale pilot plant was designed and

built as a part of this and other ongoing research. All

the activity measurements of niethanol and DME synthesis

were made on a one-liter, mechanically agitated slurry

reactor. The sketch of the slurry reactor system along

with all the peripheral units is given elsewhere (Lee,

1990a, 1990b) . A CO-rich syngas having compositions which simulate

closely to those of typical Texaco or Koppers-Totzek

syngas was used for this study. In particular, the

nominal composition of the syngas was H2:CO:C02:CH4 =

36:48:8.5:7.5. Commercial methanol synthesis catalyst

composed of CuO, ZnO, and A1203 and designated as EPJ-19

by the manufacturer United Catalysts, Inc., was used.

Methanol dehydration catalyst composed of pure

gamma-alumina and designated as AL-3916P by the

manufacturer Harshaw-Filter01 Partnership, Inc., was

used along with EPJ-19. The inert liquid phase employed

for this inverstigation was the Witco-40 white mineral

oil, manufactured by Witco Corporation. This inert oil

could be easily replaced by Witco-70, Witco-100, or

Freezene-100 oils.

After each long-term activity check was over, the

slurry containing the active catalyst was pumped out.

This active catalyst, when exposed to air, could be

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DIMETHYL ETHER SYNTHESIS PROCESS. I11 955

methanol dehydration catalyst). In the co-production of

methanol and DME, these two catalysts are slurried

together in the oil. Gamma-alumina was found to be

perfectly stable at the nominal reaction conditions

employed for the dehydration of methanol to DME (Gogate,

1990). The copper-based methanol catalyst was, however,

suspected to be far more sensitive to hydrothermal

crystal growth (Sawant et al., 1988). The purpose of

this investigation was thus to study whether the crystal

growth in the copper-based methanol synthesis catalyst

is alleviated by using it along with gamma-alumina in

the liquid phase, for the co-production of methanol and

DME, i-e., to check whether gamma-alumina exhibits any

synergistic beneficial effect on the methanol synthesis

catalyst. If so, this could be a very significant

side-benefit of the co-production approach, the primary

benefit being the fact that it has been shown to improve

reactor productivities and syngas conversions by as much

as 60% (Lee et al., 1988b, 1990~).

To qualify and quantify the problems of catalyst

crystal growth, deactivation, and hydrothermal leaching,

the following techniques were used:

(1) Thermal aging of the methanol synthesis catalyst under both continuous and batch reaction conditions, for methanol synthesis and dual catalysis (Co-production of methanol and DME).

(2) X-ray diffraction patterns for the aged catalysts.

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GOGATE ET AL. '

(3) X-ray fluorescence patterns and elemental intensities of the aged catalysts and process oils.

(4) Crystallite size distributions of the aged catalysts by the Fourier Line Profile Analysis.

(5) Average crystallite size determination.

The experimental scheme employed for this study has

been summarized in Table I. Three experiments were

conducted in a batch mode and two in a continuous mode.

The average crystal size of the freshly reduced catalyst

was 3.9 nm. The crystallite size distribution of this

catalyst is shown in Figure 1. The crystallite size

distribution has two distinct peaks, at 3 nm and at 7

nm; respectively. All the copper crystallites are in

the size range of 2-4 nm and 6-8 nm. There are

absolutely no crystallites in the 10-14 nm size range.

Crystallites in the size range 2-4 nm have a weight

function intensity of 0.5.

The crystallite size distributions of the aged

catalysts in a batch mode are shown in Figures 2-4. The

nominal compositions of the normal syngas, the CO-free

syngas, and the COZ-free syngas under which the

catalysts were aged are given in Table I. The average

crystal sizes of these three aged catalysts is 4.4 nm,

5.0 nm, and 4.6 nm, respectively. The average crystal

size is thus significantly greater than that for the

freshly reduced catalyst. Crystallites in the size

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DIMETHYL ETHER SYNTHESIS PROCESS. 111

