US2213801A - Process for the sweetening of hydrocarbon distillates - Google Patents

Description

Sept. 3, 1940.

BA A. FRoLov 2,213,801

PROCESS FOR THE SWEETENING 0F HYDROCARBON DISTILLATES 2 Sheets-Sheet 1 Filed Jan. 28, 1939 Tremed DibHHnTe I "V Ham Cooler/ Exchange Condener Caufc Alkali 901 'non W W Tank feam iripper HCM Sept 3, l940- I B. A. FRoLov 2,213,801

PROCESS FOR THE SWEETENING 0F HYDROCARBON DISTILLATES Filed Jan. 28. 19:59 2 sheets-sheet 2 Raw Condener Mamma? Caumm Alka Qomfionq JA Patented Sept. 3, 1940 UNITED STATES #PATENT OFFICE VPROCESS FOR -THE SWEETENING HYDROCARBGN DISTILLATES Application January 28, 1939, Serial No. 253,357

11 Claims.

'I'his invention relates to processes for the removal of Weak organic acids from organic water-insoluble liquids by extraction with aqueous solutions of strong bases preferably contain- 5 ing substantial amounts of solubility promoters as solutizers for said acids, and more particularly deals with a method for controlling the compositions of these aqueous solutions.

It is known that weak organic acids, such as those having dissociation constants below about 10'5, e. g., mercaptans, alkyl phenols, thiophenols, etc., are diilicult to remove from their solutions in organic Water-insoluble liquids by extraction with aqueous solutions of caustic alkali. It is further known that the extraction of these acids can be materially improved by adding4 to the aqueous solution substantial amounts of solubility promoters or solutizers for said organic acids. Suitable solutizers are organic compounds which are good solvents for the organic acids, are at least partially soluble in the aqueous solution o f the base, are substantially insoluble in the organic water-insouble solvent, and are. physically and chemically inert to the action of caustic alkalis even at elevated temperatures of steam stripping. Thus, for example the following compounds are known to be suitable solutizers of the type described: aliphatic alkanolamines and amino alkylamines in which the alkyl radicals contain two to three carbon atoms; diamino alcohols, glycols and amino glycols of three to five carbon atoms; alkyl glycerines in which the number of carbon atoms in the alkyl radicals is from one to four, diamine, di-hydroxy or amino hydroxy alkyl ethers or thioethers 'in which the alkyl radicals have from two to three carbon atoms; alkali metal and particularly potassium salts of fatty acids having fromone to six carbon atoms, amino or hydroxy fatty acids having from two to seven carbon atoms, phenyl acetic acid, hydroxy or amino phenyl acetic acids, phenol, alkyl phenols; mixtures of the above, etc. The amounts of solubility promoters dissolved in the aqueous base solution to be effective may vary between about'15% to 85%, and preferablyl 25% to 75%, although in some instances the maximum which may be added is less because o a limitedsolubility. Y

btrong bases applicable in the extractionare in particular the alkali metal hydroxldes, the

sodium and potassium yhydroxides being preferred. However,v other," strong bases, such as alkali metal hydroxides, ammonia, quaternary ammonium bases, etc., may be useful.

It is further known that thev organic solvents (Cl. 26o-609) from which the weak organic acids are to be removed, aside from being substantially insoluble in water, should also be inert to the action of the base under the conditions of the extraction,

i. e., at about normal room temperature and for a 5 period of, say,` at least l0 minutes. .4 Y

Extraction of weak rganic acids with the aid of solutizers has its most important application in the refining, and more particularly, in the sweetemng of sour gasolines, kerosenes, naphl0 thas, generally referred to as hydrocarbon distillates, i. e., in the extraction of mercaptans and other weak organic acids, such as alkyl phenols, which may be contained in sour distillates. The extraction process is usually carried out by conl5 tacting the unrened hydrocarbon distillate at a temperature between about 0 to 60 C. with the aqueous solution of the strong base containing solutizers, preferably in countercurrent in several stages or in a packed tower. The resulting ,20 treated distillate isseparated from the spent aqueous solution containing absorbed organic acids, the treated distillate is water washed if necessary, to recover small amounts of solutizers which may have been dissolved in the distillate, 25 and the resulting wash water may be combinedI with the spent aqueous solution if washing has been resorted to. The combined aqueous solution is then steam stripped to remove absorbed mer-" captans. 'I 'he stripped aqueous solution is reso turned to treat further .amounts of unrened distillate.

