US2874115A - Preparation of odorless naphthas from heavy alkylate hydrocarbons - Google Patents

Description

United Sta 2,874,115 PREPARATION OF ODORLESS NAPHTHAS FRGM HEAVY ALKYLATE HYDROCARBONS George W. Ayers, Chicago, and Walter J. Sandner, Carpentersville, Ill., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application January 5, 1956 Serial No. 557,435 4Claims. (Cl. 208- 285) The present invention relates to a method of preparing odorless naphthas and, more particularly, to a step- Z,8?d-,ll5 Patented Feb. 1?, E59

f@ in Table 11 Odor Expt. Vac.

No. dist. H O wash Alk-wash Storage Immediately after treatment 6 wks 6 mos.

No Essentially odor1ess-. Bad Very bad. No--.. Bad. No.... Do. No.-.. Present N 0.-.- No ad. Yes.-. Very bad Yes... ad. Yes... Step II... Do. Yes-.- Steps I and II... Slight Yes... No Bad.

wise process for the preparation of odorless naphthas from heavy alkylates.

The problem of preparing naphthas which are not only free of odor after treatment, but remain odor-free during storage over extended periods of time, has been of long standing. There are many claims in the art made to processes for removing ,odorous materials from hydrocarbons. In general, these processes relate to the removal of sulfur compounds and nitrogen compounds and may be classified'as sweetening processes. The steps of these prior art methods, whether chemical or physical when applied to alkylate fractions, have been found to be inadequate for the removal of odor or the prevention of odor formation during storage.

Now, in accordance with the present invention, it has beenfound that stable, odorless naphthas may be prepared from heavy alkylates and fractions thereof by the steps of vacuum distillation and thorough water washing, followed by washing with an aqueous alkali solution. In order to demonstrate the invention, a sample of heavyalkylate produced by the hydrofluoric acid alkylation of isobutane with isobutylene, and subsequent removal of the lower boiling hydrocarbons by distillation, was divided into a plurality of samples. This heavy alkylate exhibited the following distillation characteristics.

Table 1 Washed and/or alkali washed and the sequence of these operations. In Experiments 4 and 9 a double waterwash was used. In Experiments 5 and 10 a double alkali-wash was used. It is observed that only in that instance where the heavy alkylate was treated to the sequence of steps of vacuum distillation, double water washing, and alkali washing was a. product formed which not only had. no appreciable odor immediately after treatment, but i did not produce appreciable odor on storage. Reversal of the steps of treatment, single treatments with water and alkali solution, or omission of the water-washing ,step failed to produce an odor-free,

storage-stable product. The experiments clearly indicated that very thorough water washing is necessary before the caustic washing step is applied if the odorless character of the fractions is to be maintained through the caustic washing step. Although the invention is not to be limited to any theoretical considerations, it would appear that certain of the water-soluble, odorforming materials in thefdistilled naphtha are transformed into malodorous materials on contact with the caustic. The experiments also indicate that a double water wash is very effective whereas a double alkali wash or the omission of the water-Washing step is detri- AS'IYM boiling range F.) API Percent Percent Percent Odor gravity LBJ. 5% 10% rec. res. loss 1. 6 0. 4 Essentially odorless.

mental. Since the alkali-wash step is an added step in the processing, it would be desirable if the step could be eliminated and experiments were conducted to explore this possibility.

It was found that the storage stability of alkylate fractions is greatly enhanced by applying an extremely thorough water-wash step using from 5 to 7 applications of equal volumes of water, and the caustic-wash step could be eliminated in some instances. This allows the refiner to produce an odor-free stable product Where the use of a caustic-wash step may be inconvenient, that is, the facilities or materials are not available. It was found that the caustic washing of such fractions which have been exhaustively treated with water does not result in immediate odor deterioration during the caustic washing step and usually results in a more stable material on prolonged storage than where caustic treatment is not used. Thus, the caustic washing may be applied only where it is intended to subject the alkylates to storage for long periods of time. In order to demonstrate this aspect of the invention, the following examples are given:

Example 1.A 500 cc. portion of heavy alkylate, the same as previously described, was distilled under 1.5-2.0 mm. pressure in a current of nitrogen gas. The first 75% by volume of the distillate, which had the proper distillatlon range for odorless mineral spirits, was essentially odorless. On standing 70 days at ordinary temperature, in subdued light in a cork-stoppered glass bottle under air, a portion of this distillate developed an odor which made the material unsuitable as an odorless naphtha. Another portion of the fresh distillate was washed twice with equal volume portions of water, then with an equal volume of 5% sodium hydroxide solution, and finally with five equal volume portions of water. The product was essentially odorless and showed much less odor detenoratlon on standing than did the unwashed material. A third portion of the fresh distillate was washed first with an equal volume of 5% sodium hydroxide solution, and then five successive times with equal volume portions of water. The product developed a very objectionable odor during the caustic treatment which was not removed during the subsequent water washes and which made the product unsuitable as an odorless naphtha.

Example 2.-A sample of the heavy alkylate was distilled under 3 mm. pressure without the addition of inert gas or steam during the distillation. The first 85% of the distillate was essentially odorless when prepared but rapidly acquired a very pronounced odor upon storage in a cork-stonpered bottle under air at ordinary temperatures for 70 days. Thorough washing of the fresh distillate with water slowed down the odor deterioration to such an extent that the distillate was still satisfactory as odorless naphtha after 70 days standing. Thorough water-scrubbing of the deteriorated sample, which had not previously been treated with water but which had stood for 70 days, improved the odor to such an extent that the product could still be used as an odorless naphtha.

Example 3.--A sample of the heavy alkylate was distilled under 100-115 mm. pressure, using approximately 7 lbs. of steam per gallon of distillate. Thedistillate, which represented 75% of the heavy alkylate charged, was essentially odorless. On standing 70 days under air in a cork-stoppered glass bottle in subdued light at ordinary temperature, there was a slight odor deterioration of the distillate. Thorough washing of the fresh distillate with water resulted in greatly improved odor stability of the material after 70 days storage under the conditions mentioned previously. A sample of the distillate which had been washed with caustic soda solution after the water scrubbing operation did not develop additional odor during caustic washing and showed substantially no odor deterioration on storage for 70 days.

By ordinary washing with water is meant the usual 4 water washing operations as are customarily carried out in petroleum refineries where 1 or 2 washes with equal volumes (or less) of water are applied. By thorough or extremely thorough water washing is meant the use of from 3 to as high as 10 washes with equal volumes of water. The preferable range is to use from 5 to 7 applications of equal volumes of water to the alkylate. The proportions of water used in ordinary counter-current washing of hydrocarbons as applied in the refinery is not sufiicient to prevent the development of odor in heavy alkylate fractions during subsequent treatment with caustic soda solution.

Another advantage of our invention is that no special equipment is necessary in the scrubbing operations, and it is not necessary to use elevated temperatures. The ordinary batch or continuous counter-current apparatus may be used at ambient temperatures. The caustic solutions used may contain from 0.1 to 10% by weight caustic present as the alkali metal hydroxide. Although sodium hydroxide is preferred because of its cheapness, other alkalis may be applied such as potassium and lithium hydroxide.

The distillation step is carried out for the purpose of separating at least about 75% by volume of the heavy alkylate as a distillate having the proper distillation range for odorless mineral spirits. For this purpose a vacuum is applied of about 1.0 to 3.0 mm. of mercury. A current of an inert gas such as nitrogen may be employed during the distillation as a precaution against thermal degradation of the heavy alkylate. The temperatures used and the length of time employed in the distillation will depend on several factors, including the boiling range of the heavy alkylate, the amount of vacuum applied, the amount of heat available and the column efficiency. In general, the boiling range of the heavy a1- kylate distillate collected for subsequent treatment in accordance with the invention will vary from 340 F. to 410 F. For heavy alkylates boiling from 340 to 520 or 525 F. it will be necessary to remove or discard from 5 to 25% of the unvaporized ends. Since in many instances these heavy alkylates are supplied in the form of distilled or semi-purified fractions,'the invention may be applied to such fractions without the distillation step.

