US2745793A - Deleading gasoline - Google Patents

Description

limited States Patent DELEADING GASOLINE James L. Jezl, Swarthmore, and Ivor W. Mills, Glenolden, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application February 2, 1953, Serial No. 334,754

Claims. (Cl. 196-23) This invention relates to the removal of lead from gasoline by means of silica gel at elevated temperature.

Most commercial gasolines contain tetraethyl lead which has been added to increase anti-knock rating. Various situations arise Where it is desirable to remove the lead compound from the gasoline. One such instance occurs in refinery practice when the charge stock to a reforming operation which utilizes a platinum catalyst is found to contain lead. This may happen due to inadvertent mixing in the refinery of commercial gasoline containing tetraethyl lead with stocks intended for charging to the reformer operation, or due to the use of the same tanks for storing commercial gasoline and reformer stocks alternately. In cases of this kind, it is highly important that the reformer stocks be deleaded before introduction to the platinum catalyst, since lead is poisonous to the catalyst and will cause it rapidly to lose its effectiveness for promoting the desired reforming reactions.

Another situation where deleading of gasoline is desirable arises in connection with the use of certain apparatus, such as gasoline lanterns and stoves used by armed forces in the field or by farmers, which apparatus should be operated with gasoline free of lead. In such cases it may happen that the only gasoline avail able at the locus of use contains tetraethyl lead. A suitable method is then needed for deleading the available gasoline stock.

Still another instance where deleading of gasoline is desirable occurs in connection with the testing of gaso line samples. A refiner may wish to know the character of unleaded base stocks used by other refiners in producing competitive commercial gasolines. A simple procedure for deleading samples of the commercial products without substantially affecting the quality of the base stocks is therefore desirable.

Various chemical methods have been proposed for deleading gasoline but they have not been entirely satisfactory. These methods generally are not capable of achieving complete removal of lead or are objectionable in that the character of the base stock changes due to reaction with the chemicals employed.

The present invention is directed to a method of deleading gasoline which is capable of effecting substantially complete removal of the lead and which does not affect the character or quality of the base stock substantially. According to the invention, gasoline containing tetraethyl lead is contacted with silica gel at a temperature above 200 F., whereby the lead is retained in the silica gel. The treated gasoline is then separated from the silica gel, yielding a deleaded product.

The contacting step can be carried out with the gasoline either in liquid phase or in vapor phase and any suitable method of contacting at the specified elevated temperature may be used. For example, a mixture of the gasoline and a small amount of silica gel, such as 0.5- 5.0% silica gel by weight based on the gasoline, may be agitated in a pressure vessel or may be refluxed at at- 2 mosphcric pressure when the initial boiling point of the gasoline stock is sufiiciently high. Another procedure comprises adding the silica gel to the gasoline and then distilling the latter from the silica gel. Still another procedure, involving vapor phase contact only, comprises vaporizing the gasoline and passing the hot vapors through a bed of the silica gel.

In any of these methods of carrying out the contacting step, the temperature of contact should be above 200 F., preferably being in the range of 250450 F., and the time of contact at such temperature should be sufficient to effect the desired removal of lead. As a general rule, the time of contact for securing complete lead removal decreases as the contacting temperature is increased. The exact mechanism by which removal is effected is not certain; but it is believed that it involves an adsorption of the tetraethyl lead by the silica gel followed by a catalytic decomposition of the adsorbed compound into a form which is firmly held by the silica gel. The decomposition reaction, which is catalyzed by the silica gel at temperatures above 200 F., thus prevents the adsorption phenomenon from being reversible and insures complete removal of lead from the gasoline if suflicient time is allowed during contacting to permit decomposition of the tetraethyl lead to become complete. The rate of this catalytic decomposition evidently is related to temperature, so that higher temperatures allow shorter times of contact for achieving the desired result.

