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B.I.O.S. Miscellaneous Report No. 113
Additional Information on Various Catalytic Processes in Western Germany II.

(French, U.S. and British zones)

by
Dr. H. Hoog

Netherlands Military Mission, Technical Research Dept. Ministry of Economical Affairs.

Personnel of Team
A. Broek
P. Dobbelman
H. Hoog
E. Hustinx
J.C.G. de Nood
N.J.C. de Wit

1. Fischer Tropsch synthesis

2. The Formylation Process (Oxo Process)

3. Preparation of hydrogenation catalysts

Contents

Introduction.

For the same reasons as stated in the introduction to BIOS/MISC No. 112 dealing with additional information on catalytic processes in Germany, a trip was made through the French, U.S. and British zones from May 18th - June 5th, 1947 and the information collected is described in this report.

The material has again been arranged according to the processes studied rather than according to the plants or institutes visited.

    Dr. Scheuermann has studied several types of cobalt catalysts but was at present more interested in iron catalysts suitable for the preparation of high proportions of paraffin wax.  The following information was obtained on previous work with cobalt.

    It is possible to prepare catalysts consisting solely of Co.  If such a catalyst is obtained by precipitation followed by drying at 100°C and reduction at 350°C, the cobalt undergoes severe sintering and therefore the final catalyst is inactive.  If the product is reduced at 200°C the catalyst is definitely active, but deteriorates rapidly due to sintering.  It is, however, possible to avoid this collapse of structure by drying the precipitated cobalt carbonate slowly in a moist atmosphere for 24 hours at 110°C.  The final product obtained in this way contains hexagonal Co₃O₄ next to basic cobalt carbonate and the oxide obviously is a stabilizer for lattice disturbancies in the reduced catalyst.

    According to Dr. Scheuermann these disturbancies are generally favoured by slow precipitation and application of a low temperature of precipitation (20°C)    ¹).

    The function of thoria on the one hand is also that of a stabilizer of disturbancies, on the ohter hand that of a promoter.

    Catalysts prepared by the application of the above knowledge consisting of 100 Co, 28 ThO₂ and 200 kieselguhr, which have been reduced at 250°C during 5 - 10 hours, were active at 160°C and yielded a product with 35% of wax (320°C +) if the conventional synthesis gas (2 H₂: 1 CO) and atmospheric pressure were used, whereas with water gas under 12 ats pressure more olefines and branched hydrocarbons were obtained with a total product distribution of

    This type of catalyst had been operated for as long as 4 months without intermediate regeneration.

    Dr. Scheuermann had also investigated the possibility of applying kaolin, alumina and silicagel as a carrier for cobalt catalysts.  Although no outstanding results could be obtained with these materials, he had succeeded in preparing fairly active catalysts.  To this end it had been necessary to give the carrier materials a high temperature pre-treatment in order to make them less reactive towards the cobalt; it serves to modify the pore size distribution, only silica gel with narrow pores proving suitable for the purpose.

    X-ray studies of cobalt catalysts had revealed the presence of hexagonal Co. and of cubic Co in case alkali was present, no Co-carbides or Co-silicates having ever been found in these X-ray studies.

Four types of iron catalysts had been investigated in the Oppau laboratory:

1. Fused oxide catalyst ("Schmelzkontakt")
2. Knead catalyst ("kneukontakt")
3. Sinter catalyst ("Sinterkontakt")
4. Precipitation catalyst ("Fällungskontakt").

a.    Fused oxide catalyst.

    This type of catalyst had been derived from the type conventionally used in the ammonia synthesis, substituting, however, MgO for A1₂O₃.  The catalyst is prepared by blowing oxygen in an iron vessel filled with iron powder, mixed with MgO and an appropriate amount of alkali; the mixture is ignited, melts and finally solidifies.  As soon as solidification starts the pot is tipped over and the obtained product is cooled and subsequently broken into pieces of appropriate size.  Usually 3-4% of MgO was used, this amount being limited by the solubility of MgO in the molten mixture.  The quantity of alkali is partly determinant for the olefinicity of the final product as shown by the following graph:

    It should be noted that in the Ruhrland-Schwarzheide Reichsamt Comparison tests I.G. had participated with this type of catalyst containing some CaF₂, the results of which were not favourable ¹).

    A serious disadvantage of the fused oxide catalyst is its high bulk density.  Since also its preparation is rather elaborate and would require development of the procedure on a large scale, I.G. had abandoned this type.

b.    The knead catalyst

    For some time Dr. Scheuermann had worked on a catalyst prepared by combustion of finely divided iron (obtained through decomposition of iron carbonyl) with oxygen and kneading the iron oxide with a dilute solution of alkali, at the same time adding copper and magnesia and also kieselguhr, if desired.  After drying, the mixture could be shaped by applying grooved mills (compare the device considered by Ruhrchemie for preparing their "Schiffchen-kontakt").

    The representative composition of this type of catalyst was:

 c.    Sinter catalyst.

    If the dried knead catalyst is subjected to igniting at 800°C a denser form of granules is obtained (bulk density 1.5 kg/1).

d.    Precipitation catalyst.

