US1904269A - Manufacture of low boiling tar acids - Google Patents

Description

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Patented Apr.'18, 1933 TTEIS SOLOMON CAPLAN OF BROOKLYN, NEW YORK, ASSIGNOR TO COMBUSTION UTILITIES PATENT OFFICE CORPORATION, OF YORK, N. Y., A CORPORATION OF MAINE MANUFACTURE-00F Low BOILING TAR Aoins The present invention relates to the production of low boiling tar acids, and more particularly to a process for converting high boiling tar acids of-relatively low marketable value into low boiling tar acids of higher marketable value.

Low temperature tars and similar products such as blast furnace'and vertical retort tars are characterized by having a high content of relatively high boiling phenolic or phenollike bodies to which the term tar acids is generally applied. There is no appreciable present market value for these high boiling tar acids per se, whereas there is an immediate and profitable market for low boiling tar acids, notably phenol and the cresols, which are present in small quantities in coke oven tars and similar condensates obtained by the high temperature distilation of coals and the like.

The primary object of the present invention is to provide a process for treating the high boiling tar acids of low temperature and primary tar origin to increase their market value.

With this object in View one feature of the invention contemplates converting such high boiling tar acids to low boiling tar acids such as phenol and cresols.

Heretofore it has been proposed to effect the reduction of high boiling tar acids of the class above referred to, to the lower boiling tar acids, by contacting a spray of the tar acids with a current of hydrogen in a highly heated tube, the hydrogen being obtained either from an external supply orelse by interaction of steam with iron or carbon within the hot tube. It has also been proposed to use catalysts such as nickel or activated carbon in conjunction with the hydrogen reduction of the tar acids. This latter method of treatment however, wherein hydrogen is caused to react with the higher boiling tar acids in the presence of catalysts, is not at all satisfactory in the matter of yields of the lower boiling phenols, the major portion of the recovered products consisting of low boiling hydrocarbons such as benzene and toluene. Moreover, the use of catalysts involves considerable expense for the rea- Applicatien filed. September 29, 1926. Serial No. 138,571.

son that all commercial tar acids contain appreciable quantities of sulphur compounds, and such sulphur compounds quickly poison any catalyst which is used in the reducing chamber, with the result that the catalyst has to be renewed very frequently.

Accordingly another object of the present invention is to provide a. process by which high boiling tar acids of the character referred to may be cheaply and substantially completely converted into valuable low boiling tar acids.

With these and other objects and features in view the invention consists in the process for producing low boiling tar acids hereinafter described and particularly defined in the claims.

Essentially'the process for producing low boiling tar acids forming the subject of the present invention, in its preferred form, consists in passing the vapors of high boil ing tar acids together with an excess of steam through a reaction tube containing no catalyst and having no catalytic effect, the tube being heated to a temperature between 600 and 800-C., preferably about 650 0., and the time, contact, and other reaction conditions being so regulated as to effect the conversion preferably of at least 90% of the original high boiling tar acids into valuable low boiling tar acids.

The following procedure is set forth as an example of a method of treatment which has been found entirely satisfactory: A tar acid fraction of low temperature tar consisting mainly of Xylenols was distilled by means of a current of steam through asilica tube heated by an electric furnace so that the temperature inside the tube registered 650 C. About three parts by weight of steam were used'for every part of tar acids. The liquid products obtained on condensation of the reaction vapors were analyzedand found to contain a mixture of phenol and cresols. The yield of the low boiling tar acids produced was found to comprise 94.3% of thecalculated theoretical yield of cresols obtainable from the original volume of xylenols taking part in the reaction. The process has also been applied to the treatment of low'temperature tar distillates containing hydrocarbon oils and nitrogen bases in admixture with high boiling tar acids, so that the process is not limited in its application to the treatment of tar acids alone, but may be employed if desired in the direct fractional distillation of oils containing such high boiling tar acids, with the object of recovering the tar acid content in a converted low boiling form.

