US2678955A - Upgrading of crude naphthalene crystals by hot detergent washing - Google Patents

Description

May 18, 1954 c. B. OGlLVlE UPGRADING OF CRUDE NAPHTHALENE CRYSTALS BY HOT DETERGENT WASHING Filed Nov. 1, 1951 INVENTOR CLINTON B. OG/ZV/[ ATTO R N EY Patented May 18, 1954 UPGRADING 0F. CRUDE NAPHTHALENE CRYSTALS BY HOT DETERGENT WASH- ING Clinton B. Ogilvie, Martinsville, N. J., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine Application November 1, 1951, Serial No. 254,260

3 Claims.

This invention relates to an improvement in the purification of naphthalene, and more particularly, to an improvement in the separation of oily impurities from naphthalene of coal tar or petroleum origin.

The impurities associated with crude naphthalene will vary, depending upon whether the naphthalene was obtained as a by-product from coal tar or petroleum. It is common practice to combine naphthalene from both sources in storage and crude stocks will vary both in naphthalene content and in the impurities present. Our invention is applicable to the purification of naphthalene from either petroleum or coal tar sources and is particularly effective in the upgrading of naphthalene primarily derived from coal tar.

In the refining of naphthalene from coal tar sources, it is customary to remove the tar acids by suitable washing treatments with strong alkali. Naphthalene from petroleum sources does not have any considerable portion of tar acids, and therefore with such naphthalenes the Washing treatment is usually omitted. The naphthalene, free from tar acids, is then generally placed in the so-called crystallizing pans or boxes where it is permitted to stand for a long period of time, a matter of weeks or even months, until a considerable portion of the oily materials drain out. The partially purified naphthalene is then hot pressed or sometimes centrifuged to remove further amounts of oily materials, followed by sulfuric acid washing and fractional distillation. It is thus possible to obtain naphthalene of a high purity, as evidenced by its melting point of about 79.7 (3;, which represents a. purity of at least 98.5%. Naphthalene of this purity is normally required when it is to be used for dyestuff intermediates, for example, in the preparation of naphthols. Naphthalene melting at 78 C. is satisfactoryfor the preparation of phthalic anhydride.

The ordinary refining of naphthalene presents a serious problem from the standpoint of equipment capacity, particularly in the crystallizing pans or boxes, where the time of residence of the naphthalene is excessively long. The other steps such as hot pressing, sulfuric acid washing, and fractional distillation, also add to thecost of the refined naphthalene and require extensive equipment.

Various processes have been proposed for removing oily impurities from naphthalene and the separation of similar organic solids. In one process, naphthalene was crystallized in relatively large flat crystals and washed with brine. This process, while effecting some purification, was not sufiicient to replace any considerable number of the timeand equipment-consuming steps. The production of large crystals required very slow cooling and little or no agitation. While with shallow depths it is theoretically possible to cool for less than an hour, in general, the cooling extends over a number of hours, for example, six to nine. With a typical crude coal tar naphthalene, the crystals may be brought up to a setting point of a little over 74 C. This process, therefore, did not solve the problem of producing sufiiciently cheap naphthalene of phthalic anhydride intermediate grade.

Gould, in his Patent No. 1A81,197,- has described an efficient method of precipitating naphthalene in crystalline form by heating the crude naphthalene above the melting point and pouring it into cold water with agitation. The crystals when separated, however,- still occlude a large amount of the oily impurities and the napthalene must be purified further before it can be used.

According to the present invention, we have.

found that naphthalene in the crystalline form as obtained by Goulds process or some similar process, may be upgraded by hot detergent washing to produce a product melting at 73 C. or better, in a single step. It is an advantage of the present invention that when this new process improved method to'be described in conjunction with the drawing which is a diagrammatic fl'o'wsheet of my new'process.

In the drawing, l' is a tank containing the wash solution and surrounded by a heating jacket which'controls the temperature of the wash solution.

A feed pump 2 supplies the spray nozzles with the wash solution under pressure.

The washing rate is determined by means'of a flow m'eter3 and the whizzer type centrifuge 4" has'an outlet at'the bottom to permit recovery of. the used wash solution.

acvaocs In upgrading naphthalene according to my invention, I charge crude naphthalene crystals melting at about 68 C. or above into the centrifuge 4 at low speed. I then prepare the wash solution of desired composition and heat it in tank I. The centrifuge is rotated at high speed while the wash solution is forced by pump 2 through flow meter 3 to the spray nozzles within the centrifuge. After the specified volume of wash water has been applied to the crude naphthalene crystals, I wring the cake in the centrifuge for a short while. The centrifuge is then stopped and the upgraded material removed from the basket.

