ie00053a002

Ind. Eng. Chem. Res. 1991,30, 811-821 811

leged to have been among his colleagues. while an employee of E. I. du Pont de Nemours and Company. He is now Executive Director, American Institute of Chemical Engineers. 345 East 47 Street, New York, NY 10017.

Acknowledgment This tribute has been submitted for publication to In-

dustrial & Engineering Chemistry Research as well 8s to the National Academy of Sciences’ Biographical Memoirs, where it will appear in Vol. 65. The generosity of both organizations in permitting this dual publication is ap- preciated.

Richard E. Emmert received his Ph.D. degree under Dr. Pig- ford’s direction and had many consulting associations in later years

Harold S . Kemp received his.doctorate Ad joined E. I. du Pont de Nemours and Company at about the same time as Robert pigford, For many years they shared an office later, during Prof. Pigford’s academic tenure, continued their professional association on a consulting basis. Dr. Kemp, a former president of AIChE, is now retired and resides at 20 Crestfield Road, Wilmington, DE 19810.

Professors Metzner and Wilke knew Professor Pigford over many decades as a faculty colleague, the former at the University of Delaware and the latter at the University of California at Berkeley.

Catalytic Conversion of Synthesis Gas to Methanol and Other Oxygenated Products

Alvin B. Stiles,* F r a n k Chen, Jef f rey B. Harrison, Xiaodong Hu, David A. S torm, and H. X. Yang Center for Catalytic Science and Technology, Department of Chemical Engineering, The University of Delaware, Newark, Delaware 19716

This paper reports the results obtained in an extended program on the conversion of synthesis gas to methanol and higher alcohols. Modifications were made in the catalyst composition, method of fabrication, promoters, and moderators. Test conditions were also modified as a temperature, pressure, gas composition, space velocity, and production rate. Methane and other hydrocarbon production was held to less than 5% of the CO reacted. Product could be controlled as to the percent of higher alcohols in the anhydrous product to between 0 and 80%, and the identity of the alcohols could be controlled to predominantly ethanol, propanol, or isobutyl alcohol; these factors plus high production rates give the process exceptional commercial appeal. An unexpected result of the effort was observing that substantial percentages of acetaldehyde, propioaldehyde, isobutyraldehyde, and methyl ethyl ketone could be produced, which translates to acetic and propionic acids and methyl tert-butyl ether. As a result of the extensive data, a new alcohols synthesis mechanism is proposed.

The catalytic direction of synthesis gas to specific products is one of the most striking examples of the specificity and directivity of catalysts. One of the most specific reactions for synthesis gas is that of its conversion to methane over a nickel or ruthenium catalyst, the products being essentially 100% methane. The other leg of the specificity spectrum is the conversion of synthesis gas to methanol in over 99% yield and very high production rate (Berkman et al., 1940; Davies et al., 1967; Dodge, 1933; Frolich and Lewis, 1928; Stiles, 1977, 1978; Wentworth and Stiles, 1980; Casey et al., 1974; Hydrocarbon Process., 1969a-c). This is usually performed over a catalyst comprised of copper, zinc, and aluminum or chromium oxides. Between these two extremes are processes whereby synthesis gas can be converted to methanol plus high alcohols and some other oxygenated products (Klier, 1980; Larson, 1936; Morgan and Hardy, 1933; Smith and Anderson, 1983; Sabatier, 1923; Stiles, 1985; Sugier and Freund, 1978, 1981; Courty et al., 1982; Wunder, 1980). Other examples are the conversion of synthesis gas to Fischer-Tropsch products over a promoted iron, cobalt, or ruthenium catalyst (Fischer and Tropsch, 1921; 1923; Mittasch and Schneider, 1913). Other examples are the conversion of synthesis gas to ethylene glycol and to long straight-chain alcohols. The former is conducted with a rhodium catalyst, moderated with a bromine or iodine organic halide. The long straight-chain alcohols are produced at relatively high pressures and low temperatures over a ruthenium catalyst (unpublished Du Pont work)

0888-5885/91/ 2630-081 1$02.50/0

The primary objective of our work has been to economically convert synthesis gas to methanol and specific higher alcohols while simultaneously producing controlled quantities of aldehydes and methyl ethyl ketone (MEK). This research is one of the outstanding examples of cooperation between university and corporate researchers.

The development of a catalyst or a family of catalysts and process conditions has made it potentially possible for the economical, commercial synthesis of methanol and higher alcohols of both specific quantity and identity. The proportion of higher alcohols is such that the mix could be added to gasoline and have it miscible in all proportions and under all temperature conditions. This required that methanol be produced with at least 2090 higher alcohols in the crude product and preferably 30% if this level could be economically and efficiently attained. This objective has been attained, but as is customarily the case, there are incidental discoveries made during the research that make the objective more complex than as originally established. It is noteworthy and reassuring that although the synthesis of alcohols from synthesis gas has been a topic of research for a t least 75 years, there are still many valuable inven- tions to be made. A case in point is that there was no time during the course of this study that an important invention or discovery was not made in a given quarter.

In the description of our research and research results that follow, we will attempt to take the reader along our journey of effort in a manner that should show the step- by-step progress and thought-by-thought development of

0 1991 American Chemical Society

812 Ind. Eng. Chem. Res., Vol. 30, No. 5, 1991

' 2 3 4 5 h

I I -

I . Themregulator 7. Thermocouple 2. -cylinder 8. Electrodes 3. Saturated bicarbonate solution 9. Temperature indicator 4. Water IO. Recorder 5. Mixed metal nitrates solution I I . Switch board 6. Electric stirrer 12. pWmV/ion meten

Figure 1. Coprecipitation apparatus

the research program. We started with two simple primary premises. One was that the most efficient methanol synthesis catalyst available at the time would be the base line of the development. Second, the modifications would be made in this catalyst composition and operating conditions to increase the production of higher alcohols without simultaneously increasing unwanted methanation and other hydrocarbon byproducts.

Establishing the First Benchmark with a Pure MeOH Catalyst

As previously stated, when synthesizing methanol, this reaction can be conducted with such efficiency that nothing other than a product containing 99.5% methanol and 0.5% higher alcohols and aldehydes is produced. Methanation, other hydrocarbons, and dimethyl ether (DME), a frequent scourge of alcohol synthesis catalysis, are completely avoided. This catalyst is well-known in the art of having copper oxide-zinc oxide-aluminum oxide components. The ratio of copper to zinc can be varied very substantially with a ratio of 1:l to 1:6 Zn/Cu being favored. The amount of aluminum oxide can also be varied but is usually on the order of 10-20% of the total mixed oxides. The precipitation conditions and the precipitant may be varied, but usually precipitation is conducted at temperatures in the range 25-35 "C using sodium bicarbonate as a precipitant and eventually ion exchanging the sodium out of the calcined precipitate by resuspending the calcined sodium- contaminated catalyst in an ammonium bicarbonate solution (Barnes et al., 1975; Davies et al., 1967). It is generally known that sodium is a severe depressant for methanol synthesis activity and also modifies the mechanism of alcohol synthesis.

