US2771403A - Air-caustic sweetening - Google Patents

Description

United States Patent 2,771,403 AIR-CAUSTIC "SWEETENING Mathew L. Kalinowski, Chicago, and Garbis H. .Meguerian, Park Forest, 111., assignors to Standard Oil Company, Chicago, 'Ill., a corporation of Indiana No Drawing. Application April 1-6, 1954, Serial No. 423,834 3 Claims. (Cl. 196.29.)

ineffective. In the case of these refractory :sour cracked naphthas, the above process has been modified by'carrying out the contacting in the-presence of free sulfur. While this process is effective to sweeten cracked naphthas having a mercaptan number of-notrnore than 20, the use of free sulfur results in an undesirable lowering of the octane number of the sweet naphtha as compared with the octane number of the sour naphtha. An object of the invention isa sweetening process wherein the loss of octane number owing to the use of free sulfur is decreased. Other objects will become apparentin thecourse of the'detaileddescription. The process of the invention involves sweetening sour cracked 'naphthas having *mercaptannumbers of not more than .20, wherein'the naphtha is contacted with an aqueous alkaline treating agent'which contains a catalytic amount of alkyl aphenols the presence of free oxyg n and free sulfur, 'inan 'amountisufiicient to 'sweeten saidinaphtha; saidcontacting :is rcarried out at atemperature of at least about 80 F. for zastime rsuflicient to produce a productrn-aphtha that is sweet to =the'doctor te'st; said contacting is further carried out in the presence of an. eflective amount of aliphatic amine which :is essentially insoluble in water, which amine hasubecn intro: duced into the sour naphtha prior to the addition-. ofiree sulfur to said sour naphtha.

The aliphatic amines utilized in the process 'of this invention are the oil soluble amines whicharealst: essentially insoluble in water, ormorelparticularly, in-aqueous.

caustic solutions. These. aliphatic amineszinclude a=) =p' rima'ry aliphatic amines containingatleast8carbon-atoms,

for example, o ty a n decy am laury mine etylamine, sterylamine; (b) secondary aliphatic amines con taining at least 5 carbon atoms, in eachaliphatic group for example, di-n-amylamine, di-isoamylamine, anddioetyl.

amine; (c) tertiary aliphatic aminescontaini ng-atleast 3 carbon atoms in each aliphatic group, .for :eXaH-l'plQllEl-r n-propylamine, tri-iso'propylaniine, tri-nwbutylamine, triisobu'tylamine, tri-n amylamine, triisoamylamine, and triocty-l'amine. The tertiary aliphatic amines do. not react with free sulfur toform hydrogen sulfide. Since free sulfur is present in the sweet oil in virtually all thesesweetening operations, the tertiary aliphatic amines are the preferred amines. The tri-nebutylamines are preferred for reasons of costs At least an amount of the aliphatic amine'must 'be present in the oil to improve the quality of said oil. In general, at least about 0.001 weight-percent, based OII'Oil, of the aliphatic amine should be present.

Amounts'np tjoj about weight percent may be utilized. These large amounts are particularly suitable when extremely refractory oils are being treated; and when the aliphatic amine" 7 4 many 'vfr'gm'gas fo ls'with concentrated aqueous caustic solution 'suc'h'as'a 40% solution. These heavy Xylenols "2 is recovered from the sweet oil by treating the oil with an acid that- 'is reactive with the amine to form an oil insoluble salt. This salt may be decomposed by treat-, ment with aqueous caustic solutions to recover the aliphatic amine for reuse .in the process. In general, it is preferred to operate with between about 0.01 and 0.1 weight percent of aliphatic amine, v

The aliphatic amine maybe added to the sour oil prior to the addition of aqueous agent, or the aliphatic amine may be added to the mixture of sour oil and aqueous agent. In any case, the aliphatic amine must be present in the sour oil prior to contacting the sour oil with free sulfur. It is preferred to add the aliphatic amine to the sour oil prior to commencing the sweetening operation.

The feed naphtha to the process of this invention is a cracked naphtha and preferably a naphtha having an ASTM end point of not more than 425 F. The cracked naphtha may be a thermally cracked naphtha derived from refinery operations such as vis breaking, coking, gas

' cess of about 20 are not readily sweetened 'by-this process and it is p'referredtooperate'with a sour naphtha having a mercaptan numberof not more than 20.

