US2616936A - Method of sulfonation with sulfur trioxide - Google Patents

Description

Nov. 4, 1952 H. E. MAMMEN Erm.

METHOD oF suLFoNATIoN WITH SULFUR TRIXIDE Filed April 12, 1949 Patented Nov. 4, 1952 METHOD oF sLFoNA'rIoN WITH SULFUR y TRIOXIDE Howard E. Mammn, La Grange, and George L. Hervert, Berwyn, Ill., assignors to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application April 12, 1949, Serial No. 86,966

8 Claims. (Cl. 260-686) This application is a continuation-in-part Aof co-pending application Serial No. 774,630 `tiled September 17, 1947. .l

' This invention relates to a method of eiecting the sulfonation of organicV compounds whereby increased yields of sulfonated products having, a desirable color are obtained. More specically, the invention concerns an improvement in ithe method of sulfonating organic compounds which comprises effecting the sulionation reactionby contacting the charging stock at sulfonatingconditions with sulfur trioxide introduced into the sulfonation reactor suspended and/or dissolved in an inert liquid carrying medium.

It has been generally known that certain organic compounds may be sulfonated by reacting the same at selected sulfonation conditions with sulfur trioxidef'as the active sulfonating agent and that such use of sulfur trioxide as a sulfonating agent provides a highly advantageous method of effecting such reactions. Because of the ph'y's'ical instability ofthe various forms of sulfur ftrioxide and the resulting diiculties encountered in handling theireagent, particularly because of its corrosiveness to the required apparatus/irivolved, such as pumps, metering devices and mixing vessels; the'commercial use of sulfur trioxide to eiect sulfonation has been generally limited. The present invention provides a method of introducing the sulfur trioxide into the sulfonation reactor by dissolution and/or suspension inan inertcarrying medium comprising a low boiling paratlinic hydrocarbon thereby overcominglthe difficulties associated with its use inthe priorart. The so-called fpick-up procedure, as referred to herein, concerns the above method of introducing sulfur trioxid'einto a sulfonation reactor. By means of the present procedure, the advantages accompanyingthe use of sulfur trioxide as the sulfonating agent may be realized on a commercial scale applicable to many organic compounds and quality are mutually dependent factors, by a process in which discoloration and deterioration of the detersive properties of the product are substantially eliminated.

A further object of the invention is to produce sulfonated organic compounds by means of a sulfonating procedure in which high yields of the sulfonic acid product are obtained, calculated on the basis of the sulfonating agent consumed.

4Still another object of the invention is to provide a process for the production of alkyl aromatic sulfonate detergents wherein an alkyl aromatic hydrocarbon is sulfonated and the resulting sulfonic acids is subsequently neutralized with a basic neutralizing reagent to form said sulfonate detergent, effecting the sulionation reaction under conditions such that substantially none of the alkyl groups'are lost from the alkyl aromatic hydrocarbon charge and further providing for the immediate neutralization of the sulfonation reaction mixture to form the desired sulfonate detergent product without the necessity of separating the sulfonic acid from an excess of the sulfonating agent.

In one of its embodiments, the present invention concerns an improvement in the process for sulfonating a sulfonatable organic compound by contacting said compound with sulfur trioxide entrained in an inert ud carrying medium which-comprises passing said inert fluid medium selected from the `inert parannic hydrocarbons containing not more than 8 carbon atoms per molecule into a mass of sulfur trioxide main` tained in a pick-up zone at conditions selected to thereby entrain a portion of said sulfur trioxide in said inert carrying medium and thereafter mixing the inert carrying medium containing sulfur trioxide With said sulfonatable organic compound at sulfonation reaction conditions.`

In its more specific aspects, the present invention relates to a process for sulfonating a-sulfonatable organic compound WhichAV comprises passing a stream of liquid normal butane maintained at a pressure in excess of about 5 atmospheres and at a temperature of less than about 30 C. into a pick-up zone containing a mass of sulfur trioxide to thereby entrain a portion of the sulfur trioxide from the pick-up zone in v,said liquid butane, cooling the effluent thereof, to a temperature of from about `0 to about 20C. Vand admixing said eluent with said sulfonatable organic` compound in an amount corresponding to a molal ratio of sulfur trioxide to the sulfonatable organic compound. of fromabout 1:1'to about 3:1, refluxing the'butane vaporized by the heat of the resulting sulfonation reaction at a pressure sun'icient to maintain the temperature of the reaction at from about -10 to about 20 C. and thereafter vaporizing said butane from the sulfonation reaction product.