The most obvious and fruitful start for the research and development was considered to be to prepare first a highly specific and high productivity methanol synthesis catalyst. This was done following the general procedure given above. The precipitation was conducted at 35 "C. (The precipitation equipment is shown in Figure 1.) The copper, zinc, and aluminum salts were as nitrates; the concentration of the solution was approximately 1 M. The ratio of copper to zinc was 4:1, and aluminum nitrate was added in a quantity adequate to give 20% aluminum oxide in the finished catalyst. Carbon dioxide was sparged through the slurry at all times of precipitation and for 1 h after the completion of the precipitation. The reason for this is that there is evidence that the copper and zinc oxides are most active and specific when they result from the decomposition of a basic carbonate as high as possible in COS ratio.

1

1. Diaphram Compressor 1. Needle Valves 2. Rotameter 8. PunRcr 3. Flow Regulator 9. Pressure Gauge

IO. Reactor Assembly 4. Check Valve 11 . Liquid Receiver 5. Punfier

6. Hcat Exchanger I?. Back-Prrssure Regulator '>. Valco 6-pon Valve

Figure 2. Synthesis unit of alcohols.

Under normal precipitation conditions of elevated temperature and without the C02 addition, the ratio of carbonate to hydroxide in the precipitate is about 1:l. With the COz addition, it is slightly above this.

The precipitate obtained above was filtered, washed, dried, and eventually calcined at 350-400 "C. It was then pulverized and suspended in a 0.1% ammonium-bicarbonate solution to ion exchange the sodium from the precipitate. After sodium ion removal, the catalyst was dried and formed into pellets on a pharmaceutical-type pilling machine. For the laboratory test, these pellets were crushed and screened to 8-14 mesh for use in the test reactor.

After careful reduction at 250 "C, the catalyst was tested at 1200 psi using a gas comprised of 88% hydrogen, 6% C02, and 6% carbon monoxide in the equipment shown in Figures 2 and 3. Space velocity was 40000 (volumes/h)/volume of catalyst a t STP. Under these conditions, the product volume was produced equivalent to 6 (mL of methanol/h)/mL of catalyst in the reactor (equivalent to the productivity in a commercial operation of 6 (tons/day of methanol)/ft3 of catalyst bed).

For further base-line establishment, a commercial methanol plant produces at a rate of approximately 0.75 (ton/day)/ft3 of catalyst volume. Some plant operations are in the range of 0.5 ton/ft3, whereas other installations may obtain approximately 1 (ton/day)/ft3 of catalyst bed (Wentworth and Stiles, 1980). The objective is to produce as much as possible per unit volume of reactor, but because the exotherm in methanol synthesis is very high, the heat dissipation becomes a severe problem when production is higher than 1 (ton/day)/ft3 of catalyst bed. The heat dissipation requirements are even greater when higher alcohols are produced. They become unmanageable when there is a substantial amount of methanation, and this is one reason why methanation must be avoided. If it is initiated in the reaction evnironment, the exotherm is so great that it overloads the heat-exchange system and a runaway reaction with severe consequences can occur.

When the catalyst previously described was evaluated in the laboratory-scale reactor and a production rate of 6 (mL of CH30H/mL catalyst)/h was obtained, no dimethyl ether or methanation could be detected. Higher alcohols were less than of 1% of the crude product.

The First Steps in the Development of a Catalyst of Higher Alcohols

A stock lot of the catalyst previously described as a pure methanol synthesis catalyst was prepared for evaluation in the test unit. It is common knowledge that alkalies will radically modify and moderate a catalyst of copper ox-

Ind. Eng. Chem. Res., Vol. 30, No. 5, 1991 813

4" 4 -

Table I. Comparison of K. Rb, and Cs and Their Effect on the Fraction of Higher Alcohols and Methanationa feed gas CHI prod, (mL anhyd

comp HA selectivity ,d alcohols/mL T, "C P, psi CO H2 fractionb % catal.) / h SV,E km/h

4% K 400 2500 40 60 66.2 11.1 1.61 40 4% Rb 400 2500 40 60 48.2 6.3 1.62 40 4% cs 400 2500 40 60 30.0 5.8 1.67 40 2% Cs, 2% K 400 2500 40 60 46.3 5.9 1.60 40

'Cu/Zn/Mn/Co/Cr = 4/1/3/0.025/0.30. *HA = higher alcohols. cSpace velocity. dAs % of CO reacted.

5 / 0 "

4 1/16'

1 2 25"

a B

I

Figure 3. Reactor assembly and catalyst cartridge details.

ide-zinc oxide-aluminum oxide composition. Conse- quently, approximately 1 % ptassium carbonate was impregnated into the first sample and 1% rubidium carbonate into the second sample, and 1% cesium carbonate was coated onto the third sample of the methanol synthesis catalyst. When these samples were evaluated, it was evident that the catalyst was very sharply reduced in activity. Furthermore, it was necessary to raise the temperature in order for any reaction at all to take place. As the temperature was gradually raised, the productivity increased but was always sharply below 6 mL/mL of catalyst as previously reported for the catalyst producing pure methanol. Usually the productivity was less than 1 (mL/mL of catalyst)/h, which of course dropped the

productivity below the level required for a commercial plant. However, as the temperature was raised, productivity was increased and two other factors emerged. The first effect was that the quantity of total alcohols was increased and also the proportion of higher alcohols in the crude was increased. A second and very undesirable effect was that methanation began to appear as a significant product of the reaction.

When the pressure and temperature had been optimized for these catalysts, the higher alcohol content was approximately 8% of the crude with potash as the moderator, 5 % with rubidium, and approximately 3% with cesium (see Table I). The methanation characteristics of the three alkalies were just the reverse, with cesium producing approximately 2 % methanation and the potassium approximately 5 % . It is evident that the addition of alkalies had a profound effect on the catalytic performance of a so- called high-performance methanol synthesis catalyst.