The following examples are illustrative of the invention:

Example I A series of runs was made with five different leaded gasolines. The procedure comprised adding 1% by weight of 28-200 mesh silica gel to 1000 ml. of the gasoline in a distillation flask and then distilling off the gasoline through a conventional laboratory bead tower at a rate of about 5 ml. per minute. After about 95% of the gasoline had been distilled, water was added to the flask and the distillation was then continued until essentially all of the hydrocarbons had been stripped from the silica gel. The distilled gasoline was tested to determine lead content, with results as follows:

A. s. T. M. Distillation Lead g Sample No.

50% Endpoint Original Deleaded These results show that the procedure described resulted in removal of essentially all the lead from each of the gasolines except Sample No. 4 which had a small amount of lead remaining. This sample was an aviation gasoline of relatively low boiling range, so that the time of contacting at a temperature above 200 F. was considerably shorter and the maximum temperature of contact was considerably lower than with the other samples. Complete removal of lead from Sample No. 4 could have been effected by increasing the time of contact at the higher temperatures reached in the distillation or by increasing temperature as by carrying out the distillation at increased pressure. By way of comparison with the results shown above, it should be noted that distillation of a leaded gasoline in the absence of the silica gel has little if any efiect on the lead content.

Example 11 A gasoline having an A. S. T. M. boiling range of about 80-420 F. and a lead content of 3.0 cc./gal. was refluxed with 4% silica gel of 28-200 mesh for 3 hours. The temperature during this time was gradually increased to a maximum of 300 F., and 65% of the gasoline distilled off through the refluxing condenser and was recovered. The residual gasoline was separated from the silica gel by filtration, and both it and the distillate were tested for lead content. Neither material contained any detectable amount of lead.

Example III Another sample of the gasoline of Example II was refiux'ed for 2 hours with 1% silica gel, the temperature being increased to a maximum of 230 F. Analysis of the combined distillate (29%) and residual (71%) gasoline showed a lead content of 1.85 cc./ gal. This indicates that the time of contact was insufiicient at the relativel'y low temperatures employed to achieve efiective deleading.

By way of comparison, it has been found that other adsorbents, such as alumina, magnesia or clay, are not nearly as effective as silica gel. The treatment of leaded stocks with such other adsorbents at high temperature will cause some lead removal but the degree of removal is not comparable to that obtained with silica gel. It appears that these other adsorbents, while being capable of adsorbing tetraethyl lead to an extent, are inefiective in catalyzing the decomposition reaction. Hence, they will remove only the amount of tetraethyl lead dictated by the adsorption equilibrium between the solid and fluid phases, so that substantial amounts of lead will remain in the gasoline phase even after a long time of contact at high temperature. For example, it was found that treating the leaded gasoline of Example II by 4 refluxing for 3 hours with 4% alumina, the final temperature beingv 320 F. at which point 75% had distilled overhead, resulted in reduction of the lead content of the combined distillate and residuum to a value of only 1.47 cc./gal., as compared to 0.00 cc./gal. when silica gel was used as described in Example II.

We claim:

1. Method of deleading gasoline which comprises contacting a gasoline containing tetraethyl lead with silica gel at a temperature above 200 F. and separating the gasoline from thesilica gel, whereby lead is retained in the silica gel.

2. Method according, to claim 1 wherein the gasoline when contacted with the silica gel is in liquid phase and the amount of silica gel is 0.55.0% by weight on the gasoline.

3. Method according to claim 2 wherein the gasoline is contacted with the silica gel at a temperature of 250- 450 F.

4. Method according to claim 1 wherein the gasoline References Cited inthe file of this patent UNITED STATES PATENTS 2,368,261 2,571,936 Patterson et al. Oct. 16, 1951 OTHER REFERENCES Mantell, Adsorption, First Edition McGraw-Hill Book Co, Inc., New York, 1945, pages 46 and 167.

Neef Jan. 30, 1945 i

Claims (1)

1. METHOD OF DELEADING GASOLINE WHICH COMPRISES CONTACTING A GASOLINE CONTAINING TETRAETHYL LEAD WITH SILICA GEL AT A TEMPERATURE ABOVE 200* F. AND SEPARATING THE GASOLINE FROM THE SILICA GEL, WHEREBY LEAD IS RETAINED IN THE SILICA GEL.