Surrefining of coal-tar derivatives and the like
United States Patent 2346664

The present invention relates in general to the treatment of carbonaceous substances such as those produced by the destructive distillation of fuels and is more specifically concerned with improvements for enhancing the quality of products derived from coal tars; for example, phenolic compounds....

Bennett, Corson Ben
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International Classes:
C07C37/70; C07C37/82
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The present invention relates in general to the treatment of carbonaceous substances such as those produced by the destructive distillation of fuels and is more specifically concerned with improvements for enhancing the quality of products derived from coal tars; for example, phenolic compounds.

Amongst the objects.of the present invention is the provision of improved method and means whereby coal-tar derivatives such, for example, as phenols, and the like, can be cheaply, simply, and continuously produced in a high degree of refinement in respect of odor, content-of-sulphur, and also of suitability for employment in processes involving a hydrogenation step.

A further object of invention is the provision of an improved reagent and modifications thereof that are effective for the above-stated purpose, whether or not the to-be-treated coal-tar derivatives are in the liquid or in the vapor phase, and that are easily regenerative for re-use after a period of operation.

The invention has for further objects such other improvements and such other operative advantages or results as may be found to obtain in the processes or apparatus hereinafter described or claimed.

Relatively pure constituents extracted from coal-tars sometimes have admixed therewith varying small amounts of difficultly removable products that alter their normal characteristics to greater or lesser degree. In the case of phenols, for example, these associated products may be present in such minor amount as to be undetectable by the usual determinations, for example, of freezing or of boiling points, but may be present in amounts sumicient somewhat to disguise their characteristic odors and thus depreciate their commercial value. There may be also present sulphur-containing compounds that importantly reduce the effective life of a sulphursensitive catalyst when the same is employed for the hydrogenation of such phenols.

It has now been found that by bringing phenol, such as that above-described, into contact at an elevated temperature and either in its liquid or its vapor phase, with metallic copper prepared in such form that it presents a large surface to the phenol, the resultant phenol products have a greatly improved odor and that their sulphur content is so importantly reduced that they can be economically hydrogenated in processes employing a sulphur-sensitive catalyst.

In general, the more finely-divided, that is, the greater surface a given quantity of metallic copper, even when it has a minor content of its oxide, presents to the to-be-treated material, the more effective it becomes for the purpose. Considerable improvement in odor and reduction in the sulphur content of a given phenol has been brought about by passing it in vapor form over copper turnings, copper and bronze powders, and over commercial granular copper oxide that has been previously reduced by appropriately treating it with hydrogen, but, according to the present invention for improving the quality of constituents of coal tar, for example phenols, they are preferably passed in vapor form over finely comminuted metallic copper that is supported on such cheap carrier therefor as pumice, the copper being distributed over the surface of said pumice in a manner hereinafter described in connection with one of the specific examples illustrating the operation and results achievable by the present improvement. It has been found that the use of copper to achieve the stated results renders the present process commercially feasible for the purification of even relatively inexpensive products because of its cheapness and effectiveness and the ease with which it can be prepared in practical form and because, when its activity has been so reduced in operation as to render it impractical of employment, it can be restored for further use in a simple manner to close approximation of its original activity and while it is in situ in a plant lay-out. After a cycle of operation, that is interrupted when the treated phenol no longer exhibits the preferred characteristics to the desired degree, an employed mass of copperized pumice can be shunted out of the flow-path of the to-be-treated phenol and another be switched into operation for use while the former said mass is being regenerated by flowing thereover, while in its containing vessel, a current of air or oxygen-containing gas for oxidizing any deposited carbonaceous material and sulphided copper, this step being followed by a stream of hydrogen or hydrogen-containing gas for reducing the resultant oxidized 15 copper compounds. During the said regeneration steps of oxidation and reduction, temperatures not in excess of about 8000 C. and not substantially less than 200° C. for the former step are maintained in the treated mass; in some instances the copper has retained its activity when reduced from the oxide at 500* C. but the preferred temperature lies between about 200* C. and 350° C.