Before leaving the discussion of the copper oxide-zinc oxidealuminum oxide catalyst, it is well to point out that, in establishing the preferred ratio of copper to zinc, catalysts have been made approaching zero zinc and eventually zero zinc being one of the fabrications. The s i g nificant fact is that as one exceeds a 6:l ratio of copper to zinc, the activity drops sharply and when one prepares a copper oxide-aluminum oxide catalyst alone, it has essentially no activity for methanol synthesis. When one is determining the mechanism and surface effects of the methanol synthesis catalyst, this fact should be borne in mind and certainly indicates a strong influence of the zinc oxide and copper oxide on each other. Zinc chromite, on the other hand, is the catalyst used in the older high- temperature (400 "C) high-pressure (5000 psi) operations and is an acceptable catalyst under these conditions.

Step Two in the Development It has been known for decades that manganese is an

effective higher alcohol catalyst (Gresham, 1952). A t one time, a manganese chromite was used commercially to convert synthesis gas to higher alcohols and methanol, with the fraction of higher alcohols being approximately 33 % of the product of crude alcohols. It is also a historical fact that this catalyst required operation at extremely high pressures approaching 15 000 psi and produced large quantities of methane approaching 12%. Furthermore, some of the higher alcohols were almost like waxes and tended to remain on the catalyst and produce a deactivating quantity of carbonaceous deposit.

It was obvious from these historical facts that if manganese were to be added as a promoter for higher alcohols, the quantity should be kept to a relatively low level. Also it was not known what the effect of the copper and zinc combined with the manganese might have. The first step was to include manganese as 1 mol in a composition comprised of 2 mol of copper and 2 mol of zinc. The effect of manganese and the relationship between zinc, manganese, and copper was the subject of a substantial amount of our effort, with the final answer being that manganese


Table 11. Effect of Pressure on Productivity and Fraction of Higher Alcohols of Anhydrous Crude

feed gas CHI 70 anhyd prod, (mL anhyd

P, T, camp selectivity," HA in alcohols/mL psi OC CO H2 % crudeb catal.) /h

1500 400 40 60 15.5 35.0 0.8 2500 400 40 60 8.4 25.3 1.5 3750 400 40 60 4.0 14.1 2.9

"As % of CO reacted. bHA = higher alcohols.

has a deactivating effect in addition to its promoter action for higher alcohols. In fact, it seemed almost without exception that anything that increased higher alcohol production also decreased the total productivity of the catalyst.

At this time, the catalyst composition was standardized on 2 atoms of Cu:2 atoms of Zn:2 atoms of Mn, with the aluminum oxide being present at a constant 20% of the total weight. With this catalyst composition operating in a temperature range of 375-400 "C and at a pressure of 1200 (which was eventually increased to 2500 psi for an extended period of research), the higher alcohol fraction approached 20%.

Of these higher alcohols, the C2 fraction was approximately 2%, the C3 fraction (n-propanol) was approximately 1370, and the isobutyl alcohol fraction was approximately 5%. There was little or no alcohol above butanols. Since we had already learned that alkalies had a profound effect on methanation, higher alcohols production, and total productivity, we examined cesium, rubidium, and potassium in the levels of from 1% to 10% as carbonates. The maximum higher alcohols were produced with 10% potassium carbonate as moderator, but under these conditions, the productivity was less than commercially acceptable and methanation was on the order of 15-2070. A much more efficient reaction was obtained with cesium and rubidium or cesium and potassium or rubidium and potassium mixtures, but still the methanation was unacceptable and the productivity was intolerably low.

I t was previously mentioned that the pressure was increased from 1200 to 2500 psi. The effect was very significant in that the productivity increased to a very high level of approximately 2 (mL/mL of catalyst)/h. Sur- prisingly, the kinetics were such that the total quantity of higher alcohols produced was essentially the same as at the lower pressure, but the methanol production had sharply increased with the result that the percentage fraction of higher alcohols had dropped now to approximately 10%. (See Table 11.) Because of the high productivity of total alcohols a t the 2500-3500 psi pressure level, it was decided to standardize, a t least for the time being, a t the 2500 psi level and to learn how to increase the higher alcohol fraction.

Cobalt as an Additive to the Catalyst Composition Our attention at this time was called to publicity relating

to an invention at the French Petroleum Institute in which substantial quantities of cobalt were added to the composition normally producing methanol. Patents were is- sued (Sugier and Freund, 1978,1981), and this gave us an opportunity to examine cited examples. The requirement that became evident was that it was absolutely necessary to operate this catalyst at low temperature, lower than the temperature that we had been using for the high alcohols in our composition. We attempted, as a matter of fact, to raise the temperature to a point where additional productivity was obtained, but we encountered a runaway re-

action fusing the catalyst in the reactor. However, the product during a period of relative stability of the reaction did contain an unusual amount of ethanol. It became evident that the addition of cobalt in tolerable quantities might give us a catalyst that had the capability of producing ethanol, as well as propanol and isobutyl alcohol. Previous catalysts, which we had examined, those containing manganese for example, produced little or no ethanol, and it was not until the cobalt information became available to us that convincing evidence was available in- dicating that ethanol could be produced in relatively large quantities. Such information was of considerable interest to us; however, we soon learned that a commercial catalyst of the type described in the patent could not be made and operated in a plant reactor without substantial risk of severe damage or even converter meltdown (Mullen and Wigg, 1975).

Utilizing prior data, it was reasoned that a small amount of cobalt with a relatively large amount of alkaline moderator would make a catalyst having characteristics in which the higher alcohol productivity and particularly ethanol were increased. Although the patent referred to cobalt contents in the 5-5070 range, catalysts with even the low range of cobalt produced a catalyst that was un- controllable even with large quantities of alkali. As a consequence, we decreased the amount of cobalt very substantially to the point where instead of having 5-50% we had from 0.01 70 to 2.0%. It then became necessary to again optimize all ingredients in the catalyst. As a result of this optimization, the copper atomic ratio was set at 4, manganese at 3, zinc at 1, and cobalt at 0.025. All of these exploratory catalysts at this time contained 20% coprecipitated aluminum oxide.

We had noted that in earlier evaluations when we sub- stituted chromium oxide for aluminum oxide there was a tendency for an increased production of higher alcohols. Pursuing this observation, we gradually removed, the alumina and replaced it with 20% chromium oxide from chromium nitrate. It is imperative that one carefully note the fact that the chromium oxide was from chromium nitrate and not from chromic acid, an anhydride in which the valence of the chromium is 6. The significance of the difference in sources of chromium is that with chromium- (3+) the tendency for the formation of a spinel with copper and zinc is much less than with the chromium in the hexavalent state. In the hexavalent state, the chromium will form a basic copper and zinc chromate that on decomposition forms the spinel. With the chromium oxide being derived from chromium nitrate, it is necessary for a solid-state reaction to take place, and this requires substantially higher temperatures than are reached in the processing of the catalyst. We will not dwell further on the effect of the chromium oxide from two different sources, except to say that there is a very significant difference between the catalysts produced from the two sources of chromium.

