US2562767A - Sweetening of petroleum distillates - Google Patents

Description

Patented July 31, 1951 SWEETENING F PETROLEUM DISTILLATES John G. Browder, Houston, and Alvin R. Smith,

Baytown, Tex., assignors, by mcsne assignments, to Standard Oil Development Company, Elizabeth, N. J a corporation of Delaware No Drawing. Application March 23, 1950,

. Serial No. 151,516

' 11 Claims.

The present invention involves contacting a sour petroleum distillate having a boiling range of about 200 to 750 F. to which has :been added a small amount of methyl alcohol and betanaphthol in catalytic quantity with a solution of an alkali metal hydroxide to form a mixture thereof and maintaining the mixture undergoing contacting in the presence of a mild oxidizing agent in an amount sufiicient to sweeten the distillate, following which the alkali metal hydroxide is separated from the contacted distillate.

The invention is particularly adapted-to dis tillates boiling in the range from about 200 to 750 F. and has a special application to sweetening of kerosenes and the so-called solvent naphthas, the latter boiling in the range of 200 to 450 F.

The methyl alcohol may be employed in an amount in the range from about 0.1 to about 2.5% by ,volume (based on the sour distillate) with a preferred amount in the range from about 0.5 to about 1% by volume. The beta-naphthol may be employed in amounts based on the sour.

distillate varying from about 0.05 to about 1.0 gram per liter, the sum total of the methyl alcohol and beta-naphthol not being in excess of about 3.0% by volume of the sour distillate to be sweetened. The beta-naphthol and methyl alcohol are preferably added to the petroleum distillate, but may be added to the mixture of the alkali metal hydroxide and sour petroleum distillate undergoing a sweetening reaction.

The alkali metal hydroxide employed in the present invention preferably should be a solution of an alkali metal hydroxide. Preferably the solution should be an aqueous solution having a Baum gravity in the range of from about 30 "to about 50 Baum, but solutions of lower strength may be used under some conditions. An aqueous solution of sodium hydroxide of 40 Baum has been found to give satisfactory results in the practice of the present invention. Other alkali metal hydroxides besides sodium hydroxide may be used. For example, lithium and potassium hydroxidev may be used in lieu of sodium hydroxide, but the latter is to be preferred.

The temperature at which the treating operation is conducted will usually be atmospheric and may range from about 60 F. up to 200 F. and sometimes higher temperatures may be employed depending on the boiling range and the type of feed stock being treated. Apreferred temperature range may be from about to about atmospheric temperatures encountered in the Texas Gulf Coast area. 7

The process of ouriinvention may be carried out in suitable equipment which will allowv con-L tact of the sour distillateto. which methyl alcohol and beta-naphthol have been added with the alkali metal hydroxide and the mild oxidizing agent. For example, pumps, jet mixers, incorpo rators and contacting towers'may' be used. Such towers may be equipped with packing, bell cap; trays and other similar well known expedients for insuring contact between liquids and between liquids and gaseous materiaL' The present invention' will be illustrated, fur: ther by the following example:

EXAMPLE I A solvent naphtha having a copper number of less than 1 and having a boiling point in the range between 290 and 410 F. was dividedinto 1 required to sweeten the naphtha. After water washing it was also submitted to the above mentained tests. The third portion had added to it] 0.5% by volume based on the solvent naphtha of methyl alcohol andthen contacted with sodium hydroxide solutionas mentioned before, in the presence of 300% by volume of the theo-,. retical amount of oxygenrequired to sweeten. The fourth portion had added to it 0.05% by volumeof methyl alcohol and was subjected to contact with sodium hydroxide in the presence of 300% by volume of the theoretical oxygen required to sweeten same. The fifth portion had added to it 0.5 gram per liter of beta-naphthol and was then subjected: to contact with portions.- of the same sodium hydroxide solution inthe presence of oxygen in the. excess amounts -in-., dicated before. The sixth portion had added to it 0.1 gram of beta-naphthol per liter and was subjected to contact with the same (sodium hydroxide) caustic solution in the presence of 300% by volume of the theoretical amount of oxygen required to sweeten. The seventh and last por-- tion had added to it'0.05% by volume of methylalcohol and 0.1 gram of beta-naphthol per liter;

