US2578602A - Dethiolizing hydrocarbons and other organic liquids - Google Patents

Description

Dec. 11, 1951 DETHIOLIZING HYDROCARBONS AND OTHER ORGANIC LIQUIDS 1.. ROSENSTEINQ 2,578,602

2 SHEETSSHEET 1 Filed May 22, 1948 PP CENT Mf/POAPT/l/V PMOVAL /0 2.0 30 INVENTOR 25/? C/V7' ADDED WATER aw/G FasEMTE/A ATTORNEYS Dec. 11, 1951 LQROSENSTEIN 2,578,502

DETHIOLIZING HYDROCARBONS AND QTHER ORGANIC LIQUIDS Filed May 22, 1948 2 SHEETS-SHEET 2 Patented Dec. 11, 1 951 UNITED PATENT nn 'rinomzmo HYDnooaitBoNs AND OTHER ORGANIC mourns Ludwig ltfos'enstein, San Francisco, Calif., as-

signer; to egato Development Corporation, New York, N. Y., a corporation or Delaware Application May '22, 1948; Serial No. 28,623

"5 claims. (01. 196-32) This invention relates to the treatinentof hydrocarbons and other organic liquids to eiiect the removal of mercaptans and other acidic comn l c The invention is directed to the treatment of certain organic materials including hydrocarbons such as sour hydrocarbon gases and light distillates, naphtha and kerosene, with a substantially anhydrous al-kanolamine solution of alkali metal hydroxide to effect a substantially complete removal of the mercaptans contained in thehydrocarbo'ns Mercaptansare alkanethiols and hence apro oess for removing the mercaptans may aptly be termeda dethiolizing process. Sucha process is to be distinguished fromthe sweeteningprocess which is well known in the treatment of hydro; carbons. sweetening in a broad sense oonsistsof treating the hydrocarbon so as to alter sulfur compoundsco'ntained therein and produce coinpou'nds that contain no free mercaptanfs or such a small quantity of mercaptans that the material reacts negatively in the doctor test which is a sensitive, qualitative test for mercaptans. In an older sense as used in the art the term sweetening was associated with the doctorsweeten-ing proc- (ass in which the mercaptan sulfur was converted to other forms of sulfur compounds which remain in the hydrocarbon and which do not give a positive doctor test; in other words the sweetehing process produces a product which is doctor sweet although the sulfur content is not essentially iower'ed. The present invention involves a dethioliz'ing process which positively removes the inercaptans and produces a sweet product. I

Numerous e'fiorts have been made in the past to extract the inercaptans from hydrocarbons. Aqueous solutioiis bf botassii'im and sodium hydroxides usually will eiitract only a portion of the mercaptans. In some cases when only thelower molecular mercaptans are present, in general lowor than amyl 'rneicaptan, these aqueous solutions can be employed to produce a product which is negative to the doctor test provided the reagent is employed in great excess over the stoichiometric amount based on the actual mercaptan content of the hydrocarbons. In the; case of naphthas from high sulfur crudes, and-frequentlyin the case of cracked naphthas, higher molecular mercaptans are present and in spite of the fact that these reagents have been used in quantities very greatly in excess of the stoichiometric amount based on the mercaptan' content and with the most eificient methods of contacting, they '2 stoclrscontaining the higher mercaptans. The result has been that only a portion of the mercaptan content is removed andthe treated prod;- uct remains positive to the doctor test. The use of certain modifiers or solvent auxiliarieswith the aqueous caustic solution has produced improved results buteven with these expedints it has been impossible to efiect a complete removal of the higher mercaptans andproduce a sweet product. 7 Accordingly the practice has gro n up in which the hydrocarbon is first treated with the aqueous caustic hydroxide solution with or F1 out a modifier or solvent aid to enact the removal of a portion of the mercaptans and the Hydrocarbon is then subjected to a sweetening treatmerit, as sodium umane treatment or topper sweetening, by which the iiireapta'ns are 'cd'fiverted to disulfides. It is considered that when the sulfur is present the farm of disiilfids it is less harmful than when pressures mores-15 tans; although the effect or the di's'iillides on lead "ility is less than the eff of the inerapta'" pnsus 'ptibiuty the latte? are nevertheis oeeiuumunaesiiabn.