Alkaline Earths as Added Ingredients The exploratory alkaline-earth ingredients that we have

and will be considering either may be incorporated as new ingredients with basic copper, zinc, manganese, cobalt, and chromium or may be substitutes for the stabilizer that is identified at the present as either or both chromia and alumina. As we have seen, the chromium, though a stabilizer, is also a catalytically active ingredient. With regard to the alkaline earths, they are also considered to be stabilizers. In most cases, when they were added, there was a simultaneous decrease in the amount of alumina or chromia in the catalyst composition. As an example, when

Ind. Eng. Chem. Res., Vol. 30, No. 5 , 1991 815

Table 111. Effects of Added Ingredients" effect on

added shift in HA ingredient quantity, 5% productivity methanation HA ratiob components remarks Ca Sr Ba Ce La Nd mixed La Si02 TiOz ZrO,

5 5 5 5 5 5 5 5 5 5

none none increase none decrease none none none none increase

none none increase increase little little slight increase increase increase increase

none little increase increase little slight increase slight increase decrease decrease increase

little change more C3-C4 more C3-C4 no change no change no change little change more Cz's and C3's more aldehyde more aldehyde

increased DME some increased DME and aldehyde

"All are added as nitrate salts except SiOz and TiOZ, which are derived from colloidal silicia (colloidal SiOl derived from Ludox, a Du Pont product and trademark) and Tyzor (Tyzor, the source of the TiOz, is a lactic acid ester of TiOz which hydrolyzes to Ti(OH)4 in water). Effects of each of the above can be moderated (tailored) bv alkali carbonate, catalyst preparation conditions, and changes in other ingre- . - dients. HA = higher alcohols.

barium carbonate was used as an ingredient, the quantity was approximately 5% of the total weight of the catalytic material, whereas the chromium, if it were retained in the same quantity previously added, would have been 20%. However, the barium replaced 5% of the chromium so that the stabilizer quantity remained identical at 20% of which 15% was chromium and 5% was barium. In our exami- nation of alkaline earths, this was a quantity that was adequate for qualification of the effects.

Briefly, the alkaline earths were catalytically relatively inert, with barium carbonate being the only one that appeared to have any significant effect. Calcium, magnesium and strontium as coprecipitated carbonates had little de- tectable catalytic effect. However, magnesium carbonate is probably one of the best stabilizers, permitting high- temperature operation with little or no adverse thermal deactivation. In summary, the alkaline earths are basically inert and basically good stabilizers, assuring high thermal stability. Barium carbonate has a significant effect on the ratio of higher alcohol production and in the shifting of the higher alcohols toward the high end of the spectrum, that is, butanols and higher alcohols.

Effect of Lanthanides Cerium, lanthanum, and neodymium were evaluated

individually, and mixed lanthanides were also used as a single component. The mixed lanthanides are a run-of- mine product available through the primary producers but having variable composition because of the type of mineral being processed. Furthermore, some specific lanthanides may be removed because of market conditions favoring their removal and sale as individual products.

A summary of the effect of lanthanides is basically that cerium oxide has a significant effect on the production of higher alcohols but a t the expense of a strong tendency toward increased methanation. The logical next step was to attempt control of the methanation by using the alkali carbonates as moderators. The best results were experienced generally with a mixture totaling 4-6'70 potassium and cesium carbonates.

Returning to the lanthanides, it should be pointed out that cerium appears to have a beneficial effect on the stability of the catalyst toward high-temperature deactivation and also resistance to halide and sulfide poisoning. This is an observation rather than a conclusion. A second observation, however, is that a catalyst that is to be operated primarily as a methanol catalyst a t low temperatures and relatively low pressures also will be more apt to beneficially utilize the ceria when added as a minor component. In other words, when operating at low temperatures and pressures, cerium is a beneficial constituent

particularly when the crude alcohol comprises only 10% higher alcohols.

Silica, Titania, and Zirconia as Ingredients A brief summary of these three refractory oxides is as

follows. Silica as a component replacing alumina or chromia completely alters the composition of the oxygenated products. As might be expected, it has a very strong dehydration tendency and increases the dimethyl ether very substantially. For example, at elevated temperatures of 400-425 "C, as much as 10% dimethyl ether may be produced. Ordinarily, there is little or no market for the dimethyl ether; however, if there would be adequate market (for instance the conversion of the DME to gasoline or the use of the DME as a propellant in spray cans), then this would be good information to exploit.

Titania at low temperatures (that is, 230-270 "C) appears to behave only as a stabilizer. At higher temperatures, evidently there is a partial reduction of the titania with the result that it enters into the reaction but not beneficially. In contrast, zirconia tends to increase the fraction of higher alcohols when operated at high temperatures, but it also has a strong tendency to increase methanation. This could possibly be controlled by the amount and type of alkali, but there appeared to be no beneficial effect of the zirconia, which justified an extended investigation of this factor.

The catalytic effects imparted by alkaline earths, lanthanides, and the SiOz, TiOz, and ZrOz family are tabu- lated in Table 111.

Effect of Changes in Pressure The pressure of the reaction was investigated at levels

of 1200,1500,2000,2500,3500, and 4500 psi. The evidence we gathered under these pressure differences indicated that the best operating pressure for the synthesis of methanol and higher alcohols in the 20-3070 range was 2500-3500 psi. Because it is more economical to compress only to 2500 psi, most of our tests were made at this pressure. It was under these conditions that high productivity (that is, 2 (mL of alcohol/mL of catalyst)/h), low methanation (less than 5% of the reacting carbon monoxide), and controllable distribution of the higher alcohols was obtained. There has been a brief description of the effect of pressure and that will be repeated briefly as follows. When seeking higher alcohols, the pressures in the range 1200-1500 psi have the dual effects of giving unacceptable low productivity and unnecessarily high ratio of higher alcohols. The foregoing implies that a catalyst developed for 2500 psi operation must be varied in com-


1 1

0.2 -I \ \

0.c 0 100 200 300 40 0 500

Temperature (OC)

1

o'2 1 H2/CO = 2 \

c

I H2'cc \ I atm

0 IO0 200 300 400 500

Temperature ( O C )

l 2 1 a.. I 200 I." I

O 2 1 H2/CO=2 \ 0.0 , I I I I I I I

0 IO0 200 300 400 500

Temperature (OC)

Figure 4. (a, top left) Methanol equilibrium at Hz/CO of 2. (b, top right) ethanol equilibrium at Hz/CO of 2. (c, bottom left) propanol equilibrium at H2/C0 of 2. (d, bottom right) Iso-butyl alcohol equilibrium at H,/CO of 2.

position to be suitable for 1200-1500 psi operation. Con- sequently, it becomes necessary, when varying from one pressure to another, for the composition to be altered to accommodate the catalyst to the operating conditions and the desired product distribution.