In any sulfonation reactionv Where speed of reaction and yield are important factors, it becomes desirable to maintain the proportion of' sulfur trioxide in the sulfonating agent as high as possible consistent with the number of sulfonicA acid groups to be introduced into the compoundA undergoing sulfonation by maintaining thesulfonation reaction mixture as nearly anhydrousl as possible. We have discovered that by introducing pure sulfur trioxide (that is, in an anhydrous condition, free of sulfuric acid) into the sulfonation reactor entrained in an inert diluent or solvent, such as a liquid paraflinic hydrocarbon, the above desired conditions are maintained during the sulfonation reaction. Free sulfur trioxide is an active sulfonating agent such that substantially. complete monosulfonation is obtained vvhenk approximately a,A molar equivalent each of sulfur trio-xide andthe compound undergoing sulfonation are present in the sulfonation reactor. Suitable conversions may beohtained in a reaction mixture wherein the ratio ofsulfur trioxide to lcharging stock is as low as 1.: 1; molar ratio` of, the reactants, although in most;instances itA isV preferred to maintain the ratioA ofk sulfur trioxide to chargingY stock; `at slightly greater than a 1:1y molar ratio, from aboutglzl to about 2.11 in those reactions in which monosulfonation is desired. The sulfonation of,v organic compounds with sulfur trioxide 5 eliminates the problem ofseparating Vthe sulfonic acidproduct from large quantities of-excess sulfonating agent, generally required when the customaryfsulfonating agents such as sulfuric acid or the oleiuns', are ultilized. The sulfonation reaction mixture. when utilizing sulfur trioxide as thesulfonating agent may thus be neutralized directly without the consumption ofA relatively expensive neutralizing agentvto, form the, sulfate saltof the neutralizing agent vwhich is obtainable moreY cheaply froirrotlfierI sources. Theuse of Sulfur. IOXid. thetfe, eeClJS a. mafkednomyinthe usual sulfonationprocess wherein the product sulion-ic acidf is desired ingtheform4 of the-sulfonate Salt; not; only because 0i. the. reduced. quantitiesv 0f; Sulfeuating ,agent required, but alsoheceusethe.aruountof neutralizing-agent requiredfor` forming; the sulfonate salt isreprcyide. a convenient-method 3f-,introducing S111- fur.- troxide inte a. sulonetion. reaction. The method cemprseepassiue aninert .uid- .carrying medium into. a. bulls Supply of*` sulfur; trioxide maintained within a pick-up zone.Y wherein the fluid carrying medium entrans a portionof-tne sulfur. trioxide. present in the pickrup zone. and carriesthe same to the sulfonating reactor where the sulfur'trioxide, inthe presenceofthe carrying-*.medium, contactsthe organic compound to be sulfonated at.- theadesired sulfonating conditions. By theus'e. of theterm fluidcarrying medium herein, itis. contemplatedthat either gaseous or.liquid-parainic'hydrocarbons may be utilized to entrainr sulfurv trioxide in either the Vapor. liquider-dissolvedfform of thelatter reagent. When employing a liquid or liquefied normally gaseous -parafnic'hydrocarbon as the fluid carrying medium; the. reaction conditions, ves?v pecially the-temperatureof the sulfonation reaction, may be controlled within close limits by adjusting the pressure above the reaction mixture such that all or a portion of the liquid carrying medium evaporates as the exothermic heat of the sulfonation reaction isliberated.l Since one form or physical modification of the carrying medium herein specified may be an inert liquid, vaporizable at the relatively low temperatures utilized in typical sulfonation reactions, especially when the ambient. pressure is adjusted to induce vaporization. the temperature of the reaction is thereby limited to the boiling point of the carryingl medium at the particular operating pressure. The sulfonation reactor may further be attached toareflux condenser to continuously return the vaporized carrying medium during the reaction to the sulfonation zone. Alternatively, the vapors may be condensed in an auxiliary condenser and returned to the sulfur trioxide pick-up zone While additional liquid carrying mediumv in an amount sufcient to supply only that required to cool the reaction mixture by evaporation is supplied tothe sulonation zone.` The close control of the,v` temperature in this mannerH is especially advantageous when sulfonating a compound,I which is sensitive to heat andis especiallyapplicable to the sulfonation o f those compounds which undergo undesirableA color changes, (as in the case of alkyl aromatic'hydrocarbons) or which form .resinous or tarry substances at high sulfonation reaction temperatures. The introduction of the sulfur trioxide in the-presenceofy afluid carrying medium is advantageous iny other Y respects in that the sulfur trioxide Vis,ineffect,'diluted with the inertiiuid and'therefore contacts the compound tov be sulfonated gradually such that polysul- 'foriationl is'l obviatedI in those reactions Where monosulfonation is desired, as in the casev of producing benzene sulfonic acidfor subsequent conversion toga monohydroxy phenol, or in the case o f-- sulfonating` alkylA aromatic compounds for the production of sulfonate detergents therefrom. In the latter-application of the present process, dealkylation ofthe alkyl aromaticcharging stock is substantiallyrveliminated by, virtue of theabsence of water andthe gradual contact obtained between thecharge land Athe sulfurtrioxide distributed throughout an inert carrying medium. The present method eliminates the problem of dealkylation ordinarily observedwhen the charge is initially contactedv withvallor a major proportion-of the-. sulfonating agent. as, for example, when the chargeis simply. stirred into orv other- Wise. mixed with the undilutedsulfonating agent. In order-to enhance the advantages of gradual contact between the` charging stockand thel sulfur trioxide.A and, also to prevent polysulfonation, it isalso contemplated in the present process to contact the charging stock. withthe sulfonatingagent in step-Wise vbatch increments `accompaniedbyA intermediate. separation of. the sulfonic acid product-from the. reaction mixture, although the desirable monosulfonation is generally v obtainable without pol-ysulyfonation by, the continuous method of: contact WhenA the reaction conditions are maintained `vwithin the limitsL hereirrpmvided.. As @alternative t0 the. intermediateseparation of the sulfonic acidsvfrom the reactionA mixture.. .the `reaction ratel may Abe Jvlowered by decreasing; the; temperature andisimultaneously increasing; the; residence time` of the compounds, to be-,sulQIlal/ede.