The pi'eseii't invention has a distinct a vantage over the prior art pfiadtie in that the -Ijc tans can be substantially completely rem Ved nd the necessity or the 's'weeteiiig' process the mercaptans' are converted to disulfld'es is en tirayeu'mmated. g I have discovered that titativelyih reference "to the amount of alkali used. This suesests finesse-amen:

MOH-r-RSHiRSM FHzO' It seems likely however that thisequation may not represent the actual facts and that it is more probable that the allganolamine plays some part in the reaction as, for example, by combining with the water to iorm' an alkanolamine hydroxide thus lowering the activity of the water. The actual reaction may, therefore, be:

This concept of the reaction offers an airplane tion of the remarkable degree of completeness in the removal of the mercaptans.

Accordingly; in the practice of the invention the hydrocarbon or other organic liquid is treated with a substantially anhydrous alkanoiaihine solution' of an alkali metal hydroxide such as sohave been ineffective the treatment of these dium or potassium hydroxide. The solid sodium,

or potassium hydroxide is dissolved in the alkanolamine and is applied in amounts approximating the stoichiometric quantity based on the mercaptan content of the material to be treated. In practice it is desirable to use a slight excess over the stoichiometric amount but in any case it is not required to use the excessive amounts of alkali such as have previously been used with the aqueous solutions. It is preferred to have the alkali hydroxide present in the alkanolamine in concentrated or substantially saturated solution. Countercurrent contacting is considered the most effective method of contacting to obtain the quantitative reaction.

It is preferable to use an alkanolamine which is substantially insoluble in the hydrocarbon or other organic liquid to be treated. As the carbon content of the alkanolamine is increased its solubility in hydrocarbons is increased. Monoethanolamine is practically insoluble in hydrocarbons and is very highly effective as the anhydrous solvent for the alkali metal hydroxide reagent for effecting practically a 100% removal of the mercaptans. Monoisopropanolamine is equally effective and the solubility in hydrocarbons is sumciently low. The solutions of the alkali in either diethanolamine or triethanolamine are more viscous than the monoethanolamine solutions and in order to obtain the most effective use of diethanolamine and triethtanolamine it is preferable to conduct the treatment under moderately elevated temperatures such as around 120 F. In the case of the monoalkanolamines, such as monoethanolamine and monoisopropanolamine, heating is unnecessary since the viscosities of the reagent mixtures are sufficiently low at normal temperatures.

It is often advantageous to subject the hydrocarbon to a two-stage treatment in the first stage of which the hydrocarbon is treated with an alkali metal hydroxide such as an aqueous solution of sodium or potassium hydroxide and in the second stage of which it is treated with the substantially anhydrous alkanolamine solution of alkali metal hydroxide. In the first stage some lower molecular weight mercaptans are removed but the higher mercaptans are largely unaffected. When the higher mercaptans are present in a naphtha stock some 60% of the mercaptans is about as much as can be removed by the aqueous caustic regardless of the efficiency of the contacting or of the excess amount of the caustic that may be used. The treatment with the aqueous caustic will also remove any hydrogen sulfide, carbon dioxide, phenols or thiophenols or acidic substances that may be present in the hydrocarbon treated. The pretreatment may also serve to remove water present in the hydrocarbon although it will not completely remove the water dissolved in the hydrocarbon. In the second stage the hydrocarbon is treated with the substantially anhydrous alkanolamine solution of alkali metal hydroxide to thereby completely remove the mercaptans and produce a product which is negative to the doctor test.

In the further description of the invention reference is had to the accompanying drawings wherein:

Fig. 1 is a graph showing the effect of water in the treating solution.

Fig. 2 is a flow diagram illustrating a preferred method of treating hydrocarbons with regeneration of the treating solution.

Fig. 1 is a typical curve showing the effect of water in the treating solution. In obtaining the anhydrous curve.

data for Fig. l a naphtha containing 0.0484 mol per liter of amyl mercaptan was treated in a series of tests with a substantially anhydrous monoethanolamine solution of potassium hydroxide and with various amounts of water added to this solution. A laboratory grade of KOH Was dissolved in substantially anhydrous monoethanolamine to make an approximately 0.45 (by weight) molal solution. One treat was made with this solution and the other treats were made with this solution containing added amounts of water. The procedure was to batch treat separate naphtha samples by a single extraction with each of the reagents in a ratio of five volumes of naphtha per volume of reagent. The same amount of alkali metal hydroxide monoethanolamine reagent was used each time with varying amounts of water added to the reagent. In plotting the results the proportion of water in the reagent was plotted against the percentage of mercaptan removal. It was estimated that the quantity of water present in the original reagent, before the addition of any water, was about .43% and in the graph this figure was added to the actual amounts of water added in each case.