A general rule also is that, as the pressure is increased, the kinetics are such that the higher alcohols are not simultaneously increased to the degree that the methanol is (Table 11), and as a consequence, the ratio of higher alcohols is decreased. The productivity, however, and efficiency of the operation (that is, minimization of methanation) are benefited by higher pressure.

It should be reemphasized that the methanol and higher alcohol equilibrium (Figure 4) is favored by low temperature and high pressure so that if one is operating at low pressure then low temperatures must be used. However, it is evident from previous discussions that, when making a high ratio of higher alcohols, productivity may be une- conomically low. Consequently, with the types of catalyst that we have investigated, operating at low pressure and the required lower temperature essentially dictates that the higher alcohol fraction may not exceed 20% if productivity is to be economically acceptable. This probably is as high a fraction as is necessary for blending with gasoline to assure complete miscibility of all ratios of gasoline oxygenates (Most and Longwell, 1975; Mullen and Wigg, 1975; Pasquon and Dente, 1963; Powel, 1975; Flem- ing and Chamberlain; 1975; Ingamells and Lindquist, 1975; Tillman et al., 1975; Barnes et al., 1975). When operating at 2500-4500 psi, the temperature that is favored is in the range 375-440 "C. A catalyst that produces very efficient reaction at the lower temperature appeared to effect very

high methanation at higher temperatures. When this excessive methanation was first encountered,

it was naturally attributed to the catalyst. It was, however, suspected and later shown that the materials of construction of the equipment were really the problem of methanation and not the catalyst itself. This subject will be discussed more completely later in the Effect of Changes in Temperature section. Also when considering the equipment, a warning should be given that higher pressure or higher activity catalysts may produce reaction rate and exothermal heat not removable in existing reaction designs (Pasquon and Dente, 1963).

Effects of Synthesis Gas Composition Initially when we were working primarily with a pure

methanol synthesis catalyst, we used a gas composition of 88% hydrogen, 6% carbon dioxide, and 6% carbon monoxide. It has been shown in previous papers, and we agree, that carbon dioxide is highly beneficial in the gas stream when synthesizing methanol alone over copper oxideainc oxide-aluminum oxide catalyst. However, as we modified our objective from the original intent of producing a high-quality methanol synthesis catalyst and became in- terested in the production of higher alcohols, we observed the following.

In contrast to the beneficial effect of carbon dioxide when synthesizing pure methanol, it is harmful to the higher alcohol ratio, is harmful to methanation, and in general suppresses the overall productivity of the catalyst system. Carbon monoxide can be increased very substantially up to a ratio of 40% CO and 60% hydrogen with beneficial effects not only on the productivity of higher


Table IV. Effect of CO/H2 Ratio and C02 Addition on the Ratio of Higher Alcohol Distribution of Higher Alcohols" feed gas comp, 70 distribution -

CO COz H2 T, "C P,pei SV, km/h MeOH EtOH PrOH i-BuOH C,+ 20 4 76 400 2500 40 68.4 9.4 10.0 9.0 2.4 20 2 78 400 2500 40 70.3 9.0 9.5 8.8 1.6 20 0 80 400 2500 40 64.6 7.1 11.3 11.8 3.1 40 0 60 400 2500 40 47.8 8.5 13.2 20.2 7.6 40 0 60 375 2500 40 79.8 4.8 6.1 6.3 1.04

OCatalyst: Cu:Mn:Zn:CO = 4/3/1/0.025 with 10% CrZOB and 4% K2C03.

alcohols but also toward a higher ratio of propanol and isobutyl alcohol. Our observation in our laboratory-scale reactor was that the optimum CO-hydrogen feed gas was comprised of 40% CO and 60% hydrogen. These data are presented in Table IV.

As one familiar with methanol synthesis would quickly recognize, this is a ratio that present reactors simply can not handle because the reaction would be so exothermal that there would be a serious effect on the catalyst itself and the reactor shell. It should be remembered that, in an actual commercial operation, the CO content of the gas is held generally below 12%. When the carbon monoxide is a t this level, then the amount of reaction is such that equipment can readily be engineered to dissipate that heat. Furthermore, the unreacted hydrogen acts also as a heatsink and prevents the runaway reactions.

Comparison of the Heat Dissipation Problem of Alcohols versus Ammonia Synthesis

The problem of heat dissipation in alcohol synthesis is very different from that in ammonia synthesis, which is self-quenching as the temperature rises. There is no problem with using a stoichiometric 3H2:Nz ratio in ammonia syntheses because the reaction equilibrium is made less favorable as the temperature rises. Furthermore, there is no secondary reaction such as methanation.

In the case of alcohol synthesis, the reaction changes from alcohol synthesis to a methanation synthesis (an entirely different regime), and the methane synthesis is even more exothermal than is the alcohol synthesis. It is evident that temperature control is an extremely important factor and one that is presently in need of engineering attention and innovation (World Bank, 1984).

One can legitimately ask how do the authors expect to handle a gas stream that has never been handled commercially before. The answer is that we believe it could be handled in a tubular reactor with a diluted catalyst bed to reduce the intensity of the reaction and also with a multistage reactor with between-stage cooling (Wentworth and Stiles, 1980). The latter would be a very efficient operation and also permit substantial, valuable heat recovery. Briefly, it is our contention that the benefits of the high ratio of carbon monoxide are such as to justify specially designed equipment permitting its use.

Effect of Changes in Temperature Much of what we would be considering in this section

has already been mentioned previously. A brief reiteration of these factors is as follows. Low temperature favors the equilibrium for both methanol and higher alcohols; however, the kinetics are such that the higher alcohols are most efficiently produced at temperatures above 375 "C in our catalyst system. Methanol can be synthesized very efficiently a t temperatures in the range 220-320 "C, with the lower range being most favored. The tendency for methanation and other hydrocarbon formation increases as the temperature is increased. This is typically true of essentially all catalysts we have examined. However, when

we increased the temperatures, we expected methanation to increase, but in some cases, the increase was much higher than we had anticipated and did not seem to decrease with a modification in the catalyst which should have reduced methanation. It was our observation that some of the electroplating had peeled away, exposing stainless steel surfaces of the reactor. But, if we were operating at low temperatures, no effect was noted.