In order to obtain naphthalene melting at 78 C. or better, from the crude crystals melting at 68 C. or above, it is necessary to control certain steps in my process which are critical. The temperature of the Wash solution is particularly important because too low a temperature will result in a product below specification. For this reason, the temperature of the wash solution should be above 65 C. and in general, I heat the wash solution to 75 C. There is considerable cooling due to the rapid motion of the centrifuge basket and to the low temperature of the crude naphthalene crystals at the start of the washing operation. Thus, the first wash water which enters the centrifuge at 75 C. leaves the centrifuge at 53 C. and toward the end of the washing process the temperature of the effluent has increased to 74. The final temperature of the combined wash water is 59 C. For this reason, the wash solution may be heated to temperatures considerably above the setting point of i the crude naphthalene crystals and the upper limit of the temperature range would be that temperature which would result in fusion of the crude naphthalene crystals charged into the centrifuge.

The detergent used is also critical because some detergents do not produce a naphthalene of satisfactory melting point and others introduce foaming and caking. We have discovered that surface active agents which do not produce insoluble calcium salts are satisfactory in that they will produce specification grade naphthalene.

Anionic surface active agents that are derived from high molecular Weight organic sulfonates have certain operating advantages over the cationic and nonionic type. One such advantage is the lack of foaming which is particularly important with centrifuges of the size used in large commercial operations. Another advantage is the elimination of caking. Certain cationic and nonionic surface active agents although not precipitated by calcium ions, will permit the build-up of a cake on the inside jacket of the centrifuge and between the basket and the centrifuge screen. This necessitates the shutdown of equipment and the periodic cleaning of the centrifuge which naturally increases the washing cost. We particularly prefer to use di(2-ethyl hexyl) sodium sulfosuccinate in the wash water because that particular reagent keeps the centrifuge and basket clean at all times, thus enabling the operation to be used on a continuous basis without shutdown. The amount of surface active agent may be varied, but we have found approximately based on the total wash solution, was satisfactory. An increase in this amount did not give any appreciable improvement in results, but decreasing the amount gave results approaching a straight water wash which was unsatisfactory.

The amount of wash solution is related to' its temperature, but in general, approximately five parts wash water at 75 C. is used for one part crude naphthalene crystals. If less wash water is used, the temperature must be raised to obtain comparable results. Increasing the amount of wash water slows up the process and introduces new problems, so that we have found the ratio of approximately five to one to be an effective compromise.

In addition to the surface active agents, it is advantageous to add one-half of one percent sodium carbonate to the wash solution. Sodium carbonate primarily reduces the water occluded by the centrifuged crystals, and secondarily, has a beneficial effect on the setting point of the purified crystals. More than one-half of one percent sodium carbonate, however, has the opposite effect on occluded moisture and cannot be used without introducing foaming problems.

,Sodium carbonate also aids in breaking the emul- Crude naphthalene, predominantly of coal tar origin, having a setting point of 69.9 C. and containing 78.8% naphthalene, was charged into a centrifuge and washed at high speed (1450 R. P. M.) with 133 parts of wash solution containing 0.125% of aerosol OT (di(2-ethyl hexyl) sodium sulfosuccinate) at a temperature of 35 C. The wash solution was sprayed on the cake at a rate of about 25 parts per minute. The charge was wrung at high speed until essentially free of wash solution and the centrifuge then stopped. The cake when removed from the basket was approximately 92.8% pure and had a setting point of 76.83 C. This product did not meet specification because the temperature of the wash solution was too low. The yield of naphthalene recovered was better than 90% based on the naphthalene present in the centrifuge charge. The moisture content of the cake was 24.8%.

Emample 2 The procedure of Example 1 was followed, but the temperature of the wash solution was increased to 60 C. The naphthalene was upgraded from 692 C. setting point (77.6% purity) to 77.8" C. (94.8% purity), again indicating that the temperature of the wash solution was too low. The yield was approximately 88%. The final moisture content of the cake was 19.3%.

Example 3 The procedure of Example 1 was followed, using a wash solution at a temperature of 70 C. Upgrading from 690 C. S. P. (77.25% purity) to 78.50 C. S. P. (96.2% purity) was achieved with an 80% yield on the basis of naphthalene charged. Final moisture content of the cake was 12.8%.