The invention may be broadly defined as including the steps of vacuum distillation to separate at least 7% of the heavy alkylate as a distillate, condensing same, and applying the thorough water-wash step followed by the wash with an alkali metal hydroxide solution in this sequence, or simply applying the thorough water-wash and alkali metal hydroxide-wash steps to a distilled alkylate fraction, or the application of a thorough water- Wash step using from 3 to 10 applications of equal volumes of water to a distilled heavy alkylate fraction, whereby an odor-free, storage-stable product is obtained. As previously explained, the use of a thorough or extremely thorough water wash alone is only applicable to those instances where it is not intended or necessary that the product withstand very extended periods of storage. By extended periods of storage is meant more than 6 months storage.

Having thus described the invention, the only limitations attaching thereto appear in the appended claims, wherein the termheavy alkylate hydrocarbons is to be interpreted to include such products as may be produced I in the alkylation of paraffins or isoparaffins with olefins,

with subsequent removal of lower boiling hydrocarbons by distillation, such as are well known in the art. Representative processes are to be found in the prior art United States Patents 2,334,861 of Bowles, 2,335,507 of Grosse and Linn, 2,335,704 of Smith, 2,336,005 of Frey and 2,338,248 of Kassel.

What is claimed is:

1. The process for preparing odor-free naphthas from heavy alkylate hydrocarbons produced by the reaction of a paraffinic hydrocarbon with an olefinic hydrocarbon in the presence of an alkylation-promoting catalyst consisting in treating said heavy alkylate hydrocarbons to separate a fraction boiling in the naphtha boiling range, subjecting said naphtha fraction to first-stage, liquidphase Washes with from 3 to 10 substantially equal voltunes of water per volume of alkylate and a second-stage, liquid-phase wash with an aqueous alkali metal hydroxide solution and separating as the insoluble hydrocarbon phase an odor-free, stable naphtha fraction.

2. The process in accordance with claim 1 in which the heavy alkylate hydrocarbons are produced by the acid alkylation of isobutane and isobutylene and said heavy alkylate has a boiling range of about 340 to 15 4. The process for preparing an odor-free, storagestable naphtha which consists in subjecting a heavy alkylate having an API gravity of about 540 and a boiling range of 340 to 540 F. to distillation to separate a fraction-boiling in the naphtha boiling range, subjecting said naphtha fraction to liquid-phase washes with from 3 to 10 substantially equal volumes of water per volume of naphtha, subjecting the water-washed naphtha to liquid-phase treatment with an alkali metal hydroxide solution containing about 0.1 to 10% by weight of alkali metal hydroxide and removing an essentially odor-free, stable naphtha product.

References Cited in the file of this patent UNITED STATES PATENTS 2,463,601 Cranford Mar. 8, 1949 2,468,986 Legatski et al May 3, 1949 2,507,103 Heinrich et al. May 9. 1950

Claims (1)

1. THE PROCESS FOR PREPARING ODOR-FREE NAPHTHAS FROM HEAVY ALKYLATE HYDROCARBONS PRODUCED BY THE REACTION OF A PARAFFINIC HYDROCARBON WITH AN OLEFINIC HYDROCARBON IN THE PRESENCE OF AN ALKLATION-PROMOTING CATALYST CONSISTING IN TREATING SAID HEAVY ALKYLATE HYDROCARBONS TO SEPARATE A FRACTION BOILING IN THE NAPHTHA BOILING RANGE, SUBJECTING SAID NAPHTHA FRACTION TO FIRST-STAGE, LIQUIDPHASE WASHES WITH FROM 3 TO 10 SUBSTANTIALLY EQUAL VOLUMES OF WATER PER VOLUME OF ALKYLATE AND A SECOND-STAGE, LIQUID-PHASE WASH WITH AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION AND SEPARATING AS THE INSOLUBLE HYDROCARBON PHASE AN ODOR-FREE, STABLE NAPHTHA FRACTION.

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