" It has now been found that dificulty may be experienced in the above regenerative process when treating distillates. containing in addition 35 to mercaptans considerable amounts of alkyl phenols. Allwl phenols are, on the average, somewhat more strongly acidicthan mercaptans, and therefore are more diftlcult to remove from. the aqueous base solution by steam stripping. 40 As a result, there is a tendency to accumulate in the circulating aqueous base solution an amount 'of alkyl phenolates which may be harmful to the extraction. A 55 It is a purpose of this invention to prevent the, building-up of alkyl phenolates above a certain desired maximum in the circulating aqueous base solutions, which solutions are used for extracting mercaptans from sour distillates containing alkyl phenois, and which are continuously;

regenerated by steam stripping toremove absorbed mercaptans. return a portion of the extracted alkyl phenols to distillates from which they were derived without returning mercaptans. vantages will become apparent from the description below..

My process comprises the steps of extracting sour hydrocarbon distillate containing both mercaptans and alkyl phenols with an aqueous solureduce its mercaptan content to a certain maxition of a strong base capable'z of extracting at least a portion of thermercaptans'. Preferably a suilicient amount of mercaptans should be' mum level, which may be established experimentally in each individual case. Since, however, the steaming operation is relatively expensive, the Aminimum-amount 'of steam isV usedr which will barely strip mercaptans to this desired level. Under these conditions, a relatively large portionof the alkyl phenols is retained by the aqueous base solution. To remove this excess of retained alkyl phenols and to preventits building .up in the circulating aqueous solution, I now 'contact' the stripped aqueous solution with a solvent for ,alkyl `phenols under conditions unfavorable to the absorption of weak organic acids in aqueous caustic alkali. Such conditions are, for example, relatively high temperatures; low

. concentration'of the solutizer in the aqueous sowater prior to contacting it; or both.

lution, and/or of alkyl phenols in the solvent, etc. Thus, I may eiect th'e contact of the aque'- ous alkyl phenolate solution withftheV lsolvent at a temperature substantially/higher than that of thepreceding extraction, for instance, at approximately the temperature of the steam stripping; or I'may dilute the aqueous solution with l Solvents for the alkyl phenols useful removal of theflat'ter from the aqueousjbase solution are,l for example, hydrocarbon distillates, such as gasoline, kerosene, etc., benzene, toluene, Vxylene; alcohols preferably having 4 and more carbon atoms, as-butyl, amyl, etc., alcohols;

ketones, as acetone, methyl ethyl ketone, methyl propyl ketone, diethyl ketone, dipropyl ketone,

etc.; ethers, as diethyl ether, diisopropyl ether,

dibutyl ether, etc. While certain .polar solvents,

such as thediisopropylether, methyl ethyl ketone, amyl alcohols, etc., may be better solvents forv the allq'l phenols thanhydrocarbon distillates, and even may dissolve substantial amounts of the phenolate salts, I frequently prefer the use of hydrocarbon distillates which are free from mercaptans, particularly cracked distillates which, for reasons of gum stability. require the It is another purpose to Qther purposes and adrar' theA addition of gum inhibitors. By contacting such distillates with a steam-stripped aqueous base solution under the conditions described, i. e., after pre-dilution or at elevated-temperatures, or both, the double purpose of stabilizingthese distillates and removing excess alkyl phenols from the base 'solution canbe accomplished in a' single operation. Afterl the contact, the base solution may then be reconcentrated or cooled or both. as the case may require, and` the resulting aqueous solution is ready@A for extracting further amounts ofl sour hydrocarbon distillates.

Figures 1 and 2 of the' drawings represent ilow diagrams of two possible variations of my process. In Fig. l is shown the general arrangement of a preferred form in which a sour hydrocarbon distillate, containing mercaptans and alkyl phenols ise'xtracted in an extraction'zone with an aqueous solution of a caustic alkali. The resulting spent aqueous solution containing absorbed mercaptans and alkyl phenols isregenerated by steam stripping to expel mercaptans and thereafterv scrubbed with. the same distil- Alate or aseparate' solvent for alkyl phenols to remove alkyl phenols. 'I'he regenerated aqueous solution is returned to the extraction zone. Fig. 2 discloses aspecial application of my process in which a hydrocarbon distillate containing lboth mercaptans and alkyl phenols is fractionally distilled to producea light fraction containing light mercaptans but no alkyl phenols, and a heavier fraction containing the heavier'mercaptans and all of the alkyl phenols. The heavier fractionl is contacted with an aqueous caustic alkali solultion to remove mercaptans and alkyl phenols,