Suitable v charging stocks which may bev sulomated by. theV present.' procedure are,` herein; de-

scribed broadly 'as sulfonatable organic compounds,` "although the method is particularly advantageous when applied to the sulfonation of aromatic compounds, and especially when the charge stock comprises an alkyl aromatic hydrocarbon as hereinafter specified for the formation of the corresponding sulfonic acids `utilizable asA detergent intermediates. Organic compounds Within the broad class` of charging stocks include such compounds as the phenols, and alkyl phenols; alcohols of both the aliphatic and cyclo-aliphatic series; aromatic hydrocarbons such as the various benzene derivatives containing a nuclearly displaceable hydrogen atom and the polycyclic aromatics containing naphthyl, `p henanthryland anthryl nuclei; olefinic hydrocarbons such as octene, decene, etc., cyclo-olefins and their alkyl derivatives such as cyclohexene and ethylcyclohexene; heterocyclic' compounds such as thiophene, pyridine and the like; ethers and esters such as phenylmethyl ether and theA fattyacid glycerides respectively, the latter Vclass including such compounds as the glyceride mono-ester of oleic acid, etc.; acids, such asbenzoic acid; and various derivatives of the above classes of compounds containing substituents such as one or more halo, nitro, amino, keto`,carboxyl, etc. groups. The ladvantages of the present method of sulfonation are especially evident in the production of alkyl aromatic sulfonic acids which when neutralized with a suitable basic reagent such as' an alkali metal hydroxide, an amine or an alkanol amine form highly effective detergent compounds. In the latter instance, the controlv of the reaction temperature is especially important and the method herein provided for effecting gradual sulfonation of the charging stock' to be sulfonated permits sulfonation at a relatively low temperature, thereby eliminating the development Vof color bodies and dealkylation of the alkyl aromatic hydrocarbon charging stock which ordinarily occursrwhen the temperature is not controlled or whereV the charge is contacted with all or a large proportion of theV sulfonating agent. Suitable alkyl aromatic Vhydrocarbons sulfonatable by the present process include not only the alkylated polycyclic aromatic compounds such as nonyl naphthalene but also, and preferably, the alkyl benzenoid hydrocarbons wherein the alkyl group contains from about 9 to about 18 carbon atoms per'group, represented, for example, by dodecyltoluene.