    Dr. Scheuermann at present was studying iron catalysts containing various admixtures.  These products were obtained by slow precipitation with K₂CO₃.  A high activity is obtained by a low temperature of reduction.  Cu is always added in order to make reduction easier and the presence of MgO or A1₂O₃ improves the stability of the structure (maintaining the presence of lattice disturbances).

Representative data:

    The synthesis is carried out with 4 reactors in series, 5 m x 15 mm Ø, each with the gas in down-flow and with intermediate separation of wax between each 2 reactors.  The total space velocity is 400 v/v.h. to the first oven, i.e. 100 v/v.h to the total system.  The total CO-conversion in the system amounts to abt. 70%.  CO and H₂ are used in the ratio 1.0 CO : 0.9 H₂ according to the approximate equation

Another modification of this catalyst type consists of Fe, Cu, K and A1₂O₃, in which case no carrier is used.  The catalyst is active at abt. 200°C yielding somewhat less paraffin wax with a relatively low olefine content; the paraffins, however, are very little branched.

    X-Ray investigation of these iron catalysts has shown that - after use - they always contain iron carbides.  If Cu is present the carbide is definitely stabilized and it was found to be present in a new hexagonal form different from the hexagonal Fe₂C of Hägg.  The formation of this new carbide is connected with the high catalyst activity and it was found that a low reduction temperature (200°C) favours its formation.

    The Kaiser Wilhelm Institut has been working with an iron type precipitation catalyst, obtained from a 1 : 1 FeC1₃ - FeC1₂ solution via carbonate-precipitation at 60-70°C, the final composition being

Magneto-chemical studies had shown that in the used catalyst two modifications of the Fe₂C-carbide must be present, the respective Curie-points being 260°C and 380°C.  The Fe₃C-carbide, Curie-point 210°C, certainly has no significance in connection with the synthesis reaction, and it was even considered doubtful whether any role as an intermediate compound should be assigned to the Fe₂C-carbides; the rate of formation of the carbides is considerably less than that of the synthesis reaction.

    Putting together the information as from I.G.'s X-ray work and KWI's magneto-chemical and re-action velocity studies one would be inclined to conclude that preparation of iron type synthesis catalysts by precipitation with carbonate, ensuring the reduction at a relatively low temperature through the presence of copper, yields active catalysts.  The special structure to which high activity must be ascribed also seems to favour the formation of two different modifications of the Fe₂C-carbide.

2.  Iron catalysts.
Y)	Metallgesellschaft LURGI, Frankfort a/M, May 30th 1947.
		Dr. Royen	1)

    Lurgi have devoted their attention mainly to the precipitation-type of iron catalyst, to which copper and alkali are added for the reasons stated before, whereas A1₂O₃ or ZnO are added in order to improve the stability of the catalyst structure possibly through partial formation of spinels.

    They have shown that the presence of kieselguhr as a carrier yields active catalysts with less of the active material, iron, per unit volume; however, the operational temperature of the carrier-catalyst is somewhat higher.  The effect of copper is to cause the reduction to proceed more smoothly and to yield a slightly more active catalyst.

    The final catalyst is shaped through extrusion.  The following table will show some illustrative figures.

Type No. 1; precipitation with K2CO3:
100Fe	100 Fe	100 Fe
5 Cu	0 Cu	5 Cu
9 A12O3	9 A12O3	9 A12O3
5-9 K2O	5-9 K2O	5-9 K2O
120 Kieselguhr reduction during	120 Kieselguhr 1/2 h at 280°C with	0 Kieselguhr 1000 v/v.h H2
15% free Fe	5% free Fe-rest Fe0m /Fe2O3, Fe3O4
operational temp. 240°C	op. temp. 250°C	op. temp. 220°C

    Kieselguhr may be replaced by active charcoal, in which case, however, the mechanical stability of the obtained catalyst granules is very insufficient.

    The proportion of A1₂O₃ should not be increased over 9 A1₂O₃ per 100 Fe in order to prevent the formation of non-reducible Fe-A1₂O₃ compounds.  With 100 A1₂O₃ per 100 Fe e.g. no reduction of the iron could be effected and the final catalyst showed no activity whatever.

    As to the quantity of K₂O in the finished catalyst it should be noted that this compound must not be present in a concentration of over 10 K₂O per 100 Fe.  If this should be the case, due to insufficient washing out of the material, under medium-pressure conditions (20 ats. operating pressure) so much fatty acid is found that the catalyst is attacked chemically, the iron being converted into a solution of iron fatty acid salts dripping out of the catalyst space ("bleeding" of the catalyst).

    This phenomenon can be prevented by including K₂SiO₃ in the catalyst, which may be done by boiling the kieselguhr for some time with KOH prior to its use, or by impregnating the final catalyst with K₂SiO₃ as such.

