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INDUSTRIAL A N D ENGINEERING CHELMISTRY
of 320' and 370" C. The dotted line represents the conversions a t the end of the run-i. e., after the catalysts have been operated a t the higher temperature levels. Conclusions
In the absence of similar data on other catalyst mixtures it seems justifiable to conclude that the decomposition method of testing is eminently fitted for studies of the activity of catalysts for the methanol synthesis from water gas a t high pressure. While such a result had been hoped for in light of the data recorded for other catalytic reactions, the good agreement between the independent methods of testing is nevertheless surprising in view of the rather complicated nature of the methanol decomposition reactions discussed in the first paper of this series.2 It is particularly interesting to note that formation of methyl formate, by polymerization of the supposedly intermediately formed formaldehyde, does
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not occur in the high-pressure synthesis of methanol with these catalysts. I n addition to the fact that the decomposition at atmospheric pressure is a much simpler method of catalyst-testing than the direct synthesis of the alcohol a t high pressure, i t also follows from these researches that the decomposition method is greatly illuminating as a means of disclosing the mechanism of the underlying reactions. The decomposition method of catalyst study therefore promises to be a valuable tool in researches on the synthesis of higher alcohols and more complicated organic compounds. Work along this line is now in progress. Acknowledgment
The writers are indebted to E. J. Tauch for design of the high-pressure reactor used in the catalyst test, and to Miss D. Quiggle for preparation of the catalysts.
New Catalytic Processes for the Utilization of Coal-Tar Crudes' A. 0. Jaeger' THE SELDENCOMP.%XY, PITTSBURGH Pn. ,
T
HE purpose of this discussion is to focus attention on some extremely interesting possibilities for the chemical industry arising from the development of new and very effective processes for purifying various crude aromatic hydrocarbons, such as light-oil fractions, crude naphthalene, and, particularly, crude anthracene by selective catalytic oxidation. This is accomplished by the use of new classes of contact masses which, by selective action, remove part or all of the impurities. Difficulties of Anthracene Purification
To illustrate the usefulness of such new catalytic processes may be cited the difficulties involved in the recovery of anthracene of high purity from coal tar, as hitherto practiced. This has long been one of the most baffling problems in the coal-tar distillation industry. Even yet the most important source for the technical recovery of anthracene is anthracene oil or green oil. This is the last fraction coming over in the distillation of coal tar and is collected in the range of temperature of 270400" C. From this fraction 6 to 10 per cent. is recoverable as crude anthracene of 15 to 30 per cent anthracene content. The recovery of the crude anthracene from the green oil fraction is made by filtration, centrifuging,,and cold and hot pressing. By washing as well as possible with solvent naphtha or creosote oil, the adhering oil and other impurities are to some extent removed and an enriched product is obtained, which, however, still contains only 30 to 50 per cent anthracene. Many difficulties are encountered in the commercial purification of such grades of crude anthracene to such an extent that the product is sufficiently pure for the production of anthraquinone, which is the most important intermediate in the dye-making industry for alizarins and vat colors. The impurities which must be removed in this purification are many and various. Phenanthrene, acenaphthene, fluorene, carbazole, methylanthracene, acridine, etc., are all pres1 Paper presented before the Second International Conference on Bituminous Coal, Pittsburgh, Pa., November 19 to 24, 1928. 2 Technical director, The Selden Company.
ent as well as, in many cases, high-boiling paraffins such as ecosane, decosane, and the like. Other impurities are sometimes present in small amounts and the relative proportions of the different impurities will vary considerably with the nature of the coal tar from which the crude anthracene is produced. The impurities present in largest quantities, however, are carbazole and phenanthrene. Although carbazole is not the most troublesome contaminant, its removal is a critical problem. The paraffins and the alkyl derivatives of anthracene, however, are not only more troublesome to remove but are also more harmful to the quality of the product. Many processes have been worked out for the further purification of the various grades of crude anthracene. As examples may be mentioned the removal of contaminants by washing or by recrystallization. Since carbazole behaves much like anthracene in solubility in most solvents and in vapor pressure special treatments have been devised for its removal, such as conversion to potassium salt by treatment with potassium hydroxide, conversion to nitroso compounds, formaldehyde derivatives, and so on. One solvent has been found which is somewhat specific for the removal of carbazole, and that is pyridine. All of these processes are expensive and slow. Many require several repetitions in the principal operations and on that account are high in labor cost. They entail relatively high health hazards, since the crude anthracene contains many compounds which are very irritating to the skin and may even initiate cancerous growths. The processes are also very wasteful, since only certain grades of crude anthracene can be used. For example, certain coke-oven tars produce a crude having less than 24 per cent and sometimes as low as 14 to 16 per cent anthracene content. Such crudes cannot be economically worked up by the processes hitherto used. Moreover, cannel coal or other highly paraffinoid coals, when cracked, result in tar fractions containing relatively large amounts of paraffins. These contaminants cannot be satisfactorily removed by any of the methods of purification hitherto known, so that the raw materials from such tars have been quite useless for making intermediates for dyes.
