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PHASES IN THE ACTIVE LIQUID PHASE METHANOLSYNTHESIS CATALYSTAshok V. Sawant a , Sunggyu Lee a & Conrad J. Kulik ba Department of Chemical Engineering , University of Akron , Akron, Ohio, 44325b Electric Power Research Institute , Palo Alto, CA, 94303Published online: 08 Mar 2007.

To cite this article: Ashok V. Sawant , Sunggyu Lee & Conrad J. Kulik (1988) PHASES IN THE ACTIVE LIQUID PHASE METHANOLSYNTHESIS CATALYST, Fuel Science and Technology International, 6:2, 151-164, DOI: 10.1080/08843758808915881

To link to this article: http://dx.doi.org/10.1080/08843758808915881

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FUEL SCIENCE & TECHNOLOGY INT'L., 6 ( 2 ) , 151-164 ( 1 9 8 8 )

PHASES IN THE ACTIVE LIQUID PHASE

METHANOL SYNTHESIS CATALYST

Ashok V. Sawant, and Sunggyu Lee Department of Chemical Engineering

University of Akron Akron Ohio. 44325

and

Conrad J . Kulik Electric Power Research Institute

Palo Alto. CA 94303

ABSTRACT

An attempt has been made to identify the phases present in the active catalyst for liquid phase methanol synthesis. X-ray powder diffraction was used to identify the phases. Only metallic Cu was detected, while no CU' species was found to be present. A significant amount of ZnC03 was found to be present in catalysts which had been subjected to high partial pressures of COY This fact has hitherto not been reported in literature. Some speculations about the effect of ZnC03 on the life of the catalyst are made.

INTRODUCTION

This paper aims to determine the composition of

the methanol synthesis catalyst under reaction

conditions in the liquid phase methanol synthesis

process. In this process the catalyst which is a

coprecipitated mixture of CuO, ZnO. and A1203 is

Copyright0 1988 by Marcel Dckkcr, h e .

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1 5 2 SAVANT, LEE, AND KULIK

slurried with an inert mineral oil (Witco-40). The

syngas which is a mixture of C02. H2, CO. and CH4

reacts in this slurry. There are two main reactions

which are thought to occur (Parameswaran (1987)).

The kinetics, thermodynamics and mass transfer

phenomena associated with this process have been

investigated in detail (KO et al. (1987). KO (1987).

Savant (1985)).

There has been a long running controversy

regarding the existence of cut species in the active

methanol synthesis catalysts. It has been shown by

many investigators (Herman et al. (1979), Mehta et al.

(1979). Chinchen and Waugh (1986), Okamoto et al.

(1983), Sankar et al. (1986), Giamello et al. (1984).

and Tarasov et al. (1985)) that the active catalyst

contains a monovalent species of copper.

However, studies (Shimomura et al. (1978)) using

X-ray diffraction have shown that there was a complete

reduction of copper oxide to metallic copper. It has

been reported that (Fleisch and Mieville (1984 and

1986)) X-ray photo electron spectroscopy of the

catalyst shows only metallic copper and zinc oxide in

the catalyst. This result contradictsthe findings of

Okamoto et al. (Okamoto et al. (1983)) where X-ray

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ACTIVE LIQUID PHASE UETHANOL SYNTHESIS CATALYST 153

photoelectron spectroscopy was also used to study the

nature of the copper in the catalyst. Studies

(Friedrich et al. (1983) ) on Raney copper catalysts

have shown that the copper exists only in the metallic

state.

EXPERIMENTAL

Figure 1 is a schematic of the experimental

system. The syngas which was blended and stored in a

tank, passed through a forward pressure regulator

(FPR). The solenoid valve SV3 was used to turn the flow

of gases on and off. Flow of the inert N2 was

controlled by the solenoid valve SVl. The two lines

met at a junction. At any given time only one of

sither N 2 or syngas was allowed to flow. Nitrogen was

used as a purge gas. The gases were filtered t5rough

beds of fiolecular sieves and activated carbon. A Brooks

58711 mass flow control system coupled to a Brooks

5810P mass flow sensor and a Brooks 58358 mass flow

control valve were used to control the flow rate of the

syngas. The gases were fed to the 1-liter reaction

vessel manufactured by Autoclave Engineers. This vessel

was equipped with a turbine impeller and a baffle. The

product stream from the reactor passed through a

condenser where the water and methanol were condensed

out. They were collected in a collection bomb, from

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SAVANT, LEE, AND KULIK

VENT

FLOW SENSOR FOR 4NALVSlS

AUTOCLAVE-

COLLECTOR

$ FOR ANALISIS

Figure 1. Schematic of the experimental slurry reactor system.

which they were removed periodically for analysis. The

uncondensed gases exited from the condenser and their

pressure was let down by a dome loaded back pressure

regulator. BPR1. This stream was sampled by a Hevlett

Packard 5 8 9 0 A gas chromatograph equipped with a

multi-port injection valve. The mixture of H z . CO.