Table I

Summary of Crystal Size Growth Experiments for Dual Catalysts

Sample EDME14 EDME18 EDME19 EDME15 EDME16 EDME17 ........................................................ Mode of Operation R C C B B B ........................................................ Temp. (OK) 523 523 523 523 523 ........................................................ Pres. (MPa) 0.345 5.585 5.688 5.792 5.722 5.722 ........................................................ Feed Gas Composition Mole % ........................................................ Hz 5.0 59.3 33.6 37.4 59.3 33.6 N2 95.0 0.0 0.0 0.0 0.0 0.0 CO 0.0 0.0 55.4 46.3 0.0 55.4 co2 0.0 35.4 0.0 7.7 5.3 0.0 CH4 0.0 5.3 11.4 8.6 35.4 11.4 ........................................................ Time (Hours) 60 6 0 64 5 5 6 6 ........................................................ Crystal Size (nm) 3.9 5.2 5.5 4.4 5.0 4.6

Notes: 15 g MeOH Synthesis Catalyst and 1 g Gamma-Alumina was used as dual catalyst. 550 ml of Witco-40 oil was added to make the slurry. Continuous operating mode is indicated by C, and the batch operating mode is indicated by B. R indicates catalyst reduction.

range of 10-14 nm are present in all these aged

catalysts. At the same time, the weight function of the

crystallites in the size range of 2-4 nm is decreased

accompanied by a simultaneous increase in the weight

function of the crystallites in the size range of 6-8

and 10-ld nm

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Average Crystal Size = 3 . 9 nm

0 2 4 6 8 10 12 14 16

Cryetallite Sire (nm)

Figure 1 . C r y s t a l l i t e S i z e Dis tr ibut ion of Freshly Reduced Dual Cata lys t .

Figure 2 . C r y s t a l l i t e S i z e ~ i s t r i b u t i o n of An Aged Catalyst i n Normal Syngas f o r 64 Hours i n a Batch Mode.

16

0.5

0.4 -

c 0 .- .4

0.3 - c I: u .r .- ff 0.2 -

0.1 -

0 ,

Average Crystal S i z e = 4 . 4 nm

0 0

0

0 O

0 0 0

0 D 0

, C, n -

I I I I I 3 I I I I I - I = 0 2 4 6 8 10 12 14

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0'5 r- Average Crystal Size = 5 . 0 nt

0 2 4 6 8 10 12 14

Ctystollite Size (nm)

Figure 3 . C r y s t a l l i t e S i z e Dis tr ibut ion of An Aged Cata lys t i n No-CO Syngas f o r 5 5 Hours i n a Batch Mode.

I Average Crystal S i z e = 4 . 6 nm

Crystallite Size (nm)

Figure 4 . C r y s t a l l i t e S i z e Dis tr ibut ion o f An Aged Catalyst i n No-C02 Syngas f o r 66 Hours i n a Batch Mode.

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960 GOCATE ET AL.

The crystallite size distributions of the aged

catalysts in a continuous mode are shown in Figures 5

and 6. The catalyst in Figure 5 was aged for 60 hours

in the C02-free syngas having a nominal" composition of

H2:CO:CH4 = 33.6:55.3:11.1. The average crystal size of

this catalyst was 5.4 nm. The crystallite size

distribution of this catalyst falls in two distinct size

ranges of 2-6 and 8-12 nm. The catalyst in Figure 6 was

aged for 60 hours in the CO-free syngas having a nominal

composition of H2:C02:CH4 = 59.2:35.5:5.3. The average

crystallite size was 5.2 nm. The crystallite size

distribution of this catalyst was nearly trimodal in the

sense that it had three distinct peaks in the size

ranges of 2-6, 6-10, and 12-14 nm.

It was very apparent that the copper catalyst

crystals had undergone a pronounced increase in the

crystal size over only 60 hours of use, under both the

CO-free and the C02-free environment. The crystallite

size distribution also had underwent a very significant

shift in the sense that the crystals in the lower range

Of sizes (2-6 nm) had now a lower weight function and

those in the higher range (6-10 nm) were of much higher

weight function. Crystals in the size range of 10-14 nm

also appear for the first time in the aged catalysts.

To explain this shift in the crystallite size

distributions, the atomic migration model has been

applied before (Lee, 1989).

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Crystollite Size (nm)

0.4 -

C 0 0.3 - - " C

I: - L D - 0.2 - :

0.1 -

0

Figure 5. Crystallite Size Distribution of An Aged Catalyst in No-C02 Syngas for 70 Hours in a Continuous Mode.

Average Crystal S i z e = 5 . 4 nm

0 0

0

0 D

0 D

0 0

0 0 - D 0 " - I -4 I I I I I I I I I I -

0.50

Average Crystal S i z e = 5 . 2 nm

Crystollite Size (nm)

Figure 6. Crystallite Size Distribution of an Aged Catalyst in a No-CO Syngas for 60 Hours in a Continuous Mode.

