US2848374A

US2848374A - Oxygen sweetening process

Info

Publication number: US2848374A
Application number: US513362A
Authority: US
Inventors: Garbis H Meguerian; William P Fairchild
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1955-06-06
Filing date: 1955-06-06
Publication date: 1958-08-19
Anticipated expiration: 1975-08-19
Also published as: GB800984A; BE551286A; FR1213410A

Description

g- 19, 1953 G. H. IMEGUERIAN ETAL 2,848,374

OXYGEN SWEETENING PROCESS Filed June 6. 1955 is Ema km m k m Q\ m N .W M. v m wv N I QQN INVENTORS:

Garb/s H. Meguerion y William P. Fairclrlld m 9% AT T 0RIVE' Y naphthas.

'tillate.

United States Patent OXYGEN SWEETENING PROCESS Garbis H. Meguerian, Park Forest, 11]., and William P. Fairchild, Munster, Ind., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana Application June 6, 1955, Serial No. 513,362

9 Claims. (Cl. 19629) This invention relates to the sweetening of sour petroleum naphthas.

An object of the invention is the catalytic oxidation of mercaptans present in petroleum naphthas to produce a naphtha essentially free of mercaptans. Another object of the invention is a sweetening process which is particularly applicable to sour virgin naphthas. Yet another object is a sweetening process wherein refractory sour naphthas are rapidly sweetened. A further object is a process wherein sour naphthas are sweetened without considerable color degradation. Other objects Will become apparent in the course of the detailed description of the invention.

'In this process, sour petroleum naphthas are sweetened by contact with an aqueous solution in the presence of free-oxygen. The aqueous solution consists ofan alkyl phenol mercaptan solubility promoter, an alkylene polyamine mercaptan solubility promoter, alkali-metal hydroxide, a. copper-polyamine complex mercaptan oxidation catalyst and the remainder essentially water. The process is carried out at a temperature of between about 40 F. and 200 F. for a time sufficient to convert essentially all the mercaptans in the sour naphtha to disulfides. The sweet naphtha is separated from the aqueous solution.

The sour petroleum naphthas which are charged to the process of the invention may be any mercaptan-containing naphtha which is derived from petroleum or from a hydrocarbon conversion process. The process is applicable to all sour hydrocarbon fractions boiling in the naphtha range, i. e., between about 100 F. and 430" F.

at atmospheric pressure. Examples of sour petroleum naphthas are virgin light naphtha, virgin heavy naphtha, absorption naphtha, thermally cracked naphtha, catalytically cracked naphtha, and mixtures of these naphthas. Virgin naphthas are much less amenable to oxidation sweetening than are either the thermally cracked or catalytically cracked naphthas. The process'of this invention is particularly effective with these refractory virgin The process may also be utilized on materials boiling in the kerosene and distillate fuel range when these heavier-than-gasoline distillates are of moderate sulfur content and particularly are low in alkyl phenol content.

The process is carried out by contacting the sour naphtha with an aqueous solution in an amount at least suflicient to form a distinct aqueous phase. More than this amount of aqueous solution is usually utilized. In

general, between about volume percent and about 100 volume percent of aqueous solution is used, based on sour naphtha charge.

The contacting is carried out in the presence of freeoxygen which may be introduced either as air, cylinder oxygen, or in the form of an oxygen-furnishing cornpound, such as hydrogen peroxide. At least enough freeoxygen is present to produce an essentially sweet dis- Since some sweetening normally takes place in the storage tanks subsequent to the sweetening operation,

'2 it is not always'necessary to complete the sweetening in the mercaptan oxidation zone.

The process is carried out at a temperature between about 40 F. and about 200 F. It is preferred to operate at the lowest temperature that contacting time permits. In general, the lower the temperature of operation, the longer the contacting time needed to obtain complete oxidation of the mercaptan or sweetening of the sour distillate. It is preferred to operate at a temperature between about .60 F. and F.