    This was the reason for the development of a second type of iron catalysts, in which rather high proportions of alkali may be used:

    Type II; precipitation with KOH and subsequent addition of K₂SiO₃:

100 Fe	100 Fe
5-10 Cu	25 Cu
9 A12O3	18 ZnO
9K2O added as water-glass (10 K2O, 22 SiO2), moreover some 1-3 K2O may be present from the KOH used in the precipitation	9 K2O 24 SiO2
120 Kieselguhr or no carrier at all	120 Kieselguhr or no carrier at all.

    In this catalyst-type SiO₂ is set free from K₂SiO₃ and CO₂ as formed in the synthesis, Some Fe-SiO₂ structure will form during operation, but this will not hamper the synthesis under medium-pressure conditions.

    This type is active at 220°C operation temperature, a pressure of 10-20 ats. and a free iron content 5-20%.

    No major differences were found between the A1₂O₃ and the ZnO containing catalysts; they both yield, if tested in one reaction stage with water gas:

abt. 135 g/ m³ C₃+ on entry gas

abt. 70-75% CO + H₂ converted

abt. 10-16% CO  converted into CH₄ + C₂H₆ (6-10%) and C₂H₄ (4-6%)

As described previously Lurgi have developed a gas circulation process, applying recirculation of rest gas at a relatively low rate (2 : 1 or 3 : 1 cycle gas to fresh water gas).  As the CO₂ formed in the synthesis step is in this way partly fed back to the reaction space, this tends to shift the water gas - equilibrium - occurring by the side of the synthesis proper - to the CO-side:

This ensures that the gas fed to the catalyst is potentially of the appropriate composition as required by iron type catalysts:

even though ordinary water gas of abt. 1 CO + 1.3 H₂ is used as fresh gas.

Whereas all commercial Fischer-Tropsch synthesis plants in Germany have been built according to the conventional Ruhrchemie-type design, the I.G. laboratories have tackled the problem of finding a better way of carrying out the reaction from various angles.  None of the possibilities studied, viz.

1. Michael fixed-bed gas circulation process
2. Michael liquid-phase catalyst-foam process
3. Duftschmid (Winkler) fixed-bed oil circulation process, has, however, found its way into commercial praxis.

    Since an outline of these studies has been given before ¹) reference is made to the relative reports and only some additional information as obtained from Dr. Duftschmid will be reported here.  Moreover, attention is drawn to Dr. Duftschmid's survey of his own work in Addendum No. I.

    In Dr. Duftschmid's "oil circulation process" the Fischer-Tropsch reaction is carried out over a fixed bed of catalyst, the synthesis gas passing up-flow through the reaction space together with a relatively large amount of recycled liquid reaction product.  The main aim of this development was to remove the heat of reaction in large-size catalyst beds, thereby making the use of big single catalyst-space reactors (without any cooling tubes or similar devices) possible.

    The work was started with fused iron catalysts at 270°C and 100 ats. pressure, but although relatively high space time yields were reached this operation was not considered to be a paying proposition in view of the high costs of the high pressure equipment.  When iron catalysts were found to be active at lower temperatures and pressures, the operating pressure was reduced to abt. 20 ats., the same catalyst being used as by Dr. Michael (prepared through de-composition of iron carbonyl).

    The pilot plant used in the later stages of this work consisted of a reactor 6 m x 500 mm Ø, provided with a hot separator for wax and an intermediate separator for middle oil, the latter product being recycled to the entrance of the reactor (Fig. I-1) ¹).

    The temperature distribution in the reactor naturally depends on the amount of cold cycle oil.  It may, however, also be affected by the way of injecting:  if the total amount of cycle oil is introduced at the bottom a temperature distribution curve is obtained as indicated in Fig. I-2, showing a rather steep rise towards the end; if, on the other hand, part of the oil is injected near the top of the catalyst bed a much flatter temperature curve and a smaller total rise in temperature can be reached.  Dr. Duftschmid had actually reduced the temperature rise from 50°C to 20°C at 65% CO conversion by running his plant in the latter way.

    The nature of the cycle oil will also play an important role in the picture:  heavy oil, B.P. > 400°C, will not evaporate and will wherefore act according to its specific heat; light oil, B.P. > 200°C, will partly evaporate in the reactor and consequently much heat will be removed as heat of evaporation.

Dr. Duftschmid would suggest making use of both faculties when designing a large-scale plant and would introduce heavy cycle oil at the bottom of the reactor and inject light oil at various spaces in the catalyst bed as indicated in Fig. I-3.

In order to keep the temperature well in hand at least 60-70 1 of middle oil (200°C +) of room temperature must be recycled to the reactor per kg of reaction product formed and if a heavier oil (400°C+) is used this quantity would rise to a much higher value (150-200 1/kg).

Whereas in the "Hauptlaboratorium" at Ludwigshafen the "Rieselverfahren" (trickle operation) as developed by Dr. Reppe was generally used for carrying out fixed catalyst bed gas-liquid reactions with a large heat of reaction, this system had not been investigated by Dr. Duftschmid.  Model experiments in glass equipment had convinced Dr. Duftschmid that turbulency is so intesive in the reactor as to ensure a very good contact between catalyst, gas and liquid and he therefore did not expect improvement from reversing the flow through the reactor.