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Table I1

Summary of Crystal Size Growth Experiments for Methanol synthesis'

Sample EPJ 905 903 904 908 910 911 ........................................................ Mode of Operation R C C B B B

Temp. (OK) 523 523 523 523 523 ........................................................ Pres. (MPa) 6.998 6.998 5.516 5.516 5.516 5.516 ........................................................ Feed Gas Composition Mole %

H2 5.0 59.3 33.6 36.0 36.0 36.0

N2 95.0 0.0 0.0 0.0 0.0 0.0 CO 0.0 0.0 55.4 48.0 48.0 48.0

co2 0.0 35.4 0.0 7.6 7.6 7.6

CH4 0.0 5.3 11.4 8.4 8.4 8.4 ........................................................ Time (Hours) 60 6 0 100 75 5 0 ........................................................ Crystal size (nm) 2.9 10.5 8.0 4.4 4.3 4.6

(+: Sawant et al., 1988)

The crystal size growth data for the methanol

synthesis catalyst, aged under conditions of purely

methanol synthesis, have been presented in Table 11.

his and the experimental scheme in Table I were carried out under very similar reactor operating conditions.

Comparing the average crystal size for these two cases,

dual catalysts are shown to offer a very favorable

scenario for the crystal size growth and catalyst

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DIMETHYL ETHER SYNTHESIS PROCESS. I11

Table I11

Dual Catalyst Activity in Normal Syngas, No-CO Syngas and No-C02 Syngas

Operating Conditions: Catalyst 15 g of EPJ-19

I g of Gamma-Alumina Temperature 250°C Pressure 5.792 MPa Oil 550 ml of Witco-40 oil Impeller speed : 1500 rpm Feed flow rate : 1 SLPM

Syngas Type ~ormal# No-CO NO-C02 ........................................................ Reactor Feed Flow Rate and Mole Fractions

Flow, mol/h 2.6786 2.6787 2.6787

Hydrogen 0.3616 0.5920 0.3307 CO 0.4836 0.0000 0.5556 Methane 0.0790 0.0530 0.1137 Carbon dioxide 0.0757 0.3550 0.0000 ........................................................ Reactor Exit Flow Rate and Mole Fractions

Flow, mol/h 1.9557 2.5496 2.0681

Hydrogen 0.1956 0.5329 0.1949 CO 0.4469 0.0261 0.5232 Methane 0.1082 0.0557 0.1439 Carbon dioxide 0.1425 0.3257 0.0585 Water 0.0012 0.0408 0.0005 Methanol 0.0755 0.0189 0.0343 DME 0.0300 0.0000 0.0485 ....................................................... Reaction Rates (mol/kg cat (MeOH). h)

Hydrogen -39.0705 -15.1313 -33.1707 CO -28.0853 +4.4331 -26.5433 Carbon dioxide +5.0546 -8.0387 +8.0678 Water +O. 1560 +6.9281 +O. 0690 Methanol +9.8473 +3.2109 +4.1972 ....................................................... Reaction Rate (mol/kg cat (DME). h)

DME +58.6191 0.0000 +100.2266

Note: # : The data for normal syngas is at 7.0 MPa.

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964 GOGATE ET AL.

Figure 7. X-ray Diffraction Pattern of an Unreduced Methanol Synthesis Catalyst.

deactivation. This simply means that methanol synthesis

catalyst could conserve its original activity longer,

when aged along with the methanol dehydration catalyst.

This bears a very important implication: not only

higher productivities were obtained in the co-production

of methanol and DME, these productivities could be

maintained much longer than those for methanol synthesis

alone.

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DIMETHYL ETHER SYNTHESIS PROCESS. I11 965

Figure 8. X-ray D i f f r a c t i o n P a t t e r n o f Freshly Reduced Dual C a t a l y s t .

To assess the influence of reaction environment on

the average crystal size and the crystallite size

distribution, the reaction rate data from the CO-free

and the C02-free syngas case are given in Table 111. For

the CO-free syngas case, the selectivity to methanol was

only 32%. The selectivity to water was unusually high

at 68%. Absolutely no DME was formed for this case. For

the C02-free syngas case, however, the selectivity to

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COGATE ET AL.