The aqueous solution utilized in the process of this invention consists essentially of water, an alkyl phenol mercaptan solubility promoter, a water-solube alkylene polyamine mercaptan solubility promoter, free alkali-metal hydroxide, a copper-polyamine complex mercaptan oxidation catalyst and water. At least about 5 weight percent of free alkali-metal hydroxide, such as sodium hydroxide or potassium hydroxide is present in the aqueous solution. More than this amount may be present up to the saturation amount. It is preferred to operate with a free alkali-metal hydroxide concentration of between about 10 and 15 weight percent. In addition to the free alkalimetal hydroxide, the solution will contain alkali-metal small amounts of alkyl phenols appreciably increase the solubility of mercaptans in the aqueous solution. Thus as little as one volume percent or less of alkyl phenol may be present in the solution or as much as the saturation amount may be present. It is preferred to operate with an alkyl phenol concentration between about IOand 20 volume percent in the aqueous solution. The alkyl phenols may be pure compounds, such as cresol, xylenol,

.ethyl phenol, nonyl phenol, etc., or they may be mixtures of alkyl phenols. Particularly suitable mixtures are those derived from phenolic compound-containing petroleum hydrocarbons such as crackednaphthas, cycle stocks, and some distillate fuels, such as West Texas heater oil. The alkyl phenols derived by caustic treating from naphthas are commonly spoken of as petroleum cresols. Those obtained by caustic treating of cycle stocks or heater oils and which boil at about the boiling point of xylenol, about 400 F. and higher, are commonly known as petroleum xylenols. Other sources of alkyl phenols are wood tars. It is preferred to utilize petroleum cresols or xylenols.

The aqueous solution also contains another mercaptan solubilitypromoter, alkylene polyamine, where each alkylene group contains from 2 to 4 carbon atoms. Even very small amounts of-promoter polyamine in the aqueous solution increases the solubility of mercaptans in the solution. For example, as little'as one volume percent-or less. Amounts of promoter polyamine up to the saturation concentration of the solution may be utilized. The presence of large amounts of promoter polyamine in the aqueous solution may result in uneconomic losses of the promoter polyamine to the sweet oil. It has been found that by operating with not more than about 8 volume percent of promoter polyamine in the aqueous solution that the loss of material to the sweet oil may be reduced to avery low and economic amount. It is. preferred to operate with an aqueous solution containing promoter polyamine in an amount between about 3 and 8*volume percent.

- polyamine.

j propylene tetramine,

These alkylene polyamines may be utilized in C. P. grade,

However, any polyamine which is sufiiciently soluble to produce a concentration of at least the preferred amount is suitable for use in the process. Examples of polyamine which may be used as mercaptan solubility promoters are ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, propylene diamine, dipropylene triamine, tripropylene tetramine, tetrapropylene pentamine, butylene diamine, and dibutylene triamine. These promoter polyamines may be utilized alone or in admixture with each other in either the C. P. grade, technical grade, or in commercial grades. The commercial grade of diethylene triamine is a preferred source of promoter alkylene polyamine.

There is present in the aqueous solution a mercaptan oxidation catalyst which is the complex formed by the reaction of a water-soluble copper salt and a hereinafter defined alkylene polyamine. The complex is probably a chelate. 4

The copper salts utilized may be organic or inorganic salts which are appreciably soluble in water. Examples of water-soluble copper salts which are suitable for use in the. formation of the catalyst of the invention are cupric acetate, cupric bromate, cupric bromide, cupric chlorate, cupric chloride, cupric fluoride, cupric fluosilicate, cupric formate, cupric lactate, cupric nitrate, cupric sulfate, cupric methanesulfonate, cupric ethanesulfonate, benzenesulfonate, and cupric toluenesulfonate. These salts may be used either in the anhydrous form or in the hydrated form. The widely available and relatively inexpensive cupric sulfate, sold as blue vitriol, i. e.,

CuSO .5H O

is a preferred water-soluble copper salt.-

The other component of the catalyst is an alkylene The alkylene group may be either ethylene or propylene. The catalyst alkylene polyamines may contain one or more alkylene groups. It is preferred to utilize those alkylene polyamines which are very water soluble and simultaneously of relatively low oil solubility. Examples of the alkylene polyamines which may be utilized in preparing the catalyst are ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, propylene diamine, dipropylene triamine, triand tetrapropylene pentamine.

the technical grade, or the commercial purifies. The commercially available grade of diethylene triamine is a preferred source of alkylene polyamine for use in the preparation of the oxidation catalyst.