December, 1928
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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present with the heterocyclic compounds and other impurities. The product of such a catalytic purification is a highgrade anthracene containing varying amounts of phenanthrene as almost the only impurity. Even the phenanthrene may be very nearly completely removed by suitable choice of catalyst, but it is difficult to remove all of the phenanthrene by catalytic oxidation without seriously reducing the yield in anthracene, since, though phenanthrene is more sensitive to oxidation catalysis than anthracene, its sensitivity is far less than that of carbazole and the other impurities. Therefore, most catalysts which reduce the phenanthrene As a result of the lack of highly purified anthracene in large enough quantities and a t a sufficiently low cost, the to small amounts will burn up a considerable amount of the anthraquinone used in this country as intermediate for dyes anthracene. How much phenanthrene should be removed by catalysis w ill depend to a has been made almost exlarge extent on the market clusively by the synthetic One of the chief obstacles to the production of vat for phenanthrene and its deprocess. This synthesis is dyes derived from anthraquinone has been the diffirivatives. I n solubility in accomplished in two steps culty of obtaining high-grade anthracene from the many well-known solvents, -namely, the condensation crude material. Two basically different processes for phenanthrene differs very of phthalic anhydride with accomplishing this result are described. definitely from anthracene. benzene by means of alu(1) By selective catalytic oxidation in the vapor It is therefore possible by minum chloride and the ring phase the impurities present may be burned out, simple and economical reclosure of the benzoyl benyielding an anthracene of high purity. This may be crystallization processes, or zoic acid so produced. Alcondensed as such or may in the same operation be even only by washing with though the process is simpassed directly through a second specific catalyst for many solvents, to separate ple a t first glance, certain direct air oxidation to anthraquinone. the anthracene and phens e r i o u s difficulties are in(2) A specific separating solvent for anthracene a n t h r e n e practically comherent to it: (1) Aluminum has been found in furfural. By dissolving crude anpletely, so that an anthrachloride of sufficiently high cene of 90 to 99 per cent is thracene in furfural at elevated temperatures and quality is very expensive and easily obtained. Moreover, cooling the liquid, anthracene of excellent quality for difficult to store and handle; direct vapor-phase oxidation to anthraquinone sepain the subsequent utilization (2) in the condensation hyrates out. The solvent may be recovered and the losses of the anthracene by oxidadrochloric acid is produced, tion to anthraquinone, the of both solvent and solute are slight. involving all the difficult s m a l l a m o u n t of phenanproblems due to its great threne remaining is necescorrosive action: and (3) benzene is used in much more than theoretical quantities sarily destroyed. I n these recrystallization and washing procinvolving the usual difficulties and expenses in its recovery esses phenanthrene can be recovered in very pure condition from the mother liquors. ready for re-use. It is seen that as a result of this catalytic method of puriAltogether, it may be said that although this synthetic process for making anthraquinone has served as a temporary fying the anthracene, not only is the main product obtained means of overcoming the lack of suitable material for the in highly purified condition, but by-products, such as phendye industry, it cannot be called a very satisfactory per- anthrene, of high potential value can also be obtained in almost any required degree of purity. Since by these procmanent solution of the problem. esses phenanthrene of high quality is made available at Certain New Processes very reasonable costs, it is certain that methods for its utilization will be developed along the lines of making new derivaCertain new processes have been'devised for purifying tives in the dye and pharmaceutical fields. various coal-tar crudes, and these processes are dealt with in As noted above, the paraffin impurities in the crude anthrathis discussion. When applied to the purification of crude cene are completely removed in these catalytic processes. anthracene, almost any grade can be utilized, even down to This attack on the paraffin extends even to alkyl radicals 12 to 15 per cent anthracene content. Such low-grade attached to such nuclei as the anthracene grouping. This crudes are entirely out of the question for utilization in any attack probably proceeds by