The graph clearly shows that the proportion of mercaptans removed decreases as the amount of water in the reagent is increased and that beyond the critical point of 5.6 of water for this reagent the effect of increased proportions of water in reducing the mercaptan removal property is greatly accelerated. It will be seen that the data are best represented by two intersecting lines. There is definitely an aqueous curve and a substantially The anhydrous curve represents that portion of the data in which the effect of water in the reagent is very slight, added increments of water within this zone reducing the mercaptan removal property only a very slight extent. The anhydrous curve represents such small proportions of water in the reagent that as a practical matter it may be said to be substantially anhydrous. The aqueous curve represents that portion of the .data in which the effect of water is pronounced or predominating; it is that portion in which added increments of water decrease the mercaptan removal property at rates greatly accelerated over those represented by the anhydrous curve. The positions of the two curves and their point of intersection will vary somewhat with different stocks treated and with different concentrations of reagent but in every case the efiect of water will be characterized by curves of the type of Fig. 1, that ,is, with a substantially anhydrous curve representing very low water content in which the water has relatively little efiect and an aqueous curve in which the water content greatly reduces the mercaptan removal property. The invention contemplates operating within the zone represented by the substantially anhydrous curve and preferably as near the upper terminus of that curve as is practicable.

The apparatus illustrated in Fig. 2 includes a pretreating unit A, a treating unit B for treating with the anhydrous alkanolamine solution of alkali metal hydroxide and a recovery unit consisting of fractionators C and D for reactivating the used reagent.

When employing the pretreating unit the naphtha or other hydrocarbon to be dethiolized is directed through a line H) to the pretreating unit A and a concentrated aqueous solution of an alkali metal hydroxide such as potassium or sodium hydroxide is introduced through line I]. The unit A may embody a zone for the contact ing of the naphtha and reagent and may include one or more settling zones for separating the naphtha from the reagent. In the pietreating unit the naphtha is contacted with the aqueous caustic solution to effect a removal of a portion of the imercaptans, the more easily removable or lower molecular weight mercaptans. In this operation certain other constituents that maybe present are removed :-from the naphtha such as hydrogen sulfide, carbon dioxide, acids per 'se, phenols or thiophenols and the like and in the event that water is present in the naphtha a portion at least of the water is separated. In any case as has been explained, it is not possible to remove-all of the mercaptans by this treatment and the naphtha directed through a :line. i=2 to the treating zone B. The used "reagent may be withdrawn rrom the system through a line 13. Whenit is not desired to pre'trea't the naphtha it is passed directly through a line M to the treating zone B. The unit B is preferably in the for-moi a tower arranged for countercurrent contacting of the naphtha and reagent. The naphtha is introduced into the low'ersportion of the tower and a substantially anhydrous alkanol- 1 amine solution of alkali metal hydroxide is admitted-through a lihe 1-5 to an 'upperzportion of the tower. The tower preferably contains suitable "Contact material *for facilitating :effi'oient countercurr'ent contacting between the iupiiowing naphtha and down-flowing reagent. The 'line 4-5 may advantageously terminateain a spraying element' for distributing the reagent over the contact material. The =dethiolized naphtha "overflows from the tower through a line J 6 and may Y be washed with water or passed directly. to ta-hkage. V

The m'e'rcaptan content f the naphtha, as introduced from the caustic pretreater {A :or as admitted directly through the lline I4, is deter nod and in operation the iilow Slates of the naphtha and the anhydrous alkanolamine solution of -:alkali metal hyd'roxide are maintained so as to provide the =stoiehiometric quantity or ;reagent required to i remove all of the "mercaptans. In' the event that there are anyiother constituenits in the naphtha which are reactive with the re agent allbwance must,- of course, bemade'ior the presence =03? such constituents. Generally :spea-kingQ-and especially after caustic ipretreatin g, the mercaptan-analysis will indicate the necessary amount "of reagent. a practical matter the reagent may be employed .in slight excess over the stoichiometrlc quantity, such for example as "540% excess.