The catalyst is prepared by reacting, in an aqueous medium, the water-soluble copper salt and the alkylene polyamine. Sufiicient alkylene polyamine is added to the aqueous medium to complex all of the copper salt. The particular amount of alkylene polyamine added is dependent upon the particular alkylene polyamine being used. It appears that when utilizing ethylene diamine or propylene diamine that the complex is tetrahedral and contains two moles of the diamine and one gram atom of copper ion. More simply, the complex can be prepared by slowly adding the polyamine to a concentrated solution of copper salt in water until a blue precipitate appears. The presence of excess amine in the aqueous medium containing the complex salts out the complex in the form of a blue solid. The aqueous medium containing dissolved complex is a blue color. A complex essentially free of excess polyamine is obtained by decanting the aqueous medium from the precipitated blue solid and drying the solid at moderate temperature. Or a solution of complex in water of known concentration can be prepared by adding polyamine to an aqueous solution of copper salt until the first appearance of precipitate; the precipitate can be redissolved by the addition of water 4 to the preparation vessel. In any event, the presence of excess polyamine has no deleterious effect on the catalytic activity of the copper-polyamine complex.

The aqueous solution contains at least a catalytically effective amount of the copper-polyamine complex catalyst. In general, the aqueous solution will contain between about 0.02 and 1 weight percent, calculated as copper, of the catalyst. More usually the catalyst content will be between about 0.1 and 0.3 weight percent as copper. The larger amounts of catalyst have a favorable effect on the rate of mercaptan oxidation.

The results obtainable with the process of the invention are illustrated by the following Working examples. These examples are not to be considered as limiting the scope of the invention.

Two types of catalyst polyamine complexes were prepared and utilized. One complex was prepared by dissolving one gram of cupric sulfate pentahydrate in 5 ml. of Water and 2 ml. of technical grade ethylene diamine was added to the salt solution. The addition of more ethylene diamine to the solution resulted in the precipitation of a blue solid. The other solution was prepared by adding one gram of cupric sulfate penetahydrate to 8 ml. of Water and 7 ml. of diethylene triamine. The addition of more polyamine caused the precipitation of a blue solid. In all cases, the copper polyamine complex containing aqueous media were deep blue in color. To prepare the catalyst containing aqueous alkaline media, portions of the preformed complex solutions were added to the aqueous alkaline media.

Tests were carried out on sweetening of our distillates using a virgin naphtha boiling over the range of about 100 F. to 325 F. and a thermally cracked heavy naphtha boiling over the range of about 200 F. to 400 F.

TEST 1 In this test, the efiectiveness in sweetening of promoter polyamines was compared with monoethanol amine and butyl amine. The sour naphtha was a virgin naphtha having a mercaptan number of 28 (mg. of mercaptan sulfur per 100 ml. of naphtha). The aqueous solution consisted of 20 volume percent of the particular amine and the remainder was a cresylate solution providing 10 volume percent of petroleum cresols and 8% of free sodium hydroxide. The sour naphtha and the aqueous solution were contacted at F. utilizing 20% of aqueous solution based on sour naphtha charged. With each amine, after sweetening a portion of the sour naphtha, the sweet naphtha was decanted from the aqueous solution phase and the separated aqueous solution Was used to contact another portion of the sour naphtha. The catalyst was a copper-diethylene triamine complex and was present in an amount equivalent to 0.15 weight percent of copper. In Run No. l, the sour naphtha was contacted with solution containing no amine in order to determine the effectiveness of the petroleum cresols as sweetening catalysts. The results of thls test are set out in Table I.