and was subjected to contact with the same caustic solution in the presence of 300% by volume of the theoretical amount of oxygen required to sweet-en. The results of these tests are It will be seen from thefor'egoing results that the only treatment which caused the solvent naphtha to pass the doctor test was the one where both methyl alcohol and beta-naphthol were present. All of the other treatments reflected that the naphtha was =not sweetened by virtue of the fact that it did not pass (DNP) the doctor test. It is of interest to note that the treatments did not affect the color of the solvent naphtha which remained at 30, the original color of the solvent naphtha being 30. Since the alcohol may have a detrimental effect on the flash point of solvent naphthas to which it and betanaphthol are added prior to contact with caustic solution and oxygen, it may be desirable in the practice of the present invention to remove the alcohol. This may be effectively done by washing the sweetened product with water or by heating the sweetened product to remove methyl alcohol therefrom by simple distillation. Neither one of the treating operations has any effect on the color. A sample of the solvent naphtha treated in accordance with the present invention as shown in column 7 of Table I was divided into three portions. Each of these portions contained a small quantity of alcohol by virtue of the alcohol having been added thereto inadmixture with beta-naphthol. One portion was heated to 150 F., the second portion to 200 F. and the third portion to 250 F. The flash points and Saybolt colors of the heated sweetened product were then determined and are shown in Table II:

1 About 80 F.

' It will be noted that heating the solvent naphtha to 150 F. effectively removed the alcohol, was indicated by the specification flash point, and heating the solvent naphtha to as high as 250 F. did not affect the color.

EXAIVIPLE II In order to illustrate further the synergistic effect of methyl alcohol and beta-naphthol in the practice of the present invention, a high sulphur refined oil raifinate, from solvent extraction of a hydrocarbon fraction in the kerosene boiling range, having a copper number of 40 was divided into eight portions. One portion was contacted with 50 Baum sodium hydroxide solution as is in the presence of 300% by volume of the theoretical amount of oxygen required to sweeten and the copper number determines immediately after the treat and after 1, 3, 5 and 24 hours settling. Three of the remaining seven portions had methyl alcohol added to them in varying percentages and were also subjected to treatment with the sodium hydroxide solution in the presence of the aforesaid amount of oxygen. A fifth portion had beta-naphthol added to it and was also subjected to treatment in the presence of 300% by volume of the theoretical amount of oxygen required to sweeten, while the remaining three portions had both methyl alcohol and beta-naphthol added to them and were subjected to contact with the sodium hydroxide solution in the presence of 300% by volume of the theoretical amount of oxygen required to sweeten. The results of these tests showing the copper number immediately after and after 1, 3, 5 and 24 hours of settling and the percentage of reduction in copper numher after 24 hours are presented in Table III:

Table III High Sulfur Refined Oil Raflinate of 40 Copper N umber 50 Baum Caustic, Per Cent. 1.0 1.0 1.0 1.0 1.0 1.0 1.0 MethylAlcohol,Vol. Per Cent 0.05 0.1 0.2 0.05 0.1 0.2 B-NaphthoLgms/l 9.1 0.1 0.1 0.1 Oxygen, Per Cent of Theor.. 300 300 300 300 300 300 300 300 Copper No. After Treat:

- Immediately after 26 34 32 32 36 29 26 lhourafter 20 24 24 10 9 l0 3hoursalter 20 19 21 20 35 9 8 8 5hours after 21 16 8 5 7 24l1ours after 22 10 10 6 15 2-3 2 2-3 Per Cent Reduction in Copper Number After24Hours- 75 75 85 60 500.2'905002 It will be apparent from the data in Table In that treatment with sodium hydroxide solution in the presence of oxygen results in only 45% reduction in copper number, whereas treatment with varying amounts of alcohol showed reductions between 75 and 85% in the copper number. Treatment of the distillate to which beta-naphthol had been added showed a reduction of about 60% of the copper number, while in the practice of the present invention as illustrated in columns 6 to 8 of Table III, reductions of about 90% were effected. It will be seen that the reduction of the copper number in the practice of the present invention is greater than the average of that effected by the methyl alcohol and the betanaphthol alone. Thus, it appears that the methyl alcohol and beta-naphthol when used together and added to the sour raflinate has a synergistic effect thereon in catalyzing the sweetening operation.

The Saybolt colors shown in Example I were determined in accordance with the ASTM Test method D156-38 while the flash point was determined in accordance with the AS'I'M Test method D56-36.