stages in that the alkyl radicals of the processes hitherto known. The processes may be are first oxidized to carboxyl groups and the latter lose carbon briefly outlined as follows: dioxide, so that the alkyl groups are completely removed. Crude anthracene is vaporized and mixed with air, pref- I n the old processes for purification of anthracene, removal of erably by spraying the crude into heated air. The vapor- alkyl derivatives of anthracene was the most difficult problem ized mixtures are passed over a suitable catalyst which favors and was never completely solved. This was particularly untotal combustion of the heterocyclic impurities and aliphatic fortunate in that alkyl anthracenes were the most deleterious compounds. The anthracene is not attacked to any con- impurities which could be present in the final product. The siderable extent. overcoming of this difficulty by the catalytic purification procThe variety of catalysts which will accomplish this selective esses by choice of suitable conditions for the oxidation and oxidation is very large. For, surprising as it may seem, the suitable catalysts is one of the most important phases of the writer has found that carbazole and other nitrogenous com- improvement accomplished. pounds, normally considered very stable, are substantially quantitatively burned when subjected in the vapor phase t o Application to Partially Purified Crudes proper reaction conditions in the presence of suitable cataWhile the new catalytic purification processes have been lysts. At the same time, these conditions do not result in any considerable oxidation of the aromatic hydrocarbons discussed as yet only as applied to the crude anthracenes, it is
These considerations are largely responsible for the fact that, in spite of the immense production of coke, and therefore, of coal tar, in the United States, all efforts to make these domestic sources of anthracene economically available have failed of success. This is a serious handicap to the domestic alizarin and vat dye industries which are now in a condition of intensive development. The patent literature shows that the failure has not been due to the lack of welldirected efforts to overcome these difficulties. Disadvantages of Present Method for Anthraquinone
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IXDGSTRIAL AlND ENGINEERISG CHEMISTRY
evident that a semi-purified anthracene would serve as excellent material for such processes. There is a large variety of cheap solvents available which will remove the phenanthrene from crude anthracene. The semi-purified product obtained from recrystallization or washing with such solvents is eminently suitable as a material for the catalytic purification processes, since practically the only remaining impurity in large quantities is carbazole, which is completely removed in this catalytic procedure. The product of such a course of treatment is necessarily an anthracene of extremely high purity. It has been emphasized throughout the discussion that carbazole is destroyed in the course of catalytic purification. It may be desirable a t times that the carbazole be recovered, a t least in large part. One class of solvents has long been known which will remove carbazole from anthracene. This is pyridine and pyridine-like compounds. I n cases where the recovery of the carbazole is desired, a preliminary treatment with pyridine and its derivatives could be used and the semipurified anthracene obtained could then be subjected to the catalytic purification. The carbazole recovered would carry with it the phenanthrene in large part. But not only is a separation of the two possible by use of known solvents, but by proper choice of catalysts and conditions for the selective catalytic oxidation, the two could be separated so as to leave a highly purified phenanthrene. Later in this discussion, attention will be called to a new development in the way of solvents which have a selective action in the removal of carbazole and which can be used by the procedure just outlined. The last two phases of the mefulness of the new catalytic purification processes which have been discussed have dealt with the use of semi-purified anthracene as a material. When such anthracene is used, it is not necessary to stop the oxidation a t the stage of producing purified anthracene and then resume it later to make from the anthracene an anthraquinone by catalytic oxidation. The two stages in the oxidation can be combined either by passing the vapors over two layers of catalyst in the same converter or by taking the vapors of purified anthracene from the first converter and passing it through a catalyst, properly selected for its oxidation t o anthraquinone, in a second converter. In either of these two methods of combining the purification with the oxidation in vapor