Table I Sweeten- Run Amine Treats ing Time,

Minutes 1 None l 60 Butyl amine l 45 Monoethanol amine l 20 The data show that the monobutyl amine is only slightly more etfective as, a catalyst than the petroleum cresols. Monoethanolarnine is a better catalyst than monobutyl amine but is very much poorer than the alkylenepolyamines, ethylene diamine, and diethylene triamine. In this test, commercial grade diethylene triamine was used.

TEST 2 In this test, the virgin naphtha was sweetened utilizing an aqueous solution containing 4 volume percent of diethylene triamine, 20% of petroleum cresols, of free sodium hydroxide, and the remainder essentially water. The sour virgin naphtha had a color of +30 Saybolt. After sweetening, using a catalyst complex consisting of copper and diethylene triamine in an amount of 0.15 weight percent of copper, the color of the sweet naphtha was +25 Saybolt.

TEST 3 In this test, thermally cracked heavy naphtha having an initial color of 14 Saybolt was sweetened utilizing the aqueous solution of the composition shown in Test 2. The sweetening was carried out at 100 F. The color of the sweet thermally crack-ed naphtha was 4 Saybolt.

The loss of color is believed due to the presence of dihydroxybenzene compounds in the thermal naphtha which are converted to color bodies during the sweetening process.

TEST 4 In this test, the effect of a sweetening process on the octane number and lead susceptibility of the sweet naphtha was determined. The feed was a virgin naphtha having a mercaptan number of 9. The aqueous solution consisted of 10 volume percent of diethylene triamine, 18 volume percent of petroleum cresols, 9 weight percent of sodium hydroxide, water and a copper-diethylene triamine complex sufiicient to give 0.3 weight percent of copper. The sweetening was carried out at 85 F. and 4 volumes of sour naphtha were used per volume of aqueous solution. Special precautions were taken to avoid the loss of lower boiling hydrocarbons during the sweetening procedure. The sour naphtha had a CFR-R octane number of 55.8 and with 3 cc. of TEL had an octane number of 75.9. The sweet naphtha had a CPR-R clear octane number of.55.9 and with 3 cc. of TEL'had anoctane number of 76.0.

This test shows that, if anything, sweetening by the process of this invention has a slight beneficialeffect on the leaded octane number of'the sweet naphtha.

TEST 5 In this test, the eflfect of having both cresols and promoter polyamine present in the aqueous solution was studied. The sour naphtha was a virgin naphtha having a mercaptan number of 32. The sweetening was carried out at a temperature of 75 F. The catalyst consisted of a copper-ethylene diamine complex and was present in an amount sufiicient to introduce 0.2 weight percent of These data show that in the absence of the polyamine, sweetening does take place at an appreciable rate, but the color of the sweet oil is markedly reduced from the +30 Saybolt color of the sour naphtha. The promoter polyamine alone produced sweetening in a shorter time than sodium hydroxide, 10 weight percent.

TEST 6 In this test, the effect of the sweetening process on the color stability of the sweet naphtha was studied. The sour naphtha was a thermal naphtha having a mercaptan number of 7 and a color of +14 Saybolt. The sweetening was carried out at a temperature of 75 F. and the aqueous solution contained a copper-ethylene diamine complex in an amount suflicient to have present 0.4 weight percent of copper. In Run 11, the aqueous solution consisted of water, 13 sodium hydroxide, and 12% of cresols. (No promoter polyamine was present.) The sour naphtha was sweetened in 6 minutes. The sweet naphtha was water-washed to remove aqueous solution and then was exposed to the atmosphere at 75 F. for 24 hours. The color of the exposed naphtha was in the ASTM range, but was lighter than 1 ASTM. In run No. .12, the aqueous solution consisted of parts of the solution of run No. 11 and 20 volumes of ethylene diamine. The sour naphtha was sweetened in 6 minutes. The color of the sweet naphtha after exposure to the atmosphere at 75 F. for 24 hours was +8 Saybolt. These runs show that the combination aqueous solution has a very pronounced favorable eifect on the color stability of the sweet naphtha.