A practical liquid-space velocity per hour of 5 the phenols through the copperized pumice is about 2.5 where unity is that velocity obtaining when a volume of liquid phenol is passed per hour in vapor phase over an equal volume of copperized pumice; the particular space-velocity employed in any one instance will naturally depend on such factors as the activity of the purification medium, temperature and pressure of treatment, the quality of the to-be-treated starting material and that desired in the finished product. In the accompanying drawing forming a part of this specification and showing for purposes of exemplification a preferred apparatus and method in which the invention' may be embodied and practiced but without limiting the claimed invention specifically to such illustrative instance or instances, the single figure shows a diagrammatic representation partly in elevation and partly in vertical section of apparatus for carrying out the improvement provided by the present invention and further shows in diagrammatic manner apparatus wherein products resulting from its practice can be optionally hydrogenated.

In the apparatus shown in the figure the tobe-treated coal-tar product, for example phenol, is continuously flowed into the vaporizer still or preheater I through line 7. This device can be any one of those well-known in the art and employed for volatilizing or distilling materials.

Any of the usual means for supplying heat thereto can be employed, and line 8 is here shown for supplying fuel gas for its heating. The tobe-refined phenolic vapors admixed with other materials such as derivatives of sulphur .and ill-smelling constituents that may even boil within the same range as a relatively pure phenol product, leave the apparatus I through insulated line 9 at temperatures usually ranging from about 180* C. to about 200* C. and usually but not necessarily at ordinary pressures, said pressures 44 being sufficient to cause a flow of said vapors through the apparatus that follows. In specific instances, either sub- or super-atmospheric pressure will be found advantageous depending on the boiling point of the to-be-treated material. 4, From line 9, the volatilized materials thereafter flow through either one or the other of the valved branch lines 10, 11 or 12 to the respective and substantially similar treating units 2, 3 or 4.

Three of such units are shown in parallel ar- 5 rangement to permit the use of one unit for the treatment of the said phenol vapors while a second unit is being revivified or reactivated as will be hereinafter described. The third unit is a spare that allows for uninterrupted opera- 5 tion in those cases where one of the other two units is temporarily out of service. The treating unit 2 is shown in vertical section and is typical of the others. It comprises a casing or tube 13, a layer of insulation 14 and pack- 6 ing 15, said packing comprising the preferred copperized pumice provided by the invention.

Any of the well-known, commercial types of insulation can be employed to insulate tube 13, the said tube being constructed of any appropri- 6 ate material capable of resisting temperatures of about 800' C. The treating units are positioned vettically with downward flow therethrough to minimize channeling and maintain uniform contact with to-be-treated vapors throughout said 7 copperized pumice.

The to-be-refined phenolic vapors leaving still I through line 9 can flow, for example, through valved branch line 10 to the treating unit 2 and while passing through insulated tube 13 will come 1 into intimate contact with the comminuted copper purification medium 15, the said contact bringng about removal of coustituent sulphur and an advantageous improvement in odor of the phenol vapors which, thereafter, leave treating tube 13 and pass in sequence through valved branch line IS and line 19, and can be optionally flowed through valved line 20 to a hydrogenation unit 5 or, if preferred, they can be flowed through valved line 23 to a fractionating column 6.

The rate of flow of phenol vapors through said tube 13 or the liquid-space velocity per hour that is feasible to remove sulphur impurities and to edulcorate, that is, to remove foreign odors from the phenol vapors, depends on such factors as the quantity of said impurities present in the phenol vapors, the particular purification medium employed as well as its available surface for contact, and the quantity of sulphides previously accumulated on the latter.

The refined phenol vapors that leave treating tube 13 through valved branch line 16 and line 19 can flow, when valved line 20 is closed, through valved line 23 to a fractionating column 6 for the separation of a phenol product having a narrower boiling range. The vapors flowing from column 6 through line 24 enter water cooled dephlegmator 25 to be refluxed, the narrower boiling range vapors leaving through valved line 26 to be condensed and stored (not shown) while higher boiling aand condensed constituents return to fractionating column 6 through line 27. The higher boiling phenol product leaves column 6 through valved line 28 for further disposition. It is of course understood that any additional heat required in column 6 for the above-described operation ann be supplied as required. When valved line 23 is closed, the Srefined, edulcorated phenolic vapors in line 19 can flow through valved line 20 to hydrogenation apparatus 5 for conversion with a sulphursensitive nickel catalyst, for example, to cyclo hexanol. The hydrogenation apparatus 5, diagrammatically illustrated in the drawing, can be one of any well-known types of apparatus chosen with consideration for treatment of the phenol accordingly as it is to be done either in the vapor or liquid phase: The hydrogenated product leav0 ing apparatus 5 can flow either through valved line 21 to suitable storage (not shown) or through valved branch line 22 to fractionating column 6, where further separation of a narrower boiling range product can be obtained as 5 previously described for a phenolic product.