0 C 0 2 , and CHb was separated at 1 5 0 C on a Carbosieve-S

column. The mixture of water and methanol was

0 separated on the same column at 2 0 0 C.

In order to analyze the cetalysts. the slurry was

pumped out from the reactor and the catalyst separated

from the oil by filtration. The filtration was carried

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ACTIVE LIQUID PHASE UETHANOL SYNTHESIS CATALYST 155

out in a glove box under a nitrogen atmosphere in order

to prevent the oxidation of the catalyst. The catalyst

was washed with heptane and acetone (also under a

nitrogen atmosphere) in order to remove the Witco 4 0

oil. It was then sealed in an air tight vial. A Philips

3720 Automated Powder Diffraction unit was used for the

analysis of the catalysts. A copper Ka radiation of 0

1.5405 A was used for all the X-rays of the catalysts.

A crystalline solid usually has several crystal

planes on which diffraction can occur. When a beam of

X-rays is incident on a powdered sample at changing

angles of incidence, different crystal planes satisfy

Bragg's law (Cullity (1959)). Thus different crystal

planes produce a diffracted beam of X-rays with changes

in the angle of incidence of the X-ray beam. Bragg's

law is satisfied at certain discrete points of angle

values. On a recorder chart the X-ray diffraction

pattern appears as a peak where diffraction occurs.

This X-ray pattern provides information about the

interplanar spacing for a crystalline solid. An X-ray

pattern is characteristic of a given mixture of

crystalline solids. By comparing the pattern with a

set of standard patterns it is possible to identify the

compounds present in a given mixture of solids. The

process begins by attempting to match the strongest

peaks in the pattern with that of a compound suspected

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156 SAVANT, L E E , AND KULIK

of being present in the solid mixture. With

sophisticated graphics and data retrieval software

available. it is possible to call up different patterns

from a database and to superimpose them on one another

on a computer terminal. Each compound is called up by

its JCPDS (Joint Committee on Powder Diffraction

Standards (1974 and 1980)) file number. For a totally

unknown mixture of compounds, a software package called

SANDMAN (Netherlandse Philips Bedrijven. B. V . (1984))

is used. This is a pattern matching software which

attempts to match the diffraction pattern with the

patterns stored in the data base. A search match table

is produced which provides a quality of fit table which

indicates the certainty with which the compound has

been' identified. Detailed description of the concepts

presented above may be found in the text by Klug and

Alexander (Klug and Alexander (1974)).

RESULTS AND DISCUSSION

One of the controversies surrounding the nature of

the methanol synthesis catalyst in its active state is

the chemical state of copper in the catalyst. An

attempt was made to determine the state of copper in

the catalyst by X-ray diffraction. X-ray diffraction

spectra of fresh and unreduced catalysts were compared

with that of the active catalyst. Figure 2 shows the

X-ray spectrum of a fresh. unused EPJ-19 catalyst. The

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ACTIVE L I Q U I D PHASE HETHANOL SYNTHESIS CATALYST 157

Sample: epj25 F i l e : EPJ250.RD 20-FEE-86 14:32

5.88 1

Figure 2. The X-ray spectrum of the fresh and unreduced EPJ-19 catalyst.

major phase identified is CuO (Tenorite). Even though

ZnO is present, its presence is masked by that of the

much larger amount of CuO. Figure 3 shows the X-ray

spectrum of the active EPJ-19 catalyst. The CuO peak

vanishes and is replaced by rather flat and broad peaks

which could belong to either Cu20 or ZnO. It is

however difficult to draw any firm conclusions from the

above. It is very clear that the active methanol

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158 SAVANT, LEE, AND KULIK

I Sample: EPJ88 File: EPBBL.RD 13-WIR-86 18:17

Figure 3. The X-ray spectrum of the active EPJ-19 catalyst.

synthesis catalyst contains very large amounts of

metallic Cu. If the X-ray spectra of fresh and

unreduced (Figure 4) and active (Figure 5) BASE S3-85

catalyst (for this catalyst CuO and ZnO are present in

similar amounts) are compared, it is clear that the

peak appearing in place of the CuO peak is that of ZnO.

However. CuZO may be present in such small quantities

that it is not detected by X-ray diffraction. The only

firm conclusion that can be drawn is that the active

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ACTIVE LIQUID PHASE METHANOL SYNTHESIS CATALYST 159

Sample: epbael File: EPB88I.RD W-Mi-B6 11 :19

2.70 3.88 I 2.40 2.10

1.80 1.58 1 .a 0.90 0.60

Figure 4. The X-ray spectrum of the fresh and unreduced BASF S3-85 catalvst.

catalyst contains metallic Cu and ZnO. This view is

supported by some investigators (Shimomura et al.