`which makes possible a simultaneous transfer of alkyl phenols in the opposite direction, i. e., from the aqueous alkaline solution to the light distillate. The treated light and heavy frac- Since 1 tions may then be recombined to produce a sweet gasoline containing' at least a substantial portion of the alkyl Aphenols originally contained therein.

v Referring to Fig. l, sour hydrocarbonv distillate, such as a cracked 'gasoline distillate containing both mercaptans and alkyl phenols, is intro-I duced through line II into extractor 2 from a source .not shown. aqueous solution oi' a caustic alkali, e. g., sodium or potassium, hydroxide, preferably containing a substantial amount of onel or several solutizers, such as sodium isobutyrate, diamino isopropanol, butylene glycol, is admitted through line 3 to thev extractor 2 to ow in counviscosity of the aqueous solution, partial or'total solidification, etc., while at higher temperatures' than 60 C. the. extraction eiilciencybecomes so l low as to make, in general, sweetening diiilcult, if not impossible. The spent aqueous solution which` emerges from the extractor through line '4 contains dissolved a major portion of the mer- 'scrubber ls.

captans andl alkyl phenols originally contained in the distillate. This spent solution is conveyed by pump 5 to still or steam stripper 6 in which it is subjected to boiling or steam stripping, preferably in accordance with principles' disclosed in the Yabroft and White application Serial No. 174,512, led November 15, 1937. Stripping steam is injected into the stripper through line 1, and is removed together' with liberated mercaptans and alkyl phenols through` line 8 to be condensed in condenser 9. Condensate is accumulated in tank I0, where it forms two llicuid layers, a lower water layer and a layer of organic acids. The water of condensation may be returned'through line I I to the spent caustic alkali solution passing through line 4 to pre-dilute the same and to facilitate its stripping. *The layer of organic acidsconsisting predominantly of mercaptans is Withdrawn from tank I through line I2. i

Stripped aqueous caustic alkali solution which has retained a substantial portion ofthe alkyl dilution is desired; additional water may be added through line I4. Pump I5 in line I3 conveys the solution tothe top of the extractor I6, where it is further stripped -of retained alkyl phenols by scrubbing with asuitable solvent for Aalkyl phenols. If desired, at least a portion of this stripped solutizer solution may be returned by pump I5through lines I3, 33, 29 or 30, and 3 to the extractor 2 in order to maintain the desired concentration of alkyl phenols in the solutizer solution.

In the extractor-scrubber I6, conditions are maintained which are different from those in extractor 2. In extractor 2 a relatively low temperature ranging fromabout 0 to about 60 C. is maintained, and the caustic alkali solution passing through it is in a relatively concentrated state, having preferably a high content of solu- .K bility promoter. In the extractor-scrubber I6 a Aat temperatures above the normal boiling temperature of the lowest boiling substance.

Solvent for the alkyl phenols'is admitted to the extractor-scrubber I6 through line I'I.. This solvent may be supplied throughA line I8 from an outside source, not shown, or treated distillate leaving extractor 2 through line I9 may serve for this purpose. If treated distillate is used, vall or a portiony of it may be pumped by pump in line 2l through heat exchanger 22, where its temperature is raised, preferably to 60 C.- or above, and through line I'I to the extractor- Solvent, containing alkyl phenols removed from the aqueous base solution, is Withdrawn from the extractor-scrubber I6 through line 23.

scrubbed aqueous caustic alkali solution now freed from mercaptans-as well as from excess of alkyl phenols, passes from extractor-scrubber I6 through line 32 and into extractor 2, if Vno further concentration is needed, or through line 24 to still 2 5, where it is concentrated by boiling. Steam so produced may be conveyed through line 26 to stripper 6 to be used in the steam stripping operation. Ii preferred, however, it

l a full range gasoline, containing both mercaptans and alkyl phenols, are admitted from a source not shown through line '40 to fractionatin'g tower 4I, in which they are separated lby fractional distillation, into a light top fraction free from alkyl phenols containing light mercaptans, and

a heavier bottom fraction containing all of the alkyl phenols and the heavier mercaptans. The heavier fraction passes through cooler v42 and line I to extractor 2, where it is extracted with aqueous c austic alkali solution admitted through line 3. The resulting spent aqueous solution' containing heavier mercaptans and alkyl phenols passes through line 4 to steam stripper 6, where it is stripped of absorbed organic. acids as described in connection with Fig. 1. The stripped solution may be'diluted with water from line I4,

. and proceed through line I3 to extractor-scrubber I6. A portion or all of the solution may pass through cooler 43, while on its way to the extractor-scrubber I6.