Where treating unit 2, for example, has been in operation for the stated purpose a predetermined time, depending mainly on the impurity concentration of said phenol vapors, it will thereafter be necessary for continuous and efficient treatSment thereof to carry on the said refining operation in one of the other treating units while unit 2 undergoes revivification. Thereafter, the said phenol vapors in line 9 that has been previously 5 flowing through valved branch line 10, refining Sunit 2 and valved branch line 18 will flow through, for example, valved branch line I, refining unit 3 and valved branch line 17 while said valved branch lines 10 and 16 are closed as are those o numbered 12 and 18.

During operation of the instant improvement on the phenolic fraction of coal tar to highly refine it, metallic copper of the copperized pumice is usually converted to sulphides of copper and some '5 carbonaceous material as well Is accumulated thereon. In the revivification of such spent copperized pumice, the sulphides and carbonaceous material are first oxidized with air or other oxygen-containing gas and thereafter the resultant oxidized copper compounds are again reduced to metallic copper with hydrogen. For this purpose, air at gradually increasing temperatures and within a range defined by about 200" C and 800* C. is flowed through line 29, valved branch line 30 to and through tube 13. The oxidation reaction may become very vigorous, especially at the beginning thereof and can be controlled by first employing a gas of low-oxygen content, for example, air mixed with nitrogen or other inert gas in preferred ratio. The excess air and other gaseous reaction products leave said tube through valved branch line 33 that connects with vent line 36. After the said oxidation, its resulting oxidation-products in the copperized mass are extensively reduced to metallic copper with a stream of hydrogen at temperatures ranging from approximately 250* C. to 350° C., the said hydrogen also being flowed through line 29, valved branch line 30, treating tube 13, valved branch line 33 to vent line 36. Thereafter, the treating unit 2 is again ready for another cycle of operation for the stated purpose. It is preferred to minimize explosion hazards in the treating units by employing an inert, oxygen-free gas as a purge gas before the air oxidation, before the hydrogen reduction and before phenol vapors are again passed through them after revivification. For this reason, all valves should be free of leaks when closed.

In the above-given description of the instant novel process and the employed apparatus for highly refining coal-tar products to improve, for example, their odor and remove constituent sulphur, contact between the refining media, such as finePl-dividedr, or n or ofl 4--Air mr et A ppVl_ - 1-5eg0 inerts, and the to-be-treated material, is effected when the latter is in the vapor phase. It has been found that the beneficial results of the invention can be also obtained in a modification of the described process wherein a coal-tar derivative, for example phenol, is treated in the liquid phase with the copperized pumice or with other forms of finely divided copper. When the process- is practiced in the latter fashion, the to-be-refined product can be refluxed in the presence of the chosen medium. The time of contact depends on the form of the chosen refining medium and on the impurity-content of the to-be-treated material and may vary from about five to about twelve hours. Thereafter, the so-treated product can be vaporized to separate it from the refining medium and, as above described, the vapors can be directly passed to hydrogenation means or to a fractionsting column to secure a product of a preferred boiling range. Revivification of the copperizedpumice purification medium can, for example, be accomplished in a manner similar to that hereinabove described.

The following specific examples are illustrative of the results obtainable by the operation of the present process.

Example 1 A quantity of copperized-pumice refining medium was prepared by soaking pea-sized pumice inr hot, concentrated copper sulphate solution.

The'so-impregnated pumice was drained and dried and thereafter the absorbed copper sulphate was reduced to copper in a stream of hydrogen at about 300° C. Approximately 2.8 pounds of the so-prepared copperized pumice which was in this wise impregnated with 6.1 per cent by weight of comminuted metallic copper was packed to a depth of about fifty inches in an insulated iron tube having an internal diameter of 2.2 inches; the total volume occupied therein by the refining medium was about 190 cubic inches. The said iron tube was connected by an insulated pipe with a still for vaporizing the to-be-refined phenol product, which was a product known in the trade as "90% phenol," and was a coal-tar derivative having a melting point of about 36* C. This particular phenol product was chosen since it had both a foreign odor, that somewhat disguised the characteristic odor of phenol, and had a sulphur content of about 0.02 per cent by weight. It had been found previously that even a phenol fraction of narrow boiling range derived from this "90% phenol" and having a melting point of about 40° C. could not be successfully hydrogenated for any considerable period because sufficient of the sulphur-containing impurities distilled over with this relatively pure material to poison in a relatively short time the sulphursensitive nickel catalyst employed for the hydrogenation thereof to cyclohexanol.