In the foregoing examples, the improvement obtained by the practice of the present invention has been illustrated by the copper number test. This is a well known analytical procedure in the petroleum industry. A description of the method of test may be found in U. 0. P. Laboratory Test Methods for Petroleum and Its Products, Third Edition, page I-I-6l, Universal Oil Products Co., Chicago, 1947. This test is a measure of the v mercaptan sulfur content of the oil being tested Although not illustrated by the several examples, one or the particular advantages of the of the alkali metal hydroxide solution. The

alkalimetal hydroxide appears to function as a true catalyst since the small amount used may be recycled to treat large quantities of the sour petroleum distillate. A small amount of the alkali metal hydroxide solution may be entrained in the treated naphtha, and, therefore, it may be necessary to replace the entrained amount with fresh solution. In short, it is contemplated in the practice of the present invention that the alkali metal hydroxide solution will be reused over and over again since it isnotnecessary to regenerate the alkali metalh'ydroxide solution.

Hie invention has been described and illustrated by employment of a mild oxidizing agent such as oxygen. It is contemplated that mixtures of oxygen with other gases, such as air may be employed. It is also contemplated that other mild oxidizing agents such as peroxides, permanganates, and the like may be used." For example, a hydrogen peroxide solution may be employed as the mild oxidizing agent.

In practicing the present invention, it is to be understood that the petroleum distillate may be subjected to a preliminary treatment for removal of hydrogen sulfide if the distillate contains hydrogen sulfide. Such preliminary treatment may include washing with a dilute alkali metal hydroxide solution or blowing with a free oxygen-containing gas, such as air. If hydrogen sulfide or other acidic compounds are present and not removed, the alkali metal hydroxide solution employed as the catalyst may very quickly become seriously depleted in activity.

In the practice of the invention, it will be desirable to use an amount of oxygen in excess of the theoretical amount required to sweeten the sour petroleum distillate. Ordinarily, an amount of about 300% of the theoretical amount to sweeten may be employed. However, sweetening in accordance with the present invention may be obtained with considerably lesser quantities of oxygen. In other instances as much as 500% of the theoretical amount required to sweeten may be employed. In fact, sweetening may be obtained in some cases by contact with the oxygen present in the treating vessel. It will be desirable to employ an amount of oxidizing agent at least equivalent to the theoretical amount required to sweeten.

I'he invention has been described and exemplified by employment of 0.5 to 1% by volume of the catalytic alkali metal hydroxide solution. It is contemplated that as little as 0.1 and as much as 5% by volume, or more, of the alkali metal hydroxide solution, based on the sour naphtha, may be employed. Very good results. however. are obtained with 1% by volume and this amount will be preferred.

It is to be understood that after separation of the alkali metal hydroxide solution the contacted naphtha may be washed with water, if desired. to remove any alkali metal hydroxide which may be entrained therein and to remove methyl alcohol when the fraction treated is a solvent naphtha or kerosene and where the presence of the alcohol may have a detrimental effect on the flash point thereof. In most instances it will be unnecessary to treat the contacted naphtha with water or other aqueous solutions.

The nature and obiects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and secure by Letters Patent is:

if'A' 'method for sweetening a sour petroleum distillate containing mercaptans boiling below 750 F. which comprises adding to said distillate an amount of beta-naphthol and methyl alcohol, said methyl alcohol being employed in an distillate and then contacting said distillate containing methyl alcohol and beta-naphthol with a solution of an alkali metal hydroxide while adding a sufiicient amount of a mild oxidizing agent to convert the mercaptans to disulfides and to obtain a sweetened distillate.

2. A method for sweetening a sour petroleum distillate containing mercaptans boiling below 750 F. which comprises adding to said distillate an amount of beta-naphthol and methyl al-' cohol in the range, respectively, from 0.05 to 1 gram per liter of said'distillate and from 0.05% to 2.5% by volume based on said distillate, forming a mixture of an aqueous solution of sodium hydroxide and said sour petroleum distillate to which beta-naphthol and methyl alcohol have been added, and then agitating the mixture while adding a sufficient amount of a mild oxidizing agent to convert the mercaptans to disulfides and to obtain a sweetened distillate.

3. A method for sweetening a sour petroleum distillate containing mercaptans boiling below 750 F. which comprises adding to said distillate an amount of beta-naphthol and methyl a1- cohol in the range, respectively, from 0.05 to 1 gram per liter of said distillate and from 0.05 to 2.5% by volume based on said distillate, forming a mixture of an aqueous solution of sodium hy droxide and said sour petroleum distillate to which beta-naphthol and methyl alcohol have been added, and then agitating the mixture while adding a suificient amount of air to convert the mercaptans to disulfides and to cause sweetening of said distillate, separating sodium hydroxide solution from said distillate and recovering said distillate.