As previously mentioned, prior experimenters on the conversion of high boiling to low boiling tar acids have all employed hy-.

drogen as the reducing agent by which to split ofl the alkyl groups from the high boiling tar acids and thereby convert the high boiling tar acids into lower boiling phenols. Experiments have shown, however, that hydrogen is not a satisfactory agent to employ for carrying out the conversion, and the reason that hydrogen has not proven to be the best agent for this purpose is thought to be demonstrated by the following consideration of the equilibria involved in the various reactions taking place in the conversion chamber. There are apparently two main reactions taking place when hydrogen and tar acid vapors are mixed at an elevated temperature. In one of these reactions the hydroxyl group of the tar acids is split out and immediately combines with the hydrogen to form water, the tar acids being thus con verted into hydrocarbons. In the other principal reaction the alkyl side chains are split out from the tar acid and combine with the hydrogen to form gases, the tar acids being thus reduced tothe lower boiling phenols. These two reactions may be expressed as follows, the higher boiling tar acids being represented as xylenols C H (CH OH, and the lower boiling phenol products of the conversion being represented as cresols C ILCI-LOH.

1- OGHg 20H H2 C IL (CTI 2 I1 0 2. 0 11 (CH 0H H,

The reaction designated as (1) above is undesirable since it leads to a production of hydrocarbons instead of to the production of valuable low boiling phenols such as are produced by reaction (2). It is thought that the greater yields of low boiling tar acids which are obtained by the present method over the former proposed methods of produc- 111g high boiling tar acids by means of hydrogen may be explained by a consideration of the law of mass action. Thus it is believed that an application of the law of mass action to the reaction (1) above will show that this undesirable reaction would be retarded by the presence of a large molar excess 9f steam in the reaction chamber. since steam 1s one of the two products of the reaction. B37 employing steam in place of hydr g n and by carrying out the conversion reactions at a temperature far below the lowest temperature at which decomposition of steam takes place and in the absence of any catalyst for such decomposition, reaction (1) is entirely avoided by the process of the present invention. Experiments carried out in connection with the present invention have shown that steam at temperatures between 600 and800 C. and in the entire absence of catalysts is as suitable an agent as hydrogen for causing the splitting off of the alkyl side chains from high boiling tar acids, as expressed in reaction (2) above. Thus the reaction taking place when steam rather than hydrogen is employed as the dealkylating agent may be represented as follows:

Any tendency of the hydrogen which is produced in this reaction to enter into reaction with the hydroxyl group of the tar acids in accordance with the reaction (1) to produce hydrocarbons is greatly retarded, if not entirely inhibited, by the presence of the large molar excess of steam in the reaction chamber, as explained above. In fact it 1s believed that the production of hydrocarbons, as in reaction (1) above, is entirely eliminated in carrying out the preferred planof the present invention at temperatures n the neighborhood of 650 C., for experiments have shown that reaction (1) above proceeds very slowly at temperatures below 700 C., in the absence of catalysts. I

In order that the steam may not react with the walls of the hot reaction tube, with consequent conversion into hydrogen, it is preferred to use materials in the construction of the hot tube which are inert toward steam and which also will not act as catalysts for the undesirable reactions resulting in the production of hydrocarbons by reduction of the high boiling tar acids. The reaction tubes may be constructed either of a material, such as fused silica or porcelain, which is inert towards superheated steam, tar acid vapor. and their conversion products, or else the tubes may be constructed of some material which becomes quickly coated with a stable film on contact with air or steam at elevated temperatures. and becomes thereafter inert toward superheated steam, tar acid vapors, and their conversion products. As an example of the second class of materials mentioned above aluminum may be cited. On heating in air or steam aluminum becomes coated with a very stable film of oxide which is inert towards the steam and the tar acids and their conversion products. Aluminum. however, is not a satisfactory material for use in making up the reaction tubes employed in accordance with the process of the present invention, because of its low fusion point.

Calorized iron on the other hand (specifically iron having a coating of. aluminum) behaves in the same manner on heating in the presence of air or steam as does aluminum, and has been found to be a very satisfactory material for use in making up the reaction tube. There are, undoubtedly, other materials which are equally as satisfactory as calorized iron in the respects mentioned above.

Another advantage which should be noted as directly resulting from the use of steam in effecting the reduction of high boiling tar acids is that it serves to prevent any deposition of carbon in the hot reaction tube, such as might occur in the absence of steam through complete decomposition of some of the tar acids. Thus when tar acids alone, in the absence of steam, are passed through a hot tube, a considerable amount of cracking of the tar acid molecule takes place with resultant deposition of carbon and the formation of some low boiling hydrocarbons. It has been known for some time that if small quantities of steam are introduced into a hot tube wherein cracking reactions are promoted, the deposition of carbon is thereby prevented. However, so far as known, all prior processes for producing low boiling tar acids from high boiling tar acids are based primarily on thermal decomposition of the tar acid molecules, the resulting products consisting almost entirely of hydrocarbons with only small amounts of low boiling phenols. According to the process forming the basis of the present invention, on the other hand, a large molar excess of steam is employed. Thereby the tar acids are protected from thermal decomposition and the steam and tar acid molecules interact chemically in accordance with stoichiometric laws to produce substantially quantitative yields of low boiling phenols and substantially no hydrocarbon products.