F igu re 9. X-ray D i f f r a c t i o n P a t t e r n o f Dual Ca ta l ys t Aged i n Normal Syngas f o r 64 hours i n a Batch Mode.

methanol was almost 99.9%. Both DME and C02 had

significant positive synthesis rates. Thus, the

reaction environment in CO-free syngas case was

water-rich, whereas that in the C02-free syngas case was

methanol and CO-rich. The average crystal size for the

C02-free syngas case was 5.4 nm, whereas that for the

CO-free syngas case was 5.2 nm. This insignificant

difference in the crystal size of these two cases night

have been due to insufficient aging time (60 hours).

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DIMETHYL ETHER SYNTHESIS PROCESS. 111

Figure 10. X-ray Diffraction Pattern of Dual Catalyst Aged in No-CO Syngas for 55 hours i n a Batch Mode.

The X-ray diffraction patterns for the aged

catalysts are given in Figures 7-15. It is shown that

all the copper peaks in the aged catalysts have become

sharper and have more intensity when compared to that

for the freshly reduced catalyst. The best graphic

comparison is illustrated in Figures 13 and 15. In

Figure 13, the X-ray diffraction peak for the Cu(ll1) is

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GOGATE ET AL.

Figure 1 1 . X-ray Diffraction Pattern of Dual Catalyst Aged in NO-C02 Syngas for 66 hours in a Batch Mode.

compared among the freshly reduced catalyst, the

catalyst aged in the C02-Tree syngas for 60 hours in a 1

batch mode, and the catalyst aged in the COZ-free syngas 1

for 60 hours in a continuous mode. In Figure 15, a

similar comparison is made for the CO-free syngas case.

It is shown that when compared to that of the freshly

reduced catalyst, the Cu(ll1) peaks for the catalyst

aged in both batch and continuous mode are sharper and

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DIMETHYL ETHER SYNTHESIS PROCESS. I11

Figure 12. X-ray Diffraction Pattern of Dual Catalyst Aged i n No-LO2 Syngas for 60 hours in Continuous Mode.

have a much higher intensity. At the same time, the

catalyst aged in a continuous mode has a higher

intensity than that for the batch mode. This is

indicative of the fact that the thermal aging problems

are more severe in the continuous mode than in the batch

mode. This might be due to the fact that in the batch

mode, the synthesis reactions come to equilibrium very

quickly as opposed to that for the continuous mode. A

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GOGATE ET AL.

F i g u r e 13. Comparative X-ray D i f f r a c t i o n P a t t e r n s f o r Cu (111) Peak For F r e s h l y Reduced. Aged f o r 60 hours i n Batch Mode, and Aged f o r 60 hours i n Continuous Yode, i n No-COZ Syngas.

x103

similar fact is ,borne out by the average crystal size

comparison for' these cases.

The X-ray fluorescence (XRF) patterns for the fresh

and aged catalysts as well as the used process oils have

been given in Figures 16-18. The most interesting

2.00 -

1.80 '

1 .i.0

1.40 '

l.20 .

observat'ion was that in the used process oils, trace

amounts of copper and zinc were detected. The elemental

- '

No-C02 Syngas, 60 Hours, C

n

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DIMETHYL ETHER SYNTHESIS PROCESS. I11 971

Figure 14. X-ray D i f f r a c t i o n P a t t e r n o f Dual C a t a l y s t Aged i n No-CO Syngas f o r 60 Hours i n Continuous Mode.

intensities for these in Witco-40 oil are, however, very

small when compared to that for either aged or freshly

reduced catalysts. The hydrothermal leaching problems

are thus almost negligible, over the aging periods

considered in this study. However, by ' looking at the

trend in the values for the copper intensities, the

copper intensity in used Witco-40 oil was the most under

the CO-free syngas case. This case was also an

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1 .80

1.60

No-CO Syngas. 60 Hours. C 1.40 No-CO Syngas. 55 Hours, B

1.20

1 .OO

0 . m

0.60

G .40

0.28

F igu re 15. Comparative X-ray D i f f r a c t i o n Pat te rns f o r Cu (111) Peak f o r F resh l y Reduced Ca ta l ys t , Aged i n 60 Hours i n Continuous Mode. and Aged i n 55 Hours i n Batch Mode, i n No-CO Syngas.

F igu re 16. X-ray Fluoroscence P a t t e r n and Elemental I n t e n s i t i e s f o r a Fresh ly Reduced Dual Cata lys t .