TEST 7 In this test, a flow unit was used in the sweetening of virgin naphtha having a mercaptan number of about 20 underconditions to determine the loss of promoter polyamine to the sweet naphtha. In this test, the catalyst was a copper-diethylene triamine complex and was present in an amount suflicient to introduce 0.15 weight percent of copper into the aqueous solution. The aqueous solution, excluding the polyamine, consisted of water,

catalyst, petroleum cresols, 20 volume percent, and free The polyamine utilized in the tests was commercial grade diethylene triamine. The tests were carried out at about 75 F.

The flow unit consisted of a reactor, sweetening zone, having a volume of 350 ml. where the aqueous solution, sour naphtha, and air were intermingled. The naphtha residence time in the sweetening zone was 14 minutes. From the sweetening zone, the mixture passed to a disengaging zone where the aqueous solution separated from the naphtha. The naphtha residence time in the disengaging zone was 10 minutes. From the disengaging zone the oil and naphtha passed to a first settler wherein an aqueous phase was continuously separated by gravity settling from naphtha phase. The naphtha from the first settler was passed to a second settler for further removal of aqueous solution. The naphtha residence time in each settler was 20 minutes.

In all the tests, the efiluent naphtha from the disengaging space was sweet; that is, the sweetening time under these conditions was less than 24 minutes.

In the tests, an aqueous solution was used to contact 900 ml. of sour oil. The sweet oil was then analyzed for polyamine content. Another portion of sour naphtha was then sweetened utilizing the separated aqueous solution and the second portion of sweet naphtha was analyzed for polyamine content. This procedure was repeated until the amine loss had become substantially constant.

Three aqueous solutions were utilized in this test. One solution contained 11 volume percent of diethylene triamine, another solution contained 7 volume percent of diethylene triamine, and the other solution contained 4 volume percent of diethylene triamine. This amount of diethylene triamine was that present in the solution charged to the sweetening of the first portion of sour naphtha.

The results of this test are set out in the annexed figure which forms a part of this specification. The ordinate shows the grams of amine dissolved in each portion of the sweet naphtha produced. The abscissa shows the number of portions of sour naphtha sweetened. Each portion amounts to 900 ml. of naphtha. The aqueous solution utilized in the sweetening amounted to 20 volume percent of the sour naphtha charged.

The figure shows that, quite surprisingly, a decrease from an initial concentration of 11% of the polyamine to 7% results in substantially eliminating the loss of amine to the sweet naphtha. Utilizing 4 volume percent of amine in the initial solution results in only a virtually negligible amount of loss of amine to the sweet naphtha.

Thus having described the invention, what is claimed 1. A sweetening process which comprises contacting (a) a sour petroleum naphtha with (b) between about and 100 volume percent, based on said naphtha, of an aqueous solution consisting of (l) free-alkali metal hydroxide in a concentration between about.5% and saturation, (2) alkyl phenol mercaptan solubility promoter in a concentration of between about 1 volume percent and saturation, (3) water-soluble alkylene polyamine mercaptan solubility promoter in an amount between about 1 volume percent and saturation, each alkylene group containing from 2 to 4 carbon atoms, (4) a mercaptan oxidation catalyst consisting of the copper-polyamine complex formed by the reaction of a water-soluble copper salt and an alkylene polyamine wherein the alkylene group is selected from the class consisting of ethylene and propylene, in an amount between about 0.02 and 1 weight percent, calculated as copper, and (5) the remainder essentially water, in the presence of suflicient free-oxygen to convert essentially all the mercaptans in said naphtha, said contacting being carried out at a temperature between about 40 F. and 200 F. for a time sufiicient to convert essentially all of the mercaptans in said naphtha, and separating an essentially sweet naphtha from aqueous solution.