    The following figures were given for the Foam process and the oil circulation procedure:

    In the oil circulation process in one stage 50-65% CO may be converted, whereas in two stages (the second being run at a 10-20°C higher temperature) abt. 90% CO-conversion is reached.  The exit gas is composed of

    About the same applies to the Foam process.

    The gasoline must be subjected to a water treatment and further conventional refining; its octane number amounts to 65.

    The middle oil is very suitable for use as a diesel fuel; cetane number 75-80.

II.    The Formylation Process (Oxo-Process)

I. G. Farbenindustrie A. G. (Badische Anilin und Soda Fabrik) Ludwigshafen - Oppau, May 22, 23, 28 and 29, 1947.

Ludwigshafen: Dr. Kurt Schuster

                       Dr. Eilbracht

Oppau          : Dr. Nienburg

A.    Introduction

has been described in some detail by various previous investigators. ¹)  However, so far nothing has been reported on the Oxo-studies as carried out at the Ludwigshafen - and Oppau-laboratories of I.G.  These institutes have no doubt contributed largely to the development of the process from the processing point of view as well as with respect to the clarification of the kinetics of the reaction.  Therefore, the information collected when visiting these I.G. - works will be reported here in detail.

    B.    General considerations

    Whereas Ruhrchemie, the original inventors of the Oxo-reaction, had only carried it out as a batch-reaction and had accordingly designed the commercial plant of the Oxo-Gesellschaft m.b.H. at Holten, I.G. Farben did not consider this as the best possible technical proposition, and had started work on the possibilities for continuous operation at an early date.

    The solution as proposed by I.G. Leuna consisted of passing a slurry of cobalt-on-guhr catalyst in the olefine-feed together with watergas through a series of reactors whereupon the slurry was to be treated with hydrogen in a subsequent series of reactors, first to decompose dissolved carbonyls and next to hydrogenate the aldehydes formed in the first stages, without intermediate separation of catalyst.  Finally, the catalyst was to be recovered from the alcoholic product by filtration.

    On the other hand, I.G. Ludwigshafen followed a completely different course in their researches.  The essential point in their work is the application of the so-called "Rieselverfahren" (trickle-phase-or drip-phase-operation) to the Oxo-process.

    This specific way of carrying out liquid-gas-reactions had been developed at the "Haubtlaboratorium" by Dr. Walther Reppe and his co-workers.  It is characterised by the fact that the liquid feed is charged to the top of a reactor filled with catalyst and flows downward concurrently with the gas feed.  As the catalyst is always covered with a thin layer of liquid, diffusion of gas to the catalyst-surface will be relatively easy, thereby providing a high rate of reaction.  Moreover, high gas velocities may be maintained without risk of "flooding" the column, and this opens the possibility of removing the heat of reaction by the application of a high rate of circulating gas, no other cooling of the reactor being provided for.

    This reaction system has successfully been applied in commercial hydrogenation processes (e.g. in the hydrogenation of "aldol" to "butol" at the Hüls buadieno factory. ¹)

    When applying this technique to the Oxo-reaction it was realized that provisions should be made for replacing the cobalt removed from the solid cobalt catalyst in the reactor in the form of carbonyl in the products to which end cobalt-fatty acid salt was added to the feed in adequate amounts.

    The reaction product from the Oxo-stage was treated with hydrogen in a subsequent reactor, filled with pumice; the carbonyls present in the product were thereby decomposed and the cobalt-metal formed was deposited on the pumice, from which it could be recovered later in a suitable manner.

    Finally, the decobalted product was hydrogenated in a third reaction system.  As no cobalt was present in the feed to the hydrogenation-reactors, any suitable catalyst could be used in this stage.  A copper-chrome-silicagel catalyst, prepared on a commercial scale at Ludwigshafen, was usually applied.

    This general set-up offers a number of advantages over the Leuna operational scheme, viz.:

1. No suspension of solid catalyst in the olefine-feed need be prepared, maintained and pumped, only clear solutions being handled.
2. The filtration of the very small-sized catalyst particles from the final product is eliminated.
3. No provision need be made for building sufficient cooling surface inside the reactors, the heat of reaction being removed by the gas.
4. The hydrogenation can be carried out with catalysts less sensitive to CO than cobalt

    However, the Leuna-system was considered to require considerably less reaction-space than the Ludwigshafen-operation.  Since, on the other hand, feed stocks different both as regards molecular weight and olefine content were used at the two research-centres, the discrepancy in the allowable space-velocities may be partly attributed to this point.  (Dr. Eilbracht).

    At Ludwigshafen the process had been operated on a pilot plant scale by Dr. Schuster and Dr. Eilbracht of the "Hauptlabor".  This plant had been removed to Gendorf in 1944 and had only partly come back after the capitulation.  With the pumps and circulation-compressors missing, it could not be operated.

    At Oppau research work had been carried out by Dr. Nienburg of the "Ammoniaklabor" mainly in small-scale equipment; moreover, a pilot plant had been erected in 1944, which was then damaged by bombing and had not come into operation until recently.