The aqueous'treatingsageht used in'this process is present .in an amount at :least sufficient to form 'a separate phase. Sweetening can :be obtained with amounts of agent just great enough 'to :irnpart a haze to the naphtha-.-

For most operations the amount of :theaqueou's treating agent will .be-about- 1010 about 200-volzume percent based 1 on the feed: naphtha. It -is-preferred to use about 25% to about 50% by volumeof aqueous treating agentinnthis process.

The caustic component of the aqueous treating agent may besodium" hydroxide, potassium hydroxide, or mixtures thereof. The c-austiclispresent in the treating agent in the form of free-alkali and in chemical combination.

with the alkylphenols. Furthermore, :some of the caustic may be combined With acidic' contaminants in the treating agent. Free caustic must be present, preferably, at least v aboutS weightpercent. Higher concentrations of caus ti'c may be-used and -in somewcases .a saturated solution may rived from thermal crackin'g'an'd catalytic cracking processes. These alkylphenols'may 'be obtained by contacting the petroleum hydrocarbon with concentrated aqueous v causticsolution. The cresols derived from cracked naphtha have an ASTM boiling range from about 370 F. to about 440 F. Alkylphenols "occur in petroleum hydrocarbons boiling in the heavier-th'an-gasoline range, i. e.,

hydrocarbons boiling from about 350 F. to'ab'out 600 F. 'Thesealkylphneolfs are usu'ally called heavy'xylenols and may b O tain d by contac c acke gas o and Batented Nov. 20, .1956 I have an ASTM boiling range between about 375 F. and 560 F. or higher.

The alkylphenols present in the aqueous treating agent act as solutizers for the mercaptans. The alkylphenols also aid in preventing the presence of corrosive sulfur in the naphtha, and it is possible that they do this by reacting with the excess free sulfur. It is necessary to have at least a catalytic amount of alkylphenols present in the aqueous treating agent, and preferably at least about 2 volume percent. It is advantageous to have more alkylphenols present and in some cases a saturated solution may be desirable. However, these alkylphenols increase the viscosity of the agent and may produce phase separation difficulties. It may be desirable to limit the alkylphenols to about 30 volume percent when using sodium hydroxide, preferably about 20; somewhat higher amounts may be used when using potassium hydroxide. It is preferred to use between about 5 and 20 volume percent alkylphenols in the aqueous treating agent.

The free oxygen may be introduced into the process either in the form of substantially pure oxygen, i. e., cylinder oxygen, or in the form of a free-oxygen-containing gas, e. g., air. Very slight amounts of free oxygen are needed to oxidize the mercaptans in the naphtha to disulfides, but at least an amount sufficient to oxidize the easily oxidizable mercaptans is desirable since the sulfur is particularly required for the oxidation of mercaptans which are difiicult to oxidize. The amount of free oxygen required will increase with increasing mercaptan number of the sour naphtha. Usually 5 s. c. f. of air will be sufficient for the production of a sweet product. It is preferred to add between about 0.2 and 2 standard cubic feet of free oxygen per barrel of sour naphtha. When air is used, from about 1 to about s. c. f. of air are added per barrel of sour naphtha.

The amount of free sulfur must be at least an effective amount but less than the amount which gives a corrosive product naphtha. The use of free sulfur effects favorably the contacting temperature and contacting time. The amount of free sulfur required increases with increasing mercaptan number of the naphtha feed. The use of more than about 1.8 pounds of sulfur per 1000 barrels of naphtha feed per mercaptan number of the feed appears to have an adverse etfect on the TEL susceptibility of the product naphtha, and a corrosive naphtha product may result. Amounts of free sulfur as low as 0.5 lb./1000 bbls./mercaptan number or lower may be sufiicient with some naphthas. Preferably, between about 0.9 to about 1.6 pounds of sulfur per 1000 barrels of naphtha feed per mercaptan number of said feed is used to obtain a doctor sweet product with thermally cracked naphthas having a boiling range between about 120 F. and 400 F. When the particular type of mercaptans present in the naphtha are very diflicult to oxidize, the amount of sulfur required to obtain a sweet naphtha product will correspond more closely to the 1.6 figure than to the 0.9 figure; this is the case normally with naphthas having ASTM end points appreciably above 400 F.