phase, the first layer of catalyst is properly selected t o purify the anthracene and the second layer of catalyst is selected for its oxidation to anthraquinone, and by proper choice of the two catalysts an absolutely chemically pure anthraquinone can be produced in yields of 90 per cent of theory or higher. As another example of the usefulness of selective catalytic purification, phenolic substances and other impurities present in crude naphthalene fractions of coal tar can be removed so as to produce a very high grade naphthalene. The naphthalene can then be directly oxidized to such valuable products as @-naphthaquinone,phthalic anhydride, maleic acid, and the like without an intermediate isolation of the naphthalene itself. Other fractions of coal tar may also be either completely purified or greatly improved by similar treatments. Crude benzene and other crude light-oil fractions may be so treated as to remove, a t least in large part, aliphatic, alicyclic, heterocyclic, and unsaturated compounds which may be present as impurities. Classification of Catalyst Components
Although it is possible to use any suitable oxidation catalyst having a selective oxidizing effect on impurities, the writer has found that the most effective catalysts are the so-called
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"stabilized" ones. These are catalysts which contain, in addition to the specific catalytic components, compounds of the alkali metals, alkaline-earth metals, and some earth metals characterized by the fact that their oxides are difficultly reducible. These stabilizers exercise a moderating action on the catalyst and prevent or moderate its activity in oxidizing such organic compounds as anthracene, naphthalene, phenanthrene, acenaphthene, benzene, toluene, and the like. Other components, while somewhat active catalytically, are not highly specific in their action, and may be used in combination with the stabilized catalyst. I n such case4 these components appear to tone or promote the action of the stabilizer present, and in this manner highly efficient selective action of the catalyst is induced. These coniponents are therefore termed "stabilizer promoters." Complex Compounds as Catalysts
The manner in which the catalytically active componeiita are associated with the other components in the mass may affect the action of the mass very considerably. Mixtures of the various elements may be used, but it has also been found that combinations of the elements in the form of base-exchange substances, which may or may not be siliceous baseexchange substances, are also very efficient catalysts for the purposes under discussion. I n many cases it may be possible by variation of the conditions of the catalytic purification to use the same catalyst for different purposes. In other cases the same starting material may be made to yield different main products by varying such conditions as the amount of air or other oxidizing gases, the time of contact, the rate of loading, etc. The following outlines of experiments illustrate the manner of carrying out the selective catalytic purification processes. The experiments are so chosen as to illustrate the development of catalysts of highly selective activity. In the first experiments relatively simple contact mass compositions are illustrated and in later experiments these are developed to more and more complex structure, a t the same time attaining greater selectivity in their action. Experiment I
Suspend 16 t o 18 parts freshly precipitated titanium oxide in 100 cc. of water which contains 8 to 12 parts of potassium hydroxide, potassium cyanide, potassium nitrate, either singly or in admixture. Coat the suspeiision onto 200 volumes of pumice broken to pea size. When 30 per cent crude anthracene is uniformly vaporized with air in a ratio of about 1:25 by weight and passed over the contact mass a t 360" C., a product containing 65 per cent or more anthracene is obtained. KO anthraquinone and 6 per cent or less of carbazole are present in the product. At higher temperatures the product will have about the following compositions: At 380" C. the anthracene will be 66 or 67 per cent, no anthraquinone, and 4 per cent or less carbazole. At 390" C., 68 per cent or better anthracene, no anthraquinone, and less than 3 per cent carbazole. This last product when crystallized from toluene will give a product of nearly 95 per cent purity. At 400" C. the product will contain about the same amount of anthracene, no anthraquinone, and the carbazole will drop to 2l/* per cent or less. Finally a t 420" C. the product will contain 70 per cent anthracene and slightly above 1 per cent carbazole, no anthraquinone being present. I n all these products it is understood that phenanthrene makes up the remainder above the stated percentages.