4. A method for sweetening a sour petroleum distillate containing mercaptans which comprises adding 0.2% by volume of methyl alcohol and 0.1 gram per liter of beta-naphthol to said sour petroleum distillate, forming a mixture of said sour petroleum distillate to which methyl alcohol and beta-naphthol have been added with an aqueous solution of sodium hydroxide having a Baume gravity of 50, agitating the mixture while adding a sufficient amount of air to convert the mercaptans to disulfides and to cause sweetening of said distillate, separating said sodium hydroxide solution from said agitated distillate, and recovering said agitated distillate.

5. A method in accordance with claim 4 in which the amount of sodium hydroxide solution is 1% by volume based on thesour distillate.

6. A method for sweetening a sour solvent naphtha containing mercaptans having a boiling point in the range between 200 and 450 F. which comprises adding to said solvent naphtha methyl alcohol in an amount in the range between 0.1% and 2.5% by volume of said solvent naphtha and beta-naphthol in an amount in the range between 0.05 and 1.0 gram per liter of said solvent naphtha, forming a mixture of an aqueous solution of an alkali metal hydroxide and said solvent naphtha to which methyl alcohol and beta-naphthol have been added and then agitating the mixture while adding a sufiicient amount ofia mild oxidizingvagent qtorconvertthe mercapta-nsto disu-Ifidesand to obtain. a sweetenede disti-11ate...

'7. A .method 'in, accordance. with claim 6 .inwhich the alkali metal: hydoxide is. sodium hydioxide.-

8. -A:method. .in accordance.yvith claim ..6 in. which the aqueous isolutionais.employedin an amount equivalent .to. approximately. 1 by. vol. ume .of .thersolvent naphtha.

9. .A .method. ..for.. sweetening .a sour solvent naphtha. containing, mercaptanshaving. a boilingopo int in the .range between 290? and 410 F.

while. maintaining the color of said. naphtha which comprises adding to said.s01vent naphtha 0.05% byvolume of methyl alcohol based on .the

s01vent.naphtha and. 0.1 'gr amof beta-naphthol...

per. liter of said naphtha forming amixture of an aqueous solution of .sodium hydroxide insaid.

solvent ..naphtha to. which methyl alcoholand air. -itot- :eonyert mercaptansi-toc disulfides. and-stow obtain a neweeteneddistillate, andyrremovingmethylalcohol from. said sweetened distillate-:1

10..A methoddnaccordance with -c1aim=.9 in 5 which the methy1=a1coho1-.isremoved by-;wash:

ing-the-sweetened naphtha with water.

1147A :method-in accordance with.c1aim- 9 Tin!"- which, the methyLalcohol is removed .by heating the sweetened naphtha-101a temperature. of. at-,

JOHN G. BROWDER ALVIN: R." SMITH.-

REFERENCES. CITED beta-naphthol have been added, then agitating U the mixture while. adding a sufiicient amount of 2,494,687 I Bond., Jan. '17, 1950.,

Claims (1)

1. A METHOD FOR SWEETENING A SOUR PETROLEUM DISTILLATE CONTAINING MERCAPTANS BOILING BELOW 750* F. WHICH COMPRISES ADDING TO SAID DISTILLATE AN AMOUNT OF BETA-NAPHTHOL AND METHYL ALCOHOL, SAID METHYL ALCOHOL BEING EMPLOYED IN AN AMOUNT IN THE RANGE BETWEEN 0.5% TO 2.5% BY VOLUME BASED ON SAID DISTILLATE, AND SAID BETANAPHTHOL BEING EMPLOYED IN AN AMOUNT IN THE RANGE BETWEEN 0.05 AND 1 GRAM PER LITER OF SAID DISTILLATE AND THEN CONTACTING SAID DISTILLATE CONTAINING METHYL ALCOHOL AND BETA-NAPHTHOL WITH A SOLUTION OF AN ALKALI METAL HYDROXIDE WHILE ADDING A SUFFICIENT AMOUNT OF A MILD OXIDIZING AGENT TO CONVERT THE MERCAPTANS TO DISULFIDES AND TO OBTAIN A SWEETENED DISTILLATE.