2. The process of claim 1 wherein said naphtha is a virgin naphtha.

3. The process of claim 1 wherein the polyamine promotor and the polyamine in the complex is diethylene triamine.

4. The process of claim 1 wherein the alkyl phenol concentration is between about 10 and 20 volume percent.

5. The process of claim 1 wherein the promoter polyamine concentration is between about 3 and 8 volume percent.

6. The process of claim 1 wherein the free-hydroxide concentration is between 10 and 15 weight percent 7. The process of claim 1 wherein said temperature is between about F. and F.

8. The process of claim 1 wherein the catalyst concentration is between about 0.1 and 0.3 weight percent.

9. A sweetening process which comprises contacting a sour petroleum naphtha with between about 5 and 100 volume percent, based on said naphtha, of an aqueous solution consisting of (1) free alkali-metal hydroxide in a concentration between about 10 and 15 weight percent, (2) alkylphenol mercaptan solubility promoter in a concentration between about 10 and 20 volume percent, (3) alkylene polyamine mercaptan solubility promoter in an amount between about 3 and 8 volume percent, wherein each alkylene group contains from 2 to 4 carbon atoms, (4) a mercaptan oxidation catalyst consisting of the com plex formed by the reaction of a water-soluble copper salt and an alkylene polyamine wherein the alkylene group is selected from the class consisting of ethylene and propylene, said catalyst being present in an amount between about 0.1 and 0.3 weight percent calculated as copper and (5) the remainder essentially water, in the presence of sufficient free oxygen to convert all the mercaptans in said naphtha, thereby producing a sweet naphtha as determined by the Doctor test, said contacting being carried out at a temperature between about 60 F. and 100 'F. for a time sufiicient to convert all of the mercaptans in said naphtha, and separating a sweet naphtha from aqueous solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,413,945 Bolt Jan. 7, 1947 2,432,301 Fetterly Dec. 9, 1947 2,659,691 Gislon et al. Nov. 17, 1953 2,663,674 Krause et al. Dec. 22, 1953 2,744,854 Urban May 8, 1956

Claims

1. A SWEETENING PROCESS WHICH COMPRISES CONTACTING (A) A SOUR PETROLEUM NAPHTHA WITN (B) BETWEEN ABOUT 5 AND 100 VOLUME PERCENT, BASED ON SAID NAPHTHA, IF AN AQUEOUS SOLUTION CONSISTING OF (1) FREE-ALKALI METAL BY DIOXIDE IN A CONCENTRATION BETWEEN ABOUT 5% AND SATURATION, (2) ALKYL PHENOL MERCAPTAN SOLUBILITY PROMOTER IN A CONCENTRATION OF BETWEEN ABOUT 1 VOLUME PERCENT AND SATURATION, (3) WATER-SOLUBLE ALKYLENE POLYAMINE MERCAPTAN SOLUBILITY PROMOTER IN AN AMOUNT BETWEEN ABOUT 1 VOLUME PERCENT AND SATURATION, EACH ALKYLENE GROUP CONTAINING FROM 2 TO 4 CARBON ATOMS, (4) A MERCAPTAN OXIDATION CATALYST CONSISTING OF THE COPPER-POLYALMINE COMPLEX FROMED BY THE REACTION OF A WATER-SOLUBLE COOPER SALT AND AN ALKYLENE POLYMINE WHEREIN THE ALKYLENE GROUP IS SELECTED FROM THE CLASS CONSISTING OF ETHYLENE AND PROPYLENEM IN AN AMOUNT BETWEEN ABOUT ABOUT 0.02 AND 1 WEIGHT PERCENT, CALCULATED AS COPPER, AND (5) THE REMAINDER ESSENTIALLY WATER, UN THE PRESENCE OF SUFFICIENT FREE-OXYGEN TO CONVERT ESSENTIALLY ALL THE MERCAPTANS IN SAID NAPHTHA, SAID CONTACTING BEING CARRIED OUT AT A TEMPERATURE BETWEEN ABOUT 40*F. AND 200*F. FOR A TIME SUFFICIENT TO CONVERT ESSENTIALLY OF THE MERCAPTANS IN SAID NAPHTHA, AND SEPERATING AN ESSENTIALLY SWEET NAPHTHA FROM AQUEOUS SOLUTION.