December, 1928
INDUSTRIAL A.VD ENGINEERING CHEMISTRY Experiment I1
Suspend 16 parts of freshly precipitated ferric oxide in 150 parts of water and dissolve 25 parts of potassium nitrate in the suspension. Impregnate 200 volumes of pea-sized pumice with this suspension and dry it. The converters suitable for use with such contact mass may be made up of a plurality of tubes of 1 to 3 em. diameter and surrounded by a cooling bath of high heat conductivity. The bath may consist of mixed potassium and sodium nitrates or nitrites or both, or of molten metal or alloy. I n case alloy is used it is very convenient that it should be adjusted in composition to have a boiling point approximately at the temperature desired for carrying on the reaction. The inass charged into such a converter may be filled to a layer 30 to 50 cm. deep. Bath converters are not essential to the proper working of this catalyst mass, but converters containing provision for automatic cooling by the reaction gases may be used and when so used provision may also be made for the use of heatequalizing mediums of high conductivity through the catalyst. With this catalyst anthracene containing considerable paraffin, such as that resulting from the tar from distillation of cannel coal or other paraffinoid coal, may be purified. Such an anthracene of about 25 to 35 per cent is uniformly vaporized by spraying into a current of hot air, using 1 part anthracene to 15-40 parts of air by weight. The vapors are led over the contact mass a t 360-400" C. and the product contains 90 t o 95 per cent of the anthracene present in the crude material. I t 360" C. 70 per cent or better anthracene, no anthraquinone, and 6 per cent or less carbazole are obtained in the product. At 380" C. the anthracene content rises to nearly -t a per cent, no anthraquinone, and the carbazole content drops to 4 per cent. Such a product can be recrysta!lized from toluene or solvent naphtha to yield an anthracene of 90 per cent or better purity. When the temperature of the purification is raised to 400-440' C. a product of 77 to 80 per cent anthracene is obtained while the carbazole drops to 2 per cent or less. After one recrystallization such an anthracene mill give an anthracene of 94 to 96 per cent purity, having only a slight grayish shade. The materials which have been purified in the manner specified above would have been considered altogether unsuitable for commercial purification by solvent or chemical means as hitherto applied. The products contain none of the oils present in the crude material, and the yellowish contaminant, probably chrysogen, is completely removed by the crystallization from coal-tar solvent. In addition to the great reduction in carbazole content, the phenanthrene content also has been much reduced. The water usually present in such crude materials does not adversely affect the catalytic purification and a drying is obtained simultaneously with the purification since the water is carried away with the waste gases. The product as obtained from the converter is free from unpleasant odor. The analyses shorn that the carbazole is substantially completely burned out and the paraffins and liquid lubricating oils containing perhaps phenols and other impurities are also destroyed. Instead of using the crude anthracene directly, as we have discussed u p to this point, it may be given a preliminary purification. Such a semi-purified anthracene containing, say, 40 to 60 per cent anthracene and obtained by one recrystallization from a solvent suitable for phenanthrene removal yields an anthracene of 90 to 96 per cent directly from the converter. This anthracene is suitable for use immediately, by catalytic, electrolytic, or chromic acid oxidation. The anthraquinone so obtainable is of excellent
1333
purity and can be used without recrystallization as a dye intermediate. The ferric oxide used as the catalytically active component of this mass may be partly or wholly replaced by other metal oxides. For instance, copper oxide made from 55 to 60 parts of crystallized copper nitrate or nickel oxide freshly prepared from 60 to TO parts of crystallized nickel nitrate, cobalt oxide prepared from 70 to 80 parts of crystallized cobalt nitrate, or 14 parts of cerium oxide, may be used. The potassium nitrate used in the mass as a stabilizer may also be changed. For example, the hydroxide, sulfate, acid sulfate, cyanide, carbonate, chloride, chlorate, bromide, or fluoride of potassium, the various potassium phosphates and corresponding compounds of sodium, other alkalies, or alkaline-earth metals may be used in its place. The stabilizer and the catalytically active element may be introduced into the mass in the form of a complex compound. For instance, potassium ferricyanide will furnish both stabilizer and the catalytically active iron compound. Various silicates in which the catalytically active element may be a silicate or the stabilizer may be a