We had some inkling that much of the methanation was caused by the gas contacting some exposed walls of the reactor and some of the inlet lines. All surfaces reaching temperatures above 250 "C were changed to copper bronze except for the reactor into which a thin-walled copper tube was "shrink fitted". At the conclusion of these changes, the synthesis gases did not contact any surfaces except those of pure copper or copper bronze. The catalyst cartridge was fabricated from Type A brass. Two very de- sirable results were experienced. First was that methanation was sharply reduced and second was that the higher alcohol level was restored to that which had been experienced prior to the changes in the reactor and inlet and exit gas lines.

The very obvious lesson is that in the synthesis of higher alcohols, which requires temperatures 60-100 "C higher than for methanol, the reactor and any other hot exposed surfaces must be fabricated from copper, brass, copper bronze, or galvanized iron.

Equipment Used in the Catalyst Evaluations This is not typically the place where authors describe

the equipment that has been used in the program, but in this particular study, this sequence is appropriate, now that we have talked about the inadvisability of using stainless steel in the reactor itself. The equipment is shown in diagram form in Figure 2 and comprises sources of hydrogen, carbon monoxide, and carbon dioxide all from high-pressure cylinders. The cylinder gas pressure is reduced by typical diaphragm valves and then the gases are passed to rotameters, except for carbon monoxide which is first heated to 250 "C and passed at this temperature over granular y-alumina impregnated with approximately 15% sodium or potassium carbonate. The offending carbonyls, which are most likely iron or nickel, are de- composed and the resultant carbon and metal deposited on the alkalyzed alumina. This alumina must be changed frequently, for example, after passing gas equal to approximately 10 0oO volumes of the alkalyzed alumina. On removal from the purifier, the alkalyzed alumina generally is black and heavily coated with a sootlike carbonaceous deposit. The gases have now all passed through rotameters and then all pass through Brooks control valves that are supplementary to the rotameters. One gives a reassuring visual readout whereas the other is a digital, electronic readout as well as a control. After metering, the gases are combined and passed through a diaphragm compressor that increases the pressure from approximately 15 psi to the desired pressure. It is a multistage and is capable of raising the pressure as high as 5000 psi. The compressed


gases are now passed through a second purifier similar to the original one used for the purification of the carbon monoxide. This also is operated at 250 "C and is charged with y-alumina impregnated with approximately 15% either sodium or potassium carbonate. After passing through this purifier, the gases pass into the catalytic converter, which is a drilled out 2-in.-diameter stainless steel bar with a thin-walled copper tube shrink fit lining and bronze copper lead-in and exit lines. An exterior thermocouple reads the heater temperature, and an interior thermocouple measures the reaction temperature. A brass cartridge is inserted into the reactor, and this cartridge is built in such a manner that it holds approximately 10 mL of granular catalyst and a thermocouple well can be inserted down through the interior of the cartridge (Figure 3). The reactor is designed for pressures to 5000 psi and temperatures to 500 "C. These values are both above those that have been a part of our research program.

The synthesized alcohols and unreacted gases pass out of the converter into a condenser cooled with chilled water and into a receiving vessel where the liquid is collected and volume measured after a given period of time, generally 20-60 min. The condensate is analyzed for alcohols, other oxygenates, and hydrocarbons.

The gas then passes through a Grove regulating and let-down valve that controls the pressure to within 10 psi of the value to be used. After passing through the control valve, the gases are sampled and are then exhausted. The samples are analyzed to determine the carbon dioxide, carbon monoxide, hydrogen, methane, and other ingredients that might be present.

The equipment has been very reliable and has permitted the successive testing of a given type of catalyst with ac- curacy of 1-270. The equipment is essentially as originally designed with the exception of the previously described change in the inlet and exit gas lines and in the use of a copper insert rather than electrolytically deposited copper interior. A second change that should be noted by anyone intending to use high-pressure equipment is that originally the reactors were built with threaded closures. This is very clumsy and introduces many annoying problems. The reactors were redesigned and rebuilt with the top gasketed and held in place with capbolts. Since those changes, the equipment has functioned very reliably and leaks have been infrequent and minor. The equipment was fabricated by Pressure Products Company according to our design.

Changing the Distribution of Alcohols in the Higher Alcohol Fraction

If the crude alcohol is always to be used as an additive to gasoline for the purposes of giving better octane rating and permitting the use of more efficient higher compres- sion engines, then there would be little or no incentive to control the identity and quality of alcohols in the higher alcohol fraction. However, it is entirely possible that uses will be found for these alcohols in pure form for chemical application. For example, n-propanol has been evaluated as a source of three carbon molecules in the synthesis of acrolein and acrylonitrile. In work done several years ago, it was observed that the alcohol gave a higher yield of acrylonitrile than did propylene. An explanation was that the dehydration of the alcohol was endothermal, tending to make more nearly isothermal the acrylonitrile reaction. This; of course, is not at present a commercial process, but it has a potential for commercialization particularly when large quantities of alcohols are made. Isobutyl alcohol has a number of different outlets, for tert-butylamine, for example, or an isomer thereof, and it also can be dehydrated to form isobutene, which has many valuable ap-

plications. The ethanol fraction also could be dehydrated to ethylene, which also is a huge volume raw material.

At this point, it is well to recognize that when one speaks of large volumes of alcohols such as we are speaking of, one must be seeking sources of carbon other than above-ground petroleum or natural gas. This naturally means using coal or petroleum from wells that are termed exhausted simply because we do not know how to obtain the 60% or 80% heavier oil remaining therein. This raises two subjects that the authors feel are presently not receiving much research attention but deserve to receive much more. These are, first, the conversion of coal to CO and hydrogen by new and efficient processes and, second, the recovery of the petroleum as such or as synthesis gas from so-called ex- haust wells. Both of these research programs deserve research attention more than the perfunctory and unin- spired research that they have received to date (World Bank, 1984).

Now we identify those factors that can be changed in order to increase the ratio of specific alcohols in the higher alcohols. The fact that cobalt increases the ethanol content of the crude has already been mentioned. The ethanol content can be brought up to essentially 100% of the higher alcohols by coingredients with the cobalt and by suitable manipulation of temperature, pressure, and space velocity.