( 1 9 7 8 ) , Friedrich et al. ( 1 9 8 3 ) ) who have reported that

metallic Cu is the active component in the methanol

synthesis catalyst.

A very interesting and hitherto unreported

phenomenon was observed when a methanol synthesis

catalyst was used under high partial pressures of CO 2 '

ZnCO was found to be present in significant amounts in 3

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160 SAWANT, LEE, AND KULIK

I Sample: EPB00 F i l e : EPB002.RD 02-NQY-86 1 1 :40

Figure 5. The X-ray spectrum of the active BASF S3-85 catalyst.

the active catalyst. Figure 6 shovs the X-ray

diffraction spectrum of such a catalyst. Zinc carbonate

was not found to be present in large amounts in

catalysts used under lov partial pressures of COY

Thermodynamic calculations (Lee et al. (1986)) shov

that for the reaction:

The equilibrium constant K for the above reaction is a

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ACTIVE LIQUID PHASE METHANOL SYNTHESIS CATALYST 161

Figure 6. The X-ray spectrum of a catalyst showing the presence of ZnC03.

0.014 at 237 OC. and it is much higher at 25 OC. i.e..

2015. This indicates that the formation of ZnC03 takes

place only when there is a high concentration of C02 in

the reaction gas mixture. This thermodynamic reasoning

is of a qualitative nature only. However, it is

confirmed by the experimental evidence presented above.

This experimental confirmation of the formation of

ZnC03 under high partial pressures of C02 has never

been made by other investigators

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162 SAWANT, LEE, AND KULIK

CONCLUSIONS

It was shown that only metallic Cu exists in

detectable amounts in the active copper-zinc-alumina

catalyst. Any cut species which might have been

present was not detected by the X-ray diffraction

analysis used to analyze the catalysts.

Some of the catalysts which had been used under

high partial pressures of C02 showed the presence of

large amounts of ZnC03. It is possible that the

mechanjsm by which C02 interacts with the catalyst is

by the formation of ZnC03. Detailed studies have to be

conducted to clarify the role of ZnCOg in methanol

synthesis.

ACKNOWLEDGMENTS

The authors would like to thank Dr. Annabelle Foos

of the Department of Geology for all her help. Mr.

Byung Lee's and Mr. Klein Rodrigues' help with

preparation of the samples is acknowledged with

appreciation. The authors would like to thank United

Catalysts and BASF Wyandotte Corp. for the supply of

their catalysts. This work was wholly supported by

contracts RP2146-02 and RP8003-11 from the Electric

Power Research Institute. Palo Alto. CA. 94303.

REFERENCES

Chinchen. G. C., and Waugh, K. C.. J . Catal.. 97. 280(1986).

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ACTIVE LIQUID PHASE UETHANOL SYNTHESIS CATALYST

Cullity, B. D., "Elements of X-ray Diffraction", Addison Wesley Publishing Company Inc., Reading, Mass, 1959.

Fleisch. T. H., and Mieville, R. L.. J. Catal., 90, 165(1984). - Fleisch, T. H.. and Mieville, R. L.. J. Catal., 97, 284(1986). - Friedrich, J. B.. Wainright, M. S.. and Young. D. J., J. Catal., 80, l(1983).

Giamello. E.. Fubini. B., Lauro, P., and Bossi, A., J. Catal., 87, 443(1984).

Herman. R . G., Klier. K., Simmons, G. W . , Finn. B. F., and Bulko, J. B., J. Catal., 56, 407(1979).

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Joint Committee on Powder Diffraction Standards (JCPDS), Swatmore, PA - 19081, Powder Diffraction File Alphabetical Index, Inorganic Phases. 1980.

K l u g , H. P., and Alexander, L. E., "X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials", Second Edition. New York. John Wiley. 1974.

KO, M. K., Lee, S., and Kulik. C. J.. Energy and Fuels, 1. No. 2 . 211(1987).

KO, M. K.. Ph. D. Dissertation , University of Akron. May 1987.

Lee, S., Paramesvaran, V.. Savant. A. V., KO, M.. and Cho, D. H., Paper presented at the Eleventh Annual, EPRI Conference on Clean Liquid and Solid Fuels, May 5-9, 1986, Palo Alto, CA.

Mehta, S.. Simmons, G. W.. Klier. K., and Herman. R. G., J. Catal., 57, 339(1979).

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RECEIVED: July 31, 1987

ACCEPTED: September 8, 1987

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