The light fraction produced Iin fraotionator 4I l is condensed in condenser 44 situated in line45,

means of the lightdistillate fraction, but also of simultaneously extracting light mercaptans from the latter in order to sweeten it, conditions may not usually be as favorable for scrubbingl as formerly described. Obviously, the set of conditions which will result in optimum scrubbing of alkyl phenols from the aqueous caustic alkali solution with simultaneous production of sweetened light fractionwlll be chosen. What these conditions will be cannot be denitely stated, because they may vary over a wide range depending upon several factors. light fraction contains very light mercaptans only, such as Cr-Ca mercaptans, and is free from heavier mercaptans, more favorable scrubbing.

conditions, i. e., higher temperatures and/or greater degrees of dilution may be employed than if substantial amounts of heavyl mercaptans Fory example, if the were present. In other words, the boiling range y and, more particu1arly,-the end boiling point of the light fraction, has an important bearing' as Well as the degree of fractionation achieved in the fractional distillation. A well fractionated distillate is more easily sweetened than one contain- `ing high boiling portions. Likewise, much depends on the relative volumes of the two liquids countercurrently flowing through the extractorscrubber I6: the higher the ratio of aqueous solution to distillate, the more favorable may be the scrubbing conditions. Other factors are concentration of both mercaptans and alkyl phenols in the regenerated. aqueous solution entering the stages in the I tillate'fraction in extractor described.

'I'he vtwo independently sweetened ldistillate fractions, that is, the heavier one from extractor 24 which has been substantially denuded of alkyl phenols, and the light fraction i'roml extractorscrubber l 6, which has recaptured at least a portion of the alkyl phenols removed from the heavier fraction, may be joined in line 46 to produce a sweetened gasoline containing an adequate amount of natural gum inhibitors.

While in the foregoing I have described two ow diagrams of my process, it shall be understood that other variations are possible. In particular,

- the addition of pumps, by-passes, heat exchangers and other necessary equipment are considered to be within lthe skill otthe designerfor such equipment. Moreover, piecesof equipment described may be replaced by others kn`own to 'be equivalent. For example, instead of using a steam stripper 6, I may employ a simple boiler'.

I claim as my invention:v Y

1. In a regenerative process of separating mer- "at a temperature higher'than-tliat of treatingsaid stripped 'solution with a'. salient for' ikyi phenols distillate but below the boiling temperaturen! the v lowest boiling substance employed in said scrubbing. f 6. The process of claim in whichythe 'scrubbing is carried out under superatmospxheric presf 7. In a regenerativeprocess oiseparating'mercaptans from a hydrocarbon distillate .containing both mercaptans and alkyl phenols by extraction with an aqueous solutionof a strong base, the method of controlling the composition of said solution comprising the steps of treating said dlstillate with said aqueous solution underconditions to absorb mercaptanstand alkyl `phenols'in the latter and to form two liquid layers, an aqueous layer containing absorbed mercaptans and alkyl phenols, and a layer consisting essentially of treated distillate, separatingthe layers, subjecting the aqueous layer to a steam stripping tore move mercaptans and to produce a stripped soluv tion retaining a substantialv portionl'of the'absorbed alkyl phenols, and scrubbing the stripped solution with said treated distillate at la temperature which is `higher thanthe temperature of f treating said distillate.

8. In a regenerative process of separating mercaptans from a hydrocarbon distillate containing both mercaptans and alkyl phenols by extraction with an aqueous solution of a strong base', the

captans from -a hydrocarbon distillate containing both mercaptans and alkyl phenols by extraction with an aqueous solution of a strong base, the

method of controlling the composition of said solution 4comprising the steps of treating said distillate with said aqueousf solution under conditions to absorb mercaptans and alkyl phenols inthe latter and' to form two liquid layers, an aqueous layerlcontaining absorbed mercaptans and alkyl phenols and a layer consisting essentially 'of treated distillate, separating the'layers, subjecting the aqueous layer to a striping to remove mercaptans and to produce a stripped solution retaining a substantial portion of the absorbed alkyl phenols, and scrubbing thestripped solution with va solvent for' alky`1 phenols.l

2. The process of claim 1 in which 'the aqueous solution contains dissolved a substantial amount ofv a solubility promoter for mercaptans.