If one wants to increase the propanol and isobutyl alcohol, increasing the manganese level in the catalyst composition is very effective.

In describing the method of preparation of the catalyst, it was stated that the precipitant is ordinarily sodium bicarbonate. However, if potassium bicarbonate is used to replace the sodium bicarbonate, then the resultant catalyst, with all other conditions remaining the same, will produce a crude alcohol very high in ratio of propanol and isobutyl alcohol. Particularly, the isobutyl alcohol ratio has changed.

To increase the propanol a t the expense of the other alcohols, the other ingredients in the catalyst remain the same, but the manganese and chromium are reduced to the degree necessary to achieve the increase in propanol required.

It has previously been stated that increasing the ratio of CO in the hydrogen-C0 feed gas increases the ratio of higher alcohols with respect to the methanol. A further effect of the change in the carbon monoxide level is that propanol and isobutyl alcohol are increased in the spectrum of alcohols.

In addition to the change of the catalyst composition to include more cobalt, the ethanol fraction can also be increased by adding carbon dioxide to the synthesis gas. The quantity of carbon dioxide required is in the range of 0.52%. Larger quantities of carbon dioxide have a very unfavorable effect on the productivity of a given catalyst.

A tabulation of factors affecting the fraction of higher alcohols and altering their distribution is given in Table V.

Effects of Different Precipitation Methods The standard precipitation procedure comprised the

addition of sodium bicarbonate solution to the solution of several metal nitrates. The initial concentration of total ions in solution was roughly 1 mol/L, and the precipitation temperature was 35 "C. With this method of precipitation, there was a heterogeneity in composition of precipitates because of a sequential precipitation of catalyst ingredients at different pHs and time. This heterogeneity proved to be beneficial in some cases where active ingredients were precipitated last and on the surface of already precipitated


Table V. Additional Factors Affecting the Fraction of Higher Alcohols and Their Distribution HA" alcohol

fraction distribution Droductivitv methanation Gbs%utkg Cr for A1 increases none none increases increasing P decreases variable increases decreases increasing SV decreases moves to lighter alcohols increases decreases increasing 7' increases increases heavier alcohols increases to max and then decreases increases addition of Co increases largely EtOH

as an ingredient Cu decreases no effect Mn increases shift to C3+ Zn slight increase none

HA = higher alcohols.

Table VI. Comparison of the Effects of Reverse Precipitation with Normal Coprecipitation

precipitation HA," prod, CHI, catalyst method % (mL/mL)/h %

normal 22.86 0.61 9.8 reverse 20.55 0.81 8.2

BQ BR

" HA = higher alcohols.

particles. However, in other cases where all the ingredients were precipitated at almost the same time or one of the active components was precipitated earlier than other components, variable results were experienced.

As mentioned before, a serious problem with precipitation of the catalyst with Na+ salts is that Na+ is.occluded harmfully. This can be corrected by removing Na+ by ion exchange after calcination, as to be described later.

Several other percipitation methods, including reverse coprecipitation and sequential precipitation, were also employed, and several additional precipitants were used, including sodium carbonate, potassium bicarbonate, and ammonium bicarbonate. In the "Standard" precipitation (normal coprecipitation), the base is added to the solution of metal nitrates initially a t about pH 0.5 and rises to neutrality. In reverse precipitation, the solution of acidic catalytic salts is added to the basic precipitants a t about pH 9 and also ending at neutrality. In a third procedure, the selected catalyst ingredients are added to the acidic solution sequentially with the resultant obtaining homo- geneous precipitates in both crystal morphology and chemical composition.

Table VI shows the results for two catalysts with exactly the same chemical composition (Cu/Zn/Mn/Co/Cr = 4/1/1/0.03/0.62, promoted with 4% Cs) but prepared by different methods. The catalyst coded BQ was prepared by normal coprecipitation whereas that coded BR was prepared by reverse coprecipitation. It is evident that reverse precipitation results in somewhat higher productivity of total alcohols and lower methanation, but it does not affect the selectivity to higher alcohols. This beneficial effect of reverse precipitation can be attributed to the intimacy of contact between copper and zinc when they precipitate simultaneously (in normal precipitation, zinc precipitates after the copper).

The basic idea of sequential precipitation is that a desired distribution of composition along the radius of the catalyst particles can be established by adding the components in a predetermined sequence. In one experiment, the mixed cupric nitrate and zinc nitrate solution was added to the chromium and manganese that were already precipitated. The resultant catalyst produced a larger amount of alcohols than the catalyst prepared with normal coprecipitation but less than that prepared with reverse precipitation.

Precipitation with potassium carbonate (K+ was not ion exchanged from the calcined precipitate) produced some surprising results. Catalysts precipitated with potassium

increases sharply increases decreases increases (with Cu)

sharp increase increases a t high 5" increases no significant change

Table VII. Comparison of Precipitation with NaHCOS and with K2C0," - -

EtOH, PrOH, i-BuOH, prod, Dreciaitant % % % (mL/mL) / h &co3 18 48 34 1.99 NaHCO, 31 57 12 1.69

aPressure, 2500 psi; temperature, 410 OC; feed, CO/Hp 40160; catalyst Cu/Mn/Zn/Co/Cr/K,C03 = 4/41 1/0.03/0.62/4%.

showed an enhancement of total alcohols and a sharp increase in isobutyl alcohol. Table VI1 reveals this trend.

However, the selectivity to higher alcohols over the catalysts prepared with K2C03, precipitant is generally 10-15% lower than that prepared with NaHC03. An explanation of the effect of K2C03 as precipitant is that the K ion occluded in the precipate is intimately in contact with the active components and thus modifies the electronic properties particularly of active sites. The mod- erating effect of the occluded K ion is significantly different from the K2C03 added to the finished catalyst.

Mechanism of Methanol and Higher Alcohol Synthesis

Survey of Reaction Mechanisms. The reaction mechanisms of the synthesis of higher alcohols is intimately associated with the nature of the catalyst and the experimental conditions (Ford, 1971; Hougen et al., 1954; Kobe1 and Tillmetz, 1974; Mananec, 1986; Natta et al., 1955a,b; Smith and Anderson, 1982; Thomas and Portalski, 1958). Consequently, many mechanisms are required to give a satisfactory intrepretation of the product distribution brought about by a complex catalyst system such as ours. The following hypotheses have been proposed to account for the formation of higher alcohols by many researchers employing diverse catalysts.