The material herein 'designated' as the carrying medium for the sulfur trioxide sulfonating agent is more specifically described as a parain hydrocarbon which is essentially inert at the temperature specified for the particular sulfonation reaction. At'relatively high sulfonation temperatures', for example, at temperatures in theregion of about 50.to about 100 C., itis desirable tok utilize asa carrying medium for the sulfur trioxide aV normally liquid inertparaiiin hydrocarbon containing fewer than about 8 carbon atoms per' molecule such as heptane, hexane," and pentane and employing sufliciently high pressures inlsulfonation stageof the process to maintain at least a portion of the inert hydrocarbon in "substantially liquid phase. `At relativelyv low sulfonating temperatures, for example, at temperatures of'from about 20 to about 50C., low'boiling parafiinic hydrocarbons such as propane and butane ora mixture thereof are desirably utilized as the carrying medium. The latter may be passed through the sulfuritrioxide 6. pick-up zone in either vapor or liquid condition to entrain a portion of the sulfur trioxde therein.- In the subsequent sulfonation stage, the pressure therein may be increased to maintain at least a portion of the carrying medium in liquid phase. Y

It is generally preferred that the pick-up zone and auxiliary equipment leading to the sulfonation reactor be maintained at a temperature less than about 30 C., preferably at from about ,0 to about 70 C. to avoid any reaction between the carrying medium and the sulfur trioxide. For this reason and also to provide a fluid, nonviscous medium, n-butane, propane or mixtures thereof are preferred carrying media for usein the present invention, since the latter are substantially inert and readily flow at these temperatures.

In sulfonating most organic compounds and particularly in the sulfonation of alkyl aromatic hydrocarbons where undesirable coloration of the produci-l is likely to develop at higher sulfonation temperatures, the preferred temperature is in the range of from about 10 to about 20 C., and the preferred inert liquid carrying media for the reaction are the low molecular Weight normal parain hydrocarbons. The latter inert hydrocarbons may be readily distilled from the sulfonation reaction product following the completion of the sulfonation reaction and are readily recoverable .by passing the hydrocarbon vapors from the distillation through a condenser at pressures in excess of the vapor pressure of the carrying medium, although the paraiiin hydrocarbon vvapors may themselves be recovered and recycled to the pick-up zone, as desired.

The active component of the sulfonating agent herein utilized which provides the sulfonic acid radical attached to the sulfonatable organic compound during the sulfonation reaction is sulfur trioxide in any of its various physical modications. Sulfur trioxide has become available commercially in three forms, the so-called aform (a solid asbestos-like material melting at about 62 C., generally considered to be a sulfur trioxiole polymer) the -form, also a polymeric solid at normal temperatures melting at aboutV 33 C., and the 'y-form, a normally liquid modification of 'sulfur trioxide at room temperatures containing a large proportion of monomeric sulfur trioxide and melting at about 17 C. As previously' indicated, the invention contemplates utilizing any of said forms,` although the 'y-form is preferred herein because of its greater adaptability to continuous processing procedures and its more desirable handling behavior. `A c stabilized y-form is manufactured commercially under the trade name Sulfan containing an inhibitor which maintains the stabilized product in liquid condition at temperatures higher than its melting point at which temperature it would normally (in the absence of the inhibitor) be converted to the polymeric solid aand -forms. Sulfur trioxide vhas a sufficient vapor pressure that significant quantities thereof are vaporized and may be entrained in a paraffin hydrocarbon vapor by passing said hydrocarbon into the gck-up zone, even at temperatures below about The sulfur trioxide is for purposes of the present process maintained in a suitable tower or vessel containing a bulk supply thereof. In order to effect dissolution or entrainment of the sulfur trioxide in the carrying medium, the latter isV `least a portion thereof is recycled to the initial stages of the process for picking up additional amounts of sulfur trioxide from the bulk supply zone. The liquid butane for the latter alternative .operation is removed from condenser 30 through line 3| and discharged into line 35, through valve 36 into butane charging line 3 for recirculation in the process.

The sulfonation reaction product comprising alkyl aromatic sulfonic acids kand usually some residual butane carrying medium, as Well as excess sulfur trioxide depending upon Whether a molar excess of the sulfonating agent is utilized in reactor 25, is removed from reactor 25 through line 35 and valve 31 and transferred into butane separating zone 38 whereinV the butane carrying lmedium is vaporized from the remaining components of the sulfonation reaction mixture, usually at a somewhat lower pressure and/or higher temperature than are maintained in the sulfonation reactor. Butane separation zone 38 is preferably a packed fractionating column preceded by a preheater in which the incoming charge `thereto may be heated prior to introducing the mixture into zone 38. Alternatively, the incoming charge may be heated by hot butane vapors from the reboiling section of the column, as hereinafter described. The relatively high volatility of butane in relation to the other components of the reaction mixture permits the butane to be readily separated from the sulfonation reaction mixture, depositing a residue comprising predominantly alkyl aromatic sulionic acid.