Normally, the practical extremes of temperature in which sweetening will be carried out are from about 80 F. to 210 F. Temperatures below about 100 F. are preferred for use on naphthas having substantial quantities of light ends, i. e., butanes and pentanes, to avoid substantial losses of these by evaporation during the processing. It is desirable to use higher temperatures as the sweetening reaction is accelerated by higher temperatures. Therefore, for naphtha feeds boiling between about 120" F. and 400 F., temperatures of about 120 F. to about 160 F. are preferred. For naphthas which are more refractory, i. e., harder to sweeten, temperatures above 160 F. may be used.

The mixture of amine, free sulfur, agent, naphtha and free oxygen should be maintained intermingled for a,

time sufiicient to complete the sweetening reaction, i. e., to produce a naphtha having a mercaptan number substantially less than 1. The required contacting time is dependent on the mercaptan number and the type of naphtha, but normally this time will be between about 1 minute and 60 minutes. For most feeds, a contact time of from about 2 to about 20 minutes will be sufficient.

After the completion of the sweetening reaction, the mixture of treating agent and naphtha is settled for a time sufficient to separate the product naphtha from the lower aqueous phase. The aqueous phase is usually suitable for recycle to the initial contacting step. However, in the course of time there is a buildup of thiosulfates and other by-product salts which interfere with the sweeteningprocess and reduce the free caustic concentration. The cresols also build up in the treating agent, when the naphtha feed has not been prewashed with caustic to remove HzS or extracted with caustic-cresylate solution for mercaptan number reduction. It is therefore desirable to periodically discard the treating solution and use fresh solution; or to continuously withdraw a portion of the treating agent and replace it with fresh solution.

The results obtainable by the process of this invention are illustrated by the working example set out below. It is to be understood that this example is illustrative only and does not limit the scope of usefulness of the process.

Example The feed to the tests was a cracked heavy naphtha derived from the thermal cracking of a virgin gas oil. This naphtha boiled between 200 and 390 F. and had a mercaptan number of 27.6 (mg. of mercaptan sulfur per ml. of naphtha).

Test 1.A 500 ml. sample of the sour naphtha was placed into a three-necked flask. To the flask was added ml. of aqueous caustic-cresylate solution which contained about 10 weight percent of free NaOH and a cresol concentration of about 20 volume percent. These cresols had been obtained by caustic extraction of sour cracked naphtha. In this test, 69 mg. of free sulfur were added to the contents of the flask. The mixture was heated to 90 F. and air was introduced into the flask for 15 minutes. The naphtha was decanted from the aqueous agent and then water washed to remove occluded agent. The product naphtha was sweet to the doctor test.

Test 2.Another portion of the sour naphtha was sweetened as in Test 1, except that 0.005 weight percent of tri-n-butylarnine was added to the sour naphtha before the aqueous agent was added to the flask.

Test 3.-Another portion of sour naphtha was sweetened according to the procedure of Test 1 and then 0.005 weight percent of tri-n-butylamine was added to the sweet oil.

Since very slight differences in octane number are involved, the octane number change by the various methods of treating was determined by a differential procedure, using the octane number of the sour feed naphtha as a reference point. Octane numbers were determined of the naphthas as is, i. e., clear and also containing 1 imtcil 3 cc. respectively of commercial tetraethyllead sou on.

The results of these tests are set out below:

Dlfierenttal Octane Number, OFR-R Naphtha From- Clear 1.0 cc. 3.0 cc.

71. 2 79. 3 84. 4 l8? l3? 0.1 Test 3 0. 0 -0. 4 1. 0

The results of Tests 1 and 3 show that the butylamine has no beneficial effect on the leaded octane number of the sweet oil when added to the sweet oil. The results of Test 2 show that the adverse effect of sulfur on the octane number of the naphtha is completely overcome. By the use of the process of this invention, it is possible to gain between one-half and one octane number over the conventional process. This represents a significant economic saving in tetraethyl-lead usage to attain a given octane number.