Example 4 The procedure of Example 1 was followed using the wash solution at a temperature of 80 C. Upgrading from 703 C. S. P. (79.5% purity) to 79.35 C. S. P. (97.9% purity) was achieved with about 70.0% yield. Final moisture content of the cake was 6.1%.

Example 5 To the wash solution of Example 3, 0.5% soda ash was added and the procedure was repeated according to that example. Upgrading from 68.5 C. S. P. (76.3% purity) to 785 C. S. P. (96.2% purity) was achieved with better than 80% yield on the basis of real naphthalene charged. Final moisture content of the cake was 5.4%.

Example 6 Example 7 The procedure of Example 3 was followed with 0.125% by-weight of NI-l-182 (product of one mole of dimerized fatty acid and two moles of Carbo Wax #4000) being used in place of aerosol OT in the wash solution. Upgrading from 69.1 C. S. P. (77.4% purity) to 78.10 C. S. P. (95.4% purity) was achieved with an 88.6% yield on the basis of real naphthalene charged. Final moisture content of the cake was 8.2%. Considerable caking was noted in the centrifuge basket.

Example 8 The procedure of Example 3 was repeated, using the Wash solution at a temperature of 65 C. The naphthalene crystals were upgraded from 69.6 1 C. to 780 C.

Example 9 The procedure of Example 8 was repeated, but the aerosol OT (di(2-ethy1 hexyl) sodium sulfosuccinate) was replaced by an equal weight of soap. The crude naphthalene crystals were upgraded from a setting point of 68.78 C. to a setting point of 77.41 C.

Example 10 The procedure of Example 8 was repeated, but the aerosol OT (di(2-ethyl hexyl) sodium sulfosuccinate) present in the wash solution was omitted. The naphthalene crystals were upgraded from a setting point of 69.30 C. to a final setting point of 77.23 C. by washing with water alone.

Example 11 The procedure of Example 3 was repeated, but the aerosol OT (di(2-ethyl hexyl) sodium sulfosuccinate) present in the wash solution was replaced by an equal weight of mixed amylnaphthalene sodium sulfonate. The naphthalene crystals were upgraded from a setting point of 693 C. to a setting point of 78.15 C.

It will be recognized that the effluent from the centrifuge may be reheated and recycled, thus improving the overall yield of my process. In addition, the oily layer which separates from the effluent emulsion may be recycled to the crude naphthalene stock and reprecipitated in crystalline form.

I claim:

1. A process for upgrading crude naphthalene crystals which comprises washing said crystals in a centrifuge with a wash solution containing less than 1% di(2-ethyl hexyl) sodium sulfosuccinate, the temperature of said solution being above C., but insuificient to melt said naphthalene crystals.

2. A process for upgrading crude naphthalene crystals which comprises washing said crystals in a centrifuge with a wash solution containing less than 1% di 2-ethyl hexyl) sodium sulfosuccinate, and approximately one-half of one percent sodium carbonate, the temperature of said solution being above 65 C., but insufiicient to melt said naphthalene crystals.

3. A process for upgrading crude naphthalene crystals which comprises Washing said crystals in a centrifuge with a wash solution containing less than 1% di(2-ethyl hexyl) sodium sulfosuccinate, the amount of said wash solution being approximately 5 times the amount of the crude naphthalene crystals, and the temperature of said solution being above 65 C., but insufiicient to melt the naphthalene crystals.

References Cited in the file *of this patent UNITED STATES PATENTS Number Name Date 1,441,417 Gould Jan. 9, 1923 2,078,963 Miller May 4, 1937 2,403,127 Schulze July 2, 1946 2,499,236 Van Gilder et al. Feb. 28, 1950 FOREIGN PATENTS Number Country Date 611,213 Great Britain Oct. 27, 1948

Claims (1)

1. A PROCESS FOR UPGRADING CRUDE NAPHTHALENE CYRSTALS WHICH COMPRISES WASHING SAID CRYSTALS IN A CENTRIFUGE WITH A WASH SOLUTION CONTAINING LESS THAN 1% DI(2-ETHYL HEXYL) SODIUM SULFOSUCCINATE, THE TEMPERATURE OF SAID SOLUTION BEING ABOVE 65* C., BUT INSUFFICIENT TO MELT SAID NAPHTHALENE CRYSTALS.

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