        C.    Information on the processing at Ludwigshafen

    The Ludwigshafen pilot plant consisted of two reactors, each of which was 70 mm Ø and 9 m high, made of N₈-chrome steel and provided with electrical heating.  The first reactor was charged with 25 1 Co-on-pumice (1% Co) catalyst and was used for the formylation-step.  The second reactor was charged with 25 1 pumice and served for decobalting the Oxo-stage product.  This was finally hydrogenated in separate equipment.

    The plant was further equipped with pumps for the olefine-feed, a separate pump for injecting cobalt-fatty acid salt-solution, and with gas circulating compressors.

    The arrangement of the plant, located in Lu #115, is shown in the attached diagram and photos (fig.11-1-4).

    The feed stock generally used at Ludwigshafen was Michael-benzin, the gasoline produced in the Michael-modification of the Fischer-Tropsch-process for which they had a pilot plant in operation.  This feed stock contains about 60-70% of olefines, which are mainly single-branched.  Usually a fraction with 100-150°C boiling range (C₈-C₁₀) was used, but other ranges were also investigated (e.g. 100-200°C corresp. to C₈-C₁₂).

    The cobalt-solution was originally obtained from hexahydrobenzoic acid or from naphthenic acids, but as forerun-fatty acids were readily available and as the latter cobalt salts were better soluble, they were later exclusively used for this purpose.  The salts were obtained by reacting cobalt acetate with the fatty acids at abt. 150°C, distilling off the acetic acid formed under vacuum.

    Ludwigshafen had actually run their reactor once for a total duration of 3 months with many interruptions, the conversion remaining constant all through this period.

    Some confusion exists as to the allowable feed rate to the reactor:  as a representative figure Dr. Schuster stated that the production of alcohols amounted to about 0.35 kg per litre of reaction space ("8 kg Alkohol pro Liter pro Tag"), which figure would correspond to a total feed rate of abt. 0.5 kg/1.h.  However, Dr. Schuster was convinced that a higher rate would be allowable, provided that sufficient gas-circulation is maintained for removing the heat of reaction.

    The pre-treatment of the fixed catlyst used is not critical:  pumice was impregnated with cobaltnitrate and the catalyst was thereupon ignited in order to decompose the nitrate.  It was subsequently reduced with hydrogen, but it is also active without previous reduction.

    As a representative product-composition the following figures were stated:

from 1 kg olefine feed, fraction 100-150°C, olefine content 67%

were obtained:  350 grams forerun paraffin - fraction

                        700   "    Oxo-alcohols c9-C11

were obtained:    110 grams thick oil boiling > 120°C at 10 mm.

The product-distribution therefore is abt. 85% alcohols and 15% thick oil.

    The thick oil contains esters and higher alcohols as well as aldol-type condensation products; however, no ketones were found in the thick oil of this type of feed stock.

    The feed rate in the decobalting step may easily be chosen twice or more times as high as in the Oxo-step.  The pressure is not critical:  good results were obtained at lower pressures (100 ats) as well.  The use of hydrogen seems to be rather essential: with nitrogen a certain decomposition of the cobalt-carbonyl-compounds was reached, but decobalting remained less complete than with hydrogen.  The total amount of cobalt metal to be "stored" in the decobalting reacotr could not be given.  The system had once been in operation continuously for a period of over two months and was then still operating satisfactorily.  This would correspond to a total quantity of about 15 kg Co per 25 1 of pumice.

    The cobalt is not distributed evenly throughout the column, some accumulation taking place near the feed-side.  This can, however, be improved by applying a sufficiently high gas circulation rate and by a proper choice of the temperature distribution.

    It has been proposed to convert the cobalt, accumulated in the decobalter, into a solution of cobalt-tetracarbonyl by feeding Oxo-alchols and carbon monoxide under pressure (as available at Ludwigshafen) to the reactor, after this should have been loaded to capacity.  Dr. Eilbracht, however, does not consider this to be a practical proposition:  as the decobalter can be run for months on end, the cobalt-carbonyl-solution would have to be storable for the same period, and he does not consider this to be feasible.  Accordingly, in Dr. Eilbracht's opinion, the reconversion of the cobalt into the fatty-acid salt is the preferable proposition for the recovery of this material.

    The hydrogenation of the decobalted product has been effected with different catalysts, as e.g. 5% Co on silicagel, 5% Ni on silicagel, N1 on pumice or Cu-Cr on silicagel (B.B.E. catalyst).  The latter was generally used for aldehyde-and ester-hydrogenation and being available from large scale production it was later used exclusively.  Complete hydrogenation could be reached in one pass in a trickle-phase system.  The final product was said to contain only very little aldehyde:

Finally it should be noted that in the early stages of their work Dr. Schuster had used small-scale apparatus in which liquid olefine-feed (obtained from wax-cracking) and water gas were passed up-flow through a catalyst bed.  Although no direct comparisons between this system and the trickle-operation were made, the latter was generally preferred, primarily because of the supposed better contact between gas and liquid and catalyst, but also in view of the small liquid hold-up in the trickle-system.  This will offer a definite advantage in case a reactor should have to be disconnected in a large-scale plant.