Fischer and Tropsch (1923) and Fischer (1925) suggested that the chain growth might be carried out by CO insertion and acid decomposition. Natta et al. (1955a,b) proposed a mechanism resembling that of Fischer and Tropsch except that alkali salts were specifically employed to augment the reactions. However, mechanisms suggested by Natta et al., as well as Fischer and Tropsch, do not provide a good explanation for the product distribution of the oxygenates formed. That is, n-PrOH and i-BuOH, rather than the predicted EtOH (from hydrogenation of the carboxylates), were found as the main reaction products.

Storch (1951) postulated that the chain growth proceeds by condensation of hydroxycarbene moities (also known as hydroxymethylene). Again, like the mechanisms of Natta et al., the mechanisms proposed by Storch gave no explanation for the presence of abnormally high fractions of i-BuOH and n-PrOH in the liquid products.

Morgan and Hardy (1933) hypothesized that the higher alcohols (and aldehydes) arose from lower aldehydes by the consecutive reactions of aldol condensation, dehydration, and hydrogenation:


R R R R' \ \ \ / /C=O+ C=O - CHCH -

/ / \ -Hfl H WCHp HO CHO

R R' R' R' \ / +2Ht \ +2H* \ - CHCHO - CHCHpOH

/ / RCH, RCHZ

HO /c = c\cHo

Morgan and Hardy used this mechanism to rationalize the possible pathways for generation of some of the primary C3+ alcohols. However, this mechanism did not ad- dress the formation of surface species on the catalyst and failed to rationalize the formation of ethanol (it is known that the reaction 2HCHO - HCHOzCHO is not feasible under the higher alcohols synthesis conditions) or secondary alcohols (e.g., i-PrOH, 2-BuOH).

Stiles (1977) suggested a mechanism in which the ad- ditions of methylene species to the surface-adsorbed aldehydes (species I-IV) were the key steps for chain growth I. chain initiation

CHp-0 CH, 0 I I + I 1

,4"7 "7

CH3,

C o t + H; - I I - I 11. chain growlh

CHp-0 CHp CHZ - CHp - 0 CH-0 I I + I 1 - I I - I I

"77 " m / m /////////////// I I1

CH-CHp-0 C(CH3)z-0 CH3, CH3, CH-0 CHp I I + I I - I l o l l I

CH-0 CH3CH2 \

CH-CHp-0 CH3 \

I I "77

I - 1 - ///////////////

I V 111. chain termination

CH3CH2 \ CH-0 +2Ht

I I - 1-PrOH hm.+ IV

Stiles also suggested that the reaction site is a lattice- deformity site (a metal suboxide or lattice nonconformity site) rather than a metallic (or crystalline) site. This mechanism was again unable to explain why i-BuOH and n-PrOH are the major reaction products in most of the higher alcohol synthesis processes.

Other mechanisms have been proposed by Frohich and Cryder (1930), Graves (1931), and Negishi (19411, all of whom postulated "direct dehydration" mechanisms in which the condensation of lower alcohols generated the higher alcohols.

Smith and Anderson (1982) elaborated on the dehydration hypothesis by providing a quantitative description of the distribution of higher alcohols. However, this hypothesis is in disagreement with the fact that the formation

CH;OM CH3CHPM 4 CH3CHzCHzOM CH~CHZCHZCHZOM

CHgOH C H j C H P H CHjCHzCH2OH CH3CHzCHzCHzOH

Figure 5. Chain growth mechanism of higher alcohol synthesis. a = methylene group addition, b = hydrogenation to aldehyde and still adsorbed, c = formyl group formation, d = desorption of aldehyde, and e = desorption of alcohol.

of ethanol has never been achieved by the condensation of two molecules of methanol in the heterogeneous system.

Mananec (1986) recently proposed a mechanism in which a stepwise transfer of hydrogens to the coordinated CO and chain growth by CO insertion (into a metal-carbon bond of a surface-bonded aldehyde) provides the primary pathway for the construction of the higher alcohols over the metal oxide catalysts.

A mechanistic interpretation of the current results for the newly developed catalyst system (Cu/Mn/Zn/Co/ Cr/K + Cs) = 4/3/1/0.028/15%/4.0%) is presented as follows. In the product of our catalyst system, a substantial amount of aldehydes (e.g., CH3CH0, CH3CH2CH0, and (CH3)2CHCHO) were always found, while no glycol-type products were detected. A decrease in space velocity, as well as an increase in CO/H2 feed ratio, was found to increase the concentration of aldehydes in the liquid products. The carbon distribution in the liquid products was found not to follow the Anderson-Schulz-Flory distribution law, and relatively high concentrations of i-BuOH and n-PrOH were detected in most liquid products.

Carbon dioxide in the feed gas was found to increase the MeOH production rate and decrease methanation in the MeOH synthesis system, as has been repeatedly reported by others, whereas by contrast as reported herein before, carbon dioxide was found to decrease the production rate of higher alcohols and to increase methanation in the synthesis system of higher alcohols. Methane was detected as the only hydrocarbon produced in most cases of the present study, and its formation rate was increased by C02 and cobalt when both or either were present in the system.

We would like to propose the following mechanism (Hu, 1989) for our catalyst composition, test conditions, and products. This mechanism combines several probable growth pathways, including a- and @-addition of methylene groups to surface-bound aldehydes and condensation of two surface alkoxy species (Figure 5).

Finally, this mechanism predicts that an increase in the CO/H2 ratio would raise the surface concentration of one of the key reactants-the surface formyl species-and thus increase the formation of aldehydes and higher alcohols, in agreement with our results.

Acknowledgment

We express our gratitude to Alberta Gas Chemicals (now Nova Corp.) and Texaco, Inc., for their financial and

.Ind. Eng. Chem. Res., Vol. 30, No. 5, 1991 821

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Received for review February 26, 1990 Revised manuscript received June 7, 1990

Accepted June 22,1990

scientific support and cooperation. As previously stated, we believe this program is an outstanding example of cooperation between industrial enterprises and the academic research community to attain an industrially valuable objective.

Registry No. CH3CH0, 75-07-0; CH3CH2CH0, 123-38-6;

46-2; Cu, 7440-50-8; Zn, 7440-66-6; Mn, 7439-96-5; Co, 7440-48-4; Cr, 7440-47-3; CO, 630-08-0; Ca, 7440-70-2; Sr, 7440-24-6; Ba, 7440-39-3; Ce, 7440-45-1; La, 7439-91-0; Nd, 7440-00-8; Ti02, 13463-67-7; Zr02, 1314-23-4; COz, 124-38-9; NaHC03, 144-55-8; K2C03, 584-08-7; CH30H, 67-56-1; CH&H,OH, 64-17-5; CHS(C-

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