It is not intended that the above description shall be construed as limiting the invention in its scope or application to the use of any one temperature or of any one rat-i0 of steam to tar acids, nor to the treatment of any particular fraction or group of tar acids, nor to any particular method of efi'ecting the introduction of the tar acids and steam into the heated reaction tube. Thus although steam distillation was employed in treating the high boiling tar acids in the particular application of the invention cited as an example, any other method for introducing the tar acids and steam into the heated reaction tube may be employed, such for example as that of spraying the tar acids by means of a steam injector into the tube.

The term tar acids is used in the description and claims as a generic term to define all alkali-soluble hydroxy derivatives of aromatic and nonaromatic cyclic hydroresemble the phenols, cresols and the -phe-' nolic homologues of coke oven tar in some of their properties, do not come within the generally accepted definition of a phenol but are rather hydroxyl derivatives of cyclic hyv drocarbons which are nonaromatic in character, having hydrogen and alkyl side chains attached to the cyclic nucleus.

The preferred form of the invention having been thus described, what is claimed-as new'is: Y

'1. The process for converting high boiling tar acids into 'tar acids of lower boiling point, which comprises contacting vapors'of the former with a large molar excessv of steamat an elevated temperature ranging from1600'C. to 800 (3., adapted to facilitate the said conversion reactions, .in the absence of solid materials reacting with steam to generate hydrogen, and collecting the re action products. I

2. A process for converting high'boiling tar acids into tar acids of lower boiling point which comprises passing a mixture of vapors of said high boiling tar acids and superheated steam'through a reaction zone at a temperature between 600 and 800 C. in the absence of materials reacting with steam to generate hydrogen.

3. The process for converting'high boiling tar acids intotar acids of lower boiling point, which comprises contacting vapors of the high boiling tar acids with a molar excess of steam at an elevated temperature below 800 C. to cause conversion of the high boiling tar acids and to produce tar acids of lower boiling point without substantial conversion of the former to hydrocarbon products, the said conversion being conducted in the absence of catalysts adapted to facilitate hydrogenation reductions.

4. The process for converting high boiling tar acids into tar acids of lower boiling point, which comprises passing a mixture of vapors of the high boiling tar acids and steam through an independently heated unobstructed reaction chamber maintained at an elevated temperature not higher than 800 C. but sufliciently high to cause the conversion reactions to occur between the components of the mixture and to produce tar acids of lower boiling point, the inner surfaces of the reaction chamber in contact with the vapor mixture being made of a material which is nonreactive with superheated steam to generate hydrogen at the temperatures employed.

5. A process for converting high boiling tar acids into tar acids of lower boiling point which comprises passing a mixture of about one part by weight of the vapors of the high boiling tar acids and about three parts by weight of steam through a reaction zone heated to a temperature in the neighborhood of 650 C. in the absence of iron, and condensing and collecting the mixture of vapors leaving said reaction zone.

6. The process of treating low temperature tar distillates containing high boiling tar acids which comprises vaporizing the said distillate and contacting the vapors thereof with steam in amount by weight greater than the amount of high boiling tar acids present in the said distillate while maintaining an elevated temperature between 600 C. and 800 0., in the absence of any catalyst adapted to facilitate decomposition of the steam to form hydrogen at the temperatures employed.

, 7. The process of converting high-boiling tar acids into tar acids of lower boiling point which comprises, injecting vapors of the former with a molar excess of steam into a reaction zone maintained at a temperature of from 600 C. to 800 0., which zone is free of solid materials adapted to react with steam to generate hydrogen, and collecting the reaction products.

8. The process for converting high-boiling tar acids into tar acids of lower boiling point which comprises, passing a mixture of vapors of the said high-boiling tar acids and a molar excess of steam through a reaction zone maintained at a temperature within the range 600 C. to 700 C., in the absence of solid materials capable of reacting with steam at the said temperature to generate hydrogen.

In testimony whereof I afiix my signature.

SOLOMON OAPLAN.