    D.    Information on the processing at Oppau #

        1.    Laboratory studies

The small scale equipment as in use at Oppau 140 is shown in the attached flow diagram (fig. II-5) and photograph (fig. II-6).  It consists of 4 reactors, two of which are used for the formylation proper, one is used for decobalting and one for hydrogenating.

All reactors are operated trickle-phase and once-through for liquid and gas.  The total length, 2 meters, is considered by Dr. Nienburg to be the minimum which can be used successfully in trickle-phase operation and a greater length is certainly advisable:  the contact-time in this type of processing is primarily determined by gravity-flow rather than by the throughput applied; in model-experiments carried out in glass equipment with water as the trickling liquid a contact-time of abt. 2 minutes per meter is found, independent to some extent of the throughput.

Dr. Nienburg had studied the formylation of a large number of pure olefines in this equipment (vide next section) during the war.

The following representative data were given for a recent run with cyclohexene as the feed:

In the Oxo-stage 113 cm3/h product (density 0.915) was obtained, yielding through rectification:

In the decobalting stage no aldehydes were found to be hydrogenated, no saturation of unconverted cyclohexene taking place either.

The hydrogenation of the decobalted product yielded a final product, the main distillation-fraction of which was analysed as follows:

Only 30% of the cyclohexene present in the decobalted product proved to be hydrogenated in the hydrogenation stage.

        2.    Splitting hydrogenation of thick oil

The thick oil obtained in the Oxo-process may be converted partially into valuable alcohol by hydrogenation in drip-phase at higher temperatures:

Apparatus        :    laboratory type

Feed                :    thick oil from cyclohexene

Feed rate        :    100 cm³/h

Gas rate         :    2 1/h H₂ off gas

Catalyst           :    B. B. E. 1000 cm³

Pressure          :    200 ats H₂

Temperature    :    280°C

The residue may well contain C₁₄-alcohol.  In the case of cyclohexene-thick oil its constitution was not determined.  With isobutene as the feed, however, a similar residue was analysed to contain C₁₀-alcohol.

                        3.    Semi-scale experiments

In view of the availability of propene from propane-dehydrogenation Oppau started erection of a semi-scale Oxo-plant during the war (Oppau 266).  This plant was damaged by bombing but has since been repaired.  Operations had recently been resumed.  With a view to obtaining products useful for the manufacture of pharmaceutics, the plant is now being run on isobutene as the feed.  As the isobutanol-manufacture was in operation, isobutene could easily be obtained via dehydration of the isobutanol.

Dr. Nienburg intends to run the plant applying a hot separator (the product from which will be the main product) followed by a gas cooler and cold separator, the product collected in which will consist of unconverted isobutene and therefore will be recycled.  Moreover, as during the reaction a voltile cobalt compound obviously is formed, assumed by Dr. Nienburg to be cobalthydrocarbonyl, this cobalt-hydrocarbonyl may be expected to be trapped in the cold catchpot from which it will be recycled to the reaction zone.  This way of operation is expected greatly to reduce the amount of cobalt required to be fed in with the fresh feed to the plant. ¹)  So far, operations had not been successful, as the iso-amyl alcohol formed was not trapped in the hot catchpot but distilled to the cold separator.

The plant consists of one reactor for the formylation proper (being 4.5 m high and having an internal diameter of 91 mm with a 45 mm central displacer, leaving a free annular space of 200 mm).  provided with a jacket for boiling water, the temperature being controlled by the pressure.  The reactor can be operated either drip-phase or "sumpf-phase" and is provided with a gas circulation system.  It is charged with abt. 20 1 of catalyst, consisting of 2% wt. Co on silicagel.

The product from the Oxo-stage will be decobalted, "prehydrogenated" as it is called in Oppau, in either one of two decobalting ovens, 3, 5 m high and 45 mm wide, provided with electric heating and filled with pumice (7 litres).  No provisions for recirculation of gas have been made.

Finally, the decobalted product will be hydrogenated in a reactor of similar size as the Oxo-reactor.  It is, however, not fitted with a constant temperature jacket but is heated electrically.  The gas system is for once-through operation.

For the sake of completeness reference is made to the attached flow scheme and pictures of the plant (fig. II-7 -9).

Oppau intend to run the installation at a feed rate of 10 1/h isobutene, a solution of 2% wt.  Co (fatty acid salt) in butanol being added to the feed.  The life of the solid catalyst in the Oxo-stage is expected to be very long, as the small-scale reactors have been run for several months without decline of conversion.

            E.    Kinetics of the Oxo-reaction in relation to the constitution of the alcohols formed.

During the years 1940-1944 Dr. Nienburg carried out considerable research concerning the constitution of the Oxo-alcohols obtainable from various types of olefines.  A brief survey of the results was drawn up after the war and is attached to this report (vide addendum II).