The used alkanolamine alkali metal hydroxide reagent containing the merca'ptans is removed from the tower B through a line I! and directed to the'p'rimary iractionatonC. Water is added through a lin'e'TB totheused reagent, in amounts usually of about'15-25% by volume, so as to carry on an effective distillationffor the removal 'o'f'the mercaptans. When washing with water the treated naphtha "removed through line E6 "the wash water from "this operation may advantageously be utilized as the 'water introduced through line l8 to the tower C. In the event any small amounts ofrea'gent may be entrained in the treated naphtha flowing through line l6 such reagent may be readily recovered by waterwashing and returned to the system by introduction to the tower G. Live steam preferably at superatmospheric pressure or superheated is introduced through a line [9 to facilitate the distillation. The water vapor and mercaptans pass overhead to a condenser :20 thence to a receiving drum 2| wherein the mercapta'ns separate from the aqueous layer, the mercaptans being withdrawn through :line 22 and the water through line 23.

:In an alternative method a small quantity ;of naphtha brother light hydrocarbon is introduced to the tower '0 through a line 24. The addition of the hydrocarbon provides for an azeotropic distillation and the mercaptans will be largely contained in the naphtha layer which may be removed through .line :22.

From the bottom of tower'C an aqueous alkanolamine alkali metal hydroxide solution which is practically free of mercaptans is withdrawn through a line 25am: directed to the secondary fractionator D. This fractionator is heated by a heating coil "such as a closed steam coil 23 or by any suitable reboiler means. For the-distillation in towerDitiis highly desirable that .a :small amountof naphthaor other light hydrocarbon-be combined with the aqueous solution in order to conduct an azeotropic distillation for efiectually dehydrating the aqueous alkali metal hydroxide alkanolaminetsolu tion. For this purposetnaphtha is introducedthrough lineZl. The water-naphtha azeotrope is distilled overhead through a cone denser 28 to "a receiving drum 29 wherein the naphtha separates from the aqueous layer. The naphtha introduced to the tower D throughiline 2'5 may consist of recycle naphtha withdrawn from the receiver 29 through line 30 together with make-up Jnaphtha "entering through line 31.. In viewnof the fact that the aromatic ihydrocarbons such as benzol, toluol and the xylenes are highly effective in forming azeotropes with water it is advantageous to employ'such'aromatic hydrocarbons as the azeotropeformers.

The dehydrated alkali metal hydroxide alkanolamine solution is withdrawn from the tower D and either withdrawn from the system through line 32 or recycled through line 33 to the treating tower B. When recycling the reactivated reagent portions may be withdrawn from "time to time through line 32 and makeup reagent as-maybe needed is admitted through line 15.

In an alternative method of regenerating the used alkali metal hydroxide alkanolamine reagentit may be subjected to an oxidation treat' ment. The used reagent withdrawn from .the treatingtower B is blown with air to convert themercaptides Ito sulfides and thus remove'the sulfur content from the reagent. .Itis preferable to conduct the oxidizingat an elevated temperature'suflicient to remove the small amount of water which is formed in 'the treating reaction .so that the reactivated reagent willbe in a substantially anhydrous condition and adapted for recycling to the tower B. Promoters, vsuch as tannic acid and cumic acid may advantageously 'be used .in the regeneration.

The recycling of the reactivated alkali metal alkanolamine treating solution has theadvanitage that the water content of the reagent charged to the treating zone may be held at a vpoint even below the water contentof the original reagent used. An advantageous method of operation is to introduce the fresh alkali metal hydroxide alkanolamine solution to the dehydrating unit D so that any excess water content may be readily removed before introduction to the treating tower B. In this operation the dried reagent is continuously charged to the treating tower B and make-up reagent is charged aevswoe to the dehydrator D from time to time as may be-needed. By Way of example, the invention involving the two-stage treatment may be applied to a West Texas naphtha containing .02 gram mol of mercaptans per liter or 0.227 lb. mercaptan sulfur per barrel. By pretreating with 40% aqueous NaOH in 100% excess basis mercaptan content, 20% of the mercaptans may be removed in a single batch treat requiring 0.56 lb. of NaOH per barrel of naphtha with only 0.056 lb. being actually reacted which on the basis of actual caustic utilized 'for mercaptan removal involves the use of alkali reagent in 900% excess. The remaining 80% of mercaptans may then be completely removed by treating with a substantially anhydrous monoethanolamine solution of NaOH (with 1% excess caustic) requiring. 0.23 lb. of caustic per barrel and 1.7 lbs. of ethanolamine per barrel. With more efiicient contacting in the pretreating step it is possible to increase the amount of mercaptans removed so that reduced amounts of the anhydrous NaOI-I-ethanolamine solution are required in the second step. Treating the same naphtha without the caustic pretreat and using the same NaOH ethanolamine reagent requires 0.28 lb. of NaOH per barrel and 2.13 lbs. of ethanolamine per barrel to completely remove the mercaptans. The following table shows the pounds per barrel of caustic and ethanolamine in substantially anhydrous solution required for completely removing the mercaptans in the naphtha without the caustic pretreat and with caustic pretreats of various efliciencies:

Per Cent Lbs./Bbl. Required RSH Pei Cent moved b Residual Aqueous g a g \TQOH Monoeth- NaOH p anolamine No pre- 100 0. 28 2. 13

treat In the prior art practice a typical operation for treating naphtha for mercaptan removal employs some 4 lbs. of caustic per barrel of naphtha ,treated and such treatment will not completely remove the mercaptans and produce a product negative to the doctor test except in instances where only the lower molecular weight mercaptans. generally lower than amyl mercaptan, are present. When resorting to the sodium plum bite treatment for sweetening the naphtha an additional 4 lbs. of caustic per barrel and 'lb. of litharge per barrel are employed and in this case the difficultly removable sulfur compounds are not actually removed but only are changed to other forms. The advantage of the invention in saving in the quantities of reagent required and in eiiecting a complete removal of the mercaptans is readily apparent. v

The invention is adapted for the treatment of various organic fluids which are insoluble in, and nonreactive with, the non-aqueous solution of alkali metal hydroxide in monoalkanolamine for the removal of mercaptans. For example, alkylthiophanes produced by the hydrogenation of 81-1 kylthiophenes may be readily rendered sweet by the described treatment with the non-aqueous alkali metal hydroxide in monoalkanolamine.

Although a preferred embodiment of the invention has been described herein, it will be understood that various changes and modifications may be made therein, while securing to a greater or less extent some or all of the benefits of the invention, without departing from the spirit and scope thereof.

Iclaim:

l. The process of dethiolizing hydrocarbons thatcomprises countercurrently contacting the hydrocarbons with a substantially anhydrous alkanolamine solution of alkali metal hydroxide limited in quantity to supply approximately the stoichiometric amountof the hydroxide based on the mercaptan content of the hydrocarbons to thereby effect complete removal of the mercaptans.

2. The process of dethiolizing hydrocarbons that comprises charging the hydrocarbons to a reaction zone, charging to said reaction zone a substantially anhydrous alkanolamine solution of an alkali metal hydroxide at a rate limited to supply approximately the stoichiometric amount of the hydroxide based on the mercaptan content of the hydrocarbons, intimately contacting the hydrocarbons with said solution in the reaction zone to effect the complete dethiolizing thereof and removing the dethiolized hydrocarbons and used treating solution from the reaction zone.

3. The process of dethiolizing hydrocarbons according to claim 2 in which the alkanolamine is monoethanolamine.

4. The process of dethiolizing hydrocarbons according to claim 2 in which the alkanolamine is monoisopropanolamine.

5. The process of dethiolizing organic fluids which are insoluble in and non-reactive with anhydrous alkali metal hydroxide in alkanolamine that comprises charging the organic fluid to a reaction zone, charging to the reaction zone a substantially anhydrous alkanolamine solution of alkali metal hydroxide in a quantity limited to supply approximately the stoichiometric amount of the hydroxide based on the mercaptan content of the organic fluid, and intimately contacting the organic fluid with said solution to effect the complete removal of the mercaptans.

LUDWIG ROSENSTEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,152,720 Yabrofi Apr. 4, 1939 2,152,723 Yabroff Apr. 4, 1939 2,238,201 Wilson et al. Apr. 15, 1941 2,317,053 Henderson Apr. 20, 1943 2,446,507 Cauley Aug. 3, 1948 2,455,656 Cauley Dec. 7, 1948 FOREIGN PATENTS Number Country Date 557,315 Great Britain Nov. 15, 1943

Claims (1)

1. THE PROCESS OF DETHIOLIZING HYDROCARBONS THAT COMPRISES COUNTERCURRENTLY CONTACTING THE HYDROCARBONS WITH A SUBSTANTIALLY ANHYDROUS ALKANOLAMINE SOLUTION OF ALKALI METAL HYDROXIDE LIMITED IN QUANTITY TO SUPPLY APPROXIMATELY THE STOICHIOMETRIC AMOUNT OF THE HYDROXIDE BASED ON THE MERCAPTAN CONTENT OF THE HYDROCARBONS TO THEREBY EFFECT COMPLETE REMOVAL OF THE MERCAPTANS.

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