The said "90% phenol" product was pumped at an approximate rate of two gallons per hour to the still, the volatilized phenol issuing therefrom and having a temperature of from 180* C. to 190° C. was flowed into contact with copperized pumice prepared as above described, the said rate of flow corresponding to a liqiud-space velocity of about 2.5 and an approximate contact time of two seconds. The phenol vapors after this treatment were condensed. The resultant sweetened product had the fresh aromatic odor characteristic of pure phenol and was thereafter successfully hydrogenated with a sulphur-sensitive nickel catalyst to cyclohexanol, without impairing the normal efficiency of said catalyst.

About fifty gallons of a commercial "90% phenol" product were continuously refined in twentyfour hours with the same copperized pumice, a quantity equivalent to about sixty volumes of phenol product per volume of copperized pumice.

Thereafter, to maintain refining efficiency it was found necessary to oxidize the sulphided copper and deposited carbonaceous material on said comminuted copper refining medium, oxidized copper so being thereafter reduced to metallic copper. The spent copperized pumice was regenerated or revivified in situ first for about twelve hours with air increasing progressively in temperature from about 200* C. to 500* C. and thereafter for ap.s5 proximately six hours with hydrogen at about 300° C. to 350° C. Approximately seventeen cubic feet of air per hour and 1.5 cubic feet of hydrogen per hour, both measured at standard conditions, were employed for the oxidation and reduction to respectively, the efficiency of said regeneration being about 85 per cent.

Thereafter, the so-regenerated copperized pumice was again employed repeatedly for edulcorating and refining said "90% phenol" product una;, der substantially similar conditions to those .above-described and the resultant product remained comparable in purity with that produced during the said reagent's initial use. To minimize the hazard of explosion the treating unit ;7 was purged with nitrogen to sweep out gases and vapors present therein before each of the oxidation, reduction and refining steps. During the first hour or so of the oxidation step a mixture of about one part air and one part nitrogen 76 was used to limit the evolution of heat, the nitrogen content being thereafter progressively reduced until straight air was employed.

Example 2 The following is an example of the beneficial results obtained when a standard commercial "90% phenol" product was refined according to the present invention in the liquid phase while employing finely-divided copper as the refining medium. The employed finely-divided copper treating medium was prepared by adding sodium carbonate to a solution of copper sulphate also containing diatomaceous earth. The precipitate of basic copper carbonate on diatomaceous earth was separated by filtration, dried and the metallic copper obtained by reduction with hydrogen at about 300 C. The so-prepared terating medium comprised about 75 per cent copper and 25 per cent diatomaceous earth.

An admixture comprising a "90% phenol" product similar to that treated in Example 1, and the said copper treating medium in a weight ratio of about 100 to 1, respectively, was boiled under substantially complete reflux for about six hours and thereafter the copper treating medium was filtered off and the liquid portion distilled In the distillate, approximately 80 per cent ofthe starting material was recovered as phenol having a melting point of substahtially 40" C. and the characteristic odor of highly refined phenol.

A phenol product having substantially the same melting point but recovered from"the starting material without the said copper t!eatment had a decidedly less agreeable odor. The said phenol produced by the copper treatipent was hydrogenated to cyclohexanol with 1 nickel catalyst without unusual reduction in its activity due to presence of sulphur.

There has been described a process, reagents and apparatus for treating, more especially, otherwise relatively highly refined by-product derivatives of the carbonization of coal to remove therefrom contaminants that are usually relatively low in concentration in such derivative products, yet whose presence therein can appreciably reduce their commercial value for a particular purpose. The present process is adapted to be practiced per se or in combination with other processes for purification and utilization of such products; it can be used to enhance the value of an existing product by further refining the same, or it can be employed to prepare such product for conversion into a product having another chemical structure.

By specific example and description particular emphasis has been laid on the applicability of the present process for further refining phenols to produce a source material for the production of cyclohexanol through its hydrogenation. It is to be understood that the phenols are but one group of a large number of compounds resulting from the destructive distillation of fuels, for example coal, that, due to their origin, can be contaminated with relatively minor amounts of undesirable constituents, an . for the removal of which the present process is peculiarly adapted, and especially so for those malodorous constituents and for those ingredients that materially reduce the efficiency of certain hydrogenation catalysts.