silicate, or both chemically combined, may be used. When using the copper oxide catalyst, stabilized with potassium hydroxide or nitrate, with a crude of 30 to 35 per cent anthracene content a t 400-440" C., a product is obtained in which the carbazole is reduced t o below 1 per cent and the anthracene content is raised t o 70 per cent. Such a product by one recrystallization from solvent naphtha gives anthracene of 95 per cent purity. Sometimes anthraquinone in considerable quantities is formed, but the carbazole percentage is never high. Of course, the anthraquinone content has no deleterious effect and so cannot be considered as a n impurity. A yield of 90 per cent of theory or better is obtained. A nickel oxide-potassium hydroxide catalyst used with 30 per cent crude anthracene a t 400" C. yields a product containing 74 per cent anthracene, no anthraquinone, and less than 2 per cent carbazole. Cobalt oxide-potassium hydroxide and cobalt oxide-potassium nitrate catalysts are also excellent contact masses. Used with 30 per cent crude anthracene with an air ratio of 1325 a t 360" C., the product contains 72.5 per cent anthracene, no anthraquinone, and about 3.5 per cent carbazole. At 380" C. the anthracene rises to 73.3 per cent, no anthraquinone and less than 1 per cent carbazole are present. This last product by recrystallization gives anthracene of 95 per cent purity. When the catalytic purification is carried out at 400" C. the product contains 75 per cent anthracene, no anthraquinone, and practically no carbazole. The phenanthrene remaining as practically the only contaminant of this product can be removed by recrystallization or mashing with well-known solvents. The phenanthrene is recoverable from the solvent in a purity of 90 to 95 per cent. Such a contact inass is effective to a very high degree. Passing crude anthracene of 30 per cent content through a 40-em. layer of stabilized cerium oxide catalyst a t 380" C. gives a product containing i 4 per cent anthracene and only 1.4 per cent carbazole. At 400" C. an anthracene of i i per cent purity is obtained and the carbazole is practically eliminated. Such an anthracene when purified from toluene, using only a minimum amount of the solvent, yields a product of 96 to 97 per cent purity, the remainder being phenanthrene. A second recrystallization results in beautifully white anthracene of 99 to 99.8 per cent purity. It goes without saying that phenanthrene of high quality can be recovered from the toluene mother liquors.
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INDUSTRIAL AND ENGINEERING CHEMISTRY Experiment I11
The quality of the contact mass can be favorably modified by using, with the catalytically active component and the stabilizer, a stabilizer promoter. For such stabilizer promoters materials ordinarily considered as dehydrogenating and dehydrating catalysts are very effective. The following is given as an illustration of such a contact mass: Precipitate 8.7 parts of ferric oxide and 8 parts of titanium oxide from soluble salts of the two metals by means of alkali. Suspend the mixture of the oxides in 100 parts of water and add 14.2 volumes of 10 N potassium hydroxide. Coat the suspension onto 200 to 250 volumes of pea-sized pumice in the usual manner and calcine a t 400-500" C. By using with this mass a crude anthracene of about 30 per cent containing some 22 per cent carbazole, a t 380" C. with an air mixture in the ratio of 1:30, a product is obtained in which the carbazole is reduced to about 3.5 per cent. At 400" C. only 1.4 per cent carbazole remains and a t temperatures of 420" to 440" C. a Kjeldahl analysis of the product shows no carbazole. The last-named product can be purified from its phenanthrene contaminant in the usual way, to give a product of 96 to 97 per cent purity with phenanthrene available as a by-product. In this mass the ferric oxide may be replaced by other metal oxides, as also may be the stabilizer promoter, titanium oxide. It should be noted that with the ferric oxide mass described the phenanthrene is relatively little attacked. Experiment IV
Since oxides of the elements of the fifth and sixth groups, such as vanadium, molybdenum, etc., have been described in the literature for use in actual oxidation of the aromatic hydrocarbons catalytically, it might be supposed that such elements could not be used in catalysts intended only for purification. However, by proper selection of stabilizers for admixture with such elements, they also make very effective catalytic purification contact masses. For instance, prepare a manganese vanadate from 14.4 parts of vanadium pentoxide dissolved in water containing the proper amount of potassium hydroxide by adding a solution of 14.8 parts of crystallized manganese sulfate in 200 parts of water. Suspend the precipitate in water containing 10 parts of potassium bromide and spray onto 400 parts by volume of pumice. The catalyst is used in a