Thus having claimed is:

1. A sweetening process which comprises 1) adding to a sour cracked naphtha, having an ASTM endpoint of not more than 425 F., between about 0.001 and 10 weight percent of at least one aliphatic amine selected from the class consisting of (a) primary aliphatic amines containing at least 8 carbon atoms, (11) secondary aliphatic amines containing at least carbon atoms in each aliphatic group, and (c) tertiary aliphatic amines containing at least 3 carbon atoms in each aliphatic group, (2) contacting said amine-containing sour naphtha with (i) an aqueous treating agent consisting essentially of water, caustic and alkylphenols, said agent containing at least about 5 weight percent of free caustic, at least about 2 volume percent of alkylphenols and no plumbite, said described the invention, what is agent being present in an amount between about 10 and 200 volume percent, based on said amine-containing sour naphtha, (ii) free oxygen in an amount between about 0.2 and 2 standard cubic feet per barrel of said amineoontaining sour naphtha and (iii) free sulfur in an amount to render said amine-containing sour naphtha essentially sweet to the Doctor test, (3) maintaining the contents of said contacting zone of step 2 at a temperature between about F. and about 200 F. for a time at least sufiicient to convert essentially all the mercaptans in the sour naphtha and to produce an essentially sweet naphtha and (4) separating an essentially sweet aminecontaining naphtha from aqueous agent.

2. The process of claim 1 wherein said amine is trin-butylamine.

3. The process of claim 1 wherein said amine is present in an amount between about 0.001 and 0.1 percent.

References Cited in the file of this patent UNITED STATES PATENTS 1,767,356 Fischer June 24, 1930 2,143,405 Campbell et al. Jan. 10, 1939 2,411,083 Davis et a]. Nov. 12, 1946 2,589,450 Stanton Mar. 8, 1952 2,604,437 Conner et al. July 22, 1952

Claims (1)

1. A SWEETENING PROCESS WHICH COMPRISES (1) ADDING TO A SOUR CRACKED NAPHTHA, HAVING AN ASTM ENDPOINT OF NOT MORE THAN 425* F., BETWEEN ABOUT 0.001 AND 10 WEIGHT PERCENT OF AT LEAST ONE ALIPHATIC AMINE SELECTED FROM THE CLASS CONSISTING OF (A) PRIMARY ALIPHATIC AMINES CONTAINING AT LEAST 8 CARBONS ATOMS, (B) SECONDARY ALIPHATIC AMINES CONTAINING AT LEAST 5 CARBON ATOMS IN EACH ALIPHATIC GROUP, AND (C) TERTIARY ALIPHATIC AMINES CONTAINING AT LEAST 3 CARBON ATOMS IN EACH ALIPHATIC GROUP, (2) CONTACTING SAID AMINE-CONTAINING SOUR NAPHTHA WITH (I) AN AQUEOUS TREATING AGENT CONSISTING ESSENTIALLY OF WATER, CAUSTIC AND ALKYLPHENOLS, SAID AGENT CONTAINING AT LEAST ABOUT 5 WEIGHT PERCENT OF FREE CAUSTIC, AT LEAST ABOUT 2 VOLUME PERCENT OF ALKYLPHENOLS AND NO PLUMBITE, SAID AGENT BEING PRESENT IN AMOUNT BETWEEN ABOUT 10 AND 200 VOLUME PERCENT, BASED ON SAID AMINE-CONTAINING SOUR NAPHTHA, (II) FREE OXYGEN IN AN AMOUNT BETWEEN ABOUT 0.2 AND 2 STANDARD CUBIC FEET PER BARREL OF SAID AMINECONTAINING SOUR NAPHTHA AND (III) FREE SULFUR IN AN AMOUNT TO RENDER SAID AMINE-CONTAINING SOUR NAPHTHA ESSENTIALLY SWEET TO THE DOCTOR TEST, (3) MAINTAINING THE CONTENTS OF SAID CONTACTING ZONE OF STEP 2 AT A TEMPERATURE BETWEEN ABOUT 80* F. AND ABOUT 200* F. FOR A TIME AT LEAST SUFFICIENT TO CONVERT ESSENTIALLY ALL THE MERCAPTANS IN THE SOUR NAPHTHA AND TO PRODUCE AN ESSENTIALLY SWEET NAPHTHA AND (4) SEPARATING AN ESSENTIALLY SWEET AMINECONTAINING NAPHTHA FROM AQUEOUS AGENT.