In the case of n.cetene the C₁₇-alcohols formed were analysed to consist for

50% of n.C₁₇-alcohol,

20% of d-methyl C₁₆-alcohol

and 30% of d-ethyl-, propyl-, etc. alcohols.

This finding is in perfect agreement with the results of Leuna where Asinger and Berg could prove that the formylation is always accompanied by a simultaneous shift of the double bond.  This isomerisation is catalysed by Co-carbonyl.

A number of branched-chain olefines (iso-butylene, 2-methyl-butene-2, 2.3-dimethyl-butene-2, 2.4-dimethyl-pentene-2 and di-iso-butylene) were subjected to the Oxo-reaction with the aim of obtaining alcohols with highly branched chains which subsequently might be converted into paraffin hydrocarbons suitable for high octaine-number gasoline.  These attempts failed completely:  in no case a quarternary or adjacent tertiary structure was formed, a shift of the double bond always preceding the formylation proper.

However, Dr. Nienburg had studied another possibility for preparing high octane paraffins which looked very promising:  rather than adding CO and H₂ to the di-olefinic double bond, formaldehyde was made to react with the olefine at atmospheric pressure and about 80°C with 1% H₂SO₄ and water as the catalyst to form 1.3-dioxane compounds.  By subsequent hydrogenation of these compounds methanol was split off and a primary alcohol was obtained.  By this procedure the higher branched structure was always obtained (e.g. 2.3-dimethyl-butene-2 yielded 2.2.3-trimethyl-butanol-1 from which 2.2.3-trimethylpentane, triptane, was obtained.

It was also possible to decompose the dioxane over a phosphoric acid catalyst which resulted in water and formaldehyde being split off and a conjugated di-olefine being formed.

Whereas oxygen containing unsaturated compounds as allyl alcohol and acrylic osters definitely reacted with carbon oxide and hydrogen, no clearcut products were formed possibly due to concomitant polymerization reactions.

It was found possible to carry out the Oxo-synthesis with a mixture of ammonia and CO rather than with synthesis gas.  In this case the corresponding amides were obtained.

In connection with the above-reported kinetic results it may be of interest to note that Dr. Nienburg had also experienced great differenced in reaction-velocity in some cases:  whereas isobuylene reacted smoothly and at a high rate, the formylation of di-and tri-iso-butylene was rather slow.  However, with sufficient contact time any olefine could be converted practically completely.

            F.    Various applications of Oxo-alcohols

                1.    General information

According to Dr. Schuster Oxo-alcohols have been applied or have been considered as base materials for the following purposes:

    a.    Higher molecular alcohols from mainly straight chain olefines have been used successfully for the preparation of sulphonate detergents.  This type of products was mainly prepared and investigated in connection with the work of Leuna.  As stated in Dr. Nienburg's report, Oppau had investigated the possibility of applying the Oxo-alcohol from tri-isobutylene, which was not found suitable for this purpose.

        b.    Oxo-alcohols from the lower olefines have been found to be suitable as base materials for the preparation of phthalates to be used as placticizers.  This point was discussed in some detail with Dr. Kling of the Plastic Department (vide 2).

        c.    Various Oxo-alcohols as well as the corresponding aldehydes and acetates (especially those of terpenes) offer possibilities for application in the perfume industry.  For this purpose the aldehydes may be recovered from the non-hydrogenated Oxo-product via the bisulphite compound; they may also be obtained by dehydrogenation of the alcohols over copper catalysts.  Dr. Schuster had favourable experience with the Ludwigshafen B.B.E. contact for this conversion.

            d.    When reacted with acetylene in the presence of alkali, the Oxo-alcohols yield vinyl ethers, which have been applied successfully as components of polumerization feed stocks:

            e.    In special cases available olefines may be converted into alcohols useful in the pharmaceutic industry (e.g. iso-butylene as base stock for iso-amyl alcohol).

                    2.    Application of Oxo-alcohols for the preparation of placticizers

Verious batches of Oxo-alcohols prepared at Ludwigshafen or at Oppau have been converted into the corresponding di-alkyl phthalates in the department of Dr. Hambsch.  A detailed description of this manufacture has been given previously. ¹)

General tests applied to plasticizers

For the plasticizers as such the following properties are usually determined:

    1.    Boiling range

            convertional method.

    2.    Colour

            visual comparison with KJ - J₂ solutions of different concentration, the intensity of the colour being indicated a smg.J₂/litre.

        3.    Volatility

                The plasticizer is placed in an open cup and is kept for 11 days at 90°C under constant slow renewal of the air atmosphere.

The behaviour of the phthalates as plasticizers for P.V.C. was determined by milling a mixture of 60 parts by wt. of P.V.C. and 40 parts by wt. of plasticizer to sheets which were subjected to further tests.  In those cases where the plasticizer proved to possess outstanding properties, a mixture of 75 parts by wt. of P.V.C. and 25 parts by wt. of plasticizor was subjected to investigation.

Conventional practice was to determine for those P.V.C.-sheets:

1.    Compatibility

2.    Tensile strength

3.    Elongation strength

4.    Volatility index

5.    Cold flex resistance

6.    Specific electrical resistance

The volatility index was determined in the same way as with the plasticizer as such.  Evaporation loss should be less than 5% by wt.