converter and under conditions the same as those described above. Using a 25 to 30 per cent crude anthracene, an anthracene of 70 to 80 per cent is produced with the carbazole eliminated as shown by Kjeldahl analysis. The phenanthrene is attacked to a greater or less extent, depending on the operating conditions of the catalytic purification. This product by one recrystallization yields an anthracene of 90 to 95 per cent purity and with a recovery approximating theory. For the manganese vanadate in the mass described above, vanadates of iron, cobalt, nickel, titanium, aluminum, copper, and silver, singly or in admixture, may be used. Instead of vanadates, salts of the other metal acids of the fifth and sixth groups may be used alone or admixed with the vanadates. Further, the stabilizer used can be replaced in part or wholly by other halides of the alkali or alkaline-earth metals. I n these substitutions changes in the amounts of stabilizers and in the conditions of use of the resulting contact masses are usually desirable. Experiment V
The iirst four experiments illustrate the making and use of contact masses in which the components are present entirely or largely as mixtures. I n the catalytic purification of coal-tar crudes by selective oxidation of the impurities,
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results which are even more definitely controllable to the desired ends are obtainable by combining the components to complex compounds of high molecular weight. For instance, compounds of the nature of zeolites or base-exchange substances not containing silica are eminently adaptable to these purposes. Let us consider for a moment the formula of a similar zeolite and, using this formula as a starting point, show what varied changes can be made in it for use as catalysts for any given purpose : K2O.AI203.4 SiO2.X HzO
Since the potassium oxide acts as a stabilizer, the compound is already partly ready for use. However, since this oxide is replaceable to any desired extent by basic oxides, other stabilizers or stabilizer promoters or even catalytically active oxides can be introduced in this part of the molecule. Further, in making the zeolite the aluminum oxide may also be replaced to any desired degree by other amphoteric oxides, and so the nature of the final product can be modified at will by using oxides as titanium, chromic, cupric, cobaltic, ferric, or others which may serve the purposes of stabilizer promoters and catalytically active components. Lastly, having built a mass which only partly serves the purpose in hand, we have the further flexibility of being able to imbed a catalytically active oxide in the zeolite structure. As noted above, non-siliceou# base-exchange substances are also available for the uses under discussion. Such compounds are the reaction products of alkali metallates of amphoteric metal oxides with metal salt solutions maintained neutral or faintly alkaline to phenolphthalein; e. g., a solution of potassium aluminate may be treated with solutions of cobalt nitrate or ferric nitrate or with mixtures of these two salts. Such an operation results in a very effective catalyst for the selective oxidation of certain coal-tar crudes. A crude anthracene semi-purified to the extent of the removal of most of the phenanthrene by well-known solvents and then vaporized with air in the ratio of 1:35 and passed over such a catalyst a t 380400" C. produces an anthracene of 96 to 99 per cent purity. The recovery of anthracene is almost theoretical. Experiment VI
To illustrate the use of a double catalytic operation in one converter, we may have a t the top of the tubes a 30- to 40cm. layer of an anthracene purification catalyst as discussed in former experiments. Below this catalyst is a 20- to 30em. layer of a contact mass adapted to the oxidation of anthracene to anthraquinone. Zeolites containing vanadium tetraoxide as one of the amphoteric oxides are eminently adapted for this latter purpose. To make such a catalyst dilute 200 parts of 33" BB. potassium silicate solution with 1600 volumes of water and add 70 parts of Celite earth. Reduce 18 parts of vanadium pentoxide in water by means of sulfur dioxide and transform it into the corresponding potassium vanadite. Mix this solution with the silicate suspension, treat this mixture with so much manganese sulfate solution that it is neutral or slightly alkaline to phenolphthalein. Before use, calcine the mass a t 400-500" C. with 7 per cent sulfur dioxide gases. Using a semi-purified anthracene, as detailed in Experiment V, a chemically pure anthrapuinone results in yields of 90 to 93 per cent of theory. The purity of this product is such that a freezing point test is the best one to use for detecting minor variations in its quality. Variations of more than 0.1 to 0.2 degree from the freezing point of anthraquinone of the highest purity obtainable show that the operation has not been properly controlled.