3. The process ofl claim 1 in which the stripped method of controlling the composition of said solution comprising the steps of treating said distillate with said aqueous solution in anextraction zone under conditions to absorb mercaptans and alkyl phenols in the latterand to form two liquid layers', an aqueous layer containing absorbed mercaptans and alkyl phenols and a layer consisting essentially of treated distillate, separating the layers, subjecting the aqueous layer to a stripping to remove mercaptans and to produce a stripped solution retaining a substantial portion of the 'absorbedv alkyl phenols, diluting said solution with watei' at a point subsequent to the separation of f said layers, thereby producing al dilute solution,

scrubbing the dilute solution with a solvent forl alkyl phenols, boiling the scrubbed solution to vaporize water of dilution', and returning the resolution is scrubbed at a temperaturewhich isV v higher than the temperature at which the distillate is treated.

4. The process of claim 1 in which the aqueous layer is diluted with water prior tothe scrubbing.

5. In a regenerative process of separating mercaptansrom a hydrocarbon distillate containing' both mercaptans and alkyl phenols by extraction with an aqueous solution of a strong base, the

methodof controlling the composition of said solutioncomprising the steps of treating said dis-4 tillate with said aqueous solution atv a temperature between 0 and 60 C. to absorb mercaptans and alkylzphenols in the latter and to form two liquid layers, anaqueous layer containing absorbed mercaptans and alkyl phenols, and a layer consisting essentially of /treated distillate, sepa- ,rating the layers, subjectingthe aqueous layer to -a stripping to removemercaptans and to produce a stripped solution retaining a substantial portionl of the absorbed alkyl phenols, and scrubbing the sulting reconcentrated .solution to said extraction zone. 9. The process of claim 8 in which steam produced in the boiling of the stripped solution is used for stripping said aqueous layer. j.

10. In a regenerative process of separating mercaptans from a hydrocarbon `distillate containing both mercaptans and alkyl phenols by extraction with an aqueous solution of a strong base, the method of controlling the composition of said solution comprising the steps of fractionally distilling said distillate 'to'produce a low boiling fraction free from alkyl phenols`and containing low mercaptansand higher boiling fraction containing alkyl phenols .and higher mercaptans,'

treating -saidy higher boiling fractiorrin a' rst extraction zone with said aqueous solution under conditions to absorb mercaptans and. alkyl phenols in the latter and to form two liquid layers, a

i'lrstaqueous layer containing absorbed heavy mercaptans and alkyl phenols and a layer con-- sisting essentially` ofv treated higher boiling dis` till-ate, separating thelayers, subjecting the first aqueous layer to asteam stripping toremove mercaptar. "and to produce a stripped aqueous solution retaining a substantial portion of the absorbed alkyl phenols, treatingthe'low boiling.`

fraction with the stripped solution in a second 11.1n a regenerative process'l of separatingv mercaptans from a hydrocarbon distillate containingboth mercaptans and alkyl phenols by extraction with an -aqueous solution of a strong base, the lmethod of controlling the composition of I said solution comprising the steps of fractionally distilling saidl distillate to produce a low boiling fraction free from alkyl Phenols and containing low mercaptans, and higher boiling fraction containing alkyl phenols and higher mercaptans, treating said higher boiling fraction in a lirst extraction zone with said aqueous solution 25 under' conditions to absorb mercaptans and alkyl phenols in the latter and to form two liquid layers, a iirst aqueous layer containing absorbed heavy mercaptans and| alkyl phenols and a layer consisting essentially of treated higher boiling distillate, separating the layers, subjecting the iirst .aqueous layer to a steam stripping to remove mercaptans and to 4produce a stripped aqueous solution retaining a substantial portion of the absorbed alkyl phenols, diluting said solution with water at a point subsequent to the separation of said layers, thereby'producing a dilute solution, treating the low boiling fraction .withthe diluted strippedsolution runder vconditions :to absorb low mercaptans in the aqueous solution, to dissolve alkyl phenols in said low boiling fraction., and to form two liquid layers, one comprising a second aqueous layer containing absorbed mercaptans, and the other consisting essentially of the treated low boiling fractionr containing alkyl phenols,

combining the treated low and higher boiling M sulting reconcentratedaqueousy solution to said iirst extraction zone.

' marsa. FRoLov. 25

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