The resistance to cold flex was determined by bending a sheet of 6 x 1 cm to a 180° bend and dropping a weight of 200 g from 20 cm height on the bend.  The brittle point is then recorded as the temperature at which the sheet cracks.

Dr. Kling has ample experience with phthalate plasticizers prepared from various types of alcohols.  In his opinion C₄ and C₅ phthalates of any type of alcohol are too volatile, whereas C₁₀ and C₁₁ become insufficiently compatible:  sheets of 60/40 composition are greasy to the touch and the plasticizer definitely sweats out in 50/50 proportion.  However, both C₅ and C₁₁ phthalates may be incorporated in small proportions in full range mixtures, C₅-C₁₁ having been used at Ludwigshafen.

As to the influence of the specific structure of alcohols, comparisons have been made between the phthalic esters of:

1. n. C₇ - C₉ alcohol (from hydrogenation of corresponding fatty acids);

2. 2-othyl hexanol;

3. Oxo-alcohols from Michael gasoline (which contains mainly single-branched olefines).

Occasional slight differences were found in the various tests, with the exception of the cold flex resistance.  This proved to be influenced unfavourably by branching of the alcohol molecule.

The brittle point may be improved by mixing of the esters: the cold flex resistance of the mixture was found to be better than that calculated proportional to the amounts of the components used.

The cold flex resistance was not affected by preparing the plasticizers through concommittant esterification of a range of alcohols instead of by mixing the esters obtained from the separate components of such  a range:  No differences were found between the mixture of n. C₄-C₆ phthalate plus n. C₇-C₁₁ alcohols.

Prof. Dr. Walther Hieber (Techn. Hochschule, München)

Munich, May 27th, 1947

        G.    The chemistry of cobalt carbonyls

In view of the extremely important role played by cobalt carbonyl compounds in the chemistry of the Oxo-reaction, as opined by Dr. Roelen ¹), Dr. Schuster and Dr. Nienburg, Germany's expert on the chemistry of metal carbonyl compounds, Prof. Dr. Walther Hieber, was visited at his home, Kaulbachstrasse 89, Munich.

Dr. Hieber and his co-workers have investigated the formation of carbonyls from various metals and carbon monoxide under pressure, and have also studied the formation of carbonyls via the "wet way".  A survey of this work has been published during the war. ")

Prof. Hieber showed that various metal carbonyls may be obtained by treating the corresponding metal halides with carbon monoxide under high pressure in the presence of an acceptor for the halogen.  In the case of CoJ₂, when treated for 15 hours at 250°C under 200 ats CO in the presence of Cu, the cobalt could be completely converted into cobalt tetracarbonyl dimer, [Co (CO)₄]₂.  The same preparation can be applied to iron carbonyl and nickel carbonyl and it has also been proved to hold for the noble metals.

Whereas Blanchard '") has effected the synthesis of cobalt hydrocarbonyl via reaction in liquid phase and at low pressure, Hieber and co-workers have shown that the hydrocarbonyl may also be obtained by direct synthesis from cobalt compounds, hydrogen or hydrogen-containing substances and carbon monoxide under pressure.  These reactions were always carried out in small copper-lined autoclaves, and the hydrocarbonyl formed was recovered by blowing off the contents of the autoclave via a cold trap.  Although cobalt hydrocarbonyl in concentrated form rapidly decomposes at temperatures over -20°C, it is rather stable in dilution in other gases, and consequently only a minor part decomposed during the blowing-off of the autoclave (some cobalt metal deposit was always found in the expansion valve).

Since this mechanism should be tested by carrying out flow-experiments and as Prof. Hieber had not had other equipment at his disposal then small autoclave, he had no definite proof for this opinion.

When asked about the heat of formation of the tetracarbonyl and the hydrocarbonyl, Prof. Hieber stated not to have carried out any calorific measurements on these compounds.  He was inclined to assume the formation of the hydrocarbonyl from the tetracarbonyl to be an exothermic reaction:

The formation of the "full" carbonyls from the metals Ni, Co and Fe and CO is also an exothermic reaction, the relative heats of formation amounting to:

The heat of polymerisation from cobalt tetracarbonyl monomer to its dimer may be taken to be negligibly low.

Whereas the dissociation pressure of nickel-carbonyl at various temperatures is well-known, no such data have been published for iron- and cobalt-carbonyl.  According to Prof. Hieber the latter carbonyls do not give a clearcut dissociation; they decompose into lower carbonyls and CO, as follows:

and are partly converted into carbides.

However, Prof. Hieber had been able to measure the decomposition pressure for one specific iron double carbonyl, viz.: for the reaction FeJ₂ + 4 CO   Fe (CO)₄J₂, the dissociation pressure for the complex carbonyl being found at abt. 6 ats. CO at room temperature.

As stated above, no such transition pressures could be measured for those carbonyls most interesting in connection with the Oxo-synthesis, cobalt hydrocarbonyl and iron hydrocarbonyl.