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1928
New Solvent Process
It has frequently been pointed out in this discussion that the carbazole is completely destroyed in the purification processes. The fact that carbazole may become an important material for making dyes, rubber accelerators, etc., led to reconsidering the possibility of the recovery of this compound from the crudes. Liquid compounds containing the furane nucleus were found to possess an extremely high solvent power for carbazole and phenanthrene. On the other hand, the most easily available of these compounds, furfural, was found to dissolve anthracene easily a t elevated temperatures and redeposit the solute on cooling. By using this newly discovered property of furfural, recoveries of 94 to 98 per cent of the anthracene from crudes are obtained in the form of greatly purified anthracene. These yields are obtainable either by recrystallization from this solvent or merely by washing processes. Furfural is relatively cheap and has recently become available in enormous quantities. As compared with the use of pyridine as a solvent for this purpose, it is a cheaper material and one of relatively pleasant odor, h-gh boiling point, and low solubility in water. By one recrystallization of crude anthracene from furfural the anthracene content has been raised from 31 per cent to 86 per cent and a t the same time the carbazole content has been
1335
reduced from 16 per cent to approximately 6 per cent. The recovery of anthracene is about 96 per cent, although this may vary by 2 to 3 per cent depending on the nature of the crude material. Such a product is immediately usable for catalytic oxidation to anthraquinone of highest purity. It goes without saying that the phenanthrene and carbazole are recoverable from the mother liquor by known methods. By a further crystallization from the same solvent the anthracene purity can be raised to 92-96 per cent with only about 2 per cent of carbazole remaining as a contaminant. By using even cheaper solvents which remove phenanthrene and dead oils chiefly-such solvents as o-dichlorobenzene, for example-for an initial purification and following with a treatment with furfural, similar results can be obtained. The new solvent purification and the new purification by selective catalytic oxidation processes are in a sense rival procedures. By pyramiding the results of either procedure on the other the yields and quality of the product finally obtained leave nothing to be desired in this field of chemical activity. Acknowledgment Such results necessarily could not be obtained without extensive and costly research. The ample research facilities provided by The Selden Company and its policy of encouraging developments of this kind have contributed in no small degree to the successful solution of these problems.
Synthesis of Methane from Carbon Dioxide and Hydrogen' Merle Randall and Frank W. Gerard2 CHEMICAL LABORATORY, UNIVERSITY OF CALIFORNIA,
BERKELEY,CALIF.
The equilibrium in the formation of methane and HE synthesis of methide tube D. An accurately water vapor from carbon.dioxide and hydrogen and the controlled constant flow of ane from hydrogen and reverse reaction have been redetermined. The free the oxides of c a r b o n gas was obtained by means of energy of methane calculated from these experiments has been the subject of extena r e s i s t a n c e flowmeter, E. is in agreement with the value found from the direct sive investigations, references The portion below the dotted synthesis from graphite and hydrogen in the same to which may be found in the line was kept in a constant temperature range. The cause of the deposition of recent article by Hightower temperature bath. The difcarbon in the catalysts has been discussed. a n d White.a Pease a n d ference in level of the merChesebro' have also detercury in the two arms of the mined the equilibrium at a single temperature. The fol- flowmeter manometer was maintained constant within 0.2 lowing experiments were designed to give a check upon the mm. by means of the automatic pressure-regulating valves rather discordant values of the equilibrium in the reaction shown in Figure 2. As the gas pressure drops in the arm A leading to the flowmeter, the mercury falls in the arm B COzk) 4-4Hz(g) = CHdk) f 2H20k) (1) of the manometer C, opening the circuit of the electric relay and to study the efficiency of several catalysts for the reaction. D, and causing i t to close the circuit of the electromagnet F , through the relay E. The iron plunger G presses against the Apparatus pin of an ordinary tire valve, H , opening the valve and alThe apparatus consisted of three parts: (1) a device for lowing gas to flow in at J from the cylinder. As soon as the synthesizing, at definite slow rates, constant mixtures of pressure builds up again the mercury rises in B, closing the any of the gases; (2) the catalyzing furnace; and (3) means relay circuit and opening the electromagnet circuit, allowing of automatically taking a sample without disturbing the the valve to close and shut off the flow of gas. For best operation the manometer should contain a minimum amount flow of gases through the catalytic mass. of mercury, and the pressure given by the reducing valve SYNTHESIS OF GASMIXTURES-A diagrammatic sketch of the apparatus is shown in Figure 1. The carbon dioxide was should be regulated so that the automatic valve operates taken from a commercial cylinder through a pressure-reducing about every 15 seconds. A globe, C (Figure l),of about 1valve, and dried by passing through the phosphorus pentox- liter capacity was inserted between the regulating manometer B and the drying tube. The flowmeter was calibrated by 1 Received July 5, 1928. determining the quantity of carbon dioxide collected in the * Pacific Coast Gas Association Fellow, 1927-28. buret of the Burrell apparatus in a given time. The carbon 8 IND.ENG.CEEM.,SO, 10 (1928).
T
4
J . Am. Chcm. SOC.,50, 1464 (1928).
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Smith, IND.END.CHEW.,16, 22 (1924).