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DIMETHYL ETHER SYNTHESIS PROCESS. I11

CuKu

1 S1K.x i 5 C N T 10.m , 20.00 , . -, . , 3@.@0 , I , ,

I 9 . E 4 K E V 10eV/ch A E D R X

I u A E D R X

I

Figure 17. X-ray Fluorescence Pattern and Elemental Intensities for an Aged Catalyst in No-C02 Syngas for 70 Hours in a Continuous Mode.

water-rich environment, since the catalyst selectivity

to water was 68%. Thus, water-rich environment in the

methanol-DME synthesis is suspected to be detrimental in

both ways, viz., it promotes the structural degradation

of the catalyst by hydrothermal leaching, and second, it

promotes the crystallite size growth of the copper

crystallites, as evidenced by the crystal growth data.

CONCLUSIONS

The crystal size growth in the methanol synthesis

catalyst when aged in presence of the methanol

dehydration catalyst was investigated for the first

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COGATE ET AL.

Figure 18 . X-ray Fluoroscence Pattern and Elemental Intensities o f Copper and Zinc i n Witco-40 Oil f o r an Aged Catalyst under no-CO Syngas f o r 60 Hours i n a Continuous Mode.

time. Water and methanol-rich liquid phase were found

to promote catalyst crystal growth. The crystal growth

problems in the copper-based methanol catalysts when

used in the dual catalyst mode were found to be far less

severe than when the catalysts were used for methanol

synthesis alone. Thus, the co-production of methanol

and DME renders yet another advantage in the catalyst

activity maintenance.

ACKNOWLEDGEMENTS

This work was fully sponsored by the Electric Power

Redearch Institute through its research contract

RP317-6. The authors are greatly indebted to Howard, E.

Lebowitz of the Electric Power Research lnstitutelfor

his continued support and encouragement.

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DIMETHYL ETHER SYNTHESIS PROCESS. 111

REFERENCES

Air Products and Chemicals, Inc.. 1986. Liquid-Phase Methanol Process Development Unit (PDU) - 40 Day Run at LaPorte, Texas, Final Report AP-4430, Electric Power Research Institute, Palo Alto, California.

Gogate, M. R.. 1990. Kinetics of Methanol Dehydration to Dimethyl Ether. M. S. Thesis, The University of Akron.

Lee, B. G.. 1989. Regeneration and Post-Treatment of Industrial Co-precipated Methanol Synthesis Catalyst. Ph. D. Dissertation, The University of Akron.

Lee, S.. 1986. Research to Support Development of Liquid Phase Methanol Synthesis Process. Interim Report AP-4429, Electric Power Research Institute, Palo Alto, California.

Lee, S.. 1988a. Mass transfer in the Liquid Phase Methanol Synthesis ( L P M ~ O H ~ ~ ) Process. Interim Report EPRI AP-5758. Electric Power Research Institute, Palo Alto, California.

Lee, S., Parameswaran, V. R., Lee, B. G., and Gogate, M. R.. 1988b. Novel Developments and Enhancements in Methanol Synthesis. Proc. of Indirect Liquefaction Contractors' Review Meeting (USDOE/PETC), Pittsburgh, Pennsylvania, November 15-17.

Lee, S.. 1990a. Reaction Mechanisms in Liquid Phase Methanol Synthesis, Interim Report ER/GS-6715, Electric Power Research Institute, Palo Alto, California.

Lee, S.. 1990b. Methanol Synthesis Technology, CRC Press, Boca Raton, Florida, 1990.

Lee, S., Gogate, M. R., and P. Vijayaraghavan. 1990c. Development of Single-Stage, Liquid-Phase synthesis Process of Dimethyl Ether from CO-rich Syngas. Invited Paper Presented at the 15th Annual EPRI Contractors' Conference on Fuel Science and Conversion, Electric Power Research Institute, Palo Alto, California.

Sawant, A. V.. 1987. The Effect of Thermal Aging, Water, and C02 on the Liquid Phase Methanol Synthesis Catalyst. Ph.D. Dissertation, The University of Akron.

Sawant, A. V., Lee, S., and Foos, A.. 1988. Crystal Size Growth in the Liquid Phase Methanol Synthesis Catalyst. Fuel Sci. and Tech. Inttl, 6(5), 569-589.

RECEIVED: September 24, 1990 ACCEPTED: October 15 , 1990

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