The vaporized butane is removed from separating zone 38 through line 39 and valve 40 and transferred to condenser 30 by connection of line 39 with line 28 for recycling the butane as hereinabove provided. Any residual butane which is not flashed from the mixture charged to separation zone 38 is generally removed by additional heating cf the residue, for example, by contacting the latter with reboiler coil 4l in the bottom of zone 38. The residue comprising the alkyl aromatic sulfonic product acid in a substantially pure state is removed from separating zone 38, through line G2 containing valve 43 to other processing apparatus, not shown, such as a neutralization zone, Because of the substantially complete conversion of the alkyl aromatic hydrocarbon to sulfonic acids thereof in the sulfonation reactor, the problem of separating unconverted charging stock is eliminated when utilizing sulfur trioxide as the sulfonating agent charged at at 1:1 or slightly higher molar ratio of sulfur trioxide to charging stock.

The present invention is illustrated with respect to several of its specic embodiments in the following examples, which, however, are not to be considered as limitations of the invention in any of its broad aspects hereinabove specined.

Example I In a batch apparatus for the sulfonation of dodecyltoluene, liquid n-butane is passed upwardly at a rate of 2500 grams per hour through a vertical pick-up zone containing 274 grams of liquid sulfur trioxide in a column of the re- Civ agent approximately 30 inch-es high. The pick-up zone is maintained at a temperature of about 18 C. and at 5 atmospheres pressure. At these conditions the n-butane carrying medium will contain approximately 3% by Weight of sulfur trioxide. This mixture is then introduced into a sulfonation reactor containing 200 grams (0.77 mol) of dodecyl toluene. Sulfonation is effected at atmospheric pressure and at a temperature of about 0 C. obtained by vaporization of the butane. The vapors from the sulfonation reactor are condensed and a portion of the liqueed n-butane is returned to the reactor, while the remaining portion is utilized to pick up sulfur trioxide by recycling the butane to the pick-up zone. Under these conditions, approximately 97% sulfonation of the dodecyl toluene is obtained.

Example II Utilizing the apparatus and procedure employed in Example I, the butane-sulfur trioxide eiiiuent of the pick-up zone containing approximately 3% sulfur trioxide is introduced concurrently With lauryl alcohol into a stirred sulfonation reactor maintained at a temperature of approximately 0 C. at atmospheric pressure and at a rate suicient to supply about 1.1 moles of sulfur trioxide per mole of lauryl alcohol. The average residence time in the sulfonation reactor is about 15 minutes, the butane vaporizing as exothermic vheat is liberated by the resulting sulfonation reaction. The butane vapors are continuously reiluxed into the reactor by means of a Dry Ice condenser above the reactor. The resulting reaction mixture is continuously transferred to a distillation column for removal of the remaining butane and the distillation residue neutralized With caustic soda. Approximately 98% of the lauryl alcohol is sulfonated by this procedure and the product is substantially colorless.

Example III Utilizing a vertical column pick-up zone, liquid butane is vaporized at atmospheric pressure and bubbled into the bottom of said pick-up zone containing liquid sulfur trioxide at a temperature of from about 20 to about 25 C. wherein it entrains sulfur trioxide vapor. The mixture of gases is then passed into a sulfonation reactor containing dodecyltoluene and about 1.5 volumes proportion of liqueed butane which refluxes into the reactor from a Dry Ice condenser attached to the sulfonation vessel. The butane-sulfur trioxide vapors are bubbled into the reactor as the liquid hydrocarbons are rapidly stirred, the heat of the resulting sulfonation reaction vaporizing the liquid butane which refluxes at a rate sumcient to maintain the volume proportion of butane to dodecyltoluene hydrocarbons in the sulfonation zone at approximately 1.5. Over 99% sulfonation is obtained and about 1.1 moles of sulfur trioxide are removed from the pick-up zone per mole of dodecyltoluene sulfonated.