For treatment of said derivative products according to the present invention ordinary pressures are usually employed that are sufficiently above atmospheric pressure to direct the flow of said products through the treating and other process apparatus when operated under substantially atmospheric pressures. Without departing from the spirit of the invention, however, as hereinabove mentioned, pressures above or below atmospheric can be used for practicing the improvement in the case of specific products, and empirical determinations must then be made for the correct space-velocity, temperature of contact, and effective life of the reagent. Because of the favorable results obtainable thereby, the temperature chosen for treating the specific phenolic product was preferably that temperature just sufficient to maintain it at or slightly above its boiling point. However, when treating other materials having the same origin, :'their physical characteristics, the temperature at which preferred results are obtained and the ,degree to which they are to be refined will somew wht .determine the employed procedure and must be e6pirically determined.

In the above-given discussion, the action of copper alone has been described as the active reagent, but it is interesting to note that other metals in combination with copper give favorable results and consequently it is not desired broadly to limit the claimed invention specifically to the use of copper alone because metallic mixtures in which copper has an active part are of utility and in certain instances have advantages. For example, greater economy can result in consequence of a lowered temperature of hydrogen reduction to the active metallic states, Swhich in the case of copper adixed with zinc is more than about 150* C. lower thai t` e reductlon temperature for zinc, said zic, when used by itself, being an ineffective reagett. Also, the more expensive copper can be partly replaced by cheaper iron in an admixture of these metals.

For example, when a commercial phenolic product that was somewhat malodorous was brought into contact at about its boilin point and in the vapor phase with iron that thad been reduced at about 450* C., the sai4 treated product exhibited no improvement in odoi: .or reduction in its sulphur content. However, on the other hand, an admixture comprising about .70 per cent Fe2O3 and 30 per cent CuO was, after reduction in hydrogen at 200° C., an effective treating reagent and said reagent's activity to edulcorate and remove sulphur from said phenolic product was considerably greater than would be anticipated on the basis of its copper content alone; in other words its iron. content, for the instant purpose, showed activity in the presence of copper. Combinations of metals, one of whose constituents is copper are thus of economic import in the present improvement.

In the case of phenolic compounds that have been produced by the present process, the freshly prepared product is substantially colorless but gradually takes on a pinkish tint. Its color stability can, however, be increased by bringing it at elevated temperatures into contact with such absorptive bodies as clays or gels; for instance, Attapulgus clay or activated alumina. They can be simply employed in combination with the present process by packing them in a treating unit substantially similar to those alreaty described for the active copper-containing reagents and they can be incorporated advantageously Into the apparatus, shown in the drawing, between the treating units 2, 3, and 4, and the fractionating column 6. They .should be of such size as to provide a liquid-space velocity of about 1.0. in the case of Attapulgus clay, to remove color-producing constituents. A so-treated phenol product remains colorless for long periods.

The invention as hereinabove set forth is embodied in particular form and manner but may be variously embodied within the scope of the claims hereinafter made.

I claim: 1. A process of sur-reflning a phenol containing approximately .02 of sulphur which comprises, passing the same through a body of copper absorbent produced by dispersing a copper compound on an inert porous carrier and then reduced to metallic copper by means of hydrogen and heat.

2. A process of sur-refining a phenol containing approximately .02 of sulphur which comprises, passing the same through a body of copper absorbent produced by dispersing a copper compound on an inert porous carrier of pumice and then reduced to metallic copper by means of hydrogen and heat.

3. A process as claimed in claim 2, and in which the proportion of the copper to the pumice is about six per cent by weight.

4. A process of sur-reflning a phenol containing approximately .02 of sulphur which comprises, passing the same through a body of copper absorbent produced by dispersing a copper compound on an inert porous carrier of diatomaceous earth and then reduced to metallic copper by means of hydrogen and heat.

5. A process as claimed In claim 4, and in which the copper absorbent is comprised of 75 per cent copper and 25 per cent diatomaceous earth.

6. A process as claimed in claim 1, and in which the phenol is passed through the body of copper absorbent in vapor phase.

7. A process as claimed in claim 1, and in which the phenol is passed through the body of copper absorbent in liquid phase.

8. A process as claimed in claim 1, and in which the copper is associated on the carrier with at least one of the group of metals consisting of iron and zinc.