We claim as our invention:

l. In a sulfonation process wherein a sulonatable organic compound is reacted in a sulfonation zone with sulfur trioxide, the method of supplying sulfur trioxide to said zone which comprises maintaining in a pick-up zone apart from said sulfonation zone a mass of a sulfonating agent selected from the group consisting of liquid sulfur trioxide and solid sulfur trioxide, passing through said mass in the pick-up zone an inert paraiiinic 'lli mixture of gpar'aiiinic hydrocarbon and sulfur atrioxide from. the pick-up .zone andintroducing theI sameI to vsaid Asulfonation. `zone.

.2. AThe method of claim 1 further characterized in thatsaid paraiinic hydrocarbon isvliquefied butane.

13. The process of c1aim1 further charactervized in that said inert parafnic hydrocarbon is .butane.

The process of claim 1 further character- -ized in that the .'y-form of sulfur trioxide is maintained in ysaid pick-up zone.

The process of claim 1 further characterized in that said inert parainic hydrocarbon is passed into said sulfur trioxide pick-up zone at a rate suicient to supply said sulfonation zone with from about 1.1 to 1 to about 2 to Lmoles of sulfur trioXide per `mole ofsulfonatable organic compound.

'6. The process of claim 1 further characterized in that the temperature and pressure conditions A in said pick-up zone are selected to maintainlsaid parainic hydrocarbon in substantially liquid phase therein.

7. The process of claim 1 further characterized in thatsaid parainic hydrocarbon is introduced intosaid pick-up zone in thev bottom thereof and vingaseous condition ata temperature sufcient to vaporize a portion of thesulfur trioxide in `said pick-up zone to form a mixture of gases comprising said sulfur .trioxi'de and said paranic hydrocarbonand thereafter passing .said mixture 2.8. '.'The `process of claim lifurther characterized in that said paraftinicl hydrocarbon is introduced into :said pick-.up zonev in the-.bottom thereof vand ingaseousfcondition at, a Atemperature of .from

aboutl vtoabout .30 C.to .vaporize -a portion ofthe sulfur trioxide in saidxpick-up zone to form -a mixture ofgases comprising said sulfur trioxide and .said paraiinic hydrocarbon :and thereafter v`passing said mixture into '.saidfsulfonation zone.

. HQWARD ECNIAMMEN. .GEORGE IL. -I-IERVERT.

REFERENCES CIT-ED T-he:following-references'are of record in the rile -of this patent:

UNITED STATES nPATENTS .Number Name Y Date Re;:22;548 Brandt Sept.,26, 1944 1312256.41 :Grob Jui-y I1, 1922 1,956,571 f.,Gri11`et ;May 1, -1934 11,991,955 Ralston Feb. 19,;1935 A,2,111,978 `Kokotnur Mar. v 22, 1938 k2,198,595 yAmosetal. VAPL-BO, 1940 "2203x141 Oliver June-4, 1940 2,268,443 `Crowder Dec. 30, 1941 `2,285,390 A Brandt June 9, 1942 12,290,167 Datin .Iuily :21, .1942 2,480,592 vMitchell Aug. 30, l1949 l VFOREIGN PATENTS Number Country Date r539,281 -Great Brtain Sept.,.3, 194,1

Claims (1)

1. IN A SULFONATION PROCESS WHEREIN A SULFONATABLE ORGANIC COMPOUND IS REACTED IN A SULFONATION ZONE WITH SULFUR TRIOXIDE, THE METHOD OF SUPPLYING SULFUR TRIOXIDE TO SAID ZONE WHICH COMPRISES MAINTAINING IN A PICK-UP ZONE APART FROM SAID SULFONATION ZONE A MASS OF A SULFONATING AGENT SELECTED FROM THE GROUP CONSISTING OF LIQUID SULFUR TRIOXIDE AND SOLID SULFUR TRIOXIDE,PASSING THROUGH SAID MASS IS THE PICK-UP ZONE AN INERT PARAFFINIC HYDROCARBON CONTAINING FROM 3 TO 8 CARBON ATOMS PER MOLECULE AT A TEMPERATURE BELOW ABOUT 30* C. TO ENTRAIN A PORTION OF THE SULFUR TRIOXIDE IN THE PARAFFINIC HYDROCARBON, REMOVING THE RESULTANT MIXTURE OF PARAFFINIC HYDROCARBON AND SULFUR TRIOXIDE FROM THE PICK-UP ZONE OF INTRODUCING THE SAME TO SAID SULFONATION ZONE.

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